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Geology of the west Cumbria district Memoir for 1:50 000 Geological Sheets 28 Whitehaven, 37 Gosforth and 47 Bootle (England and Wales)

By MonograptusC. Akhurst et al.

Geology of the west Cumbria district Memoir for 1:50 000 Geological Sheets 28 Whitehaven, 37 Gosforth and 47 Bootle (England and Wales)

Bibliographical reference: Akhurst, M C, Chadwick, R A, Holliday, D W, McCormac, M, McMillan, A A, Millward, D, Young, B, Ambrose, K, Auton, C A, Barclay, W J, Barnes, R P, Beddoe-Stephens, B, James, J W C, Johnson, H, Jones, N S, Glover, B W, Hawkins, M P, Kimbell, G S, MacPherson, K A T, Merritt, J W, Milodowski, A E, Riley, N J, Robins, N S, Stone, P, and Wingfield, R T R. 1997. The geology of the west Cumbria district. Memoir of the British Geological Survey, Sheets 28, 37 and 47 (England and Wales).

Keyworth, Nottingham: The British Geological Survey 1997. ©NERC copyright 1997 First published 1997. ISBN 0 85272 300 8. Printed in the UK by Premier Print

The grid used on the Figures and Maps is the National Grid taken from the Ordnance Survey maps 89 (1982) and 96 (1981). © Crown copyright reserved. Ordnance Survey licence no. GD272191/1997

Authors: M C Akhurst, BSc, MSc, PhD; M McCormac, BSc; A A McMillan, BSc; D Millward, BSc, PhD; B Young, BSc British Geological Survey, Edinburgh; R A Chadwick, MA, MSc; DW Holliday, MA, PhD British Geological Survey, Keyworth.

Contributing authors: C A Auton, BSc; R P Barnes, BSc, PhD; B Beddoe-Stephens, BSc, PhD; H Johnson, BSc; K A T MacPherson, BSc, MSc; J W Merritt, BSc; P Stone, BSc, PhD British Geological Survey, Edinburgh; K Ambrose, BSc W J Barclay, BSc; BW Glover, BSc, PhD; M P Hawkins, BSc, MSc; K Ambrose, BSc; W J Barclay, BSc; B W Glover, BSc, PhD; M P Hawkins, BSc, MSc; J W C James, BSc; NS Jones, BSc, PhD; GS Kimbell, BSc; A E Milodowski, BSc; N J Riley, BSc, PhD; R T R Wingfield, BA, PhD British Geological Survey, Keyworth; NS Robins, BSc, PhD British Geological Survey, Wallingford.

(Front cover) Cover photograph St Bees Sandstone Formation exposed in the type section at St Bees Head (D04735). (Photographer: Tom Bain).

(Rear cover)

Acknowledgements

This memoir was compiled by M C Akhurst from published information (as cited) and contributions of unpublished text and information. Chapters in this memoir have been written by the following authors.

Notes

Preface

West Cumbria is an area in which the landscape and the working lives of local people are dominated by the underlying geology. The area spans the boundary between the rugged landscape of the Lake District National Park, largely underlain by Ordovician to early Devonian 'basement' rocks, and the low-lying coastal plain bordering the north-east Irish Sea, underlain by drift-covered Carboniferous and Permo-Triassic 'cover' rocks. Mining of coal from the coastal plain and adjacent offshore area provided the foundation for industry. This, coupled with the exploitation of iron ore deposits, in the sedimentary rocks that fringe the Lake District block in west Cumbria, formed the basis of a substantial mining industry that was of national strategic importance. A de­tailed understanding of the geology of the coastal plain of west Cumbria has been derived from the results of these once-extensive mining activities.

In recent years the geology of the coastal plain in west Cumbria has been subject to intense study by a wide range of sophisticated survey techniques. In­deed it would be no exaggeration to say that the basement of the Sellafield area has been more intensively studied than the basement of any other area. The investigations undertaken for United Kingdom Nirex Ltd, to determine whether the geology of the area is suitable to host an intermediate-level radio­active waste repository, have included the acquisition of 2D and 3D seismic re­flection surveys and also 27 boreholes many of which penetrate the Lower Palaeozoic basement rocks. The combination of offshore, coastal zone and onshore seismic surveys has enabled continuous interpretation of the geologi­cal structure from the Lake District to the central Irish Sea. Detailed analysis of the borehole core and geophysical logs has established the character of the rock sequences, the post-depositional geological history, the nature of faults and fractures, the character of discontinuities, the physical properties of the rocks and their potential to transmit groundwater. The results of outcrop studies, field geophysical surveys and geochemical analyses have been used to define the character of basement rocks in the subsurface as well as at outcrop. Study of the unconsolidated sediments overlying bedrock on the coastal plain and shallow offshore area has made a significant contribution to the under­standing of glaciation and postglacial history in this area. Analysis of ground­water and borehole pump tests have provided data on which a model of the hydrogeological regime in this area is based.

The Nirex-funded investigations were initially aided by existing knowledge of the local and regional geology, much of which had been derived from pub­licly funded research. More recently, a steady stream of data from the Nirex investigations has been released for integration with the information from more traditional geological surveying techniques. Thus this memoir, which summarises the geology of the west Cumbria area, demonstrates the added value derived from a combination of publicly funded scientific research with commercial exploration data and commissioned research, to further under­standing of British geology and enhance the publicly available national database of earth science information.

Peter J Cook, CBE, DSc, CGeol, FGS Director British Geological Survey Kingsley Dunham Centre Keyworth Nottingham NG12 5GG

Geology of the west Cumbria district—summary

This memoir describes the area covered by the 1:50 000 Series geological sheets 28 Whitehaven, 37 Gosforth and 47 Bootle of England and Wales. The district includes the western margin of the Lake District and the adjacent offshore area. The geological structure was interpreted from offshore and onshore geophysical surveys and inte­grated with geological mapping, borehole and other data sources onshore. Detailed description and inter­pretation of the geological succession was undertaken from sequences at outcrop and from boreholes.

Geological processes have produced many resources within the district, some of national economic impor­tance. Extraction of coal, which commenced in the last century, continues at the present day. Mining of iron ore also has a long history but has all but ceased. The effects of these mining activities as well as exploitation of other industrial and bulk minerals are now important factors for consideration in future land-use planning. Although oil and gas are important resources offshore in the East Irish Sea Basin there is currently only a small gas discov­ery at the margin of the district.

During the Lower Palaeozoic, the district lay at the leading edge of the Eastern Avalonian microcontinent, forming part of the southern margin of the Iapetus Ocean. Northward drift and closure of the ocean led to uplift and erosion of deep marine turbidites deposited on the ocean floor as subduction-related processes gen­erated magma within the crust and underlying mantle. Subaerial extrusion of andesite lavas was followed by caldera collapse and accumulation of silicic ignimbrites during the late Ordovician, and the final stage of the vol­canic cycle was marked by intrusion of granitic plutons. During late Silurian times a foreland basin sequence was deposited although it is not preserved within the district. Acadian thrusting and folding was instigated by conti­nental collision. This Caledonian basement sequence was eroded and reduced to a peneplain prior to the deposition of a sequence of Carboniferous and Permo­-Triassic cover rocks.

In early Carboniferous times, a block and basin system developed within a regime of north-south crustal exten­sion. Most of the district lay within a block that included the Lake District inlier; shallow carbonate shelf condi­tions were established, and a limestone sequence is pre­served. The north-west of the district lay within the Solway Basin where fluviodeltaic conditions were estab­lished during the early Carboniferous, and gradually extended over the block; the coal measures sequence accumulated later, in Westphalian times. Uplift and ero­sion occurred during an episode of inversion of the Solway Basin during the late Carboniferous and prior to the unconformable accumulation of a fluvial sandstone sequence. This, and later episodes of Carboniferous inversion, were the response in west Cumbria to the Variscan orogeny and marked the onset of a long period of erosion.

Permian and early Triassic times were marked by for­mation of the East Irish Sea Basin; the fault-defined boundary with the Lake District Block lies onshore in the district. A sequence of Permian alluvial fan breccia, evap­orite and shale unconformably overlie eroded Carbonif­erous and basement rocks within the basin. Subsequent­ly, rapid fault-controlled subsidence of the East Irish Sea Basin during the Triassic accommodated a thick sequence of fluvial or aeolian sandstone, mudstone and evaporite. Triassic sedimentation extended beyond the basin eastwards over the Lake District Block where a thinner sequence was deposited. Active syndepositional faulting also occurred in the Solway Basin during the Permo-Triassic. Regional subsidence in the Solway and East Irish Sea basins continued from Triassic to Caino­zoic times. Maximum depth of burial within the district is considered to have occurred during the Palaeocene. Although the youngest preserved sedimentary rocks are Jurassic in age and occur as outliers within the East Irish Sea Basin, thick sequences of Mesozoic rocks are inferred to have been present within the basinal areas and a some­what thinner sequence over the Lake District Block.

Regional uplift commenced in the early Cainozoic, as a response to development of the Icelandic plume and seafloor spreading between Greenland and Iceland, and has persisted to the present day over the Lake District Block. Episodes of inversion which also occurred within the East Irish Sea and Solway basins are mostly attributed to the Alpine Orogeny. During the long period of expo­sure most strata of Jurassic to Cretaceous age were erod­ed from the basinal areas and all Mesozoic strata were stripped from the Lake District Block.

During the last glacial-interglacial cycle of the Quater­nary the district lay at the confluence of the Lake District ice cap with the Scottish ice sheet; most Quaternary sedi­ments in the district accumulated at this time. Deposits of earlier glacial and interglacial stages are only locally present. During the last deglaciation the position of the ice margins fluctuated and phases of ice readvance have produced areas of distinctive glacitectonic deformation.

(Table 1) Geological succession of the district.

Chapter 1 Introduction

The west Cumbria district discussed in this memoir spans the rugged upland scenery at the western edge of the Lake District, the low-lying coastal plain and extends beyond the coastal zone into the Irish Sea (Figure 1), (Figure 2); (Plate 1). A concise account is given here summarising the geology of the west Cumbria district presented on the 1:50 000 Series Sheet 28 Whitehaven, Sheet 37 Gosforth and Sheet 47 Bootle (Figure 1); British Geologi­cal Survey, 1996a, in press a and b).

The mountain scenery typical of the Lake District borders the eastern edge of the district (Plate 2) and includes fells of the Ennerdale area that range up to 570 m in height (Figure 2). This area of high ground is underlain by Lower Palaeozoic volcanic and sedimen­tary rocks that are deeply dissected by glacial erosion. Interaction of erosional and depositional glacial pro­cesses and bedrock on the coastal plain in the northern part of the district has produced south-west-trending drumlins (Plate 1). The coastal plain is blanketed with Quaternary sediments deposited during and after glaciation. Glaciated valleys radiate from the Lake Dis­trict fells and are utilised by the Marron, Ehen, Calder, Bleng, Irt and Esk rivers which drain the upland area and flow across the coastal plain to the Irish Sea (Figure 2). South of Egremont the coastal plain is less than 5 km wide, has very low relief and is underlain by Trias­sic sandstones. Northwards the coastal plain is broader with hills up to 250 m in height and is underlain by Car­boniferous rocks. Offshore, water depth increases south-westwards to a maximum of about 40 m within the district over Quaternary sediments and Permo­-Triassic rocks.

Land use, population distribution and underlying geology are very closely linked in the district. The upland area of Lower Palaeozoic basement rocks is sparsely populated and lies within the Lake District National Park. The major roads and railway, the main lines of communication, are restricted to the coastal plain. The main population centres of the district, Whitehaven and Workington, are situated on the coast on the outcrop of coal-bearing Carboniferous rocks. There the Cumbrian Coalfield was worked at surface and underground, with workings beneath the sea bed extending westwards for 6 km from Whitehaven. This provided a basis for industrial development in the dis­trict. Coal mining still continues but now only as onshore opencast workings.

Carboniferous limestones around the edge of the outcrop of Lower Palaeozoic basement rocks are host to iron ore reserves of high grade and considerable volume. Mining towns such as Egremont and Cleator Moor were established at the outcrop of the mineralised limestones with the iron ore mining industry providing a catalyst for other activities such as quarrying of limestone as a flux for smelting. Mining of iron ore has now virtually ceased.

History of survey

Primary geological surveying was undertaken between 1870 to 1895 with a comprehensive resurvey from 1921 to 1927 during the peak of the coal and iron ore mining industries. A modern resurvey of the Whitehaven, Gos­forth and Bootle sheets (the west Cumbria district) has been recently completed (see Information Sources) and has incorporated data from coal mine plans and boreholes, iron ore mine plans and exploration boreholes, British Geological Survey boreholes and site investigation data including offshore and onshore investigations by Nirex. The latter includes seismic surveys, geophysical surveys and deep boreholes (Figure 3). For this account the solid geology offshore within the district is inter­preted from geophysical data.

Geological history

Lower Palaeozoic

During early Palaeozoic times a major ocean, described in the geological literature as Iapetus Ocean, separated Laurentia in the north from the microcontinent of Eastern Avalonia; the district lay on the leading edge of this microcontinent. Deep-water marine turbidites of the Skiddaw Group were deposited on the continental slope during the late Cambrian and early Ordovician; rocks of Ordovician age crop out in the north-eastern part of the district and around Muncaster Fell (Figure 1). During the Ordovician and Silurian, the Iapetus Ocean closed, as Eastern Avalonia drifted northward from high latitudes in the southern hemisphere. Uplift and erosion probably resulted from injection of large volumes of magma associ­ated with the development of subduction and the destruc­tion of oceanic crust. The culmination of this process was a short-lived but violent Caradocian volcanic episode resulting in the accumulation of the Borrowdale Volcanic Group. The initial extrusion of andesite plateau lavas was followed by accumulation of a large volume of acid tuffs and volcaniclastic rocks. The volcanic cycle ended with emplacement of the Eskdale and Ennerdale intrusions which are part of the major Ordovician composite batholith that underlies the Lake District (Figure 4).

Eventual collision of Eastern Avalonia with Laurentia instigated the Early Devonian Acadian orogeny. Evidence of the preceding late Silurian foreland basin sequence, the Windermere Supergroup, that was deposited in response to loading of the Avalonian margin by overriding Laurentia is not preserved in the district. Develop­ment of a regional cleavage associated with the Acadian deformation appears to have been a climactic event during the Early Devonian.

Carboniferous

By early Carboniferous times northern Britain had drifted northwards into tropical latitudes. An extensional block and basin regime had become established; most of the district, both offshore and onshore, lay within a rela­tively stable block area. The north-western corner of the district lay within the subsiding Solway Basin which had a faulted boundary with the adjacent block. In the basin, fluviodeltaic and marginal marine environments were established in the early Carboniferous, and this style of sedimentation probably continued unchanged into the late Carboniferous.

A marine transgression over the block during the early Carboniferous allowed the development of a carbonate shelf environment. Sea-level fluctuations and tectonic sub­sidence together, in this shallow-water setting, caused alternating periods of exposure and submergence so that a cyclical pattern of carbonate sedimentation characterises the lower Carboniferous succession. The Chief Limestone Group rests unconformably on the eroded Lower Palaeo­zoic rocks (Table 1), inside front cover, and consists of a cycli­cal succession of marine limestones separated by mud-stone and sandstone. Sedimentary cycles identified in the north of the district can be correlated with equivalent rocks around the northern margin of the Lake District. Lower Carboniferous rocks also occur concealed in the central part of the district, but these have a closer affinity with limestones of equivalent age in south Cumbria.

Later in Carboniferous times an influx of siliciclastic sediment smothered carbonate deposition over the block. Initially, deltaic conditions prevailed with occasional marine incursions, but progressively more fluviodeltaic conditions were established and coal swamps were developed. Three Upper Carboniferous sedimentary sequences are identified at outcrop in the northern part of the district: the Hensingham Group, Coal Measures and Whitehaven Sandstone Formation (Table 1). All three are predominantly of clastic sedimentary rocks, deposited in a marginal marine to terrestrial setting; the Coal Measures sequence is thin compared with other British coalfields.

Periods of nondeposition and erosion occurred during and at the end of the late Carboniferous. Reddened strata of the Whitehaven Sandstone Formation, probably deposited in fluvial to lacustrine environments, rest unconformably on coal-bearing strata. They represent an episode of basin inversion. This was a precursor to the regional uplift during latest Carboniferous times that was the response in northern Britain to the Variscan orogeny; the effects of this orogeny are more evident in continental Europe. Locally, Variscan compressive defor­mation was accommodated by structural inversion of the Solway Basin, by reversal of basin margin faults and a prolonged period of non-deposition.

Permo-Triassic

A regime of east-west extension was initiated in Early Permian times and persisted through the Triassic and Early Jurassic periods, broadly related to the opening of the north Atlantic. The East Irish Sea Basin which lies mainly to the west of the district is one of a series of north-trending extensional basins formed on the western side of Britain at this time. The north-eastern margin of the East Irish Sea Basin is defined by the Lake District Boundary Fault Zone, a section of which lies onshore within this district (Figure 4).

Initially, Permian sedimentation was restricted to the basin. The earliest Permian sediments preserved are alluvial fan breccias that accumulated in a semiarid environment. Variation in breccia thickness demonstrates both regional subsidence and syndepositional faulting.

Subsequently during the Late Permian, a marine trans­gression, part of a northern European event contempora­neous with the Zechstein cycles of the Southern North Sea Basin, flooded much of the district, and resulted in the deposition of a sequence of carbonates and evaporites. The Upper Permian sequence is restricted to the East Irish Sea Basin but thins and shows changes in depositional facies towards the Lake District Boundary Fault Zone. The youngest Permian sediments show a return to terrestrial sedimentation in a mud-flat or alluvial setting.

During the Triassic, rapid fault-controlled subsidence of the East Irish Sea Basin occurred with much slower subsidence of the Lake District Block. Sedimentation was not confined to the East Irish Sea Basin at this time, but extended over the Lake District Block where a thinner sequence was deposited. The Permian sequence is con­formably overlain by the Triassic Sherwood Sandstone Group (Table 1) which crops out over the central part of the district. It comprises three sandstone-dominated for­mations that accumulated in either fluvial or aeolian settings. Mud-flat or playa lake conditions prevailed during the accumulation of the succeeding Mercia Mud-stone Group. This crops out over most of the southern part of the district, but is not exposed onshore (Figure 1).

Jurassic

Sedimentation continued in the East Irish Sea Basin into Jurassic times. The presence of Jurassic rocks in the south-west of the district is inferred from seismic data. They are likely to correlate with the Early Jurassic Lias Group identified farther to the west, within the East Irish Sea Basin.

Regional uplift and basin inversion

There is no direct evidence of the geological history of the district from the later part of the Early Jurassic to Cainozoic (Tertiary) times, as strata of this age are not preserved within the district (Table 1). Comparison with adjacent areas indicates that the existing Permo-Triassic faults remained active and that a thick sequence of Juras­sic rocks was deposited in the East Irish Sea Basin. Thinner deposits probably covered the Lake District Block but were eroded during the Early Cretaceous. Accumulation of an Upper Cretaceous sedimentary sequence across the district followed regional subsidence as the sea floor spreading centre in the North Atlantic migrated farther from the district.

Uplift that commenced in the early Cainozoic has been virtually uninterrupted to the present day. Regional uplift was associated with the development of the igneous provinces of Northern Ireland and western Scot­land, and their radiating dyke swarms. In addition, struc­tural inversion within the East Irish Sea Basin, a response to Alpine orogenic movements, caused reversal of earlier normal faults and the formation of transpressional inver­sion structures.

Quaternary

By Pleistocene times, the British Isles had drifted north­ward to a mid-latitude position and the district experi­enced several glacial episodes during the Quaternary. Many cooling events, from temperate interglacial to cold glacial, are identified. Most of the Quaternary sediments within the district accumulated during the last glacial-interglacial cycle, over about the last 30 000 years.

The district lay at the confluence of the local Lake District ice cap with the Scottish ice sheet flowing south through the Irish Sea. The contact of these ice sheets lay within the coastal lowlands of west Cumbria, fluctuating between what is now the eastern limit of the coastal plain and the shallow offshore area. Glacigenic and glaciofluvial sediments deposited on the coastal plain are thus extremely varied, laterally discontinuous and affected by glacitec­tonism. Offshore, glaciomarine sediments deposited during and after the last glacial are more extensive.

Chapter 2 Applied geology

The district encompasses much of the Cumbrian Coal­field and the West Cumbrian Iron Orefield. Both coal and iron ore working have exercised a profound influ­ence on the economic and social history of the district and have left indelible marks on the landscape. Other mineral products include limestone, brick and refractory clays, evaporites and building stone; extraction of some of these continues today though on a much smaller scale than in former years.

Geological factors, former mining activities, present-day resources and ground stability, which should be taken into consideration in land-use and planning matters are briefly outlined here; sources of further information are indicated in Information sources (p.111). The key issues are:

Energy sources

Coal

The presence of coal seams within the Carboniferous rocks of the district is outlined in Chapter 5. Apart from the Udale Coal (Figure 24) which is high in the Namurian sequence, coal seams of economic interest are confined to the Langsettian and Duckmantian (Lower and Middle Coal Measures). Approximately 25 named seams are known (Table 4), and most consist of bitumi­nous coal of high volatile content with strong caking properties. The coal is well suited to coking, steam raising and household use; gas-making was an important use prior to the availability of natural gas. Jones (1951) gave brief descriptions of the characteristics of Cumbrian coals. Few recent analytical data have been published, although Taylor (1978) notes a volatile content from 32 to 39 per cent, calculated on a dry ash-free basis. Pyrite is common in certain seams, notably the Brassy, and is an undesirable contaminant in view of the increasing demand for low sulphur coal.

The Cumbrian Coalfield has enjoyed a long history of production with coal working from the mid-sixteenth century until the present day, although the heyday of the industry was during the latter half of the nineteenth and early part of the twentieth centuries. The district's huge reserves of coking and steam coal combined with the high-grade haematite iron ore (discussed below) pro­vided the basis for the industrial economy of west Cumbria. Histories of the Cumbrian coal industry have been published by Wood (1988) and Calvin (1992).

During the peak years of production almost the entire output of coal was obtained from underground mines. In the later years of deep mining, working became concen­trated in the coastal collieries which extended up to 5 km offshore. Cumbria's last major deep mine, Haig Colliery at Whitehaven, ceased coal production in 1984. The Main Band Colliery near Whitehaven was sunk in recent years to extract an unworked portion of the Main Band Seam beneath the St Bees area and is currently held on a care and maintenance basis.

Large-scale opencast coal production began in Cumbria in 1958, at Broughton Moor. Since then several large sites have been worked with large tonnages recov­ered from previously unworked portions of seams and from pillars of coal left as support in previous under­ground workings. Opencast extraction is currently in progress at Kidburngill [NY 060 217] and Lowca [NX 990 235]. Considerable scope exists for future opencast extraction although, with the possible exception of the Main Band Colliery, underground mining is unlikely to be resumed.

Hydrocarbons

Onshore

Johnston (1839) reported occurrences of oil in the Middle Coal Measures of the Whitehaven area. Smith (1920) described the recovery of a semi-solid hydro­carbon exuding from a sandstone in Ladysmith Pit, Whitehaven. Smith (1920) also refers to the discovery of oil seepages in the William Pit, and elsewhere in the Whitehaven area. Harrison (1975) noted the presence of hydrocarbons in purple fluorite in a chalcedony nodule in the St Bees Evaporite at Sandwith Mine and small amounts of solid hydrocarbons are recorded as veins in the First Limestone at Tendley Hill Quarry, Eaglesfield [NY 088 286] (Young and Boland, 1992; Appleton et al., 1995).

In common with most British coal-bearing sequences, the Coal Measures of west Cumbria naturally generate methane. It was common in all west Cumbrian collieries but particularly abundant in Haig Colliery, where a methane drainage system was begun in 1950. The gas recovered was used at surface for steam raising and in 1953 methane from Haig Colliery was supplied to Whitehaven gasworks. Figures are not available for the total quantities of gas produced, but Wood (1988) records that 212 million cubic feet of methane were used at the Haig Colliery boiler plant in 1971.

Offshore

Oil and gas are important resources within the East Irish Sea Basin, but all the developed fields and reported significant discoveries lie to the south of the district. The nearest significant find was reported by Clyde Petroleum in Borehole 113/28a-2, very close to the south-eastern corner of the district, which tested 0.35 Mm3 of gas per day from an unspecified reservoir within the Sherwood Sandstone Group. However, the accumulation is reported to be very small and future development here probably depends upon a production project centred on Borehole 113/28a-2 and on Amoco's small discovery (Binney) in 113/29-1 which tested 0.62 Mm3 gas per day, again from a reservoir in the Sherwood Sandstone Group. The results of recent drilling by Clyde Petroleum at Borehole 113/28a-3 within the district and at 113/29a-2 just north of Binney are not yet available.

Peat

Small amounts of hill peat are known to have been dug for domestic fuel. Trotter et al. (1937) noted that peat cutting was then still active at Cold Fell [NY 060 090] and Stords [NY 078 080].

Ore minerals

Iron ore

Earliest records of iron ore mining in west Cumbria date from the 12th century and mining is known to have been active in the 17th and 18th centuries. Large-scale and extensive iron ore mining and exploration in the district took place in the 19th century. Historical reviews of the industry include those by Daysh and Watson (1951), Hewer and McFadzean (1992) and Kelly (1994).

By the beginning of the present century many of the more northerly mines had closed and mining became concentrated in the southern, concealed, part of the orefield at Florence, Beckermet and Haile Moor (Figure 5). Here the district's largest orebodies were worked until the late 1970s when closure of the combined Beckermet–Florence mine ended large-scale iron ore mining in west Cumbria. Small-scale production continues today from shallow workings at Florence mine with the annual output of a few thousand tons of haematite employed in specialised steel making and in pigment manufacture. Reserves at Florence mine are likely to be sufficient to sustain current output levels for many years.

Comprehensive orefield production figures are not available but west Cumbria is known to have produced in excess of 100 million tons of high grade haematite iron ore. When large-scale mining ceased, total reserves were said to be limited to about 1 million tons which were in places difficult to reach (Shepherd and Goldring, 1993).

Iron ores of two main types have been worked in the district; siderite and haematite. Nodules of siderite mud- stone, also known as clay ironstone, are common in many of the Coal Measures and Hensingham Group mudstones. They may contain up to 25 per cent metallic iron (Cantrill in Strahan et al., 1920), and have been worked as a by-product of coal mining. Eastwood et al. (1931) notes working of these ores in the Harrington, Branthwaite and Clifton areas. The most recent produc­tion is recorded from the roof of the Metal Band coal seam of Clifton Colliery in 1900.

The district's most important iron ores were the huge deposits of haematite of the West Cumbrian Iron Ore­field (Figure 5). Cumbrian haematite, with an iron content of 50 to 60 per cent and a phosphorous content of less than 0.02 per cent, was ideally suited to the pro­duction of high-quality iron suitable for steel making by the acid Bessemer process. The orefield extends from near Lamplugh to Calderbridge (Kendall, 1873–75; Smith, 1924; Schnellmann, 1947). Most of the haematite deposits occur as replacements or vein-like bodies closely associated with faults, mainly within the Carboniferous rocks. Some important but smaller deposits occurred as fissure veins within the Skiddaw Group.

The west Cumbrian orebodies are composed almost exclusively of haematite, occurring as massive haematite, kidney ore, pencil ore and specularite. Details of the mineralogy of the haematite and the petrology of the ores, together with references to the most important lit­erature sources are provided by Smith (1924), Goldring and Greenwood (1990) and Shepherd and Goldring (1993). Metalliferous minerals are recorded in associ­ation with the haematite and include a number of manganese minerals, mostly oxides, pyrite, marcasite, siderite, chalcopyrite, malachite and galena but in total comprise much less than 1 per cent of the ore. Gangue minerals include aragonite, baryte, calcite, fluorite and quartz (Smith, 1924; Young, 1987). Goldring and Greenwood (1990) have demonstrated the particular abundance of fluorite in the gangue assemblage in the Egremont area and have suggested that fluorite-rich ores may be present elsewhere in the orefield.

Distribution and formation of the orebodies

Most orebodies are metasomatic replacements of lime­stone adjacent to faults or joints. That the haematite replaces limestone is clearly demonstrated where un­altered shale beds pass into the orebodies and where fossils are wholly or partly replaced by haematite. Ore-bodies vary in size from small-scale patchy alteration along joints to irregular or flat bodies that may extend for several hundreds of metres. Smith (1924) estimated reserves of 20 million tons of haematite within the Florence orebody alone. Representative sections through several important orebodies are shown in (Figure 6), many others are illustrated by Rose and Dunham (1977).

Most orebodies occur within the Chief Limestone Group although a small number of deposits have been worked within other stratigraphical units. At Lonsdale Mine, Frizington [NY 040 173] haematite was also worked from the Hensingham Grit (Namurian) and at Millyeat Mine, also near Frizington [NY 024 177], haematite occurred as a replacement of a limestone within the Millyeat Beds Member of the Whitehaven Sandstone Formation, Bolsovian (Westphalian C) to Westphalian D (Chapter 5). The Brockram has in places been replaced by haematite presumably facilitated by a local abundance of limestone clasts. True fissure vein deposits appear to be confined to Lower Palaeozoic rocks and are found at a number of widely scattered localities throughout the Lake District. The district's largest and most productive group of deposits of this type occur within the Skiddaw Group at the Kelton Fell and nearby Knockmurton mines (Figure 5). Several veins, up to 6 m wide, were worked to depths of about 180 m below surface.

The haematite deposits of west Cumbria exhibit clear lithostratigraphical and structural control. Within the Chief Limestone Group certain limestones, notably the Seventh, Fourth and First, were preferentially replaced.

Coarse-grained limestones may have been the most sus­ceptible to haematisation (Shepherd and Goldring, 1993). The association of orebodies with the overstep of the Permo-Triassic rocks onto the Carboniferous lime­stones has long been known (e.g. Trotter, 1945; Rose and Dunham, 1977) and orebodies are typically present where permeable Permo-Triassic rocks, such as St Bees Sandstone or Brockram directly overlie limestone. Where mudstones of Namurian, Bolsovian or Permian age intervene, orebodies are generally absent. To the north of Frizington most orebodies are associated with north-west-trending faults which clearly exhibit post-Triassic displacement. South of Frizington mineralisation is commonly associated with north-east-trending pre-Triassic faults known locally as 'Coal Faults'. Shepherd and Goldring (1993) have commented on the apparent absence of orebodies west of the 'Coal Faults'. This may reflect a lack of data rather than any real structural relationship.

The origin of the west Cumbrian haematite deposits has long been the subject of discussion and controversy. Early views centred on two different sources of iron-rich fluids. Kendall (1873–1875) advocated a deep-seated magmatic or hydrothermal source whereas Goodchild (1889–1890) favoured the leaching of iron by meteoric groundwaters from overlying iron-rich rocks such as the St Bees Sandstone. More recently, Shepherd and Goldring (1993) suggested that brines expelled from over-pressured sediments in the East Irish Sea Basin were driven towards the margins of the Lake District batholith. There they leached iron from the granites before being driven upwards through fractures along the western margin of the Lake District. Rose and Dunham (1977) suggested a model whereby iron, leached by warm hypersaline fluids from the Permo-Triassic sedi­ments of the East Irish Sea Basin, was forced up-dip towards the margins of the Lake District. Both models are consistent with the iron-rich mineralising fluids gaining access to the limestones via fractures as well as through permeable formations within the Permo-Triassic sequence (see ME6a (Table 2)). The presence of abundant specular haematite within the interstices of coarse-grained sandstones in the Coal Measures near Whitehaven led Young (in Jones et al., 1990) to speculate that certain Coal Measures sandstones could also have acted as mineralising aquifers in suitable structural settings. If so, as yet undiscovered orebodies may be present at depth within the concealed limestones to the south and west of the known orefield beneath Permo-Triassic and Upper Carboniferous rocks. In a recent review, Shepherd and Goldring (1993) have concluded that the mineralisation is the product of the mixing of sulphate-rich groundwaters with warm, iron-rich hypersaline brines. They advocate a downward flow of mineralising fluids to account for the distribution of orebodies within the limestones. However, the occurrence of haematite veins within Lower Palaeozoic rocks of west Cumbria, and more widely in the Lake District, and the distri­bution patterns for arsenic, barium and fluorine within these deposits suggests an upward flow of mineralising fluids. They favour a sedimentary source for the iron. Fluid inclusion data for quartz, fluorite and calcite indicate that the mineralising fluids were hypersaline brines at temperatures of up to 120°C. Palaeomagnetic data suggest a Permian or Early Triassic age for the mineralisation (DuBois, 1962; Evans and El-Nikhely, 1982; Evans, 1986) although Dunham (1984) has advocated a post-Triassic age.

Manganese ore

Manganese minerals have been reported from a number of the west Cumbrian haematite deposits (Smith, 1924; Young, 1987; Young and Nancarrow, 1990). These miner­als usually comprise only a tiny proportion of the deposit but at Wyndham Pit, Bigrigg [NY 003 126] manganese oxide minerals were found in workable amounts in lentic­ular masses near the margins of the haematite orebody (Smith, 1924; Trotter, 1945). Smith (1924) noted that 40 to 50 tons of manganese ore were recovered as a by-product of 1000 tons of haematite mined.

Lead ore

Small amounts of galena within siderite mudstone nodules in the Coal Measures (Eastwood et al., 1931) may be of diagenetic origin. Elsewhere, galena-bearing veins of clearly epigenetic origin have been worked in at least two places within the district. The mineralogy of these veins suggests an association with the widespread lead-zinc mineralisation of the Lake District for which a Carboniferous age is generally accepted (Stanley and Vaughan, 1982), though a post-Carboniferous age is also possible. The main working was at Kinniside Mine [NY 043 145], where a north-west-trending vein up to 1 m wide cuts Skiddaw Group mudstones; the galena is recorded as carrying 10 to 14 ounces of silver per ton of lead with between 4 and 16 grains of gold per ton (East­wood et al., 1931). Mining at Kinniside dates from the eighteenth and nineteenth centuries for which produc­tion figures are not available. A second, smaller north­-north-west-trending vein cutting the Skiddaw Group at Leady Moss, near Mockerkin [NY 103 236] shows evi­dence of small-scale working of unknown date.

Eastwood et al. (1931) noted the sporadic minor occurrence of galena in spoil from Crossgill haematite mine, Cleator Moor [NY 035 160]. Moorbath (1962) commented briefly on the presence of galena as a replacement of Carboniferous limestone in boreholes in the Hensingham area, adding that this was probably not connected with the haematite mineralisation. Young (1987) also records galena in several boreholes in this area but its relationship to the haematite mineralisation is unknown. This lead mineralisation within the Dinan­tian rocks may be an expression of the more widespread lead-zinc mineralisation of the Lake District in which case a post-Carboniferous age would be indicated.

Copper ore

Although traces of copper minerals have been reported from several of the district's haematite deposits (Eastwood et al., 1931; Trotter, 1945; Young, 1987) only at one site has any attempt at commercial production been attempted. This was noted by Eastwood et al. (1931) as a small working in Skiddaw Group rocks, about 0.4 km south-east of Egremont Station where the log of a bore­hole, dated 1874, notes 0.5 m of 'copper ore' at a depth of 21.4 m, although nothing is known of the mineralogy or of any ore-bearing structure. The site is said to have been worked between 1872 and 1878. Production figures are unknown though at best only a very modest output of ore is likely.

Industrial and bulk minerals

Limestone

All limestone formations within the Chief Limestone Group have been quarried and small quarries were formerly worked in the Magnesian Limestone in the Whitehaven area. Almost every village and many farms within reach of the limestone outcrop maintained a small quarry with adjacent lime kiln to provide burnt lime for mortar and for use as a soil conditioner. In west Cumbria some of these quarries expanded to supply burnt lime for export from the district. The large-scale development of iron smelting last century created a huge demand for limestone flux and most of the Chief Limestone Group were of a suitable specification for this purpose. Large quarries were established at Glints [NY 008 124] (Third, Fourth and Fifth limestones), Rowrah [NY 059 180] (Fourth Limestone), Kelton [NY 068 184] (Fourth Lime­stone), Yeathouse [NY040 170] (Fourth and Fifth lime­stones), Salter Hall [NY 060 175] (Fourth Limestone), Stockhow Hall [NY 067 176] (Fifth and Sixth limestones), Distington [NY 005 241] (First Limestone) and Overend [NX 991 165] (First Limestone). The demise of iron smelting in west Cumbria ended the local demand for limestone flux and the only limestone quarries active today, at Tendley Hill [NY 088 286] (First Limestone) and at Eskett [NY 054 170] (Fourth Limestone) (Figure 5), produce crushed rock aggregate and roadstone. However, significant expansion of production capacity has recently been made at these two quarries and investi­gations have been undertaken to establish new workings. No beds of high-purity limestone are known in the district.

Gypsum and anhydrite

Gypsum and anhydrite in the St Bees Evaporite were for­merly worked in the Whitehaven area.

Gypsum, possibly the hydrated equivalent of the Fleswick Anhydrite, was worked from a bed up to 9 m thick last century at Barrowmouth Mine in the cliffs at Saltom Bay [NX 959 158]; some alabaster for ornamental use was also produced (Binney, 1855). The presence of abundant anhydrite and the instability of the roof pre­sented considerable difficulties in mining which ceased in 1908 (Sherlock and Smith, 1938).

Until the 1970s, the Sandwith Anhydrite was exten­sively mined from beneath the coast at Sandwith Mine [NX 963 160] as a raw material for sulphuric acid manu­facture at the adjoining chemicals plant; Portland cement was produced as a by-product. The mine is today abandoned and flooded.

Sand and gravel

Extensive spreads of sand and gravel are present within the district as glaciofluvial, fluvial and beach deposits. All have been worked in the past for local use as building materials. Eastwood et al. (1931) record the working of glaciofluvial sands near Egremont as a fill for under­ground iron ore mining at Crowgarth Mine, Cleator Moor. They also comment on the use of glacial sands in the Whitehaven area as moulding sand in the local iron works. In the past few decades extraction of sand and gravel from glacial deposits has taken place at a number of locations but currently only one sand and gravel pit at Peel Place near Holmrook [NY 070 010] is active (Harris et al., 1994), working glaciofluvial outwash deposits of the Gosforth Glacigenic Formation (Chapter 8).

Extensive glaciofluvial deposits are present within the district. In particular, coarsening-upward glaciofluvial deposits east of Seascale represent a large local sand and gravel resource. Deposits of blown fine-grained sand also occur that comprise the Drigg Point Sand Formation (Chapter 8), but these lie within the national nature reserve at Ravenglass and the military firing range at Eskmeals.

Brick and refractory clay

Mudstones and some siltstones from the Coal Measures have locally been of importance as sources of brick clay. Although brick making no longer takes place today in the district former brickworks were situated at Whitehaven, Harrington, Rowrah and Branthwaite. Eastwood et al. (1931) note that glacial clays throughout the district have been employed for brick making, for example laminated clay, likely to be of glaciolacustrine origin, near Mosser and till at Winscales [NY 029 259].

Trotter et al. (1937) record that glaciolacustrine clays and loams were formerly used for tile-making near Holmrook and a bright red sandy till at Drigg, from within the extent of the Gosforth Glacigenic Formation, was also used for brick and tile making although both operations were very small.

Many of the clay seatearths which underlie the dis­trict's coal seams possess refractory properties. Fireclay was formerly worked from Wythemoor Colliery, Branth­waite (Anon., 1920), and more recently the Micklam Fireclay seam was mined. near Lowca [NX 981 223]. In recent years, seatearth clays of suitable composition have been recovered during opencast coal extraction and have been supplied to brick and refractory makers outside the district.

Ganister

Sandstone within the Hensingham Grit was formerly worked at Distington [NY 005 241] and from the Sixquarters Rock at Branthwaite Colliery [NY 059 253] as sources of ganister for manufacture of refractory prod­ucts in the local steelworks (Anon., 1920).

Building stone

Sandstones of Carboniferous and Triassic age have been widely utilised for local building stone. The best known and most extensively worked is the Triassic St Bees Sand­stone. This formation provides excellent freestone, and numerous quarries have been worked for both rough and sawn stone much of it for use outside the district. Quantities of St Bees Sandstone were exported to North America last century (Eastwood et al., 1931). Two quarries, Birkhams [NX 955 154] and Bankend [NX 992 127], near Whitehaven are in production today (Harris et al., 1994).

Carboniferous stone used for building include the Orebank Sandstone, which has been quarried at Eaglesfield, and the Hensingham Grit at Hensingham and Dist­ington. Sandstone was formerly worked from parts of the Coal Measures, for instance the Sixquarters Rock at Schoose Quarry [NY 012 278] and the Bannock Band Rock at Sandclose Quarry [NY 012 187]. However, by far the best known and most widely used of the Carbonifer­ous stones is the distinctive red to pink Whitehaven Sandstone obtained from several large quarries in the Whitehaven area. Good examples of the use of this stone may be seen in the piers of Whitehaven Harbour and in numerous buildings and railway bridges.

Water resources

The Triassic Sherwood Sandstone Group, which over­steps Permian strata eastwards to rest unconformably on Lower Palaeozoic rocks, forms a coastal aquifer that thickens seawards. Groundwater flow occurs through dilated fractures or fissures although most water in the aquifer is stored in the intergranular matrix of the rock. The outcrop of the Sherwood Sandstone Group is largely covered by extensive and varied Quaternary deposits that locally contain perched water tables and commonly a lowermost zone of confined groundwater which is in hydraulic contact with groundwater within the underly­ing sandstone. The hydraulic conductivity of the sand­stone aquifer is much greater (2 to 3 orders of magni­tude) than that of the Borrowdale Volcanic Group rocks which it directly overlies in the east of the district. These volcanic rocks form a relatively impermeable base to the aquifer, whereas the overlying Quaternary sediments are very much more permeable than even the sandstone. Groundwater flow within the Sherwood Sandstone Group is towards the west, from the higher ground in the east of the district to the coast; the water table is at an elevation of about 20 m above Ordnance Datum (OD) some 2 km from the coast rising steadily to more than 150 m above OD at the eastern edge of the aquifer. A component of river flow enters the eastern part of the aquifer but otherwise recharge occurs at outcrop or via the permeable Quaternary cover. In places where there is no Quaternary cover direct recharge may be more than 500 millimetres per year (mm a-1). Discharge from the aquifer takes place through the Quaternary sedi­ments towards the coast but also as offshore discharge to the sea.

Near-surface groundwaters in the Sherwood Sandstone Group are mainly fresh with concentrations of total dis­solved solids generally less than 500 milligrams per litre (mg l−1). The waters are of calcium bicarbonate type and the general increase in calcium, alkalinity and sulphate concentrations towards the coast is attributable to the progressive dissolution of calcite, dolomite and anhydrite from the sedimentary cover during groundwater flow towards the west (Bath et al., 1996; Nirex, 1993a). West Cumbrian coalmines do not cause risings of polluted minewater and issues are of adequate quality to dis­charge directly to surface waters. Locally enhanced con­centrations of chloride, nitrate and some other dissolved constituents may reflect the use of agricultural fertilizers. Deep drilling in the Gosforth area shows that, at loca­tions more than about 2 to 3 km from the coast, the fresh groundwaters are underlain by NaCl-dominated brackish-saline waters (with approximate Cl concentra­tions of 1000 to 20 000 mg l−1 ) which occur largely within the Borrowdale Volcanic Group. Nearer the coast, the deeper part of the Sherwood Sandstone Group (greater than about 400 m below OD) contains NaCl-dominated saline waters and brines with Cl concentrations in excess of 100 000 mg l−1. Low Br/Cl ratios in these brines are consistent with an origin through the dissolution of halite deposits, considered most likely to be within the Permo-Triassic sedimentary sequence of the East Irish Sea Basin.

Abundant good-quality surface water in the area has inhibited the need to develop groundwater as a resource. However, numerous hillside spring sources have been utilised in the past and the town of St Bees was once sup­plied by a small spring called the Holy Well. Borehole sources have been developed in the Calder Bridge [NY 042 060] and Brow Top [NY 031 066] areas and ground­water from the Sherwood Sandstone Group aquifer sup­plied the Beckermet mine. The mine complex is now closed but pumping continues at a discharge of some 10 million litres per day (M1 d−1), derived both from the sandstone aquifer and the underlying Carboniferous strata, in order to maintain the water level at about sea level. The mine water is of good quality and not a cause of pollution under the existing care and maintainence conditions. Detailed hydrogeological investigation of the Calder Bridge and Brow Top well fields indicate that the sandstone aquifer is anisotropic with the horizontal hydraulic conductivity up to 20 times greater than the vertical conductivity. Although regional transmissivity is typically in the range of 50 to 100 metres squared per day (m2d−1), locally in the vicinity of the Calder Bridge and Brow Top well fields it is in the range 1000 to 5000 m2 d−1). The Brow Top well field of four boreholes can sustain a conservative service yield of 10 M1 d−1.

Ground stability

Within parts of the district a number of natural and man­made factors affect the stability of the ground thus influencing present and potential land use.

Landslips

A number of areas of landslip occur within the district. Most of these are relatively small areas of superficial or solid rocks which have moved downslope as a result of oversteepening by stream erosion. Several rather larger landslips can also be recognised, as described below.

The most extensive area of landslipping occurs on the coast north of St Bees Head, on the south side of Saltom Bay, where coastal erosion of St Bees Shale has caused extensive rotational slipping of the overlying St Bees Sandstone. The marked offset in the course of the old inclined tramway to the Barrowmouth gypsum mine and the backward tilting of the remaining mine buildings clearly illustrates this slipping [NX 959 158]. Wave erosion of the seaward dipping Coal Measures and Whitehaven Sandstone, which form the cliffs north and south of Whitehaven, has produced extensive coastal landslips.

Large areas of landslipped Skiddaw Group form a con­spicuous feature on the north side of Crag Fell, Ennerdale [NY 095 147]. Landslipped Coal Measures mantle the hillsides west and north of Moorside Colliery [NY 055 216]. In both of these instances the landslips appear to be the result of oversteepening of slopes during the final phases of deglaciation. Such slips are now con­sidered to be largely inactive and may be regarded as comparatively stable unless disturbed by groundworks.

Swallow holes

Swallow holes are present on the outcrop of most of the district's limestones. Whereas most occur on outcrops of bare limestone, or on limestone with only a compara­tively thin cover of superficial deposits, some may locally penetrate for a considerable distance through overlying strata. For example, in the Eaglesfield area [NY 088 278] a large number of closely spaced swallow holes penetrate through up to 25 m of Hensingham Grit into the underlying First Limestone; swallow hole development is still active in this area and new holes periodically appear. Despite the local abundance of swallow holes there is little evidence for the presence of any significant cave system within the west Cumbrian limestones though small solution cavities may be present locally. The distri­bution and possible origin of these holes are discussed by Young and Boland (1992) and Boland and Young (1992).

Mining subsidence

Centuries of coal and iron ore mining have created extensive voids beneath parts of the district. Many of these workings are in various states of collapse resulting in significant problems of ground stability and potential contamination of groundwater. A clear appreciation of the exact extent, nature, depth and date of abandon­ment of underground workings is essential to land use planning. Sources of statutory abandonment and other mine plans are outlined in the Information Sources (p.111). Interpretations of the extent of undermining within 30 m of the present surface are presented for the northern part of the district by Barnes et al. (1988) and Boland and Young (1992). These authors also review aspects of undermined ground which are of relevance to the whole district. Only a brief summary is given below.

Throughout much of the coalfield one or more seams have been extracted. The proportion of coal recovered from any working depended upon the mining method employed. In older workings the pillar and stall method was adopted whereby pillars of coal were left to support the roof. Collapse of the abandoned workings, especially where competent roof beds such as sandstone were present, is typ­ically sporadic and may take place intermittently over a very long period. Modern longwall mining aims to remove all of the coal with the roof being encouraged to collapse com­pletely very soon after extraction. The major subsidence is normally expected to be complete within a year or so of mining, though some residual subsidence may take place over the following ten years. It is thus important in ground engineering to establish not only the extent of old work­ings but the method of mining used.

The voids left by iron ore mining differ substantially from those of coal mining. The west Cumbrian haematite orebodies were commonly irregular in shape and much larger in volume than coal seams. Mining aimed to extract the maximum amount of ore by a variety of mining methods, most of which resulted in the creation and abandonment of large voids, in places several tens of metres high. Backfilling for support was not generally practised in these mines. Subsidence above such iron ore workings may propagate upwards through many tens of metres of strata. Collapse of workings has long presented a major problem in the orefield. Smith (1924) describes several examples of measures taken to minimise damage caused by subsidence, including the confining of rivers in artificial channels such as the steel conduit, known as the 'black ship' which carried the River Keekle across the area of Montreal mines, Cleator Moor. A large subsidence hollow above the old Florence Mine workings near Egremont is a conspicuous land­scape feature.

Seismicity

In common with the rest of the UK, the west Cumbria district has a moderate rate of seismicity although most earthquakes are not felt. The effects of several seismic events, reviewed by Musson et al. (1984a, b) and Musson (1987, 1994), have been felt over the district. However, an earthquake of magnitude 5.0 (Musson, 1994) felt from Dublin to Aberdeen in 1786 was centred within the district, just off the west Cumbria coast near Whitehaven.

Made ground and landfill

Mining and quarrying throughout the district have pro­duced numerous accumulations of waste rock. Opencast coal operations in recent years have used considerable volumes of nearby colliery and other spoil in backfilling. Large areas of land adjacent to former opencast sites have been extensively disturbed and landscaped during restoration. Large heaps of steel works slag at Working­ton and Distington have been landscaped in recent years.

Several abandoned quarries have been employed as landfill sites for the disposal of domestic and industrial waste. Specially excavated shallow pits within superficial deposits have been used for disposal of low-level radioac­tive waste at Drigg [SD 062 990]. The large subsidence hollow above the Florence orebody near Egremont is currently used as a landfill site.

Gases

In common with most British coalfields the coal-bearing rocks of Cumbria are known to yield significant amounts of methane. Methane continues to be released into aban­doned coal workings where other gases such as carbon dioxide and hydrogen sulphide may also be generated. Discharge into the atmosphere can occur through natural fissures, boreholes, adits or shafts, through the collapse of old workings or through porous rocks such as sandstone. Advice on the treatment of old workings with regard to gas emissions and other hazards is available in a British Coal publication (National Coal Board, 1982). In a nationwide assessment, Appleton et al. (1995) con­sidered the north-eastern part of the district to be an area of moderate susceptibility to methane and carbon dioxide emissions, although the remainder of the district is within an area of low susceptibility.

Little information is available on radon concentrations in west Cumbria. However, most of the onshore part of the district has a low to moderate susceptibility for radon emissions, but areas of moderate and high susceptibility coincident with the outcrop of some Carboniferous rocks have been identified (Appleton and Ball, 1995). The presence of radon is supported by the direct measurement of mine air from the Egremont haematite mines shortly before closure which revealed up to 400 Bec­querels per litre (Bq l-1).

Landfill gas is the collective name given to the mixture of gases produced by the decomposition of waste mate­rial in landfill sites. Methane and carbon dioxide are the main constituents though other gases may be present in small amounts. Landfill gas is capable of widespread migration from its site of origin and care must be exer­cised in planning and managing such sites.

Nature conservation

The district contains several important geological sites designated as Sites of Special Scientific Interest (SSSI) and details of which may be obtained from English Nature at North Minster House, Peterborough. In addition, a number of sites with great educational value are designated as Regionally Important Geological and Geomorphological Sites (RIGS) and details of these may also be obtained from English Nature.

Most faults are mapped at base Permo-­Triassic; the Maryport Fault is mapped at base Carboniferous, and faults in the Caledonian basement (stipple ornament) are mapped at outcrop. Location of cross-sections in (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070).

Chapter 3 Structure and concealed geology

The structure and concealed geology of west Cumbria can be described in terms of three major tectonostrati­graphical units that are bounded by unconformities and whose structural complexity increases with depth and age. The lowest unit is the Lower Palaeozoic 'Caledo­nian' basement which comprises faulted, folded and cleaved rocks that crop out in the east of the district. Westward this is overlain unconformably by the two younger units, Carboniferous and Permian to Mesozoic strata, which comprise the sedimentary cover sequence. The Carboniferous succession has been tilted, faulted and locally folded. It is overstepped and mostly con­cealed by Permo-Triassic rocks that crop out over much of the district, with isolated outliers of Lower Jurassic strata. This is also tilted and faulted but only locally folded.

