Geology of the Bradford district. Sheet description of the British Geological Survey 1:50 000 Series Sheet 69 Bradford (England and Wales)

By C N Waters

Bibliographical reference: Waters, C N. 2000.  Geology of the Bradford district.  Sheet description of the British Geological Survey, 1:50 000 Series Sheet 69 Bradford (England and Wales). 41pp.

Geology of the Bradford district. Sheet description of the British Geological Survey 1:50 000 Series Sheet 69 Bradford (England and Wales)

Author: C N Waters. Contributors: A Butcher, B C Chacksfield, R A Chadwick, J D Cornwell, D E Highley, K Northmore, N J Riley and C P Royles

Keyworth, Nottingham: British Geological Survey 2000. © NERC 2000. All rights reserved. ISBN 0 85272 355 5

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Licence No: 100017897/2000. Maps and diagrams in this book use topography based on Ordnance Survey mapping.

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(Front cover) Cow and calf rock [SE 131 468] is an example of a topple rock fall, and is an important conservation and recreation site (GS 538).

(Back cover)

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Acknowledgements

This sheet description was compiled and largely written by C N Waters. R A Chadwick, J D Cornwell, C P Royles and B C Chacksfield contributed to the chapter 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 and C Hallsworth determined the heavy mineral assemblages for selected sandstones. The chapter on Applied Geology was compiled from contributions by K J Northmore on engineering geology characteristics and landslips, by D E Highley on mineral resources and by A Butcher on hydrogeological information. The report has been edited by T J Charsley and A A Jackson.

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 members of the City of Bradford Metropolitan District local authority, the Coal Authority, Mineral Valuers Office, Environment Agency (formerly National Rivers Authority and Waste Regulation Authority), Yorkshire Water, British Rail and numerous civil engineering consultants. The cooperation of landowners, tenants and quarry companies in permitting access to their lands is gratefully acknowledged.

Notes

Throughout this report the word ‘district’ refers to the area covered by the geological 1:50 000 Series 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 area upon which the site falls, for example SE 13 SE. The locations of all the boreholes referred to in the text, along with other selected significant boreholes, are shown in Chapter 8 Information sources.

Geology of the Bradford district—summary

The landscape of the Bradford district is dominated by the upland moors and ‘grit’ edges of the Millstone Grit. The Millstone Grit formed as deltaic sediments deposited at the mouths of large river systems flowing from the north about 315 million years ago. At first the rivers discharged into a deep, mostly marine basin, with the future Bradford district situated 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 that extended far beyond the district, and are now evident as the sandstones which form the edges on Rombalds Moor. The deposition of the sediments shows 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, which formed the Coal Measures we see today in the south and east of the district, are typified by the presence of prominent coal seams, the buried and compressed remnants of the mire-peats. It was the presence in the Coal Measures 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 a legacy of difficult foundation conditions and pollution.

For 310 million years following the 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 of former ice cover 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.

(Table 1) Geological succession of the district.

Chapter 1 Introduction

This Sheet Description 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 simplified map of the bedrock geology is shown in (Figure 1), and the geological succession is summarised in (Table 1). A summary of the geology is also provided by the Sheet Explanation for the 1:50 000 Series map, 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 the Calderdale District in the south-west, the Leeds District in the east and part of North Yorkshire in the north (Figure 2). 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 agricultural land with villages, and moorland.

The bedrock (Figure 1) is composed entirely of rocks deposited during the Carboniferous, about 354 to 310 million years ago. The oldest rocks proved in the Bradford district are Dinantian (Lower Carboniferous) mudstones and limestones. At depth these are believed to rest unconformably upon strongly deformed Lower Palaeozoic rocks, similar to those proved in the Ribblesdale inlier of the Settle district to the north-west (Arthurton et al., 1988). Dinantian strata occur in the north-west of the district, forming a low-lying area occupied by the town of Skipton. These rocks are overlain by the Millstone Grit of Namurian age, a thick succession of interbedded sandstones, siltstones and mudstones with subordinate thin coals, fireclays and ironstones. The Millstone Grit crops out over most of the north, and west of the district, including the high ground of Rombalds Moor. Commonly it forms upland scenery (Plate 1) with extensive moorlands associated with poor and naturally acid soils caused by the high silica content of the parent material, the lack of neutralising minerals such as lime, and the high rainfall. 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, a succession of mudstones, siltstones and sandstones and subordinate thin coals, fireclays and ironstones of Langsettian (Westphalian A) age. The Coal Measures outcrop in the south-east of the district, including the main Bradford conurbation and the outlier of Baildon Moor; they tend 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, although mineral extraction is today much reduced in scale.

History of research

The district covered by Sheet 69 Bradford was originally surveyed on the 1:10 560 County Series sheets Yorks. 168, 169, 170. 185, 186, 187, 200, 201, 202, 215, 216 and 217 by J R Dakyns, J Lucas, C Fox Strangways, R Russell, W H Dalton and W Gunn, and published on 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 on the 1:10 560 County Series sheets by J V Stephens, G H Mitchell, Wilfred Edwards and W Lloyd in 1933 to 1937 and published as Solid and Drift editions in 1949. Sheet 69 was reprinted in 1967 (Drift) and 1968 (Solid) and reconstituted to the 1:50 000 scale in 1974. The accompanying memoir for the district (Stephens et al., 1953) provides a detailed account of the geology with descriptions of localities and regional variations.

This Sheet Description provides a summary of the geology with indication of amendments or additions to the existing memoir. It is based on a second resurvey carried out on a 1:10 000 scale (except SD 94 SE which was resurveyed at the 1:10 560 scale) mainly in the period 1993 to 1996. However, some earlier work is included: the 1:10 000 map SE 25 SE was resurveyed by I C Burgess in 1977 to 1978 as part of the work on Sheet 62 Harrogate: sheets SE 23 NW/NE/SE were resurveyed by D G Tragheim and M T Dean in 1989 to 1990 as part of the applied geological mapping of Leeds (part funded by the Department of the Environment), and was described by Lake et al. (1992). The remaining geological maps were resurveyed by C N Waters, R G Crofts, N Aitkenhead, R Addison, J G Rees, N S Jones and M Stewart in 1993 to 1996. The applied geology of the part of the district covered by the City of Bradford Metropolitan District is described fully, with accompanying thematic maps and geological databases, by Waters et al. (1996b).

Concurrent with the first resurvey Hudson and Mitchell (1937) were working just to the north, 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 for Sheet 67 Garstang (Aitkenhead et al., 1992) and Sheet 59 Lancaster (Brandon et al., 1999), largely based on the scheme for the Worston Shale Group developed for the entire Craven Basin by Riley (1990). Earp et al. (1961), Arthurton et al. (1988) and Aitkenhead et al. (1992) provide accounts of the biostratigraphical schemes used in the Dinantian of the Craven Basin, with Riley (1990) providing a detailed summary of the biostratigraphical ranges of selected taxa for the Worston Shale Group and correlation of the lithostratigraphical units with the Dinantian stages and series.

The second resurvey has used recent advances in Silesian geology to make amendments to previous surveys. Following the work of Ramsbottom et al. (1978), various workers 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., 1996a) 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 includes Jowett and Muff (1904) on ‘glacial overflow’ channels and of Keen et al. (1988) on Bingley Bog. Interesting data are also provided by Price et al. (1984) as part of a mineral assessment survey.

Chapter 2 Dinantian

Dinantian rocks are the oldest strata at outcrop in the district, occurring in the extreme north-west in the vicinity of Skipton; in addition they underlie the entire district at depth. The strata occur at crop in the core of the north-east-trending Skipton Anticline, though they are poorly exposed, occurring beneath an extensive drift cover. Much of the information presented in the Bradford memoir (Stephens et al., 1957) is derived from outcrop to the north (Hudson and Mitchell, 1937) of that which has been covered by this resurvey. 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 3.4 km (see Horizontal Sections Sheet 69 Bradford).

During the late Devonian and Dinantian, a phase of crustal stretching resulted in the formation of rapidly subsiding basins, separated from relatively slowly subsiding horst and tilt-blocks by extensional faults (Leeder, 1982). The Bradford district is mainly located within the area of the Harrogate Basin, although the Dinantian strata present in the north-west of the district have affinities with the Craven (or Bowland) Basin that lies to the west (see Chapter 6 Concealed geology and structure). To the north of the district, the Harrogate Basin is separated from the Askrigg Block by the North Craven Fault.

Chatburn Limestone Group (CHL)

The Chatburn Limestone Group (Earp et al., 1961), of late Courceyan-early Chadian (Tournaisian) age, was formerly referred to as the Haw Bank Limestone and the underlying Haw Bank Limestone-with-Shales in the vicinity of Skipton (Hudson and Mitchell, 1937; Stephens et al., 1953; Arthurton, 1983). In the Bradford district, only the upper 80 to 100 m is estimated to be present at outcrop, occurring entirely within the former Haw Bank Limestone. This consists mainly of the thickly and thinly bedded, medium to dark grey, bioclastic limestones with dark grey shaly mudstone intercalations (shown as ChL on the map), with dark grey shaly mudstone or mudstone with thinly interbedded muddy limestones (shown as md/ls on the map) predominating in places. In the district, the group is conformably overlain by the Worston Shale Group. The Chatburn Limestone Group is interpreted as having been deposited in a shallow marine carbonate ramp with high influx of terrigenous muds and silts derived from the still emergent Askrigg Block (Riley, 1990).

Worston Shale Group

The Worston Shale Group (Riley, 1990) comprises three formations, in ascending order: the Clitheroe Limestone Formation, the Hodder Mudstone Formation and the Pendleside Limestone Formation. The Hodderense Limestone Formation, present between the Hodder Mudstone and Pendleside Limestone formations throughout much of the Craven Basin (Riley, 1990), has not been proved in the Bradford district; it is probably absent beneath an unconformity at the base of the Pendleside Limestone Formation.

The Clitheroe Limestone Formation (CIL), redefined by Riley (1990), was formerly referred to in the district as the Halton Shales (Hudson and Mitchell, 1937; Stephens et al., 1953). The formation, of early Chadian (Tournaisian) age, is estimated as 160 to 195 m thick. It conformably overlies the Chatburn Limestone Group and is in turn unconformably overlain by the Embsay Limestone Member of the Hodder Mudstone Formation. In the Skipton area, only the lower part of the Clitheroe Limestone is considered to be present beneath the unconformity at the base of the Embsay Limestone, with the amount of erosion considered to be greatest in the eastern part of the Skipton Anticline (Riley, 1990). The formation consists dominantly of limestone across most of the Craven Basin, but in the Skipton area the main lithology is shaly, calcareous mudstone with subordinate interbedded thin beds of dark grey limestone. Regionally, the formation was formed in a carbonate ramp environment, although the dominantly argillaceous facies observed in the Bradford district may have been located in a deeper basinal environment, or it may be a consequence of greater clastic supply to the basin at that time.

The Hodder Mudstone Formation (HoM), defined by Riley (1990), is of Arundian to Holkerian age. The formation is predominantly argillaceous with a limestone member, the Embsay Limestone Member (EL), present at the base. The Embsay Limestone, estimated to be about 20 to 25 m thick in the Skipton area of the district, overlies unconformably the Clitheroe Limestone Formation. The term Embsay Limestone was used informally by Hudson and Mitchell (1937) and Stephens et al. (1953) but has been formally defined by Riley (1990). The member comprises thin to thick-bedded, pale detrital/skeletal limestone interbedded with dark calcareous silty mudstones, calcilutites and, near to the base, limestone and mudstone lithoclast conglomerates and breccias at the type locality (Riley, 1990). The Embsay Limestone is interpreted as carbonate turbidites interbedded with hemipelagic muds (Riley, 1990). The overlying argillaceous succession was formerly referred to as the Skibeden Shales (Stephens et al., 1953). The succession, estimated to be 195 to 240 m thick in the Skipton area, is dominated by dark grey, shaly, calcareous mudstone with some thinly interbedded, fine-grained dolomitic and argillaceous limestone. The transition to the dominantly argillaceous facies is interpreted as representing a decrease in carbonate influx into the basin during Holkerian times (Riley, 1990). The formation is overlain (locally unconformably) by the Pendleside Limestone Formation.

The Pendleside Limestone Formation (PdL), of late Holkerian to Asbian age, was referred to in the Skipton area as the Draughton Limestone (Hudson and Mitchell, 1937; Stephens et al., 1953), but has been redefined formally as the Pendleside Limestone Formation over the entire Craven Basin (Riley, 1990). The formation, estimated to be 20 to 45 m thick in the district, overlies the Hodder Mudstone Formation with a local unconformity present in the area of the Skipton Anticline (Hudson and Mitchell, 1937), which may explain the absence of the Hodderense Limestone Formation. The Pendleside Limestone Formation is overlain by the Lower Bowland Shale Formation. The Pendleside Limestone Formation comprises medium to dark grey, thinly bedded and finely bioclastic skeletal/detrital limestone, and also includes a basal breccia with lithic clasts derived from the Hodderense Limestone Formation (Riley, 1990). The formation is considered to represent a return to widespread deposition of carbonate turbidites (Riley, 1990). The Embsay Limestone Member of the Hodder Mudstone Formation and the Pendleside Limestone Formation both occur above unconformities, with minimum thicknesses for both limestones apparently developed over topographic highs, such as that probably associated with the Skipton Anticline (Riley, 1990). The unconformities are believed to reflect phases of late Chadian to early Arundian and late Holkerian to early Asbian crustal extension (Riley, 1990; Kirby et al., 1994).

Bowland Shale Group

The Bowland Shale Group comprises the Lower Bowland Shale and the Upper Bowland Shale formations, and was definitively described in the adjacent Clitheroe district to the west (Earp et al., 1961). The boundary between these formations, at the base of the Cravenoceras leion Marine Band, coincides with the boundary between the Viséan (Lower Carboniferous) and the Namurian (Upper Carboniferous). The Upper Bowland Shale Formation is discussed in Chapter 3 Namurian. The rocks of the group give rise to a long concave slope to the south and east of Skipton, located beneath the scarps produced by the sandstones of the Pendle Grit Formation.

During late Asbian and Brigantian times, the development of fringing reefs at the platform margin led to a marked diminution of carbonate supply, and oxygen depletion and stratification of the water column in the basins to the south of the Askrigg Block. This resulted in the deposition of hemipelagic muds that form the argillaceous deposits of the Bowland Shale Group (Riley, 1990; Aitkenhead et al., 1992).

Stephens et al. (1953, fig. 2) identified three unconformities within the Bowland Shale Group. No evidence was found during this resurvey to confirm or disprove this. However, as the succession is thought to be entirely of basinal deep-water facies, a more probable explanation is that the apparent hiatuses are the product of the shearing effects of the intense folding of competent limestone and incompetent mudstone within the Skipton Anticline.

The Lower Bowland Shale Formation (LBS), of late Asbian and Brigantian age, is estimated to vary in thickness from about 105 to 130 m. The formation was subdivided during the previous survey into Lower Bowland Shales and Middle Bowland Shales (Stephens et al., 1953), mainly based on biostratigraphical criteria, but this subdivision was not recognised during this resurvey. The formation is conformable between the Pendleside Limestone Formation below and Upper Bowland Shale Formation above. The general lithology is shaly mudstone, generally black or dark grey, calcareous and bituminous with thin beds of argillaceous, fine-grained sandstone, scattered bullions (limestone nodules) and ammonoid-rich beds. The Lower Bowland Shale displays a reduced bioturbation in comparison with underlying Worston Shale Group (Riley, 1990; Aitkenhead et al., 1992; Brandon et al., 1999), and is generally more calcareous and more consistently marine than the Upper Bowland Shale Formation. Three calcareous bands were described in a 15 m-thick succession in the upper part of the formation by Hudson and Mitchell (1937).

