Geology of the country around Lancaster: Memoir for 1:50 000 Geological Sheet 59 (England and Wales)

By A Brandon, N Aitkenhead, R G Crofts, R A Ellison, D J Evans and N J Riley

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

British Geological Survey

Geology of the country around Lancaster: Memoir for 1:50 000 Geological Sheet 59 (England and Wales)

A Brandon, N Aitkenhead, R G Crofts, R A Ellison, D J Evans and N J Riley

Contributors

London: The Stationery Office 1998

NERC copyright 1998. First published 1998 ISBN 0 11 884526 8. Printed in the UK for The SO. J 58942 C6 10/98

The grid used on the figures is the National Grid taken from the Ordnance Survey map. (Figure 1) is based on material from Ordnance Survey 1:50 000 scale map numbers 97, 98, 102 and 103. Crown copyright reserved. Ordnance Survey licence no. GD 272191/1998.

Authors A Brandon, BSc, PhD N Aitkenhead, BSc, PhD R G Crofts, BSc R A Ellison, BSc D J Evans, BSc, PhD N J Riley, BSc, PhD British Geological Survey, Keyworth

Contributors

Other publications of the Survey dealing with this district and adjoining areas

Books

Maps

Preface

In this scenically attractive part of rural Lancashire, where there has been only minor mineral exploitation and limited industrialisation, geological interpretations were based mainly on surveys and data dating back to the 1880s. The inadequacy of the data was dramatically highlighted by an explosion of methane gas in an underground valve house at Abbeystead in 1984 which tragically resulted in 16 fatalities. Subsequent investigations confirmed the urgent need for basic up-to-date geological information. As a consequence, a detailed geological survey around Abbeystead was commissioned by North West Water plc, and eventually provided the stimulus for a multidisciplinary survey of the entire Lancaster district.

This memoir is the first comprehensive and general account of the geology of the Lancaster district to be published. It is a synthesis of many detailed geological, biostratigraphical, geophysical and petrographical investigations and includes information, both surface and subsurface, from the Survey's extensive archives and from external sources. It is best read in conjunction with the colour-printed 1:50 000 scale published geological maps.

The Lancaster district encompasses the heart of the upland Bowland Fells in the south-east, a fringe of undulating rural country, including the Lune valley, to the north and west, and the coastal plain bordering Morecambe Bay in the west. Bedrock mainly comprises the Millstone Grit Group, a 2.5 km-thick pile of lithified deltaic sands, silts and muds, introduced by large, generally southward-flowing rivers into an extensive Centre Pennine Basin in late Carboniferous times, about 315 million years ago. Small inliers in the south-east and north-west reveal earlier Carboniferous marine limestones and mudstones, laid down in a tropical sea. In the north-east, the district just touches on the Lower Coal Measure rocks of the Ingleton Coalfield. Permo-Triassic rocks in the south-west, and in a small, newly discovered basin near Lancaster, comprise red mudstones and sandstones that were deposited during relatively arid climatic conditions.

Much of the drainage, geomorphology and superficial deposits are a legacy of the late Devensian glaciation of the area, when widespread deposits of till were laid down in all but the highest places and were extensively moulded into drumlins. Deglaciation resulted locally in thick glaciofluvial sand and gravel sheets and mounds. This is splendidly illustrated in some recently processed Landsat scenes, one of which is partly reproduced in this memoir.

The survey has provided insights into the developments of the Carboniferous Craven and Central Pennine basins and the post-Carboniferous Irish Sea Basin, which have hydrocarbon potential. Resources of industrial minerals, such as sand and gravel, limestone and sandstone for use in the construction industry, siltstones and mudstones as brick clays, and sandstones and limestones as aquifers have been indicated.

The recent work in the district appreciably advances our understanding of the local three-dimensional bedrock and the superficial drift deposits, and provides a sound basis for future research. It is also intended to be of practical value to a wide range of users, from specialists in the earth sciences or related disciplines, to others who may use the findings as an aid to land-use planning and development or for mineral exploration, and to local naturalists, conservationists and amateur geologists.

David A Falvey, PhD Director, British Geological Survey, Kingsley Durham Centre, Keyworth, Nottingham. NG12 5GG

Acknowledgements

This memoir has been compiled by Dr A Brandon. The authorship of each chapter is as follows:

In addition to the authors listed above, the memoir incorporates the results of workers listed on the title page who have mostly contributed BGS Technical Reports, listed in Appendix 1, on various aspects of the geology of the Lancaster district. Mr R J Ireland, formerly of North West Water plc, Warrington, and Mr N S Robins and Mrs M A Lewis contributed the hydrogeological account. Dr N S Jones compiled (Figure 31) from a sedimentological investigation of the two boreholes. The memoir was edited by Mr T J Charsley and Dr S G Molyneux.

Grateful acknowledgement is made to organisations and individuals, including landowners, quarry operators and public and local authorities, for their willing help and cooperation during the course of the geological and geophysical surveys. The following organisations are amongst many who have kindly presented borehole data: British Gas plc, Butterley Brick Ltd, Lancashire County Council, Lancaster City Council, North West Water plc, Nuclear Electric, RTZ Mining and Exploration Ltd, Scottish Power, Shell UK Ltd, Tarmac Roadstone (Western) Ltd, Tilcon Holdings plc, Wimpey Asphalt Ltd. The authors also gratefully acknowledge the cooperation of Enterprise Oil Exploration Ltd, International Petroleum Corporation (Pendle Petroleum Ltd) and North West Water plc in granting permission both to use and publish parts of confidential seismic reflection lines across the district.

The geological survey of parts of sheets SD 55 SW, SE, NW, NE, 56 SW, 65 SW and NW was partly funded by North West Water plc, and that of parts of SD 45 NW and 46 SE by the former Central Electricity Generating Board.

Notes

History of survey of the Lancaster sheet

The district covered by the Lancaster (59) sheet of the 1:50 000 geological map of England and Wales was originally surveyed at the six-inch scale by R H Tiddeman, with the assistance of J R Dakyns and C E De Rance, and the results were published as the Old Series sheet 91 NE (New Series sheet 59) in 1884 in Solid and Drift editions. No memoir was published to accompany the geological sheets.

Revision mapping on 1:10 000 National Grid maps was initiated in 1980 by A J M Barron in the Claughton area (part of Sheet SD 56 NE) and N Aitkenhead in the Middleton area (part of Sheet SD 45 NW), though these field maps have been superseded by later work. Following the underground explosion at Abbeystead in 1984, North West Water Ltd commissioned BGS to survey an area around Abbeystead, and this work, on parts of sheets SD 55 SW, NW, SE and NE, and small parts of SD 56 SW and SD 65 SW, was completed by A A Wilson, A Brandon and E W Johnson in 1985. A confidential report in 1985, summarising the geology of the Abbeystead area, was released as a BGS technical report in 1989. During 1986, further commissioned mapping on the 1:10 000 scale around Heysham power station, for the then Central Electricity Generating Board, was carried out by A A Wilson. The confidential results of this work were not released as a BGS technical report until 1993. The marginal sheets along the southern edge of the district were mapped as part of the systematic survey of the Garstang district by R A Hughes, R G Crofts, A S Howard and T P Fletcher between 1985 and 1986. Systematic surveys of the remaining parts of the Lancaster district were carried out between 1987 and 1991 by A Brandon, N Aitkenhead, R G Crofts, R A Ellison, R A Hughes and M J C Nutt.

Copies of the fair drawn or manuscript maps may be inspected at BGS Keyworth, and purchased as black and white dyeline sheets. They are listed below with the initials of the geological surveyors and the dates of the surveys. In the case of marginal sheets, only those surveyors who mapped this district are listed. In addition to the two reports mentioned above, reports on the detailed geology of these sheets are also available as technical reports (see Appendix 1), except for sheets SD 55 SE and NE, which are component parts of the Abbeystead report area.

SD 45 SW Cockersand Abbey RGC 1985
SD 45 NW Middleton NA, AAW, MJCN 1980–89
SD 45 SE Cockerham RGC 1986
SD 45 NE Galgate RGC 1990
SD 46 SW Morecambe AAw, RGC 1986, 91
SD 46 SE Lancaster RGC 1991
SD 46 NE Bolton-le-Sands NA 1990
SD 47 SE (pt) Carnforth NA 1991
SD 55 SW Dolphinholme AAW, ASH 1984, 86
SD 55 NW Quernmore AAW, RAH 1985, 86
SD 55 SE Abbeystead EWJ, AB, RAH 1984–86
SD 55 NE Tarnbrook AB, EWJ 1984–86
SD 56 SW Caton AB 1986, 88–89
SD 56 NW Nether Kellet NA 1990
SD 56 SE Littledale AB 1989–90
SD 56 NE Hornby AB 1990–91
SD 57 SW (pt) Over Kellet NA 1991
SD 57 SE (pt) Arkholme AB 1991
SD 65 SW Trough of Bowland RAH, AB 1985
SD 65 NW Brennand Fell AB 1985, 87–88
SD 65 SE Dunsop Bridge TPF 1985
SD 65 NE White Hill RAH 1986
SD 66 SW Goodber Common RAH 1988
SD 66 NW Wray RAE 1990–91
SD 66 SE Cross of Greet RAH 1987
SD 66 NE Bentham RAE 1990
SD 67 SW (pt) Cantsfield RAE 1991
SD 67 SE (pt) Ingleton RAE 1991

Geology of the country around Lancaster—summary

The Lancaster district described in this memoir encompasses the heart of the upland Bowland Fells in the south-east, a fringe of undulating rural country, including the Lune valley to the north and west, and the coastal plain bordering Morecambe Bay in the west. This is the first comprehensive and general account of the geology of the district to be published, and is a synthesis of many detailed geological, biostratigraphical, geophysical and petrographical investigations, augmented by programmes of shallow drilling.

The oldest rocks were deposited in tropical seas during a dynamic phase of rift subsidence in the Dinantian epoch of the Carboniferous. Small inliers in the south-east reveal mudstones and limestones laid down in a subsiding Craven Basin. Conversely, coeval limestones exposed in inliers in the north-west were deposited in a clear, shallow, shelf sea above the southern part of the Lake District High. The succeeding Namurian Millstone Grit Group, underlying most of the district, comprises a 2.5 km-thick pile of lithified deltaic sands, silts and muds, derived from as far away as Greenland, and transported by large rivers, flowing generally southwards, into an extensive, thermally subsiding Central Pennine Basin in late Carboniferous times, about 315 million years ago. The lower Namurian sequence, in which three highstands are newly established, is the thickest recorded from western Europe. Deposition continued uninterrupted into the Westphalian, whose Lower Coal Measure rocks form the Ingleton Coalfield, a small part of which extends into the district in the north-east. Compressive forces during the Variscan Orogeny tilted, folded and faulted the Carboniferous rocks of the district. Unconformably overlying Permo-Triassic rocks in the south-west, and in a small, newly discovered basin near Lancaster, comprise red mudstones and sandstones that were deposited in a relatively arid climate. These rocks were in turn subject to post-Variscan faulting, mainly during the rift development of the East Irish Sea Basin which commenced in Permo-Triassic times. Mesozoic and Neogene sediments that once covered the area have long since been removed. A solitary Palaeogene basalt dyke is described.

Much of the drainage, geomorphology, and superficial deposits are a legacy of the late Devensian glaciation of the area, when widespread deposits of till were laid down in all but the highest places, and were extensively moulded into drumlins. Deglaciation resulted locally in thick glaciofluvial sand and gravel sheets and mounds. Other superficial deposits are described.

The survey has provided insights into the developments of the Carboniferous Craven Basin and the post-Carboniferous Irish Sea Basin, both of which have hydrocarbon potential. Resources of industrial minerals, such as sand and gravel, limestone and sandstone for use in the construction industry, siltstones and mudstones as brick clays, and sandstones and limestones as aquifers have been indicated. Potential risk factors, such as land-slipped ground and methane seepage, are outlined.

(Succession) Geological succession in the Lancaster district.

Chapter 1 Introduction

This memoir describes the geology of the country covered by 1:50 000 Geological Sheet 59 (Lancaster), published in solid and drift editions in 1995. The topography and geography of the Lancaster district are shown in (Figure 1) and on (Plate 1). Apart from a small segment of North Yorkshire in its north-eastern corner around High Bentham, and a tiny part of offshore Cumbria in its north-western corner, west of the Kent Channel in Morecambe Bay, the district falls entirely within the county of Lancashire. A lack of economic mineral resources, particularly coal, left the district virtually unscarred by the ravages of the Industrial Revolution that typified parts of Lancashire farther south. The principal centres of population are the City of Lancaster, a former port and now an industrial and commercial centre and university town, and nearby Morecambe, a tourist resort and retirement dormitory. Heysham and Glasson are small ports, the former near the site of the nuclear power stations. The remaining areas are mainly pastoral, moorland, coastal marshes or tidal flats.

(Figure 2) places the solid geology of the Lancaster district in a regional setting. The bedrock of the district (Figure 3) mainly comprises deltaic siltstones and sandstones of the Millstone Grit Group of Namurian age. Only to the north of Lancaster, around Carnforth, and in small outcrops in the south-east of the district do slightly older marine limestones and mudstones of Dinantian age occur in the cores of anticlinal flexures. In the north-east corner, where the district impinges on the Ingleton Coalfield, there is a small, drift-covered area of Lower Coal Measures, of Westphalian age. Red fluvial and aeolian sandstones and mudstones with evaporites of Permo-Triassic age underlie much of the drift-covered, low-lying ground in the south-west and have been discovered, during the course of the survey, to extend to a synclinal area to the west of Lancaster. (Figure 3) also indicates the approximate extent of an area in the western part of the district covered by blanket drift deposits, where the bedrock geology is largely conjectural, its delineation being dependent principally on relatively few point sources, such as boreholes, with the backing of seismic interpretation. East of the line indicated on (Figure 3), bedrock disposition is known with much greater certainty, based on many incised stream sections and crag and quarry exposures, and landform feature mapping, though even this area incorporates many tracts where boundaries are extrapolated beneath drift.

East of the Quernmore Fault (Figure 3), strata are generally inclined northwards so that the lowest Namurian formations and Dinantian strata occur in the south-east of the district, and the highest Namurian rocks plunge under the Lower Coal Measures of the Ingleton Coalfield in the north-east of the district.

Farther north, the rocks of the Ingleton Coalfield retain a capping of Permo-Trias rocks. Across this tract, the outcrops of individual Millstone Grit formations are commonly repeated by WNW–ESE-trending faults, down-throwing mainly towards the south. West of the Quernmore Fault, the general dip of the beds is southwards, the Pendle Grit and Dinantian strata occurring mainly north of Lancaster, whereas the higher Namurian strata crop out with Permo-Triassic rocks in the southern part of the district. The scissor-fault nature of the Quernmore Fault is also clearly discernible on the Bouguer gravity anomaly map ((Figure 40)A).

The district comprises several, greatly contrasting geomorphological tracts (Figures 1 and 4), whose features result partly from their underlying bedrock geology but largely from erosional and depositional events that occurred during the late Devensian glaciation. The district's central and eastern parts are dominated by the highest hills of the Forest of Bowland, commonly referred to as the Bowland FellsIn some geological publications the area is also referred to, perhaps erroneously, as the Lancaster Fells., designated as the 'Forest of Bowland Area of Outstanding Natural Beauty'. This moorland is formed mainly of thick, resistant Millstone Grit sandstones. The broad drift-free hill masses of Ward's Stone and White Hill rise to 560 m and 544 m above OD respectively. Rural areas of lower undulating hills covered by blanket till adjoin the fells, extending westwards towards the coast, northwards across the Lune, Hindburn and Wenning valleys, and along Wyresdale into the Forest of Bowland in the south. In its thicker parts, where the underlying bedrock is generally composed of less-resistant siltstones and sandstones of the Millstone Grit, the till is typically moulded into drumlin fields. The coastal plain is composed of early Flandrian Older Marine Deposits, laid down during a period of high sea level, overlying peats in places as well as glaciofluvial deposits and till. The extensive intertidal tracts of Morecambe Bay in the north-west, and the Lune estuary in the south-west, are underlain by thick drift sequences. The wide range of soil types developed across these different geomorphological areas were described by Hall and Folland (1970).

The, drainage of the district (Figure 1) has been inherited, almost totally, from the pattern of meltwater streams established during the waning episode of the last glaciation. Most of the main valleys contain dissected deposits of glaciofluvial sand and gravel. Perhaps the most dramatic feature dating from the glacial episode is the straight course of the Lune, upstream of the Crook o' Lune, with its kilometre-wide alluvial tract, and its extension southwards into the Quernmore valley. This feature is thought, record a major tunnel valley eroded beneath the ice sheet, and is now the site of subsequent thick drift accumulations.

The BGS survey of the district was partly prompted by the explosion of methane in an underground valve house at Abbeystead in 1984. The methane was deduced to have accumulated by outgassing from groundwater that had leaked from Millstone Grit sandstones into the partly empty Wyresdale aqueduct tunnel (Health and Safety Executive, 1985; Orr et al., 1991). Renewed attention to this potential hazard on industrial sites led to the geological survey of the area around Heysham power stations, and in due course to the complete survey of the district. In recent years, there has been an active search for hydrocarbons in the region, the Bowland Shale being considered the most important source rock (Lawrence et al., 1987). Some 365 km of seismic lines have been acquired across the district, and the profiles have proved to be of immense value in the interpretation of the structure of the Craven Basin.

The memoir is a generalised comprehensive account of the geology compiled from the results of this multidisciplinary research and augmented from other scientific studies. In the text, specific reference is not made to individual BGS technical reports, except for those of the two commissioned surveys (Wilson et al., 1989; Wilson and Crofts, 1992), since the relevant report is evident from the area or subject under discussion.

The geological data used in this synthesis have been largely compiled from stream sections, a limited number of quarries, and 1:10 000 mapping. Detailed logs of the two aqueduct tunnels are also important, namely the Wyresdale Tunnel (Johnson, 1981; Wilson et al., 1989) and the Bowland Forest Tunnel; unpublished geological plans of the latter were made available by North West Water plc. Structural information has also been gleaned from seismic profiling and gravity data. Unlike many more populated areas, the Lancaster district contains few boreholes that are stratigraphically useful. The wildcat hydrocarbon Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8) and the BGS Wray Borehole (Figure 22), put down to investigate the heat flow potential of a possible high heat flow anomaly over the Forest of Bowland (Gebski et al., 1987; Rollin, 1987), are notable exceptions. The environs of the Heysham power stations have been thoroughly investigated by numerous site investigation boreholes. Other useful boreholes include two drilled at the beginning of the century in the Bentham area, in connection with the exploration of the Ingleton Coalfield; those drilled by BP Minerals to investigate the metalliferous minerals of the Brennand area; boreholes put down by Tarmac Roadstone and Wimpey in connection with limestone quarrying around Carnforth; and shallow boreholes for sand and gravel resource assessment in the vicinity of Carnforth, especially those drilled by Tilcon Holdings plc. In addition, the survey has benefitted from the results of many shallow site investigation boreholes along the lines of major pipelines, including those of Shell and British Gas. Finally, numerous relatively shallow bore-holes were drilled by BGS during the geological survey of the district to investigate bedrock in its drift-covered western part, and have proved to be of immense value in understanding the disposition of the rocks. The deeper BGS Dam Head Borehole explored the Kinderscoutian stratigraphy of the Quernmore Syncline.

In the stratigraphical account which follows, all the lithostratigraphical names, unless otherwise qualified, are formalised according to recommended stratigraphical practice (Whittaker et al., 1991). Information regarding formal designation into groups, formations and members, i.e. details of type sections, boundaries, etc. has been entered into the BGS Stratigraphical Lexicon.

History of research

The earliest account of the stratigraphy and structure of the district was contained in a report by Phillips (1837) on the probable occurrences of economic coal in the vicinity of Lancaster. The work, an extension of his opus on the geology of Yorkshire (1836), which itself has several notes pertinent to this district, is remarkably perceptive for its day, and includes some illuminating horizontal sections across those parts of the district which were then being mined for coal. The primary geological survey of the district at a scale of six inches to one mile carried out mainly by R H Tiddeman with the assistance of J R Dakyns and C E De Rance around 1880, resulted in the publication of the New Series map at a scale of one inch to one mile in drift and solid editions in 1884. Unfortunately, no descriptive sheet memoir ever appeared, presumably due to Tiddeman's perfectionism (Marr, 1919), though some stratigraphical details of the Millstone Grit strata are discernible from a long and detailed horizontal section across the district (Tiddeman, 1891). Inspired, no doubt, by much contemporary debate concerning evidence for former glaciation in north-west England (for example Mackintosh, 1869), as opposed to the previously held view that boulder clay could be ascribed to marine processes (for example, Tiddeman, 1868), Tiddeman (1872) presented evidence for ice movement and till in the region, from data gathered during his survey work. His discovery of the Caton–Grindleton basalt dyke was left for Eccles (1870) to record.

Following the primary survey, the area appears to have been neglected by geologists for a considerable time. The superficial deposits of the Lune valley in the vicinity of Lancaster and of the coastal zone around Morecambe and Heysham were described by Reade (1904), together with lists of their foraminifera. Some local details of the geology encountered during the construction of Heysham Harbour were noted by Abernethy (1906).

The biostratigraphical zonation of the Carboniferous limestone outcrops near Carnforth was first briefly referred to by Garwood (1912). The earliest really perceptive observations on that area, however, were by Hudson (1936) who recognised the shelf (‘massif’) to shelf margin (‘reef’) to basin facies transition at this northern margin of the Craven Basin. Slinger (1936) was the first to make use of Bisat's (1924) high-resolution goniatite biostratigraphy of the local Namurian, and, though much quoted, his publication was little more than a summary of the nomenclature from his thesis research on the Millstone Grit stratigraphy of Caton Moor. He was also the first to recognise glacial retreat stages in the area. Trotter (1951) constructed a stratigraphy for the thick Arnsbergian sequence of the Lancaster fells following Hudson's (1944b) work on the marine bands of the area. The stratigraphy and structure of the Dinantian limestones, the Bowland Shale and lowest Millstone Grit strata encountered during the construction of the Bowland Forest Tunnel, were described by Earp in 1955, building on the pioneering work of Parkinson (1936) in the adjoining Slaidburn area. The folds affecting the Carboniferous rocks of the district were evaluated in a regional context, in terms of underlying basement controls, by Turner (1949). An account of the Westphalian succession of the Ingleton Coalfield and of the adjacent upper part of the Millstone Grit around Bentham was given by Ford (1954). A definitive paper by Moseley (1954) on the lithostratigraphy, biostratigraphy and structure of the Millstone Grit rocks of the 'Lancaster Fells' resulted from an industrious and detailed survey. Other aspects of this work resulted in an explanation of the Quaternary deposits and glacial features, including a full description of the glacial retreat stages (Moseley and Walker, 1952), an account of the joint patterns (Moseley and Ahmed, 1967), a geomorphological interpretation of the Bowland Fells (Moseley, 1961), and a description and explanation of the upper Dinantian to lower Namurian stratigraphy and structure of the Sykes Anticline (Moseley, 1962). Thewlis mapped 1:10 000 Sheet SD 56 SE (Littledale) for an unpublished undergraduate dissertation thesis (1962; see Appendix 4), which included some details not previously recorded.

Following Moseley's fruitful research, no further original work in the district was published on the bedrock geology for some time, although he later included the district in a regional tectonic history of north-west England (Moseley, 1972). Tooley (1974) documented the stratigraphy of the Quaternary sediments proved in borings for the Morecambe Bay Barrage feasibility study and encountered at the site of the Heysham nuclear power stations in a wider study of changing Flandrian sea levels. Johnson (1981) described deltaic Namurian rocks examined by BGS geologists in the Wyresdale Tunnel during an early phase of the present survey.

Recent interest in basin analysis and the relationship between tectonics and sedimentation have led to papers dealing with the Dinantian sequence by Gawthorpe (1986, 1987) and Gawthorpe and Clemmey (1985) for the Craven Basin (Bowland Sub-basin) in the southeastern part of the district, and by Horbury (1987, 1989, 1992) for the Dinantian shelf sequence in the northwestern part of the district. The northern shelf-basin transition was again alluded to by Gawthorpe et al. (1989). Several unpublished dissertation theses by undergraduate students at Lancaster University deal particularly with aspects of the local Quaternary geology, and with geophysical investigations along the Lune and Quernmore valleys. Recent alluvial fans and river terraces in the Bowland Fells have been the subject of a study by Harvey and Renwick (1987).

On a regional scale, BGS memoir accounts of the geology of the Settle (Arthurton et al., 1988) and Garstang (Aitkenhead et al., 1992) districts have been published to accompany BGS 1:50 000 maps. An unpublished regional account of the depositional history of the Pendle and Grassington grits was given in a PhD thesis by Sims (1988), and a sedimentological study of the Namurian of the Craven–Askrigg area was undertaken by Martinsen (1990, 1993). Johnson (1985) presented a synthesis outline of the glaciation of the west Pennines which included this district. Interest in hydrocarbon exploration during the 1980s has prompted several papers dealing with the structural evolution of the Craven Basin using a variety of geophysical techniques (Gawthorpe, 1987; Lawrence et al., 1987; Lee, 1988). A recent controversial interpretation of apatite fission track analyses concluded that the Pennine region was covered by up to 3 km of post-Triassic sediments, which were removed during the late Palaeogene and early Neogene (Lewis et al., 1992).

Chapter 2 Dinantian: Worston Shale Group and the shelf succession

Lower Carboniferous rocks of Dinantian age, including the Lower Bowland Shale Formation described in the next chapter, almost certainly underlie the entire district but crop out only in the north between Halton, Carnforth and Over Kellet, and in the extreme south-east (Figure 5). In the latter area, the outcrop forms two periclinal inliers in the axial part of the Sykes Anticline, one around Sykes [SD 630 515] south of the district, and the other in the area around Brennand Farm [SD 645 541] and High Laithe [SD 659 555]. These are referred to as the Sykes Inlier and the Brennand Inlier, respectively. A third small outcrop in the south-east, around Burn House [SD 682 527], forms part of the north-west limb of the Slaidburn Anticline, the major part of which lies in the three adjacent districts of Garstang, Clitheroe and Settle.

The first geological map of the Lancaster district, the One-inch Old Series Sheet 91 NE (New Series Sheet 59) published in 1884, shows the lower part of the Carboniferous rock succession to consist simply of 'Carboniferous Limestone' overlain by Toredale Rocks'. In the northern outcrop, the former includes what are now the Park Limestone and Urswick Limestone formations, while the latter are now roughly the equivalent of the Gleaston Formation and the Bowland Shale Group. In the southeast, the limestone formations forming outcrops in the axial parts of the Sykes and Slaidburn anticlines were referred to as 'Carboniferous Limestone', while the overlying, predominantly argillaceous sequence was collectively assigned to the 'Yoredale Rocks'.

Garwood (1912) subdivided the sequence in the northern part of the present district on a biostratigraphical basis, using the coral–brachiopod zonal scheme of Vaughan (1905) which was modified to utilise local assemblages of fossils. He included a new coloured geological map with his paper, reproducing the old Geological Survey boundaries for the 'Carboniferous Limestone' and 'Yoredale Rocks' but showing further zonal and subzonal subdivisions within these two groups. In the present district, these further subdivisions included the S1, S2, D1 and D2 subzones. In recent decades, it has become the practice, for mapping and descriptive purposes, to subdivide the rock succession on lithostratigraphical rather than biostratigraphical criteria. Thus in the modern succession ((Figure 5), (Table 1)), the Park Limestone Formation is roughly equivalent to Garwood's S1 and S2 beds, the Urswick Limestone Formation to D1, and the Gleaston Formation to D2. It must be stressed, however, that new evidence has enabled the recently completed Geological Survey maps to be far more accurate than those produced previously.

The general Dinantian successions and thicknesses for the various outcrops are indicated in (Figure 5), together with their location within the district. The 870 m succes sion in the Slaidburn Anticline outcrop is the thickest in the Craven Basin of the Lancaster district. The shelf succession in the north-west around Carnforth is estimated to be about 300 m thick at outcrop. The Whitmoor Borehole, drilled at a location [SD 5874 6315] midway between these two areas, proved some 494 m of Dinantian rocks (Figures 5 and 8). All these successions are of mid-to late Dinantian age, and none give any indication of what the total thickness of the Lower Carboniferous rocks might be. Seismic reflection and gravity data (Chapter Nine) indicate a thickness for the Lower Carboniferous rocks across most of the district of between 1.3 and 2 km, a value which may include some upper Devonian strata. To the south-east of the Sykes Anticline/Bowland Line, the thickness increases to about 2.75 km. The sub-Carboniferous (or sub-late Devonian) basement is generally supposed, by interpolation from adjacent regions, to consist of strongly folded Silurian rocks (see for example Wills, 1978).

Palaeogeography and depositional history

Northern England and southern Scotland were subjected to crustal stretching during late Devonian and Dinantian times (Leeder, 1982; Gawthorpe et al., 1989). As a result, a series of extensional, fault-bounded, rapidly subsiding basins formed, separated by slowly subsiding horst and tilt-block areas (Miller and Grayson, 1982). This tectonic regime had a profound effect on deposition, resulting in a relatively complete, usually thick argillaceous sequence in the basins and an incomplete, usually thin limestone sequence elsewhere. The present district (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39) lies mostly within the Craven Basin (Hudson, 1933), also called the Bowland Basin by some authors including Ramsbottom (1974), Gawthorpe (1987) and Lee (1988). The basin occupied an asymmetric graben with a southward tilt (Gawthorpe, 1987; Riley 1990), which was bounded by slowly subsiding regions referred to as the Southern Lake District High (Grayson and Oldham, 1987) to the north-west, the Askrigg Block (Hudson, 1938) to the north-east, and the Central Lancashire High (Miller and Grayson, 1982) to the south. The Southern Lake District High encroached into the north-western part of the present district (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39) arounds Carnforth and Nether Kellet. As Adams et al. (1990) imply, the boundary between this 'high' and the adjacent basin to the south was probably gradational during Chadian to Arundian times, in the form of a ramp, unlike the faulted boundaries at the margins of the other adjacent blocks. However, the rocks present on this 'high' show marked differences in facies and thickness when compared with those present in the basin, reflecting marked differences in sedimentary environments, recorded by Hudson (1936) as facies changes between Carnforth and Halton Green [SD 521 654]. Hudson had earlier (1933) noted similar contrasts between the Craven Basin rocks and those of the Askrigg Block.

Deposition in the basin may have started in late Devonian times, and certainly by the early Dinantian (Courceyan). The nature of the thick concealed succession, suggested by seismic evidence (Chapter Nine) to lie beneath the Worston Shale Group, the oldest strata exposed, can only be inferred (see Riley in Aitkenhead et al., 1992, p. 4). The deep borehole at Swinden, in the Clitheroe district to the south-east (Charsley, 1984), showed that by late Courceyan times, a thick marine sequence of shallow-water limestones and fine terrigenous clastic rocks, comprising the Chatburn Limestone Group (late Courceyan–early Chadian), had accumulated. Depth of water appears to have been relatively uniform across the basin, despite the rapid subsidence that must have occurred to accommodate these strata, estimated from seismic evidence to be more than 3 km thick locally. Towards the basin margins, a relatively thin sequence of red beds, peritidal limestones and evaporites may have accumulated, similar to the Stockdale Farm Formation in the Settle district (Arthurton et al., 1988).

This situation continued until the deposition of the Worston Shale Group (Chadian–Asbian), when differential subsidence and more-varied sediment supply began to produce the greater lateral variation in facies and thickness that occur in districts to the south and east (Riley in Aitkenhead et al., 1992, p.4), and which are inferred to occur in the present district where outcrop is more limited. During deposition of the Clitheroe Limestone Formation (early Chadian; (Table 1)), the southward tilt of the graben floor increased, resulting in the deposition of relatively shallow-water bioclastic limestones (Thornton Limestone Member) in the Slaidburn Anticline area, and deeper-water Waulsortian buildups (knoll reefs) in the adjacent districts to the south. In the Craven Basin as a whole, there is evidence for an interval of widespread submarine erosion during the closing phases of Clitheroe Limestone Formation deposition (Riley, 1990).

Deposition resumed during late Chadian times with the Hodder Mudstone Formation (late Chadian–Holkerian), which marks a change in the main supply of carbonate sediment from intrabasinal to extrabasinal sources. A hemipelagic, dysaerobic (oxygen-poor) depositional regime became established and continued for the remainder of the Dinantian. At the same time, however, renewed fault movements rejuvenated the buried intrabasinal horsts, including the Bowland High, part of which lies in the present district ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). Relatively shallow-water limestones (Hetton Beck Limestone Member), deposited on this high and represented in the Sykes and possibly Whitmoor Borehole sections, contrast markedly with the predominantly mudstone sequence of the undifferentiated Hodder Mudstone Formation which is present off the high in the Slaidburn Anticline area. By Arundian times, hemipelagic deposition was widespread, intrabasinal carbonate production had ceased and there was generally slow accumulation of fine-grained mudstones and calcisiltites in deeper water.

The change in sediment supply within the basin, referred to above, corresponded to the onset of shallow-water limestone deposition in the surrounding stable areas (highs) where carbonate ramps, and eventually platforms developed as these areas were submerged by marine transgression (Adams et al., 1990). On the Southern Lake District High, which was transgressed during late Chadian and Arundian times, these deposits are the Martin Limestone, Red Hill Oolite and Dalton Beds (Rose and Dunham, 1977). These formations are probably present at depth in the northern part of the present district but have not been proved. The flanking platforms became the main source areas for carbonate sediment supplied to the basin throughout the rest of the Dinantian. Sediment supply was variable in type and volume as relative sea level oscillated in response to eustatic and tectonic effects. During intervals of relatively low sea level, the carbonate platforms became emergent allowing rivers transporting terrigenous sand and silt to reach the basin; the Buckbanks Sandstone Member in the Garstang district is the result of one such event. Conversely, during intervals of relatively high sea level, carbonate production was optimised, and a significant amount of detrital carbonate was transported into the basin to form accumulations of limestone turbidites, such as the Rain Gill Limestone Member.

During the Holkerian, the Craven Basin became progressively starved of detrital carbonate sediment, a process that culminated in a widespread accumulation of hemipelagic cephalopod limestones, the Hodderense Limestone Formation. On the Southern Lake District High to the north, relatively high rates of shallow-water carbonate sedimentation (Park Limestone Formation) approximately kept pace with subsidence (Adams et al., 1990). However, detailed evidence is lacking in the present district where this formation is dolomitised and poorly exposed.

During late Holkerian and Asbian times, limestone turbidite supply to the basin resumed with the deposition of the Pendleside Limestone Formation. The carbonate platform environments surrounding the basin, including the Southern Lake District High, were at their maximum extent, acting as carbonate sediment factories from which copious amounts of detrital carbonate were exported into the basin. The Urswick Limestone Formation in the north of the present district, the main formation of Asbian age on this 'high', consists of cyclical sequences of facies types bounded by emergent palaeokarstic surfaces (Horbury, 1989), in common with many other Asbian platform or shelf successions to the south (Walkden, 1987), in the Peak District for example. According to Horbury (1989), sedimentation of the Urswick Limestone was controlled by an interplay of probable fault-controlled subsidence and eustatic sea level oscillations, the latter reflecting the accumulation and melting of south polar ice caps. The environmental changes on the platform were remarkable, with a variety of shallow-water environments during highstands, often with an abundance of marine organisms. These conditions alternated with periods of emergence when much of the platform area was probably flat, low-lying land with extensive vegetation (Adams et al., 1990). On rare occasions, relative uplift was greater, resulting in steep-sided valleys being eroded into the platform surface near the platform margin (Horbury, 1989).

The rocks deposited in the Craven Basin during late Asbian times (see Chapter Three) can be correlated by means of ammonoid (goniatite) biostratigraphy with the initiation and growth of fringing 'reefs', for example the 'reef-knolls' of the Cracoe area, at the boundary between the Craven Basin and the adjacent carbonate platforms ('Transition Zone' of Arthurton et al., 1988). There is some evidence that 'reefs', such as that at Swantley near Nether Kellet, may also fringe the southern margin of the Southern Lake District High. The development of these rimmed platforms tended to isolate the basin from supplies of detrital carbonate. Continuing oscillations in relative sea level led to erosion of the platform margin during lowstands, as indicated by the presence of limestone clasts and reworked foraminifera in some of the basinal limestone turbidites. This effect was also accentuated by uplift of the south-western margin of the Askrigg Block (Arthurton et al., 1988). In addition, local tectonic control is indicated by marked local variations in facies and thickness in the Gleaston Formation (latest Asbian–Brigantian) near the margin of the Southern Lake District High, both in the present district (p.00) and elsewhere (Rose and Dunham, 1977; Adams et al., 1990).

The diminution of carbonate sediment supply to the basin was eventually matched on the platform, where the limestones are predominantly dark and argillaceous with interbedded 'black' pyritic mudstones. The former, clear, well-oxygenated seas were only rarely to return, as climatic changes took place (Leeder, 1988), sea level initially rose, and the influx of terrigenous sediment subsequently increased from river deltas prograding intermittently from the north.

Classification

Lithostratigraphy

The lithostratigraphical scheme adopted for the Craven Basin rocks in the present district is shown in (Table 1). It is the same as that used in the adjacent Garstang district (Aitkenhead et al., 1992) which was largely adopted from that of Riley (1990). A comprehensive review of earlier schemes was given by Fewtrell and Smith (1980). The Clitheroe Limestone, Hodder Mudstone, Hodderense Limestone and Pendleside Limestone formations all belong to the Worston Shale Group and were formally defined or redefined by Riley (1990).

The formation names used for the carbonate shelf sequence in the north of the district (Table 1) are those of Dunham and Rose (1941) and Rose and Dunham (1977) for the western part of the Southern Lake District High. Adams et al. (1990) applied these names to the whole of the shelf outcrop south of Kendal, but noted that the nomenclature had 'never been formalised according to recommended stratigraphic practice'. It is here proposed that at least the three highest formations of Dinantian age, which crop out in the present district, be formally accepted. These are the Park Limestone Formation, the Urswick Limestone Formation and the Gleaston Formation.

Biostratigraphy and chronostratigraphy

Biostratigraphical and chronostratigraphical subdivision of the Dinantian of Britain has recently been reviewed and summarised by Riley (1993), and that of the Craven Basin succession in adjacent areas to the south of the present district by Riley (1990) and Aitkenhead et al. (1992). Corresponding subdivision of the Southern Lake District High carbonate platform sequence has been given by Rose and Dunham (1977) and Adams et al. (1990). Subdivision of the Dinantian of the present district is summarised in (Table 1).

Macrofaunas of the Park Limestone, Urswick Limestone and Gleaston formations have been recorded in detail by Garwood (1916) and Rose and Dunham (1977) to which the reader is referred. Some are also mentioned in the stratigraphical account which follows, together with significant microfossils, which have proved particularly useful in elucidating the overall stratigraphy of the Craven Basin sequence.

Shelf sequence

Park Limestone Formation

This formation was named after Park Sop [SD 213 754] near Dalton-in-Furness where it was formerly exposed (Rose and Dunham, 1977). Reference sections are designated in the type area at Stainton Quarries [SD 245 728] where the upper half of the formation and its junction with the overlying Urswick Limestone is exposed (Rose and Dunham, 1977, p.48), and at Barker Scar near Holker Hall in the Cartmel area. Here [SD 245 728], the basal 45 m of the formation is exposed, together with the junction with the underlying Dalton Beds (Rose and Dunham, 1977, p.54 and fig. 8). This section is also the stratotype for the Holkerian Stage (George et al., 1976).

The only rocks to be assigned, tentatively, to this formation in the present district, are partially dolomitised limestones that crop out over a small area in the axial part of the Leapers Wood Anticline, exposed mainly in the deepest part of Leapers Wood Quarry [SD 516 694] (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6). Here, the bedding is poorly defined due to the scarcity of other contrasting lithologies such as clays. This, together with the largely dolomitised nature of these massive, crinoidal, bioclastic pack-stones and grainstones, may distinguish this sequence from the overlying Urswick Limestone Formation. No fossils have been recovered and the assigned Holkerian age is inferred from that proved elsewhere in the south Cumbrian succession (Rose and Dunham, 1977, p. 34; Mitchell, 1978, p. 174). The subdrift outcrop to the north-west of Over Kellet is unproved.

Urswick Limestone Formation

The Urswick Limestone was named and described, with its type area in the Barrow-in-Furness district, by Dunham and Rose (1941) and Rose and Dunham (1977); formation status was assigned informally by Horbury (1989), and is formally proposed here. Stratotype reference sections occur at the Devonshire quarry complex [SD 249 728] near Dalton-in-Furness and near Kirk House in the present district [SD 5250 6976] to [SD 5265 6963]. The formation consists predominantly of alternating sequences, 3 to 24 m thick, of pale brown, massive, thickly bedded grainstones and mottled grey to pale grey-brown packstones (Horbury, 1989). Interspersed with these two major lithofacies are pale grey to dark brown carbonate mudstones and wackestones, varicoloured K-bentonitic clays, and limestone conglomerates. These are usually associated with well-defined bedding planes, in many cases showing a mamillated form due to palaeokarstic dissolution.

The lower boundary of the formation is defined as the point where poorly bedded homogeneous-textured limestones of the Park Limestone Formation pass upwards into well-bedded heterogeneous-textured limestones and 'pseudobreccias' of the Urswick Limestone. Horbury (1987, 1989) and Adams et al. (1990) found that the formation lies, with up to 20 m of unconformable onlap extending over the regional outcrop, on a palaeokarstic surface at the top of the Park Limestone. The upper boundary of the formation is taken at the point where the predominantly pale, thickly bedded Urswick Limestone passes upwards into the predominantly dark, thinner bedded limestones and 'black' shaly mudstones of the Gleaston Formation. The thickness of the formation reaches its maximum of about 180 m on the steep limb of the Hutton Monocline in the present district; the thickness range elsewhere is between 120 and 160 m (Horbury, 1989; Adams et al., 1990). The formation is essentially Asbian in age, though in places the diachronous top is earliest Brigantian.

The outcrop of the Urswick Limestone in the Lancaster district extends from the northern boundary of the 1:50 000 sheet to the vicinities of Bolton-le-Sands and Nether Kellet, and thence north-north-eastwards in a narrow faulted belt through Over Kellet where it is folded in the Hutton Monocline. Apart from two isolated but significant exposures, one in a disused quarry near Bolton-le-Sands [SD 487 681] and the other at Millhead [SD 498 714], all the western part of the outcrop is drift covered and largely unproved by drilling. The configuration of the geological boundaries and structure are therefore highly conjectural. In contrast, in the part of the outcrop that lies east of the M6 Motorway, drift is either thin or absent. As a result, the limestones are well exposed and extensively quarried.

Despite the good exposure, the base of the Urswick Limestone is not easily recognised in this district. The limestones in the basal part of the formation and the top part of the underlying Park Limestone Formation may appear similar in colour and texture, and the Holkerian foraminiferal assemblage characteristic of the lower formation has not been found in the few samples collected. The main distinguishing feature, i.e. the well-bedded character of the Urswick Limestones compared with the poorly bedded Park Limestones, is apparent in only two sections. These are located (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6) at Leapers Wood Quarry [SD 517 693] and in a disused quarry [SD 525 699] stratigraphically below the base of the long Urswick Limestone section [SD 5250 6976] to [SD 5265 6963] near Kirk House, Over Kellet. The top of the formation is also exposed in the Kirk House section and is taken at a bedding plane 5.8 m below the top of the section where the limestones become predominantly medium to dark grey in colour. The same sort of transition between the Urswick Limestone and Gleaston formations is exposed in the vertically inclined sequence at the disused Overhead Quarry [SD 529 714], but access to the quarry faces here is difficult and dangerous due to flooding.

The lithology of the Urswick Limestone has been studied in detail by Horbury (1987), who examined major quarry sections across almost the entire outcrop, including those at Leapers Wood, Back Lane and Dunald Mill quarries in the present district. Summaries of the stratigraphy and depositional models (Horbury, 1989; Horbury and Adams, 1989; Adams et al., 1990; Horbury, in press), form the basis of the following account; somewhat simplified logs of three detailed measured sections are shown in (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6).

The two principal rock associations, in order of relative abundance, are pale grey-brown, well-sorted grainstones, and grey to pale grey-brown, more-micritic limestones ranging from packstones to mudstones with some interbedded grainstones. These two associations comprise, respectively, the 'sub-wavebase facies' and the 'shoal grainstone facies' of Horbury (1987), who noted that 'compaction of some grainstones resulted in the loss of all or most depositional porosity, and consequently these appear in the field as diagenetic packstones or wackestones'. Original, commonly peloidal textures are only readily identified from acetate peels or thin sections. The grainstones occur in massive, very thick (up to 10 m), well-jointed beds that usually lack any sedimentary structures. Corals such as Siphonodendron (Lithostrotion) and Syringopora occur mostly as dispersed fragments, and rarely as more complete colonies, either rolled or in growth position. Brachiopod fragments are a common constituent, while largely unbroken productoid shells tend to occur in localised concentrations at a few levels. Peloids comprise the most abundant of the non-bioclastic grain (allochem) constituents, which also include intraclasts and ooids. Bioclasts are dominated by the alga Kamaenella (Adams et al., 1992), but include other algae such as Koninckopora, Ungdarella, Polymorphocodium and the encrusting Girvanella.

The second main limestone rock type, comprising mostly packstones, is generally much thinner bedded than the grainstones and commonly shows dark, sharply defined mottles. These give a rubbly appearance in weathered sections, and reflect the presence of Thalassinoides burrows (believed to be produced by shrimp-like crustaceans). Such burrowed packstones are most conspicuously present in a unit informally named the 'Triple Rubbly Band' by Horbury (1987), which forms a useful marker, well seen in Leapers Wood Quarry (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6).

Other rock types described by Horbury (1987) and present in the Carnforth area include pale grey to dark grey-brown carbonate-mudstones and wackestones, dark grey siliciclastic mudstones, varicoloured K-bentonitic clays, and limestones of conglomerate (rudstone), calcarenite and calcisiltite grade derived from the erosion of emergent limestones. The carbonate-mudstones and wackestones are usually present as single beds, up to 0.4 m thick, with a splintery conchoidal fracture; some beds contain small, clear, spa-filled fractures or fenestrae. The siliciclastic mudstones and K-bentonite clays are soft and weather out readily, and are rarely exposed outside quarries. The clays commonly overlie limestone beds whose top surfaces were weathered to an undulating (mamillated) form by penecontemporaneous dissolution following emergence. The upper parts of these beds may also contain evidence of roots (rhizocretions) and soil-forming processes (laminar calcretes, micritised surfaces, pedogenic micrite and pedogenic K-bentonite clay). Though these lithologies comprise only a small proportion of the total Urswick Limestone sequence, they have great significance in the interpretation of the various depositional environments which were present on the platform. Near the southern margin of the main outcrop south-east of Nether Kellet, important facies changes may be observed that indicate the proximity of the platform margin. A prominent palaeosol clay bed on an irregular eroded surface is exposed high on the west face of Dunald Mill (West) Quarry [SD 5100 6792] to [SD 5097 6810], 12 m below the top of the section illustrated in (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6). The limestones overlying this clay, have been described by Horbury (1992), who found that they consist of shoal grainstones which pass laterally northwards into a peloid cementstone algal bioherm or reef. This structure is about 11 m high and 9 m wide, and is distinguishable by its steep-sided dome shape and its apparent lack of bedding. There is an increase in the proportion of the 'shoal grainstone facies' from north to south in the quarry, and also when compared with Back Lane and Leapers Wood quarries to the north (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6). The general structure of the area of the Dunald Mill quarries is that of a broad dome so that the stratigraphical level of the palaeosol clay and overlying reef mentioned above, which lie on the western limb of the fold, is probably again exposed on the east face of the inactive Dunald Mill (East) Quarry [SD 5153 6789] to [SD 5157 6780]. This face has not been logged in detail but contains a complex array of contacts and facies, including peloidal oncolitic grainstones, concentrations of athyrid shell debris, and boulder beds. Towards the south end of the section, in the likely direction of the platform margin, several neptunian dykes and fissures occur, the latter showing a polyphase fill of crinoidal calcarenite, 'black' pyritic organic mudstone, calcisiltite and terrigenous sandstone.

Other occurrences of reefs or fine-grained limestone buildups are known in this area. One is indicated by a very small exposure [SD 5087 6752] south of Hill Top Farm but the only substantial exposure is in the Swantley Inlier (Figure 5) where it forms part of a prominent line of crags [SD 5230 6788] to [SD 5243 6766]. The reef here consists of a mass of pale grey, fine-grained limestone forming the core of what is probably a fault-bounded periclinal structure. It appears to be unbedded except at its northern margin, where it can be seen to interdigitate with coarser-grained limestones flanking the reef. The rock shows the characteristic 'reefy' fabric on a few naturally etched surfaces, together with small sparry cement-filled cavities, scattered small brachiopods and, at one point, a pocket of indeterminate ammonoids. There is also some irregular silicification which, in places, gives an indication of bedding orientation, and a neptunian dyke of dark bituminous limestone is present at the foot of the crags [SD 5239 6774].

Scattered exposures of the Urswick Limestone occur outside the Nether Kellet area, e.g. in M6 Motorway cuttings [SD 5117 7061] to [SD 5104 7045], [SD 5117 7046], and [SD 5049 6947] to [SD 5041 6913] and in disused quarries at Millhead [SD 4983 7142] and Bolton-le-Sands [SD 4871 6816]. None are of particular stratigraphical significance, but the last-mentioned quarry is the most southerly exposure of the formation and provides some constraint on the location of the platform margin, which must lie farther south.

During deposition of the Urswick Limestone, as the names of the 'shoal grainstone facies' and 'sub-wavebase facies' of Horbury (1989) indicate, contrasting environments were present on the platform, depending on whether or not the sea floor was affected by wave-induced currents. This in turn was dependent on rates of subsidence and eustatic sea-level changes. The low-energy sub-wavebase environment is indicated by the presence of carbonate-mud-bearing packstones and wackestones, 'with diverse open marine faunas and floras often in growth position and abundant bioturbation' (Horbury, 1989). The sequences in which grainstones predominate, with their low depositional lime-mud content and sparse evidence of bioturbation and macro-fossils in growth position, 'suggest an intertidal to shallow subtidal high energy, probably wave-dominated grainstone shoal complex' (Horbury, 1989).

Interbedded with the predominant rock types described above are lithofacies indicating that there were times when the platform became emergent. The evidence usually includes a bedding surface modified by palaeokarstic solution, an overlying palaeosol clay, and pedogenic (soil forming) alteration of the topmost part of the underlying limestone (Davies, 1991). Pedogenic alteration includes the production of dark laminar calcrete, micrite and micritised surfaces. The presence of the roots of vegetation which grew on the developing soils is indicated by irregular tubes, known as rhizoliths (Klappa, 1980), filled mainly with sparry calcite and sheathed by altered limestone (rhizocretions).

There were probably also a few occasions when freshwater streams eroded valleys into the emergent platform surface. An extraordinary example occurs in Leapers Wood Quarry [SD 5171 6947] (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6) and was described in detail by Horbury (1987, 1989, and in press). This valley attained a depth of nearly 30 m, and was eroded down from a palaeokarst surface that now lies strati-graphically about 24 m above the base of the Urswick Limestone. It is infilled with limestones of a quite different facies from those forming the sides of the valley ((Plate 2); (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6)), and includes, in upwards succession, dark calcisiltites, limestone conglomerates containing boulders of collapsed wall rock, and oolitic grainstones. This succession was thought by Horbury (in press) to represent the progressive infill of the valley which developed into a ria-like inlet as sea level rose.

In common with other Asbian platform sequences in Europe and North America, lithologies in the Urswick Limestone Formation tend to be arranged in regular cyclical sequences. Horbury (1989, fig. 7) identified a number of platform-wide major cycles, characterised in many sections by packstones and wackestones in the lower part and grainstones in the upper part. Three such major cycles are recognised in the basal 35 m of the Urswick Limestone in Leapers Wood Quarry (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6). Although the higher part of this section consists largely of grainstones, Horbury recognised two further major cycles by inferring correlations of some of the interbedded palaeosol clay beds with other sections across the platform, where the cycles are more clearly differentiated. In addition, he recognised some 19 minor cycles in Leapers Wood Quarry (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6), mostly bounded by emergent surfaces marked by beds or partings of palaeosol clay (Horbury, 1989). Significantly, these surfaces are developed on pedogenically altered limestones whose facies represent environments ranging from 'deep subtidal to supratidal'.

Quite different mechanisms were suggested by Horbury (1989) for the major and minor cycles. The former were attributed to movements associated with 'platform downfaulting', whereas the latter probably resulted from temporary eustatic falls in sea level caused by the growth of ephemeral ice caps at polar latitudes or high altitudes in the southern hemisphere continent of Gondwana.

Biostratigraphy of the Urswick Limestone

Foraminiferal assemblages in the Urswick Limestone are abundant and well preserved. Foraminifera of the Cf6a Subzone (lower Asbian) are particularly well represented in the lower part of the formation at the isolated quarry at Bolton-le-Sands [SD 4871 6816], and include Endothyra tynanti, Florenella llangollensis and Pojarkovella. At Swantley [SD 5239 6775], Endothyra tynanti is also present in the micritic 'knoll-reef limestone. This facies is cut by a neptunian dyke [SD 5239 6774] which contains Koninckopora inflata and poorly preserved Pojarkovella?, suggesting fissuring of the reef during the early Asbian. At Leapers Wood Quarry [SD 5160 6960], foraminifera that are typical of lower Asbian strata (Cf6α Subzone), comprising bilaminar palaeotextulariids, Vissariotaxis sp. and Bibradya inflata, occur in the strata which lies between 14.6 m below and 2.8 m above the Triple Rubbly Band (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6). Upper Asbian assemblages enter about 6 to 10 m above the Triple Rubbly Band, in a 3 m-thick band with the brachiopod Davidsonina septosa which has been located at Back Lane [SD 5100 6920] and Leapers Wood quarries. Some foraminifera of lower Asbian aspect (Cf6a Subzone) persist, with Florenella cf. llangollensis occurring some 41 m above the D. septosa band at Back Lane Quarry. However, poorly preserved Neoarchaediscus, indicative of the Cf6γ Subzone, enter 17 m above D. septosa there. The uppermost beds at Back Lane Quarry, some 77 m above the Triple Rubbly Band, yield Howchinia sp. and Saccamminopsis, allowing tentative correlation with the natural outcrop exposed at Kirk House [SD 5250 6976] to [SD 5265 6963] where the lowest Saccamminopsis band lies 16.9 m below the top of the Urswick Limestone (see below). The Triple Rubbly Band at Kirk House has not been located, but the presence of Climaccammina, an upper Asbian (Cffry Subzone) marker, 46.8 m below the top of the Urswick Limestone, indicates that it must lie within or below the lowest 87.9 m of the section there.

Dolomitisation

Dolomitisation has locally affected both the Park and the Urswick limestone formations. The alteration process has imparted a granular texture to the dolomitised limestone, and a brown colour which makes this rock conspicuous in the faces of Leapers Wood [SD 516 694], High Roads [SD 516 691] and Back Lane [SD 511 692] quarries. In Leapers Wood Quarry, much of the Park Limestone Formation is dolomitised. In the Urswick Limestone Formation, the dolomitised limestone occurs as moderately irregular bands subparallel to the bedding, in the order of 1.5 to 3.5 m thick but amalgamating in places to total about 6.0 m. Some bands probably extend laterally for at least 1 km to the limits of the quarry exposures, with about 5 per cent of the total succession dolomitised. A relatively minor amount of dolomitised limestone is also irregularly present adjacent to fault planes.

Horbury (1987) showed that the semi-stratiform dolomitisation has mainly affected limestones below palaeokarstic surfaces, and that in the platform outcrop as a whole, it is largely confined to the marginal area around Carnforth. The dolomitisation probably resulted from the late diagenetic dewatering of mudstones in nearby parts of the Craven Basin. Cements, precipitated early from marine and meteoric pore waters in the Urswick Limestone Formation and identified by cathodoluminescence studies, are composed of calcite (Horbury and Adams, 1989).

Gleaston Formation

The Gleaston Formation was first defined by Rose and Dunham (1977, p.30) to include a mixed sequence of dark mudstones, thinly bedded dark limestones and sandstones, 'above the Urswick Limestone and below the C. leion Band'. The type locality is at Gleaston in the Ulverston district of south Cumbria. George et al. (1976, fig. 11) gave its age as Brigantian, but evidence from the present district (see below) suggests that its age extends back to the latest Asbian (Table 1).

In the district, the formation is largely concealed beneath thick drift deposits and unproved by drilling, except for a recent borehole ((SD56NW/64), see below) near Nether Kellet. As a result, its outcrop is conjectured as a narrow strip around the much more extensive outcrop of the Urswick Limestone. In this marginal area, the Gleaston Formation is assumed to pass laterally and gradationally into its basinal equivalent, the Lower Bowland Shale Formation, and any boundary drawn between the two is arbitrary. The total thickness of the formation ranges from 8 m in the above-mentioned borehole, to an estimated 140 m north-east of Over Kellet where it comprises an extended sequence on the steep limb of the Hutton Monocline. The disused Overhead Quarry [SD 5287 7127] (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6), where access is difficult and dangerous, and the section near Kirk House [SD 5265 6963] expose about 30 m and 5.8 m, respectively, of the lowest beds in the formation. At both localities, the base is taken at the point where the limestones become predominantly dark grey to grey and relatively thinly bedded, in contrast to the pale, very thick limestone beds of the underlying formation.

In the Kirk House section, there is no appreciable change in the foraminiferal assemblages across the formation boundary. The dasyclad alga Koninckopora is absent above this level, however; the extinction of this genus is closely correlated with the Asbian–Brigantian boundary. The formation boundary is also exposed just north of the district in the River Keer [SD 5304 7194] (see below) near Capernwray, but there the disappearance of Koninckopora is in a 5 m-thick limestone bed, 5 m above the base of the Gleaston Formation (Figure 7). These differences in the relative position of the upper limit of Koninckopora suggest either diachroneity of its disappearance between sections, possibly due to facies control, or diachroneity of the lithostratigraphical boundary. Similar problems have been described from Derbyshire and North Wales (Chisholm et al., 1983, Somerville and Strank, 1984).

The predominant lithologies in the lower part of the extended sequence, on the steep limb of the Hutton Monocline, consist of medium to thickly bedded, cherty, dark grey wackestones and packstones with minor interbeds of grey grainstone, 'black' pyritic shaly mudstone, and dolomitic limestone. These can only be seen easily in a section on the bed of the River Keer [SD 5309 7198] to [SD 5304 7194], some 0.4 km north of the district boundary, where the lowest 43 m of the formation are exposed together with the junction with the Urswick Limestone (Figure 7). A 2.11 m bed of dark wackestone, 1.05 m above the base of this section, contains small Girvanella? nodules and probably represents the Girvanella Nodular Bed of Garwood (1913, p. 482). This is a widespread marker at or near the base of the Brigantian dark limestone sequence, both on the Southern Lake District High (see Mitchell in Rose and Dunham, 1977, p.35) and on the Askrigg (Dunham and Wilson, 1985, fig. 7) and Alston blocks (see for example Burgess and Holliday, 1979, fig. 25). Concentrations of Saccamminopsis are also widespread elsewhere in the lower part of this sequence; they occur here 15.9 m to 21.8 m above the base. The upper 22.5 m of the River Keer section, from 21.5 m above the base of the Gleaston Formation, contains a foraminiferal assemblage definitive of the Cf68 Subzone of mid-Brigantian age. These include Asterarchaediscus postrugosus, Betpakodiscus attenuates, Howchinia bradyana and Neoarchaediscus probates, and represent the most diverse assemblage of this age recovered during the survey.

About 1.8 km west of the Hutton monoclinal belt, near Hill Top Farm, Nether Kellet, a borehole (SD56NW/64) [SD 5074 6762] penetrated the entire formation in a mixed sequence only 8.1 m thick, consisting of dark mudstone, pale grey-brown limestone, and limestone conglomerates. This provides a remarkable contrast to the River Keer section outlined above (Figure 7). The mudstones yielded well-preserved miospores of the VF Zone of Brigantian age. The formation is overlain by a 3.84 m turbidite sequence, of mudstones and siltstones with a few thin sandstone beds, which has yielded NC Zone (Owens et al., 1977) miospores indicating an age within the late Brigantian to Pendleian interval. The sandstones could therefore be correlatives of those in either the upper Brigantian Pendleside Sandstones Member or the upper Pendleian Pendle Grit Formation. The latter is preferred because of the absence of marine fossils, but the former is not entirely ruled out. As a further contrast, a disused roadside quarry [SD 5065 6783] immediately below Hill Top Farm, only 224 m along strike to the north-north-west of the borehole site, exposes 4.57 m of mainly dark grey wackestones and packstones with shaly partings and some intraformational slumping.

The upwards change from the pale grainstones and packstones of the Urswick Limestone, to the dark, relatively thinly bedded cherty wackestones and pyritic mudstones of the Gleaston Formation, marks a major marine transgression (see also Harrison in Rose and Dunham; 1977, p. 39). This drowned much of the shelf and platform areas surrounding the Craven Basin, including the Southern Lake District High, so that the clear, well-oxygenated shallow shelf seas were initially replaced by deeper, often poorly oxygenated waters. At the same time, the amount of terrigenous mud and silt being brought into the area by rivers increased, probably due to a change to a wetter climate (Rowley et al., 1985). However, there are clear indications that eustatic cyclicity and local earth movements also affected sedimentation, producing marked differences in facies and thickness in places across the Southern Lake District High (Rose and Dunham, 1977, fig. 5 and p. 35; Adams et al., 1990, p. 26).

In the present district, the contrast between the rock sequence proved in Borehole (SD56NW/64) near Nether Kellet, and that 5 km away to the north-east in the River Keer section (see above), provides striking evidence of local tectonic control, although precise correlation between the two Brigantian sequences is lacking.

Basin sequence

The Dinantian rocks that crop out in the south-eastern part of the district and in the Halton Green inlier, southeast of the main outcrop around Carnforth, all lie within the Craven Basin (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39). (Figure 5) shows, in a generalised form, the sequences present in each inlier, except for that at Halton Green where rocks assigned to the Pendleside Limestone and Lower Bowland Shale formations occur. The various formations are described below in ascending stratigraphical order. All the formations, either at outcrop or proved in boreholes, belong to the Worston Shale Group, except for the Lower Bowland Shale Formation, at the top of the succession, which belongs to the Bowland Shale Group. The term Worston Shale Group was used informally by Earp et al. (1961) and is approximately the equivalent of the Worston Group of Moseley (1962). It was formally defined by Riley (1990), who also defined a number of constituent formations, some of which occur in the present district (see below).

Clitheroe Limestone Formation

The Clitheroe Limestone Formation is known in this district only in the extreme south-east, where it is represented by the Thornton Limestone Member cropping out on the steep north-west limb of the Slaidburn Anticline. The formation was redefined, and the member defined, by Riley (1990); both occur extensively to the south-east of the present district, within the Craven Basin.

There is no significant exposure in the present district but studies from the adjacent Garstang (Sheet 67) and Settle (Sheet 60) districts demonstrate that this formation contains coral–brachiopod and foraminiferal faunas referable to the C1 Coral–Brachiopod Zone and Cf4α1 Subzone of the Eoparastaffella (Cf4) Foraminiferal Zone. This correlates with the lower part of the Chadian Stage, of latest Tournaisian age (Table 1).

The Thornton Limestone Member commonly comprises wavy-bedded, mostly fine- to medium-grained, dark grey, cherty, argillaceous packstones and wackestones, with scattered corals including Syringopora, and brachiopods comprising mainly productoids, chonetoids and spiriferoids. These beds are thought to have been deposited on the shallower part of a southward-dipping submarine ramp (Riley, in Aitkenhead et al., 1992). In the present district, scattered exposures [SD 6807 5211] to [SD 6822 5230] south of Burn House contain conspicuous 'black' chert commonly replacing burrow fills.

Hodder Mudstone Formation

The Hodder Mudstone Formation, of late Chadian to Holkerian age, was first defined by Riley (1990) following completion of the BGS resurvey of the Garstang district. That district shares, with the adjacent Clitheroe district, the type locality of the formation on the bed of the River Hodder [SD 6680 4330] to [SD 7007 4070]. Over much of the previously mapped areas of the Craven Basin, the extensive outcrop was referred to as undifferentiated Worston Shales. Riley (1990) also defined ten members occurring locally in various parts of the basin, of which two, the Hetton Beck Limestone and Rain Gill Limestone members are known in the present district (Figure 5).

On a regional scale, the basal contact with the underlying Clitheroe Limestone Formation is unconformable. Though this contact (with the Thornton Limestone Member) is of very limited extent and unexposed in the present district, the relationship is assumed to be the same. The upper boundary is taken where the predominantly mudstone and siltstone sequence passes up into the pale grey-brown wackestones with dark varicoloured micritic nodules that characterise the overlying Hodderense Limestone Formation. The full thickness of the formation is present only on the north-west limb of the Slaidburn Anticline, where it is estimated to be about 450 m.

The general lithology of the undivided formation consists of dark grey to grey, blocky and fissile, silty, calcareous mudstones with subordinate thinly interbedded, silty argillaceous limestones or calcisiltites. Thin lenses and nodules of 'black' chert occur in places, and soft-sediment deformation structures such as slump folds are common. Good exposures of these rocks occur [SD 6816 5238] to [SD 6811 5251], and [SD 6783 5230] south and south-west of Burn House in the Slaidburn Anticline. The mudstones in the lower part of the first of these exposures are highly cleaved, while the second shows the boundary with the overlying Rain Gill Limestone Member (see below). The macrofossil assemblage found in the Hodder Mudstone is fairly low in both numbers and diversity, and includes solitary corals, small chonetoids, smooth spiriferoids, pectinoid and nuculoid bivalves, gastropods, cephalopods, trilobites and fish debris, indicating a sea bottom environment depleted in oxygen (Riley in Aitkenhead et al., 1992, p. 20). Evidence of bioturbation is common, in the form of small, dark, irregular burrow fills whose presence, in isolated exposures, helps to distinguish beds of this formation from those of the overlying Bowland Shale Group. Limestone turbidite beds are sporadically present in the sequence, and locally become common enough to form a mappable unit, the Rain Gill Limestone Member.

The Hodder Mudstone Formation represents deepen-ing of the carbonate ramp, which retreated northward. There is no exposure of the lowest part of the formation in the present district, but in the adjacent Garstang and Settle districts, ammonoid, conodont, foraminiferal (in turbidites) and trilobite faunas occur and are referable to the Cf4α2 Subzone of the Eoparastaffella Cf4 Foraminiferal Zone of late Chadian, basal Visean age (Table 1).

The Hetton Beck Limestone Member of latest Chadian age, is at least 80 m thick in the Sykes Anticline, and is lithologically similar to the Thornton Limestone Member of the Clitheroe Limestone Formation. In the Settle district, the Hetton Beck Limestone rests unconformably on the Thornton Limestone, but in the present district the base of the Hetton Beck Limestone has not been proved. The main outcrop, at the base of the exposed sequence at Sykes, lies just outside the district boundary (Aitkenhead et al., 1992, p. 25). However, the Hetton Beck Limestone occurs in the basal part of the sequence in boreholes in the Sykes and Brennand inliers (Figure 9), and may also be represented by undivided limestones at the base of the Whitmoor Borehole sequence (Figures 5 and 8).

The member consists of grey, fine- to coarse-grained packstones with thin partings and interbeds of shaly mudstone and scattered thin lenses and nodules of dark chert; Moseley (1962) referred to it as the 'Lower limestones with chert'. Thin, current-winnowed, crinoidal bioclastic lenses are sporadically present, together with disarticulated brachiopods and silicified overturned Syringopora; bioturbation is common. Foraminifera and algae indicate that the Hetton Beck Limestone lies in the Cf4α2 Foraminiferal Subzone, and is therefore contemporary with the hemipelagic mudstones and limestone turbidites in the basal part of the Hodder Mudstone Formation in the Slaidburn Anticline. Assemblages recovered below 174.65 m from the cores of borehole (SD65SW/25) (Figure 9) include Dainella micula, Endothyra laxa, Eoparastaffella sp., Eotextularia diversa, E. mongeri, and bilaminar Koninckopora. Foraminiferal assemblages of the Cf4a2 Subzone, comprising Eoparastaffella and bilaminar Koninckopora, also occur in limestone cuttings from the basal part of the Whitmoor Borehole (Figure 5) and (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), between 1494.5 m and 1559.0 m TD.

Synsedimentary slump structures are evident at outcrop (Gawthorpe and Clemmey, 1985) and in boreholes, notably (SD65SW/22) [SD 6372 5233] (Figure 9), and there is an increasing abundance of graded beds towards the top of the member. This evidence suggests deposition either on the lower part of a submarine ramp or on the upper part of a slope. Biostratigraphical evidence indicates that the member is coeval with at least part of the Martin Limestone of South Cumbria (Rose and Dunham, 1977), and with hemipelagic mudstones with limestone turbidites (Whitemore Limestone Member) in the Garstang district to the south. The former sequence is thought to have been deposited on the shallow proximal part of a ramp (Adams et al., 1990), and the latter in a relatively deep part of the basin.

The upward passage from the Hetton Beck Limestone Member to undivided Hodder Mudstone Formation is gradational in the Sykes and Brennand inliers, and is characterised by a gradual increase in the proportion of interbedded shaly mudstone and a corresponding decrease in the proportion of limestone. In many places, however, the original lithology is masked by pervasive silicification or chertification in this part of the sequence. In the Sykes Inlier, silicified limestone is sufficiently thick (7.62 m according to Moseley, 1962) and extensive to be shown on the 1:50 000 geological map.

In the Sykes and Brennand inliers, carbonate ramp deposition ceased by Arundian times, when the Hetton Beck Limestone was inundated by hemipelagic mudstones. Cores of thin interbedded turbidites within these mudstones in borehole (SD65SW/25) (Figure 9) have yielded foraminiferal assemblages referable to the Cf4γ Subzone and Cf5 Zone, of Arundian to Holkerian age (Table 1), including primitive archaediscids such as Glomodiscus oblongus and Paraarchaediscus sp. (at the involutus stage of coiling) at 168.9 m and possible Pojarkovella at 145.8 m. The basal Arundian Cf4β Foraminiferal Subzone has not been recognised, and it is possible that the top of the Hetton Beck Limestone is marked by a non-sequence, as in the adjacent Settle district (Eshton–Hetton Anticline). Unfortunately, this contact is obscured by chertification in the present district.

Laterally equivalent limestone sequences are also of Arundian age, and include the Rain Gill Limestone Member ((Figure 5), (Table 1)). This was defined by Riley (1990, p. 174) who designated a type section '0.45 km south-west of Rain Gill, Slaidburn' in the adjacent (Settle) district to the east, where it has a more extensive outcrop (Arthurton et al., 1988). The outcrop extends into the present district on the north-west limb of the Slaidburn Anticline, where the member is about 150 m thick. There are good sections in stream gorges [SD 6765 5213], [SD 6782 5231] and [SD 6825 5278] cut through the prominent topographical feature formed by the member near Burn House. The lithology generally comprises dark grey, turbiditic packstones and wackestones, thinly interbedded with mudstone. Twelve metres of debris-flow limestones exposed along Rams Clough [SD 6323 5238] in the Sykes Inlier may also belong to this part of the sequence. The poor representation of this member in the Sykes and Brennand inliers suggests that those areas were either too distal or bathymetrically too shallow to receive substantial turbidite supply in the Arundian.

Packstones about 24 m above the debris flow limestones of Rams Clough, in the overlying, undifferentiated, predominantly mudstone sequence, have yielded a foraminiferal assemblage that clearly indicates a late Arundian age. This mudstone sequence comprises the highest unnamed division of the Hodder Mudstone Formation in the Sykes Inlier (Figure 5). On the northwest limb of the Slaidburn Anticline, about 120 m of equivalent strata are exposed in a gorge [SD 6772 5253], west-south-west of Burn House, where they consist of dark grey, fissile mudstone with rare interbedded dark limestone. In general, these beds indicate that there was an overall decrease in the supply of skeletal carbonate sediment from the platforms surrounding the Craven Basin in late Arundian and early Holkerian times.

In the Whitmoor Borehole, limestones yielding primitive archaediscids were proved from borehole cuttings between 1442 m and 1494 m. These include Kasachstanodiscus settlensis, Glomodiscus sp.and Uralodiscus rotundus of Arundian age. Because no core was taken, it is not clear whether these strata are in a turbidite or carbonate ramp facies. They are contemporary with the ramp carbonates known as the Dalton Beds in south Cumbria (Rose and Dunham, 1977), and with limestone turbidites in the Craven Basin referable to the Embsay, Rain Gill and Chaigley limestone members. This borehole also displays a substantial thickness of limestones referable to the Cf5 Zone, of Holkerian age, between 1359 and 1442 m, with Pojarkovella nibelis and archaediscids at the concavus stage of coiling. These limestones are contemporary with ramp carbonates referable to the Park Limestone of south Cumbria (Rose and Dunham, 1977), but are much more shaly and may be turbidites. There are no substantial limestone turbidites of this age in the exposed parts of the Craven Basin. Their possible presence in the Whitmoor Borehole reflects proximity to the carbonate ramp on the Southern Lake District High. The upper part of the Hodder Mudstone Formation in the Whimoor Borehole comprises grey mudstones with thin limestones, with limestones becoming predominant in the uppermost approximately 33 m of strata.

Hodderense Limestone Formation

This unit, of Holkerian age, was recognised under the name 'Hodderense Band' and mapped in the Slaidburn Anticline outcrop by Parkinson (1936). Its outcrop was later shown on the Geological Survey One-inch Sheet 68 (Clitheroe) under the name Bollandoceras hodderense Beds (Earp et al., 1961), following Parkinson's earlier (1935) work in that district. The unit was renamed and given defined formational status by Riley (1990, p. 176), who recognised its widespread significance as a strati-graphical marker and palaeoenvironmental indicator over much of the western part of the Craven Basin (see also Riley in Aitkenhead et al., 1992, p. 26).

The formation is generally between 5 and 15 m thick, and consists mainly of thin beds of grey porcellanous wackestone, weathering to a pale cream colour, with partings and thin interbeds of mudstone showing a streaky grey to dark grey lamination and much bioturbation of the Chondrites type. The wackestones are characterised by the presence of irregularly shaped, dark bluish to brownish grey micritic nodules, up to 2 cm in diameter. In some cases, these nodules replace bioclasts, notably the ammonoid Bollandoceras hodderense from which the name of the formation is derived. This muddy facies contains a combination of nekto-pelagic (free-swimming and floating) and benthonic (sea-floordwelling) faunas (listed by Riley in Aitkenhead et al., 1992). The latter group were adapted to low oxygen levels and the facies probably represents slow deposition in a sediment-starved dysaerobic environment.

The base of the formation is taken at the first appearance of micritic nodules in the wackestones. The litho-logical change from the underlying Hodder Mudstone Formation is gradational however, marked by an increase in the proportion of grey wackestones over darker mudstone. In many places, the formation forms the basal part of the elevated topographical feature formed by the conformably overlying Pendleside Limestone Formation.

In the present district, the occurrence of the formation on the north-west limb of the Slaidburn Anticline is confirmed by a small exposure in a stream [SD 6770 5258] south-west of Burn House. Exposures of the typical nodule-bearing wackestones are present on the northern flank of the Sykes Inlier, at two places in Rams Clough [SD 6305 5233] and [SD 6332 5243], where the thickness of the formation is 4.8 m and 8.0 m respectively. Exposures in the Brennand Inlier are confined to the north-eastern area [SD 6575 5515] and [SD 6585 5513] on both limbs of the pericline. However, the beds containing the characteristic micritic nodules are here only 0.10 and 0.27 m thick, respectively, and the formation was not mapped separately. The formation is also present in the cores of mineral exploration boreholes (SD65SW/22) and (SD65SW/25) [SD 6372 5233] and [SD 6414 5368] (Figure 9), and is particularly well developed in the latter borehole, where it has a thickness of about 5.1 m, with some of the characteristic ammonoids, including B. hodderense and Nomismoceras sp., amongst the abundant bluish grey micritic nodules

Some sequences of the formation in the Sykes Anticline include limestone turbidites interbedded with cephalopod limestones, e.g. in Rams Clough (see above). These turbidites are unusual in being composed predominantly of fragments of the dasyclad alga Koninckopora inflata. Some 8 m of probable turbidite limestones also occur at this stratigraphical level in the Whitmoor Borehole, between approximate depths of 1229 m and 1237 m. Their presence in the Sykes Anticline and Whitmoor Borehole suggests that these sites were close enough to the basin margins to receive carbonate detritus from the Askrigg Block and Southern Lake District High respectively. In Rams Clough, the ammonoids Bollandoceras hodderense, Merocanites cf. applanatus and Nomismoceras rotiforme have been recovered.

Pendleside Limestone Formation

The Pendleside Limestone Formation, the uppermost formation in the Worston Shale Group, with an extensive outcrop across the Craven Basin, has long been the subject of research, going back to the work of Tiddeman (1889) (see Riley in Aitkenhead et al., 1992, p. 27). Formational status was first given by Fewtrell and Smith (1980), who defined a stratotype at Pendle Hill in the Clitheroe district. In the present district, the two contiguous conformable limestone units, namely the underlying Hodderense Limestone Formation and the overlying Ravensholme Limestone Member, have been mapped separately, where feasible. This was the practice followed in the adjacent Garstang district, but in the adjacent Settle district to the east, mapped earlier during the 1970s, both units were included in the Pendleside Limestone (Arthurton et al., 1988).

In adjacent districts to the south, the lower part of the formation consists of a mudstone-dominated sequence, the Rad Brook Mudstone Member (Riley, 1990, p. 176), the lowest mudstone bed defining the base of the formation. In the present district, the upward passage into the formation is generally gradational, with grey, cream-weathering, porcellanous wackestones and thinly interbedded bioturbated mudstones, similar to the underlying formation but without the characteristic micritic nodules. An additional distinctive interbedded lithology is also present in varying proportions, however, comprising coarsely bioclastic and lithoclastic rudstones and floatstones. These occur in beds which are commonly either unsorted or show overall upward-fining grading and sharp erosive bases, and which are associated with soft-sediment deformation and slumping in many cases. They are thought to have been transported by various gravity flow processes (Gawthorpe, 1986), particularly turbidity currents and debris flows, and to have been derived largely from sources marginal to the Craven Basin.

The formation was deposited during the Holkerian and Asbian. Foraminifera of the Neoarchaediscus Cf6 Zone enter in the lower part of this formation, and include Vissariotaxis compressa and bilaminar palaeotextulariids in the Whitmoor Borehole between 1207.01 m and 1219.2 m. In the Brennand Inlier, boreholes (SD65SW/24) and (SD65SW/25) (Figure 9) have yielded archaediscids at the angulatus stage of coiling. However, the formation also contains an allochthonous, fragmentary carbonate platform fauna and flora, probably derived from the Askrigg Block and Southern Lake District High. Borehole (SD65SW/25) has yielded foraminifera of Arundian age between 68.45 and 70.95 m, reworked from the upper part of the Eoparastaffella (Cf4) Zone and including Glomodiscus oblongus and Kasachstanodiscus sp. These observations, together with others in the adjacent Garstang and Settle districts from contiguous occurrences, suggest erosion of the footwalls of basin margin faults (footwall uplift?) and/or progressive incision of the platform edge by turbidite canyons.

The top of the formation and boundary between the Worston Shale and Bowland Shale groups is gradational over a few metres, and is marked by a colour change and a reduction in bioturbation (see p.27). The thickness of the formation ranges from 8 m in the western Rams Clough section in the Sykes Inlier [SD 6302 5232] to an estimated total of more than 75 m in the north-eastern part of the Brennand Inlier [SD 657 553]. These thickness variations seem to reflect the varying proportions of clastic limestones to wackestones in the sequence. The former were probably deposited in the form of submarine fans, while the latter represent the normal muddy background sedimentation in the basin. A basinwide analysis of these facies and thickness variations has been given by Gawthorpe (1987).

Elsewhere in the present district (Figure 5), some 2 m of limestone proved in the Whitmoor Borehole have been assigned to the formation, between depths of about 1207 and 1229 m (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8). A 2.3 m sequence, present in the Halton Green Inlier near the northern margin of the basin, is also assigned to the formation.

The best exposures of the Pendleside Limestone Formation in the Sykes and Brennand inliers occur in Rams Clough and in the Whitendale River and its tributary streams. The Rams Clough stream crosses the outcrop of the formation in two places, on the limbs of a subsidiary anticline on the northern flank of the main pericline. On the eastern limb [SD 6335 5244], where the formation is estimated to be 17.5 m thick, there are scattered exposures of thinly bedded, largely dolomitised, fine-grained limestone. On the western limb [SD 6303 5233], most of the total thickness of 8.3 m of wackestones and thinly interbedded mudstones is exposed, together with the conformable boundaries of the formation. Both rock types are intensively bioturbated, with vertical and ramifying burrow systems: the ichnogenera Chondrites, Planolites, Thalassinoides and Rhizocorallium were identified in the field. On the west bank of the Whitendale River [SD 6591 5509], just north of Whitendale Farm, the formation is represented by 27 m of grey, cream-weathering, intensely bioturbated, micritic wackestones interbedded with rare bioclastic limestones and thin (less than 0.10 m) cherts.

Several of the cored mineral exploration boreholes drilled by BP Minerals International Ltd penetrated the formation, and further demonstrate the mixture of interbedded wackestones with thin interbeds and partings of mudstone, with varying proportions of coarser bioclastic and lithoclastic beds (Figure 9). In some of the boreholes, however, e.g. (SD65SW/25) and (SD65NE/1) [SD 6414 5368] and [SD 6587 5546], the detailed stratigraphy is difficult to elucidate because of the effects of synsedimentary sliding and slumping, and later disharmonic folding and associated faulting

A small periclinal Dinantian limestone inlier of basin facies occurs about 16.5 km to the north-west of the Sykes and Brennand inliers, and 1.75 km south of the nearest Urswick Limestone outcrop, the platform equivalent of the Pendleside Limestone Formation (Figure 5). This lies on the crest of a steep slope [SD 522 655] overlooking the Lune valley near Halton Green. Most of the exposures here are of limestone boulder beds assigned to the Lower Bowland Shale Formation (see p.28). However, in a small disused quarry [SD 5217 6551] that formerly supplied an adjacent limekiln, the boulder beds are seen to rest with evident unconformity on 2.3 m of well-bedded, darkish grey to grey-brown partially dolomitised calcisiltite, with traces of shaly mudstone partings and with a few chert nodules seen on the quarry floor. These beds, which are assigned to the Pendleside Limestone, appear to lack sedimentary structures, probably because of the effects of dolomitisation, but their general character suggests that they are of turbidite facies (Horbury, 1987).

Chapter 3 Dinantian to Namurian: Bowland Shale Group

Outcrops of the Bowland Shale Group fringe those of the underlying Worston Shale Group in the Carnforth area in the north of the district, and in the Sykes, Brennand and Slaidburn areas in the south-east (see inset map in (Figure 5)). The general successions and thicknesses for the two component formations, the Lower Bowland Shale Formation and the Upper Bowland Shale Formation are shown in (Figure 5) and (Figure 11) respectively. The Lower Bowland Shale Formation forms the lower (Dinantian) part of the Bowland Shale Group, which corresponds closely to the Bolland Shale of Phillips (1836), the Bowland Shales of Tiddeman (in Hull et al., 1875), the Bowland Shale Series of Parkinson (1926) and the Bowland Shale Formation of Fewtrell and Smith (1980). Variants in the lithological nomenclature employed by workers in this and adjacent districts are given in (Table 2).

Depositional history

Near the end of Asbian times, deposition of the basinal Lower Bowland Shale Formation began with a marked regional diminution in the supply of carbonate sediment. Reefs at the margins of the Southern Lake District High and Askrigg Block probably isolated the basin from the surrounding carbonate platforms, the water column in the sea became stratified and oxygen depleted, and 'black' hemipelagic mud ( 'shale') was deposited (Riley, 1990). Another effect of the fringing reefs was partially to obstruct the import of detrital carbonate into the basin, so that there was only localised accumulation of limestone turbidites and debris flows such as the Park Style Limestone and Ravensholme Limestone members. Mud-dominated sedimentation continued as the platforms were drowned at the start of a long period of general regional subsidence (p.37). In particular, this resulted in the loss of a sharp facies differentiation between southern parts of the Southern Lake District High and the Craven Basin.

Evidence for the flushing of the basin by relatively fresh water becomes increasingly apparent upwards through the Bowland Shale sequence, and is reflected in the faunas, giving rise to discrete marine bands dominated by ammonoids and pectinoid bivalves, separated by less-black, commonly ironstone-rich, lacustrine or brackish-water shales with fish and phosphatic debris. It is the ammonoid-bearing bands which provide the key to the stratigraphy of the Bowland Shales and indeed the rest of the Namurian ((Table 3)).

