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Geology of the Nottingham district: Memoir for 1:50 000 geological sheet 126 (England and Wales)

By A S Howard G Warrington J N Carney K Ambrose S R Young T C Pharaoh C S Cheney

Bibliographical reference: Howard, A S, Warrington, G, Carney, J N, Ambrose, K, Young, S R, Pharaoh, T C, and Cheney, C S. 2009. Geology of the Nottingham District. Memoir of the British Geological Survey, Sheet 126 (England and Wales).

British Geological Survey

Geology of the Nottingham district: Memoir for 1:50 000 geological sheet 126 (England and Wales)

A S Howard G Warrington J N Carney K Ambrose S R Young T C Pharaoh C S Cheney

Contributors

Keyworth, Nottingham: British Geological Survey 2009

© NERC copyright 2009 First published 2009

Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining NERC permission.

Contact the BGS Intellectual Property Rights Manager, Keyworth, Nottingham. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

The grid used on the figures is the National Grid taken from the Ordnance Survey map. Topography is based on material from Ordnance Survey 1:50 000 scale maps. © Crown copyright reserved. Ordnance Survey licence number 100037272/2009 ISBN 978 0 85272 579 5

Printed in the UK for the British Geological Survey by Alphagraphics, Nottingham.

Acknowledgements

Numerous organisations and individuals supplied information during the resurvey of the Sheet 126 Nottingham, including British Gypsum, Blue Circle, Tarmac Brick and Hoveringham Gravels. In particular we wish to thank the Coal Authority, RJB, British Petroleum, the Environment Agency and Nottinghamshire County Council for supplying and granting permission to publish borehole and seismic data. Burrow Croker, and G Maunsell and partners also supplied borehole core material. We are most grateful to local landowners, especially the farmers and quarry owners, for their co-operation in providing access for the surveyors.

Chapters in this memoir have been written by the following authors.

Authorship

The task of compiling the memoir was started by A S Howard and taken to completion by J N Carney. The memoir was edited by R D Lake, S G Molyneux and A A Jackson; figure production was by R J Demaine and P Lappage; pagesetting by A Hill.

Notes

Throughout this memoir, the word ‘district’ refers to the area covered by the geological 1:50 000 Sheet 126 Nottingham. The district is covered by 24 full 1:10 000 series maps, each of which is given a geographical name for ease of reference.

All National Grid references are given in square brackets; all lie within the 100 km square SK.

Borehole records referred to in the text are generally given a geographical name. Locations, depths and BGS registered numbers are tabulated in the memoir.

Numbers preceded by the letter A refer to the BGS collection of photographs; those preceded by the letter E refer to the BGS sliced rock petrographical collection.

Preface

In 1990, the British Geological Survey embarked upon a major programme of geological survey (or resurvey) in Britain, in order to bring standards of mapping and of multidisciplinary geological science up to the level of detail and precision that will be required for the foreseeable future. The rationale and objectives of this programme have since been revised, as reviewed by Walton and Lee (2001). The programme is driven by an assessment of end-user requirements for geoscience information, and is carried out within the framework of what is realistically achievable given the ever-changing levels of financial and staffing resources available to the survey. This memoir and the accompanying map provide a full evaluation of the detailed stratigraphy of the Nottingham district, its mineral, hydrocarbon and water resources, and the constraints that the surface and subsurface geo-environments place on urban and rural development.

The geology of the Nottingham district has exerted an important control over its industrial development and rural land use. The form of the landscape is controlled by the nature of the underlying rocks, and the location of resources such as minerals, water, fertile soils and dry, defensible land are all determined by the local geology. Information in this memoir, and in the thematic report for the Nottingham urban area by Charsley et al. (1990), shows how geology can be applied to the effective, safe and environmentally sound development of these resources. It also provides an overview of the stratigraphy and structure, which should be of interest to amateur and professional geologists alike.

Mineral exploitation has long been important to the local economy and at present is mainly represented by the extraction of sand and gravel, brick clay and gypsum. Coal resources are present at depth and have been extensively mined in the past, although there is no current activity within the district. The concealed Carboniferous rocks are important targets for hydrocarbon exploration. The subsurface geology and structure of the district are therefore important themes, and their investigation has been facilitated by the numerous deep boreholes and seismic reflection traverses conducted in support of mineral exploration.

This memoir synthesises a mass of information for the Nottingham district, and also contains much hitherto unpublished material. Many specialist contributions highlight the emphasis placed by the current BGS programme on a multidisciplinary approach to geological mapping. It represents a major advance in the understanding of the geological history and structure of the district, and I am confident that it will play its part for many years to come in serving the needs of the scientific, planning, commercial and academic communities.

John N Ludden, PhD Executive Director British Geological Survey Kingsley Dunham Centre Keyworth Nottingham NG12 5GG

Geology of the Nottingham district—summary

This memoir describes the surface and subsurface rocks of the geological map Sheet 126, together with various aspects of the geophysical and geological structure. The district extends north-eastwards from Nottingham to the outskirts of Newark, and includes the towns of Radcliffe on Trent, Bottesford and Southwell.

At depth, much of the district is underlain by Carboniferous strata that show a marked thickening within two structural basins, the Widmerpool Half-graben to the south-west and the Welbeck–Sleaford Low in the north-east of the district. Strata include the ‘productive’ Coal Measures sequence lying at the southern edge of the concealed Nottinghamshire Coalfield, which extend southwards into the Vale of Belvoir Coalfield; in the south and east they are locally replaced by a thick sequence of basaltic volcanic rocks. This concealed geology is described in detail, and the structure has been interpreted from borehole data — lithological and geophysical (gamma-ray, sonic velocity) logs — in combination with seismic information. These structures may have implications for future coal or hydrocarbon exploration.

Apart from a small outcrop of Carboniferous rocks in the Radford area of Nottingham City, the strata at outcrop comprise a south-eastward dipping succession of Permian, Triassic and Lower Jurassic rocks. Detailed accounts are given of the Permian and Triassic groups, formations and members, and many type localities and reference sections lie within this district. The basal Triassic rocks include thickly developed sandstones that are major aquifers, replenished from their wide outcrop in the west and north of the district and present at depth elsewhere. The upper part of the Triassic sequence is largely red-brown mudstone and includes gypsum beds that have been exploited by both opencast and underground mining.

The district has been affected by only one glaciation, during the Anglian stage (MIS 12) of the Quaternary. Few outcrops of unconsolidated glacial deposits now remain, since most were removed by a sustained, largely post-Anglian period of downcutting that has moulded the present landscape. The most notable legacy of this erosion was the formation of the wide, flat-bottomed floodplain of the river Trent, and of the many large and small tributaries of that river system. Detailed Quaternary mapping of the Trent floodplain has shown a history of at least four separate phases of aggradation, including that of the modern alluvium, which have left their mark in a series of river terrace deposits, both within and adjacent to the floodplain. Such deposits are important as aquifers and as sand and gravel resources. They also delineate areas of raised ground, and their depiction on geological maps can thus help to estimate the severity of flooding that is likely to occur at a given locality.

The memoir outlines a number of potential natural geological hazards within the district, such as the possibility of near-surface gypsum solution, radon gas emission, shrink-swell clays and flooding. It also describes the man-made hazards, including, for example, ground subsidence in the former mining areas and the local contamination of water supplies by rising mine-water discharges. A further hazard, unique to the Nottingham City area, is that many caves hewn out of the Sherwood Sandstone have weak roofs and periodically cause collapses at ground level.

Many of the above factors are of relevance to farmers or conservationists in planning the management of the land, to planners considering the location of constructional or trunk route developments, and to hydrogeologists concerned with groundwater and pollution management. There is also an increasing need to provide insurers with geoscience information that can be used to assess the risk factor imposed by the geology over large areas or in site-specific case studies.

Geological succession in the Nottingham District (TableInsideFC)

Chapter 1 Introduction

This memoir describes the bedrock (Figure 1) and Quaternary geology of the Nottingham district, covered by the 1:50 000 series geological map Sheet 126 Nottingham. The district lies mainly in south Nottinghamshire, but includes small parts of north-east Leicestershire and south-west Lincolnshire. Much of the city of Nottingham occupies the south–western quadrant, with the town of Newark on Trent in the extreme north-east. The remainder is largely rural, but includes the smaller towns of Southwell, Bingham, Calverton, Burton Joyce, Radcliffe on Trent and Cotgrave.

Apart from a small outcrop of Middle Coal Measures strata in the extreme west, the geology of the district comprises a south-eastward dipping succession of Permian, Triassic and Jurassic strata, in places with a thin veneer of Quaternary deposits. The ‘productive’ Coal Measures are present at depth beneath most parts of the district, which is located at the southern margin of the concealed Nottinghamshire coalfield. Coal is no longer mined, but was formerly a major contributor to economic growth. Other geological resources of current commercial significance include sand and gravel, brick clay and gypsum. Large quantities of groundwater occur within permeable sandstones of Triassic age and make a major contribution to the water supply of the region. The district continues to be a target for hydrocarbon (oil and gas) exploration, but no commercially viable fields have been discovered.

Topographically, the district is bisected by the floodplain of the north-eastward flowing River Trent (Figure 2). The valley floor forms a nearly flat expanse of land, about 2 to 4 km wide, falling from 25 to 11 m above OD, and is bounded locally on both sides by steep bluffs rising up to 50 m above the valley floor. To the north-west of the Trent, the ground rises to a maximum of 144 m OD on the Triassic outcrop, which is dissected by a number of deeply incised stream courses known locally as ‘dumbles’. To the south of the Trent, the highest ground (70 to 80 m above OD) is formed by the immediately adjacent river bluffs developed on Triassic strata, before falling away south-eastwards into the Vale of Belvoir. The latter area is characterised by a subdued scarp and cuesta topography developed on upper Triassic and Jurassic strata. Most of the Vale of Belvoir lies below 35 m OD, and is drained by the River Devon, which joins the Trent at Newark.

History of research

The original geological survey of the district was carried out at the scale of one inch to one mile (1:63 360) by W T Aveline, E Hull, T R Polwhele, W H Holloway and J Jukes-Browne, and was published on [SK Old Series] sheets 71NE (1858 with additions in 1879), 71SE (1855 with additions in 1879) and 70 (1886). B S N Wilkinson, G W Lamplugh, W Gibson, W B Wright and R L Sherlock resurveyed the district on the scale of six inches to one mile (1:10 560) in 1903–1906, and the maps were published as Nottingham County Standards.

A few of the Nottinghamshire sheets were resurveyed in the 1950s and 1960s as National Grid Standards at 1:10 560 scale. The 1:10 560 scale sheets along the western edge of the district were resurveyed by D V Frost, E G Smith and P McC L Duff in 1963–1964, with minor revisions by J W Baldock and T J Charsley in 1989.

The most recent 1:50 000 geological map of the Nottingham district, published in 1996 and described in this memoir, was compiled from 1:10 000 National Grid Sheets following detailed geological surveys and data acquisition in the district between 1987 and 1994. The 1:10 000 National Grid Sheets included in the compilation are listed in Information sources, together with the names of the surveyors, the dates of survey and reference numbers of the accompanying Technical Reports.

The most recent 1:10 000 scale surveys augmented a study commissioned by the then Department of the Environment into the geology and applied geology of Nottingham City and its environs. The results of this work provide the earth-science background to all aspects of land-use and mineral resource planning, and are contained in the Technical Report by Charsley et al. (1990), complementary to this memoir. Other BGS data covering the district, including maps, reports and digital material, are given in the Information sources section.

Geological sequence

The geology of the district consists of three major components, namely bedrock, superficial deposits or drift, and man-made deposits. Bedrock is usually exposed only in man-made excavations, including quarries, pits, drainage ditches or boreholes; natural exposures are relatively rare. Superficial deposits, generally consisting of unconsolidated sediments such as clay, sand or gravel, are also rarely exposed. They may completely cover the bedrock to depths of several metres, as beneath the River Trent floodplain, or be thin and patchy in their distribution, as in the Nottingham City area. Man-made deposits are likely to occur wherever the land surface has been re-modelled or landscaped by the activities of man, and are widespread in all areas of human settlement.

The geological formations described in this memoir are listed on the inside of the front cover. The simplified geological map (Figure 1) shows the distribution of rock strata at the surface or at rockhead (i.e. the rocks below drift deposits). A cross-section of the strata beneath the district (e.g. section 2 at foot of 1:50 000 Sheet 126) shows that they dip gently towards the east-south-east or south-east, at an angle of 1° to 2°. Consequently, the oldest Permian rocks of the Cadeby Formation crop out in the extreme north-west and west of the district, with the youngest Jurassic rocks of the

Lias Group restricted to the extreme south-east. Apart from a small area of Radford, Nottingham, where Upper Carboniferous rocks (Coal Measures) occur at the surface, Carboniferous strata are concealed beneath Permian or younger rocks, and are therefore encountered only in boreholes or underground mines.

The recent geological survey has shown that the bedrock is more faulted than was hitherto recognised.

The structure of the concealed Carboniferous rocks is more complex than that of the overlying Permian and younger rocks, from which they are separated by an unconformity. The Carboniferous rocks are gently folded into a series of low-amplitude dome and basin structures, superimposed on a gentle regional dip of 1° to 4° to the north-east. They are also disturbed to a greater extent by faults than the overlying Permian and younger strata.

Outline of geological history

The bedrock beneath the Nottingham district (inside front cover) preserves a record of the changing geography and climate of the region over about 350 million years of geological time. For much of this period, the Earth’s geography bore little resemblance to that of the present day, with landmasses occupying completely different and gradually shifting positions as oceans opened or closed and the adjacent continents ‘drifted’. The area now occupied by the East Midlands lay below the sea for much of the time, and even when the seas retreated, the landscape and climate were very different to those of today. Evidence of landscape features such as volcanoes, ‘tropical’ swamps, semi-arid alluvial plains, desert sand dunes and salt lakes are all preserved in the rocks of the district.

The pre-Carboniferous ‘basement’ rocks of the district occur at depths of over 1200 m and have not been proved by drilling, although their top surface and some details of their structure can be inferred from geophysical evidence. They are thought to consist of strongly folded mudstone, with sandstone and perhaps volcanic horizons, and are probably of Cambrian to Ordovician age (approximately 500 million years ago), similar to lithologies proved in several deep boreholes within 10 to 20 km of the Nottingham sheet.

The oldest rocks encountered by drilling are of Dinantian (Early Carboniferous) age, dating from about 350 million years ago. Their deposition commenced when the sea transgressed across the eroded basement rocks, some 50 million years after the end-Caledonian (Acadian) earth movements. Although only 152 m of these Lower Carboniferous strata have been proved in boreholes, seismic profiles show that they are thickly developed within asymmetrical rift basins that formed as this region was undergoing crustal extension. The principal syn-Dinantian depositional basins, shown in profile on section 1 of the Nottingham geological map (Sheet 126), were the Widmerpool Half-graben (or Widmerpool Gulf) and the Welbeck–Sleaford Low, which were progressively filled by turbiditic mudstone, siltstone and thin limestone. Between these two basins was the Nottingham Shelf, a tectonic ‘high’ across which an attenuated, limestone-dominated Dinantian sequence was deposited. The south-western margin of the shelf, and the transition to the Widmerpool Half-graben, is represented by a broad monocline, broken by the Cinderhill–Foss Bridge Fault System, along which basaltic volcanism occurred in late Dinantian times. Its north-eastern margin is defined by the Eakring–Foston Fault complex, to the north of which lies the deepest part of the Welbeck–Sleaford Low.

The succeeding Namurian strata, comprising the mudstone-dominated prodelta facies of the Edale Shale Group and the deltaic sandstone and mudstone of the Millstone Grit Group, represent a largely passive sedimentary fill to the rifted basins, which accumulated when differential, fault-induced subsidence had largely ceased. Towards the end of the Namurian, sedimentation in the Millstone Grit Group periodically outpaced regional subsidence, and thickly vegetated peaty swamps were established. Fluctuations in the rate of subsidence are reflected by distinct cycles of sedimentation; each cycle begins with marine or near-marine fissile mudstone (including ‘Marine Bands’), which passes up through mudstone into deltaic siltstone and sandstone. At the top of each cycle are the products of the compaction and alteration of peat and other organic material and soils, namely coal and seatearth. In its stratigraphically higher part, the Millstone Grit Group includes three thick sandstone sequences, namely the Ashover Grit, the Chatsworth Grit and the Rough Rock. These are the deposits of river deltas that built out into the rift basins from the east and south-east.

Through Westphalian times, sedimentation of muddy, shallow-water deposits, represented by the Lower, Middle and Upper Coal Measures, continued on a wide, equatorial delta plain that had been established across the East Midlands region. The sedimentary cycles increased in number but became generally thinner up-sequence. Swamps, with an abundant and diverse flora, marked extended periods when the area was above sea level, and led to the deposition of thick peat beds that were eventually to become exploitable coal seams. The Coal Measures range between 290 and 440 m in thickness and, on a regional scale, thin gradually towards the east. In the Lower Coal Measures, this thinning is accompanied by the progressive interdigitation of basalt lavas and volcaniclastic rocks, which eventually make up virtually the whole of the Lower Coal Measures succession in the south-east of the district.

Later in Westphalian times, earth movements initiated localised uplift and altered the sedimentation patterns. The resultant change to better-drained alluvial conditions is reflected in the strata of the Barren Measures, which comprise red mudstone, siltstone and ‘espley’ sandstone of the Etruria Formation, and the sandstone with minor seatearths and coals of the Halesowen Formation. The tectonic instability culminated in uplift and block faulting which characterised the end-Carboniferous phase of the Variscan orogeny (about 300 million years ago), when the Coal Measures basin was inverted and the strata exposed to subaerial erosion.

In the early Permian, landscape denudation proceeded under a harsh, tropical desert climate. By late Permian times, some 40 million years later, substantial thicknesses of Carboniferous strata had been removed by erosion, and a largely subdued rock desert terrain occupied much of the East Midlands. The underlying Carboniferous bedrock was deeply weathered and reddened, commonly down to depths of several tens of metres beneath the Permian. The erosion surface bore a veneer of the Permian Basal Breccia, a hard, dolomite-cemented rock that superficially resembles concrete in appearance. The Basal Breccia was formed from accumulations of angular rock fragments and pebbles that lay on the desert surface, and is generally less than 1 m thick. It directly overlies the Carboniferous rocks in the district and provides a useful marker in deep exploration boreholes for coal and oil.

Global warming in the late Permian (about 260 million years ago) resulted in melting of the polar ice caps and a rapid rise in sea level. The Permian desert was flooded by a warm tropical sea, the so-called Zechstein Sea, that extended over much of north-west Europe. The East Midlands lay on the south-western margin of the sea, with the shoreline extending north-westwards though the area now occupied by the centre of Nottingham, and then eastwards across the southern boundary of the district. The Zechstein Sea was highly saline, and magnesium-rich carbonate mud and sand with common shell fragments accumulated on the sea bed near the coastline. These formed the yellowish brown dolostone and dolomitic limestone of the Cadeby Formation (formerly known as the Magnesian Limestone). In later Permian times, falling sea level led to retreat of the Zechstein Sea and the emergence of saline mudflats with temporary lakes, in which the red-brown dolomitic mudstone of the Edlington Formation was deposited. The environment was unfavourable for both plants and animals, and these rocks are therefore devoid of fossils. Finally, at the end of the Permian and into early Triassic times (about 250 million years ago), desert sand dunes, occasionally eroded and redeposited by flash floods following rainstorms, advanced across the mudflats. These sands are now preserved as the reddish brown, buff mottled, fine-grained sandstone of the Lenton Sandstone Formation (formerly known as the Lower Mottled Sandstone), the stratigraphically lowest unit of the Sherwood Sandstone Group.

The Cadeby Formation is composed in part of coarse, rhomboidal dolomite grains, which give the rock a sandstone-like appearance. This stone, quarried in the Bulwell area (‘Bulwell Stone’), has been used as a walling stone in many parts of Nottingham, and as an ornamental stone, for example in rockeries. The Edlington Formation has less resistance to erosion than adjacent formations, and forms the bedrock beneath much of the low-lying ground of the Leen valley. The Lenton Sandstone Formation generally forms the rockhead below the lower slopes on the eastern side of the Leen valley, but underlies the floor and both the western and eastern flanks of the valley in the Lenton area. Due to its fine grain size and weak cementation, it has been quarried in the past as a naturally bonded moulding sand, for use in local iron and brass foundries.

By early Triassic times (about 251 million years ago), a major river system had been established across southern Britain. The river was fed by monsoonal rainstorms that fell on the Variscan mountains, near the site of present day Brittany, eroding sandy and pebbly detritus from these mountains and carrying it many hundreds of kilometres across the semi-arid landscape to the north. The river flowed across what are now central England, Cheshire, Lancashire and the Irish Sea, but at times was diverted eastwards across the East Midlands and out towards the area now occupied by the North Sea. The pebbly sands deposited by this river now form the Nottingham Castle Sandstone Formation, previously known as the Bunter Pebble Beds and representing the youngest Triassic component of the Sherwood Sandstone Group. This sandstone forms a conspicuous outcrop northwards from the city and, being freely water bearing, it provides a major part of the water supply in the area.

As the power and capacity of the early Triassic river declined, finer grained sand, silt and mud were laid down, now preserved as the Sneinton Formation (previously called the Waterstones), the oldest part of the Mercia Mudstone Group. Broad, flat alluvial plains occupied the East Midlands. They were well vegetated in places, with seasonal freshwater or brackish lakes that teemed with fish. Fossil footprints show that reptiles, distant ancestors of modern lizards and crocodiles, inhabited the district at the time, but the true dinosaurs were yet to evolve. Generally, the Sneinton Formation gives rise to an undulating incised topography, in which the more resistant sandstone beds locally produce marked features, but alluvial deposits of the River Trent and subsidiary streams cover much of its outcrop.

Eventually, as the climate once again became more arid, the East Midlands region was occupied by a playa, a low-lying plain occupied by mudflats and seasonal saline lakes. This increased aridity is indicated in the larger part of the Mercia Mudstone Group by such features as pseudomorphs after halite. The fast-flowing rivers gave way to intermittent streams that flowed into ephemeral lakes. There were times when the region was affected by extreme climatic aridity, similar to the conditions that prevail in saline mudflat environments of modern continental regions, which led to the formation of evaporitic gypsum deposits. Throughout these episodes, windblown dust provided a significant input to the thick mudstone sequences, and at times of increased rainfall sheet floods deposited relatively thin but often widespread beds of sand or coarse silts, now referred to as ‘skerries’. The Radcliffe Formation comprises well-laminated, red–brown, pink and grey–green mudstone and siltstone with subordinate fine-grained sandstone, and is named after its most complete surface section in river cliffs at Radcliffe on Trent [SK 646 398]. The Gunthorpe Formation comprises interlayered red-brown and grey-green mudstone, siltstone and very fine-grained sandstone. Thick beds of blocky mudstone are still exploited as brick clay, although less extensively than in the past. Numerous tough dolomitic siltstone and fine-grained sandstone beds commonly form upstanding topographic features. At the base of the Edwalton Formation is the Cotgrave Sandstone, which can be traced throughout the district. Above the Cotgrave Sandstone, the strata are of a similar lithology to the Gunthorpe Formation, but the top 7 m of the Edwalton Formation comprise the alternating sandstone and mudstone of the Hollygate Sandstone. The overlying Cropwell Bishop Formation comprises the usual red-brown to grey-green mudstone and siltstone strata, but gypsum is particularly common and locally forms thick units such as the Newark and Tutbury gypsum beds, formerly and currently exploited by both opencast and underground mining. The onset of a profound change in the depositional environment is indicated by the Blue Anchor Formation in the uppermost part of the Mercia Mudstone Group. This formation comprises grey-green to yellow-green dolomitic mudstone and siltstone, with features that confirm intermittent inundation by the sea.

Argillaceous, calcareous and locally arenaceous formations of predominantly marine origin, which occur between the Mercia Mudstone Group and the base of the Lias Group, constitute the Penarth Group, the main outcrop of which occurs in the face of the prominent ‘Rhaetic’ escarpment in the south of the district. Its lowest unit in the Nottingham district, the Westbury Formation, has a sharply defined base, which suggests a period of erosion prior to its deposition. This basal unit locally contains a representative of the nationally famous ‘Rhaetic Bone Bed’, with fragmentary remains of fish and reptiles. The overlying Lilstock Formation is represented mainly by the Cotham Member, comprising mudstone with discontinuous bands of limestone nodules.

By about 205 million years ago, fully marine conditions prevailed as the first strata of the Lias Group were deposited. The district lay beneath a shallow, open sea, sufficiently remote from the coast to be beyond the reach of coarse detritus, and yet close enough to receive a constant supply of finer debris. When the sediment supply was copious, thick beds of mud were laid down. In contrast, periods of diminished sediment supply are indicated by bands of impure limestone, incorporating the shells and skeletal remains of the organisms that were able to colonise the temporarily clearer waters. The earliest Lias Group strata of the Scunthorpe Mudstone Formation, comprising the Barnstone Member, feature ammonites belonging to the genus Psiloceras, the first appearance of which marks the beginning of the Jurassic Period. The Scunthorpe Mudstone and overlying Brant Mudstone Formation are shallow marine deposits; phosphatisation of some ammonites and the boring of limestone nodules suggest reworking and periods of low sediment input. The Jurassic strata, which crop out only in the southern part of the district (Figure 1), give rise to a subdued cuesta topography of escarpments and extensive, commonly drift-covered dip-slopes to the south-east of the Penarth Group outcrop.

The faults within the Permian and younger rocks generally have throws of only a few metres, the exceptions being the Harlequin, Cinderhill–Foss Bridge and Eakring–Foston faults, which have throws of up to 40 m. The last two structures have a long history of movement, indicated by their large throws, 250 m and 1200 m respectively, in the Carboniferous rocks at depth. These and other major faults in the district were active during the Carboniferous, and it is possible that some of the very minor earth tremors recorded in historical times may have resulted from continued slight movement, especially on the Cinderhill–Foss Bridge Fault. At the present day, tectonic and seismic activities in the UK are at a very low level, and the risks posed by naturally occurring earth movements are small. However, movement along faults can be re-activated by underground coal mining activities, a process that has caused serious damage to properties in several parts of Nottingham in the past.

The present-day landscape of the Nottingham district, along with that of much of the rest of the UK, was moulded by processes of erosion and deposition over the last 500 000 years of the Quaternary, and is therefore comparatively young in geological terms. The superficial deposits or drift of the district date from the Mid Pleistocene (about 450 000 years before present) to Holocene (10 000 years BP to present day) epochs. This period of Earth history is notable for several fluctuations in global climate, which resulted at high latitudes in periodic changes from very cold intervals, commonly marked by major glacial advances, to warmer interglacial episodes. The Anglian glaciation, commencing just under 500 000 years ago, deposited sheets of till and unconsolidated glaciofluvial sand and gravel, now preserved only as patchy, erosional remnants. Retreat of this ice sheet was followed by sustained uplift through the later part of the Anglian Stage and into the Devensian, resulting in at least three generations of river terrace deposits that are best developed in the trunk valley of the River Trent. The coarser, gravelly sediments were deposited during colder climatic periods, for example in the Late Devensian when rivers were swollen by glacial meltwater. The Trent valley deposits are the thickest and most extensive drift deposits of the district; they constitute a major aggregate resource and are also a local source of water. Quaternary slope deposits, broadly included in the category ‘head’, are partly periglacial and partly colluvial in origin, and date mainly from the Late Devensian and Flandrian stages of the Quaternary. They form veneers or infills to many of the topographically lower parts of the district. The youngest (Flandrian) drift deposits were laid down mainly in the overbank environments of rivers during the present temperate period that commenced about 10 000 years ago. They consist of alluvium, alluvial fan deposits, lacustrine deposits, shell marl and peat, which are developed mainly on the low-lying and periodically inundated parts of the Trent floodplain and tributary valleys. Landslips occur rarely, but have been observed on some of the steeper slopes of the district.

The earliest evidence for human activity in the Trent valley dates from about 500 000 years before present (early Palaeolithic period), but major modification of the landscape, in the form of forest clearance, agriculture and water-course management, probably did not commence until about 4000 years ago. Large scale re-modelling of the landscape by mineral excavation and man-made deposits postdates the major industrial expansion in the district that occurred after the second half of the 19th century. Man-made deposits are likely to occur wherever there has been artificial disturbance of the ground. They are therefore ubiquitous in all areas of human settlement, and are particularly extensive in urban areas. The most extensive developments of man-made deposits are shown on the 1:50 000 geological map of the district and are classified into Made Ground and Excavations. Such ground presents a number of potential hazards and constraints to planning and development, and must be identified and evaluated by appropriate investigations prior to construction. This aspect is developed further in the following chapter.

Chapter 2 Applied geology

Geological resources and constraints relevant to planning and development are reviewed in this chapter. It incorporates information from the more detailed account of the geological background to planning and development prepared for Nottingham City and its environs by Charsley et al. (1990). The geology of the Nottingham district dictates soil quality, the potential for mineral and water resources, and the suitability of foundation conditions, and may therefore impose constraints on development. These geological factors may be considered alongside others, such as existing and proposed land use, demand for housing and industrial development, communications, conservation and amenity areas, archaeological interest and agricultural land potential. The information presented here should be used in conjunction with, but not as a replacement for the detailed and comprehensive development plans, specifications and advice (e.g. for waste disposal, water supply, flood-risk) provided by the local councils or bodies such as the Environment Agency.

Mineral resources

The Nottingham district is well endowed with mineral resources (see ‘Information sources’, p.186) and the historical prosperity of the city was founded to a large extent on their exploitation. The district remains a significant producer of gravel, sand, gypsum and brick clay, and also includes a building stone quarry. There is the potential for oil discoveries and, perhaps in the longer term, for renewed exploitation of the coal reserves. In this chapter, ‘mineral resources’ covers those minerals and other geological deposits that have the potential for economic exploitation. Mineral reserves, implying quantified deposits that could be extracted economically, are not considered in detail because many factors, such as land value, extraction costs and proximity to markets, have to be considered before reserves can be identified. This requires a comprehensive evaluation and is beyond the scope of this memoir.

Mineral workings can present problems for post-extraction land use, which are likely to be resolved only by resorting to geotechnical or hydrogeological advice. For example, the increasing use of quarries and pits for waste disposal has the potential to produce a widely developed but localised hazard from toxic leachates and dangerous gases. This is potentially a serious hazard at landfill sites situated on deposits in hydraulic continuity with an aquifer, which would be the case for those hosted in former quarries located on the Sherwood Sandstone Group or on the floodplains of major rivers or their tributaries.

Underground mining may involve local subsidence damage, and will produce waste material, the disposal of which commonly creates a demand for tip sites. Such tip sites sterilise the underlying area for further shallow mineral extraction, and present the planner with further problems regarding use of the newly made ground. In such circumstances, geological and geotechnical information on ground conditions can be used to ensure that informed decisions are made prior to allocating land for tipping.

Coal

Coal has been mined in the surrounding region, part of the Yorkshire and East Midlands Coalfield, for hundreds of years. Up to the 15th or 16th century, mining was restricted to the working of coal from its outcrop or by using shallow ‘bell pits’, and so was not important in this district. A desire to reach deeper coal reserves resulted in the introduction of the ‘pillar and stall’ mining system, and as the depth of working increased, larger pillars were required to support the roof. A new approach to deep mining was eventually provided by the development of longwall mining, beginning in Shropshire in the 17th century, and this was still the main method used until recently in the concealed coalfield of Nottinghamshire. Coal seams that have been exploited are those between (and including) the Blackshale and Ashgate seams in the Lower Coal Measures, up to (and locally including) the High Main seam of the Middle Coal Measures. Typical thicknesses of the various seams are summarised in Table 1. Coal quality varies widely, but Coal Rank Codes of between 702 and 902 (weakly caking to non-caking with over 36 per cent volatile matter) are typical, with ash contents generally in the range of 2 to 8 per cent.

The economics of deep coal mining have undergone a succession of reviews since the 1950s, resulting in progressive closure of older mines (Table 2). Calverton Colliery (Plate 1) was the last of the working mines sited in the district to close. Coal resources beneath the district remain substantial, especially in the North-East Leicestershire (Vale of Belvoir) Prospect, in the south-east of the district (Carney et al., 2004). However, the recent (1997) closure of Asfordby Colliery [SK 725 206], near Melton Mowbray<span data-type="footnote"> news item, in Mercian Geologist, 1998, Vol. 14, 102</span>, has cast considerable doubt on the future viability of exploiting the coal resources within this prospect, and the opening of new mines anywhere in the district is unlikely at the time of going to press.

Sand and gravel

The sand and gravel resource of the district consists mainly of Quaternary deposits laid down by the present and former rivers occupying the Trent valley. These include gravels beneath the recent alluvium and those constituting the river terrace deposits, both within the modern floodplain or flanking it. The extraction of gravel for use as aggregate is the primary reason for these sand and gravel quarries. However, the workings also provide sand (forming about 50 per cent of the deposits) as an important and readily marketable by-product.

The sand and gravel resources in the Trent valley itself comprise the recent alluvium and lower terrace deposits (Holme Pierrepont Sand and Gravel), although the working of such deposits is prone to disruption by high water tables and periodic flooding. Sand and gravel has been produced most recently in the district from separate operations in the Trent valley at Hoveringham [SK 71 48] and Holme Pierrepont [SK 634 394]. Downstream from Radcliffe on Trent, towards the workings at Hoveringham, there are considerable tracts of alluvium and river terrace deposits on each side of the river that remain as a substantial resource (see also Charsley et al., 1990, table 8).

The sand and gravel deposits of the Trent alluvium lie beneath an overburden that is generally less than 1 m, but locally up to 5 m thick (Spenceley, 1971). The overburden comprises a thin layer of topsoil over sandy or silty clay, with less common organic clay or peat. Spenceley (1971) showed that the thickness of the sand and gravel between Colwick and Holme Pierrepont [SK 623 397] is independent of surface form (whether beneath the floodplain or a terrace), and is related to variations in the depth of the underlying bedrock surface. In general, however, the greatest thickness has been recorded from the central parts of the floodplain: maximum values of over 4.5 m in the Colwick area (Spenceley, 1971), 10.8 m in a borehole at Wilford [SK 5742 3748] and about 10 m near Hoveringham. Sand and gravel is absent in some places where deep channels cut in the bedrock are filled with clay or silt.

Few boreholes have been drilled in the greenfield resource areas, so the presence of gravel there is in some doubt. Any calculation of reserves is dependent on detailed surveys using a grid of boreholes sited on the basis of at least one borehole every 75 m, together with geological and geophysical interpretation. Use of any published figures for sand and gravel yields per hectare may be misleading, and potential yields should be established on an area-by-area basis prior to the release of land, so that areas of low yield can be avoided. In general, average yields for the Trent valley are reported to be between 55 000 and 65 000 tonnes per hectare (George, 1984), although actual yields are between 30 000 and 100 000 tonnes per hectare, and can exceed the latter value (Nottinghamshire County Council, 1984, 1997).

Although gravel also occurs beneath the alluvium and terrace deposits of other valleys in the district, extractable volumes are limited or the land has been extensively built over. The exception occurs within an area of about 0.9 km2 of Leen Sand and Gravel north of Bestwood [SK 555 505]. The higher terrace deposits (Bassingfield, Whatton and Balderton sands and gravels), lying outside the modern Trent floodplain, also constitute a potential resource, but are patchy in their occurrence. Former workings in the Bassingfield Sand and Gravel show it to be clay-rich in part, with highly variable gravel content. Nevertheless, there is a resource area of about 1 km2, which has not been entirely built over, between Gamston [SK 605 375] and Radcliffe on Trent [SK 636 385] in the southwest of the district.

Sand

Sand is the main component of the Sherwood Sandstone Group, weakly cemented parts of which have been quarried widely in the past. Both the Nottingham Castle Sandstone and the underlying, finer grained Lenton Sandstone formations are mainly loosely consolidated, and are thus easy to work. Because of the limited demand for sand, there exists a virtually unlimited resource in the non-urbanised parts of the Sherwood Sandstone Group’s outcrop, which extends from the city outskirts northwards. In general, sand obtained from the group, particularly its lower part, is finer grained and better rounded than that of the Trent valley deposits. The sand is more suitable for building and asphalting than the latter, which typically provides the ‘sharp’, coarser grained sand required for concrete. Former underground mining of sand has left extensive cave systems just north of the Nottingham city centre, adjacent to Mansfield Road (the ‘Peel Street Caves’; see also below).

Sand with almost no pebble content has been quarried from the Sherwood Sandstone Group at several places, for use in building and construction. Quarries in the Lenton Sandstone Formation (formerly the Lower Mottled Sandstone) were worked for iron, brass and other metal foundries in the past, for example at the Queens Medical Centre in Lenton [SK 546 388] and at Bobbers Mill [SK 553 415]. The fine grain size and clay content made the sand particularly suitable as a moulding material, but there is now very little demand for sand for this purpose.

A sand quarry near Bestwood [SK 564 479] has been used as a waste disposal site. The Burntstump Quarry [SK 588 500], in the Nottingham Castle Sandstone Formation, is a resource for both sand and gravel, and the reserves in the area around the quarry are extensive.

Gypsum

Gypsum (hydrous calcium sulphate) was formerly worked from various parts of the Mercia Mudstone Group in the southern part of the district, but is now extracted only from the upper part of the Cropwell Bishop Formation. The resource is generally of mill and cement grade, with special uses in plasterboard manufacture. There are no records of alabaster quarrying. The positions of the main gypsiferous horizons in the sequence are summarised in Table 3.

Gypsum occurs mainly as veins, cross-cutting but also concordant with the bedding. Exceptionally, veins are up to 22 cm thick, but more commonly are much thinner. They are not confined to any particular stratigraphical level, but occur in both the lower parts of the Edwalton Formation and in the underlying Gunthorpe Formation. Examples of this type of occurrence can be seen in the river cliffs at Radcliffe on Trent [SK 6160 3935] and at Gunthorpe Weir [SK 6880 4370]. The mined gypsum in this area was of the fibrous satinspar variety, and was used for beads and other ornaments as well as for flooring plaster (Lamplugh et al., 1908; Du Boulay Hill, 1932). Although resources of this type of gypsum are substantial, the general thinness, impersistence and geometry of the veins mean that future extraction is unlikely.

The main mined gypsum in the East Midlands comes from the Cropwell Bishop Formation (Table 3). Although this formation is highly gypsiferous, with nodules and concordant to crosscutting veins, certain parts have been exploited more than others, and it is generally not possible to define the gypsum resources of the district without a detailed drilling programme. Gypsum is rarely present in the top few metres on the outcrop due to solution, so that surface mapping of individual gypsum beds is not possible. Over much of the Nottingham district, the Tutbury Gypsum has lost its identity as a viable gypsum resource, although it has been extensively mined as a single thick ‘seam’ farther south, around East Leake and Barrow upon Soar (Charsley et al., 1990; Carney et al., 2001, 2004).

The Newark Gypsum of the Cropwell Bishop Formation (p.128) has been the main focus for extraction by quarrying and underground mining in the district, the three principal centres of activity being around Cropwell Bishop [SK 675 355], Orston [SK 763 402] and Flawborough [SK 790 430]. Unlike the Tutbury Gypsum, it comprises multiple beds, each of which varies in form from layers of nodules (‘balls’), lenticular masses (‘bullets’ or ‘cakes’) to beds. Individual gypsum-bearing layers have been given names in the belief that they can be traced between Cropwell Bishop and Newark. However, considerable caution should be exercised due to the impersistence of many such beds. The gypsum ‘seams’ or beds recognised at Cropwell Bishop are listed here in stratigraphical order, the uppermost units first: Red Fumblers, Cocks, Pinks, Cakes, Top Rock Riders, Bottom White, Blue Rock, Rough Nodules, Rough Balls, Soft Floor Bottom Nodules and Lower Bottom.

The whole sequence of the Newark Gypsum seams spans about 18 m in the upper part of the Cropwell Bishop Formation. Purity varies, both between and laterally within beds, but generally the best quality material comes from the Bottom White and Blue Rock gypsum. The impersistence of the gypsum beds, and their considerable variation in thickness over short distances, relate partly to original local nondeposition and partly to postdepositional solution. The Cocks attains the greatest thickness, being up to 1.68 m thick in places. Of the other beds, the Pinks, in places comprising two separate beds, may be up to 0.88 m thick. Other seams typically range between 0.1 and 0.3 m thick, and are rarely more than 0.6 m.

Surface extraction from the Newark Gypsum is currently being carried out at Kilvington Quarry [SK 795 435] (Plate 16), following its re-opening by British Gypsum in 1995. The gypsum from there is processed at the nearby Jericho plant [SK 805 505] for plasterboard manufacture. A whole series of former gypsum surface workings occurs between Kilvington Quarry, in the south, and the disused Beacon Hill Quarry [SK 812 542] farther north (Nottinghamshire County Council, 1997), including Bantycock Pit [SK 810 497].

Gypsum has been quarried around Cropwell Bishop since the 19th century (Firman, 1964; Charsley et al., 1990, map 6), but this activity ceased in 1995. During later quarrying activities, the topsoil was stockpiled and gypsum extracted using a dragline or excavators and dump trucks. After the gypsum had been separated, the spoil was used as backfill so that, at any time, the open pit occupied a relatively small area (about 15 hectares). The underground mining of gypsum around Cropwell Bishop was by the ‘pillar and stall’ method (see below), and this is still the practice at the new Barrow upon Soar mine in the adjacent Melton Mowbray district (Carney et al., 2004).

Gypsum was worked from the middle and lower parts of the Mercia Mudstone Group in the East Bridgford area [SK 69 43] from the 17th or 18th century to about the 1940s (Firman, 1964), but no detailed records of the workings are known. The sites of six former shafts into the Edwalton Formation have been located in the village itself (Charsley et al., 1990, map 6), and others almost certainly exist. Gypsum was also probably worked from shallow pits near the cliffs on the River Trent north-east of East Bridgford and from local brickworks.

Gypsum mining (see also ‘Underground gypsum mining’ p.30) at Orston probably commenced in medieval times, and was first documented in the 16th century. Mining, mainly by underground pillar and stall methods, expanded greatly in the mid 19th century, with the construction of a plaster works and kilns for firing bricks and tiles derived from quarrying the associated mudstone. Underground mining ceased in 1894, following a roof collapse, but further reworking of the remnant pillars by opencast methods continued into the early 20th century. The history of mining at Orston has been documented in detail by Barnes and Firman (1991).

Brick clay

Brick clay in the UK is obtained mainly from weakly to moderately consolidated mudstone or claystone, which may require some crushing and mixing with water to provide workable ‘clays’. The main brick clays in the district occur in the Mercia Mudstone Group, particularly in the Edwalton Formation but also in the Gunthorpe Formation. The outcrops of both formations are scattered with numerous small clay pits, some of which produced tiles and pottery as well as bricks.

The sole working brick pit in the district is that run by Ibstock Brick Ltd at Dorket Head [SK 595 473]. Mudstone and siltstone are dug from the lowest 15 to 20 m of the Gunthorpe Formation. The permitted reserves here are considerable, and permission to extend the pit has been granted subject to certain conditions, including the requirement for progressive backfilling of the workings with domestic, commercial and nonhazardous industrial waste.

Elsewhere in the east and south of the district, the Gunthorpe Formation has been the main resource for large-scale brickmaking operations. Two stratigraphical levels have been traditionally favoured; the lowest beds, i.e. those still worked at Dorket Head, and a level just below the Cotgrave Sandstone at the top of the formation. This is due to the geomorphological requirements for extraction as much as the suitability of the lithology, since the presence of overlying, shallowly dipping, resistant beds at both levels results in a well-developed scarp slope, allowing easy access and creating only minimal overburden. The lithology in both cases is dominated by red-brown blocky mudstone with subordinate siltstone. Former brick pits were located at Wilford [SK 568 355], Edwalton [SK 588 362], Harlequin [SK 659 392], Carlton [SK 604 411] and Thorneywood [SK 595 414].

Limited local use has also been made of mudstone beds within the Middle Coal Measures for brick making; for example, bricks were made from mining spoil at Clifton colliery [SK 565 379].

Building stone

Stone has been quarried in the district since medieval times. It is believed that much of the sandstone for Nottingham’s Norman castle came from quarries at St. Ann’s [SK 579 408], dug into the Sneinton Formation (Waterstones). There were further quarries between Sneinton and Gedling (Lott, 2001), which are now obscured by urban development. However, in view of the difficulty of working relatively thin beds within a mudstone/siltstone sequence, and of the trend to replace natural stone in construction by reconstituted stone, the Sneinton Formation sandstone has little or no potential as a source of building stone.

The Lower Magnesian Limestone (now part of the Cadeby Formation) was the traditional building stone of the district, and has been extensively quarried as ‘Bulwell Stone’, mainly to the west of the district. This stone is presently worked only at Bulwell [SK 532 455], just west of the district, the current output being mainly rough blocks for ornamental purposes (Lott, 2001). The locations of small, disused pits to the north of Bulwell around [SK 54 48] are given by Charsley et al. (1990, map 6).

Small amounts of flaggy-bedded limestone have been excavated for local building purposes in the east of the district, from the outcrop of the Lower Jurassic Barnstone Member (Scunthorpe Mudstone Formation, Lias Group).

Mine stone

A feature of underground coal mining is the extraction of large quantities of spoil in the form of mudstone, siltstone, sandstone, ironstone, waste coal/dirt and seatearth, known collectively as mine stone. The more extensive spoil tips, adjacent to former colliery shafts, often form small, steep-sided hills, such as that at Calverton Colliery [SK 605 510]. Many of the spoil tips close to abandoned collieries have been landscaped and given over to agriculture or recreational use. Enormous reserves of mine stone exist in the district, but as many of the older tips now form landscape features, quarrying would be restricted. In addition, the use of mine stone is limited to some extent by its mineralogy, since it commonly contains pyrite, which may oxidise to produce sulphurous chemicals, and waste coal, which is combustible.

Oil

The East Midlands has been actively explored for hydrocarbons since the First World War, but it was mainly the discovery of the Eakring, Duke’s Wood, Caunton and Kelham Hills oilfields in the years 1939–1943 that stimulated further exploration (Lees and Taitt, 1946). The Nottingham district lies to the south and west of these producing wells and oilfields, but is nonetheless of interest because it includes the north-eastern margin of the Widmerpool Half-graben and the south-western margin of the Welbeck-Sleaford Low. Both of these structurally bounded basins are considered to be major sites of potential hydrocarbon generation. They were actively subsiding during Early Carboniferous times (Chapter 9), and in the case of the Widmerpool Half-graben, more than 5000 m of carbonaceous mudstones and limestones were deposited to the south of the district in Dinantian times (Ebdon et al., 1990; Carney et al., 2001, 2004).

The main oil-prone source rocks of the East Midlands oilfields are strata of the Edale Shale Group, dating from Pendleian (Carboniferous, Namurian) times (Fraser et al., 1990), which form a south-westwards-thickening sequence that attains about 650 m in the Widmerpool Half-graben, immediately to the south of the district (Carney et al., 2004). The migration and entrapment of oil was in part controlled by structures that formed along the edges of the basins during their inversion at the time of the end-Carboniferous (end-Variscan) compressive event (Fraser et al., 1990; Fraser and Gawthorpe, 1990). The latter authors consider, however, that Variscan uplift and erosion would have effectively frozen oil generation and migration, and that the success of this hydrocarbon province is partly due to a later Mesozoic phase of burial that regenerated hydrocarbon production in the Carboniferous source rocks. The Variscan traps were then re-occupied, until oil migration was subsequently arrested during regional Cenozoic tilting and uplift (Chapter 9). These conclusions bear out the suggestion of Holliday et al. (1984) that oil generation, although probably beginning in the Westphalian, later resumed in the Mesozoic and continued until at least the end of the Cretaceous, there being at all times closed structures into which the oil could migrate (Fraser and Gawthorpe, 2003). Reservoir rocks with the best potential for accumulating oil in the East Midlands are Upper Carboniferous sandstones of channel facies (Fraser et al., 1990), although Dinantian carbonates, if sufficiently fractured, could also be considered. A wide range of porosity and permeability values from Carboniferous reservoir rocks of the East Midlands oilfields has been recorded (Holliday, 1986; Berridge et al., 1999), with mean values of 12 per cent porosity and 13–14 milliDarcys permeability for sandstones of the Millstone Grit and the Lower and Middle Coal Measures. For Upper Coal Measures sandstones, the mean values were 15 per cent porosity and 60 mD permeability.

Extensive seismic exploration has been carried out in the district, and a number of deep oil exploration boreholes have been drilled (Charsley et al., 1990). To date, the oil finds with the most potential have been hosted mainly in Carboniferous sandstone reservoir rocks of Namurian to early Langsettian (Westphalian) age. However, significant oil showings have also been produced from fractures in Westphalian basaltic sills, for example, during drilling through the Norton or Kilburn Sill in the Harlequin No. 1 exploration borehole<span data-type="footnote"> Brief details of selected boreholes are given in (Table 21)</span>. Other ‘plays’ that have been considered include fractured Dinantian limestone and, to the east of the district, fractured pre-Carboniferous basement. The nearest find to the district was from the Langar No. 1 Borehole in 1958, which produced 198 barrels per day on test from a reservoir in the Kinderscout Grit (Millstone Grit Group). However, four further appraisal wells failed to get production. The Langar No. 1 well (Sheet 142) is located along the crest of the faulted monocline that delimits the north-eastern margin of the Widmerpool Half-graben, and is about 1 km north-west of the Plungar oilfield. The latter, in the adjacent Melton Mowbray district, comprised a cluster of 33 wells that collectively produced a modest amount of oil (304 067 barrels) between 1953 and 1982 (Carney et al., 2004).

Limestone, dolomite and ‘marl’

Limestone, dolomite and‘marl’(calcareous mudstone) were all previously exploited in the district, but none is regarded as having economic potential at the present day.

Limestone was formerly burnt to produce lime, suitable for the manufacture of Portland cement, as well being used for other products, including local building stone (Lamplugh et al., 1909; Carney et al., 2004). The resource occurs in the south-east of the district as a succession of separate thin beds within the Barnstone Member (Hydraulic Limestones) of the Scunthorpe Mudstone Formation (Lias Group). Charsley et al. (1990, map 6) show the distribution of former limestone pits. Of these, only the complex of quarries around Langar and Barnstone [SK 740 351] occur in the district. Fletcher (1980) described the working of limestone around Langar by a company that was formed in 1875 and at its peak was producing 2000 tons of clinker per week for the manufacture of Portland cement. Quarrying ceased in 1969, by which time the company had been importing Lower Lincolnshire Limestone from their quarry farther south, near Waltham on the Wolds [SK 813 253].

Dolomite for calcining to a dolomitic lime, and for experiments in calcium silicate brick manufacture, was obtained locally to the west of the district, from the Cadeby Formation. The main economic product of this formation, however, was building stone (Lott, 2001).

‘Marl’ pits abound on the outcrop of the Mercia Mudstone Group, and the extracted material was traditionally used in agriculture to improve sandy soil. In this instance, ‘marl’ is a misnomer since most of the extracted material lacks sufficient calcium carbonate to warrant the name, but this is well-established local terminology. Some marl pits were also dug to supply material for small-scale brick making or flooring. Many of these are shown as clay pits on the 1:10 000 scale maps of the district, and on map 6 of Charsley et al. (1990).

Base metal and uranium mineralisation

Within the Mercia Mudstone Group, green spots within red brown beds, traditionally known as ‘fish eyes’, have minute black cores composed of uranium and copper minerals (Aljubouri, 1972). They are commonly developed in the Cropwell Bishop Formation associated with gypsum. Rare occurrences of malachite, a hydrated copper carbonate mineral, have been recorded from gypsum workings at Cropwell Bishop.

Other resources

Caves

Man-made caves excavated into the relatively soft strata of the Sherwood Sandstone Group have been present under Nottingham for at least a thousand years.

During this time, they have been used for such diverse purposes as wells, cesspits, store rooms for grain, wine, fish and meat, breweries and tanneries, dwellings and hideaways, routes of communication, decorative follies, shelters in time of war (both in medieval times and in the Second World War) and as a source of building sand. At present, several of the caves are used for beer storage and as cellars under private properties, and some are promoted as tourist attractions. Charsley et al. (1990, table 10) list caves and their present usage, and highlight some that might be considered for development. Many of the caves in use at present have only limited public access and are little publicised; there exists a considerable opportunity for further tourist development. Other than for use in tourism, some of the caves still have potential to be converted into emergency shelters. It must also be remembered that the excavation of caves is a relatively simple and low cost operation and that extensions to existing caves or the creation of new ones for various purposes is possible. Cave locations and their geohazard potential are discussed below (p.31).

Waste disposal sites

The ideal site for waste disposal is a large excavation into dry, impermeable strata that can be backfilled, the waste then being compacted to the former ground level and used for construction or agriculture. Geological considerations are therefore important, not least because the site will generally be a void that has been created by economic mineral extraction. For example, it may well be a major consideration in the economics of initial mineral extraction that the excavation can be used later for profitable waste disposal. Furthermore, the planning permission granted for mineral working may be conditional on the type of backfilling and restoration work that will be carried out once extraction has ceased. Geological and geotechnical factors are also of prime importance when considering the nature of the bedrock and its structure, which together may determine the potential for unconfined toxic and explosive substances, including gases and leachates, to migrate out of the site and produce an environmental hazard. Nowadays, however, it is common practice to convert unfavourable geological sites into useful assets by the construction of sealed cells and by venting any gases created by biodegradeable waste. Airborne radiometric surveys, backed up by groundbased subsurface techniques, are increasingly being used to monitor the extent of leachate plumes around leaking landfill sites.

The spreading of waste material on derelict, unused or low-lying waterlogged land has been widely followed in Nottingham city and its environs, as described by Charsley et al. (1990). Some of the principal spreads of Made Ground are indicated on the 1:50 000 geological map (Sheet 126), and those not shown appear on the accompanying 1:10 000 scale maps. Such landfill may have the disadvantage of sterilising a resource; for example sand and gravel deposits in the Nottingham city area. In other locations, there may be environmental or nature conservation issues to consider.

Soils

Soils and drainage are major factors used to classify the quality of agricultural land. To a great extent, both are dependent on the underlying geology. Around Nottingham city, land quality varies from Grade 2 to Grade 4, Grade 3 being the most common (Dittmer, 1984). The soils and drainage contributing to the better Grade 2 land of the district are developed mainly on the outcrops of the Mercia Mudstone Group and on the Permian strata of the Edlington Formation and the upper part of the Cadeby Formation. Grade 3 land is commonly developed on the outcrop of the Sherwood Sandstone Group. Predictions as to the quality of the soils for agriculture in a given area can be made by reference to the geological map on which the bedrock units may be identified and any cover of drift deposits noted.

Geological sites of scientific and educational interest

Exposures of rocks and superficial deposits that demonstrate the geology and geomorphology of the district form a resource for educational and research purposes. The main way to preserve such sites is by designating them as Sites of Special Scientific Interest (SSSI), Regionally Important Geological Sites (RIGS) or Local Nature Reserves (LNR). There are a number of such sites within the district, and although most were designated for their ecological importance, many also display notable geological features. All such SSSIs and LNRs in the district are listed in Table 4, in which their geological interest is also indicated.

Geological site recording for Nottinghamshire has been carried out by staff at the Wollaton Natural History Museum, run by the Nottingham City Council, as part of the National Scheme for Geological Site Documentation (NSGSD), initiated in 1977 and financed by the Nature Conservancy Council. The aim of the scheme is to provide a source of information on sites of scientific and educational value for planners, educationalists, researchers and others. Information is readily available from records of the National Scheme for Geological Site Documentation or from the BGS, and advice can be obtained from the Natural England.

Also occurring in the district are some fine geological sites that are not currently preserved or protected in any way. Many parts of the geological sequence can be demonstrated at natural exposures that are unlikely to be destroyed or covered, for example the cuttings in the Lenton Sandstone Formation behind the Queen’s Medical Centre [SK 545 387] or the type section of the Nottingham Castle Sandstone Formation at Castle Rock [SK 569 394]. Other sections, equally important but at greater risk, are listed here.

Sections in the Lenton Sandstone Formation showing aeolian sand dunes in the former moulding sand quarry at Bobber’s Mill [SK 553 415]. This locality also includes sections in periglacially disturbed glacial sand and gravel.

The section at the boundary between the Lenton Sandstone and Nottingham Castle Sandstone formations in the yard of the former Bestwood Colliery [SK 558 474].

The type section of the Sneinton Formation in the former railway cutting off Colwick Road [SK 592 397].

The section in the Hollygate Sandstone in the former railway cutting at Edwalton [SK 590 396].

Water resources and flooding

This section, mainly compiled by C S Cheney, complements the detailed hydrogeological account of Nottingham City and its environs provided by Charsley et al. (1990). The resource aspects of water as well as flooding problems are discussed. In the west of the district, the average annual rainfall is 707 mm over 123 raindays (data from The Meteorological Office, 1961–1990 figures for the station at Watnall, Nottingham), declining to about 600 mm to the south and east of the River Trent. Mean annual evaporation is of the order of 460 mm. Excess precipitation is stored mainly as groundwater within the Sherwood Sandstone Group and as surface water within the River Trent and its tributaries. For these principal water resources, the situation in 1999 was that ‘...the local resources, aquifers and main rivers, meet the water needs of the major domestic, agricultural and industrial demand centres...of the East Midlands’ (Environment Agency, 1999). Currently, however, the regional trend is for a reduction in the amount of water available for use over a large part of the East Midlands. This was largely attributed to planned groundwater licence reductions to alleviate stressed aquifers, but also took into account the dryness of the present climate and the probable impact of future climatic changes. Such factors may necessitate increased abstraction from the River Trent, as well as the importation of groundwater from the Birmingham area during low flow periods.

Groundwater

The Sherwood Sandstone Group constitutes the only major aquifer in the district, and is one of the most important in Britain. The Coal Measures, Cadeby Formation and Mercia Mudstone Group form minor aquifers, but the Penarth and Lias groups only have the potential to provide extremely limited local supplies of groundwater. Allen et al. (1997) have described in detail the physical properties of the Sherwood Sandstone in the district (as part of north-east England), and Jones et al. (2000) have described the physical properties of the minor aquifers. The importance of the groundwater resource often causes restrictions to be placed on development that may cause pollution, either to the Sherwood Sandstone aquifer or to the minor aquifers.

Groundwater abstraction licence data for the Sherwood Sandstone aquifer and minor aquifers, together with water use, are shown in Table 5. In some parts of the district, surface water flows are maintained by base flow, predominantly from the Sherwood Sandstone aquifer. Abstraction licence data for surface water sources have therefore also been included in Table 5 for comparative purposes. It should be noted that the table reports maximum licensed abstraction volumes and that the actual abstraction is generally 20 to 40 per cent lower. The effect of over-abstraction within the district, causing the lowering of water levels and reductions of base flow to streams and rivers, was noted as early as 1897 in the particular case of the Dover Beck (Lamplugh et al., 1908). Over-abstraction problems still existed in 1963, but thereafter an embargo on new licences has attempted to redress the balance (Charsley et al., 1990).

The largest groundwater abstractions are from the Sherwood Sandstone aquifer for public water supplies and industry. Abstraction for public supply takes place to the north and north-east of Nottingham, whereas industrial abstraction, predominantly for laundries, bleaching and dyeing, the pharmaceutical industry and brewing, is concentrated within the Nottingham urban area. By comparison, the quantities of groundwater abstracted for general agricultural purposes are small, but the large number of licences in the riverine gravels and Mercia Mudstone Group also illustrate the importance of these minor aquifers to the agricultural community. Much larger are the total licensed quantities for spray irrigation, but this is almost entirely concentrated in the Sherwood Sandstone aquifer. The limited amounts of groundwater obtained from the Coal Measures and Cadeby Formation are commonly for industrial use.

Coal Measures

The Coal Measures constitute a complex, multilayered aquifer. Argillaceous strata predominate, and act as aquitards or aquicludes, with occasional thicker sandstone levels effectively acting as separate aquifers. However, the potential of the sandstones to act as aquifers is limited by their small outcrop area (Downing et al., 1966; Holliday et al., 1984). Furthermore, the sandstone is commonly fine-grained, micaceous, well cemented and weakly permeable, so groundwater storage and transport is largely dependent on fractures. The Coal Measures are extensively faulted, and the fracturing can connect previously isolated aquifers, although it can also lead to the development of isolated blocks of aquifer and a lack of lateral hydraulic continuity. In many places, fracturing is the effect of subsidence, the legacy of past mining.

Within the district, few boreholes, wells or shafts penetrate the Coal Measures without first passing through either the basal strata of the Sherwood Sandstone Group or the Cadeby Formation. In places, both aquifers are present in vertical sequence above the Coal Measures. Under these circumstances, it is frequently difficult to define contributions from each aquifer to the total yield. However, yields of boreholes and wells penetrating only the Coal Measures are dependent not only on penetrating a productive horizon, but also upon encountering fractures of an adequate size and lateral extent. Yields are consequently highly variable. The largest yield was from a 200 mm diameter borehole at the Raleigh Cycle Works [SK 5494 3981], which provided 23 litres per second (l/s) for a drawdown of 16.7 m. Production may decline over the long-term due to depletion of storage in the sandstones, since these have no local outcrop and receive little recharge. Generally poor yields have resulted in only limited use of the resource.

Little information is available on groundwater levels in the Coal Measures, but mine drainage problems have affected most areas. There is a considerable risk of surface and near-surface contamination from poor quality mine water, following rises in groundwater levels after the closure of collieries and the consequent cessation of pumping. In a conceptual model for the Nottinghamshire coalfield suggested by Dumpleton and Glover (1995), groups of collieries most recently being pumped were considered to form an interconnected pond, the main one being that shared between the Woodside [SK 448 444], Annesley–Bentinck [SK 488 550] to [SK 518 533] and Calverton [SK 6035 5018] collieries. Although the mine water from these is in equilibrium during pumping, cessation of pumping will result in zones of enhanced transmissivity and invasion of the overlying Permo-Triassic strata, as well as mine water discharge into surface watercourses. The non-pumped, isolated ponds, comprising closed collieries such as Blidworth [SK 594 566], Gedling [SK 612 440], Clifton [SK 565 380] and Cotgrave [SK 652 364], will almost certainly feature rising mine waters, which could contaminate the Permo-Triassic aquifers (Cadeby Formation, Sherwood Sandstone Group).

Groundwater quality is generally good at outcrop. The groundwater is of the calcium bicarbonate type, being hard to very hard with low chloride concentrations (of the order of 30 mg/l) and sulphate commonly less than 100 mg/l (Downing et al., 1966). Where the Coal Measures aquifer is confined beneath Permo-Triassic strata, the groundwater may be mineralised, of sodium chloride type, with elevated concentrations of sulphate and iron due to the dissolution of iron pyrites. Examples from near outcrop (Nottingham Dairy Co. [SK 5487 3947]) and under confined conditions (Bestwood No. 1 sump [SK 565 380]) are included in Table 6. The latter example is only a partial analysis, but serves to illustrate the more highly mineralised nature of the groundwater.

Cadeby Formation

The aquifer in the upper part of the Cadeby Formation (formerly the Lower Magnesian Limestone) ranges in thickness from about 5 to 15 m in the district, and is generally confined below the Edlington Formation. In many parts of the district, the lower part of the Cadeby Formation comprises dolomitic argillaceous siltstone or mudstone, previously termed the ‘Lower Marl’, which acts as an aquiclude and isolates the aquifer from the underlying Coal Measures. However, the ‘Lower Marl’ is not always present, and the Cadeby Formation as a whole is absent in the southern part of the district, where the Sherwood Sandstone Group aquifer directly overlies the Coal Measures.

Groundwater in the Cadeby Formation is contained within and flows through fractures. Borehole yields are entirely dependent on the size and lateral extent of the fractures that they penetrate. As a result, they are highly variable, although commonly sufficient to meet the relatively small local demand. Seasonal groundwater level variations are large, with a range of up to 7 m in some parts of the district (Charsley et al., 1990). The highest recorded yield of 13 l/s for a drawdown of 6.9 m was from a borehole of 430 mm diameter at Bagnall Road [SK 5458 4338], but yields are mostly less than 5 l/s.

Groundwater is generally potable although hard, with carbonate concentrations commonly in the range of 400 to 600 mg/l. Nitrate concentrations may be high in outcrop areas (Charsley et al., 1990), predominantly due to contamination from agricultural sources.

Sherwood Sandstone Group

The Sherwood Sandstone Group is the most prolific aquifer in the district, and is of particular importance for public water supply and industrial use (Table 5). It consists of two separate formations, the basal Lenton Sandstone Formation, composed of fine- to medium-grained silty sandstone with minor mudstone and siltstone, and the overlying Nottingham Castle Sandstone Formation, consisting of poorly cemented, medium- to coarse-grained, commonly pebbly sandstones. The Nottingham Castle Sandstone is likely to be the more significant component of the Sherwood Sandstone aquifer by virtue of its greater thickness and its lithological characteristics, but because the two formations are in hydraulic continuity, the Sherwood Sandstone Group is viewed as a single aquifer unit. The overlying and thick Mercia Mudstone Group is an argillaceous sequence that effectively confines this aquifer, although the interbedded, fine-grained sandstones and mudstones of the Sneinton Formation at its base may form a minor transitional aquifer that is commonly in hydraulic continuity with the Sherwood Sandstone. This relationship may have a significant influence on Sherwood Sandstone hydrogeochemistry. The concealed part of the Sherwood Sandstone Group aquifer thickens north-eastwards to more than 150 m across the Eakring–Foston Fault (Bridge et al., 1999). The regional structural dip produces a concomitant increase in thickness of the overlying strata towards the east; for example, in the Middlestyle Bridge Borehole, the top surface of the aquifer lies at a depth of 343 m. The underlying Permian marl, mudstone and limestone generally provide an impermeable base to the aquifer, except where faulting is present.

The lithology of the Nottingham Castle Sandstone Formation is typically medium- to coarse-grained and well-sorted sandstone, with a hydraulic conductivity of 3 to 6 m/d and porosity of about 30 per cent. The more poorly consolidated, coarse-grained, pebbly sandstone may have a hydraulic conductivity of 25 to 30 m/d and porosity of 35 to 40 per cent, whereas the rare, wellcemented layers have hydraulic conductivity of the order of tenths of a metre/day and about 20 per cent porosity (Lovelock, 1977). Lovelock determined an overall intergranular transmissivity for the aquifer of 344 m2/d, using data obtained from laboratory analyses of permeability carried out on core from a test borehole. Transmissivity determined from an aquifer test in the same borehole was 2771 m2/d, which indicated the presence of substantial secondary permeability due to fracture flow.

Bishop and Rushton (1993) identified aquifer transmissivity trends for the Sherwood Sandstone aquifer throughout much of the East Midlands. The trends were observable in both west–east and south–north directions. Transmissivity values increased from west to east across the outcropping aquifer concomitantly with increasing saturated aquifer thickness as the strata dip to the east. A more subtle transmissivity increase occurs from south to north in response to increasing saturated aquifer thickness, and results from an actual increase in thickness of the sandstone strata, from 60 to 80 m in the south to 150 to 200 m in the centre of the aquifer outcrop. In the confined aquifer section, transmissivity values decrease eastwards in parallel with an increasing degree of confinement beneath the Mercia Mudstone Group. This trend results from increasing cementation and formation compression as the overburden thickens. Within the Nottingham district, the west–east trends are observable but the northward trend is more difficult to observe. Yield-drawdown relationships expressed as specific capacity are, however, more generally available and reflect the same trends shown by the transmissivity values. The highest yields have been obtained from largediameter boreholes drilled to the west of the district as sources of public water supply. At Halam Lane Pumping Station, in the confined section of the aquifer, three boreholes of 1016 mm diameter [SK 6697 5369]; [SK 6678 5341]; [SK 6687 5354], which penetrate over 120 m of saturated sandstone, produce yields of 107 l/s for drawdowns of about 50 m. Greater yields have been obtained, for example at Bestwood [SK 579 483] (Plate 2) and Papplewick [SK 5829 5212] pumping stations, which yielded respectively 126 l/s and 158 l/s, but in both cases from pairs of large-diameter wells with associated adits and boreholes from the base of the wells. At both locations, recorded yields declined with time (at Papplewick to 82 l/s over a 27 year period), indicating that pumping rates have been excessive, causing depletion of storage. The most common borehole diameter in the Sherwood Sandstone aquifer is about 460 mm, from which yields range between about 20 and 80 l/s, while specific capacities generally range between 2 and 4 l/s/m.

Contours on the potentiometric surface of the aquifer for March 1978 are shown on (Figure 3). The contour distribution shows a major area of recharge immediately to the north-west of the district, although more general recharge may also be expected to occur across the entire outcrop area. Groundwater flow is towards the southeast, initially at a fairly gentle gradient but slackening rapidly where the aquifer becomes confined.

Although groundwater levels fluctuate with time, it is unlikely that the overall regional contour pattern changes to any great extent. Long-term trends in groundwater levels are illustrated by the hydrograph of the Hazel Hill observation borehole [SK 5663 4637] (Figure 4). The form and amount of variation is very similar to that observed on other hydrographs available for monitoring boreholes in the Sherwood Sandstone aquifer to the north of the district. Total water level variations are only 3.6 m over the 37-year record, and water level responses to periods of drought and major recharge events are very slow due to the considerable thickness of the unsaturated zone. Responses to recharge are delayed by 7 or 8 months.

The decline in groundwater abstraction within the built-up areas of Nottingham has led to a rise in groundwater levels, as illustrated by the hydrographs for the Shipstones Brewery and York House boreholes (Charsley et al., 1990, figs 22 and 23). In some parts of the city, this has led to ingress of water into some of the deeper basements and caves. The consequences for stability and safety are discussed elsewhere (p.32). Furthermore, rising groundwater levels in the aquifer beneath Nottingham City may also cause problems for building foundations. A short term solution of direct pumping has been adopted where the problem is at its worst, but should levels continue to rise, some remedial dewatering boreholes may have to be commissioned.

The hydrogeochemistry of the Sherwood Sandstone aquifer in the East Midlands has been described by Bath et al. (1979), Andrews and Lee (1979) and Edmunds et al. (1982). The study area included the northern half of the Nottingham district, but their conclusions are also pertinent to the southern part of the district, although the natural groundwater chemistry there will have been modified by human activity in the urban area. Bath et al. (1979) and Andrews and Lee (1979) defined three zones of groundwater based on age, as determined from interpretation of isotopic and inert gas data. The three zones provide a chronology for the evolution of groundwater chemistry extending over a period of 35 000 years (Edmunds et al., 1982). Zone 1 covers the whole of the unconfined section of the aquifer, extending just to the east of the outcrop boundary between the Sherwood Sandstone and Mercia Mudstone groups. Groundwater in this zone is predominantly modern and is only a few tens or hundreds of years old. Zone 2 occupies a belt about 8 km wide to the east of Zone 1, in the confined section of the aquifer, where groundwater ages range from 1000 to 10 000 years BP. Zone 3 lies to the east of Zone 2, in the more deeply confined section of the aquifer, and has groundwater ages ranging from 10 000 to 35 000 years BP. Representative groundwater compositions from each of the three zones are shown in Table 6. Edmunds et al. (1982) concluded that the established sequence of hydrogeological processes within the Sherwood Sandstone aquifer permitted recognition of three separate controls for most elements in terms of natural geochemical and anthropogenic influences:

Rainfall was largely responsible for sodium and chloride concentrations. The low concentrations in zones 2 and 3, as little as 5 mg/l, can be interpreted as the effect of recharge by meltwaters under a periglacial climate.

Maritime aerosols and industrial fallout are considered to be the source of the higher chloride concentrations in Zone 1, commonly in excess of 50 mg/l.

Human influence on groundwater quality produced the elevated sulphate and nitrate concentrations in Zone 1, compared to zones 2 and 3. Higher sulphate concentrations partly originated from rainfall polluted by industrial contaminants, as well as from agricultural activities. The latter is also the likely source of elevated nitrate concentrations.

Water-rock interaction in zones 2 and 3 is responsible for increasing concentrations of sulphate, calcium and manganese as well as some minor elements, which increase down dip. Although groundwater mineralisation due to water-rock interaction increases steadily down dip, in line with the increasing degree of confinement, the aquifer is remarkable in that potable water may be present as much as 20 km to the east of the outcrop (Edmunds and Smedley, 1992).

An evaluation of water quality (Edmunds and Smedley, 1992) found that overall changes in aquifer chemistry since the previous study, in 1975, were remarkably small. The most noticeable changes, particularly in nitrate concentrations, were restricted to outcrop areas, and were attributable mainly to anthropogenic influences, such as contamination from agriculture and mine drainage. In the confined section of the aquifer, relatively little change had occurred. In urbanised areas, some major and some minor elements were enhanced by anthropogenic contamination. Elevated concentrations of chloride, ammonia, nitrate and other elements in the aquifer beneath Nottingham provided clear evidence of contamination from leaking sewers (Lerner and Hoffman, 1993). The mining of coal deposits beneath the Sherwood Sandstone aquifer also caused contamination, due to the disposal of often highly saline mine water and the leaching of older mine spoil tips. Changes in mining practice and the closure of mines has to some extent reduced these effects in more recent years (Harris and Skinner, 1992).

Mercia Mudstone Group

The mudstone component of the Mercia Mudstone Group is effectively impermeable, and this unit is normally considered to be an aquiclude. However, there are numerous, thin, impersistent beds of cemented siltstone and sandstone (skerries), and usable supplies of water can be obtained from fractures in these beds. Such supplies are small, but of considerable importance to the agricultural community in the eastern part of the district. Numerous small springs occur on the outcrop of the Sneinton Formation, at the base of the group, which consists of laminated siltstone and sandstone and was previously known as the Keuper Waterstones, reputedly because the abundance of mica on bedding planes imparts the appearance of watered silk. Shallow wells have commonly provided adequate water supplies for domestic purposes, accounting for the clustering of villages and farms along the outcrop of this formation (Lamplugh et al., 1908).

Yields from the Mercia Mudstone Group are small, ranging from 0.5 to 1 l/s and only rarely attaining 2 l/s. Drawdown is highly variable, ranging from as little as 1 m to as much as 43 m. Natural replenishment of groundwater in the thin sandstone beds is slow due to their limited outcrop and enclosure within the mudstones. Sustainable yields may therefore diminish with time as pumping depletes the groundwater in storage.

Little information is available regarding water quality within the Mercia Mudstone Group. The water is generally potable although very hard, the available partial analyses indicating that chloride ion concentrations only rarely exceed 50 mg/l. Sulphate concentrations are commonly over 100 mg/l and may be considerably higher, due to the dissolution of gypsum contained in the mudstone.

Lower Lias Group and Penarth Group

These strata consist predominantly of mudstone interbedded with limestone. They are relatively impermeable but are capable of yielding small quantities of water when fractures are encountered in the limestone, or more rarely sandstone. Yields are invariably less than 1 l/s. No water quality data are available for the district.

Quaternary deposits

Extensive spreads of alluvial and river terrace gravel deposits are present in the district, particularly in the Trent valley. As may be expected from the highly variable nature of these deposits, yields are also highly variable, ranging from less than 0.5 l/s to as much as 16 l/s. The high-yielding sources are used for agriculture and gravel washing operations. Groundwater in these deposits is likely to be relatively shallow and in direct hydraulic conductivity with the River Trent and its tributaries.

Groundwater quality data for the superficial deposits are very sparse. In view of the wide use of the source for agricultural purposes, the water is probably potable, although it may be nitrate-rich in some locations. This groundwater source will be particularly vulnerable to surface contamination, which places constraints on its use for human supply.

Groundwater vulnerability and aquifer protection

The Environment Agency is responsible for ensuring that existing and potential groundwater resources are adequately protected, at a time when the risk of pollution is increasing, both from the disposal of waste materials and from the widespread use of potentially polluting chemicals by industry and agriculture. Groundwater vulnerability to nitrate pollution is a particular problem, mainly in the rural areas, and has been the subject of a special study for the Mansfield–north Nottingham area (Palmer, 1987). Other major concerns over groundwater quality (Environment Agency, 1999) are:

To assist with their Groundwater Protection Policy (NRA, 1992), the Environment Agency, in conjunction with BGS and the Soil Survey and Land Research Centre, have compiled a series of groundwater vulnerability maps (see Information Sources) for the UK. This vulnerability system zones the soil and geological strata in order to assess the ease with which a pollutant released at the surface would be expected to reach the underlying groundwater body (Palmer and Lewis, 1998). The detailed aquifer protection policy of the Environment Agency enables that body to meet its statutory responsibilities for the protection of groundwater from pollution. Specific details on various aspects of the policy are outlined in Charsley et al. (1990) and regular updates are available from the offices of the Environment Agency.

Surface water

The River Trent and its tributaries dominate the drainage of the district and, together with a canal system, have contributed historically to both water supply and communications. The hydrology of the surface water and drainage is beyond the scope of this memoir, and the reader is referred to Downing et al. (1966), Garland and Hart (1972) and Evans (1984) for these aspects. In addition, Severn Trent plc and the Environment Agency hold a large database of information on almost all matters pertaining to water in the district.

Over the last 30 years, the quality of the River Trent water has improved from poor to fair, due in part to improved techniques of sewage treatment, and it is now an important source of drinking water (East Midlands Regional Assembly, 1999).

Flooding and flood risk

Flooding is currently a major environmental issue, particularly in those parts of the Nottingham district that are located on the floodplain of the River Trent and its tributaries, or rely upon communications that cross it. Prior to 2000, the last major flooding of urban areas occurred in 1947, and it was after this event that a programme of flood protection works was initiated in the 1950s. Peak flows were recorded in 1955, 1960 and 1977, but these did not result in serious flooding of built-up areas. Evans (1984) provides a detailed account of the earlier river flow and flood protection schemes in parts of the district.

The Environment Agency (1999) noted that there is increasing pressure to develop floodplains, particularly for urban or industrial sites, and concluded that such developments will inevitably be at risk from flooding. Recent research suggests that, as a result of climate change, peak floods such as that experienced in the Trent valley in November, 2000 (Carney, 2001), are likely to occur more frequently and be more severe, underlining the need for legislation that gives greater control over planning and permissions on floodplains. The extent of the problem, and advice concerning areas of responsibility and potential liability on floodplains, is explained in the Planning and Policy Statement (PPS) Note 25 (ODPM, 2006). The account that follows here emphasises the important geological aspects of flooding that contribute to the assessment of risk.

In river catchment areas and floodplains, a fundamental relationship exists between geology, topography and the potential extent of flooding. In the catchment area, the permeability of bedrock units, which in the Nottingham district are mainly impermeable mudstones, can affect the rate of water absorption and hence runoff. On floodplains, Quaternary geological processes are largely responsible for the width and topography of the alluvial tracts and the volume of alluvial fill that is capable of absorbing floodwaters. The interaction of these factors with human modifications, such as the development of infrastructure, industry and housing on the floodplains, is a further important factor to be taken into account when predicting flood-risk.

The floodplain of the River Trent is characterised by extensive tracts of low-lying ground that is mapped as alluvium. The alluvium is Holocene (Flandrian) in age, and represents various types of deposit left behind following meander migration of the active river channel(s) (Figure 39). The distribution of alluvium and the ‘floodplain terrace’ (Holme Pierrepont Sand and Gravel) defines the geological floodplain, which includes the ‘active floodplain’ containing the areas that have been extensively inundated during recent flooding events (Plate 3). The 1:50 000 geological Sheet 126 Nottingham shows that the ‘floodplain terrace’, being raised above the general level of the floodplain, will include ground that is less prone to flooding. As demonstrated by the river terraces around Gunthorpe [SK 685 445], such outcrops include ground that remained largely dry during the flooding of November 2000 (Carney, 2001; Carney and Napier, 2004).

Maps designed specifically for flood-risk assessment are currently based mainly on historical information combined with river discharge data, hydrodynamic modeling and topographic surveying (digital elevation mapping). An early example is given by Charsley et al. (1990, map 9), who prepared a hydrogeological map showing areas of shallow groundwater as well as maximum flood limits along the River Trent and some of its tributaries. The maximum flood limits were taken from data supplied by the former Severn Trent Water Authority, and excluded information for the (until then exceptional) 1947 floods. Such estimates are now superseded by assessments, produced by the Environment Agency for the River Trent floodplain, which predict a number of flood-risk limits, each of which relates to the magnitude of the flood event and its statistical frequency, expressed as its ‘return period’. Hence, the ‘return period’ for floods comparable in magnitude to those of November 2000 is estimated to be 35 years. These assessments can be obtained by application to the local Environment Agency office at West Bridgford. Alternatively, the extent of the modern alluvium shown by geological maps remains a useful estimate of the likely extent of flooding.

A further aspect of this problem is that many lowlying parts of the district, away from major floodplains, could still be susceptible to flash flooding resulting from extreme, localised rainfalls. Any settlements on valley floors, or at valley entrances, particularly those situated close to unprotected stream courses, would be at risk from this type of inundation.

Geology and planning

Potentially adverse ground conditions are the main geological constraint for consideration in planning and development. Although appropriate engineering or construction works can overcome most ground problems, the early recognition of potential problems is of great importance, not least because solutions may be prohibitively expensive. Assessment of ground conditions includes not only the properties and stability of bedrock and superficial materials, but also the changes to the subsurface brought about by man, such as mining and any consequent subsidence, quarrying and landfill. These two aspects, natural geological properties and man-made modifications, are considered below.

Properties and stability of bedrock and superficial materials

The suitability of bedrock and superficial materials for foundations depends mainly on their geotechnical properties. Sound foundations for building are provided by most of the bedrock materials in the district, but problems posed locally are referred to below. These include the presence of steep slopes, peat beds, former excavations, caves, mineshafts, adits and undermined areas. In many areas, particularly on the outcrop of the Mercia Mudstone Group, small scale building work proceeds with a minimum of prior ground investigation. While building in such circumstances has little case history of failure, preliminary ground investigations should always be carried out by experienced professionals following guidelines such as those given in BS 5930:1999, ‘Code of Practice for Site Investigations’. Unexpected factors contributing to ground instability may occur, such as the presence of Head or other unconsolidated material resembling bedrock, but with relict shear planes or loose sand pockets.

The geotechnical properties of natural materials are reviewed below; more detailed geotechnical information is presented in Forster (1989) and Charsley et al. (1990). In this account, fill is treated as a geologically significant deposit, with large-scale landfill operations a relatively recent development, made necessary by a massive increase in industrial and domestic waste. Fill commonly includes chemical and organic wastes, each of which may provide locally difficult or sometimes hazardous conditions.

Geological factors other than geotechnical properties should also be taken into account when considering the suitability and stability of ground conditions for building or engineering works. These might include local geological structure and slope stability, the possible presence of solution cavities or, on a regional scale, the possibility of earthquakes. Any of these may give rise to problematical ground conditions, which then act as a major constraint to development. A further aspect to be considered is the possibility of risk to health from exposure to radioactive radon gas emanating from subsurface materials. Sitespecific investigations should always be carried out prior to development.

Geotechnical properties

The engineering geological assessment of the superficial and bedrock units in the district was based on information abstracted from published scientific papers and over 300 ground investigation reports. Data from numerous test or sample points in pits or boreholes were also used, but no new sampling or testing was undertaken so that data were to a large extent gathered from areas where development has taken place. Sample coverage of geological units is generally good, except for the Blue Anchor Formation, Penarth Group and Lias Group in the south-east. Full details of the coverage and quality of data, the methodology used in processing the data, the limitations of the results and an analysis of geotechnical properties, are provided in a separate report (Forster, 1989). The following description of geotechnical properties is summarised from the account in Charsley et al. (1990), and deals with materials in three groups, comprising fill, superficial (drift) deposits and bedrock.

Fill is a general term for man-made deposits, mainly within planned areas of landfill or backfill, but including a patchy veneer beneath most built-up areas. The distribution of various categories of man-made or disturbed ground between the city of Nottingham and Thurgarton is shown by Charsley et al. (1990, maps 4 AD and fig. 13), and further detail for the whole district is provided by the 1:10 000 scale geological maps.

The geotechnical properties of fill differ widely and are difficult to predict. Its behaviour depends not only upon the nature of the material, but also upon how it is compacted during placement. Fill placed as part of an engineering project should be selected for its geotechnical behaviour, placed in a controlled manner and compacted to a specified density. When fill is placed as part of a waste disposal operation, it may vary from relatively inert, inorganic waste, such as mine spoil or brick rubble, to organic domestic refuse. The geotechnical properties of such a site will thus vary and, in the case of organic waste, will change with time as decay proceeds. The decay of organic material in domestic refuse may cause a volume loss of up to 50 per cent, and will generate landfill gases such as methane and carbon dioxide as well as toxic leachate. Migration of these substances may then take place through the deposit or into adjacent strata by way of pores or open fissures, with potentially serious consequences as illustrated by the explosion at Loscoe in Derbyshire (Williams and Aitkenhead, 1991). Methane in an explosive concentration (5 to 15 per cent in air) may be ignited by a spark or a shock wave, either of which may be generated during pile-driving or dynamic compaction operations.

The bearing capacity of fill is generally very low and can vary over short distances, leading to highly uneven settlement. Bearing capacities quoted for domestic landfill sites in the past may not be applicable to current or future sites. For example, the amount of ash placed in landfill sites has decreased over the last fifty years whereas the amount of paper and plastic has increased.

Where past industrial activity has left contaminated ground, tests for chemical and biological contamination should be included in the ground investigation. Potential hazards to people, including those undertaking building excavation work, and possible corrosive leachate attack on services and buried concrete (Eglinton, 1979) should be assessed.

The engineering classification of superficial (or drift) deposits is shown in Table 7. In general, an engineering soil is a material formed by an aggregation of rock particles that can be separated by gentle mechanical means and excavated by digging. Fine-grained soils comprise clay and silt, whereas coarse-grained soils comprise uncemented sand and gravel. Head may be fine or coarse grained, and is dealt with separately, as are organic soils, including peat.

Fine-grained soils in the district include sandy alluvium (i.e. excluding gravel) and clay-rich varieties of lacustrine deposits. They are composed mainly of normally consolidated clay and silt, but may be locally sandy and pebbly. Organic-rich layers and channels, and beds or pockets of peat and shell marls, are also sporadically developed. Such deposits are of low to high plasticity, soft to firm consistency and medium to high compressibility with medium to very high consolidation. The moisture content typically ranges from 10 to 50 per cent, usually falling between the liquid and plastic limits of the material. The more organic-rich soils may, however, range up to several hundred per cent. Sulphate content is generally within class I of the BRE classification with some samples (20 per cent) falling in class II and a few (10 per cent) in classes III and IV. Higher sulphate values may result from groundwater contamination from nearby fill. The pH values range from 4.8 to 10.5, but are usually between 6 and 9.

Engineering problems associated with alluvium and lacustrine clay are commonly due to their low shear strength and high compressibility, and these deposits may require special foundations such as a raft or piles. Lateral and vertical differences in composition will be reflected by variations in geotechnical properties. Sulphate and acid attack on buried concrete is not a common problem, but concrete conforming to class II sulphate conditions may be required occasionally, and class III and class IV conditions may be encountered rarely. Excavations will require support, and may encounter running sand below the water table.

Till is poorly represented in the database. Tills that have been investigated are generally sandy clay with variable pebble content, of low to intermediate plasticity, medium compressibility and have a coefficient of consolidation in the range 0.1–10 m2/yr. Till samples collected near Hucknall, to the north-west of the Nottingham district, have greater cohesion (100–350 kPa), greater bulk density (2.1–2.3 Mg/m3) and lower moisture content than samples collected farther south, near Keyworth in the Melton Mowbray district. The latter have a bulk density in the range 1.8–2.1 Mg/m3 and moisture content between 15 and 30 per cent.

The sulphate content of tills indicates that class I conditions for sulphate attack on concrete largely apply. However, class III conditions apply in a small number of samples, and sulphate-resisting concrete mixes will be needed for structures below the water table.