Key locality:

Chapter 3 Namurian

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. The rocks comprise a lower, dominantly argillaceous, thin succession of the Bowland Shale Group, overlain by a thick interbedded succession of mudstone and siltstone, generally poorly exposed, and sandstone (commonly referred to as ‘grit’), which may be well exposed in natural sections and quarries. 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 (see structural contour insets on solid edition of Sheet 69 Bradford).

During the Namurian Epoch, approximately 315 million years ago, northern England lay within a large, actively subsiding basin. Extensive delta systems, fed with fluvial sediments eroded from the surrounding land surfaces to the north, built out into the basin. Coarser grained sediments, deposited along fluvial and delta systems and as turbidite fans, eventually became lithified as sandstones, whereas fine-grained background sedimentation, muds and silts, settled in more quiescent areas and became lithified as mudstones and siltstones, respectively.

The previous survey defined the Millstone Grit as a chronostratigraphical unit, the Millstone Grit Series, that comprised all strata of Namurian age, including the dominantly argillaceous Upper Bowland Shales (Stephens et al., 1953). The Millstone Grit 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 (Stephens et al., 1953). During this resurvey the Millstone Grit Group has been mapped as a lithostratigraphical unit that includes all strata of Namurian age above the base of the Pendle Grit Formation, with the Upper Bowland Shales as a formation within the dominantly argillaceous Bowland Shales Group. The use of the epithet ‘grit’ is maintained for the sandstone nomenclature where its usage is well established in the literature; grit and sandstone are considered synonymous in the following descriptive text. The Namurian Epoch is divided into seven stages (Table 2), which are in turn subdivided into chronozones (Ramsbottom et al., 1978). The boundaries of these chronostratigraphical subdivisions, are recognised biostratigraphically by the presence of diagnostic ammonoid (goniatite) fauna.

Bowland Shale Group

The group comprises the Lower Bowland Shale Formation, of Dinantian age (discussed in Chapter 2 Dinantian), and the Upper Bowland Shale Formation.

The Upper Bowland Shale Formation (UBS), of Pendleian age is estimated to be 95 to 105 m thick. The formation lies conformably upon strata of the Lower Bowland Shale Formation, with the base of the formation taken at the base of the Cravenoceras leion Marine Band, and the top is taken as the base of the lowermost quartzo-feldspathic sandstone of the Millstone Grit Group. The dominant lithology is mudstone, dark grey and fissile. In the Upper Bowland Shale Formation the 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.

Key locality:

Millstone Grit Group (MG)

The Millstone Grit present in the district comprises about 1800 m of interbedded mudstone, siltstone and sandstone. Within the group only the Pendle Grit has been assigned formation status in the district. The Pendle Grit facies, including the coarse-grained sandstones, indicate deposition from turbidity currents in relatively deep water. This contrasts markedly with the remainder of the Millstone Grit Group in which the main sandstones were deposited as delta-top sandbodies. Recent resurveys of the Garstang and Lancaster districts (Aitkenhead et al., 1992; Brandon et al., 1999) have identified further formations common to these areas which both occur within the Craven Basin. These formations cannot necessarily be correlated with the Bradford district, which is located in the separate Harrogate Basin. In the Bradford district, the succession above the Pendle Grit Formation is treated as a distinct unnamed formation with named sandstones that generally display similar petrographical and sedimentological features and can only be distinguished from one another 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, although attempts have been made to rationalise nomenclature with the adjoining districts of Leeds (Sheet 70) and Huddersfield (Sheet 77).

Glacioeustatic 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 2 to 3 m. They can be recognised across large areas, and as each marine incursion generally contains distinctive and diagnostic marine faunal assemblages, particularly ammonoids, marine bands represent important marker horizons. About 50 marine bands are recognised in the Millstone Grit of the Pennines (Holdsworth and Collinson, 1988); the principal marine bands present in this district are shown in (Table 2). The marine bands commonly pass up through claystones into siltstones and sandstones, representing a transition in sedimentation during high stands from pelagic claystone to delta slope and finally to distributary channels on the delta top. From mid-Namurian times onwards, the top of each cycle (when sea level was at its lowest) was often marked by the formation of soils and the development of a widespread cover of vegetation forming peats. Once subjected to compaction and lithification the soil horizons became seatearths, and the organic deposits coals. This pattern of deposition is repeated with each rise in sea level; the deposits of an individual cycle are known as a cyclothem. The sequence of development described above is idealised and may be interrupted or modified. Collinson (1988) has reviewed the sedimentation of the Millstone Grit.

The Pendle Grit Formation (PG), which outcrops in the north of the district, ranges in thickness from 251 to 455 m in the north-west, whereas in the north-east the full thickness is not proved. The formation, of late Pendleian age, is interpreted as comprising turbiditic facies deposited on a prodelta slope. The definition of Pendle Grit Formation as used by this resurvey was introduced by Arthurton et al. (1988) in the Settle district and formally defined by Aitkenhead et al. (1992) in the Garstang district. This formation equates with the Pendle Grit of the Clitheroe district (Earp et al., 1961), and is equivalent to the lower part of the Skipton Moor Grits of the previous survey (Stephens et al., 1953). Recent work by Brandon et al. (1995) suggests that the Pendle Grit and lower part of the Grassington Grit Formation of the Askrigg block are coeval. Here the formation is subdivided on the basis of its dominant constituent lithologies, namely sandstone (PG) and thinly interbedded siltstone and sandstone (sl/sa). Previously, the formation has been subdivided into a lower, dominantly sandstone unit, the ‘Pendle Grits’, and an upper, dominantly mudstone and siltstone unit, known as the ‘Pendle Shales’ (Eagar et al., 1985). Brandon et al. (1995) have renamed and redefined the upper unit as the Surgill Shale Member (of the Pendle Grit Formation). The limited exposures and borehole provings have prevented the identification of the Surgill Shale Member in this district. 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, although where this locally dies out laterally the boundary has been arbitrarily extended between Millstone Grit Group (undivided) and Pendle Grit Formation. The formation comprises grey, medium to coarse-grained, feldspathic sandstone, rarely conglomeratic, present in thick, massive beds with flute casts, load casts, groove and prod marks and micro-wrinkles 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 Warley Wise Grit (WWG), of latest Pendleian age, is estimated to range in thickness from about 35 m in the Otley area up to 163 m in the Langbar area, with a thinning broadly toward the east and south of the district. It is recognised in the type area of the Clitheroe district (Earp et al., 1961) and was formerly mapped in the Bradford district as the upper sandstones of the Skipton Moor Grit Group (Stephens et al., 1953). The Warley Wise Grit is probably equivalent to the upper part of the Grassington Grit Formation of the Askrigg block (Brandon et al., 1995) and the Almscliff Grit of the Harrogate district (Cooper and Burgess, 1993). The Warley Wise Grit comprises very coarse-grained, commonly pebbly, quartzo-feldspathic, cross-bedded sandstone commonly interbedded with siltstone and dark grey, micaceous, silty mudstone. This mainly fluvial facies contrasts with the predominantly turbiditic facies of the bulk of the Pendle Grit Formation.

In the north-west of the district, the Warley Wise Grit is overlain by a 45 to 90 m-thick succession of interbedded mudstone, siltstone and sandstone for which no direct equivalent is found in the north-east of the district. Approximately 10 m of dark grey mudstones immediately above the Warley Wise Grit in the Silsden and Cononley areas include the Bradley Coal (BC), recorded as 0.5 m thick where worked. This is overlain by two unnamed sandstones, both 10 to 15 m thick, fine to medium grained, quartzo-feldspathic and cross-bedded; they are separated by dark grey silty mudstone, 21 m thick, with a thin and unnamed coal near the base and marine fauna near the top, recorded in the Croft House Borehole. The two unnamed sandstones were referred to as Bradley Flags in the previous survey. However, differences in lithology and the recognition during this resurvey that the sandstones represent deposition in distinct cycles indicates that this name should be restricted to the sandstone exposed at the type locality in Bradley Quarry. The Bradley Flags (BF) show the thickest development of 25 m at Bradley. They comprise fine-grained sandstone, interbedded with micaceous mudstones. The sandstone is very micaceous, flaggy with planar bedding and lamination displaying primary current lineations, crossbedding with burrow traces in places, and both wave and current ripple cross-lamination.

The base of the Cravenoceras cowlingense Marine Band (E2a1) marks the base of the Arnsbergian (E2) Stage; it overlies directly the Bradley Flags in the north-west of the district. This marine band has not been proved elsewhere in the district, but is assumed to rest directly on the Warley Wise Grit. This is the Edge Marine Band of the previous survey. At Cononley Beck, the marine band comprises a sequence of 1.5 to 2.0 m of fissile, grey, micaceous silty mudstone, overlain by a 0.25to 0.5 m-thick sandstone that is hard, bioturbated, grey to dark grey, micaceous, calcareous and fine grained with glauconite and phosphatic bioclasts (Strong, 1996). The sandstone yields specimens of Paraconularia and an inarticulate brachiopod suggesting that it is marine. The sandstone is overlain by ammonoid-bearing mudstones, 0.7 m thick, with a thin (1 to 2 cm) bentonite present 1.8 m above the sandstone.

Above the C. cowlingense Marine Band is a succession, estimated to be between 90 and 240 m thick, with two distinct dominantly argillaceous lithologies, which because of limited exposure have not been mapped as separate units. The lower part comprises dark grey, sandy, micaceous, parallel-laminated mudstone and fine to medium-grained, sharp-based sandstone beds (up to 5 m thick), interpreted as deposits from turbidity currents. The upper part comprises dark grey, micaceous, fissile, silty mudstone with rare Sanguinolites sp., interbedded with subordinate very thin flaser-bedded sandstone lenses and thin (0.15 m), hard, planar and ripple cross-laminated, dolomitised sandstone beds. The upper lithology appears to be equivalent to the Close Hill Siltstone Member of the Roeburndale Formation, described in the Craven Basin and interpreted as delta slope to delta front deposits (Brandon et al., 1995). The Eumorphoceras ferrimontanum Marine Band (E2a2), not recorded during the previous survey, has been identified at a number of localities in the north-east, including at Holbeck [SE 198 470] where it was incorrectly identified by Stephens et al. (1953) as part of the Marchup Marine Beds. The thickness of strata between the Cravenoceras cowlingense and E. ferrimontanum marine bands has not been proved in the district. However, the E. ferrimontanum Marine Band is found associated with turbiditic sandstones comparable to those described in the lower turbiditic facies. Also, specimens identified by Yates (1962) as Eumorphoceras cf. E. bisulcatum ferrimontanum were found in loose blocks, but not in situ, at Cononley Beck. It is possible that the specimens have been incorrectly identified or have fallen from an inaccessible part of the cliff, approximately 5 to 15 m above the C. Cowlingense Marine Band.

The Marchup Grit (Mp), of Arnsbergian age, is typically 15 to 25 m thick in the north-west of the district, increasing in thickness towards the east with an estimated maximum of 65 m in the Timble area. It has been equated to the Red Scar Grit of the Harrogate district (Cooper and Burgess, 1993) and is not, as suggested by Stephens et al. (1953), equivalent to the Almscliff Grit. The Marchup Grit is generally a medium to very coarse-grained, thickly crossbedded, quartzo-feldspathic sandstone, with some log impressions. Locally, especially in the north-west of the district, the sandstone may be fine grained, micaceous and thinly planar bedded or ripple cross-laminated. The base of the sandstone is locally sharp and erosive, or gradational and upwards-coarsening; the top is typically a hard ganister.

The Marchup Grit is overlain by an argillaceous succession about 80 to 120 m. The lower part comprises the ‘Marchup Marine Beds’ of Jones (1943) and Stephens et al. (1953), a succession of mudstones that during this resurvey have been identified as containing three marine bands. These are, in ascending order: the Eumorphoceras yatesae Marine Band (E2a3) (not previously described in the district) about 1 m above the top of the Marchup Grit: the Cravenoceratoides edalensis Marine Band (E2b1) 3.5 m above the E. yatesae Marine Band: the Cravenoceratoides nitidus Marine Band (E2b2) (not previously described in the district) estimated to occur about 15 to 20 m above the Marchup Grit. A 20m thick k-bentonite is present between the E. yatesae and C. edalensis marine bands. An unnamed, laterally impersistent sandstone, up to 8 m thick, is present at Askwith. The base of the sandstone is estimated to be about 10 m above the top of the Marchup Grit, and present between the C. edalensis and C. nitidus marine bands. The sandstone is fine grained, micaceous with upward-coarsening beds grading from mudstone to sandstone. In the upper part of the argillaceous succession a further marine band is identified, the Cravenoceratoides nititoides Marine Band (E2b3). The Ben Rhydding Toll Bridge Borehole indicates that this marine band occurs 56 m above the C. nitidus Marine Band, whereas the same interval is estimated to be about 100 m in the Addingham area. This marine band is estimated to occur about 15 to 20 m below the Nesfield Sandstone.

The Nesfield Sandstone (NS), of Arnsbergian age, is estimated to be about 10 to 20 m, with the thickest development in the vicinity of Addingham. The base is gradational, with an upwards-coarsening succession of dark grey silty mudstone to grey siltstones, with thin beds of sandstone which become more common upwards. The base of the Nesfield Sandstone is taken where sandstone becomes predominant over siltstone. The sandstone is typically quartzarenitic; it is generally fine grained, well sorted and cemented, thinly planar bedded and laminated, cross-bedded and ripple cross-laminated in places, with wave and current ripples. In the Steeton and Cowling area, the sandstone is atypical, being medium grained, medium bedded and feldspathic. At Nesfield, the sandstone is interpreted by Martinsen (1990) as a proximal mouth bar.

The poorly exposed, argillaceous succession overlying the Nesfield Sandstone is estimated to be 50 to 65 m thick. Up to three marine bands, the Nuculoceras nuculum marine bands (E2c2–4), are estimated to occur between 10 and 20 m above the top of the Nesfield Sandstone, although no locality in the district has recorded more than one of these marine bands.

The Middleton Grit (Mn), of Arnsbergian age, is estimated to be a maximum of 16 to 30 m in the Addingham area, thinning and dying out towards Burley In Wharfedale to the east and Sutton-in-Craven to the west. The Middleton Grit comprises a massive or cross-bedded, quartzofeldspathic sandstone, locally with sigmoidal foresets and wave ripples. The sandstone fines southward, from medium to coarse grained and pebbly in places, at Middleton, to fine to medium grained south of the River Wharfe at Ilkley. At Middleton, the sandstone is mapped as two leaves and locally a 0.4 m coal with seatearth has been recognised within the sandstone. The sandstone is described fully by Martinsen (1990) who identifies features indicative of deposition in fluvial channels and delta-front mouth bar environments, and the presence of syndepositional growth faulting. Above the Middleton Grit is a dominantly argillaceous succession, approximately 30 to 45 m thick. Immediately above the sandstone are the Isohomoceras subglobosum marine bands (H1a1–3), the lowest of which is taken as the base of the Chockierian (H1) Stage. At least two of the three marine bands have been proved in the district. About 7 to 10 m above the Middleton Grit are mudstones which include the Homoceras beyrichianum Marine Band (H1b1).

The Brocka Bank Grit (BB) is largely restricted in extent to the Addingham area where it has a maximum thickness of 55 m. The age of this sandstone is uncertain, but is thought to be Chokierian or Alportian. The sandstone is generally coarse grained and massive or cross-bedded, although a lower leaf of fine-grained, massive bedded sandstone has been identified during this resurvey. Martinsen (1990) has proposed distributary channel and mouth-bar settings for deposition of the Brocka Bank Grit.

