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Geology of the Melton Mowbray district — brief explanation of the geological map Sheet 142 Melton Mowbray

J N Carney, K Ambrose and A Brandon

Bibliographic reference: Carney, J N, Ambrose, K, and Brandon, A. 2002. Geology of the Melton Mowbray district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 142 Melton Mowbray (England and Wales). Keyworth, Nottingham: British Geological Survey.

Keyworth, Nottingham: British Geological Survey, 2002.

Notes

The word 'district' refers to the area of the geological 1:50 000 Series Sheet 142 Melton Mowbray. National grid references are given in square brackets and all lie within 100 km square SK. Symbols in round brackets after litho-stratigraphical names are the same as those used on the geological map.

Acknowledgements

This Sheet Explanation was compiled by J N Carney and edited by A A Jackson. Full acknowledgements and bibliography are to be found within the Sheet Description.

The grid, where it is used on figures, is the National Grid taken from Ordnance Survey mapping.

© Crown copyright reserved Ordnance Survey licence number GD272191/2002.

Geology of Melton Mowbray district (summary from rear cover)

This Sheet Explanation provides a concise account of the area around Loughborough, Melton Mowbray, and Keyworth. The central and north-eastern parts of the district are occupied by the Vale of Belvoir. It is overlooked from the south by a more elevated, 'wolds'-type landscape of north-facing escarpments and broad, dissected, south-easterly slopes that reflect the prevailing tectonic dip of the outcropping strata. Mixed agriculture provides the main economy of the district, but in the past limestone and ironstone were quarried or mined from the Lower Jurassic strata, and there was limited coal extraction from the concealed Carboniferous strata of the Vale of Belvoir coalfield. Currently, sand and gravel is produced from glaciofluvial deposits, gypsum is mined from Triassic strata and there are two producing oil wells drawing from reservoirs in Carboniferous sandstones.

New information is provided for the 'basement' rocks, some of which according to borehole provings consist of Ordovician granodiorite. The stratigraphy of the concealed Carboniferous succession is synthesized from exploration drilling augmented by seismic surveys. Over 4000 m of these strata accumulated in the deepest part of a major syn-Dinantian structural basin, the Widmerpool Half-graben. The oldest of the outcropping strata are Triassic in age and form part of the Mercia Mudstone Group. End-Triassic sedimentation is recorded in the overlying Penarth Group, which is overlain by mudstones, thin limestones and subordinate sandstones and ironstones of the predominantly Jurassic-age Lias Group. The youngest rocks at crop are Middle Jurassic mudstones and limestones of the Inferior Oolite Group. An extensive Quaternary sequence is described, dating from pre-Anglian times. It includes various glacigenic deposits and a sequence of river terrace deposits in the Soar and Wreake valleys. Mass wasting deposits in 'clay vales' can be linked into the successive landscape cycles that produced the river terraces.

Earth science-related issues that should be considered when planning decisions have to be made are reviewed. Some of the principal factors include the physical properties of the rocks, slope stability, and the water and mineral resources of the district.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the district covered by the geological 1:50 000 Series Sheet 142 Melton Mowbray, published as a Solid and Drift geology edition in 2001. A more comprehensive account can be found in the Sheet Description (Carney et al., in press), and there is much detailed information in the individual Technical Reports (see Information sources for details).

The rocks at outcrop are of Triassic and Jurassic age with a thick cover of Quaternary deposits in places. Topography is subdued, but variation is provided by the low-lying Vale of Belvoir in the north, and to the south-east by a 'wolds' topography of escarpments and broad dip-slopes formed by resistant Jurassic strata. Much information has been gathered on the concealed geology of the district, during exploration for coal and hydrocarbons that has taken place intermittently since 1918.

Geological history

The oldest rocks, proved in boreholes, are Ordovician granodiorites that were intruded into a Lower Palaeozoic sedimentary and volcanic sequence. Resting on this 'basement' is a thick Carboniferous sequence, dominated by mudstones, that accumulated within the Widmerpool Half-graben or 'gulf'. To the north of the graben is a relatively thinner limestone-dominated sequence that developed on the Nottingham Shelf. The Coal Measures Group of the concealed Vale of Belvoir (North-east Leicestershire) Coalfield rest on these strata; they represent the deposits of a widespread delta plain, and intercalated with the coal-bearing strata in the east and south are thick alkali basalt lavas and volcaniclastic rocks. Earth movements associated with the onset of the Variscan orogeny initiated a change and the youngest Carboniferous rocks, the red beds of the Warwickshire Group, were deposited in better-drained alluvial conditions.

A prolonged period of erosion followed the uplift and faulting that signified the final stages of the Variscan orogeny. Permian and Triassic strata were deposited in arid continental conditions and include the Cadeby and Edlington formations and the Sherwood Sandstone Group. The overlying Mercia Mudstone Group represents the oldest strata to crop out in the Melton Mowbray district. It is characterised by red-brown mudstones deposited in aeolian and playa lake environments, with commercially important gypsum seams, reflecting evaporitic conditions, near the top. Continental sedimentation ended when the sea flooded the land in late Triassic times; the grey mudstone and siltstone of the Penarth Group mark this change in the depositional environment. Marine conditions persisted throughout most of the Jurassic Period, when a shallow tropical sea covered the area. The sediments deposited were predominantly fine-grained mud and silt, but the variety of other rock types indicate that conditions were variable: phosphatised fossils and bored phosphate nodules suggest periods of slow deposition and reworking, bioclastic limestones indicate higher energy conditions, and ooidal ironstones were deposited during a regression when sea level was relatively lower. The lower formations of the Middle Jurassic, Inferior Oolite Group were deposited in marginal-marine and estuarine conditions, but later a marine-barrier bar-lagoonal complex was established on which the ooidal and peloidal limestones of the Lincolnshire Limestone Formation accumulated.

Quaternary deposits conceal the solid rocks over much of the district. The most widespread is till, deposited during the Anglian glaciation; three types can be identified and indicate different directions of derivation and therefore of ice flow. Interleaved with the till are layers or lenses of glaciofluvial sand and gravel, and glaciolacustrine clay. However, the oldest Quaternary deposits predate the glaciation. These are sands and gravels of the ancient river Bytham, and the present-day Wreake follows part of this old river course. Following the glacial period, climatic fluctuations and adjustments to the regional base levels combined to produce at least five generations of river terrace deposits in the valleys of the Soar and Wreake rivers. In the Vale of Belvoir, episodes of periglacial slope wasting resulted in the formation of planoconcave solifluction terraces, collectively termed 'Slope Terrace Deposits'. More modern slope instability is indicated by land-slipped ground along the steeper escarpments, developed mainly on Jurassic mudstone (Plate 1). Of the younger Quaternary deposits, colluvium, head, and floodplain alluvium are locally extensive.

Current mineral production comes from sands and gravels of glaciofluvial and river terrace origin, and the underground mining of gypsum from adits at Barrow upon Soar. Oil is currently being produced from wells at Rempstone and Long Clawson, and coal was formerly mined from Cotgrave and Asfordby. The concealed Carboniferous succession has potential for further coal production, and during the period of the resurvey at least (1996–1999) continued to present a favourable target for hydrocarbon exploration.

Chapter 2 Geological description

Ordovician (concealed)

Ordovician granodiorites buried at shallow depths are the source of the large positive aeromagnetic anomalies (inset on Sheet 142 Melton Mowbray) to the south of the Normanton Hills and Sileby faults. They intrude a basement that is perhaps similar to the Lower Palaeozoic cleaved mudrocks and andesitic tuffs in the Sproxton No. 1 Borehole [SK 8451 2394], 1.4 km east of the district. The granodiorites are calcalkaline in composition (Pharaoh et al., 1993), and similar in chemistry to the exposed Mountsorrel Complex, just to the south-west of the district. An Ordovician (Caradocian) age is inferred, based on a U–Pb zircon determination of 451 to 452 Ma for the Mountsorrel intrusion (Noble et al., 1993).

The Rempstone Granodiorite (ReGd), below 1131.2 m depth in the Rempstone LN/10–1 Borehole [SK 5821 2405], is in tectonic contact with the Millstone Grit along the plane of the Normanton Hills Fault. It is a coarse-grained, inequigranular granodiorite with pink plagioclase crystals, up to 5 mm across, set in a pink, finer grained quartzo-feldspathic base; there are sporadic xenoliths of grey diorite up to 40 mm across. The Melton Mowbray Granodiorite was proved at 402 m depth in the Kirby Lane Borehole [SK 7324 1759], below the Millstone Grit (Marsdenian). The top few metres is a clay-rich weathered zone. Net-veining is locally developed, in which angular fragments of grey quartz-diorite are separated by narrow septa of pink aplo-granite.

