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Geology of the Melton Mowbray district. Sheet Description of the British Geological Survey, 1:50 000 Series Sheet 142 (England and Wales).

By J N Carney, K Ambrose, A Brandon, M A Lewis, C P Royles, T H Sheppard

Bibliographical reference: Carney, J N, Ambrose, K, Brandon, A, Lewis, M A, Royles, C P, and Sheppard, T H. 2004. Geology of the country around Melton Mowbray. Sheet Description of the British Geological Survey, 1:50 000 Series Sheet 142 (England and Wales).

Geology of the Melton Mowbray district. Sheet description of the British Geological Survey 1:50 000 Series Sheet 142 Melton Mowbray (England and Wales)

• Authors: J N Carney, K Ambrose, A Brandon, M A Lewis, C P Royles, T H Sheppard^‡1 
• Contributors:
• Stratigraphy and structure: T J Charsley, R G Crofts, A S Howard, D J Lowe, M Shaw, M G Sumbler
• Sedimentology: C R Hallsworth
• Biostratigraphy: B Cox, I Wilkinson, N J Riley, G Warrington
• Seismic interpretation and deep structure: T C Pharaoh
• Hydrogeology: M A Lewis
• Engineering Geology: A Forster
• Clay Mineralogy: S J Kemp

Keyworth, Nottingham: British Geological Survey 2004. © NERC 2004. All rights reserved ISBN 0 85272 489 6

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Licence No: 100017897/2004. Maps and diagrams in this book use topography based on Ordnance Survey mapping.

Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

British Geological Survey. Parent Body: Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU

(Front cover) Belvoir Castle stands on a small outlier of Lower Jurassic strata, the Dyrham Formation underlies the middle and lower slopes, and the Marlstone Rock Formation forms the top of the hill. The walls of the castle are built largely of ‘Sandrock’, a ferruginous sandstone bed that is widely developed at the top of the Dyrham Formation. View from the northwest [SK 820 337] (Photographer Caroline Adkin; MN39938).

(Rear cover)

Acknowledgements

This report describes the geology of the district covered by the 1:50 000 Series Sheet 142 Melton Mowbray (solid and drift). A shorter account is given in the Sheet Explanation that accompanies the map. The report was compiled by J N Carney, who also wrote the sections on the Ordovician and Dinantian strata, structure, mineral resources, and applied geology. The Permian chapter was written by K Ambrose, who also contributed, together with H Sheppard and J N Carney, to the Westphalian section. K Ambrose and J N Carney wrote the Namurian and Penarth Group sections, and A Brandon wrote the Jurassic and Quaternary chapters. This account draws heavily on the BGS Technical Reports (Table 12) that accompany each of the 1:10 000 series map sheets. N J Riley was responsible for Carboniferous faunal identifications. Heavy mineral studies were carried out by C R Hallsworth (Millstone Grit Group, Lower Coal Measures) and R W Knox (Triassic sandstone). Petrography of the Marlstone Rock was studied by R W Knox and G K Lott, and Triassic clay mineralogy by S J Kemp. T C Pharaoh provided interpretations of seismic lines, both to assist the mapping and to synthesise the shallow structure. C P Royles evaluated gravity and aeromagnetic data, including recently acquired High-Resolution airborne geophysical data, bearing on the deep geophysical structure of the district. Other contributors include A Forster (landslip) and M A Lewis (hydrogeology). The report was reviewed by N J Riley (Carboniferous), G Warrington (Permian and Triassic) and A Forster (Applied Geology). The manuscript was edited by A A Jackson; figures were drawn by R J Demaine, P Lappage and G Tuggey, BGS Cartography, Keyworth.

The cooperation of landowners and tenants in permitting access to their land is gratefully appreciated. English Nature is thanked for allowing us access to the Brown’s Hill (Holwell) SSSI. We acknowledge all those who permitted the transfer of their data records to the National Geological Records Centre, BGS Keyworth. We are especially grateful to RJB Mining (UK) Ltd for use of borehole and other interpretative data relevant to concealed strata in the Vale of Belvoir prospect. Severn-Trent Water and numerous civil engineering consultants are also thanked for their contributions of data.

Notes

Throughout this report the word ‘district’ refers to the area covered by the geological 1:50 000 Sheet 142 Melton Mowbray. The district is covered by twenty-eight 1:10 000 series maps, or part-maps, each of which is given a geographical name for ease of reference. The codes for geological units shown on the map face are indicated in parenthesis where first introduced in the text.

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

Borehole records referred to in the text are generally given a geographical name. Locations, terminal depths and BGS registered numbers are given in (Table 13).

Numbers quoted in brackets in the plate captions refer to the BGS collection of photographs. Numbers preceded by the letter E refer to the BGS sliced rock collection.

Geology of the Melton Mowbray district—summary

The bedrock of the Melton Mowbray district consists of Triassic and Jurassic strata, which are partially covered by Quaternary Superficial Deposits. Insets on the geological Sheet 142 Melton Mowbray show additional information on the concealed rocks, complemented by the results of seismic reflection profiling, and the geophysical (gravity and magnetic) properties of the geological ‘basement’.

The concealed geology of the district is described in much greater detail than before, because of the availability of information from coal and hydrocarbon exploration boreholes. These data show that the oldest proven rocks comprise late Ordovician granodiorites, representing intrusions into the lower Palaeozoic and/or Precambrian ‘basement’ of the area. They were partly unroofed by erosion later in the Palaeozoic, and are either faulted against or unconformably overlain by Carboniferous strata.

The concealed sedimentary sequence commences with Lower Carboniferous (Dinantian) strata deposited during a time of extension-induced subsidence of the East Midlands crust. Seismic investigations have shown that these strata attain 3500 m thickness in the southern part of a syn-Dinantian asymmetric rift structure, the Widmerpool Half graben (or ‘gulf’). The succeeding Namurian strata, comprising the prodelta facies Edale Shale Group and deltaic sandstones and mudstones of the Millstone Grit Group, were deposited when fault-induced subsidence had largely ceased. A wide delta plain had been established by Westphalian times, on which was accumulated the Coal Measures Group of the concealed Vale of Belvoir (Northeast Leicestershire) Coalfield. During deposition of the Lower Coal Measures, sediment transport paths were modified by the effusion of alkali olivine-basalt lavas and their associated volcaniclastic products in the east and south of the district. Later in the Westphalian, earth movements initiated a change to better drained, alluvial conditions reflected by the red beds of the Warwickshire Group, restricted to the east of the district.

Variscan faulting and block uplift inverted the Coal Measures basin and ushered in a 50 million year period of erosion. By latest Permian times, however, aggradation had commenced, depositing a thin sedimentary veneer that includes the Cadeby and Edlington formations. The overlying basal Triassic strata are of fluviatile origin and constitute the regionally important aquifer of the Sherwood Sandstone Group. They are in turn succeeded by the Mercia Mudstone Group, deposited in arid, aeolian and playa lake environments, with locally thick gypsum seams that have been mined underground. Continental sedimentation was brought to a close by the marine transgression that deposited the Rhaetian-age mudstones and siltstones of the Penarth Group. Fully marine conditions were established at the start of the Lias Group, in latest Triassic to early Jurassic times, when the district lay within a relatively stable area known as the East Midlands Shelf. The Scunthorpe Mudstone and Charmouth Mudstone formations are shallow-water marine associations characterised by slow deposition and consequent reworking suggested by the phosphatisation of some ammonites and the boring of phosphate nodules. Intercalated bioclastic limestones are nevertheless indicative of periodic higher energy environments. The overlying Dyrham Formation contains more sandy or silty detritus, and it is capped by the ironstone-rich Marlstone Rock Formation deposited under high energy conditions during a marine regression. There was a return to relatively deeper marine environments during deposition of the Whitby Mudstone Formation, but further uplift brought a change to marginal-nonmarine conditions represented by the Middle Jurassic Northampton Sand Formation. A marine barrier bar-lagoonal complex was subsequently established, and peloidal limestones of the Lincolnshire Limestone Formation were deposited, the youngest bedrock unit of the district.

The oldest representatives of the Quaternary (Superficial Deposits) occur in the south of the district, as the sands and gravels of the preglacial Bytham River Basin, the course of which was partly coincident with that of the present-day Wreake valley. The Anglian glaciation that followed produced a reasonably coherent stratigraphy of deposits across the district. The principal varieties of lodgement till are a red, north-westerly derived till bearing Triassic and Carboniferous fragments, a grey till of eastern derivation with flint and chalk, and a till containing no flint or chalk but with abundant Jurassic limestone fragments. Interleaved with these deposits are layers or lenses of glaciofluvial sand and gravel, and glaciolacustrine clay. Sustained uplift through the later part of the Anglian stage, and into the Flandrian, resulted in at least five generations of river terrace deposits in the trunk valleys of the Soar and Wreake rivers. These deposits constitute an aggregate resource and are also local suppliers of water in the district. The Quaternary evolution of ‘clay vales’, such as the Vale of Belvoir and the Stapleford vale south-east of Melton Mowbray, was dominated by successive episodes of periglacial slope wasting. The resultant landforms are plano-concave solifluction terraces, underlain by head deposits that are collectively termed ‘Slope Terrace Deposits’ on the map. Features related to modern slope instability are extensive tracts of landslipped ground along the (mostly) north-facing escarpments developed mainly on Jurassic mudstone. Of the younger Quaternary deposits, colluvium, head and floodplain alluvium are locally extensive and there are small occurrences of blown sand, shell marl and lacustrine deposits.

Current mineral production comes from deposits of glaciofluvial and river terrace sand and gravel, and the underground mining of gypsum from adits at Barrow upon Soar. Coal was formerly mined from Cotgrave and Asfordby and large deposits remain unexploited. Oil is currently being produced from wells at Rempstone and Long Clawson. The concealed Carboniferous succession is locally very thick and the district continues to present favourable targets for hydrocarbon exploration.

(Table 1) Summary of the geological succession of the Melton Mowbray district. Thickness range shown in brackets.

Chapter 1 Introduction

The district lies mainly within the Leicestershire, Nottinghamshire and Rutland administrative areas, but its extreme north-eastern corner also includes a small part of Lincolnshire. Melton Mowbray is the main town, and there are smaller population centres at Keyworth, Barrow upon Soar, Ruddington and Clifton. Outside of these, the land is given over to arable and livestock farming, the latter particularly important on the flood-prone valley floors of the rivers Soar and Wreake (Figure 1), (Figure 2).

About 450 million years of geological history are represented, by the rocks that form the succession summarised in (Table 1). The distribution of the outcropping rock sequences is indicated in (Figure 1), which also highlights those units of particular economic or environmental significance. These include, for example, the Cropwell Bishop Formation, which locally contains thick gypsum beds, and the Barnstone Member and Marlstone Rock Formation which have been mined at the surface and at shallow depths.

The oldest elements of the concealed geology, proved by drilling, are the Rempstone Granodiorite and the Melton Mowbray Granodiorite, both of Ordovician age. These rocks are the sources of coincident aeromagnetic anomaly ‘highs’ representing extensive intrusions into the Precambrian and Early Palaeozoic basement of the district. These basement rocks are unconformably overlain by Lower Carboniferous (Dinantian) strata, which were deposited on shelf areas and intervening deep basins, the latter represented by the Widmerpool Half-graben, a major asymmetric rift structure. The oldest proven component of the rift-fill consists of clastic sedimentary rocks of the Scalford Sandstone Formation. On the shelf, carbonate ramp facies are represented by the Milldale Limestone Formation, Belvoir Limestone Formation and Plungar Limestone Formation, whereas the Widmerpool Formation is of basinal turbidite facies. The Dinantian syn-rift sequence as a whole is of considerable economic importance since it provided a source for much of the oil that is currently being extracted from the Rempstone-1 and Long Clawson-2 wells. The overlying Namurian strata, of the Edale Shale Group and Millstone Grit Group, filled the remaining accommodation space in the Widmerpool Half graben; they provide both the cap-rocks and reservoirs to many oil showings in the East Midlands hydrocarbon province. By Westphalian times the Coal Measures Group was being accumulated within a gently subsiding delta plain that occupied virtually the whole of the Pennine Basin. The seams of the Vale of Belvoir Coalfield constitute a large potential resource. Sedimentation in the Lower Coal Measures was interrupted by alkali-olivine basalt magmatism, represented by intrusive peperites of the Asfordby Volcanic Formation, and by the Saltby Volcanic Formation, the latter an extrusive association supplied from centres to the east of the district. This activity had largely ceased by earliest Middle Coal Measures times, although the latter strata and the Upper Coal Measures both show an eastward attenuation across the buried volcanic pile. Local tectonism and uplift produced a major environmental change, to the accumulation of the Warwickshire Group red beds, which are largely barren of coal seams.

Variscan uplift inverted the coal basin, exposing the strata to erosion that spanned most of the Permian period. Sedimentation was resumed in latest Permian times with the deposition of calcareous sandstones of the Cadeby Formation and mudstones in the Edlington Formation. The Triassic period commenced with a major fluvial episode, depositing strata of the Sherwood Sandstone Group.

Red, argillaceous, continental-facies strata of the overlying Mercia Mudstone Group form the oldest part of the outcropping geological sequence. They are restricted to the western part of the district, where they include the Cropwell Bishop Formation, a unit that has been locally exploited for its thick seams of gypsum, and the distinctive grey to green dolomitic mudstones of the Blue Anchor Formation. The overlying strata of the Penarth Group, of Rhaetian age, mark the onset of the marine sedimentation that persisted throughout the rest of the bedrock sequence. The landscape developed on the Mercia Mudstone Group is subdued; the principal feature is a dissected escarpment that contains the Blue Anchor Formation overlain by the Penarth and Lias groups.

The Jurassic strata of the Lias Group mark the advent of fully marine conditions, following a major transgression. The strata dip gently to the south-east to produce a cuesta topography, rising to a maximum elevation of about 150 m in the east. Prominent dip-slopes are developed on relatively resistant limestones of the Barnstone Member, basal to the Scunthorpe Mudstone Formation of the Lias Group. Stratigraphically higher units of the Scunthorpe Mudstone crop out in the Vale of Belvoir, where numerous thin limestones and subordinate sandstones have been eroded differentially to produce a series of small scarps and broad dip slopes seen between Upper Broughton and Barkestone-le-Vale. Similar topography is developed in the lower beds of the overlying Charmouth Mudstone Formation, up to the foot of a prominent escarpment that rises steeply above the Vale of Belvoir and where the transition to siltstone of the Dyrham Formation occurs. The escarpment is capped by a dissected plateau developed on resistant strata of the Marlstone Rock Formation; this was deposited during a sea-level low-stand, and has been extensively worked as a source of iron ore. A more subdued escarpment feature leads up to the higher ground, in the east of the district, between Branston and Croxton. Its lower slopes consist of marine mudstone of the Whitby Mudstone Formation, the youngest division of the Lias Group. It is capped by the Inferior Oolite Group. At the base, the Northampton Sand Formation, which was deposited in nearshore high-energy conditions, is a resistant lithology that gives rise to long, gently cambered dip slopes. Above these slopes a smaller escarpment is formed by marginal marine or estuarine facies strata of the Grantham Formation. In turn, this is capped by the stratigraphically highest bedrock unit of the district, the Lincolnshire Limestone Formation, which forms a characteristic dissected plateau.

Quaternary Deposits (Drift or Superficial Deposits) are widely distributed and locally very thickly developed in the district. Pre-Anglian deposits of the Bytham Sands and Gravels are more restricted, lying within the largely drift covered trunk valley and tributaries of the preglacial Bytham River, in the south of the district. The overlying glacigenic deposits were laid down during the Anglian glaciation about 440 000 years ago. The lodgement tills of this event comprise the Thrussington Till, which is red in colour and rich in Triassic debris, and the Oadby Till, brown to grey and with chalk and flint debris but also including a Lias-rich facies that is largely devoid of flint and chalk. Outwash or melt-water sands and gravels of these tills comprise glaciofluvial deposits, whereas clays and silts of glaciolacustrine origin mainly represent the ponding of subglacial or proglacial drainage. The drift deposits are most thickly represented in the relict palaeovalley of the Bytham River, where they form a local stratigraphy in which Thrussington Till is overlain by the glaciolacustrine Rotherby Clay, and by a glaciofluvial phase represented by the Wigston Sand and Gravel; the latter is capped by Oadby Till.

Extensive Quaternary deposits underlie the floodplains of the modern Soar and Wreake rivers. They consist of modern alluvium, and remnants of earlier floodplain levels represented by the river terrace deposits, of which there are five separate generations. These are locally thick and constitute a major resource of sand and gravel in the district.

Quaternary slope deposits, of largely periglacial origin, are developed in all parts of the area, but form particularly well-differentiated sequences in ‘clay vales’, such as the Vale of Belvoir and the Stapleford vale south-east of Melton Mowbray. The Pen Hill, Langar and Harby head deposits of the former, and the equivalent Burton Lazars Head in the Stapleford vale, date back to the ‘Wolstonian’ stage. Younger deposits of Flandrian age, which includes head and colluvium, are widespread and landslips are common on the steeper escarpment slopes.

History of survey and research

The district was originally surveyed on the 1:63 360 scale by H Howell, E Hull, J W Judd, W H Holloway and A J Jukes-Browne and published on [old series] sheets 63, 64, 70 and 71 in 1855–79. The primary survey at the 1:10 560 scale, by C Fox-Strangways, W Gibson, C B Wedd, R L Sherlock, B Smith and G W Lamplugh was published as a Solid and Drift edition in 1909. The memoir (Lamplugh et al., 1909) contains much lithological and palaeontological detail. The Marlstone Rock Formation was remapped in 1939 by D A Wray, and the Northampton Sand Formation in 1941 by F B A Welch. Details of these formations was included in a new memoir (Whitehead et al., 1952). Further amendments by V Wilson were incorporated into a 1959 edition of the Melton Mowbray geological sheet. The Generalized Vertical Section, and horizontal section were updated in the 1969 edition of the map, which incorporated much new detail on Carboniferous subsurface geology.

The resurvey of the district commenced in 1987–88, with 1:10 000 series map-sheets for the north-western margin completed by T J Charsley, R G Crofts, A S Howard and D J Lowe. The remaining sheets were completed between 1996 and 1999 by the survey staff (Table 12). This final phase 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 Ordovician — Rempstone and Melton Mowbray granodiorites

These granodiorites are the only basement rocks to have been proved in the Melton Mowbray district; their descriptions are based on a few samples retained on completion of drilling. The granodiorites intrude a basement sequence that is, in part, represented by the tuffs and mudstones of probable Early Palaeozoic age proved in the Sproxton No. 1 Borehole [SK 8451 2394], located 1.4 km beyond the eastern margin of the district. T C Pharaoh (in Berridge et al., 1999, p.17–21) summarises other provings of the sub-Carboniferous basement close to this district.

Clues to the age of the Rempstone and Melton Mowbray granodiorites are provided by chemical data, discussed below, indicating that they are part of the same magmatic event that formed the Mountsorrel Complex. Zircons extracted from the exposed rocks of the Mountsorrel Complex, and dated by the U-Pb method, suggest an Ordovician (Caradoc) age of 451–452 Ma. This value was derived by Noble et al. (1993), who recalculated the data obtained by Pidgeon and Aftalion (1978) by merging it with values obtained from the nearby intrusive rocks of the South Leicestershire Diorites Suite. The former authors urge caution, however, in that the Mountsorrel age was obtained on zircons that were abraded and are significantly discordant. The age nevertheless falls within the spectrum of values between 449 ± 13 and 457 ± 20 Ma obtained from tuffs and plutonic rocks proved by drilling elsewhere in the basement of eastern England (Noble et al., 1993). This activity was thus broadly contemporaneous with the Ordovician volcanism of the Lake District and Snowdonia.

The comparative geochemistry of samples from the Rempstone (2 analysed samples) and Melton Mowbray (2 samples) granodiorite provings, and from exposures in the Mountsorrel Complex, which crops out 500 m to the southwest of the district, is discussed by Pharaoh et al. (1993). All plots lie along a single trend of magmatic variation, as also recognised by Le Bas (1972), indicating descent from common parental magma-types. Their compositions show no iron enrichment, moderate enrichment of large ion lithophile (LIL) elements (K, Rb and Ba), Th and Ce, and relative depletion of Nb (and Ta), which are patterns typical of calc-alkaline volcanic arc magmatism. Pharaoh et al. (1993) considered that the magmas were generated by the southwards-directed subduction of oceanic lithosphere beneath central England from the Tornquist Sea, or part of the Iapetus Ocean.

Rempstone Granodiorite (ReGd)

This unit was proved between 1131.2 m and terminal depth (1213.0 m) in the Rempstone LN/10-1^‡2  Borehole. The granodiorite contact with overlying Millstone Grit strata was not preserved intact; however, interpretations of nearby seismic reflection profiles suggest it is tectonic, and that the borehole has intersected granodiorite forming the local footwall to the Normanton Hills Fault (information from T C Pharaoh; see also Section 2 on Sheet 142 Melton Mowbray). The subsurface extent of the Rempstone Granodiorite is defined by a triangular-shaped aeromagnetic anomaly (see inset on Sheet 142 Melton Mowbray), which shows a body of between 6 and 8 km diameter. Its linear, west-north-west-orientated margin is controlled by the Normanton Hills Fault, which as noted is intersected in the Rempstone LN/10-1 Borehole. The south-eastern margin of the Rempstone Granodiorite is also linear, and appears to be controlled by a north-east trending structure. Geophysical modelling (Chapter 9) suggests that the top of the granodiorite is close to the surface and probably forms much of the sub-Carboniferous basement to the south of the fault. The intrusion may be linked at depth to the Mountsorrel Complex, which also gives rise to a circular magnetic anomaly to the south of the district (Chapter 9).

The two surviving core samples, from depths of 1202.2 and 1202.3 m in the borehole, show that the Rempstone Granodiorite is a coarse-grained rock with an inequigranular texture. Cream to green, prismatic plagioclase crystals, up to 5 mm across, are set in a pink, medium to fine grained quartzo-feldspathic base in which grey to black, granular mafic mineral aggregates between 2 and 4 mm across are commonly developed. A xenolithic component consists of pale grey, medium to fine-grained diorite fragments that range from 10 mm up to at least 40 mm in size; they contain sporadic plagioclase phenocrysts of similar appearance to those in the main part of the granodiorite.

A thin section (E60513) from 1202.2 m depth shows plagioclase feldspar euhedra, up to 3 mm long, which are largely replaced by granular clusters of epidote and white mica. Between the feldspars are medium-grained, hypidiomorpic-granular aggregates of plagioclase prisms and chlorite laths, the latter pseudomorphic after amphibole (and possibly also after biotite); interstitial intergrowths of quartz and turbid K-feldspar locally form granophyrictextured patches up to 3–4 mm across. A further thin section (E60514), from 1202.5 m depth, shows a quartzdiorite xenolith consisting of tightly packed plagioclase laths, much interstitial secondary chlorite, and interspersed granular quartzo-feldspathic pools. The coarse-grained granodiorite that encloses the xenoliths is similar to that described for (E60513), but shows a more accentuated development of the granophyric texture; there are no obvious signs of chilling between xenolith and host rock.

Melton Mowbray Granodiorite

This intrusion was intersected in the Kirby Lane Borehole, from 402 m to the terminal depth at 413.9 m. The borehole description mentions that the upper 8 m of intrusive rocks are weathered, with their topmost part being ‘greenish-grey speckled with soft-white kaolinitised feldspar and red and green grains’. Weathering of the intrusion is further indicated by the geophysical borehole log, reproduced in Brandon (1999, fig. 3), showing increased gamma-ray values compatible with the conversion of igneous rock to secondary clay minerals in the top 3 m of the intrusion.

Core samples from the borehole show coarsely inequigranular granodiorite with prominent pink feldspar prisms up to 5 mm across. One specimen is net-veined, with angular inclusions of grey, mafic-rich granodiorite or quartz-diorite separated by narrow septa of pink aplogranite (Plate 1). In the same sample, scattered xenoliths of grey, fine-grained diorite, are possibly the remnants of an earlier phase of basic intrusion.

The weathered surface of the intrusion is unconformably overlain by strata of the Millstone Grit Group, at a level equated by Brandon (1999) with the Marsdenian stage of the Namurian. The overlying sandstone bed, 0.34 m thick, is described as being ‘gritty’ with a soft white matrix, and it probably contains detritus reworked from the weathered top of the intrusion. The aeromagnetic anomaly map on Sheet 142 shows that the Melton Mowbray Granodiorite occupies a north-east-orientated body, just over 16 km long by about 7 km wide. Its north-western margin is linear, and in part controlled by the Sileby Fault (Chapter 9).

Chapter 3 Carboniferous

Uplift and erosion of the early Palaeozoic basement rocks produced a landscape that was eventually inundated by the marine transgression that occurred in latest Devonian or early Carboniferous (Tournaisian) times (about 355 Ma). In this district the Carboniferous strata are recognised in boreholes, but have also been imaged on many seismic reflection profiles, which form the basis for their classification in terms of seismostratigraphical sequences (e.g. Ebdon et al., 1990; see also, Chapter 8). The oldest sequences, of early Carboniferous (Dinantian) age, accumulated in a syn-rift tectonic environment, but by late Carboniferous times this tectonic regime had evolved into one of more uniform, regional-scale subsidence (post-rift thermal sag). Thus, during the Namurian, deltas encroached upon large areas of the Midlands, and ultimately, in Westphalian times, a fluvio-lacustrine delta-plain was established. The effusion of basaltic lavas and associated volcaniclastic rocks in the late Dinantian and latest Namurian to early Westphalian (Langsettian) periods was an expression of localised tectonic instability in parts of the Melton Mowbray and adjacent districts.

Dinantian

Dinantian strata were deposited within a tilted block and graben topography (e.g. Miller and Grayson, 1982), and are of widely varying lithofacies. They are part of the ‘syn-rift megasequence’ of Fraser and Gawthorpe (1990), the evolution of which is mainly interpreted from seismic data, as discussed in Chapter 8. In this district Dinantian rocks have also been proved in several deep boreholes, which have helped to constrain the correlations embodied in the seismic depth sections shown on Sheet 142. Such interpretations show that the Dinantian attains a maximum thickness of about 3500 m in the deeper, southern part of the asymmetric Widmerpool Half-graben.

The lithological and thickness variations that characterise the Dinantian succession can be related to deposition within fault or flexure-bound structural domains (Chapter 8). These comprise (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) the Widmerpool Half-graben, the Hathern Shelf (Ebdon et al., 1990) on the southern (footwall) side of the Normanton Hills Fault, and the Nottingham Shelf to the north-east of the graben. In addition, volcanic rocks of late Dinantian (Brigantian) age were extruded from several centres along the Cinderhill–Foss Bridge Fault line to the north of this district (Fraser et al., 1990; Howard et al (a), in prep.).

The five major divisions of Dinantian rocks recognised in the district are termed the Scalford Sandstone, Milldale Limestone, Belvoir Limestone, Plungar Limestone and Widmerpool formations. The Milldale, Belvoir and Plungar Limestone formations broadly equate to the ‘Carboniferous Limestone’, a term that has traditionally been used for Dinantian carbonate rocks that collectively form a unit of supergroup lithostratigraphical rank. ‘Carboniferous Limestone’ is not a formal unit, however, and this terminology is not recommended for current use (Aitkenhead and Chisholm, 1982). Lithostratigraphical revisions currently in progress (Waters et al., in prep.), but at the time of writing not yet finalised, suggest that the limestone-dominated Dinantian formations of shelfal or platform facies should all be included within a division of their own (the Peak Limestone Group). On the other hand, basinal-facies, mudstone-rich sequences, such as the Widmerpool Formation of this district, but also including Namurian strata presently referred to as the Edale Shale Group, would be placed within a separate ‘Craven Group’.

The borehole correlations of (Figure 4) show that the Widmerpool Formation attenuates, and the Dinantian as a whole displays increasing degrees of unconformity with the overlying Namurian as the floor of the Widmerpool Half graben becomes shallower to the north-east of the district. Attenuation is more abrupt in the south, across the Sileby Fault, as seen in the Kirby Lane Borehole where Dinantian strata are absent (Figure 7). These relationships are also shown by the depth sections (2 and 3) on Sheet 142.

Scalford Sandstone Formation (SfdS)

At least 123.7 m of siliciclastic strata were uniquely proved in the Scalford No. 1 Borehole, although the lithologies are only poorly documented from cuttings samples. The succession consists mainly of reddish brown, brown or green, fine to medium-grained calcareous sandstone, brown, red and purple, blocky to fissile siltstone, and grey, blocky mudstone. The beds are unfossiliferous, and consequently of uncertain age, but are ‘overlain’ by strata correlated with the Widmerpool Formation (Ambrose, 2000a). The thickness of the Widmerpool Formation, only 68 m, is considerably less than would be predicted by seismic profiling in this part of the Widmerpool Half-graben. Its apparent attenuation may suggest tectonic omission in this borehole, possibly because its junction with the Scalford Sandstone is a shear zone representing the footwall cut-out of the Normanton Hills Fault (information from T C Pharaoh; compare (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)a and (Figure 7)). The Scalford Sandstone could therefore be a basal Dinantian or even latest Devonian sequence deposited on the Hathern Shelf, in an analagous structural position to the Calke Abbey Sandstone Formation of the Loughborough district (Carney et al., 2001). It may represent an early syn-rift fluviatile or fan-delta association, containing material derived from young escarpments formed by the initiation of rifting along the Normanton Hills or Sileby faults.

Milldale Limestone Formation (Mi)

Strata correlated with the Milldale Limestone Formation (Parkinson, 1949; Aitkenhead and Chisholm, 1982) were encountered only in the north of the district, and are at least 168 m thick in the Plungar 8A Borehole; where no base to the succession was proved. The top of the unit is a probable unconformity surface, which in turn is overlain by the Belvoir Limestone Formation (see below).

The evidence of borehole cuttings suggests that the basal 50 m of the formation in Plungar 8A Borehole consists of silty, buff to grey, dolomitic limestone and dolostone interbedded with dolomitic siltstone, the latter commonly oil-stained. Above this are grey, buff or brown, ‘crystalline’ dolomitic limestones with sporadic productid fossils.

The age and correlation of this unit is based on biostratigraphical investigations of cuttings samples from the Plungar 8A Borehole. The initial report, by A R E Strank (1980; unpublished borehole log report), was superseded by that of Riley (1992), who found that the most age-diagnostic material (foraminifera and algae) came from strata between 1394.5 and 1269.5 m depth. The age proposed for this interval was either early Chadian or late Courceyan (Cf4a1 Subzone). This facies, with its abundant cyanobacteria and the calcareous alga Parachaetetes, was considered typical of the carbonate ramp lithologies developed in the lower part of the Milldale Limestones found in the continuation of the Widmerpool Half-graben in the Ashbourne district, about 40 km to the north-west. The overlying strata, between 1269.5 and 1149 m depth in the borehole, were barren of fauna, but from regional considerations it was suspected that this interval contains the top of the Milldale Limestone Formation. In other parts of the East Midlands, that surface is an unconformity or nonsequence between the early and late Chadian, and it also contains the Tournaisian–Visean boundary. Here, this unconformity is taken arbitrarily to lie at 1240 to 1250 m depth in the Plungar 8A Borehole. The overlying c. 120 m of Belvoir Limestone Formation in the Plungar 8A Borehole could therefore be of late Chadian age.

In the Ashbourne district, strata of the Milldale Limestone Formation were deposited in a carbonate ramp setting (Chisholm et al., 1988), with respect to the basinal province represented by the Widmerpool Half-graben (Ebdon et al., 1990; fig. 3).

Belvoir Limestone Formation (Bvr)

These brown to white, dolomitic, locally ooidal limestones occupy an interval about 120 m thick above the inferred early/late Chadian unconformity, discussed earlier to be at about 1240 to 1250 m depth in the Plungar 8A Borehole. Within 55 m of the top of the unit, two thin volcanic beds of ‘green ash’ are recorded. The Belvoir Limestone strata are likely to be of late Chadian age in their topmost part, since samples from above 1149 m yielded bilaminar Koninckopora, with no archaediscids present (Riley, 1992). No age-diagnostic fossils were recovered from the critical lower part of this succession, between 1269 and 1149 m depth. Although Riley (1992) inferred an unconformity at the top of the Milldale Limestone within this interval, there is no particularly obvious feature on the gamma-ray log (Figure 4) that would indicate its position.

At the top of the Belvoir Limestone Formation, Riley (1992) inferred a further unconformity or non-sequence, with overlying strata of possible late Arundian age. The latter are now referred to the Plungar Limestone Formation, and as the position of the base-late Arundian unconformity cannot be determined on faunal grounds, it is here taken as the base of the lowest sandstone bed, at 1130 m depth (Figure 4). The poor biostratigraphical definition of the hiatus could be due to the reworking of earlier faunal elements derived by erosion, although the nature of the material, from borehole cuttings, does militate against good faunal resolution.

Plungar Limestone Formation (PlLs)

This formation is named after its main proving in the Plungar 8A Borehole where it is a limestone-dominated sequence, 198 m thick, and bounded by unconformities that separate it from the (possibly late Chadian) Belvoir Limestone Formation below, and the Millstone Grit Group above.

The unconformable base of the formation on the early Chadian Belvoir Limestone Formation described above, is taken at the base of a 6 m-thick bed of grey, pebbly sandstone recorded at 1131 m depth in the borehole. The part of the formation immediately overlying this unconformity includes dolomitic limestones with two thinner sandstones in a 15 m thickness of strata. The lithological log of the borehole describes white to buff, crystalline limestones, ooidal in places, above the youngest sandstone.

The upper junction is an unconformity (Figure 4) that forms a surface across which at least some of the Brigantian, and all of the Pendleianand Arnsbergian-age strata, pinch out toward the north-east. The hiatus probably occurred during a late Brigantian episode of mild basin inversion that was documented by Ebdon et al. (1990; fig. 9) for the north-eastern margin of the Widmerpool Half-graben. The formation is interpreted as a carbonate ramp or platform lithological association. It may be represented by other limestone provings beneath the Namurian in the north-east of the district, as shown in (Figure 4) and discussed in the next section, but there is insufficient biostratigraphical information to confirm the correlations.

Age and correlation

Riley (1992) noted that faunal remains are sparse for this unit, with a Late Arundian age regarded as tentative. This conflicts with the macrofauna obtained from 140 m below the top of the unit in the adjacent Plungar No. 8 Borehole, which includes Gigantoproductus, indicative of a D1 (Asbian) age, possibly younging upwards into the Brigantian.

Undivided Dinantian limestones

Many hydrocarbon exploration boreholes were stopped only a few tens of metres into the Dinantian. Comparisons of the gamma-ray traces in (Figure 4) nevertheless suggest that beds corresponding to the Plungar Limestone Formation probably underlie the Millstone Grit across the north-east of the district. The deeper borehole sections show sufficient lithological variation to suggest that different parts of the formation may have been encountered. For example, in the Plungar No. 4 Borehole, 72 m of ‘cream-white limestone’ was described, whereas in the Barkestone No. 1 Borehole, about 2.5 km to the north-east, the lower part of a 61 m thickness of Dinantian beds consisted of ‘black shale and limestone’ intercalations. In this borehole, fossils yielded from a datum 5.2 m below the Millstone Grit included Productus cf. Davidsonaria septosa (Phillips), suggesting an Asbian age. The Redmile No. 1 Borehole proved pale grey-brown (oil-stained) limestone with crinoids and foraminifera; the sporadic grey-green mudstone partings were locally carbonaceous and pyritous.

Widmerpool Formation (WdF)

The Widmerpool Formation (Aitkenhead, 1977) represents a late Dinantian (Asbian to Brigantian) syn-rift to post-rift sedimentary sequence deposited during a general collapse of the platforms bordering the Widmerpool Half-graben. Sedimentation involved periodic carbonate gravity-flows and turbidity flows into a hemipelagic environment. A single subdivision, the Ratcliffe Volcanic Member, has been recognised. The top of the formation, and of the Dinantian, is taken at the base of the Cravenoceras leion Marine Band or, where this is not proved on faunal grounds, the corresponding feature on geophysical borehole logs. The formation was apparently bottomed in the Scalford No. 1 Borehole (Ambrose, 2000a) in the south-east of the district, but here, as previously discussed, the unit may be in faulted contact with the Scalford Sandstone Formation. Interpretations of seismic data (insets on Sheet 142 Melton Mowbray) suggest up to 1000 m thickness of the Widmerpool Formation in the south-west of the Widmerpool Half-graben, where maximum synsedimentary subsidence occurred. To the north, borehole correlations (Figure 4) show that the formation attenuates before pinching out across the Cinderhill–Foss Bridge Flexure, which delineates that margin of the graben (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)a.

The Widmerpool No. 1 Borehole, located in the central part of the Widmerpool Half-graben, proved a 480 m minimum thickness of the formation. The records are poor but suggest a sequence dominated by dark grey mudstone with interbedded thin limestones. The latter are sandy to gritty or conglomeratic, with shell detritus and quartz pebbles. In the lower 60 m of this borehole the fauna included the ammonoids Nomismoceras cf. germanicum, Beyrichoceras, ?Girtyoceras, Goniatites cf. crenistia, the conodont Hindeodella, and the marine bivalve Dunbarella. The occurrence of Beyrichoceras, if confirmed, would indicate a position within the Beyrichoceras (B) zone of Riley (1990), and therefore a probable late Asbian age. In the overlying 200 m of strata, the absence of Beyrichoceras and occurrence of Arnsbergites aff. sphaerico-striatus and the bivalve Posidonia becheri Brown suggest a position within the P1b-d subzones in the Brigantian. In the upper 220 m or so of beds, core preservation was too fragmentary for accurate age determinations on the basis of macrofaunas. The Cravenoceras leion Biozone, delimiting the top of the Widmerpool Formation, was identified in the Widmerpool No. 1 Borehole and at the base of the Colston Bassett North Borehole (Figure 4).

In the southern part of the Widmerpool Half-graben, the most extensive proving of the formation is the 330 m minimum thickness of carbonaceous, silty mudstones and interbedded bioclastic limestone turbidites encountered in the Rempstone LN/10-1 oil-producing borehole (Carney, 1999). Farther east, in the Old Dalby Borehole, sidewall cores and chipping samples indicate that the formation includes beds of grey-brown packstone with shell fragments, together with buff, dolomitic sandstone with oil shows.

In the north-east of the Widmerpool Half-graben, the Long Clawson No. 2 Borehole encountered at least 175 m of the Widmerpool Formation, below a zone of high gamma-ray values identified as the Cravenoceras leion Marine Band. The lithologies consist of mudstones intercalated with thin, quartzose to subarkosic sandstones and grey, argillaceous limestones. Thicker sandstones (up to 2–3 m), with graded siltstone and sandstone couplets, are intercalated about 50 m below the top of the formation. Beds of white to pale brown limestone and shelly limestone become numerous about 80 m lower down and limestone dominates in the lowest part of the proving, suggesting a downwards transition to the ‘Carboniferous Limestone’ Dinantian facies (Figure 4).

Ratcliffe Volcanic Member (RaV)

Thin beds of green-grey basic tuff appear between 100 and 135 m from the top of the Widmerpool Formation in the various boreholes described above (Figure 4). They are correlated with the beds named from the Ratcliffe Borehole [SK 5081 2913] of the adjacent Loughborough district (Carney et al., 2001). The tuffaceous beds in the Widmerpool No. 1 Borehole appear 60 m above the Arnsbergites aff. sphaericostriatus (P_1c) occurrence. The member is thus probably equivalent to tuffaceous strata occupying part of the P₂ zone in the cored Duffield Borehole (Aitkenhead, 1977), in the Derby district, and to the Tissington Volcanic Member of the Ashbourne district. The latter comprises a diverse basaltic sequence interleaved with strata containing ammonoids dated at between P_1c and early P₂ age, probably within the P_1d Zone (Chisholm et al., 1988, p.33). The member may also represent a partial lateral equivalent of the basaltic volcanic rocks that replace seismostratigraphical units EC4–EC6 (mid Asbian to mid-Brigantian age) along the continuation of the Cinderhill–Foss Bridge Flexure a few kilometres to the northwest of this district (Fraser et al., 1990, fig. 6). These volcanic rocks are proved to lie beneath middle to late Brigantian limestones in the Strelley No. 1 Borehole [SK 5052 4296], located about 7 km north-west of the district (Riley, 1986; Howard et al., in prep.).

In the Rempstone LN/10-1 Borehole the member is 56 m thick, compared with the 124 m found in the Ratcliffe on Soar Borehole farther west. On the gamma-ray log (Figure 4) it is distinguished by the occurrence of prominent troughs, three of which are interpreted on the completion log as tuff beds between 2 and 5 m thick, interleaved within mudstone. Cuttings samples described in the borehole log indicate that some tuff beds are pale grey to blue, dolomitic to highly calcareous lithologies with white mottles and some lamination. The member thins progressively eastwards from the Rempstone Borehole, to a thickness of 27 m in the Widmerpool No. 1 Borehole where it consists of altered, ‘palagonitic tuffs’; farther east, only 15 m of the member was identified in Long Clawson No. 2 Borehole.

Namurian

The concealed Namurian strata of the district have been proved, in many oil and coal exploration boreholes, to be in stratigraphical continuity with the succession at outcrop in the southern Pennines. Namurian strata form part of the Upper Carboniferous, ‘post-rift megasequence’ of Fraser and Gawthorpe (1990), although it is noted that the international boundary between the Lower and Upper Carboniferous lies within the Namurian, at the base of the Chokierian Stage. According to Fulton and Williams (1988), combinations of eustatic sea-level change, basinal flexuring and local faulting may have played a part in controlling Namurian sedimentation, which represents the infilling of the preceding, Dinantian tectonic basins (Figure 7).

In 1939, the discovery of oil-bearing Namurian sandstone reservoirs in the Eakring Oilfield of central Nottinghamshire provided the impetus for further exploration that led to a steady refinement in knowledge of the East Midlands Namurian stratigraphy (Lees and Taitt, 1945; Edwards, 1951; Falcon and Kent, 1960; Downing and Howitt, 1969). More recent regional syntheses of exploration data have focused on the sequence stratigraphy of the Namurian, both at a low resolution (Ebdon et al., 1990; Fraser et al., 1990; Fraser and Gawthorpe, 1990) and at higher resolutions (Church and Gawthorpe, 1994; 1997). The geophysical correlations between boreholes are aided by biostratigraphical determinations of core samples, although the biostratigraphical data points are scattered because of the limited amount of borehole core available, and such studies have enabled the identification of diagnostic faunas for some Namurian marine bands in the Melton Mowbray district.

In this district as elsewhere, the Namurian is subdivided into the Edale Shale Group, mudstones interbedded with turbidite siltstones and sandstones of prodelta facies, and the overlying Millstone Grit Group, which represents the progradation of deltas that were the precursors of the swampy, delta-plain environments of the Westphalian Coal Measures.

Edale Shale Group (ESh)

‘Edale Shale Group’ is now an obsolete name, and the strata referred to here are likely to fall within the Morridge or Bowland Shale formations (Waters et al., in prep.). The sequence consists of mudstones and silty to sandy turbidites of prodelta facies. Its lower boundary is defined at the base of the Cravenoceras leion Marine Band. The top is less satisfactorily delineated, and is taken at the base of the stratigraphically lowest ‘significant’ feldspathic sandstone typical of the overlying Millstone Grit Group (Stevenson and Gaunt, 1971). The maximum proven thickness of the unit is 649 m in the Widmerpool No. 1 Borehole. It thins southwards, to about 350 m in the Rempstone LN/10-1 and Old Dalby No. 1 boreholes, and in the north-east it pinches out across the Cinderhill–Foss Bridge Flexure, as indicated by the correlations in (Figure 4).

These strata remain poorly described in boreholes, which generally indicate a sequence of dark grey to black, commonly calcareous and pyritous mudstones, with sporadic to locally common, thin beds of pale grey, micritic limestone and graded beds of siltstone and quartzose sandstone. In the Widmerpool No.1 Borehole, the base of the Edale Shale is indicated by core samples containing ‘Cravenoceras cf. leion’, together with Eumorphoceras sp. (notes on the log). Determinations by the BGS for the same interval (1411–1409 m depth) indicate the ammonoids ?Cravenoceras sp., Girtyoceras, and Eumorphoceras ?pseudobilingue, consistent with an E_1a zonal age. Above this, at 1341 m depth, Cravenoceras cf. malhamense was identified on the log (with Caneyella mambranaica), indicative of the E_1c zone.

Other biozones, spanning the Pendleian and Arnsbergian stages, have been identified from wireline log correlations between the Duffield, Rempstone LN/10-1 and Old Dalby boreholes, as shown in (Figure 5). The top of the Arnsbergian is uncertain in the Old Dalby Borehole; two possible levels are indicated at about 1038 m and 1062 m, both lower down than documented on the completion report (1009 m). The top of the group is probably Kinderscoutian in age, but there are no definitive marine band provings of this stage, or of the older Chokierian and Alportian stages.

