Content and licensingview original scan buy a printed copy

Geological notes and local details for 1:10 000 sheets: SP28SW (Meriden) British Geological Survey Technical Report WA/89/22

M G Sumbler

Publications viewer record

For images see PDF

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

British Geological Survey Technical Report WA/89/22 Onshore Geology Series

Subject index Geology, Quaternary, Triassic, Upper Carboniferous, Cambrian

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.

© Crown copyright 1989 Keyworth, Nottingham British Geological Survey 1989 Technical Report WA/89/22

Geographical index UK, C England, Warwickshire, Meriden

Summary

The geology of sheet SP28SW (Meriden) is described, with emphasis on significant exposed sections and borehole logs. The Cambrian and most of the Carboniferous rocks are not represented at outcrop, and are known only from boreholes. Graphic logs of the cored sections of these boreholes are presented. The Carboniferous rocks occur on the west side of the Warwickshire Coalfield and are terminated by the Meriden Fault. The Triassic rocks to the west are heavily drift covered and are poorly known.

Details are given-of the lithologies and thicknesses of the drift deposits with diagrams to show their thickness and the elevation of the sub-drift topography.

Attention is drawn to the mineral resources of the area, and a schedule of boreholes is appended.

Introduction

This account describes the geology of 1:10 000 Sheet SP28SW (Figure 1). The area was first geologically surveyed on the one-inch scale by H H Howell and A C Ramsay, and is included in Old Series One-Inch Sheets 54NE and 62SE, published in 1855. The solid geology of the area is briefly described by Howell (1859).

The area was surveyed on the six-inch scale by C H Cunnington and T Eastwood in 1913 and 1915, and is included in one-inch (or 1:50 000) New Series sheets 168 (Birmingham) and 169 (Coventry), first published in 1924 and 1922 respectively. Explanatory memoirs for these sheets have been published (Eastwood and others 1923, 1925). The whole area was resurveyed on the 1:10 000 scale by M G Sumbler in 1980, with revisions by K M Bardell, R A Old and J G Rees in 1987–88. The work was supported by the Department of the Environment through its membership of the Geological Survey Consortium, and this report, originally published in 1982, has been revised in connection with a subsequent contract with the Department.

A BGS drilling programme to investigate the sand and gravel resources of this, and adjacent districts, carried out in 1980–81, is described in Cannell (1982).

The area is situated midway between Coventry and Birmingham, on the western margin of the concealed Warwickshire coalfield. It is largely given over to agriculture. The coalfield boundary fault system runs roughly north-south through Meriden. To the east, the Enville Group, with major feature forming sandstones, forms the highest ground of the area, reaching over 160 m OD. Westwards, the ground slopes gently down to heights of around 90 to 100 m OD. Most of this ground is underlain by Mercia Mudstone, although a few inliers of Bromsgrove Sandstone outcrop along the boundary fault system. The River Blythe, a tributary of the Tame, runs from south to north through the western part of the area, and near Hampton-in-Arden, the Arden Sandstone, the only mappable horizon within the Mercia Mudstone, forms steep riverside bluffs. A large part of the Mercia Mudstone outcrop, mainly east of the River Blythe, is concealed beneath thick glacial and fluvio-glacial sand and gravel, which has been extensively worked for aggregate. Along the Blythe valley, these (Figure 1). deposits have apparently been partly reworked by the river, which has cut a broad bench at around 96 m OD. River terrace deposits are not well developed in the Blythe valley, except for first terrace gravels and loams, which commonly border the floodplain. The relationship between the terrace deposits and the alluvium indicates that the River Blythe has a complex history.

Similar reports covering adjoining sheets are:

• SP18SE Elmdon (Sumbler, 1982)
• SP27NW Berkswell and Balsall Common (Old, 1987)
• SP28NW Maxstoke (Old, 1989)
• SP28SE Allesley (Rees, 1989)

Geological sequence

The geological sequence represented in the area, either proved at the surface or in boreholes, or inferred from adjacent areas is as follows:

Cambrian

Boreholes drilled by British Coal in this and adjacent areas show that the Carboniferous rocks of the Warwickshire Coalfield are underlain by Cambrian sediments. The British Coal Berryfields Farm (1977) Borehole [SP 2498 8148] proved 9.10 m of green-grey fissile mudstone with some thin (c. 5 mm) sandy and silty layers, below the base of the Productive Coal Measures at 1003.70 m. The mudstone yielded acrotretid and linguellid brachiopods, suggesting a horizon at, or above, the base of the Merevale Shales (Tremadoc) of the Nuneaton district. The beds also yielded abundant acritarchs, which suggest a late Middle Cambrian to early Upper Cambrian age.

Carboniferous

Upper Carboniferous (Westphalian) beds from the Productive Coal Measures up to the Enville Group occur at outcrop, or have been proved by boreholes, east of the Meriden Fault. They rest unconformably on the Cambrian basement. The Carboniferous sequence beneath the Triassic west of the Meriden Fault is unproven in this area, although limited seismic data suggests that the sequence is similar.