Carboniferous (concealed)

In latest Devonian or earliest Carboniferous times (about 355 Ma) a period of crustal extension resulted in rifting and block-tilting. Subsiding graben with intervening shelves, or 'highs', acted as the main structural controls during the ensuing Dinantian marine transgression. Seismic interpretations (sections 2 and 3 Sheet 142 Melton Mowbray) show up to 3500 m of Dinantian strata in the southern part of the asymmetric Widmerpool Half-graben. Southwards, across the Normanton Hills Fault (Figure 12), a more attenuated Dinantian sequence characterises the Hathern Shelf (Ebdon et al., 1990), which in turn borders the Wales–London–Brabant Massif (inset, Sheet 142 Melton Mowbray) The latter is delimited by the Sileby Fault, which also confines the Dinantian subcrop. To the north of the Widmerpool Half-graben the Dinantian sequence is attenuated across the Cinderhill–Foss Bridge Flexure, the whole sequence becoming greatly condensed on the Nottingham Shelf.

The Scalford Sandstone Formation (SfdS) (Figure 1) was proved, uniquely, in the footwall of the Normanton Hills Fault at the base of the Scalford No. 1 Borehole. These strata may represent a basal Carboniferous, or even Devonian, clastic sequence deposited on the adjacent Hathern Shelf. The Milldale Limestone Formation (Mi) (Figure 1) was penetrated in boreholes on the north-eastern margin of the Widmerpool Half-graben. The sequence of bedded limestone and dolostone contains abundant cyanobacteria and the calcareous alga Parachaetetes (Riley, 1992). The top of this formation in the Plungar 8A Borehole is interpreted as an intra-Dinantian unconformity on which rests the Belvoir Limestone Formation (Bvr) and a further unconformity marks the top of the latter unit. It is overlain by the Plungar Limestone Formation (PlLs), which contains a 6 m bed of pebbly sandstone at the base. This is succeeded by younger Dinantian and Namurian strata that onlapped across the flexured north-eastern margin of the Widmerpool Half-graben.

The Widmerpool Formation (WdF) (Figure 1) is thickest, about 1000 m, in the Widmerpool Half-graben. In the Widmerpool No. 1 Borehole [SK 6366 2958], the oldest proven strata of the formation yielded an ammonoid fauna of late Asbian age {Beyrichoceras (B) zone}. The Ratcliffe Volcanic Member (RaVo) is 15 to 56 m thick, and thins eastwards. It is identified by sporadic beds of pale grey or blue, highly calcareous tuff. In the Widmerpool No. 1 Borehole, the member lies about 60 m stratigraphically above the Goniatites aff. sphaeris-striatus (P_1c) zone of the early Brigantian.

The Edale Shale Group (Esh) (Figure 1) marks the beginning of the Silesian 'postrift' sequence. The group commences at the base of the Cravenoceras leion Marine Band, and its top, lying within the Kinderscoutian stage, is taken at the appearance of the first feldspathic sandstones of 'Millstone Grit'-type. Several ammonoid biozones, spanning the Pendleian and Arnsbergian stages, have been identified by comparing geophysical borehole logs with those containing fully cored Namurian sequences elsewhere in the region. A 12 m-thick unit of graded sandstone–siltstone in Arnsbergian strata of the Rempstone LN/10–1 Borehole is an important producing oil reservoir. Sedimentation typical of the Millstone Grit Group (MG) had advanced into the district by R1 (Kinderscoutian) times and had extended southwards across the Sileby Fault by Marsdenian times. Fauna from the marine and Lingula bands, together with geophysical logs allow the Millstone Grit to be correlated in the subsurface. Some of the earliest sandstones occur in The Chase Borehole [SK 7242 2081] where intercalated mudstones contain the Reticuloceras coreticulatum Marine Band (R_1c4), indicating a late Kinderscoutian age. Stratigraphically higher faunal markers are indicated by the sections shown on Sheet 142 Melton Mowbray. Provenance studies of the four main fluvio-deltaic sandstone bodies (Hallsworth, 2000) show that southerly sources dominated deposition of the Kinderscout Grit (up to 40 m thick). Incursions of sand from the north did not commence until well into Marsdenian times (R_2b5–R_2c1) when the Ashover Grit was deposited; this is up to 36 m but generally split into two or more units. Mixed northerly and southerly sources characterise the sandstone deposited in Marsdenian (R_2c1–G_1a1) times, and represented by the Chatsworth Grit (1–48 m), and also in the Yeadonian when the Rough Rock (up to 19 m thick) was deposited.

The Coal Measures Group underlies the district to the north and east of the line on the map representing the incrop of the Subcrenatum Marine Band (SBMB). Subdivision of the Westphalian is based on the identification of three faunal horizons: the Subcrenatum, Vanderbeckei and Aegiranum marine bands, respectively, defining the bases of the Langsettian, Duckmantian and Bolsovian stages. The Langsettian corresponds with the Lower Coal Measures lithostratigraphical unit, the Middle Coal Measures includes the Duckmantian and the lower part of the Bolsovian. The base of the Upper Coal Measures is taken at the Cambriense Marine Band, within the Bolsovian, although this has not been positively identified in the district.

Near the base of the Lower Coal Measures (LCM) (Figure 2) numerous marine bands are recorded, for example in the Wilds Bridge Borehole [SK 6738 3248]. A major fluvio-deltaic episode followed, represented by the Wingfield Flags (WF), locally up to 50 m thick.

Cyclic depositional sequences dominate the Westphalian above the Kilburn Coal. A typical small-scale cycle (Guion et al., 1995) consists of basal dark grey to black, carbonaceous and commonly pyritous mudstone containing nonmarine (lacustrine) or less commonly marine fauna. This is overlain by siltstone and sandy siltstone laid down as overbank or distal lacustrine delta deposits. The top of each cycle is generally marked by a seatearth (gleysol, palaeosol) and a coal (mire facies). Sandstone beds occur only rarely at the top of the cycles; they are more common as multistorey, intercycle channel-fill bodies orientated typically north– south.

Alkali basalt lavas erupted to the east of the district may have raised the local topography, causing many interseam cycles to attenuate eastwards. For example in the Mickley group, the Blackshale and Ashgate coals merge to produce a seam 8.18 m thick, proved in the Harby Hill Borehole [SK 7644 2706]. The Low Estheria Band consists of dark grey mudstone with the crustacean Euestheria and the nonmarine bivalve Carbonicola. It forms an important faunal marker horizon, overlying the Blackshale Coal, where complex interdigitation with volcanic rocks (Figure 3) precludes accurate coal seam correlations.

The Asfordby Volcanic Formation (AsVo) (Figure 2) is locally restricted to a narrow subsurface zone around the Asfordby Colliery site [SK 210 700]. Its margins are abruptly defined against adjacent Namurian and Langsettian strata that show local soft-sediment deformation. Basaltic peperite breccias occur in over 100 m of core from the Welby Church Borehole; they were probably intruded into unconsolidated, wet, Namurian and Langsettian sediments. The Saltby Volcanic Formation (Stby) (Figure 2) is an association of extrusive subaerial basalt lavas and coarsely fragmental rocks (Burgess, 1982), but also includes peperite breccias and pillow breccias (Carney et al., 2002). During the two main phases of activity, lava flowed from centres to the east of the district and interdigitated with Langsettian strata (Figure 3). There are many basaltic (doleritic) sills in the Lower and Middle Coal Measures. The youngest sill is intruded into Middle Coal Measures strata just above the 2nd Waterloo Coal, only slightly postdating the youngest known Westphalian tuff, which occurs below the 3rd Waterloo Coal in the Thorney Plantation Borehole [SK 7165 2142]. The Middle Coal Measures (MCM) (Figure 2) commence with the Vanderbeckei Marine Band, which pinches out north-eastwards, on to the surface of the Saltby Volcanic Formation (Figure 3). The overlying strata of the Middle Coal Measures show marked attenuation to the east and individual coal seams merge, locally forming the very thick Top Bright Coal (Figure 4). Little is known about the Upper Coal Measures (UCM) (Figure 2) due to intense reddening of strata below the Warwickshire Group or Permo-Triassic beds; the Cambriense Marine Band, defining its base, has been tentatively identified only in the Stroom Dyke Borehole [SK 7139 3455].

