Huddart, D. & Glasser, N.F. 2007. Quaternary of Northern England. Geological Conservation Review Series No. 25, JNCC, Peterborough, ISBN 1 86107 490 5.
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D. Huddart and N.F. Glasser
The later stages of the Quaternary Period, the Devensian cold stage and the Holocene temperate stage, are much more important in shaping the landscape of northern England than the preceding stages. During the Late Devensian, ice sheets developed in the highlands of Scotland and these advanced south along the east and west coasts of northern England to coalesce with independent ice-caps formed in the Lake District, the Cheviot Hills and parts of the Pennines. At its maximum extent, Devensian ice covered the whole of northern England, with the exception of small parts of Derbyshire. The sediments and landforms developed during this episode are described in this chapter. On retreat of the Devensian ice, periglacial processes modified much of the glacial landscape, and the landforms and deposits that resulted are dealt with in Chapter 6. At the end of the Devensian glaciation, rapid climatic fluctuation during the Late-glacial interstadial and stadial episodes caused significant vegetation changes in the region, together with much sediment accumulation in lakes, and these topics are covered in Chapter 7. The final stage of the Quaternary Period, the current Holocene temperate stage, saw a significant rise in sea level, reactivation of river systems and their modification of the glacial sediment cover, major changes in vegetation consequent on widespread climatic amelioration, and evidence of human modification of the landscape. These topics are covered in Chapter 8.
The traditional stratigraphical view is that the Devensian cold stage followed the end of the Ipswichian interglacial stage (Oxygen Isotope Stage (OIS) 5e) at approximately 115 ka and is subdivided into Early (115–50 ka), Middle (5026 ka) and Late (26–10 ka) sub-stages (Mitchell et al., 1973). The biostratigraphical evidence for the transition from the Ipswichian interglacial to the Devensian glacial, however, is scanty and, as Lowe and Walker (1984) have stated, once evidence from outside Britain is considered there seems to be a much more complex environmental sequence across the boundary than evidence in Britain provides. Thus, a climatic deterioration at 115 ka (OIS 5d) is followed by a warmer phase of either interglacial or interstadial rank about 100 ka (OIS 5c). This, in turn, is followed by a cool episode around 90 ka (OIS 5b) and an interglacial or interstadial episode about 80 ka (OIS 5a). Between 80 ka and 65 ka significant cooling may be correlated with OIS 4.
Several sites in northern England yield important information related to this time period but pose problems concerning their dating and whether they provide evidence of extensive Early Devensian glaciation. Chelford has provided major biostratigraphical and palaeoclimatic evidence for an early Devensian interstadial event, known as the 'Chelford Interstadial' (Simpson and West, 1958), but its precise age is uncertain. Conventional radiocarbon dating methods have provided age estimates between 25 000 and 65 000 years BP for organic sequences within the Chelford Formation, uranium-series dates have yielded an age of 86 000 years BP (Heijnis and Vanderplicht, 1992) and thermoluminescence dates suggest absolute ages in the range 90 000–100 000 years BP (Rendell et al., 1991; Rendell, 1992). The glaciogenic deposits that underlie the Chelford Formation may therefore identify an Early Devensian glaciation but equally may relate to a glacial episode preceding the Ipswichian glaciation. Similar uncertainty relates to the age of the thin peat in Mosedale on the northern fringes of the Lake District. The peat overlies the Thornsgill Till and is overlain by Late Devensian Threlkeld Till and terrace gravels. The peat has been radiocarbon dated by Boardman (1981) as >54 200 years BP and uranium-series dated at between 77 000 and 91 000 years BP, and is tentatively ascribed to an Early Devensian interstadial.
A borehole at Burland, near Nantwich (Bonney et al., 1986), revealed 1 m of peat within a 9 m sequence of organic silts and clays deposited in a lake or abandoned river channel. The pollen indicates evidence for local pine–birch forest into which spruce migrated and the minimum age of these deposits is >47 200 years BP The organic sequence is overlain by thick Devensian Till and underlain by further till correlated with the Oakwood Till at Chelford. The organic sequence therefore represents an interstadial episode of probable Chelford age, underlain by till of at least Early Devensian, but probably older age. At Four Ashes, organic sediments beneath Late Devensian till, and in contact with bedrock, have a pollen assemblage including pine, spruce and birch that is comparable with the Chelford and Burland flora. Again the insect fauna is analogous to Chelford, but overall, although the oldest stadial deposits could either pre-date or post-date the Chelford Interstadial, most of the succession is thought to be of post-Chelford age.
