Geology of the Bradford district — brief explanation of the geological map Sheet 69 Bradford

C N Waters

Bibliographic reference: Waters, C N. 1999. Geology of the Bradford district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 69 Bradford (England and Wales).

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

Keyworth, Nottingham: British Geological Survey, 1999. © NERC 2004 All rights reserved. Printed in the UK for the British Geological Survey by Hawthornes, Nottingham

(Front cover) The Doubler Stones at Rombalds Moor [SE 013 465] is an unusual stack, 2.5m high. One of the Kinderscoutian sandstones is named after this feature (GS550). (Photographer: Neil Aitkenhead.)

(Rear cover)

(Figure 1) Summary of the geological succession of the district.

Notes

The word 'district' refers to the area of Sheet 69 Bradford. National Grid references are given in square brackets; all lie within the 100 km squares SE and SD. Borehole records referred to in the text are prefixed by the code of the National Grid 25 km² are upon which the site falls, for example SE 13 SE.

Acknowledgements

This Sheet Explanation was compiled and written by C N Waters. R A Chadwick, J D Cornwell, B C Chacksfield and C P Royles contributed to the section on Concealed Geology and Structure. N J Riley identified all of the Carboniferous fossils and G E Strong provided petrographical descriptions for the Carboniferous sandstones. The section on Applied Geology was compiled from contributions by K Northmore on engineering geology characteristics and landslips, by D E Highley on mineral resources and by A Butcher on hydrogeological information. We acknowledge the assistance provided by members of the City of Bradford Metropolitan District local authority, the Coal Authority, Mineral Valuers Office, Environment Agency, Yorkshire Water, British Waterways, British Rail and numerous civil engineering consultants. Landowners, tenants and quarry companies are thanked for permitting access to their lands.

The grid, where it is used on figures, is the National Grid taken from Ordnance Survey mapping. © Crown copyright reserved Ordnance Survey licence no. GD272191/1999.

Geology of the Bradford district (summary from rear cover)

(Rear cover)

(Figure 1) Summary of the geological succession of the district.

The landscape of the Bradford district is dominated by the upland moors and 'grit' edges of the Millstone Grit. This harsh landscape is credited with inspiring the writings of the Brontë sisters and continues to attract visitors to the district. The origin of the Millstone Grit as deltaic sediments deposited at the mouths of large river systems flowing from the north about 315 million years ago is no less a remarkable story. At first the rivers discharged into a deep, mostly marine basin of which the Bradford district occurred at the northern margin. Initially the deltas could prograde only a short distance southwards, but as the basin continued to fill with sediments the deltas formed thick sheets of sand (now evident as the sandstones that form the edges on Rombalds Moor) which extended far beyond the district. The deposition of the sediments show a marked cyclicity believed to be controlled by regular fluctuations in sea level during the Carboniferous.

Eventually, with the basin almost completely filled with sediment, the Carboniferous rivers flowed across a broad and very gently sloping delta plain upon which shallow freshwater lakes and mire-swamps developed. These deposits formed the Coal Measures we see today in the south and east of the district. They are typified by the presence of prominent coal seams, the buried and compressed remnants of the mire-peats. It was the presence of coal seams, along with fireclays, ironstone and building stone, most notably the Elland Flags, which controlled the location and subsequent growth of the urban area of Bradford. The relicts of these extractive industries have left parts of the district with potential problems with foundation conditions and pollution.

For the 310 million years following deposition of the Coal Measures there is no evidence of the geological evolution of the district, until, during the Quaternary, when Britain was affected by periods of glaciation. At the peak of the last glacial period the southern margin of the ice sheet straddled the district. In areas where ice formerly occupied, now thin blankets of till remain. Scouring by glaciers and erosion by meltwater rivers resulted in the formation of the landslip-prone steep-sided valleys of Wharfedale and Airedale which subsequently were adopted by the current rivers.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the geology of the district covered by the geological 1:50 000 Series Sheet 69 Bradford published in solid and solid and drift editions in 1999. A fuller description of the geology is provided by the Sheet Description, (Waters, 1998), and detailed information can be found in the individual Technical Reports for the 1:10 000 scale geological maps.

The district lies predominantly within the county of West Yorkshire, principally in the City of Bradford Metropolitan District. It also includes small areas of Calderdale District in the south-west, the Leeds District in the east, and the county of North Yorkshire in the north. The main population centres are the conurbation of Bradford, Shipley and west Leeds; smaller towns in the valleys of the rivers Aire, Wharfe and Worth include Keighley, Bingley, Ilkley, Otley and Skipton. The population centres are separated by areas of agricultural land, with scattered villages, and expanses of moorland.

The bedrock is composed entirely of rocks deposited during the Carboniferous, about 354 to 310 million years ago. The oldest rocks proved in the district are Dinantian (Lower Carboniferous) mudstones and limestones. These are believed to rest unconformably at depth upon strongly deformed Lower Palaeozoic rocks, similar to those proved in the Ribblesdale inlier of the Settle (Arthurton et al., 1988). The Dinantian strata occur in the north-west of the district forming a low-lying area occupied by the town of Skipton. The Dinantian rocks are overlain by the Millstone Grit Group, a thick succession of interbedded sandstones, siltstones and mudstones and subordinate thin coals, fireclays and ironstones of Namurian age. The Millstone Grit occurs at outcrop over most of the north, and west of the district, including Rombalds Moor. Commonly, it forms an upland scenery with extensive moorlands associated with poor and naturally acid soils. The thick sandstones form a series of dissected escarpments or plateaux which show a general decrease in height toward the south and east, matching the regional dip of bedrock strata. The Millstone Grit is overlain by the Coal Measures of Langsettian (Westphalian A) age, a succession of mudstones, siltstones and sandstones, with subordinate thin coals, fireclays and ironstones The Coal Measures outcrop in the south-east of the district, including the main Bradford conurbation and the outlier of Baildon Moor, tending to form relatively low-lying areas although topographical slopes may be steep locally. The presence of minerals such as coal, fireclay, brickclay, ironstone and building stone within the Coal Measures stimulated the early growth of the urban areas, but today mineral extraction is much reduced in scale.

History of research

The district covered by Sheet 69 Bradford was originally surveyed on a scale of six inches to one mile and published as the 1:63 360 'Old Series' sheet 92 SE in 1878. The primary survey account of the geology of the district is given by Dakyns et al. (1879). A general description of the Yorkshire Coalfield, the northern part of which extends across the south and east of the district, is given by Green et al. (1878). The district was resurveyed at 1:10 560 scale in 1933–1937, and Sheet 69 was published at 1:63 360 scale as Solid and Drift editions in 1949; it was reprinted in 1967 (Drift) and 1968 (Solid) and reconstituted to the 1:50 000 scale in 1974. The accompanying memoir (Stephens et al, 1953) provides a detailed account of the geology of the district with descriptions of localities and regional variations. Concurrent with the survey, work was carried out just to the north by Hudson and Mitchell (1937), and the results defined most of the major lithostratigraphical units for the Dinantian.

However, the lithostratigraphical scheme employed for the Dinantian here conforms with that of Garstang (Aitkenhead et al., 1992) and Lancaster (Brandon et al., 1998), largely based on the scheme for the Worston Shale Group, developed for the entire Craven Basin by Riley (1990). Biostratigraphical schemes used in the Dinantian of the Craven Basin are given by Earp et al. (1961), Arthurton et al. (1988) and Aitkenhead et al. (1992). Riley (1990) provides a detailed summary of the biostratigraphical ranges of selected taxa for the Worston Shale Group and correlation of the lithostratigraphical units within the Dinantian stages and series.

