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Geology of the country between Loughborough, Burton and Derby. Sheet description of the British Geological Survey 1:50 000 Series Sheet 141 Loughborough (England and Wales)

By J N Carney, K Ambrose and A Brandon

Bibliographical reference: Carney, J N, Ambrose, K, Brandon, A Cornwell, J D, Hobbs, P R N, Lewis, M A, Merriman, R J, Ritchie, M A, and Royles, C P. 2001. Geology of the country between Loughborough, Burton and Derby. Sheet description of the British Geological Survey, 1:50 000 Series Sheet 141 Loughborough (England and Wales). 92pp.

Geology of the country between Loughborough, Burton and Derby. Sheet description of the British Geological Survey 1:50 000 Series Sheet 141 Loughborough (England and Wales)

Authors: J N Carney, K Ambrose and A Brandon

Contributing authors: J D Cornwell, P R N Hobbs, M A Lewis, R J Merriman, M A Ritchie and C P Royles

Keyworth, Nottingham British Geological Survey 2001. © NERC copyright 2001. ISBN 0 85272 388 1

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Ordnance Survey licence number GD 272191/2001.

(Front cover) Dinantian rocks of the Milldale Limestone Formation exposed in the face of the Breedon Hill Quarry, viewed from the east [SK 411 232]. The main pit of the quarry is below the viewing level. Breedon Hill formed a major element of the Permo-Triassic topography, before being buried by mid-Triassic strata of the Mercia Mudstone Group. The latter’s outcrop gives rise to red, clay-rich soils typified by the ploughed fields in the foreground (Photographer C F Adkin) (MN32052).

(Back cover)

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Acknowledgements

This account draws freely on data from BGS open-file reports that accompany each of the 1: 10 000 series map sheets (Table 7) and the following are acknowledged:

In this report J N Carney was responsible for overall compilation, and for sections on the Precambrian and Cambrian rocks, Structure, Concealed Geology and Mineral Resources, together with parts of the Applied Geology section. The Carboniferous section was written jointly by K Ambrose and J N Carney, and K Ambrose also contributed the account of the Triassic rocks and the Penarth Group. A Brandon wrote the sections on the Jurassic and Quaternary. The manuscript was edited by T J Charsley, A A Jackson and R D Lake.

We acknowledge the help provided by the holders of data in permitting the transfer of their records to the National Geological Records Centre, BGS Keyworth. We are especially grateful for the assistance provided by the Coal Authority, Severn-Trent Water and numerous civil engineering consultants and quarry companies. The cooperation of landowners and tenants in permitting access to their land is gratefully appreciated.

A brief account of the geology of the district with some details of the mineral resources and applied geology given here is provided in the Sheet Explanation for Sheet 141 Loughborough.

Notes

Geology of the country between Loughborough, Burton and Derby—summary

This report describes the geology of the Loughborough Sheet 141. Overlooking the district in the south-east are the uplands of Charnwood Forest, a region of numerous craggy exposures that reveal a predominantly volcaniclastic sequence, derived by eruptions from a volcanic arc that was active in Precambrian times, over 600 million years ago. Cambrian rocks are present, although very poorly exposed, on the eastern side of Charnwood Forest, and have been proved in a single borehole farther north, near Ticknall. Together with the Precambrian rocks they were folded, cleaved and mildly metamorphosed during the Acadian (Siluro-Devonian) orogeny. Mainly Carboniferous and Triassic strata occupy the remainder of the map area, with outliers of Lower Jurassic rocks in the extreme east. In many parts of the district, however, superficial Quaternary deposits cover the bedrock.

Inliers of Lower Carboniferous (Chadian to Brigantian) dolostones that include Breedon Hill are part of a largely concealed, highly variable Dinantian sequence for which a new stratigraphy has been erected. Data from boreholes and seismic records show that the Dinantian attains over 5 km thickness within the concealed Widmerpool half-graben (or ‘gulf’). Sandstones in the overlying Millstone Grit Group are part of a Namurian deltaic sequence, which can be correlated on faunal grounds with that of north Derbyshire. Stratigraphical correlations within the overlying Coal measures, and their complex structure, are discussed for the North-west Leicestershire and South Derbyshire coalfields, and the extent of the economically important fireclay resource in the South Derbyshire Coalfield is highlighted.

The result of Variscan (end-Carboniferous) deformation is spectacularly demonstrated by the uplift of Precambrian rocks against the Coal Measures along the Thringstone Fault, and by the vertical attitudes of Dinantian strata in quarries around Breedon on the Hill. Other fundamental structures of this age, and reactivated Acadian lineaments, are revealed by utilising surface observations allied to seismic interpretations and geophysical (aeromagnetic and gravity) modelling.

Triassic strata are shown to have overstepped on to a locally mountainous land-surface chiefly formed during a period of about 60 million years of erosion spanning the Permian. They commence with the Sherwood Sandstone Group, representing the deposits of former river systems and constituting a regionally important aquifer. By contrast, the overlying Mercia Mudstone Group was mainly deposited in aeolian and playa lake environments; it locally contains thick gypsum seams that have been mined underground. Rhaetianage marine beds of the Penarth Group, and the overlying Jurassic mudstones and limestones of the Lias Group, complete the preserved bedrock sequence.

Quaternary deposits include two varieties of Anglian-age till: red, Triassic-rich Thrussington Till and grey, chalky, Jurassic and Cretaceous-derived Oadby Till. Till forms a patchy cover and, together with thick developments of glaciolacustrine clay, also occurs within narrow tunnel valleys. Sustained uplift through the Anglian and Flandrian stages resulted in at least six generations of river terrace deposits in the trunk valleys. These complex deposits represent an aggregate resource and are also important suppliers of water in the district.

There is an impressive diversity of metalliferous minerals, but current economic value comes from ‘hard rock’, limestone, sand and gravel, coal, fireclay and gypsum. The legacy of centuries of mining or quarrying is, unfortunately, large areas of artificially changed ground. Geology has an important role to play, not only in delineating already despoiled land, but in predicting the constraints that the rocks and superficial deposits of the district may pose to further development.

(Table 1) Geological succession of the Loughborough district.

Chapter 1 Introduction

The Loughborough district (Figure 1) lies mainly within the Northwest Leicestershire and South Derbyshire administrative areas, but also includes small parts of Staffordshire in the west and Nottinghamshire in the northeast. The main population centres of Derby, Long Eaton, Burton upon Trent, Loughborough, Ashby-de-la-Zouch, Melbourne, Swadlincote and Church Gresley conurbations are separated by agricultural land, which include the flood-prone valley floors of the Trent, Derwent and Soar Rivers (Figure 2).

Over 600 million years of geological history are represented in this district, by rocks that form the sequence summarised in (Table 1). The distribution of the main rock groupings is indicated in (Figure 1), which also shows those units of particular economic or environmental significance, for example the Cropwell Bishop Formation. The southeast margin of the district lies on the edge of Charnwood Forest, a hilly terrain of craggy knolls, rough pasture and heathland that rises to just over 210 m maximum elevation on Ratchet Hill [SK 4467 1635]. Late Precambrian volcaniclastic rocks of the Charnian Supergroup underlie this ground, and because of their resistance to erosion they form a fossil hill range that is now being exhumed from beneath a variably thick cover of Triassic strata and drift. A younger component of this ‘basement’ are the marine mudstones of the Cambrian-Ordovician Stockingford Shale Group, which are inferred to be the principal sub-Carboniferous unit to the north and west of Charnwood Forest. These strata are not exposed, but have been proved in the Ticknall Borehole‡1 , drilled in support of this resurvey. The earliest recorded Charnian uplift dates from the Acadian orogeny of Silurian–Devonian times, when these sequences were cleaved and folded. Dinantian (‘Carboniferous Limestone’) strata form undulating country around Ticknall and appear as a line of smaller inliers farther east; they are locally tilted to the vertical, and protrude through the mantling Trias to form the spectacular landmark of Breedon Hill (Front cover), rising to 125 m OD. The Dinantian sequence thickens to over 5 km north-east of the Normanton Hills Fault. The succeeding Millstone Grit of Namurian age comprises fluvio-deltaic sandstones and siltstones intercalated with mudstones, and gives rise to a scarp and dip-slope topography around Melbourne. Westphalian strata of the Coal Measures are mainly preserved to the south-west of the Thringstone Fault in the Northwest Leicestershire and South Derbyshire coalfields. Their content of minerals such as coal, ironstone and fireclay contributed to the early growth of the urban centres, and the various phases of mining activity have also profoundly affected much of the land surface on the Productive Measures outcrop. However, today such extraction is limited to two opencast sites.

Overlying the faulted and eroded pre-Mesozoic rocks at the depth are late Permian strata of the Edlington Formation and the Permo-Triassic Lenton Sandstone Formation. The Moira Formation is regarded as a highly diachronous, Permo-Triassic basal lag deposit. The oldest truly Triassic-age strata, of the Sherwood Sandstone Group, give rise to undulating ground in the central and south-western parts; they comprise the conglomeratic Polesworth Formation and fine-grained Bromsgrove Sandstone Formation, which are both major aquifers in the district. Prominent outliers of the group commonly form steep-sided plateaux where preserved on the Coal Measures, as at Pistern Hill [SK 342 208]. Red, argillaceous strata of the succeeding Mercia Mudstone Group are the most widespread Triassic rocks and form a gently undulating, dissected terrain in the central and northern parts of the district. They include the Cropwell Bishop Formation which has been locally exploited for its thick seams of gypsum, and which can also give rise to hazardous ground in areas where the gypsum seams have dissolved at or near to the surface. The youngest bedrock components represent a reversion to marine conditions. These are mudstones, sandstones and limestones of the Penarth Group, and the overlying flaggy limestones and mudstones of the Barnstone Member (largely Jurassic in age) at the base of Lias Group. They form distinctive, steep-sided plateaux dominating the eastern margin of the district.

Unconsolidated deposits of Quaternary drift are patchily developed. The oldest drift deposits are referred to the Anglian glaciation of about 440 000 years ago, and mainly form veneers to the bedrock on the wider interfluves, or are preserved in palaeochannels. They comprise the Thrussington Till which is red in colour and rich in Triassic debris and the Oadby Till which is brown to grey with chalk and flint debris. Locally abundant are sands and gravels comprising glaciofluvial deposits, and clays and silts of glaciolacustrine origin. The most extensive Quaternary sequences either floor the trunk valleys or underlie terraces that flank them. In the former situation they were thought to consist mainly of modern alluvium, but this re-survey has proved that other river terrace deposits predominate. These are locally thick and constitute a major resource of sand and gravel in the district.

History of survey and research

The district was originally surveyed on the 1:63 360 scale by A C Ramsay, H H Howell and E Hull and published on the old series sheets 62, 63, 71 and 72 in 1852 and 1855. The primary survey at the 1:10 560 scale, by C Fox-Strangways and W W Watts, was published as a Solid and Drift edition in 1904. The Carboniferous rocks were revised and other amendments made by G H Mitchell, leading to the publication in 1950 of a second map version. A brief account of the district is given by Fox-Strangways (1905). Many of the earlier accounts concentrated on the coalfields (Hull, 1860; Fox-Strangways, 1907), which continued to be the main subject of later work by Mitchell and Stubblefield (1948) and Spink (1965). The Charnian Precambrian rocks have had a long history of research, summarised by Ford (1979) and Watts (1947), the latter work classically illustrating the geology as then known. During the post-war years surveys for hydrocarbons have provided comprehensive information on the shallow seismic structure and lithostratigraphy for the central and north-eastern parts of the district; the principal findings are discussed in Falcon and Kent (1960) and Fraser and Gawthorpe (1990).

The latest phase of re-mapping started in 1964–74, with a survey along the northern margin of the district at the 1:10 560 scale by D V Frost and J G O Smart as part of the Sheet mapping programme for Sheet 125 Derby, and on the southern margin, parts of sheets SK 21 NE, 31 NW, 41 NE and 51 NW were mapped by B C Worssam and R A Old during the resurvey of Sheet 155 Coalville. A. Horton also carried out limited mapping in association with the construction of the Melbourne Dam and Staunton Harold Reservoir, located at the northern end of Staunton Harold Reservoir. The first 1:10 000 scale resurvey was carried out by A S Howard, in 1987. The remaining 1:10 000 series sheets were completed between 1993 and 1996 by the survey staff indicated in (Table 7). This final phase, supported by the drilling of two stratigraphical boreholes, involved researchers from a wide range of geological disciplines both within and outside the BGS. Some of this work was still on-going at the time of writing, but much is also reviewed in the pages that follow.

Chapter 2 Precambrian

The Precambrian rocks represent an uplifted segment of the cratonic basement which otherwise deeply underlies this part of the English Midlands (Pharaoh et al., 1987a). They are the remnants of a latest Precambrian (Neoproterozoic III) volcanic arc, and are divisible into the bedded volcaniclastic sequence of the Charnian Supergroup, and a suite of later intrusions - the North Charnwood Diorites. These rocks are typically developed within Charnwood Forest, but they are also present farther north beneath a thin Triassic cover. They are exposed in an inlier east of Grace Dieu Brook [SK 4397 1880], and were proved below Triassic strata at 74.2 m depth in the Belton Borehole. However, the Precambrian rocks, as the immediate (pre-Carboniferous or pre-Triassic) basement, are terminated by major concealed faults within several hundred metres north of the Charnwood Forest upland (see Chapter 10). The Precambrian outcrop extends for 10 km south-east of the Loughborough sheet margin, into the Coalville district (Worssam and Old, 1988). It is limited to the west by the Thringstone Fault, and to the south and east by the south-eastward plunge of the anticline that folds the Charnian sequence (Chapter 9).

The geochemistry of the Charnian Supergroup and its associated intrusions is directly comparable with Precambrian volcanic arc rocks of the Nuneaton inlier, located 23 km to the south-west (Bridge et al., 1998). All of these Precambrian occurrences must therefore have originally formed part of a single volcanic system which is now incorporated into the basement and is termed the ‘Charnwood Terrane’ by Pharaoh et al. (1987b).

Precambrian volcanic rocks are also proved in the Orton and Glinton boreholes, to the south-east of the Loughborough district, as discussed further below. Their chemistry does not compare with that of the Charnian Supergroup, however, and they may belong to a separate volcanic arc terrane (Noble at al., 1993).

Charnian Supergroup

The lithostratigraphical scheme for the supergroup followed here (Table 2) is based on the terminology of Watts (1947) that was formalised by Moseley and Ford (1985) and modified further by Carney (1994), who gave details of most exposures in the district. All three Charnian groups are represented; they crop out in the south-east of the district in a south-east plunging anticline. The various components of the supergroup are only exposed intermittently but their inferred distribution beneath younger cover is shown in (Figure 3). The supergroup has an aggregate thickness of at least 3800 m in the district, with no base proved.

The volcanic provenance of the Charnian Supergroup has long been recognised (see Watts, 1947 and references in Ford, 1979). Chemical analyses of the primary volcanic components show that the parental magmas were calcalkaline, similar to those of modern evolved volcanic arcs founded upon oceanic or attenuated continental crust (Pharaoh et al., 1987b). Many modern intra-oceanic arc systems are largely submerged, and consequently it is the fragmental material, either eroded or ejected from the volcanic axis, that is the most likely to be preserved in the depositional basins that surround the arc. This explains why the Charnian is composed mainly of well-stratified volcaniclastic lithologies, with only a subordinate amount of primary pyroclastic rocks (terminology of Fisher and Schmincke, 1984). The general absence of cross-bedding or wave-generated structures indicates that deposition was primarily below storm wave base; other structures, such as grading, suggest that sedimentation was by debris flows, pyroclastic flows and sediment-laden turbidity currents flowing into basins that were marginal to the active volcanoes (Carney, 1999). In the north-west of Charnwood Forest a different lithological assemblage, of subvolcanic intrusions and/or domes (Whitwick Volcanic Complex) associated with very coarse-grained volcanic breccias, indicates that later in the Charnian cycle of magmatism, active volcanic centres had migrated into the district.

A late Precambrian (Neoproterozoic III) age for the extrusive phase of the Charnian arc is indicated by Ediacaran fossils, which are found throughout the sequence in this and the Coalville districts (Boynton and Ford, 1995, 1996). However, the precise age of this magmatism is currently controversial. Previous studies, based on K-Ar and Rb-Sr isotope systems, were carried out by Meneisy and Miller (1963) and Cribb (1975). The latter concluded on the basis of Rb-Sr ratios that the South Charnwood Diorites (markfieldites), emplaced within the Charnian Supergroup to the south of this district, were 552 ±58 Ma old, but the large error range renders this age difficult to interpret. For the North Charnwood Diorites, outcropping in this district, Cribb returned an age of 311 ± 92 Ma which is clearly at odds with the fact that the intrusions predate a cleavage deformation now known to be Acadian (Siluro-Devonian) in age (Chapter 9). Indirect evidence for an upper age limit comes from lithological and geochemical correlations between the South Charnwood Diorites and the similar granophyric-textured diorite intruded into volcaniclastic rocks of ‘Charnian’ type in the Nuneaton inlier, about 33 km south-south-west of this district (Bridge et al., 1998). The Nuneaton granophyric diorite has been radiometrically dated by the U-Pb method, yielding an age of 603 ± 2 Ma (Tucker and Pharaoh, 1991). According to McIlroy et al. (1998), however, this is rather older than the value of 580 Ma currently favoured for the base of the fossil-bearing Ediacarian subdivision of the Neoproterozoic, and it therefore requires further substantiation.

The age of the uppermost Charnian unit, the Brand Group, is also in doubt. Clast lithologies show that the middle part of this group contains detritus of granophyric diorite apparently eroded from the South Charnwood Diorites (McIlroy et al., 1998), suggesting a major unconformity postdating the last phase of intrusion. Furthermore, in the lower Brand Group, the Hanging Rocks Formation (exposed just south of this district, see Worssam and Old, 1988) is the first Charnian unit to contain rounded volcanic pebbles and is thus probably unconformable on the Maplewell Group. Added to this are the findings of Bland (1994) that the Swithland Formation, upper Brand Group, contains trace fossils of Teichichnus which are thought to indicate an age no older than the Lower Cambrian (Bland and Goldring, 1995).

The Precambrian volcanic rocks proved in the Orton and Glinton boreholes, to the south-east of Charnwood Forest, have yielded U-Pb isotope ages of 616 ± 6 Ma and 612 ± 21 Ma respectively (Noble et al., 1993). These rocks are not the precise chemical equivalents of those in Charnwood Forest, however, and their relevance to the age of Charnian volcanicity is therefore questionable.

Blackbrook Group

This unit corresponds to the ‘Blackbrook Series’ of Watts (1947) and was given its present name by Moseley and Ford (1985). It occurs within the central part of the Charnian anticline (Figure 3), its component formations disposed in annular outcrops reflecting the south-east plunge of the fold. The base of the group is not seen; its top is defined by the incoming of volcanic breccias comprising the Benscliffe Breccia Member of the overlying Maplewell Group. The group has an aggregate thickness of at least 1800 m. It was divided into two formations by Moseley and Ford (1985); (Table 2), to which a third and basal unit - the Morley Lane Volcanic Formation - was added by Carney (1994). The Blackbrook Group commences in massive andesitic volcanic rocks (Morley Lane Formation) passing up to grey, turbidite-facies volcaniclastic mudstones, siltstones and sandstones of the Ives Head Formation. The succeeding Blackbrook Reservoir Formation is similarly of turbidite facies, consisting of grey-green, thickly bedded and multiply graded volcaniclastic strata. A single bedding plane in the Ives Head Formation contains fossils which, although of problematic affinity, were nevertheless placed within the Ediacaran faunal assemblage by Boynton and Ford (1995, 1996).

The three formations of the Blackbrook Group together constitute an upwards-fining sequence. In the basal Morley Lane Volcanic Formation, the possible occurrence of lava flows is indicative of an initial, proximal-to-centre volcanic environment. Subsequently as water depths increased, instability in the now largely quiescent or more distal volcanic source areas contributed the sand-rich turbidite sequence of the Ives Head Formation, possibly accompanied by more proximal-facies epiclastic or pyroclastic debris flows (graded volcaniclastic sandstones and breccias). This trend culminated in the largely epiclastic Blackbrook Reservoir Formation which is dominated by medial to distal turbidites representing episodic sedimentary influxes into the basin.

Morley Lane Volcanic Formation

This unit, named by Carney (1994), represents the stratigraphically lowest Charnian subdivision. It does not crop out, and has been proved only in the BGS Morley Quarry No.1 Borehole (Pharaoh and Evans, 1987), between 541 and 835.54 m (terminal depth). It consists mainly of dark greenish grey to black flow-banded porphyritic dacite, up to 90 m thick, interpreted as lava flows. There are subordinate intercalated fine-grained tuff beds.

Ives Head Formation (IvH)

This unit is about 800 m thick and occupies an elongate outcrop in the core of the main Charnian anticline. The type section designated by Moseley and Ford (1985) is on Ives Head [SK 477 170] and the exposures at Morley Quarry [SK 4765 1785] are considered to be an important reference section (Figure 4)a & b. In Morley Quarry, the sequence consists mainly of pale grey or greenish grey, parallel bedded to laminated volcaniclastic mudstones and siltstones. These commonly grade downwards into thicker and more massive beds of coarse to very coarse-grained crystal and lithic-rich volcaniclastic sandstone (saV). These coarser beds show diffuse parallel stratification in their upper parts, but lower down they are commonly massive, consisting of coarse-grained volcaniclastic sandstone and, near the base, matrix-supported breccia (brV) with both volcanic and sedimentary clasts (Carney, 2000a). Sedimentary features are well displayed at Ives Head summit [SK 4769 1704]; they include repetitive normal grading, load structures and wavy to contorted bedding and laminae (Carney, 1994). A volcaniclastic breccia at Short Cliff [SK 4852 1719] is about 60 m thick; it encloses fragments of dacitic volcanic rock which, in thin section (E67478), show groundmass textures ranging from aphanitic to spherulitic and shardic (y-shapes). At Ives Head summit (Plate 1) a prominent bedding plane contains impressions of problematic, ?medusoid Ediacaran fossils of the genus Ivesheadia, Shepshedia and Blackbrookia (Boynton and Ford, 1995, 1996). The Ives Head Formation is capped by the South Quarry Breccia Member (SQBr), about 30 m thick. In its type section at One Barrow Plantation [SK 4639 1714] it contains folded siltstone rafts, up to 1.5 m long, in a pale grey, coarse-grained, poorly sorted crystal-lithic matrix. The beds below consist of about 4 m of medium to coarse-grained volcaniclastic sandstone which grades down into laminated siltstones and mudstones.

Blackbrook Reservoir Formation (Blk)

This formation was named by Moseley and Ford (1985), who designated the type section as the intermittent exposures around the northern end of the Blackbrook Reservoir and in Blackbrook Quarry [SK 4563 1797]. It is approximately 550 m thick, but uncertainties over this estimate are due to possible tectonic omission or repetition of strata in the north-east of the outcrop. Greenish grey, volcaniclastic mudstones, siltstones and sandstones of turbidite facies dominate the formation.

At Blackbrook Quarry the sequence consists of pale grey to greenish grey, finely laminated volcaniclastic mudstone and siltstone, with intercalated beds of fine grained sandstone. Laminae are commonly expressed on a scale of one millimetre or less, and are grouped in sets between 5 and 30 mm thick. Some of the thicker beds show normal grading, and in places the laminae are gently flexured. Above the contact with the South Quarry Breccia, the basal beds consist of laminated to massive volcaniclastic siltstone and sandstone in beds 0.2 to 0.4 m thick.

In Longcliffe and Newhurst quarries (Carney, 1994, figs. 4, 5), the formation is composed of a distinctive series of beds which are typically up to 2 m thick; they have sharply defined, planar boundaries which constitute good structural markers (Plate 17). Individual beds were deposited from multiple sedimentary events, each bed consisting of between 10 and 20 sets composed of parallel laminated, massive, or normally graded volcaniclastic mudstone and siltstone (Figure 4)c & d. More rarely, volcaniclastic sandstone (saV) forms amalgamated, massive to normally graded beds, in sequences up to 4.5 m thick; individual sandstone beds commonly grade downwards into massive matrix-supported breccia (brV), and at Newhurst Quarry such breccias are characterised by a high proportion of intraformational sedimentary clasts. Other sedimentary features common to the formation include load structures and convoluted or rafted bedding; synsedimentary brecciation is exposed at Ingleberry Rock [SK 4896 1733].

Key localities:

Maplewell Group

This group is estimated to be just over 2000 m thick, and crops out around the flanks of the main Charnian anticline. It shows lateral variations in lithology, as indicated by the Generalised Vertical Section of the 1:50 000 Series Sheet 141 Loughborough, and is here divided into two main parts, each of which contains various members, as shown in (Table 2). An eastern outcrop consists mainly of the Beacon Hill Formation, and is dominated by fine to medium-grained volcaniclastic rocks and re-worked tuffs with a locally significant pyroclastic component. A north-western outcrop consists of the Charnwood Lodge Volcanic Formation, which is composed largely of very coarse-grained to block-rich pyroclastic lithologies that were deposited nearer to the Charnian volcanic centres (Carney, 2000b). Correlation between these two sequences is aided by the mapping of a significant marker bed, the Benscliffe Breccia Member, which occurs at the base of the Maplewell Group and can be traced continuously around the nose of the main Charnian anticline to the south of this district. The Bradgate Formation represents the youngest Maplewell Group component; it is common to both eastern and western outcrops, though is generally coarser grained and more massive in the west.

In the eastern outcrop, the Benscliffe Breccia Member overlies the Blackbrook Reservoir Formation and underlies the Beacon Tuff Member. Both are well-bedded and laminated, turbiditic volcaniclastic sequences deposited subaqueously, suggesting that the Benscliffe Breccia represents the deposits of a subaqueous pyroclastic flow. It thickens north-westwards, where traced around the main Charnian anticline into the Charnwood Lodge Volcanic Formation (see below), suggesting it represents the initial episode of explosive volcanism from centres situated in that region. Further pyroclastic flows formed the dacitic lithic-crystal tuffs within the Beacon Tuff Member and capping this, the Sandhills Lodge Member may represent the deposits of a subaqueous volcaniclastic debris flow, triggered either by tectonism or a pyroclastic eruption, and involving the mobilisation of partially lithified sediments or pyroclastic deposits. A prolonged period of distal turbidite sedimentation followed, depositing the Buck Hills Member. It was accompanied by pyroclastic fall-out from distant volcanic centres that formed vitric tuff layers or laminae. The Outwoods Breccia Member represents a renewed episode of coarse sediment influx. Its content of sediment clasts suggests it was generated by slope instability and involved the mass mobilisation of a partially lithified sedimentary pile that may have formed a turbidite apron that accumulated marginally with respect to the active volcanic centre(s).

In the western part of the Maplewell Group the overall lithology of the Charnwood Lodge Volcanic Formation indicates deposition in a proximal situation with respect to active Charnian volcanic centres. Its close spatial association with the Whitwick Volcanic Complex, which possibly represents a magmatic feeder zone, further suggests this. Important petrographical and geochemical parallels can also be drawn between components of the Whitwick Volcanic Complex and Charnwood Lodge Formation. The stratified component (undivided beds) of the Charnwood Lodge Formation is interpreted as volcaniclastic accumulations which formed a debris flow apron around andesitic to dacitic volcanic centres. Some of these beds, however, could also be the deposits of long run-out pyroclastic/epiclastic debris flows originating on the flanks of more distant centres. The Swannymote Breccia shows evidence for subaqueous deposition and mixing with an unconsolidated sedimentary substrate. Clasts in that lithology and in the Cademan Breccia Member can be directly matched with massive lithologies in the Whitwick Volcanic Complex. Therefore, these breccia members probably represent the deposits of pyroclastic block flows originating from the disintegration of the volcanic domes or viscous flows represented by the Grimley Andesite or Sharpley Dacite of the Whitwick Volcanic Complex. The great thickness of the Cademan Volcanic Breccia, and its localised development, suggest that it was supplied by multiple debris flows which formed accumulations ponded within valleys, tectonic depressions or a caldera (Carney, 2000b).

The Bradgate Formation represents a change to more distal accumulations of predominantly ash-grade crystal, lithic and vitric pyroclastic material, modified by turbidity current processes. In the north-western outcrop, the presence of very coarse-grained volcaniclastic sandstones and breccias, some with vitric shards, suggests that volcaniclastic sediment gravity flows continued to be generated near to the Whitwick volcanic centre(s).

Beacon Hill Formation

This formation was formally named and subdivided by Moseley and Ford (1985), who designated various type sections in the Beacon Hill and Bradgate Park areas, south of this district. Their scheme is followed here, with some modifications indicated in (Table 2). The formation has a wide outcrop in the eastern part of the Maplewell Group, and is estimated to be about 1800 m thick. The lowest unit is the Benscliffe Breccia Member (Ben) 20 to 100 m thick. This is a volcanic breccia with poorly defined, subrounded pink to grey clasts, ranging from pea-size up to lapilli 40 mm across, enclosed in a greenish grey, medium to coarse-grained crystal-rich matrix. The clasts are predominantly of andesitic to dacitic composition (57 to 69% SiO2; unpublished BGS analyses); in thin section (E67728) they show both flow-banded and spherulitic textures. It should be noted that the Benscliffe Breccia is a widely developed unit which can be traced around the Charnian anticline and into the western outcrop, where it forms the base of, and possibly merges into, the Charnwood Lodge Volcanic Formation (see below).

The overlying Beacon Tuff Member (BcT) is about 875 m thick. It consists of hard (‘flinty’), blue-grey, parallel-laminated and graded tuffaceous mudstones and siltstones. The deposits of a pyroclastic event more significant than that which produced the Benscliffe Breccia are represented by outcrops of massive dacitic lithic-crystal tuff (ZD), estimated to be 180 m thick, within the bedded sequence near Nanpantan Hall, e.g. [SK 5031 1638]. The matrix of this tuff is crammed with lapilli-size andesitic and dacitic clasts, some with relict fluidal and spherulitic textures.

At the top of the formation are predominantly volcaniclastic units commencing with the Sandhills Lodge Member (ShL), exposed south of Home Farm [SK 5037 1617]. It consists of about 20 m of pale grey, massive, coarse grained, crystal-rich volcaniclastic sandstone with folded fine-grained sedimentary rafts. In thin section (E67502) vitric (y-shaped) shards are found both in the matrix and in lapilli of dacitic tuff. The overlying Buck Hills Member (BHM) is a fining-upwards sequence, consisting of alternations between blue-grey, parallel-laminated, graded volcaniclastic mudstones, siltstones and sandstones. Beds of massive to graded sandstone (saV) are common near the base, and from these beds a thin section (E67725) shows vitric tuff laminae packed with y-shaped glass shards. The succeeding Outwoods Breccia Member (OtB) comprises about 120 m of grey, medium to coarse-grained, massive to parallel-stratified volcaniclastic sandstone in beds 0.5 to 3 m thick, alternating with breccia. The latter beds are up to 7 m thick in the Out Woods; their matrix is coarse grained, crystal rich and lithic rich, with granule to small pebble size clasts of spherulitic dacite and welded tuff (E67681). Angular blocks and larger rafts of volcaniclastic mudstone and siltstone constitute the larger fragments, which characterise the breccia beds. Their outlines reveal that they have been affected by plastic deformation; processes involving brecciation, soft-sediment folding and stretching of pre-existing bedding are all suggested by the various clast shapes (Moseley and Ford, 1989).

Bradgate Formation (BT)

The Bradgate Formation is the youngest unit of definite Precambrian age in the Charnian sequence. It was formally named by Moseley and Ford (1985) and given a type section in the Bradgate Park–Warren Hill–Hallgate Hill area, south of the district. The formation is probably not much more than 180 m thick in this district.