Above the Brocka Bank Grit is a poorly exposed argillaceous succession estimated to be about 120 to 150 m thick. Fauna indicative of the Hodsonites magistrorum Marine Band (R1a1), which marks the base of the Kinderscoutian stage, have been recorded in the Ilkley area during this resurvey. The regional position of this marine band above the Brocka Bank Grit is uncertain as this sandstone is absent in the Ilkley area. The succession above the H. magistrorum Marine Band is dominated by siltstone and mudstone with thin interbedded turbiditic sandstones, commonly slumped, and typical of deposition on a delta slope (McCabe, 1978). A distinct facies recognised in this succession includes grey and dark grey laminites of siltstone and very fine-grained sandstone with a cyclicity that suggests a tidal origin; it is interpreted as the deposits of a prodelta environment (Aitkenhead and Riley, 1996). Locally, fine-grained, massive or parallel laminated sandstones dominate, and in the Sutton-in-Craven area reach a thickness of about 85 m. These sandstones are laterally impersistent and are interpreted as proximal turbidite channels. Formerly referred to as the Addlethorpe Grit (Stephens et al., 1953), correlation with this sandstone in the type area of the Harrogate district (Cooper and Burgess, 1993) is not proved and the isolated nature of the sandbodies has led to them not being named during this resurvey. Marine bands identified in this succession include the Reticuloceras circumplicatile Marine Band (R1a2), and possibly the Reticuloceras dubium Marine Band (R1a5) and Reticuloceras eoreticulatum Marine Band (R1b1). In the Guiseley area, a marine band referred to as the Otley Shell Bed comprises 5 to 6 m of mudstone with a thin limestone; it contains diverse marine fauna but lacks diagnostic ammonoids. The Otley Shell Bed occurs near to the base of the overlying Addingham Edge Grit and its absence in the Hag Farm Borehole may suggest that it may have been removed locally by erosion at the base of this sandstone.

The Addingham Edge Grit (AE), of Kinderscoutian age, commonly forms a prominent scarp feature in the district (Plate 1), notably at Earl Crag [SD 985 429], Addingham High Moor [SE 070 472] to [SE 088 471] (the type locality), Ilkley Crags [SE 125 465] and Caley Crags [SE 230 445]. The sandstone is estimated to be 15 to 55 m thick, with the thickest development broadly in the east of the district. In the north-west of the district, the sandstone was also referred to as the Earl Crag Grit during the previous survey. In the north-east of the district, the Addingham Edge Grit is considered to be equivalent to the Caley Crag Grit of the previous survey (Figure 3) and not as Stephens et al. (1953) proposed as equivalent to the Bramhope Grit. The sandstone is generally medium to very coarse grained, in parts pebbly, feldspathic and thickly cross-bedded, and is interpreted as having been deposited in fluvial channels.

Above the Addingham Edge Grit, a succession of three sandstones with intervening dominantly argillaceous strata have been recognised across most of the district (Figure 3). The previous survey did not name these sandstones, except in the north-east of the district, where all three sandstones were identified as the Bramhope Grit. The BGS Bradup, Hag Farm and Jaytail boreholes have permitted correlation of the three sandstones which have been named from exposures present on Rombalds Moor. In ascending order these are the Long Ridge Sandstone, Doubler Stone Sandstone and High Moor Sandstone. In the south-west of the district, the nomenclature used in the Huddersfield (Sheet 77) district is preferred with amendments.

The dominantly argillaceous succession above the Addingham Edge Grit is very variable in thickness, ranging from 10 to 60 m. Two marine bands have been identified in the Bradup and Westfield Mills boreholes, tentatively equated with the Reticuloceras reticulatum marine bands (R1c2–3) (Aitkenhead and Riley, 1996).

The Long Ridge Sandstone (LRS), of Kinderscoutian age, is estimated to range in thickness from 5 to 58 m, with the thickest development in the north-east of the district. In the Wadsworth area, the equivalent sandstone was mapped during this resurvey as a leaf of the Lower Kinderscout Grit (LK), as opposed to the Addingham Edge Grit of the previous survey. The sandstone is typically fine to very coarse grained, upwards-fining, massive or cross-bedded with a sharp erosive base; in places it is underlain by fine to medium-grained, laminated, micaceous and locally bioturbated, sandstone. A thin coal underlain by a seatearth is found locally at the top of the sandstone.

Above the Long Ridge Sandstone is a mudstone-dominated sequence, estimated to be 2 to 35 m thick. Immediately above the sandstone are mudstones of the Reticuloceras coreticulatum Marine Band (R1c4).

The Doubler Stones Sandstone (DSS), of Kinderscoutian age, is estimated to be 8 to 60 m thick, with the thickest development in the north-east of the district. In the Wadsworth area, the equivalent sandstone is the uppermost leaf of the Lower Kinderscout Grit (LK), not the lower leaf of the Upper Kinderscout Grit as mapped during the resurvey of the Huddersfield (Sheet 77) district (Wray et al., 1930). The sandstone varies from fine grained, planar-laminated, planar-bedded and micaceous to fine grained to granular and cross-bedded.

The Doubler Stones Sandstone is overlain by an argillaceous succession, 0 to 20 m thick, with the local development of the worked Morton Banks Coal, up to 1.5 m thick, in the Keighley area. The succession commonly contains a Lingula band believed to correlate with the Butterly Marine Band (Aitkenhead and Riley, 1996). Locally, in the southwest and north-east of the district, the Doubler Stones Sandstone cannot be distinguished from the overlying High Moor Sandstone, and so has been mapped as Doubler Stones Sandstone/High Moor Sandstone (undivided). Either this is the consequence of limited exposure preventing the identification of two distinct sandstones, or the intervening argillaceous sequence has been removed by erosion at the base of the High Moor Sandstone.

The High Moor Sandstone (HMS), of Kinderscoutian age, ranges in thickness from 0 to 21 m. In the Wadsworth area the equivalent sandstone is the Upper Kinderscout Grit (UK). The sandstone varies in grain size from very fine grained to very coarse grained; it is cross-bedded or massive, broadly upwards-fining, locally becoming very micaceous and very thinly bedded towards the top. The top of the sandstone is typically marked by a ganister.

The base of the Bilinguites gracilis Marine Band (R2a1) marks the base of strata of Marsdenian (R2) age. In the Bradup Borehole, the marine band is proved as two leaves with a total thickness of 16.03 m. This unusually great thickness may be due to abundant sediment supply associated with the proximity to the Askrigg Block (Aitkenhead and Riley, 1996). In the south-west of the district, the marine band is estimated to be only 3 to 4 m thick and in the Horsforth Borehole only 0.9 m thick. Typically, the marine mudstones are directly underlain by a thin (0.1 to 0.2 m), medium grey, carbonaceous and micaceous siltstone or fine-grained sandstone. The mudstone-dominated succession above the marine band ranges from 5 to 30 m.

The East Carlton Grit (EC), of Marsdenian age, ranges from thin or absent in the west of the district, up to 52 m in the Guiseley area where it forms two thick leaves. In the west, the East Carlton Grit is typically a fine-grained, micaceous sandstone with scattered Pelecypodichnus traces. In areas of thickest development, the sandstone can be medium grained, locally very coarse grained, cross-bedded with internal erosion surfaces.

In the Keighley area, the Thwaites Coal (TC), with a maximum thickness of 0.6 m, lies immediately above the East Carlton Grit. The coal is, in turn, overlain by probably the lowest Bilinguites bilinguis Marine Band (R2b1). This marine band may be the lateral equivalent of the Keighley Bluestone (BS), present locally in the west of the district. The Keighley Bluestone, 0 to 7 m thick, comprises a hard, compact, dark bluish grey, siliceous siltstone, chert and claystone with abundant spines of the sponge Hyalostelia smithi and Zoophycos traces calcareous brachiopods and crinoids occur locally. The Keighley Bluestone is interpreted as being formed from marginal marine, possibly lagoonal, silts (Waters et al., 1996a). A Lingula band found about 2 m above the Keighley Bluestone may equate with the B. bilinguis Marine Band (R2b2). A further coal, the Stanbury Coal (SC), up to 0.3 m thick, occurs locally above the Keighley Bluestone and Lingula band, and was worked west of Haworth.

The Scotland Flags (SF), of Marsdenian age, are estimated to be 0 to 30 m thick, being absent in the north-east of the district. This sandstone was formerly mapped as the lower leaf of the Woodhouse Grit (Stephens et al., 1953), but here the nomenclature used in the Huddersfield district (Wray et al., 1930) has been adopted. In the west of the district, the Scotland Flags are typically a very fineto fine-grained, micaceous sandstone. Sedimenatry features include large-scale clinoform surfaces, cross-bedding, ripple crosslamination, thinly planar bedding lamination (commonly with abundant Olivellites plummeri), and some evidence of slumping in the Cullingworth area. This is overlain by medium to coarse-grained and trough cross-bedded sandstone which thickens in the central part of the district and predominates to the exclusion of the underlying sandstone. A thin unnamed coal and seatearth occur locally in the Oxenhope area between leaves in the sandstone.

The Scotland Flags are overlain by an argillaceous succession estimated to vary from 0.2 m in the Crow Hill area to a maximum of 15 m elsewhere. This variation in thickness probably reflects erosion at the base of the overlying Midgley Grit. Lingula mytilloides is found locally in the mudstone, and in the Snail Green Borehole it occurs with Reticuloceras sp. (Deans, 1932, 1934) now interpreted as Bilinguites. This may equate with the Bilinguites bilinguis Marine Band (R2b3), although no diagnostic ammonoid fauna has been found in the district.

The Midgley Grit (MgG), of Marsdenian age, is up to 30 m thick, but is absent locally in the Guiseley area. The sandstone was previously mapped as the upper leaf of the Woodhouse Grit, or as the Brandon Grit in the east of the district (Stephens et al., 1953). The nomenclature used here follows that of Wray et al. (1930). The sandstone is generally medium to very coarse grained with granules; it is quartzo-feldpathic, thickly cross-bedded, and log impressions are fairly common near its sharp erosional base. A thin unnamed coal and a seatearth can be found at the top of the sandstone.

The argillaceous succession above the Midgley Grit is about 5 to 25 m thick with the thinnest and thickest development occurring in the south-west of the district, to the south and north of the Denholme Clough Fault, respectively. A Lingula band occurs locally, immediately above the top of the sandstone, and is considered to equate to the Bilinguites eometabilinguis Marine Band (R2b4). The Bilinguites metabilinguis Marine Band (R2b5), occurs about 3 to 4 m above the top of the sandstone. In the Keighley area, the Rough Holden Coal (RH) is present above the B. metabilinguis Marine Band as a worked seam up to 1.5 m thick, about 6 m below the base of the overlying Guiseley Grit.

The Guiseley Grit (G), of Marsdenian age, ranges from 7 to 27 m in thickness; the greatest thickness is in the Guiseley area where it occurs as two leaves. The sandstone is typically upward-coarsening; broadly it varies from fine to medium grained, with thin parallel bedding and ripple cross-lamination to medium to coarse grained, and thickly cross-bedded. In the Haworth area, the coarse-grained sandstone has a sharp base.

The dominantly argillaceous succession above the Guiseley Grit is estimated to be 7 to 25 m and includes the Bilinguites superbilinguis Marine Band (R2c1), present about 1 to 4 m above the Guiseley Grit. The Verneulites sigma Marine Band (R2c2) has not been identified in the district but may equate to a Lingula band proved in the Keighley area in Aire Valley No.1 Borehole 4 m above the top of the B. superbilinguis Marine Band.

The Huddersfield White Rock (WR), of Marsdenian age, is generally thin or absent in the south-west of the district, but reaches a maximum of 12 m thickness in the east. The sandstone is siliceous, generally fine to medium grained, thin to thickly bedded, cross-bedded and cross-laminated. In the south-west of the district, the sandstone is locally very coarse grained and cross-bedded, and was formerly referred to as the Warley Rock (Wray et al., 1930). The siltstone, interbedded with fine-grained sandstone, is about 3m thick overlain by a seatearth clay and 0.1 m-thick coal. Sandstone at Withins Foot [SD 987 355] identified as the Huddersfield White Rock by Stephens et al. (1953) was found during the current survey to be a younger, unnamed sandstone present above the Cancelloceras cancellatum Marine Band. This unnamed sandstone occurs at the same stratigraphical position as the Lower Haslingden Flags present to the west of the district, although this study has not established a correlation. A thin (up to 0.2 m) coal seam, possibly equivalent to the Upper Meltham Coal of the Huddersfield (Sheet 77) district, and underlying seatearth occur above the Huddersfield White Rock.

Above the Huddersfield White Rock is a dominantly argillaceous succession, 10 to 40 m thick. The lower part is typically dark grey mudstone with the Cancelloceras cancellatum Marine Band (Gla1), which defines the base of rocks of Yeadonian age, and Cancelloceras cumbriense Marine Band (Glb1) occurring about 0 to 7 m and 12 to 22 m above the top of the Huddersfield White Rock, respectively. The succession above the C. cumbriense Marine Band varies in thickness from 10 to 25 m and broadly coarsens upwards into siltstone and fine-grained sandstone, passing gradationally into the Rough Rock Flags. A nonmarine bivalve band, interpreted as the Anthraconaia bellula band, and a Lingula band were recorded in the Sandoz Chemical Company Borehole, approximately 17 and 19 m above the C. cumbriense Marine Band, respectively (Hudson and Dunnington, 1939).

The Rough Rock Flags (RF), of Yeadonian age, range in thickness from 1 to 32 m, the variation possibly reflecting different levels of erosion at the base of the overlying Rough Rock or the difficulty of determining the base of the markedly gradational Rough Rock Flags. The Rough Rock Flags comprise grey, commonly weathered ochreous, fineto medium-grained, (or more rarely coarse-grained) micaceous sandstone; large cross-bedding sets several metres thick are present in many places. The sandstones may also display, ripple cross-lamination and abundant Pelecypodichnus traces. Syndepositional faults have been described locally (Waters et al., 1996a). The unit is interpreted as minor distributary channel sandstones deposited in lobate shallow-water deltas, with palaeocurrent flow towards the south and west (Bristow, 1988).

The Rough Rock (R), of Yeadonian age, is estimated to be about 12 to 30 m thick. It is grey but weathers to an ochreous colour, and comprises coarse- to very coarse-grained (or medium-grained in parts), massive or crossbedded, feldspathic sandstone with small pebbles, predominantly of quartz. The base of the Rough Rock is commonly erosive with numerous Calamites logs present toward the base, with the Rough Rock generally resting directly upon the Rough Rock Flags. Locally, where the Rough Rock and Rough Rock Flags are lithologically similar, the base of the Rough Rock can be difficult to distinguish from other internal erosion surfaces. In the east of the district, a thick mudstone succession, up to 8 m thick, is locally recorded between the Rough Rock Flags and Rough Rock. The Rough Rock is interpreted as a widespread, multi-storey and multi-lateral fluvial sheet sandstone with a sharp, slightly channelled erosion surface at the base. It is interpreted as a braided river deposit which in the Bradford area had a palaeocurrent direction towards the south (Bristow, 1988). The Rough Rock is overlain by the Pot Clay Coal (0.1 to 0.2 m thick) locally referred to as the Cottingley Crow or Thin Coal, and an associated fireclay, 1 to 3 m thick.

Key localities:

Chapter 4 Westphalian

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, the pattern of sedimentation described for the Millstone Grit continued, but with increasing dominance of shallow water deposits. In general, sedimentation kept pace with the subsidence of the Pennine Basin, with major faults playing a periodically important role. In the early Langsettian (Westphalian A), deposition was in a shallow-water delta/lower delta-plain environment, passing gradationally into upper delta plain conditions in the late Langsettian (Westphalian A). Periods when the area was above sea level and land floras were abundant became more frequent and more prolonged, resulting in complicated patterns of coal seam development. Conversely, marine incursions onto the delta plain became less frequent and less prolonged, resulting in only two Westphalian marine bands being recognised in the district. The nature of sedimentation in the Coal Measures is described by Guion and Fielding (1988) and Guion et al. (1995). Chisholm (1990) provides a more specific description of depositional environments for the sequence between the Upper Band (80 Yard Coal) and Better Bed in the central and south Pennine area.

