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Geological notes and local details for 1:10,000 sheets: SP28SE (Allesley). Part of 1:63,360 Sheets 169 (Coventry). British Geological Survey Technical Report WA/89/23

J G Rees

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British Geological Survey Onshore Geology Series Technical Report WA/89/23

Bibliographic reference: Rees, J G. 1989 Geological notes and local details for 1:10,000 sheets: SP28SE (Allesley). British Geological Survey Technical Report WA/89/23.

©. Crown Copyright 1989 Keyworth, Nottingham, British Geological Survey 1989

Production of this report was funded by the Department of the Environment, but the views expressed in it are not necessarily those of the Department.

Geographical indexUK, Central England, Warwickshire, Allesley

Subject indexGeology, Quaternary, Upper Carboniferous, Cambrian

Summary

The geology of Sheet SP28SE (Allesley) is described with reference to information from rocks at outcrop and significant boreholes and shafts.

Cambrian rocks and the overlying coal bearing part of the Carboniferous sequence are known from several boreholes. Much of the dominantly red-bed Carboniferous sequence overlying these is known also from outcrop.

Glacial deposits cover much of the area, and details are given of their lithology and distribution. A diagram shows the elevation of the sub-drift (bedrock) topography.

Currently, coal mining is the only form of mineral extraction in the area.

A schedule of boreholes is appended.

Introduction

The following report describes the geology of 1:10,000 sheet SP28SE (Allesley) (Figure 1) and is designed to be used in conjunction with the 1:10,000 Geological sheet. Uncoloured dyeline copies of this map may be obtained from the British Geological Survey, Keyworth, Nottingham NG12 5GG.

Similar reports covering adjoining areas are:

SP27NE (Coventry West) (Old 1988)

SP28NE (Fillongley) (Rees 1989)

SP28SW (Meriden) (Sumbler 1989)

SP38SW (Coventry North) (Old 1989)

The map forms part of 1:50 000 Geological Sheet 169 (Coventry) for which a memoir was published (Eastwood and others 1923). The area was surveyed at 1:10 560 by C.H. Cunnington and T. Eastwood in 1913–1914. The whole of SP28SE was surveyed at the 1:10,000 scale by J.G. Rees in 1987–8 under the direction of Dr. A.J. Wadge as Regional Geologist. The survey and production of the map and this report were part-funded by the Department of the Environment. Palaeontological contributions were by Dr. A.W.A. Rushton and Dr. N.J. Riley.

Topography and land-use

The area occurs north-east of Coventry on Upper Palaeozoic rocks of the Enville Group that form higher ground than the surrounding Mesozoic rocks. The rocks of the Enville Group form sandstone dip slopes and mudstone-rich scarps. In places these are overlain by drift sequences, composed mostly of tills, that form clay plateaux. Apart from Allesley village the area of SP28SE is largely given over to agriculture. The poorly drained soils on glacial clays and Upper Palaeozoic mudstones have given rise to dairying. The better- drained soils on Upper Palaeozoic sandstones, glacial sands and gravels, river terraces and alluvium are largely used for sheep rearing. The ground is dissected by the River Sherbourne and Pickford Brook and their tributaries.

Geological sequence

The solid formations and Quaternary and Recent deposits on sheet SP28SE are listed below; the relative and absolute thicknesses of the former are shown on the map.

Cambrian

Wherever proved, the pre-Carboniferous rocks are of Cambrian age (here taken to include the Tremadoc Series).

Monks Park Shales

The upper part of this formation has been proved at the base of the Long Lady Wood and Corley Moor boreholes (Figure 2). It consists of black-pale grey, slightly calcareous mudstones with a sparse brachiopod and trilobite fauna that includes:

Broeggeria salteri (Holl) Ctenopyge fletcheri (Matthew) Orusia lenticularis (Wahlenberg) Sphaerophthalmus major (Lake)

Merevale Shales Formation

The lower part of the formation which generally lacks distinctive bio stratigraphically useful fossils has been proved at the base of Hawkes End, Meriden, and Greenways Farm boreholes. It is distinguished by bioturbated mudstones which contain thin sandstones and siltstones. The fauna within these includes:

Broeggeria salteri (Holl)

Linnarssonia belti (Davidson)

Tomaculum sp. Dictyonema sp. Lingulella sp. Orusia sp.