The first major influx of turbiditic terrigenous sand into the basin occurred in mid-Brigantian times (Pendleside Sandstones), and a second, relatively localised incursion took place in the late Pendleian (Hind Sandstone). The latter was a precursor to the huge sand influx that followed shortly afterwards to form the Pendle Grit at the base of the succeeding sandstone- and siltstone-dominated Millstone Grit Group.

Lower Bowland Shale Formation

The Lower Bowland Shale Formation is the highest formation in the Dinantian succession in both the Lancaster district and the Craven Basin as a whole. It is the lower of the two formations that constitute the Bowland Shale Group (Earp et al., 1961, p. 74), the higher one being the Upper Bowland Shale Formation of Namurian age which conformably overlies it. The Lower Bowland Shale Formation and two of its members, namely the Park Style Limestone and Pendleside Sandstones, are defined and described in the Garstang Memoir (Aitkenhead et al., 1992). A third member, the Ravensholme Limestone, has its type area in the Clitheroe district (Earp et al., 1961).

The stratotype of the Lower Bowland Shale Formation is at Little Mearley Clough in the Clitheroe district and was described by Earp et al. (1961). In the present district, the criteria by which the lower boundary with the Pendleside Limestone Formation is recognised, are those used in the Garstang district (Aitkenhead et al., 1992). These are the upwards change in colour of the mudstones (including thin partings and interbeds), from varying shades of grey, to very dark grey or 'black', and the greatly reduced occurrence of bioturbation compared with the Worston Shale Group. In this respect, the criteria differ from those used in the Settle district to the east, where the mappable landform feature at the limestone/shaly mudstone junction dictated the position of the boundary. Thus the limestone conglomerates which are locally present in the basal part of the formation and constitute the Ravensholme Limestone Member in the Clitheroe, Garstang and Lancaster districts, were placed in the Pendleside Limestone in the Settle district (Arthurton et al., 1988, fig. 19). Consequently, the base of the formation is markedly diachronous in the Settle district, ranging from B2 to P1c in age (Table 1), whereas it lies predominantly within the Beyrichoceras (B) Ammonoid Genus-Zone in the other districts, although ammonoid faunas of this and the overlying Goniatites crenistria Zone (P1a) have not been recognised in the present district. The top of the formation is taken everywhere at the base of the Cravenoceras leion Marine Band.

The formation is of late Asbian to Brigantian age. In its lower part, the ammonoid sequence is best displayed in adjacent districts to the south, in particular the Clitheroe district, where a detailed commentary was provided by Ramsbottom in Earp et al. (1961). Relatively major, fresher-water flushing events, reflected in ferruginous, fissile, fish-bearing mudstone, are apparently restricted to certain levels associated with the Pendleside Sandstones (late P1c–d zones) and the shaly strata bounding the Lyrogoniatites georgiensis Marine Band (late P2b–c zones).

The thickness of the formation ranges from about 100 m in the south-east of the district, to 148 m in the Whitmoor Borehole (Figure 5) and (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8). However, no more than 30 m may be present in the Halton Green Inlier, near the basin margin. In the general area of the basin margin, there is also inferred to be an unproved and unexposed gradational lateral passage into the Gleaston Formation.

The general lithology of the formation consists of dark grey to 'black', variably calcareous, fetid and petroliferous mudstone with a mainly blocky texture when unweathered. Fossils, especially bivalves and ammonoids, are common, usually in a crushed state of preservation. Concretionary carbonate bullions and lenses are also common, many containing uncompressed fossils which indicate that the finely crystalline carbonate is early diagenetic in origin. These rocks, when freshly broken, also commonly show mineral oil bleeds from any fractures or cavities which may be present. Detrital limestones are locally important (see below), but are usually present only as thin laminae at the sharp bases of thin blocky mudstone beds, and together the two lithologies are broadly similar to the DE-type beds of Bouma's (1962) distal turbidite facies. Scattered, sharp-based beds of fine-grained sandstone occur in the middle part of the sequence, and are commonly sufficiently prevalent to form a recognisable unit, the Pendleside Sandstones Member. A fuller description of the general lithology is given by Aitkenhead et al. (1992, pp.30–32).

The best-documented section in the Lower Bowland Shale Formation was recorded by Earp (1955) in the Bowland Forest Tunnel. Although this lies just beyond the eastern boundary of the district, it serves as the best reference section for the formation in this south-eastern area, with ten levels from which stratigraphically significant ammonoid faunas have been collected. The identities of these and their zonal and subzonal assignations, ranging from P1a to the top of P2 (see (Table 1)), are given in Earp's (1955) paper, in which the thickness of the formation is shown as 104 m.

The best surface section lies south-south-west of Whitendale, in the Whitendale River at the bridge to Whitendale Farm [SD 6597 5487]. The section (Figure 11) for location." data-name="images/P988508.jpg">(Figure 10), originally figured by Moseley (1962, fig. 3), is nearly continuous, with a total thickness of 87 m. It ranges from probable P1c Zone with the bivalve Posidonia becheri and indeterminate striatoid ammonoids, through to the P2b Zone with the ammonoid Sudeticeras splendens. There are several interesting features in this section. Most notable is the occurrence of reworked foraminiferal and algal assemblages in limestone turbidites, present in the P2a and P2b ammonoid zones in particular. These contain intraclasts with Koninckopora inflata, but lack any Cf6-y Subzone guides. Their source cannot therefore be the contemporary Gleaston Formation and equivalents. The same applies to limestone turbidites of P2b age in Borehole (SD65SW/24) at 25.8 m (Figure 9). These occurrences indicate that all the material was derived from shallow-water carbonates of pre-Brigantian age. It is unclear whether this resulted from erosion of the basin margin, or was a redistribution of previously deposited detrital carbonate within the basin.

The highest Dinantian faunal horizon, referable to the Lyrogoniatites georgiensis (P2c) Ammonoid Zone, is well exposed in Hind Clough [SD 6443 5337], where the zonal form is associated with the bivalve Posidonia corrugata, indeterminate dimorphocerafid and girtyoceratid ammonoids, fish and conodont remains.

Farther to the north-west in the Halton Green Inlier, which probably lies about 1.5 km south of the north-western margin of the basin, the formation is represented by well-exposed limestone boulder beds. These were first noted by Garwood (1913) who described them as a 'thrust breccia', thought to be derived 'by extensive thrusting' from 'knoll-reef country in the south-east' near the Craven faults. While this explanation is no longer considered plausible, the list given by Garwood of 26 fossils collected from the clasts, mostly corals and brachiopods, remains the only published indication of the macrofossil assemblage. The list is consistent with the Asbian age suggested by foraminifera identified during the present survey and by White (1992, p. 209). The boulder beds are seen in two low craggy exposures [SD 5211 6542] and [SD 5217 6551]. The second of these is the better, comprising about 6 m of clast-supported limestone pebble-to-boulder conglomerate, lying with evident unconformity on beds assigned to the Pendleside Limestone Formation (see above). Horbury (1987) recognised limestone clast lithologies that are characteristic of both the nearby platform margin and shelf interior facies of the Urswick Limestone Formation, together with a few examples which indicate erosion of the underlying Pendleside Limestone submarine slope deposits. The boulder beds are thought to have been transported and deposited by debris flow mechanisms.

The boulder beds are assumed to lie at the base of an unproved mudstone sequence underlying the 'slack' topographical feature that separates the limestone exposures from the nearest outcrop of coarse-grained Pendle Grit sandstone, some 60 m to the south-east. Though arbitrarily shown as Upper Bowland Shale on the geological maps, the possibility that these mudstones belong in part to the Lower Bowland Shale is not ruled out. It is likely that part of the sequence is missing, due to unconformity and to tectonic shearing of the incompetent mudstones, squeezed between the relatively rigid limestones below and Pendle Grit above on the flanks of the Halton Green Pericline. The sequence is probably comparable with that proved in borehole (SD56NW/64) [SD 5074 6762] (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6), near Nether Kellet, where limestone conglomerates, in this case assigned to the laterally equivalent Gleaston Formation, are unconformably overlain by a mudstone sequence (p.19 and (Figure 7)).

The only other outcrop of the Lower Bowland Shale Formation in the area of the basin's north-western margin occurs immediately east of the faulted Urswick Limestone inlier at Swantley, 2.5 km north of the Halton Green inlier. Here, the only exposures, apart from isolated patches of dark limestone immediately overlying the knoll-reef facies of the Urswick Limestone, are two small elongate crags of steeply dipping sandstone at [SD 5246 6786] and [SD 5245 6770]. They consist of up to 10 m of massive, parallel and thickly bedded, siliceous, coarse- to very coarse-grained sandstone. The lack of internal lamination in these beds and the presence in some of shale flake cavities suggests that they are of proximal turbidite facies. For this reason, the outcrop has recently been assigned to the Lower Bowland Shales, an interpretation different to that given in the technical report on the area (Appendix 1). A thin section shows the sandstone to be quartz arenite with very poor sorting and almost no porosity due to the tight quartz cement.

Three members are distinguished locally ((Figure 5), (Table 1)), namely the Ravensholme Limestone, the Park Style Limestone, and the Pendleside Sandstones members. The Ravensholme Limestone Member was first named by Earp et al. (1961) in its type area, on the northern slopes of Pendle Hill in the Clitheroe district.

In the present district, it crops out discontinuously, directly overlying the Pendleside Limestone Formation in the Sykes and Brennand inliers where it reaches a maximum thickness of at least 20 m, and possibly nearly 30 m. The member is characterised by the presence of thickly bedded, poorly sorted, commonly dolomitised, conglomeratic limestone beds, together with sharp-based, coarse packstones showing overall upward-fining grading with conglomeratic basal divisions. Thinly interbedded mudstones are dark grey to 'black', and are sparsely bioturbated compared with the Pendleside Limestone. Many of the conglomerates are floatstones, in which the constituent bioclasts and lithoclasts are not in contact but are separated by the matrix which ranges from dark grey to 'black' mudstone to grey-brown dolomitised packstone. The sequence is similar to Facies Association 6 of Gawthorpe (1986), interpreted as being deposited from debris flows and turbidity currents which transported their clastic loads from sources that included platform margin, intrabasinal high and slope regions. Debris flows were defined by Stow (1985, p. 70) as 'slurry-like flows of sand to boulder-size clasts supported by their own buoyancy in a muddy matrix. They occur commonly on slopes greater than 1–2°, and advance slowly downslope either continuously or intermittently for distances up to tens of kilometres'. This last statement is significant in that it allows for the possibility that the debris flow deposits in the Pendleside and Ravensholme limestones could have come from the Southern Lake District High or Askrigg Block platforms, some 20 km away to the north-west and north-east respectively. It is not necessary to invoke a nearby source such as the hypothetical carbonate platform on the Bowland High suggested by Gawthorpe and Clemmey (1985), Gawthorpe (1986, 1987) and Arthurton et al. (1988), for which there is no direct evidence.

The best exposures of the Ravensholme Limestone Member occur in Rams Clough and the Whitendale River. In the former, some 20 m of the sequence, with some gaps, are exposed on each flank of the subsidiary anticline on the northern flank of the main pericline [SD 6298 5231] and [SD 6350 5250] to [SD 6376 5256]. The western sequence includes several debris flow beds up to 1.2 m thick, interbedded with grey bioclastic limestones and dark grey to 'black' mudstones. In contrast, the eastern sequence largely comprises obscurely bedded debris flow beds and finer-grained carbonates, both showing extensive dolomitisation. On the west bank of the Whitendale River [SD 6569 5547], at least 12 m of the member are exposed, including 6 m of spectacular debris flow limestone with many partly silicified solitary and colonial rugose corals, and micritic lithoclasts up to 0.40 m across. The rest of the section consists of thinner (< 80 m) debris flow beds, dolomites, and graded, laterally impersistent, bioclastic packstones.

The Park Style Limestone Member was first delineated in the Garstang district to the south, where the type section is designated in Leagram Brook near Park Style (Aitkenhead et al., 1992, p. 30). Its lower part is approximately coeval with the Ravensholme Limestone Member. In the present district, it has only been tentatively recognised from chippings and geophysical logs, as an 11 m-thick sequence of pale brownish grey fossiliferous limestones and interbedded mudstones beneath the Pendleside Sandstones in the Whitmoor Borehole, between depths of 1192 and 1203 m (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8).

The Pendleside Sandstones Member was formally defined by Riley (in Aitkenhead et al., 1992, p.32), with sections described by Earp et al. (1961) on the flanks of Pendle Hill in the Clitheroe district designated as the stratotype. In the present district (Figure 5), it crops out discontinuously in the south-east and was proved in the Whitmoor Borehole.

Sandstones are interbedded with mudstones in widely varying proportions in the present district, over a maximum thickness of about 80 m. Consequently, those parts of the sequence assigned to the member in bore-holes and exposed sections were chosen arbitrarily where the interbedded sandstones were considered to comprise a significant part of the sequence. Where sandstone beds predominate, the member forms a topographical feature at outcrop, which enables it to be mapped between exposed sections. There is sufficient evidence to indicate that the discontinuous outcrop, in this and other districts in the Craven Basin, truly reflects the laterally impersistant character of the sand bodies that occur within the member. Individual beds commonly show sharp bases with sole structures such as flute, groove, bounce and load casts, and show overall upward-fining grading, although the range of sand grain size is usually limited to fine to medium. Internal sedimentary structures include massive bedding, parallel-lamination and convolute-lamination, but these have not been systematically observed or analysed. Nevertheless, this evidence suggests that these sandstones were deposited from turbidity currents, and the stacked sequences of beds which comprise the discontinuous mapped outcrops are interpreted as turbidite submarine fans deposited in fairly deep water. No systematic study of palaeocurrent evidence has been made, but the few directional sole structures that have been measured in the Sykes and Brennand inliers suggest flow from the north or north-east.

There is no direct evidence for the presence of the Pendleside Sandstones Member on the north-west flank of the Slaidburn Anticline in the district. In the Bowland Forest Tunnel, however, the sandstones at a higher level are represented by 0.3 m of sandstone in the lower part of P2, and by about 7.6 m of sandy shales with thin sandstones at the top of P2 (Earp, 1955). This mudstone-with-sandstone sequence has a total thickness of about 33 m.

In the Sykes Inlier, the characteristic sharp-based, mainly massive, medium-grained sandstones with sole structures are best seen in the western part of Rams Clough [SD 6290 5229]. A total thickness of 19.5 m in the lower part of the member, consisting of sandy mudstones, siltstones, and sandstone beds up to 0.5 m thick, is present here. There are many gaps in the exposed sections, both here and elsewhere in the inliers. Some biostratigraphical control is provided by borehole (SD65SW/24) [SD 6416 5441], from which abundant Posidonia becheri bivalves, suggesting the Plb–c zones, were recovered between depths of 106.28–108.53 m, the sandstone occurring between depths of 53.74 m and 64.10 m (Figure 9). The sandstone is described in unpublished logs (Carlon, 1983) as a medium grey, micaceous, non-calcareous, quartz arenite. The absence of lamination in the sandstone, scarcity of mudstone partings, and the presence of mudstone clasts suggests a succession of rapidly deposited, amalgamated proximal turbidite beds, stacked either in a submarine channel fill or on a fan. The total thickness of the sequence containing interbedded sandstones in this borehole is 85.38 m, in a Lower Bowland Shale succession totalling 120.15 m; the top of the formation was not proved. In the Whitmoor Borehole, the Pendleside Sandstones Member is estimated to be 80 m thick, between depths of 1112 m and 1192 m. Sandstone appears, from the chippings, to predominate from 1135 m to 1165 m, much the thickest sequence in the district.

The Pendleside Sandstones in the Whitendale River section are restricted to a single 20 cm thick bed of fine-grained sandstone (Figure 11) for location." data-name="images/P988508.jpg">(Figure 10). Two bands with the bivalve Actinopteria occur in the P1d Ammonoid Subzone below the sandstone. These bands occur within the type section of the Pendleside Sandstones at Little Mearley Clough, on Pendle Hill, in the Clitheroe District (Earp et al., 1961).

Upper Bowland Shale Formation

The Upper Bowland Shale Formation comprises the predominantly mudstone sequence between the base of the Cravenoceras leion Marine Band and the base of the conformably overlying Pendle Grit Formation (Figure 11). Formal definition as a formation was proposed by Aitkenhead et al. (1992, p. 40), but previously, the term 'Upper Bowland Shales' had long been used for the same sequence, e.g. by Bisat (1928, pl. vi), Stephens et al. (1953) and Arthurton et al. (1988) (Table 2). The base of the Cravenoceras leion Marine Band is taken at the lowest point in the succession with the key ammonoid Cravenoceras. The Cravenoceras leion Marine Band is also a major, internationally recognised boundary between the European Dinantian and Silesian subsystems. There is little change in general lithology across this lower boundary, so that accurate mapping of its position requires recognition of the C. leion Marine Band in a number of exposures. This can be done in the south-eastern part of the district, but absence of exposure means that the position of the boundary is highly conjectural elsewhere. There is one named member, the Hind Sandstone.

Outcrops of the formation fringe those of the underlying Dinantian strata in the north-west of the district around Carnforth and Halton Green, and in the southeast around the inliers at Sykes and Brennand (Figure 11). A third outcrop area fringes the Dinantian on the north-western limb of the Slaidburn Anticline in the extreme south-east. Estimates of thickness for these areas are 90 m east of Carnforth (Kellet Park Wood), 90 m to 120 m in the Sykes/Brennand area, and about 113 m at Burn Fell in the Slaidburn Anticline area. Only the Whitmoor Borehole has proved the formation outside these outcrop areas (Figure 5) and (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8). Here, a thickness of 115 m has been estimated from an interpretation of the geophysical logs.

For the most part, the rocks of the formation comprise blocky or platy beds of dark grey, weakly calcareous or dolomitic, silty mudstone and siltstone, alternating with thin intercalations of very dark grey fissile mudstone. The beds are generally parallel and of even thickness. At some levels in the sequence, especially the basal part, the diagenetic carbonate content is high enough for the beds to have the hardness and appearance of argillaceous limestones, commonly with a lensoid or ovoid concretionary form. The silt content of the blocky beds includes some quartz and mica; finely comminuted debris of carbonaceous plants and calcareous bioclasts may also be present. In some sections, a few scattered, thin, diagenetic ironstone (probably sideritic) lenses and nodules are present in the upper parts of the E1a and Elb2 sequences. In fresh unweathered sections and boreholes, the blocky beds commonly show sharp basal contacts and more gradational top contacts with the fissile mudstone intercalations, bedforms which suggest deposition from weak distal turbidity currents. Thin basal silty or bioclastic laminae may also be present. In weathered sections, the carbonate-bearing beds have become decalcified and softened to produce a yellow-brown colouration and a finely porous texture. Freshly broken surfaces of the blocky beds commonly give off a bituminous smell, and small oil bleeds are occasionally observed in the calcite-filled veinlets which are present in the harder carbonate-bearing beds. The fissile mudstone intercalations contain a few carbonised plant fragments and probably result from slow hemipelagic deposition in a dysaerobic (oxygen-poor) sea floor environment.

Marine fossils occur abundantly at several discrete levels in the sequence. The lithology of these marine bands shows an alternation of blocky and fissile beds similar to the bulk of the formation, but is noticeably more calcareous. The fossils mostly comprise a low-diversity assemblage of posidoniid bivalves, ammonoids and nautiloids, and are mainly concentrated in the fissile intercalations where they are flattened but generally unbroken. Fossils in the blocky beds tend to be fragmentary and dispersed, but exceptionally they are concentrated as a lag deposit at the bases of beds or in concretions, and may be uncrushed and very well preserved if early diagenetic carbonate crystallisation has prevented compaction from taking place.

The 'marine bands' were mostly well recognised and identified in the Upper Bowland Shale sequence penetrated by the Bowland Forest Tunnel [SD 6880 5406] to [SD 6878 5469], just to the east of the present district (Earp, 1955). They comprise the Cravenoceras leion Marine Band at the base, and, in sequence, the Tumulites pseudobilinguis (formerly Eumorphoceras pseudobilingue) and the Cravenoceras malhamense marine bands above. A further marine band, that of Cravenoceras brandoni, previously described from Ireland by Brandon and Hodson (1984), has been discovered in the outcrops in the south-eastern part of the district during the present survey. It lies between the C. leion and T. pseudobilinguis marine bands (Figure 11) and is now taken to mark the base of the E1b Ammonoid Zone. Brandon and Hodson recognised that C. brandoni (described by Palframan, 1984) has probably been determined as C. leion in other British occurrences, as for example along Carla Beck, Skipton (Stephens et al., 1953, pl. VI) where it occurs in association with Eumorphoceras (now Edmooroceras stubblefield).

The Hind Sandstone Member is present locally in the Sykes and Brennand areas, lying stratigraphically between the Tumulites pseudobilinguis and Cravenoceras malhamense marine bands. Moseley (1954) originally delineated and described this sandstone correlating it with the Newton Fells Grit of Parkinson (1936). Later, realising this correlation was uncertain, Moseley (1964) renamed it 'Hind Sandstone' and it has since been assigned member status (Aitkenhead et al., 1992), with a type locality at Hind Clough [SD 6443 5321], near Brennand, from which Moseley derived the name.

The best-exposed and longest sections through major parts of the formation are those at Hind Clough [SD 6443 5337] to [SD 6445 5321] on the north face of Whin Fell, Blue Scar [SD 6564 5459] to [SD 6568 5456] on the north-east face of Middle Knoll, in the Trough of Bowland [SD 6254 5281] to [SD 6249 5284], and on the slopes of Burn Fell [SD 6795 5301] to [SD 6789 5315] (Figure 11).

Cravenoceras leion (Ela), associated with the bivalve Obliquipecten sp. and ammonoid Tumulites sp., has been found in a 1 m-thick mudstone bed near the base of the Upper Bowland Shale Formation in Hind Clough, separated by a 3.5 m gap from the underlying Lyrogoniatites georgiensis horizon. Some 4 m above the gap, Edmooroceras medusa occurs, and marine faunas dominated by the bivalves Posidonia corrugata and P. trapezoedra persist for a further 6.5 m, giving rise to a total thickness of approximately 10.5 m for the Cravenoceras leion Marine Band. The highest E1a fauna lies 28 m below the Tumulites pseudobilinguis Marine Band (E1b2) in Hind Clough. A similar E1a sequence is present in a gully [SD 6385 5216] on the north-west slope of Staple Oak Fell. The most complete sequence was recorded in the Bowland Forest Tunnel by Earp (1955), whose published section shows four leaves present at this level in a sequence about 11 m thick. The C. brandoni Marine Band has not been confirmed at Hind Clough, and this reflects the difficulty in recognising this particular horizon which is only conspicuous where weathering has rendered it decalcified. The marine band is, however, exposed in the Trough of Bowland [SD 6256 5280] (where it is 2 m thick and separated from the T. pseudobilinguis band by 5.4 m of strata), at Blue Scar [SD 6564 5459] (at least 6.6 m thick, 12 m below the T. pseudobilinguis band), and along Folds Clough [SD 6401 5454], but has so far not yielded the eponymous ammonoid in these sections.

In a much thicker, 119 m-thick stratigraphical section on Burn Fell [SD 6780 5315] to [SD 6795 5307], the Cravenoceras brandoni Marine Band occurs at least 58 m above the top of the Cravenoceras leion Marine Band. The latter is represented there by 13 m of dark fissile mudstone and thin wackestones with rare Posidonia trapezoedra, the main ammonoid-bearing phase lying below the base of the section. Strata between these marine bands comprise fissile shales with thinly bedded calcisiltites and scattered ironstone nodules. Fauna is sparse and only fish remains have been found. The Cravenoceras brandoni Marine Band is 3 m thick, and includes the bivalve Posidonia corrugata and ammonoids Cravenoceras brandoni, Edmooroceras cf. angustum, E. hudsoni and E. cf. stubblefieldi, preserved in decalcified laminated wackestones and platy mudstones. An 11 m gap in exposure occurs above this horizon, overlain by the Tumulites pseudobilinguis Marine Band which consists of 2.5 m of tough, calcareous mudstone. The zonal ammonoid occurs with Posidonia cf. corrugata, P. trapezoedra and T. cf. stubblefieldi in 3.5 m of tough, platy, calcareous mudstone. The Cravenoceras malhamense Marine Band, yielding the bivalves Actinopteria persulcata, Chaenocardiola cf. haliotoidea and Posidonia membranacea, and the ammonoids Cravenoceras malhamense and indeterminate dimorphoceratids, is separated from the Tumulites pseudobilinguis Marine Band by 19.5 m of fissile mudstones with scattered sideritic ironstones.

The T. pseudobilinguis Marine Band is also well exposed in the Hind Clough [SD 6438 5328] and Trough of Bowland [SD 6253 5282] sections and at Blue Scar [SD 6568 5456]. At the last-named locality, the marine band lies immediately beneath the Hind Sandstone Member, in contrast to the sections at the Trough of Bowland and Hind Clough where sequences of mudstone respectively 24 m and 17.5 m thick separate the two levels (Figure 11). The anomalously thin sequence at Blue Scar may be at least partly due to the removal of the overlying, unconsolidated, muddy sediments during the formation of a sea floor palaeovalley by the currents that subsequently deposited the Hind Sandstone. The existence of such a palaeovalley is suggested by evidence of soft-sediment deformation, in the form of a probable slide plane and slumped bedding in the lower part of the Hind Sandstone. As already noted, the Hind Sandstone is only locally developed, being present in some sections and absent in others, and is very variable in thickness. The sandstone is medium to coarse grained, with the thick massive beds showing some poorly developed upward-fining grading and sharp bases. Deposition was probably from turbidity currents in laterally impersistent channels. This member is regarded as a minor precursor, in late Elb times, of the huge influx of sand, represented by the Pendle Grit Formation, that came into the Craven Basin during the E1, interval.

Due to erosion by springs issuing from the overlying Pendle Grit, the C. malhamense Marine Band is one of the best exposed in the entire Namurian sequence. For example, there are at least four exposures of the band scattered along the south-east-facing slopes of Beatrix Fell and Burn Fell [SD 66[SD 6637 5203], [SD 6732 5263], [SD 6769 5297] and [SD 6789 5315]. The thickness of the band is generally about 3 m here compared with about 2.4 m in the Trough of Bowland [SD 6249 5284], its most accessible section. At Blue Scar [SD 6568 5456], the band is 2.5 m thick, and is unusual in containing thin, isolated neptunian dykes comprising lenses of medium-grained sandstone discordant to the bedding. These probably formed by the deposition of sand into cracks at the unstable margin of a submarine channel. A 0.75 m-thick, coarse-grained sandstone bed is present at a similar level in Calf Clough [SD 6633 5498], some 4.5 m below the base of the Pendle Grit Formation.

The only place where the Upper Bowland Shale is exposed in the district outside the south-eastern area, is in the stream (Swarth Beck) in Kellet Park Wood, north-east of Over Kellet. The stream follows the north-to-south strike of the near-vertically dipping beds involved in the Hutton Monocline. At one point [SD 5306 7077], an exposure consisting of 4 m of tough, calcareous, dark grey, blocky mudstone with a few fissile fossiliferous intercalations, yielded sparse ammonoids, including Tumulites pseudobilinguis, together with an ammonoid jaw and the bivalves P. corrugata, P. membranacea and pectinoids. This identifies the strati-graphical level as that of the T. pseudobilinguis Marine Band. Most of the other small scattered exposures, both above and below the marine band, consist of interlaminated siltstones and silty mudstones. One exposure [SD 5312 7087], lying above the marine band, shows evidence of penecontemporaneous slumping. Thinly interbedded sandstones also occur in some exposures. The general content of terrigenous sand and silt in these rocks is markedly higher than that present in the formation in the south-eastern outcrops. This probably reflects the greater proximity of the northern margin of the basin.

Chapter 4 Namurian: Millstone Grit Group (upper Pendleian Yeadonian)

Most of the Lancaster district is underlain, at outcrop or at depth, by a thick pile of mainly deltaic sandstones and siltstones of Namurian age belonging to the Millstone Grit Group. The group is only absent where Dinantian rocks and the Bowland Shale Group crop out in minor inliers. Test boreholes, put down in connection with the Morecambe Bay Barrage Scheme in 1968 (Figure 3), show that Millstone Grit forms bedrock under Quaternary and Flandrian sediments offshore, north of Morecambe. Interpretations of the Bouguer gravity anomaly data support this, and indicate that the outcrop extends southwards into the Heysham area.

Following completion of the primary survey of the district in the 1880s, the local Millstone Grit received little attention for a considerable period. Gibson (1910) provided summaries of the stratigraphies and faunas of the Seat Hall and Bentham Station boreholes, and Slinger (1936) gave a brief account of the stratigraphy of Caton Moor. Hudson (1944b) worked out the sequence of marine bands in the Caton Shale which was used by Trotter (1951) in constructing his Arnsbergian stratigraphy of the Lancaster Fells. The most important work on the stratigraphy of the Millstone Grit of this district was by Moseley (1954), who described a substantial part of the drift-free area of the 'Lancaster Fells'. This was followed by his geological account of the Keasden area (1956), in the adjoining Settle district, which is relevant to the geology of the north-eastern part of this district. The only other original published work prior to this survey was by Bisat (1932; 1934) and Hudson (1944b; 1946) on aspects of the biostratigraphy of the Caton Shale. A study of the miospore assemblages in the Namurian and Westphalian rocks of the area was undertaken by Mishell (1965).

The Millstone Grit rocks of the district fall into two informal divisions that have required different treatment (see (Figure 3)). The lower division, restricted to the lower two chronostratigraphical stages, i.e. the upper Pendleian and Arnsbergian, is about 1600 m thick and comprises the bulk of the Namurian succession (Figure 12). This is the thickest sequence of its age in western Europe, the Scottish Midland Valley sequence being about 1200 m (Ramsbottom et al., 1978, fig.11). The lower division also comprises most of the outcrop of the group, including that underlying the hilly central part of the district (Figure 3). Stream sections in this division are relatively numerous and the stratigraphy is known with a fair degree of confidence. The wide expanse of Millstone Grit beneath Morecambe Bay is also thought to consist of rocks of this age, suggested by evidence of probable Pendleian miospores from two Morecambe Bay Barrage Scheme site investigation boreholes, S6 [SD 4654 6952] and C4 [SD 4098 6902].

The upper division of the Millstone Grit comprises all the remaining stages of the Namurian (Table 3) but is relatively thin, being of the order of 500 to 700 m thick. It is generally confined to drift-covered, low-lying areas (Figure 3) in the north-east of the district, around Bentham, and the south-west of the district, between Heysham and Dolphinholme, where natural exposures are few and widely scattered. Around Heysham, site investigation boreholes drilled in connection with the nuclear power stations have been particulary useful in elucidating the stratigraphy of the highest beds, i.e. those of late Kinderscoutian to Yeadonian age. The stratigraphy of the upper Millstone Grit beneath the till blanket across a large area from Dolphinholme, through Galgate, to Overton and northwards, remains poorly known, though BGS shallow borehole programmes have been successful in locating several marker marine bands. This evidence, taken in conjunction with an interpretation of seismic data supplied by oil companies and North West Water plc, has enabled the 'solid' geological map to be constructed. In the western areas in general, very little is known about the Alportian and lower Kinderscoutian sequence.

There is conflicting evidence for the thickness of the lower division of the Millstone Grit in the south-western part of the district. Seismic profiles across this area (see p.137) indicate that the base of the Millstone Grit lies no deeper than about 600 m, where a thick Roeburndale Formation would be expected to outcrop. However, near-surface biostratigraphical evidence from shallow boreholes across this western area suggests that the bedrock is of Chokierian to Kinderscoutian age at several places, for example, in the BGS Heaton Hall Borehole [SD 4398 5949], north of Overton. These conflicting lines of evidence are impossible to reconcile unless the upper Pendleian–Arnsbergian strata, represented by the Pendle Grit and especially the Roeburndale Formation, are greatly attenuated in this area (see p.53).

Classification

Lithostratigraphy

The strictly lithostratigraphical term 'Millstone Grit' or 'Millstone Grit Series' (e.g. Phillips, 1836; 1837) originally included all strata from the base of the lowest coarse-grained Carboniferous sandstone unit in the Pennine sequence, up to the base of the Lower Coal Measures. During the primary survey of the Lancaster district, the-base of the Millstone Grit was established at the base of the Pendle Grit (Geological Survey of England and Wales, 1884; Tiddeman, 1891). Later, in Geological Survey usage, 'Millstone Grit Series' took on a hybrid, partly chronostratigraphical connotation, synonymous with the Namurian (e.g. Stephens et al., 1953), and this has remained common practice until quite recently, for example in the description of the geology of the Settle district (Arthurton et al., 1988). This usage does not conform with modern stratigraphical convention (Whittaker et al., 1991), especially since the 'Millstone Grit Series' of later usage included a thick sequence of argillaceous rocks, the Upper Bowland Shales, above its chronostratigraphically defined base. To avoid the problem, the term Millstone Grit Group was introduced in the description of the geology of the Garstang district (Aitkenhead et al., 1992) for all the Namurian rocks above the base of the Pendle Grit Formation, ironically a usage that closely follows the procedure established much earlier for the present district (see above) and by Earp et al. (1961) in the Clitheroe district.

The general stratigraphy of the Millstone Grit Group in the Lancaster district is given in (Figure 12). Formerly, only 'grits' of the Millstone Grit were named, and the intervening, dominantly argillaceous rocks were generally shown on maps as 'Millstone Grit undivided'. Following the nomenclatural practice begun in adjacent districts (Arthurton et al., 1988; Aitkenhead et al., 1992), most major, region-wide sandstone units are here classed as formations. The intervening argillaceous units are also grouped into formations, where appropriate. An exception is in the upper part of the group where, because lateral facies changes are largely unknown, the rocks are depicted as Millstone Grit undivided. Certain areas concealed beneath a blanket cover of superficial deposits are similarly classified, but such areas may include small outcrops of Lower Coal Measures in the south-west of the district. Many of the formal names are adapted from those used by Slinger (1936) and Moseley (1954; 1956).

Though the named subdivisions are essentially lithological or lithofacies groupings, the general rhythmical character of the Millstone Grit has led to the repetition of similar units of strata in the sequence. Many sections cannot be placed in the stratigraphical sequence without the evidence of biostratigraphical markers or marine bands. It is the discovery and identification of these thin marine bands at numerous exposures which have been the key to the resolution of the Millstone Grit lithostratigraphy.

Many of the lithostratigraphical names used in the upper part of the group are different from those employed for the adjacent ground in the Garstang district (Aitkenhead et al., 1992). The lithological nomenclature used in the north-western part of the Garstang district was extrapolated from the succession established around Dolphinholme and Abbeystead (Wilson et al., 1989) in the Lancaster district. However, the structurally simple and better-known sequence in the north-eastern part of the Lancaster district provides a better standard upper Millstone Grit Group succession than the Dolphinholme–Abbeystead area, where the structure is complex and the succession obscured by drift cover. The lithostratigraphical nomenclature used in this memoir is based on the north-eastern area. The equivalent former nomenclature is provided under the appropriate section.

Chronostratigraphy and biostratigraphy

The chronostratigraphical classification is shown in (Table 3). The Namurian comprises seven stages, each sub-divisible into ammonoid chronozones (Ramsbottom et al., 1978) based on the presence of free-swimming ammonoids (formerly referred to as goniatites). In the Millstone Grit, the ammonoids are confined to thin but extremely widespread, dark, hemipelagic, sediment-starved 'marine bands', where their remains are commonly abundant along bedding planes. The marine bands are listed in (Table 3) along with their indices. In a fully marine context, where dysaerobic bottom conditions prevailed, the marine bands typically contain a fauna dominated by thin-shelled pectinacean and myalinid bivalves, including the genera Posidonia, Caneyella and Dunbarella, in addition to the ammonoid assemblages. Shallower, more-oxygenated marine environments are characterised by the influx of bottom-dwelling forms such as crinoids and shelly articulate brachiopods such as Crurithyris. Reduced salinities in more marginal marine situations, typically accompanied by increased sedimentation rates, are represented by restricted benthonic faunas of horny brachiopods, such as Lingula or Orbiculoidea, and bivalves such as Selenimyalina or Sanguinolites. In these more marginal situations, the eponymous ammonoids are not usually found. A selection of typical Namurian molluscs from the district is illustrated on (Plate 3).

During the course of the survey, several marine and marginal marine localities were discovered in the Roeburndale Formation (lower Arnsbergian Stage) which did not fit easily into the established marine band scheme. From a review of stratigraphies established elsewhere in the Pennines (Brandon et al., 1995; see (Figure 20)), it is now realised that two poorly documented marine highstand events within the E2a Chronozone are represented by these discoveries, namely the Cravenoceras gressinghamense (E2a2á) Marine Band, the eponymous ammonoid being a new species, and a widespread band with Sanguinolites and other sparse benthonic taxa. The latter is named the Close Hill Siltstone Member in this account, and is given the index E2a2â.

Palaeogeography and depositional history

During Pendleian to Chokierian times, deposition occurred throughout the district in a generally subsiding basin, in which thermal 'sag' subsidence (Leeder, 1982) had replaced the 'rift' subsidence prevalent throughout the Dinantian. This more widespread regional subsidence caused the Dinantian Craven Basin (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39) to lose its identity, and to merge into what has been referred to as the Central Province (Ramsbottom, 1969; Collinson, 1988), Central Pennine Trough (Reading, 1964) and the Central Pennine Basin(s) (Aitkenhead et al., 1985; Chisholm et al., 1988; Holdsworth and Collinson, 1988). The last name is preferred here. Block and basin control may have continued to affect sedimentation, to a lessening extent, throughout the Namurian, both passively by burial of pre-existing topography, and actively by reactivation of basement faults which previously controlled Dinantian deposition (Kent, 1974; Johnson, 1981; Arthurton et al., 1988; Collinson, 1988). Coal cleat orientations indicate that the main extensional forces acting during at least the early Arnsbergian to Langsettian were directed north-north-eastwards to south-south-westwards (see p.136 and (Figure 43)).

Apart from the upper Namurian, there is nearly a full complement of Namurian marine bands within the district, and no evidence that such structures as the Bowland High exerted any influence on Millstone Grit deposition, although tectonics affected sedimentation at times. The lower part of the Millstone Grit Group, i.e. from the Pendle Grit to the Claughton Formation, reflects the repeated, fairly rapid infilling of the marine bathymetric basin inherited from Bowland Shale times, by turbidite-generated sands channelled down generally southwards-facing, silty, palaeodelta slopes. These turbidite sediments originated at the fronts of major, southward-prograding river deltas situated generally to the north of the district. Instability of the delta slope is reflected by syndepositional slumps and growth faulting. On several occasions, the earliest being in the late Pendleian, the basin filled up and delta top or platform deposition extended into and across the Lancaster district. Such events are represented by sandstones with subaerial palaeosols and coals, and even subaerial desiccation cracks (in the Brennand Grit).

The cause of the dramatic northerly influx of sediment into northern Britain in late Pendleian times is still debated. Local geomorphological changes such as river avulsion or river capture have recently been proposed (Sims, 1988), but any explanation must acknowledge that the influx occurred simultaneously, and in an identical fashion, in analogous basins as far away as, for example, north-west Ireland (Brandon and Hodson, 1984). An influencing factor may have been the convergence of Gondwana and the Euramerican landmass in equatorial latitudes, leading to climatic changes (Rowley et al., 1985) and uplift of the North Atlantic continent (Reading, 1964; Hodson, 1959). The northerly drift of the Euramerican continent through the equatorial regions may also have led to climatic changes (Leeder, 1988).

Superimposed on this deltaic scenario are eustatic sea-level changes, generally accepted as being caused by glacial fluctuations in the southern hemisphere (Powell and Veevers, 1987; Maynard and Leeder, 1992). Eustatic changes in sea-level have been proposed as the cause of minor cyclicity (Holdsworth and Collinson, 1988; Leeder, 1988), affecting salinity and sedimentation throughout Namurian and Westphalian times. Periods of highstand and fully marine salinities are manifest as marine bands which, though seldom more than a few metres thick, probably represent a substantial part of Namurian time. They are composed of slowly deposited hemipelagic muds, and were formed when the basin was being starved of terrigenous sediment due to drowning of the peripheral deltas. Low sea levels were generally times of sand deposition when river water influx is thought to have maintained low basin salinity (Holdsworth and Collinson, 1988).

Martinsen (1993) proposed a sequence-stratigraphical interpretation in an overview of Namurian sedimentation in the Craven Basin–Askrigg Block region, including this district. The work did not take account of the data presented here, and he pointed out that an explanation based entirely on eustatic sea-level changes could not be applied because of the prevalence of tectonic movements at the basin margin.

Several tectonic events may have affected deposition in Pendleian and Arnsbergian times. To the east of the present district, evidence for an angular intra-E1c unconformity at the base of the Grassington and Brennand grits has been used to advocate tectonism during the later Pendleian (Mundy and Arthurton, 1980; Arthurton et al., 1988). However, there is no supporting evidence from the Lancaster district, and another interpretation of the succession is proposed (see p.44). During the present survey, evidence has been found for an extensive angular intra-E2a unconformity at the base of the Ward's Stone Sandstone, north of the Artle Beck Fault Zone. Coupled with the widespread removal of the highest members of the underlying Roeburndale Formation, which are preserved only on the southern downthrown side of certain prominent WNW–ESE-trending faults south of the Artle Beck Fault (see (Figure 26)A), the unconformity at the base of the Ward's Stone Sandstone probably partly implies down-south movement along faults with a WNW–ESE trend during early Arnsbergian times. Moreover, facies variations within the E. yatesae Marine Band, deposited slightly earlier in Arnsbergian times, indicate a submarine relief. Together with a demonstrable local angular unconformity at the base of the E. yatesae Marine Band adjacent to the Artle Beck Fault (see (Figure 24)), the submarine relief may have been generated by similar movements before the main Arnsbergian event (see below).

The base of the Millstone Grit Group is marked by the influx of coarse-grained, sand-dominated, Pendle Grit submarine fan systems across the floor of the basin. These were fed by channelised turbidite flows from delta-top margins situated to the north of the district (Sims, 1988). It appears that braid-delta deposits with associated mass-flow aprons that first reached the district in later Pendleian times as the Brennand Grit, may have been the result of an entirely separate pulse of sedimentation into the basin (Sims, 1988), following an uncertain phase of tectonism (see above). Supporting evidence for a break in upper Pendleian deltaic sedimentation is provided by a marginal marine fauna from the Surgill Shale Member, the upper siltstone unit of the Pendle Grit, in this and adjacent districts (Brandon et al., in press). Brennand Grit delta progradation culminated in basin infill and subaerial exposure over wide areas in the east of the district, resulting in arboreal growth and even local desiccation, while a deep-water environment prevailed in the west.

The onset of Roeburndale Formation sedimentation marks renewed down-sagging of the basin in late Pendleian times, and the development of a silty, generally southwards-facing palaeoslope across the district, with turbidite flows as the main mechanism of sediment transport. Periodically the slope became unstable, resulting in syndepositional slumping and growth faulting. Five eustatically controlled, early Arnsbergian highstands may be recognised by their marine faunas. Down-sagging appears to have been pulsed, for three phases of partial delta-top encroachment across the district may be recognised within the Roeburndale Formation, each with local palaeosol development. The first is represented by the upper part of the Dure Clough Sandstones Member (Figure 12) in the south-eastern part of the district, an area that appears to have remained relatively shallow since the deposition of the Brennand Grit. The second phase, which occurred shortly after the E2a2 highstand (E. ferrimontanum Marine Band), is represented by the Gavells Clough Sandstone Member, again in the east part of the area. The third, represented by the Sapling Clough Sandstone Member, was terminated either by the E2a3 highstand (E. yatesae Marine Band) or local tectonism. Cessation of delta-slope sedimentation was followed by a phase of tectonism. The highest members of the Roeburndale Formation north of the Artle Beck Fault Zone were removed, leading to an angular unconformity at the base of the overlying formation.

The ganisteroid Ward's Stone Sandstone represents a major pulse of delta-top progradation across what must have been a relatively shallow basin, for there appears to have been a minimal turbidite front. Continued tectonic control on sedimentation is suggested by marked thickening of the formation immediately south of the Artle Beck Fault Zone. Furthermore, palaeocurrents, indicated by trough cross-bedding in the upper part of the formation, are closely parallel to this major fault trend. Sandstone deposition was terminated by a marked rise in sea level, which may have been eustatically controlled. This led to a long period when the basin, far removed from a delta margin and in a stable tectonic phase, was starved of sediment. Above a non-sequence and reworked delta-top, the Caton Shale is composed entirely of marine claystones in which changes in the faunal elements reflect changing salinities (e.g. Ramsbottom et al., 1962, pp. 114–117). Equally marked is the sudden return to turbiditic siltstone and fine-grained sandstone-dominated delta-slope deposits which characterise the Claughton Formation. Conditions were analogous to those of the Roeburndale Formation and, near the end of Arnsbergian times, likewise culminated in the infilling of the basin and the district-wide progradation of delta-platform sediments. These are represented by the Silver Hills Sandstone, with associated Banister sandstones and thin coals.

Subsidence and sedimentation remained generally in balance throughout Chokierian to Yeadonian times when the upper part of the Millstone Grit Group was deposited, in contrast to the substantial fluctuations in basinal depth in the early Namurian. The Crossdale Mudstone Formation records a significant global event associated with the mid-Carboniferous boundary (Riley et al., 1987), in that it contains a non-sequence between the Arnsbergian and Chokierian stages. To the north of this district, on the Alston Block, this non-sequence is more severe, with Kinderscoutian strata resting on middle Arnsbergian rocks–a situation that is usual across much of North America, Eurasia and North Africa. South of the present district, however, in the Central Pennine Basin, no non-sequence occurs. The Lancaster district thus occupies an intermediate position between these two extremes. In addition to non-sequence on a global scale, this boundary is commonly associated with a major change in marine fauna.

Further evidence of the intermediate position of the Lancaster district comes from the Bentham area, where Alportian, Kinderscoutian and lower Marsdenian strata contain benthonic marine shelly faunas, including articulate brachiopods, crinoids and bryozoans, and rare solitary corals, trilobites and foraminifera. Marine bands in this area are thick due to abundant sediment supply, in contrast to the starved hemipelagic sequences further south. The association of predominantly shelly faunal phases and wave-influenced marine sandstones indicate nearshore conditions during marine highstands. The upper Millstone Grit sequences are characterised by intermittent progradation of sheet-like fluviodeltaic systems into relatively shallow-water environments, interspersed with periods of high stand marked by numerous, generally thin marine bands. Compared with central Lancashire (e.g. Wright et al., 1927), the upper Namurian sequence is relatively thin, suggesting that the area of maximum subsidence had transferred southward by this time. This is also born out by the abundance of fluviatile sands and the apparent absence of many of the upper Namurian marine bands (Table 12).

Provenance of Millstone Grit sediments

A continental-scale drainage system has been inferred for the river/delta of the Central Pennine Basin, prompting comparison with the modern Mississippi or Amazon (Leeder, 1988). The implications of various provenance studies (e.g. Gilligan, 1920; Muir, 1963) have been summarised by Leeder (1988). These point to a drainage basin that covered a large part of Caledonian Scotto-Scandinavia, with the hinterlands being of granitic or gneissic composition. Radiometric age determinations on detrital zircons (Drewery et al., 1987) indicate derivation from a Caledonian and Archaean sourceland that may have included areas as far afield as Fennoscandia and Greenland. Leeder (1988) concluded that the influx of coarse-grained and feldspathic pebbly sandstones into the Central Pennine Basin during the Namurian probably followed basement unroofing (Greensmith, 1965), which may have been triggered by climatic change.

Sandstones representative of all the sandstone-dominant members and formations of the Millstone Grit Group of the Lancaster district were investigated petrographically and by detailed quantitative heavy mineral analysis to verify the provenance of the sediment. Both sets of analyses indicate that there was no significant change in provenance of the northerly supply of sediment throughout the Namurian.

Heavy-mineral analyses

A quantitative study was made of the heavy minerals in 38 Millstone Grit sandstones from the district (Appendix 1; Hallsworth, 1992). The analyses also included seven samples of the highest sandstones exposed along the River Greta to the north of the district. The study compared the Millstone Grit data with similar data from potential source rocks in an attempt to test the previous ideas on the sourcelands given by Gilligan (1920) and Cliff et al. (1991).

The detrital heavy-mineral suites of the Millstone Grit sandstones contain variable amounts of eight, stable, translucent mineral species. Zircon, tourmaline and rutile are abundant throughout the sequence, zircon commonly being predominant. There is considerable variation in the abundance of both apatite and garnet. Monazite is a minor component throughout but is significant as a key mineral for provenance reconstruction. Anatase is present as an accessory mineral in most samples, and rare chrome spinels were occasionally recorded. The low diversity of the heavy-mineral suite indicates that there has been extensive dissolution of unstable minerals. Garnet is at the limits of its stability, and is only preserved in cemented units, which suggests that the pore fluid temperatures exceeded 80°C during deep burial. By analogy with the North Sea Mesozoic and Palaeogene rocks, sedimentary burial depths may have reached 3350 m. The absence or low proportion of apatite suggests that acidic groundwaters may have influenced the heavy-mineral suites. The lower part of the Millstone Grit appears to be more depleted in apatite, suggesting that it was more severely affected by percolation of acidic groundwaters. There are also more rounded zircons in this part of the sequence; one possible explanation is that sediment spent longer periods on the floodplain in the early Namurian.

There is no mineralogical evidence for a major change in source material during the deposition of the Millstone Grit in the Lancaster district. The overall drainage pattern is considered to have remained essentially similar throughout. Any differences in palaeocurrent direction are thought to have resulted from local distributary factors rather than indicating changing input from different source areas. However, the detrital input from the different source lithologies varied with time, creating a number of stratigraphical trends which may be regionally correlatable.

The heavy-mineral assemblage indicates that the Carboniferous hinterlands were composed of a high-grade metamorphic terrain, intruded by a number of granite masses that were characterised by wide variations in their abundance of monazite. In addition there was a sedimentary or metasedimentary source that decreased in importance through the Namurian. Gilligan (1920) proposed that the source lay to the north, comprising the Scottish landmass and a continental mass farther north. Although many of the source rock lithologies are found in Scotland, the major involvement of Scottish material is doubtful because these rocks do not presently provide detritus with similar heavy mineral characteristics (Hallsworth and Morton, 1991; Morton and Hallsworth, 1992; Ms C R Hallsworth, personal communication, 1993). The low involvement of Scottish material is supported by isotopic age data from zircons and monazites (Cliff et al., 1991).

The evidence suggests that the drainage basin must have included a high-grade Archaean terrain and monazite-bearing granitic bodies, probably in a more distant northerly location such as east Greenland, in aggreement with the conclusions of Drewery et al. (1987) and Leeder (1988). If this was the case, it is probable that the sedimentary and metasedimentary lithologies were also being eroded from the same region and may have been an important source of detrital sediment.

Petrographical analyses

Analyses have been made of 68 thin sections of representative sandstones from the Namurian of the district, supplemented by 5 samples of Kinderscoutian to Yeadonian sandstones exposed in the River Greta (Appendix 1; Strong, 1991).

Most of the sandstones have broadly similar detrital compositions and diagenetic mineralogy (Plate 4). The composition of the main detrital components, generally unstrained quartz, K-feldspar, albite and mica, suggests an origin from the same acid igneous and/or gneissic source area throughout the Namurian. In keeping with this, granitic lithic clasts occur as a minor component of some of the coarser samples from the Pendle Grit and Brennand Grit. The sandstones are typically quartz arenites and subarkoses composed of detrital quartz and K-feldspar (including microcline in the fresher Pendle Grit and Eldroth Grit samples), with minor plagioclase and mica (mainly albite and muscovite). Opaque minerals occur in most samples, consisting of secondary iron oxides and detrital carbonaceous clasts. The secondary iron oxides occur as pore linings and pore fillings, and may replace ferro-magnesian grains such as biotite.

The sandstones vary in feldspar content, thereby varying the classification from quartz arenite to subarkose, and in grain size distribution. These variations are consistent with changes in hydrodynamic depositional conditions. With the notable exception of those from the Ward's Stone Sandstone, all the coarser delta top sandstone samples, i.e. those from the Brennand Grit, the Nottage Crag Grit, the Eldroth Grit and the Heysham Harbour Sandstone, fall into the subarkose category, as do the coarse-grained Pendle Grit samples. Most other samples, including all those from the finer delta-slope sandstones, the finer delta-top members of the Roeburndale Formation, and the Ward's Stone Sandstone, are quartz arenites. Plagioclase is absent from 11 out of 12 samples of the Ward's Stone Sandstone analysed. This is unlikely to be due to weathering because of the presence of K-feldspar, and may be due to a change in provenance. The ubiquitous presence of detrital mica and general lack of bioclasts is consistent with a fluvial-dominated deltaic depositional environment.

Marine bioclasts (echinoids, bryozoa) and phosphate were found in a sample from the Kirkbeck Formation, the only fully marine sandstone studied.

The coarse grain size and amount of K-feldspar in some subarkoses suggests a relatively proximal source and minimal reworking of grains. In other sandstones, mostly those of finer grain size, and in some siltstones and mudstones, K-feldspar may be either absent or only a minor component, suggesting reworking of the sediment.

Chert appears as a minor detrital component of three Pendle Grit samples. The source of the chert is unclear; it may be intraformational or derived from earlier Carboniferous or older rocks. is typical of the fluvial-dominated sandstones, and may be the product of early diagenesis in a subaerial or shallow-burial environment.

The second group is characterised by the development of carbonate cements. The carbonates are calcite, ferroan calcite and, to a lesser extent, siderite. Calcite may coexist with ferroan calcite, and ferroan calcite with siderite, in the same slide, but calcite and siderite appear to be mutually exclusive in the samples inspected. The calcite and ferroan calcite generally occur as pore-filling cements, whereas siderite occurs as nodules including sphaeroids.

A few samples, e.g. from the Cocklett Scar Sandstones Member, the Barncroft Beck Member and the Eldroth Grit, show some overlap of these two assemblages, with authigenic quartz and kaolinite occurring together with a carbonate cement. No detailed paragenesis of authigenic minerals has been considered here, but it is tentatively suggested that the carbonates represent the influence of marine pore fluids associated with ephemeral transgressions.

Phosphatic cement occurs in some marine Kirkbeck Formation sandstones, associated with bioclasts. This suggests long periods of winnowing.

Sandstone diagenesis

The Millstone Grit sandstone samples (Appendix 1; Strong, 1991) generally fall into two distinct groups based on diagenetic mineral assemblages, i.e. quartzkaolinite and carbonate assemblages (see (Plate 4)). Most sandstones studied from the district belong to the quartzkaolinite assemblage, but the carbonate assemblage is characteristic of many of the sandstones from the Cocklett Scar Sandstones Member of the Roeburndale Formation and the Kirkbeck Formation. A single basal sandstone from the Barncroft Beck Member of the Claughton Formation and the only sample of the Rough Rock examined also represent the carbonate assemblage. These sandstones generally have marine affinities or lie in close proximity to marine strata.

The quartz-kaolinite group is characterised by the development of significant quartz overgrowths and cements, usually associated with later, pore-filling, vermicular kaolinite. The quartz occurs as clean syntaxial overgrowths on detrital grains, and as intergranular cement. The extent of quartz authigenesis is variable, from minor overgrowths to fully cemented 'orthoquartzites'. Significant detrital clay contents in some sandstones appear to have inhibited quartz development. The kaolinite commonly, but not exclusively, occurs in oversized pores (grain dissolution porosity), probably after K-feldspar. Remnants of severely corroded K-feldspar remain in some pore spaces. Why some K-feldspars should remain fresh while others corrode within the bounds of one thin section is not clear; microperthitic intergrowths may render some grains more susceptible than others, or there may be some permeability factor. Some K-feldspar grains show alteration to sericite, but absence of significant sericite elsewhere in the fabric of the sandstones suggests that the sericitisation is pre-depositional. The quartz-kaolinite assemblage

Pendle Grit Formation

The name 'Pendle Grit' was first used by R H Tiddeman on the Geological Survey One-inch Old Series Sheet 92SE, published in 1878, for the sandstone (grit) capping Pendle Hill in the Clitheroe district. It subsequently appeared on the first one-inch sheet of the Lancaster district, published in 1884. The name was recently formalised as Pendle Grit Formation in the Settle district (Arthurton et al., 1988). The nomenclature formerly applied to the formation in the present district and adjoining areas by the main workers is shown in (Table 2). Little Mearley Clough [SD 785 411] on the north flanks of Pendle Hill provides the type section for the base and middle parts of the formation.

The Pendle Grit crops out in two areas that have contrasting geomorphological styles. In the Bowland Fells of the south-eastern part of the district (Figure 4), the formation produces steep, essentially till-free but head-mantled escarpments above the deeply incised Sykes, Brennand and Whitendale valleys. The main outcrop extends northwards from Beatrix Fell [SD 66 52] to Croasdale Fell [SD 68 57], and then south-westwards across Whitendale Fell [SD 66 56], along the south side of Brennand Fell [SD 64 55], to Winfold [SD 62 53], Marshaw [SD 61 52] and Hawthornthwaite [SD 57 52] fells. The Bowland Forest Tunnel section of the Haweswater Aqueduct penetrated the entire formation under Croasdale Fell (Earp, 1955). Stream sections are numerous in this area but rarely continuous.

West of the Quernmore Fault, from the Lancaster area northwards, the Pendle Grit outcrop is largely covered by till and the topography more subdued. Craggy outcroppings of 'grit' in a series of anticlinal and monoclinal folds with steep limbs have been much quarried for building stone. Quarries occur at Quernmore Park [SD 51 62], at North Park [SD 517 645] and west of Escowbeck [SD 526 640] near Caton. Close by, the Pendle Grit crops out extensively along the bed of the River Lune from Crook o' Lune westwards to Halton [SD 508 646]. Further quarrying activities were undertaken at Williamson Park [SD 490 613], Bowerham [SD 482 602] and Primrose [SD 484 612], Lancaster. North of the Lune, the Pendle Grit occurs in crags, quarries and along streams in the Halton Green [SD 52 66] and Addington [SD 52 68] areas, and east of Over Kellet along Swarth Beck [SD 532 706]. Along this crop, the beds steepen on the vertical limb of the Hutton Monocline.

In the ground between the two outcrop areas, the Pendle Grit is known only from the Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8) and (Figure 13) where 402 m of strata are assigned to the formation between depths of 547 m and 949 m. At outcrop, it is generally difficult to estimate the thickness because of the absence of marker bands, and though exposures are numerous they are seldom continuous. In the south-eastern crop, the thickness is variably estimated as being between 365 m in the Trough of Bowland area and 550 m on Brennand Fell (Figure 13). These values include the thickness of the Surgill Shale Member, ranging from 20 m to about 200 m respectively. Approximately 335 m were penetrated in the Bowland Forest Tunnel (Earp, 1955) of which the topmost 180 m are ascribed here to the Surgill Shale Member. In the outcrop extending northwards from Lancaster, the formation is estimated to be up to about 350 m thick, but only 150 m may be present in the steeply inclined tract in the Over Kellet area. The 540 m formerly estimated on 1:10 000 sheets of the Lancaster City area is thought to be excessive, and to include siltstone-dominated strata now included with the Roeburndale Formation. These values compare with estimates of 340 m to 475 m for the formation in the Garstang district (Aitkenhead et al., 1992), and up to 550 m in the adjoining part of the Settle district (Arthurton et al., 1988). North-west of Lancaster, in the Barrow-in-Furness district, the Pendle Grit is correlated with the upper part of the Roosecote Mudstones (Rose and Dunham, 1977) which, despite their name, consist mainly of sandstone and siltstone above the Cravenoceras malhamense Marine Band.

In an upwardly coarsening sequence, the base of the formation is arbitrarily taken at either the base of the lowest massive sandstone or where the sandstones become predominant over siltstones and mudstones. In the south-eastern crop, the base of the formation is conformable and gradational on the Upper Bowland Shale Formation. There are no surface sections of the basal contact in the north-west crop, though a borehole near Dunald Mill Quarry (see (Figure 7)) on the crest of the Dunald Mill Dome indicates an unconformable contact on the Gleaston Formation (see p.19). Moreover, seismic profiling indicates an area north-east of Lancaster (see (Figure 42)) where there is an apparent angular unconformity at the base of the Pendle Grit. In the seismic sections, the base of the Pendle Grit appears to onlap the western side [SD 492 640] of a flexure that is probably the northwards extension of the Williamson Park Anticline, and to truncate the underlying Bowland Shale and possibly some of the underlying limestones on the eastern side [SD 520 645] of the Knots Anticline or Halton Green Pericline. The angular unconformity may have been due to syndepositional movement along the Quernmore Fault, leading to an emergent NNE–SSW trending ridge to the west of the fault in late Dinantian to early Namurian times. Seismic profiling also indicates that the Pendle Grit onlaps eastwards at an angular unconformity beneath the Claughton area [SD 565 660], where it apparently cuts out at least 150 m of uppermost Dinantian and lower Namurian strata.

The intergrading lithofacies and facies associations that make up the Pendle Grit Formation have been discussed by Sims (1988). Mainly, they constitute an evolving, vertically aggraded, sand-rich submarine fan system, with turbidity currents being the main mechanism of mass-flow sediment dispersal, largely within a hierarchy of channel complexes. In simple terms, the formation comprises medium-grained to very coarse-grained or granule-grade, feldspathic, channel-fill sandstones, interbedded with thinner siltstones with numerous interbedded fine-grained sandstones. The proportions of the two main lithologies is variable, both stratigraphically and laterally within the district, but few persistently mappable subdivisions of the thick pile of sediments are possible. In common with the practice in the Garstang district, a basal, thinly interbedded, distal turbidite sandstone and silty mudstone/siltstone unit ('sa/sl') is recognised locally, as in the Whitendale River and Trough of Bowland sections (see below). This unit has been named the 'Whitendale Member' (Sims, 1988) and ascribed to pro-channel lobes, i.e. to progradation beyond the channel mouths. A widespread, predominantly siltstone unit, the Surgill Shale Member, has been mapped at the top of the formation along the southeastern crop. Sims (1988) interpreted these siltstones as belonging to a submarine delta-slope association. They embody coarse-grained, lenticular sandstones which are thought to be feeders for the main Pendle Grit Formation fans.

Palaeocurrent data (Sims, 1988) indicate movement of Pendle Grit Formation sediments from the north-east across the south-eastern part of the Lancaster district, and from the north-east and north across the westerly outcrop around Lancaster. Sims tentatively concluded that the initial supply of sediment into the district was from the north-west of the Lancaster area, to the west of the Askrigg Block, with subsequent dispersal being directed south-westwards axially across most of the basin.

The only common fossils are plant remains and trace fossils, the latter having been described by Eagar et al. (1985). Reduced basin salinity during deposition of the main part of the Pendle Grit, coupled with a relatively high sedimentation rate, has been cited by these authors to explain the lack of an extensive fauna. Sanguinolites, a marine bivalve which appears to have tolerated a high sedimentation rate, occurs characteristically in thick, marginal marine, siltstone sequences. It has been recorded from the Surgill Shale Member in the Clitheroe district (Brandon et al., in press), from equivalent strata in the Roosecote Borehole (Rose and Dunham, 1977), and from the Whitendale River in the present district. The occurrences probably represent a previously little-known marine horizon, named the Blacko Marine Band by Brandon et al. (1995).

Within the main part of the Pendle Grit, a broad lateral change in lithofacies occurs approximately southwestwards across the south-eastern outcrop (Figure 13). In the area of Croasdale Fell and Brennand Fell, the general background lithology of the main part of the formation (i.e. that shown on the map as 'PG') is similar to that of the adjacent parts of the Settle district, and consists of undifferentiated interbedded sandstones and siltstones. More durable, thicker-bedded, coarser-grained but laterally impersistent 'grits' ('sa') occur in packets. By contrast, towards the south, on Beatrix Fell, in the Trough of Bowland area and on Hawthornthwaite Fell, the formation consists mainly of thin to thickly bedded sandstone, with subordinate, interbedded silty mudstone and siltstone ('sl' or 'sl/sa') (Figure 13).

West of the Quernmore Fault, the Pendle Grit lithology, deduced from crag and quarry exposures, consists mainly of amalgamated stacks of extremely thickly bedded, massive channel sandstones with very few siltstone partings. However, the nature of this 'background' lithology may be misleading, as the coarser, more resistant beds are preferentially better exposed in this area. A few indifferent exposures of more thinly interbedded, finer-grained sandstones and siltstones along some incised streams hint at a greater proportion of this facies than is apparent.

In the heavily drift-covered ground on the northwestern outskirts of Lancaster City, northwards to the Bolton-le-Sands area, several boreholes show thick sequences of interbedded sandstones and siltstones, including siltstone-dominated units several tens of metres thick. In the absence of biostratigraphical markers, these strata may be interpreted as falling entirely within the Pendle Grit, in which case they imply a westward facies change from the sandstone-dominated facies exposed along the west side of the Quernmore Fault. Alternatively, they may belong entirely or partly to the Roeburndale Formation as depicted on the map.

Problems of the boundary with the Brennand Grit

The upper boundary of the formation in the Croasdale area [SD 68 57] is considered to be stratigraphically higher than in the adjoining part of the Settle district (Arthurton et al., 1988). This has inevitably led to a mismatch of the geological boundaries between the two sheets. The very coarse-grained pebbly sandstones forming Reeves Edge and Bloe Greet were placed within the lower part of the Brennand Grit in the Settle memoir and map, because of cross-bedding in the higher beds and the apparently strong unconformable relationship in the Saddle Hill area [SD 69 57] (see p.49). Traced towards the west, onto Whitendale Fell [SD 66 57] in the Lancaster district, these sandstones thin out and are clearly part of a lenticular channel-fill, at or near the base of the Surgill Shale Member. This conforms with observations in the

Bowland Forest Tunnel (Earp, 1955). The lowest sandstones of the Brennand Grit, represented by the crags of Great and Little Bull Stones, are at a considerably higher stratigraphical level. Farther west, a similar extremely coarse-grained, pebbly, cross-bedded channel sandstone at the base of the Surgill Shale forms a 120 m long landform feature on the east side of the Brennand valley [SD 6330 5503].

'Whitendale Member'

In the south-eastern part of the district, the basal 'Whitendale Member' of the formation (Figure 13) grades upwards from the Upper Bowland Shale, and is typically composed of alternations of parallel-bedded, medium-grained turbidite greywacke sandstones and siltstones ('sl/sa'). The sandstones become better sorted and cleaner upwards, and also increase in thickness as the thickness of the siltstones decrease correspondingly. One of the best and most accessible sections of the unit is at Trough Scar on the west side of the Trough of Bowland [SD 6245 5286], where it is estimated to be 14 m thick. It is 35 m thick in the river section below the Whitendale Intake [SD 6536 5590], and is also exposed on the south side of Calf Clough [SD 664 550] on Whitendale Fell. Sims (1988) placed the lowest 82 m of the Pendle Grit in the Whitmoor Borehole in this member. The member has not been seen in the western outcrop.

Main part of the Pendle Grit

The sandstones of the main part of the Pendle Grit vary in thickness from more than 1 m to 100 mm or less, the thinner beds usually being finer grained. They are grey at depth, but like most other Millstone Grit sandstones are invariably weathered at the surface to a pale orange-brown or buff, due to a slight iron content. They remain indurated, unlike the sandstones of the Brennand Grit. In the Lancaster area, they are partly reddened, due to a former Permo-Trias land surface and overburden. They are typically parallel- and massively bedded with sole-marked sharp bases, commonly resting on scour surfaces. Lenticular beds are also common. The thicker beds, up to about 4 m thick, are internally graded, upward-fining units, being typically coarse to very coarse and pebbly in grain size in the lower part, and medium-grained in the upper part. The pebbles are mostly rounded, white vein quartz, up to 20 mm in diameter, and, if sufficiently abundant, form conglomerate lenses up to 0.7 m thick. Small flakes of white mica are common and are arranged subparallel to the bedding. Though the thicker sandstones are mostly massive and devoid of sedimentary structures, they develop a subhorizontal undulating jointing or 'pseudobedding' on exposure, probably caused by cryogenic processes. Current structures are generally uncommon and cross-bedding is very rare. A coarse-grained and pebbly sandstone in the upper part of the formation, and forming Reeves Edge in the Croasdale Fell area, is cross-bedded in places and was formerly placed within the Brennand Grit (see above). Typically, the upper boundaries of the sandstones are rapidly gradational. The upper parts of the sandstones are commonly current-ripple-marked; good examples occur in Folds Clough [SD 6380 5522] (Plate 5). They are also conspicuously micaceous, and may contain comminuted plant debris and lenses of intraformational conglomerate that incorporate flattened pebbles of grey siltstone or silty mudstone. Spherical ferruginous-cemented concretions, about 0.3 to 0.4 m in diameter, and known colloquially as 'mares balls', occur sporadically. Such concretions are common in a 2 m-thick, medium-grained bed at the water pumping station at North Park [SD 5185 6422]. The thinner sandstones are also commonly micaceous and may contain comminuted plant debris.

The argillaceous parts of the interbedded units consist predominantly of grey, micaceous, variably sandy, shaly siltstones which grade into shaly, silty mudstones and micaceous, platy, fine-grained sandstones. The siltstone beds range typically from a wafer to 0.4 m thick, with rarer beds up to 1.5 m or more. They contain abundant comminuted plant fragments, and pass into striped beds with ripple cross-laminated sandstones. Thin, fine- to medium-grained siliceous sandstones, mostly ranging from lamina to thin beds a fraction of a metre thick, are common to very numerous, and have sharp, sole-marked bases, typical of turbidites, and ripple-marked tops. Greywacke-type silty sandstone beds with chaotically arranged mica occur sporadically.

In a section at Folds Clough, Lee End [SD 6400 5547], a 1 m bed of striped siltstone near the top of the main unit shows synsedimentary deformation, in which individual sandstone laminae are folded recumbently with closures to N 040° E.

Sections in the main part of the Pendle Grit west of the Quernmore Fault

The Pendle Grit in this largely drift-covered area of Lancaster City has been reddened in part below a former Permo-Trias surface and overburden. Sections in the massive, thickly bedded sandstone-dominated facies are still exposed for up to 7 m at several places in the formerly extensive Williamson Park quarry workings [SD 489 611]; [SD 491 615]. The formation was also penetrated in several deep boreholes sunk to supply water to the Lancaster factories. The Greenfields Mill Borehole (SD46SE/13) [SD 4825 6161], sited at Moorlands on Pendle Grit bedrock, passed through 157 m of grey sandstones with only minor 'black shale' partings. Several other Lancaster wells, notably the St Georges Mill (SD46SE/8) [SD 4709 6219], Lune Mills (SD46SE/17) [SD 4622 6187] and Nelson (SD46SE/3) [SD 4888 6404] boreholes, sited generally down-dip of the Green-fields Mill Well, encountered reddened fine- to coarse-grained sandstone and argillaceous strata 127 m, 271 m, and 136 m thick respectively, including major siltstone-dominated units between 14 and 100 m thick. These beds may be entirely within the upper part of the Pendle Grit, but are more likely to be partly or wholly within the lower part of the Roeburndale Formation, as shown on the map. Provided there is no major faulting, the 16 m of mainly medium-grained, medium- to thickly bedded, sharp-soled sandstone turbidites, exposed during low tide along the north side of the River Lune below Carlisle Bridge [SD 4715 6245], must be part of the sequence penetrated in the Lune Mills Borehole.

Similarly, to the north of Lancaster, in the thickly drift-covered coastal tract from Carnforth to Morecambe, two boreholes have proved interbedded sandstones and siltstones devoid of biostratigraphical marker bands which may be tentatively assigned to either the Pendle Grit or the Roeburndale Formation. The exploratory BGS Slyne Borehole (SD46NE/24) [SD 4745 6529], sited just south of Slyne, penetrated 60 m of partly reddened, interbedded, fine- to coarse-grained sandstones and siltstones, provisionally assigned to the Pendle Grit. The only fossil recovered was an ostracod from a thin mudstone at a depth of 39 m. About 1 km off the coast at Bolton-le-Sands, one of the site investigation boreholes (S6) for the proposed Morecambe Bay Barrage [SD 4654 6951] proved 9 m of fine-grained, dark grey, silty micaceous and pale grey siliceous sandstones, thinly interbedded with dark grey mudstones and siltstones, which are provisionally ascribed to the Roeburndale Formation but which could be Pendle Grit.

East of Halton, there are several small crag, stream and quarry exposures in the massive coarse-grained sandstone facies around the core of the Halton Green Pericline c. [SD 52 65]. North of the pericline, Monkley Gill upstream from [SD 5210 6614] provides scattered exposures of the finer-grained, more argillaceous interbedded sandstone and siltstone facies. Two noteworthy sections are present farther north, on the vertical limb of the Hutton Monocline. The first of these, at Addington [SD 5280 6830], is the best of several quarry sections in a strong north–south ridge protruding through the drift. It consists of about 38 m of mostly amalgamated, massive, pebbly, coarse-grained sandstone beds. The second is provided by the incised glacial meltwater valley of Swarth Beck [SD 5314 7060] to [SD 5327 7060], north-east of Over Kellet. About 80 m of sandstone-dominated strata are represented, the beds being mainly massive, very thickly bedded, coarse-grained sandstones.

In the tract of ground from Quernmore northwards to the Lune, there are numerous minor sections of up to several metres of amalgamated, massive, thickly bedded, coarse-grained sporadically pebbly sandstones. Exposures are particulary plentiful in crags and small quarries around the core of the Knots Anticline in Knots Wood e.g. [SD 5123 6177], and in quarries at North Park e.g. [SD 5188 6437] and near Escowbeck House e.g. [SD 5261 6410]. The beds are tightly folded, steeply dipping and locally overturned in the latter area, in proximity to the Quernmore Fault. The best section examined during the survey was in about 26 m of sandstones in an excavation at the North West Water plc pumping station at North Park [SD 5185 6421]. Sections mainly in the massive sandstone facies also occur in the bed and banks of the River Lune around the Crook o' Lune c. [SD 522 646], and farther downstream south-east of Halton [SD 510 646]. A small quarry [SD 5085 6452] in the south bank and excavations in the north bank at old factory sites e.g. [SD 5095 6465] expose up to 7 m of partly reddened, coarse-grained, massive sandstones. An approximately 25 m-thick unit of grey, micaceous, shaly siltstone with numerous thin interbeds of fine-grained, pale orange-brown, micaceous sandstones is exposed along the Crook o' Lune [SD 5204 6475] and [SD 5203 6457].

Sections in the main part of the Pendle Grit in the south-eastern outcrop

There are few noteworthy surface sections in the south-eastern outcrop. In the Croasdale area, approximately 40 m of mainly massive, coarse-grained sandstones up to 3 m thick are exposed in the disused Baxton Fell End Quarry [SD 682 563]. Good stream exposures occur along the length of the Whitendale River [SD 65 56] and Gutter Clough [SD 653 561], with further exposures along Calf Clough [SD 667 551], Higher Stony Clough [SD 663 567], Black Brook [SD 683 560] and Croasdale Brook [SD 688 565]. On Beatrix Fell, intermittent sections in the formation are provided by Costy Clough [SD 66 53] and Stony Clough [SD 66 54]. In the Brennand Fell area, the upper part of the main unit, including the fairly well-defined top, is well exposed in sections in Folds Clough [SD 6371 5500] to [SD 6397 5546]. There are also good exposures in a tributary stream [SD 6389 5500] to [SD 6394 5512], and lower beds are exposed in Well Springs Clough [SD 6433 5500] to [SD 6441 5520].

Surgill Shale Member (new name)

This unit has been mapped in the eastern outcrop where it was first noted by Tiddeman (1891). It is widespread in the Craven Basin. The unit was named Surgill Shales in the Lothersdale area of the Clitheroe district (Bray, 1927), but Baines (1977) called it the Pendle Shale Formation, a term proposed by Sims (1988) for the unit basinwide. This practice is not followed here because having two units with the same geographical name is potentially confusing.

In the south-eastern crop, the member comprises dominantly delta-slope siltstones and silty mudstones with relatively few thin sandstones. It varies in thickness from 30 m on Beatrix Fell to up to 210 m in the Brennand Fell area. About 180 m were penetrated in the Bowland Forest Tunnel beneath Croasdale Fell (Earp, 1955) though only 40 m were determined at outcrop during mapping. In the western outcrop, where the overlying Brennand Grit fails, equivalent strata have probably been included in the basal part of the Roeburndale Formation.

It consists of medium grey, non- to moderately fissile, laminated, finely micaceous siltstones which constitute about 90 per cent of the succession. A few levels of blue-grey, shaly mudstones with siderite mudstone lenses up to 40 mm thick occur, mainly in the upper part of the unit. The best section is in about 52 m of beds in the steep north bank of Folds Clough [SD 638 553], where a few of the beds appear to be slumped. Here, the base of the unit is fairly well defined, at the boundary between dominantly medium- to coarse-grained sandstones of the main part of the Pendle Grit and the overlying siltstone-dominated sequence, though elsewhere the boundary may be gradational. There are only intermittent sections of the member along the Brennand River. The unit is also well exposed along the Whitendale River upstream of [SD 657 577]. On Beatrix Fell, the 30 m-thick unit forms 20 m-high scars along Costy Clough c. [SD 671 539]. Sanguinolites spp. were collected from a 6 m-thick section of burrowed siltstone along Whitendale River [SD 6553 5811].

Sandstones form roughly 10 per cent of the Surgill Shale Member. They may form discrete, massive to parallel-laminated beds, typically 0.1 to 0.4 m thick and less commonly up to 1.5 m, but the thickness generally varies laterally. These sandstones are grey, weathering orange-brown, arkosic, fine to medium grained, though the thicker beds tend to be medium to coarse grained. They have sharp, erosive bases, commonly with sole marks, and loaded bases. Rippled tops are common, and lenses with siltstone pellets occur sporadically e.g. [SD 6380 5532]. Sporadic grey, massive, unsorted, argillaceous greywacke beds, up to 0.2 m thick occur, with chaotic mica flakes, e.g. in Fox Clough [SD 6294 5512] and in Folds Clough [SD 6380 5528]. There are also lenticular, laterally discontinuous, topographical feature-forming beds of coarse- to very coarse-grained, granule-grade, and pebbly sandstones several metres thick which, according to Sims (1988), probably filled feeder channels. Some of these exhibit large-scale cross-stratification. Other sandstones intergrade with the siltstones. They are grey, weathering orange-brown, parallel-laminated, platy, silty, fine-grained sandstones, and range from thin ribs in siltstone up to beds 2 m thick with siltstone partings. In places, the siltstones also contain 'striped beds' with thin layers of ripple cross-laminated sandstones on the millimetre scale. All the above lithologies contain abundant mica and comminuted plant debris, and trace fossils are common at some levels.

In keeping with deposition on the delta slope, large-scale slumping is common within the Surgill Shale, and soft-sediment deformation structures have been recorded from several exposures. Contorted strata occur within a few metres of the top of the member at Fox Clough [SD 6294 5512] and in the Brennand River [SD 6304 5517], and may have been produced by loading due to rapid deposition of the massive basal part of the Brennand Grit. Local slump deformation, confined to individual siltstone or sandstone beds, has been recorded from exposures along Folds Clough [SD 6380 5532]; [SD 6390 5540].

Brennand Grit Formation

The history of lithostratigraphical nomenclature is given in (Table 4). Before the development of ammonoid biostratigraphy (Bisat, 1924), the sandstones of the Brennand Grit Formation were tentatively correlated with the much younger, but similarly coarse-grained Kinder-scout Grit of the type area in Derbyshire (Tiddeman, 1891). Later, they were locally called Brennand Grits by Moseley (1954), from a type section in a gorge along the Brennand River, and the name was recently formalised to Brennand Grit Formation (Aitkenhead et al., 1992. p.38). Regional sedimentological work (Sims, 1988) has demonstrated an apparent stratigraphical continuity of the Brennand Grit west of the River Ribble with the Grassing-ton Grit to the east of the river (Arthurton et al., 1988) and the Warley Wise Grit of the Pendle area to the southeast (Earp et al., 1961). The latter term was also applied by Earp (1955) to the formation in the Bowland Forest Tunnel section in this district. If the above correlation is accepted, the term Grassington Grit, introduced originally by Dakyns (1892) in the Grassington area of Yorkshire, would have priority. However, the occurrence of a Lingula Band within the Grassington Grit of the eastern Askrigg Block has led Brandon et al. (in press) to conclude that the lower part of the Grassington Grit Formation, as defined by Dunham and Wilson (1985, p.62), may be coeval with part of the Pendle Grit. Until these correlation difficulties are resolved, the term Brennand Grit Formation is retained.

The craggy and faulted outcrop of the Brennand Grit Formation strikes across the south-eastern corner of the Lancaster district. From the southern slopes of White Hill in the east, where the sandstones are exposed in Shooters Clough [SD 659 583] and form crags such as Little Bull Stones [SD 679 578], Great Bull Stones [SD 673 577] and Grinding Stones Rocks [SD 660 583], it can followed through Burn Fell at Sapling Crag [SD 648 569], and on to Brennand Fell with its characteristically weather-etched and fluted tors of Whitendale Hanging Stones [SD 6435 5639] and Brennand Hanging Stones [SD 6398 5585]. Close by, a gorge section upstream of [SD 6313 5523] is provided by the Brennand River. West of the gorge, the sandstones form crags such as Millers House. From here, the formation can be traced through Threaphaw Fell [SD 62 54] and White Moor [SD 60 54], to Marshaw [SD 59 53] on the north side of the Marshaw Wyre valley, where the craggy features become mantled by a cover of till. Southeastwards into the Garstang district, where it appears to die out, its presumably steadily diminishing outcrop is totally hidden by till. The highest beds of the formation also form minor inliers, exhumed by Middle Gill [SD 6680 6129], Little Moor Beck c. [SD 679 621] and Crossdale Beck [SD 685 634], across the Whiteray and Lythe fells on the north side of White Hill. It has a more extensive, though faulted outcrop from Whiteray Beck [SD 681 611] across the watershed eastwards into the Hodder valley in the Settle district. Around 1950, the Bowland Forest Tunnel cut through a faulted sequence under White Hill (Earp, 1955). An isolated outlier [SD 6685 5375] of what are taken to be the basal 15 m of the formation caps Beatrix Fell in the core of the Beatrix Fell Syncline.

The wedge of coarse deltaic sedimentary rocks forming the Brennand Grit Formation thins southwestwards at outcrop, from between about 200 m and 250 m in the White Hill and Brennand Fell areas, to 0 m north of Catshaw Fell c. [SD 558 517] on the north side of the Garstang district. The formation in the Bowland Forest Tunnel section under White Hill is faulted, and Earp (1955) concluded that much of the middle part of the division was unrepresented. The basal 18 m of a very coarse-grained, conglomeratic, arkosic, lower leaf of grits, and a 30 m-thick upper leaf of coarse-grained, pebbly, arkosic grits, the latter underlain by 16 m of siltstones and finer sandstones, were encountered in the tunnel. In the Marshaw area, at least 65 m are present on the south side of the Millers House Fault. Although Moseley (1954) considered the Brennand Grits to be present in the Caton area, the formation is now known to be totally absent east of the Quernmore Fault in the north-western part of the district, where contemporaneous beds bordering the Pendle Grit outcrop are siltstones with sandstones in the lower part of the Roeburndale Formation. In the intervening ground, in the middle part of the district, the formation lies buried beneath younger Namurian sediments, and the assumed south-westerly thinning cannot be confirmed. Some 195 m of strata penetrated in the Whitmoor Borehole [SD 5874 6315] (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), including thick units of medium-to very coarse-grained and pebbly arkosic sandstone, are included in the Dure Clough Sandstones Member of the Roeburndale Formation in this account (p.58), although a correlation with the Brennand Grit cannot be excluded.

In the western part of the Settle district, the formation is estimated to be 220 m thick at Croasdale, adjacent to the Lancaster district, but thins eastwards towards the South Craven Fault.

The base is taken at the base of the first pebbly sandstones above the Surgill Shale Member of the Pendle Grit Formation. The Brennand Grit rests sharply and erosively on siltstones with thin interbedded sandstones. The basal contact is well exposed in the Brennand gorge [SD 6305 5518] to [SD 6313 5523] where it is channeled and strongly erosional on the underlying siltstones. It was also exposed for a considerable distance in the Bowland Forest Tunnel were it 'shows all those irregularities characteristic of the erosional base of a coarse arenaceous deposit' (Earp, 1955). Evidence is presented in the account of the adjoining part of the Settle district (Arthurton et al., 1988, p.80) for an angular unconformity and non-sequence at the base of the Brennand Grit, but there is no supporting evidence forthcoming from the present district. It is probable that the re-allocation of cross-bedded pebbly channel sandstones of Reeves Edge, Bloe Greet and Saddle Hill into the Pendle Grit (p.44) removes the necessity for postulating a strong unconformable relationship.