Most of the faults identified in the district belong to a system of normal faults that cuts the sedimentary cover sequence (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). Many of these faults are reactivated basement structures, and were active during the develop­ment of the Solway and East Irish Sea basins, from Carboniferous to Cainozoic times; they divide the district into a mosaic of tilted fault-blocks. The relationship of major faults, basement and cover rocks within the district is illustrated by regional cross-sections in (Figure 8).

Lower Palaeozoic (Caledonian) Basement

The deep crystalline crust beneath the district is believed to have formed in late Precambrian times by the accretion of volcanic arcs and marginal basin com­plexes onto an ocean margin of the southern hemi­sphere supercontinent of Gondwana (McKerrow et al., 1991; Soper and Woodcock, 1990). Subsequently, a small continental fragment, Eastern Avalonia, is believed to have separated from Gondwana in early Ordovician times, to commence a protracted northward drift towards the continent of Laurentia. West Cumbria lay close to the northern edge of this microcontinent and extensional faulting, volcanotectonic deformation and penecontemporaneous emplacement of granitic intru­sions were related to subduction processes. Continued northward drift led to the gradual convergence of Eastern Avalonia with other continental masses and oblique collision with Baltica that lay to the north-east in late Ordovician or early Silurian times (McKerrow et al., 1991; Soper and Woodcock, 1990). To the north-west, the Iapetus Ocean continued to close through Silurian times, leading to the eventual collision of Eastern Avalo­nia with Laurentia, and culminating in the Early Devo­nian Acadian orogeny. By reactivating or overprinting earlier structures, Acadian deformation was responsible for the dominant regional east-north-easterly trending tectonic fabrics now observed in the Lower Palaeozoic basement. The Acadian episode is here taken to include both the late Silurian foreland thrust belt development and the Early Devonian Acadian climactic event. The early Palaeozoic history of the Lake District is sum­marised more fully by Cooper et al. (1995).

Geophysical evidence

Gravity, magnetic and locally seismic reflection data provide valuable insights into the nature of the sub­surface Caledonian basement rocks.

Concealed basement

Long wavelength, north-east-trending magnetic highs in the north-western and south-eastern parts of the district (Figure 9) have been interpreted as the expression of relatively elevated areas of a magnetic basement which lies beneath the pre-Carboniferous basement surface (Lee, 1989; Millward et al., in press). Such basement is very deep or absent to the north, beneath the Solway Basin, perhaps because of a postulated sedimentary apron to Eastern Avalonia, carried to deeper structural levels within the footwall of the Iapetus Suture Zone (Kimbell and Stone, 1995). The magnetic basement beneath the Lake District may be formed of Precam­brian crystalline rocks although alternative explanations involving pre-Skiddaw Group magnetic sedimentary rocks or deep-seated Ordovician arc magmatic rocks are possible.

Although there is a correlation between long wave­length aeromagnetic and gravity anomalies across the district (Figure 9), (Figure 10) the gravity signature can be largely explained by the presence of the Lake District batholith onshore and thickness variations in sedimen­tary cover rocks in the offshore and coastal areas. How­ever, a component of the long wavelength gravity vari­ation probably arises from intrabasement structures as is illustrated by the approximate correlation of the south­ern gravity and magnetic highs with the Skiddaw Group inlier at Black Combe to the east of the district (Figure 9), (Figure 10).

A large aeromagnetic anomaly occurs in the northern Lake District over the outcrop of the Eycott Volcanic Group which is stratigraphically equivalent to the Borrowdale Volcanic Group. This anomaly can be traced westward to the northern edge of the district (M1 in (Figure 9)) where the Eycott Volcanic Group is interpreted to lie at depths of 500–1000 m (Nirex, 1992a). Anoma­lies M2 and M3 in the northern district are probably also an expression of concealed Eycott Volcanic Group rocks at similar depths. Offshore, anomalies M4–M6 (Figure 9) are indicative of magnetic rocks at depths of 1000–2000 m; these have a shallower source than the deep magnetic basement discussed above and probably relate to the overlying Eycott or Borrowdale Volcanic groups. Anomalies M4 and M5 lie within the footwall block of the Laura Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

Borehole data indicate that relatively magnetic rocks of the Fleming Hall Formation (Chapter 4) within the concealed Borrowdale Volcanic Group are correlated with the onshore part of anomaly M7 (Figure 9); (Kimbell, 1994). Localised anomaly M8 corresponds to an exposure of the Longlands Farm Member (Chapter 4), but other magnetic units within the Borrowdale Volcanic Group may contribute to the offshore anomalies, because magnetic andesitic rocks occur lower in the sequence (for example associated with magnetic anomaly M9, (Figure 9)).

Lake District batholith

Much of the Lake District inlier is underlain by a large intrusive complex, the Lake District batholith, of late Ordovician to Early Devonian age (Figure 4), which intrudes the Skiddaw and Borrowdale Volcanic groups of early to mid-Ordovician age (Chapter 4). Modelling of the gravity data suggests that the batholith comprises up to 14 distinct granitic intrusions (Lee, 1989). Two of the components, the Eskdale and Ennerdale intrusions, of Caradocian age, crop out within the district and are the source of strong negative gravity features ((Figure 11), residual lows ES and EN, respectively). Lee (1989) mod­elled the Eskdale granite (estimated mean density 2.63 Mg m−3) as a deep-seated body, some 9000 m thick. The Ennerdale granite (2.62 Mg m−3) and Eskdale gran­odiorite (2.70 Mg m−3) were modelled as relatively thin (about 1000 m-thick) units, each underlain by a con­cealed intrusion of differing density. In Lee's model, the 'Buttermere Granite' (assumed density 2.68 Mg m−3) underlies the Ennerdale granite, whereas the 'Ulpha Granite' (2.66 Mg m−3) underlies the Eskdale granodiorite. The inferred intermediate densities of the concealed intrusions could reflect either their composition or (more likely) interleaving of lower-density granitic units with country rock (Figure 12); (Millward et al., in press). An alternative, less-favoured, explanation for the Ulpha gravity feature is that it is due to a thick sequence of low-density rocks of the Borrowdale Volcanic Group in the Ulpha syncline (Lee, 1989).

The Eskdale and Ennerdale intrusions have very different magnetic signatures (Figure 9). The response over the former is characteristic of a very low magnetisation whereas distinct magnetic disturbances over the latter are due to included zones of magnetic dioritic rocks (Lee, 1989; Millward et al., in press).

A residual Bouguer gravity anomaly low to the north of the Ennerdale granite, CR, (Figure 11) is interpreted as the expression of a high-level concealed granite beneath the Crummock Water metamorphic aureole (Figure 1); (Cooper et al., 1988; Lee, 1989). Adjoining this anomaly is a lobe of low residual gravity values centred near Frizing­ton [NY 034 172] (F, (Figure 11)) which appears to be due to the thick sequence of Upper Carboniferous rocks, proved by the Frizington Hall borehole (Chapter 5), rather than a granitic intrusion.

From the nature of its gravity signature, the western margin of the Lake District batholith is steep and locally coincides with strands of the Lake District Boundary Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). Seismic reflection data provide more detailed insights into the subsurface structure of the western edge of the batholith within the district (Figure 12); (Nirex, 1993b). Reflection-rich and reflection-poor areas are interpreted as a layered structure incorpo­rating multiple tabular intrusions (Evans et al., 1993). The Ennerdale granite is interpreted as a 1100 m-thick sheet-like intrusion, in agreement with the gravity mod­elling of Lee (1989). Beneath this, the batholith is com­posed of several poorly reflective granitic laccolithic intrusions that interfinger with more reflection-rich wedges, interpreted as pods of country rock (Figure 12). Thus, although the envelope of the western flank of the batholith dips quite steeply (more than 65°) to the west, in detail it has a rather jagged 'cedar-tree' profile (Evans et al., 1994).

Regional setting and deformation

The structure of the Lower Palaeozoic rocks in the central Lake District is dominated by large folds and zones of fault­ing that trend east-north-east (Figure 4). The Causey Pike and Eskdale faults are mapped from the central Lake Dis­trict into this district, the latter structure being prominent on satellite imagery and potential-field data (Firman and Lee, 1986; Lee, 1989). The Causey Pike Fault (Figure 4), (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) is co-incident with the Crummock Lineament of Lee (1989). It marks the boundary between domains of opposed facing directions in slumped units within the Skiddaw Group, and was also associated with southward thrusting and Acadian sinistral displacements. Geophysical information indicates that the Causey Pike Fault may be linked to deep-seated lower crustal shear zones associated with Acadian continental collision (Chadwick and Holli­day, 1991) and may be a crustal-scale feature of fundamen­tal importance. Kneller and Bell (1993) and Kneller et al. (1993) explained the structural configuration of the Lake District as a whole in terms of crustal-scale Acadian thrust­ing along a basement ramp dipping north-west.

An angular discordance and a substantial difference in the style of deformation between the Skiddaw and Borrowdale Volcanic groups is commonly observed across the Lake District. However, this may merely reflect competency contrasts between the two units because, although the Skiddaw Group was uplifted, tilted and eroded prior to volcanism, no definitively pre-volcanic tectonic folds and fabrics have been identified within it. Consequently, Hughes et al. (1993) discounted compres­sional deformation at this time and concurred with Branney and Soper (1988) that this major change in environment was probably a response to subduction ­related melting, thermal expansion and ascent of magma through the crust.

During Acadian deformation, the Lake District batholith acted as a rigid body, influencing the response of the overlying rocks to the effects of ductile shortening and concentrating strain around its margins. Sub­sequently, it was probably responsible for the continu­ation of the Lake District Block as a structural entity from Carboniferous times to the present day.

Structures within the district

The Lower Palaeozoic rocks which crop out in the east of the district and form the westernmost part of the Lake District inlier are dominated by faults with a long history of movement. Skiddaw Group rocks crop out in the north-east of the district and in a small inlier farther south, to the east of Ravenglass (Figure 1). The Borrowdale Volcanic Group crops out in the east of the district where the youngest part of the succession is preserved in the River Bleng area (Figure 13).

The principal structural elements of the Skiddaw Group in the district are north-west-dipping thrust faults. In the north, the Watch Hill Thrust emplaces the oldest exposed part of the group (Bitter Beck Formation) above younger strata. Farther south a similar situation is seen where the Loweswater Thrust emplaces the middle part of the group (Loweswater Formation) above younger beds. These two thrust structures affect the northern stratigraphical belt (Chapter 4), the southern boundary of which is marked by the major Causey Pike Fault (Cooper et al., 1995) which as described above shows both south-directed thrust and sinistral transcur­rent components of movement.

The arcuate Thistleton Fault downthrows to the west (Figure 13) and divides the Borrowdale Volcanic Group into two structurally distinct areas. The lowest part of the succession, the Birker Fell Formation, crops out to the north and east of the fault, where it is broken up into a number of fault-bound blocks. Bedding dip and strike within individual fault blocks are consistent, but between blocks the bedding strike varies by as much as 90° and the dip from moderate to very steep. The Shep­herd Crag Fault trends north-north-west and has a large westward downthrow, but has little effect on the western part of the Ennerdale granite. The fault therefore pre­dates or was synchronous with emplacement of the granite.

Although they are intensely faulted, strata exposed west of the Shepherd Crag Fault form a broad, easterly plunging asymmetrical syncline with a steeply dipping southern limb (Figure 13). The concealed Borrowdale Volcanic Group was proved in boreholes to the west of Gosforth (e.g. Sellafield 2, 4, 5, RCF1-3); it dips steeply (about 60°) south to south-east. By contrast, strata farther north in Sellafield 7A and 14A boreholes are mainly gently dipping.

Ordovician

In the Skiddaw Group south of the Causey Pike Fault, early Ordovician (Tremadoc to Llanvirn) synsedimentary deformation formed a major, submarine olistostrome deposit, designated as the Buttermere Formation (Webb and Cooper, 1988). This, and the remainder of the Skiddaw Group, were subjected to regional uplift, fault­ing and tilting in late Llanvirn times. This process brought about a change to subaerial erosion prior to eruption of the Borrowdale Volcanic Group which has an angular unconformity at its base (Hughes et al., 1993).

Many of the large- and small-scale structures within the Borrowdale Volcanic Group are regarded as the products of Llanvirn to Caradoc volcanotectonic processes and have been studied extensively in the central Lake District (Branney and Soper, 1988; Branney and Kokelaar, 1994; Millward et al., in press). The structures include volcano-tectonic faults across which there are changes in thick­ness and volcanic facies, fault block rotations, local angular unconformities, gravity collapse structures and hot-state deformation features in ignimbrite. In west Cumbria, the presence of a thick succession including rheomorphic ignimbrite, faults with large pre-Permian throws, and weakly developed cleavage, invite compari­son with the deposits in the Scafell Syncline (Figure 4), a structure that developed initially as a caldera system (Branney and Kokelaar, 1994) to be subsequently tecton­ically tightened during Early Devonian Acadian deforma­tion. Within the Sellafield boreholes, densely welded ign­imbrites of the Bleawath and Fleming Hall formations contain rheomorphic folds at a variety of scales, meso­breccia and domain breccia, indicative of deformation of hot, welded pyroclastic deposits.

The fault-block rotations in the Birker Fell Formation exposed east of the Thistleton Fault (described above) cannot be explained readily by normal extensional tec­tonic processes. This chaotic structural arrangement is seen also farther east in Wasdale and Eskdale, where Pet­terson et al. (1992) and Millward et al. (in press) showed this to be an effect of piecemeal caldera collapse follow­ing large-magnitude pyroclastic eruptions.

Acadian

Regional tectonic deformation of the Skiddaw Group occurred during the Acadian episode (Hughes et al., 1993). Thrust-related shortening commenced in late Silurian times with the initiation of large-scale upright, tight to isoclinal folds that trend east-north-east. A perva­sive slaty fabric was developed parallel to bedding in the northern part of the Skiddaw Group outcrop, but appears much more variable in attitude and intensity to the south of the Causey Pike Fault. Subsequent strain increments intensified the southward-directed thrusts and one or two crenulation cleavages were superimposed locally in the northern outcrop although they are very variable and markedly domainal. The thrusts probably failed to propagate into the rigid overlying volcanic rocks and the resultant increasing strain in the Skiddaw Group might have been accommodated by the formation of the domainal crenulation cleavages, and possibly by localised back-thrust movement along the unconformable contact between the Skiddaw and Borrowdale Volcanic groups. Thrust planes would have acted as the domainal bound­aries during this deformation, controlling the distribu­tion of the crenulation fabrics.

Volcanotectonic structures in the Borrowdale Volcanic Group were overprinted during the Acadian episode. Caldera depressions were tightened to form plunging synclines, existing faults were reactivated and a regional cleavage was developed. Within the district, cleavage in the volcanic rocks trends east to east-north-east and gen­erally dips south; it varies from a weak spaced fabric to strong and slaty. Cleavage is most noticeable east of the Thistleton Fault. Cleavage development is strongly con­trolled by lithology. Thus the massive central parts of basalt, andesite and dacite sheets in the Birker Fell For­mation commonly display little or no cleavage, whereas the flow-brecciated tops and bases are cleaved. In the upper part of the Borrowdale Volcanic Group sequence, densely welded ignimbrite and rhyolite sheets rarely show cleavage; unwelded ignimbrite and volcaniclastic sedimentary rocks may be moderately to strongly cleaved. This contrast is well illustrated in cores from the Sellafield boreholes where unwelded or weakly welded pyroclastic rocks of the Sides Farm Member and the Brown Bank Formation are strongly cleaved, but the glassy ignimbrites of the Fleming Hall and Bleawath for­mations are apparently uncleaved. The regional cleavage is also present within the Eskdale granite (discussed in Millward et al., in press).

Faulting

Faulting occurs on all scales within the Borrowdale Vol­canic Group. The larger structures have probably been reactivated several times, although it is generally not pos­sible to identify detailed increments of the displacement history. The faults range from simple fractures to zones of intense fracturing locally more than 100 m wide with cleavage development and brecciation, quartz and car­bonate cements and pervasive haematisation. Vertical displacements are commonly several hundred metres, but may exceed 1000 m; strike-slip displacements of up to 1500 m are present. Mineralogical characterisation of fault-rocks and related fracture infills in the Sellafield boreholes indicates several mineralising episodes, with evidence of fault reactivation (see below).

Faults in the Lower Palaeozoic basement at outcrop have a wide range of orientations, but north-westerly and easterly trends are dominant with a similar strike pattern apparent in borehole fault intersections. Faults inter­sected in the boreholes are generally steeply dipping to near vertical (Figure 14a). A similar orientation pattern is apparent for smaller scale fractures in the Sellafield boreholes (Nirex, 1997a) whose poles dominantly lie within a girdle defining a plane that dips about 20° south-west (Figure 14b). Fracturing in the Borrowdale Volcanic Group within the Lake District Boundary Fault Zone in the Bleng valley area shows a similar girdle, but more steeply dipping to the south-west (Figure 14c). However, east of the Thistleton Fault, fractures in the Borrowdale Volcanic Group outcrop are dominantly ver­tical (Figure 14d). The variation in the dip of fractures west of the Thistleton Fault is consistent with the dip of the Permo-Triassic rocks and suggests that vertical frac­turing formed prior to Permian deposition and has been tilted with the cover rocks in the hanging-wall of the Lake District Boundary Fault Zone.

The north-trending Lake District Boundary Fault Zone is one of the principal structures in the district (Figure 4), (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) and has a complex movement history. It marks the bound­ary between basement rocks and the younger cover sequence. Individual fault-bound blocks within the fault zone show a distinctive basement stratigraphy and also pre­serve small outliers of Permo-Triassic rocks. One of the main strands, the Thistleton Fault (Figure 13), juxtaposes the Blengdale and Birker Fell formations with a displace­ment of at least 1500 m, most of which predates the Permo­-Triassic. The fault zone also forms the western boundary of the Lake District batholith and movement on the Shep­herd Crag Fault, south of its intersection with the Windgate Fault, clearly predates or is contemporary with the emplacement of the granite (Figure 13), whereas later movement is demonstrated by juxtaposition of the Sherwood Sandstone group with the Skiddaw Group and Eskdale granodiorite south of Ravenglass (Figure 1).

The Eskdale Fault is a major east-north-east-trending feature identified in this district and Ambleside to the east (Figure 4), (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7); (British Geological Survey, in press a). The fault is locally associated with a zone of intensely fractured and haematised rock at least 100 m wide (Millward et al., in press). Its vertical displacement within the Lower Palaeozoic rocks is small, but it has a dextral strike-slip displacement of up to about 1 km. Dextral dis­placements are seen on faults of similar orientation in the cover rocks and may have developed in Mesozoic times.

The Seascale–Gosforth Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) comprises several faults of north-easterly trend in the exposed basement at the eastern margin of the district. Some were reactivated during the Permo-Triassic, but the Scale Beck Fault, with a throw about 1000 m down to the north within the basement, has no expression in the cover rocks (Figure 13).

The St Bees Fault Zone is a north-easterly trending structure of echelon faults (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) that is considered to have been generated by dextral reactivation of an underlying basement structure into the cover sequence. This structure is aligned with the Crummock Lineament and the Causey Pike Thrust (Figure 4), (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7); (Lee, 1989).

Carboniferous

In earliest Carboniferous times, northward subduction of the Rheic Ocean led to regional back-arc extension and the development of a block and basin system in northern Britain (Leeder, 1982a). In later Carboniferous times, east-west compression was possibly associated with plate collision in the Urals. Final closure of the Rheic Ocean culminated in the Variscan Orogeny and large-scale thrust and nappe emplacement in Belgium, northern France and southern Britain (Hutton and Sanderson, 1984). Variscan deformation in northern Britain, on the northern foreland of the Variscan Foldbelt, was much less pervasive, involving basin inversion and partial reversal of the earlier Carboniferous basin-controlling normal faults.

The elevated terrain of the Caledonian fold belt was eroded and peneplained prior to deposition of the Car­boniferous succession, whose oldest beds were deposited on a fairly flat, smooth basement surface. Further pene­plaination occurred after tilting and uplift of the Car­boniferous succession. Regional tilting allowed erosion to progressively deeper levels eastwards, and thus any Carboniferous rocks present were stripped from the eastern edge of the district. Carboniferous rocks are otherwise present over most of the district although mostly concealed beneath the Permo-Triassic cover (Figure 15a) and (Map 5).

Carboniferous structural development

Early Carboniferous extensional basins and blocks

In early Carboniferous (Dinantian) times regional north-south extension (Leeder, 1982a) initiated a 'syn­rift' phase of basin evolution and the formation of sub­siding basins and relatively stable blocks. Most of the dis­trict lay within a block that included the Lake District inlier and its offshore extension, the Ramsey–White­haven Ridge. The block was separated from the Solway Basin to the north-west by the Maryport Fault (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7), (Figure 8). The southern parts of the block are much less well understood, although Dinantian strata appear to thicken southwards and westwards (Nirex, 1993c). The extreme south-west of the district may extend to the Keys Embay­ment, a northerly branch of the Central Province Trough (Jackson et al., 1995, fig. 25), a major Dinantian depocentre forming the offshore extension of the Craven Basin (Kirby et al., in press).

Late Carboniferous 'sag' basin

In late Carboniferous times active crustal extension gave way to regional 'post-rift' subsidence, with a much reduced structural demarcation between the block and the Solway Basin. Namurian and Westphalian strata were deposited in a regime of regional sedimentation with little syndepositional normal faulting. Seismic reflection data acquired offshore (Nirex, 1993c) indicate that upper Carboniferous rocks thicken steadily to the west and south-west (Jackson et al., 1995).

Faults in the upper Carboniferous sequence are likely to have developed either as accommodation structures during post-rift subsidence or as later structures during either Variscan basin inversion or Permo-Triassic exten­sion. Inspection of mineplans and subsurface workings has revealed considerable local detail of structures affect­ing the upper Carboniferous rocks in the Whitehaven area, which are described elsewhere (Nirex, 1992b).

Variscan (end-Carboniferous) basin inversion

In latest Carboniferous times, basin subsidence gave way to regional uplift as components of Variscan north- and east-directed compression initiated the process of basin inversion. This was accomplished by regional basin upwarping (for example within the Solway Basin, (Figure 15b)) and localised, oblique reversals of basin margin faults. Fault reversal reduced net displacements on the deep syn-rift normal faults and produced linear zones of reverse faulting, anticlines and monoclines at shallower structural levels.

Although the main Variscan movements postdate pre­served Westphalian rocks, there is also evidence of earlier, minor episodes of basin inversion within west Cumbria. The unconformity at the base of the Whitehaven Sandstone (Chapter 5; Eastwood et al., 1931) pro­vides striking evidence of intra-Carboniferous earth movements. Still earlier Variscan precursor folding is indicated by thickness changes in the Namurian succes­sion of the adjacent Maryport and Cockermouth districts (Eastwood, 1930; Eastwood et al., 1968).

Structures within the district

Detailed information on the structure of the Carbonifer­ous succession is restricted to the Carboniferous at outcrop and within subsurface workings. Information is available on a broader scale from interpretation of seismic data.

Two orthogonal (north-east- and north-west-trending) fault sets are present in the Carboniferous outcrop (Figure 1). Many of the north-east-trending faults that were active during the Carboniferous do not displace overlying Permo-Triassic rocks; they may have a Dinan­tian origin, associated with active rifting at the Solway Basin margin. Near Cleator Moor [NY 306 517] the north-east-trending fault set defines the limit of the Carboniferous at outcrop and juxtaposes Dinantian rocks against Skiddaw Group, or Coal Measures and Hensingham Group against Dinantian strata. The north east-trending faults are commonly terminated by faults of north-west trend which show significant Triassic (cm younger) displacement. Faulting in the northern part of the district is well known, from coal mine plans and the interpretation of numerous haematite exploration boreholes, and the two fault sets are seen to curve into each other or show mutual termination relationships (Nirex, 1993c, fig. 3.3). This relationship suggests that both fault sets were active during the Carboniferous and that faults of north-west trend were reactivated in Permo-Triassic times.

The Maryport Fault is a north-east-trending syndeposi­tional normal fault that dips to the north-west at the southern margin of the Solway Basin (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7), (Figure 8); (Chadwick et al., 1993). Early Carboniferous oblique-normal displacements on the fault produced thickening of the lower Carboniferous succession by approximately 2000 m in the Solway Basin. Subsequent Variscan reversal and basin inversion generated minor reverse splay faults in its footwall block, the Ramsey–Whitehaven Ridge (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7), (Figure 8); (Chadwick et al., 1993). The axial region of the Solway Basin was folded into a north-east-trending anticline; the north-west of the district lies on its south-eastern limb. Although subsequent Mesozoic and Cainozoic tilting has greatly reduced dips in the Carboniferous strata, a marked angular unconformity with the overlying Permo-Triassic sequence remains (Figure 15b). This complex basin margin was again subject to inversion in Cainozoic times, with superimposi­tion of a younger anticline.

Anastomosing fractures with polyphase displacements (including lateral and reverse movements) can be recog­nised in Carboniferous rocks onshore within the district. These may be related to Variscan deformation (Nirex, 1992b). Lenticular inliers of Borrowdale Volcanic Group, Skiddaw Group and Carboniferous Limestone occur beneath the Permian cover along these faults. (Nirex, 1992b, c). Elsewhere, evidence of Variscan movements is less clear. Significant faulting occurred during latest Carboniferous or earliest Permian times; seismic and borehole data show that a number of faults at subcrop beneath the basal Brockram surface do not cut the Permo-Triassic sequence (Nirex, 1992c).

Much of the Variscan faulting along the Cumbria coastal plain may relate to reactivation of the Lake District Boundary Fault Zone. It is likely that Variscan displacements on this major structure were highly oblique and with a significant reverse component, as has been noted for the subparallel Pennine and Dent faults (Burgess and Holliday, 1979; Underhill et al., 1988).

Permo-Triassic

In Permian and Early Triassic times regional east-west­ or east-north-east-directed extension (Chadwick and Evans, 1995) was established as the dominant tectonic process and a system of north-trending rift basins devel­oped from the English Channel to western Scotland. The East Irish Sea Basin (Figure 27) was a rapidly subsiding part of this rift system, with this district lying on its north­eastern margin.

Earliest Permo-Triassic extensional faulting probably occurred prior to the deposition of Permian strata since faults that show greater displacement of Carboniferous than overlying Permo-Triassic rocks are widespread (Nirex, 1993c). These faults are not associated with syn­depositional thickness changes within the Carboniferous sequence and are therefore presumed to be evidence of early Permian extension during a period of subaerial exposure and erosion.

Basin development allowed deposition of the Permian sedimentary sequence, which rests with angular uncon­formity on eroded Carboniferous strata (Figure 15b), and which oversteps from Westphalian to Dinantian strata. Thickness changes within the Permian sequence are mostly gradual, indicating deposition within a regional sag basin. Abrupt thickness changes do occur locally, for example within the Brockram near the basin margin and the Collyhurst Sandstone offshore (Nirex, 1993c); these are taken as evidence of minor syndeposi­tional faulting.

Deposition of the Early Triassic Sherwood Sandstone Group marked the onset of major rift-basin formation. Rapid subsidence was controlled by syndepositional movements on the principal normal faults of the district (Figure 16). However, the thickness of the Sherwood Sandstone Group is fairly uniform across the East Irish Sea Basin from west to east (Figure 8); (Jackson et al., 1987) suggesting deposition in a roughly symmetrical graben, bounded to the west by the Lagman and Keys faults and to the east by the Lake District Boundary Fault Zone.

During the later Triassic, sedimentation extended across the Lake District Boundary Fault Zone and a thin sequence was probably deposited over the Lake District Block to the east. In the west, rapid basin development continued, driven by syndepositional normal faulting and regional post-rift subsidence. The Mercia Mudstone Group thickens westwards towards the Keys Basin which straddles the western edge of the district. It is this Late Triassic subsidence which produced the westward-deepening asymmetry of the northern East Irish Sea Basin and contributed to the regional westward dip of the Permo-Triassic cover in the district (Figure 8).

Faults associated with important thickness changes in the Permo-Triassic succession divide the district into the Solway Basin, the Lake District Block and the East Irish Sea Basin (Figure 16). These are considered separately below.

Solway Basin

The Solway Basin regained something of its early Car­boniferous structural identity in Permo-Triassic times; the base of Permo-Triassic strata now lies at depths up to 2000 m and deepens farther to the north-west (Map 4). The Solway Basin is separated from the East Irish Sea Basin by the Ramsey–Whitehaven Ridge (Figure 8) which is a north-east-trending structural block on which the Permo-Triassic sequence is less than 500 m thick or absent. The Maryport Fault defines the south-east margin of the Solway Basin and is interpreted to have thrown down the base of the Permo-Triassic succession to the north by more than 1000 m (Chadwick et al., 1993). It was subject to later reversal during Cainozoic basin inversion (Chapter 7), with development of the Solway anticline in its hanging-wall block (Figure 15b); (Chadwick et al., 1993). The southern boundary of the Ramsay–Whitehaven Ridge is defined by the Lagman Fault (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) which throws the base Permian surface down to the south by a few hundred metres within the district, although displacement increases to about 3000 m farther to the south-west (Nirex, 1992b, d). Several minor reverse faults and tight anticlinal folds in the hanging-wall block of the Lagman Fault (Nirex, 1993d), indicate reverse or oblique-reverse reactivation, probably during Cainozoic basin inversion.

Lake District Block

The history of the Lake District Block during the Permo­-Triassic is poorly understood because little strata of that age is preserved there. It is presumed to have formed a stable elevated area underpinned by the Lake District batholith, initially emergent and subsequently charac­terised by the accumulation of relatively thin sedimentary sequences (Chapter 6). In the south of the district the block is separated from the East Irish Sea Basin by the Lake District Boundary Fault Zone. South of Ravenglass the fault zone is narrow, interpreted as a single west-dipping normal fault. It juxtaposes the upper formations of the Sherwood Sandstone Group to the west against the Eskdale granodi­orite, with a minimum throw of 1800 m and corresponds to a sharp, linear residual gravity gradient (Figure 11). North of Ravenglass the Lake District Boundary Fault Zone divides into several distinct structures, some of which may join with the Seascale–Gosforth Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). The latter transfers a significant proportion of the down-to-the ­west displacement westward as illustrated by deflection of the gravity gradient (Figure 11). North of the Seascale–Gosforth Fault Zone the Lake District Boundary Fault Zone splays into several smaller faults, but with the overall westward downthrow appearing to diminish north­wards. Within the basement at outcrop, strands of the Lake District Boundary Fault Zone with substantial pre-Brock­ram displacements may have been significantly reactivated in Permo-Triassic or later times.

East Irish Sea Basin

The East Irish Sea Basin is the main Permo-Triassic depo­sitional feature within the district (Figure 16). It formed by east-west extension across faults with northerly trend (ranging from north-west to north-east, (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7)), which have mainly Permo-Triassic displacements. Within the basin these faults define a general radial pattern, from the north-east trend of the Lagman Fault in the west, to the north-north-west trend of faults onshore (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7), (Figure 16). This is consistent with the systematic southward increase in measured extension across the basin from almost zero west of St Bees Head to nearly 20 per cent in the south of the district and is interpreted as resulting from clockwise rotation of the Ramsey–Whitehaven Ridge relative to the Lake District Block (Nirex, 1993c). Within this overall pattern the East Irish Sea Basin com­prises several distinct structural elements, the Lakeland Terrace, the Ravenglass Sub-basin and the Tynwald and Keys basins.

The Lakeland Terrace

The Lakeland Terrace is the onshore and nearshore area characterised by thin preserved sedimentary cover rocks (less than 1000 m thick), at the eastern margin of the East Irish Sea Basin. It includes many faults with rela­tively small displacements rather than the fewer but larger faults mapped within the basinal parts of the East Irish Sea Basin. The south-western margin of the terrace forms a south-west-dipping slope cut by the Natasha, Harriet and Braystones fault zones (Figure 16), (Figure 17a) and (Figure 17b). Its south-eastern margin is marked by the Seascale–Gosforth Fault Zone which bounds the Ravenglass Sub-basin to the south. Within the terrace there are many northerly trending faults which are crossed by faults of east-north­east trend. Both sets of faults are considered to have been active contemporaneously and are described below.

Northerly trending faults

Onshore these structures trend north-west and dip either north-east or south-west. The north-easterly dipping faults usually dip at a relatively gentle angle (less than 50°) whereas the south-west-dipping faults are commonly steeply inclined or vertical. It may be that some of these faults developed symmetrically with respect to the bedding. If this is the case, the implication is that they were subsequently tilted to the south-west. Syndeposi­tional movement on the northerly trending faults occurred during the Permian and Early Triassic, although some structures ceased to be active during accumulation of the St Bees Sandstone. Thus, abrupt thickness changes in the Brockram are evident across faults that downthrow to the west and some down-to-the­ east structures. The facies change from Brockram to the St Bees Shale and Evaporite formations may also be locally fault controlled, for example along the Fleming Hall Fault Zone.

Offshore the faults are typically north-trending and appear to have relatively simple geometry with domi­nantly normal displacements. Fault zones with evidence of a more complex history are described in the following paragraphs.

Where it intersects the base St Bees Sandstone Forma­tion surface, the High Sellafield Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) is interpreted to be a continuous structure with normal displacement down to the east. However, at shallower levels (base Calder Sandstone Formation surface and above) it is an echelon structure consistent with a component of sinistral strike-slip. Where the fault zone is mapped onshore it includes a significant antithetic fault and has the character of a complex flower structure with oblique and reverse components of displacement.

The Natasha Fault Zone is a normal fault dipping moderately to the east with a well-developed rollover that may have a wide zone of antithetic and synthetic faulting in its hanging-wall block (Figure 17b). It has an overall maximum throw down to the east of 650 m but section balancing (Nirex, 1993c) indicates there has also been considerable oblique displacement.

The Laura Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) has an overall maximum normal downthrow to the east of 600 m. However, section restorations also suggest that there must also have been a significant component of oblique slip (Nirex, 1993c).

The Harriet Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) has an unusually complex geometry. At the base of the Permo-Triassic sequence it is a single down-west step but at higher struc­tural levels it becomes a complex zone up to 4 km wide of synthetic and antithetic faulting; it includes an open anticlinal structure with a collapse graben at the fold crest.

The arcuate Braystones Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) comprises several component structures with cumulative throw down to the east and locally developed minor folding in the hanging-wall block (Figure 17a). It links southwards into the Sarah Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) which is a probable low-angle listric' normal fault.

East-north-east-trending faults

Steeply dipping east-north-east-trending faults cross the principal northerly trending faults in the Lakeland Terrace. They correspond to underlying Caledonian basement structures and acted as transfer faults subparal­lel to the extension direction, defining distinct blocks within which the northerly trending faults developed independently.

The St Bees Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) consists of an echelon series of faults with displacement down to either the north or south, the mapped geometry indicating a component of dextral strike slip. The fault zone becomes less continuous at shallower levels and individual faults are rotated into an easterly alignment, as exposed at St Bees Head (Plate 3). The fault zone may owe its origin to reactivation of a basement structure beneath the Crum-mock Lineament and the Causey Pike Thrust (Figure 4) and (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

The Woodlands Fault (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) is well known from mine workings within the Carboniferous Limestone near Haile [NY 038 089] as a zone of steep subparallel faults. Throw is not consistent but, overall, there is slight offset of the northerly trending faults (Nirex, 1993c). Borehole information in the vicinity of the fault indicates that it does not affect the thickness of either the preserved Car­boniferous sequence or the Brockram. From the contrast in their geometry it seems likely that independent devel­opment of the northerly trending faults occurred to north and south of the Woodlands Fault during the Permo-Triassic, the fault possibly acting as a transfer zone during basin extension.

The Seascale–Gosforth Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) also acted as a transfer structure during the Permo-Triassic, defining the northern margin of the Ravenglass Sub-basin (Figure 16). The base of the Permo-Triassic suc­cession is thrown down to the south across the fault zone with displacement increasing eastwards. However, understanding of the detailed fault structure is incom­plete and the amount of displacement at the eastern end is very poorly constrained, although gravity data indicate a relatively abrupt step in this area (Kimbell, 1994).

Faults at outcrop and in boreholes

The Permo-Triassic rocks at outcrop within the Lakeland Terrace belong mainly to the Sherwood Sandstone Group (Nirex, 1992c). Bedding in the onshore expo­sures dips gently south-west (Figure 18) except adjacent to faults where dips may be steeper. In exposures around St Bees dip is less than 15°, but farther south within the district observed dip is generally steeper, 15–30°, increas­ing eastwards to 40° near the eastern edge of the Permo-­Triassic outcrop.

Faults seen at outcrop are minor and broadly eastward trending (Figure 16) and therefore differ significantly from the larger northerly trending faults. Many of the exposed faults occur in the St Bees Sandstone at St Bees Head, where an intensely faulted zone in the southern part of the headland is probably an onshore extension of the St Bees Fault Zone (Plate 3). A south-dipping fault [NX 9503 1230] with a displacement of about 20 m has one minor fault in the footwall block but 16 anti­thetic faults in its hanging-wall block, over a zone some 800 m wide. Many of these have populations of smaller-scale antithetic and synthetic fractures. The main dis­placements appear to be dip-slip with late oblique move­ment. Study of the fault rocks demonstrates a sequential development similar to that established from the Sellafield boreholes (Table 2); (Nirex, 1995a; Strong et al., 1994).

A few minor, easterly trending faults are exposed as granulation seams in the Calder and Ormskirk Sand­stone formations in the vicinity of Gosforth. In the fore­shore exposures at Seascale [NY 0340 0130] a vertical fault trending 094°, marked by a zone up to 1.2 m wide of echelon fractures with very thin quartz infills, is proba­bly part of the Seascale–Gosforth Fault Zone.

A variety of fault-rocks have been proved in the Permo-Triassic rocks intersected in the Sellafield boreholes (Nirex, 1995b; 1996a, b; 1997b). Mineralisation studies provide evidence of fault reactivation with the development of illite-mineralised gouges. Faults inter­sected within the Sherwood Sandstone Group are mostly moderate to steeply dipping and inclined to the east or north-east. Fault intersections that dip to the south-west and near-vertical faults with an easterly strike are also recorded (Figure 18). The borehole cores also provide evidence of movement on some bedding surfaces.

Ravenglass Sub-Basin

The Ravenglass Sub-basin (Figure 16) is bounded to the east by the Lake District Boundary Fault Zone and to the north by the Seascale–Gosforth Fault Zone; it passes southwards into the Tynwald Basin. The quality of seismic data is poor over much of the sub-basin but the residual gravity anomaly map very clearly distinguishes the Raven-glass Sub-basin, RG, (Figure 11) as an embayment between the Eskdale Granite and the Seascale–Gosforth Fault Zone defined by a zone of increased gravity gradi­ent. Formation of the sub-basin margin may have been associated with reactivation of east-north-easterly trending basement structures between the Ennerdale and Eskdale intrusions. The preserved Permo-Triassic sequence in the Ravenglass Sub-basin is generally more than 1000 m thick in contrast to the thinner sequence over the Lakeland Terrace to the north.

Tynwald Basin

The Tynwald Basin lies to the south of the Lakeland Terrace and is bounded by the Tynwald and Lake Dis­trict Boundary fault zones to the west and east, respec­tively (Figure 16), (Figure 19a). Within the basin the base of the Permo-Triassic sequence dips gently westwards from about 2000 to 3500 m depth (Map 4), but patterns of faulting are very complex. Low-angle listric' normal faults are common and many penetrate to a detachment surface which flattens to become bedding-parallel near to the base of the Permo-Triassic succession (Figure 19a). Above the detachment, regional extension of the Permo­-Triassic succession was accommodated by synthetic and antithetic normal faults typified by the southerly continu­ation of the Harriet Fault Zone (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). The widespread development of low-angle faulting may be associated with a thick development of salt within the Permian rocks. Particular occurrences of listric' normal faulting in the Permo-Triassic succession may coincide with heavily faulted Carboniferous strata beneath.

Open anticlinal folds are common within the Tynwald Basin (Figure 16); (Jackson et al., 1987) and have been cited as inversion-related structures (Roberts, 1989). However, they are commonly associated with listric normal faulting and probably initially formed as rollovers during extension with perhaps some enhancement by later shortening. Folding related specifically to Cainozoic basin inversion is more clearly seen in the hanging-wall block of the Lake District Boundary Fault Zone (Nirex, 1993d).

Tynwald Fault Zone

This remarkable north-trending structure separates the northern part of the East Irish Sea Basin into two struc­turally distinct provinces (Jackson et al., 1987; Arter and Fagin, 1993). To the west are the structurally simple Lagman and Keys basins with relatively minor faulting, whereas to the east, the Tynwald Basin is much more complex with abundant low-angle faulting. The fault zone is 5 to 10 km wide and comprises opposed low-angle normal faults bounding a prominent central graben (Figure 8), (Figure 19b). At the base of the Permo-Triassic sequence the net downthrow across the fault zone is gen­erally quite small because it has a roughly symmetrical profile and the eastern and western bounding faults have similar displacements (Jackson et al., 1987). Although structural attenuation of the Sherwood Sandstone Group is extreme, thinning from about 2000 m thick on either side of the fault zone to typically 500 m (locally faulted out) within the central graben, the structure can be restored by section balancing (Arter and Fagin, 1993). It is likely that low-angle detachments within the Permian St Bees Evaporite (Chapter 6) played a crucial role in the development of such structures as the central graben and detached folding of the Mercia Mudstone Group within it (Figure 19b) may be associated with salt movements.

Keys Basin

This is the deepest part of the East Irish Sea Basin and is associated with a prominent Bouguer gravity anomaly low in the south-west of the district (Figure 10), (Figure 16). The interpreted base of the Permo-Triassic lies at about 5000 m depth and is relatively unfaulted (Map 4). At higher structural and stratigraphical levels the presence of thick salt units within the Mercia Mudstone Group has facilitated development of many low-angle listric' normal faults (Nirex, 1992d). Consequently, the Mercia Mudstone Group is significantly deformed, with large 'rafts' of strata several kilometres across appearing to 'float' upon the weak salt layers (Nirex, 1992b).

Lagman Basin

The eastern edge of the Lagman Basin extends into the westernmost part of the district (Figure 16). The basin has a markedly asymmetrical profile; the base of the Permo-Triassic sequence lies between about 1000 and 2000 m and dips westward (Map 4). On the whole there appear to be relatively few faults within the Lagman Basin and its sedimentary fill is largely undeformed. The basin is bounded to the east by the Sigurd Fault Zone (Figure 16) which comprises a sinuous anastomosing network of normal faults; it is several kilometres wide and throws down to the east. Locally it is offset dextrally by east-trending transfer faults with a throw of up to 1000 m.

Fracture mineralisation

The complex and varied sequence of structural events which has affected the rocks of west Cumbria is reflected in the mineralogy of their faults, fractures and associated fault-rocks. A paragenetic sequence of nine distinct frac­ture mineralisation episodes, termed ME1 to ME9 in order of decreasing age, has been established on the basis of cross-cutting relationships and mineral textural and fabric observations in the Sellafield boreholes (Table 2); (Nirex, 1995a; Milodowski et al. 1997).

The earliest events (ME1 to 3) are restricted to the Lower Palaeozoic rocks. ME1 is dominated by silicate minerals (quartz, feldspar, chlorite and haematite) and affected by cleavage formation; it probably relates to mineralisation during early hydrothermal circulation developed shortly after accumulation of the Borrowdale Volcanic Group. Widespread, high-temperature hydro-thermal quartz-dominated silicate vein mineralisation (ME2) and later sulphide and quartz mineralisation (ME3) are probably largely associated with emplacement of the Lake District batholith. Major anhydrite vein min­eralisation (ME4) and carbonate mineralisation (ME6) events are correlated with deep burial cements formed during the diagenesis of Permo-Triassic rocks. ME5 and ME7 are dominated by clay mineralisation (Table 2) and although these are found as cements in the Permo­-Triassic rocks, they are principally associated with fault-rock development.

ME6 fracture mineralisation is subdivided into three mineralogically and temporally discrete episodes, ME6a to ME6c (dominated by calcite-haematite, dolomite ­ankerite-anhydrite and calcite, respectively), which corre­spond to diagenetic events in the Permo-Triassic rocks (Chapter 6) indicative of different phases of faulting. Manganese and iron oxyhydroxide minerals of ME8, and calcite, sulphate and sulphide minerals of ME9 were formed by geologically recent alteration and mineralisa­tion processes and may be actively forming at the present day (Milodowski, et al., 1997).

Faults with the most intense deformation and, there­fore, the greatest inferred displacement, are cemented by ME6 mineralisation. Correlation of ME6 mineralisa­tion to diagenetic events in the Permo-Triassic rocks (Chapter 6) indicates that the main episode of move­ment on the principal faults intersected by the boreholes occurred during the progressive deep burial of the Trias­sic sequence. This probably occurred during the Mid to Late Triassic, by analogy with the burial history of the East Irish Sea Basin presented by Stuart and Cowan (1991). K–Ar and Ar–Ar dating of ME7 illite mineralised fault gouge indicates that later reactivation and signifi­cant displacement took place in the period from the Mid Jurassic to the mid Cretaceous.

Chapter 4 Lower Palaeozoic

Rocks of Early Palaeozoic age crop out along the eastern margin of the district and have been proved in boreholes beneath Carboniferous and Permo-Triassic cover rocks to the west. The oldest strata present comprise the marine, Tremadoc to Llanvirn Skiddaw Group (Cooper et al., 1995 and references therein). This is overlain by the calc-alkaline Borrowdale Volcanic Group which is of Llandeilian to early Caradoc age (Molyneux, 1988; Thirlwall and Fitton, 1983). The central part of the Lake District is underpinned by a granitic batholith (Bott, 1974; Lee, 1986), represented at outcrop in the district by parts of the Eskdale and Ennerdale intrusions.

The Lower Palaeozoic rocks of the Lake District record geological events at the margin of the microconti­nental terrane of Eastern Avalonia. This had been attached to the Gondwana continent in a high southern latitude and was separated from the continent of Lauren­tia to the north, by the Iapetus Ocean (Cocks and Fortey, 1982; McKerrow, et al., 1991; Trench et al., 1991). In the early Ordovician, Eastern Avalonia rifted from Gondwana, drifted north during closure of the Iapetus Ocean and eventually collided with Laurentia in sub­tropical latitudes during the Silurian (see review by Soper et al., 1992).

The Skiddaw Group accumulated beneath deep, circumpolar water peripheral to the Gondwanan margin (Fortey et al., 1989), probably in an intracontinental extensional basin formed as part of the rift separaton of Avalonia. Cooper et al. (1995) described the strata as deep-water, continental margin slope and basin deposits. Turbidity current flow was the dominant depositional mechanism with slump movement on all scales disrupt­ing the layered sequence (Webb and Cooper, 1988). Palaeocurrent indicators show that flow was mainly from the south-east. Petrography and geochemistry (Cooper et al., 1995) indicate that the provenance was an inactive, continental volcanic arc terrane comprising siliceous extrusive rocks, acid plutons, cleaved and metamor­phosed basement rocks and sedimentary lithologies such as shale and quartzite.

Uplift and erosion of the Skiddaw Group in the mid-Ordovician was followed by a period of subaerial volcan­ism, represented in the northern Lake District by the Eycott Volcanic Group and in the south by the Borrowdale Volcanic Group (Millward and Molyneux, 1992). During the early stages of the subaerial regime the Latterbarrow Formation accumulated as a mainly alluvial deposit although parts may have had a marine, intertidal influence (Allen and Cooper, 1986).

The succeeding subaerial volcanic rocks of the Borrowdale Volcanic Group are the remnants of a sub­duction-related, calc-alkaline volcanic sequence erupted within a rift zone at the margin of Eastern Avalonia. An effusive, multiple-centred, plateau-andesite sequence formed during the first part of the volcanic cycle (Petter­son et al., 1992). A dramatic change in eruptive style fol­lowed with the emplacement of voluminous ignimbrites, associated with piecemeal caldera collapse (Branney and Soper, 1988; Branney and Kokelaar, 1994). The caldera depressions formed substantial volcaniclastic sedimen­tary basins. The last stage in the magmatic cycle involved emplacement of the Lake District batholith and minor intrusions.

Evidence of the late Ordovician to early Devonian history of the Lake District is not preserved in this dis­trict. During this period a turbidite-dominated sequence, the Windermere Supergroup, accumulated in a foreland basin that migrated southward across the Lake District in the final stages of closure of the Iapetus Ocean as Eastern Avalonia collided with Laurentia (Kneller, 1991; Hughes et al., 1993; Kneller et al., 1993).

Skiddaw Group

The Skiddaw Group comprises a succession of sandstone, siltstone and shale, up to 5000 m thick, ranging in age from Tremadoc to early Llanvirn. A comprehensive review of Skiddaw Group stratigraphy has been pub­lished recently by Cooper et al. (1995) and their termi­nology is followed in this account. Two distinct stratigraphical belts have been defined in the main Lake Dis­trict inlier and designated the Northern Fells and Central Fells belts (Cooper and Molyneux, 1990; Cooper et al., 1995). These are separated by the Causey Pike Fault (Figure 4), which trends approximately westwards, passing just south of Croasdale [NY 094 175]; it is a zone of coincident south-directed thrusting and sinistral strike-slip shear. The Northern Fells Belt has been divided into five formations (Figure 20), four of which (Bitter Beck, Watch Hill, Loweswater and Kirk Stile) are present in the district; the Central Fells Belt comprises two formations, only one of which (Buttermere) is present here.

In the northern part of the district, borehole evidence shows that the Skiddaw Group extends westwards beneath the Carboniferous strata of the Cumbrian coastal plain. Farther south, near Ravenglass in the central part of the district [NY 093 965], two small inliers of Skiddaw Group strata are preserved adjacent to the Eskdale intrusion in the footwall of the Lake District Boundary Fault Zone. There, hornfelsed mudstone con­tains metamorphic biotite and some chlorite along with tourmaline and chiastolite; beds of meta-sandstone are also present. It is not possible to assign these inliers of metamorphosed Skiddaw Group to any particular formation (Figure 1).

Bitter Beck Formation

The Bitter Beck Formation is the oldest part of the Skiddaw Group and is of Tremadoc age. It is up to 500 m thick in the district (Cooper et al., 1995) cropping out in the north-eastern corner where it lies structurally above the younger Kirk Stile Formation along the south-directed Watch Hill Thrust.

The formation is dominated by dark grey mudstone with only sporadic thin sandstone beds. A fine sedimen­tary lamination is generally present, and the beds prob­ably represent low-density turbidite deposits. Sandstone beds are pale grey and fine grained with undulose lami­nation and irregular bases and tops. Small slump folds are fairly widespread and many show bed-parallel detach­ment surfaces.

Watch Hill Formation

The Watch Hill Formation conformably overlies the Bitter Beck Formation in the extreme north-east of the district (Figure 1), where it is less than 100 m thick. The thickness increases east of the district to a maximum of almost 800 m (Cooper et al., 1995). The formation ranges in age from the latest Tremadoc to the earliest Arenig (Molyneux and Rushton, 1988). The boundary between the Watch Hill and Bitter Beck formations is gradational, marked by a relatively abrupt increase upwards in the proportion of sandstone to about 70 per cent of the sequence. Pale grey- and brown-weathered lithic wacke (Leeder, 1982b) is the most abundant sand­stone type, commonly with mudstone intraclasts. Individ­ual sandstone beds range up to 1 m thick and locally display normal grading, parallel lamination or ripple cross-lamination. Thinner beds are commonly irregular in thickness with lateral 'pinch and swell' effects, appar­ently of sedimentary origin.

Loweswater Formation

The Loweswater Formation is of mid-Arenig age (Cooper et al., 1995). It crops out in the central part of the main Skiddaw Group outcrop in the district (Figure 1), where structurally, it overlies younger Skiddaw Group forma­tions along the south-directed Loweswater Thrust. The faulted boundary skirts the south-east flank of Knock Murton [NY 095 190] before trending west towards Kirk­land [NY 073 180]. To the north of the thrust the Loweswater Formation ranges up to about 900 m thick.

The formation consists mainly of quartz-rich, felds­pathic wacke (Leeder, 1982b) but the basal beds have been variably cut out by the thrust. Above the thrust plane there is a steady increase upwards in the thickness of the sandstone beds, from 0.30 m to a maximum of about 1 m, over about 300 m of strata. The sandstones are mostly fine to medium grained, but maximum grain size increases to very coarse sand with the increase in bedding thickness. This is accompanied by a decrease in the proportion of argillaceous interbeds from almost 50 per cent to only 10 per cent. The upper part of the formation is a fining and thinning upward sequence in which bed thickness and maximum grain size decrease gradually whilst the propor­tion of mudstone increases. Most of the sandstone beds have planar bases. Scattered bottom structures include channels, groove casts and flute casts. The thinner sand­stone beds are mainly parallel laminated or ripple cross-laminated; the thicker beds may be graded at their base and pass upwards into a laminated top.