Upper Carboniferous (Westphalian-Stephanian)

Upper Carboniferous (Westphalian-Stephanian) rocks overlie the Cambrian rocks unconformably. The succession comprises mudstones, siltstones, sandstones and seatearths, and is coal bearing in its lower part. The lithostratigraphy of the group is summarised in (Table 1). The upwards passage from predominantly grey rocks of deltaic and alluvial facies, to red measures, suggests a progressive change to more arid conditions in late Westphalian and Stephanian times. The paucity of marine and non-marine fauna, particularly in the upper part of the Westphalian and in the Stephanian, makes a precise chronostratigraphic subdivision of the sequence impractical, and the ages of the younger formations can only be estimated.

Productive Coal Measures (Westphalian A, B and C) (Figure 2) & (Figure 3)

The Productive Coal Measures include all of the Westphalian strata up to the base of the Etruria Marl. The Westphalian A/B boundary is taken at the Vanderbeckei (Seven Feet) Marine Band, or in its absence, immediately above the Seven Feet Coal. The Westphalian B/C boundary is placed at the base of the Aegiranum (Nuneaton) Marine Band.

Measures below the Thick Coal

These have been proved in a programme of drilling carried out by British Coal. The succession, estimated to be between 15 m and 75 m thick, consists of mudstone, siltstone and seatearth with subordinate thin sandstones. Ironstone in the form of thin bands is common. Coals occur at several levels but none has been worked. The principal named seams, in ascending order, are the Bench, Seven Feet, and Smithy. Of these, only the Bench is widely developed and of workable thickness.

The Bench, which usually is split, is cumulatively over a metre thick in the east of the area but thins to less than 0.7 m in the west. It is of good quality but tends to become inferior towards the roof and floor. The seam is overlain by c.25 m – 40 m of planty mudstones, seatearths and thin coals. A 3 m to 8 m thick, cross and parallel laminated sandstone containing stem fragments, occurs throughout the area in the middle part of this interval.

The Seven Feet varies considerably in composition and thickness over the area. It is represented by several very thin seams in the Corley Moor, Park Hill Lane and Greenways Farm boreholes, but in other boreholes it occurs as a single seam, which in the Muzzards Wood borehole is over 0.8 m thick.

The Vanderbeckei Marine Band, which generally is represented by an impoverished Lingula fauna dominated by Lingula mytilloides lying close to, or in contact with the Seven Feet, was not detected in several boreholes (Figure 2) and (Figure 3). The 5 m – 8 m interval between it and the Thick Coal is dominated by seatearths.

The Thick Coal

The Thick Coal a combination of several seams that are separated outside the area. In ascending order these are the Nine Feet, Ell, Ryder, Bare, Two Yard and High Main coals (Fulton and Williams 1988, p.204). Over most of the area the Thick Coal varies between 5 m and 6.8 m thick. However in places it is considerably thinner, for instance in the Muzzards Wood and Meriden boreholes it is c.1.65 m thick, and in the latter it is split by a 0.3 m thick mudstone.

Measures between the Thick Coal and the Etruria Marl

The thickness of this interval varies considerably from about 60 m to 130 m thick. Over much of the area, at the base of this interval, the mudstones immediately overlying the Thick Coal contain an impoverished bivalve fauna. Above this is a 15 m–20 m thick sandstone rich interval, which in the north eastern part of the area is overlain by the Four Feet coal; a laterally impersistent seam which is less than 0.5 m thick. This in turn is overlain in parts by a shelly band containing ostracods and fish debris which is separated from the Half Yard seam by c.7 m–17 m of mudstone and seatearth and sporadic sandstones. The Half Yard which is commonly split and up to 1.4 m thick is laterally persistent over all but the north eastern part of the area.

The Aegiranum (Nuneaton) Marine Band, is separated from the Half Yard by 10 m–15 m of mudstone and sandstones. It contains faunas dominated by brachiopods including Chonetes, Orbiculoidea, Rugosochonetes cf. skipseyi, Lingula, particularly Lingula mytilloides, and productoids and by ostracods, goniatites including Anthracoceras, and fish fragments including Megalichthys.