The Warwickshire Group rests unconformably upon the Coal Measures (Figure 4) and is proved only in the extreme north-east of the district. Formerly termed the 'Barren Measures' because of its lack of exploitable coal seams, it represents a change to better drained alluvial conditions in response to intra-Westphalian tectonic uplift (Besly, 1988). In the Etruria Formation (Et) (Figure 2) varicoloured (red, purple, brown, green), ochreous siltstone with ferruginous pisoids and sedimentary structures that include ripple cross-lamination, and raindrop imprints indicate partly emergent, overbank environments. In the Halesowen Formation (Ha), micaceous, fluvial channel sandstones become more abundant in the youngest part of the sequence.

Permian (concealed)

These strata were deposited during latest Permian times, adjacent to the western edge of the Southern North Sea Basin (or Southern Permian Basin) at a time when hot, arid desert conditions prevailed. The Permian Basal Breccia (PBB) is a diachronous unit that replaces the Cadeby and Edlington formations in southern parts of the district. It represents the deposits of debris flows that filled depressions on the eroded Carboniferous landsurface, and consists of conglomerates and breccias that are red-brown to purple-brown, generally poorly cemented and matrix supported. The clasts were mainly derived from underlying Carboniferous rocks, with some acidic tuff and microgranular quartz-diorite pebbles of local basement derivation. The Cadeby Formation (CdF) represents the carbonate phase of the EZ1 Zechstein transgressive cycle (Smith et al., 1986), although in this district only marginal Zechstein facies are present. The formation consists of an equivalent of the 'Lower Marl', which comprises red-brown, muddy siltstone with mudstone and sandy laminae and thin beds of pinkish brown limestone. It is overlain by the equivalent of the 'Lower Magnesian Limestone', which consists of creamy grey to red, sandy, dolomitic limestone, siltstone, and sandstone with abundant bivalves including Bakevellia sp. and Schizodus sp. The Edlington Formation (EdF) was formed in alluvial plain, sabkha and playa lacustrine environments on the basin margin and represents the upper E1Zb cycle and the whole of the EZ2 cycle. Strata include laminated micaceous mudstone and siltstone, commonly with desiccation cracks, fine- to coarse-grained sandstone and pebbly sandstone showing small-scale fining-upward cycles. The Roxby Formation (RoF), of red mudstone or siltstone, is impersistently developed as an interdigitation within the Lenton Sandstone Formation. The equivalents farther north represent the topmost part of Zechstein Cycle EZ3 and all of cycles EZ4 and EZ5. A pronounced gamma-ray peak on geophysical borehole logs marks the top of the formation, which is taken to represent the position of the top Permian/base Triassic datum in this district.

Triassic

Triassic strata are either concealed or, if present at outcrop, poorly exposed, but the various components have distinctive geophysical signatures that allow them to be recognised in boreholes throughout the district (Carney et al., 2002). The concealed part of the Triassic begins with the Sherwood Sandstone Group (SSG). The Lenton Sandstone Formation (LnS) (Figure 5) contains a thin bed of red mudstone, identified as the Roxby Formation, thus suggesting a Permian age for the lower part of this sequence. The Nottingham Castle Sandstone Formation (NtC) is thinnest (11 m) to the south of the Normanton Hills Fault, but thickens to over 100 m in the north-east of the district. Its base may be a disconformity with the underlying Lenton Sandstone Formation. Local sources probably contributed the subangular Carboniferous limestone and volcanic clasts, and there are clasts of microgranular quartz-diorite and weakly cleaved mudrock (possibly derived from the Lower Palaeozoic basement). The Bromsgrove Sandstone Formation (BmS) is lithologically diverse and is recognised only in the west of the district.

The Mercia Mudstone Group (MMG) (Figure 5) represents a change to a mainly aeolian environment with lacustrine, playa mudflat or coastal sabkha developed locally. The average thickness is 210 m. The clay mineralogy of the group is dominated by illite and intermediate-Fe chlorite assemblages. The Sneinton Formation (Snt) is the oldest unit to crop out in the district. These strata were formerly known as 'waterstones' on account of their abundant mica, which imparts a 'watery' appearance to many bedding planes. The Radcliffe Formation (Rdc) was not recognised at outcrop, but these finely interlaminated, mud-rich strata can be identified on geophysical borehole logs. Core samples show sedimentary structures that include mud cracks, cross-lamination and load casts. The Gunthorpe Formation (Gun) gives rise typically to red or rarely green clay in ploughed fields on the outcrop. The mudstone is intercalated with numerous beds of dolomitic siltstone (0.1–0.5 m thick) that show parallel lamination, ripple cross-lamination, mudcracks, load structures and pseudomorphs after halite. Two sandstone beds can be mapped. At the base of the Edwalton Formation (Edw), the Cotgrave Sandstone Member (Cot) ranges from 1 to 7 m thick, and consists of fine- or medium-grained sandstone interbedded with mudstone. The Hollygate Sandstone Member (Hly), at the top of the Edwalton Formation, is locally up to 10 m thick, but this includes several mudstone interbeds; it has a significant content of coarse, 'millet seed' sand grains of aeolian origin. In the Cropwell Bishop Formation (Figure 5), gypsum is considerably more abundant as disseminations, veinlets and nodules. The stratigraphically lowest gypsum bed is the Tutbury Gypsum (T), up to 4 m thick. It was formerly mined underground around East Leake and is currently being extracted via an adit in the gypsum works south of Barrow upon Soar [SK 5925 1675]. At a higher level the Newark Gypsum (N), comprising several thinner seams within a vertical thickness of about 18 m, has been mined and quarried at Cropwell Bishop [SK 685 348]. The Blue Anchor Formation (BAn) is a lithologically distinctive, grey to bright green, dolomitic mudstone that was deposited in marine and fluvial/lacustrine environments.

The Penarth Group (PnG), of Rhaetian age (Rr dinoflagellate cyst biozone), crops out on the middle and upper slopes of the 'Barnstone Member escarpment', which is prominent in the west of the district. The Westbury Formation (Wby) represents the early deposits of a widespread Rhaetian transgression. It consists of fissile, dark grey mudstone with thin beds of pyritous sandstone and limestone, the latter showing desiccation cracks. The 'Rhaetic Bone Bed', just above the base of the formation, has yielded fish remains and teeth, and coprolites belonging to Ichthyosaurus platyodon and Ichthyosaurus sp. Bivalves including Rhaetavicula contorta are present at higher stratigraphical levels. The Cotham Member (Ctm) is part of the Lilstock Formation. Locally it is up to 4 m thick, but is absent from some boreholes in the south of the district. It consists mainly of pale to medium grey, slightly calcareous, olive-green weathering mudstone with thin wisps and lenticles of siltstone and very fine-grained sandstone. Fossils include an impoverished fauna of shells and, in the basal few centimetres, the branchiopod crustacean, Euestheria minuta, which is indicative of fresh to brackish water conditions. Marine microplankton are common throughout, and the member was probably deposited in a lagoonal environment with fluctuating salinity levels (Warrington and Ivimey-Cook, 1992). A thin 'White Lias' (Langport Member) facies is locally present, and in ploughed fields its presence is indicated by debris of nodular, micritic limestone from a bed above the Cotham Member.

Jurassic

The Lias Group either crops out or forms the rockhead beneath Quaternary (drift deposits) over approximately 85 per cent of the district. The strata dip at between 1º and 2º to the south-east, producing characteristic scarp and dip-slope features of varying magnitude (indicated to left side of the column in Figure 6) that are locally displaced by faulting. The group accumulated in generally warm, shallow, subtropical seas that had transgressed across much of the East Midlands. Ammonites provide good biostratigraphical control and biozones are defined with considerable precision (Figure 6), documented in detail for the equivalent strata in the Grantham district to the north-east (Brandon et al., 1990).