Kirk Stile Formation

At a few localities in the district the Loweswater Forma­tion passes conformably upwards into the Kirk Stile For­mation, but the principal outcrops of the formation are structurally confined, beneath the Watch Hill and Loweswater thrusts and north of the Causey Pike Fault. The Kirk Stile Formation is estimated at 1500 to 2500 m thick, although some of this variation may have resulted from stacking of slumped masses, and the top is never seen. It is largely of late Arenig age with the youngest beds extending into the earliest Llanvirn.

The lithology that is typical of the formation is lami­nated to thinly interbedded (less than 2 cm) dark grey siltstone and mudstone, commonly forming graded units and interpreted as very low-density turbidite deposits. Locally, there are lenticular sandstones, up to about 100 m thick, comprising thinly bedded (1–10 cm) lithic wacke with parallel and ripple lamination. The dominant clast types in the lithic wackes are volcaniclastic siltstone and altered mafic volcanic rock. Synsedimentary slump folding is widespread, generally concentrated into dis­rupted units, 2 to 40 m, thick which are sandwiched between undisturbed beds.

Within the district, biostratigraphical control for the Kirk Stile Formation is provided by a graptolite fauna from an old quarry north of Whinnah Farm [NY 1063 2419]. This has been interpreted by Dr A W A Rushton (BGS) as indicative of the upper part of the gibberulus Biozone in the sense of Cooper et al. (1995).

Buttermere Formation

The Central Fells stratigraphical belt is represented in the district only by the Buttermere Formation. It is an olistostrome deposit, at least 1500 m thick, comprising disrupted, sheared and folded mudstone and sandstone clasts (on all scales) which contain graptolite and acritarch assemblages ranging in age from Tremadoc to late Arenig (Webb and Cooper, 1988; Cooper et al., 1995). The olistostrome is thought to have been emplaced in the late Arenig by downslope movement towards the north-north-west.

Although exposure is very restricted there appears to be much evidence for slump disruption in the west of the outcrop, with a more regularly bedded mudstone sequence and sporadic thin beds of fine-grained feldspathic wacke, in the east. Within the less-disrupted zone an upper Tremadoc assemblage of trilobites and acritarchs has been described by Molyneux and Rushton (1984) and Rushton (1988) from exposures beside the River Calder [NY 0687 1178]. This may derive from a part of the succession underlying the slumped olistostrome or from a very large raft of older strata within it. However, about 1 km to the south-east, on the opposite side of Latter Barrow at Beck Grains [NY 0776 1128], late Arenig graptolite–trilobite fauna of the gibberulus or hirundo Biozone has been recorded by Allen and Cooper (1986). This proximity of disparate biostratigraphical ages is characteristic of the Buttermere Formation and encourages its interpretation in terms of stratal mixing through large-scale slump movements.

Borrowdale Volcanic Group

The group is approximately 8000 m thick, and mid-Ordovician in age. It comprises basaltic, andesitic, dacitic and rhyolitic lavas, sills and pyroclastic rocks along with abundant volcaniclastic sedimentary rocks. The group underlies most of the central Lake District and in the Ambleside district to the east its lithostratigraphy has been described in detail by Millward et al. (in press). There, the Birker Fell Formation, an andesite lava succes­sion, forms the lowest part of the sequence. In this dis­trict the Birker Fell Formation is underlain by siliciclastic rocks of the Latterbarrow Formation (Figure 21). Early descriptions (e.g. Eastwood et al., 1931; Trotter et al., 1937) included the Latterbarrow Sandstone as the youngest part of the Skiddaw Group. However, it has since been shown to overlie the Skiddaw Group uncon­formably (Allen and Cooper, 1986) and is therefore included as the lowest formation of the Borrowdale Vol­canic Group.

Large downthrow on the Shepherd Crag and Thistle-ton faults (Figure 13) has preserved thick successions of pyroclastic rocks on the western margin of the Lake Dis­trict massif which are now exposed in the lower reaches of the Bleng valley, Blengdale Forest [NY 091 068], north-east of Gosforth. Farther west, the existence of vol­canic rocks buried beneath Permo-Triassic cover has been known for many years from haematite exploration boreholes in the district (Smith, 1924; Eastwood et al., 1931; British Geological Survey, 1980), but the records are sparse. More recently, the Sellafield boreholes (Figure 3) have, for the first time, enabled the extent and significance of the volcanic sequence to be assessed (Millward et al., 1994).

The base of the Borrowdale Volcanic Group at outcrop is interpreted as an unconformity, but much of the biostratigraphical and structural evidence for this is derived from the eastern Lake District (Wadge, 1978). In the district the base of the group is nowhere exposed. There is no evidence for faulting or thrusting of the contact as considered by Eastwood et al. (1931) and Trotter et al. (1937). An unconformable relationship is supported by the change in sedimentary facies at the junction, the configuration of the mapped boundary and the palaeontological evidence for differing ages from the underlying Skiddaw Group (Allen and Cooper, 1986; see also Buttermere Formation).

Latterbarrow Formation

At the base of the Borrowdale Volcanic Group the Latter-barrow Formation comprises about 400 m of unfossilifer­ous sandstone cropping out over about 3.6 km2 between Swarth Fell [NY 065 118] and Lank Rigg [NY 091 118]. First mentioned by Ward (1876), the stratigraphy, pet­rography and geochemistry of these rocks have been dis­cussed more recently by Allen and Cooper (1986). Origi­nally it was included with the Skiddaw Group.

East of the River Calder the lowest 110 m of the forma­tion comprises grey or green, thinly bedded, fine- or medium-grained sandstone with sporadic pebbly lenses. Thinly laminated units with alternations of siltstone, very fine-grained and fine-grained sandstone are present in places. The thin sandstone beds commonly have ero­sional bases whilst the tops of the beds may contain small ripples; tabular cross-bedding is also present. These rocks pass upwards into about 250 m of massive, thickly to very thickly bedded, medium-grained sandstone which is purple or grey in the west but green or grey farther east. Beds several metres thick containing only faint discontin­uous laminae, alternate with units of similar thickness in which bedding is well developed. Graded bedding, shallow pebble-filled channels and asymmetrical ripples commonly occur within the well-bedded sandstone. At Latterbarrow Beck [NY 0710 1098] and [NY 0766 1113] and at Gill Force [NY 0670 1122] in the River Calder sporadic, discontinuous, purplish brown interbeds of mudstone, up to 30 cm thick, occur in the uppermost 40 m of the formation.

The sandstone is mainly fine- to medium-grained quartz wacke with more than 25 per cent matrix. The constituent grains are poorly sorted, subangular to sub-rounded and with moderate sphericity. Well-rounded coarse sand-size grains and pebbles are sparsely scattered through the rock and concentrated in laminae. Beds of quartz arenite within the formation are better sorted, with more closely packed and rounded coarse sand grains. Quartz grains predominate with subordinate clasts of chert, quartzite, sandstone, quartz-schist, acid volcanic rock, chloritised basic igneous rock, vitric tuff, microcrystalline quartz-sericite rock and, very rarely, mudstone. Basic igneous rock fragments are most common at the bottom and top of the formation; for example, at the base of the formation on Lank Rigg [NY 0886 1167] dark grey sandstone beds, up to 25 cm thick, contain abundant chlorite-rich clasts. The matrix of the quartz wacke is extensively replaced by iron oxide but in places comprises chlorite, with some silt-size quartz grains.

The clastic constituents of sandstones in the Latterbar­row Formation and in the underlying Skiddaw Group are compositionally similar, but those in the former are more coarse grained and include a coarse, well-rounded fraction not seen in the Skiddaw Group (Allen and Cooper, 1986). The presence of quartzite and quartz-schist clasts favours a psammitic source area. Allen and Cooper (1986) considered that the abundant feldspar (up to 16 per cent) in a few beds from the uppermost part of the formation, the illitic mudstone intercalations, basic volcanic rock clasts, chloritic matrix, and the high iron and manganese content of the Latterbarrow Forma­tion may be explained best by penecontemporaneous volcanic input.

Birker Fell Formation

The Birker Fell Formation oversteps the Latterbarrow Formation to rest unconformably on the Skiddaw Group. In the central Lake District it is almost 3000 m thick, and comprises tabular sheets of andesite interbedded with subordinate basalt, dacite and volcaniclastic rocks (Petterson et al., 1992). In west Cumbria, the Birker Fell Formation crops out in the footwall blocks of the Shepherd Crag and Thistleton faults, but is only poorly exposed compared with the type area to the east (Figure 13). Subdivision of the formation follows the scheme adopted in the Ambleside district (British Geological Survey, 1996b; Millward et al., in press) where andesite is generally shown undivided, but units of significantly dif­ferent lithology are assigned member status. Four members occur within this district, these are in upward succession, the Devoke Water, Seatallan, Craghouse and Wrighthow; the type sections or type areas for these are within the Ambleside district.

Most of the Birker Fell Formation is composed of andesite sheets, generally 20 to 100 m thick. Typical features of these include massive and flow-banded central zones, and autobrecciated lower and upper sheet margins (Petterson et al., 1992; Millward et al., in press). Interpretation of the andesite sheets, either as lavas or as high-level intrusions, is dependant on good exposure of the upper contacts and the relationship with the over­lying strata (Branney and Suthren, 1988). The presence of internal sediment, the characteristic used to distin­guish a lava from a sill, is noted in the upper autobrec­cias of many of the andesites. However, the generally poor exposure does not facilitate determination of the proportion of lavas to sills.

The andesite is varied in appearance. Dark blue-grey, highly feldspar-phyric andesite occurs in the upper reaches of the River Bleng [NY 0982 0727], in the Birker Fell Formation beneath the Seatallan Member. South of High Thistleton and near Hawkbarrow [NY 098 045] pink to grey, feldspar-phyric andesite has platy flow joints that are wavy and relatively closely spaced. Basaltic andesite crops out north-west of Thornholme [NY 066 080] and aphyric andesite overlies the Devoke Water Member in the River Calder [NY 070 094].

The andesite groundmass varies from cryptocrystalline to fine grained, locally with a well-developed hyalopilitic texture; it is commonly altered to chlorite, sericite, iron-oxide and carbonate. Euhedral to subhedral plagioclase phenocrysts and glomerocrysts, some with sieve textures, form up to 20 per cent of the rock. Also present are up to 5 per cent chlorite pseudomorphs after pyroxene; iron oxide and small apatite crystals are ubiquitous. Many of the andesites contain spherical and lenticular amygdales, up to about 1 cm diameter, of quartz or chlo­rite. Examples of these are found in Friars Gill [NY 060 101] and Scalderskew Wood [NY 090 089].

In the upper reaches of the River Bleng e.g. [NY 0983 0728] beds of andesitic tuff and lapilli-tuff occur within the formation. These rocks are massive to weakly eutaxitic, ungraded, poorly and very poorly sorted, and matrix sup­ported. Up to 25 per cent of the lapilli-tuff comprises angular to rounded lithic clasts, chiefly of altered very fine tuff. A small proportion of subhedral and broken crystals of plagioclase and altered pyroxene also occurs, within a typically very fine-grained matrix altered to quartz, feldspar, white mica, chlorite and iron oxides.

As in the western part of the Ambleside district the for­mation is extensively faulted. Many of the juxtaposed fault blocks have differing internal dip and strike direc­tions, typical of the effects of caldera collapse (Millward et al., in press), but poor exposure and the absence of distinctive marker beds precludes correlation between the blocks. Hence the thickness of the formation in this district is uncertain, although a minimum of 2600 m can be deduced.

Devoke Water Member

From Lowther Park [NY 052 119] to the flanks of Boat How [NY 092 104], coarse tuff, lapilli-tuff and pyroclastic breccia overlie the Latterbarrow Formation. The sequence thins eastwards from a maximum thickness of about 600 m. These rocks were described previously by Green (1917) and Trotter et al. (1937) as the Mottled Tuffs, but similarities in lithofacies and lithostratigraphi­cal position suggest that they should be included with the Devoke Water Member of the Ambleside district. The base of the member is exposed at three localities (Allen and Cooper, 1986). In Gill Force gorge [NY 0670 1122] the junction is sharp, markedly discordant and was prob­ably originally nearly vertical, indicative of subaerial erosion. A similar relationship is displayed at one locality in Latterbarrow Beck [NY 0699 1098], but farther east [NY 0766 1113] the relationship is unclear as the base occurs within a sequence of interbedded sandstone and cobble-bearing mudstone overlain by pyroclastic breccia.

The poorly to well-sorted tuff and lapilli-tuff is variably massive, weakly and well bedded; bedforms are typically planar and parallel. Alternating coarse- and fine-grained beds are common, with laminae of fine tuff up to 15 mm thick. Normal grading is characteristic. A pyroclastic breccia facies is spectacularly displayed on Capel Crag [NY 071 102], where clast- and matrix-supported blocks range up to 0.5 m. The breccia is polylithic, but domi­nated by well-sorted sandstone and siltstone clasts, proba­bly derived from the Latterbarrow Formation. The long axes of the clasts lie parallel to the bedding. The propor­tion of volcanic fragments in the breccia is small compared with the rest of the unit.

Throughout the member, volcanic clasts are angular to subrounded pyroclasts of generally non-porphyritic, non­amygdaloidal, microcrystalline and hyalopilitic andesite or basaltic andesite. Trotter et al. (1937) reported the pres­ence of some amygdaloidal varieties and acidic lithic clasts including, on Capel Crag, large blocks of silicified welded tuff. Fragments of sandstone, lithologically similar to those of the Latterbarrow Formation, are common. Single quartz grains and patches of quartz-rich sandy matrix between the lithic grains are probably disintegrated, poorly lithified clasts of Latterbarrow sandstone. Charac­teristically the rocks are grain supported and pressure solution effects possibly caused the flattened grain con­tacts. The small amount of matrix is made up of fine-grained chloritic and haematitic material.

Seatallan Member

Saccharoidal dacite is exposed in the upper reaches of the River Bleng [NY 095 071] and on Hollow Moor [NY 1009 0627]. It is similar in appearance to the Seatallan Dacite, defined from a type area on Seatallan, north-west of Wast Water in the Ambleside district (Millward et al., in press) and to which member it is stratigraphically assigned.

In the Bleng valley [NY 095 070] the Seatallan Member is about 460 m thick and comprises two dacitic units separated by andesite. At the base of the member is a greenish grey rhyodacite about 90 m thick. This con­tains euhedral plagioclase phenocrysts up to 3 mm long, sparse glomerocrysts of plagioclase and sieve-textured plagioclase phenocrysts with vermicular inclusions of chlorite. These are set in a very fine-grained to cryp­tocrystalline groundmass with rounded, concentrically zoned amygdales up to about 10 mm in diameter, and a distinctive epidote-clinozoisite alteration. The pheno­crysts are locally aligned parallel to a set of epidote­mineralised platy fractures, interpreted as a primary flow fabric. Overlying the rhyodacite is a feldspar-phyric andesite, approximately 70 m thick.

Most of the member is made up of the upper, massive dacite that has a rough, granular, pale greenish grey weathered surface. Flow-banding is well developed locally. On Hollow Moor the rock appears brecciated and in places e.g. [NY 0963 0710] the dacite has a clastic appear­ance with a eutaxitic-like texture enclosing abundant sub-rounded feldspars and lithic lapilli. Phenocrysts and glomerocrysts of plagioclase form up to 20 per cent of the rock and are set in a devitrified, cryptocrystalline, glassy groundmass. The plagioclase is partially replaced by epidote and/or clinozoisite, possibly with some chlorite. A few phenocrysts of chloritised biotite, K-feldspar, iron oxide and possibly pyroxene are also present. Phenocrysts are variably aligned parallel to the flow-banding.

Craghouse Member

Welded lapilli-tuff assigned to the Craghouse Member crops out in two fault blocks (Figure 13). The first and best exposed of these is just east of Crag House [NY 110 026], between the Windgate and Shepherd Crag faults. The second block is very poorly exposed between the Thistleton and Shepherd Crag faults.

The Craghouse Member is at least 1000 m thick. The lowest 70 m consists of bedded pumice lapilli-tuff, massive to weakly bedded lithic-rich unwelded lapilli-tuff and pyro­clastic breccia with interbeds of laminated siltstone and sandstone. The remainder of the member comprises mainly unstratified eutaxitic lapilli-tuff, with abundant flat­tened fiamme, broken feldspar crystals and sporadic coarse lithic lapilli set in a microcrystalline matrix. At the base of this tuff unit there are 5 m of breccia made up of angular and subangular blocks of sedimentary rocks in an unwelded, fine tuff matrix; this is interpreted as a co­ignimbrite lag breccia. In the upper part of the member, pumice becomes less abundant and the lithic content gradually becomes dominated by granitic clasts and non­amygdaloidal, possibly juvenile fragments with cumulose margins. The upper part of the uniform lapilli-tuff appears to be less densely welded than the lower part.

In the Blengdale Forest [NY 094 068] polymict, very poorly sorted, matrix- to clast- supported pyroclastic breccia and coarse lapilli-tuff are included within the member. The subangular to subrounded lapilli and blocks include parataxitic crystal-rich tuff, dacite, hyalo­pilitic andesite and chloritised tuff.

Wrighthow Member

The Wrighthow Member comprises about 200 m of dark greyish green, massive and scoriaceous, autobrecciated basalt lava. It is exposed north of Hollins around Wrighthow Crags [NY 108 037] and has been interpreted by Petterson et al. (1992) and Millward et al. (in press) as a compound aa-lava. The basalt has a microcrystalline groundmass, and is typically aphyric to clinopyroxene-­phyric with subordinate microphenocryts of plagioclase. The top of the Wrighthow Member is cut out by faulting.

Volcanic succession north and east of Gosforth

West of the Thistleton Fault the Borrowdale Volcanic Group comprises up to 1550 m of poorly exposed vol­caniclastic rocks (Figure 13), (Figure 21). The base is not seen and the sequence is overlain unconformably by Permo­-Triassic breccias and sandstones (Chapter 6). Three for­mations are present, in ascending order they are the Fleming Hall, Lowcray and Blengdale. Two deep boreholes, Sellafield 8A and 9A, have proved the lower part of the succession (Figure 3). The uppermost unit, the Blengdale Formation, contains the youngest Borrowdale Volcanic Group rocks known from the district.

Fleming Hall Formation

A succession of mostly welded andesitic tuff and lapilli­tuff in Sellafield 8A and 9A boreholes and at outcrop north and east of Gosforth are correlated with the Fleming Hall Formation identified in the Sellafield boreholes farther to the west (Millward et al., 1994). There, three members have been distinguished, the Town End Farm, Sides Farm and Longlands Farm in upward succes­sion. However, only the uppermost has been confidently identified in the Gosforth area. The upper part of the formation is exposed in the Bleng valley (Figure 13) and the lower parts proved in Sellafield 8A and 9A boreholes (Figure 3), (Figure 21); the base has not been seen.

The lower part of the Fleming Hall Formation was proved in the Sellafield 8A and 9A boreholes (Figure 3) penetrating 800 and 485 m, respectively. Three stratigraphical units are recognised, comprising two thick, geochemically uniform andesitic welded lapilli-tuffs, interpreted as ignimbrites, separated by silicic rocks. Several large faults were encountered in the boreholes which introduce stratigraphical uncertainty (Figure 21). The andesitic ignimbrites are texturally varied, dark greenish grey to reddish grey, massive, coarse tuff and lapilli-tuff with eutaxitic and parataxitic fabrics. The uppermost unit contains sporadically fresh clinopyrox­ene and is considered to be part of the Longlands Farm Member. The lowest unit is probably the Town End Farm Member, described from the Sellafield boreholes to the west.

The fault-bounded central part of the succession in Sellafield 8A and 9A boreholes contains three lithologi­cal units; a lowermost massive tuff is overlain by eutaxitic lapilli-tuff and felsite. The felsite is massive and spherulitic at the base and flow-banded in the upper part. This faulted succession is not referred to a member because lithological and geochemical similarities can be drawn to either the Sides Farm member or the older Brown Bank Formation (Figure 22).

The uppermost part of the Fleming Hall Formation, the Longlands Farm Member, is exposed around Table Rock [NY 0885 0360], in Scale Beck [NY 0886 0559] and near Farmery [NY 0732 0695] where it comprises parataxitic tuff; columnar jointing occurs at Table Rock (Trotter et al., 1937, plate IIB). Varied orientation of the welding fabric, flow-folds and plastic deformation of attenuated fiamme indicate that it is a high-grade rheo­morphic tuff. In the vitroclastic matrix are subhedral and broken crystal fragments of plagioclase (10–15%), iron oxide (2–3%), and clinopyroxene (2–5%). The crystals are generally fresh, although in places pyroxene is replaced by chlorite. Lithic clasts, between 0.4 and 5.0 mm across, form less than 10 per cent of the tuff and include andesite, various fine tuffs and sporadic felsite. Locally, there are lithic-rich lapilli-tuff layers dominated by angular to subrounded tuff clasts in a densely welded vitroclastic matrix.

Lowcray Formation

The Lowcray Formation is poorly exposed in the lower part of the River Bleng. The rocks include crystal-rich parataxitic tuff and lithic-rich coarse lapilli-tuff, locally with a weak eutaxitic fabric. Generally, the rocks are intensely haematised and silicified so that primary textures are unrecognisable. The tuff comprises 5 to 25 per cent subhedral and fragmented crystals of sericitised plagio­clase, minor K-feldspar, pyroxene, iron-oxide, quartz and apatite in a devitrified, very fine-grained matrix.

Blengdale Formation

The Blengdale Formation crops out in the rivers Bleng (type section) and Calder and also on Ponsonby Fell, north-west of the Scale Beck Fault (Figure 13). This pink to pale grey, rheomorphic rhyolitic ignimbrite is one of the most differentiated units within the Borrowdale Volcanic Group. The main rock type is a glassy, parataxitic, tuff, containing up to 10 per cent crystal fragments of sericitised plagioclase and K-feldspar locally aligned parallel to the welding fabric. The apparently K-feldspar-rich and possibly spherulitic matrix also contains feldspar microlites and small lithic clasts in places. A jigsaw-fit autobreccia is present locally.

The upper part of the formation, the Ponsonby Fell Member, comprises a breccia dominated by clasts of the rhyolitic ignimbrite. It is seen as scattered small exposures and large boulders north-west of the summit of Ponsonby Fell [NY 081 072]. The characteristic lithology is a massive, ungraded, clast- or matrix-supported polylithic, coarse breccia; clasts are angular to locally sub rounded and consist of parataxitic rhyolitic tuff and subordinate andesite and andesitic tuff. Some rounded clasts of polycrystalline to cryptocrystalline quartz and rare monocrystalline quartz crystal fragments are also present. The matrix is fine grained and haematised.

Concealed Borrowdale Volcanic Group

Three geographically distinct volcaniclastic successions are recognised from boreholes which penetrate the con­cealed volcanic rocks of the district (Millward et al., 1994). These occur around Longlands [NY 056 040], near Calder Hall and near the coast around Seascale (Figure 22). Five formations are identified in the Longlands area, the Moorside Farm, Broom Farm, Bleawath, Brown Bank and Fleming Hall formations, within a sequence which is about 1140 m thick. The type section for these formations is the Sellafield 2 Borehole. To the north, in the Calder Hall area, two formations are identi­fied in Sellafield 7A and 14A boreholes; the Newton Manor and, overlying Yottenfews formations (Figure 22). In the Seascale area, the volcaniclastic succession in Sellafield 3 and 13A boreholes are quite distinct from each other and from those elsewhere; they have no formally assigned lithostratigraphy (Figure 22). Some of the pyro­clastic lithofacies are illustrated in (Plate 4). Thicknesses given are uncorrected for dip or for deviation of the borehole trajectory from vertical.

Moorside Farm Formation

The Moorside Farm Formation occurs at the base of the Sellafield 2 Borehole (Millward et al., 1994). It comprises welded lithic-rich lapilli-tuff passing up into more than 114 m of massive, poorly sorted, clast- and matrix-sup­ported, coarse pyroclastic breccia. The upper part of the breccia is unwelded and rich in andesite clasts, whereas angular, glassy juvenile rhyolitic clasts and some col­lapsed pumice clasts dominate the lower part. The pro­nounced upward geochemical zonation from rhyolite to andesite is ascribed to the increase in the content of non-juvenile andesite clasts.

Broom Farm Formation

The formation is 13.5 m thick and overlies the Moorside Farm Formation in the Sellafield 2 Borehole (Millward et al., 1994). It consists of coarse-grained and pebbly vol­caniclastic sandstone, intercalated with laminated fine-grained volcaniclastic sandstone and siltstone. The coarse-grained sandstone is medium- to thickly bedded and commonly with convoluted laminations.

Bleawath Formation

The Bleawath Formation is up to 416 m thick in the type Sellafield 2 Borehole (Millward et al., 1994). It consists of several sheets of blocky and coarse pumice lapilli-tuff, and displays zonation from andesite to rhyodacite. Eutaxitic, parataxitic and locally rheomorphic fabrics indicate dense welding throughout. Cognate lithic clasts are abundant; they are glassy, crystal-rich, but variably angular, subrounded or elongate, and weakly to non-vesicular. Non-juvenile, crystalline andesite lithic clasts are rare. The moderately high crystal content comprises altered plagioclase, pyroxene and iron oxide. The lower part of the formation, seen only in the Sellafield 2 Bore­hole, is crudely layered and rich in pink, acidic lithic clasts; weakly parallel-bedded, coarse-grained sandstone and pebbly sandstone occur about 12 m above the base. Sellafield 4, 5 and 10A boreholes do not penetrate the base of the formation (Figure 22).

Brown Bank Formation

This is a heterogeneous ignimbrite succession consisting of poorly sorted, lithic-rich tuff, lapilli-tuff, tuff-breccia and pyroclastic breccia (Millward et al., 1994). The ignimbrites are weakly to densely welded and locally rheomorphic. Most of the units are massive, though the uppermost tuff and lapilli-tuff member has layers with abrupt variations in crystal, fiamme and lithic clast content. Correlation has been facilitated by the presence of several silicic ignimbrites, particularly the widespread and distinctive Seascale Hall Member (Figure 22). The base of the formation is defined by the lowest lithic-rich pyroclastic rock overlying pumice-rich lapilli-tuff of the Bleawath Formation. The Brown Bank Formation over­laps north-eastwards onto the Bleawath Formation, indi­cating an unconformable relationship between them. Thus, the Brown Bank Formation thickens abruptly south-westwards as the number of component members increases.

Sellafield RCF1 Borehole proved a thick, flow-banded and flow-folded feldspar-phyric felsite in the Brown Bank Formation below the Seascale Hall member (Figure 22). It is locally amygdaloidal and has some eutaxitic-like fabrics in the lowest part. The uppermost few metres are autobrecciated, with interstitial finely laminated sand­stone and siltstone. The characteristics of this unit are typical of felsic lavas and lava-like ignimbrites, both of which are present in the Borrowdale Volcanic Group in the central Lake District (Branney et al., 1992; Kneller et al., 1993). However, the origin of the felsite remains uncertain because details of its extent and thickness vari­ation are essential to any interpretation.

The Seascale Hall Member is of particular stratigraphi­cal importance (Millward et al., 1994). It is a eutaxitic to parataxitic rhyolitic tuff interpreted as a rheomorphic ignimbrite and contains particularly conspicuous small, white, subangular, aphyric felsite clasts. Geophysical logs indicate a subtle compositional zoning. The thin sequence in the Sellafield 5 Borehole is wholly auto­brecciated, and at the base of the member in the Sellafield RCF1 Borehole, a thin fine-grained reverse-graded basal layer, is overlain by unbedded, poorly sorted, polymict, coarse lapilli-tuff and tuff-breccia inter­preted as co-ignimbrite lag breccia.

Within the Brown Bank Formation thin sequences of volcaniclastic sandstone, tuff, pumice lapilli-tuff and accretionary lapilli-tuff separate some of the ignimbrites. Accretionary lapilli are locally abundant within cross-laminated tuff that also contains lenticular and wavy bedding, abrupt grain-size changes and reverse grading. Beds of ashfall and/or pyroclastic surge origin are associ­ated with the Seascale Hall Member and the lava-like felsite (above) in the Sellafield RCF1 Borehole. Under­lying the felsite are nearly 6 m of bedded pumice-rich lapilli-tuff and laminated fine tuff, and beneath the Seascale Hall Member are about 2 m of medium- to thickly bedded, pumice lapilli-tuff. The pumice in these beds is intensely flattened, probably as a result of loading compaction following alteration of the pumice to clay minerals (Branney and Sparks, 1990). Bedded, medium-to coarse-grained, and locally pebbly, sandstone and lam­inated siltstone occur at the base of the formation in the Sellafield 2 and 10A boreholes.

Fleming Hall Formation

Densely welded, medium to fine andesitic tuff and lapilli­tuff form the Fleming Hall Formation (Figure 22). These rocks are high-grade, rheomorphic tuffs, as indicated by the ubiquitous presence of flattened vitroclastic textures, variations in the welding fabric dips, small-scale intrafo­lial folds, shears, boudinaged fiamme and penecontem­poraneous microfaults. Small, dark greyish green, het­erolithic clasts occur throughout. The formation comprises two compound ignimbrites, the Town End Farm and Longlands Farm members, separated by coarse lapilli-tuff and breccia constituting the Sides Farm Member (Figure 22). A marked change in lithology, geo­chemistry and crystal content occurs at the base of the formation distinguishing it from the underlying Brown Bank Formation. In the Longlands area, the Fleming Hall Formation is overlain unconformably by cover sequence rocks.

At the base of the formation, the Town End Farm Member comprises massive, eutaxitic and parataxitic lapilli-tuff with characteristically smooth geophysical log traces and geochemical homogeneity. The crystal content is generally 15 to 18 per cent by volume, pre­dominantly plagioclase and pyroxene. Lithic clasts are a minor component. The uppermost part, as seen in the Sellafield RCF2 and RCF3 boreholes, is particularly rich in coarse lapilli-grade pumice. Parts of the unit in the Sellafield RCF1–3 and RCM1–3 boreholes contain domain breccia of the type described from ignimbrites within the Airy's Bridge Formation of the Scafell area of the Lake District by Branney and Kokelaar (1994) who inferred that it formed by hot-state autobrecciation during emplacement and welding. Polymict, poorly sorted, clast ­to matrix-supported, coarse lapilli-tuff and breccia occur at the base of the member and are interpreted as a co-­ignimbrite lag breccia.

Overlying the Town End Farm Member in all except the Sellafield 2 and 4 boreholes is the Sides Farm Member. In the Sellafield 5 Borehole this consists of about 70 m of unbedded, poorly sorted, clast-supported, blocky coarse breccia of mostly welded tuff blocks up to 3 m, some of which show in-situ cracking and brecciation. These brec­cias were emplaced either as syn-eruptive debris-fall avalanche breccias, or as non-cohesive debris flows. In the Sellafield RCF and RCM boreholes, the member is more heterogeneous, with thick beds of graded, clast- and matrix-supported tuff-breccia and breccia. Though some of the beds are lithic breccia, others are rich in weakly abraded pumice blocks, particularly in the upper parts. The matrix-supported pumice-rich beds are debris flow deposits or unwelded ignimbrite.

The Longlands Farm Member is geochemically homoge­neous, glassy, densely welded and locally rheomorphic, welded acid-andesitic lapilli-tuff commonly with fresh clinopyroxene and plagioclase. Geochemically, the Longlands Farm Member is indistinguishable from the Town End Farm Member. The base is defined sharply by the con­trast in lithology between the welded tuff and the unwelded breccias of the Sides Farm Member below; this break coincides with a marked change in the geophysical log signatures. The Longlands Farm Member contains more varied lithofacies than the Town End Farm Member and includes massive tuff, massive eutaxitic and parataxitic lapilli-tuff, layered lapilli-tuff and domain breccia (Branney and Kokelaar, 1994). Massive tuff occurs in the uppermost part; with layering, 3 to 40 m thick, present in the central and lowest parts. Each of the layers becomes progressively more lithic rich downwards so that abrupt changes in the geophysical logs are noted at the base of each layer as the increase in the concentration of pale coloured lithic clasts within layers is matched by lower spectroscopy gamma-ray values. The layered facies is mostly densely welded, except in Sellafield RCF3 and RCM1 boreholes where part of it is lithic rich and unwelded.

Newton Manor Formation

The type section for this formation is the Sellafield 7A Borehole (Figure 22) in the Calder Hall area (Millward et al., 1994). The thickness of the formation, and included andesite sills, in Sellafield 7A Borehole is 240 m; the base is not seen. The formation consists mainly of volcani­clastic sandstone in Sellafield 7A and 14A boreholes (Figure 22). The sandstone is mainly medium- to thickly bedded, moderate to well sorted and coarse to very coarse grained. Other facies present include: parallel-laminated siltstone and well-sorted very fine- to medium-grained sandstone, in places normally graded and commonly with load casts and centimetre-scale microfaults; cross-lami­nated medium- and fine-grained sandstone containing rip-up clasts and microfaults: medium- and coarse-grained sandstone with abundant synsedimentary deformation. Beds containing angular pebbles and cobbles are usually reverse graded, with a fine- to medium-grained basal layer. Steep contacts at the base of some beds indicate possible channel fills.

Pyroclastic rocks form a small component of the for­mation, particularly in the upper part (Figure 22). Thin ignimbrites comprise poorly sorted, matrix-supported, unwelded tuff and lapilli-tuff with abundant, normally graded, non-vesicular, cognate lithic clasts, some of which are plastically deformed around, or against, adja­cent fragments. Beds of graded pumice lapilli-tuff and accretionary lapilli-tuff are interpreted as pyroclastic fallout deposits.

Yottenfews Formation

The Yottenfews Formation comprises three rheomor­phic welded tuffs in the type section in the Sellafield 7A Borehole (Millward et al., 1994). At the base is the Sella Park Member, a high-silica rhyolitic welded tuff. It con­tains K-feldspar crystals and the eutaxitic to parataxitic fabrics have been extensively silicified. This welded tuff is locally abundantly spherulitic, with well-preserved, radial, sheaf-like intergrowths of alkali feldspar and quartz. Many spherulites are nucleated on feldspar crys­tals and some have central cavities filled with carbonate, chlorite and epidote. The spherulites have grown across the welding fabric and clearly postdate welding. The lowest 5 m of the member are unwelded and a weak lay­ering is shown by variations in pumice and crystal con­centrations. The Sella Park Member is overlain by a welded, crystal poor, parataxitic lapilli-tuff with auto­breccia at the top, intrafolial breccias and strong, platy foliation in the lower part. Geochemical analysis demon­strates a very potassic composition (Millward et al., 1994). The uppermost tuff is an acid andesitic, glassy, parataxitic tuff containing a small proportion of crystals, mainly plagioclase, and pale-coloured lithic clasts. Overall, there is geochemical similarity between these units and the Blengdale Formation.

Volcaniclastic rocks of Sellafield 3 and 13a boreholes

The sequence proved in these coastal boreholes cannot be correlated with the other Borrowdale Volcanic Group formations. The volcanic succession proved in Sellafield 3 Borehole comprises four welded ignimbrites, each from 26 to 78 m thick, intercalated with tuff, lapilli-tuff, volcaniclastic breccia, sandstone and siltstone (Figure 20). The welded ignimbrites comprise massive tuff and lapilli-tuff ranging in composition from acid andesite to rhyolite. Crystals of plagioclase and minor pyroxene gen­erally comprise 10 to 20 per cent of the rock, although up to 40 per cent is present in crystal-rich zones. K-feldspar is a minor constituent of the uppermost unit. Lithic clasts generally account for less than 10 per cent of the rocks although concentrations up to 40 per cent occur in places. The lowest two ignimbrites are densely welded, but the ignimbrite above them is characterised by small fiamme and a weak eutaxitic texture. The upper­most ignimbrite becomes increasingly welded down­wards; weak layering in the top 30 m passes progressively into eutaxitic and parataxitic lapilli-tuff with parataxitic textures towards the base containing small-scale intrafolial folds, faults and shear planes indicative of rheomorphism.

Separating the ignimbrites are bedded volcaniclastic sedimentary and pyroclastic lithofacies (Figure 22). The sedimentary component comprises parallel-laminated, medium- to coarse-grained sandstone, the coarser parts containing large proportions of elongate, chloritised pumice. Channelling, cross-bedding and soft-sediment deformation structures are locally abundant. The pyroclas­tic beds are 1 to 6 m thick and include massive, homoge­neous, poorly sorted, unbedded, pumice lapilli-tuffs inter­preted as unwelded ignimbrites. The weak eutaxitic texture in some of these units was probably produced by com­paction following alteration of the pumice to clay minerals (Branney and Sparks, 1990). The lowest 20 m of the bore­hole succession comprise medium- to coarse-grained sand­stone that becomes progressively more disrupted upwards with an increasing number of lapilli-tuff blocks.

In the Sellafield 13A Borehole, 104.4 m of ignimbrite were cored beneath Carboniferous strata. The base of the ignimbrite was not reached. Variations in grain size and component concentrations in the poorly sorted, lithic-rich fine lapilli-tuff have produced a crude thick layering. Fiamme are reverse-graded in places and a weak eutaxitic fabric is present. The crystal component is up to 10 per cent feldspar. The clast population is heterolithic and most clasts are 2 to 15 mm across with a maximum of 55 mm.

Intrusive rocks

Borrowdale Volcanic Group-related intrusive rocks

In the central Lake District, sills are an integral part of the Birker Fell Formation and are abundant within the volcaniclastic successions of the Borrowdale Volcanic Group (Beddoe-Stephens et al., 1995; Millward et al., in press). Many are shallow level intrusions, with peperitic margins. Two thick, peperitic andesite sills have been identified in the Brown Bank Formation of the Sellafield RCF1, RCF3, RCM1 and RCM2 boreholes (Figure 22). Characteristically, the sill margins are brecciated, with angular to subrounded clasts set in disrupted country rock. This passes progressively inwards through andesite breccia with andesite matrix into massive andesite, rich in euhedral feldspar and mafic phenocrysts. The upper of the sills generally comprises multiple leaves separated by screens of wall rock. Borehole core shows that the Newton Manor Formation is host to several andesite sills, up to 97 m thick in the Sellafield 7A Borehole (Figure 22). Within the Yottenfews Formation is a vesicular, feldspar-phyric dacite sill.

Lake District batholith

The westernmost parts of two major granitic bodies, the Ennerdale and Eskdale granites extend into the district (Figure 1). These plutons form a major part of the Lake District batholith. U-Pb isotopic ages of 450 ± 3 and 452 ± 4 Ma on zircon from the Eskdale and Ennerdale intrusions, respectively, indicate a Caradoc emplacement age (Hughes et al., 1996). Interpretation of seismic reflection profiles and modelling of the gravity anoma­lies in west Cumbria shows that the western margin of the Lake District batholith largely coincides with the Lake District Boundary Fault Zone, and that the granites are part of a cedar-tree laccolith (Evans et al., 1993; 1994). The Ennerdale and Eskdale intrusions have been described in detail from the Ambleside district (Millward et al., in press).

Ennerdale intrusion

The Ennerdale intrusion, commonly referred to as the Ennerdale Granophyre, intrudes the Skiddaw and Borrowdale Volcanic groups and has a metamorphic aureole that widens northwards within the Skiddaw Group (Figure 1). Geophysical studies suggest that the intrusion is a relatively thin, tabular body, less than 2000 m thick, underlain by denser, less silicic plutonic rocks (Lee, 1989; Evans et al., 1993).

In the district the intrusion is generally poorly exposed. Pink, leucocratic, fine-grained, slightly por­phyritic granite, commonly with granophyric texture is the dominant lithology. Biotite was probably the main mafic component although it is now altered to chlorite. On the southern side of Ennerdale Water are diffuse enclaves of doleritic and hybridised dioritic rocks. More extensive diorite facies are developed in the Bleng valley [NY 125 085] in the Ambleside district.

Eskdale intrusion

The Eskdale intrusion comprises two, approximately coeval plutons, the Eskdale granite and the Eskdale gran­odiorite. In the district the granite crops out on Muncaster Fell [SD 100 960] and the granodiorite is to the south of this. In the contact metamorphic aureole the hornfels is, in places, cut by a spaced cleavage.

Exposures of the Eskdale granite on the western part of Muncaster Fell comprise locally haematised medium-to coarse-grained biotite granite that is petrographically similar to the main granite outcrop farther east. Variably porphyritic microgranite masses within the outcrop may be either intrusions or xenoliths. The contact with Skiddaw Group rocks is exposed west of Muncaster Castle [SD 0991 9616], where the granite shows a 20 cm-wide marginal chilled zone of porphyritic microgranite. Elsewhere at the margin of the intrusion is quartz-mica greisen which locally contains large plates of mica. The greisen and granite are cut by veins of country-rock breccia up to 40 cm wide.

Within the Eskdale intrusion, granodiorite is exposed mainly around Newtown Knott [SD 095 953]. The rock is aphyric, medium to coarse grained, dark coloured and biotite rich; it is composed of oligoclase, microperthite, quartz, chloritised biotite, iron oxide, apatite and zircon. Near its margin, the granodiorite is finer grained and contains many xenoliths of dolerite and volcanic country rock from 0.01 to 5 m across. The larger xenoliths are veined by granodiorite and there is a 2 cm-wide chilled zoned adjacent to them.

An oval-shaped mass of grey porphyritic microgranite crops out east of Newtown [SD 096 956] and is in contact with the granodiorite. It is lithologically distinct from other microgranites seen elsewhere in the Eskdale intru­sion. The varied phenocryst content is mostly of euhe­dral orthoclase, sericitised euhedral plagioclase and some biotite; some rare, ragged quartz phenocrysts are present. The groundmass of quartz, feldspar and biotite is texturally distinct with spherulites up to 0.5 mm in diameter set in a mosaic of anhedral crystals. Greisen occurs at one locality [SD 0985 9576].

Minor intrusions

Thin basalt and dolerite sills and dykes crop out through­out the district. They are generally fine grained, in part doleritic, and aphyric to variably plagioclase- and pyrox­ene-phyric; many are amygdaloidal. Two geochemical groups are present: a predominant basaltic andesite with less than 1.5 per cent TiO2 that is probably related to the Borrowdale Volcanic Group, and subordinate basalt with greater than 2 per cent TiO2, probably of tholeiitic affin­ity. Similar groupings were reported from intrusions within the Birker Fell Formation of Eskdale and Wasdale (Macdonald et al., 1988).

Rhyolite intrusions, up to about 2 m wide, also occur at outcrop and in the Sellafield boreholes. The dykes are nearly vertical, pale pink to buff weathered, aphyric to sparsely feldspar-phyric and locally spherulitic. A number of dykes with a north-north-easterly trend occur south­east of Flat Fell [NY 055 130], but elsewhere a northerly trend is also seen. Similar dykes are commonly associated with the margins of the Ennerdale and Eskdale intru­sions in the Ambleside district (Millward et al., in press).

Chapter 5 Carboniferous

At the beginning of Carboniferous times, following Caledonian tectonism and intrusion, erosion reduced the west Cumbrian landscape to a peneplain. The district lay within a continental crustal plate just south of the equator, and from there drifted north during the remainder of the Carboniferous (Scotese et al., 1979). In Britain to the north of the Wales–Brabant Massif, north-south extension and rifting during the Dinantian resulted in block and basin formation; most of the dis­trict lay on the stable Lake District Block, separated by the syndepositional Maryport Fault from the subsiding Solway Basin to the north-west (Chapter 3; Jackson et al., 1995, fig. 25). Regional dip of the block surface was to the south, and in the south-west of the district there was a gradual passage into the basinal facies that accumu­lated in the Keys Embayment of the Central Province Trough (Jackson and Johnson, 1996); the offshore exten­sion of the Craven Basin.

Carboniferous sedimentation was controlled by an interplay of tectonic, climatic and eustatic factors. Dinan­tian rocks record alternate periods of emergence and in­undation by shallow, tropical marine waters. In late Dinantian times there was a northward and eastward transition to Yoredale facies which comprises a sequence of limestone, shale, sandstone and coal that records repeated cycles of marine transgression and regression. These cycles represent the depositional response of a sili­ciclastic-influenced carbonate platform to rapid and re­peated oscillations of sea level caused by glacio-eustasy. The facies can be traced from this district into the Cock­ermouth, Brampton and North Pennine areas, with pro­gressive thinning of the limestones and thickening of the intervening clastic beds (Trotter and Hollingworth, 1932a; Eastwood et al., 1968; Young and Armstrong, 1989). From the Namurian to mid-Westphalian, the influx of terrestrial sediment from the north-west and north-east broadly balanced local subsidence to establish and maintain a freshwater deltaic environment with lagoons and coal swamps, periodic marine incursions produced thin marine bands. Later in Westphalian times, the district took on a continental aspect and red beds accumulated, before regional uplift terminated sedimentation.

Permo-Triassic sediments were deposited across the eroded surface of the Carboniferous rocks. Carbonifer­ous rocks crop out in the onshore and adjacent offshore areas of the northern part of the district where the unconformable cover has been eroded (Figure 1). Else­where in the district, Carboniferous rocks remain con­cealed beneath Permo-Triassic strata. The widespread occurrence of concealed Carboniferous rocks offshore is confirmed by interpretation of seismic reflection data. Onshore the outcrop is concealed by extensive drift cover, but there are exposures at the coast and in quar­ries and stream sections (Eastwood et al., 1931). Most data on the onshore succession are derived from explo­ration and working of coal, iron ore and limestone.

At outcrop, the Carboniferous succession is divided into four major units (Table 1). In ascending order these are: the Chief Limestone Group, a cyclical succession shelf limestones predominantly Dinantian in age: the Hensingham Group, mostly clastic marine and deltaic facies of Namurian age: Westphalian Coal Measures of deltaic and lagoonal facies: and the Whitehaven Sand­stone Formation, a sandstone-dominated red bed succes­sion. This nomenclature is based on Eastwood et al. (1931). The lower three units were recognised by Young and Boland (1992) in the north-east and can be mapped across the district; equivalents have been recognised off­shore (Jackson and Johnson, 1996). In addition, the newly redefined Whitehaven Sandstone Formation, described in this memoir, may be recognised in the Whitehaven area (Sheet 28).

Detailed examination of the Dinantian rocks proved in boreholes in the Sellafield area reveals that these exhibit rather closer stratigraphical and sedimentological affini­ties to the equivalent rocks of south Cumbria than to those at outcrop in west Cumbria. During the revision survey of the district, detailed lithological, sedimentologi­cal and palaeontological studies have been undertaken only for parts of the sequence. These investigations, which include a revised correlation of Carboniferous lithostratigraphy across the whole of northern England, are as yet incomplete and will be the subject of future BGS publications. In this memoir the Carboniferous rocks of the outcrop area are described in accordance with the classification adopted on the published 1:50 000 scale maps of the district.

Carboniferous Limestone

The traditional classification of the Carboniferous Lime­stone in west Cumbria (Table 3) and (Figure 23) was erected during the peak of the haematite mining indus­try (Kendall, 1885; Edmonds, 1922; Eastwood et al., 1931) and is retained for the exposed succession. Fossilif­erous marker beds, such as the Girvanella, Orionastraea and Erythrospongia bands (Figure 23) provide stratigraphical correlation within the limestone succession. The Girvanella Band is widespread throughout northern England near to the Asbian/Brigantian stage boundary (Burgess and Mitchell, 1976).

The limestone-dominated Dinantian succession in the Sellafield boreholes has more similarity with that of south Cumbria and north Lancashire than with that of north Cumbria. A lithostratigraphical classification was proposed by Barclay et al. (1994) for the concealed strata recovered in the Sellafield boreholes (Table 3). The south Cumbrian name Martin Limestone (Rose and Dunham, 1977) was proposed for the late Chadian strata, the Seventh Limestone (of Holkerian age) was renamed the Frizington Limestone by Barclay et al., (1994). The south Cumbrian name Urswick Limestone (Rose and Dunham, 1977) was used for the overlying late Asbian limestones of similar facies in the concealed sequence, equivalent to the Sixth, Fifth and lower part of the Fourth Limestone, including the White Limestone, of the exposed Carboniferous sequence (Table 3); (Figure 23). Thus, the Chief Limestone Group is described sepa­rately from those formations within the concealed sequence that are equated to the Dinantian sequence in south Cumbria. Several major non-sequences were recog­nised by Barclay et al. (1994).

Chief Limestone Group

The stratigraphy of the group, which comprises lime­stones separated by thinner, laterally persistent mud-stones and sandstones is summarised in (Figure 23). The group rests unconformably on Lower Palaeozoic rocks. In the north-east of the district, where it crops out in a narrow belt and is proved in boreholes beneath the west Cumbria coalfield, it overlies the Skiddaw Group. In the central and south-east of the district it is concealed beneath Permian and Triassic rocks and rests on the Borrowdale Volcanic Group.

The subdivisions of the Chief Limestone Group were derived from the results of exploration for and mining of iron ore deposits in the Whitehaven area (Smith, 1924).

Seven main limestones are numbered from the First Limestone at the top, to the Seventh Limestone at the base of the sequence (Figure 23). The intervening clastic rocks are known as 'shales' but include sandstone, silt-stone, mudstone and claystone; they are numbered from the First Shale to the Seventh Shale. The 'limestones' also include thin mudstone beds and a number of com­ponent limestones have been distinguished within the Fourth Limestone (Figure 23).

The limestones, formerly assigned to Dinantian faunal zones S2 to D3 of Garwood (1913) by Edmonds (1922), range in age from Holkerian to Pendleian (George et al., 1976; Ramsbottom et al., 1978; Mitchell et al., 1978) (Figure 23).

During an earlier survey (Eastwood et al., 1931), the group was relatively well exposed in quarries and mines in the northern part of the district. Access to many of these exposures is now lost, but active quarrying contin­ues in the Fourth Limestone at the Eskett Quarry [NY 054 170] and near Pardshaw [NY 099 258] and in the First and Second Limestones near Eaglesfield [NY 089 288]. The 'shales' typically form hollows in the landscape and are poorly exposed but the First, Second, Fourth and Fifth shales can be seen in some quarry sections.

Limestones form more than 90 per cent of the Chief Limestone Group. They range from very dark to very pale grey in colour, but locally may be brown or purple adjacent to mineralised faults or joints. Grain size ranges from lime mudstone to coarse-grained bioclastic lime­stone and shelly layers include corals, productoid bra­chiopods and crinoid debris. Algae such as Saccamminop­sis sp. (formerly classified as the foraminifer Saccammina) and the cyanophyte Girvanella sp. are locally conspicuous (Eastwood et al., 1931). Detailed studies of the Dinantian limestones of west Cumbria were undertaken by Stabbins (1969) and Thurlow (1996).

The limestones are generally massive, but include sty­lolitic partings, commonly with a thin residue of clay. Within the Fourth Limestone, highly irregular palaeokarst surfaces have hollows and potholes filled with siliciclastic deposits. Palaeokarsts and palaeosols were described from the concealed Dinantian rocks of the district by Barclay et al. (1994). Several beds within the Fourth Limestone, the 'spotted beds' of Garwood (1913) and the 'Spotted Lime­stone Unit' of Eastwood et al. (1931), are distinguished by colour-mottling termed 'pseudobrecciation'. Limestones of this type are common in the Asbian of northern England, weathering to give a characteristic rubbly appear­ance at outcrop. Mitchell et al. (1978) suggested that pseudobrecciation resulted from bioturbation but it may also be linked to the formation of calcretes (Vanstone, 1996). Most of the limestones are recrystallised to some extent but extensive dolomitisation, except where associ­ated with mineralisation (Chapter 2), is not known. Some of the limestones are bituminous (Eastwood et al., 1931; Young and Boland, 1992). Chert nodules occur in the First and upper parts of the Fourth limestones (Eastwood et al., 1931), nodular anhydrite has been recorded in the Seventh Limestone near Egremont (Llewellyn et al., 1968).