Coarse-grained soils consist mainly of gravelly alluvium, which in the Trent valley occurs below a capping of silty clay alluvium. Lenses of sand occur in the gravels (sand content varies from about 30 to 50 per cent), and silt and clay occur sporadically. Standard penetration tests (SPT) commonly show gravels to be associated with a tripartite layering of relative densities, in which a unit of mainly medium density, with average SPT values of 25, overlies a very dense unit (SPT values over 50). A third deposit of loose density, with an SPT value of about 10, may be present at the surface. Density and moisture content data for gravels should be treated with caution, due to the difficulty in obtaining samples of gravel in an undisturbed state. Sulphate test results indicate that groundwater in gravels normally conforms to class I conditions for sulphate attack, but class II conditions were indicated in 25 per cent of the tests, and a single determination recorded class III conditions. The average pH of the groundwater was 7.5, with values ranging from 5 to 10. Precautions against acid attack on buried concrete are unlikely to be required. As most gravel is composed of quartzite and quartz, with minor chert or flint, problems with alkali aggregate reaction are unlikely when used in concrete aggregate.

Gravels offer good foundation-bearing capacity, with low compressibility. They have a high to medium permeability (6.2 3 10-2 to 6.2 3 10-4 m/sec) and, where excavated, will require support and measures to control groundwater inflow if below the water table.

River terrace deposits form a category of coarsegrained soils that are poorly represented in the database. The 44 samples considered here consist of gravel, sand and sandy to gravelly clay from the Gamston [SK 605 375] and Clifton Bridge [SK 565 360] areas, both situated on the Holme Pierrepont Sand and Gravel. SPT values indicate the sampled material to be medium dense to dense, and occasionally very dense. The clay fraction of the clayrich component has low to intermediate plasticity. The very limited information on sulphate content (3 values) indicates class I conditions. Considerable differences in properties are to be expected for sand and gravel underlying river terraces elsewhere. Although they are medium-dense to dense, terrace sand and gravel become loose on disturbance so that excavations require support. Glaciofluvial sand and gravel and sandy till varieties of the coarse-grained soils are likely to have similar properties to the river terrace deposits, although little geotechnical information is available. They are presumed to offer good bearing capacity, with low settlement characteristics. Excavations will require support.

Head is derived from the weathering and downslope movement of pre-existing deposits. It may have a periglacial origin as a solifluction deposit, or result from hillwash processes (as colluvium). Its composition is highly variable, and reflects the upslope source material. It may be crudely stratified, but is generally unstructured in appearance; this could be deceptive, however, since relict subhorizontal shear planes may exist, and may be reactivated if disturbed during excavation, causing landsliding.

Head may be composed of fine-grained material of a soft to stiff consistency, but can include coarse-grained material with a loose to dense relative density. Excavations in Head will require support, and water inflow may cause collapse.

Head is commonly a thin surface deposit, which is usually removed before foundations are placed. If it is not removed, or is of greater than usual thickness, its low strength and high compressibility can lead to excessive settlement. Where it veneers slopes, Head may suffer instability problems due to its inherent weakness and/or the reactivation of relict shear surfaces. Movement may be instigated by undercutting at the foot of the slope, loading at the top, or by the build-up of high pore water pressures within the slope.

Organic soils, including peat, shell marl, and clay, silt or sand rich in organic matter, occur mainly as channel fills within alluvium and river terrace deposits, or may be associated with lacustrine deposits. The geotechnical properties of local peats, which are summarised in Charsley et al. (1990), correspond with those of peats found elsewhere (Hobbs, 1986). Engineering problems caused by peat and organic-rich soils are due to their low strength, high compressibility and aggressive groundwater content. Their moisture content may be as high as 420 per cent.

As peat occurs in relatively small discrete bodies, for example along the line of a former stream, foundations may be laid across both highly compressible peat and other, less compressible materials, with ensuing differential settlement and severe structural damage to the building. Concrete foundations may suffer damage due to sulphate or acid attack by groundwater, and excavations will require support. Organic soils generate methane and their burial may introduce the risk of an explosive build-up of gas. Engineering solutions to these problems include the removal of peat and its replacement by inert fill, the use of raft foundations and piled foundations, and the use of cement mixes resistant to chemical attack for buried concrete.

Of the bedrock materials, mudstone is a predominantly overconsolidated lithology that may include thin beds of siltstone, fine-grained sandstone and limestone. It weathers to variably silty and sandy clay. Depending upon stratigraphical position, three mudstone types have been encountered in near-surface geotechnical investigations (Table 8).

In the Sneinton Formation, the sequence comprises overconsolidated mudstone interbedded with siltstone and fine-grained sandstone, which weather to firm clay and dense sand. Standard penetration test values are moderate to high (25 to 50>); undrained cohesion for clay averages 59 kPa (weathered) to 25 Mpa (unweathered). Settlementis moderate in clay, and low in sandstone. Sulphate attack on buried concrete is unlikely.

California Bearing Ratio results indicate that some sandstone is excellent for road sub-base material. Excavations in weathered rock may be made by digging, but ripping may be required in sandstone and unweathered bedrock. Support is required in weathered material. Slopes of 35º have been used in cuttings, where there is adequate protection from surface water to prevent erosion.

Sandstone comprises generally weak to moderately strong fine-, mediumand coarse-grained, sometimes pebbly sandstone, weathering to sand. The depth of weathering penetrates up to about 8 m. Standard penetration test values range from low (3) in weathered material, to high (50+) in unweathered material; likewise, unconfined compressive strength ranges from 1 MPa (weathered) to 22 MPa (unweathered). Sulphate attack on buried concrete is unlikely.

Excavation is usually possible by scraper or bulldozer, with ripping necessary in harder beds, and where bedding and jointing are widely spaced. Blade wear rate is commonly high due to abrasive quartz grains. Nearvertical faces (70º) are stable in the short term, although cuts at 35º, if protected from runoff, are required for long-term stability. Excavated material can be used for road sub-bases. The sandstones of the Nottingham city area may contain man-made excavations at shallow depth, which may be empty or rubble filled. The problem of caves is discussed separately on p.32.

The upper part of the Cadeby Formation is strictly a dolostone with thin mudstone layers. However, it is commonly described in ground investigation reports as sandstone, weathering to silty or gravelly sand with clay. At the surface, a widely developed remanié deposit of clay, up to about 1 m thick, results from partial solution of the carbonate. The consequent wide range in lithology gives rise to considerable variation in geotechnical properties. Standard penetration test values range from 20 to 50 at depth. Together with data on moisture content, the SPT results suggest that there is an abrupt change in geotechnical properties at the boundary between weathered and unweathered material. Fine-grained weathered material is of low plasticity, with undrained cohesion in the range 30 to 370 kPa. The unweathered rock has a compressive strength in the range 22 to 32 MPa, and gives an average Rock Quality Designation (RQD) value of 31 per cent (q 21), although the range is between 0 and 80 per cent. Sulphate attack on buried concrete is unlikely.

The rock is well jointed. The joints are commonly a focus for solution, reducing the rock to granular dolomitic sand along the joint. Further solution may produce enlarged fissures and cavities, but these are generally less than a few centimetres in width. However, cambering on valley sides may open joints to form large fissures that can either be filled with superficial material or remain open at depth but be bridged with rubble at the surface. A similar effect has been observed where mining subsidence has opened pre-existing fractures.

Geological structures

Foundation conditions may be affected by deep-seated faults and folds, and by superficial structures confined to the few metres below the ground surface. Major fault zones cross the district, but folding is of little importance, being mainly of very low amplitude with most bedrock dips being less than 4º. Movement on deep basement faults may cause earthquakes (p.28) with the potential for damage, although there is no evidence that the district has been much affected. However, faults can juxtapose rock types that have different geotechnical properties, so that loading by buildings that straddle them may cause differential settlement. In areas of undermining, collapse of old workings on one side of a fault may lead to extensive subsidence damage along the line of the fault. This is the only type of fault-related differential movement that has been noted in the district (see below).

Joints are fractures along which no displacement has taken place. They are common in the more massive sandstones and in the dolostones of the Cadeby Formation. They may have a direct effect on the stability of rock slopes, where water or tree roots may induce slab failure, as occurred at Castle Rock in January 1969 (see below). Mining-induced differential subsidence may widen joints to produce open fissures, a phenomenon that has been widely reported in the Cadeby Formation, with joints widened to 5 cm or more. The effects of solution along joints, or of squeezing material into open joints, must be considered when designing foundations in areas that are likely to be affected.

Superficial structures that occur in mudstone or clayrich Quaternary deposits include folds and faults that are not attributable to deep-seated tectonic causes, as well as cryoturbation structures. In many deep, steepsided valleys on the Mercia Mudstone Group there are asymmetrical folds with wavelengths of only a few metres and orientations invariably parallel or subparallel to the valley sides. Minor faulting is commonly associated with the folds, which are caused by valley bulging in association with cambering on the valley sides. These structures most probably originated under periglacial conditions in the Devensian Quaternary Stage. They indicate zones of potential instability and possible residual stress in the bedrock, and are a potential hazard where deep excavations in mudstone are planned within narrow valleys.

Periglacial cryoturbation is widespread in weathered rock and superficial deposits close to the ground surface. Convoluted fold structures are locally present, and many profiles show stones that have been rotated so that their long axes are vertical. Generally, cryoturbated materials have less strength than their parent deposits.

Slope stability

Slope stability relates to the potential for a slope to fail. The stability of slopes is dependent on slope angle, the nature, structure sand strength of the underlying material (bedrock, superficial deposits or fill), and the influence of water.

Undisturbed natural slopes have generally attained a considerable degree of stability in our present climate. However, construction can disturb this equilibrium and may cause problems in some circumstances. Slopes at a wide range of angles are common in the Nottingham district (Charsley et al., 1990, map 5), but most present little hazard to development if undercutting by rivers or human agencies is avoided. Charsley et al. (1990, fig. 19) recorded landslips and incipient unstable ground from various locations, and also classified the main slope types. Clay is a major constituent of the mudstone and interbedded mudstone and sandstone lithologies that underlie more than two-thirds of the district, and is the material most susceptible to mass movement. The stability of clay slopes is related mainly to local structural and hydrogeological conditions, and the scarps and dip slopes that dominate the geomorphology of the district give rise to generally stable situations. Undercutting by the river is the main cause of the landslips and instability along the cliffs and bluffs facing the River Trent [SK 651 410].

Mass movement of head, colluvium and talus overlying bedrock on steep faces contributes to many landslips, in part because deeply weathered bedrock, and material derived from it such as head is weak and relatively more permeable than fresh substrate. The weathered zones of slopes will therefore be susceptible to movement if there is an increased ingress of water from natural or artificial sources. Under the present climate, natural water input is not generally sufficient to promote movement, except near spring lines. However, under the wetter freeze-thaw periglacial conditions of the Devensian movement may have occurred as shallow landslips or solifluction. The degraded mass movements produced by these processes may be preserved unrecognised, and may include relict shear surfaces, which could be reactivated if the slope is undercut or water is introduced from drains or soakaways.

In those bedrock lithologies that lack significant clay content (i.e. the Sherwood Sandstone Group and the dolostones of the Cadeby Formation) the main modes of slope failure are rockfall, slab displacement or undercutting of steep faces. All these types of failure are associated with the exposed sandstone rock faces in the Nottingham city area, as discussed by Charsley et al. (1990) and Waltham and Cubby (1997). The main contributory causes of such failure are wedging by tree roots, widening of joints by flowing water or undercutting by erosion. These generally act on major planar structures, which in addition to joints include faults, bedding planes and cross-bedding. The best-documented example of such failure occurred in January 1969, when a slab weighing about 18 tons fell from beneath Castle Rock [SK 569 394]. Remedial work required the construction of concrete buttresses and rock bolting. Erosion of sandstone faces by granular disintegration is presently taking place, so the undercutting of faces and overlying walls can present a significant hazard that should be monitored.

The types of failure noted in the Sherwood Sandstone Group are also a potential problem in newly cut excavations in the Cadeby Formation. The outcrop area of the latter has been extensively undermined, so that joints and faults may have been widened locally due to subsidence, leading to increased risk of instability. Acid rain attack on free faces may also lead to widening of joints and undercutting due to solution.

Gypsum solution

Due to its solubility in free-flowing groundwater, extensive dissolution of gypsum has taken place within the Mercia Mudstone Group, in a zone several metres thick, the so-called solution zone, below the base of the subsoil or superficial deposits (Elliott, 1961). Much of the dissolution may have resulted from groundwater flow along bedding planes, joints and fissures (Firman and Dickson, 1968), and although it is believed to have occurred mainly under glacial or periglacial conditions, the process may continue today, albeit much more slowly(Firman and Dickson, 1968). In parts of the sequence, gypsum veins and nodules may constitute more than 30 per cent of the total thickness of borehole cores retrieved from below the base of the solution zone. However, almost no gypsum is exposed at outcrop in the Nottingham district, except where the rate of erosion exceeds the rate of solution, for example in river cliffs or man-made excavations (Firman and Dickson,1968). The depth of the solution zone is controlled mainly by groundwater circulation, and is normally only a few metres thick. However, it may extend down as much as 30 m in the vicinity of faults and heavily jointed areas (Elliott, 1961). Where a deep solution zone is present, a larger volume of gypsum will have been removed from the subsurface. Lowering of the land surface will be greater in such areas. Solution features created by this process occur mainly on the outcrop of the highly gypsiferous Cropwell Bishop Formation, as irregular, commonly closed depressions that cannot be explained by normal patterns of surface erosion. There are four possible circumstances in which gypsum solution may produce a geotechnical hazard in the district.

  1. Collapse of underground solution voids This factor is the principal cause of subsidence in the Ripon area (Cooper, 1986), where groundwater solution along joints in thick beds of gypsum produces large underground caves. These subsequently collapse, causing foundering of overlying strata. It is much less likely to occur in the Nottingham district, as discussed by Charsley et al. (1990). Only in the thick Tutbury and Newark gypsum horizons could significant cavities form. However, in view of the probable very slow rate of gypsum solution, it is unlikely that such large cavities could develop under natural conditions of groundwater flow. Nevertheless, there is documentary evidence that underground solution of gypsum at Orston [SK 770 410] led to ‘frequent reparations’ of the parish church and that gypsum subsidence hollows influenced planning and construction in the village (Barnes and Firman, 1991). Gypsum solution hazards should therefore be considered where development is proposed on the outcrop of the upper part of the Cropwell Bishop Formation.
  2. Collapse of former gypsum mine workings This hazard could occur in areas of former underground mining, around East Bridgford, Cropwell Bishop and Orston (see above). Extraction of gypsum was by bell pitting or pillar-and-stall methods, and as there is little surface evidence for collapse of the workings, it can be assumed that voids are present. Since most workings are below the water table and groundwater flow is probable, solution of the remaining pillars, or of disseminated gypsum in the walls or roof of workings, may lead to collapse and to subsidence at the surface. Very few plans of gypsum workings are currently on public file at the BGS, and reference should therefore be made to British Gypsum Plc (East Leake offices) for further details of mine locations.
  3. Slow solution of gypsum          If occurring below a major structure, this process could cause uneven settlement resulting in damage, as discussed by Seedhouse and Sanders (1993).
  4. Unconsolidated ‘pocket’ sediments Where deposited within natural solution depressions, ‘pocket’ deposits may be highly compressible and could cause excessive and possibly uneven settlement, leading to damage.

Earthquakes

Earthquakes that have been felt around Nottingham are listed in Table 9. In a country of low seismicity, such as Britain, assessment of seismic risk is based on historical research.

The main seismic risk in the district is a repeat of the intensity 6–7 ‘Derby’ earthquake of the 11th February 1957. During this earthquake, reviewed by Carney et al. (2001 and references therein), the worst damage consisted of movement and cracks in the masonry of the Blackbrook Reservoir dam near Loughborough. Chimney stack collapses and falls, cracks in roofs and ceilings, tiles falling from roofs, cracked walls and broken windows were also reported, but there were no burst water or gas mains.

A slightly lesser effect was produced by the earthquake of 30th May 1984, which had an instrumental epicentre close to County Hall, West Bridgford, and a magnitude of 3.1 on the Richter Scale. Its maximum felt effect, measured in terms of intensity, was 5 MSK in the area between Loughborough and Leicester, with an intensity of 3–4 in the Nottingham–Hucknall area.

Movement on major faults at varying depths is a possible cause of many earthquakes. For example, the 1984 West Bridgford earthquake had its focus at a depth of 15 km, within the pre-Carboniferous basement. The 1984 Bulwell earthquake, with a focus at only 6.5 km, resulted from more shallow movement, perhaps reflecting reactivation of the Cinderhill Fault or a closely related fracture. Since the Nottingham district is crossed by several major faults extending into the pre-Carboniferous basement, further seismic activity is to be expected. Detailed analysis of local seismic risk to major constructions can be obtained from the BGS Global Seismology Unit.

Radon

The National Radiological Protection Board (NRPB) has established that the general population may be exposed to relatively high levels of radon within certain buildings. This type of radon exposure may be responsible for up to 6 per cent of lung cancer cases in Britain (Clarke and Southwood, 1989; Hughes et al., 1988). The radon originates from geological materials, soil and groundwater, with only a minor contribution from building materials. Thus, the problem is confined mainly to buildings of up to two storeys. During a countrywide ground-survey, a single high radon value was recorded in Nottingham. Work conducted on homes situated on the Sherwood Sandstone and Mercia Mudstone groups has found little radon in either rock type (Waltham, 1991). On the other hand, the lower part of the Lias Group, which crops out in the southeast of the district, has given high summertime soil-gas readings and may thus yield radon to houses situated on permeable materials above (Sutherland, 1992). Additional research is required to pinpoint the geological reasons for these radon levels that are higher than average and the need for further action should be assessed when the original measurement has been fully explained.

Advice on potential radon hazard and measures for the alleviation of radon build-up in properties can be obtained on application to the Enquiries Desk at the British Geological Survey, Keyworth.

Human activities affecting ground conditions

Modification of the land surface and subsurface by human activities takes two forms:

  1. Excavation and removal of material to leave voids or pits, as in mining and quarrying
  2. Addition of material as fill, either into former excavations or as constructed landfill

Many constraints are placed on development by these changes, and developers in the district must exercise particular care since many of these activities started before written records were kept. In Nottingham city, for example, man-made caves pose an ever-present problem for development in the parts underlain by sandstone. The following sections review the constraints imposed by former land use and mining.

Coal mining

Coal has been mined to the west of the district since at least the Middle Ages, and probably earlier. Much of the wealth of the Willoughby family, who constructed Wollaton Hall in the 16th century, and that of other Nottingham landowners, was founded on mining of the exposed or shallowly concealed coalfield west of the hall. This activity has left a legacy of largely undocumented abandoned mine shafts and shallow workings in the Radford area [SK 549 404], in the extreme southwest of the district (Charsley et al., 1990). Later, deeper seams were extracted by the pillar-and-stall method, with 40 to 50 per cent extraction. Panel working, introduced in the 18th century, gave way to longwall mining, which considerably increased the recovery ratio in the concealed part of the coalfield. Following the 1872 Coal Mines Regulation Act, accurate plans were lodged with the Mines Inspectorate. However, these only showed the extent of mining and did not record levels or geological information. The sites of known or suspected shafts and adits in the city area are shown in detail on maps 8A and 8B of Charsley et al. (1990). However, such records will be incomplete and responsibility for locating shafts at or close to these sites rests with the site owner or developer.

A large part of the Nottingham city area has been undermined from collieries (Charsley et al., 1990, maps 7, 8A, 8B), and commonly more than one seam has been extracted beneath a given site. Records of this activity for the period since 1872 are lodged with the Coal Authority (see Information sources for address). The coals worked beneath the city area, for which records exist, are given in Table 10. Any associated subsidence in the city is assumed to have ceased almost completely, apart from any potential subsidence that might result from the most recent workings of the Gedling and Cotgrave collieries, but developers should seek advice from the Coal Authority.

Surface subsidence is mainly a function of the thickness of the extracted seam and the depth to the workings. In general, the greater the depth to the workings, the more the effects of differential subsidence at the surface will be dispersed and damage to property lessened. Subsidence starts within hours of extraction, but its full effects are transmitted upwards more slowly and it may be more than 10 years before the surface is completely stable (McLean and Gribble, 1985). Even then, collapse of formerly supported sections, such as some roadways, may still take place. Dramatic differential subsidence may occur when a fault plane is reactivated by subsidence, especially when coal has been extracted from one side of a fault only. Such subsidence effects should be carefully considered when planning sites straddle faults. Generally, faults are not single planes, but consist of a series of subparallel fractures that form a complex fault zone, which may be tens of metres wide. During mining from Clifton Colliery in the 1950s, some houses in West Bridgford suffered severe structural damage associated with differential subsidence along major fault planes in the area between the Melton Mowbray, Boundary and Ellesmere roads [SK 585 360]. The effect of subsidence on surface structures with reference to geological factors has been the subject of a detailed study in the area north-west of the city. Further examples reported from the Nottingham urban area (Papplewick, Aspley, Hucknall), and from other locations close to the district, are discussed by Donnelly (2000).

Following the abandonment of workings, dangerous gases such as methane and carbon monoxide may accumulate in any voids remaining after subsidence. Escape of these gases along faults and from shafts is a remote but real possibility, even from deep mines, and the gases could enter higher-level workings, such as those for gypsum, or even near-surface excavations for foundations.

Coal mining produces large quantities of spoil, for example 10 million cubic metres annually in the early 1980s (Nottinghamshire County Council, 1997). Although some has been sold as mine stone for fill (p.23), the bulk of it remains in waste tips, most of which are shown as Made Ground on Sheet 126. The tips are mainly steepsided and consist of compacted shale, mudstone, siltstone and sandstone. Internal drainage is poor. Combustion of contained fragmentary coal can take place, leading to heat generation and subsidence. For these reasons, colliery tips are considered unsuitable sites for building and their potential instability may place a constraint on the use of the surrounding land for construction, unless extensive and costly engineering works are undertaken. Given the large areas that the tips cover, however, they present an opportunity as well as a constraint for development. Conversion to amenity or agricultural areas is an option that is being increasingly adopted in the region.

Underground gypsum mining

Shallow underground gypsum mining has taken place at East Bridgford, Orston and Cropwell Bishop. In view of the consequent risk of subsidence, a cautious approach is required to development in these areas.

Little is known of the extent of mining at East Bridgford, but a cluster of six former shafts have been located (Charsley et al., 1990, map 6) around [SK 694 430]. Others almost certainly exist. As in other types of mining for satinspar veins, it is probable that mining followed the better veins rather than adopting a more uniform pattern of extraction such as the pillar and-stall method. Voids left by mining may thus be highly irregular in shape and some could be close to the surface. The depth of the workings is not generally known. However, at one site [SK 6947 4323], which may be typical, the primary County Series geological map records ‘Satinspar mine 25 feet to gypsum bed which is 9 inches thick, fibrous and remarkably bright and pure’. The risk of collapse of unlocated or incompletely backfilled shafts, or of subsidence into old workings, may be high. Further development should be conditional on ground investigations to establish the extent of former workings and whether voids are present. Where development already exists in such areas, special note should be taken of any evidence for structural damage in properties.

The undermined area at Cropwell Bishop [SK 675 355] can be relatively well defined using mine abandonment plans (see Charsley et al., 1990, map 6). However, there is a possibility that workings extend to the north of those documented. Gypsum was probably extracted from several levels within the Newark Gypsum (p.128) by a combination of mining out from the base of a shaft (similar to bell-pitting) and the pillar-and-stall method. Generally, the latter does not lead to early subsidence because of the roof support provided by the pillars. However, solution of gypsum or degradation of mudstone in the pillars could eventually lead to collapse, especially in the longer term if water enters into or flows within disused shallow workings. Evaluation of this risk may be difficult, because ground investigation boreholes may penetrate pillars, leading to an underestimation of the extent of former workings.

Near Orston [SK 763 402] in the Vale of Belvoir, the Newark Gypsum was mined underground using the pillar-and-stall method with access from both shafts and adits (Barnes and Firman, 1991). Remnant pillars were locally re-worked by opencast methods. Subsidence hollows are associated with these workings, together with flooded opencast pits.

Quarries and pits

The constraints that former excavations place on development relate to three aspects.

Knowledge of the presence and type of former excavations can resolve most problems for development at the planning stage.

Until well into the 20th century, the surface extraction of minerals in the district was almost entirely from a number of small operations. This pattern has changed so that present workings for sand and gravel, brick clay and gypsum are centred on a few large-scale excavations. Former quarries, pits and artificially dug ponds are present throughout the district. Many have been backfilled (shown as Made Ground), others are partially filled and degraded, some are flooded, and a few remain in their quarried state, with steep backwalls and limited fill in their bases. The sites of former quarries, pits and ponds have been located using BGS archives and old editions of Ordnance Survey maps, and are indicated by Charsley et al. (1990). Other excavations certainly exist. Where delineated, the boundaries of excavations are based on the best information available and are likely to be imprecise in detail. In areas where former workings are known or where a resource exists, ground investigations should allow for the possible presence of backfilled excavations.

The increasing use of quarries and pits for waste disposal has produced a widely developed but localised hazard. Liquid toxic residues, either as a primary component of fill or generated secondarily by chemical or biological reactions, can migrate both within the deposit and into adjacent permeable strata. This is potentially a serious hazard at landfill sites situated on deposits in hydraulic continuity with the Sherwood Sandstone aquifer or, in the case of gravels, with the River Trent or its tributaries. Toxic and explosive gases, particularly methane, can be generated within waste tips and landfill sites. Such gases can migrate, sometimes through adjacent porous strata or along fissures, and accumulate within buildings or excavations, either nearby or some distance away, as occurred at Loscoe in Derbyshire in 1986 when an explosion resulted (Aitkenhead and Williams, 1987).

Constructional landfill

Artificial landforms are created where fill is placed on an original ground surface. The larger artificial landforms, of which colliery spoil tips are the most obtrusive, are shown as Made Ground on Sheet 126. Road, rail, canal and flood protection embankments are present throughout the district, and may form distinctive landforms. Less obvious are major spreads of fill, such as those in the Dunkirk–Lenton Lane area [SK 55 37] and south of Wilford Road [SK 57 36], which have significantly altered the local landscape by forming artificial terraces, several metres above the floodplain of the River Trent. Landscaping schemes have also produced artificial mound sand terraces of fill in places, and have involved excavation of bed rock in others. The levelling of playing fields or amenity areas is ubiquitous.

Constraints are placed on development where the fill is composed of materials of low strength or high compressibility, or consists of organic waste, which may generate methane, other noxious gases or toxic residues (see also p.23). Additional problems exist where artificially steep slopes have been created, as on some embankments and the edges of major constructional landfill sites. Poorly managed groundwater flow can produce catastrophic failure of poorly compacted embankments, spoil heaps and other steep-sided landforms. Consideration must also be given to the nature of the underlying surface. For example, some river valley areas e.g. [SK 553 414]; [SK 480 547] were prone to flooding prior to tipping, with the development of marshy conditions and ponds. Settlement of peat, organic soils and alluvial clays probably occurs beneath the cover of fill in these areas, together with the generation of methane from decaying organic material.

Caves

The sandstone beneath most of central Nottingham would provide sound reliable foundations almost everywhere, were it not for the presence of man-made caves. A register of all caves in the city of Nottingham for which there is documentary evidence was commissioned by the Department of the Environment and is available separately (Owen and Walsby, 1989). Further information is given in Charsley et al. (1990) and Walsby et al. (1990). These reports provide major sources of reference to more than 400 caves or cave systems for planners, building control officers, architects, engineers, developers and members of the public.Additional information,which includes historical and geotechnical assessments of cave-related problems, is provided by Waltham (1992, 1993, 1996) and Waltham and Cubby (1997). Caves considered as a resource rather than a constraint are reviewed elsewhere (p.13).

The first caves were almost certainly cut into the bluffs and cliffs facing the River Trent as human shelters and byres. From about the 13th century, the Broadmarsh or Drury Hill cave system was developed, and in the 16th century housed a tanning works with access to the Trent floodplain. Later caves were mainly excavated downwards into the sandstone, for storage, sand extraction and waste disposal, or as cellars for houses, particularly beneath public houses where they were used as beer or wine cellars. The Victorians, especially during the development of The Park area of Nottingham in the mid 19th century, dug caves as decorative follies, and many were modified or extended during the Second World War when they were used as air raid shelters. The long history of excavation, and the large number of caves recorded, point to the presence of unrecorded sites, particularly in the central parts of the city and certain outlying areas such as Arnold. The cave plans in the register (at a scale of 1:2500; Owen and Walsby, 1989) therefore serve the dual purpose of (i) showing the distribution of known caves and (ii) the gaps between groups of caves where others may be found.

The distribution of caves closely follows the outcrop of the Nottingham Castle Sandstone Formation (Charsley et al., 1990, map 11), although they are not confined to that formation. The sandstone can be easily carved or excavated, yet stands in vertical cuts and is strong when compressed or loaded. It is soft and friable, and component grains can be scraped away with a penknife. Weathering may weaken what little intergranular cement there is, and can cause grain-by-grain erosion of a free face. Jointing may initiate instability in steep faces (see also p.27).

Although roads have occasionally collapsed into caves, there is no record of building subsidence. Modern construction work in the city has invariably allowed for the presence of caves, some of which have been filled whereas others have been left as a feature. However, given the known extent of cave networks and the lack of a complete record of caves, the possibility of localised subsidence is always present.

All ground investigations in areas underlain by Triassic sandstone, particularly the Nottingham Castle Sandstone Formation, should assume that caves are present. The aim of the investigation would then be to prove the absence of caves by a programme of borehole drilling, trial pitting, trenching and using geophysical methods, such as ground-probing radar. Ideally, ground investigations should not be conducted until existing buildings are demolished and the site has been cleared to the former basement level. Accurate evaluation of the often intricate patterns of cellars, sometimes on two levels, passages and deeper levels of caves can then be made, and new buildings designed accordingly.

Where caves are present, the engineering solutions most commonly adopted for foundations are (i) infilling of the cavities by concrete or (ii) total excavation to the lowest cave floor level, incorporating deep basements in the design. Alternative approaches, which may be possible locally and are likely to be less costly, are to use pad and stem foundations founded on the floors of caves or a thick concrete raft to straddle the caves. Both methods have the advantage that the caves are preserved for present use or future research.

Recent rises in the water table beneath the city see (Figure 4) have resulted in the flooding of some caves retained as basements, threatening the stability and safety of premises. Freestanding water will have a deleterious effect on pillars and walls, and may cause undermining of foundations. Where the rock surrounding a cave is load bearing, pumping to reduce water levels, as carried out in the Broadmarsh system, is recommended. The effect of groundwater flow beneath cave systems at different levels may also reduce the strength of the sandstone by removing natural cementing materials. The underground water regime beneath the lower lying parts of the city may therefore need carefully monitoring. Changes to the ventilation of caves as water levels rise could lead to accumulations of stale air and harmful gases (see above) or to the expulsion of such gases into adjacent caves or buildings.

Chapter 3 Pre-Carboniferous rocks

Pre-Carboniferous rocks have not been proved in the Nottingham district, but evidence for their probable age and nature comes from exploration boreholes in the surrounding area. Basement lithologies provide the physical constraints that enable realistic models of the deep geology to be constructed from geophysical and seismic information (Chapter 10). The structural history of the basement rocks is also relevant to discussion of the factors that control the distribution of faults at the surface (Chapter 9).

The Foston No. 1 Borehole [SK 8491 4146], located on the Foston structural ‘High’ about 2 km east of the district (Figure 42), proved 134 m of purple and olive metasiltstone beneath unconformable Dinantian strata (Pharaoh in Berridge et al., 1999). The metasiltstone has a penetrative slaty cleavage, associated with the growth of white mica and chlorite in strong preferred orientation, crosscut by a crenulation cleavage (Berridge et al., 1999; plate 2a). Greenschist-facies metamorphic conditions are inferred from a white mica-crystallinity value of 0.22°2θ (Pharaoh et al., 1987). Phemister (in Kent, 1967) previously correlated these ‘slates’ with the ‘Brand series’, the youngest basement unit of Charnwood Forest, which at that time was considered to be of Precambrian age. An early Palaeozoic age for the Foston basement is now considered to be more likely (Pharaoh et al., 1987; Pharaoh in Berridge et al., 1999); indeed the Brand Series (now the Brand Group) may itself be of Early Palaeozoic age (see discussion in Carney et al., 2001).

The Ironville No. 5 Borehole [SK 4299 5141], located about 11 km west of the district, proved 95 m of weakly metamorphosed, grey, bioturbated sandstone and siltstone. They are interbedded with black mudstone that yielded an acritarch flora of probable early Ordovician, Tremadoc or Arenig age (Molyneux, 2001). The metasedimentary rocks dip eastwards at 55° to 70° (Pharaoh et al., 1987), and the argillaceous layers are affected by an intense, penetrative cleavage that becomes more spaced in the silty and sandy lithologies. The cleavage postdates a bedding-parallel mica fabric that possibly developed during diagenesis and/or burial metamorphism, and has in turn been folded by kink-bands on gently inclined axial surfaces, observable on both microscopic and mesoscopic scales. Mica crystallinity values for three samples are in the range 0.28 to 0.29°2θ, compatible with metamorphism under high anchizonal conditions (Merriman et al., 1993). Numerous highly altered basic sheets of lamprophyric affinity, from 0.5 to 5 m thick and with chilled margins, intrude the metasedimentary strata. In thin section, they contain pseudomorphs after pyroxene or amphibole, and probably also after olivine; the main alteration effects are carbonation and argillisation. Geochemical data (T C Pharaoh and N Brewer, BGS unpublished data) suggest that the sheets are part of the spessartitic lamprophyre suite that commonly intrudes CambroOrdovician strata in the Midlands (Thorpe et al., 1993) and was termed the Midlands Minor Intrusive Suite by Bridge et al. (1998). This subduction-related magmatic suite (Pharaoh et al., 1993) may have been emplaced at various times from the Tremadoc onwards; the only radiometric date, obtained using the U-Pb method, is from the Nuneaton area, and gives a latest Ordovician age of about 442 Ma (Noble et al., 1993).

The Eakring No. 146 Borehole [SK 6807 5948], located 5 km north of the district on Sheet 113 Ollerton, proved 84 m of grey, phyllitic mudstone and subordinate sandstone beneath a coarse clastic sequence of latest Devonian or earliest Carboniferous age (Edwards, 1967). Phosphatic fragments were noted by C J Stubblefield (in Edwards, 1967) from between 7218 and 7228 ft (i.e. 2201–2204 m) depth. He concluded that they might be from an Acrotreta-like brachiopod, suggesting that these rocks are Phanerozoic, possibly Cambrian, in age. Bedding dips range from 40° to 70° and the mudstone is locally fractured and brecciated, listricated and affected by veining and slickensides. Two samples yielded white mica crystallinity values in the range 0.26–0.28°2θ (Pharaoh et al., 1987; Merriman et al., 1993), comparable with values from Ironville No. 5 Borehole. Thin flows, less than 10 m thick, of altered andesite and dacite lava are intercalated with the sedimentary rocks at depths of 2204 m (BGS sliced rock numbers (E20700), (E20701)) and 2240 m (E20702), (E20687). The chemical composition indicates that they belong to a calc-alkaline magmatic series (Pharaoh et al., 1991).

The Cox’s Walk No. 1 Borehole [SK 8412 3808], located on the Foston ‘High’ in a similar structural location to Foston No. 1 (Figure 42), proved 243 m of andesite, dacite and rhyolite lavas beneath an unconformable Dinantian cover (Pharaoh et al., 1991; Pharaoh in Berridge et al., 1999). Although the lavas are affected by chloritic alteration and are well jointed, fractured and veined, primary igneous features such as amygdales, flowage textures and zoning in plagioclase are well preserved, and penetrative deformational fabrics are absent (Pharaoh in Berridge et al., 1999; (Plate 2b, c). The lavas exhibit a calc-alkaline fractionation trend, showing geochemical similarities to the lavas proved in the Eakring No. 146 Borehole. A Rb-Sr isochron age of 466 ± 11 Ma, or mid-Ordovician on the timescale of Gradstein and Ogg (1996), was interpreted as that of eruption, given the lack of penetrative deformation (Pharaoh et al., 1991). This interpretation requires confirmation from U-Pb mineral dating, which has demonstrated the ease with which the Sr isotopic system can be reset by low-grade metamorphism (Noble et al., 1993), but it is corroborated by findings farther to the south.

In the Rempstone No. 1 Borehole [SK 5821 2405], 11 km south of the district, 82 m of granodiorite were proved in the footwall of the Normanton Hills (Hoton) Fault, which delimits the southern margin of the Widmerpool Half-graben (Pharaoh et al., 1993; Carney et al., 2004). The granodiorite is xenolithic, but otherwise similar to rocks of the Mountsorrel Complex, in the Leicester district [SK 560 150]. The Mountsorrel granodiorites have yielded a U-Pb age of about 450 Ma (Noble et al., 1993; recalculated from Pidgeon and Aftalion, 1978). Together with the Rempstone and Kirby Lane rocks, they evidently belong to a co-magmatic series of small calc-alkaline plutons in the East Midlands basement (Le Bas, 1982) that were generated above a subduction zone in mid-Ordovician (Caradoc) time (Pharaoh et al., 1993).

In summary, the pre-Carboniferous basement is likely to consist of early Palaeozoic (Cambro-Ordovician) metasedimentary rocks (Foston No. 1, Ironville No. 5 boreholes), locally interbedded with acid metavolcanic lithologies (Eakring No. 146; Cox’s Walk No. 1). The geochemistry of the volcanic lithologies supports their generation in a magmatic arc located along a subduction zone. Furthermore, the limited isotopic evidence for a mid-Ordovician age, combined with other petrographical and geochemical attributes, suggests broad contemporaneity with the Ordovician volcanism of Wales and the Lake District (Pharaoh et al., 1993; Noble et al., 1993). The volcano-sedimentary sequences formed the host rocks to two suites of intrusions: Caradocian granodiorite plutons (Rempstone No. 1 Borehole and Mountsorrel Complex) and spessartite lamprophyre sheets of similar or slightly younger (Caradoc–Ashgill) age (Ironville No. 5).

Chapter 4 Carboniferous

Carboniferous rocks ranging from Dinantian to Westphalian in age are present throughout the district, but are only seen at outcrop in the Radford area [SK 545 404] of Nottingham. Nevertheless, a considerable body of data, derived from numerous boreholes and reflection seismic surveys, is available for the rest of the district, where the Carboniferous rocks are concealed beneath Permian to Jurassic strata.

Deep exploration boreholes were first drilled in the search for a concealed continuation of the productive Nottinghamshire coalfield, which is exposed to the west of the district. These boreholes proved potentially productive Westphalian (Coal Measures) strata at depth, and were the basis for the development of numerous collieries in the western half of the district. The gradual deepening of the Westphalian strata eastwards meant reduced prospectivity, and consequently a lower density of borehole provings east of the A46 trunk road (the Fosse Way) until the search for oil began in the East Midlands (Lees and Cox, 1937; Lees and Taitt, 1946). Thereafter, clusters of borings through the Westphalian into the underlying Namurian and Dinantian strata were completed in conjunction with reflection seismic profiling across much of the district, in order to identify and investigate structures that might trap oil in the Carboniferous strata.

Data from boreholes drilled in the late 19th and early 20th centuries are generally of limited value, with no geophysical logs and only poorly preserved core runs or chippings from which cursory descriptions were made, commonly by the driller. As drilling techniques developed, so the data became more voluminous and reliable. Recovery of core through the productive zones of both the Westphalian and Namurian strata improved, and detailed descriptions by Geological Survey, Coal Board and oil company geologists provide an irreplaceable data source. The development of geophysical logging techniques provided an additional data source, especially after the advent of reliable gamma-ray logging tools, and such data are commonly used to provide a framework to which the lithological detail is added.

The refinement of onshore seismic surveying techniques over the past two decades has provided an abundance of high quality seismic data from which structural and stratigraphical detail can be obtained (Chapter 9), often in combination with the full suite of geophysical logs now run in exploration boreholes. Sidewall cores and mud chippings provide material for direct lithological and palaeontological study where full cores are not taken.

Geophysical potential field data constitute an additional source of information on the concealed strata of the district. Maps of magnetic and gravity anomalies (Chapter 10) give an indication of the nature of the deeply buried strata and, when well constrained, may provide details of strata beyond the reach of other geophysical techniques.

Work on the sedimentation and tectonic history of the Carboniferous of eastern and northern England has been ongoing for some time. It includes studies by Lees and Taitt (1946), Turner (1949), Wills (1956, 1973), Falcon and Kent (1960), Kent (1968a), Francis (1970, 1978), Leeder (1976, 1982, 1988), Smith and Smith (1989), Fraser et al. (1990) and Fraser and Gawthorpe (1990, 2003). Three key collections of papers are those edited by Miller et al. (1987), Besly and Kelling (1988) and Arthurton et al. (1989). Further work, including individual papers from these collections, is quoted widely in the text that follows.

The palaeogeography of the East Midlands at the close of the Devonian was probably that of a low-lying, undulating terrain exposing Cambrian and Ordovician rocks that had been cleaved and folded during an orogeny, some 50 million years previously. This landscape was subsequently inundated by a marine transgression depositing the first dateable Carboniferous sedimentary rocks in the region. These occur to the south-west of the Nottingham district, and are referred to the earliest part of the Dinantian, the Tournaisian, commencing about 360 Ma ago (George et al., 1976). The Dinantian succession of the Nottingham Shelf includes lithologies that are typical of the shelf-facies of Carboniferous Limestone exposed in Derbyshire, but grading laterally into mudstone-rich strata that were thickly developed within rifted basins, the Widmerpool Half-graben and Welbeck–Sleaford Low (Figure 42). By Late Carboniferous times, the tectonic regime had evolved into one of more uniform, regional-scale subsidence (postrift thermal sag), and the more widespread Pennine Basin became established. Synsedimentary movements of the structures controlling the Widmerpool Half-graben and Welbeck–Sleaford Low appear largely to have ceased, and these rifted basins were progressively infilled during the Namurian, first by prodelta turbidites of the Edale Shale Group and then by deltaic deposits of the Millstone Grit Group. The Namurian sequence, with its broad coarsening-upward trend, indicates that sedimentation was outpacing subsidence, and by Westphalian times, a low-lying fluviolacustrine delta-plain, in which strata of the Coal Measures were deposited, dominated the region. These measures show little variation of thickness across the district, indicating continued shelf stability; they consist of grey mudstone, siltstone and sandstone with numerous coals, seatearths and marine bands indicative of both local tectonic activity and eustatic sea-level variations. Towards the end of Westphalian times, compressional tectonic movements caused localised uplifts, which in turn promoted a change to better drained alluvial conditions, reflected by sedimentation styles in the Barren Measures.

The periodic effusion of basaltic lavas and associated volcaniclastic deposits is a significant feature of the Carboniferous stratigraphy, carrying as it does the implication that associated tectonic activity may have partly controlled sedimentation in this part of the Pennine Basin. Carboniferous volcanic activity and related intrusions are discussed in a separate section of this chapter.

Dinantian (now named Tournaisian and Viséan)

Carboniferous strata of Dinantian age were proved in 28 boreholes in the district, and are overlain unconformably by Namurian strata. The Dinantian strata have also been imaged on seismic profiles, which show that they are present at depth throughout the district. The combined seismic and borehole evidence show thickness and facies changes within the Dinantian, and demonstrate that the Dinantian strata at depth in the Nottingham district are in stratigraphical continuity with Dinantian strata at outcrop in the Derbyshire Peak District. The base of the Dinantian succession was not proved by any of the boreholes in the Nottingham district, although several boreholes within 10 km of the district did reach pre-Carboniferous basement (Chapter 3).

Although ‘Carboniferous Limestone’ has always been considered an informal lithostratigraphical unit of supergroup ranking, it is probable that this name will not feature when a formalised lithostratigraphical scheme is eventually erected for these strata. It is therefore not recommended for current use (Aitkenhead and Chisholm, 1982). Lithostratigraphical revisions in progress (Waters et al., in prep.) suggest that the limestone-dominated Dinantian formations of shelf or platform facies should all be included within a division of their own (Peak Limestone Group). The basinal, mudstone-rich facies of the district, which would include equivalents of the Widmerpool Formation described farther south (Carney et al., 2004) and west (Chisholm et al., 1988), would be placed within a ‘Craven Group’, which would also include Namurian strata presently referred to the Edale Shale Group.

The Dinantian strata were deposited in a tilted block and graben topography that formed at a time of widespread crustal extension across the English Midlands (e.g. Miller and Grayson, 1982). They are considered to form part of a ‘syn-rift megasequence’ (Fraser and Gawthorpe, 1990), and have been subdivided on the basis of the seismic sequence stratigraphy erected for the East Midlands hydrocarbon province by Fraser et al. (1990) and Ebdon et al. (1990). Riley (1993) has pointed out the limitations of the seismostratigraphical approach, in terms of chronostratigraphical precision, but it does provide a useful framework in which to consider Dinantian stratigraphical evolution. The seismostratigraphical scheme has also helped to elucidate the early Carboniferous structural history of the district (Chapter 9), by showing that many of the lithological and thickness variations within the Dinantian succession can be related to differential movements between tectonically bounded depositional domains (e.g. Ebdon et al., 1990). The domains are shown in (Figure 42).

Sedimentation is thought to have occurred throughout the Dinantian in parts of the district. Locally, however, the sequence is attenuated and stratal packages are missing. For example, a basement ‘high’, the Foston High (Figure 42) was emergent in Holkerian (late Dinantian) times in the south-east of the district (Strank, 1987; Ebdon et al., 1990), and a late Dinantian to intra-Namurian unconformity may be present elsewhere (Strank, 1987). A reactivation of extension and subsidence occurred in late Asbian to early Brigantian times in the Widmerpool Half-graben (Ebdon et al., 1990), and was broadly coeval with the basaltic magmatism proved by the Strelley LN/4-2 Borehole (see below), just to the west of the district. In early to mid-Brigantian times, and probably overlapping with this volcanism, further subsidence (and/or sea-level rise) produced a southwards-prograding carbonate grainstone facies along the northern margin of the Widmerpool Half-graben (Ebdon et al., 1990). These authors also noted a late to post-Brigantian episode of mild basin inversion, which was superseded by regional thermal subsidence leading to the encroachment of prodelta facies mud in early Silesian (Namurian) times.

Some indication of the age and thickness of Dinantian strata is given by deep boreholes located outside but close to the district. The Ironville No. 5 Borehole [SK 4299 5141], 11 km to the north-west of the district, proved 621 m of Dinantian strata overlying Lower Palaeozoic basement. The Plungar No. 8A Borehole, located only 2 km to the south-east of the district, proved 486 m of Dinantian strata (unbottomed), ranging in age from Chadian (and ?late Courceyan) to Arundian and possibly younger (Riley, 1992; Carney et al., 2004). In the Nottingham district, however, boreholes have only penetrated the uppermost part of this sequence, and the paucity of information precludes any meaningful lithostratigraphical subdivision of these rocks. Most of the borehole logs are based on chippings samples, with full core descriptions available for only three boreholes, Bingham No. 1, Langar No. 1 and Cropwell Butler No. 1 (Figure 42). Only the broadest possible inferences on lithostratigraphy and lithofacies are therefore possible. No new biostratigraphical research has been carried out during the present study. BP has carried out micropaleontological investigations of a number of boreholes (Strank, 1987), but precise details remain confidential.

The Dinantian succession in the Welbeck–Sleaford Low is up to 2500 metres thick adjacent to the Eakring–Foston Fault (Figure 42), thinning steadily north-eastwards as shown by Section 1 of the published 1:50 000 geological map (Sheet 126). According to the interpretation of Fraser et al. (1990, fig. 7), it commences with sequence EC2, deposited adjacent to the Eakring–Foston Fault as a wedge of subaerial clastic conglomerates of late Devonian to Courceyan age. Of the remaining five sequences, EC3 (late Chadian to early Asbian) and EC5 (early to mid Brigantian) are substantially thicker than on the Nottingham Shelf to the south-west, indicating increased subsidence of the Welbeck–Sleaford Low during these periods. The topmost 78 m of the Dinantian has been proved in Normanton No. 4 Borehole, and probably represents the Brigantian sequences EC5 and EC6. Eleven other boreholes penetrated the Dinantian in the Welbeck–Sleaford Low, although none have proved more than 40 m of strata. These typically consist of moderately fossiliferous, pale brown, brown-grey, or dark grey crystalline or granular limestone with very thin beds of mudstone, and probably represent shallow-water, platform carbonates. ‘Igneous rocks’, described from 5 m below the top Dinantian in the Rolleston G2 Borehole, are likely to be intrusive.

The Dinantian sequence is about 350 m thick along the western margin of the Nottingham Shelf, adjacent to the Widmerpool Half-graben, and thins steadily northeastwards to only 200 m adjacent to the Eakring–Foston Fault. Dinantian limestone was encountered in 16 boreholes, the maximum penetrations being 46 m in Screveton No. 1 and 40.2 m in Langar No. 1 (Figure 42). The lithologies are mainly pale grey, finely crystalline limestone that is rather more fossiliferous than that encountered in the Welbeck–Sleaford Low, with common crinoids, brachiopods and corals. Stylolites are recorded in some logs. Typically, these strata occur in packages between 3 and 10 m thick, separated by thin beds of pyritic mudstone. Geophysical logs through the limestones generally show very low gamma-ray log values and a low interval transit time (i.e. high sonic velocity). The presence of thin mudstone interbeds is reflected by the spikiness of many gamma-ray traces, and such sequences, for example in the Screveton No. 1 Borehole, produce characteristically serrated gamma-ray profiles. However, there is no reliable correlation of these mudstone beds between boreholes.

Seismostratigraphical studies suggest that strata of Courceyan age (sequence EC2) are absent on the Nottingham Shelf. The remaining five seismostratigraphical sequences consist mainly of shallow-water, platform carbonates (Fraser et al., 1990, fig. 8). The relative attenuation of the Nottingham Shelf succession is attributable mainly to the thinness of sequences EC3 and EC5, compared to their equivalents in the Welbeck–Sleaford Low and Widmerpool Half-graben (Fraser et al., 1990). Sequences EC4 to EC6 (Asbian–Brigantian) are locally absent on the shelf below the basal Silesian unconformity, but their presence elsewhere is suggested by the occurrence of typical late Viséan (Brigantian, D2) faunas. These include the late Brigantian assemblage of Spirifer bisulcatus and Productus (Gigantoproductus) latipressus recorded from limestone at the base of the Cropwell Butler No. 1 Borehole (W H C Ramsbottom, 1958; note included with borehole log), and the Gigantoproductus sp. recorded from a similar level in the Langar No. 1 Borehole (W H C Ramsbottom, BGS report PD/58/20). Cores from the Bingham No. 1 Borehole have yielded a macrofauna that includes Productus sp. and a zaphrentid species. An indistinct microfauna is also present, but is not diagnostic of age. Core samples of limestone from the Bottesford Nos 1, 3 and 4, and Granby Nos 1 and 2 boreholes, collected more than 8 m beneath the base of the Namurian, have yielded microfaunas that indicate an Holkerian age. Farther north, in strata comprising part of the hanging-wall block of the Eakring–Foston Fault, the highest Dinantian beds in the Farndon No. 1 Borehole are of late Brigantian age, whereas strata within a few metres of the basal Namurian in the Rolleston No. 1 Borehole are late Asbian.

Between the Harlequin and Foss Bridge faults, tuffaceous mudstone overlies Dinantian strata (Saxondale No. 1 and Cropwell Butler No. 1 boreholes; (Figure 7). The volcanic rocks may be of Namurian age, or may equate with the thick succession of Dinantian basalts in the Strelley LN/4-2 Borehole, to the west of the district. Their lithology and age are discussed below (end of Chapter 4).

Seismic profiles show up to 2500 m of Dinantian strata in the Widmerpool Half-graben, the upper part of which is equivalent to the Widmerpool Formation of Asbian–Brigantian age in the Melton Mowbray district (Carney et al., 2004). The succession thickens progressively southwestwards, to about 5500 m against the Normanton Hills Fault at the opposite margin of the half-graben (Carney et al., 2001). Interpretation of seismic profiles (Ebdon et al., 1990; Fraser et al., 1990) and data from oil exploration boreholes (Carney et al., 2001) indicate that the succession consists of basinal carbonates, mudstones and calciturbidites (carbonate ramp to rimmed shelf facies) belonging to sequences EC2 to EC6 (Chadian to mid-Brigantian). The initial synrift, clastic wedge associations of sequence EC2 occur farther south, but are probably absent beneath the Nottingham district.

Namurian

Concealed strata of this age in the Nottingham district are the stratigraphical equivalents of the Edale Shale and Millstone Grit groups seen at outcrop in the southern Pennines. Following the discovery in 1939 of oil-bearing Namurian sandstone reservoirs in the Eakring Oilfield of central Nottinghamshire, further borehole and seismic investigations were undertaken, and the Namurian succession summarised in (Figure 5) was established (Lees and Taitt, 1946; Edwards, 1951; Falcon and Kent, 1960). The fact that Namurian strata provide both source and host rocks for the hydrocarbon reserves of the East Midlands has led to several attempts at stratigraphical correlation between the concealed and exposed successions (e.g. Downing and Howitt, 1969; Church and Gawthorpe, 1994). Recent regional syntheses of exploration-derived data on the Namurian have focused on the sequence stratigraphy, at both low resolution (Ebdon et al., 1990; Fraser et al., 1990; Fraser and Gawthorpe, 1990, 2003) and high resolution (Church and Gawthorpe, 1994, 1997).

To date, the Namurian strata of the Nottingham district are known from numerous hydrocarbon exploration boreholes, 28 of which prove the complete succession. Exploration has mainly targeted potential sandstone reservoirs on the crests or flanks of low amplitude Variscan inversion anticlines. As a result, borehole provings of Namurian strata are mostly clustered into two zones. A north-eastern cluster of boreholes date mainly from the late 1940s and 1950s, and possess summary lithological logs based on chippings and limited core runs, but no geophysical logs. However, full geophysical log suites are available for the more recent boreholes Parkhill No. 1 and Newark No. 1A (Figure 6), inset). The boreholes of the second zone are clustered in the south-east of the district, between the Cinderhill–Foss Bridge and Harlequin faults (Figure 7), and mostly date from the early 1960s onwards. Most have gamma-ray logs, which are supplemented by full log suites in two more recent boreholes, Saxondale No. 1 and Cropwell Butler No. 2. Of the sporadic provings of Namurian strata between these two zones, the most useful information comes from the Fiskerton and Screveton No. 1 boreholes (Figure 6), both of which have geophysical logs.

The major structures bounding the Nottingham Shelf (Figure 6), inset continued to control early Namurian sedimentation in the district. Active rifting and differential subsidence of the Widmerpool Half-graben had largely ceased (Ebdon et al., 1990; Fraser and Gawthorpe, 1990), but a substantial bathymetric low remained, enabling accumulation of the thick, basinal sequence of Pendleian to Alportian strata that constitute the Edale Shale Group. On the Nottingham Shelf, seismic stratigraphical interpretations, together with borehole provings farther south, indicate that lower to middle Pendleian strata are absent, and that the upper Pendleian to Alportian strata are highly condensed compared to their equivalents in the Widmerpool Half-graben. Referred to by Fraser et al. (1990) as the ‘gamma active shales’, these strata with their characteristic basinal or ‘gulf’ facies are dominated by organic-rich, calcareous mudstone. Sandstone, where present, is typically quartzitic.

The Kinderscoutian to Yeadonian succession of the Millstone Grit Group is dominated by coarse-grained, feldspathic sandstone with interbedded mudstone, siltstone and fine-grained sandstone, accompanied by minor seatearth and coal. The succession records the general southwards progradation of a major delta system across the Pennine Basin during the Namurian, and thus has a highly diachronous lower boundary. Practical difficulties arise when it comes to defining this boundary in boreholes in the Nottingham district, because the logs lack critical information on the feldspar content of the sandstones. In this memoir, the lower boundary of the Millstone Grit Group is drawn at the base of the lowest laterally persistent thick bed of coarse-grained sandstone, regardless of its mineralogy. So defined, this boundary also coincides generally with the base of the sandstone-dominated, upper part of the Namurian succession (?Kinderscoutian–Yeadonian), which also includes siltstone and mudstone with seatearth and minor coal (Figure 5). The Millstone Grit Group is well developed on the Nottingham Shelf, and there is regional evidence for thickening across the Cinderhill–Foss Bridge Fault into the Widmerpool Half-graben (Carney et al., 2004). However, there is no corresponding thickening into the Welbeck–Sleaford Low. Instead, the evidence indicates that the whole Namurian succession becomes attenuated north-eastwards, across the Eakring–Foston Fault (Figure 6). The Welbeck–Sleaford Low thus had no inherited bathymetric expression in the later part of the Namurian, and may have undergone minor tectonic inversion before that time.

Correlation of the Namurian throughout north-west Europe is greatly assisted by the presence within the succession of discrete marine bands, each containing a distinctive ammonoid fauna. Several of the important marine bands within the Marsdenian to Yeadonian succession have been proved in the district, and can be traced between boreholes by their distinctive geophysical log signature (Figure 6); (Figure 7). Subdivision of the succession based on these marine bands therefore provides a useful descriptive framework for the Millstone Grit Group, and also enables recognition of the major named sandstone units in this part of the Namurian, namely the Ashover Grit, Chatsworth Grit and Rough Rock. In contrast, there are no reliable provings of any marine bands below the base of the Marsdenian in the district, and hence no attempt has been made to subdivide the Edale Shale Group on a similar basis.

At least three separate episodes of Namurian volcanism are suggested by the borehole provings in the Nottingham district (see below). Volcaniclastic beds occupy restricted intervals in the lowermost part of Edale Shale Group in the south of the district, and within the Millstone Grit Group near the northern sheet boundary. Volcanic rocks of latest Namurian age occur in the east, but represent the basal parts of a long-lived phase of volcanism that spanned the Langsettian.

Edale Shale Group

The Edale Shale Group has since been renamed as the Bowland Shale Formation of the Craven Group (Waters et al., in prep). It is best developed to the south and west of the district, in the deeper parts of the Widmerpool Half-graben. There, it constitutes a prodelta succession of early Namurian (Pendleian–Alportian) age, comprising more than 600 m of calcareous, organic-rich mudstone with subordinate beds of turbiditic sandstone and argillaceous limestone (Falcon and Kent, 1960; Downing and Howitt, 1969; Fraser et al., 1990; Carney et al., 2004). In the Widmerpool No. 1 Borehole [SK 6366 2958], for example, 7 km south of the district, the succession is 649 m thick (Falcon and Kent, 1960; Carney et al., 2004). This characteristic, thick, basinal mudstone ‘gulf’ facies has not been proved in boreholes in the Nottingham district, all of which are located on the Nottingham Shelf (Figure 6). The shelf facies is more attenuated than the characteristic ‘gulf’ facies, with evidence of periodic emergence. A localised volcanic interval is also present near the base. Organic-rich, calcareous and pyritic mudstone remains the dominant lithology, however, reinforcing assignment to the Edale Shale Group.

In the shallower part of the Widmerpool Half-graben, occupying the south-west corner of the Nottingham district (Figure 6), approximately 250 m of the Edale Shale Group is inferred from seismic profile data. The character of this succession is indicated by the Colston Bassett North Borehole [SK 7100 3382], which lies only 3 km to the south of the district. The borehole proved 260 m of Edale Shale (Carney et al., 2004), consisting mainly of dark grey, variably calcareous, carbonaceous and pyritic mudstone, with subordinate beds of muddy or silty limestone. Sandstone is rare except in the uppermost 50 m, where a few beds of mainly finegrained, argillaceous sandstone are present, associated with mudstone, seatearth and ganister horizons. The Cravenoceras leion Marine Band has been proved at the base of the Edale Shale Group in the borehole, but there is no firm biostratigraphical evidence for the age of the upper boundary. If, as suggested below, the sandstones at the base of the overlying Millstone Grit Group correlate with the Kinderscout Grit of the southern Pennines, the implication is that the Edale Shale Group ranges in age from Pendleian to Kinderscoutian.

Like the prodelta ‘gulf’ facies, the Edale Shale strata of the Nottingham Shelf are dominated by mudstone, which is variably micaceous, calcareous, pyritic and organic-rich. There are, however, numerous seatearth and ganister beds throughout the succession. Thin beds of sandstone, commonly calcareous, are common, and one such bed, which grades to a sandy limestone, lies at or just above the base of the group in most boreholes. These strata, with their lack of marine bands and abundance of rootlet horizons, indicate a marginal facies of the Edale Shale Group, characterised by frequent periods of emergence and substantial fluvial influence. The environment of deposition was probably within an interdistributary bay, with sporadic thin sandstone beds deposited by episodic floods. The thicker, coarse-grained sandstone beds recorded in Langar No. 1 Borehole (Figure 7) probably represent a local minor distributary channel and associated proximal crevasse splay deposits. The strongly pyritic, calcareous mudstones that are particularly common near the base were probably laid down during sea level highstands, but the lack of a marine fauna suggests brackish water with significant fluvial influence.

The thickest provings of the shelf sequence are in the Saxondale No. 1 (73 m) and Cropwell Butler No. 1 (55 m) boreholes (Figure 7), where volcanic rocks are also well developed (see below). These boreholes are located close to the transition between the Nottingham Shelf and Widmerpool Half-graben. Elsewhere on the shelf, the Edale Shale Group varies from 15 to 30 m thick (excluding intercalated intrusive igneous rocks), with a general thinning towards the east. Some of the thickest (up to 3 m) upwardfining beds of sandstone with coarse-grained bases have been recorded in Langar No. 1 Borehole, but not elsewhere. The lowest few metres of mudstone in many boreholes are typically strongly pyritic and organic-rich, with a high gamma-ray log response. In the Normanton No. 4 Borehole, these mudstones have yielded Cravenoceras sp. and Cravenoceratoides sp., indicating a late Pendleian to Arnsbergian age. This supports the conclusion from seismic stratigraphy (Fraser et al., 1990) that much of the Pendleian (seismic sequence LCN2a) is absent on the Nottingham Shelf. It also suggests that, locally at least, a complete Arnsbergian to Alportian succession (seismic sequence LCN2b) may be present, albeit highly condensed. As in the Widmerpool Half-graben, the topmost Edale Shale beds on the Nottingham Shelf are tentatively inferred to be of Kinderscoutian age.

The Edale Shale Group is absent from the Newark No. 1A Borehole, in the extreme north-east of the district (Figure 6), and probably also from the whole of the area formerly occupied by the Welbeck–Sleaford Low.

Millstone Grit Group

In the southern Pennines and adjacent areas, the term Millstone Grit is now formally defined in the sense intended by Stevenson and Gaunt (1971), as that part of the Namurian succession dominated by coarse-grained feldspathic sandstone interbedded with mudstone, siltstone and fine-grained sandstone, accompanied by minor coal and seatearth. It is no longer broadly equivalent to the Namurian, as it excludes the mudstone and subordinate quartzitic sandstone of the underlying Edale Shale Group. In the Nottingham district, information on the mineralogy of the sandstones is usually lacking in borehole logs, so for practical purposes the lower boundary of the group is drawn at the base of the lowest persistent coarse-grained sandstone (Figure 5). This bed lies just below the principal consistently identifiable chronostratigraphical marker in the Namurian of the Nottingham district, namely the Bilinguites gracilis Marine Band. No marine bands have been proved below this sandstone, so its age cannot be determined with certainty, but it most likely correlates with the Kinderscout Grit of the southern Pennines, which is late Kinderscoutian (R1c) in age. The top of the group is drawn at the base of the Subcrenatum (Pot Clay) Marine Band, which has been proved in the Langar No. 1 and Langar No. 4 boreholes, and is recognisable on geophysical logs in several other boreholes in the district.

In the Nottingham district, the Millstone Grit Group ranges from a maximum of 121 m thick in the Parkhill No. 1 Borehole to only 23 m in the Newark No. 1A Borehole. The latter, in conjunction with the other provings shown in (Figure 6), illustrates the attenuation of the group eastwards across the Eakring–Foston Fault, a feature suggesting the inversion earlier in the Namurian of the Welbeck–Sleaford Low basin. Greater thicknesses of the Millstone Grit are likely below the western part of the district, as it is known that the group thickens westwards on the Nottingham Shelf and southwards into the Widmerpool Half-graben (Church and Gawthorpe, 1994; Carney et al., 2004). In the Nottingham district, however, there is no borehole evidence to substantiate this. At outcrop farther west, on the eastern flanks of the Derbyshire Dome, the group is typically about 300 to 400 m thick (Frost and Smart, 1979).

Church and Gawthorpe (1994, 1997) have described the stratigraphy of much of the Millstone Grit succession (Marsdenian to Yeadonian) to the east of Nottingham. They divide the succession into a number of sequences, each of which represents the response of the Namurian fluviodeltaic depositional system to a complexity of processes (not necessarily related to eustacy) that have brought about changes in the patterns of sedimentary stacking (Church and Gawthorpe, 1997). Thick fluvial channel sandstones are interpreted as the fills of incised valleys formed during periods of relative sea level fall (lowstand systems tracts). Transgressive systems tracts were deposited during the ensuing rise in relative sea level, and contain a variety of lithofacies that indicate gradual submergence of the delta plain. Marine bands represent the maximum flooding surface of each sequence, when marine waters inundated the delta plain. Highstand systems tracts overlying the marine bands again comprise a variety of lithofacies, but generally represent periods of delta progradation as rates of sediment accumulation exceeded rates of relative sea level rise. Church and Gawthorpe (1994) named each sequence after the marine band forming its maximum flooding surface. Most of the sequences are thin and represented only by the transgressive and highstand systems tracts. The only lowstand systems tracts preserved in the Nottingham district are the locally developed fluvial channel sandstones of the Ashover Grit and Rough Rock. The stratigraphical correlations presented in this memoir (Figure 6); (Figure 7) differ little from those of Church and Gawthorpe (1994), except that the base of the Marsdenian (Bilinguites gracilis Marine Band) has been drawn at a higher level in Screveton No. 1 Borehole. Interpretations of the depositional environment of various stratigraphical units are also based largely on the geophysical ‘log facies’ of Church and Gawthorpe (1994).

Upper Kinderscoutian (R1c) strata

Except in the Newark No. 1A Borehole, where pre-Marsdenian strata are absent (Figure 6), the Bilinguites gracilis Marine Band, marking the base of the Marsdenian, is underlain by a sandstone-dominated series consisting of beds of fine to medium or, less commonly, coarse-grained sandstone, up to 3 m thick, interbedded with subordinate siltstone and mudstone with minor seatearth. More substantial beds of medium to coarse-grained sandstone, up to 7 m thick with basal, granule-grade lags, are noted in some logs. This sandstone-dominated series is typically 12 to 15 m thick, reaching a maximum of 20 m in the Bingham No. 1 Borehole and declining rapidly eastwards to only 5 m in the Granby No. 2 and Bottesford No. 4 (Figure 7) boreholes. No marine bands have been recorded within or below these strata, but they most likely correlate with the Kinderscout Grit of the southern Pennines, implying a late Kinderscoutian (R1c) age.

These strata display considerable variability, even between closely spaced boreholes, with a wide range of gamma-ray log signatures. The latter include serrated motifs, indicating interbedding of sandstone and siltstone or mudstone beds, and funnel-shaped motifs, suggesting upward-coarsening units. Thicker beds of coarse-grained sandstone with granule lags have more barrel-shaped profiles. This variability probably indicates a complex association of delta front and lower delta plain depositional environments, including crevasse splays (interbedded units), distributary mouth bars (upward-coarsening units) and minor distributary channel-fills (thicker sandstone units).

Marsdenian (R2) strata

The base of the Marsdenian Stage is placed at the base of the Bilinguites gracilis Marine Band, and the base of the succeeding Yeadonian Stage at the base of the Cancelloceras cancellatum Marine Band. On the eastern flanks of the southern Pennines, the stage includes two persistent coarse-grained sandstone units, the lower Ashover Grit being of R2b age and the higher Chatsworth Grit of R2c age. Both units have been interpreted as delta top distributary channel fills (Collinson, 1988; Steele, 1988). Their equivalents have long been recognised in boreholes in the Nottingham district, and have been the targets of extensive exploration for hydrocarbons (Lees and Taitt, 1946; Falcon and Kent, 1960).

The Bilinguites gracilis Marine Band has been proved in the Cropwell Butler No. 1 and Langar No. 1 boreholes (BGS Biostratigraphy Report PD/58/20). In the former (Figure 7), it is separated from the overlying Bilinguites bilinguis Marine Band by about 1.5 m of mudstone with common fish remains. The close spacing of these two marine bands produces a distinctive double serration on the gamma-ray log that can be recognised in most other boreholes in the district.

Strata between the Bilinguites bilinguis and B. bilinguis (late form) marine bands are typically 8 m thick, with a maximum of 20 m proved in the Parkhill No. 1 Borehole (Figure 6). The succession generally thins eastwards and has not been recorded in the Newark No. 1A Borehole, where the high gamma-ray peak at the base of the Namurian succession may be an amalgamation of the B. gracilis, B. bilinguis and B. bilinguis (late form) marine bands. This interval consists mainly of mudstone, but several boreholes record beds of argillaceous sandstone and seatearth towards the top. The gamma-ray log has a funnel-shaped profile suggesting an overall upward-coarsening trend. The B. bilinguis (late form) Marine Band has been proved palaeontologically in the Cropwell Butler No. 1, Langar No. 1 (BGS Biostratigraphy Report PD/58/20) and Screveton No. 1 boreholes, and correlated elsewhere by its geophysical log signature. In the Fiskerton (Figure 6) and Bingham No. 1 boreholes, geophysical log correlation suggests that the B. bilinguis (late form) Marine Band has been removed either by faulting or by erosion below the Ashover Grit.

The interval between the Bilinguites bilinguis (late form) and B. superbilinguis marine bands includes the local correlatives of the Ashover Grit of the eastern flanks of the southern Pennines. In the northern part of the district, this interval reaches a maximum thickness of 37 m in the Parkhill No. 1 Borehole, declining eastwards to only 12 m in Newark No. 1A (Figure 6). Eastwards thinning is also evident in the southern part of the district, from a maximum of 46 m in the Saxondale No. 1 Borehole to only 27 m in Bingham No. 2. In the Bottesford No. 4 Borehole (Figure 7), the interval is probably less than 10 m thick and dominated by igneous rocks (see below).

The thickest and most characteristic development of the Ashover Grit in the district lies in the lower part of the interval between the Bilinguites bilinguis (late form) and B. superbilinguis marine bands, below an unnamed marine band identified by Church and Gawthorpe (1994). The sandstones at this level generally occur within a single, pebbly-based unit, 5 to 17 m thick, with a barrel-shaped gamma-ray log profile. These sandstones are generally recorded in boreholes as coarseor very coarse-grained, and are interpreted by Church and Gawthorpe (1994) as the infill of an incised fluvial channel formed during a fall in relative sea level. A persistent thin coal seam, here informally named the Ashover Coal, either directly overlies the sandstone or is separated from it by up to 5 m of seatearth with beds of ganister (Figure 7). The coal produces a distinctive low ‘kick’ on gamma-ray logs in most boreholes in the district.

The unnamed marine band of Church and Gawthorpe (1994) overlies the Ashover Coal and was proved in the Wild’s Bridge Borehole in the adjacent Melton Mowbray district, where it contains Lingula but no ammonoids. A Lingula Band has been proved at this level in the Cropwell Butler No. 1 Borehole, and is identified elsewhere in the Nottingham district by its high gamma-ray log response. The strata above this marine band form a general, upward-coarsening progradational succession of mudstone, siltstone and fine-grained sandstone, 5 to 20 m thick, overlain by the Bilinguites superbilinguis Marine Band. Thicker beds of coarse-grained sandstone, up to 12 m thick, with barrel-shaped gamma-ray log profiles, occur just below the B. superbilinguis Marine Band in some boreholes, notably Parkhill No. 1 and Fiskerton (Figure 6), and may represent locally developed minor distributary channel fills.

The Bilinguites superbilinguis Marine Band has been proved in the Bingham Nos 1 and 2, Langar No. 1 and Cropwell Bishop No. 1 boreholes (Figure 7), and also in the Colston Bassett North Borehole, just south of the district (Carney et al., 2004). As well as ammonoids, the band contains abundant Lingula, marine bivalves and fish remains. In the southern Pennines, the interval between the Bilinguites superbilinguis and Cancelloceras cancellatum marine bands (R2c) includes another thick fluvial channel sandstone complex, the Chatsworth Grit. At outcrop in the adjacent Derby district, the R2c interval is generally about 60 m thick (Frost and Smart, 1979), but the equivalent in the Nottingham district ranges from 7 to 30 m in thickness, thinning eastwards across the Eakring–Foston Fault (Figure 6). Based on palaeontological determination of specimens from the Wild’s Bridge Borehole in the Melton Mowbray district, provided to BP by the BGS (N J Riley, written communication), Church and Gawthorpe (1994) identified another marine band, that of Verneulites sigma, 3 m above the B. superbilinguis Marine Band. A bed with high gamma-ray values, 3 to 5 m stratigraphically above the latter marine band in the Nottingham district (Figure 7), is correlated with the Verneulites sigma Marine Band.

Above the Verneulites sigma Marine Band, an upwardcoarsening succession, 8 to 25 m thick, is indicated by a funnel-shaped gamma-ray log profile. This cycle culminates a few metres below the Cancelloceras cancellatum Marine Band. Most of the succession was cored in the Cotgrave Bridge Borehole, where it coarsens gradually upwards from micaceous siltstone with scattered plant and fish remains at the base, to ripple cross-laminated, fine-grained sandstone interbedded with micaceous siltstone at the top. Large worm burrows have been recorded towards the top, together with abundant plant remains. By analogy with the log facies of Church and Gawthope (1994), the succession is interpreted as a progradational, prodelta to distributary mouth bar sequence. Other boreholes in the south of the district generally record a few thin beds of fine-grained sandstone towards the top of this upward-coarsening succession, which is commonly capped by a ganister. The only true representatives of the Chatsworth Grit fluvial channel sandstone facies to be proved in the district are coarse-grained sandstone units, respectively 10 and 12 m thick, recorded in the Fiskerton and Parkhill No. 1 boreholes. These have sharp-based, barrel-shaped gamma-ray log motifs (Figure 6) suggesting distributary channel fills (compare with Church and Gawthorpe, 1994). However, the spacing and distribution of boreholes means that thick unproved developments of Chatsworth Grit could be present below other parts of the district, especially in the north-west.

Church and Gawthorpe (1994) placed a sequence boundary at the top of the upward-coarsening succession, which they regarded as a progradational highstand systems tract. They interpreted the strata above the boundary as the transgressive systems tract of a separate sequence. The relationship to this sequence boundary of the thick channel sandstones in the Fiskerton and Parkhill No. 1 boreholes is unclear. They may represent the incised valley fills of a lowstand systems tract related to the upper sequence or, alternatively, may be fluvial channel fills associated with the culmination of delta plain progradation in the underlying highstand systems tract. The latter is considered more likely, given the lack of evidence within the district for substantial incision at the bases of the channels.

A thin, 3 to 7 m thick interval, consisting predominantly of siltstone with beds of sandstone, seatearth and ganister, and characterised by a steadily increasing gamma-ray log signature, intervenes between the top of the upward-coarsening succession and the Cancelloceras cancellatum Marine Band. A thin coal, probably correlating with the Ringinglow Coal of the adjacent Derby district (Frost and Smart, 1979), has been proved immediately above the top of the upward-coarsening sequence in the Bingham No. 1, Granby No. 1 and Langar Nos 2 and 6 boreholes. A Lingula Band overlies the coal in Bingham No. 1 and has been proved at a similar stratigraphical level in other boreholes, notably those at Cotgrave Bridge, Tithby and Holme Pierrepont. Thin sandstones above this coal may be the local equivalent of the Redmires Flags of the southern Pennine Basin (Frost and Smart, 1979; Stevenson and Gaunt, 1971).

In the Cropwell Butler No. 1, Cropwell Butler No. 2 and Saxondale No. 1 boreholes, most of the R2c succession down to the Verneulites sigma Marine Band has been removed by erosion below an unusually thick development of the Rough Rock (Figure 7). Church and Gawthorpe (1994) have interpreted this as a lowstand incised valley fill, which was eroded during an episode of relative sea level fall in the Yeadonian.

Yeadonian (G1) strata

The base of the Yeadonian Stage is placed at the base of the Cancelloceras cancellatum Marine Band, and that of the succeeding Westphalian Series at the base of the Subcrenatum Marine Band. Another widespread marine band, characterised by Cancelloceras cumbriense, occurs within the Yeadonian. The Rough Rock, a major sheet-like fluvial sandstone deposit (Bristow, 1988, 1993), occurs between the Cancelloceras cumbriense and Subcrenatum marine bands and is recognisable over much of the Pennine Basin.

In the Nottingham district, the Cancelloceras cancellatum and C. cumbriense marine bands have been identified separately only in the Cotgrave Bridge Borehole. There, they each consist of up to 2 m of dark grey, silty, pyritic mudstone with abundant large Lingula, marine bivalves and fish remains. Orbiculoidea was recorded in the C. cumbriense Marine Band, and only this marine band contains ammonoids, analogous to the situation in the adjacent Derby district where the C. cancellatum Marine Band has an impoverished linguloid fauna with no ammonoids (Frost and Smart, 1979). The marine bands are separated by a 3 m thick succession that coarsens upwards from grey micaceous siltstone to fine-grained ganisteroid sandstone. A thin coal seam lies immediately below the C. cumbriense Marine Band. Cancelloceras cancellatum has also been recorded in the Bingham No. 1, Holme Pierrepont and Cropwell Bishop No. 1 boreholes, and in the Colston Bassett North Borehole just south of the district. A Lingula band occurs at the corresponding level in the Tithby and Langar Nos 1 and 6 boreholes, and produces a characteristic geophysical log signature that is recognisable in many other boreholes (Figure 7).

The interval between the Cancelloceras cumbriense and Subcrenatum marine bands (G1b) maintains a near constant thickness of between 8 and 10 m in most boreholes in the district. It consists mainly of mudstone and siltstone with abundant rootlets. The lower two thirds of the interval has a funnel-shaped, upward-decreasing gamma-ray log profile, and is capped by a thin (2–3 m) ganisteroid sandstone. Above this, 2 to 4 m of rootletbearing mudstone and siltstone with a steadily increasing gamma-ray log response underlie the Subcrenatum Marine Band.

In the Saxondale No. 1, Cropwell Butler Nos 1 and 2 and Bulcote (Edwards, 1951) boreholes, the Subcrenatum Marine Band is underlain by a sandstone-dominated succession, 28 to 35 m thick, totally unlike the succession in other boreholes in the district. The base of the sandstone typically lies just above the Bilinguites superbilinguis or Verneulites sigma Marine Band and has clearly cut out the Cancelloceras cancellatum Marine Band, together with about 20 to 30 m of the underlying succession (Figure 7). The sandstone has a barrel-shaped geophysical log profile with an abrupt base, and fines upwards internally from coarse-grained at the base to very fine-grained with siltstone partings in the upper half. On the basis of log facies, Church and Gawthorpe (1994) identified it as a locally developed fluvial channel sandstone. They argued that the sandstone represents the local incised valley fill of a lowstand systems tract formed during an episode of relative fall in sea level. The Subcrenatum Marine Band is interpreted as the maximum flooding surface at the top of a thin transgressive systems tract that overlies the lowstand deposit. Church and Gawthorpe (1994) equated the channel sandstone with the Rough Rock of the southern Pennines, which they also argue, perhaps more controversially, to be an incised lowstand succession. The correlation is reinforced by an identification of the ‘Sand Rock Mine’ non-marine fauna, diagnostic of the Upper Rough Rock sequence, about 3 m below the Subcrenatum Marine Band in the Wilds Bridge Borehole, about 2 km south of the Nottingham district (Riley, 1984).

Westphalian

The Westphalian rocks of the district commence at the base of the Subcrenatum Marine Band. They consist mainly of the ‘productive’ Coal Measures, but an overlying, relatively thin Barren Measures sequence is preserved locally. Westphalian strata only crop out in a very small area in the west, around Radford [SK 545 404] in the city of Nottingham. Almost all the information reviewed here is derived from borehole and mining data. The dataset is generally very extensive for the Coal Measures, due to the intensity of coal mining and coal exploration in the district, especially in the west. Farther east, however, where coal exploration boreholes are fewer, there is a paucity of detailed lithological information, although the abundance of oil exploration boreholes does help to provide details of the Westphalian stratigraphy there.

Westphalian nomenclature in the Pennine Basin has evolved along both lithostratigraphical and chronostratigraphical lines, leading to a plethora of names for the same or similar sequences. The lithostratigraphical nomenclature developed for the exposed coalfield east of the Pennines has remained in general usage, despite the advances in chronostratigraphical correlation of the Westphalian successions across Europe. Various other faunal and floral schemes have been used to correlate Westphalian strata in the Pennine Basin; these were reviewed by Ramsbottom et al. (1978) and some are indicated in Table 11. They are not discussed further in this account. The limitations of a borehole-based dataset are such that lithostratigraphical nomenclature is more difficult to apply than a chronostratigraphical scheme, especially in the cyclicity-dominated Westphalian. The Coal Measures and Barren Measures are recognised as major units on the Nottingham map (Sheet 126) but it should be noted that there has been a revision of Westphalian lithostratigraphical nomenclature since publication of the map. The Coal Measures now have group ranking and the Lower, Middle and Upper divisions (Table 11) each constitute a formation (Powell et al., 2000). A chronostratigraphical element is implicit in this nomenclature for those units that have boundaries defined at a faunal datum, represented by the marine bands. For the minor subdivisions, lithostratigraphical names are used for certain sandstone units, coal seams and marine bands.

Coal Measures (Pennine Coal Measures Group)

The intensive coal mining activity in the district (see Chapter 2) has ensured that the stratigraphy of the concealed Coal Measures sequence is well known. Early work on the Coal Measures of the East Pennine Coalfield, including the concealed part beneath the Nottingham district, was summarised by Edwards (1951). There has been little additional work on the broader nature of the Westphalian sequence since that time (although see Howitt and Brunstrom, 1966), but a number of researchers have concentrated on the tectonic and sedimentological history of the Coal Measures beneath the district, using borehole data and information obtained during mining operations; summaries are given in Eden (1954), Calver (1969), Besly (1988a, b) and Guion and Fielding (1988), as well as the many other works cited below.

Table 11 presents a summary of the terminology used in this account and its relationship to other nomenclature in the literature. The Subcrenatum (Pot Clay), Vanderbeckei (Clay Cross) and Aegiranum (Mansfield) marine bands define the chronostratigraphy of the Westphalian, and as they are also identified in most core and on geophysical logs, they are obvious correlation markers as well as approximate time lines. The base of the Coal Measures is placed at the Subcrenatum Marine Band, and the Langsettian–Duckmantian (Westphalian A–Westphalian B) boundary is taken at the base of the Vanderbeckei Marine Band, which also coincides with the junction between the Lower and Middle Coal Measures. The Duckmantian–Bolsovian (Westphalian B–Westphalian C) boundary is placed at the base of the Aegiranum Marine Band, and is somewhat lower in the sequence than the Middle–Upper Coal Measures junction, which is taken at the top of the Cambriense (Top) Marine Band. The latter marine band is not well developed in the Nottingham district, and so this lithostratigraphical boundary is difficult to locate accurately.

The lithostratigraphical boundary between the Coal Measures and the overlying Barren Measures is taken at the base of the Etruria Formation, which marks the first occurrence of primary red beds in the Westphalian succession and is probably diachronous. The base of the Etruria Formation can be difficult to identify where only written or chippings logs core are available because of the abundance of secondary reddening beneath the Barren Measures. The formation does have a characteristic wireline log signature (Figure 17), however, and using this, the base of the Etruria Formation, and therefore the contact between the Coal Measures and Barren Measures, can be inferred with reasonable accuracy across the district. The base of the Etruria Formation in the Nottingham district is generally of early to middle Bolsovian age, although it is somewhat older in the south-east and may locally be of latest Duckmantian age.

Conditions of deposition

During much of Westphalian times, subsidence was fairly uniform, with little differential uplift along active faults, allowing a thick sedimentary succession to accumulate in environments that fluctuated between a lower delta plain setting, with frequent marine incursions, and fluvialdominated upper delta plain conditions. The strata, which characterise the Coal Measures throughout the Pennine Basin, consist of grey mudstone, siltstone and sandstone with subordinate coal, seatearth and ironstone deposited in cyclic sequences (cyclothems). A typical small-scale interseam cycle (Guion et al., 1995) commences with a basal dark grey to black, carbonaceous and commonly pyritous mudstone, containing nonmarine or less commonly marine fauna (lacustrine or marine conditions). The succeeding strata generally become coarser with siltstone and sandy siltstone (overbank or distal lacustrine delta). They pass in turn up into sandstone (proximal delta or channel), with the top of each interseam cycle generally being marked by a seatearth (gleysol, palaeosol) and a coal (mire facies). Plant remains and debris are common throughout these cycles. Some sandstone bodies do not form the tops of cycles, but occur instead within cycles as channel fill bodies. Basaltic volcanism profoundly affected Lower Coal Measures sedimentation in the east of the district, and there is some evidence for extrusive activity in neighbouring areas, persisting into early Middle Coal Measures times. Concomitant intrusive activity is recorded at various levels throughout the Lower Coal Measures.

The laterally extensive marine bands in the succession represent major periods of widespread marine transgression. Other, usually localised incursions led to deposition of mudstones with Lingula and Estheria, indicating semimarine conditions (Calver, 1969). The Vanderbeckei (Clay Cross) Marine Band represents the only significant marine incursion throughout much of the later Langsettian and early Duckmantian, and occurs throughout the Pennine Basin. By latest Duckmantian and early Bolsovian times, there was a decline in the abundance and thickness of coal seams and a corresponding increase in the number of marine bands, suggesting a change to lower delta plain conditions. A predominantly alluvial, coal-bearing environment is invoked for the Upper Coal Measures, above the Cambriense Marine Band, such strata being present only in the north-west of the Nottingham district.

Lower Coal Measures

A summary of the main variations in Lower Coal Measures strata in different parts of the district is given in (Figure 8), and typical seam thicknesses are indicated in (Table 1). South-west of the Eakring–Foston Fault System, there is an overall eastwards thinning of the formation, a trend which is offset in the south-east, where strata are replaced laterally, and the sequence thickened, by basaltic volcanic rocks. Basalt lavas and breccias dominate the 336.8 m thickness of Lower Coal Measures in the Bottesford No. 4 Borehole, for example, whereas in the Granby No. 1 Borehole, located only some 4 km to the south-west, the sedimentary component is predominant (Figure 19), with an aggregate thickness of about 205 m. An increased thickness of 232 m was proved farther west, in the Harlequin No. 1 Borehole, and 223 m of Lower Coal Measures strata were proved in the Parkhill No. 1 Borehole farther north (these values are exclusive of basaltic sills). A thickness of only 158 m was recorded for the Lower Coal Measures in the Farndon No. 1 Borehole, which is situated on the north-eastern side of the Eakring–Foston Fault System.

Sedimentation early in Langsettian times was very similar to that in the Millstone Grit Group, with lower delta plain to shallow water deltaic environments prevailing. It is characterised by abundant fluvial sand bodies, representing the thicker accumulations of distributary systems. Units such as the Crawshaw Sandstone, Loxley Edge Rock and Wingfield Flags are readily identifiable in the exposed coalfield and are correlatable into the concealed coalfield to the east. The Belperlawn, Alton and Norton coals represent the only significant development of delta top swamps at the time. The progradation of deltas was punctuated by periodic sea level highstands that provided conditions for the deposition of sheet-like, dark grey to black, fissile mudstone containing the marine and semi-marine bands. In addition to their ammonoid and other faunas, which can be widely correlatable, these horizons have characteristically high gamma-ray peaks on wireline logs and can therefore be used extensively as regional geophysical correlation markers. In addition to the basal Westphalian Subcrenatum Marine Band, the Langsettian strata beneath the Blackshale Coal contains a number of other marine and semi-marine bands, many of only local development. These include the Listeri (Alton) Marine Band and a number of Lingula bands including the Amaliae (Norton) Lingula Band (Figure 8).