In the eastern part of the Out Woods [SK 5149 1656] it comprises alternations between pale and dark grey parallel-laminated vitric tuff, tuffaceous siltstone and massive to parallel-bedded sandstone. In thin section (E67756) the tuffs show silty layers containing subhedral to angular plagioclase crystals interspersed with sliver shaped shards of recrystallized glass. In the north-west of the Charnian outcrop, beds tentatively correlated with the formation were exposed in a sewer outfall excavation in Thringstone [SK 4335 1659]; they consist of grey, coarse grained, crystal-rich volcaniclastic sandstone with granule to small-pebble size clasts of volcanic rock and maroon siltstone.

Key localities:

Charnwood Lodge Volcanic Formation (CLV)

This unit is equivalent to the ‘Charnwood Lodge Member’, which Moseley and Ford (1985) included within the Beacon Hill Formation. The same rocks were called ‘Charnwood Lodge Agglomerate’ by Worssam and Old (1988). Formational status is preferable for this unit because it is capable of further subdivision into the members shown in (Table 2). The lowest division, the Kite Hill Tuff Member of Carney (1994), is not shown on Sheet 141 Loughborough, but is included within the undivided beds of the formation. The Charnwood Lodge Volcanic Formation is re-defined as the succession of massive to thickly stratified coarse-grained tuffs, lapilli tuffs and volcanic breccias, between 950 and 1280 m thick, which lies between the Blackbrook Reservoir and Bradgate Formations. In accordance with the scheme of Moseley and Ford (1985), the formation is considered to be contemporary with, and therefore laterally equivalent to, the Beacon Tuff Member, which comprises the lower part of the Beacon Hill Formation on the north-eastern side of the Charnian anticline.

Moseley and Ford (1985) designated the type section for this unit as the area in the Charnwood Lodge Nature Reserve between Flat Hill [SK 4650 1606] and Warren Hills [SK 4605 1481], on the southern margin of the Loughborough district. Here, however, exposures are too sporadic to be considered representative of the unit as a whole, and it may therefore be preferable to regard this as a type area.

Undivided beds of the formation comprise massive to thickly bedded andesitic volcanic breccia (comparable with the ‘bomb rocks’ of Watts, 1947) intercalated with parallel-bedded lithic-lapilli or lithic-crystal tuff, as seen at Gunhill Rough and at Strawberry Hill Plantation [SK 4558 1710]. These lowermost beds of the formation are lateral equivalents of the Benscliffe Breccia Member. That unit was mapped at the base of the Charnwood Lodge Formation farther south and east (Worssam and Old, 1988), but it is not differentiated here since it is considered to have merged with the main coarse-grained component of the Charnwood Lodge Formation. The St. Bernard Tuff Member (SBT), about 100 m thick, occupies a synclinal structure, but its true stratigraphical position is not known; it may pass south-eastwards into the unexposed lower lying ground of the Charnwood Lodge Nature Reserve, south of Collier Hill (Figure 3). In the Mount St. Bernard type area [SK 3575 1626] (Carney, 1994), the member consists of a lower unit, about 60 m thick, of massive lithic-crystal tuff, with abundant andesitic lapilli, passing up to volcanic breccia, and overlain by a 2.7 m-thick lapilli tuff bed. The last unit shows in thin section (E675170) common y-shaped glass shards in the matrix. The uppermost beds, immediately west of the Abbey building, are probably less than a metre thick and consist of repetitively graded, medium to fine-grained crystal tuffs.

There are two further members showing close spatial and compositional affinities with rocks of the Whitwick Volcanic Complex. The Swannymote Breccia Member (SB), some 120 m thick, forms isolated outcrops in close association with Sharpley Porphyritic Dacite of the Whitwick Volcanic Complex. At Swannymote Rock, it comprises pale grey, coarse-grained dacitic tuff grading to monomictic volcanic breccias. The latter’s clasts are most commonly represented by subangular to rounded blocks of porphyritic (plagioclase and green quartz) dacite identical to the Sharpley Porphyritic Dacite (see below). Close by to the west, irregular-shaped masses of grey volcaniclastic siltstone are intermixed with the breccia matrix, the latter containing clasts with spherulitic textures seen in thin section (E67527). At Ratchet Hill there is a sharp contact between Sharpley Dacite and Swannymote Breccia [SK 4474 1634]. Nearby, the breccia contains rafts of grey siltstone with internal laminae sharply truncated by the host breccia. The Cademan Volcanic Breccia (CVB), up to about 450 m thick, is most typically developed around Calvary Rock. It has a coarse-grained, green-grey crystal-lithic matrix, which encloses abundant lapilli and angular to subangular blocks of a uniform, fine-grained, high-silica andesite lithology that is identical both chemically and petrographically to massive rocks of the Grimley Andesite (see below). The blocks average about 0.3 m across with some ‘outsize’ blocks in excess of 2 m; in places they are closely packed (Plate 2), suggestive of a ‘jig-saw’ type of breccia, as at Grace Dieu Wood [SK 4353 1746].

Key localities:

Whitwick Volcanic Complex

This is an assemblage of lithologies named by Moseley and Ford (1985) and re-defined by Carney (2000b) to include only those massive to autobrecciated components which occupy no particular stratigraphical position and may be bounded either by intrusive or faulted contacts. Unfortunately, exposures of contacts are exceedingly rare; those in Whitwick Quarry are invariably faulted, and are the site of ductile shear zones (Carney, 1994, fig. 10). The three components of the Whitwick Complex are all named after the varieties of ‘porphyroid’ described by previous workers (for example, Watts, 1947), and are: Peldar Dacite Breccia, Sharpley Porphyritic Dacite and Grimley Andesite.

These three units are interpreted to be either subvolcanic intrusions or subvolcanic to extrusive domes emplaced into the Charnian volcanic centres. Disintegration of these domes would have caused pyroclastic flows and lahars characterised by the incorporation of ‘Grimley’ type blocks in Cademan Breccia and ‘Sharpley’ blocks in Swannymote Breccia (Carney, 2000b). Intense but localised autobrecciation seen in the Grimley Andesite may be attributed to an early stage of the disintegration process, but the Sharpley Dacite is not brecciated, and may be interpreted as a relatively late-stage subvolcanic intrusion that rose into a previously brecciated carapace. The Peldar Dacite Breccia, with no obvious representatives in the Charnwood Lodge Formation, may represent a subvolcanic dome (cryptodome) that failed to reach the surface. Its spherulitic textures, denoting chilling of the magma to a glass or near-glass, the extreme granulation of its matrix, and complex mixing of the latter with unconsolidated sediment are features suggesting interaction between dacitic magma and wet sediments. Quench-brecciation of the dacite resulted from this process, producing a type of hyaloclastite lithology (Carney, 2000b).

Peldar Dacite Breccia (PDB)

This unit, estimated to be about 520 m thick, has its type section in Whitwick Quarry (Carney, 1994; fig. 10) which lies mainly in the Coalville district to the south (Sheet 155). It is a heterogeneous lithology (Plate 3) with three principal components:

  1. numerous rounded to elliptical or cuspate enclaves, from millimetre to decimetre-size, of black, fine-grained, porphyritic (plagioclase and green quartz) dacite
  2. small (10 to 500 mm) rounded inclusions of pale green medium-grained quartz microdiorite
  3. a grey, medium-grained crystal-rich matrix which encloses abundant slivers of dark grey dacite (Plate 3). In thin section (E67547C), the dacite slivers have a pervasive, globulose texture caused by abundant quartzofeldspathic micro-spheruliths

In the central part of the quarry, a 150 m-long raft of maroon volcaniclastic siltstone and mudstone is enclosed within the breccia; at its margins coarse-grained lenticles of breccia matrix are admixed with the siltstone, and wisps of maroon siltstone occur within the adjacent breccia matrix.

Sharpley Porphyritic Dacite (SyP)

The Sharpley Porphyritic Dacite was named by Carney (1994) and equates to the ‘Sharpley-type’ porphyroid of Watts (1947). It is a massive, texturally homogeneous rock with a dacitic composition confirmed by chemical analyses indicating between 70% and 72% SiO2 (unpublished BGS data). The unit, which is restricted to the Whitwick Complex, forms numerous scattered outcrops and cannot be traced with much confidence beneath the younger cover. In (Figure 3) it is interpreted as a bifurcating, sheet like body, in part fault-controlled. The dacite is up to 600 m thick in places and its type locality is on High Sharpley [SK 4485 1707].

Sharpley Dacite has a similar phenocryst suite to the Peldar Dacite Breccia (i.e. large white plagioclase and green quartz), but these occur within a medium to pale grey or lavender matrix. It is identical in lithology, petrography and geochemistry to the blocks in the Swannymote Breccia Member. Although it is commonly massive, on High Sharpley [SK 4485 1707] it exhibits prominent planar surfaces whose dip, towards the south-west, is apparently parallel to the regional Charnian dip. On these surfaces there is developed a system of rectangular to polygonal shaped joints, spaced at between 0.5 and 1 m, which in sections perpendicular to the ‘dip’ divide the rock into attenuated lozenges. This structure is not produced by the Charnian cleavage, which here trends west-north-west, and is instead reminiscent of a relict columnar-jointing system. A ‘pseudo-brecciate’ structure, produced by systems of curved joints, is visible at a further exposure to the south of High Sharpley [SK 4474 1682].

Grimley Andesite (GyA)

This name of this unit (Carney, 1994) is derived from the ‘Grimley-type’ porphyroid mentioned by Watts (1947). Farther south apparent equivalents have been called the ‘Bardon Good Rock’ and ‘Bardon Breccia’ (Jones, 1926). Its main outcrop extends (Figure 3) from the railway cutting west of Grace Dieu Wood [SK 4313 1753] south-eastwards to the exposure near High Tor Farm [SK 4594 1542], just outside the southern margin of the district. The type area is designated as the ground between Whitwick Quarry [SK 4468 1619] and the crags around Cademan Street in Whitwick [SK 4370 1637]. A thickness of 940 m hereabouts must remain a rough estimate due to the paucity of exposures.

Grimley Andesite forms extensive masses but has also been found as more restricted occurrences, for example within the Cademan Volcanic Breccia outcrop at High Cademan [SK 4424 1689]. It is mostly a green to greyish green, moderately plagioclase-phyric high-silica andesite or dacite, with silica contents between 57 and 63% (unpublished BGS analyses). Locally it shows intense autobrecciation, as in the outcrops at Cademan Street, Whitwick, and at Hob’s Hole [SK 4360 1740]. In Whitwick Quarry [SK 4468 1619] fresh faces show incipient breccia development in the form of anastomosing stringers of dark grey medium-grained andesite which divide the lithology into metres-scale diamondshaped slivers. In the last location, a small intrusion of Grimley Andesite shows a chilled margin against Peldar Dacite Breccia, this being the only evidence for relative age of emplacement within the Whitwick Complex.

Key localities

Brand Group

The Brand Group was formerly thought to be entirely of Precambrian age, but recent work has shown that this is probably only true for its lower part (the Hanging Rocks Conglomerate); (Figure 3), which does not crop out in this district. To the south, beds of the overlying Swithland Formation contain the trace fossil Teichichnus which is considered to be no older than Lower Cambrian (Bland and Goldring, 1995; McIlroy et al., 1998). Within the Brand Group, therefore, a major unconformity must occur in strata below the Swithland Formation. The latter unit has a small outcrop in this district and is described below (see Chapter 3).

Precambrian intrusions

In this district there are two types of Precambrian intrusions: the North Charnwood Diorites and the Lubcloud Microgranite (although it is also possible that the latter may be from a separate, Ordovician phase of intrusion). The South Charnwood Diorites include the occurrences of granophyric diorite (markfieldite); they crop out in the Coalville district, farther south, and are described by Worssam and Old (1988).

The North Charnwood Diorites (HD) suite (Worssam and Old, 1988) is represented by near-vertical to inclined diorite sheets, up to 60 m wide. They show north-westerly and easterly orientations (Figure 3), and in the Longcliffe and Newhurst quarries [SK 492 170]; [SK 484 179] they intersect Charnian bedding at a high angle (Carney, 1994, figs. 4, 5). Typical lithologies are grey with a coarsely mottled texture. In thin section (E67485) this mottling consists of white, subhedral plagioclase crystals, 2 to 5 mm across, enclosed within a grey, granular quartzo-feldspathic mesostasis containing several percent of granophyric intergrowths. The intrusive contacts show chilling to a fine-grained diorite. Adjacent to such contacts, the Charnian country rocks become pale grey and develop green-grey thermal spots. The ellipsoidal shapes of these spots, as seen at the southern end of Longcliffe Quarry [SK 4940 1678], is due to the penetrative cleavage deformation that postdated diorite emplacement (Boulter and Yates, 1987 see also, Chapter 9).

A second intrusive type, the Lubcloud Microgranite (FG), is exposed south of Ives Head summit where it occurs as a 9 m-wide north-west-trending dyke. It consists of common white plagioclase phenocrysts set in a red, saccharoidal quartzo-feldspathic matrix.

Key localities

Chapter 3 Cambrian

Cambrian strata represent the deposits of a widespread marine transgression across the eroded Precambrian landmass (Taylor and Rushton, 1971). This chapter includes the Swithland Formation, traditionally regarded as part of the Charnian Supergroup but now believed to be Lower Cambrian in age (see Brand Group in Chapter 2).

Swithland Formation (SG)

The Swithland Formation was named by Moseley and Ford (1985), who designated the type section on ‘The Brand’ estate and in Swithland Wood, Sheet 155 Coalville. It is largely unexposed in the Loughborough district, but is probably at least 200 m thick. The Swithland Formation is still referred to the upper part of the Brand Group, although this may be revised in view of the Early Cambrian age established by the discovery of the trace fossil Teichichnus south of the district (Bland and Goldring, 1995; McIlroy et al., 1998). Farther south in the Coalville district the formation consists largely of slaty mudrocks (Worssam and Old, 1988). In the Loughborough district, the formation is exposed only in a small quarry east of Nanpantan [SK 5103 1739], where it consists of purple or maroon siltstones and poorly sorted coarse-grained, lithic-rich and crystal-rich sandstones. These beds probably occupy a stratigraphical position near the base of the formation. They contain detritus from the underlying Charnian Supergroup that was eroded and deposited rapidly, probably from sediment-gravity flows.

Stockingford Shale Group (SSh)

The Stockingford Shale Group was named by Taylor and Rushton (1971) and has its type area between Mancetter and Nuneaton in Warwickshire (Bridge et al., 1998; Worssam and Old, 1988). The unit does not crop out in this district, but was proved over 39 m at the base of the Ticknall Borehole (Figure 7). The principal lithologies are black, dark grey and pale grey, pyritous, laminated mudstones and silty mudstones. Green and red colours prevail for 11 m below the unconformity with the Calke Abbey Sandstone Formation; this is attributed to pre-Dinantian weathering of the Stockingford Group. The beds dip steeply, about 50 to 70°, giving a true thickness of about 25 m, and the sequence displays a pervasive, near vertical, penetrative cleavage attributed to Acadian (Silurian-Devonian) compression (see Chapter 9).

The Middle or early Late Cambrian age of these beds is based on a fragmentary fauna which includes the trilobite Agnostus pisiformis (Rushton, 1995) and sparse acritarchs (Molyneux, 1995). Together with obvious lithological similarities, this age proves the unit’s correlation with the Stockingford Shale Group whose type area occurs around Nuneaton (Taylor and Rushton, 1971; Bridge et al., 1998). A further proving of the Stockingford Shale Group, beneath Dinantian strata, was made in the BGS Rotherwood Borehole [SK 3458 1559], located 8 km south-south-west of the Ticknall Borehole (Worssam and Old, 1988).

Chapter 4 Carboniferous

After the Acadian deformation and uplift, no geological record of the next 60 million years has survived in the stratigraphy of the district. It is likely that this was a period of erosion, moulding a landscape that was flooded by a marine transgression in latest Devonian or early Carboniferous (Tournaisian) times (about 355 Ma). The initial deposits of this transgression probably accumulated in restricted basins which had subsided differentially (syn-rift) as a result of faulting and flexuring. By Westphalian times regional-scale subsidence due to post-rift thermal sag allowed large areas of the Midlands to be submerged and covered by sediments. The early Carboniferous topography was probably developed mainly upon Cambrian and Ordovician rocks, and in the south the basement rocks of the Charnwood Massif formed a ‘palaeo-high’, part of the northern margin of the Wales–London–Brabant Massif (Corfield et al., 1996).

Dinantian (‘Carboniferous limestone’)

Dinantian strata were deposited within a tilted block and graben topography formed at a time of widespread crustal extension across the English Midlands (e.g. Miller and Grayson, 1982), and are considered to form part of a ‘synrift megasequence’ (Fraser and Gawthorpe, 1990). In this district, many of the lithological and thickness variations within the Dinantian succession can be related to particular structural domains. These comprise (Figure 6)." data-name="images/P946471.jpg">(Figure 5a) the Widmerpool Half-graben, the Hathern Shelf (Ebdon et al., 1990), on the south-western (footwall) side of the Normanton Hills Fault, and the Platform (incorporating the Charnwood Massif), consisting of an uplifted and relatively un-faulted region to the south and west of the faults bounding the Hathern Shelf. The lateral relationships between the various Dinantian formations traced across these structural domains are summarised in (Figure 5b). Correlations of strata between the limited number of available boreholes are shown in (Figure 6). The nomenclature of the exposed strata in the Breedon–Ticknall area is summarised in (Table 3).

These strata were traditionally included within the ‘Carboniferous Limestone’, which may be considered to be an informal lithostratigraphical unit of supergroup ranking representing strata deposited through the Dinantian period. However, Carboniferous Limestone is not a formal unit, and this terminology is not recommended for current use (Aitkenhead and Chisholm, 1982).

Hathern Shelf Sequences

The only outcrops of Dinantian strata in the district belong to the Hathern Shelf structural province, and are confined to a narrow zone, extending between Ticknall and Grace Dieu. These strata were uplifted and locally steeply tilted by the combined movements on the Breedon and Thringstone faults (Figure 1). Elsewhere their sub-Triassic distribution is inferred from seismic interpretation, constrained by several deep boreholes. Parsons (1918), Mitchell and Stubblefield (1941) and Monteleone (1973) described the outcropping sequences. As a result of this resurvey the nomenclature, age and correlation of the units has been further refined (Ambrose and Carney, 1997 a, b), (Table 3), and has been extended to the concealed parts of the shelf sequence. A significant finding of this resurvey is that the entire Early Chadian carbonate sequence exposed around Breedon is absent from the Ticknall Borehole, indicating either that it has thinned out westwards, or was removed by uplift and erosion prior to deposition of the Holkerian to Brigantian strata (Figure 5b).

Hathern Anhydrite Formation (HaA)

This is the oldest recorded Dinantian unit in the district and has been proved only in the Hathern No.1 Hydrocarbon Borehole (Figure 6) where 97 m were recorded above terminal depth. The overlying limestones are of early Chadian age (George et al., 1976). The anhydrite is interpreted as a basal facies, at least locally, on the Hathern Shelf and was equated by Ebdon et al. (1990) with their EC1 tectono-stratigraphical sequence. Palynological evidence (Llewellyn et al., 1969) indicates that the Hathern Anhydrite is of Courceyan age, equivalent to the CM Zone of Clayton et al. (1977). The unit comprises bedded to nodular anhydrite alternating with limestone, dolostone and mudstone. This association is interpreted as cyclically layered sabkha deposits by Llewellyn and Stabbins (1970). It probably indicates a restricted marine influence as parts of the region began to subside (Ebdon et al., 1990).

Milldale Limestone Formation (Mi)

This unit is correlated with strata exposed in north Derbyshire and named by Parkinson (1949). In this district it is exposed in Breedon Hill and Cloud Hill quarries (Ambrose and Carney, 1997b, figs. 2, 3), where the minimum thicknesses are estimated to be 380 m and 130 m respectively. A single subdivison, the Holly Bush Member named by Ambrose and Carney (1997b), is recognised only at Cloud Hill Quarry. The Milldale Limestone comprises grey to buff, thin to thickly bedded, fine to coarse-crystalline dolostones, with pebbles and sand grains common in the Holly Bush Member.

Secondary dolomitisation has obscured many of the original sedimentary structures, and hence the origin of the Milldale Limestone Formation. At Cloud Hill Quarry, however, the overall character of the succession suggests deposition on a carbonate shelf, largely in high-energy, storm dominated environments which are suggested by brachiopod coquinas and the possible presence of hummocky cross-stratification. A proximal shallow water shelf setting is further indicated by the clastic component (Holly Bush Member), and the commonly high bioclastic content of these beds. By contrast, Milldale Limestone at Breedon Hill Quarry contains a mud-mound (Waulsortian) reef and thus represents a more distal, carbonate ramp setting, with water depths of 220 to 280 m suggested for the comparable mud-mound reefs of north Derbyshire (Bridges and Chapman, 1988).

At Cloud Hill Quarry, the bedded part of the Milldale Limestone shows undulating bounding surfaces throughout (Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6) (GS 1006)." data-name="images/P946491.jpg">(Plate 4), with many partings of green and grey, commonly bituminous clay, shaly mudstone and siltstone. In part, this bedding may represent hummocky cross-stratification that was emphasised by non-sutured stylolites developed during dolomitisation. One package of beds which are not dolomitised shows that the formation comprises beds of fine to coarse-grained, bioclastic, locally ooidal, pelloidal grainstone. This facies is similar to that developed within undolomitised Milldale Limestone in its type area of Milldale in Derbyshire. The dolomitised beds contain chert nodules which have yielded foraminifera suitable for dating: the assemblages (Cf4a1 subzone) are indicative of an Early Chadian age (information from N J Riley, 1999). In keeping with this age are coquinas containing the brachiopod Levitusia humerosus, for which Cloud Hill is the type locality. Other fossils include brachiopods, crinoids, gastropods, corals and echinoids.

In the upper part of the formation in Cloud Hill Quarry, the Holly Bush Member is 61 m thick although it is impersistent, dying out northwards over about 200 m in the quarry. The member is composed of bedded dolostones with a high quartz or lithic sand content, and with sporadic pebbles. One pebble is a tuff which resembles in thin section (E71013) certain of the Charnian Precambrian lithologies; other pebbles are micrites with fenestral structures indicating sources from lithified Dinantian peritidal deposits as well as basement.

In Breedon Hill Quarry, the Milldale Limestone is represented by similar but less fossiliferous strata, overlain to the west of a major fault by about 100 m of finely crystalline, unbedded, fossiliferous dolostone of mud-mound (Waulsortian) reef facies (mmr). Massive dolostone represents the core of the mound and an overlying bedded sequence, just below the observed top of the formation, probably represents accumulations of debris on the flanks of the mound. Volume changes due to secondary dolomitisation are probably responsible for the abundance of vuggy cavities in these carbonates. Despite this, relict structures such as sheet spars, typical of Waulsortian fabrics, can still be discerned. The Early Chadian reefs of south Derbyshire/north Staffordshire are undolomitised examples of the mound at Breedon Hill. About 90 per cent of their volume is composed of micrite, with the remainder comprising skeletal carbonates containing fenestrate bryzoa, sponge spicules and common crinoids (e.g. Bridges and Chapman, 1988; Bridges et al., 1995). The Breedon Hill mud mound contains a diverse fauna of this type with additionally, nautiloids and ammonoids, including Fascipericyclus fasiculatus, of Early Chadian age.

In the Hathern Hydrocarbon Well No. 1, 149.6 m of thickly bedded grey, brown and black, fine-grained limestones with thin shaly beds overlie the Hathern Anhydrite. They are probably of Chadian, C1/C2 age (George et al., 1976; Ebdon et al., 1990), and are equated here with a local development of the Milldale Limestone. The overlying 110 m of grey to black, laminated calcareous mudstones are undated (George et al., 1976), but if they are equivalent to the Widmerpool Formation (see below), a substantial unconformity must be present at the top of the Milldale Limestone here (Figure 6).

Key localities

Calke Abbey Sandstone Formation (CAS)

This formation is a new unit, named by Ambrose and Carney (1997a) and proved only in the Ticknall Borehole where it is 70.6 m thick. Its base, at 171.9 m depth, is a major unconformity with the Cambrian Stockingford Shale Group, and it is overlain abruptly at 101.3 m by pale green, fine-grained sandstones of the Arch Farm Sandstone Formation (Ambrose and Carney, 1997a). The Calke Abbey Sandstone is barren of fossils and its age is consequently unknown.

The larger part of the formation (Figure 7) consists of medium to thick-bedded, brown to green-grey, medium to coarse-grained pebbly sandstones and conglomerates (Plate 5a); they show parallel stratification or low-angle cross-bedding. Finer-grained components consist of laminated to thinly bedded sequences of green or red mudstones and siltstones which include thin, sharp-based and commonly graded layers of sandstone; the principal sandstone beds are feldspathic and classified as litharenites or sublitharenites (Strong, 1996). There are numerous reddened layers, consisting of poorly sorted, generally structureless, mudstones, siltstones and argillaceous sandstones. They commonly show vermicular red to grey rootlet mottles and also contain rare examples of silt-filled near-vertical fissures (Plate 5b): such lithologies resemble alluvial palaeosols described by Bown and Kraus (1987). In the basal conglomerate that is about 13 m thick, the chemistry of volcanic pebbles (unpublished BGS analyses) indicates a contribution of material from a Charnian-type Precambrian source, which presumably is Charnwood Forest situated 9 km to the south-east. The overlying sandstones nevertheless contain abundant K-feldspars (Strong, 1996), commonly visible as prominent pink grains in hand specimens, which are not typical of the Charnian and indicate an additional contribution from a granitoid basement.

The main clastic part of the Calke Abbey Sandstone has not yielded any dateable fossil remains, although it must be older than Asbian (NM biozone), which is the age of the base of the Cloud Hill Dolostone proved higher in the Ticknall Borehole. The formation could be a local equivalent of the Caldon Low Conglomerate, of Asbian age, in the Ashbourne district (Chisholm et al., 1988 p. 28). On the other hand, the arenaceous beds are also lithologically similar to the Redhouse Sandstones, of the same district, which are considerably older, being at least Courceyan in age (Chisholm et al., 1988). A further possibility is that the sandstones may be lateral and thus more proximal equivalents of the pebbly beds represented by the Holly Bush Member of the Early Chadian Milldale Limestone (see above) exposed in Cloud Hill Quarry to the south-east. The latter two possibilities suggest that within the Ticknall Borehole, there could be a major unconformity developed on Early Chadian, Courceyan or even late Devonian strata represented by the main part of the Calke Abbey Sandstone sequence.

The depositional environment of the Calke Abbey Sandstone was probably that of a distal alluvial fan with episodic influxes of gravelly debris flows and sheetflood sands, interspersed with quiescent periods during which the alluvial deposits were pedogenically modified. At times of extended overbank sedimentation, or when bodies of standing water may have existed, the thicker mudstone and siltstone sequences accumulated; the graded sandstone interbeds are interpreted as the subaqueous continuations of sheetfloods. A change to nearshore marine environments is indicated by the incoming of Lingula debris in the overlying Arch Farm Sandstone Formation.

Arch Farm Sandstone Formation (ARFS)

Ambrose and Carney (1997a) named this 9 m-thick unit for the strata between 92.3 and 101.3 m depth in the Ticknall Borehole; it has not been seen at outcrop. The formation consists mainly of sandstone, in beds up to 1.7 m thick, which are commonly green to grey, fine to medium-grained and laminated or cross-laminated. They contain pebble-rich lenticles, and shelly lags containing fragments of Lingula. Partings up to several centimetres thick consist of green mudstone and siltstone, some with Lingula, and these lithologies also occur as rip-up clasts in the basal parts of sandstone beds. The upper 4 m of the formation is particularly coarse grained and conglomeratic, containing calcareous sandstones which commonly show significant pedogenic fabrics. For example, in the highest bed, 0.9 m thick, there are abundant anastomosing stringers and veinlets of white calcareous material and the bed is capped by green mudstone with numerous listric surfaces and sporadic small ferruginous concretions.

The base of the Arch Farm Sandstone is interpreted as a major marine flooding surface, which also corresponds to a prominent indentation on the gamma-ray log (Figure 7). The overlying laminated sandstones containing Lingula were deposited in moderate to high energy, nearshore or shoreface settings. The upper part of the formation contains conglomerates and coarse-grained sandstones and appears devoid of Lingula, perhaps indicative of a return to fluvial conditions. Episodes of emergence and soil formation are indicated here, by pedogenic fabrics developed in strata comprising the upper 2 m of the formation.

Cloud Hill Dolostone Formation (CHD)

The name of this unit (Ambrose and Carney, 1997b) is modified from the ‘Cloud Hill Dolomite’ of Monteleone (1973). The strata rest unconformably on Milldale Limestone at Cloud Hill and Breedon Hill, and are also present in the Barrow Hill inlier. They have been proved above the Arch Farm Sandstone in the Ticknall Borehole, between 55.4 and 92.3 m (Figure 7). Subdivisions of the formation include the Cloud Wood Member, in Cloud Hill Quarry (Ambrose and Carney, 1997b), and the Scot’s Brook Member in the Ticknall Borehole (Ambrose and Carney, 1997a).

The type section for the formation is at Cloud Hill Quarry [SK 413 215], where a minimum thickness of 125 m is exposed. Here, the base of the Cloud Hill Dolostone rests on Early Chadian strata and is both an angular unconformity and a possible intraformational slide surface, named the Main Breedon Discontinuity (Ambrose and Carney, 1997b, fig. 3). In the north of the quarry, the Cloud Wood Member forms the basal division of the formation; mudstone samples taken from this member just above the basal unconformity have yielded a Late Holkerian to Early Asbian palynological age (Turner, 1996). The basal unconformity therefore represents a substantial time gap; no strata of late Chadian and Arundian age, and possibly none of Holkerian age, are present. The top of the formation, intersected in the Ticknall Borehole, is a karstified surface overlain by strata of the Ticknall Limestone Formation.

The Cloud Wood Member is about 36 m thick in the north of Cloud Hill Quarry, where it occupies the base of the Cloud Hill Dolostone. It comprises a lower sequence, up to 9 m thick, of mudstones and dolomitic siltstones with thin dolostones. These beds are grey, greenish grey, purplish brown and red-brown in colour, commonly well laminated and locally shell-rich. The upper 20 to 30 m consist of dolostones that are grey to greenish grey and red-stained, thin to thickly bedded, and fine to coarsely crystalline. Red or grey, clay or shaly mudstone/siltstone partings commonly separate these beds.

The Scot’s Brook Member was named by Ambrose and Carney (1997a) and is the basal unit of the Cloud Hill Dolostone in the Ticknall Borehole, between 88.85 and 92.3 m. This unit consists of carbonate-veined, pedogenically modified argillaceous sandstones intercalated with grey, argillaceous and calcretic palaeosols. Near the base there is a 0.7 m-thick bed of white, micritic limestone containing ostracods; it is capped by green mudstone with rounded, elliptical carbonate nodules. At the top, green calcareous mudstone of the member is succeeded sharply by nodular, micritic limestone of the Cloud Hill Dolostone.

A mud-mound reef facies (mmr) of dolostone lies above the Cloud Wood Member in the north of Cloud Hill Quarry, and is also seen at Barrow Hill. This is a buff to grey, massive, generally finely crystalline, fossiliferous dolostone which contains brachiopods, crinoids, corals, gastropods, nautiloids and ammonoids. Ammonoids include Goniatites, which indicates a Late Asbian to Brigantian age for these beds. Similar Asbian reefs on the northern flanks of the Widmerpool Gulf are composed of microbialite, with sponges, bryzoan and corals as secondary constituents (Mundy, 1994); however, at Cloud Hill coral debris is not commonly preserved. The lower contact of the reef on the Cloud Wood Member is sharp and apparently conformable, whereas southwards it is faulted against undivided beds of Cloud Hill Dolostone (Ambrose and Carney, 1997b, fig. 3). Shear deformation within the mudstones, and locally intense folding and thrust imbrication of the whole of the Cloud Wood Member, become progressively more pronounced northwards in the quarry, culminating in a sequence with tectonically incorporated slivers of mud-mound reef (Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6). This deformation is discussed further in Chapter 9.