Siliciclastic lithologies include the named 'shales' (Eastwood et al., 1931) and thin mudstone beds within the main limestone units. The 'shales' are mostly less than 10 m thick with the notable exception of the Second Shale, which consists of the 20 m-thick Orebank Sandstone. Sandstones are typically pale grey to buff, fine to medium grained, micaceous and cross-bedded; they grade into calcareous siltstone and shale. Some thin beds of white or pale grey, fine-grained sandstone are termed 'whirlstone' in old borehole logs, a name also applied to some haematised or dolomitised limestone. Black car­bonaceous mudstones, grey-black marine shales and pale grey calcareous siltstones are present in the Fifth Shale. Calcareous mudstones comprise much of the Fourth Shale and grade up into nodular limestone at the base of the Fourth Limestone (Eastwood et al., 1931). Claystone occurs as thin intra-limestone partings, commonly brick red or mottled pale blue and green. Some are bentonitic and may be altered air-fall tuffs (Walkden, 1972; Vanstone, 1996).

Depositional environment

A thin, basal red bed succession represents a range of depositional environments, including coastal alluvial plain, fluvial channels and shallow peritidal zone; all contain locally derived, weathered Lower Palaeozoic detritus. Marine transgression was initiated in late Chadian times, with the development of a carbonate ramp on the gently south-dipping surface of the Lake District Block where sediment accumulated in proximal, inner ramp and coastal environments. Marine transgres­sion was not continuous through into the Holkerian as there are intra-Dinantian unconformities. The base of the Holkerian onlaps over the late Chadian and Basal Beds. The later Holkerian succession represents deposi­tion in generally deepening water, and indicates a range of environments from shallow inshore to successively more offshore inner ramp settings. At the close of the Holkerian, prolonged exposure of the inner ramp allowed the development of a thick soil profile, with a workable coal in the Maryport district. The late Asbian and Brigantian platform carbonate succession accumu­lated in water generally less than 20 m deep, rendering wide areas of the platform emergent during lowstands of sea level. The succession shows a cyclicity similar to that in the southern Lake District and north Lancashire (Horbury, 1989), with shoaling cycles truncated by palaeokarstic surfaces, some of which are overlain by bentonitic palaeosols indicating volcanic ash falls from an unknown source that may have been some distance from the district.

Repeated cycles of rising and falling sea level related to glacio-eustatic and tectono-eustatic influences also resulted in rhythmical changes within the Dinantian limestone facies (Ramsbottom, 1973; Horbury, 1989; Vanstone, 1996; Stabbins, 1969). Periodically, the shelf was inundated by incursions of fluviodeltaic sediments, in particular, the First, Second, Fourth and Fifth shales mark the development of fluviodeltaic conditions. Silici­clastic deposits were transported from the north-east by a major delta system although there may also have been a locally derived component from the Lake District inlier (Stabbins, 1969). The 'shales' commonly have evidence of a marine influence, such as crinoid debris (Young and Boland, 1992), suggesting deposition at the seaward limit of the delta system. This cyclothemic pattern of Yoredale­type sedimentation occurs throughout the Carboniferous of the district and is widespread across much of northern England (Taylor, et al., 1971). Significant non-sequences and disconformities have been detected within Chadian strata; Arundian and early Asbian strata are missing (Table 3).

Stratigraphical succession

Detailed descriptions of the Chief Limestone Group and its component units have been given by Edmonds (1922), Smith, (1924), Eastwood et al. (1931), Butcher (1974),Trotter et al. (1937), Mitchell et al. (1978), Stabbins (1969), Thurlow (1996) and Young and Boland (1992). Only a brief description is presented here and summarised in (Figure 23).

Onshore in the northern part of the district the Seventh Shale ('Basal' or 'Basement' beds of Eastwood et al., 1931 and Mitchell et al., 1978) rests unconformably on reddened Skiddaw Group. To the north of Frizing­ton, the Seventh Shale consists of 1 to 2 m of shale and, in places, conglomerate. Farther south, the unit thickens to 9 m, and comprises mottled shales, coarse-grained sandstones and conglomerates.

The Seventh Limestone comprises thinly bedded, pale grey or brownish grey limestones with interbedded silt-stones and distinctive hummocky cross-bedded calcare­ous sandstones. It thickens southward from 30 to 60 m. Sections in quarries near Wilton [NY 0485 1088] and Frizington Parks [NY 0405 1560] are described by Barclay et al. (1994) who proposed the name Frizington Limestone for this unit. Nodular calcretes occur near the top of the Frizington Limestone in the Sellafield boreholes and in Mousegill Quarry [NY 0485 1090].

The Sixth Shale, 3 to 6 m thick, comprises black shale that may be sandy and interbedded with black nodular limestone. It contains a palaeosol in the Gosforth area and a coal in the Maryport district, which mark the major unconformity between the Holkerian and late Asbian. The upper and lower limits of the unit are poorly defined locally at outcrop, as thin shale interbeds are present in both the overlying and underlying limestones.

The Sixth Limestone is more massive and darker blue-grey than the Seventh Limestone. The upper 10 m is exposed in old quarries at Stockhow Hall [NY 0665 1755] where it is thinly bedded with stylolytic surfaces. It is characterised by subspherical or irregular patches of dark grey limestone, up to 10 cm in diameter, within a paler limestone groundmass, and is attributed (Vanstone, 1996) to development of a calcrete profile.

The Fifth Shale is up to 10 m thick, and comprises a distinct upper and lower section. The lower section con­sists of interbedded dark grey limestone and black car­bonaceous mudstone that grades upwards into a dark grey seatearth. The upper section comprises a coarsen­ing-upwards sequence from dark grey marine shale with chonetid brachiopods and ironstone nodules to pale grey calcareous siltstone and sandstone containing plant remains.

The Fifth Limestone, the lowest of the massive lime­stones, comprises a 20 m-thick sequence of limestone, divided into an upper and lower unit by a thin mudstone bed. The lower limestone unit is dark grey and thickly bedded; the upper limestone unit is paler and more thinly bedded. 'Pseudobreccia' texture is commonly developed. The Fifth Limestone was much quarried and a full section is exposed at Stockhow Hall Quarry [NY 0665 1755].

The Fourth Shale is well known from borehole records although there are now relatively few exposed sections. At Glints Quarry [NY 0080 1240], a 5 m-thick section consists mainly of calcareous mudstone that grades upwards into pale pink or grey micaceous siltstone. Fine-grained silty sandstone is seen at other localities within the district.

The Fourth Limestone comprises 70 m of massive limestone separated by thin mudstone beds and promi­nent palaeokarst surfaces. Subdivisions of the limestone are named according to characteristics such as colour, texture or included fauna (Eastwood et al., 1931; Smith, 1924) (Figure 23). The limestone is exposed in quarries at Glints [NY 0080 1240], Eskett [NY 0540 1680], Salterhall [NY 0600 1750], Kelton [NY 0680 1840], and Pardshaw [NY 0990 2570] and numerous other smaller workings. The named units are, in ascending order, White Limestone, Rough Limestone, Spotted Limestone, Potholes Limestone, Saccammina Limestone, Junceum Limestone and Cherty Limestone.

The White Limestone is a pale grey limestone, 15 to 20 m thick that is 'pseudobrecciated' and characterised by rubbly weathering. It has a nodular or brecciated base intercalated with brick-red clay. True breccias and poss­ibly stromatolitic limestones were reported by Eastwood et al. (1931). Within the limestone, there are thin, red or colour-mottled mudstone beds. The topmost of these, which contains the dasycladacean alga Saccamminopsis sp. distinctive nodular masses of the cyanophyte Girvanella sp., the annelid Spirorbis sp. and ostracods is known as the Girvanella Band (Girvanella Nodular Bed of Burgess and Mitchell, 1976). The Girvanella Band, which is recog­nised widely in northern England, is known to lie just above the base of the Brigantian Stage as defined by coral and brachiopod faunas (Figure 23); (Burgess and Mitchell, 1976; Mitchell et al., 1978).

The Rough Limestone, believed to have been named from its rough appearance on weathered surfaces, is 15 to 20 m thick and bituminous. The Spotted Limestone is pale grey, 6 to 9 m thick, and conspicuously 'pseudobrec­ciated'; alga Saccamminopsis sp. or coral fragments are preserved within the darker nodules. The Potholes Lime­stone is a thick- bedded, pale grey limestone, 6 to 14 m thick, with its top commonly indented by penecontempo­raneous karstic hollows up to 2 m deep, filled with sand­stone and siltstone; the potholes are readily seen at Glints Quarry [NY 0080 1240]. The Orionastraea Band near the top of the Potholes Limestone is a widely corre­lated coral bed containing species of Corwenia, Nemistium and Orionastraea (Mitchell et al., 1978). The Saccammina Limestone is a grey crinoidal limestone with common Saccamminopsis sp. Its upper surface contains penecon­temporaneous karstic hollows filled with red mudstone with abundant Saccamminopsis sp. and a limestone that may be representative of the Erythrospongia Band marker bed. The Junceum Limestone is dark to pale grey and its component beds are characterised by a rubbly texture; the coral Siphonodendron junceum (Fleming, 1828) is locally conspicuous. Chert nodules are common throughout and included fossils may be silicified. It is not easily distinguished from the overlying Cherty Limestone, at the top of the Fourth Limestone, which is also dark grey, thin bedded and rubbly with black chert nodules. The two limestones are together approximately 20 m thick.

The Third Shale comprises 2 m of shale grading upward into sandstone. The shale contains plant debris and the sandstone is described as crinoidal (Eastwood et al., 1931). It increases in thickness from less than a metre near Whitehaven to over 6 m at the northern margin of the dis­trict; it is absent at Hensingham, east of Whitehaven.

The Third Limestone is typically up to 5 m thick. There are very few exposures and little detailed description is available. It is pale to dark grey and contains much crinoid debris.

The Second Shale is also known as the Orebank Sand­stone. It is laterally extensive and comprises shale and sandstone in variable proportion. In the type area at Bigrigg [NY 005 126] it is up to 20 m thick and predomi­nantly of sandstone (Eastwood et al., 1931). Traced northwards to the vicinity of Lamplugh, it becomes thinner and more shaly (Eastwood et al., 1931). It is rela­tively thick north of Lamplugh (Young and Boland, 1992) and sandstones become dominant with a seatearth present in the Broughton area. The sandstones are gen­erally white to buff, fine to medium grained and cross-bedded. They are quartz-rich and contain micaceous layers, rootlets and crinoid debris. Shales and mudstones above and below the sandstone are black, laminated and contain abundant marine fossils.

The Second Limestone is poorly exposed, 5 to 10 m thick, and described as medium to dark grey, argilla­ceous and wavy-bedded with a nodular or rubbly top (Eastwood et al., 1931; Stabbins, 1969).

The First Shale (Little Whirlstone Shale) is laterally extensive, 5 to 7 m thick, and consists of grey to black shale with plant debris and rootlets. It grades up into fine- to medium-grained, pale brown sandstone (Young and Boland, 1992; Stabbins, 1969). Eastwood et al. (1931) recorded a coal at Hensingham.

The First Limestone consists of a medium to dark grey, thickly bedded bioclastic limestone with thin, black shaly partings (Young and Boland, 1992) and is typically 15 to 20 m thick. Vertical joints cut the full thickness of the limestone and are intruded by thin sedimentary dykes of sandstone; discontinuous layers of shell sand are preserved locally in hollows on the bedding planes (East­wood et al., 1931). The limestone is not as abundantly fossiliferous as in many other parts of northern England but contains the Chaetetes Band near the base (Johnson, 1958). The First Limestone was extensively worked in the Hensingham and Distington areas although these work­ings are now infilled. It is still actively quarried at Tendley Hill [NY 088 286].

Concealed formations

Dinantian beds, unconformably overlying Lower Palaeo­zoic rocks but concealed beneath Permo-Triassic strata, are widespread in the district, including the offshore area (Nirex, 1993a). Little is known of these Carbonifer­ous strata that rest unconformably mostly on the Borrowdale Volcanic Group. Six Sellafield boreholes proved a maximum recovered thickness of 149 m of strata of late Chadian to late Asbian age. A thin diachronous silici­clastic facies, of uncertain age, at the base, is overlain by three limestone formations (Barclay et al., 1994).

Basal Beds

Siliciclastic beds up to 2.6 m thick, a diachronous facies at the base of the Dinantian, overlie the sub-Carbonifer­ous unconformity. They consist mainly of poorly sorted, red-brown and grey-brown, crystal-rich pebbly and tuffa­ceous sandstone, siltstone and some conglomerate with interbedded lime mudstone and thin sandy limestone, which were deposited in alluvial to peritidal environ­ments. Barclay et al. (1994) give no evidence for the age of the Basal Beds, but note that in some boreholes they pass into the lowest beds of the Frizington Limestone, suggesting a Holkerian age, but in others they are trun­cated by an erosion surface and may be of Courceyan age as at Blindcrake Gill [NY 1494 3456].

Martin Limestone

The Martin Limestone (Rose and Dunham, 1977; Barclay et al., 1994) has been proved in three of the Sellafield boreholes and ranges in thickness from 6 to 12 m. It is assigned a late Chadian age, from the included foraminiferal assemblage (Barclay et al., 1994), and does not appear to have any correlatives at outcrop to the north. It comprises a thinly bedded succession of sandy packstones, lime mudstones (Dunham, 1962) and fine-grained sandstones. The top of the formation is an erosion surface, overlain by sandstone which is locally conglomeratic. The lithologies reflect mixed carbonate-siliciclastic deposition in a shallow inshore setting with colonisation of the sediments by burrowing organisms and vascular plants.

Frizington Limestone

The Frizington Limestone, equivalent of the Seventh Limestone at outcrop to the north, has been proved in six of the Sellafield boreholes (Barclay et al., 1994). It comprises up to 100 m of thin- to thick-bedded tabular limestone with thin shale interbeds. Two informal members are recognised. The lower member is less than 16 m thick and consists mainly of thin- to medium-bedded sandy and silty limestone which is intensely bio­turbated by burrows and roots. Fenestral lime mudstones and tabular to hummocky cross-bedded sandstones also occur. The upper member is 28 to 73 m thick and comprises mainly medium- to thick-bedded, foraminifera-rich bioclastic packstone and grainstone (Dunham, 1962), in which lithostrotionoid sheets are common, and thin shale and sandy limestone beds. Closely spaced palaeokarstic surfaces and siliciclastic and calcrete palaeosols occur near the top of the formation.

The Frizington Limestone records a change from peri­tidal deposition for the lower member to a shallow sub-tidal environment for the upper member. The sandy lithologies that comprise the relatively thin lower member represent sediment accumulation in close prox­imity to the siliciclastic sediment source. Rhizoliths and fenestral fabrics in the lower member demonstrate colonisation by vascular plants and blue green algae, respectively. The bioclastic limestones within the upper member accumulated in a high energy environment, deposited as shoals and sheets of skeletal carbonate sand within fair-weather wave base. The apparent lack of sedi­mentary structures is probably due to bioturbation. The rocks contain no ooids but micritised peloids are abundant. The development of coral thickets indicates deposi­tion in open marine conditions near fair-weather wave base. The presence of siliciclastic sediment suggests derivation by erosion from the nearby landmass or reworking within the coastal zone. Evidence of sediment deposition under storm conditions is provided by shell coquinas and hummocky cross-stratified sandstone. The presence of lime mudstone that may have fenestral fabrics or are algal laminites indicate deposition in a tidal flat environment. Siliciclastic mudstone and silt-stone beds within the upper member reflect periods of low energy deposition either in deeper water below wave base or in a shallow water lagoonal setting. The geo­chemical characteristics of one mudstone bed in Sellafield 3 Borehole suggest that the bed may be an illitised bentonite. Calcretes, palaeokarst surfaces and terrige­nous deposits are evidence of emergence and subaerial exposure at the top of the formation, marking the break in sedimentation between Holkerian and late Asbian times.

Urswick Limestone

The Urswick Limestone (Rose and Dunham, 1977; Barclay et al., 1994), the concealed correlative of the Sixth, Fifth and lower part of the Fourth limestones was proved in two Sellafield boreholes, with a maximum thickness of 42 m. Several diagnostic foraminifera and coral faunal assemblages demonstrate a late Asbian age for this formation. The formation comprises thin- to very thick-bedded peloid grainstones, with abundant algal bioclasts and foraminifera, as well as packstones and wackestones. The grainstones are interpreted to have been deposited in high-energy shoals, the packstones and wackestones generally in deeper water environ­ments. The formation is characterised by numerous palaeokarst surfaces, formed during periods of subaerial exposure, each overlain by a thin red-brown and green bentonitic palaeosol indicating a component of volcanic dust within the soil. Pseudobreccias are also charac­teristic of the uppermost beds.

Hensingham Group

The Hensingham Group includes rocks between the top of the First Limestone (Chief Limestone Group) and the Subcrenatum Marine Band at the base of the Coal Measures (Taylor, 1961; Mitchell et al., 1978). It com­prises a succession of mudstones, laminated siltstones and sandstones with thin coals. In contrast to other Car­boniferous rocks of the district, the group has been little investigated by boreholes, being relatively poorly exposed and generally of little economic importance. However, important new evidence on the nature of the succession has been obtained recently from British Geo­logical Survey boreholes (Figure 24) at Distington [NX 9967 2331] and Rowhall Farm in the adjacent Maryport district, as well as a new road section at Hensingham.

The Hensingham Group crops out in the northern part of the district to the west of the Chief Limestone Group, where the outcrop is discontinuous and offset by several north-west-trending faults. The main exposures are in disused quarries at Brigham [NY 083 302] (Young and Boland, 1992) and Bigrigg [NY 0052 1270] (East­wood et al., 1931). The group also crops out as inliers at Distington and Hensingham (Figure 1). Stream sections and cuttings in the Hensingham inlier include the sec­tions at Snebro Gill [NX 9835 1685]. The group thickens to the north and east, from 50 m in the Lamplugh area (Young and Boland, 1992) to 110 m and 140 m thick in the Distington and Rowhall Farm boreholes, respectively (Figure 24). This relatively thin Namurian succession on the Lake District Block is separated from the Solway Basin to the north-west by the syndepositional Maryport Fault (Barnes et al., 1988; Chadwick et al., 1995).

In the offshore part of the district, rocks of the Hens­ingham Group or its equivalents are inferred to be widespread from seismic reflection data, and also from boreholes beyond the boundary of the district, but no detailed information is available.

Sporadic faunal evidence confirms the Namurian age of the Hensingham Group (Mitchell et al., 1978; Ramsbottom et al., 1978). Rocks of Pendleian to Arnsber­gian E2b age are proved from the Snebro Gill section and from boreholes at Ullock and Rowhall Farm (Ramsbot­tom et al., 1978; Young and Boland, 1992). Fossiliferous shales and limestones of Arnsbergian age, equivalent to part of the Snebro Gill Beds, have been identified in the Distington Borehole (Figure 24), and near Hensingham. Younger strata formerly exposed at Bigrigg (Mitchell et al., 1978), and in the Ullock boreholes, contain ammonoid faunas proving a Yeadonian to Langsettian age (Eastwood et al., 1931; Young and Boland, 1992). The goniatite Cancelloceras cumbriense (Bisat, 1924) has been found at its type locality in these beds at Bigrigg [NY 0010 1305]. However, these younger strata are absent from the Rowhall Farm Borehole where a major non-sequence has been inferred at the base of the West­phalian (Figure 24).

Stratigraphical succession

At outcrop, the basal part of the group generally com­prises a prominent sandstone, the Hensingham Grit, which is 10 m thick at Hensingham (Eastwood et al., 1931). It thickens northwards to over 30 m at Brigham (Young and Boland, 1992) where, in disused quarries, it forms 10 m high faces of white to buff, fine- to medium-grained flaggy sandstone, containing mica and kaolinised feldspar, with thin mudstone partings. Cross-bed foresets indicate current flow to the south-west.

The overlying parts of the Hensingham Group com­prise a varied succession of mudstone, siltstone, sand­stone, argillaceous limestone and coal (Figure 24). It is not yet possible to erect a single, common succession of named units although correlation between the boreholes and the main natural sections (Figure 24) can be attempted with some confidence.

The sandstones of the group are typically fine to medium grained, white to pale brown, commonly bio­turbated and locally with rootlet beds. Limestones occur as thin beds or lenses within thicker shale units. They are dark grey and contain a diverse marine fauna in which crinoid debris is common. Examination of argilla­ceous rocks proved in boreholes suggest they have a wide range of properties. In the Distington Borehole (Figure 24), mudstones in the Yeadonian part of the succession have a listric fracture and may be carbona­ceous, containing abundant plant remains. In the same borehole, thick beds of dark grey siltstone are finely laminated with laminae and wisps of fine-grained, pale grey sandstone. Mudstones in both the Distington and Rowhall Farm boreholes are very dark grey and give high values on the borehole gamma-ray logs. Coals are generally only a few centimetres thick. They characteris­tically overlie pale grey to greenish grey mudstone or siltstone seatearths.

Cyclical Yoredale-type sedimentation established in the Dinantian continued, in modified form, into the Namurian (Taylor, et al, 1971; Chadwick et al., 1995). Six Yoredale-type cycles can be identified in the Hensingham Group of the Rowhall Farm and Distington boreholes (Figure 24). In the latter borehole, no limestone beds are present but a similar pattern of cyclothems from marine shale through to sandstone with coal can be correlated.

In the first cycle, the Hensingham Grit is interpreted as the deposits of an extensive river system that pro-graded from the north and terminated the shelf carbon­ate deposition of the First Limestone (Ramsbottom, 1977; Young and Boland, 1992). After this initial influx, the supply of coarse-grained sediment diminished and a cyclic sequence of mainly fine-grained rocks, mudstone, siltstone and coal, marks a change from marine to deltaic conditions. Impure limestone and mudstones within the Snebro Gill Beds were deposited during periodic marine incursions. Coarse-grained sandstone and a thin coal, the Udale coal, top the Snebro Gill Beds. At or above the base of the coal, a significant non-sequence has been inferred between strata of Arnsbergian and Yeadonian age, although no angular unconformity has been recorded (Eastwood et al., 1931; Mitchell et al., 1978) (Figure 24). The district may have been emergent during this period, or sediment may have continued to accumu­late prior to later erosion. Dark grey carbonaceous mud-stones, grading into siltstones with seatearths, complete the section up to the base of the Westphalian.

The cyclical sedimentation pattern of the Namurian rocks and rapid evolution of the included fauna allows correlation throughout Northern England (e.g. Ramsbottom et al., 1978; Chadwick et al., 1995). A key correlation point within each cycle is the basal marine facies, which typically comprises limestone or thin dark grey mudstone with high gamma-ray responses in geo­physical logs. Some mudstone beds contain a characteris­tic ammonoid fauna but only rare examples have been recorded in west Cumbria. The correlation between the First Limestone and the Great Limestone of the North­ern Pennines is long established (Edmonds, 1922; Ramsbottom et al., 1978). Equivalents of the Little Limestone and perhaps, less certainly, the Crag, Upper and Lower Felltop limestones and Coalcleugh Shell Bed of the Northern Pennines are recognised in the Rowhall Farm and Distington Boreholes (Figure 24).

Coal Measures

The district includes the southern part of the West Cumbria Coalfield in which workings extend for up to 5 km offshore from Whitehaven. Onshore, the Coal Measures are 300 to 400 m thick; they are considerably thinner but of similar lithology to those found in most other English coalfields. Offshore, in the north-west of the district, Westphalian strata thicken into the Solway Basin; a thinner sequence is preserved in the south­west district (Taylor, 1961; Jones, 1992; Jackson et al., 1995).

The first comprehensive account of the Coal Measures by Eastwood et al. (1931) did not attempt a biostratigraphical classification. Expansion of the coal mining industry after World War II produced a wealth of data from which Calver (in Taylor, 1961) compiled a correlation of the fossil faunas and divided the Cumbrian Coal Measures into standard bivalve zones. Eight key marine bands within the succession were also defined. Only two contain ammonoids, the remainder contain a restricted assemblage with foraminifera, Lingula sp. and fish remains. In a later synthesis, Calver (1968) proposed a correlation with other coalfields and identified the subdi­visions Westphalian A, B, C (now renamed Langsettian, Duckmantian and Bolsovian) and Westphalian D within the Cumbrian succession (Ramsbottom et al., 1978) (Figure 25).

The position of the Subcrenatum Marine Band defin­ing the base of the Langsettian is well established from boreholes throughout the area (Taylor, 1961). The succeeding Honley, Listeri, Amaliae and Langley marine bands may all be present in the northern part of the Coal Measure crop, but over much of the Whitehaven area their stratigraphical position is occupied by a thick sand­stone, the Harrington Four Foot Rock.

The Vanderbeckei Marine Band, defining the base of the Duckmantian, is poorly developed in the coalfield. Its position has been inferred from a 'mussel' band (Eastwood et al., 1931) or the presence of fish remains (Taylor, 1961). The Aegiranum Marine Band, defining the base of the Bolsovian, and the preceding Haughton Marine Band are recorded from the Whitehaven coastal collieries and to the north of Distington (Taylor, 1961). However, over most of the district the Aegiranum Marine Band, and higher marine bands appear to be cut out below the unconformable base of the Whitehaven Sand­stone, although the sandstone is itself never older than the Cambriense Marine Band (Figure 25).

The Coal Measures crop out in the northern part of the district to the west of the Chief Limestone and Hensingham groups (Figure 1). They are exposed continuously in cliff sections from Harrington [NX 986 242] to Saltom Bay [NX 961 163], but inland much of the outcrop is concealed beneath Quaternary deposits and there are few natural exposures. Sections described by Eastwood et al. (1931) include stream gullies in the valley of the Distington Beck, for example at Stubsgill [NY 015 230], and the Dean Moor escarpment, for example Thief Gill [NY 047 225]. Apart from temporary sections in opencast pits, exposures are mainly confined to aban­doned workings in sandstones and claystones, for example Barngill Quarry [NX 9985 2190] (Sixquarters Rock), Whitehaven brickclay quarry [NX 9720 1672] and Colingate [NY 0385 2308] (Main Band Rock).

Sandstones are abundant in many parts of the succes­sion, and are prominent in coastal cliffs. They are gener­ally fine to medium grained and pale grey in colour, although generally they are either stained brown or orange by iron oxides or darkened by finely dissemi­nated carbonaceous material. Fine-grained, thinly lami­nated, micaceous, typically buff-coloured sandstone forms thick units such as the Main and Bannock Band rocks. Individual channel units with erosive bases, pebble lags and abundant ironstone nodules are exposed at Lowca [NX 978 220] in the Tenquarters and Bannock Band rocks (Figure 25).

Mudstone and siltstone occur within coarsening-upwards sequences. Black mudstone forms distinct thin units, usually massive or with a fine 'papery' lamination, which grade into carbonaceous shale and soft coal. Dark mudstone of this type is characteristic of the marine or Lingula beds. Blue-grey or pale grey, laminated mud-stone or shale that grades into siltstone is more common and apart from abundant plant material, these beds are typically unfossiliferous. Clay ironstones occur within some mudstones and have been worked locally.

Coals form only a minor component of the succession. Individual seams range from a few centimetres up to 3 m thick, as in the Main Band Coal. Low in the succession, coal occurs as single seams, but at higher levels split seams separated by seatearths or shales are common. The general thickening of the measures towards the north-west is associated with thickening of strata between split seams (Taylor, 1961). Pyrite is common in some seatearths and coals. Seatearths occur throughout the Coal Measures and may be much thicker than the associated coal seam. Lithologically, they range from hard siliceous sandstone (ganis­ter) to siltstone or claystone. Some clay-rich seatearths constitute fireclays which have been worked locally.

Depositional environment

The depositional environment of the west Cumbria Coal Measures is typical of the north European Westphalian. The succession was deposited on a gently subsiding delta plain, traversed by a sediment-charged river distributary system. Silt and mud were deposited in a low-energy envi­ronment and periodic emergence allowed the develop­ment of coal swamps. These low-energy conditions were recurrently and abruptly terminated by episodic floods that swept sand and silt into the area, mainly from the west (Jones, 1992; Rippon, 1996). River channels, com­monly infilled by sandstone, eroded through the under­lying strata creating 'wash-outs'. Locally, several channel sandstones are stacked vertically together, for example, the Bannock Band Rock directly overlies the Main Band Rock (Figure 25).

Episodes of marine encroachment from the west (Calver, 1968) occurred briefly at the beginning of the Langsettian and again the end of the Duckmantian; other incursions were of brackish water. Periodically, extensive freshwater lagoons developed sufficient depth to allow localised lacustrine delta formation (Jones, 1992).

Stratigraphical succession

Very detailed geological successions are recorded from mine workings. Since the advent of systematic opencast exploration a more standard nomenclature has been established for the Cumbria coalfield. Alternative seam names, some still in use but others obsolete, are widely used on mine plans and borehole records and these are presented in (Table 4). Palaeontological study of both marine and nonmarine fossils has provided a chronostratigraphical framework for the coalfield (Ramsbottom et al., 1978; Taylor et al., 1971). The local nomenclature of coal seams, sandstones and prominent fossiliferous shales is shown in (Figure 25).

The Lower Coal Measures have a relatively uniform thickness across the coalfield. Several coarsening-upward cycles are present, each culminating in a thick fluvial sandstone. Coals are few in number but laterally persistent.

The lowest coal, the Harrington Four Foot, is recog­nised across the whole coalfield and has been worked in a number of places, notably near Distington. It is a few metres above the Subcrenatum Marine Band. It is over­lain by the Harrington Four Foot Rock, a 30 m thick sandstone found in all but the extreme north of the outcrop. The Harrington Four Foot Rock is commonly the only stratigraphical marker indicating the base of the Coal Measures in old borehole records. Northwards, it passes laterally into a sequence of shale with four marine bands and a set of thin coals known collectively as the Albrighton or Albright coals (Figure 25).

The Lower and Upper Threequarters coals are closely spaced, and may include a third higher seam called the Wythemoor Parrot. These were worked only in the north of the outcrop area and are associated with the overlying Threequarters Rock sandstone (Figure 25). The Lower Threequarters Coal is also called the Micklam Fireclay Coal (Table 4) from its association with the seatearth for­merly worked at the Micklam brickworks at Lowca [NX 981 223].

The next cycle contains the Sixquarters Coal and over­lying Sixquarters Rock sandstone. The seam is one of the prime coals of the area, both onshore and offshore. The overlying sandstone is a regionally prominent channel sandstone body which has also been worked for building stone, for example from Barngill Quarry [NX 9985 2190] and Schoose Quarry [NY 0124 2784]. The overlying sequence of mudstones contains minor discontinuous sandstones and three main coals, the Lickbank, also seen in Barngill Quarry, and the Eighteen Inch and Little Main seams.

The Vanderbeckei Marine Band, which occurs approx­imately 15 m above the Little Main seam, marks the base of the Duckmantian Middle Coal Measures. Above this marine band the lower 30 m of the Middle Coal Mea­sures are fine-grained with a number of stratigraphically significant 'mussel' bands (Eastwood et al., 1931) and coals which are mainly of indifferent quality except for the Yard Coal (Figure 25).

The Middle Coal Measures above the Yard Seam show a more pronounced cyclicity. Relatively thin units of mud-stone with coal occur between 25 to 35 m-thick sandstones. This sequence contains the Main Band and Bannock Band coals which are the most widely exploited seams of the dis­trict; both seams are commonly split into several leaves which may be named separately (Figure 25). The seams are overlain by the Main Band and Bannock Band rocks that are typically thick successions of fine-grained, thin-bedded sandstones. The base of both these sandstone units is erosive and 'wash-outs' are common.

The Bannock Band Rock is overlain by a 50 to 70 m of strata that consist mostly of mudstone and includes three major coals. The Tenquarters, Slaty and White Metal coals form an evenly spaced triplet easily identified in borehole records. In the north of the district the Tenquarters Rock sandstone, overlying the lowest coal, forms a prominent coastal cliff north of Parton.

The Countess Pit Sandstone above the White Metal Coal is extensive and thick; it forms a 20 m-high coastal cliff from Parton southwards to Whitehaven and is encountered in boreholes throughout the coalfield. The Countess Pit Sandstone marks the upper limit of major workable seams in the district. The sedimentary sequence between the top of this sandstone and the base of the Whitehaven Sandstone (described below) is char­acterised by marked lateral variations in lithology. A number of coal seams are present but are thin, with the exceptions of the Black Metal and Brassy seams. Where the coals have no long-established local name, or obvious regional correlative, the Opencast Executive has included them as 'unnamed' seams in their standard nomenclature (Table 4), (Figure 25). Barnes et al. (1988) introduced local names for some of these coals.

In the coastal collieries, the strata between the Countess Pit and Whitehaven sandstones comprise several mudstone and sandstone cycles with coals and the Haughton, Aegiranum and Cambriense marine bands (Figure 25). The Aegiranum Marine Band marks the boundary between rocks of Duckmantian and Bolsovian age (Jones, 1992). Eastwards, this succession is progressively dominated by mudstones with a few unnamed thin coals which cannot be easily correlated with the coastal section; no marine bands have been recognised. This change may be due to thinning of the section coupled with erosion at the unconformable base of the overlying Whitehaven Sandstone.

Whitehaven Sandstone Formation

The Whitehaven Sandstone Formation is a red bed suc­cession, at least 300 m thick overlying the Coal Measures. The name was introduced by Kendall (1896) and used by Eastwood et al. (1931); here it is termed the Whitehaven Sandstone Formation to conform with current stratigraphical use. The rocks were first described by Sedgwick (1832) who classified the sandstones as Permian despite recognising the presence of plant debris indicative of Carboniferous rocks. He also suggested that the forma­tion had an unconformable base. The discovery of the annelid Spirorbis sp. led Brockbank (1891) to include the beds with the Westphalian Coal Measures. The formation comprises two members, the Whitehaven Sandstone and Millyeat Beds members (Figure 26).

The stratigraphical position of the rocks is problemati­cal. In common with other British late Carboniferous red beds, their exact age and relationship to apparently coeval but un-reddened Coal Measures have long been a topic of debate. The key issue had been whether the rocks were a separate red bed formation resting uncon­formably on the Coal Measures or alternatively, part of the Coal Measures succession which had undergone sec­ondary reddening.

Kendall (1896) and Eastwood et al. (1931) favoured the first interpretation, the latter mapping the Whitehaven Sandstone with an unconformity at the base and noting also that certain lithological features of the Whitehaven Sandstone are not seen in the underlying Coal Measures. An origin due to secondary reddening was favoured by Taylor (1961) who described reddening of normal Coal Measures strata below unconformable Permian strata in boreholes at St Bees. He asserted that in light of regional work on red beds by Trotter (1953) the whole of the Whitehaven Sandstone should be regarded as reddened Coal Measures, a view supported by Barnes et al. (1988) and Young and Boland (1992). However, recent sedimentological studies have demon­strated that the Whitehaven Sandstone Member has a sedimentological architecture that distinguishes it from unconformably underlying Coal Measures and is here regarded as within a separate overlying formation (Jones, 1992). Although, neither an erosion surface nor an angular discordance is seen at outcrop, a comparison of borehole records across the district demonstrates that the base of the Whitehaven Sandstone Formation is unconformable, overlying beds down to the Aegiranum Marine Band or, locally, older strata (Figure 25). Boreholes at the Studfold Opencast Coal Site [NY 040 212] indicate that there the Whitehaven Sandstone may overlie the Fireclay Coal, although the succession there is likely to have been disturbed by landslip.

The age of the Whitehaven Sandstone Formation is poorly constrained but is assumed to be Bolsovian to Westphalian D (compare Taylor, 1978). The Whitehaven Sandstone has yielded very few fossils with only plant remains and a single zonal nonmarine bivalve Anthraco­nauta phillipsii (Williamson, 1836) listed by Eastwood et al. (1931). Kidston, quoted by Eastwood et al., assigned the plant remains to the Staffordian which, together with the bivalve evidence, is compatible with a late Bolsovian or Westphalian D age for the upper part of the forma­tion. A Westphalian D Tenuis Zone fauna occurs in similar strata farther north-east in the Cockermouth dis­trict (Eastwood et al., 1968), but a reliable correlation with the Whitehaven area cannot be established.

Whitehaven Sandstone Member

The Whitehaven Sandstone Member is over 100 m thick; it forms spectacular coastal cliffs at Whitehaven and caps the area of high ground to the east and north-east of the town. It consists mainly of cross-bedded, micaceous, medium- to coarse-grained sandstones with a characteris­tic red to deep purple or purplish brown colour. The coarsest beds commonly include angular grains, and some have been described as having an 'ashy' appear­ance due to grains of kaolinised feldspar (Eastwood et al., 1931). Clasts of mudstone, termed 'clay galls' by East­wood et al. (1931), are common throughout the sand­stones and, locally, red sandstone clasts up to boulder size occur at the base of individual channels. Coal frag­ments may also be present. Coarse- to very coarse-grained, deep red, cross-bedded sandstones with clay galls were exposed in the River Keekle diversion in the Keekle Extension Opencast Coal Site [NY 01 17]. Lami­nated and cross-bedded mudstone and siltstone, gener­ally pink to red or grey in colour, are interbedded within the sandstone. Thin palaeosols containing rootlets with a marked concentric colour zonation are locally present.

Millyeat Beds Member

The Millyeat Beds Member is a lithologically varied suc­cession of fine-grained red beds that was not previously named. It is here defined from the type section in the Frizington Hall Borehole [NY 019 171], in the vicinity of Millyeat; it is also proved in a borehole at Millyeat [NY 023 178] and is exposed in the Dub Beck [NY 022 175] (Brockbank, 1891; Eastwood et al., 1931). It is a sequence of mudstone, sandstone and marl with thin coals and includes thin beds of limestone with Spirorbis sp. In the type section the member is 180 m thick, its base is marked by a bed of claystone and marl which overlies a thick sandstone sequence of the Whitehaven Sandstone Member. The top of the member is marked by the unconformity at the base of overlying Permo-­Triassic rocks. Eastwood et al. (1931) considered that these beds overlay lateral equivalents of the Whitehaven Sandstone exposed at the coast, a view supported here although unconfirmed as no borehole has penetrated the full succession. The stratigraphy of the formation is summarised in (Figure 26).

The Millyeat Beds Member at outcrop in Dub Beck [NY 022 175] consists of white, red or colour-mottled shale and mudstone. In Frizington Hall Borehole, Brock-bank (1891) described green or mottled marls and grey fireclays; the latter are presumed to be seatearths. Two white, cream or purple limestones, each up to 1 m thick and containing Spirorbis sp. and ostracods were recorded from the Millyeat Beds Member (Eastwood et al., 1931). Three thin coals were also reported from boreholes and one crops out near Whitehaven Harbour [NX 974 192]. They are only a few centimetres thick and of no commer­cial value. Eastwood et al. (1931) speculated that they may be equivalent to the Senhouse High Band Coal, the highest seam worked in the Maryport district.

Depositional environment

The Whitehaven Sandstone Member is interpreted as a multistorey and multilateral sand body complex, deposited by a major braided river system which flowed across the area from the north-east. Laterally equivalent strata may be present in the Canonbie Coalfield 50 km to the north-east (Lumsden et al., 1967; Taylor et al., 1971; Picken, 1988). Abundant, coarse-grained detritus trans­ported by this river system differed from that which formed the underlying Coal Measures sandstones. Between the river channels, areas of vegetation growth and limited coal swamps were established showing that the environment was not arid at that stage.

During accumulation of the overlying Millyeat Beds Member the river system either switched to a position away from the district, or the sediment supply became restricted. Deposition of fine-grained sediment in inter-distributary or lacustrine environments became domi­nant, but minor river channels continued to deposit laterally impersistent sand beds. Coal-forming conditions rarely developed. The appearance of limestone with Spirorbis sp. and marls (Figure 26) is interpreted as a change to a drier climatic regime. Under these condi­tions the limestone is considered to have formed in shallow, well-oxygenated lakes that were possibly brackish due to high evaporation rates (Besley, 1983).

Red colouration is a notable characteristic of the Whitehaven Sandstone Formation. Much of the iron may have been deposited directly as haematite, under oxidis­ing conditions (primary reddening) or transformed from other states by pedogenic or diagenetic processes including interaction with meteoric water (secondary reddening). The presence of palaeosols and rootlet beds, which indicate that waterlogged conditions existed from time to time, suggest that some at least of the red­dening may be of secondary diagenetic origin. The dif­ference in colour between lithologies indicates that per­meability may have been a controlling factor. Red rocks of the Whitehaven Sandstone Formation are juxtaposed against un-reddened Coal Measures by pre-Brockram faulting so the process of reddening is most likely to be late Carboniferous in age. Reddening may have been associated either with a syndepositional change to an oxidising environment or with post-depositional Variscan uplift.

The widespread reddening of Carboniferous and older rocks beneath the sub-Permo-Triassic unconformity is considered in Chapter 6.

Chapter 6 Permian and Triassic

Permo-Triassic rocks crop out in the coastal area of west Cumbria and are extensively developed offshore in the East Irish Sea Basin beneath Quaternary deposits (Arthurton et al., 1978; Jackson et al., 1987, 1995; Nirex, 1993a) (Map 4), (Figure 1), (Figure 27). Onshore, Permo-Triassic forma-dons are well exposed around St Bees Head and along the valley of the River Calder but elsewhere exposures are patchy and detail is scarce (Eastwood et al., 1931; Trotter et al., 1937; Barnes et al., 1994). Additional information is available from the abandoned Sandwith anhydrite mine (Arthurton and Hemingway, 1972) and from numerous boreholes, including the Sellafield boreholes (Figure 3); (Nirex, 1993a; Michie and Bowden, 1994; Barnes et al., 1994; Jones and Ambrose, 1994; Strong et al., 1994). Apart from a few shallow boreholes, there is no direct informa­tion relating to Permo-Triassic rocks in the offshore dis­trict, but their structure and distribution have been deduced from the study of seismic reflection profiles (Jackson et al., 1987, 1995; Nirex, 1993a) (Figure 28).

The district straddles the north-eastern margin of the East Irish Sea Basin, which is the largest and deepest of a series of linked Permo-Triassic extensional basins on the western side of Britain, extending from the Worcester and Cheshire basins, in the south, to Northern Ireland and the Firth of Clyde, in the north (Jackson et al., 1987, 1995) (Figure 27). The East Irish Sea Basin was initiated by extensional, fault-controlled subsidence, locally associated with alkali basalt volcanism, which began during the Permian, and continued periodically throughout Triassic into Jurassic times (Chapter 3). Initially, in Permian times, sedimentation was restricted to the area west of the Lake District Boundary Fault. Subsequently, all younger Permo­-Triassic formations thinned stratigraphically onto the block (Figure 28). From Late Permian into Early Jurassic times, sedimentation gradually spread onto the footwall blocks of structural highs (Jackson and Mulholland, 1993). In Late Triassic times local sediment sources were probably buried, as a single regional pattern of deposition was established throughout the basin and beyond.

For ease of description and understanding, current onshore lithostratigraphical nomenclature is also employed offshore in this account, although this differs in some important details from that recently proposed for the offshore East Irish Sea Basin by Jackson and Johnson (1996) (Table 5). Rocks of the Appleby, Cumbrian Coast and Sherwood Sandstone groups crop out onshore and are present throughout much of the offshore district (Figure 1). The overlying Mercia Mudstone Group is extensive off­shore, but does not crop out onshore in the west Cumbria district. The Late Triassic Penarth Group has not been con­firmed, but it is probably present beneath the Early Jurassic rocks which occur locally in the East Irish Sea Basin and which are thought to extend into the south-western part of the district (Figure 1); (Jackson et al., 1995; Nirex, 1993a).

Sub-Permian Unconformity

During the main pulses of the late Carboniferous Variscan Orogeny (Chapter 3), and into Early Permian times, the district underwent a long period of erosion. On the Lake District Block, all of the Carboniferous cover was removed locally so that Lower Palaeozoic rocks were exposed (Figure 29). In the north-west of the district up to 5 km of Carboniferous rocks were eroded away and rocks as old as early Dinantian were exposed over a significant area.

The seismic reflection data suggest that in much of the dis­trict the sub-Permian unconformity is generally subparallel with, or at a low angle to, the dip of the underlying Car­boniferous strata (Figure 28). Study of the seismic data and the limited exposure of the unconformity around the Lake District suggests that, by Early Permian times, the district had been largely peneplained with only local relict relief (Jackson et al., 1987; Nirex, 1992d). This situation was dra­matically changed by the initiation of Early Permian rifting and associated sedimentation.

Sub-Permian reddening

A characteristic feature of the sub-Permian unconformity is the pervasive and locally deep reddening of the under­lying strata (Taylor, 1978; Jackson et al., 1987). It affects every pre-Permian formation, is related to the Early Permian land surface and developed during the long period of non-deposition (20–30 Ma) associated with the Variscan Orogeny. The most extensive reddening is com­monly associated with fractured and faulted ground. The zone of reddening is characterised by the oxidation of ferrous iron minerals and the precipitation of ferric oxides and ranges in thickness from a few centimetres to locally more than 500 m below the unconformity. The normally grey Hensingham Group, together with the Lower and Middle Coal Measures are reddened below the unconformity, with coal and carbonaceous matter largely oxidised and pyrite converted to haematite and gypsum. The Dinantian limestones are commonly dolomitised close to the unconformity, and Lower Palaeozoic rocks are also locally altered and reddened.

Stratigraphical interpretation is made more difficult by the presence of originally red Carboniferous strata, such as the Bolsovian to Westphalian D, Whitehaven Sand­stone Formation (Chapter 5). These may be difficult to distinguish from secondarily reddened rocks underlying the pre-Permian unconformity, for example, reddened strata in some East Irish Sea Basin hydrocarbon wells, once thought to be Permian, were reclassified because they are now known to be Carboniferous in age (Jackson et al., 1987).

The origin of the reddening has not been fully estab­lished. It may reflect, in part, deep oxidative weathering under arid climatic conditions during the Permian, when the contemporary water table would have been at a low level (Johnson et al., 1997). The reddening may also be related to hydrothermal fluid movement along highly permeable zones beneath the unconformity surface. In this respect, it may be related to the major regional hydrothermal haematite mineralisation which is exten­sively developed in the district (Chapter 2).

Appleby Group

Brockram and Collyhurst Sandstone Formation

Brockram is a general lithological term traditionally applied to Permo-Triassic breccias and conglomerates in north-west England. In west Cumbria it also has a more formal lithostratigraphical definition as the basal unit of the Permo-Triassic succession. The Brockram, on the western periphery of the Lake District Block, was formerly considered to be a lateral equivalent of the St Bee Evaporite, St Bees Shale and lower part of the St Bee Sandstone formations (Trotter et al., 1937; Arthurton et al., 1978). A breccia beneath the St Bees Evaporite around St Bees Head, which is only a few metres thick was believed to be a distinct older deposit and termed 'Basal Breccia' by Arthurton and Hemingway (1972) However, boreholes in the central district, notably the Sellafield 3 Borehole, have proved more than 150 m of Brockram below the St Bees Evaporite, indicating that much of the Brockram is older than previously supposed However, close to the Lake District Block, the upper part of the Brockram, which locally comprises interbedded breccia, sandstone, siltstone and claystone, is thought to be equivalent to the St Bees Evaporite/Shale (Nirex 1993e) (Figure 30a), (Figure 30b), (Figure 30c), (Figure 30d), (Figure 30e), (Figure 30f), (Figure 31) and (Figure 32).

The western limit of the Brockram is presently unknown. At the same stratigraphical level, beyond the district in the East Irish Sea Basin, well-rounded and sorted, medium- to coarse-grained, cross-bedded aeolian sandstones of the Collyhurst Sandstone have bees proved in many boreholes (Jackson et al., 1995). It is probable that these sandstones interfinger with the Brockram offshore within the district. A similar inter-fingering of Brockram and sandstones of aeolian and fluvial facies (Penrith Sandstone) is known to the east of the Lake District in the Vale of Eden (Arthurton et al., 1978).

The Brockram comprises coarse, poorly bedded, poorly to moderately sorted, generally massive, matrix- or clast-supported breccias. Details of the main facies types recognised are summarised in (Table 6). Clasts range from granule to cobble grade, but are typically of pebble grade. Most are local in origin and are subangular to angular with only a few that are subrounded to rounded. Clasts of Carboniferous Limestone are abundant at outcrop; in the Sellafield boreholes they are largely restricted to the lower parts of the Brockram where it immediately overlies the Dinantian rocks. Elsewhere in these boreholes, the clasts are almost exclusively derive, from the Borrowdale Volcanic Group, with minor debris of granitic composition likely to have been derived from the Eskdale and Ennerdale intrusions; rare intraformational clasts also occur.

Olivine basalt lavas, or breccias with basalt clasts, are locally associated with the Early Permian rocks in the Irish Sea and Morecambe Bay (Rose and Dunham, 197; Penn et al., 1983; Jackson and Johnson, 1996), but non are known within the district.

Coarse-tail grading, in which the maximum clast size decreases upwards, and inverse coarse-tail grading, in which the maximum clast size increases upwards, are common. The matrix ranges from mudstone to very poorly sorted fine- to very coarse-grained sandstone granules and very small pebbles; it is generally weakly calcareous. The matrix shows inverse and normal grading in places. Imbrication is locally visible, but cross-bedding is rare.

Marked, localised thickness changes in the Brockram suggest that contemporary faulting was a major influence on sedimentation. Coarse, locally derived, poorly sorted and commonly angular detritus within the Brockram may also be indicative of actively eroding fault-scarps. Seismic reflection data (largely to the north of the district) show clear evidence of thinning and pinch out of the Appleby Group onto the Lake District Block (Figure 28).

Conditions of deposition

The Brockram is interpreted to be the deposits of a series of alluvial fans, which formed in response to an abrupt change in gradient at the faulted western margin of the Lake District Block, probably in response to the onset of normal faulting following post-Carboniferous erosion and peneplaination (Figure 30a). The Brockram has much in common with modern-day alluvial fan deposits, exemplified by the localised nature of the deposit, rapid thickness changes, locally derived sediment, coarse grain size, angularity of clasts and dominance of gravity flow pro­cesses. In detail the Brockram shows affinities with modern day, gravity flow (semi-arid) fans, which are common in tectonically active, semi-arid to arid set­tings in which debris flow deposition is the dominant process (Schumm, 1977, p.246; Collinson, 1996, p.59). Debris flows are generated by periods of intense, heavy rainfall; they are often associated with sheet flood and sieve deposits as flood events wane. Intermittent depo­sition on these fans is indicated by the occurrence in some of the Sellafield boreholes of immature soil pro­files (calcrete).

Cumbrian Coast Group

St Bees Evaporite Formation

Following deposition of the relatively thin early Permian succession in the East Irish Sea Basin, a major period of widespread subsidence and sedimentation commenced, with expansion of the area of deposition. Apart from the immediate vicinity of the Lake District Block, the whole of the district seems to have been inundated by the marine transgression of the Bakevellia Sea (Arthurton et al,. 1978; Jackson et al., 1987, 1995; Smith and Taylor, 1992) which led to the deposition of the St Bees Evapor­ite Formation (Table 5). Only the basal carbonate member (formerly Magnesian Limestone)is well exposed onshore, notably in Saltom Bay (Eastwood et al., 1931; Arthurton and Hemingway, 1972). The remainder of the formation is known principally from boreholes (Figure 32); (Arthurton and Hemingway, 1972) and, near Whitehaven, from old mine workings.

The St Bees Evaporite Formation comprises a varied sequence of limestone, dolomitic limestone, dolomite, anhydrite (hydrated to gypsum near surface), sandstone, siltstone and mudstone (Arthurton and Hemingway, 1972; Arthurton et al., 1978; Jackson et al., 1987, 1995; Nirex 1993a). Halite has been proved in East Irish Sea Basin boreholes, beyond the margins of the district, and is probably present within the district in offshore areas. Siliceous nodules in anhydrite at the Sandwith Mine near St Bees have been described by Harrison (1975). The for­mation is up to 50 m thick in the St Bees area (Arthurton and Hemingway, 1972) and in the Sellafield boreholes (Nirex, 1993a), and locally exceeds 200 m offshore, par­ticularly where the succession is dominated by halite (Jackson et al., 1987, 1995).

A broadly defined facies distribution can be recognised within the St Bees Evaporite Formation. Carbonate and siliciclastic rocks occur largely on the totally or partially fault bounded, western margin of the basin. Farther from the margins, anhydrite is typically the main rock type developed, with halite commonly the main lithology in the basin centre (Jackson et al., 1987). The formation is largely of sabkha and shallow water origin near to the basin margin (Arthurton and Hemingway, 1972). Not enough is known of the evaporites of the basin centre to assess their depositional environment with certainty.