Coal Measures

The Coal Measures present in the district consist of about 310 m of interbedded mudstone, siltstone and sandstone, with subordinate coal, seatearth and ironstone, deposited in cyclic sequences about 310 million years ago. Stephens et al. (1953) provide a detailed account of the geology of the Coal Measures, with descriptions of localities and regional variations within the district. Their stratigraphical nomenclature has been amended here.

The Coal Measures are divided for convenience into Lower, Middle and Upper divisions; only the Lower Coal Measures (LCM), of Langsettian (Westphalian A) age, (Ramsbottom et al., 1978) 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

Typically, the mudstones are grey to black, weathering to orange-brown, mottled pale grey, planar laminated and micaceous or massive; commonly they contain nonmarine bivalves (Figure 4) that may be used as chronostratigraphical indicators. The Langsettian (Westphalian A) contains three nonmarine bivalve chronozones, in ascending order, the Lenisulcata, Communis and Modiolaris chronozones (Trueman and Weir, 1946). Ironstone nodules are common, ranging in size from a few millimetres to tens of centimetres in diameter. The mudstones are commonly overlain gradationally by siltstones.

The siltstones are typically medium grey and contain plant debris. They grade both vertically and laterally into sandstones and mudstones, and are commonly interbedded with both. Sedimentary structures include flaser and lenticular bedding, ripple cross-lamination and parallel lamination.

The sandstones commonly form positive, mappable, topographical features, and are thus distinguished on the map from the mudstones and siltstones that are shown as Lower Coal Measures (undivided). As a generalisation for the area, the sandstones in the lower part of the Lower Coal Measures are thin and laterally impersistent, whereas in the middle and upper parts of the sequence there are a number of thick, laterally persistent sandstones (Figure 4). The sandstones are mainly fine grained, varying from very fine to medium grained, and comprise subangular to subrounded quartz and feldspar 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, especially on micaceous bedding surfaces. Trace fossils may be present in Coal Measures sandstones. The commoner Upper Carboniferous ichnofacies has been described by Eager et al. (1985).

Seatearth is the name given to palaeosols which developed during a period of subaerial exposure and floral colonisation. They are developed in all lithologies, being referred to as ganister when developed in sandstone and fireclay when formed in mudstone. They are characterised by the presence of rootlets, commonly Stigmaria. In general, the pedification has destroyed primary sedimentary structures.

Coal seams are extensive, many being developed on a regional scale, but 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 (Table 3).

Marine bands are thin beds of black mudstone with a marine fauna, which commonly overlie coals or seatearths. They are generally a few centimetres thick, but may rarely attain thicknesses of 2 to 3 m. They commonly grade upwards into grey or black mudstones and siltstones with a nonmarine fauna. Marine bands can be recognised across large areas, representing eustatically controlled flooding events and are thus important isochronous marker horizons. Two marine bands are recognised in the district, the Subcrenatum and Listeri Marine Bands, although a number of Lingula bands have been proved which may correlate with marine bands found elsewhere in the Pennine Basin. Marine band faunas are discussed more fully by Calver (1968).

The base of the Lower Coal Measures succession occurs at the base of the Subcrenatum Marine Band (SMB), formerly known as the Pot Clay Marine Band, which varies from 0.9 to 3.7 m thickness in the district. This is overlain by 8 to 25 m of a mudstone-dominated, poorly exposed succession, with a nonmarine bivalve band recorded about 5.5 m below the Soft Bed Coal. The mudstone succession is, in turn, locally overlain by the Soft Bed Flags (SBF), which are thin and laterally impersistent. Typically, the flags vary from 0 to 8 m in thickness, but thicknesses of up to 15 m are recorded in the Horsforth area where two leaves are present. The Soft Bed Flags comprise fine-grained, commonly micaceous, thinly bedded, cross-laminated sandstone, passing laterally into siltstone. The top of the sandstone may be ganisteroid where present immediately beneath the Soft Bed Coal. The Soft Bed Coal (SB), lowest worked coal seam in the district, is typically between 0.4 and 0.6 m thick, but ranges from 0.2 to 0.9 m with its thickest development in the Shipley area.

The measures above the Soft Bed Coal, which are 3 to 11 m thick, are mudstone-dominated with several nonmarine bivalve-rich beds and a Lingula band. At the top of this succession, the Middle Band Rock (MBR) or Middle Band Stone is a laterally impersistent sandstone estimated to vary in thickness from 0 to 5 m. This is overlain by the Middle Band Coal (MB), a laterally impersistent coal which ranges from 0 to 0.2 m, too thin to be worked.

The sequence above the Middle Band Coal, estimated to be 6 to 13 m thick, is dominated by mudstones and siltstones, with the development of a thick seatearth, up to 2.6 m thick, immediately beneath the overlying Hard Bed Coal. A Lingula band has been described from the roof of the Middle Band Coal by Hudson and Dunnington (1940) and is interpreted as the equivalent of the Honley Marine Band. In the Clayton area, the Fairweather Green Borehole proves the interseam thickness to be 21 m; this local thickening is the result of the unusual presence of 8.8 m of thinly interbedded shale and micaceous flags (Hudson and Dunnington, 1940). The Hard Bed Coal (HB), locally referred to as the Halifax Hard Bed, varies in thickness from 0.5 to 1.0 m, with a thin mudstone parting recorded in the Denholme area. This coal was extensively worked across the area of Coal Measures outcrop.

The mudstone-dominated measures above the Hard Bed Coal range from 4 to 25 m. The coal is immediately overlain by the Listeri Marine Band (LMB), a 0.1 to 1.2m thick, black to dark grey, fissile mudstone distinguished by the presence of Gastrioceras listeri, commonly in association with Dunbarella and Posidonia. In the City of Bradford area, the marine band is recorded in the Sandoz Chemical Works Borehole as three distinct leaves within 3.4 m of shale (Hudson and Dunnington, 1939). The mudstone above the marine band is typically dark grey, micaceous with scattered ironstone nodule bands that become increasingly silty upwards. The mudstone succession is generally overlain by the Stanningley Rock (SR), or 32 Yard Rock, which is a laterally impersistent sandstone, and ranges in thickness from 0 to 29 m with the thickest development in the Horsforth area. In the west of the Coal Measures outcrop, the sandstone is relatively thin and is typically pale grey, fine to medium grained, micaceous, siliceous, thinly to thickly bedded, locally ripple crosslaminated, commonly with roots and a ganister top. In the Bingley and Shipley areas, the sandstone is commonly thicker; the lower part comprises medium sandstone beds with sharp tops and bases, interbedded with medium grey mudstone and siltstone beds, locally bioturbated or slumped. A thin coal seam (0.12 m) about 4 m below the top of the Stanningley Rock was recorded in the Shipley area in a borehole for the Manningham Storm Sewage. This may equate with the Hard Bed Band of the Huddersfield district (Wray et al., 1930), which, because of its proximity to the 36 Yard Coal, has often resulted in the two coals to be mistakenly considered synonymous. Consequently, the sandstone mapped in many places as Stanningley Rock may belong to two separate cycles, and would have been mapped as two distinct sandstones but for the paucity of field evidence. In the Shipley, area up to 6 m of strata, dominantly mudstone and siltstone, occur between the Stanningley Rock and the overlying 36 Yard Coal, and includes a Lingula band interpreted as the equivalent of the Parkhouse Marine Band. The 36 Yard Coal (36Y), or 36 Yard Band Coal, varies in thickness from 0 to 0.6 m with the thickest development in the Clayton area. The 36 Yard Coal was generally too thin to be economic to work at depth, although the underlying fireclay was formerly worked in the Clayton and Shipley areas.

The measures immediately above the 36 Yard Coal comprise a mudstone and siltstone dominated sequence, 8 to 25 m thick, with a locally thick sandstone present at the top of the cycle. A Lingula band with associated Teichichnus trace fossils was proved in the roof of the 36 Yard Coal in Manningham Storm Sewage System Boreholes and is interpreted as the equivalent of the Meadow Farm Marine Band. A nonmarine bivalve band is recorded 5 m above the 36 Yard Coal in the Sandoz Chemical Borehole (Hudson and Dunnington, 1939). The 48 Yard Rock (48YR) is a sandstone that is fine grained, cross-bedded and crosslaminated, micaceous, and commonly rooted. The sandstone is upward-coarsening with a gradational base. The thickness is estimated to range from 0 to 19 m, the thickest development being on Baildon Moor. The 48 Yard Rock is locally overlain by the 48 Yard Coal (48YC), up to 0.2 m thick, with associated seatearth.

The 48 Yard Rock is overlain by about 5 to 22 m of mudstone and siltstone. A nonmarine bivalve band, interpreted to be the Laisterdyke Shell Band of Eagar (1956), has been proved in the Manningham Storm Sewage System boreholes and the Sandoz Chemical Works Borehole. The argillaceous succession is locally overlain by the 80 Yard Rock (80YR), mistakenly equated with the Gaisby Rock by Stephens et al. (1953). This sandstone is 0 to 15 m thick, with the thickest development in the Bingley and Clayton areas. In the Shipley and City of Bradford areas, the 80 Yard Rock is considered to be absent or thin (about 1.5 m thick). The 80 Yard Rock is locally overlain by the 80 Yard Coal (80YC), up to 0.4 m thick in the Lowroyd Dyeworks Borehole, but it is commonly absent in the district. More typically only the associated seatearth is found.

The 80 Yard Rock is overlain by an argillaceous succession about 10 to 40 m thick, although locally in the Shipley area the base of the Elland Flags appear to be at a stratigraphically low level and the 80 Yard Rock is postulated to be absent. The Elland Flags (EF) comprise up to four thick sandstone leaves separated, predominantly, by mudstone; the total thickness is estimated at 35 to 72 m. The sandstone is generally fine grained, micaceous and parallel bedded or cross-bedded and has been extensively quarried for flagstone and locally mined (Godwin, 1984). The main quarries are typically present within the thick lower leaf (Plate 2) which east of Bradford Beck, in the Shipley area, has been locally referred to as the Gaisby Rock. This lower leaf commonly comprises a lower planar laminated and bedded part with a strong primary current lineation, possibly deposited in a proximal mouth bar. It is overlain by a dominantly trough cross-bedded sandstone with marked internal erosion surfaces, possibly deposited within channels (Waters et al., 1996a). At Bolton Woods Quarries, the lower leaf is overlain by up to 1.8 m of mudstone with a thin coaly mudstone, up to 0.15 m thick, which fails in the northern part of the north quarry. This coaly mudstone was considered by Stephens et al. (1953) to be the 80 Yard Coal and hence that the underlying Gaisby Rock was the equivalent of the 80 Yard Rock. This interpretation is now discounted, and the unnamed coaly mudstone is considered to be only present locally. The upper part of the Elland Flags comprise several sheet-like sandstones with parallel lamination and bedding and crossbedding, interbedded with micaceous, silty mudstones and siltstones, commonly parallel laminated.

The measures above the Elland Flags comprise a mudstone-dominated succession with a total thickness of 40 to 60 m, with two lithologically distinct sandstones, the Greenmoor Rock and Grenoside Sandstone. Both sandstones were formerly referred to as leaves of the Elland Flags (Stephens et al., 1953), although Chisholm (1990) and Chisholm et al. (1996) have demonstrated the correlations with sandstones in the southern Pennines. Typically, a few metres above the uppermost sandstone of the Elland Flags there is a change in the nature of the argillaceous rocks from typically neutral grey, micaceous mudstones present immediately above the Elland Flags to a greenish grey, poorly micaceous mudstone. This is interpreted as a primary feature associated with sedimentation from distinct sources (Chisholm, 1990; Chisholm et al., 1996); however, because of the paucity of exposure it was not possible to map these greenish grey mudstones as a distinct member. The greenish grey mudstones are overlain in places by laterally impersistent Greenmoor Rock (GN). This is a very fine-grained, greenish grey, poorly micaceous sandstone, with current and wave ripples and burrows. It occurs as one or two leaves up to 6 m thick, and is commonly overlain by a well-developed seatearth. The top of this cycle is marked by a thin coal seam, equivalent of the Dibhole Coal of Lancashire, which is only proved in the district in the CWS Creamery Borehole (Figure 4).

The succession above the Greenmoor Rock is marked by 4 to 10 m of medium to dark grey, micaceous mudstone and siltstone, coarsening upward into the Grenoside Sandstone (GR). This sandstone, estimated to be 7 to 16 m thick, is typically micaceous, fine grained and cross-laminated or cross-bedded. The Better Bed Coal (BB) is present up to 10 m above the top of the Grenoside Sandstone, and ranges in thickness from 0.2 to 0.9 m. The coal occurs at outcrop in the City of Bradford area, and in a graben at Bolton Outlanes [SE 17 20].

The succession above the Better Bed Coal is up to 35 m thick. It includes the Thick Stone (TS), a fine-grained, thinly bedded sandstone, 0 to 16 m thick. Regionally, the Thick Stone occurs only between the Better Bed Band (a thin coal that is present above the Better Bed Coal but has not been proved in the district) and the Black Bed Coal. However, during this resurvey, it was not possible to identify two distinct cycles, and any sandstone present between the Better and Black Bed coals has been recorded as Thick Stone. The sandstone occurs at outcrop in the City of Bradford area and in a graben at Bolton Outlanes [SE 17 20]. The top of the cycle is marked by the Black Bed Coal (Bl), proved in boreholes to range from 0.5 to 1.1 m. The coal occurs at outcrop in the City of Bradford area and in two graben at Fairweather Green [SE 12 33] and Girlington [SE 14 34].

The Black Bed Coal is overlain by an argillaceous succession about 5 to 15 m thick. The Black Bed Ironstone rests directly on the coal; it comprises 3.6 m of alternating shale, 0.1 to 0.3 m thick, with ironstone beds and nodules between 1 and 3 cm thick (Green et al., 1878). Locally, in the City of Bradford area, the ironstone may be absent where a laterally impersistent unnamed sandstone (up to about 3 m thick) is present above the Black Bed Coal. The sandstone is directly overlain by the Crow Coal (Cr). This coal is proved to occur as two leaves, a total of 0.3 m thick, at Broomfields [SE 172 323], and from mine plans it occurs at outcrop in a graben at Fairweather Green [SE 12 33].

The argillaceous succession above the Crow Coal is estimated to be 25 m thick, and in the Huddersfield district includes two thin coals, the 22 Yard and 32 Yard coals (Wray et al., 1930), neither of which have been proved in Bradford. The uppermost sandstone in the district is the Clifton Rock (CR), or Oakenshaw Rock. Regionally, this occurs in two leaves, although in the Bradford district, only the lower leaf and part of the intervening mudstone are proved. The sandstone, which is not exposed in the district, occurs at outcrop at Bowling [SE 18 32] and Scarr Hill [SE 18 34]; the lower leaf is estimated to be 10 m thick.

Key localities:

Chapter 5 Quaternary

About 60 per cent of the district is covered by drift (natural superficial) deposits. This includes glacial deposits, such as till, hummocky (moundy) glacial deposits, glaciolacustrine deposits and glaciofluvial deposits, and periglacial or postglacial deposits, such as head, peat, alluvium, alluvial fan deposits, river terrace deposits and landslips. The limits of the deposits have been taken as those defined during the previous geological survey of the district, unless data collected during this resurvey have revealed errors in the pre-existing geological maps. The new data may include field observations, such as recent open sections, topographical features and auger holes, or available borehole data.