The Scunthorpe Mudstone Formation (SMd) (Figure 7) is a thick succession of grey, variably calcareous mudstone with numerous thin beds of limestone that locally have a rich shelly fossil fauna (Plate 2); (Plate 3), particularly near the base and in the upper part. The Barnstone Member (Figure 7) was previously termed 'Hydraulic Limestone' on account of its former importance for cement-making (e.g. Lamplugh et al., 1909). It contains strata that mark the base of the Jurassic Period, which is defined at the level where ammonites of the genus Psiloceras first appear. This datum occurs a few metres above the base of the Barnstone Member; thus the basal ('Pre-Planorbis') beds are latest Triassic in age. The overlying, ammonite-bearing grey mudstone contains numerous limestone beds, between 0.1 and 0.3 m thick; they are poorly exposed but can be seen at Barrow upon Soar Station [SK 5780 1720] and in the disused quarry at Langar [SK 7352 3499] (Plate 5). In the many former limestone quarries around Barrow-upon-Soar the shelly faunas of the Barnstone Member are accompanied by marine vertebrate remains famed for their soft tissue preservation. (See review in Carney et al., 2002). The Barnby Member consists mainly of blue-grey, faintly laminated mudstone with sporadic beds or ellipsoidal concretions of pale grey micritic limestone with shelly fossils in places. The Granby Member is the oldest Scunthorpe Mudstone unit to show deposition in conspicuous cycles; each cycle consists of basal laminated mudstone passing upwards, as oxygenation of the water improved, to calcareous mudstone and thence to bioturbated and commonly richly fossiliferous limestone. Named units (Figure 7) consist of groups of individual limestones that are typically about 0.1 m thick. The hard, shelly and bioclastic varieties (packstone and packstone/grainstone) are sparsely distributed, occurring as lenses, but they are durable and form most of the brash seen at outcrop. The Beckingham Member contains a single division, the Dry Doddington Nodule Bed, distinguishable in ploughed fields by scattered calcite-mudstone nodules. A feature-forming mudstone bed at the top of the member (Figure 6) contains numerous phosphate nodules, together with phosphatised ammonites. The Foston Member approximates to the strata formerly known as the 'Ferruginous Limestone' (Lamplugh et al. 1909). It marks a reversion to cyclic mudstone-limestone deposition, but the limestone units (named and described in Figure 7) become increasingly influx of terrigenous material, possibly due to the proximity of the shoreline. At several levels there are laterally persistent mudstone beds with numerous phosphate nodules and phosphatised ammonites; these and other shell debris are shot with minute borings,msuggestive of increased reworking at times of condensed deposition. The beds named as the Stubton Limestones were formerly known as the 'Plungar Ironstone' and were worked at Barkestone-le-Vale [SK 7785 3484]; [SK 7833 3492]; at surface the soil is a characteristic rich, rusty brown, silty loam. The highest bed of the Stragglethorpe Grange Limestone forms a poorly defined dip-slope covered with a finely sandy loam.

The Charmouth Mudstone Formation (ChM) (Figure 8) crops out most extensively along the slopes of the prominent scarp that is capped by the Marlstone Rock Formation. The faunal stages are well documented for these strata (Figure 6) in Brandon et al. (1990). The Glebe Farm Bed is mainly detected by ditch diggings of siderite-mudstone with abundant ferruginous ooids. Fragments of siderite-mudstone nodules, typically 0.05 to 0.1 m across and with the ammonite Gagaticeras sp., were dredged from one ditch [SK 7853 3286]. They belong to the overlying Sand Beck Nodule Bed, which is not easily differentiated in this district. The Brandon Sandstone (Figure 8) forms little or no brash, although it gives rise to a very distinctive sandy soil. It is a buff-weathering, fine-grained calcareous sandstone with scattered specks of mica and abundant burrows. The Brandon Sandstone is separated from the Loveden Gryphaea Bed by 25 m of mudstone that contains layers with phosphate nodules and abundant large, ovoid, argillaceous limestone nodules. The Loveden Gryphaea Bed (Figure 8) can be recognised in ploughed fields and ditches by abundant fossils including the bivalve Gryphaea. Above the Jericho Gryphaea Bed (Figure 8) occur grey mudstone with sporadic calcite-mudstone nodules. Both the Loveden and Jericho gryphaea beds contain a small component of platy, bioclastic limestone.

The Dyrham Formation (DyS) (Figure 8) crops out on the upper slopes of the escarpment capped by the Marlstone Rock Formation and its natural exposures are mainly small sections in landslip backscarps. Some beds contain siderite-mudstone nodules, and there are impersistent beds of well cemented, fossiliferous sandstone and ferruginous limestone. At the top, and commonly seen in sharp contact with the overlying Marlstone Rock Formation, is the 'Sandrock', typically consisting of calcareous sandstone, ferruginous sandstone and shell-detrital wackestone with a siderite mudstone matrix. The Marlstone Rock Formation (MRB) (Figure 8) is relatively resistant to erosion and forms a cap to the escarpment that overlooks the Vale of Belvoir. On the broad dip-slopes, ploughed fields show abundant ironstone brash in soils of a distinctive deep orange-brown colour. The original constituents, of chamosite (berthierine) ooids (Whitehead et al., 1952) and sideritic cement, are now altered to limonite which imparts the rusty brown colours. Most of the outcrop was quarried away during the late 19th and early 20th centuries, when numerous exposures were created. At the Brown's Hill Quarry SSSI, Holwell, the Marlstone Rock Formation, locally with a basal pebble bed, rests sharply on 'Sandrock' of the underlying Dyrham Formation. Here the Marlstone includes 3.3 m of cross-bedded, shell-detrital and ooidal ironstone (Plate 4); foresets indicate that the depositional currents flowed towards the east-south-east and south-east. Broken and abraded belemnite debris are scattered on the topmost bedding plane suggesting a non-sequence at the junction with the overlying Whitby Mudstone Formation. In the quarry east of Branston, the Marlstone is a massive, finely limonite-ooidal and shell-fragmental ironstone with conspicuous nests of brachiopods and sporadic belemnites. The Whitby Mudstone Formation (WhM) (Figure 8) rests sharply upon the underlying Marlstone Rock. At Brown's Hill Quarry the lower part of the formation consists of well laminated, olive-green to dark blue-grey, fissile mudstone.

The Inferior Oolite Group was deposited in early Aalenian (early Middle Jurassic) times. The Northampton Sand Formation (NS) (Figure 9) underlies broad dip slopes in the east of the district, around Waltham [SK 805 247] and Lings Hill [SK 815 282]; it was formerly known as the 'Northampton Sand Ironstone Formation'. In this district, it is represented by a sand-rich facies and the grade was insufficient for exploitation as iron ore. The outcrop is marked by dark reddish brown, sandy loam soils with abundant brash of hard, limonite-cemented quartzose sandstone and ooidal ironstone. The Grantham Formation forms the low scarp just below the Lower Lincolnshire Limestone. Sandy and clayey loam soils are developed on the Grantham Formation; brash consists of mottled greenish grey and bluish grey, commonly fissile mudstone. To the north-west of Stonesby [SK 8166 2489] there is a prominent sandstone at the top, over 1.5 m thick. The Lincolnshire Limestone Formation is represented at outcrop by the informally named Lower Lincolnshire Limestone (LLL) (Figure 9), which crops out on the high plateau between Waltham and Croxton Kerrial. It forms long, eastwards-facing dip-slopes characterised by pale brown, clayey soils strewn with abundant tabular brash of cream-coloured limestone. In Waltham Quarry [SK 813 252] (Stonesby Quarry or Bescaby Lane Quarry), the few remaining exposures of the higher beds commonly show coarse ooidal and bioclastic muddy limestone, with local hardgrounds developed in well cemented, pale brown 'calcarenite'. A rich marine fauna consisting mainly of lamellibranchs with gastropods, brachiopods, echinoderms and corals has been identified in the Lincolnshire Limestone (Lamplugh et al., 1909). The Upper Lincolnshire Limestone (ULL) is inferred to subcrop beneath the Quaternary in the east; 18 m of equivalent strata were proved in a borehole [SK 8324 2772] just east of the district.

