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Geology of the Dudley district — brief explanation of the geological map Sheet 167 Dudley

C N Waters, D M Bridge, A J Humpage, W J Barclay and N J P Smith

Bibliographic reference: Waters, C N, Bridge, D M, Humpage, A J, Barclay, W J, and Smith, N J P. 2013. Geology of the Dudley district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 167 Dudley (England and Wales).

Keyworth, Nottingham: British Geological Survey, 2013.

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

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(Front cover): Severn Valley, Bridgnorth, cutting through Permian and Triassic rocks. (P598024).

(Rear cover)

(Geological succession) Summary of the geological succession in the district.

Notes

The area covered by geological Sheet 167 Dudley is referred to as 'the district'. Ordnance Survey National Grid references are given in square brackets: [8862 8333]. Unless otherwise indicated, all should be preceded by the letters SO. Symbols in round brackets after lithostratigraphical names are those used on the geological map. Plate captions include the registration number in the National Archive of Geological Photographs, held at the BGS. Boreholes are identified by their BGS Registration Number e.g. (SO88SW/10), where the prefix indicates the 1:10 000 scale National Grid sheet.

Acknowledgements

This Sheet Explanation was written by C N Waters, D M Bridge, A J Humpage, W J Barclay and N J P Smith and was edited by M A Woods and J E Thomas; figures were produced by J Smalley, BGS Cartography, Keyworth. We acknowledge the help provided by the holders of data in permitting the transfer of these records to the National Geosciences Records Centre, BGS Keyworth. We are especially grateful for the assistance provided by Local Authorities, the Coal Authority, Environment Agency, Dudley Museum and Art Gallery, and numerous civil engineering consultants. Landowners, tenants and quarry companies are thanked for permitting access to their lands. The National Grid and other Ordnance Survey data © Crown Copyright and database rights 2013. Ordnance Survey Licence No. 100021290.

Geology of the Dudley district (summary from rear cover)

An explanation of sheet 167 (England and Wales) 1:50 000 series map

(Rear cover)

Limestone and calcareous mudstone of Silurian age occur at crop in the cores of periclines in the South Staffordshire Coalfield. These inliers also include uppermost Silurian to Upper Devonian alluvial floodplain red-beds of the Old Red Sandstone Supergroup, which also crop out across much of the western part of the district.

Mid Devonian Acadian deformation caused the folding evident in the South Staffordshire Coalfield and produced a regional tilting of the Lower Palaeozoic strata. Subsequent erosion was followed by deposition of the Westphalian Pennine Coal Measures Group, present within the Wyre Forest and South Staffordshire coalfields. During the late Westphalian there is a transition to dominantly alluvial red-beds of the Warwickshire Group. These were deposited during the closing phases of the Variscan Orogeny, associated with renewed folding and faulting. A phase of microgabbro (dolerite) and basalt intrusion and limited formation of volcaniclastic deposits occurred during Bolsovian times.

During the early Permian, alluvial fan deposits of the Clent Formation and aeolian deposits of the Bridgnorth Sandstone Formation accumulated in an arid environment. During the Triassic, the dominantly fluvial Sherwood Sandstone Group was deposited, but is now preserved only within the Stafford Basin and the Bratch Trough, formed during a phase of Permo-Triassic extensional faulting.

The Anglian glaciation of about 500 000 years ago is thought to have extended across the district. However, most of the unconsolidated Quaternary deposits present in the region were formed during the late Devensian glaciation, which ceased about 11 000 years ago. In addition to glacial and glaciofluvial deposits, the district has significant spreads of periglacial head deposits, landslide deposits and postglacial (Holocene) alluvial and terrace deposits associated with the modern courses of the rivers Severn and Stour and their tributaries.

Industrial minerals, such as coal, ironstone, fireclay, brick clay, microgabbro (dolerite) and limestone contributed to the early growth of the urban centres. Sand and gravel is sourced from Quaternary deposits and Sherwood Sandstone Group, the latter also providing building stone and represents a major aquifer.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the geology of the district covered by the geological 1:50 000 Series Sheet 167 Dudley published as a bedrock and superficial edition in 2012.

The district lies in the counties of Shropshire, Worcestershire, Staffordshire and the metropolitan district of the West Midlands. The main population centres are in the east of the district, within the Black Country conurbation that includes Bilston, Wednesbury, Sedgley, Tipton, Dudley, Brierley Hill, Kingswinford, Halesowen and Stourbridge. Scattered villages and the town of Bridgnorth lie in the west. The western and central parts of the district comprise mainly farmland and woodland, including the northern part of the Wyre Forest. The elevation of the district is typically in excess of 75 m above OD, with the highest point within the district, at 315 m above OD, in the Clent Hills in the south-east. The district is drained by the rivers Severn and Stour, which flow from north to south across the western and central parts of the district, respectively.

The bedrock of the district (Figure 1) is composed of mainly sedimentary rocks that were deposited during the Silurian, Devonian, Carboniferous, Permian and Triassic periods, between 428 and 237 Ma. The oldest strata proved are of early Wenlock to Ludlow (Silurian) age (Figure 2), which crop out in a series of inliers in the cores of anticlines and periclines in the South Staffordshire Coalfield (Figure 1). They also occur at depth beneath Carboniferous strata elsewhere in the coalfield (Figure 3). The latest Silurian (Pridoli) to Late Devonian (Famennian) red-bed succession, of the Old Red Sandstone Supergroup, (Figure 4) crops out extensively across the western part of the district, as well as in the Trimpley inlier in the south and within the South Staffordshire Coalfield inliers.

The Silurian–Devonian succession is overlain unconformably by paralic fluviodeltaic strata of the Pennine Coal Measures Group, of Langsettian to Bolsovian (Westphalian) age (Figure 5), (Figure 6) and the predominantly red-bed alluvial Warwickshire Group of Bolsovian to early Permian age. These strata crop out in the Wyre Forest in the south-west (Figure 7), and South Staffordshire Coalfield in the east (Figure 8), and occur at depth beneath the Sherwood Sandstone Group in the central and northern parts of the district (Figure 9). The Pennine Coal Measures and Warwickshire groups have yielded abundant coal, fireclay, brickclay and ironstone, the exploitation of which stimulated the growth of the urban areas in the late 18th and 19th centuries.

During the early Permian, alluvial fan deposits of the Clent Formation and aeolian deposits of the Bridgnorth Sandstone Formation accumulated in an arid environment. During the Triassic, the dominantly fluvial Sherwood Sandstone Group was deposited across the region, but is now preserved in the district only within the Stafford Basin and the Bratch Trough (Figure 9).

Following the deposition of the Sherwood Sandstone Group, there is a nonsequence with no record preserved of the geological evolution of the district until the Quaternary Period. An Anglian ice-sheet is believed to have extended across the district, although there is little evidence of deposits associated with this glaciation. During a subsequent late Devensian glaciation, ice reached as far south as Eardington and Enville (Figure 10). To the north, the topography was eroded and glacial materials, such as till, were deposited. To the south, meltwaters deposited outwash glaciofluvial deposits and incised deep and narrow valleys. During the Flandrian, alluvial and river terrace deposits were deposited by the larger stream and river systems. Mass movement deposits, including landslide and head deposits, probably formed during the latter part of the Devensian through to the Flandrian.

Chapter 2 Geological description

Silurian

Silurian strata of the Wenlock and Ludlow series (Figure 2) occur mainly at crop in a series of inliers present in the cores of anticlines developed within the South Staffordshire Coalfield (Figure 1), (Figure 3).

Strata of Wenlock age comprise, in ascending order, the Barr Limestone, Coalbrookdale and Much Wenlock Limestone formations. The formational nomenclature used is that of Bassett (1989), with relationships to former terminology shown in (Figure 2).

The Barr Limestone Formation is only proved at depth in the district, from workings associated with Springfield Colliery No. 1 Shaft [SO 958 884] (Powell et al., 2000). It is attributed to all, or part of, the riccartonensis Zone of the Sheinwoodian Stage (Bassett, 1974), and comprises about 10 m of interbedded grey, fine-grained limestone and grey mudstone with calcareous nodules and thin bentonitic clays.

The upper part of the Coalbrookdale Formation (Cbrd) crops out in the cores of the periclines of Castle Hill [SO 945 910], Wren's Nest [SO 937 923] and Hurst Hill [SO 928 940] (Figure 3) and is of Sheinwoodian to Homerian age (Cocks et al., 1992). The formation comprises about 200 m of greyish green to greenish grey, fossiliferous calcareous mudstone with thin beds of limestone nodules. The fossils are mainly benthic shelly types. The base of the formation is gradational, placed where there is a decrease in thickness and number of limestone beds in the underlying Barr Limestone Formation, and concomitant increase in mudstone beds. About 10 m thickness of the formation is interpreted to occur at the base of the Smestow Borehole [SO 8563 9286] (Glover, 1991).

The Much Wenlock Limestone Formation (Bassett, 1989) crops out in the anticlines of Castle Hill [SO 945 910], Wren's Nest [SO 937 923] and Hurst Hill [SO 928 940]. The Wren's Nest National Nature Reserve [SO 937 923] provides excellent exposure of the formation ((Plate 1); Siveter, 2000). Correlation of the formation, which is of Homerian age, with its equivalent in the Welsh Borderland type area remains contentious as the base and top of the formation is considered to occur in different graptolite biozones between the two areas (Cocks et al., 1992). Formal members identified in the type area (Bassett, 1989) have not been unequivocally recognised in the Dudley district, where the formation is locally subdivided into three members (Powell et al., 2000). The Lower Quarried Limestone Member (LQL) comprises 12 to 16 m of hard, blue-grey, fine- to medium-grained, medium-bedded, bioclastic limestone with mudstone partings, the latter occurring especially near the base and top. The beds are mainly 8–15 cm thick, and locally up to 30 cm. The member includes large bioherms (patch reefs) of fossiliferous micritic limestone, up to 6 m in diameter, with biostromes about 30 cm thick (Cutler et al., 1990). The Nodular Limestone Member (NL) is 31 to 38 m thick and comprises nodular, shelly limestone interbedded with thin partings of grey-green calcareous mudstone and siltstone. The limestones are typically in 1–10 cm-thick beds and locally up to 0.7 m (Cutler et al., 1990). The Upper Quarried Limestone Member (UQL) comprises 9 to 10 m of hard, thin- to medium-bedded (5–30 cm), coarse-grained bioclastic limestone. Nodular and flaggy limestones with mudstone partings, and stromatoporoid bioherms up to 1 m thick, occur near the base and top.

Strata of Ludlow age comprise the Lower Ludlow Shales Group and Aymestry Limestone and Whitcliffe formations. The formational nomenclature used is based on that of Bassett (1989) and Lawson and White (1989). Relationships to former classifications are shown in (Figure 2).

The Lower Ludlow Shales Group (LLS) crops out on the flanks of the Castle Hill [SO 945 910], Wren's Nest [SO 937 923] and Hurst Hill [SO 928 940] anticlines and at The Hayes [SO 929 844] (Figure 3). This informal stratigraphical name is retained until the correlation with the Ludlow succession in the Welsh Borderland is determined (Lawson and White, 1989). The group comprises about 150 m of pale grey and greenish grey, buff-weathering mudstones and sandy mudstones, slightly calcareous with impersistent beds and nodules of pale to medium grey, fine- to medium-grained limestone and thin bentonite beds. The group was formerly exposed at Dudley College [SO 9446 9072] and proved in boreholes in the Kate's Hill area of Dudley (Poole, 1970).

The Aymestry Limestone Formation (Ay) crops out in the core of the anticlines at Sedgley [SO 92 94], Turner's Hill [SO 908 917] and The Hayes, Lye [SO 930 846] (Whitehead and Pocock, 1947; Ball, 1951). It is absent from the crest of the Castle Hill [SO 945 910] and Wren's Nest [SO 937 923] anticlines, removed below the unconformity at the base of the Pennine Coal Measures Group. The forma tion, formerly referred to as the Sedgley Limestone, is considered to be of Gorstian to Ludfordian age at Turner's Hill (Cocks et al., 1992), and slightly younger than the Aymestry Limestone of the type area in the Welsh Borderland. It comprises about 8 m of grey and blue, argillaceous, nodular, bioclastic limestone, with a thin impersistent bone bed near the top at Turner's Hill (Ball, 1951).

The Whitcliffe Formation (Wc), of Ludfordian age, crops out in the cores of the anticlines at Sedgley [SO 92 94], Turner's Hill [SO 908 917], The Hayes, Lye [SO 930 846] and at Saltwells near Netherton (Whitehead and Pocock, 1947; Ball, 1951). Correlation with the Upper and Lower Whitcliffe formations of the Welsh Borderland is made by Cocks et al. (1992). The formation is between 9 and 15 m thick. At the base it comprises blue-grey nodular and flaggy argillaceous limestone, overlain by grey, olive, buff and brown shales and flaggy sandstones, passing up into more massive, buff, silty sandstones and mudstones. Important exposures were recorded at Netherton [SO 9356 8735] and The Hayes [SO 9298 8447] (Whitehead and Pocock, 1947).

Late Silurian–Devonian

The latest Silurian (Pridoli) to Devonian succession of the Old Red Sandstone Supergroup crops out extensively across the western part of the district. It forms rolling agricultural country incised by stream gullies, which provide almost all the available exposures. It also crops out in an inlier east of the River Severn around Trimpley, and in small inliers in the South Staffordshire Coalfield at Turner's Hill, Saltwells near Netherton and The Hayes at Lye (Figure 1), (Figure 3).

The Old Red Sandstone Supergroup is subdivided into the Lower and Upper Old Red Sandstone groups (Figure 4).

Pridoli–Emsian: Lower Old Red Sandstone Group

The Lower Old Red Sandstone Group comprises the Downton, Ditton and Brecon subgroups.

Downton Subgroup

The Downton Castle Sandstone Formation (DCS), of early Pridoli age (Figure 4) (White and Lawson, 1989), is about 20 m thick in the district. It crops out at Turner's Hill [SO 910 920], Brewin's Bridge near Netherton [SO 935 875], Lodge Farm [SO 9356 8735] and The Hayes [SO 930 845] (Whitehead and Pocock, 1947; Siveter and Lane, 2000). It also occurs at Gornal [SO 920 920], where a yellow and olive-buff, massive or cross-bedded sandstone with a limonitic cement was erroneously correlated as part of the Coal Measures during the previous survey. The base of the formation is marked by the Ludlow Bone Bed, which comprises up to 0.6 m of coarse-grained, calcareous sandstone, rich in brachiopods and winnowed, phosphatised fish remains (Whitehead and Pocock, 1947), typically resting on a sharp erosion surface. The bone bed is overlain by buff, silty sandstone and mudstones, which pass upwards to yellow-buff, fine-grained, micaceous, cross-bedded sandstone.