In the south of Cloud Hill Quarry, undivided Cloud Hill Dolostone consists of dolostones that are variably grey, pale buff and reddish grey, fine to coarsely crystalline and thin to very thickly bedded, with non-sutured stylolites and partings of clay and shaly mudstone (Plate 7). Crinoid debris is common to abundant and brachiopods and corals are locally present. Stratigraphically higher beds are characterised by a high moldic porosity.

The north-western face of Breedon Hill Quarry exposes a few metres of Cloud Hill Dolostone which unconformably overlies Milldale Limestone. A reddened bedding plane crowded with the trace fossil Thallasinoides (Plate 8) marks the unconformity surface. A specimen of the colonial coral Lithostrotion found nearby, assumed to have fallen from an inaccessible part of the Cloud Hill Dolostone, indicates a Viséan, post-Arundian age for the supra-unconformity strata.

In the Ticknall Borehole, Cloud Hill Dolostone occurs between 54.65 and 92.3 m (Figure 7). It is dated as Early Asbian age, on account of the presence of the foraminifera Pojarkovella nibelis together with Dainella holkeriana and Asbian miospores about 5 m above the base (Riley, 1997a). At the junction with the overlying Brigantian dolostones of the Ticknall Limestone Formation, the latter’s base consists of about 1 to 2 m of heterogeneous friable siltstones and sandstones bearing carbonate clasts. These lithologies resemble deposits laid down on a karstified top surface, suggesting that the Cloud Hill Dolostone is unconformable with the overlying Ticknall Limestone Formation.

The environment of deposition of the Cloud Hill Dolostone was that of a carbonate shelf, with deeper water occurring to the east (Breedon area) suggesting that the shelf floor may have sloped in that direction. In the southern part of Cloud Hill Quarry, the undivided beds of the Cloud Hill Dolostone (like the underlying Milldale Limestone Formation) were probably deposited during storm events on the shelf. Farther north in the quarry, deeper water environments are indicated for the Cloud Wood Member by the higher mudstone content, particularly above the basal unconformity which may, in part, represent a flooding surface. Up-sequence the incoming of the platform-rim mud-mound reef facies suggests that by Late Asbian times shallower water conditions prevailed, since the analogous Asbian-age cracoean buildups described by Mundy (1994) were probably developed in water depths not exceeding 170 m. This facies cannot be directly related to the sequences in the south of the quarry because the magnitude of the intervening faulting (Ambrose and Carney, 1997b; fig. 3) is not known. The strata seen in the Ticknall Borehole were deposited mainly in shallow-water, high-energy environments with periodic shoaling and emergence leading to the development of sabkha-peritidal carbonates (lime mudstones); peritidal conditions are further indicated by the ‘birds-eye’ textures found at some levels. Emergent conditions at the base of the formation are indicated by the grey, calcretic palaeosols in the Scot’s Brook Member.

Key localities

Ticknall Limestone Formation (TL)

This unit, named by Monteleone (1973), crops out in the inliers around Ticknall, Calke Abbey, Staunton Harold and Worthington. It forms the topmost beds exposed at Cloud Hill Quarry (Ambrose and Carney, 1997b), and comprises the poorly exposed sequences of the Grace Dieu and Osgathorpe inliers. It has also been proved in the Ticknall and Worthington boreholes (Ambrose and Carney, 1997a, b). The type area for the formation is the former limestone quarries near Ticknall [SK 3626 2370] to [SK 3573 2422], with reference sections in the two boreholes. Foraminiferal determinations and macrofossils are consistent with a Brigantian age for the unit (Riley, 1997a). Oil shows occur in the Ticknall Borehole.

The formation consists of bedded limestones, dolostones and thinly interbedded carbonate and dark grey mudstone sequences. The last is well exposed (Plate 9) in former quarries at Ticknall [SK 360 238], together with massive dolostones and sandy dolostones which form the uppermost few metres of the formation. In the Ticknall and Worthington boreholes (Ambrose and Carney, 1997a, b) the formation includes about 10 m of strata comprising nodular carbonate associated with partings and thicker developments of dark grey, commonly shell-rich mudstone. This distinctive facies correlates with similar beds described from the Rotherwood Borehole of the Coalville district (Worssam and Old, 1988). Palaeosols, and karstic surfaces with green clayey drapes are typical of the formation (Figure 7), as are large gigantoproductid brachiopods.

The formation is at least 54.6 m thick in the Ticknall Borehole and estimated to be about 60 m thick in total around Ticknall; it is possibly up to 90 m between Worthington and Cloud Hill Quarry. In the Ticknall Borehole its base consists of a soft, red-brown and green mottled, silty mudstone overlain by red-brown, weakly calcareous sandstone with subrounded carbonate clasts, occurring below the more typical dolostone lithology. These sandy and muddy beds are interpreted as deposits laid down unconformably on a karstic surface developed on underlying Early Asbian strata (Riley, 1997a) of the Cloud Hill Dolostone. The higher beds in the borehole consist of buff to pale grey, fine to medium-grained dolostones and dolomitic limestones, with beds of lime mudstone and a few mudstone partings (Ambrose and Carney, 1997a). Visible bioclastic debris is rare but the presence of numerous bioclastic moulds suggests the unaltered rock contained a high proportion of bioclastic debris. In certain fine-grained limestone beds ‘birds-eye’ textures are preserved.

In the southern part of Cloud Hill Quarry the base of the formation is taken at the base of the lowest palaeosol. Above this is a sequence about 14 m thick consisting of predominantly thickly bedded dolostones.

In the Grace Dieu inlier, dolostones have been assigned a Brigantian age, based on the presence of Gigantoproductus (Kent, 1968), and are therefore correlated with the Ticknall Limestone Formation. Current exposures show only medium to thick-bedded dolostones (Carney, 1994), but earlier sections showed interbedded dolostones and mudstones, similar to those seen at Ticknall (Hull, 1860), with, in addition, calcareous conglomerates containing Charnian clasts (Kent, 1968). Kent suggested that the Grace Dieu strata were shoreline accumulations around the Charnian landmass, and Charnian rocks are indeed exposed only 100 m south of the outcrop. Little information is available for the Osgathorpe inlier and it is assumed to be Ticknall Limestone of similar Brigantian age. Dolostone blocks forming the walls of Osgathorpe Church include poorly sorted carbonate-clast conglomerates and coarse-grained lithologies with granules and pebbles of vein quartz, pink feldspar and pink granite. These building stones were probably worked locally, from former quarries on the Osgathorpe limestone outcrops.

Key localities

Widmerpool Half-Graben Sequences

Basinal Dinantian strata are confined to the Widmerpool Half-graben, which is delimited to the south by the Mackworth and Normanton Hills faults (Figure 6)." data-name="images/P946471.jpg">(Figure 5a). Despite their deep concealment beneath Namurian and/or Triassic cover, the thicknesses and to some extent the lithology of these off-shelf sequences are reasonably well constrained by seismic interpretations (see section on Sheet 141 Loughborough) and by deep hydrocarbon exploration boreholes.

Long Eaton Formation (LE)

This formation is named for the sequence of mudstones and predominantly thin-bedded limestones proved in the Long Eaton No.1 Hydrocarbon Borehole (Brandon, 1996); it has also been identified in the Ratcliffe on Soar Hydrocarbon Borehole (Carney and Cooper, 1997; see (Figure 1) for location). It is the principal syn-rift sequence within the Widmerpool Half-graben, corresponding to seismostratigraphic units EC3 to EC5 of Ebdon et al. (1990). At least 1867 m of these strata were proved to terminal depth in the Long Eaton No.1 Hydrocarbon Borehole. Seismic interpretations further show that the formation thickens progressively south-westwards, above the inclined floor of the half-graben, to attain a maximum of about 4000 m in the hanging wall of the Normanton Hills Fault.

The lithology of borehole chip samples suggests that the formation consists mainly of grey or brown, thinly interbedded calcareous mudstones and siltstones with beds of bioclastic limestone and graded calcisiltite, packstone and grainstone (Brandon, 1996; Carney and Cooper, 1997). Deposition of these strata was probably by sediment gravity flow mechanisms and the beds are interpreted as turbidites. Below 1980 m depth in the Long Eaton No.1 Borehole, evaporitic minerals occur in the form of anhydrite pseudomorphs after gypsum (electron microprobe determinations by T Milodowski, cited in Riley, 1997b). These occurrences may imply periodic exposure to surface evaporation but could also be due to later tectonic activity, which caused ponding of saline groundwaters within the Widmerpool Half-graben.

Microfaunas show an Early Chadian to Asbian age range for the cored strata. However, the apparent absence of Arundian and Late Chadian beds in deeper sections proved by the Long Eaton Borehole (Riley, 1997b) suggests a hiatus which is in a similar stratigraphical position to that represented by the unconformity (Main Breedon Discontinuity) within the shelf sequences exposed at Cloud Hill Quarry. The same break was recognised in the seismic stratigraphy of the Widmerpool Half-graben and attributed to a late Holkerian phase of basin inversion by Fraser and Gawthorpe (1990).

Lockington Limestone Formation (Loc)

This unit is 185 thick in the Long Eaton No.1 Hydrocarbon Borehole, from where it was first named (Brandon, 1996), and 143 m are present in the Ratcliffe on Soar Hydrocarbon Borehole (Carney and Cooper, 1997). It was recognised in part by its distinctively serrated signature on wireline logs (Figure 8). The formation consists mainly of packages 15, to 30 m thick, of brown, argillaceous to sandy turbidite-facies limestone. These are separated by thinner sequences of pyritic, carbonaceous mudstone.

Widmerpool Formation (WdF)

The Widmerpool Formation (Aitkenhead, 1977), of Late Asbian and Brigantian age, has a maximum thickness of 741 m in the Widmerpool Half-graben. It is not confined to that structure, however, since its attenuated equivalents, 110 to 130 m thick, have also been identified at depth on parts of the Hathern Shelf. The unit does not crop out, but boreholes suggest small subcrops beneath the Trent floodplain north-east of Melbourne [SK 395 269]. In the Long Eaton No.1 Borehole, the base of the formation is taken at the upper surface of the Lockington Limestone Formation, which is easily recognisable on wireline logs (Brandon, 1996). This boundary occurs within a broad interval of time spanning about 100 m of strata marking the change from Asbian to Brigantian-age microfaunal assemblages (Riley, 1997b). The top of the unit is taken at the base of the Namurian, Cravenoceras leion biozone; identification of this biozone in the Ratcliffe on Soar Borehole is based on a comparison (Figure 8) with the wireline log of the fully cored Duffield Borehole (Aitkenhead, 1977).

The Ratcliffe on Soar Hydrocarbon Borehole (Figure 8) proved the maximum thickness for the formation in the Widmerpool Half-graben. The limited core and chip samples show that the principal lithologies comprise dark to pale brown, calcareous and locally carbonaceous, pyritic mudstones grading to argillaceous limestone or calcareous sandstone (Carney and Cooper, 1997). Near the top of the formation, the Ratcliffe Volcanic Member (RaV) is about 124 m thick. It comprises five tuff beds intercalated with green or brown mudstones. The member can be correlated, on the basis of its wireline log signatures, with similar tuffaceous beds occupying the P2 Zone in the Duffield Borehole of the Derby district (Aitkenhead, 1977). This in turn suggests an equivalent age to similar units farther north, for example the Tissington Volcanic Member of the Ashbourne district (Chisholm et al., 1988).

On the Hathern Shelf, attenuated equivalents of the Widmerpool Formation have been tentatively identified in some of the deeper boreholes (Figure 6), although the borehole descriptions are generally not detailed enough to confirm the correlation. The absence of the formation from the outcropping shelf sequences around Melbourne, Ticknall and Breedon, and from the Worthington Borehole, suggests that the western parts of the Hathern Shelf remained uplifted at this time, relative to the northern and eastern parts.

About 130 m of mudstones and argillaceous limestones occurring between the Ticknall Limestone Formation and Edale Shale Group in the Ashby No. G1 Borehole are referred to the Widmerpool Formation (Brandon, 1997).

The formation may be represented in the Hathern Hydrocarbon No.1 Borehole, where 110 m of grey to black calcareous mudstones with a fauna of brachiopods, crinoid ossicles and fish remains occur between limestones of Chadian age (that possibly correlate with the Milldale Limestone Formation) and the Namurian Edale Shale Group. The age of these calcareous mudstones is not known (George et al., 1976). Their lithology and stratigraphical position suggests that they may be part of the Widmerpool Formation, but this could imply that the base of that unit is a major unconformity (Figure 6).

Limited information provided by borehole chip samples suggest that the Widmerpool Formation can be interpreted as a deep-water turbidite sequence that accumulated by sediment gravity flow processes. The formation is considerably thicker in these boreholes than the 130 m recorded on the Hathern Shelf, suggesting that subsidence within the Widmerpool Half-graben continued well into Brigantian times. In fact, Ebdon et al. (1990) suggested active subsidence during the early Brigantian (their EC5 seismostratigraphical sequence), accompanied by the inundation of some shelf margins and the uplift of others. Later in the Brigantian, subsidence waned concomitantly with the onset of volcanic activity and increased tectonic instability at the north-eastern margin of the graben; this later period of time equates with the ages of the EC5 and early LC1 seismostratigraphical sequences of Ebdon et al. (1990).

Platform Sequences

The nature of the Dinantian strata deposited within the structural Platform domain (Figure 6)." data-name="images/P946471.jpg">(Figure 5a) is not known. In the Coalville district, to the south, the Rotherwood Borehole [SK 3458 1559] showed that between Cambrian basement and Millstone Grit there occurs 114 m of Brigantian-age dolostones. The sequence includes nodular limestone beds thinly intercalated with dark grey mudstones (Worssam and Old, 1988), which is an association typical of that seen in the Ticknall Limestone Formation of the Ticknall and Worthington boreholes. Carbonates of the Platform domain are therefore inferred to represent lateral extensions of the Ticknall Limestone Formation.

Namurian

Namurian strata record the commencement of the ‘post-rift megasequence’ of Fraser and Gawthorpe (1990). Broadly speaking the Dinantian/Namurian boundary corresponds to a change in regional tectonism, from one of faulting and rift development to a regime dominated by passive thermal subsidence. Interpretations by Fulton and Williams (1988) suggest that factors such as eustatic sea-level change, basinal flexuring and local faulting also played a part in controlling Namurian sedimentation.

In this district, a broad, twofold subdivision of Namurian strata is recognised, similar to that seen farther north in the main Pennine Basin. In the model of Fulton and Williams (1988), the earliest sequences, here correlated with the Edale Shale Group, represent infilling of the remaining tectonic basins by mudstones interbedded with turbidite siltstones and sandstones. The succeeding Millstone Grit Group represents the progradation of shallower water deltas, precursors to the swampy, upper delta-plain environments of the Westphalian Coal Measures.

Edale Shale Group (ESH)

The Edale Shale Group is generally defined as the mudstone and turbidite sequence which commences at the base of the Cravenoceras leion Marine Band and terminates at the base of the first feldspathic sandstone typical of the Millstone Grit Group (Stevenson and Gaunt, 1971). It is not exposed in the district, and its top surface is particularly difficult to place, but its general distribution can be inferred from seismic records and a few deep boreholes. In the Ratcliffe on Soar Borehole (Carney and Cooper, 1997), 166 m of strata lying below the Triassic unconformity were identified as Edale Shale Group on the basis of wireline log correlations with the Duffield Borehole (Figure 8), located within the graben in the Derby district (Aitkenhead, 1977). In the Ratcliffe Borehole, the base of the group is taken at the lower surface of a 70 m-thick package of strata identified as the Pendleian-age (E1a) Cravenoceras leion biozone. All of the other Pendleian zones in the Duffield Borehole, up to and including Cravenoceras malhamense (E1c), are also present in the Ratcliffe Borehole. The lithologies of the core samples suggest a sequence composed of dark grey, calcareous mudstone. Sandstone packages average about 9 m thick, but are not common; their gamma-ray ‘lows’ identify them. They correspond to the graded, turbiditic sandstones proved at the same stratigraphical levels in the Duffield Borehole.

On the Hathern Shelf, the Ashby G1 Borehole (Brandon, 1997) proved, below the Trias, 130 m of calcareous mudstones containing Eumorphoceras bisulcatum (=E. ferrimontanum), that is indicative of an Arnsbergian age, younger than the highest Edale Shale beds in the Ratcliffe Borehole. The Hathern No.1 Hydrocarbon Borehole (Brandon, 1994) proved at least 137 m of the group above possible Widmerpool Formation strata. Samples from this sequence yielded remains of Orbiculoidea sp. and the ammonoids ‘Eumorphoceras’ and ‘Anthracoceras’. Like the Widmerpool Formation, the Edale Shale Group may be absent from the Worthington Borehole, and from around Melbourne (Figure 9), but it is also possible that the group may interdigitate with the lower part of the Millstone Grit Group.

Millstone Grit Group (MG)

The Millstone Grit Group (Stevenson and Gaunt, 1971) comprises a sequence of mudstone with interbedded sandstones that lies below the Subcrenatum Marine Band. In its type area of north Derbyshire it has been divided into a number of thick sandstone-dominated packages (the ‘grits’), none of which is as yet formally defined. In this district the group is principally exposed north-east of the Thringstone Fault, around Melbourne and Staunton Harold, with smaller inliers located close to the fault on the upthrown side near Thringstone, Pegg’s Green and Newbold. It is exposed at Carver’s Rocks and has also been penetrated in many of the deeper shafts and exploration boreholes in the Northwest Leicestershire and South Derbyshire coalfields, to the south-west of the Thringstone Fault. No provings of Millstone Grit have been made to the north-east of the Normanton Hills Fault, but the group is inferred from seismic profiles to underlie Coal Measures or Triassic strata across much of the east and north-east of the district (Figure 16).

The thickness of the Millstone Grit is considerably less than that recorded in the Derby district (Sheet 125) (Frost and Smart, 1979); however, the precise details of the attenuation are not everywhere clear owing to the lack of marine-band control over most of this district. The Melbourne and Worthington boreholes proved complete, but highly attenuated sequences, with respective thicknesses of 156.25 m and 115.2 m (Figure 9). Significant local attenuations additionally occur at the top of, and within, the Millstone Grit, for example at Worthington. Southward thinning of the unit (towards the Wales–Brabant Barrier) is apparent between the Melbourne outcrops and Worthington Borehole, and between the latter and the Rotherwood Borehole in the Coalville District (Worssam and Old, 1988), in keeping with the trend indicated by the isopach diagram of Fulton and Williams (1988). Although the group consists mainly of mudstones and interbedded sandstones, minor siltstones, coals and seatearths are also present. Marine bands and Lingula bands occur throughout the sequence, with up to ten recognised between various boreholes. Sandstones in the lower part of the sequence are commonly crossbedded, pebbly and locally conglomeratic, with mainly well-rounded vein quartz and quartzite pebbles; those in the middle part of the group contain a conspicuous pink variety of feldspar as sand to small pebble-size clasts (white feldspar is also present).

The Millstone Grit sandstones have long been regarded as being of deltaic origin. They are characteristically rich in feldspar grains derived from a northerly source (e.g. Trewin and Holdsworth, 1973; Jones, 1980) which was deflected to the north-north-west along the Widmerpool Gulf by the Wales–Brabant landmass which lay to the south of the district. Ongoing heavy mineral studies (Hallsworth, 1998) suggest significant variations in heavy mineral ratios and garnet geochemistry for the sandstones of this district. The unnamed sandstones in the lower part of the sequence, below the Ashover Grit, are monazite-poor whereas sandstones of the Ashover Grit, and those above, are monaziterich and thus more typical of the northerly derived Millstone Grit in Yorkshire. Possibly the monazite-poor source region included the upland area of the Wales–Brabant Massif, lying to the south of the district.

Throughout the district the Millstone Grit overlies Dinantian strata with varying degrees of unconformity. In the Worthington Borehole (Figure 9), the lowest identifiable marine band, 5 m above the base, contains Cravenoceras subplicatum, probably indicating the Cravenoceratoides nitidus Zone E2b2, of Mid-Arnsbergian age (Riley, 1998). This suggests that the Pendleian and at least part of the Arnsbergian stages may be absent from the south-western part of the Hathern Shelf (Figure 6)." data-name="images/P946471.jpg">(Figure 5a). The occurrence of a thick, feldspathic sandstone bed immediately above Dinantian carbonates in the Worthington and Melbourne boreholes may indicate that the Edale Shale Group is not present. On the other hand, the two boreholes show thick ‘Edale’-type turbiditic mudstones and siltstones above this sandstone, suggesting interdigitation with the Millstone Grit lithology. Farther south, inliers of Millstone Grit around Thringstone include the Bilinguites gracilis Marine Band, and are therefore a little older than basal Marsdenian in age (Carney, 1994). Similarly in the Rotherwood Borehole (Worssam and Old, 1988), located within the Platform domain, the Millstone Grit only just extends downwards into the Kinderscoutian which rests directly on Dinantian strata.

In the main outcropping part of the Millstone Grit, boreholes around Staunton Harold Reservoir have proved marine bands of Arnsbergian and Late Alportian–Kinderscoutian age. The Bilinguites gracilis Marine Band (R2a1), marking the base of the Marsdenian stage, has been proved in the Melbourne and Worthington boreholes (Ambrose and Carney, 1997a, b). Above the Bilinguites gracilis Marine Band at Worthington, the Bilinguites bilinguis (R2b1) and Bilinguites metabilinguis (R2b5) marine bands were proved, separated by a thin sandstone. A local non-sequence here cuts out the R2b2, R2b3 and R2b4 marine bands, and no marine bands were proved in the equivalent part of the Melbourne Borehole (Figure 9). The Yeadonian stage is either very thin or absent hereabouts, but has been identified below the Subcrenatum Marine Band farther south in the Newbold inlier [SK 4003 1937] by the occurrence of the Cancelloceras cancellatum Marine Band (Mitchell and Stubblefield, 1948). The latter and the Cancelloceras cumbriense Marine Band are of widespread occurrence in deep boreholes in the South Derbyshire Coalfield (Barclay, 1996a; Carney, 1996a).

Beds between Dinantian strata and the Ashover Grit (MG, sa)

Apart from the borehole provings (Figure 9), arenaceous beds from this part of the succession are known from several small exposures summarised by Ambrose (1997a) and Ambrose and Carney (1997a). The sandstones are fine, medium and coarse-grained, reddish brown to pale grey lithologies. Up to 8 m are exposed in an old quarry in Calke Park [SK 362 226].

In the Worthington Borehole (Figure 9), much of the sequence between 90 m and the top of the basal sandstone at 128 m depth consists of ‘striped’, pale grey and dark grey, interlaminated mudstones, siltstones and thin, sharpbased sandstones. Graded bedding, load structures and cross-lamination are common, with the beds commonly burrowed and in places microfaulted and slumped. This sequence resembles the turbidite lithofacies beds described from the upper part of the Pendleian and lower/middle Arnsbergian stages in the Duffield Borehole (Aitkenhead, 1977), and it possibly represents an interdigitation of the Edale Shale Group lithology. Between 90 m and the base of the Ashover Grit at 36.6 m depth in the Worthington Borehole, the sequence includes marine bands in the range between R2b5 and E2b-c. It consists mainly of siltstones, but also contains sandstone beds which increase upwards both in number and thickness. Six marine bands, three of which are named, are present in the associated mudstones, as shown on (Figure 9). Palaeosol horizons and iron pans are present, and Riley (1998) noted that much of the mid-Marsdenian sequence has been lost through erosion.

Ashover Grit (AsG)

This is the lowest major mappable sandstone of the district. Its recognition in the Melbourne and Worthington boreholes (Figure 9) is based on the overlying Bilinguites superbilinguis (R2c1) Marine Band. In the Melbourne Borehole, it is the highest sandstone containing distinctive pink K-feldspars. The equivalent outcropping sandstone is at Stanton by Bridge, where a disused quarry [SK 373 274] exposes about 8 m of grey, fine to very coarse-grained, cross-bedded sandstone (Plate 10). Palaeocurrents measured here and at a nearby exposure [SK 3760 2723] show dominant trends to the north and north-west, with minor variations to the west, south-west, south and north-east. Outcrop and borehole evidence prove a thickness of around 33 m near Stanton by Bridge, compared to 21.74 m in the Melbourne Borehole and only 9 m in the Worthington Borehole. Away from Stanton, the Ashover Grit splits into several beds of sandstone, separated by mudstones.

Beds between the Ashover Grit and Chatsworth Grit

These are exposed in a railway cutting by King’s Newton [SK 3941 2607]. Up to 3 m of section is visible at any one place, consisting of fine to coarse-grained, slightly fining up sandstones; palaeocurrents are variable, to the west, north-north-west, north-north-east and east (Ambrose, 1997a). These beds are absent from the Worthington Borehole, due to the presence of unconformities (Figure 9).

Chatsworth Grit (ChG)

This unit shows rapid thickness variations. In places it is absent, for example in the Worthington Borehole (Figure 9), but more commonly it is split into three or four thin beds, as in provings in the South Derbyshire Coalfield (Carney, 1996a), and in the Melbourne Borehole where 6.6 m are present. The unit is mainly exposed in the Melbourne area (Ambrose, 1997a), around Highfields where a disused quarry shows a fine to coarse-grained sandstone. A further exposure [SK 374 249] is in weathered coarse-grained sandstone showing a current direction to the north-west.

Rough Rock (RR)

The Rough Rock is separated from the underlying Chatsworth Grit by a mudstone and seatearth sequence which, as in the Melbourne Borehole, commonly includes both the Cancelloceras cancellatum (G1a1) and Cancelloceras cumbriense (G1b1) marine bands.

At Melbourne Quarry the Rough Rock is at least 15 m thick and consists mainly of medium-grained, crossbedded sandstones with rare basal, pebbly lags. At the base of this sequence, current directions are towards the westsouth-west and west-north-west, but upwards they successively change to predominantly north-north-west, north, and north to north-east directions. Farther east the Rough Rock splits into several thin beds about 2 to 4 m thick. To the south, it is at least 3 m thick in the Newbold inlier (Mitchell and Stubblefield, 1948), and to the west 21.6 m was proved in the Matts Yard Colliery Borehole (Barclay, 1996a). At the Carver’s Rocks inlier, the exposed sequence comprises about 10 m of medium and coarse-grained, feldspathic pebbly sandstone (Barclay, 1996b); Fulton and Williams (1988) recorded north-west and westerly current flow directions from this locality.

In the Worthington Borehole, the uppermost Millstone Grit strata above the Bilinguites superbilinguis Marine Band are represented by only 4 m of mudrocks, indicating that the Chatsworth Grit and Rough Rock are absent (Figure 9), having been cut out at the base-Westphalian unconformity.

Key localities

Westphalian

In this district Westphalian strata are represented mainly by the Coal Measures; there is only a single borehole proving the overlying Warwickshire Group. The Coal Measures crop out principally within faulted, synclinal basins to the west of the Thringstone Fault. Eastwards they are represented by small outliers between Melbourne and Worthington (Figure 1), and they are inferred beneath Triassic strata in the north-east corner of the district (Figure 16). The measures have been extensively exploited, by underground and opencast methods in the North-west Leicestershire and South Derbyshire coalfields.

Coal Measures

The Coal Measures comprise a mudstone-dominated sequence, which at present is not formally named or defined. It started to accumulate at about 310 Ma, an event marked by the marine transgression which deposited the Subcrenatum (Pot Clay) Marine Band. The strata represent a continuation of the sedimentation pattern described for the Millstone Grit, but by Langsettian times (Westphalian A) water depths had shallowed to the extent that deposition occurred mainly within a delta-plain environment that was largely above sea level.

The Coal Measures sedimentation was cyclic in character. A typical small-scale cycle (Guion et al., 1995) consists of basal dark grey mudstones (lacustrine or marine conditions), with mussel bands, marine bands or ironstone nodules. The succeeding strata are dominantly mudstones (claystones) and siltstones (overbank/lacustrine delta). They in turn pass up into sandstones (proximal delta/channel) surmounted by pale grey ganisteroid sandstones forming the seatearth (palaeosol) of many coals (mires). Deposition within the Pennine Basin was characterised by regional-scale progressive thinning of the sequence southwards, on to the Wales–London–Brabant Barrier (Fulton and Williams, 1988). In this district the measures also thin eastwards, across an axis represented by the Boothorpe Fault and/or the Ashby Anticline (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) and (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11). This structure has been used to define the boundary between the North-west Leicestershire Coalfield, to the east, and the South Derbyshire Coalfield on the western flank of the anticline (Mitchell and Stubblefield, 1948); (Figure 16).

The Coal Measures attain a maximum aggregate thickness of 760 m in the South Derbyshire Coalfield. Their subdivision is based on identification of three faunal horizons: the Subcrenatum, the Vanderbeckei and Aegiranum marine bands. These three horizons mark, respectively, the bases of three stages Langsettian, Duckmantian and Bolsovian (formerly Westphalian A, B and C Series). The Langsettian corresponds with the Lower Coal Measures, but the Middle Coal Measures covers both the Duckmantian and the lower part of the Bolsovian. The base of the Upper Coal Measures is taken at the Cambriense Marine Band, within the Bolsovian.

On Sheet 141 Loughborough, the inter-coalfield seam correlations follow the scheme of Spink (1965), which is modified from that of Fox-Strangways (1907) and Mitchell and Stubblefield (1948), while the names are mainly those used in the Coalville district by Worssam and Old (1988). Virtually all of the worked coal seams lie within the ‘Productive Coal Measures’ (Figure 1), whose base is the Kilburn seam.

In the following account, descriptions of the Coal Measures are given in summary form, with reference to sets of comparative stratigraphical columns, arranged east-west across the district, which also give typical thicknesses of the principal coal seams (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) and (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11). It should be noted that the records on which these are based commonly lack details of seatearths and fossil horizons, but their absence from the sections does not necessarily mean that they do not occur in the sequence. For more detail the reader is referred to the early accounts of Fox-Strangways (1907) and Spink (1965), and to recent work by Barclay (1996a, b) and Carney (1994, 1996a, b).

Measures north-east of the Thringstone Fault

Small outliers of Lower Coal Measures were proved to the north-east of the Thringstone Fault, as shown on Sheet 141 Loughborough. The most southerly of these was proved in the Worthington Borehole (Figure 9), confirming the findings of earlier coal exploration drilling nearby. In the Worthington Borehole, Riley (1998) identified the Subcrenatum Marine Band at 9.56 to 16.65 m depth. He further noted that a thin conglomerate at around 21 m is in depositional continuity with the marine band; this conglomerate is not the Rough Rock, and its base marks a major hiatus which spans the Yeadonian and uppermost part of the Marsdenian Stage. The strata near Worthington may extend south-westwards beneath the Trias to another proving of measures, which includes the Subcrenatum Marine Band, in the Ferrer’s Opencast Site Borehole, located on the upthrown side of the Thringstone Fault (Ambrose and Carney, 1997b).

North-west Leicestershire Coalfield

In this coalfield the measures are preserved within an asymmetric synclinal structure against the Thringstone Fault (Chapter 9). The strata, described in Carney (1994), Worssam and Old (1988) and Spink (1965), range from the Subcrenatum Marine Band, at the base of the Langsettian (Lower Coal Measures), to just above the Minge seam in the Duckmantian (Middle Coal Measures).