The Westphalian Series is divided into four stages, A–D in ascending order. This chronostratigraphic subdivision is difficult to apply rigorously in Warwickshire, due to the lack of palaeontological evidence at some horizons. The base of Westphalian B is defined by the Vanderbeckei (Seven Feet) Marine Band, which occurs just above the Seven Feet (and Thin) coals in the northern part of the coalfield. In this area, it is absent, but its horizon probably lies close below the Thick Coal. The base of Westphalian C is drawn at the Aegiranum (Nuneaton) Marine Band which has not been found within this area, although it has been proved to the east (Rees, 1989). Its absence in this area is due to the Etruria Marl facies occuring at this stratigraphic level (Fulton and Williams, 1988). Due to paucity of fossil evidence, the position of the Westphalian C–D boundary is uncertain, but it probably corresponds approximately with the base of the Halesowen Formation. No Carboniferous beds younger than Westphalian D are represented in the area.

Productive Coal Measures

The upper part of the Productive Coal Measures was penetrated in the Packington Borehole [SP 2471 8479], drilled in the early part of this century, but the only information for the whole sequence from this area comes from the Berryfields Farm Borehole (Figure 2), for which the detailed written log is confidential. The thickness of the Productive Coal Measures is about 130 m to 140 m; Westphalian A being of the order 40 m to 50 m thick, and Westphalian B perhaps 80 m to 90 m thick; Westphalian C is largely represented by Etruria Marl.

The Productive Coal Measures are predominantly composed of mudstones, with a few sandstones in some parts of the sequence. A number of coal seams occur, the most important being the composite Thick Coal, near the base of Westphalian B. The identification of the other named seams (Figure 2) is tentative.

In the Packington Borehole, 36.6 m of Productive Coal Measures was penetrated below the base of the Etruria Marl at 575.8 m as follows:

Etruria Marl Formation

The Etruria Marl Formation is probably entirely of Westphalian C age. It consists of red-brown and grey mottled mudstones and siltstones, with mudstone flake breccias, and a few grey beds of Productive Coal Measures aspect, including rare inferior coals. The mudstone flake breccias ('pellet rocks') are probably mainly intraformational, but may include flakes of Cambrian Shale. The coarse sandstones and breccias ('espleys') characteristic of the Etruria Marl in the northern part of the Warwickshire Coalfield are almost entirely absent in this area.

In the Packington Borehole the Etruria Marl was 101.1 m thick, and in the Berryfields Farm Borehole c. 137.5 m. The boundary between the Etruria Marl and the underlying Productive Coal Measures is diachronous and gradational, with sporadic reddish and ochreous stained beds occurring below the lower limit of the more consistently red Etruria Marl.

Halesowen Formation

The Halesowen Formation marks a return to an environment similar to that in which the Productive Coal Measures were laid down. Its base is very sharp, and unconformable on the Etruria Marl, accounting for some of the thickness variation of the latter (Mitchell 1942, p.13, Old and others, 1989).

The Formation consists predominantly of grey sandstone, particularly in its lower part, together with mudstone and thin coal seams. The base of the Formation in the Packington Borehole is placed where grey mudstone passes down into red Etruria Marl mudstone (Figure 2). The boundary was not cored at Berryfields Farm and the base has been taken below the thick basal sandstone recognisable on geophysical logs.

In the Packington Borehole the top of the Formation is taken above a grey sandstone at 394.4 m, but the mudstones beneath to 426 m are described in the log as 'red and blue marl', and their base could be taken as the top of the Halesowen Formation (Figure 2). These alternatives give thicknesses of 82 m and 51 m respectively for the Formation. At Berryfields Farm the top of the Halesowen is tentatively placed at 681 m, below which the chipping samples are predominantly grey, giving a thickness of 54 m for the Formation.

The basal sandstone is 34.6 m thick in the Packington Borehole and 33 m in Berryfields Farm, and is the equivalent of the '100 ft sandstone' of earlier writers (e.g. Eastwood and others, 1923). It is overlain in the Packington Borehole by 0.15 m of grey 'Spirortis' limestone which is probably the Index Limestone, a marker widely developed in the Warwickshire Coalfield (Eastwood and others, 1923, p. 73). The limestone is overlain by 14.7 m of grey, gritty and 'shalt'' sandstone interbedded with grey sandy mudstone, followed by 'red and blue marl'.

Keele Formation

The Keele Formation probably averages about 275 m in thickness in the area, although its lower and, more particularly, its upper boundaries are rather indefinite. In the Packington Borehole it is 260.0 m thick, and in the Berryfields Farm Borehole, c. 293 m. It consists predominantly of red mudstones with subordinate beds of red and grey sandstone, which are more common in the upper part of the formation. In the Packington Borehole, mudstone flake conglomerates ('pellet rocks') occur at several horizons. According to Eastwood and others, (1923, pp 89–90), the Maxstoke Spirorbis Limestone lies at 170.1 m in the borehole, i.e., 224 m above the base of the Keele Formation. Possibly the same Limestone was mapped at outcrop just to the west by C.H. Cunnington, but no trace of this band could be found during the present survey and the outcrop shown on the map is taken from Cunnington's survey.