The main clastic interval in the Rempstone LN/10-1 Borehole occurs between 750 and 640 m depth, in strata of Arnsbergian age. It consists of two graded sedimentary packages, each fining upwards from grey, fine to medium grained quartzose sandstones and siltstones to mudstones with thin interbedded limestones. The 12 m-thick sandstone between 663 and 655 m depth is the main oil reservoir of this producing well (Chapter 11). Wireline log correlations suggest that this bed could be equivalent to the sequence of graded turbiditic sandstones, siltstones and mudstones between 170 and 204 m depth in the Duffield Borehole (Aitkenhead, 1977). The clastic sequence proved at 1223 to 1239 m depth in the Edale Shale Group of the Old Dalby Borehole includes about 10 m of matrix supported subangular conglomerate with clasts of ‘granite’; the ‘granite’ was possibly derived locally, from the Melton Mowbray or Rempstone granodiorites.

Millstone Grit Group (MG)

The Millstone Grit Group (Stevenson and Gaunt, 1971) comprises a sequence of mudstones with interbedded sandstones lying below the Subcrenatum Marine Band, which delimits the base of the Westphalian. In its type area of north Derbyshire, the Millstone Grit has been divided into a number of thick sandstone-dominated packages (‘grits’), none as yet formally defined. The base of the group is taken to be the base of the stratigraphically lowest sandstone of ‘Millstone Grit’ type, although in the absence of detailed lithological information its delineation can be somewhat arbitrary. In this district, the Millstone Grit represents the progressive culmination of sedimentary infilling of the Widmerpool Half-graben. The infilling was also reflected by a change from the marine to brackish conditions, which prevailed during deposition of the Edale Shale Group, to predominantly deltaic conditions with only sporadic marine incursions during high stands of sea level.

The Millstone Grit is thickly developed in the south of the Widmerpool Half-graben, with at least 200 m in the Rempstone LN/10-1 Borehole and a maximum 141 m in Great Framlands Borehole. Elsewhere, it thins onto the flanks of the Widmerpool Half-graben, as shown by thicknesses of around 60 to 70 m in the north (Figure 4) as well as in the south-east of the district. The group consists mainly of mudstone, siltstone and interbedded sandstone, with thin (up to 1.2 m) inferior coals and seatearths present in minor proportions. These alternations make up a number of sequences, each representing the response of the Namurian fluvio-deltaic depositional system to a complexity of processes that have effected changes in the patterns of sedimentary stacking (Church and Gawthorpe, 1997). In a study of late Namurian (Marsdenian–Yeadonian) strata in the Wilds Bridge Borehole of this district, Church and Gawthorpe (1994) identified seven sedimentary geophysical log facies. These are:

• facies A marine band
• facies B prodelta to delta front siltstones and sandstones
• facies C distributary mouth bar
• facies D fluvial channel sandstones, with subfacies (I) active fill and subfacies (II) abandonment fill
• facies E interdistributary bay and swamp mudstones and siltstones
• facies F minor mouth bar and crevasse splay sandstones
• facies G minor distributary channel and crevasse channel sand bodies

Marine bands and Lingula bands occur throughout the succession and are considered by Church and Gawthorpe (1994; 1997) to represent maximum flooding surfaces. Their faunas, in combination with geophysical log signatures where no faunas were recovered, are the basis for correlating these strata throughout the subsurface (Figure 4) and (Figure 5). Such considerations suggest that the base of the Millstone Grit Group in this district is probably located within the R₁ (Kinderscoutian) stage of the upper Namurian. It is also a surface of unconformity and overstep at either margin of the Widmerpool Half-graben, as shown by (Figure 4); this proves that in the north-east the Millstone Grit crosses the base of the Edale Shale Group, to rest directly on Dinantian strata. To the south of the graben and Hathern Shelf, the Dinantian and much of the Namurian are missing and the Millstone Grit overlies the basement in the Kirby Lane Borehole (Figure 7), and possibly in the Sproxton No. 1 Borehole [SK 8451 2394] that lies to the east of the district.

A characteristic feature of Millstone Grit fluvio-deltaic sandstones in the Pennine Basin is that they are rich in feldspar grains derived from a northerly source (Drewery et al., 1987). However, a significant contribution of sedimentary detritus from the south has been recognised in the Staffordshire Basin (Trewin and Holdsworth, 1973), and more recently in the Loughborough district (Hallsworth, 1998). Palaeocurrents indicate that in the southernmost part of the Pennine Basin the Millstone Grit sediment transport path was commonly deflected to the north-north-west (Fulton and Williams, 1988), parallel to the trend of the Widmerpool Half-graben. This also reflects the influence of the Wales–London–Brabant landmass, which was a Carboniferous tectonic margin in part controlled by the Normanton Hills and/or Sileby faults (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3). The interplay between northerly and southerly source regions in the present district is demonstrated by heavy mineral studies of sandstone samples collected from various boreholes. The results (Hallsworth, 2000) indicate that southerly sourced sediment transport systems dominated sedimentation during deposition of the Kinderscout Grit and associated sandstones in pre-R₂ or Marsdenian time, although the southerly derived sandstones of this district are more feldspathic than their analogues in the Staffordshire Basin. The northerly derived sand incursions into this district commenced in R_2b (Marsdenian) times, when the Ashover Grit was deposited, but then waned to produce mixing between northern and southern sources during deposition of the subsequent Chatsworth Grit and Rough Rock (Yeadonian) sandstones.

Biostratigraphical information for the strata of the Asfordby Hydro, Holwell Works and The Chase boreholes (Riley, 1983a,b; (Figure 13)), in conjunction with geophysical wireline log correlations, enable distinctive datum to be traced across the district. The Kinderscout Grit (KG) and associated Reticuloceras coreticulatum Marine Band were proved from faunas in the Asfordby Hydro and The Chase (Figure 13) boreholes, in both cases with the zonal ammonoid Reticuloceras coreticulatum (R_1c4) identified. The sandstone attains 40 m thickness in the Great Framlands Borehole, and 35 m in the Widmerpool No. 1 Borehole (Downing and Howitt, 1969) and in the Old Dalby Borehole (Figure 5), where two upward-coarsening cycles reflect successive phases of delta progradation. Farther north the Kinderscout Grit is considerably thinner (Figure 4). Lower marine horizons with Lingula have also been proved; the presence of Vallites in The Chase Borehole suggests a correlation with strata of Alportian (H_2c) to Kinderscoutian (R_1c) age.

The Bilinguites gracilis Marine Band (R_2a1), marking the commencement of the Marsdenian, was identified in the Asfordby Hydro Borehole on the basis of a fragment of Bilinguites sp. and its close proximity to the underlying Reticuloceras coreticulatum Marine Band. It has also been identified from its gamma-ray signature in the boreholes farther north (Figure 4). The Asfordby Hydro Borehole has also proved the Bilinguites bilinguis (R_2b1-3), B. eometabilinguis (R_2b4), B. metabilinguis (R_2b5), and B. superbilinguis (R_2c1) marine bands. Within the Marsdenian sequence, sandstones occurring between the Superbilinguis and Bilinguis marine bands have been correlated with the Ashover Grit (AsG). This forms a single bed in places (e.g. Great Framlands Borehole), and in the Widmerpool No. 1 Borehole it may be 36 m thick (correlation of Downing and Howitt, 1969), but elsewhere is commonly represented by two or more thin sandstone beds (Figure 4). The Ashover Grit in this district was deposited at a time when the Widmerpool Half-graben was a dominant sediment pathway, according to Church and Gawthorpe (1997); it is generally a fineto medium-grained sandstone, which is locally coarse and ‘gritty’. Intraformational mudstone, siltstone and sandstone and derived quartzite clasts have been noted.

Above the Ashover Grit, the Verneulites sigma Marine Band (R_2c2), has been tentatively identified in the Holwell Works Borehole (Riley, 1983a; (Figure 13)) and may be present in the Great Framlands Borehole. The overlying Chatsworth Grit (ChG) is subject to large local variations in thickness around Asfordby; it is commonly very thin (1–3 m), but in the Old Dalby Borehole there is a thickness of 48 m (Figure 5). The latter includes two coarsening upward, prodelta to delta front cycles, followed by sandstone that indicates the establishment of active fluvial channel facies akin to that identified by Church and Gawthorpe (1994). In the Wilds Bridge Borehole, Church and Gawthorpe (1997) identified the Chatsworth Grit as part of a transgressive sequence. The succeeding Cancelloceras cancellatum (G_1a1), and C. cumbriense (G_1b1), marine bands are identified in most of the Asfordby area boreholes studied by Riley (1983a), as well as in provings farther north (Figure 4). They generally form a distinctive double peak on gamma-ray logs.

The Rough Rock (RR) is commonly interpreted as a major, sheet-like fluvial sandstone body (Bristow, 1993). It generally forms a single unit, but locally splits into two or three beds. The thickest provings include 12.66 m for a single sandstone in the Great Framlands Borehole, and 19.44 m in the Asfordby Mine Site No. 6 Borehole where there are two sandstones, separated by seatearth mudstone and a thin coal. The Rough Rock is commonly a fine to coarse-grained, locally coarse and pebbly sandstone, interlaminated with siltstone. The pebbles are generally derived quartzite or intraformational siltstone and mudstone, but igneous clasts have also been noted. The Rough Rock is thinnest in the north of the district, averaging only 1 to 3 m there (Figure 4). The uppermost few metres of the Millstone Grit consist of mudstone, siltstone and seatearth. In places, a thin coal underlying the Subcrenatum Marine Band marks the top of the group.

Westphalian

Westphalian rocks occur in about 80 per cent of the subsurface of the district (Figure 27), beneath the Permo-Triassic cover. Despite this deep burial, much information on the lithology and structure of the Westphalian is available from successive exploration programmes for oil and coal, utilising intermediate-depth drilling and seismic reflection profiling. These investigations have shown that the Westphalian rocks have a generalised dip to the north or north-east, but are locally faulted and folded. The most significant structures are the Foss Bridge Fault and the adjacent Plungar Dome, and the series of anticlines and synclines developed along the Normanton Hills and Sileby faults farther south (Chapter 8).

The main Westphalian divisions in this district are the Coal Measures Group and the overlying and unconformable red beds of the Warwickshire Group. In addition, there are locally thick developments of basaltic lavas and fragmental rocks represented by the Asfordby Volcanic Formation, and Saltby Volcanic Formation.

Coal Measures Group

The Coal Measures Group is a new formal lithostratigraphical term (Powell et al., 2000) for strata previously referred to as the ‘Coal Measures’. Its base corresponds to the onset of the marine transgression that deposited the Subcrenatum (Pot Clay) Marine Band, which rests conformably on the Millstone Grit Group, and its top is an unconformity with either the Warwickshire Group or Permo-Triassic strata. In this district the unit attains a maximum thickness estimated to be around 800 m and forms the larger part of the wholly concealed Vale of Belvoir (North-east Leicestershire) Coalfield. There is no current exploitation of coal, but underground mining has taken place in the recent past, around Cotgrave in the north-west and Asfordby in the south (Chapter 11). The local Westphalian stratigraphy is summarised in (Figure 6) together with the scheme of coal seam nomenclature, which closely follows that for the adjoining Nottinghamshire Coalfield (Lamplugh et al., 1908; Charsley et al., 1990; Howard et al., in prep (a)). The most comprehensive treatment of the Vale of Belvoir Coalfield is that by Sheppard (2003).

The chronostratigraphical subdivision of the Coal Measures Group is based on the identification of three faunal horizons: the Subcrenatum, Vanderbeckei (Clay Cross) and Aegiranum (Mansfield) marine bands (Calver, 1968). These datum define the bases of three stages, which are respectively Langsettian, Duckmantian and Bolsovian (formerly Westphalian A, B and C). The Langsettian corresponds with the Lower Coal Measures lithostratigraphical unit, 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 (Top) Marine Band, within the Bolsovian, although that faunal marker has not been positively identified in the district. The Upper Coal Measures, and parts of the Middle Coal Measures, are progressively overstepped eastwards along the erosional unconformity marking the base of the Warwickshire Group.

The earliest strata are the Lower Coal Measures of Langsettian age. They represent a continuation of sedimentation from the Millstone Grit Group, but with an increasing dominance of interchannel, lacustrine depositional environments up-section. This change reflects the longer periods in which land floras were allowed to develop, within the mires that produced the coal seams. The depositional regime was predominantly that of a coastal plain, although in the east this sedimentation pattern was periodically modified or destroyed by repeated marine glacioeustatic transgressions, and by the local build-up of basaltic shields or lava aprons. Later in the Langsettian an upper delta to alluvial plain had been established over the whole district and this environment persisted through the Duckmantian and into the early part of the Bolsovian, when the Middle and Upper Coal Measures were being deposited. The unconformably overlying Warwickshire Group marks a change to better drained alluvial conditions and strata indicate deposition within fluvial channels and overbank environments, the latter commonly distinguished by ferruginous palaeosol horizons.

Most of the detailed borehole logs in this district support the view that Coal Measures sedimentation was cyclic in character. A typical small-scale interseam cycle (Guion et al., 1995) consists of basal dark grey to black, carbonaceous and commonly pyritous mudstone containing nonmarine or less commonly marine fauna (lacustrine or marine conditions). The succeeding strata are generally coarser grained, with siltstone and sandy siltstone (overbank or distal lacustrine delta) and pass up to sandstone (proximal delta or channel). The top of each interseam cycle is generally marked by a seatearth (gleysol, palaeosol) and a coal (mire facies). Plant remains and debris are common throughout these cycles. The sandstones of this district only rarely occur at the tops of cycles, occurring instead mainly as intercycle channel-fill bodies. They are grey and mainly fine to medium grained, commonly cross-bedded and of multistorey type. Typical sedimentary structures preserved in the siltstone and sandstone include parallel lamination, flaser bedding, lenticular bedding, cross-bedding and climbing ripple cross-lamination. In this part of the Pennine Basin, the Coal Measures sequence thins progressively southwards, on to the Wales–London–Brabant Barrier (Fulton and Williams, 1988). Such a trend can be demonstrated for this district, although an additional complexity has been imposed by synsedimentary faulting and volcanic activity in Lower Coal Measures times. In particular, the Saltby Volcanic Formation (see below) represents lava aprons or shields that periodically encroached westwards, into the main Coal Measures depocentres.

The summary of the Coal Measures, herein, is based on borehole transects arranged to show the main directions of interseam variation in the district (Figure 7); (Figure 8); (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) and (Figure 11). Thicknesses of the principal coal seams are depicted on an areal basis in (Table 2) and (Table 3), but the main details of interseam lithological variations can be found in Sheppard (2003), and in the technical reports prepared during the mapping of this district (Table 12). The coal seam nomenclature generally follows that for the Nottingham district (Howard et al., in prep (a)). A number of seams merge, as summarised in (Figure 6), and the names change to reflect this. Thus the Low Bright, Brinsley, High Hazels, Cinderhill Main and an unnamed coal merge to form the ‘Top Bright Coal’ in the north-east of the district.

Lower Coal Measures (LCM)

The Lower Coal Measures are present at depth to the east and north of the line on Sheet 142 Melton Mowbray representing the surface projection of the incrop of the Subcrenatum Marine Band at the Permo-Triassic unconformity. The strata occupy a structural basin (Figure 27), formed by folding and faulting at the time of the end-Carboniferous (Variscan) inversion event, and they are locally overstepped by Permo-Triassic strata to the west and the south. In the northern part of the district, the thickness of Lower Coal Measures varies from about 430 m in the west, to 340 m in the east. (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) shows that the progressive eastwards thinning of Lower Coal Measures sedimentary strata on to the underlying Saltby Volcanic Formation (see below) is largely augmented by thickening of the volcanic rocks in the same direction. The complex stratigraphical relationships between the volcanic rocks and sedimentary strata (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), and (Burgess, 1982; fig. 6) commonly precludes the accurate correlation of coal seams in the east, which tend to occur as attenuated packages of beds, sandwiched within the thicker parts of the volcanic succession. The Subcrenatum Marine Band has been replaced by the Saltby Volcanic Formation before the Harston No. 1 Borehole [SK 8452 3165] is reached, just beyond the eastern margin of the district. Similarly at the top of the Lower Coal Measures, the Vanderbeckei Marine Band disappears as it onlaps the top surface of the Saltby Volcanic Formation (Figure 13)." data-name="images/P946224.jpg">(Figure 12); for example, it is missing from the Woolsthorpe Bridge Borehole [SK 8434 3488], located outside the district. The Lower Coal Measures thin southward across the Normanton Hills Fault (Figure 7); (Figure 8).

Subcrenatum Marine Band to Kilburn Coal: To the west of the area affected by penecontemporaneous volcanic activity, this part of the Lower Coal Measures succession shows a slight, general northwards thickening accentuated by synsedimentary movements along the Normanton Hills Fault (Figure 8); concomitantly, many of the coals show attenuation (e.g. Kilburn, Belper Lawn). At the base, the Subcrenatum Marine Band has locally yielded a diagnostic fauna; for example in the Wilds Bridge Borehole the ammonoids Anthracoceratites sp. and Gastrioceras subcrenatum were identified in addition to marine bivalves Caneyella sp. or Posidonia sp., Dunbarella sp., and fish debris (Riley, 1984). Elsewhere, although the marine band is distinguishable on geophysical logs, the faunas are generally non-diagnostic and include ammonoids, horny brachiopods Lingula and Orbiculoidea, trace fossils such as Planolites and fish debris. The overlying Crawshaw Sandstone (CrS) amalgamates and thickens northwards (Figure 8), but is locally of variable thickness, within a range of between 5 and 12 m overall. Above the Crawshaw Sandstone, a number of Lower Coal Measures marine bands is suggested by wireline geophysical data showing gamma-ray peaks in many boreholes. In the Wilds Bridge Borehole these marine bands occur within 20 m of strata and, with a few exceptions, are identified as dark grey, carbonaceous mudstones with fish debris and Lingula mytilloides (Riley, 1984). They include, from base to top, the Springwood or Honley Marine Band, Listeri Marine Band (immediately above the Alton Coal, and containing Gastrioceras listeri, Anthracoceratites sp., Posidonia sp., Dunbarella papyraceai), Lower Parkhouse (including foraminifers Ammodiscus sp. and the conodont Idiognathodus sp.) and Upper Parkhouse marine bands. A nonmarine fauna including the bivalve Carbonicola extenuata separates the last two. Above the Upper Parkhouse Marine Band, the Forty Yard (Meadow Farm) and Amaliae (Norton) marine bands were identified from the distinctive signature on the geophysical logs. Farther south, in the Sheep Pens Borehole, as well as in other provings in the Asfordby area (Figure 13), Lingulabearing mudstones represent the following marine bands (from base to top) Holbrook, Springwood, Honley, Listeri and Amaliae (Ambrose, 1999); (Table 4). An impersistent sandstone found between the Listeri and Forty Yards marine bands in the Hoe Hill Borehole is an off-white, gritty sandstone with pebbly layers, and is equated with the Loxley Edge Rock, the correlation of which is discussed further in Eden (1954). It should be stressed that there are rapid lateral variations in the coals and marine bands of the Asfordby area, as indicated, for example, by the northwards thickening of the Subcrenatum Marine Band to Kilburn Coal interval in (Figure 8). This is attributed mainly to synsedimentary tectonic uplift along the Normanton Hills Fault, but with the added complication of soft-sediment deformation that was associated with emplacement of the Asfordby Volcanic Formation, see below, and (Figure 13). The major clastic interval represented by the Wingfield Flags (WF) mirrors the trend seen in the Crawshaw Sandstone by generally amalgamating and thickening northwards (Figure 8). It is up to 50 m thick locally, although as little as 8 m has also been recorded, and consists of fineto medium-grained sandstones that are thinly bedded and micaceous; interbeds of siltstone or sandy siltstone are common, and climbing ripple cross-lamination is a typical sedimentary structure.

Kilburn Coal to Blackshale Coal: In this interval, the northward thickening noted above continues (Figure 8), and is accompanied by complex splitting of the Mickley coals. The Blackshale and Ashgate coals show a tendency to merge over most of the district, and in the south-east they join with the Mickley 1–3 coals to form a seam up to 8.18 m in the Harby Hill Borehole (Ambrose, 2000b). This merging together of the seams reflects stratal thinning in areas where the Lower Coal Measures lap onto the Saltby Volcanic Formation. Similar eastwards thickening, of the Parkgate, Blackshale and Ashgate and Norton coals, is seen in the south of the district (Table 2).

Blackshale Coal to the Vanderbeckei Marine Band: Above the Blackshale (and Ashgate) Coal, the Low Estheria Band acts as an important faunal marker horizon for those successions where attenuation and/or interdigitation with volcanic rocks precludes accurate coal seam correlations. Generally, it consists of dark grey to black, carbonaceous and micaceous mudstone with a nonmarine to brackish fauna of the crustacean Euestheria, the bivalve Carbonicola, fish debris and fish trace fossils including Cochlichnus. The volcanic rocks in the east of the district that are sporadically intercalated in this part of the succession (Figure 8) are probably the distal equivalent of Phase 1 activity in the Saltby Volcanic Formation (see below). The measures overlying the Blackshale/Ashgate coals maintain a fairly constant overall thickness from south to north, allowing for the intercalation of sills and lavas referred to Phase 2 of the Saltby Volcanic Formation (Figure 7; (Figure 8) and (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9). The Parkgate seam split is complicated and, as summarised in (Figure 6), in contrast to previous interpretations, the Threequarters and Tupton coals are not involved. Splitting of the Deep Main coals takes place in a north-north-west direction across the middle of the map sheet and is also reported from the Scalford area in the south-east (Ambrose, 2000a).

Local thickening of the sequence between the Yard and Joan/Brown Rake coals, in part, reflects the intercalation of Phase 2 lavas of the Saltby Volcanic Formation (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9). The various channel sandstone bodies intercalated in this part of the succession commonly have a north-south orientation (Figure 10), suggesting diversion or ponding of successively developed drainage systems against the western flanks of the lavas. In the south-east of the district, the succession between the Deep Main Coal and the Vanderbeckei Marine Band thins eastward due to the onlap of the strata across the surface of the Saltby Volcanic Formation. The full upward-coarsening cycle is seen, for example in the Harby Hill Borehole (Ambrose, 2000b), but is missing farther east, in the Waltham Lane Borehole, where the Deep Main, Joan and Brown Rake coals have all combined to form a seam that is 2.56 m thick.

Syn-depositional tectonism during deposition of the Lower Coal Measures is suggested by the stratal thickening noted above. Additionally, (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) shows an apparent truncation of strata at the disconformity formed by the local base of the Saltby Volcanic Formation, in the Plungar No. 23 Borehole. Here, the absence of the Yard and Blackshale/Ashgate coals broadly corresponds to the axis of folding related to the Plungar Dome. The pattern of interdigitation between the Lower Coal Measures and Saltby Volcanic Formation indicated by (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) shows that the Tupton, Parkgate and Deep Main coals successively onlap the volcanic rocks over a 2 km distance north-eastwards, between Plungar 23 and Grimmer boreholes. This could suggest a relatively steep western flank to the volcanic pile, which was perhaps accentuated by syn-volcanic faulting and flexuring in that area.

Middle Coal Measures (MCM)

The subsurface occurrence of the Middle Coal Measures on Sheet 142 Melton Mowbray is to the east and north of the line representing the incrop of the Vanderbeckei Marine Band at the Permo-Triassic unconformity (Figure 27). The unit is conformably overlain by the Upper Coal Measures in parts of the north and east of the district, but is also extensively overstepped by the Warwickshire Group and Permo-Triassic rocks and is absent from the subsurface in large areas of the south and west. The thickness of the Middle Coal Measures is at least 240 m in the north-west of the district.

Vanderbeckei Marine Band to Cinderhill Main/Top Bright Coal: The Vanderbeckei Marine Band, marking the base of the Middle Coal Measures, is up to 12 m thick in the north-west of the district. It consists of dark grey, generally laminated mudstone with common burrows, some pyritised, pyrite nodules and thin beds or nodules of ironstone. The base is locally black and carbonaceous or canneloid, with common plant remains including Calamites and Pecopteris. The brachiopods Lingula and Orbiculoidea were noted. Other fossils recorded are the marine bivalves, Dunbarella, Myalina, Pecten, and ?Posidoniella; gastropods including Euphemites, Platyconcha and Soleniscus; productids, ammonoids, ostracods including Geisina, foraminifera, the crustacean Euestheria; fish debris, coprolites and trace fossils including Cochlichnus, Planolites opthalmoides, ?Tomaculum and the worm tube Spirorbis. Nonmarine bivalves, including Carbonicola, Anthracosia, Anthraconaia, Anthracosphaerium and Naiadites have also been recorded and all typically occur interbedded with the marine fauna. The marine band has been proved persistently across the district, although it onlaps the volcanic rocks in the extreme east, e.g. (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9); (Figure 13)." data-name="images/P946224.jpg">(Figure 12); one exception is in the Hoe Hill Borehole, where it has been washed out by sandstone. Across the transect shown in (Figure 11), the Vanderbeckei Marine Band thins noticeably, from an average thickness of 12 m in the west to 2 m or less in the east. For example, in Croxton Banks Borehole, the marine band consists of only 2 m of dark grey, pyritous mudstone with Lingula, the nonmarine bivalve Anthracosia, foraminifera, ostracods and fish debris, accompanied by a flora of Mariopteris.

The northern part of the district contains the most complete sections through the Middle Coal Measures. The unit shows marked attenuation to the east where it is also overstepped progressively by the Warwickshire Group. This eastwards thinning was attributed by Burgess (1982) to the relatively low degree of compaction of rocks comprising the Saltby Volcanic Formation, in the underlying Lower Coal Measures. The thinning is, however, most accentuated in strata above the Third Waterloo Coal, as shown by (Figure 11). Thus over a horizontal distance of several kilometres the thickness of the Third Waterloo to Brinsley/Low Bright Coal interval reduces from 82 m, in the Coach Gap Farm Borehole, to 50 m in the Calcrofts Close Borehole. Sandstone bodies occupy correspondingly larger proportions of the measures farther east, some representing multistorey channel bodies forming the basal parts of interseam cycles. An example in the Stathern South Borehole is the 9.7 m thick sandstone above the Dunsil/1st Waterloo Coal, which is composed of five amalgamated sandstone beds, the thickest being at the base. The sandstones are pale green and fine grained, with ripple cross-laminated sets present throughout. The overlying strata comprise several siltstone beds characterised by sandy laminae and ripple-drift cross-lamination, with contorted bedding and burrows in some beds. The siltstones are capped by 1.5 m of seatearth, consisting of siltstone with ironstone nodules passing up to mudstone, which is overlain by the Top Hard group of coals.

Cinderhill Main/Top Bright Coal to Cambriense Marine Band: Complex splits and mergers of seams in the interval between the Cinderhill Main and Low Bright coals accompany an overall eastward attenuation of the upper part of the Middle Coal Measures (Figure 11). Thus in the Grimmer Borehole these coals have merged to produce the Top Bright seam of 2.6 m thickness. This is in turn overlain by a major channel sandstone body, 23.3 m thick in total, comprised of four amalgamated beds. The rest of the overlying 28 m of strata in the Grimmer Borehole, up to the junction with the Warwickshire Group, consists of interbedded siltstone and sandstone. These beds are lateral replacements of the Main Bright Coal, as well as the Maltby Marine Band, which occur at the same stratigraphical level within the thicker sequence farther west.

Above the Two Foot Coal (or where the latter is absent, the High Hazles to Low Bright coals), the sequence changes to one with relatively thin seam intervals and correspondingly thick seatearths (up to 3–4 m), and is punctuated by marine bands. The earliest of these is the Maltby (Two Foot) Marine Band, present over 5.6 m of strata in Stathern South Borehole. A note with the log by M A Calver (1977) draws attention to the co-existence of the marine ostracod Cypridina cf. phillipsi with nonmarine bivalves such as Naiadites augustus, suggestive of proximity to the shoreline at this time. In the same borehole the Aegiranum (Mansfield) Marine Band, defining the junction between the Duckmantian and Bolsovian stages, is identified by blocky, dark grey mudstones with Lingula mytilloides, the annelid Serpuloides stubblefieldi and productid bivalve fragments. This assemblage is supplemented by the nonmarine bivalve Anthracosia, and a marine fauna of Edmondia and Orbiculoidea in Stroom Dyke Borehole. The Edmondia and overlying Shafton marine bands were tentatively identified together in the Hills Farm Borehole within a thickness of 8.4 m of siltstone and muddy siltstone containing fucoids, Mariopteris and Alethopteris and bivalves including the nonmarine Anthraconaia pruvosti. The bivalves may indicate the presence of the Main Estheria Band, which normally occurs between the Edmondia and Shafton marine bands. The Cambriense (Top) Marine Band, whose top also defines that of the Middle Coal Measures, is tentatively identified over about 5 m of strata in the Stroom Dyke Borehole, where it may be faulted; it consists of poorly laminated, pyritous mudstone with fucoids, fish debris and ostracods.

Upper Coal Measures (UCM)

These strata are thin and discontinuous due to their removal by erosion at the unconformities with the Warwickshire Group or Permo-Triassic sequence. Their identification depends upon recognition of the Cambriense Marine Band, the top of which is taken to be the base of the Upper Coal Measures. The marine band has only been tentatively identified, however, from the Stroom Dyke Borehole described above. There, it is overlain by about 10 m of mudstone and brick red micaceous siltstone with a bed of ‘grit’ (1 m thick), which contains subangular fragments of acid and basic igneous rock. A red colouration, accompanied by ochreous mottling, is typical of the topmost Coal Measures strata in this district. This is a secondary feature, caused by staining below the Permo-Triassic strata or (where present) the Warwickshire Group.

Westphalian volcanic and intrusive rocks

Alkali basaltic magmatism in the eastern and central parts of the district possibly commenced in the latest Namurian and continued throughout the Langsettian (Lower Coal Measures). The complex relationships caused by interdigitation between the extrusive rocks and Coal Measures strata are summarised in (Figure 7) and (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), and the areal distribution of the two main igneous formations is shown in (Figure 13)." data-name="images/P946224.jpg">(Figure 12). Burgess (1982) and Kirton (1984) provided brief reviews of this activity, and two formations have been formally named during this resurvey.

The Asfordby Volcanic Formation is a thick but areally restricted sequence of basaltic peperite breccias. They are possibly intrusive, and were emplaced into strata below the Kilburn Coal in the south of the district. The Saltby Volcanic Formation is a more widespread development of basaltic extrusive rocks. The base lies close to the Namurian–Westphalian boundary and the top between the Yard and Parkgate seams in the Lower Coal Measures sequence.

Basic intrusive rocks, mainly sills, some of which have been named, occur throughout the Lower Coal Measures and lower part of the Middle Coal Measures, but have not been encountered above the Dunsil/1st Waterloo seam (Figure 6). Sills have also been encountered in the Namurian and Dinantian sequences of the district.

Asfordby Volcanic Formation (AsVo)

The Asfordby Volcanic Formation, named by Ambrose (1999), is confined to a narrow subsurface zone around the Asfordby Colliery site. Its southern limit is not known, but may be taken at the Sileby Fault (Figure 13)." data-name="images/P946224.jpg">(Figure 12). The formation consists mainly of fragmental basaltic rocks, some of which are referred to as ‘agglomerates’ on borehole logs. It should be stressed that many of the classifications previously used for these rocks cannot now be supported, and as discussed below certain lithologies formerly described as ‘agglomerate’ may in reality be peperite breccias.

The precise age of the Asfordby Volcanic Formation is not known with any certainty because of doubts as to the extrusive or intrusive origin of these rocks, discussed below. The earliest (stratigraphically lowest) proving is in The Chase Borehole, where the formation occurs at a late Kinderscoutian to Early Marsdenian level; the Coreticulatum Marine Band (Kinderscoutian), and sandstones correlated with the Kinderscout Grit, have been proved respectively 25 m and 10 m below the first basalt. The top of the basalt pile in the Asfordby Farm Borehole lies within Langsettian strata (Figure 13), just below the seam identified as the Kilburn Coal. If an intrusive mode of origin is adopted, the latter datum, being part of the ‘roof’ to the Asfordby Formation, would approximate to the maximum possible age of the magmatism.

A maximum 141 m thickness of the Asfordby Volcanic Formation was proved in The Chase Borehole. The northerly limit of the formation is well constrained by borehole evidence in the Asfordby Colliery area, and is a remarkably abrupt interface across which the basaltic rocks disappear over distances that in some cases are as little as 50 m from the main mass (Figure 13). Even close to the formation’s margin, basalt is found interdigitating with Lower Coal Measures strata only in the Asfordby Mine Site Nos. 2, 4 and 5 boreholes, all being within 100 m of the subcrop. The exception to this is in the Asfordby Hydro Borehole, about 25 m below the Kilburn Coal, where there are layers of basalt that show partly crenulated or ‘pillowed’ contacts against sedimentary rocks (Old and Riley, 1983). Beds rich in basaltic fragments are found in conjunction with disturbed sedimentary strata, that in places assume near-vertical attitudes, in the Holwell Works and Asfordby North Shaft boreholes. The disturbed Namurian strata in the Asfordby Hydro Borehole, just below the level of the Cumbriense Marine Band, show features indicative of soft-sediment deformation. Away from the mine area, to the north, north-west and west, the limits of the formation are poorly constrained, in part due to boreholes terminating higher in the Coal Measures sequence.

The thick basaltic rocks in the Asfordby North Shaft, Asfordby Farm, Osier Bed and Welby Church boreholes (Figure 13) were described as lava flows by Old and Riley (1983), with individual layers from 1 to 17 m thick recognised in many cores. Inter-layer weathering was not obvious, however, and many internal contacts were described as ‘firmly welded’. Mudstone and siltstone fragments, apparently showing few signs of baking, occurred within some of the basalt layers, and in the Osier Bed Borehole, Old and Riley (1983) noted a sedimentary component enclosing poorly developed basaltic pillows. The present authors have found that coarsely fragmental lithologies are present in layers that are metres thick, and are interleaved with more massive basalt throughout the Welby Church Borehole where the formation is over 100 m thick. In these rocks the larger (block-size) basalt fragments commonly show curviplanar to amoeboid margins, similar to fragments of pillows (e.g. Carlisle, 1963; Staudigel and Schmincke, 1984). The matrix between these fragments is remarkably heterogeneous, with two principal components recognised (Plate 2). In a thin section (E72703), one component consists of abundant fragments of amygdaloidal basaltic scoria with smoothly rounded to cuspate margins. Each fragment is surrounded by a thin, dark grey, glassy, nonvesicular rim. Separating the scoria fragments, the second component consists of fine-grained to amorphous, locally amygdaloidal, chloritised material, possibly representing highly altered sediment. The mudstone immediately overlying the main basalt sequence is variously described in completion logs as being baked (Welby Church, The Chase boreholes), or heavily veined with calcite (Laneside, Substation Asfordby). The best description of the top contact of the formation comes from the horizon at 517.72 m depth in the Asfordby Mine Site No.1 Borehole. There, dark grey mudstone of the Lower Coal Measures sequence sharply overlies dark greenish grey, nonvesicular basalt. This contact is described as ‘highly irregular with many fragments of igneous rock in sediments for 15 cm; contact selvedges slightly paler and finer grained’. Just one metre below this upper contact, ‘pillowed masses’ were noted in the basalt.

Old and Riley (1983) considered the possibilities that the Asfordby basalts were extruded either as lava flows, contemporaneously with late Namurian to early Langsettian sedimentation, or as lavas of entirely Langsettian age that, due to their heat and weight, burrowed downwards through the sediments into Namurian strata. It is difficult to envisage the first of these alternatives, requiring large volumes of basalt to be erupted over a fairly extended period, within about 100 m of a normally accumulating Namurian to Langsettian sedimentary sequence (Figure 13). On the other hand, it is possible that basaltic magma was rapidly emplaced by multiple sheet intrusion at shallow levels into unconsolidated wet sediments, the resulting complex interactions causing the observed pervasive development of peperitic breccias (White et al., 2000). Such a mechanism would account for the lack of weathering seen in other provings of the top of the formation, as well as the weak baking and calcite mineralisation noted in the immediately overlying mudstone. Intrusion would also give rise to the apophyses of peperitic material found in the adjacent strata, as in the Asfordby Hydro Borehole; a forcible intrusive mode explains the synsedimentary deformation of these strata.

An intrusive mode of origin, with the Kilburn Coal and higher strata forming the roof to the sedimentary carapace enclosing the Asfordby Volcanic Formation, requires that this magmatism was younger than its stratigraphical position suggests. Phreatomagmatic extrusive activity, contemporaneous with the basalt intrusion, may indeed have given rise to the tuffs, spatially related to the Asfordby Volcanic Formation, overlying the Kilburn Coal in boreholes north of the Asfordby Mine Site (Figure 13). There are further tuff beds in the Steelworks Borehole, which are also of Early Langsettian age, occurring between the Listeri and Amaliae marine bands.

Saltby Volcanic Formation (Stby)

This formation was named by Ambrose (2000a), who designated a type section in the Egypt Plantation Borehole, about 1.5 km to the east of this district [SK 8660 2786]. It represents a complex association between basaltic lavas, pyroclastic and epiclastic rocks and basic sills. The formation is widely distributed in the subsurface of the eastern part of the district (Figure 13)." data-name="images/P946224.jpg">(Figure 12), and it both thickens and amalgamates eastwards, towards the presumed volcanic source region, achieving about 280 m thickness in the Harston No. 1 Borehole (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), just outside the district. The latter record suggests that volcanism had commenced, possibly just after deposition of the Subcrenatum Marine Band. The termination of activity was placed by Burgess (1982; fig. 6) immediately after deposition of the Vanderbeckei Marine Band, corresponding to the Langsettian–Duckmantian boundary. In this district, however, younger pyroclastic fall-outs, in early Duckmantian times, are also suggested by the thin ash-grade tuff beds occurring in the Thorney Plantation Borehole between the 4th and 3rd Waterloo Coals and between the 3rd Waterloo Coal seam split in the Middle Coal Measures.

In an overview of this volcanism, Burgess (1982) pointed out the limitations of the subsurface data and the difficulties this imposed for distinguishing between the various classes of igneous or extrusive basaltic rock. Despite these problems the borehole correlations (Figure 7); (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) point to there being two major expansions of volcanism, broadly equivalent to the main pulses of activity suggested by Burgess (1982), although not by Kirton (1984, fig. 3). In this account, they are designated as Phase 1 and Phase 2, each representing the construction of a basaltic lava shield or outflow apron westwards across the northern part of the district (Figure 13)." data-name="images/P946224.jpg">(Figure 12).

Phase 1 Volcanism between the Subcrenatum Marine Band and Mickley/Ashgate coal grouping

This activity denoted the first major westwards encroachment of basalt, which may locally have been directed along the foot of the Cinderhill–Foss Bridge Flexure (Figure 13)." data-name="images/P946224.jpg">(Figure 12). It commenced at about the level of the Crawshaw Sandstone in the east of the district, where an early pyroclastic episode is suggested by gamma-ray interpretations of the Harston and Redmile boreholes. The volcanic products also include basalt flows (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), and in the Plungar area lavas postdate the Kilburn coal. The base of the volcanic rocks is thus diachronous, becoming progressively younger farther west, whereas volcanism was more or less continuous in the east, where the main centres of eruption were probably located. The surface of the lavas is, by definition, a plane of disconformity, and as sedimentation recommenced it was progressively onlapped to the east, first by the Mickley coals and later by the Blackshale/Ashgate and Yard coals.

About 200 m of ‘tuff’ extending between the Rough Rock and Morley Muck Coal in the Colston Bassett South Borehole (see Section 1 on the Sheet 142 Melton Mowbray) is also attributed to Phase 1. Descriptions of the borehole chip samples (Sabine, 1963) indicate an abundance of ‘scoria’ fragments, and thus a probable pyroclastic-dominated sequence. Sabine concluded that such a great thickness of pyroclastic rocks must be due to the presence of a volcanic centre, here termed the ‘Colston Bassett Centre’ (Figure 13)." data-name="images/P946224.jpg">(Figure 12).

Volcanic breccias and fine-grained tuffs of Langsettian age in the southern part of the district are located within one kilometre of the main development of the Asfordby Volcanic Formation and are described above, although their true affinities are not known. Various other provings show thin beds of ash-grade tuff between the Subcrenatum Marine Band and the Kilburn Coal.

Phase 2 Volcanism between the Yard Coal and Parkgate/Tupton coal

This phase marks a second westwards expansion of basalt lava flows and associated pyroclastic rocks, particularly in the north of the district (Figure 13)." data-name="images/P946224.jpg">(Figure 12). The volcanism superseded the Yard Coal in the north-east (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), but like Phase 1 the base is diachronous, as indicated by extrusive rocks at relatively low stratigraphical levels, just above the Blackshale Coal, in the Harby Hill, White Lodge and Goadby Gorse Boreholes. The upper surface to the Phase 2 pile is estimated to have had an average 1° westwards slope, and it formed a major topographic feature across which the Tupton Coal and strata up to and including the Vanderbeckei Marine Band pinched out progressively eastwards (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9); (Figure 13)." data-name="images/P946224.jpg">(Figure 12). Possible airfall products of this volcanism are also seen farther south, as the beds of tuff between the Threequarters and Tupton coals in the Stonepit Spinney Borehole. As noted above, tuffs have also been recognised at higher stratigraphical levels, up to the 3rd Waterloo Coal in the Thorney Plantation Borehole. These latter occurrences may suggest a still younger phase of volcanism in other parts of the East Midlands region.

Surficial weathering of Phase 2 rocks, prior to renewed Coal Measures sedimentation, is suggested by the log of the Woolsthorpe Bridge Borehole describing ‘tuff’ with red layers and ironstone concretions at the top of the volcanic sequence. A possible horizon of reworked volcanic material is seen in the Stathern South Borehole, where notes by I C Burgess describe a pale grey ‘tuff’ with rootlets and a seatearth fabric between the Tupton and Parkgate coals. In the same borehole, the top surface of the main lava sequence, below the Tupton Coal, is altered to a 1.8 m-thick ‘bole’ consisting of basalt weathered to dark green material (notes of I C Burgess). In the Freeby View Borehole, a 3.69 m-thick ‘bole’ caps the basalt lava sequence. A well developed soil profile occurs at the top of some of the older Phase 2 tuffs, just above the Blackshale Coal, in the Harby Hill and White Lodge boreholes.

Interpretation of the main volcanic lithologies in Phase 2 is aided by the annotated descriptions of I C Burgess and by the present author’s own interpretations of core samples from the Grimmer Borehole.

Basalt lava flows: These are represented in the upper part of the Grimmer volcanic succession. Notes on the completion log, and the evidence of the gamma-ray profile (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14), indicate that flow sequences average about 10 m in thickness, and some are separated by thin sedimentary layers. The preserved core samples show that individual flow sequences are of compound type, comprising layers of 2 to 4 m average thickness with some interflow basaltic breccias. A thin section of lava (E72603) shows abundant zeolitised plagioclase laths in a turbid, intersertal matrix composed of granules and leafy acicular aggregates of Fe-Ti oxides; euhedra and granules of chloritised olivine are scattered throughout. Rounded, compound amygdales are infilled by chlorite-zeolite, possibly quartz and Fe-Ti oxides. This specimen contains a single, small, angular ultramafic xenolith consisting of granular chloritised aggregates pseudomorphic after olivine, and dark brown possibly picotite spinel; two similar occurrences from the Vale of Belvoir Carboniferous volcanic rocks were noted by Kirton (1984). Farther south, in the Freeby View borehole, Burgess identified at least five separate lava flows, all showing evidence of subaerial exposure. Two have a well-developed pale green to reddish grey ‘bole’ at the top, and the remainder are capped by reddened basalt, commonly showing spheroidal weathering.

Tuff: This is commonly fine to medium-grained, and pale greenish grey in colour. In the Grimmer Borehole it is massive or only faintly laminated. In a thin section (E72612) of tuff from 739.7 m depth in the Croxton Abbey Borehole, a platy fabric is imparted by the parallel alignment of elongate shards of chloritised glass, resembling Pele’s hair pumice and suggestive of distant subaerial lava fountaining (e.g. Williams and McBirney, 1979, p.130). Alternations of fine-grained and coarse to lapilli grade tuffs were described by Burgess (1976, notes accompanying borehole log) from the top of the Saltby Volcanic Formation in Stathern South Borehole.