Lower Coal Measures (LCM)

This unit, about 340 m thick, comprises the strata below the base of the Vanderbeckei Marine Band (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10). The borehole provings are poorly documented for the lower part, but the Listeri Marine Band was indicated in the Dole’s Farm Borehole. The overlying sequence includes the Wingfield Flags (WF), about 30 m thick where exposed around Ashby-de-la-Zouch, composed of brown to greenish grey, fine to medium-grained, thinly bedded, silty and carbonaceous sandstone (Carney, 1996b). The first seam above these beds is the Kilburn (K), marking the start of the Productive Measures; it shows local thickening to 3.8 m around Heath End [SK 3725 2098], one of the few places where it has been worked underground (Ambrose and Carney, 1997a). A further sandstone, up to 11 m thick, occurs just below the Vanderbeckei Marine Band and is responsible for the split between the Upper Main(UM) and High Main (HM) seams which are locally up to 2 m thick. Other similarly thick seams are the Lower Main(LM, upper and lower) and the Nether and Middle Lount (NL, ML). In the former Lounge opencast site [SK 385 185], the latter seams are washed out locally by narrow palaeochannels containing sandstones showing east-south-east current flow (Jones, 1994; Jones et al., 1995); associated channel bank listric collapse structures formed by recumbently folded Coal Measures strata were observed during this resurvey in 1993 at the Lounge opencast site [SK 395 185], now fully restored.

Middle Coal Measures (MCM)

A partial sequence of these strata is present, totalling 120 to 140 m thickness (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11). The New Main (NMA), Splent (SP) and Minge (MI) seams, each locally up to 1.5m thick, are among the more important to have been worked. Sandstone intercalations are generally thin (1 to 2 m but locally up to 6 m), but become particularly numerous above the New Main Rider (NMR) seam.

South Derbyshire Coalfield

This coalfield is divided by structure into three sectors (Figure 18). To the east of the Boothorpe Fault only the Lower Coal Measures crop out, from the Subcrenatum Marine Band upwards to the Stockings (ST) seam, the former coming in just to the south of the district. West of the Boothorpe Fault, Bolsovian beds of the Upper Coal Measures crop out in a broad syncline that closes to the north-west, thus also bringing to crop progressively older strata of the Middle and Lower Coal Measures, down to the Well (W) seam. West of the Coton Park and Netherseal faults (Figure 18) a largely complete sequence, up to and including the Warwickshire Group, is concealed beneath Triassic strata of the Needwood Basin.

Lower Coal Measures (LCM)

This division thickens westwards (Fulton and Williams, 1988), from about 330 m south of Woodville to about 420 m around Caldwell in the concealed coalfield. In its lower part it contains the Wingfield Flags which are up to 65 m thick if siltstones and sandy siltstones are included (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10). The thickest coal seams are the Stockings (up to 2.4 m), Woodfield (WD, to 2 m) and, just below the Vanderbeckei Marine Band the Maingroup. The Nether Main (NM) and Over Main (OM) locally unite to form a seam up to 5.5 m thick (Hull, 1860), with a thickness of 3.7 m recorded in the Rawdon Pit Shaft. Farther west the Main seams are locally separated by up to 16 m of mudstone (Carney, 1996a).

Middle and Upper Coal Measures (MCM, UCM)

These strata average 350 to 400 m thick across the coalfield (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11), the principal seams being the Little (L), Block (B) and Upper Kilburn (UK), each between 1 and 2 m thick.

Above the Upper Kilburn, coal seam nomenclature changes to the ‘P’ series, devised by Jago (in Worssam et al., 1971), commencing with P44. Above this, coal seams become increasingly numerous, their vertical separation decreases and seatearth thicknesses increase. Several marine bands are intercalated, as reviewed by Carney (1996a) and shown in (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11), including the Aegiranum Marine Band (AMB), located above the P31 (Derby) coal seam, which marks the Duckmantian/Bolsovian boundary, and the Cambriense Marine Band (CMB), above P17, representing the Middle/Upper Coal Measures boundary. The floor of the P40 seam, or top of the underlying sandstone (Hill Farm Sandstone of Worssam and Old, 1988), mark the base of the commercially important ‘Pottery Clays’ formation (informal name), whose type section in the BGS Hanginghill Farm Borehole is documented by Worssam (1977, see also (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11)). The biostratigraphical correlations demonstrate that the 140 m minimum thickness of these beds represents part of a condensed sequence that is about a quarter of the thickness of the equivalent stratigraphical unit in North Derbyshire and Nottinghamshire (Frost and Smart, 1979).

The ‘Pottery Clays’ include the upper part of the middle Coal Measures (Plate 11) and all of the Upper Coal Measures of South Derbyshire. Seatearths up to 4 m thick form the principal fireclay resources and historically the most important were those between the P34 (Ell) and P31 (Derby) seams; their local nomenclature is discussed by Mitchell and Stubblefield (1948), whose stratigraphy is summarised as follows:

Seam

Named Fireclay Horizon

Approx. Thickness (m)

P31 (Derby)

Marl

1.0

Crucible clay/ Main Fireclay/ Derby Fireclay

1.0–3.0

Bottle Clay

1.2–3.7

P32 Rider

Seat earth, no name

0–1.8

P32

—

—

P33

Deep Fireclay/ White Fireclay

1.5–4.0

Deep Clunch/ Brown Clay

P34 (Ell)

—

Warwickshire Group

This division, formally known as the ‘Barren Measures’, constitutes a ‘red bed’ association which commenced deposition at the start of the late Carboniferous, Variscan inversion event (Corfield et al., 1996). At this time, earth movements involving local block uplifts initiated a change from swampy environments to better drained, alluvial conditions.

In this district, these beds are proved only in the Caldwell No. 2 Borehole, where 44.7 m of strata beneath the Trias is correlated with the Etruria Formation (Et). The sequence comprises reddish brown, massive mudstones with purple, yellow, green and blue-grey mottles, and with a thick bed of coarse-grained sandstone in the middle part; it rests with a sharp, probably unconformable base on the Upper Coal Measures which are reddened and colour mottled for several metres below the contact.

Chapter 5 Permian

Permian strata were proved only at depth, in the northeastern corner of the district, where the Chilwell Borehole and Central Ordnance Borehole showed, respectively, 1.6 m and 14.3 m of red mudstone or marl which was assigned to the Edlington Formation (Edl) by Howard (1989). In the Chilwell Borehole, the mudstone is overlain by 37.9 m of sandstone and pebbly sandstone, of which the lowermost 20.3 m may be Lenton Sandstone Formation (LnS) (Charsley et al., 1990), the latter of uppermost Permian to Scythian age and included for convenience in the Sherwood Sandstone Group (Chapter 6).

Chapter 6 Triassic

The lithostratigraphical subdivision of the Triassic rocks adopted herein follows Warrington et al. (1980) but incorporates the modifications that Charsley et al. (1990) applied to the local stratigraphy erected by Elliott (1961).

In latest Permian and earliest Triassic times (about 250 Ma; Gradstein and Ogg, 1996), mainly continental-facies deposits began to accumulate, a process that culminated in the burial of a landscape that had evolved over about 60 million years of erosion, initiated by late Carboniferous (Variscan) block uplift. The depositional surface was generally planar to gently undulating, but with rugged palaeo-hill ranges developed on the Precambrian outcrops of Charnwood Forest and the steeply dipping Dinantian strata around Breedon. Thick Triassic sequences filled actively subsiding basins. These included the Hinckley Basin, to the south-west (Worssam and Old, 1988), and the Needwood Basin whose margin lies within the western and north-western parts of the district (Figure 16).

Moira Formation (MO)

This formation was earlier referred to as the ‘Permian breccias and marls’ (Fox-Strangeways, 1905, 1907) and the ‘Breccia and Marl of Moira’ on the earlier version of the Sheet 155 Coalville. Its present name was first used by Barclay (1996a, b). The formation accumulated in pockets on the eroded land surface. Consequently, it is of variable thickness, with maxima of 42.6 m proved in the Caldwell No. 2 Borehole and possibly 52.4 m at Coton Park Colliery in the south-west of the district. A Permian age for parts of the unit cannot be ruled out, although it is highly diachronous: indeed, recent palaeomagnetic investigations of samples from the West Midlands concluded that a possibly equivalent unit - the Hopwas Breccia - is of earliest Triassic age (information from J H Powell, BGS, 1995). In the Ashbourne district, Chisholm et al. (1988) equated similar beds at the base of the Triassic, named the Huntley Formation, with the Moira/Hopwas breccias.

The formation includes beds of angular conglomerate (‘breccias’), sandstone and mudstone. The conglomerates are poorly sorted with a clast suite derived mainly from local Carboniferous, Lower Palaeozoic and Charnian (Precambrian) terrains (Brown, 1889; Carney, 1996a). Their deposition was by debris flows, which formed two distinct lobes extending north and westwards from the Charnian uplands. Distal facies exposed between Ingleby [SK 349 279] and Swadlincote, at Castle Donington (Ambrose, 1997b) and near Ticknall (Ambrose and Carney, 1997a), comprise red-brown, locally green or ochreous mottled, silty, micaceous mudstones of possible lacustrine and/or aeolian origin, and red to buff, fine to medium-grained sandstones representing fluvial or sheet flood interludes.

In the Charnwood Forest area, impersistent breccias filling the central parts of palaeovalleys on the Triassic unconformity are informally termed ‘Basal Breccia’ (Carney, 1994). They are typically up to 4 m thick, but locally up to 11 m, and are composed of very poorly sorted angular Charnian rock fragments set in a carbonate-cemented sand matrix. At Grace Dieu, they additionally include breccias made up of Carboniferous Limestone clasts. Such breccias have also been found at higher stratigraphical levels, for example within the overlying Mercia Mudstone Group in exposures close to an irregular unconformity surface, as at Breedon on the Hill (Breedon Member, see below).

Key localities

Sherwood Sandstone Group

This group forms an unconformable sequence cropping out mainly in the central and western parts of the district, and onlaps various pre-Triassic rocks. It is predominantly arenaceous and includes the most important bedrock aquifers of the district. Overall the succession fines upwards, both by a reduction in mean grain size of the sandstones and by an increase in the abundance of intercalated mudstone or siltstone beds, from the Polesworth Formation to the Bromsgrove Sandstone Formation at the top.

In the Ashbourne district, on the north-western and northern side of the Needwood Basin, the equivalents of the Polesworth and Bromsgrove Sandstone formations are the Hawksmoor and Hollington formations respectively (Chisholm et al., 1988).

Polesworth Formation (PoF)

This formation is mainly confined to the western half of the district. It consists of poorly cemented, medium to coarse-grained, pebbly sandstones and matrix or clast supported conglomerates. The larger clasts typically comprise well-rounded vein quartz or quartzite pebbles whose composition and origin were discussed by Worssam and Old (1988, p.56). The unit corresponds to the ‘Bunter Sandstone’ or ‘Bunter Pebble Beds’ of previous workers (e.g. Fox-Strangways, 1905). Its present name was introduced by Warrington et al. (1980, p.38) and the type area designated by Worssam and Old (1988, p.56) as the outcrop between Polesworth and Warton, on the eastern side of the Warwickshire Coalfield. The formation belongs to a distinctive early Triassic (Scythian age) association of coarse-grained sedimentary rocks. The equivalent strata have been recognised throughout the English Midlands, but they commonly form basal infills to isolated Triassic depositional basins and so are seldom seen in demonstrable lateral continuity on a regional scale. This prompted Warrington et al. (1980, p.38) to recommend that the strata should have local formation names in their various areas of outcrop. The Polesworth Formation represents the strata within or fringing the Hinckley and Needwood basins; it is equivalent to the Kidderminster and possibly the Wildmoor Sandstone formations of the Worcester Basin, and to the Nottingham Castle Sandstone Formation of south Nottinghamshire (Warrington et al., 1980, table 4; Worssam and Old, 1988, table 3).

The base of the Polesworth Formation is irregular and unconformable; in the former Wragg’s Clay Pit [SK 311 195], close to the mapped Boothorpe Fault, evidence was found for tilting of the Moira Formation prior to deposition of the first sandstone beds (Brown, 1889). The formation is largely absent from the Triassic sequence east of the Boothorpe Fault, but west of the fault it thickens to over 150 m due to synsedimentary subsidence within and along the margin of the Needwood Basin. Such thickening is not uniform, and it has been shown (Carney, 1996a) that the formation thins across the horst of Carboniferous rocks formed by the Netherseal and Overseal faults, and across a further possible buried horst to the north-west, suggesting active faulting during deposition. The outcrop limits of the formation further indicate that during early Triassic times the entire area between Swadlincote and Breedon, and possibly as far east as the Soar valley, was one of relative uplift and non-deposition.

The formation represents a major period of fluvial activity involving rivers draining northwards across the district from as far as north-west France (Wills, 1970; Warrington and Ivimey-Cook, 1992). Outcrop considerations suggest that the river valleys were probably broad and occupied by braided systems; palaeocurrent indicators reflect predominantly northerly flow.

A coherent sequence is difficult to establish for the Polesworth Formation, since its outcrops are strewn with pebbles and cobbles regardless of the underlying lithology. Non-conglomeratic sandstone beds have been mapped at the surface, but commonly cannot be followed laterally for more than a few hundred metres. Most of the better-documented boreholes show that true conglomerates form less than 50 per cent of a given section, and that within the sequence as a whole there are all gradations between conglomerate, pebbly sandstone and medium to coarse grained sandstone devoid of pebbles.

Beds exposed near Council Farm, Church Gresley (Plate 12), are typical of the formation in showing planar or trough cross-bedding throughout; current directions are between north-west and north or north-east (Figure 12). Similar sequences were recorded around Foremark Reservoir and at Gravel Pit Hill where a significant additional component of south-easterly current flow was found (Barclay, 1996b). In these more northern and eastern occurrences, the Polesworth Formation typically averages about 40 m thickness.

In the north-east of the district, the Polesworth Formation is thought to pass gradually into the Nottingham Castle Sandstone Formation (Charsley et al., 1990). The transition is everywhere concealed but outrops in the adjacent Derby district (Sheet 125) demonstrate an eastwards decrease in size and abundance of pebbles (Frost and Smart, 1979), concomitant with a continuing gradation into typical Nottingham Castle Sandstone Formation. This formation may occur locally in the east of the district, as in the Central Ordnance Depot (Chilwell) Borehole (Howard, 1989) and possibly in the Hathern No. 1 and other deep boreholes in the Normanton on Soar area (Fox-Strangways, 1905; Brandon, 1994). It generally consists of sandstones and pebbly sandstones which, in the Normanton on Soar and Long Eaton boreholes, include Charnian and Carboniferous clasts indicative of local derivation by fluvial and/or debris flow processes.

Bromsgrove Sandstone Formation (BmS)

The Bromsgrove Sandstone (Warrington et al., 1980) was formerly the ‘Lower Keuper Sandstone’. It onlaps the Polesworth Formation and equivalent formations, and represents a significant extension of alluviation across the district. The formation is absent from the areas of Breedon and Charnwood Forest, which persisted as topographical highs throughout the later part of the Triassic. Its age is generally considered to be Anisian but there are no fossils, apart from a few reptilian footprints (Sarjeant, 1974). The Bromsgrove Sandstone was not recognised in the Derby (Frost and Smart, 1979) and Nottingham (Charsley et al., 1990) districts. The top of the formation is gradational over a few metres into the mudstone-siltstone-sandstone sequence of the Sneinton Formation, the lowest unit in the Mercia Mudstone Group. Its base is locally disconformable on the Polesworth Formation or Moira Formation, and in places it oversteps these to rest unconformably on pre-Triassic rocks.

The formation has an average thickness of 30 to 50 m but this is exceeded in the south-west of the district where the Caldwell Hall Borehole, for example, indicates that up to 110 m is present at the Needwood Basin margin (Carney, 1996a). This thickening is also due in part to syndepositional fault movements, which have been proved across both the Burton Fault and the Boothorpe Fault (Barclay, 1996b). Between these two structures, to the south-east of Burton upon Trent, the Bromsgrove Sandstone Formation onlaps the Polesworth Formation and cuts it out northwards against the Coal Measures crop. Southwards along the same depositional onlap zone, the Polesworth Formation is downfaulted to the west by the Coton Park Fault, and flexured, dipping at up to 22° to the west. This structure is interpreted as a fault-monocline system (Figure 16) which developed at the time of Needwood Basin subsidence, and persisted at least during Bromsgrove Sandstone sedimentation.

The Bromsgrove Sandstone comprises buff, fine to medium-grained, cross-bedded and parallel laminated sandstones and subordinate red and green mudstones and siltstones; typical lithologies were seen in a quarry by Chellaston East Junction (Ambrose, 1997b). In the Ticknall–Repton area a prominent basal bed, up to 10 m thick, is composed mainly of red mudstone (Brandon, 1997). Locally, the basal few metres are conglomeratic, but above this there is a general absence of quartz and quartzite pebbles. Of the 15 current orientation measurements taken most indicate flow towards the north, as near Lawn Plantation (Ambrose and Carney, 1997a), with variations towards the north-west, north-east and south-east. In the Belton Borehole, dune bedding was reported (written communication attached to log, R E Elliot, 1971) from a sequence equated here with the Bromsgrove Sandstone Formation; such a structure has not been found elsewhere in the district, however.

Alternations between sand and mud-dominated lithologies are interpreted to indicate the presence of upward fining alluvial cycles throughout the Bromsgrove Sandstone Formation (e.g. Worssam and Old, 1988). This association is suggestive of deposition within a meandering fluvial system. Ongoing heavy mineral studies indicate a local provenance particularly noticeable in the stratigraphically lower beds of the Bromsgrove Sandstone Formation (Knox, 1996); these contain abundant lithic grains which, being rich in chlorite, are thought to reflect derivation from greenschist-facies rocks of the Charnian Supergroup.

The Shepshed Sandstone Member (ShS) is a distinctive mappable subdivision confined to the area within and around Charnwood Forest. It is a local facies in the Bromsgrove Sandstone Formation, and may be equivalent also to part of the Sneinton Formation. It is recognised by the commonly massive internal nature of its beds, as in the cutting near Blackbrook Hill House, and by the presence of angular to subangular Charnian clasts that locally form thin breccia beds at the type section in Newhurst Quarry (Carney, 1994). The variable thickness of the member is due to deposition across an irregular topography. An example of this occurs in the concealed sub-Triassic palaeovalley beneath the present Black Brook valley [SK 457 175], where seismic and geophysical investigations have shown the unit to thicken to about 50 m in the centre of the palaeovalley (BGS unpublished information). Heavy mineral studies (Knox, 1996), and the identification of sandstones with local Charnian clasts, indicate that the Shepshed Sandstone is present in the basal 10 to 15 m of Triassic beds in the Belton Borehole.

Key localities

Mercia Mudstone Group (MMG)

The Mercia Mudstone Group is the formal name (Warrington et al., 1980) for strata formerly known as the ‘Keuper Marl’. With an average thickness of about 220 m (range 190 to 250 m), it is the most widespread unit at outcrop in the district. (Figure 13) summarises the stratigraphic relationships of the six component formations and two members, together with their characteristic gamma-ray and sonic log profiles. Geophysical borehole logs of this type are commonly the principal means of correlating and comparing the group across the East Midlands. The generalised thicknesses in (Figure 13) are exceeded in boreholes sited just to the south-west of the district, in Burton upon Trent, where the Radcliffe (14 to 20 m), and Gunthorpe (93 to 103 m) formations thicken appreciably westwards across the Burton Fault at the Needwood Basin margin.

The group has a basal siltstone and sandstone-rich unit, the Sneinton Formation, which represents deposition within a broad alluvial plain crossed by ephemeral streams and sheet floods, with bodies of standing water and accumulations of wind blown sediment. A possible early marine influence has also been detected (see below) in these beds. The beds of the overlying siltstone/mudstone sequence comprising the Radcliffe Formation are finely laminated and of lacustrine origin. The succeeding three mudstone-rich divisions, which constitute the bulk of the group (Gunthorpe, Edwalton and Cropwell Bishop formations), represent the extended accumulation of wind-blown sediments in arid playa mudflat or sabkha environments, with both continental and marine influences present (Taylor, 1983). Periods of standing water - playa lakes - and short-lived sheet flood episodes contributed the intercalated siltstone and sandstone beds, with sandstones of the Cotgrave and Hollygate members reflecting more prolonged fluvial sheet flood events. The presence of gypsum is indicative of a high water table, charged with sulphate rich water, particularly during deposition of the Cropwell Bishop Formation. The stratigraphically highest division, the Blue Anchor Formation, is a transitional unit; both marine and continental water sources may have been involved in its formation (Taylor, 1983).

Upstanding massifs of Carboniferous dolostone at Breedon on the Hill were subjected to karstic dissolution and underground fluvial circulation in late Carboniferous to early Triassic times. The resultant caves (Ambrose and Carney, 1997b) were locally infilled with Triassic sediments (Plate 13), probably during the deposition of the Gunthorpe Formation. Vertebrate remains have been reported from cave and fissure fills at Breedon Hill Quarry (Fraser, 1994 p.216), but the age of this fauna has not been determined. Deposition of the Mercia Mudstone Group probably accompanied widespread regional subsidence, although with continued fault/flexure control along the edge of the Needwood Basin east of Burton upon Trent, where the Sneinton Formation onlaps beds of the Bromsgrove Sandstone. It is probable that the whole district, including the highest points of the Charnwood Forest palaeo-hill range, was buried beneath sediments by mid-Triassic times.

Sneinton Formation (Snt)

This unit was formerly known as the ‘Waterstones’. It is generally between 20 and 30 m thick, where not onlapping against the sub-Triassic basement. The few exposures show sequences of interbedded, laminated and varicoloured micaceous mudstones, siltstones and fine-grained sandstones; some of these form scarp and dip slope features. Sandstone debris found in fields commonly shows parallel lamination, cross-lamination, symmetrical and asymmetrical ripples (respectively indicating formation by wave and current activity) and pseudomorphs after halite. Microfossils from Sneinton Formation laminites at Newhurst Quarry include a colonial alga (Plaesiodictyon mosellanum) indicative of brackish water conditions (Warrington, 1994), and bedding planes in the intercalated flaggy sandstones have revealed footprints of the reptile Chirotherium (M. King, in Carney, 1994). Exposures at Cloud Hill Quarry [SK 4124 2175]; (Plate 14), only tentatively referred to the Sneinton Formation (Ambrose and Carney, 1997b), yield Mid-Triassic microfossils together with tasmanitid algae indicative of deposition in marine or brackish waters (Warrington, 1996).

Radcliffe Formation (Rdc)

This formation varies from 0 to 15 m thick across the district. It represents a predominantly lacustrine association, and consists of very finely laminated, red-brown, brick-red, pinkish red and grey-green mudstone, siltstone and very fine-grained sandstones, with subordinate thicker beds of structureless mudstone and fine-grained sandstone. In places, the Sneinton and Radcliffe formations cannot be separated with confidence and are locally very thin or absent. The Radcliffe Formation is assigned a Mid-Triassic (Anisian to Ladinian) age.

Gunthorpe Formation (Gun)

The Gunthorpe Formation is about 75 m thick, and comprises red-brown, mainly structureless, silty mudstones with subordinate laminated beds. It is usually micaceous in the lowermost few metres. Thin beds of greenish grey siltstone and very fine-grained sandstone, the ‘skerries’ of former terminology, are common throughout and not all are indicated on the accompanying map. They show parallel lamination, cross-lamination, ripple marks, pseudomorphs after halite, convolute bedding and load structures. The formation is assigned a Ladinian (late Mid-Triassic) age. A distinctive greenish grey bed of mainly siltstone and fine-grained sandstone, the Diseworth Member (Dis), up to 5 m thick, has been identified in the Mercia Mudstone Group outcrop. It maintains a stratigraphical position between 15 and 20 m above the base of the Gunthorpe Formation (Ambrose and Carney, 1997b), and broadly corresponds in stratigraphical position to the ‘Plains Skerry’ grouping in the upper part of the Carlton Formation of earlier terminology (Elliott, 1961).

The Breedon Member (Br) crops out around Breedon Hill and Barrow Hill, occurring at several levels in the Gunthorpe Formations. At the north end [SK 405 237] of Breedon Hill Quarry, 5 m of the member unconformably overlies Dinantian dolostones; it contains angular to subangular clasts of partially rotted dolostone, varying from a few to several centimetres across, supported by a matrix of dark red-brown, very fine-grained, clayey sandstone. Debris flows from the Breedon palaeo-hill range probably produced such breccias at various times throughout deposition of the Gunthorpe Formation.

Edwalton Formation (Edw)

This unit is about 35 to 50 m thick. It is generally more sandy than the Gunthorpe Formation, and locally contains hard and siliceous sandstone or siltstone beds. Gypsum as thin, anastomosing veins, is particularly common in its upper part. The unit can be recognised on geophysical logs (Figure 13) but in the field its recognition usually depends on identifying two relatively thick sandstones, the Cotgrave and Hollygate members, whose lower and upper surfaces respectively delineate the formation boundaries. The formation is late Ladinian to Carnian in age.

At the base of the formation, the Cotgrave Sandstone Member (Cot) comprises red-brown, grey and buff, fine to medium-grained, commonly parallel laminated sandstone, with local thin red and green mudstone beds. It is poorly exposed, but a ditch section for the Derby Southern Bypass [SK 3497 2970] revealed about 3 m of the sequence. It consists of sandstone, pale brown to reddish brown in colour, fine grained and with parallel and cross-laminated beds up to 0.6 m thick; this is intercalated with reddish brown sandy siltstone (Brandon, 1997). By contrast, in boreholes near Ratcliffe on Soar Power Station [SK 498 295], the member comprises a sandstone bed, 4.25 m thick, with a further 1.45 m-thick bed close above it (Carney and Cooper, 1997). Miospores found at this level in the Leicester Forest East Borehole in the Coalville district indicate a Ladinian-early Carnian age (Worssam and Old, 1988, p.67).

The Hollygate Sandstone Member (Hly) is the upper division of the formation and a correlative of the Arden Sandstone of the West Midlands (Warrington, 1970). It is very poorly exposed, but borehole provings indicate that it is locally up to 11 m thick. Former exposures in cuttings for the A564 [SK 3752 2945] showed almost 6 m of strata consisting of red-brown to greenish grey, fine-grained, structureless to parallel-laminated dolomitic sandstone in beds up to 1.7 m thick, alternating with subordinate beds of red-brown to green, silty, locally micaceous mudstone (Ambrose, 1997a). Elsewhere, borehole provings show that the sandstone component is locally medium-grained, and rarely coarse-grained, with the intervening mudstones commonly gypsiferous.

Cropwell Bishop Formation (CBp)

This formation, up to 66 m thick, forms a series of fault bounded outcrops in the north and east of the district (Figure 1), and is mostly covered by Trent alluvium or river terrace deposits. It comprises red-brown mudstones and siltstones, but is characterised by an abundance of gypsum as veinlets, nodules, disseminations or thick beds. The formation is assigned a Norian (mid Late Triassic) age.

The principal massive gypsum bed, the Tutbury Gypsum (T), commonly ranges between 3 and 5 m thick. Its propensity to dissolution near to the surface, or beneath drift deposits, was well displayed in excavations for the Derby Southern Bypass (Cooper, 1996) and is further suggested by descriptions of voids in borehole records along the A453 where it crosses the River Soar floodplain [SK 4846 2838] (Brandon and Carney, 1997). The Tutbury Gypsum was exposed at the time of the survey in a cliff section along the River Soar [SK 4923 3039] to [SK 4923 3052], as a red mudstone, about 2 to 5 m thick, containing large (up to 0.2 m) gypsum nodules (Brandon, 1996). The stratigraphically higher Newark Gypsum (N) comprises several thinner (0.5 to 1.5 m) gypsum beds within a vertical section about 10 m thick (Carney and Cooper, 1997).

Both of these gypsum resources have been exploited. Details of the geology, quarrying, mining and potential hazards of the Tutbury gypsum occurrences around Chellaston [SK 3870 3000] and Aston-on-Trent are summarised by Cooper (1996), and mining activities around Gotham and Ratcliffe on Soar by Cooper and Carney (1997); further information is given in Chapter 12 Bedrock dissolution and Mined ground and shafts.

Blue Anchor Formation (BAn)

The Blue Anchor Formation (formerly the ‘Tea-green Marl’) varies between 7 and 10 m thick. In ploughed fields it gives rise to dark grey, clayey soils with abundant fragments of green to greyish green mudstone. The junction with red mudstone of the underlying Cropwell Bishop Formation is generally very sharp in the few places it has been seen. The formation consists largely of dolomitic siltstone and silty mudstone (Brandon, 1994). Exposures are generally limited to a few cuttings, as on Rushcliffe Golf Course where the typically blocky, green lithology was seen. The transition between the Norian and Rhaetian stages occurs within this unit (Figure 13).

Key localities

Penarth Group

The Penarth Group (Warrington et al., 1980), of Rhaetian age, crops out in the extreme east of the district where it is generally poorly exposed. The two component formations were formerly well exposed in the Normanton Hills railway cutting and tunnel (Browne, 1895; Fox-Strangways, 1905), and in nearby lime pits (Kent, 1937), as summarised in Brandon (1994). The group was laid down during a major marine transgression.

Westbury Formation (Wby)

This lowermost unit of the Penarth Group is 4 to 6 m thick and comprises dark grey to black, fissile, pyritous, shaly mudstones with a few thin beds of siltstone and sandstone. It has an impoverished bivalve fauna of principally Protocardia rhaetica, Rhaetavicula contorta and Eotrapezium concentricum. The ‘Rhaetic Bone Bed’ is locally present just above the base.

Lilstock Formation

Only the Cotham Member (Ctm) at mapping scale represents this formation. It is about 4 m thick, and consists of pale grey to greenish grey, silty, calcareous mudstone with small limestone nodules and a thin basal limestone. The overlying Langport Member, 0.25 m thick, is represented by a hard, pale grey micrite, which has only been recognised in the Normanton Hills railway cutting. In specimens from this locality, Swift (1995) noted the presence of conodonts and a sparse palynomorph assemblage; the latter is consistent with a position no higher than the lowest (latest Triassic) beds in the Lias Group (Warrington, personal communication in Swift, 1995).

Key locality

Chapter 7 Jurassic

Lias Group

The Lias Group (Powell, 1984) represents the main phase of a marine transgression which occurred in Lower Jurassic times across central and Southern England (Cope et al., 1980). Brandon et al. (1990) described the group and erected a formal lithostratigraphy for its various components in the East Midlands. The gently inclined rocks of this group sharply but conformably overlie the Penarth Group in three plateau-like hill cappings along the eastern periphery of this district, namely on Gotham Hill [SK 52 30], West Leake Hills to Winking Hill [SK 53 28] and Normanton Hills [SK 53 24]. The last outlier is bounded by the Normanton Hills Fault on its southern side.

Only the lowest division of the group is present and is up to 11 m thick; named the Barnstone Member (formerly Hydraulic Limestones), it forms the base of the Scunthorpe Mudstone Formation (Brandon et al., 1990). The resistance of this member to erosion probably causes the plateau surfaces to approximate to the gradational top of the member known from other areas (Brandon et al., 1990). However, a well-preserved schlotheimiid ammonite found in the northerly derived Thrussington Till at Hathern (Brandon, 1994) suggests that prior to the Anglian glaciation (see Chapter 8) higher parts of the Scunthorpe Mudstone Formation, including the Granby Member (formerly Granby Limestones), may have cropped out locally.

Barnstone Member (Bst)

This member comprises 9 to 11 m of alternating beds of grey argillaceous calcilutite limestone and grey calcareous mudstone. The upper boundary is not apparently preserved in any of the outliers. Individual beds are laterally persistent and it is estimated that limestones form about 30 per cent of the sequence; generally there are about 8 individual beds, between 0.1 and 0.3 m in thickness. Limestones in the lowest 2 to 3 m of the member are rich in shell debris, but others are markedly laminated and bituminous. The member is generally considered to be of shallow marine facies.