The sequence between the Aegiranum Marine Band and the base of the Etruria Marl is very variable, and consists dominantly of mudstones seatearths, sandstones and coal seams, several of which are between 0.5 m and 1 m thick.

(Table 1) Summary of Westphalian-Stephanian Lithostratigraphy

Etruria Marl Formation (Westphalian C)

A sequence of mudstones, sandstones, and breccio-conglomerates, mainly grey in colour but also variegated red, brown and yellow, occurs between the Productive Coal Measures and the overlying Halesowen Formation. The boundaries of the formation are rather indefinite but the base is taken at the lowest occurrence of red beds or breccio-conglomerates of ‘espley’ facies, and the top at the incoming of grey sandstones of the Halesowen Formation. As thus defined, the thickness of the formation varies between 26 m and 86 m. Parts of the formation were cored in several boreholes (Figure 2) and (Figure 3).

Halesowen Formation Westphalian D

The Halesowen Formation is dominated by grey sandstones, greenish grey mudstones, seatearths and rare coals and limestones. The thickness of the formation recorded in boreholes in the area mostly ranges between 60 m and 153 m, though interpretation of geophysical data in the Hawkes End borehole suggests that in places the formation is less than 30 m thick. In the absence of better evidence, the base of Westphalian D is arbitrarily taken at the base of the formation. The formation was cored only in the Meriden borehole.

Sandstones predominate in the lower part of the formation, where they are associated with impersistent coals, including the Milton which is widely developed in the area to the south. The Index Limestone (Eastwood and others 1923) forms a useful marker horizon at about 30 m below the top of the formation. The beds above the Index Limestone are dominantly mudstones which are mostly grey but locally are chocolate-brown, yellow or red. The junction with the overlying Keele Formation is transitional but is taken at the change to a predominantly red-bed facies.

In 1943 G.H.Mitchell collected a flora from the Halesowen Formation of the Meriden borehole which contained Neuropteris scheuchzeri, Neuropteris flexuosa, Neuropteris ovata, Neuropteris tenuifolia, Neuropteris heterophylla and Alethopteris lonchitica. Floral and faunal evidence of the age of the Halesowen Formation give a Westphalian D age (Cleal 1984).

Keele Formation (Westphalian D-Stephanian?)

The Halesowen Formation is overlain by a red-bed sequence consisting mainly of mudstone, but including subordinate sandstones and rare thin beds of porcellaneous limestone. The formation is estimated to be between 170 m and 300 m thick. The top of the formation is defined by a thick sandstone at the base of the overlying Coventry Sandstone Formation. The Keele Formation was only cored in the Meriden borehole in which reddish brown mudstones with grey and yellow streaks are interbedded with impersistent sandstones. In the absence of reliable palaeontological data the formation is tentatively ascribed a Westphalian D to Stephanian age (Besly 1988).

Enville Group

Coventry Sandstone Formation (Westphalian D-Stephanian)

The Coventry Sandstone Formation consists of an alternating sequence of sandstones, mudstones and thin conglomerates of red-bed facies. Sandstones, although not everywhere dominant over mudstones, make up most of the sequence, being predominant in the lower 50 m, and from the base of the Corley Member to the top of the formation. Many of the sandstones and mudstones are laterally very impersistent; this well illustrated by the logs of the Meriden Waterworks boreholes, (SP28SE/6) and (SP28SE/7) (Figure 4), which were drilled less than 7 m apart. The predominance of sandstones in the formation serves to distinguish it from the underlying Keele Formation. The age of the formation was tentatively placed by Besly (1988) as Stephanian though definitive biostratigraphical evidence is lacking.

The sandstones are mostly moderately to well sorted, fine to coarse grained. They often fine upwards, from bases, which are commonly erosional or have an often imbricated pebbly lag. Many coarser sandstones are massive in texture except for ‘floating’ extraclasts, or mudstone ‘rip up’ clasts that they contain. Trough cross-lamination is common in many of the coarser sandstones as can be seen in (Figure 5) and (Figure 6). The variation in the azimuths of dipping laminae of these suggest considerable variation in palaeocurrent direction. Most finer sandstones are parallel laminated, and flaggy in appearance, e.g. those exposed at Farrow Oak [SP 2599 8425]. The mudstones in the sequence are mostly poorly laminated. Most mudstones, and several sandstones in the formation contain green-blue reduced areas or discrete spots. Some breccias and conglomerates in the formation, such as those exposed in the Meriden Hill cutting, are very poorly sorted, and have random clast geometries and irregular tops.