Enville Group

Two formations have been recognised within the Group in this area. The lower — the Coventry Sandstone Formation — probably averages about 400 m in thickness, of which the uppermost 300 m come to crop. There is some evidence that the Formation thickens northwards at the expense of the overlying Tile Hill Mudstone Formation. Near Berkswell, just south of the sheet margin, geophysical logs of British Coal boreholes suggest that the Coventry Sandstone is approximately 300 mm to 320 mm in thickness (Old 1987), but in the Berryfields Farm Borehole, which commenced very close to the top of the Formation, c. 388 m of Coventry Sandstone was proved.

The Coventry Sandstone Formation consists essentially of alternating sandstone and mudstone beds, in about equal proportions. Individual sandstone beds are commonly up to 10 m thick, and are dominantly red-brown in colour, although some minor grey colouration results from secondary reduction. The sandstones vary from fine grained and flaggy, interbedded with muds tone, to coarse grained and massive, commonly with mudflake breccias in their lower part. The mudstones are almost exclusively red-brown in colour, though some are spotted green-grey. At outcrop, the sandstones form loamy soils, commonly with a sandstone brash, and the thicker ones form strong topographic features. The mudstones give rise to red clay soils. Individual beds of both sandstone and mudstone are lenticular, and can rarely be traced any great distance, making structural interpretation somewhat uncertain. However, mapping and borehole evidence suggests that the upper and lower parts of the Formation contain relatively more mudstone and less sandstone than the middle part, and recognition of these broad subdivisions has permitted the mapping of several faults.

In the Packington Borehole, a Spirorbis limestone occurs at a depth of 17.6 m, i.e., 116.8 m above the base of the Formation (Eastwood and others, 1923 P 73).

In an old quarry [SP 2474 8380], 3 m of apparently massive, coarse, red-brown sandstone is exposed, dipping south at c. 15°. This dip may be partly due to cross-bedding, as the general dip in the area appears to be south-easterly.

The brash on the valley sides near Berryfields Farm [SP 246 814]; [SP 248 811] and, in particular, immediately east of the margin of the area [SP 801 814] contains a significant amount of silicified wood, in association with sandstone. This wood is variously black, red and cream coloured. The structure of the original wood can generally be clearly seen on weathered surfaces, though it is usually rather obscure in cross-section due to recrystallisation. Mapping shows that the fossil wood originates from a single sandstone bed which, near Berryfields Farm [SP 246 814], includes a lens of conglomerate with clasts of Carboniferous Limestone and Spirorbis limestone (Eastwood and others, 1923 p 87).

The only other locality in the region where such fossil wood has been found is at Allesley [SP 301 805], about 5 km to the east, in the 'Allesley Conglomerate' (Eastwood et al 1923, p 87), close to the top of the Coventry Sandstone Formation. Here, the wood has been identified as Cordaites brandlingi. The occurrence in the present district undoubtedly represents the same bed.

Probably about 50 m of the overlying Tile Hill Mudstone Formation crop out in the south east of the area. The Formation is similar to the Coventry Sandstone in its lithologies, but contains a higher proportion of mudstone relative to sandstone, perhaps about 70%.

Triassic

The Triassic rocks were laid down in the Knowle Basin, which is bounded to the east by the Meriden Fault and associated sub-parallel north-south faults. All these faults were probably active in Triassic times and the Triassic formations probably thicken westwards. The uppermost part of the Bromsgrove Sandstone Formation and nearly the full thickness of the Mercia Mudstone Group are represented at outcrop. Borehole and seismic evidence from adjacent areas, suggests that the Bromsgrove Sandstone is underlain by older Triassic strata (probably Kidderminster Formation) which may exceed 400 m in thickness, thinning eastwards to zero as the Meriden Fault is approached, where the Bromsgrove Sandstone probably rests directly on Upper Carboniferous rocks (Old 1987, 1989).

Bromsgrove Sandstone Formation

The uppermost 20 m or so of the Bromsgrove Sandstone crops out in faulted inliers west of the Meriden Fault. Lower beds are unproved in this district, but the Formation may be 200 m or more in thickness, probably thining eastwards towards the Meriden Fault.

The Formation consists of sandstone, with subordinate beds of mudstone. The sandstones are generally grey to green grey, but weather to buff, pink and brown. They are mostly soft, poorly cemented, fine to medium grained and commonly micaceous. The mudstones are red-brown or green-grey in colour, and are commonly sandy or silty to varying degrees. The Bromsgrove Sandstone gives rise to a sandy loam soil. It rarely, if ever, gives rise to a sandstone brash, although lumps of sandstone are often thrown out from ditches.