The second resurvey was carried out largely on the 1:10 000 scale. Map SE 25 SE was produced as part of the resurvey of the Sheet 62 Harrogate and maps SE 23 NW/NE/SE were resurveyed as part of the applied geological mapping of Leeds, part funded by the Department of the Environment, with the applied geology described by Lake et al. (1992). The remaining geological maps were resurveyed by C N Waters, R G Crofts, N Aitkenhead, R A Addison, J G Rees, N S Jones and M S Stewart in 1993–1996. The applied geology of the City of Bradford Metropolitan District is described fully by Waters et al. (1996a), with accompanying thematic maps and geological databases.

Recent advances in Silesian geology has necessitated some amendments to the previous surveys. Following the work of Ramsbottom et al. (1978), various publications have addressed regional and local aspects of the cyclicity (Holdsworth and Collinson, 1988), sedimentology (Collinson, 1988; Bristow, 1988; Guion and Fielding, 1988; Chisholm, 1990; Guion et al., 1995; Chisholm et al., 1996; Waters et al., 1996b) and palaeontology (Trueman and Weir, 1946; Calver, 1968; Eager et al., 1985) of the Namurian and Westphalian. Leeder (1982) provided insights into the regional structural history of the Carboniferous.

Other than during the geological surveys, the Quaternary deposits have been little studied this century. Work of note include Jowett and Muff (1904) on 'glacial overflow' channels and of Keen et al. (1988) on Bingley Bog. Interesting data is also provided by Price et al. (1984) as part of a mineral assessment survey.

Chapter 2 Geological description

Dinantian rocks

Dinantian rocks are the oldest strata at outcrop in the district, occurring in the extreme northwest in the vicinity of Skipton (Figure 1). The strata occur at crop in the core of the north-east-trending Skipton Anticline, but they are poorly exposed, occurring beneath an extensive drift cover. Much of the information presented in the Bradford memoir is derived from an area of outcrop to the north of the district. A maximum thickness of 700 m of Dinantian strata has been estimated at outcrop, whereas seismic data suggests a total thickness, including concealed strata, of up to 3.4 km.

During the late Devonian and Dinantian a phase of crustal stretching resulted in the formation of relatively rapidly subsiding basins, separated by extensional faults from more slowly subsiding horst and tilt-blocks (Figure 2). The Bradford district lies mainly within the area of the Harrogate Basin, separated from the Askrigg Block to the north by the North Craven Fault. The Chatburn Limestone Group is interpreted as having been deposited in a shallow marine carbonate shelf during a period of high influx of terrigenous muds and silts derived from the Askrigg Block. Further subsidence resulted in a deeper water environment in which the Worston Shale Group was deposited. This group consists dominantly of hemipelagic muds with two prominent carbonate turbidites, the Embsay Limestone Member and Pendleside Limestone Formation. Unconformities mark the base of both these limestones, and the minimum thicknesses of the limestones occur over topographical highs, such as that associated with the Skipton Anticline. During late Asbian and Brigantian times, the development of fringing reefs at the platform margin led to a marked diminution of carbonate supply, oxygen depletion and stratification of the water column in the basin to the south of the Askrigg Block, allowing deposition of the hemipelagic muds that formed the argillaceous deposits of the Bowland Shale Group.

Chatburn Limestone Group

Chatburn Limestone Group (Earp et al., 1961), of Tournaisian age, was formerly referred to as the Haw Bank Limestone in the vicinity of Skipton. The group comprises well-bedded, medium to dark grey, bioclastic limestones with dark grey shaly intercalations (shown as ChL on the map), but dark grey shaly mudstone or mudstone with thinly interbedded muddy limestones (shown as md/ls on the map) predominate in places.

Worston Shale Group

Worston Shale Group (Riley, 1990) conformably overlies the Chatburn Limestone Group. The Worston Shale Group comprises three formations, described in ascending order. The Clitheroe Limestone Formation (ClL), formerly referred to as the Halton Shales, is of Chadian age. Only the lower part of the formation is present beneath the unconformity at the base of the overlying formation. The main lithology is shaly, calcareous mudstone with subordinate interbedded thin beds of dark grey limestone. The Hodder Mudstone Formation (HoM) is of Arundian to Holkerian age. It is predominantly argillaceous, but the Embsay Limestone Member (EL) occurs at the base. The member is estimated to be about 20 to 25 m thick in the Skipton area, and rests unconformably on the Clitheroe Limestone Formation. It comprises thinly to thickly bedded, pale limestone interbedded with dark calcareous silty mudstones, calcilutites, and at the type locality limestone and mudstone lithoclast conglomerates and breccias occur near to the base. The overlying argillaceous succession was formerly referred to as the Skibeden Shales, and is estimated to be 195 to 240 m thick in the Skipton area. It is dominated by dark grey, shaly, calcareous mudstone with some thinly interbedded, fine-grained dolomitic and argillaceous limestone. The Hodder Mudstone Formation is overlain, locally unconformably, by the Pendleside Limestone Formation (PdL) of Asbian age, which was formerly referred to in the Skipton area as the Draughton Limestone. The formation consists mainly of medium to dark grey, thinly bedded and finely bioclastic limestone, but it also includes a basal breccia.

Bowland Shale Group

Bowland Shale Group comprises the Lower Bowland Shale and the Upper Bowland Shale formations, and was definitively described by Earp et al. (1961). The Upper Bowland Shale Formation, which is Namurian in age, is discussed in the succeeding section. The group forms a long concave slope to the south and east of Skipton, located beneath the scarps produced by the sandstones of the Pendle Grit Formation. The group conformably overlies the Worston Shale Group. The Lower Bowland Shale Formation (LBS) is of late Asbian and Brigantian age. The subdivision during the previous survey into Lower Bowland Shales and Middle Bowland Shales, based mainly on biostratigraphical criteria, was not recognised during this resurvey. The formation consists of shaly mudstone, generally black or dark grey, calcareous and bituminous, with thin beds of argillaceous, fine-grained sandstone, scattered bullions and ammonoid-rich beds. In general, the formation is more calcareous and more consistently marine than the Upper Bowland Shale Formation.

Namurian rocks

Namurian rocks outcrop over much of the north and west of the district and occur at depth beneath Westphalian rocks in the south and east. They comprise a dominantly argillaceous succession, the upper part of the Bowland Shale Group, conformably overlain by the Millstone Grit Group: a thick succession of interbedded mudstone and siltstone (generally poorly exposed) and sandstone (traditionally referred to as 'grit'; (Plate 1)). A maximum thickness of 1900 m of Namurian strata has been estimated at outcrop, with seismic data suggesting that the total thickness diminishes to about 1000 m towards the south of the district.

During the Namurian period, approximately 315 million years ago, northern England lay within a large, actively subsiding basin, the Pennine Basin. Extensive delta systems built out into the basin, supplied with sediments derived from the land surfaces to the north. Variations in sea level are reflected in the Millstone Grit by distinct cycles of sedimentation, each beginning at a high sea-level stand with the deposition of marine or near-marine shales, including fossiliferous marine bands. The marine bands are generally a few centimetres thick, but may attain thicknesses of several metres. They can be recognised across large areas, and as each marine band generally contains distinctive and diagnostic marine faunal assemblages, they are important marker horizons. About 50 marine bands are recognised in the Millstone Grit of the Pennines (Holdsworth and Collinson, 1988). The marine bands commonly pass up through mudstones into siltstones and sandstones, representing a transition from sedimentation in the delta slope to deposition within distributary channels on the delta top. During late Namurian times, the top of each cycle (when sea level is at its lowest) was often marked by the formation of soils and the development of a widespread cover of vegetation. Once subjected to compaction and lithification the soil horizons become seatearths, and organic deposits coals. This pattern of deposition is repeated with each rise in sea level, and the deposits of an individual cycle are known as a cyclothem. The ideal cyclotherm described above may be interrupted or modified.