The formation is a wedge of delta-top facies and, as the name implies, is characterised by generally very coarse-grained or granule-grade, arkosic sandstones. These main sandstones, several tens of metres thick, form topographical features and are separated by poorly exposed strata consisting of, or presumed to consist of siltstones and thin, interbedded, fine- to medium-grained sandstones. Four main sandstone units, not necessarily correlative, are commonly differentiated, and have been mapped on the south slopes of White Hill, on Burn Fell, and along the scarps from Threaphaw Fell to Marshaw. All four units, particularly the uppermost unit, are intermittently exposed in Shooters Clough c. [SD 660 583] and nearby crags, on the southern slopes of White Hill. In the Brennand Fell area, only two coarse-grained sandstone units, each up to about 100 m thick, are differentiated, these being Moseley's (1954) Lower and Upper Brennand Grits. The higher beds are apparently cut out against the Millers House Fault to the north.

From sedimentological work, Sims (1988) concluded that the formation in this area comprises an upward sequence of facies associations, typical of the Grassington Grit of the Askrigg Block. Upwards, the sequence is characterised by shallow-water, fluvial, and locally delta-platform sediments that were deposited in response to the progradation of a braid delta southwards into the 'Lancaster Fells Basin'. The present area lies close to the gradational line between these shallow deposits to the north and sediments characteristic of the Warley Wise Grit facies to the south. Sims (1988) described the latter as being characterised by deeper-water, braid-delta sediments with giant 'Gilbertian' foresets, fronted by mass-flow apron deposits. Locally in the present district, as in the Brennand River section, the delta appears to have been fronted by a mass-flow apron.

The sandstones are generally coarse to very coarse and granule grade in grain size and may be pebbly or even conglomeratic. Beds of medium-grained sandstone also occur. There is a general upwards decrease in grain size within each sandstone unit. Apart from the lower massive, in places conglomeratic mass-flow parts of the lower sandstone, as exposed in the Brennand gorge and described from the Bowland Forest Tunnel (Earp, 1955), the beds exhibit sedimentological features that are characteristic of major delta-top distributary channel sandstones. Large-scale, tabular planar cross-bedding with internal parallel lamination, and trough cross-bedding are both found. The higher sandstones contain ripple-marked surfaces. Sims (1988) indicated consistent palaeocurrent directions from the north-north-west. The sandstones of the Brennand Grit are typically weathered to a pale orange-brown friable condition which is quite distinct from the hard sandstones of the Pendle Grit.

The part-channelised nature of the two lower sandstones is discernible by local thickening of the units in the scarps and crags on the south side of White Hill. Lenticular channelised bodies comprising Great Bull Stones [SD 673 577] are apparent when observed from the opposite side of Croasdale valley.

A siliceous ganisteroid sandstone palaeosol, 0.4 to 0.7 m thick, is found at the top of the uppermost main Brennand Grit sandstone unit in the east of the district (Figure 14). This is medium to coarse grained, with concentrations of quartz pebbles on a characteristically hummocky surface, and is penetrated by abundant rootlets and stigmarian roots. The bed forms large bedding plane exposures in the four small stream-cut inliers of Middle Gill [SD 668 613], Crossdale Beck e.g. [SD 6867 6329], Little Moor Beck e.g. [SD 6780 6212] and Whiteray Beck [SD 681 610], in the Whiteray and Lythe fells area. At one place along Little Moor Beck [SD 6809 6207], polygonal dessication cracks filled with white sandstone occur in a 0.2 m-thick olive-green sandstone which overlies the Banister. Although a palaeosol is present in the adjoining part of the Settle district (Arthurton et al., 1988), there is no evidence of a palaeosol at the top of the formation along its outcrop to the south-west, and it may have failed in more distal parts of the delta system. It has not been found at Shooters Clough on the south side of White Hill, and in a small inlier along Dale Beck upstream of [SD 6603 5980] to the north, where sandstones with synsedimentary slumps apparently occur at the top of the formation.

The uppermost sandstone unit is exposed extensively in the headwaters of the Brennand River, along Round Hill Water [SD 6330 5594] to [SD 6345 5656] and Brown Syke [SD 6337 5607] to [SD 6392 5659], on the north-west side of the Millers House Fault. It comprises coarse- to very coarse-grained, cross-bedded sandstones, and numerous associated pebbly lenses and interbeds of medium-grained sandstones with comminuted plant remains and current-rippled surfaces. These beds are overlain by synsedimentary slumped siltstones and sandstones of the Roeburndale Formation.

The only fossils in the formation are carbonaceous plant fragments in the siltstones and finer sandstones, sporadic drifted large plant fragments, and trace fossils.

Flattened, pale, sand-lined tubes, subparallel to the bedding in a siltstone rip-up clast [SD 6312 5539] in the lower sandstone unit at Brennand gorge, are ascribed to cf. Phoebichnus (Häntzschel, 1975, p.W93; Frey and Howard, 1990).

Brennand gorge section

The Brennand Gorge section exposes a basal sandstone unit overlain in turn by a siltstone unit and then a second sandstone. The lower sandstone unit, also exposed in Fox and Little Fox tributary cloughs, is estimated to be up to 100 m thick, and can be divided broadly into a massive conglomeratic lower part, recognised only in the gorge, and a thickly cross-bedded, less-pebbly upper part. The lower part is a thickly and massive-bedded, extremely coarse-grained, conglomeratic to pebbly arkosic sandstone, becoming pale orange-brown and very friable on weathering. The beds are thought to be mass-flow deposits. The subrounded to rounded pebbles are mostly white quartz up to 40 mm across. There are less common pink quartz, grey quartz and feldspar pebbles. The unit broadly fines upwards, and generally the higher beds are not as pebbly as the basal beds. There are some non-pebbly, medium-grained lenses and levels with angular siltstone rip up clasts, commonly up to 0.4 m across, with comminuted plant debris.

The upper half of the lower sandstone is a less conglomeratic, very coarse-grained sandstone, and contains both trough and low-angle, tabular cross-bedding typical of a delta-top sandstone. In the gorge, there is a 2 m-thick lens of grey sandy, shaly siltstone interbedded with medium- to coarse-grained sandstones with loaded bases [SD 6310 5550]. There are numerous siltstone pellets and rip up clasts, some with rolled up lamination. Towards the top, grey, sandy, micaceous siltstones, up to 4 m thick, are interbedded with numerous thin, grey, fine- to medium-grained, platy, planty sandstones with current-rippled surfaces [SD 6309 5552]. Some faulting may be due to syndepositional movements or growth faulting. North-east of the gorge, there is no trace of the massive conglomeratic lower beds, and very coarse-grained, pebbly, cross-bedded sandstones in the basal few metres of the formation form the crags at Brennand Hanging Stones [SD 6398 5585], Whitendale Hanging Stones [SD 6435 5639] and Sapling Crag [SD 6483 5691] to [SD 6494 5700].

The siltstone unit between the lower and upper sandstones is well exposed in the gorge, where it is 26.5 m thick. It has only been mapped for up to 400 m on either side of the gorge, beyond which lateral continuity is uncertain. It consists of pale to medium grey, shaly to platy, micaceous, sandy siltstones, with numerous thin beds of pale grey, fine- to medium-grained, platy, parallel- to ripple cross-laminated, micaceous sandstones. The proportion of sandstone varies, but is typically about 25 per cent to 30 per cent of the beds. Individual sandstones are commonly lenticular, and mostly range from a wafer to about 0.3 m thick, with a few up to 2.5 m thick. They contain abundant siltstone clasts and comminuted plant debris, and some beds are finely laminated. At the top of the unit, at a waterfall capped by the higher sandstone unit [SD 6304 5562], 2 m of similar siltstones and sandstones fill a discordant channel. They are gently folded and cut by oblique faults which may be synsedimentary.

The lower beds of the higher sandstone unit are well exposed in Brennand gorge and the highest beds are well displayed along its western tributary, Sapling Clough c. [SD 630 557]. The base is erosional and channeled. The thickness preserved up to the Millers House Fault is estimated at about 100 m. This higher sandstone unit consists mostly of medium- to coarse-grained, thickly bedded, arkosic sandstones. Some levels are pebbly, but the unit is never as coarse grained and pebbly as the lower sandstone unit. Cross-bedding is well displayed in weather-etched crag exposures. Approximately the lowest 80 m of beds have predominantly low-angle tabular cross-bedding on a large scale, and parallel-lamination. About 22 m above the base of the unit, and well exposed where the Brennand River bifurcates [SD 6303 5568], there is a 2 m-thick bed of grey, shaly, micaceous siltstone with lenticular sandstones. A 0.5 m-thick lens of siltstone occurs 2 m higher stratigraphically. Higher sandstones, exposed in Sapling Clough, are trough cross-bedded, and the highest beds exposed near the Millers House Fault [SD 6289 5578]; [SD 6282 5575] are medium-grained with corn-minuted plant debris.

Roeburndale Formation

The term Roeburndale Formation was first used in the Settle district (Arthurton et al., 1988) for the thick sequence of siltstones and subordinate sandstones between the top of the Brennand Grit Formation and the base of the Caton Shale Formation. In those parts of the Garstang district (Aitkenhead et al., 1992) where the Brennand Grit is absent, the base of the Roeburndale Formation was taken at the top of the Pendle Grit Formation. In the Lancaster district, the top of the formation is redefined as the base of the Ward's Stone Sandstone Formation.

The origin of the name is complex (see (Table 4)). As used in the Settle and Garstang districts, it is synonymous with the 'Roeburndale Grit Group' (Moseley, 1956) of the Keasden area near Settle. This latter term had earlier been applied in a slightly different sense to the 'Lancaster Fells' (Moseley, 1954), where it excluded the 'Tarnbrook Wyre Marine Beds' (including the Cravenoceras cowlingense and Eumorphoceras ferrimontanum marine bands) above the 'Brennand Grits' (see for example Johnson, 1981). In describing the Bowland Forest Tunnel sequence, Earp (1955) referred to the 'Roeburndale Sandstones'. A further complication is that Moseley (1954, 1956) coined his name for a 'group' of strata, up to and including the delta-top 'Roeburndale Grit' (Slinger, 1936), which was mapped but not named in the Settle and Garstang areas (Arthurton et al., 1988; Aitkenhead et al., 1992). This distinctive and widespread sandstone is here given separate formational status as the Ward's Stone Sandstone Formation (see below). Thus, the top of the Roeburndale Formation is now redefined at the base of the 'Roeburndale Grit' of Slinger (1936) with the result that the application of the geographical prefix 'Roeburndale' has changed radically since its original use.

The formation has the most extensive outcrop of any Carboniferous formation over a large area of the central part of the district, both at surface and concealed beneath drift. Although there are no complete sections available, parts of the formation, including several component members, are well exposed in deeply incised gullies in the upland areas, where the drift cover is relatively thin. The 'Lancaster Fells' are the type area for the formation whose extent northwards into the Kirkby Lonsdale district is poorly known.

There are numerous gully sections, the main ones being detailed below. Sections in the lower and upper parts of the formation are almost mutually exclusive. The best sections in the lower part, up to just above the E. ferrimontanum Marine Band, are mainly confined to the south-eastern side of the 'Ward's Stone range', along the headwater streams of the Tarnbrook Wyre, Brennand

River and River Hindburn (Figure 14). Good sections in the upper part, from just below the C. gressinghamense Marine Band, occur to the north of the 'Ward's Stone range', along the rivers Roeburn and Hindburn, Foxdale Beck and their tributaries, and along incised tributaries of the River Lune (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19). Other sections are provided by the Whitmoor (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8) and Wray (Figure 22) boreholes, and the Bowland Forest Tunnel (Earp, 1955) which supposedly penetrated the entire formation. The Wyresdale . Tunnel provided sections in the lower part of the formation (Johnson, 1981).

The general stratigraphy of the formation is shown in (Figure 12). The Roeburndale Formation consists mainly of delta-slope siltstones and interbedded sandstones and siltstones, with subordinate, pro-delta, sideritic mudstones and impersistent delta-top sandstones. Thin but widespread 'black' marine mudstones, up to a few metres thick, occur at four levels, and have proved useful in correlating sections. The various lithofacies listed below form generally mappable units which have been used to subdivide the formation, and some have been named as members.

1. Marine bands: widespread, relatively thin, typically 0.5 to 4 m-thick units, comprising hemipelagic, dark grey ( 'black'), tough, shaly to platy, silty mudstones with sharp bases, and containing argillaceous limestone (wackestone) beds and nodules ('bullions'). The marine bands are generally calcareous and typically contain numerous small phosphate nodules. They contain marine faunas, dominated by thin-shelled, pectinacean bivalve and ammonoid molluscs. The presence of thick-shelled ammonoids in the main part of the marine bands indicates fully marine salinities, whereas impoverished faunas, without thick-shelled ammonoids, in the basal and upper parts of the marine bands probably indicate less-saline conditions (Ramsbottom et al., 1962; Holdsworth and Collinson, 1988). This type of marine facies occurs at four levels, named in upward sequence the Cravenoceras cowlingense, Eumorphoceras ferrimontanum, C. gressinghamense and E. yatesae marine bands. The E. ferrimontanum Marine Band maintains a uniform facies, but where there was emergence at the top of the Brennand Grit, the C. cowlingense Marine Band probably may pass laterally into fissile grey mudstones with Lingula or Sanguinolites and ostracods. The E. yatesae Marine Band probably passes laterally into similar mudstones with Selenimyalina or Lingula, where it directly overlies the ganisteroid Sapling Clough Sandstone. These marginal marine faunas probably indicate less-saline conditions.

2. Marginal marine siltstone: uniform grey, shaly, sandy, micaceous, calcareous siltstones, containing numerous, thin, fine-grained sandstones on the centimetre scale, cemented with ferroan calcite. There are also several levels of large lenticular calci-siltite nodules. The facies contains, in addition to abundant trace fossils, a generally sparse marine fauna, including the bivalve Sanguinolites, bellerophontid and glabrocingulid gastropods and ostracods, which may have been tolerant of a muddy environment with relatively high sedimentation rates (Brandon et al., 1996). It is gradational with facies 5 and is represented by the Close Hill Siltstone Member.

3. Pro-delta mudstone: dark grey to bluish grey, shaly, finely micaceous mudstones, with lenticular nodules of siderite mudstone typically up to 50 mm thick. The facies, which is gradational with facies 4, contains sparse, comminuted, nonmarine fish debris.

4. Delta-slope siltstone: grey, shaly, sandy, micaceous siltstones with comminuted carbonaceous plant debris, and subordinate, thin, sharp-soled sandstones, commonly with ripple cross-laminated tops. The facies grades into facies 5.

5. Delta-slope sandstones and siltstones: heterolithic interbeds of very fine- to medium-grained sandstones and grey, shaly, sandy, micaceous, planty, laminated siltstones. At some levels the siltstones predominate, and vice versa. The beds were probably laid down in a distal to proximal delta-slope environment by a mixture of density currents and suspension. They are represented by the Dure Clough Sandstones and Cocklett Scar Sandstones members and the unnamed unit above the Close Hill Siltstone Member. The sandstones are of several types:

a)         The predominant type consists of relatively clean, grey, brown-weathering, fine-grained, generally parallel bedded, massive, graded, micaceous, sole-marked turbidite sandstones with parallel and ripple cross-laminated tops in which the Bouma (1962) sequence of internal structure is present in various degrees of completeness. These sandstones usually range from a few tens of millimetres to less than a metre in thickness, but there are stacked sandstone units up to 4 m or more thick. The thicker sandstones have commonly been differentiated on the 1:10 000 scale maps. The sandstones may contain intraformational conglomerates with silty mudstone or siltstone pebbles. Locally, the sandstones may have a lenticular form where they fill channels. At some levels, particularly in the Cocklett Scar Sandstones and Close Hill Siltstone members, the sandstones are commonly cemented with ferroan calcite or calcite.

b)        Associated with the above sandstones are 'striped beds' (Johnson, 1981) of grey, thinly interlaminated siltstones and paler grey, very fine- to fine-grained sandstones with gradational boundaries; ripple cross-laminated levels are common.

c)         Sporadic grey, sharp-soled, silty, greywacke-type sandstones, typically up to 100 mm thick. These have a chaotic unsorted fabric and may be debris-flow deposits.

d)        Grey, silty, parallel- and ripple-laminated, micaceous sandstones, typically up to 100 mm thick, with gradational boundaries with the interbedded grey micaceous siltstones. These sequences are commonly strongly bioturbated, and were probably deposited near the top of the delta fans.

6. Fluvial or distributary channel sandstones of coastal plains: grey, weathering to pale orange-brown, fine- to coarse-grained, clean sandstones with siliceous palaeosols (ganister sandstones) and rare thin coals. This facies is represented by the Gavells Clough and Sapling Clough sandstone members, and locally by the upper part of the Dure Clough Sandstones Member.

In the eastern part of the district, the base of the formation is taken at the top of the Brennand Grit Formation, where there is commonly a sharp junction with underlying ganisteroid sandstones, for instance in the River Hindburn headwaters [SD 66 61]. In more westerly localities, where the Brennand Grit is absent, the formation overlies the Pendle Grit Formation directly, and the boundary can either be sharp, as for instance in Great Ugly Clough [SD 5119 6112], or more gradational. In the largely drift-covered area from Lancaster northwards, the base of the formation is ill defined, and it is uncertain whether sequences of siltstone-dominated strata encountered in boreholes lie within the upper part of the Pendle Grit Formation or the lower part of the Roeburndale Formation (see Pendle Grit section).

From the evidence pieced together from partial sections and the geometry at outcrop, the formation is estimated to be between 500 and 650 m thick across the area. Lack of complete sections precludes an assessment of more precise variations in thickness. The formation reaches 500 m on Burn Moor in the adjacent part of the Settle area (Arthurton et al., 1988), but thins considerably eastwards. In the north-western part of the Garstang district (Aitkenhead et al., 1992), a thickness of 450 m is estimated. The strata continue to thin south-eastwards across the district to become part of the Sabden Shale Formation, as for example at Saleswheel (Riley, 1985).

The Roeburndale Formation is apparently 518 m thick in the Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), between depths of 29 m and 547 m, although the identification of the lowest part of the formation is equivocal (see pp.48,58). A thickness of only 208 m is estimated from the log of the Bowland Forest Tunnel (Earp, 1955), compiled from beneath the upper reaches of the River Hindburn c. [SD 65 61] where the entire thickness of the formation is supposed to have been penetrated. A fault shown on the tunnel section, 12 000 feet from the North Portal, may have cut out part of the sequence. In the western part of the district, the thickness of the Roeburndale Formation may be greatly attenuated (see pp.33,137).

In the nonmarine, delta-slope siltstones and sandstones, animal remains are rare, only a possible Paracarbonicola and cypridinid ostracods having been recorded, but trace fossils such as Aulichnites, Monocraterion and Diplocraterion are commonly found and indicate activity by gastropods and various types of worms (Eagar et al., 1985). Drifted carbonised plant debris, usually in comminuted form, is abundant in the nonmarine siltstones and sandstones. More rarely, recognisable remains such as Calamites are present. In-situ stigmarian roots and rootlets have been recorded locally from ganister sandstones in the Dure Clough Sandstones and the Sapling Clough Sandstone.

The mainly nonmarine mudstones, siltstones and sandstones of the Roeburndale Formation were aggraded in various prodelta and delta-slope situations after the basin had deepened rapidly, following the retreat of the Brennand Grit fluviodeltaic systems. The overlying Ward's Stone Sandstone marks the return of a basinwide coastal, delta-top environment. A simple delta-progradational sequence is complicated by incomplete minor cycles, caused by four fully marine, glacio-eustatically induced (e.g. Maynard and Leeder, 1992) transgressions, and at least one marginal marine episode. Fully marine conditions were normally dysaerobic, as indicated by the specialised fauna, but more oxygenated bottom conditions are suggested by benthonic elements, for example crinoids, brachiopods and Selenimyalina, particularly in the E. yatesae Marine Band. Delta-top environments were established locally during Roeburndale Formation deposition.

Palaeocurrent data of the delta-slope deposits, derived mainly from current-ripple marks (39 observations), primary current lineations (16), orientated plant debris (9) and sole marks (21), indicate that the palaeoslope faced southwards throughout deposition of the Roeburndale Formation. Current flow ranged between south-south-west and south-south-east, with no discernible variation in direction corresponding to stratigraphical position. A general southwards-facing palaeoslope was also deduced from the direction of slumping of delta-slope deposits and channel axes in the Wyresdale Tunnel (Johnson, 1981).

Intraformational movements during Roeburndale Formation deposition

Syndepositional movements on the delta slope occurred at periods throughout the deposition of the Roeburndale Formation, and are evidenced by numerous examples of slumped, microfaulted or deformed strata, listric or growth faulting, local lateral stratigraphical changes over short distances, and a local unconformity at the base of the Eumorphoceras yatesae Marine Band. Examples are documented in the appropriate section. A graphic description from the lower part of the formation encountered in the Bowland Forest Tunnel, and not readily ascribed to a particular level in the stratigraphy, was given by Earp (1955): 'In the lower part of this group there is a bed nearly 20 ft thick showing large-scale intra-formational disturbance. The sandy component is rolled and drawn-out into elongate masses in which the bedding is much folded. In places the structures simulate current-bedding; in others recumbent folding. The shaly component exhibits a sort of flow-shearing where it has accommodated the masses of sandstone. The disturbed bed occupies nearly 200 ft of tunnel. Large recumbent slump folds were also recorded in the Wyresdale Tunnel by Johnson (1981) (Plate 6).

Large-scale, syndepositional growth faulting in the Brennand Great Hill area [SD 62 56] may account for the apparent local thinning of strata between the E. ferrimontanum and E. yatesae marine bands (see (Figure 19) section 10), including the possible absence or gross thinning of the Close Hill Siltstone. A complicated fault pattern in the area may have a syndepositional origin.

The movements probably resulted in part from slope instability or gravitational overloading which produced subaqueous landslides, a superficial type of growth faulting. These may in turn have been triggered by deep-seated, synsedimentary tectonic activity, a mechanism which could also explain the widespread angular unconformity at the base of the Ward's Stone Sandstone Formation (see below). This unconformity is demonstrated by mapped relationships, and is actually discernible in a few sections where the sandstone rests on various members in the upper part of the Roeburndale Formation, and where dips in the Ward's Stone Sandstone are gentler and in a different direction to those in the underlying beds (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18).

As in the Claughton Formation, the more intensely deformed zones occur on the downfaulted south-southwestern sides of a few prominent faults with an approximate north-west to south-east trend. Particularly good examples are to be found in the severely slumped Close Hill Siltstone along the River Roeburn and Warm Beck [SD 59 63], on the south side of the Claughton Fault. This fault is similarly associated with deformed siltstones and sandstones of the Claughton Formation in the Claughton area [SD 56 66], 4 km to the north-west (see p.84). The same strata are severely deformed on the south side of the Smeer Hall Fault along Snab Beck [SD 56 68], and this fault is associated with slumping of a sandstone in the Roeburndale Formation along the River Roeburn at Hill Kirks Scar [SD 6055 6637]. Contemporaneous movements in a down-south sense along faults with this trend, particularly the Artle Beck and Foxdale Beck faults, are suggested to explain also the local preservation and facies changes of the E. yatesae Marine Band (see below), which is cut out by the unconformity below the Ward's Stone Sandstone to the north of these faults (see (Figure 26)A).

These movements were probably intimately connected with the local development of the basin of deposition, which was largely subsiding due to regional thermal sag. In summary, six periods are recognised during which there are known to have been widespread syndepositional events. The first three may relate purely to gravitational overloading of the delta slope, but the others may have been caused by syndepositional fault movements.

(i)     In late Pendleian times, between the deposition of the Brennand Grit and the C. cowlingense Marine Band, there was widespread slumping on the delta slope and the injection of sand dykes.

(ii)  There was some slumping and injection of sand dykes in early Arnsbergian times, during the deposition of the Dure Clough Sandstones.

(iii)        In early Arnsbergian times, shortly after the deposition of the E. ferrimontanum Marine Band, slumping affected the deposition of the Gavells Clough Sandstone at several places.

(iv)        There was a phase, marked by widespread slumping, during the deposition of the Close Hill Siltstone in early Arnsbergian times. Slumps are particularly evident close to certain north-west to south-east faults.

(v)  The Sapling Clough Sandstone is locally affected by soft- sediment microfaulting, adjacent to a fault which may have been active in early Arnsbergian times.

(vi)        Movement around the time of deposition of the E. yatesae Marine Band in early Arnsbergian times resulted in a local unconformity at its base and facies changes within the band.

Stratigraphy of the Roeburndale Formation

Strata up to the base of the Cravenoceras cowlingense Marine Band

These beds are generally poorly exposed and there are few sections where the sequence is unequivocal. The superb sections seen in the Wyresdale Tunnel (Johnson, 1981; Wilson et al., 1989) were originally thought to have included strata at this level, but faulting and the absence of sound biostratigraphical data make this uncertain. The sections in the tunnel have therefore been omitted from (Figure 14), which shows the most important sections through the lower part of the formation.

The unit is mainly composed of siltstones, in some cases interbedded with thin, fine-grained sandstones (facies 4 and 5 above). Many of the sandstones are evidently turbidites, and possess sharp soles with well-developed solemarks. Others have gradational bases. A few thicker, fine- to medium-grained sandstones occur locally, and particular packets interbedded with siltstones were previously named in the Abbeystead area, including the Wyresdale Tunnel (e.g. Wilson et al., 1989), and in the north-western part of the Garstang district (Aitkenhead et al., 1992) as the Caw Mill, Long Bridge and Hall Gill sandstones, recorded as being up to 22 m, 8 m and 26 m thick respectively. The stratigraphical position of these beds in relation to the marine bands is uncertain, and the names have not been retained in this account. Comminuted carbonaceous plant fragments are generally abundant. Sideritic shaly mudstones form a subordinate facies in places, particularly near the top (see (Figure 14)). Syndepositionally slumped beds, in the form of isoclines, monoclines and balled-up sandstones, have been recorded in the Wyresdale Tunnel (Johnson, 1981) and in nearby sections e.g. [SD 5599 5296] along the Wyre and its tributaries (Wilson et al., 1989). Similar soft-sediment deformation occurs along Brown Syke [SD 6365 5661], in the Brennand River catchment and in Spreight Clough [SD 598 551], a tributary of the Tarnbrook Wyre. Sandstone dykes up to 2 m wide penetrate sideritic mudstones in the tunnel section, and a 1.8 m-thick dyke in similar rocks is exposed in nearby Cam Clough [SD 5356 5467].

Estimates of thickness within the district (Figure 14) include about 55 m at Great Ugly Clough [SD 511 612] in the Quernmore area, 71 m at Pedder Potts Reservoir [SD 533 704] in the Over Kellet area, between 120 m and 170 m in the Wyresdale Tunnel sections at Abbeystead [SD 55 55], where the precise level of the overlying marine band is equivocal, and at least 90 m in the Spreight Clough [SD 598 551] to Screes End [SD 603 551] area higher up Tarnbrook Wyre. The strata are about 12 m thick at Pedder's Wood in the Garstang district. In the Brennand River headwaters [SD 63 56], the overlying marine band has not been located, probably due to faulting, so that the thickness is uncertain. Farther north-east, in the headwaters of the River |Hindburn, the C. cowlingense Marine Band has not been identified with certainty, but is probably represented by the pale grey mudstone with Sanguinolites in Middle Gill [SD 6671 6137], estimated to lie only 8 m above the Brennand Grit, and by a Lingula band less than 1 m above the top of the grit in Crossdale Beck [SD 6847 6346]. The unit must therefore thin considerably towards this area. Moreover, the marine band was not found during the construction of the Bowland Forest Tunnel, in spite of a prolonged search in 12 m of dark shale overlying the Brennand Grit (Earp, 1955).

A BGS borehole at Aldcliffe [SD 4627 6021], south-west of Lancaster, encountered 63 m of partly purple, shaly, sandy siltstones, with sandstone beds in the upper part and sparse ostracods at depths of 38.2 m and 47.6 m. These strata probably lie in the lower part of the Roeburndale Formation, and may belong to this stratigraphical interval.

Cravenoceras cowlingense Marine Band (E2a1)

The marine band crops out extensively along the western and southern outcrops of the formation (Figure 15), and can be identified with certainty at five exposures and with less certainty at three. Apart from the two exposures referred to by Moseley (1954), these are new records.

The band is completely exposed in the back scarp of the Screes End Landslip [SD 603 551], Tarnbrook, where it comprises up to 3 m of tough, dark grey, shaly mudstone or 'black shale' (facies 1). A dark grey, micaceous sandy bed at its base is rich in C. cowlingense and Posidonia lamellosa (Plate 3). Other localities in this area include Delph Beck [SD 5985 5540] (subdrift debris), the hillside north of Delph Beck [SD 6022 5568] to [SD 6039 5567], and a former exposure along Tarnbrook Wyre [SD 5846 5562] near Ouzel Thorne. At Pedder Potts Reservoir [SD 5334 7039], Over Kellet, the band unusually consists of 0.5 m of dark grey limestone containing Posidonia corrugata and Cravenoceras sp., with a cone-in-cone breccia in the upper half of the bed. In the Quernmore area, the band is partially exposed in Great Ugly Clough [SD 5119 6112], where 'bunions' yielded the eponymous ammonoid and Eumorphoceras grassingtonense, and was represented in slabs dug from a gas pipe line excavation [SD 501 607].

The composite fauna, collected from unequivocal C. cowlingense Marine Band exposures within the district, includes: the bivalves Chaenocardiola sp., nuculoids, Obliquipecten costatus, Posidonia lamellosa and P. corrugata; orthocone nautiloids; the ammonoids Anthracoceras sp., Cravenoceras cowlingense, Eumorphoceras grassingtonense and Metadimorphoceras sp.; entomozoacean ostracods; and conodont and fish debris.

The marine band is known from Pedder's Wood [SD 5117 4782], to the south of the district (Aitkenhead et al., 1992), where it is partly cut out by slumping in the overlying beds. It has not been identified with certainty in the eastern parts of the Lancaster district, either in the Brennand, Crossdale Beck, Hindburn or Hodder headwaters, where there is reasonable exposure, or during the construction of the Bowland Forest Tunnel, despite a prolonged search (Earp, 1955). Furthermore, it was not recorded from the Settle district, farther east (Arthurton et al., 1988). It is unlikely that such a regionally widespread transgressive marine event, even reaching onto the Askrigg block (Dunham and Wilson, 1985), failed to penetrate the eastern part of this district. Two explanations are possible. Firstly, in the eastern area, the marine band may have been deposited but subsequently removed by local slope failure or scouring. Secondly, the marine band may be extremely thin and possess an unusual marginal marine fauna. Three candidates for the latter scenario occur in the upper reaches of Crossdale Beck and the rivers Hindburn and Hodder, and this is considered to be the most likely explanation:

a.     The horny brachiopods Lingula mytilloides and Orbiculoidea cincta, and conodont Cavusgnathus naviculus occur in 0.24 m of mudstone and coarse-grained sandstone which form an inlier along Crossdale Beck [SD 6847 6346], about 4 m above a ganister that is thought to be the top of the Brennand Grit.

b.    Pale grey silty mudstones with sparse Sanguinolites sp., forming an inlier in Middle Gill [SD 6671 6137], a tributary of the River Hindburn, occur about 8 m above a ganister that is thought to be the top of the Brennand Grit.

c.     Sanguinolites sp. and ostracods occur abundantly in 0.6 m of dark grey fissile mudstone just to the east of the district, in a tributary to Far Costy Clough [SD 6878 5923] in the headwaters of the River Hodder. Faulting obscures the precise relationship to the Brennand Grit which may occur stratigraphically only a few metres below. A cursory investigation of the ostracods (I P Wilkinson, personal communication, 1993) identified several benthonic, shallow-marine species, including Hollinella?, several Amphissites and Cavellina, as well as several other taxa including a possible fragment of an entomozoacean.

Strata between the Cravenoceras cowlingense and Eumorphoceras ferrimontanum marine bands

The only places where this sequence is reasonably well exposed, and where the overlying marine band has been positively identified are in the headwaters of the Tarnbrook Wyre and Brennand River, where it is estimated to be of the order of 130 m thick ((Figure 14), sections 5 and 6). It is probably considerably thicker elsewhere, and may be at least 253 m thick in the Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8). It consists mainly of delta-slope siltstones with thin, fine-grained, sharp-soled sandstones (facies 4), and with important sideritic shaly mudstones (facies 3) in the basal and topmost few metres and at other levels. Wherever sections permit, the middle part of the sequence is seen to comprise packets of sandstones and interbedded and interlaminated sandstones and siltstones which have been mapped as the Dure Clough Sandstones Member (facies 5 and 6; see below).

Widespread slumping has been described from this general level only in the Wyresdale Tunnel section (Plate 6), but the exact stratigraphical level there is uncertain. Slumped siltstones with thin contorted sandstone beds occur about 13 m above the Dure Clough Sandstones in Green Pot Clough [SD 6363 5726], in the Brennand headwaters.

Sandstone injections have been found at a number of locations. In the Wyresdale Tunnel, four subvertical sandstone dykes, 10 to 150 mm wide, were encountered in silty mudstones (Johnson, 1981) at a level that may underlie the Dure Clough Sandstones. Although the dykes are lithologically and texturally similar to thickly bedded sandstones that are thought to have been their source, the relationship was not exposed. Dykes were also recorded in the Tarnbrook Wyre headwaters area, cutting mudstones near what is taken as the top of the Dure Clough Sandstones Member in Swine Clough. At one locality [SD 6084 5562], a solitary vertical 10 to 20 mm-wide dyke, orientated south-south-west to north-north-east, penetrates mudstone through a height of 1.2 m, and is boudinaged in places. At another place [SD 6093 5565], four 20 to 50 mm-thick, subvertical to oblique injections of pale grey, fine-grained sandstone, orientated between north–south and north-northwest to south-south-east, emanate from a 100 mm-thick source bed which thins steadily eastwards. The dykes are disposed vertically at their bases, but upwards become oblique and merge into a 20 to 80 mm-thick, sill-like intrusion, only a few degrees oblique to the bedding. On the south-eastern side of nearby Gables Clough [SD 6096 5635], in siltstones about 25 m higher, a vertical 140 to 380 mm-thick dyke emanates from a 0.13 m-thick sandstone bed. The dykes are thought to have been injected upwards prior to dewatering and compaction. They are typically plicate and commonly boudinaged due to subsequent compression on compaction. Johnson (1981) deduced from the east–west trend of the Wyresdale Tunnel dykes that they formed parallel to the palaeoslope, but the examples given above would not suggest this.

At Swine Crag [SD 606 559], on the White Side of Tarnbrook Fell, about 20 m of partly landslipped, coarse- to very coarse-grained, massive sandstones, with pebbles of vein quartz up to 15 mm in diameter, are very local in extent, and are thought to occupy a palaeochannel on the otherwise silt-dominated delta slope. A 1 m- to 2.3 m-thick medium-grained, massive sandstone with pebbles of siderite- mudstone in the basal part, occurs in the surrounding area e.g. [SD 6108 5646], [SD 6113 5659], [SD 6098 5626], [SD 6303 5700] about 25 to 30 m below the E. ferrimontanum Marine Band, and is probably a more extensive lateral equivalent of the channel-fill.

Apart from plants and burrows, fossils are rare in these delta slope deposits. A poorly preserved bivalve, possibly Paracarbonicola, was recorded in siltstones about 9 m below the E. ferrimontanum Marine Band, in an unnamed tributary to Small Clough [SD 6107 5627].

Dure Clough Sandstones Member (new name)

The member, typically of the order of 80 to 100 m thick and mainly of delta-slope facies, is named from a fine partial section along Dure Clough [SD 634 570] (Figure 16) in the Brennand River headwaters, where it gives rise to a strong scarp feature. There are also faulted partial sections along Sapling [SD 628 559] and Green Pot [SD 636 571] cloughs ((Figure 14), section 6).

The unit is present at outcrop across the southern part of the district, and may be represented by approximately 300 m of interbedded and commonly slumped sandstones, siltstones and striped beds, penetrated on the north-western limb of the anticline in the Wyresdale Tunnel (Johnson, 1981) and formerly named the Rowton Brook Sandstone (Wilson et al., 1989). The excessive thickness here may be due to slumping. The member has not been proved in the northern part of the district. In the Whitmoor Borehole [SD 5874 6315] (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), it is probably represented by 195 m of strata, comprising thick units of medium- to very coarse-grained and pebbly arkosic sandstones, separated by generally thinner units of interbedded siltstones and fine-grained sandstones between depths of 297 m and 492 m. The lack of core and biostratigraphical control are a serious handicap to positive identification, however, and a correlation with the Brennand Grit cannot be excluded (see p.48). In the Quernmore area, a steep gully on Lythe Brow [SD 522 617] exposes about 41 m of delta-slope, interbedded, sole-marked sandstones and siltstones that have been provisionally ascribed to this member. In the eastern part of the district, the unit forms White Hill and is exposed on its northern slopes in the River Hindburn and in several tributary streams. In the adjacent north-western part of the Garstang district (Aitkenhead et al., 1992), beds probably equivalent to the Dure Clough Sandstones form the Park Wood Sandstones Member and total about 250 m in thickness. In the headwaters of the Tarnbrook Wyre and Brennand River, the base lies about 30 m above the C. cowlingense Marine Band, but in the headwaters of the River Hindburn, only about 22 m of siltstones separate the member from the Brennand Grit (Figure 14).

The base is rarely exposed, but along Middle Gill [SD 666 614] the lowest sandstone of the basal interbeds of sandstone and siltstone sharply overlies siltstones. The sharp upper boundary is only exposed in the east, where the unit passes laterally into a delta-top facies.

In the type area of the Brennand headwaters, the member consists mostly of delta-slope sandstones, variably interbedded with siltstones. In the lower part of the member, the two lithologies are generally more equant, or siltstones and more rarely silty mudstones predominate through several metres of strata. In the upper part of the sequence, there are few siltstone beds and the sandstones can form stacked units up to 18 m thick. Slumped tabular cross-bedding has been observed on loose blocks on Brown Syke Hill [SD 6388 5695], and parts of the upper unit may have been deposited on a delta top. A 14 m-thick silty mudstone separates the two sandstone parts of the member. The sandstones are pale grey when fresh, weathering to pale orange-brown, micaceous, and fine to medium grained. They occur as parallel beds typically 0.3 to 1.2 m thick. The bases are sharp and uncommonly channelled, and sole marks have been recorded. Intraformational conglomerate lenses are common in the lower parts of some sandstones. These contain mostly siltstone intraclasts that are commonly imbricate, but a sandstone pebble bed was noted [SD 6281 5591]. The sandstones are typically micaceous and platy, with parallel laminations and current-orientated plant debris. With an incoming of fine siltstone laminae, the beds pass upwards into siltstones and striped beds, in which ripple cross-lamination and current-generated ripples are common. Both the siltstones and sandstones contain much plant debris, largely in a corn-minuted state, and the only fossils recorded are the bibbed burrow cf. Aulichnites and the U-shaped burrow cf. Arenicolites. Sandstone injections occur in the highest beds in Swine Clough [SD 6093 5565] (see above). Primary current lineations, current-orientated plant debris, current-generated ripple marks and channelling suggest a SSW-facing palaeoslope.

Around the headwaters of the River Hindburn and Crossdale Beck, and underlying Botton Head Fell and White Hill to the south, the equivalent beds to the upper sandstone unit in the Brennand headwaters area are probably fluvial or distributary channel deposits of delta-top facies. They comprise about 35 m of thickly bedded, medium- to coarse-grained, tabular and trough cross-stratified sandstones that are commonly current-rippled in their upper parts. These constitute the Botton Head Grit of Moseley (1954) but are not differentiated on the map. Fine- to medium-grained, siliceous Banister sandstones with rootlets and stigmarian roots occur at more than one level. The best section is provided by Middle Gill [SD 66 61] ((Figure 14), section 7) and there are partial sections in Whiteray [SD 68 61], Little Moor [SD 67 62] and Middles Moor [SD 67 61] becks, in the River Hindburn and its tributaries [SD 65 61], and in the Crossdale Beck area [SD 68 63] ((Figure 14), section 8). Cross-bedding indicates palaeocurrents on the delta top from the east and south-east. The sharp top of the member is exposed at the confluence of the River Hindburn and Kiln Clough [SD 6562 6185], and in Middle Gill [SD 6630 6217].

Eumorphoceras ferrimontanum Marine Band (E2a2)

This marine band has proved a persistent and valuable marker bed in helping to unravel the stratigraphy and structure of the Roeburndale Formation. It has been found in at least 31 localities across the district, only two having been previously recorded (Moseley, 1954). Most of the exposures occur in the south, in the headwaters of the Brennand and Tarnbrook Wyre rivers and around Ward's Stone (Figure 17). The band has not been proved in the west due to drift cover. North of the 'Ward's Stone range', the marine band is partially exposed in Sweet Beck [SD 5508 6108] and an adjacent stream [SD 5514 6101] in the Littledale area (Figure 19), its most northerly exposure. In the northern parts of the district, the marine band probably does not crop out. It was not identified during the survey of the Settle district (Arthurton et al., 1988). Revision mapping along that district's western margin during work on the Lancaster Sheet, however, has revealed one possible occurrence of the band (see below). In addition, the band probably corresponds with the gamma peak at a depth of 253 m in the Whitmoor borehole, 44 m above the presumed top of the Dure Clough Sandstones Member. At this level, 'black' shaly mudstone chips collected through about 3 m of strata have yielded P. corrugata. The band has been found at several places in the Garstang district.

The marine band typically consists of up to 4 m of uniform tough, dark grey, platy, silty mudstone with scattered phosphatic nodules (facies 1; (Figure 17)). A basal transgressive phase underlies the 'black shale' facies, comprising more fissile, blue-grey, finely micaceous mudstone with a restricted fauna (see below) in its top metre. The base of the band is therefore gradational, as is the top. The 'black shale' facies is calcareous in the lower 1 m, and contains wackestone limestone bullions at Abbeystead House that have yielded uncrushed fossils particularly Anthracoceras. Locally, in the Tarnbrook Wyre and Brennand headwaters area, the marine band is thinner, the uppermost beds having been removed by the erosive base of the overlying Gavells Clough Sandstone (see (Figure 17)). Unusually, on Salter Fell, where abundant debris of the band from the local bedrock is common in the head in gullies [SD 647 598]; [SD 649 602], the lithology is partly dark grey, platy, silty, fine-grained sandstone, although retaining the typical faunal elements.

The fully developed marine fauna is regionally uniform, and is characterised by: the bivalves Chaenocardiola footii, Dunbarella yatesae, Myalina sp., Obliquipecten costatus, Posidonia corrugata, Pseudamussium sp. and Streblopteria sp.; and the ammonoids Anthracoceras glabrum, Cravenoceras gairense, Eumorphoceras erinense, E. ferrimontanum, Kazakhoceras scaliger and Metadimorphoceras saleswheelense. Sponge spicules, crinoid debris, orthocone and coiled nautiloids, scolecodonts, conodonts and fish debris also occur. Entomozoacean ( 'fingerprint') ostracods referable to Maternalla (Steinachella) sp. have been recovered from the band in this district (Wilkinson and Riley, 1990). P. corrugata occurs sporadically in the top metre of bluish grey shaly mudstones underlying the 'black' platy mudstones.

The most important sections are shown in (Figure 17). The band is only completely exposed and fully developed in the west bank of Sapling Clough [SD 6262 5628], although exposure is also virtually complete along the Tarnbrook Wyre [SD 5675 5445], near Abbeystead House.

On the eastern margin of the Settle district, along Outlow Gill [SD 6874 6415], 0.25 m of shaly mudstone between sandstones (see (Figure 14), section 8) contains poorly preserved platform conodonts, including Gnathodus bilineatus and G. ex gr. girtyi, which indicate an Arnsbergian or pre-Arnsbergian age. The stratigraphical relationships are confused by faulting, and either the E. ferrimontanum Marine Band or the C. gressinghamense Marine Band may be represented.

Strata between the Eumorphoceras ferrimontanum (E2a2) and the Cravenoceras gressinghamense (E2a2á) marine bands

This relatively thin unit is poorly known and incompletely exposed. Moreover, the two constraining marine bands are not exposed in the same areas. In the Tarnbrook Wyre and Brennand River headwaters, in the southern part of the district, only the lowermost few metres of strata of this interval are exposed above sections containing the E. ferrimontanum Marine Band (Figure 14), sections 5 and 6, and (Figure 17). The uppermost beds, up to and including the C. gressinghamense Marine Band, are exposed farther north along Gressingham Beck, in tributaries to the River Roeburn around Wray, and along Badger Ford Beck (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19), sections 1 to 3, and (Figure 21). The thickness of the sequence is uncertain but may be of the order of 20 m. South of High Bentham, in the Badger Ford Beck area, the thickness may be more than 100 m, due to a local thickening of what is taken to be the Gavells Clough Sandstone in the Badger Ford Bridge Borehole (see below).

The interval consists mainly of siltstones with thin, fine-grained sandstones (facies 4) and interbedded sandstones and siltstones (facies 5) of delta-slope origin. Many of the thin sandstones are turbidites and have sharp soles with bounce marks and groove casts. In places, e.g. along Sweet Beck [SD 5508 6108] and the Tarnbrook Wyre at Abbeystead House [SD 568 544], the basal 7 m or so consist of shaly mudstones with siderite mudstone lenses (facies 3).

Sand-filled cylindrical burrows of Monocraterion (Skolithos) occur in the siltstones in the lower part of the interval, e.g. along Small Clough [SD 6132 5625] and Sapling Clough [SD 6252 5637]. Similarly, along the River Roeburn [SD 6053 6677], south of Wray, a bedding plane on grey, very fine-grained sandstone, a few metres below the C. gressinghamense Marine Band, is full of current-orientated, equispaced burrows of cf. Skolithos. Here the burrows are 2 to 3 mm wide and 5 to 10 mm apart, lined with pale fine sand, and inclined at about 30° to 40° from the vertical. This trace fossil is characteristic of the shallow-water conditions of the upper delta-slope and delta-top environments, and is considered to be the dwelling structure of a small worm-like organism (Eagar et al., 1985, p. 140).

A 3 m-wide, irregular sandstone dyke pinches out downwards in siltstones about 10 m above the E. ferrimontanum Marine Band in Sapling Clough ((Figure 17), section 7). In the Tarnbrook Wyre and Brennand River areas, the Gavells Clough Sandstone Member, a thickly bedded, medium-grained sandstone, occurs immediately or a short distance above the E. ferrimontanum Marine Band. Similar sandstones at the equivalent stratigraphical level elsewhere are assumed to be the same member.

Gavells Clough Sandstone Member (new name)

The member is named from the Gavells Clough area [SD 6124 5663] in the Tarnbrook Wyre headwaters. It is exposed along many of the small streams in that area (Figure 17), and forms the much faulted, craggy topographical features thereabouts, including Dog Crag [SD 6160 5607] and White Crag [SD 6160 5583], and possibly also the White Crag [SD 6440 5738] to the north-east. Occurrences north of grid line 58 are uncertain.

In the type area, the member is probably mostly of delta-top facies (facies 6), and consists of grey weathering to pale orange-brown, mainly medium-grained but also coarse-grained, micaceous, thickly bedded, orthoquartzitic sandstones, up to about 5 m thick. Both tabular and trough cross-bedding occur, but the rock commonly appears massive. In Gavells Clough, the uppermost 1.5 m contains numerous, well-rounded pebbles of silty siderite mudstone, up to 0.1 m across. In the backscarp of the Swine Crag landslip [SD 6086 5580], the basal part, resting sharply on the E. ferrimontanum Marine Band, is a greywacke with mudstone clasts. Elsewhere in this area, the member is probably of delta-slope origin. For example, along the Tarnbrook Wyre at Abbeystead House [SD 5682 5444] ((Figure 17), section 1), the basal part of the sandstone is slumped, and groove casts and graded bedding suggest a turbidite origin. The basal boundary of the member is always sharp and probably disconformable on siltstones and mudstones. In places in the type area, the sandstone rests directly on mudstones of the E. ferrimontanum Marine Band, but at others, shaly mudstones or siltstones with thin fine-grained sandstones intervene (see (Figure 17)).

The member may be represented in part by the sandstone exposed beneath the C. gressinghamense Marine Band in Gressingham Beck [SD 5640 6992], Gressingham ((Figure 21), section 1). There, about 4 m of planar cross-bedded, medium-grained sandstones are separated from the marine band by 7 m of shaly siltstone with indeterminate fossils and sparse wackestone nodules.

In the Badger Ford Bridge Borehole [SD 6909 6774], south of High Bentham on the western side of the Settle district, about 40 m of medium- to coarse-grained and pebbly, feldspathic, thickly bedded sandstone, with a ganister and seatearth mudstone near the top, were penetrated. This sandstone is estimated to be about 38 m below the C. gressinghamense Marine Band exposed in the adjacent beck. The same ganister sandstone is also exposed in Stonegrove Wood [SD 6925 6712] nearby.

Cravenoceras gressinghamense Marine Band (E2a2α) (new name)

This newly discovered marine band (Figure 20) is known to occur at only seven localities in the north-eastern part of the district. Brandon et al. (1995) recognise it as far south as the Widmerpool Gulf, in the English Midlands. These occurrences were previously described and assigned in BGS technical reports to either the E. ferrimontanum or E. yatesae marine bands. Exposures are present along Gressingham Beck [SD 5644 6996], at two nearby sections along High Dam Beck [SD 5673 7055] and [SD 5692 7050] near Gressingham, at Hunt's Gill [SD 6056 6702], Sandy Syke [SD 6035 6713] and at two nearby localities in Roeburndale, near Wray. Two further exposures of the marine band have been located along Badger Ford Beck [SD 6927 6808] to [SD 6913 6771], Mewith, south of High Bentham, just within the Settle district. The latter localities were previously thought to represent attenuated Caton Shale (Arthurton et al., 1988, p.83). Several other fossiliferous mudstone localities, currently ascribed to the E. yatesae Marine Band (see footnote, p.70), could conceivably be exposures of this marine band.

Sections through the member are shown in (Figure 21). The member varies in thickness between 0.4 and 1.7 m, and is consistent in its lithofacies, mainly comprising fossiliferous dark grey, fissile mudstone with abundant, small, irregular phosphatic nodules. Limestone (wackestone) nodules are fairly common, and at Gressingham Beck have yielded an uncrushed fauna that includes the eponymous ammonoid ((Plate 3); described by N J Riley in Brandon et al., 1996). The mudstones tend to be sheared, and the irregular disposition of the limestone nodules suggests slumping. At all three Gressingham localities, the upper 0.2 to 0.3 m consists of grey, fissile mudstone without phosphate nodules, and a 0.8 m-thick limestone with cone-in-cone structure separates these upper mudstones from the lower, phosphate-bearing part of the marine band. A 0.3 m-thick limestone with cone-in-cone structure is also present at Hunt's Gill (Figure 21), and the same structure occurs along Badger Ford Beck.

At Gressingham Beck, the fauna includes: the bivalves Chaenocardiola footii, pectinoid indet., Posidonia corrugata and Selenimyalina sp.; orthocone nautiloids; the ammonoids Cravenoceras gressinghamense, Eumorphoceras sp. and Metadimorphoceras cf. saleswheelense; conodonts; and fish debris. At Hunt's Gill, the band has yielded: the bivalve P. corrugata; the ammonoids Anthracoceras or dimorphoceratid indet. and Cravenoceras sp.; and fish debris. The fauna collected from Badger Ford Beck consists of the bivalves cf. Obliquipecten sp., Posidonia corrugata, P. lamellosa and cf. Pseudamussium sp.; orthocone nautiloids; the ammonoids Anthracoceras or dimorphoceratid indet., Cravenoceras sp. and Cravenoceras cf. gairense; the worm tube Serpuloides sp.; arthropod fragments and conodont debris.

Strata between the Cravenoceras gressinghamense Marine Band and the Close Hill Siltstone Member

The beds are well exposed in the Littledale area, particularly along Foxdale Beck [SD 576 609], Udale Beck [SD 554 615] and Closegill Beck [SD 570 621], in the Aughton area [SD 55 67], and west of Gressingham. Elsewhere, these beds have not been identified with certainty, but they probably outcrop along the River Roeburn [SD 60 66], in the Wray area, and at localities to the east. The sequence is composed mainly of the Cocklett Scar Sandstones Member. At Lythe Brow [SD 5234 6182] and below Cocklett Scar [SD 5773 6090], 6 m of shaly mudstones with siderite mudstone lenses directly underlie this member ((Figure 19), sections 7 and 8), but the C. gressinghamense Marine Band has not been located.

Cocklett Scar Sandstones Member (new name)

The name of the member is derived from the Cocklett Scar Flags of Slinger (1936). Thickness variations are shown in the generalised sections in (Figure 19). Impressive sections occur in the cliffs of Cocklett Scar [SD 576 609] (Plate 7), on the north side of Foxdale in the Littledale area. The member is also well exposed along several of the valleys in this area (see below), where it reaches a maximum thickness of about 65 m. Along Gressingham Beck, the member is only 8 m thick. Elsewhere the estimates are less certain. In the Quernmore area, the member may be slightly thicker than at Littledale, but farther north, in the Nether Kellet and Over Kellet areas, only 40 m and 50 m, respectively, are assigned to the member. At least 60 m of strata are estimated to be present south of Arkholme [SD 57 70], and 33 m near Wray. In the Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), the member is only provisionally identified as about 77 m of interbedded sandstones and siltstones between depths of 80 m and 157 m.

The base of the member is sharp to broadly gradational, at the incoming of abundant sandstones. It is exposed along Foxdale Beck [SD 5773 6090] and on Lythe Brow [SD 5230 6181], Quernmore. Along Gressingham Beck [SD 5645 6995], and in Hunt's Gill [SD 6056 6702] and Sandy Syke [SD 6037 6713], its base sharply overlies the C. gressinghamense Marine Band (Figure 21).

The beds consist of delta-slope sandstones interbedded with siltstones and striped, interlaminated siltstones and sandstones, and are similar to the delta-slope facies of the Dure Clough Sandstones. Siltstones are generally predominant in the lower part and sandstones in the upper part. Individual sandstone and siltstone beds vary from partings up to individual beds about 3 m thick. The interlaminated striped beds are commonly up to several metres thick. The thicker sandstones are grey, weathering brown or orange-brown, fine to medium grained, and commonly cemented with ferroan calcite or calcite. They are typically thinly to medium-bedded, parallel-laminated and sharp soled, commonly with scours, groove casts, bounce marks and load casts. Ripple cross-laminated beds, possible hummocky cross-lamination, and lenses of siltstone pebble conglomerate also occur. Individual beds can vary in thickness, lensing is common, and many of the sandstones may have been deposited in channels. Most of the sandstones were probably deposited by density currents. Packets of thicker sandstones are differentiated on the 1:10 000 scale maps; these typically occur in the uppermost part of the member, and can be up to 10 m or more thick. Apart from comminuted plant debris, which is commonly abundant along bedding planes, the only other fossils are trace fossils. Sole marks, primary current lineations, and current-orientated plant debris suggest a south-facing palaeoslope. Synsedimentary slumps and small faults occur at the base of the sandstone dominant facies along the River Roeburn [SD 6065 6600]; [SD 6053 6636].

Exposures occur along Foxdale Beck for about 1 km eastwards and westwards of Cocklett Scar [SD 569 615] to [SD 586 605]. Other sections occur along Closegill [SD 570 621], along Ragill Beck and around the confluence with Crossgill [SD 579 620], and along Udale Beck and its tributary, Sweet Beck [SD 553 615]. The most westerly exposures of the member are in gullies e.g. [SD 526 623] and [SD 523 618] on the steep slope of Lythe Brow ((Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19), section 7). The uppermost 33 m of the member are exposed in a pit and along the adjacent stream [SD 553 656] in the Claughton area. North of the River Lune, the member has an extensive outcrop but exposures are scattered and disconnected, the best sections occurring along streams [SD 550 675] and [SD 552 672] and in adjacent pits at Aughton. The uppermost few metres of beds are exposed in Willie Gill [SD 5976 7061] and along the west bank of the Lune [SD 579 706], south-west of Melling. The beds are well exposed in the Wray area, in Backsbottom Quarry [SD 6055 6614], Hill Kirks Scar [SD 6055 6637] and farther north along Roeburndale as far as the confluence with the River Hindburn, and in long strike sections along the River Hindburn for a distance of about 2 km e.g. [SD 6150 6745]; [SD 6233 6744]. The only complete section in the member is along Gressingham Beck ((Figure 21), section 1), where it is atypically thin.

Close Hill Siltstone Member (new name)

The name is derived from Slinger's (1936) summary stratigraphy of Caton Moor, in which he uses the term 'Close Hill Shales' for the shaly siltstones between the 'Cocklett Scar Flags' and the 'Roeburndale Grit' (Ward's Stone Sandstone). Subsequently, the member was not recognised as a distinct lithofacies until the present survey, either in this district (Moseley, 1954), or in the Settle or Garstang districts (Arthurton et al., 1988; Aitkenhead et al., 1992). Close Hill [SD 581 610] lies adjacent to Ragill Beck, where the member is well exposed.

A marginal marine facies occurs at this stratigraphical level throughout the Lancaster district, and probably extends well beyond, as coeval marine faunas of the Saleswheel Marine Band (E2a2â) have been found as far away as Ribchester near Blackburn and the Widmerpool Gulf ((Figure 20); Brandon et al., 1995). There are numerous widely distributed partial sections, exposing several tens of metres of beds in the deeply incised valleys to the north of the upland fell watershed (i.e. north of grid northing 59; see below), but no complete section is available. The Wray Borehole [SD 6320 6570] penetrated the member between a depth of 189.24 m and the terminal depth at 310 m, and this is taken as the type section (Figure 22). The member is not exposed in the Tarnbrook Wyre or Brennand headwaters.

The 120.76 m of strata allocated to this member in the Wray Borehole represents a minimum thickness in the type section, as the base of the member was not reached. Where the member is not directly overlain by the Ward's Stone Sandstone, its thickness at outcrop is variably estimated at between 60 m and 110 m. Some of this variation is probably due to growth faulting (see below). Where the member is unconformably overlain by the Ward's Stone Sandstone, the thickness can be reduced to as little as 30 m, for example on Flodden Hill [SD 528 625], south of Caton. In the Brennand Great Hill area [SD 62 56], the thickness of the unexposed member appears to be radically reduced ((Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19), section 10), possibly due to growth faulting or erosion. In the Whitmoor Borehole (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8), 45 m of siltstone, between depths of 35 and 80 m, are provisionally identified as the Close Hill Siltstone.

Where exposed, the basal boundary is generally easily recognised at the base of the platy, sandy siltstone sequence overlying interbedded sandstones and micaceous siltstones; it is either sharp or gradational over a few metres, and is well exposed along Gressingham Beck [SD 567 699] and Udale Beck [SD 553 616].

The member is mainly of marginal marine facies (facies 2), consisting of fairly uniform, grey, shaly to platy, finely laminated, finely micaceous, commonly calcareous siltstones (Plate 8), which grade into platy, silty, very fine-grained, calcareous sandstones. There are also finer shaly mudstone to clayey siltstone intercalations, particularly in the middle part of the member, and tougher calcareous levels. The latter contain layers of large oblate septarian concretions, comprising fine sandy calcisiltite and typically being 2 m across and 0.5 m thick. Discrete thin parallel beds of rusty-brown-weathering, very fine-grained, commonly ripple-marked sandstone, up to 10 mm thick, occur at intervals of a few 10 mm throughout the member (Plate 8). Thicker fine-grained sandstones up to 1 m thick are uncommon, except near the bottom and top of the member in the gradational zones. The sandstones are typically cemented with ferroan calcite or calcite. The current-ripples indicate a southward-facing palaeoslope, and the thin sandstones were probably deposited by density currents.

In the Melling and Gressingham areas, a few metres at or near to the top of the member consist of grey, silty, finely micaceous, fissile mudstone with sporadic fish debris. The facies is exposed in a tributary to Gressingham Beck [SD 5545 7017] and in a small stream south of Melling [SD 5971 7048]. Up to 11 m of shaly, blue-grey mudstones with siderite mudstone lenses, possibly at this stratigraphical level, are exposed in two gullies in the Littledale area [SD 558 618] and [SD 561 619] and along Udale Beck [SD 5595 6092].

The marginal marine bivalve Sanguinolites spp. (Plate 3) occurs sporadically in the sandy siltstones, and can be fairly abundant at some levels in the finer shaly mudstones. The bivalve has been collected from numerous localities, including most of the major sections. Other bivalves include Anthraconeilo sp., cf. Naiadites tumidus (Plate 3) and Myalina sp. (similar to Curvirimula but lacking the characteristic radial cracks). Other fossils include bellerophontid, naticopsid and turreted gastropods, the last including Glabrocingulum, bivalve spat, ostracods and fish debris. This characteristic association has been recovered from several localities including the Wray Borehole (Figure 22), where it occurs in about 60 m of strata between depths of 218 and 277 m. This range corresponds to that part of the member which includes less sandy siltstones and mudstones, in which the fauna is more abundant and preferentially better preserved.

Bioturbation is common throughout the member. Characteristic trace fossils include sinuous bilobed bedding-plane trails cf. Aulichnites, probable gastropod burrows, and subvertical burrows assigned to Pelecypodichnus, which are bivalve resting and escape burrows (Eagar et al., 1985). The latter were probably produced by Sanguinolites; in the Wray Borehole, several are aligned with the palaeocurrent. Planolites has been recorded from the Wray Borehole.

Comminuted plant debris occurs but, apart from near the top and bottom of the member, is not as conspicuous as in adjacent delta-slope units. Sporadic Calamites remains have been recorded from the uppermost 4 m of the member along Lambclose Syke [SD 5999 6191], Hamstone Gill [SD 5947 6628] and Artle Beck [SD 540 630].

The sediments were prone to synsedimentary faulting on the subaqueous palaeoslope, and many sections, particularly in the Roeburndale area, display listric faulting and soft-sediment slump deformations. Small-scale slump features have been noted in the lowest 15 in of the Wray borehole, and examples, many of which are intrafolial, occur in the uppermost few metres of the member along Foxdale [SD 5922 6048], at Lambclose Syke [SD 5999 6192] in the Littledale area, along the River Hindburn [SD 6393 6651] and its tributary, Force Gill [SD 6340 6671], south of Bentham along Burbles Gill c. [SD 674 674], and at several places along Roeburndale e.g. [SD 6185 6100]. Lower down Roeburndale, within or close to the Claughton Fault Zone, larger-scale deformation is prevalent, forming highly deformed beds several metres thick, commonly between regular upper and lower dis continuities. The Claughton Fault may have been active during deposition, causing the gravitational sliding and slumping. Sections in these severely deformed beds, from which Sanguinolites has been collected, occur along the River Roeburn between [SD 6005 6301] and [SD 6038 6402] and up Warm Beck [SD 599 639].

South of the Clougha escarpment, 22 m of slumped Close Hill Siltstones with Sanguinolites are well exposed in a cliff section along Rowton Brook [SD 5407 5909]. The siltstones are cut by a listric fault which flattens out westwards from 45° to horizontal. The beds below the fault are nearly horizontal and those above the fault dip at 45° parallel to the fault plane. This is compatible with larger-scale rotational slip directed towards the east.

Further evidence of soft-sediment deformation, probably within this member, comprises a number of anastomosing, fine- to medium-grained sandstone dykes, up to 50 mm wide, cutting through siltstones and silty sandstones along Long Gill [SD 6015 6103].

Sections in the member occur for a considerable distance along the River Roeburn between [SD 617 611] and [SD 610 652] and its tributaries, Marking Fold Beck [SD 617 598], Mallow and Colros gills [SD 60 60] to [SD 60 61], Azers Gill [SD 598 613], Bladder Stone Beck [SD 59 62] and Pedder Gill [SD 60 63]. In the Littledale area, there are numerous sections along Closegill Beck between [SD 561 621] and [SD 587 623] and its tributaries Ragill Beck [SD 58 61] and Foxdale Beck [SD 58 60] and [SD 59 60]. In the Caton area, there are excellent sections along Artle Beck [SD 538 633] to [SD 550 627], and in the Quemmore area along Rowton Brook [SD 526 593] to [SD 542 591]. South of Hornby, there are continuous sections along Hamstone, Rantree and Sooby gills [SD 58 66] to [SD 59 66]. Near Aughton, the member is well exposed in gullies [SD 532 660]; [SD 536 661]; [SD 544 667] incised through the steep northern slope of the Lune valley, on the north bank of the River Lune [SD 540 660] and along Snab Beck [SD 554 684]. The lowest few metres of the member are exposed along Gressingham Beck [SD 567 699], and sections occur south of Melling, along Spinks Gill [SD 592 701] and an unnamed stream [SD 597 706]. West of Wray, sections occur along the River Hindburn [SD 631 672]; [SD 636 668]; [SD 65 62] to [SD 65 63] and its tributaries, and in a series of gullies on its south-west bank, e.g. an unnamed gully at Powley Wood [SD 613 673], Deep Gill [SD 617 672], Hunt's Gill [SD 624 674], Force Gill [SD 634 668] and Cod Gill [SD 641 661]. The member is also well exposed along Gill Beck upstream of [SD 685 677] in the Bentham area.

Two boreholes at Heysham power stations ((SD45NW/247) and (SD46SW/236)) [SD 4075 5966] and [SD 4067 6001] proved the member on the east side of the Money Close Lane Fault.

Strata between the Close Hill Siltstone Member and the Eumorphoceras yatesae Marine Band

This sequence consists of interbedded delta-slope sandstones and siltstones, overlain locally by the delta-top Sapling Clough Sandstone Member. Because of the tectonism at the close of Roeburndale Formation deposition, and the resultant widespread unconformity at the base of the overlying Ward's Stone Sandstone Formation, some or all of these strata are locally absent, probably due to erosion rather than non-deposition.

Interbedded sandstones and siltstones above the Close Hill Siltstone Member

The unit, shown on the geological map as 'sa/sl', is found over large parts of the area north of the 'Ward's Stone range' but is locally absent, for example along Hamstone and Sooby gills [SD 58 65] to [SD 58 66], south of Hornby, and between Lythe Brow and Pott Yeats [SD 52 62] to [SD 54 61], south of Caton, due to the unconformity at the base of the Ward's Stone Sandstone (see (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19), sections 4 and 7; (Figure 25), section 2). Good sections are numerous, typical examples being given in (Figure 25) (see also below). The best-documented section is the Wray Borehole (Figure 22) ; (Figure 25), section 4). The beds have not been named as there is some uncertainty over whether they represent one coeval facies.

Estimates of thickness vary widely, mainly due to the unconformity at the base of the Ward's Stone Sandstone. Up to 35 m are estimated at outcrop in the Caton, Littledale and Hornby areas, and 46.29 m are assigned to the unit in the Wray Borehole between depths of 142.95 m and 189.24 m. The unit is estimated to include about 66 m of beds in the Nether Kellet area. About 26 m were penetrated in the Lowgill No. 2 Borehole [SD 6526 6498], where the base was not reached. Where exposed, the basal boundary is readily discerned at the base of interbedded sandstones and siltstones overlying siltstones with few sandstones. The boundary is either sharp or gradational within 1 m. It is well exposed along Artle Beck e.g. [SD 5381 6333].

The unit consists mainly of interbedded delta-slope sandstones and shaly, micaceous siltstones rich in plant debris (facies 5), similar those found in the Dure Clough and Cocklett Scar sandstones. The sandstones, typically a fraction of a metre thick but commonly up to 2 m, are grey, weathering to brown or orange-brown, fine to medium grained, micaceous and commonly carbonate cemented. They generally appear to be massive or finely parallel-laminated, though ripple-cross lamination is also common, and have sharp bases with sole marks, particularly groove casts and bounce marks. Minor scour channels parallel to the sole marks are associated with lensing of some of the sandstone beds. Many of the sandstones appear to be turbidites. Primary current lineations, sole marks, scouring and current-generated ripple marks indicate that deposition was on a generally southward-facing palaeoslope.

In the Roeburndale to Caton area, a basal fine-grained, thick-bedded sandstone packet, totalling 3 to 8 m of strata, sharply overlies the Close Hill Siltstone. The sandstones are cemented with ferroan calcite, contain irregular beds of siltstone, and are partly slumped in exposures through Winder Wood and along Warm Beck north of [SD 5984 6350]. Other exposures of these basal sandstones occur at Lambclose Syke [SD 5991 6190] and at several places along Artle Beck e.g. [SD 5450 6295]. The same packet is probably exposed along Tarn Brook [SD 5437 6396], up to a thickness of at least 9 m.

North-west of Aughton, very thickly bedded, massive, medium-grained sandstones with ferruginous concretions and siltstone flakes, occur near the top of the unit. They total at least 5 m and may represent a series of stacked channel infills, and have been worked from three small quarries to the west and north of Whinney Hill e.g. [SD 5411 6795].

In the lower reaches of Closegill [SD 562 622] and along Artle Beck [SD 551 626], sandstones are locally subordinate to siltstones. Many of the sandstones are highly bioturbated, have gradational boundaries, and are probably not turbidites.

In poorly exposed ground, it is possible that the Sapling Clough Sandstone has been included within the sequence. Tabular cross-stratified beds in the lower part of the Snab Beck section ((Figure 25), section 1), for instance, are atypical, and may be of delta-top facies.

Comminuted plant debris is abundant, and bioturbation is prevalent on some levels. In a quarry [SD 5924 7004] in Spinks Gill Wood, south of Melling, a 4.5 m thick, very thickly bedded, fine-grained sandstone, overlying the Close Hill Siltstone, contains U-shaped Diplocraterion burrows throughout. There is a possibility that this sandstone is the Sapling Clough Sandstone (see below). Trails of cf. Aulichnites are particularly common in platy micaceous sandstones along Bank Head Gutter [SD 6373 5975], on Salter Fell.

Sections in the unit occur in unnamed northern tributary gullies of Closegill Beck [SD 5774 6235]; [SD 580 623]; [SD 5874 6237]; along Lambclose Syke [SD 596 618] to [SD 599 619], Azers Gill [SD 59 61] and Ragill Beck [SD 585 612]; and particularly in faulted sections along Warm Beck Gill and its tributary, Crogley Gill [SD 59 63]. South of Hornby, the unit is mostly missing, but it is present in a section in the upper reaches of Hamstone Gill Beck [SD 599 659]. South of Caton, the unit is exposed along Tarn Brook [SD 544 638]; [SD 556 632], and is well exposed in numerous, much faulted sections along Artle Beck between [SD 5374 6337] and [SD 5526 6246]. It is also present along the River Conder [SD 5215 6081], being largely missing in the intervening ground.

West of Aughton, on the north side of the Lune valley, sections are provided by Highfield Beck upstream of [SD 5319 6587] and an unnamed gully to the west upstream of [SD 5359 6601]. In the Gressingham area, excellent sections occur along Snab Beck upstream of [SD 5602 6866] and a tributary [SD 5635 6874]. North of Hornby, the beds are exposed in a quarry on the west side of Windy Bank [SD 5895 6975], in a stream on its south side [SD 5967 6926], and in a quarry along Spinks Gill [SD 5924 7004]. The unit is present at outcrop east of Wray, for example along Cod Gill [SD 641 661], and it has been proved at depth in the Wray Borehole. It has not been recognised in the till-covered ground south of Bentham, and was not differentiated during the survey of the Cross of Greet and Goodber Common sheets, but nevertheless may be represented in the headwaters of the Hindburn and Roeburn rivers, and has been recognised on Salter Fell [SD 632 598].

In the Lower Heysham area, the unit may be represented by 2.4 m of fine- to medium-grained sandstone overlain by 11.6 m of interbedded, fine-grained, ripple cross-laminated and parallel-laminated sandstones and siltstones, in the axial part of an anticline below the Ward's Stone Sandstone Formation, south of Throbshaw Point [SD 4081 6148].

Sapling Clough Sandstone Member (new name)

The stratigraphical position of this delta-top sandstone is shown in (Figure 12) (see also footnoteFootnote. An alternative identification for at least the non-ammonoid marine band occurrences with Selenimyalina variabilis at Sapling Clough and Foxdale ((Figure 23), sections 2, 3) is with the C. gressinghamense Marine Band. This marine band is now also known to contain S. variabilis (Brandon et al., 1995). Support for this alternative is the presence of a similar delta top sandstone below the C. gressinghamense Marine Band at Gressingham and Badger Ford becks (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and (Figure 19); (Figure 21), section 1). This alternative model has important consequences for the stratigraphy between the E. ferrimontanum and E. yatesae marine bands, which differs significantly from that adopted in this memoir and accompanying 1:50 000 map. In this model: i. the Sapling Clough Sandstone is placed immediately below the C. gressinghamense Marine Band. Therefore the delta top sandstones at Gressingham and Badger Ford becks, referred to as the ?Gavells Clough Sandstone (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18), (Figure 19), (Figure 21) becomes the Sapling Clough Sandstone. Moreover, according to this alternative model, the position of the Sapling Clough Sandstone in the general stratigraphy shown on 1:50 000 Sheet 59 (Lancaster) is incorrect. It may be significant that the E. yatesae Marine Band exposed along Artle Beck is not underlain by delta top sediments. In other words, it is not clear whether the Sapling Clough Sandstone underlies the C. gressinghamense Marine Band or the E. yatesae Marine Band. ii. the base of the Ward's Stone Sandstone south of the Foxdale Beck Fault, between the Ward's Stone and Brennand Great Hill areas, must be strongly unconformable on the Roeburndale Formation. Strata containing the Close Hill Siltstone and E. yatesae Marine Band must have been removed prior to the deposition of the Ward's Stone Sandstone. In this context, it may be pertinent that the Close Hill Siltstone has never been observed in stream sections over this general area, although it was deduced to be greatly reduced in thickness (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18), (Figure 19), rather than completely absent.). Its type section is along Sapling Clough [SD 6240 5655], in the Brennand River headwaters, east of Brennand Great Hill. The outcrop of the member is extremely patchy due to unconformity, and over large areas, where the Ward's Stone Sandstone rests on older strata, the member is missing. As a consequence, exposures are few and scattered (see (Figure 23)). Moreover, in poorly exposed ground, the member may have been inadvertently incorporated into the underlying 'sa/sl' unit, or into the base of the Ward's Stone Sandstone. Apart from the type locality, it is only known from two gullies [SD 5842 6044]; [SD 5865 6038] on the south side of Foxdale Beck, other exposures being equivocal (see below).

The member is estimated to be at least 15 m thick along Sapling Clough, and about 20 m thick along Foxdale Beck. Its base is unexposed. Along Sapling Clough, 0.7 m of siltstones separate the ganisteroid top of the member from the overlying E. yatesae Marine Band.

The member consists mainly of pale orange-brown weathering, siliceous, fine- to medium-grained, thickly bedded delta-top sandstones, with thin ganisters, coals and siltstones rich in plant debris, and is similar to the upper part of the Ward's Stone Sandstone. In the Sapling Clough waterfall section, the sandstones are stacked in parallel beds about 1 m thick, and some levels are platy and parallel- or ripple cross-laminated. The beds were evidently cut by microfaults prior to lithification, a probable result of penecontemporaneous movement along a nearby fault.

Along Foxdale Beck, the sandstones are very thickly bedded, with low-angle tabular cross-stratification. Carbonaceous plant debris is plentiful in some of the finer sandstone beds. Ganisters occur in the top of the member in both Sapling Clough and Foxdale Beck, and in the latter section a thin shaly coal, associated with an irregular ganister, occurs in the lower beds; the base of the member is there faulted out. The only fossils recorded are plant fragments and rootlets.

Strata assigned tentatively to the member are:

i.   The 4.5 m-thick sandstone with Diplocraterion burrows exposed in the quarry in Spinks Gill Wood, south of Melling (see above), and currently assigned to the underlying 'sa/sl' unit. The trace fossil is characteristic of a delta-top environment, and is common in the Ward's Stone Sandstone.

ii.The 5 m of ripple-marked and ganisteroid sandstones exposed beneath a 13 m-thick siltstone in Claughton Beck, and currently assigned to the Ward's Stone Sandstone ((Figure 25), section 3).

iii.The trough cross-bedded sandstones in Snab Beck [SD 560 687] which are currently included in the 'sa/sl' unit ((Figure 25), section 1).

Eumorphoceras yatesae Marine Band (E2a3)

As with other strata in the upper part of the Roeburndale Formation, the marine band is only locally present, and is generally absent beneath the unconformity at the base of the Ward's Stone Sandstone. It is known from only six localities, all new discoveries, except the Artle Beck section (Thewlis, 1962) for which the main sections are shown in (Figure 23). The marine band has not been found north of the Artle Beck Fault Zone (see (Figure 26)A). It was recognised in the Garstang district (Aitkenhead et al., 1992), but has been reported from the Settle district, although a thin Lingula band exposed between ganisteroid sandstones along Cowsen Gill [SD 7259 6260], a tributary of Keasden Beck (Arthurton et al., 1988, p. 83), is inferred here to be the band between the Sapling Clough Sandstone and the Ward's Stone Sandstone.

The basal boundary is sharp, where fissile mudstone with marine fossils overlies siltstone. Along Artle Beck, this boundary is an angular unconformity (Figure 24).

The marine band is very variable in thickness, biofacies and lithofacies (Figure 23). It reaches its greatest thickness of 18 m along Artle Beck. Where fully developed, as along Artle Beck, the band consists mainly of fossiliferous, medium to dark grey, shaly, silty, finely micaceous mudstones, containing a fully marine fauna (see below) that is dominated by ammonoids and thin-shelled pectinacean bivalves, but with an appreciable benthonic faunal element that includes crinoids, brachiopods and Selenimyalina. These mudstones are commonly calcareous in the lower part of the band, with thin beds and nodules of argillaceous micritic limestone; small phosphate nodules are abundant on some levels.

In Artle Beck, there is a basal conglomerate consisting of reworked irregular limestone nodules, several of which have long axes orientated at between N 180° E and N 200° E, possibly aligned parallel to the local palaeoslope. The conglomerate also includes massive blocks of calcite-veined micritic limestone up to 3 m across, embedded in the underlying siltstone, and draped around with shaly mudstone due to differential compaction. The orientation of some complete crinoids within the mudstone indicates a palaeocurrent from the south-south-west. Not only do sections measured along Artle Beck (Figure 24) clearly demonstrate an angular unconformity at the base of the overlying Ward's Stone Sandstone, but they also show that the basal conglomerate of the marine band itself rests with an angular unconformity on the unit of interbedded siltstones and sandstones below. This is probably the result of syndepositional movement along local faults.

The richest fauna was collected from Artle Beck, and consists of: the brachiopods Orbiculoidea sp., Crurithyris sp. and Nudirostra cf. papyracea; the bivalves Dunbarella yatesae, Posidonia corrugata, P. corrugata elongates, P. lamellosa and Selenimyalina variabilis; orthocone and coiled nautiloids; the ammonoids Anthracoceras sp., dimorphoceratids indet., Cravenoceras gairense, C. sp., Eumorphoceras yatesae (Plate 3) and Kazakhoceras scaliger; crinoids, conodonts and fish debris.

South-eastwards from Artle Beck, the marine band thins and changes facies. On the southern side of Foxdale Beck [SD 5825 6040] and [SD 5850 6026], the marine band is very poorly exposed and the full thickness is unknown. Up to 0.3 m of blue-grey shaly mudstone with a thin bed of siderite mudstone have yielded a fauna of the bivalves Posidonia corrugata and Selenimyalina variabilis, and the ammonoids cravenoceratid indet. and Anthracoceras sp. or dimorphoceratid indet. Only 1 km to the south, along Whitespout Gutter [SD 5839 5927] to [SD 5836 5939] on the northern side of Ward's Stone, up to 3.5 m of land-slipped fissile grey mudstone with siderite mudstone lenses have yielded sparse Lingula and P. corrugata. Along Sapling Clough [SD 6234 5678] to [SD 6246 5644], the band consists of about 3 m of fissile grey mudstones or 'paper shales' with thin beds of laminated siderite mudstone, and contains a sparse fauna of Selenimyalina variabilis with Lingula sp. near the base. A similar mudstone sequence is poorly exposed in the left bank of Gavells Clough [SD 6173 5688].

A further possible exposure of this band occurs along a small stream [SD 5313 5943], north of Rowton Brook. The fauna is non-diagnostic, and consists of the bivalves Obliquipecten sp. and Posidonia corrugata, orthocone nautiloid fragments and crinoid ossicles.

The Artle Beck occurrence is the only one identified with certainty as the E. yatesae Marine Band. All the other localities are without diagnostic ammonoids and are only ascribed to this level on the basis of their positions close to the base of the Ward's Stone Sandstone, although in most cases this conclusion is also supported by the occurrence of Selenimyalina variabilis. This assumption places the Sapling Clough Sandstone immediately below the E. yatesae Marine Band. However, an alternative model is possible (see footnote) as current knowledge is insufficient to provide the required resolution.

Strata above the Eumorphoceras yatesae Marine Band

This sequence is known from the same localities as the E. yatesae Marine Band ((Figure 23) and (Figure 26)A), and its thickness is very variable because of the unconformity below the Ward's Stone Sandstone. A maximum of 12 m are preserved along Artle Beck, and only about 5 m are present in Sapling Clough. The basal siltstone, sandstone or conglomerate sharply overlies the fossiliferous mudstone of the underlying marine band.

The sequence consists of delta-slope siltstones, with thin beds of fine- to medium-grained sandstone in the upper part (Figure 23). A thin, basal, silty, pebbly sandstone, including reworked phosphate pebbles from the underlying marine band, occurs along Artle Beck, where the overlying beds mostly comprise grey, micaceous, shaly, silty mudstones and siltstones, with siderite mudstone lenses. These siltstones are progressively cut out downstream by the unconformity at the base of the Ward's Stone Sandstone (Figure 24). Along Sapling Clough, apart from two very thin bioturbated, ?glauconitic sandstones at the base, the 5 m sequence coarsens upwards, from shaly mudstone with siderite mudstone lenses in the lower part, to interbedded siltstones and fine-grained sandstones underlying the Ward's Stone Sandstone. The only fossils known are corn-minuted plant debris and trace fossil bioturbations.

Ward's Stone Sandstone Formation

The Ward's Stone Sandstone Formation (new name) is synonymous with the Roeburndale Grit (Slinger, 1936; Moseley, 1954, 1956), a defunct term used previously in the Lancaster area (see (Table 4)). It is applied to a distinctive, topographical-feature-forming, delta-top sandstone of Arnsbergian (E2a3) age, lying between the Roeburndale Formation and the Caton Shale Formation. The sandstone was originally called the Caton Coal Grit (Tiddeman, 1891). The term Ward's Stone Sandstone was first used in the Abbeystead area (Wilson et al., 1989) for only the lower part of the formation, the upper coal-bearing part there being referred to as the Pott Yeats Sandstone. In the headwaters of the Brennand River [SD 62 56], Moseley's (1954) Long Crag Sandstone is now considered to be mostly growth-faulted Ward's Stone Sandstone, although it was previously placed within what would now be taken to be the Roeburndale Formation.

The sandstone crops out over a large part of the district east of the Quernmore Fault, but to the west it is known only from the Heysham area, including the impressive cliff section on Heysham Head [SD 408 613] and borehole (SD45NW/3) [SD 4101 5912] at Whittam Hill. The formation is present over a wider area. It was mapped as a continuous but unnamed, 2 to 40 m-thick, coal-bearing sandstone at the top of the Roeburndale Formation in the western part of the Settle district, where it was also proved at the base of the Knott Coppy borehole (Arthurton et al., 1988, fig. 23). Moseley (1956, p. 335) states: 'It is a persistent horizon which can easily be mapped across the entire Lancaster Fells and into the Keasden area'. A thin, unnamed, poorly exposed sandstone has been mapped at this level in the northern part of the Garstang district, but apparently fails farther south (Aitkenhead et al., 1992).

The formation is best documented from the Wray Borehole, between depths of 120.45 m and 142.95 m ((Figure 22) and (Figure 25)), and this complete 22.5 m sequence is taken as the type section. Though stream and crag exposures are numerous in the district, complete or nearly complete sections are few; a selection is shown in (Figure 25). Some key sections exposing the base and top of the formation are shown in (Figure 23), (Figure 24) and (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27).

Where the formation is thickest, it gives rise to the most prominent topographical feature in the district, here termed the 'Ward's Stone range' (Figure 4), stretching from Clougha [SD 54 59] in the west, via Ward's Stone and Wolfhole Crag, to Esp Crag [SD 649 580] in the east. The lowest component sandstones are exposed in a series of craggy escarpments, fronted by copious jumbled blocks of sandstone, along the ridge's southern margin. Along the 'Ward's Stone range', good sections through more than a few metres are scarce. A section through about 38 m of strata is exposed along Gables Clough [SD 611 575] in the headwaters of the Tarnbrook Wyre. On the north side of the 'Ward's Stone range', sandstones are exposed along dip slopes extending down into the valleys of the Conder headwaters, Foxdale, Roeburndale and Mallowdale.