Quaternary history

The present-day topography is largely the result of glacial processes active during the Pleistocene. The district has probably been affected by glaciation at least three times during the Pleistocene, although evidence for earlier phases has been obliterated by the final, Devensian, phase. During the Devensian cold stage, land was exposed to periglacial weathering beyond the limits of the ice sheet which built up in the Lake District and southern Scotland. The intense cold caused shattering and weathering of rock due to freezethaw processes and the development of permafrost conditions in the subsoil. Temporary thawing of the ground surface during the short summers resulted in water-saturation of the products of weathering, which could then flow downhill over the still frozen subsoil to form head deposits.

The maximum southward advance of the Devensian ice sheet reached a line approximately crossing the south of the district (Figure 5). During the maximum advance of the ice, glaciers would have covered both valleys and upland areas. However, for much of the time, at the southern margin of the ice sheet, glaciers would have occupied only areas of low ground, such as the Aire and Wharfe valleys. Dramatic fluctuations in temperature, as identified from studies of the flora and fauna present in peat at Bingley Bog [SE 115 386] (Keen et al., 1988), would have caused the valley glaciers to advance and retreat several times during the late Devensian.

The valleys of the modern Rivers Wharfe and Aire broadly coincide with buried, drift-filled channels, locally in excess of 50 m deep (Figure 5). These channels are obscured by a cover of alluvium, but are proved from borehole data to be filled with a complex interdigitation of glaciofluvial sand and gravel, glaciolacustrine silt and clay and till, occupying a channel with a U-shaped cross-section and an elliptical longitudinal profile. These channels probably formed by either glacial scouring and subsequent infill with outwash material and sediments deposited in temporary lakes, or in response to subglacial erosion by meltwater under high hydrostatic pressure at the base of the glacier. In addition to these large buried channels, there are a series of smaller late-glacial, meltwater channels present in the valley sides and upland areas. These have been recognised by Jowett and Muff (1904) and Stephens et al. (1953) throughout the district, but are particularly common in an arc from west of Keighley to Bradford and Shipley (Figure 5). These features, commonly termed ‘glacial overflow channels’, typically have a broad east-west to northwest trend, approximately parallel to the Devensian ice front. The channels usually have steep sides and flat bottoms, locally bifurcate and commonly start and end abruptly (Plate 3). Most meltwater channels have been abandoned and are dry or contain only small ‘misfit’ streams, incapable of eroding such large valleys. Jowett and Muff (1904) and Stephens et al. (1953) considered that the channels represent overspills from glacier-dammed lakes. Alternatively, as for the buried channels of Airedale and Wharfedale, these channels may have developed due to erosion by subglacial meltwater.

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. In Wharfedale, three terraces and their associated surface deposits have been recognised (Price et al., 1984), in contrast to Airedale, where only a single river terrace is recognised (Stephens et al., 1953). The terraces represent fluvial depositional surfaces which have become isolated on valley sides due to repeated entrenchment of the river systems during the Flandrian. Alluvium represents the alluvial deposits of the current floodplain level. In abandoned meltwater channels, thin deposits of lowland peat accumulated, whereas more extensive, although thin, upland peat deposits accumulated on the moors in the west of the district. Landslips are a common feature of the district, occurring in both bedrock and drift deposits. Some landslips may have been initiated during the late stages of the Devensian glaciation, although many are Flandrian in age, and some landslips are still active. Artificial (man-made) deposits are mostly associated with the Industrial Revolution and subsequent development of the district.

Glacial deposits

Till (boulder clay) is the main glacial deposit in the district, forming extensive, featureless spreads, generally less than 5 m in thickness. Price et al. (1984) recognised several different types of till in Wharfedale, and it is probable that these occur widely across the district, with variations in the types of boulders found dependent upon local differences in the underlying bedrock. Lodgement till, which was plastered beneath a moving glacier, comprises stiff, overconsolidated, blue-grey clay with scattered, subrounded, pebbles and cobbles of Millstone Grit or Coal Measures sandstones and Carboniferous limestones. Drumlins, which are mounds of lodgement till elongate parallel with the direction of ice flow, have been recognised in the district only along the eastern margin of Rombalds Moor, from Burley-in-Wharfedale to Menston. Flow till formed by the mass movement of glacial debris following release from the glacial ice; commonly, it comprises brown sandy clay with angular sandstone fragments and may show crude bedding or flow lamination. Deformation till, which formed by squeezing or pressing of glacial debris at the base of the glacier, usually overlies strongly weathered mudstone bedrock, and comprises a firm to very hard clay with abundant mudstone fragments. Melt-out till formed from the slow release of glacial debris during glacial melting and retreat. It is normally consolidated, comprising unsorted sandy, silty boulder clays. Owing to the lack of natural sections and insufficient information recorded in most borehole records, no subdivision of the till has been shown on the map.

Hummocky (moundy) glacial deposits form circular or elongate mounds of drift, comprising an unsorted mass of boulders and cobbles in a variably sandy or clayey matrix. These deposits are difficult to distinguish from till, with which they are commonly associated. During the resurvey they were distinguished from the featureless sheets of till by their prominent hummocky topographical features. The majority of these deposits are interpreted as terminal or lateral moraines (Figure 5) that formed at an active ice front. 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. However, hummocky features can also result from the melting of masses of stagnant ice, which may remain within till deposits for some time after the retreat of the main glacier. Hummocky (moundy) glacial deposits occur both in the main valley bottoms, especially the valley of the River Aire, and in upland areas in the vicinity of Wilsden [SE 08 36] and Keighley Moor [SD 98 39]. At Bingley [SE 113 387], these deposits contain many limestone boulders, formerly worked for lime production.

Glaciofluvial deposits occur as small isolated patches, from Oakworth Moor [SE 01 40] to Leaventhorpe [SE 12 33], and are present both in valleys and on plateaux. Further deposits have been proved in boreholes to occur in the buried channels present in the valleys of the rivers Aire and Wharfe. The deposits comprise bedded sands and gravels, with some thin, laterally impersistent beds of clay. The sand and gravel deposits which form sheets on the plateau between Haworth and Cullingworth [SE 060 354] and [SE 050 366] probably represent outwash deposits (Stephens et al., 1953). Deposits present at the foot of glacial meltwater channels, for example at Leaventhorpe, are interpreted by Jowett and Muff (1904) and Stephens et al. (1953) as lake delta deposits, but an origin as subglacial deposits cannot be discounted.

Glaciolacustrine deposits outcrop only at Bingley [SE 10 40], although they have been proved to occur extensively beneath the alluvium and river terrace deposits of the rivers Aire and Wharfe, occupying buried channels. In the Keighley area, there is up to 42 m of silty clay and silt; sand laminae are common, small stones are rare and are interpreted as dropstones released from melting ice masses present on the lake. Late Devensian to early Flandrian lacustrine deposits are proved  at Bingley South Bog [SE 115 386] to comprise about 7 m of silty and sandy, calcareous mud (Keen et al., 1988). In Wharfedale, boreholes show the glaciolacustrine deposits to comprise finely laminated clay with grain-thick silty partings or rhythmic graded sequences of fine sand, silt and clay (Price et al., 1984). Glaciolacustrine deposits are laterally impersistent, interdigitating with till and glaciofluvial deposits. In both Airedale and Wharfedale, they were probably deposited in small lakes dammed by terminal moraines. However, some may have been deposited in kettle holes, small circular depressions formed from the melting of stagnant ice masses within till, for example Bingley South Bog (Keen et al., 1988).

Glacial to postglacial deposits

Head is a poorly consolidated deposit derived by slow downhill movement, under the influence of gravity, of drift deposits or weathered bedrock. It may develop in response to solifluction and/or colluvial processes. Colluvial processes of hill creep and hill wash are locally active at present. Head is an unsorted deposit, commonly a diamicton, the composition of which closely reflects that of the upslope source material. The deposits may be difficult to distinguish from weathered bedrock or till, particularly in borehole records. Head is probably widespread throughout the district, but has been mapped only where it exceeds 1 m thickness, and where it is readily distinguishable from either weathered bedrock or till. The deposits have accumulated in hollows or at the bases of steep slopes, such as below the scarp of the Rough Rock in the Aire valley [SE 103 394].

Landslips are a common feature of the district, particularly on the steep north-facing slopes of Airedale and Wharfedale, especially between Keighley and Bingley and in the vicinity of Ilkley. Landslips are also common in a number of small tributary valleys, including the Worth valley, Newsholme Dean, around Silsden Reservoir and adjacent to Bradup Beck (Plate 4). Landslips have developed where natural slopes are steep (usually in excess of 10°), and in a number of different situations: for example where there is a thick cover of glacial till or deeply weathered mudstone, where a permeable water-bearing sandstone capping an impermeable mudstone dips into a valley, where a fault is associated with extensive fracturing of mudstone, and in the presence of springs or seeps. These are also conditions susceptible to future landslipping.

Scree, or talus, deposits have been mapped on the steep slopes of the western flanks of Farnhill Moor [SE 005 475]. The deposits accumulated as rockfalls from crags in the Warley Wise Grit.

Postglacial deposits

River terrace deposits are principally found in the valleys of the rivers Wharfe and Aire. In Wharfedale there are three river terraces. The Third and Second River Terraces are present as discontinuous features in the vicinity of Burleyin-Wharfedale, occurring between 3 and 12 m, above the present floodplain (Price et al., 1984). Although the Third and Second river terraces are mappable features, the associated deposits are proved by borehole and geophysical data to be very varied, and are difficult to distinguish from underlying till (Price et al., 1984). The First River Terrace of the River Wharfe forms laterally continuous features at Ilkley and Addingham, occurring 3 to 9 m above the present floodplain. The deposits associated with this lowest terrace include silt and sand with gravel lenses. In Airedale, only isolated areas of First River Terrace have been identified, at Steeton [SE 040 445] and Esholt [SE 19 39]. This terrace is associated with sand and gravel deposits. Locally, in Harden Beck [SE 098 382], two terraces are present, occurring about 2 and 4 m above the floodplain.

Alluvial fan deposits have been recognised where the River Worth meets the River Aire, at Keighley. The deposits form a triangular fan, with the apex present in the Worth valley at Ingrow [SE 060 402]. The surface of the deposits falls gently towards the north-east, from 110 m OD at Ingrow to 85 m OD at Aireworth [SE 072 418]. The deposits are proved in boreholes to comprise sand and gravel, up to 17 m thick. A similar, although much smaller, alluvial fan occurs where Holden Beck flows into the River Aire [SE 050 445].

Alluvium is present as wide, laterally persistent spreads in Wharfedale and Airedale, and as small, discontinuous, thin strips in their tributary streams. These deposits are typically heterogeneous. In Wharfedale, the deposits comprise brown silt and fine sand with gravel lenses; organic clay lenses at the floodplain margins represent former oxbow lakes (Price et al., 1984). Similar deposits have been proved by boreholes in the Aire valley.

Peat deposits occur in both lowland and upland locations in the district. Lowland peat forms small, thin, isolated patches within poorly drained, enclosed hollows, such as Bingley South Bog [SE 115 386], and in glacial meltwater channels, such as at Pitty Beck [SE 08 34]. At Bingley South Bog, the peat ranges in thickness up to 3.1 m, resting directly upon glaciolacustrine deposits, and is proved to be of Flandrian age (Keen et al., 1988). Wide spreads of peat also occur beneath alluvium in the Aire valley, west of Bingley. Upland peat forms extensive, thin veneers on the moorland areas in the west of the district, such as Keighley and Oxenhope moors. Upland peat accumulates in areas of acid soils through the decomposition of dead plant material, under conditions of relatively low temperatures, poor aeration due to waterlogging, and low evaporation rates. Upland sandstone escarpments are relatively well drained and vegetated with heather, and the peat rarely exceeds 1 m in thickness; in many places it forms only a dark peaty soil. Where mudstone or till occur at outcrop in moorland areas, the area is generally poorly drained, vegetated with sphagnum moss or cotton grass, and peat may exceed 1 m thickness and thicknesses of up to 3 m have been recorded at Will’s Allotment [SE 021 328]. The extent of the deposits was determined from aerial photographs, used in conjunction with field mapping and auger holes. The peat mapped during this resurvey is significantly reduced in comparison with that of the previous survey which showed extensive areas of peat less than 1 m thick. Also, since the previous survey there has been active erosion to form a network of gullies, or ‘haggs’, up to 3 m deep. Peat was also formerly worked in the west of the district, often with detrimental effects to the moorland floral and faunal habitats, for example Stake Hill [SE 02 33]. Peat working, heather burning and air pollution may all contribute to increased peat erosion and reduction in the extent of the deposits.

Artificial (man-made) deposits

The long history of industrial development in the district has left an extensive legacy of human modification of the natural environment. 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.

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 constructions such as road and railway embankments and reservoir dams; spoil from mineral extraction industries such as colliery and quarry spoil; building and demolition rubble; waste from heavy industries such as foundry sand, slag from ironworks, ashes and cinders from textile mill boilers; domestic and other waste in raised landfill sites, including those occupying topographical depressions such as glacial meltwater channels, for example Sugden End [SE 050 374]. The most extensive areas of made ground are in the main urban centres of Bradford, Shipley, Bingley and Keighley. In these areas the topographic features associated with specific areas of made ground, especially colliery spoil, have been smoothed over prior to development. Construction has commonly taken place on compacted rubble and deposits left by previous uses. 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 been used in the district for the disposal of waste materials, and some, quarries have been partly filled with spoil after the cessation of mineral extraction. However, in most cases quarrying operations produced voids suitable for infilling with imported waste. 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 backfilled 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, but these areas shown 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 indicated where ill-defined, surface mineral workings include a complex association of excavations, subsidence induced by near-surface mineral workings and made ground, for example areas of bell pits and shallow mine workings at Baildon Moor [SE 14 40], and Rough Holden [SE 07 45]. Landscaped ground has not been mapped during this resurvey. It comprises areas where the original surface has been extensively remodelled, and it is impractical or impossible to delineate areas of cut or made ground. This category is associated with constructional developments such as housing estates or golf courses. It should be assumed that landscaped ground is a feature of most areas of urban development.

Chapter 6 Concealed geology and structure

In earliest Carboniferous times a collision-type orogenic belt developed in the Iberian–Armorican–Massif Central region. Northward subduction of the Rheic Ocean led to regional back-arc extension and the development of a major Dinantian rift basin system in northern England (Leeder, 1982). Extension was much diminished in Namurian and Westphalian times and a regional ‘post-rift’ or ‘sag’ basin developed. In latest Carboniferous times (about 290 million years ago), closure of the Rheic Ocean occurred during the Variscan Orogeny, with large-scale thrust and nappe emplacement in Belgium, northern France and southern Britain. On the foreland to the north of the Variscan Foldbelt, deformation was much less pervasive, and in northern England it was largely restricted to partial reversal of the basin-controlling normal faults that had developed during the Dinantian, and associated folding, basin inversion and regional uplift.

Structure of the Carboniferous rocks at outcrop

The district occurs 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. Kilometre-scale open folds are present in the northwest and north of the district in a structural zone referred to as the Ribblesdale Fold Belt (Arthurton, 1984). The folds are commonly asymmetrical with steep inversion on the north-western limbs. In the north-west the folds have dominantly north-east-trending axes. The Lothersdale Anticline, which largely crops out in the Clitheroe district (Earp et al., 1961), extends into the Bradford district and is truncated to the east by the South Craven Fault. Also with north-east trending fold axes, but present to the north-east of the South Craven Fault are the Skipton Anticline, the Bradley Syncline and Bradley Anticline. The Bradley Syncline and Bradley Anticline occur parallel with and, respectively, to the north-west and south-east of the north-east-trending Bradley Fault. Folds with north-east-trending axes extend across the southern part of the Pateley Bridge district (Jones, 1943). The southernmost of the anticlines, the Norwood Anticline, which is present on the northern margin of the Bradford district, has an east-trending fold axis whose crest is coincident with a ridge of Warley Wise Grit. This structure appears to be a continuation of the north-east-trending Harrogate Anticline present in the Harrogate district (Cooper and Burgess, 1993). The folds of the Ribblesdale Fold Belt developed in response to Dinantian to early Namurian dextral shear on the faults of the Craven Fault System (Arthurton, 1984).