The coals at the base of the Lower Coal Measures are generally thin and laterally discontinuous. Economic potential is nevertheless high for these lower measures, in that the fluvial sandstone bodies, especially the Crawshaw Sandstone, act as reservoir rocks for hydrocarbons that are exploited in the oil fields immediately north of the district.

In the exposed coalfield, the fluvial sandstones of the Lower Coal Measures show an upward stratigraphical transition from coarse-grained types, which occupy wide, low-sinuosity channels, to more sinuous, narrow bodies of finer grained sandstone that are intepreted as major distributaries. This reflects a change from lower delta plain to upper delta plain sedimentary environments through the middle part of the Langsettian (Fielding, 1986). It is generally accepted that a level immediately beneath the Kilburn Coal marks the onset of upper delta plain conditions (Guion and Fielding, 1988) and is thus a good ‘divider’ of the Langsettian sequence. There is a concomitant increase in the development of coalproducing swamps up-section, resulting from sediment being distributed via wide channels into shallow freshwater lakes that periodically filled and became covered with vegetation. The strata from the Blackshale Coal upwards to the Vanderbeckei Marine Band are typical of the ‘productive measures’, and include a number of the worked coal seams of the district. Some of the thicker coals, such as the Tupton and Top Hard, can be correlated over very large areas, and represent prolonged periods of swamp development. The discontinuous sandstone units within this sequence represent distributary channel fills with highly variable palaeocurrent directions indicative of high sinuosity and a complex localised fluvial palaeogeography on the upper delta plain. A fauna of nonmarine bivalves dominates this part of the sequence, including Anthracosia, Anthraconaia and Naiadites. Named sandstones include the Tupton Rock and the Parkgate Rock, with further, generally unnamed sandstones occuring above the Yard and Roof Soft coals. The only other marine influence recorded in these strata is the ‘Low Estheria’ Band, which is locally represented at a level immediately above the Blackshale Coal, although this is nowhere developed to the extent that it is farther north. The remainder of the sequence records cyclic filling of and subsequent swamp development on freshwater lakes, with mudstone and siltstone interspersed with coal seams and thin sandstones.

There is little evidence for synsedimentary faulting during deposition of the Lower Coal Measures, although some seam splits may be associated with fault movement along some of the long-lived crustal lineaments of the district. The evaluation of such tectonism is complicated by the probability that large thicknesses of peaty deposits within the sequence have caused differential compaction-induced subsidence in some of the inter-distributary basins, with effects similar to tectonic faulting. Inspection of stratal variation between the Bulcote and Newark No. 1A boreholes suggests that, if the intercalated basaltic sills are not considered, the sedimentary component of the Lower Coal Measures, particularly the sequence between the Subcrenatum and Amaliae marine bands, thins north-eastwards (Figure 9). The cause of this is uncertain, but may be related to syndepositional movements associated with the Eakring–Foston Fault System. A degree of local tectonic instability may be inferred from the fact that the district was affected by magmatism throughout Langsettian time, as demonstrated by the extrusive basaltic rocks that dominate the sequence in the south-east. Volcanic activity of latest Langsettian age is furthermore indicated by the occurrence of basic tuffs in the north-east, around Newark, and by ash-grade volcanic beds intercalated at the Black Rake horizon (see below).

Subcrenatum Marine Band to top of the Kilburn Coal

The measures in this interval are mainly recorded from the older, fully cored coal exploration boreholes in the south and centre of the district, some of which have geophysical logs. There are no provings in the northwest of the district, and sections in the north-east and south-east are restricted to oil exploration boreholes with sketchy lithological descriptions based on cuttings, although the more recent wells have good suites of geophysical logs (Figure 9). Eden (1954) described the stratigraphy of much of this interval in the centre and south of the district in some detail, using information from cored boreholes. Only the Tithby Borehole offers a combination of geophysical logs and cores, and has been used here to establish a geophysical log stratigraphy for the strata between the Subcrenatum and Listeri marine bands (Figure 9). The latter constitutes an important correlation datum throughout the East Midlands by virtue of its distinctive, very high gamma-ray peak (Knowles, 1964; Taylor and Howitt, 1965). The Kilburn Coal, or its equivalent datum where coal is not developed, is identifiable in many boreholes, where it locally overlies sandstone with distinctive bronze and green micas (Taylor and Howitt, 1965). A thin chamositic mudstone and siltstone bed underlies the same sandstone, and is correlated with the so-called ‘Kilburn Marker’ of the East Midlands oilfield (Falcon and Kent, 1960; Taylor and Howitt, 1965). Despite the availability of these markers, however, the presence of basaltic sills in much of the eastern part of the district, and the incoming of volcanic rocks in the south-east, introduces a degree of uncertainty for stratal correlations in those areas, especially towards the base of the interval. None of the coals have been exploited in the district, although the Kilburn Coal was extensively worked in the Derby district to the west (Frost and Smart, 1979; Charsley et al., 1990).

The Subcrenatum Marine Band is proved by records of the ammonoid Gastrioceras subcrenatum or G. cf. subcrenatum in the Bulcote, Cropwell Bishop No. 1 and Langar Nos 1 and 4 boreholes. As well as the eponymous ammonoid, the marine band contains Lingula, Orbiculoidea, marine bivalves and fish remains; Eden (1954) gives a full faunal list. The marine band is absent beneath the erosive base of the Crawshaw Sandstone in the Holme Pierrepont Borehole (see below and Figure 9). In several other boreholes, it can be identified by its characteristic high gamma-ray response (Figure 9) and, in some cases, by an association with Lingula and unidentified ammonoid fossils. In the Bulcote Borehole, the marine band is 1.9 m thick and consists of dark grey, fissile, pyritic mudstone with nodular ironstone layers.

The stratigraphy between the Subcrenatum and Listeri marine bands is complicated by doleritic sills (Figure 9) and Eden, 1954, plate IIB, which substantially thicken those parts of the succession that have been intruded. Where sills are absent, the interval is typically 35 to 40 m thick in the centre and south of the district, thinning to only 9 m in the Newark No. 1A Borehole in the extreme north-east. Regionally, five cyclothems occur within this interval, all of which are represented in the Nottingham district (Eden 1954). In upward sequence, the coals within this interval are the Belperlawn, Holbrook, 2nd Smalley, 1st Smalley and Alton seams; they are typically thin (mostly less than 0.3 m), laterally impersistent and, with the exception of the Alton Coal, commonly washed out (Eden, 1954). The Holbrook, Springwood and Honley marine bands are represented by Lingula-bearing mudstones recorded above the Holbrook, 2nd Smalley and 1st Smalley coals respectively (Eden, 1954). The mudstone and siltstone within this interval is notable for its paucity of nonmarine bivalve and fish remains (Eden, 1954), when compared with other areas outside the district.

The most significant development of sandstone within this interval occurs between the Subcrenatum Marine Band and the Belperlawn Coal, and thus correlates with the Crawshaw Sandstone of the eastern margin of the southern Pennines. The sandstone is thickest (12–27 m) in the centre and south of the district (Figure 8); (Figure 9), where it consists predominantly of medium- to very coarse-grained sandstone with sporadic pebbly lags; on geophysical logs it is characterised by a barrel-shaped gamma-ray log profile with a low response. In the Holme Pierrepont Borehole, the pebbly base of the Crawshaw Sandstone lies with erosional contact on the Rough Rock, cutting out the Subcrenatum Marine Band. The coarse-grained development of the Crawshaw Sandstone strongly resembles the sandstones of the underlying Millstone Grit, especially the Rough Rock, in terms of both lithology and distribution. It probably represents the infill of major braided fluvial channels, with local incision possibly resulting from minor contemporaneous tectonic movement along faults. Similar incision through the Subcrenatum Marine Band by the Crawshaw Sandstone is recorded in the Ruddington Borehole to the south of the district (Eden, 1954), and in the Bothamsall oilfield in the Ollerton district to the north (Taylor and Howitt, 1965). The Crawshaw Sandstone channel is believed to have entered the region from the east (although with an ultimate source in the north) and to have flowed north-westwards along the margin of the Widmerpool Gulf (Guion and Fielding, 1988, fig. 13.11). The equivalent, interbedded sandstone and siltstone beds in the north and east of the district occur at the top of a succession that is characterised by an upwardsdeclining gamma-ray log response, suggestive of upward coarsening. They probably represent progradational delta front and interdistributary deposits.

The Listeri (Alton) Marine Band was proved in the Cotgrave Bridge Borehole by the identification of Gastrioceras listeri (see Eden, 1954), and indeterminate ammonoids were found at the equivalent datum in the Burton Joyce and Holme Pierrepont boreholes; Eden (1954) gives full faunal lists. In the Cotgrave Bridge Borehole, the marine band consists of 1.8 m of dark grey mudstone and siltstone with nodular ironstone beds. Ammonoids and marine bivalves are restricted to the basal 0.5 m, the remainder containing a brackish marine fauna dominated by Lingula and fish remains. Uncrushed G. listeri occur in bullions at the base of the marine band. Orbiculoidea is rare, in contrast with the Subcrenatum and Cancelloceras cancellatum marine bands. In some boreholes, a discrete Lingula band is split from the main marine band by up to 1.8 m of mudstone with scattered fish remains but no marine fossils. In oil boreholes in the south-east and north of the district, the Listeri Marine Band is identifiable by its very high, sharp-peaked gamma-ray log response (Figure 9) and sporadic records of Lingula.

The interval between the Listeri Marine and Amaliae Lingula bands is commonly intruded by sills. However, a maximum unintruded thickness of 32 m was proved in the Stragglethorpe (Foss Way) Borehole, with a minimum of 9 m in the Newark No. 1A Borehole (Figure 9). Three Lingula bands are recognised within this interval in the district. The lower two may correlate with the Lower and Upper Parkhouse marine bands, which are well developed in the adjacent Derby district (Frost and Smart, 1979). The highest of the three Lingula bands, the Forty Yard (Meadow Farm) Marine Band, is underlain by the thin (less than 0.3 m), impersistent Forty Yard Coal. The Norton Coal, which lies just below the Amaliae (Norton) Lingula Band, is the only persistent coal within the interval. It has been proved in most boreholes in the centre and south of the district where it is up to 0.6 m thick and underlain by a ganister that is commonly oil-impregnated. The remainder of the interval is dominated by unfossiliferous mudstone and siltstone of probable prodelta facies, although lacustrine mudstone with sporadic nonmarine bivalves occurs immediately above the Listeri Marine Band. The only persistent sandstone occurs below the Forty Yard Coal and correlates with the Loxley Edge Rock of the Sheffield area (Eden 1954). This sandstone is typically less than 4 m thick and varies from fine-grained, thinly bedded sandstone with siltstone and mudstone partings in some sections, to coarse-grained sandstone with pebbly layers in others. Saturation with oil was recorded in the Holme Pierrepont Borehole (Figure 9) and oil shows were noted in several other wells.

The Amaliae (Norton) Lingula Band was proved in the Burton Joyce, Bulcote, Cotgrave Bridge and Harlequin boreholes, and consists of 0.15 m or less of dark grey mudstone with Lingula, marine bivalves, foraminifera, conodonts and fish remains (Eden, 1954). None of these boreholes have geophysical logs at this level, but the Lingula band probably correlates with a marked gammaray ‘high’ at a similar stratigraphical position in many other boreholes of the district (Figure 9).

The interval between the Amaliae Lingula Band and the Kilburn Coal thickens steadily from around 23 to 30 m in the north-east of the district e.g. in the Fiskerton and Newark boreholes; (Figure 9) to 120 m in the south-west (West Bridgford Borehole). The level of the Upper Band is indicated by a persistent seatearth, 5 to 8 m above the Amaliae Lingula Band, but neither the Upper Band Coal nor the overlying Upper Band Marine Band have been recorded in the district. A very thin bed of mudstone with conodonts and Lingula?, lying 6 m above the Upper Band seatearth datum in the Burton Joyce Borehole (Eden, 1954) correlates with a marine faunal bed in the nearby Chesterfield district and was formally named the Burton Joyce Marine Band by Smith et al. (1967). The Burton Joyce Marine Band has not been identified in the other boreholes of the Nottingham district.

The succession above the inferred level of the Burton Joyce Marine Band coarsens upwards, a gradation that is well displayed on geophysical logs by an upwardsdeclining gamma-ray response. Capping this sequence are the Wingfield Flags, which consist of thinly bedded, fine-grained, pale grey sandstone with subordinate thin beds and laminae of siltstone. Wavy lamination, bioturbation, slumping and conglomeratic beds with intraformational mudstone, siltstone and ironstone pebbles have been described from cored boreholes. The top of the Wingfield Flags is commonly marked by a seatearth without a coal, and two or three less persistent layers with rootlets occur in the topmost 10 m. The Wingfield Flags are thickest (49 m) in the West Bridgford Borehole (Figure 9), but thin markedly to the east and north, where they consist of a few thin beds of fine-grained sandstone interbedded with siltstone. A dolerite sill intrudes and partly replaces the Wingfield Flags in much of the eastern and central part of the district. Wingfield Flags sandstones have a distinctive greenish hue with common small mica flakes and abundant plant fragments. They are typical of the ‘green facies’ of Chisholm (1990), the colour of which was attributed to the presence of degraded chloritic lithoclasts. They correlate with the Greenmoor Rock of Yorkshire and are thought to be derived from the west, in contrast to the predominantly northerly provenance of underlying sandstones of the Coal Measures and the Millstone Grit Group (Chisholm, 1990; Chisholm et al., 1996; Glover et al., 1996). The Wingfield Flags represent the progradation of a distributary mouth bar succeeded by interdistributary bay fill and abandonment facies (compare Chisholm, 1990).

Between 3 and 20 m of strata separate the top of the Wingfield Flags from the Kilburn Coal, with an evident trend of thickening towards the south-west (Figure 9). Beds of dark grey mudstone and siltstone dominate the lower half of the interval and commonly contain abundant fish scales and the nonmarine bivalve Carbonicola. This fauna is the local representative of the Daubhill mussel fauna (Stubblefield and Calver in Magraw et al., 1957), which occurs at this stratigraphical position throughout the Pennine Basin (Chisholm, 1990). It represents the lowest significant development of lacustrine facies mudstone in the Coal Measures of this district. One or more thin beds of green, chamositic granules have been noted within this mudstone in several oil boreholes in the north-east of the district (Farndon No. 1; Rolleston Nos G1 and G2; Thorpe No. 1) and correspond to the Kilburn Marker of Strong (in Falcon and Kent, 1960). The upper half of the interval consists of siltstone and thin, weakly micaceous sandstone with sporadic burrows, and with a thick, sphaerosideritic seatearth below the Kilburn Coal. The Kilburn Sandstone, which underlies the Kilburn Coal in the oilfields of central and north Nottinghamshire and is distinguished by its distinctive bronze and green micas (Taylor and Howitt, 1965), has a sporadic record in the Nottingham district. The Kilburn Coal forms a significant seam only in southern central parts of the district, where it is typically 0.4 m thick and locally reaches 0.9 m. Elsewhere, the position of the seam is indicated by a thin bed of black carbonaceous mudstone. The coal has not been worked, although it has been exploited in the Derby district to the west (Frost and Smart, 1979; Charsley et al., 1990).

Top Kilburn Coal to base of Vanderbeckei Marine Band

The interval (Figure 10); (Figure 11) records a more typical ‘Coal Measures’ style of sedimentation, characterised by deposition on an upper delta plain environment with greatly reduced marine influence. In the Nottingham district, it contains the lowest significant coal in terms of workable potential, the Blackshale–Ashgate seam.

The interval between the Kilburn and Ashgate/Blackshale coals is up to 75 m thick in the West Bridgford and Cotgrave areas, thinning eastwards to 44 m in the Tithby Borehole (Figure 10). The Parkhill No. 1 Borehole proved a thickness of 54 m (Figure 11), but comparisons with other areas are hampered by the presence of basaltic sills up to 45 m thick in the north and south of the district. Due to the paucity of boreholes and the presence of washouts and sills, seam correlation within this interval is uncertain. Only in the south of the region is there sufficient information to compare the succession with the better-known stratigraphy of neighbouring districts. The most consistently traceable seam occurs 16 to 23 m above the Kilburn Coal and probably correlates with the Morley Muck Coal of the Derby district (Frost and Smart, 1979). Most boreholes in the south of the district record a sandstone bed up to 10 m thick with a blocky gamma-ray log profile up to 5 m below the Morley Muck Coal (Figure 10). Where cored, the mudstones beneath these sandstones have yielded fish remains and sporadic nonmarine bivalves referred to Carbonicola and Curvirimula (formerly Anthraconauta).

The strata above the Morley Muck Coal include a number of seams that are loosely correlated in coal borehole logs with the Mickley group of coals of the Chesterfield district (Smith et al., 1967). In the Nottingham district, these seams are commonly numbered Mickley 1 to 4 in downward sequence; correlation of individually numbered seams can be made with confidence in the south of the district and in the adjacent Melton Mowbray district (Carney et al., 2004), but is open to doubt elsewhere. The Mickley 3 and Mickley 2 coals probably equate with the Lower Brampton and Upper Brampton (Mickley Thin) coals of the Derby district. The cycles below the Mickley 4 and Mickley 3 coals, like their equivalents in the Derby district, are dominated by lacustrine mudstone with abundant nonmarine bivalves (mainly the zonal form Carbonicola pseudorobusta, Curvirimula and Naiadites), ostracods and fish. The three higher cycles, overlain by the Mickley 2, Mickley 1 and Ashgate Floor coals, are dominated by bioturbated siltstone and thinly bedded, ripple cross-laminated sandstone with common soft sediment deformation, probably overbank crevasse splay and minor distributary channel facies. The sandstone below the Mickley 1 Coal has a distinct green colour. Only the Mickley 1 Coal is significant in terms of thickness, although it is commonly washed out below an overlying channel sandstone. Nonmarine bivalves and fish are restricted to thin beds of mudstone immediately above the Mickley 2 and Mickley 1 coals. Where split, the Ashgate Floor and Ashgate coals are separated by no more than 5 m of dark grey mudstone, commonly with rootlets throughout. The Ashgate Floor Coal may be confused with the Mickley coals in some boreholes in the north of the district.

The interval between the Ashgate Coal and the top of the First Piper Coal constitutes the most stratigraphically variable interval within the Coal Measures of the district. This is due mainly to complex patterns of seam splitting and the presence of locally thick but discontinuous distributary channel sand bodies, notably the Tupton Rock. In general, the interval thins from north-west (about 80 m) to south (about 40 m) across the district (Figure 10); (Figure 11) and seams tend to unite in the same direction, although complications in seam splitting patterns occur locally. Additional complexity is introduced by volcanic rocks and intrusive sills in the south-east of the district (Figure 10). Rocks of the Saltby Volcanic Formation erupted contemporaneously, with interdigitation taking place up to at least the Parkgate Coal in the Melton Mowbray district to the south (Carney et al., 2004).

The coals within the interval can be assigned to one of three composite groups of seams, in upward sequence:

The Ashgate Coal takes its name from a village about 3 km to the west of Chesterfield, where the seam was once worked extensively. The name has been applied to a seam at a comparable stratigraphical level in the Nottingham district, but correlation with the Ashgate Coal of the Chesterfield (Smith et al., 1967) and Derby districts (Frost and Smart, 1979) is uncertain. The seam is best developed in the south-west of the district. The Ashgate Floor Coal splits from the Ashgate Coal in the Cotgrave area. The former has also been recorded in the Newstead T1s Borehole in the north-west of the district.

The interval between the Blackshale and Yard coals is locally absent in the north (Figure 11), where the two seams combine. Farther south, a separation of around 17 m is proved in the Sunrise Blidworth Borehole, where the basal 3 m or so is predominantly sandstone. The interval averages 12 m thick in the Cotgrave area, where it is locally intruded by a basic sill, and thickens eastwards to 25 m in the Rundle Beck Borehole; it is dominated by mudstone and siltstone. The Low Estheria Band is developed locally at the base, just above the Blackshale Coal (Figure 8). It is a dark grey to black, carbonaceous mudstone with poorly developed ironstone nodules, Euestheria, fish debris, ostracods, nonmarine bivalves, burrows and pyritised plant debris; in many boreholes, only burrows have been recorded. Lingula and foraminifera have been recorded from the Low Estheria Band in the Stragglethorpe (Foss Way) Borehole.

The interval between the Yard and Threequarters coals thickens from around 15 m in the Cotgrave area, to 31 m in the north-west of the district (compare (Figure 10) and (Figure 11). Generally it has a lacustrine facies at the base, from which fish debris, ostracods and Curvirimula have been recorded, although this is absent in the Brunts Lane Borehole. The northward thickening is due mainly to the presence of a sandstone, referred to locally as the Yard Rock, which occurs as lower (15 m thick) and upper (25 m thick) bodies in the Turncroft Borehole. This sandstone is grey and generally fine-grained with locally common siltstone laminae, micaceous and carbonaceous bedding planes and some ironstone nodules and veins; in the extreme north-west, it comprises four beds of sandstone in the Barbers Wood Borehole. Sandstone is locally present at the same stratigraphical level in the Cotgrave area, resulting in thicker inter-seam intervals, as seen in the Holme Pierrepont Borehole (Figure 10). The principal seam splits of this interval are the Yard Upper Leaf, which occurs in the west and south of the district (Figure 10), and the Threequarters Coal Lower and Upper leaves in the Lowdham area (Ambrose, 1989). Many coal seams show variations in thickness across the district and most fail locally, either because of washout, pinch-out or nondeposition, but there are some specific trends; for example, the Tupton Coal is thickest in the north-west (Figure 11). In the north of the district, a lacustrine facies of dark grey mudstone, up to 10.5 m thick, is commonly well developed at the base of the interval between the Tupton and First Piper coals, and is overlain by the Tupton Rock. Clift and Trueman (1929) recorded abundant Carbonicola communis, C. robusta and C. rhomboidalis, common Naiadites triangularis, N. carinata and N. quadrata, together with ostracods, Spirorbis and fish remains.

The Tupton Rock comprises a grey to greenish grey, fine to medium-grained and locally coarse-grained sandstone with locally common siltstone laminae. Pebbly layers occur, commonly as lags or along foresets, and there are local thin conglomerates with intraformational mudstone, siltstone and ironstone clasts. It is variably massive, cross-bedded and cross-laminated, with ripples and climbing ripple cross-lamination. Micaceous, plant-rich bedding planes and coalified plant debris are common throughout. Upward-fining cycles have been recorded in some boreholes, as indicated by the upwards-increasing gamma-ray values of the Tupton Rock in the Salterford Farm and Parkhill No. 1 boreholes (Figure 11). The overall shape of these gammaray profiles suggests that the Tupton Rock is a major fluvial distributary channel sand body, about 27 m thick in the Parkhill No. 1 Borehole and fining upwards in the uppermost 8 m. This interpretation is consistent with log facies D of Church and Gawthorpe (1994), described for Namurian sandstone bodies in the Vale of Belvoir. Other boreholes record two or three fining upward cycles, with the Second Piper, Tupton Roof, Tupton and Threequarters coals being absent locally, either due to seam washout or pinching out against an active channel occupied by the Tupton Rock. Sheppard (2003) proposed the latter hypothesis for the Tupton Rock in the Melton Mowbray district to the south. Locally, pauses in sedimentation allowed the development of palaeosols and sometimes coal seams within the Tupton Rock cycles. Towards the margin, the Tupton Rock commonly splits into several thin leaves, probably representing crevasse splays. The eastern margin of the Tupton Rock channel is well defined in the south of the district, but farther north its position is less certain owing to lack of precise correlations between a number of oil wells. In the north it averages 20 to 25 m thick, reaching a maximum thickness of 37 m in the Oxton No. 1 Borehole; southwards the Tupton Rock splits into at least four separate channels, and into several leaves (Figure 10).

In the Cotgrave area to the south, the Tupton Roof, Hospital, Second Piper and First Piper coals merge to form the Parkgate Coal (Figure 10). A close association of the Tupton Roof Coal with the overlying Parkgate Coal was demonstrated in the Melton Mowbray district (Sheppard, 2003), thus confirming that the former is not a split from the Tupton Coal. The Tupton Roof Coal is thickest in the south, around Cotgrave. The succession from the Second Piper Coal to First Piper Coal thickens locally, as in the Gunthorpe and Bulcote boreholes (Figure 11), with a maximum of about 16 m recorded in the Gedling Colliery Top Hard 2 Pit Bottom Borehole. Here and in neighbouring boreholes, this interval is predominantly siltstone, with some mudstone and local thin sand bodies. A lacustrine facies containing fish debris and burrows has been noted locally at the base. The Gamston Bridge Borehole shows a thin channel sand body within the lacustrine strata, above which ostracods and Carbonicola were recorded. Farther north, the Second Piper Coal dies out. Notable seam splits of this interval include the First Piper Lower and Upper leaves in the Gunthorpe and East Bridgford area.

A thick nonmarine bivalve-rich bed (lacustrine facies) with Carbonicola, Spirorbis, fish debris and burrows occurs at the base of the interval between the First Piper and Deep Hard coals in the north of the district. The interval as a whole averages about 10 m in thickness, increasing southwards to around 17 m in the Cotgrave area, where the basal lacustrine facies is less developed. The thickening results from the interbedding of minor sandstone and an increased development of siltstone; a sill is also intercalated locally in the Cotgrave area. Like the Tupton Roof Coal, the Deep Hard coal is thickest in the south, around Cotgrave (Figure 10).

The interval between the Deep Hard and Deep Soft coals thickens rapidly westwards and northwards to around 10 m. In the extreme south and east, the two coals merge together with the Roof Soft Coal to form the Deep Main Coal, as in the Granby No. 1 Borehole (Figure 10). The Deep Main Coal extends across much of the Melton Mowbray district to the south and formed the only seam worked in the Asfordby prospect (Carney et al., 2004). The interval consists predominantly of mudstone with minor siltstone. The nonmarine bivalves Curvirimula, Carbonicola and Naiadites have been recorded, together with burrows, and lacustrine facies are commonly developed at the base of the cycle and locally within it. Where thin, as in the Nottingham city area (Clift and Trueman, 1929), this cycle commonly consists entirely of seatearth. The Top Soft Coal appears locally in the north-west and central parts of the district. The Black Rake and Brown Rake coals are identified in the west of the district (Figure 11), but in central parts the level of the Black Rake Coal is represented mainly by tuffaceous strata (see below). The Joan and Brown Rake coals occur close together and locally combine in the Cotgrave area (Figure 10). Farther north, however, they become separated, and the Joan Coal is largely absent.

Middle Coal Measures

The Middle Coal Measures occur at depth across most of the district, except in the south where the highest beds are cut out beneath the Permo-Triassic unconformity. Stratigraphical summaries of the succession are shown for various parts of the district in (Figure 12). The sequence is thickest in the north, north-west and west, with 328 m proved in the north Nottingham city area (Dean, 1989). Thinning takes place to the east and south, with a minimum recorded thickness of 197 m in the Eady Farm Borehole. In the extreme south-east of the district, the stratigraphically youngest Middle Coal Measures are devoid of coal seams and marine bands, and are generally reddened; there they have been both cut out and affected by weathering beneath the unconformity at the base of the Barren Measures. In the adjacent Melton Mowbray district to the south, the full Middle Coal Measures sequence, where preserved, shows a similar trend of southward and eastward thinning (Carney et al., 2004).

The Middle Coal Measures accumulated on an upper delta plain under conditions very similar to those that prevailed before deposition of the Vanderbeckei Marine Band. Coals dominate the sequence, and include a number of worked seams. The identification of specific seams is reliable in the west of the district, due to the extensive borehole coverage, but is problematical in the east where little detailed information is available. Between the Top Hard Coal and the Aegiranum (Mansfield) Marine Band, nonmarine environments that supported coal formation continued, but marine incursions increasingly affected sedimentation in the stratigraphically higher beds. There was a reversion to lower delta plain environments above the Main Bright Coal, which continued into the early Bolsovian (Guion and Fielding, 1988). In addition to the Aegiranum Marine Band, which marks the Duckmantian–Bolsovian stage boundary, two further marine bands are well developed in the district, namely the Maltby (Two Foot) and Haughton marine bands. The Edmondia and Shafton marine bands have also been identified, although they are of more local importance. Coals become thinner and less continuous above the High Main Coal, at which datum there commences an upward, diachronous facies change to a dominantly alluvial environment; part of the alluvial coal-bearing facies association of Besly (1988a) and Besly and Fielding (1989). It should be noted that although the beds above the High Main Coal are characterised by freshwater faunas, the branchiopods of the Main Estheria Band denote a brackish water facies. Tonsteins have been recorded at the level of the High Main Coal, although there is no evidence for source volcanic areas of this age within the district. Further marine bands occur in the uppermost part of the Middle Coal Measures sequence, although the detailed stratigraphy of these higher beds is poorly known due to a lack of cored boreholes through this interval. An added complexity is the reddening and weathering of strata below the Etruria Formation. The unconformable base of the latter is diachronous within the district, locally cutting down to levels below the Aegiranum Marine Band.

The interseam intervals are dominantly of mudstone and siltstone throughout the district, with generally thin and discontinuous sandstone. Some sandstone beds can be traced between boreholes and mapped out in the subsurface; their distributions are suggestive of anastomosing channels orientated north–south or north-west to south-east (Figure 13). Such variations in channel orientation occur throughout the sequence and may reflect factors such as local tectonism or differing rates of subsidence and/or compaction. Nonmarine bivalves are common at several levels, particularly in the lower part of the sequence, as noted also by Edwards (1951).

Most coal seams of this succession are discontinuous, either failing or washed out locally. Nevertheless, the Dunsil, Top Hard, Coombe, Cinderhill Main, High Hazles, Brinsley, Main Bright and High Main have all been worked. Comparative stratigraphical columns, with seam terminologies, are given for the central/northern part (Figure 14) and the southern part (Figure 15) of the district, and a summary of typical seam thicknesses is given in Table 1.

Vanderbeckei Marine Band to the Blidworth/Top Hard Coals

The Vanderbeckei Marine Band can be as much as 12 m thick; for example in the Cropwell Grange Borehole. It marks the base of the Middle Coal Measures and indicates a major marine transgression across the delta plain. The marine band is represented by dark grey, generally laminated mudstone with common burrows, some pyritised, with pyrite nodules and thin beds or nodules of ironstone. The basal beds are locally black and carbonaceous or canneloid, with common plant remains including Calamites and Pecopteris. The marine band has been proved persistently across the district, although locally it is washed out by sandstonefilled channels. Edwards and Stubblefield (1948) described the marine band in detail, noting a vertically restricted development of nonmarine bivalve beds at the base, with a fauna of Anthracosia and Euestheria, overlain by marine strata. The lowest 0.3 m of the marine beds contains Lingula and the ostracod Hollinella, representing transitional, brackish water environments. This in turn is overlain by mudstone with Anthracoceratites vanderbeckei, Dunbarella, Myalina, horny brachiopods and gastropods. Although this is a fully marine assemblage, the mudstone also contains layers with nonmarine bivalves (Anthracosia), Spirorbis and other fauna (Edwards and Stubblefield, 1948). Above the marine mudstone, there is a return to predominantly nonmarine facies with Anthracosia, although Edwards (1951) reported Lingulabearing layers interdigitating with the nonmarine phases in an upper bed. Edwards and Stubblefield (1948) gave comprehensive faunal lists for the marine band, which has also yielded fish debris, ostracods and foraminifera.

The interval overlying the Vanderbeckei Marine Band, up to the Second Ell Coal, is generally 10 to 15 m thick, thinning in the south-east to around 5 m above the rising surface of the volcanic rocks (Figure 15). Four boreholes prove more than 20 m, a maximum of 28.5 m being present in the Radcliffe Barn Farm Borehole. Mudstone and siltstone dominate the interval, but the succession coarsens upwards and locally contains sandstone up to 3 m thick; sandstone locally forms the Second Ell Coal seatearth. In the south, between Radcliffe on Trent and Cotgrave, a locally developed channel sand body, up to 12 m thick and with a north–south orientation, can be traced at the base of the cycle, where it washes out the Vanderbeckei Marine Band. To the south of Cotgrave, in the adjacent Melton Mowbray district, this channel swings south-westwards before being cut out by the unconformity at the base of the Permo-Triassic.

The succeeding interval, up to the First Ell Coal, is generally 10 to 15 m thick, thinning slightly southwards to between 8 and 12 m around Cotgrave, and to between 5 and 6 m in the east of the district. The beds at the base are principally mudstone of lacustrine facies, with Anthracosia, Anthraconaia, Anthracosphaerium, Naiadites, Spirorbis, ostracods and burrows. A maximum 8.5 m thickness of this facies was proved in the Brockley Borehole, but it dies out in the extreme east of the district. The interval generally coarsens upwards to siltstone, and locally to sandstone. A sandstone up to 5 m thick in the middle part of the interval occupies a north–south trending channel that widens to 10 km in the south of the district, between Carlton and East Bridgford, before splitting farther south into at least three separate channels. In the south of the district, around Cotgrave, the First Ell Coal splits locally into 2 or 3 thin seams. Elsewhere, it is locally absent, and may have been washed out in the Parkhill No. 1 Borehole (Figure 14).

The Waterloo group of coals comprise, in upward sequence: the Fourth, Third and Second Waterloo coals, the Waterloo Marker Coal in the north-east of the district (also referred to as the Markham Coal), the First Waterloo Coal and the Dunsil Coal. East of Cotgrave, the First Ell and Fourth Waterloo coals combine (Figure 15), although the split line is poorly defined. Similarly, in the extreme south-east, the First Waterloo and Dunsil coals combine. The Fourth Waterloo to Third Waterloo interval generally thickens southwards into the Cotgrave area, but thins in the extreme south-east corner of the district. The Third to Second Waterloo interval is of variable thickness throughout the district, and that between the Second and First Waterloo shows slight eastward and southward thinning. All four Waterloo coals, and possibly the Dunsil Coal, are locally split into two or three leaves, and in places fail altogether. Mudstone and siltstone, with generally only minor sandstone, dominate the various interseam cycles. Lacustrine mudstone with nonmarine bivalves is commonly developed above all of the seams, including the Waterloo Marker Coal; the lacustrine beds have yielded Anthracosia, Anthraconaia, Anthracosphaerium, Naiadites, Spirorbis, ostracods, fish and burrows. Sandstone beds are minor constituents, but a major channel body up to 32 m thick has been proved to the west of Southwell, in the Halloughton, Brockley and Turncroft boreholes. This sandstone is fine- to medium-grained and variably crossbedded to massive, with common ironstone nodules and coal-rich laminae. It has a restricted lateral extent (about 2 km wide), and cuts out the Fourth and Third Waterloo coals and locally the First Ell Coal. Thin sandstone beds are commonly present between the Fourth and Second Waterloo coals, and some, with typical northwesterly orientations, are shown in (Figure 13)a. A further sand body between the First Waterloo and Dunsil coals is generally thin, but about 10 m has been recorded in the Salterford Farm Borehole (Figure 14); it has a similar north-westerly trend. A number of anastomosing channels are suggested by the complex of sandstone beds at this level in the Cotgrave–Radcliffe–Bingham area, but they cannot easily be traced between boreholes.

Blidworth/Top Hard Coals to the Aegiranum Marine Band

This interval commences with a group of coals that comprises, in upward succession, the Blidworth, Top Hard, Lower Coombe, Upper Coombe and Main Smut. These seams split and merge in a complex fashion across the entire district, although all have been identified locally. The Upper Coombe is absent in places in the centre and north of the district, and the Blidworth Coal is locally absent in the south and south-east. The Blidworth and Top Hard coals are merged in the central to northern part of the district (Figure 14), and all the seams are generally combined (Figure 15) in the extreme south-east, where only the Blidworth or Upper Coombe coals are locally separated (although the Blidworth Coal is absent locally). The interval that includes these coals is very variable in thickness over most of the district, ranging from 11.8 to 35.7 m and thinning markedly in the extreme south-east, to between 4.5 and 7 m (Figure 15). The strata consist predominantly of mudstone and siltstone. Above the Dunsil Coal, they feature a persistent lacustrine mudstone that has yielded the nonmarine bivalves Anthracosia, Anthraconaia and Naiadites as well as Spirorbis, ostracods, fish and burrows. A similar fauna has been obtained from higher levels above the Dunsil Coal. Clift and Trueman (1929) recorded the following fauna from mudstone in the the roof of the Top Hard Coal, collected from the spoil heaps at Gedling Colliery: Naiadites carinata, N. triangularis, N. cf. modiolaris, N. cf. subtruncata, Anthraconaia polita, A. confusa, Anthracosia nitida, A. cf. aquilina, A. transversa, Anthracosphaerium cf. turgida and A. cf. affinis.

Sandstone occurs at three main levels: below the Blidworth Coal, below the Top Hard Coal and below the Main Smut Coal. The sandstone beds are invariably thin (about 2 m but locally up to 8 m below the Blidworth Coal) and commonly occur in 2 or 3 leaves. A sandstone also occurs locally between the Top Hard and Coombe coals. The sandstone below the Blidworth Coal is confined mainly to the west of the district and maps out as two distinct channels that appear to combine in the north–west (Figure 13)b. The westernmost, north–south channel is up to 5 km wide, whereas the eastern channel, which is better constrained by borehole data, is 1–2 km wide with gentle meanders, passing beneath Burton Joyce and Cropwell Butler. Sandstone was also proved at around the same level in several boreholes in the south-east of the district; for example, over 19 m of sandstone was proved in the Middlestyle Bridge Borehole, washing out the Dunsil Coal. The succeeding sandstone, below the Top Hard Coal, appears to form a north–south-trending channel that is well constrained on its eastern margin, between Tollerton and Calverton, narrowing southwards to between 1 and 2 km. Sandstone was also proved at this level in the extreme southwest of the district and at three localities in the east, suggesting a complex of subparallel, possibly anastomosing channels. The sandstone below the Main Smut Coal, where adequately proven, forms a series of north–southtrending anastomosing channels, each generally 1–2 km wide (Figure 13)c. Locally, the Main Smut Coal is not developed, for example in the Woodborough Borehole where it is washed out by a sandstone body.

The interval between the Main Smut and High Hazles coals contains from one to seven seams, a complex situation that is also found at this level in the adjacent Melton Mowbray district to the south (Carney et al., 2004). Over most of the district, the interval averages 30–40 m in thickness, ranging up to 49 m in the Swing Bridge Borehole. Thinning takes place south-eastwards, down to a minimum of 12.1 m in the Eady Farm Borehole. The coals are generally thin and locally inferior. The lower seams combine south-eastwards into an unnamed seam, seen above the Main Smut Coal in the Redmile No. 2 Borehole (Figure 15). The upper seams unite around the Cinderhill Main Coal, and this grouping is commonly seen to split or merge across the district (Figure 15). In the extreme south-east, the Cinderhill Main Coal comes close to merging with the High Hazles Coal and overlying Brinsley Coal; the three seams do merge to the south, to form the Top Bright Coal (Carney et el., 2004). Mudstone and siltstone beds dominate the interseam cycles of this interval, with lacustrine facies widely developed above the Main Smut Coal, indicated by a persistent mudstone with a nonmarine fauna of Anthracosia, Anthracosphaerium, Naiadites, Spirorbis, ostracods, fish and burrows. Localised lacustrine mudstone rich in nonmarine bivalves occurs at several other levels above the Main Smut Coal, and commonly overlies the coals of the various seam splits. Mudstone of this type also occurs between the Cinderhill and High Hazles coals, locally overlying the Cinderhill Main Coal; it is up to 12 m thick in the Cropwell Grange Borehole. Sandstone beds occur at three levels: above the Main Smut Coal, below the Cinderhill Main Coal, and between the Cinderhill and High Hazles coals. All are generally thin (2–3 m) and locally split into more than one leaf. They map out as anastomosing channels that are generally 1 to 3 km wide. The sandstone channels above the Main Smut Coal are orientated mainly north-west to south-east, as shown by (Figure 13)d. The coal is washed out locally by the lower sandstone, which has a maximum recorded thickness of 16 m in one of the washouts, in The Limes Borehole near Cotgrave. The sandstone body immediately below the Cinderhill Main Coal has a maximum recorded thickness of around 6 m and a north–south orientation (Figure 13)e. That between the Cinderhill Main and the High Hazles coals is up to 12 m thick and occupies a series of north–south channels (Figure 13)f. In the Burton Joyce–Bingham area, it forms a bifurcating body at least 5 km wide.

The interval between the High Hazles and Brinsley coals consists mainly of mudstone and siltstone beds, and averages 10 to 15 m in thickness in the north of the district. A maximum thickness of 23 m has been proved in the Sherwood Lodge Borehole, but the interval thins southwards and eastwards to around 8 to 10 m in the Cotgrave area. In the extreme south-east, the High Hazles and Brinsley coals approach closely (Figure 15) and in places merge. Elsewhere the Brinsley Coal splits locally into two or three seams, the lowest of which is variably called the Brinsley 2 or Brinsley Floor Coal. Where three leaves are present, the upper two are generally named the Brinsley Upper and Lower leaves. Above the High Hazles Coal, a persistent lacustrine mudstone, up to 10 m thick, has yielded a nonmarine fauna of Anthracosia, Anthraconaia, Naiadites, Spirorbis and ostracods. The facies is poorly developed in the south and south-east where it has only been recorded in a few boreholes. Sandstone beds within the interval are generally thin (1–3 m), although the lowest locally attains about 4.5 m. Channel trends are not clearly defined from borehole provings for any of the three sandstone bodies present, but appear to be approximately north–south in the lowest sandstone, above the High Hazles Coal at Gedling Colliery. There, Guion (1987) noted climbing ripple foresets, which showed east-north-east-flowing palaeocurrents. The roof and succeeding sequence of the High Hazles Coal at Gedling were also described in some detail, and the mudstone above the High Hazles Coal interpreted as being deposited within a prograding lacustrine delta complex. The mudstone is succeeded by a sequence that coarsens upwards, from siltstone and sandy siltstone deposits of a distal bar mouth environment, to sandstone and siltstone deposited in the inner/proximal mouth bar environment of the delta front, and ultimately to distributary channel sandstone of the delta plain.

The interval between the Brinsley and Low Bright (Abdy) coals is locally very thin, with the Low Bright and Brinsley coals virtually merged, but thickens up to a possible maximum of 12.1 m in the central part of the district (Figure 14). The Low Bright Coal splits with a lower, Low Bright Floor Coal present locally. The interval is predominantly of mudstone and siltstone, but sandstone is commonly developed at several levels and is locally up 8 m thick, forming most of the cycle.

The interval between the Low Bright and Two Foot (Mid Bright) coals is highly variable, between 1.2 and 22.5 m thick, with no obvious trends in the variations. The Two Foot Coal is commonly absent in the south and south-east of the district, and correlation of the higher coal seams is therefore uncertain. Elsewhere, the Two Foot Coal splits into two leaves, as in the Salterford Farm Borehole (Figure 14). Mudstone and siltstone dominate the interval, with lacustrine conditions developed locally above the Low Bright Coal and at higher levels within the cycle. Spirorbis, fish debris and burrows have been recorded from a lower bed, and Anthracosia at a higher level. Two sandstones occur in the cycle. Sandstone up to 6 m thick is well developed in the lower part of the interval around Cotgrave, and is sporadically present elsewhere. Near the top of the interval there is a further, generally thin channel sandstone body; it has a north–south trend and attains a maximum thickness of around 5.5 m in the Gedling HHB3s Borehole.

The interval between the Two Foot and Main Bright coals ranges from 0.6 to 15.7 m in thickness, but is usually less than 10 m. It consists mainly of mudstone and siltstone; sandstone is only rarely developed at the top or bottom of the cycle. An exceptional succession was recorded in the Cotgrave Colliery Shaft Pillar Borehole, which proved mainly sandstone that has washed out the Main Bright Coal and Maltby Marine Band. The Maltby (Two Foot) Marine Band overlies the Two Foot Coal, in places with an intervening thin sandstone. The Maltby Marine Band is locally up to 5 m thick and consists of dark grey mudstone. A nonmarine bivalve fauna of Anthracosia and Naiadites indicates that fully marine conditions were not generally established. Lingula has been recorded locally, however, together with foraminifera and ostracods. Unidentified ammonoids have been recorded from the marine band in the Cropwell Bridge and Rundle Beck boreholes in the south of the district, along with the ostracod Carbonita. Edwards and Stubblefield (1948) noted that Anthracosia atra occurred above and below the marine phase in Nottinghamshire, with Lingula mytilloides present throughout. They reported that marine forms died out with southwards thinning of the marine band; however, recent boreholes have proved marine faunas at this level south of the Nottingham district (Carney et al., 2004).

The strata between the Main Bright Coal and the Aegiranum Marine Band show a variable thickness range, superimposed on an overall south and eastwards thinning. In the north of the district, the interval is 30 to 50 m thick (Figure 14), but thins to 15 to 25 m in the Cotgrave area and is less than 15 m thick in the southeast (Figure 15). The interval includes three main coal seams, the Manton, Clowne and Swinton Pottery coals, the last forming up to 5 leaves; all seams are impersistent and rarely developed in the south of the district. Seam correlations are uncertain in this thinner part of the sequence, and many coals fail above the Brinsley Coal. Over much of the district, however, there is a thin unnamed coal, locally split into two leaves, below the Aegiranum Marine Band. The whole interval indicates a reversion to lower delta plain depositional environments (Guion and Fielding, 1988). Mudstone and siltstone form the predominant interseam lithologies, with lacustrine facies developed. Anthracosia, Naiadites, Euestheria, fish debris and burrows were recorded from above the Main Bright Coal, and Euestheria, bivalves, ostracods and fish debris above the Clowne Coal. Sandstone occurs at three levels, with a persistent bed between the Main Bright and Manton coals, particularly across the western part of the district where it is about 14 m thick in the Oxton Borehole, directly above the Main Bright Coal. The Haughton Marine Band occurs just above the Swinton Pottery Coal (Figure 12), although it appears to be sporadically developed in south Nottinghamshire and has only been proved in a few, widely scattered boreholes. It comprises dark grey mudstone and has a maximum thickness of over 6 m in the Newstead M3s Borehole in the north-west of the district. There are very few faunal determinations, mainly ostracods. Edwards and Stubblefield (1948) noted palaeoniscid scales, Radinichthys sp. and Lingula in the basal 0.3 m in the Calverton Lodge Borehole and, west of the Nottingham district, at Cinderhill Colliery [SK 520 475]. In the interval above the Haughton Marine Band in the north-west of the district, there are up to three sandstone beds, the most laterally persistent of which underlies the unnamed coal below the Aegiranum Marine Band.

Aegiranum to Cambriense Marine Bands

The stratigraphy of this interval is summarised in (Figure 12). The sequence thins south-eastwards across the district, and is also progressively cut out in the same direction by the unconformity at the base of the Barren Measures. The Aegiranum Marine Band is itself cut out locally by unconformities at either the base of the Barren Measures or the base of the Permo-Triassic. It consists of dark grey, fossiliferous mudstone and is generally 1 to 4 m thick; the 14 m thickness of marine mudstones in the Elston Grange Borehole is exceptional, and includes the merged Haughton and Aegiranum marine bands. Edwards and Stubblefield (1948) reported that the marine band thinned southwards across the Pennine Basin into the Nottingham area. In this district only its lower half contains a fully marine fauna, with nonmarine bivalves occurring locally in the upper part, as seen in the Calverton Lodge Borehole. The fauna is diverse, and includes Lingula mytilloides, Chonetes, Hollinella cf. bassleri, Dunbarella, Rhabdoderma, Donetzoceras, Platyconcha hindi, Homoceratoides jacksoni, Orbiculoidea, O. cf. nitida, Naticopsis, productids, sponge spicules, crinoid debris, conodonts, foraminifera, ostracods and fish debris. Smith (1913) recorded Nucula, Pseudamusium, Syncylonema, Posidoniella sulcata and Pterinopecten carbonarius.

The interval between the Aegiranum Marine Band and High Main Coal thins from around 30 m in the north-west of the district to 10 m in the Cotgrave area, and is cut out at the base of the Barren Measures in the extreme south-east (Figure 12). The High Main Coal seam may split into two leaves in the southern part of the district, but there is some uncertainty in the correlation and it may also merge with the overlying Edmondia Coal. The Wales Coals can number between one and five seams; locally, however, all of these may fail (Figure 12). Mudstone and siltstone dominate the interval, with lacustrine facies seen locally at two levels above the Wales Coals. The lower of these, immediately overlying the highest Wales seam, has yielded Naiadites, fish debris, ostracods and burrows. Sandstone occurs locally below and within the Wales Coals, and a particularly persistent sandstone, up to 4.5 m thick, is seen below the High Main Coal. This sandstone is well developed in the north of the district (Figure 12) and was deposited in northwest-trending channels.

The uppermost interval of the Middle Coal Measures, between the High Main Coal and the top of the Cambriense (Top) Marine Band, has been proved only in its entirety in nine boreholes. Only the lowermost beds are present below the Permo-Triassic unconformity in the Cotgrave area in the east, and very few coals or marine bands have been proved in the south-east, making correlation difficult. A variable thickness can be demonstrated, ranging from 56.75 m in the Salterford Farm Borehole in the north of the district, thinning southwards to 29 m in the Ploughman’s Wood Borehole. This interval contains an upwards facies change from deltaic to dominantly alluvial depositional environments. It commences with a persistent lacustrine mudstone with bivalves, ostracods and Euestheria that overlies the High Main Coal. The lacustrine bed was recorded only in the north of the district, where it is succeeded by an equally persistent sandstone, up to 6 m thick. The overlying Edmondia Coal is present across most of the district although, as noted above, it may merge with the underlying High Main Coal in the south. The Edmondia Coal is succeeded by the Edmondia Marine Band, which is well developed across most of the district. It comprises a dark grey, variably laminated or massive micaceous mudstone with ironstone layers, lenses and nodules and pyrite nodules. The fauna includes Edmondia, Myalina, Naiadites triangularis, Lingula, Euestheria, Agathammiina, Ammonema, Ammodiscus, Geisina subarcuata, foraminifera, fish debris including Rhabdoderma, Rhadinicthys cf. wandi, Rhizodopsis sp. and palaeoniscids, pyritised plant fragments and burrows. Edwards and Stubblefield (1948) reported that the Edmondia Marine Band in Nottinghamshire commonly has a nonmarine Euestheria phase at the base. The overlying marine phase is very restricted and dominated by the bivalve Edmondia, with sporadic Myalina, gastropods, ostracods, foraminifera and rare horny brachiopods and nautiloids. Above the marine band, the succession is dominated by mudstone and siltstone, with sandstone developed locally, and is topped by a thin coal in the north of the district. The overlying Main Estheria Band is contained within a lacustrine mudstone of widespread occurrence. It has yielded: Euestheria simoni, Naiadites, Megalichthys sp. and the ostracod Carbonita. Edwards and Stubblefield (1948) reported that Euestheria occurred at the base and was overlain by a nonmarine bivalve phase; they also recorded Carbonita and fish debris.

Cycles above the Main Estheria Band are dominated by mudstone and siltstone, with a few sandstone beds and coal seams developed locally. Euestheria occurs at one or two levels, with one bed referred to locally as the Extra Estheria Band. The succession includes the Anthraconaia pruvosti Band and the Shafton Marine Band. Both have been proved only sporadically and mainly in the north and north-west of the district. The Anthraconaia pruvosti Band has yielded Euestheria, A. pruvosti, Carbonita fabulina, Orbiculoidea cf. nitida, Ammonema, Agathammena, Elonichthys, Lingula and fish debris including palaeonsicids. The Shafton Marine Band fauna includes Euestheria, Lingula, Orbiculoidea, Anthraconaia, Naiadites and fish debris. The top of the Middle Coal Measures is marked by the Cambriense Marine Band, which has been proved in scattered boreholes across the district. It consists of a dark grey, fissile mudstone, locally black and carbonaceous at the base, with ironstone layers and lenses. The fauna includes Lingula mytilloides, Orbiculoidea sp., O. cf. nitida, Nuculana, N. attenuata, Dunbarella sp., D. cf. macgregori, Euestheria, Curvirimula, Naiadites, Ammonemia, Agathammina, Donetzoceras?, Chonetes landiensis, Rhabdoderma, Rhadinicthys, Elonichthys. Productids, gastropods, conodonts, echinoid debris, pyritised plant fragments and burrows are also present.

Upper Coal Measures

These strata occur at depth across much of the western part of the district, but have generally been removed to the east and south by a combination of intraand post-Carboniferous erosion, with unconformities developed at the base of the overlying Etruria Formation or Permo-Triassic strata (Figure 12). Upper Coal Measures may be present locally in the south-east, for example in the Tithby Borehole, which proved the Cambriense Marine Band. Other boreholes, including Poplars Farm, Rundle Beck and Station Farm, proved more than 50 m of generally reddened strata above the Wales Coal that may include some Upper Coal Measures. Complete sequences of the Upper Coal Measures, of varying thicknesses, have been proved in a number of cored boreholes (Figure 16), and geophysical logs and core samples are both available for the Salterford Farm and Hartswell Farm boreholes. Boreholes with geophysical logs in which the characteristic gamma-ray profile of the overlying Etruria Formation has been identified (Figure 17) indicate Upper Coal Measures thicknesses of between 69 and 112 m. A thickness of around 160 m may be present in the uncored Papplewick Hall Borehole where the Etruria Formation geophysical log signature is not developed and, in consequence, all the relevant strata are correlated with the Upper Coal Measures. In the Derby district to the west, the Upper Coal Measures are everywhere overlain unconformably by Permian strata (Frost and Smart, 1979); a maximum thickness of 106.7 m has been proved in the Linby No. 1 Borehole [SK 5356 5043]. In the neighbouring Grantham district to the east, beds assigned to the late Bolsovian and correlated with the Etruria Formation rest on Middle Coal Measures (Berridge et al., 1999). In the Melton Mowbray district to the south, evidence for the Upper Coal Measures is confined to one borehole in the north (Carney et al., 2004).

In those cored boreholes with no geophysical logs, the top of the Upper Coal Measures cannot always be located accurately because of the deeply penetrating weathering that has resulted in lithological similarity to the overlying red beds of the Etruria Formation. A maximum 53 m of these equivocal strata were proved in the Hartswell Farm Borehole, comprising grey, green, yellow, purple and red mottled mudstone, siltstone, sandstone and seatearth.

Thin coals and mussel bands have also been proved in this altered zone. Reddening has also been observed over a few metres below the Permian unconformity.

The Upper Coal Measures is a very variable sequence, in which there is an overall reduction in the number of coals accompanied by thinning of the interseam intervals as the succession is traced southwards across the district (Figure 16). Sandstone is well developed in the northwest where it generally forms thin beds between 1 and 4 m thick. In that area, the sandstone beds commonly overlie mudstone and form the tops of individual sedimentary packages; they can also occur within or near the base of upward-fining sedimentary cycles. Elsewhere, mudstone is the principal lithology; lacustrine facies are developed at several levels, with faunas dominated by the nonmarine bivalve Curvirimula, which is particularly common in the Salterford Farm Borehole. Spirorbis, Euestheria, ostracods, fish debris and burrows also occur. Up to 12 coal seams have been proved in individual boreholes (Figure 16); most are thin, but a seam about 1.1 m thick was proved in the Bestwood Colliery Borehole. This is the lowest of a group of up to five seams that are informally termed the Hucknall coals. Two further coals are named in the adjacent Derby district as the Annesley and Manor coals (Frost and Smart, 1979), and the latter has also been identified in Nottinghamshire (Edwards, 1951); both coals can be traced across the Nottingham district (Figure 16). The Annesley Coal, locally referred to as the Musters Coal, occurs 17 to 32 m above the Cambriense Marine Band and has a maximum proven thickness of 0.74 m in the Goosedale Farm Borehole. The Manor Coal, 80 to 90 m above the Cambriense Marine Band, has a maximum proven thickness of 0.6 m in the same borehole.

Barren Measures (Warwickshire Group)

The Barren Measures of the East Pennine Coalfield are poorly known in comparison with the productive Coal Measures because of the lack of exploitable coal seams, their absence at crop and their generally patchy distribution at depth. There are, however, numerous borehole provings in the north, central and eastern parts of the Nottingham district, which provide ample opportunity to address the problems of stratigraphy and distribution of these strata within the southern part of the concealed East Pennine Coalfield. Some of the boreholes have geophysical logs and others good core sample descriptions, so that it is possible both to characterise these strata lithologically and to estimate their subcrop below Permo-Triassic strata (Figure 17). Early descriptions of Barren Measures from the Nottingham district (Gibson, 1901; Lamplugh et al., 1908) were based on provings by the Thurgarton and Oxton No. 1 boreholes. Strata correlated with the formerly named Keele, Newcastle and Etruria Marl divisions of the West Midlands were described from the Thurgarton Borehole, whereas the nearby Oxton No. 1 Borehole was thought to prove Etruria Marl immediately beneath the sub-Permian unconformity. Other borings at Farnsfield, immediately to the north of the district, appeared to confirm the findings at Thurgarton (Edwards, 1951, 1967), as discussed below.

The absence of Barren Measures in the exposed part of the East Pennine Coalfield precludes a lithostratigraphical correlation of sequences in the Nottingham district with those in the West Midlands type area. Sedimentological continuity is nonetheless demonstrated by the successions proved in coal and oil exploration boreholes, which indicate a broad lithostratigraphical similarity between the two areas. Advances in developing a coherent, regionally applicable model of lithostratigraphy have been made during BGS mapping projects farther west (e.g. Powell et al., 1992; Bridge et al., 1998; Rees and Wilson, 1998). These involved detailed studies of borehole core and wireline geophysical logs from the concealed parts of the Potteries, South Staffordshire and Warwickshire coalfields (e.g. Besly, 1988b). Building on this body of evidence, the newly formalised lithostratigraphical scheme for these strata (Powell et al., 2000) dispenses with the term ‘Barren Measures’, which is now replaced by ‘Warwickshire Group’. The former term is retained for the purposes of this memoir, however, since the change was made after publication of the accompanying Nottingham 1:50 000 scale geological map (Sheet 126). The two subdivisions recognised in the Nottingham district, the Etruria Formation and overlying Halesowen Formation, are defined in Powell et al. (2000). The Hartswell Farm Borehole in the central northern part of the Nottingham district is the only borehole through the Barren Measures with both a cored sequence and accompanying geophysical logs. This borehole is therefore designated as the local reference section for both the Etruria Formation and lower part of the Halesowen Formation; the more complete section of the upper part of the Halesowen Formation in the Parkhill No. 1 Borehole is used as the continuation of the reference section. Additional information has been incorporated from other boreholes where necessary in order to give a complete description of each formation (Figure 17).

The Etruria Formation has a characteristic bow-shaped gamma-ray log signature (Figure 17), the base of which is used as one of the principal criteria to define the unconformable junction between the Coal Measures and Barren Measures. This datum commonly coincides with the base of the deeply coloured measures, and in the south-east of the district also coincides with the incoming of beds containing derived volcanic fragments. It correlates well with the base of the Etruria Formation as identified in chippings logs of those boreholes for which geophysical logs are not available. A criterion that is particularly useful for boreholes that lack geophysical logs is the selection of the base of the lowest ‘espley’-type gritty sandstone as the base of the Etruria Formation and hence of the Barren Measures (e.g. Bridge et al., 1998). In the Nottingham district, this level (i.e. the base of the lowest ‘espley’-type sandstone) commonly coincides with the base of a zone of ‘deep coloration/staining’ identified by Gibson (1901), and appears to correlate with the base of the distinctive gamma-ray profile seen in more recent boreholes drilled nearby through the Etruria Formation. The datum truncates a significant thickness of Upper Coal Measures strata in the north and cuts down to around the level of the Aegiranum Marine Band in the extreme south-east of the district (Figure 12).

It should be noted that red-stained Coal Measures up to 30 m thick can also occur where the Barren Measures are absent, immediately beneath the sub-Permian unconformity. In the West Midlands, this reddening was evidently part of a major Permian (as opposed to Triassic) secondary oxidation and remagnetisation event (Johnson et al., 1997). Carboniferous strata so reddened have been distinguished from true Barren Measures by means that include facies analysis, although the lithological distinction between primary and secondary reddening is not always clear (see Besly et al., 1993 for further discussion). In the Nottingham district, the absence of the characteristic Etruria gamma-ray log signature above the base of reddening has been used to indicate the absence of the Barren Measures.

Biostratigraphical information is not sufficient to demonstrate the precise age of these uppermost Carboniferous strata. Evidence from other areas suggests a Westphalian C (Bolsovian) age for the Etruria Formation and a mostly Westphalian D age for the Halesowen Formation (Calver, 1969; Bridge et al., 1998).

Etruria Formation

The total thickness of this unit varies from about 97 m in the Epperstone Park Borehole in the north-west of the district, to about 25 m in boreholes farther to the south-east. The full bow-shaped profile of the gamma-ray log is present even where the Etruria Formation is thin (Figure 17), suggesting that the thinning may be syndepositional. This is in contrast to the situation in the Warwickshire and South Staffordshire coalfields (Bridge et al., 1998; Waters et al., 1994), where thinning of the formation is attributed to an unconformity below the Halesowen Formation. The western limit of the subcrop of this unit in the Nottingham district (Figure 17) cannot be located accurately due to the lack of geophysical logs and the difficulties of identifying the base of the Etruria Formation lithologically. The most westerly proving in the district is in the Salterford Farm Borehole; southwards from there the variable level and degree of secondary reddening beneath the sub-Permian unconformity makes identification of Etruria Formation strata difficult. The formation is almost certainly present in the old coal borings at Burton Joyce (Station Field) and Woodborough, but appears to be absent in some of the intervening boreholes.

The original correlation of the Barren Measures sequence in the Nottingham district with that in North Staffordshire was made by Gibson (1901) on two main criteria. One was the presence of a coal-bearing grey measures sequence (here, the Halesowen Formation) between two thicker red measures sequences and the other was the presence of ‘espleys’ within the siltstone and mudstone-dominated lower reddened sequence. Gibson (1901) thought that this lower unit clearly correlated lithologically with the Etruria Marl of Staffordshire, and described it in summary as ‘red marl with bands of green grit’ (espleys). The original log for the Thurgarton

Borehole, and a further summary in the old Nottingham memoir (Lamplugh et al., 1908), suggested that the base of the Etruria Formation be placed at a depth no higher than 418.8 m (1374 feet), within or at the base of a zone described as ‘cycles with coloured/stained tops’. Given the likely diachronous nature of the base of secondary reddening of the Coal Measures, however, a more appropriate base of the Etruria Formation in the Thurgarton Borehole has been selected at 373.1 m (1224 feet). This level is at the conglomeratic base of a sandstone bed identified by Gibson in his original log as the lowest ‘espley’ in the sequence.

The Etruria Formation has a generally low to very low gamma-ray response, with the lowest levels in the middle part of the formation contributing to the distinctive bow shape of the profile (Figure 17). The gamma-ray log trace would, on a conventional interpretation, suggest that the formation is dominantly sandy, with the coarsest sandstones in the middle part. This is not borne out by core logs, however, all of which suggest a sequence composed dominantly of mudstone with only thin sandstone beds. The anomaly is best explained by the mineralogy of the mudstones, which in the Stoke district (Rees and Wilson, 1998) have a large kaolinite and detrital quartz component. This is further substantiated by chemical analyses, which show low values of K2O and K2O/Al2O3 in the Etruria Formation, suggesting that kaolinite, rather than illite, is the dominant clay mineral (Haslam, 1993). The mineralogy could be explained by a particularly high intensity of weathering during deposition of the middle beds of the formation, with concomitant leaching-out of the mobile elements (Haslam, 1993). Sonic logs available for four boreholes proving the Etruria Formation all show a progressive decrease in velocity upwards through the unit, possibly indicating a fining-upward trend.

The commencement of Etruria Formation deposition indicates a regional reorganisation of sedimentation patterns in response to the initiation of intra-Westphalian tectonism (Besly, 1988a, b). This produced a change from the poorly drained alluvial plain facies association of the Upper Coal Measures strata to a better drained alluvial plain red-bed association in which pedogenic processes are thought to have been important (Besly, 1988b; Besly and Fielding, 1989). The distinctive mottling and variegation found in the mudstone of the Etruria Formation is one effect of pedogenesis, the yellow-brown mottling being related to the presence of goethite pigment, and the purplegrey mottling to hematite pigment. Weathering was also responsible for the secondary staining and alteration of a variable thickness of measures below the base of the primary red-beds. The thin sandstone units found intermittently through the formation are here interpreted as crevasse splay deposits, whereas thicker sandstones may represent meandering fluvial channels.

Plant fragments have been logged in many of the boreholes at various levels in the formation, but no identifiable fauna or flora has been noted. In the West Midlands, Curvirimula phillipsi and Anthraconaia cf. saravana (Gibson, 1901) indicate a Westphalian C (Bolsovian) age (Ramsbottom et al., 1978).

In both the Hartswell Farm and Carr Bank boreholes, the basal sandstone of the Etruria Formation has a sharp, irregular base and consists of a coarse- to very coarsegrained, grey-green, feldspathic, pebbly sandstone. The grey-green, generally coarse-grained sandstone beds found in other parts of the sequence appear to be best developed in the Thurgarton Borehole (Gibson, 1901). They commonly have very coarse or conglomeratic bases, and, although somewhat finer grained, are equated with the espleys described from the Etruria Formation in its type area in the West Midlands. The remainder of the Etruria Formation consists predominantly of red-brown siltstone and mudstone, massive to laminated in part and with grey, green, purple and yellow mottling. Much of the mudstone and siltstone is fissured and veined with carbonate, and there are numerous layers that display listric surfaces and seatearth (rootlet) fabrics. Other structures of probable pedogenic origin include sideritic or hematitic pellets and nodules, and carbonate nodules (Figure 17). A distinctive siltstone bed at the top of the Etruria Formation in the Carr Bank and Hartswell Farm boreholes contains black pellets, likely to be ironstone nodules. Chippings logs from other boreholes in the north of the district suggest that there is little variation in lithology locally, although the abundance of espleys is difficult to assess from either chippings or geophysical logs.

The Etruria Formation proved by boreholes in the centre and east of the district differs only slightly from the formation farther north-west. The characteristic bowshaped gamma-ray trace remains well developed, as in the Elston Grange Borehole (Figure 17). The formation again consists predominantly of siltstone and mudstone with a red-brown colour, commonly mottled to grey-green, purple and yellow. Thin, coarse-grained sandstone and conglomerate has been logged at several levels; these coarser beds cannot be correlated between boreholes, but may represent espley-type beds.

In the south-east of the district, distinct ‘espley’ sandstones are absent and the Etruria Formation, as logged in boreholes, comprises predominantly red-brown, purple and mottled blue-green lithologies, described on the logs as tuff, lapilli tuff, agglomerate and beds containing accretionary lapilli. The characteristic bowshaped gamma-ray log profile is still evident, however, and its base appears to coincide with the incoming of volcanic material. Previously unpublished work by the British Geological Survey, as well as that carried out in the Melton Mowbray district to the south (Carney et al., 2004), shows that these beds (Figure 17) consist of secondary (epiclastic) rather than primary (pyroclastic) lithologies. They possibly represent detritus eroded from extinct Westphalian volcanic massifs that had been unroofed to the south or east of the district.

Halesowen Formation

The description of distinctive grey measures within a thick red measures sequence in the Thurgarton Borehole was used as partial evidence for correlation of the red-bed sequence with that in Staffordshire (Gibson, 1901). The grey measures were previously ascribed to the Newcastle Group (now an informal formation), but are here referred to a more widespread correlative, the Halesowen Formation (Powell et al., 2000), and have since been proved in a number of boreholes across the district. These strata give a spikey gamma-ray response (Figure 17), similar to that of the Coal Measures. Overlying the grey measures, the upper red-bed sequence, previously correlated with the Keele Group (or Keele Formation) of north Staffordshire, is here also referred to the Halesowen Formation, in line with most recent thinking on regional correlation of the red measures across the Midlands (Powell et al., 2000). This upper sequence is dominated by sandstone and gives a gammaray trace that is clearly distinct from that of the lower part of the formation (Figure 17). However, the similarity in sandstone type between the upper and lower units makes their formal definition as distinct members unsustainable. The onset of Halesowen Formation deposition indicates a return to the coal-bearing alluvial association of pre-Etruria Formation times. The dominant facies association is characterised by overbank deposits of mudstone, siltstone and thin sandstone, interbedded with channel and crevasse splay sandstone. A lacustrine facies association is likely to be present locally, and periods of swamp development led to the formation of the thin coal seams. The lack of marine influence suggests a depositional environment involving freshwater delta complexes. In north Staffordshire, strata exposed in the lower part of the formation include a lacustrine facies that comprises thin micritic limestone interbedded with mudstone (Pollard and Wiseman, 1971). Although this facies association cannot be positively identified in the few core logs available, it may be present locally in the Nottingham district. The upper part of the Halesowen Formation shows a reversion to the red-bed alluvial facies association, possibly a result of drainage reorganisation following renewed tectonic uplift and/or fault rejuvenation. The return to red colours and mottling indicates a well-drained flood plain with palaeosol development.

The lower part of the Halesowen Formation correlates with the informally named Newcastle formation (Rees and Wilson, 1998) of north Staffordshire. It overlies the Etruria Formation, from which it is distinguished primarily by colour, although the colour change from red-brown to grey also coincides with the top of the characteristic bow-shaped gamma-ray profile of the Etruria Formation (Figure 17) and with a lithological change. This part of the Halesowen Formation is seen in its entirety in a number of boreholes, and shows little significant thickness variation across the area, averaging about 40 m in the north, decreasing to 25 m in the south-east. It is similar in lithology to the productive Coal Measures, comprising dominantly sandstone, siltstone and grey mudstone with thin coal seams and seatearths. The latter, and other pedogenically modified layers, commonly exhibit rootlet and/or listric structures (Figure 17). Two coal seams of particular note have been logged towards the base of the Halesowen Formation in many boreholes, although they die out south-eastwards. They probably have widespread correlatives, as far afield as Warwickshire and Oxfordshire. Other individual coal seams are difficult to correlate, due to the lack of suitable core descriptions. However, a single seam up to 0.7 m thick can be traced across most of the district, generally thinning and dying out towards the southeast. This seam occurs in the middle part of the grey measures and is always the highest coal. Coal is therefore absent from the upper half of the grey measures and from all of the overlying red measures of the Halesowen Formation. Limestone beds, which are found in other Halesowen Formation sequences, are apparently absent in this district, although this may be the result of a relatively limited data set. Sandstone beds throughout the formation are micaceous and many have sharp, irregular, possibly erosional bases; such sandstone is well described in core from the Stenwith Borehole.

Plant and root fragments are found in great abundance throughout the lower part of the Halesowen Formation, and mussels, ostracods and fish remains have also been recorded. The flora identified from boreholes within the district includes Pinnularia, Cordaites, Calamites, Lepidodendron, Sigillaria, Alethopteris, A. aquilina (Schloth), Lepidostrobus sp., Neuropteris, Sphenophyllum sp., Holcospermum sp. and Annularia cf. A. sphenophylloides. Faunal identification is limited to Curvirimula, although the Farnsfield No. 3 and Carr Bank boreholes, immediately to the north of the district, yielded Spirobis sp., Anthroconauta minima, A. phillipsii, A. tenuis, Carbonita pungens, C. salteriana and Hilboldtina wardiana (Edwards, 1951, 1967). This assemblage suggests the A. tenuis Zone (Table 11) and, in the absence of better biostratigraphical data, the base of the Halesowen Formation in the district is correlated with the base of the Westphalian D stage (Stephanian), as in the West Midlands.

The upper part of the Halesowen Formation in the Nottingham district is correlated with the lower part of the (informal) Keele formation of north Staffordshire (Rees and Wilson, 1998). Overall it is red-brown in colour, with common purple, grey-green and yellow mottling. Stacked channel sandstones dominate the sequence, each sandstone bed being characterised by an erosional base and sporadic pebbly lags. The sandstone beds show various sedimentary structures (Figure 17) and are generally described as micaceous throughout this sequence, strongly supporting a Halesowen Formation assignation. Overbank deposits are represented by thin intercalated beds of mudstone, siltstone and breccia, with sedimentary structures such as climbing ripple cross-lamination. Pedogenic features such as rootlets, ferruginous nodules and carbonate pellets or nodules are also present. Caliche, which characterises the upper part of the Halesowen Formation and the overlying Radwood/Enville Formation (Rees and Wilson, 1998) elsewhere in the Midlands, has not been recognised in any of the core logs from boreholes in the district.

The very top of the Halesowen Formation is marked elsewhere by a regional gamma-ray high and a well-developed palustrine sequence. Such an association has not been proved in the Nottingham district, except perhaps at the Three Shire Oak Borehole, where the maximum preserved thickness of about 127 m is recorded. There, the top 15 m of the sequence is described as red, brown, maroon and purple mudstone in the cuttings log. It is possible, however, that these uppermost strata, which occur above a gammaray high, may be Late Permian in age.

Carboniferous volcanic and intrusive rocks

Carboniferous magmatism resulted in the widespread intrusion of basaltic sills and the more localised, but commonly thicker extrusions of basalt lava and volcaniclastic rocks. For convenience of description the extrusive sequences have been grouped according to age and their distribution in the subsurface is shown in (Figure 18). Due to the inadequacy of many borehole descriptions of these rocks and the lack of borehole coverage in parts of the district, the geographical limits of the various extrusive groupings must be regarded as approximate. A number of volcanic facies have been recognised in suitably long core runs, mainly from the Melton Mowbray district farther south (Carney et al., 2004). These facies commonly have characteristic wireline geophysical log signatures (Figure 19), enabling their recognition in other boreholes that have geophysical logs, but lack adequate volcanological descriptions. The volcanism was episodic, with the most significant extrusive phases occurring along the Cinderhill–Foss Bridge Fault System in late Dinantian times, and in the eastern and south-eastern parts of the district throughout the Langsettian. The flanks of the Langsettian basaltic shield have largely replaced the age-equivalent Lower Coal Measures strata in the east, a relationship that can also be demonstrated in the adjacent Melton Mowbray district (Carney et al., 2004).

Detrital volcanic material is present in the Etruria Formation of the Barren Measures, particularly in the south-east of the district. Its presence indicates that the Langsettian volcanic edifices had been unroofed and were undergoing dissection by Bolsovian times.

Late Dinantian and ?early Namurian volcanism

This volcanic episode was restricted to the south-west of the district (Figure 18) and was located along the southern edge of the Nottingham Shelf, coincident with the major monoclinal structure that includes the Cinderhill–Foss Bridge Fault System. On the seismic profiles of Ebdon et al. (1990, fig. 7) and Fraser et al. (1990, fig. 6), the extrusive sequence appears as a convex-topped, shield-like mass about 500 m thick. The edifice laterally replaces Dinantian strata that are mainly correlated with the early to mid-Brigantian seismostratigraphical sequence (EC6 of Fraser et al., 1990). The Strelley 1 Borehole, located about 4 km west of the district (Figure 18), penetrated these rocks fully, but their thickness of 372 m suggests that the borehole may have sampled the flank of the shield. The descriptions in the borehole log indicate that the sequence is made up of a lower volcaniclastic part, 236 m thick, consisting of pale grey, ash-grade tuff and pale green lapilli-tuff, the latter apparently ‘welded’ and flow-foliated. The upper 136 m comprises green to purple-green basaltic lava with sporadic red, crumbly ‘lateritic bole’ interflow horizons. Cuttings samples of basalt observed from this upper part were glassy and vesicular (oral communication, N J Riley, 2002).

The maximum age of the Strelley basalt sequence is further constrained by fossils found within 9 m of brown to white, shell-rich limestone that overlies the volcanic rocks in the Strelley Borehole. A fauna that contains archaediscids of the genus Asterarchaediscus associated with Valvullinella sp. suggests that these limestones are of mid to late Brigantian age (Riley, 1986a), equivalent to the upper part of the Monsal Dale or Bee Low limestones of Derbyshire and to the Widmerpool Formation (Aitkenhead and Chisholm, 1982). The volcanic episode may therefore have been in part, contemporary with the Fallgate Volcanic Formation (Aitkenhead and Chisholm, 1982), found in the adjacent Chesterfield district to the northwest and of Asbian and Brigantian age. The mudstone that overlies the limestone in the Strelley 1 Borehole is correlated with the Edale Shale Group, but the geophysical log does not provide much evidence of age. The borehole log concludes that these strata are Arnsbergian, but they could be younger, perhaps Chokierian or Alportian; sandstone that might be the Kinderscout Grit lies 90 m above the top of the limestone. The limestone that underlies the Strelley volcaniclastic rocks includes micritised grainstone–packstone and coarse–grained peloidooid grainstone, with volcanic fragments seen in some borehole cuttings (Riley, 1986b). Their microfaunas were only poorly preserved, but contain doubtful Koninckopora fragments suggesting a broadly Viséan age.

The thickest proving of the equivalent volcanic beds in the Nottingham district was 53 m in the Saxondale No. 1 Borehole. On the accompanying log, they are described as green, crumbly and crystal-rich tuffaceous mudstone. The gamma-ray profile (Figure 7) shows larger amplitude serrations in the upper 25 m of this sequence, which could therefore contain lavas, as in the Strelley Borehole. However, this signature could also be produced by lithologies such as block-rich volcanic breccias. The same volcanic sequence, although only 30 m thick, was proved in the Cropwell Butler No. 1 Borehole, resting on Dinantian limestone. These volcanic rocks are reported to contain a 6 m-thick sheet of a hard, dark green, igneous lithology that may be either a sill or a lava flow. Farther along strike to the south-east, the Bingham No. 1 Borehole records only 3.5 m of ‘dark grey, white-spotted pyritic tuff’ occurring near the base of strata correlated with the Edale Shale Group. The Bingham No. 2 Borehole has 6 m of ‘dark green igneous rock, off-white and pyritic at top’ at a similar stratigraphical level, just above Dinantian limestones (Figure 7). A ‘teschenite’ sill, 21 m thick, separates Namurian strata from Carboniferous limestone in the Screveton No. 1 Borehole (Figure 6).

The absence of overlying limestone in the Saxondale No. 1 and Cropwell Butler No. 1 boreholes indicates that the ‘Strelley’ volcanic sequence there formed part of a topographic ‘high’ that was onlapped by the Edale Shale Group (Figure 7). The upper boundary of the volcanic succession in the Saxondale No. 1 Borehole is only 25 m below strata correlated with the Kinderscout Grit (compared to a possible 90 m in the Strelley Borehole), although its base rests on Dinantian limestone. Different relationships are indicated by seismic profile interpretations across the thickest part of the pile, which show that seismostratigraphical sequence EC6 (early to mid Brigantian) both laps onto and attenuates across the convex top of the Strelley volcanic pile (e.g. Fraser and Gawthorpe, 2003). An early Kinderscoutian age for cessation of the Saxondale equivalents of these volcanic rocks would be possible if their eruption was longer lived in that area. It is more likely, however, that their upper contact with the Namurian strata is a significant disconformity, representing the progressive burial of an extinct edifice that is largely of Brigantian age, as proved at Strelley.

Possible attenuated lateral equivalents of the early pyroclastic phase at Strelley may occur to the south of the Nottingham district as the tuffaceous beds of the Ratcliffe Volcanic Member, which is part of the Widmerpool Formation. In the Widmerpool No. 1 Borehole, 7 km south of the district, the Ratcliffe Member is faunally dated as early Brigantian (P1c ammonoid zone) and was equated with the Tissington Volcanic Member of the Ashbourne district by Carney et al. (2004). The Tissington succession contains diverse basaltic rocks, and also includes sedimentary strata that yielded ammonoids indicating an age between P1c and early P2, probably within the P1d Zone of the latest early Brigantian (Chisholm et al., 1988, p. 33).

Overview

In late Dinantian times, basaltic lava and associated volcaniclastic lithologies were voluminously erupted to the south-west of the district, and probably extended into the district at least as far east as the Saxondale and Cropwell area. This activity probably commenced in the late Arundian and lasted into late Brigantian times; the pile was probably extinct when Namurian strata of the Edale Shale Group eventually lapped across it. The magmas may have exploited zones of tension along the crest or flanks of a major monoclinal flexure that includes the Cinderhill–Foss Bridge Fault System. This complex structure was active throughout the Dinantian syn-rifting episodes, when it acted as a major tectonic hinge-line that separated the Widmerpool Halfgraben from the Nottingham Shelf (compare (Figure 20) and (Figure 42).

Late Namurian to earliest Langsettian volcanism

In the east of the district, the Bottesford No. 4 Borehole shows that basaltic rocks overlie the Kinderscout Grit and apparently replace Marsdenian strata that elsewhere include the Ashover Grit (Figure 7); (Figure 19). The volcanic succession was identified on the borehole log over a thickness of about 38 m, but this also includes a significant intercalation of Namurian mudstone and sandstone. Similar beds may in part account for the serrated gamma-ray profile of the interval (Figure 19). The brief lithological log recorded‘ dark green igneous rocks’, perhaps thin lava flows or volcanic breccias, alternating with thin sandstone and dark grey mudstone beds. The basaltic rocks do not appear have to dilated the thickness of the succession, supporting their extrusive origin.

Equivalents of this volcanic episode may be the apparently discrete succession of volcanic rocks proved by boreholes between Kelham and Southwell, at the northern margin of the district (Figure 19). The log of the Normanton No. 4 Borehole, for example, shows about 32 m of ‘altered shaly sandstone and shale with igneous bands’ between depths of 693 m and 661 m. From the meagre descriptions, these lithologies might be tuffaceous sedimentary strata interbedded with air-fall tuffs, or admixed tuff and sediment. The sequence is dated as late Namurian, as it occurs between strata correlated with the Ashover and Chatsworth grits on the log. Further ‘dark grey-green igneous’ rocks occur stratigraphically higher in the sequence, spanning the Namurian–Langsettian boundary, although whether this younger basaltic episode represents extrusive rocks or sills is uncertain. In the nearby Upton No. 2 Borehole, an 83 m thickness of basaltic rocks was recorded, commencing just above the inferred top of the Namurian (Millstone Grit); one interval was described as consisting of ‘interbedded igneous and shale’. All of these late Namurian and early Langsettian volcanic sequences could include lavas and proximal pyroclastic rocks, although intrusions could also be present. The apparently isolated geographical situation of the Kelham–Southwell occurrences (Figure 18) suggests that they were extruded from source(s) separate from that of the main development of basaltic rocks in the east of the district.

Late Namurian to late Langsettian volcanism

This major development of basaltic rocks in the east and south-east of the district is co-extensive with and therefore part of the Saltby Volcanic Formation of the adjacent Melton Mowbray district (Carney at al., 2004). There, interdigitating relationships between basaltic rocks and Lower Coal Measures indicate two major culminations of basalt lava extrusion, probably from a centre, or centres, located farthereast. Phase 1, the earlier eruptive event, commenced at or just before deposition of the Subcrenatum Marine Band, and ceased just after deposition of the Kilburn Coal, before deposition of the Mickley–Ashgate coal seam grouping. Phase 2 occurred between deposition of the Yard Coal and the Parkgate–Tupton coals. In the Melton Mowbray district, the surface of the Phase 2 lava apron formed a topographical feature that caused pinch-out of the Tupton Coal and overlying strata, up to and including the Vanderbeckei Marine Band.The distribution of phases 1 and 2 lavas and the Vanderbeckei Marine Band onlap in the Nottingham district are indicated in (Figure 18) (see also Burgess, 1982, fig. 4). The edifice or outflow apron formed by these basalts terminates at approximately gridline SK50N, to the south of Balderton, as also noted by Burgess (1982).

Only a very few boreholes in the district penetrated the entire (phases 1 and 2) volcanic succession, and those that do, although supplemented by wireline geophysical logs, lack useful lithological descriptions. The thickest proving in the Nottingham district, in the Bottesford No. 4 Borehole, shows that volcanism commenced at about the level of the Ashover Grit and forms about 90 per cent of the upper Namurian to upper Langsettian interval. An aggregate thickness of 369 m of basaltic rocks is indicated, in which phases 1 and 2 form a single amalgamated sequence with the only significant break being at the level of the Kilburn Coal (Figure 19). There are no descriptions of the volcanic rocks in the Bottesford No. 4 Borehole, nor were samples available for examination, but comparison with the Grimmer Borehole in the Melton Mowbray district, for which partial core runs are still available (Carney et al., 2004), gives some indication of the likely volcanic lithologies. Comparison of the wireline geophysical logs from those boreholes suggests that the Bottesford 4 succession is dominated by basalt lava with a relatively minor content of basalt sills (Figure 19). Just above the lavas forming the base of the Phase 2 sequence in the Bottesford No. 4 Borehole, however, is a succession, about 70 m thick, characterised by a gamma-ray trace that is rather more indented than is typical of lavas. By analogy with a similar occurrence at the base of Phase 2 in the Grimmer

Borehole, the lithology is interpreted as peperite breccia. Peperite (sensu White et al., 2000) comprises fragmental volcaniclastic lithologies that formed as a result of interactions between magma and wet, unconsolidated sediments. In the Grimmer Borehole, the peperite consists of basalt blocks, commonly with curviplanar margins, set in a poorly sorted matrix of amygdaloidal basaltic scoria intermixed with silty sediment (Carney et al., 2004).

The log of the Redmile Bridge Borehole see (Figure 18) provides one of the best descriptions through the upper part (Phase 2) of the Langsettian volcanic pile (notes by I C Burgess), and some drillcore is also available. The top of the basaltic sequence lies at a depth of 597 m, immediately beneath the seatearth of the Joan–Brown Rake Coal. Its top surface consists of basalt lava weathered to a grey-green, stratified bole, 0.88 m thick, beneath which the effects of weathering are detected over a further 1.5 m down-section. The fresher rocks below are generally dark grey-green compound basalt flows with strongly amygdaloidal layers. The latter might be the tops and/or bases of individual flow units, which evidently range between 1.5 m and 5.5 m in thickness. Some flow units are separated by sedimentary intercalations comprising seatearths that are commonly surmounted by fine-grained, green, weathered basaltic tuff with graded bedding visible locally. One of these interflow zones, at a depth of 608 to 609 m, contains a coal identified as the Deep Main. In the several metres of basalt below 650 m, individual flows, from 1 to 2.25 m thick, are separated by equally thick developments of ‘basaltic rubble’. Drillcore through one rubbly horizon, at 650 to 652 m, contains rounded masses of basalt resembling pillow fragments in a matrix of pale green tuff intermixed with dark grey mudstone (Plate 4). Beneath this lava sequence are about 0.8 m of tuff and lapilli tuff that rest at a depth of 658 m on a prominent bole that is 2.98 m thick. This bole surmounts a further compound lava flow sequence, in which a prominent interval of dark grey mudstone interbedded with greygreen, fine-grained tuff occurs between 667 and 669 m. A dyke between 669 and 669.8 m in the Redmile Bridge Borehole has a curviplanar margin that is locally fragmented and invaded by the host sediment, the latter showing wispy and disrupted bedding (Plate 5). Burgess described further basaltic sills in the lowest c. 6 m of the Phase 2 succession, which terminates at a depth of 678 m, about 5 m above the Blackshale–Ashgate seam.

The rapid westwards thinning of the Langsettian volcanic sequence, commensurate with the increasing thickness of the Lower Coal Measures sedimentary strata, is shown by a comparison of the Bottesford No. 4 and Granby No. 1 boreholes (Figure 19). The thickness of the ‘normal’ Langsettian succession in the west is less than that of the volcanic rocks that replace it eastwards. Burgess (1982) attributed this relationship to the higher degree of compaction experienced by sedimentary sequences. One of the most westerly occurrences of Phase 2 lavas is in the Station Farm Borehole (Figure 19); on the log, the notes of I C Burgess describe a sequence of three basalt flows with individual flow units ranging from 1.5 to 2.5 m thick.