To the north of the 'Ward's Stone range', the formation is considerably thinner, and the resistant bedrock ridge which it forms is more often than not masked by till. However, the sandstones, overlying silty strata of the Roeburndale Formation, typically form waterfalls along incised former meltwater gullies or gills.

In the Quernmore area, the formation is well exposed in places along prominent escarpments on both flanks of the Quernmore Syncline, where the beds are typically inclined at more than 40°. Exposures occur in and around the quarry at Little Fell [SD 5085 5995] and at Stockabank [SD 51 60], along the River Conder [SD 523 608], and northwards along the length of Lythe Brow [SD 52 61] and [SD 52 62] as far as William Bank [SD 529 633], south of Caton. Numerous craggy outcrops occur to the east around Potts Hill [SD 545 624], and north of the hill there are many excellent faulted sections along the Artle Beck meltwater gorge as far as the Littledale area [SD 533 631] to [SD 562 623] ((Figure 25), sections 6 to 9). Other much faulted sections occur along Crossgill [SD 560 628], and along four unnamed tributaries to Closegill Beck [SD 577 625] to [SD 587 625]. The coarse basal part of the formation forms a small outlier at Haylot Crag [SD 588 614].

The formation crops out around the northwards-plunging Goodber Syncline. On its western limb, sections occur in Browskill Wood [SD 613 648] and along Pedder Gill [SD 613 634]. In the drift-free ground around the southern axial part of the syncline, the sandstones are well exposed along a strong escarpment feature along which runs the Hornby Road [SD 619 616] to [SD 636 597], and the uppermost beds are exposed along Goodber Beck [SD 630 607]. On the east limb of the syncline, sections occur at the confluence of Hawkshead Gill and Lordset Syke [SD 646 612], in waterfalls along Mill Beck [SD 648 636] and Well Beck [SD 647 637], and along the River Hindburn [SD 649 643] and [SD 653 637]. The formation is recognisable as the '20 ft of fine Banister' in the Bowland Forest Tunnel drivage south of Mill Beck c. [SD 650 627] (Earp, 1955).

South of Bentham, the narrow arcuate crop is largely hidden beneath till, but sections occur along Branstone Beck [SD 674 676], along a tributary to Branstone Beck [SD 679 679], and in Linghaw Quarry [SD 6854 6852]. Good sections are also present farther west, in proximity to the Smeer Hall Fault along the River Hindburn [SD 6446 6600], at Force Gill waterfall [SD 6337 6664], and along Hunt's Gill [SD 6214 6623].

In the Hornby area, the sandstone forms an outlier at Windy Bank [SD 592 695]. On the northern slopes of Claughton Moor [SD 57 66] to [SD 58 65], numerous sections in the lower beds are provided by incised gullies such as Sooby Gill, Hamstone Gill, Rantree Gill and Washfold Gill, and all but the basal beds crop out along Claughton Beck upstream of [SD 5671 6656] and against the Claughton Fault in a brick pit at Claughton [SD 5665 6620] ((Figure 25), section 3). North of the River Lune, a complete section occurs along Snab Beck downstream of [SD 5602 6866] ((Figure 25), section 1), and there are exposures along Gressingham Beck and in nearby pits [SD 562 699]. Between Aughton and Nether Kellet, the formation forms an outlier disposed around the axis of the Oaken Head Syncline [SD 53 68]. Here there are several exposures in disused quarries, the best of which is located [SD 5362 6870] near Swarthdale.

Across the district, the overall thickness of the formation varies between 3 m and 130 m ((Figure 26)B). Much of this is due to variation of the lower unit (see below), which ranges from 0 m to about 100 m. The upper unit (see below) is typically about 15 m thick, and varies between 3 m and 23 m. From the limited amount of reliable data available, it appears that the significant thickness changes occur across certain WNW–ESE-trending faults. The implication is that there was some synsedimentary movement along the faults which affected deposition. The greatest thickness change occurs in the lower unit, across a line that closely corresponds to the outcrop of the Foxdale Beck Fault along the northern margin of the 'Ward's Stone range' ((Figure 26)B). To the south-south-west of the line, the thickness of the lower unit increases rapidly to the order of 100 m beneath the 'Ward's Stone range'. Between the line of the Foxdale Beck Fault and that of the Claughton Fault, the lower unit is usually less than 15 m thick and may be absent, and the overall thickness of the formation is typically up to about 25 m. On the north side of the Claughton Fault, there is an increase in thickness up to a local maximum of roughly 35 m in the Claughton area.

The base of the Ward's Stone Sandstone is well defined, and basal, medium- to very coarse-grained sandstones are sharply separated from Roeburndale Formation siltstones or interbedded sandstones and siltstones by an erosion surface ((Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18), see below). An exception is found in sections along Hamstone and Sooby gills and their tributaries, where the basal sandstone is silty and bioturbated ((Figure 25), section 2). The silt was presumably redistributed by organisms from the unconsolidated upper layers of the underlying Close Hill Siltstone.

The Ward's Stone Sandstone represents a delta-top facies, comprising mainly stacked distributary fluvial channel sandstones. Throughout most of the Lancaster district, two broad informal units of the formation are recognised: a lower unit comprising generally coarse-grained, low-angle tabular cross-bedded sandstones; and an upper unit of mainly fine- to medium-grained, troughcross-bedded and ripple-cross-laminated, siliceous sandstones. The latter contains sandstone palaeosols, thin coal seams and subordinate siltstones. Locally in the Heysham area, the formation has been subdivided into three sandstone units separated by two 25 m-thick siltstone-dominated units. The lower two sandstones, approximately 35 m and 30 m thick respectively, and the intervening siltstone at Heysham are probably equivalent to the lower unit elsewhere, while the upper siltstone and 20 m-thick sandstone are probably equivalent to the upper unit.

Lower unit,  Ward's Stone Sandstone Formation

The lower unit of the formation comprises pale orange-brown weathering, medium- to very coarse-grained, thick to very thick-bedded sandstones, with subordinate and very poorly exposed, grey, shaly, micaceous siltstones or silty sandstones containing comminuted carbonaceous plant remains. The sandstones predominantly exhibit large-scale, low-angle tabular cross-bedding, and are weakly to conspicuously parallel-laminated. They readily develop a flaggy or platy fissility, with micaceous surfaces exhibiting primary current lineations. The coarsest beds contain sporadic, angular, small, vein-quartz pebbles, rarely more than 10 mm in diameter. Soft-sediment deformation, due to the slumping of oversteepened foresets, may be commonly observed (e.g. on Haylot Fell [SD 5894 6125] and in Baines Cragg [SD 5434 6181]). The upper parts of some beds are fine to medium grained, trough cross-stratified and ripple marked. Many excessively thick, apparently massive beds, such as the 8 m-thick bed capping Wolfhole Crag [SD 635 578], may have resulted from mass movement or possibly rapid water escape which destroyed their internal structure. Sporadic palaeosols with a few rootlets and stigmarian roots occur in the lower unit, for example along Hare Syke [SD 6068 5788], southeast of Ward's Stone, but are never as well developed as in the upper unit.

In the Heysham area, the base of the formation is well exposed in a cliff section south of the headland [SD 408 613], overlying 14 m of interbedded siltstones and fine-grained sandstones that are presumed to be at the top of the Roeburndale Formation. The upward-fining sequence continues southwards in a cliff section to the north side of Half Moon Bay [SD 407 611], where the highest beds of the lowest sandstones, with abundant burrows including Diplocraterion, and the lower part of the overlying bioturbated siltstones are well exposed. The higher beds are locally stained red and purple.

On the north-east side of the Claughton Fault at Claughton, sections along Claughton Beck and a brickpit adjacent to Barncroft Beck ((Figure 25), section 3) expose a 13 m-thick grey, shaly siltstone, underlain by at least 3 m of current ripple-marked, fine-grained sandstones and a 2.5 m thick ganisteroid sandstone with a reddened top. This 'split' by siltstone was considered by Moseley (1954, p. 431) to be of widespread significance north of a line from Caton, via Littledale to Botton [SD 65 62], but it has not been confirmed by the present survey. There is even a possibility that the lower sandstones at Claughton represent the Sapling Clough Sandstone Member, but the siltstone above has failed to yield a marine fauna.

Upper unit,  Ward's Stone Sandstone Formation

The upper unit of the formation comprises pale orange-brown weathered, fine- to medium-grained, thinly to thickly bedded, trough-cross-bedded and ripple-cross-laminated, siliceous, fluvial channel sandstones, with massive, hummocky-topped ganisters, up to 1 m thick, riddled with rootlets and stigmarian roots. Three or more ganister horizons are commonly present (Figure 25), and six were recorded along the River Roeburn [SD 621 607] in about 7 m of sandstones. Several thin, probably impersistent coals occur in the unit (see below), and are most commonly developed in the lower part of the unit where they are closely associated with thin beds and lenses of grey carbonaceous siltstone (Figure 25). Along a tributary to Branstone Beck [SD 679 679], south of Bentham (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27), the upper unit, below the topmost marine bioturbated sandstone, comprises 6 m of sandy siltstones with thin, fine-grained sandstones resting on a ganister bed. The equivalent of the upper unit is indifferently exposed in the Heysham area, but has been proved in a few boreholes, for example, Trimpell Refinery boreholes 2 and 3a ((SD45NW/2) and (SD45NW/3)) [SD 4182 5938] and [SD 4101 5912 respectively].

The top surface of the formation is invariably sharp and hummocky, and there are signs of reworking and winnowing in a marine environment (see below). The highest few tens of millimetres are typically bioturbated, and along Snab Beck contain pebbles of calcite mudstone ((Figure 25), section 1).

Moseley (1954, p.431) referred to two fairly persistent coal seams, namely a lower 'two-foot' Smeer Hall Coal and an upper 'six-inch' Crow Coal. Phillips (1837) was of the opinion that only a lower coal, of a thickness between lft Sin and 2ft 6in was worked, and that there was an upper coal, varying from a trace to 9in thick, lying between 5 m and 9 m higher. Tiddeman (1889) recorded that the lower coal was generally called the Caton Coal. It appears more likely that individual seams vary in thickness and are impersistent, since coals could have developed locally above any one of the numerous Banister palaeosols. Many sections, including the Wray Borehole (Figure 25), contain two thin coals in a few metres of strata, each ranging in thickness from a wafer to about 0.3 m. Along Artle Beck [SD 5448 6285], three thin coals are exposed within 2.5 m of strata. In places, some of the seams were of suitable thickness and quality to have been exploited. For example, near Gresgarth Hall, a 0.45 to 1.25 m-thick seam is exposed along the side of the track [SD 5352 6314] ((Figure 25), section 9), and has been worked from lines of adits along the sides of the beck.

Measurements of the directions of primary current lineations (12 observations), orientated plant debris (2) and current-generated ripples (22) from both the lower and upper units, and tabular cross-bedding foresets (11) from the lower unit, indicate that palaeocurrents were directed generally towards the south and south-south-west. However, cross-stratified troughs (32 observations) in the upper unit north of the 'Ward's Stone range' are aligned mostly from west-north-west to east-south-east, and indicate that palaeocurrents were predominantly directed towards the east-south-east. These directions are parallel to both the trend of the major faults and the isopach elongation, which suggests a possible causal link ((Figure 26)B).

The only fossils encountered in the formation below its marine bioturbated top (see below) are plant remains and trace fossils. Comminuted plant remains are abundant in the siltstones and fine silty sandstones, and larger coaly plant fragments, which were originally logs, are common in some of the sandstones. During the survey, casts of the bark of Lepidodendron and other trees were found occasionally on the surfaces of loose blocks. On Little Fell [SD 5089 6000], an in-situ fossilised tree stump base, complete with stigmarian roots, is displayed on a steeply inclined bedding surface. The siliceous Banisters and seatearths characteristically contain stigmarian roots, and are riddled with minor rootlets. U-shaped burrows are the commonest trace fossils, generally apparent as paired holes on bedding surfaces. Those with spreiten, attributable to Diplocraterion, are abundant on some well-exposed bedding planes in the upper unit of the formation. Excellent examples occur on bedrock surfaces capping the dip-slopes e.g. [SD 6408 5888]; [SD 6390 5881]; [SD 6345 5933] of Mallowdale Fell, north-east of Wolfhole Crag. As observed, the paired burrows are typically about 5 mm wide, 80 mm deep and 40 mm apart, and are connected by a narrow groove formed by the spreiten. They are indicative of shallow water (Eagar et al., 1985). This trace fossil is also abundant in the highly bioturbated sandstones that are correlated with the lower unit of the formation and are exposed on the north side of Half Moon Bay [SD 407 611], Lower Heysham. Elsewhere in the lower unit of the formation, both Diplocraterion and Arenicolites, a U-shaped burrow without spreiten, have been found sporadically. Arenicolites are interpreted as dwelling structures of either suspension or deposit-feeding invertebrates, probably worms (Eagar et al., 1985). A 90 mm-wide, 400 mm-long horizontal burrow of cf. Beaconites occurs on Salter Fell [SD 6335 5992] in the upper unit of the formation. Platy slabs of sandstone, full of narrow, obliquely inclined tubes of cf. Skolithos, can be found in wallstone adjacent to a small quarry [SD 5619 6989], the presumed source, near Brookdale Farm, Gressingham.

At the very top of the formation, bioturbation of probable marine origin is evident (Figure 25) and (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27), and the sandstone is reworked by the marine transgression associated with the base of the Caton Shale. In a stream bed near Hawkshead Farm [SD 5348 6301], south of Caton, Zoophycus burrows are common in the topmost few centimetres of the formation. Sandy calcareous concretions, cemented onto the hummocky reworked upper surface of the formation, contain the sponge Hyalostelia, brachiopods in the form of a chonetoid and Crurithyris debris, the ammonoid Anthracoceras sp., and crinoid ossicles. At Wild Carr Wood [SD 5603 6820], Aughton, lenticular, medium-grained, crinoidal pack-stones, up to 3 cm thick, have yielded a foraminiferal fauna with Neoarchaediscus sp. and Asterarchaediscus sp., together with Lingula sp., turreted gastropods and fish debris.

Unconformity at the base of the Ward's Stone Sandstone

There is strong evidence for a regional angular unconformity and non-sequence at the base of the Ward's Stone Sandstone. This unconformity has been demonstrated regionally by mapping, where the Ward's Stone Sand-stone is shown to overstep on to different units of the upper part of the Roeburndale Formation. Moreover, the unconformity is discernible in a few well-exposed stream sections. Along Artle Beck (Figure 24), for example, the Ward's Stone Sandstone progressively oversteps several units of the Roeburndale Formation in a downstream direction. In several sections, the angular nature of the unconformity is apparent where dips in the Ward's Stone Sandstone are gentler and/or in a different direction to those in the underlying beds. Well-exposed examples occur along Crogley Gill [SD 5935 6370] and [SD 5933 6365] in Roeburndale, and along Washfold Gill [SD 5843 6529] on the northern slopes of Claughton Moor, and the unconformity is apparent from the outcrop pattern in the upper reaches of nearby Rantree Gill [SD 592 651].

Over large areas of its outcrop, the boundary is inadequately exposed, and the upper beds of the Roeburndale Formation are not sufficiently differentiated to indicate that its higher parts are missing. However, the available evidence indicates that there was a regional phase of tectonic activity which folded and faulted the Roeburndale Formation prior to the deposition of the Ward's Stone Sandstone. Subsequent subaerial exposure or submarine slumping, preceding the encroachment of the Ward's Stone delta into the area, effectively trimmed the earlier deposits. In most places, the Ward's Stone Sandstone appears to rest on the unnamed interbedded sandtone/siltstone sequence above the Close Hill Siltstone. The formation oversteps directly onto the latter on the northern slopes of Claughton Moor [SD 58 65] to [SD 58 66], south of Pott Yeats [SD 54 61] to [SD 55 62], and along Lythe Brow [SD 52 62]. These areas may be eroded anticlinal areas. The Ward's Stone Sandstone rests on higher Roeburndale strata, i.e. the Eumorphoceras yatesae Marine Band and the overlying beds, only in the 'Ward's Stone range', from Sapling Clough to Foxdale Beck. Here, the higher beds are patchily preserved on the downthrown side of the Foxdale Beck and adjacent Artle Beck and Woodyards faults (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) and ((Figure 26)A), implying that these faults moved prior to the deposition of the Ward's Stone Sandstone. Comparison of (Figure 26)A and (Figure 26)B suggests that the zone around the line of the Artle Beck and the Foxdale Beck faults was particularly active towards the end of early Arnsbergian times.

Synsedimentary deformation within the Ward's Stone Sandstone

There are several good examples of features indicative of intraformational growth faulting in the Ward's Stone Sandstone.

  1. Small normal faults, with throws of up to 0.25 m, cut parallel-laminated sandstone in loose blocks along the Ward's Stone Sandstone escarpments, at Long Crag [SD 6262 5660] and [SD 6258 5675] (Plate 9) and Wolf Hole Crag [SD 635 578]. The faulting preceded cementation but occurred while the sediment was cohesive, and is ascribed to syndepositional movement. Furthermore, the disposition of the escarpment feature of Long Crag indicates that the Ward's Stone Sandstone has a low dip, contrary to inclinations between 26° and 35° recorded on the dip-slope of the feature [SD 628 569]. Several of the faults mapped in this general area may be growth faults.
  2. Synsedimentary movement is indicated by a section along the River Roeburn [SD 6277 5986], north of Mallow-dale. Abrupt thickness and lithological changes occur across a 3 m-wide zone, orientated NNE–SSW, and are associated with the splitting of a Banister sandstone.
  3. Growth faulting appears to have been particularly prevalent between Clougha and Quernmore, and to have affected strata from the Close Hill Siltstone of the Roeburndale Formation (see above) to the Ward's Stone Sandstone. Candidates for slumped, 'out of place' masses of Ward's Stone Sandstone include 45 m of fault-bounded, medium-grained, thickly bedded sandstone between Rowton Brook and Fell End Farm [SD 532 595], and the ridge-forming sandstones, mapped as part of the Roeburndale Formation, exposed east of Greenahs Farm [SD 5155 5805] to [SD 5225 5757] in a fault-bounded block. The direction of slumping is uncertain but may have been directed eastwards, as with the local Close Hill Siltstone.

Caton Shale Formation

The term Caton Shale Formation, first formalised in the Garstang district (Aitkenhead et al., 1992), is synonymous with the Caton Shales, used previously in this district (Slinger, 1936; Moseley, 1954) and the Settle district (Arthurton et al., 1988) for the 'calcareous shales (fossiliferous)' of the primary survey (Geological Survey of England and Wales, 1884).

The formation crops out extensively north of the 'Ward's Stone range' where it is well exposed along several incised stream sections. The outcrop forms a continuous strip, flanking the Goodber Common Syncline northwards from near Hawkshead [SD 63 60], and is found as a downfaulted outlier along Roeburndale [SD 63 59] to the south. Between Wray and Bentham, the outcrop forms an arcuate belt of shallowly flexured strata. It forms the lower slopes around Caton Moor and occurs on the north side of the Lune valley in the cores of the Gressingham [SD 56 68] and Oaken Head [SD 53 68] synclines. To the south-west, it caps the hill near Potts Wood [SD 54 62], and extends westwards into the core of the northern part of the Quernmore Syncline c. [SD 530 625] on the eastern side of the Quernmore Valley. Its southernmost surface outcrop forms the steeply dipping western limb of the Quernmore Syncline at Stockabank [SD 5131 6023], west of Quernmore Church.

Across the low-lying ground to the west of the 'Ward's Stone range' the outcrop of the formation is largely hidden beneath superficial deposits. To the south of Lancaster, subdrift outcrops were proved by BGS borings near Ellel Grange [SD 4839 5345], Hampson Green [SD 4953 5431]; [SD 5001 5441], and Brantbeck Farm [SD 4689 5761]. There is also evidence of outcrop around Middleton (see below). Unproven and conjectural outcrops may occur along the River Wyre.

The formation maintains a thickness of between 60 m and 70 m throughout its outcrop in the Lancaster district. It is 67.95 m thick in the Wray Borehole (Figure 22), and is estimated to be 64 m thick at Branstone Beck, the longest continuously exposed section (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). Some 52 m are inferred from the drillers log and downhole gamma log of the Lowgill No. 2 Borehole [SD 6526 6498], but the top is uncertainly placed and the amount of faulting is unknown. These values compare with estimates of 40 m in the Settle district (Arthurton et al., 1988) and 50 m to 70 m in the Garstang district (Aitkenhead et al., 1992).

The general stratigraphy of the formation is shown in (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). It is one of the most distinctive and readily identifiable formations in the district, containing marine fossils throughout, although these are abundant at some levels and scarce at others. It comprises a fairly uniform sequence of dark grey, weathering to bluish grey, shaly, fossiliferous mudstones or claystones with beds of tougher, calcareous, platy, fossiliferous mudstone. Nodular to lenticular concretions, composed of several types of carbonate mudstone, occur at many levels and are commonly septarian. The larger concretions, up to the order of 0.4 m thick, occur most commonly in the more calcareous mudstone beds, and can coalesce into more extensive lenticular beds. Smaller nodules and thin lenses occur sporadically throughout the formation. In the upper half of the formation, thin siderite mudstone lenses, typically about 40 mm thick, occur at intervals of a few metres. Silty beds with conspicuous mica and rare thin sandstones are generally only present in the transgressive and regressive zones, i.e. the basal few tens of millimetres and the uppermost 0.5 m of the formation.

Two thin potassium (K-) bentonites were recorded from the Caton Shale of the district. They are waterlain volcanic ashfalls, each of which can be traced over wide areas of northern England, particularly around north Staffordshire and Derbyshire (e.g. Trewin, 1968; Trewin and Holdsworth, 1972; Aitkenhead, 1977; Chisholm et al., 1988, fig. 14), and in the Harewood Borehole, Yorkshire. The bentonites in the Caton Shale are 10 mm or less thick and have the sharp bases and graded tops typical of air fall tuffs. Generally, these pyritous bentonites are greenish grey in the fresh state, but weather to a soft, unctuous, ochreous clay.

Vaughan (1977; see Appendix 4) showed that the concretions collected along Greenholes Beck could be grouped chemically into two main types. The smaller nodules are sideritic and the larger ones are mainly composed of calcite, many with pyrite-rich outer zones.

The mudstones in several of the sections in the area are cut by low-angle, oblique, listric surfaces which may have developed during growth faulting. They are common in the Wray borehole (Figure 22), in the cored interval between a depth of 100 m and the formation base at 120.45 m, and are lined with calcite. They are particularly common in the top 15 m of the formation along Westend Beck [SD 5618 6591], Claughton.

The base of the formation is invariably sharp. It is taken at the base of the uniform fossiliferous mudstone sequence overlying the uppermost bioturbated sandstone of the Ward's Stone Sandstone Formation (see (Figure 25) and (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27) ; the lowest part of the mudstone may be silty. In the Wray Borehole, the base lies at a depth of 120.45 m (Figure 22). The general absence of the lowest faunal horizons of the Ct. edalensis Subzone (see below), points to a localised non-sequence at the base of the formation in the district, corresponding to a widespread marine transgression over a substrate of considerable local relief. The absence of the Ct. edalensis horizon implies that the sea encroached on this district later than on regions to the south. The thickness of the uniform marine claystone points to deposition in moderately deep water below the affect of wave action for a considerable period. The faunal associations indicate variable salinities (see below). The absence from the Caton Shale of the Cravenoceratoides nititoides faunal horizon, which is associated with a relatively low eustatic sea level (Holdsworth and Collinson, 1988, fig. 12.6), implies a non-sequence at the top of the formation, unless deposits of this age are represented by the lower part of the Claughton Formation.

Biostratigraphy of the Caton Shale

The biostratigraphy of the Caton Shale was investigated in the area by Bisat (1932; 1934), Hudson (1944b; 1946) and Moseley (1954). As only the lowest 20.45 m were cored in the Wray Borehole (Figure 22), the two most complete and unfaulted surface sections were logged systematically to enable a comprehensive faunal sequence to be compiled (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). Crossgill, and its eastwards continuation into Greenholes Beck [SD 5648 6304] to [SD 5694 6327] on the western slopes of Caton Moor, provides a sequence from just below the Eumorphoceras leitrimense horizon to the top of the formation. Farther down the stream, exposures in stratigraphically lower beds are discontinuous and faulted. Almost a complete section of the formation is exposed in Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826], south of High Bentham. A third logged section, in the upper reaches of Goodber Beck [SD 6302 6078], south of Goodber Common, provides the best exposure of the impersistent basal Ct. edalensis faunal horizon, and was logged up to the base of the E. leitrimense horizon.

The faunal associations in the formation are of two main types, namely a less-saline marine 'background' phase, characterised by the thin-shelled ammonoids Anthracoceras or dimorphoceratids, and a more-fully marine, thick-shelled ammonoid phase, usually confined to thin 'marine bands' (Ramsbottom et al., 1962). The background fauna includes the thin-shelled ammonoids Anthracoceras glabrum, Metadimorphoceras saleswheelense and Monograptus ribblense, the myalinid bivalve Selenimyalina variabilis, and the pectinacean bivalves Posidonia corrugata and rare Pseudamussium sp. Other fossils include turreted gastropods, rare naticopsid and bellerophontid gastropods, orthocone and coiled nautiloids, the ?scaphopod Coleolus sp., the smooth spiriferoid brachiopod Crurithyris sp., ostracods and fish debris. The burrows Planolites and Protopalaeodictyon were recorded from the Wray Borehole. The horny brachiopod Lingula mytilloides and the spicules of sponges including Hyalostelia sp. were recorded from the transgressive phase in the basal few tens of millimetres. L. mytilloides reappears in a sparsely fossiliferous bed in the lower part of the Ct. nitidus Subzone, and in the regressive phase of the top 0.5 m of the formation.

Against this general faunal background, several species of thick-shelled ammonoids, belonging to the genera Cravenoceras, Cravenoceratoides, Fayettevillea and Eumorphoceras, form the basis of more detailed biostratigraphical subdivision (e.g. Bisat, 1932; Hudson, 1944b; 1946). Some of these ammonoid genera are confined to discrete beds of darker, generally more calcareous, platy mudstone, of the order of 1 m in thickness, containing a richer marine fauna that includes abundant P. corrugata. The Ct. edalensis faunal horizon, at or very near the base of the formation, is only known from Goodber Beck and possibly Lary Syke (see below); despite good exposure, it is generally absent elsewhere. Approximately 17 m higher, the Ct. nitidus or Eumorphoceras leitrimense faunal horizon is extremely widespread (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). The Ct. nititoides horizon, so well represented in Derbyshire and other places, is inexplicably absent from the Lancaster district.

The eponymous ammonoids indicate that the Caton Shale Formation of the Lancaster district belongs to the Ct. edalensis (E2b1) and Ct. nitidus (E2b2) ammonoid subzones of the E2b Chronozone of the Arnsbergian Stage (Table 3).

Stratigraphy of the Cravenoceratoides edalensis Subzone(E2b1) (the Ct. lirifer beds of Moseley, 1954)

The lowest faunal horizon of the subzone, i.e. a lower Cravenoceras subplicatum leaf below Ct. edalensis recorded from Saleswheel (Riley, 1985) in the Garstang district, has not been recognised in the Lancaster district, probably due to the non-sequence at the top of the Ward's Stone Sandstone Formation. The Ct. edalensis faunal horizon is represented along Goodber Beck (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27) by a 0.37 m-thick bed of reworked limestone nodules. It also contains phosphate nodules and a fauna of Ct. edalensis, Cravenoceras cf. subplicatum, Metadimorphoceras sp.,Anthracoceras sp. and S. variabilis. Ct. cf. edalensis was recorded from about 4 m above the Ward's Stone Sandstone along nearby Lary Syke [SD 6300 5955], a tributary of the River Roeburn, but the marine band is very poorly exposed there and involved in landslip.

C. subplicatum ranges above Ct. edalensis in this subzone. In the Wray Borehole [SD 6320 6570] (Figure 22), the Ct. edalensis faunal horizon was not recognised. There, C. subplicatum first occurs 1.04 m above the base of the formation, and ranges upwards through 7.6 m of strata, its highest level being 6.3 m below the gamma peak that represents the E. leitrimense faunal horizon in the Ct. nitidus (E2b2) Subzone. A similar stratigraphy occurs in Branstone Beck (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27) and, from a comparison of the gamma logs, in the Lowgill No. 2 Borehole [SD 6526 6498]. Within the range of C. subplicatum, a prominent layer of coalesced calcite mudstone lenses forms an extensive limestone bed, up to 0.8 m thick, which is useful in local correlation. It occurs 3.35 m above the base of the formation in the Wray Borehole, at a depth of 117.1 m, and at Branstone Beck, Snab Beck [SD 5624 6849] and several other localities. A K-bentonite, documented from several localities about mid-way through the range of C. subplicatum, correlates with the B7 bentonite of north Staffordshire and Edale (Trewin, 1968). In the Wray borehole, where a sharp base and graded top are evident, it occurs at a depth of 113.67 m, 6.75 m above the base of the formation (Figure 22). This bentonite is also identified as being about 10 mm thick, 6 m to 8 m above the base of the formation and associated with mudstones bearing C. subplicatum along Crossgill [SD 5590 6259], Snab Beck [SD 5628 6845] and a tributary stream [SD 5627 6859], south of Gressingham. In the Goodber Beck section (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27), what is taken to be the same bentonite is only 2 mm thick, and occurs 2.98 m above the base of the formation and the Ct. edalensis faunal band, and below a prominent nodular limestone bed. This demonstrates that correlation on the basis of secondary carbonates has to be treated with caution.

Stratigraphy of the Cravenoceratoides nitidus Subzone (E2b2)

The E. leitrimense faunal horizon, approximately 1 m thick at the base of the subzone, includes a basal 0.2 m-thick argillaceous limestone with commonly coalesced bullions, named the 'Cravenoceratoides nitidus limestone' by Moseley (1954). Ct. nitidus (Plate 3) is generally found in the upper part of the limestone, which is variably estimated as being between 8 m and 18 m above the base of the formation, depending on the local magnitude of the non-sequence at the base of the Caton Shale. In the Wray Borehole (Figure 22), the E. leitrimense horizon corresponds with a gamma peak at a depth of 105.8 m, 14.65 m above the Ward's Stone Sandstone; core removal prevented biostratigraphical investigation. In the Lowgill No. 2 Borehole, the corresponding gamma peak occurs only 10 m above the Ward's Stone Sandstone. The E. leitrimense horizon lies 13.16 m and about 18 m above the formation base at Branstone Beck and Goodber Beck respectively. The fauna collected from the limestone and the overlying mudstone comprises P. corrugata (Plate 3), S. variabilis (Plate 3), orthocone nautiloids, Anthracoceras sp., Ct. nitidus (Plate 3), dimorphoceratids indet., E. leitrimense, (Plate 3) Kazakhoceras sp. and fish fragments.

A 4 to 5 m-thick mudstone, lying between 6 and 8 m above the base of the E. leitrimense horizon in the Crossgill and Branstone Beck sections (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27), is either barren of fauna or contains a sparse fauna.

A 5 mm-thick, pinkish grey K-bentonite was recorded about 24.26 m below the top of the formation, and 2 m below the Tylonautilus nodiferus horizon (see below) in Greenholes Beck [SD 5685 6317]. The same bed, sea green in colour, is also present in Branstone Beck (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). It probably correlates with the K-bentonite below the level of F. holmesi described by Trewin and Holdsworth (1972) from Staffordshire.

The coiled nautiloid Tylonautilus nodiferus characterises a level between the upper K-bentonite and the F. holmesi beds, i.e. about 22.5 m below the top of the formation, and large uncrushed specimens have been collected from several localities. It was collected from Greenholes Beck (Vaughan, 1977, plate 7; see Appendix 4) during the present survey [SD 5690 6320] (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27), and from Warm Beck [SD 5907 6437]. Superb examples were collected by R H Tiddeman at the time of the primary survey from 'Claughton brick pit', now believed to be the site of Potter Hills Wood [SD 556 652] (Plate 3). The species was also recorded by Moseley (1954, p.434) from a thin shelly bed about 2 m above the 'Ct. nitidus limestone'.

The ammonoid Fayettevillea holmesi, indicating a higher horizon within the subzone, ranges through 4.7 m of mudstones with calcite mudstone nodules, about 30 m above the base of the E. leitrimense horizon or some 16 m below the top of the formation. These are the Cravenoceras holmesi beds of Moseley (1954). Fayettevillea holmesi and F. kettlesingense (now considered to be a juvenile form of F. holmesi) were collected by Bisat (1932) from Tarn Brook [SD 558 634], approximately half-way through the Caton Shale, the locality being the type locality of the former species. F. holmesi was also collected from this locality during the present survey [SD 5615 6336] and [SD 5626 6334]. The F. holmesi beds are exposed in Greenholes Beck [SD 5691 6321] (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). Moseley (1954) recorded the species from Branstone Beck [SD 676 681], near Bentham, about 9 m below the top of the formation, at a level that corresponds approximately with a gap in the section in (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). F. holmesi and F. kettlesingense were recorded from the upper part of the formation in the Knott Coppy Borehole in the Settle district (Arthurton et al., 1988). In the local absence of the Ct. nititoides faunal horizon, it is likely that the Ct. nitidus Subzone extends to the top of the formation. Hudson (1944b) recorded Ct. stellarum from a limestone near the top of the Caton Shale in Greenholes Beck. This would indicate the later Nuculoceras stellarum Subzone of the E2 Chronozone but is probably a misidentification, as the thin limestone is known to be at the top of the F. holmesi beds.

Sections in the Caton Shale

i Caton and Claughton moors

In the Littledale area, sections in the Caton Shale occur along Crossgill upstream of [SD 5590 6259] as far as Greenholes Beck [SD 5693 6328]. The Ct. edalensis Subzone with C. subplicatum is exposed [SD 5602 6289] in the Crossgill Fault Zone, and the E. leitrimense horizon is exposed near Tunnel Plantation [SD 566 630]. An excellent section in the upper part of the formation, including the F. holmesi beds, occurs in Greenholes Beck (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27) (see also Hudson, 1944b, p.238). Neighbouring sections in the upper part of the formation, including the F. holmesi beds and the top boundary, are to be found upstream of the dyke in Tarn Brook [SD 5600 6336], and the upper contact is also well exposed in a tributary of Mears Beck [SD 5560 6465] (Figure 28). Good sections in the lower part of the formation occur along Warm Beck upstream of [SD 5934 6405]. These expose the basal contact of mudstones with C. subplicatum on Ward's Stone Sandstone, and include the E. leitrimense horizon.

In the Claughton area, sections in the lower part of the formation, including the basal contact and mudstones with C. subplicatum, occur along Claughton Beck upstream of [SD 5709 6605], and along Mears Beck upstream of [SD 5551 6537] into Potter Hills Wood. The top of the formation is well exposed along Westend Beck [SD 5618 6591].

ii Gressingham Syncline

Between Aughton and Gressingham, continuous sections through the lowest 16 m are to be found along Snab Beck and a tributary [downstream of 5616 6860], and along a beck in Wild Car Wood c. [SD 561 681]. These expose mudstones with C. subplicatum in the Ct. edalensis Subzone.

iii Potts Hill and the Quernmore Syncline

The basal contact is well exposed along a stream near Hawkshead Farm [SD 5348 6301], Caton (see p.77). An estimated 58 m of Caton Shale, dipping at up to 46°, are continuously and well exposed in a gorge section along Artle Beck, near Gresgarth Hall [downstream of 5329 6335], but no thick-shelled ammonoid band has been identified, and the lowest

10 m or more of beds are probably faulted out against the Ward's Stone Sandstone. The E. leitrimense horizon is poorly exposed in several gullies in Stacks Wood e.g. [SD 5450 6263].

iv Roeburndale

The E. leitrimense horizon, with a 0.25 m-thick, decalcified 'Ct. nitidus limestone', is exposed in the north bank of the River Roeburn [SD 6273 5994], and is apparently separated by a fault from the Ward's Stone Sandstone Formation in the river below. The E. leitrimense horizon is also exposed along Ranteryhole Syke [SD 6315 5928].

v Goodber Syncline

A well-exposed section in the lowest 12.4 m of the formation occurs along Goodber Beck [SD 630 607], north-west of Hawkshead, where the Ct. edalensis faunal horizon crops out (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27). Discontinuous sections occur along Hawkshead Gill, and the base of the formation is exposed [SD 6460 6113] just upstream from the confluence with Lordset Syke. Discontinuous sections through the entire formation occur along Helks Brow [SD 646 637]. There are extensive exposures in the banks of the River Hindburn, and the E. leitrimense horizon with a well-developed 'Ct. nitidus limestone' is exposed at one locality [SD 6486 6466]. The Bowland Forest Tunnel cut through an undisturbed sequence of the lowest 38 m of the formation, overlying the Ward's Stone Sandstone, in the drivage south of Mill Beck c. [SD 649 628]. A section given by Earp (1955) records only the turreted gastropod Glabrocingulum, the bivalve S. cf. variabilis and the ammonoid Anthracoceras. The Lowgill No.2 Borehole [SD 6526 6498] penetrated the entire formation, and although no detailed biostratigraphy is available, a gamma log allows correlation with the Wray Borehole.

vi Wray and Bentham areas

South-east of Wray, the best-documented section is in the Wray Borehole (Figure 22), which penetrated the formation from a depth of about 55 m to the formation's base at a depth of 120.45 m. Discontinuous sections along Hunt's Gill [SD 62 65], south of the Smeer Hall Fault, include the E. leitrimense horizon with the 'Ct. nitidus limestone' at two places [SD 622 656]; [SD 623 658] (Moseley, 1954). To the east, a small, isolated, fault-bounded outcrop of the Caton Shale is exposed along the River Hindburn in the Smeer Hall Fault Zone.

South of Bentham, the most complete section through virtually the entire formation occurs along Branstone Beck and a southern tributary [SD 6770 6826] to [SD 6783 6786] (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27)

vii Heysham

The Caton Shale Formation was exposed in excavations [SD 414 594] at the former petroleum refinery, north-west of Middleton. The Shell Refinery No. 3a Borehole [SD 4101 5912] in this area proved the Ct. nitidus Subzone within a faulted sequence of shattered and probably faulted mudstones. A fauna of the bivalves P. corrugata and S. variabilis and the ammonoids C. subplicatum, Ct. nitidus and Metadimorphoceras sp. was collected. Site investigation borehole (SD46SW/236) [SD 4067 6001] at Heysham power stations penetrated mudstone with C. subplicatum at a depth of 42.38 m, and yielded Lingula sp. at a depth of 46.70 m, 0.44 m above the base of the formation.

viii Galgate area

Beds belonging to the Ct. nitidus Subzone were proved in the BGS Crag Hall Borehole [SD 4839 5345] near Ellel Grange, south of Galgate. A fauna of the bivalves S. variabilis and P. corrugata, orthocone and stroboceratid nautiloids, and the ammonoids Anthracoceras sp. and Ct. cf. nitidus was collected from 47 m of grey mudstone, the eponymous ammonoid being confined between depths of 29 m and 31 m. About 8 m of shattered mudstone with a sparse fauna of S. variabilis, Anthracoceras or dimorphoceratid indet. and Ct. cf. nitidus were encountered beneath 28 m of till in the BGS Hampson Green No. 3 Borehole [SD 4953 5431], 1.5 km to the north-east. Caton Shale with a non-diagnostic fauna, including S. variabilis, Anthracoceras sp. and cravenoceratid indet., was also penetrated to a depth of 24.33 m in the nearby BGS Hampson Green No. 4 Borehole [SD 5001 5441]. About 35 m of mudstones with a non-diagnostic fauna of abundant P. corrugate were penetrated in the BGS Tarnwater Borehole, put down near Brantbeck Farm [SD 4689 5761], and are also assigned to the Caton Shale.

Claughton Formation (new name)

The name Claughton Formation (new name) is adapted from and synonymous with the Claughton Flags (Moseley, 1954), the term used previously in the Lancaster district (see (Table 5)). On Caton Moor, Slinger (1936) divided the local succession into (in upward succession) : the Claughton Flag Series, the Nottage Crag Grit, the Claughton Moor Shales and the Moorcock Flags with the Hawkshead Grit. All but the last of these units are recognised herein, and under modified names have been given member status within the Claughton Formation. In the western part of the Settle district to the east, Moseley (1956) coined the term Keasden Flags for strata equivalent to the Claughton Flags, and this was adopted by the Geological Survey (Arthurton et al., 1988). In the thickly drift-covered ground around Dolphinholme and Ellel, within the present district, strata equivalent to the Claughton Formation were included in the Heversham House Sandstone (Wilson et al., 1989), a poorly defined unit which extends into the adjacent part of the Garstang district where it was given formational status (Aitkenhead et al., 1992). The Heversham House Sandstone is now included in the Silver Hills Sandstone Formation.

The Claughton Formation crops out extensively throughout the district. It extends northwards into the Kirkby Lonsdale district where its distribution is unknown. As the Keasden Flags, it has been mapped across the western part of the Settle district (Moseley, 1956; Arthurton et al., 1988). Its southwards extension, under a blanket of till, into the Garstang district (Aitkenhead et al., 1992) is conjectural.

North of the 'Ward's Stone range' the formation forms the outlier of Caton Moor c. [SD 58 64] and its northern extension, Claughton Moor. Further extensive outcrop occurs around the Goodber Syncline, including the outcrops on Goodber Common and Goodber Fell c. [SD 63 62]. The formation extends northwards between the Stauvin and Smeer Hall faults c. [SD 64 65] onto Tatham Fells c. [SD 66 64], and forms a continuous belt encircling the southern margin of the Ingleton Coalfied, from around Wennington c. [SD 61 71] to the Forest of Mewith c. [SD 68 68] and beyond into the Settle district. Minor outcrops of the Claughton Formation occur south of the Smeer Hall Fault in the Lune valley c. [SD 57 68], and in the core of the Quernmore Syncline, south of Caton c. [SD 53 62].

To the south-west and west of the 'Ward's Stone range', the outcrop is largely concealed by till, and the Claughton Formation is poorly known and undifferentiated. The formation forms part of the core of the Quernmore Syncline at Quernmore c. [SD 51 59]. To the south-west of the Mount Vernon Fault, fault-bounded outcrops extend southwards from north of Dolphinholme c. [SD 52 55] to the sheet boundary. The formation has also been traced around the southern extension of the Lancaster Moor Syncline on the west side of the Quernmore Fault, and around the eastern limb and nose of the Heysham Anticline in the Middleton area c. [SD 42 59].

The formation comprises mainly grey, sandy, micaceous siltstones and fine-grained sandstones of probable delta-slope facies, but sandstones of delta-top type and siltstones with a restricted marine fauna occur as minor facies. The base of the formation is defined at the base of the lowest sandstone or unfossiliferous micaceous sandy siltstone above the marine mudstones of the Caton Shale Formation. The contact is sharp and conformable. The formation maintains a thickness of about 150 m in most parts of the district. The equivalent strata in the adjacent parts of the Settle district are estimated to be only between 45 m and 60 m thick (Arthurton et al., 1988).

The formation is best exposed in the gullies and quarries on the northern slopes of Caton and Claughton moors, although the highest beds may not be preserved there. The sequence, first established there by Slinger (1936), was confirmed during this survey, and differs from the succession proposed by Moseley (1954) in two important respects. Firstly, the sandstone containing a ganister and thin coal at the Claughton brickworks [SD 5665 6619], thought by Moseley to be within the Claughton Formation, is here reinterpreted as Ward's Stone Sandstone disposed against the Claughton Formation on the north-east side of the Claughton Fault. Secondly, Moseley interpreted the Nottage Crag Grit as being more or less equivalent to the Moorcock Flags at the top of sequence, and equated both with the Crossdale Grit, i.e. with the Silver Hills Sandstone Formation of this account. Slinger's sequence is probably applicable to other outliers north of the 'Ward's Stone range'.

The only marine fossils found in the formation are the pectinacean bivalve Dunbarella and indeterminate molluscan fragments from the Claughton Moor Siltstone Member and equivalent strata. None of these are zonally diagnostic. The fossils are associated with an abundant ichnofauna. The stratigraphical position of the formation suggests that this horizon probably represents the N. stellarum Marine Band (E2c1) or one of the Nuculoceras nuculum marine bands (E2c2–3) of the basinal sequence (Table 3), though the zonal ammonoids have not been found. The scanty marine fauna is basinal in aspect but clearly diluted by an abundant supply of silt. The hemipelagic ammonoid facies of this marine cycle may lie in the unexposed sequence immediately overlying the Nottage Crag Grit.

Barncroft Beck Member (new name)

The unit is equivalent (Table 5) to the 'Claughton Flag Series' of Slinger (1936) and has only been differentiated on the northern slopes of Caton and Claughton moors. Equivalent beds are present on the southern parts of the hill and elsewhere, but cannot be separated from the Claughton Moor Siltstone Member due to the failure of the Nottage Crag Grit southwards. On Caton and Claughton moors, the thickness is variable up to an estimated thickness of about 85 m.

The member is well exposed along incised stream gullies and adjacent former brickpits along Barncroft Beck [SD 5650 6617] to [SD 5685 6577], Westend Beck [SD 5620 6591] to [SD 5665 6566], along an unnamed beck to the south-west [SD 5604 6561] to [SD 5635 6530] and in a gully along Mears Beck [SD 5590 6520]. A continuous but faulted section, through approximately 70 m of the member into the Caton Shale Formation, occurs along Green-holes Beck [SD 5688 6314] to [SD 5737 6340] (Figure 28). Good exposures of the sharp contact of the base of the member on the Caton Shale Formation occur along Westend Beck and Greenholes Beck. A further good section of the lowest 29 m and the basal contact is to be found in a gully formed by an eastern tributary of Mears Beck [SD 5559 6466] to [SD 5571 6465], and the lowest 9 m and basal contact are exposed along Tarn Brook [SD 5634 6334] . The member also forms the three minor outliers at the north end of the Quernmore Syncline, between Caton and Quernmore.

The member comprises very variably interstratified siltstones and sandstones of delta-slope origin. The siltstones are grey, micaceous, shaly to platy and sandy, commonly grading into very fine-grained sandstones. Comminuted plant debris is ubiquitous. Calcareous nodules are rare. The siltstone units are several metres thick on average, up to about 12 in thick near the top of the member. They commonly contain thin, current-ripple-marked, fine-grained sandstone beds, up to a few cen timetres thick, and channel-filled sandstone lenses. The thicker sandstones are brown-weathering, grey, fine-grained, micaceous, massive to parallel-laminated beds, typically up to about 3 m thick ranging to a thickness of 7 m. These sandstones probably fill channels and generally have erosive bases, commonly overlain by siltstone pebble conglomerates. Many of the sandstones are cemented with ferroan calcite or siderite, and weather to a conspicuous orange-brown. The sandstones are generally sharp-soled with groove casts, bounce marks and flute casts (9 observations) which, along with primary current lineations (2), indicate a south-facing palaeoslope. Bioturbated beds are common. Individual sandstones usually cannot be traced laterally, and only a few have been mapped.

Low-angle slickensided planes, pre-diagenetic microfaults in the sandstones, locally discordant bedding, and large-scale syndepositionally slumped beds are common, and imply that the member has been affected strongly by growth faulting. This probably accounts for the great variability in recorded dips. Syndepositionally slumped beds are exposed at numerous places along Snab Beck [SD 5631 6835] to [SD 5635 6810], and a low-angle listric fault is exposed along Claughton Beck [SD 5745 6518]. Slumped siltstones and sandstones are also exposed at several places along Greenholes Beck (Figure 28). The Nottage Crag Grit and higher members of the formation are unaffected by such deformation, and the angular unconformity at the top of the Barncroft Beck Member probably indicates trimming by wave erosion preceding the advancing Nottage Crag Grit delta.

The only fossils recorded are trace fossils and plant remains. ? Aulichnites burrows are abundant along bedding planes at several levels, particularly on the surface of the second main sandstone in the Greenholes Beck sequence (Figure 28), 34 m above the base of the formation. The third main sandstone in the Greenholes Beck section, 44 m above the base of the formation, is highly bioturbated.

Sections in equivalent beds elsewhere in the district

Helks Brow c. [SD 643 638] on Goodber Common provides a discontinuous section through an estimated 84 m of siltstones and fine-grained sandstones, containing abundant plant debris, probably equivalent to parts of both the Barncroft Beck and Claughton Moor Siltstone members. An 8 m-thick, medium- to coarse-grained sandstone, mapped near the base of the Claughton Formation, caps Hawkshead Hill at the south end of the Goodber Syncline. This was named the Hawkshead Grit by Slinger (1936) and equated with the Moorcock Flags of Caton Moor, although Moseley (1954) placed it much higher in the Millstone Grit sequence. The sandstone is probably of delta-top facies, and trough cross-bedding indicates palaeocurrents from the north-west. There appear to be no lateral equivalents of the sandstone; its apparently low stratigraphical position would probably rule out a correlation with the Nottage Crag Grit.

Farther north, intermittent sections through up to about 15 m of siltstones and sandstones of the Barncroft Beck Member are exposed along the River Hindburn, for example at Colgate Scar [SD 6439 6584], along several western tributaries, such as Friar Gill [SD 645 656] and Stirk Close Gill [SD 645 652], and in a landslip backscarp to the south [SD 6450 6507]. The lowest 63 m were penetrated in the Lowgill No. 2 Borehole [SD 6526 6498].

There are few good sections in the drift-covered tract south of Bentham. The basal 8 m of the Barncroft Beck Member, comprising siltstones with thin, fine-grained sandstones full of plant debris, and its contact with the Caton Shale are exposed along Branstone Beck [SD 6772 6833]. About 25 m of interbedded siltstones and sandstones of the Barncroft Beck Member are also exposed in two quarries c. [SD 625 685] near Outlay, and further sections occur in the adjacent valley sides of the tributary to Clear Beck.

Equivalent beds in the heavily drift-covered Lancaster Moor Syncline area, north of Galgate, may be partly represented by an estimated 40 m of sandy siltstones with thin sandstones, poorly exposed along the deep cutting for the Lancaster Canal, north of Brantbeck Bridge [SD 4726 5740].

Nottage Crag Grit Member

The member is synonymous with the Nottage Crag Grit as previously used by Slinger (1936) and Moseley (1954). It appears to have a very restricted distribution, and is only known from the northern slopes of Caton and Claughton moors where it forms a prominent craggy escarpment [SD 561 647] to [SD 570 657], including Nottage Crag, between the Claughton and Deep Clough faults. Sections up to 6 m high occur in crag and small quarry exposures along Nottage Crag [SD 5624 6508] to [SD 5703 6569], the best being in the small pits on the west side of the crag c. [SD 564 654]. The member is also exposed along Claughton Beck [SD 575 651] to the east. The member either thins considerably, or fails completely, on the south side of Caton Moor.

It consists mainly of pale orange-brown weathering, medium- to very coarse-grained, very thickly bedded, micaceous sandstone of delta-top facies. The sandstones are typically low-angle tabular cross-stratified, and feebly parallel-laminated, some foresets being slumped e.g. at [SD 5663 6539]. A limited amount of measurement of tabular cross-bedding indicates delta progradation from the west. The sandstones contain sporadic, small quartz pebbles up to about 10 mm across, but the only fossil remains are plant fragments. The member has a maximum estimated thickness of about 20 m along Nottage Crag; along Claughton Beck where it is represented by mostly medium-grained sandstone, the member is reduced to only 4 m.

The sharp base to the coarse-grained sandstone sequence, resting on sandy siltstones with fine-grained sandstones of the Barncroft Beck Member, is exposed along Claughton Beck. Along the northern side of Nottage Crag, the basal contact of the sandstone has not been directly observed, though from the gently inclined disposition of the member over variably inclined strata of the Barncroft Beck Member, the relationship is clearly one of angular unconformity. The top of the Nottage Crag Grit is nowhere exposed.

Claughton Moor Siltstone Member (new name)

The unit is equivalent to the Claughton Moor Shales of Slinger (1936)). The member is only differentiated on the northern slope of Caton and Claughton moors where the Nottage Crag Grit is present, but equivalent beds are probably much more widely distributed. Claughton brick pit [SD 578 648] and nearby Claughton Beck [SD 5756 6493] to [SD 5836 6444] (Plate 10) provide continuous sections in all but the basal few metres of the unit, which are nowhere exposed. The gradational top of the unit is well exposed on the south side of Claughton brick pit [SD 579 646].

The member comprises about 25 m, mainly of siltstone in a marginal marine facies, closely resembling the Close Hill Siltstone Member of the Roeburndale Formation (Plate 10). The siltstones are medium grey, micaceous, variably sandy, shaly, laminated and bioturbated, and at some levels grade into very fine-grained, silty, platy sandstones. Within the siltstones, discrete, thin, pale grey, very fine-grained, micaceous, current-ripple-marked sandstones, up to about 10 mm thick, occur at intervals of a few tens of millimetres, and rare lenses of parallel-laminated sandstones, up to about 0.2 m thick, are also present. At several levels, there are sporadic concretionary lenses of orange-brown weathering, grey, laminated, micaceous, calcisiltite or calcareous sandstone, some of which contain septarian veins of calcite.

Some beds contain comminuted plant debris, or trace fossils including burrow casts and ?Aulichnites. Scattered shells of Dunbarella (Plate 3) occur on at least one bedding plane in the upper part of the unit, based on its occurrence on loose blocks in the brickpit; the shells are preserved in white calcite. The range of this marine bivalve within the unit is unknown, and it is not clear whether one or more bedding planes are represented. A sparse marine fauna, including Dunbarella carbonarius, was recorded from what are probably coeval beds in the Keasden Flags of the BGS Knott Coppy Borehole, in the Settle district (Arthurton et al., 1988).

Sections in equivalent beds elsewhere in the district

The Claughton Moor Siltstone Member is probably represented by sections along a landslip backscarp on the west side of the Hindburn valley where, at one place [SD 6439 6477], siltstones have yielded Dunbarella. These siltstones are also well exposed in river cliffs near the confluence of the River Hindburn and Crossdale Beck at Mosit Shoe Wood [SD 6468 6576] to [SD 6469 6565]. A thin siltstone bed there shows evidence of synsedimentary deformation. The highest 7 m of Claughton Moor Siltstone Member are exposed in a gully [SD 6573 6809] near Close House, south-west of High Bentham.

Moorcock Sandstones Member (new name)

The member is equivalent to the Moorcock Flags of Slinger (1936), and is only known from Caton and Claughton moors where it forms a small outlier on the hilltop. Numerous degraded pits, south of the derelict Moorcock Hall, provide small sections; the best is at Claughton Quarries [SD 5700 6422]. The lowermost approximately 10 m are exposed on the south side of the Claughton brickpit [SD 579 646]. About 18 m are estimated to be present in the outlier, but the upper contact is not preserved. The member passes up from the Claughton Moor Siltstone Member with the incoming of numerous sandstones, 0.2 m to 0.3 m thick, in a few metres of siltstone. The only section of the basal beds is provided by the south face of Claughton brick pit.

The sandstones are grey, weathering to brown, fine-grained, micaceous, parallel-laminated and ripple cross-laminated, platy to flaggy, commonly with thin, sandy, siltstone partings. Many of the bases are gradational. The siltstones are grey, shaly, micaceous and sandy, and generally contain numerous thin, fine-grained sandstone beds. The two lithologies typically form packets between 0.5 m and 2 m thick. Bedding planes contain abundant Aulichnites burrows.

Silver Hills Sandstone Formation

The sandstone was formerly known as the Crossdale Grit in the Bentham area (Moseley, 1954). In the Settle district to the east, it has been called the Silver Hills Grit (Moseley, 1956) and the Silver Hills Sandstone (Arthurton et al., 1988). It is regarded as being equivalent to the top part of the Heversham House Sandstone, the whole of the Starbank Wood Sand-stone, and the intervening thin mudstone unit, described by Wilson et al. (1989) in the Dolphinholme area. These two names are now considered to have been superseded. Although the formation has not yielded a diagnostic flora or fauna, it is known to be late Arnsbergian from the age of the basal marine band of the overlying Crossdale Mudstone. It is coeval with the Lower Follifoot Grit in the Fewston area of Wharfedale.

The main exposures are in the Wennington area [SD 62 70] to [SD 63 68], in the Crossdale Beck valley [SD 65 65] to [SD 66 65], on the flanks of the Goodber Syncline [SD 61 64] to [SD 64 63] and in the Dolphinholme area [SD 51 55] to [SD 52 52]. The assignment to the formation of strata in the Quernmore Syncline [SD 51 59], south of Galgate [SD 53 48] to [SD 54 48] and in the Middleton area [SD 42 58] is uncertain. The formation may maintain a thickness in the order of 10 m over the north-eastern part of the district, though it has not been mapped between County Bridge [SD 649 679], Eskew Beck [SD 649 679], and Greystonegill [SD 686 691] due to lack of evidence. A maximum thickness of about 65 m is estimated in the Dolphinholme area.

In general, the Silver Hills Sandstone consists of fine- to very coarse-grained sandstones with beds of siliceous, ganisteroid sandstone, some with stigmarian roots, thin mudstone seatearths and coals. These are interpreted as having been deposited in a delta-top environment. Trough cross-bedding in sets up to 0.5 m thick, planar cross-bedding, small-scale cut-and-fill structures, syndepositional faults and slump structures have been recorded. Coalified plant debris occurs abundantly along bedding planes. An impersistent coal, 0.3 m to 0.6 m thick and overlying 1.9 m of grey mudstone seatearth, occurs in the middle of the formation in the Crossdale Beck valley [SD 6574 6515]. Evidence of bell pit workings, presumed to have been dug for coal at this horizon, occur around Parkside [SD 619 687]. In addition, two thin allochthonous coals without seatearths are exposed in the back scar of a landslip beside Damas Gill [SD 5213 5478], in the Dolphinholme area, and a lens of allochthonous coal lies near the top of the formation in a section in the banks of the River Wyre [SD 5272 5366].

The best exposures are in the valleys of the River Wenning [SD 6230 7009] and Crossdale Beck [SD 6481 6571] to [SD 6483 6568] in the north-eastern part of the district, and the valleys of the River Wyre [SD 5275 5369] to [SD 5272 5366] and Damas Gill [SD 5194 5508] to [SD 5207 5524] in the Dolphinholme area. In the Crossdale section, there is evidence of localised channels eroded through at least 0.5 m of ganisteroid sandstone and thinly bedded, fine-to medium-grained sandstone, the channels being filled with fine-grained, ganisteroid sandstone.

Damas Gill and adjacent small quarries [SD 5194 5508] to [SD 5207 5524] at Dolphinholme expose a 34 m-thick sequence; the lowest bed is presumed to be within a few metres of the base of the formation. The sandstones are fine- to very coarse-grained, massive and parallel-laminated, with granule-grade lenses and two thin ganisters. These beds were described as the Heversham House Sandstone by Wilson et al. (1989). The overlying 10 m, seen in a small section lower down in Damas Gill [SD 5213 5479], are unfossiliferous mudstones with siderite mudstone nodules. These beds are overlain in turn by up to 13 m of fine-grained sandstones, with two thin allochthonous coals without seatearths, described formerly as the Starbank Wood Sandstone (Wilson et al., 1989). Beds close to the top of the formation, exposed in the south bank of the River Wyre [SD 5275 5369] to [SD 5272 5366], include a thin allochthonous coal and dark grey, fissile, pyritous claystone with spirorbids, plant fragments and small rotted siderite mudstone nodules.

There are few exposures of what are taken to be Silver Hills Sandstone in the drift-covered Quernmore Syncline, the outcrop in this area being calculated on the basis of exposures and dip values in adjacent formations.

Crossdale Mudstone Formation

This formation is equivalent to the Crossdale Shales described by Moseley (1954) in the Bentham area and by Wilson et al. (1989) in the Dolphinholme area. The name was formalised in the account of the Garstang district (Aitkenhead et al., 1992). Six marine bands, ranging in age from late Arnsbergian (E2c) to Chokierian (H1b), have been identified (Figure 29), whereas only the Homoceras beyrichianum Marine Band (H1b1) was known previously (Moseley, 1954). The record of younger beds with an undetermined marine band of R1a age in the Knott Coppy Borehole, in the adjacent Settle district (Arthurton et al., 1988), is no longer supported, as that interpretation was due to confusion of the then unknown Isohomoceras sp. nov. Marine Band (Riley et al., 1987) with homoceratid-bearing mudstones of Kinderscoutian age.

The principal outcrop areas with exposures are in the Crossdale Beck valley [SD 64 65] to [SD 66 65], on the eastern flank of the Goodber Syncline [SD 63 63], and in the Dolphinholme area [SD 50 56] to [SD 51 54]. The formation remains unproved in the Quernmore Syncline [SD 51 59] and in the Galgate area. An isolated, faulted outcrop of Crossdale Mudstone was identified from dark grey, shaly, fossiliferous mudstone debris, dug from a pipe trench [SD 4872 5159] at Forton. The fauna includes the bivalve Caneyella semisulcata and poorly preserved homoceratid ammonoids.

The formation comprises mainly blocky, medium to dark grey, laminated mudstones and silty mudstones, which become fissile on weathering and which contain sporadic levels of siderite mudstone lenses and nodules. There are several, relatively thin marine bands, composed of dark grey, platy mudstone with scattered oblate septarian carbonate nodules. Thin beds of sandstone occur sporadically, and are particularly common in the highest few metres. The basal boundary is placed at the marked change from the sandstone-dominated Silver Hills Sandstone to a predominantly mudstone sequence.

There is considerable thickening in a south-westwards direction, from between 13.5 m and 22.5 m in Crossdale, to an estimated 165 m in the Dolphinholme area. This thickness variation is probably due to the presence of a non-sequence (Owens et al., 1990), accounting for the absence of the lowest two of three Isohomoceras subglobosum marine bands from the Crossdale area ((Figure 29), sections 4 to 6).

The formation was mainly deposited in a hemipelagic marine setting, but with periods of shallowing leading to hiatuses and some erosion. In comparison, the equivalent part of the Sabden Shales in the centre of the basin, south of this district (Earp et al., 1961; Riley et al., 1987), contain a full sequence of marine bands. In the Well Beck section ((Figure 29), section 3), upper Arnsbergian miospore assemblages from the lower part of the Crossdale Mudstone (Owens et al., 1990), below a distinctive sandstone, indicate nearshore conditions, with significant amounts of terrestrial organic debris. Miospore assemblages from the mudstones overlying the sandstone in the same section indicate an early Chokierian age and an environment which oscillated from open-marine conditions during deposition of the marine bands, to a more restricted marine environment dominated by the input of terrestrial organic debris. The top part of the formation exposed at Crossdale, of probable late Chokierian age, contains coarser clastic sediments, indicating deposition in relatively shallow water with increased sediment supply.

Strata up to the Homoceras beyrichianum Marine Band

At the base of the formation at Lowgill in Crossdale [SD 6511 6546] ((Figure 29), section 5), a 50 mm-thick, dark grey mudstone with abundant marine fossils, including the brachiopods Lingula mytilloides and Nudirostra papyracea, the bivalves Posidonia corrugata and Selenimyalina variabilis, orthocone nautiloids, anthracoceratid or dimorphoceratid ammonoids, and arthropod and fish debris, probably represents one of the four marine bands in the E2c chronozone. It is not present in exposures about 300 m upstream [SD 6540 6526], where the lowest beds of the formation contain only phosphate nodules and fish debris, and a slight hiatus is inferred. This part of the succession has not been seen elsewhere, and therefore the extent of the hiatus is not known.

An important exposure, where unconformity has been demonstrated (Owens et al., 1990), occurs in the north-east of the district. The banks of Well Beck [SD 6398 6360], near Summersgill, expose 4.63 m of dark grey shaly mudstones with the H. beyrichianum Marine Band and one of the I. subglobosum marine bands ((Figure 29), section 3), the latter presumed to be close to the unexposed base of the formation. Other marine bands may be present but have not been recognised on account of the deep weathering (Owens et al., 1990). The H. subglobosum Marine Band (H1a3) consists of about 0.60 m of grey, platy mudstone, with a decalcified bullion about 0.20 m thick close to the base, and has yielded the bivalves Caneyella semisulcata and Dunbarella cf. carbonaria in addition to the ammonoid Isohomoceras subglobosum. About 0.2 m below, a weathered, limonitic, orange-brown, medium-grained sandstone, 20 mm to 50 mm thick, contains phosphate nodules and fish debris, and has an erosive base. This sandstone contains a mixture of Arnsbergian and Chokierian conodonts, indicating reworking of late Arnsbergian and early Chokierian marine sediments. The miospore assemblage from mudstones directly below this sandstone is latest Arnsbergian (E2c4), and the mudstones above have yielded a Chokierian assemblage (Owens et al., 1990). These assemblages are sufficiently different from those of the stratotype at Stonehead Beck, 40 km to the south-east (Riley et al., 1987), to suggest that the upper part of chronozone E2c4 and at least part of the lower E2c4 deposits were removed by erosion at the base of the sandstone.

A more complete sequence, including the three I. subglobosum marine bands (H1a1 to H1a3), occurs in the lower part of the formation in a stream section at Cocker Clough Wood [SD 5078 5590] to [SD 5095 5578], north of Dolphinholme. The marine bands lie in a sequence of about 10 m of fissile, (black) mudstone with limestone bullions and a bed of nodular ironstone ((Figure 29), section 1). The section is cut by a small fault between the middle and upper marine bands and thus the thicknesses shown in (Figure 29) are estimates. The fauna of the lower band [SD 5093 5583] and [SD 5095 5578] includes the bivalve cf. Caneyella semisulcata and the ammonoids anthracoceratid or dimorphoceratid indet. and Isohomoceras subglobosum, the latter preserved uncrushed in limestone nodules. The middle band [SD 5090 5583] contains the bivalves C. cf. semisulcata, cf. Dunbarella carbonaria and Selenimyalina sp., and the eponymous ammonoid Isohomoceras subglobosum. The upper band [SD 5078 5590] and [SD 5085 5595] has yielded the bivalve cf. Myalina sp., ammonoids which include anthracoceratid or dimophoceratid indet. and Isohomoceras subglobosum, and condont debris. One of the I. subglobosum marine bands is also exposed, but for less than a metre, in Damas Gill [SD 5190 5596]. A further exposure of the highest band, with the eponymous ammonoid, occurs along Whitley Beck [SD 5062 5671] farther west, an estimated 10 m below the H. beyrichianum Marine Band.

A distinctive, 0.08 m-thick bed of medium grey, slightly calcareous sandstone, about 16 m below the top of the Crossdale Mudstone in Foss Bank Wood [SD 6582 6515] ((Figure 29), section 6), contains subrounded quartz grains up to 1 mm in diameter, subangular to rounded clasts of brown, ?ferroan calcitic claystone up to 5 mm in diameter, phosphatic nodules up to 10 mm in diameter, and subangular, dark green, lithic fragments less than 1 mm across. It is correlated with a very fine-grained sandstone with small phosphate nodules, generally less than 10 mm in diameter, and numerous fish fragments, 6.9 m below the top of the formation in a section downstream of the roadbridge [SD 6511 6546] at Lowgill ((Figure 29), section 5). This bed represents a period of reworking and winnowing during an hiatus, as at Well Beck. and is probably responsible for the non-deposition of the lower two Isohomoceras subglobosum marine bands in the Crossdale area with the hiatus increasing northwards from Well Beck.

Homoceras beyrichianum Marine Band (H1b1)

The Homoceras beyrichianum Marine Band is probably the most widespread in the formation. It consists of less than 1 m of dark grey, fissile to platy claystone and mudstone, with thin beds of calcareous mudstone. It was recorded 8.3 m above the base of the formation at Lowgill along Crossdale Beck ((Figure 29), section 5); an estimated 75 m above the base and approximately 10 m above the highest I. subglobosum Marine Band north of Dolphinholme (Figure 12); and in Well Beck (Figure 29). The composite fauna of the marine band includes the bivalve Caneyella semisulcata, the ?scaphopod Coleolus sp. and the ammonoids Anthracoceras sp. or dimorphoceratid indet., Homoceras beyrichianum, H. cf. diadema and Isohomoceras sp.

In the river bank section [SD 6511 6546], 170 m downstream of the Lowgill roadbridge ((Figure 29), section 5), the marine band consists of two, thinly laminated beds of calcareous, fine-grained sandstone, each less than 0.1 m thick and separated by 0.15 m of dark grey mudstone with the eponymous ammonoid. Other exposures are in the river bank on the west side of Crossdale Beck [SD 6515 6549] and in a slipped block in the river bank at Foss Bank Wood [SD 6582 6515]. Moseley (1954) identified the marine band at two further localities: in spoil around a former shaft (probably [SD 6542 6806] ) dug for coal in the outcrop, 1.5 km south-west of High Bentham, and 'in the stream near Lanshaw [SD 671 650]' where he recorded Homoceras sp.'. In places, this gully [SD 6707 6503] to [SD 6714 6514] now exposes unfossiliferous mudstones and, at the upstream end, grey-brown, fine-grained sandstone with small burrows, probably close to the top of the Crossdale Mudstone Formation.

South of Crossdale, the H. beyrichianum Marine Band crops out in the banks of Well Beck [SD 6398 6360] ((Figure 29), section 3). It is exposed also in small sections between Dolphinholme and Quernmore, in a tributary to Damas Gill at Nook House [SD 5164 5484], and along Whitley Beck [SD 5053 5668], the latter an estimated 10 m above the highest I. subglobosum Marine Band exposed nearby [SD 5062 5671].

Strata above the Homoceras beyrichianum Marine Band

About 0.60 m above the H. beyrichianum Marine Band at Lowgill [SD 6511 6546] ((Figure 29), section 5), a 10 mm-thick sandy mudstone with Lingula sp. marks the base of the Isohomoceras sp. nov. Marine Band (H1b2). It consists of 1.4 m of fissile mudstones with bivalves and ammonoids, the best preserved being in a 2 mm-thick, weakly cemented, thinly laminated, ?ferroan calcitic, fine-grained sandstone. The fauna includes the bivalve Dunbarella carbonaria, dimorphoceratid indet. and fragmental homoceratid ammonoids in addition to Isohomoceras sp. nov., and the worm tube Serpuloides sp. This marine band is also exposed about 370 m upstream from the bridge at Lowgill [SD 6562 6524] ((Figure 29), section 4), where it consists of about 2 m of dark grey mudstone. At the same locality, the top 1.5 m of the formation are mudstones with poorly preserved spat and Caneyella sp. This fossiliferous bed appears to be absent in the river cliff at nearby Foss Bank Wood [SD 6582 6515] ((Figure 29), section 6), where the top 3 m of Crossdale Mudstone are interbedded grey mudstones and buff, finely laminated siltstones with hummocky cross-stratification and bioturbation.

Accerhill Sandstone Formation

The Accerhill Sandstone, first mapped in the Settle district (Arthurton et al., 1988), is equivalent to the Clintsfield Grit or 'Lower Bentham Grit' described by Moseley (1954) in the Bentham area, and was formerly known as the Wellington Crag Sandstone in the Dolphinholme area (Wilson et al., 1989). An age of late Chokierian (H1b) to early Alportian (H2a) is constrained by the Isohomoceras sp. nov. Marine Band (H1b2) near the top of the underlying Crossdale Mudstone, and the H. undulatum Marine Band at the base of the overlying Kirkbeck Formation.

The formation crops out in a north to north-east-dipping tract south and west of Bentham, in the Crossdale Beck valley, the Goodber Syncline and the Dolphinholme area. In the Galgate Syncline there are no exposures, and the outcrop is inferred. The formation may occur at depth farther west in the Overton area, but has not been proved.

The formation reaches its greatest thickness, estimated at 70 m, north of the River Wenning in the north of the district. Between 10 m and 12 m are estimated to be present in the Crossdale area and 23 m to 60 m in the Dolphinholme area.

The formation consists mainly of medium- to coarse-grained sandstones with abundant plant debris on bedding and lamination surfaces, interpreted as being of delta-top facies. Planar and trough cross-bedding, with sets up to 0.8 m thick, are common, with trough axes ranging in strike from north-north-west to north-northeast in exposures in the River Wenning [SD 6263 7019]. Subordinate siltstones with hummocky cross-stratification and burrows occur in the lower part of the formation and thin coals occur at the top and base. The base of the formation is defined at the incoming of a thickly bedded sandstone-dominated sequence.

A coal, named the Clintsfield Coal by Moseley (1954), was formerly mined in a small colliery at Clintsfield [SD 6298 6979], and won from numerous small bell pits and shallow shafts along the crop south and south-east of High Bentham, between Close House [SD 657 682] and Ridding Lane [SD 6825 6890]. The coal is inferred to be at or near the top of the Accerhill Sandstone, and there is little evidence of fragments of Accerhill Sandstone in the spoil heaps around the former shafts. The coal was worked during the 17th to 19th centuries but the full extent of the workings are unknown (see Economic Chapter).

The principal exposures in the basal beds of the Accerhill Sandstone are in Crossdale, at the river cliffs in Foss Bank Wood [SD 6588 6517] to [SD 6598 6520], where about 2 m of fine- to coarse-grained, cross-bedded sandstone are underlain by 0.8 m of grey siltstone with thin lenses of allochthonous coal ((Figure 29), section 6). Equivalent beds with a total thickness of about 6 m exposed in the valley of the River Wenning [SD 6260 7019] include a 0.2 m allochthonous coal, sandstone seatearth and a hummocky cross-stratified, fine- to medium-grained sandstone with a burrowed top ((Figure 29), section 2).

The highest beds of the formation are exposed below the Kirkbeck Formation in the Eskew Beck valley [SD 6500 6806]. They consist of 0.7 m of ganisteroid, fine-grained sandstone, overlain by a 1.6 m-thick, pale grey mudstone seatearth carrying a 0.01 m-thick coal ((Figure 30), section 3).

What has been interpreted as the Accerhill Sandstone outcrop in the Dolphinholme area forms a ridge affected by faulting, principally between Crag End [SD 5085 5555] and south of Wellington Crag Farm [SD 512 546]. The sandstone is not well exposed but can be seen in several small crags and former pits [SD 5130 5465]; [SD 5125 5492] near Wellington Crag Farm.

Kirkbeck Formation (new name)

Hitherto in the north-east of the district, strata assigned to this formation were included in the 'Bentham Grit Group' (Moseley, 1954). In the adjacent Settle district (Arthurton et al., 1988), the beds were mostly mapped as undivided Millstone Grit but include strata assigned to the Knott Coppy Grit. In the south-west of the district around Dolphinholme (Wilson et al., 1989), and in the adjoining Garstang district (Aitkenhead et al., 1992), the succession is poorly known, and beds that are possibly equivalent to the lower part of the Kirkbeck Formation were mapped as the Dolphinholme Mudstone and the overlying Ellel Crag Sandstone ((Figure 12); see below). In these areas, beds equivalent to higher parts of the Kirkbeck Formation were regarded as Millstone Grit undivided. In more general terms, the Kirkbeck Formation is correlated with part of the Sabden Shales, which are well developed in the deeper part of the basin to the south of the district, where a complete sequence of hemipelagic mudstones occurs throughout with a full complement of marine bands.

The Kirkbeck Formation crops out in a roughly east to west tract south of Bentham, in the Crossdale Beck valley, the Goodber Syncline, and areas around Dolphinholme, Galgate and Overton. The main exposures are referred to in the appropriate generalised sections on (Figure 30). In the west, where there is a thick cover of drift deposits, there are few exposures and the formation is not known in detail.

The formation includes all strata between the Accerhill Sandstone Formation and the Eldroth Grit Formation. The type section is near Kirkbeck in the Eskew Beck valley [SD 6500 6806] to [SD 6489 6833] ((Figure 30), section 3) where the lowest 48 m of the formation are exposed. Reference sections, higher in the formation, are at Bentham Weir [SD 650 691], Moulterbeck [SD 664 684], and Eskew Beck [SD 650 682] ((Figure 30), section 3).

In general terms, the formation consists of silty mudstones, siltstones and fine-grained sandstones of shallow-marine and delta-top facies. The shallow-marine siltstones are characteristically wave-ripple or hummocky cross-stratified and bioturbated, and contain several, thin, ?ferroan calcite-cemented beds with a marine fauna that is dominated by brachiopods and crinoid debris. To the south-west, a deeper water environment is suggested by an outcrop of turbiditic sandstones and siltstones of probable Chokierian to Alportian age, in the lower part of the formation at Mount Vernon [SD 504 586] in the Quernmore Syncline.

Ganisteroid siltstones and fine-grained sandstones occur at several horizons. Two impersistent, medium- to coarse-grained sandstone members, the Lanefoot Sandstone and the Knott Coppy Grit (Figure 30) were recognised in the Bentham area, varying from a few metres to tens of metres in thickness. In the Dolphinholme area, the Ellel Crag Sandstone, up to 70 m thick and well exposed at Ellel Quarry [SD 504 548], probably lies within the lower half of the Kirkbeck Formation, although extensive drift cover and structural complexity make this far from certain. The possibility of the sandstone at the quarry being Ward's Stone Sandstone or Silver Hills Sandstone cannot be ruled out. It may correlate with two, unnamed, medium- to coarse-grained sandstones, separated by 10 m of siltstone and claystone, that crop out near Parkside Farm [SD 469 559] in the Galgate Syncline.

The base of the Kirkbeck Formation is placed at the incoming of marine siltstones and mudstones above the Accerhill Sandstone, whose top beds in the north-east of the district are a thin coal and its associated seatearth.

The maximum thickness in the north-east of the district is 167 m, calculated from a composite section including exposures at Bentham Weir [SD 650 691], Moulterbeck [SD 664 684] and Eskew Beck [SD 650 682] ((Figure 30), section 3). Equivalent beds in the Settle district to the east (Arthurton et al., 1988) are about 110 m thick. A regional southwards thickening is indicated by the estimate of 300 m in the south-west of the district and a similar amount for coeval beds in the Garstang district (Aitkenhead et al., 1992), but these figures depend to some extent on the age of the Ellel Crag Sandstone. In the Preston district (Price et al., 1963), coeval, sediment-starved basinal beds are only about 44 m thick.

The age of the Kirkbeck Formation ranges from Alportian to mid-Kinderscoutian, if possible Chokierian strata that are only tentatively assigned to the formation in the area between Dolphinholme, Galgate and Overton, are excluded. The Homoceras undulatum Marine Band (H2b1) occurs in the lowest beds in the type area, and the Reticuloceras stubblefieldi Marine Band (R1b3) is found close below the Eldroth Grit, near the top of the formation (Figure 30). The Reticuloceras dubium Marine Band (R1a5), probably the best-developed marine band in this part of the sequence, has been located in both the north-eastern and western outcrops, in the Bentham Station Borehole [SD 6659 6893] and in a small stream gully near Greenhalls Farm [SD 5128 5780] respectively. Other marine bands have been proved in the Bentham Station Borehole and the River Greta section (Figure 30) but the full marine band sequence is unproved. Identification of the Kirkbeck Formation in the largely drift covered south-western parts of the district is mainly based on the discovery of marine bands in BGS boreholes. None of them has yielded definitive ammonoid faunas, and their presumed ages are based on molluscs, conodonts and miospores.

The succession in the Bentham area

The Kirkbeck Formation in this area is well known from several well-exposed stream sections, including the type section at Eskew Beck ((Figure 30), section 3) and the Bentham Station Borehole ((SD66NE/1)) [SD 6659 6893]. The top 80 m are also exposed in the section in the River Greta valley, about 3 km north of High Bentham, in the adjoining Kirkby Lonsdale district.

At the base of the type section, the boundary with the underlying Accerhill Sandstone is not exposed. However, its position is well constrained, below 0.30 m of bioturbated, grey, muddy, fine-grained sandstone with calcareous brachiopods which is overlain by a ?ferroan calcitic, sandy siltstone with small fragments of broken brachiopods and molluscs, and phosphate nodules up to 4 mm in diameter. The sandstone and siltstone comprise the basal part of the Homoceras undulatum Marine Band (H2b1). The fauna from this part of the sequence at Eskew Beck includes: conulariid fragments; the brachiopods Lingula mytilloides, Crurithyris sp., cf. Lissochonetes sp., Plicochonetes sp., productoid debris and Rugosochonetes sp.; turreted gastropod debris; the bivalves Caneyella semisulcata (Plate 3) and Sanguinolites sp.; the orthocone nautiloid Brachycycloceras sp.; the ammonoids Homoceras undulatum (Plate 3) and H. cf. smithi (Plate 3); and conodont and fish debris. Overlying the basal part of the succession is about 1 m of dark grey, silty mudstone with Lingula and orthocone nautiloids, which grades up into grey siltstones with shelly horizons dominated by schizophoriid and productoid brachiopods, including Schizophoria connivens, Kozlowskia sp nov. ex gr. subcarbonaria and Productus carbonarius, and the sponge Hyalostelia. These siltstones contain large siderite ironstone nodules, and several beds of calcareous siltstone to fine-grained sandstone, up to 30 mm thick, with scattered coarse sand grains and abundant crinoid debris. The best developed of these lies about 8 m above the base of the formation, and has a sharp base overlain by a basal lag of ironstone nodules. It has internal hummocky cross-stratification and contains the first recorded foraminifera from the British Alportian, comprising Archaediscus, Asterarchaediscus, Betpakodiscus, Neoarchaediscus and pluriloculars indet. From 14.2 m to 26.4 m above its base, the type section consists of an upward-coarsening sequence of silty, fine-grained sandstones. Hummocky cross-stratification and ripple lamination are commonly developed, but in places have largely been destroyed by bioturbation. Scattered brachiopods and bryozoans are present. About 26.4 m above the base, a rather rubbly weathered horizon may be a palaeosol or condensed bed ((Figure 30), section 3), and its base is taken to be the top of the H. undulatum Marine Band. Above this rubbly bed, the type section exposes mainly sandy siltstones with sporadic beds containing coquinas dominated by Schizophoria sp. Their precise age within the Alportian or early Kindersoutian is unknown.

In a stream section [SD 6557 6557] near Low Gill Church, a rich decalcified brachiopod assemblage occurs in hummocky cross-stratified sandstones which are probably the same age as those exposed at Eskew Beck. It includes the articulate brachiopods dictyoclostid indet., Kozlowskia sp. nov. ex gr. subcarbonaria, Orthotetes cf. hindi, Pugilis cf. serpukhovensis, Rugosochonetes sp. and Spiriferellina cf. perplicata.

The Bentham Station Borehole [SD 6659 6893], though not well documented, provides a comparative section with which surface exposures can be correlated. It penetrated the top 154.7 m of the formation ((Figure 30), section 4), in which four marine bands have been recognised. The lowest, between depths of 170.08 m and 183.49 m, contains: the brachiopods Lingula mytilloides, Orbiculoidea nitida, cf. Lissochonetes sp., Productus carbonarius, and Rugosochonetes sp.; the bellerophontid gastropod Euphemites sp.; and crinoid debris; it is ascribed to one of the marine bands of the R1a chronozone (Table 3).

Between depths of 114.9 m and 168.2 m, the succession in the borehole is described (on the log) as mainly 'sandstone' with some 'shale bands' and 'shale partings' This sandstone-dominated sequence is here informally named the Lanefoot Sandstone, after Lanefoot Quarry [SD 669 685] where it was formerly worked for building stone. The quarry is now back- filled, and there is only one small exposure [SD 6692 6850] of medium-grained sandstone. Elsewhere at crop, the sandstone, with its base an estimated 57 m above the base of the Kirkbeck Formation, is poorly exposed, but appears to be thinner than in the Bentham Station Borehole. The best exposure is in a waterfall at the southern end of the deeply incised part of Moulterbeck [SD 6643 6840], which exposes about 6 m of medium- to coarse-grained sandstone with basal groove casts and with trough cross-bedded sets up to 0.8 m thick ((Figure 30), section 3). It is also exposed in the Eskew Beck valley [SD 6444 6900].

The top 80 m of the formation exposed in the River Greta valley, north of Bull Bank [SD 6170 7223] to [SD 6300 7210], consists mainly of sandstone with numerous Banisters and thin coals ((Figure 30), section 6); the R. stubblefieldi Marine Band (R1b3) has been recorded 14 m below the top of the formation. There is a nearly complete 12 m section above the Lane Foot Sandstone in the Moulterbeck valley, about 0.5 km south of High Bentham, extending from the waterfall [SD 6645 6852] to the mouth of the valley [SD 6644 6858] ((Figure 30), section 3). It comprises fissile, dark grey, micaceous siltstone and muddy siltstone, with incipient clay ironstone nodules and discontinuous lenses, up to 50 mm thick, of pale grey, splintery, ferruginous limestone. The horny brachiopod Orbiculoidea cf. nitida and indeterminate anthracoceratid ammonoids were recorded from the section during the recent survey, and by Moseley (1954) who identified, in addition, the orthocone nautiloid Cycloceras sp. and the bivalve Dunbarella sp. This 12 m section is correlated with beds in the Bentham Station Borehole that contain the Reticuloceras dubium Marine Band (R1a5). The fauna from the latter includes: the horny brachiopod Lingula mytilloides; the nuculoid bivalves Anthraconeilo laevirostrum and Phestia sp.; the bellerophontid gastropod Euphemites jacksoni and indeterminate turreted gastropods; the coiled nautiloids Ephippioceras sp. and stroboceratid indet.; the ammonoid Reticuloceras dubium; and crinoid debris. This part of the succession is also well exposed in the Eskew Beck valley [SD 6447 6908], where there are two casts of tree stumps in growth position.