In detail the stratigraphy of these beds is complex and correlation between the onshore boreholes around St Bees and Gosforth, and between these and the offshore boreholes, is problematical. In the type area around St Bees, the succession has been divided into three carbonate-evaporite cycles by Arthurton and Hemingway (1972): Saltom, Sandwith and Fleswick (Figure 31). Four evaporite cycles have been recognised offshore (Jackson et al., 1987 and 1995) but the relationship between the offshore and onshore cycles, and their correlation with the well-established standard Zechstein cyclic succession and sequence stratigraphy of the Southern North Sea Basin (Taylor, 1990; Tucker, 1991), is poorly understood (Jackson, 1994).

A marine fauna is present locally in the carbonate beds, comprising principally the bivalves Bakevellia binneyi (Brown, 1841), Permophorus costatus (Brown, 1841) and Schizodus obscurus (J. Sowerby, 1821) and a micro-flora is known from the basal part of the formation (Pattison, 1970; Arthurton and Hemingway, 1972; Nirex, 1993e). These assemblages suggest a correlation with the first two cycles of the Southern North Sea Basin Zechstein succession.

St Bees Shale Formation

The only significant outcrop of the St Bees Shale Forma­tion within the district is at Saltom Bay, where the uppermost few metres are exposed (Eastwood et al., 1931). The nature and variation of the formation, there­fore, has been largely inferred from boreholes. The for­mation is, in part, a lateral equivalent of the St Bees Evaporite Formation forming, with the higher parts of the Brockram, a siliciclastic facies association around the margins of the evaporite basin (Figure 31). Higher beds, overlying the carbonate-anhydrite-halite rocks, are transitional with the overlying St Bees Sandstone. The position of the Permian/Triassic boundary is placed near the top of the St Bees Shale (Warrington et al., 1980; Holliday, 1993a).

The St Bees Shale Formation consists of siltstone and very fine-grained sandstone, with subordinate claystone and fine- to medium-grained sandstone. The formation is known in detail from the Sellafield boreholes, in which interlaminated anhydrite and siltstone beds occur in the lowest 20 m of the succession. Gypsum veins are present throughout, mostly as anastomosing or regular networks of fibrous veins associated with evaporite dissolution col­lapse breccias. Nodules of gypsum, anhydrite, dolomite and silica are also locally present, becoming more common toward the base of the succession. Interbedded breccia facies, containing clasts that are more rounded and finer grained than within the Brockram, occur near the margin of the Lake District Block.

Offshore, in Borehole 112/25A-1, there are around 100 m of shales between the evaporites and the overlying St Bees Sandstone (Jackson et al., 1987 and 1995). The formation thins abruptly towards the Lake District Block and is overlapped by the St Bees Sandstone Formation (Jackson et al., 1987). In detail, however, there is much thickness variation, particularly where the St Bees Evap­orite Formation is well developed. The maximum thick­ness in marginal areas, where there was only limited evaporite deposition, is around 200 m in south Cumbria (Arthurton et al., 1978).

The top of the formation is taken at the base of the first significant sandstone bed of the St Bees Sandstone For­mation (Barnes et al., 1994). The junction is transitional, with alternations of sandstone and mudstone above this level. Study of the Sellafield boreholes demonstrates that there is an abrupt change in the nature of locally derived clastic sediment at or close to this boundary (Nirex, 1993e). Coarse proximal breccias die out abruptly just below the St Bees Shale/St Bees Sandstone boundary. Above, only a scattering of small clasts and lithic sand grains derived from the Borrowdale Volcanic Group are present over a limited thickness.

Three main facies types have been noted within the formation in the Sellafield boreholes, an irregularly lami­nated facies, a regularly laminated facies, and a clay­stone-siltstone facies. These facies are considered to be typical of the district as a whole. They are interbedded with beds of matrix- and clast-supported breccia (in places, as described above).

Irregularly laminated facies

This facies consists of beds of siltstone and very fine-grained sandstone 0.5 to 5 m thick. The most conspicu­ous feature is an irregular wavy lamination due to the presence of contorted, convoluted lenses of sandstone (Plate 5). The lenses (sand patches of Smoot and Olsen, 1988) are of fine- to medium-grained sandstone, 1 to 2 cm thick and 3 to 6 cm in length, which typically contain granule-sized lithoclasts. Rarely, sets of cross-lamination are preserved within the sandstone lenses. The surround­ing sediment is more fine grained, and consists of an admixture of laminated siltstone and very fine-grained sandstone. Vertical variation in the abundance of sand­stone lenses, on a decimetre scale, defines bedding within the facies. Carbonate concretions, typically con­centrated around sandstone lenses, are sporadically developed throughout, their margins varying from sharp to gradational.

The facies is interpreted as the product of sediment deposition from a combination of water laid and wind­blown processes on an irregular surface. This surface was probably covered by an irregular efflorescent salt crust formed by evaporation of saline groundwater (compare Smoot and Olsen, 1988; Smoot and Castens-Seidell, 1994). During periods of sheet flooding, lenses of rippled sand infilled the hollows within the crusts; subsequent dissolution of the salt crusts then resulted in deformation and convolution of the sand lenses. Wind-blown silt adhered to the wet sediment surface to form the thin laminae that coated the salt crust and sand lenses. Pre­cipitation of dolomite and calcite nodules probably resulted from a high rate of evaporation of carbonate-rich groundwater

Regularly laminated facies

This facies consists of reddish brown, laminated siltstone and very fine-grained sandstone with subordinate clay-stone. These lithologies commonly form upward-fining units, some of which have granules or coarse-grained sandstone at the base. Cross-lamination and climbing ripple cross-lamination occur within sandstone and silt-stone; load casts, convolute lamination and dewatering structures may also be present. Claystone, locally with desiccation cracks, occurs as thin to thick laminae. Extraformational clasts, up to granule size, are scattered throughout the succession and, in places, within thin breccia beds. Intraformational mudstone clasts and, locally, carbonate nodules are present in this facies.

The laminated nature of this facies indicates deposi­tion from unconfined sheet floods. Ripple cross-bedding demonstrates that tractional processes were dominant; high rates of fallout from suspension accompanying the ripple migration led to the formation of climbing ripples. The sheet floods were either deposited on a sub-aerial mudflat or in a lake, with some ponding of water subsequent to flooding allowing deposition of mud from suspension. The presence of desiccation cracks indicates that these bodies of water were ephemeral features.

Claystone-siltstone facies

This facies comprises reddish brown, structureless, interbedded claystone and siltstone. Sand to granule size extraformational clasts are scattered throughout the succession, locally concentrated in thin beds or laminae. Sandstone lenses may also be locally present. Characteris­tically, sedimentary structures are uncommon but desic­cation cracks have been noted. Carbonate and gypsum/ anhydrite nodules are common in places and siliceous nodules occur at some levels.

Accumulation was probably by accretion of fine-grained sediment supplied as windblown dust and by settling from suspension after periodic sheet floods. The massive nature of the facies is probably a function of complete disruption of the sediment by the combined effects of desiccation and the interstitial growth and dissolution of evaporite minerals.

Conditions of deposition

The inferred relationship of the Permian strata below the St Bees Sandstone is illustrated in (Figure 31). Deposition of the St Bees Evaporite was initiated by a marine transgres­sion (Bakevellia Sea) into the East Irish Sea Basin. Arthurton et al. (1978) have suggested that carbonate sedimenta­tion built up a shallow coastal shelf/platform sequence near the western margin of the Lake District Block (Figure 30b). This marginal facies, the Magnesian Limestone of older classifications, is a component of the Saltom Cycle (see above) which is exposed at Saltom Bay (Eastwood et al., 1931), and proved in the more easterly boreholes of Arthurton and Hemingway (1972) around St Bees, and also in Sellafield 3 Borehole (Nirex, 1993a, e). The restricted marine fauna in these and succeeding carbonate rocks suggests deposition in sea water of higher than normal salinity. The Magnesian Limestone appears to pass westwards into thinner, finer grained clastic deposits (Saltom Siltstone, (Figure 31)) which were laid down in a restricted, perhaps starved and relatively deep water basin (Arthurton and Hemingway, 1972; Arthurton et al., 1978).

The succeeding part of the Saltom Cycle, (Saltom Dolomite, (Figure 31)) does not extend over the marginal facies to the basin margin and may have been deposited during a period of lowered sea level. Rising sea level led to the deposition of dolomite of the overlying Sandwith Cycle but again this also did not fully extend to the basin edge or cover the earlier marginal carbonates. Later, halite and, more peripherally, the Sandwith Anhydrite were deposited and spread towards the basin margin where interbedded conglomerate (Brockram) and shale (St Bees Shale) were laid down, onlapping the platform dolomite.

Deposition of dolomite, as part of the overlying Fleswick cycle, suggests that at least one further marine incursion influenced sedimentation in the landward area during the remainder of Late Permian time (Figure 31). The succeeding evaporites, mainly halite in basin centre areas, but comprising the Fleswick Anhydrite towards the margins, pass into interbedded conglomerates and shales (Figure 30c) and (Figure 31).

Later, a mudflat environment was established over much of the basin. Sediment deposition was by the accre­tion of fine wind blown and sheet flood detritus (St Bees Shale), with periodic establishment of evaporitic condi­tions. These mudflat sediments pass into alluvial fan breccia deposits towards the basin margin (Figure 30d) as illustrated by the Sellafield boreholes.

Sherwood Sandstone Group

The Bees Shale Formation and, towards the basin margin, the Brockram, pass up into a thick sandstone succession which correlates regionally with the Sherwood Sandstone Group (Arthurton et al., 1978; Warrington et al., 1980; Barnes et al., 1994). Onshore, the sandstone succession had been referred to an undivided St Bees Sandstone (Eastwood et al., 1931; Trotter et al., 1937; Arthurton et al., 1978) despite the suggestion of Gregory (1915) that at least two formations could be recognised. Offshore, the group consists of the Ormskirk and St Bees sandstones, the latter comprising the Rottington and Calder Sandstone members (Jackson et al., 1987, 1995; Jackson and Johnson, 1996). The lateral equivalents of these offshore units have now been traced onshore where they are known as the St Bees, Calder and Ormskirk sandstone formations (Barnes et al., 1994; Jackson and Johnson, 1996) (Table 5). The nomenclature of Barnes et al. (1994), with some later additions, is followed in this account.

St Bees Sandstone Formation

The St Bees Sandstone Formation is spectacularly exposed in the cliffs around St Bees Head [NX 940 140] (see cover photograph) and in several nearby quarries and outcrops, which together comprise the type locality. It is of Early Triassic (Scythian) age (Eastwood et al., 1931; Arthurton et al., 1978; Warrington et al., 1980, Barnes et al., 1994) and has been penetrated by the Selafield boreholes (Jones and Ambrose, 1994) an numerous iron-ore exploration boreholes in west Cumbria. The maximum thickness recorded onshore is the district is about 600 m and a similar thickness has been proved offshore in boreholes 112/25A-1 and 113/26-1 (Figure 27); (Jackson et al., 1987, 1995). Seismic reflection data show that the St Bees Sandstone is present in almost all offshore parts of the district, probably reaching a maximum thickness of about 1000 m (Map 3).

The St Bees Sandstone is typically a uniform fine-grained, sporadically micaceous, reddish brown sand­stone. Medium to very thick (up to 5 m) tabular, com­posite beds, have flat or gently undulating erosion sur­faces, locally accentuated by thin mudstone beds, which are characteristic of the lower part of the formation (Barnes et al., 1994; Jones and Ambrose, 1994). A wide range of sedimentary structures is displayed: parallel and low-angle lamination, planar tabular and trough cross-bedding, convoluted bedding and rare cross-lamination. The sandstones are variably non-calcareous to strongly calcareous and many are dolomitic. The lower part of the formation, which contains numerous siltstone and claystone beds (about 10%), has been distinguished as the North Head Member (Figure 33).

Sandstones rich in intraformational mudstone clasts are present throughout the formation, but become less common towards the top. The lower boundary of the for­mation is gradational (see above), whereas the boundary with the overlying Calder Sandstone Formation is sharp and marked by changes in colour, lithology and sedi­mentary structures (Nirex, 1993e).

Three facies associations have been recognised in the St Bees Sandstone; a sheet flood association (Table 7), a fluvial channel association (Table 8) and an aeolian association (Table 9) (compare Jones and Ambrose, 1994). The North Head Member comprises the sheet-flood facies association, with channel sandstones (Table 7) occurring in the upper part of the member. The remainder of the formation is dominated by the fluvial channel association, typically stacked channel sandstones separated by thin mudstone beds. The aeolian association is not common (<1% by thickness), having been docu­mented in only the Sellafield 12A and 14A boreholes.

Detailed geophysical log correlations between the Sellafield boreholes, and the investigation of seismic reflection data, have shown that periodic normal faulting took place during deposition of the St Bees Sandstone. Many of the major offshore faults, such as the Keys, Lagman and Tynwald faults, as well as several other smaller structures, were active at this time (Chapter 3) and markedly affect the thickness of the formation (Jackson et al., 1987, 1995).

Palaeocurrents and provenance

Regional palaeocurrent patterns for the St Bees Sand­stone derived from outcrop data indicate a dominant northerly to north-westerly flow in the district (Jones and Ambrose, 1994) compatible with a broadly southerly source inferred throughout the formation (Warrington et al., 1980; Burley, 1984). Locally, however, the pattern of flow appears to be more variable, with additional west­erly and west-south-westerly directed palaeocurrents from the Lake District Block. Preliminary analysis of dip-meter and borehole imagery data (FMS/FMI) for the Sellafield boreholes suggests the following trends:

  1. The sheet flood-dominated lower part of the North Head Member has palaeocurrent directions that trend toward the north-east (040°).
  2. South-westerly to westerly directed palaeoflow (average 240°) becomes increasingly important above the North Head Member, and in the upper part of the formation this direction is dominant.
  3. The vertical changes in palaeoflow directions are gradational, but individual channels commonly contain unidirectional palaeocurrent trends.

However, these palaeocurrent directions derived from the borehole data differ in part from those inferred from other lines of evidence. Petrographical studies and heavy mineral analyses indicate that the Lower Palaeozoic rocks of the Lake District Block provided detritus during deposition of the Brockram and lower­most parts of the St Bees Sandstone Formation, that is the sheet flood facies association of the North Head Member, implying dominantly westerly directed flow at that time (Nirex, 1993e; Barnes et al., 1994; Strong et al., 1994). However, in higher parts of the formation, Lake District detritus has not been unambiguously iden­tified, which is consistent with a more distal southerly sediment source.

Further information on provenance is provided by chemostratigraphical analysis. Systematic variations in whole-rock trace element geochemical data for the St Bees Sandstone, from some of the Sellafield boreholes, appear to correlate with the inferred changes in the local palaeocurrents (Nirex, 1993e, 1997c) although the reso­lution is low because of the relatively small number of analyses currently available.

The vertical variation in the chrondite-normalised rare earth element (REE) distribution patterns of samples from Sellafield 2 Borehole is illustrated in (Figure 34). The Brockram has REE characteristics similar to the Borrowdale Volcanic Group and other local Lower Palaeozoic sources, supporting the stratigraphical and petrographical evidence for a Lake Dis­trict provenance. However, although the lower part of the St Bees Sandstone, including the North Head Member, contains Lake District debris, it is significantly enriched in Ce and La and has a composition similar to that of 'average continental crust'. This is interpreted to reflect a dominant more distal, southerly sediment source consistent with the regional northerly directed palaeoflow. The Lake District detritus also present in the North Head Member is thus inferred to have entered the basin to the south of Sellafield and been carried to its present position by the northerly directed currents. The upper part of the formation is more variable, but many samples have REE patterns similar to the Brock-ram (Figure 34). This indicates a change in source of sediment supply, and is good, but not unequivocal evi­dence of renewed input of Lake District detritus and is consistent with the locally observed broadly westerly directed palaeocurrents.

These strands of evidence suggest that the dominant direction of palaeoflow in the district was to the north and that the Sellafield boreholes are in a distal position relative to a major sediment source to the south. The Lake District Block was probably also a significant local source from time to time, particularly during accumula­tion of the North Head Member and again during the latter part of St Bees Sandstone deposition. However, westerly flowing streams were probably only locally present and their sediment load was transported and dis­persed by the northerly flowing system. Although the REE geochemistry reveals a Lake District provenance in the upper St Bees Sandstone, the lack of visible petro­graphical evidence for a Lake District Block source for the upper part of the formation suggests that topo­graphic relief was low and that only highly diluted fine-grained detritus was supplied.

Conditions of deposition

The basal beds of the St Bees Sandstone, that is the lower part of the North Head Member, are dominated by the sheet flood facies association, indicating that sedi­mentation at this time was marked by unconfined flood events fed by a fluvial system flowing from the south (Figure 30e). Higher in the St Bees Sandstone, this fluvial system progressively evolved into the fluvial channel facies association. This is indicated by the upward transition from sheet floods to thin, single storey, channel sandstones interbedded with overbank mudstones which, in turn, pass upwards into multistorey channel sandstones. The channels are stacked vertically and laterally to form a thick multistorey and multilateral channel sandbody complex. The dominant direction of current flow was towards the north-west (Jones and Ambrose, 1994). The narrow range of palaeocurrent directions, coupled with the dominance of sandstone, rarity of mudstones, and the general absence of laterally accreted barforms, indicates that the channels were probably of low sinuosity, or perhaps variably sinuous within the confines of a linear channel belt. Therefore, the fluvial channel facies association comprises the deposits of an extensive sandy, low-sinuosity braided river channel system (Figure 30f).

During periods of high stage flow, channel bases would have been covered by variably sized sinuous-crested dunes and ripples and, more rarely, straight-crested dunes. These migrated downstream and laterally, under lower flow regime conditions. Upper flow regime conditions developed in areas of high flow velocity and/or shallow depths, and led to the deposition of parallel laminated sands. Thin mudstone beds were common within the channels, indicating lower energy conditions during periods of waning flow. These mud-stone beds typically became exposed during periods of low flow, with the formation of desiccation cracks which were reworked during subsequent floods to yield intraformational mudstone clasts.

Abandonment of channels is indicated by the deposi­tion of finer-grained sediment, the reduction in the size of bedforms and the deposition of thick mudstone beds. Abandoned channels were filled by finer-grained sedi­ment supplied by overbank flows, wind-borne sediment and/or restricted channel flows. However, mudstones deposited in this way have a low preservation potential due to erosion by later fluvial channels.

Trotter (1929a), Arthurton et al. (1978) and Holliday (1993b) have suggested that the Lake District Block ceased to be an area of high topographic relief and source of sediment during deposition of the St Bees Sandstone, which they inferred was laid down over the formerly emergent area. (Figure 30f) shows deposition of the St Bees Sandstone on the footwall-block of the Lake District Boundary Fault Zone. However, as noted previ­ously, it is probable that the Lake District Block was periodically emergent, forming an area of low relief and localised sediment supply, particularly during the accu­mulation of the upper part of St Bees Sandstone.

Calder Sandstone Formation

The Calder Sandstone Formation (Barnes et al., 1994) is the sandstone-dominated succession above the St Bees Sandstone (Table 5). The type section is in Sellafield 10B Borehole (Barnes et al., 1994; Jones and Ambrose, 1994) and it is also exposed as discontinuous sections in the banks of the River Calder (Trotter et al., 1937; Barnes et al., 1994). The formation is also recognised in the Carlisle Basin and offshore in the East Irish Sea Basin from geophysical log data (Map 2); Barnes et al., 1994; Jones and Ambrose, 1994). Onshore, the formation con­sists of dark reddish brown, fine- to coarse-grained sand­stone with common, well-rounded and frosted 'aeolian' grains. It is generally, though not everywhere, poorly cemented and friable. Sedimentary facies analysis indi­cates that most of the onshore Calder Sandstone is aeolian in origin, but aeolian sand grains were reworked during several fluvial episodes. The resulting fluvial sand­stones are finer grained, less porous and better cemented than the aeolian sandstones, with geophysical log responses similar to those of the St Bees Sandstone (Figure 33). There is little direct evidence of the nature of the Calder Sandstone in the offshore district but else­where in the East Irish Sea Basin, its lateral equivalents contain greater proportions of strata deposited in a fluvial setting than is the case onshore (Jones and Ambrose, 1994).

The base of the Calder Sandstone is taken at the sharp upward lithological change from the generally fine-grained, well-cemented, fluvial sandstones of the St Bees Sandstone, to coarser, more friable sandstones with abundant, well-rounded frosted grains and sedimentary structures typical of aeolian deposition (Barnes et al., 1994; Jones and Ambrose, 1994). This junction is an important seismic reflector and coincides with a sharp upward increase in interval transit times and an abrupt upward decrease in the gamma-ray values (Figure 33). Equivalent to the 'Top Silicified Zone' in offshore boreholes (Colter and Barr, 1975; Colter 1978) and the 'Brown' reflector of Jackson et al. (1987), it is traceable offshore over much of the East Irish Sea Basin and beyond. This boundary appears to mark a relatively short period of erosion or non-deposition. Another widely recognised feature offshore, both as a borehole log marker and as a seismic reflector ('Yellow' reflector of Jackson et al., 1987), lies within the lower part of the Calder Sandstone and may mark the top of a widespread well-cemented fluvial sandstone within the formation.

The top of the Calder Sandstone in onshore boreholes, which is recognised on lithological and geophysi­cal criteria (discussed below), is taken at the top of a thick fluvial sandstone unit (Figure 33).

Two main facies associations have been recognised within the Calder Sandstone from exposures and the Sellafield boreholes; an aeolian association and a fluvial channel association (Table 10a) and (Table 10b). The former comprises most of the formation (80%) and is dominated by an aeolian dune sandstone facies. Cross-bedded sets typi­cally form amalgamated packages with an average thick­ness of 3.3 m. These are generally separated by sand­stone of the damp interdune facies, although less common dry interdune sandstone may also occur. The fluvial association forms up to 20 per cent of the forma­tion, and is dominated by a minor channel facies.

The offshore seismic data suggest that active rifting continued during the deposition of the Calder Sand­stone (Jackson et al., 1987; Nirex 1992d). Boreholes within the district and adjacent offshore areas prove thicknesses of up to 650 m (Jackson et al., 1987). The maximum thickness in the East Irish Sea Basin, close to faults active during Calder Sandstone deposition, may approach 1000 m.

Conditions of deposition

The Calder Sandstone marks a significant, abrupt change in the style of sedimentation from fluvial to aeolian, perhaps after a short period of non-deposition. The lateral extent of the formation indicates a widespread cessation or diversion of the fluvial system, which affected the whole of the East Irish Sea and several adjacent basins. The lower part of the Calder Sandstone accumulated within an extensive aeolian dune field (Figure 30g). Vertical stack­ing of the dune sandstone facies indicates aggradation into dune fields or draas which were separated from each other by flat, damp interdune areas, probably of limited lateral extent. The palaeowind direction was from the north-east (Jones and Ambrose, 1994).

Several fluvial units occur higher in the Calder Sand­stone and indicate wetter periods and a change in the style of sedimentation. These fluvial sandstones contain medium to coarse, well-rounded quartz grains, perhaps indicative of contemporary erosion of aeolian dunes by river channels. The channel flow was towards the west-south-west (Jones and Ambrose, 1994), a significant change from the north-westerly directed channels of the St Bees Sandstone, which may be related to a change in provenance and/or in palaeoslope direction.

Ormskirk Sandstone Formation

The Ormskirk Sandstone Formation is the highest subdi­vision of the Sherwood Sandstone Group in west Cumbria. Exposures on the shore at Seascale [NY 0340 0130] and in the valley of the River Calder at Sellafield [NY 0285 0320] to [NY 0273 0293], previously described by Gregory (1915) and Trotter et al. (1937), are referred to this formation. Elsewhere, there are few exposures so that the formation has been proved principally by means of onshore borehole logs and from offshore seismic reflection and borehole data.

The term Ormskirk Sandstone was first used in place of 'Keuper Sandstone' on the Institute of Geological Sci­ences 1:50 000 Series Sheet 84 (Wigan) (British Geologi­cal Survey, 1977) and mentioned briefly by Warrington et al. (1980). However, none of these authors formally defined the formation and no type section was desig­nated. Barnes et al. (1994) adopted the term in west Cumbria because the name had been used previously in adjacent offshore areas (Jackson et al., 1987, 1995), where the formation is the main reservoir in the More­cambe Gas Field. The first formal definition of the Ormskirk Sandstone has been provided by Jackson and Johnson (1996), based principally on geophysical and lithological criteria in offshore boreholes. There is as yet insufficient evidence to recognise or define any sub­divisions of the formation onshore. According to Warrington et al. (1980), the Ormskirk Sandstone is Scythian–Anisian in age.

The base of the Ormskirk Sandstone has been equated by Warrington (1970) with the Hardegsen Disconfor­mity, a major break in sedimentation throughout much of north-west Europe (Trusheim, 1963). There is no evi­dence for any break in the East Irish Sea Basin sequence at this level (Cowan et al., 1993), although Evans et al. (1993) demonstrated a slight angular unconformity in the Cheshire Basin from seismic reflection profiles.

The main feature distinguishing the Ormskirk and Calder sandstones from each other is their grain size, the former is generally finer grained and better sorted, whereas the latter contains common to abundant coarse to very coarse (1–2 mm), frosted quartz grains. The aeolian sandstones, below and above the fluvial unit at the top of the Calder Sandstone, show a gradual upward decrease in the abundance of the coarse grains over a thickness of about 10 m in the Calder Sandstone and the lowermost 5 m in the Ormskirk Sandstone. At outcrop, the orange-brown colour produced by weathering of the Ormskirk Sandstone is locally another distinguishing feature.

The base of the formation is not exposed onshore within the district but has been defined in the Sellafield boreholes using geophysical log data and by correlation with offshore boreholes. It is taken at an upward decrease in gamma-ray values and an increase in interval transit times as illustrated in (Figure 33). In the core from Sellafield 13B Borehole, this corresponds to a sharp upward change, from fine- to coarse-grained fluvial sandstone, forming the top of the Calder Sandstone, to medium-grained aeolian Ormskirk Sandstone. The sonic log of Sellafield 13B Borehole shows a gradual upward increase in mean interval transit time values from around 90 to 110 ps. The gamma-ray and sonic log signatures are more serrated than those of the underlying Calder Sandstone. In the district, this formation is characterised by laterally continuous reflections on seismic reflection pro­files, which may be indicative of widespread continuous bedding planes or temporary breaks in sedimentation. However, there is insufficient evidence from the field exposures to fully assess this possibility.

In the East Irish Sea Basin, the Ormskirk Sandstone Formation is about 250 m thick (Jackson et al., 1987 and 1995; Jackson and Johnson, 1996), but there are no boreholes to provide direct information as to the nature of the formation within the district offshore.

Onshore, Sellafield 13B Borehole proved a thickness of 176.42 m of Ormskirk Sandstone. Here, the formation is predominantly aeolian in origin, laid down by palae­owinds directed to the west or south-west (Jones and Ambrose, 1994). Fluvial strata are more abundant in the formation in the central parts of the East Irish Sea Basin (Cowan et al., 1993).

Two main facies have been recognised onshore. A pre­dominant aeolian dune facies comprises cross-laminated sandstone, with foresets of either alternating finer and coarser laminae or, more rarely, low-angle, 'pinstripe' lamination; low-angle, planar truncation surfaces separate individual sets. A damp interdune facies (Figure 30h) comprises well-cemented, fine- to medium-grained, poorly sorted sandstone with common thin, irregular to wavy, silty laminae. Small-scale convolutions, loading and dewater­ing structures are common. The interdune facies gener­ally occurs as thin (about 0.1 m, rarely up to 1 m, thick) interbeds within the dune facies.

Mercia Mudstone Group

The Mercia Mudstone Group of the East Irish Sea Basin comprises a mudstone facies that is dominantly reddish brown in colour, commonly with beds of halite and minor amounts of dolomite, dolomitic mudstone and anhydrite (Jackson et al., 1987 and 1995; Wilson, 1990). The group attains a maximum thickness of 3700 m in the East Irish Sea Basin (Wilson, 1990), but it has not been recognised onshore within the district (Trotter et al., 1937; Barnes et al., 1994). However, interpretation of seismic reflection profiles, suggests that it probably extends to less than 2 km offshore south of Seascale (Figure 1) and (Map 1). Just beyond the south-eastern margin of the district, the Mercia Mudstone Group is preserved beneath Quaternary cover onshore in the Furness district of south Cumbria (Rose and Dunham, 1977; Arthurton et al., 1978; Wilson, 1990).

The group has been subdivided by Wilson (1990) and Jackson and Johnson (1996) in other parts of the East Irish Sea Basin, but no attempt has been made to map these divisions in the offshore part of the district because of the limited borehole data and the complex structure. The latter is in part the result of halokinesis (Jackson et al., 1987; Jackson and Mulholland, 1993) and extensive brecciation occurs where the halite beds have been dis­solved away by groundwater (Wilson, 1990).

The Mercia Mudstone Group is believed to have accumulated by a combination of water-laid and aeolian processes (Talbot et al., 1994). Predominantly arid con­ditions are inferred, with deposition occurring on a broad, low relief mudflat or playa. The massive or struc­tureless nature of much of the mudstone is likely to be related to early disruption of the sediment fabric by a range of pedogenic and evaporitic processes including desiccation, evaporite mineral growth and dissolution, wetting and drying cycles, and the effects of churning by plants and animals (Talbot et al., 1994). Wetter periods, whether due to rising sea or lake level or increased rain­fall, led to the development of standing bodies of water. Muds deposited during these periods are typically lami­nated, but the occurrence of desiccation cracks testifies to ephemeral conditions. The mudflat was probably largely continental, but appears to have been subjected to periodic marine influence, perhaps akin to the large modern coastal flats of the Rann of Kutch in India (Arthurton et al., 1978).

The uppermost part of the group has not yet been penetrated by drilling in the East Irish Sea Basin (Wilson, 1990). The presence and nature of higher strata can only be inferred from seismic reflection data and by compari­son with sequences proved well beyond the boundaries of the district. In addition, the Late Triassic and Early Jurassic Penarth and Lias groups, are present offshore in parts of the Keys Basin (Jackson et al., 1987 and 1995; Jackson and Johnson, 1996) (Figure 1), where grey mudstones of the Lias have been proved in a shallow borehole.

Diagenesis

From the time of deposition to the present day, the Permo-Triassic sedimentary rocks have undergone diage­netic modification. Changes in temperature, pressure and groundwater chemistry during progressive burial and later uplift have caused dissolution, mineralogical alteration and replacement of the primary detrital com­ponents, and also the precipitation and dissolution of interstitial authigenic cements. Within the district, diage­netic studies have been carried out on the St Bees Evap­orites in the vicinity of the Sandwith Mine (Arthurton and Hemingway, 1972), the St Bees Sandstone (Burley, 1984) and on Permo-Triassic rocks from all formations proved in the Sellafield boreholes (Nirex, 1993e, 1995a; Strong et al., 1994).

Eleven principal diagenetic episodes (DE1–11) have been recognised from the study of the Permo-Triassic rocks of the Sellafield boreholes (Nirex, 1995a) (Table 11). The early events (DE1–3) are in part diachronous and relate largely to synsedimentary and early burial dia­genesis; events DE4–9 relate to progressively deeper burial and DE10–11 result from post-uplift alteration pro­cesses. These episodes are summarised in (Table 11), together with their related fracture mineralisation episodes (ME4–9) (Chapter 3); (Table 2).

The main synsedimentary, near-surface diagenetic pro­cesses (eodiagenesis) (DE1–2) brought about the inter­stitial deposition of gypsum, anhydrite and perhaps halite in evaporitic sabkhas and the development of infil­trated clay coatings around detrital grains. The decom­position of unstable ferromagnesian minerals, such as biotite, magnetite and chlorite, resulted in the liberation of fine-grained ferric oxides to form haematite grain coatings which has resulted in reddening of the sand­stone and shale. Some early carbonate cements, mainly nodular concretions of dolomite, were precipitated at this time. The style of alteration of the Permo-Triassic rocks in the Sellafield boreholes is typical of early red-bed diagenesis (compare Walker et al., 1978), and is also characteristic of the Sherwood Sandstone Group in other UK Permo-Triassic basins (Burley, 1984; Strong and Milodowski, 1987).

Further diagenetic changes were brought about during burial (mesodiagenesis). Modification and further precipitation of carbonate cements, and dehydra­tion of gypsum to anhydrite, occurred during early, shallow burial (DE3) (Table 11). However, the main cementing phase of the Sherwood Sandstone Group probably occurred during moderate to deep burial in mid-Triassic to Cretaceous times (Chapter 7). Detailed petrographical evidence of complex and varied mineral precipitation and dissolution is indicative of varying ground water chemistry with time (DE4–8), most prob­ably related to the expulsion of deep brines from the East Irish Sea Basin. Much of the matrix cementation associated with mesodiagenesis can be correlated with the episodes of faulting and fracture mineralisation (ME4–9) described in Chapter 3. There is strong evi­dence (Strong et al., 1994, Nirex, 1993e) that for much of this period a major part of the Sherwood Sandstone Group was cemented by an evaporite mineral, probably anhydrite (DE6). This cement has been removed by later dissolution in groundwater. It appears to have been abundant in the originally more porous, clay-free aeolian sandstones where it protected the sandstones from com­paction during burial. The initially less porous and more poorly sorted fluvial sandstones appear to have been more extensively compacted possibly because they were not protected by the early anhydrite cement. These fluvial sandstones subsequently became wholly or par­tially cemented by later diagenetic carbonate minerals. The fault-controlled, metasomatic haematite orebodies replacing the Carboniferous Limestone of west Cumbria, and also locally the Brockram and St Bees Evaporite, may have formed during Early Triassic times contemporane­ous with DE8 (ME6) (Chapters 2 and 3).

Cainozoic uplift, basin inversion (Chapters 3 and 7) and invasion by dilute meteoric groundwaters led to further diagenetic modification (telodiagenesis). Early in this period there was widespread dissolution of the evaporite cement and precipitation of fibrous pore-bridging illite (DE9) in the Sherwood Sandstone Group, leaving rocks of aeolian origin generally less well cemented and more friable than the fluvial sandstones. Conversion of anhydrite in the St Bees Evaporite to gypsum, and the dissolution of both minerals, began at this time and probably continues to the present day. Important diagenetic events contemporary with the current groundwater regime (DE10–11) are the dissolu­tion of carbonate cements (dolomite and to a lesser extent calcite) in the near surface (to depths of about 200 m below ground level), and the precipitation of late iron, manganese and manganese-barium oxyhydroxide: (DE10) and calcite (DE11) at greater depths.

No detailed information of any diagenetic changes within the Mercia Mudstone Group of the district is available. By comparison with areas elsewhere in the East Irish Sea Basin (Wilson, 1990), dissolution of interbedded halite and, to a lesser extent, gypsum and anhydrite, was probably widespread, leading to the collapse and brecciation of the overlying beds.

Chapter 7 Jurassic to Neogene

With the exception of a small outlier of Early Jurassic rocks and local basic intrusives of Cainozoic age there is no record of sedimentation in the district for a period of about 200 Ma between the Late Triassic and the Pleisto­cene. The Cainozoic Fleetwood Dyke of Arter and Fagin (1993) is an echelon intrusion that has been mapped mainly from aeromagnetic anomalies immediately to the south-west of the district ((Figure 9), feature M10; Nirex, 1992a) although it is poorly resolved by the widely spaced survey lines of the national aeromagnetic survey. Because of this paucity of direct evidence, the Mesozoic and Cainozoic evolution of north-western England and the adjacent Irish Sea has long been a subject of contro­versy. In particular, two aspects have been much debated: the thickness and nature of any former Mesozoic sequence that may have covered Palaeozoic rocks in structural highs such as the present-day upland areas of the Lake District Block, and the thickness of strata removed from the surrounding Mesozoic basins. In many palaeogeographical reconstructions (Wills, 1951; Ziegler, 1990; Cope et al., 1992), the north-eastern part of the district has been depicted as emergent through most of Mesozoic time. Conversely, other workers (Trotter, 1929a; Eastwood, 1935), have suggested that relatively thick and complete Mesozoic successions once covered the Lake District and Pennines.

Despite the very limited stratigraphical record, there are several indirect lines of evidence that, taken together, can be used to assess the Mesozoic and Cainozoic deposi­tional history of the district, and to estimate the thickness of eroded overburden and the amount of uplift. For example, comparisons can be made with neighbouring areas where a more complete stratigraphical sequence has been preserved, and depth of burial studies can provide quantitative estimates of the thickness of former cover sequence.

Structural setting

The Jurassic to mid-Cretaceous development of the dis­trict was characterised by episodes of regional crustal extension which reactived and modified existing Permo­-Triassic and earlier structures. The position of the dis­trict, straddling the boundary between the Lake District Block to the north-east and the deep basins of the Irish Sea to the west, was of fundamental importance in deter­mining its post-Triassic evolution. There is good evi­dence that the East Irish Sea and Solway basins contin­ued to subside through Jurassic times, with syndeposi­tional normal displacements on their marginal and intrabasinal faults (Chadwick et al., 1993). The nature of the Lake District Block in post-Triassic times is less well understood, because any strata deposited there have been subsequently eroded; compelling evidence that it formed a Permo-Triassic structural high (Chapter 6; Chadwick et al., 1994), and that it behaved in a similar manner during its subsequent evolution.

Post-Triassic extension (Jurassic and early Cretaceous)

The principal post-Triassic extensional structures are likely to have been broadly similar to those active during the Permo-Triassic (Figure 16). Their nature is inferred from the offshore area where the most complete stratigraphical sequences are preserved. However, even there, unequivocal evidence of post-Triassic faulting is generally lacking because strata younger than Triassic in age are only preserved in isolated, fault-bounded outliers of Jurassic rock (Jackson et al., 1995).

In the western East Irish Sea Basin, a few kilometres to the west of the district, the base of the Triassic Mercia Mudstone Group is downthrown by more than 500 m on the Lagman Fault, and up to 2000 m on the Keys Fault (Figure 38)." data-name="images/P947414.jpg">(Figure 35) (Jackson et al., 1995). Some of this displace­ment was undoubtedly syndepositional, but the remain­der was post-Triassic in age. The relative magnitude of post-Triassic displacement is uncertain, but Jackson and Mulholland (1993) suggested that it accounts for roughly one third of the total displacement on the Keys Fault. Similar arguments have been applied to the other major Permo-Triassic basin-controlling normal faults, such as the Maryport Fault in the north-west of the district (Chadwick et al., 1993), which are also likely to have significant post-Triassic normal displacements. Inter­preted seismic profiles from the offshore area indicate that significant post-Triassic listric or detached normal faulting also occurred, particularly within the Tynwald Basin (Figure 19a); (Nirex, 1992b). Most of these faults detached on salt units within the Mercia Mudstone Group, though some penetrated to the Permian evaporites.

Comparison with more complete sequences in basins elsewhere in the UK (Whittaker, 1985; Kirby and Swallow, 1987; Badley et al., 1989) indicates that exten­sion occurred principally in the Early Jurassic and again in Late Jurassic to Early Cretaceous times. During this period most of the west Cumbria district lay within a depositional regime in which thick sedimentary sequences were laid down in the basinal areas and thinner sequences on the Lake District Block. The Lias outliers of the East Irish Sea Basin lie just west of the dis­trict and have an inferred maximum preserved thickness of approximately 600 m (Jackson et al., 1995) whereas, onshore, the preserved Lias of the Carlisle Basin to the north is estimated at just 70 m thick (Ivimey-Cook et al., 1995). These outliers are undoubtedly just remnants of a much thicker, formerly more widespread sequence and although the Lias thins markedly towards the present onshore area it probably once covered the Lake District Block (Bradshaw et al., 1992; Holliday, 1993b).

The history of the district from Middle Jurassic to Early Cretaceous times is difficult to assess because of the lack of direct evidence and the relative remoteness of the nearest preserved strata of this age. It is likely that widespread deposition continued well into Late Jurassic times but became increasingly restricted to basinal areas during the Early Cretaceous, when a fall in relative sea-level led to development of the regional Late-Cimmerian unconformity (Fyfe et al., 1981; Rawson and Riley, 1982; Whittaker, 1985). Late-Cimmerian erosion was most severe on the block areas with any Jurassic strata prob­ably removed at this time (Chadwick et al., 1994).

Regional shelf subsidence (middle Cretaceous to early Palaeocene)

Extension had effectively ceased by middle Cretaceous times (e.g. Whittaker, 1985) as sea-floor spreading propa­gated northwards into the North Atlantic region. Post-extensional regional shelf subsidence became established and structural demarcation between blocks and basins was much diminished. Extrapolation of the uniform Upper Cretaceous sequence preserved elsewhere in the UK implies deposition of chalk, perhaps 300 to 500 m thick, across the district. Apatite fission-track palaeotem­perature data (see below) indicate that maximum post­-Variscan burial of the district was probably attained at some time during the early Palaeocene.

Regional uplift and basin inversion (Palaeocene to Pleistocene)

Regional uplift commenced in early Palaeocene times (Lewis et al., 1992) and triggered a period of erosion which has probably continued, certainly onshore, with relatively minor interruptions to the present day. It is likely that uplift was caused by a combination of two dis­tinct tectonic processes. In Palaeocene times the UK region underwent major epeirogenic uplift, probably as a peripheral effect of the development of the Icelandic Plume (e.g. Brodie and White, 1994; Nadin and Kuznir, 1995). The event was associated with emplacement of the Tertiary igneous province of north-west Britain and, more locally, with intrusion of the Fleetwood Dyke, dated at 63 Ma (Arter and Fagin, 1993). Superimposed upon this regional uplift were more localised upwarps associ­ated with compressional basin inversion, including rever­sal of earlier normal faults and associated minor folding. Inversion structures are common in the East Irish Sea Basin (e.g. Knipe et al., 1993), though many of the best-preserved examples are found outside the district, for example at the margins of the Ramsey–Whitehaven Ridge. Within the district, inversion of the Solway Basin was particularly pronounced with the development of a major anticlinal structure in the hanging-wall block of the Maryport Fault (Chadwick et al., 1993). Only the north-western limb of this anticline is now fully preserved, in the north-west corner of the district (Figure 16), as a north-west-facing monoclinal fold in Permo-Triassic rocks underlain by reverse faulting in the Carboniferous. Farther south there are numerous anticlinal folds (e.g. the Selker Rocks Anticline), but many of them are found in the hanging-wall blocks of listric normal faults and it is uncertain whether they formed during basin inversion or as rollovers during earlier extension.

Development of the inversion structures was not necessarily coeval with the regional uplift. It presumably corresponded to one of the two principal inversion episodes documented in southern Britain, either the Late Cretaceous inversion in the southern North Sea (Glennie and Boegner, 1981; Badley et al., 1989), or the main Oligo Miocene inversion of southern Britain and the southern North Sea (Van Hoorn, 1987, Badley et al., 1989, Chadwick, 1993). The latter event corresponded to major Alpine nappe development and is likely to have constituted the principal inversion event in the district though earlier, minor phases cannot be ruled out.

Depth of burial studies

The amount of Mesozoic extension-related subsidence and subsequent Cainozoic uplift in the East Irish See Basin and the Lake District Block can be estimated from depth of burial studies using borehole geophysical log data and apatite fission-track results (Chadwick et al. 1994). In order to place the district into a regional context it is necessary to assess burial data from a larger surrounding area (Figure 38)." data-name="images/P947414.jpg">(Figure 35).

Sonic and density borehole logs

Depth of burial is assessed from the decrease in porosity and associated increase in density and sonic velocity, caused by compaction of a sequence during burial. Because a sedimentary rock largely retains its com­paction when the overburden is subsequently removed (Issler, 1992), its degree of overcompaction can provide a measure of its maximum depth of burial. By comparing this with its present depth of burial, an estimate of the amount of overburden that has been removed by erosion can then be made, as well as the amount of any subse­quent uplift.

Shale compaction studies have received most attention in the literature and several standard burial curves have been proposed (Marie, 1975; Magara, 1976). Sandstone and limestone also compact with burial, although the possibility of porosity being influenced by factors other than mechanical compaction, such as externally sourced cements or dissolution, may render burial estimates subject to greater error.

The available compaction data are mostly geophysical logs from the Sellafield boreholes where the preserved sedimentary cover is dominated by rocks of the Sher­wood Sandstone Group. The only shale sequence pene­trated, the St Bees Shale Formation, is unsuitable for compaction studies because it is thin and of varied lithology. Normal burial curves for density and transit-time (the reciprocal of sonic velocity) for the St Bees Sand­stone and Calder Sandstone formations have been estab­lished (Chadwick et al., 1994) (Figure 36a), (Figure 36b) and (Figure 36c), from which estimates of eroded overburden for each borehole were made. The variation in estimates for any particular borehole was reasonably small and their arithmetic mean was taken as the eroded overburden thickness. This was then converted to absolute uplift, allowing for present borehole site elevation, pre-uplift water-depths and eustatic sea-level variations (Table 12).

Uplift values for the boreholes are plotted on (Figure 36d). The range of values between boreholes is thought to be within the potential range of error in any one esti­mate and a single average uplift value of about 1900 m may reasonably be taken as representative of the district. Conversion of the eroded overburden values from the Sellafield boreholes to a restored post-St Bees Sandstone sedimentary thickness indicates that, in the vicinity of the boreholes, the post-St Bees Sandstone succession thick­ened south-westward from less than 2000 m to over 2600 m (Figure 36d). This abrupt thickening is in the same direction as fault-controlled thickening noted in the underlying Permian strata and St Bees Sandstone and is thus consistent with down-to-the-west syndeposi­tional normal faulting subsequent to deposition of the St Bees Sandstone. Approximately 600 to 800 m of this post-St Bees Sandstone thickness comprises the overlying Calder Sandstone and Ormskirk Sandstone formations. A few kilometres offshore, younger rocks of the Mercia Mudstone Group are preserved. They are believed to have once extended over the west Cumbria coastal plain and probably accounted for a significant part of the remaining post-St Bees Sandstone thickness.

Apatite fission-track palaeotemperature data

Apatite fission-track analysis gives valuable information on subsurface burial temperatures attained by rocks in the geological past. The technique is based on the trails of radiation damage (fission-tracks), produced within apatite grains at a more or less constant rate throughout geological time by the spontaneous fission of 238U. Above 50°C, the fission-tracks are shortened by the process of annealing, and are completely erased above 110°C. By measuring the length and distribution of apatite fission-tracks it is possible to determine palaeotemperatures up to 110°C and also the time at which cooling from the maximum temperature began.

Though subject to various errors and uncertainties, fission-track palaeotemperatures represent the largest currently available dataset suitable for estimating eroded overburden in the west Cumbria district and surround­ing area (Green, 1986; Lewis et al., 1992). Palaeotemper­atures for various locations range from <80 to >110°C (Table 13). The time at which maximum temperature was attained varies somewhat across the region but is esti­mated to average 65 ± 5 Ma (Lewis et al., 1992), consis­tent with a maximum depth of burial in Palaeocene times.

By assuming that geothermal gradients in the eroded overburden were identical to the present-day mean gradient (30°C km-1), these palaeotemperatures- have been interpreted as indicating that up to 3000 m of Mesozoic rocks were formerly present over the Lake Dis­trict Block, with even greater thicknesses in the basins (Green, 1986; Lewis et al., 1992). Holliday (1993b) argued that such values were not in accord with known preserved thickness trends in surrounding basins, and concluded that a former sedimentary cover over the Lake District of about 1500 m was more likely. Conduc­tive thermal modelling of the apatite fission track data using laterally variable heatflows similar to present-day values (Table 13), demonstrates that geothermal gradi­ents in the eroded overburden varied laterally and, because thermal conductivity increases with burial com­paction, were systematically higher than present-day gradients in preserved strata (Nirex, 1993d; Chadwick et al., 1994). On this basis the values of eroded overburden and absolute uplift obtained (Table 13) are in general agreement with the estimates of Holliday (1993b). They range from more than 2000 m over the basins to about 1500 m or less over the Lake District Block, an important factor in deriving quite thin overburdens over the latter area being the high heafflow over the radioactive gran­ites of the Lake District batholith.

Discussion of borehole log and fission-track results

Absolute uplift values from the geophysical log and fission-track burial studies are plotted and contoured in (Figure 37). In the vicinity of the Sellafield boreholes, where burial estimates have been derived by both methods, the estimates are in substantial agreement. Localised palaeotemperature anomalies, due to fluid flows undoubtedly exist but overall there is a good measure of agreement and regional consistency in the computed uplift values. This suggests that conductivity-based geothermal modelling is an appropriate method of obtaining burial depths on a regional basis from fission-track palaeotemperatures.

The contoured data in (Figure 37) shows that post-early Palaeocene uplift of the central Lake District Block is about 1500 m, increasing northwards, westwards and southwards towards the surrounding sedimentary basins. Uplift in the Solway Basin is typically greater than 2000 m, increasing to 3000 m in the north-east of the basin. Uplift values are about 2000 m on the west Cum­brian coast, increasing westward to over 2200 m in the East Irish Sea Basin. Uplift exceeds 2500 m in the More­cambe Bay area. The amount of inversion at the north­east margin of the East Irish Sea Basin, as distinct from regional uplift, may have been quite small in the district since the Alpine compression produced overall north- or north-west-directed shortening (compare with Knipe et al., 1993). Thus the dominantly north- to north-north­east-trending faults at the north-east basin margin were subject to oblique displacements. Much greater inversion of the basin may have taken place at its north-west margin where reversal would have been near-orthogonal across the Lagman Fault (Figure 16).

Although it did not undergo structural inversion in the strict sense (Chadwick, 1993), the Lake District Block has also suffered considerable uplift from the early Palaeocene. This regional uplift was tectonically distinct from basin inversion due to crustal shortening, and prob­ably corresponded, at least in part, with epeirogenic uplift associated with development of the Iceland Plume (see above). Thus, uplift in the region appears to be the consequence of two distinct processes, a regional uplift of some 1500 m (as typified in the Lake District), and superimposed localised uplifts associated with compres­sive basin inversion. Uplift may have continued to the present day, associated with regional eastward tilting towards the North Sea Basin. Evidence from elevated erosion surfaces in the Pennines (Walsh et al., 1972) sug­gests that considerable uplift has occurred since the beginning of the Neogene. In addition, short-lived events, such as glacial loading and erosion, will have caused more recent uplift anomalies through isostatic rebound following deglaciation.

A regional cross-section, prepared from the depth of burial studies and regional geological information is pre­sented in (Figure 38) (Whittaker, 1985; Lee, 1986; Jackson et al., 1987, 1995; Holliday, 1993b; Nirex, 1993d). A present-day section together with a reconstruction of the putative eroded overburden and a section restored to an early Palaeocene datum are shown. They illustrate the development of the region through Mesozoic and Cainozoic time. Permo-Triassic extension resulted in sub­sidence of the East Irish Sea and Vale of Eden basins but the Lake District and Alston blocks, buttressed by granitic intrusions, remained as structural highs and sub­sided at a slower rate than the surrounding basins. This pattern continued into and through much of the Juras­sic. In latest Jurassic and, particularly, early Cretaceous times, relative uplift of the block areas and lowering of relative sea level led to development of the Late-Cimmerian unconformity. The Lake District and Alston blocks suffered considerable erosion at this time with the removal of any Jurassic rocks, but subsidence and deposi­tion may have continued in the adjacent basins. In the East Irish Sea Basin, for example, it is likely that middle to Upper Cretaceous beds were deposited uncon­formably upon Jurassic and possibly Lower Cretaceous strata, overstepping eastwards on to older, Triassic beds on the Lake District Block. The precise nature of this overstep cannot be ascertained, because of uncertainty in stratal thicknesses. The cross-section restored to an early Palaeocene datum (Figure 38), illustrates the structural configuration of the region at its maximum depth of burial, immediately prior to the Cainozoic uplift and erosion which ultimately resulted in the present-day structure of the district.

Chapter 8 Quaternary

The Quaternary of Cumbria has been the subject of much research during the last 150 years. Much of the modern onshore research summarised and referenced recently by Boardman and Walden (1994) stems from the early studies by the Geological Survey (Eastwood, 1930; Eastwood et al., 1931, 1968; Trotter et al., 1937). Recent reviews include those by Pennington (1978), Boardman (1991) and Huddart (1991). The interpreta­tion of the onshore deposits has been controversial with evidence presented for and against readvances of ice and marine inundations.

More recently detailed investigations of the onshore and offshore Quaternary geology of the district have been undertaken (Nirex, 1992a, d, 1993a, f, 1995c, d, 1997d, e, f, g, h, i, j, k. Field mapping, logging and sampling of natural sections, trial pits and boreholes (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) and ground geophysics programmes have been aimed at char­acterising the Quaternary in terms of lithological sequences, lithostratigraphy, origin and age with the objective of reconciling previous interpretations of the glacial history and sea-level change (Figure 40a), (Figure 40b), (Figure 40c), (Figure 40d), (Figure 40e), (Figure 40f) and (Figure 40g) past and present near-surface hydrogeological regimes and evi­dence of deformation of glacial and tectonic origin.