Distal equivalents of the Langsettian volcanic rocks might occur in the west of the district, where kaolinite-rich ‘tonstein’ (altered volcanic ash) beds have been identified. Berridge (1980a) described a particularly prominent volcanogenic bed from a datum in the C. communis Zone, at about the level of the Kilburn Coal, in the Cotgrave Colliery H53s Borehole. This 50 mm-thick bed has a coarse-grained, ‘gritty’ appearance, with a yellowish buff colour, and consists of abundant angular to subrounded grains of partially calcitised and kaolinitised vesicular basalt clasts. Berridge (1979, 1980b) described other thin beds of carbonated volcaniclastic rocks from the westerly Langsettian sequences, although the borehole records needed to determine their precise stratigraphical positions have not been found. Carbonated lapilli tuff beds have been noted in several boreholes between the Kilburn and Blackshale coals (Burgess, 1982), and are the probable distal fall-out products of Langsettian volcanism. Up to eight thin kaolinite horizons, at least some of which may be tonsteins, have been recorded within Langsettian and high Duckmantian strata in the region (Eden et al., 1963), the higher of which were probably supplied by centres outside the district.

The Screveton No. 1 Borehole (Figure 19) records about 150 m of basaltic rocks below the Wingfield Flags, but as there are no lithological descriptions, the proportion of extrusive to intrusive basalt is far from clear. However, the basalt in question is about four times thicker than the equivalent interval in the Granby No. 1 Borehole, suggesting that this part of the succession in the Screveton No. 1 Borehole has been thickened by multiple sill injection.

Late Langsettian, ‘Black Rake’ volcanism

The tuffaceous rocks forming the Black Rake (‘Black Rake Carbonate Rock’ of Edwards, 1951) represent a more stratigraphically restricted and generally younger episode of volcanism than Phase 2 of the Namurian to late Langsettian volcanic sequence described above. The Black Rake occupies the highest part of the Langsettian sequence; its top is a few metres below the Brown Rake Coal. The tuffaceous facies of the Black Rake in the Nottingham district averages 0.38 m in thickness and has a striking laminated appearance caused by up to 50 successive graded tuffaceous layers (Francis et al., 1968a). In the north and central part of the district, however, the Black Rake thickens up to 1 m and is composed mainly of tuffaceous layers in which accretionary lapilli are conspicuous; good examples are found in the Fishpool, Hartswell, Burton Joyce and Woodborough boreholes (Plate 6); (Plate 7). The distribution of the accretionary lapilli tuffs (Figure 18) is based on incomplete data coverage, but could suggest that they were deposited within a fall-out plume that settled on the central northern part of the district. This would imply a volcanic source region geographically separate from that supplying the thick Langsettian basaltic sequence described (above) in the south-eastern part of the district. A correlative of the Black Rake was encountered in the Epperstone (Wash Bridge) Borehole, where 24.5 m of basaltic rocks immediately underlie the Vanderbeckei Marine Band and extend down to the First Piper Coal. The lithologies consist of basaltic tuff admixed with sediment, an association that has been interpreted by Francis et al. (1968a) as a type of gas-fluidised tuffaceous vent deposit. Considering the position of this borehole with respect to the other occurrences of the Black Rake (Figure 18), it is possible that this vent was part of the eruptive source region(s) that produced the accretionary lapilli deposits.

Overview of Langsettian volcanism

In a discussion of the Saltby Volcanic Formation of the adjacent Melton Mowbray district, Carney et al. (2004) concluded that volcanism would have been most continuous, and its record most complete, closer to the magmatic source region(s) that lay to the east. Evidence from the Bottesford No. 4 Borehole, in which the volcanic sequence is particularly thick and generally devoid of sedimentary intercalations, suggests that this situation probably also pertains in the south-eastern part of the Nottingham district. As in the adjacent Melton Mowbray district, two major culminations of activity (phases 1 and 2) are recognised, each of which resulted in the outflow of basalt lava westwards across the Coal Measures delta plain. Each of these lava outflows would have formed a broad volcanic apron or shield, that of the Phase 2 lavas evidently forming a partial barrier to sedimentation that caused the eastward pinching out of strata up to and including the Tupton Coal and Vanderbeckei Marine Band (Figure 19). Preliminary 3-D modelling work for the north of the Melton Mowbray district suggests that the surface of the Phase 2 shield had a very gentle westward slope angle, of about 0.5 to 1.5°, steepening up to the east (information from S Dumpleton, BGS, 2002). Evidence from the Grimmer Borehole of the Melton Mowbray district, and possibly the Bottesford No. 4 Borehole of this district, suggests that volcaniclastic lithologies such as peperite breccia formed a significant part of the Phase 2 succession. They are the approximate lateral equivalents of sills and basaltic lavas in other boreholes. Some of these breccias may be the fragmental products of shallow-level intrusions into wet sediments, the presence of the latter being suggested by soft-sediment deformation noted in the vicinity of an intrusive contact in the Redmile Bridge Borehole (Plate 5). On the other hand, peperite breccia could represent the fragmentation of subaerial lavas as they entered lakes or foundered into swampy pockets on the Coal Measures delta plain. Features suggesting this latter process are seen in one of the fragmental volcanic layers in the Redmile Bridge Borehole, where pillow-like basalt masses occur within a zone of sediment invasion.

The Black Rake volcanism, which appears to have been restricted in time to the end of the Langsettian, contributed tuff with accretionary lapilli. The latter are indicative of phreato-magmatic activity (e.g. Williams and McBirney, 1979), which would probably have been driven by pressurised vapour produced when magma was erupted into lakes or water-soaked sediment, with the build-up of tuff cones or maars above the feeder vents. One such centre may have been intersected in the Epperstone (Wash Bridge) Borehole.

Intrusive basaltic rocks

Basic intrusive sills in the Nottingham district are part of an alkaline dolerite complex that is extensive in the subsurface of much of the East Midlands (Falcon and Kent,1960).These sills are locally up to several tens of metres thick and generally have a sporadic occurrence in Dinantian and Namurian strata. They reach their greatest concentration in Lower Coal Measures (Langsettian) strata, which could indicate that they are in part contemporary with and in part slightly younger than the magmatism that produced the Saltby Volcanic Formation and possibly the Black Rake volcanic rocks.

The principal mineral assemblage in the sills consists of olivine, pyroxene, plagioclase (labradorite–bytownite) and Fe-Ti oxides. Kirton (1984) described the intrusive lithologies as ‘olivine-dolerites’, although it is noted here that sills, like lavas, may have intergranular (basaltic) textures, and that the subophitic (‘doleritic’) textures typical of thick sills can also develop in the internal parts of thick lava flows. Consequently, sills and lavas cannot be differentiated on textural grounds alone, and the most conclusive criterion to distinguish them is the observation, in preserved borehole core-runs, that sills have markedly chilled, sharp, planar margins with the country rock, particularly along their top surfaces. Insufficient chemical data are available to compare the composition of the different sills, and thus to deduce whether there might have been contrasting sources of magma and/or different phases of intrusion.

Among the stratigraphically lowest intrusions is the 25 m thick dolerite sill that intrudes Namurian (Marsdenian–Yeadonian) strata in the Parkhill No. 1 Borehole (Figure 6). A 9 m-thick bed of ‘green igneous rocks’ at the same stratigraphical level in Screveton No. 1 Borehole, thought to be extrusive by Falcon and Kent (1960), also dilates the succession and is probably intrusive. In support of this is the ‘blocky’ to finely serrated appearance of the gamma-ray trace, which lacks the deeper serrations more typical of the compound basaltic lava flows seen in the Grimmer and Bottesford No. 4 boreholes (Figure 19). These intrusions, like those in the Lower Coal Measures (see below), may have been emplaced during Westphalian C (Upper Coal Measures) times as suggested by Burgess (1982), although an older age, more closely associated with the main Langsettian volcanism, is also possible and is suggested by at least one observation (Plate 5) of intrusions emplaced into unconsolidated Langsettian sediments.

The stratigraphically higher sills intruded into Westphalian strata occur at a number of levels. In the adjacent Melton Mowbray district (Carney et al., 2004), they are discontinuous and of widely varying thickness. A persistent sill is recognised immediately above the Subcrenatum Marine Band in some boreholes (Figure 9), and corresponds with the Subcrenatum Sill of the Melton Mowbray district. The other sills identified above this level are the Alton Sill (above the Listeri Marine Band) and Norton Sill (above the Amaliae Lingula Band), the latter being 53 m thick in the Harlequin No. 1 Borehole. The Norton Sill, also termed the ‘Kilburn Sill’ locally, is of economic importance since it has yielded small flows of oil from its fractures (see Chapter 2). A particularly thick (150 m) basalt, which greatly thickens the local succession and is interpreted as a development of the Norton–Kilburn Sill, occurs below the Kilburn Coal in the Screveton No. 1 Borehole. It is noteworthy that these sills are absent from the equivalent interval in the Newark No. 1A Borehole (Figure 9), which is located across the Eakring–Foston Fault and farthest from the centre of magmatism represented by the Saltby Volcanic Formation. Sills above the Kilburn Coal show a general eastwards increase in thickness across the southern part of the area (Figure 10); one of these, the 40 m-thick body just below a depth of 700 m in the Screveton No. 1 Borehole, correlates with the Mickley Thin Sill of the Melton Mowbray district. Farther north, in the Bulcote Borehole (Figure 11), the Kilburn and Blackshale sills are present. A 65 m-thick basalt correlated with the Blackshale Sill occurs below the Threequarters Coal in the Fiskerton No. 1 Borehole.

The stratigraphically highest intrusion of basalt occurs several metres below the Deep Main Coal in the Tithby Borehole and has the Parkgate Coal below it in the Granby No. 1 Borehole (Figure 10), suggesting a correlation with the Parkgate Sill of the Melton Mowbray district (Carney et al., 2004). Farther south, Burgess (1982) and Carney et al. (2004) found sills higher than this, the youngest occurring above the Second Waterloo Coal of the Middle Coal Measures (Duckmantian).

Geochemical information

Langsettian lavas and sills of this magmatic province are included in the studies of Kirton (1981, 1984). These rocks comprise a spectrum of petrographical types, ranging from basalt and basanite through to hawaiite. Tholeiitic to alkaline or subalkaline compositions are typical, with most rocks consisting of olivine basalts with TiO2 in the range 1.6 to 2.5% (Kirton, 1981); all basalts, whether extrusive or intrusive, fall within the same chemical compositional fields and thus share the same type of intraplate tectonic setting. Plotting relatively immobile trace elements on discriminant diagrams reveals a wide distribution between the alkaline and tholeiitic fields (Zr/TiO2 vs Nb/Y) and alkaline and subalkaline fields (Nb/Y vs Zr/P2O5). In these respects, the East Midlands samples show a greater range of magmatic affinity than the more alkaline West Midlands suites.

Age

The age of extrusive basaltic magmatism in the district is constrained stratigraphically, to between latest Namurian and very latest Langsettian times. Build-up of the Saltby Volcanic Formation commenced around the time of deposition of the Ashover and Chatsworth grits and persisted through most of the Langsettian before terminating just after formation of the Tupton Coal. On the timescale of Opdyke et al. (2000), these eruptions would have occurred from about 316 Ma to 314–313 Ma, the younger age also being the minimum age of the more restricted Black Rake phreatomagmatic event. The timescale of Opdyke et al. (2000) is partially calibrated from high-precision uranium-series ages on volcanic rocks interbedded within the Namurian and Westphalian sequences in various parts of Europe.

Ages determined for the intrusive basalts of the district are significantly younger than those estimated on stratigraphical grounds for the lavas and volcaniclastic rocks. Estimations based on the K-Ar method have yielded latest Carboniferous (Stephanian) dates of 296 ± 15 Ma and 302 ± 20 Ma (Francis et al., 1968b; Fitch et al., 1970) for samples from the Harlequin No. 1 Borehole. However, the large errors preclude these dates from being accurate constraints for the ages of emplacement, and as yet there are no precise dates for the Westphalian intrusive event(s) in the district.

Chapter 5 Permian

The Permian succession of the Nottingham district (Table 12) attains a maximum thickness of about 100 m. Permian strata crop out only in the extreme western part of the district, where more resistant beds, mainly constituting the Cadeby Formation, flank the western side of the River Leen valley. Across the rest of the district the sequence dips to the south-east and is overlain by Triassic strata.

The Permian rests unconformably on Westphalian rocks throughout much of the district, but oversteps in the east on to Namurian strata brought up within the Rolleston Anticline (Figure 45), a Variscan inversion structure developed in the hanging-wall block of the Eakring–Foston Fault. Although the youngest Carboniferous rocks preserved in the district are the Halesowen Formation, of probable early Westphalian D age, Carboniferous strata younger than this were probably deposited but eroded in the period that followed the end-Carboniferous phase of Variscan compression and uplift (Chapter 9).

Classification

The chronostratigraphical subdivision and correlation of Permian and Triassic rocks in Great Britain is hampered by a scarcity of diagnostic fossils. The bases of both systems are located, with considerable uncertainty, within continental strata that are largely barren of fossils. Consequently, correlations based variously on concepts of cyclic, event and sequence stratigraphy have been proposed for much of the succession.

No formal biostratigraphical or chronostratigraphical classification has been applied to the Permian of the British Isles, but it is informally divided into lower and upper parts. In eastern England, the base of the upper Permian is drawn at the incoming of marine strata (Smith et al., 1974). Offshore, in the Southern North Sea Basin (Figure 20), the top of the Permian is placed at a lithostratigraphical boundary (Warrington et al., 1980; Johnson et al., 1993), namely the base of the Bröckelschiefer, which immediately overlies the highest Permian evaporite deposit. Onshore, this evaporite is represented by the Littlebeck (formerly Top) Anhydrite, which is proved at depth in North Yorkshire and Lincolnshire (Whittaker et al., 1985) but pinches out westwards (Smith et al., 1986; Smith, 1989) and does not reach outcrop. Beyond the limits of the Littlebeck Anhydrite, the ‘base Triassic’ is placed within the Roxby Formation (formerly ‘Upper Permian Marl’), which passes laterally in Nottinghamshire into the Lenton Sandstone Formation, the lower division of the Sherwood Sandstone Group. In this memoir, the base of the Triassic is taken arbitrarily at a marked non-sequence at the base of the Calverton Breccia, which also corresponds to a distinctive lithological and geophysical marker. This datum cuts across the boundaries between the Roxby, Brotherton and Edlington formations, and separates the lower and upper divisions of the Lenton Sandstone Formation (Figure 21); (Figure 24); it may be a sequence boundary of regional importance in eastern England.

The part of the Permian sequence described here comprises shallow marine deposits and associated argillaceous red beds that are entirely of late Permian age (informal classification — see above). The lithostratigraphical nomenclature applied to these strata largely follows the proposals of Smith et al. (1986) and is summarised in (Table 12). The term ‘Zechstein Group’ is applied to the equivalent Permian sequence offshore, where the deeper part of the Southern North Sea Basin contains five, basin-wide, transgressive-regressive cycles (Johnson et al., 1993). The cycles can generally be recognised in the upper Permian of the subsurface of eastern England, and were assigned group names by Smith et al. (1986). In the thinner basin-margin sequence seen at or near outcrop in the Nottingham district, however, many of the cycle boundaries fall within formations and cannot be traced either at surface or in borehole sections. The multi-group classification is therefore not followed in this account, although reference is made to the Zechstein cycles for descriptive and comparative purposes because of their general familiarity. Since the publication of Nottingham Sheet 126, all of the Permian strata in the district have been referred to a single division, the Zechstein Group.

Applying the concepts of sequence stratigraphy, Tucker (1991) identified seven sequences in the upper Permian succession of north-east England and the adjacent offshore area. The sequence boundaries identifiable in the Nottingham district are compared with the Zechstein transgressive-regressive cycles in (Table 12). As with those cycles, relative changes in sea level are interpreted as the mechanism producing each of the sequences, but the principal discontinuities within the succession are placed at the bases of the sea-level lowstand deposits, that is the evaporites and their lateral equivalents. Extension of sequence stratigraphy to the basin-margin succession is impeded by problems similar to those that beset the cyclic stratigraphical approach, limiting its application in the Nottingham district.

The outcrop of Permian strata in west and north-west Nottingham lies mainly on the adjacent Derby sheet. Numerous surface sections there, together with a few in the Nottingham district, were described by Lamplugh and Gibson (1910) and Frost and Smart (1979). In the Nottingham district, exploration for coal and hydrocarbons has provided a large amount of subsurface information (Figure 22), (Figure 23)a, b. Colliery shaft sections and a few cored boreholes provide the best lithological data, although these are mainly located in the west and south of the district. Logs of other boreholes are generally based on chippings samples and provide less reliable lithological records, unless supported by geophysical logs. Correlations of Upper Permian and Lower Triassic strata in selected boreholes in the district are illustrated in (Figure 24), (Figure 25) and (Figure 26), which show west–east stratigraphical profiles across the northern, central and southern parts of the district respectively. A schematic interpretation of this part of the succession, based on these profiles, together with data from other boreholes, is illustrated in (Figure 21).

Palaeogeographical setting

By the end of the Carboniferous Period, Variscan compression had established a mountain chain through south-west England and across northern France into eastern Europe. To the north, widespread late Carboniferous uplift was followed in the Permian and Triassic by phases of crustal extension related to the early stages of rifting in the North Atlantic and the eventual break-up of the Pangaean supercontinent (Bott, 1982; Glennie, 1995). In the west Midlands and north-west England, these extensional movements produced a number of small, rapidly subsiding basins with graben or half-graben structure, bounded by growth faults that inherited earlier Malvernoid, Charnoid or Caledonoid trends (Chadwick and Evans, 1995). Eastern England (Figure 20)a lay on the western margin of the Southern North Sea Basin (or Southern Permian Basin), a large post-orogenic basin that extended from eastern England through northern Germany to Poland (Ziegler, 1990). Subsidence associated with either lithospheric extension or thermal relaxation (Coward, 1995) in the central parts of the basin accommodated very thick Permo-Triassic deposits, but eastern England was situated on a more gently subsiding ‘shelf’ on the western periphery of the main basin. The Nottingham district lay at the south-western extremity of the Eastern England Shelf, flanked to the west by uplands in the area of the present Pennines and to the south by the London–Brabant Massif (Figure 20)a. The region lay only a few degrees north of the Equator in early Permian times (Smith and Taylor, 1992), with steady northwards continental drift to a latitude of 15°–20°N by the end of the Triassic (Warrington and Ivimey-Cook, 1992).

In the early Permian, the climate of what is now northern Europe was hot and arid. Harsh, desert erosion prevailed and thick continental sequences (‘Rotliegendes’) accumulated in the deeper parts of the Southern North Sea Basin (Cameron et al., 1992). The surface of the Eastern England Shelf was a gently undulating rock peneplain formed mainly on deeply weathered and reddened Upper Carboniferous rocks (Smith, 1989). The peneplain was mantled partly by a thin residual piedmont breccia (‘Basal Breccia’) and localised accumulations of aeolian sand. In the later Permian, a combination of rifting in the proto-Atlantic fracture zone (Ziegler, 1990) and glacio-eustatic sea level rise (Smith, 1980) established a new seaway between the Permian basins of north-west Europe and the Boreal Ocean to the north of Scandinavia. Like many modern desert basins, the floor of the Southern North Sea Basin is thought to have lain substantially below sea level, and its inundation by the marine waters of the Zechstein Sea may have been extremely rapid, perhaps taking only a few years (Glennie and Buller, 1983). The remainder of the Permian witnessed further marine incursions, each separated by episodes of lower sea level that isolated the basin from the Boreal Ocean to the north and led to the evaporation of large, virtually landlocked bodies of hypersaline water (Smith, 1989). This produced the Zechstein sequence comprising a cyclic repetition of basinal carbonates and evaporites in the basin centre, and shelf carbonates (Cadeby and Brotherton formations), marginal sabkha and playa deposits (Edlington Formation), and fluvial deposits (lower division of the Lenton Sandstone Formation) on the Eastern England Shelf (Smith, 1989). The final Permian marine incursion was followed by the spread of continental deposits, mainly playa muds (Roxby Formation and equivalents) and more marginal aeolian and fluvial sands (upper division of the Lenton Sandstone Formation and equivalents), across the whole of the basin.

Permian Basal Breccia

Throughout much of Nottinghamshire and Yorkshire, the Permian strata are underlain by a widespread but usually thin veneer of conglomeratic deposits (see for example Smith, 1989) containing a high proportion of angular clasts derived mainly from the underlying weathered and denuded Carboniferous rocks. The informal term ‘Basal Breccia’ is normally applied to these conglomerates. Smith et al. (1974) regarded the breccia as Early Permian in age, but Carney et al. (2004) suggested that its equivalents farther south are more likely to be Late Permian, based on geophysical log correlations. In south Nottinghamshire, Leicestershire and south Derbyshire, a similar breccia (locally termed ‘Moira Breccia’, Hains and Horton, 1969) extends westwards far beyond the depositional margin of Late Permian strata, and is overlain by the Sherwood Sandstone Group or, locally, by the Mercia Mudstone Group. In these areas, it is likely that deposition of such breccias continued well into later Permian times (Smith et al., 1974), and possibly into the early part of the Triassic.

The Permian Basal Breccia crops out mainly in the eastern part of the adjacent Derby district; only a small part of the outcrop extends into the Radford area of Nottingham. Numerous borehole and shaft sections provide records of the Basal Breccia elsewhere in the Nottingham district (Figure 24), (Figure 25), (Figure 26). The unit, although thin, is remarkably persistent, being proved in all boreholes cored through the base of the Permo-Triassic in the district. It may pinch out locally, however, as noted in the Derby district (Frost and Smart, 1979).

Where overlain by other Permian strata, the Basal Breccia generally varies in thickness from a few centimetres up to about 1.2 m. Locally, in the south-eastern part of the district, thicknesses of 1.5 to 2.5 m are more typical, with a maximum of 3.0 m recorded in the Rundle Beck Borehole (Figure 22). In the south-west corner of the district, beyond the depositional margin of the Zechstein sequence, the Basal Breccia is typically 1 to 3 m thick, but locally thickens considerably, reaching a maximum of 7.8 m in the Deering School Borehole, Wilford. Farther east, similar thicknesses were proved just to the south of the district, where the Colston Bassett North and Grimmer boreholes (Figure 22) proved 13 m and 7 m, respectively, overlain in both cases by the Lenton Sandstone Formation. A temporary section exposing 2.4 m of Basal Breccia overlain by Lenton Sandstone Formation was recorded by Shipman (quoted in Lamplugh et al., 1908) at the former Radford Gasworks around [SK 548 400]. No other sections have been documented in the Nottingham district, but Frost and Smart (1979) noted several nearby exposures in the Derby district to the west. There, the Basal Breccia is made up of angular to subangular lithic clasts, varying from very coarse sand to pebble grade, in a matrix of strongly cemented, yellowish grey, sandy, dolomitic limestone. The dominant clast types are red or green, weathered Coal Measures mudstone and siltstone, with lesser quantities of subangular to subrounded, commonly purple-stained quartz and quartzite. Other clasts include ironstone and sandstone, also derived from the Coal Measures, and clasts of probable Charnian origin. Small vugs up to 10 mm in diameter are lined with calcite crystals. Pyrite and galena pellets were noted in the Basal Breccia in the Bestwood Colliery adit [SK 5554 4755]. The lithologies of the Basal Breccia in boreholes in the Nottingham district compare closely with those in the adjacent Derby, Loughborough and Melton Mowbray districts, where clasts of undoubted Charnian provenance are locally common in sub-Triassic breccias (Carney et al., 2001). Thin intercalations of redbrown siltstone and sandstone, together with mudstone clasts, occur within the thicker breccia developments towards the south of the district. Where sufficiently thick to produce a resolvable geophysical log response, the Basal Breccia is represented by very low gamma-ray and very high sonic velocity values, producing sharp-peaked, low-amplitude deflections on the log traces, as in the Newark No. 1A Borehole (Figure 24).

The Permian Basal Breccia has been interpreted as residual piedmont gravel similar to that covering many modern stony deserts (Smith, 1989). It may originally have been distributed more unevenly with intervening patches of bare rock, and subsequently redistributed by reworking at the onset of the Zechstein transgression (Taylor, 1968). The dolomitic cement was probably precipitated when Zechstein sea water infiltrated interstitial pore spaces within the breccia. The thicker developments of Basal Breccia west of the Zechstein Sea margin accumulated over a longer period and may include distal alluvial fan deposits with intercalations of wind-blown sand.

Marl Slate Formation

Many authors have applied the term ‘Marl Slate’ to all silty and argillaceous strata of Permian age (the ‘Lower Marl’) underlying the ‘Lower Magnesian Limestone’ in Nottinghamshire and Yorkshire. In its current sense (Smith et al., 1986), the term ‘Marl Slate Formation’ has a restricted application to a thin but distinctive sequence of very finely laminated, sapropelic, argillaceous dolostone at the base of the upper Permian succession. The formation is absent at outcrop in Nottinghamshire (Smith et al., 1974), but has been recorded in some borehole sections to the east, generally where the overlying Cadeby Formation is more than 35 m thick (Smith, 1989). Although thin, the unit produces a characteristic, sharp ‘high’ on gamma-ray logs (Gaunt, 1994). The formation contains transported plant remains and a restricted but distinctive marine fauna of lingulid brachiopods and palaeoniscid fish scales (Pattison et al., 1973). It is believed to have been deposited in poorly oxygenated bathymetric lows on the basin floor, following the initial EZ1 transgression (Smith, 1989).

The characteristic lithology of the Marl Slate has not been described from any boreholes in the Nottingham district. However, the Parkhill No. 1 Borehole, near Southwell (Figure 24), proved a 3 m-thick unit with the characteristic, high gamma-ray log response of the Marl

Slate immediately above the Basal Breccia. The same borehole proved the thickest Cadeby Formation succession known in the district (56 m), suggesting that this area was a local topographical low prior to inundation by the earliest Zechstein transgression.

Cadeby Formation

The term Cadeby Formation was introduced for the rocks of the carbonate phase of the EZ1 cycle (Smith et al., 1986). In most parts of the Yorkshire outcrop, the formation is equivalent to the former ‘Lower Magnesian Limestone’. Farther south, at outcrop along the border between Nottinghamshire and Derbyshire, it encompasses two phases of sedimentation that are here identified by their former names: the dolomitic, argillaceous siltstone usually termed ‘Lower Marl’ or ‘Lower Permian Marl’ and the overlying dolomitic limestone of the ‘Lower Magnesian Limestone’. Smith et al. (1986) recommended that the term ‘Lower Marl’ should be abandoned on the grounds that it is not a true marl and merely represents a siliciclastic facies variant of the lower part (Wetherby Member) of the Cadeby Formation. However, both the ‘Lower Marl’ and ‘Lower Magnesian Limestone’ are mappable at surface in Nottinghamshire and Derbyshire, and can be clearly distinguished in the subsurface in the Nottingham district. The use of informal facies names for these subdivisions was suggested by Smith et al. (1986), but the continued usage of ‘Lower Marl’ and ‘Lower Magnesian Limestone’ as informal divisions of the Cadeby Formation is preferred in this memoir because of their familiarity and convenience for descriptive purposes.

The formation has been subdivided into a lower Wetherby Member and an upper Sprotbrough Member (e.g. Pattison, 1986). This differentiation relies on the identification of the Hampole Beds, a thin but distinctive sequence of finely laminated sapropelic mudstone and dolostone that overlies an important non-sequence, the Hampole Discontinuity. The Hampole Discontinuity defines the boundary between EZ1 subcycles a and b, and is thought to represent a brief episode of relative sea level fall and erosion (Smith, 1989); it was identified as a sequence boundary by Tucker (1991). At outcrop south of Mansfield, however, the Hampole Beds lose their distinguishing characteristics and are recognisable in only a few of the available sections (Smith, 1968; Frost and Smart, 1979), for example in a quarry at Bulwell [SK 5336 4528], just to the west of the district (Frost and Smart, 1979). The Wetherby and Sprotborough members have not been recognised either at surface or at depth in the Nottingham district.

The Cadeby Formation of the Nottingham district consists of a highly variable sequence of carbonates, mainly dolostone, interdigitating with carbonate-rich mudstone, siltstone, sandstone and conglomerate. The location of the district close to the basin margin produces complex stratigraphical relationships between the various lithofacies, complicated further by the probable presence within the succession of at least one significant nonsequence that equates with the Hampole Discontinuity. The ‘Lower Marl’ is absent in the extreme south-west towards the basin margin, where it is overlapped by the ‘Lower Magnesian Limestone’. The local absence of the ‘Lower Magnesian Limestone’ beneath the Bingham and Granby areas can be ascribed with reasonable confidence to lateral passage into siliciclastic ‘Lower Marl’-type facies. In the outcrop to the west and north-west of Nottingham, the ‘Lower Magnesian Limestone’ forms a gentle, east-south-east-dipping dip slope up to 5 km in length. Most of this outcrop lies within the Derby district, where Frost and Smart (1979) described numerous good sections. Records of surface sections in the Nottingham district are limited to a few temporary exposures documented in Lamplugh et al. (1908) and Frost and Smart (1979, p. 152). There is, however, much information available from shaft and borehole sections (Figure 22).

Subsurface provings show that the Cadeby Formation is present at depth below much of the district, reaching a maximum thickness of 56 m in the Parkhill No. 1 Borehole in the north (Figure 24). It thins and eventually dies out towards the south and east (Figure 23)a. The southern limit of deposition can be delineated with reasonable precision from borehole evidence. It trends south-eastwards below the centre of the city of Nottingham before turning eastwards, running approximately along the southern boundary of the district (Figure 23)a. This line is generally taken as the local margin of the Zechstein Sea but, as noted by Taylor (1974), that sea may once have extended beyond the limits of the preserved marine deposits. The formation is absent in the Claypole and Foston boreholes in the adjoining Grantham district to the east (Berridge et al., 1999; (Figure 22), but the depositional margin is poorly known there due to a paucity of borehole information. The formation continues southwards and is present in the subsurface in the northernmost part of the adjoining Melton Mowbray district (Carney et al., 2004).

Miospores have been recorded (in a note by R F A Clarke attached to the borehole log) from the lowest 8 m of the Cadeby Formation in the Salterford Farm Borehole (Figure 24). The assemblages, from within the ‘Lower Marl Unit’, contain numerous taeniate bisaccate pollen (Lueckisporites virkkiae, Lunatisporites spp., Protohaploxypinus spp., Vittatina hiltonensis), together with non-taeniate bisaccates, including Klausipollenites schaubergeri, and a monosaccate, Perisaccus granulosus (Table 13). Comparable assemblages are known from the ‘Lower Marl’ to the west, at Kimberley [SK 503 453] (Clarke, 1965) and Cinderhill [SK 522 438] (BGS palynology preparations MPA 25651–25655) in adjacent parts of the Derby district, and to the east, from the Woolsthorpe Bridge Borehole in the adjoining Bourne district (Warrington, 1980; Berridge et al., 1999). The age of these assemblages is interpreted as Late Permian. In the classical Permian of Russia, Lueckisporites virkkiae characterises the Kazanian and younger Permian succession, which corresponds with the upper Roadian (Middle Permian) to Changhsingian (Upper Permian) of current Permian stage and series nomenclature.

A major magnetic reversal aids more precise assignment; the Illawara Reversal, near the top of the Middle Permian Wordian Stage, occurs in the Tatarian in Russia and below the Zechstein in Germany. The Tatarian sequence is regarded as older than much of the Zechstein, which is thus considered to be Late Permian, Wuchiapingian or possibly Changhsingian, in age (Holliday et al., 2001), between about 260 Ma and 251 Ma according to current timescale information (Wardlaw and Schiappa, 2001).

‘Lower Marl’

Formerly equated with the ‘Marl Slate’ of County Durham (Wilson, 1876; Lamplugh and Gibson, 1910), these strata were first termed ‘Lower Marl’ in 1921–22 on six-inch scale geological maps of the eastern part of Derbyshire. The ‘Lower Marl’ does not crop out in the Nottingham district, but has been seen in several surface sections close by in the adjacent Derby district (Frost and Smart, 1979), where it consists predominantly of grey, dolomitic, argillaceous siltstone or mudstone. The silt grade fraction includes grains of dolomite as well as quartz. Beds of dolostone or dolomitic limestone become increasingly common towards the top, with a gradual upward passage by interdigitation into the ‘Lower Magnesian Limestone’. Miospores have been recorded from a number of sections in the vicinity of Nottingham (see Table 13), and carbonaceous plant debris, consisting largely of conifer leaves and scales, is common at many levels (Stoneley, 1958). Shelly macrofossils are abundant in some beds but the faunal assemblage, listed by Frost and Smart (1979), is of low diversity and consists mainly of brachiopods, bivalves and crinoids.

Across the northern part of the Nottingham district, the ‘Lower Marl’ thickens eastwards from 18.8 m in the Bestwood Colliery adit (Figure 22) to a maximum of 30.4 m in the Norwood Borehole, before thinning to only 8 m below the Newark area. The Bestwood Colliery adit proved pale to medium grey siltstone, variably calcareous or dolomitic, with common plant remains. Calcite-lined cavities occur at the top of the sequence. The Calverton Colliery shaft (Figure 24) encountered 22 m of similar strata, with nodules and veins of pyrite and galena towards the base; Lingula sp., nautiloids (Peripetoceras sp.), bivalves (Schizodus obscurus and pectinoids) and palaeoniscid fish scales were also recorded. Lithological logs based on chippings samples from percussion-drilled or open-hole rotary boreholes in the north of the district typically record grey or purplish grey, dolomitic mudstone or siltstone with thin carbonate beds. In geophysical logs of boreholes, the gradual upward increase in the proportion of carbonate beds produces an upward decrease in gamma-ray log response, for example in the Salterford Farm Borehole (Figure 24). The logs of the Salterford Farm and Parkhill No. 1 boreholes have a serrated character, reflecting intercalation of beds with variable carbonate content. A log correlation suggests that a lateral change into carbonate facies affects progressively lower strata of the Cadeby Formation eastwards from the Salterford Farm Borehole. Thus the ‘Lower Marl’ thins gradually to only 8 m in both the Fiskerton and Newark No. 1A boreholes, and to 5 m in the Kelham Coal borehole. The division is absent in the Stragglethorpe and Broach Road boreholes (Figure 22), to the east of Newark (Berridge et al., 1999).

The ‘Lower Marl’ varies from approximately 10 to 16 m in thickness beneath the central part of the district (Figure 25). The Elston Grange Borehole provides the only cored section from this area, proving 13 m of grey, strongly cemented (probably dolomitic) siltstone. Brachiopods including ?Horridonia sp. were recorded sporadically near the base. The bivalves Bakevellia antiqua, B. bicarinata, Permophorus costatus and Schizodus sp. were recorded towards the base of the ‘Lower Marl’ in one of the Gedling Colliery boreholes.

Several cored boreholes in the south and south-west of the district (Holme Pierrepont, Station Farm, Rundle Beck and Eady Farm; (Figure 22) proved variegated purplish grey and red-brown siltstone with common beds of finegrained sandstone. The fauna includes bivalves (Bakevellia sp., Schizodus sp.) and, less commonly, worms (Spirorbis sp.), brachiopods, turreted gastropods and ostracods. The thickness of the ‘Lower Marl’ decreases steadily towards the depositional margin (Figure 21); (Figure 23)a, as documented in the adjacent Derby district (Frost and Smart, 1979). The Holme Pierrepont Borehole, about 3 km from the depositional margin, cored 10.4 m of ‘Lower Marl’ (Figure 26). Boreholes or shafts closer to the depositional margin, for example Newcastle Colliery, Saxondale No. 1, Cropwell Butler Nos 1 and 2, Eady Farm and Redmile No. 2, proved thicknesses ranging from 1.5 to 5 m. The unit is absent in the Cotgrave Colliery No. 1 shaft and the Foss Way (Stragglethorpe) Borehole, where the ‘Lower Magnesian Limestone’ lies directly on the Basal Breccia. Locally, below the Bingham and Granby areas, the ‘Lower Magnesian Limestone’ is absent, probably due to a facies change. Boreholes thereabouts, notably Bingham No. 2 (Figure 26), Station Farm and Rundle Beck, proved the entire Cadeby Formation to consist of 5 to 10 m of typical ‘Lower Marl’ facies, comprising red-brown or purplish brown dolomitic mudstone with beds of siltstone and very fine-grained sandstone.

‘Lower Magnesian Limestone’

Sections to the west of the Nottingham district (Frost and Smart, 1979) show that the ‘Lower Magnesian Limestone’ consists typically of reddish brown, thin to medium-bedded dolostone with a medium to coarsegrained saccharoidal texture. Superficially, the rock resembles sandstone in appearance but closer examination reveals that the ‘sand’ grains are composed of rhomboidal dolomite crystals. Finely crystalline, pinkish white calcareous dolostone occurs as thin beds towards the base of the unit, and forms nodular masses higher in the sequence. Quartz sand grains tend to be concentrated in a few discrete sandy beds and occur only sporadically at other levels; the abundance of sandy beds increases considerably in the more southerly sections, in proximity to the basin margin. The bedding planes are commonly wavy and stylolitic, or may be accentuated by very thin beds or laminae of red-brown micaceous mudstone. Cross-lamination and asymmetric wave ripples are common in some sections. Herringbone cross-stratification was seen in granular dolostone in a former quarry face by the A610 road at Cinderhill [SK 532 435]. The Hampole Beds, comprising 0.2 m of buff, finegrained, shelly dolostone, were identified about 3.5 m below the top of the ‘Lower Magnesian Limestone’ in a quarry [SK 5336 4528] outside the district at Bulwell (Frost and Smart, 1979, p. 151), but have not been recognised in other sections. Shelly macrofossils are concentrated in a few thin beds and are uncommon at other levels. The fauna, listed in full by Frost and Smart (1979), is of low diversity and dominated by the bivalve genera Bakevellia, Liebea, Permophorus and Schizodus.

Lamplugh et al. (1908) provided brief details of a few former surface sections, but the numerous borehole and shaft sections in the Nottingham district offer better information, which is summarised in (Figure 24), (Figure 25), (Figure 26). The granular dolostone lithofacies, typical of the outcrop in the Derby district, is restricted to the north-west of the Nottingham district. It is best recorded in the Bestwood Colliery adit, which proved 6.1 m of buff to red-brown dolostone, granular towards the base, with lenses and streaks of grey-green mudstone and a few clay-filled cavities. In the Calverton No. 2 shaft, only 5 km to the north-east, the ‘Lower Magnesian Limestone’ is represented by 11.9 m of more finely crystalline, pale grey or pinkish grey calcareous dolostone, sandy towards the top, with partings of greenish grey mudstone. Gamma-ray logs of the unit in the north-west of the district typically show very low responses with a blocky profile (Figure 24). The boundary with the underlying ‘Lower Marl’ is marked in the Goosedale Farm Borehole by a distinctive, high gamma-ray peak. Farther east, gamma-ray and sonic logs of boreholes in the Southwell area suggest that the ‘Lower Magnesian Limestone’ thickens rapidly at the expense of the ‘Lower Marl’, probably due to an increase in the carbonate content of successively lower strata within the Cadeby Formation. The ‘Lower Magnesian Limestone’ reaches a maximum thickness of 41 m in the Parkhill No. 1 Borehole before thinning and becoming sandier in the north-east of the district (Figure 24). In the Newark No. 1A Borehole, the unit is 12 m thick and consists of fine-grained dolomitic calcareous sandstone. The ‘Lower Magnesian Limestone’ is also represented mainly by dolomitic sandstone in the Stragglethorpe and Broach Road boreholes (Figure 22) to the east of Newark (Berridge et al., 1999).

In the centre and east of the district, the ‘Lower Magnesian Limestone’ is developed in a sandstone and dolostone facies (Figure 23)a. The whole sequence thins markedly southward and, as in the Derby district, interdigitates with breccia towards a depositional margin to the south. This is well demonstrated by a former section at Bobbers Mill [SK 552 415], Nottingham (Wilson, 1876), which showed the ‘Lower Magnesian Limestone’ passing southwards from granular dolostone to breccia over a distance of only 200 m. A southwards overlap of the underlying ‘Lower Marl’ and passage into ooidal limestone with breccia intercalations are also illustrated by a number of sections in the south of the district. The Holme Pierrepont Borehole, about 3 km from the depositional margin, proved 5.3 m of ‘Lower Magnesian Limestone’ overlying ‘Lower Marl’. The former consists of pale buff, pink and brown mottled, crystalline dolostone with mudstone partings and stylolites; cavities lined with calcite or pyrite are common. A sparse fauna includes productid brachiopods and Schizodus sp. Nearer the depositional margin, the Cotgrave Colliery No. 1 shaft and Foss Way (Stragglethorpe) Borehole encountered 6.8 m and 4.4 m, respectively, of ‘Lower Magnesian Limestone’ overlying Basal Breccia. In both sections, the unit consists mainly of grey, pink or reddish brown, finely crystalline dolostone with pockets of ooidal limestone. Cavities lined with calcite, pyrite or galena are common throughout, as are partings and stylolitic films of grey-green mudstone. Two boreholes at the depositional margin, Wolds Hill (Cotgrave) in the adjacent Melton Mowbray district and Cropwell Bishop No. 1 (Figure 22), both proved only 1.8 m of intercalated ooidal limestone and breccia. In the Melton Mowbray district, the ‘Lower Magnesian Limestone’ passes rapidly southwards into the Edlington Formation and Permian Basal Breccia (Carney et al., 2004).

The ‘Lower Magnesian Limestone’ is locally absent beneath the Bingham and Granby areas (see above), where the entire Cadeby Formation is in ‘Lower Marl’ facies (Figure 26). It re-appears in the south-east of the district, where cores from the Eady Farm borehole (Figure 26) showed 8.4 m of sandy dolomitic limestone intercalated with dolomitic siltstone and sandstone. Macrofossils include abundant bivalves (Bakevellia sp. and Schizodus sp.), with plant fragments, worms (Spirorbis), turreted gastropods and ostracods. The ‘Lower Magnesian Limestone’ is also present in Cox’s Walk Borehole (Figure 26), in the neighbouring Grantham district to the east (Berridge et al., 1999).

Depositional environment

Regionally, the Cadeby Formation is interpreted as a shelf carbonate wedge, constructed in two successive phases of sea-level highstand separated by an episode of erosion caused by a fall in sea level (Smith, 1989; Tucker, 1991). Interpretation of the depositional environments of these rocks frequently presents problems due to the destruction of primary depositional fabrics by dolomitisation. Moreover, few details of sedimentary structures have been recorded in borehole logs from the district. The argillaceous rocks of the ‘Lower Marl’ indicate quiet water environments of deposition. Marine conditions are suggested by the abundant macrofauna, although the low species diversity might be the result of slightly elevated salinities. Reddening of the ‘Lower Marl’ in the south of the area is almost certainly secondary, probably due to deep terrestrial weathering later in the Permian. The fine-grained, terrigenous clastic detritus and plant debris was probably derived from streams draining the land area to the south and west (see, for example, Taylor, 1968; Smith, 1989). The detritus is thought to have occupied a lower energy lagoonal embayment in the south-western part of the Eastern England Shelf, fringed and sheltered by ooid shoals to the north (Smith, 1989). The stratigraphical relationships of the ‘Lower Marl’ and ‘Lower Magnesian Limestone’ indicate that siliciclastic sedimentation, which took place over much of the Nottingham district in the first part of cycle EZ1, was gradually displaced southwards by carbonate deposition as clastic input declined with time. Nevertheless, the sand and clay mineral content of the ‘Lower Magnesian Limestone’ in the central and eastern parts of the district indicates that siliciclastic input remained significant throughout the deposition of the entire formation. A small clastic delta may have persisted in the Bingham area, where the entire formation is in ‘Lower Marl’ facies.

The ‘Lower Magnesian Limestone’ seen at outcrop in the Derby district is thought to have been deposited as an ooidal carbonate (Frost and Smart, 1979), and to have acquired its present granular texture following dolomitisation. Cross-stratification seen in some sections suggests shallow, moderate to high-energy subaqueous conditions, with some evidence of tidal current activity provided by local occurrences of herringbone cross-stratification. In both the Derby and Nottingham districts, intercalations of sandy breccia towards the southern depositional margin may have been introduced following coastal flooding and erosion by storm surges, with transport of quartz sand and breccia clasts into the foreshore and shoreface zones by storm generated currents. Isolated quartz sand grains scattered through the rock may be of aeolian origin.

Edlington Formation

The Edlington Formation (Smith et al., 1986) corresponds to the former Middle (Permian) Marl division mapped at outcrop in Nottinghamshire, Derbyshire and Yorkshire. It represents a basin-margin facies of the upper part of cycle EZ1b and the whole of cycle EZ2, both of which are more fully developed in the subsurface below eastern England and the southern North Sea (Smith et al., 1986, fig. 2; Smith, 1989). At outcrop in north Nottinghamshire and Yorkshire, the formation is clearly defined by the carbonates of the Cadeby Formation below and those of the Brotherton Formation above. In the Nottingham district, a similarly complete sequence occurs only in the Newark No. 1A Borehole in the extreme north-east (Figure 24). Elsewhere, the underlying Cadeby Formation is the only Zechstein carbonate present, and the Edlington Formation passes gradually upwards, by interdigitation, into the lower division of the Lenton Sandstone Formation (Figure 21).

Regionally, the formation is dominated by reddish brown mudstone and siltstone, with subordinate beds of sandstone, dolostone, conglomerate and sulphate (Smith et al., 1986; Smith, 1989). In north Nottinghamshire, the upper half of the formation consists largely of sandstone resembling that of the Lenton Sandstone Formation in lithology (Edwards, 1967; Smith et al., 1973). Similar sandstone-dominated sequences also occur in the Nottingham district (Figure 21), forming lateral replacements to the mudstone and siltstone successions. In the absence of the intervening Brotherton Formation, these sandstone successions cannot be mapped separately from the Lenton Sandstone and so, for convenience, they are included as the ‘lower division’ of the latter unit (see below).

The Edlington Formation crops out in a narrow strip along the Leen valley in the north-west of the district, where it is extensively covered by alluvium and river terrace deposits. Elsewhere, the formation gives rise to low-lying, commonly poorly drained ground with a reddish brown, silty clay soil, locally with a veneer of sand and rounded quartzite pebbles derived from the Sherwood Sandstone Group outcrop to the east. Exposure is poor, and a few sections in field drains show 1 m or less of purplish brown or reddish brown mudstone, usually weathered to a stiff clay. Lamplugh et al. (1908) noted a few former sections in the area, and several more informative sections were recorded from the neighbouring Derby district to the west (Frost and Smart, 1979, p. 151). Southwards, the formation has been traced at depth in boreholes across most of the Melton Mowbray district, although it is locally absent (Carney et al., 2004).

The Edlington Formation has been proved in borehole and shaft sections in most parts of the district. The position of the gradational upper boundary with the Lenton Sandstone Formation is, however, difficult to place with consistency in the lithological logs of percussion or open-hole rotary boreholes. The isopachytes shown in (Figure 23)b have been compiled from the more reliable data yielded by cored boreholes, shaft sections and geophysical logs. The formation is thickest in the north-east of the district (Figure 24), and thins southwards and westwards due to a lateral facies change into the lower division of the Lenton Sandstone Formation (Figure 21). It is typically only 4 to 6 m thick at outcrop in the north-west of the district, and only 2.1 m thick in the Bulwell Forest Borehole (Figure 25). It is absent towards the southern margin of the district, where the Lenton Sandstone Formation rests directly on the Cadeby Formation (Figure 21).

In the north-west of the district, the best sections are provided by the Bestwood Colliery adit and Calverton Colliery No. 2 shaft (Figure 24), which proved 8.0 m and 6.1 m, respectively, of red-brown calcareous mudstone (‘marl’) with pale green mottles. Beds of pale green or reddish brown sandstone are common, and are typically fine grained and dolomitic. In the Calverton No. 2 shaft, the base of the formation is sharp and marked by shrinkage cracks; as in the adjacent Derby district (Frost and Smart, 1979), the lowest few centimetres of mudstone are grey-green. As elsewhere, the transition upwards into the lower division of the Lenton Sandstone Formation is gradational.

Farther east across the northern part of the district, information is derived mainly from geophysical logs and chippings samples (Figure 24). The formation is characterised by a strongly serrated gamma-ray log profile reflecting interbedding of mudstone and sandstone, contrasting with the low response, blocky profile of the underlying Cadeby Formation. The boundary with the overlying Lenton Sandstone Formation is marked by a transition into a mildly serrated gamma-ray log profile with a consistently lower response. Sonic log profiles are also serrated, although less markedly so than the gammaray logs. The formation thickens steadily eastwards as far as the Fiskerton Borehole, where it is 13 m thick, then thickens more rapidly to 48 m in the Kelham Coal Borehole and 56 m in the Newark No. 1A Borehole. Beds of dolomite and gypsum have been noted in the chippings logs of a few boreholes in the north-east of the district.

The southward thinning and lateral facies change in the formation are well illustrated by three cored boreholes in the eastern parts of the district. The Elston Grange Borehole (Figure 25) proved the formation to be 22 m thick. The cored sequence consists mainly of siltstone, interlayered reddish brown and pale green, with beds of red-brown, fine-grained, micaceous sandstone becoming thicker and more common upwards. Thin beds of gypsum occur in the lowermost 9 m. Evidence of desiccation is common throughout, in the form of shrinkage cracks and large pseudomorphs after halite. Plant debris and burrows occur sporadically. Interbedding of siltstone and sandstone gives rise to a strongly serrated gamma-ray log profile. The Eady Farm Borehole (Figure 26) proved about 5 m of Edlington Formation, consisting mainly of reddish brown siltstone with subordinate beds of red-brown, fine- to coarse-grained sandstone. As in the Elston Grange Borehole, upwards coarsening is evident within the sequence. Grey-green ‘fish-eye’ mottles occur in both the siltstone and sandstone beds, with shrinkage cracks, sandstone dykes and microfaults recorded in the argillaceous beds towards the base of the unit. In the Station Farm Borehole, 5 km south-west of Eady Farm (Figure 22), the laterally equivalent strata have been replaced by the lower division of the Lenton Sandstone, consisting of fine to mediumgrained, brick red sandstone with subordinate siltstone and thin pebbly layers.

Depositional environment

Regionally, the argillaceous and silty sediments of the Edlington Formation are interpreted as the deposits of distal alluvial plain, sabkha and playa environments (Smith, 1989). Gypsum beds and nodules within the sequence were probably precipitated from interstitial brines or by evaporation of localised playa lakes, and may not necessarily correlate with the evaporites of the basinal succession. Intercalations of aeolian and fluvial sandstone thicken towards the west and south. The depositional environment of the lower division of the Lenton Sandstone, which replaces the Edlington Formation laterally, is discussed in Chapter 6.

Brotherton Formation

Formerly known as the ‘Upper Magnesian Limestone’ (Table 12), the Brotherton Formation (Smith et al., 1986) represents the carbonate phase of cycle EZ3. The formation is present both at outcrop and in the subsurface in Yorkshire and north Nottinghamshire, but is absent south-west of a line between Worksop and Newark (Edwards, 1951, fig. 37). In the Nottingham district, the formation has only been proved in the Newark No. 1A Borehole (Figure 24). Geophysical log correlation suggests that its absence elsewhere in the district could be due to erosion beneath the Calverton Breccia, as demonstrated by (Figure 21), rather than wedging out against a contemporaneous shoreline.

In the Newark No. 1A Borehole, the formation comprises 5.5 m of white to cream, finely crystalline dolostone; no fossils have been recorded. Geophysical logs display a characteristically very low gamma-ray and high sonic velocity response (see for example Whittaker et al., 1985, fig. 24), enabling correlation with cored boreholes in the adjacent Grantham and Melton Mowbray districts (Berridge et al., 1999; Carney et al., 2004). In the former area, wavy bedding and a distinctive low diversity association of algae (Calcinema permiana) and bivalves (Schizodus sp.) are features of the formation.

Depositional environment

The formation was deposited following marine flooding of the marginal sabkha environments of the underlying Edlington Formation. Regionally, the depositional environment is interpreted as a shallow marine, storm-dominated shelf(Smith, 1989; McKie, 1994) with slightly elevated salinities (Smith and Taylor, 1992).

Roxby Formation

At or near outcrop in Yorkshire and the East Midlands, the name Roxby Formation (Smith et al., 1986) is applied to a sequence of reddish brown, predominantly argillaceous strata intervening between the Brotherton Formation and the base of the Sherwood Sandstone Group. Basinwards, where higher Zechstein carbonate and evaporite units are present, use of the name is restricted to strata overlying the highest such units. The formation corresponds to the ‘Upper Permian Marl’ or ‘Upper Marls’ division of previous terminology, such as that used for the Ollerton district (Table 12).

Strict application of the above definition in the Nottingham district confines the Roxby Formation to the extreme north-east, where the underlying Brotherton Formation is present. However, using gamma-ray logs, equivalent strata can be traced to the west and southwest, forming an argillaceous interval within the Lenton Sandstone Formation immediately above the Calverton Breccia (Figure 24); (Figure 25). Lateral facies change into sandstone takes place in the west and south of the district.

The Newark No. 1A Borehole provides the only proving of the Roxby Formation in the district. Geophysical logs enable close comparison of the stratigraphy in this borehole with an equivalent, cored succession in the Broach Road Borehole, 10 km to the east-north-east (Figure 24). There, the formation comprises 22 m of interbedded mudstone, siltstone and micaceous sandstone, mainly reddish brown, with common ripple marks, shrinkage cracks and mudflake breccias (Berridge et al., 1999). A breccia, 5.4 m thick and midway within the sequence, is marked by a very low response, blocky, gamma-ray log profile and probably correlates with the Calverton Breccia of the Nottingham district (see pp.100). It contains pebbles up to 5 cm across of pink and white limestone, green siltstone, brown and white quartzite and green ‘hard rock’, in a matrix of red-brown sandstone. Little lithological information is available from the Newark No. 1A Borehole, where the formation is 23 m thick. The chippings log records samples of orange-brown mudstone and medium- to coarse-grained sandstone; the Calverton Breccia was not recorded, but its presence is inferred on the gamma-ray log, midway within the formation (Figure 24).

Depositional environment

Like the Edlington Formation, the Roxby Formation was probably deposited in an arid, alluvial plain or playa setting. Gradual advance of aeolian and fluvial sands north-eastwards across this plain in latest Permian to Early Triassic times gave rise to the overlying upper part of the Lenton Sandstone Formation.

Chapter 6 Triassic

The Triassic strata of the Nottingham district average between 400 and 500 m in thickness, and comprise mainly continental red beds overlain by a thin marine development (Penarth Group). They form rockhead beneath about 80 per cent of the district, and are locally covered by thin Quaternary deposits. The sequence dips south-eastwards, eventually passing beneath the mainly Jurassic-age Lias Group. The resurvey of the Nottingham 1:50 000 sheet has shown that the Triassic outcrop is traversed by numerous faults, most with throws of 5 m or less. The largest faults (Harlequin, Eakring–Foston and Cinderhill–Foss Bridge faults) locally have throws of 40 m or more, and their movement reflects the reactivation of major Carboniferous structures (see Chapter 9).

Classification

In the Southern North Sea Basin, the base of the Triassic sequence is arbitrarily placed at a lithostratigraphical boundary, the base of the Bröckelschiefer, which immediately overlies the highest (Permian) evaporite deposit (Warrington et al., 1980; Johnson et al., 1993). Onshore in eastern England, the equivalent evaporite (Littlebeck Anhydrite) pinches out westwards (Smith et al., 1986). Beyond its limits, the base-Triassic datum lies within the Roxby Formation (formerly ‘Upper Permian Marl’). Where the Roxby Formation passes laterally into the upper division of the Lenton Sandstone Formation (Figure 21); (Figure 24), as in the Nottingham district, the base-Triassic datum is more conveniently located at the base of the Calverton Breccia, which also constitutes a marked non-sequence in this part of the East Midlands (Figure 21). The breccia forms a distinctive lithological and geophysical marker and an important sequence boundary that truncates the Roxby, Brotherton and Edlington formations, as discussed at the beginning of the previous chapter.

The lithostratigraphical classification of Triassic strata in Britain largely follows the proposals of Warrington et al. (1980), but is presently under review (Table 14). In upward stratigraphical order, the main divisions are the Sherwood Sandstone, Mercia Mudstone and Penarth groups. In southern Nottinghamshire, the lower part of the Sherwood Sandstone Group consists of the Lenton Sandstone Formation. That unit contains a lower division of sandstones that are lateral equivalents of the Late Permian Edlington Formation, but for convenience they are described in this chapter. The uppermost Triassic strata form the basal few metres of the Lias Group and are included for descriptive purposes with the remainder of that group in Chapter 7.

The chronostratigraphy of Triassic rocks in the British Isles is based mainly on palynomorph assemblages (Warrington et al., 1980). As with the Permian strata of Great Britain, however, it is hampered by a scarcity of diagnostic fossils. Due to the poor recovery of palynomorphs in the Nottingham district, the positions of stage boundaries within the Triassic succession there (Table 14) are necessarily approximate and partly dependent on correlations with other regions where better results have been obtained. For example, the baseTriassic datum, which is arbitrarily located at the base of the Calverton Breccia, occurs within essentially unfossiliferous continental strata. The top of the Triassic is better constrained and is placed at the lowest occurrence of ammonites of the genus Psiloceras, which is typically slightly above the base of the Lias Group in England and Wales (Cope et al., 1980; Warrington et al., 1980, 1994).

Palaeogeographical setting

Phases of crustal extension related to the early stages of rifting in the North Atlantic area and the eventual break-up of the Pangaean supercontinent (Bott, 1982; Glennie, 1995) continued to influence sedimentation during the Triassic. As in Permian times, eastern England formed part of a more gently subsiding ‘shelf’ on the western periphery of the Southern North Sea Basin. The Nottingham district lay at the south-western extremity of this Eastern England Shelf, flanked to the west by uplands in the area of the present Pennines and to the south by the London–Brabant Massif (Figure 20)b. During the Triassic, the region experienced steady northwards continental drift, moving from subequatorial latitudes in the Late Permian to a latitude of 15° to 20°N by the end of the Triassic (Warrington and Ivimey-Cook, 1992).

The final Permian marine incursion was followed by the spread of continental deposits across the whole of the basin, mainly playa mud (Roxby Formation and equivalents) and more marginal aeolian and fluvial sand (Lenton Sandstone Formation and equivalents). By earliest Triassic (Induan) time, a further pulse of crustal extension led to renewed growth faulting and subsidence in existing basins (Chadwick and Evans, 1995), and to the development of further depocentres in central England (Figure 20)b. The Eastern England Shelf was separated from the Needwood Basin by a high, the ‘Pennine–Charnwood Bar-zone’ of Wills (1970), which also formed the northern extremity of the London–Brabant Massif.

A regional climatic change in Early Triassic times was possibly due to the continuing northwards drift of the Pangaean continent. A monsoonal climate was established over the remnants of the Variscan mountain chain, resulting in increased denudation rates and the initiation of a major river system flowing northwards across southern and central England (Wills, 1970; Warrington and Ivimey-Cook, 1992). This carried pebble-grade detritus from sources in the Armorican Massif, which occupied the present northern France–English Channel region (Audley-Charles, 1970). The rivers drained north and north-westwards into the Cheshire and Irish Sea basins, and north-eastwards into the Southern North Sea Basin. On the Eastern England Shelf, they deposited pebbly, fluvial channel sand (Nottingham Castle Sandstone Formation), which becomes generally finer grained and pebble-free distally, towards the north-east.

Regional uplift and erosion in Olenekian (late Early Triassic) times resulted in a major non-sequence, the Hardegsen Disconformity, which can be traced from northern Germany (Geiger and Hopping, 1968). Slow, thermal relaxation subsidence prevailed in most basins in the central England region through the remainder of the Triassic, with strata overlapping progressively onto adjacent highs. Following the Hardegsen uplift phase, fluvial sedimentation recommenced in basins in the central and west Midlands that were temporarily separated from the Eastern England Shelf (Warrington and Ivimey-Cook, 1992; Figure 20)b. Pebbly alluvial fan sand and silt, derived locally, were deposited in the Nottingham area, forming the lower part of the Sneinton Formation. These passed rapidly north-eastwards into distal alluvial-plain silt and mud. Evaporitic conditions prevailed in the centre of the Southern North Sea Basin at this time (Cameron et al., 1992; Johnson et al., 1993), principally resulting in deposition of the Röt Halite. Connection with basins farther west, in the central Midlands, was re-established in early Anisian (Mid Triassic) times, when alluvial-plain and lacustrine sand and silt of the upper part of the Sneinton Formation and the Radcliffe Formation prograded across the Eastern England Shelf from the west. These passed basinwards into brackish water, possibly estuarine silt and mud, and eventually into the marginal marine dolomitic mud of the Muschelkalk of the Southern North Sea Basin (Figure 20)c.

By late Anisian to Ladinian (Mid Triassic) times, sediment source areas had essentially been peneplaned (Warrington and Ivimey-Cook, 1992), and the burial of whole mountain landscapes beneath red beds was initiated, resulting in the rugged sub-Triassic topographies of areas such as Charnwood Forest (Carney et al., 2001). The succeeding Ladinian to Norian (late Mid to Late Triassic) sequence (Gunthorpe, Edwalton, Cropwell Bishop and lower Blue Anchor formations) of the Eastern England Shelf was deposited mainly on playa mudflat or distal alluvial-plain environments, periodically under either subaqueous or subaerial conditions. In the Southern North Sea Basin, equivalent sequences include thick evaporites (Cameron et al., 1992; Johnson et al., 1993).

In the early Rhaetian (latest Triassic), the accumulation of marginal marine mud and silt of the Blue Anchor Formation throughout much of England and Wales foreshadowed the more widespread establishment of marine environments in mid-Rhaetian times (Figure 20)d. Deposition of organic-rich marine mud and silt (Westbury Formation) was followed in the late Rhaetian by more restricted lagoonal mud and silt (Lilstock Formation: Cotham Member) containing slump structures; elsewhere in Britain, such sedimentary structures have been attributed to contemporaneous tectonic activity (Mayall, 1983). Fully marine conditions were established before the end of Rhaetian times and persisted throughout the Early Jurassic.

Sherwood Sandstone Group

In England and Wales, the term Sherwood Sandstone Group (Warrington et al., 1980) encompasses strata formerly assigned to the ‘Bunter’ and the arenaceous lower part of the overlying ‘Keuper’. However, the lower part of the ‘Keuper’ in the Nottingham district, unlike that elsewhere in the Midlands, is predominantly argillaceous and is now assigned to the Mercia Mudstone Group. The Sherwood Sandstone Group of the district therefore comprises strata formerly assigned to the ‘Bunter’, these being the Lenton Sandstone (formerly ‘Lower Mottled Sandstone’) and the Nottingham Castle Sandstone (formerly ‘Bunter Pebble Beds’) formations (Table 14). There is one complexity, in that the lower division of the Lenton Sandstone Formation passes laterally into strata of the Edlington, Brotherton and Roxby formations. It is therefore latest Permian in age (Figure 24), and may equally well be regarded as an arenaceous lateral facies variant of the Edlington Formation (see also, previous chapter). The remainder of the group is regarded as Early Triassic (Induan and Olenekian) in age (Table 14).

The group crops out below most of the central and northern parts of the city of Nottingham, where there are several good surface sections in addition to numerous underground sections in excavated ‘caves’ (p. 31). Its outcrop broadens to the north of Nottingham and occupies the area between the River Leen in the west, and the villages of Calverton and Oxton in the east. Numerous wells, boreholes and shafts have been directed at groundwater resources within the group itself, or at coal and hydrocarbon prospects at greater depth in the underlying Carboniferous rocks. From such records, the lower boundary of the group can usually be recognised on outline or summary lithological logs of uncored boreholes. It is often more difficult to place the upper boundary because the lowest unit of the overlying Mercia Mudstone Group (Sneinton Formation) is commonly described as a sandstone; however, both boundaries can be reliably placed if geophysical logs are available. Core descriptions are available for only a few boreholes and refer mainly to the Lenton Sandstone Formation; detailed information on the Nottingham Castle Sandstone is derived mainly from surface sections.

The district lies near the southern extremity of the main eastern England outcrop of the Sherwood Sandstone Group, which extends northwards from Nottinghamshire through Yorkshire to the Cleveland coast. The thickness of the group increases steadily northwards across the district, from 78 m in the Deering School Borehole at Wilford in the south-west, to 168 m in the Kelham Coal Borehole (Figure 22); (Figure 27)a. This trend is consistent with a regional north-eastwards thickening that occurs across the Eastern England Shelf (Taylor, 1968, fig. 30; Audley-Charles, 1970, plate 8). To the east, the broadly coeval Bunter Sandstone Formation of the Bacton Group in the central Southern North Sea Basin is up to 700 m thick (Cameron et al., 1992). To the south and west of the district (Taylor, 1968, fig. 30), the group thins and is overlapped by the Mercia Mudstone Group on the margins of the London–Brabant Massif, as seen at Charnwood Forest (Carney et al., 2001).

Lenton Sandstone Formation

The Lenton Sandstone Formation (Warrington et al., 1980) corresponds to the ‘Lower Mottled Sandstone’ (Table 14) or ‘Lower Red and Mottled Sandstone’ of earlier nomenclature. The type section is in a disused quarry on the northern side of the Queen’s Medical Centre site, Nottingham. In the western part of the district, the formation crops out mainly along the eastern side of the valley of the River Leen. North of Bestwood Village, it gives rise to gently undulating land with sandy, easily worked, but rather infertile soils. South of Bestwood, the outcrop is extensively urbanised, but some good exposures remained in disused moulding sand quarries at the time of this survey. The formation has been proved at subcrop in numerous boreholes, although most of the logs provide little lithological detail. Core descriptions are limited to a few boreholes in the south and south-east of the district, and detailed lithological descriptions were recorded during shaft-sinking at Bestwood and Calverton collieries.

The formation consists mainly of deep red-brown, fine-grained, friable sandstone. The term ‘mottled sandstone’, formerly applied to the unit, referred to large ovoid or irregular buff-grey patches and mottles, which tend to be developed mainly in the higher beds (Frost and Smart, 1979). Micaceous laminae and thin partings and beds of reddish brown or grey mudstone and siltstone occur throughout the formation, but are especially common near the base; intraformational mudclasts are common at many levels. Extraclast pebbles form one persistent bed, the Calverton Breccia, but otherwise occur mostly in thin, isolated layers, particularly in the lower part of the formation. Extraclasts are generally smaller and more angular than those in the overlying Nottingham Castle Sandstone, and a larger proportion are of local Charnian, Carboniferous and Permian provenance.

Lower and upper divisions of the Lenton Sandstone Formation, separated by an unconformity, can be recognised in the subsurface from geophysical and lithological logs (Figure 24), (Figure 25), (Figure 26). The unconformity, which is arbitrarily taken to represent the base-Triassic datum in the district, is overlain by a distinctive and persistent bed, described from the Calverton Colliery shaft and termed the Calverton Breccia by Wills (1956). At outcrop, the lithological differences between the lower and upper divisions are subtle, and the problem of differentiation is compounded by the paucity of exposure. Consequently, the two subdivisions cannot be mapped separately in the field and have been assimilated within the general outcrop of the Lenton Sandstone Formation. As previously suggested, the Lower Lenton Sandstone division is essentially a lateral variant of the Edlington Formation and therefore, where it can be recognised, it could equally be regarded as a component of that unit. This is further suggested by the presence of thick sandstone at the top of the ‘Middle Permian Marl’ (= Edlington Formation) farther north, although those sandstones differ in being predominantly medium- to coarse-grained (Smith et al., 1973).Thin breccias have been noted at outcrop in several sections in the Nottingham district and in the adjoining Derby district to the west (Wilson, 1876; Sherlock, 1911; Frost and Smart, 1979), but none can be correlated satisfactorily with the Calverton Breccia on the basis of the published information.

The Lenton Sandstone, including intercalations of the Calverton Breccia and Roxby Formation, is 70 m thick in the Fiskerton Borehole in the north-eastern part of the district (Figure 24), and thins southwards and westwards; it is approximately 21 m thick in the Holme Pierrepont Borehole in the south-west of the district (Figure 26). It pinches out to the west, in the Derby district (Frost and Smart, 1979), and to the south-west and south, in the Loughborough and Melton Mowbray districts. Thickness variations in the formation result from the thinning of both the lower and upper divisions towards the west and south, and the erosional truncation, in the same direction, of successively lower beds in the lower division and their overstep by the Calverton Breccia (Figure 21). The preserved limit of the lower division corresponds approximately with the depositional margin of the Permian in this region (Figure 23)a. To the south and west of that limit, the upper division rests unconformably upon the Permian Basal Breccia, as in the Deering School Borehole (Figure 22).

Lower division

Lithological details of this division are derived mainly from borehole and shaft records. Only one good surface section was observed in the district during this survey (Rathbone, 1989a; see below), but Lamplugh et al. (1908) and Sherlock (1911) documented several others. Borehole correlations (Figure 24), (Figure 25), (Figure 26) indicate that the lower division of the Lenton Sandstone Formation is a lateral equivalent of the mudstone and siltstone comprising the main body of the Edlington Formation, and is thus latest Permian in age.

The Calverton Colliery Shaft section, where the division is 17.7 m thick, provided the best available lithological description. There it consists mainly of weakly dolomitic, fine-grained sandstone, typically deep redbrown with greenish grey patches, but predominantly pale greenish grey in the lowest 5 m. Beds, lenses and intraformational clasts of ‘chocolate’-coloured mudstone decrease in abundance upwards. Similar lithologies were also reported in cores from the Eady Farm Borehole in the south-east of the district, where the division is 13.5 m thick. Thin, laterally impersistent ‘lenticles’ of breccia have provisionally been described from several surface sections in the district (Wilson, 1876; Sherlock, 1911; Lamplugh et al., 1908; Frost and Smart, 1979).

The base of the division was proved at 108.5 m depth in the Calverton Colliery Shaft. In a surface section [SK 5547 4940] to [SK 5541 4931] north of Bestwood Village, a sharp lower boundary was noted (Rathbone, 1989a). Elsewhere, however, the division passes downwards by interdigitation into the mudstone and thin sandstone of the underlying Edlington Formation (cf. Wilson, 1876; Sherlock, 1911; Lamplugh et al., 1908; Frost and Smart, 1979). This prompted Sherlock (1911) to use the term ‘passage beds’ for the lower part of the Lenton Sandstone Formation. The top of the division, defined by the base of the Calverton Breccia, was proved at 90.8 m in the Calverton Colliery Shaft. The gamma-ray profile of the division is characterised by pronounced serrations and a general uphole decrease in response, reflecting the interdigitation of sandstone and mudstone beds, with the former becoming dominant upwards. Where available (e.g. the Parkhill No. 1 Borehole; Figure 24), sonic logs show a weakly serrated profile, indistinguishable from that of the upper division of the formation (see below).

Thickness variations within the lower division reflect the interplay of two factors: lateral facies change into the mudstone and siltstone of the Edlington Formation, and erosional truncation beneath the Calverton Breccia (Figure 21). In the north of the district, the division reaches a thickness of 19 m in the Fiskerton No. 1 Borehole, but it is absent in the Newark Borehole only 8 km to the north-east, where equivalent strata comprise red-brown mudstone interbedded with subordinate dolomitic sandstone, typical of the Edlington Formation. The division ranges in thickness from 8 to 14 m in boreholes in the south-east of the district. It thins towards the south-west of the district (Figure 21), (Figure 24), (Figure 25), (Figure 26), where it is eventually truncated below an erosion surface overlain by the Calverton Breccia. It is absent in boreholes on the Nottingham University Campus (Taylor, 1965) and at Deering School, Wilford, both of which prove the upper division of the Lenton Sandstone resting upon the Permian Basal Breccia.

Upper division

The upper division of the Lenton Sandstone is unconformable on the lower division. In the south-west of the district, its base is marked by the Calverton Breccia (Figure 21), whereas it grades down into the underlying Roxby Formation in the north-east. In the Calverton Colliery Shaft, the Calverton Breccia was recorded as being 1.37 m thick, with sharp lower and upper boundaries. Pebbles, including both well-rounded and ‘dreikanter’ forms, and mostly of quartzite but including ‘greenish’ and ‘chocolate coloured’ mudstone clasts, are common in the lowest 0.3 m. The matrix was described as fine-grained, dark brown, marly sandstone. The Calverton Breccia was also noted in the lithological descriptions of the Bulwell Forest Borehole in the north-west of the district, and in the Deering School, Wolds Hill (Cotgrave) and Foss Way (Stragglethorpe) boreholes in the south. It was cored in the Eady Farm, Rundle Beck and Station Farm boreholes in the south-east of the district, where it is described as a breccio-conglomerate containing angular and subangular quartzite pebbles, ‘Charnian’ pebbles, and ‘green grit’ pebbles in a matrix of poorly sorted, coarse dolomitic sandstone.

The upper division of the Lenton Sandstone Formation was formerly quarried for moulding sand at numerous sites in the Nottingham area, and Lamplugh et al. (1908) and Sherlock (1911) described several of the resulting sections. Few of these remain, and no exposures of the base of the division were recorded during the present survey. The top of the division was seen in disused sand pits [SK 5544 4165], [SK 5530 4154] near Bobbers Mill, where dark red, fine-grained sandstones of the Lenton Sandstone Formation pass gradationally upwards into coarser grained, buff to red pebbly sandstones of the Nottingham Castle Sandstone Formation (Dean, 1989). This boundary was also formerly exposed in a disused railway cutting at the former Bestwood Colliery site, Nottingham [SK 5521 4727], where the uppermost 0.5 m of the Lenton Sandstone Formation, with many locally derived subangular extraclasts, were exposed below the sharp, channelled base of the Nottingham Castle Sandstone Formation (Rathbone, 1989a; see also below).

The best sections of the division occur in the Lenton area, in former sandstone quarry faces adjacent to the Cripps Computing Centre on the Nottingham University Campus (Plate 8), and close by on the north-west perimeter of the Queen’s Medical Centre site [SK 5462 3880]. The latter was defined as the type section of the Lenton Sandstone Formation by Warrington et al. (1980). Both sections have been described, notably by Swinnerton (1910), Taylor (1965), Frost and Smart (1979) Mader (1992) and Howard (2003). Each exposes up to 10 m of deep red-brown, fine- to medium-grained sandstone with pale yellowish brown mottles. The sandstone is typically weakly cemented, although Swinnerton (1910, 1948) noted lenses of strongly cemented dolomitic sandstone in the lower beds (now obscured) of the University Campus section. Planar and trough cross-stratification is common throughout, in sets ranging from a few centimetres to 1 m thick; planar lamination also occurs sporadically. The numerous borehole sections elsewhere in the district record similar lithologies but with red-brown and grey-green mudstone interbeds, micaceous laminae, mudcracks, intraformational mudclasts and ripple cross-lamination.

In geophysical (gamma-ray) logs, the base of the division is placed at a low gamma-ray marker that coincides with the top of the Calverton Breccia. This marker is identifiable in boreholes in most parts of the district (Figure 24), (Figure 25), (Figure 26) and correlates with a distinctive breccia bed cored in the Broach Road Borehole in the Lincoln district to the north-east. The upper boundary of the division is marked by an upward change to the generally lower response and more weakly serrated gamma-ray profile of the Nottingham Castle Sandstone Formation. The thickness of the upper division is consistently greater than that of the lower division of the formation, and ranges from 16 m (Gedling Colliery Shaft) to 52 m (Fiskerton No. 1 Borehole). Gamma-ray profiles from boreholes in the northern and east-central parts of the district show a higher response in the lower 10 to 20 m of the division than in the upper part. This feature is either absent or only weakly developed in profiles from the southern part of the district (Figure 24), (Figure 25), (Figure 26). Such variations may reflect a gradual increase in argillaceous content as the lower beds of the division pass north-eastwards into the mudstone-dominated facies of the Roxby Formation.

Depositional environment

The Lenton Sandstone Formation has been interpreted as the deposit of an aeolian dunefield, with interdune sheet sand and minor reworking by fluvial processes (Mader, 1992). The greater abundance of intraformational mudclasts and mudstone interbeds in the lower division implies an environment characterised by a more substantial fluvial and alluvial influence, with aeolian and fluvial sheet sand interdigitating with the distal alluvial plain, sabkha and playa mud and silt of the Edlington Formation (see above). The angular extraformational clasts in breccia lenses of the lower division were probably transported into the aeolian dunefield by ephemeral floods that reworked contemporaneous alluvial fans to the south and west; these clasts were further concentrated into thin stone pavements by aeolian deflation. The Calverton Breccia represents a more extended period of non-deposition and erosion of possible regional extent.

The formation has not yielded any age-diagnostic fossils. The lower division is a marginal, sandy facies equivalent of the Edlington Formation and is therefore inferred to be latest Permian in age. It may be coeval with similar arenaceous beds present in the Edlington Formation in north Nottinghamshire (Edwards 1951, 1967; Smith et al., 1973). An earliest Triassic (Induan) age is assigned to the upper division, as discussed at the beginning of this chapter.

Nottingham Castle Sandstone Formation

The Nottingham Castle Sandstone Formation corresponds to the ‘Nottingham Castle Formation’ of Warrington et al. (1980) and the ‘Bunter Pebble Beds’ of earlier terminology (Table 14). The formation crops out in the western part of the district, to the north of the River Trent and mainly to the east of the River Leen; its type section is Castle Rock, Nottingham (see cover). South of Bestwood Village, the outcrop is 1.5 to 4 km wide and is extensively urbanised, although good exposures abound, notably in Nottingham city centre near the type section. North of Bestwood Village, the outcrop broadens to 6 to 8 km and the formation gives rise to gently undulating land with well-drained, easily cultivated, pebbly sand or sandy loam soils. The outcrop typically has a west-facing scarp feature that is complemented by a gentle south-east-facing dip slope dissected by numerous dry valleys.

The formation is a major aquifer of regional importance (see Chapter 2), contributing substantially to Nottingham’s water supply. The sandstone is easily excavated due to its friable consistency, which has encouraged its exploitation for aggregate in several quarries to the north of Nottingham, and the excavation of numerous ‘caves’ for various purposes throughout the Nottingham city area (p. 32).

To the east of its outcrop, the formation has been recorded beneath the Mercia Mudstone Group in numerous boreholes. Most borehole records provide little lithological detail however, and the position of the boundary with the underlying Lenton Sandstone Formation is difficult to place with accuracy. On geophysical (gamma-ray) logs, the base is marked by a weak uphole decrease in the gamma-ray response, which reflects the change from the finer grained, more argillaceous and micaceous sandstone of the Lenton Sandstone Formation to the coarser, less argillaceous sandstone of the Nottingham Castle Sandstone Formation. The top of the formation is marked by the change to the predominantly finer grained strata of the Mercia Mudstone Group; this boundary is traceable at surface by a change of soil type, coinciding with the foot of a scarp feature formed by the overlying Sneinton Formation. On geophysical (gamma-ray) logs, the top of the formation is marked by a prominent uphole increase in the gamma-ray response (Figure 24), (Figure 25), (Figure 26).

The formation consists of yellow-brown or grey-brown, less commonly red-brown, fine- to coarse-grained, poorly sorted, cross-stratified sandstone containing numerous intraformational mudstone clasts and extraformational pebbles. Typically, the sandstone is only weakly cemented by carbonate, limonite and clay minerals; it can be easily disaggregated with a penknife and in some cases crumbled between the fingers. Intercalations of red-brown mudstone with very thin beds of grey siltstone occur, but are rare. They are generally less than 2 m thick and laterally impersistent due to erosional truncation below overlying beds.

During the survey, the lower boundary of the formation was observed in disused sand pits [SK 5544 4165], [SK 5530 4154] at Bobbers Mill (Dean, 1989) and at the former Bestwood Colliery site [SK 5521 4727], near Bestwood Village (Rathbone, 1989a). The boundary is gradational at Bobbers Mill, but sharp and erosive at Bestwood Colliery. Sections in the higher beds can be observed in numerous places in Nottingham city centre, but the most celebrated is at Nottingham Castle Rock [SK 5695 3938], a magnificent 30 m-high river cliff carved in the sandstone (see Front Cover). Another excellent section in the city centre is located at the Park Tunnel (Charsley, 1989; Lowe et al., 1990; Jones, 1993; Howard, 2003). Here, the three-dimensional geometry of the cross-stratification within the sandstone (Plate 9) is beautifully displayed in the sides and arched roof of the tunnel. Outside the city centre, sections in the middle part of the formation have been described by Rathbone (1989a) at the former Bestwood Colliery site [SK 564 480], and by Lawley (1993a) at Burntstump Quarry [SK 5864 5023], Wildman’s Wood Quarry [SK 5676 5263], and a quarry at Ravenshead [SK 5659 5378]; up to 40 m were visible in Burntstump Quarry. Beds within the upper 26 m of the formation were observed in a railway cutting [SK 6000 5216] to [SK 6123 5089] leading to Calverton Colliery, and in smaller exposures around Oxton. Some of the latter also display the contact with the overlying Mercia Mudstone Group (Lawley, 1993b). That contact was formerly well exposed in two sections [SK 5924 3968] and [SK 5918 3970] adjacent to a disused railway cutting at Colwick Road, Sneinton (Lamplugh et al., 1908), but the lowermost part of this section, including the boundary itself, is no longer visible.

On geophysical logs, the formation is characterised by low, slightly upwards decreasing gamma-ray values with a blocky, very mildly serrated profile (Figure 24), (Figure 25), (Figure 26). Sharp-peaked, high gamma-ray deflections represent thin, sporadic, mudstone and siltstone intercalations, which are most common in the lower and middle parts of the formation. Few sonic logs are available for the formation; those of the Cotmoor Lane and Parkhill No. 1 boreholes in the northern part of the district, and the Saxondale No. 1 and Cropwell Butler No. 1 boreholes in the south, display a weakly serrated, near-uniform response, indistinguishable from that of the underlying Lenton Sandstone. There is a marked contrast with the more fluctuating response and generally higher velocity evident in the sonic logs of the overlying Mercia Mudstone Group.

The formation thickens from about 55 m in the southwest of the district to 102 m in the north-east. The thickening trend continues eastwards into the adjoining Grantham district, where 122 m was recorded in the Stragglethorpe Borehole (Berridge et al., 1999). In the Melton Mowbray district to the south, the formation ranges from 11 to 100 m in thickness, but is commonly less than 60 m. Here also, a similar overall north-eastward thickening is apparent (Carney et al., 2004).

Most surface sections show the cross-stratified nature of the sandstone, but the true geometry of the bedforms is best displayed in the larger sections such as Castle Rock and the Park Tunnel (Howard, 2003;(Plate 8); (Plate 9). Subplanar cross-stratification is the dominant structure, characterised by foresets with a gently curving form and asymptotic bases (Bryant and Burley, 1986). These cross-stratified sets are typically 1 to 3 m thick and bounded by undulatory erosion surfaces that can normally be traced along the entire length of an exposure (Jones, 1993). Cross-bedding azimuths measured in Park Tunnel (Jones, 1993) indicate north-easterly directed palaeocurrents with a low dispersion about the mean. Trough cross-stratification is also common, but tends to be on a smaller scale and to display a greater spread of palaeocurrent directions (Bryant and Burley, 1986). Planar lamination also occurs but is less common. Pebbles and mudstone clasts are common as lags overlying erosion surfaces, especially above depressions in those surfaces; they are also strewn along foresets (Plate 9).

The intraformational mudstone and siltstone clasts are predominantly reddish brown or greenish grey in colour, and vary in shape from angular laths to wellrounded ovoids. The greenish grey clasts commonly have reddish brown rims; the reverse case is much less common. Extraformational clasts generally consist of well-rounded ellipsoidal pebbles, composed mainly of brown or grey quartzite, greenish brown or reddish grey, fine-grained sandstone, and grey or white vein quartz. Locally derived extraclasts tend to be more angular in shape; they include Charnian igneous and metamorphic rocks, Carboniferous limestone, sandstone and chert, and Permian dolostone. Wind-faceted ‘dreikanter’ pebbles have been recorded throughout the formation in numerous surface exposures and boreholes.

Petrographical analyses of samples from Park Tunnel and the Cropwell Bridge Borehole (Jones, 1993) indicate that the sandstones are lithic subarkoses, feldspathic litharenites or litharenites. Sorting is poor to moderate, with angular to subrounded grains varying from fine to coarse sand grade. Monocrystalline quartz grains predominate over the polycrystalline variety. Potassium feldspar comprises up to 10 per cent of the detrital grains, and is commonly partly replaced by clay minerals. Lithic fragments are common, particularly igneous grains comprising quartz and feldspar or quartz and mica. Also present are clasts of metaquartzite and quartz-mica schist. Sedimentary rock fragments comprise mainly mudstone and chert. The principal authigenic minerals are iron oxide, quartz, potassium feldspar, kaolinite, non-ferroan and ferroan dolomite, non-ferroan calcite and illite. Iron oxide occurs as grain coatings and was precipitated prior to the authigenic overgrowths of quartz and potassium feldspar. Porosity is high and of secondary origin through dissolution of cements and local corrosion of grains.

Depositional environment

The Nottingham Castle Sandstone Formation represents the deposits of a braided river system, with the largescale, sub-planar cross-stratification produced by downstream migration of sand bars and dunes within river channels during periods of high discharge (Bryant and Burley, 1986; Mader, 1992). Cross-stratification measurements indicate that, locally at least, current flow and bar migration was towards the north-east (Bryant and Burley, 1986; Jones, 1993). Smaller scale trough cross-stratification formed during periods of waning discharge by migration of sinuous megaripples around the margins of dunes. Beds of mud and silt were deposited by overbank floods and in channels during low discharge periods, but most were subsequently reworked by erosion at channel margins and re-deposited as clasts. Although the preserved sedimentary features are dominantly fluvial, there is evidence of aeolian processes. Aeolian deflation on the sandy braidplain produced surface mantles of well-rounded, frosted grains (Bryant and Burley, 1986), stones and dreikanter (Mader, 1992), which were subsequently reworked and incorporated into the channel sandstones. Mader (1992) also interpreted some planar laminated beds towards the top of the formation as aeolian sheet sandstones, but gave no details of location.

Bryant and Burley (1986) suggested a provenance from upland areas to the west, and dismissed earlier interpretations (e.g. Wills, 1956) of a major northward flowing river system. They did not, however, account for the common, well-rounded quartzite pebbles, for which there is no local source (cf. Bonney, 1900; Matley, 1914), or for the relative scarcity of extraclasts with a definite local provenance. The palaeogeographical interpretations by Wills (1956, 1970) and Warrington and IvimeyCook (1992) do account for these features by depicting a major fluvial system draining northwards through the Central Midlands, from where it bifurcated north-westwards into the Cheshire and Irish Sea basins, and northeastwards through the East Midlands into the Southern North Sea Basin.

Diagenetic studies (Burley, 1984) suggest that the sandstone was originally cemented by authigenic carbonates, sulphates and halite. These were subsequently dissolved by recent circulating meteoric groundwaters to produce the weakly cemented sandstone with extensive secondary porosity now seen at outcrop. The groundwaters were also responsible for ‘bleaching’ the sandstone from a primary red colour to its present pale yellowish grey (Mader, 1992). Where an early diagenetic, pore-filling, barytes cement occurs, as at Stapleford Hill in the adjacent Derby district (Taylor and Houldsworth, 1973), the bleaching effect was inhibited and the primary red colour of the sandstone is preserved (Mader, 1992).

No fossils have been recorded from the formation in the district. There is no direct biostratigraphical evidence for the age of the formation, which is conventionally and arbitrarily dated as Early Triassic (early to mid-Scythian, Induan to Olenekian).