Basaltic breccias: Many coarsely fragmental lithologies in the Saltby Volcanic Formation have been described on coal exploration completion logs as ‘agglomerate’. Unfortunately with these log descriptions, critical details of fragment shapes and outlines have not been provided. It is therefore uncertain whether the fragments are true volcanic bombs, or fragments of bombs, which are necessary to be present in the majority for such a term to be applied (Fisher and Schmincke, 1984). In the limited runs of core samples from the Melton Mowbray district examined by the present authors, however, most of the fragments lack the contorted or fluidal outlines typical of volcanic bombs, and are in reality ‘blocks’. The nongenetic term ‘breccia’ is thus more appropriate for these lithologies. Breccias form much of the lower part of the Saltby Volcanic Formation in the Grimmer Borehole (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9); (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14); they are preserved as partial core-runs, the examination of which suggests the following bipartite division.

• The lower part of the core in (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14), from about 692 m down to at least 701 m depth, is dominated by green-grey, very coarsely fragmental lithologies interpreted here as peperite breccia, a lithology whose definition is discussed by White et al. (2000). The distinctively serrated appearance on the gamma-ray log suggests that this is a thickly bedded lithology (on a scale of several metres), a structure possibly related to variations between the proportion of mudstone matrix and basalt fragments. The latter are up to 0.15 m in dimension and consist of irregular-shaped blocks with curviplanar margins. There are also sporadic angular to irregularly shaped rafts and slivers of dark grey mudstone, these commonly showing baked reaction rims against the matrix. The matrix consists of green grey, medium-grained tuff intimately mixed with dark grey silty mudstone (Plate 3). In a thin section (E72605), the matrix tuff component consists of amygdaloidal basaltic scoria fragments, many with finely serrated margins; some have sliver-like shapes, and these commonly show flattened or tube-like internal vesicle forms. The margins of many scoria fragments are delicately preserved against the adjacent silty mudstone, which forms globular to wispy patches. The sediment is locally vesicular and in places it anastomoses between individual scoria fragments.
• The upper fragmental component, between about 672 m and 692 m depth (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14), consists of green-grey basaltic pillow breccia. It is thickly stratified on the scale of the peperite breccia described above. Many layers consist of dispersed basalt fragments with curviplanar margins and are reminiscent of the ‘pillow-fragment breccia’ or ‘scoria pillow breccia’ facies described from elsewhere by Staudigel and Schmincke (1984). Many basaltic blocks have chilled rims and some show in situ brecciation into angular clusters penetrated by green grey, fine-grained basaltic hyaloclastite. Some irregular shaped, non-blocky fragments have feathery or amoeboid outlines (Plate 4), identical to the descriptions of scoria pillow fragments by Staudigel and Schmincke (1984) but also similar to the ‘equant globular’ clasts of some peperite breccias (Doyle, 2000). Other clasts, in various stages of disintegration, appear to consist of pale grey, very fine-grained tuff or tuffaceous mudstone. There is no obvious sedimentary component in the matrix of these breccias, which in a thin section (E72604) is mainly of lapilli grade, consisting of angular to rounded or globulose, closely packed fragments of vesicular, dark brown basaltic glass cemented by carbonate. Interleaved within the pillow breccia, at 682 m depth, is a 2 to 3 m-thick peperite layer showing in situ fragmentation textures, with jigsaws of angular basalt blocks surrounded by chilled margins separated by a tuff/sediment matrix.

Overview of phase 2 volcanism

The record for Grimmer Borehole indicates that at least locally, the peperite breccias form the stratigraphically oldest part of Phase 2 in the Saltby Volcanic Formation. These lithologies may be of rather limited areal distribution, although more studies are needed to accurately determine this. They are the approximate lateral equivalents of sills and basaltic lavas in adjacent boreholes (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9), and so could represent either (a) the products of shallow-level magma intrusions into wet sediments, or (b) zones of magma/sediment interaction caused by the invasion and burrowing of subaerial lavas into ‘wet pockets’ of the substrate. With (a) the pillow breccias of Grimmer could represent re-sedimented basaltic material that was deposited from debris flows avalanching down the sides of a subaqueous edifice that had emerged above the sediment/water interface. Alternatively, with model (b) the pillow breccias could represent talus from the disintegrating front of a subaqueous lava flow, following an earlier episode during which the substrate had been peperitised. The capping of compound lava flows would reflect the establishment of a subaerial flow apron during the final stage of volcanic build-up.

Intrusive rocks

Basic intrusive sills occur at a number of levels in the Coal Measures (Figure 6). Burgess (1982) noted that they are most abundant in the south, where the lowest sills occur in late Dinantian strata and the highest found is above the 2nd Waterloo Coal of the Middle Coal Measures. Farther north sills are confined to the Lower Coal Measures, mainly between the Alton and Parkgate coals (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9). The sills form part of an alkaline dolerite complex that extends over much of the East Midlands (Falcon and Kent, 1960).

The principal mineral assemblage in the sills consists of olivine, pyroxene, plagioclase (labradorite-bytownite) and Fe-Ti oxides. In one study, it was noted that texturally, the sills differ from the lavas in being more even grained and rather less vesicular (Old and Riley, 1983). Kirton (1984) described them as ‘olivine-dolerites’, although it is noted here that sills, like lavas, may have intergranular (basaltic) textures, and that the subophitic (‘doleritic’) textures, typical of thick sills, can also develop in the internal parts of thick lava flows. Consequently, sills and lavas commonly cannot be differentiated on textural grounds alone and the most conclusive criterion is the observation that sills have markedly chilled, sharp, planar margins with the sediment, particularly along their top surfaces. There is insufficient chemical data available to compare the composition of the different sills, and thus to deduce whether there may have been contrasting sources of magma and possibly different phases of intrusion. In this account, informal names are given to the main sills, taken from the underlying coal seam or marine band (Figure 6).

In the southern part of the district, around Asfordby, the presence of basic sills was a significant contributor to problems that caused the failure of the scheme to exploit the local coal resources (see note in Mercian Geologist, 1998; p.102). In order to rationalise their distribution, Ambrose (1999) divided them into two suites, one intruded into the Lower Coal Measures and the other into the Middle Coal Measures ((Figure 15)a, b respectively). Sills in the Lower Coal Measures appear at progressively higher stratigraphical positions northwards from the Asfordby area (Figure 15)a, perhaps indicating that the ‘younger’ sills emanated from the magmas that were feeding the two phases of Saltby Formation volcanism. Elsewhere in the early Langsettian, sills occur at three main levels up to the Kilburn Coal (Figure 6). Most of these are concentrated adjacent to the Fosse Bridge Fault (Figure 15)a, which possibly acted as a magma feeder zone. The Alton Sill has not been proved in the Melton Mowbray district but probably extends into it from farther north. On the other hand, the Norton Sill and the sill below the Wingfield Flags have only been proved in the south of the district. The stratigraphically highest sill in the Lower Coal Measures is the Parkgate Sill, which occurs extensively in the north-east of the district as well as in the Cotgrave area, to the north-west.

Sills in the Middle Coal Measures occur on five stratigraphical levels (Figure 6) and are of comparatively restricted lateral extent, in the south of the district. Around Asfordby most were supplied by one feeder pipe centred just to the west of the Asfordby Mine site. This feeder may have been closely associated with the zone of basalt up-rise that supplied the Asfordby Volcanic Formation, compare (Figure 15)b and (Figure 13)." data-name="images/P946224.jpg">(Figure 12). It may also have fed the Subcrenatum Sill and western part of the Kilburn Sill, compare (Figure 15)a and (Figure 15)b). The Joan Sill was evidently intruded from two different feeder pipes.

Geochemistry and absolute age of the basaltic rocks

Information on the lavas and sills of the Melton Mowbray district is provided by the studies of Kirton (1981, 1984) and Webb and Brown (1989). Based on the freshest samples, Kirton concluded that these rocks comprise a spectrum of petrographical types, ranging from basalt and basanite through to hawaiite. Olivineand nepheline-normative varieties dominate, although some rocks showed normative quartz. Tholeiitic to alkaline or subalkaline chemical compositions are typical. Webb and Brown (1989) state that the tholeiitic suite is dominant, but also note that the most alkaline composition represented in the Westphalian volcanic rocks of the East Midlands is recorded from the Vale of Belvoir (Egypt Plantation Borehole, just to the east of the Melton Mowbray district). Most rocks consist of olivine basalts with TiO₂ in the range 1.6 to 2.5% (Kirton, 1981). The geochemical studies of Kirton (1984) showed that all Vale of Belvoir basalts, whether of extrusive or intrusive origin, fall within the same chemical compositional fields and thus share the same tectonic setting. Relatively immobile trace elements, when plotted on discriminant diagrams by Kirton (1984) and Webb and Brown (1989), reveal a wide distribution between the alkaline and tholeiitic fields (Zr/TiO₂ versus Nb/Y) and alkaline and subalkaline fields (Nb/Y versus Zr/P₂O₅) and, in these respects, the East Midlands samples showed a greater range of magmatic affinities than did the more alkaline West Midlands suites. Webb and Brown nevertheless concluded, on the basis of the Ti-Zr-Y discriminant diagram, that all of the Vale of Belvoir basalts are of ‘within-plate’ type. The ultramafic nodule-bearing samples from the Melton Mowbray district were, as expected, from rocks of more alkaline geochemistry.

The age of extrusive basaltic magmatism, which in this district is represented by the Saltby Volcanic Formation, is constrained to the Westphalian Epoch commencing around the datum of the Subcrenatum Marine Band, and terminating just above the Tupton Coal (i.e. intra-Westphalian A). On the recent time scale of Opdyke et al. (2000), this part of the Westphalian represents a restricted time-range of between 316 and 313 Ma. Such values, constrained by uranium-series methods on interbedded volcanic rocks in various parts of Europe, are more precise than the available radiometric (KAr) data so far obtained from sills in this part of the UK. For example in the Harlequin Borehole [SK 6684 3981], 4 km north of this district, rather younger (Stephanian) dates of 296 ± 15 Ma and 302 ± 20 Ma (Francis et al., 1968) are implied. The large error ranges preclude these radiometric data from being accurate estimations of emplacement age, although the Duckmantian (Westphalian B) sills obviously represent intrusive magmatism postdating the extrusive sequence of the district (Figure 6).

Warwickshire Group

Warwickshire Group is the formal name for the red-bed formations and relatively coal-poor, grey formations that overlie the Coal Measures Group in the Pennine Basin and Warwickshire (Powell et al., 2000). It replaces terms such as ‘Barren Measures’, previously used to qualify these strata. Information on this group is restricted to certain boreholes in the north-east part of the district. These show that there are variations within the group from west to east, and that the base of the Warwickshire Group is an unconformity that cuts down eastwards into the Coal Measures (Figure 11).

The group represents a change in the depositional environment to one that was dominated by better drained alluvial conditions, thus allowing the development of reddened, ferruginous palaeosol horizons. It signifies localised uplifts in this region that were related to the onset of the end-Carboniferous, Variscan deformation (Besly, 1988 and see Chapter 8).

In this district, the Warwickshire Group includes strata of Duckmantian and Bolsovian age. It is subdivided into the mudstone-dominated Etruria Formation and the overlying sandstone-rich Halesowen Formation.

Etruria Formation (Et)

The Etruria Formation is bounded by unconformities and its thickness is consequently variable, ranging from zero to about 60 m. Its unconformable base is poorly constrained in this district, but is discussed in some detail by Howard et al. (in prep. (a)), for the area to the north. There, it is commonly taken at the base of the first gritty sandstone of ‘espley’ type, but can also be identified on geophysical logs, which show a marked change of gamma-ray profile between the Etruria Formation and underlying Coal Measures. In this district the junction commonly coincides with an abrupt lithological change, from a multi coloured seatearth with hematite stringers and pisoidal ironstone inclusions, typical of lithologies in the Etruria Formation, to the underlying Middle Coal Measures composed of grey-brown mudstone with coaly plant and rootlet fragments. It is stressed, however, that secondary weathering of the Coal Measures can produce lithologies of a similar appearance to those in the Etruria Formation.

In one of the thickest cored sequences (56 m in Terrace Hills Borehole), the formation consists almost entirely of red-brown, grey-green, maroon and ochreous siltstone beds. These are massive to laminated, with colour variations and contain pisoids of sphaerosiderite and hematite. Sedimentary structures include (rare) ripple-drift cross-lamination, tracks and raindrop imprints; some siltstone beds contain horizons with rootlet traces. Intercalated beds showing more extensive pedogenic modification are from about 1 to 7.5 m thick and many are described as ‘seatearth’ in the borehole log. Such beds contain abundant rootlet traces and some have a brecciated appearance, with muddy listric surfaces and highly contorted sandy patches. ‘Concretionary’ layers, with hematite pisoids, were also noted on the borehole log. Sandstones are rare in this borehole; one 1.3 m-thick bed, was described as being green, medium-grained to ‘gritty, micaceous and slightly calcareous, with plant remains and layers with small pisoliths and oolitic concretions’.

Lithological variation within the unit is demonstrated by the succession in the Barkestone Bridge Borehole. There, a bed of ‘volcanic ash’ (6 m thick) is recorded within the normal sequence of red to green, pisoidal mudstones. The ‘ash’ consists of graded beds containing sedimentary clasts intermixed with green ‘chloritic’ minerals; subordinate ‘breccia’ (subangular conglomerate) contains dark green (possibly igneous) rock fragments. Volcanism contemporaneous with the Etruria Formation has been described from the Birmingham district of the West Midlands (Glover at al., 1993). In the Melton Mowbray district, however, these ‘ash’ beds are considered to be merely the reworking of the detritus produced by uplift and erosion of the Saltby or Asfordby volcanic sequences (Burgess, 1982). For example, thin sections [E 72613, E 72614] of Warwickshire Group breccia-conglomerate in the Swallow Hole Borehole [SK 8437 3279], just to the east of the district, showed highly oxidised basalt clasts but no pristine volcanic material.

Halesowen Formation (Ha)

Typically, this formation consists of grey-green micaceous sandstone and mudstone with thin coals, intraformational conglomerate and, in places, red beds (Powell et al., 2000). It is about 60 m thick in the north-east of the district, where it is locally preserved beneath the base Permo- Triassic unconformity (Figure 27).

The red-bed facies of the Halesowen Formation is represented by about 35 m of sandstones intercalated with mudstone and siltstone in the Croxton Banks Borehole. The sandstones, which range between 0.4 and 2.5 m thick, are present in an increasing abundance upwards through the formation. They are medium-grained, red-brown to greyish purple and micaceous, with cross-laminated structures in places. Some contain intraformational hematitic clasts, and in the stratigraphically highest sandstones, just below the Permo-Triassic unconformity, calcareous concretions are locally abundant. The thickest sandstone (8.21 m) is coarse-grained, micaceous, and, according to the borehole log, shows ‘vaguely inclined laminations’. The intercalated beds of purplish red to brown or blue-green siltstone are up to 2.4 m thick, and commonly described as ‘coarse’ and ‘sandy’; many are micaceous and some show weak development of rootlet traces. Mudstones form sporadic beds, some are up to 2.8 m thick; most are seatearth-like, with rhiozocretions, sphaerohematitic concretions, rootlet fabric, listric surfaces and admixed silty layers. The base of the Halesowen Formation in this borehole is arbitrarily taken as the base of the lowermost sandstone that rests, with apparent conformity, on purplish red to brown siltstone equated with the top of the Etruria Formation.

Chapter 4 Permian

Permian strata do not crop out in the district but occur widely at depth as shown by subsurface provings. The thickness ranges between zero to about 45 m and reflects accumulation in pockets, on an irregular unconformable surface that truncates strata of the Millstone Grit, Coal Measures Group and Warwickshire Group.

The subdivision of Permian rocks in this district is based on the evidence of cored boreholes and geophysical logs. The correlations (Figure 16) show that the Permian strata conform to the standard East Midlands lithostratigraphical sequence (Smith et al., 1986), as adopted for the adjacent Nottingham district by Charsley et al., (1990) and Howard et al. (in prep. (a)).

Regionally, the top of the Permian succession is taken at the top of the Littlebeck Anhydrite (formerly Top Anhydrite) of North Yorkshire and Lincolnshire (Whittaker et al., 1985). This bed dies out southwards, however (Smith et al., 1986), and in this part of the East Midlands the top-Permian datum lies within the Roxby Formation. This in turn passes laterally into the Lenton Sandstone Formation, in which Howard et al. (in prep. (a)) place the datum at a non-sequence forming the base of the Calverton Breccia. Howard et al. identify the Calverton Breccia at the top of the Edlington Formation in the Eady Farm Borehole of the Nottingham district (Figure 16). A similar breccia occurs in the Woodlands Farm and Barkestone Bridge boreholes of the Melton Mowbray district, but here we consider it to lie at a lower stratigraphical level, and, therefore, it is not the Calverton Breccia. The position of the top Permian-base Triassic datum is therefore uncertain, and in this account it is taken at the most recognisable feature on wireline logs. This is a gamma-ray high that coincides with mudstone attributed to the Roxby Formation, and is consistent with the evidence cited above for the top Permian datum level. The Lenton Sandstone of the Melton Mowbray district is thus partly Triassic in age (Figure 16). It is included in the Sherwood Sandstone Group and described in the next section.

Accumulation of the Permian strata followed prolonged erosion of East Midlands Precambrian and Palaeozoic rocks that had been uplifted at the end of the Variscan orogeny. During the Permian, Eastern England lay at the western margin of the Southern North Sea Basin (or Southern Permian Basin), a foreland basin that extended from Eastern England to Poland (Ziegler, 1982). Hot, arid desert conditions prevailed, and initially terrestrial deposits, such as piedmont breccias and aeolian sediments, accumulated. Late in Permian times, rapid inundation by the Zechstein Sea flooded the deeper, central parts of the basin. This was followed by a series of sea level changes, which caused cyclic repetitions in deposition; basinal carbonates and evaporites accumulated in the basin centre, with marginal shelf carbonates (Cadeby Formation) extending into the northern fringes of this district. The Cadeby Formation was succeeded by other marginal facies, commencing with a complex association of sabkha, playa, fluvial and aeolian deposits (Edlington Formation), succeeded by aeolian and fluvial sands (Lenton Sandstone Formation) and playa muds (Roxby Formation).

Permian Basal Breccia (PBB)

The Permian Basal Breccia is present across much of the district, and is contiguous with similar lithologies in areas to the north (Howard et al., in prep. (a); Smith, 1989). To the west, the part-equivalent lithology was termed the Moira Breccia (Hains and Horton, 1969), or Moira Formation (Barclay, 1996a, b; Carney et al., 2001). In the Melton Mowbray district, borehole correlations (Figure 16) suggest that the Permian Basal Breccia is diachronous, and is a local lateral equivalent of the Cadeby and Edlington formations in the south.

The Permian Basal Breccia is impersistent and generally up to about 5 m thick, but has a maximum proven thickness of 30.43 m in the Melton Spinney Borehole. It consists mainly of red to purple-brown, generally poorly cemented, conglomerate, with subangular clasts of 10 to 100 mm across in a fine to coarse-grained sandstone or argillaceous sandstone matrix. In the Willow Farm Borehole, the conglomerates have both clast and matrix-supported fabrics, occurring either as massive beds or, where there are variations in clast sizes, as beds with parallel bedding or cross-bedding. Some individual beds show normal grading, and there are cyclic stratal packages that fine upwards from breccia to pebbly sandstone. Visual inspections of core samples indicate a diverse clast suite, including various clastic sedimentary rock types, as well as limestone, ironstone, basic igneous rocks, metasedimentary rocks and granite. In the Willow Farm Borehole, clasts include basic igneous rocks of probable Carboniferous (Namurian–Westphalian) derivation; small pebbles and granules include fine-grained acidic tuff, in places with a poorly defined cleavage, as well as various types of microgranular quartz diorite (E72606), and were probably derived from the local sub-Carboniferous basement (see Chapter 2).

The gamma-ray logs (Figure 16) show moderately serrated signatures with generally low values, and many feature a gradual upward increase in gamma-ray values, possibly reflecting a progressive increase in mud content through the unit. The variations between clast and matrix supported fabrics suggest that both fluvial (alluvial fan) and debris flow processes deposited the Permian Basal Breccia.

Cadeby Formation (CdF)

The Cadeby Formation (Smith et al., 1986) comprises strata equivalent to the carbonate phase of the EZ1 Zechstein cycle. In the East Midlands, it encompasses the dolomitic limestone formerly known as ‘Lower Magnesian Limestone’, as well as an underlying argillaceous unit, variously termed the ‘Lower Marl’ or ‘Lower Permian Marl’ in previous accounts (Aveline, 1880). The formation is generally interpreted as a shelf carbonate wedge, constructed in two successive phases of sea level high stand that were separated by an episode of erosion caused by a relative sea level fall (Smith, 1989; Tucker, 1991). In this district, a highly serrated gamma-ray signature reflects the high sandstone and siltstone content of the formation, for example in the Eady Farm Borehole (Figure 16) located just beyond the northern margin. The lithology is suggestive of a basin-margin facies that received clastic material from the nearby East Midlands landmass. Geophysical log correlations (Figure 16) utilising gamma-ray ‘markers’ show that the formation passes laterally southwards into the Edlington Formation and Permian Basal Breccia.

The main provings in the Eady Farm Borehole and Woolsthorpe Bridge Borehole [SK 8434 3488] lie outside this district, to the north and east respectively, but the formation may be present in the north-eastern corner. The Newlands House Borehole, proved 2.06 m of calcareous sandstone that has been correlated with the Cadeby Formation.

In the Eady Farm Borehole, the lower 3.89 m of strata equates to the ‘Lower Marl’. It consists of red-brown, muddy siltstone with mudstone and sandy laminae and thin beds of pinkish brown limestone; shell casts are common, together with burrows and a few plant remains. The upper 7.57 m of the formation, assigned to the ‘Lower Magnesian Limestone’, consist of creamy grey to red, sandy, dolomitic limestone with intercalated red to purplish brown siltstone and sandstone. Macrofossils include abundant bivalves (Bakevellia sp. and Schizodus sp.), together with turreted gastropods, ostracods, brachiopods (productids), plant fragments, burrows and worm tubes (including Spirorbis). Sedimentary structures noted in the Cadeby Formation include desiccation cracks, load casts, ripple marks and slump structures. In the Woolsthorpe Bridge Borehole the formation commences with 2.45 m of brick red, micaceous siltstone with mudstone laminae, equating with the former ‘Lower Marl’ division. This bed has yielded Bakevellia sp. and Schizodus sp., together with fish scales, plant debris, burrows and trails; it also contains a typical Zechstein miospore assemblage (Warrington, 1980; Berridge et al., 1999) which includes Crustaesporites cf. globosus, Klausipollenites schaubergeri and Lueckisporites virkkiae. The overlying bed, correlated with the former ‘Lower Magnesian Limestone’, consists of 2.55 m of brick red, laminated, micaceous, calcareous sandstone with common small siliceous pebbles, indeterminate bivalves and burrows. In the Newlands House Borehole, the Cadeby Formation comprises 0.7 m of fine to very fine-grained, micaceous, weakly calcareous sandstone with a few mud flakes, quartzitic granules and vague ripple sets, overlain by 1.36 m of reddish brown, coarse-grained, strongly calcareous sandstone.

Edlington Formation (EdF)

The Edlington Formation (Smith et al., 1986) corresponds to the former ‘Middle Permian Marl’ subdivision in the East Midlands. It represents the basin margin facies of the upper part of the E1Zb cycle, and the whole of the EZ2 cycle of Smith et al., 1986). The formation rests conformably, with a sharp base, on the Cadeby Formation or Permian Basal Breccia, and is unconformable on Carboniferous rocks. It has a gradational passage upwards into the Lenton Sandstone Formation and the top is taken immediately above the highest lithology that is not sandstone and which may be mudstone, siltstone or breccia (Figure 16). This boundary also corresponds to a marked displacement of the gamma-ray trace in some of the boreholes.

The formation has been wholly or partially cored in several coal exploration boreholes across the district. They show that it is well developed in the north-east, where it attains a maximum thickness of 28.25 m in the Barkestone Bridge Borehole (Figure 16), but that it thins to the south and east where it is locally absent. The gamma-ray signature is variable and usually distinct from that of the overlying Lenton Sandstone Formation in being more serrated, with generally higher gamma-ray values. The thicker sandstones, however, have more subdued signatures, with lower gamma-ray values. Towards the base of the Edlington Formation a prominent gamma-ray low can be traced laterally on to the top surface of the underlying Cadeby Formation (Figure 16).

The strata are generally red-brown in colour, with some beds showing green mottles or reduction spots. Included are argillaceous lithologies such as laminated and interlaminated, micaceous mudstone and siltstone, commonly with desiccation cracks, as well as fine to coarse-grained sandstone and pebbly sandstone; small-scale fining upward cycles are present. The sandstones are variably massive, parallel-laminated, cross-bedded or cross-laminated, with aeolian (‘millet seed’) sand grains in parts; some contain muddy laminae and intraformational mud flakes. Subangular conglomerates interdigitate with the argillaceous strata in most sequences and their clasts are similar lithologically to those of the Permian Basal Breccia, with intraformational mudstone fragments also present. Sedimentary structures include desiccation cracks in mudstone laminae, slump structures and load and pillow structures.

Rapid lithological variations occur both laterally and vertically, suggesting that the Edlington Formation represents a complex facies association. The depositional environment was probably that of a broad alluvial plain on which fluvial (sheet floods), alluvial fan, debris flow, sabkha and playa lacustrine deposits were accumulated. The desiccation cracks indicate frequent episodes of subaerial exposure, and millet seed sand grains are attributed to the reworking of contemporary aeolian dunes.

Roxby Formation (RoF)

The Roxby Formation, formerly the ‘Upper Permian Marl’, has been correlated with a thin (up to 1 m) bed of red mudstone or siltstone occurring, for example, in the Eady Farm, Barkestone Bridge and possibly also in Wycomb boreholes (Figure 16) where it is intercalated in the lower part of the Lenton Sandstone Formation. It is marked by a pronounced gamma-ray peak, which is seen in a number of other boreholes where the formation is otherwise not proven on lithological grounds. Farther north this formation represents the topmost part of Zechstein Cycle EZ3 and all of cycles EZ4 and EZ5 of Smith et al. (1986).

Chapter 5 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). A new Triassic lithostratigraphy is also in preparation (Howard et al., in prep. (b), and although not utilised here it is shown for comparison in (Figure 17). The main subdivisions are the Sherwood Sandstone Group, which does not occur at outcrop, the Mercia Mudstone Group, and the Penarth Group. The base of the Jurassic is placed, in Britain, at the level of the appearance of ammonites of the genus Psiloceras (Cope et al., 1980, see also (Plate 5)a). This occurs a few metres above the base of the Lias Group, the basal (Pre-Planorbis) beds of which are thus latest Triassic in age. These beds are considered, for convenience, with the Jurassic part of the Lias Group, in Chapter 6.

Sherwood Sandstone Group (SSG)

These strata were encountered in many deep boreholes, and are among the most important bedrock aquifers of the East Midlands region. The group oversteps Permian strata, to rest unconformably upon the Carboniferous in the southwest and south-eastern parts of the district. The component units are the Lenton Sandstone Formation and the Nottingham Castle Sandstone Formation overlain by the Bromsgrove Sandstone Formation; the last is mainly confined to the west of the district. The group as a whole 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.

Lenton Sandstone Formation (LnS)

The Lenton Sandstone Formation, formerly the ‘Lower Mottled Sandstone’ (Warrington et al., 1980), subcrops over most of the northern part of the district, where it has a maximum proven thickness of about 34 m in the Barkestone Bridge Borehole (Figure 16), but is absent locally. The Calverton Breccia (Wills, 1956), which is developed in the Lenton Sandstone in the Nottingham district to the north (Howard et al., in prep. (a)), was not proved in any of the cored boreholes in the Melton Mowbray district. The Permian-Triassic datum is nevertheless recognised within the Lenton Sandstone, at the top of the intercalated mudstones equated with the uppermost Permian Roxby Formation (Figure 16); Chapter 4. An Early Triassic (Induan–Olenekian) age is assigned to the upper part of the formation in the Nottingham district (Howard et al., in prep. (a)), although its lower part may be Permian.

The formation consists of fine-, medium or coarse-grained, friable sandstones that are deep red-brown or, more rarely, greenish grey or buff-grey. The strata show cross-bedding or cross-lamination, and some beds are parallel laminated. The description of ‘mottled’ that was applied to the formation referred to the large ovoid or irregular, buff-grey patches that are developed mainly in the higher beds. Micaceous laminae and beds of reddish brown or greenish grey mudstone and siltstone occur throughout the formation but are particularly common near the base; intraformational mudclasts are common in the sandstones at many levels. These argillaceous components, and also possibly the micaceous layers, produce the sporadic serrations in what is an otherwise generally subdued gamma-ray signature (Figure 16). The lowermost part of the formation is coarse and pebbly locally, with extraformational quartz and quartzite pebbles and some locally derived pre-Carboniferous and Carboniferous clasts. Such clasts are generally smaller and more angular in comparison with those in the overlying Nottingham Castle Sandstone Formation.

The Lenton Sandstone Formation has been interpreted as the deposits of an aeolian dunefield and interdune sheet sand, with minor reworking by fluvial processes. (Mader, 1992). The locally abundant intraformational mudclasts and mudstone interbeds, however, also imply a substantial fluvial and alluvial influence. The extraformational clasts were probably transported into the aeolian dunefield by ephemeral floods that reworked alluvial fans established on the South Permian Basin margin to the south and west of the district. Such clasts would have been further concentrated into thin stone pavements by aeolian deflation.

Nottingham Castle Sandstone Formation (NtC)

The Nottingham Castle Sandstone Formation, of Induan–Olenekian age (Howard et al., in prep a), is proved in many boreholes in the district. It shows a considerable thickness range, from about 11 m in the south (Figure 17) to as much as 100 m in the north-east (Belvoir No. 1 Borehole). The formation was deposited in a fluvial system that drained northwards from north-west France (Audley-Charles, 1970; Warrington and Ivimey-Cook, 1992). However, some subangular limestone and volcanic clasts that have been observed indicate a local provenance in part. The formation was usually only partially cored or ‘openholed’, and thus was incompletely described. Core runs available during this resurvey show that the formation consists mainly of red-brown and greenish grey, fine to coarse-grained, cross-bedded, cross-laminated or parallellaminated sandstone. Small quartzite pebbles are scattered throughout, and where common give rise to conglomerate or subangular conglomerate (breccia) beds. Intraformational clasts of mudstone and siltstone are also present, and igneous (dolerite) clasts have been recorded in several boreholes. A thin section (E 72611) of a conglomerate about 12 m from the top of the formation in the Willow Farm Borehole showed a predominance of quartzite clasts, but also a significant proportion of less well-rounded clasts consisting of microgranular quartz diorite and weakly cleaved mudrock and possibly of local basement derivation. The base of the formation is commonly marked by 5 to 15 m of subangular conglomerate, suggesting that this datum represents a significant sedimentary hiatus and a possible disconformity with underlying Lenton Sandstone strata. In the Belvoir Borehole, the basal bed, about 12 m thick, is purple to red in colour and very poorly sorted, with both well-rounded and angular to subrounded fragments. These clasts variously consist of quartz, quartzite, sedimentary and igneous rock-types, essentially the same assemblage that occurs in the Permian Basal Breccia (see above).

Bromsgrove Sandstone Formation (BmS)

These strata are equated with the ‘Lower Keuper Sandstone and Marls’ of the adjacent Loughborough district (Fox-Strangways, 1905), which have been more recently described by Carney et al. (2001). Typically, they comprise fluvial sequences of red to grey or brown, fine to medium-grained sandstone with subordinate interbedded mudstone and siltstone. The unit is 50 m thick in the Rempstone LN10/1 Borehole, in the west of the district (Figure 17). Farther east, however, it thins out across the Nottingham Castle Sandstone Formation, from which it is distinguished by being less pebbly and containing thick mudstone interbeds. In the Rempstone LN/10-1 Borehole, the cored interval shows a highly serrated gamma-ray signature indicating the presence of several mudstone beds. The sandstone component, recovered as chippings, was described as red and fine to coarse grained.

Mercia Mudstone Group

Mercia Mudstone Group (MMG) was formerly known as the ‘Keuper Marl’ (Warrington et al., 1980). The middle to upper parts of this group either crop out or underlie thin Drift deposits in the west of the district; elsewhere the group is present at depth. Many borehole provings indicate that the group is between 180 and 240 m thick, with an average of about 210 m. The selection of borehole data in (Figure 17) summarises the stratigraphy, newly revised terminology, and gamma-ray signature of the group. Geophysical logs are commonly the principal means of correlating and comparing the group in boreholes across the East Midlands, particularly when calibrated against fully cored lithological sections, as in the Asfordby Hydro Borehole (Figure 17).

The group has a basal siltstone and sandstone-rich unit, the Sneinton Formation, which represents deposition on a broad alluvial plain crossed by ephemeral streams and sheet floods, with bodies of standing water and accumulations of wind-blown sediment. The beds of the overlying siltstone/mudstone sequence comprising the Radcliffe Formation are finely laminated and of lacustrine origin. The succeeding 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; Jefferson et al., 2002). Periods of standing water in 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 may indicate a high water table, charged with sulphate-rich water, or a greater degree of marine influence with precipitation in shallow water (Mader, 1992) particularly during deposition of the Cropwell Bishop Formation. The stratigraphically highest division, the Blue Anchor Formation, is transitional to the Penarth Group; both marine and continental water sources were possibly involved in its formation (Taylor, 1983).

The age-range of the components of this group is expressed in terms of international stages based on successions outside of the UK. Very few of the 45 samples from the Mercia Mudstone Group of the Asfordby Hydro Borehole that were examined for palynomorphs proved productive. Assemblages from the Cotgrave Sandstone Member, with Ovalipollis pseudoalatus and Porcellispora longdonensis?, and from the Hollygate Sandstone Member, with Vallasporites ignacii?, afford only poor evidence of a Ladinian to Carnian (late Mid to early Late Triassic) age for those units (Warrington, 1997). A Ladinian to early Carnian age for the Cotgrave Sandstone Member is supported by better assemblages from the Nottingham district, where it yields Echinitosporites iliacoides, O. pseudoalatus, P. longdonensis and R. perforatus (Warrington, 1993; 1994a,b).

The clay mineralogy and maturity of the Mercia Mudstone Group in the Asfordby Hydro Borehole was studied by Kemp (1999), and the results are summarised on a stratigraphical basis in (Figure 18). The principal findings mirrored those of previous studies of the Mercia Mudstone from the Nottingham district (Bloodworth and Prior, 1993). They show that the Sneinton, Radcliffe, lowermost 2 to 3 m of the Gunthorpe, upper Cropwell Bishop and Blue Anchor formations are characterised by illite and intermediate-Fe chlorite assemblages. On the other hand, the Edwalton and lower Cropwell Bishop formations contain high concentrations of smectite/corrensite ‘swelling’ clay minerals; the geotechnical implications of this are discussed in Chapter 11.

Boreholes in areas to the west of the district (Carney and Cooper, 1997) indicate that the subcropping parts of the Mercia Mudstone Group are weathered, commonly down to at least 20 m; weathering zones IV to II of Chandler and Davis (1973) are identified. The degree of heterogeneity imposed by this weathering is further exacerbated where gypsum dissolution has occurred, and such zones may be associated with enhanced permeability (Chapter 11).

Sneinton Formation (Snt)

The Sneinton Formation (Charsley et al., 1990) is widely distributed in the East Midlands, and was termed the ‘Waterstones’ in older literature (e.g. Fox-Strangways, 1905). In the Melton Mowbray district, numerous boreholes prove an average thickness of about 45 m, and a variation of between 33 and 69 m, the latter recorded in the Redmile Borehole. The formation is inferred to crop out in the extreme south-western corner of the district, on the upthrow (southern) side of the Sileby Fault north of Quorndon, although it is largely covered by Drift deposits.

The formation varies in grain size and mud content, producing a characteristically serrated gamma-ray profile in boreholes (Figure 17). The strata comprise interbedded and interlaminated red-brown and grey-green mudstone, siltstone and fine to medium-grained sandstone; locally the sandstones contain mudstone clasts. Normal grading is commonly present on a small scale. There are calcite-filled vugs in some sandstones, and thin gypsum veins may be present. Sedimentary structures noted from borehole samples include parallel lamination, cross-lamination, ripple marks, desiccation cracks and dewatering structures including convolute bedding and load casts. All of these strata are distinctively micaceous, resulting in a ‘watery’ appearance to bedding planes. The lowermost beds are predominantly grey-green, and as in the adjacent Nottingham district (Howard et al., in prep (a.)) include conglomerate with ‘exotic’ clasts of possible local basement origin. Thin sections from the Willow Farm Borehole (E 72609, E 72610) show that these clasts include various types of microgranular diorite, very fine-grained acid igneous rocks and tuffs, and cleaved metasiltstone. Similar clasts are found in the Nottingham Castle Sandstone and Permian Basal Breccia of the Melton district (see above).

Boreholes in the central, eastern and southern parts of the district show a distinctive basal sequence, up to 18 m thick, consisting of red, silty mudstone and siltstone. These strata give rise to a prominent gamma-ray indentation at the base of the unit (Figure 17), and are correlated with the Woodthorpe Member of the Sneinton Formation (Howard et al., in prep (a.).

Radcliffe Formation (Rdc)

The Radcliffe Formation varies in thickness from 5 to 15 m across the district. It has not been recognised at outcrop, but in subsurface provings is readily identified by its gammaray signature (Figure 17). The formation comprises a distinctive association of micaceous mudstone and siltstone, which are interlaminated and variegated in red-brown, brick-red, purple-brown, pink and greenish grey colours. There are sporadic thin beds of very fine to fine-grained sandstone. Gypsum veins and calcite-filled vugs are present in parts. Sedimentary structures include pseudomorphs after halite, mud cracks, cross-lamination and load casts.

Gunthorpe Formation (Gun)

The Gunthorpe Formation (Charsley et al., 1990) ranges between 63.5 and 75.5 m in thickness. It crops out in small areas in the north-west and south-west of this district. There are few exposures, but during the resurvey it was seen in the bank [SK 5652 3496] of the Fairham Brook at Clifton, where 0.4 m of thinly interbedded red-brown siltstone, very fine-grained sandstone and mudstone were noted (Charsley, 1989).

The formation is identified in many subsurface provings by its geophysical (gamma-ray) signature (Figure 17). Borehole descriptions indicate that it consists mainly of red-brown mudstone, with green reduction spots and gypsum/anhydrite veins; these lithologies are generally structureless, but some show lamination. There are common interbeds of greenish grey, dolomitic mudstone, siltstone and sandstone. These dolomitic lithologies are identified on borehole gamma-ray logs by numerous small amplitude troughs (Figure 17), and at outcrop were formerly known as ‘skerries’. They are parallel-laminated or ripple cross-laminated, and may show convolute bedding, load structures, injection structures and pseudomorphs after halite. Because of their compact, commonly fissured nature they can behave as minor aquifers in this region. One particular development of dolomitic siltstone occurs in the middle part of the formation and shows a pronounced gamma-ray trough (Figure 17). It appears too high in the stratigraphy to be correlated with the ‘Plains Skerry’ formerly distinguished in the Nottingham district (Elliott, 1961), or the Diseworth Member of the Loughborough district (Carney et al., 2001).

Edwalton Formation (Edw)

This formation ranges between 35 and 50 m in thickness across the district. It generally has a higher content of detrital sand than the Gunthorpe Formation, and locally contains hard and siliceous sandstone or siltstone beds. Gypsum, as thin anastomosing veins, is particularly common in the upper part, and the unit also has a higher smectite clay mineral content than the Mercia Mudstone Group in general (Kemp, 1999) (Figure 18); Chapter 11. The formation is readily identified on geophysical logs (Figure 17), as well as in the field, due to the occurrence of two relatively thick sandstones. These are the Cotgrave Sandstone Member and Hollygate Sandstone Member, the lower and upper surfaces of which respectively delineate the formation boundaries. The formation is late Ladinian to Carnian in age.

Cotgrave Sandstone Member (Cot): This is from 1 to 7 m thick. It comprises red-brown, grey, grey-green and buff, fine to medium-grained, commonly parallel laminated sandstone, with some thin red and green mudstone beds present locally. Many boreholes show a distinctive geophysical log signature indicating an upper and lower bed of sandstone, separated by mudstone (Figure 17). The member crops out in the north-western and western parts of the district, where it locally gives rise to a small escarpment surmounted by a dip-slope, as seen to the south of Glapton Lane in Clifton [SK 552 345]. The only exposure in the district is in the Nature Reserve at Wilwell Farm Cutting, where 0.1 m of yellow-brown, very fine to fine-grained sandstone was seen. Farther south, the unit is inferred to form the flat to gently east-sloping feature along the floor of the King’s Brook valley [SK 560 230], in places offset by minor west-north-west faults. The sandy soils on this feature contain numerous fragments of green to grey, fine-grained sandstone.

Hollygate Sandstone Member (Hly): This member forms the long dip slopes, interrupted by faulting, in the north-west around Ruddington [SK 590 346], where exposures are confined to sporadic ditch sections. In the subsurface, the gamma-ray signature in boreholes (Figure 17) readily identifies the member, which is estimated to be between 3 and 10 m thick across the district. The member generally consists of greenish grey and red-brown, fine to medium-grained sandstone interbedded with subordinate sandy siltstone and mudstone, the latter commonly gypsiferous. The sandstones show poor lamination and bedding, and are poorly to well sorted, with both subangular and well-rounded grains present. In the outcrop around Ruddington some laminae have extremely well rounded grains with frosted surfaces, which are of aeolian derivation (Charsley, 1989). One of the most detailed descriptions of the member is the log of the Wilford Hill No. 1 Borehole, which shows nine sandstone beds in a 9 m section. Individual beds are brick-red to off-white in colour, are between 0.15 and 3.13 m thick and are fine to medium grained and argillaceous (Charsley, 1989).

Key locality

Cotgrave Sandstone Wilwell Farm Cutting [SK 5664 3474]

Cropwell Bishop Formation (CBp)

This formation (Charsley et al., 1990) varies between about 28 and 70 m thick across the district. It crops out in the north-west and west, where borehole provings indicate it is thickest (Figure 17). Here, the stratigraphically lowest gypsum seam, the Tutbury Gypsum (T) is thick enough to be mined underground, formerly around East Leake and currently at Barrow upon Soar (Chapter 11). Farther to the north-east, where the formation is thinner, the stratigraphically higher Newark Gypsum (N) seam was the main target for exploitation, with both underground mining and opencast quarrying occurring at Cropwell Bishop [SK 685 348].

The formation consists largely of reddish brown, gypsiferous mudstone and siltstone, which are mostly blocky but may locally be laminated. Beds of indurated greyish green siltstone and fine-grained sandstone occur at several levels, some shown on the map and some indicated in boreholes by their gamma-ray troughs (Figure 17). One of the sandstone beds within the formation is exposed in the deepened part of the Fairham Brook [SK 5804 2933], south of Bunny, where at least 0.2 m of grey-green, fine-grained sandstone is overlain by 0.7 m of red mudstone containing a further, 0.1 m thick sandstone.

The formation contains abundant gypsum as amorphous, nodular and vein varieties. The Tutbury and Newark gypsum seams are widespread throughout the district, and although seldom exposed they are indicated on borehole gamma-ray logs by pronounced troughs (Figure 17), and on the sonic logs by high velocity (low t values). These records show that the Tutbury Gypsum is up to 4 m thick in the west, where it is 27 to 30 m above the top of the Hollygate Sandstone Member (i.e. above the base of the Cropwell Bishop Formation). Farther east, where the Cropwell Bishop Formation as a whole is thinner, the Tutbury horizon is only 10 to 15 m from the base of the formation (Figure 17) and its gypsum content is much reduced.