Smaller scale folds (10 to 100s m across) are tighter, and were caused by the ‘drag’ of strata against fault planes during fault movement. Dips of up to 50° are common in the vicinity of major faults, such as close to the Denholme Clough Fault.

The district has been affected by extensive faulting, with dominant fault trends at outcrop of north-west to east-west; subordinate faults show a north-east trend. The faults display dominantly normal and strike-slip displacement. They are considered to be, in part, late Carboniferous features, but with further tensional movements during Permo-Triassic and later Mesozoic times. Possible Palaeogene compressive stresses may have resulted in reactivation of many of the faults. The north-west-trending Aire Valley Fault and west-trending Hewenden Fault appear to mark the northward continuation of a major linear structure, the Morley–Campsall Fault, which is thought to have had a history of dominantly strike-slip displacement (Giles, 1989). Slickenside striae found on exposed north-west-trending fault planes are invariably subhorizontal. The main faults affecting Carboniferous strata are described in (Table 4), with the amount of downthrow at surface estimated from field relations in most cases. Dramatic thickness variations within the Millstone Grit across the Denholme Clough Fault, in the area of Oxenhope, suggest syndepositional movement on the fault during Kinderscoutian and Marsdenian times.

Faults may occur as a single discrete plane, or as a zone up to several tens of meters 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. Only rarely are faults exposed in the district; their position may be based on the interpretation of topographical features, surface outcrops, site investigation data and underground mining data. Whatever the evidence, it is rarely sufficient to locate a fault precisely. In areas of thick and extensive superficial deposits, the positioning of faults relies almost entirely on projection from underground mining information.

Concealed geology

In the Bradford district, the Dinantian extensional basin system is largely concealed by Namurian and Westphalian post-rift strata. Seismic reflection data show the subsurface basin architecture to comprise a mosaic of fault-bounded tilt-blocks bounded by large east-north-east-trending syn-rift normal faults, with throws commonly of several hundred meters (see Base Dinantian structure-contour inset on Sheet 69 Bradford, Solid Geology). These structures do not correspond in a simple way to the dominantly west-northwest to north-west-trending faults mapped at surface in Namurian and Westphalian rocks. These latter faults are typified by the Gargrave–Aire Valley–Morley–Campsall fault system which may overlie a pre-existing basement structure. Surface displacements of the north-west-trending faults are generally small compared to the subsurface displacements of the east-north-east-trending basin-controlling syn-rift faults, nevertheless there is evidence that the former acted as transfer structures during extension, effectively compartmentalising strain on the larger normal faults.

The Bradford district is located in the Harrogate Basin (Figure 6) occurring to the east of the Bowland Basin and offset from it by the South Craven–Morley Campsall Fault System (Kirby et al., 1994). The basin is interpreted as a south-west-shallowing asymmetrical graben. To the north it is separated from the Askrigg Block by the North Craven Fault. To the south, the basin is bound by the Central Lancashire High and Askern–Spittal High (Kirby et al., 1994).

The pre-Carboniferous basement is assumed to comprise Lower Palaeozoic rocks deformed during the Caledonian orogeny. Basement depths are less than 2500 m on fault bounded horsts, such as the Bingley and Central Lancashire highs. These syn-rift structures are characterised by relatively thin Dinantian sequences dominated by platform carbonates (see Horizontal-section Sheet 69 Bradford Solid). Elsewhere, thicker, more basinal Dinantian sequences are found, typified by the Harrogate Basin in the north-east of the district and the Bowland Basin in the far north-west, where basement depths are considerably greater than 3000 m. The post-rift (Namurian and Westphalian) strata of the district are also dominated by west-north-west and northwest-trending faults (see Base Namurian structure-contour map Sheet 69 Bradford Solid). Some of these may have been active as Dinantian transfer faults, while others may have a Variscan or even younger origin. Other major Variscan structures comprise east-north-east-trending folds and reverse faults belonging to the Ribblesdale Foldbelt. These are 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 of the district by the south-western extremity of the Harrogate Anticline. 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.

Seismic interpretation

A horizontal section interpreting seismic reflection data is shown on the solid edition of Sheet 69 Bradford. The base of the Dinantian is not everywhere well resolved, particularly in the southern part of the section, but the gross subsurface structural configuration can nevertheless be discerned. The northern half of the cross-section traverses the western part of the Harrogate Basin, which here forms a southward-deepening tilt-block. The syn-rift Dinantian sequence here has a mostly basinal aspect, and appears to thicken southwards (down-dip) from about 1600 m at the northern end of the cross-section to more than 2000 m thick in the central part. South of this, on the Bingley High, the Dinantian succession is much thinner (about 1300 to 1500 m thick) and is characterised by platform carbonates, principally of Chadian age, which build out northwards into the Harrogate Basin (Evans and Kirby, 1999).

The post-rift Namurian and Westphalian successions are of more uniform thickness along the line of section, but with a slight southward stratigraphical thinning. This principally affects lower Namurian strata where the Millstone Grit units show particularly significant southward thinning and pinch out. The cause of this thinning is uncertain, but may relate to differential compaction of the underlying Dinantian sequence during burial. Thus, the thin platform carbonate succession of the Bingley High would show less compaction than the thicker sequence of the Harrogate Basin, providing less depositional space for the overlying Namurian sequence. This effect would gradually diminish with time.

A number of faults are shown on the cross-section. These have mostly normal displacements which decrease markedly upwards. It is evident that the faults were principally associated with Dinantian block faulting, but nevertheless continued to move, albeit to a much lesser extent, in Namurian and Westphalian times. Some of the faults are associated with minor rollover ‘reverse-drag’ folding in their hangingwall blocks. Large-scale folding is restricted to the northwest end of the section which impinges onto the southern limb of the Skipton Anticline, a major Variscan structure within the Ribblesdale Foldbelt. To the south-east of this, the much smaller Bradley Anticline forms an asymmetrical fold showing north-west vergence with evidence of minor reverse faulting in its (steeper) north-western limb (mapped at surface as the Bradley Fault). It is likely to have resulted from Variscan reverse reactivation of underlying southeast-dipping normal faults. 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.

Geophysical interpretation

The Bouguer anomaly map (inset map Sheet 69 Bradford Solid Geology) shows gravity highs to the north-west and south-west of the district; these decrease eastwards to form a central low at the eastern margin. The highs may represent areas where denser pre-Carboniferous basement rocks occur relatively close to the ground surface. The gravity high in the north-west is associated with the Ribblesdale Foldbelt where Dinantian strata crop out; the high in the south-west occurs in the area of the Central Lancashire High. The general eastward decrease in values reflects the gradually increasing thickness of lower density Namurian and Westphalian rocks and, farther eastwards, Permian and younger rocks.

Superimposed on these main anomalies are anomaly gradients that generally correspond with the two main contrasting structural trends within the district. The linear northeast-trending gradients in the northern part of the district are associated with faults within the Harrogate Basin where lower density Namurian rocks within the basin are faulted against denser rocks, notably along the Pendle Fault. The main axis of the Harrogate Basin is marked by a gravity trough through the centre of the district. The north-west trending contours in the southern part of the district run parallel to the Aire Valley–Morley–Campsall Faults. In the extreme south-west of the district, the contours swing round to a north-south direction, parallel to the base-Dinantian structure contours within the Central Lancashire High, reflecting thinning of Namurian rocks towards the west.

The aeromagnetic anomaly map (inset map Sheet 69 Bradford Solid Geology) is dominated by an increase in values to the east, culminating in a north-west-trending high just to the north-east of the district. The source of this anomaly is probably due to the presence of a deep magnetic basement. Within the district, a contour ‘bulge’ superimposed on the flank of the broad magnetic high represents a magnetic source lying at a shallower depth than the deep magnetic basement. It is thought to be a continuation of the elongated north-west-trending magnetic anomaly present to the south-east of the district that is associated with the Morley–Campsall Fault. The magnetic anomaly over the Morley–Campsall structure continues as far north as the Pendle Fault, and persists to the south-east for a total distance of about 50 km. The source of the anomaly is not known, but it appears to have the form of a steeply dipping igneous body. A second north-west-trending magnetic anomaly to the south-west of the district is the northernmost extent of another persistent magnetic anomaly with the same trend as the Morley–Campsall anomaly.

Earthquakes

Geological faults in this area are of ancient origin and are currently mainly inactive. However, the 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 near Skipton, a depth of focus of about 13 km (Tillotson, 1974), and an inferred local magnitude of 4.8 (Musson, 1994). In northern England, historic seismicity has concentrated along the Pennine, Dent and Craven fault systems, with movement on the latter possibly causing the Skipton earthquake. 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 7 Applied geology

This chapter provides a brief insight into the earth science issues that should be taken into account by planners, developers and other interested parties involved in the planning and development process. Geological factors have had a significant role in the industrial expansion of Bradford and neighbouring towns. Former mining and quarrying activities 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 information 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 are 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. (1996b) as of particular significance in the City of Bradford Metropolitan District, which occupies much of Sheet 69 Bradford.

These are:

Mineral resources

Mineral resources present in the district are those minerals that can be won at or near to the surface, as the economics of underground mining are unlikely to be favourable in the future. The main factors hindering extraction are: significant thicknesses of overburden, including natural drift deposits and man-made deposits; sterilisation of resources by urban development; 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.

Sandstone is the principal mineral currently extracted in the district, and demand for this resource is likely to continue in the future. The sandstones of the Millstone Grit and Coal Measures of Yorkshire are marketed under the generic term ‘York Stone’. The main resources identified are those sandstones which have been historically, and are still being worked in the district, namely the Elland Flags, Rough Rock, Rough Rock Flags, Midgley Grit and Scotland Flags. These sandstones occur at outcrop across much of the central and south-east of the district. At the time of survey, there were 12 working sandstone quarries in the district (Waters et al., 1996; Cameron et al., 1998). The sandstones are very resistant to attack by acid rain water, although they readily discolour from buff to black when exposed to polluted atmosphere. Subtle differences in colour, texture and natural markings provide a range of attractive building stones suitable for walling, paving and cladding. Coarse-grained sandstones (`grits’), formerly worked for grindstones, pulpstones and millstones, are now worked for construction fill and occasionally for sand. In general, the sandstones are too weak, porous and susceptible to frost damage for them to be used for good quality roadstone or concrete aggregate. They may be used in road construction below the level of possible frost damage and for some of the less demanding concrete applications.

Sand and gravel resources in the district are relatively small, and limited to areas of alluvium, river terrace deposits and buried glaciofluvial deposits present in Airedale and Wharfedale. Alluvial gravels have been worked until recently for aggregate in the Wharfe valley; the last pit ceased operation in 1996 at Otley [SE 1946]. The deposits include alluvium and river terrace deposits comprising silt and fine sand with gravel lenses. These deposits may be underlain, locally, by glaciofluvial deposits, which in Wharfedale consist predominantly of gravel with sand lenses (Price et al., 1984). Small areas of glaciofluvial sands and gravels occur on the interfluves, and limited working of the sand has been recorded in the past. The principal uses of sand are as a fine aggregate in concrete, in mortar and in asphalt; the main use of gravel is as concrete aggregate. Sand and gravel is also used as a source of constructional fill.

Coal is no longer worked in the district, although its extraction was formerly of great importance to the industrial development of Bradford. Coal-bearing strata are almost entirely confined to the outcrop of the Coal Measures, which underlie the south and east of the district. Over much of this area the resource has been sterilised by urban development. The majority of coal was worked underground, either from bell-pits, adits or shafts. The coal seams range from 0 to 1.1 m in thickness; their former uses are indicated on (Table 3). The lowest Coal Measures coal seam, the Soft Bed Coal, was formerly worked because of its low sulphur content. The Hard Bed Coal has been extensively worked both at outcrop and in mines, despite having a high sulphur content. The Better Bed Coal has been extensively mined in the limited area where it is present in the district, and is noted for its low sulphur content. The Black Bed and Crow coals both have had a limited area of extraction to the south-east of the City of Bradford. A number of sites have been investigated as potential coal opencast sites though, as yet, none have come into operation.

Fireclays mainly occur in the Lower Coal Measures. Fireclays associated with the 36 Yard Coal and Hard Bed Coal were formerly worked in the Clayton and Denholme areas, largely for lining furnaces and making crucibles, the manufacture of salt-glazed pipes and sanitary ware. The only active fireclay workings are in the clay present beneath the Hard Bed Coal at the Dog and Gun quarry, Oxenhope [SE 093 343], where the bed is in excess of 1.1 m thick. This fireclay is used for the manufacture of refractory pots used for melting speciality glasses such as lead crystal glasses.

Brickclay is no longer worked in the district, and historically was only of minor importance because of the local availability of sandstone for building purposes. The generally heterogeneous character of the mudstones and till in the district limits their future use.

Peat occurs as thin veneers across parts of the upland areas of the district. Despite its thinness and limited extent, peat was formerly worked for fuel on a limited scale at Rombalds Moor [SE 101 462], Foreside [SE 056 318], Middle Moor [SD 991 346] and Oxenhope Moor [SE 021 331]. The historic extraction of peat has had a detrimental impact on the environment, leaving patches of ground comprising coarse sand and sandstone fragments without a soil horizon, hindering the re-establishment of vegetation cover. The peat is unsuitable for horticultural purposes, and anything more than limited working for fuel is unlikely.

Mine and quarry waste is present over much of the area of Coal Measures outcrop; it has been little utilised to date. The inert nature of sandstone spoil makes it ideal for bulkfill, in particular for the construction of road embankments. Colliery spoil, or mine stone, consists of shale, siltstone, sandstone, ironstone, waste coal and fireclay. Mine stone can be utilised as fill, although the use is limited and requires controlled usage. Detrimental effects to concrete foundations may result from the decomposition of disseminated pyrite to iron sulphate. Waste coal or carbonaceous matter may generate methane and possibly undergo combustion unless precautions are taken to exclude air. Burnt shales are more suitable for bulk-fill purposes, as combustion has already removed the carbonaceous material from the spoil.

Limestone occurs at outcrop in the Skipton area, but has not been worked within the district. However, hummocky (moundy) glacial deposits present in Airedale are locally rich in limestone boulders, and during the 17th and 18th centuries the limestone boulders were extensively worked at Bingley to produce lime for agricultural use or as a flux in ironworks. The deposits have not been worked during this century, and are no longer of economic importance.

Ironstone occurs as nodules or thin beds of siderite (iron carbonate) within mudstones, principally in the Coal Measures. The main ironstone formerly worked in the district occurs above the Black Bed Coal, although the majority of workings were in the Huddersfield district. The deposits are no longer of economic significance.

Surface mineral workings

Former or active quarries or pits which have not been backfilled represent an important resource as they may provide a suitable void for waste disposal; they may be reopened as a source of minerals or may be developed as local nature reserves for educational, recreational and wildlife value. Such sites may be a constraint to development as steep rock faces may be unstable. Quarries and pits are distributed throughout the district. The majority of open excavations are in sandstone, but fireclay, sand and gravel, and brickclay have been extracted from surface workings in the past. Most options for landfill sites have already been utilised, adding pressure to use remaining disused sandstone quarries, many of which are present in rural areas.