Most coarser sandstones, particularly those which are erosional or have pebbly bases are interpreted as channel sandstones. The cross bedding formed in longitudinal or point bars e.g. (Figure 6) of a channel, whilst some of the poorly sorted conglomerates and breccias are interpreted as debris flows. The fine grained sandstones are interpreted as overbank sandstones, and mudstones as lagoonal mud deposits. Further information on the environment of deposition of the formation is given by Besly (1987, 1988).

The cross-stratification was probably formed by lateral accretion of channel sands. Bases of sandstone sets are shown by heavy lines.

From the interpretation of geophysical logs of un-cored boreholes, the cored sequence of the Meriden borehole and trigonometric calculation the Coventry Sandstone Formation is c.420 m–550 m thick.

The Corley Member

The Corley Member encompasses a sequence of pebbly sandstones and conglomerates in the middle part of the Coventry Sandstone Formation. As pebbly sandstones and conglomerates occur in the Coventry Sandstone Formation below and above the Corley Member, the boundaries, particularly the upper boundary of the member are rather indefinite. The base and top of the member are diachronous.

The conglomerates and pebbly sandstones of the formation are best developed in the area around Marsland Farm [SP 295 850], Hollyberry End [SP 2675 8364], west of Couchman's Farm [SP 2708 8300] to [SP 2760 8330] and at Muzzard's Wood [SP 2977 8419]. Pebbles and cobbles in pebbly sandstones at a temporary exposure at the latter site consisted predominantly of quartz veined doleritic suites, micro greywackes and quartzites, which are interpreted to have been derived from Lower Palaezoic or Pre-Cambrian rocks. These are mostly angular to sub- rounded with a low sphericity.

Most smaller clasts consist predominantly of angular cherty fragments. The sandstone in which the clasts occur is composed of medium, well rounded grains. At other localities, such as west of Couchman's Farm [SP 2728 8242] algal and oolitic limestones of probable Dinantian age occur in a suite of clasts similar to that described above. The regional pattern of clast types is described in detail by Shotton (1927).

The Tile Hill Mudstone Formation (Stephanian?)

The Tile Hill Mudstone Formation consists of mudstones and sandstones of red-bed facies. The thickness of the formation exposed on the sheet is estimated to be c.60 m. As the lower part of the formation is sandstone rich and the upper part of the underlying Coventry Sandstone Formation is mudstone rich, the junction is transitional. The base of the Tile Hill Mudstone Formation has been placed at the base of the lowest laterally extensive mudstone.

Structure

Pre-Carboniferous structures

Viewed in their regional setting (Old and others 1987, (figure 2)) the Cambrian rocks lie on the NW limb of a broad, presumably Caledonian, NE–SW trending syncline, which has been identified by plotting the faunal zones proved in boreholes. The varied dips proved in the boreholes in the appendix are not necessarily in accord with this structure and the folding of these beds is evidently more complicated in detail.

Intra Carboniferous movements

From the borehole evidence on the 1:10,000 map it is evident that there are large lateral thickness variations of the Carboniferous formations in the area. These may be attributed to different sedimentation patterns on either side of syn-sedimentary faults. The unconformity at the base of the Halesowen Formation (Old and others 1987) may have been created by the movement of similar faults in adjoining districts (Mitchell 1948), and possibly also beneath the Enville Group (Besly 1987). Non-sequences at these levels are not easily demonstrated in the present area.

Post-Carboniferous structures

Following the deposition of the Enville Group the Carboniferous rocks were gently folded during the Hercynian earth movements. The area occurs towards the centre of an open, southerly plunging syncline that contains several smaller, very shallow folds which trend between NNW0SSE and NE–SW. Several SW–NE or SE–NW faults probably are related to this folding as they rarely throw consistently in any direction yet are mostly oriented perpendicular to the direction of dip. Most faults in the area have small (less than 5 m) throws.