Mercia Mudstone Group

The term ‘Mercia Mudstone Group’, introduced by Warrington et al. (1980), encompasses the mainly argillaceous strata that were formerly included within the ‘Keuper Marl’. South Nottinghamshire was the first area in Britain where the ‘Keuper Marl’ was fully divided (Table 14) into formally defined formations (Elliott, 1961), each differentiated mainly on lithological characteristics observed in borehole core. Warrington et al. (1980) slightly modified Elliott’s original formational names and boundary definitions. The recent resurvey of the Nottingham district (see also Charsley et al., 1990) has shown that not all of Elliott’s formations are mappable at surface, although they can be recognised in borehole cores and differentiated on geophysical logs. In this memoir, some of the formations introduced by Elliott (1961) and modified by Warrington et al. (1980) have been downgraded to member status and combined into newly named formations.

Six formations, in ascending order the Sneinton, Radcliffe, Gunthorpe, Edwalton, Cropwell Bishop and Blue Anchor formations, now constitute the group. They encompass much of Triassic time, ranging in age from late Early Triassic (Olenekian) or early Mid Triassic (Anisian) at the base, to latest Triassic (Rhaetian) at the top (Warrington et al., 1980). New names are likely to be introduced for certain members and formations (Table 14), owing to a nationwide rationalisation of Triassic nomenclature that is currently being undertaken (Howard et al., in press). The group rests unconformably on the Nottingham Castle Sandstone Formation of the Sherwood Sandstone Group, and is overlain disconformably by the Westbury Formation of the Penarth Group.

The Nottingham district lies at the southern end of the main eastern England outcrop of the Mercia Mudstone Group, which extends northwards through Nottinghamshire and Yorkshire to the Cleveland coast. The outcrop continues south-westwards through the district and is confluent with that in adjoining areas of Derbyshire and Leicestershire. Within the district, the group generally dips gently (1°–2°) towards the south-east or east-south-east, producing a broad outcrop between 12 and 20 km wide that occupies about two thirds of the the total area of the district. To the north of the River Trent, the outcrop consists entirely of the Sneinton, Radcliffe and Gunthorpe formations, and is dissected by a number of deep valleys known locally as ‘dumbles’. To the south of the river, the outcrop comprises the upper part of the Gunthorpe Formation, together with the Edwalton, Cropwell Bishop and Blue Anchor formations. In this area, each formation has a parallel, north-east-striking outcrop, locally interrupted and displaced by a number of faults including the major north-west to south-east trending Cinderhill–Foss Bridge and Eakring–Foston structures. Resistant beds of dolomitic siltstone and sandstone give rise to a succession of north-west-facing scarps complemented by broad, southeast-facing dip slopes. The outcrop here is less dissected by streams than to the north of the River Trent, but is more extensively masked by Quaternary deposits, particularly on the outcrop of the Cropwell Bishop Formation in the eastern and south-eastern parts of the district.

The group has been penetrated by numerous wells, boreholes and shafts, directed at coal resources or hydrocarbon prospects in Carboniferous rocks or groundwater resources in the Sherwood Sandstone Group. Numerous shallow boreholes were also drilled into the group by the National Coal Board in the vicinity of Gedling and Cotgrave Collieries, with the aim of locating faults near the surface that may have displaced coal seams at depth. Cores from these fault-proving boreholes formed the basis for the formations recognised on detailed lithological and sedimentological characters by Elliott (1961). The full succession has been proved and geophysically logged, although not cored, by several boreholes in the south-east of the district. A complete succession was also penetrated by several boreholes in the adjoining Grantham district to the east (Berridge et al., 1999) and the Melton Mowbray district to the south (Carney et al., 2004). A near complete sequence (excluding the uppermost 25 m or so) was cored in the Cropwell Bridge Borehole (Figure 28), enabling calibration of geophysical logs with the lithostratigraphy and providing a reference section for correlation with other boreholes. Other fully cored successions with gamma-ray and sonic logs are those of the Fulbeck No. 1 Borehole (Figure 29) in the Grantham district (Berridge et al., 1999, fig.16), and the Asfordby Hydro Borehole in the Melton Mowbray district (Carney et al., 2004, fig. 18).

Both the lower and upper boundaries of the Mercia Mudstone Group are readily mappable at surface and are easily identified in most boreholes, even when cuttings logs are the only information available; both boundaries are well-defined on geophysical logs. The group is 237 m thick in the Redmile No. 2 Borehole (Figure 30) and thickens north-eastwards to 263 m in the Fulbeck No. 1 Borehole in the Grantham district (Figure 29). This is consistent with a regional north-eastwards thickening across the Eastern England Shelf into the Southern North Sea Basin, where coeval strata of the Haisborough Group are over 900 m thick in the Sole Pit Trough (Cameron et al., 1992; Johnson et al., 1993). To the south and south-west of the district, the group thins towards the London–Brabant Massif and the Charnwood High respectively.

In the East Midlands, the Mercia Mudstone Group consists largely of red-brown, less commonly greygreen, mudstones and argillaceous siltstones. These are commonly gypsiferous, variably dolomitic, and may have laminated, deformed or structureless textures. Thin beds of greenish grey or grey, strongly cemented dolomitic siltstone or sandstone (‘skerries’) occur at intervals within the succession, some forming mappable, cuestalike topographical features. The Cotgrave Sandstone and Hollygate Sandstone members, both of which form prominent mappable features, consist of several, closely spaced beds of sandstone and define the base and top respectively of the Edwalton Formation. Other units, such as the Radcliffe and Blue Anchor formations, are mappable on the basis of distinctive soil colours and textures.

The clay mineralogy of the group has been analysed by Jeans (1978) and more recently by Bloodworth and Prior (1993). The quantitative determinations of Bloodworth and Prior (1993), based on detailed sampling in the Cropwell Bridge Borehole, indicate an assemblage dominated by illite and mixed layer illite/smectite (‘shrink-swell clay’) with minor chlorite. The relative proportions of illite and illite/smectite vary substantially through the succession in a reciprocal relationship (Figure 28). Similar analyses, confirming such variations to be stratigraphically related, were carried out in the Fulbeck No. 1 Borehole of the Grantham district, in boreholes at Keyworth (Bloodworth and Prior, 1993), and in the Asfordby Hydro Borehole (Kemp, 1999), the last two studies being from the Melton Mowbray district. Sepiolite is restricted to a level just above the base of the Cropwell Bishop Formation, confirming earlier determinations by Jeans (1978). Jeans’ results from other boreholes and surface sections in the region also indicate comparable stratigraphical variation in the clay mineral assemblage, although sampling in individual sections was less comprehensive and the relative proportions of the clay minerals were not quantified. Comparison of the gamma-ray profile of the group with the illite curve in the Cropwell Bridge Borehole (Figure 28) shows a close relationship between the illite content and gamma-ray response; the more minor fluctuations on the gammaray log are produced by thin beds of gypsum, sandstone and dolomitic siltstone. Balchin and Ridd (1970) demonstrated that the Mercia Mudstone Group could be correlated throughout the subsurface of eastern England using gamma-ray logs; this implies that the clay mineralogical variations controlling the gamma-ray log response may be of regional stratigraphical significance.

Recent interpretations of Mercia Mudstone Group palaeoenvironments in the East Midlands suggest deposition in playa mudflats or sabkhas, into which distal fluvial systems drained periodically from the south and west (Warrington and Ivimey-Cook, 1992; Mader, 1992). Shallow hypersaline seas periodically extended westwards into the region from the Southern North Sea Basin (Figure 20)c. Laminated mudstones were deposited subaqueously, probably in ephemeral lakes, whereas the structureless mudstone facies probably represents aeolian dust deposits (Wills, 1970), perhaps reminiscent of the modern parna of the south-eastern Australian desert (Jefferson et al., 2002). Such deposits adhere to damp mudflats on which ‘ploughed ground’ may have developed as a result of evaporite crystal growth and solution (Arthurton, 1980). The thicker sandstones in the Sneinton and Edwalton formations might have been deposited by overbank floods from low sinuosity rivers (Warrington and Ivimey-Cook, 1992; Mader, 1992); thinner sandstones might have been deposited from sheet floods across mudflats following rainstorms. Gypsum was precipitated from interstitial brines that were of mixed continental and marine origin, with the proportions varying through time in the top part of the group (Taylor, 1983). The persistent gypsum beds in the upper part of the group (Cropwell Bishop Formation) have been interpreted as the products of incursions from an adjacent hypersaline sea (Taylor, 1983; Mader, 1992). At the top of the group, the supratidal and intertidal sabkha environments of the Blue Anchor Formation (Warrington and Ivimey-Cook, 1992) were precursors to the marine or marginal marine environments represented in the overlying Penarth Group.

Sneinton Formation

The Sneinton Formation is approximately equivalent to the ‘Keuper Waterstones’, which Lamplugh et al. (1908) recognised as a mappable unit between the ‘Bunter Pebble Beds’ and the ‘Keuper Marl’. Other workers (e.g. Smith, 1912; Swinnerton, 1918) restricted the use of ‘Waterstones’ to the upper part of this unit and termed the lower part ‘Keuper Basement Beds’. These subdivisions were later renamed as ‘Colwick Formation’ (Warrington et al., 1980) and ‘Woodthorpe Formation’ (Elliott, 1961) respectively (Table 14). However, as these units could not be mapped separately at surface, Charsley et al. (1990) proposed their combination into a single unit, which they named the Sneinton Formation. The revised classification is adopted in this memoir, although the Woodthorpe and Colwick divisions are retained as members on account of their distinctive lithologies and geophysical log signatures.

The type section of the Sneinton Formation is in the Cropwell Bridge Borehole, between depths of 170.7 and 213.8 m; a complete core is held in the National Geological Records Centre core store at BGS Keyworth, Nottingham. A type area for the formation was designated in Sneinton [SK 592 397], on the east side of Nottingham (Charsley et al., 1990). A good reference section is exposed at the southern end of the former Great Northern Railway cutting at Colwick Road, Sneinton [SK 5924 3968] to [SK 5920 3980] and has been described in detail by Lamplugh et al. (1908) and Charsley (1989).

Wilson and Shipman (1879), Lamplugh et al. (1908), Swinnerton (1914, 1918) and Elliott (1961) have discussed stratigraphical relationships at the base of the formation. The boundary is at the change from the pebbly, large-scale cross-stratified sandstone of the uppermost Nottingham Castle Sandstone Formation to finely laminated, interbedded, fine-grained sandstone and mudstone with scattered small, angular pebbles and granules. A thin, calcareous conglomerate containing wind-faceted pebbles rests locally on the Nottingham Castle Sandstone (Wilson and Shipman, 1879; Lamplugh et al., 1908) and was proved to a thickness of 0.5 m in the Cropwell Bridge Borehole (Plate 10). It may indicate a significant depositional hiatus with subaerial exposure (Swinnerton, 1914, 1918; Elliott, 1961) and deflation prior to deposition of the Sneinton Formation. Smith and Warrington (1971) suggested that this hiatus is the local expression of the Hardegsen Disconformity (cf. Geiger and Hopping, 1968), which resulted from relative uplift and erosion over much of north-west Europe in the mid to late Scythian. The Sneinton Formation onlaps south-westwards onto this top Sherwood Sandstone Group deflation surface (see below and Smith and Warrington, 1971). The upper boundary of the Sneinton Formation is gradational, with thinly bedded sandstone interdigitating with finely interlaminated siltstone and mudstone characteristic of the overlying Radcliffe Formation.

The formation crops out in the western half of the district, mainly to the north of the River Trent, and also occurs within several, fault-bounded subcrops beneath the alluvial deposits of the Trent valley between West Bridgford and Radcliffe on Trent. It was encountered in excavations (now infilled or flooded) for gravel on the floodplain on both sides of the Trent between Colwick and Holme Pierrepont. Its top is occasionally visible when the river level is low, at the foot of the river cliff at Radcliffe on Trent, around [SK 6461 3987] (Lowe, 1989a; Howard, 2003). To the north of the floodplain, the main outcrop is generally less than 1 km wide, extending north and north-eastwards from Sneinton through Arnold, Calverton and Oxton. The formation also floors the deep valleys at Gedling, Woodborough and Halam, and small outliers occur in the Bestwood area. It tends to form steep, undulating slopes incised by broad, deep gullies, and generally crops out on the lower part of a scarp slope capped by resistant dolomitic siltstones at a higher stratigraphical level in the Mercia Mudstone Group (Gunthorpe Formation, see p.116). The associated soils are typically brown or red-brown, silty or clayey loams with, when ploughed, abundant fragments of brown weathering, fine-grained, micaceous sandstone containing numerous pinhead-sized solution cavities. One such sandstone bed has been mapped at the top of the formation over much of the northern part of the outcrop around Arnold, Calverton, Woodborough and Oxton.

The Sneinton Formation is 43.1 m thick in the Cropwell Bridge Borehole, the type section. It thickens from about 25 to 30 m in the Nottingham city area to over 60 m in the north-east of the district (Figure 27)b. This variation is accounted for almost entirely by northeastwards thickening of the Woodthorpe Member, whereas the thickness of the overlying Colwick Member remains virtually constant. The thickening continues north-eastwards into the Grantham district (Berridge et al., 1999), where 72 m was recorded in the Fulbeck No. 1 Borehole.

The formation consists dominantly of interbedded, very fineand fine-grained sandstone, siltstone and mudstone. The mudstone beds are typically brown; the sandstone is paler and generally grey-green or yellowbuff. Both the sandstone and siltstone have laminae coated with abundant small flakes of white mica, said to resemble watered silk (e.g. Woodward, 1887) and giving rise to the term ‘waterstones’. Coarser grained, poorly sorted sandstone with granules and small pebbles occurs in the lower part of the formation (Woodthorpe Member), which also tends to have more vivid colours than the upper part, with deep purple or blue-green hues evident in both the mudstone and sandstone beds. Sandstone in the upper part of the formation (Colwick Member) is almost exclusively fine grained and pale yellow-brown; the interbedded mudstone and siltstone are typically dull reddish brown. The clay mineralogy of the mudstone is dominated by detrital illite and minor chlorite; mixed layer chlorite/smectite is absent (Bloodworth and Prior, 1993). Gamma-ray and sonic geophysical logs through the formation both display strongly serrated profiles, contrasting with the blocky profile of the underlying Nottingham Castle Sandstone Formation and the more mildly serrated profile of formations higher in the Mercia Mudstone Group.

Woodthorpe Member

The Woodthorpe Member corresponds to the ‘Keuper Basement Beds’ described by Wilson and Shipman (1879) and Swinnerton (1918, p.25), and to the Woodthorpe Formation of Elliott (1961). Wilson and Shipman (1879) and Swinnerton (1918) described the ‘Keuper Basement Beds’ as a distinctive heterogeneous unit made up of rhythmic alternations of sandstone similar to the underlying ‘Bunter Pebble Beds’ (now Nottingham Castle Sandstone Formation), and siltstone resembling the overlying ‘Waterstones’ (now Colwick Member). They were distinguished from both these units, however, by their generally brighter and more variable colour, which is mainly bluish green with subordinate purplish brown patches and beds, and by the presence of quartz or quartzite pebbles that are appreciably smaller and more angular than those of the underlying ‘Bunter Pebble Beds’. Swinnerton (1918) placed the base of the ‘Keuper Basement Beds’ at the subaerially eroded surface of the underlying ‘Bunter’ (Nottingham Castle Sandstone), and the top at a supposed surface of planation beneath a thin conglomerate at the base of the overlying ‘Waterstones’ (‘Waterstones Conglomerate’). Elliott (1961) also identified a non-sequence below the ‘Waterstones Conglomerate’ but, on lithological grounds, included that bed within his Woodthorpe Formation. Using evidence from boreholes, temporary sections and previously published descriptions (Wilson and Shipman, 1879; Wilson, in Aveline, 1880; Gibson et al., 1908; Lamplugh et al., 1908), both Swinnerton (1918) and Elliott (1961) illustrated the lateral thickening and facies change of the ‘Keuper Basement Beds’/Woodthorpe Formation from a thin, sandstone-dominated unit resembling the underlying ‘Bunter’ in Nottingham, eastwards into a thicker, mudstone-dominated unit resembling the overlying ‘Waterstones’.

Although the Woodthorpe Formation of Elliott (1961) cannot be mapped separately, it is readily distinguishable in boreholes and surface sections (Swinnerton, 1918, Elliott, 1961) and is thus retained in this memoir as a member of the Sneinton Formation. The supposed non-sequence at or near the top of the member (Swinnerton, 1918; Elliott, 1961), overlain by the ‘Waterstones Conglomerate’, is not substantiated by geophysical log correlation, which instead suggests south-westwards onlap of the Sneinton Formation onto the surface of the Nottingham Castle Sandstone Formation (Figure 29); (Figure 30). This relationship is supported by a regional study of the stratigraphy and palynology (Smith and Warrington, 1971), which suggests that the basal beds of the Mercia Mudstone Group in Nottinghamshire become successively younger towards the south-west (cf. Warrington, 1974). The Woodthorpe Member, as defined below, represents a proximal, coarse-grained facies of this onlapping series of strata and is therefore diachronous.

The base of the Woodthorpe Member was proved at 213.8 m in the Cropwell Bridge Borehole, defined here as the type section. The upper boundary is more difficult to place because the more brightly coloured, bluish green and purplish brown beds of the member pass gradually upwards, by alternation, into the duller, brown and grey colours of the overlying Colwick Member. Furthermore, beds of pebbly sandstone occur well above the highest brightly coloured beds, for example over 18 m higher in the Fulbeck No. 1 Borehole (Figure 29) in the adjacent Grantham district. In this memoir, the boundary is taken either at the top of the highest pebbly sandstone bed or at the top of the highest vivid bluish green bed over 0.5 m thick, whichever is the higher in any particular section. In the Cropwell Bridge Borehole, it is drawn at 197.2 m depth, which marks the highest development of vivid, bluish green strata and lies 2.8 m above the highest bed of pebbly sandstone.

In the Cropwell Bridge Borehole, the member consists mainly of interbedded mudstone, siltstone and very fine- to medium-grained sandstone. The rhythmicity alluded to by Swinnerton (1918) and Elliott (1961) is not evident, but ill-defined, upward-fining units about 3 m thick occur at the base and top of the member. Vivid bluish green and purplish brown colours are characteristic, with the sandstone beds being slightly paler in colour than the interbedded mudstone and siltstone. Sandstone beds or laminae range from 3 to 200 mm in thickness, with 8 to 20 mm being most typical. Thicker beds amalgamate at some levels to form composite sandstone units between 0.3 and 2.2 m thick. The sandstone is typically fine grained, but the lower beds in the composite units are commonly very poorly sorted and contain abundant, angular to subangular granules and pebbles of quartz or lithic fragments, together with frosted, aeolian sand grains. Planar lamination, low-angle cross-lamination and current ripple lamination, all defined by strongly micaceous laminae, are common in the sandstone beds, and angular mud flakes are abundant at their bases. Primary bedding and lamination are disrupted throughout the member by soft sediment deformation and shrinkage cracking; in some of the mudstone-rich intervals, only vestiges of the original stratification remain. Spheroidal nodules of calcite, 5 to 8 mm in diameter, are common throughout the member. The Epperstone–Timmermans Borehole proved a full thickness (6.1 m) of the member, with the basal 1.94 m comprising red mudstone with thin siltstone layers; wave ripples and pseudomorphs after halite were also noted (Ambrose, 1989). Petrographically, the sandstones are lithic arkoses characterised by a common and diverse assemblage of lithoclasts (Jones, 1993).

The member is very poorly exposed in the district. The base was recorded by Dean (1989) at Hungerhill Recreation Ground [SK 5794 4137] to [SK 5794 4138] and by Lawley (1993b) in a field drain at Moorfields Farm [SK 6240 5335], north of Oxton. Sections showing beds higher in the member were recorded by Rathbone (1989a) near Redhill School [SK 5837 4630] and at Ramsdale [SK 5917 4883]. Temporary sections described by Wilson (in Aveline, 1880) at Rough Hill Wood, Sneinton, and by Swinnerton (1918) at Woodthorpe and Ramsdale remain the most complete records of the member at surface. Both Swinnerton (1918) and Rathbone (1989a) recorded erosively based beds of trough cross-stratified, coarse-grained sandstone with small angular pebbles towards the top of the member. In the section at Colwick Road, Sneinton [SK 5924 3968], the lowest strata now exposed consist of cross-stratified, medium to coarse-grained, greenish grey sandstone with small angular quartzite pebbles, thin lenticular beds of red-brown mudstone and common mudstone clasts (Charsley, 1989; Howard, 2003). This sandstone is equivalent to Bed 5 of the more complete section formerly seen at this locality by Lamplugh et al. (1908, p.37), who also noted plant remains within the mudstone lenses. Lamplugh et al. (1908) recorded the thickness of this sandstone as 3.1 m, underlain by 1.6 m of well-stratified, red, green and brown mudstone with thin sandstone beds (Beds 2–4). In turn, 0.9 m of coarse, pebbly sandstone, (Bed 1 of Lamplugh et al., 1908), described as ‘normal Bunter Pebble Beds’, was recorded below the mudstone. Lamplugh et al. included their Beds 2–5 in the ‘Bunter Pebble Beds’, but Swinnerton (1918) later re-assigned these strata to the ‘Keuper Basement Beds’. Taken collectively, the lithology of Beds 2–5, together with the presence of plant remains, is more typical of the Woodthorpe Member than the underlying Nottingham Castle Sandstone Formation, and these beds are therefore included in the former unit in this memoir. Bed 6 of Lamplugh et al. (1908), described by Charsley (1989) as a thin (0.10 to 0.16 m) bed of yellow, laminated, very fine-grained sandstone with small, angular pebbles and lenses of green and brown siltstone, is defined here as the uppermost bed of the Woodthorpe Member at this locality. In the northern part of the district, the lowest 6 to 10 m of the member is predominantly green in colour (Ambrose, 1989; Lawley, 1993b, Waters, 1993), and passes laterally into the more argillaceous ‘Green Beds’ (now termed Retford Formation, after Warrington et al., 1980) mapped in the Ollerton and Retford districts to the north (Smith, 1912; Edwards, 1967; Smith and Warrington, 1971; Smith et al., 1973).

On gamma-ray logs, the Woodthorpe Member produces a very strongly serrated profile, with an upward increase in the intensity of fluctuations between the sharp lows on the pebbly sandstone beds and the peaks on the intercalated mudstone-rich intervals (Figure 29); (Figure 30). Sonic velocity generally increases upwards through the member, along with a gradual decline in the intensity of fluctuations.

Due to the paucity of lithological information, thickness variation across the district is based largely on geophysical log correlation, using the high gamma-ray mudstone at the base of the Colwick Formation in the Cropwell Bridge Borehole as a correlation datum. The member is 16.6 m thick in this borehole, thickening eastwards to 31 m in the Redmile No. 2 Borehole (Figure 30) and north-eastwards to 36 m in the Elston Grange Borehole (Figure 29). The member thins markedly towards the west of the district; Swinnerton (1918) measured only 5.2 m at Woodthorpe [SK 5830 4374] and 3.7 m at Ramsdale, 2 km west of Calverton. The former, more complete section at Colwick Road, Sneinton (Lamplugh et al., 1908; Swinnerton, 1918) proved a thickness of 4.8 m (see above). Wilson and Shipman (1879) and Aveline (1880) recorded several other sections in and around Nottingham, each less than 2 m thick and consisting of micaceous sandstone with small angular pebbles and lenticular mudstone partings. The member is present to a maximum thickness of about 6 m in adjoining parts of the Derby district to the west (Taylor, 1965; Frost and Smart, 1979), but is absent locally and has not been recorded to the west of the River Derwent.

Colwick Member

The Colwick Member corresponds to the Colwick Formation of Warrington et al. (1980), which was introduced as a replacement name for the ‘Waterstones Formation’ of Elliott (1961). Although lithologically distinct from the underlying Woodthorpe Member, it cannot be mapped separately at surface and is therefore, in this memoir, reduced to the status of a member within the Sneinton Formation. It is not equivalent to the ‘Waterstones’ unit of Lamplugh et al. (1908), which included strata assigned here to the Woodthorpe Member.

Unlike the underlying Woodthorpe Member, the Colwick Member is well exposed at several localities in the district, mainly in Nottingham itself (Howard, 2003). Only the Cropwell Bridge Borehole provides a complete section, however, and is thus chosen as the stratotype. A near-complete reference section, exposing the lower boundary of the member (see above) and about 21 m of overlying beds, is located at Colwick Road, Sneinton [SK 5924 3968] and was described by Charsley (1989) and Howard (2003). Other good sections were noted in a disused railway cutting at Woodthorpe [SK 5954 4435] (about 19 m; Dean, 1989), in the cutting (Plate 11) on the A60 Mansfield Road at Redhill [SK 5835 4689] to [SK 5837 4713], where about 7.0 m of strata were observed by Rathbone (1989a), and at a nearby engineering works [SK 5828 4681] (about 9.2 m; Rathbone, 1989a). A section of about 7.0 m of the upper part of the member, showing the upwards gradation into the Radcliffe Formation, is exposed in a disused quarry [SK 6006 3974] at Colwick Wood and in the cutting of the Nottingham–Newark railway about 50 m to the north-east [SK 6055 3996] (Lowe, 1989a). The top of the member is also exposed at or just below water level beside the River Trent at Radcliffe on Trent around [SK 6461 3987] (Lowe, 1989a; Howard, 2003). Numerous other smaller sections in and around Nottingham are recorded in BGS Technical Reports (see Information Sources).

Difficulties in defining the boundary with the underlying Woodthorpe Member are discussed above. In the Cropwell Bridge Borehole, the top of that member is placed at a depth of 197.2 m. It is overlain by a 2 m-thick succession of purplish brown, thinly interlaminated mudstone, siltstone and very fine-grained sandstone basal to the Colwick Member. These beds produce a sharp gamma-ray ‘low’ that is also recognisable in other boreholes in the eastern part of the district (Figure 29); (Figure 30) and provides a useful, local correlation datum. The boundary with the overlying Radcliffe Formation (see below) is at 170.7 m in the Cropwell Bridge Borehole (Figure 28).

The member consists of interbedded mudstone, siltstone and sandstone characterised by pale brown or dull reddish brown colours; there are no green beds thicker than 0.5 m and most are less than 0.1 m. Individual sandstone laminae and beds range from 3 to 400 mm in thickness, with 10 to 40 mm being most typical. Thinner (less than 20 mm) sandstone beds are usually intercalated with siltstone and mudstone to form heterolithic units up to 4 m thick, but thicker beds are commonly amalgamated into composite units up to 3 m thick. The sandstone is typically very fine to fine-grained and pale buff-grey in colour, with an orange tint in places. Micaceous planar lamination, current ripple cross-lamination and sporadic convolute lamination occur within sandstone beds, and the tops are commonly current rippled. The bases of individual sandstone beds are commonly slightly erosional and incorporate abundant mudflakes. The thicker composite sandstone beds occupy shallow channels at some sections, most notably at Redhill (Plate 11), but the depth of erosion is generally less than 1 m. Petrographically, the sandstones consist mainly of monocrystalline quartz with minor potassium feldspar and, in contrast to those of the Woodthorpe Member, lithic fragments are rare (Jones, 1993). The dominant cement is gypsum, with less common dolomite and ferroan calcite; secondary dissolution of the cement is common. Siltstones and mudstones within the heterolithic units are dominantly dull reddish brown in colour. Primary stratification in the more argillaceous parts of the member was extensively disrupted by penecontemporaneous soft-sediment deformation, desiccation cracking and halite crystal growth and solution, imparting a blocky weathering habit when exposed at surface. Beds of finely interlaminated siltstone and mudstone, with only minor deformation, increase in abundance towards the top of the member, as it grades upwards into the overlying Radcliffe Formation. Nodular gypsum and small, spheroidal calcite nodules are common in the Cropwell Bishop Borehole, but at outcrop are dissolved by meteoric water in the near surface and are not seen in surface sections. Desiccation cracks and pseudomorphs after halite are common and best observed on the bases of thin sandstone beds within the more argillaceous parts of the member.

The member produces a strongly serrated profile on gamma-ray logs, with a generally lower response than both the Woodthorpe Member below and the Radcliffe Formation above. In the Rolleston Borehole, the sonic logs also display a moderately to strongly fluctuating response, with an overall slight upward decline in velocity (Figure 29). In general, two units can be recognised in the Cropwell Bridge Borehole (Figure 28) and in surface sections. The lower half of the member is dominated by argillaceous, heterolithic lithologies, with a few composite sandstone beds less than 0.5 m thick. The upper half of the member forms an upward-fining sequence, marked by a general decline in the frequency and thickness of sandstone beds. This is reflected on the gamma-ray log by a gradual upward increase in response. The thickest (up to 2 m) composite beds of sandstone within the member occur at the base of this upwardfining sequence, although a 1 m-thick composite sandstone bed is developed locally at the top of the member.

The sandstone is seen in the Cropwell Bridge Borehole and at Radcliffe on Trent [SK 6461 3987], and forms a mappable feature in parts of the district (see above). The member maintains a near-constant thickness throughout the district, being 26.5 m thick in the Cropwell Bridge Borehole, and ranging from 23 to 28 m elsewhere.

The Sneinton Formation has yielded fossils at a number of localities in the west of the district, including trace fossils, plants and fish. Supposed ‘annelid tracks’ were noted in the Woodthorpe Member at Redhill [SK 582 468] (Elliott, 1961), and a Cheirotherium (sic.) footprint trace was reported from the lowermost bed of the Colwick Member at Colwick (Irving, 1874, 1876). Vertebrate tracks collected by Swinnerton (1910, 1913) from temporary exposures of the ‘Woodthorpe Formation’ in the Mapperley Park area were later described in detail by Sarjeant (1967, 1970). Sarjeant (1996) reappraised the tracks and assigned them to the ichnogenera Chirotherium, Synaptichnium, Paratetrasauropus and Swinnertonichnus. However, King and Benton (1996), studying the same specimens, have suggested that the Paratetrasauropus and Swinnertonichnus specimens should be attributed to Chirotherium, and that Sarjeant’s (1996) specimen of Chirotherium might be inorganic. Plant remains (Schizoneura paradoxa) were recorded from a thin, lenticular mudstone bed in the lowermost part of the Woodthorpe Member in the Colwick Road section (see above) by Lamplugh et al. (1908, pp.37, 42) and Vernon (1910). A supposed fossil plant specimen from the Colwick Member, which was identified as Equisetites (Wilson, 1887), might be a sedimentary or diagenetic feature (Elliott, 1961). Fish remains discovered in the roof of the Leen Valley Outfall Sewer tunnel under Colwick Wood (Wilson, 1887) were identified by Newton (1887) as Semionotus. They originated from the basal 10 cm of the Colwick Member. Temporary exposures of the same horizon in the Woodthorpe area around [SK 583 437] (Swinnerton, 1918) yielded other Semionotus specimens (Swinnerton, 1910, 1928) and Woodthorpea wilsoni, a catopterid fish (Swinnerton, 1925). McCune (1986) considered Semionotus metcalfei, a species introduced by Swinnerton (1928), to be a nomen dubium, and that the specimen, if a Semionotus, is indistinguishable from S. kapffi Fraas 1861.

None of the fossils described above provide evidence of age. Miospores from comparable beds (‘Keuper Waterstones’ and ‘Green Beds’) in the Ollerton and East Retford districts to the north were considered to indicate a late Early Triassic (Olenekian) to early Mid Triassic (Anisian) age (Smith and Warrington, 1971; Smith et al., 1973). Miospores from the ‘Green Beds’, the lowest part of the Mercia Mudstone Group in those districts, include Angustisulcites spp. and Stellapollenites thiergartii. By comparison with miospore assemblages reported from independently dated Triassic successions elsewhere in Europe, this association is now regarded as indicating an Anisian age. A similar age is likely for the Sneinton Formation.

Depositional environment

The presence of lamination throughout the Sneinton Formation suggests mainly subaqueous deposition, although the extensive disruption of the more argillaceous intervals by soft sediment deformation, brecciation and shrinkage-cracks indicates oscillation of the water table and periodic wetting and drying of the substrate. Each of the individual sandstone beds probably represents a single, short-lived depositional event, preceded by erosion of the substrate and followed by settling of mud and silt from suspension. The reptile tracks and fish together indicate a shallow water environment with temporary water bodies present at times and a more permanent water cover at others. The inarticulate brachiopod Lingula tenuissima occurs in comparable beds (the ‘Waterstones’) in the adjacent Ollerton district to the north (Rose and Kent, 1955), and implies marine influence on deposition. In combination, this evidence suggests a coastal mud and sand flat environment. Mader (1992) has suggested that sand was introduced by a weakly braided, low sinuosity fluvial channel system, with sandstone beds being deposited by episodic channel surges, crevassing or overbank sheet floods. The thicker composite sandstone beds seen in both the Woodthorpe and Colwick members may thus represent channel or proximal crevasse splay deposits. The spheroidal calcite nodules and deeper red-brown and bluish green colours of the Woodthorpe Member suggest immature to submature palaeosol development (Mader, 1992).

During late Olenekian and early Anisian times, after the phase of relative uplift responsible for the Hardegsen Disconformity, the south-western margin of the Southern North Sea Basin was temporarily separated from the Triassic basins of the central Midlands (Warrington and Ivimey-Cook, 1992, Figure 20)c. Initially, the coastal plain sediments of the Sneinton Formation gradually onlapped south-westwards onto the subaerially eroded surface of the Sherwood Sandstone Group, with the pebbly, texturally immature sandstone of the Woodthorpe Member being deposited in alluvial fans sourced locally from the Sherwood Sandstone Group and possibly from Charnian-type Precambrian rocks to the west and south. The more texturally mature sandstones of the Colwick Member probably have a more distant provenance to the west and, as originally suggested by Swinnerton (1918), are thought to have been deposited after a connection was re-established with basins in the Central Midlands (cf. Warrington and Ivimey-Cook, 1992). Initially, this led to the northeastwards progradation of distal fluvial plain environments across the region, although this episode was short-lived due to a regional decline in fluvial activity throughout the English Midlands in the later Anisian. In the Nottingham district, the decline in fluvial deposition led to the upward transition into more argillaceous, playa mudflat environments represented by the overlying Radcliffe Formation.

Radcliffe Formation

The Radcliffe Formation was named by Elliott (1961), who selected the section in the river cliff at Radcliffe on Trent [SK 6461 3987] as the stratotype; the section has since been redescribed by Lowe (1989a). The formation was proved between depths of 156.7 and 170.7 m in the Cropwell Bridge Borehole; a reference section from that borehole is held in the NGRC core store at BGS, Keyworth.

The formation crops out largely in the western half of the district, mainly to the north-west of the River Trent. The most southerly and westerly outcrops are heavily faulted and largely masked by the Trent valley alluvial deposits. The main outcrop is highly irregular and, due to the low dip, sinuous in form. It is generally less than 0.5 km wide and parallel to that of the underlying Sneinton Formation, although a broader outcrop underlies the town of Southwell. Much of the outcrop underlies Nottingham and is heavily urbanised. Typically, the formation occupies the steep, middle part of a scarp slope capped by resistant dolomitic siltstone in the overlying Gunthorpe Formation.

Despite the generally poor exposure, the formation can be readily mapped in the district on account of its finely laminated character and distinctive colour variegation. The outcrop of the formation is usually marked by pink, brown and green clayey soils which, on arable land, can be readily distinguished from the duller, reddish brown soils of the formations above and below, especially when viewed from a distance. Fragments of finely laminated mudstone and siltstone are common in freshly ploughed soils and are also brought up by handaugering. Thin beds of siltstone or fine-grained sandstone locally form mappable topographical features and distinctive brash in soils (Lowe, 1989c; Lawley, 1993b; Waters, 1993).

The type section at Radcliffe on Trent [SK 6461 3987] exposes the full thickness of the formation (about 12.1 m), overlying a thick sandstone bed (normally below river level) at the top of the Sneinton Formation, and underlying red-brown, blocky gypsiferous mudstones of the Gunthorpe Formation (Lowe, 1989a; Howard, 2003). The Cropwell Bridge Borehole furnishes the only other complete section (14.0 m thick) of the formation in the district (Figure 28). The lowest 7 m are seen resting on the Sneinton Formation in a section that extends eastwards from a disused quarry [SK 6006 3974] in Colwick Wood into the cutting of the Nottingham–Newark railway line [SK 6055 3996]. Higher beds occupy the upper faces of a disused quarry [SK 5888 4129] near St Ann’s Well Road (about 9.2 m; Dean, 1989). The uppermost 8.2 m, overlain by the Gunthorpe Formation, is visible in another disused quarry [SK 5828 4222] to [SK 5833 4216] in the Coppice Recreation Ground, Mapperley Park (Dean, 1989). The top of the formation is also exposed in the floor of Dorket Head Brick Pit [SK 5959 4718] (Rathbone, 1989a, fig. 8), in Lambley Dumble [SK 6181 4495] to [SK 6190 4500] (Rathbone, 1989b) and in the shooting range [SK 6604 4848] near Epperstone (Ambrose, 1989). Numerous other surface sections, most exposing less than 3 m of the formation, are documented in BGS Technical Reports covering the district (see Information Sources).

The distinctive, finely laminated lithology is produced by intercalations of mudstone with siltstone or very finegrained sandstone on a 0.5 to 3 mm scale. Very thin to thin beds (up to 40 mm) of very fine to fine-grained micaceous sandstone are common at some levels. Mudstone laminae are typically pinkish red or red-brown, contrasting with the pale grey or pinkish grey of the intercalated siltstone or sandstone. Predominantly green intervals up to 1 m thick occur at some levels, in some cases with interlayering of red and green coloured laminae. Individual siltstone and sandstone laminae are sharpbased, and are either internally structureless or display normal grading. Thicker sandstone beds commonly have a mudflake conglomerate at their base, and show a variety of structures including planar lamination, convolute lamination, wave and current ripple lamination and normal grading. Rain and/or hail pits were reported by Rathbone (1989b). The regularity of the laminated texture is disrupted to varying degrees (Plate 12) by desiccation cracks, fluid escape structures, microfaulting and pseudomorphs after halite, but not to the extent seen in other formations. Syndepositional slumping and folding also occur, and are commonly confined to layers a few centimetres thick (‘slip layers’; Elliott, 1961), separated from the undeformed strata above and below by décollement surfaces. Stratification is commonly curled upwards adjacent to larger shrinkage cracks, some of which are filled by gypsum nodules. Gypsum also occurs as bedding parallel or subparallel veins of satin spar, and as a cement within thin sandstone beds; dolomite is also common as a cement. The clay mineralogy of the mudstone is dominated by detrital illite (70–85 per cent) and subordinate chlorite (15–30 per cent); mixed layer chlorite/smectite is absent (Bloodworth and Prior, 1993), in contrast to formations higher in the Mercia Mudstone Group.

Both the lower and upper boundaries of the formation are gradational. At the base, the distinctive lithologies of the laminated Radcliffe Formation are intercalated with sandstone of the uppermost Sneinton Formation. In the Cropwell Bridge Borehole, the boundary is drawn above a thick (more than 1 m) composite bed of finegrained sandstone, and in the type section it is placed above a similar sandstone bed that lies at or just above river level (Lowe, 1989a). At the top of the formation, there is interdigitation with the intensely deformed and disrupted, blocky weathering siltstones of the lower part of the Gunthorpe Formation.

On gamma-ray logs, the formation has a less strongly serrated profile than the Sneinton Formation (Figure 29); (Figure 30), although the boundary cannot be picked with certainty in the absence of detailed lithological information. The lower half of the formation shows a slight upward decrease in average gamma-ray log response, and the upper half a gradual upward increase. The top of the formation lies immediately below a prominent shoulder in the gamma-ray log, above which the log values decline steadily towards the upper part of the Gunthorpe Formation. Sonic logs display fluctuating values, superimposed on a generally constant background velocity thoughout the formation.

The Radcliffe Formation ranges from about 11 to 16 m thick in the Nottingham district. Farther east, it is 15 m thick in the Fulbeck No. 1 Borehole (Figure 29). It was not differentiated in the Ollerton and Retford districts, to the north, but has been proved to thicknesses of 10 to 15 m in the adjoining Melton Mowbray and Loughborough districts to the south and south-west, respectively (Carney et al., 2004, 2001), and is up to 35 m thick south of the Loughborough district in the Coalville district (Worssam and Old, 1988).

The formation has yielded very few fossils. Lowe (1989c) noted small burrows in a section [SK 6190 4500] in Lambley Dumble, and Elliott (1961) reported a possible ‘large conchostracan’ from the Lees Barn No. 4 Borehole near Radcliffe on Trent. A palynological preparation from the formation at 167.72 m in the Cropwell Bridge Borehole (Warrington, 1993a) yielded herkomorph acritarchs (Dictyotidium), possible tasmanitid algae, and remains of a colonial alga (Plaesiodictyon mosellanum). These fossils are not diagnostic of age, but are indicative of depositional environment. The age of the formation can be constrained as Anisian (early Mid Triassic) on the basis of palynological evidence from the Sneinton and Gunthorpe formations in districts to the north (Smith and Warrington, 1971).

Depositional environment

Subaqueous environments subject to marine influence are indicated by the presence of Dictyotidium and tasmanitid algae. These occur in nearshore marine facies, but the alga Plaesiodictyon mosellanum is known from deposits considered to represent brackish conditions in estuarine and similar environments (Wille, 1970). The abundant lamination is compatible with deposition in a subaqueous environment, with episodes of strong current activity interspersed with longer periods of sediment fall-out from suspension, although the shrinkage cracks and pseudomorphs after halite suggest periods of drying and possible emergence. Mader (1992) has interpreted the depositional environment as one of alluvial mudflats and brackish lakes in a semi-arid climatic setting, with the siltstone-sandstone laminae or thin beds representing the deposits of discrete, weak flood surge events.

Gunthorpe Formation

The Gunthorpe Formation (Table 14) encompasses the former ‘Carlton’ and ‘Harlequin’ formations of Elliott (1961), who placed the boundary between these units immediately above a distinctive bed containing ‘flow-type’ breccias. The boundary lies slightly above a thin, dolomitic sandstone considered by Smith (1913) to cap the large plateau of Mapperley Plains in northeast Nottingham. Elliott (1961) named this resistant sandstone the ‘Plains Skerry’. Geological mapping of the district has shown, however, that several resistant dolomitic siltstone and sandstone beds occur in this part of the succession, and that the Mapperley Plains plateau is not attributable solely to any one of these beds. There is therefore no mappable marker horizon separating the ‘Carlton’ and ‘Harlequin’ formations, and for this reason the units have been amalgamated into the Gunthorpe Formation (Charsley et al., 1990). The name originates from Gunthorpe weir [SK 6886 4367], where the middle part of the sequence is well exposed (Rathbone, 1989c; Howard, 2003). The type section is defined in the Cropwell Bridge Borehole between depths of 84.9 and 156.7 m, curated core of which is held in the NGRC core store of the BGS at Keyworth.

The outcrop of the formation forms a broad belt extending from Clifton in the south-west of the district to Newark in the north-east. The formation forms the rockhead beneath much of the Trent valley alluvial deposits between Radcliffe on Trent and Newark. The main drift-free outcrops lie to the north-west of the Trent valley between Sneinton and Southwell, where the lower half of the formation forms two large outliers separated by the valley of Dover Beck. Higher beds crop out to the south-east of the River Trent. Several fault-bounded outcrops underlie parts of West Bridgford and extend beneath the Trent alluvium in the Wilford, Clifton and Beeston areas. The upper half of the formation forms the steep, lower slopes of the river bluffs extending along the south-east side of the Trent valley from Radcliffe on Trent to East Stoke.

The outcrop of the formation is characterised by heavy but fertile, generally deep red, silty clay soils. Beds of greenish grey mudstone, which are particularly common in the lower part of the formation, are commonly marked by stripes in ploughed fields (Lawley, 1993b). Resistant beds of mainly grey-green, dolomitic siltstone or very fine-grained sandstone form locally mappable cuesta or bench features, associated with a brash of siltstone and/or very fine-grained sandstone fragments. A series of such resistant beds, about 15 to 20 m above the base of the formation, gives rise to several, extensively dissected plateaux between Arnold and Southwell, including Mapperley Plains. In the West Bridgford area, higher beds of the formation form the steepest part of a scarp slope capped by the overlying Cotgrave Sandstone Member of the Edwalton Formation.

Although exposures of the formation are numerous in the district, sections of more than 5 m are uncommon, and only the Cropwell Bridge Borehole (Figure 28) proves a complete succession. The best surface section is at Dorket Head Brick Pit (Rathbone, 1989a), where the lowest 23.8 m of the formation, resting on the Radcliffe Formation, has been recorded in the advancing worked faces [SK 5963 4740] to [SK 5973 4737]; [SK 5967 4735] to [SK 5957 4714]; [SK 5972 4716] to [SK 5980 4713]. The base of the formation is also exposed overlying the Radcliffe Formation in the type section of the latter unit [SK 6461 3987] at Radcliffe on Trent (Lowe, 1989a), and at the shooting range [SK 6604 4850] near Epperstone (Ambrose, 1989). Approximately 14.4 m of the middle part of the formation are exposed in river cliffs at Radcliffe on Trent weir [SK 6507 4053] (Rathbone, 1989c). At Gunthorpe [SK 6886 4367], 7.85 m are exposed at a slightly higher stratigraphical level, again in a low river cliff. The topmost 8.5 m of the formation, including the junction with the overlying Cotgrave Sandstone Member, is seen in a partly soil-covered exposure in the sides of a sunken lane that descends the river cliffs to the north-west of Kneeton [SK 7087 4622]. The upper boundary of the formation was also exposed in small sections in the disused brickclay pits at Wilford [SK 5708 3555] (1.7 m) and West Bridgford [SK 5890 3616] (Charsley, 1989). A 15 m section of the upper part of the formation in Harlequin brickpit [SK 660 393], recorded by Lamplugh et al. (1908), is now obscured.

The formation consists of interbedded red-brown and grey-green mudstone, siltstone and very fine-grained sandstone, with four main lithofacies.

The laminated lithofacies consists of reddish brown mudstone, interlaminated or very thinly interbedded with pale brown or greenish grey siltstone or very fine sandstone. This lithofacies resembles the underlying Radcliffe Formation, but is less brightly coloured and is usually more extensively disturbed by features such as desiccation cracking and brecciation, water/gas escape structures and microfaulting; pseudomorphs after halite are common. This facies forms units between 0.1 and 0.8 m thick, and is common in the upper half of the formation where it is intercalated with the ‘structureless’ lithofacies, and in the basal 5 m where it is intercalated with the deformed lithofacies.

The heterolithic lithofacies consists typically of very thin to thin beds of greyish green dolomitic siltstone or very fine-grained sandstone, interbedded with greyish green or reddish brown mudstone with siltstone laminae. Sandstone beds display a variety of sedimentary structures, including planar and low-angle lamination, current and climbing ripple cross-lamination, wrinkle marks and, at the bases of beds, common pseudomorphs after halite which exceptionally reach up to 80 mm across. Individual sandstone beds commonly amalgamate to form composite beds up to 0.4 m thick. Desiccation cracks are very common and in places may be sufficiently extensive to form the ‘vein-type’ penecontemporaneous breccias described by Elliott (1961). This lithofacies is dominant in the middle part of the formation between 15 and 30 m above the base, but also occurs less commonly at other levels. It tends to occur in sequences 0.15 to 1.5 m thick, commonly forming mappable topographic features, and separated by beds of the other lithofacies.

In the Cropwell Bridge Borehole, between depths of 133.9 and 138.5 m, a series of units of the heterolithic lithofacies are deformed by extensive loading, slumping and fluidisation. This is largely confined to the sandstone beds, where the original lamination has been extensively convoluted and in some cases virtually destroyed. Load casts and ball-and-pillow structures are common. In places, brecciated fragments of sandstone with an early dolomitic cement are caught up in slump folds, forming the structure described by Elliott (1961) as ‘flow breccia’. Slumped sandstone has been observed at the same stratigraphical level, near the top of former quarry faces at Dorket Head [SK 597 472], and at the base of the section at Radcliffe on Trent weir [SK 6507 4053]. Although this slumping is distinctive and not seen in other formations of the Mercia Mudstone Group in the district, it is not confined to a single mappable sandstone bed (i.e. the ‘Plains Skerry’ of Smith, 1913, and Elliott, 1961).

The deformed lithofacies consists of penecontemporaneously deformed and brecciated argillaceous siltstone or sandy siltstone that weathers to a blocky texture. Both the ‘flow-type’ and ‘vein-type’ breccias described by Elliott (1961) are common, but do not occur together. The dominant colour is dull reddish brown, with diffuse greenish grey mottles or layers; in places the colour variations have an almost wispy appearance. A number of processes were responsible for the deformation, including desiccation, soft sediment deformation, growth and solution of interstitial evaporite crystals, and differential compaction of zones cemented by early authigenic dolomite. Where visible, remnant stratification consists of interbedding, on a scale of 10 to 30 mm, of red-brown silty mudstone and pale grey-brown sandy siltstone. This lithofacies is dominant in the lowest 15 m of the formation, within the beds assigned to the ‘Carlton Formation’ by Elliott (1961), and is also intercalated with the heterolithic lithofacies in the middle part of the formation.

The ‘structureless’ lithofacies consists of superficially structureless, reddish brown mudstone and siltstone, weathering to a blocky habit where exposed at the surface. However, on closer examination, vestigial thin interlamination of mudstone and siltstone, and discontinuous irregularly shaped ‘wafers’ of fine- to mediumgrained sandstone containing scattered, coarser ‘aeolian’ sand grains are locally apparent. ‘Wafers’ are generally less than 8 mm thick and usually structureless, although some show poorly preserved, deformed planar or ripple lamination. Greenish grey reduction zones occur as small spheroids (‘reduction spots’) or form larger haloes around sandstone wafers. The uppermost 12 m of the formation is composed largely of this lithofacies, and thinner intervals are intercalated with the heterolithic lithofacies in the middle part of the formation.

Gypsum is fairly common in all four lithofacies, occurring as small nodules (5–40 mm in diameter), satin spar veins and as a cement within sandstone beds. Satin spar veins may be up to 0.2 m thick and are generally subparallel to bedding, although thinner, high angle veins also occur in many surface sections, commonly filling joints. A 0.2 m-thick bed of satin spar gypsum, within 5 m of the top of the formation, was formerly worked on a small scale in and around East Bridgford (Firman, 1964; Rathbone, 1989c) (see p.30). Gypsum nodules and cements were probably precipitated from interstitial brines, either penecontemporaneously or soon after deposition (e.g. Aljubouri, 1972; Wills, 1976; Arthurton, 1980), whereas the satin spar veins formed secondarily, following solution, mobilisation and re-precipitation of primary gypsum. Those filling high-angle joints in surface sections may be of very recent origin.

Mixed-layer chlorite/smectite appears as a component of the clay mineral assemblage immediately above the base of the formation (Bloodworth and Prior, 1993). It generally makes up 25 to 40 per cent of the assemblage throughout most of the rest of the formation (Figure 28). The remainder of the clay assemblage consists mainly of detrital illite with minor chlorite. The mixed-layer chlorite/smectite is interpreted as having been formed by the authigenic transformation of detrital illite due to reaction with alkaline, magnesium rich groundwater, with subsequent modification during burial diagenesis (Bloodworth and Prior, 1993).

In the Cropwell Bridge Borehole, the base of the formation is placed below the lowest bed of heavily deformed silty mudstone, although intervals of laminated lithologies typical of the Radcliffe Formation persist up to 5 m above this level. At Dorket Head brickpit, several beds of fine-grained, mainly greenish grey sandstone are interbedded with deformed siltstones in the basal 3 m of the formation; these give rise to a distinctive soil brash of sandstone fragments and can be mapped locally in the surrounding area. The sharp base of the overlying Cotgrave Sandstone Member, which forms a mappable feature, defines the top of the formation.

Both the upper and lower boundaries are well defined on geophysical logs (Figure 29); (Figure 30). The base lies immediately below a pronounced ‘shoulder’ on the gamma-ray log, a feature that was termed the ‘Regional Gamma Ray Log Marker’ by Balchin and Ridd (1970) and was correlated in the subsurface beneath much of eastern England. Gamma-ray profiles through the formation show small to moderate variations in amplitude and an overall slight upward decrease in response. Sonic logs are available for the lower part of the formation in just two boreholes in the district, Saxondale No. 1 and Rolleston No. 3; in the latter and in the Fulbeck No. 1 Borehole in the Grantham district, a marked upward decline in sonic velocity occurs about 20 m above the base of the formation. The top of the formation is marked by a sharp uphole decrease in the gamma-ray response, corresponding to the base of the Cotgrave Sandstone Member.

There is little variation in the thickness of the formation within the district, although a slight north-eastwards increase is evident. The formation is 71 m and 73 m thick in the Cropwell Bridge Borehole and the Cotgrave Colliery No. 1 shaft, respectively, thickening eastwards to 76 m in the Bottesford No. 4 Borehole. A maximum thickness of 86 m was recorded in the Elston Grange Borehole in the north-east of the district. Similar thicknesses were recorded in boreholes in the Melton Mowbray district to the south (Carney et al., 2004).

Palynomorphs are the only fossils known from the formation in the district. A sample collected in 1990 from the lower part of the formation in Dorket Head brickpit [SK 596 472] contained the miospores Alisporites grauvogeli, A. toralis, and ?Illinites chitonoides, regarded as possibly Anisian (early Mid Triassic) in age (Warrington, 1993b). This is supported by the palynology of sequences in north Nottinghamshire (Smith and Warrington, 1971), where miospore associations including Angustisulcites spp. and Stellapollenites thiergartii occur in strata ranging from levels equivalent to the Sneinton Formation up to the Clarborough Beds; the latter may correlate with beds around the ‘Plains Skerry’ (see above), some 20 m above the base of the formation. Poorly preserved miospores from 2.1 m below the top of the formation in a borehole [SK 6996 4150] near East Bridgford provided no evidence of age (Warrington, 1994a), but a colonial chlorophycean alga (Plaesiodictyon mosellanum) from the same sample may indicate brackish water conditions in an estuarine or similar environment (Wille, 1970). Miospores from a sample at the top of the formation, immediately below the Cotgrave Sandstone Member in Wilford Hill brickpit [SK 569 356] were originally dated by Warrington (1970) as Carnian (early Late Triassic). This assemblage includes Retisulcites perforatus, which by comparison with records from independently dated Triassic sequences elsewhere in Europe, is now considered to be indicative of a late Mid Triassic to earliest Late Triassic (Ladinian–early Carnian) age. The top of the formation may, therefore, be slightly older than previously proposed. Samples collected from several horizons in the type section of the formation in the Cropwell Bridge Borehole proved to be barren.

Depositional environment

The depositional environment of the Gunthorpe Formation is interpreted as that of a widespread, saline, playa mudflat (Mader, 1992). Episodic sheet floods deposited the thin beds of laminated sandstone and also formed temporary, localised, brackish water lakes in which mud settled out from suspension to blanket the sandstone sheets. Subsequent evaporation formed desiccation cracks, gypsum nodules and, on the mudflat surface, crusts of halite crystals; the latter were dissolved and the resulting voids infilled by sediment from the next sheet flood to form pseudomorphs after halite. The alternate wetting and drying of the mudflat and oscillation of the water table, with associated growth and solution of interstitial salts (cf. Hardie et al., 1978), disrupted the primary depositional fabric of the sediment to varying degrees, producing the deformed textures of the laminated, heterolithic and deformed lithofacies. The ‘laminated’ and ‘heterolithic’ lithofacies probably represent the infills of broad channels that acted as conduits during the main flood surges, with the ‘structureless’ lithofacies deposited on slightly elevated areas of the mudflat that escaped periodic flooding. In these areas, sediment accumulated on the damp and uneven surface of the mudflat mainly by the accretion of wind-blown mud pedicles and sand grains (cf. Taylor et al., 1963; Arthurton, 1980).

Edwalton Formation

The Edwalton Formation was named by Elliott (1961), who selected a section of the lower part of the formation in Edwalton Hill (also known as Ludlow Hill) brickpit [SK 589 363] in the south-western corner of the district as the (partial) stratotype. Part of this section [SK 5890 3616] was described by Charsley (1989). The formation was proved between depths of 35.80 and 84.85 m in the Cropwell Bridge Borehole (Figure 28); a reference section from that borehole is held in the NGRC core store at BGS, Keyworth. The lower boundary of the formation is placed at the base of the Cotgrave Sandstone Member, and the upper boundary at the top of the Hollygate Sandstone Member. These boundaries correspond to those originally defined by Elliott (1961); they are mappable throughout the district and are also easily recognised in the subsurface in both borehole cores and geophysical logs.

The outcrop of the formation lies almost entirely to the south-east of the Trent valley, extending from Clifton in the south-west to Newark in the north-east. Numerous minor faults trending north-west to south-east disrupt the outcrop between West Bridgford and Stragglethorpe. North-east of the Cinderhill–Foss Bridge fault, the outcrop is up to 5 km wide and strikes north-eastwards, although with substantial displacements across the Harlequin and Eakring–Foston faults. Between East Stoke and Newark, the formation is largely masked by the alluvial deposits of the Trent valley and associated Quaternary river terrace deposits. The formation is very poorly exposed at surface, but has been proved in numerous cored boreholes in the district. Many of the latter were drilled by the National Coal Board, with the aim of using displacements of the Cotgrave Sandstone and other marker horizons to prove the near-surface positions of faults that may have disrupted the underlying Coal Measures at depth.

The topographical expression of the formation is characterised by a series of low cuestas dipping gently southeastwards, each formed on more resistant sandstone beds within the formation. The Cotgrave Sandstone and Hollygate Sandstone members both form strong and persistent topographical features. The base of the formation lies about 2 to 3 m downslope from the crest of a scarp or bench feature formed by the Cotgrave Sandstone Member, and the top corresponds to the foot of a long, gentle dip slope formed on the Hollygate Sandstone Member. A thin but strongly cemented dolomitic and siliceous sandstone unit about 25 m above the base of the formation also forms a strong cuesta feature with a long dip slope, notably to the south of Bingham and at Syerston airfield. The formation gives rise mainly to dark reddish brown, heavy clay soils, but dip slopes on the sandstone members and other more minor ‘skerries’ have sandy clay soils containing blocks or slabs of indurated sandstone or siltstone.

The thickness of the formation is remarkably uniform across the district. Along the southern boundary of the district, 49 m were recorded in the Cropwell Bridge Borehole and 50 m in the Redmile No. 2 Borehole (Figure 30). Comparable thicknesses (51 m and 47 m) occur in the nearby Stenwith and Cox’s Walk boreholes in the Grantham district. The full thickness of the formation was not proved in any boreholes in the north of the district, but 44 m and 43 m were recorded in the Fulbeck No. 1 (Figure 29) and Stragglethorpe boreholes, respectively, in the Grantham district (Berridge et al., 1999). Similar thicknesses have been recorded in boreholes across the adjacent Melton Mowbray district to the south (Carney et al., 2004).

The formation consists dominantly of mudstone and siltstone with beds of very fine to medium-grained sandstone, commonly with dolomitic or siliceous cements. Sandstone beds are thickest and most common in the Cotgrave Sandstone and Hollygate Sandstone members, although both these units contain an appreciable proportion of mudstone. Mudstone and siltstone lithologies are typically reddish brown, with irregularly shaped greenish grey mottles. Borehole cores indicate that gypsum is abundant throughout the formation as nodules and veins, and as a cement within the sandstones, but is usually absent in surface exposures due to solution by groundwater. The mudstone and siltstone typically weather to a stiff blocky clay or silty clay. Weathering of the gypsum-cemented sandstone tends to produce weakly cemented friable sand in which thin, dolomitic or siliceous horizons stand out as more resistant ribs.

The clay mineralogy of the mudstone is dominated by detrital illite and authigenic mixed-layer chlorite/smectite (Figure 28); detrital chlorite forms a minor component. The proportion of authigenic mixed-layer clays within the Edwalton Formation is higher than in the other formations of the Mercia Mudstone Group, reaching a maximum of 70 per cent of the total clay mineral assemblage in the Hollygate Sandstone Member. Such a composition has implications for the plasticity and shrink/swell properties of this part of the formation (Chapter 2).

Gamma-ray logs through the formation show a moderately serrated profile reflecting the intercalation of mudstone and sandstone beds. The gamma-ray log response is generally lower than in other formations of the Mercia Mudstone Group, and close correspondence between the abundance of detrital illite and the overall gamma-ray values (excluding minor fluctuations) is evident in the Cropwell Bridge Borehole (Figure 28). The base of the formation is marked by a sharp upward decline in gamma-ray response within the Cotgrave Sandstone Member; this feature can be correlated across the district (Figure 29); (Figure 30) and into the Grantham district to the east (Berridge et al., 1999, fig 15 and 16). The Hollygate Sandstone Member at the top of the formation produces a similarly low response. Sonic logs have not been run through the formation in any boreholes in the district, but are available for the Fulbeck No. 1 Borehole of the Grantham district, as illustrated in (Figure 29).

Cotgrave Sandstone Member

Thismemberisapersistent,feature-formingunitcomprising pale greenish grey or yellowish grey, very fine to finegrained sandstone, interbedded with dark greenish grey mudstone. The earliest name known to have been applied to the member was ‘Cotgrave Place Skerry’ (unpublished BGSrecords),aftertheeponymousfarm[SK 6315 3712],where the member produces a marked topographical feature (Lowe, 1989a). Elliott (1961) made no reference to this earlier usage when introducing the name ‘Cotgrave Skerry’, an unfortunate choice because the unit does not crop out either in or near Cotgrave village, which is sited partly on the Hollygate Sandstone Member at the top of the formation. Nevertheless, the name Cotgrave Skerry Member was formalised by Warrington et al. (1980), and subsequently modified to Cotgrave Sandstone Member by Charsley et al. (1990).

The principal outcrop of the member runs along the steep, upper slopes of the river bluffs on the southeastern side of the Trent valley between Newton and East Stoke, where it is mappable as an ill-defined bench. Between West Bridgford and Radcliffe on Trent, the outcrop is discontinuous due to faulting; the member can be traced between faults as a marked bench or crest. Well-developed dip slopes are uncommon, but notable examples occur at Cotgrave Place [SK 6330 3700], Malkin Hill [SK 6550 4080] and north-west of Elston [SK 7500 4860]. Sandy clay soils formed on these dip slopes contain slabs of indurated dolomitic or siliceous sandstone locally brought up by ploughing.

Charsley (1989) recorded several sections through the Cotgrave Sandstone Member in the West Bridgford and Edwalton areas, the better sections occurring in former brick pits at West Bridgford [SK 5890 3616] and Wilford Hill (Plate 13). The member is also well exposed in the river cliff [SK 5405 3492] at Clifton, just outside the district to the south-west (Howard, 1989). Sporadic exposures occur along the main outcrop of the member between Newton and East Stoke; the most complete section is located along a sunken lane that descends the river cliffs to the northwest of Kneeton [SK 7087 4622]. The member was proved between depths of 80.4 and 84.9 m in the Cropwell Bridge Borehole, and was also cored in several site investigation boreholes along the A46 trunk road between Cotgrave and East Stoke (SK74NW/18 [SK 74272 47773], SK74SW/33 [SK 70087 41616], SK74SW/34 [SK 70882 42886], SK74SW/37 [SK 72257 44947]). Cores from one of these boreholes (SK74SW/34) are archived in the NGRC Core Store at the BGS, Keyworth. The member was also cored in several coal exploration and fault-proving boreholes in the Radcliffe on Trent area (Lowe, 1989a).

The outcrop and borehole sections show that the member consists of interbedded sandstone and mudstone in approximately equal proportions. The sandstone is typically very fine- to fine-grained and pale greenish grey when fresh, weathering to a yellowish grey when exposed. Sandstone beds have sharp bases and either sharp or gradational tops, and range from 0.05 to 2.5 m thick, with all sections containing at least one bed more than 0.5 m thick. Sedimentary structures within the sandstones are vaguely defined and commonly deformed due to postdepositional modification of the sandstone fabric by early diagenetic growth and dissolution of interstitial evaporite minerals. Traces of planar lamination, low-angle cross-stratification and current ripples remain in places. Samples from sandstone beds within the member in the Cropwell Bridge Borehole are classified petrographically as arkose or subarkose (Jones, 1993). Grains are mostly subrounded to rounded, and sorting is generally poor. Gypsum is the dominant cement, although thin beds cemented by dolomite or by quartz overgrowths are common. In surface sections, the gypsum cements are removed by groundwater solution, leaving a weakly cemented sandstone or uncemented sand. The more resistant dolomitic or siliceous beds stand out as ribs and are preferentially preserved as brash on dip slopes; these beds commonly contain small vugs produced by the solution of gypsum nodules. The thicker sandstone beds are probably composite, representing several discrete depositional events. They are laterally impersistent and may take the form of broad, shallow channels, although data are insufficient to determine their geometry and orientation. The interbedded mudstone is typically medium or dark greenish grey and commonly contains starved ripples of very fine- to fine-grained, weakly cemented sandstone. Diffuse, red-brown mottles occur in the mudstone in surface sections.

The member varies in thickness from 1.5 to 5.5 m, with the thickest developments occurring in the Bingham, East Bridgford and Flintham areas. It forms a distinctive geophysical log marker (Figure 29); (Figure 30) that can be correlated in the subsurface throughout the district and into the Grantham district to the east (Berridge et al. 1999) and the Melton Mowbray district to the south (Carney et al., 2004). The gamma-ray log response of the member is substantially lower than that of the underlying Gunthorpe Formation due to the low illite content of the mudstone and the presence of thick sandstone beds.

Beds between the Cotgrave and Hollygate sandstone members

The sequence between the Cotgrave Sandstone and Hollygate Sandstone members ranges from 36 to 40 m in thickness. At outcrop, the beds are marked by heavy, dark reddish brown or grey-brown soils. Several resistant beds of dolomitic or siliceous siltstone and very fine-grained sandstone in the lower half of the succession give rise to mappable cuesta features. A notably persistent dolomitic and siliceous sandstone unit occurs about 20 m above the top of the Cotgrave Sandstone Member, and forms a long dip slope to the south of Bingham, to the north of East Bridgford and at Syerston Airfield. This unit is exposed in several places along a ditch near Tythby Grange e.g. [SK 7079 3780]; [SK 7188 3821], where it consists of only 0.5 m of thinly bedded, dolomitic and siliceous, very fine-grained sandstone with mudstone partings. Large slabs of sandstone with common pseudomorphs after halite on their bases are ploughed up on the dip slopes. Resistant, feature-forming beds are less common in the upper half of the interval and are impersistent.

The beds between the Cotgrave and Hollygate sandstones are very poorly exposed and, except for the Cropwell Bridge Borehole, few detailed records remain of borehole provings. The best sections expose the lower part of the succession in a disused railway cutting at Bingham [SK 7012 3934] and in a sunken lane at Kneeton [SK 7087 4622]. Other sections are mostly restricted to freshly cleaned-out field drains and temporary excavations, and are typically highly weathered; examples in the West Bridgford area were described by Charsley (1989), in the Radcliffe on Trent area by Lowe (1989a) and Rathbone (1989c), and in the Car Colston area by Young (1992). The sections figured by Elliott (1961) from the former Edwalton and Wilford Hill brick pits are now highly degraded and obscured.

In the Cropwell Bridge Borehole (Figure 28), the lower half of the interval resembles parts of the underlying Gunthorpe Formation, with similar intercalations of heterolithic, structureless and deformed lithofacies. The principal difference is colour, the brown and dark green colours of the Edwalton Formation contrasting with the brighter red-browns and grey-greens of the Gunthorpe Formation. Sandstone beds of the heterolithic lithofacies are also more strongly cemented in the Edwalton Formation, and some are highly siliceous. The upper half of the interval is dominated by brown structureless mudstone and siltstone lithofacies with a few thin units of heterolithic lithofacies, but includes intervals of gypsiferous mudstone with a highly distinctive fabric. The mudstone is dominantly brown with diffuse dark green layers and mottles, and contains up to 30 per cent by volume of gypsum. The latter is preserved as small (up to 7 mm diameter) subspherical nodules (Plate 14) and is concentrated in layers up to 20 mm thick, folded into corrugations with an amplitude and wavelength of 50 to 80 mm. This lithofacies was also observed in cored site investigation boreholes for the A46 trunk road near Cotgrave (SK63NE/172) and Saxondale (SK63NE/188) and appears to be restricted, in the Nottingham district at least, to the upper half of the Edwalton Formation.

Hollygate Sandstone Member

Originally referred to as the ‘Hollygate Lane Skerries’ in borehole records in the BGS archives, this mappable unit of interbedded sandstone and mudstone was first systematically described as the ‘Hollygate Skerries’ by Elliott (1961). The more formal name Hollygate Skerry Member was applied by Warrington et al. (1980). The term Hollygate Sandstone Member was introduced by Charsley et al. (1990). Correlation of the member with the Dane Hills Sandstone Member near Leicester and the Arden Sandstone Formation farther west in the Midlands was inferred by Warrington et al. (1980).

The Hollygate Sandstone Member is a composite unit, consisting of up to six thick beds of pale greenish grey to brownish grey sandstone interbedded with red-brown and grey-green mudstone. The member typically forms a cuesta with a long, although undulatory dip slope, and gives rise to sandy loam soils with, on arable land, ploughedup blocks of weakly cemented, pale brown weathering sandstone with abundant small cavities. The base of the member commonly lies just below the top of the scarp, with higher beds cropping out in succession down the dip slope. The cuesta can be traced from Tollerton airfield and the eponymous Hollygate Lane and Hollygate Farm area east of Cotgrave, as far north-eastwards as Elston and Hawton, although the outcrop is substantially displaced by the Foss Bridge, Harlequin and Eakring–Foston faults. The member is very poorly exposed; small sections in Edwalton railway cutting [SK 5919 3547] were described by Charsley (1989), those south-east of Tollerton airfield [SK 6236 3577] by Lowe (1989a), and those south-east of Cropwell Butler [SK 6898 3615], [SK 6951 3605] by Lowe (1989b). Farther northeast, small sections were observed in field drains near Hawksworth [SK 7557 4309] and Top Green [SK 7663 4447] by Young (1992).

The member was penetrated in two cored boreholes along the A46 trunk road, SK63NE/172 and SK63NE/188, which proved 5.7 m and 5.4 m, respectively. The Cropwell Bridge Borehole (Figure 28) provides the best section, 6.1 m thick, consisting of sandstone and mudstone in approximately equal proportions. Sandstone occurs in six beds ranging from 0.2 to 0.9 m thick, with the thickest bed at the base. The sandstone beds strongly resemble those of the Cotgrave Sandstone Member in terms of composition, texture and sedimentary structures, although some beds are coarser in grain size. Gypsum is the dominant cement, the near-surface solution of which accounts for the mainly uncemented nature of the sandstone in surface sections. In contrast to the Cotgrave Sandstone Member, the interbedded silty mudstones are mainly reddish brown, with greenish grey patches. They form beds up to 0.6 m thick and resemble the structureless mudstone facies of the Gunthorpe Formation.

The Hollygate Sandstone Member corresponds with a pronounced gamma-ray low on borehole geophysical logs that can be correlated in the subsurface throughout the Nottingham, Grantham (Berridge et al., 1999) and Melton Mowbray (Carney et al, 2004) districts. The feature correlates with a minimum in the illite content and a corresponding maximum in the mixed layer chlorite/smectite content of the Mercia Mudstone Group clay mineral assemblage (Figure 28), and is accentuated by small troughs formed by individual sandstone beds. The base and top of the member cannot be precisely delineated on geophysical logs, without supporting lithological information from cores.

Surface mapping in the Tollerton, Radcliffe on Trent and Cropwell Butler areas indicates thicknesses ranging from 6.0 to 9.0 m. The member thins steadily north-eastwards from Bingham, with 4 to 5 m present in the Hawksworth area and 3 to 4 m around Elston and Hawton [SK 780 500]. This trend continues north-eastwards into the adjacent Grantham district, where only 2.65 m was proved in the Fulbeck No. 1 Borehole (Berridge et al., 1999; Figure 29).

The only fossils known from the Edwalton Formation in the district are palynomorphs recovered from immediately above the Cotgrave Sandstone Member in the Cropwell Bridge Borehole (Warrington, 1993a), and from the Cotgrave Sandstone Member in site investigation boreholes for the A46 road near East Bridgford (Warrington, 1994a) and Bingham (Warrington, 1994b). Samples from other stratigraphical levels in the formation were barren.

The palynological assemblages include the miospores Retisulcites perforatus and Echinitosporites iliacoides, which are considered to indicate a late Mid Triassic to earliest Late Triassic (Ladinian–early Carnian) age based on their ranges in independently dated Triassic sequences elsewhere in Europe. As noted above, the Hollygate Sandstone Member, at the top of the formation, is a probable correlative of the Dane Hills Sandstone near Leicester and the Arden Sandstone Formation of the west Midlands. The latter has yielded miospores of late Carnian (early Late Triassic) age (Old et al., 1991; Barclay et al., 1997).

Other miospore taxa present include Carnisporites spiniger, Porcellispora longdonensis, Aratrisporites tenuispinosus, Cucullispora cuneata, ?Samaropollenites speciosus, Protodiploxypinus doubingeri, P. gracilis, ?Ellipsovelatisporites plicatus, Staurosaccites quadrifidus, Cuneatisporites radialis, Triadispora obscura, T. plicata, Institisporites crispus, Angustisulcites klausii, ?Infernopollenites sulcatus, Illinites chitonoides, Ovalipollis pseudoalatus, Lunatisporites acutus and Striatoabieites balmei. However, bisaccate pollen grains are the dominant forms in the palynological assemblages. The association reflects a contemporary land flora that consisted largely of gymnosperms, producing the bisaccate pollen, but also included lycopsids, which produced the monolete spore Aratrisporites, a bryophyte, indicated by the spore Porcellispora longdonensis, and ferns. The fern and bryophyte spores suggest damp habitats. Remains of Plaesiodictyon mosellanum, a colonial chlorophycean alga, were also recovered and are indicative of brackish water conditions in an estuarine or similar environment (Wille, 1970).

Depositional environment

Like those of the Gunthorpe Formation, the rocks of the Edwalton Formation have been interpreted as the deposits of a saline playa mudflat (Mader, 1992), with the Cotgrave and Hollygate Sandstone members representing brief incursions of a weakly braided fluvial system into the region. Sandstone bed geometry in the Cotgrave Sandstone Member indicates deposition by episodic flash floods within broad, shallow channels. Such geometry cannot be reliably inferred in the Hollygate Sandstone due to the paucity of sections, but the strong lithological similarity to the Cotgrave Sandstone implies similar depositional environments. The suggestion that the Hollygate Sandstone represents sheet flood deposits (Aljubouri, 1972) on the grounds of lateral persistence of individual sandstone beds, cannot be corroborated. Mader (1992) suggests that both these fluvial incursions were induced by enhanced precipitation in source areas, the Hollygate Sandstone Member perhaps correlating with a widespread, late Carnian ‘pluvial’ event postulated by Simms and Ruffell (1990). Warrington and Ivimey-Cook (1992) suggest that this regionally increased precipitation, erosion and run-off in the late Carnian was triggered by a relative rise of sea level and expansion of the contemporary Tethyan Ocean. Although the Hollygate Sandstone Member contains no indication of marine conditions, this interpretation is reinforced by strong evidence of a marine connection in the estuarine and deltaic facies of the equivalent Arden Sandstone Formation of the central Midlands (Warrington and Ivimey-Cook, 1992).

Cropwell Bishop Formation

Elliott (1961) subdivided the strata between the Edwalton Formation and the Penarth Group (then the ‘Rhaetic’ beds) into the ‘Trent’ and ‘Parva’ formations, the latter including the distinctive ‘Tea-green Marls’ in its upper part (Table 14). Warrington et al. (1980) introduced the term Blue Anchor Formation for the ‘Tea-green Marls’ and renamed the remaining, lower part of the Parva Formation as the Glen Parva Formation. The boundary between the Blue Anchor and ‘Glen Parva’ formations is readily mappable at surface, but that between the ‘Glen Parva’ and ‘Trent’ formations, defined on characters recognised in cored boreholes (Elliott 1961), cannot be recognised between the sporadic surface sections. Charsley et al. (1990) therefore amalgamated the ‘Trent’ and ‘Glen Parva’ formations into the Cropwell Bishop Formation (Table 14). The name is derived from the village in the south central part of the district, where much of the formation was formerly exposed in now-backfilled gypsum quarries (Lowe, 1989b). The lower 28.4 m, comprising core from 7.4 to 35.8 m in the Cropwell Bridge Borehole (Figure 28), and a composite section of the entire formation (about 52 m) comprising cores from two closely spaced boreholes (SK63SW/36 and 38) at Keyworth (in the adjacent Melton Mowbray district), are held in the NGRC core store of the BGS at Keyworth.

The formation crops out to the south-east of the River Trent. Typically, it forms low-lying ground and much of it is covered by fluvial and lacustrine deposits of Quaternary age. The most southerly occurrences, between Edwalton and the Foss Bridge Fault near Cropwell Bishop, are highly faulted and there is a larger, less disturbed outcrop up to 2.5 km wide that extends north-eastwards from the Foss Bridge Fault to Newark. The formation is highly gypsiferous throughout, and the near-surface solution of gypsum, together with the paucity of dolomitic and siliceous sandstone beds, contributes to the low erosional resistance of the formation. Gypsum solution since the late Devensian cold period locally lowered the land surface by up to 3 m below local drainage base level in some areas, for example east of Nottingham Airport (Tollerton), north-east of Cropwell Bishop, and to the north of Bingham, resulting in the formation of lakes and bogs and the deposition of lacustrine clays, peat and shell marl. Between Cropwell Bishop and Newark, the outcrop is exploited by all the principal surface drainage courses, notably the rivers Devon, Smite and Whipling. The outcrop is urbanised in the Newark–Balderton area and, to a lesser degree, at Cropwell Bishop and around Cotgrave.

Where free of Quaternary deposits, the formation gives rise to heavy, red-brown, silty clay soils. Sporadic beds of dolomitic siltstone and very fine-grained sandstone within the formation (notably the Windmill Hill Sandstone, see below) locally form low cuesta features, although none are traceable for any great distance. The lower boundary of the formation lies at the foot of the dip slope formed on the underlying Hollygate Sandstone Member of the Edwalton Formation. The upper boundary is mapped at the change to the grey-green, silty clay soils characteristic of the overlying Blue Anchor Formation. This boundary typically lies at or near the base of the scarp slope capped by the Barnstone Member at the base of the Lias Group.

During the survey, the upper part of the formation, corresponding to the Newark Gypsum (see below), was exposed in four opencast gypsum mines. Sections of the upper part of the formation were observed in the Cropwell Bishop Mine [SK 6780 3534] (see also Lowe, 1989b) and at Bantycock Pit (Plate 15), together with cored sections of the formation in boreholes either in or close to the district. A comparatively poor exposure in Kilvington Quarry [SK 7900 4300] was described by Young (1992), but a former, more complete section from there is illustrated in(Plate 16). Lamplugh et al. (1908) published sections in former gypsum quarries around Beacon Hill, east of Newark; a few small exposures remain [SK 8144 5451]; [SK 8136 5438] (Waters, 1992). Apart from gypsum quarries, the formation is very poorly exposed. Lowe (1989a) recorded small sections in ditches [SK 6244 3619]; [SK 6626 3542]; [SK 6262 3517] near Nottingham Airport, and in the partially infilled Windmill Hill Brickpit [SK 6437 3574], near Cotgrave. Other sections were noted in the banks of the rivers Smite and Whipling [SK 7524 3896]; [SK 7501 3826] east of Aslockton (Glover, 1992), and along a field drain [SK 7623 4398] to [SK 7638 4386] northeast of Hawkesworth (Young, 1992). Nodular gypsum is exposed in the banks of the River Smite south of Shelton [SK 7766 4375], and the River Devon west of Cotham Grange [SK 7817 4638]. A temporary section [SK 7696 4110] to [SK 7713 4100] at Orston showed red-brown mudstones with chaotic collapse-type structures suggestive of near-surface solution of gypsum (Young, 1992).

The formation contrasts with those lower in the Mercia Mudstone Group in that it is thicker in the south-western part of the district than in the north-eastern part. About 52 m was proved in a composite section of three cored boreholes at Keyworth [SK 615 315], whereas the mapped thickness in the area around the Cropwell Bridge Borehole site is estimated to be 48 m. In contrast, a thickness of 33 m was proved in the Redmile No. 2 Borehole in the south-eastern corner of the district, and the Cox’s Walk Borehole in the south-western corner of the adjacent Grantham district proved 29 m (Figure 30). In the adjacent Melton Mowbray district, the formation is thicker, 60 to 70 m in the west around Rempstone and East Leake, but farther north and east it is generally in the range 30 to 40 m (Carney et al., 2004).

The formation consists largely of red-brown or brown mudstone, resembling the structureless lithofacies described from the Gunthorpe Formation (see above). Grey-green spots and ‘fish-eyes’ are common. Elliott (1961) recorded ‘vein-type breccias’ and scattered aeolian sand grains in the lower half of the formation. Beds of indurated, grey-green siltstone and mudstone with pseudomorphs after halite are generally rare in this formation, although a few examples locally form mappable cuestatype features, as to the north of Barnstone [SK 735 364] and at Flawborough [SK 785 432]. Up to three beds of dolomitic sandstone, resembling those of the Hollygate Sandstone Member in lithology, occur 10 to 12 m above the base of the formation. This grouping of beds was collectively termed the ‘Windmill Skerry’ by Elliott (1961), and is renamed as the Windmill Hill Sandstone in this memoir (Figure 28). An indurated, feature-forming, red-brown dolomitic siltstone occurs 10 to 12 m below the top of the formation in the Cropwell Bishop area (Lowe, 1989b).

Several beds of dull greenish grey, laminated mudstone with buff-grey, dolomitic patches, ranging from 0.1 to 0.75 m in thickness, occur in the upper part of the formation, between the top of the Newark Gypsum (see below) and the base of the Blue Anchor Formation (Elliott, 1961).

These are interbedded with the structureless, red-brown mudstone typical of the rest of the Cropwell Bishop Formation. Elliott (1961) regarded the fish remains and bone fragments recorded from these laminated beds as a sufficient basis for their separation as the ‘Parva Formation’.

Taylor (1983) identified two distinct, stratigraphically significant clay mineral suites within the formation, results that have been replicated by Bloodworth and Prior (1993). The lower half of the formation is characterised by an assemblage dominated by mixed-layer chlorite/smectite with subordinate illite and chlorite (Figure 28). Sepiolite occurs just above the Hollygate Sandstone Member (Bloodworth and Prior, 1993). The upper half is characterised by an illite-dominated assemblage with subordinate mixed-layer chlorite/smectite and chlorite. Taylor (1983) used these contrasting assemblages to define two subdivisions, the Fauld and Hawton members, of the former ‘Trent Formation’. Apart from the clay mineralogy, there are no lithological characteristics to distinguish these units in surface sections or cores, and the boundary between them is not mappable at the surface. However, this boundary can be identified in geophysically logged boreholes, because the proportion of potassium-rich illite within the clay mineral assemblage strongly influences the gamma-ray log response. Gamma-ray values gradually increase upwards in the lower half of the formation, with a sharp increase at about the middle of the formation (Figure 28), (Figure 29), (Figure 30), corresponding to the boundary between the ‘Fauld’ and ‘Hawton’ members of Taylor (1983). The gamma-ray log profile is interrupted at several levels throughout the formation by sharp troughs representing beds of gypsum; the Windmill Hill Sandstone produces one or two less pronounced troughs. The formation has a generally lower gamma-ray signature than the overlying Blue Anchor Formation but the boundary is not clearly marked on gamma-ray logs. Borehole sonic logs have not been run through the formation in the district, but are available for the Fulbeck No. 1 Borehole of the Grantham district, as illustrated in (Figure 29).

Gypsum is abundant throughout the formation, occurring as nodules, veins and beds. Nodules occur in a wide range of sizes, from a few millimetres to over 2 m in diameter, although the larger nodules can usually be seen to have formed from the coalescence of smaller ones. Nodular gypsum is typically ‘massive’, white and semitransparent to opaque; ‘pink’ and ‘blue’ colours seen in some nodules are formed by impurities of red-brown and grey-green mud particles. Larger inclusions of mudstone are common in the more sizeable nodules and sometimes form ‘chicken wire’ fabric. Some nodules are anhydritecored. The nodules may have resisted compaction, or have acted as nuclei for gypsum precipitation, causing disruption to the regularity of bedding within the formation.

Gypsum veins are formed either of satin spar or of small, coalesced nodules. Veins of the latter type are generally 3 to 20 mm wide and commonly occur at a high angle to the bedding. Individual veins show both upward and downward terminations and are commonly curved in profile view. Satin spar veins are usually 1 to 10 mm wide, subhorizontal, and crosscut the older nodular veins. Larger, vertically orientated shrinkage cracks, up to 50 mm wide and filled with nodular gypsum, occur at some levels; examples observed in plan view at Bantycock Mine form large polygonal networks and taper downwards to a depth of up to 1 m. Similar, sulphate-filled desiccation cracks have been described from recent playa environments (Hardie et al., 1978). The smaller nodular veins may also fill shrinkage cracks, although the variety of orientations and the upward terminations imply that these cracks formed by in situ synaeresis within the sediment rather than by subaerial desiccation (Plate 17).

Fossils recorded from the district comprise fish scales and bone fragments (Elliott, 1961) and sporadic pollen grains. Elliott (1961) used the appearance of fish remains above a sharp, irregular boundary visible in borehole cores to separate his ‘Trent’ and ‘Parva’ formations, although as previously discussed this boundary is not mappable. A possible specimen of Classopollis,a pollen genus that ranges from the Late Triassic (Norian–Rhaetian) into post-Triassic deposits, was recovered from 1.5 m below the top of the formation at Bantycock Mine (Warrington, 1993c; Table 15a). Samples from other stratigraphical levels in the Cropwell Bridge and other boreholes proved devoid of determinable or stratigraphically useful palynomorphs. The Cropwell Bishop Formation overlies the Hollygate Sandstone Member, which is correlated with the Arden Sandstone Formation of late Carnian age, and is succeeded by the Blue Anchor Formation, considered to be at least partly Rhaetian. Its age is therefore considered to be post-Carnian, Norian to early Rhaetian.

Tutbury and Newark gypsum beds

Gypsum has been mined from two main levels in the Cropwell Bishop Formation of the East Midlands. The Tutbury Gypsum lies just below the boundary between the ‘Fauld’ and ‘Hawton’ members of Taylor (1983). This gypsum is best developed in the Burton-on-Trent area of Staffordshire and the Barrow-on-Soar area of Leicestershire (Carney et al., 2004), where it forms a near continuous bed up to 4 m thick. Nearer to Nottingham, the Tutbury Gypsum has been mined at Gotham and East Leake, where the bed is still up to 3 m thick but is less continuous and may occur as large nodules separated by highly gypsiferous mudstone. In the Nottingham district, the Tutbury Gypsum correlates with structureless mudstone with vein and nodular gypsum of no economic value, present at a depth of approximately 15 m in the Cropwell Bridge Borehole (Figure 28). Farther south, the Tutbury Gypsum forms a recognisable datum on geophysical logs across the entire Melton Mowbray district, but as a discrete gypsum bed it is thickly developed and commercially important only in the south and west (Carney et al., 2004).