The offshore Quaternary deposits have been investi­gated using shallow seismic reflection profiles, short vibrocores, less than 6 m long, and deeper boreholes with up to 200 m penetration below the sea bed (Institute of Geological Sciences, 1983; Nirex, 1992a, d, 1993f, 19971; Jackson et al., 1995). Additionally, BGS boreholes have been drilled to pre-Quaternary rockhead (Figure 39b).

The onshore and offshore Quaternary deposits differ in their nature and origin. The intervening coastal zone is dominated by erosion so that physical continuity between the succession offshore and the fragmentary deposits onshore is generally lacking. Variable sediment preservation potential, localised datasets and different sampling and analytical techniques have hindered lithos­tratigraphical correlation between onshore and offshore deposits although progress has been made recently (Nirex, 1997f, k).

Sediments of mid to late Quaternary age are recognised offshore on seismic profiles by their unconformable re­lationship with pre-Quaternary strata and by subhorizontal stratification (Jackson et al., 1995). The offshore sediments are extensive but generally less than 50 m thick, although up to 100 m are present in channels incised in rockhead (Institute of Geological Sciences, 1983; Jackson et al., 1995, fig. 65). Glacigenic sediments and substantial accumula­tions of glaciomarine and marine sediments comprise the bulk of the offshore record. Unconformities occur within the sediments (Figure 41), (Figure 42) indicating changes in sea level due to eustatic and isostatic events, as well as variations in glacial environment, climate and sediment input.

Onshore, the Quaternary record is fragmentary although sequences up to 90 m thick are present in places (Nirex, 1993a). The sediments comprise mainly glacigenic deposits of the Late Devensian glaciation and its associated ice readvances together with sediments deposited during deglaciation and Flandrian (Holocene) times. Locally, pockets of pre-Late Devensian deposits are preserved.

Summary of the Quaternary history of west Cumbria

Biostratigraphical and oxygen isotope evidence from cored ocean floor sediments indicates that there have been at least 16 major cold events during the Quaternary (the last 1.8 Ma) (Bowen, 1978; Shackleton and Opdyke, 1973, 1976; Boulton, 1992). Some 14 climato-stratigraph­ical stages of alternating glacial (cold) and interglacial (temperate) conditions are recognised in the British Isles (Boulton, 1992; Jones and Keen, 1993) but it is unlikely that each of the cold events produced ice sheets and till deposits on the British landmass. During the last 115 ka, evidence is noted for two major ice advances (McCabe, 1987; Bowen, 1989). The earlier glaciation developed at about 70 ka before present (BP) (within the Early Deven­sian substage), and the second during the Dimlington Stadial at about 26 ka BP (at the beginning of the Late Devensian substage) (Rose, 1989; Boulton, 1992; Gordon and Sutherland, 1993) (Table 14).

Pre-Late Devensian deposits

Most of the onshore Quaternary deposits in the district can be attributed to the Devensian glacial-interglacial cycle. Pre-Devensian sediments were largely removed by erosion during the Devensian glaciations. There are however records of older deposits in Cumbria of pre­sumed pre-Ipswichian age (more than 128 k calendar years BP) (Table 14); (Boardman, 1985, 1991; Carter et al., 1978; Thomas, in press). Immediately south-east of the district Rose and Dunham (1977) described possible pre-Late Devensian sequences of peat beneath boulder clay from records of 19th century boreholes in the Duddon estuary, north of Barrow-in-Furness. Within the district, mid to early Late Devensian marine and lacustrine deposits overlying weathered diamicton of possible Wolstonian age have been proved in boreholes at Drigg [SD 055 981] and Carleton [SD 081 990] (Nirex, 1997k). A basal, weathered diamicton of possible Wolstonian age has also been reported in a river cliff section of the Calder River [NY 069 119] (Nirex, 1997k).

Late Devensian erosion was less complete offshore. Thus glacially over-ridden deposits, the products of earlier glaciations, occur extensively (Jackson et al., 1995).

Dimlington Stadial

Growth of the ice sheet

The latest ice sheet glaciation (Figure 40a) is here assumed to have occurred during the Dimlington Stadial. This assumption is based on regional mapping in northern Britain of glacial deposits, some of which are underlain by radiocarbon-dated sediments such as subtill, moss-bearing silts yielding radiocarbon dates of about 18.5 ka BP at the type site at Dimlington, Yorkshire (Rose, 1985; Catt, 1991a, b). This main Late Devensian glaciation (Table 14) commenced with the growth of glaciers in the mountains of the Western Highlands and western Southern Uplands of Scotland in response to increasing precipitation and a cooling climate (Boulton et al., 1991). During the first 3 ka of the Dimlington Stadial these centres of ice accumulation nourished radi­ating patterns of expanding glaciers until Highland ice became confluent with ice caps developing over the Southern Uplands and the Lake District (Figure 40a), (Figure 40b) and (Figure 40c). The main Late Devensian ice sheet continued to expand and at its maximum extent some 22 ka BP covered most of Scotland, much of England and the adjacent continental shelf. From theoretical reconstruc­tions, Boulton et al. (1977) estimated that at the time of its maximum extent the relative elevation of the ice-sheet surface over Cumbria may have been in excess of 1600 m. Revised glacio-isostatic models indicate ice thick­nesses in the order of 500 to 750 m (Boulton et al., 1985) and 750 to 1000 m (Boulton et al., 1991). A thickness of 600 to 700 m is predicted in the glacio-hydro-isostatic model of Lambeck (1996).

Erosion and re-deposition

Quantification of glacial erosion suggests that a single glaciation may have removed an average thickness of about 20 m of pre-Quaternary sedimentary rock from the contemporary land areas (Nirex, 1994). The sediment thus derived during the Dimlington Stadial was consid­ered (Nirex, 1994) to have contributed to the prograda­tion of the outer continental shelves around Britain and Ireland. However, a large volume of debris was also deposited on the inner continental shelf (Tappin et al., 1994) as:

  1. subglacial deposits, mostly tills;
  2. glacial-margin moraines, mostly sands, gravels and boulders;
  3. ice-proximal outwash, both subaerial outwash and glaciolacustrine deposits, ranging from muds to gravels;
  4. ice-proximal to ice-distal glaciomarine deposits (McCabe, 1986).

Ice-sheet flow directions

Patterns of glacial striae, distribution of erratics, glacial bedforms (e.g. drumlins) and till lithologies have enabled the reconstruction of local centres of Late Devensian ice accumulation in northern England(Johnson, 1985; Hollingworth, 1931; Taylor et al., 1971 Trotter, 1929b; Trotter and Hollingworth, 1932b (Figure 40a). Detailed, local mapping commonly show considerable variation with marked deviations from the regional trend (Mitchell, 1991).

Erratics from Criffel in the Southern Uplands (Figure 40a) and from Ailsa Craig (Charlesworth, 1957) and found within glacial deposits exposed in coastal section flanking the Irish sea. This evidence supports the contention that Scottish ice flowed into the Irish Sea Basil and impinged upon the coastal lowlands of west Cumbria (Figure 40a), (Figure 40c). Scottish ice appears to have beer deflected around the northern Lake District (inferred from drumlin orientations in the north of the district (Plate 1)), by a local ice cap, which flowed radially out of the Cumbrian mountains (Figure 40a), (Figure 40b), an hypothesis supported by a lack of Scottish and other exotic erratic within the mountainous parts of the Lake District. The noticeable decline in the abundance of Scottish erratic downwards in multi-till sequences onshore within the district (Nirex, 19970 also suggests that Scottish ice arrived after the local ice cap had developed.

The distribution of Scottish erratics and distinctive Lake District rocks (such as those of the Borrowdale Volcanic Group) together with the orientation of glacial striae and drumlin landforms, indicate that the Scottish and Lake District ice masses coalesced during the main Late Devensian Glaciation (Figure 40c).

Deglaciation and ice-sheet readvances

Opinions differ on the pattern of deglaciation and the presence or absence of evidence for glacial readvance across the Solway lowlands and the coastal area of west Cumbria. Deglaciation resulted in the widespread deposition of glaciofluvial sands and gravels in the form of kames and eskers, proglacial sandur, deltaic sands and gravels and glaciolacustrine silts and clays (Figure 40d) Inland, for about 5 to 10 km from the coast, these glacial meltwater deposits show indications of having been over ridden by later readvances of ice (Figure 40e) and are capped by red, sandy diamictons which are locally extensive but laterally discontinuous on a regional scale (Trotter et al., 1937). The diamictons have variously been interpreted as deposits of late readvances of Scottish ice (Trotter et al., 1937; Huddart, 1991, 1994; Nirex 1995c) or as a drape of glaciomarine mud deposited by meltwater plumes discharging from tidewater glacier: during deglaciation (Eyles and McCabe, 1989). The latter authors envisaged high relative sea levels (more than 150 m above OD) but there are no indisputable biostratigraphical or sedimentological indications of contemporaneous marine influence within the glacigenic sediments at this elevation (Huddart, 1994; Nirex 1997e). Although the readvance model was dismissed Evans and Arthurton (1973) and Thomas (1985), both the readvance concept and the sequence of events a: originally envisaged by Trotter et al. (1937) have gained renewed support from the more recent recognition o: evidence for glacitectonic deformation and glacial over riding in the district (Nirex, 1993f; 1995c; 1997g).

Evidence for a pulsed series of readvances of the ice sheet during stages of deglaciation in west Cumbria was presented by Trotter (1929b) and Trotter et al. (1937). Ice-limit features mapped in the Gosforth area were referred to the 'Gosforth Oscillation' and were regarded as forming in response to the encroachment of Scottish ice streaming to the south and south-east (Figure 40e). The limits or ice front positions were defined by suites of ice-marginal drainage channels (identified by Smith, 1932) cut into bedrock within and to the east of the dis­trict (Figure 39b). The ice over-rode substantial thick­nesses of older glacigenic sediments that had accumu­lated in glacially over-deepened valleys (e.g. Ehen, Lower Wasdale) following the retreat of the main Late Deven­sian ice sheet (Figure 40d). At various times during read­vance, Scottish ice may have dammed the Calder valley and Lower Wasdale (Figure 40a), forming large proglacial lakes in which meltwater deltas developed (Figure 40e), (Figure 40f) and (Figure 40g). Local, Lake District ice probably still occupied the upper parts of the main valleys during the Gosforth Oscillation (Nirex, 1997e). A late-stage readvance, termed the 'Scottish Readvance' by Trotter et al. (1937), appears to have affected only a narrow coastal zone (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)b and (Figure 40g) producing the glacitectonically deformed St Bees Push Moraine (see below; Nirex, 1993f, 1995c, 1997g).

Glacitectonism

The series of readvance events described above pro­duced two styles of glacitectonic deformation, subglacial and proglacial; the Glacially Overridden Terrain and the Glacitectonic Thrust Terrain, respectively (Nirex, 1995c).

The Glacially Overridden Terrain, delimited by the inland limit of the 'Gosforth Oscillation' ice (Figure 39b) is distinguished by glacially streamlined landforms including modified kames and 'hill-hole pairs' in which sediment infilling hollows was excavated by the ice and redeposited in ice-push ridges (Aber et al., 1989). Sands and gravels were subglacially modified during the Gosforth Oscillation ice readvance and exhibit exten­sional normal faults and localised shearing; fine-grained deposits have been additionally affected by plastic deformation.

The Glacitectonic Thrust Terrain occupies the narrow coastal strip affected by the Scottish Readvance (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)b, and (Figure 40g). There, deposits have been subjected to severe proglacial thrusting, folding and faulting, seen to best effect in the St Bees Push Moraine (Nirex, 1993f, 1995c). Sediments have been affected by both compres­sional and extensional dislocations and are generally overconsolidated. A distinctive geomorphology is defined by elongated kettleholes and subparallel ridges, aligned north-east to south-west. Most of the kettleholes probably formed after the melting of slices of glacier ice incorporated in the tectonised package of sediments.

Glacially transported rafts of bedrock are also recog­nised in the district (Nirex, 1995c; B Young, 1997, written communication). For example, at Drigg Cross Quarry [NY 059 009] Permo-Triassic sandstone recorded beneath thin till within an area of thick (40 m) drift deposits is probably a raft. Whether rafting was effected during a major glaciation or a local ice readvance is not known.

Buried valleys

Several buried valleys, infilled with meltwater deposits and concealed beneath the products of later ice re-advances, have been identified in the onshore part of the district (Trotter et al., 1937; Nirex, 1997d). A deep buried valley to the west of the Ehen valley (Nirex, 1997d, Enclosure 3) is infilled with sandy sediments (determined as the Ehen Valley Sand and Gravel Member of the Seascale Glacigenic Formation, Nirex, 1997k), sandwiched between tills of contrasting nature. Other overdeepened and buried valleys infilled with pre­dominantly glaciolacustrine and estuarine deposits include the St Bees–Whitehaven valley (Plate 1), (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39), the Calder and Ehen valleys and Lower Wasdale (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) (Nirex, 1997f, k). Sequences in the Calder, Ehen and Lower Wasdale valleys are capped locally by diamictons laid down by the readvance of ice during the Gosforth Oscillation (see above) (Figure 40e).

Offshore channels

Offshore within the district, channel-like features incised in bedrock trend principally parallel to the coast (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39); (Nirex, 1992a, d, 1997f; Jackson et al., 1995). It is not apparent from the evidence available that these channels extend onshore.

Windermere Interstadial and Loch Lomond Stadial

West Cumbria was probably deglaciated by about 14 ka BP. The record provided by assemblages of insects including beetles (sensitive indicators of climatic change) and pollen preserved in organic sediment shows that a rapid amelioration of climate took place after about 13.6 ka BP marking the beginning of the Winder­mere Interstadial (about 13–11 ka BP according to Coope and Pennington, 1977) (Table 14). Cold condi­tions once again prevailed through the Loch Lomond Stadial (about 11–10 ka BP) when the climate in west Cumbria was very similar to that of the Dimlington Stadial. During the Loch Lomond Stadial corrie glaciers reappeared in the central Lake District and permafrost was widespread (Sissons, 1980).

Flandrian Stage

Following the Loch Lomond Stadial, temperatures rose rapidly and reached their interglacial maximum at around 7 ka BP during the Flandrian stage (Table 14). Onshore deposits include raised marine and estuarine sediment, coastal dune sand, peat, scree, lake sediment and recent alluvium (sand, silt and gravel) of rivers and streams.

Sea-level variation and isostatic uplift

Sea level varied during Late Quaternary times, princi­pally due to changes in the worldwide volume of ice (glacio-eustasy) and to subsidence or uplift brought about by differential loading and unloading of the litho­sphere by ice sheets (glacio-isostasy) (Boulton, 1990). Other causes included sediment accumulation, sedi­ment/rock removal, water loading and unloading (hydro-isostasy) and gravitational attraction of the sea towards continental ice sheets. Loading and unloading produce subsidence and uplift respectively, though there may be a time lag between load imposition or removal and the resulting sea level changes. Several conflicting analyses of sea-level changes, relevant to the district, have been published recently (Boulton, 1990; Eyles and McCabe, 1989; Lambeck, 1993a, b, 1995, 1996; Wingfield, 1995).

During the Late Devensian just after the last glacial maximum, about 20 to 18 ka BP, worldwide sea level is estimated to have fallen by about 120 m (Fairbanks, 1989) and parts of the southern Irish Sea basin might have been emergent at this time. However, because glacio-isostatic depression exceeded glacio-eustatic sea level fall, relative sea level was theoretically high in the west Cumbria district (Boulton, 1990; Eyles and McCabe, 1989; Lambeck, 1993a, b, 1995, 1996; Wing­field, 1995).

By about 17 to 14 ka BP, during deglaciation of the northern Irish Sea and the surrounding uplands, relative sea level in that region stood at an unknown, and dis­puted, height above present mean sea level. Highstands, with sea level elevations up to 150 m above OD on both sides of the Irish Sea, were proposed by Eyles and McCabe (1989), but are not supported by the glacio ­hydro-isostatic models of Lambeck (1993a, b, 1995, 1996). In Cumbria, available evidence suggests the sea may only have flooded the present coastal lowlands to about 10 to 15 m above OD after about 15 ka BP (Nirex, 1997f).

Following the Scottish Readvance, isostatic recovery exceeded eustatic sea level rise in the eastern Irish Sea basin and relative sea level fell to reach a possible low-stand of 55 m below OD in the early Flandrian (10 and 9.5 ka BP) (Pantin, 1977, 1978; Wingfield, 1995). Sea-level graphs based on onshore data show a fall in relative sea level to only about 20 m below OD although the timing of the lowstand is similar (Lambeck, 1993a, 1995, 1996; Zong and Tooley, 1996).

The early Flandrian lowstand was followed by the rapid rise in relative sea level known as the Main Flandrian (Holocene) Transgression. Recently acquired evidence from the Cumbrian coast suggests that raised beaches at 6 to 7 m above OD and raised estuarine flat sediments at 8 m above OD relate to a relative sea-level maximum in the mid-Flandrian (about 6.5 ka) for the north-east Irish Sea (Nirex, 1997f). When palaeotidal ranges of between 8.6 and 8.2 m are taken into account, a peak in mean sea level of at least 3.5 m above OD is indicated at about 6.5 ka BP.

From 5 ka BP to the present day relative sea level has fallen although small-scale fluctuations probably occurred (Long and Shennan, 1993; Shennan, 1992; Tooley, 1978, 1985; Zong and Tooley, 1996).

Stratigraphical succession

Onshore stratigraphy

The onshore lithostratigraphy in this account (Table 14) is based mainly on type sections described by Huddart et al (1977), Huddart (1991) and Nirex (1997k) and integrated where appropriate, the stratigraphy of Northern England, presented by Thomas (in press). Only broad regional correlation is possible with the stratigraphy of the Irish Sea which is largely determined seismically (Nirex, 1997: Jackson et al., 1995). Onshore, in the west Cumbria district a formational framework has been established within three groups (Nirex, 1997k): the Solway Drift, West Cumbria Drift and Central Cumbria Drift (Table 14). The formations comprise many members which are only included in this summary where appropriate.

The three groups (Table 14) are broadly geographically defined and comprise varied deposits of a range 43 origins and ages. The Solway Drift Group is composed of present day, Flandrian and latest Devensian estuarine and fluvial deposits of river valleys, hollows and low-lying coastal areas (BGS, 1996a, in press a and b). The West Cumbria Drift Group consists of glacigenic deposits present on the coastal lowlands of west Cumbria of Late Devensian age formed during glaciation and deglaciation (Figure 39b). The Central Cumbria Drift Group comprises glacigenic deposits, mainly of Late Devensian age, originating from ice streams and meltwater emanating from the Lake District mountains. Deposits of this group are present in the eastern and southern part of the onshore district (Figure 39b). Constituent formations are relatively thin and laterally variable sequence of sediments. Pockets of fine-grained deposits and diamictons which may be older than Late Devensian in age are present within both the West Cumbria Drift am Central Cumbria Drift groups.

Pre-late Devensian

Onshore evidence for early to mid-Devensian deposit; was recently acquired from boreholes in the Drigg area (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39). These proved shelly sand of possible marine origin overlying blue-grey organic silt, both of the Glannoventia Formation (Nirex, 1997k) (Table 14). Shells have yielded amino acid ratios consistent with an age of about 60 k calendar years BP (Nirex, 1997k). These lacustrine-marine sequences are observed to overlie weathered, brown sandy diamicton of the Drigg Till Formation (Table 14). The weathered nature and sporadic occurrences of the latter indicate they may be remnant of a more extensive cover of subglacially deposited till laid down possibly during the Wolstonian Stadial (Table 14); (Nirex, 1997k).

Other pockets of pre-Devensian deposits may be present in the district. A weathered, basal diamicton in a river cliff in the River Calder [NY 069 119] is here con­sidered a possible equivalent of the Thornsgill Formation (Thomas, in press) of pre-Ipswichian age (Table 14); (Nirex, 1997k).

At Carleton Hall (QBH2A) and Hall Carleton (QBH 20/20A) (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) boreholes have proved laminated muds underlying the Devensian Blengdale Glacigenic Formation (Nirex, 1997i, k). The upper part of the lami­nated sequence, which contains marine microfossils, is assigned to the Glannoventia Formation. The lower part of the sequence is the Carleton Silt Formation of glacio­lacustrine origin and studies of varves indicate sedimen­tation over a period of more than 2000 years (Nirex, 1997i).

Dimlington Stadial

Deposits of the main Late Devensian Glaciation

Sequences of lodgement tills and interbedded glacioflu­vial deposits, both of the Seascale Glacigenic Formation (West Cumbria Drift Group, (Table 14)) (Nirex, 1997k), are widespread over the onshore coastal part of the dis­trict. Although not dated, the distribution and nature of these sediments suggest that they formed during the main Late Devensian glaciation (Nirex, 1997e). The tills comprise generally red, stony, overconsolidated, clay-rich diamictons. They are dominated by locally derived mate­rial with varying amounts of debris from the Southern Uplands. The tills are of variable thickness and are absent in places (Eastwood et al., 1931; Trotter et al., 1937; Nirex, 1995c).

The Blengdale Glacigenic Formation (Central Cumbria Drift Group) in Wasdale and Blengdale (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) comprises lodgement tills deposited from ice streams and supra- and englacial gravels and glaciolacustrine laminated silts deposited by meltwater emanating from the Lake District. They are named after the type sections in the valley of the river Bleng, north-east of Gosforth (Nirex, 1997k). These deposits occupy most of the eastern part of the district. South of Seascale they extend to the coast where they are concealed by deposits of the West Cumbria Drift Group.

Deposits of the Gosforth Oscillation

Deposits associated with the main Late Devensian deglaciation and subsequent readvances of ice during the Gosforth Oscillation are assigned to the Gosforth Glacigenic Formation and the Aikbank Farm Glacigenic Formation (Table 14); (Nirex, 1997k). The Gosforth Glacigenic Formation comprises sequences of ice contact sand and gravel, proglacial sandur and glaciolacustrine deposits, and thin red diamictons found widely dis­tributed up to about 100 m above OD. Although the tills are not generally of lodgement origin, there is a conver­gence of lithological, sedimentological and structural evi­dence suggesting that they result from significant inter­mittent glacial readvances. Glaciofluvial and glaciolacus­trine sediments underlying the till are commonly glaci­tectonised. Commonly, the uppermost till of the Gosforth Glacigenic Formation forms the surface deposit. For example, a flow till formed as the Gosforth Oscillation ice decayed, rests on sandur deposits (Peel Place Sand and Gravel Member of Nirex, 1997k) which prograded into bodies of standing water ponded by ice at Peel Place [NY 070 010] in Lower Wasdale south of Gos­forth. In this area (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39), ice-dammed proglacial lake deposits are recognised from lacustrine/diamicton sequences assigned to the Aikbank Farm Glacigenic Formation which is well documented from the type section in borehole Aikbank Farm 2 (Nirex, 1997k), and also Aikbank Farm 1 and QBH16 boreholes (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39); (Table 14); (Nirex, 1997i, k). These boreholes show glaciolacus­trine/glaciomarine sequences overlain by a flow till, pos­sibly formed during the Gosforth Oscillation, which is in turn overlain by lacustrine sediments. At Santon Bridge, near the postulated margin of the ice-dammed lake, the sequence proved in Borehole QBH5 (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) is domi­nated by deltaic sand and gravel.

Glacitectonised coastal sequences

The St Bees Push Moraine is located at the south­western end of the St Bees–Whitehaven glacial meltwa­ter channel (Plate 1), (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)b and is the best exposed sequence of glacitectonised sediments of the Seascale and Gosforth glacigenic formations. It con­tains a glacitectonically thrust and folded series of glaci­genic and glaciofluvial sediments preserved beneath pockets of peat and sand of Windermere Interstadial age and Flandrian age (Table 14); (Nirex, 1997d). The moraine extends from Gutterfoot [NX 960 118] to the south-eastern end of the St Bees beach [NX 983 083] (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39); (Table 14). The stratigraphical sequence of deposits forming the moraine (Table 15); (Nirex, 1995c), broadly follows that established by Huddart and Tooley (1972).

The basal part of the sequence in the moraine is referred to the Seascale Glacigenic Formation formed during the main Late Devensian Glaciation (Table 15). Above a lodgement till (Lowca Till Member), a sequence of outwash deposits (St Bees Silt and St Bees Sand and Gravel members) are preserved. Huddart and Tooley (1972) infer that these deposits formed a proglacial coarsening-upwards sequence. The sediments were probably deposited as an outwash fan/delta from meltwaters discharging south-westwards through the St Bees–Whitehaven channel (Nirex, 19970, during decay of the main Late Devensian ice sheet (Nirex, 1997e). Elements of the St Bees sequence have been correlated southwards to Nethertown and Warborough Nook (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39). At Nethertown, a boulder gravel (Town-head Boulder Gravel Member, Nirex, 1997k), inferred to have formed during a jokulhlaup event is correlated with part of the St Bees Sand and Gravel Member. The underlying St Bees Silt Member pinches out over a dis­tance of 150 m between the main St Bees section and Gutterfoot.

Sediments of the upper part of the St Bees Push Moraine associated with the Gosforth Oscillation and Scottish Readvance are defined within the Gosforth Glacigenic Formation (Table 15); (Nirex, 1997k). The genesis of the St Bees Till Member, remains unclear. It was interpreted by Huddart and Tooley (1972) as a basal meltout till formed by the Scottish Readvance ice sheet. Although it has undergone local glacitectonic deforma­tion it is lithologically distinct from deposits mapped farther inland and is thought to have been derived from the Irish Sea basin and redeposited beneath the Irish Sea ice stream during the Gosforth Oscillation. The deposit is dark reddish brown, very stiff, calcareous, pebbly, silty, clay diamict in which clasts are well dispersed. It passes up into a stone-free, silty fine-grained sand. These lithological characteristics suggest accumulation initially in an aqueous environment (possibly as glaciomarine 'water-lain till'). The well dispersed clasts in the deposit may be ice-rafted dropstones. Although Eyles and McCabe (1989) concluded that the St Bees Till was of glacioma­rine origin, the results of recent microfossil and paly­nomorphic analyses by BGS are equivocal.

The St Bees Till Member grades from sandy silts and silty sands up to fine- to medium-grained sands (Units 7 and 8, (Table 15)). Soft sediment deformation structures are common and the entire sequence is glacitectonised; a glaciolacustrine or distal glaciofluvial origin is suggested. The uppermost metre or so of Unit 8 (after Huddart and Tooley, 1972) is of stratified sand and gravelly diamicton (Peckmill Sand and How Man Till members Nirex, 1997k), considered to be the main deposit of the Scottish Readvance (Nirex, 19970. It is interpreted as debris flow and sheetwash from the associated ice mass, although till was locally emplaced subglacially.

Windermere Interstadial, Loch Lomond Stadial and Flandrian

Coastal, alluvial and organic deposits of the Windermere Interstadial, Loch Lomond Stadial and Flandrian are included in the Solway Drift Group (Table 14) (Nirex, 1997k; Thomas, in press).

Windermere Interstadial and Loch Lomond Stadial

Fine-grained, organic and inorganic sediments of the Win­dermere Interstadial and the Loch Lomond Stadial are referred to the Blelham Peat Formation (Table 14) (Nirex, 1997k). Raised beach and estuarine sediments of the Hall Carleton Formation (Table 14), of probable latest Deven­sian age are recognised in boreholes QBH19 at St Bees and QBH2O at Hall Carleton (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) (Nirex, 1997i).

The type section of the Windermere Interstadial peat is a dissected kettlehole [NX 9665 1118] at St Bees (Walker, 1956; Coope and Joachim, 1980; Coope, 1994). Nearby, peat collected at a depth of 2.5 to 2.7 m from Borehole QBH19 (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39), sited on the floodplain of the Pow Beck, was dated at 11 780 ± 90 14C years BP (Nirex, 1997j). The pollen evidence, however, suggests a Loch Lomond Stadial age. The peat rests on estuarine deposits of the Hall Carleton Formation which formed after final deglaciation (Nirex, 1997k).

At Hallsenna Moor (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)b an accumulation of organic-rich sediment provides a palynological record of the late Devensian to Flandrian (Nirex, 1997k). Core samples at depths of 1.3 m and 1.7 m yielded dates of 11 215 ± 65 14C and 13 220 ± 180 14C years BP, respec­tively, confirming an age range spanning the start of the Windermere Interstadial for the lower part of the organic infill. The pollen spectra record a plant succes­sion, during the interstadial, from an initial phase of open habitat conditions, through the development of juniper and willow scrub to the establishment of open birch woodland. The end of the Windermere Interstadial is marked by a depositional hiatus at Hallsenna Moor. This appears to reflect a drying out of the site, initially under a period of cold, arid conditions.

During the Loch Lomond Stadial, the district experi­enced a return to conditions of arctic severity. This led to the re-establishment of a tundra landscape in which steppe and halophytic taxa associated with bare and moving soils were the dominant components. South of Ennerdale Water (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39), moraine, till, gelifluction and scree deposits (Wolf Crags Formation) formed in response to the development and decay of small corrie and valley glaciers (Sissons, 1980).

Flandrian Stage

Flandrian organic and inorganic sediments within the Blelham Peat Formation are found in lake basins, kettle-holes and in coastal sections (Nirex, 1997k). Exposures on the shore at St Bees and at Drigg (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) reveal peat and woody material in clay, the remnants of a sub­merged forest (Eastwood et al., 1931; Trotter et al., 1937). Shells from these deposits have been 14C dated at 8640 to 8230 years BP (Nirex, 1997e). A piston-sample of peat at 2.1 to 2.2 m depth in Borehole QBH19 at St Bees (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) yielded a 14C date of 7360 ± 80 years BP, con­firming a mid Flandrian age (Nirex, 1997j). The pollen spectrum from Flandrian sediments deposited less than 7.5 ka 14C years BP at Hallsenna Moor yielded mixed woodland species, predominantly birch, oak, elm, alder and hazel (Nirex, 1997k). There are indications in the upper levels of the cored profile for a gradual opening up of the woodland cover. A more complete but undated Flandrian peat succession is recorded at Gibb Tarn [NY 003 071] (Walker, 1956 and 1966).

Flandrian raised marine and estuarine sequences of the Hall Carleton Formation, lying at about 8 m above OD at Hall Carleton (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) crop out from beneath a veneer of blown sand (Drigg Point Sand Formation). The Hall Carleton sediments fine upwards from sands into silts and clays and are interpreted to represent an upward transition from a tidal channel into an estuarine environment. They have yielded marine microfossils and terrigenous plant remains. Two samples of humic sedi­ment from the fossiliferous strata yielded dates of 2520 ± 100 14C years BP and 8200 ± 110 14C years BP, confirm­ing a Flandrian age for the brackish-marine silts. Raised beaches formed by gravels of the Hall Carleton Forma­tion (Older Storm Beach of BGS, in press a) occur sporadically between Nethertown and Drigg with upper surfaces at elevations of 7.3 to 8 m above OD (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) (Nirex, 1997k).

Deposits of water-sorted sand, gravel and silt present on alluvial floodplains of rivers in the district comprise the Ehen Alluvial Formation (Table 14). Beneath the valley floors of small streams the deposits are typically between 1 and 3 m thick, but in the principal valleys they may be more than 10 m thick.

Offshore stratigraphy

In the northern Irish Sea east of the Isle of Man, Pantin (1977) established a general succession for the Quaternary sediments from an interpretation of grab samples, cores, boreholes and seismic reflection profiles. This showed bedrock or till (diamicton) overlain sequentially by both glaciomarine and lacustrine sediments (proglacial) and marine sediments. He interpreted this three-fold offshore Quaternary succession in terms of deposition during the Late Devensian deglaciation, subsequent eustatic sea-level rise and glacio-isostatic recovery. Pantin (1977) mostly interpreted unconformities within and below the marine sediments as periods of changing sea level during the latest Devensian and Flandrian.

Subsequently, a formal seismostratigraphy was erected for the whole of the Irish Sea which comprises six forma­tions (Hession, 1988; BGS, 1990; Jackson et al., 1995). Only the three youngest formations are thought to be present within the district namely, in upward succession, the Cardigan Bay, Upper Western Irish Sea and Surface Sands formations (Table 14); (Figure 41), (Figure 43), which broadly equate respectively to the basal diamicton, overly­ing glaciomarine deposits and marine sediments of Pantin (1977).

A further refinement of this formal seismostratigraphy has been possible for the 12 km offshore from the coast between St Bees Head and the Ravenglass Estuary, pri­marily through the interpretation of a grid of boomer seismic reflection profiles (Nirex, 1997f, 1). Six seismic sequences have been recognised and numbered 1 to 6 (Figure 42) with a seventh locally developed sequence numbered 3A. The major sequence boundaries are unconformities which may pass into correlative confor­mity. Other localised and laterally impersistent unconfor­mities have also been recognised. Sequence 1 is corre­lated with the Cardigan Bay Formation, Sequences 2 to 4 with the Upper Western Irish Sea Formation and Sequences 5 and 6 with the Surface Sands Formation (Table 14); (Figure 41), and (Figure 42). Because the depth penetra­tion of the boomer system is limited to about 60 m, older sediments within and beneath the Cardigan Bay Forma­tion may not be resolved, especially within deeper channels.

Cardigan Bay Formation

The Cardigan Bay Formation is primarily a glacigenic deposit of diamict and glacial sand and gravel. It lies unconformably on bedrock and is unconformably overlain by the Upper Western Irish Sea Formation. The bulk of the Cardigan Bay Formation is believed to be of Late Devensian age although in the deeper offshore channels there may be older sediments at depth (Figure 41). It has a chaotic seismic signature with discontinuous and irreg­ular seismic reflectors a common feature.

In the district, Sequence 1, the oldest seismically resolvable sequence, is considered to correlate with the Cardigan Bay Formation and possibly the lower part of the Western Irish Sea Formation (Table 14). It exhibits chaotic reflectors and sits unconformably upon either the underlying folded Triassic rocks, or older (pre-Sequence 1) Quaternary sediments. Sequence 1 is gener­ally less than 10 m thick, but thickens into channel margins and can be up to 25 m thick in rockhead depres­sions. Offshore boreholes (71/41, 71/62), located close to seismic profiles, suggest that Sequence 1 is charac­terised by tills, with subordinate associated sands and gravels. Rapid facies changes are typical and are inter­preted as glaciproximal sediments deposited in a proglacial environment interbedded with subglacial tills. Deposition is thought to have been associated with the Late Devensian ice sheet. Towards the coast, especially off St Bees Head, Sequence 1 thickens to about 30 m and comprises clay, sand and gravel, probably similar to the deposits of the Seascale Glacigenic Formation exposed in the adjacent St Bees cliffs.

Upper Western Irish Sea Formation

The Upper Western Irish Sea Formation is a seismically well-ordered sequence of laterally extensive reflectors exhibiting features such as drape, onlap, progradation. truncation and transparency that are commonly associ­ated with glaciomarine and marine sedimentation. The formation is dominantly composed of clay and silt with locally significant sand content. It is believed to be the dominant formation in terms of volume and thickness of sediment offshore in the district (Figure 43) and to be of Late Devensian to early Flandrian age (Jackson et al., 1995).

The Upper Western Irish Sea Formation is correlated with Sequences 2 to 4. Sequence 2 is 1 to 5 m thick and seismically transparent. It disconformably drapes Sequence 1 and is locally absent over topographic highs, due to either nondeposition or erosion. The sequence is thought to have been deposited in a low-energy glacio­lacustrine or glaciomarine environment from floating ice.

Sequence 3 is aggradational, it unconformably overlies Sequence 2 and is characterised by continuous, parallel to subparallel, high amplitude reflectors. It attains a maximum thickness of about 30 m over the offshore channels, thinning over topographic highs to about 5 to 10 m. Boreholes 71/61, 71/62 and 71/41 (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)a show that Sequence 3 is dominated by clay, silt and mud, that are thought to have been deposited in progressively deeper marine, perhaps distal lagoonal, glaciomarine, conditions (Pantin, 1977).

In the nearshore area Sequences 2 and 3 are cut out by the 'X unconformity' (Figure 41), (Figure 42) which separates Sequences 1 to 3 from the overlying Sequences 4 to 6 (Nirex, 1997f, 1). The unconformity is considered to be the result of a period of erosion brought about by a series of ice readvances, probably including both the Gosforth Oscillation and the Scottish Readvance (Nirex, 19970. However, over parts of the district there is little or no truncation of the underlying sequences' at the level of the 'X unconformity', suggesting a localised rather than a widespread erosive event.

Sequence 3A has a chaotic seismic character and sits unconformably on the 'X unconformity'. It is only locally developed and is interpreted as being a tongue of till (Nirex, 1997f, 1).

Sequence 4 is an aggradational sequence, similar to Sequence 3, and characterised by continuous, subparal­lel, subhorizontal reflectors on seismic profiles. Typically it ranges in thickness, from about 5 to 10 m, but thickens to 20 m to the west of the Sequence 1 coastal wedge, and is about 25 m thick just to the west of the Coulderton Channel (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39). To the east of the Coulderton Channel, the angular unconformable relationship between Sequence 4 and the underlying Sequences 2 and 3 is particularly clear.

Boreholes 71/41 and 71/62 (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) reveal that Sequence 4 is dominated by very fine-grained silt and clay, with sporadic pebbles and shells. The fine grain size of lithologies and the subparallel continuous nature of the seismic reflectors suggests a slow rate of sedimenta­tion in a glaciomarine to boreal-marine environment which developed during the Windermere Interstadial (Table 14). Pantin (1977) interpreted the pebbles proved in cores from the dominantly fine-grained silt to clay sequence as dropstones released from floating ice, indicative of Arctic conditions. Possible iceberg-plough­marks have been identified in the lower part of the sequence.

Surface Sands Formation

The Surface Sands Formation within the district com­prises two members; an upper SL1 and a lower SL2, described in detail by Pantin (1978). A third member, the Sea Bed Depression member (Jackson et al., 1995) is not recognised in the district. Pantin (1978) based his account of the SL1 and SL2 members on a detailed interpretation of vibrocore samples up to about 5 m in length, therefore this part of the formal stratigraphy is based primarily on lithostratigraphy rather than seismic interpretation. He describes an unconformity at the base of the SL2 member above the Upper Western Irish Sea Formation (Figure 41). Most of the sediments in the SL2 member consist of sand and gravel with little or no mud. These were apparently deposited on beaches or tidal flats, during the later stages of the Flandrian sea level rise.

A disconformity is recognised at the base of the SL1 member. The character of the disconformity corre­sponds to the nature of SL1 sediments at a given locality. It may be overlain by mobile sediment subject to modern wave and current activity and therefore an active discon­formable surface, or overlain by non-mobile accumu­lated sediment and therefore a moribund surface. The later sediments can be over 4.9 m in thickness and are fine grained, containing sand and mud in various pro­portions; they are interpreted as subtidal sediments (Pantin, 1978).

Whether Sequence 5 and 6 can be correlated with the SL2 and SL1 members respectively is not clear. The origi­nal interpreted logs of Pantin (1978) have not been cor­related with the boomer seismic reflection profiles used to interpret Sequences 5 and 6. Where Sequence 5 is present, an unconformity, termed the 'Y unconformity' (Figure 41), (Figure 42), separates it from the underlying Sequence 4 (Nirex, 1997f, 1).

Sequence 5 is characterised by a series of continuous reflectors which downlap onto the 'Y unconformity' surface (Figure 42). It is a north-westward prograding sequence, associated with an offshore bar, deposited during a period of relatively low sea level in the early Flandrian (Table 14). In core, the progradational part of the sequence is 6 m thick and composed of fine silty sand whereas the offshore bar sediments consist mainly of medium to coarse sand and are approximately 4 m thick. Subaerial exposure of Sequence 5 is indicated by erosion and downcutting into the top of the sequence. Mollusc shells from the offshore bar sediments have been 14C dated to 8310 ± 160 years BP (Nirex, 19970.

Sequence 6 is characterised by subparallel, subhori­zontal seismic reflectors which onlap Sequence 5; cores demonstrate that the sequence is dominated by silt. Within it there are many in situ bands of the gastropod Turritella communis (Risso, 1826), one of which, 3 m above the 'Y unconformity', has been 14C dated at 6600 ± 160 years BP (Nirex, 19970. Sequence 6 represents passive infill during the Flandrian transgression.

Information Sources

Further geological information held by the British Geological Survey relevant to the west Cumbria district is listed below. It includes published maps, memoirs and reports and open-file maps and reports. Other sources include borehole records, mine plans, fossils, rock samples, thin sections, hydrogeological data and photographs.

Searches of indexes to some of the collections can be made on the Geoscience Index system in British Geological Survey libraries. This is a developing computer-based system which carries out searches of indexes to collections and digital databases for specified geographical areas. It is based on a geo­graphic information system linked to a relational database management system. Results of the searches are displayed on maps on the screen. At the present time (1997) the data sets are limited and not all are complete. The indexes which are available are listed below.

Maps

Geological maps

Applied geology maps

Geophysical maps

Geochemical atlases

The Geochemical Baseline Survey of the Environment (G-BASE) is based on the collection of stream sediment and stream water samples at an average density of one sample per 1.5 km2. The fine (minus 150 pm) fractions of stream sediment samples are analysed for a wide range of elements, using auto­mated instrumental methods.

The samples from the Lake District were collected in 1978–80. The results (including Ag, As, Ba, Be, Bi, B, CaO, Cd, Co, Cr, Cu, Fe2O3, Ga K2O, La Li, MgO, Mn, Mo, Ni, Pb, Rb, Sb, Sn, Sr, TiO2, U, V, Y, Zn and Zr in stream sediments, and pH, conductivity, fluoride, bicarbonate and U for stream waters) are published in atlas form (Regional geochemistry of the Lake District and adjacent areas, 1993). The geochemical data, with location and site information, are available as hard copy for sale or in digital form under licensing agreement. The coloured geochemical atlas is also available in digital form (on CD-ROM or floppy disk) under licensing agreement. BGS offers a client-based service of interactive GIS interrogation of the G-BASE data.

Hydrogeological map

Books and reports

Memoirs and reports relevant to west Cumbria arranged by topic. Most are not widely available but may be purchased from BGS or consulted at BGS and other libraries.

General geology

BARNES, R P, YOUNG, B, FROST, D V, and LAND, D H. 1988. Geology of Workington and Maryport. British Geological Survey Technical Report, WA/88/3.

CHADWICK, R A, HOLLIDAY, D W, HOLLOWAY, S, and HULBERT, A G. 1995. The Northumberland–Solway basin and adjacent areas. Subsurface Memoir of the British Geological Survey.

COOPER, A H, MILLWARD, D, JOHNSON, E W, and SOPER, N J. 1992. A field guide to the Lower Palaeozoic rocks of the northern Pennines and the Lake District. British Geological Survey Technical Report, WA/92/69.

EASTWOOD, T. 1930. The geology of the Maryport district. Memoir of the Geological Survey, Sheet 22 (England and Wales).

EASTWOOD, T, DIXON, E E L, HOLLINGWORTH, S E, and SMITH, B. 1931. The geology of the Whitehaven and Workington district. Memoir of the Geological Survey of Great Britain, Sheet 28 (England and Wales).

EASTWOOD, T, HOLLINGWORTH, S E, ROSE, W C C, and TROTTER, F Monograptus 1968. Geology of the country around Cockermouth and Caldbeck. Memoir of the Geological Survey of Great Britain, Sheet 23 (England and Wales).

FORTEY, N J. 1988. Petrography of minor intrusions in the northwestern Lake District. British Geological Survey Technical Report, WG/88/24.

HARRISON, R K. 1975. Jasperoid and chalcedonic concretions in anhydrite, Sandwith Mine, St Bees, Cumbria. Bulletin of the Geological Survey of Great Britain, No. 52, 55–60.

HUGHES, R, and FETTES, D. 1994. Geology of the 1:10 000 sheet NY11NW (Floutern Tarn). British Geological Survey Tech­nical Report, WA/94/70.

JACKSON, D I, JACKSON, A A, EVANS, D, WINGFIELD, R T R, BARNES, R P, and ARTHUR, M J. 1995. United Kingdom offshore regional report: the geology of the Irish Sea. (London: HMSO for the British Geological Survey.)

LEE, M K. 1988. Density variations within Lake District granites and Lower Palaeozoic rocks. British Geological Survey Technical Report, WK/88/9.

LEE, M K. 1989. Upper crustal structure of the Lake District from modelling and image processing of potential field data. British Geological Survey Technical Report, WK/89/1.

MILODOWSKI, A E. 1990. Petrographic and sedimentological characteristics of drift sediments from the radiotracer experiment array at Drigg, Cumbria. British Geological Survey Technical Report, WE/90/24.

ROBERTS, J L, and PEACHEY, D. 1970. Trace metal contents of borehole samples from the marine Permian in west Cumberland. British Geological Survey Technical Report, WI/AC/70/51.

RUNDLE, C C. 1992. Review and assessment of isotopic ages from the English Lake District. British Geological Survey Technical Report, WA/92/38.

TAYLOR, B J, BURGESS, I C, LAND, D H, MILLS, D A C, SMITH, D B and WARREN, P T. 1971. British regional geology: northern England (4th edition). (London: HMSO for Institute of Geological Sciences.)

TROTTER, F M, HOLLINGWORTH, S E, EASTWOOD, T, and ROSE, W C C. 1937. Gosforth District. Memoir of the Geological Survey of Great Britain, Sheet 37 (England and Wales).

WEBB, B C. 1983. Accretion and collision tectonics during closure of the Iapetus Ocean. Report of the Institute of Geological Sciences, WA/SL/83/6.

WEBB, P C, and BROWN, G C. 1984. The Lake District granites: heat production and related geochemistry. British Geological Survey Technical Report, WJ/GE/84/14.

WRIGHT, J E, HULL, J H, MCQUILLAN, R, and ARNOLD, S E. 1971. Irish Sea investigations 1969–70. Report of the Institute of Geological Sciences, No. 71/19.

YOUNG, B. 1985. Mineralisation associated with the Eskdale Intrusion, Cumbria. British Geological Survey Technical Report, WA/LD/85/3.

YOUNG, B. 1987. A glossary of the minerals of the Lake District and adjoining areas. (Newcastle-upon-Tyne: British Geological Survey.)

Mineral resources

CAMERON, D G, COOPER, D CJOHNSON, E W, ROBERTS, P D, CORNWELL, J D, BLAND, D J, and NANCARROW, P H A. 1993. Mineral exploration in the Lower Palaeozoic rocks of south-west Cumbria. Part 1: Regional surveys. British Geological Survey Technical Report, WF/93/4.

COOPER, D C, CAMERON, D G, YOUNG, B, CORNWELL, J D, and BLAND, D J. 1991. Mineral exploration in the Cockermouth area, Cumbria. Part 1: Regional surveys. British Geological Survey Technical Report, WF/91/4.

COOPER, D C, CAMERON, D G, YOUNG, CHACKSFIELD, B C, and CORNWELL, J D. 1992. Mineral exploration in the Cockermouth area, Cumbria. Part 2: follow-up surveys. British Geological Survey Technical Report, WF/92/3 (BGS Mineral Reconnaissance Programme Report 122).

EASTWOOD, T. 1921. The lead and zinc ores of the Lake District. Special Report on the Mineral Resources of Great Britain, Memoir of the Geological Survey of Great Britain, Vol. 22.

MILLWARD, D, and YOUNG, B. 1984. Catalogue of mining information (other than coal, fireclay and slate) for the Lake District and South Cumbria held by the Northern England Office of the BGS. British Geological Survey Technical Report, WA/LD/84/1.

SHERLOCK, R L, and SMITH, B. 1924. Gypsum and anhydrite (3rd edition). Special Report on the Mineral Resources of Great Britain, Memoir of the Geological Survey of Great Britain, Vol. 3.

SMITH, B. 1924. Iron ores: Haematites of west Cumberland, Lancashire and the Lake District (2nd edition). Special Report on the Mineral Resources of Great Britain, Memoir of the Geological Survey of Great Britain, Vol. 8.

TAYLOR, B J, and CALVER, M A. 1961. The stratigraphy of exploratory boreholes in the west Cumberland coalfield. Bulletin of the Geological Survey of Great Britain, No. 17, 1–74.

Non-mineral resource assessment

GLOVER, B W, HOLLOWAY, S, and YOUNG, S R. 1993. An evaluation of coalbed methane potential in Great Britain. British Geological Survey Technical Report, WA/93/24.

HARRIS, P Monograptus 1993. Review of information on onshore sand and gravel resources in England. British Geological Survey Technical Report, WA/93/35.

Land-use planning

APPLETON, J D. 1995. Radon, methane, carbon dioxide, oil seeps and potentially harmful elements from natural sources and mining areas: relevance to planning and development in Great Britain. British Geological Survey Technical Report, WP/95/4.

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

APPLETON, J D, and BALL, T K. 1995. Radon and background radioactivity from natural sources: characteristics, extent and relevance to planning and development in Great Britain. British Geological Survey Technical Report, WP/95/2.

APPLETON, J D, HOOKER, P J, and SMITH, N J P. 1995. Methane, carbon dioxide and oil seeps from natural sources and mining areas: characteristics, extent and relevance to planning and development in Great Britain. British Geological Survey Techni­cal Report, WP/95/1.

BOLAND, M P, and YOUNG, B. 1992. Geology and land use-planning: Great Broughton–Lamplugh area, Cumbria. Part 2. Land-use planning. British Geological Survey Technical Report, WA/92/55

YOUNG, B, and BOLAND, M P. 1992. Geology and land-use planning: Great Broughton–Lamplugh area, Cumbria. Part 1: Geology. British Geological Survey Technical Report, WA/92/54.

Seismicity

MUSSON, R M W, NEILSON, G, and BURTON, P W. 1984a. Macroseismic reports on historical British earthquakes. I: North-west England and south-west Scotland. British Geological Survey Technical Report, WL/GS/84/207 (BGS Global Seismology Unit Report 207a).

MUSSON, R M W, NEILSON, G, and BURTON, P W. 1984b. Macroseismic reports on historical British earthquakes. I: North-west England and south-west Scotland. British Geological Survey Technical Report, WL/GS/84/207 (BGS Global Seismology Unit Report 207b).

MUSSON, R M W. 1987. Seismicity of southwest Scotland and northwest England; with a catalogue of earthquakes within 75 km of Chapelcross. British Geological Survey Technical Report, WL/GS/87/316 (BGS Global Seismology Unit Report 316).

Hydrogeology

LOVELOCK, P E R. 1971. Core analysis results from boreholes in the St Bees Sandstone, West Cumberland. Report of the Insti tute of Geological Sciences, No. WD/ST/15.

LOVELOCK, P E R. 1977. Aquifer properties of Permo-Triassic sandstone in the United Kingdom. Bulletin of the Geological Survey of Great Britain, No. 56.

Biostratigraphy

Pattison, J. 1970. A review of the marine fossils from the Upper Permian rocks of Northern Ireland and north-west England. Bulletin of the Geological Survey of Great Britain, No. 32 123–163

There is also a collection of internal British Geological Surve biostratigraphical reports, details of which are available fron the Biostratigraphy Group in the Keyworth office.

Environmental geology

HARRISON, I, HIGGO, J J W, LEADER, R, SMITH, B, NOY, D, WEALTHALL, G P, and WILLIAMS, G Monograptus 1991. The migration of colloidal particles through glacial sand. British Geological Survey Technical Report, WE/91/11.

HOLMES, D C, and HALL, D H. 1980. The 1977–1979 geological and hydrogeological investigations at the Windscale Works, Sellafield, Cumbria. Report of the Institute of Geological Sciences, No. 80/12.

ROBINS, N S. 1980. The geology of some United Kingdom nuclear sites related to the disposal of low and medium level radioactive wastes - Part I UKAEA and BNFL sites. Report of the Institute of Geological Sciences, WE/EN/80/5.

WEST, J M, ROWE, E J, WEALTHALL, G P, and ALLEN, M R. 1989. The geomicrobiology of the Drigg research site. British Geological Survey Technical Report, WE/89/8.

WILLIAMS, G M, STUART, A, and HOLMES, D A C. 1985. Investigation of the the geology of the low-level radioactive waste burial site at Drigg, Cumbria. Report of the British Geological Survey, Vol. 16, No. 3.

Remote sensing

BERRANGE, J P. 1991. Linear analysis of Landsat Thematic Mapper imagery of the English Lake District and environs. British Geological Survey Technical Report, WA/91/30.