Quaternary

Glacial deposits, consisting mainly of till, but also including waterlain sands, silts and clays cover much of the area. Conventionally, these deposits have been attributed to the Wolstonian Glaciation (Shotton and West 1969), but the stratigraphic basis of this glaciation is now considered questionable, and the deposits are regarded by many workers as Anglian in age (Sumbler 1983; Bowen and others 1986).

The glacial drift was deposited on a surface with considerable topographical variation (Figure 7). As boreholes have rarely penetrated the base of the drift, true drift thickness may be considerably greater than are shown (Figure 8).

Although a formal nomenclature has been applied to the stratified glacial deposits to the south east of the area (Shotton 1953), the classification is more difficult to apply in the present area, and a more generalised terminology has been adopted.

Glacio-lacustrine silts and clays

Silts and clays, which, are generally stoneless, occur sporadically at the base of the main till sheet and appear to have been laid down in glacial lakes formed near the ice- margin. They are dominated by laminated silts and clays which range in colour between whitish- yellow and dark chocolate brown. The clay-rich lithologies tend to be finely laminated as can be clearly seen in samples augured at Hill Fields Farm [SP 280 830]. The silts tend to be more massive, and slightly more red-brown in colour. Several laminated clay and silt beds occur within the main till sheet e.g. (Figure 7) but have not been mapped.

Fluvioglacial sand and gravel

Sands and gravels in the area are-commonest at the base of the till sheet, and normally overlie any glacio-lacustrine silts and clays. They are mostly composed of well washed, poorly to well sorted pale yellow, or yellow-orange sands, such as occur north of Marlbrook Hall [SP 265 843] and near Showell Lane [SP 2615 8250].

However variations in colour are common; for instance very dark brown sands occur at the Trusthouse Forte Hotel [SP 2910 8100], and most of the sands and gravels alongBridle Brook Lane [SP 292 832] are red. Where colour changes occurs within an area of outcrop, it does not appear to be sharp. It is possible that the red sands and gravels are composed of locally derived sediments of the Enville Group. The sands and gravels usually contain a large proportion of well-rounded to angular pebbles and cobbles. These are compositionally similar to the erratics in the till sheets (see below). ‘Pods’ of sands and gravels also occur within the main till sheet. One of these was drilled by boreholes (SP28SE/101)-(SP28SE/102) (Appendix 2). Several sand and gravel beds occur within the main till sheet though have not been mapped out e.g. (Figure 9).

Till (Undivided)

The main areas of till occur North West of Allesley, and on the southern margin of the area. Where the main till sheet does not lie directly on rocks of the Enville Group, it is usually underlain by glacio-lacustrine silts and clays or fluvioglacial sands and gravels. The main till was intercepted by shallow boreholes (SP28SE/100) (A-D), (SP28SE/101)–(SP28SE/102) (Appendix 2), though was mostly mapped using a hand auger. The till consists of a stiff, brown or reddish brown, sandy clay with a variety of exotic and locally derived erratics. Pebbles of ‘Bunter’ quartzite and Enville Group lithologies (sandstones and siltstones) are ubiquitous. In most areas the till contains a high proportion of brown-weathering quartzite blocks of the Cambrian Hartshill Quartzite. Other common clast varieties are shales, probably from the Cambrian north of the coalfield, and skerry sandstone and siltstone fragments from the Triassic Mercia Mudstone Group west of the coalfield. The abundance of these, particularly towards the top of the till sheet (Appendix 2), would suggest that the ice sheet depositing the tills had come from the North West. The base of the till sheet is generally sharp where it overlies the Enville Group, though where it overlies glacio-lacustrine clays the junction is often made indefinite by local interdigitation or near-surface shearing of the till by surface creep. Fluvio-glacialsand and gravel and glacio-lacustrine clay occur within the main till sheet, for instance near Windmill Farm [SP 286 816], [SP 289 817] and north of Oaklands Farm [SP 285 836]. Several other stringers of sand and gravel and laminated clay and silt were not separately mappable, and have been included within the till. Boreholes (SP28SE/100) (A–D) and (SP28SE/101), (SP28SE/102), (SP28SE/103), (SP28SE/104), (SP28SE/105), (SP28SE/106) demonstrate the complexity of parts of the main till sheet in the Allesley area.

River Terrace deposits

River terrace deposits of the River Sherbourne occur in the vicinity of Stone House Farm, Allesley [SP 294 821]. The terrace is between 0.5 m and 2 m above the river alluvium, and consists mainly of sand and fine to coarse gravel in a dark brown silty clay matrix.