Quaternary

The Quaternary Period, covering approximately the last two million years, is marked in Britain by extreme oscillations of climate, ranging from periods dominated by severely cold glacial or periglacial to mildly temperate conditions. These oscillations are reflected in the scheme of marine oxygen isotope stages, to which the Quaternary deposits (Drift) are tentatively referred on (Figure 10). The oldest of these sediments predate the Anglian glaciation, and are thus the Pre-glacial Deposits. They comprise the Bytham Sands and Gravels, representing the main channel and river terrace deposits of the east-flowing Bytham palaeoriver. Its trunk stream e.g. [SK 780 211] and tributary valleys have courses outlined by hachuring on Sheet 142 Melton Mowbray. The continental ice sheets that advanced across the district during the Anglian cold stage destroyed this topography. The resultant glacial deposits, summarised in (Figure 11), include, in the south of the district, a stratified sequence, up to 60 m thick, which filled the Bytham palaeovalley. A trans-Pennine lobe of the ice sheet advanced first, depositing the Thrussington Till; striae seen locally on the underlying bedrock surface suggest ice movement from the north-north-west. A further ice lobe encroached slightly later, depositing the Oadby Till. Though its clayey matrix is dominantly brown to dark grey in colour, it is locally a red-brown Triassic-rich variant, suggesting some mixing with the Thrussington Till. Striations on underlying bedrock, prove that the normal grey-facies of the Oadby Till was deposited by ice moving from the east-north-east. An earlier variant, Lias-rich Oadby Till, is locally developed and probably represents material brought by ice travelling along the Jurassic outcrop, from the north-north-east. The Rotherby Clay is a tabular body of fine-grade sediment laid down after the Thrussington Till, probably in a large proglacial or subglacial lake formed within the remains of the Bytham palaeovalley, prior to advance of the ice that deposited the Oadby Till. Other Glaciolacustrine deposits were laid down in bodies of standing water, and are commonly associated with glaciofluvial deposits. The Wigston Sand and Gravel is a nearly continuous sheet of glaciofluvial deposits intercalated between Rotherby Clay and Oadby Till in the Wreake valley area. The presence of abundant flint fragments suggests it represents proglacial outwash of the Oadby ice as it advanced into the Bytham palaeovalley. Other glaciofluvial deposits (Figure 11) have a patchy distribution and many of the narrower outcrops represent the fill of palaeochannels. For example the east–west-trending Fox Hill palaeochannel contains up to 13 m of glaciofluvial sand and gravel intercalated with layers of red, laminated, glaciolacustrine clay. Quarrying of this deposit south of East Leake [SK 562 247] exposed flint-free gravels with northerly derived clasts that include chert and silicified Carboniferous limestone. A younger generation of glaciofluvial deposits, rich in flint, forms spreads around Ruddington [SK 57 32]. It is also seen at the base of the Oadby Till extending from Walton on the Wolds [SK 5960 1980] to near Tithe Farm [SK 5830 1872].

The present-day drainage of the district was initiated along meltwater routes during the waning phases of the Anglian glaciation. The River Terrace Deposits are later fluvial sediments that now occur as flights of terraces along the main valleys such as the Soar and Wreake. They were formed under a wide range of conditions and record episodic climate change, coupled with continuing regional isostatic uplift that produced successive lateral and vertical incision from Anglian through to Flandrian times (Figure 10). The terrace deposits are of variable thickness and lithology (Figure 11). Stone clasts vary between the two main valleys, although 'Bunter pebbles' and shattered flints are always prevalent. The Hemington Terrace and to a lesser extent the Syston Terrace are only slightly raised above the alluvium and are considered as part of the Soar and Wreake floodplains.

Periglacial slope-wasting processes, involving solifluction, occurred during the Anglian glaciation and the cold periods that followed. They helped to promote the development of head as the Slope Terrace Deposits (Figure 11) of clay vales such as the Vale of Belvoir and the smaller Stapleford vale south-east of Melton Mowbray. These mudstone vales contain up to three planoconcave solifluction terrace levels, which can be correlated with named fluvial terraces of the adjacent river valleys (Figure 10). Blown Sand (Figure 11) probably dates to Late Devensian and may have been derived from unvegetated Triassic outcrops in this part of the East Midlands. It occurs banked up along the lower parts of deeply cut coombes within the Marlstone Rock dip slope in the Belvoir area, where it has been worked locally [SK 801 323]. Only the thicker deposits of Head are shown on the map. It is mostly a Flandrian accumulation of colluvium or surface hill wash that has not reached the floodplain. It is almost ubiquitous on low-lying ground, where it floors the many narrow valleys of the district. It is generally sandier and lighter in texture than the periglacial head, with layers of fluvial sand and/or organic-rich material.

Flandrian (Recent) deposits of Alluvium (Figure 11) underlie the seasonally flooded tracts, water meadows and meander belts of the main rivers and tributary streams. Lacustrine Deposits floor certain shallow bedrock depressions, such as the Ruddington–Gotham–Bunny 'Moor' [SK 550 297]; the formation of the moor is commonly attributed to dissolution-induced subsidence above the gypsiferous Cropwell Bishop Formation. Shell Marl, found at Flawforth [SK 587 333], predates the adjacent alluvium and is probably early Flandrian in age.

Landslips occur along many of the steeper slopes underlain by argillaceous bedrock or clayey superficial drift deposits, producing areas marked by hummocky landforms. Natural land slippage along the Marlstone Rock escarpment, overlooking the Vale of Belvoir (Plate 1), is commonly associated with spring lines in the Dyrham and Marlstone Rock formations. It has involved large-scale rotational movement in the bedrock, with the toe-zones grading into mudflows revealed by the presence of lobate features and semi-circular backscarps. To the south-east of Long Clawson, a multiple retrogressive rotational failure on the east side of Brook Hill railway tunnel [SK 746 265] may have been triggered by excavation of the ground in front of the tunnel. On the escarpment of the Middle Jurassic cuesta a large area of natural slippage extending from south of Eaton [SK 79 28] to Croxton Kerrial [SK 82 29] includes coalescing backscars, associated mudflow lobes and back-tilted rotational slips.

Artificially Modified Ground has been mapped where human influences have changed the natural topography and physical character of bedrock and superficial drift deposits. Material that has been deposited on a natural or modified ground surface is shown as Made ground; this includes industrial sites, road and railway embankments, colliery and quarry spoil tips and landfill sites. Made ground is most extensive, if not ubiquitous, in the main urban centres. Infilled ground comprises areas where excavations have been partly or wholly backfilled, such as workings for sand and gravel, ironstone, brick clay and disused railway cuttings. The infilling materials may include excavation and overburden waste, construction and demolition materials, domestic refuse and industrial waste. In places where no surface indication of the original void has remained, the delineation of infilled ground relies on archival sources and may thus be imprecise. Worked ground represents those voids from which natural material has been extracted, for example open quarries and pits, road and railway cuttings and general landscaping. Disturbed ground is not shown on the 1:50 000 Series map for reasons of clarity, but is shown on the 1:10 000 Series maps. It is an important category of modified ground, and may include areas that have been mined on more than one occasion. Examples are where the Barnstone Member has been worked for limestone, either by quarrying or, as around Barrow upon Soar, by shallow subsurface techniques. Small areas of the Marlstone Rock that were undermined at shallow depths are also marked as Disturbed ground, for example to the east of Brown's Hill Quarry near Holwell [SK 744 234], where crown-holes periodically form over collapsed pillar and stall workings. Landscaped Ground is shown only on the 1:10 000 Series maps.

Structure

The most important structures are the Normanton Hills and Sileby faults. The aeromagnetic anomaly map inset on Sheet 142 Melton Mowbray shows that their sinuous, predominantly west-north-west orientations reflect deep-seated fracturing around the margins of Ordovician-age plutons, such as the Rempstone and Melton Mowbray granodiorites. Those plutons, as well as major faults and cleavage domains formed during the Caledonian (Acadian) orogeny (Siluro-Devonian) (Carney et al., 2002), have acted as 'formers' for the structures generated during the subsequent Carboniferous and Mesozoic/Cainozoic tectonism.

Early Carboniferous extension formed a deep asymmetric basin, the Widmerpool Half-graben, and the adjacent Hathern Shelf (see inset on Sheet 142 Melton Mowbray). Seismostratigraphical studies (Ebdon et al., 1990) indicate that the Dinantian 'syn-rift' fill to the Widmerpool Half-graben consists of wedge-shaped sedimentary packages of Tournaisian to Brigantian age. These strata thicken southward, toward the hanging wall of the Normanton Hills Fault (Figure 12) which has an estimated aggregated, syn-Dinantian, northerly downthrow of about 3500 m. The opposite, northern margin of the Widmerpool Half-graben is by contrast a faulted monocline, the Cinderhill– Foss Bridge Flexure. The entire Dinantian sequence thins across it, to about 350 m on the Nottingham Shelf, which includes strata of early Chadian to Brigantian age.

The Hathern Shelf, to the south of the Widmerpool Half-graben, also has a relatively thin sedimentary fill. It is bounded by the Sileby Fault, which had an aggregate syn-Dinantian northerly downthrow of at least 1750 m. Seismic evidence indicating that Dinantian sedimentation was confined within the Hathern Shelf to the north of the Sileby Fault is corroborated by the Kirby Lane Borehole [SK 7324 1759], which proves Millstone Grit directly overlies basement granodiorite.