Popular publications

Satellite image poster. The Lake District and surrounds.

1:200 000-scale satellite image of the Lake District. Full colour (simulated), flat only.

Discovering geology: the Lake District. Multimedia CD-ROM application for Mac/PowerMac and IBM compatible computers.

Other information

Documentary collections

Borehole and site investigation record collection

BGS holds collections of borehole and site investigatior records, which may be consulted and copies purchased at BGS Edinburgh. The collections from the district currently consist of the sites and logs of approximately 2500 boreholes within Sheet 28 Whitehaven, 760 on Sheet 37 Gosforth and 3 boreholes on Sheet 47 Bootle. Index information for these boreholes has been digitised. The logs are either hand-written or typed and many of the older records are drillers logs. A small-scale plot of the distribution of these borehole sites in given in (Figure 44).

Key boreholes used for the interpretation of the geology in the district are listed in (Table 17).

Mine plans

BGS maintains a collection of plans of underground mines for minerals other than coal. More than 100 plans are held, mostly of haematite workings, that fall within the district; virtually all lie within Sheet 28.

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

Material collections

British Geological Survey photographs

More than 300 photographs illustrating aspects of the geology of the district are deposited for reference in the libraries at BGS, Murchison House, West Mains Road, Edinburgh EH9 3LA and BGS, Keyworth, Nottingham NG12 5GG. Sheet albums of the more recent photographs are also held in the BGS Information Office at the Natural History Museum Gal­leries, Exhibition Road, London SW7 2DE.

Most of the photographs were taken from 1922 to 1938 and are in black and white; later photographs are in colour. They depict rocks and sediments in natural or man-made exposures, general views illustrating the influence of geology and exam­ples of mining activity and its effect on the landscape. Copies of the photographs can be purchased as black and white or colour prints, and 50 x 50 mm transparencies.

Petrological collections

The petrological collections from the district of more than 300 rock specimens and thin sections. Most specimens and thin sec­tions are from the Lower Palaeozoic Borrowdale Volcanic Group, Skiddaw Group and related intrusions. Samples from the Upper Palaeozoic cover sequence include mineral sepa­rates from the Triassic St Bees Sandstone Formation.

Borehole core samples and core

At present (January 1997) registered rock and biostratigraphi­cal specimens from 226 boreholes within the district are held. Over 4700 rock samples, mostly from coal- or iron-ore-bearing strata, and a limited number of borehole cores are held.

Palaeontological collections

Collections of biostratigraphical specimens are taken from surface, temporary exposure and boreholes throughout the dis­trict. There are currently more than 2600 registered biostrati­graphical samples from borehole core.

Addresses for data sources

British Geological Survey (Headquarters), Keyworth, Nottingham NG12 5GG. Telephone 0115 936–3100 Telex 9378173 BGSKEY G Fax 0115–936 3200

London Information Office at the Natural History Museum Earth Galleries, Exhibiton Road, South Kensington, London SW7 2DE. Telephone 0171–589 4090 Telex 0171–938 9056/9057 Fax 0171–584 8270

British Geological Survey, Murchison House, West Mains Road, Edinburgh EH 93 LA. Telephone 0131 667 1000, Telex 727343 SEISED G, Fax 0131–668 2683.

References

Most of the references listed below are held in the libraries of the British Geological Survey at Murchison House, Edinburgh and at Keyworth, Nottingham. Copies of the references can be purchased from the Keyworth office subject to the current copyright legislation.

ABER, J S, CROOT, D G, and FENTON, F Monograptus 1989. Glaciotectonic landforms and structures. (Dordrecht, The Netherlands: Kluwer Academic Publishers.)

ALLEN, P M, and COOPER, D C. 1986. The stratigraphy and composition of the Latterbarrow and Redmain sandstones, Lake District, England. Geological Journal, Vol. 21, 59–76.

ANON. 1920. Refractory materials: ganister and silica-rock­sand for open-hearth steel furnaces- dolomite. Special Report on the Mineral Resources of Great Britain, Memoir of the Geological Survey of Great Britain, Vol. 6.

APPLETON, J D, and BALL, T K 1995. Radon and background radioactivity from natural sources: characteristics, extent and relevance to planning and development in Great Britain. British Geological Survey Technical Report, WP/95/2.

APPLETON, J D, HOOKER, P J, and SMITH, N J P. 1995. Methane, carbon dioxide and oil seeps from natural sources and mining area: characteristics, extent and relevance to planning and development in Great Britain. British Geological Survey Technical Report, WP/95/1.

ARTER, G, and FAGIN, S W. 1993. The Fleetwood Dyke and the Tynwald fault zone, Block 113/27, East Irish Sea Basin. 835–843 in Petroleum geology of Northwest Europe: proceedings of the 4th Conference. PARKER, J R (editor). (London: The Geological Society.)

ARTHURTON, R 5, 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 HEMINGWAY, J 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.

BADLEY, M E, PRICE, D, and BACKSHALL, L C. 1989. Inversion, reactivated faults and related structures: seismic examples from the southern North Sea. 201–219 in Inversion tectonics. COOPER, M A, and WILLIAMS, G D (editors). Geological Society of London Special Publication, No. 44.

BARCLAY, W J, RILEY, N J, and STRONG, G E. 1994. The Dinantian rocks of the Sellafield area, west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 37–49.

BARNES, R P, AMBROSE, K, HOLLIDAY, D W, and JONES, N S. 1994. Lithostratigraphical subdivision of the Triassic Sherwood Sandstone Group in west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 51–60.

BARNES, R P, YOUNG, B, FROST, D V, and LAND, D H. 1988. Geology of Workington and Maryport. British Geological Survey Technical Report, WA/88/3.

BATH, A H, MCCARTNEY, R A, RICHARDS, H G, METCALFE, R, and CRAWFORD, M B. 1996. Groundwater chemistry in the Sellafield area: a preliminary interpretation. Quarterly Journal of Engineering Geology, Vol. 29, 539–857.

BEDDOE-STEPHENS, B, PETTERSON, M G, MILLWARD, D, and MARRINER, G F. 1995. Geochemical variation and magmatic cyclicity within an Ordovician continental-arc volcanic field: the lower Borrowdale Volcanic Group, English Lake District. Journal of Volcanology and Geothermal Research, Vol. 65, 81–110.

BESLY, B Monograptus 1983. Sedimentology and stratigraphy of red beds in the Westphalian A to C in central England. Unpublished PhD thesis, University of Keele.

BINNEY, E W. 1855. 255 in On the Permian beds of the north west of England. Memoirs of the Literary and Philosophical Society of Manchester, Series 2, Vol. 12.

BOARDMAN, J. 1985. The Troutbeck Paleosol, Cumbria, England. 231–260 in Soils and Quaternary landscape evolution. BOARDMAN, J (editor). (Chichester: Wiley.)

BOARDMAN, J. 1991. Glacial deposits in the English Lake District. 175–183 in Glacial deposits in Great Britain and Ireland. EHLERS, J, GIBBARD, P L, and ROSE, J (editors). (Rotterdam: Balkema.)

BOARDMAN, J, AND WALDEN, J (editors). 1994. The Quaternary of Cumbria: Field Guide. (Oxford: Quaternary Research Association.)

BOLAND, M P, and YOUNG, B. 1992. Geology and land-use planning: Great Broughton–Lamplugh area, Cumbria. Part 2. Land-use planning. British Geological Survey Technical Report, WA/92/55.

BOTT, M H P. 1974. The geological interpretation of a gravity survey of the English Lake District and the Vale of Eden. Journal of the Geological Society of London, Vol. 130, 309–331.

BOULTON, G S. 1990. Sedimentatry and sea level changes during glacial cycles and their control on glacimarine facies architecture. 15–52 in Glacimarine environments: processes and sediments. DOWDESWELL, J A, and SCOURSE, J D (editors). Geological Society of London Special Publication, No. 53.

BOULTON, G S. 1992. Quaternary. 413–444 in Geology of England and Wales. DUFF, P M D, and SMITH, A J (editors). (London: The Geological Society.)

BOULTON, G S, JONES, A S, CLAYTON, K M, and KENNING, M J. 1977. A British ice-sheet model and patterns of glacial erosion and deposition in Britain. 231–246 in British Quaternary studies: recent advances. SHOTTON, F W (editor). (Oxford: Claredon Press.)

BOULTON, G S, PEACOCK, J D, and SUTHERLAND, D G. 1991. Quaternary. 503–543 in Geology of Scotland (3rd edition). CRAIG, G Y (editor). (London: The Geological Society.)

BOULTON, G S, SMITH, G D, JONES, A S, AND NEWSOME, J. 1985. Glacial geology and glaciology of the last mid-latitude ice sheets. Journal of the Geological Society of London, Vol. 142, 447–474.

BOWEN, D Q. 1978. Quaternary geology: a stratigraphic framework for multidisciplinary work. (Oxford: Pergamon Press.)

BOWEN, D Q. 1989. The last interglacial-glacial cycle in the British Isles. Quaternary International, Vols 3/4, 41–47.

BRADSHAW, M J, and 7 OTHERS. 1992. Jurassic. 107–129 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.

BRANNEY, M J, and KOKELAAR, B P. 1994. Volcanotectonic faulting, soft-state deformation and rheomorphism of tuffs during development of a piecemeal caldera, English Lake District. Geological Society of America Bulletin, Vol. 106, 507–530.

BRANNEY, M J, KOKELAAR, B P, and MCCONNELL, B J. 1992. The Bad Step Tuff: a lava-like rheomorphic ignimbrite in a calc­alkaline piecemeal caldera, English Lake District. Bulletin of Volcanology, Vol. 54, 187–199.

BRANNEY, M J, and SOPER, N J. 1988. Ordovician volcano-tectonics in the English Lake District. Journal of the Geological Society of London, Vol. 145, 367–376.

BRANNEY, M J, and SPARKS, R S J. 1990. Fiamme formed by diagenesis and burial-compaction in soils and subaqueous sediments. Journal of the Geological Society of London, Vol. 147, 919–922.

BRANNEY, M J, and SUTHREN, R J. 1988. High-level peperitic sills in the English Lake District: distinction from block lavas and implications for Borrowdale Volcanic Group stratigraphy. Geological Journal, Vol. 23, 171–187.

BRITISH GEOLOGICAL SURVEY. 1977. Wigan. England & Wales Sheet 84. Solid. 1:50 000. (Southampton: Ordnance Survey for Institute of Geological Sciences.)

BRITISH GEOLOGICAL SURVEY. 1980. Gosforth and Bootle. England and Wales Sheets 37 and 47. Solid and Drift. 1:50 000. (Keyworth, Nottingham: British Geological Survey.)

BRITISH GEOLOGICAL SURVEY. 1990. Anglesey Sheet 53°N 06°W including part of Dublin 53°N 08°W. Sea bed sediments 1:250 000. (Keyworth, Nottingham: British Geological Survey.)

BRITISH GEOLOGICAL SURVEY. 1996(a). Bootle. England Sheet 47. Solid and Drift. 1:50 000. (Keyworth, Nottingham: British Geological Survey.)

BRITISH GEOLOGICAL SURVEY. 1996(b). Ambleside. England and Wales Sheet 38. Solid. 1:50 000. (Keyworth, Nottingham: British Geological Survey.)

BRITISH GEOLOGICAL SURVEY. In press(a). Gosforth. England Sheet 37. Solid and Drift. 1:50:000. (Keyworth, Nottingham: British Geological Survey.)

BRITISH GEOLOGICAL SURVEY. In press(b). Whitehaven. England Sheet 28. Solid and Drift. 1:50 000. (Keyworth, Nottingham: British Geological Survey.)

BROCKBANK, W. 1891. On the occurrence of the Permian, Spirorbis Limestones, and Upper Coal Measures at Frizington Hall in the Whitehaven district. Memoir of the proceedings of the Manchester Literary and Philosophical Society, Vol. 4, 418–426.

BRODIE J, and WHITE, N. 1994. Sedimentary basin inversion caused by igneous underplating: northwest European continental shelf. Geology, Vol. 22, 147–150.

BURGESS, I C, and HOLLIDAY, D W. 1979. Geology of the country around Brough-under-Stainmore. Memoir of the Geological Survey of Great Britain, Sheet 31 (England and Wales).

BURGESS, I C, and MITCHELL, Monograptus 1976. Visean Lower Yoredale limestones on the Alston and Askrigg Blocks, and the base of the D2 zone in northern England. Proceedings of the Yorkshire Geological Society, Vol. 40, 613–630.

BURLEY, S D. 1984. Patterns of diagenesis in the Sherwood Sandstone Group (Triassic), United Kingdom. Clay Minerals, Vol. 19, 403–440.

BUTCHER, C E. 1974. Carboniferous miospore distributions in Cumberland with special reference to those in the Hensinghan Group. Unpublished PhD thesis, University of Aston.

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

CALVIN, R. 1992. Coal. 149–164 in Beneath the Lakeland Fells, Cumbria's mining heritage. (Cumbria Amenity Trust Mining History Society). (Cumbria: Red Earth Publications.)

CARTER, P AJOHNSON, G A L, and TURNER, J. 1978. An interglacial deposit at Scandal Beck, N W England. New Phytologist, V ol. 81, 785–790.

CATT, J A. 1991a. Late Devensian glacial deposits and glaciations in eastern England and the adjoining offshore region. 61–68 in Glacial deposits of Great Britain and Ireland. EHLERS, J, GIBBARD, P L, and ROSE, J (editors). (Rotterdam, Netherlands: A A Balkema.)

CATT, J A. 1991b. The Quaternary history and glacial deposits of east Yorkshire. 185–191 in Glacial deposits of Great Britain and Ireland. EHLERS, J, GIBBARD, P L, and ROSE, J (editors). (Rotterdam, Netherlands: A A Balkema.)

CHADWICK, R A. 1993. Aspects of basin inversion in southern Britain. Journal of the Geological Society of London, Vol. 150, 311–322.

CHADWICK, R A, and EVANS, D J. 1995. The timing and direction of Permo-Triassic extension in southern Britain. 161–192 in Permian and Triassic rifting in Northwest Europe. BOLDY, S A R (editor). Geological Society of London Special Publication, No. 91.

CHADWICK, R A, EVANS, D J, and HOLLIDAY, D W. 1993. The Maryport Fault: the post-Caledonian tectonic history of southern Britain in microcosm. Journal of the Geological Society of London, Vol. 150, 247–250.

CHADWICK, R A, and HOLLIDAY, D W. 1991. Deep crustal structure and Carboniferous basin development within the Iapetus convergence zone, northern England. Journal of the Geological Society of London, Vol. 148, 41–53.

CHADWICK, R A, HOLLIDAY, D W, HOLLOWAY, S, and HULBERT, A G. 1995. The Northumberland–Solway Basin and adjacent areas Subsurface memoir of the British Geological Survey.

CHADWICK, R A, KIRBY, G A, and BADLY, H E. 1994. The post-Triassic structural evolution of north-west England and adjacent parts of the East Irish Sea. Proceedings of the Yorkshire Geological Society, Vol. 50, 91–102.

CHARLESWORTH, Jr K. 1957. The Quaternary era with special reference to its glaciation. (London: Edward Arnold (Publishers) Ltd.)

COCKS, L R M, and FORTEY, R A. 1982. Faunal evidence for oceanic separations in the Palaeozoic of Britain. Journal of the Geological Society of London, Vol. 139, 465–478.

COLLINSON, J D. 1996. Alluvial sediments. 37–82 in Sedimentary environments: processes, fades and stratigraphy (3rd edition). READING, H G (editor). (Oxford: Blackwell Science

COLTER, V S. 1978. Exploration for gas in the Irish Sea. 503–516 in Key-notes of the MEGS-II (Amsterdam, 1978). LOON, A J v (editor). Geologie en Mijnbouw, Vol. 57.

COLTER, V S, and BARR, K W. 1975. Recent developments in the geology of the Irish Sea and Cheshire Basins. 61–73 in Petroleum and the continental shelf of northwest Europe. WOODLAND, A W (editor). (Barking, Essex: Applied Science Publishers Ltd.)

COOPE, G R. 1994. The Lateglacial coleoptera from St Bees, Cumbria. 86–89 in The Quaternary of Cumbria: field guide. BOARDMAN, J, and WALDEN, J (editors). (Oxford: Quaternary Research Association.)

COOPE, G R, and JOACHIM, M J. 1980. Lateglacial environmental changes interpreted from fossil Coleoptera from St Bees, Cumbria, NW England. 55–68 in Studies in the Lateglacial of North-west Europe. LOWE, J J, GRAY, J M, and ROBINSON, J E (editors). (Oxford: Pergamon Press.)

COOPE, G R, and PENNINGTON, W. 1977. Discussion: The Windermere Interstadial of the Late-Devensian. 337–339 in Fossil coleopteran assemblages as sensitive indicators of climatic changes during the Devensian (last) cold stage. Philosophical Transactions of the Royal Society of London, Series B, Vol. 280, 321–340.

COOPER, A H, and MOLYNEUX, S G. 1990. The age and correlation of the Skiddaw Group (early Ordovician) sediments in the Cross Fell inlier (northern England). Geological Magazine, Vol. 127, 147–157.

COOPER, A H, and 5 OTHERS. 1995. The stratigraphy, correlation, provenance and palaeogeography of the Skiddaw Group (Ordovician) in the English Lake District. Geological Magazine, Vol. 132, 185–211.

COOPER, D C, and 6 OTHERS. 1988. The Crummock Water aureole: a zone of metasomatism and source of ore metals in the English Lake District. Journal of the Geological Society of London, Vol. 145, 523–540.

COPE, C W, INGHANO K, and RAWSON, P F (editors). 1992. Atlas of palaeogeography and lithofacies. Memoir of the Geological Society of London, No. 13.

COWAN, G, OTTENSEN, C, and STUART, I A. 1993. The use of dipmeter logs in the structural' interpretation and palaeocurrent analysis of Morecambe Fields, East Irish Sea Basin. 867–882 in Petroleum geology of Northwest Europe: proceedings of the 4th conference. PARKER, J R (editor). (London: The Geological Society.)

DAYSH, G H J, and WATSON, E Monograptus 1951. Cumberland with special reference to the West Cumberland development area. A survey of industrial facilities. (Whitehaven: The Cumberland Development Council Ltd and the West Cumberland Industrial Development Co. Ltd.)

DUBOIS, R L. 1962. Magnetic characteristics of a massive hematitic body. Journal of Geophysical Research, V ol. 67, 2887–2893.

DUNHAM, K C. 1984. Genesis of the Cumbrian hematite deposits. Proceedings of the Yorkshire Geological Society, Vol. 45, 130.

DUNHAM, R J 1962. Classification of carbonate rocks according to depositional texture. 108–121 in Classification of carbonate rocks. HAM, W E (editor). American Association of Petroleum Geologists Memoir, 1.

EASTWOOD, T. 1930. The geology of the Maryport district. Memoir of the Geological Survey of Great Britain, Sheet 22 (England and Wales).

EASTWOOD, T. 1935. British regional geology: Northern England. (London: His Majesty's Stationery Office.)

EASTWOOD, T, DIXON, E E L, HOLLINGWORTH, S E, and SMITH, B. 1931. The geology of the Whitehaven and Workington district. Memoir of the Geological Survey of Great Britain, Sheet 28 (England and Wales).

EASTWOOD, T, HOLLINGWORTH, S E, ROSE, W C C, and TROTTER, F Monograptus 1968. Geology of the country around Cockermouth and Caldbeck. Memoir of the Geological Survey of Great Britain, Sheet 23 (England and Wales).

EDMONDS, C. 1922. The Carboniferous Limestone Series of West Cumberland. Geological Magazine, Vol. 59, 74–83 and 117–131.

EMILIANI, C. 1955. Pleistocene temperatures. Journal of Geology, Vol. 63, 538–578.

EVANS, A Monograptus 1986. Comments on Sir Kingsley Dunham's paper: age and origin of the Cumbrian hematite. Proceedings of the Cumberland Geological Society, Vol. 4, 405–406.

EVANS, A M, and EL-NIKHELY, A. 1982. Some palaeomagnetic dates from the west Cumbrian hematite deposits, England. Transactions of the Institution of Mining and Metallurgy (Section B: Applied earth science), Vol. 91, B41-B43.

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.

EVANS, D J, ROWLEY, W J, CHADWICK, R A, KIMBELL, G S, and MILLWARD, D. 1994. Seismic reflection data and the internal structure of the Lake District batholith, Cumbria, northern England. Proceedings of the Yorkshire Geological Society, Vol. 50, 11–24.

EVANS, D J, ROWLEY, WI CHADWICK, R A, and MILLWARD, D. 1993. Seismic reflections from within the Lake District batholith, Cumbria, northern England. Journal of the Geological Society of London, Vol. 150, 1043–1046.

EVANS, W B, and ARTHURTON, R S. 1973. North-west England. 28–36 in A correlation of Quaternary deposits in the British Isles. MITCHELL, G F, PENNY, L F, SHOTFON, F W, and WEST, R G (editors). Geological Society of London Special Report, No. 4.

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.

FAIRBANKS, R G. 1989. A 17 000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature, London, Vol. 342, 637–642.

FIRMAN, R J, and LEE, M K. 1986. The age and structure of the concealed English Lake District batholith and its probable influence on subsequent sedimentation, tectonics and mineralisation. 117–127 in Geology in the real world — the Kingsley Dunham volume. NESBITT, R W, and NICHOL, J (editors). (Institution of Mining and Metallurgy.)

FORTEY, R A, OWENS, R M, and RUSHTON, A W A. 1989. The palaeogeographic position of the Lake District in the early Ordovician. Geological Magazine, Vol. 126, 9–17.

FYFE, J A, ABBOTTS, I, and CROSBY, A. 1981. The subcrop of the Mid-Mesozoic unconformity in the UK area. 236–244 in Petroleum geology of the contential shelf of NW Europe: proceedings of the 2nd Conference. ILLING, L V, and HOBSON, G D (editors). (London: Heyden.)

GARWOOD, E J. 1913. The Lower Carboniferous succession in the north-west of England. Quarterly Journal of the Geological Society of London, Vol. 68, 449–572.

GEORGE, T N, and 6 OTHERS. 1976. A correlation of Dinantian rocks in the British Isles. Geological Society of London Special Report, No. 7.

GLENNIE, K W, and BOEGNER, P L E. 1981. Sole Pit inversion tectonics. 110–120 in Petroleum geology of the continental shelf of NW Europe: proceedings of the 2nd Conference. KLING, L V, and HOBSON, G D (editors). (London: Heyden.)

GOLDRING, D C, and GREENWOOD, D A. 1990. Fluorite mineralization at Beckermet iron ore mine, Cumbria, north England. Transactions of the Institution of Mining and Metallurgy, Section B: Applied earth science, Vol. 99, B113-B119.

GOODCHILD, H G. 1889–1890. Some observations upon the mode of occurrence and the genesis of metalliferous deposits. Proceedings of the Geologists' Association, Vol. 11, 45–69.

GORDON, J E, and SUTHERLAND, D G (editors). 1993. Quaternary of Scotland. (Geological conservation review series: 6). (London: Chapman and Hall.)

GREEN, J F N. 1917. The age of the chief intrusions of the Lake District. Proceedings of the Geologists' Association, Vol. 28, 1–30.

GREEN, P F. 1986. On the thermo-tectonic evolution of Northern England: evidence from fission track analysis. Geological Magazine, Vol. 123, 493–506.

GREGORY, J W. 1915. A deep bore at Seascale in Cumberland. Geological Magazine, Vol. 62, 146–149.

HARRIS, P M, HIGHLEY, D E, HILLIER, J A, and WHITWOOD, A, (compilers). 1994. Directory of mines and quarries 1994 (4th edition). (Keyworth, Nottingham: British Geological Survey.)

HARRISON, R K. 1975. Jasperoid and chalcedonic concretions in anhydrite, Sandwith Mine, St Bees, Cumbria. Bulletin of the Geological Survey of Great Britain, No. 52, 55–60.

HESSION, M A I. 1988. Quaternary geology of the South Irish Sea. Unpublished PhD thesis, University of Wales.

HEWER, R, and MCFADZEAN, A. 1992. Iron. 85–106 in Beneath the Lakeland Fells, Cumbria's mining heritage. (Cumbria Amenity Trust Mining Society). (Cumbria: Red Earth Publications.)

HOLLIDAY, D W. 1993(a). Geophysical log signatures in the Eden Shales (Permo-Triassic) of Cumbria and their regional significance. Proceedings of the Yorkshire Geological Society, Vol. 49, 345–354.

HOLLIDAY, D W. 1993(b). Mesozoic cover over northern England: interpretation of apatite fission track data. Journal of the Geological Society of London, Vol. 150, 657–660.

HOLLINGWORTH, S E. 1931. Glaciation of western Edenside and adjoining areas and the drumlins of the Edenside and Solway Basin. Quarterly Journal of the Geological Society of London, Vol. 87, 281–359.

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.

HUDDART, D. 1991. The glacial history and glacial deposits of the North and West Cumbrian lowlands. 151–167 in Glacial deposits of Great Britain and Ireland. EHLERS, J, GIBBARD, P L, and ROSE, J (editors). (Rotterdam, Netherlands: AA Balkema.)

HUDDART, D. 1994. The late Quaternary glaciogenic sequence: landforms and environments in coastal Cumbria. In The Quaternary of Cumbria: field guide. BOARDMAN, J, and WALDEN, J (editors). (Oxford: Quaternary Research Association.)

HUDDART, D, and TOOLEY, M J (editors). 1972. Field guide to the Cumberland Lowland. (Cambridge: Quaternary Research Association.)

HUDDART, D, TOOLEY, M J, and CARTER, P. 1977. The coasts of North West England. 119–154 in The Quaternary history of the Irish Sea. KIDSON, C, and TOOLEY, M J (editors). Geological Journal Special Issue. 7 edition.

HUGHES, R A, COOPER, A H, and STONE, P. 1993. Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia. Geological Magazine, Vol. 130, 621–629.

HUGHES, R A, EVANS, J A, NOBLE, S R, and RUNDLE, C C. 1996. U-Pb chronology of the Ennerdale and Eskdale intrusions supports sub-volcanic relationships with the Borrowdale Volcanic Group (Ordovician, English Lake District). Journal of the Geological Society of London, Vol. 153, 33–38.

HUTTON, D H W, and SANDERSON, D J (editors). 1984. Variscan tectonics of the North Atlantic region. Geological Society of London Special Publication, No. 14.

INSTITUTE OF GEOLOGICAL SCIENCES. 1983. Lake District. Sheet 54°N-04°W. Sea bed sediments and Quaternary geology. 1:250 000. (London: Institute of Geological Sciences.)

ISSLER, D R. 1992. A new approach to shale compaction and stratigraphic restoration, Beauford–Mackenzie Basin and Mackenzie corridor, northern Canada. Bulletin of the American Association of Petroleum Geologists, Vol. 76, 1170–1189.

IVIMEY-COOK, H C, WARRINGTON, G, WORLEY, N E, HOLLOWAY, S, and YOUNG, B. 1995. Rocks of Late Triassic and Early Jurassic age in the Carlisle Basin, Cumbria (north-west England). Proceedings of the Yorkshire Geological Society, Vol. 50, 305–316.

JACKSON, D I. 1994. Discussion of "Geophysical log signatures in the Eden Shales (Permo-Triassic) of Cumbria and their regional significance" Proceedings, Vol. 49, pp. 345–354, 1993. Proceedings of the Yorkshire Geological Society, Vol. 50, 173–184.

JACKSON, D I, and 5 OTHERS. 1995. United Kingdom offshore regional report: the geology of the Irish Sea. (London: HMSO for British Geological Survey.)

JACKSON, D I, and JOHNSON, H. 1996. Lit hostratigraphic nomenclature of the Triassic, Permian and Carboniferous of the UK offshore East Irish Sea Basin. (Nottingham: British Geological Survey.)

JACKSON, D I, and MULHOLLAND, P. 1993. Tectonic and structural 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, 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 North West Europe: proceedings of the 3rd Conference. BROOKS, J, and GLENNIE, K (editors). (London: Graham & Trotman.)

JOHNSON, G A L. 1958. Biostromes in the Namurian Great Limestone of Northern England. Palaeontology, Vol. 1, 30–31.

JOHNSON, R H. 1985. 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.)

JOHNSON, S A, GLOVER, B W, and TURNER, P. 1997. Multiphase reddening and weathering events in Upper Carboniferous red-beds from the English West Midlands. Journal of the Geological Society of London, Vol. 154, 735–745.

JOHNSTON, PROFESSOR. 1839. On the origin of petroleum, and on the nature of the petroleum from Whitehaven. Report of eighth meeting of the British Association for the Advancement of science; Newcastle, Vol. 7, 60.

JONES, J H. 1951. Report on the Cumberland Coalfield. 76–84 in Cumberland with special reference to the West Cumberland ievelopment area. A survey of industrial facilities. DAYSH, G H J, and WATSON, E M (editors). (Whitehaven: Cumberland Development Council Ltd and the West Cumberland Industrial Development Co Ltd.)

JONES, N S. 1992. Sedimentology of Westphalian coal-bearing strata and applications to opencast coal mining, West Cumbrian Coalfield, UK Unpublished PhD thesis, University Df Oxford Brookes.

JONES, N S, and AMBROSE, K 1994. Triassic sandy braidplain and aeolian sedimentation in the Sherwood Sandstone Group Df the Sellafield area, west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 61–76.

JONES, N S, GUION, P D, DICKINS, D, and YOUNG, B. 1990. Coal Measures palaeoenvironments in West Cumbria. Field meeting 1989. Proceedings of the Yorkshire Geological Society, Vol. 48, 119–120.

JONES, R L, and KEEN, p H. 1993. Pleistocene environments in the British Isles. (London: Chapman and Hall.)

KELLY, D. 1994. The Red Hills. Iron mines of west Cumberland. (Ulverston, Cumbria: Red Earth Publications.)

KENDALL, J D. 1873–1875. The haematite deposits of Whitehaven and Furness. Transactions of the Manchester Geological Society, Vol. 13, 231–283.

KENDALL, J D. 1885. The Carboniferous rocks of Cumberland and North Lancashire, or Furness. Transactions of the North of England Institute of Mining and Mechanical Engineering, Vol. 34, 125–136.

KENDALL, J D. 1896. The Whitehaven Sandstone Series. Transactions of the Institution of Mining Engineers, Vol. 10, 202–224.

KIMBELL, G S. 1994. The interpretation of gravity and aeromagnetic data for the geological investigation of the Sellafield area, west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, Pt I, 103–112.

KIMBELL, G S, and STONE, P. 1995. Crustal magnetization variations across the Iapetus Suture Zone. Geological Magazine, Vol. 132, 599–609.

KIRBY, G A, and 9 OTHERS. In press. The structure and evolution of the Craven Basin and adjacent areas. Subsurface Memoir of the British Geological Survey.

KIRBY, G A, and SWALLOW, P W. 1987. Tectonism and sedimentation in the Flamborough Head region of north-east England. Proceedings of the Yorkshire Geological Society, Vol. 46, 301–309.

KNELLER, B C. 1991. A foreland basin on the southern margin Df Iapetus. Journal of the Geological Society of London, Vol. 148, 207–210.

KNELLER, B C, and BELL, A Monograptus 1993. An Acadian mountain front in the English Lake District: the Westmorland Monocline. Geological Magazine, Vol. 130, 203–213.

KNELLER, B C, KING, L M, and BELL, A Monograptus 1993. Foreland basin development and tectonics on the northwest margin of eastern Avalonia. Geological Magazine, Vol. 130, 691–697.

KNIPE, R J, COWAN, G, and BALENDRAN, V S. 1993. The tectonic history of the East Irish Sea Basin with reference to the Morecambe Fields. 857–866 in Petroleum geology of Northwest Europe: proceedings of the 4th Conference. PARKER, R (editor). (London: The Geological Society.)

LAMBECK, K 1993a. Glacial rebound of the British Isles - I. Preliminary model results. GeophysicalJournal International, Vol. 115, 941–959.

LAMBECK, K. 1993b. Glacial rebound of the British Isles - II. A high-resolution, high precision model. Geophysical Journal International, Vol. 115, 960–990.

LAMBECK, K. 1995. Late Devensian and Holocene shorelines of the British Isles and North Sea from models of glacio-hydroisostatic rebound. Journal of the Geological Society of London, Vol. 152, 437–448.

LAMBECK, K 1996. Glaciation and sea-level change for Ireland and the Irish Sea since Late Devensian/Midlandian time. Journal of the Geological Society of London, Vol. 153, 853–872.

LEE, M K. 1986. A new gravity survey of the Lake District and three-dimensional model of the granite batholith. Journal of the Geological Society of London, Vol. 143, 425–435.

LEE, M K 1989. Upper crustal structure of the Lake District from modelling and image processing of potential field data. British Geological Survey Technical Report, WK/89/1.

LEEDER, M R. 1982(a). 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. 1982 (b) . Sedimentology - process and product. (London: George Allen & Unwin.)

LEWIS, C L E, GREEN, P F, CARTER, A, and HURFORD, A J. 1992. Elevated K/T palaeotemperatures througout northwest England: three kilometres of Tertiary erosion? Earth and Planetary Science Letters, Vol. 112, 131–145.

LLEWELLYN, P G, MAHMOUD, S A, and STABBINS, R. 1968. Nodular anhydrite in Carboniferous Limestone, west Cumberland. Transactions of the Institution of Mining and Metallurgy (Section B: Applied earth science), Vol. 77, B18-B25.

LONG, A J, and SHENNAN, I. 1993. Holocene relative sea-level and crustal movements in southeast and northeast England, UK Quaternary Proceedings, No. 3, 15–19.

LUMSDEN, G I, TULLOCH, W, HOWELLS, M F, and DAVIES, A. 1967. The geology of the neighbourhood of Langholm. Memoir of the Geological Survey, Scotland.

MACDONALD, R, MILLWARD, D, BEDDOE-STEPHENS, B, and LAYBOURNPARRY, J. 1988. The role of tholeiitic magmatism in the English Lake District: evidence from dykes in Eskdale. Mineralogical Magazine, Vol. 52, 459–472.

MAGARA, K. 1976. Thickness of removed sedimentary rocks, paleopore pressure and paleotemperature, southwestern part of Western Canada Basin. Bulletin of the American Association of Petroleum Geologists, Vol. 60, 554–565.

MARIE, J P P. 1975. Rodiegendes stratigraphy and diagenesis. 205–210 in Petroleum and the continental shelf of north-west Europe: proceedings of 1st Conference. WOODLAND, A W (editor). (London: Applied Science Publishers.)

MCCABE, A Monograptus 1986. Glaciomarine facies deposited by retreating tidewater glaciers: an example from the late Pleistocene of northern Ireland. Journal of Sedimentary Petrology, Vol. 56, 880–894.

MCCABE, A Monograptus 1987. Quaternary deposits and glacial stratigraphy in Ireland. Quaternary Science Reviews, Vol. 6, 259–299.

McKERROW, W S, DEWEY, J F, and SCOTESE, C R. 1991. The Ordovician and Silurian development of the Iapetus Ocean. 165–178 in The Murchison Symposium. BASSETT, M G, LANE, P D, and EDWARDS, D (editors). Special Papers in Palaeontology, No. 44.

MICHIE, U McL, and BOWDEN, R A. 1994. UK NIREX geological investigations at Sellafield. Proceedings of the Yorkshire Geological Society, Vol. 50, 5–9.

MILLWARD, D, BEDDOE-STEPHENS, B, WILLIAMSON, I T, YOUNG, S R, and PETTERSON, M G. 1994. Lithostratigraphy of a concealed caldera-related ignimbrite sequence within the Borrowdale Volcanic Group of west Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 25–36.

MILLWARD, D, JOHNSON, E W, BEDDOE-STEPHENS, B, and YOUNG, B. In press. Geology of the Ambleside district. Memoir of the British Geological Survey, Sheet 38 (England and Wales).

MILLWARD, D, and MOLYNEUX, S G. 1992. Field and biostratigraphic evidence for an unconformity at the base of the Eycott Volcanic Group in the English Lake District. Geological Magazine, Vol. 129, 77–92.

MILADOWSKI, A E, GILLESPIE, M R, and METCALFE, R. 1997. Relationships between minerological transformations and groundwater chemistry at Sellafield, N W England: a tool for studying Quaternary palaeohydrogeology. 30–33 in Geofluids II '97, Contributions to the second international conference on fluid evolution, migration and interaction in sedimentary basins and orogenic belts. HENDRY, J P, CAREY, P F, PARNELL, J, RUFFELL, A H, and WORDEN, R H (editors). (Belfast: The Queen's University of Belfast.)

MILODOWSKI, A E, AND ZALASIEWICZ, J A. 1991. Redistribution of rare earth elements during diagenesis of turbidite/ hemipelagite mudrock sequences of Llandovery age from central Wales. 101–124 in Developments in sedimentary provenance studies. MORTON, A C, TODD, S P, and NAUGHTON, P D W (editors). Special Publication of the Geological Society of London, No. 57.

MITCHELL, M, TAYLOR, B J, and RAMSBOTTOM, W H C. 1978. Carboniferous. 168–177 in The geology of the Lake District. MOSELEY, F (editor). Occasional Publication of the Yorkshire Geological Society, No. 3.

MITCHELL, W A (editor) . 1991. Western Pennines: field guide. (London: Quaternary Research Association.)

MOLYNEUX, S G. 1988. Micropalaeontological evidence for the age of the Borrowdale Volcanic Group. Geological Magazine, Vol. 125, 541–542.

MOLYNEUX, S G, and RUSHTON, A W A. 1984. Discovery of Tremadoc rocks in the Lake District. Proceedings of the Yorkshire Geological Society, Vol. 45, 123–127.

MOLYNEUX, S G, and RUSHTON, A W A. 1988. The age of the Watch Hill Grits (Ordovician), English Lake District: structural and palaeogeographical implications. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 79, 43–69.

MOORBATH, S. 1962. Lead isotope abundance studies on mineral occurrences in the British Isles and their geological significance. Philosophical Transactions of the Royal Society of London Series A, Vol. 254, 295–360.

MUSSON, R M W. 1987. Seismicity of southwest Scotland and northwest England; with a catalogue of earthquakes within 75 km of Chapelcross. British Geological Survey Global Seismology Report, No. 316.

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

MUSSON, R M W, NEILSON, G, and BURTON, P W. 1984a. Macroseismic reports on historical British earthquakes 1: Northwest England and Southwest Scotland. British Geologic Survey Global Seismology Report, No. 207(a).

MUSSON, R M W, NEILSON, G, and BURTON, P W. 1984b. Macroseismic reports on historical British earthquakes 1: Northwest England and Southwest Scotland. British Geologic Survey Global Seismology Report, No. 207(b).

NADIN, P A, and KUSZNIR, N J. 1995. Palaeocene uplift and Eocene subsidence in the northern North Sea Basin from 2D forward and reverse stratigraphic modelling. Journal of the Geological Society of London, Vol. 152, 833–848.

NATIONAL COAL BOARD. 1982. The treatment of disused mine she and adits. (London: NCB Mining Department.)

NIREX. 1992(a). The geology of the region around Sellafield: report of the regional geology joint interpretation team. UK Nirex Ltd Report, No. 264.

NIREX. 1992(b). Report of the structural geology joint interpretation team. UK Nirex Ltd Report, No. 265.

NIREX. 1992(c). A revised geological map (solid) of the Sellafiel District. UK NIREX Ltd, No. 258.

NIREX. 1992(d). An interpretation of regional seismic reflection data offshore Sellafield. UK NIREX Ltd Report, No. 270.

NIREX. 1993(a). The geology and hydrogeology of the Sellafield area. Interim Assessment December 1993. UK NIREX Ltd Repo No. 524.

NIREX. 1993 (b) . Interpretation of intra-basement seismic reflection events at Schofield. UK NIREX Ltd Report, No. 341.

NIREX. 1993(c). The geological structure of the Sellafield area: December 1993 update. UK Nirex Ltd Report, No. 520.

NIREX. 1993(d). Jurassic to Neogene structural evolution of the Sellafield area: December 1993 update. UK Nirex Ltd Report, No. 518.

NIREX. 1993(e). The Permo-Triassic rocks of the Sellafield area. December 1993 update. UK Nirex Ltd Report, No. 517.

NIREX. 1993 (f) . The Quaternary geology of the Sellafield area. UK NIREX Ltd Report, No. 519.

NIREX. 1994. Glaciation of the British Isles: an approach seekin to determine the role of glaciation in landform development over the million years. UK NIREX Ltd Report, No. NSS/R337.

NIREX. 1995(a). Flow-zone characterization: mineralogical and fracture orientation characteristics in the PRZ and Fleming Hall Fay Zone area boreholes, Sellafield. UK Nirex Ltd Report, No. SA/95/001.

NIREX. 1995(b). The 3D geology and hydrogeology of the RCF south shaft location: summary report. UK NIREX Ltd Report, No. S/95/007.

NIREX. 1995 (c) . Characterisation of the onshore Quaternary deposits around Sellafield, Cumbria: Phase II. UK NIREX Ltd Report, No. 768.

NIREX. 1995(d). Factual report: compilation of maps and drawings. UK NIREX Ltd Report, No. SA/95/002.

NIREX. 1996 (a) . The Seascale–Gosforth Fault Zone Final Repo? UK NIREX Ltd Report, No. SA/96/001.

NIREX. 1996 (b) . The 3D geological structure of the PRZ: Marc! 1996 update. UK NIREX Ltd Report, No. SA/96/004.

NIREX. 1997(a). Structural atlas of the Sellafield boreholes. U Nirex Ltd Report, No. SA/96/005.

NIREX. 1997(b). The 3D geological structure of the Sellafield Sii UK NIREX Ltd Report, No. SA/96/017.

REFERENCES 123

NIREX. 1997(c). A synthesis of data used to assess the hydraulic character of the Sherwood Sandstone Group at Sellafield. UK NIREX Ltd Report, No. SA/97/064.

NIREX. 1997(d). Synthesis of the hydrogeological characteristics of Quaternary sequences in the Sellafield area. UK NIREX Ltd Report, No. SA/97/001.

NIREX. 1997(e). Quaternary evolution of the Sellafield area, Cumbria. UK NIREX Ltd Report, No. SA/97/002.

NIREX. 1997(1). A summary of the correlation and nature of onshore and offshore Quaternary sediments of the Sellafield area. UK NIREX Ltd Report, No. SA/97/003.

NIREX. 1997(g). A synthesis of the nature and origin of deformation features within the Quaternary sequences, Sellafield. UK NIREX Ltd Report, No. SA/97/004.

NIREX. 1997(h). Assessment of geological and hydrogeological data from the 1995 Quaternary drilling programme. UK NIREX Ltd Report, No. SA/97/005.

NIREX. 1997(i). Logging and interpretation of Nirex Quaternary Boreholes (QBH) drilled in the Sellafield area during 1996. UK NIREX Ltd Report, No. SA/97/043.

NIREX. 1997(j). Analytical studies of the provenance, micropalaeontology and chronology of Quaternary sediments from the Sellafteld area, 1996. UK NIREX Ltd Report, No. SA/97/044.

NIREX. 1997(k). The Quaternary lithostratigraphy of the Sellafield district. UK NIREX Ltd Report, No. SA/97/045.

NIREX. 1997(1). Interpretation of the BNFL/Nirex offshore high resolution seismic data. UK NIREX Ltd Report, No. SA/97/042.

PANTIN, H Monograptus 1977. Quaternary sediments of the northern Irish Sea. 27–54 in The Quaternary history of the Irish Sea. KIDSON, C, and TOOLEY, M J (editors). Geological journal Special Issue, 7.

O'BRIEN, C, PLANT, J A, SIMPSON, P R, and TARNEY, J. 1985. The geochemistry, metasomatism and petrogenesis of the granites the English Lake District. Journal of the Geological Society of London, Vol. 142, 1139–1157.

PANTIN, H Monograptus 1978. Quaternary sediments from the northeast Irish Sea: Isle of Man to Cumbria. Bulletin of the Geological Survey of Great Britain, Vol. 64, 1–43.

PATTISON, J 1970. A review of the marine fossils from the Upper Permian rocks of Northern Ireland and North-West England. Bulletin of the Geological Survey of Great Britain, No. 32, 123–163.

PENN, I E, and 7 OTHERS. 1983. The Larne No. 2 Borehole: discovery of a new Permian volcanic centre. Scottish Journal of Geology, Vol. 19, 333–346.

PENNINGTON, W. 1978. Quaternary geology. 207–225 in The geology of the Lake District. MOSELEY, F (editor). Occasional Publication of the Yorkshire Geological Society, No. 3.

PETTERSON, M G, BEDDOE-STEPHENS, B, MILLWARD, D, and JOHNSON, E W. 1992. A pre-caldera plateau-andesite field in the Borrowdale Volcanic Group of the English Lake District. Journal of the Geological Society of London, Vol. 149, 889–906.

PICKEN, G S. 1988. The concealed coalfield at Canonbie: an interpretation based on boreholes and seismic surveys. Scottish Journal of Geology, Vol. 24, 61–71.

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. 1977. Major cycles of transgression and regression (mesothems) in the Namurian. Proceedings of the Yorkshire Geological Society, Vol. 41, 261–291.

RAMSBOTTOM, W H C, and 6 OTHERS. 1978. A correlation of Silesian rocks in the British Isles. Geological Society of London Special Report, No. 10.

RAWSON, P F, and RILEY, L A. 1982. Latest Jurassic-Early Cretaceous events and the 'Late-Cimmerian Unconformity' in the North Sea area. Bulletin of the American Association of Petroleum Geologists, Vol. 66, 2628–2648.

RIPPON, J H. 1996. Sand body orientation, palaeoslope analysis and basin-fill implications in the Westphalian A-C of Great Britain. Journal of the Geological Society of London, Vol. 153, 881–900.

ROBERTS, D G. 1989. Basin inversion in and around the British Isles. 131–150 in Inversion tectonics. COOPER, M A, and WILLIAMS, G D (editors). Geological Society of London Special Publication, No. 44.

ROSE, J. 1985. The Dimlington Stadial/Dimlington Chronozone: a proposal for the naming of the main glacial episode of the Late Devensian in Britain. Boreas, Vol. 14, 225–230.

ROSE, J. 1989. Stadia( type sections in the British Quaternary. 45–67 in Quaternary type sections: imagination or reality? ROSE, J, and SCHLUCHTER, C (editors). (Rotterdam: Balkema.)

ROSE, W C C, and DUNHAM, K C. 1977. Geology and hematite deposits of South Cumbria. Memoir of the Geological Survey of Great Britain, Sheets 58, part 48.

RUSHTON, A W A. 1988. Tremadoc trilobites from the Skiddaw Group in the English Lake District. Palaeontology, Vol. 31, 677–698.

SCHNELLMANN, G A. 1947. The West Coast haematite bodies. Mining Magazine (London), Vol. 76, 137–151.

SCHUMM, S A. 1977. The fluvial system. (New York: John Wiley & Sons.)

SCOTESE, C R, BAMBACH, R K, BARTON, C, VAN DER V00, R, and ZIEGLER, A Monograptus 1979. Palaeozoic base maps. Journal of Geology, Vol. 87, 217–277.

SEDGWB K, A. 1832. On the new Red Sandstone Series in the Basin of the Eden, and north-western coasts of Cumberland and Lancashire. Transactions of the Geological Society, Vol. 4, Series 2nd, 383–407.

SHACKLETON, N J. 1969. The last interglacial in the marine and terrestrial records. Proceedings of the Royal Society of London, Series B, Vol. 174, 135–154.

SHACKLETON, N J, and OPDYKE, N D. 1973. Oxygen isotope and palaeomagnetic stratigraphy of equatorial Pacific core V28–238: oxygen isotope temperatures and ice volumes on a 105 year and 106 year scale. Quaternary Research, Vol. 3, 39–55.

SHACKI.ETON, N J, and OPDYKE, N D. 1976. Oxygen isotope and palaeomagnetic stratigraphy of Equatorial Pacific core. V28–239, Late Pliocene to Latest Pliestocene. 449–464 in Investigation of late Quaternary palaeoceanography and palaeoclimatology. CLINE, R M, and HAGS, J D (editors). Geological Society of America Memoir, No. 145.

SHENNAN, I. 1992. Late Quaternary sea-level changes and crustal movements in eastern England and eastern Scotland: an assessment of models of coastal evolution. 161–173 in Impacts of tectonics on Quaternary coastal evolution. NELSON, A R, and BERRYMAN, K R (editors). Quaternary International, Vol. 15/16.

SHEPHERD, T J, and GOLDRING, D C. 1993. Cumbrian hematite deposits, north-west England. 419–445 in Mineralization in the British Isles. PArnuot, R A D, and POLYA, D A (editors). (London: Chapman and Hall.)

SHERLOCK, R L, and SMITH, B. 1938. Gypsum and anhydrite, celestine and strontianite. Special Reports on the Mineral Resources of Great Britain. Memoir of the Geological Survey of Great Britain, Vol. 3.

SISSONS, J B. 1980. The Loch Lomond Advance in the Lake District, northern England. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 71,13–27.

SMITH, B. 1920. Cumberland. 5–6 in Mineral oil, Kimmeridge oil-shale, lignites, jets, cannel coals, natural gas, England and Wales (2nd edition). STRAHAN, A. Special Report on the Mineral Resources of Great Britain. Memoir of the Geological Survey of Great Britain, Vol. 7.

SMITH, B. 1924. Iron ores: haematites of west Cumberland, Lancashire and the Lake District (2nd edition). Special Report on the Mineral Resources of Great Britain. Memoir of the Geological Survey of Great Britain, Vol. 8.

SMITH, B. 1932. The glacier-lakes of Eskdale, Miterdale and Wasdale, Cumberland; and the retreat of the ice during the main glaciation. Quarterly Journal of the Geological Society of London, Vol. 88,57–83.

SMITH, D B, and TAYLOR, J C Monograptus 1992. Permian. 87–96 in Atlas of palaeogeography and lithofacies. (Memoir of the Geological Society of London). COPE, J C W, INGHAM, J K, and RAWSON, P F (editors). (London: The Geological Society, London.)

SMOOT, J P, and CASTENS-SEIDELL, B. 1994. Sedimentary features produced by efflorescent salt crusts, Saline Valley and Death Valley, California. 73–90 in Sedimentology and geochemistry of modern and ancient saline lakes. RENAUT, R W, and LAST, W M (editors). SEPM (Society for Sedimentary Geology) Special Publication, No. 50.

SMOOT, J P, and OLSEN, P E. 1988. Massive mudstones in basin analysis and paleoclimatic interpretation of the Newark Supergroup. 249–274 in Triassic Jurassic rifling, continental breakup and the origin of the Atlantic Ocean and passive margins. Part A. MANSPEIZER, W (editor). (Amsterdam, Oxford, New York, Tokyo: Elsevier.)

SOPER, N J, ENGLAND, R W, SNYDER, D B, and RYAN, P D. 1992. The Iapetus suture zone in England, Scotland and eastern Ireland: a reconciliation of geological and deep seismic data. Journal of the Geological Society of London, Vol. 149,697–700.

SOPER, N J, and WOODCOCK, N H. 1990. Silurian collision and sediment dispersal patterns in southern Britain. Geological Magazine, Vol. 127,527–542.

STABBINS, R. 1969. The depositional history of the Lower Carboniferous rocks of west Cumberland. Unpublished PhD thesis, University of London.

STANLEY, C J, and VAUGHAN, D J. 1982. Copper, lead, zinc and cobalt mineralization in the English Lake District: classification, conditions of formation and genesis. Journal of the Geological Society of London, Vol. 139,569–579.

STRAHAN, A, GIBSON, W, CANTRILL, T C, SHERLOCK, R L, and DEWEY, H. 1920. Pre-Carboniferous and Carboniferous bedded ores of England and Wales. (2nd edition). Special Report on the Mineral Resources of Great Britain, Memoir of the Geological Survey of Great-Britain, Vol. 13.

STRONG, G E, and MILODOWSKI, A E. 1987. Aspects of the diagenesis of the Sherwood Sandstones of the Wessex Basin and their influence on reservoir characteristics. 325–337 in Diagenesis of sedimentary sequences. MARSHALL, D (editor). Geological Society of London Special Publication, No. 36.

STRONG, G E, and 5 OTHERS. 1994. The petrology and diagenesis of Permo-Triassic rocks of the Sellafield area, Cumbria. Proceedings of the Yorkshire Geological Society, Vol. 50, 77–89.