The Namurian Epoch is divided into seven stages, in order of decreasing age, Pendleian (E₁), Arnsbergian (E₂), Chokierian (H₁), Alportian (H₂), Kinderscoutian (R₁), Marsdenian (R₂) and Yeadonian (G₁) stages; these, in turn, are subdivided into chronozones (Ramsbottom et al., 1978). The boundaries of these chronostratigraphical subdivisions are recognised biostratigraphically by the presence of diagnostic ammonoid (goniatite) fauna. Formerly the Millstone Grit was defined as a chronostratigraphical unit, the Millstone Grit Series (Stephens et al., 1953), which consisted of all strata of Namurian age, including the dominantly argillaceous Upper Bowland Shales. The 'Series' was subdivided into six groups defined as goniatite genus-zones, namely: the Skipton Moor Grit (E₁); Silsden Moor Grit (E₂); Middleton Grit (H); Kinderscout Grit (R₁), Middle Grit (R₂) and Rough Rock (G₁) groups. To conform with current usage the Millstone Grit Group has been mapped as a lithostratigraphical unit that includes all strata of Namurian age above the Upper Bowland Shales Formation, which is dominantly argillaceous and therefore part of the Bowland Shales Group. Important modifications of the Kinderscoutian (R₁) succession have arisen from new BGS boreholes on Rombalds Moor, described by Aitkenhead and Riley (1996).

Bowland Shale Group

Bowland Shale Group comprises the Lower Bowland Shale Formation, of Dinantian age, and the Upper Bowland Shale Formation (UBS), of Pendleian age. The base of the latter formation is taken as the base of the Cravenoceras leion Marine Band, which coincides with the boundary between the Viséan (Lower Carboniferous) and the Namurian (Upper Carboniferous). The dominant lithology is mudstone, dark grey and fissile. Marine bands are fewer, more discrete and better defined, and the mudstones are generally less calcareous, darker grey and more fissile than within the underlying Lower Bowland Shale Formation.

Millstone Grit Group

Millstone Grit Group (MG) comprises about 1800 m thickness of interbedded mudstone, siltstone and sandstone. Within the group only the Pendle Grit has been assigned formation status in the district. The Pendle Grit Formation (PG) is of Pendleian age. It outcrops in the north of the district near Skipton and comprises a turbiditic facies deposited on a prodelta slope; it is lithologically distinct from the remainder of the group. The formation, defined by Aitkenhead et al. (1992) in the Garstang district, is equivalent to the lower part of the Skipton Moor Grits of the previous survey. Here the formation is subdivided on the basis of its dominant constituent lithologies, namely sandstone (PG) and thinly interbedded siltstone and sandstone (sl/sa). The bottom of the formation is defined as the base of the lowest coarse-grained turbiditic sandstone present above the Upper Bowland Shale Formation. Locally, the lowermost sandstone is laterally impersistent and where it is absent the base of the formation is placed conjecturally within mudstones. The top of the formation is taken as the base of the lowermost sandstone of the Warley Wise Grit, but locally where this dies out the boundary has been extended between Millstone Grit Group (undivided) and Pendle Grit Formation. The formation comprises feldspathic sandstone that is grey, medium to coarse grained, rarely conglomeratic, and occurs in thick, massive beds; flute casts, load casts, groove and prod marks and micro-wrinkles have been recorded on the bases of beds. The sandstones are typically 5 to 10 m thick and display a lensoid pseudo-cross-bedding. The sandstones are laterally impersistent, and interdigitate with interbedded siltstone, very thin sandstone beds and subordinate mudstone.

The succession above the Pendle Grit Formation is treated as a distinct unnamed formation with named sandstones. The sandstones show similar petrographical and sedimentological features, and can be distinguished from one another only by their position relative to known marine bands. The intervening mudstones and siltstones are, with the exception of the Keighley Bluestone, shown on the map as Millstone Grit (undifferentiated). The sandstone nomenclature is broadly the same as that used during the previous survey, but some attempt has been made to rationalise nomenclature with the adjoining districts of Leeds (Sheet 70) and Huddersfield (Sheet 77). Descriptions of named sandstones and coals are provided in (Figure 3) and (Figure 4), respectively.

Westphalian rocks

Westphalian rocks outcrop over much of the south and east of the district, including the main urban area of Bradford and the outlier of Baildon Moor. During Westphalian times, about 310 million years ago, the pattern of sedimentation described for the Millstone Grit continued, but as sedimentation kept pace with subsidence of the Pennine Basin shallow-water conditions were eventually established. In Langsettian times, deposition occurred in a delta-plain environment that was above sea level for much of the time and land floras were abundant.

Coal Measures

Coal Measures are divided for convenience into Lower, Middle and Upper divisions, of which only the Lower Coal Measures (LCM) of Langsettian (Westphalian A) age are present in the district. The Coal Measures rest conformably upon the Millstone Grit, with the base taken as the base of the Subcrenatum (Pot Clay) Marine Band. The Coal Measures consist of interbedded mudstone, siltstone and sandstone, with subordinate coal, seatearth and ironstone, deposited in cyclic sequences. The mudstones are grey to black, weathering to orangebrown, mottled pale grey, planar laminated and micaceous, or massive. Commonly, they contain non marine bivalves, for example the Laisterdyke Shell Bed, which may be used as chronostratigraphical indicators. Between the Elland Flags and Grenoside Sandstone the mudstones are distinctively greenish grey and mica-poor. Generally, ironstone nodules are common in mudstones, ranging in size from a few millimetres to tens of centimetres in diameter. The mudstones are commonly overlain gradationally by siltstones, which are typically medium grey with flaser and lenticular bedding, ripple cross-lamination and parallel lamination and commonly contain plant debris. The siltstones grade both vertically and laterally into sandstones. The sandstones (Figure 5) commonly form positive, mappable, topographical features, and are thus distinguished on the map from the mudstones and siltstones, which are shown as Lower Coal Measures (undivided). In the lower part of the succession the sandstones are thin and laterally impersistent, whereas in the middle and upper parts there are a number of thick, laterally persistent sandstones. The sandstones are mainly fine grained, varying from very fine to medium grained, and comprise subangular to sub-rounded quartz and feldspar grains with a variable mica content. They are grey where fresh, but weather to yellowish brown. Sedimentary structures include planar lamination, cross-bedding and climbing ripples, together with flaser and lenticular bedding. Coalified plant fragments are common, as locally are trace fossils. Seatearths are palaeosols which developed during floral colonisation and are characterised by the presence of rootlets, commonly Stigmaria. They occur in all lithologies, being referred to as ganister where they are developed in sandstone, and fireclay where they are formed in mudstone. In general the pedification has destroyed primary sedimentary structures. Coal seams are extensive, and many are developed on a regional scale, but they vary laterally in thickness and composition, chiefly by variation in the number of dirt partings present within the seam. The coals generally cap upward-coarsening sedimentary cycles, and are underlain by seatearths. Nine named seams are identified in this area (Figure 4). Marine bands are thin beds of black mudstone with a marine fauna; commonly they overlie coals or seatearths. They are generally a few centimetres thick, but may rarely attain thicknesses of 2 to 3 m. Marine bands can be recognised across large areas; they represent eustatically controlled flooding events and are thus important isochronous marker horizons. The Subcrenatum Marine Band and the Listeri Marine Band are recognised in the district, but a number of Lingula bands have been proved which may correlate with the Honley, Parkhouse and Meadow Farm marine bands found elsewhere in the Pennine Basin. Marine band faunas are discussed fully by Calver (1968).