The Temeside Mudstone Formation (TM) (Figure 4) is restricted at crop to inliers at Turner's Hill [SO 915 920], the Brewin's Bridge section at Netherton [SO 9366 8767], Lye [SO 928 848] and Wollescote [SO 924 836]. The formation, of Pridoli age, consists of about 10 to 13 m of purple and olive green mudstone and siltstone, with purple and green, micaceous, fine-grained sandstone. Locally, thin 'bone beds' contain abundant fish remains, as, for example at Brewin's Bridge. Hard, buff, grey and green mudstones and sandstones are common near the top of the formation at Turner's Hill. The formation was formerly exposed in a small inlier 300 m north-west of The Hayes [SO 9284 8480] (Whitehead and Eastwood, 1927).

The Raglan Mudstone Formation (Rg) of Pridoli Series (late Silurian) to Lochkovian (Early Devonian) age (Lawson and White, 1989) was termed the Ledbury Formation in the Birmingham district (Powell et al, 2000). The main outcrop in the west of the district is poorly exposed, and much of its northern outcrop is covered by Quaternary deposits. Hereabouts it comprises 170 m thickness of red mudstones/siltstones with sporadic sandstones, interpreted as a coastal alluvial plain mudstone-dominated succession, with fish beds indicating marine influence at times (White and Lawson, 1989). The argillaceous beds are mostly pedified to varying degrees, with original sedimentary lamination largely destroyed. At outcrop, these beds weather to heavy, stiff clay. Small calcrete nodules are common, and locally form mature, coalesced nodular limestones. The topmost calcrete is a massive, rubbly nodular limestone correlated with the Bishop's Frome Limestone Member (BFL). This member was formerly referred to as the Psammosteus Limestone and included within the overlying Ditton Series (Figure 4). Devil's Hole [SO 672 929] is the best documented section in the main outcrop, exposing the topmost beds of the formation (Barclay, 2004; Dineley, 1999). At Trimpley, the formation is restricted in outcrop to the flanks of a syncline located mainly north of the Park Attwood Fault (King, 1934; Whitehead and Pocock, 1947). The thickness of the formation in the area is poorly constrained, but is thought to be greater than 140 m. In South Staffordshire, the formation occurs at crop in small inliers north of Turner's Hill [SO 91 92], at Wollescote [SO 921 838] and Brewin's Bridge [SO 9363 8770]–[SO 9371 8765] at Netherton (Plate 2). The formation also occurs extensively at subcrop beneath the unconformity at the base of the Pennine Coal Measures Group (Figure 3), with up to 80 m proved in the Lye area and 45 m at Baggeridge Colliery No. 1 Shaft [SO 8978 9297].

Ditton Subgroup

The St Maughans Formation (SMg), of Lochkovian–?Pragian age, comprises a 340 m-thick succession of interbedded sandstones and mudstones deposited in an alluvial floodplain setting in a semi-arid climate. In the main outcrop in the west, the sandstone-dominated basal part of the formation forms a bold escarpment south of Morville [SO 670 930] southwards to Harpswood [SO 680 910]. The sandstones are mainly channelised, fluvial sand bodies with sharp erosive bases and planar cross-bedding. They range from red-brown to pale green, purple and brown, and generally fine upwards from medium-grained at the base to fine-grained at the top, passing upwards through rippled, fine-grained sandstones and siltstones into the overlying mudstones. The sand bodies are up to about 1.5 m thick, locally coalescing to give thicker packets of stacked sandstones. The sandstones are low-angle cross-bedded and variably calcareous, and are generally too soft to form persistent features. Intraformational (or intraclast) conglomerates occur mainly as lenticular sheets at the base of the sandstones. They comprise red-brown/purple and pale green varieties, all containing an abundance of calcrete clasts. Fish fragments have been recorded mainly from these conglomerates, but also occur in the sandstones, particularly in the bases of channelised units. The mudstones are red-brown and locally mottled and leached to pale green to a greater or lesser degree. Laminated mudstones are common, but equally commonly, they were affected by pedogenic alteration resulting in the destruction of the primary bedding and lamination. Increased pedogenesis is represented by massive, red-brown, green and purple mottled mudstones and calcretes (pedogenic limestones) displaying a range of maturity. Small calcrete nodules show increasing size with maturity, eventually coalescing to give massive, rubbly, hard pan calcrete. Mudstones dominate the overall succession, forming about 60 per cent of the total thickness.

In the main outcrop in the west of the district, good stream exposures of intraformational conglomerate occur in an unnamed tributary of Horsfield Brook [SO 6756 8823], Borle Brook [SO 6803 8970] and Crunell's Brook [SO 6970 8668]. In the Trimpley inlier, the formation is about 335 m thick and is restricted in outcrop to the core of a syncline located to the north of the Park Attwood Fault and the composite Trimpley Anticline and Syncline to the south of the fault (King, 1934; Whitehead and Pocock, 1947).

Brecon Subgroup

A single formation of Emsian age, the Clee Sandstone Formation (ClF), represents the Brecon Subgroup in the district. Although originally referred to the Brownstones by King (1925, 1934), Greig et al. (1968) referred all the correlative beds on the adjoining Church Stretton sheet to the Clee Group, and this name is applied in this account to the Dudley district, but downgraded to formation status (Figure 4). A small, largely fault-bounded outcrop of strata, about 300 m thick, tentatively referred to the Clee Sandstone Formation, occurs in the extreme south-west of the area where beds are exposed in a stream [c. 6710 8057] south-east of Prescott and east and south of Harcourt [SO 6923 8305]–[SO 6974 8292]; [SO 6880 8226]–[SO 6927 8244]. The correlation is uncertain, and based on more extensive outcrops on the adjoining Church Stretton sheet to the west (Greig et al., 1968). The formation comprises mainly medium- to coarse-grained, quartz-rich, green-grey and purplish grey, cross-bedded, flaggy sandstones. There is also some red-brown, finer-grained, micaceous sandstone and some green and purple intraformational conglomerate lenses and interbedded red mudstones. Calcrete occurs at the base of the sandstone beds in a northerly stream tributary [SO 6923 8305] and may correlate with the lower of the Abdon limestones of the Clee Hills (the Hillside Dolomitic Formation of Allen (1961).

Famennian: Upper Old Red Sandstone Group

Regionally, the Upper Old Red Sandstone Group rests unconformably upon strata of the Lower Old Red Sandstone Group. The Farlow Sandstone Formation (Frl) of Famennian (Late Devonian) age is recognised in a small area in the south-west of the district. It comprises about 60 m thickness of buff or yellow, cross-bedded, soft sandstones that are locally pebbly and conglomeratic. Some of the coarse beds are pale green and grey. There are few good sections or exposures, apart from river cliffs and a road cutting close to the west of the district around Prescott (Greig et al., 1968; Dineley, 1999), from which fossil fish fragments have been recovered. The outcrop is fault-bounded on its southern margin by the Billingsley Fault, with sandstones tentatively correlated with the Clee Sandstone Formation being faulted against it in the extreme south-west (see above).

Carboniferous

Carboniferous strata of Tournaisian to Namurian age are absent within the district. During this time, the district occupied part of an upland area known as the Wales–Brabant High and if any terrestrial deposition occurred, the deposits were eroded prior to the commencement of Westphalian deposition. The preserved Westphalian to Stephanian sedimentary rocks, present at crop within the Wyre Forest and Staffordshire coalfields, record deposition during the gradual change in climate from humid to semi-arid conditions, in response to northward plate migration. This is reflected in the transition from mainly coal-forming environments during the Langsettian to Duckmantian, represented by the Pennine Coal Measures Group, to the red beds of the Warwickshire Group. This deposition occurred during the closing phases of the Variscan Orogeny, with localised uplift, folding and erosion particularly affecting rocks of the Warwickshire Group.

Westphalian: Pennine Coal Measures Group

The Pennine Coal Measures Group (PCM) crops out in the Wyre Forest and South Staffordshire coalfields. A detailed description of the stratigraphy was provided by Whitehead and Pocock (1947) and Whitehead and Eastwood (1927). Some deep mining operations in both coalfields postdate these memoirs and in particular provide information on the extent of the concealed extensions of the coalfields.

The Pennine Coal Measures Group is divided into Lower, Middle and Upper formations using regionally developed marine bands. The base of the Pennine Lower Coal Measures Formation (PLCM) is placed at the base of the Subcrenatum Marine Band. However, this band is not proved in the district, and the base of the formation is instead taken at the base of the predominantly grey, coal-bearing succession which rests with an angular unconformity upon Silurian and Devonian strata (Plate 2). The base of the Pennine Middle Coal Measures Formation (PMCM) is placed at the base of the Vanderbeckei Marine Band, which is proved in both coalfields. The Cambriense Marine Band, the top of which marks the base of the Pennine Upper Coal Measures Formation, is not proved in the district and the Pennine Upper Coal Measures Formation is considered to be absent.

The group consists of interbedded grey mudstone, siltstone and sandstone, with subordinate coal, seatearth and ironstone, deposited in cyclic sequences. The rocks are nonmarine, except for the Vanderbeckei, Maltby and Aegiranum marine bands. Rootlet-bearing palaeosols (seatearths) include sandstone (ganister) and mudstone (fireclay) types. Unlike the Pennine Coal Measures Group over most of the Pennine Basin, the lowermost, mainly Langsettian, part of the group in the Wyre Forest Coalfield and southern part of the South Staffordshire Coalfield includes primary red beds, similar to the Etruria Formation of the Warwickshire Group.

The sediments of the Pennine Coal Measures Group are mainly fluviolacustrine deposits that accumulated at the southern margin of the Pennine Basin, on the northern flank of the Wales–Brabant High. The mudstones and siltstones were deposited in interdistributary bay or lacustrine environments, with laterally persistent coals recording extensive swamp conditions (Guion and Fielding, 1988). Laterally impersistent sandstones were deposited as lacustrine deltas, crevasse splays and channels. Larger sandbodies represent major distributary channel deposits. The localised development of red beds probably represents deposition in a comparatively well-drained, alluvial floodplain environment, with brunified palaeosols and sandstones locally sourced from the Wales–Brabant High representing single channel fill or multilateral or multistorey channel fills.

Wyre Forest Coalfield

The Carboniferous igneous intrusive rocks of the Wyre Forest Coalfield belong to the Clee Hill Microgabbro Sill-Swarm and in the district include the Kinlet Microgabbro Sill and the Shatterford Microgabbroic Sill.

The northern part of the coalfield crops out in the south-west of the district, and occurs as small outliers resting unconformably upon the Lower Old Red Sandstone Group and on the western flank of the north-north-east-trending inlier at Shatterford. The eastward concealed extension of the Pennine Coal Measures Group reaches beyond the Enville Fault to the Western Boundary Fault (see the cross-section on the 1:50 000-scale map). The Pennine Coal Measures Group thickens towards the south, and ranges from 124 m in the Claverley Borehole to 200 m in the Schoolhouse Lane Borehole, in an embayment of the Wales–Brabant High (Figure 5). The group was formerly included in the lower part of the Kinlet Group (Whitehead and Pocock, 1947), a local name erected because of the difficulty in distinguishing the Coal Measures from the overlying Etruria Formation (Warwickshire Group) in parts of the Wyre Forest Coalfield. The nomenclature used in the nearby South Staffordshire Coalfield and elsewhere in the Midlands (Powell et al., 2000) has been applied in this account.

The base of the group typically includes a hard, grey or white ganister up to 12 m thick, or a fireclay and grey sandstone with plant remains. The overlying succession, up to 90 m thick, comprises red and grey mudstone, fine-grained sandstone and siltstone, coarse-grained sandstones more typical of the Etruria Formation (Warwickshire Group), seatearth clays and thin coals. The upper 110 m or so of the Pennine Coal Measures Group in the subsurface comprises grey measures more typical of the Coal Measures found elsewhere within the Pennine Basin. Thin coal seams, seatearth clays and mottled mudstones are common. Locally the mudstones are red in the upper part, below the Aegiranum Marine Band (Figure 5).

A 0.4 m thick Lingula band, proved in the Highley No. 4 Underground BH [SO 7781 8549], is correlated as the Vanderbeckei Marine Band. As the marine band is locally absent, the succession is shown at outcrop as undivided Pennine Coal Measures Group. The lowermost main coal seam, the Wyre Forest Thick Coal, occurs about 8 m above the Vanderbeckei Marine Band in this borehole, comprising fifteen leaves with a total thickness of 2.6 m. It is also proved in the Alveley No. 4 Borehole [SO 7972 8638] and Alveley No. 2 Borehole [SO 7888 8491] (Figure 5). The Wyre Forest Thick Coal appears to split into leaves and thin southward toward the margin of the basin. For example, in the Kinlet and Schoolhouse Lane boreholes (Figure 5), it comprises sparse and thin coals that cannot be correlated with those of the Wyre Forest Thick Coal to the north. The number of leaves and proximity to the base of the Pennine Middle Coal Measures Formation suggest that this seam equates with the Staffordshire Thick Coal of the South Staffordshire Coalfield.

Above the Wyre Forest Thick Coal there are four principal, laterally extensive coal seams within a 7 to 9 m thick succession (Figure 5). In ascending order, they are the Two Foot (TF) (0–0.9 m), Four Foot (FF) (0.3–0.8 m), Half Yard (HY) (0–0.8 m) and Highley–Brooch (HB) (0.2–1.2 m). Correlation of these seams with those in the South Staffordshire Coalfield remains uncertain.

The Aegiranum Marine Band, locally known as the Eymore Farm Marine Band, is a thin, dark grey mudstone with the goniatite Donetzoceras aegiranum Schmidt and the brachiopods Lingula mytilloides (J Sowerby) and Productus rimberti (Waterlot) in the railway cutting near Eymore Farm, Upper Arley [SO 769 790] (Whitehead and Pocock, 1947; Cleal and Thomas, 1996) and in nearby boreholes (Poole, 1966). The transition from grey measures to red measures of the Etruria Formation occurs 4 to 15 m above the Aegiranum Marine Band. Further to the north, a Lingula band about 33 m below the base of the Etruria Formation in the Alveley No. 2 Borehole [SO 7888 8491], and 30 m below the base of the formation in the Alveley No. 4 Borehole [SO 7972 8638], is correlated with the Aegiranum Marine Band (Figure 5). This suggests that the base of the Etruria Formation becomes progressively younger towards the north of the coalfield. To the north of the district, the Symon Unconformity has been demonstrated to occur at the base of the Etruria Formation (Hamblin and Coppack, 1995, fig. 13; Smith et al. 2005, fig. 33). Although no angular unconformity can be demonstrated in the Wyre Forest Coalfield, the variable level of the base of the Etruria Formation may reflect the presence of such an unconformity.