Alluvium

Thin spreads of alluvium occur along the valleys of the River Sherbourne, Pickford Brook and their tributaries. The deposits, which are rarely more than 2 m thick, consist principally of sandy, silty, pale reddish-brown loam, above a basal gravel. Where the alluvium overlies rocks of the Enville Group it usually contains a high proportion of red-brown sand.

Head

The head deposits occur towards the bottom of valleys and are usually a mixture of till and sandy wash from the Enville Group. The clays and silt within the head often have a vague lamination, possibly caused by shearing during down-hill creep.

Made Ground

There are several sites of made ground in the area. Most of these were created to level the ground surface, either by infilling of existing depressions, or building a ramp on a slope. The three main sites of made ground:

1.       The Reservoirs on Meriden Hill [SP 260 820]; these have been constructed largely of local materials including tills.

2.       The embankments and car parks at the Jaguar factory, Allesley [SP 298 815], which are up to 4 m thick.

3.      The site of the Triumph motor cycle factory. A new housing estate [SP 267 827] has been built on the rubble of the factory which had been covered by a thin skin of boulder clay.

Economic geology

Coal

Although a small amount of ground near Corley has been undermined from Coventry Colliery, the western part of the district occurs at the northern end of the South Warwickshire Prospect (National Coal Board 1985, British Coal 1987). This is a coalfield completely concealed by younger rocks. Details of the coal-bearing strata are given in the Westphalian section of this report. All of the recoverable reserves are in the Thick Coal.

Sand and gravel

Although there are large outcrops of fluvio-glacial sands and gravels, most production of sand and gravel in the past was very localised, and was derived from the de-cemented regolith of the Coventry Sandstone.

Stone

There are no good building stones in the area, and no quarrying of stone is currently being undertaken. In the past however, the Coventry Sandstone, particularly the Corley Member, has furnished stone for local use.

Water supply

Although numerous water-wells have been drilled in the Coventry Sandstone Formation in the past (Butler 1946), today water is only pumped from the wells at the Meriden Water Works (SP28SE/6), (SP28SE/7), [SP 2624 8262], [SP 2623 8262] and at Brailles Farm (SP28SE/99) [SP 2516 8285].

References

BESLY, B.M. 1987. Late Westphalian to early Autunian red-bed sedimentation and the tectonic evolution of the Variscan foreland of the English Midlands. Field Guide. Yorkshire Geological Society–British Sedimentological Research Group. 1987.

BESLY, B.M. 1988. Palaeogeographic implications of late Westphalian to early Permian red-beds, Central England. 200–221 in BESLY, B.M. and KELLING, G. (editors) Sedimentation in a Synorogenic Basin complex: the Upper Carboniferous of Northwest Europe. Blackie: Glasgow and London.

BRITISH COAL CORPORATION 1987. Proposed Colliery at Hawkhurst Moor: Statement to accompany applications for planning permission. British Coal: Coleorton.

BUTLER, A.J. 1946. Water supply from underground sources of the Birmingham- Gloucester district. Part III Geological Survey Wartime Pamphlet. No.32.

COPE, K.G. and JONES, A.R.L. 1970. The Warwickshire Thick Coal and its mining environment. Sixième Congres International de Stratigraphie et du Géologie du Carbonifère. Sheffield 1967. 585–598.

EASTWOOD, T., GIBSON, W., CANTRILL, T.C. and WHITEHEAD, T.H. 1923. The geology of the country around Coventry. Memoir of the Geological Survey of Great Britain.

FULTON, I and WILLIAMS, H 1988. Palaeogeographical change and controls on Namurian and Westphalian A/B sedimentation at the southern margin of the Pennine Basin, Central England. 178–199 in BESLY, B.M. and KELLING, G. (editors) Sedimentation in a Synorogenic Basin Complex: The Upper Carboniferous of Northwest Europe. Blackie: Glasgow and London.

MITCHELL, G.H. 1948. The Geology of the Warwickshire Coalfield. Geological Survey Wartime Pamphlet, No.25.

NATIONAL COAL BOARD 1985. South Warwickshire Prospect. A consultation paper. (National Coal Board. South Midlands area).