Immediately west of the Meriden Fault at Cornet's End [SP 2393 8114], uppermost Bromsgrove Sandstone is exposed in a ditch. It consists of interbedded green-grey fine sandstone and red mudstone. The beds are highly disturbed and broken, due to the proximity of the fault, but appear to dip gently westward, the dip increasing as the fault is approached.

Cunnington (1913) noted exposures in two quarries now largely obscurred. At Meriden Hall [SP 2420 8175], he recorded 6 m of medium grained yellow-white sandstone, massive and false bedded, with much mica, irregularly bedded with red marl. Near Old Hall Farm [SP 2418 8287], he noted 2.4 m of grey-brown coarse, friable sandstone, often maganese stained, the lowest part being very friable, coarse and greenish and containing pellets of green marl and small black pebbles; the sandstone rested on 0.6 m of pinkish red marl. Cunnington believed this exposure to fall within the Enville Group, but his description, its westerly dip and evidence from the present survey all suggest that it is Bromsgrove Sandstone.

Around Cornet's End [SP 232 809] a number of confidential gravel trial bores have terminated in Bromsgrove Sandstone beneath drift. The evidence of these bores suggests that the outcrop is limited westwards by a fault, which probably passes through the disused eastern section of Cornet's End Gravel Pit. The quarry manager reports that blocks of sandstone were dug from the pit floor near Keepers Cottage [SP 233 810].

Mercia Mudstone Group

From borehole and seismic data in adjacent areas, the full thickness of the Mercia Mudstone Group hereabouts is estimated to be of the order of 350 m to 400 m. The bulk of this is represented in the present area, only the uppermost part (including the Blue Anchor Formation) being absent. The Group consists mainly of red-brown mudstones, giving rise to a red clay soil, with a few thin green grey mudstone and siltstone beds (skerries).

The only mappable subdivision is the Arden Sandstone Member, an estimated 300 m above the base of the Group. It is unlikely that all of this 300 m of strata reaches outcrop in the area: there is a faulted contact between the Mercia Mudstone and the Bromsgrove Sandstone to the west of the Meriden Fault, and other sub-parallel faults with a westward downthrow may occur in the drift-covered ground to the west.

The Mercia Mudstone outcrop is dotted with small pits where the mudstone was dug for brickmaking and 'marling' the soil, but these are now mostly overgrown, and the only major section of the red mudstones is at Jackson's Brickworks (Arden Brick Co. Ltd.). The quarry [SP 205 826] is about 15 m deep but, as the beds dip at c. 5° to the north east, a total of about 25 m of beds are exposed. The precise stratigraphic position of the section within the sequence is uncertain, although it probably lies close above the Arden Sandstone. The composite section is as follows:-

Beds 9a and 9b, and to a lesser extent bed 2, form striking colour bands in the face. Beds 4 to 7 inclusive form a hard band, but this has no significant topographic expression in the adjoining fields.

An exploratory borehole, drilled for the North Warwickshire Water Co. in 1903 (SP28SW/181), is sited near Mouldings Green Farm [SP 218 822] and a summary log given on the map. A more complete log is given by Butler and Lee (1943, p 68). The exact borehole site is uncertain, but the presence of probable Arden Sandstone at a depth of 42.4 m suggests that a fault separates the borehole and an outcrop of Arden Sandstone mapped 0.3 km to the south [SP 218 819].

Arden Sandstone Member

The Arden Sandstone consists of pale green-grey sandstone, siltstone and mudstone, interbedded with red mudstone. At several localities, dark grey mudstones have been noted. The thickness of the member is variable, but probably reaches up to 10 m. In the area to the west there is some evidence that it thins to zero (Sumbler 1982); such thinning may account for the apparent absence of the bed between Molands Bridge [SP 220 820] and Little Packington [SP 220 847]. No evidence was found for the outcrops in this area shown on the current One Inch Sheet 168 (Birmingham) (1924 edition).

The Arden Sandstone forms bold features on the western flank of the Blythe Valley near Hampton in Arden. Here, it includes a bed of red mudstone, perhaps several metres thick. The beds above the red mudstone include much fine sandstone, but the beds beneath are made up dominantly of green-grey siltstone and mudstone.

South of Hampton in Arden, debris from a gas pipeline trench [SP 2040 8018] to [SP 2048 8009] consisted largely of thinly bedded green-grey siltstone and grey sandstone, commonly ripple-marked, with thin mudstone layers bearing shrinkage cracks. An exposure in the stream to the south [SP 2073 8010] showed 0.4 m of green-grey silty mudstone beneath First Terrace loam.

Arden Sandstone caps the steep bluff at Siden Hill Wood. Old pits, presumably for building stone, occur at the north end of the wood [SP 2123 8073]; all are now filled, but pieces of grey sandstone can be found in the debris. The lower part of the member crops out at the base of the bluff; in a ditch (from [SP 2137 8065] northwards), interbedded red mudstone and green-grey mudstone and siltstone were exposed to a maximum depth of 0.5 m.