Gypsum extraction in the Nottingham district has concentrated on the Newark Gypsum (Chapter 2), a series of mostly thin, gypsum-bearing beds spanning much of the upper half of the formation. Individual beds or ‘seams’ may be nodular (‘balls’), lenticular (‘bullets’ or ‘cakes’) or semi-continuous, and are spread over a vertical interval of up to 18 m. Interbedded mudstone is of the structureless type and contains many small nodules and veins of gypsum. The base of the Newark Gypsum interval lies no more than 4 to 5 m above the level of the Tutbury Gypsum: the top lies up to 10 m below the base of the Blue Anchor Formation in the Cropwell Bishop area but only 2.8 m below that datum at Bantycock Mine, near Newark. Up to 12 individual gypsum-bearing seams have been worked in any one quarry. Names have been applied to the more productive seams, although nomenclature varied between different quarry operators. The scheme adopted by British Gypsum plc (Chapter 2) has been applied across the district from Cropwell Bishop to Newark, although many beds are known to be impersistent and some correlations may be doubtful. Seams in the lower half of the sequence are mostly less than 30 cm thick but tend to form the more continuous and persistent beds, whereas seams in the upper half are less continuous. The uppermost ‘seams’ at Bantycock and Kilvington pits (Plate 15) and (Plate 16) comprise large, discontinuous nodular masses up to 2 m thick. The Newark Gypsum interval has been identified on geophysical logs across the entire Melton Mowbray district to the south, although only up to three discontinuous beds are discernible using such techniques (Carney et al., 2004).

Gypsum has largely been removed in the shallow subsurface through solution by meteoric groundwaters. The solution zone typically extends to a depth of 2 to 10 m, increasing to 30 m in the vicinity of faults or heavily jointed zones (Elliott, 1961). Hazards associated with gypsum solution are discussed in Chapter 2.

Depositional environment

Isotopic analysis by Taylor (1983) suggested that each of the individual gypsum beds within the Newark Gypsum represented a discrete marine incursion. The Tutbury Gypsum, however, has a different isotopic signature, suggesting that the source brines were charged with sulphate derived from erosion of Lower Carboniferous anhydrites around the margin of the Charnwood Massif (Taylor, 1983). Based on the abundance of gypsum, Mader (1992) also suggested a greater degree of marine influence during the deposition of the Cropwell Bishop Formation than during deposition of lower formations in the Mercia Mudstone Group. He concluded that the formation was deposited in a coastal sabkha setting, with gypsum precipitated from shallow water bodies and interstitial brines fed by periodic influxes of seawater. As with similar facies elsewhere in the Mercia Mudstone Group, the structureless mudstone accumulated on a damp and uneven mudflat surface by accretion of wind-blown mud pedicles and sand grains (cf. Taylor et al., 1963; Arthurton, 1980). Jefferson et al. (2002) compared the structureless mudstone of the Cropwell Bishop Formation to ‘parna’, a recent loess-like aeolian deposit composed of silt-grade pellets of clay deposited in the semi-arid Murray–Darling Basin of Australia. The laminated mudstones with fish and bone fragments were probably deposited in fairly long-lived, brackish water lakes.

Blue Anchor Formation

The Blue Anchor Formation, named by Warrington et al. (1980), forms the highest unit in the Mercia Mudstone Group in England and Wales. Throughout the English Midlands, it consists of near-uniform, grey-green dolomitic mudstone and siltstone, formerly known as the ‘Tea Green Marl’ (or ‘Tea-green Marl’). The type section of the formation is in west Somerset (Warrington and Whittaker, 1984), where a more lithologically heterogeneous development occurs. In the Nottingham district, the Blue Anchor Formation corresponds to the upper part of the ‘Parva Formation’ of Elliott (1961; Table 14).

The formation has a narrow outcrop that extends from Cropwell Bishop to Newark but is broken in places by faulting. The outcrop typically occupies the concave lower slopes of a scarp capped by resistant limestones of the Barnstone Member (Lias Group, Chapter 7). The formation gives rise to yellowish grey or greenish grey, stiff, silty clay soils that contrast with the reddish brown soils formed on the underlying Cropwell Bishop Formation and the very dark grey-brown, ‘sticky’ clay soils of the overlying Westbury Formation (Penarth Group, see below). Exposure is generally very poor, although complete sections were well exposed at the time of survey in gypsum quarries at Cropwell Bishop [SK 678 353] and south of Balderton [SK Staple Pit, 805 492; Bantycock Pit, 810 497]. The quarries at Cropwell Bishop and Staple Pit are now exhausted, and in 1998 were being backfilled. Complete cored sections of the formation were also proved in site investigation boreholes on the A46 trunk road to the east of Cotgrave, just outside the district.

The formation consists of pale greenish grey, dolomitic mudstone or siltstone; some dark greenish grey, pyritic laminae are present, particularly near the base, and scattered, coarse, aeolian quartz sand grains have been recorded (Elliott, 1961; Sykes et al., 1970). In fresh sections, the beds have a blocky or conchoidal fracture, and although superficially structureless, have an indistinct ‘wispy’ lamination that is moderately to strongly deformed or convoluted (Plate 18). Small angular clasts of early authigenic, cream-coloured dolomite are common, and were presumably brecciated by the same deformation processes that disturbed the host mudstone. These textures and structures may reflect syndepositional sediment deformation caused, as in the underlying formations of the Mercia Mudstone Group, by repeated wetting and drying of the substrate. However, other indications of evaporation, such as desiccation cracks, pseudomorphs after halite and primary gypsum nodules, are absent. Some of the convolution is more reminiscent of the penecontemporaneous slumps in the Cotham Member (Penarth Group; see below), which have been interpreted as the product of seismic shock. In addition, the Blue Anchor Formation and overlying Penarth Group show features indicating that they have been deformed together as a result of very large-scale slumping or sediment loading (Plate 18). Nodular layers of dolomitic mudstone, up to 5 cm thick, occur at several levels; these postdate deformation of the mudstones and are probably of diagenetic origin.

The lower boundary is placed at the prominent colour change from the red-brown mudstone of the underlying Cropwell Bishop Formation. When viewed from a distance in quarry faces, the boundary appears remarkably sharp and planar (Plate 15). Seen in closeup, however, the colour change is slightly diffuse over a vertical interval of 3 to 5 mm and is not accompanied by a change in sediment texture or grain-size. This diffuse colour change is due to reduction of the uppermost part of the underlying Cropwell Bishop Formation. The upper boundary is sharp and disconformable (Plate 15); a bored and slightly channelled surface on the grey-green mudstone is overlain by dark grey to black, fissile mudstone of the Westbury Formation (Penarth Group; see below). At Bantycock Pit, narrow fissures or joints filled with black mudstone penetrate more than 2.5 m down into the Blue Anchor Formation from the base of the Westbury Formation.

There are no boreholes through the formation in the Nottingham district that have both a cored section and geophysical logs. The geophysical log character of the formation is therefore illustrated from the cored Fulbeck No. 1 Borehole (Figure 29) in the adjacent Grantham district (Berridge et al., 1999). Both gamma-ray and sonic logs of the formation show a more weakly serrated, blocky response than the underlying Cropwell Bishop Formation, although the boundary is not clearly defined. The upper boundary of the formation is marked by a sharp peak on the gamma-ray log and a corresponding sharp decline in sonic velocity.

The thickness of the formation is 6 to 7.5 m in the Cropwell Bishop area (Lowe, 1989b), about 5 m in the Redmile area (Glover, 1992), 4.5 m in the Orston and Staunton area (Young, 1992), 5.2 m at Bantycock Pit, Balderton, and 6 m in the north-eastern corner of the district (Waters, 1992). Carney et al. (2004) recorded similar thicknesses across the Melton Mowbray district to the south, with minima and maxima of 3 m and 10 m.

Scattered fish scales have been recorded from the Blue Anchor Formation in the Nottingham district and in the northern part of the adjoining Melton Mowbray district (Elliott, 1961; Ivimey-Cook and Elliott, 1969). The upper surface of the formation is penetrated by borings that reflect colonisation of the Blue Anchor Formation substrate after the onset of Penarth Group deposition. A very sparse palynomorph assemblage from the lowest metre of the formation at Bantycock Pit, Balderton (Warrington, 1993c; Table 15b) includes sporadic dinoflagellate cysts (Rhaetogonyaulax rhaetica) indicative of a marine environment. Assemblages from the upper 2 m of the formation at that site are richer and more diverse; they are dominated by miospores, but include algal and other remains. The miospore associations are dominated by circumpolles (Classopollis spp.), produced by cheirolepidacean conifers, and bisaccate pollen, principally Ovalipollis spp., together with moderate numbers of Rhaetipollis germanicus and Ricciisporites tuberculatus; most other miospore taxa are represented by very few specimens (Table 15a). The sparse associations of algal and other remains from this level are dominated by dinoflagellate cysts (Dapcodinium priscum, Rhaetogonyaulax rhaetica and Suessia swabiana), but include rare specimens of the acritarch genera Cymatiosphaera and Micrhystridium and test linings of foraminifera. Suessia swabiana has not been found above this level at Bantycock (Table 15b). The assemblages are indicative of a Rhaetian (Late Triassic) age and a position within the Rr dinoflagellate cyst biozone of Woollam and Riding (1983); they are comparable with those recorded from the same stratigraphical level in a borehole at Bunny, in the adjacent Melton Mowbray district (Morbey 1975).

Depositional environment

The Blue Anchor Formation is thought to reflect a transition from a supratidal to a low-energy intertidal sabkha, prior to the main marine transgression that marked the onset of deposition of the overlying Westbury Formation (Warrington and Whittaker, 1984; Warrington and Ivimey-Cook, 1992). An alternative interpretation (e.g. Mayall, 1981; Taylor, 1983) is that deposition occurred in a low-salinity, lacustrine environment. A lack of gypsum suggests less evaporative conditions and less saline groundwater than during the deposition of lower formations in the Mercia Mudstone Group. A general increase in marine influence during the deposition of the formation is, however, indicated by oxygen isotope values (Taylor, 1983) and the increasingly diverse assemblages of marine palynomorphs (Table 15b). The grey-green colour has been regarded as primary (e.g. Dunham in Stevenson and Mitchell, 1955) or the result of secondary reduction of primary red beds (e.g. Elliott, 1961). Evidence of marine influence, the abundance of organic remains and pyrite, and the general lack of evaporitic features, such as salts and desiccation cracks, all point to an amelioration of the arid, highly oxidising conditions that prevailed during deposition of the underlying red beds. This, together with the regularity of the base of the formation, supports a primary origin for the green coloration.

Penarth Group

The Penarth Group (Warrington et al., 1980) comprises the Westbury and overlying Lilstock formations, both of which crop out in the district. Two members were recognised in the Lilstock Formation by Warrington et al. (1980), but only the lower, Cotham Member is consistently present in the East Midlands; the overlying Langport Member is thin and impersistent (Kent, 1953, 1968b, 1970; Swift, 1989, 1995a). The group is Rhaetian (Late Triassic) in age (Warrington et al., 1980).

The group crops out in a narrow belt, up to 250 m wide, in the southern and eastern parts of the district, between Cropwell Bishop and Newark. Faulting displaces the group around Cropwell Bishop and between Flawborough and Cotham. It is largely masked by Quaternary deposits in the Cotham–Beacon Hill (Newark) area. The outcrop is characterised by ‘sticky’ clay soils, with either a dark grey-brown (on the Westbury Formation) or an olive green-grey tint (on the Cotham Member). Exposure is usually poor; Wilson (1882), Lamplugh et al. (1908) and Kent (1953) published records of former sections, and good sections were available during the survey in active gypsum workings at Cropwell Bishop and south of Balderton. A section in Barnstone railway cutting, described by Sykes et al. (1970), lies within a Site of Special Scientific Interest (Table 4); it is usually in an overgrown state and only fragmentary exposures were visible at the time of survey. Complete cored sections of the group were also proved in site investigation boreholes on the A46 trunk road to the east of Cotgrave, just outside the district. Other boreholes penetrate the group in the south-east of the district (Figure 30), but none have core descriptions.

On geophysical logs, a peak on the gamma-ray trace marks the base of the group, and the top is placed at a sharp reduction in gamma-ray response. The gamma-ray profile is less serrated than those produced by the units above and below (Figure 30). No sonic logs are available from the Nottingham district, but in the Fulbeck No. 1 Borehole of the Grantham district (Figure 29) (Lott and Warrington, 1988), the base is marked by a sharp reduction in velocity compared with the Blue Anchor Formation below, and the top is placed below a strong increase in sonic velocity. This last feature corresponds to the lowest limestone in the overlying Barnstone Member, the basal unit of the Scunthorpe Mudstone Formation (Lias Group, Chapter 7). Low sonic velocities in the lower part of the group correspond broadly with the Westbury Formation; higher velocities characterise the overlying Cotham Member of the Lilstock Formation.

Both formations of the group consist largely of grey to dark grey mudstone. The boundary between the Westbury Formation and the overlying Cotham Member is defined by subtle changes in colour, sedimentary structures and carbonate content. It can be recognised in fresh exposures and borehole cores, but is not usually traceable with precision at outcrop.

Thickness data are insufficient for the construction of an isopach map for the group. Thickness variations do, however, correspond broadly with those documented regionally by Kent (1968b). The group is 14.1 m thick at Bantycock gypsum mine [SK 810 497]; it thins southwestwards along the outcrop to between 5.5 and 8.5 m in the Orston–Staunton area (Young, 1992), and 8.5 to 9 m in Barnstone railway cutting [SK 739 358] (Sykes et al., 1970). The group is 12.6 m thick in borehole SK63NE/168 [SK 6635 3509] near Cotgrave; in northwestern parts of the adjacent Melton Mowbray district it averages 9.1 m (Crofts, 1989a, b). Thicknesses of 4 to 5 m proved in boreholes around the south-eastern corner of the Nottingham district accord with a zone of thinning, noted by Kent (1968b, p.179), between Leicester and Sleaford. These thickness variations of the Westbury Formation explain much of the variation within the group as a whole. In the adjoining Melton Mowbray district, however, the group thins southwards and the Cotham Member is locally missing (Carney et al., 2004).

Westbury Formation

The Westbury Formation is a thin but distinctive unit that forms the lower part of the Penarth Group throughout much of the British Isles (Warrington et al., 1980). In the East Midlands, it corresponds with the ‘Lower Rhaetic’, ‘Black Shales’ or ‘Avicula contorta Beds’ of earlier authors (Berridge et al., 1999; table 5). Typically, it crops out in the middle part of a scarp capped by resistant limestones of the Barnstone Member of the Lias Group, and is characterised by ‘sticky’, dark greybrown soils with a ‘rusty’ tint. Exposure is generally poor. During the survey, the best sections were available in gypsum mines at Cropwell Bishop [SK 676 353] and south of Balderton, Staple Pit, [SK 805 492]; Bantycock Pit, [SK 810 497]. The quarries at Cropwell Bishop and Staple Pit are now worked out and backfilled. Lamplugh et al. (1908, p.56) and Johnson (1950) recorded former exposures in Beacon Hill Quarry around [SK 813 538], east of Newark.

The formation consists of dark grey to black, platy or fissile mudstone (Plate 15); (Plate 18) with very thin laminae and beds of coarse siltstone or very fine-grained sandstone. It usually weathers to ‘rusty’ grey clay, commonly with a yellow sulphurous tint produced by the breakdown of pyrite. ‘Bone beds’, mostly thin remanié layers with abundant vertebrate remains, phosphatic nodules and coprolites, are present at several levels; the most persistent lies between 0.6 and 1.4 m above the base of the formation and has been recorded at several localities in the district (see below). Macrofossils are scarce in the beds below this level, but the overlying beds contain a diverse marine macrofauna dominated by bivalves such as Rhaetavicula contorta, Protocardia rhaetica and Eotrapezium concentricum. Ichnofossils, principally Chondrites and Teichichnus, are common, but tend to be concentrated at a few discrete levels. Palynomorph assemblages (Table 15A) and (Table 15B) are dominated by miospores but include algal and other remains.

The formation ranges in thickness from 5 to 7 m in the north-east of the district (Waters, 1992), and is 6.1 m thick in borehole SK63NE/168, near Cotgrave, and only 2.5 m at Barnstone [SK 739 358]. It is likely to be thinner still in the south-east corner of the district, where the Penarth Group as a whole is attenuated (see above) and the Westbury and Lilstock formations cannot be differentiated on geophysical logs. In the Melton Mowbray district to the south, the Westbury Formation thins southwards to around 2 m in the Asfordby area (Carney et al., 2004).

The stratigraphy and lithology of the formation at five localities in the district are illustrated in (Figure 31). The best section, and the one logged in greatest detail, was seen in Bantycock gypsum pit (Plate 15); (Plate 18) near Balderton. Three sedimentologically and faunally distinct units, A to C in ascending order, were distinguished in this section and are recognisable in most of the others (Figure 31). The following descriptions relate to the Bantycock section, unless otherwise indicated.

Unit A

Unit A is 1.2 and 1.35 m thick at Bantycock and Cropwell Bishop mines, respectively, and about 1.2 m at Staple Pit mine (Martill and Dawn, 1986). It corresponds to the ‘Pre-Bone Bed Black Shale’ (0.6 m) at Barnstone railway cutting (Sykes et al., 1970). Unit A consists largely of dark grey to black fissile mudstone with laminae or, less commonly, discontinuous lenticles, 0.5 to 10 mm thick, comprising coarse, micaceous siltstone or very fine-grained sandstone. Internally, individual silt or sand laminae show normal (upward fining) grading or, less commonly, planar lamination, low-angle cross-lamination or wave ripple lamination. Indistinct bioturbation occurs locally. Pyrite is common as small irregular nodules or as cement within the sandstone. The lower boundary of the unit is sharp and disconformable. Burrows (including forms similar to Arenicolites and Zoophycos), borings, and desiccation cracks filled with dark grey Westbury Formation mudstone penetrate several centimetres down into the underlying Blue Anchor Formation. The basal 50 mm of the unit consists of a distinctive bluish grey claystone with a ‘soapy’ feel, and contains small angular clasts of Blue Anchor Formation mudstone. The basal claystone is overlain by up to 15 mm of very hard, fine- to medium-grained, siliceous, pyritic sandstone. Unit A contains a very sparse, low-diversity bivalve fauna (Table 16), together with coprolites and scattered vertebrate remains, the last being most common in the basal claystone. Palynomorph assemblages from this unit at Bantycock gypsum pit (Table 15A) and (Table 15B) are comparable with, but slightly more diverse than those from the top of the Blue Anchor Formation; a considerable increase in the relative abundance of Ricciisporites tuberculatus occurs in the highest sample from this unit.

Unit B

Unit B corresponds to the ‘bone bed’ described from Staple Pit mine (Martill and Dawn, 1986) and Barnstone railway cutting (Sykes et al., 1970), and probably to that recorded by Harrison (in Jukes-Browne, 1885) in the railway cutting west of Elton and Orston station [SK 7655 4007]. It is characterised by the presence of abundant fish and reptile remains. The thickness averages 0.16 m at Bantycock, with slight variation along the section. The base and top of the unit are marked by low-angle cross-laminated or wave ripple laminated, poorly sorted, fine- to medium-grained, pyritic sandstone with mudstone partings. The middle part of the unit consists of grey, argillaceous siltstone, intensively burrowed by Chondrites, Teichichnus and horizontal Planolites-like traces (Plate 19). Vertebrate remains are common throughout the unit but are concentrated, along with rolled, phosphatised coprolites and granules of coloured, translucent quartz, in lags associated with the laminated sandstones at the base and top. The upper laminated sandstone bed was not recorded at Staple Pit mine or Barnstone railway cutting, where the unit averages 0.15 m and 0.08 m thick, respectively. Vertebrate faunas from these localities were documented by Sykes (1971, 1974a, b, 1979), Sykes et al. (1970) and Martill and Dawn (1986).

Unit C

Unit C is 3.8 m thick at Bantycock gypsum pit; at Barnstone cutting it includes the ‘Black Shale Beds’ and ‘Sandy Beds’ of Sykes et al. (1970). It resembles Unit A in lithology but has some thicker beds (up to 0.05 m) of very fine-grained sandstone with wave ripple lamination. Calcareous septarian nodules occur at a few horizons. The macrofauna (Table 16) is richer and more diverse than that of Unit A. Monospecific shell pavements, containing numerous disarticulated bivalve shells of a single species, and of similar size, occur on many bedding planes. Bioturbation, represented by Chondrites, Teichichnus and indeterminate horizontal pyritic tubes, occurs at a few discrete levels, mainly in the upper half of the unit. Vertebrate remains are scattered throughout, but tend to be more abundant in the bioturbated levels. The upper boundary of the unit is marked by a sharp subtle lithological change to the paler grey, less well-laminated, calcareous mudstone of the Cotham Member. Palynomorph assemblages from this unit at Bantycock gypsum pit (see (Table 15A) and (Table 15B)) are comparable with those from Unit A but become more diverse upwards; the dinoflagellate cyst Rhaetogonyaulax rhaetica occurs in much greater numbers in this unit than in Unit A.

In geophysical logs of the Fulbeck No. 1 Borehole in the Grantham district (Lott and Warrington 1988; Berridge et al., 1999), the base of the formation is marked by a prominent high gamma-ray peak and a sharp reduction in sonic velocity. The upper boundary is not clearly marked on gamma-ray logs but may be broadly indicated by an uphole increase in sonic velocity (Figure 29).

Palynomorph assemblages from the formation at Bantycock gypsum pit (Table 15A) and (Table 15B) are comparable with those recorded from boreholes in the Melton Mowbray district (Orbell, 1973, as reviewed in Carney et al., 2004; Morbey, 1975; Fisher, 1985). Assemblages from Unit A at Bantycock are similar in character and composition to those from the uppermost Blue Anchor Formation there, but become slightly more diverse upwards. They are dominated by miospores, principally Classopollis torosus, Ovalipollis spp., Rhaetipollis germanicus and Ricciisporites tuberculatus, the last showing a considerable increase in relative abundance in the highest sample from the unit (Table 15a). Taxa that appear in Unit A at Bantycock include the trilete spores Perinosporites thuringiacus and Polycingulatisporites bicollateralis and the bisaccate pollen Quadraeculina anellaeformis. This association persists upwards into Unit C where additional taxa, including Densosporites fissus, Ephedripites tortuosus,but Perinopollenites elatoides, Tsugaepollenites ? pseudomassulae and representatives of the genera Osmundacidites, Stereisporites and Todisporites appear in small numbers. Algal associations from Unit A (Table 15b) include Beaumontella langii, definite Cleistosphaeridium mojsisovicsii and remains comparable with Reduviasporonites. Algal associations from Unit C are mostly dominated by dinoflagellate cysts, principally Rhaetogonyaulax rhaetica, which shows a considerable increase in relative abundance in the upper 2 m of the unit; tasmanitids and other algal remains, acritarchs (Cymatiosphaera spp., Micrhystridium spp.), and test linings of foraminifera are also present. The palynomorph assemblages are indicative of a Rhaetian (Late Triassic) age and a position within the Rr dinoflagellate cyst Biozone of Woollam and Riding (1983).

Depositional environment

The Westbury Formation was deposited during and immediately after a widespread mid to late Rhaetian (Late Triassic) marine incursion (Warrington and Ivimey-Cook, 1992). The first indication of marine influence is provided by dinoflagellate cysts in the underlying Blue Anchor Formation, and the onset of fully marine conditions is marked by the colonisation of a firm, shrinkage-cracked and locally cemented Blue Anchor Formation substrate by burrowing and boring marine organisms. The acritarchs, dinoflagellate cysts and other algal remains, the test linings of foraminifera, and the macrofauna recorded from the Westbury Formation indicate that it accumulated in a shallow, low-energy marine environment. Although the macrofaunal diversity of the formation as a whole is moderately high, the diversity of the benthic associations at any given horizon is low. Together with the general lack of bioturbation, this suggests restricted bottom water circulation and poor oxygenation during deposition (cf. Wignall and Hallam, 1991). Strata rich in vertebrate remains, notably Unit B, are associated with high levels of bioturbation and may reflect more effective water circulation, associated with regionally significant reductions or breaks in sedimentation during periods of relative sea-level rise (MacQuaker, 1994). Thin silt and sand beds may have been derived, during storms, from sands fringing the Anglo-Brabant landmass to the south.

Lilstock Formation

In central and southern England, the Lilstock Formation comprises the Cotham and Langport members (Warrington et al., 1980). The Langport Member is represented locally in the Nottingham region by a thin bed of porcellanous limestone that contains a sparse marine fauna, unlike the thin limestone beds in the Cotham Member (Swift, 1995a). The base of the formation is marked by a sharp transition from the dark grey, fissile mudstone of the Westbury Formation into paler grey, blocky-weathering, calcareous mudstone. The upper boundary is generally located immediately below the fissile mudstone and platy limestone of the Barnstone Member at the base of the Scunthorpe Mudstone Formation (Lias Group; Chapter 7). The lower boundary is not clearly marked on geophysical logs, but the upper boundary is marked by a prominent reduction in the gamma-ray response and a sharp increase in sonic velocity at the base of the overlying Lias Group (Figure 29).

Cotham Member

The Cotham Member comprises pale grey and greenish grey calcareous mudstone with thin, discontinuous or nodular beds of limestone. It weathers to a silty, yellow and grey-brown mottled clay with common small, irregular, white to buff calcareous nodules (‘race’ of Lamplugh et al., 1908). The outcrop of the member typically forms the upper part of a scarp slope capped by resistant limestones of the Barnstone Member (Lias Group; Chapter 7), with the upper boundary of the member lying just below the crest. Fragments of nodular porcellanous limestone with a conchoidal fracture form a field brash on parts of the outcrop; the nodules have a blue-grey centre and cream-weathering outer layer, and are commonly septarian.

Boreholes near Cotgrave (SK63NE/166 and 168), and A46 Borehole 12, sited just to the south of the district, proved the member to be between 6.5 and 7.1 m thick. It is 4.6 m thick in the Barnstone railway cutting, where it includes the ‘Blocky Beds’, ‘Cotham Marls’ and ‘Nodular Limestone’ of Sykes et al. (1970). A 4.9 m section was formerly seen in a railway cutting at Kilvington [SK 7987 4275] (Jukes-Browne, 1885; Young, 1992). The member thickens towards Newark, with about 8.8 m logged at Bantycock gypsum pit, south of Balderton (Figure 31). It thins southwards into the Melton Mowbray district, and dies out around Asfordby (Carney et al., 2004).

The section at Bantycock gypsum pit [SK 810 497] was the only well exposed, complete surface section of the member seen in the district during the survey. Two lithological subdivisions, a lower ‘blocky’ unit and an upper ‘laminated’ unit, were distinguished in this section and can also be recognised in boreholes east of Cotgrave and in the section logged by Sykes et al. (1970) at Barnstone cutting.

The lower ‘blocky’ unit is 3.7 m thick at Bantycock, thinning to 2.7 m at Barnstone and 2.3 m near Cotgrave (Figure 31). It consists of medium grey calcareous mudstone. The blocky weathering habit is due to the disturbance of the primary, laminated depositional fabric by penecontemporaneous slumping (Plate 20). Vestiges of thin (less than 1 cm thick) siltstone beds containing planar and ripple lamination can be picked out within the slumps, commonly defining recumbent folds with amplitudes of more than 1 m.

The upper ‘laminated unit’ consists of olive-grey or brownish grey ‘soapy’ claystones with abundant, very thin (2–15 mm) beds of very fine-grained sand or coarse silt. The sandstone and siltstone beds display normal vertical grading, planar and/or low-angle cross-lamination and, more rarely, wave and current ripple lamination. Sandfilled erosional scours, up to 0.15 m deep and 1.5 m across, occur sporadically and are commonly strongly cemented by calcite. Minor slumps occur in places, also preferentially cemented by calcite. The unit is 5.1 m thick at Bantycock, thinning to 3.8 m at Cotgrave and 1.9 m at Barnstone.

A sparse bivalve fauna (Table 16) was recorded in the basal few centimetres of the member at Bantycock, and thin discontinuous or nodular limestones contain an impoverished macrofauna of branchiopod crustaceans (Euestheria minuta), indicative of fresh to brackish water conditions. However, associations of algal and other remains have similar composition, diversity and relative abundances to those from the Westbury Formation here (Table 15b) and in the Melton Mowbray district (Fisher, 1972; Orbell, 1973, as reviewed in Carney et al., 2004; Morbey, 1975), and indicate a comparable marine influence.

Miospore associations from the member at Bantycock gypsum pit (Table 15a) are comparable with those recorded from boreholes in the Melton Mowbray district (Fisher, 1985; Orbell, 1973; Morbey, 1975). The associations in the boreholes comprise the taxa recorded from lower in the succession at Bantycock (i.e. the lower ‘blocky’ unit) with the exception of Ephedripites tortuosus, but are slightly more diverse. Differences in relative abundances and other characteristics are also apparent. The forms dominant at lower levels remain so in the lower part of the member but Ovalipollis spp., Rhaetipollis germanicus and Ricciisporites tuberculatus all show a decrease in relative abundance in the upper part of the member, where they are replaced in importance by Convolutispora microrugulata and Deltoidospora spp. (Table 15a). Taxa that appear in the Cotham Member at Bantycock include monolete lycopsid spores (Aratrisporites spp.), but are predominantly trilete spores, including Calamospora mesozoica, Camarozonosporites rudis, Converrucosisporites luebbenensis, Intrapunctisporis toralis, Sellagosporis mesozoicus and Semiretisporis gothae, together with representatives of the genera Contignisporites, Kyrtomisporis, Triancoraesporites and Zebrasporites (Table 15a). Miospore associations dominate palynomorph assemblages from the lower part of the member, but they are subordinate at higher levels, in the ‘laminated’ unit, to the associations of algal and other remains (Table 15b). Within the miospore associations, the relative abundance of trilete spores increases from the ‘blocky’ unit into the ‘laminated’ unit, and this group of palynomorphs dominates associations at the top of the latter. The change partly reflects the incoming of a greater diversity of such forms and an increase in the numbers of specimens of taxa such as Convolutispora microrugulata and Deltoidospora spp., but is also a result of a decrease in the numbers of circumpolles and taxa such as Ovalipollis spp. and Ricciisporites tuberculatus. A noteworthy record at the top of the ‘laminated’ unit is the occurrence of Porcellispora longdonensis, a bryophyte spore (Table 15a). Algal associations from the Cotham Member are dominated by dinoflagellate cysts, principally Rhaetogonyaulax rhaetica, but include smaller numbers of Beaumontella langii, Dapcodinium priscum and Rhombodella kendelbachia in addition to sporadic occurrences of the acritarch genera Cymatiosphaera and Micrhystridium and, at the top of the member, Veryhachium. Test linings of foraminifera also occur, mainly in the lower part of the member (Table 15b). These associations are subordinate to miospores in the lower part of the member, but increase in relative abundance upwards and are the dominant component in some palynomorph assemblages from the ‘laminated’ unit. Like those from the Westbury Formation, the palynomorph assemblages from the Cotham Member are indicative of a Rhaetian (Late Triassic) age and a position within the Rr dinoflagellate cyst Biozone of Woollam and Riding (1983).

The Cotham Member has been interpreted as being deposited in a regionally extensive lagoon that was subject to fluctuating salinity but was dominated by marine conditions (Mayall, 1983; Warrington and IvimeyCook, 1992). The thin beds of sandstone and siltstone probably represent storm deposits. The widespread occurrence of slumping in the Cotham Member has been attributed to seismic shock (Mayall, 1983; Simms 2007).

Langport Member

The Langport Member is represented in the Nottingham district by a thin, impersistent, hummocky bed of thinly laminated, ‘splintery’ micritic limestone between the Cotham Member and the base of the Lias Group. A 0.17 m-thick bed is present at Bantycock gypsum mine (Swift, 1995a), and 0.24 m was recorded in A46 Borehole 12 near Cotgrave (Figure 31). In the Barnstone railway cutting, however, this bed is missing, and a nodular bed at the top of the Cotham Member is succeeded by basal Lias Group lithologies. Similar relationships occur along the northern margin of the Melton Mowbray district, with a micrite bed present around Clipston [SK 640 342], but not present in an exposure [SK 683 342] and boreholes near Owthorpe (Swift, 1995a). Fragments of the bed were noted in a gypsum pit at Beacon Hill, east of Newark, by JukesBrowne (1885), who compared it to the ‘sun-bed’ of the White Lias of southern England. The ‘sun-bed’ was also recorded by Lamplugh et al. (1908), Trueman (1915, 1918) and Kent (1970) in a section at Cotgrave Gorse [SK 658 345], just to the south of the district (Figure 31). Swift (1995a) has reviewed other documented occurrences of the Langport Member in the East Midlands.

Swift (1995b) recovered a conodont (Chirodella verecunda) from the Langport Member in Bantycock pit, but this is of limited stratigraphical value as it is known from Middle to Upper Triassic strata elsewhere. However, at Cotgrave Gorse [SK 658 345] in the Melton Mowbray district, and Normanton Hills [SK 537 246] in the Loughborough district, the member has yielded other conodonts, including Misikella coniformis, which is known from Upper Triassic, including late Rhaetian, strata elsewhere (Swift, 1995b) and supports the late Rhaetian age inferred for the member from the ages of stratigraphically contiguous units. Kent (1970) observed U-shaped Diplocraterion burrows in the bed in the Cotgrave Gorse section, but no other fossils have been recorded from the member in the district.

Swift (1995a) interpreted the Langport Member as the product of a quiet lagoonal carbonate mud-flat environment, and suggested that its discontinuous nature might indicate an uneven sea floor rather than partial erosion of a formerly continuous bed. The Diplocraterion burrows described by Kent (1970) might indicate brief emergence.

Chapter 7 Jurassic

Jurassic strata occur at surface and at rockhead beneath thin Quaternary deposits in the east and south-east of the district. The sequence has a regional dip to the southeast of 1° or less. It is affected by numerous faults with throws of generally 5 m or less, which locally produce substantial displacements of the otherwise simple, southwest to north-east-striking outcrops (Chapter 9). The Eakring–Foston Fault has a larger throw of up to 40 m, and there are other faults and periclinal folds associated with this structure that complicate the outcrop pattern around Staunton in the Vale [SK 82 43].

The Jurassic strata of the Nottingham district represent the lower half of the Lias Group (Figure 32), with stratigraphically higher strata cropping out in the Grantham and Melton Mowbray districts to the east and south, respectively (Berridge et al., 1999; Carney et al., 2004). The base of the Jurassic in Britain is placed at the lowest occurrence of ammonites of the genus Psiloceras (Cope et al., 1980; Warrington et al., 1980). In the Nottingham district, this typically occurs about 3 m above the base of the Lias Group; the lowest beds of which, being devoid of ammonites, are assigned to the Rhaetian stage of the Triassic. For descriptive purposes, however, these lowest strata are considered here along with the remainder of the Lias Group. As noted below, the discovery of conodonts provides further support for the Triassic age of these lowermost, ‘Pre-Planorbis beds’ of the Lias Group. The youngest Jurassic strata in the district are of probable early Pliensbachian age.

Biostratigraphical control in the early Jurassic of England and Wales based on ammonite biozones (Dean et al., 1961; Brandon et al., 1990) is excellent. In the following account, the ammonite biozones are treated conventionally with the nominal taxa printed in italics. The stages in the Lower Jurassic were originally based on groupings of these biozones, and are now recognised as chonostratigraphical subdivisions by most Jurassic stratigraphers. Exposures and boreholes in the adjacent Grantham district have yielded an extensive collection of ammonites, enabling detailed biostratigraphical subdivision of the Lower Jurassic in that area and correlation with the standard sequence of stages (Brandon et al., 1990; Brandon, in Berridge et al., 1999). The sequence in the Nottingham district (Figure 32); Table 17) is correlated with that of the Grantham area mainly by mapping of the component lithostratigraphical units, supported by diagnostic ammonites, some of which along with other common fossils are illustrated in (Plate 21).

Palaeogeographical setting and depositional environments

A continuation of the relative rise in sea level that commenced in Late Triassic times resulted in widespread flooding of much of north-west Europe during the Early Jurassic. The Nottingham district probably lay at latitudes of about 40°N, with a climate that was substantially more humid than in the preceding Triassic Period (Bradshaw et al., 1992). The Jurassic seas of Britain were generally warm and shallow, with a diverse marine biota, and were flanked by topographically subdued and well-vegetated land areas. In north-west Europe, the disposition and configuration of sedimentary basins and intervening highs in the Early Jurassic was largely inherited from the Triassic. A phase of regional lithospheric extension during the Early Jurassic, related to rifting in the north Atlantic, resulted in rapid subsidence of some basins and the accommodation of thick, Early Jurassic sequences (Holloway, 1985). In contrast, the East Midlands, as in the Triassic Period, formed part of a more gently subsiding shelf (the so-called East Midlands Shelf) on the periphery of the Southern North Sea Basin (Figure 33). This area was separated from the more rapidly subsiding Cleveland Basin to the north by the Market Weighton High, and was bounded to the south by the Anglo-Brabant Landmass (also termed the London Platform).

Poorly oxygenated bottom waters were widespread during the early stages of this transgression, resulting in deposition of faunally restricted, laminated, organicrich sediments in many basins (Wignall and Hallam, 1991). On the East Midlands Shelf, such a facies occurs within the Barnstone Member, the lowest part of the Lias Group. The generally low taxonomic diversity seen in the macrofauna of this member indicates a fully marine environment of deposition, probably in an offshore, open shelf setting. The bituminous mudstones and limestones tend to be devoid of bottom-dwelling fauna, but contain the skeletal remains of ichthyosaurs and plesiosaurs and, in some sections in the East Midlands, fish and insect remains (Sumbler, 1993). Strata rich in benthic fossils such as bivalves represent colonisation of the substrate following periodic improvements in oxygen levels.

As sea level continued to rise, there was a transition to hemipelagic shelf environments (Weedon, 1986) in which the Scunthorpe Mudstone and Brant Mudstone formations were deposited. Transgression also resulted in southward onlap of successively younger strata of the Scunthorpe Mudstone Formation on to the Anglo-Brabant Landmass (Donovan et al., 1979). The Market Weighton High was probably submerged from the late Triassic onwards, but very low rates of subsidence led to the deposition of an attenuated sequence there (Gaunt et al., 1980; Brandon et al., 1990). The accumulation of carbonates and argillaceous sediments with a diverse marine fauna characterised sedimentation in the Scunthorpe Mudstone and Brant Mudstone formations of the district. Cyclic deposition in the Scunthorpe Mudstone Formation, involving beds of laminated mudstone passing up into calcareous mudstone and thence to bioturbated limestone, generally commences at the base of the Granby Member. The cycles result from variations in bottom water oxygen conditions, from anoxic with a limited benthic fauna, to better oxygenated, coarsergrained substrates with a more diverse fauna, the underlying causes being complex (Waterhouse, 1999).

Lias Group

The Lias Group (Powell, 1984) is a mudstone-dominated sequence resting on the Late Triassic Penarth Group. In the East Midlands, it is overlain by the Middle Jurassic Northampton Sand Formation. The entire group is present in the adjacent Grantham district, where it is about 270 to 280 m thick, but only the lower 150 m crops out in the Nottingham district. This part of the group is composed mainly of grey fissile mudstone with subordinate beds of limestone and ironstone with thin sandstone laminae. The mudstone component also contains layers of calcareous (limestone) nodules, ferruginous (ironstone) nodules and smaller phosphatic nodules. Most of the sequence is highly fossiliferous, but macrofossils are more abundant in a number of bioclastic limestone beds, where the shells are commonly worn and fragmented. Generally the macrofauna is dominated by bivalves, of which the oyster Gryphaea is particularly conspicuous within and at many levels above the Claypole Limestones of the Granby Member. Ammonites, gastropods, belemnites, crinoids and brachiopods (Plate 21) are all common, and bioturbation by several ichnogenera is evident at many levels.

Lithostratigraphical nomenclature in the East Midlands (Table 17) is based largely on work by Brandon et al. (1990) around Fulbeck Airfield [SK 900 510] in the adjacent Grantham district. The beds present in the Nottingham district comprise two formations. The Scunthorpe Mudstone Formation consists mainly of mudstone with numerous thin limestone beds (Figure 32). The overlying Brant Mudstone Formation is also mudstone dominated, but is characterised by abundant limestone and ironstone nodules and generally lacks persistent limestone beds. In a revision of Lias Group nomenclature that followed publication of the Sheet 126 Nottingham, the Brant Mudstone was renamed the Charmouth Mudstone Formation (Cox et al., 1999).

Quarrying of limestone in the lowermost part of the group (the Barnstone Member of the Scunthorpe Formation) provided several well-documented sections in the district, but exposures elsewhere in the group are sparse. The more resistant beds, usually of bioclastic limestone, are commonly seen as ploughed-up fragments or ‘field brash’. Rock fragments dredged up during excavations of drainage ditches also yield useful lithological and faunal information. Care is needed, however, in making biostratigraphical inferences from such material because the samples are not necessarily collected in situ. The Lias Group has been penetrated, although not cored, by several coal and hydrocarbon exploration boreholes, and these provide useful geophysical logs.

Scunthorpe Mudstone Formation

The type area for the Scunthorpe Mudstone Formation is in the Kingston upon Hull and Brigg district, where Gaunt et al. (1992) nominated the Blyborough Borehole [SK 9206 9428] as the type section. Two further boreholes at Fulbeck airfield, within the Grantham district 8 km east of Newark, provide reference sections. A complete sequence was proved in the Fulbeck No. 5 Borehole [SK 9062 5076], and this provided the type section for the constituent members of the formation (Brandon et al., 1990). The Fulbeck No. 1 Borehole encountered all but the highest beds of the formation (Berridge et al., 1999). Halved cores from both boreholes are stored at the BGS, Keyworth. The formation is 107 m thick in the Nottingham district, compared with average thicknesses of 115 m and 128 m in the Grantham and Melton Mowbray districts respectively (Berridge et al., 1999; Carney et al., 2004).

The Scunthorpe Mudstone Formation is characterised by grey, variably calcareous mudstone containing numerous thin limestones. In the type area, it becomes increasingly ferruginous towards the top and the Frodingham Ironstone Member is developed locally. In the Nottingham district, the greater part of the sequence comprises dark grey, fissile mudstone with a calcium carbonate content typically between 10 and 20 per cent. More strongly calcareous mudstone, with up to 50 per cent carbonate, occurs at some levels, and is generally a paler, medium grey colour and has a more blocky fracture. The mudstone throughout the formation tends to decalcify on weathering to stiff, blue-grey or brownish grey silty clay, and typically gives rise to heavy, brownish grey clay soils. Limestone beds, typically 0.05 to 0.25 m thick, contain 60 to 70 per cent calcium carbonate. They form mappable cuesta features of varying magnitudes (Figure 32), even though they are relatively insignificant components of the formation. Some are primary bioclastic limestone units that include lenticular beds indicative of reworking by waves or winnowing by currents, signifying episodic higher energy environments than those that prevailed during the deposition of the mud. Such limestone units were subsequently indurated by carbonate cement and are highly resistant to weathering, readily forming field brash material. Other limestone units are strong, well-cemented calcite mudstones (‘cementstones’), partly of secondary origin, as are the calcite mudstone nodules within the mudstone (Hallam, 1964). These beds, which only rarely form brash, tend to be more prone to decalcification and readily weather to yellowish grey, crumbly clay.

In south Lincolnshire and the Vale of Belvoir (including the Nottingham district), the Scunthorpe Mudstone Formation is divided into five members (Table 17). Three of these, the Barnstone, Granby and Foston members, consist of mudstone with limestone beds (Figure 32). The Barnstone Member has a substantial proportion of limestone throughout (Figure 34), whereas the limestone in the other two members occurs typically in groups of several closely spaced beds separated by 2 to 5 m of mudstone (Figure 35). Individual groups of limestone beds in all three members are laterally persistent, and form topographical features that can be mapped in the region (Brandon et al., 1990; Sumbler, 1993). Some can be recognised in boreholes across extensive areas of the East Midlands Shelf (Berridge et al., 1999).

The three limestone-rich members are separated by the Barnby and Beckingham members, which consist of mudstone accompanied by only sporadic limestone beds. These various members and individual groups of limestone beds are readily recognised and correlated in the subsurface using gamma-ray logs (Figure 35). The Barnstone Member, in particular, is readily identifiable on gamma-ray logs, due to its distinctive, strongly serrated, upward-increasing signature.

The Scunthorpe Mudstone Formation ranges in age from latest Rhaetian to Late Sinemurian. It contains a diverse shelly macrofauna in which bivalves are dominant, accompanied by common ammonites, gastropods and crinoids; vertebrate faunas are also present, as ichthyosaur and plesiosaur remains. Together with the evidence provided by abundant trace fossils, these faunas indicate deposition in a shallow marine environment.

Barnstone Member

The Barnstone Member was formerly known locally as the ‘Hydraulic Limestones’ (Table 17), reflecting its use in the manufacture of hydraulic cement. It is named after the village of Barnstone [SK 733 354], where the limestone was formerly quarried at several sites. These alternating beds of mudstone and limestone are highly resistant to weathering compared to the mudrocks above and below. The member caps a prominent cuesta, 20 m high, broken and displaced in places by faulting, in the eastern part of the district between Cotgrave and Newark. The underlying Penarth Group forms the scarp slope of the cuesta, and the crest is underlain by the basal part of the Barnstone Member. The ‘dip slope’ forms a planar surface that is typically 1 km long, but up to 4 km in places; it is inclined at a slightly lower angle than the true bedding dip, so that successively younger strata crop out downslope. The outcrop is marked by a brown or yellowish brown clay soil with a brash of limestone slabs.

Several good exposures of the member formerly existed either within or just outside the district, mostly in limestone quarries and railway cuttings. The better local sections were documented by Jukes-Browne (1885), Lamplugh et al. (1908), Kent (1937, 1964) and Sykes et al. (1970), although the level of detail in the logs varies considerably. These sections are shown in (Figure 34), together with others (Trueman, 1915, 1918; Ivimey-Cook and Elliott, 1969) from the Melton Mowbray district to the south. Most are now obscured, but the minor exposures afforded by field drains or streams were useful for mapping purposes, although none displayed more than 2 m of section. The combined evidence from exposures and field brash provides a fairly detailed picture of the range of lithologies within the member.

The base of the member, and of the Lias Group, rests sharply on the Lilstock Formation of the Penarth Group. A non-sequence at or just above the boundary has been inferred at former sections in Barnstone railway cutting [SK 7408 3561] (Sykes et al., 1970), and in boreholes and sections around the village of Owthorpe [SK 680 339] (Trueman, 1915; Ivimey-Cook and Elliott, 1969; Swift, 1989) in the adjacent Melton Mowbray district. In contrast, an exposure at Bantycock gypsum pit [SK 8123 4949], south of Newark, showed no evidence of a hiatus. The upper boundary of the member is gradational, with the proportion of limestone gradually declining upwards into the overlying Barnby Member. The thickness of the Barnstone Member shows a slight north-eastward increase across the district, from about 8 m around Cotgrave and Cropwell Bishop to about 10 m near Newark.

Limestone typically makes up about 30 per cent of the sequence (Figure 34). It consists mainly of grey calcite mudstones (‘cementstones’), mostly 0.05 to 0.2 m thick and rarely exceeding 0.3 m. Some limestone beds, especially in the lower half of the succession, are highly fossiliferous, but commonly contain only one or two bivalve species. Other less fossiliferous beds are markedly laminated and bituminous or, less commonly, structureless. Kent’s (1937, 1964) suggestion that some of the limestone beds are laterally persistent across the East Midlands is borne out by correlation of geophysical borehole logs (Brandon et al., 1990). Nevertheless, bedby-bed correlation of sections is difficult, probably due to the pinching out or splitting of some limestone beds. The mudstone intercalations within the member are characteristically up to 0.9 m thick. They are mainly finely laminated, dark grey, fissile, bituminous ‘paper shales’ with laminae of silty limestone, but medium grey, blocky, calcareous mudstones also occur.

Ammonites of the genus Psiloceras (Plate 21)a first occur a little way above the base of the Barnstone Member. The underlying Pre-Planorbis Beds (Trueman, 1915; Kent, 1937) of the Lias Group (and Barnstone Member) are by current definition (Cope et al., 1980) of late Triassic, Rhaetian age, and are from 2 to 3 m thick in the Nottingham district (Figure 34). The overlying, ammonite-bearing part of the member is of early Hettangian, planorbis Zone age (Figure 32); (Figure 34).

Kent (1937) described in detail a complete section (Figure 34) of the member at the Barnstone quarries, although an incorrect location was unfortunately cited. Hallam (1968, p.208) later reproduced the section, giving the correct location [SK 739 348], just within the adjacent Melton Mowbray district. There, the member is 8.3 m thick and the Pre-Planorbis Beds make up the lowermost 3 m.

The overlying 1.9 m of strata contain P. planorbis Sowerby and are assigned to the planorbis Subzone; the uppermost 3.35 m, which bears Caloceras (Plate 21)b, including the species C. johnstoni (Sowerby), are assigned to the johnstoni Subzone. Bed-by-bed lists of other macrofossils were given by Kent (1937). The Pre-Planorbis Beds contain a characteristic bivalve fauna dominated by Pteromya tatei, Modiolus minimus and Liostrea hisingeri, with less common Atreta intusstriata, Plagiostoma giganteum and Palmoxytoma longicosta. Of these, only L. hisingeri and P. giganteum were recorded above the Pre-Planorbis Beds, where a more diverse assemblage of bivalves occurs, with pectinids, limnids and other species of Liostrea and Modiolus (Plate 21)c, d. Echinoid spines occur throughout the member, but are particularly common just around the base of the planorbis Zone. Plesiosaur and ichthyosaur remains are also common; an ichthyosaur forelimb from the Pre-Planorbis Beds, described by Delair (1974), showed evidence of dislocation during the animal’s lifetime. A partial skeleton of an ichthyosaur found at Elton around [SK 768 387], and credited to W Stukeley in 1719, was probably from the Barnstone Member; it is thought to have been the first fossil reptile described from Great Britain.

The section in Barnstone railway cutting [SK 7408 3561] was described by Jukes-Browne (1885) and Sykes et al. (1970). The latter noted a 3 m-thick section of the lower part of the member, which was devoid of ammonites and was therefore assigned to the Pre-Planorbis Beds. The characteristic bivalves M. minimus, P. tatei and L. hisingeri were recorded, together with ostracods and foraminifera. The discovery of conodonts supports a Triassic age for the Pre-Planorbis beds of the Lias Group. Misikella posthernsteini, the index species of the highest Triassic conodont zone, was found at Barnstone (Swift, 1989, 1995b) and a probable fragment of Chirodella verecunda, known from Middle to Upper Triassic strata, was recovered from these beds at Owthorpe, at the northern margin of the Melton Mowbray district (Swift, 1995b).

Palynomorph assemblages from the basal Lias in the Owthorpe 1–4 boreholes (Orbell, 1973, reviewed in Carney et al., 2004) of the Melton Mowbray district, and from the higher beds in the Barnstone cutting section (Fisher, 1972), are dominated by Gliscopollis meyeriana and are much less diverse than those from the underlying Penarth Group; acritarchs and dinoflagellate cysts occur, indicating marine conditions. The basal mudstone in the member at Bantycock gypsum pit, Newark, has yielded a similar palynomorph assemblage, dominated by miospores and of limited diversity compared with those from the Cotham Member. Few of the taxa recorded from the latter are present in the Barnstone Member at Bantycock. The miospore association (Table 15a) consists largely of circumpolles but includes small numbers of a few trilete spores, principally Kraeuselisporites reissingeri but including Nevesisporites bigranulatus, in addition to sporadic bisaccate pollen and rare specimens of Ricciisporites tuberculatus. Other remains comprise the dinoflagellate cyst Dapcodinium priscum and acritarchs (Micrhystridium spp.) (Table 15b). The presence of Dapcodinium priscum and absence of Rhaetogonyaulax rhaetica indicates a position within the Dp dinoflagellate cyst Biozone of Woollam and Riding (1983), of latest Rhaetian to Sinemurian (latest Triassic to Early Jurassic) age.

Kent (1964) described the section and fauna at a former limestone quarry about 800 m south of Askerton Hill [SK 8044 4582]. Formerly known as the ‘Reverend Staunton’s Pit’ or ‘Cotham Quarry’, this is now largely backfilled and flooded, and only about 1.5 m of section remains visible above water level. The lower 6.2 m of the member was formerly exposed here, overlying the Penarth Group, and the lowest Psiloceras sp. was recorded 2.2 m above the base of the member.

Former sections in railway cuttings at Kilvington [SK 7987 4275] and Staunton Grange around [SK 7981 4555] were noted by Jukes-Browne (1885). A small exposure remains in the cutting about 500 m south-east of Cotham village [SK 7994 4719], comprising 0.8 m of fissile calcareous mudstone with subordinate argillaceous limestone. A more complete section was formerly exposed here (Jukes-Browne, 1885), showing the lowermost 5.6 m of the Barnstone Member above the Penarth Group (Figure 34). The lowest ammonites were noted 2.3 m above the base of the member.

At Bantycock Pit [SK 8123 4949], the advancing quarry face (Plate 18) revealed the lowermost 1.05 m of the member (Figure 34), comprising grey fissile mudstone with laminae of silty limestone and subordinate thin beds of buff weathering, grey or purplish grey, argillaceous, micritic limestone. The base of the member is marked by a thin (10 mm) but distinctive coquinoid limestone with small pyritic nodules and mudstone clasts; this bed rests on a porcellanous limestone of the uppermost Penarth Group. The coquina contains Liostrea hisingeri and fragments of Modiolus sp (Table 16). The higher beds yielded L. hisingeri, M. hillanoides, Palmoxytoma longicosta, Pteromya tatei, Modiolus sp. and ichthyosaur vertebrae. Psiloceras was absent, so these strata are of late Rhaetian age. Several small sections of the upper, ammonite-bearing part of the member were noted in the Shire Dyke [SK 8156 4829] to [SK 8238 4834], 1.5 km to the south-east. Excavations along the A1 road, east of Newark, temporarily exposed a near-complete section of the member. The lowermost part of the member, exposed in deep bridge foundations [SK 8243 5413], consists of 0.9 m of grey fissile mudstone overlain by 0.1 m of thinly bedded argillaceous limestone. The limestone yielded the bivalves Modiolus laevis, M. minimus, Pteromya sp. and P. tatei, typical of the Pre-Planorbis Beds. As at Bantycock Pit, the base overlies a distinctive porcellanous limestone that marks the top of the Penarth Group (see p.136). The upper part of the Pre-Planorbis Beds (probably comprising 1–1.5 m of strata) was not exposed here, but much of the remainder of the member was revealed in the road cutting about 700 m to the south-east [SK 8267 5334] where 7.6 m of greenish brown, weathered, fissile mudstone with subordinate beds of argillaceous limestone, overlain by 3 m of gravels (Eagle Moor Sand and Gravel, p.154), were seen. The lower 2 m yielded Psiloceras planorbis, and Caloceras sp. was recorded in the upper 2.5 m. Both the planorbis and johnstoni subzones were therefore proved, although the boundary between them could not be located precisely. Other fossils recorded include the bivalves Plagiostoma giganteum, Liostrea hisingeri, Modiolus laevis, M. minimus and Cardinia cf. hennoquii, together with crinoid ossicles, vertebrate remains and woody fragments.

Barnby Member

The Barnby Member, named after the village of Barnbyin-the-Willows in the adjacent Grantham district, corresponds to the Angulata Clays (Swinnerton and Kent, 1949) and Barnby Clays (Swinnerton and Kent, 1976) of earlier nomenclature (Table 17). Typically it underlies ground to the south-east of the Barnstone Member dip slope where it is largely concealed by alluvium or river terrace deposits. At outcrop, the member is marked by heavy grey or brownish grey clay soils. The sparse exposures are mostly restricted to streams and ditches.

The Barnby Member consists mostly of grey or bluish grey, blocky, calcareous mudstone, typically weathering to stiff grey or bluish grey silty clay. A few beds of argillaceous silty limestone occur, making up about 1 per cent of the sequence in the Fulbeck No. 5 Borehole. This member, which is about 21 m thick in the Nottingham district and the surrounding region (Sumbler, 1993) is entirely of Hettangian, liasicus Zone age (Brandon et al., 1990; (Figure 32).

The lower 6.4 m of the member were formerly exposed in the limestone quarries at Barnstone [SK 739 348] (Carney et al., 2004), overlying the Barnstone Member (Kent, 1937; Hallam, 1968). The section showed mainly grey mudstone, with three beds of massive argillaceous limestone, each up to 0.15 m thick. The fauna, listed by Kent (1937), consists of bivalves, ammonites, nautiloids, echinoid spines and plates, and ichthyosaur and plesiosaur remains. The ammonites all belong to the genus Waehneroceras (Plate 21)l, supporting a liasicus Zone age. Small exposures, collectively proving the lowest 5 m of the member, were noted along the Shire Dyke [SK 8111 4739] to [SK 8134 4825] at Bennington Fen. These exposures showed mainly bluish grey mudstone, with a few thin to medium beds of silty limestone containing planar laminae of very fine-grained micaceous sandstone. The bivalves Liostrea, Pseudolimea and ?Lucina occur in the mudstones.

A continuous section through the uppermost 5.8 m of the member was exposed by dredging operations along The Grimmer [SK 7841 3720] to [SK 7842 3713]. The sequence consists mainly of grey or blue-grey mudstone, weathering to clay, with a few beds of calcareous nodules and a more persistent 0.08 m bed of limestone about

1.3 m below the top. Ammonites in the BGS collection, donated by P E Kent and originating from the uppermost few metres of the member in the A1 road cutting at Costa Hill near Long Bennington [SK 830 446], include Alsatites sp. and Waehneroceras sp (Plate 21)k, l. Their mode of preservation as phosphatised, fragmentary remains, is typical of the district.

Granby Member

The Granby Member corresponds to the Granby Limestones of Kent (1937, 1980) and is named after Granby in the south of the district, although the village actually stands on the outcrop of the Barnstone Member. The Granby Member crops out in a tract, 1.5 to 3 km wide, extending from south-east of Granby [SK 765 361] to Costa Hill, Long Bennington [SK 833 450]. The outcrop east of Staunton in the Vale is complicated by minor faults and folds associated with the Eakring–Foston Fault. There is little Quaternary cover and the member is characterised by heavy grey or brownish grey clay soils, in places containing abundant limestone brash.

The member is generally poorly exposed in the district, although a nearly complete section was exposed in The Grimmer [SK 7842 3713] to [SK 7916 3612] by dredging operations in early 1992 (Figure 35). Supplementary lithological and faunal information comes from field brash and other ditch dredgings. The Granby Member consists of grey calcareous mudstone with numerous thin limestone beds that comprise about 15 to 20 per cent of the sequence. The limestone beds typically occur in packages of closely spaced units, each package giving rise to subtle, but nonetheless mappable scarp and dip features, as indicated in (Figure 32). The main limestone groupings are named on Sheet 126 Nottingham and in (Figure 32), following Brandon et al. (1990); this memoir follows the latter’s scheme, in which many of the units are in the plural, for example ‘Fen Farm Limestones’. Each limestone package can usually be identified in the field by a combination of lithology and faunal content, and each package also produces a distinctive signature on gammaray logs (Figure 35). Within a single package, individual limestone beds are typically about 0.1 m thick, and are predominantly of silty, argillaceous calcite mudstone. More lenticular beds of brown-weathering, blue-grey, well-cemented bioclastic limestone are less common, but because of their greater resistance to weathering, they are the dominant component of the brash found on the dip slopes. The mudstones within the member are typically grey or bluish grey and calcareous, with a fissile to blocky fracture.

The Granby Member is 26 m thick in The Grimmer section (Figure 35), and a similar thickness is probably maintained elsewhere in the district. It ranges in age from the angulata Zone (Hettangian) to the early bucklandi Zone (Early Sinemurian) (Figure 32). The biota is diverse, and along with the lithology, indicates deposition in a low-energy, shallow marine environment with well-oxygenated bottom waters. The fauna collected in the adjacent Grantham district (Brandon et al., 1990; Berridge et al., 1999) includes bivalves, ammonites (which are locally common in the limestones), nautiloids (in the lowest limestone beds), brachiopods, gastropods, corals, crinoids, ostracods and foraminifera. Large conical burrows (Kulindrichnus, or ‘turnip stones’; Hallam, 1960), preserved as casts with well-cemented fills of bioclastic limestone, are commonly ploughed up on the dip slopes.

The original definition of the Holm Farm Limestone by Brandon et al. (1990) has been extended downwards (Berridge et al., 1999) to encompass their limestones ‘X’ and ‘Y’. As re-defined, the base of the Holm Farm Limestone thus corresponds with the base of the Granby Member. The limestone crops out on the lower valley sides to the south-east of The Grimmer and the River Devon, commonly forming a subtle, single or double bench-like feature without a well-developed dip slope. The lower part of the Holm Farm Limestone was temporarily exposed in ditches alongside the new Bottesford bypass [SK 7852 3850] to [SK 7900 3833], east of Orston Grange (Brandon et al., 1990). This part of the unit included a rubbly limestone up to 0.5 m thick with the bivalves Cardinia hybrida, Modiolus hillanoides and the subzonal ammonite Schlotheimia cf. extranodosa. The section in The Grimmer [SK 7842 3711] showed that the whole unit was 2.6 m thick and comprised three limestone beds separated by thicker mudstone intercalations (Figure 35). The lowest limestone bed, 0.29 m thick, yielded the nautiloid Cenoceras cf. latidorsatus, but no ammonites diagnostic of age. The middle of the three limestone beds, probably corresponding to limestone ‘Y’ of Brandon et al. (1990), also yielded S. cf. extranodosa, together with the bivalves Modiolus sp. (Plate 21)d, Cardinia sp., ?Placunopsis and Pseudolimea hettangiensis.

The Cross Lane Limestone generally forms a welldeveloped escarpment. The dip slope locally reaches over 500 m in length with an abundant brash of bioclastic limestone. The brash yields a very diverse bivalve assemblage but Gryphaea is very rare, unlike faunas from higher limestones of the Granby Member. In The Grimmer section [SK 7876 3692], where the Cross Lane Limestone is 1.1 m thick, there are five limestone beds interbedded with grey calcareous mudstone (Figure 35). The second limestone bed up from the base is richly bioclastic, with the bivalves Liostrea sp. (Plate 21)c, Pseudolimea sp. and Plagiostoma giganteum, and the ichnofossil Kulindrichnus sp. The remaining limestones are less fossiliferous, silty and argillaceous.

The Claypole Limestone forms a long dip slope at Normanton airfield [SK 820 420], but a less well-developed, bench-like feature elsewhere along the outcrop. The unit is well exposed in The Grimmer section [SK 7885 3672], where it totals 1.7 m in thickness and consists of seven beds of mainly argillaceous limestone with calcareous mudstone intercalations (Figure 35). One markedly lenticular bioclastic limestone occurs about the middle of the sequence, and contains abundant Gryphaea arcuata, with Pseudopecten sp. (Plate 21)t and the gastropod Pleurotomaria sp. Bioclastic limestone brash on the outcrop of the Claypole Limestones contains abundant Gryphaea, in contrast to the Cross Lane and Holm Farm limestones.

The Blackmires Limestone forms a more subdued and less persistent scarp and dip feature than the other limestone packages in the Granby Member. The associated field brash is distinctive, however, consisting of pebblesized fragments of nodular, commonly richly crinoidal bioclastic limestone with common loose specimens of Gryphaea and the solitary coral Montlivaltia haimea. In The Grimmer [SK 7903 3651] (Figure 35), this unit is 2.2 m thick and represented by three beds of mainly argillaceous limestone, separated by calcareous mudstone with thin nodular beds of bioclastic limestone. The latter contain abundant Gryphaea sp. and Pentacrinus debris (Plate 21). Trueman (1918, p.71) recorded a section in a former brick pit at Bottesford around [SK 8064 3943], probably in this limestone, containing a rich fauna of bivalves, crinoids, echinoid spines, fish teeth and foraminifera. Arietites bucklandi was also recorded, indicating a bucklandi Zone age.

The Fen Farm Limestone, at the top of the Granby Member, forms a moderately strong cuesta with a broad dip slope north-east of Bottesford [SK 825 403]. A more subdued discontinuous feature is developed elsewhere. Brash is common and consists of pale brown-weathering, medium grey bioclastic limestone that contains abundant Pentacrinus columnals (Plate 21)g and small, thin-shelled bivalves; loose specimens of Gryphaea are abundant and Kulindrichnus is common. In The Grimmer [SK 7915 3620] (Figure 35), the Fen Farm Limestone totals 0.48 m in thickness and comprises two beds of argillaceous limestone separated by calcareous mudstone with thin, discontinuous beds of bioclastic limestone. South-east of Eady Farm [SK 8005 3722], ditch dredgings of this limestone yielded the ammonite Vermiceras cf. solaroides, indicating the conybeari Subzone of the bucklandi Zone.

Beckingham Member

The Beckingham Member corresponds to the Bucklandi Clays of Swinnerton and Kent (1949, 1976) (Table 17). It crops out in a tract 0.5 to 1 km wide in the south-east of the district, and in a downfaulted block within the Eakring–Foston Fault system east of Staunton in the Vale. The outcrop is largely free of drift and gives rise to brownish grey clay soils. Exposure is restricted to a few small and highly weathered ditch sections.

The Beckingham Member consists predominantly of bluish grey fissile mudstones with rare thin beds of argillaceous limestone. Ferruginous limestone nodules are common within the Dry Doddington Nodule Bed, near the top of this sequence. The member has a near constant thickness of 22 m within the district. In the adjacent Grantham district (Berridge et al., 1999), typical fossils include the bivalves Gryphaea and Pseudopecten (Plate 21)f, ammonites of Early Sinemurian (bucklandi Zone to semicostatum Zone) age and sporadic pentacrinoid fragments.

The Dry Doddington Nodule Bed has been mapped only to the east of Staunton in the Vale and around Bottesford. Roughly 2 m thick, this bed lies about 17 to 18 m above the base of the member. Its outcrop is characterised by numerous ovoid, ochreous, yellow-skinned, grey, ferruginous limestone nodules, typically 0.05 to

0.20 m across, in a brownish grey clay soil. The nodules are generally unfossiliferous but are locally crowded with small Modiolus (Plate 21)d. Sections in the Grantham district (Berridge et al., 1999) indicate that the ferruginous limestone nodules occur as sparse thin layers.

The Lincoln Hill Limestone, above the Dry Doddington Nodule Bed, lies 3 to 4 m below the top of the Beckingham Member. It is 0.15 to 0.3 m thick in the adjacent Grantham district (Berridge et al., 1999). Although probably laterally persistent, the limestone is only mappable in the Nottingham district to the west of Redmile [SK 785 355], where it forms a well-developed dip slope. The associated brash consists of small slabs of medium grey, silty, shelly, bioclastic limestone. Gryphaea is common within the brash, both as single loose specimens and as ‘nests’ of several individuals cemented within bioclastic limestone.

Foston Member

The Foston Member is named after Foston Beck, near the villageofFostonintheadjacentGranthamdistrict(Brandon et al., 1990). It is approximately equivalent to the Ferruginous Limestone Series (Table 17) of Swinnerton and Kent (1949). The outcrop lies mainly between Redmile and Muston [SK 81 36]. The Stubton Limestone at the base of the member also caps Folly Hill, to the east of Staunton in the Vale, and forms a long dip slope to the east of Bottesford [SK 825 390].

This member, 30 to 32 m thick, consists mainly of grey mudstone, with thin limestone beds making up about 10 per cent of the sequence. As in the Granby Member, the limestone beds tend to occur in groups that form scarp and dip features. The limestone beds become increasingly silty and sandy upwards through the member (Berridge et al., 1999). Persistent beds of phosphatic nodules occur (Figure 32), commonly at the base of limestone beds (for example at the base of the Stubton Limestones). Many of the nodules are penetrated by minute, penecontemporaneous borings, suggesting at least one episode of erosional reworking.

The member ranges from the semicostatum Zone up into the turneri Zone (Lower Sinemurian), and possibly into the obtusum Zone (Upper Sinemurian) (Brandon et al, 1990). Bivalves including Camptonectes, Cardinia, Gryphaea, Lucina, Oxytoma, Protocardia, Pseudolimea and Pseudopecten (Plate 21)f, together with ammonites, dominate the fauna, as listed by Brandon et al. (1990). Foraminifera, ostracods and palynomorphs are also present.

The Stubton Limestone equates with the Lower Ferruginous Limestone or Plungar Ironstone of earlier terminology (Lamplugh et al., 1909). This unit generally forms an extensive dip slope, notably on Folly Hill [SK 823 434] and to the east of Bottesford [SK 825 390]. In the Grantham district, boreholes have shown the Stubton Limestone to consist of up to four beds of limestone interbedded with mudstone. The grouping of beds is up to 2.4 m thick, of which limestone comprises about half. The limestone units are mostly argillaceous, but include, towards the top, a brown and grey mottled, ferruginous bioclastic limestone that is intensely burrowed, Gryphaearich, and contains siderite or goethite ooids. Regionally, this ferruginous limestone produces a rich, rust-brown silty soil with a copious and distinctive brash in ploughed fields. The numerous Gryphaea commonly show contemporaneous abrasion and borings, and occur together with Kulindrichnus and ammonite fragments. Limonitic ooids are common in some limestone fragments, as are irregular, orange-brown ‘limonite’ veins and patches. Small, orange-skinned phosphatic pebbles also occur in the brash, derived from a nodule bed at the base of the Stubton Limestones.

A small exposure of the Stubton Limestone in a ditch [SK 8156 3704] south-east of Toston Hill yielded a diverse assemblage of molluscan fossils. This comprised gastropods including Procerithium sp., scaphopods, bivalves including Cardinia hybrida, C. cf. crassiuscula, Chlamys sp., Gryphaea sp. juv. and Pseudolimea sp., and the ammonite Arnioceras sp. Ammonites collected from brash on dip slopes near Redmile [SK 788 351] and Hill Farm [SK 807 367] included Arnioceras sp., A. cf. semicostatum (Plate 21)j and an indeterminate coroniceratid. These indicate a probable early semicostatum Zone, lyra Subzone age.

The Lodge Farm Limestone produces a weak to moderate dip and scarp feature between Redmile and Muston. Slabs dredged from ditches consist of hard, pale brown-weathering, grey, silty, bioclastic limestone with abundant Gryphaea and Pseudopecten valves. Boreholes in the Grantham district (Brandon et al., 1990) proved several thin limestones with mudstone interbeds, totalling about 1.5 m in thickness.

The Fenton Limestone has a narrow outcrop between Redmile and Muston and lies on the lower part of a scarp slope associated with the overlying Littlegate Limestone. Although the Fenton Limestone does not form a strong topographical feature, it can be traced locally from ditch dredgings. It is present in the south bank of the River Devon [SK 8311 3754] south-east of Muston, where it consists of a single limestone bed about 0.25 m thick with a sharp, erosional base. The bed is a distinctive, hard, olive-grey, finely sandy, silty, sparsely shelly limestone. It contains pectinid bivalves and small ammonites, but unlike older limestones, generally few Gryphaea. A small exposure in a roadside excavation [SK 8305 3805], north-east of Muston Church, yielded Arnioceras cf. miserabile and A. cf. semicostatum, indicating a semicostatum Zone age. More precisely, this limestone can be assigned to the latest scipionianum Subzone because, south-west of Muston, ditch dredgings [SK 8212 3743] of the immediately overlying mudstone yielded Euagassiceras donovani of the resupinatum Subzone.

The Littlegate Limestone forms a prominent cuesta between Redmile and Muston, although brash is rather sparse on the long dip slope. Boreholes in the Grantham district (Berridge et al., 1999) proved two beds of limestone, each 0.20 m to 0.25 m thick, separated by about 1 m of mudstone; in some boreholes a third thin bed of limestone was recognised. The lower limestone is a hard, compact, shelly rock; the upper one is less shelly and contains a high proportion of fine-grained quartz sand. No exposures have been recorded in the Nottingham district. Ditch dredgings and brash show grey, weathering to orange-brown, hard, bioclastic limestone. This lithology contains the bivalves Cardinia? and Gryphaea maccullochi var. arcuatiformi, the brachiopod Spiriferina walcotti and the ammonites Arnioceras sp. and Euagassiceras terquemi.

The Mill Lane Limestone generally forms a weak feature, although a more marked scarp and dip feature [SK 825 370] is developed about 1 km south of Muston. The outcrop is characterised by a greyish brown loam, generally with little or no brash. In the Grantham district (Berridge et al., 1999), boreholes show that this unit consists of several limestone beds within a vertical interval of 2 to 3 m. Several drainage ditches to the south of Muston yielded debris of grey, weathering buff to ochre, silty, finely sandy, shelly limestone grading into calcareous siltstone. The rock contains Gryphaea, numerous pectinid bivalves and a few belemnites, and is commonly intensely burrowed. Limestone slabs dredged from one ditch [SK 8161 3620] contained Arnioceras miserable, Arnioceras semicostatum (Plate 21)j and Arnioceras sp., indicating a semicostatum Zone age.

The Highfield Farm Limestone forms a weak feature, but can be recognised by material dredged from ditches at several places. The dredgings generally consist of fragments of bluish grey, weathering yellowish brown, silty, slightly sandy, platy, bioclastic limestone. This characteristically contains large amounts of pyrite, both finely disseminated and in denser masses, which weathers to a brownish ochre; reworked phosphatic nodules also occur. Gryphaea, some abraded and bored, are abundant and pectinid bivalves are common. Boreholes in the Grantham district (Berridge et al., 1999) showed either one or two beds of limestone, in the latter case separated by up to 0.35 m of mudstone. Both the limestone beds and the intervening mudstone contain pyritised shells and shell fragments.

The Stragglethorpe Grange Limestone is the highest named limestone within the Foston Member, lying about 6 m below the top. It forms a poorly defined feature and is traceable mainly by ditch dredgings. A finely sandy loam with rare limestone brash marks the outcrop. Limestone slabs from ditches are grey, weathering pale brown, finely sandy, silty, shelly and compact, with numerous Gryphaea and Pseudopecten (Plate 21)f, resembling the Mill Lane Limestones. An exposure in a ditch [SK 8183 3605] north of Muston Grange Farm showed 0.1 m of sandy limestone with the bivalve Hippopodium ponderosum; Kent (MS, 1963) recorded Asteroceras from the same locality, indicating an obtusum Zone age. Boreholes in the Grantham district (Berridge et al., 1999) proved either one bed or, less commonly, two closely spaced beds of bioturbated, sandy bioclastic limestone, each ranging from 0.1 to 0.35 m in thickness.

Brant Mudstone Formation

The formation shown as the Brant Mudstone Formation on the Nottingham Sheet 126 was renamed the Charmouth Mudstone Formation by Cox et al. (1999). To be consistent with the map, the original name is used in this memoir.

The Brant Mudstone Formation comprises the poorly defined Obtusum-Oxynotum Clays, Sandrock and ‘Upper Clays’ of Swinnerton and Kent (1949, 1976), as shown on earlier editions of BGS Geological Sheets 114 and 127 (Table 17). It equates with the lower part of the Coleby Mudstone Formation of Gaunt et al. (1992). No members have been defined, but Brandon et al. (1990) assigned informal names to several mappable beds within the formation.

The stratigraphically lower part (about 45 m) of the formation crops out in the extreme south-east corner of the district and is largely free of drift. Higher strata occur in the adjoining districts to the east and south, where the formation varies from 110 to 150 m thick (Sumbler, 1993).

The Brant Mudstone Formation consists mainly of grey fissile mudstone with abundant layers of phosphatic siderite mudstone (ironstone) and calcite mudstone nodules, some of which are mappable. Limestone beds such as those that characterise the Scunthorpe Mudstone Formation are rare. The part of the formation occurring in this district includes finely sandy mudstones, and typically gives rise to grey or brownish grey, silty clay soils. The Brandon Sandstone (see below) is the only unit within the formation that forms a strong scarp and dip feature (Figure 32).

The base of the formation is marked by a thin pebbly ferruginous oolite (Glebe Farm Bed), which rests erosively and non-sequentially on grey mudstone of the underlying Scunthorpe Mudstone Formation. The top is not seen in the district, but elsewhere is defined by the base of the Dyrham Formation. The formation as a whole ranges from the oxynotum Zone of the Upper Sinemurian to the davoei Zone of the Upper Pliensbachian, but strata above the jamesoni Zone (Lower Pliensbachian) are absent from the Nottingham district. The fauna is dominated by bivalves, including Cardinia, Gryphaea, Hippopodium (Plate 21)h, Pholadomya, Pseudolimea and Pseudopecten (Plate 21)f, together with ammonites and belemnites (Berridge et al., 1999). Like the Scunthorpe Mudstone Formation, the Brant Mudstone was deposited in a shallow marine, low-energy shelf setting with generally well-oxygenated bottom waters.

The Glebe Farm Bed does not form a mappable topographical feature, but its outcrop is traceable by ditch dredgings. In the Grantham district (Berridge et al., 1999), the bed consists of two distinct units. The lower consists of up to 0.1 m of grey, weathering yellowish brown, bioclastic limestone, with abundant bivalve fragments and argillaceous limestone pebbles up to 0.08 m in diameter. These pebbles contain numerous borings and are evidently reworked calcareous nodules, implying a significant erosional hiatus at the base of the bed. The upper unit, typically about 0.3 m thick, is a ferruginous ooidal limestone, brownish grey when fresh, weathering to deep orange brown. It contains goethite ooids in a patchily cemented, argillaceous limestone matrix. It commonly contains scattered small, brown, polished, ovoid phosphatic pebbles (probably reworked nodules), up to 30 mm in diameter, some of which contain minute borings. The rock contains a few shells, commonly abraded and bored, and burrows are present.

In the Nottingham district, both the lower bioclastic limestone and the upper ferruginous ooidal limestone can be recognised from debris produced by ditch dredgings; both weather to orange brown. From a ditch adjacent to the Grantham Canal at Muston Gorse [SK 8192 3598], the upper unit yielded Gagaticeras sp. (Plate 21)i, indicating an Early Pliensbachian, oxynotum Zone age.

The Sand Beck Nodule Bed (Figure 32), not shown on Nottingham Sheet 126, consists of 3 to 5 m of grey mudstone with numerous ovoid, siderite mudstone nodules, which are typically 0.05 to 0.1 m across. The nodules dredged from ditches weather orange brown to red in colour, and are commonly veined with calcite and pyrite. Ammonites collected in the adjacent Grantham district (Berridge et al., 1999) indicate an oxynotum Zone age.

The Brandon Sandstone (the Sandrock of Swinnerton and Kent, 1949, 1976) occurs about 15 m above the base of the Brant Mudstone Formation. Estimated to be about 1 or 2 m thick at outcrop, it forms a strong and persistent scarp and dip feature, offset by minor faults, to the west of Muston Gorse [SK 825 356]. The dip slope is characterised by a brown, silty, finely sandy soil with little or no brash. Ditch dredgings reveal sandstone that is pale grey weathering buff, silty, shelly, calcareous and fine grained, with scattered specks of mica and abundant Chondrites burrows. Fossils tend to be concentrated in lenses, and include Gryphaea and the large, deep-burrowing bivalve Pholadomya, the latter commonly in life position. Ammonites collected in the Grantham district (Berridge et al., 1999) indicate that the Brandon Sandstone is of raricostatum Zone age.

The 22 m of mudstone separating the Brandon Sandstone from the Loveden Gryphaea Bed commonly contains large, ovoid, calcite mudstone nodules. A nodule-rich layer, 2 m thick, occurs about 7 m above the Brandon Sandstone and was located by ditch dredgings from several localities near Muston Gorse [SK 825 356]. A bed of grey bioclastic limestone, up to 0.03 m thick and yielding numerous Pseudopecten and Gryphaea, also occurs at this level; it commonly contains reworked limestone and phosphatic nodules.

The Loveden Gryphaea Bed, about 22 m above the Brandon Sandstone, does not produce a topographical feature, but is nevertheless a useful marker; it may correlate with the ‘70 Marker’ Member of the south Midlands (Horton and Poole, 1977). About 6 m of mudstone overlying the Loveden Gryphaea Bed crops out [SK 830 351] to the east of Mansel’s Barn. Abundant red-brown siderite mudstone nodules up to 0.2 m in diameter were dredged from ditches at several places. The ditch dredgings also showed a thin bed of bioclastic limestone, associated with calcareous mudstone containing abundant large Gryphaea valves and common Pseudopecten and belemnites. These strata are the youngest Jurassic rocks seen in the district and are of late raricostatum Zone or possibly early jamesoni Zone age. The Loveden Gryphaea Bed is known to be of raricostatum Zone, macdonnelli Subzone age in the adjacent Grantham district (Berridge et al., 1999).

Chapter 8 Quaternary

No strata between the Pliensbachian (Lower Jurassic) and Middle Pleistocene are preserved in the district. Recent research (Whittaker et al., 1985; Green et al., 1993) suggests that an estimated 1.8 km of Jurassic to early Palaeocene strata were deposited over the East Midlands, and were removed subsequently by denudation following uplift that commenced in the Palaeocene, about 60 Ma (Green et al., 1993). The present landscape of the region has been shaped essentially by events that commenced in the Middle Pleistocene. These relate mainly to climatic fluctuations, and include glaciation during the Anglian cold stage plus several subsequent episodes of fluvial aggradation and modification of the drainage pattern by rejuvenation and diversion.

The Quaternary deposits (‘drift’) in the district fall into four main groups. Glacigenic deposits such as tills and glaciofluvial sand and gravel occur sporadically as dissected remnants on the higher interfluves, mainly in the western part of the district. Two small patches of glaciofluvial outwash deposits occur on hilltops to the east of Newark. River terrace deposits and Alluvium are extensively developed along and adjacent to the floodplain of the River Trent (Plate 3), where they locally reach up to 10 m in thickness. Substantial spreads of these deposits, generally less than 3 m thick, are also associated with the River Devon and its tributaries to the south-east of the Trent, and with the River Witham in the extreme east of the district. The older fluvial deposits, consisting mainly of sand and gravel, are preserved as the higher terraces flanking most of the major drainage courses. The most extensive tracts of Lacustrine deposits in the district occur to the east of Nottingham (Tollerton) Airport and to the north of Bingham. Mass movement deposits, mainly classified as head and originating principally from periglacial solifluction and/or colluvial processes, are ubiquitous on slopes and as partial valley fills in the district. Most of the deposits classified as diamictons, preserved on low interfluves between Bingham and Tollerton, probably represent the dissected remnants of older head deposits. Small landslips have been mapped locally but are uncommon. Organic deposits, peat and shell marl, are commonly associated with lacustrine deposits, but only rarely do they form discrete mappable outcrops.

Stratigraphical framework

Although the Quaternary evolution of the East Midlands has been the subject of considerable research since the latter part of the 19th century, much remains to be resolved. Considerable debate persists regarding the age of the last glaciation to affect the middle and lower Trent basin and the pattern of preglacial drainage. Unravelling the sequence of events in the region is hampered further by general uncertainties concerning the chronology of the British Quaternary.

Globally, the Quaternary is characterised by marked climatic oscillations between cold and warm phases. These fluctuations are recorded by variations in the oxygen isotopic composition of the tests of deep ocean foraminifera, reflecting changes in global ice volume and oceanic temperature (Emiliani, 1955; Shackleton, 1975; Jones and Keen, 1993). In high latitudes, including the British Isles, extensive lowland ice sheets developed at times during some of the cold periods, with temperate climates prevailing during the intervening ‘interglacials’. These cold-warm alternations and their associated deposits provide the basis for chronostratigraphical subdivision of the Quaternary sequence (Table 18), which in Britain is based on the framework of Mitchell et al. (1973). Their scheme recognises three major cold stages in the mid to late Pleistocene, namely the Anglian, Wolstonian and Devensian in order of decreasing age (Table 18).

In central England there is direct evidence of glaciation during the first and last of these stages (Hains and Horton, 1969), which included extreme cold (stadial) episodes. The extent of any Wolstonian ice sheet has been hotly debated, however, in a controversy centred on the age of some glacigenic deposits of the English Midlands and Lincolnshire. The classic work of Shotton (1953) assigned the ‘Wolston Series’ glacial succession of Warwickshire to a glaciation that occurred between the Hoxnian and Ipswichian stages, subsequently defined as the Wolstonian Stage by Mitchell et al. (1973). Chalky tills in East Midlands and Lincolnshire, contiguous with those of the upper part of the ‘Wolston Series’, were likewise thought to be of Wolstonian age (Clayton, 1953; Posnansky, 1960; Straw, 1963; Rice, 1968a). Doubt was cast on this interpretation by Perrin et al. (1979), who correlated the chalky tills of Lincolnshire with the pre-Hoxnian (Anglian) Lowestoft Till of Norfolk on the basis of till fabric analysis. This alternative interpretation implies that the Midlands were not glaciated between the Hoxnian and Ipswichian stages, and seriously undermines the status of the stratotype of the Wolstonian Stage (Sumbler, 1983; Rose, 1987). Support continues to increase for this alternative view (for example Bowen et al., 1986; Rose, 1989), which is strengthened further by a Hoxnian date yielded by organic deposits immediately overlying the ‘Wolston Series’ in the Warwick district (Bowen, 1992). Despite this, the term ‘Wolstonian’ continues to be used semi-formally by many workers to describe the period between the Hoxnian and Ipswichian (Bowen et al., 1999).

Considerable problems arise when attempting to correlate the fragmentary onshore records of cold–warm cycles with the more complete chronology provided by the oceanic record. There is general agreement that the last interglacial, the Ipswichian, corresponds to Marine Isotope substage 5e, and that the last major glaciation in the Late Devensian correlates with stage 2 (Table 18). Greater uncertainty surrounds the correlation of the Anglian–Hoxnian–Wolstonian sequence. The chronology most widely accepted (Bowen et al., 1986, 1989) matched the Anglian glaciation with Stage 12. This has subsequently been challenged, however, with the suggestion (Sumbler, 1995) that the Anglian Stage may have comprised two separate glaciations corresponding to Marine Isotope stages (MIS) 12 and 10, with an intervening stage (11) represented by the ‘Swanscombian Interglacial’. It is noted, however, that many workers now suggest that the Hoxnian interglacial could also be referred to MIS 11 (e.g. McMillan, 2005). There followed a complex series of warm and cold intervals represented by stages 8, 7 and 6, respectively, spanning the period assigned to the Wolstonian by Mitchell et al. (1973), which may extend to Stage 10.

Of the mid to late Pleistocene glaciations, the Anglian is widely considered to have had the greatest extent, with the ice margin reaching as far south as the present Thames valley. There is also general agreement that most of the Midlands and southern England remained unglaciated during the Late Devensian glacial maximum. The interpretation of the series of river terraces preserved in the Trent drainage basin remains the principal method for determining the chronology of Quaternary events in the East Midlands. While not entirely conclusive, the evidence strongly supports an Anglian age for the last glaciation of the region (Brandon and Sumbler, 1988, 1991; Howard, 1992). Dating of individual Quaternary deposits is shown in Table 18 and discussed below, and the Quaternary evolution of the district is summarised in the final section of this chapter.

In this account, the various Quaternary deposits have been named informally to correspond with the nomenclature used on Sheet 126 Nottingham. Since publication of the map, a new scheme of subdivision has been published, in which many of the current geographical names were nevertheless retained (Bowen et al., 1999; McMillan, 2005).

Glacigenic deposits

Till

The previous 1:10 560 scale geological survey of the Nottingham district identified several extensive areas of Till (‘Boulder Clay’ described by Lamplugh et al., 1908) in the south-eastern part of the district between Wiverton Hall [SK 714 364] and Shelton [SK 767 437]. The new survey has shown these to be of fluvial origin and they have been reclassified as either undifferentiated river terrace deposits or Whatton Sand and Gravel. Other tills mapped in the vicinity of Cotgrave are classified here as undifferentiated diamictons (see p.165).