Engineering ground conditions

Three important considerations relevant to construction and development are the suitability of the ground to support structural foundations, ease of excavation and the use of the ground materials in engineered earthworks and fills. These issues are summarised for the main engineering geological units in the district in (Table 5) and discussed more fully by Waters et al. (1996b). 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 differential settlement, particularly in the urban and industrial areas. Colliery spoil may contain iron sulphides (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-resistant cement. This oxidation process may also result in expansion and differential heaving of foundations constructed upon such deposits. Large volumes of quarry spoil are common in the district, and the areas affected may have poor foundation conditions if large cavities are present or material was deposited on steep slopes.

Subsidence risk due to undermining

The underground mining of coal, fireclay, ironstone and sandstone are no longer carried out in the district. However, mining was formally an important industry, largely restricted to the area of outcrop of the Coal Measures in the south and east of the district, including much of urban Bradford. Small centres of coal mining are also recorded where Millstone Grit coals are present near to Stanbury and Keighley. Sandstone mining was largely limited to working of the Elland Flags, the history of which was reviewed by Godwin (1984), and to a lesser extent the Rough Rock Flags and Scotland Flags, although 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. (1996b).

In areas of former coal and sandstone mining the principal concerns relate to ground instability caused by the collapse of unsupported shallow workings. This may be evident as general ground subsidence or as the development of crown-holes. 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), which also provides information on the sandstone mining industry of West Yorkshire. Records of shafts and abandoned mines are lodged with the Coal Authority, who should be consulted prior to development in the former coalfield areas.

Slope stability

Development, particularly for housing, has been forced to extend beyond the prime flat lowland areas of the main valleys onto the steep valley sides. Construction on these existing landslip, and where thicker head deposits, containing relict shear surfaces have accumulated on the lower parts of the slopes (see Glacial to Postglacial deposits in Chapter 5). In many cases, the landslips present in the district developed in response to oversteepening 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 large volumes of water are introduced, such as may occur due to alteration of drainage patterns during development.

Pollution potential and leachate movement

Artificial (man-made) deposits may contain toxic residues, either as a primary component or generated secondarily by chemical or biological reactions; these can migrate both within the deposit and into adjacent permeable strata. Waters et al. (1996b) identified a number of industrial land-uses in the district which may be associated with potential pollution. One of the greatest concerns for potential generation of pollution are old landfill sites; these are common within the district, particularly associated with infilled quarries and disused railway cuttings. Leachates may be a particular problem from old sites in which tipping was uncontrolled and little attempt was made to prevent pollution migration. The problem may be exacerbated where sites occur within areas of faulted bedrock as the faults may provide possible pathways for leachate migration. Areas of former gasworks, chemical works, textile mills, iron and steel works, railway land and sewage works may all be associated with contamination.

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

Leachate migration occurs where rain water or groundwater percolates through waste and becomes enriched in soluble components including inorganic, organic and microbial 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. Historically, landfill operations in the UK practised a policy of ‘dilute and disperse’ within uncontained sites. Such a method could potentially lead to reduction of water quality and consequently, newer landfill sites have tended to be engineered containment sites with treatment of leachates.

Gas emissions

The main potential gas hazards in the area are associated with the accumulation of methane, carbon dioxide, carbon monoxoide, and radon in poorly ventilated enclosed spaces such as basements or foundations. 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. Methane is potentially explosive, may act as an asphyxiant and may cause vegetation die back. Carbon dioxide is toxic in high concentrations; it may act as an asphyxiant and may cause vegetation die back. Carbon monoxide is potentially explosive and is toxic at low concentrations. Radon is potentially carcinogenic. Hazards associated with radon, methane, carbon dioxide and carbon monoxide are discussed fully by Hooker and Bannon (1993), Appleton (1995), and for the Bradford district by Waters et al. (1996b).

Mine gas may be generated in coal or colliery-based workings or from areas of colliery spoil, largely present in the area of Coal Measures outcrop. The main gases present include methane, often referred to as firedamp, carbon dioxide, often occurring as blackdamp a combination of carbon dioxide and nitrogen, and carbon monoxide.

Artificial (man-made) deposits, in particular landfill sites, may contain organic matter which can biodegrade to form methane and carbon dioxide. The nature of landfill gas characteristics is discussed by Williams and Aitkenhead (1991) and Hooker and Bannon (1993).

Natural gas emissions may develop in response to burial, compaction and heating of marine sediments rich in microorganisms. Dinantian and Namurian strata present beneath the district may provide a suitable source, as in the case of the Abbeystead disaster caused by the explosion of methane probably derived from Millstone Grit carbonaceous shales (Health and Safety Executive, 1985). A number of explosions have been recorded early this century in water boreholes which may be sourced by natural methane, although a source from mining cannot be ruled out. Methane may also be generated in areas of swamp or marsh, peatlands, lakes including mill ponds associated with the textile industry.

Radon is a naturally occurring radioactive gas derived from rocks, soils and groundwater containing uranium and thorium. In the district, levels of natural uranium and thorium are generally low, although locally higher concentrations may be associated with marine bands, other carbonaceous shales and coal seams in the Millstone Grit and Coal Measures (Ball et al., 1991). Radon may also occur in higher concentrations in high permeability rocks, such as sandstone or sand and gravel deposits, present above a source.

Water resources

Reservoirs provide the principal source of water for domestic supplies; some reservoirs are sited in the 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, historically, have provided significant volumes of potable water, for example Manywells Spring [SE 072 356], White Wells [SE 118 467], the latter supplying the Roman Bath at Ilkley.

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 Coal Measures and Millstone Grit in the area are markedly heterolithic 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 thickness, 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. (1996b).

Flooding and land drainage

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 in the moorland catchment areas of the main rivers, the Wharfe and Aire, where the predominance of V-shaped valleys, and relative impermeability of bedrock and drift deposits, result in a rapid runoff in response to heavy rainfall. 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 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 which have no natural drainage outlet. However, over recent drought years the dominantly clayey soils associated with till tend to retain moisture longer than areas where bedrock occurs at crop, and hence have provided better pasture during summer months.

Conservation sites

Many of the sites identified in the district as of importance to earth science research and teaching and for recreational purposes 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].

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, 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 available are:

Maps

Geology maps

Geophysical maps

Geochemical atlases

Hydrogeological map

Books

British Regional Geology

The Pennines and adjacent areas, 3rd edition, 1954.

Memoirs

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

(Table 6) shows the reference number for the technical reports covering the geology of individual or combined 1:10 000 scale geological 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. 1996b.

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 (Table 7) 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, British Geological Survey, Keyworth, Nottingham NG12 5GG.

Mine plans

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

Coal, ironstone and fireclay

Copies of all known abandonment plans are held by the Mining Records Office, Coal Authority, Bretby Business Park, Ashby Road, Burton upon Trent, Staffordshire DE15 0QD. These plans are held by the Coal Authority in the public domain, but are not available for reference at BGS

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 Sheet 69 Bradford 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 the BGS Web site: http://www.bgs.ac.uk.

Material collections

Palaeontological collection

Macrofossils and micro-palaeontological 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.

Borehole 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 photographs used in this report 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 (for address see below).

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 is 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.

References

Most of the references listed below are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies of the references may be purchased from the Library subject to the current copyright legislation.

AITKENHEAD, N, BRIDGE, D McC, 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.

APPLETON, J D. 1995. Potentially harmful elements from “natural” sources and mining areas: characteristics, extent and relevance to planning and development in Great Britain. British Geological Survey, Technical Report, WP/95/3.

ARTHURTON, R S. 1983. The Skipton Rock Fault an Hercynian wrench fault associated with the Skipton Anticline, northwest England. Geological Journal, Vol. 18, 105–114.

ARTHURTON, R S. 1984. The Ribbesdale fold belt, NW England - a Dinantian-early Namurian dextral shear zone. 131–138 in Variscan tectonics of the North Atlantic region. HUTTON, D H W, and SANDERSON, D J (editors). Special Publication of the Geological Society of London, No. 14, 270pp.

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.)

BALL, T K, CAMERON, D G, COLMAN, T B, and ROBERTS, P D. 1991. Behaviour of radon in the geological environment: a review. Quarterly Journal of Engineering Geology, Vol. 24, 169–182.

BRANDON, A, AITKENHEAD, N, CROFTS, R G, ELLISON, R A, EVANS, D J, and RILEY N J. 1999. 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.

CAMERON, D G, HIGHLEY, D E, HILLIER, J A, JOHNSTONE, T P, LINLEY, K A, MILLS, A J, SMITH, C G, and WHITE, R. 1998. Directory of mines and quarries 1998. 5th edition. (Keyworth, Nottingham: British Geological Survey.)

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, Part 1, 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, 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 92SE.

DEANS, T. 1932. A borehole section in the Millstone Grits of Rombalds Moor. Transactions of the Leeds Geological Asscociation, Vol. 5, Pt. 1, 9–16.

DEANS, T. 1934. A second boring in the Millstone Grits of Rombalds Moor. Transactions of the Leeds Geological Asscociation, Vol. 5, Pt. 2, 75–85.

EAGAR, R M C. 1956. Additions to the non-marine fauna of the Lower Coal Measures of the North-Midlands coalfields. Liverpool and Manchester Geological Journal, Vol. 1, 329–369.

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). Society of Economic Palaeontologists and Mineralogists, Special Publication 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).

EVANS, D J, and KIRBY. G A. 1999. The architecture of concealed Dinantian carbonate sequences of the Central Lancashire and Holme Highs, Northern England. Proceedings of the Yorkshire Geological Society, Vol. 53, 297–312.

GILES, J R A. 1989. Evidence of syn-depositional tectonic activity in the Westphalian A and B of West Yorkshire. 201–206 in The role of tectonics in Devonian and Carboniferous sedimentation in the British Isles. ARTHURTON, R S, GUTTERIDGE, P, and NOLAN, S C (editors). Yorkshire Geological Society Occasional Publication, No. 6.

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, UK. 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.

HEALTH AND SAFETY EXECUTIVE. 1985. The Abbeystead explosion - A report of the investigation by the Health and Safety Executive into the explosion on 23 May 1984 at the valve house of the Lune/Wyre water transfer scheme at Abbeystead. (London: HMSO.)

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.)

HOOKER, P J, and BANNON, M P. 1993. Methane: its occurrence and hazards in construction. Construction Industry Research and Information Association (CIRIA), Report No. 130, 137pp.

HUDSON, R G S, and DUNNINGTON, H V. 1939. A boring in the Lower Coal Measures and Millstone Grit at Bradford. Proceedings of the Yorkshire Geological Society, Vol. 24, 129–136.

HUDSON, R G S, and DUNNINGTON, H V. 1940. A borehole section in the Carboniferous at Fairweather Green, Bradford. Proceedings of the Yorkshire Geological Society, Vol. 24, 206–218.

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. (London: HMSO.)

JONES, T W. 1943. The geology of the Beamsley Anticline. Proceedings of the Leeds Philosophical Society (Scientific Section), Vol. 4, Pt. 2, 146–166.

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, AG, 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.

LEEDER, M R. 1982. Upper Palaeozoic basins of the British Isles: Caledonide inheritance versus Hercynian plate margin processes. Journal of the Geological Society London, Vol. 139, 481–494.

MCCABE, P J. 1978. The Kinderscoutian delta (Carboniferous) of northern England; A slope influenced by density currents. 116–126 in Sedimentation in submarine canyons, fans and trenches. STANLEY, D J, and KELLING, G (editors). (Stroudsburg: Dowden, Hutchinson and Ross.)

MARTINSEN, O J. 1990. Interaction between eustacy, tectonics and sedimentation with particular reference to the Namurian E1c–H2c of the Craven–Askrigg area, northern England. Unpublished Dr. Sc. thesis, University of Bergen, Norway.

MUSSON, R M W. 1994. A catalogue of British earthquakes. British Geological Survey Technical Report, WL/94/04.

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. Geological Society of London Special Report, 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.

RILEY, N J, CLAOUÉ-LONG, J, HIGGINS, A C, OWENS, B, SPEARS, A, TAYLOR, L, and VARKER, W J. 1995. Geochronometry and geochemistry of the European Mid-Carboniferous Boundary Global Stratatype proposal, Stonehead Beck, North Yorkshire, UK. Annales de la Societe geologique de Belgique, Vol. 116, 275–289 (imprinted 1994)

STEPHENS, J V, MITCHELL, G H, and EDWARDS, W. 1953. Geology of the country between Bradford and Skipton. Memoir of the Geological Survey of Great Britain, Sheet 69 (England and Wales).

STRONG, G E. 1996. Petrography of Namurian rock samples from the Bradford area: 2 (1:50,000 Sheet 69). British Geological Survey Technical Report, Mineralogy and Petrology series, WG/96/31.

TILLOTSON, E. 1974. Earthquakes, explosions and the deep underground structure of the United Kingdom. Journal of Earth Sciences Leeds, Vol. 8, Part 3, 353–364.

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Figures, plates and tables

Figures

(Figure 1) Solid geology of the Bradford district.

(Figure 2) Principal physical features of the district.

(Figure 3) Correlation of Kinderscoutian strata in the northern part of the district.

(Figure 4) Correlation of sandstones and coals of the Lower Coal Measure from selected boreholes.

(Figure 5) Location of meltwater channels, drumlins and moraines, and the approximate position of the Devensian ice front (based on Stephens at al., 1953, with the inclusion of new data form this resurvey).

(Figure 6) Principal early Carboniferous (syn-extension) structures of the region (after Kirby et al., 1994).

(Figure 7) Location of 1:10 000 scale maps within Sheet 69 Bradford.

Plates

(Front cover) Cow and calf rock [131 468] is an example of a topple rock fall, and is an important conservation and recreation site (GS 538).

(Plate 1) Kinderscoutian sandstone crag at Addingham High Moor. A cut millstone is lying amongst the rock fall [SE 07 47] (GS 539).

(Plate 2) Two leaves of the Elland Flags exposed in Bolton Woods South Quarry (Berry and Marshall, Bolton Woods, Ltd) with redundant crushing plant in the foreground [SE 163 362] (GS 537).

(Plate 3) Bifurcating glacial meltwater channel near Newsholme Dean [SE 002 410] (GS 540).

(Plate 4) Shallow rotational slide at East Morton [SE 104 427] (GS 536).

(Back cover)

Tables

(Table 1) Geological succession of the district.

(Table 2) Western European Namurian marine bands (after Riley et al., 1995).

(Table 3) Proved thickness range of named coal seams and mean thickness of inter-seam strata of the Lower Coal Measures.

(Table 4) Principal named faults in the district with an indication of the approximate maximum downthrow at surface.

(Table 5) Main engineering geological units of the district.

(Table 6) Component 1:10 000 scale maps, technical reports, and survey details of Sheet 69 Bradford. * denotes availability in digital format

(Table 7) Boreholes cited in the text and selected boreholes in and adjacent to the district are listed alphabetically, together with their National Grid Reference, BGS registered number (1:10 000 scale quarter-sheet number) and total depth.