OLD, R.A. 1988. Geological notes and local details for 1:10,000 sheets: SP27NE (Coventry West) (Keyworth: British Geological Survey).

OLD, R.A. 1989. Geological notes and local details for 1:10,000 sheets: SP38SW (Coventry North) British Geological Survey Technical Report WA/89/25 (Keyworth: British Geological Survey).

OLD, R.A., SUMBLER, M.G. and AMBROSE, K. 1987. Geology of the country around Warwick. Memoir of the British Geological Survey, Sheet 184 (England and Wales).

REES, J.G., 1989. Geological notes and local details for 1:10,000 sheets: SP28NE (Fillongley) British Geological Survey Technical Report WA/89/21 (Keyworth: British Geological Survey).

SHOTTON, F.W. 1927. The conglomerates of the Enville Series of the Warwickshire Coalfield. Quarterly Journal of the Geological Society of London, Vol.83, 604–621.

SHOTTON, F.W. 1953. The Pleistocene deposits of the area between Coventry, Rugby and Leamington, and their bearing on the topographic development of the Midlands. Philosophical Transactions of the Royal Society of London Series B, Vol. 237, 209–260.

SHOTTON, F.W. and WEST, R.G. 1969. Stratigraphic table of the British Quaternary. In: Recommendations on a stratigraphic usage. Proceedings of the Geological Society of London. No.1656, 155–157.

SUMBLER, M.G. 1989. Geological notes and local details for 1:10,000 sheets: SP28SW (Meriden). British Geological Survey Technical Report WA/89/22. (Keyworth: British Geological Survey).

SUMBLER, M.G. 1983. A new look at the type Wolstonian glacial deposits of Central England. Proceedings of the Geological Association. Vol.94, 23–31.

Appendix 1 borehole schedule for SP28SE

Detailed logs of non-confidential boreholes may be examined at the BGS National Geosciences Data Centre, Keyworth, by prior appointment and payment of the current fees.

c. Denotes confidential records, details of which may only be released to a third party by permission of the original client.

Appendix 2 BGS Drift Boreholes Drilled Near Allesley, Coventry 1988

These boreholes were drilled by a ‘Minuteman’ rig with screw flights and barrel using a wireline. The cores were retained in removable plastic lining tubes within the barrel. These tubes were sealed, and re-opened for examination at a later date.

Boreholes (SP28SE/100) A-D

These boreholes, sited at Windmill House Farm, were drilled to determine the nature of the junction between the main till sheet and under laying fluvio-glacial sand and gravel. Geological mapping proved that this junction passes under the main Coventry Birmingham Road at this point; tills occur at Windmill House Farm to the north of the road, and sands and gravels occur at a lower level to the south of the road in the vicinity of the Windmill Farm Hotel see (Figure 10).

Drilling problems necessitated the drilling of four boreholes, A-D. Core recoveries were as follows:

Logs of the cored sections are shown in (Figure 10). The cores represent a cumulative sequence of c.12.5 m. which is dominated by silty and sandy calcareous tills interbedded with sandy, generally non-pebbly, calcareous silts and sands and gravels. The junction between most beds is gradational. Clasts within the tills consist of Enville Group sandstone and siltstone and mudstone fragments, ‘Bunter’ pebbles, greywacke fragments, quartz, and shale and quartzite fragments that were probably derived from the Cambrian outcrops to the north east, near

Nuneaton, and greenish sandstones and siltstones which probably represent skerry fragments from the Triassic Mercia Mudstone Group. Most of the greywacke, quartz and ‘Bunter’ pebbles are moderately well rounded, whilst other varieties of clast are more angular to sub-angular. These tills are characterised by an abundance of clasts of Enville Group lithologies which in combination with their silty and sandy texture, and red colour, suggest that they were largely derived from local Enville Group rocks.

The generally pebble-free silts, which are also characterised by a laminated fabric, fine upwards from sand or pebble beds. The lamination and absence of pebbles within these suggest that they were water-lain.