The Newark Gypsum is represented by 15 to 20 m of strata just below the junction with the Blue Anchor Formation. Borehole records show that several gypsum beds are commonly present, although on geophysical logs only a few of these can be differentiated. In the various provings, the stratigraphically highest, and also the thickest (up to 2 m) gypsum is the ‘Cocks’ seam, with the stratigraphically lowest being the ‘Blue Rock’. At the time of survey good exposures were afforded by the cuttings at the Safewaste landfill site (formerly Baldwin’s brick pit), located on the middle to lower part of the escarpment south of Bunny [SK 578 285]. The 13.8 m sequence measured here (Carney, 1999) consists mainly of red-brown, blocky to poorly laminated, silty mudstone with five gypsiferous horizons. None of these are continuous gypsum seams, rather the gypsum forms regularly spaced, discrete ellipsoidal masses up to 0.2 m thick and 2 m long, concentrated along prominent clayey parting planes. The central parts of the gypsum masses are fibrous to structureless, with the margins commonly surrounded by a thin selvage of fibrous gypsum. Many gypsum masses show smooth or ribbed surfaces against the surrounding mudstone, indicative of karstic dissolution. The mudstone between the gypsum masses is commonly brecciated and gypsum-veined. The topmost gypsiferous horizon, about 3 m below the landsurface, is believed to be the ‘Cocks seam’. It consists of isolated gypsum masses up to 1.3 m thick, whose rounded outlines are a karstic feature indicative of gypsum solution. The mudstones below and intervening between the gypsum masses have a platy fabric due to concentrations of bedding-parallel, discontinuous and bifurcating fibrous gypsum veins up to 15 mm thick. Bedding in the overlying mudstone is disrupted above those parts of the gypsum seam that are most affected by solution. To the west of the Safewaste site a prominent, bench-like feature along the lower part of the scarp slope represents a continuation of the Cocks seam outcrop. A further exposure of that seam occurs in the cutting leading to the adit of the Silver Seal Mine [SK 5855 2865], where in a section about 2 m thick, red mudstone contains abundant fibrous gypsum veins and larger gypsum masses up to 1 m across. Anomalous surface features on the outcrop of the Cropwell Bishop Formation occur to the east of the Silver Seal adit and are attributed to natural gypsum solution (Chapter 11). Other examples of such ground occur farther north (Crofts, 1989a), for example south of Bradmore Lane between Blackcliffe Hill [SK 6010 3205] and Plumtree House Farm [SK 6130 3290]. Further exposures of the Newark Gypsum occurred in the lower part of the quarry at Cropwell Bishop [SK 677 346], but this is now partly infilled.

Blue Anchor Formation (BAn)

The Blue Anchor Formation (formerly the ‘Tea-green Marl’; Warrington et al., 1980) is the youngest Mercia Mudstone Group formation, and is of Norian to Rhaetian age. It ranges between about 3 and 10 m in thickness, and consists mainly of grey to green, dolomitic siltstone and mudstone with an irregular blocky fracture. The base of the formation is defined at the first appearance of the green grey beds. The junction can be seen below the arch of the bridge over the railway cutting adjacent to the British Gypsum factory north of East Leake [SK 5518 2764]. There, red, laminated, calcareous mudstone of the Cropwell Bishop Formation is abruptly overlain by green fissile mudstone of the Blue Anchor Formation. In the west and north of the district, the formation has a narrow outcrop, displaced by faults, along the middle and lower slopes of an embayed escarpment that is capped by the Penarth and Lias groups. The clayey soils developed on this formation may be green-tinged, but more commonly are dark grey, with abundant fragments of green to greyish green mudstone. The formation cannot always be easily identifiable on geophysical logs; its upper boundary is commonly seen as a sharp gamma-ray peak and a correspondingly sharp decline in sonic velocity (Figure 17).

Exposures in the Blue Anchor Formation are few, and generally limited to cuttings, as on the Rushcliffe Golf Course, where green, blocky mudstone is seen [SK 5429 2813]. Further small exposures, many now overgrown, were noted by Crofts (1989a); they include those in the Normanton Railway cutting, which were also described by Lamplugh et al. (1909), and a 3.5 m section in a river meander scar east of Normanton-on-the-Wolds. In the banks of the Walton Brook [SK 5833 2664] the top of the formation consists of green to cream, weathered blocky mudstone, which is overlain by several centimetres of very dark grey, ochreous, fissile mudstone typical of the Westbury Formation (Penarth Group). The junction is gently flexured, suggesting that these strata may have been affected by periglacial mass movement processes. The formation was formerly well exposed in the quarry at Cropwell Bishop [SK 677 347].

Key localities

Normanton Railway cutting [SK 625 323] to [SK 628 321]

River bank east of Normanton-on-the-Wolds [SK 6365 3313]

Penarth Group (PnG)

The Penarth Group is a mudstone-siltstone sequence that forms narrow outcrops in the escarpment below the Barnstone Member of the Lias Group in the west and north-west of the district. Elsewhere it is identified in the subsurface by gammaray traces obtained from boreholes (Figure 17). These provings suggest that the group averages about 8 m in thickness in the north and west, but that elsewhere it is between 2 and 5 m thick, with only 2 to 3 m recorded in the Asfordby Hydro Borehole (Figure 17). Warrington et al. (1980) introduced the term ‘Penarth Group’ as a substitute for ‘Rhaetic’, which was the term used in the original memoir for this district (Lamplugh et al., 1909). The Penarth Group, as defined in the Nottingham district (Howard et al., in prep (a.)), corresponds exactly with the ‘Rhaetic’ of the primary geological surveys. The boundaries of the group do not, however, coincide with those of the Triassic Rhaetian Stage, which encompasses strata between the middle of the underlying Blue Anchor Formation (Mercia Mudstone Group) and the lowest part of the Barnstone Member (Lias Group).

The group comprises the Westbury Formation and the overlying Lilstock Formation. In the Lilstock Formation, the Cotham Member is succeeded by the Langport Member (Warrington et al., 1980); however, the latter has not been mapped even though it is probably present in many parts of the district (Swift, 1995a). In the south and south-east of the district, the group is particularly thin, and the Cotham Member is absent in cores from boreholes such as Welby Church, Holwell Mouth and Asfordby Hydro Such provings contrast with those outside the district, which show a full Penarth Group sequence up to 10 m thick (for example in the Fulbeck No. 1 Borehole [SK 8889 5053] of the Grantham district; Berridge et al., 1999).

The Penarth Group represents a change from the mainly continental environment that characterised most of the Triassic period, to the marine conditions of the overlying Jurassic. In the Nottingham and surrounding districts (Howard et al., in prep. (a)) sedimentation occurred in shallow, generally low-energy, marine environments on the gently subsiding East Midlands Shelf (Chapter 8). The Westbury Formation was deposited immediately after a widespread Rhaetian (Late Triassic) transgression (Warrington and Ivimey-Cook, 1992). Kent (1968) suggested a return to continental conditions after deposition of that formation and in the Nottingham district, Howard et al. (in prep (a) note an impoverished macrofauna of branchiopod crustaceans (Euestheria minuta), indicative of fresh to brackish water conditions in the basal few centimetres of the Cotham Member. However, marine microplankton occur throughout the Penarth Group in the region (e.g. Fisher, 1972; Orbell, 1973; Morbey, 1975) and the Cotham Member is thought to have been deposited in a lagoonal environment, with fluctuating salinity levels (Mayall, 1983; Warrington and Ivimey-Cook, 1992). The local absence of the Lilstock Formation (Cotham Member) is attributed to a major sea-level fall in latest Rhaetian times (Hallam, in prep).

The study by Orbell (1973) of samples from the Owthorpe 1–4 boreholes indicates the distribution and abundance of miospores and marine microplankton throughout the Penarth Group and Barnstone Member of the Lias Group (Table 4). The Westbury Formation and Cotham Member assemblages are indicative of a Rhaetian (Late Triassic) age and a position within the Rr dinoflagellate cyst biozone of Woollam and Riding (1983). Swift (1995a) discussed the occurrence of a thin ‘White Lias’ (Langport Member) facies above the Cotham Member in the district and neighbouring areas. These strata, and the succeeding ‘Pre-planorbis Beds’ of the Barnstone Member (Lias Group, see below), have yielded conodonts in the Melton Mowbray and adjacent districts (Swift, 1989, 1995a, b; Swift and Martill, 1999). The records from the Penarth Group of the district are summarised as follows:

Detailed listings of the macrofaunas sampled from the Penarth Group in the Owthorpe 1–4 boreholes are given in Ivimey-Cook and Elliott (1969).

Westbury Formation (Wby)

This lower formation of the Penarth Group averages between 2 and 4 m in thickness across the district. It corresponds to the ‘Lower Rhaetic’, ‘Black Shales’ or ‘Avicula contorta Shales’ of earlier authors (Lamplugh et al., 1909) and consists of dark grey to black, fissile, fossiliferous mudstones with sandy and some pyritic laminae, and a few thin beds of sandstone. The ‘Rhaetic Bone Bed’ occurs just above the base, but vertebrate fossils also occur higher in the formation.

The unit is very poorly exposed, and cannot easily be distinguished by shallow augering since it weathers to nondescript yellow or silvery grey, plastic clays. The principal exposure is currently the quarry at Cropwell Bishop, where A S Howard (BGS, 1995 field notes, pp.kw0000548–9) measured the following strata:

Exposures described by Lamplugh et al. (1909) were mainly in road or railway cuttings through the escarpment capped by the Barnstone Member, and most of these are now overgrown or otherwise inaccessible. The main locality was the railway cutting north-west of Stanton-on the-Wolds [SK 6355 3130]. Here, Wilson (1882, in Lamplugh et al., 1909) recorded a 4.1 m-thick section in black ‘shales’ with thin beds of pyritous sandstone and limestone, the latter showing desiccation cracks. A ‘bonebed or coprolite seam’ one-inch thick was noted 0.8 m above the junction with the Blue Anchor Formation, and yielded a rich fauna that included teeth and coprolites of Temnodontosaurus platyodon and Ichthyosaurus sp.

A further exposure of these strata was investigated by H G Fryer (cited in Sykes, 1977), and although the grid reference given [SK 573 173] is imprecise it presumably refers to the railway cutting through the Westbury Formation at Barrow upon Soar. The section, totalling 3.77 m in thickness, consists mainly of black, fissile mudstone with fine-grained sandstone beds and common traces of bone material; there are also two beds of nodular limestone, 0.15 and 0.62 m thick, in the upper 2 m of the succession. Four bone beds were recorded in the lower 1.7 m of the section, the principal one, 0.05 m thick, resting on the basal contact with the overlying Blue Anchor Formation; no faunal details were given. Throughout this sequence, ‘trace’ bone-beds occurred in close association with sand-rich sedimentary layers, and this ‘incipient’ development of bone-beds was attributed to the action of currents, which also sorted the sand grains.

The macrofauna collected from the formation in the Welby Church Borehole included Eotrapezium concentricum, Modiolus sp., Protocardia rhaetica, Rhaetavicula contorta, Tutcheria cloacina and fish debris (Ivimey-Cook, 1993). Ambrose (1999) assigned all the 2.18 m measured thickness of those strata to the Westbury Formation. Details of palynomorphs and conodonts obtained from the formation were given earlier.

Lilstock Formation

Cotham Member (Ctm)

Only the Cotham Member is shown at mapping scale; however, limestone of the overlying Langport Member has been identified in a few places. As previously noted, the Cotham Member is absent in the south-east, but elsewhere it averages about 4 m in thickness. The outcrop of the member in the west and north forms the upper part of a scarp slope capped by resistant limestones of the Barnstone Member, with the upper boundary of the Cotham Member lying just below the crest. The lower boundary, with the Westbury Formation, is exposed at the Cropwell Bishop Quarry (see above). Elsewhere, it commonly forms a slight concave break in slope about 4 m lower down from the crest of the feature formed by the Barnstone Member.

In Cropwell Bishop Quarry [SK 677 346], 1.5 m of the member is exposed (field notes of A S Howard). It consists of pale to medium grey, slightly calcareous, olive-green weathering mudstone with thin wisps and lenticles of siltstone and very fine-grained sandstone. Fossils are not abundant, but there is debris of shells, and possibly of the branchiopod crustacean, Euestheria. The base is gradational upwards from the Westbury Formation. Elsewhere, the Cotham Member comprises pale grey and greenish grey, calcareous, silty mudstone with thin, discontinuous or nodular beds of limestone, the latter with an impoverished fauna (Sykes et al., 1970) consisting of Euestheria minuta. It weathers to silty, yellow and grey-brown mottled clay, with common ‘race’ consisting of small, irregular, white to buff calcareous nodules. On borehole logs the member commonly has gamma-ray values slightly lower than those of the underlying Westbury Formation, and markedly higher than the overlying Barnstone Member of the Lias Group.

Langport Member

Field identifications and former records of a limestone intervening between the Cotham Member and the ‘Pre-Planorbis beds’ of the Barnstone Member were taken by Swift (1995a) as evidence for the presence of the Langport Member. The limestone was noted at the small abandoned limestone pits north of Hoton, and at Cotgrave Gorse, these localities yielding the conodont faunas summarised earlier. During this resurvey a small bench-like feature, strewn with micritic limestone brash, was observed, indicating an outcrop of the Langport Member north of Taft Leys [SK 5610 2755].

Field recognition of the member is assisted by the debris strewn about, consisting of nodular, porcellanous limestone with a conchoidal fracture. The nodules have a blue-grey centre and cream-weathering outer layer and are commonly septarian. Nodular limestone near the top of the member is a particularly distinctive septarian variety with an irregular surface, although it is generally visible only as ploughed-up blocks with the more flaggy limestones of the Barnstone Member in close proximity up-slope. The septarian limestone is exposed in a tributary of the Normanton Brook [SK 6415 3120], and in the River Smite [SK 6938 3276]. Field debris of the lithology can be examined west of the junction of Hall Lane and Owthorpe Road [SK 6915 3350], west of Foss Cottages [SK 660 349] and west of Nottingham Road [SK 5791 1877].

Key localities

Westbury Formation: quarry at Cropwell Bishop [SK 677 346]

Lilstock Formation (Langport Member): old quarry at Cotgrave Gorse [SK 658 345]; disused quarry north of Hoton [SK 571 232]

Chapter 6 Jurassic

The Lower Jurassic Lias Group and part of the Middle Jurassic Inferior Oolite Group crop out within the district. The sequence dips at about one degree to the south-east, and is affected by faults that locally produce substantial displacements of the scarp and dip-slope features formed by the more resistant beds.

The Jurassic strata accumulated in warm, shallow, subtropical seas that covered the East Midlands Shelf, on the periphery of the Southern North Sea Basin (Chapter 8). Hallam (2001) attributed rapid flooding of the East Midlands Shelf to a major sea-level rise during the Rhaetian transgression. In the early stages of that event, poorly oxygenated bottom waters resulted in deposition of a dysaerobic facies of faunally restricted, laminated, organic-rich sediments (Wignall and Hallam, 1991), recognised within the Barnstone Member of the lowest Lias Group. With rising sea level, and a consequent transition to hemipelagic shelf environments (Weedon, 1986) well-oxygenated conditions became established leading to the accumulation of carbonate and argillaceous sediments with a diverse marine fauna in the Scunthorpe Mudstone and Charmouth Mudstone formations. ‘Cyclic’ deposition, consisting of beds of laminated mudstone passing up to calcareous mudstone and thence to bioturbated limestone, has long been recognised in strata of the Scunthorpe Mudstone Formation, and is generally developed above the base of the Granby Member. The underlying causes of this cyclicity are complex (Waterhouse, 1999) and involve variation in bottom-water oxygen conditions. Anoxic conditions supported only a limited benthonic fauna, while better oxygenated conditions and coarser grained substrates supported a more diverse fauna. The Dyrham Formation and in particular the ferruginous Marlstone Rock Formation, with its locally prominent cross-bedding, may represent a regressive, high-energy episode on the East Midlands Shelf. The overlying Whitby Mudstone Formation was deposited in deeper water and more quiescent conditions. This reversion represents one of the most important transgressive events of the Jurassic period (Hallam, 2001). A regressive event of equal importance occurred in the early Aalenian (Hallam, in prep) ushering in an abrupt change, to the relatively shallow-water environments of the Inferior Oolite Group. The latter commences with the ferruginous Northampton Sand Formation, representing near-shore, high-energy deposition. The succeeding Grantham Formation is of probable marginal marine, estuarine origin, and in the Grantham district shows some channelisation into the Northampton Sand (Berridge et al., 1999). The highest beds, the Lincolnshire Limestone Formation, are considered to be typical of marine barrier bar-lagoonal complexes (Ashton, 1977).

Lias Group

The Lias Group (Powell, 1984) has an aggregate thickness of about 330 m in the district and occupies a large proportion of the Jurassic outcrop. On the East Midlands Shelf (Chapter 8) it comprises in upward sequence: the Scunthorpe Mudstone, Charmouth Mudstone (formerly Brant Mudstone Formation), Dyrham, Marlstone Rock and Whitby Mudstone formations (Brandon et al., 1990; Brandon, in Berridge et al., 1999).

Biostratigraphical control in the early Jurassic of England and Wales is based on ammonite biozones that are defined with considerable precision (Dean et al., 1961). The stages in the Lower Jurassic of the East Midlands have been well documented for strata in the nearby Grantham district (Brandon et al., 1990; Berridge et al., 1999), with which the sequence described here (Figure 19) is correlated. No systematic fossil collecting was carried out during this survey, although the authors commonly carried out field identifications. Illustrations of some of the more common fossils, which may for example be encountered as brash in fields or in ditch diggings, are given in (Plate 5) and (Plate 6).

Many of the formational names of the Lias Group follow the scheme of Brandon et al. (1990), except that the ‘Brant Mudstone Formation’ of those authors is now termed the Charmouth Mudstone Formation (Cox et al., 1999). The lowermost 2 to 3 m of the Lias Group is devoid of ammonites and is therefore, by definition, of late Triassic age, since the base of the Jurassic is drawn at the lowest occurrence of ammonites of the genus Psiloceras. For descriptive purposes, however, these strata, of the lower Barnstone Member, are included below with the remainder of the Lias Group. The youngest Lias Group strata in the district are of Toarcian age.

Scunthorpe Mudstone Formation (SMd)

This formation is about 128 m thick in the Vale of Belvoir (Brandon et al., 1990), and as defined by Gaunt et al. (1992), it consists of grey, variably calcareous mudstone containing numerous thin beds of limestone and calcareous siltstone, particularly near the base and in the upper part. Where not at crop, the various components of the Scunthorpe Mudstone can be recognised from their geophysical signatures recorded in deep boreholes penetrating through the younger cover, as shown in (Figure 20). The weakly calcareous mudstone has a low sonic velocity (leftward-pointing troughs on (Figure 20)) and high gammaray activity (rightward peaks). Conversely, limestone has a high sonic velocity and low gamma-ray activity. The moderately calcareous mudstones show intermediate values.

The limestone beds generally contain 60 to 70 per cent of calcium carbonate, and are of two main types. The mapped, feature-forming beds are mainly primary bioclastic limestones and indicate episodes of higher energy sedimentation; lenticular bedforms are typical, and are interpreted as wave-reworked or current-winnowed deposits, subsequently indurated by a carbonate cement. The other limestone type, found particularly in the Barnstone Member, but also the Granby Member and, sporadically in the Barnby and Beckingham members, are well-cemented, argillaceous calcite-mudstones (‘cementstones’). Such lithologies also occur as nodules within mudstone and may, in part, be of secondary origin (e.g, Hallam, 1964). The intervening strata comprise dark grey, weak, fissile mudstone or claystone, with calcium carbonate content typically between 10 per cent and 20 per cent. There are also successions with relatively well-cemented mudstone and siltstone in which carbonate may range up to 50 per cent.

The faunas of the Scunthorpe Mudstone Formation indicate an age ranging from latest Rhaetian to latest Early Sinemurian. Subdivision of the formation into five members (Figure 19) is based on the relative frequency of thin limestone beds, which form distinctive scarp and dipslope features of varying magnitude. Limestone forms between 10 and 30 per cent of the limestone-rich members and less than 5 per cent of the limestone-poor members. In the Granby and Foston members, each limestone bed has been informally named after a locality where it is exposed, or where the associated feature is particularly well developed.

Barnstone Member (Bst)

The Barnstone Member, formerly termed the ‘Hydraulic Limestone Series’ (e.g. Lamplugh et al., 1909), comprises a distinctive lithological association of thin, grey, argillaceous limestone interbedded with finely laminated, fissile (‘papery’) calcareous mudstone. The member varies from about 8 to 12 m thick, the latter value being recorded in boreholes around Barrow upon Soar. The base generally rests sharply and apparently conformably on a nodular limestone identified as the Langport Member of the underlying Lilstock Formation (e.g. Swift, 1995a); however, where this is absent, as in the south of the district, a minor hiatus or disconformity is possible.

In this district, as elsewhere (Trueman, 1918, p.66), the member has yielded faunas indicating that it ranges in age from the latest Triassic (Rhaetian) to early Jurassic (Hettangian). The lowest beds are devoid of ammonites and the informal name ‘Pre-Planorbis Beds’ has been assigned to them (Trueman, 1915; Kent, 1937; Chapter 5). Latest Triassic conodont faunas have been discovered from the ‘Pre-Planorbis Beds’ (Swift, 1989, 1995) at two sites:

1. Barnstone railway cutting [SK 739 358] Misikella posthernsteini, Pa element (the only specimen so far discovered in the UK)
2. Blue Hill, Owthorpe, disused quarry on west bank of canal [SK 682 342] Chirodella verecunda, dextral M element

These occurrences confirm a Rhaetian age for the top of the Penarth Group (Chapter 5) and, more importantly, for the ‘Pre-planorbis Beds’, as M. posthernsteini is the index fossil of the youngest Triassic conodont zone in the late Rhaetian, and conodonts are not known from any independently dated Jurassic strata. The base of the Hettangian - and hence of the Jurassic - in Britain is taken at the lowest occurrence of ammonites of the genus Psiloceras, shown in (Plate 5)a (Cope et al., 1980).

The macrofaunas of the Barnstone Member were well studied in the many former limestone quarries around Barrow upon Soar, particularly the marine vertebrate faunas and their notable soft tissue preservation. These works include descriptions of Ichthyosaurus communis and Leptonectes tenuirostris; Rhomaleosaurus megacephalus, otherwise known as the ‘Barrow Kipper’ (Plate 7), and a Pistosaurus-like animal, the respective references are: Martin et al. (1986), Taylor and Cruickshank (1989), Cruickshank (1994) and Cruickshank (1996). The invertebrate fossils, described by Hallam (1968) and Fox-Strangways (1903), include echinoids and crustaceans as well as the bivalves Modiolus minimus, Pleuromya tatei var. wilmcotensis and Liostrea irregularis var. hettangiensis. The ammonites Psiloceras planorbis and P. johnstoni were recorded by Browne, as related by Fox-Strangways (1903). Hallam (1968) attributed the preservation of insects and vertebrate remains to anaerobic environments. Detailed listings of Rhaetic and Lower Jurassic macrofauna from the Owthorpe 1–4 boreholes are provided by Ivimey-Cook and Elliott (1969).

The ‘Hydraulic’ connotation refers to the former use of limestones from this member for hydraulic cement manufacture (Chapters 10; 11). Brandon et al. (1990), in redefining the member, renamed it after a village in the Vale of Belvoir [SK 734 354] where it was worked for this purpose. The limestone beds that generally make up about 30 per cent of the Barnstone Member are 0.1 to 0.2 m thick, rarely up to 0.3 m, and consist mainly of uniformly grey, argillaceous calcite-mudstone (‘cementstone’). Those in the lowest 2 to 3 m are rich in shell debris, but others are markedly laminated and bituminous, suggesting deposition in very quiet anaerobic conditions. Ploughed fields on the outcrop are characterised by sticky, yellowish brown, clay-rich soils and the surface is littered with slabs of fine-grained limestone.

Lamplugh et al. (1909) and Fox-Strangways (1903) briefly described a number of sections in former quarries or minor cuttings in the Barrow upon Soar area. The principal of these was 37 ft (11.2 m) of strata observed by Harrison (1877) in a former quarry located to the south of the railway line [SK 5926 1629]. The measured section utilises the local quarry mens’ nomenclature for the various limestone beds and also indicates the stratigraphical positions of invertebrate and vertebrate fossils (Fox Strangways, 1903; p.22). The thickest limestones are the ‘Four Foot Calf’ at the base, and the ‘Good-for-nothing-Calf’, each being 0.3 m thick. A section through these strata in the now overgrown Darby’s Pit at Cream Lodge [SK 5915 1863] was illustrated in Lamplugh et al. (1909, plate II), and the origin of the folded bedding seen there is discussed in Chapter 8. There is a further photographic illustration (Lamplugh et al., 1909; plate IV), showing strata in the former quarry to the north-west of Paudy Lane [SK 5840 1770]. During this resurvey, about 1 m of pale grey siltstone and laminated, calcareous mudstone, with fissile micaceous mudstone, was visible in then unfilled Trueman’s Pit [SK 5980 1602]. The cutting by the platform of Barrow upon Soar Station showed intermittent exposures up to 1 m thick in dark grey-green laminated mudstone with beds several centimetres thick of hard, pale grey, parallel-laminated micritic limestone.

In the Vale of Belvoir outcrop, Crofts (1989b) described several sections to the north-west of Kinoulton, including an extensive one through the Barnstone Member in the River Smite. It showed eight beds of pale grey, laminated limestone separated by dark grey, fissile mudstone, the latter poorly exposed. Farther to the north-west, most of the Barnstone workings have been infilled by council waste, but some sections are still open. For example, a quarry section near Langar revealed up to 6.42 m of poorly fossiliferous strata in a shallow, broad anticline (Brandon and Carney, 2000). The lithologies exposed comprise friable, laminated grey mudstone intercalated with beds of massive to laminated, hard, calcite-mudstone up to 0.3 m thick (Plate 17)." data-name="images/P946251.jpg">(Plate 8). Strata formerly exposed at Langar are described by Kent (1937) and Fletcher (1980). Kent (1937) included extensive faunal listings for the Langar and Plumtree Wolds quarries [SK 6335 3249], and for a quarry at Owthorpe where beds of the Barnstone Member are still exposed.

Key localities

Barrow upon Soar Station, [SK 5780 1720]; River Smite near Kinoulton [SK 6943 3293]; Quarry at Langar [SK 7352 3499]-[SK 7317 3453]; Quarry at Owthorpe [SK 675 341].

Barnby Member (Bby)

This member ranges from 22 to 28 m thick across the district, and in the subsurface it can be readily recognised by its geophysical signature on wireline logs (Figure 20). It consists of grey calcareous mudstone with rare thin argillaceous limestones, which make up about 2 per cent of the sequence. The member was formerly known as the Angulatum (or Angulata) Clays (Swinnerton and Kent, 1949) or the Barnby Clays (Swinnerton and Kent, 1976) after the village of Barnby in the Willows. The present name was formalised by Brandon et al. (1990). The member was extensively deposited across the East Midlands Shelf (Brandon et al., 1990, fig. 7), and thickens northwards into south Yorkshire at the expense of the Barnstone Member.

At outcrop the member gives rise to dark grey to yellow brown, clayey soils commonly mantled by sandy colluvium or head. Augering reveals yellow to grey, or blue-grey, stoneless clay, with nodules of carbonate ‘race’ in the weathered mudstone bedrock. Intermittent natural exposures, as seen in the brook south-west of Seagrave, seldom reveal more than 1.5 m of strata, a typical example [SK 6169 1668] consisting of blue-grey, faintly laminated mudstone with discontinuous beds, or ellipsoidal nodules, of pale grey, hard, nonlaminated micritic limestone, in places with shelly lags. The limestones are up to 70 mm thick, but brash in the stream indicates that they attain at least 0.12 m locally. The beds at these exposures invariably show flexuring and folding, possibly a result of periglacial mass wasting (Chapter 8). In the Vale of Belvoir outcrop the member is largely unexposed, and forms low-lying ground, much covered by head, between Colston Bassett and Barnstone.

The fauna of the Barnby Member includes the bivalves Liostrea (Plate 5)d, Cardinia listeri (Plate 5)b and Lucina etc. The ammonite fauna includes Alsatites cf. laqueolus, Caloceras sp. (Plate 5)c, Saxoceras sp., and Waehneroceras sp. Fossils collected by Kent (see Brandon et al., 1990) outside the district from the Shire Dyke, west of Barnby in the Willows [SK 8111 4739] to [SK 8134 4825], confirm that the Barnby Member exposed there is probably entirely of liasicus Zone age.

Granby Member (Gby)

This member averages 40 m in thickness across the district. Its name is synonymous with the ‘Granby Limestones’ (Swinnerton and Kent 1949, 1976; Kent 1980), and the unit is included within the ‘Clays below Ferruginous Limestone’ category of Lamplugh et al. (1909). The name is taken from the village of Granby [SK 751 363], just to the north of the district, although that village is actually sited on the outcrop of the Barnstone Member. The reference section is taken from the Fulbeck No. 1 Borehole of Lincolnshire and is described in more detail elsewhere (Brandon in Berridge et al., 1999; Ivimey Cook et al., in press).

The Granby Member consists of grey, calcareous mudstone with numerous thin and laterally persistent limestones comprising rather more than 10 per cent of the sequence. These typically occur as groups of several closely spaced beds at vertical intervals of a few metres and their contrast with the intervening mudstone produces the characteristically serrated appearance on geophysical logs (Figure 20). The limestones are individually thin (typically about 0.1 m), and consist of argillaceous calcite-mudstone with numerous harder, well-cemented, grey, relatively clean, shelly and bioclastic limestone lenses. Weathered limestone brash on the dip slopes formed by the limestones is predominantly of the more durable bioclastic type. However, ditch dredgings and rare exposures show that the shelly limestones form only a minor part of each limestone group, which consist predominantly of the calcite-mudstone. Petrographical analyses of thin sections of the bioclastic limestones show them to be mostly packstones and packstone/grainstones (Dunham 1962); most are biosparites (Folk 1959).

The main limestone beds, or combinations of closely spaced limestone beds, give rise to readily mappable cuesta features that are of variable magnitude (Figure 19), such outcrops being characterised by limestone brash in a brownish grey clayey soil on the dip slopes. These limestones can usually be distinguished by a combination of lithology and faunal content. They are (in ascending order) Holm Farm Limestones (HF), Cross Lane Limestones (CL), Claypole Limestones (Cp), Blackmires Limestone (Bm) and Fen Farm Limestones (FF). The lowest two limestone packages, present in Fulbeck Borehole 5, were referred to as limestones ‘X’ (lowest) and ‘Y’ by Brandon et al. (1990), but as they do not generally form separately mappable features they are best included within the definition of Holm Farm Limestones.

The Granby Member was deposited mainly during the Hettangian, Schlotheimia angulata Zone, and also the earliest part of the Lower Sinemurian Arietites bucklandi Zone. The fauna, reviewed in Lamplugh et al. (1909), is dominated by the bivalves Liostrea ((Plate 5)d; common in the lower limestones), Gryphaea arcuata ((Plate 5)e; common from the Claypole Limestones upward), and Camptonectes, Cardinia, Mactromya (in the Claypole Limestones), Plagiostoma (Plate 5)f, Pseudolimea and Pseudopecten (Plate 5)g. Ammonites such as Schlotheimia angulata (Plate 5)h are locally common in the limestones; the nautiloid Cenoceras is found principally in the lower two limestones of the Holm Farm Limestones, and the gastropods Ptychomphalus and Pleurotomaria occur sporadically. The Blackmires and Fen Farm limestones contain conspicuous amounts of pentacrinoid ossicles (Plate 5)i. Internal casts of Kulindrichnus burrows (‘turnip stones’), composed of bioclastic limestone, are common in the brash on the dip slopes. The simple coral Montivaltia is common in the Blackmires Limestones and occurs rarely in the Fen Farm Limestones. The brachiopod Calcirhynchia (Plate 5)j occurs in the Claypole Limestones.

Exposures are confined mainly to ditch sections of up to 1 m of strata. The best exposure [SK 7235 3227], thought to represent part of the Holm Farm Limestone, was north of the Harby Lane bridge over Wash Dyke. The detailed bed stratigraphy of the member is known to be extremely uniform laterally, and it is likely that there are no significant differences in bed lithology and faunal content from the sections described for the Grantham area (Brandon et al., 1990; Brandon, in Berridge et al., 1999).

Beckingham Member (Bkg)

This member has a wide distribution on the East Midlands Shelf. Average thickness in the district is 21 m. The strata are dominated by bluish grey, fissile mudstone, and show predominantly high gamma-ray values on borehole geophysical logs (Figure 20); there are also a few thin limestones. Limestone nodules are common at one level, and at the very top of the member, immediately below the Stubton Limestones, there is a feature-forming mudstone bed containing numerous phosphate nodules. These occur together with phosphatised ammonites, a lithological association not found in lower beds but which is common in the overlying Foston Member.

The member is equivalent to the ‘Bucklandi Clays’ of Swinnerton and Kent (1949, 1976). As the mudstone contains beds of both bucklandi and semicostatum Zone (Lower Sinemurian) age, however, it has been renamed the Beckingham Mudstone Member by Brandon et al. (1990), who designated a type section in the Fulbeck No.5 Borehole of Lincolnshire. Typical fossils, some illustrated in (Plate 5), include the bivalves Gryphaea arcuata and Pseudopecten, ammonites and sporadic pentacrinoid fragments.

In this district, the Beckingham Member contains a persistent tripartite unit, the Dry Doddington Nodule Bed (DDN), which comprises a mudstone (about 2 m thick) with calcite-mudstone nodules between two thin bioclastic limestones. The outcrop of this bed is marked by scattered calcite-mudstone nodules and a strong to subdued escarpment feature. It can be traced in many parts of the Vale of Belvoir, particularly north of Plungar [SK 767 343] to [SK 776 350] and east of Stathern Lodge, around [SK 757 326].

Foston Member (Fst)

This member averages 35 m in thickness across the district. It is a distinctive association of grey mudstone interbedded with numerous, laterally persistent feature-forming limestone beds constituting about 10 per cent of the sequence. The limestones are all named according to the scheme of Brandon et al. (1990), as shown in (Figure 19). This unit approximates to the strata formerly known as the ‘Ferruginous Limestone Series’ (Swinnerton and Kent, 1949), and ‘Ferruginous Limestone’ (Lamplugh et al. 1909). In this earlier terminology the ‘Lower Ferruginous Limestone’, or ‘Plungar Ironstone’ (Lamplugh et al., 1909) is evidently equivalent to the Stubton Limestones unit that now defines the base of the Foston Member. The single exception to the Foston Member stratigraphy of Brandon et al. (1990) and Berridge et al. (1999) is that in the Vale of Belvoir the sandy Mill Lane Limestones appear to fail south-westwards; the datum is characterised only by the calcite-mudstone nodule bed that occurs beneath the limestone in the north-east.

The member ranges in age from the semicostatum Zone up into the turneri Zone of the Lower Sinemurian and possibly into the obtusum Zone of the Upper Sinemurian. The latter may be absent, however, owing to a disconformity at the base of the overlying Charmouth Mudstone Formation. The fauna (Brandon et al., 1990) is dominated by bivalves of the genera Camptonectes, Cardinia, Gryphaea arcuata, G. maccullochii (Plate 6)a Lucina, Oxytoma (Pteria) inequivalvis (Plate 6)b, Protocardia, Pseudolimea, and Pseudopecten; ammonites such as Arnioceras spp. (Plate 6)f are generally common in the limestones. Belemnites are first noted in the local Lias sequence in the Littlegate Limestones. The rhynchonellid brachiopod Calcirhynchia (Plate 5)j is found in the Stubton, Fenton and Mill Lane limestones and Spiriferina in the Fenton, Littlegate and Mill Lane limestones. The gastropod Pleurotomaria occurs sporadically in the Stubton Limestones. Some of the more sandy levels, such as the Mill Lane Limestones, are intensely burrowed with Chondrites and also contain the bivalve, Pholadomya.

The limestone beds of the Foston Member become increasingly silty and sandy up-section. This influx of terrigenous material may imply a change of climate or current regime, or closer proximity to the shoreline. At several levels there are laterally persistent mudstone beds with numerous phosphate nodules that are shot with minute borings, indicative of reworking. These beds, which also contain well preserved phosphatised ammonites, may therefore represent periods of condensed deposition. Calcite-mudstone nodules, of the type found in the Dry Doddington Nodule Bed of the Beckingham Member, are larger than the phosphate nodules, and are present in beds forming the upper part of the member. No surface sections in the district exceed about 1 m; however, the member and its individual beds are readily identifiable from their geophysical log signatures (Figure 20).

The Stubton Limestones (StL) are about 1 m thick and locally form a long dip slope [SK 759 330], although the crest of the feature is typically occupied by the underlying phosphate nodule bed. These beds (formerly ‘Plungar Ironstone’) were worked for ironstone at Barkestone-le-Vale [SK 7785 3484]; [SK 7833 3492]. They produce a rich, rusty-brown, silty loam soil, with copious brash of orange-brown weathered, ferruginous, shelly or coquinoidal, bioclastic limestone containing numerous Gryphaea, which are commonly abraded and bored. Geothitic ooids are abundant in some pieces and there are common irregular, orange-brown iron hydroxide veins and patches. Fossils are abundant and suggest a probable early semicostatum Zone, lyraSubzone age (Brandon et al., 1990). The Lodge Farm Limestones (LfL) are about 3.5 m thick and produce a weak to moderate feature, as seen to the south of Plungar [SK 775 338], with brash of grey, bioclastic limestone. Slabs from ditches and small sections, such as that in the River Smite [SK 7007 2723], consist of hard, pale brown-weathering, grey, silty, bioclastic limestone with numerous Gryphaea and Pseudopecten (Plate 5)g valves. The Gryphaea are commonly abraded and bored and there are local patches of iron hydroxide. The Fenton Limestone (Fn) is a single bed, seldom feature-forming, less than 1 m thick, that typically crops out on the lower part of the scarp slope formed by the Littlegate Limestones feature. The limestone found in numerous ditch dredgings [SK 7147 2817]; [SK 7206 2901] is a distinctive olive-grey, finely sandy to silty lithology with few shells. The bed is characterised by common pectinids and numerous small ammonites and, unlike the other limestones, generally contains few Gryphaea. The fauna from the Fenton Limestone indicate the scipionianumSubzone of the semicostatum Zone (Brandon et al., 1990). The Littlegate Limestones (Lt) are 2 m thick and form long clayey dip slopes, for example near Hose [SK 742 295]. The crest of the feature is invariably formed of the underlying phosphate nodule-rich mudstone, with limestone brash confined to the lower part of the dip slope. Well-exposed sections through the Littlegate Limestones occur below alluvium along Dam Dyke [SK 7270 2867] to [SK 7253 2855] and show grey, argillaceous, shelly and ferruginous limestones of massive and compact aspect; they include Gryphaea maccullochii (Plate 6)a and Pseudopecten (Plate 5)g. Calcite-mudstone nodules with sparse Modiolus have been dug out of some ditches [SK 7226 2818]; [SK 7208 2809], from a level just below the Mill Lane Limestones. The Littlegate Limestones, which contain the oldest recorded belemnites in the local succession, date to the resupinatumSubzone of the semicostatum Zone (Brandon et al., 1990). The Mill Lane Limestones (ML) are impersistent, but present in the north-east of the district, where they are nodular and generally form only a weak feature surmounted by a greyish brown, finely sandy soil that has little or no brash [SK 772 327] to [SK 784 330]. A more persistent feature is formed by mudstone containing micrite limestone nodules, directly below the Mill Lane Limestones. Ditches yield debris of fawn to ochreous-weathering, silty or finely sandy shelly limestone grading into highly calcareous siltstone. One ditch [SK 7468 2978] to [SK 7482 2957] provided more or less continuous dredgings, through the nodular Mill Lane Limestones up to the Stragglethorpe Grange Limestone; grey mudstone with phosphate nodules and phosphatic Arnioceras sp. predominated. The fauna of the Mill Lane Limestones and associated siltstones and mudstones (Brandon et al., 1990) indicates a late semicostatum Zone age. The Highfield Farm Limestones (HfF), about 1.5 m thick, form a weak feature, and where covered by head deposits can be inferred from distinctive ditch dredgings. Typical Highfield Farm Limestones slabs [SK 7722 3224]; [SK 7816 3325]; [SK 7868 3362] consist of tough platy limestone that is yellowish brown-weathering, bluish grey-hearted, silty to slightly sandy, shelly or coquinoidal. The bed characteristically contains large amounts of pyrite, both finely disseminated and in denser masses, which weathers to brown ochre giving the rock a pock-marked appearance. Reworked phosphate nodules are common. Gryphaea maccullochii is abundant, some specimens being abraded and bored, and there are common pectinids. The fauna collected indicates the turneri Zone (Brandon et al., 1990). The Stragglethorpe Grange Limestone (SG) is a single bed less than 1 m thick, which forms a poorly defined dip slope covered with a finely sandy loam. Brash is rare, but slabs from ditches [SK 7728 3217] consist of a pale brown weathering, grey, silty to finely sandy, compact shelly limestone with numerous Gryphaea maccullochii, Pseudopecten and Hippopodium (Plate 6). The fauna so far found is not zonally diagnostic (Brandon et al., 1990).

Charmouth Mudstone Formation (ChM)

This formation varies between 110 and 130 m thick across the district. The lower part forms low-lying, commonly drift-covered ground, whereas the higher beds underlie the steepening scarp slopes capped by the Marlstone Rock Formation. The strata consist mainly of grey, fissile mudstone and there are several levels with abundant calcite-mudstone, phosphate or siderite-mudstone nodules. Prior to a reclassification of some of the East Midlands Jurassic sequence (Cox et al., 1999), this unit was called the ‘Brant Mudstone’ (Brandon et al., 1990), with a type section in the Copper Hill Borehole [SK 9787 4265] (Berridge et al., 1999; Ivimey-Cook et al., in press). The formation comprises the poorly defined ‘Obtusum-Oxynotum Clays’, ‘Sandrock’ and ‘Upper Clays’ of Swinnerton and Kent (1949; 1976). Its base is defined by the distinctively ferruginous Glebe Farm Bed, which rests erosively and non-sequentially on the underlying Scunthorpe Mudstone Formation. The top of the Charmouth Mudstone Formation is gradational into the Dyrham Formation.

There are a few persistent, lenticular beds of bioclastic limestone in the lower part of the formation. The Loveden Gryphaea Bed is a very fossiliferous mudstone associated with thin beds of platy bioclastic limestone and abundant Gryphaea occurring in the middle part of the formation, which can readily be mapped from numerous ditch dredgings. A similar bed at a higher stratigraphical level, the Jericho Gryphaea Bed, has been traced locally.

The formation ranges in age from the oxynotum Zone of the Upper Sinemurian to an undefined biostratigraphical level approximately around the davoei/margaritatus zonal boundary (Lower/Upper Pliensbachian boundary). There are a very few minor stream sections in the district but most exposures are afforded by temporary sections associated with ditch digging and cleaning, only the most important being referred to in this account (but see Brandon and Carney, 2000).

The Glebe Farm Bed (GF) forms a subdued feature at certain places [SK 781 328]. It is composed of a distinctive peloidal ironstone or pebbly ferruginous oolite containing reworked phosphate and calcite-mudstone nodules, and is commonly revealed by the numerous pieces of siderite-mudstone with abundant ferruginous ooids dug from ditches. Fragments of siderite-mudstone nodules typically 0.05 to 0.1 m across with Gagaticeras sp. (Plate 6)d, indicating the oxynotum Zone, were also dredged out at one place [SK 7853 3286]. These belong to a slightly younger unit, the Sand Beck Nodule Bed, recognised by Brandon et al. (1990) but not easily differentiated in this district.

The Brandon Sandstone (BrS), the ‘Sandrock’ of Swinnerton and Kent (1949, 1976), lies about 15 m above the base of the Charmouth Mudstone. Estimated to be up to 3 m thick, it forms a strong and persistent dip slope that is covered in a brown, finely sandy soil with little or no brash. The rock is of pale grey, buff-weathering, fine-grained calcareous sandstone with scattered specks of mica and abundant burrows. At the Muxlow Hill brickyard [SK 6830 2655], near Upper Broughton, former exposures described by Lamplugh et al. (1909) showed ‘micaceous sand rock’, ‘clayey sands’ and ‘compact sand-rock’. The fauna from here included Gryphaea cymbium (Plate 6)e, Cardinia sp., Pholadomya sp., common pectinids, Ostrea and ammonites (Arnioceras semicostatum being a probable misidentification). A section [SK 7075 2562] along the River Smite showed just over 1 m of the Brandon Sandstone, which includes thin beds of brown, finely sandy siltstone and silty, hard, grey-weathering sandstone. Ammonites collected from the Brandon Sandstone in the Copper Hill Borehole (see above) suggest that the major part of the unit belongs to the raricostatoidesSubzone of the raricostatum Zone. The mudstones between the Brandon Sandstone and Loveden Gryphaea Bed (approximately 25 m) contain levels with phosphate nodules and abundant large, ovoid, argillaceous limestone nodules of the same type as found in the Dry Doddington Nodule Bed.

The Loveden Gryphaea Bed (LG) locally forms a weak feature. In subsurface provings it is recognised by a pronounced gamma-ray ‘low’, showing that it is commonly between 2 and 7 m thick, and thus is a useful marker that correlates with the ‘70’ Marker Member of the Midlands (Horton and Poole, 1977). The unit consists of bluish grey, fissile calcareous mudstone yielding abundant large Gryphaea maccullochii (Plate 6)a; a thin bed of grey, platy, shelly limestone is also present, its fauna detailed in Brandon et al. (1990). There are sparse exposures of the Loveden Gryphaea along the River Smite [SK 7150 2503], where about 0.4 m of unweathered, blue-grey, shaly mudstone with sporadic Gryphaea represents some part of it. The faunas examined from this level by Berridge et al. (1999) show that the Loveden Gryphaea Bed is of macdonnelliSubzone age, of the raricostatum Zone.