The succession proved in the Claverley Borehole [SO 8035 9133] has several characteristics atypical of its northerly position in the Wyre Forest Coalfield. Firstly, the Pennine Coal Measures Group is thin (about 125 m), whereas it would be expected to thicken northwards away from the basin margin. The Aegiranum Marine Band occurs only 9 m below the inferred base of the Etruria Formation, whereas the general trend elsewhere (Figure 5) would have predicted an interval in excess of 30 m. Finally, the coal seams are relatively sparse and thin and correlation with the main seams found in the Wyre Forest Coalfield is not possible. Dextral strike-slip displacement on the north-east to south-west-trending Kinlet Hall–Pattingham Fault may have juxtaposed a more proximal basin-margin succession to the north against a thicker succession to the south, or this is a basinal 'high' on the footwall of this fault.

The outcrop of Pennine Coal Measures Group at Shatterford extends as a narrow north-east to south-west belt, up to 450 m wide, immediately north-west of the Trimpley inlier and typically faulted against the Lower Old Red Sandstone Group. The strata mainly dip steeply toward the north-west. The sandstones are greenish ochre, buff or ochreous weathered, fine- to medium-grained and thin- to medium-bedded. Coal seams are sparse at outcrop, but the Highley–Brooch and Four Foot coals are tentatively recognised in the Shatterford Borehole [SO 7901 8103]. They are thinner (0.2 and 0.3 m respectively) and more widely separated than in the Alveley Shaft [SO 7533 8417].

South Staffordshire Coalfield

The Carboniferous igneous intrusive rocks of the South Staffordshire Coalfield belong to the Brierley Hill Cluster, which in the district comprises the Rowley Regis Microgabbro Lopolith, and the Dudley Basaltic Sill-and-Vent Swarm including the Barrow Hill Basaltic Vent, Brewin's Bridge Microgabbro Dyke, London Fields Basalt Sill and unnamed igneous intrusive rocks.

The coalfield occupies a broad area in the north-east of the district, to the east of the Western Boundary Fault (Figure 1). The Pennine Coal Measures Group occurs widely in the subsurface, broadly beneath the Warwickshire Group. The group also occurs below Permo-Triassic strata to the west of the fault, in the Bratch Trough (see the cross-section on the 1:50 000-scale map). In contrast to the Wyre and South Staffordshire embayment areas, the Pennine Coal Measures Group of the Bratch Trough was probably deposited on a promontory of the Wales–Brabant High. Much information about the succession has been obtained from colliery shafts and exploratory boreholes (Figure 6). The minimum thickness of 30 m, recorded in the Smestow Borehole [SO 8563 9286] (Figure 6), is considered to represent a condensed succession deposited on the Smestow High (Glover, 1991). The thickest development of 162 m is in the Netherton Ironworks Borehole [SO 9472 8752] (Figure 6). The broad southward regional decrease in thickness across the coalfield is considered to reflect reduced subsidence toward the Wales–Brabant High (Besly, 1988a).

The Pennine Coal Measures Group rests with angular unconformity upon strata of Silurian to Devonian age (Figure 3). The widespread development of the Vanderbeckei Marine Band permits subdivision of the group into Pennine Lower and Middle Coal Measures formations. Where the Vanderbeckei Marine Band is absent or unproven, the base of the Pennine Middle Coal Measures is taken at the top of the underlying Stinking Coal. The Pennine Lower Coal Measures Formation is up to 96 m thick in the Netherton Ironworks Borehole (Figure 6). The basal beds of the group typically include a conglomerate (Plate 2) or coarse-grained sandstone referred to as the Ludgbridge Conglomerate (LC). The overlying succession comprises grey mudstone, fine-grained sandstone and siltstone, abundant ironstones, seatearth clays, ganisters and coals, the last being thickest in the upper part of the formation. There are five main coal seams, in ascending order, the Bottom Holers (BoH), Bottom (Bo), Fireclay (F), New Mine (NM) and Stinking (S). There is a southward migration of the southern limit of progressively younger coals, which reflects the southward onlap of the succession onto the Wales–Brabant High during the Langsettian.

The Vanderbeckei Marine Band, locally referred to as the Stinking Marine Band, typically rests upon the Stinking Coal (Figure 6). It contains Lingula mytilloides, but lacks a diagnostic ammonoid fauna. The band is 3.1 m thick in the Dudley Dock No. 5 Borehole [SO 9378 8985] (Poole, 1970), decreasing to the west and south of Dudley. It was exposed in the disused Yew Tree Hill Quarry, Netherton [SO 9400 8780] as a 5 cm-thick bed of Lingula-bearing ironstone nodules about 3 m above the Stinking Coal (Wilson and Waters, 1991). It is absent in the southern margin of the coalfield, where the Stinking Coal is also absent or poorly developed.

The Pennine Middle Coal Measures Formation is up to 117 m thick (Prestwood Colliery SO88NE 2) and comprises grey measures more typical of the Coal Measures found elsewhere within the Pennine Basin. Thick coal seams, ironstones and seatearth clays are particularly common towards the base of the formation. Mudstones, although predominantly grey, are locally red in the upper part of the formation, showing a gradation through interdigitation with the predominantly red and purple mudstones of the overlying Etruria Formation (Plate 3).

The five main coal seams are, in ascending order, the Heathen (H), Thick (TC), Flying Reed (FR), Brooch (BR) and Two Foot (TF). Only the Thick Coal occurs throughout the coalfield as a recognisable coal seam. It comprises 14 leaves, some with thin dirt partings, with a total thickness of 12 m. The Flying Reed Coal is a split from the roof of the Thick Coal, with the interseam thickness increasing dramatically to the west of the Western Boundary Fault, reaching over 50 m in the Wombourne area (Waters et al., 1994). In the southern part of the coalfield, the Thick Coal typically splits into three main seams, with the sediments of the splits derived from the Wales–Brabant High to the south. Many of the other coal seams in the north-east of the district thin markedly or fail, either towards the Wales–Brabant High to the south, or the Smestow High to the west (Figure 6).

The Maltby Marine Band, locally termed the Sub Brooch Marine Band, is restricted to the northern part of the South Staffordshire Coalfield. The marine band thickens eastwards to 0.9 m in the Kate's Hill No. 1 Borehole [SO 9522 8991] (Poole, 1970). The Aegiranum Marine Band, locally named the Charles' Marine Band, is recorded in Himley Clay Pit [SO 898 903] as a 2.5 m succession of dark grey silty and micaceous mudstone with marine fossils (Glover, 1991). Here, the transition from grey measures to the red measures of the Etruria Formation occurs immediately above the Aegiranum Marine Band, showing that the base of the Etruria Formation is progressively younger toward the north of the coalfield, a comparable relationship with that seen in the Wyre Forest Coalfield.

Westphalian and Stephanian: Warwickshire Group

The Warwickshire Group of the Wyre Forest Coalfield occurs at crop in the west and central parts of the district as a broadly east- or north-east-dipping succession, bounded to the east by the Enville Fault. The succession is locally steeply dipping to the north-west on the western flank of the north-north-east-trending Trimpley inlier, and disrupted by numerous faults. In the South Staffordshire Coalfield, the group mainly occurs at outcrop to the east of the Western Boundary Fault, although north of Himley it is also present to the west, located to the east of the Lloyd House Fault (Figure 1). Between the Enville and Lloyd House faults the extent and thickness of the Warwickshire Group is poorly constrained. The nomenclature of the Warwickshire Group red-bed succession of the Wyre Forest and South Staffordshire coalfields is that defined for the English Midlands (Powell et al., 2000). It comprises, in ascending order, the Etruria, Halesowen, Salop and Clent formations. Prominent unconformities occur at the base of the Halesowen and Clent formations. The Clent Formation is considered to be of Permian age (Waters et al., 1995).

In the Wyre Forest Coalfield, the base of the Warwickshire Group overlies progressively younger strata towards the south (Figure 1). In the north-west, the base of the group rests on an angular unconformity at the base of the Halesowen Formation, overlying the Raglan Mudstone Formation (Silurian–Devonian) west of Astley Abbotts [SO 68 97]–[SO 69 90] and the St Maughans Formation (Early Devonian) west of Chelmarsh [SO 69 90]–[SO 71 87]. The Etruria Formation is absent north of the Kinlet Hall–Pattingham Fault. In the south-west of the Wyre Forest Coalfield, the base of the group and of the Etruria Formation appears to rest conformably on the Pennine Coal Measures Group (Figure 7). In the South Staffordshire Coalfield, a similar relationship is seen, with the base of the group occurring widely at the base of the Etruria Formation, although locally in the north, as in the Penn No. 5 Borehole (Figure 8), the base lies at the angular unconformity at the base of the Halesowen Formation.

The Etruria Formation (Et) occurs at outcrop in the Wyre Forest Coalfield in the south-west of the district, being absent in the northern part of the coalfield, below the unconformity at the base of the Halesowen Formation. The maximum thickness in the Wyre Forest Coalfield (90 m) is proved in the Schoolhouse Lane Borehole [SO 7426 8292] (Figure 7), with thickness decreasing northwards as the unconformity cuts down through stratigraphically lower beds. The formation also occurs in the South Staffordshire Coalfield, east of the Western Boundary Fault. In the northern part of the coalfield, up to 61 m are recorded in the Baggeridge Colliery No. 2 Shaft (Figure 8), although the formation is locally absent, as in the Penn No. 5 Borehole (Figure 8). The variable thickness reflects a phase of folding and faulting prior to deposition of the Halesowen Formation (Waters et al., 1994). The thickest development, up to 250 m, occurs west of the Russell's Hall Fault in the Rowley Regis and Halesowen areas.

The formation comprises purple and red mottled mudstones dominated by brunified alluvial palaeosols, with some grey or green beds, seatearth clays and thin coals and 'espley'-type sandstones, interpreted as well-drained alluvial floodplain deposits (Plate 4). Other pedogenic horizons are gley, semi-gley and pseudo-gley palaeosols, ferralitic and ferruginous palaeosols and polygenetic palaeosols (Glover et al., 1993). In the South Staffordshire Coalfield there are a number of thin sulphurous coal seams. The Little (Sulphur) Coal occurs about 45 m above the Two Foot Coal, and near to the base of the Etruria Formation across much of the northern part of the coalfield. The sandstones were typically derived from erosion of the Wales–Brabant High to the south, and occur as sharp-based, channel-fill or tabular, fine- to coarse-grained sandbodies with extraformational pebble lags (Glover et al., 1993). A subordinate facies comprises granular and pebbly mudstone and muddy pebble-conglomerate, rich in rounded coarse sand- to small pebble-grade clasts, mainly of igneous material (Glover et al., 1993). In the Wyre Forest Coalfield, the sandstones are commonly micaceous, ochreous-weathered, greenish ochre or greenish grey, fine- to coarse-grained, locally granular to pebbly, mainly with rounded quartz granules. Beds are commonly trough cross-bedded, and with either sharp and erosive or gradational bases. In the south-western part of the district there are more sandstones, and they are thicker and appreciably coarser than those within other parts of the outcrop to the north. The base of the formation in the south-west is marked by an 'espley'-type sandstone up to 16 m thick, as, for example in Alveley Shaft [SO 7533 8417] (Figure 7), which rests on grey, mottled red and yellow seatearth. Elsewhere, the base of the formation is gradational, with interdigitation of grey mudstones of the Pennine Coal Measures Group and red or purple mudstone of the Etruria Formation. The base of the latter is placed at the base of the predominantly red mudstone succession (Plate 3), which occurs from just above to 32 m above the Aegiranum Marine Band (Figure 5), indicating a Bolsovian age for at least its lower part.

The type area of the Halesowen Formation (Ha) is in the southern part of the South Staffordshire Coalfield. The formation also crops out in the Wyre Forest Coalfield along the valley of the River Severn, east of the Romsley Fault, and on the western flank of the Trimpley inlier. The base of the formation is marked by a slightly angular unconformity (Plate 4). The top of the formation occurs at an upward change from grey-green beds (Halesowen Formation) to red beds (Salop Formation), except where the Halesowen Formation is itself red; in this case the boundary is drawn arbitrarily, above the top of the highest litharenite sandstone. In the South Staffordshire Coalfield an important basal section of the formation is provided by a disused tramway track at Oldnall [SO 9318 8401]. The top of the formation is seen in a stream section at Uffmoor Wood [SO 956 811]–[SO 951 811]. The formation is about 200 m thick in the Wyre Forest Coalfield, 100 m in the steeply dipping succession north of Shatterford, and 110 m around Halesowen, where the lower part of the formation is dominated by three laterally persistent upward-fining cycles (Glover and Powell, 1996). These comprise thick, sheet-like bodies of grey-green, micaceous sandstone (litharenite), which pass up into grey-green mudstone with thin coals, Spirorbis limestones and local intraformational conglomerates. The formation represents deposition in fluvial channel to floodplain environments, with relatively high water tables and development of rheotrophic swamps and deposition of lacustrine carbonates (Glover and Powell, 1996). Cross-bedding in the sandstones, in both the Wyre Forest and South Staffordshire coalfields, indicates palaeocurrents mainly toward the west. However, their petrography is indicative of a distant southerly source (Besly, 1988b; Glover and Powell, 1996). In the type area, the upper part of the formation, the Dark Slade Member, comprises a pale grey, ochreous and red mottled, laminated mudstone-dominated succession with weakly developed palaeosols (Figure 8). Locally, the strata are reddened, which in the past has hindered distinction from the overlying Alveley Member of the Salop Formation.

In the Wyre Forest Coalfield there are three main worked coal seams in the Halesowen Formation (Whitehead and Pocock, 1947). In ascending order these are the Bank Farm (or Main) Coal (BF) (up to 1.1 m thick), the Bind Coal (or Main Sulphur Seam) (B) (up to 0.43 m), and the Brock Hall (or Brockholes) Coal (BH) (up to 0.6 m). Interseam thicknesses generally decrease toward the north (Figure 7). Two cream-coloured, thin Spirorbis limestone beds occur in the lower part of the formation, between the Bank Farm Coal and lowermost main sandstone, and between the Bind and Brock Hall coals (Whitehead and Pocock, 1947). A coal from Little London Brook, Alveley [SO 755 834], contains a miospore assemblage indicative of a late Bolsovian or early Asturian age (Owens, 1990). This coal was shown as occurring within the Alveley Member on the previous 1:50 000 map, but is now interpreted to lie within the Dark Slade Member (Besly and Cleal, 1997). In the South Staffordshire Coalfield there are a number of thin coal seams. In the south, the Uffmoor Coal occurs near the top of the formation, also within the Dark Slade Member (Figure 8).