A few small areas of till occur, mainly in the south and west of the district. Till deposits, up to about 4 m thick, cap a series of prominent ridges around Gaunt’s Hill [SK 568 469] at 115 to 125 m above OD. A smaller patch, 1 to 2 m thick, caps the river cliff at Colwick [SK 597 399] at about 90 m OD. Both of these outcrops consist of stiff, red-brown sandy clay with abundant pebbles of quartzite and quartz derived from the Sherwood Sandstone and lesser amounts of Carboniferous sandstone, together with slabs of smoothed and striated Mercia Mudstone ‘skerry’. Both areas were classified as Glacial Sand and Gravel by Lamplugh et al. (1908). A section in a former gravel pit in the deposits at Colwick, described by Shipman (unpublished MS, quoted in Lamplugh et al., 1908), included vertically orientated pebbles, suggestive of later, probably Late Devensian, cryoturbation; no other details of till fabric have been recorded. Both these occurrences are of a similar lithology to the Thrussington Till, mapped in the Melton Mowbray district farther south (Carney et al., 2004); they contain a northwesterly derived, ‘Pennine’ erratic suite, indicating deposition by a glacier flowing from that direction (see p.167). The red-brown matrix was probably derived mainly from Triassic sandstones and mudstones.

Around East Bridgford [SK 697 430], south of Mill Farm [SK 680 419] and west of Newton Airfield [SK 697 406] outcrops of clayey to sandy till typically have a ‘Pennine’ clast suite, with many fragments of sandstone and rounded quartzite. The clay matrix is brown to grey green in colour, in places becoming red brown below about 2 m (Rathbone, 1989c). Tills of uncertain provenance occur at rather lower elevations (generally below 40 m OD) in the south of the area, around Cotgrave village [SK 636 355]. Lowe (1989a) notes that they consist mainly of grey clay with pebbles. Around Radcliffe on Trent, similar grey-brown till was proved by augering and in temporary excavations [SK 6402 3925] to underlie deposits of the Bassingfield Sand and Gravel (Lowe, 1989a). The grey-brown colour of the clay matrix, combined with the absence of Chalk or flint erratics, indicates that all of these diamictons may be equivalent to the ‘Lias-rich’ facies of the Oadby Till mapped farther south (Carney et al., 2004), suggesting derivation from the main Jurassic outcrop either within or to the north-north-east of the district.

Glaciofluvial sand and gravel

Deposits of glaciofluvial sand and gravel are patchily distributed in the western part of the district, occurring mainly as highly dissected remnants on interfluves. Most lie on the outcrop of the Nottingham Castle Sandstone Formation and produce pebbly, sandy soils, which can be difficult to distinguish from those resulting from weathering of the underlying bedrock. They may be recognised by their erratic content, notably Carboniferous sandstone and limestone, and less commonly, Cretaceous flint and Jurassic limestone.

Several patches of glaciofluvial sand and gravel occur at elevations of 90 to 120 m above OD to the north of Bestwood. Rathbone (1989a) described 0.8 m of very poorly sorted, pebbly sand and silt occupying a channel cut in the Nottingham Castle Sandstone Formation at Bestwood quarry [SK 5674 4775]. Erratics recorded include ‘altered’ volcanic rocks and Carboniferous sandstone. Lamplugh et al. (1908) noted about 2 m of red, stratified sand and gravel in a former pit at Bestwood Lodge. They recorded erratics of Lower Palaeozoic andesite and Carboniferous sandstone, as well as the ubiquitous pebbles derived from the Sherwood Sandstone Group.

Further small outcrops of sand and gravel occur along or near to the Leen valley. Those in the Bulwell Forest area [SK 548 457] are not exposed, but lie over 15 m higher than the Leen floodplain and almost certainly represent glaciofluvial deposits. Farther south, in the Radford and Basford areas, sand and gravel outcrops form bench-like features on both sides of the valley at elevations of 7 to 10 m above the alluvium. These are possibly the dissected remnants of postglacial deposits laid down by a precursor of the Leen rather than glaciofluvial deposits. The best sections occur in disused sand pits at Bobbers Mill [SK 5544 4165]; [SK 5530 4154], where up to 2.8 m of cryoturbated, orange-red gravelly sand were logged by Dean (1989). Lamplugh et al. (1908) recorded boulder-sized erratics of ganister and andesite hereabouts, possibly from these pits.

Glaciofluvial sand and gravel capping Wilford Hill [SK 580 355] lies at an altitude of about 90 m above OD. Exposures in trenches, recorded by Charsley (1989), showed about 3 m of red-brown, pebbly sand with pockets of clay. Sands with northwards-inclined, low-angle cross stratification were noted towards the base of the excavations. Vertical pebble orientation and flame-like injection structures indicate intense postdepositional cryoturbation. Lamplugh et al. (1908) described similar sections in temporary excavations for a reservoir nearby. Charsley (1989) noted that the dominant clast types within the gravels are quartzite pebbles derived from the Sherwood Sandstone with subordinate Carboniferous sandstone. Although numerous, rounded, black Cretaceous flints also occur in the soil herabouts, it is possible that these represent a remanié derived from younger glacigenic deposits.

Depositional environment

Local channelling into the underlying bedrock and the cross-stratified nature of the gravels indicate deposition by subglacial or proglacial meltwater. Intercalations of pebbly clays (diamictons) in the Wilford Hill deposit, the sporadic boulder-sized erratics and, farther south, the associated local patches of till (Carney et al., 2004) indicate that both the glaciofluvial sand and gravel and tills are remnants of a formerly more extensive, complex deposit produced by the advance and subsequent waning and melt-out of an ice sheet, the age of which is discussed later (see p.168).

River terrace deposits<span data-type="footnote">Further information on the river terraces and other deposits is given in the Quaternary Research Association Field Guide on the Trent Valley and adjoining regions (2007)</span>

The correlation and chronology of these economically important deposits is shown in Table 18. As noted above, the nomenclature of these and other Quaternary deposits has recently been formalised, the main changes being that the various ‘Sand and Gravel’ units of this account, although retaining their geographical names, are now regarded as separate members of a new unit, the Trent Valley Formation (Bowen et al., 1999; McMillan, 2005). A detailed account of the geomorphological development and archaeology of the Trent Valley is given by Knight and Howard (2004).

Eagle Moor Sand and Gravel

Regionally, the Eagle Moor Sand and Gravel (Brandon and Sumbler, 1988) forms a series of hilltop outliers extending north-eastwards from Newark, with a more extensive spread from Danethorpe Hill to Eagle Moor [SK 84 57], west of Lincoln. The altitude of these outliers descends steadily towards the Lincoln Gap. In the Nottingham district, two small outliers east of Newark form highly dissected terrace remnants with upper surfaces lying at about 35 m above OD, and with a possibly planar base on bedrock at about 30 m above OD. About 2 km to the west, the Trent floodplain lies at 8–9 m above OD.

A borehole near Coddington Windmill [SK 8324 5359] (Gozzard, 1976) proved 3.9 m of sand and gravel, clayey towards the top. In bulk, the deposit comprised 58 per cent gravel, 30 per cent sand and 12 per cent fines. The gravel fraction comprised Sherwood Sandstone-derived quartzite and quartz pebbles, Lias mudstone clasts, Cretaceous flint and Carboniferous chert.

Depositional environment and age

The flint content of the Eagle Moor Sand and Gravel indicates that its deposition postdates deposition of the chalkand flint-rich tills of the East Midlands. Swinnerton (1937) suggested that the deposit was terraced outwash from a retreating Pennine glacier, formed as meltwater drained north-eastwards through a pre-existing Lincoln Gap. A sedimentological study (Howard, 1992) of sections in a gravel pit at Potter Hill, about 10 km north-east of Newark, appears to confirm aggradation in a proglacial braid-plain environment. At Newark, the base of the Eagle Moor Sand and Gravel is elevated up to 20 m higher than the base of the Balderton Sand and Gravel (Figure 36)a. The latter has been dated as late ‘Wolstonian’ (MIS 6) by Brandon and Sumbler (1991), further suggesting an age substantially older than late Wolstonian for the Eagle Moor Sand and Gravel.

Balderton Sand and Gravel

The Balderton Sand and Gravel (Brandon and Sumbler, 1988, 1991) covers an area of about 10 km2 in the northeast corner of the district. The ‘Balderton Terrace’, upon which most of Newark and Balderton are built (Frontispiece), also includes surficial deposits consisting of aeolian coversands and periglacial ‘gelifluctates’ are present locally elsewhere in the East Midlands (Brandon and Sumbler, 1991). North-eastwards, the Balderton Sand and Gravel occurs continuously as far as Lincoln, forming a slightly sinuous, gravelly tract up to 4 km wide.

The deposit is well exposed in a number of quarries, mostly located just to the north-east of the Nottingham district, between Newark and Lincoln. The deposit generally consists of 7 to 8.5 m of orange-brown gravel with a medium- to coarse-grained sand matrix. An overall upwards-fining trend is evident as coarse, poorly stratified gravels pass upwards into better stratified, commonly trough cross-bedded sandy gravels. Channels filled with laminated sand, silt and clay occur in the lower part of the deposit, and have yielded a rich assemblage of floral and faunal remains (Brandon and Sumbler, 1991). Ice-wedge casts are common throughout; many are truncated by subplanar intraformational erosion surfaces indicating penecontemporaneous cryoturbation. The pebble content resembles those of the Eagle Moor Sand and Gravel, with mean counts of 76 per cent Sherwood Sandstone-derived quartzite and quartz, 16 per cent Cretaceous flint and 6 per cent Triassic sandstone and siltstone (Gozzard, 1975, 1976; Jackson, 1977). Less common exotic pebbles include Carboniferous limestone, sandstone and chert, Lower Palaeozoic volcanic rocks, probably derived from the Lake District, and Charnian tuffs (Brandon and Sumbler 1991). Clasts derived from the underlying bedrock are common towards the base of the deposit.

Within this district, the Balderton Sand and Gravel is typically from 6 to 8 m thick, with a maximum of 8.8 m proved by a borehole at Bridge Farm [SK 8333 5188]. Between Balderton and Beacon Hill [SK 815 532], the deposit occupies a planar-based channel, 1.5 km wide, incised into the foot of the scarp slope formed by the Penarth Group and Barnstone Member. Elsewhere, the original channel margins have been removed by later erosion. The terrace surface lies 17 to 19 m above OD, which is about 7 m above the local level of the Trent floodplain. Particle size analyses from local boreholes (Gozzard, 1976) typically indicate proportions of gravel ranging from 45 to 70 per cent, sand and fine gravel from 25 to 50 per cent, and fines from 1 to 5 per cent.

Waters (1992) described exposures that typically displayed only the uppermost 1 to 2 m of the deposit. This consisted mainly of orange-brown pebbly sand with lenses of gravel, the latter commonly cemented strongly by red-brown hematite to form a ferricrete. Quartz, quartzite and flint pebbles are the dominant clast types.

Depositional environment and age

The lithology and sedimentology of the Balderton Sand and Gravel indicates aggradation by a low sinuosity braided river (Brandon and Sumbler, 1991). Penning (in Jukes-Browne, 1883) and later Swinnerton (1937) suggested deposition by a precursor of the River Trent, flowing to the east of its present course downstream of Newark and continuing through the Lincoln Gap. This interpretation has not been seriously disputed since, but determining the age of the deposit was problematical. Reconstructions of the theoretical thalwegs of the Trent terrace deposits led most workers (Swinnerton, 1937; Clayton, 1953; Posnansky, 1960; Rice, 1968a; Straw and Clayton, 1979) to correlate the Balderton Terrace with the Beeston Terrace, over 30 km upstream. On similar grounds, these authors equated the Beeston Terrace with the Early Devensian Allenton Terrace of the lower Derwent valley (Table 18), the underlying deposits of which have yielded a hippopotamus fauna indicating aggradation during the Ipswichian interglacial stage (Bemrose and Deeley, 1896; Jones and Stanley, 1974). More recently, Brandon and Sumbler (1988, 1991) have demonstrated an alternative assignment of the Balderton Sand and Gravel to the preceding (late Wolstonian) cold stage. Amongst the considerable body of evidence cited in favour of this correlation has been the determination of a pre-Ipswichian cold-stage mammalian fauna from the Balderton Sand and Gravel (Lister and Brandon, 1991). Of further significance are the syndepositional ice-wedge casts, demonstrating contemporaneous permafrost during deposition of the Balderton Sand and Gravel. Electron spin resonance dating of mammoth and elephant teeth from the deposit gave an age range of predominantly 130 000 to 190 000 years BP, supporting a post-Hoxnian–pre-Ipswichian (late Wolstonian, MIS 6) age for this cold stage (R Grün, in Brandon and Sumbler, 1991). Just below the Balderton Terrace surface, the latter authors noted palaeosols that had been rubified by pedogenesis in the succeeding (Ipswichian) warm phase, but then extensively cryoturbated during a subsequent (Late Devensian) cold period.

Whatton Sand and Gravel (new name)

North-eastwards from Northfield Farm [SK 724 360] to Cotham [SK 805 476], isolated patches of sandy gravel occur as thin cappings on interfluves. More patches occur near Thorpe Lodge [SK 784 495] and Honey Lane Farm [SK 788 505], to the north-west of Cotham. The rockhead elevation beneath the deposits declines steadily from 32 m above OD at Northfields Farm to around 14 m above OD at Honey Lane Farm, representing a gradient of about 1 m per kilometre (Figure 37). These gravelly patches probably represent the dissected and degraded remnants of a formerly continuous deposit, newly named after the village of Whatton, which lies close to one of the larger crops [SK 745 388]. Lamplugh et al. (1908, p.8) tentatively interpreted these deposits as ‘Boulder Clay’, while noting a clay matrix derived locally from the Mercia Mudstone or Lias groups. No sections were described, however, and it seems likely that they observed weathered bedrock into which pebbles from the overlying thin spread of gravel had been incorporated by cryoturbation and deep ploughing. Such comparable mixed lithologies were observed during this resurvey.

A matrix of yellowish brown clayey gravel was encountered in a few places on these deposits. The dominant clasts are Cretaceous flints and Sherwood Sandstonederived quartzite and quartz pebbles, with lesser quantities of Mercia Mudstone-derived siltstone and very fine-grained sandstone, Lias Group ferruginous limestone, and worn Gryphaea valves.

Depositional environment and age

The northward-declining bedrock surface beneath the deposit approximates to the typical graded thalweg of a fluvial channel or channel system. Together with a similarity in composition to other river gravels in the Devon, Witham and Smite valleys, this indicates that the Whatton Sand and Gravel is the remnant of a formerly more extensive tract of fluvial sand and gravel. The longitudinal profile of the deposit appears to grade approximately to the base of the Balderton Sand and Gravel (Figure 37). The Whatton Sand and Gravel may therefore have been deposited during the late Wolstonian by a northward flowing tributary of the Trent, with a confluence at Balderton. The deposits were substantially incised by the rivers that aggraded terrace deposits of probable Devensian age in adjacent valleys (Figure 38). Near Farndon, for example, the deposits are up to 7 m higher than the base of the Late Devensian Holme Pierrepont Sand and Gravel. Thus the Whatton Sand and Gravel must substantially predate Late Devensian time (Table 18).

Bassingfield Sand and Gravel

The outcrops of the Bassingfield Sand and Gravel (Charsley et al., 1990) extend along the southern margin of the Trent floodplain between West Bridgford and Radcliffe on Trent. The deposits lack a typical terrace morphology, but instead form a low discontinuous ridge on which the villages of Gamston and Bassingfield stand.

The highest point on the ridge lies at 29 m above OD, which is some 6 to 7 m above the local level of the Trent floodplain and 5 m above the Holme Pierrepont Terrace surface (Figure 36)b. Site investigation boreholes drilled at intervals along the A52 road between Gamston and Radcliffe on Trent proved sandy gravels grading upwards into sands with sparse pebbles, between 4 and 5.6 m thick in total. The rockhead surface descends steadily to the north-east. Scattered poor exposures (Lowe, 1989a) showed up to 2.5 m of orange-brown to brown, generally poorly sorted, clayey sand and gravel; vague clast imbrication was evident in places. Auger evidence indicated that the lower part of the deposit locally interdigitates with clays and diamictons. Ploughed soils on the outcrop suggest that the gravel fraction consists predominantly of medium-size pebbles that are generally well rounded. Sherwood Sandstone-derived quartz and quartzite are the dominant pebble types, together with abundant (?Carboniferous) sandstone and Cretaceous flint, and less common igneous rocks.

Depositional environment and age

The lithology and geomorphology of the Bassingfield Sand and Gravel indicate aggradation in a fluvial environment with clasts derived mainly from reworking of pre-existing Quaternary deposits. There is, however, little sedimentological evidence to determine palaeoenvironments in more detail. Deeley (1886, p.471) figured a former section of the deposit at Gamston showing extensive convolution of virtually the full thickness of the gravels. These structures almost certainly indicate extensive cryoturbation of the deposit, but may relate to a postdepositional periglacial episode, probably in the Late Devensian.

(Figure 36)b shows that the deposit is elevated substantially higher than and therefore predates the Holme Pierrepont Sand and Gravel, which is probably of Late Devensian age (see below). Deeley (1886) and Posnansky (1960) correlated the Bassingfield and Beeston terraces on geomorphological grounds, but degradation of the terrace at Bassingfield by subsequent denudation must introduce considerable uncertainty into this interpretation. This leaves the possibility that the Bassingfield Terrace is a correlative of the Balderton and Whatton deposits of the district (Table 18).

Holme Pierrepont Sand and Gravel

The Holme Pierrepont Sand and Gravel is equivalent to the Flood-plain Terrace deposits of Posnansky (1960) and the Floodplain Sand and Gravel of Brandon and Sumbler (1988). The new name is derived from the village of Holme Pierrepont [SK 629 392] and was introduced by Charsley et al. (1990) to overcome the confusion implicit in the earlier terminology. Although the deposits crop out within the confines of the Trent floodplain, their upper surface forms a terrace (the Holme Pierrepont Terrace) standing up to 2.5 m above the level of the floodplain (Plate 3). The abandoned pits to the north-west of Holme Pierrepont have been landscaped to form the National Water Sports Centre.

This terrace is extensive along the Trent valley in the Nottingham district, where some tracts of these deposits cover an area of several square kilometres. It is commonly bounded by a substantial step down to the adjacent floodplain, but locally the transition is marked by only a slight break of slope. The well-drained sandy soil of the terrace surface contrasts strongly with the much heavier soil of the adjacent floodplain alluvium.

The Holme Pierrepont Sand and Gravel, although lithologically similar to alluvial sand and gravel, may be distinguished from it in good sections on the basis of sedimentology, organic remains and artefacts. Former sections in gravel pits near Holme Pierrepont village (Cummins and Rundle, 1969) and at Colwick (Salisbury et al., 1984) proved alluvial sand and gravel lying directly on bedrock (see below). Thus, beneath the Trent floodplain in those areas and probably elsewhere, the Holme Pierrepont Sand and Gravel has been completely removed by Flandrian (Holocene) reworking. Boreholes show that the rockhead is generally slightly lower below the floodplain than below the Holme Pierrepont Terrace. This was illustrated by Posnansky (1960) and it indicates that, locally at least, Flandrian incision extended below the level of the base of the Holme Pierrepont Sand and Gravel (see below and (Figure 36). However, geotechnical data from a few boreholes indicate that there is also a distinct basal zone of very dense gravel (Forster, 1992), which may comprise isolated remnants of the Holme Pierrepont Sand and Gravel. Incision and reworking of the Holme Pierrepont Sand and Gravel during Flandrian times has produced the extensive deposits of alluvial sand and gravel that occur beneath the silt and clay of the modern floodplain (Figure 36)b.

The Holme Pierrepont Sand and Gravel is typically 6 to 7 m thick, ranging up to a maximum of 9 m to the west of Newark. Exploration for sand and gravel in the Trent valley has yielded numerous borehole provings (see for example Spenceley, 1971; Price and Rogers, 1978), but little lithological detail is provided by such sources. The best exposures are provided by active gravel quarries, which are kept dry by pumping and provide fresh faces for study.

At the time of survey, the only quarries working these deposits were near Holme Pierrepont itself [SK 618 382] (Lowe, 1989a) and at Hoveringham [SK 695 475] (Ambrose, 1989). At Hoveringham (Plate 22), the deposit consists dominantly of poorly sorted, clast-supported gravel, 6 to 9 m thick, with a medium- to coarse-grained sand matrix. Pebbles are generally less than 50 mm across, but larger pebbles range up to 0.1 m. They are mostly rounded, but subrounded to angular shapes also occur. The uppermost 2 to 3 m of the deposit appears unstratified and the remainder shows subhorizontal stratification or, less commonly, trough cross-stratification. Locally, the long axes of pebbles show horizontal orientation, imparting a pronounced fabric to the deposit; imbrication is rare. Lenses of fine- to medium-grained sand are present at a few levels. These may be planar laminated or, more commonly, planar or trough cross-stratified with foreset azimuths orientated downstream to the north-east. Ice-wedge casts are preserved at two levels, one truncated by the upper unstratified gravels and the second truncated by a further intraformational erosion surface 1 to 2 m below.

The deposits to the west of Newark (Price and Rogers, 1978) show mean proportions of 60 per cent gravel, 40 per cent sand and less than 2 per cent silt and clay. In places, the uppermost 1 to 1.5 m of the deposit consists of pebbly, medium-grained, clayey sand with up to 40 per cent silt and clay in some samples. Posnansky (1960), and Price and Rogers (1978) recorded pebble count data from the Nottingham district, but these counts include pebbles from the overlying alluvial sand and gravel (see below). The dominant pebble types, usually making up to 70 per cent by number, are quartz and quartzite derived from the Sherwood Sandstone Group. Also common (comprising between 5 and 10 per cent) are flints derived from the Chalk, sandstone derived from strata of the Sherwood Sandstone Group and Sneinton Formation, and sandstone, limestone and chert derived from Carboniferous strata. Jurassic limestone and ironstone, igneous rocks and coal also occur but are less common.

Depositional environment and age

Comparable gravels were described by Howard (1992) in the lower part of the Holme Pierrepont Sand and Gravel at Besthorpe quarries [SK 820 630] between Newark and Lincoln. This sedimentological study indicated aggradation in a glacial meltwater-charged, braided river system with a high sediment load. The truncated icewedge casts at Hoveringham provide further evidence of aggradation in a periglacial climatic regime, and pebbly sands, found in places at the top of the deposit, may contain a component of wind-blown fine-grained sand and silt. A further important cold climate indicator is a specimen of musk-ox, Ovibos moschatus, collected from a former quarry at Holme Pierrepont and held at Wollaton Hall Museum, Nottingham. A probable Late Devensian age for these deposits (Table 18) is further supported by unpublished finds of Mousterian flint implements (Posnansky, 1960). Radiocarbon dating of organic-rich sediments at the base of the Holme Pierrepont Sand and Gravel in Holme Pierrepont Quarry (SK625 385) gave an age of 11 300 years BP, suggesting that this particular phase of aggradation occurred at around the beginning of the Loch Lomond Stadial (Howard, A J et al., in prep.).

Leen Sand and Gravel

These deposits (Charsley et al., 1990) form a discontinuous terrace along the Leen valley [SK 555 505], lying up to 2 m above the floodplain. The terrace is best developed south and south-east of Papplewick, and smaller patches occur at intervals as far south as Lenton.

Rare temporary exposures include a few described by Shipman (quoted in Lamplugh et al., 1908). Sporadic exposures occur in field drains to the south-east of Papplewick (Rathbone, 1989a; Lawley, 1993a). They indicate that the deposit consists of crudely stratified and very poorly sorted pale grey silt, sand and ‘pea’ gravel, up to 2.4 m thick. Shipman (cited in Lamplugh et al., 1908) recorded up to 3 m of ‘Torrential Gravel’ and sand in a temporary section in this deposit; also noted were pebbles of quartz, flint, sandstone and chert in the gravels of the Leen valley, although their provenance was not specified.

Depositional environment and age

The Leen Sand and Gravel is a fluvial deposit aggraded by a precursor of the modern River Leen. The low elevation of its terrace surface implies equivalence with the Holme Pierrepont Sand and Gravel and hence a Late Devensian age (Charsley et al., 1990).

Undifferentiated river terrace deposits

Devon, Smite and Whipling catchments

Tracts of fluvial sand and gravel are developed in many places along these valleys and their tributaries. Typically, they form low terraces elevated 1 to 2.5 m above the adjacent alluvium. In places, a bedrock step of up to 1 m is evident between the modern floodplain surface and the base of the gravels. The sand and gravel deposits locally range up to 2 m thick, but thicknesses of 1 m or less are more common. The deposits are thickest at Bottesford, Sibthorpe and Hawton, where they consist of up to 1.2 m of gravelly fine-grained sands, locally clayrich, overlying a basal gravel 0.5 to 1 m thick. Elsewhere only the basal deposits are preserved, typically consisting of orange-brown to grey-brown sandy gravels, with small to medium pebble-sized clasts of Chalk-derived flint, Sherwood Sandstone-derived quartz and quartzite, and Lias-derived limestone, ironstone and Gryphaea valves. In some tracts, for example the Whipling valley at Wiverton Hall [SK 713 364] and east of Whatton Manor [SK 745 374], only a very thin remanié gravel is present. This produces a pebbly soil with a reddish brown clayey matrix derived from the underlying weathered Mercia Mudstone bedrock. The remanié gravels were misinterpreted as glacial ‘Boulder Clay’ by the earlier surveyors (Lamplugh et al., 1908). Many of these deposits have been subjected to intense cryoturbation, showing involutions and pods of gravel descending as much as 2.5 m into the underlying weathered and contorted bedrock. In many places, the depth of cryoturbation has led to the preservation of remnant pods of gravel beneath the incised base of the alluvium of adjacent floodplains (Figure 38). This was well demonstrated by exposures in field drains south of Brocker Farm [SK 7260 3958] and to the west of Elton [SK 755 386] (H G Fryer, written communication, 1992).

The distribution of these deposits attests to several diversions of drainage following deposition. In particular, an extensive tract of sand and gravel extending from Aslockton [SK 743 403] to Wensor Bridge [SK 785 458] via Hawksworth was probably deposited by a precursor of the Smite before diversion to its present course to the east, which has no associated terraces. Similarly, a tract of sand and gravel trending north-westwards through Orston Grange [SK 777 388] represents a drainage route now abandoned in favour of a route to the south-west via Granby [SK 732 362]. In view of such drainage diversions, the chronology of these deposits is likely to be complex. Mammalian faunal remains, comprising elephants, ox, deer and a human skull, were recorded at Bottesford (Jukes-Browne, 1885), but were poorly located and inconclusive of age or environment. Near Hawton [SK 788 505] and Farndon, the terraces lie at a similar elevation to the Holme Pierrepont Terrace, indicating a comparable Late Devensian age. The local removal of the upper sandy parts of the deposits may have been largely accomplished by aeolian deflation towards the end of the Devensian.

Witham valley

Extensive tracts of sand and gravel occur around the Shire Dyke (in the Witham valley) at Bennington Fen [SK 815 476]. Typically, they form a discontinuous low terrace up to 1 m higher than the adjacent alluvial plain. The sandy and gravelly loam soils are bounded by barely perceptible breaks of slope. Abundant sections in the drainage ditches crossing Bennington Fen show variable thicknesses of the deposit, up to a maximum of 2.5 m. The base locally displays marked channelling into the underlying Barnby Member bedrock, for example at Shire Bridge [SK 8257 4849]. The deposits consist of yellow-brown gravelly sand or sandy gravel, dominated by smallto medium-sized pebbles of ferruginous limestone and ironstone derived from the Lias. Flints, Lincolnshire Limestone pebbles, Gryphaea valves and crinoid columnals are also common clast types. Sherwood Sandstone-derived quartz and quartzite pebbles do occur, but are less common than in the terrace deposits of the River Devon catchment.

A good exposure at a new fishpond west of Pasture Lodge Farm [SK 8218 4696] showed the entire thickness of gravel to be preserved as a single set of eastward-dipping, low-angle cross-strata, suggestive of lateral accretionary bedding produced by point bar migration in a meandering (high sinuosity) river system. Cryoturbation is absent. The uppermost 0.5 m of the gravel is decalcified, with secondary rubified patches in places. The gravel is overlain by a distinctive, sharp-topped layer of dark grey organic-rich clay, 40 mm thick, overlain in turn by up to 1.1 m of brown silty alluvial clay. The organic-rich clay probably represents a palaeosol, and patchy rubification of the underlying gravels may indicate temperate conditions (see for example Rose et al., 1985). This implies subaerial exposure of the terrace and a significant hiatus prior to deposition of the overlying Flandrian alluvium.

The lower elevation and lack of cryoturbation implies a younger age for these deposits than those of the Devon catchment. No older terraces are known along the present course of the Witham between Long Bennington [SK 830 455], to the east of the district, and Bassingham (13 km south-west of Lincoln), suggesting that this is a comparatively recent route, initiated by headward erosion of the narrow gap to the east of Long Bennington and capture of a former course of the Witham to the east. Capture probably took place towards the end of Devensian times, enabling transport of sands and gravels reworked from older river terrace deposits upstream in the Witham valley and re-deposition downstream of the Long Bennington gap at Bennington Fen. The gravels may have been deposited originally by a braided river in the Late Devensian, but were subsequently reworked by a meandering river channel as the climate ameliorated in early Flandrian times.

Greet valley

Two large tracts of sand and gravel (one classified on the map as ‘post-Anglian’) occur along the south-west side of the Greet valley to the north and east of Southwell. Smaller patches of probably equivalent deposits crop out at Upton [SK 736 546] and Brinkley [SK 721 525]. The larger tracts lack a typical terrace morphology, and show upper surfaces that slope gently down to the Greet floodplain. Little information is available on lithology and thickness. A borehole (SK75 SW/12 [SK 7143 5353]) on the large tract to the east of Easthorpe proved only 1.8 m of silt and sand with subordinate gravel. Soils on all four tracts are commonly loamy, with abundant pebbles and cobbles of siltstone and sandstone derived from the lower part of the Mercia Mudstone Group, and quartz and quartzite pebbles originating from the Sherwood Sandstone Group.

These deposits may represent the remnants of two or more terraces that have degraded and apparently merged due to solifluction and colluvial processes. The topographically highest deposits lie about 9 m above the neighbouring Holme Pierrepont Terrace, indicating that they substantially predate the Late Devensian, but their equivalence with any of the higher Trent terraces is speculative.

Alluvium

Alluvium represents the detritus deposited by Flandrian fluvial activity along the floodplains of the River Trent, its tributaries and other river systems of the district. It typically consists of clayey or very fine-grained sandy silt overlying sand and gravel. The silt deposits are the fine-grade material laid down on the floodplains by episodic overbank flooding, and give rise to poorly drained, heavy, dark brown soils. The sand and gravel is mostly derived from older river terrace deposits, or their reworked equivalent, and this component of the alluvium is only seen in excavations or boreholes.

Extensive spreads of alluvium are associated with the Trent and its south bank tributary system formed by the rivers Devon, Smite and Whipling. Broad alluvial flats also occur in the Witham valley at Bennington Fen on the eastern edge of the district. North bank tributaries of the Trent tend to have more deeply incised valleys and comparatively narrow floodplains; the alluvial tracts associated with the rivers Leen, Dover Beck and Greet are rarely more than 400 m wide. Small tracts of alluvium occur in places along other minor drainage courses.

Trent valley

Broad spreads of alluvial silt are present on the floodplain of the Trent, and are most extensive where migration of river meanders during the Flandrian incised broad tracts (up to 2 km wide) through the Holme Pierrepont Sand and Gravel, leaving terrace remnants at the margins of the floodplain. This has occurred between Beeston [SK 36 54] and Shelford [SK 663 423], and again to the north-east of Bleasby [SK 717 495]. Between Shelford and Bleasby, narrow tracts of alluvium separate numerous patches of the Holme Pierrepont Terrace, as at Gunthorpe (Figure 39), indicating that periodic channel avulsion in addition to gradual meander migration has been an important process hereabouts. Some of the narrowest tracts of alluvium probably relate to tributaries or chute channels rather than the main channel.

The floodplain surface is generally almost flat, but in a few places the topography undulates by up to 1.5 m where abandoned channels, bars and levees are present. An example of this occurs in the vicinity of the large meander south-east of Burton Joyce [SK 650 430]. There, the alluvial features show up faintly on the ground and on aerial photographs, but are dramatically revealed by remote high-resolution topographic surveying, as shown in (Figure 39) (Carney and Napier, 2004).

The alluvial deposits vary considerably in thickness due to their irregular upper and lower surfaces. They generally average 3.5 to 4 m thick, reaching a maximum of 8 m. Locally, the deposits thin to 2 m or less over bedrock ‘highs’, for example at Wilford, where bedrock was observed on the river channel floor (Lamplugh et al., 1908). The numerous boreholes drilled through the gravels enable detailed contouring of the rockhead in many places. Lateral profiles constructed across the valley indicate that, below the floodplain, Flandrian incision has generally removed the Holme Pierrepont Sand and Gravel apart from a few local remnants (see above and (Figure 36)b, leaving alluvial sand and gravel overlying rockhead. In longitudinal (along-stream) profile and excluding local irregularities, the rockhead falls gradually from 14 m above OD at Wilford [SK 568 370] to 3.5 m above OD at Farndon [SK 770 527], a gradient of 0.4 m per km. Below Farndon there is a steepening of the rockhead profile to 1 m per km, possibly representing a former knickpoint.

The best sections have been described from abandoned gravel pits north of Holme Pierrepont village (Cummins and Rundle, 1969) and at Colwick (Salisbury et al., 1984). The deposits vary from 2 to 6 m thick and are developed as a single set of large scale cross-strata dipping at low angles towards the south. Cummins and Rundle observed pebble imbrication indicating current flow towards the east. They therefore interpreted the cross-stratification as the product of lateral accretion due to point bar migration in a meandering channel system. Boreholes beneath the Trent floodplain west of Newark (Price and Rogers, 1978) indicate that the upper parts of the deposit are decidedly more silty and clayey, a feature typical of point bar deposits (Leopold et al., 1964). Lenticular beds of dark grey, organic-rich clays, up to 1.5 m thick, have been noted both at the top (Cummins and Rundle, 1969) and within the gravels (Rathbone, 1989b), representing the fills of abandoned river meanders see also (Figure 39). They contain partings of silt or very fine-grained sand, introduced by episodic flooding events, and an abundant fauna of freshwater gastropod and bivalve molluscs, listed by Cummins and Rundle (1969).

The alluvial silt varies in thickness from a feather-edge to 4 m, with 1.5 to 2.5 m being the dominant range. Exposures abound along the banks of the Trent and in drainage ditches, and show that the deposit typically consists of brown to dark brown clayey silt or silty clay, which is variably sandy. A reddish hue is evident along the north-western side of the floodplain, reflecting a high content of detritus derived from tributaries draining the Mercia Mudstone outcrop to the north-west. The silty alluvium generally lacks stratification due to slow accumulation rates and disturbance by burrowing organisms and plant root systems. Thin, impersistent beds and lenses of gravelly sand, locally cross-stratified, seen in a few sections, were probably deposited by higher energy channelised flows during floods. Deposits representing the fills of abandoned channels are seen as beds, up to 1.5 m thick, of dark grey to black silty and peaty clay, or in some cases clayey peat. They have been described from several quarry sections, notably at Sneinton and Colwick (Lamplugh et al., 1908) and Holme Pierrepont (Cummins and Rundle, 1969). Such beds are laterally impersistent and are usually developed at the boundary between the alluvial silt and the underlying sand and gravel. They commonly contain decayed wood fragments and an abundant fauna of freshwater bivalves and gastropods. Detailed faunal lists are given by Cummins and Rundle (1969).

Leen valley

Most information on this alluvium is derived from boreholes and temporary sections, notably those described by Shipman (quoted in Lamplugh et al., 1908) at Radford and Basford. Typically, sections show a tripartite sequence of grey or brown silty clay, up to 1.3 m thick, overlying peat up to 1.6 m thick, which in turn overlies yellow grey or white gravelly sand up to 1.8 m thick. The basal sands have most likely been reworked from the Leen Sand and Gravel, and then gleyed by waterlogging and reduction associated with the overlying peat deposits. In the Bestwood area, many parts of the floodplain are now permanently flooded due to mining subsidence and the creation of artificial ponds (Rathbone, 1989a).

Cocker Beck, Dover Beck and River Greet catchments

These streams drain the Mercia Mudstone outcrop between Arnold and Southwell, joining the Trent valley to the southeast. Smaller tributary streams in these catchments are deeply incised, forming steep-sided valleys known locally as ‘dumbles’(Doornkamp,1971).They are commonly floored by head, with only a few patches of alluvium.

The alluvium typically shows a twofold division, with a basal angular gravel overlain by silt or silty clay (Ambrose, 1989). The gravel varies from 0.8 to 1.4 m thick and consists of clasts of reddish brown or greenish grey siltstone and very fine-grained sandstone derived from the Mercia Mudstone Group; downstream-orientated clast imbrication is common. The overlying silts and silty clays are up to 2 m thick, red-brown and unstratified. Lamplugh et al. (1908) described a dark greenish grey silt below the angular gravels in Cocker Beck, 700 m east of Harlow Wood Farm [SK 647 475]; mammal bones (including a human femur) and an extensive molluscan fauna were collected from these silts, as were flint flakes that were described as Neolithic.

River Devon and tributaries

The River Devon and its tributaries, principally the Smite and Whipling, drain an area of more subdued topography than the tributaries to the north-west of the Trent. This drainage system consists of a series of broad alluvial plains occupying strike-parallel valleys along the outcrops of the less competent parts of the Mercia Mudstone and Lias groups, namely the Cropwell Bishop Formation and the Barnby Member, respectively. Narrow strike-normal valleys have been cut through interfluves at Whatton [SK 746 400] and Wensor Bridge [SK 790 455] where faulting has displaced the Cropwell Bishop Formation’s outcrop.

The floodplains of these rivers are underlain by 1 to 2.5 m of brown to dark brown, locally peaty, silty clays. In some places, mainly along the main valleys occupied by the Smite and the Devon, up to 1 m of alluvial gravels intervene between the clays and bedrock. These were probably reworked from the adjacent river terrace deposits.

Witham valley

In the east of the district, the Witham floodplain forms a broad area of low-lying, formerly poorly drained land known as Bennington Fen [SK 815 480]. The present course of the river lies just beyond the eastern boundary of the district. Exposures of alluvium in the many ditches and dykes display up to 2 m of brown to dark brown, structureless, silty clay. Freshwater gastropods are common at the base of the alluvium in the north-west part of Bennington Fen, suggesting temporary development of lacustrine conditions.

The alluvium typically overlies river terrace deposits, but overlaps directly on to bedrock in many places, notably towards the west of Bennington Fen. The preservation of a former soil profile at the top of the river terrace deposits indicates that the alluvium has draped the former terrace surface without significant incision.

Depositional environment and age

The alluvial sand and gravel deposits of the Trent valley were formed by Flandrian (Holocene) incision and reworking of the Late Devensian Holme Pierrepont Sand and Gravel. The transition from the high discharge, braided river regime of the Holme Pierrepont Sand and Gravel to the single channel, meandering river system responsible for deposition of alluvial sand and gravel probably marks the climatic amelioration towards the end of the Devensian, probably at about 10 000 years BP. Organic remains and artefacts within the deposits indicate that reworking continued up to at least medieval times (Cummins and Rundle, in MacCormick, 1969).

Uprooted and transported trunks of large trees (‘bog oaks’) are common; examples from Colwick yielded radiocarbon and tree ring (dendrochronological) dates of between 3500 and 5500 years BP (Salisbury et al., 1984). Dug-out canoes, a spoked wheel (MacCormick, 1969) and reworked fish weir timbers (Salisbury et al., 1984) have been found in places towards the base of the deposit and indicate ages ranging from Iron Age or Roman to medieval times. Many more examples of human modification of the Trent valley landscape through time are given by Knight and Howard (2004). More recently, navigation and flood management schemes have locally reinforced the riverbanks, largely preventing further channel migration.

Lacustrine deposits

Spreads of lacustrine deposits occur in two parts of the district. The first lies to the south of the Trent valley in the Edwalton and Tollerton areas, the second to the north and east of Bingham. Deposits in both areas contain freshwater molluscs characteristic of semipermanent lakes or pools, distinguishing them from fluvial alluvium.

Two tracts of lacustrine alluvium, at Edwalton [SK 603 355] and to the east of Nottingham Airport, Tollerton [SK 625 360], were described by Lowe (1989a). The latter tract is the larger of the two, and has yielded more lithological and faunal data. Its deposits consist of up to 3 m (generally 1.5 to 2.5 m) of grey or grey-brown, clayey and sandy silts, commonly structureless but with signs of lamination at some levels. Thin layers of peat and molluscan debris are common. Bones, rootlets and woody fragments also occur throughout. Molluscan faunas were listed by Lamplugh et al. (1908) and were studied and interpreted in more detail by McMurray (1993). The fauna consists entirely of extant Flandrian freshwater and terrestrial species, and is characteristic of habitats fluctuating from shallow lacustrine to marsh and grassland, with a gradual trend towards the last as sediment accumulation progressed. One freshwater gastropod species, Theodoxus fluviatilis (Linné), has been recorded from the Trent alluvium nearby at Holme Pierrepont (Cummins and Rundle, 1969), but not from the lacustrine alluvium at Tollerton. On the grounds that this species is not known in the UK before about 6600 years BP, McMurray (1993) suggested that its absence implied that the ‘Tollerton lake’ had silted up by that date. It is likely, however, that marshy conditions persisted until the recent artificial drainage of the area (Lowe, 1989a).

The lacustrine alluvium north of Bingham [SK 700 404] was described by Rathbone (1989b). The deposits average 1 m in thickness, locally reaching 3 m, and closely resemble those at Tollerton, though with thicker beds of peat up to 1.5 m. They produce a dark grey to black, heavy soil with abundant shell debris. The boundary with alluvial deposits to the east is gradational.

Shell marls and peaty layers occur within the extensive tracts mapped as alluvium to the north of Barnstone [SK 73 36] and between Cropwell Bishop and Wiverton Hall [SK 705 360]. Although lacustrine conditions may have prevailed temporarily in these areas, it has not proved practical to map these deposits separately from the adjacent alluvium.

Depositional environment and age

These lacustrine deposits are all located on the outcrops of either the Cropwell Bishop Formation or the upper part of the Edwalton Formation, which are the most gypsiferous parts of the Mercia Mudstone Group. It is therefore likely that the lakes formed in broad, shallow depressions produced by the dissolution of interstitial gypsum within the bedrock and resultant gradual lowering of the land surface. The gypsum solution process may have been enhanced by cryoturbation of the bedrock in Late Devensian times, and the lakes probably formed in the more temperate climate of the early Flandrian after about 10 000 years BP. The lake waters were partly fed by minor streams and by occasional inundations of floodwater from nearby larger rivers.

Mass movement deposits

Head

The term ‘head’ is applied to slope deposits produced by a range of periglacial mass movement processes (see for example Harris, 1987), of which solifluction is usually the dominant agent. Head is composed of weathered material derived from upslope. In areas that have not been glaciated since the Anglian period, such as the Nottingham district, head deposits have probably accumulated over an extended period of denudation spanning several climatic fluctuations from stadial to interglacial. This has been demonstrated by the successive flights of Wolstonian and Devensian-age head terrace features that have been mapped and named in the adjacent Melton Mowbray district to the south (Brandon, in Carney et al., 2004). Hence, the deposits of the Nottingham district may be of diverse age and origin; some processes, such as rain-wash and soil creep, operated during more temperate conditions and still continue today, depositing mainly colluvial head or ‘colluvium’. Although it is impracticable in most cases to differentiate between head deposits of different age or type, most of the deposits classified as diamictons (see below) in the Nottingham district may represent older (possibly pre-Late Devensian) head deposits, preserved on low interfluves following changes in patterns of drainage and incision.

Thin veneers of head are probably ubiquitous on most slopes throughout the district, but deposits have only been mapped where they are likely to exceed 0.5 to 1 m in thickness. Thin spreads or scatterings of exotic pebbles and cobbles are common in many parts of the district, being most noticeable on interfluves and gentle slopes underlain by the Mercia Mudstone Group. The pebbles consist mostly of quartzite and quartz derived from the Sherwood Sandstone Group. Less abundant clasts include Cretaceous flint, Jurassic limestone, Carboniferous sandstone and limestone, wind-polished Mercia Mudstone dolomitic siltstone (skerry) slabs, and worn, Lias-derived Gryphaea valves. Some larger boulders of granite and olivine-dolerite were recorded on the Sherwood Sandstone outcrop to the north of Nottingham by Shipman (in Lamplugh et al., 1908). These exotic clasts were derived from the denudation of local but formerly more extensive glacial or glaciofluvial deposits.

Thicker deposits of head, up to 3 m, typically occur as aprons at the foot of slopes or as more extensive spreads in valley bottoms. They are commonly poorly consolidated and show randomly orientated, pebble to cobble-sized angular clasts set in a finer grained matrix. Less commonly, crude stratification is evident. The deposits are highly variable in composition, reflecting the parent material cropping out upslope. Nevertheless, two main types of head can be distinguished. The first is derived mainly from the principal mudstone-rich bedrock types, the Mercia Mudstone or Lias groups, and commonly consists of a soft to plastic silty clay with angular fragments (litho-relicts) of less weathered bedrock materials. The second is derived from the Sherwood Sandstone Group and consists of unconsolidated pebbly sand. Both types of head contain a proportion of exotic clasts, mainly quartzite and flint pebbles, derived from superficial deposits. In some cases these clasts indicate the former presence up-slope of glacigenic deposits, since removed by denudation.

In the north-east of the district, near East Stoke and Thorpe [SK 775 502], small outcrops of deposits classified as ‘sandy head’ have been distinguished. These deposits consist of up to 1.4 m of pale brown, silty, fine-grained sand with weathered ‘skerry’ fragments derived from the local Mercia Mudstone bedrock. The deposits to the east of Thorpe contain small pebbles of flint, quartz and quartzite, derived from the Whatton Sand and Gravel that caps the low interfluve to the east. The high sand content of these deposits appears to be anomalous because of the lack of sufficiently sandy source material up-slope. The situation of these deposits on north and east-facing slopes overlooking the Trent valley may indicate a wind-blown origin, derived largely from the Holme Pierrepont Sand and Gravel when unvegetated periglacial environments prevailed during the Late Devensian. Extensive spreads of aeolian deposits (Blown Sand) occur on the eastern flanks of the Trent valley in the Ollerton district to the north (Edwards, 1967).

Shipman (in Lamplugh et al., 1908) described 0.6 to 1.8 m of ‘Glacial drift’ beneath the Leen Sand and Gravel at Basford, consisting of mottled red-brown and yellowish green pebbly sand. The ‘kneaded and crumpled’ structure with ‘puckered strings of pebbles’ probably indicates involutions resulting from post-depositional cryoturbation. The low elevation of these deposits argues against a glacial origin; they most likely represent head deposits derived from the Lenton and Nottingham Castle Sandstone formations upslope.

Diamicton

Several patches of pebbly clays with interstratified sands and gravels have been mapped between Edwalton and East Bridgford. A nongenetic lithological classification is assigned to these deposits due to their uncertain origin. They occupy typically low interfluves, but also occur on gently sloping valley sides and in valley bottoms. At Gamston [SK 605 375], the deposits underlie and interfinger with the lowermost part of the Bassingfield Sand and Gravel (Lowe, 1989a). Between Nottingham Airport, Tollerton and Stragglethorpe [SK 635 360], the deposits lie at low elevations (27 to 32 m above OD), flanking the lacustrine deposits in that area and locally underlying them. Other outcrops between Saxondale and East Bridgford lie at elevations between 40 and 55 m above OD. They occupy gently sloping, low-lying interfluves that are probably underlain by resistant dolomitic siltstone and sandstone of the Edwalton Formation. None of the deposits exceed 2.5 m in thickness.

Near Saxondale village, drainage ditches [SK 6737 4059]; [SK 6706 4114] showed about 1.7 m of brown or greenish brown silty and clayey sand, poorly sorted, with a layer of greenish grey clay (0.6 m thick) towards the middle (Rathbone, 1989b). Some sand grains have the frosted, millet-seed appearance characteristic of aeolian transport. Abundant pebbles and cobbles occur throughout, including wind-polished cobbles of grey dolomitic siltstone derived from the Mercia Mudstone Group and less common exotic pebbles of flint, quartz and quartzite. Contorted bedding in the underlying bedrock indicates disturbance by cryoturbation. Temporary sections near Holme House [SK 6309 3813] showed about 2.4 m of similar deposits underlying the Bassingfield Sand and Gravel (Lowe, 1989a).

The occurrence of these deposits at generally low topographical levels argues against their interpretation as tills. However, the exotic clast content may relate to partial derivation from pre-existing till deposits. The deposits may represent solifluction material with wind blown sand and polished bedrock fragments incorporated during transportation. The deposits between Saxondale and East Bridgford may be of local derivation. Those between Tollerton and Stragglethorpe may have been derived from tills present on Clipstone Wolds, 2 km to the south, in the adjacent Melton Mowbray district.

Landslips

Landslips are uncommon in the district and of generally small areal extent (mostly less than one hectare). Some are too small to be shown at 1:50 000 scale, but they are delineated on the 1:10 000 scale source maps. All the landslips occur on the outcrop of the Mercia Mudstone Group and most are located on the steep bluffs bordering the Trent floodplain. On the south-east side of the Trent, several landslips are developed on bluffs near Radcliffe on Trent and between Gunthorpe and East Stoke. Thereabouts, the Trent flows close to the foot of the bluffs and has promoted failure by undercutting the slope. The landslipped material includes both bedrock and superficial slope deposits. These slips are probably of Flandrian origin, but a larger slip north of Radcliffe on Trent [SK 6525 4105] displays a more rounded, degraded morphology; now stabilised; it may date from the Late Devensian.

The potential hazards posed by landslips and other forms of slope instability are discussed in Chapter 2.

Organic deposits

Peat

Peat is common as layers or lenticular beds within alluvial and lacustrine deposits throughout the district. It has formed by the slow accumulation of humic debris within abandoned river channels, marshes or shallow lakes. The only discretely mappable peat deposits are located along a former river channel at the margin of the Trent floodplain to the west of Morton [SK 720 513]. A borehole in these deposits (SK75SW/17 [SK 7223 5156]) near Poplar Farm proved peat to a depth of 3.4 m, separated from bedrock by a thin (0.4 m) layer of sandy gravel.

Shell marl and tufa

Shell marls commonly occur within lacustrine alluvium in the district (p.164). Other significant deposits have been mapped along Halam Beck to the west of Southwell [SK 6635 5335]; [SK 6685 5385], and about 400 m south of Southwell Minster [SK 703 534, mapped as Lacustrine deposits]. Those in Halam Beck consist of soft, white or pale grey calcareous clay with abundant freshwater gastropods; they give rise to a light, pale brown soil. The Southwell deposits are more peat-rich, producing a dark grey to black soil. Thickness is likely to be less than 2 m but has not been proved. Calcareous tufa is associated with the most north-eastern outcrop in Halam Beck [SK 6685 5385], ploughing up as orange-buff, ‘cindery’ fragments. Tufa also mantles bedrock along other parts of Halam Beck, notably east of Challands Farm [SK 657 529].

Both the shell marls and tufa are associated with former marshes and small meres fed by springs issuing from sandstone-rich parts of the Sneinton and Radcliffe formations. The tufa is produced by accumulation of inorganic calcium carbonate precipitates, derived from the dissolution of carbonate cement in the sandstones. Flow from these springs has reduced considerably in recent decades, due to lowering of the water table, but they are still evident as patches of damp ground, despite the excavation of field drains. The tufa near Challands Farm still accumulates sufficiently quickly to block drainage pipes periodically.

Evolution of the Trent drainage basin in the district

Preglacial topography and drainage

The construction of a subglacial rockhead surface to reflect the preglacial topography presents problems due to the patchy distribution of glacigenic deposits and the considerable extent of postglacial denudation in the district. The available information suggests a preglacial land surface declining gradually southwards in altitude, from at least 144 m above OD at Loath Hill [SK 636 537], north of Oxton, to 95 to 120 m between Bestwood and Ravenshead and 80 m at Wilford Hill [SK 582 351], immediately south of the district. Patches of diamicton mapped to the west of Newton [SK 675 405] probably represent local soliflucted tills, and these lie at about 50 m OD.

In the Aslockton area, outcrops of ‘Boulder Clay’, shown at elevations as low as 19 m above OD on the 1908 edition of the Sheet 126 Nottingham prompted Straw (1963) and Rice (1968b) to suggest that the Vale of Belvoir was lowered to its present level by glacial erosion. Reinterpretation of these deposits as fluvial gravels leaves the Vale of Belvoir free of glacigenic deposits, a conclusion also reached following resurvey of the adjacent Melton Mowbray district (Carney et al., 2004). Glacial striae formerly observed near Wartnaby in the Melton Mowbray district (Lamplugh et al., 1909) nonetheless leave little doubt that the Vale of Belvoir area was traversed by ice moving from north to south. Considerable subsequent denudation has taken place, as the precursors of the rivers Witham and Devon and their tributaries regraded to successive incisions of the Trent.

Lamplugh et al. (1908) took the similar elevations of glacial deposits at Colwick and Wilford Hill, on opposite sides of the Trent, to indicate that the deeply incised course of the Trent valley between Long Eaton and Newark must be a postglacial feature. The origins of this so-called ‘Trent Trench’ (see below) and the preglacial drainage pattern in the area have been discussed subsequently by many authors. Swinnerton (1937) invoked a Neogene drainage system with eastwards flowing master rivers draining through the Lincoln and Ancaster gaps. Linton (1951) later extended considerably the proposed course of the Ancaster River, linking it to a proto-Trent trunk stream believed to have flowed eastwards across the Midlands. This model was elaborated later by Straw (1963), who plotted the course of the proto-Trent through the Ruddington, Tollerton and Cropwell Butler areas, then across the Vale of Belvoir to the Ancaster Gap. Shotton (1953) suggested that a major preglacial river drained northwards into this proto-Trent, essentially along the same route as the present-day Soar. This river was a continuation of the ‘proto-Soar’ system of central England in which were deposited fluvial gravels and sands that were later termed the Baginton Formation (Maddy and Lewis, 1991).

Although the ‘proto-Trent theory’ has been widely quoted in textbooks, no fluvial deposits of preglacial age have ever been found to support it. Furthermore, the topographical evidence for a palaeovalley along the route proposed by Straw (1963) must be considered highly speculative in view of the extent of postglacial erosion. Work on preglacial sediments elsewhere in the Midlands throws further doubt on the existence of a proto-Trent river. For example, Rose (1987, 1989) has plotted an alternative route of the proto-Soar, renaming it as the Bytham River and suggesting that it turned eastwards near Syston (Figure 40)a to drain more or less parallel to the Wreake valley (cf. Wyatt, 1971), eventually flowing across East Anglia. Analyses of pebble derivations by Rice (1991) and heavy minerals by Bateman and Rose (1994) suggest that this Bytham River was joined to the west of the Wreake valley by a tributary from the north-west (Derby River of Brandon, 1997), carrying Carboniferous detritus from the southern Pennines. Consideration of (Figure 40)a indicates that such an interpretation must preclude the existence of an eastward-flowing proto-Trent immediately prior to the Anglian glaciation. Together with the limited evidence on the nature of the preglacial topography, it implies that the western half of the Nottingham district formed an interfluve separating the proto-Derwent valley in the west from the catchment of a preglacial Lincolnshire River to the east or north-east. The latter may have drained north-eastwards through the Lincoln Gap or northwards towards the Humber. Streams draining the Mercia Mudstone outcrop to the north of Nottingham may once have contributed to a smaller Ancaster River (Swinnerton, 1937), creating a high level ‘Ancaster Gap’ through the Lincolnshire Limestone escarpment. There is, however, no evidence of a former watershed between the Ancaster and Lincolnshire rivers, so it is likely that the Lincolnshire River captured the headwaters of the Ancaster River long before the Anglian glaciation. Immediately prior to glaciation, drainage in the Vale of Belvoir may thus have been towards the north (Figure 40)a. The present morphology of the Ancaster Gap may relate to incision by glacial meltwaters (Pocock, 1954; Berridge et al., 1999).

Glaciation

Since the work of Deeley (1886), it has been recognised that two main types of glacial tills occur in the East Midlands, distinguished by the provenance of their erratics. The first, variously termed the Northern or Pennine Drift, is typically red-brown in colour and contains a preponderance of Triassic and Carboniferous-derived material, with lesser amounts of igneous erratics derived from Cumbria. The second, traditionally referred to as the Eastern Drift or Chalky Boulder Clay, typically has a blue-grey matrix with erratics derived mainly from the Jurassic and Cretaceous rocks of Lincolnshire. In many parts of the Midlands, most noticeably in Warwickshire and Leicestershire, there is an overlap in the geographical distribution of the two tills, with the Pennine Drift generally showing relationships indicative of an older age. This led to the view that ice first advanced over the Midlands from the north and north-west, followed later by a more vigorous advance from the north-east or east. Deeley (1914) later suggested that separate glacial advances deposited the Pennine Drift and Chalky Boulder Clay within a single glacial stage. However, like some later workers (West and Donner, 1956; Posnansky, 1960), he maintained that substantial parts of the Pennine Drift should be assigned to an earlier and separate glacial episode.

Significant advances in understanding the glacial sequence of the Midlands resulted from the work of Shotton (1953) in the Coventry, Rugby and Leamington Spa areas. An initial encroachment of ice across the region from a north or north-westerly direction, depositing tills rich in Triassic material, was invoked. Slight retreat to the north resulted in the damming up of a proglacial lake (Lake Harrison), with the deposition of glaciolacustrine sands, silts and clays. A later, more vigorous advance of ice from a more north-easterly direction then over-rode the area, depositing the ‘chalky’ tills rich in Jurassic and Cretaceous erratics. Clayton (1953) and Straw (1963), working farther north in the Trent Basin, concurred with Shotton that both these glacial advances took place during a single glacial episode between the Hoxnian and Ipswichian interglacials, and this was later defined as the Wolstonian by Mitchell et al. (1973). As summarised in the introduction to this chapter, however, and discussed further below, it is now accepted that at least part of this glaciation was Anglian in age. A source of further confusion, which has not yet been resolved, is the possibility that the Anglian and Wolstonian timespans of the Middle Pleistocene may be much closer to each other than previously thought, provoking the suggestion by Keen (1999) that the Wolstonian be discontinued as a stage name.

Apart from the controversy over the age of glaciation, and of the Anglian/Wolstonian chronology, doubts have also been cast over whether any significant time-gap existed between the arrival of the ice sheets that carried the two tills. Rice (1981), Sumbler (1983) and Bridge et al. (1998) noted that the stratigraphically lower Triassic-rich till, now termed the Thrussington Till (Rice, 1968a), interdigitates with chalky tills to the north-east of Coventry. This indicates an early encroachment of eastern ice into the Midlands, prior to the formation of Lake Harrison. Similarly, the chalky tills, now termed the Oadby Till (Rice, 1968a), contain subordinate intercalations of Triassic-rich till.

The rather scattered tills and glaciofluvial deposits of the Nottingham district contain dominantly north or north-westerly derived erratics (Figure 40)b, and almost certainly represent the denuded remnants of a formerly more extensive, but probably thin sheet of ‘Thrussington’ glacigenic deposits (Lamplugh et al., 1908). The incoming of younger chalky, Oadby-type tills, of northeastern derivation, takes place in the south of the district, and is best seen between Cotgrave and Stanton on the Wolds (Lamplugh et al., 1909; Crofts, 1989a). Many authors (Lamplugh and Gibson, 1910; Swinnerton, 1937; Clayton, 1953; Posnansky, 1960) have referred to the Trent Basin as the contact zone between separate Pennine and Eastern ice sheets although, in reality, there is a broad zone in which tills of both ice sheets are present. Thus Cretaceous flints occur as far north as Heanor (Frost and Smart, 1979) and Jurassic limestones have been recorded at Bestwood, north of Nottingham (Rathbone, 1989a). Furthermore, a tripartite glacial stratigraphy is mapped farther south, across large parts of the Melton Mowbray district (Carney et al., 2004), where Thrussington (Pennine) Till is succeeded in places by a Lias-rich variant of Oadby Till, which is in turn overlain by the typical, chalk-rich Oadby Till. The picture of ice first invading the region from the north, and subsequently being displaced by an advance from the north-east or east (Lamplugh and Gibson, 1910; Clayton, 1953; Posnansky, 1960; Straw, 1963) may therefore be an oversimplification. It is nevertheless possible that a margin to one of the north-eastern ice sheets may have lain broadly parallel to the present course of the Trent (see for example Posnansky, 1960), playing an important part in determining the pattern of postglacial drainage in the Nottingham district, as discussed below.

Recent work in the Nottingham district (Brandon and Sumbler, 1988, 1991; Howard, 1992), principally on the Trent terraces, provides as yet inconclusive local evidence that the glaciation was Anglian in age (Table 18). This arises from interpretation of the Eagle Moor Terrace as representing glaciofluvial outwash that had aggraded during deglaciation of the Oadby Till ice sheet, in Late Anglian times (Brandon and Sumbler, 1988, 1991). Howard (1992) has demonstrated that successively younger river terrace deposits of the Trent contain steadily declining proportions of exotic clasts derived from outside the Trent drainage basin. This indicates that there has been no fresh input of exotic clasts during the formation of the terrace sequence and confirms that the region has not been glaciated since the Anglian Stage.

Late Anglian drainage and the origin of the Trent Trench

The ‘Trent Trench’ is the name given by many authors to the incised linear section of the Trent valley between Long Eatonand East Stoke. Thetrenchmaintainsafairlyconstant width of 2 to 3 km, and is bounded on either side by local steep bluffs (King, 1972). These are typically 30 to 40 m high, but reach a maximum of almost 60 m at Syerston Airfield [SK 722 477]. The valley appears to be floored only by Flandrian alluvium and the Late Devensian Holme Pierrepont Sand and Gravel (Figure 36)b.

After Lamplugh et al. (1908), there has been general agreement that the Trent Trench did not exist prior to glaciation. Lamplugh and Gibson (1910) suggested that the feature was excavated by meltwaters derived from a decaying Pennine ice sheet and that these waters were guided north-eastwards along the margin of a stagnant ice lobe occupying the Vale of Belvoir area. In contrast, Swinnerton (1937) suggested that the trench was cut solely by headward erosion of powerful meltwater streams emanating from a decaying Pennine ice sheet. Later workers, notably Posnansky (1960) and Straw (1963), have favoured Lamplugh and Gibson’s hypothesis, invoking the lobe of stagnant ‘Eastern’ ice to explain the diversion of the Trent from a supposed preglacial course across the Vale of Belvoir area. They maintained that, on deglaciation, meltwaters flowed along the margin of the stagnant ice lobe and escaped north-eastwards through the Lincoln Gap, initiating the Trent Trench and aggrading the Eagle Moor Sand and Gravel (Figure 40) c, d. The present morphology of the Trent Trench, including both its lateral and longitudinal profile, has been considerably modified by further incision since the end of the Anglian Stage. The precise mechanism of its formation may never, therefore, be resolved with any certainty. The evidence that there was no proto-Trent flowing across the Vale of Belvoir area in preglacial times does, however, require modification of the models proposed above for the formation of the Trent Trench.

Certain elements of Lamplugh and Gibson’s (1910) model remain attractive, particularly the supposition that the Trent Trench was formed along the contact zone between Pennine and Eastern ice sheets. Objections can be raised to other aspects, however. In particular, it is unlikely that stagnant Eastern ice could have continued to block the Vale of Belvoir area without also blocking the Lincoln Gap, thus preventing the eastwards escape of meltwaters. Without an outlet to the east or north, meltwaters could not have developed sufficient erosive power to excavate the Trent Trench. It seems more likely, therefore, that the trench was initiated upon deglaciation. This would have enabled free flow of meltwater towards the Lincoln Gap, as well as the aggradation of proglacial outwash deposits represented by the Eagle Moor Sand and Gravel. It is suggested that, as climate ameliorated towards the end of the Anglian stage, englacial meltwaters were unable to drain eastwards through the preglacial Bytham valley, adopting instead a new route across the watershed between the former proto-Derwent and Lincolnshire river basins. The meltwaters may have exploited a zone of structural weakness in the ice, marking a former suture where Pennine and Eastern ice originally coalesced (Figure 40)b. Alternatively, they may simply have found the shortest route between the two drainage basins. Flowing initially along tunnels excavated within the ice (Figure 40)c, the meltwaters eventually impinged on the underlying bedrock, cutting a subglacial meltwater channel across the former watershed (Howard, 1992). In support of this hypothesis, a series of extensive, east–west orientated subglacial palaeochannels, or tunnel valleys, have been mapped beneath the Trent valley floodplain deposits in the Loughborough district, to the south-west (Brandon, 1996; Carney et al., 2001). As deglaciation gathered pace and the land surface was exhumed, the Bytham valley remained blocked by glacial deposits. Meltwaters thus continued to be guided through the incipient Trent Trench, first deepening and widening the channel and then, as their erosive power waned, aggrading the proglacial outwash deposits of the Eagle Moor Sand and Gravel. All traces of these outwash deposits were subsequently removed from the Trent Trench by post-Anglian erosion.

The deeply incised valleys (‘dumbles’) of streams draining the Mercia Mudstone outcrop to the northwest of the Trent were probably formed initially in latest Anglian times, as streams charged with proglacial meltwater graded rapidly to the newly incised Trent Trench (Figure 40)d. Further deepening of the dumbles has occurred since the Anglian in response to rejuvenations of the Trent drainage system.

Hoxnian–Wolstonian drainage

With the possible exception of the Eagle Moor Sand and Gravel, no deposits intervening in age between the Late Anglian (MIS 12) and late Wolstonian (MIS 6) are known in the Nottingham district (Table 18). The area would have experienced at least one cold climatic period during this episode, represented by the early Wolstonian Stage 8. No terraces are preserved from this period, but it is highly likely that the Trent continued to flow through the Trent Trench. As proposed by Penning (in Jukes-Browne, 1883), the later course of the Trent through the Lincoln Gap (Figure 40)c, d is marked by outcrops of the Balderton Sand and Gravel, the dating of these deposits indicating that this aggradation occurred during the late Wolstonian (MIS 6; Brandon and Sumbler, 1991). Some authors (Pocock, 1929; Straw, 1963; Howard, 1992) have considered that the Trent flowed northwards to the Humber before aggradation of the Balderton Sand and Gravel, and various explanations have been offered to explain its subsequent diversion through the Lincoln Gap. One model, invoking blockage of the Humber route by Wolstonian ice (Howard, 1992), is compatible with the late Wolstonian age of the Balderton Sand and Gravel alluded to above. On the other hand, other explanations, notably those by Jukes-Browne (1883), Swinnerton (1937) and Brandon and Sumbler (1988, 1991), consider that the Trent did not flow to the Humber until after aggradation of the Balderton Sand and Gravel, i.e. after the late Wolstonian. This controversy is not likely to be resolved until more information has been compiled on the dating of Quaternary deposits in the lower Trent basin and elsewhere in Lincolnshire.

The Bassingfield Sand and Gravel could date from the late Wolstonian, although it may equally represent a later Ipswichian aggradation. The Whatton Sand and Gravel was deposited by a tributary flowing northward across the Vale of Belvoir area, joining the Trent at Balderton (Figure 37).

Ipswichian drainage

No deposits of definite Ipswichian age are known in the district, although the Bassingfield Sand and Gravel may date from this period rather than the late Wolstonian. The Trent continued to incise its course along the Trent Trench, but abandoned its late Wolstonian route through the Lincoln Gap and adopted a course northwards towards the Humber, terminating aggradation of the Balderton Sand and Gravel (Brandon and Sumbler, 1988, 1991). Capture of the Trent by a Humber tributary has been suggested as the mechanism responsible for diversion (Jukes-Browne, 1883; Swinnerton, 1937). Alternatively, the Trent may have resumed a pre-Wolstonian route to the north, following wasting of Wolstonian ice blocking the Humber estuary (Howard, 1992).

Devensian–Flandrian (Holocene) drainage

Little evidence remains of the deposits that must have formed during Early to Mid-Devensian times, although aggradation of some of the river terrace deposits in the Devon catchment possibly commenced prior to the Late Devensian. The latter period is marked by extensive aggradation of fluvial sands and gravels by the Trent and its tributaries (Table 18). The Holme Pierrepont Sand and Gravel aggraded along the Trent Trench, and the Leen Sand and Gravel along the Leen valley. These deposits show evidence of transport in powerful braided rivers with a high sediment load, and farther west they have been interpreted as valley sandar deposited from an ice front higher up in the Trent catchment system (Brandon, 1996). Similar sand and gravel deposits also aggraded in the River Devon catchment, accompanied by several drainage diversions (p.160). An older, more easterly course of the River Witham was captured by headward erosion of the gap [SK 835 455] at Long Bennington, to the east of the district, leading to deposition of Late Devensian gravels along a new course across Bennington Fen. The intensely cold periglacial conditions led to extensive cryoturbation of bedrock and involution of older drift deposits. Accelerated gypsum solution caused subsidence and formation of low depressions on the outcrops of the Edwalton and Cropwell Bishop formations near Bingham and Tollerton. Shallow lakes later occupied the depressions in the early Flandrian.

With climatic amelioration in the Flandrian, the rate of discharge and sediment flux to the Trent drainage basin became reduced, resulting in a widespread transition from dominantly braided channel systems to single thread, meandering channels (Figure 39). Incision and reworking of Late Devensian sand and gravel deposits has left a series of low terraces (including the Holme Pierrepont Terrace) along the main drainage courses. Shallow lakes near Bingham and Tollerton silted up rapidly, probably before 6600 years BP.

Chapter 9 Structure

The tectonic structures of the district fall into two principal categories: fundamental structures that define domains related to Palaeozoic basin formation and deformation, and the relatively minor faults, flexures or folds that have been mapped in areas of Triassic or Jurassic outcrop. The most important structures are the Cinderhill–Foss Bridge and Eakring–Foston fault complexes. Although they displace Mesozoic rocks at the present land surface, these structures also extend downwards as deep-seated, crustal-scale lineaments and boundaries that are of regional importance (Lee et al., 1990), as indicated by the geophysical information discussed in Chapter 10. The coincidence between surface and deep structure indicates that these major faults, as well as other displacements in the district, are the ‘posthumous’ rejuvenations of pre-existing basement discontinuities, as discussed by Swinnerton and Kent (1949) and Turner (1949).

Pre-Carboniferous deformation

The pre-Carboniferous ‘basement’ is likely to consist mainly of Ordovician metasedimentary and metavolcanic sequences intruded by granodiorite plutons, all of these lithologies having been penetrated by boreholes outside the district (Chapter 3). The metasedimentary and metavolcanic rocks bear the imprint of a penetrative cleavage, and were metamorphosed under high anchizonal to greenschist facies conditions during a major event that has been correlated with the Acadian Phase of the Caledonian Orogeny (Pharaoh et al., 1987; Merriman et al., 1993).

Further evidence for the nature of pre-Carboniferous Structure is provided by the exposures of Charnwood Forest, 18 km to the south-west of the district. There, the Precambrian and Cambrian basement rocks are folded along a principal north-west axis, which is cut across by a penetrative west-north-west-trending cleavage (Carney et al., 2001). Radiometric (Ar/Ar) dating has shown that the mica forming the cleavage fabric crystallised during a Siluro–Devonian phase of the Caledonian Orogeny (Carney et al., 2008). Together with the alignment of Ordovician plutons, such as the Rempstone Granodiorite, and of possible major thrust and shear zones within the basement (Carney et al., 2004), these west-north-westerly structural elements appear to have been of fundamental significance, acting as the precursors for the faults and folds generated during subsequent Carboniferous and Mesozoic-Cenozoic tectonism in the district.

Structural elements with north-north-west orientations are also present and may reflect the influence of a major tectonic boundary to the south-west of the district. That junction separates the concealed ‘Eastern Caledonides’ fold/thrust belt of eastern England, which forms the basement to the Nottingham district, from a relatively less tectonised crustal block known as the Midlands Microcraton (Pharaoh et al., 1987).

Early Carboniferous syn-rift structural history

The Nottingham district lies at the southern edge of a mosaic of Early Carboniferous basins (Figure 41) that are located within a wide zone to the north of the Wales–London–Brabant Massif. One of the earliest reviews of the distribution of these basins and their intervening ‘highs’ was that by Falcon and Kent (1960; see also, Kent, 1968b). Most of these basins have the geometry of an asymmetric half-graben, with margins controlled by syndepositional faults and flexures that have predominant west-north-west and north-west orientations. The half-graben basins and their intervening tilted shelves in turn reflect localised subsidence caused by the relaxation of suitably orientated basement structures, the triggering mechanism being an early Carboniferous phase of lithospheric extension across this region (Leeder, 1982). Their evolution is now much better understood, thanks to detailed seismostratigraphical studies of reprocessed high quality seismic reflection data (Ebdon et al., 1990; Fraser et al., 1990; Fraser and Gawthorpe, 2003). These studies have demonstrated that Dinantian syn-rift sedimentation was characterised by phases of fault-controlled subsidence alternating with periods of relative tectonic quiescence, punctuated by episodes of mild basin inversion. The importance of the rift-bounding structures diminished later in the Carboniferous, when the tectonic regime changed to one characterised by postrift regional thermal subsidence. However, some of the faults were reactivated during Variscan compression and basin inversion at the end of the Carboniferous Period.

Three principal Early Carboniferous structural domains occur within the Nottingham district (Figure 42). The most extensive of these, occupying most of the district, comprises the East Midlands Platform of Fraser and Gawthorpe (1990), here termed the Nottingham Shelf. The shelf is bounded to the south-west by the Cinderhill–Foss Bridge Fault System and an associated flexure, which marks the north-eastern limit of the Widmerpool Half-graben (Fraser et al., 1990). The latter is an early Carboniferous asymmetric basin (Kent, 1967), the main depocentre of which lies to the south-west of the district (Figure 42); (Figure 44). The north-eastern boundary of the shelf is defined by the Eakring–Foston–Denton Fault System, which in turn delineates a further asymmetric basin, the Welbeck–Sleaford Low.

Seismic reflection data indicate that Dinantian strata on the Nottingham Shelf are attenuated compared with strata in the adjacent basins (Figure 43), (Figure 44). They exhibit a very gradual north-eastwards direction of thinning across the shelf (Chapter 4), which in part may have been caused by the tilting produced by footwall uplifts during mild syn-Dinantian inversion events along the Eakring–Foston Fault System. The seismic data also show that the subCarboniferous unconformity lies at an average depth of about 1250 m below OD beneath the shelf.

The transition between the Nottingham Shelf and Widmerpool Half-graben is represented by a complex, west-north-west-trending structure, the crest of which lies about 1 km north of the similarly orientated Cinderhill–Foss Bridge Fault System (Figure 42). Seismic reflection data show that for pre-Namurian strata this structure has the form of a faulted monoclinal flexure (Figure 43), and this has been termed the ‘CinderhillFoss Bridge Flexure’ in the adjacent Melton Mowbray district (Carney et al., 2004). Dinantian strata thicken progressively south-westwards across this structure, from the Nottingham Shelf into the Widmerpool Half-graben. Basaltic magmatism was located along this structure in Brigantian times (~P1d), and as shown in (Figure 44), it replaces laterally parts of seismic sequence EC6 of Ebdon et al. (1990). The main development of volcanic rocks was proved in the Strelley No. 1 Borehole, which is located 4 km west of the district. It has been suggested (Chapter 4) that this phase of volcanism may reflect the rise of magmas that exploited a zone of tension as the monoclinal structure developed. On the evidence of boreholes, the Strelley volcanic rocks extend along the Cinderhill Fault into the present district, and may be represented by the attenuated basaltic sequences seen in the Saxondale No. 1 Borehole (Chapter 4), adjacent to the Harlequin Fault.

Up to 2.5 km of Dinantian strata are indicated in the Widmerpool Half-graben by seismic profiles, such as that shown on (Figure 44), in the south-west corner of the Nottingham district. Farther south, these strata attain a thickness of 5.5 km in the deepest part of the halfgraben, against the Normanton Hills Fault (Carney et al., 2001). As boreholes provide only a very limited penetration of this sequence (Chapter 4), evidence for the tectonic and stratigraphical history of the Widmerpool Half-graben is necessarily derived from seismic reflection data. Ebdon et al. (1990) and Fraser et al. (1990) recognised six sequence units (EC1–6) within the syn-rift phase, and two sequences (LC1–2) within a late Brigantian to late Bolsovian (Westphalian C), post-rift phase (Figure 44). Sequences EC1, 3 and 5 have wedge-shaped geometries, thickening onto the basin-bounding fault and thinning up the hanging wall dip-slope, and are interpreted as tectonically driven sequences arising from periods of lithospheric extension. Such events were also characterised by strong sedimentary onlap, the drowning of hanging wall carbonate margins and uplift of footwall zones (Ebdon et al., 1990). The intervening sequences, EC2, 4 and 6, reflect the development of prograding carbonate ramps and are interpreted as stillstand or regressive sequence tracts deposited during tectonically quiescent periods. In the south-west part of the Nottingham district, such strata probably dominate the Dinantian sequence occupying the upper hanging wall dip-slope of the half-graben (Figure 44). They are interpreted as comprising successive carbonate ramps that rimmed the adjacent shelf and prograded south-westwards, supplying calciturbidites to the deeper parts of the basin. The most rapid phase of subsidence of the halfgraben occurred during deposition of sequences EC1–3 (Courceyan to Arundian), when up to 3 km of strata accumulated in the axis of the Widmerpool Half-graben.

Sequences EC4–6 (Holkerian to Brigantian) comprise up to 1 km of strata. The contrast with the Nottingham Shelf, for example the sequence proved by the Ironville No. 5 Borehole (Chapter 3), is notable. Here, on the uplifted shoulder of the rift, sequences EC1–3 are half the thickness of EC4–6, reflecting the rapid extension in the early history of the rift.

The Welbeck–Sleaford Low (‘Welbeck Low’ on the structure inset of the Sheet 126 Nottingham) is a Dinantian half-graben basin located on the north-eastern flank of the Nottingham Shelf. Its new name here emphasises the fact that, although segmented by the Eakring–Foston Fault System, it is broadly continuous with the Sleaford Low of the Grantham district (Figure 41) and the Welbeck Low farther north. The southern margin of the basin is delimited by the Eakring–Foston Fault System, and by the Barkston Fault to the east of the district (Figure 41); (Figure 42). On previous compilations (e.g. by Ebdon et al., 1990), no basin was shown in this position. However, seismic reflection data indicate its presence, with at least 2 km of Dinantian strata in the hanging wall of the Eakring–Foston Fault System (Figure 43). For the latter, a Dinantian syndepositional displacement of about 1400 m down to the northeast can be inferred.

Mid And Late Carboniferous post-rift structural history

By early Namurian times, the East Midlands tectonic regime reflected a more uniform type of regionally distributed subsidence (post-rift thermal sag), in which faulting was of relatively minor importance (Fraser et al., 1990). The ensuing phase of sedimentation progressively filled the Dinantian rift-basins and is well documented by seismostratigraphical studies. Sequence LC1a (late Brigantian–late Pendleian in age) comprises prodelta mudstones, mainly of the Edale Shale Group, representing distal sedimentation related to the advancing Silesian delta system, which had already filled the basins of northern England (Fraser et al., 1990). Sequence LC1b (late Pendleian–Alportian), representing the stratigraphically higher part of the Edale Shale Group, is condensed over the Nottingham Shelf, the Widmerpool Half-graben being starved of sediment at the time. This may reflect large-scale switching of delta lobes in the southern North Sea region, or climatic changes in the hinterland to the north affecting the rate of sediment supply (Fraser and Gawthorpe, 1990). Sequence LC1c (Kinderscoutian–late Westphalian A) represents the main phase of Millstone Grit and Lower Coal Measures sedimentation, the Millstone Grit phase being characterised by the continued and widespread progradation of the Kinderscout, Ashover and Chatsworth–Crawshaw delta systems into the Widmerpool Half-graben. The Ashover Delta entered the half-graben longitudinally in a south-east to north-west direction, following the inherited Dinantian structural grain.

It is probable that filling of the former half-graben basins was in the main accomplished ‘passively’, without significant differential movements along faults. Reactivation of structures along the Cinderhill–Foss Bridge tectonic hinge line is suggested, however, by the attenuation of Namurian strata (Edale Shale equivalents, or Sequence LC1a, b of Ebdon et al., 1990) on to the Nottingham Shelf in the adjacent Melton Mowbray district (Carney et al., 2004; see also Figure 44). Minor inversion may also have reactivated former listric faults with north-north-west orientations (Ebdon et al. 1990) following the deposition of Brigantian strata (EC6), but prior to the accumulation of sequences LC1–2 (Namurian–Westphalian). Such inversion may be reflected by the attenuation of Namurian (Edale Shale Group) strata north-eastwards across the Eakring–Foston Fault System, into the area formerly occupied by the Welbeck–Sleaford Low (Figure 6).

The culmination of basin infilling is reflected by the prevalence of lower delta plain sedimentary environments over much of northern England in Lower Coal Measures times, at the end of deposition of seismostratigraphical sequence LC1 (Guion and Fielding, 1988). At the same time, localised early Westphalian (Langsettian) tectonism is suggested by the extrusion of a thick sequence of basaltic rocks in the south-east of the district (Chapter 4). In many parts of the world, such intraplate magmatism is typical of plume-related extensional tectonic settings. The trends of overall thickening towards the east, and the general distribution of the volcanic rocks, indicate that the lavas represent outflows from centres that might have been controlled by extensional movements along precusor(s) to the Denton Fault, as noted by Carney et al. (2004), and/or the Eakring–Foston Fault System of this district (Figure 42). The main episode of volcanism occurred over a relatively brief interlude (possibly 2–3 Ma), and terminated just before the regional flooding event that deposited the Vanderbeckei Marine Band. Following the latter, continued thermal subsidence established predominantly upper delta-plain environments in the Middle and Upper Coal Measures (Westphalian A–C), representing sequence LC2 of Ebdon et al. (1990).

Variscan inversion structures

An intense episode of block uplift and basin inversion occurred throughout the district during the culminating phase of the Variscan Orogeny, in late Westphalian D and Stephanian times. This event, documented for the region by, among others, Fraser et al. (1990) and Corfield et al. (1996), was a response to foreland compression that occurred towards the end of nappe emplacement within the Variscan orogenic belt, which at that time lay across southern Britain. It was anticipated by the red-bed depositional regime of the Barren Measures, interpreted as representing the onset of better drained conditions in response to a general lowering of base-levels during the initiation of intra-Westphalian tectonic uplift (Besly, 1988b). In the Nottingham district, the Variscan movements reactivated basement structures and reversed the throws of the Dinantian normal faults that controlled the margins of the Nottingham Shelf, the principal effect being the inversion of the Welbeck–Sleaford Low (Figure 45).

Among the Variscan structures that formed in the East Midlands region were long-wavelength inversion anticlines in the hanging wall blocks of the major westnorth-west-trending syndepositional faults, for example the Normanton Hills Fault and associated Rempstone Anticline farther south, in the Melton Mowbray district (Carney et al., 2004). In contrast, north-north-westto north-west-trending structures, such as the Denton Reverse Fault (Berridge et al., 1999; fig. 6) and its continuation in this district, the Eakring–Foston Fault System, showed relatively less Dinantian syndepositional growth, and movements during the Variscan were characterised by shallower detachments and tight inversion anticlines adjacent to the faults. Such structures, which may have commenced growth early in the Namurian (see above), constitute the majority of hydrocarbon-bearing traps in the East Midlands (Fraser and Gawthorpe, 1990). In the Nottingham district, they include part of the Rolleston Anticline (Figure 45), related to inversion controlled by compression along the Eakring–Foston Fault System (Figure 43). Along the crest of the anticline, the baseNamurian was uplifted by about 450 m relative to its position on the Nottingham Shelf, 1.5 km to the southwest. About 250 m of this uplift was achieved by reversal of the fault and the rest by growth of the inversion anticline. Subsequently, Middle and Upper Coal Measures strata were eroded from the crest of the fold prior to deposition of Permian strata. Other, much smaller inversion anticlines with variable amplitudes occur between the Harlequin and Cinderhill–Foss Bridge fault systems (Figure 43).

(Figure 45) illustrates other structures that are most probably related to Variscan deformation. The Carboniferous succession is tilted towards the north-east, and in the south-west of the district is displaced by a plethora of faults with west-north-west orientations and downthrows of up to about 150 m, mainly to the south. These displacements represent rejuvenations of movement along the Cinderhill–Foss Bridge axis of Dinantian thickening. The Harlequin Fault, with a northerly throw of about 50 m in the Carboniferous, delimits the northern margin of a horst, and a zone of mild anticlinal folding, roughly coincident with the crest of the former monocline. Structures that cut across the regional tectonic ‘grain’ are faults and, farther north, gentle folds, with north-easterly and north-north-easterly orientations. These may reflect rejuvenation of subsidiary basement structures, which are more ‘visible’ here due to the relatively thin Carboniferous cover on the Nottingham Shelf.

Permian and Mesozoic basin evolution

By Permian time, the Carboniferous structural elements described above were no longer recognisable, and Variscan inversion structures were eroded and overstepped by Permian strata. The Permian and Mesozoic strata of the district were deposited within a different tectonic regime to that prevailing in the late Carboniferous, and form part of an entity termed the ‘East Midlands Shelf’ by Green et al. (2001), although this name should not be confused with the ‘East Midlands Platform’ syn-Dinantian province of other authors (e.g. Berridge et al., 1999). The general dip of these strata, at 1° to the east and south-east, indicates regional tilting in post-Jurassic times. Mild rejuvenation along the Rolleston Anticline and Eakring–Foston Fault System, probably during the same tilting event(s), is suggested by the northwest-trending domal structure developed on Barnstone Member strata around White House Farm [SK 815 460]. Other faults and periclinal folds associated with this structure give rise to a complex outcrop pattern in the Jurassic strata to the east of Staunton in the Vale [SK 82 43]

Reactivation of Variscan faults is shown by the many examples of normal displacements affecting Permo-Triassic and Lower Jurassic strata along the Eakring–Foston and Cinderhill–Foss Bridge fault systems. The most significant of these occur on the Harlequin Fault (locally 40 m; downthrow to the north), the Cinderhill–Foss Bridge Fault System (up to 35 m; downthrow to the south-west) and the Eakring–Foston Fault System (up to 40 m; downthrow to the north-east).

There is no direct evidence for the age of this deformation, other than it being post-Early Jurassic. Data based on apatite fission track analysis and vitrinite reflectance, summarised by Green et al. (2001), suggest, however, that the East Midlands Shelf experienced two well-defined uplift and erosion events, dated respectively as Early Tertiary and Late Tertiary (Cenozoic). The favoured explanation (Green et al., 2001) is that these events indicate the relative ease of deformation of the structurally controlled Carboniferous domains of the district, such as the Widmerpool Half-graben and Nottingham Shelf.

Chapter 10 Geophysical evidence for concealed geology

Regional gravity and magnetic data are available for the Nottingham district from the BGS databanks (see Information Sources). The district has been included within a number of regional studies, such as those by Busby et al. (1993) and Cornwell and Walker (1989), the former providing information on the deep geology of an area stretching from Yorkshire to the south coast of England. The maps based on these datasets (Figure 46); (Figure 47) provide valuable structural information by indicating the presence of geophysical anomalies. Some of the anomalies clearly reflect structures defined by geological and seismic evidence, but others have no obvious surface structural expression and may be related to non-reactivated structures or igneous contacts within the basement (pre-Carboniferous) rocks of the district. The interpretation of the anomalies leads to an improved understanding of variations within the basement, where little other information is available (Chapter 9), and it demonstrates that certain structures in the district are of regional importance. The interpretations are in part based on modern processing and imaging techniques that now allow the more subtle anomalies to be studied. Certain of the gravity and aeromagnetic features of the district can be correlated with major structural lineaments indicated on the published tectonic map (British Geological Survey, 1996). The origins and significance of the regional-scale gravity and magnetic anomalies are discussed in Lee et al. (1990, 1991).