The sand beds are variably pebbly and consist almost exclusively of well sorted and rounded grains. These beds may be the result of removal of fines from the till by water, deposition by water below an ice sheet, or alluvial or aeolian deposition on the margins of an ice sheet. The lack of pebbles within some sands suggests that they were not formed by removal of fines from the till by water. The top of borehole D occurs at about the same level as the uppermost fluvio-glacial sands and gravels on the south side of the Birmingham Road next to the Windmill Farm Hotel. Consequently it is probable that the sequences in the borehole and exposed next to the hotel are laterally equivalent.

Boreholes (SP28SE/101) and (SP28SE/102)

These boreholes, sited on the hill behind the tractor factory at Windmill House Farm, were drilled to determine the nature of fluvio- glacial sand and gravel ‘pods’ mapped within the main till sheet.

Drilling problems necessitated the drilling of two boreholes, (SP28SE/101) and (SP28SE/102) see (Figure 11). Core recoveries were as follows:

The sequence in these boreholes is dominated by sands with variable clay, silt, granule and pebble contents and silty, very pebbly tills. The sands are generally very well rounded and well sorted, probably reflecting a local Enville Group source, rather than aeolian deposition. The clasts that they contain are generally distributed throughout the beds. Angular to sub-angular clasts include fragments of Enville Group sandstone and siltstones as well as mudstones and quartzites of probable Cambrian age. Better rounded clasts include quartz, greywacke and ‘Bunter’ pebbles. The mode of deposition of the sands is unclear, though it is probable that at least those which are almost pebble free were not formed by removal of fines from the till sheet.

The junction between the sands and gravels are mostly gradational. For instance, the very poorly sorted, pebbly bed between 2.2 m–1.4 m in (SP28SE/102) which is interpreted as a very silty sandy till, grades up from the underlying generally granule and pebble free sands. Also the clay rich till below 6.8 m in borehole (SP28SE/101) grades up into relatively well sorted sands over c.0.6 m.

Boreholes (SP28SE/103), (SP28SE/104), (SP28SE/105) and (SP28SE/106)

These boreholes, sited north of Ley's Farm, c.300 m east of Hill Fields Farm on Harvest Hill Lane. They were drilled to determine the character of some of the higher tills in the Allesley area.

Core recoveries were as follows:

The sequence in these boreholes consists of tills interbedded with laminated, generally stone-free silts and sands. All the lithologies in these boreholes are notably calcareous, particularly the clay rich tills which contain large amounts of secondary calcite in places see (Figure 12). Both silty and clayey tills occur. The silty varieties mostly have a vague lamination, occasionally accentuated by clay laminae, within them. The clasts in the sandy and silty tills, which make them very distinctive, are angular to sub-angular skerry fragments from the Mercia Mudstone Group of Triassic age. Other angular and sub-angular clasts include mudstones and quartzites, probably from the Cambrian sequence, sandstones and mudstones from the Enville Group, and coal as well as moderately to well-rounded greywacke, quartz and ‘Bunter’ pebbles.

The sand and silt beds within the tills contain few granules or pebbles, and the silts they contain are laminated. Probably these beds were water-lain.

Figures and tables

Figures

(Figure 1) Area of this report relative to area of whole contract is shown with bold outline

(Figure 2) Comparative sections of the Productive Coal Measures (North eastern part of SP 28 SE)

(Figure 3) Comparative sections of the Productive Coal Measures (South western part of SP 28 SE).

(Figure 4) Sections of the Coventry Sandstone Formation in the Meriden Waterworks Boreholes

(Figure 5) Logs of principal sections of the Coventry Sandstone Formation exposed on sheet SP 28 SE

(Figure 6) Field sketch of Coventry Sandstone Formation at a quarry SW of Meriden Shafts [SP 2667 8288]

(Figure 7) Sub-drift rock head elevation

(Figure 8) Thickness of drift

(Figure 9) Key to Logs of Boreholes (SP28 SE/100) A-D (Figure 10), (SP28SE/101) (SP28SE/102) (Figure 11), (SP28SE/103) (SP28SE/104) (SP28SE/105) (SP28SE/106) (Figure 12)

(Figure 10) Windmill House Farm Boreholes (SP 28 SE/100) A-D. For Key see (Figure 9)

(Figure 11) Windmill House Farm Hill. For Key see (Figure 9)

(Figure 12) Ley's Farm Boreholes. For Key see (Figure 9)

Tables

(Table 1). Summary of Westphalian–Stephanian Lithostratigraphy