The Salop Formation occurs at outcrop extensively along the eastern margin of the Wyre Forest Coalfield, and in the South Staffordshire Coalfield in the south-east of the district and in the area between the Lloyd House and Western Boundary faults. It consists of red and red-brown mudstone, and red-brown (mostly sublitharenite) sandstone. The succession is divided into the Alveley Member and overlying Enville Member (Powell et al., 2000). The formation represents a return to well-drained, distal (Alveley Member) to proximal (Enville Member) semi-arid alluvial plain settings, with localised shallow lake formation. The siliciclastic material is derived from erosion of the Wales–Brabant High.

The village of Alveley [SO 76 84], in the south-west of the district, is the type area for the Alveley Member (Aly) (Besly and Cleal, 1997), formerly named the Keele Formation (or Beds). The member is up to 220 m thick in the Claverley Borehole (Figure 7) in the north of the Wyre Forest Coalfield. It is 270 m thick in the Penn No. 5 Borehole in the north of the South Staffordshire Coalfield, thinning to 50 m in the Daleswood Farm Borehole in the south (Figure 8). Regionally, the member comprises red mudstone and sandstone, thin dark blue-grey Spirorbis limestone beds and pedogenic limestone (calcrete). The mudstones have been locally worked for brick clay (Plate 5). The sandstones are mostly fine- to medium-grained sublitharenites with a sheet-like geometry traceable over several kilometres. The base of the member is conformable, with a transitional-gradational boundary, arbitrarily taken at the base of the first major red-bed stratum, overlying the grey mudstone-dominated succession of the Halesowen Formation. Where exposure of this interval is good it has been possible to identify a boundary within a mudstone-dominated succession. Elsewhere, the base of the member is taken at the base of the lowermost sublitharenite. The lower part of the member is dominated by a number of relatively thick sandstone beds, some of which were formerly extensively quarried e.g. Alveley Quarry [SO 758 848] (Cleal and Thomas, 1996). Cross-bedding in the Wyre Forest Coalfield typically indicates palaeocurrents toward the west or north-west, though with a significant number to the east or north-east. The upper part of the member is mudstone-dominated and tends to form flat-lying countryside with comparatively few exposures.

The Enville Member (En) was formerly known in the district as the Enville Beds (Whitehead and Eastwood, 1927), the Bowhills Formation (Ramsbottom et al., 1978) and the Enville Formation (Besly, 1988b). Its type areas are at Bowhills [SO 77 84] and Enville Sheepwalks [SO 81 85], between Alveley and Enville villages, where it is 145 m thick; in the South Staffordshire Coalfield it is up to 90 m thick. The member comprises red mudstone and red-brown, fine- to coarse-grained, locally pebbly sandstone, and lenticular beds of conglomerate. The sandstone is mostly sublitharenite, and the conglomerate clasts are mostly of Carboniferous limestone and red or ochreous silicified mudstone (commonly referred to as chert). The sandstones are typically thicker, browner, coarser and contain more extraformational clasts (Plate 6) than sandstones in the underlying Alveley Member. They are mainly lenticular, but have a high degree of interconnectivity. Foresets within the sandstones indicate palaeocurrents mainly to the east or north-east in the Wyre Forest Coalfield, whereas in the South Staffordshire Coalfield a north-eastward palaeoflow is more typical (Glover and Powell, 1996). The lower boundary is poorly defined and taken arbitrarily at the base of a sandstone-dominated succession that overlies the Alveley Member. The basal sandstone typically forms a prominent topographical feature in the area, and was locally quarried for building stone (Plate 6).

Carboniferous igneous rocks

The igneous rocks of the district are entirely of Carboniferous age, mainly comprising intrusive bodies of alkaline olivine microgabbro (dolerite) and basalt (Kirton, 1984). Volcaniclastic deposits are limited to the Etruria Formation of the Tansey Green area of the South Staffordshire Coalfield. The microgabbro (dolerite) and basalt typically intrude strata of the Pennine Coal Measures Group and the Etruria Formation of the Warwickshire Group. Their absence in strata of Asturian (Westphalian D) age suggests a Bolsovian age, consistent with the Bolsovian age of the volcanic rocks at Tansey Green.

Wyre Forest Coalfield

The Kinlet Microgabbro Sill (KS) is a large olivine basalt and Microgabbro sill intruded at, or just above, the position of the Highley–Brooch Coal, formerly interpreted as a lava (Whitehead and Pocock, 1947). The basalt is typically vesicular and spheroidally weathered, and is over 15 m thick at Raggits Quarry, Knowle Hill [SO 693 818]. In the subsurface, igneous rocks have been proved in the Kinlet [SO 7271 8173] and Claverley [SO 8035 9133] boreholes (Figure 5). In the Kinlet Borehole, thin basalts occur above the Highley–Brooch Coal and immediately above and below the Half Yard Coal. A 2.1 m-thick breccia of blocks of basalt, fragments of sandstone and quartz pebbles in a seatclay matrix occurs above the Highley–Brooch Coal. These rocks appear to be lateral equivalents of the Kinlet Microgabbro Sill. In the Claverley Borehole, a 7 m-thick microgabbro (dolerite) is present at a slightly higher level in the Pennine Middle Coal Measures.

The Shatterford Microgabbroic Sill (SS) trends north-north-east to south-south-west and extends 3.6 km from Arley Wood [SO 801 828] to Eymore Wood [SO 781 797]. The intrusive nature of the olivine basalt, with baked country rock and chilled margins, was demonstrated by Whitehead and Pocock (1947), and the upper contact shows complex interfingering of the basalt and the country rock, indicative of an intrusive contact (Marshall, 1942). The sill cuts across bedding ranging from the middle part of the Pennine Coal Measures Group in Eymore Wood in the south [SO 782 797], to the lower part of the Etruria Formation near Witnells End in the north [SO 795 815]. It is exposed in a series of disused quarries [SO 7984 8216]–[SO 7968 8175] and was proved at depth in the Shatterford Deep Sinking [SO 7901 8103], with 8.6 m present at the bottom of the shaft. The sill displays the same steep tectonic dips as in the Carboniferous country rock, suggesting that intrusion occurred prior to the late Carboniferous phase of deformation.

South Staffordshire Coalfield

The Rowley Regis Microgabbro Lopolith (RRL) is the largest Carboniferous basic igneous intrusion in the West Midlands. It mainly occurs in the Birmingham district, where it extends about 3 km, forming a north–south trending ridge, and is up to 100 m thick (Powell et al., 2000). The intrusion thins markedly towards the margins, with the north-western margin extending into the Dudley district at Tansley Hill [SO 956 894]. Formerly referred to as a laccolith (Eastwood et al., 1925; Marshall, 1942), the lopolithic geometry was demonstrated by Waters (1991), with the planar upper contact and markedly downward convex lower contact both displaying chilled margins. The basal contact in places is almost vertical, possibly reflecting sagging of the intrusion within an active graben, bounded to the west by the Knowle Fault and to the east by the Portway Fault (Waters, 1991). The intrusion has been almost entirely undermined for coal and no evidence of a feeder pipe has been found (Eastwood et al., 1925), suggesting that the intrusion was fed laterally through marginal sills. Thin sills of amygdaloidal olivine alkaline basalts, up to 1 m thick, have been recorded within the vicinity of the lopolith. A sill was formerly seen at outcrop in a brick pit within the Etruria Formation near Tansley Hill [SO 9545 8905].

The Barrow Hill Basaltic Vent (BHC) [SO 915 896] is a microgabbro (dolerite) pipe intruded within vent agglomerates and country rock. The vent agglomerate comprises fault-bounded blocks of volcanic breccia with clasts of Etruria Formation and Pennine Coal Measures mudstones, coal and rounded quartzite pebbles in a tuffaceous matrix (Marshall, 1946). The microgabbro (dolerite) is also fault bounded and contains abundant Pennine Coal Measures and Etruria Formation xenoliths up to 4.5 m diameter. The complex occurs within, and adjacent to the west–east-trending Tansey Green Trough, and is interpreted as a high-level phreatomagmatic intrusion (Wilson and Waters, 1991). A similar igneous intrusive body at Cooper's Bank [SO 914 900]; [SO 918 904] is shown as undifferentiated igneous intrusive rock on the 1:50 000-scale map.

At Tansey Green [SO 911 896], the Etruria Formation includes volcaniclastic deposits associated with tuffisitic and agglomeratic dykes and pipes and alkaline basalt dykes (Glover et al., 1993; Waters, 2003). The bedded volcaniclastic sequence comprises 31 m of volcanic breccia, scoriaceous lapilli tuff and tuffaceous mudstone and siltstone. The lapilli tuff preserves conifer stems in growth position (Galtier et al., 1992; Glover et al., 1993). An agglomerate pipe, up to 10 m in diameter, and a single alkaline basalt dyke (0.3 m width) are present at Tansey Green, and are similar to the intrusive rocks present in the nearby Barrow Hill Basaltic Vent (Glover et al., 1993).

Additional small areas of igneous intrusive rocks, the Brewin's Bridge Microgabbro Dyke and London Fields Basalt Sill, are shown on the 1:50 000-scale map. The Brewin's Bridge Microgabbro Dyke (BBDy) is about 180 m long, trends north-west to south-east [SO 9349 8778]–[SO 9364 8770], and is exposed in the Dudley Canal cutting. The dyke comprises ophitic olivine microgabbro (dolerite). It occurs within the core of the north-north-east to south-south-west-trending Netherton Anticline, mainly intruding the late Silurian Temeside Mudstone Formation, but also the basal part of the Pennine Lower Coal Measures at its north-western limit. The intrusion has been interpreted as post-dating movement on a north-east-trending fault, which it follows in part (Whitehead and Pocock, 1947).

The London Fields Basalt Sill (LFS) crops out at London Fields [SO 929 905]; [SO 931 907]. The sill is interpreted as a single transgressive intrusion that cuts strata between the Thick Coal (Pennine Middle Coal Measures) and Bottom Coal Coal (Pennine Lower Coal Measures). It is up to 22 m thick, as proved in the Russell's Hall No. 19 pit [SO 9322 9028].

Additional undifferentiated igneous intrusive rocks, intrude levels within the Pennine Coal Measures Group at Sandfield Bridge [SO 908 906], Dibdale [SO 920 906] and Dudley [SO 946 898]. A micro-ophitic olivine basalt was recorded in Warren's Hall Colliery (Whitehead and Pocock, 1947). Also, a 0.5 m-thick porphyritic Micrograbbro (dolerite) in Kates Hill Borehole No. 1 (SO98NE/89), intrudes between two thin coals below the Herring Coal (present beneath the Brooch Coal), neither of which displays thermal alteration (Poole, 1970). Only the larger outcrops are shown on the 1:50 000-scale map.

Permo-Triassic

The northern and central parts of the district, between the Wyre Forest and South Staffordshire coalfields, are underlain by Permo-Triassic strata, preserved in fault-bounded half-grabens or grabens. The Stafford Basin, which extends into the district from the north, has poorly defined depocentres to the west of the Pattingham–Billingsley faults, with an estimated thickness of 600 m of Permo-Triassic strata present. The Bratch Trough, bounded on the west by the Enville Fault, and on the east by the Western Boundary Fault, links the Stafford Basin with the deeper Worcester Basin to the south. The form of the basins is illustrated by (Figure 9).

Clent Formation

The Clent Formation (Cle), considered to be of Permian age (Waters et al., 1995), is assigned to the mainly Carboniferous Warwickshire Group. In the type area of Clent Hills [SO 930 800] it consists of 137 m of coarse-grained breccia set in a soft, red-mauve mudstone matrix, interpreted as alluvial fan deposits. Clasts comprise volcanic igneous rocks derived from the Precambrian basement of the Wales–Brabant High. The formation is rarely exposed, but it gives rise to a distinctive, strongly serrated topography. The proportion of breccia decreases northwards of the Clent Hills, and in the Baggeridge area consists of up to 243 m of mudstone and siltstone, with thin beds of sandstone and lenses of small pebbles. The base of the formation in the south rests with angular unconformity (or disconformity) upon the Enville Member, the unconformity becoming less marked towards the north (Powell et al., 2000). The succession is also present in the Enville Sheepwalks [SO 81 85], showing a similar thinning of breccia beds to the north, failing at Bobbington [SO 81 90].

Bridgnorth Sandstone Formation

The Bridgnorth Sandstone Formation (Bri) (Warrington et al., 1980) crops out in a relatively narrow belt on the western margins of the Stafford Basin, where it rests unconformably on strata of the Warwickshire Group and dips eastwards beneath younger strata. The thickness of the formation is highly variable due to irregularities on the pre-existing topographical surface, and to syndepositional movements on major basin-bounding faults. However, the general trend is one of thickening in a sub-basin to the west of the Pattingham–Billingsley faults, and southwards into the Bratch Trough. Thicknesses in these areas may well exceed 300 m, although no boreholes have penetrated the base. There are no unequivocal provings to the east of the Lloyd House Fault, suggesting that this fault, together with the Stapenhill Fault, marked the western boundary of a topographical high.

Lithologically, the sandstone is dull red-brown, fine to medium grained and pebble free. Grains are well rounded, many resembling 'millet seed', and are weakly cemented by a thin layer of iron oxide. Large-scale, high angle (dune) cross-stratification is characteristic (Plate 7), and in many sections it is the dominant bedform. The depositional environment was one of a dry sand desert in which aeolian crescentic and linear dunes accumulated under a predominantly easterly wind direction (Karpeta, 1990). Planar bedding is much less common and represents interdune dry sandsheets. Quartz is the dominant constituent with minor feldspar and volcanic grains. Good sections exposed in and around Bridgnorth include Castle Hill Gardens [SO 717 928], High Rock Cliff [SO 724 939] and the Bridgnorth Cliff Railway. At Kinver [SO 836 835], the famous Holy Austin rock houses, carved out of the sandstone, were inhabited until the 1950s.

Sherwood Sandstone Group

The dominantly fluvial Sherwood Sandstone Group comprises, in ascending order, the Kidderminster, Wildmoor Sandstone and Bromsgrove Sandstone formations.