A number of authors have suggested an Early Devensian glaciation in eastern England (Straw, 1979c) and it has been suggested that at around 70 000 years BP there was a limited build-up of ice in Scotland and upland Cumbria (Nirex, 1997b); a suggestion made earlier by Huddart (1971b) to explain Southern Scottish erratics in the Vale of Eden and the lower tills in the sequences in the valleys of the northern fringes of the Lake District. Supporting evidence for an Early Devensian glacial comes from Norway where Baumann et al. (1995) provided evidence for extensive glaciations on three occasions during the Devensian. Despite this possibility Worsley (1991a) concluded that there was a paucity of convincing stratigraphical or chronological data and that on balance there is no good evidence for an Early Devensian glaciation in Britain. Bowen et al. (1986) also argue that such a concept remains unproven.
In the Peak District, Elder Bush Cave has produced a vertebrate fauna transitional between those of the Ipswichian and Devensian, including woolly rhinoceros, cave bear, bison, cave lion and hyaena (Bramwell, 1964; Bramwell and Shotton, 1982). Extensive cave sedimentation occurred in the Peak District during the Early Devensian (Briggs and Burek, 1985), and the Hope Terrace of the Derwent valley, formed in the Ipswichian, received a cover of soliflucted sediment in the Early Devensian (Waters and Johnson, 1958; Briggs and Burek, 1985). Robin Hood's Cave (Cresswell Crags) has produced Mousterian artefacts and Early Devensian pollen spectra from its basal stratigraphy (Campbell, 1977; Roe, 1981). At Pin Hole Cave, two separate Middle Palaeolithic industries and many vertebrate remains have been discovered in a probable Early Devensian context (Jenkinson et al., 1985).
Farther north, at Stump Cross Cave in northern Yorkshire, cave sediments containing Pleistocene mammal remains that include reindeer, wolverine, wolf, red and arctic fox have been uranium-series dated to 83 000 years BP using flowstone that encased them (Sutcliffe et al., 1985). Hence a cold environment existed at this period within OIS 5b, as wolverine and the animal that comprises the major part of its diet, the reindeer, currently have a circumboreal distribution that reaches the tundra. Recently more precise dates for these sediments come from flowstone enclosing the wolverine bones and these are close to 74 ka (Gilmour, pers. comm., quoted in Currant and Jacobi, 2001).
| Homo species | artefacts |
| Lepus timidus | mountain hare |
| Spermophilus major | red-cheeked suslik |
| Canis lupis | wolf |
| Vulpes vulpes | red fox |
| Ursus arctos | brown bear |
| Mustela erminea | stoat |
| Mustela putorius | polecat |
| Crocuta crocuta | spotted hyaena |
| Panthera leo | lion |
| Mammathus primigenius | woolly mammoth |
| Equus ferus | wild horse |
| Coelodonta antiquitatis | woolly rhinoceros |
| Megaloceros giganteus | giant deer |
| Rangifer tarandus | reindeer |
| Bison priscus | bison |
Uranium-series dating of speleothems has further clarified the pattern of environmental change in this period. Gascoyne et al. (1983) reported low speleothem growth in north-west England between 90 000 and 45 000 years BP, which implies the existence of a non-glacial tundra-like climate. Gordon et al. (1989) have pointed to a clear fall in speleothem growth frequency after a peak at 95 000 years BP, with a minimum at 80 000 years BP considered to mark the boundary between the last interglacial and the last cold stage. Peaks of speleothem growth at 76 000, 57 000 and 50 000 years BP have been proposed as indicators of Devensian interstadi-als. It is clear though that this Early Devensian period is still not well known and climatic changes and the timing of events in northern England are known only from a few sites, with little stratigraphical continuity.
This period of the Devensian is within the limits of 14C dating, yet often there is still some doubt related to age determinations. It appears that the climate was cold for much of this period, with an amelioration that gave rise to the Upton Warren Interstadial. The key site is Four Ashes, where sandy detritus peat and organic clay within sands and gravels have given 14C ages of between 42 000–30 000 years BP (Morgan, A.V., 1973). However, there is evidence of a cold phase between the Chelford Interstadial and prior to 43 500 years BP, based mainly on insect evidence, with indications of a continental climate with cool summers. Between 42 500 and 38 500 years BP there were significant changes in the insect fauna, indicating a climate of reduced continentality, with warmer summers than previously. Tree growth would have been possible but there is an absence of tree pollen and no wood-eating insects. After about 38 000 years BP the numbers of northern and eastern stenothermic insects increased in a tundra landscape. Cold polar desert conditions ensued after 30 000 years BP and the Late Devensian ice advance was after this date in southern Staffordshire.