The Jericho Gryphaea Bed (JG), approximately 27 m above the Loveden Gryphaea Bed, is of similar lithology to the latter and comprises about 1 to 2 m of grey mudstone with numerous Gryphaea; also present are a thin platy bioclastic limestone and sporadic calcite-mudstone nodules. A valdaniSubzone (ibex Zone) age has been clearly established in the Copper Hill Borehole of the Grantham district (Brandon in Berridge et al., 1999). The bed is known only from rare ditch dredgings [SK 7196 2541] containing numerous Gryphaea cf. gigantea and platy bioclastic limestone fragments.

Strata other than the named units above are described from indifferent exposures in various parts of the district (Lamplugh et al., 1909). The railway cutting at Old Dalby [SK 683 235] has received particular attention (Trueman, 1918; Kent, 1937, 1973); some 15 m of strata are described, consisting mainly of blue-grey to buff fossiliferous mudstone and sandy, micaceous, fissile mudstone. Ambrose (1998) summarised these findings, and suggested a fault close to the northern end of the tunnel, juxtaposing the jamesoni and oxynotum zones. To the east of the Old Dalby tunnel, near Greenhill Farm, an exposure [SK 695 237] showed up to 4 m of grey and ochreous, silty ferruginous mudstones with belemnites, Gryphaea, Pholadomya, pentacrinoid fragments, and the ammonites Uptonia and Platypleuroceras (Cox, 1998) indicating the jamesoni Zone. From the southerly (Grimston) end of the Old Dalby tunnel [SK 6919 2199], analysis of microfauna (foraminifera and ostracods) from exposed mudstone yielded taxa suggesting a stratigraphical position within the ibex Zone (Wilkinson, 1998).

Dyrham Formation (DyS)

This formation is between 15 and 25 m thick across the district. It corresponds to the ‘Sandy clays’ division on the previous edition of Sheet 142 Melton Mowbray and to the ‘Clays above the Semicostatus Beds’ of Lamplugh et al. (1909). An uppermost component that is commonly seen in sharp contact with the overlying Marlstone Rock Formation was informally known as ‘Sandrock’. Although in the past this bed has commonly been regarded as part of the Marlstone Rock (Jukes-Browne, 1885; Lamplugh et al, 1909; Berridge et al., 1999), here it is included within the Dyrham Formation in accordance with the scheme of Cox et al. (1999). The formation probably spans the upper part of the daveoi and margaritatus zones.

The narrow outcrop is located at the top of the well wooded and commonly landslipped escarpment capped by the Marlstone Rock Formation. Natural exposures are uncommon, but several small sections in landslip backscarps show that the lower part of the formation consists of grey, ochreous-weathering, generally poorly cemented micaceous siltstone and very fine to fine-grained sandstone. Some beds contain siderite-mudstone nodules, and there are impersistent beds of well-cemented, fossiliferous sandstone and ferruginous limestone. Jukes-Browne (1885) noted a section probably from this part of the formation ‘on the east side of the brook at Scalford’. It consisted of micaceous mudstone with thin layers of micaceous sandstone that yielded ‘Cardium truncatum, Avicula inaequivalvis’ and ‘Ammonites sp. (?spinatus); the last is more likely to be Amaltheus margaritatus, given the probable stratigraphical position of these beds 5 to 10 m below the Marlstone Rock (Ambrose, 2000b).

The upper ‘Sandrock’ component of the formation is up to 5 m thick, although it is impersistent and locally absent. It is typically revealed by field brash that includes calcareous sandstone, ferruginous sandstone and shell-detrital wackestone with a siderite mudstone matrix. The ‘Sandrock’, typically yellow-brown and friable, is exposed beneath the Marlstone Rock Formation at Brown Hills Quarry SSSI (see below). Calcareous microfaunas from the ‘Sandrock’ at this quarry included Lenticulina muensteri acutiangulata (Wilkinson, 2002), an important marker form, which in onshore Britain is indicative of a margaritatus Biozone age. ‘Sandrock’ was formerly seen in a cutting for the mineral railway [SK 763 287], north-north-west of Hill Top Farm, where exposures showed 4.6 to 6.1 m of flaggy, calcareous, fossiliferous sandstone overlying soft, sandy, micaceous mudstone (from unpublished BGS manuscripts). The bed has a conglomeratic base, 0.45 m thick, and shows numerous phosphatic concretions. In a further disused railway cutting [SK 7543 2588] to [SK 7604 2561], ferruginous and calcareous sandstone and grey, micaceous siltstone are exposed (Ambrose, 2000b). Immediately to the west of Hill Farm [SK 759 273], where the sandstone has died out, a thin bed of sandy ironstone and ferruginous, bioclastic grainstone forms a pronounced feature about 5 m below the top of the formation. A further exposure near Eaton [SK 7962 2952] shows only 0.15 m of soft, fine to very fine-grained, grey, micaceous sandstone immediately beneath the Marlstone Rock Formation. Lamplugh et al. (1909) give details of several other minor exposures in the district, together with some faunal information. The fossils included: Astarte striata-sulcata, Protocardia cf. truncata, Pseudomonotis cf. substriata, Limasp. and Pecten sp.

Marlstone Rock Formation (MRB)

The Marlstone Rock Formation (formerly Marlstone Rock Bed) varies between about 1 and 5 m in thickness across the district. It is relatively resistant to erosion, and forms the crest of the prominent scarp that delimits the Vale of Belvoir in the south-east. A broad dip slope is developed behind this escarpment, and in parts where the formation has a high iron content much of this outcrop has been quarried away or worked underground as a source of ironstone (Chapter 11).

Marlstone Rock weathers to a deep rusty brown colour and produces soils of a characteristic deep orange-brown. Field brash shows three main facies of ironstone, which are, in order of decreasing abundance: near-pure ooidal ironstone with very little matrix; ooidal ironstone with common shells and shell debris; and iron-packstone/wackestone comprising ooids in an iron-mudstone matrix, with some shells and shell debris. A basal pebble bed is widespread. Petrographically, the formation is a shell detrital limestone with a sideritic cement. Ooids originally were thought to be composed of chamosite (Whitehead et al., 1952), but are more likely to be of berthierine. In this district weathering of both chamosite and siderite produces limonite (Hallam, 1968; (Plate 9)a), which accounts for the rusty weathering colours of the rock.

The ooidal ironstone facies of the formation has a rich fauna, with many fossils described from this district by Lamplugh et al. (1909). They include the terebratulid Lobothyris punctata and the rhynconellid Tetrarhynchia tetrahedra (Plate 6)g, commonly aggregated into clusters with Pseudopecten (Plate 5)g. Berridge et al. (1999) demonstrated that the ooidal facies of the formation in the Grantham district included the late spinatum Biozone, with the tenuicostatum Biozone present near the top, which is thus of earliest Toarcian age. Hallam (1968), however, had earlier suggested that the Marlstone Rock Formation is a condensed sequence, with the spinatum Biozone absent in parts of the Midlands. The diagnostic ammonite, Pleuroceras spinatum, which was identified in the Grantham district (Berridge et al., 1999), does not appear in any of the faunal listings so far published for the Melton Mowbray district. Recent work (Wilkinson, 2002) on the calcareous microfaunas from Brown’s Hill Quarry indicates that only the lower metre or so of the Marlstone Rock Formation is of the spinatum Biozone age (uppermost Pliensbachian), with the rest of the formation being of the tenuicostatum Biozone, and thus Toarcian in age.

Large-scale iron ore extraction once afforded numerous exposures, mainly in the period from around 1880 into the 1950s. These sections are comprehensively described by Whitehead et al. (1952) and Wheeler (1967), with additional data in unpublished BGS manuscripts. Lamplugh et al. (1909) and Jukes-Browne (1885) have also described sections. Nowadays most of the shallow pits on the long dip slopes have been restored to agriculture, but a few clean sections remain.

The unfilled workings east of Holwell locally expose a full 4.2 m thickness of the Marlstone Rock Formation. At Brown’s Hill Quarry SSSI, it rests sharply on the upper sandstone (‘Sandrock’) of the underlying Dyrham Formation, with a pebble bed locally present at the base. The formation here consists of a basal massive bed of ooidal ironstone, 0.9 m thick (Plate 9a), overlain by 3.3 m of medium to thickly bedded and cross-laminated shell-detrital, ooidal ironstone. Foreset bedding, of planar and trough type, is accentuated by grain-size variations and by concentrations of bioclastic debris mainly consisting of crinoid fragments (Plate 10). Length sections of the crinoid columnals and belemnites are commonly orientated north-eastwards, perpendicular to the dominant current directions measured from cross-lamination and cross-bedding foresets that are inclined mainly towards the east-south-east and south-east (Figure 21). The formation becomes coarse-grained and shell-rich in the uppermost few centimetres and the top is a bedding plane strewn with broken and worn belemnites. This surface may represent a nonsequence at the base of the overlying Whitby Mudstone Formation (e.g. Clements, 1989).

The disused ironstone pits to the north-east and southwest of Eaton Lodge expose up to 4 m of the formation. The rocks consist of fine-grained ferruginous oolite, massive in the lowermost 1 m but, as at Brown’s Hill Quarry, cross-laminated higher up. Other noteworthy exposures described from this area by Ambrose (2000b) include the quarries to the south of Eaton [SK 7997 2846], in which the upper 1.5 m of the formation consists of ochreous, fine-grained, cross-laminated and finely crossbedded iron-oolite. The facies rests on a belemnite-rich lag, in turn underlain by 0.65 m of massive, shelly ironoolite. The same two-fold subdivision, into a lower massive ironstone overlain by the cross-laminated facies is seen in a former quarry face [SK 7984 2826] to [SK 7953 2826] that exposes up to 4 m of the formation.

Marlstone Rock revealed in the disused railway cutting near Cranyke Farm [SK 7549 2587] to [SK 7544 2588] shows up to 2.5 m of thinly bedded iron-oolite or ferruginous, ooidal limestone, coarse and pebbly in the lowermost part where the contact with the upper sandstone of the underlying Dyrham Formation is seen.

A roadside quarry east of Branston shows lithologies that differ from those seen at Holwell. Here, the Marlstone Rock overlies 1 m of Dyrham Formation sandstone and consists of 2.4 m of massive, finely limonite-ooidal and shell-fragmental ironstone (Plate 9b), with conspicuous nests of brachiopods and sporadic belemnites (Plate 11). A similar section is visible in former quarry faces to the west of Eaton Grange [SK 8024 2880]. There, the uppermost sandstone bed of the Dyrham Formation appears to be as ferruginous as the overlying Marlstone Rock, and has evidently been worked for ironstone.

Key localities

SSSI at Brown’s Hill Quarry, near Holwell, [SK 741 234]; Ironstone pits near Eaton Lodge, [SK 783 296]; Disused quarry east of Branston [SK 8136 2944]

Whitby Mudstone Formation (WhM)

The term Whitby Mudstone Formation was defined by Powell (1984) for the Yorkshire basin, and its usage was extended throughout the East Midlands by Cox et al. (1999). It largely replaces the ‘Upper Lias’ of former use. The formation consists mainly of grey mudstone with a few beds of nodular limestone, and with calcareous siltstone beds especially near the base. It is 55 m thick, on average, but is largely covered by drift except in the east, where it forms the lower part of the steep escarpment capped by the Northampton Sand Formation. Lamplugh et al. (1909) followed previous workers (e.g. Jukes-Browne, 1885) in adopting a four-fold division for these strata, although this cannot be used as a basis for mapping. In the Grantham district, the base of the unit is disconformable on the underlying Marlstone Rock (Berridge et al., 1999), and a sharp contact is seen in the exposures at Brown’s Hill Quarry of this district. The basal beds of the formation in the Grantham district belong to the Harpoceras falciferum Biozone, whereas the upper part is in the Hildoceras bifrons Biozone. Calcareous microfaunas from Brown Hills Quarry are consistent with a falciferum Biozone age for the basal part of the sequence (Wilkinson, 2002).

At Brown’s Hill Quarry, intermittent exposures above the Marlstone Rock consist of well laminated, olive green to dark blue-grey, fissile mudstone (Plate 12), part of the ‘Dumbleton Beds’ of Lamplugh et al. (1909). Many former exposures were described by those authors, to which the reader is referred for details. For example, at the Stanton Company’s ironstone quarry [SK 742 238], Lamplugh et al. (1909) measured about 4.3 m of ‘Dumbleton Beds’ consisting of pale blue ‘shaly clay’, which are still visible in places. The lowest part of this division, immediately above the Marlstone Rock, comprised several centimetres of buff or ochreous clay with calcareous layers and cream-coloured nodules containing fish debris, and may be an equivalent of the ‘Transition Bed’ of Hallam (1968). In the overlying strata at the Stanton Quarry, Lamplugh et al. (1909) recovered a fauna of abundant Pseudomonotis sp., together with Astarte (Plate 6)h, Dactylioceras annulatum (Plate 6)i, Harpoceras sp., and Belemnites cf. elongatus. The uppermost part of the formation was formerly exposed below the Northampton Sand in the Stonesby brick-pit [SK 8204 2433], but was overgrown even at the time of the original survey (Lamplugh et al., 1909; p.53). It showed a few metres of unfossiliferous blue clay with pyritous and calcareous nodules.

Key locality

Brown’s Hill Quarry, near Holwell [SK 741 234]

Inferior Oolite Group

This sequence, formerly known as the ‘Inferior Oolite’ (Lamplugh et al., 1909) constitutes the stratigraphically youngest Jurassic division exposed in the district. Its base coincides with the base of the Middle Jurassic (Aalenian Stage). Only the three lower formations of the group are represented here and are, from the base upwards: Northampton Sand Formation, Grantham Formation and Lincolnshire Limestone Formation.

Northampton Sand Formation (NS)

This unit is composed of fine-grained, ferruginous sandstone and iron oolite of Aalenian, Leioceras opalinum Zone age. It crops out in the east of the district, around Waltham, where it is 4 m thick, on average. The unit was formerly known as the ‘Northampton Beds’ (Lamplugh et al., 1909) and ‘Northampton Sand Ironstone Formation’ (Taylor, 1949), and is the lateral equivalent of the ‘Northampton Ironstone’ of Hallam (1968). To the east and south of this district the unit, in its type development, has a varied lithology. Here, however, it is clear from Taylor (1949, plate II) that only the ‘sandy marginal facies’ of the ‘Northampton Sand Ironstone Formation’ is mainly represented. Consequently, these strata have not been worked to any great extent as a source of iron ore (Chapter 11).

The formation is relatively resistant to erosion and gives rise to a prominent bench that caps the Whitby Mudstone escarpment along Lings Hill [SK 815 282] and around Waltham [SK 805 247]. Soils on the outcrop are of dark reddish brown sandy loam with abundant brash of hard, limonite-cemented quartzoze sandstone and some ooidal ironstone. Cambering, producing slopes towards the Whitby Mudstone scarp, is a pronounced feature of the outcrop particularly to the south-east of Waltham. Complex flexuring and fracturing of the formation and adjacent units was described to the west of Waltham (Lamplugh et al., 1909) and are periglacial phenomena related to cambering (Chapter 8).

The original survey by Lamplugh et al. (1909) noted only one good exposure, in a small pit at Croxton Park, ‘680 yards due west of Croxton House’ [SK 8176 2750]. There, 2.5 m of weathered ochreous ‘ironstone’ contained a fauna of Terebratula trilineata, Lima sp., Modiola cf. cuneata and Pecten paradoxus. Partial exposures formerly occurred along the top face of the brick pit near Stonesby [SK 8204 2433], as 4.2 m of ‘unfossiliferous brown ironstone and ferruginous sandstone’ (Lamplugh et al., 1909, p.53), but nowadays only debris can be seen.

Grantham Formation (GrF)

The Grantham Formation (formerly the Lower Estuarine Series) crops out in the east of the district, just below the Lower Lincolnshire Limestone which is unconformable upon it in the Grantham district (Berridge et al., 1999). It is 4 m thick on average, but locally thin or absent, for example to the south-west of Croxton Kerrial. The strata are mainly of nonmarine and paralic facies, consisting of interbedded sandstones and pale grey mudstones. They give rise to sandy and clayey loam soils with brash of mottled greenish grey and bluish grey, commonly fissile mudstone ploughed up in places. Sandstone beds occur at various levels; for example, near the top of the formation to the north-west of Stonesby [SK 8166 2489] a pit (1.5 m deep) exposed yellow sand with relict tablets of hard, grey, medium-grained quartzose sandstone.

Apart from these temporary sections, the Grantham Formation is very poorly exposed in the district. It has, however, been recorded at the Sproxton Quarry SSSI [SK 864 253], about 1.5 km to the east of Sheet 142, where it is 3.8 m thick (Richardson, 1939; Cox et al., in prep), though only the topmost 0.3 m are currently exposed [SK 865 247]. These accounts show that the lower part of the formation is dominated by sandstone, which is overlain by a seatearth-like mudstone in turn succeeded by the ‘Stainby Member’, consisting of dark grey, fissile mudstone with silty laminae.

Lincolnshire Limestone Formation

This formation, of Aalenian to Bajocian age, crops out on the high plateau between Waltham and Croxton Kerrial, at the eastern margin of the district. The estimated 20 m of beds that are represented consist mostly of the Lower Lincolnshire Limestone, but the top few metres possibly belongs to the Upper Lincolnshire Limestone; these are informally named members of the formation (Kent, 1966). A rich marine fauna consisting mainly of lamellibranchs with gastropods, brachiopods, echinoderms and corals was reported by Lamplugh et al. (1909), although they mainly referred to the faunal lists given in Jukes-Browne (1885). Additional details that include ostracod and microfaunal identifications from the Grantham district are given by Berridge et al. (1999).

The basis for the twofold division of the Lincolnshire Limestone in this account comes from the thickness of strata encountered in Borehole (SK82NW/47), located about 100 m to the east of the district. The sequence in the borehole is poorly documented; the stratigraphical placement of the Lower/Upper boundary is based on A. crossi and must be regarded as dubious for reasons discussed below.

Lower Lincolnshire Limestone (LLL)

This unit is estimated from the borehole (above) to be 16 m thick. It gives rise to long, eastwards dip slopes characterised by pale brown, clayey soils strewn with abundant tabular brash of cream-coloured limestone. Between Waltham and Stonesby the underlying Northampton Sand Formation appears to dip northwards, suggesting that in this southerly part of the outcrop flexuring may in part be responsible for preservation of these strata.

Much of the Lower Lincolnshire Limestone Formation in this district appears to be dominated by massive to thickly bedded, uniformly fine-grained ‘calcarenite’-textured limestone of obscure internal constitution (possibly a very fine-grained shell-detrital, ooidal and peloidal limestone), which weathers to a pale brown platy brash. Although the formation has been mapped as a single unit, its overall thickness, and the evidence of the above borehole, suggest that it probably encompasses the ‘Sproxton’ and ‘Greetwell’ members, which are the two stratigraphically lowest divisions of the formation proposed by Ashton (1980). Based on this correlation, a discites Biozone age is probable (Berridge et al., 1999; table 8).

In Waltham Quarry [SK 813 251] (Stonesby Quarry or Bescaby Lane Quarry), the lower part of the formation was described by Lamplugh et al. (1909) as a ‘variable sequence of massive and thinly-bedded limestones’. These lower strata are either ooidal or structureless, and micritic, with interbedded grey mudstone, micaceous sandstone or sandy limestone. From this part of the sequence a fauna of Ceromya cf. bajociana, Cyprina?, Lima (Plagiostoma) pontonis and ?Natica cincta was listed by Lamplugh et al. (1909). At the same locality F B A Welch (1941, see the fieldslip for Leics 13 SE/E) recorded nearly 6 m of strata and a similar thickness was also recorded as a graphic section by Ashton (1977, 1980). During this resurvey, M G Sumbler noted that there are still a few exposures of these higher beds that are not overgrown; the best are in the southern part of the quarry complex that comprises the Stonesby Quarry Nature Reserve. One exposure there showed about 1.5 m of coarse ooidal and bioclastic muddy limestone (possibly Welch’s ‘oolite’, see (Plate 13)) resting on hard, pale brown ‘calcarenite’. The latter has a hardground top, enabling correlation with Ashton’s record of this quarry in which, however, the beds below the hardground are (mistakenly?) ornamented as peloidal limestones. The presently exposed beds are of similar appearance to (and possibly equate with) Ashton’s ‘Sproxton Member’ (‘fine grained, homogeneous silty dolomitic biomicrite’), or the ‘Blue Beds’ of Richardson (1939). If this is so, however, they must be somewhat thicker (totalling about 5 m) than at the type section of Sproxton Quarry, to the east of this district [SK 864 253], where the member is only 1.8 m thick. This is further indicated by the borehole evidence discussed above, which shows 3.4 m of the member.

The stratigraphically higher beds of the formation comprise variably peloidal and shell-fragmental wackestone and packstone and, more rarely, almost pure lime mudstone, typical of the Greetwell Member of Ashton (1980). This part of the formation is apparently almost 14 m thick in the borehole described above, if the ‘clay parting’ is taken to be the equivalent of that separating the two members in Berridge et al. (1999, fig. 21). On the outcrop, F B A Welch mapped ‘oolite’ around Waltham Quarry (above the ‘calcarenites’ described above), and ‘pisoidal limestone’ in various places. The latter lithologies are actually medium to coarse-grained peloidal packstones and there are no dominantly pisoidal limestones in this district. He also identified the so-called ‘Crossi Bed’, mapped south of Croxton, which appears to be mostly of pure lime mudstone. This supposed marker bed was at that time used to define the top of the Lower Lincolnshire Limestone on the adjacent Bourne Sheet, and it has been used, for example in the classification of the sequence in Borehole (SK82NW/47) (see above). It is, however, a lithology that recurs at various levels, and the correlative value of the eponymous Acanthothyris crossi is now known to be minimal (see Ashton, 1979).

Key locality

Stonesby Quarry Nature Reserve, [SK 813 251]

Upper Lincolnshire Limestone (ULL)

This informal member is inferred to subcrop beneath Drift in the extreme east. It is tentatively equated with the uppermost 18 m of strata proved in Borehole (SK82NW/47) (see above), located just east of the district. No lithological details are available.

Chapter 7 Quaternary

Uplift of the region from the Palaeogene through into Quaternary times (Chapter 8) and the concomitant erosion resulted in the complete removal of all but the lowest part of the thick marine Jurassic and Cretaceous sequences that once covered the district (Green et al., 2001). Relict patches of near-sea level early Neogene strata (Walsh et al., 1972) and an early Quaternary nonmarine mammal fauna that is preserved only in the highest karst of the Peak District (Spencer and Melville, 1974), testify to the amount of uplift and erosion that has taken place. The Quaternary Period, covering the last 2 million years, is marked in Britain by extreme oscillations of climate ranging from severely cold glacial or periglacial to mild 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 5).

The Quaternary sequence of the Melton Mowbray district commences with Preglacial Deposits, that are fluvial in origin, and probably date back to at least Neogene times (Rose, 1989; Brandon, 1999). They accumulated from rivers flowing within the Bytham river basin, the trunk stream of which transported quartzite-rich, sandy and gravelly sediments eastwards into the North Sea. When ice sheets subsequently advanced across the English Midlands during the severely cold Anglian stage (o.i. stage 12) Glacial Deposits were laid down, thickening into, and completely infilling, the Bytham river basin. There are two principal varieties of till, together with their related glaciofluvial sands and gravels. These deposits commonly interleave with glaciolacustrine silts and clays where they are thickly accumulated in palaeovalleys.

The present-day drainage was initiated along meltwater routes (Brandon, 1996, 1999) during the waning phases of the Anglian glaciation. The River Terrace Deposits are the valley sandar and later fluvial sediments, which now occur as flights of terraces along the trunk valleys. They record climate change coupled with continuing uplift and lateral and vertical incision. It is this regime of erosion that is responsible for much of the present-day topography of the district.

Widespread deposits of head, which include deposits related to terrace cryoplanation, are evidence for periglacial conditions occurring at various times following the Anglian glaciation. The clay vales, such as the Vale of Belvoir, developed through repeated episodes of periglacial slope mass movement, the various stages being partly reflected by the head that forms the Slope Terrace Deposits (Brandon, 1999; Brandon and Carney, 2000). Landslippage is a further slope process, which has occurred along the steeper escarpment slopes. Flandrian (o.i. stage 1) events are marked by further fluvial incision and terracing of Late Devensian and early Flandrian sediments along the trunk valleys, together with the formation of the alluvium of the modern floodplains. Man’s influence has led to accelerated colluviation linked to deforestation and modern farming practises and a change of hydrodynamic styles brought about by the introduction of flood prevention schemes.

Permanent sections in the Quaternary deposits are rare and are only mentioned in the text if significant.

Geomorphological framework

Quaternary erosional as well as depositional processes are responsible for the landforms of the Melton Mowbray district. This section therefore considers the ‘Superficial Deposits’ in the context of nine more or less clearly defined geomorphological domains, shown in (Figure 22).

1 Ruddington clay vale

A low-lying and extensive area of Mercia Mudstone bedrock with a patchy covering of ‘Superficial Deposits’. The uneven floor of the vale is marked by minor cuesta and gravel-capped hills. A prominent subdomain is the flat lowland of Ruddington Moor (1A), drained by the Fairham Brook. The formation of the moor may have been facilitated by gypsum dissolution (Lamplugh et al., 1909), and it is underlain by thin head, lacustrine and alluvial deposits.

2 Barnstone Member dip slope and ‘Rhaetic escarpment’

The cuesta formed by the Barnstone Member has a prominent dip slope underlain mainly by hard limestone beds. The complementary scarp, capped by the Barnstone Member, is formed mainly of mudstone of the Penarth Group and the underlying Blue Anchor Formation. The domain is masked in places by remnants of the ‘Till capped plateau’ (see below).

3 Vale of Belvoir

An extensive post-Anglian clay vale bounded in the south-east by the Marlstone Rock escarpment and in the west by a ‘Till-capped plateau’. Its northern margin is taken at the foot of the Barnstone Member dip slope. Thin veneers of Slope Terrace Deposits and Flandrian head cap the bedrock, which consists of Lias mudstone with thin limestones and sandstones that locally form small cuesta on the floor of the vale.

4 Marlstone Rock dip slope

An extensive surface tilted to the south-east, underlain by the Marlstone Rock Formation. It is deeply dissected by combes and valleys excavated into the siltstone and sandstone of the underlying Dyrham Formation.

5 Middle Jurassic dip slope

A minor area underlain by Northampton Sand and Lincolnshire Limestone, with an escarpment in the northern part underlain by the Whitby Mudstone.

6 Till-capped plateau

A dissected plateau generally lying at elevations greater than about 80 m above OD. It is a cryoplanation surface underlain mainly by Anglian-age Oadby Till and other glacial deposits. Valleys deeply incised into bedrock bound the periphery of the plateau. Thicker deposits, such as sand and gravel, occur only in buried channels. The Bytham Subdomain (6A) in the south-east is dissected by the present-day Wreake valley. It is underlain by a thick accumulation of stratiform glacigenic deposits capped by Oadby Till, which infills the pre-Anglian Bytham valley. This subdomain extends along three tributary infillings of the Bytham valley as far as the Vale of Belvoir escarpment.

7 Wreake valley

The floodplains, river terraces and valley slopes of the Wreake river system.

8 Stapleford vale

A small post-Anglian clay vale opening out into the Wreake valley. The outcrops consist mainly of thin solifluction deposits although there are remnants of till plateau; these deposits overlie Lias mudstone bedrock.

9 Soar valley

The floodplains, terraces and valley slopes of the Soar river system.

Preglacial deposits

These deposits are mostly confined to the Bytham river basin (e.g. Rose, 1989; Brandon, 1999), and its associated tributary valleys (Figure 23). The trunk stream flowed north-eastwards from the Coventry and Leicester areas, and thence across the Melton Mowbray district (Wyatt, 1971) where its graded floor declines in the inferred direction of flow, from about 60 m above OD in the west to 50 m farther east. The minor valleys shown in (Figure 23) represent tributary streams, in which early Quaternary fluvial deposits have been found. The Scalford and Waltham valleys drain southwards and although subsequently filled by Anglian till they are still conspicuous because, as Sheet 142 Melton Mowbray shows, they break the Marlstone Rock dip slope and escarpment of the Vale of Belvoir.

Preglacial deposits are poorly exposed, but they constitute an important local aggregate resource and are consequently known from recent subsurface exploration programmes (e.g. Rice, 1991; Brandon, 1999).

Bytham Sands and Gravels

Bytham Sands and Gravels is the collective name for all of the pre-Anglian fluvial deposits of the Bytham River and its tributaries occurring in this district. In the Wreake valley it was referred to as the ‘Older Sand and Gravel’ by Lamplugh et al. (1909), who also hinted at its preglacial age. The deposits were later named the ‘Thurmaston sand and gravel’ by Rice (1968), but this was later changed to the term ‘Baginton Sand and Gravel’ (Rice, 1991). The latter is here considered to represent only the last cycle of aggradation of the Bytham Sands and Gravels on a graded floor of the Bytham valley. The ‘Bytham Terrace Deposits’ of Brandon (1999) form raised outcrops and relate to earlier periods of sediment aggradation along the valley; they are included within the Bytham Sands and Gravels but are referred to informally below.

During this resurvey, a combination of fieldwork, borehole syntheses and interpretations of coal exploration high-resolution seismic data helped to confirm a course for the Bytham River very similar to that suggested by Wyatt (1971). Research drilling was then employed by BGS (Brandon, 1999) and the Welby Grange Borehole (Figure 23) proved till to 14.65 m resting on 5.35 m of sandy deposits overlying bedrock at 67.91 m above OD. The proving suggested a location on the southern flank of the Bytham valley and the borehole may have penetrated a buried sequence of ‘Bytham Terrace Deposits’. The BGS Potters Hill Borehole succeeded in proving the deposits of a deep and narrow Bytham channel indicated by the seismic investigations. The sequence encountered below till comprised 7 m of red sand on 10.8 m of very coarse grained sand with gravel, the top lying at 70.04 m above OD. The bipartite lithology of these deposits, with fine grained red sand overlying coarser sand and gravel, supports them being part of the ‘Baginton Sand and Gravel’. The course of the Bytham valley to the north-east of Melton Mowbray (e.g. Wyatt, 1971) is not well constrained, but the Abbot Lodge Borehole may have penetrated the Bytham deposits since the log indicates 57.9 m of till on 7.3 m of sand and clay, resting on 2.1 m of sand overlying probable ‘Lias’ bedrock at 52 m above OD.

The detailed stratigraphy, clast composition, provenance and sedimentology of the Bytham Sands and Gravels of the lower and middle Wreake valley were described by Engineering Geology Ltd (1985a) and Rice (1991). The far-travelled gravel clasts fall into two compositional suites, the most important constituents (Rice 1968) being rounded quartzite and quartz derived from the Sherwood Sandstone Group. Of slightly lesser importance are Upper Carboniferous sandstone and Lower Carboniferous chert and limestone fragments; they probably had a northerly derivation from Derbyshire, via the Derby River (Brandon, work in progress). The remaining constituents are locally derived, composed of Jurassic limestone and ironstone, and Triassic siltstone and mudstone. Up river, in what is now the Soar valley area, the Baginton Sand and Gravel has been seen to contain syn-depositional ice-wedge casts that imply deposition under periglacial conditions (e.g. Rice, 1991, p.47).

Terrace remnants of the Bytham Sands and Gravels are identified (Figure 23) in places where the base of the deposits is raised above the typical height range for the Baginton Sand and Gravel. The outcrop on the north side of the Wreake valley, between Hoby [SK 670 172] and Austen Dyke [SK 683 182], was encountered in boreholes that proved up to 7.3 m of sand and gravel with bedrock at about 64 m above OD. On the south side of the valley, to the east of Rotherby [SK 676 168] to [SK 686 173], mapping indicates a second outcrop with rockhead at 65 to 68 m above OD; a borehole [SK 6794 1680] shows 1.6 m of sand on 1.4 m of gravel.

Around Asfordby the correlation of the deposit mapped as Bytham Sands and Gravels is equivocal, for although it maintains the same character as farther west, the basal gravel is generally absent and the base of the deposit is at too high an elevation. Deeley (1886, p.455) referred to this deposit as the ‘Melton Sand’, and its distribution in the district is shown in (Figure 23). Borehole evidence shows that the sand can be up to 7.3 m thick, with values above 3 m being common. Basal gravel has been recorded at only three locations, the thickest value being 1.6 m [SK 7321 1815]. At the Leicester Road Industrial Park west of Melton Mowbray, a number of boreholes (Brandon, 1999) through the deposit proved about 8.3 m of reddish brown to orange-brown, silty sand, with some fine gravel lying between about 66 and 74 m above OD. Lewis (1989) described a temporary section [SK 736 174] as consisting of thin head underlain by 1.5 m of dark brown sand with conspicuous coal fragments. The deposit was planar crossstratified above the base, becoming ripple laminated towards the top; palaeocurrent measurements on individual planar foresets and ripples indicated a flow direction from west-south-west to east-north-east.

Reddish brown ‘Melton Sand’, lying between bedrock and the Oadby Till, crops out marginal to the Wreake and Eye floodplain at several places eastwards of Melton Mowbray (Figure 23). All these occurrences are probably part of the Bytham valley fill and some of the higher ones may represent former, pre-Anglian river terrace deposits. Mapping and boreholes east of Brentingby show that the sand is at least 8.5 m thick in places. It has been worked from two small pits [SK 7822 1860]; [SK 7838 1865] at Brentingby. At Wyfordby, a relatively thin sand bed occurs at about 85 m above OD between Oadby Till and bedrock, and presumably was worked from a small pit [SK 7908 1900]. A section available in 1998 showed ‘Lias’ clay at the base of the pit with incorporated, probably cryoturbated, pods of reddish brown sand.

The main channel deposits (Baginton Sand and Gravel) of the Bytham Sands and Gravels typically form a fining upwards sequence (Rice, 1991), of basal gravel overlain by red sand. The thicknesses of the gravel and sand units, where clearly differentiated, are summarised by Brandon (1999); the basal gravel ranges between about 1 to 6.5 m in thickness (average about 2.5 m) and the upper sand unit ranges between about 0.5 to 5.5 m with about 2 m being typical. These deposits crop out as terrace-like features on the northern and southern flanks of the Wreake valley; a typical example is the outcrop lying some 7.5 to 10 m above the Wreake floodplain and extending along the southern valley flank as far east as Rotherby [SK 676 167]. West of Frisby, there is a further terrace-like outcrop along the south flank of the Wreake valley. Deeley (1886, p.446) refers to a former pit section [SK 6966 1791] near the mill at Frisby consisting of ‘a light, clean, bedded sand, with occasional pebbly beds; it much resembles the Aylestone sand. The false-bedding indicates currents from the west’. An analysis of a gravel sample from a borehole in this district is given in Brandon (1999, table 5).

Tributary valley deposits of the Bytham Sands and Gravels are known from the Scalford valley (Figure 23). South of Long Clawson [SK 72 26], an outcrop contains deposits of red sand that occur beneath Thrussington Till. The Croxton Kerrial valley and its tributaries also contain material of possible pre-Anglian age in the shallow valleys east of Bescaby [SK 828 264]; [SK 828 260]. The gravelly deposits contain large Lincolnshire Limestone clasts accompanied by sporadic Bunter pebbles. Their outcrops appear to be terminated abruptly by the till infill of the Croxton Kerrial buried valley, however, suggesting that they are the older remnants of an infill to a tributary of that valley.

Glacial deposits

Various deposits were accumulated during the Anglian glaciation, which involved two principal ice sheets: a trans-Pennine ice sheet initially covered the district from the north-west, and was followed by the advance of ice from 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 glacigenic suites. Thus the distinct ice advances correspond, respectively, to the Thrussington and Oadby tills (Rice, 1968), both representing mainly lodgement facies, and their associated meltout deposits. Ice striae on bedrock which support the different ice movements have long been known from two localities within the district. Striae and roche moutonnée developed on Marlstone Rock Formation, proving glacial movement towards the south-south-east (150°-170°), were noted during ironstone working at Wartnaby [SK 704 233], about 3 km to north of Asfordby (Lamplugh, 1909, pp. 64, 70). Though the overlying till appears to be mainly the Liasrich variety of the Oadby Till, distinguished separately on Sheet 142 Melton Mowbray, clasts of Upper Carboniferous sandstone and Lower Carboniferous limestone up to boulder size indicate a thin remanié of Thrussington Till at the base. Striae on bedrock below the Lias-rich facies of the Oadby Till orientated south-west (230°), the probable direction of ice advance, are recorded on the ‘Lias’ limestone floor in Stanton Railway Tunnel [SK 637 307] (Deeley, 1886, pp.458, 461). An orientation of only a few degrees from south-west was quoted by Lamplugh et al. (1909, pp.64, 77) for the same locality. The earlier glacigenic suite is not known south-east of Melton Mowbray and it could be that that area was never covered by the Thrussington ice sheet.

In the absence of any intervening interglacial sediments the current consensus 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 at about 80 m above OD, that is now much dissected by the development of the modern drainage system.

Thicknesses of glacial deposits beneath the plateau areas vary greatly from place to place. On the Till plateau (Figure 22), total thicknesses are typically less than 15 m but more intact, variable and thicker deposits, up to about 60 m, are preserved in palaeochannels cut into the bedrock. A network of such channels was proved between Wymeswold, Wysall and East Leake (Carney, 1999; fig. 5), some of which are indicated by narrow outcrops of glaciofluvial deposits (see below) that form the infills. Thus the Fox Hill palaeochannel [SK 245 570] has a narrow valley floor that declines in elevation westwards from East Leake to Kingston on the edge of the River Soar valley (Brandon, 1994). The Wysall palaeochannel [SK 593 241] appears to empty southwards into the east-west valley of the King’s Brook, but can also be followed northwards into the upper reaches of the Fairham Brook. The floor of this palaeochannel does not have a uniform gradient and borehole evidence suggests that it may be overdeepened to the south-east of Rempstone (Carney, 1999). This is typical of tunnel valleys, which have been carved by pressurised (subglacially confined) sediment-laden water into the underlying bedrock at the time of occupancy of the area by Anglian ice sheet(s).

Within the preglacial Bytham valley, in the present Wreake valley area, there is a well-differentiated stratiform glacigenic sequence (Rice, 1968), comparable to the ‘Wolston Glacial Succession’ that was deposited in the continuation of the Bytham valley farther west in Warwickshire (Bridge et al., 1998). It comprises the following sequence:

• Oadby Till, locally with a basal Lias-rich facies
• Wigston Sand and Gravel
• Rotherby Clay
• Thrussington Till (locally resting on Bytham Sands and Gravels)

Thrussington Till

The Thrussington Till (Rice, 1968), or the ‘Older Boulderclay’ of Lamplugh et al. (1909), is of widespread occurrence in the central and western parts of the district. On the higher parts of the Till plateau (Figure 22) it commonly rests directly on the bedrock, and there it is locally attenuated or missing due to overstep by the Oadby Till, as for example to the west of Kinoulton [SK 653 296]. The till is a diamicton characterised by a matrix of brown to reddish brown, silty or sandy clay and is largely derived from Carboniferous and Triassic argillaceous rocks. Stones within the till, like those of the associated glaciofluvial outwash or tunnel valley deposits, include abundant Carboniferous sandstone, chert, coal and limestone from the Pennine regions, Triassic rocks (particularly quartzite and quartz pebbles) and minor constituents including igneous erratics from as far afield as Scotland and the Lake District. In the Brooksby area (Brandon, 1999) the till incorporates rip-up clasts of ‘Liassic’ mudstone and Bytham Sands and Gravels. The Thrussington glacigenics are commonly locally preserved beneath a more extensive cover of Oadby Till. They are very poorly exposed, although were described from a number of temporary sections during this resurvey. Borehole records of Thrussington Till exist in the Wreake valley area, where the unit was commonly penetrated during exploration of the underlying Bytham Sands and Gravels aggregate resource, as summarised in Brandon (1999).

Near to or within sediment-filled palaeochannels (see above), the Thrussington Till commonly shows complex interleaving with glaciofluvial sands and gravels, and with sand-rich diamictons, as seen in fields between Wysall and Wymeswold [SK 5945 2548]. Thrusting up of slices of the underlying Thrussington Till may have formed mixed tills of this type.

Oadby Till

The Oadby Till (Rice, 1968), is a bipartite unit, consisting of a lower till rich in Liassic limestone fragments, but largely devoid of chalk or flint, and an upper till with abundant chalk and flint.

The Lias-rich till facies has an outcrop extending from the Wreake valley area northwards along the eastern and central parts of the district. In those parts it is commonly developed at the base of the chalky facies of Oadby Till. The Lias-rich facies is chalk and flint-free, and is composed almost entirely of Lower Jurassic rock fragments in a grey to brown or yellow-brown matrix. In places there is a gradation downwards into it, from the normal ‘chalky’ Oadby Till. The deposit was previously misidentified on geological maps as ‘Lias’ mudstone bedrock. It may be locally be up to 20 to 30 m thick, and in the northern spur of the Till plateau, west of Kinoulton and around Keyworth [SK 655 305] it is the only superficial deposit present. This part of the Quaternary sequence can be complex, with a Triassic-rich till variant of the Oadby Till also identified locally, as near Wysall (Carney, 1999).

The chalk-rich facies of Oadby Till, known to Lamplugh et al. (1909) as ‘Chalky Boulder-clay’, underlies the wide expanse of the Till-capped plateau (Figure 22), from around Clipston [SK 64 33] in the north to Barrow upon Soar [SK 59 17] in the south. It also forms the higher parts of the Bytham valley sediment sequence, localised around the present-day Wreake valley, with a broad outcrop extending eastwards through Melton Mowbray. Two conspicuous spurs of till point northwards to the Vale of Belvoir and mark the courses of the two sediment-filled Bytham tributary valleys - the Scalford and Waltham valleys; a third, Croxton Kerrial valley lies just east of the district (Figure 23). A thickness of at least 26 m for the deposit has been recorded for the Oadby Till where it infills the Bytham valley, or the Waltham paleaovalley (Ambrose, 2000a), and boreholes on the crest of the Till plateau (Figure 22) near to a major junction on the A46 (SK61NW/70), indicate a similar thickness.

Outcrops of Oadby Till are characterised by yellowish brown, clayey soils strewn with abundant angular, granule to boulder-size fragments of flint, Jurassic limestone, ironstone and rounded quartz pebbles; Gryphaea shells are particularly conspicuous and chalk fragments additionally occur in fields that have been deeply ploughed. When augered, the upper leached part of the Oadby Till is commonly yellowish brown and contains small flint fragments but no chalk. Chalk does not occur in abundance until about 0.4 to 0.6 m lower down; its appearance coincides with a change to pale grey or medium grey clay, corresponding to the less-weathered part of the till. The fresh Oadby Till matrix is largely derived from Jurassic mudstone rocks and is generally grey. A flinty remanié deposit commonly indicates a former Oadby Till cover to Thrussington Till outcrops.

Heterogeneity within the Oadby Till was described by Carney (1999) in ploughed fields to the south of the Rempstone Road [SK 5940 2380], where fragments of red, Triassic-rich till and grey, chalky till occur together. Freshly dug graves in the cemetery nearby [SK 5952 2376] revealed a deposit consisting of aggregated, angular to subangular fragments of these two components.

Rotherby Clay

The Rotherby Clay, first named by Rice (1968), corresponds to the ‘Glacial Lake Deposits’ of the 1976 edition of the Sheet 142 Melton Mowbray, and was considered part of the ‘Older Boulder-clay’ category of Lamplugh et al. (1909). The deposit forms narrow outcrops in the south of the district, along the various tributary valleys of the River

Wreake, and is probably 3 to 7 m thick on average. It consists of clay and silt, and represents sediments accumulated where glacial or subglacial water was ponded within the remains of the Bytham palaeovalley. Rotherby Clay occupies a distinct stratigraphical position, between Thrussington Till and the Wigston Sand and Gravel, and it is thus analogous to, although not contiguous with, the Wolston Clay outcrops farther west in Warwickshire (Bridge et al., 1998).

The Rotherby Clay was formerly worked at the Rotherby brick pit [SK 679 163] and in the brickyard [SK 6455 1622], now overgrown, to the north-west of Thrussington. It was described by Lamplugh et al. (1909), partly from drilling, as comprising 6.4 m of ‘laminated brick-clay or sandy loam of a reddish colour with a pebble here and there’. An exposure of glaciolacustrine clay some distance from the main outcrop of Rotherby Clay was found in a stream bed [SK 6307 1802] near North Hill Farm. It consists of at least 1.0 m of red, grey or green mottled clay with sporadic ‘Bunter pebbles’ and Triassic siltstone fragments; these are probably dropstones.