Strata above those in the Moulterbeck section are exposed in the degraded faces of Low Quarry [SD 6447 6910] and in the bed of the River Wenning [SD 6439 6924]. They consist of 15 m to 20 m of medium- to thickly bedded, fine-grained sandstones and sandy siltstones with hummocky cross-stratification, strongly developed wave-ripple lamination, and a few burrows. They are overlain by a thin coal and seatearth, exposed on the north side of the river [SD 6426 6932]. This part of the succession includes a marine band in the Bentham Station Borehole, but no evidence of it was found at outcrop. The fauna from the Bentham Station Borehole includes the brachiopods Lingula mytilloides, Cleiothyridina sp. and Productus carbonarius, and crinoid debris, and the marine band is interpreted as either the R. nodosum (R1b2) or R. eoreticulatum (R1bl ) Marine Band.

The sandstone between depths of 65.23 m and 71.02 m in the Bentham Station Borehole ((Figure 30), section 4) is correlated with the Knott Coppy Grit, described from between the Reticuloceras dubium and R. stubblefieldi marine bands in the Settle district (Arthurton et al., 1988). It has not been seen at outcrop in the present district.

The best exposures in the top 50 m or so of the formation (Figure 30) are along the River Wenning downstream of Bentham Weir [SD 6513 6906], along a southern tributary of the River Wenning west of Hilltop [SD 654 688], and in the bed and banks of the River Wenning south of Bentham [SD 6638 6874] to [SD 6658 6871]. Much of this sequence is attributable to the Reticuloceras stubblefieldi Marine Band (R1b3). The last locality contains up to 100 mm-thick, lenticular, calcareous siltstones or fine-grained sandstones with crinoid debris. In thin section, these are seen to contain numerous brachymetopid trilobites and the foraminifera Earlandia sp.,Endothyra sp., Globovalvulina sp., lasiodiscid indet., Palaeonubecularia sp. and calcispheres. Other fauna noted in this section include brachiopods, and bellerophontid and turreted gastropods. In the sections in the vicinity of Bentham Weir, an estimated 35 m to 40 m below the Eldroth Grit, the lowest beds exposed [SD 6507 6902] are interpreted as shore-face deposits and consist of 2.2 m of ripple-laminated, fine-grained sandstones with silt-filled burrows, some of which are Diplocraterion. The sandstones contain brachiopod debris and Lingula sp. The rippled bedding surfaces display 'tuning fork' wave-ripple crests and are guttered in places. Ripple-crest azimuths on successive beds only millimetres apart may diverge by up to 90°, and indicate flows from between north-east and north-west. The overlying 1.6 m of upward-coarsening, fossiliferous marine mudstone and silty mudstone are exposed in an inaccessible cliff on the south bank of the river [SD 6508 6902], and 50 m west of the weir on the north bank [SD 6507 6906]. The fauna from the latter locality includes: the brachiopods Orbiculoidea nitida, Productus carbonarius, Rhipidomella mitchelini and Rugosochonetes sp.; the bivalves Aviculopecten sp. and Parallelodon semicostatus; the ?scaphopod Coleolus sp.; a coarsely ornamented Reticuloceras sp. ammonoid; and crinoid debris. The mudstone is tentatively interpreted as the R. stubblefieldi Marine Band (R1b3), and is correlated with a marine band between depths of 37.49 m and 65.23 m in the Bentham Station Borehole. The overlying 0.55 m of strata form a rib in the bed of the River Wenning [SD 6502 6911], and consist of thinly bedded, finely laminated, ?ferroan calcitic siltstone with burrows, brachiopod and crinoid fragments, and a bed with phosphate nodules up to 15 mm in diameter.

The succession in the area between Dolphinholme, Galgate and Overton

A large area in the south-west of the district, thought to be underlain by Kirkbeck Formation, is covered by thick drift deposits. As a consequence there are few exposures, and some sequences in exposures and boreholes can only be tentatively placed in the stratigraphy. The stratigraphy and structure of this area are interpreted largely from the results of a programme of shallow drilling undertaken during the field survey, augmented by data derived from seismic profiling.

The thickness of the Kirkbeck Foramation in this area is estimated to be about 300 m. The lowest 60 m to 80 m are probably predominantly mudstones, equivalent to the Dolphinholme Mudstone of Wilson et al. (1989) and Aitkenhead et al. (1992). Exposures occur in the east bank of the River Wyre [SD 5198 5317] and in the deeply incised gully [SD 5184 5346] at Dolphinholme. In the latter section, about 1 m below the top of the mudstone sequence, approximately 0.9 m of medium grey, fissile mudstones with siderite mudstone nodules have yielded Caneyella semisulcata, a bivalve restricted to the Chokierian and Alportian stages. The BGS Five Lane Ends Borehole [SD 5050 5398], situated 1.5 km to the west-north-west, probably penetrated the same part of the succession beneath 17 m of till. It proved 13 m of medium to dark grey, silty claystone containing two marine bands of relatively dark grey, pyritic mudstone. Conodonts and the bivalves Caneyella semisulcata and Dunbarella cf. carbonaria indicate a Chokierian to Alportian age for the marine bands. Strata probably at around this level also crop out farther north in the Quernmore Syncline. Mudstone in a small gully exposure [SD 5038 5856] near Mount Vernon, on the steep northern limb of the syncline, has yielded C. semisulcata and the conodonts Declinognathodus noduliferus and cf. Neognathodus symmetricus, indicating a Chokierian to Alportian age. This exposure is of particular interest as the siltstones and thin sharp-soled sandstones overlying the marine band are probably turbiditic in origin.

The Ellel Crag Sandstone is a thick sandstone, interpreted as being mainly of delta-top facies, that crops out only in the Dolphinholme area. The type section is at Ellel Crag Quarry [SD 504 549], and there are possible correlatives at Croft Height Wood [SD 514 540], Welby Crag [SD 515 568] and Mainstones [SD 520 565]. On account of poor exposure and faulting, the stratigraphical position of the Ellel Crag Sandstone is uncertain. On the assumption of a reasonably consistent westwards dip between exposures of the Crossdale Mudstone Formation in the Damas Gill valley [SD 518 549] and the sandstone at Ellel Crag Quarry, the member is tentatively estimated to be between 60 m and 80 m above the base of the Kirkbeck Formation in this area. Palynology has provided a probable Kinderscoutian age. A 2 m-thick carbonaceous siltstone within the sandstone, exposed on the north side of Ellel Crag Quarry [SD 504 549], contains Kinderscoutian or younger miospores. Palynological analyses of three samples from the sandy siltstones beneath the sandstone in the quarry suggest an age not older than Kinderscoutian. Comparison of the miospore sequence in these three samples with the Kinderscoutian miospore sequence from the siltstones beneath the Eldroth Grit in the BGS Dam Head Borehole (see below) suggests that the Ellel Crag Sandstone is older. However, the possibility of the Ellel Crag Sandstone equating with a delta-top sandstone at a lower stratigraphical level, such as the Silver Hills or Ward's Stone sandstones, cannot be ruled out, especially since the Caton Shale has been proved in nearby BGS Hampson Green 3 and 4 boreholes [SD 4953 5431] and [SD 5001 5441]. The Ellel Crag Sandstone appears to be absent in the Quernmore Syncline.

The sandstone is up to about 50 m to 70 m thick. In the faulted, well-exposed sections at Ellel Crag Quarry, the sandstone overlies a 12 m, upward-coarsening sequence of grey mudstones and sandy siltstones, presently worked as a brick clay. The latter contains levels of calcareous nodules, up to 0.3 m across, and numerous burrows, including Monocraterion, Rhizocorallium and Zoophycus, the latter suggesting a marine environment. In the upper part of the sequence below the Ellel Crag Sandstone, a few sharp-soled sandstones with groove casts appear. The lowest 10 m of the sandstone member here comprise mainly medium-grained, thinly bedded sandstones, with abundant plant debris, allochthonous coaly lenses and thin siltstone interbeds, and may be of delta-slope origin. The highest 18 m exposed in the quarry consist of fine- and medium-grained sandstones with large-scale cross-bedding, and are of delta-top type. Exposures of fine- to medium-grained sandstone in former quarries at Welby Crag [SD 5152 5682]; [SD 5153 5671] and Mainstones [SD 5189 5655]; [SD 5191 5640] show current-ripple lamination and trough cross-bedding.

Most of the Kirkbeck Formation probably crops out in the Galgate Syncline. At an estimated 65 m above the base, near Parkside Farm [SD 469 559], two unnamed 10 m-thick sandstones, separated by 10 m of siltstone and mudstone, were mapped largely on the evidence of topographical features. The lower sandstone, pale grey, medium- to coarse-grained and thickly bedded, is not exposed but was formerly quarried [SD 4688 5615] to build Parkside Farm. The upper sandstone is pinkish grey, fine- to medium-grained and medium-bedded, and is exposed at several places between Parkside Farm and Lower Burrow [SD 4735 5720]. Higher beds proved in the BGS Parkside Borehole [SD 4715 5552], drilled up-dip of the sandstones, comprise 5.8 m of fossiliferous, greyish purple and greyish dark red claystone beneath 11.5 m of till. The fauna from these higher beds, which includes the bivalves Caneyella sp. and Dunbarella rhythmics, and the ammonoids Reticuloceras sp. and Vallites striolatus, is Kinderscoutian in age. The Caneyella sp. may be C. squamula, in which case the horizon is no older than the R. eoreticulatum Marine Band (R1bl) and is ascribed to the upper part of the Kirkbeck Formation, although an age younger than the Eldroth Grit cannot be excluded.

The BGS Sellerley Borehole [SD 4778 5465], also in the Galgate Syncline, penetrated an undetermined marine band between depths of 23 m and 27.8 m. It contains a strongly ribbed but poorly preserved homoceratid of probable late Chokierian to Alportian age (H1b to H2b Zones), and a conodont fauna indicating a Chokierian (H1b) to Kinderscoutian (R1c4) age. This information suggests that the marine band is most likely to be in the lower part of the Kirkbeck Formation, though a Crossdale Mudstone horizon cannot be ruled out.

Evidence for the sequence in the poorly exposed upper part of the formation comes from the Quernmore Syncline. On its eastern limb, the R. dubium Marine Band (R1a5) is well exposed at the base of a stream section [SD 5127 5781] near Blackwood End Farm. The marine band comprises at least 6.23 m of dark grey mudstone interbedded with argillaceous limestones, and has yielded the ammonoid Reticuloceras dubium, conodonts cf. Declinognathodus lateralis and cf. Neognathodus bassleri, and fish debris. Up to 100 m of beds, provisionally assigned to the Kirkbeck Formation, are estimated to be present above the R. dubium Marine Band in the core of the syncline. There are small stream sections [SD 5051 5758]; [SD 5126 5786] of interbedded silty mudstones, siltstones and fine-grained sandstones on the southern limb of the syncline. The BGS Dam Head Borehole [SD 5065 5800], sited along the Conder valley in the core of the Quernmore Syncline, penetrated 56.18 m of these beds beneath the Eldroth Grit. The uppermost 22.70 m comprises mostly rhythmically layered, pale grey, fine-grained sandstone and darker grey siltstone beds which resemble some recently described tidal rhythmites (Williams, 1991). The layers range between 4 mm and 20 mm thick, and the beds are arranged in groups, typically a fraction of a metre thick, in which the layers are very uniform in thickness. The lower beds are grey, fine sandy siltstones with thin, mostly turbiditic sandstones becoming less numerous downwards. The sequence in the Dam Head Borehole was determined to be of Kinderscoutian age, based on palynological analyses of six core samples. The miospore species Crassispora kosankei is predominant throughout, and suggests assignment to the KV Zone of Owens et al. (1977).

Around Middleton [SD 425 588] and Overton [SD 436 580], the Kirkbeck Formation is concealed by drift, but is estimated to be 300 m thick, assuming an average southwards dip of 15° between the sandstone outcrop in the quarry alongside Downeyfield Road [SD 4365 5960] and exposures of the Eldroth Grit at Overton (see below). About 4 m of unnamed, pale reddish brown, medium-bedded, fine-grained sandstone exposed at Downeyfield Road Quarry is probably the same as that penetrated in the BGS Heaton Hall Borehole [SD 4398 5949]. There, the sandstone comprised 15.1 m of pale greyish white, thickly bedded, micaceous, fine-grained sandstone with thin siltstone and sandy siltstone interbeds and partings. This sandstone may lie roughly at the level of the Ellel Crag Sandstone farther east, although correlation with the Accerhill Sandstone cannot be discounted. In the borehole, a 1.9 m-thick, dark grey, pyritous mudstone, with the brachiopod Lingula sp. and conodonts was proved 30.8 m below the base of the sandstone in a 42.7 m siltstone-dominant sequence. The conodonts Declinognathodus noduliferus and D. inaequalis indicate an assemblage that is most likely to be in the Declinognathodus noduliferus Zone, extending from near the base of the Chokierian (H1a2) to the base of the Kinderscoutian Stage. Within this age range, between the Isohomoceras sp. nov. (H1b2) and Hudsonoceras proteum (H2a1) marine bands, there are unnamed marine horizons which characteristically lack a thick-shelled ammonoid phase in the Craven Basin (Moore, 1930). It is to this late Chokierian interval that the marine band in the Heaton Hall Borehole is tentatively referred. The adjacent strata have been mapped locally as 'Millstone Grit undivided', as it is not clear whether they should be included in the top of the Crossdale Mudstone or the lower part of the Kirkbeck Formation.

West of the conjectural Overton Fault [SD 43 58], there is no surface or subsurface information on an estimated 460 m of strata above the Silver Hills Sandstone Formation, which are therefore shown as undifferentiated Millstone Grit.

Eldroth Grit Formation

This predominantly sandstone unit was named by Bisat and Hudson (1941). Its type area is near Clapham, to the east of the present district. It was included in the lower part of the Bentham Grit Group by Moseley (1954) but is now mapped separately, following Arthurton et al. (1988) in the adjacent Settle district. It is of mid- to late Kinderscoutian age (R1b3 to R1c), equivalent to the Kinderscout Grit of the Clitheroe district (Earp et al., 1961) and regions of the Pennines farther south.

The base of the Eldroth Grit is taken at the base of a predominantly sandstone sequence overlying siltstones. The bulk of the formation consists of trough cross-bedded, feldspathic, medium- to coarse-grained sandstones deposited in a braided, fluvial delta-top channel system. The sandstones are generally thickly bedded with upwards-fining units, some with basal lag deposits of very coarse sand to granule-grade quartz clasts. Ganister palaeosols occur locally near the top of the formation. Trough orientations measured at exposures near Bentham and at Near Naze, Heysham Harbour, indicate palaeocurrents from between the north-east and north-north-east. The top of the formation is taken at the top of the highest sandstone, commonly containing rootlets, overlain by mudstones or siltstones.

The thickness is estimated at 30 m in the Bentham area, 50 m around Overton, up to about 41 m in boreholes on the Heysham power stations site [SD 40 60], 51.68 m in the BGS Dam Head Borehole [SD 5065 5800] in the Conder valley, and 60 m in the adjacent Settle district. Apart from the Dam Head Borehole, the main sections are shown in (Figure 30).

The best exposures in the Bentham area are in the bed of the River Wenning, south-west of High Bentham [SD 6555 6910]; [SD 6573 6907]; [SD 6615 6895]. There, the sandstones are commonly stained red-brown, indicating the proximity of the former cover of Permo-Triassic strata.

The full succession is well documented in borehole cores from the Heysham area ((Figure 31)). The lower 18.5 m or so are an alternation of cross-bedded, medium-grained sandstones with few burrows and ripple-laminated siltstones with horizontal burrows of the Teichichnus type. The middle 14 m of the formation are largely cross-bedded, medium-grained sandstones with some convoluted lamination caused by soft-sediment deformation, and the top 8.5 m are thinly bedded alternations of upward-fining, ripple-laminated, fine- to medium-grained sandstones with a palaeosol.

A complete sequence of the Eldroth Grit was also penetrated between depths of 29.20 m and 80.88 m in the Dam Head Borehole, in the core of the Quernmore Syncline ((Figure 12)). Most of the formation below 41.51 m consists of several, metre-thick, upwards-fining channel units of red to pink, coarse-grained to granule grade, cross-bedded sandstones, though there are some thin beds of mudstone and siltstone. Several palaeosol levels with rootlet casts occur in the thinner-bedded mudstones and fine- to medium-grained sandstones in the upper part of the formation.

A well-exposed coastal section of the Eldroth Grit can be examined at the headland of Near Naze [SD 4035 6063], just north of Heysham Harbour and now partly covered by the harbour works. The section comprises about 14 m of partly reddened, coarse- to very coarse-grained, trough cross-bedded, arkosic sandstone with lenses of quartz granules; trough alignment indicates a palaeocurrent directed towards the south-west. A sandstone, only tentatively identified as this formation because of lack of biostratigraphical evidence, is exposed at several places in the Overton area to the south. Up to 14.2 m are exposed in disused quarries [SD 4334 5790]; [SD 4330 5785]; [SD 4424 5754] at Overton, about 3 m on the foreshore [SD 4435 5755] south of Overton, and 1.4 m on the foreshore [SD 4366 5675] at Bazil Point.

Millstone Grit Group between the Eldroth Grit Formation and Heysham Harbour Formation Sandstone Formation

These strata are 15 m thick in the River Greta section [SD 6337 7187] to [SD 6345 7202] ((Figure 30), section 6), just north of the Lancaster district, 8 m thick in the Seat Hall Borehole near Low Bentham ((Figure 30), section 5), and about 43 m thick in boreholes at Heysham where cores are cut by small faults (Figure 31). They consist mainly of siltstones with fine-grained sandstone laminae, mudstones and sporadic mudstone seatearths, interpreted as interdistributary bay deposits.

Two thin mudstones, both containing Lingula sp. and directly above a palaeosol in the basal 4 m of this sequence in Borehole 45 NW/229 at Heysham power stations (Figure 31), are probably the same marine band repeated by a small fault. Other fossils associated with this level in nearby boreholes include sponges, the brachiopod Productus sp., and a ribbed pectinoid bivalve. In the BGS Dam Head Borehole [SD 5065 5800] (Figure 12), 5.15 m of mostly weathered grey mudstone and siltstone, with the bellerophontid gastropod cf. Euphemites sp. and the nuculoid bivalve Anthraconeilo sp. in the uppermost 0.9 m, were penetrated between till and the Eldroth Grit. This marine band was not identified in the Seat Hall Borehole ((Figure 30), section 5), but crops out directly above the Eldroth Grit in the River Greta section [SD 6337 7187], where it yielded the brachiopods Lingula mytilloides, cf. Ambocoelia sp., cf. Derbyia, cf. Lissochonetes, productoid debris, cf. Rugosochonetes and Schizophoria sp., bryozoan debris and the worm tube Serpuloides stubblefieldi. The band is probably equivalent to one of the Reticuloceras reticulatum marine bands (R1c1 to Rlc3).

Reticuloceras coreticulatum Marine Band (R1c4)

This marine band was penetrated about 6 m above the Eldroth Grit in several site investigation boreholes at Heysham power stations (e.g. Borehole (SD45NW/229), (Figure 31)), where it comprises about 4 m of grey mudstone with a composite fauna of: the brachiopods Lingula mytilloides and Productus carbonarius; the worm tube Serpuloides stubblefieldi; the bivalves Caneyella squamula, Dunbarella rhythmica and Posidonia obliquata; the ?scaphopod Coleolus sp.; orthocone nautiloids; a stroboceratid? coiled nautiloid; the ammonoids anthracoceratid or dimorphoceratid indet., Homoceratoides divaricatus, R. coreticulatum and R. reticulatum; and indeterminate cypridinid ostracods. It was also identified in the Seat Hall Borehole, and is probably represented by 0.3 m of dark grey mudstone with the brachiopod Lingula sp. and the bivalve Anthraconeilo sp. in exposures in the River Greta section [SD 6342 7193] (Figure 30). The Butterly Marine Band, recently established between the R. coreticulatum and B. gracilis marine bands (Aitkenhead and Riley, 1996), is presumed to have been removed by erosion before deposition of the Heysham Harbour Sandstone.

Heysham Harbour Sandstone Formation

The Heysham Harbour Sandstone Formation is described for the first time in this account. It is defined from well-documented borehole evidence and surface exposures in the Heysham area ((Figure 30), sections 1 and 2, (Figure 31)). There is no surface evidence in the north-eastern crop, though it is probably represented by one of the thin sandstones between depths of 145 m and 155 m in the Seat Hall Borehole of the Bentham area. It is also probably equivalent to the Upper Bentham Grit described in the River Greta section (Ford, 1954), and is equivalent to part of the 'Kinderscout Grit Group' of the Preston district (Price et al., 1963) and the Upper Kinderscout Grit in the Clitheroe and Nelson district (Earp et al., 1961).

The base of the Heysham Harbour Sandstone is taken at the base of a predominantly sandstone sequence overlying predominant siltstones. The formation consists mainly of thickly laminated to medium-bedded, grey, medium- to coarse-grained sandstones, commonly with ganisteroid tops. Trough cross-bedded, medium- to coarse-grained sandstones occur in the lower part of the formation. The upper 5 m of the formation are predominantly fine-grained sandstones with ripple cross-lamination, bioturbation, soft-sediment deformation structures and angular mudstone rip-up clasts, and include thin siltstone beds. The succession is interpreted as a sequence of distributary channel deposits. The top of the formation is defined at the top of the highest sandstone, commonly with rootlets, which is overlain by siltstones or mudstones including the Bilinguites gracilis Marine Band. The formation is of late Kinderscoutian (R1c4) age.

The formation crops out at several localities in the area around Heysham power stations. It was formerly exposed on Far Naze [SD 403 604] and in rock scars south of this headland, but these exposures are now covered by the harbour works, except for a partial section through 5 m of strata in the east wall of Heysham Harbour [SD 4033 6028]. The best section was in the road cutting and disused quarry on the approach to Heysham power stations [SD 4050 5998] to [SD 4055 6010], where a full thickness of 33.3 m was formerly exposed but, due to degradation and vegetation growth, only the lowest 20 m are now visible. Boreholes at Heysham power stations penetrated a complete sequence of about 15 m of the sandstone ((Figure 31)). The core of Heysham power stations borehole (SD45NW/229) [SD 4045 5989] between depths of 37.75 m and 23.20 in is designated as the type section.

The exposures in the Heysham Harbour area contain radioactive nodules, 10 to 90 mm across, pellets and irregular impregnations, enriched in hydrocarbon, scattered throughout the sandstones (Harrison, 1970). The nodules have a concentric structure of alternating hydrocarbon-rich and hydrocarbon-free sandstone. The origin of the hydrocarbon and the time and method of its emplacement, are uncertain, but the localised occurrence and absence of feeders to the nodules suggests progressive diagenesis of pockets of organic-rich debris.

Millstone Grit Group above the Heysham Harbour Sandstone Formation

The Millstone Grit Group above the Heysham Harbour Sandstone crops out in a narrow tract north of High Bentham, and in a steeply inclined and much faulted zone adjacent to the Ocean Edge Fault at Heysham. The beds are poorly known in the district, and sections (Figure 30) occur only in boreholes at the Heysham power stations and nearby exposures, and in the Seat Hall Borehole and two small exposures in the Bentham area. At all these localities, the highest Millstone Grit strata are not seen. The beds are also well exposed along the River Greta [SD 6345 7204] to [SD 6398 7191], less than 1 km north of the Lancaster district, where the section continues up into the overlying Lower Coal Measures.

The strata comprise siltstones and mudstones, interbedded with prominent beds of cross-bedded, fine-to coarse-grained sandstone with palaeosol horizons. Several marine bands, notably the B. gracilis Marine Band (R2a1) and the C. cancellatum Marine Band (G1a1), are well developed and have greatly facilitated correlation of the few isolated sections.

The total sequence is 155 m thick in the River Greta section, of which the lowest 82 m represent strata up to the base of the C. cancellatum Marine Band ((Figure 30), section 6). The latter beds thicken to about 137 m in the Seat Hall Borehole ((Figure 30), section 5). The equivalent thicknesses around Heysham are uncertain due to lack of exposure in the upper part of the sequence ((Figure 30), sections 1 and 2).

Bilinguites gracilis Marine Band (R2a1) and adjacent strata

The Bilinguites gracilis Marine Band is a widespread and readily identifiable horizon in the district, having been recorded at outcrop and in boreholes both in the Heysham power stations and Bentham areas (Figure 30). It occurs at or near the base of a variable sequence, predominantly of siltstone with thin sandstones and numerous bioturbated levels, between the top of the Heysham Harbour Sandstone and base of the Greta Grits. This sequence is up to 30 m thick in the Heysham power stations boreholes (Figure 31). The marine band comprises grey shaly mudstone, which in the Heysham area is reddened by proximity to a former Permo-Triassic cover. Regionally, it is 1 m to 2 m thick, but in the Seat Hall Borehole, about 17 m of mudstones have yielded a shelly marine fauna that includes: agglutinating foraminifera; the worm tube Serpuloides stubblefieldi; the brachiopods Lingula mytilloides, Orbiculoidea bulla, O. cincta, O. nitida, Productus carbonarius, Rugosochonetes sp. and Tornquistia cf. polita; the bivalves Aviculopecten sp., Caneyella rugata, Dunbarella speciosa and myalinid indet.; and the ammonoid Bilinguites gracilis. This suggests that deposition in the Bentham area occurred in a relatively marginal basin setting compared to the area to the north where, in the River Greta section [SD 6345 7204], the marine band is only 1.5 m thick and is less shelly, with: the brachiopods Lingula sp., Orbiculoidea sp., Crurithyris sp, and Productus carbonarius; the bivalves Caneyella sp. and Dunbarella sp.; and the ammonoid Bilinguites gracilis. In the Bentham area, the marine band was also recorded about 1 km east of High Bentham in the Fowgill Beck Valley (Ford, 1954), probably close to a small exposure [SD 6766 6916] where 1 m of unfossiliferous, rather fissile mudstone with small ironstone nodules is currently exposed. In the north bank of the River Wenning [SD 6578 6917], an exposure of about 1.5 m of unfossiliferous grey muddy siltstone may be close to the locality from which B. gracilis was recovered by Bisat and Hudson (1941).

The general thickness in the Heysham area is 1.8 m. A complete section is provided by the road cutting on the approach to Heysham Harbour [SD 4049 5994] and was penetrated in several nearby site investigation boreholes (e.g. (SD45NW/229) and (SD45NW/230), (Figure 31)). The composite fauna from the section and the boreholes includes: the brachiopods Lingula mytilloides, Orbiculoidea sp. and Productus sp.; bellerophontid gastropods including Euphemites urei; the bivalves cf. Anthraconeilo sp., Caneyella rugata, Dunbarella speciosa, cf. Nuculopsis sp. and cf. Phestia sp.; the nautiloid Huanghoceras sp.; the ammonoids anthracoceratid or dimorphoceratid indet., Anthracoceratites sp. and Bilinguites gracilis; and fish debris. In borehole (SD45NW/258) [SD 4069 5970], an orthotetoid brachiopod was recovered at a depth of 36.56 m, from a claystone 16.88 m above the base of the B. gracilis Marine Band. This level may correlate with the shelly upper part of the relatively thick marine band recorded in the Seat Hall Borehole of the Bentham area.

Greta Grits (R2a-R2b)

The Greta Grits occur in the north-eastern part of the district, where they underlie the village of High Bentham. Based on exposures in the River Greta valley, the beds were classified as Greta Grit Group by Ford (1954). Both there and in the Seat Hall Borehole he identified two main sandstones, the lower of which he named the Greta Grit. Three principal beds of sandstone ((Figure 30), section 6) are now distinguished in both these sections. However, these sandstones and the intervening mudstones and siltstones, known collectively and informally as the Greta Grits, are not differentiated on the geological map. This is because of the sparsity of exposure, due to drift cover, and the absence of any intervening Marsdenian marine bands which are developed south of the present district. The Greta Grits probably correlate with the successive Revidge, Fletcher Bank and possibly Helmshore grits of central Lancashire.

The Greta Grits sequence is 88.7 m thick in the Seat Hall Borehole, and about 60 m thick in the River Greta section. In this general area, it consists largely of trough cross-bedded, feldspathic, medium- to coarse-grained sandstones, interpreted as fluviodeltaic deposits including mouth bar sediments. Locally, they are pebbly, with granules up to 2 mm in diameter in the lower part, and there are sporadic ganister horizons. The sandstones at outcrop are commonly stained dark orange to red-brown by their former proximity to Permo-Triassic strata, whereas the lowest 2.8 m of sandstone in the Seat Hall Borehole were recorded on the log as 'green tinted'. Interbeds of bioturbated mudstone and silty mudstone, less than 5 m thick, occur in the Seat Hall Borehole and River Greta section. They have not yielded faunas, but may mark Marsdenian marine events in more central parts of the Central Pennines Basin to the south of the district. The best exposures of the Greta Grits in this area are in Lairgill Beck [SD 6704 6917], where at least 6 m in the middle part of the sequence are exposed, and in former sandstone quarries [SD 6844 6964] north of Greystonegill.

The Greta Grits sequence is also known from boreholes and exposures in the Heysham area. The sandstones are dominantly fine to medium grained, and the sequence includes an important Bilinguites bilinguis Marine Band (R2b1–3), though it is not clear which one. The lowest 20.3 m of beds above the B. gracilis Marine Band, correlated with the lower part of the Greta Grits in the Bentham area, are exposed on the east side of the approach road to Heysham Harbour [SD 4049 5994] to [SD 4047 5988], and comprise fine-grained sandstones and siltstones. Limulid burrowing traces and bilobate burrows of Isopodichnus? sp. were found in a ripple-marked sandstone [SD 4047 5988]. A similar sequence was penetrated in nearby site investigation boreholes (SD45NW/230) (Figure 31) and 258. Higher strata, including a B. bilinguis Marine Band, occur in a well-exposed, 25.4 m-thick sequence in the sea cliffs west of Middleton Towers [SD 4094 5866] to [SD 4102 5847] ((Figure 30), section 1). Fine-grained sandstones and siltstones predominate, and ganister palaeosols occur both below and above the B. bilinguis Marine Band (R21,1–3). Here, the marine band consists of about 1.2 m of purplish grey mudstone, with the horny brachiopod Lingula mytilloides, bivalves Phestia sp. and Caneyella cf. rugata, and the ammonoids Anthracoceratites sp. juv. and Bilinguites sp. juv. (ex gr. bilinguis). A prominent, upward-coarsening sequence overlies the marine band in the sea cliffs. It consists of 11 m of grey, fine- to coarse-grained sandstones, bioturbated in places, with hummocky cross-stratification and two ganisteroid beds. An estimated 35 m of beds above the higher ganister are cut out by faults in the Middleton area. The same B. bilinguis Marine Band was probably penetrated between depths of 24.16 m and 26.75 m in borehole (SD45NW/133) [SD 4033 5966] at the Heysham power stations.

A sandstone exposed on the foreshore at Bazil Point [SD 4370 5680], to the west of the conjectural Bazil Fault [SD 4374 5678], is tentatively interpreted as being between the Bilinguites gracilis (R2a1) and Cancelloceras cancellatum (G1al) marine bands, and may correlate with sandstones in the Middleton Towers section ((Figure 30), section 1). About 7.5 m of cross-bedded, very fine- to coarse-grained sandstones are exposed in a generally upward-fining sequence. Trough alignment suggests a palaeocurrent from the north to north-west. A ganisteroid sandstone occurs in the middle of the sequence, and the highest bed, seen in the cliff, has a well-developed ganisteroid top with stigmaria. Within the base of the till exposed in the cliff [SD 4359 5685] a short distance to the west, poorly fossiliferous, dark grey mudstone fragments may be derived from a marine band above the ganister.

Strata between the Greta Grits and the Cancelloceras cancellatum Marine Band

Above the Greta Grits, the Seat Hall Borehole ((Figure 30), section 5) proved about 30 m of mainly 'shale', which Ford (1954) classified as 'Rough Rock Shales'. They contain a marine band and one or several nonmarine bivalve horizons. The marine band, between depths of 36.58 m and 44.20 m, contains the horny brachiopod Orbiculoidea nitida, the nuculoid bivalves Anthraconeilo sp. and cf. Nuculopsis sp., orthocone nautiloid indet. and fish debris, and is most likely to be correlated with the Bilinguites superbilinguis Marine Band (R2c1) because of its position below the C. cancellatum Marine Band (G1al). This fauna indicates a significant supply of terrigenous clastic sediment and variable salinity, conditions unfavourable for either a shelly fauna, seen in other mid- to late Namurian marine bands in this area, or the hemipelagic ammonoid–bivalve facies present to the south in central Lancashire.

A nonmarine fauna, collected between depths 17.07 and 30.48 m in the Seat Hall Borehole, may be from one or more levels in the mudstone sequence (Figure 30). The fauna includes the bivalves Anthraconaia angulosa, A. cf. lenisulcata and Carbonicola sp., the worm Spirorbis sp., and the ostracod Geisina arcuata, and constitutes a relatively diverse nonmarine assemblage of probable late Marsdenian age. The fauna is consistent with deposition in a relatively aerobic, terrigenous clastic-influenced, lacustrine environment, the bivalves, particularly the A. angulosa, being relatively deep burrowers. The overlying, unnamed sandstone is equivalent to the Holcombe Brook Grit of central Lancashire (for example Wright et al., 1927).

Strata represented in the Seat Hall Borehole are to be seen at outcrop only along Ellergill Beck [SD 6586 6973] and along a tributary [SD 6573 6996]; [SD 6573 6989], where no marine bands are exposed. Equivalent strata in the River Greta section are shown in (Figure 30). The same beds are not exposed in the Heysham area, though boreholes ((Figure 30), section 1) indicate that the uppermost 17 in of equivalent strata comprise interbedded fine-grained sandstones and siltstones overlain by mudstones.

Cancelloceras cancellatum Marine Band (G1a1)

This widespread and easily recognised marine band has been identified in the River Greta section, in the Seat Hall Borehole, and in several boreholes at Heysham power stations ((SD45NW/87) [SD 4026 5994], SD 45 NAV/132/28 [SD 4031 5956] and (SD45NW/136) [SD 4032 5963]). It is generally about 1 m thick and comprises dark grey mudstone with phosphate nodules. The fauna from the Heysham boreholes includes: the brachiopod Lingula mytilloides; the bivalves Caneyella multirugata and Dunbarella sp.; the ammonoids Agastrioceras carinatum, Anthracoceratites sp., Bilinguites superbilinguis, Cancelloceras cf. branneroides, C. cancellatum, C. crencellatum and Homoceratoides aff. divaricatus; and fish debris. In the River Greta section, where there is an impersistent basal nodular limestone up to 0.1 m thick, the band yielded Lingula sp., orthotetoid indet., Productus carbonarius, cf. Agastrioceras sp.,Cancelloceras crencellatum and C. cf. cancellatum. In the Seat Hall Borehole, where it was incorrectly assigned to the C. cumbriense Marine Band by Ford (1954), it has yielded the brachiopod Productus carbonarius, and the ammonoids C. branneroides and C. cancellatum. C. branneroides is typically associated with a shelly fauna, indicative of deposition in a relatively nearshore marine setting, within the hemipelagic facies.

Strata between the Cancelloceras cancellatum and Subcrenatum marine bands

These beds are not exposed within the district, but crop out beneath drift deposits in the north-east crop, north of Bentham, and at Heysham, in a narrow tract to the east of the Ocean Edge Fault. The whole sequence is well exposed, however, in the Greta section, to the north of the district ((Figure 30), section 6), where it comprises 73 m of mainly siltstones and mudstones with comminuted plant debris, but includes the Rough Rock.

The lowest beds were penetrated in boreholes at Heysham, for example borehole (SD45NW/132/6) [SD 4025 5959], and consist of about 38 m of mudstone with thin siltstones and fine-grained sandstones. Nonmarine bivalves in this interval include Anthraconaia sp. in the lower beds and Carbonicola cf. lenicurvata, Naiadites sp. and Anthraconaia sp. in the upper beds. Overlying these strata are about 20 m of reddish brown mudstone with thin beds of fine-grained sandstone. Higher strata of the Millstone Grit Group were not proved in the Lancaster district.

The Cancelloceras cumbriense Marine Band (G1b1), approximately 1 m of dark grey fossiliferous mudstone, occurs about 31 m above the C. cancellatum Marine Band in the Greta section (Figure 30), in the adjoining part of the Kirkby Lonsdale district. It has yielded a fauna that includes the brachiopod Lingula sp., the bivalve Caneyella multirugata, and the ammonoids anthracoceratids indet., Cancelloceras cf. cumbriense and Homoceratoides sp. It is overlain in this section by the Rough Rock, a widespread, typically coarse-grained, fluviodeltaic, sheet-like sandstone (Bristow, 1988) that has long been identified as the highest grit of the Millstone Grit Group (see for example Stephens et al., 1953). The sandstone in the River Greta section comprises 8 m of reddened, medium- to coarse-grained, cross-bedded sandstone with plant fragments. Ganisteroid beds and pyrite nodules occur in the higher beds.

Chapter 5 Westphalian: Lower Coal Measures

The Lancaster district covers the southern margin of the Ingleton Coalfield, an outlier of Lower Coal Measures resting conformably on the Millstone Grit Group where two main seams were formerly mined (Ford, 1954). The succession, well known outside the district from exposures in the River Greta valley and exploratory boreholes and shaft sections, was informally subdivided by Ford in 1954. The lowest approximately 210 m of Coal Measures strata below the two main coal seams crop out in the north-east corner of the district. They are poorly exposed and thus undivided; the only exposures within the Lancaster district occur along the Aspland Beck valley [SD 6857 7080] to [SD 6765 7128].

The Subcrenatum Marine Band, defining the base of the Westphalian, is exposed in the River Greta valley [SD 6436 7204], 1 km north of the present district, where a fauna including the bivalve Dunbarella cf. papyracea, the ammonoid Gastrioceras cf. subcrenatum and fish debris was collected. It may also occur east of this district in the exposure of silty mudstone with plant debris and Lingula sp. directly overlying the Rough Rock in the Aspland Beck valley [SD 6938 7077], an horizon interpreted by Ford (1954, p.237) as being above the Greta Grit. The lowest 200 m to 300 m of Lower Coal Measures are well exposed just north of the district in the River Greta valley, south and east of Burton-in-Lonsdale, and have been proved in boreholes in the Ingleton Coalfield, the nearest being the Nutstile Beck Borehole (SD67SE/5) [SD 6933 7140]. They consist of an interbedded sequence of red, purple-grey and pale grey mudstones, siltstones and fine-grained micaceous sandstones with several nonmarine bivalve horizons. Ford (1954) included the Mill Hill Shales, the Parks Wood Sandstones and the Burton Bridge Sandstones in this succession. There is insufficient evidence to map these units in the present district.

The lowest Lower Coal Measures strata exposed within the district, estimated to lie roughly 80 m above the base of the Westphalian, are approximately 85 m of mainly micaceous, fine- to medium-grained sandstones, some stained red-purple. They occur in a series of small sections along the Aspland Beck valley [SD 6857 7080] to [SD 6778 7097]. At a locality [SD 6774 7092] corresponding to a strati-graphical position a short distance above these sand stones, Mr R H Tiddeman recorded shale with ironstone and Anthracosia' during the primary survey. This is probably the same faunal band directly overlying the Burton Bridge Sandstones from which Ford (1954, p.242 and fig. 6) recorded the nonmarine bivalve Carbonicola aff. pseudorobusta and variants and fish, indicating a level within the Carbonicola pseudorobusta Zone of mid Langsettian age. Ford also noted Anthraconauta minima (Hind) [SD 677 710], now attributed to Curvirimula, at a slightly higher level.

A 0.12 m coal, underlain by a seatearth and silty mudstone, is exposed along Aspland Beck [SD 6765 7130], just north of the present district. It is interpreted to be the Blaeberry Coal (Ford, 1954), estimated to lie 204 m above the Subcrenatum Marine Band.

From the general disposition of the highest Millstone Grit at Heysham, it is very likely that Lower Coal Measures, with or without coals, are present directly beneath the cover of Permo-Triassic strata on the western, down-thrown, side of the Ocean Edge Fault, both onshore and offshore (see (Figure 36) for sections A–B, C–D)." data-name="images/P988531.jpg">(Figure 33)).

Carboniferous strata were proved in several site investigation boreholes for the Heysham power stations. The thickest known succession is in borehole SD 45 NW 132/4 [SD 4022 5948] between depths of 59.60 m and 100.70 m; however, interpretation was made difficult because the cores, which were incomplete, showed the beds to be steeply dipping, badly shattered and full of listric surfaces. Corrected for dip, approximately 30 m of strata are represented. The lowest 13 m consist of reddened, fine-grained, micaceous sandstones with parallel bedding and current ripple-lamination, and with some interbedded mudstones. These are overlain by 17 m of reddish brown silty mudstones with rare Anthraconaia sp., for example in the above mentioned borehole at a depth of 63.65 m. This nonmarine bivalve is of little stratigraphical use without specific determination, as it ranges from the Marsdenian Stage to the Stephanian Series. No marine bands are known and any spores which may have been present have been oxidised by Permo-Triassic weathering so that the age of the beds cannot be determined, but it is likely that they lie within the highest Millstone Grit or the Lower Coal Measures.

Chapter 6 Permo-Triassic

The collision of continental crustal plates that produced the Hercynian (or Variscan) orogeny in latest Carboniferous and earliest Permian times eventually resulted in the removal by erosion of large thicknesses of Carboniferous rocks. This episode of great earth movement is represented by a major unconformity at the base of the Permian sequence. In addition, the exposed Carboniferous rocks were subjected to oxidation and reddening in the prevailing arid climate (see below and (Figure 32)), a process which was probably continued by groundwater circulation beneath the subsequent deposits of primary red sediments.

Rocks of Permian and Triassic age are known, from boreholes and a few coastal exposures, to crop out in the westernmost part of the district, where they are largely overlain by a thick and extensive cover of drift. Site investigation boreholes at the Heysham power stations indicate the presence there of an attenuated or 'feather edge' equivalent of the St Bees sequence of Cumbria (see below). In the Morecambe area to the north-east, the probable presence of a growth-faulted graben with an extended sequence that includes the Collyhurst Sandstone, is suggested by the Bouguer gravity anomaly map (Figure 40) and sparse borehole data.

Classification

There is evidence for the presence of subdrift outcrops of Permian and Triassic rocks in the western part of the district, both on land and offshore. However, the formations identified in borehole sections cannot all be delineated on geological maps. Rather than classify the outcrops using the chronostratigraphical term 'Permian and Triassic undivided', two new lithostratigraphical 'group' names are formally introduced for the Permian sequence of the Lancashire–Cumbria region, namely the Appleby Group and the Cumbrian Coast Group ((Table 6) and (Figure 32)). The former includes rocks equivalent to the Collyhurst Sandstone of Lancashire, and the Penrith Sandstone and Brockram of the Vale of Eden. The latter group includes equivalents of the St Bees Evaporites and St Bees Shales formations of Cumbria, and the Manchester Marls of Lancashire (see for example Smith et al., 1974, table III, and Arthurton et al., 1978, figs. 65 and 66), and is overlain conformably by the undivided Sherwood Sandstone Group, formerly known as the 'Bunter Sandstone' (see Warrington et al., 1980). In the absence of positive palynological evidence from this district (G Warrington, personal communication), the chronostratigraphical subdivision of the sequence ((Table 6) and (Figure 32)) has had to be inferred from regionally established subdivisions.

There is evidence that strata belonging to the Mercia Mudstone Group crop out just beyond the western boundary of the district, on the downthrown western side of the inferred projected position of the Ocean Edge Fault. Here [SD 38943 69178], Morecambe Bay Barrage Site Investigation Borehole A3 proved 3.55 m of reddish brown silty mudstone with gypsum veins, at a depth of 47.75 m below drift deposits. Miospores of late Scythian or early Anisian age have been recovered from the mudstone by Dr G Warrington (unpublished internal report PDL 70/76, BGS Biostratigraphy and Sedimentology Group).

Appleby Group (new name)

The Appleby Group is here proposed as a new name for the lower Permian rocks of north-west England and the eastern Irish Sea, with its type section in the Penrith Sandstone Formation at Hilton Beck [NY 7151 2037] to [NY 7195 2055] near Appleby, Cumbria (Burgess and Holliday, 1979, p.70). The group consists predominantly of red aeolian and fluviatile sandstones and conglomerates or 'breccias ('Brockram'), interbedded in varying proportions. It rests with strong unconformity on Carboniferous or older rocks and is overlain conformably by interbedded carbonates, evaporites and argillaceous rocks of the Cumbrian Coast Group (see below). The group locally comprises the Penrith Sandstone Formation and 'Brockram' in Cumbria and the coeval Collyhurst Sandstone Formation in Lancashire.

Collyhurst Sandstone Formation

The Collyhurst Sandstone is present locally in Lancashire and the East Irish Sea Basin at or near the base of the Permian sequence (Smith et al., 1974; Jackson and Mulholland, 1993, fig. 2). Its localised distribution probably reflects the relief of the early Permian land surface, caused mainly by penecontemporaneous rifting following the Variscan folding. In the type area, Collyhurst in Manchester, the formation is known mainly from boreholes, and descriptions have been provided by several authors, e.g. Hickling (1918), Tonks et al. (1931), and Poole and Whiteman (1955).

In the present district, rocks of probable early Permian age are thought to consist of an outcrop of Collyhurst Sandstone concealed by thick drift, forming the north-western and southern parts of a basin east of Morecambe (Figure 32). The presence of this basin, here named the Torrisholme Basin, is indicated by a Bouguer gravity anomaly (p.143) and by the Belmount Farm Borehole (SD46NE/23) [SD 4669 6511] which proved strata interpreted as belonging to the St Bees Shales (see below). Only two boreholes, Lune Crossing No.6 ((SD46SW/283) [SD 4483 6152]), and White Lund Farm ((SD46SW/498) [SD 4442 6227]), penetrated sandstone tentatively assigned to the Collyhurst Sandstone, the latter proving 20 m of red, fine- to medium-grained, well-sorted, laminated sandstone characterised by the presence of conspicuous rounded to well-rounded 'millet seed' quartz grains. A thin section (E67172) of one sandstone sample from a depth of 12 m in the White Lund Farm Borehole shows it to be a quartz arenite, with dominant quartz in fine, angular and subangular grains, plus some sub-rounded to rounded grains of medium sand size. There are also minor amounts of K-feldspar, albite, and rounded opaque grains. The fabric (Plate 4) generally has an open texture and high (approximately 30 per cent) porosity, probably of secondary origin, mostly after cement dissolution. The formation has not been found in the site investigation boreholes in the area of the Heysham power stations [SD 401 594] where beds assigned to the St Bees Evaporites appear to lie unconformably on Carboniferous strata.

Cumbrian Coast Group (new name)

The Cumbrian Coast Group is proposed as a new name for the predominantly marine, upper Permian sequence of interbedded carbonates, evaporites and argillaceous rocks in north-west England and the east and north Irish Sea. The type section, 36.6 m thick, is on the Cumbrian Coast at Saltom Bay [NX 9584 1592] to [NX 9543 1551] described by Smith (1924, p.291). A nearby borehole, (NX91SE/190) [NX 9488 1492], provides a complete and detailed 82.7 m representative section (Arthurton and Hemingway, 1972), comprising the component St Bees Evaporites and St Bees Shales formations. The lower boundary on the Appleby Group is usually sharp but the upper boundary with the St Bees Sandstone (Sherwood Sandstone Group) is gradational, taken at the point in the sequence where sandstone becomes predominant.

St Bees Evaporites Formation

The St Bees Evaporites are known to occur at depth around the Heysham power stations and foreshore of the Lune estuary (Figure 32) and (Figure 36) for sections A–B, C–D)." data-name="images/P988531.jpg">(Figure 33). The formation also probably crops out beneath drift east of Morecambe in the Torrisholme Basin. However, neither here, nor in the subdrift outcrops around the Lune Estuary, is there sufficient evidence to warrant subdividing the conjectural outcrop of the Cumbrian Coast Group, by attempting to delineate its two constituent formations on the geological map.

The St Bees Evaporites sequence was first defined as a formation, with a number of dolomite, siltstone and anhydrite members, by Arthurton and Hemingway (1972). Its type area is around St Bees Head on the west coast of Cumbria. A similar sequence occurs in the Furness area (Dunham and Rose, 1949; Rose and Dunham, 1977). There, part of the succession includes three members, defined by Smith et al. (1974, p.39), which are, in ascending order: the Gleaston Dolomite, the Haverigg Haws Anhydrite and the Roosecote Anhydrite. These are correlated (Smith et al., 1974, table III) with the Sandwith and Saltom dolomites, the Sandwith Anhydrite and the Fleswick Anhydrite, respectively, of the St Bees area.

The sedimentological interpretation of the west Cumbria rock succession given by Arthurton and Hemingway (1972) is taken to be generally applicable to both the Furness district and the present area, where poor core recovery and preservation precluded detailed description and analysis. In late Permian times, much of the region between the Isle of Man and the coastal areas of west and south Cumbria and Lancashire was occupied by an isolated arm of the sea, known as the 'Bakevellia Sea' (Smith et al., 1974; Smith and Taylor, 1992), in which sea level fluctuated in a cyclical manner. Arthurton and Hemingway (1972) recognised three sedimentary cycles, each with an early marine transgressive phase represented by laminated siltstones or shelly dolomites, and culminating in a later regressive phase of evaporite deposition. The latter is represented successively by the Saltom Dolomite containing anhydrite pseudomorphs, the Sandwith Anhydrite and the Fleswick Anhydrite. Complete cycles are thought to reflect a change in environment from shallow marine to supratidal sabkha during the duration of the cycle.

Six site investigation boreholes drilled at the Heysham power stations proved thicknesses for the formation ranging from 11.2 m to 18.7 m (Figure 36) for sections A–B, C–D)." data-name="images/P988531.jpg">(Figure 33). Apart from a few spot checks, no detailed mineralogical or sedimentological study was made. Four of these boreholes, (SD45NW/132/4) [SD 4022 5948], (SD45NW/132/20) [SD 4016 5946], (SD45NW/132/22) [SD 4020 5947] and (SD45NW/132/39) [SD 4019 5947], correlated by Wilson and Crofts (1992, fig.2), show two evaporite members. These members are correlated with the Haverigg Haws Anhydrite and the Roosecote Anhydrite, and are separated by a sequence of mainly red-brown mudstone. One, (SD45NW132/40) [SD 4019 5952], penetrated an 11.2 m sequence, consisting mainly of gypsum and anhydrite with minor interbedded dolomite and red mudstone. The sixth borehole, (SD45NW/132/51) [SD 4022 5942], proved a mixed succession of red mudstone with thin sandstones, gypsum and dolomite, all brecciated in part, separating evaporite units above and below.

The complete reference section for the formation occurs outside the Lancaster district, between depths of 125.03 m and 157.28 m in the BGS Roosecote Borehole (SD26NW/19) [SD 2304 6866] of the Barrow-in-Furness district, some 19 km to the west-north-west (Rose and Dunham, 1977, p.134). Neither the basal 'Grey Beds' at Roosecote, nor the underlying 0.85 m breccia (Rose and Dunham, 1977, p.134), are present in Heysham boreholes, where the formation appears to rest directly on deeply reddened Carboniferous beds. The only borehole at Heysham proving a possible correlative of the overlying Gleaston Dolomite ('Magnesian Limestone': Rose and Dunham, 1977, p.134) at Roosecote, is (SD45NW/132/39), in which this member is 1.18 m thick compared with 4.01 m at Roosecote. The rock is brecciated in part and in places shows a cryptalgal interlamination of dolomite and gypsum, suggestive of an intertidal flat depositional environment. In the other Heysham boreholes, the likely correlative of the Haverigg Haws Anhydrite, present between depths of 137.60 m and 143.75 m at Roosecote, forms the basal member of the formation resting directly on Carboniferous beds. The thickness of the member around Heysham ranges from 3.5 m to 6.48 m, compared with 6.15 m at Roosecote. Both anhydrite and gypsum are present in varying proportions. The overlying clastic sequence consists mainly of red to red-brown silty mudstone, and ranges in thickness from 0.42 m to 4.1 m in the Heysham boreholes. This compares with 2.1 m of mainly red and brown mudstone and siltstone at Roosecote, where these beds are overlain by a 0.43 m porcellanous dolomite known informally as the Roosecote Dolomite. The latter probably correlates with a unit of brecciated dolomite with gypsum laminae, about 0.6 m thick at a depth of 67.3 m, in borehole (SD45NW/132/22) at Heysham. The overlying Roosecote Anhydrite, the highest member of the formation, is 9.92 m thick at Roosecote, compared with a range of 1.2 m to 4.7 'm in the Heysham boreholes where gypsum, rather than anhydrite, appears from the field logs to be the predominant mineral.

Outside the Heysham area, only one borehole, Salt Ayre No.1 (SD46SE/38) [SD 4526 6200], is considered to have encountered the formation (Figure 32). It proved 10.5 m of red-brown, laminated, silty clay with gypsum and anhydrite, immediately below 14 m of drift. The only possible surface indication of the formation is a note on an early (c.1880) map by Mr R H Tiddeman that gypsum was reported in a former railway cutting [SD 469 625] near Lancaster, with exposures of 'magnesian limestone' along the adjacent north bank of the River Lune showing anomalously steep dips. No indication of these occurrences were found during the recent BGS survey.

St Bees Shales Formation

The St Bees Shales conformably overlie the St Bees Evaporites at Heysham and, by inference, in the Torrisholme Basin and around the Lune estuary. The formation is not delineated on the geological maps but is included in the undivided outcrop of the Cumbrian Coast Group (see above and (Figure 32)).

The formation was first defined by Arthurton and Hemingway (1972) in the type area around St Bees, Cumbria, where it largely consists of red siltstones and silty mudstones, with some sandstones, millet-seed sand grains, mudstone-breccias and gypsum veins. The base of the formation is defined simply as 'the base of the main red clastic sequence'. In reality, gypsum veins are common in places in the basal part of the formation, and the junction is taken where red mudstones and siltstones become predominant over evaporites. In south Cumbria, Rose and Dunham (1977) took the base of the St Bees Shales down to the top of the 'Grey Beds', thereby including beds equivalent to the St Bees Evaparotes of this account in the formation. However, the evidence from the Roosecote Borehole (see above) supports the stratigraphical scheme proposed by Smith et al. (1974, table III, column 11) which recognises the St Bees evaporites as a discrete unit, and this is the scheme used here.

In the present district, the formation is known only from a few boreholes (Figure 32), including those proving the St Bees Evaporites mentioned above. The lithologies are substantially the same as those in the type area, but thicknesses differ significantly, up to an estimated maximum of 85 m for the Torrisholme Basin. There, an incomplete sequence of 54 m was penetrated in the BGS Belmount Farm Borehole (SD46NE/23) [SD 4669 6511], neither the base nor the top of the formation being proved. At Heysham, the complete sequence averages only 15.8 m in boreholes. Such thickness differences may indicate control of subsidence and sedimentation rates by synsedimentary faulting, perhaps on the east and west margins of the developing Torrisholme Basin while the Heysham area remained relatively upstanding. Smith and Taylor (1992) envisage the St Bees Shales to have been deposited on a 'vast sedimentary plain'. This would have occupied the site of the former 'Bakevellia Sea' in which the St Bees Evaporites had previously accumulated.

Palynological analyses of samples taken from Heysham and the Belmont Farm Borehole have not yielded positive results (G Warrington, personal communication).

Sherwood Sandstone Group

The Sherwood Sandstone Group comprises the youngest 'solid' rocks of the district, underlying a considerable area in the extreme south-west, both onshore and offshore (Figure 32). The base of the group is gradational and probably diachronous, and is arbitrarily taken at a point in the succession where sandstone becomes predominant over siltstone and mudstone. The succession is undivided and is represented by an estimated 150 m of sandstone, perhaps equivalent to the lowest 20 to 25 per cent of the more complete sequence beneath the Fylde in the adjacent district to the south (Aitkenhead et al., 1992). A much thicker succession is present in the East Irish Sea Basin (Jackson et al., 1987; Jackson and Mulholland, 1993). The group is generally regarded as being of early Triassic age, possibly extending back into the latest Permian (Smith et al., 1974). During this time, the present outcrop area is thought to have formed part of the sandy floodplain of a great braided river system that flowed northwards from the Armorican mountains in the northern France–English Channel region (Audley-Charles, 1970). Some aeolian sands were also deposited under the prevailing arid conditions.

In the Heysham area, much of the lowest 120 m of the Sherwood Sandstone Group is either exposed on the shore at Red Nab [SD 401 592] or is known from excavations and boreholes at the nearby Heysham power stations (Wilson and Crofts, 1992). In general, the sequence consists of red-brown, fine-grained sandstones in which cross-bedding, including trough cross-bedding, is common, alternating with parallel-laminated strata. Convoluted strata and disturbed cross-bedding occur at Red Nab. Red-brown mudflakes and scattered bands of grey to pale grey sandstone have been commonly reported in boreholes. The latter are probably the equivalent of the prominent pale yellowish brown patches of bleached sandstone present on the shore at Red Nab (Plate 11) and near Crook Farm [SD 430 550]. A well-bedded sequence of predominantly pale grey sandstone is exposed around Plover Scar Light [SD 421 541], north-west of Cockersands Abbey. In hand specimen, the sandstone resembles the bleached variety, but the possibility that it represents a faulted inlier of Carboniferous age is not entirely ruled out. On the shore [SD 427 533], nearer the abbey, red-brown sandstones of probable aeolian origin are exposed, showing prominent rounded to well-rounded quartz grains and thick cross-bedded units. A thin section (E67173) of a sample of this rock (Plate 4) shows it to be a medium-grained subarkose, composed of quartz (including chert), K-feldspar and albite, together with opaque grains, igneous lithic clasts, traces of mica and some secondary Fe-oxide. The grains are generally more angular and compacted than in the Collyhurst Sandstone sample described above, and the porosity is slightly lower (20 to 25 per cent), probably due to cement dissolution.

Reddened Carboniferous strata

Before deposition of the Permo-Triassic sequence, the Carboniferous strata were deeply weathered and eroded in an arid environment. Over a large area of the western part of the district, either beneath or peripheral to outcrops of Permo-Triassic rocks, originally grey Millstone Grit strata have been secondarily oxidised to various shades of red, pink or purple by the formation of haematite. The oxidisation has also removed most of the original carbon from the rocks. The haematite was probably introduced by groundwater permeating down either from the former land surface or from a later overburden of Permo-Triassic rocks. This cover may have been removed relatively recently, probably during the Quaternary; perhaps by glacial erosion in the late Devensian. (Figure 32) indicates the extent of this discoloration and therefore the approximate extent of the postulated Permo-Triassic cover.

The Millstone Grit rocks are variably affected by this reddening. Permeable sandstones show the effect most intensely, as, for example, in the core from the Dam Head Borehole (see below). In the Heysham area, borings and sections, e.g. of the B. gracilis Marine Band and adjacent strata [SD 4048 5996], show that beneath the present outcrop of Permo-Triassic rocks, and closely bordering it, the Millstone Grit strata are completely reddened down to a depth of about 100 m. Beyond this zone, there is a diffuse zone where reddening is either patchy and commonly confined to sandstones, or occurs along particular bedding planes or joint fractures, the interbedded argillaceous deposits commonly being unaf fected. This zone extends about 5 km eastwards from the present Permo-Triassic outcrop, particularly along the Lune valley in the Halton area e.g. [SD 5105 6467], where jointed Pendle Grit sandstones are selectively reddened almost as far upstream as the Crook o' Lune. Several isolated occurrences of reddening are known, for example in the porous, coarse-grained Eldroth Grit penetrated by the BGS Dam Head Borehole [SD 5065 5800] in the core of the Quernmore Syncline, and in the Ellel Crag Sandstone [SD 5054 5484] near Ellel Crag.

A similar, formerly more extensive cover of Permo-Triassic rocks across the Ingleton Coalfield is indicated by reddening of the Eldroth and Greta grits in exposures in the High Bentham area.

The Millstone Grit strata within the intensely reddened zone contain cross cutting veins of secondary satin spar gypsum along joints. Examples were recorded in many confidential boreholes at Heysham power stations, at a depth of 322 m in the Lune Mills Borehole (SD46SE/17) [SD 4622 6187], and between depths of 11 m and 15 m in the BGS Parkside Borehole (SD45NE/136) [SD 4715 5552]. No such examples were recorded from surface exposures, but it is conceivable that R H Tiddeman's note of gypsum being discovered on the north bank of the River Lune [SD 469 625] during construction of the Morecambe branch railway (see p.105), may have referred to veins in reddened Millstone Grit, though the strata in question are now tentatively assigned to the Cumbrian Coast Group.

Chapter 7 Palaeogene igneous rocks: Caton Dyke

The Caton Dyke, a subvertical sheet of strongly altered, pale green, vesicular olivine-basalt, traverses Caton Moor in a north-west to south-east direction. The 'dolerite' was first noted by R H Tiddeman in the summer of 1864 (Eccles, 1870; Hull et al., 1875) during the primary survey of the area, and is known from three stream exposures. It is 1.5 m wide and strikes at N 145° E in the south bank of Crossgill [SD 5632 6302], about 20 m below the road bridge. It is of comparable width, trending at N 150° E, where exposed in the north bank and bed of Tarn Brook [SD 5601 6336]. Here it becomes irregular in the higher part of the bank section where it dips at up to 50°, thinning upwards to less than 0.6 m and incorporating slices of country rock. At its most northerly exposure, in the south bank of Mears Beck (Anas Gill) [SD 5550 6502], the south-west margin is not exposed, but the dyke is estimated to be at least 5.2 m wide, striking at N 145° E. In its general trend, the dyke is subparallel to the main faults in the area, e.g. the Deep Clough and Crossgill faults.

The dyke intrudes blue-grey, shaly, fossiliferous clay-stones with sporadic carbonate mudstone nodules of the Caton Shale Formation. Contemporaneous spheroidal weathering has reduced most of the central parts of the dyke to a soft brown rottenstone, but cores of hard, strongly altered, pale green to bluish grey vesicular basalt remain. The dyke has chilled margins in which aligned vesicles, indicating flow foliation, lie parallel to a closely spaced set of joints in the adjacent host rock. Otherwise, the host rock does not appear to be much affected by the intrusion. A detailed petrography of rock specimens from the dyke and their geochemistry is given by Fortey (1991; see Appendix 1). The rock is described as a strongly altered micro-porphyritic basalt.

Extent of the dyke

The Caton Dyke appears to be non-magnetic, or only weakly magnetic, due probably to the alteration of primary magnetite. It cannot be identified on the Aeromagnetic Map of Great Britain and a detailed magnetic survey was unable to trace it within the extent of outcrop indicated by the three known exposures (Smith, 1988; see Appendix 1). The dyke is depicted as having a continuous outcrop over this sector, but it has not been proved to reach the surface everywhere. It has long been thought to be contiguous with the olivine-basalt Grindleton Dyke [SD 754 471], about 25 km to the south-east near Clitheroe (Eccles, 1870; Hull et al., 1875, Earp et al., 1961). Although the Grindleton Dyke is less altered in that augite is preserved both as phenocrysts and in the groundmass, the two dykes share the same trend and are very closely aligned. In the poorly exposed ground between the two dykes, Eccles (1870) with Tiddeman (in Hull et al., 1875) recorded a basalt fragment on a dump from the Whitewell or Brennand lead mine c. [SD 652 549], situated on the col between Brennand and Whitendale farms. Tiddeman (in Hull et al., 1875) further reported an unworn, angular fragment of dolerite on the surface near White Hill House [SD 740 580], now north-east of Stocks Reservoir, that he thought may have come from an exposure nearby. However, despite these tentative indications, the dyke has not been shown to reach the surface between Caton Moor and Grindleton, and it is noted that no dyke was intersected during construction of the Bowland Forest Tunnel (Earp, 1955).

Age of the dyke

Isotopic determination of the age of the Caton Dyke has not been attempted in view of its strongly altered condition. However, Earp et al. (1961) noted that the Grindleton Dyke intersects probable late Armorican folds, and in keeping with its trend, is likely to be Palaeogene in age. Similarly, the Caton Dyke, in common with other intrusions with an analogous regional trend, is deduced to be the same age, and may be a distant extension of the Mull dyke swarm of about 60 Ma. Recent zircon fission track analyses of the Butterton and Cleveland dykes have given dates of this age (Lewis et al., 1992).

The Gleaston Dyke, a strongly altered olivine-dolerite dyke intruded into Namurian mudstone at Gleaston [SD 2584 7073], near Barrow-in-Furness (Binney, 1868; Rose and Dunham, 1977, p.51) has the same north-west trend as the Caton Dyke, and is probably also part of the Mull dyke swarm. However, the multiple dykes, known as the Fleetwood Dyke Group, which have been identified from magnetic anomalies in the Irish Sea between Blackpool and the Isle of Man (Kirton and Donato, 1985; Jackson, 1987), have a more west-north-westerly trend, and are probably associated with an Antrim dyke swarm.

The composition of the Caton Dyke (see below), and its possible extension at Grindleton, has been compared with that of the small number of Palaeogene basalt dykes in Staffordshire and Shropshire (J Winchester, personal communication, 1992). It is similar to the relatively alkaline, north-north-west-trending dykes at Yarnfield and Butterton (see Gibson et al., 1925; Whitehead et al., 1927) but identical to neither of these, leading Dr Winchester to conclude that a series of distinct magma pulses formed these dykes. All of these are chemically different from the north-west-trending tholeiitic dyke at Grinshill in north Shropshire (Pocock and Wray, 1925).

Mineralogy

At Anas Gill, the dyke consists of grey, strongly altered, micro-porphyritic basalt. Rock from the central part of the dyke (E62808) contains abundant calcite and chlorite pseudomorphs in small clusters, after minute olivine and pyroxene phenocrysts, accompanied by less-frequent turbid phenocrysts of plagioclase. The holocrystalline groundmass consists largely of slender plagioclase laths altered to albite and saussuritic material, accompanied by chlorite, carbonate and minute granules of opaque goethitic material. In addition, the ground-mass contains minute flakes of biotite and interstitial patches of possible analcime. No quartz is present. A sample of pinkish grey rock from the dyke margin (E62809), within 0.2 m of its contact with the host Caton Shale, contains abundant calcite pseudomorphs after minute olivine phenocrysts, commonly in small clusters, and a small number of plagioclase phenocrysts, 1 to 2 mm wide, which tend to occur singly. The dark, devitrifled glassy groundmass contains slender plagioclase laths and abundant minute calcite rhombs. Calcite is also present in fracture veinlets, and in more irregular gashes related to flowage and gas release during intrusion. Flow banding is also expressed in thin section by variation in glass content, especially where detached fragments of relatively crystalline basalt are entrained in the more glassy material ((Plate 12)a). Although the marginal rock evidently underwent a degree of chilling, baking of the host shale is hardly apparent.

At Tarn Brook, the rock seen in the stream bed is strongly altered, vesicular olivine-basalt. Olivine phenocrysts, now replaced by calcite, occur in a turbid groundmass of slender plagioclase laths ((Plate 12)b), accompanied by minute grains of calcite, opaque material, chlorite and minute biotite flakes (E62810). Flow banding is indicated by mm-scale bands of clear, calcite-poor groundmass which contain ovoid vesicles now filled by coarsely crystalline calcite. The groundmass associated with the vesicles contains conspicuous plates of biotite and oligoclase laths ((Plate 12)c). A sample from one of the overlying basalt veins (E62811) consists of calcite pseudomorphs after olivine phenocrysts, again set in a groundmass of interlocking plagioclase laths accompanied by interstitial, intergrown chlorite and opaque granules after ophitic pyroxene. The ground-mass also contains traces of possible interstitial analcime. Vesicles contain amygdales of calcite and pale chlorite, surrounded by margins of dark, devitrified glassy groundmass.

At Crossgill, the basalt is strongly altered and reddened and no thin section work was carried out. Thewlis (1962; see Appendix 4) recorded pyrite-lined vesicles at this locality.

Geochemistry

Analyses of three samples by X-ray fluorescence spectrometry are given in (Table 7). Modification of the original magma composition during the alteration suffered by the dyke is indicated by the low Si02 and high losson-ignition results obtained, and is probably responsible for much of the variation seen in Fe, Mg, Ca, K, Zn, Rb, Sr and Ba. The consistency between the low Si02 concentrations of the three samples suggests dilution, principally by precipitation of calcite in vesicles and fractures. The Si02 results of 37 per cent or less can be corn-pared with normal concentrations of more than 45 per cent in basalts. However, a greater degree of variability is shown by the other elements, suggesting that addition and subtraction took place. K shows considerable enrichment, as emphasised by plotting K2O + Na2O versus K2O/K2O + Na2O (after Hughes, 1972). If, on this basis, sample LC991 is regarded as the least altered, then its relatively high MgO and low CaO contents indicate a loss of Mg and a gain of Ca during the alteration that affected samples LC990 and LC992, consistent with the destruction of olivine and the precipitation of calcite during the alteration.

Consistent results from the three samples were obtained for several elements, including Ti, Al, Y, Zr, Nb, La and Ce, which display low mobility during low-temperature alteration by connate or meteoric fluids. Behaviour of the transition elements is more equivocal. Ni and V show only limited variation between the samples, but Cr appears to be more variable.

Use of ratios between the more immobile elements to classify the rock is permissible, but use of their absolute concentrations should be treated with caution because of the likely dilution (by 20 per cent or so). On the Zr/TiO2–Nb/Y and Zr/TiO2–Ce diagrams of Winchester and Floyd (1977), and the Ti02-Zr/P205 diagram of Winchester and Floyd (1976), the Caton dyke samples plot as alkali basalt. On the Ti/100-Zr–Y.3 diagram of Pearce and Cann (1973), the results fall in the 'Within Plate Basalt' field, being distinguished from 'Ocean Floor Basalt' by a relatively low yttrium content. Thus, use of stable trace elements indicates that the Caton Dyke is a within-plate alkali olivine-basalt.

Chapter 8 Quaternary

Quaternary deposits lie unconformably on folded and faulted sedimentary strata that range in age from Carboniferous to Triassic. Between Triassic and Quaternary times, the district is likely to have been covered by a sequence of later Mesozoic and Palaeogene sedimentary rocks, which must have been removed by erosion during uplift in later Palaeogene and early Neogene times. Regional apatite fission track studies (Green, 1986; Lewis et al., 1992) imply that 2.7–3.3 km of post-Triassic strata may have been present, though consideration of the thicknesses of strata in adjacent basins would reduce this to 1.2–1.8 km (Holliday, 1993). A study of the garnet dissolution in Millstone Grit sandstones of the Lancaster district (see p.39) implies an overburden thickness of 3.4 km, including a substantial thickness of Coal Measures strata. Possible relict surfaces in the Bowland Fells have been discussed by Moseley (1961) in terms of Neogene subaerial erosion, though they may be a legacy of one or more extensive glaciations that probably affected the district prior to the ultimate glaciation.

The Quaternary era began approximately 1.6 to 2.4 million years ago and is characterised by great climatic fluctuations, ranging from warm temperate conditions during the relatively short-lived interglacial episodes to glacial or periglacial conditions during the stadial stages of longer duration. These climatic changes form the basis of the present chronostratigraphical classification.

Although the district was very probably glaciated on several occasions, its Quaternary deposits (with the possible exception of minor cave deposits) date mainly from the later part of the last, or Devensian, glacial stage (see below). The piedmont ice sheets, which built up and encroached into the area some 20 000 years ago in the Dimlington Stadial (part of oxygen isotope stage 2), reaching their acme about 18 000 years BP, effectively removed any previous drift deposits, or perhaps in places submerged remnants of them beneath a blanket of glacial till along with any possible relict preglacial valleys and other topographical features. Pre-late Devensian sediments may be discovered as limestone quarrying in the Nether Kellet and Over Kellet areas reveals sections of them in old cave and fissure systems beneath glacial till (see below). A famous nearby example of cave sediments dating back to the Ipswichian Interglacial about 130 000 years ago, and containing the fossil remains of such exotic mammals as hippopotamus, Hippopotamus amphibius, and the extinct straight-tusked elephant, Palaeoloxodon antiques, has been recorded from Victoria Cave in the Settle district (Boylan, 1977).

Much of the district is covered by extensive spreads of drift, which can be divided into two major categories: glacial deposits, wholly of Dimlington Stadial (late Devensian) age, and postglacial deposits, of later Devensian to Flandrian age. The latter were the result of diverse processes that acted after the ice had melted some 13 000 to 14 500 years BP (Gale, 1985). In the absence of datable material, nonglacial late Devensian processes and deposits cannot be distinguished readily from those of the Flandrian, defined as commencing 10 000 years BP. The drainage pattern of the district is dominated by the River Lune and the upstream River Wyre or Tarnbrook Wyre and their tributaries (Figure 1), which were established on the landscape during deglaciation. Drainage systems that might have been established and reached maturity between the last and previous glaciations have been obliterated, covered over, or perhaps remoulded by the ensuing glaciation. However, valleys such as that of the River Wenning which are relatively open, shallow and in part bottomed by till may be re-exhuming preglacial courses.

The district has attracted little attention fr'om Quaternary researchers. Prior to Tiddeman's primary survey in the 1870s and his paper (1872) on ice movement in the region, the only known publications were by Crofton (1867) and Mackintosh (1869), who made basic observations on coastal sections and some railway cuttings. Reade (1904) sampled tillq on the coast and in the Lune valley for foraminifera in order to establish whether the till originated from ice spreading inland from the Irish Sea Basin or from land ice to the north. From the lack of foraminifera in these samples, he concluded that the latter scenario was correct. Slinger (1936) recognised that the district contained signs of meltwater drainage; the extent and significance of this was eventually documented by Moseley and Walker (1952). Recent work has tended to concentrate on coastal Flandrian sediment correlation and sea level changes (e.g. Tooley, 1974, 1982, in Robinson and Pringle, 1987; Zong and Tooley, 1996), or has provided regional overviews (e.g. Johnson, 1985a and b), the latter often within the context of the Irish Sea Basin and its environs (e.g. Eyles and McCabe, 1989).

Rockhead

Although many boreholes have been put down in the Quaternary deposits, particularly in the areas west and south of Lancaster, rockhead provings are sporadic or clustered. Additionally many areas have little or no borehole coverage. Geophysical data has augmented the database in specific areas, but because of the sparsity of data, a subdrift contour plot has only been attempted for the western part of the district (Figure 34). The high borehole density in the Heysham area allows the resolution of small-scale structures, including a 'late glacial', drift-filled channel cut to a base level of at least 30 m below OD. In contrast, only three boreholes out of over 300 have proved rockhead around Morecambe [SD 43 64]. These provide some information about the lithology at rockhead but no hint of the nature of the rockhead surface.

In general, if it were not for the drift accumulations, the greater part of low-lying ground to the west of Lancaster (Figure 4) would lie below sea level, with Ordnance Datum roughly following the inland limit of Quaternary marine deposits. In this area, bedrock highs occur between Heysham and Middleton [SD 41 60], between Heaton and Overton [SD 44 59], and at Cockersand Abbey [SD 42 53] (see (Figure 34)).

Glacial deposits

During the latter part of the Devensian cold phase, ice streams radiating from centres around the Howgill Fells in the northern Pennines (Johnson, 1985b; Mitchell, 1991) coalesced into sheet glaciers that advanced southwards across the central and eastern parts of the district. Farther west, southward flowing ice from the eastern and south-eastern Lake District, including ice from Shap Fell, incorporated Triassic bedrock into its load. It could be assumed from the general absence of erratics over the highest fells of the district, and from the pattern of ice movement depicted in (Figure 35), that the high fells remained permanently above the ice as nunataks. However, it is more likely that at their maximum expansion the late Devensian ice sheets covered the entire Lancaster district, and that any glacial drift deposited in the upland areas was subsequently removed by periglacial processes, for the following reasons:

  1. Glacial striae were recorded by Mr R H Tiddeman during the primary survey at about 470 m above OD [SD 595 574] on the south flank of Ward's Stone, and striae on glazed surfaces of Ward's Stone Sandstone were noted during the present survey at about 400 m above OD on the south side of the Roeburndale col [SD 6407 5852]; [SD 6417 5837], near Esp Crag (see (Figure 35)). It is thought unlikely that such features could have survived from a previous glaciation.
  2. Till was recorded to over 430 m above OD on Rowton Brook Fell [SD 55 58].
  3. Two misfit gorges [SD 566 583] and [SD 592 574] gouged in the Ward's Stone escarpment, at 420 m and 455 m above OD respectively, testify to the generation of meltwater from large amounts of decaying ice above those heights.
  4. Several dry channels cut into bedrock on cols, such as that of the Trough of Bowland, indicate meltwater routes across the main watershed of the district.
  5. Thick and extensive till underlies the broad Wyre valley around Abbeystead, in the lee of the 'Ward's Stone range'.
  6. The till margin against the upland fell appears to be one of erosion and there are no lateral or terminal moraines.

The glacial deposits and associated topographical features fall broadly into two categories, related to glacial advance and glacial retreat phases respectively. The depositional product of the former is predominantly till, which forms a clayey ground moraine covering much of the ground below 300 m. During glacial retreat, down-wasting of the ice sheets is believed to have occurred rapidly, and was largely achieved by in-situ stagnation and decay of ice that had ceased to move (Longworth, 1985). During this phase, large volumes of water were released, flowing below and within the ice, and eventually proglacially. These waters cut a network of channels, and deposited gravelly sediments, now preserved as hummocky ground, eskers, kames and flat spreads.

Following the glacial maximum, the upland region above the ice margin suffered the affects of a periglacial climate, and the resultant deposits, known as head, form broad gelifluction terraces in moorland areas above the mapped upper limit of the till. These deposits are described with postglacial head deposits (see p.00). On lower ground, glaciofluvial sediments commonly overlie the till sheet. Head deposits became more widespread on the total withdrawal of glaciers from the district.

Till and constructional features related to glacial advance

The general pattern of ice movement is given by glacial striae, in places discernible in relict glazed patches on the surfaces of gritstone outcrops, and by drumlin orientations (Figure 35). The flow-alignments of the regional drumlin fields, including those of the present district, are clearly illustrated on Landsat imagery (Plate 1).

Across the lowland in the western part of the district, the ice sheet moved in a broad arc around the western margin of the Bowland Fells, from a south-west direction in the north of the district, to a south-south-east direction in the south. There is scant evidence of the flow direction across the upland fell area. The col between Roeburndale and Whitendale [SD 645 590] was probably eroded into bedrock by ice moving southeastwards into the Croasdale and Whitendale areas. Apart from the rare glacial erratic, glacial drift is absent from this area, as in other upland fell areas in the district, but south-eastwards directed ice striae (Figure 35) on glazed surfaces of Ward's Stone Sandstone were recorded on the south side of the col during the survey.

All parts of the district except the upland fells are covered by extensive deposits of till laid down during glacial advance. The till comprises an ill-sorted mixture of rock fragments up to boulder size, set in a matrix composed of sandy clay, silty clay or clayey sand derived from weathered and pulverised rock and pre-existing superficial deposits. Its composition varies across the district, depending on the source of the ice, the nature of the local bedrock, and the mode of deposition. The composition also varies stratigraphically, for the basal metre or so of the till typically comprises a high proportion of broken-up local bedrock, commonly formed only of one rock type. For example, the fossiliferous locality along Delph Beck [SD 5985 5540], Tarnbrook, comprises slabs of mudstone from the Cravenoceras cowlingense Marine Band in a dark grey clay matrix. Two till types, reddish brown and grey, have been recognised as being geographically distinct (Figure 35), although in places the reddish brown type overlies the grey (see below). To the west of Lancaster, till is reddish brown with a matrix rich in the debris of Triassic rocks; to the east, and over most of the district, the till is dark grey with a matrix derived mainly from pulverised Lower Palaeozoic and Carboniferous rocks. Evidence suggests that both tills have a generally northern provenance: the first deposited from ice traversing the eastern and southeastern Lake District and the second originating in the Pennines around the Howgill Fells (see below). These coalescing ice sheets generally correspond to the 'Lake District Glaciers' and the 'Lonsdale Glacier' of Moseley and Walker (1952).

Drumlin fields

In the lowland areas in the western and northern parts of the district, and generally less than 100 m above OD, both types of till form a drumlin terrain (Figure 35). The area west and north of a line from Galgate [SD 47 55] through east Lancaster, Caton [SD 53 65] and Wray [SD 60 68] to High Bentham [SD 67 69], provides a superb example of a drumlin landscape, sometimes referred to as 'basket of eggs topography'. A cross-section through part of this topography is shown in (Figure 37). This drumlin field is part of a much larger regional field (Plate 1). To the east of this line, only isolated drumlins e.g. at Askew Hill [SD 5255 6180], and subdued till ridges, as in the Caton Green area [SD 550 650], occur, and the till forms a generally smooth cover to the bedrock. The Lancaster drumlin field was first noted by Mackintosh (1869), who was not convinced of any correlation with the extensive Irish drumlin fields recorded by Close (1867). The formation of drumlins from pre-existing subglacial deposits, as well as the formation of tunnel valleys (see below), is now seen as characterising periods of fast glacier flow caused by rapid calving at ice margins. The extensive drumlin belts peripheral to the northern part of the Irish Sea are thought to have formed during the basinwide 'drumlin event' which was related to a southwards ice surge, and was triggered by a glacio-isostatically controlled rise in sea level in the southern Irish Sea Basin at around 17 000 years BP (Eyles and McCabe, 1989). This high relative sea level peripheral to the ice margin followed an earlier global glacio-eustatically controlled fall in sea level.

The drumlins are generally of large proportions, some being more than 1 km long. One such example, centred on Norbreck Farm [SD 452 535], is up to 300 m wide, and over 20 m high. They generally occur where the till is thicker, being noticeably rare around Heysham, an area of thin till over a bedrock high. However, in areas of generally thin till, there are three known examples of rock-cored drumlins: at Lane House [SD 4835 5470] near Galgate, near the Heysham power stations [SD 406 598] (Figure 36), and exposed in a road cutting [SD 512 704] to the east of Carnforth.

In the west of the district, the drumlins form an arcuate pattern (Figure 35) reflecting deflection of the lowland ice sheet around the Bowland Fells at the time of drumlin formation. To the east of Wray [SD 602 675], the drumlins are generally smaller and show no preferred orientation.

This area lay between a south-westwards moving ice sheet to the west, and ice moving south-eastwards along the Wenning valley into the Ribblesdale area (Raistrick, 1933, fig. 28; Arthurton et al., 1988, fig. 24).

Reddish brown till

This is restricted to the western third of the district (see (Figure 35)) where much of it is buried beneath younger deposits of Flandrian age. It has been encountered in many boreholes which prove it to be very variable in thickness. A maximum thickness of 30 m was recorded in the Old Glasson Borehole (SD45NW/270) [SD 4438 5538]. The most extensive sections in this till are on the coast, 15 m being seen south-west of Red Bank Farm at [SD 4702 6792] and 7 m in the car park [SD 4286 6407] adjacent to Morecambe Railway Station. There are also many minor exposures of the till in old marl pits.

The reddish brown till invariably comprises a reddish brown, silty, sandy, clay matrix with abundant erratics up to boulder size. The erratics are chiefly Lower Palaeozoic greywacke 'sandstones, Borrowdale volcanic rocks, Lower Carboniferous limestones and Upper Carboniferous sandstones. Rare stones of Shap Granite and Eskdale Granite have been recorded from coastal sections of the red till. Shap Granite has been recorded from Hest Bank and Bolton-le-Sands (Tiddeman, 1872; Reade, 1904, p.179), and Eskdale Granite from coastal sections of the Cross Stones drumlin [SD 415 625], south of Morecambe, by Crofton (1876) and Reade (1904, p.176). However, Longworth (1985, fig. 10.6a) considered that Eskdale and Scottish granite erratics typify an Irish Sea/Lake District ice stream which did not impinge upon this district, and should not be expected to occur commonly. A rounded, mussel-encrusted block of Shap Granite, 2 m in diameter and known locally as Conger Rock [SD 4042 6264], lies on the shell bank at Foot Skear, 1.2 km north-west of Heysham Village. The block is probably embedded in till which is exposed locally beneath the thin shell bank deposits.

Ice striae are common on the Lower Carboniferous limestone clasts, but occur only rarely on sandstone blocks. The limestone clasts are commonly absent from the upper metre or so of the till due to decalcification. Reade (1904) described a 9 m section [SD 472 617] of red till in an excavation at Lancaster railway station, where the deposit was so tough, presumably being cemented with calcium carbonate, that it had to be drilled and blasted. Crofton (1876) recorded the marine molluscs 'Mytilus edulis, Cardium edule, Ostrea edulis, Littorina littoralis and Buccinum undatum' from the red till in coastal sections of two drumlins [SD 415 625] and [SD 414 620] between Morecambe and Heysham.