Quaternary deposits

About 60 per cent of the district is covered by drift (natural superficial) deposits, which comprise glacial, periglacial and postglacial deposits. The nature of these deposits are shown on (Figure 6) and (Figure 7). The limits of the deposits have been taken as those defined during the previous geological survey of the district except where new data, such as field observations, recent open sections, topographical features, auger holes or borehole data, has revealed errors in the pre-existing geological maps. The drift deposits and bedrock are locally covered by artificial (man-made) deposits, the product of human modification of the natural environment, notably in areas of industrial development. The man-made deposits shown on the map represent those that were identifiable at the date of survey. They were delineated by recognition in the field and by examination of documentary sources, in particular topographical maps, aerial photographs and site investigation data. Only the more obvious man-made deposits can be mapped by these methods and the boundaries shown may be imprecise. Only deposits known to be broadly in excess of 1.5 m thickness are shown.

The present-day topography is largely the result of glacial processes active during the Pleistocene (Plate 2). The district was probably affected by at least three glaciations, although evidence for earlier phases has been obliterated by the final, Devensian, phase. The maximum southward advance of the Devensian ice sheet reached a line approximately crossing the south of the district. The glaciers would have occupied only areas of low ground, such as the Aire and Wharfe valleys, except during the maximum advance of the ice when they would have also extended over upland areas, resulting in broad blankets of till. Lodgement till was plastered beneath moving ice, locally forming drumlins elongate in the direction of ice movement in the Skipton area and eastern side of Rombalds Moor. Flow till formed by the mass movement of glacial debris following release from the glacial ice. Deformation till formed by squeezing or pressing of glacial debris at the base of the glacier. Melt-out till formed from the slow release of glacial debris during glacial melting and retreat. Dramatic fluctuations in temperature, as identified from studies of the flora and fauna present in peat at Bingley Bog (Keen et al., 1988), would have caused the valley glaciers to advance and retreat several times during the late Devensian. During the final stage of ice-retreat, the valley glaciers probably retreated in a series of pulses, with the halt-stages marked by terminal moraines (especially evident in Airedale) with lateral moraines left on valley sides (for example Lanshaw Delves, in the Bingley Moor area). These deposits are mapped as hummocky (moundy) glacial deposits.

The valleys of the modern rivers Wharfe and Aire broadly coincide with buried, drift-filled channels, locally in excess of 50 m deep. These channels have a U-shaped cross-section and an elliptical longitudinal profile. They probably formed by either glacial scouring and subsequent infill with outwash material (glaciofluvial deposits) and sediments deposited in temporary lakes (glaciolacustrine deposits), or in response to subglacial erosion by meltwater under high hydrostatic pressure at the base of the glacier. A series of smaller late-glacial, meltwater channels, formerly termed 'glacial overflow channels' are present in the valley sides and upland areas. These have been recognised especially in an arc from west of Keighley to Bradford and Shipley. These features typically have a broad east–west to SE–NW trend, approximately parallel to the Devensian ice front. They usually have steep sides and flat bottoms, locally bifurcate and commonly start and end abruptly. Most meltwater channels have been abandoned and are dry or contain only small 'misfit' streams, incapable of eroding such large valleys.

Periglacial weathering occurred in areas not covered by ice during the glacial periods. The intense cold caused the development of permafrost conditions in the subsoil, and shattering and weathering of rock due to freeze–thaw processes. These processes helped to promote the formation of head, landslips and scree deposits (Figure 7). Landslips are prone to develop in areas associated with natural slopes usually in excess of 10°, on slopes with a thick cover of till or deeply weathered mudstone, in the presence of a permeable water-bearing sandstone cap dipping into the valley and overlying an impermeable mudstone, in the presence of a fault associated with extensive fracturing of mudstone, and the presence of springs or seeps (Plate 3).

Following the Devensian glaciation, the modern drainage pattern became established, with alluvial deposition within the broad valleys of Airedale and Wharfedale, and associated tributary streams. River terraces deposits represent fluvial deposits, with erosion surfaces forming the terrace feature, which have become isolated on valley sides due to repeated entrenchment of the river systems during the Flandrian. In Wharfedale three terraces occur between 3 and 12 m above the present floodplain, whereas in Airedale only the First River Terrace has been identified, occurring between 2 and 12 m above the floodplain. Alluvium represents the alluvial deposits of the current floodplain level. Where two river systems meet alluvial fan deposits may accumulate with the apex pointing up the tributary river and the toe merging into the alluvium of the main river. In abandoned meltwater channels, thin deposits of lowland peat accumulated, whilst more extensive, though thin, upland peat deposits accumulated on poorly drained moors in the west of the district. Peat working, heather burning and air pollution may have all contributed to increased erosion over recent years, often forming a network of gullies or 'haggs'.

Made ground represents areas where the ground is known to be deposited by man on the natural ground surface. The main categories include civil engineering works, spoil from mineral extraction industries, building and demolition rubble, waste from heavy industries, and ashes and cinders from textile mill boilers and domestic and other waste in raised landfill sites. The most extensive areas of made ground are in the main urban centres. In these areas the topographical features associated with specific areas of made ground may have been smoothed over prior to development. In such areas, the extent of made ground is based largely on site investigation data. Infilled ground comprises areas where the natural ground surface has been removed and the void partly or wholly backfilled with man-made deposits. Mineral excavations and disused railway cuttings have frequently been used in the district for the disposal of waste materials. The common types of fill include excavation waste, construction and demolition waste, domestic refuse and industrial waste. Where quarries and pits have been restored and either landscaped or built on, there may be no surface indication of the extent of the back-filled void. In such cases, the location of these sites is taken from archival sources, in particular old topographical and geological maps.

The 1:50 000 scale geological map does not show areas of worked ground and disturbed ground, though they are delineated on the constituent 1:10 000 scale geological maps. Worked ground is where material is known to have been removed, for example in unfilled quarries and pits, excavations for roads and railways and general landscaping. Disturbed ground is associated with ill-defined surface mineral workings, such as bell pits, in which shallow excavations, subsidence and made ground are complexly associated with each other. Landscaped ground has not been mapped during this survey. This comprises areas where the original surface has been extensively remodelled, but where it is impractical or impossible to delineate areas of cut or made ground. Most areas of urban development are associated with landscaped ground.

Structure and concealed geology

In earliest Carboniferous times a major rift basin system developed in northern England (Figure 1) in response to regional back-arc extension, caused by northward subduction of the Rheic Ocean. Extension was much diminished in Namurian and Westphalian times and a regional 'post-rift' or 'sag' basin developed. In latest Carboniferous times (about 300 million years ago), final closure of the Rheic Ocean culminated in the Variscan Orogeny, with large-scale thrust and nappe emplacement in southern Britain. However, to the north of the Variscan Foldbelt deformation was much less pervasive; in northern England it was largely restricted to partial reversal of the earlier Carboniferous basin-controlling normal faults, associated folding and minor basin inversion and regional uplift.

In the Bradford district, the Dinantian extensional basin system is largely concealed by Namurian and Westphalian post-rift strata. Seismic reflection data show a mosaic of tilt-blocks bounded by large east-north-east-trending syn-rift normal faults, with throws commonly of several hundred metres. Basement depths are less than 2500 m on fault-bounded horsts such as the Bingley and Central Lancashire highs, the latter associated with a gravity high. These syn-rift structures are characterised by relatively thin Dinantian successions (about 1300 to 1500 m thick), dominated by platform carbonates, principally of Chadian age. Thicker, more basinal Dinantian sequences (in excess of 2000 m thick) are present in the Harrogate Basin in the north of the district and the Bowland Basin in the west, where basement depths considerably exceed 3000 m. These areas tend to be associated with gravity lows.