Glaciolacustrine deposits, undifferentiated

Sporadic and discontinuous outcrops of grey to red-brown clay or silty clay have been mapped that generally occur as lenses within glaciofluvial deposits, for example to the north of Burton on the Wolds [SK 590 215]. Borehole records suggest that glaciolacustrine deposits may occupy a substantial proportion of certain palaeochannel fills. Thus the mainly glaciofluvial sequence in the Fox Hill palaeochannel, near East Leake, contains beds up to 2 m thick consisting of sandy clay or pebbly clay (possibly diamicton).

In a former brick pit at Melton Mowbray [SK 757 196], glaciolacustrine clay consisting of 6 m of red, laminated and silty clay with rare pebbles was reported by Lamplugh et al. (1909, p.67; see also, Brandon, 1999). This sequence was highly contorted, according to Deeley (1886).

Wigston Sand and Gravel

This deposit (Rice, 1968) is between 2 and 6 m thick, and has been mapped as a part-continuous sheet of glaciofluvial sand and gravel at the base of the Oadby Till in the Wreake valley area (Brandon, 1999; Carney, 1999). In the few former exposures, described for example by Deeley (1886) and Lamplugh et al. (1909), its base was described as gradational with the Rotherby Clay but its upper contact was invariably a sharp junction with the Oadby Till. The Wigston Sand and Gravel is flint-rich and may represent proglacial outwash of the Oadby ice sheet into what remained of the Bytham valley, after the Thrussington Till glaciation and subsequent Rotherby Clay lacustrine environment.

There are few remaining exposures; however, the deposit can locally be traced in the field, where it gives rise to a small scarp and ledge feature. Samples obtained by auger consist of red, grey or yellow sand with common to abundant pebbles of ‘Bunter’ quartz and numerous flints.

Glaciofluvial deposits, undifferentiated

Patchy but locally very thick occurrences of sand and gravel have been mapped throughout the district. Their field relations and constituent clasts indicate that they represent material laid down during both the Thrussington Till (non-flinty sands and gravels) and the Oadby Till (flint-rich sands and gravels) ice-sheet regimes.

Narrow sand and gravel outcrops in the west of the district typically represent the infills of palaeochannels (see above) excavated as possible tunnel valleys during the Thrussington Till ice advance. One of the largest and deepest of these is the east-west trending Fox Hill palaeochannel (Carney, 1999; fig. 5), which is currently being exploited as a source of sand and gravel (Chapter 11). The part closest to East Leake [SK 565 247] has a topography of about 30 m and a remnant infill composed of up to 13 m of non-flinty glaciofluvial sand and gravel with intercalated layers of red, laminated, glaciolacustrine clay up to 2 m thick. Recent excavations to the east of Home Farm Cottages [SK 562 247] show sequences of red, fine to medium-grained, clayey sand with 1 to 2 m-thick gravel bodies, the latter with pebbles of quartz or quartzite, cherts and silicified Carboniferous limestone. Locally derived fragments of the Blue Anchor Formation are conspicuous in places. Near-surface zones in which discshaped clasts show near-vertical orientations indicate cryoturbation of the deposit. On the south side of the Fox Hill palaeochannel, former workings at Riseholme Farm [SK 5553 2502] revealed scars showing up to 0.4 m of red, coarse grained sand and granule-grade gravel containing pebbles of quartz (85%), cherts (5%) and green mudstone (possibly Blue Anchor Formation). Diffuse cross-stratification and pebble imbrication indicated a current flow towards the south-east (120°), against the presumed westwards gradient of the channel. Farther to the east, a northerly elongated belt of non-flinty sand and gravel corresponds to glaciofluvial deposits filling the Wysall palaeochannel. Here, the original topography has been inverted, so that the sands and gravels now form a pronounced ridge across the valley to the east of Wolds Farm [SK 5980 2540]. A borehole (SK52NE/55), inferred to be close to the axis of the Wysall palaeochannel, showed 19.5 m of ‘glacial clay and gravel’. The outcrops [SK 593 257] mapped between this borehole and Wolds Farm to the west suggest that glaciofluvial sand and gravel is interleaved with Thrussington Till. On more speculative grounds, the northerly continuation of the Wysall palaeochannel may be represented by the deposits of nonflinty gravel north of the Fairham Brook [SK 619 291].

Flint-rich glaciofluvial deposits commonly occur in palaeochannels at the base of the Oadby Till, or as layers within it. An example of the latter mode of occurrence is the narrow sand and gravel outcrop extending from the southern outskirts of Walton on the Wolds [SK 5960 1980] south-westwards to near Tithe Farm [SK 5830 1872], where pits indicate former workings. This deposit forms a lens within the Oadby Till near Walton on the Wolds, but farther west its base cuts down into the underlying Thrussington Till. There are no exposures of these deposits, but augering shows that they consist of red, brown or yellow, medium grained sand with abundant pebbles of ‘Bunter’ quartz and flint. A further body of sand and gravel occurs between Oadby Till and bedrock at Burton Lazars. It was much pitted in the past, and at one such working [SK 766 168] a note on the field slip indicated at least 6.1 m of yellow, ‘wavybedded’ sand with gravel layers. A particularly thick development of flinty glaciofluvial sand and gravel, around 15 m thick, was noted near to the village of Thorpe Arnold, overlain by chalky Oadby Till. It is exposed in a road cutting west of the village [SK 7696 2009] as brown silt, silty sand and fine-grained sand. Further extensive developments of flinty sands and gravels, locally just over 5 m thick, occur around Ruddington [SK 57 32] and Bradmore (Charsley, 1989).

At the Melton Mowbray brick pits [SK 757 196] glaciofluvial deposits were formerly seen as a ‘bed’ of yellow, cross-bedded sand which, dipping eastwards, formed part of a complex and heterogeneous, contorted sequence (Deeley, 1886; Lamplugh, 1909). The deposit was also encountered in boreholes in the town, such as at the Cattle Market [SK 751 195].

Postglacial deposits

River terrace deposits

These postglacial deposits reflect Late Anglian river basin initiation and later incision associated with the development of the Trent, Soar and Wreake catchment systems. They occur as parallel sheet-like spreads of sand and gravel, rarely more than 5 m thick, and mark periods when deposition outpaced erosion in the valleys of the Soar and Wreake.

The deposits generally comprise sand-rich, matrix supported, trough cross-bedded gravels deposited on braid plains in periglacial climates. Terrace deposit nomenclature, correlation and tentative assignment to the o.i. stages are shown in (Table 5). The names were modified by Brandon (1999) from those used by Rice (1968) although, to avoid confusion, the terrace form, main coarse-grained deposit, and undifferentiated deposits will here be termed separately, as in Syston Terrace, Syston Sand and Gravel and Syston Terrace Deposits. It should be noted that the Quorndon Terrace of Rice (1968) is equivalent to the Syston Terrace of this account.

As with other major valleys in the Trent basin (Brandon, 1996, 1997), altimetric information and constructed terrace thalwegs (Figure 24) for the Wreake valley indicate about 7 m of incision between each successive cold stage aggradation (Brandon, 1999). Stone clasts derive from reworking of the older ‘Superficial Deposits’ and bedrock within the river catchment and the proportions of the main constituents vary between the valleys, although ‘Bunter’ pebbles and shattered flints are always prevalent, generally in similar proportions. Later head accumulation and cryoplanation (see below) typically modify the terrace form. The degree of cryogenic involution generally increases with the age of the deposit.

Because of the repeated cycles of fluvial incision and periglaciation, the preservation of the terrace deposits is inversely proportional to the age of the deposit. No traces appear to remain of the valley sandbar deposits that were contemporary with the initiation of the Soar and Wreake valleys. Possible small outcrops of the Knighton Sand and Gravel are the remnants of the oldest and highest terrace, however. They occur along the Soar valley at Barrow upon Soar [SK 576 176], at about 63 m above OD, and along the Wreake valley near Hoby [SK 663 173]. In Barrow upon Soar, a former pit [SK 5780 1770] through the deposit may have been the source of a complete skeleton of the straight-tusked elephant ‘Elephas antiques Falconer’, which was unearthed during excavations for Barnstone Member limestone (Plant, 1859). The species lived in an interglacial environment and therefore could not be derived from any cold-stage gravel. Patches of Birstall Sand and Gravel have been mapped along the Soar valley north of Barrow [SK 570 196] and on the opposite bank at Quorndon [SK 55 16] to [SK 55 17]. In the Wreake valley this deposit survives as small patches at Hoby [SK 670 175], Asfordby [SK 702 190] and Kirby Park [SK 725 177] and a few other places. A degraded pit at Kirby Park may have been the source of pygmy mammoth molars (Adams, 1879; Brandon, 1999).

The Wanlip Sand and Gravel is particularly widespread with numerous remnants, situated on rocksteps about 2 m above the alluvium, occurring along the flanks of the Soar and Wreake valleys. No less than fourteen patches occur along both sides of the Wreake valley between Rearsby and Stapleford. However, the most extensive remnants, with outcrops as wide as 350 m, occur along the Soar valley, particularly around the confluence of Walton Brook with the Soar [SK 56 19] to [SK 55 20]. A borehole through this terrace deposit (SK51NE/179) showed Mercia Mudstone overlain by a basal sandy gravel 0.8 m thick, on which rested 3.2 m of brown, clayey to gravelly sand. A section through a former incised channel of the river system that deposited the Wanlip Sand and Gravel is suggested by Borehole (SK51NE/177), which recorded 7.25 m of mainly sand and gravel that included a 2.3 m intercalation of clayey to sandy silt.

The Syston Sand and Gravel occurs as a terrace 1 to 1.5 m above alluvium and also forms the lower part of the coarse deposit beneath the alluvium of the Soar and Wreake valleys. Subsurface provings in the Soar valley suggest that a thickness of between 2.5 and 3.5 m is typical, but locally where the deposit is channelised it attains 5.5 m (Carney, 2000). Early Flandrian incision by anastomosing and chute channels has resulted in this deposit forming dissected low terraces and isolated eyots above the Hemington Terrace Deposits and alluvium. There are numerous outcrops in both the Soar and Wreake valleys, the largest spread extending northwards from Quorndon [SK 56 16] to [SK 55 19]. In a borrow pit [SK 555 182], Syston gravels with syndepositional ice wedge casts were exposed (noted in 1993), this working also revealing lenses of organic silt. The latter yielded pollen remains indicating a glacial or early Late glacial environment of deposition (Brown et al., 1994). A 14C age determination on material from a further organic layer, just above bedrock, gave an older limiting value of about 28 000 years BP for deposition of these sands and gravels, an age that closely predates the onset of the Late Devensian cold cycle, which lasted between about 26 000 and 13 000 BP (Rose, 1985). Thus the borrow-pit floras could be considered as representing early glacial to glacial conditions in the upper part of the Devensian Quaternary stage. The Holme Pierrepont Sand and Gravel, which is a direct correlative of the Syston Sand and Gravel (Table 5) in the Trent valley catchment area, has a small outcrop on the outskirts of Edwalton [SK 560 352].

Along the Soar valley, the Flandrian ‘floodplain alluvium’ has been subdivided into Hemington Terrace Deposits and Alluvium (see below). Both deposits are similar and comprise a basal point-bar gravel, up to 5 m thick, overlain by overbank-facies deposits consisting of grey and brown mottled clayey silt, up to 2 m thick on average. The silty to clayey soils on these deposits give rise to somewhat marshy, poorly drained conditions in contrast to the light, sandy soils of the older terraces. The Hemington Terrace Deposits typically form broadly convex, subdued terrace features rising to about 0.5 m above the alluvium, as for example to the south of Barrow upon Soar [SK 580 165]. Ridge and furrow cultivation (Plate 14) commonly marks such ground, indicating that it is beyond the range of low-magnitude, seasonal flooding in historical times. The Hemington Terrace Deposits were also mapped along the Wreake valley but, since the distinction with the modern alluvium is not clear in many places, on the published map they are depicted as Alluvium, undivided. The same is true along the upper reaches of many tributary valleys where the narrow tracts of alluvium commonly interdigitate with, or pass beneath colluvium. One valley in which the distinction between the Hemington deposit and alluvium is particularly well marked (though not shown on the published map) is that of Whissendine Brook, in the extreme south-east of the district, around [SK 830 158].

The Bunny Sand and Gravel forms a low, wide terrace at 35 to 40 m above OD where the Fairham Brook enters the eastern end of the Ruddington–Gotham–Bunny Moor (Figure 22). Typically, the deposit (Carney, 1999; Charsley, 1989) consists of between 2 and 4 m of flint-rich gravel and sand with layers of clay. It was correlated with the Holme Pierrepont Sand and Gravel of the River Trent system by Charsley (1989), making it also equivalent to the Floodplain Terrace of Posnansky (1960). Brandon (1996) correlates the Holme Pierrepont Sand and Gravel with the Syston Sand and Gravel. Thus, it follows that the latter and Bunny Sand and Gravel were deposited contemporaneously although in different parts of the Trent–Soar catchment system.

River terrace deposits, undifferentiated

These deposits constitute the minor occurrences of terraced sands and gravels along various tributary streams. They are generally too isolated to be classified with the named river terrace deposits, although they are probably all of Devensian age. Some minor patches of terrace deposits are numbered in order to differentiate aggradations of different ages, although the numbering implies no correlation between different valleys. For example, both First and Second river terrace deposits have been mapped higher up the Fairham Brook valley [SK 6120 2895]; [SK 6150 2876]. A First River Terrace Deposit has been mapped along the Devon valley [SK 82 31] and is thought to correlate with the Holme Pierrepont Sand and Gravel of the River Trent. Small areas of undifferentiated river terrace deposits are also mapped along Fishpool Brook [SK 59 18].

Slope terrace deposits

The distinction of Slope Terrace Deposits is an innovative feature of the Quaternary mapping carried out during this resurvey and is explained in more detail in Brandon and Carney (2000). All such deposits consist of head, the origin of which is discussed further below.

Slope Terrace Deposits comprise some of the most extensive deposits of head in the district, occurring in clay vales (Figure 22) such as the Vale of Belvoir (Brandon and Carney, 2000), the smaller Stapleford vale south-east of Melton Mowbray (Brandon, 1999) and also possibly the low-lying tracts near Ruddington [SK 56 31]. These mudstone vales have developed through successive episodes of periglacial slope wasting during the cold stages. A staircase of plano-concave solifluction terraces, their correlations shown on Sheet 142 Melton Mowbray, and (Table 5), has resulted from fluvial incision during the warm interglacial stages. This incision, induced by regional uplift, has led to continual base level lowering throughout the Trent–Soar catchment and hinterland, and consequently there is a close correspondence between the solifluction terrace staircase and the fluvial terrace staircase of the adjacent river valley.

Subsurface investigations carried out during this resurvey in the Vale of Belvoir (Brandon and Carney, 2000) showed that the Slope Terrace Deposits comprise two or three layers, each about 1 m thick (Figure 25). The lower layer consists of brecciated grey mudstone and grey clay, which overlies undisturbed, grey, Lower Jurassic mudstone. The middle layer rests on a basal shear plane (Plate 15) and comprises slickensided and sheared grey clay. It is overlain by a layer of sand and gravel containing abundant oxidised siderite mudstone fragments; this upper layer is commonly involuted with, and thus appears part of, the middle slickensided layer.

Three phases of the Slope Terrace Deposits have been recognised and mapped, and in the Vale of Belvoir their distribution in relation to other ‘Superficial Deposits’ and major landforms is given in (Figure 26). The Pen Hill Head survives only as a capping to Pen Hill [SK 716 304] near Long Clawson. Its base hereabouts lies at between 50 and 54 m above OD, which is 7 to 10 m above the Harby Head, and the deposit is thought to be equivalent in age to the Egginton Common Sand and Gravel of the Trent valley (i.e. oi. stage 6). The Harby Head of the Vale of Belvoir and the equivalent Burton Lazars Head of the Stapleford vale occur as dissected terrace remnants that once formed continuous tracts along low-lying areas. Their terrace edges typically lie 2.5 to 3.5 m above the adjacent alluvium, colluvium or Langar Head. The Stapleford Head merges with the back of the contemporary Wanlip Sand and Gravel of the Wreake, which is Early Devensian in age (oi. stage 4). The Langar Head of the Vale of Belvoir (Figure 26) and the equivalent Stapleford Head of the Stapleford vale form low and commonly extensive terraces, typically lying between 0.5 and 1.5 m above adjacent tracts of alluvium or colluvium. These deposits are Late Devensian in age (oi. stage 2), as the Stapleford Head merges with the back of the Syston Sand and Gravel of the Wreake valley. The Stapleford Head has been mapped along with ‘Head, undifferentiated’, on Sheet 142 Melton Mowbray, but on 1:10 000 series maps is shown separately (see also, Brandon, 1999).

Alluvium

The Flandrian ‘floodplain alluvium’ forms deposits that are similar to those of the Hemington Terrace Deposits (see above). In the Soar valley, the alluvium typically consists of a basal point bar gravel, up to 5 m thick, overlain by overbank-facies deposits of grey and brown mottled clayey silt, generally about 2 m thick but exceptionally almost 4 m in thickness, as in Borehole (SK51NE/218).

Alluvium of the minor tributary valleys is seldom more than 3 m thick and is generally composed of brown to grey, clayey silt or organic-rich silt. Thin lenticles or more continuous bodies of coarse, flint-rich gravel are common at or near to the base of such deposits. An unusual occurrence of detrital peaty silt occurs along the unnamed valley south of Long Clawson, above [SK 7278 2620]. It appears to have been formed by the blockage of the narrow valley by a slipped mass of till.

Lacustrine deposits

These deposits, of mainly Flandrian age, form extensive spreads underlying the Ruddington–Gotham–Bunny Moor [SK 550 297], which is drained by the Fairham Brook. A further broad expanse is mapped to the east of Tollerton [SK 62 35], at the foot of the Hollygate Sandstone dip slope. The origin of these ‘moors’ (Figure 22) is complex and may involve subsidence due to gypsum, or even salt dissolution, in the underlying Mercia Mudstone strata (Lamplugh et al., 1909). In this respect it is noted that the inferred outcrop of the 3 to 4 m-thick Tutbury Gypsum closely coincides with the present area of Bunny–Gotham Moor. The Lacustrine Deposits and their associated Shell Marl probably originated during the periodic filling of shallow lakes ponded within these depressions. Gradients between the headwaters of the streams and the River Trent are very low and it is likely that much of the silty deposition results from ponding of floodwater throughout the Flandrian (Charsley, 1989). A recent study of the former Tollerton lake basin suggests that it commenced during locally high water levels around 10 200 BP and persisted until about 7000 BP (McMurray, 1993).

Deposits of the Bunny–Gotham Moor are commonly less than 2 m thick and produce a black, organic-rich sandy clay soil, which is locally abundant in bivalve shells. The lower part is generally of cryoturbated sand and gravel less than 1 m thick, which was laid down by currents flowing from the west and north-east (Charsley, 1989). The coarse deposit is overlain by a similar thickness of greyish brown silt and fine-grained sand. A thin layer of dark brown and black peaty clay, and less commonly silt, with thin lenses of peat, covers broad areas of the outcrop. Ploughing in fields south of Moor Lane [SK 5442 2970] produced slabs of dark grey, well-laminated silty clay and silty sand with bivalves (Carney and Cooper, 1997), as well as a gravel component suggested by locally abundant ‘Bunter’ quartz pebbles in patches of dark grey, organic-rich sandy soil [SK 5440 2958]. A typical exposure of these deposits, in a cutting for a horse-jump [SK 5471 2954], showed the following section (Carney and Cooper, 1997):

The similar broad expanse of Lacustrine Deposits northeast of Tollerton consists mainly of grey-brown silt and clay with thin peaty and shelly layers. Early Flandrian gastropods have been recorded from here (Lowe, 1989). Two further small areas of Lacustrine Deposits in the Bradmore area [SK 588 325]; [SK 593 306], which were mapped as Fluvio-lacustrine Deposits on the 1:10 000 sheet, comprise up to 2 m of brown and grey clay found in depressions.

Shell Marl

A small occurrence of Shell Marl, which predates the adjacent alluvium and is probably early Flandrian in age (Charsley, 1989), was mapped at Flawforth [SK 587 333].

Blown Sand

Blown Sand of probable Late Devensian age occurs in patches banked up along the lower parts of deeply cut coombes within the Marlstone Rock dip slope (Figure 22) in the Belvoir area, where it has been pitted, e.g. [SK 801 323]; [SK 816 328] to [SK 818 323]. A more extensive tract occurs along the steep eastern flank of the Devon valley, between Knipton and Woolsthorpe [SK 831 320] to [SK 834 332]. Blown Sand is typically a pale pinkish to orange-brown, fine grained, homogeneous sand, which was probably derived from unvegetated Triassic outcrops in this part of the East Midlands.

Head, undifferentiated

Head sensu stricto is a periglacial deposit formed during the Anglian–Devensian cold stages. It is of extremely widespread occurrence, can be as much as 3 m thick, and is important because of its commonly hazardous geotechnical properties (Chapter 11), although it can be difficult to differentiate from other diamictons such as till. Head accumulated as a result of several closely related processes and it underlies extensive ‘solifluction terrace’ aprons on the flanks of many valleys.

The composition of head mainly depends on the nature of the source bedrock and/or superficial deposits up slope. It generally consists of grey to brown silty clay with a variable content of dispersed stones. Although most of the surviving head is Late Devensian in age, it was a product of all stadial periods and older head (not generally mapped separately) can be identified by the cumulative affects of periglacial processes during later stadials. For example, such older head, where accumulated on the Wanlip Terrace, displays vertical stone orientation and is typically severely cryogenically involuted into the underlying sand and gravel and even bedrock. Such processes contributed to cryoplanation of the older terrace features. Other periglacial features observed in the district include cambering and small-scale valley bulging structures affecting Jurassic bedrock, as described in Chapter 8.

The undifferentiated head deposits mapped in narrow strips along many minor valleys [SK 737 205], and near the base of steeper slopes containing sand and gravel and friable sandstone bedrock, is mostly a Flandrian accumulation of colluvium or surface hill wash that has not reached the floodplain. The wider spreads of colluvial head material are indicated separately on Melton Mowbray Sheet 142. These deposits are up to a few metres thick, and though variable are generally sandier and lighter in texture than periglacial head; they may also contain layers of fluvial sand or peat in the valley-floor situation. Commonly, periglacial head or alluvium may underlie colluvial head. On some of the component 1:10 000 mapsheets, colluvium has been mapped separately from other types of head for the Vale of Belvoir and the Stapleford vale areas.

Landslips

Slope instability is inherent in the district along many of the steeper valley slopes and larger cuesta escarpments underlain by argillaceous bedrock or clayey superficial deposits. The resulting landslips have their origins mainly in mudstone or clay strata that contains thin permeable beds, and they are characterised by hummocky landforms. The brief descriptions below are based on observations made by the authors during field mapping, and on ground visits following aerial photographic interpretations of selected areas by A Forster (written communication, 1998). The geohazard potential of such landslipped ground is discussed in Chapter 11.

Land slippage is a characteristic feature of the Marlstone Rock escarpment that overlooks the Vale of Belvoir, although some parts of it appear to be unaffected. Largescale complex slippage involving rotational movement in the bedrock has usually occurred in association with spring lines in the Dyrham and Marlstone Rock formations. The toe of the landslip is commonly difficult to delineate where it grades into mudflow. Typical examples of hummocky, landslipped ground are to be found from Old Dalby [SK 67 23] to Holwell Mouth [SK 72 24], west of Eastwell [SK 74 26] to [SK 76 28], through Stathern, Plungar and Barkestone woods [SK 78 30] to [SK 79 32] and south-west of Belvoir Castle [SK 80 32]. Along this escarpment, A Forster (BGS, written communication, 1998) confirmed that in addition to rotational failures there is abundant evidence for mudflow activity in the presence of lobate flow-forms and semi-circular backscarps (Plate 16); landforms indicative of solifluction activity were also identified. To the south-east of Long Clawson, a landslide on the east side of the portal of the Brook Hill railway tunnel [SK 746 265] was interpreted as a multiple retrogressive rotational failure that may have been triggered by excavation of the ground in front of the tunnel.

Smaller scale slips, in which till is partly involved, also extend along the flanks of some of the deeper valleys initiated in the escarpment, for example south of Long Clawson [SK 72 26] and south-east of Stathern [SK 77 30]. Discrete rotational slips occur in the Dyrham Formation along spring lines in many of the combes incised through the Marlstone Rock dip slope in the Eaton [SK 79 28] to Knipton [SK 81 32] area. The rotational slips on the northern slopes of Hickling Standard [SK 68 28] are mainly in Lias mudstone although Oadby Till is also involved in places; hereabouts, small-scale terracettes indicate recent creep in the superficial zones of larger landslips.

The escarpment of the Middle Jurassic cuesta is marked by slippage, and an almost continual outcrop of hummocky, foundered Whitby Mudstone has been mapped from aerial photographs south of Eaton [SK 79 28] to Croxton Kerrial [SK 82 29]. On the hill to the west of Eaton [SK 792 287], A Forster (BGS, written communication, 1998) identified a number of different landslide features. These included coalescing backscars and associated mudflow lobes and, on the south-facing hill slope, a large back-tilted rotational feature adjacent to a translational slab slide showing possible multiple retrogressive failure. The fact that the latter postdates a ridge and furrow cultivation pattern indicates a relatively recent age of movement.

Hummocky ground associated with rotational movement of bedrock, mudflows and terracettes is found locally along the ‘Rhaetic escarpment’, and involves strata of the Penarth Group, Blue Anchor Formation and possibly the upper part of the Cropwell Bishop Formation. Examples can be found to the south of Cotgrave [SK 651 343], at Rough Hill [SK 56 28] between Bunny and East Leake, south of Stanford Hall [SK 560 235], south of Rempstone [SK 575 240], along the south side of the Walton Brook valley [SK 583 197].

Chapter 8 Structure

The tectonic structures of the district fall into two principal categories: fundamental structures that define domains related to Palaeozoic deformation, and the relatively minor faults, flexures or folds that have been mapped in areas of Triassic or Jurassic outcrop. The most important structures are the Normanton Hills and Sileby faults. Although they displace Mesozoic rocks at the surface, these structures also give rise to deep-seated geophysical lineaments and boundaries (Chapter 9) that are of regional importance (Lee et al., 1990, 1991), as shown by the aeromagnetic inserts on Sheet 142 Melton Mowbray. This coincidence between surface and deep structure indicates that these major faults, as well as other displacements in the district, are the ‘posthumous’ rejuvenations of pre-existing basement discontinuities (Turner, 1949). A third category of structure is of superficial origin, attributed to periglacial mass-wasting in Quaternary times.

Pre-Carboniferous (Acadian) deformation

Major crustal structures in the pre-Carboniferous ‘basement’ of the district have been imaged as north dipping planes on seismic profiles beneath the Widmerpool Half-graben. They are interpreted by T C Pharaoh as the possible traces of Caledonide thrusts, some of which may also have experienced listric movement during Dinantian extension. Gravity and aeromagnetic studies, as discussed in Chapter 9, have detected these and many other deepseated crustal structures in the Melton Mowbray district.

The nearest surface expression of this basement deformation are folds, and a penetrative east-south-east-trending cleavage, in the Precambrian and Cambrian rocks of Charnwood Forest, about 3 km to the west of this district (Carney et al., 2001). Those structures were formed during the Acadian (Siluro-Devonian) event (BGS, work in progress), and are elements of the concealed, ‘Eastern Caledonides’ orogenic system, which underlies this part of the East Midlands (Pharaoh et al., 1987; Lee at al., 1991). Together with the alignment of earlier, Ordovician plutons, of which the concealed Rempstone and Melton Mowbray granodiorites of this district are representatives, the Acadian structures have acted as ‘formers’ for the faults and folds generated during the subsequent Carboniferous and Mesozoic/Cainozoic tectonism in the district.

Early Carboniferous faulting and basin development

During the Dinantian, progressive extension of the East Midlands crust resulted in the formation of deep, sediment filled, fault-bounded basins, separated by tectonic ‘highs’ (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)b across which Dinantian strata are attenuated. The Widmerpool Half-graben and adjacent Hathern Shelf of the district comprise one of these basinal systems, and their bounding structures are the locations of small oil accumulations (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)a.

The sedimentological and structural evolution of the Widmerpool Half-graben and Hathern Shelf have been constrained by the detailed seismostratigraphical studies of reprocessed, high-quality, seismic reflection data presented by Ebdon et al. (1990, fig. 7) and Fraser et al. (1990). The results of this analysis indicate the presence of six sequence units (EC1-6) within the Dinantian syn-rift phase. The seismic data available during this resurvey have not been reprocessed and are of poor quality compared to those described by Ebdon et al. (1990) and Fraser et al. (1990); consequently it has not been possible to carry out such a detailed seismostratigraphical analysis as did those authors. The units interpreted by T C Pharaoh and portrayed on the depth sections 2 and 3 on Sheet 142 Melton Mowbray are, instead, based on a lithostratigraphical correlation of seismic sequences, constrained where possible by borehole information.

The depth sections together indicate an asymmetric Dinantian fill to the Widmerpool Half-graben, consisting of wedge-shaped sedimentary packages of Tournaisian to Brigantian age, the latter including the Widmerpool Formation (EC5/EC6 of Ebdon et al., 1990). These packages attenuate northwards and thicken in the opposite direction, towards the hanging wall of the Normanton Hills Fault. Along the latter structure an aggregate, syn-Dinantian, northerly downthrow of about 3500 m is estimated from Section 2, using the pre-Namurian sediment thicknesses as a rough guide but ignoring the effects of periodic syn-Dinantian basin inversion (Ebdon et al., 1990) and compaction. Depth section 3 shown on Sheet 142 Melton Mowbray, and the seismic profile of Ebdon et al. (1990, fig. 4), confirm that faulting along the northern margin of the Widmerpool Half-graben was accompanied by significant monoclinal flexuring. This complex structural belt is here termed the Cinderhill–Foss Bridge Flexure (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3). Relative uplift across the flexure was maintained at least into Brigantian times, causing northward pinching out of the Widmerpool Formation shown in (Figure 4). The entire Dinantian sequence ultimately thins to about 350 m on the Nottingham Shelf (e.g. Howard et al., in prep.). The attenuated succession on the shelf is punctuated by unconformities that separate the early Chadian-age Milldale Limestone from the ?late Chadian Belvoir Limestone Formation (respectively representing units EC2 and EC3 of Ebdon et al., 1990), and the latter from the ?Late Arundian to Brigantianage Plungar Limestone Formation (?EC5 and EC6).

To the south of the Normanton Hills Fault, the Hathern Shelf (Ebdon et al., 1990, fig. 7) depositional province represents a relatively less subsided compartment of the regional Dinantian rift system. It is bounded to the south by the Sileby Fault, which also forms the southerly limit of detectable syn-Dinantian rifting and the northern margin of the Wales–London–Brabant Massif (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3). Stratal thickness variations (depth section 2 Sheet 142) suggest an aggregate syn-Dinantian northerly downthrow of at least 1750 m along the Sileby Fault. This confined Dinantian sedimentation to the north of the fault, as indicated by the Kirby Lane Borehole, where Namurian (Millstone Grit) strata rest directly on basement granodiorite (Figure 7). Section 2 Sheet 142 shows that the Hathern Shelf is characterised by wedge-shaped stratal packages that attenuate northwards, towards the Normanton Hills Fault. This configuration suggests intra-Dinantian footwall uplift and back tilting along the Normanton Hills Fault at broadly the same time as normal movements occurring along the Sileby Fault. A local unconformity of Arundian–Asbian age is detected along the most elevated part of the footwall to the Normanton Hills Fault, possibly suggesting accelerated uplift, and local emergence, in response to one or more of the basin inversion phases documented by Ebdon et al. (1990, fig. 9). No Dinantian strata of the Hathern Shelf were penetrated save, perhaps, for the Scalford Sandstone Formation, which may represent an early clastic wedge association equivalent to the EC1 seismostratigraphic unit of Ebdon et al. (1990).

Convergence between the Normanton Hills, Sileby and Cinderhill–Foss Bridge systems causes narrowing of the Widmerpool Half-graben and Hathern Shelf in the east of the Melton Mowbray district, as shown by (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3). Farther to the east of the district the graben terminates, against the Foston High, at the Denton Fault (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)b.

Post-rift structure in Namurian and Westphalian times

At this time the East Midlands lay within a post-rift tectonic regime characterised by regional thermal subsidence. Progressive infilling of the Dinantian basins culminated in the establishment of the delta plain environments of the Westphalian (Langsettian to Bolsovian) Coal Measures successions (Sequence LC2 of Ebdon et al., 1990). Although it is probable that graben filling was largely accomplished without differential movements (e.g. (Figure 7); depth section 3 Sheet 142), tectonism along the Cinderhill–Foss Bridge Flexure was at least, in part, responsible for the attenuation of early Namurian strata (Edale Shale equivalents, or Sequence LC1a,b of Ebdon et al., 1990) on to the Nottingham Shelf (section 3 Sheet 142), where Marsdenian and possibly Kinderscoutian strata (Sequence LC1c) directly overlie Dinantian limestones (Figure 4). Early Westphalian faulting at the southern margin of the Widmerpool Half-graben is similarly suggested (Figure 8) by the apparent attenuation of pre-Kilburn Lower Coal Measures strata across the Normanton Hills Fault (Ambrose, 1999).

Localised early Westphalian tectonism presumably accompanied alkali olivine basalt magmatism in the Asfordby and Saltby volcanic formations. The distribution of the Asfordby Volcanic Formation may suggest magma uprise either along or near to the Sileby Fault (Figure 13)." data-name="images/P946224.jpg">(Figure 12). The more widespread basalts of the Saltby Volcanic Formation recall a style of magmatism that in many parts of the world is typical of extensional tectonic settings. Local extension could have reactivated the Cinderhill–Foss Bridge Flexure, causing slight southwards diversion of lavas during Phase 1 activity (Figure 13)." data-name="images/P946224.jpg">(Figure 12). Thickening trends for the Saltby Volcanic Formation, discussed in Chapter 3, nevertheless indicate that its centre lay to the east of the district, in which case the feeder zone(s) could have been controlled by a precursor structure to the Denton Fault (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)b.

Variscan inversion event

Late Carboniferous basin inversion (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 was presaged by the red-bed depositional regime exhibited by the Warwickshire Group, interpreted as representing the onset of better drained conditions in response to a general lowering of base-levels during the initiation of intra-Westphalian tectonic uplift (Besly, 1988). In this district, Variscan movements reactivated basement structures and reversed the throws of the principal Dinantian normal faults that controlled the Widmerpool Half-graben and Hathern Shelf, so inverting the Carboniferous basins. Among the structures that formed (Figure 27), the Rempstone Anticline is a long-wavelength inversion anticline located to the north of the reversed Normanton Hills Fault. The Rempstone oil well is situated on this anticline (section 2, Sheet 142), which was rejuvenated in post-Jurassic times (see below). Farther east, the Normanton Hills Fault decreases in throw, and splays in complex fashion (Ambrose, 1999, fig. 10). In this area, a further inversion anticline may have controlled the location of the reservoir tapped by Long Clawson 2 oil well. The Rempstone Anticline and related periclinal folds occur in close association to the various strands of the Normanton Hills and Sileby faults. In this complex structural belt fold axes are commonly oblique to the faults (Figure 27), suggesting a mild transpressive component to the deformation.

Reactivation of the Cinderhill–Foss Bridge Flexure, along the north-eastern margin to the Widmerpool Half graben, produced a swarm of north-westerly fault systems, some with throws of up to 150 m (estimated from the base Westphalian structure contours, (Figure 27)), significantly in excess of their post-Jurassic rejuvenated extensions seen at the surface. A broad anticline developed along the crest of the flexure, and is offset by north-easterly cross-faults. This interference may be related to the development of the Plungar Dome, on which the Plungar oilfield is situated. Farther to the north-east there are broad, en échelon periclinal structures (collectively the ‘Bingham–Harston High’ of BP Petroleum Development), developed on the downthrown side of the Denton Reverse Fault (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3)b, and see also (Berridge et al., 1999).

Post-Jurassic deformation

Syn-Triassic movements are possibly suggested by thinning of the Nottingham Castle Sandstone Formation across the Normanton Hills Fault, although this may also be the result of palaeotopography, and by the north-eastward thinning of the Cropwell Bishop Formation (Figure 17). For convenience, however, all of the surface bedrock structures of the district are regarded as having last been active in post-Jurassic times. The district is considered to lie across the junction between the two Mesozoic tectonic provinces of Green et al. (2001), the Midland Platform to the south and the East Midlands Shelf to the north. The boundary between these provinces is ill-defined, but in this district it broadly coincides with the Normanton Hills and Sileby faults. The principal post-Jurassic structure of the district is the regional south-easterly dip of the Mesozoic strata, but important modifications to this have occurred along faults and folds, many of which have orientations that reflect their inheritance from pre-Carboniferous structures.

The Sileby Fault has an estimated post-Jurassic, northerly downthrow of 130 to 140 m in the west of the district, decreasing farther east to around 40 m near Hoby [SK 654 155]. Although mapped at the surface as a broadly arcuate structure, geophysical evidence (Chapter 9) suggests that at depth the Sileby Fault is a composite of intersecting west-north-west and west-south-west structures. East of Asfordby it splays, and merges with the southern strand of the Normanton Hills Fault. The Normanton Hills Fault is, in reality, a complex of parallel faults and associated flexures, which splays into two main strands east of Six Hills [SK 654 204]. In the west near Hoton [SK 575 327] the fault has a northerly downthrow of about 80 m. There, Triassic and Jurassic strata are folded (Carney, 1999, fig. 6) across a structure that coincides precisely with the Rempstone Anticline, which has a Variscan inheritance (see above). The presence of this fold indicates that compression against the Normanton Hills Fault, probably resulting in some reverse movement, has occurred at some stage of post-Mesozoic time, and that the normal downthrow referred to above represents only an aggregate summation of all movements in a complex post-Mesozoic structural history. Farther to the east, the throw on the Normanton Hills Fault is variable due to complex flexuring of strata between the various splays (Ambrose, 1999, fig. 12) possibly suggesting a transpressive component to the faulting, as was suggested for the Variscan movement phase.

North-west-trending post-Jurassic structures, which include the Foss Bridge Fault, generally have throws of 5 to 25 m. They represent rejuvenation of the Variscan, Cinderhill–Foss Bridge Flexure. The southerly termination to the Foss Bridge Fault may also reflect Variscan tectonic inheritance (Figure 27). It consists of north-east-trending faults, generally with throws of several metres or less, many of which cross the Plungar Dome. The north-easterly structural orientation represents a basement control that is most strongly imprinted in areas of shallower Carboniferous and Mesozoic cover, outside the Widmerpool Half-graben. It reappears, for example, to the south of the Normanton Hills Fault where north-east-trending faults are mapped around Barrow and Hoton.

There is no direct evidence for the actual age of this post-Jurassic deformation. Data based on apatite fission track analysis and vitrinite reflectance summarised by Green et al. (2001) nevertheless suggest that on the East Midlands Shelf (i.e. north of the Normanton Hills Fault) there were two well-defined uplift and erosion events dated at Early and Late Tertiary. Farther south, however, these events were considerably less marked on the Midland Platform. The favoured explanation (Green et al., 2001) is that uplifts on the East Midland Shelf reflect the relative ease of deformation of Carboniferous basins such as the Widmerpool Half-graben and Hathern Shelf of this district.

Superficial structures caused by periglacial activity

Cambering typically occurs in association with resistant Jurassic strata that cap steeply sloping escarpments or valley sides. It accentuates the regional south-eastward dips and produces anomalous reversals of this dip as seen, for example, in the north-westerly dip slopes recorded on the Marlstone Rock Formation above Knipton Reservoir [SK 819 302].

Some of the most spectacular examples of cambering and superficial faulting are not related to present topography, but probably occurred in Anglian or immediately post-Anglian times and can now be seen along the partially exhumed slopes of sediment-filled palaeovalleys (Figure 23). For example, along the palaeovalley margin due west of Waltham on the Wolds [SK 800 255], periglacial mass-wasting associated with cambering has caused the foundering and complex faulting of a large sliver of the Lower Lincolnshire Limestone and Grantham Formation. The structures produced by this process include sediment-filled ‘gulls’ that were revealed in a former ironstone working and are illustrated in Lamplugh et al. (1909, fig. 5). Similar structures were formerly seen in Marlstone Rock workings to the north of White Lodge (Plate 17), and were described elsewhere by Whitehead et al. (1952, p.155).

Complex fold structures in Jurassic mudstone are another manifestation of periglacial activity, visible where exposed in the streambeds of certain wide valleys, and probably prevalent throughout the district. Exposures in the bed of the brook leading from the southern margin of the district north-eastwards [SK 6169 1668] show Lias Group mudstone folded into attitudes of between 10° and 40° to the north-east and south-west. The folds are commonly asymmetrical with axes parallel to the northeasterly trend of the valley in which the brook is situated. The folds, being related to the local topography, are thought to be entirely superficial in nature and analagous to those in South Derbyshire that were attributed to periglacial heaving or doming in Devensian times (Jones and Weaver, 1975). A further possible example of disturbed bedding was recorded in Barnstone Member strata exposed in the now overgrown limestone quarry (Darby’s Pit) at Cream Lodge [SK 5915 1863], as illustrated in Lamplugh et al. (1909, plate II). The structure, of a relatively large magnitude, was described as a tight anticlinal fold with an axis parallel to the valley of the Fishpool Brook, in which the quarry is situated.

Chapter 9 Geophysical information on the concealed geology

The patterns shown by the Bouguer gravity and aeromagnetic anomaly insets Sheet 142 Melton Mowbray reflect the presence of deep-seated structures rooted in the crust of the district. The principal features, together with information from other compilations and geophysical profiles (Royles, 1998) are summarised and labelled on the composite interpretation map (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28).

The Bouguer gravity anomaly pattern over the district is dominated by a deep ‘low’, G1 of (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28), with an amplitude of 13 mGal. Most of this anomaly coincides with the area of thickest Carboniferous sediment accumulation in the central and southern parts of the Widmerpool Half-graben. It is probably the rapid attenuation of these strata, across the Normanton Hills Fault, which is responsible for the steep gravity gradient along the southern anomaly edge. The anomaly minima extends outside the half-graben, to the north of the Cinderhill–Foss Bridge Flexure System (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28); (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29), where the Carboniferous rocks are considerably thinner. Its shape and magnitude were possibly influenced by the presence in the basement of material that is of low density, relative to predictable basement densities (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). The source of this lower density basement was suggested to be diorite or tonalite with a density ranging between 2.73 and 2.68 Mg/m³ (Busby et al., 1993). Such bodies were presumably coeval with the Ordovician-age Rempstone and Melton Mowbray granodiorites of the district (Chapter 2). In (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29) the bodies (C6 and 7) have been modelled extending to approximately 7 km, with a density of 2.69 Mg/m³, contributing to the gravity low north of the Widmerpool Half graben. As the physical properties of these deep bodies are poorly constrained many alternative situations would result in similar anomalies. The northern margin of the Widmerpool Half-graben is defined by the Cinderhill–Foss Bridge Flexure (Chapter 8) along which faulting was relatively minor and across this boundary there is only a small inflexion of the Bouguer gravity contours, compare (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28) and (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Also shown on (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28), although lying outside the district, is a prominent gravity ‘high’ (G2), referred to as the ‘Foston High’ and thought to represent shallow Precambrian or Lower Palaeozoic basement that was uplifted along the south-western margin of the Denton reverse fault system (Berridge et al., 1999).