In the Loughborough district, as elsewhere in the East Midlands (Trueman, 1918), the lower part of the member is devoid of ammonites, although a marine bivalve fauna is present. The name ‘Pre-Planorbis Beds’ has been assigned to these strata (Trueman 1915; Kent, 1937) and remains a useful informal descriptive term. As the base of the Hettangian - hence the Lower Jurassic - in Britain is taken at the lowest occurrence of ammonites of the genus Psiloceras (Cope et al., 1980), the ‘Pre-Planorbis Beds’ are assigned to the Triassic, uppermost Rhaetian Stage. These beds are 2.92 m thick in the Normanton Hills area, where the member is at least 9.78 m thick. Typical fossils include the bivalves Liostrea spp., Modiolus minima, pectinids, Plagiostoma giganteum and Pteromya tatei and the ammonites Psiloceras spp., including P. sampsoni, and Caloceras spp.

About 9 m of these strata occur on Gotham Hill (Howard, 1989) and West Leake Hills (Carney and Cooper, 1997), but although pits in the latter area once afforded sections these are now either overgrown or infilled. There is nevertheless a thorough documentation of former exposures in quarries and along an adjacent railway cutting [SK 537 244] (the latter now much overgrown) at Normanton Hills (Fox-Strangways, 1905; Lamplugh et al., 1909; Kent, 1937; Brandon, 1994). Fox-Strangways (1905) illustrated the beds exposed in a tight syncline against the Normanton Hills Fault.

Chapter 8 Quaternary

Continued uplift of the region from the Palaeogene through into Quaternary times and the concomitant erosion led to the complete removal of all but the lowest part of the thick marine Jurassic and Cretaceous sequence that must have once covered the district. Relict patches of near-sea level early Neogene strata (Walsh et al., 1972) and a terrestrial early Quaternary mammal fauna (Spencer and Melville, 1974), preserved only in the highest karst of the Peak District, testify to the amount of uplift and erosion that has taken place. The Quaternary Period, covering the last 2 million years, was also marked in Britain by extreme oscillations of climate ranging from periods dominated by severely cold glacial and periglacial to mildly temperate conditions. These oscillations, of the order of 100 000 years periodicity, are reflected in the scheme of marine oxygen isotope (o.i.) stages to which the deposits of this district are tentatively referred (Table 4).

The oldest Quaternary sediments, consisting of till, glaciofluvial and glaciolacustrine deposits, were laid down by continental ice sheets which advanced across the district during the Anglian cold stage (o.i. Stage 12), obliterating the pre-existing drainage system. Glaciofluvial outwash during the waning phases of the Anglian glaciation initiated the present day drainage (Brandon, 1996). The valley sandar and later fluvial sediments, largely confined to flights of terraces along the main valleys, record climate change coupled with continuing uplift and lateral and vertical incision (Brandon, 1997). Towards the end of the last main cold stage, during the Late Devensian stage (o.i. Stage 2), an Irish Sea ice sheet advanced eastwards into the Trent and Dove catchments around Uttoxeter. These ice sheets were the source of the thick accumulations of outwash down river through this district.

Periglacial conditions are evidenced by widespread deposits of head, and by cryogenic disruption of earlier deposits leading to terrace cryoplanation. Flandrian (o.i. Stage 1) events are marked by fluvial incision and terracing of the outwash and coeval sediments along the major valleys. They also reflect the influence of man in causing accelerated colluviation linked to deforestation and modern farming practices, and in affecting hydrodynamic styles by the introduction of flood prevention schemes. Permanent sections in the Quaternary deposits are rare and are only mentioned in the text where they are significant.

Pre-Anglian drainage system

The main valley of this ancient system, which drained southwards into the Bytham River (Rose, 1994), was that of the Derby River (‘Proto-Derwent’), whose course is still marked by the line of the present Derwent and lower Soar valleys (Brandon, 1994, 1996, fig. 1). The Fox Hill Palaeovalley is identified as a possible relict left-bank tributary valley, extending eastwards towards Rempstone, which is partly infilled with sand (Brandon, 1994). Judging by the fall of the till base into the Black Brook (Carney, 1996c) and Kingston Brook (Carney and Cooper, 1997) valleys, these brooks may have partly re-exhumed ancient right and left bank tributary valleys of the Derby River. A possible continuation of the former into the Belton area (Ambrose and Carney, 1997b) is partly infilled with a complex of glacigenic deposits. In the south-west of the district the preglacial Lullington valley (Worssam and Old, 1988) drained northwards towards Castle Gresley where its deposits may be represented in part by sand and gravel mapped as of glaciofluvial origin (Carney, 1996a).

Older drift deposits: Anglian glaciation

The Anglian glaciation involved two principal ice sheets; a trans-Pennine ice sheet initially covered the district from the north-west, and was succeeded by the advance of a second sheet from Lincolnshire in the east and north-east. There is ample evidence for this from both within and outside the district in the form of superimposition of the two glacigenic suites. These distinct advances correspond respectively to the Thrussington and Oadby tills (Rice, 1968), both mainly representing lodgement facies, and their associated melt-out deposits. In the absence of any intervening interglacial sediments, the current consensus of opinion is that both glaciations date from the same severely cold stage (o.i. Stage 12; Bowen et al., 1999). The glacigenic deposits were once ubiquitous, veiling a previous landscape and forming a plateau lying generally above about 60 m above OD that is now much dissected by the development of a post-Anglian drainage system (Brandon, 1997). Till mapped at about 230 m above OD on Bardon Hill in Charnwood Forest, Coalville district, confirms the suggestion of Ford (1967) that ice completely overrode this hilly area. Cryoplanation and other erosive agencies have completely annihilated any glacigenic landforms that once existed. Remaining thicknesses of individual types of deposits beneath the plateau areas vary greatly from place to place but thicknesses greater than 7 m are unusual. More intact deposits are preserved in tunnel valleys (see below).

Thrussington Till

The matrix of this till is typically brown to reddish brown and is largely derived from Carboniferous and Triassic argillaceous rocks. Its stone content, like those of the associated outwash deposits, includes abundant Carboniferous sandstone, coal and limestones from the Pennine regions and Triassic rocks (particularly quartzite and quartz - ‘Bunter pebbles’). Minor constituents include igneous erratics from as far afield as Scotland and the Lake District.

The Thrussington glacigenic deposits commonly have an irregular basal contact and are characterised by wide variations in thickness; one proving in an M1 borehole [SK 4812 2157] showed 15.2 m present, but this may be exceptional. Commonly, Thrussington Till is locally preserved beneath a more extensive cover of Oadby Till: for example, on Aston Hill [SK 410 303], the Thrussington Till is partly confined to gypsum dissolution cavities beneath the Oadby Till (Brandon, 1996).

Oadby Till

The Oadby Till matrix is largely derived from Jurassic mudrocks, and is grey, weathering to brown. Its original extent was much greater than present-day outcrops suggest, since in many places, particularly the south-east of the district, outcrops of Thrussington Till are veneered by a flinty remanié deposit that indicates a former Oadby Till cover.

The typical stone suite is composed mostly of flint and chalk from the Lincolnshire Cretaceous outcrop and various limestones and fossils from the Jurassic; Gryphaea shells are particularly conspicuous. Locally, a particularly Triassic-rich till with red-brown to grey matrix occurs at the base. Mixed tills, also common at the base, were formed by the incorporation of material from the lower till. A Triassic-rich variant of the Oadby Till, consisting of a brown to red-brown clay matrix with flint, chalk and Triassic rock fragments is also present locally.

Glaciolacustrine deposits, including tunnel valleys

Glaciolacustrine deposits, representing the localised ponding of glacial meltwaters, occur sporadically within the district and are most thickly developed within deep channels, or tunnel valleys, carved by debris-laden pressurised subglacial water into the underlying bedrock. A group of four such valleys has been mapped trending roughly parallel to the present-day Trent valley (Figure 15). Numbers inside Elvaston Palaeochannel indicate height of floor of channel in metres OD." data-name="images/P946481.jpg">(Figure 14). They are typically under 1 km wide, with slightly sinuous courses and undulating bases, and cut down to below 25 m above OD locally in enclosed basins (Brandon, 1997). Their infillings are known from boreholes, and in the case of the Elvaston and Swarkestone channels from temporary sections along the Derby Southern Bypass. They comprise mainly glaciolacustrine clays and silts, commonly laminated and with channeled fluvial sand bodies, between partly slumped tills; gravels are not common.

The Stretton Palaeochannel and much of the Elvaston Palaeochannel were cut by the Thrussington and Oadby ice sheets respectively (Brandon, 1997). The Elvaston Palaeochannel is largely filled with the Findern Clay (Figure 15), a grey to brown, horizontally laminated glaciolacustrine clay with dropstones and flow tills of Oadby Till derivation. The Swarkestone Palaeochannel (Ambrose, 1997b) and possibly the Elvaston Palaeochannel in its eastern part (Brandon, 1996) are more complex and contain glacigenic suites of Thrussington and Oadby till types. The Swarkestone Palaeochannel contains a lower infill of Thrussington Till-related glacigenic deposits surmounted by a complex Oadby Till-related glacigenic sequence which shows minor thrust-imbrication in its upper part (Plate 15), in a manner suggesting glaciotectonic deformation (Ambrose, 1997b). Samples collected from the Oadby glacigenic deposits yield palynofloras appropriate to Jurassic (Toarcian–Bajocian and Callovian–Oxfordian) stages, together with Late Carboniferous (Westphalian) and Rhaetian forms (Riding, 1995). Glaciolacustrine and glaciofluvial deposits also partly infill the narrow Isley Walton Palaeochannel (Ambrose and Carney, 1997b).

Glaciofluvial deposits

Glaciofluvial deposits occur sporadically throughout all parts of the district, and are generally rather thin. They mainly represent the products of river systems originating from the melting of the ice sheets. Those occurring in association with the Thrussington Till ice sheet have a clast suite dominated by Triassic ‘Bunter’ quartz pebbles together with the more resistant Carboniferous and Triassic rock fragments.

The Hathern Gravel (Brandon, 1994) is a localised basal glaciofluvial deposit [SK 503 215] rich in Lower Carboniferous rocks that were being transported southwards along the Derby River (see above) from the Peak District. About 2.5 m of glaciofluvial sand and gravel is well exposed below the arches of the Tickow Lane bridge [SK 4629 1864], south-west of Shepshed; it consists of red to brown, medium-grained poorly sorted to cross-bedded sand with gravelly lenses containing Triassicand Carboniferous-derived clasts. Measurements of the foresets indicate currents flowing to the south-west, south-east and east-north-east, suggestive of deposition within a high sinuosity river system (Carney, 1994).

Local occurrences of glaciofluvial sand and gravel have also been mapped or proved in association with the Oadby Till. Around Belton, the Westmeadow Brook and its tributaries [SK 443 213] are flanked by deposits of flinty sand and gravel associated with glaciolacustrine deposits. The deposits are in places overlain by Oadby Till and they variably overlie or are cut into Thrussington Till or the bedrock; they are interpreted as subglacial in origin (Ambrose and Carney, 1997b).

River terrace deposits

These deposits reflect Late Anglian Trent basin initiation and later incision. They occur as parallel, sheet-like spreads of sand and gravel (Brandon, 1996, 1997), rarely more than 5 m thick, and mark periods when deposition outpaced erosion in the major valleys.

The deposits generally comprise sand-rich, matrix supported, trough cross-bedded gravels deposited on braid-plains in periglacial climates. Valley sandar of glaciofluvial origin are also included because of problems of differentiation. Terrace deposit nomenclature, correlation and tentative assignment to the o.i. stages are shown in (Table 4). The terrace form, main coarse-grained deposit, and undifferentiated deposits are named separately, as in Beeston Terrace, Beeston Sand and Gravel and Beeston Terrace Deposits.

The constructed terrace thalwegs indicate about 7 m of incision between each successive cold stage aggradation, for the rivers Derwent and Trent (Brandon, 1996, 1997). Interglacial deposits with age-diagnostic fossils are confined to bedrock-cut channels and are rarely exposed. Stone clasts derive from reworking of the older drift deposits and bedrock within the river catchment; the proportions of the main constituents vary between the valleys although ‘Bunter pebbles’ and shattered flints are always prevalent. Carboniferous limestone and chert are common in the Derwent valley, flint is particularly abundant in the Soar valley, and Charnian clasts are prominent on the terrace deposits of the Black Brook. The terrace forms are modified by later head accumulation and cryoplanation (see below). The degree of cryogenic involution (Plate 16a) generally increases with the age of the deposit; the converse is true of the degree of shattering of the flint clasts (Brandon, 1997).

The highest and most scattered terrace patches, named the Eagle Moor Sand and Gravel (Brandon and Sumbler, 1988), occur just below the Oadby Till ‘plateau’ and are thought to represent the Anglian valley sandur (o.i. Stage 12) at the initiation of the Trent valley (Brandon, 1997, 1996) although deposits reworked during o.i. Stage 10 cannot be excluded. The deposit incorporates a greater proportion of unshattered flints than the lower terrace deposits, and is composed predominantly of sand with subordinate gravel. The largest remnants occur on Willington Hill [SK 293 296] (Brandon, 1997) and at Etwall [SK 293 320] (Brandon and Cooper, 1997). Remnants of a rubified temperate palaeosol, the Hykeham Soil (Brandon and Sumbler in Bowen et al., 1999), of probable Ipswichian (o.i. Stage 5e) age subsequently cryoturbated in the Devensian (Brandon and Sumbler 1991), occur in the upper part of the Etwall Sand and Gravel and Egginton Sand and Gravel deposits of the Trent valley (Brandon and Cooper, 1997). All three of these terraces (and their deposits) were previously included within the ‘Hilton Terraces’ of Clayton (1953) and Posnansky (1960).

The most extensive surviving remnants of Birstall Sand and Gravel in the district occur along the Kingston Brook valley, from Sutton Bonington to West Leake (Carney and Cooper, 1997). Beneath the terrace of the Allenton Sand and Gravel of the Derwent valley at Allenton [SK 3707 3256] (Bemrose in Bemrose and Deeley, 1896) and Boulton Moor [SK 382 317] (Jones and Stanley, 1974), south of Derby, the Crown Inn Beds (Brandon in Bowen, et al. 1999) contain the remains of Hippopotamus amphibius and other large temperate mammalian species indicative of the Ipswichian Stage (o.i. Stage 5e). This also helps date the correlative Wanlip Sand and Gravel and the Beeston Sand and Gravel of the Soar and Trent respectively.

The Holme Pierrepont Sand and Gravel of the Trent and Dove valleys were formed as Late Devensian valley sandar from an ice front situated upriver of the district. Their base levels lie about 7 m below the present-day floodplain. Coeval periglacial braid plain deposits occur along the Derwent and Soar valleys, for example the Syston Sand and Gravel. Early Flandrian incision by anastomosing chute channels has resulted in these deposits forming dissected low terraces and isolated eyots above the Hemington Terrace Deposits.

The Hemington Terrace Deposits, of Flandrian (Recent) age, overlie either bedrock or Holme Pierrepont Sand and Gravel. Organic silts infilling shallow troughs at the base have yielded Devensian to early Flandrian pollen assemblages and radiocarbon dates in the range of 10 300 to 12 500 years (Brandon, 1996).These deposits comprise a lower layer, the Hemington Gravel and equivalents, up to 5 m thick, and an upper overbank deposit of grey and brown mottled clayey silt with stones, up to 2 m thick. The relatively thick and commonly coarse-grained accumulations formed by the combined Holme Pierrepont Sand and Gravel and the Hemington Gravel are the principal resource of aggregate in the Trent valley. Good temporary sections occur in the various pits, for example at Shardlow (Plate 16b) and Hemington (Brandon, 1996) and Barrow upon Trent (Brandon, 1997).

The Hemington Terrace is generally beyond the range of annual floods and is commonly marked by ridge and furrow and older settlements. Chute channels 60 to 200 m wide carry water across the terrace when the rivers are in spate.

Small facets of Undifferentiated River Terrace Deposits, partly underlain by sand and gravel, have been mapped along some minor valleys, e.g. along the ‘Castle Gresley’ valley (Carney, 1996a). They are probably mostly of Late Devensian age.

Head (and related periglacial features)

Head (sensu stricto; see below for colluvium) is a periglacial deposit generally formed during the Anglian–Devensian cold stages. It is an extremely widespread deposit that is important because of its commonly hazardous geotechnical properties, although it can be difficult to differentiate from other diamictons such as till deposits. It accumulated as a result of gelifluction processes and underlies extensive ‘solifluction terrace’ aprons on valley flanks.

Head is extremely variable in composition, depending on the nature of the source bedrock and superficial deposits up slope, but typically it is a stony clay-silt up to a few metres thick. Accumulations of scree-like head rich in angular Charnian clasts are extensively developed in Charnwood Forest: they are exposed as a layer, about 1 to 2 m thick, mantling Charnian and Triassic rocks at Morley Quarry [SK 4770 1786].

Although much of the surviving head is Late Devensian in age, it was a product of all periglacial periods. Older head (not generally mapped separately) can be identified since it is commonly affected by periglacial processes during later stadials, which contributed to cryoplanation of the older terrace features. Up to 3 m of head has accumulated on the backs of those river terraces at least as old as the Beeston Terrace (and equivalents). Such older head, displaying vertical stone orientation, is typically severely cryogenically involuted into the underlying sand and gravel and even bedrock (Brandon, 1997). Good sections of this older head were seen in the upper parts of the Etwall, Egginton Common and Beeston terrace deposits during construction of the Derby Southern Bypass (Brandon, 1997).

Other periglacial features observed in the district include: valley bulging and both syndepositional and epigenetic ice wedge casts affecting the Beeston Sand and Gravel in a borrow pit [SK 301 296] at Willington (Brandon, 1997); patterned ground visible from aerial photographs on the Wanlip Terrace [SK 477 278] (Brandon and Carney, 1997); roots of syndepositional ice wedge casts in pit sections of the Holme Pierrepont Sand and Gravel at Hemington [SK 464 306] and Shardlow [SK 427 309]. In the Hemington locality the ice wedge casts are truncated at the base of the Older Alluvium (Brandon, 1996). A section of cryoturbated Allenton Sand and Gravel with possible roots of ice wedge casts is exposed along the northern bank of the Derwent [SK 4280 3347], near Draycott Sewage Works.

The head mapped in strips along many minor valleys is mostly a Flandrian (or Recent) accumulation of colluvium or surface hillwash that has not reached the floodplain and been moved down valley by fluvial action. It is a variable deposit up to a few metres thick, commonly with a basal sand and gravel, and is generally sandier and lighter in texture than periglacial head which commonly underlies it.

Alluvium

This Flandrian-age deposit is widespread within the larger river valleys and their tributaries, although its area of outcrop in the main valleys has been reduced considerably as a result of this resurvey. It is underlain mainly by bedrock, Holme Pierrepoint Sand and Gravel or Hemington Terrace Deposits.

The present-day floodplains of the Trent and Soar lie 0.5 to 1 m lower than the Hemington Terrace and correspond to the water meadows or river meander belts. In this situation, the deposits of alluvium overlie bedrock and comprise up to 5 m of gravel overlain by up to 2 m of mottled grey and brown clayey silts of overbank facies. Historical artefacts, ranging from fish weirs to medieval bridges, have come to light by gravel extraction (Salisbury, 1995). Hemington Terrace Deposits and alluvium have not been mapped separately along the minor streams.

A small area of sandy and gravelly Alluvial Fan Deposits has been mapped at Stanton by Bridge [SK 370 274].

Lacustrine deposits

These deposits floor possible dissolution depressions above the gypsiferous Cropwell Bishop Formation, the largest of which is Sinfin Moor [SK 360 310] and, lying close to the eastern margin of the district, Gotham Moor. Though wide in areal extent, the deposits are thin, and under the Sinfin Moor site are up to 2.8 m thick and comprise blue or grey clay, containing molluscs, ostracods and interbedded detrital peat and sand layers. These deposits overlie a marginal gravel up to 1.2 m thick (Champion, 1969).

The south part of Sinfin Moor is occupied by up to about 2 m of dark grey clay and greenish grey sandy clay of the Older Lacustrine Deposits underlying, with a raised bedrock step, a 1 to 3 m high terrace (Brandon, 1996).

Landslips

Landslips mapped along the Kingston Brook [SK 5455 2685] may affect only superficial deposits and probably occurred from Late Devensian into Flandrian times. The landslides at Brands Hill, near Barton in Fabis [SK 532 334], occur where the Mercia Mudstone Group is overlain by till; those on Gotham Hill [SK 524 308], are developed on Mercia Mudstone overlain by the Penarth Group and Lower Lias. Fossil landslides have been mapped on the western flank of the West Leake Hills [SK 5352 2695], on an outcrop of the Penarth Group, and at Gotham Hill [SK 524 308], on Mercia Mudstone overlain by the Penarth Group and Lower Lias. On one of the steepest slopes in the district, immediately west of Hemington [SK 4540 2775], recent soil creep is indicated by terracettes. Farther west [SK 4533 2774], three prominent parallel ridges are interpreted as degraded block slides formed by the slippage of Bromsgrove Sandstone strata, resting on mudstone, close to the trace of the Normanton Hills Fault. Similarly, south of Ingleby [SK 352 267], the landslip on the north-facing escarpment developed on the Sherwood Sandstone Group has been caused by the seepage of water from above mudstone at the base of the Bromsgrove Sandstone Formation (Ambrose, 1997b). At the base of the Bromsgrove Sandstone escarpment, at Pistern Hill [SK 3587 1977], hummocky mounds are interpreted as slipped or slumped packages of Triassic strata. Marshy hollows at the base of this oversteepened scarp, and a spring issuing from near the Coal Measures/Triassic junction, suggest that water outflow may have contributed to the movement.

Chapter 9 Structure and Metamorphism

The structures of the district can be broadly divided into two categories: fundamental structures that define structural domains related to Palaeozoic deformation, and the relatively minor faults, flexures or folds that have been mapped in areas of Triassic or Jurassic outcrop. Structures relating to the domains are summarised in (Figure 16), which also shows the outcrop and inferred subcrop of the pre-Triassic rocks. They commonly either coincide with or are defined by geophysical lineaments and boundaries that are of regional importance (Lee et al., 1990, 1991), as shown by the aeromagnetic and gravity inserts on Sheet 141 Loughborough, and see Chapter 10. Such coincidence indicates that many structures mapped at the surface must also extend to deep crustal levels; they are thus considered to be the ‘posthumous’ rejuvenations of pre-existing basement discontinuities (Turner, 1949).

The orientations of the major structures shown in (Figure 16) reflect convergence between two principal systems. The northerly ‘Malvernian’ basement trends, seen mainly in the west, are inherited in part from Precambrian structures, while the north-westerly ‘Eastern Caledonide’ trends and subsidiary north-easterly cross-faults, seen farther east, largely reflect a younger, Caledonide inheritance. This fault pattern is a consequence of the district’s location astride the junction between the Midlands Microcraton and Eastern Caledonides basement provinces (Pharaoh et al., 1987a; Smith, 1987).

Pre-Carboniferous (Acadian) deformation and metamorphism

The imprint of this deformation is widespread throughout Charnwood Forest. It is correlated with the event that folded the Charnian Supergroup into a south-east-plunging anticline and imposed a pervasive transecting cleavage which cuts obliquely in an anticlockwise sense across the axis of the anticline (Figure 3). However, poor exposure precludes accurate positioning of the axial plane trace of the fold. The distribution of the principal structures in the Charnian basement is shown in Carney (1994, fig. 1).

The age of this deformation has long been controversial, because the Charnian rocks have shown a spread of radiometric (K-Ar) dates, which could be variously attributed to eruptive and deformational events in Precambrian, early and late Caledonian (Acadian) or Carboniferous times (Meneisy and Miller, 1963). BGS work currently in progress has constrained the cleavage age by utilising the more precise Ar39 /Ar40 techniques on fabric-forming mica from the Swithland Formation and ductile shear zones in Whitwick Quarry, just south of the district [SK 446 159]. The results indicate a very strong late Silurian to early Devonian imprint, suggestive of major crystallisation at the time of the Acadian (late Caledonian) orogenic event. By implication, the cleavage fabric in the Stockingford Shale Group of the Ticknall Borehole is of the same age.

On the north-eastern flank of the main Charnian anticline, a major structural belt, seen in Longcliffe and Newhurst quarries [SK 493 168]; [SK 485 177], shows asymmetric folds with amplitudes of at least 80 m and locally vertical to overturned limbs (Plate 17). The inferred tectonic transport direction deduced from the facing of these major folds was towards the north-east at Newhurst Quarry and north-west at Longcliffe Quarry; the latter orientation was possibly caused by the deflection of fold axes against the Abbot’s Oak Fault (Carney, 1994).

The main north-westerly structural grain of Charnwood Forest is cut across by post-cleavage faults that have northeasterly to northerly directions. Offsets to geological boundaries suggest both sinistral and dextral movement on these cross-faults, although there are no exposures of the fault planes. The largest cross-fault is the Abbot’s Oak Fault (Figure 3), with a dextral displacement of about 1300 m (see discussion in Carney, 1994). During this episode the Charnian structural block was uplifted, relative to the Cambrian basement seen in the Ticknall Borehole farther north, probably along major faults now concealed beneath the Trias and Carboniferous strata (Chapter 10).

Regional metamorphism, appropriate to low, high and very high epizonal (metapelitic) white mica crystallinity grades, is widely distributed in the Charnian mudrocks, as shown by Merriman and Kemp (1997). That study indicated that the highest grades, appropriate to burial at depths in excess of 12 km, occur to the north-west of the Abbot’s Oak Fault, in the core of the anticline, with a more complex pattern to the south-east of the fault. Metamorphic grades in the Cambrian-age Stockingford Shale Group of the Ticknall Borehole (Kemp, 1997) are, by contrast, diagenetic to low-anchizonal (metapelitic), considerably lower than at Charnwood as is further emphasised by the more finely crystallised microtextures in the Ticknall samples.

Within the context of a single Acadian event, it would appear that the Charnwood Forest basement sequences represent crust that was cleaved and metamorphosed during an initial phase of the Acadian orogeny that involved compression and tectonic burial. This was followed by tectonic exhumation, probably along major bounding structures such as the Thringstone Fault, as well as along the faults, shown in (Figure 16) along the northern margin of the Charnwood structural block. Evidence for major fault-controlled uplift is found in Whitwick Quarry where east-south-east-trending ductile shear zones are geometrically related to the prevailing strike of the cleavage. They are characterised by smaller grain size of the phyllonitic fabrics containing a faint mineral elongation lineation that is invariably orientated down the dips of the foliation planes. One of the Acadian recrystallisation ages mentioned above was obtained from a Whitwick Quarry phyllonite. The pre-Carboniferous age of this later uplift phase is further demonstrated by the overstep of Dinantian strata on to Charnian rocks at Grace Dieu (Chapter 4 Ticknall Limestone Formation).

Syn-Dinantian deformation

Syn-Dinantian faulting is well documented in this district, as discussed in Chapter 4. It was dominated by regional crustal extension to the north and east of the Sileby and Thringstone faults which delimit the Hathern Shelf structural province from the relatively upstanding Platform domain (Figure 6)." data-name="images/P946471.jpg">(Figure 5a). The Widmerpool Half-graben was the locus of maximum subsidence, estimated to be at least 5500 m without considering the effects of later reversals (see inset on Sheet 141 Loughborough). This subsidence was greatest in the immediate hanging wall of the graben’s south-western bounding fault system, defined by the Mackworth and Normanton Hills (Hoton) faults (Ebdon et al., 1990); (Figure 6)." data-name="images/P946471.jpg">(Figure 5a).

Along the northern margin of the Charnwood Massif, seismic reflection surveys suggest that major faults downthrowing to the north are present beneath the Trias. One of the most southerly profiles, terminating on the M1 Motorway [SK 488 197], shows reflections interpreted as a combined Dinantian/Namurian sequence (information from T C Pharaoh, BGS, 1996) thickening southwards to 1250 m only 1.7 km from the nearest Charnian exposures. This thickening may outline part of a syn-Carboniferous rollover structure, towards the major normal faults bounding the northern margin of the Charnian basement. Those faults may in turn represent the westerly extension of the Sileby fault system (Figure 16). Gravity evidence bearing on the locations of such faults is discussed in Chapter 10.

Important syn-Dinantian unconformities are displayed in Cloud Hill Quarry, Breedon (Ambrose and Carney, 1997b, fig. 3). The earliest is represented by three stratal breaks of which the most important is the Main Breedon Discontinuity, separating Early Chadian (Milldale Limestone Formation) strata from overlying, possibly Holkerian to early Asbian age, strata of the Cloud Hill Dolostone Formation (Plate18). This structure represents a hiatus of perhaps 7 to 10 Ma and is also an angular unconformity beneath which the Milldale Limestone is locally tilted to near-vertical, relative to the more gently dipping strata above. Three further lines of evidence suggest that it is also of regional distribution. First, it corresponds to a major faunal hiatus in the basinal limestone sequence of the Widmerpool Half-graben, as seen in the Long Eaton No.1 Borehole (Riley, 1997b). Second, it is in the same stratigraphical position as a major non-sequence within the graben that was correlated by Fraser and Gawthorpe (1990) with a Holkerian inversion event. Farther afield, the unconformity may also be related to the event that caused the Arundian–Holkerian erosional interval seen at Caldon Low in the Ashbourne district (Chisholm et al., 1988), 36 km to the north-west.

Folded bedding is a second major manifestation of syn-Dinantian structure at Cloud Hill Quarry. It occurs within the mudstone-rich Cloud Wood Member, in the north of the quarry, but also includes tectonic slivers of the overlying Late Asbian mud-mound reef. The folded beds comprise thrust-imbricated strata thrown into asymmetric structures (Plate 20) (GS 1023)." data-name="images/P946508.jpg">(Plate 19) facing towards the east (Ambrose and Carney, 1997b; fig. 8b). Possibly this disturbance reflects the slumping of a largely lithified sequence during a period of tectonic instability on the Hathern Shelf. In a regional context, it is noteworthy that in the Ashbourne district, Chisholm et al. (1988, p.29) described possible slumped bedding in an Asbian sequence (‘Unit D’) which rests unconformably upon the Milldale Limestone. The age of the disturbance at Cloud Hill (which is Late Asbian, the age of the mud-mound reef, or younger) could suggest it was triggered by an end-Asbian to early Brigantian phase of rifting and footwall uplift documented elsewhere within the Widmerpool Half-graben system (Ebdon et al., 1990).

Namurian to Westphalian deformation

Movements along the Widmerpool Half-graben bounding faults may have continued during the earlier part of this period, but overall the region experienced progressive subsidence. Carbonate deposition was widespread to the north and west of the Charnian structural block during the Brigantian, with strata overstepping on to the Charnian Precambrian rocks at Grace Dieu [SK 435 180]. By early Namurian times, however, much of the central and western part of the district was characterised by non-deposition, implying that it was uplifted, with Pendleian strata of the Edale Shale Group confined to the eastern and northern parts of the Hathern Shelf (Chapter 4 Edale Shale Group). Millstone Grit sedimentation did not reach the remaining parts of the Hathern Shelf until the mid-Arnsbergian, while on the Platform Province, beds no older than Kinderscoutian are present in the Rotherwood Borehole of the Coalville district (Figure 9). The deformation which characterised the post-rift tectonic environment was summarised by Fulton and Williams (1988): it involved limited faulting in response to thermal subsidence, one of the consequences, during the Westphalian, being a westwards thickening of the Coal Measures across the Boothorpe Fault/Ashby Anticline (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) and (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11). Thickening of the Millstone Grit west of the sheet margin is indicated by seismic profiles (information from T C Pharaoh). The Netherseal Fault was a possible displacement involved in this, but data for the present district is insufficient to prove this with any certainty.