Reddish brown till has been observed to overlie grey till at some localities. This relationship was recorded in the cliffs between Morecambe and Heysham by Reade (1904), but the sections were reappraised by Moseley and Walker (1952) who re-interpreted Reade's upper till as hill wash. The cliffs are now landscaped or covered by sea defence works, but a temporary section [SD 4891 6190] showing 3.5 m of reddish brown till overlying 8.0 m of grey till was seen 200 m to the west of Lancaster Cemetery during this survey. This occurrence is close to the suggested boundary between the red and grey till types (Figure 35) and (Figure 37), and implies that the ice stream depositing the grey till reached this particular locality before the ice stream depositing the red till.

Grey till

Much of the remainder of the district, apart from the high moorland in the south-east of the area, is covered by grey till. Ice striae on bedrock [SD 6407 5852]; [SD 6417 5837] are known from the till-free area near Esp Crag, but erratics are rare, suggesting that the ice covering these high moorland areas may have been clean of far-travelled stones. The till on the lower ground is generally less than 4 m thick over much of this area, but thicknesses in excess of 10 m are not uncommon. There are many minor exposures of up to a few metres of till along incised streams throughout this area, including many instances where the till directly overlies bedrock. A synthesis of till thickness in the Abbeystead area (Wilson et al., 1989, fig. 4) illustrates this variability. A borehole (SD55SE/2) [SD 5564 5428] near Abbeystead proved 34.5 m of till, the maximum recorded thickness anywhere in the district. Up to 15 m has been seen at outcrop in landslip scars [SD 6107 6508] in the Wray area.

The till generally consists of a grey, clayey, sandy silt matrix, invariably weathered to orange-brown in the top few metres, with abundant erratics up to boulder grade. The erratic suite is dominated by sandstones from the Millstone Grit Group, but also includes less durable Millstone Grit Group lithologies such as siltstones, mudstones, limestone and ironstone nodules, and coal. Greenish grey Lower Palaeozoic turbidite sandstones and Lower Carboniferous limestones are also common, and there are rarer occurrences of chert and igneous rocks. Ice striae are common on the tough Lower Palaeozoic sandstone clasts. Locally, the till composition commonly reflects the local bedrock geology, e.g. south of Knots Wood [SD 508 612] where the till comprises Pendle Grit sandstone clasts in a very sandy matrix. Generally, the basal metre or so of the till is composed predominantly of the local bedrock.

The Lune-Quernmore Tunnel Valley

Modelling of Bouguer gravity anomaly data has identified a drift-filled channel, or tunnel valley, beneath the present course of the Lune between Caton and Claughton ((Figure 34); Appendix 1: Busby and Cornwell, 1993). The rockhead surface of the tunnel valley climbs south-westwards, from about 54 m below OD near Claughton to 8 m below OD at Caton. In this stretch, the channel is filled with till and glaciofluvial and glaciolacustrine deposits. Site investigation boreholes at Claughton Brickworks (see p.121) indicate that sands, gravels, clays and silts overlie till at 7 m below OD. Although there are no data upstream of Claughton, it is probable that the tunnel valley continues beneath the River Lune towards Melling [SD 59 71]. Detailed gravity traverses in the Quernmore valley suggest that the tunnel valley continues south-westwards, with rockhead rising steadily to 50 m above OD near Knotts Farm [SD 515 612]. To the south-west of Knotts Farm, its presumed continuation as a 300 to 500 m-wide, drift-filled channel has been traced as far as Dam Head [SD 501 577] by the disposition of solid outcrops, and sporadic boreholes.

The formation of the Lune–Quernmore Tunnel Valley is thought to be related to the Irish Sea Basin 'drumlin event' (see above) when rapidly moving ice and increased subglacial water-flow-enhanced erosion of the underlying rocks (Eyles and McCabe, 1989), promoting the formation of tunnel valleys (Woodland, 1970). The Quernmore valley is therefore considered to have been initiated during the late Devensian, and not to be the preglacial course of the River Lune as previously suggested (e.g. Hall and Folland, 1970, p.107).

Glaciofluvial deposits

Boreholes reveal that glaciofluvial deposits are more widespread than is suggested by mapping. Considerable thicknesses of gravel, sand, silt and clay are present beneath a covering of marine and estuarine deposits in the Lune estuary, and beneath till elsewhere. The principal deposits occur in three main, genetically interrelated settings: areas of hummocky terrain, in which glaciofluvial sands, gravels, silts and clays were deposited in close association with stagnant and decaying ice; as eskers and kames, formed en- or supraglacially, but now found as distinct constructional features on the till surface; as stratified spreads underlying flat terrace features. The first two categories are described below under Glaciofluvial Ice-contact Deposits and the last under Glaciofluvial Sheet Deposits. However, this distinction is not always clear and one category can merge into another, as seen in the Lune valley [SD 49 64] downstream of Halton, and around Quernmore [SD 518 602]. The main outcrops of glaciofluvial deposits are shown in (Figure 38).

Glaciofluvial ice-contact deposits

These are essentially 'late glacial' deposits, formed as the ice was waning when sands and gravels were deposited next to ice masses. They comprise mainly immature, ill-sorted, proximal gravels with clasts up to boulder grade, poorly stratified with sands. Subsequent melting of the adjacent ice resulted in slumping and deformation, and the formation of generally heterogeneous deposits incorporating englacial dirt bands and laminated clays and silts from ponding. The deposits typically underlie hummocky ground in which kettleholes may be present–a terrain known as kettle-kame moraine. The main occurrences of these deposits are: around Carnforth [SD 500 700]; along the Lune valley to the north and south of Hornby [SD 585 685] and west of the Crook o' Lune [SD 520 645]; along the Quernmore valley [SD 520 630]; along the Wenning valley to the east of Low Bentham [SD 649 693] ; around Chipping House [SD 506 533] near Dolphinholme; and in the Morecambe–Bare–Torrisholme area c. [SD 45 65]. The moundy deposits around Quernmore church [SD 5180 6032] were thought to mark a terminal moraine by Moseley and Walker (1952), but they are now considered to be dissected remnants of ice-contact deposits. Good examples of kettleholes in a kettle-kame topography occur in Quernmore Park [SD 52 63] and south-west of Williamsland Farm, near Torrisholme at [SD 461 644]. A classic example of a single kettlehole [SD 4980 6430] occurs on the south bank of the River Lune, 150 m east of the M6 Motorway.

There are many small exposures of up to a few metres of mostly ill-sorted gravel. In a quarry [SD 5123 6459] on the south bank of the River Lune, south of Halton, about 4 m of ill-sorted gravel are visible, overlying till. Sections which exhibit slumping are not common. One of the best sections, of 6.9 m of stratified sands and coarse gravels inclined at 18°, is in the south bank of Bull Beck [SD 5423 6489], near Caton Green. About 3 m of slumped gravels were also exposed in temporary excavations for silage tanks [SD 5725 6715], near Farleton. A group of boreholes at Claughton brickworks [SD 561 663] proved about 3.5 m of sand and gravel overlying till and beneath glaciolacustrine silts and clays (see below). These deposits fill the Lune–Quernmore Tunnel Valley at Claughton.

The deposits have been extensively worked for sand and gravel in the Carnforth area [SD 497 707] but most of the pits are now backfilled. However, sections are visible in a few former sand and gravel pits, the most extensive being through 12.5 m of coarse, poorly sorted and partly cemented gravels with thin sand lenses in the former Mount Pleasant pit [SD 491 688] to the south of the town. More than 16 m of sands, gravels and stony clays have been proved in boreholes in this area. Mackintosh (1869) recorded a 30 m exposure in the railway cutting [SD 492 702], south of Carnforth Railway Station. Around Carnforth, glaciofluvial deposits swamped part of the drumlin field. It is possible therefore, that thicknesses in excess of 30 m may occur in the slacks between drumlins.

Although the clast content of these glaciofluvial deposits generally reflects the erratic suite of the till, the gravels at some localities are composed largely of local bedrock. For example, some of the gravels between Brookhouse and Caton, and exposed in a pit [SD 5358 6467], are composed mainly of clasts of mudstones and siltstones from the Roeburndale Formation and Caton Shale. In most of these cases, the deposits occur at the mouths of meltwater channels incised through bedrock.

Moulin kames

These occur as strings of isolated gravelly mounds which probably mark locations where meltwaters flowing on the ice surface plunged into crevasses or moulins close to the ice margin possibly at a stillstand during glacial retreat. They are commonly associated with ice-marginal meltwater channels. Several good examples are found in the district. A well-marked train of conical gravelly moulin kames occurs along the north side of the Haylott (Closegill) meltwater channel from [SD 573 625], and extends eastwards for nearly 4 km across Roeburndale to a mound [SD 608 638] near Lower Salter (Figure 38). Swaintley Hill [SD 586 625] is a prominent example from this group (Frontispiece). The line of moulin kames is clearly related to the now virtually dry Haylott channel. It probably formed during a stillstand when ice, retreating northwards, had not cleared the area of what became lower Roeburndale, and caused drainage from the upper part of the valley and the ice margin to divert westwards along the Haylott channel. Another string of small, conical, gravelly mounds interpreted as moulin kames stretches for nearly 4 km on the north side of the Crossdale Beck valley, from the Swine Knott mound [SD 648 661] near Lower Stock Bridge in the west, to a mound [SD 685 665] south of Gruskham in the east (Figure 38). This series appears to be connected to a set of short, parallel, west-south-west-trending meltwater channels, disposed generally to the north of the string of mounds. There are also irregular hummocks of gravel extending southwards from the main tract across Tatham Fells to near Swans at [SD 658 633]. Upper Crossdale itself probably originated as a meltwater channel about this time when ice was retreating northwards into the Wenning valley. The irregular sinuous tract of gravelly mounds along the Wyre valley from near Rotten Hill [SD 556 576] on Abbeystead Fell, via Chapel House Farm [SD 552 549] to west of Dolphinholme c. [SD 50 53] may, in part, have had a similar origin.

Eskers

Distinct eskers and kames are not common in the district. However, sinuous gravel ridges, identified as eskers by Arthurton (1987), occur to the east and south of Carnforth. Other eskers have been identified near Dam Head [SD 502 575], and at Thursland Hill, where a quarry [SD 4455 5390] revealed a 4 m sequence dipping at 25° to the south-south-east, and comprising mainly coarse gravels with thin beds of sand.

Glaciofluvial sheet deposits

These consist of undeformed, well-bedded sands and gravels underlying flat terrace features. They were deposited proglacially, or relate to a slightly later period than the local ice-contact deposits, when the ice had melted from the vicinity of the site of deposition. There were once continuous spreads of such valley sandar along all the major valleys. Broad fans are found emanating from meltwater channels (Figure 38), a good example being that at Caton [SD 530 644] formed by meltwater from the Artle Beck channel ((Plate 13); see below). The most extensive outcrops of glaciofluvial sheet deposits, other than around Caton, occur: in the Lune valley north of Hornby [SD 585 685] and in the Skerton area between Halton and Lancaster [SD 475 630]; in the Quernmore valley as outwash from the Conder at [SD 520 605] and Birk Beck at [SD 510 590] meltwater channels; west of Stodday [SD 466 586] ; and north of Conder Green [SD 460 560] Many of the deposits lie beneath relict high-level terraces. In the lower reaches of the principal rivers that were graded to a late Devensian low sea level, the rapidly aggraded thick fluvioglacial spreads that formerly filled the valleys can now be found both beneath higher terraces and underlying the present day floodplains, an example being in the Lune valley between Halton [SD 500 647] and Lancaster [SD 483 624]. Here, the terrace surface lies at about 20 m above OD and boreholes (for example (SD46SE/3) [SD 4888 6404] ) show that these deposits extend to 10 m below OD, giving an estimated sediment thickness of 30 m. This thick accumulation and its extension upstream to Caton indicates that drainage down the proto-Lune valley was already in the direction of Lancaster rather than Quernmore. The truncated front of the Caton Terrace emanating from Artle Beck (Figure 38) is at c.25m above OD. Flandrian incision of these deposits into underlying till and bedrock led to the formation of the Crook o' Lune gorge [SD 521 645]. Minor terrace remnants of glaciofluvial sheet deposits occur in smaller valleys, as for example Udale Beck [SD 555 615] where the terrace surface is 30 m above the present incised stream level.

Good sections are uncommon. The majority of exposures show up to a few metres of undeformed, coarse, ill-sorted gravel with clasts to boulder grade (Plate 13). The clast lithologies are similar to those of the glaciofluvial ice-contact deposits, and most of the pebbles and larger clasts are well rounded. Palaeocurrents are readily determined from imbrications of the more tabular clasts and from foreset bedding. As an example of such gravels, about 5 m are exposed in a landslip backscarp [SD 5552 6238] on the north side of Crossgill valley. A 9 m section in undeformed, well-bedded, cross-stratified, poorly to well-sorted silts, sands and gravels, was formerly exposed at a pit [SD 580 689] near Hornby.

Glaciofluvial sand and gravel beneath Morecambe and offshore, generally concealed by younger marine deposits, may form part of a large sandur (Knight, 1977). Boreholes in the Morecambe area have proved more than 10 m of deposits, including laminated silts, sands and clayey gravels.

Glaciolacustrine deposits

Laminated clay beneath the Kent Channel, was proved by several Morecambe Bay Barrage boreholes ((Figure 37); Knight, 1977). The clay infills a hollow in the till surface and was probably deposited in a lake during late Devensian low sea level. Three minor outcrops of grey and brown laminated soft clay and silt occur along the Wenning valley at Low Bentham [SD 6487 6959]; [SD 6395 6927]; [SD 6430 6920], 10 to 20 m above river level. They might be part of a larger tract of glaciolacustrine deposits beneath till.

Glaciolacustrine clays and silts also occur along the line of the former Lune–Quernmore Tunnel Valley (Figure 38).

'Lake Claughton'

These deposits occur beneath the broad alluvial tract of the Lune and have been proved in a group of site investigation boreholes (SD56NE/1), (SD56NE/2), (SD56NE/3), (SD56NE/4), (SD56NE/5), (SD56NE/6), (SD56NE/7), (SD56NE/8), (SD56NE/9), (SD56NE/10), (SD56NE/11), (SD56NE/12), [SD 561 663] at Claughton Brickworks (Figure 38). Beneath about 3 m of alluvial silts that overlie between 4 m to 6.9 m of ?fluvial sand and fine to coarse gravel, the boreholes show up to 21.2 m of stoneless, grey and brown, finely laminated clays with fine silt layers, resting on up to 3.5 m of glaciofluvial sand and gravel on till. The clays and silts are barren of Quaternary pollen and spores (Dr A P Bonny, personal communication, 1989). The lake deposits are probably coextensive with the Lune–Quernmore Tunnel Valley upstream of Crook o' Lune for some considerable distance (Figure 34). As the boreholes are located close to the valley side and the bedrock floor of the channel is suggested by BGS geophysical traverses to be as low as 54 m below OD (see above), the maximum thickness of these lake deposits may be much greater. The thick accumulation of clays and silts indicates that the lake must have been in existence for a considerable time, during which the drainage down the proto-Lune must have been of low energy, insufficient to infill the lake with coarse sediment. This might be explained by the lake having been formed subglacially within the tunnel valley.

'Lake Quernmore'

An extensive, flat, low-lying area [SD 520 613], 2 km long by 300 m to 500 m wide north of Quernmore church, is probably the site of a former major kettlehole (Figure 38). The depression is surrounded by terraced glaciofluvial sheet deposits. Its floor is mainly underlain by soft grey silty clay of probable glaciolacustrine origin, proved in site investigation boreholes (e.g. (SD56SW/38) [SD 5193 6130]) to be at least 8 m thick. Possible drop stones in the clay have produced a deposit which was described as 'till' by Moseley and Walker (1952, fig. 5). 'Lake Quernmore' eventually drained southwards into the River Conder, incising the deep misfit channel [SD 516 603] through bedrock near Quernmore Church (Figure 38). A small peaty ponded area remained in the central part of the kettle hole [SD 517 612] well into Flandrian times (Moseley and Walker, 1952; see below).

Meltwater channels and features related to glacial retreat

During the waning of the ice sheet, a complex system of marginal drainage was inaugerated. These glacial meltwater channels, which were in part subglacial, are distinguished from postglacial valleys by being almost dry or a gross misfit with the drainage they now carry. A large number of meltwater channels that continued to be utilised by streams until the present day are generally greatly modified and less readily recognisable. The distribution of meltwater channels, recorded on the surface during the present survey, is shown in (Figure 38). The channels can be broadly classified into three types: incised watershed cols that carried meltwater between the Lune and Hodder catchments during an early stage of glacial retreat; those formed as meltwaters flowed westwards, parallel or subparallel to the ice margin during its retreat northwards away from the high ground of the 'Ward's Stone range' and 'Upland fell' into the Lune valley; a series of lowland channels in the western part of the district that carried waters southwards after much or all of the ice had disappeared, prior to the establishment of the modern Lune drainage.

Watershed cols

Several dry cols were probably initiated by meltwaters flowing eastwards or south-eastwards over the main upland watershed into the Hodder drainage system during a relatively early period, when ice sheets still covered much of the higher ground (Figure 38). They occur at the head of Whiteray Beck [SD 683 607], Brennand Tarn [SD 626 546] and Trough of Bowland [SD 622 532]. A fourth example, at Salter Fell [SD 649 587], may have partly resulted from scouring by ice moving south-eastwards, as indicated by local glacial striae (Figure 35).

Ice-marginal channels

Ice-marginal channels occur as a complex of well-defined channels, as well as a large number of short channels and step-like features. They are well developed parallel or subparallel to the contours of the 'Incised slope terrain' (Figure 4) and (Figure 38) in a belt stretching from High Bentham to Quernmore. Many of the channels are deeply incised into till and bedrock (Frontispiece). They commonly carry misfit streams, whereas others have been modified by Flandrian drainage to varying degrees. The channel courses are commonly crossed by narrower, more deeply incised present-day stream gullies flowing more directly down the hill slopes, or in some cases a stream may still flow along a channel for part of its course before descending abruptly to a lower level. This series of channels was thought to have formed at successive stages of retreat of the ice margin northwards (see below) and involved meltwaters flowing westwards into the Lune and Conder systems. They were first recognised by Slinger (1936), and documented by Moseley and Walker (1952, pp.42–46, fig. 2), who identified eight possible stages of northerly retreat. The complex pattern of drainage channels from Quernmore to Bentham is now understood to have formed partly subglacially.

A series of south-south-east-aligned channels, incised mainly through till to a depth of over 20 m in places, occurs in the area between Quernmore and Abbeystead (Figure 38). Many of these channels, for example Sparrow Gill [SD 532 559], are greatly modified by Flandrian drainage. They were probably initiated by ice-marginal meltwater flowing southwards into Wyresdale at successive stages as the ice front withdrew westwards. At an early stage, some of the meltwater may have been carried around the western end of Clougha from the north side of the 'Ward's Stone range'.

Between the 'Ward's Stone range' and the Lune valley (Figure 38), three main phases of ice decay have been recognised. Firstly, as the ice withdraw from the 'Ward's Stone range', ice-marginal drainage flowed westwards initiating the proto-Conder valley and incising a complex of channels in bedrock north of Clougha. Fluvioglacial sediments carried by these melt-waters formed the Quernmore Terrace at Quernmore. Secondly, on further ice decay, meltwaters flowing along the upper Roeburn valley were diverted westwards into the large Haylott channel while ice remained in the area of the lower Roeburndale valley. These were augmented by meltwaters from farther east which were fed down the Salter Beck and Harterbeck channels, across what is now Roeburndale. These melt-waters drained via the Artle Beck channel to form the thick fan of coarse bouldery gravels of the Caton Terrace at Caton. The final phase of ice-marginal drainage in this area occurred as the ice margin retreated into the proto-Lune valley, down the northern slope of Caton and Claughton moors. During this phase, lower Roeburndale eventually became ice free. At an early stage of this phase, a series of subhorizontal, generally step-like escarpment features or one-sided channels cut in till was formed by meltwater flowing south-westwards into the Artle Beck channel. Glacial ice is thought to have formed the northern sides of these ephemeral channels which were generally too short lived to have been cut into bedrock. Later, meltwater from the lower Roeburn cut the presently dry Rantree, Nottage Crag and Anas Gill system of channels from which the sediment-laden meltwaters emerged to form the Brookhouse Terrace. In the final stage, westerly flowing meltwaters from the lower Roeburn carved the Farleton Beck channel through till.

Lowland channels

The drift-covered lowland area in the west of the district is traversed by a series of channels of generally low gradient. Many have a surface expression as dry valleys or carry small misfit streams. They appear to be graded to a late Devensian sea level, perhaps 40 m below present sea level (BGS, 1984). They are now mostly filled with glaciofluvial deposits and follow sinuous courses around drumlin topography. A good example is the Slyne Channel from east of Bolton-le-Sands [SD 496 682] to Skerton [SD 4762 6372], the A6 trunk road following its route to the south of Slyne [SD 477 656]. The sinuous channels to the south of Lancaster probably continued to carry meltwater from an ice front situated to the north, after deglaciation of the immediate area but before the present-day Lune drainage was established.

Buried valleys

The Lune Channel is a buried, drift-filled channel beneath the Lune estuary. It runs southwards from Lancaster to Bank End [SD 440 528], east of the Cockersand Abbey to Heaton bedrock 'highs' (Figure 34). Boreholes in the Lune valley at Lancaster suggest that the Lune Channel continues northwards at least as far as the Motorway crossing [SD 496 645], rockhead being proved at 14 m below OD in borehole (SD46SE/3) [SD 4888 6405] and 44 m below OD in borehole (SD46SE/17) [SD 4622 6187] to the north and west of the city, respectively. The channel cannot extend farther upstream as rockhead occurs well above OD between Halton [SD 500 647] and the Crook o' Lune [SD 521 645]. The channel appears to be graded to a late Devensian low sea level, and it is tentatively suggested that it may connect offshore with the Lune Deep, 20 km to the west-south-west of Sunderland Point [SD 423 552], where rockhead is at about 116 m below OD (BGS, 1984). The presence of the channel indicates that the Lune's present course south-westwards from Lancaster was established in late-glacial times.

Postglacial deposits

These deposits were laid down in the late Devensian (late glacial') and Flandrian, a period between the complete disappearance of the ice sheets and the present day. The early postglacial history of the district involved river incision and terrace formation, the accumulation of peat and lacustrine alluvium in some kettleholes (Barnes, 1975), and the formation of head deposits and major landslips. Later, following a rapid, glacio-eustatically controlled rise in sea level in early Flandrian times (Tooley, 1974), marine and estuarine silts and clays were deposited in the low-lying ground in the west of the district. Peat developed extensively in both upland and lowland areas, hill wash or colluvium accumulated on lower slopes, and alluvium was deposited in the lowland areas. In the upland areas, terrace formation through incision and aggradation at times of spate continues on juvenile streams, and hill peat now suffers more erosion than accumulation. The influence of man has been increasing in historic times, culminating in the refashioning of the land surface by mineral extraction, drainage ditches and the dumping of made ground.

Head

Head comprises heterogeneous deposits, derived by downhill movement, through gelifluction and solifluction, of oversaturated drift deposits and near-surface bedrock. The optimum period of head formation spans the time from the early stages of glacial retreat, when the ice sheets were clearing the upland areas and periglacial processes were widespread, to the total deglaciation of the district in 'late glacial' times, when periglacial conditions existed in the Loch Lomond Interstadial. During the Flandrian, further downslope movement of surface materials took place by solifluction. Because they are difficult to distinguish from head, some Flandrian gravitational creep and slope downwash deposits, or colluvium, are probably included.

Head was probably deposited on most slopes, but has only been mapped where it is consistently over 1 m thick. Slope deposits derived from bedrock underlie extensive gelifluction terraces in the upland valleys of the Bowland Fells in the south-eastern corner of the district, in the headwaters of the Whitendale c. [SD 65 56], Tarnbrook Wyre c. [SD 60 56], Brennand c. [SD 65 53], Hindburn c. [SD 65 60] and Roeburn c. [SD 62 60] rivers, and on the flanks of Marshaw Fell c. [SD 58 52] and the slopes c. [SD 57 57] below Ward's Stone. It comprises poorly consolidated, sandy silt to silty sand, with ill-sorted, angular sandstone fragments up to boulder grade, as well as more clay-rich deposits derived from till. The deposits are generally thin on the steeper slopes, but may be up to 5 m or more thick on more gently sloping ground.

Head is also present in the west and north of the district, where the ground is mainly till covered. It infills low ground and generally comprises a yellowish brown stony clayey silt derived from till on the higher slopes.

Marine and estuarine deposits

An almost flat spread of estuarine, marine and shoreline deposits covers much of the western part of the district (shown in (Figure 4) as the 'coastal plain' and intertidal flats), where the sea invaded low-lying parts of the post-glacial surface. Deposition probably commenced some 9000 to 8000 years BP (Tooley, 1974, 1985), associated with a rapid rise in sea level from 20 to 15 m below OD caused by the rapid decay of the Laurentide Ice sheet and a landward expansion of a 'proto-Morecambe Bay'. General sea level continued to rise more slowly after about 7000 years BP, by a succession of marine transgressions separated by regressive phases (Tooley, 1974, 1985; Huddart et al., 1977), culminating at about the present sea level some 6000 years ago. This led to a landscape very different from that of today, with parts of the 'drumlin belt' isolated as two larger islands from Morecambe to Middleton [SD 41 62] to [SD 41 57] and Heaton to Overton [SD 43 61] to [SD 43 57]. Individual drowned drumlins formed smaller islands between Morecambe, Bolton-le-Sands [SD 484 680] and Lancaster (Figure 37), and south of Glasson [SD 444 561]. (Figure 36) shows a section through one at the Heysham power stations. Most buried peats encountered in site investigation boreholes in the Heysham area (see p.00) are probably the older, early Flandrian peat level and do not signify these later regressive stages, although peats encountered in a few boreholes, e.g. (SD46SW/23) [SD 4376 6404] and (SD46SW/222) [SD 4230 6120], may lie within the Older Marine Deposits. Thin peaty levels in Older Marine Deposits are known from the Morecambe Bay Barrage Boreholes ((Figure 37); Tooley, 1974).

Older marine deposits

The 'Coastal plain', underlain by early Flandrian older marine deposits from Carnforth [SD 495 705] to Cockerham [SD 463 523], covers an area of some 100 km2 and extends inland for up to 6 km (Figure 4). Much of the area lies within the range of the highest tides and would be flooded were it not for the protection afforded by sea walls constructed over the last 250 years. There are many minor exposures of dark bluish grey clay or pale greyish brown silty clay and silt in the myriad of drainage ditches across the area. Boreholes have proved more than 10 m of these sediments, but thicknesses of 2 m to 5 m are more general. Reade (1904, plate XII; redrawn by Tooley, 1974, fig. 3b) provided a section through up to 15 m of these deposits, exposed during the Heysham Harbour excavations, overlying the early Flandrian peat and 'late glacial' silt and sand. The lower part is a foraminiferarich clay overlain, apparently unconformably, by shelly fine sands with lenses of oyster shells which may, at least in part, be tidal flat deposits. Older marine deposits in the area of the Heysham power stations are shown in (Figure 36).

Tidal flat deposits

Tidal flat deposits cover an area of approximately 70 km2 in the extreme west of the district. This area is subject to daily tidal effects and periodic storms which may expose older underlying strata from time to time, such as the 'windows' of till exposed on the foreshore at Morecambe [SD 41 63] and Half Moon Bay [SD 406 608]. Boreholes drilled offshore prove the sediment to consist mainly of fine- and medium-grained sand with shell fragments. These deposits are known to thicken rapidly offshore (Figure 37). Confidential boreholes have recorded thicknesses of 10 m within 300 m of the coastline, although thicknesses of 3 to 4 m are more common. Further boreholes show that the thickness increases to more than 25 m about 3 km offshore.

Tidal river or creek deposits

These deposits occur in the tidal estuaries of the rivers Lune, Conder and Cocker, and consist mainly of greyish brown muddy silt. For convenience, their inland limit is taken at the modern tidal limit. The thickness of the deposit varies from zero in the channel bottoms up to 4.3 m (as proved in borehole (SD46SW/347) [SD 4468 6117] ) close to the boundary with the saltmarsh.

Storm beach and older storm beach deposits

The saltmarsh and tidal flat deposits are commonly terminated landwards at the high-tide mark by a narrow strip of storm beach, which has been built up by storm waves to a height of about 1 m to 2.5 m above the surrounding terrain. These beach sediments generally consist of coarse sand, shingle and cobble gravel. The range of clast sizes depends partly on the width of any protecting saltmarsh and on the availability of fresh material from nearby eroding till deposits.

Inland from the present coastline, a low gravel ridge [SD 424 563] at Sunderland and another [SD 446 535] northwest of Cockerham are interpreted as former storm beaches. The gravel thicknesses are unknown.

Saltmarsh deposits

These deposits are limited to the area of approximately 10 km2 covered by salt-tolerant vegetation. Their main occurrence borders the Lune estuary, from around Sunderland c. [SD 42 55], through the Glasson area [SD 45 56] and Colloway Marsh c. [SD 45 58], to Aldcliffe Marsh c. [SD 45 60]. They also form coastal flats around the mouth of the River Keer c. [SD 48 71], between Bolton-le-Sands and Hest Bank [SD 47 68] to [SD 46 66] and north of Sunderland Point c. [SD 41 56]. The sediment is mainly fine sand and silty mud. At spring tides, the Lune estuary below Lancaster resembles a lake, with the saltmarsh completely flooded. Beyond the sea walls and saltmarsh edge, sediment deposition and erosion is finely balanced. Through comparison with the limits indicated on the 1972 Ordnance Survey 10 000 scale maps, the saltmarsh is known to be accreting in the Lune estuary and around Sunderland Point, and to be eroding to the north of Hest Bank.

Shell bank

Banks of mussel beds occur along the coast in the intertidal zone, particularly offshore from Morecambe and Heysham. The deposit is probably thin and is strewn with boulders derived from the red till below, which is occasionally exposed during the formation of ephemeral gullies. The shell banks are composed of shell debris shingle, sporadic stones and incorporated intertidal silt, the whole being covered by colonies of living mussels. A feature of the banks, for example Foot Skear [SD 410 630], is the abundance of oyster shells which must have once flourished in the area.

River terrace deposits

The drainage system of the district is relatively immature, being essentially derived from the pattern of meltwater erosion established during deglaciation. As a consequence, most upland rivers and streams are juvenile, and are still actively downcutting to a lower base level through drift and bedrock so that incision is more important than lateral channel migration and aggradation on the valley-floor. Terrace formation is extremely irregular in these upland areas, with innumerable, small, undifferentiated terrace facets, underlain by 2 to 4 m of coarse imbricate bouldery gravels, resulting from cut-and-fill processes during large flood events. Work on coarse-grained flood deposits elsewhere in the northern Pennines (Macklin et al., 1992) suggests that accelerated rates of channel entrenchment and terrace formation in late Roman times and during the eighteenth century were caused by increased runoff and flood magnitude, associated with a wetter and cooler climate. Flow was augmented by early historical woodland clearance, and drainage of the catchment in more recent times.

Typical juvenile rivers are the Wenning, Hindburn and Roeburn. Along their courses, at levels up to 2 or 3 m above the present stream surface, individual terrace facets and their underlying gravels are typically juxtaposed, and so have been mapped as undifferentiated terrace deposits. At higher levels above the present stream level, e.g. up to 11 m along the Artle Beck gorge [SD 551 626], relict individual facets occur, underlain by coarse gravels which may be partly of glaciofluvial origin. Along juvenile streams, the terrace deposits consist mostly of horizontally stratified, ill-sorted, coarse, cobbly, bouldery gravels up to 4 m thick with subordinate lenses of gravelly sand.

More continuous aggradational river terrace deposits are developed in the more distal parts of the river valleys as the long-profile gradient declines. These sectors are typically underlain by glaciofluvial deposits. Examples are to be found along the River Conder around Galgate [SD 484 553], along the River Wyre downstream of Catshaw [SD 547 536], and along the south bank of the River Lune between the Motorway crossing [SD 496 645] and Skerton Bridge [SD 480 623]. In these examples it is likely that thick glaciofluvial deposits are being reworked in part.

Along the River Conder three terrace facets are developed at about 2 m, 4 m and 6 m respectively above the present floodplain, the lowest being the most extensive. The underlying deposits consist mostly of well-sorted sand and gravel up to 5.3 m thick. The higher terraces mark local, discontinuous erosion surfaces that developed as the glaciofluvial infill of the Conder valley was reworked. Only the lowest terrace can possibly be related to a single aggradational event.

Two terrace-flats developed along the River Wyre appear to represent two distinct phases of aggradation. The deposits beneath the first terrace have been worked to the south of Dolphinholme, where sections in gravel pits [SD 517 522] showed up to 4 m of gravel overlying 1.5 m of well-laminated sand and silt. Along the River Lune, sand and gravel up to 9.5 m thick has been recorded from boreholes (e.g. (SD46SE/2)) [SD 4860 6354] put down on a terrace about 2 m above the present floodplain.

Alluvial fan deposits

Minor cones and fan-shaped deposits are invariably found at the foot of steeply inclined stream gullies where they enter larger valleys. They vary in size from simple cones, e.g. the pair formed where Great Ugly and Little Ugly cloughs descend onto the 'Lake Quernmore' flat [SD 516 613], to more extensive sheets, e.g. at the mouth of Moulter Beck [SD 6645 6865], along the River Wenning. They may be more than 5 m thick. They generally consist of variably interbedded sediments, ranging from silts to imbricated bouldery gravels. These deposits may also contain woody matter, e.g. at the mouth of Shooters Clough [SD 683 563] below Croasdale Fell. Much of the cone and fan formation is likely to have taken place in late prehistoric to early historic times as a result of man-induced vegetation changes (Harvey, 1985). However, larger fans may have a long, but intermittent, history of sedimentation, commencing with the final stages of deglaciation. A small, simple cone, developed where Gutter Clough joins the Whitendale River [SD 6535 5607], has been investigated by Harvey and Renwick (1987) as part of a wider study of the alluvial fans of the Bowland Fells. A radiometric date of 1200 years BP was obtained on wood from an organic layer beneath the cobble to boulder gravel of the fan. Their work indicates that two main phases of Flandrian erosion can be identified with debris cone/fan deposition, one between 5400 and 1900 years BP and the other at about 900 years BP.

Alluvium

Riverine deposits have been mapped along all but the smallest streams. The most extensive alluvial flats occur: along the River Lune, upstream of Crook o' Lune, and along its east bank tributary, the River Wenning; in the Conder and Wyre catchments; and in the Keer valley. The alluvium typically consists of an upper overbank layer of yellowish to greyish brown silt or sandy silt, which is up to a 4 m thick in the case of the River Lune, overlying a channel deposit of coarse, imbricated, cobbly, bouldery gravel with sandy lenses. The gravels vary greatly in thickness, and in places may be up to 5 m thick. The thicker deposits are probably reworked glaciofluvial sediments. The alluvium of the smaller upland streams generally consists of imbricated boulder gravels. In the lower reaches of the rivers, the superficial fine-grained alluvium merges imperceptibly into estuarine deposits, but boreholes (e.g. (SD46SE/3) [SD 4888 6404] ) prove that gravel at least 6.5 m thick is present at depth. Misfit meltwater channels, as for example that used by the Lancaster Canal to the east of Aldcliffe [SD 470 600], are generally floored by grey-brown and grey silt and clay, commonly overlain by peat. These were formerly marshy areas with minor streams which spread their sediment during periods of flooding.

Older alluvium

Several narrow strips of older alluvium have been mapped in the Galgate area, flooring glacial meltwater channels abandoned because of stream diversion in post-glacial times. The deposits are up to a few metres thick, and comprise clayey to sandy silt underlain by gravel. They typically form flats intermediate in level between those of the glaciofluvial sheet deposits and the present-day alluvium at the downstream ends of the channels. Two examples are associated with Burrow Beck. One occurs along the valley associated with Ou Beck [SD 481 569], which was formerly fed by that part of Burrow Beck upstream of Burrow Beck Bridge [SD 480 584]. The other occurs farther down Burrow Beck and northwards from Conder Green [SD 461 560], where a now-dry valley was formerly used by the beck before its diversion westwards at Ashton Hall [SD 462 573].

Lacustrine deposits

Minor patches of lacustrine alluvium infill irregular enclosed depressions which were originally the sites of 'late glacial' lakes initiated during deglaciation. Most lakes probably continued into historical times but are now largely drained. Fine examples of lacustrine alluvium, typically with a cuspate polygonal outline and about 300 m across, infill intra-drumlin hollows in the drumlin field c. [SD 55 70] to the north of Aughton, where many are interlinked by minor streams. Many of the kettleholes in the glaciofluvial ice-contact terrain, for example the kettlehole [SD 522 633] in Quernmore Park where a pond still exists, are also infilled with lacustrine deposits. Few glacial bedrock depressions infilled with these deposits are known. Two small examples [SD 506 616] occur in Pendle Grit south of Knots Wood.

There are few sections in the lacustrine deposits, which probably consist mainly of silts and clays with peaty layers. Some of the lower deposits are likely to be glaciolacustrine in origin.

A small ponded area remained in the central part of the site of glacial 'Lake Quernmore' well into Flandrian times. A borehole [SD 5171 6102] proved an upward sequence, up to 6 m thick, of grey clay, greyish green calcareous Chara mud with layers of silt, dark micaceous silt or sand, and peat with Potamogeton (Moseley and Walker, 1952). The calcareous mud yielded a temperate freshwater fauna typical of fresh clear shallow water, including the gastropods Limnea pereger (Muller) and Planorbis sp., and the ostracods Cypridopsella villosa Uurine), Pionocypris elongates (Kaufmann) and Candona candida (Muller).

Peat and 'late glacial' deposits

Peat formation began at the end of the Devensian cold stage and has continued in parts of the district to the present day. There are numerous, small, scattered deposits in the lowlands, and more extensive but largely dissected spreads on the 'upland fell' and 'Ward's Stone range'.

Buried 'Late Glacial' deposits and early Flandrian coastal peat

Thin buried peats, typically a fraction of a metre thick, have been encountered in many site investigation boreholes in the Heysham and Morecambe areas and in the Morecambe Bay Barrage Feasibility Survey. They occur up to about 1 m above till, and are separated from it by a thin bed of clay, silt or sand. The peat is commonly described as a hard, consolidated, dry, laminated deposit. Heights of the peat in boreholes range between about 17 m below OD offshore to about 3 m above OD inland. It occurs around 10 m below OD on the coast at Bare (boreholes (SD46SW/52),  (SD46SW/53),  (SD46SW/54),  [SD 443 649] ) and Heysham Sands ((SD46SW/344) [SD 4095 6230] ); 4 m below OD at Heysham Moss ((SD46SW/123) and ((SD46SW/124) [SD 427 610] ) and inland west of Bare (e.g. (SD46SW/480) [SD 4454 6452] ); within 1 m of OD south of Heysham Moss ((SD46SW/116), ((SD46SW/118) and ((SD46SW/121) [SD 421 604] ), inland from Morecambe (e.g. (SD46SW/71) [SD 4305 6349] and (SD46SW/360) [SD 4260 6229] ) and south of Heysham Harbour (e.g. (SD45NW/265) [SD 4074 5976] ); and 3 m above OD at Torrisholme ((SD46SE/21) [SD 4553 6424]), Bolton-le-Sands (augerhole at [SD 4735 6760] ) and near Crag Bank, Carnforth (e.g. (SD47SE/12) [SD 4860 7018]).

These records probably mainly represent one discontinuous, generally seaward-sloping peat horizon, and evince an early Flandrian topography that was drowned by the postglacial eustatic rise in sea level and covered by older marine deposits ((Figure 37); Tooley, 1974). Based on excavations during the construction of Heysham Harbour, Reade (1904, plate XII) showed the peat to overlie a thin bed of silt or sand above till, and to fall seawards at a gradient of 1 in 34, parallel to the surface prior to marine submergence. From evidence of mammal remains, given below, the silt or sand beneath the peat is known to be at least partly 'late glacial' in age. The peat is likely to be diachronous. Samples collected between 16–17.5 m below OD in three boreholes offshore from Heysham power stations [SD 393 599] have yielded radiocarbon dates between c. 8925 and 9270 years BP, and a peat at 16 m below OD in Morecambe Bay Feasibility Survey borehole C6 [SD 4486 6645] has produced a date of c. 8330 BP (Tooley, 1974, figs. 3a and 4). Coastal peat in the Carnforth area, varying from near-surface to at-surface, is recorded as up to 4.9 m thick (in borehole (SD46NE/1) [SD 4879 6987] ) and probably postdates the mid-Flandrian marine transgression (5200 to 7600 years BP) (Shimwell, 1985).

The peat and the underlying, possibly late-glacial deposits have been exposed at several places along the coast, where the older marine deposits have been removed. Reade (1904) referred to sections at a number of places along the shore north of Heysham Harbour, at the level of high spring tides prior to construction of the sea wall. These exposed peat containing trunks of oak, underlain by a thin bed of varicoloured, root-bearing clay that rested on till. Crofton (1876) described what may be the same peat horizon resting on blue organic clay, exposed occasionally beneath the drifting shingle of the coast at Morecambe c. [SD 430 645] and Bare [SD 445 651]. Moreover, a bed of peaty mud is frequently exposed on the foreshore [SD 414 620] near the former site of the lime kiln north of Heysham village, from where birch trunks were recorded by Crofton (1876). Moseley and Walker (1952) described this site as a 'submerged forest' with 'upright stumps of trees, rooted in the underlying clay', and recorded a section comprising 1.7 m of organic muds, with wood and plant fragments, resting on 0.16 m of stoneless, clayey mud and silt, overlying till. They suggested from pollen analyses that the organic muds belonged to the Atlantic period and pollen zone VIIa of West (1968), dated at about 6–7000 years BP. Local fishermen still trawl up tree trunks and branches from 'Heysham Lake' c. [SD 400 620] which lies offshore from the village.

Mammal remains (now in the City Museum, Lancaster; (Plate 14)) were discovered between till and this early Flandrian peat during construction of Heysham Harbour. The skull and attached horns of an aurochs, Bos primigenius, were found [SD 401 602] 9 m below OD, in the thin bed of grey silt or sand that overlies till and is directly overlain by a 0.3 m-thick bed of peat (Reade, 1904, p.182; Hogarth, c. 1930, p.61; index card, Lancaster City Museum). The antlers (2.35 m span) and adjoining part of the skull of a male giant deer, Megaloceros giganteus, were recovered from the same excavations (index card, Lancaster City Museum), very probably from the same silt bed. After the late Devensian Dimlington Stadial glaciation of Britain and Ireland, the giant deer is known to have been restricted to the mild interstadial conditions of late-glacial pollen zone II, or the Windermere Interstadial, between c. 13 000 and 11 000 years ago, during which time it flourished and then became extinct (Stuart, 1982). Crofton (1876) recorded washed up lumps of hard peat, wood and several antlers of red deer, Cervus elaphus, along the shore between Heysham and Morecambe. These were probably derived from the same peat and underlying sediments lying offshore.

Other lowland peat

In addition to the peat lying buried offshore or along the coast, lowland peat occurs inland in many small enclosed areas, many of which are kettle holes or intradrumlin hollows. Deposits are found north-east of Carnforth [SD 510 714], east of Nether Kellet [SD 528 689], at Bolton-le-Sands [SD 483 682], east of Torrisholme e.g. [SD 462 644], near Potters Brook [SD 493 522], on Heysham Moss [SD 423 610] and many other places. Lowland peat also floors meltwater channels, for example the channel [SD 470 596] near Aldcliffe, and former lake sites, such as 'Lake Quernmore' (see below). In general, the lowland peat is up to 1 m thick, but is known to be 2 m thick on Heysham Moss [SD 423 608] where a radiocarbon date of c. 4000 years BP has been obtained (Huddart et al., 1977). Pollen analyses of samples from a borehole [SD 5171 6102] through a thin peat capping lacustrine sediments at 'Lake Quernmore' (Moseley and Walker, 1952) demonstrate its post-Boreal development in a former lake.

Upland or blanket peat

Much of the high moorland in the south-eastern part of the district is covered by dissected blanket peat. Hill peat is commonly up to 2 m thick, and exceptionally more than 3 m. It typically overlies head or a kaolinised and bleached regolith from the Millstone Grit. Moore (1975) suggested that the formation of blanket peat began around 5000 years BP, and that it was initiated as Neolithic farmers began to clear or thin the forest. In this upland area, the cover of hill peat is thought to have been almost complete in the past, with maximum coverage at about 1000 AD (Mayfield and Pearson, 1972). It has since suffered dissection and deflation, accelerated in recent years by drainage and burning (Thompson, 1987). Gullying has given the hill peat a convoluted outline, and there are many isolated hags. In some areas, e.g. around Ward's Stone [SD 592 587], the peat has suffered almost complete erosion and only a few prominent hags remain. Elsewhere, for example on Red Mire [SD 680 656], the deposit is still reasonably intact. Pollen analyses of hill peat at Brownley Hill [SD 566 593] and White Moss [SD 638 643] were given by Moseley and Walker (1952). At the former site, they concluded from the high frequency of alder and the low frequency of pine pollen that the peat had formed since the Boreal–Atlantic transition. At the latter site, the data were less precise but gave an overall indication that peat at White Moss began to grow in the post-Boreal period. During the present survey, scattered Neolithic flint and chert flake artefacts were found on gritstone surfaces across the fells where the peat cover had been eroded. The most interesting find (by AB) was of thirteen late Neolithic flint flakes at a depth of 0.5 m in the face of a 2 m-thick peat stack [SD 6245 5742], at about 473 m above OD on Brennand Fell. The flakes were derived from marine pebbles, probably originating on the Yorkshire coast. They were illustrated by Matthews (1990; see Appendix 4), who also demonstrated from palynological analysis that the peat spans Flandrian pollen zones I to III of West (1968) .

Scree

Discontinuous, narrow aprons of coarse scree occur along the foot of the rocky Ward's Stone Sandstone escarpment, on the south side of the 'Ward's Stone range' from below Birk Bank [SD 532 608], Clougha, in the west, to Tarnbrook Fell [SD 61 57] in the east. The deposit comprises jumbled angular blocks and is unlikely to be more than a few metres thick.

Cave deposits

Over the years, cave and fissure systems, partially or wholly filled with sediment, have been revealed by quarrying of the Urswick Limestone in the Nether Kellet area. During the survey, one small cave [SD 5101 6953] at Leapers Wood Quarry was found to contain an unfossiliferous 6 m sequence comprising finely laminated grey and pale brown clay, resting on brown stony clay, with reddish brown and orange-brown clay and sand at the base. The colour of the lowest deposits may indicate derivation from a temperate, interglacial palaeosol, and deposition of the sequence may span the last interglacial/glacial cycle.

Blown sand

Blown sand occurs in a linear belt along the present-day coastline, northwards from Sunderland Point [SD 413 554] to [SD 416 574]. It forms a ridge up to 2 m high and 250 m wide. Other small areas of blown sand occur at Potts' Corner [SD 413 572], and in a 50 m-wide strip [SD 411 590] at Middleton Tower. The sand is generally yellowish brown and fine-grained. The thickness of this deposit is uncertain.

Vincent and Lee (1981) described widespread silts, up to 2 m thick, of probable loessic origin overlying limestone outcrops around Morecambe Bay, to the north of the district. Unmapped brown silty loam with dispersed pebbles in the Carnforth area, e.g. overlying till in a trial pit [SD 5081 6972], may be partly loessic in origin.

Landslips

Landslips affecting both Millstone Grit and superficial deposits are common on steep slopes in the central and eastern parts of the district. Many of the larger examples were initiated during late Devensian deglaciation when glacially oversteepened slopes were left unsupported. An example of this type is the large slip complex forming an apron along the south slopes of Ward's Stone c. [SD 57 57], which affects an area of over 4 km2. Similar extensive slip complexes also occur on the south side of the Udale Beck valley [SD 566 603] and on the eastern slope of Whitmoor [SD 590 635].

Many rotational slips on steep valley sides have been caused by the active downcutting of glacial meltwater and later fluvial processes. Good examples occur along Foxdale Beck [SD 570 613] to [SD 593 601] and the Hindburn [SD 64 64] valley.

Major slips have also occurred where the dip of the Millstone Grit strata is concordant with the hill slope. Examples of such bedding plane slides occur at Screes End [SD 602 553], Swine Crag [SD 609 559] and on Mallowdale Fell [SD 60 60], the latter affecting an area of over 1 km2.

Slips that involve mainly till are also extensively developed in many of the incised smaller river valleys, e.g. along the Conder valley [SD 497 570] to [SD 500 575] and along the upper reaches of Tarn Brook [SD 565 635], Udale Beck [SD 55 61] and Greenholes Beck [SD 577 634]. Slipping is mainly caused by stream incision or toe removal, though several active slips in till have been partly induced by road construction (see Economic Geology).

Made ground

Extensive areas of made ground occur in the vicinity of Lancaster, Morecambe, Heysham and Carnforth. The deposit was generally dumped on marine deposits to raise the land surface prior to development, e.g. at Balm Hill [SD 441 634] and in the area around the Heysham power stations (Figure 36). Materials are either of local origin or have been imported. Made ground also forms embankments carrying roads e.g. [SD 489 569], railways e.g. [SD 482 557] and canals e.g. [SD 478 553], with material derived from cuttings or local borrow pits. Other embankments serve as coastal defences e.g. [SD 420 634].

Small pits and quarries, for example Scotch Quarry [SD 4845 6115], and many former marl pits in the west of the district, have been partially or wholly infilled. Some quarries are known to be infilled with domestic waste, for example the former sandstone quarry [SD 4690 5613] to the north of Parkside Farm. Former gravel workings around Carnforth [SD 49 70] have been backfilled with unknown material.

Chapter 9 Structure

The Lancaster district lies within the northern part of the Dinantian Craven Basin, in which a number of important basin margin and intrabasinal structures have been recognised ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). Some of the latter were identified from Bouguer gravity anomalies ((Figure 40)A). Since Hudson (1933) introduced the term Craven Basin, its precise definition and limits have been the subject of much discussion, particularly with regard to its north-western extent. The term Craven Basin is used in this account in the wider sense suggested by Grayson and Oldham (1987), Riley (1990) and Aitkenhead et al. (1992). It encompasses the area bounded to the north by the Southern Lake District High and the Askrigg Block and to the south by the Central Lancashire High. It is thus broadly equivalent to at least part of Ramsbottom's (1974) Bowland Basin. The latter term has subsequently been widely used to define slightly differing areas (Gawthorpe, 1987; Lee, 1988; Gawthorpe et al., 1989; Horbury, 1989; Fraser and Gawthorpe, 1990). We here refer to the main Craven Basin depocentre, bounded by the Bowland High, Askrigg Block and the Central Lancashire High, as the Bowland Sub-basin (see below).

The northern margins of the Craven Basin are formed by the southern limits of the Southern Lake District High (Grayson and Oldham, 1987) and the Askrigg Block ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). Intrabasinal structures include the Lancaster Fells Basin (Gawthorpe et al., 1989), referred to here as the Lancaster Fells Sub-basin ((Figure 40)A, anomaly E), which is associated with the Westphalian strata of the Ingleton Coalfield and is separated from the Askrigg Block by the north-west–south-east South Craven Fault Zone ((Figure 40)A, lineament F). To the south of the sub-basin, gravity values increase to a broad high under the Bowland Fells ((Figure 40)A, anomaly A), forming part of the Bowland High of Lawrence et al. (1987) (the continuation of the Bowland Block of Arthurton et al., 1988). This marks the development of a northwards dipping tilt-block, the south-eastern limit (or crest) of which is marked by the gravity feature ((Figure 40)A, anomaly C) known as the Bowland Line (Arthurton et al., 1988; or 'Sykes Line' of Lawrence et al., 1987). This feature is closely associated with the Sykes and Catlow anticlines. Gravity values decrease rapidly to the south-east of this anomaly, indicating deepening of the basement to form the main depocentre of the Craven Basin in the Bowland Sub-basin (Bowland Basin of Lawrence et al., 1987; Gawthorpe et al., 1989). The northern limits of the South Fells Tilt Block (Lawrence et al., 1987) lie along the southern boundary of the district ((Figure 40)A, anomaly B). Superimposed upon the anomaly, the Nicky Nook Anticline and the Luddocks Fell–Hareden Syncline have been recognised as a weak local Bouguer gravity high and low respectively (Aitkenhead et al., 1992).

The Carboniferous rocks of the district were folded and faulted most intensely during the Hercynian (or Variscan) orogeny at the end of the Carboniferous Period, to produce a group of structures that form part of the Ribblesdale Fold Belt (Phillips, 1836). Some profound earth movements also took place in this region at intervals through Dinantian and early Namurian times (Arthurton, 1984; Gawthorpe, 1987).

The Permo-Triassic rocks of the western part of the district are mostly concealed beneath Quaternary deposits, and their structure is largely conjectural. However, from the few boreholes and from seismic reflection data, it appears that the Permo-Triassic rocks are mostly unaffected by the type of folding and faulting prevalent in the Carboniferous tract to the east. The structural picture is dominated by north–south faulting, with the Permo-Triassic rocks preserved in the newly discovered, but poorly defined, Torrisholme Basin (Figure 32), (Figure 37) and (Figure 41), and the onshore extension of the East Irish Sea Basin. This structural trend is subparallel to that affecting Carboniferous rocks over a wider area of Lancashire. Faults with a similar trend cut the Silurian rocks in southern Furness and bound the Permo-Triassic rocks of the East Irish Sea Basin (Jackson et al., 1987). Wilson and Evans (1990, p.33) suggested 'that many of these structures lie on inherited end-Silurian lines which were intermittently active at least until Jurassic times'.

Structures within the Permo-Triassic rocks have also been recognised from geophysical investigations. In order to facilitate the description of the structures within the district, the results of the interpretation of the Bouguer gravity and aeromagnetic anomalies (Appendix 1; Busby and Cornwell, 1993) are included in this section. Appendix 2 contains a brief explanation of the physical properties of the rocks and the derivation of the potential field (Bouguer gravity and aeromagnetic) maps. Seismic reflection data used to illustrate the account have been calibrated with reference to the Whitmoor Borehole (refer to (Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8) and (Figure 42)C).

Variscan Plate Cycle

The geological setting of the adjacent Settle district during the Lower Palaeozoic and the possible nature of its pre-Carboniferous basement have been described by Arthurton et al. (1988). Much of the discussion probably applies to the Lancaster district and will only briefly be dealt with here. From the trend of Caledonide tectonic features, the district lies within the North-West England Caledonian Province of Fraser et al. (1990). This province, dominated by north-east–south-west-trending structures, lies to the north of the Midlands Microcraton around which the Lower Palaeozoic (Caledonian) structural fabrics swing. The microcraton, interpreted as acting as an indenter during the closing of the Iapetus Ocean in early Palaeozoic times (Soper et al., 1987), had a profound effect upon the basement structure of this part of Britain, and ultimately upon the orientation and development of Carboniferous basins. Many of the folds mapped in the district (Figure 41) may be related to the underlying Lower Palaeozoic basement fabric.

Intra-Carboniferous movements

Direct evidence for intra-Carboniferous movements is limited and widely dispersed, but there is reason to suppose that tectonic events affecting more distant parts of the Craven Basin would have had some effect in the district. Sedimentological studies of Dinantian strata reveal conglomeratic carbonate rocks, unconformities, non-sequences, erosional palaeovalleys on the platform edges, and intraformational slump or slide structures (Gawthorpe, 1986; Horbury, 1989; Riley, 1990; (Plate 2)). Intra- formational slumps and slides may be caused by earthquakes, or by an increase in the slope of the sea floor, or simply by rapid sediment accumulation.

The observed sedimentary features of the Dinantian rocks indicate abrupt increases in the relief of the basin margins. Such increases were probably due to movement on marginal faults or on structures controlling the intrabasinal 'highs' and 'lows'. Arthurton (1984) and Arthurton et al. (1988) presented evidence that structures within the Ribblesdale Fold Belt came into existence during the Dinantian, the result of periods of compression, transpression or transtensional stresses. Tilting of the sea floor may therefore have resulted from compressive events during sedimentation or movement of fault-bounded crustal blocks during extensional phases. However, though tectonic activity probably accounts for the observed sedimentary features, the possible effects of regressive eustatic sea-level fluctuations, perhaps related to glaciation, cannot be ruled out (Ramsbottom, 1973; Horbury, 1989).

There is good evidence for tectonic movement in Namurian times (Pendleian to Arnsbergian). Within the Pendleian, an angular unconformity is thought to occur at the base of the Grassington Grit in the adjoining part of the Settle district (Arthurton et al., 1988; Sims, 1988), but no evidence of this is forthcoming from the present district at the base of the Brennand Grit. A widespread Arnsbergian angular unconformity can be demonstrated within the Lancaster district at the base of the Ward's Stone Sandstone, and another of more local importance occurs at the base of the Nottage Crag Grit Member of the Claughton Formation. Syndepositional movements along some west-north-west–east-south-east faults, such as the Claughton and Smeer Hall faults (Figure 41), have disrupted siltstones and sandstones of the Roeburndale and Claughton formations. A considerable increase in thickness of the Ward's Stone Sandstone across the Foxdale Beck Fault implies that this fault also moved, at least during Arnsbergian times (see also Chapter Four).

Seismic reflection data indicate that the Knots Anticline, parallel and in proximity to the Quernmore Fault and Quernmore Syncline (Figure 41), may be an important inversion structure, possibly active during late Dinantian to early Namurian (Pendleian) times. The basal Namurian Pendle Grit apparently rests with angular unconformity upon truncated sequences, interpreted as comprising Bowland Shale and older strata of late Dinantian age ((Figure 42)B).

Variscan deformation

The Variscan cycle extends from mid-Devonian times, marking the end of the Caledonian cycle with the closure of the Iapetus Ocean and the formation of the Laurasian mega-continent in early Devonian times, to the late Carboniferous–early Permian consolidation of the Pangaean supercontinent (e.g. Ziegler, 1990). The early phases were associated with rifting that produced a complex series of extensional basins, probably along the lines of the pre-existing Caledonian framework. The later stages were associated with compressional tectonics during which the inversion of earlier extensional structures occurred. However, there is much debate surrounding the present-day structural configuration of the Craven Basin, particularly the causal mechanism of, and relationship between, the folding and faulting, and the timing of such movements relative to the main depositional cycles. Some models invoke transpressive movements during the Dinantian, whilst others attribute the structures observed at outcrop entirely to end-Carboniferous Variscan deformation.

The control of basement structures on the late Devonian and Dinantian basin development makes determination of the causal stress fields during Dinantian rifting difficult. The folds and faults observed in the Basin, may be variously interpreted to infer three distinct stress fields and crustal extension directions. These are:

  1. east–west extension (Haszeldine, 1984, 1988, 1989; Haszeldine and Russell, 1987);
  2. large-scale dextral shear during the Dinantian. This may have occurred: either in a shear zone related to right lateral transform faulting in the Canadian Maritime Provinces which lay to the south-west at that time (Dewey, 1982); or in response to transpressional movements on basement faults in an east–west dextral shear regime, initiated during sedimentation (Arthurton, 1984); or as a result of back-arc stretching within a regional dextral shear system (Lawrence et al., 1987), crustal stretching and thinning being in response to Rheic subduction (Leeder, 1982; Bott, 1987);
  3. pulsed north–south or north-west–south-east extension (Bott, 1987; Gawthorpe, 1987; Gawthorpe et al., 1989; Fraser et al., 1990). Gawthorpe (1987) considered models involving large-scale strike slip to be inappropriate, because the facies variations can still be traced across the basin.

Rift subsidence

From possibly late Devonian (Frasnian–Fammenian) to early Dinantian times, the region formed part of an intracratonic rift province, with several fault-bounded and linked rift basins including the Craven Basin, referred to as the northern England extensional province by Fraser and Gawthorpe (1990). It was situated some 500 km north of the main Rheno-Hercynian back-arc, from which it was separated by the London–Brabant massif. The classic 'block and basin' model for the network of Carboniferous basins (e.g. Kent, 1966; Bott and Johnson, 1967; Johnson, 1967) has been questioned, with Leeder (1982) and Miller and Grayson (1982) proposing a tiltblock/half-graben model for the evolution of the Carboniferous Dinantian basins. The basins formed as a result of lithospheric stretching, and within these basins thick sedimentary sequences accumulated (Johnson, 1967; Leeder, 1982; Kimbell et al., 1989; Fraser et al., 1990; Fraser and Gawthorpe, 1990). The intervening areas of Lower Palaeozoic strata formed basement highs or blocks, commonly cored by granitic plutons (Bott, 1967; Wills, 1978). The Askrigg Block and Lake District Massif are two such areas which directly affected sedimentary processes across the district.

Extension and synsedimentary faulting accompanied the deposition of possibly upper Devonian to lower Carboniferous strata, marking the main period of rift-controlled subsidence in the Craven Basin. The 1500 m of known Tournaisian and lower Visean strata in the Craven Basin, with an unproven base, contrasts with the total Dinantian thickness of some 500 m in the Holme Chapel Borehole, and attests to the fact that many of the structures controlling sedimentation were active during the late Devonian to early Carboniferous. These structures remained active and controlled much of the sediment transfer and deposition throughout the rest of the Dinantian.

Further periods of relatively minor extension (pulsed rifting) or enhanced tectonic activity variously affected the deposition of the remaining Dinantian succession. The more significant episodes were during the late Chadian to early Arundian and the mid to late Asbian (e.g. Gawthorpe, 1987; Gawthorpe et al., 1989; Fraser et al., 1990; Fraser and Gawthorpe, 1990), with movements continuing into the early Brigantian (Fraser et al., 1990). The intervals between the tectonic events (e.g. late Arundian–Holkerian) mark periods of tectonic quiescence, with slower subsidence during post-rift sag of the basin (e.g. Adams et al., 1990; Fraser and Gawthorpe, 1990). The late Asbian and Brigantian episode of enhanced tectonic activity caused the break-up of marginal reefs along the northern margin of the basin, and marked the end of major carbonate deposition in the basin (Gawthorpe, 1987).

Regional subsidence

The influx of fluviodeltaic sequences at the start of the Silesian is broadly taken to represent the switch from dominantly rift subsidence to regional and essentially thermally driven ('sag') subsidence (Leeder, 1982; Fraser and Gawthorpe, 1990). The evidence indicates that thermal subsidence was probably ongoing during the Brigantian, and may have started even earlier. To the north, Chadwick et al. (1993) have suggested that sedimentation of Asbian and younger sequences in the Northumberland–Solway Basin was in response to regional thermal relaxation subsidence.

In summary, the late Devonian/Dinantian (Courceyan to early Chadian) probably represented an initial period of synsedimentary fault activity, when the greatest rift-induced subsidence occurred. Thereafter, sedimentation was affected by a combination of periods of relatively minor tectonic activity (pulsed rifting) and intervening periods of relative quiescence, when sedimentation was controlled by either isostatic compaction or thermally driven subsidence. From the Brigantian to the end of the Westphalian, sedimentation was mainly in response to thermal relaxation subsidence, although the switch from rift to thermally driven subsidence may have occurred earlier in the Dinantian.

Variscan compression

The final closure of the Rheic Ocean far to the south, with continent-to-continent collision in southern England and central Europe, culminated in the Variscan Orogeny from Bolsovian to early Permian times (the joining of Laurussia and Gondwana to form the Pangaean super-continent). There was regional crustal shortening, with thrust and nappe emplacement in southern England, through France and into Belgium. In northern England, this was reflected in the inversion of pre-existing Dinantian extensional faults, with the folding and erosion of Carboniferous sediments.

The most obvious expression of these movements are the structures which constitute the Ribblesdale Fold Belt, the existence of which was first recognised by Phillips (1836). The Lancaster district generally lies north of the Ribblesdale Fold Belt, the only major fold of this belt impinging on the south-east of the district being the Sykes Anticline (Figure 41). However, folding of Carboniferous strata is present elsewhere in the district, for example in the Grizedale and Heysham anticlines and in the Hutton Monocline with its associated belt of steep dips (Figure 41). Faulting of the Carboniferous strata is dominated by approximately north-west–south-east-orientated faults.

The orientation, relationships and origins of structures within the Craven Basin have been variously interpreted. Based on a comparison with similarly orientated structures modelled experimentally in cover sequences above basement faults (e.g. Tchalenko, 1970; Wilcox et al., 1973), Arthurton (1984) argued that structures developed in cover sequences of the basin (the Ribblesdale Fold Belt) resulted from lateral displacements on basement fractures in a region of dextral shear between the Askrigg Block and the Central Lancashire High during the Dinantian to early Namurian ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). Late Carboniferous lateral displacement on structures in the Craven Basin had previously been proposed by Wager (1931), Hudson and Mitchell (1937), Earp et al. (1961) and Moseley (1962). Gawthorpe (1987), however, suggested that the local unconformities and sediment thickness variations observed in the Dinantian sequences could be related to buried Dinantian extensional faults, many of which were postulated to have suffered reverse movement during the Variscan orogeny, producing the folds in the cover sequences. The Pendle Monocline (Gawthorpe et al., 1989; Fraser et al., 1990) and the Thornley Anticline (Aitkenhead et al., 1992) are two examples of folds cited as inversion structures above concealed and re-activated extensional basement faults. Gawthorpe (1987) argued that the present-day structural configuration of the Craven Basin is the result of a northwest–south-east or north–south-orientated compressive/transpressive regime, active during the late Carboniferous.

The orientation and relationships of folds to faults in the district do not necessarily support the dextral shear model. Indeed, the relationships and angles between folds and faults (Figure 43) support arguments against their generation within the sort of dextral shear environment envisaged by Arthurton (1984). Structures in the district are more readily accounted for by the model of Gawthorpe (1987). Even so, an alternative kinematic interpretation of the structures is possible.

North of the east–west-trending structures of the Variscan Fold Belt and associated Variscan Front in Britain, the Carboniferous rocks are affected by folds whose axial orientation generally lies between north-west and north-east. The Carboniferous strata are unconformably overlain by Permo-Triassic strata, demonstrating a Variscan age for the major deformation. Shiells (1964) advocated an approximately east–west compression to account for structures of this orientation in northern England, a view supported by Benard et al. (1990) and Chadwick et al. (1993). One interpretation of the relationships between folds and faults and their associated slickensides in the district might also indicate a regional west-north-west–east-south-east compression during the Variscan orogeny (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39). Additionally, this direction of compression could also account for the inversion structures seen in the Craven Basin. North-east–south-west-orientated inversion structures of the Northumberland–Solway Basin have been attributed to such an approximate east-west compressional regime (Chadwick et al., 1993). Where the compressive stress field re-activated obliquely oriented structures, severe localised strike-slip and oblique-slip patterns are observed in the Northumberland–Solway Basin (Chadwick et al., 1993), as they are in the Lancaster district.

Observations of cleat orientations in intraformational coal clasts indicate that cleat formed during coal diagenesis (Gayer and Pesek, 1992), and the main cleat is thought to form parallel to the maximum compressive stress (Kulander and Dean, 1993, p.1382). The main cleats recorded from the Arnsbergian, Chokierian and Langsettian coals of the Lancaster district and adjoining part of the Ingleton Coalfield ((Figure 43); Ellison, 1992) are orientated west-north-west-east-south-east, supporting a west-north-west-east-south-east-orientated Variscan compressional regime, with an associated north-northeast-south-south-west extensional element as early as the Namurian.

Deep structures beneath the Carboniferous outcrop

The northern margin of the Craven Basin during the Dinantian was formed by two stable, relatively positive areas of Lower Palaeozoic basement. To the north-west lay the Southern Lake District High, and to the northeast, the Askrigg Block (Hudson, 1938, 1944a). At present these areas correspond to regions where magnetic basement is relatively shallow ((Figure 40)B). The magnetic anomalies of the Lake District have been interpreted as part of a 200 km-long belt of such features, disrupted by the Dent Fault, extending from the Lake District to the Wash (the Furness-Ingleborough-Norfolk ridge of Wills, 1978). The anomalies are probably due to magnetic rocks subcropping at the pre-Carboniferous basement surface, and these could be similar to the magnetite-bearing lower Ordovician sedimentary rocks proved in the borehole at Beckermonds Scar (Wilson and Cornwell, 1982).

In the north-west of the district, the sequences of Dinantian age were deposited close to the south-eastern limits of the Southern Lake District High. To the northwest, the data indicate that a discrete magnetic body with a relatively low susceptibility (about 0.01 SI units) lies at a depth of 2–3 km beneath the Silurian (Ludlow) sedimentary rocks of the Cartmel area ((Figure 40)B). The anomalies over the western part of the Lancaster district appear to be continuous with the Cartmel anomaly of the southern Lake District, but indicate that the magnetic rocks responsible lie at greater depths.

The Askrigg Block, together with the Craven Fault Zone forming its southern margin, lies just to the northeast of the district. Over the block, magnetic anomalies indicate that magnetic basement (possibly the Ingleton Group) lies at a depth of a few hundred metres (Arthurton et al., 1988). Silesian strata forming the Ingleton Coalfield crop out in the north-east of the district, obscuring the basin margin structure. A line of Bouguer gravity anomaly lows, interpreted as arising from a thick sediment pile against a fault scarp, suggests that the transition from block to basin, expressed in the Settle area by the Craven Fault Zone, continues west-north-westwards into the Dent Fault Zone.

The observed magnetic gradient into the Craven Basin suggests the presence of magnetic material at considerable depths, perhaps some 8–12 km (Arthurton et al., 1988), indicating that the Craven Basin is underlain by a great thickness of Carboniferous and older sedimentary rocks.

Gawthorpe (1987) interpreted the main structure of the Craven Basin as a half graben, differential subidence increasing from north to south against the Pendle Fault. However, Hudson (1938) and recent studies (e.g. Arthurton et al., 1988; Horbury, 1989; Riley, 1990) have shown that syndepositional faulting also occurred at the northern margin of the basin, indicating that the basin's structure is more akin to an asymmetrical graben. During the Dinantian, important structural elements partitioned the Craven Basin in the present district. These syndepositional highs and lows, initially inferred from Bouguer gravity anomaly data, were the northern limits of the South Fells Tilt Block, the Lancaster Fells Sub-basin and the Bowland High. Seismic reflection data have been used to elucidate both the structural configuration of the basement and the relationship of the folds to the underlying basement structures. These data illustrate (Figure 42) that top seismic (possibly Lower Palaeozoic) basement over the Bowland High lies between 1.0 and 1.3 secs two-way travel time (TWTT), a depth of about 2.3 to 3.0 km below OD. Over most of the area of the Bowland High, the Dinantian sucession is interpreted to be some 0.8 secs TWTT (about 2 km) thick. However, to the east-north-east of the Whitmoor Borehole, the Dinantian succession appears to be only 0.5 to 0.6 secs TWTT thick (about 1.3 to 1.5 km), with seismic basement at about 0.8 secs TWTT (about 1.8 km depth) from where it deepens south-eastwards across a fault to some 1.2 secs TWTT (about 2.8 km depth).

In the northern parts of the district, the top of the seismic basement is thought to lie at about 1.0 sec TWTT (some 2 to 2.5 km depth) beneath the southern limit of the Ingleton Coalfield, and perhaps 1.3 to 1.4 secs TWTT (about 2.9 km depth) beneath the Quernmore Syncline, in what is interpreted to be the footwall block to the Quernmore Fault ((Figure 42)B). In both of these areas the Dinantian would appear to be some 0.6 to 0.7 secs TWTT thick (about 1.5 to 1.8 km). To the west of the Quernmore Fault, seismic data are generally poor, and the actual age of the top seismic basement is poorly constrained. However, from the seismic character of the entire Carboniferous succession, this appears to be the same seismic reflection as that interpreted to be the top of the Lower Palaeozoic elsewhere in the district, and lies between 0.8 and 1.1 secs TWTT (about 1.8 to 2.5 km depth) in the west of the district, with the Dinantian some 0.5 to 0.7 secs TWTT thick (about 1.3 to 1.8 km) and thinning to the north-west. If this seismic reflection is close to the top of the Lower Palaeozoic, then the seismic data suggest an apparently considerable westwards thinning of the Namurian sequence. Combined with borehole data, it seems that it is part of the pre-Alportian sequences, almost certainly the Pendle Grit and Roeburndale formations, which are thinner here than in the north- east (see also Chapter Four, pp.33, 53).

Two basic interpretations exist for the Bouguer gravity anomaly termed the Bowland Line. Arthurton et al. (1988) attributed it to an inclined density boundary sloping into what he termed the Craven Basin, i.e. the Bowland Sub-basin of this account, the Bowland Line coinciding approximately with the upper edge of the slope. No fault was inferred along the line. The alternative interpretation is that the gravity gradient marking the south-eastern edge of the Bowland High is the result of a concealed Dinantian syndepositional fault (Lawrence et al., 1987; Aitkenhead et al., 1992). Seismic reflection data reveal that the top of the seismic basement reaches depths of about 2 km (about 1.0 sec TWTT) in the area north-west of the Sykes Anticline/ Bowland Line ((Figure 42)A). To the south-east, basement reaches some 3.5 km (1.2 to 1.4 secs TWTT) across a concealed syndepositional fault, attaining a depth of some 5 km farther east within the main basin. The data confirm the importance of the geophysical feature and support the interpretations of Lawrence et al. (1987) and Aitkenhead et al. (1992). The structure probably continues south-westwards as the Thornley–Doeford faults recognised by Aitkenhead et al. (1992). It is offset by the north-west–south-east-trending Clitheroe Fault Zone which acted as a transfer zone.

Structure of the Carboniferous rocks at outcrop

Folds

The Carboniferous rocks cropping out over much of the district have been locally folded into a series of shallow anticlines and synclines with a predominantly north-north-easterly axial trend (Figure 43), and some fold axes appear to be offset across faults with a northwesterly trend (Figure 41). Evidence for some of the structures is limited, particularly to the west of the Quernmore Fault.

As indicated above, only the north-easterly trending Sykes Anticline of the Ribblesdale Fold Belt impinges on the south-eastern corner of the district ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). Moseley (1962) described this as a complex anticline characterised by disharmonic folding, the degree of deformation varying considerably at different strati-graphical levels within the fold. This is shown by the variations in dips in (Figure 9). At the level of the late Dinantian limestones in the core of the structure, it comprises three folds, producing the isolated inliers of the Sykes, Brennand and Whitendale periclines. The limbs of the folds are commonly steep to overturned, and appear crumpled. Additionally, boreholes across the structure reveal that low-angle faulting is common, and slip planes parallel to bedding are ubiquitous in the Bowland Shale and Worston Shale groups (Carlon, 1983). At the level of the Pendle Grit, the structure appears to be a single, flat-topped anticline, the limbs dipping away at about 30°. To the south-east lies the broad, shallow Beatrix Fell Syncline, the core of which is marked by an outlier of Brennand Grit.

Seismic reflection data indicate that the Sykes Anticline is probably a Variscan inversion structure, associated with concealed north-east–south-west-trending basement faults that define the edge of the Bowland High (Bowland Line) and were active during the Dinantian ((Figure 42)A). Sequences of Dinantian age, particularly those predating the Chatburn Limestone, i.e. early Chadian and older, thicken southwards across the fault, in contrast to those of Namurian age which are largely unaffected by it. Subsequent Variscan compressive/transpressive events reactivated the fault, reversing movements and generating the fold in the overlying sedimentary sequences.

In the north-eastern part of the district, Silesian rocks are affected by broad synclinal flexures at outcrop. The north–south-trending Goodber Syncline appears to pass northwards across north-westerly trending faults into a similar broad flexure, part of the Ingleton Coalfield Syncline (e.g. Ford, 1954; Moseley, 1972). The latter is itself intimately associated with the Craven Fault belt. A group of five broad and open folds, with a west-southwest–east-north-easterly trend, affects the Roeburndale Formation in the Wyresdale Tunnel. The Grizedale Anticline, the most important fold of the group, has dips of up to 20° on the steepest limb adjoining the parallel Dunkenshaw Syncline. The Grizedale Anticline may pass east-north-eastwards, under thick drift cover, into the similarly trending Ward's Stone Dome, a broad, periclinal flexure seen to mostly affect the Ward's Stone Sandstone around the summit of Ward's Stone.

West of the Gressingham, Quernmore and Dolphinholme synclines in the western part of the district, the trend of the folds is north-north-easterly (Figure 41) and parallel to the Quernmore Fault, in contrast to the more north-easterly trend of folds in the Ribblesdale Fold Belt. Dips on the limbs of these folds are commonly 15° to 20°, while the east-south-easterly limb of the Quernmore Syncline dips at up to about 50°. The Heysham Anticline, a southwards plunging fold in lower Arnsbergian strata between Heysham and Middleton, is the only north–south-rending fold.

The Knots Anticline is a major asymmetrical fold with a steeper eastern limb, typically dipping at 45° to 50° although near- vertical to overturned in a group of quarries at Escowbeck near Caton [SD 526 642]. It probably consists of a number of en échelon periclinal folds. The anticline diminishes northwards towards the River Lune but may be related to the en échelon Halton Green Pericline on the north side of the Lune. The Knots Anticline, and southerly continuations that are evident on seismic traverses, is associated with the Quernmore Fault ((Figure 42)B). The fault appears to have had an eastwards directed component of reverse movement, and the fold to the west is interpreted as an inversion structure.

A north–south-trending gravity gradient ((Figure 40)A) is associated with the Quernmore structures and continues northwards into the Hutton Monocline, indicating that the structures may be co-incident or closely related. While the Hutton Monocline is probably related to basement fault movements, the evidence in seismic reflection data is poor and the genesis of the structure remains problematical. The Hutton Monocline (Hudson, 1936; Moseley, 1972) has a near-vertical east-facing limb represented by a belt of strata 0.6 to 0.8 km wide. At Pedder Potts Reservoir [SD 533 702], the vertical dip of the strata decreases to horizontal over a distance of only about 40 m, and no faulting was observed.

Folds are variably affected by the main faults in the district (Figure 41). The fold axes of the Oakenhead, Gressingham, Quernmore, Lancaster Moor and Knots structures appear to be offset by faults with north west–south-east and west-north-west–east-south-east trends. However, those of the Thwaite House, Leapers Wood, Aughton, Wards Stone, Dunkenshaw and Grizedale (Johnson, 1981) structures continue across fault traces with no apparent offset. Other folds appear to be restricted to certain fault blocks, e.g. the unnamed fold pair south of the Woodyards Fault.

Faults

The thick drift deposits present to the west of the Quernmore structure make recognition of structures there difficult. This account will largely address the structure of the Carboniferous to the east and north of the district. Faults affecting both the Carboniferous and Permo-Triassic strata at Heysham are dealt with below, under Permo-Triassic structures.

Many of the faults were observed in gully sections, commonly recognised by the increase in joint density and shattered, brecciated zones. Several of the faults were named by Moseley (1954) and the resurvey of the district has, where possible, followed the nomenclature of previous workers. The faults fall into two main trends.

West-north-west–east-south-east and north-west–south-east faults

The near-surface structure of the district is dominated by a set of approximately west-north-west–east-south-easttrending, subvertical, normal faults (Figure 41). The Hawksheads, Millhead, Gressingham Beck, High Dam Beck, Claughton, Cross of Greet, Foxdale Beck, Smeer Hall, Ellel, Artle Beck, Marshaw and Abbeysteads faults or fault zones are typical of these structures. These faults have been mapped over long distances, typically with a spacing of about 1 km. Throws vary considerably, although the downthrow is generally to the south. This prevailing downthrow direction, coupled with the generally northwards dip of strata, accounts for the repetitive and wide outcrop of Arnsbergian strata across the central part of the district. Slickensides, if present, are generally associated with the faults in this group, and predominantly those of the west-north- west to east-south-east set (Figure 43). The slickensides are horizontal to low angle oblique (i.e. up to 25° from horizontal), with the exception of a few vertical slickensides recorded on faults and accompanying joints in the Littledale area c. [SD 56 62]. A number of faults which affect strata in the Roeburndale and Claughton formations display features associated with syndepositional faulting, e.g. slump folds within sediments (see above and Chapter Four).

Artle Beck Fault Zone

The Artle Beck Fault Zone consists of a complex of closely associated faults over a width of 100 m to 150 m. Many of the faults are well exposed along Artle Beck [SD 54 62]. They are steeply inclined normal faults, with fault planes dipping at 60° to 75°. Individual faults within the zone have throws in opposing senses, so that the effective throw across the zone is only in the order of a few tens of metres at outcrop. The largest fault, named the Artle Beck Fault (Moseley, 1954), downthrows to the south-south-west by the order of 40 m, and has a fault plane dipping at 60° to 65°. The fault zone and other faults to the east-north-east are imaged in seismic reflection data ((Figure 42)C), and in common with a fault of opposing throw just to the south, the fault zone can be identified on satellite images along much of its length. A narrow horst, seen in Artle Beck [SD 543 630], is created along some of the fault zone's length by a parallel fault, 10 m to 15 m to the north and downthrowing to the north-north-east, notably south of Ravenscar Farm.

The Foxdale Beck Fault, locally termed the Cragg Wood Fault by Moseley (1954), downthrows to the south-south-west by up to 255 m and is exposed in Sweet Beck [SD 5505 6103], the fault plane dipping at 60° to the south. The fault forms the northerly extension of a complex fault zone, merging southwards with the northward throwing Green Pot Fault which itself joins the southward throwing Woodyards Fault (Figure 41).

Abbeystead Fault Zone

A complex series of faults with opposing senses of throw form the Abbeystead Fault Zone. Two faults were recorded as broad shatter zones near the Abbeystead Portal. The northern fault of the pair, seen at Gallows Clough [SD 5447 5463], is thought to downthrow to the south, whilst the southern fault dips north at 14°. The fault zone is seen in the seismic reflection data which reveal it to be complex, the dominant fault switching throw along the length of the fault zone. In the west, the main fault downthrows to the south, whereas in the east, itdownthrows to the north. This fault zone, together with the Marshaw Faults (Figure 41), may represent the north-westerly continuation of the Clitheroe Fault Zone ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A). The Bouguer gravity data ((Figure 40)A) reveal that part of lineament (C) coincides with the position of the fault zone, and is interpreted as marking the southern edge of the Bowland High ((Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39)A).

Swaintley Hill Fault, Long Crag Fault, Crossgill Fault and Deep Clough Fault

In many cases, the west-north-west–east-south-east-trending faults are associated with splinter faults that strike in a more north-west–south-east direction. Typical of the latter trend are the Swaintley Hill, Long Crag, Crossgill and Deep Clough faults (Figure 41), the last of these being superbly exposed in a cliff section along Greenholes Beck [SD 5698 6332]. They appear to be genetically related to the main through-going west-north-west–east-south-east-trending faults, as shown by the relationship of the Crossgill and Deep Clough faults to the Artle Beck Fault. The many unnamed faults in this category show both northward and southward downthrow directions, throws to the north being slightly more common.

Hawksheads Fault

The Hawksheads Fault is inferred to trend north-west–southeast to account for the marked change in the strike of the Pendle Grit and adjacent (Dinantian) limestones around Stub Hall [SD 507 667]. The fault has been linked with the Lindale Fault in the Cartmel district, both on the 1:250 000 series Lake District sheet, and by Moseley (1972) who named it the Cartmel–Artle Beck Fault. However, it is proposed that the southern continuation of the fault at Cartmel is the Lindale–Hest Bank Fault. In this case the Hawksheads Fault is either a splay to the latter or terminates against it.

Millhead Fault

The Millhead Fault follows the same trend, with a coarse calcitic breccia that is well exposed at Millhead quarry [SD 4981 7141] and just to the north of the district at Scout Crag [SD 4858 7231]. Shattered sandstones and siltstones in a zone 2 m wide were observed in exposures of the northward-throwing High Dam Beck Fault [SD 5696 7048] to [SD 5706 7034]. To the south-east, this fault merges with the southerly throwing Gressingham Beck Fault. Between these two faults, a north-westerly trending horst contains the apparently offset axis of the Gressingham Syncline (see (Figure 41)).

Claughton Fault

The Claughton Fault is well exposed in a north-east face of a former brick pit at Claughton [SD 5666 6617]. The fault plane dips at 80° to the south-west, with the lower member of the Claughton Formation downthrown against brecciated, siliceous Ward's Stone Sandstone. To the north-west, the Claughton Fault branches into two unnamed faults as it crosses the Millstone Grit outcrop to the south of the Smeer Hall Fault. To the south-east, the fault is associated with several splinter faults, some of which throw to the north, effectively decreasing its throw.