By early Namurian times the East Midlands lay within a post-rift tectonic regime of more uniform subsidence. The rifted Dinantian basins were progressively filled with sediment, which spread out across their margins later in the Namurian, as the Millstone Grit deltas advanced across the region. Continued subsidence culminated in the widespread delta plain environments of the Westphalian Coal Measures. Residual tectonism is nevertheless implied by alkali-basalt magmatism of the Asfordby and Saltby volcanic formations.

End-Carboniferous basin inversion was a response to the final phases of the Variscan orogeny across southern Britain. In this district, the 'red-beds' of the Warwickshire Group were deposited in better-drained conditions created by the initial intra-Westphalian tectonic uplifts (Besly, 1988). Subsequent and larger Variscan movements reversed the throw of the earlier Dinantian faults that controlled the Widmerpool Half-graben and Hathern Shelf, 'inverting' the Coal Measures basin. The principal inversion structures, which have furnished traps for oil accumulation, include the Rempstone Anticline (Figure 12) formed within a zone of compression and reverse movement along the Normanton Hills Fault. Farther north, reactivation of the Cinderhill–Foss Bridge Flexure produced a swarm of west-north-westerly fault systems, some with throws of up to 150 m, which is significantly in excess of the post-Jurassic rejuvenated extension that is mapped at the surface. The Plungar Dome is a broad interference structure formed by the interplay between north-west and north-east structural trends.

Post-Jurassic deformation caused regional south-easterly tilting of the Mesozoic strata, as well as folds and flexures formed locally along faults, many of which were rejuvenations of Carboniferous or even 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]. The Normanton Hills Fault, with its plethora of parallel faults and associated flexures, forms a complex that splays into two main strands east of Six Hills [SK 654 204]. Near Hoton [SK 575 327] the fault downthrow is 80 m to the north. The adjacent Triassic and Jurassic strata are folded across a compressional structure that is a rejuvenation of the Rempstone Anticline, indicating that at least one episode of post-Jurassic reverse movement occurred along the Normanton Hills Fault. A swarm of post-Jurassic north-westerly faults, which include the Foss Bridge Fault, generally have throws of 5 to 25 m, and many are rejuvenated Variscan structures that formed along the Cinderhill–Foss Bridge Flexure. The latter is locally cross-cut by north-east-trending faults and folds, particularly the strata above the Variscan-age Plungar Dome. The north-easterly faults represent a basement control that is most strongly imprinted in areas of shallower Carboniferous and Mesozoic cover.

It should be noted that geological faults in this district are of ancient origin and are currently inactive. However, in common with other parts of Britain this district is affected from time to time by earthquakes (p.31).

Periglacial structures include cambering that either accentuates the regional south-eastwards dips, or 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]. Cambering and superficial faulting in Anglian times is indicated by the complex faulting along the partially exhumed slopes of sediment-filled palaeovalleys; for example, due west of Waltham on the Wolds [SK 800 255] (see also Lamplugh et al., 1909, fig. 4). Complex fold structures in mudstones are another manifestation of periglacial activity that are visible in the stream beds of certain wide valleys [SK 6169 1668].

Chapter 3 Applied geology

Geological factors have played a significant role in the development of the Melton district, and should always be taken into account during or before urban, industrial or rural planning processes. Natural variations in ground conditions can occur 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. The mineral resources of the district have locally influenced development, in areas around Barrow upon Soar, Asfordby, Cotgrave and along the belt of mines and quarries that follows the Marlstone Rock outcrop. 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, if necessary, prior to 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.

Mineral resources

Current and past mineral extraction in the district is summarised in (Figure 13). The economics of underground mining are unlikely to be favourable in the near future, so that with the notable exceptions of gypsum and oil, potential resources are those which can be won at or near to the surface. The main factors hindering extraction are significant thicknesses of overburden, including Quaternary deposits and man-made deposits, sterilisation of resources by urban development and conflicts with other forms of land-use, with possible detrimental effects on the landscape. In addition, the extraction of mineral resources may lead to problematical engineering ground conditions, depending on the types and methods of backfill, and can act as a constraint to future development of a site. Surface mineral workings, such as quarries or pits that have remained open, represent an important resource as they may provide a suitable repository for waste disposal or may be re-opened for further mineral extraction (Plate 5). The increasing use of abandoned workings for waste disposal has the potential for producing a localised hazard from toxic leachates and dangerous gases. This can be a particular problem where infilled workings are located on substrates that are in hydraulic continuity with a floodplain or a bedrock aquifer. Quarries may also furnish conservation sites with educational, recreational and wildlife value, however (see below).

Water resources and flooding

Springs issue mainly from the base of the Lias Group (Barnstone Member) and the base of the Marlstone Rock Formation that, historically, supply Melton Mowbray. Groundwater is supplied mainly from deep boreholes that tap the major aquifer of the Sherwood Sandstone Group, in the west and north of the district. Yields are unpredictable (maximum 17 litres per second on test), and water quality is variable. The Mercia Mudstone generally acts as an aquiclude, but the interbedded sandstones can provide sustainable yields if not over-pumped (about 1 l/s). Local and small supplies have also been obtained from limestone beds within the various formations of the Lias Group, the Brandon Sandstone and the 'Sandrock' that occurs at the top of the Dyrham Formation (Figure 6). The Marlstone Rock and Northampton Sand formations have been exploited for water where the aquifer is confined; the former yields up to 14 l/s of hard, commonly ferruginous water. Useful local water supplies have also been obtained from the Quaternary deposits, particularly the Bytham Sands and Gravels (up to 4 l/s). Higher and more sustainable yields were obtained from the River Terrace Deposits (up to 7.6 l/s) and alluvium. On floodplains these constitute an interconnected aquifer in hydraulic continuity with surface water in the main river channels. Such supplies are therefore prone to pollution.

The district receives between 600 and 700 mm of rainfall annually and surface water is conveyed through the large floodplains and tributaries of the rivers Wreake/ Eye and Soar. Numerous smaller valleys feed these in turn; many are moderately incised and the streams can be prone to flash flooding. More widespread and severe floodplain inundation of the Soar and Wreake valleys last occurred in October/November, 2000. Sheet 142 Melton Mowbray shows the distribution of alluvium, which allows tracts of floodable ground to be readily recognised. The map also shows significantly large areas of river terrace deposits, which delineate ground that is topographically higher than the modern alluvium tracts and thus less likely to flood. The interaction of floodplain geology with human modifications, such as infrastructure and industrial/residential developments on the floodplains, should also be considered when predicting floodrisk. Flood-risk assessments are currently based mainly on historical and hydrological information combined with high-resolution topographic surveying, and are available for the Soar and Wreake floodplains from the local Environment Agency office at West Bridgford.

Geology and planning

Geological assessments are becoming increasingly necessary for the purpose of planning for land-use development, the control of natural resources and the prediction of areas with potential geohazards. There is also a growing awareness of the value of the geological heritage in the rock outcrops, quarry exposures and natural landscape. These considerations are set in the context of the continuing need to provide land for housing, commercial, industrial, waste disposal and other developments. In this district, the maximisation of mineral resources such as coal, oil, sand and gravel are further issues that may arise in the future.

The key parameters relevant to construction and development of a site or area are all part of the foundation conditions — the suitability of the ground to support structural foundations, the ease of its excavation and its worth in engineered earthworks and fills. These issues are summarised for the main engineering geological units in the district in (Figure 14). The substrate can affect the foundation conditions in a number of ways, for example:

• natural occurrence of sulphates (gypsum) in the Mercia Mudstone Group, can produce deleterious effects on concrete
• weathering of the Mercia Mudstone, and much of the Lias Group, increases the natural moisture content, plasticity and swelling potential
• peaty deposits or lenses of running sand in alluvium can result in areas of highly compressible ground.

Factors such as geological structure, slope stability, the presence of undermining and potential for flooding are also locally important. The seismic history of this district is also relevant, as it has shown the potential for significant earthquakes to occur. Variable man-made conditions, encountered in landfill sites and areas of colliery spoil, is a further potential problem with respect to severe differential settlement. Colliery spoil, as in the Asfordby area [SK 717 210], may contain iron pyrites that is prone to oxidise and produce sulphate-rich, acidic leachates, which could be harmful to concrete present in foundations or buried services.