Variscan inversion event

This late Carboniferous deformation (Fraser et al., 1990; Corfield et al., 1996) was a response to foreland compression occurring towards the end of nappe emplacement within the Variscan orogenic belt which at that time lay across southern Britain. It reactivated basement structures and reversed the throws of the principal Dinantian normal faults. Broad inversion anticlines formed to the north of the Mackworth and Normanton Hills fault systems (Figure 16), but deformation was more extreme along the north-west-oriented structures. A strongly asymmetric syncline developed in Coal Measures strata on the downthrown (south-western) side of the Thringstone Fault (Figure 17), which is a major reverse fault with a hade of 40o to the north-east determined from its extension in the Coalville district, farther south (Worssam and Old, 1988). Locally, the Coal Measures strata are vertical in a zone about 200 to 300 m wide on the south-western (downthrown) side of the fault, as near Thringstone [SK 420 176]. In this district, the combined throw along the Thringstone Fault and associated syncline is about 500 m down-to-the-west near Thringstone, decreasing to about 300 m just south of Ticknall. North of Ticknall, the fault is offset by easterly trending structures and its influence is considerably diminished (Figure 16).

A second major north-westerly reverse fault is the concealed, and hence largely conjectural, Breedon Fault. Evidence for its presence is provided at Breedon Hill and Cloud Hill quarries. In the latter, Dinantian strata steepen progressively eastwards to become locally near-vertical (Plate 20) or overturned, with bedding plane movements indicated by the formation of flexural-slip thrust faults (Ambrose and Carney, 1997b; fig. 3). This structural style is comparable with that described above, along the Thringstone Fault (Carney, 1996b). Spink (1965) attributed the Breedon deformation to diapirism resulting from the mobilisation of an underlying anhydrite layer. The geometrical relationship of both the Breedon and Thringstone faults to a major north-west-trending gravity boundary (inset on Sheet 141 Loughborough), however, strongly suggests a mechanism of basement-cored uplift, with lower-density crust to the east overriding a higher density gravity ‘ridge’. Seismic information further suggests that the Dinantian sequence hereabouts is little more than several hundred metres thick and, as it rests upon rigid, Cambrian basement, it is unlikely that diapirs could be developed, on the scale required.

Farther west, coalfield inversion structures summarised in (Figure 17) and (Figure 18) indicate that northerly, north-westerly and north-easterly oriented basement structures were reactivated. The principal Variscan structures include the Ashby Anticline flanked to the west by the Boothorpe Fault. The fault has an estimated minimum throw of about 260 m to the west, to which must be added at least 58 m to take account of a reversal of this throw during Triassic times (see below). A 1 km-wide, complex, north-westerly trending belt of faults and broad periclinal structures in the Coal Measures, which includes the Overseal and Mount Pleasant synclines and the Overseal Anticline, marks a major Variscan compressive zone. This is coincident with the positions of the convergent Netherseal (downthrow to the west of about 500 m), Overseal and Coton Park faults (the latter with a downthrow to the west of about 190 m). The Overseal Fault had a reversed throw in Variscan times, with an estimated displacement of 140 m down to the west when post-Triassic reactivation is taken into account. All these structures (Figure 18), and the Burton Fault (Figure 16), have northerly trends indicating they represent reactivations of deep-seated ‘Malvernian’ crustal boundaries.

Sinistral transcurrent faulting of Variscan age may be responsible for an apparent offset of the Early Chadian/ Holkerian unconformity when traced under the Triascovered area northwards from Cloud Hill Quarry in to Breedon Hill Quarry. On (Figure 16) this displacement, shown to affect the Dinantian/Namurian junction, is suggested to be along a west-north-west-trending structure representing an extension of the Derby Hills Fault, although given the lack of Carboniferous rock exposure hereabouts, other explanations are possible.

Syn-Triassic deformation

The principal movements, occurring in Scythian to Anisian or early Ladinian times, are mainly detected in the southwest. They are a response to extension and subsidence along the margin of the developing Needwood Basin (Figure 16). The Polesworth Formation forms a partial fill to a highly uneven landsurface, with tectonism suggested by attenuation of the beds over fault-blocks, of Coal Measures strata, including the horst formed by the Netherseal and Overseal faults (Carney, 1996a); (Figure 18). Northwards, along the line of the Coton Park Fault, whose Triassic throw was about 70 m to the west, the Polesworth Formation dips consistently westwards at angles of up to 22Þ, suggesting associated monoclinal flexuring (Figure 16). Along this monocline, near Burton upon Trent, the Bromsgrove Sandstone Formation oversteps the Polesworth Formation (Chapter 6 Polesworth Formation). The contact between these two units is irregular, suggesting an intervening period of intra-Triassic faulting and flexuring (Carney, 1996a), but both formations thicken to the west in response to contemporaneous subsidence and faulting (e.g. the Burton Fault) within the Needwood Basin. Movements attributed to rejuvenation of the Boothorpe Fault locally caused an angular unconformity between the Moira and Polesworth formations, as described by Brown (1889) at Swadlincote. Later in the Triassic, movement of the Boothorpe Fault is detected farther north. Boreholes showing 58 m of the Polesworth Formation immediately to the east of the fault, but none to the west, indicate a down-to-the-east Triassic movement, the reverse of the Variscan throw on the fault described above (Barclay, 1996a).

Post-Jurassic deformation

Significant post-Jurassic movements are demonstrated by flexuring and a maximum displacement of about 95 m in the Lias Group along the Normanton Hills Fault (Brandon, 1994) and, as indicated in the Leicester district (Sheet 154), along the Sileby Fault. Monoclinal flexuring along north-west and north-east axes is typical of the minor structures affecting Triassic and Lias Group strata around Gotham [SK 525 300], as indicated by gypsum mine plans (Carney and Cooper, 1997). Elsewhere, post-Jurassic deformation probably caused the northerly to west-north-westerly faulting and gentle synclinal warping of the Trias along and to the east of the Thringstone Fault, and further movements of the syn-Triassic fault systems on the northeastern Needwood Basin margin, around Burton upon Trent (Figure 1).

Palaeogene to Quaternary deformation

This is principally manifested by the flights of Anglian to Flandrian-age river terraces developed along the major drainage systems (Chapter 8 River Terrace Deposits). They are in part attributed to drainage renewal within a regime of regional uplift that can be traced at least as far back as the early Neogene (Walsh et al., 1972). That the district is not entirely tectonically quiescent is indicated by its seismicity (Chapter 12 Earthquakes). This includes one of the most damaging earthquakes to be recorded in the UK this century, the Derby earthquake of February 1957.

Chapter 10 Geophysical information on the concealed geology

The following account is largely based on the report of Cornwell and Royles (1998) which gives a review of geophysical information and previous work, accompanied by listings of physical properties for all the main bedrock and superficial units. The resulting ‘deep’ geological synthesis may be summarised by the interpretations of gravity and aeromagnetic lineaments in the district, shown in (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19).

The insets on Sheet 141 Loughborough show that the district is dominated by a north-west-trending, ridge-like Bouguer gravity anomaly. Its margins are in part delimited by the Thringstone and Breedon faults in the north-east and the Boothorpe Fault in the south-west, and it is compartmented by an east-west structure coinciding with the Barrow Fault. Combined gravity and magnetic modelling along a profile closely corresponding to the cross-section on the map (Figure 20) suggested a moderately high density (2.78 Mg/m3) for the rocks giving rise to the north-western elongated gravity high. This anomaly is bounded by well-defined linaments, in particular the Boothorpe Fault along its south-western margin, indicating deep-seated fault control. The density, shown in the model (Figure 20), ‘B1’, is about 0.08 Mg/m3 higher than the assumed background density and is the minimum realistic density to produce the contrast required. The nature of this dense basement is unknown but it could represent:

  1. Precambrian rocks. These would need to have a different overall composition to those exposed in Charnwood Forest, which generally have lower densities and are not associated with a gravity high. The data given in Cornwell and Royles (1998) suggests that a high proportion of diorite intrusions and/or slaty mudrocks would increase the average density to the value required. The lack of magnetic contrast could be explained if this high density basement overlies the deep magnetic basement.
  2. Lower Palaeozoic greywackes of the type seen in the Rotherwood Borehole (Worssam and Old, 1988). If thickly developed, these would form a sequence with the requisite high density. This alternative explains the absence of an associated magnetic anomaly but the assumed density (2.78 Mg/m3) is about the maximum expected for rocks of this type. The considerable depth (possibly in excess of 7 km) of the high density body in the profile of (Figure 20), and the low velocity (4.67 km/s) of the Lower Palaeozoic rocks in the Rotherwood Borehole, are factors that argue against this alternative.

Weaker linear gravity features coincide with the Normanton Hills and Sileby faults (respectively G9 and G5 on (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19)), and there is evidence that the Breedon Fault (a composite of G3 and G2b,d) extends south-eastwards, into the Charnian basement terrane. The distribution of Precambrian basement north of Charnwood Forest was clarified by a gravity infill survey of the area between Loughborough and Shepshed, carried out in support of this resurvey. This indicated that the Charnian, as the immediate sub-Carboniferous or sub-Triassic basement, is terminated, probably against Stockingford Shale-type Cambrian basement, along systems of intersecting north-westerly, easterly or north-easterly orientated faults, as shown in (Figure 16). Evidence supporting this is provided by seismic refraction data across the Charnian/Dinantian contact at Grace Dieu [SK 4321 1813]; the interpreted profile (Whitcombe and Maguire, 1981) showed the sudden appearance of a reflector at several hundred metres depth, attributed to the downfaulted Precambrian/Cambrian junction.

The magnetic anomaly inset on Sheet 141 Loughborough shows localised highs corresponding to shallowly buried granodiorite intrusions proved in boreholes at Rempstone [SK 5821 2405] and Kirby Lane [SK 7324 1759], to the east of the district. A further anomaly, located just beyond the south-east corner of the district, coincides with the exposed Mountsorrel granodiorite complex (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19). A late Ordovician (early Caradoc) age for the grandiorite complex is based on the rather imprecise U-Pb determination of 463 + 32 Ma obtained by Pidgeon and Aftalion (1978; value recalculated by Noble et al., 1993). In this district the prominent oval-shaped west-north-west elongated aeromagnetic anomaly centred over Diseworth is, by implication, part of the same Ordovician batholith suite (labelled MH5 on the map of Lee et al., 1991). Its northern margin may have controlled the location of the Normanton Hills Fault (lineaments G9 and M2, (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19)), which also represents the margin of the Widmerpool Halfgraben. Three-dimensional modelling (Cornwell and Royles, 1998) suggests that the Breedon and Thringstone (G2a,c; M7) lineaments have compartmented the intrusion, although equally, separate intrusions could have controlled the fault locations. Combined gravity-magnetic profiles modelled across this ‘Diseworth intrusion’ suggest it has a flat top which in places may lie at less than 1000 m depth (Figure 20).

Of the other geophysical features shown in (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19) the coincident lineaments G2a and M7, are significant in possibly representing a structure associated with the westerly pinch-out of Early Chadian strata between Breedon and Ticknall (Figure 5b) and (Figure 6). This axis may be related to the Thringstone Fault at depth, but appears to lie midway between that structure and the Breedon Fault. It may be a better choice for the western margin of the Hathern Shelf than the Thringstone Fault shown by Ebdon et al. (1990). More speculatively, it could be related to a rejuvenation of structures defining the north-eastern edge of the Midlands Microcraton, which otherwise was taken at the Thringstone Fault by Lee et al. (1990, 1991).

M1 is one of the dominant central Midlands magnetic lineaments; it represents the ‘top’ edge of a south-west dipping interface possibly extending from 3 to 12 km depth, and may be geometrically related to the other deep seated gravity lineament, G1. The latter, and parallel M6 lineament, broadly correspond to the position of the Boothorpe Fault (Figure 16). Farther west, the paired lineaments G6 and M9 coincide with the Netherseal Fault and with the western edge of the domain containing the major Variscan fault/fold zone, described above, which includes the Mount Pleasant and Overseal synclines. Compare (Figure 18) and (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19). All of these important structures are believed to reflect the rejuvenation of pre-existing discontinuities within the underlying basement.

Specific field geophysical investigations in support of the remapping (Cornwell and Royles, 1998) included gravity and resistivity surveys carried out in conjunction with shallow seismic profiling of the Black Brook Triassic palaeovalley by Dr I A Hill of Leicester University. Preliminary results indicated that in places the palaeovalley axis lay at 90 m below the present surface, and that it is infilled by up to about 50 m of Shepshed Sandstone strata (Chapter 6 Bromsgrove Sandstone Formation).

Chapter 11 Artificial (man-made) deposits

Only selected categories of man-made deposits, or ground otherwise modified by human activity, are shown on 1:50 000 Series Sheet 141 Loughborough. Descriptions of the other categories are nevertheless included in this account since they have a bearing on the local ground conditions; they are shown in their full complexity on the 1:10 000 Series map sheets upon which the 1:50 000 Series map is based. Artificial deposits are the legacy of a long history of human modification of the natural environment. They were delineated by recognition in the field and by compilations from documents including topographical maps, aerial photographs, site investigation reports and mine or quarry abandonment plans. In places where these data are absent, the boundaries shown may be imprecise.

Made ground

Made Ground represents areas where material is known to be deposited by man on the natural ground surface. The main categories include industrial sites, road and railway embankments, reservoir dams, colliery and quarry spoil, building and demolition rubble, waste from heavy industries and domestic and other waste in raised landfill sites. Made Ground is most extensive, if not ubiquitous, in the main urban centres where it is not shown on the 1:50 000 Series map. In other areas, where the topographical features associated with specific areas of Made Ground, especially colliery or quarry infill spoil, were smoothed over prior to redevelopment, the extent of Made Ground is based largely on site investigation data.

Infilled ground

This comprises areas where the natural ground surface has been removed and the void partly or wholly backfilled with man-made deposits. Mineral excavations for sand and gravel, coal, fireclay and brick clay and disused railway cuttings are to date the principal repositories for the disposal of waste materials. The latter may include excavation and overburden waste, construction and demolition waste, domestic refuse and industrial waste. Where excavations have been restored and either landscaped or built on, no surface indication of the original void may remain and their delineation relies on the availability of archival sources. During this resurvey incomplete documentation existed for many of the large restored fireclay pits between Swadlincote, Woodville and Church Gresley; these are listed in Carney (1996a).

Worked ground

This is included within the category of ‘Infilled Ground’ on the accompanying 1:50 000 Series map, but it is shown separately on the 1:10 000 Series sheets. It represents those areas where material is known to have been removed, for example in unfilled quarries and pits, road and railway cuttings and general landscaping.

Disturbed ground

Areas of Disturbed Ground are shown on the 1:10 000 Series geological maps of this district but for reasons of clarity they have been left off the 1:50 000 Series geological map. Disturbed Ground is an extremely important and locally extensive category of modified ground in this district. In the coalfield areas, it commonly encompasses ground that has experienced the effects of more than a single phase of mineral extraction, involving combinations of surface, shallow subsurface and deep underground mining techniques that have evolved over the centuries. Consequently a number of different processes contributing to ground instability may be operative within a single small area (Chapter 12 Mined ground and shafts).

Landscaped ground

This category is shown only on the 1: 10 000 Series maps. It represents areas where the original surface has been extensively remodelled, but where it is impractical or impossible to delineate areas of cut or Made Ground. Constructional developments such as housing estates, playing fields or golf courses, and most areas of urban development, are associated with Landscaped Ground.

Chapter 12 Applied geology

This chapter provides a brief overview of those earth science matters which should be taken into account during or before urban, industrial or rural planning and development processes. In the Loughborough district, the wide variety of rock types at surface or at shallow depths means that a broad spectrum of mineral resources are present, whilst considerable natural variations in ground conditions could occur over small areas; this diversity in geotechnical properties may be further exacerbated within a single rock unit by considering the superimposed effects of weathering. Geology has also played a highly significant role in the industrial expansion of Loughborough, Derby and Burton upon Trent, and the urban conurbations of the coalfields. Particularly within the coalfields, the legacy of mineral extraction by deep-mining or quarrying, and the resultant heavy industrial development, is areas of undermined, derelict and otherwise despoiled land which have their own unique and highly variable geotechnical and chemical characteristics. However, by considering the interplay between natural geological and artificial, man-made factors at an early stage in the planning process, appropriate remediation or mitigation measures can be taken prior to a site’s development. Geological and geotechnical information may also be used to identify opportunities for development, particularly in respect of leisure, recreation and protection of sites of nature conservation interest.

It should be noted that this chapter mainly collates the available earth science data of relevance to planning and development. It should be used in conjunction with, but not as a replacement to, the detailed and comprehensive development plans and specifications (e.g. for waste disposal, water supply) that are produced by the local councils (Leicestershire, Derbyshire, Nottinghamshire and Staffordshire). The topics considered in this section are:

Mineral resources

Minerals of current interest include those which can be won at or near to the surface, as the economics of underground mining are unlikely to be favourable in the near future. The main factors hindering extraction are significant thicknesses of overburden, including natural drift deposits and man-made deposits, sterilisation of resources by urban development and conflicts with other forms of land-use, and possible detrimental effects on the landscape. The extraction of mineral resources may lead to problematical engineering ground conditions, depending on infill materials and methods of compaction, and this can limit a site’s future development. Past mining activities are important for their impact on current ground conditions, and their visible surface effects have been indicated on various map editions, as discussed in Chapter 11.

Coal

Coal has long been a major resource of the district, and its extraction was undoubtedly occurring for a considerable time before the earliest mining records, for Swannington, which date to 1204 AD (Owen, 1984). Deep mining reached peak production during the mid-20th century, as documented by Owen (1984), Worssam and Old (1988) and Boucher (1994) among others, but by the late 1980s most pits were closing and at the time of the survey (1993–1996) none was producing coal. The coal is generally of high volatile, weak or non-coking type, commonly with high inherent moisture content (Coal Ranks 702, 802, 902 generally). Virtually all seams over 0.5 m thick, down to and including the Kilburn seam, have been worked at least locally, and consequently large parts of the ‘Productive Measures’ outcrop on either side of the Ashby Anticline (Figure 1) are undermined. Post-war development involved the construction of shafts and the driving of long underground drifts westwards from Castle Gresley, beneath the concealed part of the South Derbyshire Coalfield where large resources still remain.

Opencast operations at any large scale are summarised in the various reports accompanying the 1: 10 000 Series maps of the district. They date back to the 1940s, at Limby Hall and Smock Windmill [SK 414 166]–[SK 413 173], and continued through to 1960 particularly around Ashby-de-la-Zouch (Carney, 1996b). Subsequently, open casting occurred along the line of the proposed A42 [SK 382 180], with the major Lounge opencasts complex closing in 1993. Quarries open at the time of the survey include those developed in areas of industrial dereliction around Swadlincote and Moira, the largest being Nadin’s site [SK 280 195]. By contrast, the currently working Shellbrook site, immediately south of Norris Hill [SK 330 162], was opened in a ‘greenfield’ setting.

Fireclay

The Swadlincote area has been the UK’s most important fireclay producer this century. Extraction was originally closely associated with that of underground coal mining, at least since 1825 (Owen, 1984), but opencast working was well underway by the turn of the century (Fox-Strangways, 1907). This activity had greatly expanded by the time of the 1939 geological survey, as documented by Mitchell and Stubblefield (1948), and continues intermittently at the Donnington Extension [SK 3062 1760]; (Plate 11) and Albion [SK 3188 1725] sites. The resources are the seatearths occurring within the 150 m-thick ‘Pottery Clays’ formation. Mining was initially concentrated between seams P34 (Ell) and P31 (Chapter 4 Coal Measures) but nowadays strata down to the P41 seam may be worked. The fireclays were formerly used in the manufacture of clay pipes for sewage and surface-water drainage, but present uses are mainly for facing bricks, vitrified clay pipes and refractory products (Highley and Cameron, 1995). They exhibit a wide range of compositions according to Highley (1982), with a maximum of 35.6 per cent alumina proved in the Hanginghill Farm Borehole (Worssam, 1977). A detailed account of the ‘Pottery Clays’, their composition and history of mining is given in Worssam and Old (1988, p.127).

A further important source of fireclay are the Lower Coal Measures mudstones between the Woodfield and Little Woodfield seams, which were recently exploited at Bretby Brick Works [SK 279 212]. Around Ticknall and Heath End, the working of pale grey clays from the Lower Coal Measures and Millstone Grit formerly supported a local earthenware industry, but this was in decline by the late 18th century (Owen, 1984).

Brick and agricultural clay

Clay for brick-making or agricultural use was formerly worked from the Mercia Mudstone Group in numerous small pits shown on the 1:10 000 Series maps. Large operations included the Hathern brickyard [SK 515 242], but at the time of survey the only working brick pit was that of Charnwood Forest Brick Company at Shepshed [SK 4792 1796]. Other former sources of brick clay are the Millstone Grit and Moira Formation mudstones, around Derby Hills [SK 373 233], and till.

Gypsum

This has principally been worked from the Tutbury seam of the Cropwell Bishop Formation in two areas. Around Chellaston [SK 385 303] and Aston-on-Trent, alabaster-grade gypsum has been mined since the Middle Ages. Nineteenth century mining and quarrying was for both alabaster and plaster manufacture; extraction was still continuing into the 1960s but has now ceased. Comprehensive accounts of the alabaster production were given by Young (1990), and reviews of the geology, extraction history and geohazard potential of this occurrence by Cooper (1996 see also, below). In the second area, the Tutbury seam was extensively worked underground from Triassic strata underlying the Jurassic outcrops around Gotham Hill [SK 525 305] and the West Leake Hills [SK 535 285]. Much of this mining took place between 1900 and 1990 (Carney and Cooper, 1997) and has now ceased; however, a large plasterboard manufacturing complex remains at East Leake, just to the east of the district.

Crushed rock

Rock suitable for road surfacing is a major resource mainly extracted from the Precambrian intrusive and volcaniclastic rocks of the Charnian Supergroup. Its history of extraction in Charnwood was summarised by Boucher (1994) and Worssam and Old (1988), the latter giving details of physical properties. The currently working quarries of Charnwood (Longcliffe and Newhurst) and Whitwick reported an output of 900 000 and 800 000 tonnes respectively, averaged over five years from 1991 (source: Midland Quarry Products, Shepshed). Carboniferous limestone was formerly quarried from all of the inliers described earlier (Chapter 4 Hathern Shelf Sequences), particularly around Ticknall [SK 357 238], but production is now confined to the large quarries of Breedon on the Hill [SK 407 233] and Hill Cloud [SK 413 215] where material for road surfacing and ornamental gravel is extracted.

‘Lime’

Carboniferous carbonate rocks generally have a high magnesium content, those in the BGS Ticknall Borehole analysing between 10 and 18 per cent MgO (Colman, 1997). However, the equivalent strata were formerly worked for lime at Ticknall [SK 360 238] and Dimminsdale [SK 375 219]. Limestone of the Barnstone Member may have been worked for lime as well as building stone (see below).

Ironstone

Ironstone occurs as nodule-rich seams in the Lower Coal Measures; the resource was formerly worked from numerous bell-pits in South Wood [SK 363 208] and formed the basis for a local iron smelting industry with records going back to 1306 AD (Owen, 1984).

Sand and gravel

Workings to date have been mainly centred on the River Trent terrace deposits. Brandon (1996) identified an early phase of small-scale, dry extraction, dating back to the 19th century and utilising the higher terrace deposits such as the Allenton Sand and Gravel. With the recent increased demand, attention switched to the lower terraces, such as the Hemington Terrace Deposits and Holme Pierrepoint Sand and Gravel, and the floodplain gravel, which are commonly worked extensively below the prevailing water table. At present there remain a few working pits, as around Hemington Fields [SK 463 303]. Outcrops of glaciofluvial deposits have commonly been worked in the past, as have areas of weathered bedrock developed on the Bromsgrove Sandstone and Polesworth formations.

Building stone

In early times, building stone was extensively worked from a number of small quarries in the Charnian Supergroup. However, its use was strictly local, since there are few examples of Charnian building stone outside the Charnwood Forest–Shepshed–Loughborough area. Sandstone constituted a local resource around the Millstone Grit outcrop, with the Rough Rock being the principal stone worked at Melbourne Quarry [SK 382 249]. Lower Coal Measures sandstones of the Wingfield Flags were worked around Southwood House [SK 3587 2165] and in Ashby-de-la-Zouch [SK 3598 1699]. The Bromsgrove Sandstone constitutes a minor source of sand (see below) but has also locally been worked as a building stone, e.g. south of Lockington [SK 4556 2735]. Jurassic limestone of the Barnstone Member was worked from several pits, the largest being at Stonepit Wood [SK 520 301]. Around Breedon and Melbourne, Carboniferous limestone was sporadically used in buildings and walls.

Precious metals

Gold in Charnwood Forest was reported in 1880, but the first well-documented in situ find was of ‘rare filigree gold’ in a quartz vein system cutting Precambrian rocks in Bardon Quarry, in the adjacent Coalville district (King, 1967). During this survey, Colman (1997) reported up to 10 ppb Au from quartz veins in a shear zone intersected by the Morley Quarry Borehole. Gold grains panned by R C Leake during this resurvey from the Black Brook [SK 459 188], at the northern edge of the Charnwood Forest Precambrian outcrop, show a strong association with copper and silver. They may have been derived from the erosion of localised, extremely small-scale enrichments of ‘red-bed’ affinity that were formed by the action of solutions circulating at the unconformity between Charnian rocks and Triassic strata (Colman, 1997).

Base metals

Lead–zinc–(molybdenum) minerals

Lead–zinc–(molybdenum) mineralswere formerly worked underground, from shafts between Staunton Harold and Dimminsdale [SK 378 216], as documented by King (1983). Russell (in King, 1983) suggested that the orebodies occurred just above the junction between Millstone Grit and Dinantian dolostones (Carboniferous Limestone), and died out not far below this, while King (1968) stated that the mineralisation was in north-south veins within the limestone. Among the minerals listed by Ford and King (1968), and King (1982) were galena, baryte, sphalerite, pyrite, cinnabar, marcasite and a hydrocarbon compound, hosted in dolomitised limestone. The molybdenum mineral wulfenite was described from this paragenesis (King, 1978), and wulfenite with possible molybdic wad from cave-filling clays in the dolostones at Breedon Hill Quarry (King, 1991). King (1983) also noted galena in these beds at Cloud Hill Quarry: it features a skin of chalcopyrite oxidised to goethite, malachite, cuprite and native copper. Galena has also been found within basal Triassic breccia at Newhurst Quarry (King, 1983), and, in association with wulfenite, in strata of the Shepshed Sandstone Member at the former Tickow Lane Mine near Shepshed [SK 4269 1864] (King and Ludlam, 1969; King, 1983).

Copper

Copper mineralisation is of similar widespread occurrence to lead. In Cloud Hill Quarry, chalcopyrite occurs in association with galena, as described above, and also occurs locally with marcasite, calcite, baryte, aurichalcite and cinnabar (King, 1982). At Breedon Hill Quarry [SK 408 323] it occurs in calcite vein systems, or within anastomosing clayey veinlets (stockworks) in the dolostones. All of these occurrences are hosted within brecciated dolostones occupying a 100 m-wide zone to the north-west of a north-north-east-trending fault that traverses the quarry (Ambrose and Carney, 1997b, fig. 2). The open cavities, which are commonly associated with thick calcite vein systems developed around rectangular masses of bitumen-stained dolostone, are spectacularly lined by scalenohedral calcite which (Plate 21) is studded with small crystals of chalcopyrite, minor sphalerite and spherules of malachite (Colman, 1997). A limestone quarry at Calke Park [SK 370 226] was said to have yielded copper as a byproduct (Hull, 1860). Native copper was formerly revealed at Newhurst Quarry [SK 487 181], as a sheet-like body within a joint traversing Charnian rocks immediately below the Triassic unconformity (King, 1967). Close to this locality, which is also an SSSI, King and Wilson (1976) noted an occurrence of the vanadium mineral, vesigniéite, within a zone of Triassic oxidation of veins containing the primary assemblage of bornite, chalcocite and chalcopyrite. The vanadium-bearing magnetite, coulsonite, has also been described from here. Mottramite, a complex ore of lead, copper and vanadium, was described from a quartz vein in the south-west of Whitwick Quarry; it is thought to be related in age to the greenschist-facies metamorphism of the host Charnian rocks (Faithfull and Ince, 1992). During this survey, a thin Triassic sandstone bed that was heavily mineralised was recorded, intercalated in mudstones within a palaeovalley excavated at Whitwick Quarry [SK 4449 1619]. The dominant malachite surrounds masses of cuprite and tyrolite with cores of native copper (Colman, 1997). Chalcopyrite also commonly forms impregnations in the sandy matrix of Triassic breccias immediately above the unconformity in Newhurst Quarry [SK 4872 1786].

Zinc

Zinc is represented by the mineral sphalerite. In addition to its occurrence in association with copper and lead, described above, it has also been found associated with siderite in Coal Measures strata (King, 1993).

Uraniferous minerals

A uraniferous hydrocarbon compound occurring in association with galena and well-crystallised baryte was noted in the Polesworth Formation at the disused quarry at Midway [SK 3020 2080], east of Burton upon Trent (King, 1968). At Breedon Hill Quarry, a small (10 mm), grey radioactive nodule assaying more than 1 per cent uranium was found within the Triassic fill to a cave in Dinantian dolostone; the nature of the mineral species was not clear at the time of writing (Colman, 1997).

Hydrocarbons

Hydrocarbons have been the target of post-war exploration programmes involving seismic surveys across the central and eastern parts of the district, and this activity resulted in the drilling of four deep exploration boreholes (Figure 6)." data-name="images/P946471.jpg">(Figure 5a). Exploration in the East Midlands region was still in progress at the time of writing, the principal target being the thick, basinal Carboniferous sequences of the Widmerpool Half-graben (Figure 6)." data-name="images/P946471.jpg">(Figure 5a). Hydrocarbons have not yet been found in commercially exploitable amounts in the Loughborough district, but three showings of oil have been reported. These all occurred outside the Widmerpool Half-graben: in Bromsgrove Sandstone exposed in road cuttings at Winshill and Bladon [SK 2610 2327] (Fox-Strangways, 1905); within the Ticknall Limestone Formation intermittently between 137 and 176 m depth in the Worthington Borehole (Ambrose and Carney, 1997b); and in the Hathern No.2 Borehole, between 182 and 183 m depth as ‘oily matter in joints and cleats’ within strata correlated here with the Edale Shale Group (Richardson, 1931).

Groundwater

The water resources of the district are administered by the Midlands Region of the Environment Agency. The account that follows is mainly taken from the report of Lewis (1998). The regional direction of groundwater flow is north-eastward, but locally the flow reflects the surface drainage, except where affected by abstraction. The aquifers with the highest yielding sources are the river terrace deposits, the Sherwood Sandstone Group and the Millstone Grit Group. However, the outcrops of the last two aquifers are limited and abstraction, particularly from the Millstone Grit, is relatively low. In fact, the licensed abstractions indicate that nearly as much groundwater is taken from the Quaternary floodplain deposits as from the Sherwood Sandstone Group.

The floodplain gravels (e.g. alluvium and river terrace deposits), particularly those of the River Trent system, constitute major aquifers in this district. In the area around Burton upon Trent they are in hydraulic continuity with the river and yields are high, although probably at the expense of flow in the Trent. The highest yields of 20 l/s are obtained from large-diameter wells, which are up to 9 m deep, at Dove Bridge [SK 271 276]. Nearly 14 l/s was obtained in Burton upon Trent [SK 25 25] from a 240 mm-diameter borehole 7.5 m deep for a drawdown of only 1.9 m.