STUART, I A, and COWAN, G. 1991. The South Morecambe Field, Blocks 110/2a, 110/3a, 110/8a, UK East Irish Sea. 527–541 in United Kingdom Oil and Gas Fields 25 Years Commemorative Volume. Assorts, I L (editor). Memoir of the Geological Society of London, No. 14.

TALBOT, M R, HOLM, K, and Williams, M A J. 1994. Sedimentation in low-gradient desert margin systems: a comparison of the Late Triassic of northwest Somerset (England) and the late Quaternary of east-central Australia. 97–117 in Paleoclimate and basin evolution of playa systems. ROSEN, M R (editor). Geological Society of America Special Paper, 289.

TAPPIN, D R, CHADWICK, R A, JACKSON, A A, WINGFIELD, R T R, and SMITH, N J P. 1994. United Kingdom offshore regional report. The geology of Cardigan Bay and the Bristol Channel. (London: HMSO for British Geological Survey.)

TAYLOR, B J. 1961. The stratigraphy of exploratory boreholes in the west Cumberland coalfield. Bulletin of the Geological Survey of Great Britain, No. 17,1–74.

TAYLOR, B J. 1978. Westphalian. 180–187 in The geology of the Lake District. MOSELEY, F (editor). Occasional Publication of the Yorkshire Geological Society, No. 3.

TAYLOR, B J, and 5 OTHERS. 1971. British regional geology. Northern England (4th edition). (London: HMSO for Institute of Geological Sciences.)

TAYLOR, J C Monograptus 1990. Late Permian-Zechstein. 153–190 in Introduction to the petroleum geology of the North Sea (3rd edition). GLENNIE, K W (editor). (Oxford: Blackwell Scientific Publications.)

TAYLOR, S R, and MCLENNAN, S Monograptus 1985. The continental crust: its composition and evolution. (Oxford: Blackwell Scientific Publications.)

THIRLWALL, M F, and FITTON, J G. 1983. Sm-Nd garnet age for the Ordovician Borrowdale Volcanic Group, English Lake District. Journal of the Geological Society of London, Vol. 140, 511–518.

THOMAS, G S P. 1985. The Quaternary of the northern Irish Sea basin. 143–158 in The geomorphology of North-west England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

THOMAS, G S P. In press. Northern England. In A correlation of the Quaternary rocks of the British Isles. BOWEN, D Q (editor). Geological Society of London Special Report.

THURLOW, A. 1996. Sedimentary style in a mixed carbonatesiliclastic depositional setting: the Late Dinantian of Northwest Cumbria. Unpublished PhD thesis, University of Manchester.

TOOLEY, M J. 1978. Sea-level changes in north-west England during the Flandrian stage. (Oxford: Clarendon Press.)

TOOLEY, M J. 1985. Sea-level changes and coastal morphology in north-west England. 94–121 in The geomorphology of northwest England. JOHNSON, R H (editor). (Manchester: Manchester University Press.)

TRENCH, A, TORSVIK, T H, SMETHURST, M A, WOODCOCK, N H, and METCALF, R. 1991. A palaeomagnetic study of the Builth Wells–Llandrindod Wells Ordovician Inlier, Wales: palaeogeographic and structural implications. Geophysical Journal International, Vol. 105,477–489.

TROTTER, F Monograptus 1929(a). The Tertiary uplift and resultant drainage of the Alston Block and adjacent areas. Proceedings of the Yorkshire Geological Society, Vol. 21,161–180.

TROTTER, F Monograptus 1929(b). The glaciation of the Eastern Edenside, the Alston Block, and the Carlisle Plain. Quarterly Journal of the Geological Society of London, Vol. 85, 549–612.

TROTTER, F Monograptus 1945. The origin of the west Cumbrian haematites. Geological Magazine, Vol. 82, 67–80.

TROTTER, F Monograptus 1953. Reddened beds of Carboniferous age in north-west England and their origin. Proceedings of the Yorkshire Geological Society, Vol. 29, 1–20.

TROTTER, F M, and HOLLINGWORTH, S E. 1932(a). The geology of the Brampton district. Memoir of the Geological Survey of Great Britain, Sheet 18 (England and Wales).

TROTTER, F M, and HOLLINGWORTH, S E. 1932(b). The glacial sequence in the North of England. Geological Magazine, Vol. 69, 374–380.

TROTTER, F M, HOLLINGWORTH, S E, EASTWOOD, T, and ROSE, W C C. 1937. Gosforth District. Memoir of the Geological Survey of the Great Britain, Sheet 37 (England and Wales).

TRUSHEIM, F. 1963. Zur Gliederung des Buntsandsteins. Erdoel Zeitschrift, Vol. 7, 277–292.

TUCKER, M E. 1991. Sequence stratigraphy of carbonate-evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea. Journal of the Geological Society of London, Vol. 148, 1019–1036.

UNDERHILL, J R, and 5 OTHERS. 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.

VAN HOORN, B. 1987. Structural evolution, timing and tectonic style of the Sole Pit inversion. Tectonophysics, Vol. 137, 239–284.

VANSTONE, S D. 1996. The influence of climatic change on exposure surface development: a case study from the Late Dinantian of England and Wales. 281–301 in Recent advances in Lower Carboniferous geology. STROGEN, P, SOMERVILLE, I D, and JONES, G L (editors). Geological Society of London Special Publication, No. 107.

WADGE, A J. 1978. Classification and stratigraphical relationships of the Lower Ordovician rocks. 68–78 in The geology of the Lake District. MOSELEY, F (editor). Occasional Publication of the Yorkshire Geological Society, No. 3.

WALKDEN, G Monograptus 1972. The mineralogy and origin of interbedded clay wayboards in the Lower Carboniferous of the Derbyshire Dome. Geological Journal, Vol. 8, 143–160.

WALKER, D. 1956. A Late-glacial deposit at St Bees, Cumberland. Quarterly Journal of the Geological Society of London, Vol. 112, 93–101.

WALKER, D. 1966. The Late Quaternary history of the Cumberland lowland. Philosophical Transactions of the Royal Society of London, Series B, Vol. 251, 1–210.

WALKER, T R, WAUGH, B, and GRONE, A J. 1978. Diagenesis in first-cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico. Geological Society of America Bulletin, Vol. 89, 19–32.

WALSH, P T, BOULTER, M C, IJTABA, M, and URRAisa, D Monograptus 1972. The preservation of the Neogene Brassington Formation of the southern Pennines and its bearing on the evolution of Upland Britain. Journal of the Geological Society of London, Vol. 128, 519–559.

WARD, J C. 1876. The geology of the northern part of the English Lake District. Memoir of the Geological Survey of Great Britain.

WARRINGTON, G. 1970. The stratigraphy and palaeontology of the 'Keuper' Series of the central Midlands of England. Quarterly Journal of the Geological Society of London, Vol. 126, 183–223.

WARRINGTON, G, and 8 OTHERS. 1980. A correlation of Triassic rocks in the British Isles. Geological Society of London Special Report, No. 13.

WEBB, B C, and COOPER, A H. 1988. Slump folds and gravity slide structures in a Lower Palaeozoic marginal basin sequence (the Skiddaw Group), North West England. Journal of Structural Geology, Vol. 10, 463–472.

WHITTAKER, A (editor). 1985. Atlas of onshore sedimentary basins in England and Wales: post- Carboniferous tectonics and stratigraphy. (Glasgow: Blackie.)

WILLS, L J. 1951. A palaeogeographic atlas of the British Isles and adjacent parts of Europe. (London, Glasgow: Blackie & Son.)

WILSON, A A. 1990. The Mercia Mudstone Group (Trias) of the East Irish Sea Basin. Proceedings of the Yorkshire Geological Society, Vol. 48, 1–22.

WINGFIELD, R T R. 1995. A model of sea-levels in the Irish and Celtic seas during the end-Pleistocene to Holocene transition. 209–242 in Island Britain: a Quaternary perspective. PREECE, R C (editor). Geological Society of London Special Publication, No. 96.

WOOD, O. 1988. West Cumberland Coal 1600–1982/3. Cumberland and Westmorland Antiquarian and Archaeological Society, Extra Series 24.

YOUNG, B. 1987. Glossary of the minerals of the Lake District and adjoining area. (Newcastle Upon Tyne: British Geological Survey.)

YOUNG, B, and ARMSTRONG, Monograptus 1989. The applied geological mapping of the Dearham and Gilcrux area, Cumbria. British Geological Survey Technical Report, WA/89/70.

YOUNG, B, and BOLAND, M P. 1992. Geology and land-use planning: Great Broughton–Lamplugh area, Cumbria. Part 1. Geology. British Geological Survey Technical Report, WA/92/54.

YOUNG, B, and NANCARROW, P H A. 1990. Hausmannite from west Cumbria. Journal of the Russell Society, Vol. 3, 29–30.

ZIEGLER, P A. 1990. Geological atlas of western and central Europe (2nd edition). (Shell Internationale Petroleum: Maatschappij B.V.)

ZONG, Y, and TOOLEY, M J 1996. Holocene sea-level changes and crustal movements in Morecambe Bay, northwest England. Journal of Quaternary Science, Vol. 11, 43–58.

Figues, plates and tables

Figures

(Figure 1) Geological map of the west Cumbria district.

(Figure 2) Topography of the district.

(Figure 3) Location map of the Sellafield boreholes within the district.

(Figure 4) Principal structural features of the Lake District Block and the west Cumbria district. (Modified from Nirex, 1993c).

(Figure 5) Map of the West Cumbrian Iron Orefield.

(Figure 6) Sections through haematite orebodies, west Cumbria, after Smith (1924, figs 6,9 and 16). Locations shown on (Figure 5).

(Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7) Principal faults identified in the district. Most faults are mapped at base Permo-Triassic; the Maryport Fault is mapped at base Carboniferous, and faults in the Caledonian basement (stipple ornament) are mapped at outcrop. Location of cross-sections in (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070).

(Figure 8) Regional cross-sections, locations on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). Modified from Nirex (1995d figs. 010055 and 010056).

(Figure 9) Aeromagnetic map (total field) of the district. Bold line indicates the extent of detailed surveys conducted for Nirex in 1990–91, with surveys flown at an elevation of 300 m in the offshore area (500 m survey line spacing) and 100 m above terrain in the onshore area, continued to 300 m for this image (200 m survey line spacing). Surrounding BGS data flown in 1958–59 at an elevation of 305 m (1000 ft) above terrain and with survey line spacings of 2 km, increasing to 4 km within the south-western quadrant. An empirical datum shift has been applied to the more recent survey values to provide an approximate fit to the reference field used for the earlier survey. Colour levels are defined on an equal-area basis; illumination is from the north. Ml-M10 = features discussed in the text, BC = Black Combe inlier, EN = Ennerdale intrusion, ES = Eskdale intrusion.

(Figure 10) Bouguer gravity anomaly map of the district, based on data from BGS, Nirex and Western Geophysical. Contour interval = 1 mGal (= 10-5 ms-2). Bold line indicates extent of detailed gravity data in the offshore area (survey line density is much lower outside this area and apparent contour inflections at the boundary may be spurious). Reduction density = 2.7 Mgm-3 (onshore and detailed marine data) and 2.2 Mgm-3 (remainder of offshore area). BC = Black Combe inlier.

(Figure 11) Residual Bouguer gravity anomaly map of part of the district after removal of a third-order polynomial surface (calculated over an area of 40 X 35 km). Contour interval = 0.5 mGal. CR, ES, EN, F, RG = features discussed in the text.

(Figure 12) True-scale cross-section in the eastern part of the district showing the western edge of the Lake District batholith and putative Caledonian basement rocks beneath the sedimentary cover. Inset shows seismic reflection data over the Lake District batholith. A, B granitic laccoliths (part of the component of the Lake District batholith underlying the Ennerdale granite); BVG Borrowdale Volcanic Group in the Sellafield boreholes and at outcrop; SD Seatallen Member.

(Figure 13) Geological map of the area to the north and east of Gosforth.

(Figure 14a) Stereographic plots of fault and fracture orientation in the Borrowdale Volcanic Group in boreholes and at outcrop. Poles to planes. Lower hemisphere, equal area projection. Faults orientated from vertical, Sellafield boreholes. Terzaghi weighted contours.

(Figure 14b) Stereographic plots of fault and fracture orientation in the Borrowdale Volcanic Group in boreholes and at outcrop. Poles to planes. Lower hemisphere, equal area projection. Orientated discontinuity data, Terzaghi weighted, Sellafield RCF3 Borehole.

(Figure 14c) Stereographic plots of fault and fracture orientation in the Borrowdale Volcanic Group in boreholes and at outcrop. Poles to planes. Lower hemisphere, equal area projection. Fracture orientation from exposures in the Bleng valley area within the Lake District Boundary Fault Zone.

(Figure 14d) Stereographic plots of fault and fracture orientation in the Borrowdale Volcanic Group in boreholes and at outcrop. Poles to planes. Lower hemisphere, equal area projection. Fracture orientation in the footwall block of the Thistleton Fault.

(Figure 15a) Carboniferous tilt-blocks beneath thick Permo-Triassic cover, East Irish Sea Basin. Note putative normal faults which do not penetrate base Permo­-Triassic unconformity.

(Figure 15b) Marked unconformity in the Solway Basin provides evidence for repeated basin inversion. Thus, at the onset of Permo-Triassic deposition Carboniferous strata dipped steeply to the south-east, on the limb of a major Variscan anticline. Subsequent inversion in Cainozoic times tilted Permo-Triassic strata to the north-west, on the limb of an Alpine anticline in the hanging-wall block of the Maryport Fault, which lies a few kilometres to the south-east of seismic line. Location of seismic lines shown on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

(Figure 16) Principal Permo-Triassic and younger structural elements of the west Cumbria district. Black denotes Permo-Triassic and younger normal faults, sepia denotes Cainozoic contractional (inversion) features. BrF Braystone Fault; HaF Harriet Fault; HseF High Sellafield Fault; LaF Lagman Fault; LDBFZ Lake District Boundary Fault Zone; NaF Natasha Fault; SiF Sigurd Fault; TyF Tynwald Fault.

(Figure 17a) Faulting in the Permo-Triassic cover of the offshore district. Braystones Fault (SSL84M-2). Location of seismic lines shown on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

(Figure 17b) Faulting in the Permo-Triassic cover of the offshore district. Natasha Fault (SSL84M-7). Location of seismic lines shown on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

(Figure 18) Stereographic plot of faults within the Sherwood Sandstone Group, based on data from outcrop and Sellafield boreholes. Poles to planes. Lower hemisphere, equal area projection.

(Figure 19a) Detached normal faulting in the Tynwald Basin with development of hanging-wall block rollover. The normal fault at the north-east end of the section is probably a splay from the Lake District Boundary Fault Zone. For key to abbreviations see (Figure 17b).

(Figure 19b) Tynwald Fault Zone in the southern part of the district. The Sherwood Sandstone Group is severely structurally attenuated beneath the downfaulted central block, but thickens eastwards due to the overall down-to-the-east geometry. Note development of detached folding within the Mercia Mudstone Group of the central fault-block. Location of seismic lines shown on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7). For key to abbreviations see (Figure 17b).

(Figure 20) Summary stratigraphy of the Skiddaw Group, after Cooper et al. (1995); not to scale. Causey Pike Fault is shown on (Figure 8) and seismic lines in (Figure 15a), (Figure 15b), (Figure 17a), (Figure 17b), (Figure 19a) and (Figure 19b) are also shown. (Modified from Nirex, 1995d fig. 010070)." data-name="images/P947373.jpg">(Figure 7).

(Figure 21) Generalised lithostratigraphy of the Borrowdale Volcanic Group north and east of Gosforth.

(Figure 22) Lithostratigraphy of the Borrowdale Volcanic Group in the Sellafield boreholes. With the exception of Sellafield RCF1 Borehole, which was deviated from the vertical, all boreholes are nominally vertical. The thicknesses of the successions in the boreholes are not corrected for dip of the beds.

(Figure 23) Stratigraphy of the Chief Limestone Group in the district. *After Barclay et al. (1994).

(Figure 24) Stratigraphy of the Hensingham Group in the Distington Borehole and correlation with the Rowhall Farm Borehole in the Maryport district.

(Figure 25) Generalised vertical section of the Coal Measures in the district. 1. After British Coal Opencast Executive. 2. After Ramsbottom et al., 1978.

(Figure 26) Generalised stratigraphy of the Whitehaven Sandstone Formation.

(Figure 27) Main Permo-Triassic structural features of the region (modified from Jackson et al., 1995).

(Figure 28) Carlisle Basin seismic reflection profile. Location of seismic line shown on (Figure 27).

(Figure 29) Sub-Permian geological map, modified from Nirex (1993e).

(Figure 30a) Depositional model of the Permo-Triassic rocks of the eastern part of the district. Brockram.

(Figure 30b) Depositional model of the Permo-Triassic rocks of the eastern part of the district. St Bees Evapourite – basal dolomite.

(Figure 30c) Depositional model of the Permo-Triassic rocks of the eastern part of the district. St Bees Evapourite – anhydrite.

(Figure 30d) Depositional model of the Permo-Triassic rocks of the eastern part of the district. St Bees Shale.

(Figure 30e) Depositional model of the Permo-Triassic rocks of the eastern part of the district. St Bees Shale/ St Bees Sandstone transition.

(Figure 30f) Depositional model of the Permo-Triassic rocks of the eastern part of the district. St Bees Sandstone.

(Figure 30g) Depositional model of the Permo-Triassic rocks of the eastern part of the district. Calder Sandstone.

(Figure 30h) Depositional model of the Permo-Triassic rocks of the eastern part of the district. Ormskirk Sandstone.

(Figure 31) Stratigraphical relationships in the Appleby and Cumbrian Coast groups (not to scale).

(Figure 32) Borehole correlation Appleby and Cumbrian Coast groups.

(Figure 33) Borehole correlation Sherwood Sandstone Group. Gamma-ray in sepia: sonic log in black.

(Figure 34) REE geochemistry and inferred provenance of the St Bees Sandstone Formation in Sellafield 2 Borehole.

(Figure 38)." data-name="images/P947414.jpg">(Figure 35) Simplified geological map of the region with locations of apatite fission-track sites, selected boreholes and line of cross-section (Figure 38).

(Figure 36a) Depth of burial studies. Solid lines denote assumed normal compaction curves. Calder Sandstone Formation densities

(Figure 36b) Depth of burial studies. Solid lines denote assumed normal compaction curves. Calder Sandstone Formation transit times.

(Figure 36c) Depth of burial studies. Solid lines denote assumed normal compaction curves. St Bees Sandstone Formation transit times.

(Figure 36d) Map of selected Sellafield boreholes showing absolute uplift at each site and thickness of post-St Bees Sandstone Formation overburden (in brackets) in metres.

(Figure 37) Computed values and contours of post-early Palaeocene uplift in north-west England. Uplift values in metres are based on apatite fission-track palaeotemperatures and borehole log compaction studies.

(Figure 38) Regional cross-section, for location see (Figure 37). a. Present-day showing putative eroded overburden. b. Restored to early Palaeocene datum.

(Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39) a. Location of boreholes proving the Quaternary succession and localities mentioned in the text. Offshore channels infilled with up to 100 m of sediment shown in stipple. Position of seismic line in (Figure 42) and inset for (Figure 42) and inset for (Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels." data-name="images/P947421.jpg">(Figure 39)b also shown. b. Distribution of glacigenic sediments, ice movement direction and glacial drainage channels.

(Figure 40a) General pattern of ice-flow direction in northern England during the last glaciation (Taylor et al., 1971).

(Figure 40b) Build-up of the main Late Devensian ice sheet about 26 ka BP.

(Figure 40c) Main Late Devensian glaciation about 25–22 ka BP.

(Figure 40d) Retreat of ice of the main phase of the Late Devensian glaciation after 18 ka BP.

(Figure 40e) Readvance of Irish Sea ice about 16 ka BP (Gosforth Oscillation).

(Figure 40f) Retreat of ice after the Gosforth Oscillation.

(Figure 40g) The Scottish Readvance about 14 ka BP.

(Figure 41) Schematic section showing relationships of seismostratigraphical formations and seismic sequences offshore within the district (modified after Jackson et al., 1995; Nirex, 1997f, 1).

(Figure 42) Seismostratigraphical architecture of the offshore Quaternary, an interpretation of seismic lines 89/29, shotpoints 2621–2630 (from Nirex, 1997l).

(Figure 43) Distribution, thickness and facies of the Western Irish Sea Formation (from Jackson et al., 1995).

(Figure 44) Location of recorded boreholes in the district.

Maps

(Map 1) Base Mercia Mudstone Group, depth contours in metres relative to OD.

(Map 2) Base Calder Sandstone, Sherwood Sandstone Group, depth contours in metres relative to OD.

(Map 3) Base St Bees Sandstone, Sherwood Sandstone Group, depth contours in metres relative to OD.

(Map 4) Base Appleby Group (base Permo-Triassic), depth contours in metres relative to OD.

(Map 5) Base Carboniferous, depth contours in metres relative to OD.

(Map 6) Top Lower Palaeozoic basement, depth contours in metres relative to OD.

Plates

(Front cover) Cover photograph St Bees Sandstone Formation exposed in the type section at St Bees Head (D04735). (Photographer: Tom Bain).

(Plate 1) Landsat image of the west Cumbria district. Processed by BGS Keyworth. Bands 4, 5 and 7, edge-enhanced, geometrically corrected to British National Grid.

(Plate 2) West Cumbria landscape looking eastwards from Lostrigg Beck [NX 043 273] across boulder clay covered Coal Measures to the rugged topography of the Lower Paleaozoic Loweswater Fells on the eastern margin of the district (D04653).

(Plate 3) Part of the St Bees Fault Zone exposed in the St Bees Sandstone Formation at St Bees Head [NX 9503 1230]. South-dipping faults in the northern part of the fault zone showing conjugate arrays of fractures in the intervening blocks. Cliff is 70 m in height, looking east-north-east (MNS5973/6–7).

(Plate 4) Textural features in the volcaniclastic rocks of the concealed Borrowdale Volcanic Group. a. Eutaxitic fabric defined by prominent chloritised fiamme in the Longlands Farm Member of the Fleming Hall Formation within Sellafield 4 Borehole (430 m below OD). Rheomorphism is indicated by microfolding of some fiamme (lower right) (GS0460/a). b. Eutaxitic fabric and characteristic angular, white felsitic lithic clasts in the Seascale Hall Member of the Brown Bank Formation within Sellafield 2 Borehole (906 m below OD) (GS0460/b). c. The Sella Park Member of the Yottenfews Formation within Sellafield 7A Borehole (706 m below OD). This very densely welded, rhyolitic ignimbrite is characterised by common well-preserved spherulites and perlitic cracks (GS0460/c). d. Bedded volcaniclastic sandstone and siltstone in the Newton Manor Formation within Sellafield 14A Borehole (723 m below OD) displaying syn-sedimentary deformation and microfaulting (GS0460/d).

(Plate 5) Irregularly laminated facies, St Bees Shale Formation (MN27924).

(Back cover)

Tables

(Table 1) Geological Succession of the district.

(Table 2) Fracture mineralisation chronology, principal associated minerals and mineralisation types in the Sellafield boreholes. From Nirex (1995a). Phases shown in bold are volumetrically dominant at the present day, though one or more of the other phases listed may be dominant locally.

(Table 3) Summary of mid-Dinantian classification of the district. The precise age of the Basal Beds is unknown and may be as old as Late Devonian. They are also likely to be diachronous and may locally be as young as Holkerian. Vertical hatching denotes significant non-sequences.

(Table 4) Standard and local coal seam names.

(Table 5) Lithostratigraphy of Permo-Triassic rocks in west Cumbria and the East Irish Sea basin from Barnes et al. (1994) and Jackson and Johnson (1996).

(Table 6) Brockram facies.

(Table 7) St Bees Sandstone Formation sheet-flood facies association. IMC = intraformational mudstone clast.

(Table 8) St Bees Sandstone Formation fluvial channel facies association.

(Table 9) St Bees Sandstone Formation aeolian facies association.

(Table 10a) Calder Sandstone Formation fluvial facies association.

(Table 10b) Calder Sandstone Formation aeolian facies association.

(Table 11) Summary of diagenetic events identified in Permo-Triassic rocks below the Mercia Mudstone Group and their relationship with fracture mineralisation events.

(Table 12) Eroded overburden and uplifted estimates (metres) from geophysical log compaction studies (Nirex, 1993d). NA = No logs available. ID = Insufficient log data.

(Table 13) Fission-track sites: palaeotemperatures, heatflows and estimates of eroded overburden and uplift, based on conductive thermal modelling (Nirex, 1993d). * Includes overburden present in borehole (i.e. depth in borehole) † Location and palaeotemperatures from Lewis et al., 1992 ‡ Mean of more than one analysis

(Table 14) Quaternary stratigraphy of the district. † Calendar years BP. *14C years BP.

(Table 15) Stratigraphical sequence within the St Bees Push Moraine.

(Table 16) Survey history of 1:10 000-scale geological maps of the district, showing initials of geological surveyors and dates of survey. The surveyors were: P M Allen, C A Auton, R G Crofts, B Beddoe-Stephens, A M Bell, M P Boland, R P Barnes, D J Fettes, D V Frost, R A Hughes, E W Johnson, N A Matthieson, M McCormac, J W Merritt, D Millward, M G Petterson, A J Reedman, N M S Rock, B C Webb and B Young.

(Table 17) Key boreholes used for the interpretation of the geology of the district.

Tables

(Table 2) Fracture mineralisation chronology, principal associated minerals and mineralisation types in the Sellafield boreholes

Mineralising episode Principal associated minerals Dominant type of mineralisation
ME1 K-feldspar/adularia ±quartz, ±chlorite, ±albite, ±haematite Silicate
ME2 Quartz ±epidote, ±calcite, ±chlorite, ±apatite, ±K-feldspar, ±albite, ±sericite, ±haematite Silicate (& carbonate)
ME3 Pyrite ±traces of chalcopyrite, arsenopyrite, marcasite, galena sphalerite, Bi-Se sulphosalts and quartz Sulphide (& silicate?)
ME4 Anhydrite ±barite, ±fluorite, ±haematite, ±quartz, ±siderite (?), ±K-feldspar Sulphate
ME5 Albite, K-feldspar, kaolinite, illite, ±haematite Silicate
ME6a Early ME6a ferroan/manganoan carbonate now replaced completely by specular haematite and calcite with abundant inclusions of Fe- and Mn-oxides. Late ME6 calcite and haematite Carbonate
ME6b Dolomite, ferroan dolomite, ankerite, ±siderite, ±quartz, ±anhydrite, ±ferroan calcite ±Sulphate
ME6c Calcite (usually ferroan), ±barite, ±fluorite, ±haematite, ±pyrite, ±sphalerite, ±galena ±Sulphate
ME7 Illitic clay and haematite Silicate and oxide
M E8 Mn- and Fe- oxides/oxyhydroxides Oxide
ME9 Calcite ±pyrite, ±anhydrite, ±gypsum Carbonate ±sulphate ±sulphide
  • From Nirex (1995a).
  • Phases shown in bold are volumetrically dominant at the present day, though one or more of the other phases listed may be dominant locally.

(Table 4) Standard and local coal seam names

Standard names Alternative seam names
Unnamed J Siddick
Unnamed I Isabella
Unnamed H Ellen
Unnamed G Senhouse Senhouse High Band
Unnamed F Watergate, Crow
Unnamed E Gale
Brassy
Black Metal Weddicar Asby Surface Lamb Hill coals
Fireclay
White Metal Cleator Moor Six Foot Upper Metal
Slaty Cleator Moor Four Foot Preston Isle (Haig Pit)
Tenquarters Cleator Moor Five Foot China Preston Isle (Wellington Pit)
Bannock Band
Main Band Prior
Yard Metal Band
Half Yard
Little Main Two Foot
Eighteen Inch Potash
Lickbank
Sixquarters Yard
Wythemoor Parrot
Upper Threequarters
Lower Threequarters Micklam Fireclay
Albrighton
Harrington Four Foot Virgin

(Table 5) Lithostratigraphy of Permo-Triassic rocks in west Cumbria and the East Irish Sea basin

GROUP WEST CUMBRIA

EAST IRISH SEA BASIN
Lias Group

Not present onshore in district

Lias Group
Penarth Group

Penarth Group
Mercia Mudstone Group

Mercia Mudstone Group (Formations not listed)

Sherwood Sandstone Group

 Ormskirk Sandstone Fm

Ormskirk Sandstone Fm
Calder Sandstone Fm

St Bees Sandstone Fm

 Calder Sst Mb.
St Bees Sandstone Fm North Head Member at base Rottington Mb.

Cumbrian Coast Group

 St Bees Shale Fm

Barrowmouth Mudstone Fm
St Bees Evaporite Fm

St Bees Evaporite Fm
Appleby Group Brockram

Collyhurst Sandstone Fm
  • from Barnes et al. (1994) and Jackson and Johnson (1996).

(Table 6) Brockram facies

Facies (% volume) Description Interpretation
Matrix-supported conglomerate (77%) Pebble- to cobble-grade, matrix-dominated conglomerate, poorly sorted and massive. Some coarse-tail and inverse coarse-tail grading, rare vertically inclined clasts. Matrix up to 50%, comprising mudstone or poorly sorted muddy sandstone. Clast types dominantly extraformational, rare intraformational mudstone clasts. Uncommon calcrete development. Weakly bedded, 0.5 to 2.0 m thick. Debris flow: cohesive or non-cohesive depending on the mud content.
Clast-supported conglomerate (8%) Granule- to pebble-grade, clast-supported, moderately sorted, erosively based conglomerate. Common normal grading, rare imbrication and cross-bedding with sets up to 0.1 m. Matrix comprises poorly sorted mudstone to very coarse-grained sandstone. Uncommon calcrete development. Moderately to well bedded, 0.05 to 0.5 m thick Tractional sheetflood deposit.
Thinly bedded sandstone

(3%)

 Very fine- to fine-grained sandstone, in thin beds that gradationally overlie matrix-supported conglomerate. Parallel lamination, rare convolute lamination. Well bedded, gradational base, 0.01 to 0.05 m thick Water-laid deposit, formed during waning of a debris flow, results in reworking and winnowing of fines.
Thickly bedded sandstone

(5%)

 Very fine- to fine-grained muddy sandstone, parallel laminated and cross-laminated, with normal grading. Well bedded, sharp based, 0.05 to 0.2 m thick Unconfined tractional sheetflood
Irregularly laminated sandstone and siltstone

(2%)

 Very fine- to fine-grained muddy sandstone, siltstone and rare claystone. Irregular to poor lamination, cross- lamination, load casts, minor desiccation, and rare adhesion structures. Common calcrete lenses and nodules. Poorly bedded, 0.1 to 2.0 m thick. Mixed tractional, suspension and wind-blown deposits, modified by pedogenesis.
Laminated mudstone (3%) Claystone or siltstone, reddish brown, commonly interlaminated. Rare sandy laminae, parallel laminated, rare current and wave ripples, and rare desiccation cracks Facies occurs near the top of the Brockram. Well bedded, 0.05 to 0.3 m thick Suspension and tractional deposition in ephemeral lakes.
Destratified mudstone (2%) Claystone or siltstone, reddish brown, massive or faint disrupted wavy parallel lamination, and rare sandy lenses. Common calcrete or silcrete nodules and desiccation cracks. Poorly bedded, 0.1 to 1.0 m thick Waterlaid and wind­blown deposits, modified and disrupted by pedogenic processes.

(Table 7) St Bees Sandstone Formation sheet-flood facies association. IMC = intraformational mudstone clast

Facies (% volume) Description Interpretation
Sheetflood sandstone

(60%)

 Fine- to medium-grained, sharp-based, parallel or cross- bedded, reddish brown sandstone; fines upwards, may contain cross-lamination at the top of the bed. Sole marks may be present at the base of each bed. Up to 1 m in thickness, may be hundreds of metres in lateral extent. Deposition from unconfined, bedload­dominated, short-lived tractional flows.
Playa mudflat (30%) Reddish brown, massive, cross-laminated or parallel- laminated mudstones. May contain desiccation cracks. Up to 3 m in thickness, may be 100s to 1000s m in lateral extent. Deposition from

suspension in relatively small ephemeral lakes
Minor channel sandstones (10%) Fine- to medium-grained, erosively based, cross-bedded sandstone. More than one set of cross-bedding commonly present. IMCs common. Up to 2 m in thickness; unknown lateral extent. Confined bedload­dominated deposition in small ephemeral streams: possible down­stream-dominated accretion.

(Table 8) St Bees Sandstone Formation fluvial channel facies association

Facies (% volume) Sub-facies Description Interpretation

Major and minor channel (99%)

 Trough cross-bedded sandstone (55%) Fine- to medium-grained, trough cross-bedded sandstone. Sets up to 1.5 m thick, with concave-upwards set bases and asymptotic foresets. Wide, open trough forms common, with low-angle foresets. Rare mudstone clasts along foresets and at set bases. Channel sandstone typically 2 to 5 m thick. Dewatering and convolute lamination may occur near the top of channels Sinuous-crested dune bedforms generated by lower flow regime, unidirectional currents. Larger sets occupied the deeper parts of channels.
Planar cross-bedded sandstone (20%) Fine- to medium-grained sandstone, planar cross-bedded. Sets up to 1.5 m thick, with planar set bases and tops and asymptotic or angular foresets. Rare mudstone clasts along foresets and at set bases. Straight- to linguoid-crested dune bedforms generated by lower flow regime, unidirectional currents.
Planar-bedded sandstone

(7%)

 Fine- to medium-grained sandstone, well-defined parallel lamination or low-angle lamination with primary current lineation. Upper flow regime conditions related to high-velocity flows and shallow water depth. A grain traction carpet is developed and parallel lamination becomes the dominant bedform. Primary current lineation generated by streaks close to the bed.
Cross-laminate sandstone

(5%)

 Very fine- to fine-grained sandstone, cross-laminated. Sets up to 5 cm, laterally persistent for up to 10 m. Foresets asymptotic, trough-shaped lower bounding surfaces. Rare climbing ripples and ripple form sets occur. Asymmetrical ripples, formed by low energy tractional currents. Commonly associated with early stages of channel abandonment or episodes of waning flow. Climbing ripples form during periods of bedload transportation associated with abundant fallout of suspended sediment. Form sets represent the preserved ripple morphology.
Parallel- laminated sandstone (3%) Very fine- to fine-grained sandstone, with poorly formed parallel lamination; rare cross-lamination, and abundant mica. Low-energy deposit formed from a combination of suspended sediment clouds and bedload. Ripples produced at slightly higher flow velocities. Abundant mica inhibits ripple formation.
Conglomerate (5%) Beds of pebble conglomerate with common intraformational mudstone, and rare extraformational lithic clasts, in a sandstone matrix. Typically occur overlying channel bases, less commonly occur lining set or coset bases. Generally massive and clast supported; rarely imbricated and cross- bedded. Clasts vary in shape from angular to rounded. Lag deposits, representing coarsest sediment transported by the flow: clast-supported texture produced by winnowing. Clast angularity related to the degree of transportation.
Thinly bedded mudstone

(3%)

 Beds of claystone and siltstone, up to 0.1 m thick and 10s to 100s m in length. Massive or laminated, with common desiccation cracks. Channel drape, deposited from suspension during periods of low flow. Desiccation cracks formed during periods of exposure.
Thickly bedded mudstone (2%) Beds of claystone and siltstone up to 1 m thick and 10s to 1000s m in length. Commonly forms part of an upward- fining sequence. Minor interbedded sandstone. Massive or parallel laminated, desiccation cracks common. Deposition from suspension within an abandoned channel. Upward-fining indicates a reduction in flow velocities. Sandstones represent bedload deposition from infrequent, higher-energy flows.
Floodplain (1%) Floodplain mudstone Beds of claystone and siltstone from 1.0 to 2.0 m thick and 10s to 1000s m in length. Massive or parallel laminated, desiccation cracks. Laterally extensive sheet deposits. Suspension deposition in ephemeral lakes.

(Table 9) St Bees Sandstone Formation aeolian facies association

Facies (% volume) Description Interpretation
Dune sandstone (86%) Medium-grained, reddish brown sandstone, in beds from 0.2 to 1.5 m thick. Cross- bedded, with sets up to 0.2 m thick consisting of bimodally sorted foresets and some grainflow lamination. Rare convolute lamination and slump fold structures. Common, scattered, well-rounded, frosted grains. Small aeolian dunes formed by reworking of channel sands. Sorting characteristics typical of aeolian processes. Grainflow laminae produced by avalanching processes. Convolute and slump structures produced when when the dunes were wet.
Damp interdune
sandstone (12%)		 Fine- to medium-grained, poorly sorted sandstone and silty sandstone, in beds from 0.05 to 0.15 m thick. Common flat-lying, silt-lined wavy and convolute lamination. Accumulation of sediment in localised troughs between dunes. Deposition occurs on a damp, probably uneven sediment surface with irregular accretion of windblown silt and sand.
Dry interdune sandstone (2%) Fine- to medium-grained sandstone, in beds from 0.05 to 0.2 in thick. Well-defined, parallel or low-angle pinstripe lamination. Accumulation of sediment in localised troughs between dunes. Sediment surface was dry and covered with wind ripples. Each pinstripe lamina was produced by the migration of a single migrating wind ripple set.

(Table 10a) Calder Sandstone Formation fluvial facies association

Facies (% volume) Description Interpretation
Minor channel (16%) Fine- to coarse-grained reddish brown sandstone Common frosted, well-rounded grains and red mudstone clasts. Trough and planar cross-bedding and cross-lamination. Occurs in erosively based units from 0.6 to 2.3 m in thickness, unknown lateral extent. Deposition by tractional processes in minor fluvial channels. Lower flow regime subaqueous dunes and ripples are dominant bedforms. Well-rounded frosted grains indicate fluvial reworking of aeolian deposits.
Floodplain mudstone (1%) Reddish brown laminated and massive siltstone and claystone. Beds less than 1 m thick and laterally discontinuous. Locally cross-laminated, some desiccation cracks, and micaceous in places Subaqueous deposition of silt and clay from suspension on unconfined floodplain, local tractional deposition, sediment drying locally important.
Sheet sandstone (3%) Fine- to medium-grained micaceous sandstone, in sharp-based, upward-fining beds up to 1 m thick. Some scattered intraformational clasts. Cross-bedded, with rare parallel lamination and climbing ripples. Aeolian grains common. Unconfined tractional sheetflood deposits, carrying a sandy bedload. The presence of aeolian grains indicates fluvial reworking of aeolian deposits. Possibly minor aeolian reworking at tops of beds.

(Table 10b) Calder Sandstone Formation aeolian facies association

Facies (% volume) Description Interpretations
Dune sandstone (40%) Sandstone, fine- to coarse-grained, well sorted, with common well-rounded, frosted medium and coarse grains. Cross-bedded throughout, with sets from 0.1 to 0.7 m. Well-defined grainfall and grainflow foreset lamination; moderate- to high- angle foresets. Sets are stacked into cosets from 2 to 17 m thick. Sets of cross-bedding formed by migration of small wind-blown dunes. Thick cosets may indicate superimposition of dune sets to form larger draas. Grainfall and grainflow lamination combined with absence of of mud clasts and lack of erosion surfaces highly indicative of aeolian deposits.
Damp interdune sandstone (22 %) Poorly sorted, very fine- to fine-grained silty sandstone in beds up to 1 m thick. Scattered medium and coarse sand grains. Irregularly shaped, wavy lenses of sandstone, surrounded by thin wavy, discontinuous dark coloured silty laminae. The sand lenses are generally distorted, loaded or deformed. Dewatering structures and convolute lamination present. Interbedded with sediments of dune facies. Interbedding with aeolian dunes suggests deposition in interdune area; sedimentary structures indicative of deposition on a damp interdune by the irregular accretion of sand. Water-laid and wind-blown sand accumulates as lenses in salt-encrusted surface depressions. Salt dissolution causes deformation of lenses. Matrix accumulates by deposition of mud carried by wind.
Dry interdune sandstone (16%) Fine- to coarse-grained sandstone, in beds up to 0.5 m thick, occurs interbedded with dune sands. Low-angle to horizontal lamination: rare wind ripple lamination: sporadic deflation lags of medium to coarse sand. Interbedding with aeolian dunes suggests deposition in interdune area: sedimentary structures indicative of dry environment: wind ripple and low-relief bedform migration processes important, some minor deflation.
Wet interdune mudstone (2%) Laminae or thin beds of claystone and siltstone up to 0.2 m thick. Massive, with desiccation cracks, and some load casts. Deposition of mud in ephemeral pools of water in the interdune area.

(Table 11) Summary of diagenetic events identified in Permo-Triassic rocks below the Mercia Mudstone Group and their relationship with fracture mineralisation events

Diagenetic episode Principal mineralogical characteristics Equivalent mineralisation episode Diagenetic stage Age
DE1 Shallow/near surface 'red bed' diagenesis with development of infiltrated clay coatings, haematite grain coatings, haematite + anatase replacement of detrital ferromagnesian minerals, micronodular non-ferroan calcite and dolomite cement (calcrete, dolocrete, cornstones), anhydrite cements, interstitial precipitation of gypsum and anhydrite in sabkhas etc.

No corresponding fracture mineralisation events

EODIAGENESIS Synsedimentary near surface processes

PERMIAN­ EARLY TRIASSIC Diachronous
DE2 Early diagenetic precipitation of smectite grain coatings + minor K-feldspar overgrowths
DE3 Neomorphism of early carbonate cements and precipitation of idiomorphic non-ferroan dolomite and calcite overgrowth cements. Precipitation of ferroan dolomite and calcite as late- stage overgrowths. Conversion of gypsum to anhydrite; some dissolution of anhydrite EARLY MESODIAGENESIS Shallow burial

EARLY-MID TRIASSIC BURIAL
DE4 Precipitation of quartz, K-feldspar and albite overgrowths

ME4

MIDDLE MESODIAGENESIS Moderate burial
DE5 Precipitation of minor haematite, dissolution of earlier calcite and dolomite
DE6 Precipitation of major pore-filling evaporite cement (?anhydrite) prior to major compaction
DE7 Dissolution of earlier carbonate and evaporite cements, precipitation of kaolinite, illitisation of kaolinite, illite precipitation (evident only in Brockram) ME5

LATE MESODIAGENESIS Deep burial
DE8a Precipitation of ferromanganoan calcite and major collomorphic haematite (in Brockram only, preserved as relicts) ME6a
DE8b Corrosion of calcite, precipitation of non-ferroan dolomite, becoming ferroan in later stages (all formations). Precipitation of anhydrite

ME6b
DE8c Corrosion of dolomite, precipitation of ankerite (all formations)
DE8d Corrosion and dissolution of earlier carbonates and anhydrite, precipitation of barite (all formations)

ME6c
DE8e Precipitation of traces of fluorite, sulphides and selenides (fluorite only seen in Brockram)
DE8f Precipitation in two stages of ferromanganoan calcite, traces of pyrite (all formations)
DE9 Extensive dissolution of evaporite cements particularly in the Sherwood Sandstone Group, and some dissolution of feldspar grains, precipitation of fibrous and platey illite in secondary rejuvenated porosity ME7 POST-MID­TRIASSIC
DE10 Late-stage oxidative dissolution of carbonate cements, hydration and dissolution of anhydrite, associated precipitation of iron and manganese oxides and oxyhydroxide alteration products. In part contemporaneous with present-day groundwater alteration ME8

TELODIAGENESIS Uplift and meteoric invasion

PALAEOCENE–RECENT
DE1 1 Late-stage precipitation of euhedral calcite (all formations), locally also gypsum or anhydrite, in secondary porosity in Brockram and dissolution cavities after anhydrite nodules in St Bees Shale: hydration of anhydrite to gypsum and dissolution of gypsum (St Bees Evaporite and Shales) ME9

(Table 12) Eroded overburden and uplifted estimates (metres) from geophysical log compaction studies

Borehole St Bees Sst ΔT (m) Calder Sst ΔT (m) Calder Sst Density (m) Estimate of average overburden (m) Absolute uplift (m)
Sellafield 1A 2014 2093 1903 2003 1931
Sellafield 2 1818 1781 1821 1807 1772
Sellafield 3 2020 2044 2254 2106 2022
Sellafield 4 2065 NA NA 2065 2039
Sellafield 5 2062 1765 1379 1914 1900
Sellafield 7A 1858 1635 1755 1749 1702
Sellafield 7B 1910 ID ID 1910 1863
Sellafield 10A 2037 NA NA 2037 1977
Sellafield 12A 2034 1932 2002 1989 1934
Silloth 1 2355 2211 NA 2283 2193
113/26-1 2551 1988 NA 2270 2204
112/25-1 2623 2068 2338 2343 2281
  • (Nirex, 1993d).
  • NA = No logs available.
  • ID = Insufficient log data.

(Table 13) Fission-track sites: palaeotemperatures, heatflows and estimates of eroded overburden and uplift, based on conductive thermal modelling

Site Fission-track temperature (°C) Surface heatflow (mWm-2) Eroded overburden (m) Absolute uplift

(m)
1 >110 62 >3200 >3175
2 >110 64 >2900 >2850
3 90–100 70 1675 1625
4 90–100 72 1600 1725
5 100–110 67 2300 2250
6 100–110 68 2225 2250
7 100–110 73 1900 1950
8† >110 73 >2150 >2225
9† >110 74 >2100 >2150
10 100–110 68 2225 2125
11 >110 80 >1825 1850
12 >110 99 >1450 >1750
13 >110 101 >1425 >1750
14 >110‡ 90 >1600 >1800
15 100–110 80 1625 1650
16 90–100 86 1275 1350
17 90–100 87 1400 1600
18 90–100 86 1400 1475
19 95–105‡ 66 2100 2025
20 100–110 82 1825 1850
21 70–90 89 1325 1400
22 70–90 86 1150 1350
23 90–100‡ 77 1575 1850
24 90–100 82 1325 1350
25 >110 76 >1975 >2125
26 100–110 77 1825 2000
27 70–90 73 1175 1250
28 90–100 76 1500 1575
30 95–105‡ 82 1600 1550
31 >110 81 >1925 >2000
32 90–100 73 1675 1775
33 100–110 72 1950 2050
34 >110 76 >1950 >2100
35 100–110 70 2000 2025
36† >110 64 >2550 >2500
37 90–100 56 2750 2700
41 70–90 77 1275 1600
42 >110 89 >1625 >1950
43 90–100 77 1475 1550
44 100–110 82 1575 1650
Sellafield 3 Borehole >110 65 >2825* >2033
  • (Nirex, 1993d).
  • * Includes overburden present in borehole (i.e. depth in borehole)
  • † Location and palaeotemperatures from Lewis et al., 1992
  • ‡ Mean of more than one analysis

(Table 15) Stratigraphical sequence within the St Bees Push Moraine

Lithological units (Huddart and Tooley, 1972)

Formations and members (Nirex, 1997k)

8 Sandy clays, gravels and sands

Gosforth Glacigenic

 How Man Till
Peckmill Sand
7 Sandy clay passing up into sands Gutterfoot Sand
6 Pebbly silty diamicton St Bees Till
5 Gravels

Seascale Glacigenic

St Bees Sand and Gravel
4 Sandy gravel and sands
3 Clays and silts St Bees Silt
2 Lodgement till Lowca Till
1 Bedrock St Bees Sandstone

(Table 16) Survey history of 1:10 000-scale geological maps of the district, showing initials of geological surveyors and dates of survey

Sheet Name Surveyor Date
NX 90 NE Nethertown RPB, RAH 1989–1990
NX 91 NE Whitehaven RPB, MMCC 1990, 1995–1996
NX 91 SW St Bees Head RPB, MMCC 1990, 1996
NX 91 SE St Bees RPB, MMCC 1990, 1995–1996
NX 92 NE + NW Workington DVF 1985–1986
NX 92 SE Lowca MMCC 1995
NY 00 NW Beckermet RPB, RAH, CAA 1989, 1989, 1996
NY 00 NE Cold Fell MGP, RPB, CAA, RGC 1990, 1990, 1993–1995, 1993
NY 00 SW Seascale MGP, RPB, CAA 1989, 1989, 1993, 1996
NY 00 SE Gosforth MGP, RPB, RGC, CAA 1990, 1990, 1990, 1993
NY 01 NW Frizington MMCC 1995
NY 01 NE Kirkland MMCC, RAH 1995
NY 01 SW Egremont RAH, RPB, MMCC 1990, 1990, 1996
NY 01 SE Kinniside PMA, MGP, DJF, JWM 1984–1985, 1990, 1996, 1996
NY 02 NW Stainburn BY 1985–1986
NY 02 NE Greysouthern BY 1989–1990
NY 02 SW Pica MMCC 1995
NY 02E Lamplugh MPB, BY 1989–1990
NY 10 NW Seatallan and Greendale MGP, BBS, AJR 1987–1989
NY 10 SW Santon Bridge BBS, MGP 1987–1988
NY 11 NW Floutern Tarn RAH, DJF 1993
NY 11 SW Haycock MGP, RMSR, BBS, DJF, JWM 1988–1989, 1988, 1996, 1996, 1996
NY 12 NW BCW, BY 1983–1986, 1990
NY 12 SW BCW 1983–1986
SD 09 NW Barn Scar BY, CAA 1992, 1996
SD 09 NE Ravenglass PMA, RAH, BY, CAA 1985, 1989, 1992, 1993
SD 09 SE Eskmeals MGP, BY 1991, 1992
SD 19 NW BY, PMA, BBS, DM 1983–1987
SD 19 SW BY, DM 1983–1985
SD 08 NE Hycemoor MGP, BY 1991,1992
SD 18 NW Black Combe & Bootle AMB, EWJ, NAM, BY 1984–1993
SD 18 SW Silecroft AMB, EWJ, NAM 1984–1993
  • The surveyors were: P M Allen, C A Auton, R G Crofts, B Beddoe-Stephens, A M Bell, M P Boland, R P Barnes, D J Fettes, D V Frost, R A Hughes, E W Johnson, N A Matthieson, M McCormac, J W Merritt, D Millward, M G Petterson, A J Reedman, N M S Rock, B C Webb and B Young.

(Table 17) Key boreholes used for the interpretation of the geology of the district.

Borehole Easting Northing GR Borehole registration number
Sellafield 1/1A 3202 2706 [NY 03202 02706] (NY00SW/34)
Sellafield 2 5543 3412 [NY 05543 03412] (NY00SE/28)
Sellafield 3 2596 2646 [NY 02596 02646] (NY00SW/35)
Sellafield 4 5639 3457 [NY 05639 03457] (NY00SE/29)
Sellafield 5 5160 3872 [NY 05160 03872] (NY00SE/30)
Sellafield 7A 3857 4903 [NY 03857 04903] (NY00SW/36)
Sellafield 7B 3854 4853 [NY 03854 04853] (NY00SW/37)
Sellafield 8A 7208 4983 [NY 07208 04983] (NY00SE/38)
Sellafield 8B 7214 5015 [NY 07214 05015] (NY00NE/30)
Sellafield 9A 8525 4269 [NY 08525 04269] (NY00SE/43)
Sellafield 9B 8532 4252 [NY 08532 04252] (NY00SE/46)
Sellafield 10A 4312 3061 [NY 04312 03061] (NY00SW/38)
Sellafield 10B 4268 3080 [NY 04268 03080] (NY00SW/40)
Sellafield 10C 4343 3094 [NY 04343 03094] (NY00SW/43)
Sellafield 11A 6792 1663 [NY 06792 01663] (NY00SE/34)
Sellafield 12A 4934 2644 [NY 04934 02644] (NY00SW/39)
Sellafield 13A 4521 0146 [NY 04521 00146] (NY00SW/41)
Sellafield 13B 4506 0184 [NY 04506 00184] (NY00SW/42)
Sellafield 14A 2486 5692 [NY 02486 05692] (NY00NW/451)
Sellafield RCF1 5795 3907 [NY 05795 03907] (NY00SE/35)
Sellafield RCF2 5506 4170 [NY 05506 04170] (NY00SE/36)
Sellafield RCF3 5565 3932 [NY 05565 03932] (NY00SE/37)
Sellafield RCM1 5568 3961 [NY 05568 03961] (NY00SE/41)
Sellafield RCM2 5598 3942 [NY 05598 03942] (NY00SE/40)
Sellafield RCM3 5785 3896 [NY 05785 03896] (NY00SE/39)
Sellafield PRZ2 5661 3444 [NY 05661 03444] (NY00SE/44)
Sellafield PRZ3 5186 3852 [NY 05186 03852] (NY00SE/42)
Distington 972 334 [NX 9972 2334] (NX92SE/84)