The magnetic anomaly inset on Sheet 142 Melton Mowbray shows localised, major magnetic highs (red colours), which are labelled M1-6 on (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28) and can also be seen on (Figure 30). These anomalies are the expressions of shallow-depth Ordovician granodiorite intrusions, which were proved in boreholes at Rempstone (located over M1) and Kirby Lane (M4) as described in Chapter 2. A smaller anomaly (M2), just outside the south-western corner of the district, coincides with exposed granodiorites of the Mountsorrel Complex. Further anomalies of a similar character occurring to the west of the district, near Diseworth (M5), are discussed in Carney et al. (2001). They are part of a regionally distributed, arcuate belt of similar anomalies (labelled MH5 by Lee et al., 1990) extending over 125 km to the south-east of Derby. The anomalies in the vicinity of the Melton Mowbray district have been modelled by Arter (1982) as cupola-like bodies with upper surfaces either at or close to the surface and extending to depths of around 7 km, although the lower boundaries of such bodies are poorly constrained in such models. The major geophysical lineaments L1 and L2, which coincide with the footwall of the north-dipping Normanton Hills Fault, compare (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28) and (Figure 30), define the northern margin of the Diseworth and Rempstone granodiorite anomalies (M5, M1). Farther south, the Sileby Fault is a composite of two intersecting lineaments, L3 and L4. The former is related to the col separating the Rempstone Granodiorite anomaly from that of the Mountsorrel Complex. Lineament L4 is strongly controlled by the north-western margin of the Melton Mowbray Granodiorite (M4), and possibly at greater depth its continuation (M3) farther south. These bodies are only seen as subtle contour deviations in the Bouguer gravity map (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28), due to the dominance of the anomaly G1 gradient, but they can be seen in residual anomaly images (Royles, 1998). It is noteworthy that samples of Melton Mowbray Granodiorite from the Kirby Lane borehole produced a low-density value (2.57 Mg/m³). The small, sharp magnetic anomaly (eastern part of C1) at 30 km on (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29) occurs in the footwall of the Sileby Fault and suggests magnetic material within 1 km of the surface. Bodies C2/3 lie beneath the Hathern Shelf and equate to the eastward continuation of the Rempstone Granodiorite anomaly, M1 of (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28).

East of the district, the Denton Fault gives expression to a series of very prominent, narrow, north-west-trending magnetic anomalies (Figure 30). They are caused by Variscan uplift of magnetic basement that may include volcanic rocks (see below).

The 1998 High-Resolution aeromagnetic survey of the East Midlands has provided information that is particularly useful for defining narrow or fine-scale magnetic anomalies that were not adequately shown on the earlier 1955 survey. The compilation of this data (Figure 30) shows a series of sinuous, discontinuous anomalies in the basement beneath the Widmerpool Half-graben, extending from the central part of the district towards its northwestern corner. These anomalies have a collective trend broadly parallel to structures bounding either side of the half-graben, such as the Normanton Hills Fault and Cinderhill–Foss Bridge Flexure. They are tentatively interpreted as the expression of a major, Acadian-age, northdipping thrust complex of the type that has been detected on seismic profiles to the south of the Normanton Hills Fault (Chapter 8; section 2 Sheet 142).

In the east and south of the district, thickly developed basaltic lavas and volcaniclastic rocks of the Saltby Volcanic Formation and Asfordby Volcanic Formation occur (Figure 13)." data-name="images/P946224.jpg">(Figure 12) which, lying at relatively shallow depths, might be expected to produce aeromagnetic anomalies on the High Resolution compilation of (Figure 30). To evaluate this possibility, magnetic susceptibility measurements were made on extrusive rocks in core from the Egypt Plantation Borehole [SK 8660 2786], just to the east of the district. The results showed that the Saltby Volcanic Formation was magnetically highly variable but contained significant volumes of material with susceptibilities of 50 x 10^{− 3} SI or more, and with average values of 20 x 10-3 SI, between 700 m and 950 m depth in the borehole. Samples from the Grimmer Borehole gave similarly variable values, with the most magnetic rocks (between 5 and 35 x 10^{− 3} SI) represented by the basaltic lava flows and sills encountered between 647 and 670 m depth (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14). Samples of peperite breccia from the Asfordby Volcanic Formation, between 516 and 616 m depth in the Welby Church Borehole, were generally lower than 1 x 10^{− 3} SI, although with one short interval (516-524 m depth) averaging 4 x 10⁻³ SI and an individual reading (at 588 m) of 12 x 10⁻³ SI. Interflow weathering considerably reduced the magnetic susceptibility of rocks in all the boreholes examined.

The above measurements suggest that large volumes of highly magnetic material, such as unweathered basalts (seen most abundantly in Egypt Plantation Borehole), if at relatively shallow depths (less than 1 km), should give rise to a magnetic signature measurable at the surface, or at low altitudes. In the north-east of the district, this may explain the coincidence between the arcuate, northerly trending magnetic anomaly gradient straddling the Cinderhill–Foss Bridge Flexure, and the inferred western edge of the Saltby Volcanic Formation, compare (Figure 30) and (Figure 13)." data-name="images/P946224.jpg">(Figure 12).

Chapter 10 Artificially modified ground

Only selected categories of man-made deposits, or ground otherwise modified by human activity, are shown on Sheet 142 Melton Mowbray. 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 Sheet 142 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 opencast mine 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 in this district include industrial sites, road and railway embankments, colliery and quarry spoil, building and demolition rubble, waste from light industries and domestic and other waste in raised landfill sites. Made Ground is most extensive, if not ubiquitous, in the main urban centres such as Melton Mowbray, 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 quarry infill spoil, were smoothed over prior to re-development, the extent of Made Ground is based largely on earlier records.

Worked ground

This represents those areas where material is known to have been removed, for example in unfilled ironstone quarries on the Marlstone Rock outcrop and in smaller pits, road and railway cuttings.

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, brick clay, ironstone, limestone and disused railway cuttings are 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, some of which may be imprecise. During this resurvey incomplete documentation existed for some of the large, restored or partially restored ironstone quarries on the Marlstone Rock Formation outcrop.

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 omitted from the 1:50 000 series geological map. Disturbed Ground is nevertheless an extremely important and locally extensive category of modified ground in this district. It commonly encompasses ground that has experienced the effects of more than a single phase of mineral extraction. This may have involved combinations of surface and shallow subsurface mining techniques, and as a consequence a number of different processes may have contributed to ground instability within a single small area (Chapter 11). Disturbed Ground is commonly found where the Barnstone Member has been worked, for example along the northern side of the Fishpool Brook [SK 5840 1840]. Small parts of the Marlstone Rock outcrop that were undermined at shallow depths are also marked by Disturbed Ground, as to the east of Brown’s Hill Quarry, near Holwell [SK 744 234], where the periodic development of crown-holes (Plate 18) signifies the continued collapse of pillar and stall workings.

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 11 Applied geology

This chapter provides a brief overview of those earth science matters that should be taken into account during or before urban, industrial or rural planning and development processes. In the Melton Mowbray district there are some natural variations in ground conditions over small areas and the resultant diversity in geotechnical properties may be further exacerbated within a single rock unit by considering the superimposed effects of weathering. Only small amounts of exploitable mineral resources are present, but they played a significant role in the development of areas located close by, such as Barrow upon Soar, Asfordby, Cotgrave and the belt of mines and quarries that follows the Marlstone Rock outcrop. In such parts of the district, the legacy of mineral extraction by deep-mining or quarrying 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 section 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, Nottinghamshire and Rutland).

Mineral resources

Minerals of current interest include those that can be won at or near to the surface, as well as high-value commodities such as petroleum. The main factors hindering bedrock mineral extractions are significant thicknesses of overburden, including natural drift deposits and manmade 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 surface or shallow subsurface mining activities are important for their impact on current ground conditions, and their visible surface effects, mainly in the form of Disturbed Ground, have been indicated on various map editions, as discussed in Chapter 10.

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 with an aquifer, which is the case for those sand and gravel quarries located along the major rivers or their tributaries.

Coal

There are very considerable potential coal reserves in the district, but no current exploitation. The subsurface of the district contains virtually the whole of the Vale of Belvoir Coalfield (otherwise known as the North East Leicestershire Prospect). The coal formerly exploited from Cotgrave Colliery, just beyond the north of the district, is considered to be co-extensive with the Nottinghamshire Coalfield (Howard et al., in prep (a)).

The Vale of Belvoir Coalfield was first proved in this district during the 1920s when the D’Arcy Exploration Co. Ltd, later to become British Petroleum, was drilling for both coal and oil (A R L Jones, 1977, written communication NCB). This drilling largely delineated the Coal Measures subcrop and the Westphalian stratigraphy was subsequently refined by NCB exploratory drilling between 1973–76 (Hope, 1978). By the latter date, the NCB exploration was largely complete, with some 80 boreholes and 400 km of high-resolution seismic surveys proving reserves of 510 million tonnes (Lewis, 1978), making this the largest unworked coalfield in western Europe (Mann, 1980). Coal quality is generally fair to good, with Coal Rank Codes of 802–902 and ash content of between 4–10 per cent typical for the district.

A public enquiry concerning the further development of the Vale of Belvoir resource was convened between October 1979 and May 1980 (Mann, 1980). It examined a wide range of issues, including the possible effects of subsidence and the environmental effects of colliery spoil disposal. The final outcome was that Asfordby was chosen as the only permissible site for a colliery. This mine-site was located in a highly unfavourable geological situation, characterised by structural complexity (Figure 27) and a Carboniferous succession containing numerous basaltic sills (Figure 15). Work commenced on its development in 1984 and later the pit was taken over by RJB Mining (UK) Ltd. Full production on the first longwall face in the Deep Main seam commenced in April 1995, but by that Autumn was encountering severe geological difficulties. A series of intrusive sills, which lie above the operating seams, created unusual rock fracturing patterns, resulting in heavy weighting of the face, severe damage to the face equipment and ingress of water. Several alternative mining systems were considered, but severe weighting problems recurred. On the 12 August 1996, there was further ingress of water and the face became unsafe. Closure was announced in August 1997, by which time Asfordby had produced 1.5 million tonnes of coal. As of late 1998, the two shafts have been filled and capped for safety (Reported in Mercian Geologist, 1998, Vol. 14 (3)).

The economics of deep coal mining in the East Midlands have undergone a succession of reviews since the 1950s resulting in progressive closure of older mines. As a consequence of this, and of geological complexities caused mainly by faulting, the other working colliery, at Cotgrave, closed in 1992.

Oil

In the concealed Carboniferous sequences of the East Midlands region the identification of structural ‘highs’, such as anticlines, has furnished potential targets for oil since exploration commenced in 1918 (Lees and Cox, 1937). These activities were renewed in 1935, when gravity, magnetic and seismic methods were employed by the D’Arcy Exploration Co. Ltd (later to become British Petroleum). They met with some success but the principal finds were all located to the north of the district, around Eakring, Duke’s Wood, Caunton and Kelham Hills (Lees and Taitt, 1945). Oil exploration was extended into the Melton Mowbray district towards the end of the Second World War (Falcon and Kent, 1960) and was continuing at the time of the present resurvey (1996–1999) in a few licence areas. The district has experienced oil production in three fields, with current extraction restricted to the wells at Rempstone and Long Clawson (Department of Trade and Industry, 2000). (Table 6) summarises the available oil production figures, main drill stem tests and reservoir information in other wells.

The largest extraction area was the circular cluster, about 2.5 km diameter, of 33 oil wells that constituted the now-disused Plungar oilfield. The expectation of a field here was fulfilled in 1953 and crude oil production figures by the end of 1959 had reached 18 650 tons, as compared to the 267,928 tons yielded at Eakring (Falcon and Kent, 1960). Final production in 1980 is aggregated at 43,788 tonnes (304 067 barrels; Huxley, 1983). The Plungar Dome, a probable Variscan inversion structure (Figure 27), provided favourable conditions for oil accumulation at this field. Given the possibility of secondary Mesozoic oil generation in this region (see below), however, the post-Jurassic faults that cross the dome, shown on Sheet 142, may have provided additional structural traps during Mesozoic or Cainozoic oil migration.

Oil is currently being pumped from a single installation at the head of the Rempstone LN/10-1 well, which was discovered in 1985 following extensive exploration in the district by BP Petroleum Development Ltd. The main oil reservoir occupies a 12 m-thick sandstone, informally called the ‘Rempstone Sandstone’, located between 665 and 653 m depth, which is here correlated with Pendleian or Arnsbergian-age strata of the Edale Shale Group (Figure 5). At the time of writing, recoverable reserves of 0.23 million tonnes and peak production of 0.01 million tonnes per annum are estimated from this reservoir, which was also tapped by a deviated well (Rempstone LN/10-2Z), now disused, located 1 km to the north-north-west of LN/10-1. The Rempstone find is so far unique in the East Midlands, on account of its older (Arnsbergian–Pendleian) age, turbiditic sandstone reservoir and location on the southern margin of the Widmerpool Half-graben. It is similar to other finds, however, in being located on the crest of a Variscan inversion structure (Rempstone Anticline, (Figure 27); information from T C Pharaoh). These structures are obvious ‘traps’ for migrating hydrocarbons, but interpretations of confidential gypsum exploration records additionally show that the Rempstone Anticline was reactivated as a fold in post-Jurassic times (Carney, 1999; Chapter 8), and may therefore have been re-occupied during the possible Mesozoic phase of oil generation discussed below.

The Long Clawson oil well is located in a similar structural setting to Rempstone (Figure 27). It has recoverable reserves of 0.2 million tonnes and a peak production of 0.012 million tonnes per annum (Department of Trade and Industry, 2000) from the Chatsworth Grit reservoir. The first year of peak production was 1997.

Past studies (Falcon and Kent, 1960) have emphasized the important oil-generating capacity of deep, sediment filled Carboniferous basins, such as the Widmerpool Half graben and Hathern Shelf of the district (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3). In a modern assessment of the East Midlands hydrocarbon play, Fraser et al. (1990, p.438) and Fraser and Gawthorpe (1990) acknowledge that it is the Variscan inversion anticlines, formed within or at the edges of these basins (Figure 27) that are the potential ‘traps’ for migrating hydrocarbons. They note, however, that Variscan uplift and erosion would have effectively frozen source rock oil generation and migration. The success of this hydrocarbon province is therefore partly due to a later, Mesozoic phase of burial that regenerated hydrocarbon production in the Carboniferous source rocks. The Variscan traps were reoccupied, with oil migration subsequently arrested during regional Cainozoic tilting and uplift (Chapter 8). These conclusions bear out the suggestion of Holliday et al. (1984), that oil generation probably began in the Westphalian but continued until at least the end of the Cretaceous, there being at all times closed structures into which the oil could migrate. A particularly good example in this district of post-Jurassic reactivation and subsequent oil productivity is the Rempstone Anticline, which also affects Triassic and Jurassic strata (Chapter 8). Oil shows in post-Carboniferous strata are very uncommon, suggesting that the traps have not been badly breached.

Gypsum

Commercial gypsum deposits have been worked in three areas of the district, but at the time of writing exploitation is confined to underground mining of the Tutbury Gypsum from the adit at the British Gypsum Works south of Barrow upon Soar [SK 5290 1675]. Undermining currently extends north-eastwards, almost to Walton on the Wolds, where the seam begins to split and thin. The adit was completed in 1987 and mining commenced in 1989 with extraction by the room and pillar method, using continual cutting machines. The main product, manufactured at the Barrow works, is bagged building plaster (Information from British Gypsum Ltd in prep).

Underground extraction of the Tutbury seam commenced around 1900 at East Leake, from what is now the British Gypsum plasterboard-manufacturing factory. Lamplugh et al. (1909) noted that the mines were originally accessed by adits on the western slopes of Sharpley Hill [SK 5554 2785], Crow Hill (precise locality uncertain) and Hotchley Hill [SK 5556 2845]. The oldest workings avoided the partially dissolved and collapsed, marl-rich material, left as pillars, and in some practices robbed the good quality gypsum that formed the ‘roof ballstone’, just before abandonment. Subsequently operations were greatly expanded, and an adit added at the Silver Seal Mine, south of Bunny [SK 5854 2863]. These modern workings extend over large areas to the west and east of the East Leake factory [SK 5550 2820], but ceased in 1990. The undermined area largely coincides with the higher ground occupied by outcrops of the Blue Anchor Formation and Lower Lias strata extending from the East Leake works to just beyond Highfields [SK 5855 2745] and southwards to Costock. All of the modern workings for gypsum have been carried out on a regular, reticulate, well-engineered pattern of pillar and stall workings designed on careful rock mechanics principles.

The Newark Gypsum has been extracted by quarrying and underground mining south of Cropwell Bishop [SK 685 350] since the 19th century (Firman, 1964; Howard et al., in prep (a)), but this activity had ceased in the Melton Mowbray district by 1976. Unlike the Tutbury Gypsum it comprises up to 18 m of multiple beds, each of which varies in form from layers of nodules (‘balls’), lenticular masses (‘bullets’ or ‘cakes’) to beds. Individual gypsum-bearing layers have been given names in the belief that they can be traced between Cropwell Bishop and Newark; however, considerable caution should be exercised due to the impersistence of many of the beds. The gypsum ‘seams’ or beds recognised at Cropwell Bishop are listed in Howard et al. (in prep (a)). Purity varies both between and laterally within beds, but generally the best quality material comes from the Bottom White and Blue Rock gypsum. The Cocks seam is commonly the thickest, being up to 1.68 m in places. Of the other beds, Pinks may be up to 0.88 m thick but other seams typically range between 0.1–0.3 m thick. Gypsum at the Cropwell Bishop workings was most recently extracted by opencast quarrying, but all activities ceased in 1995 and the quarries are now undergoing restoration.

Brick and agricultural clay

Brick clay is obtained mainly from weakly consolidated mudstone or claystone, which may require some crushing and mixing with water to provide workable ‘clays’. The main brick clays in the area occur in the Mercia Mudstone Group and mudstone of the Lias Group. There are minor workings in Quaternary deposits of the Rotherby Clay, north-west of Thrussington [SK 6455 1620], and near Rotherby [SK 679 163], in Glaciolacustrine Deposits around Melton Mowbray, e.g. Barne’s Brick pit, [SK 7572 1965], and there are numerous small pits in the various tills of the district.

One of the largest workings, from which gypsum was also extracted, was the Baldwin’s Brick pit, located in the Cropwell Bishop Formation to the south of Bunny [SK 578 285] and now occupied by the Safewaste landfill site. The other noteworthy former pits are in the Cropwell Bishop Formation south of Prestwold [SK 5730 2024] and in the Gunthorpe Formation at Quorndon [SK 5563 1700].

Limestone

Limestone was formerly quarried or worked underground from the outcrop of the Barnstone Member. Its uses were for cement and concrete products, building stone and agricultural purposes (Lamplugh et al., 1909), but it is no longer commercially exploited.

A major area of former extraction was centred on and around the village of Barrow upon Soar. Brief histories of these operations are given in the reports of Arup Geotechnics (1990) and Wardell Armstrong (1987), and there are useful historical accounts in Martin et al. (1986) and Joyce (1997). The earliest documentary evidence for this activity dates from 1159 AD (Martin et al., 1986) and these medieval workings involved the sinking of numerous shafts and pits, from which short headings, or ‘delphs’, 3 to 4 m in height, were then driven horizontally into the strata. The workings were at this time apparently located throughout the outcrop, as well as within Barrow upon Soar village (Arup Geotechnics, 1990), giving rise to the extensive areas of Disturbed Ground mapped in the surrounding countryside (Carney, 2000; Chapter 10). According to Wardell Armstrong (1987), 84 pits existed in 1481, and were increasingly worked in the 16th and 17th centuries for the reputed bonding qualities of the lime. During the 18th and through to the 19th century mining was on an increasingly larger scale and was extended underground using the pillar and stall extraction method. Subsurface limestone workings were encountered during recent site investigations of the urban and industrial parts of Barrow upon Soar and are potential causes of localised subsidence (see below).

Fletcher (1980) has described the other principal concentration of limestone workings in the Barnstone Member, around Langar [SK 725 347]. The company was formed in 1875 to mine limestone on a large scale, and at its peak was producing 2000 tons of clinker per week for the manufacture of Portland Cement. Quarrying (Plate 19) ceased in 1969, by which time the company had been importing Lower Lincolnshire Limestone from the quarry near Waltham on the Wolds [SK 813 253]. Other pits in the Barnstone Member north of gridline 330 are shown on Map 6 of Charsley et al. (1990).

Ironstone

The principal ironstone resource in the district is the Marlstone Rock Formation, which has been quarried out in many parts of its outcrop (Whitehead et al., 1952, plate VI). The ore has been worked since ancient times, when it was commonly used for building, road metalling and lime burning. The greatest expansion of the workings around Holwell [SK 741 234] commenced in 1875 and those in the Wartnaby (Lamplugh et al., 1909, plate I) and Kettleby areas in 1878 (Hewlett, 1935; Whitehead et al., 1952; see also the account in Swift and Reddish, 2002). The Branston, Eaton and Eastwell works were opened between 1882 and 1891. The ore was initially sent for smelting to the iron furnaces in Yorkshire and Derbyshire, but blast furnaces were later built at Asfordby and the first of these was tapped in 1881. The only underground workings mentioned by Whitehead et al. (1952, p.110) were accessed by adits from Brown’s Hill Quarry (Plate 20) and adjacent quarries near Holwell. Most surface workings ceased production in the 1930s, but Holwell remained open until 1963. The ore in the district was of variable quality, with local enrichment due to secondary oxidation and the development of limonite (Plate 9a). Iron content was typically between 25 to 40 per cent in the dried ore (e.g. Lamplugh et al., 1909, p.92; Whitehead et al., 1952).

The Northampton Sand Formation is the lateral equivalent of the ‘Northampton Ironstone’ farther south, but has not been worked for ironstone in this district. Trial pits dug around Waltham on the Wolds showed an average of only 20 per cent iron, which is far below the 30 to 50 per cent of the workable ironstone in other parts of the Midlands (Lamplugh et al., 1909; p.96).

Sand and gravel

The sand and gravel resource of the district has been summarised by Mathers and Colleran (1987):

• Deposits of the pre-Anglian drainage systems - the Bytham Sands and Gravels
• Glaciofluvial Deposits intercalated within the Anglian Drift
• Alluvium and River Terrace Deposits of the Soar and Wreake valleys.

There is no current exploitation of the Bytham Sands and Gravels, but a drilling programme (Engineering Geology Ltd, 1985a, b; Rice, 1988) has highlighted the potential of this resource.

Current exploitation of Glaciofluvial Deposits commenced in 1999 at a quarry by Holm Farm Cottages, near East Leake [SK 562 247]. The deposit is possibly up to 13 m thick and forms part of the infill to the Fox Hill Palaeochannel (Chapter 7). Elsewhere in the district, other workings for Glaciofluvial Deposits are on a considerably smaller scale.

Alluvium of the Wreake valley, which may also include equivalents of the Hemington and Syston sands and gravels, was formerly extracted between the 1940s and mid-1970s in the Frisby area [SK 695 183] and around Asfordby and Kirby Bellars [SK 71 18]. In the Soar valley, there have been limited workings in alluvium and/or the Hemington Terrace Deposits to the south-west of Barrow upon Soar [SK 570 165]. The workings to the north-west of Quorndon [SK 5545 1820] constituted a borrow-pit for the construction of the Quorn–Mountsorrel Bypass. The Wanlip Sand and Gravel was formerly worked from a small pit at Mill Spinney [SK 5570 1595].

Building stone

The Marlstone Rock Formation and underlying cemented sandstone (‘Sandrock’) at the top of the Dyrham Formation have both furnished building stone, seen in the distinctive, rust-brown coloured houses and churches at villages such as Holwell, Branston and Wartnaby. The tabular-bedded limestones of the Barnstone Member also constituted a former building stone resource, which was used very locally to the outcrop (e.g. Lamplugh et al., 1909; Lott, 2001).

Water resources

The Melton Mowbray district is drained to the River Trent via the rivers and tributaries of the Wreake/Eye, Soar and Fairham Brook, and the water resources are the responsibility of the Midlands Region of the Environment Agency. The mean annual rainfall varies from less than 600 mm over the low ground in the north of the district to more than 700 mm in the south-west, around Quorndon [SK 57 17] (Meteorological Office, 1977). The mean annual evapotranspiration is 509 mm (data derived using MORECS figures; Thompson et al., 1981).

The hydrogeology of the area was first described by Lamplugh et al. (1909), and Richardson (1931) provides further information. The principal aquifer in the district is the Triassic Sherwood Sandstone Group; of lesser importance are the Dyrham and Marlstone Rock formations (Lias Group) and the Quaternary deposits. (Table 7) details the licensed groundwater abstractions for the district; it indicates that 83 per cent of the local water is abstracted from the Sherwood Sandstone aquifer, by four sources, for industrial and agricultural use.

Bedrock water sources

No water from Carboniferous strata has been utilised in the district. The 1006 m-deep Barkestone No. 1 Borehole terminated in Dinantian dolomitic limestone with an artesian flow of 3.4 l/s, at a pressure head of 1090 m, equivalent to a piezometric level as much as 84 m above ground level. The water was brackish, as also was water encountered in deep boreholes penetrating the Millstone Grit and Coal Measures groups (Table 8). Holliday et al. (1984) and Downing and Howitt (1969) give further information on groundwater from Carboniferous strata in the north of the district.

The Sherwood Sandstone Group aquifer, which does not crop out at the surface, provides water to deep boreholes in the west and north of the district. Borehole core samples of Sherwood Sandstone at depth beneath Loughborough [SK 5435 2081] had a mean porosity value of 23.2 per cent and vertical hydraulic conductivity values of between 0.64 and 0.97 m/d.

Details

At East Leake [SK 5530 2775], a 251 m-deep, 200 mm diameter borehole yielded 17.7 l/s during a 15 day test for a drawdown of 16.4 m, from 58.8 m of saturated Sherwood Sandstone. The rest water level was 167 m above the surface of the sandstone. However, a nearby 152 mm borehole of similar depth [SK 5534 2774] yielded only 4.2 l/s for a drawdown of 14.6 m. The water is of the calcium sulphate type and brackish, with a sulphate ion concentration of 888 mg/l (Table 8).

At Edwalton Nurseries, West Bridgford [SK 5872 3437], a borehole 228.6 m deep, yielded 15 l/s from the Sherwood Sandstone, during a three-day test for a drawdown of 26.5 m. The main yielding horizons were in the Nottingham Castle Sandstone Formation, between 213.4 m depth and the bottom of the borehole; the water had high sodium, calcium, chloride and sulphate ion contents (Table 8).

A deep borehole at Ruddington [SK 650 3243] penetrating Sherwood Sandstone between depths of 142.3 and 209.5 m, encountered water ‘so hard as to be unusable’ and a depth sample from the Sherwood Sandstone in a borehole at Plungar [SK 7720 3347] had a total dissolved solids content of over 4000 mg/l.

The Mercia Mudstone and Penarth groups generally act together as an aquiclude, confining water in the underlying Sherwood Sandstone Group.

Details

At Widmerpool [SK 6200 2882], a 71.6 m deep borehole penetrating through till, Charmouth Mudstone and the Penarth and Mercia Mudstone groups struck water at 8.8 m depth, possibly in the top of the Cotham Member, yielding 0.2 l/s. However, a second borehole nearby [SK 6202 2886], 39.8 m deep, yielded no supply.

At Longcliffe Farm, Wysall [SK 6030 2864], a further borehole yielded 0.6 l/s for 0.3 m drawdown, during a two-day test in 1969. The depth at which water was struck was not recorded, but the borehole was open to a small thickness of Barnstone Member, the underlying Penarth and the uppermost Mercia Mudstone groups. By 1983 it had silted up below 18.3 m and after cleaning out to the original depth, was tested at 1.4 l/s, but this could only be sustained for 20 minutes and it produced only 0.15 l/s for 16.8 m of drawdown. The most probable cause of this was poor borehole design, either due to insufficient open area on the well screen, leading to high entry velocities mobilising fines which then clogged the screen, or to the wrong slot size allowing fines to enter the well.

Lamplugh et al. (1909) commented that in the area underlain by Mercia Mudstone Group water is generally supplied by shallow wells in the overlying ‘Superficial Deposits’. Although some of these wells are now dry, the thin dolomitic siltstone and sandstone beds (skerries) intercalated with the mudstone can yield small supplies, generally less than 1 l/s. Samples from sandstone in the Gunthorpe Formation, at a depth of 120 m beneath Loughborough [SK 5435 2081], had a mean porosity of 24.3 per cent and mean vertical and horizontal hydraulic conductivities of 0.0056 m/d and 0.23 m/d, respectively. Successful Mercia Mudstone boreholes are concentrated in the north-west of the district, where the strata are at or near outcrop. The water is commonly very hard due to the high gypsum content of the mudstones. Although chloride ion concentrations are generally less than 50 mg/l, higher values are possible where saliferous marls are present.

Details

A 50 m deep borehole at Loughborough [SK 5440 1947] recorded the highest yield; though capable of 13.8 l/s, 1 l/s was the normal abstraction rate, with the water probably coming from a sandstone in the Gunthorpe Formation.

At Ruddington [SK 5872 3316], a 24 m-deep borehole drilled into ‘marl with skerries’ (Hollygate Sandstone Member) yielded 0.44 l/s for a drawdown of 0.8 m after an eight hour test.

A 50.3 m deep hole at Burton-on-the-Wolds [SK 5781 2022] yielded up to 0.9 l/s, this obtained from the Cropwell Bishop Formation.

In Plumtree [SK 6139 3309], a 26.2 m-deep shaft and borehole yielded only 0.4 l/s.

At Keyworth [SK 6132 3168], a 61.3 m deep borehole supplied up to 45 m³/d, but was unable to pump for more than three or four hours at a time, before having to allow the water level to recover for an hour.

At Melton Mowbray [SK 7580 1881], a 300 m-deep borehole yielded 0.07 l/s for a drawdown of 50.3 m. The depth of the water strike was not recorded but the borehole was open to strata between the Granby Member (Scunthorpe Mudstone Formation) and the Mercia Mudstone Group, beneath cased out alluvium and glacial deposits.

Lamplugh et al. (1909) stated that the lower part of the Lias Group yields water only from sporadic thin limestone beds, or from the sandy limestones at or near the top of the Semicostatus Zone (Foston Member) of the Scunthorpe Mudstone Formation. A few small springs were also observed to issue from strata of the Scunthorpe Mudstone, and precarious supplies to wells were yielded from the junction with underlying low-permeability strata of the Penarth Group. The thin limestones that occur throughout the Scunthorpe Mudstone Formation are well jointed and collectively form a multilayered aquifer, in which water is confined by the interbedded mudstones. Several boreholes have obtained small yields, generally of less than 1 l/s, from these limestone bands, and yields are commonly less than 0.5 l/s.

Details

At Asfordby Hill [SK 725 197], a 64 m-deep borehole produced 0.8 l/s during a three-day test for a drawdown of 2.8 m; the transmissivity of the Scunthorpe Mudstones was calculated as 24 m²/d.

A 51.8 m-deep borehole at Barn Farm, Wymeswold [SK 5972 2403] is an example of a source with higher than average yields. It supplied 0.9 l/s for three days for a very small drawdown from the Barnstone Member, beneath 11.9 m of Thrussington Till.

At Willoughby Lodge Farm [SK 6488 2783], a 57.9 m deep borehole yielded 0.7 l/s, for 11.6 m of drawdown, mainly from a 0.3 m-thick limestone, probably in the Barnstone Member, at a depth of 57.0 m.

At Hickling Pastures [SK 6619 2761], a borehole yielded 0.5 l/s from five limestones probably within the Granby Member.

At Stathern Railway Station [SK 7606 3088], a dug well and borehole to a total depth of 66.4 m, into the Granby Member, was completely dry, while a nearby dug well [SK 7607 3083] yielded only 0.01 l/s for a drawdown of 5.5 m.

At The Yews in Upper Broughton [SK 6830 2630], a 32.3 m deep, 152 mm diameter borehole yielded between 5 and 6 l/s at a depth of 31.1 m, from a limestone probably in the Foston Member. Another borehole in Upper Broughton [SK 6834 2598] obtained water, from the same horizon. When pumped at 2.5 l/s for three days in April 1941 it lowered the water level in the borehole at The Yews by 12.2 m and considerably diminished the yield of springs 400 m away. When pumped at 4 l/s for 14 days in March 1935, it dried up the other wells and springs in the village. The water here is hard and of the sodium sulphate type, with a sulphate ion concentration of 997 mg/l, a sodium ion concentration of 617 mg/l and a total dissolved solids content of 2145 mg/l (Table 8).

The Charmouth Mudstone Formation yields small supplies, generally of less than 0.5 l/s, from levels that include the Brandon Sandstone. A borehole at Cumberland Lodge, Scalford [SK 7688 2309] penetrated a 0.9 m-thick limestone (possibly the Jericho Gryphaea Bed) at a depth of 57.6 m; this yielded 0.63 l/s for 1.5 m drawdown during a five hour test.

The yields in siltstone and sandstone of the overlying Dyrham Formation are generally low and dry boreholes are not unknown.

Details

At Scalford Pumping Station [SK 7655 2435], a 76.2 m deep borehole into the Dyrham Formation yielded 1.1 l/s for 49 m drawdown, during a 12 hour test. Another 57.6 m deep borehole nearby [SK 7652 2428] yielded only 0.2 l/s borehole for 15 m drawdown over a six hour period. A third, 61 m deep [SK 7655 2435], is recorded as yielding 8.8 l/s before collapsing due to pump vibration; however, this quantity probably includes water from seven shallow wells and springs issuing from the Marlstone Rock farther up the valley and piped to the pumping station.

At Wartnaby [SK 7095 2290], a 26.5 m-deep borehole yielded 4.9 l/s, from ‘sandrock’ at the top of the Dyrham Formation, during a 14 day test for 3.8 m of drawdown.

At Ab Kettleby [SK 7223 2307], a further borehole yielded 2.25 l/s from the ‘Sandrock’, during a 132 day test for 3.7 m of drawdown. Other boreholes in Ab Kettleby had significantly lower yields; one at the Poultry Farm [SK 71510 23530], penetrating 28 m of sandy clay with limestone beds up to 0.4 m thick, had an initial yield of 0.15 l/s but this had decreased seven years later to only 0.08 l/s.

North of Scalford [SK 7664 2555], a 4 m-deep shaft yielded 2.5 l/s for a few hours each day, possibly from ‘sandrock’. A partial analysis of water from the Dyrham Formation is given in (Table 8).

The outcrop area of the Marlstone Rock Formation is generally too small and its thickness too limited in this district for it to provide significant volumes of water. As it overlies deposits of lower permeability, however, springs commonly issue from its base and it thus yields supplies to local wells and boreholes. Melton Mowbray itself was historically supplied by several such springs in the valleys north of Scalford. Their combined flows in 1902 varied from 2.0 to 5.8 l/s (Lamplugh et al., 1909). The groundwater is contained in a regionally developed fracture system.

The aquifer is utilised by boreholes only where it is confined, since the Marlstone Rock Formation is generally unsaturated at outcrop. Boreholes penetrating it have moderate yields, varying from less than 1 l/s to more than 14 l/s. The quality of the water from the Marlstone Rock is generally good but often ferruginous (Table 8). At Holwell Spring [SK 7517 2377] the water was good but hard, with a total dissolved solids content of 482 mg/l, a total hardness of 325 mg/l (as CaCO₃) and a chloride ion concentration of 19 mg/l.

Locally the Marlstone Rock is dry, with water only encountered when the underlying Dyrham Formation is penetrated. A borehole at Chadwell [SK 7807 2457], for example, penetrated 3.4 m of Marlstone Rock beneath 8.2 m of till and Whitby Mudstone. Water was only struck at a depth of 18.6 m, when a yield of 1 l/s was obtained from a 2.7 m thickness of saturated Dyrham Formation. A nearby 25.9 m deep borehole [SK 7792 2454] struck water at the base of the Marlstone Rock and yielded 1.26 l/s during a 14 day test.

Details

At Holwell Spring, Scalford [SK 7516 2377], two shallow bores, about 6 m deep, and associated springs together yielded 12.6 l/s from the Marlstone Rock. Another 18.3 m deep bore [SK 7517 2377] yielded 14.8 l/s for 14 days for a drawdown of 1.0 m during a 14 day test.

At Waltham on the Wolds [SK 7965 2608], a 1.8 m diameter shaft yielded 3.8 l/s for 14 days from 3 m of Marlstone Rock. The water level rose 3 m above the top of the Marlstone Rock.

At Eaton [SK 8048 2785], a 72.4 m deep borehole obtained 0.5 l/s from the Marlstone Rock, for no noticeable drawdown.

Small supplies of water were formerly obtained from dug wells into the Whitby Mudstone Formation around Waltham-on-the-Wolds.

The Northampton Sand Formation, although permeable and constituting a minor aquifer farther south, is hardly utilised for water supply in this district due to its localised occurrence and generally unsaturated nature. A well in Waltham on the Wolds [SK 8020 2509] obtained water from the sand at a depth of 4.3 m, but another borehole [SK 7997 2432], penetrating 5.9 m of Northampton Sand above the Whitby Mudstone, Marlstone Rock and Dyrham Formation, yielded nothing. In another borehole at Eaton [SK 8048 2785], the Northampton Sand water strike was cased out, presumably due to insufficient quantity, and a supply of 0.5 l/s obtained from the Marlstone Rock at depth.

The Grantham Formation will act as a lower permeability horizon, separating water in the Lincolnshire Limestone above, from that in the Northampton Sand below.

The Lincolnshire Limestone Formation is a significant aquifer in eastern England, but is unimportant in this district due to its limited outcrop. The only record in the National Well Record Archive, in the Lincolnshire Limestone, is a disused domestic supply at Croxton Park [SK 8157 2619], currently used as an observation borehole for monitoring water levels. It shows annual fluctuations in excess of 18 m, but has been dry in six out of the twelve years between 1989 and 2000.

Quaternary water sources

Useful water supplies have locally been encountered in the Quaternary deposits; however, it should be noted that any shallow groundwater is highly vulnerable to contamination from both diffuse and point source pollutants due to the thinness of the unsaturated zone. Successful aquifer remediation is difficult, prolonged and expensive, and therefore the prevention of pollution is important.

In the Bytham Sands and Gravels, water has been encountered at Frisby-on-the-Wreake [SK 6892 1731], where a 152 mm trial bore, penetrating 9.6 m of Bytham Sands and Gravels above Scunthorpe Mudstone, yielded 3.9 l/s for 4.1 m drawdown during a five day test. A 1.4 m diameter 6.1 m deep well with two 304 mm diameter, 7.9 m deep boreholes in the base, was later constructed and this yielded 4.0 l/s during a 14 day test for 4.8 m drawdown. A chemical analysis of the water is shown in (Table 8). This resurvey has shown the potential for significant thicknesses of this sand and gravel, which constitutes a perched reservoir, to be present in the basal part of the fill to the concealed Bytham palaeovalley (Figure 23). Its course, indicated on Sheet 142 Melton Mowbray, has been traced around the north of Melton Mowbray [SK 71 21] and extends eastwards beyond the margin of the district.

Small domestic supplies of groundwater have been obtained from sand and gravel lenses within the lower part, or at the base, of the various sheets of till, but its main hydrogeological significance is that it reduces recharge into underlying formations. Examples of higher than average yields from till are:

Near Seagrave [SK 6220 1905], a 62.5 m-deep borehole which penetrated 61.3 m of Oadby Till and yielded 0.6 l/s during an 8 hour test.

At Wymeswold [SK 6220 2410], a 61 m-deep borehole penetrating 36.3 m of Oadby Till with a yield of 0.6 l/s.

At Six Hills [SK 6445 2090], a borehole penetrating 4.4 m of sand and gravel beneath 55.3 m of Oadby Till struck water at a depth of 56.4 m and yielded 0.9 l/s for 3 m of drawdown.

Lower yields and unsuccessful boreholes are also known and supplies therefore tend to be marginal:

At Willoughby-on-the-Wolds [SK 6459 2528], a borehole yielded only 0.1 l/s for 6.9 m drawdown during a one day test from 3 m of ‘silty sand and fossil shells’ (possibly bedrock) below 22.3 m of Oadby Till. The borehole was deepened to 76.2 m but obtained only 0.05 l/s from the Scunthorpe Mudstones and was then abandoned.

In Welby Lane, Melton Mowbray [SK 7411 2022], a 1.2 m diameter well and 127 mm diameter bore, to a total depth of 13.7 m, yielded only 0.08 l/s from gravel layers within the Oadby Till.

Glaciofluvial Deposits commonly occur as isolated outcrops with limited recharge. Supplies are likely to be affected by seasonal variations in water level, but despite this, they have been utilised for small domestic supplies in the past.

River Terrace Deposits are generally in hydraulic continuity with the river. Yields are therefore higher and are more likely to be sustained than other sources in the Quaternary deposits. Such groundwater is shallow, however, and liable to surface pollution. Typical yields are as follows:

Details

In Loughborough [SK 5415 1943], a 2.7 m diameter well 7.6 m deep, with headings probably connecting it to a second well, yielded 7.6 l/s of water for a drawdown of 3 m during a 10 hour working day. The water, from the Wanlip Sand and Gravel, had a total hardness of up to 500 mg/l.

At the railway pumping station in Melton Mowbray [SK 7452 1942], four 76 mm diameter bores 11.9 m deep, plus a 152 mm bore that was 10.7 m deep were sunk into the sands and gravels. They had a combined yield of 3 l/s and were pumped for 12 hours/day. The water was hard (587 mg/l as CaCO₃) but otherwise of good chemical quality (Table 8).

At Moor Lane Farm, Loughborough [SK 550 192], a 101 mm diameter borehole penetrating 11.1 m of sand and gravel above 4.1 m of Mercia Mudstone yielded 0.57 l/s for a 1.1 m drawdown during a four day test.

At Quorn Field’s Farm [SK 560 184], a shallow well yielded water with a total hardness of 670 mg/l (as CaCO₃) from the Syston Sand and Gravel.

A 1.5 m-diameter well penetrating 2 m of gravelly floodplain alluvium, beneath 3.5 m of subsoil and clay in Melton Mowbray [SK 7570 1914], yielded 0.8 l/s for 1.8 m of drawdown during an eight day test. This gravel is likely to be in hydraulic continuity with the river; its transmissivity was calculated as 15 m²/d.

Groundwater vulnerability and aquifer protection

The Environment Agency is responsible for ensuring that existing and potential groundwater resources are adequately protected, at a time when the risk of pollution is increasing both from the disposal of waste materials and from the widespread use of potentially polluting chemicals by industry and agriculture. Groundwater vulnerability to nitrate pollution is a particular problem in rural areas, since the majority of groundwater sources in the district obtain water from shallow, minor aquifers. Shallow groundwater is highly vulnerable to contamination from both diffuse (e.g. nitrates and pesticides) and point source (e.g. storage tanks) pollutants due to the thinness of the unsaturated zone. Successful aquifer remediation is difficult, prolonged and expensive, and therefore the prevention of pollution is important. Water in the deeper Sherwood Sandstone aquifer is confined and well protected from pollution.

Other major concerns over groundwater quality (Environment Agency, 1999) are: the cost of pollution problems associated with contaminated land clean-up operations; pollution incidents due to illegal waste disposal practices; and the closure of mine workings that may cause the rise of poor quality minewater and its ingress into major aquifers. To assist with their Groundwater Protection Policy (NRA, 1992), the Environment Agency, in conjunction with the BGS and Soil Survey and Land Research Centre have compiled a series of groundwater vulnerability maps (see Information sources) for the UK. This vulnerability system zones the soil and geological horizons in order to assess the ease with which a pollutant released at the surface would be expected to reach the underlying groundwater body (Palmer and Lewis, 1998).

A potential concern in parts of the district is the risk of surface and near-surface contamination from poor quality minewater, following further rises in groundwater levels after closure of collieries and consequent cessation of pumping. In the conceptual model for the Nottinghamshire coalfield suggested by Dumpleton and Glover (1995), there are nonpumped, isolated ponds, comprising closed collieries such as Cotgrave [SK 651 363], just to the north of this district. In such situations, which may now include the recently closed Asfordby Colliery [SK 725 205], rising minewaters may be generated, which could ingress the Permo-Triassic aquifer.

Flooding

Flooding is a major potential geohazard in many low-lying parts of this district during heavy falls of rain. Prolonged rain can result in widespread floodplain inundation, whereas shorter, much heavier bursts of rainfall can result in flash flooding.

On floodplains a broad relationship exists between geology, geomorphology and the potential extent of flooding. The permeability of bedrock units in the catchment area can affect the rate of runoff, whereas Quaternary geological processes are largely responsible for the width and topography of floodplain tracts and the volume of alluvial fill that is capable of absorbing flood waters. The edge of the modern alluvium broadly correlates with the deposits left behind by previous maximum-flood events, and therefore this boundary approximates to the maximum flooding limit. This resurvey has shown that the major floodplains, particularly that of the River Soar, also contain significant areas of ground that are topographically higher than the modern alluvium tracts. These elevated areas correspond to outcrops of the River Terrace Deposits, and their distribution allows zones of generally lower flood frequency to be recognised within the floodplain. The interaction of these factors with infrastructure modifications and industrial/residential developments on the floodplains, is a further important factor to be taken into account when predicting flood-risk. An example of floodplain topography resulting in flood-retardant zones, during the major flooding of late October/November, 2000 in the River Soar, is shown in (Plate 14).