Physical properties

The accuracy of geophysical models based on gravity and magnetic data depends on the constraints imposed by the physical properties of the rocks in the district. The physical property measurements, summarised in Table 19, have been made by many workers in the East Midlands region (Arter, 1982; El-Nikheli, 1980), but also include data gathered during recent surveys of the adjacent Loughborough, Melton and Grantham districts.

The majority of the gravity and magnetic anomalies in (Figure 46; (Figure 47) have been picked from lines or zones of steep potential field gradient. They are interpreted as representing zones of rapid variations in physical properties of the basement rocks, such as may occur where different rock types are juxtaposed across faults or intrusive contacts, either close to the surface or at considerable depth.

Main gravity anomalies

The gravity anomaly pattern for the district is shown in (Figure 46), and can be seen in its regional context by referring to the Bouguer gravity anomaly map (British Geological Survey, 1997). The regional gravity data coverage is generally good (1 station per 1.4 km2) and has been augmented by additional data collected during resurvey of the Loughborough and Melton Mowbray districts.

The Bouguer gravity anomaly pattern in Figure 46 is dominated by a deep ‘low’ (GI), the centre of which lies just to the south, in the Melton Mowbray district. The gravity minimum (-13 mGal in the Melton Mowbray district) broadly coincides with the thickest accumulations of Carboniferous strata in the central and southern parts of the Widmerpool Half-graben, but the width of the body is restricted, with only a very minor elongation noted parallel to the trend of the half-graben. The northward prolongation of the anomaly takes it across the Cinderhill–Foss Bridge fault and flexure system, and the anomaly margins show only minor interruption by this structural axis, indicated by lineaments GL1 and GL2 of (Figure 46). In discussing the origin of G1 in the Melton Mowbray district, C P Royles (in Carney et al., 2004) noted that its shape and magnitude may be influenced by the presence of material in the basement that is of lower density than predicted local basement densities. The source of this lower density basement was suggested to be diorite or tonalite, with densities ranging between 2.73 and 2.68 Mg/m3 (Busby et al., 1993); such bodies were presumably coeval with the Rempstone and Melton Mowbray granodiorites of Ordovician age, encountered by drilling in the Melton Mowbray district (Carney et al., 2004).

Gravity anomaly G2, to the north-east, has a similar geometry to G1, and may be the continuation of the latter. If so, it would have been offset by about 7 km along a dextral strike-slip basement displacement coincident with the Eakring–Foston Fault, the latter showing prominently as gravity lineament GL3 on (Figure 46). Anomaly G2 was termed the ‘Newark Low’ by Berridge et al. (1999), but its origin is uncertain; it may be either a basin of pre-Carboniferous rocks or a buried granitic pluton, as discussed by Berridge et al. (1999).

The gravity lineament (GL3) marks the deep crustal trace of the Eakring–Foston Fault splays at their southeastern extremity in the Nottingham district. As shown in (Figure 42), and discussed by Berridge et al. (1999, fig. 8c), the northerly strand of the lineament (GL3a) corresponds to the Barkston Fault and the southerly strand (GL3b) to the Denton Fault. The latter is a major high-angle reverse fault that is part of the Eakring–Kirklington–Rolleston inversion axis (Chapter 9). The ground between the two strands forms the Foston High (G3 on (Figure 46), which was emergent until Late Dinantian (Holkerian) times in the Grantham district, and continued to act as an axis of restricted sedimentation into Namurian times (Berridge et al., 1999). The anomaly itself reflects the shallow depth of relatively high density basement material, of probable Lower Palaeozoic age, brought up in the hanging wall of the Denton Fault and proved in the Foston No. 1 and Cox’s Walk boreholes (Berridge et al., 1999; (Figure 42)).

Although the Cinderhill–Foss Bridge Fault system gives rise to only weak gravity anomaly lineaments in the Nottingham district (GL1 and GL2), it is part of a major regional geophysical and tectonic feature that extends west-north-westwards towards the Derbyshire Peak District. There, it is coincident with the Cronkston and Bonsall Heath Fault zone (Cornwell and Walker, 1989; (Figure 41)), and is shown on the tectonic map of the British Geological Survey (1996).

The shaded relief grey-tone gravity image inset in (Figure 46) shows the major anomalies, G1 and G2, and the linear anomaly GL3 corresponding to the EakringFoston Fault. It also shows a number of other linear features, which, with north-north-westerly trends, converge with the Eakring–Foston trend. Fainter linear features in the south-west of the district have west-northwest orientations, and these are broadly coincident with the Cinderhill–Foss Bridge fault system.

Aeromagnetic anomalies

The original aeromagnetic data for the East Midlands were acquired in 1955 during the first regional component of the National Aeromagnetic Survey. The data were surveyed at an elevation of 1000 feet (305 m), on flight lines 1 mile (1.6 km) apart. They were recorded in analogue form and subsequently digitised (Smith and Royles, 1989), and it is the digital dataset that has been used for most recent regional studies. In 1999, the Nottingham district was included in the BGS High Resolution Environmental Survey programme (HiRes 1). World Geoscience Corporation flew this survey at an elevation of 90 m on lines spaced 200 m and 400 m apart, all data being recorded digitally. The survey provided data of a much higher resolution, with large amounts of information gained about features nearer to the surface. Innovative noise removal techniques have been developed at BGS in order to optimise the geological content of the signal. Presentations of the data from the HiRes 1 survey can be found in the HiRes GIS at the BGS (Cuss and Kimbell, 2001).

The principal features of the magnetic data, labelled as magnetic lineaments (ML) and anomalies (M), are summarised in the Reduced-to-Pole magnetic anomaly map shown in (Figure 47). The production of this map has involved transforming the data to correct for the inclination on the geomagnetic field. Reduction-to-the-pole is a technique that should produce magnetic anomalies positioned directly over their source body at depth. In addition, the data have been statistically ‘smoothed’ as the high frequency content of the HiRes 1 data results in overly complex contours and small closures. The aeromagnetic anomalies of this district are shown in their regional context on the magnetic anomaly map (British Geological Survey, 1998).

The magnetic compilation for this memoir (Figure 47) shows a large number of coherent features, many of which reflect the ‘structural grain’ of the Nottingham district. In the east of the district, lineament ML3 is subparallel with ML2 (see below), but is attributed more directly to the linear zone of Variscan basement uplift containing the axis of the Rolleston Anticline (compare with (Figure 45); (Figure 47). Close by, anomaly ML4 is interpreted as the trace of the Eakring–Foston Fault System at depth.

Lineament ML2 marks the edge of an extensive magnetic high that underlies much of the Nottingham district and extends westwards into adjacent districts. It is clearly related to the Eakring–Foston–Denton fault system, but is offset to the south-west, relative to that structure, and to ML4. The Bouguer gravity anomaly G1 (see above) is partly contained within the magnetic high. The southerly prolongation of ML2 is coincident with the gravity feature GL3b (Figure 46), which as noted above is related to the Denton Fault margin of the Foston High. The latter is defined by the coincident anomalies GL3 and ML3 (Figure 45); (Figure 46) producing a strong geophysical expression that reflects the presence of shallow basement, which includes the sequence of intermediate lavas of Ordovician age intersected in the Cox’s Walk Borehole (Chapter 3). The uplift of the Foston High basement is attributed to end-Carboniferous movements along the Denton Fault, which acted as a high angle reverse fault during the Variscan inversion event (Berridge et al., 1999; fig. 6).

To the south-west of ML2 is a further parallel lineament, ML1, which marks the north-eastern edge of the complex, annular-shaped magnetic high labelled M1 on (Figure 47). This body, which is particularly well seen on the shaded relief image in (Figure 47), is attributed in part to the presence in the basement of magnetic and relatively low density rocks, such as granodiorite. They would lie at deeper levels than those described in the adjacent Melton Mowbray district (Carney et al., 2004), possibly below 5 km. The localised, superimposed magnetic highs, M1a and b, form a magnetic ridge system, possibly offset in places but with a distinctly north-west to southeast orientation that is parallel to ML1. They may be parallel to the orientation of basement thrusts. Further local magnetic highs, M4 and M5, are superimposed on the regional high, and a granodioritic source is also postulated for these.

The high frequency content of the HiRes 1 aeromagnetic data is best viewed as a shaded relief image, such as that shown in (Figure 48). For this compilation, a regional field has been calculated by continuing the data upwards by 200 m (i.e. processing the data to appear equivalent to the anomalies that would be observed at the higher elevation, losing some of the high frequency content). The upward-continued field has then been subtracted from the original data, leaving and thereby accentuating the shorter wavelength anomalies, which include those caused by near-surface geology. The horizontal gradient of these residual (short wavelength) anomalies was then calculated and displayed as a ‘grey-shaded topography’ illuminated from the north. Many of the high-resolution linear features on (Figure 48) are orientated in a west-north-west direction, broadly parallel to structures such as the Foss Bridge–Cinderhill Fault and Eakring–Foston Fault; the Harlequin Fault, with a more westerly direction, also shows on this type of compilation. Although these lineaments correlate well with surface structure, they evidently have a more deep-seated origin. They may indicate basement discontinuities of late Caledonian age, such as northdipping thrusts of the type detected on seismic profiles to the south of the Normanton Hills Fault in the Melton Mowbray district (T C Pharaoh, in Carney et al., 2004).

Magnetic susceptibility measurements were made on Westphalian basalts in various borehole cores from the Melton Mowbray district and are summarised in Table 19. These rocks are magnetically highly variable, locally over 300 m thick (Chapter 4), and if faulted, could be expected to form some of the low amplitude, high frequency anomalies in the south-eastern corner of (Figure 48).

Information sources

Further geological information relevant to the Nottingham district and held by the British Geological Survey is listed below. It includes published material in the form of maps, memoirs and reports, and unpublished maps and reports. Also included are other sources of data held by BGS in a number of collections, including borehole records, site investigation reports, mine plans, fossils, rock samples, thin sections, bore core samples and photographs.

Searches of indexes to some of the collections can be made through the Geoscience Data Index (GDI) on the BGS website (www.bgs.ac.uk) and via a more comprehensive version at the National Geoscience Records Centre at Keyworth. This is a computer-based system that carries out searches of indexes to collections and digital databases for specified geographical areas. It is based on a geographical information system linked to a relational database management system. Results of the searches are displayed on maps on the screen. Some of the indexes currently available (2004) for the Nottingham district are listed below:

Other items on the BGS web site (www.bgs.ac.uk) include a Lexicon to which definitions of all the named rock units in the UK are currently being added.

Maps

Copies of these maps may be consulted at the Library or National Geological Records Centre of the British Geological Survey, Keyworth. Those still in print can be purchased from the Sales Desk or ordered via the web site (address above).

Geological maps

1:1 500 000

1:625 000

1:250 000

1:63 360 (one inch to one mile)

1:50 000 and 1:63 360 (England and Wales); Nottingham and adjacent districts

(1:63 360 map reprinted at 1:50 000 scale) Sheet 126 Nottingham, Solid and Drift, 1996 Sheet 127 Grantham, Solid and Drift, 1996 Sheet 141 Loughborough, Solid and Drift, 2001

1:10 560 (six inches to one mile)

The maps produced by B S N Wilkinson, G W Lamplugh, W Gibson, W B Wrightand R L Sherlock on the six-inch scale during resurvey of the district in 1903–1906 were published as Nottingham County Standards. They are listed below together with the surveyor’s initials and the date of the survey:

Sheet No. Surveyor Date
33NW RLS 1904–5
33NE RLS 1905
33SW RLS 1904–5
33SE RLS 1905
34NW BSNW 1903
(additions by GWL 1906)
34NE BSNW 1903
(additions by GWL 1906)
34SW BSNW 1904
(additions by GWL 1906)
34SE BSNW 1904
(additions by GWL 1905)
35NW RLS 1905
35NE RLS 1905
35SW RLS 1905
35SE RLS 1905
38NW RLS 1904–5
38NE RLS 1904–5
38SW RLS 1904–5
38SE RLS 1904
39NW GWL 1905
39NE GWL & WBW 1905
39SW GWL & WBW 1905
39SE GWL & WBW 1905
40NW RLS & WBW 1905
40NE RLS 1905
40SW WBW 1905
40SE WBW 1905
42NW WG & RLS 1904–5
42NE RLS 1904–5
42SW RLS 1904–6
42SE RLS 1904–6
43NW RLS & WBW 1905
43NE WBW 1905
43SW WBW 1905
43SE WBW 1905
44NW WBW 1904–5
44NE WBW 1904
44SE WBW 1904
44SW WBW 1904–5

1:10 000

Since the 1960s, the standard large-scale map for recording field survey information has been the 1:10 000 National Grid Sheet. Those sheets that were resurveyed and included in the compilation of Sheet 126 Nottingham are spatially indexed at the foot of the map sheet. They are listed in Table Info 1 with their surveyor and date of survey, and full bibliographic references to the technical reports covering most of these sheets are given in the reference list.

Applied geological maps (for land-use planning)

A series of thematic maps compiled for the western part of the district (Nottingham City and environs) to accompany a planning and development report (Charsley et al., 1990).

The maps are also available separately from the report, and include: Boreholes and Trial Pits (1:50 000); Bedrock geology (1:50 000); Distribution and thickness of superficial deposits (1:50 000); Distribution of made and disturbed ground (1:25 000); Geomorphology, drainage and slopes (1:50 000); Mineral resources, mining and quarrying (excluding coal) (1:50 000); Underground deep coal mining (1:50 000); Coal: opencast mining, mine shafts and shallow mining (1:25 000); Hydrogeology and flood limits (1:50 000); Engineering geology of bedrock materials (1:50 000); Engineering geology of superficial (drift) deposits (1:50 000); Distribution of (sandstone) caves (1:25 000).

A BGS Mineral Resources Map (2002) for Nottingham and Nottinghamshire, at a scale of 1:100 000, gives information on planning permissions and mineral production statistics. This map can be supplied in single sheet print-on-demand format, or with an accompanying report.

Geophysical maps

1:1 584 000

1:1 500 000

1:1 000 000

1:625 000

1:250 000

Geochemical atlases

1:500 000 Colour classified digital maps

Hydrogeological maps

1:625 000

1:500 000

1:100 000

1:100 000 Groundwater vulnerability maps

Bulk mineral assessment maps

The following report includes 1:50 000 maps for the Soar valley, north Leicestershire, south Leicestershire and north Northamptonshire.

1:25 000 Mineral Assessment Maps

1:1 000 000

1:1 500 000

1:1 584 000

1:2 500 000

Publications

Memoirs, books, reports and papers relevant to the Nottingham district arranged by subject. They may be consulted or purchased at BGS and other libraries.

Books and memoirs

Memoirs

These accompany the 1:50 000 and 1:63 360 geological maps for Nottingham and adjacent districts.

Sheet description

Technical reports

Technical reports giving details of the geology accompany the 1:10 000 maps listed above for the Nottingham district. The authors are given in Table 20. No reports are available for sheets SK73NW, SK74SW, SK74NW, SK74NE, SK75SW, SK75SE, SK83NW and SK84NW.

Other Technical Reports relating to the Nottingham area include the following.

General geology

Reports not otherwise included in the References are:

Economic geology

Hydrogeology

Engineering geology

Biostratigraphy and sedimentology<span data-type="footnote"> See also References under Warrington, G</span>

Popular publications

Lott, G K, and Cobbing, J. 1996. Nottingham: heritage in stone. Holiday geology guide (includes city map). Keyworth: British Geological Survey.

Documentary Collections

Basic geological survey information, which includes 1:10 000 or 1:10 560 scale field slips and accompanying field notebooks, is archived at BGS Keyworth. Charges and conditions of access to these records are available on request from the Manager, National Geological Records Centre.

Borehole records

BGS holds collections of borehole records, collated according to quarter sheet map reference number. These can be consulted at BGS Keyworth or (if not held confidentially) can be ordered via the sales desk or website. For the Nottingham district, the collection consists of logs for over 4000 boreholes. For some boreholes, index information, which includes site references, has been digitised. The logs are either hand-written or typed, and many of the older records are drillers’ logs. Summary details of the selected boreholes mentioned in this memoir are given in Table 21.

Site investigation reports

The collection comprises reports of investigations into foundation conditions carried out by contractors prior to construction. There are more than 60 such reports, digitally indexed, for the Nottingham district.

Mine plans

The BGS maintains a collection of approximately 327 miscellaneous plans relating to mining activity in the Nottingham area. The most inclusive set of coal abandonment plans is that held by the Coal Authority (Mining Reports, 200 Lichfield Lane, Mansfield, Nottinghamshire, NG18 4RG).

Coalfield geological data

Interpretative geological data from the Nottinghamshire and Vale of Belvoir coalfields, previously held by the Coal Authority and including cross-sections and coal seam isopachyte maps, is now held in the National Geological Records Centre at BGS. This information does not include the mine abandonment plans, which have been retained by the Coal Authority and can be examined at the address given above.

Material Collections

Geological Survey photographs

About 35 photographs illustrating aspects of the geology of the Nottingham district are deposited for reference in the Library at BGS Keyworth, Nottingham. The photographs were taken mainly during the early 1900s and the remainder between 1964 and 1972. They depict details of the various rocks and sediments exposed either naturally or in excavations, and also include some general views. A list of titles can be supplied on request. The photographs can be supplied as black and white or colour prints, or 2 3 2 colour transparencies, at a fixed tariff.

Petrological collection

The BGS petrological collection district includes several hundred hand specimens and thin sections from the Nottingham, which can be viewed by arrangement.

Borehole core collection

Samples have been collected from over 60 cores taken from boreholes in the district. These include sections of intact core and individual samples. Digital data sheets giving the locations of boreholes, and depths at which the core was sampled, can be obtained on application to the Manager, National Geological Records Centre.

Palaeontological collection

There is a large collection of biostratigraphical specimens taken from surface and temporary exposures and from boreholes throughout the Nottingham district. The palaeontological collection, which is a working collection and is used for reference, can be examined by arrangement with the Chief Curator, BGS Keyworth.

Addresses for data sources

References

Most of the references listed below are held in the Library of the British Geological Survey, Murchison House, Edinburgh, and at Keyworth, Nottingham. Copies of the references can be purchased subject to current copyright legislation. BGS Library catalogue can be searched online at: http://geolib.bgs.ac.uk

Aitkenhead, N, and Chisholm, J I. 1982. A standard nomenclature for the Dinantian formations of the Peak District of Derbyshire and Staffordshire. Report of the Institute of Geological Sciences, No. 82/8.

Aitkenhead, N, and Williams, G M. 1987. Geological evidence to the Public Inquiry into the Gas Explosion at Loscoe. British Geological Survey Technical Report, FP/87/8/83AS.

Aljubouri, Z A. 1972. Geochemistry, origin and diagenesis of some Triassic gypsum deposits and associated sediments in the East Midlands. Unpublished PhD Thesis, University of Nottingham.

Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, Wagstaff, S J, and Williams A T. 1997. The physical properties of major aquifers in England and Wales.

Allen, D J, Bloomfield, J P, and Robinson, V K (editors). British Geological Survey Technical Report, WD/97/34; Environment Agency R&D Publication, 8. (Keyworth, Nottingham: British Geological Survey.)

Ambrose, K. 1989. Geology of the Lowdham district: 1:10.000 Sheet SK64.NE. Part of 1:50.000 Sheet.126 (Nottingham). British Geological Survey Technical Report, WA/89/14.

Andrews, J N and Lee, D J. 1979. Inert gases in groundwater from the Bunter Sandstone as indicators of age and palaeoclimatic trends. Journal of Hydrology, Vol..41, 233–252.

Arter, G. 1982. Geophysical investigations of the deep geology of the East Midlands. Unpublished PhD Thesis, University of Leicester

Arthurton, R S. 1980. Rhythmic sedimentary sequences in the Triassic Keuper Marl (Mercia Mudstone Group) of Cheshire, north-west England. Geological Journal, Vol..15, 43–58.

Arthurton, R S, Gutteridge, P, and Nolan, S C. 1989. The role of tectonics in Devonian and Carboniferous sedimentation in the British Isles. Yorkshire Geological Society Occasional Publication, No..6.

Audley-Charles, M G. 1970. Triassic palaeogeography of the British Isles. Quarterly Journal of the Geological Society of London, Vol..126, 49–89.

Aveline, W T. 1880. The geology of parts of Nottinghamshire, Yorkshire and Derbyshire (second edition). Memoir of the Geological Survey of Great Britain, Sheet 82 NE (England and Wales). (London: HMSO.)

Balchin, D A, and Ridd, M F. 1970. Correlation of the younger Triassic rocks across eastern England. Quarterly Journal of the Geological Society of London, Vol..126, 91–101.

Barclay, W J, Ambrose, K, Chadwick, R A, and Pharaoh, T C. 1997. Geology of the country around Worcester. Memoir of the British Geological Survey, Sheet.199 (England and Wales). (London: Stationery Office.)

Barnes, P, and Firman, R J. 1991. Gypsum working in the parish of Orston, Nottinghamshire Bulletin of the Peak District Mines Historical Society, Vol..11, 167–182.

Bateman, R M, and Rose, J. 1994. Fine sand mineralogy of the early and middle Pleistocene Bytham Sands and Gravels of Midland England and East Anglia. Proceedings of the Geologist’s Association, Vol..105, 33–39.

Bath, A H, Edmunds, W M, and Andrews, J N. 1979. Palaeoclimatic trends deduced from the hydrochemistry of a Triassic sandstone aquifer, United Kingdom. 545–568 in Isotope hydrology 1978: Proceedings of an International Symposium on Isotope Hydrology, Vol..2. (Vienna: International Atomic Energy Agency.)

Bemrose, H H A, and Deeley, R M.1896. Discovery of mammalian remains in the old river gravels of the Derwent near Derby. Quarterly Journal of the Geological Society of London, Vol..52, 497–510.

Berridge, N G. 1979. Suspected tuffaceous bands beneath the Deep Soft Coal, Cotgrave Colliery, Nottingham. British Geological Survey Technical Report, WG/PE/LD/79-3.

Berridge, N G. 1980a. Suspected tuff 161.5.m below the Deep Hard Coal, Cotgrave Colliery, Nottingham. British Geological Survey Technical Report, WG/PE/LD/80–11.

Berridge, N G. 1980b. Suspected tuff horizons in the Westphalian: Cotgrave Colliery, Nottingham. British Geological Survey Technical Report, WG/PE/LD/80–6.

Berridge, N G, Pattison, J, Samuel, M D A, Brandon, A, Howard, A S, Pharaoh, T C, and Riley, N J. 1999. Geology of the Grantham district. Memoir of the British Geological Survey, Sheet.127 (England and Wales). (London: Stationery Office.)

Besly, B M. 1988a. Late Carboniferous sedimentation in northwest Europe: an introduction. 1–7 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow: Blackie.)

Besly, B M. 1988b. Palaeogeographic implications of late Westphalian to early Permian red-beds. 200–221 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow: Blackie.)

Besly, B M, and Fielding, C R. 1989. Palaeosols in Westphalian coal-bearing and red-bed sequences, central and northern England. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol..70, 303–330.

Besly, B M, and Kelling, G. 1988. Sedimentation in a Synorogenic basin complex: the Upper Carboniferous of northwest Europe. (Glasgow: Blackie.)

Besly, B M, Burley, S D, and Turner, P. 1993. The late Carboniferous ‘Barren Red Bed’ play of the Silver Pit area, southern North Sea. 727–740 in Petroleum geology of northwest Europe: proceedings of the 4th conference. Parker, J R (editor). (London: The Geological Society of London.)

Bishop, T J, and Rushton, K R. 1993. Water resources study of the Nottinghamshire Sherwood Sandstone aquifer system of Eastern England. Mathematical model of the Sherwood Sandstone aquifer. (Birmingham: Unpublished report from the Department of Civil Engineering, University of Birmingham for the National Rivers Authority.—.Severn-Trent Region.)

Bloodworth, A, and Prior, S V. 1993. Clay mineral stratigraphy of the Mercia Mudstone Group in the Nottingham area. British Geological Survey Technical Report, WA/93/29.

Bonney, T G. 1900. The Bunter Pebble-Beds of the Midlands and the source of their materials. Quarterly Journal of the Geological Society of London, Vol..56, 287–303.

Bott, M H P. 1982. The interior of the earth: its structure, constitution and evolution. Second edition. (London: Edward Arnold.)

Bowen, D Q. 1992. Aminostratigraphy of non-marine Pleistocene mollusca in southern Britain. 65–69 in Quaternary stratigraphy, glacial morphology and environmental changes. Robertsson, A–M, and Lundgvist, J (editors). Forskningsrapporter Sveriges Geologiska Undersökning, No..81. (Uppsala: Sveriges Geologiska Undersökning.)

Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. Special Report of the Geological Society of London. No..23.

Bowen, D Q, Rose, J, Sutherland, D, and McCabe, A M. 1986. Correlation of Quaternary glaciation in England, Ireland, Scotland and Wales. Quaternary Science Reviews, Vol..5, 299–340.

Bowen, D Q, Hughes, S, Sykes, G A, and Miller, G H. 1989. Land-sea correlations in the Pleistocene based on isoleucine epimerization in non-marine molluscs. Nature, Vol..340, 49–51.

Bradshaw, M J, Cope, J C W, Cripps, D W, Donovan, D T, Howarth, M K, Rawson, P F, West, I M, and Wimbledon, W A. 1992. Jurassic. 107–129 in Atlas of palaeogeography and lithofacies. Cope, J C W, Ingham, J K, and Rawson , P F (editors). Memoir of the Geological Society of London, No..13.

Brandon, A. 1996. Geology of the lower Derwent valley: 1:10.000 sheets SK33SE, 43SW and 43SE. British Geological Survey Technical Report, WA/96/07.

Brandon, A. 1997. Geology of the Stretton and Repton areas: 1:10.000 sheets SK22NE and 32NW. British Geological Survey Technical Report, WA/97/02.

Brandon, A. 1999. Geology of the Wreake valley (SK61NE, SK71NW, SK71NE and SK81NW (western part). British Geological Survey Technical Report, WA/99/17.

Brandon, A, and Sumbler, M G. 1988. An Ipswichian fluvial deposit at Fulbeck, Lincolnshire and the chronology of the Trent terraces. Journal of Quaternary Science, Vol..3, 127–133.

Brandon, A, and Sumbler, M G. 1991. The Balderton Sand and Gravel: pre-Ipswichian cold stage fluvial deposits near Lincoln, England. Journal of Quaternary Science, Vol..6, 117–138.

Brandon, A, Sumbler, M G, and Ivimey-Cook, H C. 1990. A revised lithostratigraphy for the Lower and Middle Lias (Lower Jurassic) east of Nottingham. Proceedings of the Yorkshire Geological Society, Vol..48, 121–141.

Bridge, D McC, Carney, J N, Lawley, R S, and Rushton, A W A. 1998. The geology of the country around Coventry and Nuneaton. Memoir of the British Geological Survey, Sheet.169 (England and Wales).

Bridge, D McC, Bowden, A, and Barnett, A. 1999. Report on a 3-D modelling study of the Permo-Triassic succession of South Nottinghamshire and Derbyshire. British Geological Survey Technical Report, WA/99/54.

Bristow, C R. 1988. Controls on sedimentation in the Rough Rock Group. 114–131 in Sedimentation in a Synorogenic Basin Complex: the Upper Carboniferous of northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow: Blackie.)

Bristow, C R. 1993. Sedimentology of the Rough Rock: a Carboniferous braided river sheet sandstone in northern England. 291–304 in Braided Rivers. Best, J L, and Bristow,.C.R (editors). Geological Society of London Special Publication, No..75.

British Geological Survey. 1996. Tectonic map of Britain, Ireland and adjacent areas. Pharaoh, T C, Morris, J H, Long, C B, and Ryan, P D (compilers). 1:1.500.000 scale. (Keyworth, Nottingham: British Geological Survey.)

British Geological Survey. 1997. Colour shaded relief gravity anomaly map of Great Britain, Ireland and adjacent areas. Smith, I F, and Edwards, J W F (compilers). 1:1.500.000 scale. (Keyworth Nottingham: British Geological Survey.)

British Geological Survey. 1998. Colour shaded relief magnetic anomaly map of Great Britain, Ireland and adjacent areas. Royles, C P, and Smith, I F (compilers). 1:1.500.000 scale. (Keyworth, Nottingham: British Geological Survey.)

Bryant, I D, and Burley, S D. 1986. The Sherwood Sandstone of the Nottingham area. Field excursion guide for the 1986 annual meeting of the British Sedimentological Research Group (unpublished report).

Burgess, I C. 1982. The stratigraphical distribution of Westphalian volcanic rocks in the area east and south of Nottingham, England. Proceedings of the Yorkshire Geological Society, Vol..44, 29–44.

Burley, S D. 1984. Patterns of diagenesis in the Sherwood Sandstone Group (Triassic), United Kingdom. Clay Minerals, Vol..19, 403–440.

Burton, P W, Musson, R M W, and Neilson, G. 1984. Macroseismic reports on historical British earthquakes: IV Lancashire and Yorkshire. British Geological Survey, Global Seismology Research Group Reports, WL/GS/84/219.

Busby, J P, Kimbell, G S, and Pharaoh, T C. 1993. Integrated geophysical/geological modelling of the Caledonian and Precambrian basement of southern Britain. Geological Magazine, Vol..130, 593–604.

Calver, M A. 1969. The Westphalian of Britain. Comptes Rendus, 6ième Congrès Internationale de Stratigraphie et de Géologie de Carbonifère, (Sheffield, 1967). Vol..1, 133–254.

Cameron, T D J, Crosby, A, Balson, P S, Jeffery, D H, Lott, G K, Bulat, J, and Harrison, D J. 1992. United Kingdom offshore regional report: the geology of the southern North Sea. (London: HMSO for the British Geological Survey.)

Smith, W C. 1963. Description of the igneous rocks represented among pebbles from the Bunter pebble beds of the Midlands of England. British Museum (Natural History). Mineralogical Bulletin, Vol..2 (1).

Carney, J N. 2001. Trent valley geology and flooding. Mercian Geologist, Vol..15, 126–127.

Carney, J N, Ambrose, K, and Brandon, A. 2001. Geology of the country between Loughborough, Burton and Derby. Sheet Explanation of the British Geological Survey, 1:50.000 Series Sheet 141 Loughborough (England and Wales).

Carney, J N, Ambrose, K, Brandon, A, Lewis, M A, Royles, C P, and Sheppard, T H. 2004. Geology of the country around Melton Mowbray. Sheet Description of the British Geological Survey, 1:50.000 Series Sheet 142 Melton Mowbray (England and Wales).

Carney, J N, and Napier, B. 2004. Floodplain management: Visualising floodplains through geological maps. Earthwise issue.20, 24–25 (Keyworth, Nottingham: British Geological Survey.)

Carney, J N, Alexandre, P, Pringle, M S, Pharaoh, T C, Merriman, R J, and Kemp, S J. 2008 40Ar–39Ar isotope constraints on the age of deformation in Charnwood Forest, UK. Geological Magazine, Vol. 145, 702–713.

Chadwick, R A, and Evans, D J. 1995. The timing and direction of Permo-Triassic extension in southern Britain. 161–191 in Permian and Triassic rifting in northwest Europe. Boldy, S A R (editor). Geological Society of London Special Publication, No..91.

Charsley, T J. 1989. Geology of the Nottingham (South) district. 1:10.000 Sheet SK53NE. Part of 1:50.000 Sheet.126 (Nottingham). British Geological Survey Technical Report, WA/89/4.

Charsley, T J, Rathbone, P A, and Lowe, D J. 1990. Nottingham: a geological background for planning and development. British Geological Survey Technical Report, WA/90/1.

Chisholm, I. 1990. The Upper Band-Better Bed sequences (Lower Coal Measures, Westphalian A) in the central and south Pennine area of England. Geological Magazine, Vol..127, 55–74.

Chisholm, J I, Charsley, T J, and Aitkenhead, N. 1988. Geology of the country around Ashbourne and Cheadle. Memoir of the British Geological Survey, Sheet.124 (England and Wales).

Chisholm. J I, Waters, C N, Hallsworth, C R, Turner, N, Strong, G E, and Jones, N S. 1996. Provenance of Lower Coal Measures around Bradford, West Yorkshire. Proceedings of the Yorkshire Geological Society, Vol..51, 153–166.

Church, K D, and Gawthorpe, R L. 1994. High resolution sequence stratigraphy of the late Namurian in the Widmerpool Gulf (East Midlands, UK). Marine and Petroleum Geology, Vol..11, 528–544.

Church, K D, and Gawthorpe, R L. 1997. Sediment supply as a control on the variability of sequences: an example from the late Namurian of northern England. Journal of the Geological Society of London, Vol..154, 55–61.

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Clayton, K M. 1953. The glacial chronology of part of the Middle Trent Basin. Proceedings of the Geologists’ Association, Vol..64, 198–207.

Clift, S G, and Trueman, A E. 1929. The sequence of non-marine lamellibranchs in the Coal Measures of Nottinghamshire and Derbyshire. Quarterly Journal of the Geological Society of London, Vol..85, 77–108.

Collinson, J D. 1988. Controls on Namurian sedimentation in the Central Province basins of northern England. 85–101 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of northwest Europe. Besly, B M, and Kelling, G (editors). (Blackie: Glasgow.)

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Corfield, S M, Gawthorpe, R L, Gage, M, Fraser, A J, and Besly, B M. 1996. Inversion tectonics of the Variscan foreland of the British Isles. Journal of the Geological Society of London, Vol..153, 17–32.

Cornwell, J D, and Walker, A S D. 1989.Regional geophysics. in Metallogenic models and exploration criteria for buried carbonate-hosted ore deposits.—.a multidisciplinary study in eastern England. Plant, J A, and Jones D G (editors). (Keyworth, Nottingham: British Geological Survey; London: The Institution of Mining and Metallurgy.)

Coward, M P. 1995. Structural and tectonic setting of the Permo-Triassic basins of northwest Europe. 7–39 in Permian and Triassic rifting in northwest Europe. Boldy, S A R (editor). Geological Society of London Special Publication, No..91.

Cox, B M, Sumbler, M G, and Ivimey-Cook, H C. 1999. A formational framework for the Lower Jurassic of England and Wales (onshore area). British Geological Survey Research Report, RR/99/01.

Crofts, R G. 1989a. Geology of the Keyworth district. 1:10.000 Sheet SK63SW. Part of 1:50.000 Sheet.142 (Melton Mowbray). British Geological Survey Technical Report, WA/89/11.

Crofts, R G. 1989b. Geology of the Kinoulton district. 1:10.000 Sheet SK63SE. Part of 1:50.000 Sheet 142 (Melton Mowbray). British Geological Survey Technical Report, WA/89/12.

Cummins, W A and Rundle, A J. 1969. The geological environment of the dug-out canoes from Holme Pierrepont, Nottinghamshire. Mercian Geologist, Vol..3, 177–188.

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Dean, M T. 1989. Geology of the Nottingham (north) district. 1:10.000 Sheet SK54SE. Part of 1:50.000 sheet.126 (Nottingham). British Geological Survey Technical Report, WA/89/8.

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Doornkamp, J C. 1971. East Midlands Landforms II. The Keuper Cuesta and the Dumbles. East Midlands Geographer, Vol..5, 222–223.

Donovan, D T, Horton, A, and Ivimey-Cook, H C. 1979. The transgression of the Lower Lias over the northern flank of the London Platform. Journal of the Geological Society of London, Vol..136, 165–173.

Downing, R A, and Howitt, F. 1969. Saline ground-waters in the Carboniferous rocks of the English East Midlands in relation to geology. Quarterly Journal of Engineering Geology, Vol..1, 241–269.

Downing, R A, Land, D H, Allender, R, Lovelock, P E R and Bridge, L R. 1966. The hydrogeology of the Trent river basin. British Geological Survey Technical Report, WD/WD/66/2.

du Boulay Hill, A. 1932. East Bridgford, Nottinghamshire. (London: Oxford University Press.)

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East Midlands Regional Assembly. 1999. Viewpoints on the East Midlands Environment.

Ebdon, C C, Fraser, A J, Higgins, A C, Mitchener, B C, and Strank, A R E. 1990. The Dinantian stratigraphy of the East Midlands: a seismostratigraphic approach. Journal of the Geological Society of London, Vol..147, 519–537.

Eden, R A. 1954. The Coal Measures of the Anthraconaia lenisulcata Zone in the East Midlands. Bulletin of the Geological Survey of Great Britain, No..5, 81–104.

Eden, R A, Elliott, R W, and Young, B R. 1963. Tonstein bands in the coalfields of the East Midlands. Geological Magazine, Vol..100, 47–58.

Edmunds, W M, Bath, A H, and Miles, D L. 1982. Hydrochemical evolution of the East Midlands Triassic sandstone aquifer, England. Geochimica et Cosmochimica Acta, Vol..46, 2069–2081.

Edmunds, W M, and Smedley, P L. 1992. The East Midlands Triassic aquifer: hydrogeochemical evolution 1975–1992. British Geological Survey Technical Report, WD/92/23R.

Edwards, W. 1951. The concealed coalfield of Yorkshire and Nottinghamshire. Third edition. Coalfield Memoir of the Geological Survey of Great Britain.

Edwards, W N. 1967. Geology of the country around Ollerton. Memoir of the Geological Survey of Great Britain, Sheet.113 (England and Wales).

Edwards, W N, and Stubblefield, C J. 1948. Marine bands and other faunal marker-horizons in relation to the sedimentary cycles of the Middle Coal Measures of Nottinghamshire and Derbyshire. Quarterly Journal of the Geological Society of London, Vol..103, 209–260.

Eglinton, M. 1979. Chemical considerations on filled ground. Proceedings of the symposium on the engineering behaviour of industrial and urban fill. Midlands Geotechnical Society, B11–15.

Eisenbud, M. 1987. Environmental radioactivity. (London: Academic Press Inc.)

El-Nikhel, A H D. 1980. Seismic reflection, gravity and magnetic studies of the geology of the East Midlands. Unpublished Ph.D. thesis, University of Leicester.

Elliott, R E. 1961. The stratigraphy of the Keuper Series in southern Nottinghamshire. Proceedings of the Yorkshire Geological Society, Vol..33, 197–234.

Emiliani, C. 1955. Pleistocene temperatures. Journal of Geology, Vol..63, 538–578.

Entwisle, D C. 1993. Density, porosity and sonic velocity determinations on twelve rock samples from 1202–1203.m of the Rempstone Borehole, near Rempstone, Loughborough, Leicestershire. British Geological Survey, Engineering Geology and Geophysics Group Laboratory Report, No..93/16.

Evans, A J. 1984. Hydrology and water supply. 13–25 in A new geography of Nottingham. Brazier, S, Hammond, R, and Waterman, S R (editors). (Nottingham: Trent Polytechnic.)

Falcon, N L, and Kent, P E. 1960. Geological results of petroleum exploration in Britain, 1945–1957. Memoir of the Geological Society of London, No..2.

Fielding, C R. 1986. Fluvial channel and overbank deposits from the Westphalian of the Durham Coalfield, NE England. Sedimentology, Vol..33, 119–140.

Firman, R J. 1964. Gypsum in Nottinghamshire. Bulletin of the Peak District Mines Historical Society, Vol..2, 189–203.

Firman, R J, and Dickson J A D. 1968. The solution of gypsum and limestone by upward flowing water. Mercian Geologist, Vol..4, 401–408.

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Figures, plates and tables

Figures

(Figure 1) Simplified bedrock geology map of the Nottingham district.

(Figure 2) Topographical map of the district.

(Figure 3) Contours (in metres relative to OD) on the potentiometric surface of the Sherwood Sandstone aquifer in March 1978 and the location of public supply pumping stations (after the Hydrogeological Map of the North East Midlands, Institute of Geological Sciences, 1981).

(Figure 4) Groundwater hydrograph for Hazel Hill Borehole [SK 5663 4637]. The scale on the vertical axis is in metres below datum. The level of the measured datum is 106.76 m AOD. (Provided by the Environment Agency, West Bridgford).

(Figure 5) Dinantian and Namurian rocks of the district, generalised vertical sections based mainly on boreholes.

(Figure 6) Correlation of lithological and geophysical logs for Namurian strata in selected boreholes in the centre and north of the district. The depths are in metres below local ground level. For explanation of the lithologies, see (Figure 7).

(Figure 7) Correlation of lithological and geophysical logs for Namurian strata in boreholes in the centre, south and east of the district. The depths are in metres below ground level.

(Figure 8) Generalised Lower Coal Measures stratigraphy of the district, based on boreholes.

(Figure 9) Correlation of the Lower Coal Measures (Subcrenatum Marine Band to Kilburn Coal) in selected boreholes. The depths are in metres below local ground level. Gamma Ray log (GR) calibrated in API units.

(Figure 10) Correlation of the Lower Coal Measures (Kilburn Coal to Vanderbeckei Marine Band) in selected boreholes in the south of the district. The depths are in metres below local ground level. For explanation of the lithologies, see (Figure 9). Gamma Ray log (GR) calibrated in API units.

(Figure 11) Correlation of the Lower Coal Measures (Kilburn Coal to Vanderbeckei Marine Band) in selected boreholes in the north of the district. For explanation of the lithologies, see (Figure 9). Gamma Ray log (GR) calibrated in API units.

(Figure 12) Summary of Middle and Upper Coal Measures stratigraphy in the district.

(Figure 13) Channel trend of selected sandstone bodies in the Middle Coal Measures.

(Figure 14) Correlation of the Middle Coal Measures (Vanderbeckei to Aegiranum marine bands) in the central and northern parts of the district. The depths are in metres below local ground level. For explanation of the lithologies, see (Figure 9). Gamma Ray Log (GR) calibrated in API units.

(Figure 15) Correlation of the Middle Coal Measures in the south of the district. The depths are in metres below local ground level. For explanation of the lithologies, see (Figure 9).Gamma Ray Log (GR) calibrated in API units.

(Figure 16) Correlation of Upper Coal Measures strata. For explanation of lithologies, see (Figure 9).

(Figure 17) Correlation of Barren Measures strata using core and geophysical logs. Gamma Ray Logs (GR) are calibrated in API units. Inset shows the subcrop map of the Barren Measures and isopachytes for the Etruria and Halesowen formations.

(Figure 18) Subcrop map showing the Carboniferous volcanic rocks.

(Figure 19) Borehole logs illustrating the Westphalian volcanic and extrusive rocks. The calibration of lithology with gamma-ray signature is based on examination of extensive core sample runs for the Grimmer Borehole (see Carney et al., 2004). Gamma Ray log (GR) calibrated in API units. The borehole locations are shown in (Figure 18).

(Figure 20) Late Permian and Triassic palaeogeography, simplified from (a) Smith and Taylor, 1992, and (b–d) Warrington and Ivimey-Cook, 1992). a Zechstein Group b Sherwood Sandstone Group c Mercia Mudstone Group d Penarth Group Principal depositional basins: CB Cheshire Basin; EB Eden Basin; HB Hinckley Basin; NB Needwood Basin; WB Worcester Basin

(Figure 21) Schematic, south-west to north-east profile showing the stratigraphical relationships of Upper Permian strata. Based on borehole correlations shown in (Figure 22).

(Figure 22)(Figure 22) Simplified map of Permian and Triassic strata in the Nottingham and adjacent districts, showing the locations of principal boreholes mentioned in the text.

Figure 23 Isopachytes and facies maps of the Permian strata of the district. a. Cadeby Formation isopachytes and distribution of principal lithofacies in the ‘Lower Magnesian Limestone’ b. Edlington Formation isopachytes and the subsurface distribution of the Brotherton Formation

(Figure 24) Borehole logs illustrating the Upper Permian strata and Sherwood Sandstone Group in the north of the district. Depths are in metres below ground level.

(Figure 25) Borehole logs illustrating the Upper Permian strata and the Sherwood Sandstone Group in the central part of the district. Depths are in metres below ground level. For explanation of lithologies see (Figure 24).

(Figure 26) Borehole logs illustrating the Upper Permian strata and the Sherwood Sandstone Group in the south of the district.

(Figure 27) Isopachyte maps. a. Sherwood Sandstone Group b.Sneinton Formation

(Figure 28) Detailed log of the Cropwell Bridge Borehole, incorporating clay mineral determinations from Bloodworth and Prior (1993).

(Figure 29) Borehole logs illustrating the Mercia Mudstone Group of the central and northern parts of the district. The depths are in metres below local ground level.

(Figure 30) Borehole logs illustrating the Mercia Mudstone Group in the southern part of the district. The depths are in metres below local ground level.

(Figure 31) Comparative sections of the Penarth Group in or adjacent to the Nottingham District. Staple Pit Mine section after Martill and Dawn (1986); Barnstone cutting after Sykes et al. (1970).

(Figure 32) Generalised stratigraphical and biostratigraphical column in the Lias Group, modified for the Nottingham district using information from Brandon et al. (1990) and Berridge et al. (1999). The relative magnitude of the topographical features formed by the beds is indicated on the left of the lithostratigraphy column. The subzones highlighted by grey shading are those proved by findings of subzonally diagnostic ammonites in the district.

(Figure 33) Early Jurassic palaeogeography, eastern England (modified after Ziegler, 1990, and Bradshaw et al., 1992).

(Figure 34) Correlation of Barnstone Member sections in the Nottingham district and in adjacent areas of the Melton Mowbray district.

(Figure 35) Correlation of the Lias Group in sections and boreholes in the Nottingham district and adjacent parts of the Grantham district. Abbreviations used for individual groups of limestone beds correspond to those of (Figure 32). Casing corrections have been applied to the Redmile 2 and Cox’s Walk gamma-ray logs. Fulbeck No. 5 Borehole section modified after Brandon et al. (1990).

(Figure 36) Generalised profiles across the Trent valley near Newark (section a) and Nottingham (section b), showing the relationships of the principal Quaternary deposits. Note that in the key, the main alluvial units are listed in descending order of decreasing age, with the oldest, and highest, terrace deposits at the top.

(Figure 37) Reconstructed longitudinal profile of the Whatton Sand and Gravel between Wiverton and Newark, and its relationship with the Balderton Sand and Gravel.

(Figure 38) Schematic section (not to scale) showing topographical relationships of fluvial deposits in the valleys of the rivers Devon and Witham.

Plate 22 Exposure of the Holme Pierrepont Sand and Gravel in Hoveringham Quarry [SK 70 48], showing an ice-wedge cast indicative of cryoturbation (P692322).

(Figure 39) Floodplain geology of part of the River Trent on a background of coloured, high-resolution topography generated from the airborne LiDAR (Light Detection and Ranging) technique. The arcuate features in the alluvium south of Burton Joyce represent successive developments of scroll bars caused by sediment accretion on point bars forming on the inside of a northwards-migrating meander. North of the Trent, a meandering abandoned channel is visible as the narrow tract of low-lying ground (blue colours). The LiDAR data were provided by the Environment Agency, West Bridgford office, and digitally reprocessed at the BGS by B Napier.

(Figure 40) Drainage evolution in the East Midlands during the Quaternary. Prior to the Anglian glaciation. The Nottingham district forms a major watershed between protoDerwent/Bytham and Lincoln pre-glacial river basins. The course of the Bytham River (‘proto-Soar’) incorporates modifications from Brandon (1999). Anglian glaciation. Preglacial drainage totally suppressed. The ‘Eastern Ice’ has advanced across the earlier ‘Pennine Ice’. Late Anglian. Deglaciation commences, with the Trent Trench being initiated by meltwater that exploits a zone of structural weakness within the ice, marking the former contact zone between Pennine and Eastern ice sheets. Latest Anglian. Deglaciation continues, with widening and deepening of the Trent Trench by proglacial meltwater, and deposition of the Eagle Moor Sand and Gravel. The geological boundaries shown are those of the present day.

(Figure 41) Principal tectonic elements of the Carboniferous basin complex of the East Midlands and eastern England, modified from Berridge et al. (1999). Incorporates subsurface mapping of Dinantian structures and half-grabens published by Ebdon et al. (1990) and Fraser et al. (1990), as well as unpublished BGS maps.

(Figure 42) Principal Dinantian synsedimentary structures and tectonic provinces. Those shown for the western part of the Grantham district are modified from Berridge et al. (1999). Shows selected boreholes proving Dinantian rocks. For an interpretation of the seismic line BP 83–38, see Berridge et al. (1999, fig. 6).

(Figure 43) Seismic reflection profile BP NT-81-07/8 and interpretation. This seismic line includes the whole of Section 1 of the Sheet 126 Nottingham; its path is also indicated on (Figure 42). Abbreviations for seismic stratigraphical surfaces: BMMG Base of Mercia Mudstone; BP Base of Permian; TC Top of Carboniferous; TH Top Hard Coal; DM Deep Main Coal; TMG Top Millstone Grit; TD Top Dinantian; BC Base of Carboniferous

(Figure 44) Diagrammatic representation of a seismostratigraphic interpretation of the western part of the Widmerpool Half-graben. Reproduced by kind permission of Ebdon et al. (1990) and the Geological Society of London, with minor modifications. Note that the precise location of this line was not given in the original publication, but probably lies close to the western margin of the district (i.e. just to the west of area shown in (Figure 42)).

(Figure 45) Sub-Permo-Triassic map showing the distribution (incrops) of Carboniferous strata and of the principal Variscan structural elements of the district. The structure contour data and fault lines are modified from a compilation by Holliday et al. (1984, encl. No. 22).

(Figure 46) Bouguer gravity anomaly map of the Nottingham district (inset) and surrounding area (see text for explanation).

Contours are at 1mGal intervals. Brown tones indicate positive and grey tones negative values. The Bouguer reduction density has been varied to allow for the range of densities across the area. Lineaments have been selected from various enhanced images of the gravity data (see the smaller diagram) and highlight local variations in the gravity gradients, such as those seen across faults. The most important lineaments are depicted by solid lines and are labelled. The inset map is a grey-toned relief image of the same data, illuminated from the south-west and showing linear features superimposed on or flanking the main gravity anomalies.

(Figure 47) Magnetic anomaly map (reduced-to-pole) of the Nottingham district (inset) and surrounding area (see text for explanation).Contours are at 25 nT intervals. Brown tones indicate positive and grey tones negative values. Lineaments have been selected from various enhanced images of the magnetic data (see (Figure 48)) and highlight local variations in the magnetic gradients, such as those seen across faults. The most important are depicted by solid lines and are labelled; the dashed lines indicate minor lineaments. The inset is a grey-toned image of the same data, illuminated from the south-west.

(Figure 48) Shaded relief, grey-tone, high-resolution aeromagnetic image of the Nottingham district, illuminated from the south. Mapped surface faults are superimposed in white. Their continuations at depth are indicated in (Figure 45).

Plates

(Cover photograph) Type section of Nottingham Castle Sandstone Formation at Castle Rock [SK 569 394] Nottingham. (Photograph T Cullen; P627174).

(Frontispiece) View of Newark Castle from the south, with the canalised Newark Branch of the River Trent in the foreground. The castle is built on naturally raised ground corresponding to a river terrace feature formed by the Balderton Sand and Gravel, the deposition of which took place under cold, periglacial conditions during the ‘Wolstonian’ Quaternary stage. The lower- lying area to the left of the water is underlain by modern alluvium of the River Trent floodplain (P692300).

(Plate 1) View of Calverton Colliery, the last to close in the Nottingham district (P692301) (1999).

(Plate 2) Bestwood Pumping Station, which draws groundwater for public supply from the Sherwood Sandstone aquifer (P692302).

(Plate 3) Aerial view of the Trent valley between Gunthorpe and Caythorpe [SK 680 450] looking downstream, towards the north-east, at midday on 9 November, 2000, about 24 hours after the main flood peak had passed. The alluvium of the modern floodplain is completely inundated. The areas remaining dry correspond to tracts of naturally raised ground coinciding with outcrops of the Holme Pierrepont Sand and Gravel (from Carney, 2001). (P692303).

(Plate 4) Sample of drillcore from 652–653 m in the Redmile Bridge Borehole, showing a fragmental, peperitic facies of the Langsettian basalt sequence. The large rounded basalt fragment (upper left) shows pronounced flattening of amygdales parallel to its chilled margin and may be a disaggregated pillow. Note also the curviplanar marginal fracture systems of other fragments near the bottom of the photo. The matrix consists of mudstone (dark grey areas) with abundant finely comminuted fragments of glassy basalt. The specimen is 0.19 m in length (P692304).

(Plate 5) Sample of drillcore from 669 m in the Redmile Bridge Borehole, showing a basalt dyke (at left) intruded into Langsettian strata. The dyke has a curviplanar, slightly crenulated, chilled margin. The mudstones (dark grey) and interbedded siltstones (paler grey) into which the dyke is intruded show wispy, disturbed bedding. Synsedimentary deformation, resulting in the attenuation of a siltstone bed along a carbonate-filled fracture believed to have been associated with dyke intrusion, is demonstrated in the centre of the photo. The specimen is 0.22 m in length (P692305).

(Plate 6) Sample from about 648 m in the Woodborough Borehole, showing medium-grained tuff with highly vesicular basalt fragments (dark grey) interpreted as pumice. Note also the presence of shadowy spheroidal clasts, which may represent highly altered accretionary lapilli (E21479A). Magnification ×50, (MLD 3521, from Francis et al., 1968a, (Plate 16), figure 3) (P692306).

(Plate 7) A slightly flattened accretionary lapillus from 647.8 m in the Woodborough Borehole (E21478A). Magnification ×50, (MLD 3519, from Francis et al., 1968a, plate 16, figure 5) (P692307).

(Plate 8) Exposure in planarbedded and cross-bedded strata from the ‘upper division’ of the Lenton Sandstone Formation at Nottingham University campus [SK 5440 3863] (P692308).

(Plate 9) Exposure showing crossstratification in pebbly facies of the Nottingham Castle Sandstone Formation exposed at the Park Tunnel, which is accessible via steps from Upper College Street. Ruler is 1.45 m long. [SK 5652 3996] (P692309).

(Plate 10) Drillcore from 214 m in the Cropwell Bridge Borehole, showing the conglomerate marking the base of the Sneinton Formation. The core section is about 0.15 m long (P692310).

(Plate 11) Sneinton Formation strata exposed in a cutting on the A60 Mansfield Road at Redhill [SK 5835 4689] to [SK 5837 4713]. The prominent sandstone bed in the middle of this section thickens from left to right, and also cuts down into the beds beneath (P692311).

(Plate 12) Finely laminated strata of the Radcliffe Formation at 165.5 m in the Cropwell Bridge Borehole. Note the locally disturbed and rafted lamination, irregular developments of gypsum (white) and possible desiccation crack (at base). The core section is about 0.5 m long (P692312).

(Plate 13) Cotgrave Sandstone Member (pale grey bed at top left of picture) exposed above the Gunthorpe Formation at Wilford Hill brickpit [SK 5708 3555] during quarrying operations in 1965. (P692313).

(Plate 14) Drillcore showing the highly gypsiferous upper part of the Edwalton Formation at 47 m in the Cropwell Bridge Borehole. The gypsum (white areas) exhibits a distinctive fabric (at top) of subspherical nodules and abundant anastomosing gypsum veinlets beneath. The core section is about 0.5 m long (P692314).

(Plate 15) Exposure of uppermost Triassic and lowermost Jurassic strata at Bantycock gypsum pit [SK 8123 4949]. The lower part of the face is occupied by the Cropwell Bishop Formation, with seams of the Newark Gypsum (white) visible. The grey-green overlying bed is the Blue Anchor Formation, and the overlying beds are in turn the Westbury Formation of the Penarth Group (dark grey) and Cotham Member of the Lilstock Formation, Penarth Group (pale grey). The latter is succeeded by dark grey mudstone with pale grey limestone beds of the Barnstone Member (Lias Group) (P692315).

(Plate 16) Exposure of the Cropwell Bishop Formation at Kilvington Quarry, with seams of the Newark Gypsum (white layers). The Blue Anchor Formation occurs near the top of the face (P692316).

(Plate 17) Drillcore from 17.7 m in the Cropwell Bridge Borehole showing complex cross-cutting relationships between successive generations of gypsum veins. The core section is about 0.5 m long (P692317).

(Plate 18) Exposure in the Bantycock gypsum pit [SK 8123 4949], showing the sharp contact between the Blue Anchor Formation and the overlying Westbury Formation. The succession has been affected by large-scale synsedimentary slumping, with the Westbury Formation either folded or loaded into the Blue Anchor Formation at left-centre of the photograph. Bedding in the Blue Anchor Formation also appears to have experienced contortion (lower right). The higher beds in the left background consist of the Barnstone Member of the Lias Group, at the top of the quarry face, overlying the Cotham Member, the latter comprising the topmost bed of the Penarth Group (P692318).

(Plate 19) Exposure of a ‘bone bed’ in the Westbury Formation of the Penarth Group at Bantycock gypsum pit, showing dark grey, fissile mudstone with abundant irregular burrows (pale grey areas) (P692319).

(Plate 20) Contorted calcareous mudstone in the Cotham Member at Bantycock gypsum pit (P69232).

(Plate 21) Fossils typical of the Lias Group. (Note that not all of the specimens shown here are from the Nottingham district). The actual dimensions are in brackets. a. Psiloceras (50 mm); b. Caloceras (80 mm); c. Liostrea (120 mm); d. Modiolus (27 mm); e. Gryphaea arcuata (55 mm); f. Pseudopecten (65 mm); g. Pentacrinus ossicles and columnals (10 mm ossicles); h. Hippopodium (60 mm); i. Gagaticeras (35 mm); j. Arnioceras semicostatum (45 mm); k. Alsatites sp. (85 mm); l. Waehneroceras sp. (55 mm) (P692321).

Tables

(TableInsideFC) Geological succession in the Nottingham District

(Table 1) Coal seam thickness (‘S’ refers to a split seam interval).

(Table 2) Colliery closures since 1950.

(Table 3) Main worked gypsum units.

(Table 4) Sites of Special Scientific Interest (SSSI).

(Table 5) Licensed abstraction data for the Nottingham district, indicating the relative importance of different sources of water to the various users. The units shown are in cubic metres per annum (M3/a). Bracketed numbers indicate the number of licences in any particular category. The tabulation is derived from data provided by the Environment Agency, Severn-Trent Region (about 1993–1994 formerly National Rivers Authority).

(Table 6) Typical chemical analyses of groundwater in the Nottingham district.

(Table 7) Engineering geological classification of superficial deposits.

(Table 8) Engineering geological classification of bedrock materials.

(Table 9) Main earthquakes (after 1750) affecting the Nottingham area (after Neilson, Musson and Burton, 1984).

(Table 10) Colliery-worked coals in the Nottingham City area.

(Table 11) Classification of the Westphalian in the Nottingham district. New lithostratigraphical names are in brackets.

(Table 12) Comparison of current lithostratigraphical divisions of the Permian rocks in the Nottingham district with previous nomenclature, and correlation with chronostratigraphical, cyclic and sequence stratigraphical subdivisions identified in the Southern North Sea Basin. The wavy lines denote unconformities.

(Table 13) Miospores from the lower Cadeby Formation, Salterford Farm Borehole. The numbers of specimens of each taxon identified in a count of 300 miospores from each sample are indicated (from a report to the Geological Survey by R F A Clarke, 19 August 1964).

(Table 14) Comparative stratigraphical nomenclature of Triassic rocks in the Nottingham and adjacent districts.

(Table 15a) Distribution of miospores in the upper Mercia Mudstone Group, Blue Anchor Formation, Penarth Group and basal Lias Group at Bantycock Pit near Balderton [SK 8123 4949]. Examination and determinations by G Warrington. For key, see Figure 15b.

(Table 15b) Distribution and relative abundances of algae and other remains and relative abundances of principal groups of palynomorphs in the upper Mercia Mudstone Group,Blue Ancher Formation, Penarth Group and basal Lias Group at Bantycock pit near Balderton [[SK 8123 4949]. Relative abundance expressed as percentage based upon countsof 200 specimens. Specimens curated in the palynology collections (MPA series) at BGS,Keyworth. Examination and determinations by G Warrington.

(Table 16) Macrofauna of the Penarth Group and adjacent strata at Bantycock Mine, near Newark [SK 8123 4949]. All strata are Rhaetian (Late Triassic) in age.

(Table 17) Lithostratigraphical nomenclature of upper Triassic and lower Jurassic strata for Nottingham and adjacent districts. Note that the ‘Brant Mudstone Formation’ has been renamed as the Charmouth Mudstone Formation (Cox et al., 1999).

(Table 18) Chronostratigraphy of the principal Quaternary deposits in the Nottingham district and correlation with adjacent areas. Modified mainly from A Brandon (in Carney et al., 2001, 2004) and Bowen (1999; table 10). * signifies that the terrace deposit is ascribed a marine isotope stage on the basis of biostratigraphy, absolute age determination, detailed stratigraphy and sedimentology or presence of palaeosol. Other deposits are ascribed to a stage mainly on the basis of altimetry. Some river terrace deposits for the Nottingham district are of uncertain age, as indicated by the bracket. Key to the shaded rows: blue cold (glacial); grey cold (periglacial); yellow warm (temperate). ** Alternative age of Hoxnian warm period. *** Marine Isotope Stage.

(Table 19) Physical properties of the principal rock units seen at outcrop, including a selection of lithologies likely to be present in the subsurface of the Nottingham district. Compiled from various sources. The figures in brackets refer to the values most commonly used for seismic interpretations in the East Midlands region, and were provided by T C Pharaoh (BGS, written communication, 2002).

(Table 20) Availability of BGS Technical Reports, and index of authors to 1:10 000 scale map-sheets.

(Table 21) Summary details and alphabetic listing of a selection of the principal boreholes mentioned in the text.

Tables

(Table 1) Coal seam thickness (‘S’ refers to a split seam interval).

Unit/Seam Thickness (m)
Upper Coal Measures
Manor 0.24–1.0
Hucknall
Musters/Annesley 0.05–0.74
Middle Coal Measures
Edmondia 0.02–0.82
High Main 0.15–6.5 S
SWP 0.10–3.1 S
Clowne 0.01–3.5 S
Main Bright 0.23–1.49
Two Foot 0.03–5.03 S
Low Bright Floor and Low Bright 0.75–1.97
Brinsley, Low Bright Floor and Low Bright 1.80–2.68
High Hazles, Brinsley 2, Brinsley, Low Bright Floor and Low Bright 2.12
Cinderhill, HH, B2, B, LBF and LB 0.74 S
Abdy/Low Bright 0.1–3.3 S
Brinsley and Low Bright Floor 0.30–2.09
Low Bright Floor 0.06–0.92
Brinsley 0.06–1.03
Brinsley 2 0.01–0.61 S
High Hazles 0.05–3.0 S
Cinderhill 0.02–4.8 S
Main Smut 0.13–4.4 S
Coombe 0.27
Top Hard, Lower Coombe and Upper Coombe 0.42–2.68
Blidworth, Top Hard, Lower Coombe and Upper Coombe 0.63–2.60
Upper Coombe 0.03–0.53
Top Hard and Lower Coombe 0.45–1.93
Blidworth, Top Hard and Lower Coombe 0.40–2.17
Lower Coombe 0.01–0.94 S
Blidworth and Top Hard 0.67–1.57
Top Hard 0.13–3.4 S
Blidworth 0.06–0.91 S
1st Waterloo Upper Leaf and Dunsil 0.3–0.66
Dunsil 0.05–4.59 S
1st Waterloo 0.14–1.42
1st Waterloo Upper Leaf 0.02–1.14
1st Waterloo Lower Leaf 0.01–0.97
Waterloo Marker 0.01–0.45
2nd Waterloo 0.04–4.8 S
3rd Waterloo 0.02–7.9 S
1E and 4W 0.15–1.67
4th Waterloo 0.05–4.3 S
1st Ell 0.02–3.1 S
2nd Ell 0.04–11.4 S
Lower Coal Measures
Joan and Brown Rake 0.20–1.35
Joan 0.01–1.00
Brown Rake 0.02–0.70
Black Rake
Top Soft 0.03–0.4
Roof Soft 0.08–0.86
Deep Hard and Deep Soft 0.29–4.3 S
Deep Soft 0.7–4.8 S
Deep Hard 0.28–9.2 S
Hospital, 2P and 1P 0.67–2.96
CKSH, Hospital, 2P and 1P 0.07–2.59
1st Piper 0.12–6.5 S
Hospital and 2P 0.42–0.97
2nd Piper 0.08–0.70
Hospital 0.11–1.14
Tupton and CKSH 1.23–2.54
CKSH 0.06–0.62
Threequarters Lower and Upper Leaves and Tupton 1.17–1.54
Tupton 0.15–2.1
Threequarters 0.10–1.15
Threequarters Upper Leaf 0.13–0.51
Threequarters Lower Leaf 0.08–0.50
Yard and Yard Upper 0.44–1.35
Yard Upper Leaf 0.04–2.0 S
Blackshale, Yard Upper Leaf and Yard 0.83–3.17
Yard 0.03–2.8 S
Ashgate and Blackshale 0.52–2.27
Blackshale 0.19–2.13
Ashgate 0.01–3.15 S
Ashgate Floor 0.06–0.28
Kickley 1 0.04–0.59
Morley Muck 0.05–1.12
Kilburn 0.1–0.8

(Table 2) Colliery closures since 1950.

Colliery Year opened Year closed
Babbington (Cinderhill) 1842 1988
Bestwood 1871 1967/68
Calverton 1948 1999
Cotgrave 1964 1993
Clifton 1868 1968/69
Gedling 1902 1991
Hucknall 1862 1987/88
New Hucknall 1876 1982
Radford/Wollaton 1874 1965
Watnall 1893 1950

(Table 3) Main worked gypsum units.

Group Formation Worked Gypsum

Mercia Mudstone

 Blue Anchor No workable gypsum
Cropwell Bishop Newark gypsum
Edwalton 'Main' East Bridgeford gypsum
Gunthorpe Minor satinspar veins
Radcliffe No workable gypsum (rare satinspar veins only

(Table 4) Sites of Special Scientific Interest (SSSI).

Name Grid reference [SK] Main reason for special site status Geological interest
Colwick cutting [SK 600 397] ‘Type’ section of Colwick Formation of Elliot (1961) Section shows boundary between Sneinton and Radcliffe formations
Barnstone railway cutting [SK 740 356] Sections through the Blue Anchor Formation, Cotham Member and lower part of the Lias Group (Barnstone Member) Section shows transition from the Late Triassic (Norian and Rhaetian stages) into the Early Jurassic (Hettangian stage)
Grantham Canal [SK 780 345] Canal with aquatic habitats Views of Lias Group scarp and cuesta features
Hoveringham Pastures [SK 707 465] Wetland habitat by side of River Trent Views of Holme Pierrepont Terrace and adjacent floodplain alluvium
Muston Meadows [SK 823 366] Lowland meadow habitat Subdued scarp and cuesta features near top of the Foston Member
Wilford Claypits [SK 571 344] Marsh and mire plants Exposures of Cotgrave Sandstone and other ‘skerries’ in Mercia Mudstone

(Table 5) Licensed abstraction data for the Nottingham district, indicating the relative importance of different sources of water to the various users. The units shown are in cubic metres per annum (M3/a). Bracketed numbers indicate the number of licences in any particular category. The tabulation is derived from data provided by the Environment Agency, Severn-Trent Region (about 1993–1994 formerly National Rivers Authority).

Use

Water supply

Agriculture

 Fish Farming

Industrial
Aquifer Public Private General Spray irrigation General Gravel working Mining Electricity generation Total
River gravels — 159

(2)

 39 325

(9)

 49 796

(9)

 — 54 949

(4)

 2157077 — — 2 301 306

(36)
Lower Lias — — 3140

(6)

 — — — — — — 3140

(6)
Mercia Mudstone — 3410

(1)

 36 980

(26)

 25 298

(4)

 — 272 760

(1)

 — — — 338 448

(32)
Sherwood

Sandstone

 38 321 953

(9)

 501 327

(2)

 12 725

(6)

 854 475

(11)

 1 401 422

(2)

 5 980 455

(22)

 — 1 009 212

(2)

 — 48 081 569

(54)
Lower Magnesian Limestone — — — — — 855 912

(2)

 — — — 855 912

(2)
Coal Measures — — — — — 33 186

(1)

 — — — 33 186

(1)
Total 38 321 953

(9)

 504 896

(5)

 92 170

(57)

 929 569

(24)

 1 401 422

(2)

 7 197 262

(30)

 2 157 077

(2)

 1 009 212

(2)

 — 51 613 561

(131)
Surface waters — — 7502

(2)

 1 637 609

(67)

 11 302

(2)

 3 566 251

(16)

 418 560

(2)

 1 182 400

(2)

 986 472 090

(1)

 993 295 714

(92)

(Table 6) Typical chemical analyses of groundwater in the Nottingham district.

Location Nottingham Diary Bestwood No.1 Sump Far Balker BN3 Halam BH1 Clay Lane
NGR [SK 5487 3947] [SK 5555 4740] [SK 6121 5431] [SK 6700 5365] [SK 8109 5352]
Source type borehole mine shaft borehole borehole borehole
Aquifer Coal Measures Coal Measures Sherwood Sandstone (Zone 1) Sherwood Sandstone (Zone 2) Sherwood Sandstone (Zone 3)
Date of analysis 24.5.1954 18.5.1945 1992 1992 1992
pH 7.8 6.7 8.10 8.28 7.60
Conductivity SEC = S/cm NR NR 537 282 567
Calcium (Ca2+) mg/l 131.9 409.8 47.0 18.7 60.8
Magnesium (Mg2+) mg/l 35.8 134.6 23.0 20.0 19.8
Sodium(Na+) mg/l 134.0 NR 10.1 5.1 13.7
Potassium (K+) mg/l NR NR 2.8 1.8 4.3
Bicarbonate (HCO3-) 830.9 103 141 211
Sulphate (SO42-) 19.8 131.5 63.7 4.4 76.0
Chloride (Cl-) mg/l 48.0 3500 30.5 10.0 15.1
Nitrate (NO-3) mg/l nil NR 13.5 2.5 0.07
Iron (Fe3+) mg/l nil NR <0.015 <0.015 0.222

Data provided by the National Rivers Authority, Severn-Trent Region.

(Table 7) Engineering geological classification of superficial deposits.

Engineering geological unit

Lithostratigraphical unit
HEAD

Head
ORGANIC SOIL

Peat Alluvium (excluding gravel)

Lacustrine clay
FINE-GRAINED SOIL

Till (Boulder Clay)

COARSE-GRAINED SOIL

 Alluvial gravel
Holme Pierrepont Sand and Gravel

Deposits of lower river terraces
Leen Sand and Gravel
Beeston Sand and Gravel

Deposits of upper river terraces
Bassingfield Sand and Gravel
Balderton Sand and Gravel
Whatton Sand and Gravel
Eagle Moor Sand and Gravel
Glacial Sand and Gravel
Sandy Till Glacial deposits

(Table 8) Engineering geological classification of bedrock materials.

Engineering geological category Lithostratigraphical unit

Mudstone

various plasticity, with some siltstone, fine sandstone and limestone

 A Scunthorpe Mudstone Formation
Cotham Member
Westbury Formation
Blue Anchor Formation
Parts of Cropwell Bishop and Edwalton formations
B Cropwell Bishop Formation
Edwalton Formation
Gunthorpe Formation
Radcliffe Formation
C Edlington Formation
Cadeby Formation (mudstone)
Middle Coal Measures
Lower Coal Measures
Interbedded Sandstone and Mudstone Sneinton Formation

Sandstone

 Nottingham Castle Formation
Lenton Sandstone Formation
Lower Magnesian Limestone Cadeby Formation (dolomite)

(Table 9) Main earthquakes (after 1750) affecting the Nottingham area (after Neilson, Musson and Burton, 1984).

Date Macroseismic epicentre Maximum intensity in area MSK scale Location where felt in Nottingham area
23.8.1750 ?Off coast of Lincolnshire 3–4 Nottingham
30.9.1750 Uppingham 1795 Derby ?3–4

?

 Nottingham

?
17.3.1816 Mansfield area 5–6 Bingham, Carlton, Nottingham
4.8.1893 A few km NW of Leicester ?3–4 Cropwell Bishop
24.3.1903 A few km NE of Ashbourne 4–5 Bingham, Bulwell, East Bridgford, Hucknall, Nottingham
3.7.1904 SW of the Peak District 3–4 Nottingham and district
27.8.1906 Matlock Bath area 4 Nottingham and district
14.1.1916 Chebsey district ?3–4 Nottingham and district
3.3.1924 Sutton-in-Ashfield 3 Hucknall
6.3.1924 Kirby-in-Ashfield 5 Gedling, Hucknall, Mapperley, Nottingham
4.4.1924 South Normanton 4 Nottingham
20.4.1924 South Normanton 5–6 Hucknall
10.1.1956 Area NW of Leicester (Charnwood Forest) ?5 Bramcote, Nottingham
12.2.1957 Diseworth [~450 250] 6–7 (Magnitude 5.3) Throughout the area
2.6.1981 North of Arnold [58 48] 3+ (Magnitude 2.7) Nottingham
16.3.1983 Gunthorpe [688 441] 2+ (Magnitude 1.7) Woodborough
22.3.1984 East Retford ? (Magnitude 3.2) Arnold
30.5.1984 County Hall, West Bridgford [58197 38008]

(Depth 15 km)

 4–5 (Magnitude 3.1) Nottingham and district
23.8.1984 Bulwell [535 451] (Magnitude 2.2)
28.10.2001 North of Melton Mowbray [770 283] 5+ (Magnitude 4.1) Nottingham and district

Guide to disturbance for each point on the MSK scale: 1 Not noticeable; 2 Scarcely noticeable (very slight); 3 Weak; 4 Largely observed; 5 Effects noticed widely (strong); 6 Slight damage; 7 Damage to buildings; 8 Destruction of buildings; 9–12 Widespread devastation

(Table 10) Colliery-worked coals in the Nottingham City area.

Middle Coal Measures

 High Main
Main Bright
Low Bright
*High Hazles
Cinderhill
Coombe
Top Hard
1st Waterloo
2nd Waterloo

Lower Coal Measures

 Deep soft
Deep Hard*
Piper
Tupton (Low Main)
Threequarters
Yard
Blackshale*
Kilburn
* Seams worked in recent past

(Table 19) Physical properties of the principal rock units seen at outcrop, including a selection of lithologies likely to be present in the subsurface of the Nottingham district. Compiled from various sources. The figures in brackets refer to the values most commonly used for seismic interpretations in the East Midlands region, and were provided by T C Pharaoh (BGS, written communication, 2002).

Density (Mg/m3) Susceptibility (x 10-3SI units) Seismic velocity (km sec -1) Reference
STRATIFORM ROCKS
Jurassic:
Lias Group 2.49 2.4 Bridge et al. (1998)
Permo-Triassic: (2.5–2.8)
Mercia Mudstone Group 2.45 3.2–3.4 Bridge et al. (1998)
Sherwood Sandstone 2.49–2.55 Berridge et al. (1999)
Carboniferous:
Westphalian (2.9–3.5)
Westphalian 2.48 Worssam and Old (1988)
Namurian (3.5–4.0)
Namurian 2.54 Evans and Allsop (1987)
Dinantian (4.5–6.0)
Dinantian 2.75 Evans and Allsop (1987)
Dinantian 2.66–2.70 Berridge et al. (1999)
Dinantian 2.65–2.70 6.22 Worssam and Old (1988)
Ordovician?:
Andesite, Coxs Walk Bh 2.69 0.67
Cambrian:
Stockingford Shale Group (4.5–6.0)
Stockingford Shale Group 2.5–2.75 0.1–0.3 Bridge et al. (1998)
Stockingford Shale Group in Ticknall Borehole 2.7 Carney et al. (2001)
?Stockingford Shale Group in Ironville 5 Bh 2.68 n/d
Precambrian:
Charnian Supergroup 2.63–2.78 0.5–0.8 5.4–5.7

(5.7–6.1)

 Worssam and Old (1988)
IGNEOUS ROCKS
Carboniferous basalt:
Saltby Volcanic Formation Oct-50 Carney et al. (2004)
Ordovician intrusions:
Granodiorite (Croft/Sapcote) 2.7 0.16–0.70 5.0–5.78 Worssam and Old (1988)
Granodiorite (Mountsorrel) 2.65 26.4 6 Worssam and Old (1988)
Granodiorite (Rempstone Bh) 2.69–2.71 6 Entwisle (1993)
Granodiorite (Kirby Lane Bh) 2.57 0.8 3.31
Midlands Minor Intrusive Suite:
Lamprophyre 2.71 0.72 5.61 Worssam and Old (1988)
Diorite 2.74 0.4–50.0 Bridge et al. (1998)
Precambrian:
South Charnwood Diorite 2.72–2.84 0.49–41.00 4.9–6.2 Worssam and Old (1988)
North Charnwood Diorite 2.91 1.13 6.36 Worssam and Old (1988)
Basic Intrusions, Nuneaton 2.8 0.4–2.0 Bridge et al. (1998)

(Table 20) Availability of BGS Technical Reports, and index of authors to 1:10 000 scale map-sheets.

Map Sheet Report No. Geologist Date of Survey
SK53NE WA/89/4 T J Charsley 1987–88
SK54NE WA/89/7 P A Rathbone 1988
SK54SE WA/89/8 M T Dean 1988
SK55SE WA/93/21 R S Lawley 1993
SK63NW WA/89/9 D J Lowe 1987–88
SK63NE WA/89/10 D J Lowe 1987–88
SK64NW WA/89/13 J R A Giles & D J Lowe 1987–88
SK64NE WA/89/14 K Ambrose 1988
SK64SE WA/89/16 P A Rathbone 1987–88
SK64SW WA/89/15 P A Rathbone 1987–88
SK65SW WA/93/20 R S Lawley 1992/3
SK65SE WA/93/33 C N Waters 1993
SK73NE WA/92/30 B W Glover 1992
SK74SE WA/92/47 S R Young 1992
SK84SW WA/92/47 S R Young 1992
SK85SW WA/92/2 C N Waters 1992

(Table 21) Summary details and alphabetic listing of a selection of the principal boreholes mentioned in the text.* denotes boreholes located outside of the district.

Borehole/Shaft name NGR BGS borehole number Max. depth (m)
A46 Borehole 12 [SK 6592 3447] SK635E/86
Asfordby Hydro* [SK 7252 2061] SK72SW/71 657
Bagnall Road (Old Basford) [SK 5458 4338] SK54SW/526 30
Barbers Wood [SK 5603 5413] SK55SE/31 807
Bestwood Colliery [SK 5562 4745] SK54NE/200 202
Bestwood Pumping Station [SK 5792 4827] SK54NE/16A 71.6
Bingham No.1 [SK 7252 3935] SK73NW/3 900
Bingham No.2 [SK 7169 3956] SK73NW/1 829
Bottesford No.1 [SK 7907 3886] SK73NE/1 988
Bottesford No.3 [SK 7861 3919] SK73NE/2 994
Bottesford No.4 [SK 7859 3881] SK73NE/3 995
Broach Road* [SK 9292 5455] SK95SW/7 907
Brockley [SK 6595 5400] SK65SE/12 980
Brunts Lane [SK 6936 4251] SK64SE/93 no data
Bulcote (Lowdham Lodge) [SK 6651 4547] SK64NE/19 964
Bulcote Farm [SK 6629 4404] SK64SE/18 510
Bulwell (Forest) [SK 5518 4473] SK54SE/597 104
Burton Joyce [SK 6538 4427] SK64SE/38 150
Burton Joyce (Station Field) [SK 6452 4304] SK64SW/21 882
Calverton Colliery No.2 Upcast shaft [SK 6028 5015] SK65SW/52 514
Calverton Colliery shaft [SK 6035 5018] SK65SW/58 523
Calverton Colliery No.1 Downcast Shaft [SK 6034 5019] SK65SW/6 432
Calverton Lodge [SK 6215 5081] SK65SW/17 788
Carr Bank (Farnsfield)* [SK 6397 5579] SK65NW/2 939
Claypole No.1* [SK 8451 4934] SK84NW/3 669
Colston Bassett North* [SK 7100 3382] SK73SW/2 1306
Cotgrave (no name) [SK 6670 3606] SK63NE/172
Cotgrave (no name) [SK 6635 35097] SK63NE/168
Cotgrave (no name) [SK 6621 3514] SK63NE/166
Cotgrave Bridge [SK 6385 3669] SK63NW/39 613
Cotgrave Colliery No.1 shaft [SK 6511 3642] SK63NE/9 626
Cotgrave Colliery H53s [SK 6480 3525] SK63NW/17 240
Cotgrave Wolds Hill* [SK 6489 3433] SK63SW/17 862
Cotmoor Lane [SK 6615 5235] SK65SE/14 1003
Cox’s Walk No.1* [SK 8412 3808] SK83NW/10 800
Cropwell Bishop 1 [SK 6878 3812] SK63NE/11 914
Cropwell Bridge [SK 6773 3547] SK63NE/28 670
Cropwell Butler No.1 [SK 6813 3869] SK63NE/12 980
Cropwell Butler No.2 [SK 6797 3824] SK63NE/73 967
Cropwell Grange [SK 6863 3766] SK63NE/50 666
Eady Farm [SK 7958 3713] SK73NE/40 395
Eakring No.146* [SK 6808 5948] SK65NE/68 2278
East Bridgford (no name) [SK 6996 4150] SK64SE/73 20
Elston Grange [SK 7820 4601] SK74NE/2 842
Epperstone (Wash Bridge) [SK 6535 4787] SK64NE/20 713
Epperstone Park [SK 6414 4896] SK64NW/14 800
Epperstone-Timmermans [SK 6508 4750] SK64NE/37 63
Farndon No.1 [SK 7716 5350] SK75SE/1 805
Farnsfield No.1* [SK 6422 5742] SK65NW/3 474
Farnsfield No.3* [SK 6564 5588] SK65NE/107 901
Fishpool* [SK 5995 5540] SK55NE/3 792
Fiskerton [SK 7294 4979] SK74NW/9 834
Fiskerton No.1 [SK 7355 4983] SK74NW/10 1110
Forest Lane Papplewick [SK 5551 5099] SK55SE/14 698
Foss Way (Stragglethorpe) [SK 6577 3795] SK63NE/2 74
Foss Way Stragglethorpe [SK 6657 3619] SK63NE/1 902
Foston No.1* [SK 8489 4146] SK84SW/3 748
Fulbeck No.1* [SK 8889 5053] SK85SE/25 396
Fulbeck No.5* [SK 9062 5076] SK95SW/17 138
Gamston Bridge [SK 6031 3774] SK63NW/44 445
Gedling Colliery B11s/ug [SK 6346 4485] SK64SW/4 193
Gedling Colliery HHB3s [SK 6302 4375] SK64SW/5 173
Gedling Colliery Top Hard 2 Pit Bottom [SK 6118 4393] SK64SW/2 182
Goosendale Farm [SK 5639 4942] SK54ne/22 669
Granby No.1 [SK 7532 3684] SK73NE/4 939
Granby No.2 [SK 7689 3745] SK73NE/5 909
Grimmer* [SK 7908 3404] SK73SE/50 711
Gunthorpe Bridge (East Bridgford) [SK 6841 4351] SK64SE/11 534
Gunthorpe Grange Farm [SK 6724 4482] SK64SE/23 688
Halloughton [SK 6948 5141] SK65SE/11 950
Harlequin No.1 [SK 6684 3981] SK63NE/21 669
Hartswell Farm [SK 6444 5442] SK65SW/16 788
Hazel Hill Water Observation [SK 5663 4637] SK54NE/194
Holme Pierrepont [SK 6307 3932] SK63NW/28 792
Ironville No.5* [SK 4299 5141] SK45SW/67 c
Kelham Coal [SK 7716 5386] SK75SE/8 798
Keyworth (no name) [SK 6210 3314] SK63SW/36 50
Keyworth (no name) [SK 6194 3178] SK63SW/38 62
Langar No.1 [SK 7199 3558] SK73NW/4 946
Langar No.4 [SK 7217 3536] SK73NW/5 905
Langar No.6 [SK 7090 3612] SK73NW/9 822
Lees Barn No.4 ‘South??’ [SK 6398 3795] SK63NW/16 57
Linby Colliery No.1 [SK 5356 5043] SK55SW/13A 419
Longhedge Lane [SK 7944 4097] SK74SE/3 821
Middlestyle Bridge [SK 8085 3615] SK83NW/12 729
Newark No.1A [SK 8290 5248] SK85SW48 747
Newcastle Colliery [SK 5459 4220] SK54SW/38A 66
Newstead M3s [SK 5589 5316] SK55SE/56 142
Newstead T1s [SK 5701 5390] SK55SE/51 50
Newark-Widmerpool [SK 7088 4288] SK74SW/34 20
Newark-Widmerpool [SK 6996 4150] SK64SE/68 20
Newark-Widmerpool [SK 6901 4021] SK64SE/73 20
Normanton No.4 [SK 7220 5443] SK75SW/4 871
Norwood Borehole* [SK 6959 5497] SK65SE/2 929
nr Poplar Farm [SK 7223 5156] SK75SW/17 5
Oxton [SK 6116 5303] SK65SW/5 65
Oxton No.1 [SK 6652 5164] SK65SE/1 1277
Papplewick Hall [SK 5468 5213] SK55SW/31 694
Papplewick Pumping Station [SK 5829 5212] SK55SE/76 84
Parkhill No.1 [SK 7044 5285] SK75SW/23 372
Ploughman’s Wood Lowdham [SK 6428 4688] SK64NW/30 845
Plungar No.8A [SK 7745 3336] SK73SE/27 1418
Poplars Farm [SK 7627 3722] SK73NE/10 764
Radcliffe Barn Farm [SK 6639 3806] SK63NE/53 618
RaleighCycleWorks(noname) [SK 5494 3981] SK53NE/16A 137
Redmile Bridge [SK 7947 3568] SK73NE/11 733
Redmile No.2 [SK 8070 3609] SK83NW/13 648
Rolleston G1 [SK 7578 5161] SK75SE/4 614
Rolleston G2 [SK 7530 5135] SK75SE/5 667
Rolleston No.1 [SK 7612 5191] SK75SE/3 725
Rolleston No.3 [SK 7541 5119] SK75SE/11 510
Ruddington* [SK 5560 3260] SK53SE’/20 570
Rundle Beck [SK 7578 3524] SK73NE/13 748
Salterford Farm [SK 6057 5282] SK65SW/19 809
Saxondale (no name) [SK 6864 3964] SK63NE/188 26
Saxondale No.1 [SK 6775 3931] SK63NE/74 1058
Screveton No.1 [SK 7307 4348] SK74SW/1 1104
Sherwood Lodge [SK 5733 5080] SK55SE/67 701
Shipstones Brewery [SK 5568 4208] data missing
SK54NE/15B [SK 556 475] data missing
Station Farm [SK 7429 3592] SK73NW/46 690
Stenwith* [SK 8335 3683] SK83NW/11 720
Strelley LN/4-2* [SK 5052 4296] SK54SW/560 1450
Sunrise Blidworth* [SK 5729 5480] SK55SE/48 821
Swing Bridge [SK 6696 3651] SK63NE/55 669
The Limes [SK 6742 3721] SK63NE/49 202
Thorpe No.1 [SK 7693 5054] SK75SE/6 692
Three Shire Oaks Long Bennington [SK 8221 4303] SK84SW/21 982
Thurgarton [SK 7003 4842] SK74NW/6 259
Tithby [SK 7009 3713] SK73NW/2 798
Turncroft* [SK 6562 5473] SK65SE/13 1026
Upton No.2 [SK 7323 5293] SK75SW/6 822
West Bridgford [SK 6002 3640] SK63NW/48 714
Widmerpool No.1* [SK 6366 2958] SK62NW/1 1891
Wild’s Bridge [SK 6738 3248] SK63SE/30 935
Wilford Deering School [SK 5741 3748] SK53NE/2 50
Woodborough [SK 6215 4808] SK64NW/9 803
Woolsthorpe Bridge* [SK 8432 3488] SK83SW/99 239
York House [SK 5730 4040] SK54SE/583 no data
* denotes boreholes located outside of the district.