The post-rift Namurian and Westphalian successions are generally of more uniform thickness than the underlying Dinantian strata, although the lower part of the Namurian succession shows a significant southward thinning. The thinning probably relates to the basinward thinning and fining of deltaic deposits infilling a relatively deep basin during early Namurian times. The basinal argillaceous deposits are both more condensed and prone to greater compaction than the deltaic sands. The post-rift strata are dominated by west-north-west- to north-west-trending faults, as mapped at surface. Some of these may have been active as Dinantian transfer faults, whilst others may have a Variscan or even younger origin. These faults belong to the Gargrave–Aire Valley–Morley–Campsall fault system, evident as a steep aeromagnetic anomaly gradient. Surface displacements of the north-west-trending faults are generally small, typically in tens of metres, compared to the subsurface displacements of the east-north-east-trending basin-controlling syn-rift faults.

The district is situated on the eastern limb of the north-trending axis of the Pennine Anticline and generally the strata have a broadly consistent dip of 2 to 5° toward the south and east. Small-scale (tens to hundreds of metres) tight folds, caused by the 'drag' of strata against fault planes during fault movement may result in dips of up to 50°, such as in the vicinity of the Denholme Clough Fault. Large-scale (km) open folds are present in the north of the district forming part of the Ribblesdale Fold Belt. This major Variscan structure comprises broadly east-north-east-trending folds and reverse faults, typified in the north-west part of the district by the Lothersdale and Skipton anticlines and the much smaller Bradley Anticline, and in the north-east by the Norwood Anticline, the south-western extremity of the Harrogate Anticline. In the north-west of the district, the foldbelt is associated with a gravity high, presumably because denser pre-Carboniferous basement occurs at relatively shallow depths (as little as 1600 m below OD). The lack of stratigraphical thinning across these folds, in both Dinantian and preserved Namurian strata, suggests that folding postdated deposition of these rocks, and was most probably of end-Carboniferous age. It is likely that the north-west-trending structures acted as transfer faults during development of the folds, exemplified by the way the Gargrave Fault offsets the Skipton and Lothersdale anticlinal axes. The Bradley Anticline is asymmetrical, with north-west vergence and evidence of minor reverse faulting in its steeper north-western limb, mapped at surface as the Bradley Fault. The anticline is likely to have resulted from reverse reactivation of underlying south-east-dipping normal faults.

At outcrop faults may occur as a single, discrete plane, or as a zone up to several tens of metres wide containing several fractures, each accommodating some of the displacement. The portrayal of such faults as a single line on the map is therefore a generalisation. The position of a fault may be based on the interpretation of topographical features, surface outcrops, site investigation data and underground mining data but the evidence is rarely sufficient to locate a fault precisely. Only rarely are faults exposed in the district. In an area of thick and extensive superficial deposits, the positioning of faults relies almost entirely on projection from underground mining information. Geological faults in this area are of ancient origin and are currently mainly inactive. However, the Bradford district, in common with other parts of Britain has been affected historically by minor earthquakes. Of note was an earthquake on 30th December 1944 with a macroseismic epicentre beneath Skipton, a depth of focus of about 13 km and an inferred magnitude of 4.8 (Musson, 1994). Minor earthquakes may also arise through reactivation of faults by undermining, when general subsidence effects may be concentrated along them. Underground mining has ceased in the district, and although minor residual subsidence may still occur, it is increasingly unlikely that this will result in significant fault reactivation.

Chapter 3 Applied geology

Geological factors have had a significant role in the industrial expansion of Bradford and neighbouring towns. A history of mining and quarrying associated with the development of heavy industry has left a legacy of areas of derelict and despoiled land. By considering the nature and location of earth science issues at an early stage in the planning process appropriate action may be taken to ensure that the site and development are compatible, and that appropriate mitigation measures can be taken prior to development. The information may also be used to identify opportunities for development, particularly in respect of leisure, recreation and protection of sites of nature conservation interest. The key issues, given below, were identified and discussed in detail by Waters et al. (1996a) for the City of Bradford Metropolitan District and Lake et al. (1992) for the Leeds district.

Mineral resources

The economics of underground mining are unlikely to be favourable in the future so that potential mineral resources are those which can be won at or near to the surface. The main factors hindering extraction are significant thicknesses of overburden, including natural drift deposits and man-made deposits, sterilisation of resources by urban development and conflicts with other forms of land use and possible detrimental effects on the landscape. In addition, extraction of mineral resources can lead to problematical engineering ground conditions, depending on the types and methods of infilling, and can act as a constraint to future development of a site. The main historically important mineral resources in the district are described in (Figure 8).

Surface mineral workings

Quarries (Plate 4) or pits that have not been backfilled, represent an important resource as they may provide a suitable void for waste disposal, may be reopened as a source of minerals or may be developed as sites of educational, recreational and wildlife value. However, they can also be a constraint to development as steep rock faces may be unstable. Quarries and pits are distributed throughout the district with the majority of open excavations in sandstone. Most options for landfill sites have already been utilised, adding pressure to use remaining disused sandstone quarries, many of which occur in rural areas.

Engineering ground conditions

Three of the most important ground conditions relevant to construction and development are the suitability of the ground to support structural foundations, the ease of excavation and the use in engineered earthworks and fills. These issues are summarised for the main engineering geological units in the district in (Figure 9). Foundation conditions are not only affected by the engineering properties of the bedrock and superficial deposits, 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 total and differential settlement, particularly in the urban and industrial areas. Colliery spoil may contain iron pyrites that is prone to oxidise and produce sulphate-rich, acidic leachates, which may be harmful to concrete present in foundations or buried services, thus requiring the use of sulphate-resisting cement. This oxidation process may also result in expansion and differential heaving of foundations constructed on such deposits. Large volumes of quarry spoil are common 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.

Subsidence risk due to undermining may be a constraint in areas of former underground mining of coal, fireclay, ironstone, sandstone and lead. Coal mining in particular was formerly an important industry, largely restricted to the area of outcrop of the Coal Measures in the urban south and east of the district. Sandstone mining was largely limited to working of the Elland Flags (Plate 5), the history of which is reviewed by Godwin (1984); as there are few abandonment plans for such workings their extent is poorly known. The distribution of known underground workings and shafts is presented by Waters et al. (1996a). In areas of former coal and sandstone mining, the principal concerns relate to ground instability caused by the collapse of unsupported shallow workings. Structures straddling a fault may be susceptible to uneven settlement in areas prone to mining subsidence. Collapse of shaft fill, linings or cappings may also result in surface subsidence. A review of mining instability in the UK is provided by Arup Geotechnics (1991). Records of shafts and abandoned mines are lodged with the Coal Authority, who should be consulted prior to development in a coalfield area.

Mine-drainage waters may also be a problem in areas of disused coal or colliery-based workings, such as those prevalent in the south-east of the district. Where mine drainage waters reach the surface, their high pH, in addition to iron precipitation and the often elevated levels of manganese, aluminium and sulphates, can result in the complete extermination of flora and fauna.

Slope stability is an issue particularly where housing and infrastructure development has been forced to extend beyond the prime flat lowland areas of the main valleys onto the steep valley sides. Construction on these steep slopes may encounter stability problems, in areas of existing landslip and where thicker head deposits containing relict shear surfaces have accumulated on the lower parts of the slopes. In many cases, the landslips present in the district developed in response to oversteepening and weakening of slopes during the last phases of glaciation, and the majority of the features may be considered currently inactive. However, renewed instability may occur if the slope is adversely disturbed by undercutting or top-loading or if increased volumes of water are introduced, such as may occur due to alteration of drainage patterns during development.