Detailed flood-risk maps, based on hydrology and historical information, augmented by micro-topographic surveying, are available for the larger floodplains such as those in the Soar and Wreake valleys, and can be obtained from the West Bridgford office of the Environment Agency (Midlands). For smaller tributary valleys, where detailed historical and topographical information is not available, the distribution of alluvium and/or valley head (colluvium) deposits, shown on Sheet 142 Melton Mowbray, can be used as an approximation to the maximum flooding limits. It should be stressed, however, that the alluvium represents only those preserved deposits of flooding events: the waters that deposited them may have extended further, beyond the alluvium boundary as mapped.

The Melton Mowbray district features numerous valleys; many are moderately incised but some are seen as little more than gentle depressions and revealed only during this survey by the mapping of narrow strips of alluvium or valley colluvium (including head deposits). Such narrow valley systems, e.g. [SK 80 22] focus runoff, resulting in flash flooding at times of short-lived and localised, but exceptionally heavy, bursts of rain. One of the many examples of this type of flooding was experienced through the centre of East Leake [SK 554 264] on 18 July, 2001. It followed a cloudburst, recorded by the BGS weather station at nearby Keyworth, which resulted in 96.3 mm of rain falling in less than 24 hours on the catchment of the Sheepwash Brook, behind the village. Localised flooding can also be caused by drainage overflows, as occurred around Asfordby during the heavy rains of April and June 1998.

Ground conditions and geohazards

In considering the stability of engineering structures, the geotechnical properties of the substrate must be examined, as well as geological factors such as: local geological structures, slope stability, bedrock weathering and/or dissolution, and seismicity. Any of these may either enhance or 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 10) are therefore intended only as a general guide to the expected behaviour of the strata described." data-name="images/P946273.jpg">(Table 9) and (Table 10), which are based on the findings of more detailed geotechnical reports for adjacent districts (Hobbs, 1998; Howard et al., in prep (a); Berridge et al., 1999; Charsley et al., 1990). There are a few large-scale landfill or backfill operations in the district, but colliery waste is limited to the reclaimed tips north-west of Asfordby Colliery [SK 716 207].

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, but geotechnical coverage of geological units is generally good. 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).

Mudstone, of either Triassic or Jurassic age, is the dominant bedrock type and underlies about 40 per cent of the district; it is these lithologies that are often at most risk of weakening by natural agencies such as weathering. The Mercia Mudstone Group generally consists of stiff to hard silty clays of low to intermediate plasticity. The locally high content of smectite clay minerals in the Edwalton and lower Cropwell Bishop formations (Figure 18) nevertheless indicates a potential for shrink/swell clays to be present in this part of the Triassic succession. The net allowable bearing capacity of Mercia Mudstone is in the range of 100 to 600 kPa, with moderate, rarely high, settlement. Sulphate attack on buried concrete is possible, so that class 2 or class 3, rarely class 4 or 5, concrete mixes may be required locally (Building Research Establishment, 1996). Excavations on Mercia Mudstone can generally be carried out by digging, or by ripping in harder parts, and support is required in weathered material.

Clays of the Penarth, Lias and Inferior Oolite groups can be of intermediate to very high plasticity, with strength generally increasing with depth as weathering and stress relief effects decline. Such clays may be subject to slope instability and high compressibility, as well as shrinkage and swelling problems. Excavations can generally be carried out by digging, but ripping may be necessary for sequences with strong limestone beds. Water may flow along joints in limestone beds causing flooding to excavations.

Slope stability

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

• slope angle
• nature, structure and strength of the underlying material (bedrock, superficial deposits or fill)
• influence of water

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. Natural slopes of varying steepness characterise this district. The steeper ones include the escarpment, about 80 m high, capped by the Marlstone Rock Formation, which overlooks the Vale of Belvoir. Relatively smaller escarpments include the slopes leading up to the Northampton Sand Formation, and the low, embayed feature capped by the Barnstone Member. Steep slopes are also developed along the deep valleys that dissect the Marlstone Rock dip slope around Knipton Reservoir [SK 800 300]. A geotechnical database assembled for the Grantham district (Forster, 1992) indicated a residual angle of internal friction ’ for the Scunthorpe Mudstone in the range 13° to 19° with a median value of 16°. If a median bulk density, , of 1.97 Mg/m³ is assumed then using the Skempton Delory equation the theoretical threshold slope for stability ranges from 6.5° to 9.6° with a median value of 8.0°. These values are close to the angles measured for scarp slopes in Charmouth Mudstone near Old Dalby, but are exceeded in places on the steeper Dyrham Formation outcrop (Table 11).

The surface geotechnical properties of a given bedrock or superficial lithology generally determines its susceptibility to mass movement. Mudstone and interbedded mudstone and sandstone are normally strong enough to sustain steep slopes without failure. Deeply weathered bedrock and material derived from it, such as head, is much weaker and has a reduced permeability. The weathered zone of slopes, and slopes mantled by Quaternary deposits, are consequently 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 or following exceptionally heavy and sustained rainfall. However, under the wetter freeze-thaw periglacial conditions during the Devensian, movement may have occurred, forming shallow landslips or solifluction aprons. The degraded products of such processes are today preserved as the numerous outcrops of head and Slope Terrace Deposits. Relict shear surfaces (Chapter 7) within heads indicates that they have the potential to be reactivated by loading, undercutting or excavating, or by introducing water into the slope from drains or soakaways.

The main types of landslide are described in Chapter 7, and selected areas with such features were studied by A Forster (written communication, 1998). On the Marlstone Rock escarpment to the east of Old Dalby [SK 685 235], a two-stage history of slope instability was suggested for slopes developed on sandy clays of the Charmouth Mudstone. The first stage is now represented by a mature, possibly stable, uniform slope with an angle of about 10°; however, the remaining facets of this slope appear to be covered by shallow lobate mudflows, the development of which is perhaps consistent with solifluction of the active surface layer under periglacial conditions. In a second stage, the uniform slope was deeply dissected by gully erosion, with fresh-looking block slumps and slides at the top and larger more distinct flows issuing from the gullies (Plate 16). This second phase of development may have occurred when the climate was warmer and wetter, allowing the thawed-out ground to sustain a greater flow of water that emerged as a spring line at the base of the Marlstone Rock Formation. It is further possible that quarrying of the ironstone has enhanced drainage into the ground, resulting in a greater concentration of water at the spring line, which caused renewed activity.

For bedrock lithologies without significant clay, such as the Marlstone Rock Formation, 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.

Bedrock dissolution

Bedrock solution may be anticipated in the western parts of the district that are underlain by the Mercia Mudstone Group, in particular by the Cropwell Bishop Formation with its locally thick gypsum beds. Typically, gypsum dissolution occurs in the presence of freely flowing groundwater, within a ‘solution zone’ that is several metres thick, below the base of the subsoil or superficial deposits (Elliott, 1961). The process is mainly accomplished by groundwater flow along bedding planes, joints and fissures, and although commonly attributed to glacial or periglacial conditions it may be continuing, albeit much more slowly, today (Firman and Dickson, 1968). The occurrence of anomalous depressions in ground on the outcrop of the Newark Gypsum near Bunny, to the east of the Silver Seal Mine adit [SK 590 287], may indicate subsidence resulting from natural gypsum solution. Farther north, Crofts (1989a) described similar features south of Bradmore Lane, between Blackcliffe Hill [SK 6010 3205] and Plumtree House Farm [SK 6130 3290]. Areas where the solution zone is particularly deep, and greater volumes of gypsum were dissolved, may coincide with the wide depression in which the Lacustrine Deposits of the Ruddington–Gotham–Bunny Moor are located (Chapter 7). The circumstances in which gypsum solution may produce a geotechnical hazard are discussed more fully by Cooper (1996) and in Carney et al. (2001). In this district they include: the collapse of natural underground solution voids, collapse of former gypsum mine workings (see below), and the slow, natural solution of gypsum. The latter process occurs within zones of enhanced groundwater flow, and could cause uneven settlement resulting in damage to heavy man-made structures; it has been predicted in ground adjacent to the Ratcliffe on Soar Power Station, to the west of the district (Seedhouse and Sanders, 1993).

Mined ground and shafts

Mining activities in this district have occurred in association with the extraction of coal, gypsum, limestone and ironstone (see above). Underground mining may involve local subsidence damage and will produce waste material, the disposal of which commonly creates a demand for tip sites. The area tipped over becomes sterilised for shallow mineral extraction, and presents the planner with further problems regarding use of the new artificial landforms. Information on ground conditions, as determined by the geology and former land-use, can be used to ensure that informed decisions are made prior to land allocation for tipping.

Coal mining has been carried out from beneath overburdens that are at least 170 m thick in the north-west of the district, where extraction was from Cotgrave Colliery, and in excess of 500 m around Asfordby Colliery. General ground subsidence caused by the progressive collapse of roadways and working faces in abandoned deep mines, has probably occurred and may still be occurring throughout the undermined areas, but no specific examples of damage are known to the authors. Collapse of individual mine shafts is possible if these have not been adequately backfilled or grouted. For information about local coal mining subsidence and shaft locations, contact: Coal Authority, Mining Reports, 200 Lichfield Lane, Mansfield, Nottinghamshire NG18 4RG Tel. 0845 762 6848.

Gypsum mining has occurred in three areas (see above): south of Cropwell Bishop, around East Leake and to the south of Barrow upon Soar. The gypsum was worked from shafts or adits and quite commonly the early 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. As noted above, however, the modern workings for gypsum are all based on careful rock mechanics principles. Abandoned gypsum mines could pose stability problems in three ways.

• If the workings have not completely collapsed, voids at shallow depths could exist.

• 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.

• In areas of old mine workings, or around former shafts, natural gypsum dissolution could continue within the workings thus destabilising these areas in the future.

Only a very few plans of gypsum workings are currently on public file at the BGS, and reference to British Gypsum Ltd. (East Leake offices) should therefore be made for further details.

Limestone mining has been limited to the subsurface of outcrops of the Barnstone Member, around Langar and Barrow upon Soar (see above). This resurvey has added much new detail on the distribution of Disturbed Ground (Chapter 10) caused by these activities, which reflects combinations of surface and shallow subsurface workings. Disturbances caused by shallow subsurface workings for Barnstone Member limestone include the localised collapses of ground within Barrow upon Soar between 1976 and 1987. The occurrences prompted intensive ground investigations and surveys of former mining activities, the results being summarised in the reports of Wardell Armstrong (1987) and Arup Geotechnics (1990). The three principal types of hazard identified by these studies were: the collapse of former mine roofs causing crownholes, the settlement of poorly consolidated fill in the large-diameter shallow access shafts, and the uneven settlement of backfill in the former quarries. In the case of the two former categories, follow-up investigations involving the drilling of numerous shallow boreholes typically encountered widespread areas of partially collapsed and choked mine workings, with voids 2 to 3 m in diameter, below an extremely thin (1 to 3 m) ‘roof’. The reports cited above have identified ‘proven’, ‘suspect’ and ‘remainder’ mining areas in the urbanised and/or industrialised parts of Barrow upon Soar. The reader is referred to them for detailed analysis of subsidence mechanisms and possible causes, and strategies for remediation and prevention.

Ironstone mining of the Marlstone Rock Formation (see above) is restricted to an area immediately east of Brown’s Hill Quarry, near Holwell [SK 745 235]. Access to the shallow underground workings was through adits driven at shallow angles in to the resource, from faces opened up in the surface quarries (Plate 20). Pillar and stall methods were utilised for extraction, and as this occurred beneath a minimal overburden the ground is now unstable, with numerous small subsidence pits marked on the Ordnance Survey 1:10 000 scale topographical map, e.g. [SK 745 234]. There is still a high risk of subsidence in this area (Swift and Reddish, 2002), with some collapses reported as recently as the winter of 1998–99 (Plate 18). Plans showing the distribution of these workings (Permissions Nos 349 and 458) are currently lodged with the Planning Department of Leicestershire County Council.

Surface quarrying

Until well into the 20th century, the surface extraction of minerals was almost entirely from a number of small operations, and there are many disused pits in the district, indicated on the 1:10 000 series maps (Table 12), that date from this phase. This pattern has changed so that the present workings for sand and gravel, and former workings for limestone and ironstone, are centred on a few large-scale excavations. Many quarries have been backfilled and others, particularly the ironstone workings of the Marlstone Rock Formation, are partially filled and degraded. Only 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 and that other excavations may 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.

Constraints to the further development of worked-out excavations are related to geotechnical problems of variable ground conditions, including drainage, between the natural surface and the fill. Problems of settlement may occur within some of the larger infilled quarry sites of the district. The properties and nature of the backfilled material must also be considered, in particular its possible interaction with the wall-rocks of the repository, and any risks associated with the migration of gases, including potentially explosive methane, or leachates from the fill into the surrounding geological deposit (see below).

The increasing use of quarries and various types of pit (Plate 18) 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 with permeable bedrock or, in the case of the 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 noted below.

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 (Plate 18), 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, or units rendered susceptible to fluid flow as a result of faulting and/or jointing (e.g. Mercia Mudstone Group, Lias Group). Permeability may also be enhanced in mudrocks by zones of solution (e.g. 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.

Mine gas is caused mainly by the migration of methane from former coal mine workings. Although it is released when coal seams are disrupted by mining, it can also migrate naturally, for example along fault zones, and is known to be a potential hazard in underground workings for gypsum.

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. Many modern sites pack waste material densely and contain it within impermeable barriers, venting the gas through pipes to the surface. Other sites, if not contained or vented, may present a risk from gas or leachate migration. Gases can migrate, sometimes through adjacent porous strata or along faults and 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). 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 that 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. Higher than normal concentrations of carbon dioxide may result from the oxidation or combustion of organic materials, such as methane and coal from colliery spoil. 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 with ground 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 Melton Mowbray district it is anticipated that natural radon levels will be generally low except over the outcrops of Lias Group. Studies by Sutherland (1992) and Sutherland and Sharman (1996) show that elsewhere in the East Midlands the Marlstone Rock Formation is a significant radon generator, with the Northampton Sand, Charmouth and Scunthorpe Mudstone formations ranking slightly lower in this respect. These conclusions are borne out by the airborne Hi-Res (High-Resolution) radiometric survey recently carried out in this part of the East Midlands (see Information Sources). 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 groundwater, returning to a gas phase in areas of water turbulence or pressure decrease (e.g. waterfalls and springs). Radon may therefore occur in high permeability rocks present above a source rock. 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 ground surface. 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.

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

Earthquakes

Earthquakes present a considerable hazard to development in certain parts of the world; however, in a country of low seismicity such as Britain, much historical research is required to assess seismic risk. The largest seismic event to be recorded in the district was the Melton Mowbray earthquake of 28 October, 2001, the epicentre of which was located [SK 770 283] several hundred metres to the west of Eastwell (Figure 27). With a magnitude of 4.1 ML (intensity 5+ EMS), this was the fourth largest event to have been recorded by instruments in the region (information from BGS Global Seismology Unit). It was felt across much of the East Midlands, and as far afield as Warwickshire, and caused minor damage to chimneys and the walls of some houses. The cause of the earthquake is unknown, but the focus, on a north-dipping plane at an estimated depth of 11.6 km (Information from the UK Seismic Monitoring and Information Service, BGS Edinburgh), could reflect movement due to readjustments along either the Normanton Hills or Sileby faults (News item in Mercian Geologist, 2002, Vol. 15 (3)).

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 (aftershock: 4.2 ML) and maximum intensity of 6 to 7 EMS, it was one of the most damaging UK earthquakes of the 20th century and was felt over the English Midlands, and as far as Hartlepool, Pwllheli, Norwich and Topsham (near Exeter). The epicentre was located 9 km west of the district, near to Diseworth [SK 450 250] (Dollar, 1957; Lees, 1957; Neilson et al., 1984; and see review in Carney et al., 2001). There was widespread damage to chimneys and roofs in the Derby–Nottingham- Loughborough areas. Other earthquakes recorded in the adjacent Nottingham district include a magnitude 3.1 ML, Nottingham event of 30 May 1984, with a maximum intensity of 5 EMS (Marrow, 1984); a discussion of this and other Nottingham events is given in Charsley et al. (1990). Detailed information including analysis of local seismic risk to major developments 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 geological SSSIs, which comprise the Marlstone Rock Formation outcrop at the Brown’s Hill ironstone quarries [SK 741 234] and the Lower Lincolnshire Limestone Formation at Waltham Quarry [SK 813 252].

Information sources

Further geological information relevant to this district and held by the British Geological Survey is listed below. Searches of indexes to some collections can be made on computerised databases, either held at BGS or available on the BGS web site http://www.bgs.ac.uk. The latter contains details of BGS activities, services and data, including: summaries of BGS projects, BGS products and contact points for advice on a wide range of issues. A Geoscience Data Index (GDI) is available on the web site, with details of borehole and seismic line locations; topographical backdrops based on various map scales; large-scale geology of the UK and many other items of data. Geological information is also available by enquiry to the BGS Sales Desk at Keyworth. Digital geological coverage of the UK at 1:50 000 scale (DIGMAP) is now available, by enquiry to the BGS Sales Desk at Keyworth.

Maps

Geological maps

• 1:625 000
• Solid geology map UK South Sheet, 2001; Quaternary geology, 1977
• 1:500 000
• Tectonic map of Britain, Ireland and adjacent areas, 1996.
• 1:250 000
• East Midlands, Solid geology, 1983
• 1:100 000
• Mineral resources maps for Leicestershire/Rutland and Nottinghamshire (both 2002)
• 1:50 000 and 1:63 360
• Sheet 126 Nottingham (Solid & Drift), 1996 Sheet 141 Loughborough (Solid & Drift), 2001
• Sheet 142 Melton Mowbray (Solid & Drift), 1909, 2002 Sheet 143 Bourne (Solid & Drift), 1964 (Last reprinted 1971)
• Sheet 156 Leicester (Solid & Drift), 1903 (Last reprinted 1975)
• 1: 10 000 and 1:10 560
• Details of the original geological surveys are listed on editions of the 1:63 360 geological sheets. Copies of maps of these earlier surveys may be consulted at the BGS Library, Keyworth. The maps at six-inch to one mile or 1:10 000 scale covering the 1:50 000 Series Sheet 142 are listed in (Table 12), together with the surveyors’ names and reference numbers of accompanying Technical Reports.

Geophysical maps

• 1:1 500 000
• Colour shaded relief gravity anomaly map of Britain, Ireland and adjacent areas (1997). Smith, I F and Edwards, J W F (compilers), British Geological Survey.
• Colour shaded relief magnetic anomaly map of Britain, Ireland and adjacent areas (1998). Royles, C P and Smith, I F (compilers), British Geological Survey
• 1:50 000
• High-resolution airborne geophysical and radiometric surveys Print-on-demand maps giving high-resolution gravity and aeromagnetic information, in addition to the surface distributions of a range of radioactive elements are available on enquiry to the BGS Sales Desk.

Geochemical atlases

• A baseline geochemical survey (G-base) has been completed for this district and the processed results will be available in the near future.

Hydrogeological map

• 1:625 000
• England and Wales (1977)
• 1:100 000
• Groundwater vulnerability (Sheets 23 & 24)

Digital geological map data

In addition to the printed publications noted above, many BGS maps are available in digital form, which allows the geological information to be used in GIS applications. These data must be licensed for use, and details are available from the Intellectual Property Rights Manager at BGS Keyworth. The current availability can be checked on the BGS web site at: http://www.bgs.ac.uk/products/digitalmaps/digmapgb.html

Books and reports

Memoirs, books, reports and papers published by BGS and relevant to the district and adjacent area are arranged by topic. Some are 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

Central England, 1969

Memoirs

Geology of the Melton Mowbray district (Sheet 142), 1909 Geology of the country around Nottingham, in preparation Geology of the country near Leicester (Sheet 156), 1903

Economic geology: ironstone

The Liassic ironstones (The Mesozoic ironstones of England),

Memoir Geological Survey of Great Britain, 1952

Petrology of the Northampton Sand ironstone formation (The Mesozoic ironstones of England), Memoir Geological Survey of Great Britain, 1949.

Hydrogeology

Wells and springs of Leicestershire. Memoir Geological Survey of Great Britain, 1931

Sheet Description

Geology of the country between Loughborough, Burton and Derby (Sheet 141), 2001

Documentary collections

Basic geological survey information, which includes 1:10 000 or 1:10 560 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 13).

Mine plans

BGS maintains a partially complete collection of plans of underground and opencast mines for coal, ironstone 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 from coal and hydrocarbon exploration programmes is available for the whole of the district.

BGS Lexicon of named rock unit definition

Definitions of the rocks and superficial deposits shown on BGS maps, including those shown on the 1:50 000 Series Sheet 142 Melton Mowbray, are held in the Lexicon database, available through the BGS web site (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, and are indexed in the BGS web site. Colour or black and white prints and transparencies can be supplied at a fixed tariff.

Material collections

Petrological collections

The petrological collections for the district include hand specimens and 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 some of the boreholes in this district. 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, 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. Copies of some of these plans are held in BGS, Keyworth.

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

Other plans, which include those of ironstone workings, may be held at the relevant office of Leicestershire County Council.

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

• BGS Hydrogeology Enquiry Service: wells, springs and water borehole records.
• British Geological Survey, Hydrogeology Group, Maclean Building , Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB. Telephone 01491 838800
• Fax 01491 692345
• London Information Office at the Natural History Museum Earth Galleries, Exhibition Road, South Kensington, London SW7 2DE
• Telephone 0171 589 4090
• Fax 0171 584 8270
• British Geological Survey (Headquarters)
• Kingsley Dunham Centre Keyworth, Nottingham, NG12 5GG Telephone 0115 936 3100
• Fax 0115 936 3200
• Web site http://www.bgs.ac.uk
• Email: sales@bgs.ac.uk

References

Most of the references listed below are held in the Library of the British Geological Survey at keyworth, Nottingham. Copies of the references can be purchased, subject to current copyright legislation. BGS Library catalogue can be searched online at http://geolib.bgs.ac.uk

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AITKENHEAD, N. 1977. The Institute of Geological Sciences borehole at Duffield, Derbyshire. Bulletin of the Geological Survey of Great Britain, No. 59, 1–38.

AITKENHEAD, N, and CHISHOLM, J I. 1982. A standard nomenclature for the Dinantian formations of the Peak District of Derbyshire and Staffordshire. Report of the Institute of Geological Sciences, No. 82/8.

AMBROSE, K. 1998. Geology of the Old Dalby area (SK 62 SE). British Geological Survey Technical Report, WA/98/16.

AMBROSE, K. 1999. Geology of the Ab Kettleby area (SK 72 SW). British Geological Survey Technical Report, WA/99/20.

AMBROSE, K. 2000a. Geology of the Scalford area (SK 72 SE). British Geological Survey Technical Report, WA/00/06.

AMBROSE, K. 2000b. Geology of the Eastwell area (SK 72 NE). British Geological Survey Technical Report, WA/00/07.

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ASHTON, M. 1979. A re-appraisal of the value of Acanthothyris crossi (Walker) in the correlation of the Lincolnshire Limestone Formation (Bajocian, Jurassic). Transactions of the Leicester Literary and Philosophical Society. Vol. 73, 65–76.

ASHTON, M. 1980. The stratigraphy of the Lincolnshire Limestone Formation (Bajocian) in Lincolnshire and Rutland (Leicestershire). Proceedings of the Geologists’ Association, Vol. 91, 203- 223.

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AVELINE, W T. 1880. The geology of parts of Nottinghamshire, Yorkshire and Derbyshire. Memoir of the Geological Survey of England and Wales, Sheet 82NE. (London: HMSO.)

BARCLAY, W J. 1996a. Geology of the Winshill–Newhall area: 1:10 000 Sheet SK22SE. British Geological Survey Technical Report, WA/96/77.

BARCLAY, W J. 1996b. Geology of the Hartshorne area: 1:10 000 Sheet SK32SW. British Geological Survey Technical Report, WA/96/78.

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BRANDON, A. 1994. Geological notes and local details for 1:10 000 Sheet SK52SW (Normanton on Soar). British Geological Survey Technical Report, WA/94/60.

BRANDON, A. 1996. Geology of the lower Derwent valley: 1:10 000 sheets SK33SE, 43SW and 43SE. British Geological Survey Technical Report, WA/96/07.

BRANDON, A. 1997. Geology of the Stretton and Repton areas: 1:10 000 sheets SK22NE and 32NW. British Geological Survey Technical Report, WA/97/02.

BRANDON, A. 1999. Geology of the Wreake valley (SK61NE, SK71NW, SK71NE and SK81NW (western part). British Geological Survey Technical Report, WA/99/17.

BRANDON, A, SUMBLER, M G, and IVIMEY-COOK, H C. 1990. A revised lithostratigraphy for the Lower and Middle Lias (Lower Jurassic) east of Nottingham, England. Proceedings of the Yorkshire Geological Society, Vol. 48, 121–141.

BRANDON, A, and CARNEY, J N. in prep. Geology of the Vale of Belvoir (SK62NE, SK72NW, SK73SW, SK73SE and SK83SW western part). British Geological Survey Technical Report, WA/00/36.

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CARNEY, J N. 2000. Geology of the Barrow-upon-Soar and Seagrave areas: 1:10 000 sheets SK51NE and SK61NW. British Geological Survey Technical Report, WA/00/21.

CARNEY, J N and COOPER, A H. 1997. Geology of the West Leake area: 1:10 000 Sheet SK52NW. British Geological Survey Technical Report, WA/97/46.

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Figures plates and tables

Figures

(Figure 1) Simplified map of the main bedrock units and geological structures.

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

(Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) Dinantian geological setting. a. Dinantian structures and depositional provinces in relation to the oil-producing areas. The locations of boreholes used in (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999).

(Figure 4) Comparative stratigraphical columns in Dinantian and Namurian strata, showing gamma-ray variation. Depths in metres from the drilling platform are shown down the left side of each record. See (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) for borehole locations and structural setting.

(Figure 5) Millstone Grit and Edale Shale strata of the Rempstone and Old Dalby boreholes, see (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) for locations, and their correlation with the Duffield Borehole of the Derby district. Named marine bands are indicated by italicised script. The gamma-ray log is to the left, sonic log (where available) to the right of each column. Depths in metres from the drilling platform are shown down the left side of each record (Modified from Ambrose, 1998).

(Figure 6) Summary of Westphalian stratigraphy, coal seam splits and magmatic activity (modified from Burgess, 1982).

(Figure 7) True-depth cross-section in the Coal Measures Group, from north to south, modified from an original British Coal compilation based on borehole correlations and seismic investigations. Note that for many of these boreholes, the classification of igneous rock types is regarded as tentative. See (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) for borehole locations and structural setting.

(Figure 8) Comparative stratigraphical columns in the Lower Coal Measures, with selected coal seams. Depths in metres from the drilling platform are shown down the left side of each record. See (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) for borehole locations and structural setting.

(Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) Comparative stratigraphical columns in the Lower Coal Measures and Saltby Volcanic Formation, showing selected coal seams and volcanic facies. For borehole locations, see (Figure 13)." data-name="images/P946224.jpg">(Figure 12).

(Figure 10) Sequential palaeogeographical maps of the Lower Coal Measures in the eastern part of the district, showing the influence of the Saltby Volcanic Formation lava pile on the deposition of strata between the Tupton and Joan/Brown Rake coals (diagrams and interpretations are from Sheppard (2003)).

(Figure 11)Comparative stratigraphical columns in the Middle and Upper Coal Measures, showing selected coal seams. Depths in metres from the drilling platform are shown down the left side of each record. See (Figure 4), (Figure 7), (Figure 8) and (Figure 11) are also indicated. b. Principal early Carboniferous tectonic features of the region, with outline of the Melton Mowbray district (modified from Berridge et al., 1999)." data-name="images/P946215.jpg">(Figure 3) for borehole locations and structural setting.

(Figure 13)." data-name="images/P946224.jpg">(Figure 12) Subsurface distribution of Phases 1 and 2 of the Saltby Volcanic Formation, and of the Asfordby Volcanic Formation, based on available borehole evidence, showing the locations of boreholes featured in (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9) and (Figure 13).

(Figure 13) Comparative stratigraphical columns showing the lateral relationship between the Asfordby Volcanic Formation and adjacent strata of the Millstone Grit Group and Lower Coal Measures. For borehole locations, see (Figure 13)." data-name="images/P946224.jpg">(Figure 12).

(Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14) Stratigraphical column and gamma-ray variations through Phase 2 basaltic lavas and volcaniclastic rocks of the Saltby Volcanic Formation proved in the Grimmer Borehole. The stratigraphical positions of selected petrographical samples (‘E’ numbers) and (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 13)." data-name="images/P946224.jpg">(Figure 12)." data-name="images/P946221.jpg">(Figure 9).

(Figure 15) Areal distribution of basic intrusive sills in the subsurface around and to the north of Asfordby. a) in the Lower Coal Measures, and b) in the Middle Coal Measures.

(Figure 16) Comparative stratigraphical columns illustrating lithological and gamma-ray variations (higher values to the right) in Permian strata from north to south across the district. The red lines denote geophysical marker horizons that can be correlated between boreholes; two have been numbered to show their position across the diagram. Depths in metres from the drilling platform are shown down the right side of each record.

(Figure 17) Comparative stratigraphical columns in the Mercia Mudstone Group, with gamma-ray variations indicated on the left side of each record, and depths in metres from the drilling platform on the right. A proposed new lithostratigraphical scheme for the Mercia Mudstone (Howard et al., in prep. (b)) is shown at extreme left. For borehole locations, see (Figure 16).

(Figure 18) Variations in clay mineralogy relative to stratigraphy in the Mercia Mudstone Group of the Asfordby Hydro Borehole (determinations by S J Kemp).

(Figure 19) Stratigraphical and biostratigraphical column in the Lias Group, from the Barnstone Member to the top of the Marlstone Rock. Modified for the Melton district using information from Brandon et al. (1990) and Berridge et al. (1999). The relative magnitude of the topograhical features formed by the beds is indicated on the left of the column. The graduated scale on the right is in 10 metre intervals and mainly refers to stratal thicknesses in the Grantham district.

(Figure 20) Comparative stratigraphical columns in the Scunthorpe Mudstone Formation and lower part of the Charmouth Mudstone Formation, with gamma-ray and sonic logs on the left and right, respectively, of each column. Depths in metres from the drilling platform. For borehole locations, see (Figure 16).

(Figure 21) Rose diagram of current directions measured from foreset inclinations in the Marlstone Rock Formation exposed to the east of Holwell, at Brown’s Hill Quarry, and in the small quarry immediately to the north [SK 7415 2368]. The radius of arc of each class sector is proportional to the number of readings in the class (n = 32).

(Figure 22) Distribution of principal geomorphological domains in the Melton Mowbray district.

(Figure 23) The course of the Bytham valley near Melton Mowbray (modified from Brandon, 1999). All heights are in metres above OD.

(Figure 24) River terrace thalwegs (long profiles) in the Wreake valley (from Brandon, 1999). Most of the place names are indicated on (Figure 23).

(Figure 25) Schematic section of a typical profile through a periglacial Slope Terrace Deposit of the Vale of Belvoir, as revealed by pitting in the Harby–Hose area (see Brandon and Carney, 2000). The scale is approximate.

(Figure 26) Geomorphology, and distribution of the Quaternary deposits in the Vale of Belvoir, excluding thin belts of Flandrian alluvium and colluvium (modified from Brandon and Carney, 2000).

(Figure 27) Map showing the inferred incrop of Carboniferous strata and selected major Variscan structures truncated at the Permo-Triassic unconformity. The compilation is modified from a BPPD interpretion using borehole and seismic information (1977; E/GL/77/31).

(Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28) Geophysical summary map, showing Bouguer gravity anomalies (black contours), Magnetic highs (red hatching), principal lineaments (dashed blue lines) and line of section ABCD (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text.

(Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29) Bouguer gravity anomalies, magnetic anomalies and modelled section along line ABCD (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Numbered features G1-2 and M1-6 are gravity and magnetic features referred to in the text." data-name="images/P946240.jpg">(Figure 28) and (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above.

(Figure 30) Coloured relief image of magnetic, horizontal gradient data. The data north of grid line 315 km N are from the HI-Res1 survey and have been reduced to pole (transformed so that the anomaly should overlie the source). The data have been manually de-cultured, although some anomalies of non-geological origin may still exist. The line of section ABCD refers to the geophysical model shown in (Figure 30). Solid colour polygons have been defined from seismic data (information from T C Pharaoh). Physical properties used to compute the model are listed in the table above." data-name="images/P946241.jpg">(Figure 29). Abbreviations: M Mountsorrel Complex; NHF Normanton Hills Fault; SF Sileby Fault.

Plates

(Front cover) Belvoir Castle stands on a small outlier of Lower Jurassic strata, the Dyrham Formation underlies the middle and lower slopes, and the Marlstone Rock Formation forms the top of the hill. The walls of the castle are built largely of ‘Sandrock’, a ferruginous sandstone bed that is widely developed at the top of the Dyrham Formation. View from the northwest [SK 820 337] (Photographer Caroline Adkin; MN39938).

(Plate 1) Sample of heterogeneous facies in Melton Mowbray Granodiorite from the Kirby Lane Borehole. Scale: core is 9 cm in width (GS1198).

(Plate 2) Core sample (JNC 868) of peperite breccia from the Asfordby Volcanic Formation at 535 m depth in the Welby Church Borehole. A large clast of fine-grained basalt with curviplanar outlines and chilled margins is enclosed within an emulsion-textured matrix consisting of chlorite-rich mudstone (black areas) and irregular masses of basaltic scoria (pale green areas). Sample is 205 mm in length (GS1199).

(Plate 3) Core sample (JNC 856) of matrix-rich part of a peperite breccia in the Saltby Volcanic Formation, from 700.5 m depth in the Grimmer Borehole, see (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14). The black areas represent a sedimentary component of mudstone, which also occurs as larger clasts, some of which are rimmed. Intimately mixed with the mudstone are wispy to globular masses (pale yellow-grey areas) of basaltic scoria. Sample is 150 mm in length (GS1200).

(Plate 4) Core sample of Saltby Volcanic Formation pillow breccia, from 679 m depth in the Grimmer Borehole, see (Plate 3) and (Plate 4) are shown. Double-headed arrows represent the intervals where core sample is available for examination. The base of the local Phase 2 volcanic sequence is estimated to lie just below this column, see (Figure 9)." data-name="images/P946226.jpg">(Figure 14). Note the amoeboid outline of the pillow fragment at centre/right, and the chilled margin of the fragment to upper left of this. The matrix is of very coarse to lapilli-grade basaltic hyaloclastite. Sample is 150 mm in length (GS1201).

(Plate 5) Some fossils of the Lias Group, mainly found in the Scunthorpe Mudstone Formation (GS1202). The actual dimensions are in brackets. a) Psiloceras (50 mm); b) Cardinia listeri (50 mm); c) Caloceras (80 mm); d) Liostrea (120 mm); e) Gryphaea arcuata (55 mm); f) Plagiostoma (110 mm); g) Pseudopecten (65 mm); h) Schlotheimia angulata (65 mm); i) Pentacrinus ossicles and columnals (10 mm ossicles); j) Calcirhynchia (13 mm).

(Plate 6) Lias Group fossils commonly found in the upper Scunthorpe Mudstone Formation, and the Charmouth, Marlstone Rock and Whitby mudstone formations (GS1203). The actual dimensions are in brackets. a) Gryphaea maccullochii (90 mm); b) Oxytoma (Pteria) inequivalvis (25 mm); c) Hippopodium (60 mm); d) Gagaticeras (35 mm); e) Gryphaea cymbium (70 mm); f) Arnioceras semicostatum (45 mm); g) Tetrarhynchia (27 mm); h) Astarte (20 mm); i) Dactylioceras annulatum (72 mm).

(Plate 7) Neotype of the pliosaur Rhomaleosaurus megacephalus, locally called the ‘Barrow Kipper’, which measures 5.3 m from tip to tail. It was purchased in 1851 from one William Lee and was found in or near to Barrow upon Soar, at a former limestone working, the location of which is uncertain (information from M. Evans of Leicester City Museums, 2000). This photograph is reproduced with kind permission of the Curator of the New Walk Museum at Leicester, where the specimen (LEICT G221.1851) is currently housed (GS1204).

(Plate 17)." data-name="images/P946251.jpg">(Plate 8) Strata of the Barnstone Member exposed in a former limestone quarry at Langar (GS1205). Note the pale grey, laminated calcite-mudstone (‘cementstone’) beds. See also, (Plate 17).

(Plate 9a) Photomicrographs of lithologies in the Marlstone Rock Formation, described by G K Lott (written communication, 2001; (GS1206)). In Brown’s Hill Quarry, Holwell; calcareous ironstone from the top of the basal massive ironstone facies. It is dominated by fine to medium-grained, ferruginous oolitic grains with bioclastic fragments (bivalves and echinoids). The rock shows pervasive oxidation to yellow-brown limonite. Field of view is c.1.0 mm.

(Plate 9b) Photomicrographs of lithologies in the Marlstone Rock Formation, described by G K Lott (written communication, 2001; (GS1206)). From a roadside quarry near Branston, detail of yellow-brown bioclastic ironstone. The framework grains are mainly of ferruginous oolite, which are commonly deformed and pervasively oxidised; they are accompanied by bivalve and echinoid debris and forasmininera tests. The field of view is approximately 1 mm.

(Plate 10) Cross-bedding in bioclastic ironstone of the Marlstone Rock Formation at Holwell Quarry, see (Figure 21) for current direction analysis; (GS1207). Note the abundance of white crinoidal debris, here seen mainly in cross-section.

(Plate 11) Massive ironstone of the Marlstone Rock Formation, with pale grey, weathered-out brachiopod clusters, exposed by the roadside east of Branston (GS1208).

(Plate 12) Laminated, fissile mudstones of the Whitby Mudstone Formation exposed about 3 m stratigraphically above the Marlstone Rock Formation at Brown’s Hill Quarry (GS1209). These mudstones are barren of calcareous microfauna and ostracods, and are of probable dysaerobic facies (Wilkinson, 2002).

(Plate 13) Ooidal and bioclastic muddy limestone from the Lower Lincolnshire Limestone exposed in Waltham (Stonesby) Quarry [SK 813 251] (GS1210). The texture is that of a lime mudstone to packstone, with sporadic grainstone patches (Dunham, 1962). As well as shell debris, the grains include brown-rimmed ooliths, rare pisoliths and common foraminifera. Large, sharp-sided, mudfilled burrows disrupt the fabric in the lower part of the rock. The uppermost part of the slab (not seen) is a bored hardground or omission surface along which truncation of grains has occurred (written communication, G K Lott, 2001). The area viewed here is 80 mm in width.

(Plate 14) River Soar floodplain south of Barrow, taken on the 9 November, 2000, about 48 hours after the main flood peak. The view is to the south-east and covers the junction of the canal (bottom and left of photo) with a meander loop of the main Soar channel converging from the right [SK 577 167]. Meadow View Farm is to right of canal at bottom edge of the picture. The emergent area at upper right defines the Hemington Terrace, which is also distinguished by its ancient, ridge and furrow cultivation pattern. The alluvial tract of the modern River Soar floodplain is incompletely flooded to the left of the terrace, probably because material had been added to it during deepening and canalization of this part of the river. Photograph by S Footit, Nottingham Evening Post; (GS1211).

(Plate 15) Trial pit in the Harby–Hose area [SK 747 330], showing a profile through Slope Terrace Deposits of the Langar Head (GS1212). The topsoil is underlain by a c. 0.5 m thick layer of ochreous sand and gravel. This rests on 1 m of sheared clay with a prominent basal slickensided zone (shear planes are in blue-grey clay). Brecciated clay lies beneath the latter. Scale bar shows 1 cm graduations. See also, (Figure 25).

(Plate 16) Slope instability features near Greenhill Farm, looking east-south-east from [SK 6945 2393]. The scarp shows a uniform mature slope with an angle of about 10°, which is cut by a series of bowls feeding active mudflows from the Charmouth Mudstone. At the foot of the scarp there is a broad apron of material formed from coalesced, degraded, ancient mudflows, mudslides and related mass movements. Photograph by A Forster; (GS1213).

(Plate 17) View of a former ironstone quarry to the north of White Lodge [SK 7835 2785]. The quarry face shows the Marlstone Rock Formation displaced and rotated by a number of small step-faults as a result of Quaternary slope instability. The throws are down to the east, in the direction of the slope down to the Waltham palaeovalley. Photograph by J Rhodes, 1931 (A05558).

(Plate 18) Circular collapse feature in ground disturbed by shallow subsurface mining for ironstone, to the east of Brown’s Hill Quarry, approximately [SK 7442 2346]. Note that the pit is being filled with domestic refuse, increasing the potential for pollutants to enter the local groundwaters. Photograph was taken in 1999; (MN31610).

(Plate 19) Quarry in the Barnstone Member at Langar [SK 735 347], in 1966, viewed looking southwards. The pale grey beds of hard, calcite mudstone, constituted the resource for cement manufacture. Photograph by G Warrington; (GS1214).

(Plate 20) Former adit entrance at Brown’s Hill ironstone quarry [SK 741 234] (GS1215).

(Back cover )

Tables

(Table 1) Summary of the geological succession of the Melton Mowbray district. Thickness range shown in brackets.

(Table 2) Summary of seam stratigraphy and thicknesses for the Lower Coal Measures. The division into geographical sectors is colour coded, and location of individual 10 000 map-sheets is shown below. Grey lines denote groups of seams that have merged, with name given at left of table, for scheme of seam mergers, see (Figure 6). Map-sheets with no proven Coal Measures are omitted from the table. ng seam present, but thickness not given.

(Table 3) Summary of seam stratigraphy and thicknesses for the Middle Coal Measures. The division into geographical sectors is colour coded, and location of individual 10 000 map-sheets is shown below. Grey lines denote groups of seams that have merged, with name given at left of table, for scheme of seam mergers, see (Figure 6). Map-sheets with no proven Coal Measures are omitted from the table. ng seam present, but thickness not given.

(Table 4) Palynomorph distribution in Penarth Group and Barnstone Member, Owthorpe 1-4 boreholes (after Orbell, 1973 table 3 and modified by G Warrington, 2001, with the author’s permission). * Names modified where appropriate, some species transferred between genera. Revision by G Warrington.

(Table 5) Correlation of the Quaternary glacigenic, fluvial and slope deposits of the district (modified from Brandon, 1999). blue - cold; glacial. green - cold; periglacial. red - warm, temperate. * 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.

(Table 6) Summary of oil well and oil field locations, reservoirs and production details (Source: Department of Trade and Industry, 2000). *DST Drill stem test.

(Table 7) Licensed groundwater abstractions in the Melton Mowbray district in m³/a (Source: Environmental Agency, May 2001).

(Table 8) Chemical composition of selected groundwater in the district.

(Table 10) are therefore intended only as a general guide to the expected behaviour of the strata described." data-name="images/P946273.jpg">(Table 9) Engineering and geotechnical properties of the Quaternary deposits of the district. Lithostratigraphically defined Quaternary deposits and bedrock may be grouped in terms of their predominant behaviour to give engineering geological units. However, it is inherent in the nature of many geological materials that they show variation in their geotechnical properties, both vertically and horizontally, due to depositional variation and to the effects of weathering. (Table 10) are therefore intended only as a general guide to the expected behaviour of the strata described." data-name="images/P946273.jpg">(Table 9) and (Table 10) are therefore intended only as a general guide to the expected behaviour of the strata described.

(Table 10) Engineering and geotechnical properties of the bedrock units. Lithostratigraphically defined Quaternary deposits and bedrock may be grouped in terms of their predominant behaviour to give engineering geological units. However, it is inherent in the nature of many geological materials that they show variation in their geotechnical properties, both vertically and horizontally, due to depositional variation and to the effects of weathering. (Table 10) are therefore intended only as a general guide to the expected behaviour of the strata described." data-name="images/P946273.jpg">(Table 9) and (Table 10) are therefore intended only as a general guide to the expected behaviour of the strata described.

(Table 11) Average and median slope angle for the scarp slope formed by the Marlstone Rock Formation, Dyrham Formation and Charmouth Formation near Old Dalby. Measured from contours on OS 1:10 000 topographic sheets SK62SE and SK72SW.

(Table 12) BGS 1:10 000 Series sheets in the district.

(Table 13) Brief details of boreholes mentioned in this report.

Tables

(Table 6) Summary of oil well and oil field locations, reservoirs and production details

(Table 7) Licensed groundwater abstractions in the Melton Mowbray district in m³/a

(Table 8) Chemical composition of selected groundwater in the district

(Table 11) Average and median slope angle for the scarp slope formed by the Marlstone Rock Formation, Dyrham Formation and Charmouth Formation near Old Dalby.

Measured from contours on OS 1:10 000 topographic sheets SK62SE and SK72SW.

(Table 12) BGS 1:10 000 Series sheets in the district.

(Table 13) Brief details of boreholes mentioned in this report.