The Mercia Mudstone Group generally acts as an aquiclude confining groundwater in the underlying Sherwood Sandstone Group. However, thin sandstones (skerries) within the mudstone yield small supplies of up to 1 l/s of hard water. Where overlain by superficial deposits, yields from Mercia Mudstone may be augmented. Because of its large outcrop area the Mercia Mudstone is widely used for small agricultural supplies, so significant volumes are abstracted, of the same magnitude as from Carboniferous rocks.

The Sherwood Sandstone Group forms a single hydrogeological unit, the infrequent marl bands only having a limited effect on the restriction of water movement. Generally, the Polesworth Formation is a better aquifer than the Bromsgrove Sandstone Formation, due to the coarser grained and less well-cemented nature of the former. In the northern part of the district, 300 mm diameter boreholes in Sherwood Sandstone have yielded up to 30 l/s at Long Eaton [SK 4787 3380] and Chilwell [SK 5088 3506], the former from below more than 100 m of Mercia Mudstone Group. Yields of 5 to 20 l/s are more common, however. Farther south, where the aquifer thins against the Palaeozoic basement, yields decrease and several sites abstract from a combination of the Sherwood Sandstone and the underlying Moira Formation and/or Carboniferous rocks. Water levels are still above or near the surface over parts of the Trent valley. At outcrop the groundwater is of the calcium bicarbonate type, but with increasing depth of burial beneath the Mercia Mudstone Group the groundwater becomes calcium-bicarbonate-sulphate type.

The individual sandstones in the Coal Measures and Millstone Grit act as separate aquifers, with no common water table or hydraulic continuity between them except where they are brought into contact by faulting. The sandstone above the Eureka seam (‘Eureka Rock’) and the Wingfield Flags locally yield water. However, yields from the Coal Measures are generally low and the water may be of adverse chemical and bacteriological quality. In the Millstone Grit, yields in the range 4 to 8 l/s have been recorded from 150 to 250 mm-diameter boreholes intersecting one or more grits located either on the outcrop or beneath Mercia Mudstone. The highest yields are obtained from groups of wells connected by adits, which maximise the chance of intersecting water-bearing fissures; at Stanton [SK 3745 2715] one such grouping yielded 46 l/s in total. In some cases the uppermost sandstones were dry and only the lowermost sandstone (‘Bottom Grit’) yielded water, often under considerable pressure. Yields from both boreholes and springs vary seasonally and are known to dry up in summer due to the considerable annual variations in water level. Water quality is good with total hardness up to 400 mg/l (as CaCO3) and a chloride ion concentration generally less than 30 mg/l.

Groundwater quality is controlled primarily by bedrock composition but will be influenced by other factors relevant also to surface water quality. These may include sewage and/or industrial effluent, also landfill operations (particularly back-filled opencast sites), acid mine drainage (in former coalfield areas), infiltration by non-aqueous phase liquids and diffuse pollution from fertilisers and pesticides.

Groundwater vulnerability is depicted by a series of maps, at 1:100 000 scale, covering England and Wales, produced for the Environment Agency (formerly National Rivers Authority) by the British Geological Survey and the Soil Survey and Land Research Centre, Cranfield University. The concepts and rationale behind the vulnerability classification system were explained by Palmer and Lewis (1998). The Loughborough district is covered as part of maps 22 and 23 of the series.

Flooding

Flooding and surface water in general are directly influenced by geological factors. Flooding could be evaluated by the preparation of a hydrogeological map showing areas of shallow groundwater along the Trent and Soar rivers and their tributaries (e.g. Charsley et al., 1990, Map 9). Information on flood-risk boundaries is also provided by the Environment Agency at their West Bridgford office near Nottingham.

The resurvey of the 1:50 000 Series Sheet 141 Loughborough shows that the major river floodplains are dominated by River Terrace Deposits, which, being upstanding relative to the modern alluvium, consequently define areas of varying but generally lower flood frequency. The distribution of these deposits and their relationship to the micro-topography of the flood plain, should therefore form the basis of any plan to manage flood risk. This aspect of the Quaternary geology also explains why many settlements such as Shardlow [SK 435 305], the older parts of which were built on the higher ground of the Holme Pierrepont terrace, are located within the confines of the floodplain. It is noted that during the major floods of early November, 2000, all of the modern alluvium and most of the slightly higher ground formed by the Hemington Terrace Deposits (Plate 22) were inundated, as were the degraded and consequently lower edges of the Holme Pierrepont and Syston terraces.

Rising groundwater

A significant concern for the district relates to the potential pollutant and destabilising effects of rising groundwater within the mining areas of the North-west Leicestershire and South Derbyshire coalfields. General recommendations for monitoring this problem were made by Dumpleton and Glover (1995). More specifically, a study of the North-west Leicestershire Coalfield by Smith (1995) concluded that minewater has continued to rise since the last pumping ceased at Church Hill [SK 416 174] in 1989. This had possibly caused localised subsidence (see below Mining subsidence), and farmers had encountered problems during the wetter winters. It was predicted that in the near future, all surface watercourses draining to the north and north-east on the exposed coalfield are likely to be adversely affected by increased pollution. The South Derbyshire Coalfield may experience similar problems involving rising, polluted mine groundwaters, with the added possibility that these waters may travel westwards and contaminate the adjacent, lower lying Sherwood Sandstone Group aquifers around Burton upon Trent. However, there is at present no evidence for or against the hydraulic connection necessary to cause such contamination.

Ground conditions and geohazards

In considering the stability of engineering structures several geological factors, in addition to geotechnical properties, must be examined; these include local geological structure and slope stability, the possible presence of solution cavities, or, on a regional scale, earthquakes. Any of these may give rise to problematical ground conditions and geohazards which then act as a major constraint to development. Site specific investigations should always be carried out prior to development.

Geotechnical properties

The suitability of bedrock and superficial materials of the district for foundations and other aspects of construction work depends mainly on their geotechnical properties. A summary is provided in (Table 5), which is based on the findings of a more detailed report on the geotechnical aspects of this district prepared by Hobbs (1998). It is noteworthy that mudrocks of either Carboniferous or Triassic age underlie about 75 per cent of the district. These lithologies are often at most risk of weakening, either by natural agencies such as weathering and faulting, or by the effects of human activities at surface or at shallow depths. Large-scale landfill or backfill operations are common in the district, are a relatively recent development, and are likely to remain important into the future because of the massive projected increase in industrial, mining and domestic waste. Colliery fill is especially common, and has given rise to uneven settlement conditions along parts of the A42 that cross the former Lounge opencast site [SK 380 178]. Fill commonly includes chemical and organic wastes, each of which may provide difficult or sometimes hazardous conditions locally (see below Surface quarrying).

The engineering geological assessment of the superficial and bedrock units in the district was based on information abstracted from published scientific papers. No new sampling or testing was undertaken. Geotechnical coverage of geological units is generally good except for the Coal Measures mudrocks, Blue Anchor Formation, Penarth Group and Lias Group. Full details of the coverage and quality of data, the methodology used in processing the data, the limitations of results and analysis of geotechnical properties are provided in the various references given in Hobbs (1998).

Slope stability

Slope stability relates to the potential for a slope to undergo landslippage. The stability of slopes is dependent on three main factors:

Undisturbed natural slopes have generally attained a considerable degree of stability in our present climate; however, construction of any sort disturbs this equilibrium and may present problems in certain circumstances. Slopes of varying degrees of steepness characterise this district. The steeper ones include those flanking the deep valleys of Charnwood Forest and those leading down from the plateaux covered by the Jurassic Barnstone Member in the east. Farther west, locally steep slopes are developed on the Sherwood Sandstone Group capping the Coal Measures; local cliffs and bluffs flanking the southern margin of the Trent valley may also be steep.

The geotechnical properties of material at the surface in the district determines their susceptibility to mass movement. In general, mudstone and interbedded mudstone and sandstone are strong enough to sustain steep slopes without failure. Deeply weathered bedrock and material derived from it, such as head, were much weaker and have a reduced permeability. The weathered zone of slopes, and slopes mantled by Quaternary deposits, are both therefore susceptible to movement if there is 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 during the Devensian, movement may have occurred as shallow landslips or solifluction. The degraded results of these processes may be preserved unrecognised and may include relict shear surfaces which could be reactivated by loading, undercutting or excavating into slopes, or by introducing water into the slope from drains or soakaways.

Within the bedrock lithologies without significant clay, that is the Sherwood Sandstone, Millstone Grit sandstones, Dinantian carbonate rocks and Charnian Supergroup, the main modes of slope failure are by rockfall, slab displacement or undercutting of steep faces. Such types of failure are most likely to occur associated with quarrying operations, and the potential causes of failure are generally related to major planar structures such as joints, faults, bedding planes and cross-bedding.

The occurrence of landslides in the district is described in Chapter 8 Landslips. In most places natural slopes, which in this district are considerably less than 20Þ, present little hazard to development if undercutting by rivers or human agencies is avoided; however, former landslips and incipient unstable ground have been recorded from various locations. Superficial deposits such as Head, Till, and Glaciofluvial Deposits may contain internal planes of potential movement and may become destabilised if oversteepened by excavation, as would be the case with road or quarry cuttings.

Bedrock dissolution

Gypsum solution

Due to its solubility in freely flowing groundwater, extensive dissolution of gypsum has taken place within the Mercia Mudstone in a zone (the so-called solution zone) several metres thick below the base of the subsoil or superficial deposits (Elliott, 1961). Much of the solution seems to have been accomplished by groundwater flow along bedding planes, joints and fissures (Firman and Dickson, 1968). Although much of the solution of gypsum is believed to have taken place during glacial or periglacial conditions, the process may be continuing, albeit much more slowly, today (Firman and Dickson, 1968).

The outcrops of the Triassic Cropwell Bishop Formation (Figure 1), which contain the major gypsum resources of the district, represent the areas most at risk from gypsum dissolution. In borehole cores through the solution zone, gypsum is rarely encountered and voids commonly reported, whereas below the base of the solution zone, gypsum veins and nodules may constitute over 30 per cent of the total thickness in parts of the sequence. Gypsum is only rarely exposed at crop in the district, the exceptions being areas where the rate of erosion exceeds the rate of solution, for example on river cliffs (Chapter 6, Cropwell Bishop Formation) or in man-made excavations (Firman and Dickson, 1968).

The depth of the solution zone is mainly controlled by groundwater circulation conditions. Normally, the zone is only a few metres thick. However, in the vicinity of faults and heavily jointed areas, the depth of the solution zone may be as much as 30 m (Elliott, 1961). In areas where the solution zone is deep, lowering of the land surface will be enhanced due to the removal of a greater volume of gypsum from the subsurface. A major solution depression created by this process is suspected to have formed Sinfin Moor [SK 360 310] (Champion, 1969), occupied by lacustrine deposits (Chapter 8). Irregular, commonly closed depressions that cannot be explained by normal patterns of surface erosion are reported from the outcrop of the Cropwell Bishop Formation in the Nottingham district (Charsley et al., 1990) but were not convincingly demonstrated during this resurvey.

There are four possible circumstances in which gypsum solution may produce a geotechnical hazard in this area.

  1. Collapse of underground solution voids. This occurs in certain circumstances where sufficient water flow in caves and cavities can cause rapid enlargement followed by instability and collapse (Cooper, 1986). Evidence for this process in the district comes from the area around Chellaston and Aston Hill, where various cuttings for the Derby Southern By-Pass, examined at the time of survey, revealed drift-filled cavities up to 4 m diameter and at least 2 m depth. These are interpreted to have propagated upwards from the Tutbury Gypsum, about 5 m beneath (Brandon, 1996; Cooper, 1996). Cavities have also been intersected in boreholes through the Cropwell Bishop Formation in its outcrop beneath River Soar alluvium and terrace deposits, as described in Chapter 6 Cropwell Bishop Formation. There is little field evidence for subsidence hollows produced by sudden collapse on the crop of the Cropwell Bishop Formation. This could be due in part to the antiquity of such hollows, and consequent tendency for them to have been obscured by infilling drift and/or slope deposits, as noted previously.
  2. Collapse of former gypsum mine workings (see next section).
  3. Slow solution of gypsum. This process occurring beneath heavy man-made structures could cause uneven settlement resulting in damage. It is probably initiated when fibrous gypsum veins, nodules and thicker beds dissolve producing cavities or promoting water flow. The host Mercia Mudstone may become brecciated, collapse and produce ground conditions of low bearing strength. Such conditions were encountered in the ground adjacent to the Ratcliffe on Soar Power Station [SK 50 30], where dissolution of gypsum produced subhorizontal ‘gravelly’ zones in the Cropwell Bishop Formation. These zones represent the escape routes for warm water leaking from cooling ponds, and Seedhouse and Saunders (1993) predicted that excessive differential settlement of the cooling towers would occur if additional superstructure loading was carried by the existing foundations.
  4. Unconsolidated ‘pocket’ sediments. Unconsolidated sediments deposited within natural solution depressions (‘pocket’ deposits) may be highly compressible and could cause excessive, and possibly uneven, settlement leading to damage. Evidence for such deposits occurring in this district is discussed above.

Carbonate rock solution

Caves up to 60 m length, either empty or filled with Triassic calcareous mudstone and cave breccia, occur in Carboniferous dolostones adjacent to a major fault zone in Breedon Hill Quarry (Ambrose and Carney, 1997b). Carbonate breccias, attributed to cave or fissure infills, have also been observed in the old limestone quarries at Grace Dieu (Carney, 1994). The possibility that caves may exist close to the surface in the main area of limestone outcrop between Ticknall and Staunton Harold therefore cannot be entirely discounted, although none has been reported.

Mined ground and shafts

A brief history of coal and fireclay mining operations in the district and of underground gypsum extraction is given in Chapter 12. For a fuller account of the techniques likely to have been employed for coal mining, the reader is referred to Waters et al. (1996, p.44).

Coal and fireclay mining

In the Coal Measures outcrop, the various techniques of mining that have evolved over the previous eight centuries of recorded mining history (Owen, 1984) have left a legacy of complex surface modification. The most ancient examples of mining, involving the sinking of numerous bell-pits and shallow subsurface pillar and stall workings, tend to be widely distributed. The features left by them can be mapped in rural areas, and are portrayed on the 1:10 000 Series maps within the Disturbed Ground category of modified ground (Chapter 11). In addition, there are a considerable number of larger mine shafts, for which there is no documentation; the shafts were probably sunk before the middle part of the 19th century. Some of these shafts were encountered during underground mining and are depicted on mine abandonment plans. Many other, hitherto undocumented, shafts were located during this re-survey, either by direct observation in the field or from of interpretations of 1:10 000-scale colour aerial photographs. Good examples are the numerous shafts located on the 1:10 000 Series Sheet SK31NE, to the north-east of Coleorton Hall [SK 39 17]. It is stressed, however, that the accuracy, completeness or reliability of mine entry locations shown on any of these maps is limited by the amount of data available at the time of survey. For example, there are almost certainly old shafts or adits for which records were never made, or have been obscured by landscaping or urban development. The responsibility for locating and treating shafts at or close to development sites rests on the site owner or developer. Enquiries concerning the location of colliery-based mine shafts and other mine entries should be made to the Coal Authority and BGS.

Mining subsidence is likely to have been widespread throughout the crop of the Productive Coal Measures (Figure 1), which has been worked extensively down to the Lower Main Coal, and locally the Kilburn Coal of the Leicestershire Coalfield, and the Well Coal of the South Derbyshire Coalfield. Areas of visible subsidence are portrayed on 1: 10 000 Series maps of the district, as part of the Disturbed Ground category (Chapter 11).

Disturbances reflecting surface workings

Disturbances reflecting surface workings represent a complex association between ground that has been cut away and ground that has been wholly or partially infilled by a variety of materials (see also, Infilled Ground). Such areas were mostly identified in fields by observing anomalous or hummocky small-scale features, commonly associated with angular unweathered or partially weathered rock debris and man-made waste in the soil. In the Coal Measures outcrop, such ground represents mainly sites of ancient outcrop mining; it has been identified north of Lount [SK 383 194], around Heath End [SK 3715 2143], and at several other locations.

Collapse of individual mine shafts

Collapse of individual mine shafts, generally those which have been inadequately backfilled or grouted, can be sudden and catastrophic. No specific examples are known from this district, but many old and hitherto unrecorded shafts have been detected in the course of this resurvey, as mentioned earlier in this section.

Disturbances caused by shallow subsurface workings

Disturbances caused by shallow subsurface workingsare developed in areas that formerly experienced mineral extraction by the bell-pit or pillar and stall methods. They are recognised by the occurrence in fields of numerous roughly circular mounds, or by a generally uneven, hummocky type of ground. In the Coal Measures outcrop such features are commonly accompanied by angular rock waste and colliery waste in the soil, and by uneven ground which signifies localised subsidence caused by underground collapse, as seen in the area of bell-pitting around Coleorton [SK 4005 1710] and near Lount [SK 304 194]. Because the recognition of this category of ground is essentially visual, its distribution on the 1:10000 Series maps has not generally been extrapolated into adjacent sites of urban development, or beneath roads and railways, where it cannot be seen. It is nevertheless widespread in such areas; for example BGS records for the Coal Measures areas include a number of cases where cavernous ground, attributed to partially collapsed bell-pits or shallow subsurface stalls, has been encountered during site excavations, particularly in the urban areas of Swadlincote, Church Gresley and Newhall.

General ground subsidence

General ground subsidence caused by the progressive collapse of roadways and working faces in abandoned deep mines, has probably occurred throughout the undermined area on the Productive Coal Measures outcrop (Figure 1). It may still be occurring as a result of the weakening effect of rising mine groundwaters on underground workings (Smith, 1995). Examples of surface disturbance caused by subsidence-induced earth movements reactivating old fractures have been reported from the South Derbyshire Coalfield (Donnelly, 2000). They include ground in the vicinity of the Boothorpe Fault around Woodville and Norris Hill [SK 32 16], and scars and terracettes in fields on the upthrow side of the Moira Fault west of Hanging Hill [SK 3114 1658]. In fields north of Cappy Farm [SK 287 182] there are systems of well-defined escarpments, 1 to 3 m high, which broadly reflect the courses of underground roadways and mined panels depicted on local Coal Authority mine abandonment plans. They are believed to have resulted from the differential subsidence of mined areas whose boundaries were determined by fault lines in the Coal Measures (Carney, 1996a). In the Leicestershire Coalfield, Smith (1995) and Donnelly (2000) described stepped scars, which were attributed to subsidence, in fields close to the former Church Hill pumping station, Swannington [SK 416 174]. Past episodes of subsidence have permanently weakened many buildings, resulting in the programmes of demolition being carried out in Swadlincote at the time of this writing. However, subsidence may also prove to be a continuing problem in areas of the most recent mine abandonments, exacerbated by the weakening effect of rising groundwaters (Smith, 1995). Advice about subsidence in specific areas, and mine plans showing the extent of undermining, can be obtained from the Coal Authority (address on p.51).

Gypsum mining

Gypsum has principally been worked from the Tutbury seam of the Cropwell Bishop Formation (Chapter 12), around Chellaston [SK 385 303] and Aston-on-Trent, and farther east below the plateaux capped by Jurassic strata around Gotham Hill [SK 525 305] and the West Leake Hills [SK 535 285].

The development of gypsum quarries and mines in the Chellaston area is described by Cooper (1996), and several mine plans are held at BGS. The gypsum was worked from shafts or adits and quite commonly the miners followed the best stone by picking out a network of randomly orientated tunnels. Some of the workings were limited at the intersection with the water table, where dissolution of the gypsum resource would have occurred. The abandoned gypsum mines of the Chellaston area are at shallow depths and could pose stability problems in three ways:

  1. If the workings have not completely collapsed, voids at shallow depths could exist.
  2. If they have collapsed, the foundered material may be of a much lower load-bearing strength than the unaffected areas remaining over the pillars. In the latter case differential settlement may occur and provision for such eventualities should be made.
  3. In areas of old mine workings, natural gypsum dissolution could continue within the workings thus destabilising these areas in the future.

Disturbed Ground attributed to the effects of gypsum mining was observed in the vicinity of former surface workings for the exploitation of the Tutbury and Newark gypsum seams, as described around Bellington Hill [SK 4105 3046] near Aston-upon-Trent (Brandon, 1996; Cooper, 1996), and around Chellaston Hill (Ambrose, 1997b).

The extensive gypsum mines beneath Gotham Hill and the West Leake Hills followed a similar extraction pattern to that just described (Carney and Cooper, 1997). The oldest workings went in to the hillside from near the outcrop, followed the best stone and left the collapsed and mudstone-rich material as pillars. Places where very little material was left as pillars generally define the areas where later subsidence will occur. In addition to leaving small pillars, just before abandonment, some of the earlier mining companies robbed the good quality gypsum that had formed the ‘roof ballstone’, further weakening the areas of extraction. Further potential areas of subsidence are around incompletely filled shafts. The hazards posed are similar to those for collapsing coal mining shafts, but the area of collapse could be widened by enhanced gypsum dissolution due to waters ponded within the shaft. Ground subsidence due to the extraction of gypsum deposits has not been reported on any large scale for the area of undermining between Thrumpton and the West Leake Hills. Smallscale collapse around old shafts has been observed, however, as on the slopes south of Gotham [SK 5398 2870]. Similarly the collapse of ground above former shallow surface workings may have given rise to a subsidence depression, about 80 m across, next to the abandoned Cuckoo Bush Farm [SK 5330 2877], and subsidence was reported to have occurred near the former Kingston Mine Works [SK 5240 2886]. There are very few plans for the Gotham–West Leake mine workings on public file and reference to British Gypsum Ltd. should be made for further details.

In the areas of gypsum outcrop within the Cropwell Bishop Formation, natural ground subsidence is likely to occur. Its surface manifestations have proved difficult to identify in the district, in part due to later drift coverings, as described in Bedrock dissolution above. It should be noted that the extensive broad trough-shaped depression occupied by Sinfin Moor [SK 360 310] has been attributed to the effects of gypsum dissolution by Champion (1969).

Surface quarrying

There are numerous quarries and pits throughout this district. Until well into the 20th century, the surface extraction of minerals was almost entirely from a number of small operations; this pattern has changed so that present workings for sand and gravel, coal, fireclay and roadstone are centred on a few large-scale excavations. The locations of former quarries, pits and artificially dug ponds are shown mainly on the 1:10 000 Series maps and described in the accompanying Technical Reports (Table 7). Many have been backfilled, others are partially filled and degraded, some are flooded while a few remain in their quarried state with steep backwalls and limited fill in their bases. It is important to note that many former quarries, pits and ponds have been sited using BGS archives and old editions of Ordnance Survey maps but that other excavations certainly exist. The boundaries of those delineated are based on the best information available, and some are likely to be imprecise in detail. In areas where former workings are known or where a resource exists, site investigations should allow for the possible presence of backfilled excavations.

The largest and deepest of the quarries still working are those at Longcliffe [SK 492 170], Newhurst [SK 486 179] and

Whitwick [SK 448 160], exploiting Charnian Supergroup strata and Precambrian intrusive rocks (Carney, 1994), and at Cloud Hill [SK 413 215] and Breedon on the Hill [SK 407 235], in Dinantian dolostone. All extract material for hardrock aggregate.

Constraints to the further development of worked-out excavations are related to:

The increasing use of quarries and pits for waste disposal has the potential for producing 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 either with the Sherwood Sandstone aquifer or, in the case of the many sand and gravel quarries, with the major rivers or their 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 (Williams and Aitkenhead, 1991).

Leachate movement and gas emissions

The main potential hazards are associated with the formation of toxic leachates derived from landfill sites and other areas of man-made disturbance, and the incursion of methane, carbon dioxide and radon gases into buildings and engineering works.

In old or modern landfill sites with inadequate containment structures, the migration of leachate into surface watercourses and groundwater could occur where permeable geological conditions are present. These could be represented by permeable superficial deposits (e.g. Glaciofluvial Deposits, River Terrace Deposits, Alluvium) or minor aquifers (see above Groundwater), or units rendered susceptible to fluid flow as a result of faulting and/or jointing (e.g. Mercia Mudstone Group, Charnian Supergroup). Permeability may also be enhanced in mudrocks by zones of solution (e.g. caves in Dinantian carbonate rocks, or gypsum dissolution in Triassic mudrocks of the Cropwell Bishop Formation).

Leachate plumes migrate in response to groundwater flow, which may be difficult to predict in areas of faulting and complex structure, such as in the highly fractured Precambrian rock sequences of Charnwood Forest. In parts of the Coal Measures outcrop, leachate migration from landfill sites may be enhanced where conditions of rising groundwater prevail (see above).

When not properly contained, gases can migrate in response to factors such as a drop in barometric pressure, pressurisation due to rising groundwater levels, migration through permeable rocks, such as sandstone or carbonates, along open joints or fractures, faults and bedding planes, through man-made disturbances and along major faults.

Mine gas is caused mainly by the migration of methane from former coal mine workings. However, it is released only when coal seams are disrupted, either by geological disturbances, such as faults, or by mining and/or subsidence disturbance. The principal areas of coal workings prone to contamination by mine gas are the undermined areas located on the outcrop of the Productive Coal Measures (Figure 1), or in the concealed westerly extension of the South Derbyshire Coalfield.

Landfill gas is a type of bacteriological methane, formed by the biodegradation of organic matter in landfill sites under anaerobic conditions. It has a lower density than air and thus has the potential to migrate from the landfill site, both vertically and laterally. The time taken for landfill sites to completely stabilise with respect to methane varies depending upon the type of containment structures. Many modern sites pack waste material densely and contain it within impermeable barriers, venting the gas through pipes to the surface, as at the former Lounge opencast site [SK 3906 1960]. Other sites, usually not contained or vented, present a possible risk from gas or leachate migration (Williams and Aitkenhead, 1991). As a general rule none of the bedrocks of the district should be considered for the disposal of degradeable waste material without suitable arrangement for its safe containment.

Carbon dioxide is a colourless, odourless, non-combustible gas which is very soluble, forming the potentially corrosive carbonic acid. The gas has a high density relative to air, and thus tends to accumulate in low areas; it can accumulate in depressions, such as trial pits, replacing air and resulting in the potential for asphyxiation. The escape of carbon dioxide at surface and underground has been reported from near Swadlincote (Appleton et al., 1995, appendix A/83).

Higher than normal concentrations of carbon dioxide may result from the oxidation or combustion of organic materials, such as methane and coal, both from in situ coal and colliery spoil. In disused mine workings or shafts, carbon dioxide to methane ratios (expressed as a percentage) are generally less than 10 per cent. However, carbon dioxide is typically a major constituent of landfill and sewage derived gases; it commonly makes up 40 per cent of the volume of a typical landfill gas, but can vary between 16 to 57 per cent (Williams and Aitkenhead, 1991). Carbon dioxide to methane ratios from landfill sources are typically 30 per cent.

Radon (Rn-222) is a naturally occurring gas which is derived from rocks, soils and groundwater containing uranium (U) and thorium (Th). Nationally, the main areas of relatively high levels of radon are associated both with areas underlain by rocks, or their weathering products, containing enhanced concentrations of uranium, and areas underlain by permeable rocks, superficial deposits and their weathering products. For the district, natural radon levels are thought to be low, though local concentrations may occur in marine bands, coals and certain carbonaceous mudrocks of the Coal Measures and possibly the Millstone Grit. Uraniferous minerals have been found within Dinantian dolostones at Breedon Hill Quarry (Chapter 12), suggesting this as a further possible source rock for radon generation.

Radon tends to migrate from the source rocks by association with other gases, in particular methane and carbon dioxide. It may also be transported in solution, returning to a gas phase in areas of water turbulence or pressure decrease (e.g. waterfalls and springs). Radon may occur in high permeability rocks present above a source rock. High radon levels are known to occur in Coal Measures sandstones elsewhere in the country (BGS, unpublished data). Major faults can act as conduits for radon migration while impermeable surface deposits, such as till, may form a surface capping, reducing levels of radon reaching the groundsurface. Although concentrations of radon in open air normally do not present a hazard, in poorly vented confined spaces the gas can accumulate and may cause problems to individuals exposed to it for long periods of time.

Earthquakes

Earthquakes present a considerable hazard to development in certain parts of the world. In a country of low seismicity, such as Britain, much historical research is required to assess seismic risk, and this account presents the results of this research together with the record of contemporary seismicity for the region. The latter data is shown in (Table 6), with epicentres plotted in (Figure 21).

A simple guide to the degree of disturbance for each intensity of the EMS-92 (European Macroseismic Scale 1992) is as follows (after Grünthal, 1993):

1 - Not felt. 2 - Scarcely felt. 3 - Weak. 4 - Largely observed-felt indoors by many, outdoors by very few. 5 Strong - felt indoors by most, outdoors by a few. 6 - Slightly damaging-felt by most indoors and outdoors, slight damage to many buildings. 7 - Damaging-Furniture shifted, many buildings moderately damaged e.g. small cracks in wall, fallen chimneys. 8 - Heavily damaging-furniture overturned, buildings damaged with large cracks appearing in walls, partial collapse. 9–12 - Widespread devastation.

Examination of the historical database shows that the main seismic risk in the district is a repeat of the Derby earthquake of 11 February 1957. With a magnitude of 5.3 ML and maximum intensity of 6 to 7 EMS, it was one of the most damaging UK earthquakes this century and was felt over the English Midlands, and as far as Hartlepool, Pwllheli, Norwich and Topsham (near Exeter). The epicentre was located just to the north of Diseworth [SK 450 250] and the felt area was 83 000 km2 (isoseismal 3) (Dollar, 1957; Lees, 1957; Musson, 1994; Neilson et al., 1984b; Principia Mechanica, 1983). There was widespread damage to chimneys and roofs in the Derby–Nottingham–Loughborough areas. The 29 m high dam of the Blackbrook Reservoir [SK 4575 1778], about 10 km south of the epicentre, suffered the most significant damage recorded in the UK to a dam by an earthquake (Charles et al., 1991). All coping stones on the dam parapet were shaken into different positions, each weighing three-quarters of a ton. Cracks in drainage gallery and upstream and downstream dam faces were recorded, and displacements of 30 mm were recorded in the Charnian bedrock. Drainage water levels increased from 500 gallons a day to 200 000 gallons per day on the downstream side of the dam, eventually returning to normal. A magnitude 4.2 ML aftershock occurred the following day causing further damage to already weakened structures. It was felt from Hull to Gloucester and on the east coast to Norfolk. The maximum intensity was 5 EMS and the felt area was 20 000 km2 (isoseismal 3).

Examination of contemporary seismicity records for the district between 1970 and 1998 reveals that during the past 28 years only six earthquakes have occurred, all with epicentres within 10 km of the district margins (Figure 21). The most significant of these was the magnitude 3.1 ML, Nottingham event of 30 May 1984 which was felt over an area of 13 000 square kilometres with a maximum intensity of 5 EMS (Marrow, 1984), and the Nottingham event of 23 August 1984, with a magnitude of 2.2 ML. All felt areas quoted describe the area inside the isoseismal 3 contour.

None of these felt earthquakes was associated with surface rupture. In the case of the Derby earthquake, with a focus at 13 km depth, movement on a deep-seated fault controlled basement boundary is suggested to be the cause (Ambrose and Carney, 1997b). It is noteworthy that the Breedon Fault and Thringstone Fault are located 4.5 and 7.5 km respectively to the south-west of the epicentre (Figure 16), and that they represent Variscan reverse faults whose movement planes dip north-eastwards, towards the epicentre. For the Breedon Fault to be the causative displacement, a north-easterly hade of 70º would be required for the fault plane to intersect the epicentre at the required depth, with about 65º in the case of the more distant Thringstone Fault. Location errors, on the hypocentre, however, are 5 km for the epicentre location and around 5 km for the depth, making it difficult to identify the causative fault.