Pollution potential

Artificial (man-made) deposits may contain toxic residues, either as a primary component or generated secondarily by chemical or biological reactions and are thus potential sources of pollution. Significant sites of potential pollution include areas of landfill and former gasworks, chemical works, textile mills, iron and steel works, railway sidings and sewage works. Leachate migration may be a problem where rain water or groundwater percolates through waste and becomes enriched in potentially harmful soluble components. The resultant leachate may permeate into surface water and groundwater depending on factors such as the permeability of superficial deposits and bedrock adjacent to the site, presence of containment structures and depth of the unsaturated zone. The problem may be enhanced where sites occur within areas of faulted bedrock as the faults may provide possible pathways for leachate migration. One of the greatest concerns for potential generation of pollution are old landfill sites which are prevalent across the district, particularly associated with infilled quarries and disused railway cuttings. Leachates may be a particular problem where tipping was uncontrolled and little attempt was made to prevent pollution migration.

Gas emissions

Gas emissions may represent a hazard in areas associated with the accumulation of methane, carbon dioxide and radon in poorly ventilated enclosed spaces such as basements or foundations (Figure 10). These gases can sometimes migrate considerable distances through permeable strata and accumulate within buildings or excavations. Fissures and faults or broken ground due to subsidence and mine workings may act as pathways for such gas migration. Prolonged exposure to radon gas will increase the risk of lung cancer. Methane is potentially explosive, may act as an asphyxiant and may cause vegetation die back, and is a 'greenhouse gas'. Carbon dioxide is toxic in high concentrations, may act as an asphyxiant, may cause vegetation die back and is also a 'greenhouse gas'. Carbon monoxide is potentially explosive and is toxic at low concentrations.

Water resources

Reservoirs provide the principal source of water for domestic supplies; some reservoirs are sited in upland areas in the west of the district. Springs discharge onto slopes where groundwater flow in sandstone aquifers is interrupted by impermeable mudstones. They are abundant in the district and have historically provided significant volumes of potable water, but are less used today. Groundwater provides water supply to isolated farms in the upland areas and licenced water abstraction for industrial purposes throughout the district. There are no groundwater abstractions for public domestic supply. The bedrock units in the district are classified as minor aquifers, with complex sandstone aquifers interbedded with mudstone aquitards or aquicludes. The Millstone Grit sandstones are considered to provide higher quality groundwater supplies than Coal Measures sandstones, which tend to have high concentrations of sulphates, iron and trace metals. This suggests that future supplies of good quality, potable groundwater may be abstracted from the north and west of the district. Faults may act as a conduit for groundwater flow, potentially increasing yields from water boreholes, however, faults with large displacements may reduce the interconnectivity of aquifer sandstones, thus limiting groundwater flow. The presence of clay-rich drift deposits (particularly till) where generally in excess of 5 m thick may seriously limit recharge to aquifers and reduce the potential usage of groundwater for significant volumes of extraction. Details of porosities, permeabilities and transmissivities of the main aquifer sandstones in the district and groundwater abstraction licence data are provided by Waters et al. (1996a). Flooding has long been a serious issue in the district and the city centre of Bradford has suffered serious disruption by floods in 1946, 1947, 1962 and 1982. The problem is caused by the predominance of v-shaped valleys and relative impermeability of bedrock and drift deposits in the moorland catchment areas of the rivers Wharfe and Aire, which result in a rapid runoff in response to heavy rainfall events. The problem was somewhat alleviated by the construction of numerous dams in the valleys of the west of the district in the 19th century, and more recently by channel improvements and construction of flood defences. One of the most important tools for flood control is the designation of washlands; areas of land along rivers which provide essential space for the storage of floodwater. In the district, the main areas of washland are parts of the natural floodplains of the rivers Aire and Wharfe. It is these flat, lowland areas lying close to the main transport routes which are under greatest pressure to be developed for industrial or housing purposes. Rising groundwater is not currently recognised as a significant problem in the area. During the peak of the textile industry in Bradford and neighbouring towns in the 19th and early 20th centuries large quantities of groundwater were extracted. With the decline of this industry in the area over recent decades groundwater levels in the urban areas are likely to have risen in response to decreased abstraction. An important aspect of rising groundwater in low-lying areas is that contaminants could be leached into the groundwater and water courses. Land drainage may be a significant issue where till deposits are present. Till, which extends across much of the district, is associated with areas of relatively poor drainage. In areas where underdrainage has been developed the land can be suitable for pastoral farming. Where no artificial drainage is provided the ground may become marshy, the soils become acidic and peat may accumulate. The poor drainage of till deposits is exacerbated locally by the presence of broad hollows and glacial meltwater channels that have no natural drainage outlet. However, over recent drought years the dominantly clayey soils associated with till tend to retain moisture longer than soils developed where bedrock occurs at crop, and hence have provided better pasture during summer months.

Conservation sites

Several sites have been identified in the district as important to earth science research and teaching and for recreational purposes. Many of these are in disused quarries and pits. There is increasing pressure to use such sites for landfill, particularly those sites near to urban centres. Yeadon Brickworks and railway cutting [SE 193 408] has been designated as a Site of Special Scientific Interest (SSSI) on account of its special geological interest. Additional locations have been recognised by the local authorities to have special geological importance and have been designated as Sites of Ecological or Geological Importance (SEGIs). These include Baildon Moor [SE 147 409], Shipley Glen [SE 131 388] and Chellow Dene [SE 123 346].

Chapter 4 Information sources

Further geological information held by the British Geological Survey relevant to the Bradford district is listed below. It includes published material in the form of maps, memoirs and reports and unpublished material, including maps, reports and other sources of data held by BGS in a number of collections. Searches of indexes to some of the collections can be made on the Geoscience Index System in BGS libraries. At the present time (1998) the datasets are limited and not all are complete. The indexes which are available are listed below:

• Index of boreholes
• Topographical backdrop based on 1:250 000 scale maps
• Outline of BGS maps at 1:50 000 and 1:10 000 scale and 1:10 560 scale County Series
• Chronostratigraphical boundaries and areas from BGS 1:250 000 maps
• Geochemical sample locations on land
• Aeromagnetic and gravity data recording stations
• Land survey records

Maps

• Geology maps
• 1:1 500 000
• Tectonic map of Britain, Ireland and adjacent areas, 1996
• 1:625 000
• United Kingdom (South Sheet) Solid Geology, 1979; Quaternary Geology, 1977
• 1:250 000
• 53N 04W Liverpool Bay, Solid Geology, 1978
• 53N 02W Humber–Trent, Solid Geology, 1983
• 53N 04W Liverpool Bay, Quaternary Geology, 1984
• 1:50 000 and 1:63 360
• Sheet 69 Bradford (Solid; Solid & Drift) 1999
• Sheet 60 Settle (Solid 1989; Drift 1991)
• Sheet 62 Harrogate (Solid 1987; Drift 1985)
• Sheet 68 Clitheroe (Solid 1960; Drift 1975)
• Sheet 70 Leeds (Solid 1974; Drift 1970)
• Sheet 76 Rochdale (Solid 1967; Drift 1974)
• Sheet 77 Huddersfield (Solid & Drift) 1978
• Sheet 78 Wakefield (Solid & Drift) 1998
• 1:25 000 and 1:50 000 Thematic Maps
• Leeds: BGS Technical Report WA/92/1
• City of Bradford Metropolitan District: BGS Technical Report WA/96/1
• 1:10 000 and 1:10 560
• Details of the original geological surveys are listed on editions of the 1:50 000 or 1:63 360 geological sheets. Copies of the fair-drawn maps of these earlier surveys may be consulted at the BGS Library, Keyworth.
• The maps covering the 1:50 000 Series Sheet 69 Bradford are listed below together with the surveyor's initials and the date of survey. The surveyors were: R A Addison, N Aitkenhead, I C Burgess, R G Crofts, M T Dean, N S Jones, J G Rees, M S Stewart, D G Tragheim and C N Waters. The maps are not published but are available for public reference in the libraries of the BGS in Keyworth and Edinburgh and the BGS London Information Office in the Natural History Museum, South Kensington, London. Uncoloured dyeline copies are available for purchase from BGS Sales Desk; some sheets are available in a digital format (marked with *).