Abandoned mineworkings

Abandoned mineworkings are a potential constraint in areas of former limestone, ironstone, coal and gypsum extraction. The two areas of coal mining are to the south of Cotgrave (overburden in excess of 170 m) and around Asfordby (overburden in excess of 500 m). Here, the principal concerns relate to ground instability caused by the collapse of worked-out seams and underground roadways. The Coal Authority can provide information about local coal mining subsidence and shaft locations (see Information sources). Gypsum mining was largely limited to workings in the Newark and Tutbury seams (Figure 13). The main concerns relate to ground instability including uneven settlement caused by voids or foundered workings, exacerbated by natural gypsum dissolution continuing within the abandoned workings. Records of underground mining activities of the gypsum resources around East Leake, Barrow upon Soar and Cropwell Bishop are lodged with British Gypsum PLC, East Leake offices. Limestone mining has been limited to the shallow subsurface of the Barnstone Member outcrops, around Langar and Barrow upon Soar. Ground disturbed by these activities includes crown-holes that opened in Barrow upon Soar between 1976 and 1987 (Carney et al., 2002). Ironstone mining of the Marlstone Rock Formation occurred immediately east of Brown's Hill Quarry, near Holwell [SK 745 235], from adits (Plate 6) driven at shallow angles from the surface quarries. This activity took place beneath a minimal overburden and the ground is now unstable, with new subsidence pits appearing periodically.

Bedrock solution

Bedrock solution due to groundwater circulation is a potential risk in outcrops of the Cropwell Bishop Formation, which contain the major gypsum deposits of the district. The solution zone may locally contain cavities and is controlled by surface topography and bedrock lithology or structure; it can reach depths of up to 30 m below the surface. Anomalous ground depressions near Bunny [SK 590 287] and between Blackcliffe Hill [SK 6010 3205] and Plumtree House Farm [SK 6130 3290] are examples of possible subsidence resulting from natural gypsum solution.

Slope stability

Slope stability is a potential issue particularly where building development is extended on to steep valley sides. Many of the landslipped areas (Plate 1) that are shown on Sheet 142 Melton Mowbray may have formed under the wetter freeze-thaw periglacial conditions that prevailed during the Devensian times. These areas, together with outcrops of head and Slope Terrace Deposits that may contain relict shear surfaces, have the potential to be reactivated by loading, undercutting or excavating into slopes, or by introducing water into the slope from drains or soak-aways. Unstable conditions would be favoured by increased ingress of water from natural or artificial sources, and at times of exceptionally heavy and sustained rainfall.

Artificial (man-made) deposits

Artificial (man-made) deposits may contain toxic residues, either as a primary component or generated secondarily by chemical or biological reactions, and are thus potential sources of pollution. Significant sites in this district would include areas of landfill and colliery spoil, railway sidings and sewage works. In old or modern landfill sites with inadequate containment structures, leachate migration into surface watercourses and groundwater could occur if developed on permeable Quaternary deposits (e.g. Glaciofluvial Deposits, River Terrace Deposits, Alluvium). Minor aquifers, or impermeable lithologies of the Mercia Mudstone and Lias groups, may also be rendered susceptible to fluid flow as a result of faulting, jointing or gypsum dissolution.

Gas emissions

In areas associated with the accumulation of the 'greenhouse gases' (methane and carbon dioxide), radon and carbon monoxide, gas emissions may represent a hazard. Mine gas, mainly methane, can be generated naturally from the concealed Coal Measures strata, or from the decomposition of materials in landfill sites. It can migrate considerable distances through permeable strata and can accumulate in enclosed spaces such as building foundations or gypsum mineworkings. Landfill gas is a type of bacteriological methane, formed by the biodegradation of organic matter in landfill sites under anaerobic conditions; it can migrate from the landfill site through permeable substrates, or along faults and joints, both vertically and laterally. Radon (Rn-222) is a naturally occurring gas, which is derived from rock, soil and groundwater containing uranium (U) and thorium (Th). In the Melton Mowbray district natural radon levels are generally low except over the outcrops of Lias Group and in particular the Marlstone Rock Formation. The Northampton Sand, Charmouth and Scunthorpe Mudstone formations rank slightly lower in this respect (Sutherland and Sharman, 1996). 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). 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, BGS, Keyworth.

Earthquakes

Earthquakes, although of generally small magnitude, nonetheless pose a potential problem in the East Midlands, which is one of the more seismically active parts of the UK. The largest earthquake to be recorded in the district was the Melton Mowbray earthquake of 28th October, 2001, the epicentre of which was located [SK 770 283] several hundred metres to the west of Eastwell. 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, and it caused minor damage to chimneys and the walls of some houses. The historical database shows that greater damage would be caused by a repeat of the Derby earthquake of 11 February 1957, 9 km west of the district, with a magnitude of 5.3 ML (aftershock: 4.2 ML) and maximum intensity of 6 to 7 EMS. The BGS Global Seismology Unit can provide a detailed analysis of these events and assessments of local seismic risk to major constructions.

Conservation sites

Exposures of rocks and Quaternary 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 principal 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

Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. Geological advice for this area should be sought from the Regional Geologist, Integrated Geological Surveys (South), BGS, Keyworth.

Other geological information held by the British Geological Survey includes borehole records, fossils, rock samples, thin sections, hydrological data and photographs. Searches of indexes to some of the collections can be made on the Geoscience Data Index system available in BGS libraries and on the web site (see back cover for addresses). BGS catalogue of geological maps and books is available on request.

BGS Hydrogeology Enquiry Service (wells, springs and water borehole records) can be contacted via BGS web site or at: British Geological Survey, Hydrogeology Group, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OXO 8BB. Telephone 01491 838800. Fax 01491 692345.

Maps

• 1:625 000
• United Kingdom (South sheet) Solid, 1979; Quaternary Geology, 1977
• 1:50 000
• Sheet 142 Melton Mowbray (Solid & Drift), 2002
• 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 or 1:10 000 scale covering the 1:50 000 Series Sheet 142 are not published but are available for examination at BGS Keyworth, or may be purchased as dyeline copies. They are listed in below, together with the surveyors’ initials and reference numbers of accompanying Technical Reports. Surveyors are K Ambrose, A Brandon, J N Carney, T J Charsley, A H Cooper, R G Crofts, A S Howard, M Shaw, M G Sumbler.

• Geophysical maps
• 1:1 500 000
• Colour shaded relief gravity anomaly map of Britain, Ireland and adjacent areas, 1997
• Colour shaded relief magnetic anomaly map of Britain, Ireland and adjacent areas, 1998
• High-resolution airborne geophysical andradiometric surveys
• High-resolution gravity and aeromagnetic information is available, in addition to the surface distribution of a range of radioactive elements. Enquiries to 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 maps
• 1:625 000
• England and Wales (1977)
• 1:100 000
• Groundwater vulnerabilty (Sheets 23 & 24)

Publications

Memoirs, books, reports (see above) and papers of the BGS relevant to the district arranged by topic. Most are not widely available, but may be consulted at BGS and other libraries.

• British Regional Geology
• Central England, 1969
• Memoirs and Sheet Descriptions
• Grantham district (Sheet 127). Memoir, 1999
• Loughborough, Burton and Derby (Sheet 141). Sheet Description, 2001
• Melton Mowbray (Sheet 142). Sheet Description, (in press)
• Melton Mowbray district (Sheet 142). Memoir, 1909
• Leicester (Sheet 156). Memoir, 1903†
• Economic geology: ironstone
• The Liassic ironstones (The Mesozoic ironstones of England), Memoir Geological Survey of Great Britain, 1952†
• Hydrogeology
• Wells and springs of Leicestershire. Memoir Geological Survey of Great Britain, 1931†
• † out of print; facsimile copies may be purchased from BGS libraries at a tariff set to cover the cost of copying

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, names and depths for these boreholes can be accessed through the BGS web site, where copies can also be ordered.

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 are available for the whole of the district.

BGS Lexicon of named rock unit definition

Definitions of the rocks and Quaternary deposits shown on the 1:50 000 Series Sheet 142 Melton Mowbray are held in the Lexicon Database, available through the BGS web site. Further on the database can be obtained from the Lexicon Manager, BGS, Keyworth.

BGS (Geological Survey) photographs

Copies of the photographs used in this report, and of others taken during this and 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.

Materials 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 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, including many from the Melton Mowbray district, is held by the Minerals and Geochemical Surveys Division of the BGS.

Relevant collections held outwith BGS

Coal abandonment plans are held by the Coal Authority, Mining Reports, 200 Lichfield Lane, Mansfield, Notts NG18 4RG Tel. 0845 762 6848.

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.