Kidderminster Formation

The Kidderminster Formation (Kdm) (Warrington et al., 1980), known formerly as the Bunter Pebble Beds, gives rise to prominent hills or escarpments, with its outcrop repeated across the district by north-north-east-trending faults. Thicknesses range from 80 m to a maximum of 148 m, proved in the Bellington No. 2 Borehole in the Bratch Trough to the south of the district (Figure 9). The formation lies unconformably on the Bridgnorth Sandstone Formation, except in the north-east around Penn and in the south-east near the Clent Hills, where it rests unconformably on the Clent Formation. Throughout the district, the sequence commences with a lower unit, 40 to 60 m thick, mainly of texturally mature pebble/cobble conglomerates (Plate 7) which in the Clent Hills is mapped as a distinct unit. These are composed largely of fine-grained quartzite together with red sandstone, quartz and rare porphyritic igneous rocks. The beds show weak horizontal stratification and planar or trough cross-stratification. Interfingering sandstones, pebbly sandstones and red-brown, micaceous mudstones form a minor part of the sequence. Non-pebbly, red-brown sandstone increases upwards through the succession. The formation is fluvial in origin and was probably deposited in piedmont alluvial fans that prograded from marginal horsts into a rift valley, drained by a northward-flowing braided river system. Exposures include those at The Hermitage, Bridgnorth [SO 7277 9355] (Plate 7), Wolverley car park [SO 8282 7937] and Church Hill, Kinver [SO 8480 8297].

Wildmoor Sandstone Formation

The Wildmoor Sandstone Formation (WrS) (Warrington et al., 1980), formerly Upper Mottled Sandstone, crops out in the Bratch Trough and in the western part of the Stafford Basin. The maximum thicknesses are inferred to occur to the west of the Pattingham Fault, where a borehole at Hilton Waterworks [SO 7768 9593] proved 188 m of strata; the southern part of the Bratch Trough may contain a comparable thickness. The formation is dominated by weakly cemented, micaceous, fine-grained sandstone. The intense red colour of the sandstone is distinctive, and derives from iron oxide coatings on the sand grains. Red-brown and grey-green mudstones are present in beds less than 30 cm thick, but exceptionally reach a few metres towards the top of the formation. Bedforms comprise low-angle, trough cross-bedding, low-angle planar bedding and ripple cross-lamination. The formation was deposited in a fluvial environment, predominantly in a distal braid-plain setting. Mudstone interbeds probably represent the deposits of temporary lakes. The junction with the underlying Kidderminster Formation is transitional, and difficult to recognise, but is drawn conventionally at the point above which the sequence becomes pebble-free.

Bromsgrove Sandstone Formation

The Bromsgrove Sandstone Formation (BmS) (Warrington et al., 1980), formerly the 'Lower Keuper Sandstone', gives rise to a fairly well-featured topography of ridge and valleys, offset by north-north-east-trending faults, around the southern margin of the Stafford Basin. The formation is also preserved in the central part of the shallow Stourbridge Syncline, to the south of Stourbridge. The basal sandstones rest disconformably on the Wildmoor Sandstone Formation (the Hardegsen Unconformity of Powell et al. (2000) in the Birmingham district) and are markedly better cemented than the sandstones of the underlying formation. The top of the formation is not seen. The formation consists of dark red and brown, calcite-cemented, locally micaceous, medium- to coarse-grained sandstone with beds and lenses of pebbly, conglomeratic sandstone. Well-rounded quartz granules and pebbles, and intraformational red mudstone rip-up fragments are common. Thin beds of red mudstone and siltstone, and lensoid beds of calcrete conglomerate are locally present. Large-scale trough cross-bedding in the sandstones commonly passes up into rippled siltstone. The sandstone grains are noticeably more angular and more poorly sorted in comparison to the underlying Wildmoor Sandstone Formation. The Bromsgrove Sandstone was deposited in a semi-arid, northward-flowing river system, predominantly as a braided channel facies, with highly fluctuating stream velocities and sediment supply.

Quaternary

Most of the unconsolidated Quaternary deposits in the region were formed during the late Devensian glaciation, the limit of which crosses the district (Figure 10). The ice was derived from the north, flowed across the Irish Sea Basin and the Cheshire Plain, and at its maximum extent (the 'Wolverhampton Line') reached Eardington in the Severn valley and Enville in South Staffordshire.

There is indication of earlier glacial activity in the district. Gravel pits around Trysull and Seisdon, South Staffordshire, have exposed probable Anglian age glacially incised meltwater channels (Plate 8) infilled with outwash gravels, overlain by organic-rich, calcareous silts. The outwash gravels are believed to be late Anglian, and the silts have been assigned to the Hoxnian Interglacial (Morgan, 1973; Morgan and West, 1988). South of Stourbridge, patches of high-level, probably glaciofluvial gravels have been ascribed to a pre-Devensian origin (Maddy et al., 1995), whilst glacial till, in isolated patches around the Clent Hills and forming more extensive spreads east of Dudley, is of probable Anglian age and equates to deposits east of the district in the Quinton area (Horton, 1989).

The late Devensian glaciation influenced the landscape of the northern part of the district, although the direct effects were muted; landforms were streamlined and rounded, particularly those on the soft Permo-Triassic rocks, and some glacial materials were deposited. The greatest impacts were seen south of the ice limit, in the southern half of the district, where meltwater incised deep narrow valleys in the higher ground formed by the Devonian and Carboniferous rocks, and eroded wide valleys in the softer Permo-Triassic outcrop. Prior to that time, the proto River Severn flowed northwards towards the Dee (Wills, 1938). There is also some evidence to indicate that prior to the late Devensian glaciation, the dominant drainage in the western half of the district was south-eastwards towards the Stour valley, where a major pre-Anglian river existed (Maddy, 1997), possibly crossing the Trimpley anticline where some dry valleys and misfit streams occur. The subsequent diversion of the Severn through the Ironbridge Gorge, to the north of the district, dissected this earlier drainage pattern, the remnants of which are reflected in the orientation of valleys that form the right-bank tributaries of the Borle Brook, which lay beyond the Devensian glacial limit.

In addition to glacial and glaciofluvial deposits, the district has significant spreads of periglacial head deposits, landslide deposits and postglacial (Holocene) alluvial and terrace deposits associated with the modern courses of the rivers Severn and Stour and their tributaries referred to as the Severn Valley Formation.

Pre-Devensian

Till of probable Anglian age occurs in the district as isolated patches around the Clent Hills [SO 915 790] and generally comprises in red-brown sandy clay. The surface expression of these deposits is characterised by the very pebbly nature, the clasts being predominantly red-brown quartzite, vein quartz and conglomerates derived from the Clent and Kidderminster formations, with subordinate clasts of mudstone and sandstone derived from the Pennine Coal Measures Group.

Undifferentiated glaciofluvial deposits occur between Kidderminster and Stourbridge, on the high ground between the Stour valley and the Hurcott Brook at about 90–130 m above OD, and at a similar elevation east of the Smestow Brook. The deposits are the remnants of a dissected sheet of sand and gravel that formerly lay in a shallow valley extending south-south-west towards Churchill, where isolated patches capping knolls survive (Whitehead and Pocock 1947). Sand and gravel workings at Gibbet Wood [SO 865 845] and in Norton Covert have exposed strongly cross-bedded sands with lenses of moderately coarse gravel, containing erratics that probably originate from northern Britain (Whitehead and Pocock 1947). More recent investigations at the Gibbet Wood site (Goodwin et al. 1997), now largely backfilled, identified a diamict and deformation structures within an overlying sand-dominated unit, interpreted as a possible lacustrine or glaciolacustrine deposit. Maddy et al. (1995) considered that the sequence at this location was deposited during a glacial event which occurred after the Anglian, but which immediately predated the deposition of the Kidderminster Station Member (see below). These deposits also occupy channels in the Seisdon Sand Pit [SO 8495 9470] (Plate 8).

The Kidderminster Station Member (formerly the Kidderminster Terrace of Wills, 1938) forms extensive high-level terraces along the valley of the River Stour between Kidderminster and Stourton (Figure 10), with the most extensive spreads of sand and gravel lying on the west bank of the Stour south of Kinver [SO 845 816]. This terrace, absent in the Severn valley, lies over 30 m above modern river level locally, and in places cuts into the older undifferentiated high-level gravels described above. Maddy et al. (1995) have assigned it to Oxygen Isotope Stage (OIS) 6, implying pre-Ipswichian (?Wolstonian) glaciofluvial deposition during cold climatic conditions. Isolated terrace remnants at Amblecote [SO 899 850] in Stourbridge are considered to be Ipswichian river terrace deposits (Powell et al., 1992). They comprise sand and pebbly sand, with gravel lenses up to 3 m thick, and may have been deposited by a pre-Devensian proto-Stour river. Included within the Holt Heath Sand and Gravel Member as the Stourbridge Beds (Maddy et al., 1995) they have been assigned to OIS 5e (Ipswichian) (Maddy, 1997). The deposit has yielded a varied fauna of mammalian bone fragments including hippopotamus, mammoth and woolly rhinoceros (Boulton, 1917), although these records are of uncertain value, with the likelihood of reworking of earlier deposits.

Devensian

The late Devensian glacial record is poorly preserved. Although the northern half of the district was affected by this glaciation, the glacial deposits or geomorphological features are not readily distinguishable from earlier glaciations. Fragmentary patches of till form an irregular line across the district from Eardington Mill to Enville (Figure 10), probably marking the late Devensian glacial maximum (Whitehead and Pocock, 1947). There is no well-defined 'limit' between Bridgnorth and Claverley, but the distribution of till and associated features suggests that, within the most southerly limit, there may have been minor oscillations or re-advances of the of the ice margin. Some east–west orientated streams, such as the Mor Brook, may have been marginal meltwater channels subsequently exploited by postglacial drainage.

The most extensive areas of Till lie on the outcrop of the Sherwood Sandstone Group east of Bridgnorth and north of Wombourne (Figure 10). Only around Morville [SO 690 930] and Bobbington are there significant spreads of glacial deposits. Much of the till is a chocolate brown sandy clay or reddish loam, with abundant rounded, locally boulder-sized clasts. At Eardington Mill [SO 718 900], a small section exposed a till deposit probably sourced from the immediate surrounding bedrock, as it is dominated by massive blocks of sandstone and coal fragments derived from the Alveley Member and Halesowen Formation. However, many erratics have a northern origin, and even where till is absent, granitic boulders of a probable Lake District or Scottish source, are commonly found scattered across the area north of the glacial limit.

The poorly defined nature of the ice margin across the district, compared to elsewhere along the Devensian glacial limit in the West Midlands, may be a consequence of local variations in the dynamics of the ice sheet. It is considered that the ice margin, after advancing rapidly into the district, became static or stagnant, with little active glacial erosion. However, localised ice streams within the ice sheet may have formed more active small-scale marginal lobes, capable of eroding and depositing more material, and this may account for the more extensive till deposits around Bobbington.

Generally of limited extent, glaciofluvial ice contact deposits form ridges and mounds. Deposited as ice-marginal features, they are more heterolithic than glaciofluvial sheet deposits laid down on outwash sandur. Whilst composed predominantly of poorly sorted sand and gravel, they also commonly contain tills and silts and clays of possible glaciolacustrine origin. A distinctive ice contact ridge at Ludstone Hall [SO 799 945], near Claverley, lies within the late Devensian glacial limit, and further deposits are present southwards towards Bobbington (Figure 10). East of Dudmaston Hall [SO 745 890] are a series of progressively dissected fan surfaces, with associated glaciofluvial fan deposits . They issue from the well-developed, but now dry Morfe Valley, below Burf Castle [SO 762 908], and feed south-westwards into the Severn valley west of Quatt (Figure 10). Three fan surfaces have been identified, the lowest (and youngest), being the most extensive. The highest fan deposits are restricted to a narrow terrace along the valley margins. During the previous survey, these deposits were recorded as the third to fifth terraces of the River Severn and undifferentiated glaciofluvial gravel deposits.

Further east, patches of glaciofluvial fan deposits occur around Enville [SO 830 865] (Figure 10). These deposits, usually less than 2 m thick, are considered to be an ice front margin sandur fan south of Highgate Common, which merges with other valley side fans issuing from tributary valleys in the Trimpley inlier immediately to the west, as evidenced by the proportion of clasts derived from the Clent Formation breccias. Further extensive fan deposits lie below the western face of the scarp of Kinver Edge, these deposits being dominated by 'Bunter' pebbles derived from the Kidderminster Formation that forms the Edge. These deposits, located in tributaries of the River Stour, suggest the development of a glaciofluvial system parallel to the main Stour valley, but largely separated from it by the scarp formed by the Kidderminster Formation.

Glaciofluvial fan deposits occur in the Stourbridge–Hagley area (Figure 10), comprising brown sandy loam with quartz pebbles and fragments of Clent Formation breccia, less than 5 m thick. These deposits are the eroded remnant of a large fan in which local material sourced from the Clent Hills was deposited at the foot of the scarp. Glaciofluvial sheet deposits are found down the length of the Severn valley (Figure 10) and equate with the previously mapped third or 'Main' terrace of the River Severn. These deposits lie about 30 m above current river level, at an elevation of about 60 m above OD, and were formed in a low sinuosity, high energy environment in an extensive valley sandur issuing from the late Devensian ice margin at Eardington. The material is coarse sand and gravel, with boulders up to 2 m in diameter (Dawson, 1985), and an abundance of exotic igneous clasts. Extensive spreads of gravel still remain, although the largest areas on the west bank of the River Severn around Eardington and Hampton Loade have largely been worked out for aggregate. Pods of diamict recorded during sand and gravel extraction in these deposits at Chelmarsh, above Hampton Loade, are considered to be blocks of frozen glacial till which were transported during periods of high flow (Dawson, 1989).

Further extensive sheet deposits occur in the vicinity of Claverley in the Worfe valley (Figure 10). These deposits, at a higher elevation of 75 m above OD, fall gently towards the south and lie within the late Devensian glacial limit. As a consequence, they may not directly correlate with the deposits within the Severn valley, but instead are associated with a retreating ice margin lying to the north of the district.

Undifferentiated Glaciofluvial Deposits of late Devensian age occur marginal to and within the glacial limit, as spreads of sand and gravel rising up gentle slopes east of Shipley [SO 820 962], as isolated patches between Morville and Bridgnorth, and as an undulating spread north of Lower Penn [SO 860 970]. These deposits have no distinctive morphological expression and frequently overlie till. In Bridgwalton Sand and Gravel Pit, Morville [SO 6871 9206], they occur with glaciolacustrine clay and sand.