Longmoor, Mount Vernon and Five Lane Ends faults

Within the group of north-west-trending faults, several important structures affect the Namurian strata beneath drift in the Dolphinholme–Galgate–Quernmore area, namely the Longmoor, Mount Vernon and Five Lane Ends faults and two unnamed and more conjectural faults to the west. Much of the evidence for the inferred presence of the faults and the contraints on their subdrift outcrop is derived from stratigraphical information provided by BGS shallow drilling. Their large vertical displacements—up to c. 1000 m in the case of the Mount Vernon Fault and Five Land Ends faults—imply a different origin to that proposed for structures such as the Crossgill and Deep Clough faults mentioned above, and they might be related to similarly trending faults affecting the Permo-Triassic cover to the west. Strata downfaulted in a graben between the Five Lane Ends Fault and the Mount Vernon Fault are locally reddened (Figure 32), indicating that they may be preserved in a structure that postdates the Permo-Triassic reddening.

West-south-west–east-north-east faults

With the exception of the Millers House Fault [SD 622 556], faults with this trend are generally of minor importance. The Millers House Fault is enigmatic, displaying an arcuate east–west trend, parallel to the Bowland Line, with a downthrow to the north. It separates an area to the north, where the structure is dominated by a series of west-north-west–east-south-east faults, from an area of steeply inclined strata to the south. To the south, the faults trend approximately west-south-west–east-northeast and north–south, directions associated with the Sykes Anticline just to the south-east (see above). The fault may be related to the basement fault underlying the Sykes Anticline (see below), which is the cause of the gravity feature termed the Bowland Line.

North-north-east to south-south-west faults

Other than the Rushy Lee and Quernmore faults and an unnamed fault at Heysham Head, faults of this orientation are generally of minor importance. The northnorth-east–south-south-west fault exposed at Heysham Head [SD 4082 6150] cuts the similarly trending Heysham Head Anticline. The fault and several minor splinters have a reverse throw and are associated with barytes veining.

Rushy Lee Fault

The Rushy Lee Fault displays a north-north-east–south-southwest trend, and appears to truncate the Artle Beck and Foxdale Beck faults, two of the main west-north-west–eastsouth-east-trending fault zones in the district. The fault is clearly seen in the River Conder at Rushy Lee Farm [SD 5313 6125], where sandstones of the Ward's Stone Sandstone are severely shattered, with vertical slickensides along joints, and where strata are vertically inclined in places, in a zone 30 m wide. It lies some 2 km to the east of, and has a trend close to that of the Quernmore Fault.

Quernmore Fault

The Quernmore Fault, though not exposed, is one of the largest structures in the Lancaster district. The Pendle Grit sandstones at outcrop are tightly folded against the fault, the folds displaying very steeply inclined or inverted limbs. The Quernmore Fault is associated with a prominent gravity gradient ((Figure 40)A), with gravity values decreasing from west to east, indicating that basement is generally shallower to the west of the fault. Several smaller faults with this orientation are present to the west, some of them being associated with barytes mineralisation. Seismic reflection data indicate the fault is a reverse fault or thrust, probably associated with an inversion structure (the Knots Anticline); from the seismic section, the inferred base of the Pendle Grit has a vertical displacement of 500 to 700 m across the fault ((Figure 42)B). Another appoximately north–south-trending gravity gradient, lineament H ((Figure 40)A), defines the eastern edge of a general low on the Bouguer gravity anomaly map ((Figure 40)A, feature I). It is probably related to the combined effects of the Mount Vernon, Longmoor and Five Lane Ends faults, and is linked to the gravity gradient associated with the Quernmore Fault.

The northerly continuation of the Quernmore Fault

The southern continuation of the Dent Line or Dent Fault, and the nature of the northern margin of the Craven Basin have long been debated. Turner (1935) believed that the Dent Fault continued southwards into the Hutton Monocline, ultimately to disappear beneath the Triassic rocks of west Lancashire. From the gravity data, the Quernmore Fault continues northwards into the Hutton Monocline along lineament G ((Figure 40)A), and thence northwards beyond the, present district to Priest Hutton [SD 530 738], where dips of the Dinantian Urswick Limestone and Gleaston formations and the Pendle Grit increase to near-vertical against an easterly throwing, north–south-trending fault (Turner, 1935). The Hutton Monocline dies out north of Priest Hutton, but a fault continues northwards into the Kendal Fault and a faulted monocline extends north-eastwards to Hutton Roof. The Kendal Fault downthrows westwards with Dinantian Limestones preserved in the hanging-wall block, the foot-wall block comprising Lower Palaeozoic rocks (Moseley, 1972). Other north–south-trending faults and monoclinal structures e.g. the Silverdale Anticline or Disturbance (Moseley, 1972; Underhill et al., 1988) form important embayments into the southern margin of the Southern Lake District High.

Seismic reflection data across the Quernmore Fault ((Figure 42)B) and to the north, near Priest Hutton, suggest that the Dinantian sequences thicken eastwards into the structure. The Urswick Limestone reaches its maximum thickness of about 180 m on the vertical limb of the monocline in the Kirk House section near Over Kellet [SD 5250 6976]. The evidence might indicate the presence of a north–south-trending, eastwards dipping, Dinantian half graben. Similar eastwards thickening of sequences into the north–south-trending Dent Fault Zone, to the north of the district, have been described (e.g. Underhill et al., 1988). One implication is that the south-eastern margin of the Southern Lake District High may have been dissected by a series of small, north–southtrending Dinantian half-graben structures, whose orientations were inherited from pre-existing and long-lived basement structures. Turner (1949) recognised the importance of basement faults for the subsequent structural development of northern England.

Joints

Joint patterns measured in central parts of the district are complex, but appear to show a consistent relationship with the main fault zones (see (Figure 43)). Joint density generally increases as faults are approached, and a predominant north-west–south-east set is developed, associated with a minor set of west-north-west–east-southeast-oriented joints. They are subvertical, generally perpendicular to the beds, and are commonly associated with horizontal or oblique slickensides (up to 25° from horizontal). Joints of this nature may be more correctly referred to as shear joints. Vertical slickensides are rare. On the well-exposed dip slope of Clougha [SD 545 600], certain joints are so well developed as to be clearly seen on aerial photographs. Deep gullies have formed along the joints, the result of the action of glacial meltwater. A further minor set, oriented north-north-east–southsouth-west and best developed in the Caton and Brennand Fell areas, is parallel to a group of minor faults. These joints are not generally associated with slickensides. Slickensides in the district point to subhorizontal movements on many of the west-north-west–eastsouth-east faults and joints, but they probably only reflect the last phases of movement on structures already in existence and modified by late stress fields.

As Moseley and Ahmed (1967) discovered, a joint set may have the same trend as an associated fault but a different inclination, whilst there are equally prominent joint sets at right angles or oblique to the fault trends. As joints are generally perpendicular to the bedding, they may be dragged into a fault with the bedding. Moseley and Ahmed (1967) interpreted this to mean that the joints predate the important fault movements, although the joints and faults may be related in some way. However, it is difficult to assess the magnitude of later post-Carboniferous faulting and its effects on pre-existing joint sets.

Post-Variscan deformation

The faults affecting Permo-Triassic strata display the same regional trend as the structures defining sub-basins and platforms in the Irish Sea Basin (e.g. Jackson et al., 1987). Thus, faults within the district affecting strata of Permo-Triassic age are probably synsedimentary faults initiated in Permo-Triassic times, and are controlled by fractures in the underlying Lower Palaeozoic basement (e.g. Colter, 1978; Jackson et al., 1987).

Development of the East Irish Sea Basin commenced during Permo-Triassic times in response to Atlantic rifting (e.g. Ziegler, 1990), and therefore many of the structures associated with the Permo-Triassic strata of the district are probably of this age. The post-Carboniferous history of the district is not well known or constrained, particularly that relating to post-Triassic evolution. Post-Triassic fault movement has probably taken place, but the evidence is scanty. Hailwood et al. (in Maddock, 1992) present evidence that the remnant magnetism obtained from a slickenside on a fault cutting Carboniferous rocks in Lancashire is indistinguishable from the geomagnetic field vector predicted for the locality for the Neogene to Recent. The East Irish Sea Basin may provide clues for the history of the onshore areas. The post-Triassic history offshore may best be summarised as one of intermittent subsidence, Cretaceous and Palaeogene uplift and faulting, and Palaeogene igneous activity (Jackson et al., 1987). There is evidence for Upper Triassic and Lower Jurassic strata being buried to little more than 2 km to 2.5 km, both offshore (Bushell, 1986; Woodward and Curtis, 1987) and onshore in the Cheshire Basin (Evans et al., 1993), although apatite fission track analysis suggests some 3 km of strata were removed during late Palaeogene and early Neogene erosion throughout north-west England (Lewis et al., 1992; see also p.112).

Structure of the Permo-Triassic rocks at outcrop

Faults and folds affecting the Permo-Triassic rocks in the district are found around and to the south of Heysham. Evidence for their existence beneath the drift cover is scarce. The district lies within the West Lancashire Basin, effectively the onshore extension or feather-edge of the East Irish Sea Basin (Jackson et al., 1987). The Permo-Triassic rocks in the south-west of the district correlate with the area of a relatively low Bouguer gravity anomaly ((Figure 40)A). Seismic reflection data from the northern area do not satisfactorily image the contacts between the Carboniferous and Permo-Triassic rocks. These relationships have been elucidated by gravity modelling along selected profiles (Appendix 1: Busby and Cornwell, 1993).

North–south-trending faults affect the Permo-Triassic strata that crop out in the area south of Heysham. Structures with similar trends affecting strata of this age have been described to the south of the district by Wilson and Evans (1990) and Aitkenhead et al. (1992). The development and location of major Permian and Mesozoic faults was strongly influenced by pre-existing Variscan and older fault zones (e.g. Chadwick, 1985, 1986). These were reactivated during succeeding crustal extension phases, controlling the development of faults and sedimentary basins. A strike-slip component of displacement may be present, unless the extension vector was perpendicular to the older structures.

The only well-documented structures affecting rocks of Permo-Triassic age, and therefore undoubtedly post-Hercynian in age, are the faults in the Heysham area. However, on the shore at Red Nab [SD 403 592], the Sherwood Sandstone Group is affected by the minor Red Nab Syncline. It is a gentle, open structure with a southward plunge on the western side of the Ocean Edge Fault.

To the north-west of Lancaster, a small, sharply defined gravity low, elongated north to south with an amplitude of around 3.0 mGal (the Torrisholme anomaly; (Figure 40)A, anomaly M) extends from the River Lune northwards into Morecambe Bay. The steep gradients to the west and east of the feature indicate that the margins of the anomaly are bounded by north–south-trending faults. To the west of this is an elongate, north–southtrending gravity high ((Figure 40)A, anomaly N), which correlates with the denser Millstone Grit rocks in the core of the Heysham Anticline. The Torrisholme anomaly has been interpreted as a graben, termed the Torrisholme Basin, between the Lindale–Hest Bank and Overton faults (Figure 41). The BGS Belmount Farm Borehole (SD46NE/23) penetrated strata of Permo-Triassic age and proved that the Torrisholme anomaly cannot be explained as a drift-filled, fault-bounded hollow within the Carboniferous. Gravity modelling revealed that it cannot be modelled as a single structure. There is a near-surface Permo–Triassic component, proved by boreholes (Figure 32), with a maximum thickness of 300 m, underlain by a probable syncline in a Carboniferous sequence which forms a lower unit. Commercial-in-confidence seismic reflection data reveal a change in the ground conditions, but a possible base to the Permo-Triassic strata within the basin is only sporadically indicated. Rarely, reflections from strata of assumed Namurian age appear to be truncated beneath a reflection which may be from the base of the Permo-Triassic succession.

The Lindale–Hest Bank Fault defines the eastern extent of the Permo-Triassic rocks in the Lancaster–Morecambe area, and is inferred from the disposition of strata in boreholes (SD46NE/24) and (SD46NE/23) (see (Figure 32)). The throw on the fault is likely to be in the order of 100 m to 200 m to the west, and the fault is thought to be a southwards continuation of the important Lindale Fault on the southern margins of the Lake District. To the south, the Bilsborrow Fault, with a similar trend and downthrow direction, also affects the Permo-Triassic outcrop, and the two faults may form an en échelon fault pair. To the west, the Overton Fault has a similar trend but with an eastwards direction of downthrow, and defines the western extent of the Permo-Triassic outcrop in the Torrisholme Basin. The amount of downthrow is likely to be in excess of 100 m.

To the south of the Heysham Anticline, the general north–south to north-north-west–south-south-east-trending Trimpell Tanks, Moneyclose Lane and Ocean Edge faults were mapped at surface. The Trimpell Tanks Fault downthrows to the east, whereas the Moneyclose Lane and Ocean Edge faults downthrow to the west. The magnitude of the throws is variable. The latter two faults are probably part of the system of westwards-throwing faults that are close to or define the northern and eastern margins of the West Lancashire Permo-Triassic Basin.

The Moneyclose Lane Fault, or a splinter, is exposed to the south of Heysham. Correlation of site investigation boreholes at the Heysham Power Stations [SD 40 59] indicates probable post-Triassic movement along the fault. Boreholes situated to the west of the fault (e.g. (SD45NW/229) and (SD45NW/230); (Figure 31)) penetrate deeply reddened mudstones and sandstones of Kinderscoutian to Marsdenian age. However, boreholes to the east of the fault (e.g. (SD46SW/236) and (SD45NW/247)) encountered completely unaltered grey strata of Arnsbergian age, ranging from the Roeburndale Formation to the Caton Shale.

The Ocean Edge Fault, can be traced northwards across Morecambe Bay, east of Morecambe Bay Barrage Site Investigation Borehole A3 [SD 3894 6918], to the Humphrey Head Fault in Cartmel (e.g. Moseley, 1972; Jackson et al., 1987). It marks the boundary between Carboniferous and Triassic rocks and broadly correlates with the southern part of lineament J ((Figure 40)A). The gravity data ((Figure 40)A) suggest that the Permo-Triassic rocks to the south-west of the Ocean Edge Fault form a low-amplitude Bouguer gravity anomaly. This has been modelled as a uniform or gentle northward thickening of the Sherwood Sandstone Group succession (including a thin St Bees Shales). The south-western limit of this area, beyond the margin of the district, is marked by lineament K ((Figure 40)A), interpreted as a fault, across which the Sherwood Sandstone Group thickens rapidly. The structure appears to be the offshore extension of the Preesall Fault in the Blackpool area (e.g. Jackson et al., 1987; Wilson and Evans, 1990).

Lineament L ((Figure 40)A) also marks the boundary between Carboniferous and Permo-Triassic strata, and is traced southwards as the Bilsborrow Fault in the Garstang district (Aitkenhead et al., 1992). However, there is a possibility that lineaments K and L may represent structures that are sinistrally offset by an unmapped transfer fault.

Earthquakes

As in many parts of Britain, there are reports of minor earthquakes affecting the Lancaster district in historical times. Records compiled by Davison (1924) and Burton et al. (1984a and b) for the north-west of England were summarised by Aitkenhead et al. (1992, table 1). There have been no recent events to require an update of that table, though the epicentre for the 17th March, 1871, North Pennines earthquake has now been put in the Appleby–Alston area (Dr R M W Musson, personal communication, 1992). The list included only those earthquakes with epicentres in northern England. Those with more distant epicentres, e.g. the 26th December, 1979, earthquake in the Carlisle area, and those of the 19th July, 1984, and 2nd April, 1990, in Wales, were not included but may have been weakly felt in the district. None of the earthquakes known to have affected the Lancaster district appear to have had epicentres within the district.

Chapter 10 Economic geology

Mineral resources

The district owes its unscathed rural and moorland beauty to a general paucity of those economical mineral deposits whose exploitation, during the Industrial Revolution, so ravaged the countryside in more southerly parts of Lancashire. Inferior deposits of coal and iron ore from the Millstone Grit were worked on a minor scale within the district. Small-scale deposits of lead and zinc were mined locally in the limestone outcrops of the Brennand and Whitendale valleys. Small excavations, formerly worked for building stone, aggregate, brick-clay and lime, mostly for local use, are also common. Larger stone quarries in the Pendle Grit at Lancaster provided building stone for many of the fine buildings in the city. Sizeable sand and gravel extraction was carried out at Hornby and in the Carnforth area until comparatively recently. Sandstone, limestone and sand and gravel aggregate quarries were formerly exploited opportunistically, such as during the construction of the M6 Motorway. Modern mineral working is now confined to quarrying of siltstones of the Claughton Formation on Claughton Moor [SD 577 648] for brickmaking at Claughton works, and the large-scale quarrying of the Urswick Limestone south-west of Carnforth to produce aggregate for roadstone, concrete and constructional fills. The hydrocarbon potential of the region has recently been investigated by programmes of seismic profiling. The results remain confidential, though so far no drilling has been done. The potential of the glaciofluvial and terrace deposits of the district as mineral sand and gravel resources largely remains to be assessed.

Brick clay

Caton Shale Formation

The less calcareous mudstones of the Caton Shale Formation were formerly worked for brick making. Pits up to 10 m deep occur at 'Brookhouse brickyard' along Crossgill [SD 562 629] and [SD 5647 6303]. Numerous reject bricks around the east pit are imprinted 'Lune 1965'. The Brookhouse Brick Company works [SD 563 631] has been demolished, but Thewlis (1962; see Appendix 4) reproduced a photograph as it was in the 1960s and gave some details of the yields and operations involved since work began about 1900. Pyrite and calcite in the Caton Shale would have a deleterious effect, and the lack of these minerals in the siltstones of the Claughton Formation may partly explain why the latter are now exploited. Other disused brickpits occur in Potter Hills Wood c. [SD 555 653], Claughton; the local brickyard was probably located along the main road to the north [SD 5540 6582].

Claughton Formation

The Barncroft Beck Member was formerly worked on a moderate scale for brickmaking at several places adjacent to Barncroft Beck [SD 5656 6617] and [SD 5645 6607] and Westend Beck [SD 5623 6592] and [SD 5625 6580], south of Claughton, in spite of the appreciable content of sandstone beds. The brickpits are terraced in places, the result of leaving the thicker sandstones unworked. The pits are now very much overgrown.

The sandy siltstones of the Claughton Moor Siltstone Member (Plate 10) are currently (1992) extensively worked for brick making at Claughton brick pit [SD 578 648]. After being allowed to weather, the blasted rock is transported by two aerial ropeways to the Claughton brickyards [SD 560 662] and [SD 563 664].

Kirkbeck Formation

Siltstones exposed below the Ellel Crag Sandstone in the floor of Ellel Quarry [SD 504 549] were worked opportunistically by J A Jackson Ltd in 1992 and transported to Preston for brick manufacture.

Superficial deposits

Bricks have been made in the past from several types of superficial deposits. For example, Older Marine Deposits were dug up to a depth of 3 m at the White Lund Brickworks [SD 4375 6270], and till was utilised at a pit near Quernmore (Reade, 1904).

Coal mining

Though Westphalian coals of the Ingleton Coalfield were formerly worked just outside the sheet boundary, workings did not extend into the district. In addition, based on borings made in the early part of this century just to the north of the area, it is likely that only thin and impersistent seams of this age are present in the district.

As early as 1837, Phillips concluded that what he believed to be the one thin coal worked around Lancaster belonged to the 'Millstone Grit Series' and that there was no prospect of finding more profitable seams. Two main coal horizons are known to have been worked. The thin, probably impersistent coal seams in the upper unit of the Ward's Stone Sandstone Formation were exploited locally at several places between the Quernmore and Wray areas, but seam thicknesses were seldom greater than 0.5 m. The Clintsfield Coal in the Accerhill Sandstone was worked in the Tatham and Bentham areas.

Mining dates from historical times but documentary evidence shows that most activity was in the late 17th, 18th and early 19th centuries, a long period for such unremunerative workings. Working mainly ceased around the mid 19th century, by which time the construction of the Preston to Kendal Canal allowed coal to be brought in from south Lancashire. The workings are marked mainly by clusters of bell pits with some drifts in open ground, and by adits along the sides of incised valleys, such as Artle Beck. Some sites were probably opencast from small pits, and many were probably unproductive trials. The coal-bearing formations and main centres of exploitation are set out below. Details are mainly documented by Phillips (1837), Docton (1971; see Appendix 4) and Clare and Hudson (1987), and may also be found in BGS Technical Reports for the relevant areas (Appendix).

Ward's Stone Sandstone Formation

Coals in the Ward's Stone Sandstone were worked in the Quernmore area near Askew Hill Farm c. [SD 528 611 (King Charles' Colliery), c. 5[SD 25 616], c. [SD 527 619], south of Little Fell c. [SD 508 598] and near Mount Vernon [SD 506 588]. A survey of an adit dug by a local coal merchant, working a seam up to 0.8 m thick as late as 1926 or 1930 alongside the River Conder, near Mount Vernon, is documented by Clare and Hudson (1989). South of Caton, old workings have been recorded at many places in and around the Artle Beck valley, e.g. between Short Reks [SD 529 631] and Flodden Hill c. [SD 529 628], near Hawkshead c. [SD 535 630], along Artle Beck gorge from near Gresgarth Home Farm [SD 5339 6355] to near Potts Wood [SD 5474 6272], and around Hawes House c. [SD 563 625]. Two coals were possibly worked in the Farleton area c. [SD 578 672] and c. [SD 575 665]; thicknesses are recorded (Phillips, 1837) as up to 0.61 m. The upper coal is exposed in Farleton Beck [SD 5760 6692]. Remains of bell pit workings are also present at Coal Pit Lot c. [SD 539 682] in the Swarthdale area, and in the Wray area around Parkside [SD 620 687] and south of Smeer Hall [SD 624 658] to [SD 619 651], where the coal is up to 0.5 m thick (Phillips, 1837). There were also several shafts dug through till on the east side of Roeburndale [SD 613 651] and [SD 614 648]. South of Heysham, a 0.6 m-thick coal was found during construction work in 1948. It was probably the same seam as that worked by the Coal Board during excavations for the local electricity substation [SD 417 601] (Clare and Hudson, 1987, p.14).

Accerhill Sandstone Formation

The Clintsfield Coal in the Accerhill Sandstone is the only other coal known to have been worked in the district. The seam, reported to be up to 0.5 m thick (Phillips, 1837), was worked from several shafts between the 17th and 19th centuries, including those at Tatham and Clintsfield collieries c. [SD 629 697] (Catalogue of plans of abandoned mines, 1928, p.31). Tatham Colliery was worked until after 1834, and Clintsfield Colliery reopened in 1855 (Clare and Hudson, 1987, pp.6–7). The building housing the winding gear of the Clintsfield Colliery is still extant [SD 6295 6981]. South of Bentham, numerous old bell pits and shafts follow the crop of the Clintsfield Coal for 3 km along strike from Close House to Ridding Lane [SD 654 680] to [SD 683 689]. Phillips (1837) gives a thickness of up to 0.46 m for the lower coal and 0.25 m for an upper coal in this area. These pits and shafts were worked at least in the period 1810 to 1842 (Clare and Hudson, 1987, p.7).

Hydrocarbons

The hydrocarbon source potential of upper Dinantian to lower Namurian sequences of north and central England has long been suspected, following the discovery, for example, of oilfields in the east midlands (Falcon and Kent, 1960). As long ago as 1940–1950, a reconnaissance survey of the Heysham Anticline was carried out by A E Gunther and A H Noble of the Shell Company, but the prospect was not drilled. In 1966–67, the 'wildcat' exploratory Whitmoor No. 1 Well [SD 58744 63150] (referred to as the Whitmoor Borehole in this report) was drilled by the then Place Oil and Gas Company (UK) Ltd, to explore the hydrocarbon potential of these rocks in the central part of the present district. The borehole terminated at 1559 m, with a trace of methane in the Upper Bowland Shale at 1006 to 1036 m depth being shown on the log by Exploration Logging Robertson Ltd.

In recent years, with the discovery of the Morecambe gas field (Levison, 1988) only 50 km west of Lancaster (where Coal Measures are the probable source and Sherwood Sandstone the reservoir), there has been a rekindling of interest in hydrocarbon potential of Dinantian and Namurian rocks of the Craven Basin. Within the Lancaster district, exploration licences have been taken out by several companies, including Enterprise Oil Exploration Ltd and Pendle Petroleum Ltd, and approximately 365 km of seismic traverse have been shot, accompanied by sampling and analysis of possible source and reservoir rocks from exposed outcrops. As yet, no new exploratory boreholes have been put down within the Lancaster district, though British Gas have recently drilled several 'wildcat' wells in the Garstang and Preston districts to the south.

The hydrocarbon source potential of upper Dinantian to lower Namurian rocks, and the factors controlling maturation, migration and trapping in a porous reservoir rock, have been summarised for the adjacent Garstang district (Aitkenhead et al., 1992). As similar strata are also found in the present district, the same principles and criteria apply and will not be detailed here. It seems that the main hydrocarbon source rocks are likely to be the thick upper Dinantian and lower Namurian marine sequences such as the Bowland Shale and Caton Shale, and probably also the Coal Measures, and that the prime host reservoirs are the Collyhurst and Sherwood sandstones (Fraser et al., 1990). The latter sandstone is present in the south-western part of the district, where it is underlain by Namurian and probable Westphalian strata that include potential source rocks. However, there is no obvious retaining cap rock, such as the Mercia Mudstone, within the district. Although there are plunging anticlinal folds within the Namurian which could provide hydrocarbon traps, e.g. the Heysham Anticline, the degree of faulting is potentially deleterious and the local Namurian sandstones are not likely to be porous enough to host commercial quantities of hydrocarbon. Moreover, the overburden estimates of Aitkenhead et al. (1992), based on conodont maturation studies which concluded that post-Carboniferous burial had little temperature-enhancing effect (Metcalfe et al., in press), are likely to be understated. Fission track analyses imply that most rocks presently at outcrop within the district were subjected to palaeotemperatures greater than 90°C during the latest Cretaceous or Palaeogene (Lewis et al., 1992), and that several kilometres of post-Namurian sedimentary cover over the Pennines may have been removed by Tertiary erosion. This is supported by studies on garnet grains in the Millstone Grit sandstones of the present district (p.39) which deduced that pore fluid temperatures exceeded 80°C during a burial of the order of 3.3 km. This would suggest that any hydrocarbon discoveries would be of gas.

The explosion disaster at Abbeystead in 1984 highlighted the presence of quantities of methane, though well below commercial levels, lodged in an anticlinal structure in lower Namurian strata and possibly of deep origin (Wilson et al., 1989; On et al., 1991; Hooker and Bannon, 1993). Methane in easily detectable quantities was also found in groundwater and soil gas, in areas affected by faulting in the Namurian outcrop and by the Ocean Edge Fault at the Heysham power stations, although the decay of recent organic remains may have been at least partly responsible for the gas production (Dr T K Ball, personal communication 1993). Evidence for either gas migration or degassing within a 100 m-wide zone of Sherwood Sandstone parallel to the Ocean Edge Fault is evidenced by numerous, irregularly shaped, reduced zones in the sandstone, both in exposures at Red Nab (Plate 11) and in former excavations at the power stations. These zones are up to 1 m long and, though many are flattened parallel to the bedding, their long axes in plan lie subparallel to the fault. It is inferred that gaseous hydrocarbons, streaming up joints and fractures in the past, reduced the haematitic state of the iron to ferrous iron compounds. The gas may have migrated eastwards under an evaporite cap rock, from a Collyhurst Sandstone reservoir situated more centrally in the Permo-Triassic basin into the thin basal marginal breccia at Heysham, and may then have been released along the fractured passage-way of the Ocean Edge Fault zone.

Further evidence for hydrocarbon migration in this area comes from the Namurian Heysham Harbour Sandstone. Disseminated, late diagenetic, non-volatile residues of hydrocarbon were found in samples of the sandstone from boreholes (SD45NW/10) and (SD45NW/14) [SD 4046 5917] and [SD 4043 5938]. Harrison (1970) described radioactive spheroidal to ellipsoidal hydrocarbon-rich nodules, 10 to 90 mm across, from exposures [SD 4031 6029]; [SD 4053 5999] of the sandstone in the Heysham Harbour area.

Hydrocarbon traces are widespread in the Dinantian limestones. In the Over Kellet area, the presence of hydrocarbons is evident in the small oil bleeds and residues that are occasionally found in the limestone quarries, particularly Dunald Mill. The Thornton Limestone Member of the Clitheroe Limestone Formation in the Sykes Anticline also contains hydrocarbon traces. Fresh rock surfaces give off a pungent smell of oil. Hydro- carbon fluid inclusions were numerous in BP Minerals borehole cores of the Hodder Mudstone and Pendleside Limestone formations in this area (see (Figure 9)). Methane was especially troublesome during the operations of the Whitewell Mine c. [SD 652 549] (see p. 148), when the system was periodically shut down to allow the dispersal of gas.

Limestone

The presence of a thick sequence of Carboniferous Limestone with an extensive outcrop close to the town of Carnforth, a railway junction and former centre of iron smelting, led to the development of limestone quarrying as an important industry in that part of the district. The building of the M6 Motorway in the 1960s, and later, the local A601 (M) access link road, gave a major boost to this industry and greatly improved access to distant markets for the quarry products.

Much of the limestone outcrop around Carnforth itself is deeply drift-covered. East of the M6 Motorway and south of the northern boundary of the district, however, it is estimated that limestone of potentially good quality, covered by little (<3 m) or no overburden, crops out over an area of about 265 hectares. Existing quarries, including those that are active (see below), inactive and disused, cover about 86 hectares of this area. There is probably some margin for enlarging and deepening these quarries, subject to planning contraints, especially in the higher area south of the Carnforth to Over Kellet (B6254) road where the water table is likely to be low relative to the ground surface.

Most of the outcrop referred to above is formed by the Urswick Limestone Formation which forms a very valuable resource, generally consisting of rock that is classified as having either a very high (>98.5% CaCO3) or a high purity (>97% CaCO3) classification (Harrison et al., 1990). However, the presence of intercalated, partially dolomitised limestone, thin interbedded clays, and drift-filled joints, fissures and caves, tends to reduce the overall bulk purity. Many of these occurrences, though minor, are difficult to predict and occasionally cause problems for the quarry operators, not least in producing excessive waste. The Park Limestone Formation, which underlies the Urswick Limestone, has been worked in the lowest part of Leapers Wood Quarry (see below) where it is partially dolomitised but lacking in clay or mudstone interbeds; it is likely to occur at depth below the other working quarries. This formation also constitutes a valuable resource.

Of the five major limestone quarries in the Carnforth area, three are currently in production: Leapers Wood [SD 513 694] (Wimpey Asphalt); Back Lane [SD 507 694] (ECC Quarries); and Dunald Mill [SD 513 680] (Tarmac Roadstone–North West). These three working quarries produce aggregates for roadstone, concrete and constructional fills, as well as armourstone which comprises large blocks used for local coastal sea defences. A fourth quarry, High Roads [SD 515 683] (ECC Quarries), is currently a location for manufacturing cement-based products, while the fifth, Overhead [SD 529 714], said to have been opened to supply stone for construction of the M6 Motorway, is disused and deeply flooded.

Elsewhere in the district, the limited outcrops of Carboniferous Limestone of basin facies have been used on a small scale, in former times, for building stone, hard core and lime making. The remains of limekilns in disused limestone quarries in the Pendleside Limestone and Lower Bowland Shale formations at Halton Green [SD 521 655], and in the Rain Gill Limestone Member near Hey [SD 676 521], provide evidence of this last usage. However, these outcrops are unlikely to be of much interest to modern industry because of their variable purity, inferred from adjacent areas (Harrison, 1982), remoteness from major road and rail networks, and their location in the designated Forest of Bowland Area of Outstanding Natural Beauty. In the 19th century, a limekiln situated along the shore [SD 415 622] to the south of Morecambe (Crofton, 1876) probably used limestone blocks on the shore as raw material.

Marl

As in adjoining parts of Lancashire (Binns, 1982), numerous small marl pits were dug in the first half of the 19th century in the calcareous till in the western part of the district. The pits were located particularly along the crestlines of drumlins, to facilitate the spreading of till over the nearby ground as an agricultural dressing in order to enrich the soil with lime and encourage grass growth. Larger stones within the till were probably incorporated into local walling. None of the pits is dug today, and former sites are commonly used either as cattle-watering holes, or as disposal sites for local domestic or agricultural refuse.

Metalliferous sulphide deposits

Metalliferous minerals, comprising some of the primary sulphides of lead, zinc, copper and iron, together with their alteration products, are known in the district but are not being exploited. They occur mainly in the limited areas where Dinantian limestone strata crop out: in the northern part of the district around Carnforth and, in particular, in the south-east in the periclinal inliers within the Sykes Anticline. Though not themselves of any economic significance, the occurrences outlined below do illustrate the general setting for metalliferous mineral deposits which may help in any future exploration.

In a broad sense, the mineralisation is similar to that of the much more extensive North Pennine Orefield to the north-east, described by Dunham and Wilson (1985). There, as well as in other Pennine orefields (Plant and Jones, 1989; 1991), the minerals, in Carboniferous limestone and sandstone host rocks, are thought to have crystallised out of hot brines. These hydrothermal fluids were expelled from Carboniferous basinal argillaceous rocks which had been heated and pressurised during deep burial and intervals of high tectonic stress, mainly during the late Carboniferous and Permian. The brines had probably leached out metal ions absorbed on clay minerals in the basinal mudstones.

The primary ores, mainly pyrite (FeS2), galena (PbS), sphalerite (ZnS) and chalcopyrite (CuFeS2), deposited by the processes outlined above, were subsequently altered by oxygen-bearing groundwaters, probably assisted by microbial action (Erlich, 1981). There were then further intervals of alteration, remobilisation and deposition of secondary minerals.

Sykes Anticline

Of the three mineralised Dinantian periclines within the Sykes Anticline, that centred on Sykes itself lies mostly in the adjacent Garstang district and was referred to in the corresponding memoir (Aitkenhead et al., 1992). The other two, at Brennand and Whitendale, have been worked for lead. The main mineralised area, and the remaining traces of the associated workings, are located mostly on the col between Brennand Farm [SD 645 541] and Whitendale [SD 661 550]. These include a collapsed adit [SD 6462 5429] on the slope opposite Brennand Farm and the remains of shafts and vein workings associated with what was known as the 'Whitewell or Brennand Lead Mine'. The history of mining here, which goes back at least to 1630, has been described by Raistrick (1973, pp.163–168) and Gill (1987, pp.46–48). A number of veins or lodes were worked, most of which are shown on the BGS geological maps, having been largely transcribed from old plans held in BGS archives. At the time of the primary geological survey, De Rance (1873) was able to examine workings in the 'Brennand Lode' or 'Brennand and Whitewell Lead Vein' shortly before the mine finally closed in 1874, and gave brief but vivid descriptions of the orebodies. The main host rock is referred to as the 'Red Bed Limestone' which appears to be the equivalent of both what is now the Ravensholme Limestone and at least part of the underlying Pendleside Limestone. De Rance also noted that, in general, 'lodes' with a directional trend across the anticlinal axis are richer in lead ore while those trending subparallel to the strike of the beds are richer in zinc. Gill noted that no attempt appears to have been made to exploit the zinc ores. However, some silver was probably produced from galena, though there is no direct evidence.

The results of the BGS mineral reconnaissance survey of the area in the 1970s (Wadge et al., 1983), part of a basinwide study funded by the Department of Industry, encouraged a more intensive survey shortly afterwards by BP Minerals International Ltd. This work included the drilling of a number of boreholes, some of which were cored to depths of between 114 m and 267 m; logs of a selection of these are shown in (Figure 9). The results of this exploration show that the mineralisation is stratabound, being concentrated in disseminated and veinlet form particularly in two sequences (Carlon, 1983). These are, firstly, in the upper division of the 'Clastic Limestone Formation' (Ravensholme Limestone), and secondly, in a sequence spanning a lower division of the 'Worston Shale Formation' and the upper part of the underlying 'Sykes Limestone Formation'. In current BGS terms, this latter sequence lies in the Hodder Mudstone Formation (and Worston Shale Group), within and just above the Hetton Beck Limestone Member (see (Figure 5), column 2, and (Figure 9). The upper sequence 'is characterised by a complex association of dolomitisation, silicification and mineralisation by zinc-lead sulphides; the lower unit is characteristically veinlet style sphalerite in totally silicified mudstone (cherts)' (Carlon, 1983). Some pyrite is commonly disseminated in the mudstones, particularly in the Lower Bowland Shales. Baryte and fluorite occur as gangue minerals, but in no great quantity.

Since the research noted above, the Sykes/Brennand mineralisation has been further studied by Mr J Gaunt (personal communication, January 1993) who has contributed the following summary of his conclusions. 'The mineralisation occurred in three episodes characterised in turn by: (1) dominant pyrite, (2) sphalerite-galena, and (3) galena with baryte and fluorite. The second episode was the principal one, and this was separated from the first and third episodes by the emplacement of multiple vein carbonates. Hydrocarbon fluid (liquid) inclusions, indicate a period of petroleum expulsion prior to the sphalerite-galena mineralisation episode, these hydrocarbons, and the sulphides of all three episodes having migrated via basin margin faults. At Spire Farm, Cow Ark (in the adjacent Garstang district) there are also three successive assemblages, namely (1) marcasite-pyrite, (2) galena and (3) galena with baryte. This suggests a genetic relationship with the Sykes/ Brennand mineralisation. This relationship is further supported by comparable sulphide assemblages, geochemistries and sulphur isotopes for equivalent mineralisation episodes; and by the presence of hydrocarbons at both localities which predate both second mineralisation episodes. The mineralisation at Cow Ark is related to local faults. The mineralisations at both localities were the consequence of three periods of basin dewatering, the expulsed fluids having been metalliferous brines at temperatures of 100 to 1400C (pressure corrected). It is proposed that mineralisation was a consequence of an elevated geothermal gradient and increased rate of basinal dewatering post Westphalian C–Permian basin inversion'. It should be noted that the 'basin' referred to above is that referred to in this memoir (p. 130) as the Bowland Sub-Basin.

Carnforth area

In the Carnforth area, some relatively minor mineralisation is present in the southern part of the Dinantian shelf limestone outcrop at Swantley [SD 524 678], south-east of Nether Kellet. In broad terms, this area lies at or near the late Dinantian shelf margin, and on the crest of the Hutton Monocline where a gentle southerly plunge carries the limestone beneath the unconformably overlapping Namurian mudstones and sandstones. In detail, the Swantley outcrop is a knoll-reef which, with adjacent strata belonging to the Urswick Limestone, is situated in the core of a faulted subsidiary anticline, the main vertical limb of the monocline flanking its eastern side. The slopes to the east of the line of crags at Swantley are pockmarked with old diggings in partially silicified and dolomitised limestone, with traces of galena, sphalerite, azurite and malachite. Descriptions of these occurrences, when they were better exposed, have been given in an unpublished report by Kendall (1921). Traces of metallic sulphides have also been noted on joint surfaces in the various limestone quarries in the area, and in the disused quarry on the crest of the periclinal limestone inlier [SD 5217 6551] near Halton Green (p. 28).

Other hydrothermal occurrences

While the main host rocks for mineralisation are upper Dinantian limestones, a few examples of mineralisation occur in Namurian strata. These include traces of galena and sphalerite in nodules from the Ct. edalensis Subzone of the Caton Shale exposed adjacent to the Crossgill Fault along Crossgill Beck [SD 5602 6289] (Thewlis, 1962, p.29; see Appendix 4), and galena with drusy quartz in a sedimentary breccia from the Close Hill Siltstone Member exposed in the River Roeburn [SD 6016 6387] near Lower Salter.

Barytes

A few thin veins of white or pink baryte are associated with joints and faults that affect Namurian sandstones. Examples occur in the Pendle Grit of the Knots Anticline e.g. [SD 5070 6243], in nearby probable mine spoil near Stanley Farm [SD 5057 6218], along a fault cutting the Surgill Shale in a gully [SD 6380 5532] at Lee End, in faulted Dure Clough Sandstone in a disused quarry at Delph Beck [SD 6044 5533] in the Tarnbrook Wyre area, and in jointed Ellel Crag Sandstone at Ellel Crag Quarry [SD 5055 5482]. High values of barium in three single stream sediment samples were found during geochemical mapping of part of the district (Dr N Breward, personal communication 1993). The values (in ppm) are 1999 [SD 6272 6137], 1218 [SD 6614 5979] and 2192 [SD 6522 6161], the first two localities being in proximity to westnorth-west–east-south-east-trending faults.

Iron ore

Several sites of iron production, active between the 13th and 18th centuries to meet local demands, have been identified by the presence of low-temperature bloomery slag (Hudson and Price, 1989). They include sites in the Hindburn valley between Lowgill [SD 652 649] and Furness Ford Bridge [SD 636 669], at Outhwaite [SD 615 654] and Barkin Bridge [SD 601 639] in Roeburndale, and in the Quernmore valley [SD 527 605]; [SD 5130 5820]; [SD 5160 5870]; [SD 513 576]. The source of the ore was probably the nodular sideritic mudstones of the local Millstone Grit sequence.

Peat

Lowland peat at Heysham Moss [SD 422 608], east of Heysham, was formerly dug as fuel, probably this century. Approximately 12 hectares of peat, at least 2 m thick, remain as a raised area. Other lowland peat deposits along the coastal tract between Heysham and Carnforth are buried beneath younger deposits, or are too thin or too small to be regarded as a resource. Dissected hill peat still covers large areas of the Forest of Bowland, commonly to a thickness of 2 m. It is reasonable to believe that it was formerly exploited extensively as a fuel by the rural community, though there are very few places where it is known to have been dug. Peat up to 2 m thick was worked on Thrushgill Fell [SD 636 616] until recent times, and a 2 m-thick deposit was also dug at White Moor [SD 611 550]. A largely undissected area of peat up to 3 m thick occurs to the east of Ward's Stone at [SD 597 590].

Sand and gravel

Deposits that are a potential resource for sand and gravel aggregate include Glaciofluvial Ice-contact and Glaciofluvial Sheet deposits, River Terrace Deposits, Storm Beach and Older Storm Beach deposits, Alluvial Fan Deposits and Blown Sand. In many instances, these deposits may be partly or completely concealed by more recent spreads of alluvial and marine deposits. The Glaciofluvial Ice-contact Deposits may occur as pods totally surrounded by till. With future drilling, therefore, it is likely that new resources will be discovered.

To date, the main centres of exploitation have been in Glaciofluvial Ice-contact Deposits in a number of large quarries around Carnforth, notably the Lundsfield Quarries [SD 497 694] and Crag Bank Quarry [SD 493 704] to the east and west of the town respectively, which cover a total area of about 100 hectares, and in River Terrace Deposits and alluvial floodplain gravels of the River Wyre, south of Dolphinholme, at the northern extension of Scorton Quarry [SD 517 523]. Within the confines of the district, there are no extant workings in either of these areas, but Tilcon Ltd have workings to the west of Tewitfield [SD 518 735], and Tarmac Ltd have workings near Scorton [SD 502 489] (Aitkenhead et al., 1992), 1.5 km and 3 km to the north and south of the district respectively. The output from these areas has mainly been of gravel used for concrete aggregate and motorway construction.

There are many indications of sand and gravels being formerly worked on a less-intensive scale throughout the district. About 10 m of well-bedded sands and gravels of the Glaciofluvial Sheet Deposits were worked on a commercial basis until 1981 near Priory Farm at [SD 580 689], Hornby. Minor working of Glaciofluvial Ice-contact and Glaciofluvial Sheet deposits was formerly carried out at various localities between Halton and Hornby e.g. [SD 502 645], [SD 537 649], [SD 578 678] and River Terrace Deposits have been worked on a small scale in the Galgate area e.g. [SD 483 557] and [SD 488 565].

Allott and Lomax (1990) gave a broad indication of the resources of sand and gravel in the region. Although their report was prepared before the most recently completed mapping in the north of the district, it identifies several areas, particularly to the north of the City of Lancaster, where sand and gravel is likely to be present within the till sheet. Similar deposits, particularly those immediately to the north of Carnforth, were assessed by Arthurton (1983), and the area has been explored by Tilcon Ltd in recent years. The present survey confirms that although many of the resources around Carnforth have been exploited, the main area still to be worked lies between Carnforth and the M6 Motorway [SD 508 704]. Allott and Lomax (1990) also identified the Lune valley, upstream of Crook o' Lune [SD 520 647], as part of a main target area for future investigations. The present survey has identified extensive areas of glaciofluvial gravels around Halton, Caton, Quernmore and Hornby that may be worthy of future assessment. These lie in the Bowland Forest Area of Outstanding Natural Beauty, however, and may therefore be subject to planning constraints. Glaciofluvial deposits lying beneath the flood-plain of the River Lune, downstream of Lancaster, were assessed by Patrick (1978). He identified a major resource but noted possible ecological side effects of exploitation. Other prospects in the Lancaster and Morecambe areas, such as the Glaciofluvial Sheet Deposits underlying the Scale Hall area [SD 463 627], have been sterilised by urban development.

Sandstone

Walling stone and building stone

All the named sandstones in the Millstone Grit Group have been quarried on a small scale for local use as building and walling stone, generally more than a century ago. A large number of buildings in the district are built of local stone. The majority of quarries are less than 100 m across, many are partially backfilled with general agricultural waste, but most provide small exposures. There are currently no actively working stone quarries in the area, though probably numerous quarries have been opened up even in the last few decades for the production of local stone and aggregate to meet temporary local demands. Examples are the expansion of the Ellel Quarry [SD 504 549] in the Ellel Crag Sandstone during construction of the M6 motorway; the exploitation of Pendle Grit at Baxton Fell End Quarry on Croasdale Fell for use in the construction of the nearby Stocks Reservoir; and quarrying in the Ward's Stone Sandstone in the Quernmore area [SD 536 611] during the construction of the adjacent Thirlmere Aqueduct. The resources of sandstones for walling stone and building stone in the district are considerable.

The main workings were as follows:

Pendle Grit Formation

The outcrops of thickly bedded, medium- to coarse-grained, sandstone-dominated Pendle Grit have been much quarried for building stone, particularly in the more populated areas around Lancaster, Halton and Caton. Many of the fine buildings in Lancaster are built of this durable freestone won from nearby quarries, and reddened Pendle Grit was employed in some of the older walls of the castle. The City Hall is of Pendle Grit, imported in 1908 from the Longridge quarries near Preston (Watson, 1911). In the Lancaster area, the largest group of workings is now restored as a recreational garden facility at Williamson Park [SD 490 613]. Other Lancaster quarries, now largely backfilled or degraded, were Scotch Quarries [SD 484 612] at Primrose (source of the 'Lancaster Freestone' of Watson, 1911, p.279), Park Road Quarry [SD 485 616] at Moorlands, and Bowerham Quarry [SD 482 602] at Bowerham. Small workings were also carried out at Aldcliffe [SD 4677 6008]. In the Halton area, red sandstone was formerly worked at a small quarry [SD 4945 6455] along the north bank of the Lune, and rock was formerly worked on a small scale in the south bank of the Lune [SD 5085 6453] and [SD 5120 6457].

In the Caton area, the sandstones were quarried from numerous small pits situated in Knots Wood at Quernmore Park [SD 51 62], at North Park [SD 517 645] and west of Escowbeck [SD 526 640]. North of the River Lune, small disused quarries occur in the Halton Green area [SD 5192 6541]; [SD 5251 6569] and at Addington [SD 5285 6805]; [SD 5280 6830]; [SD 5272 6858].

Sandstone was extracted from the large disused Baxton Fell End Quarry on Croasdale Fell for the construction of the nearby Stocks Reservoir.

Brennand Grit Formation

The major coarse-grained sandstones were worked from several small pits near High Barn e.g. [SD 5880 5385] and New Barn e.g. [SD 5950 5369], in the Marshaw area.

Roeburndale Formation

The thicker sandstones in the upper part of the Cocklett Scar Sandstones Member have been quarried on a small scale for local walling stone or building stone: e.g. at Aughton Church [SD 5512 6764] ; near Holehouse Farm [SD 5528 6557], Claughton; north of Gressingham [SD 5728 7109] and [SD 5763 7056] ; and at Backsbottom Quarry [SD 6055 6614], Roeburndale. The thicker sandstones in the interbedded sandstones and siltstones unit above the Close Hill Siltstone have been worked for local walling stone. A basal 4.5 m-thick sandstone was worked from a small pit in Spinks Gill Wood, south of Melling [SD 5924 7004]. In the northern part of the district, thick sandstones in the upper part of the unit were worked. Quarries occur north-west of Aughton [SD 5411 6795]; [SD 5417 6837]; [SD 5441 6907].

Ward's Stone Sandstone Formation

The hard, siliceous, thickly bedded sandstones and Banisters in both units of the formation were formerly worked on a small scale for building stone, wall stone and road aggregate from numerous small pits. Several pits were worked in the Swarthdale area, such as Brockholes Crag Quarry [SD 5362 6870]. Workings occur: west of Gressingham, around Brookdale Farm c. [SD 560 696] ; on Windy Bank hill, north-east of Hornby c. [SD 592 696] ; and adjacent to Hamstone Gill [SD 5885 6675], south of the town. They occur on Whitmoor, on both the north side of the hill [SD 590 652] and [SD 593 648] and on the south side c. [SD 590 630]. Disused pits occur around Outhwaite e.g. [SD 6176 6505], south-east of Wray, and the sandstones were worked at Linghaw Quarry [SD 6854 6852], south-east of Bentham. To the south, the sandstones were formerly exploited in the Higher Thrushgill area [SD 650 625] and [SD 647 614]. In the Littledale area, pits occur near Crossgill [SD 563 626], [SD 564 629] and [SD 562 623], and near Pott Yeats [SD 551 623]. In the Quernmore area, the sandstone was worked along the River Conder [SD 5223 6085], along Otter Geer Clough [SD 5360 6110] and at Little Fell [SD 509 599] to [SD 512 603].

Claughton Formation

A sandstone within the Barncroft Beck Member was quarried at a small pit on Caton Moor [SD 5748 6318]. The sandstones were also worked from two quarries c. [SD 625 685] and an adit mine [SD 6251 6861] west of Perry Moor. The Nottage Crag Grit has been worked in the past for walling stone from numerous small pits along its outcrop near Nottage Crag on the north side of Caton Moor e.g. [SD 564 654], [SD 570 657] and [SD 576 653].

Silver Hills Sandstone Formation

The Silver Hills Sandstone was worked at two adjacent quarries [SD 520 551] along Damas Gill north of Dolphinholme. South of Galgate, medium- to coarse-grained, thickly bedded sandstones that are classed as Silver Hills Sandstone were worked from pits at Quarry Wood [SD 4830 5415] and Ellel Grange [SD 4817 5388].

Accerhill Sandstone

Sandstones ascribed to this formation were worked south of Galgate at Richmond Quarry [SD 4852 5221] and Berries Head Wood [SD 4742 5290] and at several small quarries to the east of the town near Middle Crag e.g. [SD 5130 5465].

Kirkbeck Formation

A pale grey, medium- to coarse-grained, thickly bedded sandstone was exploited at a now-backfilled quarry [SD 4694 5615] to build nearby Parkside Farm. A further unnamed sandstone was worked at Downeyfield Road Quarry [SD 4365 5960]. Up to 20 m of medium to thickly bedded, fine-grained sandstones were extracted from Low Quarry [SD 6447 6910], Low Bentham, for constructing local buildings, and in particular during the building of the railway for bridges and other constructions. The Lane Foot Sandstone Member was formerly quarried in an area extending 200 m along strike at Lane Foot Quarry [SD 6692 6850], 1 km south of High Bentham.

The Ellel Crag Sandstone has been worked intermittently at Ellel Crag [SD 504 549], the largest sandstone quarry in the district, for 100 years. The quarry was reopened in 1973 by J A Jackson Ltd of Preston, though stone production recently ceased. Most of the output was crushed for road construction, but a creamy buff, fine-grained building stone, known as 'Galgate', was used in nearby Morecambe for sills, mullions and lintels in housing. In 1985, a sculpture of a medieval knight carved in 'Galgate' was commissioned to stand outside the Lancaster Law Courts (Leary, 1986). Ellel Crag Sandstone [SD 5151 5682] from Welby Crag quarry was used for lining the Haweswater aqueduct tunnel.

Eldroth Grit

Reddened sandstones ascribed to this formation were worked from several small, disused quarries at Overton e.g. [SD 433 579] and [SD 442 575].

Heysham Harbour Sandstone

Sandstone from the partially backfilled quarry on the approach road to Heysham power stations [SD 4047 5985] was probably used during the construction of Heysham Harbour (Abernethy, 1906).

Greta Grit

Gritty, coarse-grained sandstone from a quarry [SD 6844 6964] along Fowgill Beck, High Bentham, was used for local building and walling stone.

Flagstone

Ward's Stone Sandstone

Flagstone is known to have been worked from Ward's Stone Sandstone at two localities north-west of Aughton [SD 5398 6808] and [SD 538 676].

Claughton Formation

The sandstones of the Moorcock Sandstones Member were formerly worked for flagstone on Caton Moor, from numerous pits, now degraded, arranged in an east–west line south of the derelict Moorcock Hall; the largest workings were Claughton Quarries [SD 5700 6422].

Stone slate

Millstone Grit sandstones with a strong platy fissility were formerly worked for roofing slate. The low-angle, tabular, cross-bedded, delta-top sandstones with parallel lamination appear to have been the most favoured material.

Brennand Grit Formation

Parallel laminated, platy, medium-grained Brennand Grit sandstone has been worked, probably for local farmhouse slate, from a small quarry along the Brennand valley [SD 6300 5538].

Roeburndale Formation

Parallel laminated, fine- to medium-grained sandstones in the Dure Clough Sandstones have been worked for slate and possibly flagstone from a small pit along Delph Beck [SD 605 553], in the Tarnbrook area.

Ward's Stone Sandstone Formation

A strong platy fissility along the parallel lamination is commonly developed in the low-angle, tabular, cross-stratifled sandstones of the lower unit of the Ward's Stone Sandstone. The rock was exploited for roofing slate, mostly in the 19th century, over the western part of the 'Ward's Stone range', the most accessible part of the fell to Lancaster and nearby settlements. There are numerous former small pits and trials, marked by copious amounts of waste material, dotted around Black Fell [SD 54 60], [SD 55 60] and Clougha [SD 55 59]. Larger workings occurred on Birk Bank [SD 532 605] and Clougha [SD 556 595]. The pits were accessed by tracks up the fell side, and although long abandoned, are still readily discernable. Stone slate was also taken from the upper unit from two quarries [SD 539 627] and [SD 543 626] near Potts Wood, south-east of Caton.

Millstones

Brennand Grit Formation

The coarse-grained, pebbly sandstones of the Brennand Grit have been made into millstones at the crag outcrops of the Millers House area e.g. [SD 6201 5523] and Grinding Stones Rocks [SD 6605 5828]. Partially complete to complete millstones are scattered around this area.

Ward's Stone Sandstone Formation

The coarser granular sandstones of the lower unit of the Ward's Stone Sandstone were locally worked into millstones. Hudson (1989) documents several sites around Quernmore, some of which date from at least the early 14th century, and gives details of the finds and the working methods employed. Baines Cragg [SD 543 618] was a site of manufacture and many partly worked blanks to nearly complete millstones are to be found there. Hudson describes other sites at Cragg Wood [SD 542 616], Millstone Rake Stead c. [SD 544 607], Birk Bank c. [SD 533 605], Fell End [SD 543 601], and at several places on Black Fell e.g. c. [SD 546 606].

Hydrogeology and water supply

Most of the district is located within the lower Lune catchment. To the south, the land surface reaches over 550 m above OD between Black Fell and Mallowdale Fell to form the main watershed between the catchments of the rivers Lune and Wyre, the latter draining the southwestern part of the district. The north-western part of the district is drained by the River Keer, whilst the southeastern corner is drained by the River Hodder, a tributary of the River Ribble. Apart from the main watershed, the interfluves rise to between 100 m and 130 m above OD. The River Lune is tidal as far inland as the weir in north Lancaster [SD 482 633].

There are a number of river and stream intakes in both the Lune and Wyre catchments which are used for public supply. Reservoirs which are fed by these collector systems are located at Langthwaite [SD 498 591], Blea Tarn [SD 494 585] and Damas Gill [SD 527 574]. Large volumes of water are taken from the River Lune near Halton and pumped via the Quernmore pipeline and Wyresdale Tunnel to the River Wyre at Abbeystead for subsequent abstraction at Garstang. This Lune/Wyre transfer forms one element of the Lancashire Conjunctive Use Scheme, a major network of integrated water sources of regional importance in public water supplies in the north-west of England (Law, 1965).

The district experiences an average annual rainfall of 900 mm along the coast in the south, rising to more than 2000 mm in the Forest of Bowland, with annual potential evapotranspiration of nearly 425 mm. Much of the district experiences a soil moisture deficit during late summer. Groundwater is recharged during the winter months but infiltration of rainfall is inhibited wherever clayey till is present.

Aquifer development potential within the district is limited. Fractured massive Dinantian limestones, occurring within the Carnforth and south-eastern parts of the district, have moderate groundwater potential. In the former a number of springs issue from the contact between these limestones and overlying Namurian rocks. Boreholes in the Dinantian limestones usually yield small quantities of hard groundwater. At Crawshaw Farm [SD 6937 5143] near Newton, just outside the district on the Clitheroe 1:50 000 geological sheet (68), a 37 m-deep borehole penetrating the Chatburn Limestone under till yielded 0.5 litres per second (1/sec) for a drawdown of 17 m after two days of pumping. A 27 m borehole at Parrock Head Farm near Slaidburn [SD 6974 5264] on the adjacent Settle 1:50 000 geological sheet (60), yielded groundwater at the rate of 1 1/sec for a drawdown of 0.6 m from the same horizon. The groundwater is hard (Table 8) with an alkalinity of about 270 milligrams per litre (mg/1).

Namurian sandstones and shales occur at or near the surface over much of the district, and are the principal source of groundwater (Table 9) even though they are largely concealed by superficial deposits. Persistent sandstone horizons form a multi-layered aquifer system within which there are many perched water tables. Springs may occur at the base of sandstone layers and at the margins of overlying till sheet deposits. Spring flows fluctuate in response to rainfall, ceasing altogether during long dry periods.

Borehole yields of 1 to 5 1/sec can be expected from Namurian sandstone aquifers. Higher yields have been obtained at several localities, but only in larger diameter (300 m to 450 mm) boreholes. A 122 m borehole in Pendle Grit at Foot Holme [SD 6527 5288] produced 50 1/s for a drawdown of 37 m, and at Heysham [SD 4183 5904] 26 1/sec was sustained from a 144 m borehole in Ward's Stone Sandstone for a drawdown of 29 m. Significant yields were also obtained at Lancaster [SD 4860 6355] where a 140 m overflowing borehole in Pendle Grit was pumped at 16 1/s in which the dynamic water level was drawn to 10 m below ground level, and along Whiten-dale River [SD 6554 5344] where a 122 m borehole, also in Pendle Grit, yielded 151/s for a drawdown of 42 m.

Groundwater from Namurian strata tends to be good quality, of calcium-bicarbonate type with alkalinity less than 350 mg/l. Under anaerobic conditions, Namurian groundwater is reducing in form with concentrations of up to 2 mg/1 iron and 1.8 mg/1 manganese. Stable isotope determinations indicate the presence within the district of groundwaters with a wide range of residence times, and mixed flow systems (Bath et al., 1985). Methane-bearing groundwaters were shown to have contributed to the explosion at Abbeystead (Health and Safety Executive, 1985), but Orr et al. (1991) concluded that the gas and water were of deep origin, remote from the shallow groundwater flow regime.

There is little potential for groundwater within the Westphalian strata. A 52 m borehole at High Bentham [SD 6730 7078] yielded 1 1/sec for a drawdown of 8 m.

Within the district, the Sherwood Sandstone Group is composed of fine- to very fine-grained sands, much of the formation either underlying Morecambe Bay or mantled by a thick and extensive cover of till on the adjacent land mass. The superficial deposits prevent recharge of rain water to the formation which in consequence has limited development potential. Some recharge may occur from the Namurian sandstones at fault contacts within the Torrisholme Basin. The 40 m deep Mitchell's Brewery Borehole (SD45SE/2) at Cockerham [SD 4653 5222], which had a low yield of 0.6 1/sec of very hard water, is the borehole water supply on record from the Sherwood Sandstone.

Permeable glacial sand and gravel horizons within widespread till deposits supply small amounts of groundwater for agricultural usage. Many small supplies from springs and shallow wells have been developed, supplying farms and field troughs. Yields are generally small, typically between 0.1 and 1 1/s, as at Dolphinlee, Lancaster [SD 4838 6367] where 1 1/sec is obtained from a well for a drawdown of 11 m. However, an adjacent well at the same location and with the same dimensions demonstrates how changeable the strata can be over a short distance, as this source can sustain 15 l/s with an 8 m drawdown. Other high-yielding examples from this same vicinity are: 15 1/s for a 10 m drawdown [SD 4878 6390] ; 24 1/s for a drawdown of just over 1 m [SD 4871 6395] ; and 121/s for 8 m drawdown [SD 4869 6395]. Water quality within the superficial deposits is generally good. The recently recharged groundwaters in these deposits are vulnerable to surface pollutants and may contain elevated concentrations of nitrate.

Potential geological risk factors

This section is intended as a summary of the main geological hazards to engineering structures identified in the area at the last date of survey. It is not exhaustive and should not be used as a substitute for any part of a geotechnical site investigation.

Geological maps give the essential first indication of ground conditions and facilitate the most efficient and effective planning of site-investigations. It is emphasised that BGS maps, even at 1:10 000 scale, do not provide information detailed enough for site-investigation purposes, and that site specific investigations should always be carried out prior to any development. Unlike many urban areas, for which BGS has a large geotechnical database consisting largely of site-investigation borehole records, there is little geotechnical information available for the present district. However, certain hazards associated with particular mapped deposits are mentioned below.

Head

Head deposits are generally poorly consolidated and may be susceptible to further downslope movement following periods of heavy rain, snow or frost, especially if undercut or loaded by an overlying structure. Head deposits are likely to occur on and at the foot of steep slopes. They may be locally thick and are likely to be difficult to distinguish from the underlying drift deposits.

Landslip

This is one of the main hazards of the deeply incised, immature, hilly landscape typical of the district. Landslips of a wide range of scales, and affecting both bedrock and drift deposits, occur commonly on the steep valley sides, particularly of actively downcutting streams. Although many of the slips are of ancient origin and are effectively stable, they are prone to slippage if further undercut by streams or road construction, especially during wet periods. Slippage may range from slow creep to catastrophic movement. There should be caution in undertaking constructions on sloping ground, especially if landslips are mapped in the immediate area.

During the period of survey, several slips affecting road construction were encountered. An active slip in till on the north side of Artle Beck [SD 551 627] seriously damaged the Littledale road in 1990. A slip also occurred in the steep side of Crossdale Beck during the same year, affecting the Crossdale Mudstone beneath the Accerhill Sandstone and causing part of the road at Low Wood [SD 6519 6551] to collapse into the valley. In the Bowland Fells, hillsides can be very unstable. A typical example is the hillside composed of Pendle Grit on the east side of the Whitendale River where the road in the valley bottom [SD 659 543] needs constant attention.

Several examples are known on slopes in the district, where a superficial peat deposit has recently slipped on, and exposed, a till surface. One such slide occurred in 1984 on the northern slope of Swine Clough [SD 6015 5557], Tarnbrook, and was notable in revealing several unexploded mortar shells which had lodged in the till from firing practice during the last war.

Limestone dissolution and karst

The Carboniferous limestone surface has been modified by dissolution at various times to produce enlarged joints and vertical shafts, which may lead to subsurface cave systems (Ashmead, 1974, pp.221–223). The effect of ice erosion during the last glaciation was to abrade a fairly even surface, relatively free of superficial solution-enlarged joints, and this surface is likely to have been largely protected from renewed dissolution where there is still a till cover whose permeability has not been increased by decalcification. However, preglacial potholes and caves are still likely to be present in places. These are likely to be choked with unlithified deposits and may cause problems if they are undetected or not allowed for in construction design. This hazard will be greater on ground where the drift cover is thin and porous because of either decalcification or a low clay content. The areas where dissolution of limestone has been most active since the last glaciation are in the relatively low ground surrounding and adjacent to the limestone outcrops, especially where the drift cover is porous, thin, or absent altogether.

Made ground

Man-made deposits represent a potential hazard in three main ways:

  1. Areas of backfill may have been poorly compacted when constructed or may contain materials likely to rot or corrode. The composition of the filling material can be very variable from site to site and within short distances on a single site. This may lead to unpredictable bearing capacity and uneven settlement. Additionally, the backfilling material may be water soluble, and the slow dissolution by water over time may result in the formation of voids and unpredictable ground conditions. If the spoil is dumped on a slope, any buried soil/organic layer may form a plane of weakness and therefore might form a potential failure surface. Poorly managed groundwater flow in embankments and spoil heaps may allow pore pressures to build up in these deposits, resulting in catastrophic failure.
  2. Toxic residues, either as a primary component of the man-made deposit or generated secondarily by chemical or biological reactions, can migrate both within a deposit itself, and into adjacent permeable strata. The problem is particularly pertinent where waste infills former quarries in porous or well-jointed sandstones or sand and gravel.
  3. Toxic or explosive gases, particularly methane, can be generated within waste tips and landfill sites. Such gases can migrate (sometimes through adjacent permeable strata) and accumulate within buildings or excavations either nearby or some distance away (Williams and Aitkenhead, 1991). Sandstone quarries or gravel pits being backfilled with domestic waste present the greatest potential problems.

It must always be borne in mind that, in the more industrial areas of the district that have long histories of development, such as Lancaster, Morecambe, Heysham and Carnforth, man-made deposits are widespread. Those shown on the 1:10 000 geological sheets were delineated principally by recognition in the field and the examination of documentary sources. As such, only the more obvious man-made deposits can be mapped by this method and the boundaries shown are likely to be approximate.

Marine and estuarine deposits

Many of the marine and estuarine deposits of the western part of the district are low lying, soft, sandy to clayey silts that are likely to be saturated with water and may tend to liquify when loaded or disturbed. Additionally, they commonly conceal layers of peat and peaty sediment. Organic deposits such as these are normally highly compressible compared to surrounding deposits, and could give rise to excessive and differential settlement of overlying structures.

Methane in groundwater

The section on hydrocarbons gives examples of relatively small amounts of methane found in the upper Dinantian and lower Namurian rocks of the district. Made ground and organic deposits in hydraulic continuity with appropriate bedrock may be further sources of underground methane. Methane readily dissolves in groundwater, especially under pressure, and presents a potential hazard in underground constructions at levels well below commercial quantities. This was tragically illustrated by the explosion in the underground valve house at Abbeystead on 23 May 1984, resulting in the death of 16 local people. In that particular case, the methane was deduced to have accumulated by outgassing from groundwater that had leaked into the partly empty Wyresdale aqueduct from Millstone Grit sandstones in the core of an anticline (Health and Safety Executive, 1985). Structures built or founded in Carboniferous rocks, or in porous younger rocks providing hydraulic continuity with them, should be designed to allow free air ventilation.

Peat, lacustrine deposits and alluvium

Large areas of peat occur in the moorland parts of the district and there are small areas of surface lowland peat, especially in coastal areas. Additionally, as in the case of Marine Deposits, there may be concealed peaty or organic strata within areas mapped as alluvial, terrace and lacustrine deposits, particularly in kettle holes within till and glaciofluvial terrains. Such peaty layers would be expected to be of low strength, high compressibility and acidic water content. Because some bodies of peat, such as those formed in kettle holes, are laterally restricted, they could give rise to severe differential settlement of building foundations if not removed before construction. Organic deposits also generate methane, and their burial may introduce a risk of explosive gas concentration.

Underground water bursts

Underground excavations may encounter large quantities of water under great pressure when unexpectedly breaking into zones of faulting or jointing, or meeting a water-charged porous or well-jointed rock from an impervious medium. A dramatic event occurred during the construction of the Forest of Bowland Tunnel and is documented by Earp (1955). Water under pressure within the basal part of the Brennand Grit, a short distance above the roof of the tunnel, caused the siltstone roof of the tunnel to split with considerable violence along a 60 m length with an inrush of copious amounts of water. Unknown bodies of water-charged sand and gravel within impervious till might provide a possible drift analogy.

References

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

ABERNETHY, G N. 1906. The Midland Railway Company's Harbour at Heysham, Lancashire. Minutes of Proceedings of the Institution of Civil Engineers, Vol. 166, 229–241.

ADAMS, A E, HORBURY, A D, and ABDEL AZIZ, A A. 1990. Controls on Dinantian sedimentation in south Cumbria and surrounding areas of northwest England. Proceedings of the Geologists' Association, Vol. 101, 19–30.

ADAMS, A E, HORBURY, A D, and RAMSEY, A T S. 1992. Significance of palaeoberesellids (Chlorophyta) in Dinantian sedimentation, UK. Lethaia, Vol. 25, 375–382.

AITKENHEAD, N. 1977. The Institute of Geological Sciences borehole at Duffield, Derbyshire. Bulletin of the Geological Survey of Great Britain, No. 59, 1–38.

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, CHISHOLMJ I, and STEVENSON, I P. 1985. Geology of the country around Buxton, Leek, and Bakewell. Memoir of the British Geological Survey, Sheet 111 (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, 115–126.

ALLOTT and LOMAX. 1990. Sand and gravel resources of Lancashire: report for the Department of the Environment. Volumes 1 and 2 and summary report.

ARTHURTON, R S. 1983. DOE Carnforth Project. British Geological Survey Technical Report, WA/83/15.8.

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

ARTHURTON, R S, BURGESS, I C, and HOLLIDAY, D W. 1978. Permian and Triassic. 189–206 in The geology of the Lake District. MOSELEY, F (editor). Occasional Publication of the Yorkshire Geological Society, No.3.

ARTHURTON R S, and HEMINGWAYJ E. 1972. The St Bees Evaporites - a carbonate-evaporite formation of Upper Permian age in West Cumberland, England. Proceedings of the Yorkshire Geological Society, Vol. 38, 565–592.

ARTHURTON, R SJOHNSON, 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).

ASHMEAD, P. 1974. The caves and karst of the Morecambe Bay area. 201–226 in The limestones and caves of north-west England. WALTHAM A C (editor). (Newton Abbot: David and Charles, for the British Cave Research Association.)

AUDLEY-CHARLES, M G. 1970. Triassic palaeogeography of the British Isles. Quarterly Journal of the Geological Society of London, Vol. 126, 49–89.

BAINES, J G. 1977. The stratigraphy and sedimentology of the Skipton Moor Grits (Namurian Elc) and their lateral equivalents. Unpublished PhD thesis, University of Keele.

BARNES, B. 1975. Palaeoecological studies of the late Quaternary period in north west Lancashire (Fylde). Unpublished PhD thesis, University of Lancaster.

BATH A H, CAVE M R, and DARLING W G. 1985. Wyresdale Tunnel investigations, notes on hydrochemical investigations. Unpublished report prepared for the North West Water Authority by Fluid Processes Research Group, British Geological Survey, Keyworth.

BENARD, F, MASCLE, A, LE GALL B, DOLIGEZ, B, and Rossi, T. 1990. Palaeo-stress fields in the Variscan foreland during the Carboniferous from microstructural analysis in the British Isles. Tectonophysics, Vol. 177, 1–13.

BINNEY E W. 1868. Description of a dolerite at Gleaston in Low Furness. Memoirs of the Literary and Philosophical Society of Manchester, Vol. 7, 148–154.

BINNS, G R. 1982. Lancashire marl pits. Lancashire Magazine, January/February edition.

BISAT, W S. 1924. The Carboniferous goniatites of the north of England and their zones. Proceedings of the Yorkshire Geological Society, Vol. 20, 40–124.

BISAT, W S. 1928. The Carboniferous goniatite-zones of England and their continental equivalents. Compte Rendu Congres International de Stratigraphie et de Geologie du Carbonifere (Heerlen, 1927), 117–133.

BISAT, W S. 1932. On some lower Sabdenian goniatites. Transactions of the Leeds Geological Association, Vol. 5, 27–36.

BISAT, W S. 1934. Anthracoceras from the E2 zone of the Namurian. Transactions of the Leeds Geological Association, Vol. 5, 112–117.

BISAT, W S and HUDSON, R G S. 1941. The lower Reticuloceras (R1) goniatite succession in the Namurian of the north of England. Proceedings of the Yorkshire Geological Society, Vol. 24, 383–440.

BOTT, M H P. 1967. Geophysical investigations of the northern Pennine basement rocks. Proceedings of the Yorkshire Geological Society, Vol. 36, 139–168.

BOTT, M H P. 1987. Subsidence mechanisms of Carboniferous basins in northern England. 21–32 in European Dinantian environments. MILLER, J, ADAMS, A E, and WRIGHT, V P (editors). (Chichester: John Wiley and Sons.)

BOTT, M H P, and JOHNSON, G A L. 1967. The controlling mechanisms of Carboniferous cyclic sedimentation. Journal of the Geological Society of London, Vol. 122, 421–441.

BOUMA, A H. 1962. Sedimentology of some flysch deposits; a graphic approach to facies interpretation. (Amsterdam and New York: Elsevier.)

BOYLAN, P J. 1977. Victoria Cave. 52–53 in Guidebook for Excursion C7. Yorkshire and Lincolnshire, INQUA X Congress, United Kingdom. CATO A (editor). (Norwich: Geo Abstracts for International Union for Quaternary Research.)

BRANDON, A, and HODSON, F. 1984. The stratigraphy and palaeontology of the late Visean and early Namurian rocks of north-east Connaught. Special Paper of the Geological Survey of Ireland, No. 6.

BRANDON, A, RILEY, N J, WILSON, A. A and ELLISON, R A. 1995. New marine bands in the upper Pendleian (Elc) and lower Arnsbergian (E2a) of northern England. Proceedings of the Yorkshire Geological Society, Vol. 50, 333–355.

BRAY, A. 1927. The Carboniferous sequence between Lothersdale and Cowling (Colne). Journal of the Manchester Geological Association, Vol. 1, 44–57.

BRISTOW, C R. 1988. Controls on the 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 Northwest Europe. BESLY, B M and KELLING, G (editors). (Glasgow and London: Blackie.)

BRITISH GEOLOGICAL SURVEY. 1983. Lake District Sheet 54°N-04°W. 1:250 000 series, sea bed sediments and Quaternary geology.

BRITISH GEOLOGICAL SURVEY. 1984. Liverpool Bay Sheet 53°N-04°W. 1:250 000 series, sea bed sediments and Quaternary geology.

BURGESS, I C, and HOLLIDAY, D W. 1979. Geology of the country around Brough-under-Stainmore. Memoir of the British Geological Survey, Sheet 31 (England and Wales).

BURTON, P W, MUSSON, R M W, and NEILSON, G. 1984a. Marcroseismic reports on historical British earthquakes IV: Lancashire and Yorkshire. British Geological Survey Global Seismology Unit, Reports, Nos. 219a and 219b (2 volumes).

BURTON, P W, MUSSON, R M W, and NEILSON, G. 1984b. Studies of historical British earthquakes. British Geological Survey Global Seismology Unit, Report, No. 237.

BUSHELL, T P. 1986. Reservoir geology of the Morecambe Field. 189–207 in Habitat of Palaeozoic Gas in North West Europe. BROOKS, J, GOFF, J, and VAN HOORNE, B (editors). Special Publication of the Geological Society of London, Vol. 23, 189–207.

CARLSON, CI 1983. Mineral exploration in the Sykes, Brennand, Whitendale and Stocks project area, Bowland Basin. Unpublished report in support of the Mineral Exploration and Investment (MEIGA) Grant. BP Minerals International.

CATALOGUE OF PLANS OF ABANDONED MINES. 1928. Vol. 1. Cheshire, Cumberland, Durham, Lancashire, Northumberland, Westmorland, Isle of Man. (London: His Majesty's Stationery Office.)

CHADWICK, R A. 1985. Seismic reflection investigations into the stratigraphy and structural evolution of the Worcester Basin. Journal of the Geological Society of London, Vol. 142, 187–202.

CHADWICK, R A. 1986. Extension tectonics in the Wessex Basin, southern England. Journal of the Geological Society of London, Vol. 143, 465–488.

CHADWICK, R A, HOLLIDAY, D W, HOLLOWAY, S, and HULBERT, A G. 1993. The evolution and hydrocarbon potential of the Northumberland/Solway Basin. 717–726 in Petroleum geology of NW Europe: Proceedings of the 4th Conference. PARKER, J R (editor). (London: Geological Society.)

CHARSLEY, T J. 1984. Early Carboniferous rocks of the Swinden No. 1 Borehole, west of Skipton, Yorkshire. Report of the British Geological Survey, No. 84/1, 5–12.

CHISHOLM, J I, CHARSLEY, T J, and AITKENHEAD N. 1988. Geology of the country around Ashbourne and Cheadle. Memoir of the British Geological Survey, Sheet 124 (England and Wales).

CHISHOLM, I, MITCHELL, M, STRANK, A R E, Cox, F C, and HARRISON, D J. 1983. A revision of the stratigraphy of the Asbian and Brigantian limestones of the area west of Matlock, Derbyshire. Report of the Institute of Geological Sciences, 83/10, 17–24.

CLARE, J, and HUDSON, P J. 1987. Notes on coal and coalmining in western Lunesdale and Quernmore. Contrebis, Vol. 13, 2–17.

CLIFF, R A, DREWERY, S E, and LEEDER, M R. 1991. Sourcelands for the Carboniferous Pennine river system: constraints from sedimentary evidence and U-Pb geochronology using zircon and monazite. 137–159 in Developments in sedimentary provenance studies. MORTON A C, TODD, S P, and HAUGHTON, P D W (editors). Special Publication of the Geological Society of London, No. 57.

CLOSE, M H. 1867. Notes on the general glaciation of Ireland. Journal of the Royal Geological Society of Ireland, Vol. 1, 207–242.

COLLINSON, J D. 1988. Controls on Namurian sedimentation in the Central Province basins on northern England. 85–101 in Sedimentation in a synorogenic basin complex. The Upper Carboniferous of Northwest Europe. BESLY, B M and KELLING, G (editors). (Glasgow and London: Blackie.)

COLTER, V S. 1978. Exploration for gas in the Irish Sea. Geologie en Mijnbouw, Vol. 57, 503–516.

CROFTON, A. 1876. Drift, peat, etc., of Heysman [Heysham], Morecambe Bay. Transactions of the Manchester Geological Society, Vol. 14, 152–154.

DAKYNS, J R. 1892. On the geology of the country between Grassington and Wensleydale. Proceedings of the Yorkshire Geological Society, Vol. 12, 133–144.

DAVIES, J R. 1991. Karstification and pedogenesis on a late Dinantian carbonate platform, Anglesey, North Wales. Proceedings of the Yorkshire Geological Society, Vol. 48, 297–321.

DAVISON, C. 1924. A history of British earthquakes. (Cambridge: Cambridge University Press.)

DE RANCE, C E. 1873. On the occurrence of lead, zinc and iron ores in some rocks of Carboniferous age in the north-west of England. Geological Magazine, Vol. 10, 64–74.

DEWEY, J F. 1982. Plate tectonics and the evolution of the British Isles. Journal of the Geological Society of London, Vol. 139, 371–412.

DREWERY, S E, CLIFF, R A, and LEEDER, M R. 1987. Provenance of Carboniferous sandstones from U-Pb dating of detrital zircons. Nature, London, Vol. 325, 50–53.

DUNHAM, K C, and ROSE, W C C. 1941. Geology of the iron ore field of south Cumberland and Furness. Wartime Pamphlet of the Geological Survey of Great Britain, No. 16.

DUNHAM, K C, and ROSE, W C C. 1949. Permo-Triassic geology of South Cumberland and Furness. Proceedings of the Geologists' Association, Vol. 60, 11–40.

DUNHAM, K C, and WILSON, A A. 1985. Geology of the Northern Pennine Orefield: Volume 2, Stainmore to Craven. Economic Memoir of the British Geological Survey.

EAGAR, R M C, BAINES, J G, COLLINSON, J D, HARDY, P G, OKOLO, S A, and POLLARD, J E. 1985. Trace fossil assemblages and their occurrence in Silesian (Mid-Carboniferous) deltaic sediments of the central Pennine basin, England. 99–149 in Biogenic structures; their use in interpreting depositional environments. CURRAN H A (editor). Special Publication of the Society of Economic Palaeontologists and Mineralogist.

EARP J R. 1955. The geology of the Bowland Forest Tunnel, Lancashire. Bulletin of the Geological Survey of Great Britain, No. 7, 1–12.

EARP, J R, MAGRAW, D, POOLE, E G, LAND, D H, 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).

ECCLES, J. 1870. On two dykes recently found in North Lancashire. Transactions of the Manchester Geological Society, Vol. 9, 26–28.

ELLISON, R A. 1992. Observations of cleat in British coalfields. British Geological Survey Technical Report, WA/92/85.

EHRLICH, H L. 1981. Geomicrobiology. (New York: Marcell Drekker, Inc.)

EVANS, D J, REES, J G, and HOLLOWAY, S. 1993. The Permian to Jurassic stratigraphy and structural evolution of the central Cheshire Basin. Journal of the Geological Society of London, Vol. 150, 857–870.

EYLES, N, and MCCABE, A Monograptus 1989. The late Devensian (<22 000 BP) Irish Sea Basin: The sedimentary record of a collapsed ice sheet margin. Quaternary Science Reviews, Vol. 8, 307–351.

FALCON, N L, and KENT P E. 1960. Geological results of petroleum exploration in Britain 1945–57. Memoir of the Geological Society of London, No. 2.

FEWTRELL, M D, and SMITH D G. 1980. Revision of the Dinantian stratigraphy of the Craven Basin, N England. Geological Magazine, Vol. 117, 37–49.

FORD, T D. 1954. The Upper Carboniferous rocks of the Ingleton Coalfield. Quarterly Journal of the Geological Society of London, Vol. 110, 231–265.

FRASER, A J, and GAWTHORPE, R L. 1990. Tectono-stratigraphic development and hydrocarbon habitat of the Carboniferous in northern England. 49–86 in Tectonic events responsible for Britain's oil and gas reserves. HARDMAN, R F P, and BROOKS, J (editors). Special Publication of the Geological Society of London, No. 55.

FRASER, A J, NASH, D F, STEELE, R P, and EBDON, C C. 1990. A regional assessment of the intra-Carboniferous play of northern England. 417–439 in Classic petroleum provinces. BROOKS, J (editor). Special Publication of the Geological Society of London, No. 50.

FREY, R W, and HOWARD, J D. 1990. Trace fossils and depositional sequences in a clastic shelf setting, Upper Cretaceous of Utah. Journal of Paleontology, Vol. 64, 803–820.

GALE, S J. 1985. The Late and Post-glacial environmental history of the southern Cumbrian massif and its surrounding lowlands. 282–298 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

GARWOOD, E J. 1912. The Lower Carboniferous succession in the north-west of England. Quarterly Journal of the Geological Society of London, Vol. 68, 449–586.

GAWTHORPE, R L. 1986. Sedimentation during carbonate ramp-to-slope evolution in a tectonically active area: Bowland Basin (Dinantian), northern England. Sedimentology, Vol. 33, 185–206.

GAWTHORPE, R L. 1987. Tectono-sedimentary evolution of the Bowland Basin, northern England, during the Dinantian. Journal of the Geological Society of London, Vol. 144, 58–71.

GAWTHORPE, R L, and CLEMMEY, H. 1985. Geometry of submarine slides in the Bowland basin (Dinantian) and their relation to debris flows. Journal of the Geological Society of London, Vol. 142, 555–565.

GAWTHORPE, R L, GUTTERIDGE, P, and LEEDER, M R. 1989. Late Devonian and Dinantian basin evolution in northern England and North Wales. 1–23 in The role of tectonics in the Devonian and Carboniferous sedimentation in the British Isles. ARTHURTON R S, GUTTERIDGE, P, and NOLAN S C (editors). Occasional Publication of the Yorkshire Geological Society, No. 6.

GAYER, R A and PEŠEK, J. 1992. Cannibalisation of Coal Measures in the South Wales Coalfield - significance for foreland basin evolution. Proceedings of the Ussher Society, Vol. 8, 44–49.

GEBSKI, J S, WHEILDON, J, and THOMAS-BETTS, A. 1987. Detailed investigations of the UK heat flow field (1984–1987). Final report (unpublished) for the British Geological Survey. Geology Department, Imperial College of Science and Technology.

GEOLOGICAL SURVEY OF ENGLAND and WALES. 1884. Sheet 91 N.E. (Lancaster) (New Series Sheet 59). (Southampton: Ordnance Survey for Geological Survey.)

GEORGE, T NJOHNSON, G A L, MITCHELL, M, PRENTICE, J E, RAMSBOTTOM, W H C, SEVASTOPULO, G D, and WILSON, R B. 1976. A correlation of Dinantian rocks in the British Isles. Special Report of the Geological Society of London, No. 7.

GIBSON, W. 1910. Notes on three borings in the Ingleton Coalfield. Summary of Progress of the Geological Survey for 1909, 71–72.

GIBSON, W, WEDD, C B, and SCOTT, A. 1925. The geology of the country around Stoke-on-Trent. Memoir of the Geological Survey of Great Britain, Sheet 123 (England and Wales).