Linkage of the two 1984 Nottingham earthquakes to fault structures was suggested by Charsley et al. (1990). Since this district contains several basement-rooted faults, with long history of repeated movement up to and beyond Triassic or Jurassic times, further seismicity is to be expected and major structures should be engineered to take account of this. Detailed analysis of local seismic risk to major constructions can be obtained from the BGS Global Seismology Unit.

Conservation—geological sites of scientific and educational interest

Exposures of rocks and superficial deposits which can demonstrate the geology and geomorphology of the area are a considerable resource for educational and research purposes. The main way such sites can be preserved is by their being made into Sites of Special Scientific Interest (SSSI) or Local Nature Reserves (LNR).

Within the district there are two of these sites. The upper level of the north-eastern end of Newhurst Quarry [SK 488 179] is preserved as an SSSI because Triassic strata just above the Precambrian unconformity contain the rare vanadium mineral, vesigniéite (King and Wilson, 1976). Farther west, Morley Quarry [SK 4753 1798] is preserved as a Local Conservation Site of the Charnwood Borough Council. It contains an excellent section through the Ives Head Formation of Precambrian age and is one of the few places outside the working quarries where the unconformity between the Charnian and Triassic strata can be viewed.

There are many excellent geological sites in the district, some of which are not preserved or protected at present in any way. These comprise virtually all of the Charnian Supergroup exposures, described in this report and in Carney (1994). Others which are worthy of consideration, are listed below.

  1. Sections in the upper galleries of the five main roadstone quarries highlighted in under Surface quarrying.
  2. Tickow Lane bridge, Shepshed [SK 4629 1864]. Rare exposure of glaciofluvial deposits; nearby sections in Shepshed Sandstone. The entrance to a former lead mine is also located here.
  3. Roadside cuttings near Council Farm, Church Gresley [SK 2721 1930]; an exposure of the Polesworth Formation about 20 m long (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11).
  4. Cliffs on the south bank of the River Trent around Anchor Church, Ingleby [SK 3355 2710] to [SK 3440 2723]. Good, permanent sections up to 11 m high in Polesworth Formation (Brandon, 1997, p.10).
  5. Cliffs on south bank of River Trent east of Newton Solney [SK 2725 2568] to [SK 2753 2568]. Sections in Sneinton Formation; also similar beds exposed in banks of a trackway [SK 2800 2584] in the village (Brandon, 1997, p. 14).
  6. 6.Backyard of the Crown Inn [SK 3705 3256] at Allenton. Site of Derby Hippo find during excavations in 19th century (Bemrose and Deeley, 1896; Brandon, 1996, pp. 48–49). This site is of major importance for the stratigraphy of the Trent Basin Quaternary deposits and could be re-excavated.
  7. North bank of River Derwent [SK 4277 3347] to west of Draycott. Permanent section in cryoturbated Allenton Terrace Deposits on Mercia Mudstone Group, overlain by undisturbed head or later alluvium (Brandon, 1996, p. 52).
  8. Cliff [SK 4922 3046] on east bank of River Soar at Redhill Lock. Good section in Cropwell Bishop Formation including Tutbury Gypsum seam at top of section (Brandon, 1996, p.24).
  9. Carver’s Rocks [SK 3310 2265]. Exposures of the Rough Rock (Millstone Grit).

Information sources

Further geological information relevant to this district and held by the British Geological Survey is listed below. Searches of indexes to some of the data collections can be made on the computer based Geoscience Data Index in BGS libraries. The indexes which are available are:

Other items of information are available on the BGS Website (http//www.bgs.ac.uk); they include, for example, a Lexicon to which is currently being added definitions of all the named rock units in the UK.

Maps

Geological maps

Geophysical maps

Geochemical atlases

Hydrogeological map

Publications

Memoirs, books, reports and papers relevant to the district arranged by topic. Most are either out of print or are not widely available, but may be consulted at BGS and other libraries. Some of these publications are cited in the Bibliography.

British Regional Geology

Memoirs

Economic geology: coal and ironstone

Hydrogeology

Geothermal potential

Engineering and applied geology

Documentary collections

Basic geological survey information, which includes 1:10 000 or 1:10560 scale field slips and accompanying field notebooks are archived at the BGS. Charges and conditions of access to these records are available on request from the Manager, National Geological Records Centre.

Boreholes and site investigation reports

BGS holds collections of borehole records which can be consulted at BGS Keyworth, where copies of records in the public domain may be purchased. Index information, which includes site references, for these boreholes has been digitised. Summary details of the selected boreholes mentioned in this report are given in (Table 8).

Mine plans

BGS maintains a partially complete collection of plans of underground and opencast mines for coal and gypsum.

Hydrogeological data

Records of water boreholes, wells and springs and aquifer properties are held in the BGS (Hydrogeology Group) database at Wallingford.

Gravity and magnetic data

These data are held digitally in the National Gravity Databank and the National Aeromagnetic Databank at BGS Keyworth. Seismic reflection data is available for the south-western (Needwood Basin) and central (Widmerpool Half-graben and Hathern Shelf) parts of the district.

BGS Lexicon of named rock unit definitions.

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Series Sheet 141 Loughborough are held in the Lexicon database, available through the BGS Website (see below). Further information on the database can be obtained from the Lexicon Manager at BGS Keyworth.

BGS (Geological Survey) photographs.

Copies of the photographs used in this report, and of others taken during the present resurvey or previous surveys are deposited for reference in the BGS library, Keyworth. Colour or black and white prints and transparencies can be supplied at a fixed tariff.

Materials collections

Petrological collections

The petrological collections for the district consist of about 700 hand specimens and 500 thin sections. Information on the databases of rock samples, thin sections and geochemical analyses can be obtained from the group manager, Mineralogy and Petrology Section, BGS, Keyworth.

Borehole core collections

Samples have been collected from core taken from boreholes. They are registered in the borehole collection at BGS Keyworth.

Palaeontological collections

The collections of biostratigraphical specimens are taken from surface and temporary exposures, and from boreholes throughout the district. The samples are held at BGS Keyworth. Enquiries concerning all the macrofossil material should be directed to the Curator, Biostratigraphy Collections, BGS Keyworth.

Geochemical samples

A database of silicate and trace element analyses, including many from the present district, is held by the Minerals and Geochemical Surveys Division of the BGS.

Collections held outwith BGS

Coal abandonment plans are held by the Coal Authority, Mining Reports, 200 Lichfield Lane, Mansfield, Nottinghamshire, NG18 4RG.

Gypsum mine plans are held by British Gypsum Limited, East Leake, Loughborough, Leicestershire, LE12 6JQ.

Sites of Special Scientific Interest are the responsibility of the Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough, PE1 1JY.

Addresses for data sources

References

Most of the references listed below are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies of the references may be purchased from the Library subject to the current copyright legislation.

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Figures, plates and tables

Figures

(Figure 1) Simplified map of the main bedrock units and geological structures. Abbreviations: Hydrocarbon boreholes A Ashby G1, LE Long Eaton, R Ratcliffe on Soar, H Hathern, BGS stratigraphical boreholes, T Ticknall, W Worthington, M Melbourne

(Figure 2) Principal physical features and drainage of the district.

(Figure 3) Distribution of Precambrian and Cambrian rocks of the Charnian Supergroup, inferred beneath younger cover.

(Figure 4) Sections in the Ives Head Formation (a, b) and Blackbrook Reservoir Formation (c, d).

(Figure 6)." data-name="images/P946471.jpg">(Figure 5a) Distribution of inferred major Dinantian depositional provinces. Lithological summaries of the boreholes (1–5) and quarry section (Cloud Hill) are shown in (Figure 6).

(Figure 5b) Schematic cross-section along line A-B above, showing the inferred relationships between strata of the Hathern Shelf and Widmerpool Half-graben at the time of deposition of the Millstone Grit (not to scale).

(Figure 6) Correlation of Dinantian strata in boreholes and exposed sections (Cloud Hill Quarry) on the Hathern Shelf and Platform. For locations and structural setting see (Figure 6)." data-name="images/P946471.jpg">(Figure 5a).

(Figure 7) Summary of lithological and gamma-ray variations in the Ticknall Borehole [SK 3591 2363].

(Figure 8) Comparison of Carboniferous basinal sections from the Duffield and Ratcliffe on Soar boreholes. Depths are in metres from the drilling platform (data for the Duffield cored section is from Aitkenhead, 1977).

(Figure 9) Correlation of Millstone Grit strata in BGS stratigraphical boreholes. Gamma-ray profiles are shown for Rotherwood and Worthington (left); resistivity profiles for Worthington (right) and Melbourne.

(Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) Comparative sections in the Lower Coal Measures. For locations of sections see (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield).

(Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11) Comparative sections in the Middle and Upper Coal Measures, for explanation see (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10). For locations of sections, see (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield).

(Figure 12) Section in the Polesworth Formation (Sherwood Sandstone Group) exposed near Council Farm [SK 2721 1930].

(Figure 13) Lithological section, showing gamma-ray (left) and sonic log (right) profiles of the Sherwood Sandstone and Mercia Mudstone groups.

(Figure 15). Numbers inside Elvaston Palaeochannel indicate height of floor of channel in metres OD." data-name="images/P946481.jpg">(Figure 14) Palaeochannels infilled with glacigenic sediments in the Trent valley downstream of Burton upon Trent and the Derwent valley downstream of Derby. A cross-section along line A-B is shown in (Figure 15). Numbers inside Elvaston Palaeochannel indicate height of floor of channel in metres OD.

(Figure 15) An approximately east-west cross-section, A-B in (Figure 15). Numbers inside Elvaston Palaeochannel indicate height of floor of channel in metres OD." data-name="images/P946481.jpg">(Figure 14) of the Elvaston palaeochannel deposits constructed from boreholes along the Derby Southern Bypass transect. Note that intense cryoturbation and involution affects the highest parts of the infill deposits, com-prising the upper Oadby Till, Findern Clay and also the overlying Etwall Sand and Gravel and head. The vertical scale is exaggerated by 40. Numbers below the boreholes are the registered numbers in the BGS archive. In addition, the positions of a selected number of critically positioned, unregistered boreholes are indicated.

(Figure 16) Main structures, and sub-Triassic geology of the district.

(Figure 17) Coal Measures structure, North-West Leicestershire Coalfield. Stratigraphical columns in the named boreholes and shafts are given in (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) and (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11).

(Figure 18) Coal Measures structure, South Derbyshire Coalfield. Stratigraphical columns in the named boreholes and shafts are given in (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield)." data-name="images/P946477.jpg">(Figure 10) and (Figure 17) (North-west Leicestershire Coalfield) and (Figure 18) (South Derbyshire Coalfield). " data-name="images/P946478.jpg">(Figure 11).

(Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19) Interpretation of major gravity (G) and aeromagnetic (M) lineaments. The crosshatched areas within the district boundary represent the outline of the magnetic anomaly modelled as C1 (Figure 20) and interpreted as due to the ‘Diseworth’ Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998).

(Figure 20) Combined gravity and aeromagnetic (‘Gravmag’) profile along the line of crosssection A-B on (Figure 20) and interpreted as due to the �Diseworth� Ordovician intrusion. Comparable bodies to the east and south-east are the Rempstone and Mountsorrel intrusions (from Cornwell and Royles, 1998)." data-name="images/P946486.jpg">(Figure 19). Abbreviations and physical properties: NHF Normanton Hills Fault; TF Thringstone Fault; BS Breedon Structure; RBH Rotherwood Borehole.

Model

Geology

Density (Mg/m3)

Susceptibility (x 10–3 SI units)

PT

Permo-Trias

2.45

0

WN

Westphalian and Namurian

2.50

0

LC

Lower Carboniferous

2.65

0

BB

Basal Carboniferous beds

2.48

0

C

Cambrian

2.70

0

CI

Caledonian(?) Intrusions

2.70

0.013

B

Basement

2.70

0

BI

High density basement

2.78

0

MB

Magnetic basement rocks

2.73

0

(Figure 21) Distribution of earthquake epicentres in the district. The double-circle symbol south of Castle Donington represents the main shock (outer circle) and aftershock (inner circle) of the Derby earthquake of February, 1957.

Plates

(Front cover) Dinantian rocks of the Milldale Limestone Formation exposed in the face of the Breedon Hill Quarry, viewed from the east [SK 411 232]. The main pit of the quarry is below the viewing level. Breedon Hill formed a major element of the Permo-Triassic topography, before being buried by mid-Triassic strata of the Mercia Mudstone Group. The latter’s outcrop gives rise to red, clay-rich soils typified by the ploughed fields in the foreground (Photographer C F Adkin) (MN32052).

(Plate 1) Volcaniclastic strata of the Ives Head Formation at Ives Head summit. The highest crag exposes a tuffaceous sandstone turbidite bed, 2.5 m thick. It grades upwards, from a massive coarse-grained base to a middle section with parallel bedding and thence to a laminated muddy and silty top (A12332).

(Plate 2) Cademan Volcanic Breccia Member (Charnwood Lodge Formation) exposed in Grace Dieu Wood. The andesite blocks have highly angular outlines, indicating rapid deposition with a minimum of reworking. Those occurring in clusters with ‘jig-saw’ fit (as at right) represent a particularly large block that was in the process of disintegrating when the deposit came to rest (GS1004).

(Plate 3) Slabbed specimen of Peldar Dacite Breccia (JNC531) from Whitwick Quarry. The contrast is enhanced to show dark-toned areas that represent scattered, cognate fragments of porphyritic dacite with phenocrysts of euhedral plagioclase and rounded, radially fractured quartz. The paler toned matrix consists of slivers of dacite showing spherulitic texture and smaller crystals. The specimen is 10 cm wide (GS470).

(Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6) (GS 1006)." data-name="images/P946491.jpg">(Plate 4) Vertical bedding in dolostones of the Milldale Limestone Formation, exposed on the southern face of Cloud Hill Quarry. The undulating nature of individual bed surfaces may be an original depositional feature, enhanced by nonsutured stylolites developed during dolomitisation, see also (Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6) (GS1006).

(Plate 5a) Calke Abbey Sandstone Formation from the Ticknall Borehole. Stratified conglomerate from 143.4 m depth, showing separation into diffusely bounded clast and matrix-supported layers. The core section is 230 mm long (GS1007).

(Plate 5b) Calke Abbey Sandstone Formation from the Ticknall Borehole. Pedogenically modified layer from 116.7 m depth, showing silt-filled desiccation crack within a poorly sorted and probably clay-illuviated sandstone host. This core section is 100 mm long (GS1008).

(Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6) Strata of the Cloud Hill Dolostone Formation in Cloud Hill Quarry, viewed northwards, on the quarry face to the west (left) of locality ‘x’ in (Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS1009).

(Plate 7) Bedding in Cloud Hill Dolostone on the western face of Cloud Hill Quarry. Individual beds have undulating boundaries produced by nonsutured stylolites. The dark grey interbeds consist of mudstone with concentrations of bioclastic debris resulting from the stylolitisation process (GS1010).

(Plate 8) Bedding plane with Thallasinoides, taken to represent the unconformable base of the Cloud Hill Dolostone in Breedon Hill Quarry (GS1011).

(Plate 9) Ticknall Limestone Formation in former quarries at Ticknall [SK 3610 2358] showing part of a mudstone bed containing nodular masses of limestone (pale grey) (GS1012).

(Plate 10) Exposure of the Ashover Grit in a former quarry near Stanton by Bridge. Shows cross-bedded, coarse to medium-grained feldspathic sandstone deposited by currents flowing towards the north or north-west (from left to right). A coarse lag occurs at the base of a foreset near the top of the photograph (GS1013).

(Plate 11) Strata of the Middle Coal Measures, ‘Pottery Clays Formation’ in the north-east face of the Donnington Extension opencast site [SK 3064 1765]. The pale grey sandstone at the base of the section occurs just above the Aegiranum Marine Band and represents a section through the laterally-accreting bar deposit of a former river channel. It is in turn overlain by the base of another channel. The exposed shaft is probably of pre-19th century construction, with metal hoops and wooden supporting struts (GS1014).

(Plate 12) Exposure of pebbly sandstone in the Polesworth Formation, viewed in a roadside cutting near Council Farm, Castle Gresley [SK 2721 1930]. See also (Figure 12) (GS1015).

(Plate 13) Cave resulting from solution of Carboniferous dolostones, on the eastern face of Breedon Hill Quarry. The cave is filled mainly by Triassic mudstone and siltstone (red with green margins) tentatively correlated with the Gunthorpe Formation (GS1016).

(Plate 14) View of the upper western face at Cloud Hill Quarry showing the sharp unconformity between steeply dipping Carboniferous dolostones and thinly-bedded red to grey-green mudstones, siltstones and sandstones tentatively correlated with the Triassic Sneinton Formation (GS1017).

(Plate 15) Cross-bedded, medium and coarse-grained sands of probably glaciodeltaic origin exposed at a former excavation in the Swarkestone Palaeochannel [SK 389 294]. The sand-filled low angle thrust plane displacing bedding above the coin is probably a manifestation of glaciotectonic disturbance of the palaeochannel succession (GS1018).

(Plate 16a) Relationships in the River Terrace Deposits. Remanié of the Allenton Sand and Gravel forming involutions in the top of the Mercia Mudstone, as revealed in excavations for the Alvaston spur of the Derby Southern Bypass [SK 405 310] (GS1019).

(Plate 16b) Relationships in the River Terrace Deposits. Unconformity between basal gravel of the Hemington Terrace Deposits, with secondary iron staining, and underlying pinkish brown, trough cross-bedded sand and sandy gravel of the Holme Pierrepont Sand and Gravel, at Shardlow pit [SK 435 295] (GS1020).

(Plate 17) Asymmetric fold in strata of the Blackbrook Reservoir Formation in Longcliffe Quarry, viewed along the fold axis towards the south-west. Pronounced partings separate these strata into beds 2 to 3 m thick; they are interpreted as pause-planes between multiple episodes of turbiditic sedimentation. The vertical height of this exposure is 70 m and the horizontal distance across the base is about 30 m (GS1021).

(Plate 18) Strike-section in the western face of Cloud Hill Quarry showing the Cloud Hill Dolostone resting on the Main Breedon Discontinuity (sloping from left to right). The brecciated beds with subhorizontal apparent dip below the discontinuity are tentatively correlated with the Milldale Limestone Formation (GS1022).

(Plate 20) (GS 1023)." data-name="images/P946508.jpg">(Plate 19) Folding in dolostone (pale brown beds) and mudstone (dark grey beds) at the base of the Cloud Hill Dolostone Formation. This structure, and the imbrication shown in (Plate 20). Thinly bedded dolostones and red mudstones of the Cloud Wood Member show synsedimentary folding and thrust imbrication, with incorporated slivers of brecciated mud-mound reef facies dolostone (pale yellow, unbedded lensoid masses) (GS 1009)." data-name="images/P946494.jpg">(Plate 6), possibly resulted from the detachment and slumping of packages of poorly consolidated beds; the asymmetry of the fold suggests an original palaeoslope dipping to the east (from left to right). The location of this photograph is shown as ‘X’ in (Plate 20) (GS1023).

(Plate 20) Cloud Hill Quarry looking northwards, showing Dinantian rocks of the Milldale Limestone Formation (at lowermost right) with near-vertical dips (dashed line) imposed by Variscan rotation along the Breedon Fault, farther to the east (right) of this view. The Milldale Limestone is overlain along the Main Breedon Discontinuity (arrowed) by the Cloud Hill Dolostone. Location of the disturbed beds shown in (Plate 20) (GS 1023)." data-name="images/P946508.jpg">(Plate 19) is indicated by ‘X’ (MN 27976) (GS1024).

(Plate 21) Detail of a mineralised cavity in dolostones from Breedon Hill Quarry, showing scalenohedral calcite crystals encrusted with sulphide minerals that include chalcopyrite and sphalerite. This specimen measures about 80 mm across (GS1025).

(Plate 22) Aerial view taken at mid-day on the 9th November 2000, about 24 hours after the flood had peaked in this part of the River Trent. This shows the confluence between the Trent (left) and River Soar (right), looking east-south-east with Sawley Cut and marina [SK 473 311] to lower left and Ratcliffe Power Station in the background. The flooded areas include former gravel pits to the right of the marina, but are mainly on modern alluvium and Hemington Terrace Deposits. In the centre of the photograph, the green emergent areas just beyond the railway line represent the higher parts of the feature formed by the Hemington Terrace. Photo by A Forster (BGS) (GS1026).

(Back cover)

Tables

(Table 1) Geological succession of the Loughborough district

(Table 2) Lithostratigraphy of the Charnian Supergroup

(Table 3) Comparative stratigraphical terminology of the Dinantian rocks of the Breedon area.

(Table 4) Correlation of the glacigenic and fluvial deposits of the Trent, Soar, Derwent and Dove valleys. *Signifies that the terrace deposit is ascribed to an oxygen isotope (o.i.) 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. The shaded rows denote interglacial or warm interstadial periods.

(Table 5) Geotechnical data for the main geological units in the district.

(Table 6) Earthquake data recorded within or close to the district.

(Table 7) Listing of BGS Technical Reports covering individual geological 1:10 000 Series sheets in the district

(Table 8) Brief details of boreholes mentioned in this report

Tables

(Table 5) Geotechnical data for the main geological units in the district.

Engineering Considerations

Engineering Geological Units

Engineering Geological Units

Geological Units (see maps)

Description/ Characteristics

Foundations

Excavations

Engineering Fill

Site Investigation

Soils

Mixed

Loose - dense

Till (boulder clay)

Stiff/very stiff stony sandy clay, /variable

Generally good but depends on water bearing sand/ silt layers/ lenses

Diggable. Ponding of water. Short term stability good except when saturated

Suitable if selected. Laminated & high plasticity clays unsuitable

Determine depth, lithology, presence of sand / silt layers. Drilling difficult

Cohesive/ non-cohesive

Seatearth, Head

Soft-firm clay, sandy Silty clay. Highly variable (head)

Generally poor due to high variability, presence of relict shears & plasticity

Diggable

Generally poor Unpredictable properties. High plasticity

Determine thickness variation, lithologies, plasticity (Seatearth)

Soils

Soft - firm

Alluvium, Lacustrine alluvium, Glaciolacustrine deposits

Soft-firm, loose-dense, fine-coarse, clay, silt, sand, gravel

Soft, highly compressible (organic?) zones. Dense gravels good

Diggable. Poor stability. Running condition in sand and silt. Flooding hazard

Generally unsuitable

Determine depth and extent of soft, compressible zones. Probing and geophysics useful

Non-cohesive soils

Medium - Dense

River terrace deposits, Glaciofluvial deposits

Medium dense sand & gravel with laminated silts

Generally good. Variable thickness in channels

Diggable. Poor stability. De-watering may be required

Sand & gravel suitable

Determine depth and extent of buried channel infill. Geophysics may be useful

Man-made deposits

Made Ground, Infilled Ground

Highly variable in composition, depth & density

Very variable. May be very compressible. Pollution hazard

Diggable. Poor stability. Toxic/flammable gas hazard

Generally unsuitable unless inert or origin is known.

Determine depth, extent, material & source. Measure pollution

Landslide deposits

Landslide

Variable. Content as per origin but weaker; voided, saturated?

Generally unsuitable unless special measures taken to stabilise ground

Usually diggable unless large or involving rock. Support essential

Generally unsuitable

Determine extent, stability, history. Probing and geophysics useful

Rock

Weak sandstone

Mercia Mudstone Group

Very weak to strong, thinly bedded, flaggy sandstone, sand

Generally good depending on thickness, cementation, & weathering state

Generally diggable. May need ripping or breaking. Water seepage?

May be suitable as bulk fill, but uneconomic. Unsuitable as rock fill

Determine depth, weathering state. Bearing tests may be required

Strong sandstone

Coal Measures, Millstone Grit

Strong to extremely strong, thickly bedded, blocky sandstone

Good foundation. Presence of open joints, block movement possible on slopes?

Breaking or blasting required. Possible rockfall hazard

May be suitable as rock fill, but uneconomic

Determine depth, weathering state, jointing. Sampling at exposure may be required

Mudrocks

Soft - hard

Penarth Group, Lias Group, Mercia Mudstone, Coal Measures

Soft mudrock-hard clay. Fissured, jointed, shaly?. Plasticity generally low but locally high

Generally good, but variable. If high plasticity, subject to heave. Slaking on exposure. Sulphate attack on concrete

Generally diggable. May require ripping & occasionally breaking. Stability generally good

Suitable if properties known. Pyrite oxidation may cause heave, acid ground water

Determine plasticity, strength, sulphate content, presence of gypsum. Voids due to natural solution or mining

Limestones

Carboniferous Lst, Barnstone M Lst, Penarth Group

Strong to extremely strong limestone & muddy limestone

Generally good if nonvoided, non-karstic. Mining subsidence hazard

Generally requires breaking, blasting

Generally suitable. Unsuitable combined with pyritic mudrock, acid groundwater

Determine presence of voids, irregular bedrock profile, possible karstic surface

Very strong volcanic & metam. Rocks

Charnian Supergroup

Strong to extremely strong bedded volcaniclastics.

Highly jointed & faulted

Generally good. Removal of loose / weathered material may be required

Very strong, hard, abrasive. Requires breaking, blasting. Weaker near ground level

Generally suitable as rock fill, aggregate. Fault rock / shales unsuitable

Determine rock type, faulting, bedrock profile. Geophysics may be useful

(Table 6) Earthquake data recorded within or close to the district.

Year/Month/Day

Hours/minutes/seconds

Latitude

Longitude

NGR

Depth

Magnitude

Locality

Int

1893/08/04

18/01

52.72

−1.22

[SK 527 139]

10.0

3.7

Leicester

5

1940/07/14

22/09

52.69

−1.41

[SK 399 105]

3.7

Coalville

5

1956/01/10

08/01

52.72

−1.27

[SK 493 139]

4.0

3.6

Ashby

6

1957/02/11

15/03

52.82

−1.33

[SK 451 250]

13.0

5.3

Derby

6–7

1957/02/12

23/09

52.82

−1.33

[SK 451 250]

12.0

4.2

Derby

5

1984/05/30

02/53/59.4

52.87

−1.12

[SK 589 308]

17.8

3.0

Nottingham

5

1984/08/23

09/09/38.4

53.00

−1.20

[SK 535 451]

6.5

2.2

Nottingham

1984/09/19

20/17/00.5

52.71

−1.16

[SK 567 129]

1.1

1.8

Loughborough, Leics

1997/09/27

06/12/56.1

52.73

−1.14

[SK 578 152]

16.9

1.7

Loughborough, Leics

1997/12/12

10/56/40.5

52.94

−1.56

[SK 298 385]

7.3

1.7

Derby, Derbyshire

1998/04/23

04/43/29.9

52.65

−1.14

[SK 581 064]

8.7

0.9

Leicester, Leics

(Table 7) Listing of BGS Technical Reports covering individual geological 1:10 000 Series sheets in the district

Report

Map sheet (sk)/ area(s)

Authors

Special topics

WA/97/03

23SE; Etwall

A Brandon, A H Cooper

Trent terraces

WA/97/64

33SW; Littleover

A H Cooper

WA/96/07

33SE, 43SW & 43SE; Allenton, Borrowash & Long Eaton

A Brandon

Long Eaton F., Soar, Derwent & Trent terraces

WA/89/05

53SW; Attenborough

A S Howard

Penarth & Lias groups

WA/97/02

22NE, 32NW; Stretton & Repton

A Brandon

Dinantian., Widmerpool F., Edale Shale; Trent & Dove terraces, Stretton & Elvaston palaeochannels

WA/97/40

32NE; Melbourne

K Ambrose

Coal Measures, Millstone Grit, Elvaston palaeochannel

WA/96/41

42NW; Castle Donington

K Ambrose

WA/97/04

42NE; Kegworth

A Brandon, J N Carney

Trent & Soar terraces

WA/97/46

52NW; West Leake

J N Carney, A H Cooper

Long Eaton F., Widmerpool F., Edale Shale, Penarth & Lias Groups

WA/96/77

22SE; Winshill-Newhall

W J Barclay

Coal Measures (S. Derbyshire) Dinantian, Millstone Grit

WA/96/78

32SW; Hartshorne

W J Barclay

Coal Measures (S. Derbyshire)

WA/97/17

32SE; Calke Abbey

K Ambrose, J N Carney

Cambrian, Dinantian, Millstone Grit, Coal Measures (NW Leicestershire)

WA/97/42

42SW; Breedon

K Ambrose, J N Carney

Dinantian, Millstone Grit, Coal Measures

WA/96/100

42SE; Long Whatton

J N Carney

WA/94/60

52SW; Normanton on Soar

A Brandon

Hathern Anhydrite, Dinantian, Widmerpool F., Edale Shale, Soar terraces

WA/96/11

31NW, 21NE; Swadlincote & Church Gresley

J N Carney

Cambrian, Dinantian, Millstone Grit, Coal Measures (S. Derbyshire)

WA/96/02

31NE; Ashby-de-la-Zouch

J N Carney

Millstone Grit, Coal Measures (NW Leicestershire)

WA/94/08

41NW, 41NE & 51NW; Thringstone, Shepshed & Loughborough

J N Carney

Precambrian, Dinantian, Millstone Grit, Coal Measures (NW Leicestershire)

(Table 8) Brief details of boreholes mentioned in this report. * denotes borehole drilled by BGS

Borehole/Shaft Name

NGR (SK)

BGS Number (SK)

Depth (m)

Ashby G1 Hydrocarbon

[SK 3134 2524]

(SK32NW/42)

288.9

Belton

[SK 4437 1957]

(SK41NW/46)

81.4

Cadley Hill

[SK 2775 1887]

(SK21NE/14)

541

Caldwell Hall

[SK 2532 1721]

(SK21NE/26)

708.7

Caldwell No.2

[SK 2568 1672]

(SK21NE/25)

481.6

Chilwell Shell-filling factory

[SK 5059 3431]

(SK53SW/64)

119.3

Central Ordnance Depot, Chilwell

[SK 5090 3501]

(SK53NW/373)

61.6

Coton Park Colliery No.2

[SK 2732 1792]

(SK21NE/33)

232.6

Dole’s Farm

[SK 3797 1830]

(SK31NE/2)

193

Ferrer’s Opencast Site

[SK 3887 2039]

(SK32SE/26)

88.4

George Inn

[SK 4076 1726]

(SK41NW/37)

221

Granville Colliery No.2

[SK 3070 1907]

(SK31NW/1)

357.2

* Hanginghill Farm

[SK 3135 1672]

(SK31NW/141)

155.7

Hathern No.1 Hydrocarbon

[SK 5158 2416]

(SK52SW/3)

634.59

Hathern Brickyard No.2

[SK 515 241]

(SK52SW/1b)

184.4

Long Eaton No.1 Hydrocarbon

[SK 4640 3166]

(SK43SE/161)

2747.25

Matts Yard Coliery

[SK 2882 2107]

(SK22SE/18)

482.5

* Melbourne

[SK 3820 2374]

(SK32SE/39)

169.1

* Morley Quarry

[SK 4765 1787]

(SK41NE/30)

835.5

New Lount Colliery

[SK 3996 1848]

(SK31NE/14)

137

Ratcliffe on Soar Hydrocarbon

[SK 5081 2913]

(SK52NW/72)

2242

Rawdon Pit Shaft

[SK 3127 1626]

(SK31NW/30)

331

Swannington Colliery

[SK 4203 1694]

(SK41NW/26)

232.6

* Ticknall

[SK 3591 2363]

(SK32SE/103)

209.04

* Worthington

[SK 4045 2104]

(SK42SW/204)

179