Of limited extent, undifferentiated glaciofluvial terrace deposits occur in the Stour valley in the vicinity of Prestwood [SO 872 865]. They are of probable Devensian age with a surface elevation of about 70 m OD, and are incised by the younger Holt Heath Member.

In the Stour valley, late Devensian glaciofluvial sheet deposits are named the Holt Heath Sand and Gravel Member (Maddy et al., 1995). They are probably contemporaneous with the extensive undifferentiated late Devensian sheet deposits in the Severn valley. The member typically forms a surface about 60–65 m above OD, and is most extensively developed around Kinver and Stourton, but can be traced up the valley to the Devensian glacial maximum at Seisdon (Figure 10).

Head has accumulated as a result of a combination of solifluction and colluvial processes. Extensive solifluction took place during the late Devensian glacial period, when the district was located just to the south of the main ice front and periglacial conditions prevailed. Similar conditions possibly persisted into the early Flandrian. Accumulations of colluvial material have been forming throughout the Flandrian and are still being deposited at the present.

Head was not mapped during the previous survey. The deposit is probably widespread throughout the area on valley sides and bottoms, but its extent is often difficult to determine as the composition commonly closely reflects that of its upslope source material and may resemble in situ weathered bedrock. Head contains unsorted and angular blocks of locally derived sandstone and siltstone in a matrix of sandy clay.

The deposits have been mapped during the present resurvey only where a significant thickness (greater than 1.0 m) is found. The mapped areas generally occur at the bases of steep slopes, as in the Morfe Valley and east of Chelmarsh Hall [SO 722 880], or as valley fill deposits in the deeply dissected landscape of the Wyre Forest Coalfield west of the River Severn (Figure 10), such as within the Borle Brook and its tributaries. Locally, head forms lobes or aprons resting on or grading into other Quaternary deposits, such as till or the glaciofluvial sheet deposits in the Severn valley.

Postglacial

Alluvial fan deposits occur where tributaries intersect main valleys and emerge from the confines of their channels. They typically form small cone-shaped features and are composed primarily of sandy clay and silty sand with gravel. Most of the fans were probably mainly active during the late glacial transition, when large amounts of water and sediment were available and there was relatively little vegetation. However, deposition continues to the present and modern changes in landuse can initiate a new phase of fan deposition. Numerous small alluvial fans have been identified in the Severn valley.

Undifferentiated river terrace deposits of the Severn Valley Formation are the preserved remnants of older alluvial tracts which have subsequently been incised. Only in the north-west of the district, upstream of Eardington in the Severn valley, and along its tributary the River Worfe, upstream of the probable glacial meltwater gorge cut through the Kidderminster Formation at Burcote [SO 747 954], has their been any extensive postglacial Flandrian river terrace development. There are two named river terrace deposits in the district. The first terrace, associated with the Power House Sand and Gravel Member , mainly rises no more than a few metres above current river level, and is predominantly sandy silt with lenses of gravel. The second terrace, associated with the Worcester Sand and Gravel Member can be as much as 10 m above river level and has a greater gravel content. Elsewhere in the district, terrace development within the Severn and Stour valleys is patchy, as continued fluvial activity has eroded the older terraces, although even in these larger systems there are no more than two postglacial terraces.

Alluvium occurs as almost continuous tracts in the modern floodplain of the larger rivers, and as isolated patches within the smaller tributary valleys (Figure 10). The widest alluvial spreads occur within the relatively easily eroded Permo-Triassic rocks north of Chelmarsh along the River Severn, and in the Stour valley north of Kidderminster. Where undrained for agricultural purposes, the alluvium typically forms flat, commonly waterlogged ground with reed beds and evidence of abandoned channels. It is laterally highly variable and consists of clay, silt sand and gravel with varying proportions of peat and lacustrine deposits. A basal gravel lag is common. Lacustrine alluvium is mapped in a small area near to Mere Hall, Bobbington [SO 822 892] and is likely to comprise a thin deposit of organic clay and silt.

Peat is mapped in a small area in the north of the district at Rushy Marsh [SO 833 973], west of Black Brook (Figure 10). Augering has proved at least 0.5 m, which rests upon poorly drained till deposits.

Landslides within the district are largely confined to bedrock, although small failures can occur where watercourses undercut slopes within superficial deposits. The largest landslides are along the Mor Brook at Thatchers Wood [SO 700 903] and at the confluence of the Borle Brook with the River Severn [SO 753 817]. Both landslides occur within Carboniferous strata, which seem particularly prone to failure on deeply incised, steep valley sides that are common beyond the Devensian glacial limit. Some of the failures may have been initiated during the Devensian. Subsequently, toe erosion by streams, and the presence of springs at the base of sandstones in the Halesowen Formation and at the boundary between the Etruria and Halesowen formations, resulted in shallow rotational failures developing into larger complex failures. This movement continues to the present.

Artificial ground

West of the River Stour, man-made deposits are of generally limited extent, commonly being associated with mineral workings, transport routes or industrial developments. However, within the heavily urbanised Black Country, large swathes of the district have been heavily modified by exploitation of resources and subsequent remediation or development.

Worked ground includes areas where the ground is known to have been cut away by man. The majority of excavations in the district are now disused sandstone quarries, sand and gravel pits for aggregate (e.g. Eardington where excavations extended to bedrock [SO 730 905]) and clay pits (commonly at brick works, for example [SO 708 850]), although recently quarrying has restarted at Knowlesands [SO 718 915] at the former Bridgnorth brickworks site, supplying clay to the brickmaking industry (Plate 5). Other modern excavations include numerous fish ponds for commercial and recreational use, and railway and road cuttings. There are also some ancient road cuts, such as the Holloway in Wolverley [SO 829 795]. Some pits, such as Dalton's Clay Pit [SO 936 870], remain open because of their unique geological and/or biological features, and have statutory or local protection from redevelopment (Cleal and Thomas, 1996).

Made ground consists of material deposited on top of the original land surface, although in some cases the top and subsoil may have been removed first. It includes areas of spoil from the numerous sandstone quarries and ironworks, and colliery spoil heaps either from surface workings or adjacent to shafts. In parts of the Black Country coalfield area, around Tipton and Coseley, much of the spoil was spread across the surface prior to urban development and so does not form distinct topographical features, but its extent can be recognised from borehole data. In the west of the district, one of the largest areas of spoil is at the former Alveley Colliery, which has been landscaped at Severn Valley Country Park [SO 752 840]. Smaller areas of spoil are associated with the former Highley Colliery [SO 745 831].

Made ground also includes embankments for railways, roads and dams associated with the fish ponds. Large reservoir embankments are found in the Severn valley at the Trimpley Works [SO 767 789]–[SO 775 787] and at Chelmarsh Reservoir [SO 735 873]. Tipping of domestic refuse, as at Stack Pool [SO 835 780], has created a recreational park in an area formerly prone to flooding.

Infilled ground comprises areas where the natural ground has been cut away and partially or wholly backfilled with made ground. Backfilled sandstone quarries and small clay pits are common across the district. Many sand and gravel pits, such as those at Hay Farm [SO 727 895] and Barnsley [SO 758 926] are in the process of being backfilled with either quarry waste or inert domestic refuse, whereas some older pits, such as south of The Heath [SO 751 821] have been completely infilled and restored. Recent opencast coal workings at Amblecote and Bilston have been backfilled in a controlled fashion, with monitoring, and venting, and compaction of the waste to make it suitable for redevelopment.

Disturbed ground encompasses those areas of shallow mineral working, which resulted in areas of hummocky ground. The most extensive occurrences are west of Billingsley [SO 707 845] and an area of numerous bell pits in woods east of Cherry Orchard Farm [SO 761 790].

Structure

Four dominant fault orientations, with approximate north, north-west, north-east and west trends are recognised in the district (Figure 1). With the exception of the west-trending faults, the larger faults were probably initiated as pre-Carboniferous lines of structural weakness, which may have been repeatedly reactivated during the Variscan Orogeny in the latest Carboniferous and by Mesozoic and/or Cenozoic earth movements (Waters et al., 1994). Most faults have normal displacements at the surface, but many of the major structures have a complex history with components of reverse movement.

The South Staffordshire Coalfield, in the eastern part of the district, is a broadly north-trending horst block, the Western Boundary Fault defining the western margin of the horst. The fault, which broadly throws Permo-Triassic strata down to the west against the Carboniferous strata of the South Staffordshire Coalfield to the east, is north-east- to north-north-east-trending to the north of Himley and north-north-west- to north-trending to the south. The fault splays repeatedly to form fault-bounded slivers up to 3 km long. The north-west-trending Russell's Hall Fault, which extends east of the prominent bend in the Western Boundary Fault, displays a net reverse displacement. The fault separates a condensed succession of Pennine Coal Measures Group and Etruria Formation to the north-east (hanging wall) and an atypically thick succession to the south-west (footwall). South-west of the Russell's Hall Fault the main structures are north-north-east-trending, including the Shut End and Brockmoor faults, all of normal displacements down to the west, and the Hayes Fault, with a net reverse displacement. The Netherton Anticline occurs parallel with, and in the hanging wall of, the Hayes Fault. West-trending faults are also present, including the Brierley Hill Trough faults and the Cradley and Wollescote faults. To the north-east of the Russell's Hall Fault are a series of en echelon periclinal folds of the Dudley Ridge, including the Hurst Hill, Wren's Nest and Castle Hill anticlines. To the east of the Dudley Ridge there are a number of west-trending faults, including the Coseley–Wednesbury and Tipton–Hill Top faults, mainly with throws down to the south (Waters et al., 1994).

A series of major north-trending faults, including the Western Boundary Fault and the Lloyd House and Stapenhill faults, occupy the eastern flank of the graben of the Bratch Trough, which is bound to the west by the Enville Fault. The Stourbridge Syncline, which is subparallel with and located between the Stapenhill and Western Boundary faults, deforms Permo-Triassic strata. The axis of the Stourbridge Syncline appears to be offset dextrally by a set of west-trending faults. The Smestow Borehole (Figure 6), (Figure 8) proved a condensed succession of Pennine Coal Measures Group and Etruria Formation, representing deposition on the Smestow High (Figure 1). This may have formed a passive topographical feature at the time of deposition, or was actively uplifting in response to reverse displacements on the bounding Enville and Stapenhill faults (Glover, 1991).

To the west of the Enville Fault, in the Wyre Forest Coalfield, the dominant faults are north-east- and north-north-west- to north-north-east-trending. There are also east–west oriented faults, mainly with small throws down to the north. The north-east-trending set has generally large throws (in the order of tens to hundreds of metres) mainly down to the north-west. The main fault is the Kinlet Hall–Pattingham Fault. A steeply inclined reverse fault of this trend forms the western margin of the Trimpley inlier. In the vicinity of Shatterford, the Siluro-Devonian succession in the hanging wall to the south-east is folded into a syncline and anticline with fold axes parallel with the fault. In the footwall to the west, Carboniferous strata are steeply dipping toward the north-west, with dips steepening as the fault is approached. The eastern margin of the Trimpley inlier is defined by the Enville Fault, which comprises two faults to the east of Trimpley. Within the inlier, the Lower Old Red Sandstone Group is cut primarily by faults of east–west trend, the main being the Park Attwood Fault, which appears to have variable directions of throw along its length. Further north-north-east-trending faults appear to cut the fold axes of an upright syncline and anticline at Trimpley.

There are two main north-north-west-trending faults, the Alveley and Romsley faults, which extend south of the Kinlet Hall–Pattingham Fault forming a prominent graben. Mining from Alveley Colliery was restricted west and east of the graben. The two faults join south of Romsley. A further graben formed by north-north-west-trending faults is defined by the Station Fault to the west and the Arley Park Fault to the east.

Structural history

There is limited evidence for Caledonian deformation in the district. The north-north-west-trending periclinal folds of the Dudley Ridge appear to show two phases of deformation about the same fold axis. The earlier phase, assigned to the Acadian phase of the Caledonian Orogeny, resulted in the regional tilting and localised folding of the Silurian and Devonian succession (Figure 3). The culmination of the Variscan Orogeny was during late Carboniferous to Permian times. However, evidence for tectonic influence on sedimentation suggests that deformation occurred as early as Westphalian times (Waters et al., 1994). Synsedimentary faulting is indicated by thickness variations in the Pennine Coal Measures Group, which parallel the major structures, and the presence of seam splitting across faults, most notably in the seam split between the Flying Reed and Thick Coal. The interseam thickness increases dramatically from zero to over 50 m between the Coseley–Wednesbury Fault and Tipton and Hill Top Fault (Waters et al., 1994) and to the west of the Shut End Fault.

During the Bolsovian to Asturian (Westphalian D) an important event, marked by the inversion of a number of pre-existing structures and regional uplift, resulted in the development of the angular unconformity at the base of the Halesowen Formation (Plate 4). This event activated faults and produced folds with a north–south to north-north-east–south-south-west trend. The periclinal folds of the Dudley Ridge (Figure 3) may have developed in response to sinistral displacement on the Russell's Hall Fault (Waters et al., 1994). The major microgabbro (dolerite) intrusions, of Bolsovian age, occur in proximity to some of the major faults (Figure 1) and it is probable that displacements on these faults, in response to east–west or north-west–south-east compression, permitted the upward migration of the igneous bodies. The intrusions at Kate's Hill and London Fields are adjacent to the Russell's Hall Fault, the Barrow Hill intrusion occurs within the Tansey Green Trough, and the Kinlet Microgabbro Sill occurs between several splays of the Kinlet Hall–Pattingham Fault (Figure 1).

The Kinlet Hall–Pattingham Fault may have controlled sedimentation during the end-Variscan deformation event, as it delineates the area of Bridgnorth Sandstone Formation limited to the north-west of the structure, and the Clent Formation is restricted to the south-east. In the South Staffordshire Coalfield, regional uplift of the Wales–Brabant High occurred at this time, producing an angular unconformity at the base of the Clent Formation. To the north, in the Himley area, the Clent Formation rests conformably upon the Salop Formation.

The Bratch Trough (Figure 9) and the major north-trending faults developed in response to east–west extension during Permo-Triassic times, which also resulted in development of the Stafford and Cheshire basins to the north and the Worcester Basin to the south. This phase of extension resulted in reactivation of the Western Boundary Fault.

Chapter 3 Applied geology

The key geoscience constraints likely to influence land use, development and conservation are described below. Powell. et al. (1992) provided details for the eastern part of the district.

Mineral resources

The district is endowed with abundant mineral resources, principally coal, ironstone, fireclay, brick clay, limestone, microgabbro (dolerite), sand and gravel and building stone. The main factors hindering extraction are significant thicknesses of overburden, sterilisation of resources by urban development and possible detrimental effects on the landscape and environment.