In a shallow cutting on Meriden Road, Hampton in Arden [SP 2155 8145], pale to dark green grey thinly bedded siltstone is poorly exposed over a distance of about 80 m. To the north east [SP 2127 8157], green-grey sandstone and siltstone forms the bed of the River Blythe. In the adjacent river bank, 1 m of red mudstone is exposed above 1 m of interbedded pale green-grey siltstone and mudstone.

The steep river bluff south west of Mouldings Green Farm [SP 214 818] is capped by Arden Sandstone, which forms a dense brash of green siltstone and pale grey sandstone in the fields. Cunnington (1913) recorded an exposure of red marl with a coarse whitish green sandstone at the top, containing fish scales. The Arden Sandstone has been quarried at two sites nearby [SP 2147 8182]; [SP 2168 8189].

A skerry, probably the Arden Sandstone, crops out in the valley west of Diddington Lane. Pieces of grey sandstone occur amongst red mudstone debris in an old pit [SP 2076 8223], and 0.5 m red and green-grey mudstone is exposed in the stream to the north east [SP 2069 8231]. The outcrop has been mapped as a north eastward dipping inlier, bounded by a fault to the south west. No evidence was found to justify the continuous outcrop of Arden Sandstone between this point and the outcrops at Hampton in Arden (described above) as shown on the current edition of One-Inch Sheet 168.

The Arden Sandstone is brought to crop by faulting in the Blythe valley at Little Packington [SP 220 848]. The presence and position of the faults which bound the outcrop to the south west and north, beneath alluvium and terrace gravels, are inferred from the evidence of gravel trial boreholes. In the backface of an old quarry [SP 2187 8452], a section showed 0.1 m of grey flaggy sandstone beneath 0.3 m of red and green-grey laminated mudstone. The base of the Arden Sandstone was exposed in the river bluff close to the north [SP 2191 8468]. Above red mudstone, the section showed:

Quaternary

Glacial Deposits

The glacial deposits mapped in the district have been classified (somewhat arbitarily) as Glacial Sand and Gravel, and Fluvio-Glacial Gravel. The latter has only been recognised in the eastern part of the district, where it clearly post-dates the Glacial Sand and Gravel. The possibility that some of the high level deposits designated 'Glacial Sand and Gravel' west of the River Blythe are in fact consanguineous with the Fluvio-Glacial Gravel cannot be discounted. The thickness of these deposits is shown in (Figure 3).

Glacial Sand and Gravel

Glacial Sand and Gravel covers a broad north-south trending swathe of ground on the east side of the river Blythe; and is overlapped by fluvio-glacial gravels along its eastern margin. West of the Blythe, scattered outliers occur on hilltops, and the north west part of the district includes the south eastern corner of a broad tract of glacial sand and gravel that stretches several kilometres to north and west. The deposits give rise to sandy soil, invariably containing scattered pebbles. In sections, however, they are seen to vary widely in lithology, through all intermediates between fine silty sand and poorly sorted boulder gravel. Pebbles are dominantly of Bunter quartzite, with some Triassic sandstones (Bromsgrove and ?Arden Sandstone), and extremely rare flints. Boulders of Cambrian quartzite and Enville Sandstone have been dug from the base of the deposit at Cornet's End. Shotton (1977, p 18) also records granite, rhyolite, ignimbrite, andesite and andesitic tuff from North Wales, the Lake District or Scotland.  

An attempted reconstruction of the bedrock topography, beneath the glacial drift, based on outcrop levels and borehole data is given in (Figure 4). In the south, the main element in this topography is an elongate depression, up to 1.5 km across. Along its eastern margin, the bedrock falls steeply (locally perhaps at up to 15°) from around +120 m OD to below +80 m OD in the base of the depression. A portion of the western margin of the depression is preserved south and east of Patrick Farm [SP 217 810], but elsewhere has been destroyed by the cutting of the Blythe valley. In the north, information is less complete, but the base of the Glacial Sand and Gravel appears to dip gently towards the Blythe valley, the dip steepening in the valley itself, suggesting that the modern valley follows the line of the more ancient depression, and has cut down below its base.

Cross-bedding in the Glacial Sand and Gravel at Cornet's End [SP 233 813] and the Somers [SP 225 823] dips southwards indicating deposition from the north which accords with the pebble and boulder content of the gravels. However the floor of the depression undulates or falls gently northwards suggesting that the deposits infill a pre-glacial valley or depression and its infilling represents the course of a sub-glacial channel.

A number of sections of Glacial Sand and Gravel have been recorded at Meriden Quarry, Cornet's End [SP 233 814], operated by Tilcon Ltd. A composite section of the 1980 working face, (around [SP 2357 8155]) was as follows:

Farther west in the pit, the basal sand is more pebbly, and boulders of up to 0.3 m across have been dredged from the base of the deposit by dragline. In a ditch immediately east of the face, 1.3 m of red-brown, poorly bedded silty clay, with a few layers of brown silt and rare Bunter quartzite pebbles, was exposed beneath fluvio-glacial gravels. This material does not appear in the pit face, and seems to be restricted to the margins of the sand, possibly representing reworked Mercia Mudstone from the channel walls.