GILL, M C. 1987. The Yorkshire and Lancashire lead mines: a study of lead mining in the south Craven and Rossendale districts. Northern Mine Research Society. British Mining, No. 33.

GILLIGAN, A. 1920. The petrography of the Millstone Grit of Yorkshire. Quarterly Journal of the Geological Society of London, Vol. 75, 251–293.

GRAYSON, R F, and OLDHAM, L. 1987. A new structural framework for the northern British Dinantian as a basis for oil, gas and mineral exploration. 33–59 in European Dinantian environments. MILLER, J, ADAMS, A E, and WRIGHT, V P (editors). (Chichester: John Wiley and Sons.)

GREEN, P F. 1986. On the thermo-tectonic evolution of Northern England: evidence from fission track analysis. Geological Magazine, Vol. 123, 493–506.

GREENSMITH, J T. 1965. The petrology of the sedimentary rocks. 4th edition. (London: Murby.)

HALL, B R and FOLLAND, C J 1970. Soils of Lancashire. Bulletin of the Soil Survey of Great Britain, No. 5.

HALLSWORTH, C R, and MORTON, A C. 1991. Heavy minerals derived from the Moine metamorphic basement of NW Scotland. British Geological Survey Technical Report, WH/91/222R.

HANTZSCHEL, W. 1975. Trace fossils and problematica. Part W (Miscellanea, Supplement 1) . W1-W258 in Treatise on invertebrate paleontology. TEICHERT, C (editor). (Boulder, Colorado and Lawrence, Kansas: Geological Society of America and University of Kansas.)

HARRISON, D J. 1982. The limestone resources of the Craven Lowlands: description of parts of 1:50 000 Geological Sheets 59, 60, 61, 67, 68 and 69. Mineral Assessment Report of the Institute of Geological Sciences, No. 116.

HARRISON, D J, HUDSON, J H, and CANNELL, B. 1990. Appraisal of high-purity limestones in England and Wales. British Geological Survey Technical Report, WF/90/10.

HARRISON, R K. 1970. Hydrocarbon-bearing nodules from Heysham, Lancashire. Geological Journal, Vol. 8, 101–110.

HARVEY, A Monograptus 1985. The river systems of North-west England. 122–142 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

HARVEY A M, and RENWICK W H. 1987. Holocene alluvial fan and terrace formation in the Bowland Fells, northwest England. Earth surface processes and landforms, Vol. 12, 249–257. (Chichester: John Wiley and Sons.)

HASZELDINE, R S. 1984. Carboniferous North Atlantic palaeogeography: stratigraphic evidence for rifting, not megashear or subduction. Geological Magazine, Vol. 121, 443–463.

HASZELDINE, R S. 1988. Crustal lineaments in the British Isles: their relationship to Carboniferous basins. 53–68 in Sedimentation in a syn-orogenic basin complex. The Upper Carboniferous of Northwest Europe. BESLY, B M and KELLING, G (editors). (Glasgow and London: Blackie.)

HASZELDINE, R S. 1989. Evidence against crustal stretching, north-south tension and Hercynian collision, forming British Carboniferous basins. 25–33 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.

HASZELDINE, R S, and RUSSELL, M J. 1987. The Late Carboniferous northern North Atlantic Ocean: implications for hydrocarbon exploration from Britain to the Arctic. 1163–1175 in Petroleum geology of North West Europe. BROOKS, J, and GLENNIE, K (editors). (London: Graham and Trotman.)

HEALTH and SAFETY EXECUTIVE. 1985. The Abbeystead explosion. (London: Her Majesty's Stationery Office.)

HICKLING, G. 1918. The geology of Manchester as revealed by borings. Transactions of the Institution of Mining Engineers, Vol. 54, 367–417.

HOGARTH, F W. circa 1930. A history of Heysham. Privately published.

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 Northwest Europe. BESLY, B M, and KELLING, G (editors). (Glasgow and London: Blackie.)

HOLLIDAY, D W. 1993. Mesozoic cover over northern England: interpretation of apatite fission track data. Journal of the Geological Society of London, Vol. 150, 657–660.

HOOKER, P J and BANNON, M P. 1993. Methane: its occurrence and hazards in construction. Construction Industry Research and Information Association Report 130. (London: CIRIA.)

HORBURY, A D. 1987. Sedimentology of the Urswick Limestone in south Cumbria and north Lancashire. Unpublished PhD thesis, University of Manchester.

HORBURY, A D. 1989. The relative roles of tectonism and eustacy in the deposition of the Urswick Limestone in South Cumbria and North Lancashire. 153–169 in The role of tectonics in Devonian and Carboniferous sedimentation in the British Isles.

ARTHURTON, R S, GUTTERIDGE, P, and NOLAN, S C (editors). Occasional Publication of the Yorkshire Geological Society, No. 6.

HORBURY, A D. 1992. A late Dinantian peloid cementstonepalaeoberesellid buildup from north Lancashire, England. Sedimentary Geology, Vol. 79, 117–137.

HORBURY, A D. In press. A Dinantian karst valley and its infill in north Lancashire.

HORBURY, A D, and ADAMS, A E. 1989. Meteoric phreatic diagenesis in cyclic late Dinantian carbonates, northwest England. Sedimentary Geology, Vol. 65, 319–344.

HUDDART, D, TOOLEY, M J, and CARTER, P A. 1977. The coasts of northwest England. 119–154 in The Quaternary history of the Irish Sea. Geological Journal Special Issue, No. 7. KIDSON, C, and TOOLEY, M J (editors).

HUDSON, P J. 1989. Old mills, gritstone quarries and millstone making in the Forest of Lancaster. Contrebis, Vol. 15, 35–64.

HUDSON, P J, and PRICE, J. 1989. Ironworking sites in the Lancaster Fells. Contrebis, Vol. 15, 68–77.

HUDSON, R G S. 1933. The geology of the Yorkshire Dales. I, The scenery and geology of north-west Yorkshire. Proceedings of the Geologists' Association, Vol. 44, Pt. 3, 228–255.

HUDSON, R G S. 1936. The Lower Carboniferous south of Carnforth. British Association for the Advancement of Science: Report of the Annual Meeting, Blackpool, 1936, 344–345.

HUDSON, R G S. 1938. I, The general geology and topography of the Harrogate district; II, The Carboniferous rocks. 295330 in The geology of the country around Harrogate. Proceedings of the Geologists' Association, Vol. 49, 295–352.

HUDSON, R G S. 1944a. A pre-Namurian fault-scarp at Malham. Proceedings of the Leeds Philosophical and Literary Society (Science section), Vol. 4, 226–232.

HUDSON, R G S. 1944b. The faunal succession in the Ct. nitidus zone in the mid-Pennines. Proceedings of the Leeds Philosophical and Literary Society (Science section), Vol. 4, 233–242.

HUDSON, R G S. 1946. The Namurian goniatites Cravenoceratoides bisati Hudson and Ct. lirifer n. sp. Proceedings of the Yorkshire Geological Society, Vol. 25, 375–386.

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.

HUGHES, C J. 1973. Spilites, keratophyres and the igneous spectrum. Geological Magazine, Vol. 109, 513–527.

HULL, E, DAKYNS, J R, TIDDEMAN, R H, WARD J C, GUNN, W, and DE RANCE, C E. 1875. The geology of the Burnley Coalfield and of the country around Clitheroe, Blackburn, Preston, Chorley, Haslingden and Todmorden. Memoir of the Geological Survey of Great Britain.

JACKSON, D I, JACKSON, A A, EVANS, D, WINGFIELD, R T R, BARNES, R P, and ARTHUR, M J. In press. United Kingdom offshore regional report: the geology of the Irish Sea. (London: HMSO for the British Geological Survey.)

JACKSON, D I, and MULHOLLAND, P. 1993. Tectonic and strati-graphic aspects of the East Irish Sea Basin and adjacent areas: contrasts in their post-Carboniferous structural styles. 791–808 in Petroleum geology of Northwest Europe: Proceedings of the 4th Conference. PARKER, J R (editor). (London: The Geological Society of London.)

JACKSON, D I, MULHOLLAND, P, JONES, S M, and WARRINGTON, G. 1987. The geological framework of the East Irish Sea Basin. 191–203 in Petroleum geology of Northwest Europe. BROOKS, J, and GLENNIE K W (editors). (London: Graham and Trotman.)

JOHNSON, E W. 1981. A tunnel section through a prograding Namurian (Arnsbergian, Eta) delta, in the western Bowland Fells, north Lancashire. Geological Journal, Vol. 16, 93–110.

JOHNSON, G A L. 1967. Basement control of Carboniferous sedimentation in northern England. Proceedings of the Yorkshire Geological Society, Vol. 36, 175–194.

JOHNSON, R H. 1985a. The geomorphology of the regions around Manchester: an introductory review. 1–23 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

JOHNSON, R H. 1985b. The imprint of glaciation on the west Pennine uplands. 237–262 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

KENDALL, P F. 1921. Report on the economic minerals at Nether Kellet. Unpublished manuscript held in BGS archives and reproduced in verbatim in BGS Report, WA/92/27.

KENT, P E. 1966. The structure of the concealed Carboniferous rocks of NE England. Proceedings of the Yorkshire Geological Society, Vol. 35, 323–352.

KENT, P E. 1974. Structural history. 13–28 in The geology and mineral resources of Yorkshire. RAYNER, D H, and HEMINGWAYS, J E (editors). Occasional Publications of the Yorkshire Geological Society, No. 2.

KIMBELL, G, CHADWICK, R A, HOLLIDAY, D W, and WERNGREN, 0 C. 1989. The structure and evolution of the Northumberland Trough from new seismic reflection data and its bearing on modes of continental extension. Journal of the Geological Society of London, Vol. 146, 775–787.

KLAPPA, C F. 1980. Rhizoliths in terrestrial carbonates, classification, recognition, genesis and significance. Sedimentology, Vol. 27, 613–629.

KNIGHT, D J. 1977. Morecambe Bay feasibility study - subsurface investigations. Quarterly Journal of Engineering Geology, Vol. 10, 303–19.

KULANDER, B R and DEAN, S L. 1993. Coal-cleat domains and domain boundaries in the Allegheny Plateau of West Virginia. Bulletin of the American Association of Petroleum Geologists. Vol. 77, 1374–1388.

LAW F. 1965. Integrated use of diverse resources. Journal of the Institution of Water Engineers, Vol. 19, 1–24.

LAWRENCE, S R, COSTER, P W, and IRELAND, R J. 1987. Structural development and petroleum potential of the northern flanks of the Bowland Basin (Carboniferous) north-west England. 225–233 in Petroleum geology of north-west Europe. BROOKS, J and GLENNIE, K (editors). (London: Graham and Trotman.)

LEARY, E. 1986. The building sandstones of the British Isles. Building Research Establishment Report. Department of the Environment. (Garston, Watford: Building Research Establishment.)

LEE, A G. 1988. Carboniferous basin configuration of central and northern England modelled using gravity data. 69–84 in Sedimentation in a synorogenic basin complex. The Upper Carboniferous of Northwest Europe. BESLY, B M and KELLING, G (editors). (Glasgow and London: Blackie.)

LEEDER, M R. 1982. Upper Palaeozoic basins of the British Isles - Caledonide inheritance versus Hercynian plate margin processes. Journal of the Geological Society of London, Vol. 139, 479–491.

LEEDER, M R. 1988. Recent developments in Carboniferous geology: a critical review with implications for the British Isles and NW Europe. Proceedings of the Geologists' Association, Vol. 99, 73–100.

LEVISON, A. 1988. The geology of the Morecambe gas field. Geology Today, Vol. 4, No. 3, 95–100.

LEWIS, C L E, GREEN, P F, CARTER, A, and HURFORD, A J. 1992. Elevated K/T palaeotemperatures throughout northwest England: three kilometres of Tertiary erosion? Earth and Planetary Science Letters, Vol. 112, 131–145.

LONGWORTH, D. 1985. The Quaternary history of the Lancashire Plain. 178–200 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

MACKINTOSH, D. 1869. On the correlation, nature and origin of the drifts of north-west Lancashire and a part of Cumberland, with remarks on denudation. Quarterly Journal of the Geological Society of London, Vol. 25, 407–431.

MACKLIN, M G, RUMSBY, B T, and HEAP, T. 1992. Flood alluvia-don and entrenchment: Holocene valley-floor development and transformation in the British uplands. Bulletin of the Geological Society of America, Vol. 104, 631–643.

MADDOCK, R H. 1992. Absolute dating of fault movements. Journal of the Geological Society of London, Vol. 149, 249–250.

MARR, J E. 1916. The geology of the Lake District and the scenery as influenced by geological structure. (Cambridge: Cambridge University Press.)

MARR, J E. 1919. Obituary to Richard Hill Tiddeman. The Quarterly Journal of the Geological Society of London, Vol. 74, liv-lv.

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.

MARTINSEN, O J. 1993. Namurian (late Carboniferous) depositional systems of the Craven-Askrigg area, northern England: implications for sequence-stratigraphic models. Special Publications International Association of Sedimentologists, Vol. 18, 247–281.

MAYFIELD B, and PEARSON, M C. 1972. Human influences with the north Derbyshire blanket peat. East Midlands Geographer, Vol. 5, 245–251.

MAYNARD J R, and LEEDER, M R. 1992. On the periodicity and magnitude of Late Carboniferous glacio-eustatic sea-level changes. Journal of the Geological Society of London, Vol. 149, 303–311.

MILLER, J, and GRAYSON, R F. 1982. The regional context of Waulsortian facies in northern England. 17–33 in Symposium on the paleoenvironmental setting and distribution of the Waulsortian Facies. BOLTON, K, LANE, R H, and LE MONE, D V (editors). (El Paso: El Paso Geological Society and the University of Texas.)

MISHELL, D R F. 1965. Namurian and Westphalian miospores from the Bowland Fells and Ingleton Coalfield. Unpublished PhD thesis, University of Sheffield.

MITCHELL, W A. 1991. Dimlington Stadial ice sheet in the western Pennines. 25–42 in Western Pennines: field guide. MITCHELL, W A (editor). (London: Quaternary Research Association.)

MOORE, E W J. 1930. A section in the Sabden Shales on the River Darwen, near Blackburn. Journal of the Manchester Geological Association, Vol. 1, 103–108.

MOORE, P D. 1975. Origin of blanket mires. Nature, London, Vol. 256, 267–269.

MORTON A C, and HALLSWORTH C R. 1992. Heavy mineral assemblages supplied by the basement rocks of northern Scotland: the Northern Highlands west of the Moine Thrust. British Geological Survey Technical Report, WH/92/142R.

MOSELEY, F. 1954. The Namurian of the Lancaster Fells. Quarterly Journal of the Geological Society of London, Vol. 109, 423–454.

MOSELEY, F. 1956. The geology of the Keasden area, west of Settle, Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 30, 331–352.

MOSELEY, F. 1961. Erosion surfaces in the Forest of Bowland. Proceedings of the Yorkshire Geological Society, Vol. 33, 173–196.

MOSELEY, F. 1962. The structure of the south-western part of the Sykes Anticline, Bowland, West Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 33, 287–314.

MOSELEY, F. 1972. A tectonic history of northwest England. Journal of the Geological Society of London, Vol. 128, 561–598.

MOSELEY, F, and AHMED, S Monograptus 1967. Carboniferous joints in the north of England and their relation to earlier and later structures. Proceedings of the Yorkshire Geological Society, Vol. 36, 61–90.

MOSELEY, F, and WALKER, D. 1952. Some aspects of the Quaternary Period in North Lancashire. The Naturalist, Vol. 841, 41–54.

MUIR, R O. 1963. Petrology and provenance of the Millstone Grit of Central Scotland. Transactions of the Edinburgh Geological Society, Vol. 43, 331–340.

MUNDY, D J C, and ARTHURTON, R S. 1980. Field meetings: Settle and Flashy. Proceedings of the Yorkshire Geological Society, Vol. 43, 32–36.

ORR W E, MUIR-WOOD A, BEAVER J L, IRELAND R J, and BEAGLEY D P. 1991. Abbeystead Outfall Works: background to repairs and modifications - and the lessons learned. Journal of the Institution of Water and Environmental Management, Vol. 5, 7–20.

OWENS, B, NEVES, R, GUEINN, K J, MISHELL, D R F, SABRY, H S M Z, and WILLIAMS, J E. 1977. Palynological divisions of the Namurian of northern England and Scotland. Proceedings of the Yorkshire Geological Society, Vol. 41, 381–398.

OWENS, B, VARKER, W J, and HUGHES R A. 1990. Lateral biostratigraphical consistency across the Mid-Carboniferous boundary in northern England. Courier Forschungsinstitut Senckenberg, Vol. 130, 237–244.

PALFRAMAN, D F B. 1984. A new species of Cravenoceras from the Namurian of County Leitrim, Ireland. Bulletin of the Geological Survey of Ireland, Vol. 3, 211–219

PARKINSON, D. 1926. The faunal succession in the Carboniferous Limestone and Bowland Shales at Clitheroe and Pendle Hill, Lancashire. Quarterly Journal of the Geological Society of London, Vol. 82, 188–249.

PARKINSON, D. 1935. The geology and topography of the limestone knolls in Bolland (Bowland), Lancs. and Yorks. Proceedings of the Geologists' Association, Vol. 46, 97–120.

PARKINSON, D. 1936. The Carboniferous succession in the Slaidburn district, Yorkshire. Quarterly Journal of the Geological Society of London, Vol. 92, 294–331.

PEARCE, J A, and CANN, J R. 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth and Planetary Science Letters, Vol. 19, 290–300.

PHILLIPS, J. 1836. Illustration of the geology of Yorkshire. Part 2 The Mountain Limestone district. (London: John Murray.)

PHILLIPS, J. 1837. A report on the probability of the occurrence of coal and other minerals in the vicinity of Lancaster. (Lancaster: William Barwick.)

PLANT, J A, and JONES, D G (editors). 1989. Metallogenic models and exploration criteria for buried carbonate-hosted ore deposits - a multidisciplinary study in eastern England. (Keyworth, Nottingham: British Geological Survey. London: The Institution of Mining and Metallurgy.)

PLANT, J A, and JONES, D G (editors). 1991. Development of regional exploration criteria for buried carbonate-hosted mineral deposits: a multdisciplinary study in northern England. British Geological Survey Technical Report, WP/91/1C.

POCOCK, R W, and WRAY, D A. 1925. The geology of the country around Wem. Memoir of the Geological Survey of Great Britain, Sheet 138 (England and Wales).

POOLE, E G, and WHITEMAN, A J. 1955. Variations in thickness of the Collyhurst Sandstone in the Manchester area. Bulletin of the Geological Survey of Great Britain, No. 9.

POWELL, C MCA, and VEEVERS, J J. 1987. Namurian uplift in Australia and South America triggered the main Gondwanan glaciation. Nature, London, Vol. 326, No. 6109, 177–179.

PRICE, D, WRIGHT, W B, JONES, R C B, TONKS, L H, and WHITEHEAD, T H. 1963. Geology of the country around Preston. Memoir of the Geological Survey of Great Britain, Sheet 75 (England and Wales).

PRINGLE, J and JACKSON, J W. 1928. Tylonautilus nodiferus gen. nov. = (Nautilus (Discites) nodiferus Armstrong) : a Carboniferous guide fossil. The Naturalist, 1928, December 1, 373–378.

RAISTRICK, A. 1933. The glacial and post-glacial periods in west Yorkshire. Proceedings of the Geologists' Association, Vol. 44, 263–269.

RAISTRICK, A. 1973. Lead mining in the mid-Pennines. (Truro: Bradford Barton.)

RAMSBOTTOM, W H C. 1969. The Namurian of Britain. Sixieme Congres International de stratigraphie et de geologic. du Carbonifere, Sheffield., 1967, Vol. 1, 219–232

RAMSBOTTOM, W H C. 1973. Transgressions and regressions in the Dinantian: a new synthesis of British Dinantian stratigraphy. Proceedings of the Yorkshire Geological Society, Vol.39, 567–607

RAMSBOTTOM, W H C. 1974. Dinantian. 47–73 in The geology and mineral resources of Yorkshire. RAYNER, D H, and HEMINGWAY J E (editors). (Yorkshire Geological Society.)

RAMSBOTTOM W H C, CALVER M A, EAGAR, R M C, HODSON, F, HOLLIDAY, D W, STUBBLEFIELD, C J, and WILSON, R B. 1978. A correlation of Silesian rocks in the British Isles. Special Report of the Geological Society of London, No. 10.

RAMSBOTTOM, W H C, RHYS, G H, and SMITH, E G. 1962. Boreholes in the Carboniferous rocks of the Ashover district, Derbyshire. Bulletin of the Geological Survey of Great Britain, No. 19, 75–168.

READE, C E. 1904. Glacial and post-glacial features of the lower valley of the River Lune and its estuary. Proceedings of the Liverpool Geological Society, Vol. 9, 163–196.

READING, H G. 1964. A review of the factors affecting the sedimentation of the Millstone Grit (Namurian) in the central Pennines. Developments in Sedimentology, Vol. 1, 340–346.

RILEY, N J. 1985. Asturoceras and other dimorphoceratid ammonoids from the Namurian (E2) of Lancashire. Proceedings of the Yorkshire Geological Society, Vol. 45, 219–224.

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

RILEY, N J. 1993. Dinantian (Lower Carboniferous) biostratigraphy and chronostratigraphy in the British Isles. Journal of the Geological Society of London, Vol. 150, 427–446.

RILEY, N J, VARKER, W J, OWENS S, B, HIGGINS, A C, and RAMSBOTTOM, W H C. 1987. Stonehead Beck, Cowling, North Yorkshire, England: a British proposal for the mid-Carboniferous boundary stratotype. Courier Forschungsinstitut Senckenberg, Vol. 98, 159–177.

ROBINSON, N A and PRINGLE, A W (editors). 1987. Morecambe Bay: An assesment of present ecological knowledge. Resource paper of the Centre for North-West Regional Studies. Published in conjunction with the Morecambe Bay Study Group.

ROLLIN, K E. 1987. Catalogue of geothermal data for the land area of the United Kingdom. Third revision: April 1987. Investigation of the Geothermal Potential of the UK, British Geological Survey. (Keyworth, Nottingham: British Geological Survey.)

ROSE, W C C, and DUNHAM, K C. 1977. Geology and hematite deposits of South Cumbria. Economic Memoir of the Geological Survey of Great Britain, Sheets 58, part 48.

ROWLEY, D B, RAYMOND, A, PARRISH, J T, LOTTES, A, SCOTESE, C R, and ZEIGLER, A Monograptus 1985. Carboniferous paleogeographic, phytogeographic and paleoclimatic reconstructions. International Journal of Coal Geology, Vol. 5, 7–42.

SHIELLS, K A. 1964. The geological structure of northeast Northumberland. Transactions of the Royal Society of Edinburgh, Vol. 65, 449–484.

SHIMWELL, D W. 1985. The distribution and origins of lowland mosslands. 299–312 in The geomorphology of north-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

SIMS, A P. 1988. The evolution of a sand-rich basin-fill sequence in the Pendleian (Namurian, Etc) of north-west England. Unpublished PhD thesis, University of Leeds.

SLINGER, F C. 1936. Millstone Grit and glacial geology of Caton Moor, near Lancaster. Report of the British Association for the Advancement of Science, Blackpool. 1936, 345.

SMITH, B. 1924. On the west Cumberland brockram and associated rocks. Geological Magazine, Vol. 61, 289–308.

SMITH, D B, BRUNSTOW, R G W, MANNING, P I, SIMPSON, S, and SHOT-TON, F W. 1974. A correlation of Permian rocks in the British Isles. Special Report of the Geological Society of London, No. 5.

SMITH, D B, and TAYLOR, J C Monograptus 1992. Permian. 87–96 in Atlas of palaeogeography and lithofacies. COPE, J C W, INGHAM, J K, and RAWSON, P F (editors). Memoir of the Geological Society of London, No. 13.

SMITH, K, SMITH, N J P, and HOLLIDAY, D W. 1985. The deep structure of Derbyshire. Geological Journal, Vol. 20, 215–225.

SOMERVILLE, J D, and STRANK, A R E. 1984. The recognition of the Asbian/Bigantian boundary fauna and marker horizons in the Dinantian of North Wales. Geological Journal, Vol. 19, 227–237.

SOPER, N J, WEBB, B C, and WOODCOCK, N J. 1987. Late Caledonian (Acadian) transpression in North West England: timings, geometry and geotectonic significance. Proceedings of the Yorkshire Geological Society, Vol. 46, 175–192.

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).

STOW, D A V. 1985. Deep-sea clastics: where are we and where are we going? 67–93 in Sedimentology: recent developments and applied aspects. BRENCHLEY, P J, and WILLIAMS, B P J (editors). Special Publication of the Geological Society of London, No. 18.

STUART, A J. 1982. Pleistocene vertebrates in the British Isles. (London and New York: Longman.)

TCHALENKO, J S. 1970. Similarities between shear zones of different magnitudes. Bulletin of the Geological Society of America, Vol. 81, 1625–1640.

THOMPSON, D. 1987. Battle of the bog. New Scientist, Vol. 113, No. 1542, 41–44.

TIDDEMAN, R H. 1868. The valleys of Lancashire. Geological Magazine, Vol. 5, 39–40.

TIDDEMAN, R H. 1872. On the evidence for the ice-sheet in North Lancashire and adjacent parts of Yorkshire and Westmorland. Quarterly Journal of the Geological Society of London, Vol. 14, 471–491.

TIDDEMAN, R H. 1889. On a concurrent faulting and deposit in Carboniferous times in Craven, Yorkshire, with a note on Carboniferous reefs. Report of the British Association (Newcastle), 600–603.

TIDDEMAN, R H. 1898. Geology of Bowland Knotts. Yorkshire Naturalist's Union. Supplement to Circular of 136th Meeting, at Clapham.

TIDDEMAN, R H. 1891. Sections illustrating the geology of the country between Slaidburn and Ingleton, and between Morecambe Bay and Settle. Horizontal Section, Sheet 147. Geological Survey of England and Wales.

TONKS, L H, JONES, R C B, LLOYD, W, SHERLOCK, R L, and WRIGHT, W B. 1931. The geology of Manchester and the South-East Lancashire Coalfield. Memoir of the Geological Survey of Great Britain, Sheet 85 (England and Wales).

TOOLEY, M J. 1974. Sea-level changes in the last 9000 years in north-west England. The Geographical Journal, Vol. 140, 18–42.

TOOLEY, M J. 1982. Sea-level changes in northern England. Proceedings of the Geologists' Association, Vol. 93, 43–51.

TREWIN, N H. 1968. Potassium bentonites in the Namurian of Staffordshire and Derbyshire. Proceedings of the Yorkshire Geological Society, Vol. 37, 73–91.

TREWIN, N H, and HOLDSWORTH B K. 1972. Further K-bentonites from the Namurian of Staffordshire. Proceedings of the Yorkshire Geological Society, Vol. 39, 87–88.

TROTTER, F M, 1951. Sedimentation facies in the Namurian of north-western England and adjoining areas. The Liverpool and Manchester Geological Journal, Vol. 1, pt.1, 77–112.

TURNER, J S. 1935. Structural geology of Stainmore, Westmorland, and notes on the late-Palaeozoic (late Variscan) tectonics of the north of England. Proceedings of the Geologists' Association, Vol. 46, 121–151.

TURNER, S. 1949. The deeper structure of the north of England. Proceedings of the Yorkshire Geological Society, Vol.27, 280–297.

UNDERHILL, R, GAYER, R A, WOODCOCK, N H, DONNELLY, R., JOLLEY, E J, and STIMPSON, I G. 1988. The Dent Fault System, northern England - reinterpreted as a major oblique-slip fault zone. Journal of the Geological Society of London, Vol. 145, 303–316.

VAUGHAN, A. 1905. Palaeontological sequence in the Carboniferous Limestone of the Bristol area. Quarterly Journal of the Geological Society of London, Vol. 61, 181–307.

VINCENT, P J, and LEE, M P. 1981. Some observations on the loess around Morecambe Bay, north-west England. Proceedings of the Yorkshire Geological Society, Vol. 43, 281–294.

WADGE, A J, BATESON, J H, and EVANS, A D. 1983. Mineral reconnaissance surveys in the Craven Basin. Mineral Reconnaissance Programme Report, Institute of Geological Sciences, No. 66.

WAGER, L R. 1931. Jointing in the Great Scar Limestone of Craven and its relation to the tectonics of the area. Quarterly Journal of the Geological Society of London, Vol. 87, 392–424.

WARRINGTON, G, AUDLEY-CHARLES, M G, ELLIOTT, R E, EVANS, W B, IVIMEY-COOK, H C, KENT, P E, ROBINSON, P L, SHOTTON, F W, and TAYLOR, F Monograptus 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No. 13.

WATSON, J. 1911. British and foreign building stones: a descriptive catalogue of the specimens in the Sedgwick Museum, Cambridge. (Cambridge: University Press.)

WEST, R G. 1968. Pleistocene geology and biology with special reference to the British Isles. (London: Longman.)

WHITE, F Monograptus 1992. Aspects of the palaeoecology and strati-graphic significance of late Dinantian (early Carboniferous) foraminifera of Northern England. Unpublished PhD thesis, University of Manchester.

WHITEHEAD, T H, DIXON, E E L, POCOCK, R W, ROBERTSON, T, and CANTRILL, T C. 1927. The geology of the country between Stafford and Market Drayton. Memoir of the Geological Survey of Great Britain, Sheet 139 (England and Wales).

WHITTAKER, A, and ten others. 1991. A guide to stratigraphical procedure. Journal of the Geological Society of London, Vol. 148, 813–824.

WILCOX, R E, HARDING, T P, and SEELY, D R. 1973. Basic wrench tectonics. Bulletin of the American Association of Petroleum Geologists, Vol. 57, 74–96.

WILKINSON I P, and RILEY N J. 1990. Namurian entomozoacean Ostracoda and eustatic events. 161–172 in Ostracoda and global events. WHATLEY, R, and MAYBURY, C (editors). (London: Chapman and Hall.)

WILLIAMS, G E. 1991. Upper Proterozoic tidal rhythmites, South Australia: sedimentary features, deposition, and implications for the earth's paleorotation. 161–178 in Clastic tidal sedimentology. SMITH, D G, REINSON, G E, ZAITLIN, B A, and RAHMANI A (editors). Memoir of the Canadian Society of Petroleum Geologists, No. 16.

WILLIAMS, G M, and AITKENHEAD, N. 1991. Lessons from Loscoe: the uncontrolled migration of landfill gas. Quarterly Journal of Engineering Geology, Vol. 24, 191–207.

WILLS, L J. 1978. A palaeogeographic map of the Lower Palaeozoic floor below the cover of Upper Devonian, Carboniferous and later formations. Memoir of the Geological Society of London, No. 8.

WILSON, A A, BRANDON, A, and JOHNSON, E W. 1989. Abbeystead: geological context of the Wyresdale tunnel methane explosion. British Geological Survey Technical Report, WA/89/30.

WILSON, A A, and CORNWELL, J. 1982. The Institute of Geological Sciences borehole at Beckermonds Scar, North Yorkshire. Proceedings of the Yorkshire Geological Society, Vol. 44, 59–88.

WILSON, A A, and CROFTS, R G. 1992. Geology of the Heysham area. British Geological Survey Technical Report, WA/92/88.

WILSON, A A, and EVANS, W B. 1990. Geology of the country around Blackpool. Memoir of the British Geological Survey, Sheet 66 (England and Wales).

WINCHESTER, A, and FLOYD, P A. 1976. Geochemical magma type discrimination: application to altered and metamorphosed basic igneous rocks. Earth and Planetary Science Letters, Vol. 28, 459–469.

WINCHESTER, J A, and FLOYD, P A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, Vol. 20, 325–343.

WOODWARD, K, and CURTIS, C D. 1987. Predictive modelling for the distribution of production-constraining illites - Morecambe Gas Field, Irish Sea, Offshore UK. 205–213 in Petroleum geology of North West Europe. BROOKS, J, and GLENNIE, K (editors). (London: Graham and Trotman.)

WRIGHT, W B, SHERLOCK, R L, WRAY, D A, LLOYD, W, and TONKS, L H. 1927. The geology of the Rossendale Anticline. Memoir of the Geological Survey of Great Britain, Sheet 76 (England and Wales).

ZIEGLER, P A. 1990. Geological atlas of Western and Central Europe (2nd edition.) (Mijdrecht: Drukkerij Verweij B.V. for Shell Internationale Petroleum.)

ZONG, Y, and TOOLEY, M J. 1996. Holocene sea-level changes and crustal movements in Morecombe Bay, northwest England. Journal of Quaternary Science, Vol. 11, 43–58

Appendix 1 BGS reports

Land Survey technical reports

Open-file reports containing geological details additional to those shown on the 1:10 000 maps are listed below. They can be consulted at BGS libraries or purchased from the same outlets as dyeline maps.

Biostratigraphical technical and other reports

These reports do not have open-file status but may be consulted along with enquiries on additional data on application to the manager, Biostratigraphy and Sedimentology Group, BGS, Key-worth. Note that prior to 1988 the reports are group reports rather than technical reports. Reports with negative results are not listed.

Dinantian palynology

Dinantian macropalaeontology

Namurian palynology

Namurian marine macropalaeontology and conodonts

Miscellaneous technical reports

These reports generally do not have open-file status but may be consulted by application to the manager of the relevant unit at BGS, Keyworth. Note that prior to 1988 the reports are group reports rather than technical reports.

Appendix 2 Physical properties of rocks, gravity and aeromagnetic data

Physical property measurements on rocks from the district are scarce and restricted to density measurements, the majority having been carried out by students from Lancaster University (B Robinson, personal communication, 1992). Consequently, published density data from adjacent areas (Arthurton et al., 1988; Aitkenhead et al., 1992) have also been utilised in the modelling. The bulk density values used in the detailed interpretations of the Permo-Triassic basins and drift-filled channels carried out to complement geological mapping in the Lancaster district are: superficial deposits 1.85 Mg/m3; Sherwood Sandstone Group ranging between 2.24 and 2.60 Mg/m3 with an average of 2.30 Mg/m3; Millstone Grit sandstones 2.40 Mg/m3; Bowland Shale 2.54 Mg/m3; Dinantian limestone 2.66 Mg/m3.

Regional gravity surveys

Bouguer gravity anomaly data for the district were collected by the BGS and by RTZ Oil and Gas. The RTZ data were restricted to the upland regions where positions and heights were obtained by tacheometric surveying. The BGS gravity stations were located on Ordnance Survey (OS) benchmarks and spot heights. These data result in an average coverage of 1.3 gravity stations per km2. Some additional data in the Quernmore Valley, to the south of Caton, and along the coastal strip to the west of Lancaster and Galgate have been collected by the BGS and students from Lancaster University.

A Bouguer correction density of 2.55 Mg/m3 has been used to reduce the gravity data to sea-level. This density was found to give the least correlation between the Bouguer gravity contours and topography and is an accepted average value for mixed Namurian and Dinantian sequences (Aitkenhead et al., 1992). The resulting Bouguer gravity anomaly map is shown in (Figure 40). The map extends beyond the Lancaster district so that trends from adjoining regions can be discerned.

Aeromagnetic survey

The aeromagnetic data for the Lancaster district were acquired in 1958 at a flight altitude of 305 m mean terrain clearance along 2 km spaced east–west flight lines. The original analogue data have subsequently been put into digital form for the BGS data bank.

Appendix 3 Selected boreholes

This list includes the BGS permanent registration number, name, original owner and number where appropriate, grid reference, total depth and stratigraphical range (down to formation rank) of the boreholes. The registration number of onshore boreholes is in the form (SD45NW/103), where SD 45 NW is the 1:10 000 geological sheet number. The sites and brief abstract logs of most of the holes listed are shown on the relevant maps listed in the front of the memoir. Offshore borehole numbers relate to latitude and longitude and are in the form 54-03/22. These and other non-confidential borehole records are held on open file in the Survey's archives. Copies of these records may be obtained from the British Geological Survey, Keyworth, Nottingham NG12 5GG, at a fixed tariff. * and f denote that sliced half core and chippings respectively are held at BGS Keyworth. Biostratigraphical and miscellaneous samples from other boreholes have also been retained.

(SD36NE/54-03/7) Morecambe Bay Barrage Site Investigation A3(1968) [SD 3894 6918] 47.8 m: drift, Mercia Mudstone *

(SD45NW/2) Heysham No. 2, Trimpell Refinery (1954) [SD 4182 5938] 103.9 m: drift, Caton Shale, Ward's Stone Sandstone

(SD45NW/3) Heysham No. 3a, Trimpell Refinery (1956) [SD 4101 5912] 132.9 m: Till, Caton Shale, Ward's Stone Sandstone

(SD45NW/14) Pre-Stage 1 No. 10, Heysham Power Stations (1966) [SD 4043 5938] 49.7 m: drift, Millstone Grit Group (undivided), Heysham Harbour Sandstone

(SD45NW/87) Stage 1 No. 60, Heysham Power Stations (1967) [SD 4026 5994] 23.9 m: drift, Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/97) Lune Foreshore D, Heysham Power Stations (1975) [SD 4170 5637] 15.0 m: drift, St Bees Shales

(SD45NW/99) Lune Foreshore E2, Heysham Power Stations (1975) [SD 4087 5517] 30.8 m: drift, St Bees Evaporites

(SD45NW/103) Lune Foreshore L, Heysham Power Stations (1975) [SD 4067 5934] 50.6 m: Millstone Grit Group (undivided), Heysham Harbour Sandstone

(SD45NW/132/4) Stage 2 No. 4, Heysham Power Stations (1978) [SD 4022 5948] 100.7 m: Made Ground, drift, Sherwood Sandstone Group, St Bees Evaporites, ?Lower Coal Measures

(SD45NW/132/5) Stage 2 No. 5, Heysham Power Stations (1978) [SD 4024 5949] 42.4 m: Made Ground, drift, Sherwood Sandstone Group, St Bees Shales, Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/132/6) Stage 2 No. 6, Heysham Power Stations (1978) [SD 4025 5959] 60.9 m: Made Ground, drift, Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/132/14) Stage 2 No. 14, Heysham Power Stations (1978) [SD 4009 5944] 100.6 m: Made Ground, drift, Sherwood Sandstone Group

(SD45NW/132/20) Stage 2 No. 20, Heysham Power Stations (1978) [SD 4017 5947] 108.7 m: Made Ground, drift, Sherwood Sandstone Group, St Bees Shales, St Bees Evaporites, ?Lower Coal Measures

(SD45NW/132/22) Stage 2 No. 22, Heysham Power Stations (1978) [SD 4020 5947] 91.5 m: Made Ground, Sherwood Group, St Bees Shales, St Bees Evaporites, ?Lower Coal Measures

(SD45NW/132/28) Stage 2 No. 28, Heysham Power Stations (1978) [SD 4031 5956] 41.9 m: Made Ground, drift, Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/132/39) Stage 2 No. 39, Heysham Power Stations (1978) [SD 4015 5947] 104.2 m: Made Ground, drift, Sherwood Sandstone Group, St Bees Shales, St Bees Evaporites, ?Lower Coal Measures

(SD45NW/133) Stage 2 No. 214, Heysham Power Stations (1982) [SD 4033 5966] 37.5 m: Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/136) Stage 2 No. 217, Heysham Power Stations (1982) [SD 4032 5963] 40.3 m: drift, Millstone Grit Group (undivided) above Heysham Harbour Sandstone

(SD45NW/229) Dry Buffer Store (DBS) 101, Heysham Power Stations (1989) [SD 4045 5989] 150.2 m: Made Ground, drift, Millstone Grit Group (undivided), Heysham Harbour Sandstone, Millstone Grit Group (undivided), Eldroth Grit, Kirkbeck Formation *

(SD45NW/230) Dry Buffer Store (DBS) 103, Heysham Power Stations (1989) [SD 4050 5963] 120.2 m: Made Ground, drift, Millstone Grit Group (undivided), Heysham Harbour Sandstone *

(SD45NW/240) Dry Buffer Store (DBS) 133, Heysham Power Stations (1989) [SD 4053 5972] 84.5 m: Made Ground, drift, Millstone Grit Group (undivided), Heysham Harbour Sandstone *

(SD45NW/247) Dry Buffer Store (DBS) 142, Heysham Power Stations (1989) [SD 4075 5966] 99.6 m: Made Ground, drift, Eldroth Grit, Caton Shale, ?Ward's Stone Sandstone, Roeburndale Formation *

(SD45NW/268) Heaton Hall, BGS (1991) [SD 4398 5949] 64.1 m: Till, ?Kirkbeck Formation

(SD45NW/269) Overton, BGS (1991) [SD 4397 5724] 77.2 m: drift, ?Eldroth Grit, ?Kirkbeck Formation

(SD45NE/135) Tarnwater, BGS (1991) [SD 4689 5762] 51.0 m: drift, Caton Shale

(SD45NE/136) Parkside, BGS (1991) [SD 4715 5552] 19.3 m: Till, Kirkbeck Formation

(SD45SE/2) Manor Inn well, Cockerham, Mitchell's Brewery (pre-1956) [SD 4655 5222] 41.7 m: drift, Sherwood Sandstone Group

(SD45SE/73) Sellerley, BGS (1991) [SD 4778 5465] 60.0 m: drift, Kirkbeck Formation

(SD45SE/74) Crag Hall, BGS (1991) [SD 4839 5346] 54.0 m: Till, Caton Shale

(SD45SE/75) Launds Farm, BGS (1991) [SD 4631 5365] 30.2 m: Till, Cumbria Coast Group

(SD45SE/78) Hampson Green 3, BGS (1993) [SD 4953 5431] 35.9 m: Till, Caton Shale

(SD46NW/54-03/8) Morecambe Bay Barrage Site Investigation C4 (1968) [SD 4097 6902] 70.3 m: drift, Millstone Grit Group undifferentiated *

(SD46NW/54-03/9) Morecambe Bay Barrage Site Investigation C5 (1968) [SD 4209 6826] 53.7 m: drift, Millstone Grit Group undifferentiated *

(SD46NW/54-03/10) Morecambe Bay Barrage Site Investigation A4 (1968) [SD 4326 6721] 78.3 m: drift, Millstone Grit Group undifferentiated *

(SD46NW/54-03/11) Morecambe Bay Barrage Site Investigation S5 (1968) [SD 4432 6671] 78.0 m: drift, Millstone Grit Group undifferentiated *

(SD46NW/54-03/12) Morecambe Bay Barrage Site Investigation C6 (1968) [SD 4486 6645] 41.5 m: drift, Millstone Grit Group undifferentiated *

(SD46NW/54-03/17) Morecambe Bay Barrage Site Investigation A9 (1968) [SD 4278 6587] 74.9 m: drift, Millstone Grit Group undifferentiated *

(SD46NE/23) Belmount Farm, BGS (1991) [SD 4669 6511] 69.0 m: Till, St Bees Shale t

(SD46NE/24) Slyne, BGS (1991) [SD 4745 6529] 69.0 m: drift, Pendle Grit t

(SD46NE/54-03/22) Morecambe Bay Barrage Site Investigation S6 (1968) [SD 4653 6951] 47.1 m: drift, ?Roeburndale Formation

(SD46SW/19) Well, LMS Railway Company (1905-7) [SD 4156 6020] 126.5 m: Ward's Stone Sandstone, Roeburndale Formation

(SD46SW/152) Heysham Harbour Link Sewer No.10, Lancaster Corporation (1984) [SD 4161 6108] 9 m: Made Ground, drift, Roeburndale Formation

(SD46SW/236) Dry Buffer Store (DBS) 102, Heysham Power Stations (1989) [SD 4067 6001] 100.0 m: drift, Eldroth Grit, Caton Shale, ?Ward's Stone Sandstone, Roeburndale Formation

(SD46SW/498) White Lund Farm, BGS (1991) [SD 4442 6227] 30.0 m: drift, Collyhurst Sandstone

(SD46SE/2) Well, Lansil Ltd (1931) [SD 4860 6354] 139.6 m: drift, Pendle Grit

(SD46SE/3) Well, Nelson's Silk Mill (1950) [SD 4888 6404] 156.9 m: drift, ?Roeburndale Formation, Pendle Grit

(SD46SE/13) Well, Greenfield Mills, (1900–2) [SD 4825 6161] 157.5 m: Pendle Grit

(SD46SE/17) Well, Lune Mills (1894) [SD 4622 6187] 322.3 m: drift, Roeburndale Formation, ?Pendle Grit

(SD46SE/38) Salt Ayre No. 1, Lancashire County Council (1975) [SD 4526 6200] 24.5 m: drift, St Bees Evaporites

(SD46SE/264) Aldcliffe, BGS (1991) [SD 4627 6021] 74.7 m: drift, Roeburndale Formation

(SD55NW/12) Dam Head, BGS (1993) [SD 5065 5800] 137.1 m: Till, Millstone Grit Group (undivided), Eldroth Grit, Kirkbeck Formation *

(SD55SW/14) Hampson Green 4, BGS (1993) [SD 5001 5441] 24.3 m: Till, Caton Shale

(SD56NW/28) Well, Whinney Hill (1972) [SD 5426 6793] 67.1 m: Head, Roeburndale Formation

(SD56NW/64) Dunald Mill No. 3/92, Tarmac Roadstone plc. (1992) [SD 5074 6762] 89.4 m: ?Pendle Grit, Gleaston Formation, Urswick Limestone

(SD56NW/66) Dunald Mill No. 14/93, Tarmac Roadstone plc. (1993) [SD 5095 6753] 42.8 m: Till, Gleaston Formation, Urswick Limestone

(SD56SW/8) North Park site investigation DH 106, Lancashire River Authority (1972) [SD 5177 6424] 64.6 m: drift, Pendle Grit

(SD56SW/26) Well, Rectory, Stockabank (1972) [SD 5143 6097] 76.2 m: Made Ground, ?Ward's Stone Sandstone, Roeburndale Formation

(SD56SE/1) Whitmoor, Place Oil and Gas Company (1966–7) [SD 58744 63150] 1559.1 m: Caton Shale, Ward's Stone

Sandstone, Roeburndale Formation, Pendle Grit, Upper Bowland Shale, Lower Bowland Shale, Pendleside Limestone, Hodderense Limestone, Hodder Mudstone

(SD65NE/2) BP Minerals BHD 7 (1982) [SD 6554 5539] 152.0 m: drift, Lower Bowland Shale, Pendleside Limestone, Hodder Mudstone

(SD65SW/21) BP Minerals BHD 5 (1982) [SD 6497 5434] 156.6 m: drift, Lower Bowland Shale, Pendleside Limestone, Hodderense Limestone, Hodder Mudstone

(SD65SW/22) BP Minerals BHD 9 (1983) [SD 6372 5233] 220.8 m: drift, Pendleside Limestone, Hodderense Limestone, Hodder Mudstone *

(SD65SW/24) BP Minerals BHD 11 (1983) [SD 6416 5441] 188.5 m: drift, Lower Bowland Shale, Pendleside Limestone

(SD65SW/25) BP Minerals BHD 12 (1983) [SD 6414 5368] 266.7 m: drift, Lower Bowland Shale, Pendleside Limestone, Hodderense Limestone, Hodder Mudstone *

(SD65SE/39) BP Minerals BHD 2 (1982) [SD 6519 5491] 255.4 m: drift, Lower Bowland Shale, Pendleside Limestone, Hodderense Limestone, Hodder Mudstone

(SD66NW/5) Wray, BGS (1987) [SD 63200 65700] 310.0 m: Claughton Formation, Caton Shale, Ward's Stone Sandstone, Roeburndale Formation *

(SD66NE/1) Bentham Station, Ingleton Collieries Ltd (1904) [SD 6659 6893] 183.5 m: drift, Eldroth Grit, Kirkbeck Formation

(SD66NE/2) Seat Hall, Ingleton Collieries Ltd (1904) [SD 6603 6982] 183.3 m: drift, Millstone Grit Group (undivided), Greta Grit, Millstone Grit Group (undivided), Eldroth Grit

(SD66NE/3) Badger Ford Bridge well, Craven Water Board (1971) [SD 6909 6774] 116.7 m: Till, Roeburndale Formation

(SD66SE/5) Lowgill No. 2 well, North West Water Authority (1982) [SD 6526 6498] 152.6 m: Till, Claughton Formation, Caton Shale, Ward's Stone Sandstone, Roeburndale Formation

(SD67SE/5) Nutstile Beck, Ingleton Collieries Ltd (1906) [SD 6933 7140] 182.9 m: Lower Coal Measures

Appendix 4 Dissertation theses and other unpublished works referred to in the Memoir

Copies of those marked by an asterix are held at the BGS Library, Keyworth.

Author citations for fossil species

To satisfy the rules and recommendations of the international codes of botanical and zoological nomenclature, authors of cited species are listed below.

Chapter 2 Dinantian: Worston Shale

Chapter 3  Dinantian to Namurian

Chapter 4  Namurian

Chapter 5 Westphalian

Chapter 6 Permo-Triassic

Chapter 8 Quaternary

Figures, plates and tables

Figures

(Figure 1) Topography and geography of the Lancaster district.

(Figure 2) Regional setting of the Lancaster geological sheet.

(Figure 3) General bedrock geology of the Lancaster district and reliability. The approximate boundary is shown between the area where bedrock geology is well known, based on numerous stream and quarry exposures and detailed landform mapping, and where an extensive drift cover restricts knowledge of bedrock to scattered boreholes, isolated sections, and seismic profile interpretations. Important stratigraphical boreholes and the line of the Wyresdale and Bowland Forest tunnels are shown. Pecked lines denote uncertainty.

(Figure 4) Principal geomorphological areas.

(Figure 5) Generalised vertical sections through the Dinantian sequence; inset map shows the areas where Dinantian rocks crop out.

(Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6) Logs of sections in the Urswick Limestone Formation (after Horbury, 1987, with additional information 1991). The relative stratigraphical positions of the sections are based partly on BGS observations. Approximately 10 m of beds, obscured during the BGS survey, were recorded by Horbury below the bases of the Dunald Mill and Back Lane quarry sections. See (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text.

(Figure 7) Contrasting sections of the Gleaston Formation from Borehole (SD56NW/64) near Dunald Mill Quarry and exposed in the River Keer, just north of the district boundary (see (Figure 7) for key. Inset shows location of section in (Figure 7) and other sites cited in text." data-name="images/P988504.jpg">(Figure 6) for locations).

(Table 3) are tentative. See(Figure 5) for location." data-name="images/P988506.jpg">(Figure 8) Stratigraphy of the Whitmoor Borehole [SD 5874 6315]. The lithostratigraphy is based on descriptions of chippings with depths modified slightly to fit gamma-ray (GRA) and sonic (BHCA) down-hole geophysical logs below a depth of 180 m. Depths are given in metres below ground level, 3.2 m below the drilling platform. The geophysical logs do not reach to 1559 m TD. The identifications of the Pendleian and lower Arnsbergian marine bands, denoted by their indices as given in (Table 3) are tentative. See (Figure 5) for location.

(Figure 9) Stratigraphy and mineral occurrences in selected BP Minerals (BHD Series) boreholes in the Sykes, Brennand and Whitendale periclines. All the boreholes were vertical except for BHD 11, which was inclined at 60° towards 112° to magnetic north. Note the steep dips have the effect of greatly increasing the apparent thicknesses.

(Figure 11) for location." data-name="images/P988508.jpg">(Figure 10) Section in the Lower Bowland Shale Formation in the Whitendale River [SD 6597 5487]. See (Figure 11) for location.

(Figure 11) Generalised sections of the Upper Bowland Shale Formation. WR = location of the Lower Bowland Shale Formation Whitendale River section shown in (Figure 11) for location." data-name="images/P988508.jpg">(Figure 10).

(Figure 12) Generalised stratigraphy of the Millstone Grit of the Lancaster district. A. Lower part of the Millstone Grit (Pendleian to late Arnsbergian). B. Comparative generalised sections in the upper part of the Millstone Grit (late Arnsbergian to Yeadonian) of the Bentham and Heysham to Dolphinholme areas. Note that the two parts of the Millstone Grit are at different scales and that the unornamented parts of the sequence are undifferentiated siltstones and mudstones with thin sandstones. See (Figure 44) for key.

(Figure 13) Generalised compiled sections of the Pendle Grit Formation. Apart from 8A (Bowland Forest Tunnel section, after Earp, 1955) and 6 (Whitmoor Borehole) these are as mapped and represented on 1:10 000 maps. See (Figure 44) for key.

(Figure 14) Comparative compiled generalised sections of the lower part of the Roeburndale Formation (minor gaps omitted). See (Figure 44) for key.

(Figure 15) Sections in the Cravenoceras cowlingense Marine Band. See (Figure 44) for key.

(Figure 16) Sections in the Dure Clough Sandstones, Brennand River headwaters. See (Figure 44) for key.

(Figure 17) Comparative sections in the E. ferrimontanum Marine Band and Gavells Clough Sandstone and adjacent strata. See (Figure 44) for key.

(Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18) Ribbon diagram of the upper part of the Roeburndale Formation from the E. ferrimontanum Marine Band up to the unconformity at the base of the Ward's Stone Sandstone Formation. Selected faults which are thought to have partly moved prior to the deposition of the sandstone are shown. Note that the E. yatesae Marine Band is confined to locations south of the Artle Beck Fault. Localities where an angular unconformity is exposed are denoted by A. See (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See (Figure 44) for key.

(Figure 19) Comparative generalised sections in the upper part of the Roeburndale Formation. Each section is typically compiled from several closely grouped stream sections and also the Wray and Badgerford Bridge borehole sections where appropriate. The locations of the groups of sections are shown in (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18). In this model, the C. gressinghamense Marine Band is assumed to lie a short distance above the E. ferrimontanum Marine Band. The top of all the sections is an unconformity at the base of the Ward's Stone Sandstone Formation. See (Figure 44) for key.

(Figure 20) Marine bands between the E. ferrimontanum (E2a2) and E. yatesae (E2a3) marine bands. Faunal symbols are not shown for the previously established marine bands. Nonmarine fish debris not indicated. Note that the northern Bowland Fells sequence is at half the scale of the other sections. See (Figure 44) for key.

(Figure 21) Comparative sections in the C. gressinghamense Marine Band and adjacent strata. See (Figure 44) for key.

(Figure 22) Stratigraphy of the Wray Borehole [SD 6320 6570]. Note that the lithology above the start of coring at 100 m is based on the geophysical logs. See (Figure 44) for key.

(Figure 23) Comparative sections in the Sapling Clough Sandstone and the Eumorphoceras yatesae Marine Band. See (Figure 44) for key.

(Figure 24) Generalised sections through the upper part of the Roeburndale Formation and lower part of the Ward's Stone Sandstone Formation near the scout camp, Artle Beck, Littledale, Caton. The cartoon, taken from the field notebook and not to scale, illustrates the possible relationships of the units. See (Figure 44) for key.

(Figure 25) Selected sections of the Ward's Stone Sandstone Formation north of the 'Ward's Stone range'. See (Figure 44) for key.

(Figure 26) Evidence related to syndepositional fault movement during the early Arnsbergian. a. Localities where the E. yatesae Marine Band and higher strata occur beneath the Ward's Stone Sandstone. In all cases preservation is on the down-thrown side of faults which may have moved prior to the deposition of the Ward's Stone Sandstone. Localities are as follows: 1 Artle Beck; 2 Foxdale Beck; 3 Foxdale Beck; 4 Whitespout Gutter; 5 Rowton Brook area; 6 Gavells Clough; 7 Sapling Clough b. Isopachs for the Ward's Stone Sandstone Formation. A single number indicates total thickness in metres. The lower and upper fractionated numbers give the thickness of the lower and upper units respectively, where known. The arrow indicates predominant palaeocurrent direction deduced from trough alignment in the upper part of the formation.

(Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27) Stratigraphy of the Caton Shale Formation. The generalised stratigraphy with the ranges of the principal fossils is shown on the left. Note that for Posidonia corrugata and Selenimyalina variabilis, the ranges where they are abundant are indicated. See inside back cover for key. Comparative sections in the Caton Shale Formation are: 1. Crossgill, and its easterly continuation into Greenholes Beck [SD 5648 6304] to [SD 5694 6327]. The section is logged down to the base of the E. leitrimense faunal horizon and is continued upwards in (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon).

(Figure 28) Sections in the lower part of the Barncroft Beck Member, Claughton Formation, Caton Moor. The Greenholes Beck section is continued downwards in (Figure 28) 2. Branstone Beck and a right bank tributary [SD 6783 6786] to [SD 6770 6826] 3. Goodber Beck [SD 6302 6078] (logged up to the E. leitrimense faunal horizon)." data-name="images/P988525.jpg">(Figure 27)A. The general stratigraphy of the Claughton Formation on Caton Moor and the stratigraphical range of the most important sections are also indicated by inset A. See inside back cover for key.

(Figure 29) Comparative sections in the Crossdale Mudstone and Accerhill Sandstone formations. See inside back cover for key.

(Figure 30) Comparative sections in the Kirkbeck Formation and higher Namurian strata.See inside back cover for key.

(Figure 31) Log of the upper part of the Kirkbeck Formation and overlying strata penetrated in Heysham power stations boreholes (SD45NW/229) and (SD45NW/230). Sliced cores of these boreholes are lodged at BGS, Keyworth. See inside back cover for key.

(Figure 32) Outcrop and the general stratigraphy of the Permian and Triassic rocks in the western part of the Lancaster district. Thickness data for borehole provings and the extent of reddened Millstone Grit at outcrop and in boreholes are also depicted.

(Figure 36) for sections A–B, C–D)." data-name="images/P988531.jpg">(Figure 33) WSW–ESE natural scale horizontal section (E–F) at the Heysham power stations site based on borehole data. (See (Figure 36) for sections A–B, C–D).

(Figure 34) Subdrift bedrock topography of the district.

(Figure 35) Landforms and other features in the Lancaster district related toglacial advance. The direction of ice flow can be discerned from the orientation of glacial striae and drumlins.

(Figure 36) Horizontal sections showing the relationships of the drift deposits in the area of the Heysham power stations. The lines of the sections are shown in (Figure 36) for sections A–B, C–D)." data-name="images/P988531.jpg">(Figure 33) (inset). Vertical scale exaggeration x 5. All borehole numbers should be prefixed with SD 45 NW. Section A–B depicts a rock-cored drumlin which formed an island during an early part of the Flandrian.

(Figure 37) Generalised sections of superficial deposits along the line of the Morecambe Bay Barrage boreholes (A–B) and from Heysham to Halton (C–D). Vertical scale exaggeration x 25. Section A–B is compiled from borehole data and seismic profiles (Knight, 1977) and section C–D from borehole data.

(Figure 38) Topographical features in the Lancaster region related to glacial meltout. Abbreviations are as follows: CT, Caton Terrace; QT, Quernmore Terrace; BT, Brookhouse Terrace; Co, Conder Channel; CW, Cragg Wood Channel, OGC, Otter Geer Clough Channel; BB, Birk Bank Channel; Hh, Hollinhead Channel; AB, Artle Beck Channel; AG, Anas Gill Channel; NG, Nottage Crag Channel; FB, Farleton Beck Channel; Rt, Rantree Channel; GB, Greenholes Beck Channel; Hb, Harterbeck Channel; Hy, Haylott Channel; Bh, Bellhill Channel; SB, Salter Clough Channel.

(Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39) Main structural elements of the Lancaster district in their regional context and a kinematic analysis of the structures observed in the Lancaster district: A. Relation of structures to those in the Craven Basin. Also shown (brown arrows) is the dextral wrenching model of Arthurton (1984) whereby the stuctures within the Ribblesdale Fold Belt are generated within a regional 'distributed zone of shear' caused by the relative displacement of the Askrigg Block and Central Lancashire High. B. Summary of the main fault, fold and joint trends in the district (see (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alternative kinematic analysis for the structures within the Craven Basin—that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation.

(Figure 40) Geophysical maps of the Lancaster district and adjoining areas (Appendix 2): A. Bouguer gravity anomaly map, reduced using a Bouguer correction density of 2.55 Mg/m3. Letters denote structures as follows: A, Bowland High; B, Nicky Nook Anticline; C, Bowland Line and the southern limit of the Bowland High; D, Sykes Anticline; E, Ingleton Coalfield; F, South Craven Fault Zone; G, Quernmore Fault; H, I, J and K, see text; L, Bilsborrow Fault; M, Torrisholme anomaly; N, Heysham High; WF, Woodsfold Fault. B. Aeromagnetic anomaly map with contours at 10 nT intervals. Anomalies over built-up areas have been removed.

(Figure 41) Principal structural features of the Lancaster district. Abbreviations are as follows: A Anticline; P Pericline; S Syncline; F Fault; TTF Trimpell Tanks Fault. Pecked lines denote uncertainty

(Figure 42) Seismic reflection lines across the district. The inset map shows the locations.  A. W–SE line (and line interpretation) illustrating the Sykes Anticline, interpreted to be an inversion structure overlying a Dinantian syndepositional fault. B. SW–NE traverse illustrating the main structures in the Quernmore area. An erosional boundary interpreted to be at the base Pendle Grit shows onlap onto the Knots Anticline from the west. C. Line (and line interpretation) across the Artle Beck Fault Zone and illustrating the tie to the Whitmoor Borehole.

(Figure 43) Rose diagrams illustrating the main trends of the surface structures mapped and recorded in the Lancaster district east of the Quernmore Fault. A summary of the trends is given in (Figure 43)). Note that the high angle made between the main fold trend and the main fault trend with oblique/horizontal slickensides (OB/HS) is probably the result of pre-existing basement structures/fractures. C. Predicted and observed structures from pure shear and dextral shear/transpression models with which to compare the angular relationships between the folds and fractures of the district when assessing the kinematic model. A possible alterna­tive kinematic analysis for the structures within the Craven Basin – that of a general west-north-west to east-south-east pure shear or compression is depicted in A by the large arrows. A more WNW–ESE-directed pure shear reactivates Dinantian syndepositional faults and pre-existing basement structures at any angle to the compression direction. NW–SE faults move as wrench faults, generating horizontal/oblique slickensides, although it is recognised that these structures may only define the very closing stages of deformation." data-name="images/P988537.jpg">(Figure 39). NB. Data on joints observed at exposures; trends of faults and fold axes are as mapped. Data are compiled from 1:10 000 sheets SD 55 NE, SD 56 NE, SW and SE, 57 SE, SD 65 NW, SD 66 NW and NE. The inset diagram shows the coal cleat directions.

(Figure 44) Key to symbols used on Millstone Grit figures. See (Figure 12),  (Figure 13),  (Figure 14),  (Figure 15),  (Figure 16),  (Figure 17),  (Figure 19) for sections used to compile generalised stratigraphies about the locations numbered. Members are initialed as follows: Sapling Clough Sandstone, SpCS; Close Hill Siltstone, C1HS; Cocklett Scar Sandstones, CoSS; Gavells Clough Sandstone, GvCS. See inside back cover for key." data-name="images/P988516.jpg">(Figure 18),  (Figure 19),  (Figure 20),  (Figure 21),  (Figure 22),  (Figure 23),  (Figure 24),  (Figure 25),

Plates

(Front cover) Cover photograph Black Fell, Clougha, looking west-north-west towards the Lancaster/Morecambe conurbation, Morcambe Bay and the Lake District. Quernmore valley and the partly wooded Stocka-Bank/Knots Wood ridge can be seen in the middle distance with Heysham Nuclear Power Station to the left. Heather and bilberry survives on the leached outcrop of Ward's Stone Sandstone, which dips to the north-west. Parallel lamination in the sandstone has allowed it to be used locally as a roofing slate but the quality is poor. A small trial working is marked by a heap of stones to the left of the picture [SD 539 607]. (MN28017) (Photographer: Paul Tod)

(Frontispiece) Swaintley Hill ([SD 586 625]), a conical moulin kame, the Haylott meltwater channel and upper Roeburndale, viewed from the north-west. Mallowdale Pike lies in the right middle distance and White Hill in the far distance on the left (A15504).

(Plate 1) Landsat image centred on the Bowland Forest and the Lancaster district (outlined). The image is part of an infrared false-colour composite of Landsat Thematic Mapper scene 204–022 (Copyright BGS/NERC 1992). It was processed by the BGS Remote Sensing Group and forms part of their database of enhanced imagery covering the UK mainland. Most of this image is also part of a BGS 1:200 000 scale poster The Lake District and surrounds'. Pendle Hill is situated in the SE part of the view and the lowlands of The Fylde in the SW. The Craven fault system is clearly discernable in the NE. The Lyth Valley to Grange-Over-Sands area on the southern fringes of the Lake District are included in the NW part of the image. The differently vegetated areas are depicted by false-colours as follows: blue, unvegetated areas such as mudflats around the coast, quarries and rocky areas inland and conurbations; yellowish green, moorland areas; orange, farmland; dark russet, forest.

(Plate 2) A steep-sided palaeovalley seen in cross-section in the Urswick Limestone in Leapers Wood Quarry [SD 5171 6947] near Carnforth. The dark erosive contact between the lenticular-bedded valley-fill limestones and the more parallel-bedded platform limestones into which the valley was eroded, is clearly visible, especially on the right of the photograph. The bottom of the valley is concealed beneath rubble. Photograph taken by A Horbury in 1985 (GS 446).

(Plate 3) Selected Namurian marine ammonoids, nautiloids and bivalves from the Lancaster district. a. Eumorphoceras yatesae, lateral view of crushed late adolescent conch (RH 5111) x 2. Eumorphoceras yatesae Marine Band (E2a3), Roeburndale Formation, Arnsbergian Stage, Artle Beck [SD 5524 6245], Littledale. b, c. Cravenoceratoides nitidus, lateral and ventral views respectively of an early adolescent conch (RH 4095) x 4. Eumorphoceras leitrimense faunal horizon (E2b2), Caton Shale Formation, Arnsbergian Stage, River Hindburn [SD 6485 6466], Lowgill. d. Selenimyalina variabilis, lateral view of exfoliated left valve (AB 1349) x 2.5. Cravenoceratoides edalensis Subzone (E2b1), Caton Shale Formation, Arnsbergian Stage, Crossgill [SD 5632 6302], Littledale, Caton. e. Metadimorphoceras cl ribblense, lateral view of exfoliated, septate, adolescent conch (RH 5379) x 6.5. From a loose nodule with Fayettevillea holmesi, in the upper part of Cravenoceratoides nitidus Subzone (E2b2), Caton Shale Formation, Arnsbergian Stage, Warm Beck Gill [SD 5921 6427], Whit Moor. f, g, m. Cravenoceras gressinghamense, Cravenoceras gressinghamense Marine Band (E2a2a), Roeburndale Formation, Arnsbergian Stage, Gressingham Beck [SD 5644 6996], Gressingham. f. lateral view of exfoliated mature conch (holotype RHR 333) x 1.5. g. lateral view of part exfoliated mature conch (paratype RHR 331) x 1.75. m, apertural view of exfoliated, septate, adolescent conch (paratype RHR 313) x 4. h. cf. Naiadites tumidus, lateral view of left valve (AB 1479) x 3. Close Hill Siltstone Member (E2a2B), Roeburndale Formation, Arnsbergian Stage, left bank tributary [SD 5920 6620], Hamstone Gill Beck, Farleton. i.  Eumorphoceras leitrimense, lateral view of crushed adolescent conch (RH 4953) x 4. Cravenoceratoides edalensis Subzone (E2b1), Caton Shale Formation, Arnsbergian Stage, south bank of Crossgill [SD 5630 6300], west side of Caton Dyke, Littledale, Caton. j. Sanguinolites sp. 1, lateral view of external mould of left valve (RH 5130) x 3. Close Hill Siltstone Member (E2a2â), Roeburndale Formation, Arnsbergian Stage, right bank of Rowton Brook [SD 5412 5910], Quernmore. k. Sanguinolites sp. 2, lateral view of left valve (AB 1494) x 3. Close Hill Siltstone Member (E2a2â), Roeburndale Formation, Arnsbergian Stage, Sooby Gill [SD 5833 6633], Farleton. l. Posidonia corrugate, external mould of left valve (AB 1504) x 2. Cravenoceratoides edalensis Subzone (E2b1), Caton Shale Formation, Arnsbergian Stage, Greenholes Beck [SD 5613 6295], Caton. n, r. Tylonautilus nodiferus, part exfoliated mature conch, lateral and ventral views respectively (GSM 48355) x 0.5. Previously figured by Pringle & Jackson (1928) and labelled "Claughton Brickworks", probably from the now disused brick pit at Potter Hills Wood, Claughton [SD 555 651]. o. Caneyella semisulcata, part exfoliated, lateral view of the right valve (RH 5481) x 4. Base of the Homoceras undulatum Marine Band (H2b1), Kirkbeck Formation, Alportian Stage, Eskew Beck [SD 6502 6813], Low Bentham. p. Homoceras undulatum and H. smithi, centre and top respectively, lateral views of crushed, part exfoliated adolescent, conches (RH 5492) x 2. Homoceras undulatum Marine Band (H2b1), Kirkbeck Formation, Alportian Stage, Eskew Beck [SD 6502 6813], Low Bentham. q. Dunbarella sp., lateral view of exfoliated left valve (AB 1391) x 4. Claughton Moor Siltstone Member (E2c?), Claughton Formation, Arnsbergian Stage, Claughton brick pit [SD 5790 6469], Claughton. s. Posidonia lamellosa, lateral view of exfoliated right valves (Ro 9641) x 1. Base of the Cravenoceras cowlingense Marine Band (E2a1), Roeburndale Formation, Arnsbergian Stage, Screes End [SD 6029 5515], Tarnbrook.

(Plate 4) Photomicrographs of Millstone Grit and Permo-Trias sandstones. In all photographs pore spaces are coloured blue and scale bar = 0.5 mm. a. (E66068) Pendle Grit Formation, quarry on south bank of River Lune [SD 5085 6454]. Very coarse-grained subarkose, composed of quartz (white), K-feldspar (stained yellow), with some secondary iron oxides (opaque). Quartz overgrowths and cements and some grain contact pressure-welding is evident. b. (E66034) Brennand Grit Formation, Brennand River gorge [SD 6309 5547]. Medium- to coarse-grained subarkose, composed of quartz (white), K-feldspar (stained yellow), and minor albite (not stained, upper right). Quartz overgrowths and cements are well developed. Porosity is intra- and intergranular, mainly grain dissolution porosity. c. (E66051) Cocklett Scar Sandstones Member, Foxdale Beck [SD 5837 6062]. Coarse- to very coarse-grained calcareous sandstone composed of quartz, carbonaceous fragments, pellets of laminated micrite, and minor K-feldspar. The origin and significance of the pellets is not clear. d. (E66029) Ward's Stone Sandstone Formation, Gables Clough [SD 6116 5747]. Medium- to coarse-grained quartz arenite, with minor K-feldspar. Quartz overgrowths and cements are well developed. e. (E66073) Eldroth Grit Formation, Borehole (SD45NW/229) [SD 4045 5989], Heysham power stations, at 120.1 m. Fine-grained subarkose, ferruginous, composed of quartz, with minor K-feldspar and plagioclase, and secondary iron oxide. Grain dissolution porosity postdates the secondary iron oxide. There are minor developments of quartz overgrowths and cements. f. (E66075) Heysham Harbour Sandstone Formation, Borehole (SD45NW/230) [SD 4050 5963], Heysham power stations at 93.61 m. Coarse- to very coarse-grained subarkose, composed of quartz, K-feldspar, albite with secondary iron oxides, kaolinite. There are minor developments of quartz overgrowths and cements. g. (E67172) Collyhurst Sandstone Formation, White Lund Farm Borehole (SD46SW/498) [SD 4442 6227] at 12 m. Fine- to medium-grained quartz arenite/subarkose, composed of angular to subangular quartz, K-feldspar and albite. Open porosity and minimal compaction suggests that most of the porosity is secondary after cement dissolution. h. (E67173) Sherwood Sandstone Group, foreshore near Cockersands Abbey [SD 4270 5336]. Medium-grained subarkose, composed of quartz (including cherts), K-feldspar, albite and some very fine-grained igneous lithic clasts. Porosity is probably secondary after both cement and grain dissolution.

(Plate 5) Inclined ripple-marked surface of a sandstone bed in the Pendle Grit, Folds Clough [SD 6380 5522], River Brennand headwaters (GS448).

(Plate 6) Syndepositionally slumped, interbedded, fine-grained sandstones and siltstones, 975 m south of the Rowton Portal, Wyresdale Tunnel [SD 5307 5887]. The strata are of delta slope origin and ascribed to the Dure Clough Sandstones Member of the Roeburndale Formation. The geometry indicates a southward inclined palaeoslope (to the left) and the observer's hand rests on the subhorizontal slide plane at the base of the slump. Incipient fold mullions occur in the sandstone, and in places the less-competent siltstones are intensely deformed (L1713).

(Plate 7) Interbedded, generally fine-grained sandstones and siltstones of the Cocklett Scar Sandstones Member at Cocklett Scar [SD 576 609], on the north side of Foxdale. Note variations in the thickness of individual sandstone beds and the discordant bedding with probable slumped siltstones on the right-hand side of the view (A15516).

(Plate 8) Close Hill Siltstone Member, Roeburndale Formation, Rowton Brook [SD 5412 5910]. The grey sandy siltstones, with regular, parallel interbeds of fine-grained, ferruginous sandstone, are typical of this marginal marine deposit and contain a sparse fauna, including Sanguinolites sp. The sandstones are probably distal turbidites. Length of hammer is 38 cm (GS449).

(Plate 9) Syndepositional faults cutting very coarse-grained Ward's Stone Sandstone in a fallen block below Long Crag [SD 627 568], Brennand Valley. The scale is graded in centimetres (GS445).

(Plate 10) Sandy siltstones with thin sandstone ribs in the Claughton Moor Siltstone Member of the Claughton Formation, Claughton brick pit [SD 5764 6480]. The scale is marked in centimetres (A15488).

(Plate 11) Reduced patches in cross-bedded Sherwood Sandstone on the foreshore at Red Nab [SD 4031 5915]. The view is taken looking northwest, 25 m west of the Ocean Edge Fault (GS447).

(Plate 12) Photomicrographs of basalt samples from the Caton Dyke. For sample provenances see (Table 7).a. (E62809), field 3 x 2 mm) Flow-banding: boundary between wholly crystalline basalt and glassy basalt containing detached autoclasts of the more crystalline variety. b. (E62810), field 3 x 2 mm) Pseudomorphs after euhedral olivine phenocryst in altered basalt. c. (E62810), field 3 x 2 mm) Calcite-filled vesicle surrounded by clear, possibly recrystallised basalt rich in biotite flakes and laths of oligoclase.

(Plate 13) Ill-sorted bouldery gravels of the Glaciofluvial Sheet Deposits exposed in the east bank of Artle Beck [SD 5329 6371], Caton. The gravels underlie the Caton Terrace and the imbricate tabular clasts indicate a palaeocurrent to the north (right to left in the photograph). The scale is marked in centimetres (A15497).

(Plate 14) Late-glacial, Windermere Interstadial mammal remains discovered 9 m below OD during the construction of Heysham Harbour [SD 401 602] in 1901. a. Incomplete skull and horn cores of an aurochs, Bos primigenius (unregistered, Lancaster City Museum). b. Frontal skull and antlers of a giant deer, Megaloceros giganteus (LM 72.6/1, Lancaster City Museum).

Tables

(Table 1) Dinantian stratigraphy and classification.

(Table 2) Lithostratigraphical nomenclature of strata from the Bowland Shale Group to the Brennand Grit Formation used in the Lancaster district and adjoining areas (no scale implied).

(Table 3) Ammonoid-based biostratigraphy and chronostratigraphy for the Namurian of north-west Europe. Regional non-ammonoid marine bands are omitted.

(Table 4) Lithostratigraphy of the lower Arnsbergian strata of the Lancaster Fells (no scale implied).

(Table 5) Lithostratigraphical nomenclature of the Claughton Formation.

(Table 6) General classification and stratigraphy down to formation level of the Permian and Triassic rocks in the Lancaster district compared with adjacent districts (no scale implied).

(Table 7) Analyses of basalt samples from the Caton Dyke. X-ray fluorescence analyses carried out by BGS Analytical Chemistry Unit. Major elements were analysed using fused beads, and trace elements using pressed powder pellets. Fe2O3t - total iron given as Fe2O3; LOI-loss-on-ignition. LC990 (E62808)-grey basalt from the central part of the Caton Dyke at Anas Gill; LC991 (E62809)-pink-grey basalt from the dyke margin at Anas Gill; LC992 (E62810)-grey basalt from the central part of the dyke at Tarn Brook.

(Table 8) Typical chemical analyses of groundwaters in the Lancaster district.

(Table 9) Licensed abstractions in the Lancaster district (in Ml/a).

(Succession) Geological succession in the Lancaster district.

Tables

(Table 3) Ammonoid-based biostratigraphy and chronostratigraphy for the Namurian of north-west Europe

Regional non-ammonoid marine bands are omitted.

Stage Genus-zone Chronozone Marine bands Index A B

Yeadonian

 Cancelloceras G1b Cancelloceras cumbriense G1b1 MG
Cancelloceras G1a Cancelloceras cancellatum G1a1 yes MG

Marsdenian

 Bilinguites R2c Donetzoceras ? sigma R2c2 MG
Bilinguites R2c Bilinguites superbilinguis R2c1 ?* MG
Bilinguites R2b Bilinguites metabilinguis R2b5 MG
Bilinguites R2b Bilinguites eometabilinguis R2b4 MG
Bilinguites R2b Bilinguites bilinguis R2b3 MG
Bilinguites R2b Bilinguites bilinguis R2b2 ?* MG
Bilinguites R2b Bilinguites bilinguis R2b1 yes MG
Bilinguites R2a Bilinguites gracilis R2a1 yes MG

Kinderscoutian

 Reticuloceras R1c Reticuloceras coreticulatum R1c4 MG
Reticuloceras R1c Reticuloceras reticulatum R1c3 ?* MG
Reticuloceras R1c Reticuloceras reticulatum R1c2 MG
Reticuloceras R1c Reticuloceras reticulatum R1c1 MG
Reticuloceras R1b Reticuloceras stubblefieldi R1b3 KbF
Reticuloceras R1b Reticuloceras nodosum R1b2 ?* KbF
Reticuloceras R1b Reticuloceras eoreticulatum R1b1 ?* KbF
Reticuloceras R1a Reticuloceras dubium R1a5 yes KbF
Reticuloceras R1a Reticuloceras todmordenense R1a4 KbF
Reticuloceras R1a Reticuloceras subreticulatum R1a3 KbF
Reticuloceras R1a Reticuloceras circumplicatile R1a2 KbF
Reticuloceras R1a Hodsonites magistrorus R1a1 KbF
Homoceras H2c Homoceratoides prereticulatus H2c2 KbF

Alportian

 Homoceras H2c Vallites eostriolatus H2c1 KbF
Homoceras H2b Homoceras undulatum H2b1 yes KbF
Homoceras H2a Hudsonoceras proteum H2a1 ?* KbF

Chokierian

 Homoceras H1b Isohomoceras sp. nov H1b2 yes CroM
Homoceras H1b Homoceras beyrichianum H1b1 yes CroM
Homoceras H1a Isohomoceras subglobosum H1a3 yes CroM
Homoceras H1a Isohomoceras subglobosum H1a2 yes CroM
Homoceras H1a Isohomoceras subglobosum H1a1 yes CroM

Arnsbergian

 Eumorphoceras E2c Nuculoceras nuculum E2c4 CroM
Eumorphoceras E2c Nuculoceras nuculum E2c3 Clau
Eumorphoceras E2c Nuculoceras nuculum E2c2 Clau
Eumorphoceras E2c Nuculoceras stellarum E2c1 Clau
Eumorphoceras E2b Cravenoceratoides nititoides E2b3 Clau
Eumorphoceras E2b Cravenoceratoides nitidus E2b2 CSh
Eumorphoceras E2b Cravenoceratoides edalensis E2b1 CSh
Eumorphoceras E2a Eumorphoceras yatesae E2a3 Rbl
Eumorphoceras E2a Cravenoceras gressinghamense E2a2α yes Rbl
Eumorphoceras E2a Eumorphoceras ferrimontanum E2a2 yes Rbl
Eumorphoceras E2a Cravenoceras cowlingense E2a1 yes Rbl

Pendleian

 Eumorphoceras E1c Cravenoceras malhamense E1c1 yes UBS
Eumorphoceras E1b Tumulites pseudobilinguis E1b2 yes UBS
Eumorphoceras E1b Cravenoceras brandoni E1b1 yes UBS
Eumorphoceras E1a Cravenoceras leion E1a1 yes UBS

Column A indicates the marine horizons recognized in the Lancaster district and column B their lithostratigraphical contexts. * denotes a non-ammonoid fauna in the Lancaster district.

(Table 7) Analyses of basalt samples from the Caton Dyke

X-ray fluorescence analyses carried out by BGS Analytical Chemistry Unit. Major elements were analysed using fused beads, and trace elements using pressed powder pellets. Fe2O3t - total iron given as Fe2O3; LOI-loss-on-ignition. LC990 (E62808)-grey basalt from the central part of the Caton Dyke at Anas Gill; LC991 (E62809)-pink-grey basalt from the dyke margin at Anas Gill; LC992 (E62810)-grey basalt from the central part of the dyke at Tarn Brook.

Sample LC990 LC991 LC992
major elements (weight percentages).
SiO2 37.01 36.35 36.92
TiO2 2.01 2.12 1.92
Al2O3 14.16 14.34 13.95
Fe2O3t 12.03 12.97 8.67
MnO 0.26 0.30 0.26
MgO 3.61 8.27 3.79
CaO 11.01 8.82 14.12
Na2O 1.11 1.72 1.68
K2O 4.60 1.64 3.23
P2O5 0.36 0.50 0.35
Cr2O3 0.03 0.02 0.04
LOI 12.88 12.78 14.27
Total 99.07 99.84 99.19
trace elements (ppm except for Ti)
Ti(%) 1.004 1.233 0.932
V 193 230 179
Cr 152 168 206
Ni 100 114 103
Cu 37 61 45
Zn 175 421 35
Rb 131 35 68
Sr 195 421 312
Y 18 24 20
Zr 136 138 128
Nb 34 35 31
Ba 1017 858 459
La 20 23 22
Ce 49 41 48
Th 5 5 5
U 3 2 2

(Table 8) Typical chemical analyses of groundwaters in the Lancaster district

Location (SD65SE/12) Newton in Bowland (SD46SE/2) Caton Road, Lancaster (SD46SW/8) Lancaster (SD66SE/1) Lowgill No.1 46/2b *

Caton Road, Lancaster
NGR [SD 6937 5145] [SD 4860 6354] [SD 4709 6219] [SD 6528 6498] [SD 4841 6368]
Type of source 36.6 m deep borehole 139.6 m deep borehole 137.2 m deep borehole 68.0 m deep borehole 7.6 m deep shaft
Aquifer Chatburn Limestone Pendle Grit Roeburndale Formation and Pendle Grit Claughton Formation Superficial deposits
Date of analysis 9/12/65 1955 18/5/33 ? 20/12/60 1955
pH 7.2 7.1 7.2 7.6
Total dissolved solids mg/1 360 740 350 280
Bicarbonate (HCO3-) mg/1 329 295 440 55 366 295
Sulphate (S042-) mg/1 136 61 58 23 14
Chloride (C1-) mg/1 13 175 30 50 20 24
Fluoride (F-) mg/1 nil 0.12 nil
Nitrate (NO-3-N) mg/1 0.5 7 nil 6
Calcium (Ca2+) mg/1 120 102 30 80 70
Magnesium (Mg2+) mg/1 16 35 7 21 16
Sodium (Na+) mg/1 112 31.8 32.5 20 12
Potassium (K+) mg/1
Iron (total) mg/1 0.2 0.05 1.0 1.7
Manganese (total) 0.2

Data from National Well Record Collection, BGS Wallingford. * denotes that this shaft does not have a BGS permanent registration number (see Appendix 3) and is listed under the National Well Record Collection number. The sample from borehole (SD46SW/8) was taken from the base of the borehole.

(Table 9) Licensed abstractions in the Lancaster district (in Ml/a)

Dinantian

Namurian

Westphalian

Superficial deposits

Total  groundwater

Total surface water*
Agriculture — (0) 57 (19) 10 (1) 63 (27) 130 (47) — (0)
Spray irrigation — (0) — (0) — (0) 3 (1) 3 (1) 2 (2)
Fish farming — (0) — (0) — (0) — (0) — (0) 8894 (2)
Industry

(including cooling)

 9 (1) 2365 (5) — (0) — (0) 2374 (6) 25771 (6)   
Fire fighting — (0) — (0) — (0) — (0) — (0) 864 (1)
Public water supply — (0) 2792 (4) — (0) 415 (1) 3207 (5) 126207 (7)   
Domestic supply — (0) — (0) — (0) 4 (10) 4 (10) — (0)
Total 9 (1) 5214 (28) 10 (1) 485 (39) 5718 (69) 161737 (18)
  • * excluding non-consumptive uses and seawater
  • (Figures in brackets indicate the number of licences).
  • Complied from data supplied by the National Rivers Authority, North-West Region.