Tables

(Table 2) Western European Namurian marine bands (after Riley et al., 1995)

MARINE BANDS
STAGE INDEX AMMONOIDS

YEADONIAN G1

 G1b1 Cancelloceras cumbriense*
G1a1 Cancelloceras concellatum*

MARSDENIAN R2

 R2c2 Verneulites sigma
R2c1 Bilinguites superbilinguis*
R2b5 Bilinguites metabilinguis**
R2b4 Bilinguites eometabilinguis*
R2b3 Bilinguites bilinguis
R2b2 Bilinguites bilinguis
R2b1 Bilinguites bilinguis*
R2a1 Bilinguites gracilis*

KINDERSCOUTIAN R1

 R1c4 Reticuloceras coreticulatum****
R1c3 Reticuloceras reticulatum*
R1c2 Reticuloceras reticulatum*
R1c1 Reticuloceras reticulatum
R1b3 Reticuloceras stubblefieldi
R1b2 Reticuloceras nodosum
R1b1 Reticuloceras eoreticulatum*
R1a5 Reticuloceras dubium*
R1a4 Reticuloceras todmordenense
R1a3 Reticuloceras subreticulatum
R1a2 Reticuloceras circumplicatile*
R1a1 Hodsonites magistrorum*

ALPORTIAN H2

 H2c2 Homoceratoides prereticulatus
H2c1 Vallites eostriolatus
H2b1 Homoceras undulatum
H2a1 Hudsonoceras proteum

CHOKIERIAN H1

 H1b2 Isohomoceras sp. nov.*
H1b1 Homoceras beyrichianum**
H1a3 Isohomoceras subglobosum*
H1a2 Isohomoceras subglobosum*
H1a1 Isohomoceras subglobosum*

ARNSBERGIAN E2

 E2c4 Nuculoceras nuculum*
E2c3 Nuculoceras nuculum*
E2c2 Nuculoceras nuculum*
E2c1 Nuculoceras stellarum
E2b3 Cravenoceratoides nititoides*
E2b2 Cravenoceratoides nitidus*
E2b1 Cravenoceratoides edalensis*
E2a3 Eumorphoceras yetesae*
E2a2a Cravenoceras gressinghamense
E2a2 Eumorphoceras ferrimontanum*
E2a1 Cravenoceras cowlingense*

PENDLEIAN E1

 E1c1 Cravenoceras malhamense*
E1b2 Tumulites pseudobilinguis
E1b1 Cravenoceras brandoni*
E1a1 Cravenoceras leion*

(Table 3) Proved thickness range of named coal seams and mean thickness of inter-seam strata of the Lower Coal Measures

Coal seam name (alternative name) Former use Thickness (m) min       Thickness max Inter-seam thickness
Crow gas & household 0.1 0.5
5–15
Black household, engine & gas coals 0.4 1.1
36
Better Bed coking coals 0.3 0.9
c. 120
80 Yard 0.0 0.4
10–25
48 Yard 0.0 0.2
20
36 Yard (Upper Band) 0.0 0.6
20–27
Hard Bed (Halifax Hard Bed) engine coals 0.5 1.0
6–13
Middle Band 0.0 0.2
3–11
Soft Bed (Halifax Soft Bed) coking coals 0.2 0.9

(Table 4) Principal named faults in the district with an indication of the approximate maximum downthrow at surface

Fault name Orientation Maximum downthrow and downthrow direction Description
Gargrave NW–SE 75 m to SW also known as South Craven Fault
Bradley NE–SW 60 m to NW reverse fault
Glusburn WNW–ESE 300 m to SSW associated with lead workings in Cononley area
Aire Valley NW–SE 100 m to SW fault zone with switching throw directions
Wharfe Valley WNW–ESE 60 m to SSW position beneath thick drift uncertain
Drake Hill NW–SE 60 m to NE
Rivock NW–SE 340 m to SW
Graincliffe NW–SE 340 m to NE
Weecher NW–SE 160 m to SW
Reva NW–SE 200 m to NE
Burley Moor NW–SE 205 m to SW
Hewenden WNW–ESE 90 m to SSW intermittently bounds graben to the SSW
Denholme Clough WNW–ESE 150 m to NNE intermittently bounds graben to the NNE
Calverley NE–SW 100 m to SE bounds graben to the SE - the Calverley Trough
Billing Hill W–E 50 m to S
Horsforth–Tinshill NE–SW 80 m to SE
Bramley W–E 50 m to S

(Table 5) Main engineering geological units of the district

Engineering consideration Engineering consideration Engineering consideration Engineering consideration
Engineering geological units Geological units Description/ characteristics Foundations Excavation Engineered fill Site investigations
Soils

Mixed cohesive/ non-cohesive soils

 Stiff/ dense Till

(boulder clay)

 Stiff to very stiff, stony sandy CLAY; variable. Generally good, unless water bearing sand and silt layers/lenses are present. Diggable; generally stable in short term. Ponding of water may be problem. May be suitable if care is taken in selection and extraction. Important to determine thickness and lithology.
Soft firm Head Soft to firm sandy silty clay with stones; low to medium plasticity and compressibility; highly variable. May contain relict shear surfaces of low shear strength. Relict shear surfaces may cause stability problems on shallow slopes. Limited thickness may allow economical removal. Diggable. May be suitable as bulk fill; may be too wet to achieve satisfactory compaction. Important to determine thickness/ extent and presence of relict shear surfaces.
Soft/ loose Alluvium Glaciolacustrine deposits Very soft to firm, sandy, silty clays and silts, with impersistent peat; and loose to dense fine to coarse-grained sands and gravels with clay lenses. Soft, highly compressible zones may be present, with risk of severe differential settlements. Diggable. Immediate trench support required. Running conditions likely in granular material. High water tables may cause flooding problems. Generally unsuitable. Important to ascertain the presence, depth and extent of soft compressible zones and depth to sound strata. Closely spaced boreholes my be required.
Non-cohesive soils Medium dense Alluvial fan deposits River terrace deposits Glaciofluvial deposits Hummocky (moundy) glacial deposits. Medium dense, fine to coarse-grained sands and medium dense to dense gravels with some cobbles. Sandy clays and silts may occur locally. Generally good. Thick deposits in buried channels may be significant in foundation design. Diggable. Trench support required. May be water-bearing. Sands and gravels suitable as granular fill. Important to identify presence and dimensions of buried channels and characteristics of infilling deposits. Geophysical methods may be advisable.
Organic soils Very soft Peat Fibrous/amorphous peat. Very poor; very weak, highly compressible; acidic groundwater. Diggable. Generally wet ground conditions may require immediate trench support and dewatering. Unsuitable. Important to determine extent and depth. Groundwater acidity should be determined prior to selection of buried concrete.
Highly variable artificial deposits Made ground Infilled ground Highly variable depth and geotechnical properties. Very variable. May be highly compressible. Hazardous waste may be present. Usually diggable. Highly variable. Some material may be suitable. Essential to determine depth, extent, condition and type of fill and chemistry of ground waters.
Landslip deposits Landslip Variable, as for source; usually containing slip surfaces of low strength. Rockfall detritus may be extensive below scarps. Generally unsuitable for building development, unless appropriate remedial works to stabilise ground. Usually diggable. Large sandstones blocks and boulders may cause difficulties locally. Generally unsuitable. Essential to ascertain stability conditions of slip site and adjacent slopes prior to any development and/or design of remedial works.
Bedrock
‘Strong’ sandstone Sandstones of the Millstone Grit and Coal Measures. Moderately to well-joined, thinly to thickly bedded, fine to coarse-grained sandstones. Strong to moderately strong when fresh or slightly weathered. Usually good foundation conditions. Bed thickness and depth of weathered zone important in design. Dependent of joint spacing. Ripping, pneumatic tools or blasting. Suitable as high grade fill if care taken in selection and extraction; suitable as bulk fill if uneconomic to separate from mudstone interbeds. Important to determine depth and properties of weathered zone.

In situ loading tests advisable to assess bearing strengths.
Mudrocks Mudstones, shales, claystones and siltstones of the Millstones Grit and Coal Measures; calcareous mudstones of the Chatburn Limestone, Worston Shale and Bowland Shale groups. Fissured, weak to moderately strong, mudstones, shales, claystones, siltstones weathering to a firm to stiff silty clay. Tendency to deteriorate and soften when exposed/wetted. Generally good. Dependent on nature and thickness of weathered zone. Foundation levels may need protection in open excavations. Weathered mudrocks are diggable; ripping or pneumatic breakers may be required at depth or for major excavations. Suitable as fill under controlled compaction conditions. Important to determine depth and properties of weathered zone.

In situ loading tests advisable to assess bearing strengths at selected sites.
Limestones Limestone of the Chatburn Limestone Group, Embsay Limestone and Pendleside Limestone. Thin to thick-bedded, generally strong limestones, locally conglomeratic, interbedded with calcareous mudstones. Usually good, but bed thickness, and presence of highly weathered zones need to be accounted for in design of shallow foundations. Dependent on joint spacing and mudstone interbeds. Ripping, pneumatic tools or blasting. Suitable as high grade fill if care taken in selection and extraction. Important to ascertain possible presence of local highly weathered zones.

(Table 6) Component 1:10 000 scale maps, technical reports, and survey details of Sheet 69 Bradford. * denotes availability in digital format

Sheet No. Sheet name Surveyor Date Technical report
SD93NE Crow Hill CNW 1994 WA/97/7
SD93SE Wadsworth CNW 1996 WA/97/7
SD94NE Cononley RA 1995 WA/97/22
SD94SE Sutton-in-Craven RGC 1995 WA/94/79
SD95SE Skipton NA 1995
SE03NW Haworth NA 1994 WA/96/79
SE03NE Cullingworth JGR 1993 WA/94/79
SE03SW Oxenhope CNW 1994 & 1996 WA/97/7
SE03SE Denholme CNW 1993 & 1996 WA/97/8
SE04NW Silsden RA 1994–1995 WA/97/22
SE04NE Addingham NA 1994
SE04SW Sutton-in-Craven & Steeton RGC 1994 WA/94/79
SE04SE* Keighley RGC 1993 WA/94/80
SE05SW Embsay & Draughton NA 1994–1995
SE05SE Beamsley & Bolton Abbey NA 1995
SE13NW* Bingley JGR 1993–1994 WA/94/75
SE13NE* Shipley NSJ 1994–1995 WA/97/80
SE13SW* Clayton CNW 1993–1994 WA/95/32
SE13SE* City of Bradford CNW 1994 WA/95/39
SE14NW Ilkley MS 1994 WA/96/40
SE14NW Ilkley CNW 1995
SE14NE Burley-in-Wharfdale MS 1994 WA/96/40
SE14NE Burley-in-Wharfdale CNW 1995
SE14SW Bingley Moor NA 1993 WA/95/41
SE14SE Guiseley NA 1994–1995 WA/97/52
SE15SW Middleton Moor CNW 1995 WA/96/40
SE15SE Timble CNW 1995 WA/96/40
SE23NW* Horsforth DGT 1990 WA/91/40
SE23NE North-west Leeds MTD 1990 WA/91/41
SE23SW* Pudsey RA 1994–1995
SE23SE South-west Leeds MTD 1989 WA/91/42
SE24NW Otley RGC 1995 WA/97/60
SE24NE Huby RGC 1995 WA/97/60
SE24SW Yeadon NSJ 1995 WA/97/59
SE24SW Yeadon RGC 1996
E24SE Bramhope RGC 1996 WA/97/59
SE25SW Norwood RGC 1995 WA/97/60
SE25SE Beckwith ICB 1977–1978

(Table 7) Boreholes cited in the text and selected boreholes in and adjacent to the district are listed alphabetically, together with their National Grid Reference, BGS registered number (1:10 000 scale quarter-sheet number) and total depth

Borehole name Grid reference BGS number Total depth (m)
Aire Vale Dyeworks [SE 2384 3663] (SE23NW/8) 155
Aire Valley No.1 [SE 0882 4036] (SE04SE/12) 60
Aire Valley No.2 [SE 0887 4045] (SE04SE/13) 35
Aire Valley No.3 [SE 0890 4050] (SE04SE/14) 36
Aire Valley No.4 [SE 0892 4056] (SE04SE/15) 40
Aire Valley No.6 [SE 0899 4057] (SE04SE/17) 55
Aire Valley No.7 [SE 0890 4061] (SE04SE/18) 58
Aire Valley No.28 [SE 1040 3911] (SE13NW/22) 41
Aire Valley No.P21 [SE 0981 3973] (SE03NE/8) 51
Alston Works [SE 1463 3340] (SE13SW/17b) 199
Barkerend Mills [SE 1736 3339] (SE13SE/25a) 276
Bingley Mills [SE 1079 3953] (SE13NW/16) 101
Birkshall Gasworks [SE 1823 3245] (SE13SE/35) 257
Bradford Moor No.3 [SE 1838 3378] (SE13SE/77) 70
Bradford Power Station [SE 1634 3398] (SE13SE/33) 223
Bradup [SE 0914 4417] (SE04SE/774) 203
Britannia Mills [SE 1649 3254] (SE13SE/13) 188
Broom Mills [SE 2232 3543] (SE23NW/3) 123
Butterbowl Mills [SE 2572 3252] (SE23SE/4) 198
Canal Works, Shipley [SE 1474 3790] (SE13NW/6) 77
Carlton Moor [SE 2242 4247] (SE24SW/14) 275
Cotopa Ltd., Horsforth [SE 2219 3716] (SE23NW/7) 198
Cumberland Works No.1 [SE 1376 3325] (SE13SW/14a) 189
CWS Creamery [SE 1731 3206] (SE13SE/10) 308
Fairweather Green [SE 1338 3330] (SE13SW/15) 379
Farnley Ironworks [SE 2559 3181] (SE23SE/3229) 215
Grange Mills [SE 1211 3366] (SE13SW/7) 107
Hag Farm [SE 1583 4461] (SE14SE/52) 137
Horsforth Steam Laundry No.2 [SE 2403 3824] (SE23NW/11) 145
Horton Dyeworks [SE 1492 3334] (SE13SW/9) 214
Jaytail Farm [SE 0624 4419] (SE04SE/775) 57
Keighley Co-operative Laundry [SE 0580 4113] (SE04SE/6) 145
Kirkstall Brewery Well [SE 2581 3551] (SE23NE/2) 70
Ladywell Mills [SE 1692 3221] (SE13SE/4) 171
Leaventhorpe Mill [SE 1214 3261] (SE13SW/6) 194
Lees Moor Railway Tunnel [SE 0502 3774] (SE03NE/21) 90
Low Hall Road, Horsforth [SE 2214 3747] (SE23NW/6) 82
Low Lane Dyeworks [SE 2485 3850] (SE23NW/25) 91
Low Mills, Rawdon [SE 2184 3769] (SE23NW/4a) 115
Lowroyd Dyeworks [SE 1452 3340] (SE13SW/12) 291
Manningham Mills [SE 1442 3487] (SE13SW/10a) 220
Midland Railway Well [SE 2514 3640] (SE23NE/1) 85
New Lane Mills [SE 1909 3285] (SE13SE/34) 287
Newsholme Dean Reservoir No.4 [SE 0228 4067] (SE04SW/6) 72
Newsholme Dean Reservoir No.7 [SE 0229 4035] (SE04SW/9) 41
Newsholme Dean Reservoir No.9 [SE 0228 4020] (SE04SW/12) 60
Ondura [SE 068 422] (SE04SE/56) 92
Park Mills [SE 2192 3888] (SE23NW/24) 76
Ross Gelatines Ltd., Newlay [SE 2428 3688] (SE23NW/10) 61
Saltaire Mills [SE 1415 3802] (SE13NW/3) 152
Sandoz Chemical Works [SE 1638 3438] (SE13SE/30) 218
Snail Green (composite log) [SE 1180 4241] (SE14SW/2) 232
Sunnybank Mill [SE 2168 3535] (SE23NW/1a) 196
Top Mill [SE 1186 3443] (SE13SW/5) 165
Vale Dyeworks [SE 1641 3443] (SE13SE/16a) 106
Victoria Mills [SE 1732 3215] (SE13SE/9) 282
Waterloo Mills [SE 1642 3253] (SE13SE/17) 341
Wellington Mills [SE 2472 3554] (SE23NW/9) 107
Westfield Mills [SE 2047 4099] (SE24SW/1) 360
Whetley Mills [SE 1471 3372] (SE13SW/11) 329
Woodbottom Mills [SE 2204 3782] (SE23NW/2) 76