Shotton (1977, p 18) recorded a section of the pit, showing 4 m of level-bedded sands ('Upper lacustrine sands'), underlain by 3.5 m of coarser level bedded yellow sand with gravel layers ('Middle Sand Series'), in turn underlain by up to 12 m of cross-bedded coarse gravel and sand ('Lower Gravel Series'). The thickness of the Glacial Sand and Gravel in the sections described above is up to 19.5 m. The deposits are overlain by Fluvio-Glacial Gravel at about +80 m OD, implying a total original thickness of about 28 m. A graphic section of the 1988 working faces is shown in (Figure 5).

In 1987 the gravel pits to the south of Cornet's End Lane, operated by Western Aggregates Ltd., exposed much more varied deposits than those to the north.

At the north end of the workings the following section was seen [SP 2259 8097]:

At the south end of the workings the section was [SP 2257 8032]:

At the Somers [SP 224 824], about 1 km to the north west, extensive workings in Glacial Sand and Gravel are now flooded, and used as a coarse fishery. At the southern end of the workings [SP 2257 8207] there are rather degraded exposures showing up to 5 m of horizontally bedded and trough cross-bedded brown sand with seams of pebbles. Borehole records show that, in the workings, the deposits were up to 11.6 m thick, extending down to about +82 m OD. The deposits proved in the boreholes are laterally very variable, but consist dominantly of sand (as described above), commonly underlain by more gravelly beds. The worked section was generally overlain by 1 m to 2 m of brown and grey silty and clayey sand overburden, locally underlain by leached grey-white gravelly sand which rarely extends more than 2.4 m below the ground surface. It is possible that these upper beds represent glacial deposits reworked by the River Blythe (see below), or Head derived from the fluvio-glacial gravels to the east.

A small area of sand and gravel workings to the east of Somers Road is largely backfilled, and no exposures remain. In the eastern part of the pit (Figure 5). [SP 2306 8276], Cunnington (1913) noted 3 m of "streaked whitish and yellowish-red sand with occasional earthy layers. Thin lenticular layers of fine angular pebbles including flints.

North west of Packington Old Hall [SP 228 849], flooded workings are now used as a trout fishery. Some poor exposures of up to 3 m of buff to brown gravelly sand can be seen.

West of the River Blythe, 6 m of red sand, with only a few pebbles, are poorly exposed in slips in the railway cutting 0.4 km south east of Park Farm [SP 2087 8374]. In a gravel pit immediately east of the railway [SP 2090 8364], Eastwood and others (1925, p119) noted 12 ft (3.7 m) of well bedded gravel with occasional flints, the upper 5 ft (1.5 m) disturbed and clayey in the north east part.

In 1963, during construction of the underpass north of Park Farm [SP 2062 8414], R J Wyatt (BGS unpublished field notes) recorded c. 6 m of 'medium grained, clean well-graded bedded sand, predominantly bright orange or orange-brown in colour, showing distinct false bedding; few scattered pebbles occur in uppermost 8 ft (2.4 m) and very impersistent strings of small pebbles in 4 ft (1.2 m) below: a few thin lenticular bands of pebbly gravel occur (generally up to c. 1 ft thick) consisting of abundant well rounded pebbles in sandy matrix'.

West of Little Packington [SP 211 849], a formerly extensive gravel pit is now incorporated into the major Little Packington Landfill Site. In the south east face, adjacent to Packington Lane, many poor exposures of red and brown sand with scattered pebbles were seen in 1980. About 5 m of sand and gravel have been removed and Mercia Mudstone was sporadically exposed in ditches in the pit floor.

Fluvio-Glacial Gravels

Fluvio-Glacial gravels have been recognised only east of the River Blythe, where they overlap the margins of the Glacial Sand and Gravel. They consist of poorly sorted, commonly clayey, sand and gravel, containing bodies of till-like clays. The pebble content of the gravel resembles that of the glacial gravels, being dominated by Bunter quartzite, but also includes small proportions of (?Welsh) Lower Palaeozoic rocks, which have not been recorded (at least in the same quantity) in the glacial gravel. The clays are dominantly red brown in colour, and contain Bunter quartzite pebbles and fragments of Enville and (?Triassic) sandstones and a little coal. They have not been mapped separately, but have been recorded in boreholes and in a section (see below). The pebble content of the deposits suggest a roughly northerly derivation, as for the Glacial Sand and Gravel.

The Fluvio-Glacial Gravel forms a thin sheet, overlapping the steep margins of the possibly sub-glacial channel (see above). Farther north, the deposits are not so readily separated, and mapping is largely on the basis of a slight topographic feature, which, it is thought, marks the western margin of the Fluvio-Glacial Gravel where it overlies Glacial Sand and Gravel.