• Geophysical maps
• 1:1 500 000
• Colour shaded relief gravity anomaly map of Britain, Ireland and adjacent areas, 1997 Colour shaded relief magnetic anomaly map of Britain, Ireland and adjacent areas, 1998
• 1:625 000
• United Kingdom (South Sheet) Aeromagnetic map, 1965
• 1:250 000
• 53N 04W Liverpool Bay, Aeromagnetic anomaly, 1978
• 53N 02W Humber-Trent, Aeromagnetic anomaly, 1977
• 53N 04W Liverpool Bay, Bouguer gravity anomaly, 1978
• 53N 02W Humber-Trent, Bouguer gravity anomaly, 1977
• 1:50 000
• Geophysical information maps; these are plot-on-demand maps which summarise graphically the publicly available geophysical information held for the sheet in the BGS databases. Features include:
• Regional gravity data: Bouguer anomaly contours and location of observations.
• Regional aeromagnetic data: total field anomaly contours and location of digitised data points along flight lines.
• Gravity and magnetic fields plotted on the same base map at 1:50 000 scale to show correlation between anomalies.
• Separate colour contour plots of gravity and magnetic fields at 1:125 000 scale
• Location of local geophysical surveys
• Location of public domain seismic reflection and refraction surveys
• Location of deep boreholes and those with geophysical logs
• Geochemical atlases
• 1:250 000
• Point-source geochemical data processed to generate a smooth continuous surface presented as an atlas of small-scale colourclassified digital maps.
• Geochemical Survey Programme data are also available in other forms including hard copy and digital data.
• Hydrogeological map
• 1:625 000
• Sheet 1 (England and Wales) 1977
• 1:100 000
• Southern Yorkshire and adjoining areas (Sheet 12), 1982
• Groundwater Vulnerability Map, South Pennines (Sheet 11); produced by the Environment Agency.

Books

• General geology
• British Regional Geology
• The Pennines and adjacent areas, 3rd edition, 1954
• Memoirs
• Geology of the country between Bradford and Skipton (Sheet 69), 1879
• Geology of the country between Bradford and Skipton (Sheet 69), 1953
• Geology of the country around Settle (Sheet 60), 1988
• Geology of the country around Harrogate (Sheet 62), 1993
• Geology of the country around Clitheroe and Nelson (Sheet 68), 1961
• Geology of the district north and east of Leeds (Sheet 70), 1950
• Geology of the country around Huddersfield and Halifax (Sheet 77), 1930
• The geology of the Yorkshire Coalfield, 1878 The structure and evolution of the Craven Basin and adjacent areas, Subsurface memoir, in press.
• Technical Reports
• Technical reports relevant to the district are arranged below by topic. Most are not widely available but may be purchased from BGS or consulted at BGS and other libraries.
• Geology
• Reference number for the technical reports covering the geology of individual or combined 1:10 000 scale geological sheets are shown under listing of 1:10 000 and 1:10 560 geological map sheets.
• Geology and land-use planning
• Parts of the district are covered by the following BGS Technical Reports and accompanying thematic geological maps dealing with land-use planning and development:
• Lake et al., 1992; Waters et al., 1996a.
• Mineral resources
• Price et al. (1984) provides details of sand and gravel resources in Wharfedale. Further information on mineral resources is available from the Minerals Group, Keyworth.
• Engineering Geology
• Cooper (1984) provides details of landslips at Otley. Further information on engineering geology is available from the Coastal and Engineering Geology Group, Keyworth.
• Biostratigraphy
• There is a collection of internal British Geological Survey biostratigraphical reports, details of which are available from the Biostratigraphy Group, Keyworth.
• Sedimentology
• Hallsworth (1994) provides information on heavy minerals and provenance of Millstone Grit and Coal Measures sandstones.
• Hallsworth, C R. 1994. Mineralogical evidence for variations in provenance of the Millstone Grit and Lower Coal Measures of the Bradford district. British Geological Survey Technical Report, WH/95/200R. Strong, G E has produced three internal reports detailing the petrography of Carboniferous sandstones.

Documentary collections

Boreholes and shafts

Borehole and shaft data for the district are catalogued in the BGS archives (National Geosciences Records Centre) at Keyworth on individual 1:10 000 scale sheets. For the Bradford district the collection consists of the sites and logs of about 11 100 boreholes, for which index information has been digitised. For further information contact: The Manager, National Geosciences Records Centre, BGS, Keyworth.

Mine plans

BGS maintains a collection of plans of underground mines for minerals other than coal, mostly for sandstone and fireclay.

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 the north and central parts of the district. The profiles are from surveys by Toredo Petroleum Plc. Geophysical logs are available for the Low Bradley Borehole (SE04NW/363) (Toredo Petroleum Plc) and BGS boreholes at Bradup (SE04SE/774), Jaytail (SE04SE/775) and Hag Farm (SE14SE/52).

Hydrogeology

Data on water boreholes, wells and springs and aquifer properties are held in the BGS (Hydrogeology Group) database at Wallingford.

BGS Lexicon of named rock unit definitions

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Series Bradford Sheet 69 are held in the Lexicon database. Information on the

database can be obtained from the Lexicon Manager at BGS Keyworth. The database can be consulted on BGS internet site.

Material collections

Palaeontological collection

Macrofossils and micropalaeontological samples collected from the district are held at BGS Keyworth. Enquiries concerning all the macrofossil 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 by the Mineralogy and Petrology Group at BGS Keyworth. The Group Manager should be contacted for further information, including methods of accessing the database. Charges and conditions of access to the collection are available on request from BGS Keyworth.

Bore core collection

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

BGS photographs

Copies of these photographs are deposited for reference in the BGS library, Keyworth. Colour or black and white prints and transparencies can be supplied at a fixed tariff.

Other relevant collections

Coal abandonment plans

Coal abandonment plans are held by The Coal Authority, Mining Records Department, Bretby Business Park, Ashby Road, Burton on Trent, Staffs, DE15 0QD.

Groundwater licensed abstractions, Catchment Management Plans and landfill sites

Information on licensed water abstraction sites, for groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, details of aquifer protection policy and extent of Washlands and licensed landfill sites are held by the Environment Agency.

Earth science conservation sites

Information on the Sites of Special Scientific Interest present within the Bradford district is held by English Nature, Headquarters and Eastern Region, Northminster House, Peterborough.

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.

Aitkenhead, N, Bridge, D Mc C, Riley, N J, and Kimbell, S F. 1992. Geology of the country around Garstang. Memoir of the British Geological Survey, Sheet 67 (England and Wales).

Aitkenhead, N, and Riley, N J. 1996. Kinderscoutian and Marsdenian successions in the Bradup and Hag Farm boreholes, near Ilkley, West Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 51, 115–125.

Arthurton, R S, Johnson, E W, and Mundy, D J C. 1988. Geology of the country around Settle. Memoir of the British Geological Survey, Sheet 60 (England and Wales).