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 the current copyright legislation. A full bibliography for this district may be found in Carney et al. (in press).

Besly, B M. 1988. Palaeogeographicalimplications of Westphalian to early Permian red beds, Central England. 200–221 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G. (editors). (Glasgow: Blackie).

Brandon, A. 1999. Geology of the Wreake Valley (S K61N E, 71N W, 71S W and 81N W). British Geological Survey Technical Report, WA/99/17.

Brandon, A, and Carney, J N. 2000. Geology of the Vale of Belvoir (S K72N W, S K73S W, S K73S E and S K83S W western part). British Geological Survey Technical Report, WA/00/36.

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.

Burgess, I C. 1982. The stratigraphicaldistribution of Westphalian volcanic rocks in the area east and south of Nottingham, England. Proceedings of the Yorkshire Geological Society, Vol. 44, 29–44.

Carney, J N, Ambrose, K, and Brandon, A. 2001. Geology of the country between Loughborough, Burton and Derby. Sheet description of the British Geological Survey, 1:50 000 Series Sheet 141 Loughborough (England and Wales)

Carney, J N, Ambrose, K, Brandon, A, Royles, C P, and Shepherd, T H. 2002. Geology of the Melton Mowbray district. Sheet description of the British Geological Survey, 1:50 000 Series Sheet 142 Melton Mowbray (England and Wales)

Ebdon, C C, Fraser, A J, Higgins, A C,Mitchener, B C, and Strank, A R E. 1990. The Dinantian stratigraphy of the East Midlands: a seismotectonic approach. Journal of the Geological Society of London, Vol. 147, 519–537.

Guion, P D, Fulton, I M, and Jones, N S. 1995. Sedimentary facies of the coal-bearing Westphalian A and B north of the Wales–Brabant High. 45–78 in European coal geology. Whateley, M K G, and Spears, D A. (editors). Geological Society Special Publication, No. 82.

Hallsworth, C. 2000. Interplay of northern and southern sources in the Melton area of the Widmerpool Gulf during the Namurian. British Geological Survey Technical Report, WH/00/41R

Lamplugh, G W, Gibson, W, Wedd, W,Sherlock, R L, and Smith, B. 1909. The geology of the Melton Mowbray district and south-east Nottinghamshire. Memoir of the Geological Survey of Great Britain, Sheet 142 (England and Wales).

Noble, S R, Tucker, R D, and Pharaoh, T C. 1993. Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes. Geological Magazine, Vol. 130, 835–846.

Pharaoh, T C, Brewer, T S, and Webb, P C. 1993. Subduction-related magmatism of late Ordovician age in eastern England. Geological Magazine, Vol. 130, 647–656.

Rice, R J. 1968. The Quaternary deposits of Central Leicestershire. Philosophical Transactions of the Royal Society of London, Vol. 262(A), 459–508.

Riley, N J. 1992. Faunal Biostratigraphy of Plungar 8A Bh. Interval 3280–4615 British Geological Survey Technical Report, W H92/199C

Smith, D B, Harwood, G M, Pattison, J, and Pettigrew, T H. 1986. A revised nomenclature for the Upper Permian strata in eastern England. 9–17 in The English Zechstein and Related Topics. Harwood, G M, and Smith, D B (editors). Geological Society of London Special Publication, No. 22.

Sutherland, D S, and Sharman, G. 1996. Radon — in Northamptonshire? Geology Today, Vol. 12, 63–67.

Warrington, G, and Ivimey-Cook, H C. 1992. Triassic. 97–106 in Atlas of palaeogeography and lithofacies. Cope, J C W, Ingham, J K, and Rawson, P F (editors). Geological Society of London Memoir, No. 13.

Whitehead, T H, Anderson, W, Wilson, V, and Wray, D A. 1952. The Liassic Ironstones. Memoir of the Geological Survey of Great Britain.

Index to the 1:50 000 Series maps of the British Geological Survey

The map below shows the sheet boundaries and numbers of the 1:50 000 Series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased.

(Index map)

The area described in this sheet explanation is indicated by a solid block.

Printed in the UK for the British Geological Survey by B&B Press Ltd, Rotherham.

Figures and plates

Figures

(Figure 1) Dinantian and Namurian rocks proved in boreholes in the district.

(Figure 2) Descriptions of Westphalian rocks concealed beneath younger strata.

(Figure 3) Sections in the Lower Coal Measures and Saltby Volcanic Formation. Figures to left side of columns denote depths below the surface.

(Figure 4) Middle Coal Measures and Warwickshire Group. Figures to left side of columns denote depths below the surface.

(Figure 5) Sherwood Sandstone and Mercia Mudstone groups.

(Figure 6) Stratigraphy of the Scunthorpe and Charmouth mudstone formations.

(Figure 7) Lithological description of the members within the Scunthorpe Mudstone Formation.

(Figure 8) Lithological description of Charmouth Mudstone, Dyrham, Marlstone Rock and Whitby Mudstone formations.

(Figure 9) Lithostratigraphical description of the Inferior Oolite Group.

(Figure 10) Quaternary chronology and correlation. (Modified from Brandon, 1999).

(Figure 11) Morphology and lithology of the Quaternary deposits.

(Figure 12) Principal structures and concealed Carboniferous geology.

(Figure 13) Mineral deposits.

(Figure 14) Geotechnical properties of the principal lithological units.

Plates

(Plate 1) Slope instability features between Stonepit Spinney (left) and Green Hill (right) [SK 6945 2393] looking east-south-east towards the scarp of the Charmouth Mudstone Formation capped by the Marlstone Rock Formation. 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; GS1215.).

(Plate 2) Fossils of the Lias Group, found mainly in the Scunthorpe Mudstone Formation. Actual dimensions are in brackets. i Psiloceras (50 mm); ii Cardinia listeri (50 mm); iii Caloceras (80 mm); iv Liostrea (120 mm); v Gryphaea arcuata (55 mm); vi Plagiostoma (110 mm); vii Pseudopecten (65 mm); viii Schlotheimia angulata (65 mm); ix Pentacrinus ossicles and columnals (10 mm ossicles); x Calcirhynchia (13 mm).

(Plate 3) Fossils of the Lias Group, commonly in the upper Scunthorpe Mudstone Formation, Charmouth, Marlstone Rock and Whitby mudstone formations. Actual dimensions are in brackets. i Gryphaea maccullochii (90 mm); ii Oxytoma (Pteria) inequivalvis (25 mm); iii Hippopodium (60 mm); iv Gagaticeras (35 mm), v Gryphaea cymbium (70 mm), vi Arnioceras semicostatum (45 mm); vii Tetrarhynchia (27 mm); viii Astarte (20 mm); ix Dactylioceras annulatum (72 mm).

(Plate 4) Cross-bedding in bioclastic ironstone of the Marlstone Rock Formation, Holwell Quarry [SK 741 234] (GS1207).

(Plate 5) Quarry in the Barnstone Member at Langar, in 1966. The pale grey beds of hard, calcite mudstone were worked for cement manufacture [SK 73 34]. (Photograph by G Warrington; GS1214.).

(Plate 6) Former adit entrance at Brown's Hill ironstone quarry [SK 741 234] (GS1215).

(Front cover) Belvoir Castle stands on a small outlier of Lower Jurassic strata; the Marlstone Rock Formation forms the top of the hill and the Dyrham Formation underlies the middle and lower slopes. 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 north-west [SK 820 337] (MN39938).

(Rear cover)

(Geological succession) Geological succession in the Melton Mowbray district.

(Index map) Index to the 1:50 000 Series maps of the British Geological Survey.

Figures

(Figure 1) Dinantian and Namurian rocks proved in boreholes in the district

(Figure 2) Descriptions of Westphalian rocks concealed beneath younger strata

(Figure 5) Sherwood Sandstone and Mercia Mudstone groups

(Figure 7) Lithological description of the members within the Scunthorpe Mudstone Formation

Fossils (in bold print) are illustrated in (Plate 2) and (Plate 3).

(Figure 8) Lithological description of Charmouth Mudstone, Dyrham, Marlstone Rock and Whitby Mudstone formations

Fossils (in bold print) are illustrated in (Plate 2) and (Plate 3).

(Figure 9) Lithostratigraphical description of the Inferior Oolite Group

(Figure 10) Quaternary chronology and correlation. (Modified from Brandon, 1999)

(Figure 11) Morphology and lithology of the Quaternary deposits

(Figure 13) Mineral deposits

(Figure 14) Geotechnical properties of the principal lithological units