Around 1.2 m of Fluvio-Glacial Gravel is exposed at the top of the eastern and northern faces of Cornet's End Gravel Pit [SP 234 811]; [SP 236 815]; [SP 236 817]. It consists of grey, brown and ochreous clayey sand and sandy clay with Bunter quartzite pebbles. No bedding could be distinguished, but the whole deposit is cryoturbated, with frost-wedge structures extending to 1.3 m down into the underlying Glacial Sand and Gravel (Figure 5).

At Outwoods, 2 m of red-brown clay containing pebbles and large blocks of red Enville sandstone were exposed in a pipeline trench [SP 2383 8484]. Fluvio-Glacial gravels have been penetrated in a number of gravel trial bores (confidential). Three BGS boreholes (Cannell, 1982), proved a large proportion of till in the deposit. The Park Farm Borehole (SP28SW/335) [SP 2328 8016] proved 2.5 m of brown sandy gravel, underlain by 4.9 m of red-brown stony clay, above bedrock. The Hampton Lane Borehole (SP28SW/32) [2346 8216] proved 5 m of red-brown sandy pebbly clay, above glacial sand. The Harding's Wood Borehole (SP28SW/325) [SP 2351 8323] proved red-brown pebbly clay, with a bed of brown sand to 13.6 m, above 2.1 m of brown sand with scattered pebbles, on bedrock: the lower sand may represent Glacial Sand and Gravel.

River Terrace Deposits

River Terrace Deposits, mainly sand and gravel, commonly flank the flood-plain of the Blythe. In addition, a broad bench cut into the Glacial Sand and Gravel may be the result of reworking by the river at an early stage of downcutting. South of the district, the bench is well preserved, and falls gently in height to the north, but within the district the bench is too dissected for any consistent gradient to be discerned. It is clearest on the eastern side of the valley, where the Glacial Sand and Gravel forms a plateau at around +95 to +99 m OD. It is particularly obvious south of The Somers [SP 225 819], where it is about 500 m wide and bounded on the east by a pronounced rise of about 5 m (capped by Fluvio-Glacial Gravel) that trends roughly parallel to, and just east of, Somers Lane. No deposits have been mapped on the bench, although the upper part of the Glacial Sand and Gravel may have been reworked.

Deposits of the Second Terrace have been recognised at three localities near Molands Bridge [SP 217 814]; [SP 222 818]; [SP 219 821]. They form gently sloping spreads, with a poorly preserved bench about 3 m to 5 m above the modern river floodplain. The deposits consist of brown sandy gravel, similar in composition to, and evidently derived from, the older glacial and fluvio-glacial sands and gravels, from which they are distinguishable solely on the basis on their situation and form.

Deposits of the First Terrace are more widespread than those of the Second Terrace, and form well-defined benches bordering the floodplain, generally about 1 m to 1.5 m above the alluvium and rising gently to about 2 m further from the river. The deposits consist of loamy sand and gravel, in parts very clayey or silty. Gravel trial bores suggest that the deposits average about 1.5 m in thickness, but locally reach up to 3 m, thus extending below the level of the floodplain.

West of Packhorse Bridge, Hampton in Arden [SP 210 801], dark grey clays have been assigned to the First Terrace. In a ditch running across the terrace, grey and grey brown clay up to 1.3 m thick is exposed above Mercia Mudstone [SP 2080 8006]. Near the bridge, the terrace is about 1 m above the modern floodplain, but it grades imperceptibly downstream to the north into the modern alluvium, and is clearly slightly younger than the terrace gravels on the opposite side of the stream. To the south, the clayey deposits can be seen to mark an abandoned river coarse, which diverges from the present course of the Blythe at Barston Bridge (Old 1987), at which point [SP 216 784] the clay terrace corresponds in height with the gravel terrace on the present course of the Blythe (ie, about 3 m to 4 m above the modern floodplain). These relationships suggest that the Blythe originally flowed along its present course, depositing the terrace gravel. Following diversion, the clay terrace was then deposited, though downcutting did not proceed further upstream than Packhorse Bridge, above which the clay and gravel terraces correspond in height. The river then resumed its original course, downcutting proceeded upstream, and the modern floodplain was formed.

Alluvium

Alluvium forms the floodplain of the River Blythe, and floors the tributary valleys. It consists of grey or brown loamy clay and silt, commonly containing sandy and peaty lenses, generally with a thin basal lag deposit of gravel. Along the Blythe, boreholes indicate that the alluvium may locally exceed 3 m in thickness, although 2 m is probably a more usual average. The alluvium of the streams draining the Glacial Sand and Gravel at Cornet's End [SP 221 802]; [SP 227 814] is, in places, conspicuously gravelly. At Mercote Lodge [SP 220 802] the stream deposits appear to grade into the first terrace bench, suggesting that the alluvium here is in part contemporaneous with the First Terrace gravels.