Arup Geotechnics. 1991. Review of mining instability in Great Britain. Report to the Department of the Environment, Arup Geotechnics, Ove Arup and Partners. (London: HMSO.)

Brandon, A, Aitkenhead, N, Crofts, R G, Ellison, R A, Evans, D J, and Riley, N J. 1998. Geology of the country around Lancaster. Memoir of the British Geological Survey, Sheet 59 (England and Wales).

Bristow, C S. 1988. Controls on sedimentation of the Rough Rock Group (Namurian) from the Pennine Basin of northern England. 114–131 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Calver, M A. 1968. Distribution of Westphalian marine faunas in Northern England and adjoining areas. Proceedings of the Yorkshire Geological Society, Vol. 37, 1–72.

Chisholm, J I. 1990. The Upper Band-Better Bed sequence (Lower Coal Measures, Westphalian A) in the central Pennine area of England. Geological Magazine, Vol. 127, 55–74.

Chisholm, J I, Waters, C N, Hallsworth, C R,Turner, N, Strong, G E, and Jones, N S. 1996. Provenance of Lower Coal Measures around Bradford, West Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 51, 153–166.

Collinson, J D. 1988. Controls on Namurian sedimentation in the Central Province basins of northern England. 85–101 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Cooper, A H. 1984. The geology, hydrology and stability of the landslips between Otley and Old Pool Bank, West Yorkshire. British Geological Survey Technical Report.

Cooper, A H, and Burgess, I C. 1993. Geology of the country around Harrogate. Memoir of the British Geological Survey, Sheet 62 (England and Wales).

Dakyns, J R, Fox-Strangways, C, Russell, R and Dalton, W H. 1879. The Geology of the Country between Bradford and Skipton. Memoir of the Geological Survey of Great Britain, Quarter Sheet 92S E.

Eagar, R M C, Baines, J G, Collinson, J D, Hardy, P G, Okolo, S A, and Pollard, J E. 1985. Trace fossil assemblages and their occurrence in Silesian (mid-Carboniferous) deltaic sediments of the Central Pennine Basin, England. 99–149 in Biogenic structures; their use in interpreting depositional environments. Curran, H A (editor). Special Publication of the Society of Economic Palaeontologists and Mineralogists, No. 35.

Earp, J R, Poole, E G, and Whiteman, A J. 1961. Geology of the country around Clitheroe and Nelson. Memoir of the Geological Survey of Great Britain, Sheet 68 (England and Wales).

Godwin, C G. 1984. Mining in the Elland Flags: a forgotten Yorshire Industry. Report of the British Geological Survey, Vol. 16, No. 4, 17pp.

Green, A H R, Russell, R, Dakyns J R, Ward, J C, Fox-Strangways, C, Dalton, W H, and Holmes, T V. 1878. The geology of the Yorkshire Coalfield. Memoir of the Geological Survey of Great Britain.

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 North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

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

Holdsworth, B K, and Collinson, J D. 1988. Millstone Grit cyclicity revisited. 132–152 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of North West Europe. Besley, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Hudson, R G S, and Mitchell, G H. 1937. The Carboniferous geology of the Skipton Anticline. Summary of Progress of the Geological Survey for 1935, 1–45.

Jowett, A, and Muff, H B. 1904. The glaciation of the Bradford and Keighley district. Proceedings of the Yorkshire Geological Society, Vol. 15, 193–247.

Keen, D H, Jones, R L, Evans, R A, and Robinson, J E. 1988. Faunal and floral assemblages from Bingley Bog, West Yorkshire, and their significance for Late Devensian and early Flandrian environmental changes. Proceedings of the Yorkshire Geological Society, Vol. 47, No. 2, 125–138.

Kirby, G A, Aitkenhead, N, Baily, H E, Chadwick, R A, Evans, D J, Holliday, D W, Holloway, S, Hulbert, A G, Pharaoh, T C, and Smith, N J P. In press. The structure and evolution of the Craven Basin and adjacent areas. Subsurface Memoir of the British Geological Survey.

Lake, R D, Northmore, K J, Dean, M T, and Tragheim, D G. 1992. Leeds: A geological background for planning and development. British Geological Survey Technical Report, WA/92/1, 83pp.

Price, D, Carruthers, R M, Lowe, D J, and Pattison, J. 1984. The sand and gravel resources of the Wharfe Valley between Ilkley and Collingham. (Keyworth, Nottingham: British Geological Survey.)

Ramsbottom, W H C, Calver, M A, Eager, 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 Publication of the Geological Society of London,No. 10, 82pp.

Riley, N J. 1990. Stratigraphy of the Worston Shale Group (Dinantian) Craven Basin, north-west England. Proceedings of the Yorkshire Geological Society, Vol. 48, Part 2, 163–187.

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Waters, C N, Aitkenhead, N, Jones, N S, and Chisholm, J I. 1996b. Late Carboniferous stratigraphy and sedimentology of the Bradford area, and its implications for the regional geology of northern England. Proceedings of the Yorkshire Geological Society, Vol. 51, 87–101.

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.

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 Earth Galleries, and from BGSapproved stockists and agents.

Figures and plates

Figures

(Figure 1) Summary of the geological succession of the district.

(Figure 2) Early Carboniferous syn-extension structures of the region (after Kirby et al., in press).

(Figure 3) Sandstones of the Millstone Grit above the Pendle Grit Formation.

(Figure 4) Coal seams of the Coal Measures and Millstone Grit.

(Figure 5) Principal sandstones of the Coal Measures.

(Figure 6) Glacial deposits.

(Figure 7) Periglacial and postglacial deposits.

(Figure 8) Principal mineral resources of historical importance in the district.

(Figure 9) Principal engineering geological units in the Bradford district. The presence of undermining, the presence of faults and variable depths and degrees of weathering need to be considered in addition to the described engineering properties of the bedrock and superficial deposits. Note that limestone strata occur almost entirely beneath Superficial deposits.

(Figure 10) Main sources of gas emissions in the district.

Plates

(Plate 1) Kinderscoutian sandstone crag at Addingham High Moor. A cut millstone is lying amongst the rock fall [SE 07 47]. (GS539).

(Plate 2) Bifurcating glacial meltwater channel near Newsholme Dean [SE 002 410]. (GS540).

(Plate 3) Shallow rotational slide at East Morton. (GS536).

(Plate 4) Two leaves of the Elland Flags exposed in Bolton Woods South Quarry. Berry and Marshall (Bolton Woods) Ltd. [SE 16 36]. (GS537).

(Plate 5) Underground sandstone workings in the Elland Flags at Ellcliffe Quarry [SE 114 348] showing evidence of roof collapse. (GS551/L3014).

(Front cover) The Doubler Stones at Rombalds Moor [SE 013 465] is an unusual stack, 2.5m high. One of the Kinderscoutian sandstones is named after this feature (GS550). (Photographer: Neil Aitkenhead.)

(Rear cover)

(Index map) Index to the1:50 000 Series maps of the British Geological Survey.

Figures

(Figure 1) Summary of the geological succession of the district

(Figure 3) Sandstones of the Millstone Grit above the Pendle Grit Formation

(Figure 4) Coal seams of the Coal Measures and Millstone Grit

(Figure 5) Principal sandstones of the Coal Measures

(Figure 6) Glacial deposits

(Figure 7) Periglacial and postglacial deposits

(Figure 8) Principal mineral resources of historical importance in the district

(Figure 9) Principal engineering geological units in the Bradford district

The presence of undermining, the presence of faults and variable depths and degrees of weathering need to be considered in addition to the described engineering properties of the bedrock and superficial deposits. Note that limestone strata occur almost entirely beneath Superficial deposits

(Figure 10) Main sources of gas emissions in the district