Coal and associated ironstone have been mined in the South Staffordshire Coalfield since medieval times, but by the late 19th century, with exhaustion of seams, deep mining operations moved to the Himley and Baggeridge mines, west of the Western Boundary Fault, and the Highley area of the Wyre Forest Coalfield. Deep coal mining in the district ceased in the South Staffordshire Coalfield with closure of Baggeridge Colliery in 1968 and in the Wyre Forest Coalfield at Alveley Mine in 1969. The economics of underground mining are currently unfavourable and consequently mineral resources are those that can be worked close to surface. Bituminous coal (Plate 3) and associated fireclay and ironstone resources mainly occur in the Pennine Coal Measures Group. The Thick Coal is a thick seam, up to 12 m, throughout the South Staffordshire Coalfield. In the north-east of the district, coals beneath the Thick Coal are thicker and of better quality than their correlatives south of Dudley. The Bottom Holers, Mealy Grey (present below the Bottom Holers coal) and Stinking coals are generally of poor quality, the last being very sulphurous. In the south of the coalfield, around Lye and Halesowen, the lowermost coal seams fail and are replaced by fireclays. The refractory and semi-refractory clays were used in the manufacture of firebricks, sanitary ware, drain pipes and pottery. Ironstone, sourced from nodules of siderite (iron carbonate), has not been worked in the district since the 1920s.

Brick clay has historically been extracted mainly from the Etruria Formation (Plate 4) and Alveley Member (Plate 5). The Etruria Formation clays produce very high quality bricks of various colours, and the high iron oxide content facilitates production of the strong engineering (blue) brick. The clays of the Alveley Member are generally too calcareous for brick making and have a low iron content.

The main source of road aggregate and coated stone is from the numerous microgabbro (dolerite) igneous intrusive bodies, the largest of which, at Rowley Regis, is the only one still being worked. Sand and gravel for aggregate and building sand was formerly worked from superficial deposits, including glaciofluvial (Plate 8) and river terrace deposits, and also from sandstones of the Sherwood Sandstone Group. The Wildmoor Sandstone Formation was formerly worked for moulding sand in the iron and steel industry.

Limestone was formerly extracted from the Silurian Aymestry Limestone, Much Wenlock Limestone (Plate 1) and Barr Limestone formations, and used as a flux in the iron industry, as agricultural lime and in cement production.

Quarries that have not been backfilled are an important resource in providing suitable sites for waste disposal; they may also be reopened as a source of minerals or developed as sites of educational, recreational and wildlife value, such as Doulton's Clay Pit [SO 935 870], now forming part of the Saltwells Local Nature Reserve (Cleal and Thomas, 1996).

Ground conditions

The most important ground conditions relevant to construction and development are the suitability of the ground to support structural foundations, the ease of excavation of ground material and its use in engineered earthworks and fills. These are summarised in (Figure 11). Foundation conditions are not only affected by the engineering properties of the local geology, but also by factors such as the geological structure, slope stability, the presence of undermining and the depth and degree of weathering. Variable man-made ground conditions, notably from landfill sites and areas of colliery spoil, may be a potential problem with respect to severe differential settling. Colliery spoil may contain iron pyrites that is prone to oxidise and produce sulphate-rich, acidic leachates, which may be harmful to concrete in foundations or buried services, thus requiring the use of sulphate-resistant cement. This oxidation process may also result in expansion and differential heaving of foundations constructed on such deposits. Large volumes of quarry spoil are present in the district, and the areas affected may present poor foundation conditions if large cavities are present, or where the spoil was deposited on steep slopes.

Mining subsidence

In the exposed coalfields mining subsidence represents a significant hazard, largely due to the collapse of abandoned underground workings and their access shafts and adits. Coal mines tend to be shallower and older in the eastern part of the district, where the Pennine Coal Measures Group occurs at crop in the South Staffordshire Coalfield. Older mines, using partial extraction methods such as pillar and stall, produce more concentrated subsidence features than modern long-wall methods, which tend to affect larger areas but less severely. Deeper, more recent, mining activity has taken place to the west of the Western Boundary Fault and in the Wyre Forest Coalfield, mostly by long-wall extraction. Faults can be reactivated by mining subsidence, resulting in linear subsidence features.

Shafts represent a hazard, particularly where either incompletely or poorly backfilled. Similarly, adits may have been blocked without being backfilled. Mine collapse may be delayed for many years following abandonment, depending on the type and size of working and changes in the ground water regime.

Slope stability

There are 38 landslides mapped within the district. A large proportion of the more extensive landslides are situated along the Severn Valley and in tributary valleys in the west of the district (Figure 10), most notably where the rivers and streams have incised steep valley margins within the Halesowen Formation.

A landslide indicates significant ground movement in the past and/or present and represents a hazard. Ancient landslides may be reactivated by earthmoving and other engineering operations, by natural erosion, and by water leakage or drainage failure. Where possible, any form of development on landslides should be avoided. Special precautions should be taken when site investigations are carried out on or near landslides. Landslides in man-made spoil are hazardous, particularly where spoil becomes saturated and long run-outs are available.

Pollution potential

This is particularly applicable to artificial (man-made) deposits that may contain toxic residues, either as a primary component or generated secondarily by chemical or biological reactions. Significant sites of potential pollution include areas of landfill and former gasworks, chemical works, textile mills, foundries, railway sidings and sewage works. Leachate migration may be a problem where groundwater percolates through waste and becomes enriched in potentially harmful soluble components. The problem may be enhanced in fractured bedrock because the discontinuities may provide pathways for leachate migration. Mine-drainage waters may also be a problem near former mine workings because of their high pH, iron precipitation and the common elevated levels of manganese, aluminium and sulphates.

Mine gas may be generated from both underground colliery workings and from colliery spoil. The gas includes methane, carbon dioxide, and carbon monoxide. Gases, in particular methane, can also be generated from natural deposits such as carbonaceous mudstones and from man-made deposits, such as domestic refuse in landfill sites. Such gases are able to travel significant distances from their source through fissures, either natural or related to mining subsidence. Where these gases are allowed to collect, fire or explosion may result.

Radon is a natural radioactive gas produced by the radioactive decay of radium and uranium. It is found in small quantities in all rocks and soils, although the amount varies from place to place. Radon that enters poorly ventilated enclosed spaces such as some basements, buildings, caves, mines, and tunnels may reach high concentrations. Inhalation of the radioactive decay products of radon gas increases the chance of developing lung cancer. BR211 (BRE, 1999) provides guidance on protective measures for new dwellings and defines areas where geological assessment should be carried out. Within the district, the areas of significant radon potential are limited to the part of the South Staffordshire and Wyre Forest coalfields where the Pennine Coal Measures Group occurs at crop, and in the vicinity of Bridgnorth, in the north-west of the district.

Water resources

Groundwater provides water supply and licensed water abstraction for industrial purposes. The major aquifer in the district comprises the Permian Bridgnorth Sandstone Formation and overlying Triassic Sherwood Sandstone Group, which supplies large quantities of water to Stourbridge, Wombourne and Wolverhampton (Powell, et al., 1992). The aquifer typically forms a single hydrogeological unit, but at least two aquifers are recognised in the Stourbridge area, with a confining layer within cemented pebbly horizons and mudstones towards the base of the Kidderminster Formation (basal Sherwood Sandstone Group). Although water quality is generally good, the upper aquifer (including the Kidderminster and Wildmoor Sandstone formations) has a tendency for high nitrate contents, derived mainly from nitrate-based fertilisers (Powell, et al., 1992; Allen et al., 1997). The Bromsgrove Sandstone Formation includes mudstone interbeds which cause it to act as a multiple aquifer system. Faults may act as conduits for groundwater flow, potentially increasing yields from boreholes, but faults with large displacements may reduce the interconnectivity of aquifer sandstones, thus limiting groundwater flow. Pumping tests indicate transmissivity ranges from 2 to 5200 m²/d, and maximum core porosities for all of the Permo-Triassic formations are typically about 35 per cent (Allen et al., 1997).

Carboniferous sandstone units in the district, especially those of the Warwickshire Group, are minor aquifers. The quality of the groundwater in the coalfield areas is naturally poor due to metals and sulphate and chloride minerals in the rock (Powell, et al., 1992). In the coalfield areas, groundwater quality is also affected by contamination associated with heavy industry. The closure of much heavy industry in the coalfield area in the east of the district has resulted in reduced groundwater abstraction and a consequent rise of groundwater levels.

Information sources

Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. For information on wells, springs and water borehole records contact: BGS Hydrogeological Enquiries, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB Telephone 01491 838800 Fax 01491 692345.

Other geological information held by the British Geological Survey includes borehole records, fossils, rock samples, thin sections and hydrogeological data. Searches of indexes to some of the collections can be made on the website, which also gives access to the BGS Lexicon of named rock units and photographic collection. The BGS catalogue of maps and books is available on request (see back cover for addresses).

Maps

• Geological maps
• 1:50 000
• Sheet 167 Dudley (Bedrock and Superficial) 2012
• 1:10 000
• The maps covering the 1:50 000 Series Sheet 167 Dudley are not published, but are available for public reference in BGS libraries in Keyworth and Edinburgh and the London Information Office in the Natural History Museum, South Kensington, London. Full colour digital copies are available for purchase from the BGS Sales Desk. Copies of the fair-drawn maps of the earlier surveys may be consulted at the BGS Library, Keyworth. Many BGS maps are available in digital form, which allows the geological information to be used in GIS applications. These data must be licensed for use. Details are available from the Intellectual Property Rights Manager at BGS Keyworth. The current availability can be checked on the BGS website.
• Geophysical maps
• 1:1 000 000
• Colour shaded relief gravity anomaly maps (UTM series), 2006
• Colour shaded relief magnetic anomaly maps (UTM series), 2006
• Geochemical atlases
• 1:250 000
• Point-source geochemical data has been processed to generate a smooth continuous surface presented as an atlas of small-scale colour-classified digital maps.
• Data from the Geochemical Baseline Survey of the Environment (G-BASE) are also available in other forms including hard copy and digital data.
• Hydrogeological maps
• 1:625 000
• Sheet 1 (England and Wales) 1977
• 1:100 000
• Groundwater Vulnerability Maps, South Staffordshire and east Shropshire (Sheet 22), Worcestershire (Sheet 29); produced by the Environment Agency.

Books and reports

British Regional Geology

Central England. Third edition, 1969

Memoirs

Sheet 167 Dudley, 1947, reprinted 1987

Geology and land-use planning report

Powell, J H, Glover, B w, and waters, c n. 1992. A geological background to planning and development in the Black Country. British Geological Survey Technical Report, WA/92/33.

Documentary collections

Boreholes and shafts

Borehole and shaft data are catalogued in the BGS archives at Keyworth. For the Dudley district, the collection consists of the sites and logs of about 10 000 boreholes. For further information contact: The Manager, National Geosciences Records Centre, BGS, Keyworth.

Mineplans

BGS maintains a collection of plans of underground mines for minerals other than coal, mainly ironstone, fireclay and limestone.

Geophysics

Gravity and aeromagnetic data are held digitally in the National Gravity Databank and the National Aeromagnetic Databank at BGS Keyworth. Seismic reflection data is available for parts of the district.

Material collections

Palaeontological collection

Macrofossils and micropalaeontological samples collected from the district are held at BGS Keyworth. Enquiries concerning the material should be directed to the Curator, Biostratigraphy Collections, BGS Keyworth.

Petrological collections

Hand specimens and thin sections are held in the England and Wales Sliced Rocks collection at BGS Keyworth. A collection database is maintained and charges and conditions of access to the collection are available on request from BGS Keyworth.

Borehole core collection

Samples and entire core from a small number of boreholes in the Dudley district are held by the National Geosciences Records Centre, BGS, Keyworth.

BGS photographs

Photographs used in this report are held in the BGS library, Keyworth. Copies can be supplied at a fixed tariff.

Other relevant collections

Coal abandonment plans

Coal abandonment plans are held by The Coal Authority (for address see below).

Licensed water abstraction sites

Information on licensed water abstraction sites, for groundwater, springs and reser voirs, Catchment Management Plans with surface water quality maps, and extent of washlands and licensed landfill sites are held by the Environment Agency.

Earth science conservation sites

Information on Sites of Special Scientific Interest (SSSI) is held by Natural England, Northminster House, Peterborough, PE1 1UA. Information on Regionally Important Geological and Geomorphological Sites (RIGS) is held by UKRIGS, National Stone Centre, Porter Lane, Middleton by Wirksworth, Derbyshire DE4 4LS.

Addresses for data sources

Mine plans

Coal, ironstone and fireclay

Copies of abandonment plans are held by the Mining Records Office, Coal Authority, 200 Lichfield Lane, Berry Hill, Mansfield, NG18 4RG, Telephone 01623 638233. These plans are held by the Coal Authority in the public domain, but are not available for reference at BGS.

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. BGS Library catalogue can be searched online at: http://geolib.bgs.ac.uk

Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, Wagstaff, S J, and Williams, A T. 1997. The physical properties of major aquifers in England and Wales. British Geological Survey Technical Report, WD/97/34. Environment Agency R&D Publication, No. 8.

Allen, J R L. 1961. The highest Lower Old Red Sandstone of Brown Clee Hill, Shropshire. Proceedings of the Geologists' Association, Vol. 72, 205–219.

Allen, J R L. 1977. Wales and the Welsh Borders. 40–54 in A correlation of Devonian rocks of the British Isles. House, M R, Richardson, J B, Chaloner, W G, Allen, J R L, Holland, C H and Westoll, T S (editors). Special Report of the Geological Society of London, No. 8.

Ball, W H. 1951. The Silurian and Devonian rocks of Turner's Hill and Gornal, South Staffordshire. Proceedings of the Geologists' Association, Vol. 62, 225–236

Ball, W H, and Dineley, D L. 1952. Notes on the Old Red Sandstone of the Clee Hills. Proceedings of the Geologists' Association, Vol. 63, 207–214.

Ball, W H, and Dineley, D L. 1961. The Old Red Sandstone of Brown Clee Hill and the adjacent area. Bulletin of the British Museum, Natural History, Vol. A5, 177–242.

Barclay, W J. 2004. Devil's Hole, Shropshire. 228–9 in The Old Red Sandstone rocks of Great Britain. Barclay, W J, Browne, M A E, McMillan, A A, Pickett, E A, Stone, P, and Wilby, P R (editors). Geological Conservation Review Series, No. 31. (Peterborough: Joint Nature Conservation Committee.)