The hill east of Patrick Bridge [SP 218 811] is encircled by alluvium, a broad alluvial flat east of the hill joining the Blythe floodplain alluvium to the north and south [SP 218 817]; [SP 216 808]. This alluvial flat may mark a former coarse of the River Blythe, although this seems unlikely, for First Terrace gravels border the modern Blythe floodplain north of the hill [SP 216 816] showing that the Blythe followed its present course prior to formation of the alluvial flat to the east. The flat was more probably formed by capture of the stream north of Hornbrook Farm [SP 223 813], (that originally drained northwards), by the stream to the south [SP 223 809]; all the drainage now flows around the south of the hill, and the northern part of the alluvial flat is virtually dry.

Economic geology

Brickclay

Mercia Mudstone is dug for brickmaking at the Jackson's Brickworks (Arden Brick Co. Ltd.) [SP 205 828]. After crushing and forming the clay, the bricks are fired in gas-fuelled kilns. A variety of different colours of facing bricks are produced by the use of additives. Resources are virtually unlimited, although there are obvious practical limits to the depth and extent of quarrying.

Coal

The western margin of the South Warwickshire Prospect, a major area of unworked Thick Coal is formed by the Meriden Fault. Details of the prospect have been published by British Coal (National Coal Board, 1985; British Coal Corporation, 1987).

Sand and gravel

Glacial Sand and Gravel was extensively worked by the Amey Roadstone Corporation at Little Packington [SP 210 849], Great Packington [SP 228 849] and The Somers [SP 223 824]. The currently working pits are at Cornets End [SP 235 819]; [SP 225 806]. The former operated by Tilcon Ltd. currently produces mainly sand, used largely as building sand, and, with additives, as moulding sand. The latter, operated by Western Aggregates Ltd. produces sand and gravel.

Of the remaining unworked areas of Glacial Sand and Gravel, the most promising in terms of thickness are those north of Middle Bickenhill [SP 202 841] and at Harding's Wood [SP 233 832].

Fluvio-Glacial gravels and river terrace deposits are generally likely to be too clayey, too thin, or too limited in extent to be of commercial interest, although First Terrace gravels were worked on a small scale at Packhorse Bridge [SP 213 802].

A fuller account of the sand and gravel resources of the district is given by Cannell (1982).

References

BUTLER, A J and LEE, J. 1943. Water supply from underground sources of the Birmingham-Gloucester district. Wartime Pamphlet No. 32, Part II. Geological Survey of Great Britain. 70 pp.

BRITISH COAL CORPORATION, 1987. Proposed colliery at Hawkhurst Moor. British Coal Corporation: Central Area.

CANNELL, B. 1982. The Sand and Gravel Resources of the Country East of Solihull, Warwickshire. Description of parts of 1:25 000 sheets SP 17, 18, 27 and 28. Mineral Assessment Report of the Institute of Geological Sciences No. 115.

CUNNINGTON, C H. 1913. Six-inch geological field maps Warwickshire 15 and 20. British Geological Survey, unpublished.

EASTWOOD, T, GIBSON W, CANTRILL, T C and WHITEHEAD, T H. 1923. The Geology of the Country around Coventry. Memoir of the Geological Survey.

EASTWOOD, T., WHITEHEAD, T H and ROBERTSON, T, 1925. The Geology of the Country around Birmingham. Memoir of the Geological Survey.

HOWELL, H H. 1859. The geology of the Warwickshire coalfield and the Permian rocks and Trias of the surrounding district. Memoir of the Geological Survey.

MITCHELL, G H. 1942. The geology of the Warwickshire coalfield. Wartime Pamphlet No. 25, Geological Survey of Great Britain. 40 pp.

NATIONAL COAL BOARD, 1985. The South Warwickshire Prospect. National Coal Board: South Midlands Area.

OLD, R A. 1987. Geological notes and local details for 1:10 000 sheets: SP27NW (Berkswell and Balsall Common). Keyworth: British Geological Survey.

OLD, R A. 1989. Geological notes and local details for 1:10,000 sheets: SP28NW (Maxstoke). British Geological Survey Technical Report WA/89/20.

OLD, R A., BRIDGE, D McC and REES J G. 1989. The geology of the Coventry area. British Geological Survey Technical Report WA/89/29.

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

SHOTTON, F W. 1977. The English Midlands. Guidebook for excursion A2 X INQUA Congress, 51 pp. Norwich: Geo Abstracts Limited.

SUMBLER, M G. 1982. Geological notes and local details for 1:10 000 sheets: SP18SE (Elmdon). Keyworth: Institute of Geological Sciences.

Appendix: Schedule of boreholes on Sheet SP28SW

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

c Denotes confidential records, details of which may only be released by permission of the original source.

Figures, plates and tables

For images see PDF

Figures

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

(Figure 2). Comparative Westphalian successions in cored boreholes

(Figure 3). Thickness of drift

(Figure 4). Rockhead elevation at the base of the drift

(Figure 5). Generalised section of sand and gravel workings, Meriden Quarry [SP 233 818]