Bassett, M G. 1974. Review of the stratigraphy of the Wenlock Series in the Welsh Borderland and South Wales. Palaeontology, Vol. 17, 745–777.

Bassett, M G. 1989. The Wenlock Series in the Wenlock area. 51–73 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Besly, B M. 1988a. Late Carboniferous sedimentation in northwest Europe: an introduction. 1–7 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Besly, B M. 1988b. Palaeogeographical implications of late 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 and London: Blackie.)

Besly, B M, and Cleal, C J. 1997. Upper Carboniferous stratigraphy of the West Midlands (U K) revised in the light of borehole geophysical logs and detrital compositional suites. Geological Journal, Vol. 32, 85–118.

Boulton, W S. 1917. Mammalian Remains in the Glacial Gravels at Stourbridge. Proceedings of the Birmingham Natural History and Philosophical Society, Vol. 4, 107.

B R E, 1999. Radon: guidance on protective measures for new buildings. C RC Ltd.

Cleal, C J, and Thomas, B A. 1996. British Upper Carboniferous Stratigraphy. Geological Conservation Review Series, No. 11 (London: Chapman and Hall.)

Cocks, L R M, Holland, C H, and Rickards, R B. 1992. A revised correlation of Silurian rocks in the British Isles. Special Report of the Geological Society of London, No. 21.

Cutler, A, Oliver, P G, and Reid, C G R. 1990. Wren's Nest National Nature Reserve. Geological Handbook and Field Guide. (Dudley Leisure Services Department.)

Dawson, M R. 1985. Environmental reconstructions of a late Devensian terrace sequence: some preliminary findings. Earth Surface Processes and Landforms, Vol. 10, 237–246.

Dawson, M R. 1989. Chelmarsh. 80–85 in West Midlands: Field Guide. Keen, D H (editor). (Hampshire: Quaternary Research Association.)

Dineley, D L. 1999. Devil's Hole. 119–125 in The fossil fishes of Great Britain. Dineley, D L, and Metcalfe, S J (editors). Geological Conservation Review Series, No. 16. (Peterborough: Joint Nature Conservation Committee.)

Eastwood, T, Whitehead, T H, and Robertson, T. 1925. The geology of the country around Birmingham. Memoirs of the Geological Survey of Great Britain, Sheet 168 (England and Wales).

Galtier, J, Scott, A C, Powell, J H, Glover, B W, and Waters, C N. 1992. Anatomically preserved conifer-like stems from the Upper Carboniferous. Proceedings of the Royal Society of London, Vol. 247, 211–214.

Glover, B W. 1991. Geology of the Wombourne District. British Geological Survey Technical Report, WA/90/74.

Glover, B W, and Powell, J H. 1996. Interaction of climate and tectonics upon alluvial architecture: Late Carboniferous–Early Permian sequences at the southern margin of the Pennine Basin, U K. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 121, 13–34.

Glover, B W, Powell, J H, and Waters, C N. 1993. Etruria Formation (Westphalian C) palaeoenvironments and volcanicity on the southern margins of the Pennine Basin, South Staffordshire, England. Journal of the Geological Society of London, Vol. 150, 737–750.

Goodwin, M, Maddy, D, and Lewis, S G. 1997. Pleistocene Deposits at Gibbet Hill (Stewponey Pit), Stourbridge, Staffordshire. 91–94 in The Quaternary of the South Midlands and the Welsh Marches: Field Guide. Lewis, S G, and Maddy, D (editors). (Hampshire: Quaternary Research Association.)

Greig, D C, Wright, J E, Hains, B A, and Mitchell, G H. 1968. Geology of the country around Church Stretton, Craven Arms, Wenlock Edge and Brown Clee. Memoir of the Geological Survey, Sheet 166 (England and Wales).

Geomorphological Services L TD. 1987. National review of research into landsliding in Great Britain. Report to the Department of the Environment.

Guion, P D, and Fielding, C R. 1988. Westphalian A and B sedimentation in the Pennine Basin, U K. 153–177 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Hamblin, R J O, and Coppack, B C. 1995. Geology of Telford and the Coalbrookdale Coalfield. Memoir of the British Geological Survey, parts of sheets 152 and 153 (England and Wales).

Horton, A. 1989. Quinton. 69–76 in The Pleistocene of the West Midlands: Field Guide. Keen, D H (editor). (Cambridge: Quaternary Research Association.)

King, W W. 1921a. The plexography of South Staffordshire in Avonian times. Transactions of the Institute of Mining Engineering, Vol. 61, 155–168.

King, W W. 1921b. The geology of Trimpley. Transactions of the Worcestershire Naturalists' Club, Vol. 7, 319–322.

King, W W. 1925. Notes on the 'Old Red Sandstone' of Shropshire. Proceedings of the Geologists' Association, Vol. 36, 383–389.

King, W W. 1934. The Downtonian and Dittonian strata of Great Britain and north-western Europe. Quarterly Journal of the Geological Society of London, Vol. 90, 526–567.

Karpeta, W P. 1990. The morphology of Permian Palaeodunes — a reinterpretation of the Bridgnorth Sandstone around Bridgnorth, England, in the light of modern dune studies. Sedimentary Geology, Vol. 69, 59–75.

Kirton, S R. 1984. Carboniferous volcanicity in England, with special reference to the Westphalian of the East Midlands. Journal of the Geological Society of London, Vol. 141, 161–170.

Lawson, J D, and White, D E. 1989. The Ludlow Series in the Ludlow area. 73–90 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Maddy, D, Green, C P, Lewis, S G, and Bowen, D Q. 1995. Pleistocene Geology of the Lower Severn Valley, U K. Quaternary Science Reviews, Vol. 14, 209–222.

Maddy, D. 1997. Midlands Drainage Development. 7–18 in The Quaternary of the South Midlands and the Welsh Marches: Field Guide. Lewis, S G, and Maddy, D (editors). (Hampshire: Quaternary Research Association.)

Marshall, C. 1942. Field relations of certain of the basic igneous rocks associated with the Carboniferous strata of the Midland counties. Quarterly Journal of the Geological Society, London, Vol. 98, 1–25.

Marshall, C. 1946. The Barrow Hill Intrusion, South Staffordshire. Quarterly Journal of the Geological Society of London, Vol. 101, 177–205.

Morgan, A V. 1973. The Pleistocene geology of the area north and west of Wolverhampton, Staffordshire, England. Philosophical Transactions of the Royal Society of London, B265, 233–297.

Morgan, A V, and West, R G. 1988. A pollen diagram from an interglacial deposit at Trysull, Staffordshire, England. New Phytologist, Vol. 109, 393–397.

Owens, B. 1990. Palynological report on a coal sample from Little London Brook, Alveley, Shropshire. British Geological Survey Technical Report, WH/90/254.

Poole, E G. 1966. Trial boreholes on the site of a reservoir at Eymore Farm, near Bewdley, Worcestershire. Bulletin of the Geological Survey of Great Britain, Vol. 24, 131–156.

Poole, E G. 1970. Trial boreholes in Coal Measures at Dudley, Worcestershire. Bulletin of the Geological Survey of Great Britain, Vol. 33, 1–41.

Powell, J H, Glover, B W, and Waters, C N. 1992. A geological background to planning and development in the Black Country. British Geological Survey Technical Report, WA/92/33.

Powell, J H, Glover, B W, and Waters, C N. 2000. Geology of the Birmingham area. Memoir of the British Geological Survey, Sheet 168 (England and Wales).

Ramsbottom, W H C, Calver, M A, Eagar, R M C, Hodson, F, Holliday, D W, Stubblefield, C J, and Wilson, R B. 1978. A correlation of Silesian rocks in the British Isles. Special Report of the Geological Society of London, Vol. 10.

Siveter, D J. 2000. Wren's Nest (S O 937 920). 191–198 in British Silurian Stratigraphy. Palmer, D, Siveter, D J, Lane, P, Woodcock, N, and Aldridge, R (editors). Geological Conservation Review Series, No. 19. (Peterborough: Joint Nature Conservation Committee.)

Siveter, D J, and Lane, P D. 2000. Brewin's Canal. 438–440 in British Silurian Stratigraphy. Palmer, D, Siveter, D J, Lane, P, Woodcock, N, and Aldridge, R (editors). Geological Conservation Review Series, No. 19. (Peterborough: Joint Nature Conservation Committee.)

Smith, N J P, Kirby, G A, and Pharaoh, T C. 2005. Structure and evolution of the south-west Pennine Basin and adjacent areas. Subsurface memoir of the British Geological Survey.

Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W, and Taylor F M. 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No. 13.

Waters, C N. 1991. Geology of the Rowley Regis District (S O98N E). British Geological Survey Technical Report, WA/91/55.

Waters, C N. 2003. Carboniferous and Permian igneous rocks of central England and the Welsh Borderland. 279–316 in Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front. Stephenson, D, Loughlin, S C, Millward, D, Waters, C N and Williamson, I T (editors). Geological Conservation Review Series, No. 27. (Peterborough: Joint Nature Conservation Committee.)

Waters, C N, Glover, B W, and Powell, J H. 1994. Structural synthesis of S Staffordshire, U K: implications for the Variscan evolution of the Pennine Basin. Journal of the Geological Society of London, Vol. 151, 697–713.

Waters, C N, Glover, B W, and Powell, J H. 1995. Discussion on structural synthesis of south Staffordshire, U K: implications for the Variscan evolution of the Pennine Basin. Journal of the Geological Society of London, Vol. 152, 197–200.

White, D E, and Lawson, J D. 1989. The Přídolí Series in the Welsh Borderland and south-central Wales. 73–90 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Whitehead, T H, and Eastwood, T. 1927. The geology of the southern part of the South Staffordshire Coalfield. Memoir of the Geological Survey of Great Britain.

Whitehead, T H, and Pocock, R W. 1947. Dudley and Bridgnorth. Memoir of the Geological Survey of Great Britain, Sheet 167 (England and Wales).

Wilson, D, and Waters, C N. 1991. Geological notes and local details for 1:10 000 Sheet S O98N W (Brierley Hill). British Geological Survey Technical Report, WA/91/62.

Wills, L J. 1938. The Pleistocene Development of the Severn from Bridgnorth to the Sea. Quarterly Journal of the Geological Society of London. Vol. 94, 161.

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.

British geological maps can be obtained from sales desks in the Survey's principal offices, through the BGS London Information Office at the Natural History Museum, and from BGS-approved stockists and agents.

Figures and plates

Figures

(Figure 1) Bedrock map summarising the distribution of bedrock units and main structures of the district

(Figure 2) Summary of Silurian lithostratigraphical nomenclature for the Staffordshire Coalfield (for Pridoli succession see Figure 4).

(Figure 3) Distribution of Silurian–Devonian strata at outcrop and at subcrop below the Pennine Coal Measures Group and younger strata, and equivalent of the Acadian unconformity where overlain by Upper Devonian strata. Contours at variable intervals and key boreholes show depth to Acadian unconformity taken at the base of the Pennine Coal Measures Group (metres relative to OD). Colour of borehole indicates age of strata proved beneath the unconformity: colours as for key.

(Figure 4) Present and previous classifications of the Old Red Sandstone Supergroup rocks of the district. ORS - Old Red Sandstone.

(Figure 5) Correlation of Pennine Coal Measures Group strata from selected borehole (BH) and shaft records in the Wyre Forest Coalfield.

(Figure 6) Correlation of Pennine Coal Measures Group strata from selected borehole (BH) and shaft records in the South Staffordshire Coalfield.

(Figure 7) Correlation of Warwickshire Group strata from selected borehole (BH) and shaft records in the Wyre Forest Coalfield.

(Figure 8) Correlation of Warwickshire Group strata from selected borehole (BH) and shaft records in the South Staffordshire Coalfield.

(Figure 9) Structure contours on the Variscan unconformity, taken at the base of the Bridgnorth Sandstone Formation where present, or the Sherwood Sandstone Group. Selected boreholes with level of the Variscan unconformity in metres relative to OD (negative values are above sea level, NP shows not penetrated).

(Figure 10) Quaternary deposits and ice limits in the Dudley district.

(Figure 11) Engineering ground conditions of bedrock and superficial deposits

Plates

(Plate 1) Wren's Nest Hill, Dudley. Quarries and pillars in the Much Wenlock Limestone Formation [SO 9400 9200] (P201915). The Wren's Nest National Nature Reserve [SO 937 923] is one of the most famous geological sites in Britain, and the source of excellent Silurian fossils in many museum collections (Siveter, 2000).

(Plate 2) Brewin's Bridge [SO 9366 8767]. Ludgbridge Conglomerate, at the base of the Pennine Coal Measures Group, resting unconformably upon the Raglan Mudstone Formation (see Whitehead and Pocock, 1947, fig 3; Cleal and Thomas, 1986; Siveter and Lane, 2000). View looking to the north-east (P201903).

(Plate 3) Opencast section at Brettell Lane site, Brierley Hill with about 35–40 m of Pennine Middle Coal Measures Formation with a thin veneer of Etruria Formation on top of section. a) Brooch Coal (upper part) about 0.9–1.0 m thick; b) Measures about 10 m;1. Stinking Coal about 0.6 m, overlain by dark to black shales about 4.5 m; (central parts); 2. Measures, up to 15 m thick; e) Thick Coal, up to 12 m thick (partly exposed lower left) [SO 90660 86050] (P211756).

(Plate 4) Face up to 13 m high at Ketley Quarry [SO 898 890]. View to south-east is of pale purple mudstone with 2 m thick composite espley sandstone, overlain unconformably by Halesowen Formation, the lower 1–2 m being a pebbly sandstone. The low angular unconformity is irregular with small scours (P708646).

(Plate 5) Knowlesands Clay Pit, near Bridgnorth. Mudstones (Alveley Member, Salop Formation) dug for brick making. View towards the west [SO 7175 9148] (P598215).

(Plate 6) Basal Enville Member (Salop Formation) sandstone and conglomerate lenses. Visible face about 3 m high in disused quarry near Hillhouse Farm [SO 7840 8128] (P598060).

(Plate 7) The Hermitage, Bridgnorth. Unconformity between the Kidderminster Formation basal conglomerate (above) and the Bridgnorth Sandstone Formation (below) [SO 7277 9355] (P598172).

(Plate 8) Seisdon Sand Pit. Channel-fill glaciofluvial deposits [SO 8495 9470] (P598242).

(Front cover): Severn Valley, Bridgnorth, cutting through Permian and Triassic rocks. (P598024).

(Rear cover)

(Geological succession) Summary of the geological succession in the district.

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

Figures

(Figure 11) Engineering ground conditions of bedrock and superficial deposits