Currant and Jacobi (2001) use the Pin Hole Cave as the type locality for their Middle Devensian (OIS 3) mammalian assemblage (see
At the Oxbow opencast coal site in the Aire valley, Gaunt et al. (1970) described a silt, deposited in standing or quietly flowing water on a floodplain. The flora and fauna indicated a tundra environment, with some snow patches. A mammoth tusk from this sediment was dated by 14C to 38 600 years BP and its age is considered applicable to the deposit it was contained in. The flora included dwarf birch, fringed sandwort, alpine cinquefoil, Thalictrum alpinum, Armeria maritima, Salix herbacea, Allium schoenoprassum and Empetrum species. July temperature values of around 10°C and a continental climatic regime have been suggested.
Again by means of uranium-series dates Gascoyne et al. (1983) have deduced overall low speleothem growth in the Craven District of north-west England from 85 000 to 35 000 years BE For the period 44 000–34 000 years BP, a minor increase in the number of dated speleo-thems occurs, which may indicate episodes of milder climate. No ages were obtained for 34 000–13 000 years BP, which has been interpreted as demonstrating the existence of continuous permafrost, then ice, in this area. However, Atkinson et al. (1986) suggest that groundwater recharge was possible in this area at 39 000 years BP and 26 000 years BE Intermittent growth was also suggested by dates published by Sutcliffe et al. (1985) of between 44 000 and 29 000 years BP from Stump Cross caverns. This means that there was discontinuous rather than continuous permafrost present in this area during this period to as late as 26 000 years BP. At Pin Hole Cave in Cresswell Crags, earlier Upper Palaeolithic artefacts have been recorded from the Upper Cave Earth Uenkinson et al., 1985) and at Robin Hood's Cave in the same area similar artefacts also have been found, and a 14C date of 28 500 years BP has been obtained from bone of Ursus arctos (Campbell, 1977). Recent dates for spotted hyaena remains from the Cresswell area are given in
During the Nirex investigations (1997b) in west Cumbria, Mid-Devensian marine and lacustrine deposits were found to overlie a weathered till of possible Wolstonian age in boreholes at Drigg and Carleton. In the Drigg borehole a shelly silt of possible marine origin, below a till and overlying a blue-grey organic silt, yielded amino acid ratios corresponding to an age of 45 000 years BP These deposits are important for an interpretation of Middle Devensian sea levels, but it is conceivable that they are not in situ, although Wingfield et al. (1997) suggest that as they have been located in four boreholes separated by up to 0.5 km it is unlikely they form a raft. At Carleton Hall and Hall Carleton boreholes have proved laminated muds underlying the Late Devensian Blengdale Glaciogenic Formation (Nirex, 1997b). The upper part of the laminated sequence, which contains marine microfossils, has been assigned to the Glannoventia Formation of possible OIS 3 age. The lower part is of glacio-lacustrine origin and studies of varves indicate sedimentation over a period of over 2000 years (Nirex, 1997b). This unit has been tentatively correlated with OIS 4, although it is possible that the microfossils are reworked into a glacio-lacustrine sequence of Late Devensian age. This again emphasizes the tentative nature of much of the environmental reconstructions for this period of the Early and Middle Devensian in northern England.
| Robin Hood Cave | OxA-6115 | 22 800 | ± 240 |
| Robin Hood Cave | OxA-6114 | 22 980 | ± 480 |
| Church Hole | OxA-5800 | 24 000 | ± 260 |
| Ash Tree Cave | OxA-5798 | 25 660 | ± 380 |
| Church Hole | OxA-5799 | 26 840 | ± 420 |
| West Pin Hole (Dog Hole) | OxA-5803 | 29 300 | ± 420 |
| Robin Hood Cave | OxA-5802 | 31 050 | ± 500 |
| Pin Hole | OxA-1206 | 32 200 | ± 1000 |
| Robin Hood Cave | OxA-5801 | 33 450 | ± 700 |
| Pin Hole | OxA-1207 | 34 500 | ± 1200 |
| Pin Hole | OxA-4754 | 37 800 | ± 1600 |
| Pin Hole | OxA-1448 | 42 200 | ± 3000 |
Northern England has played an important historical role in the development of conceptual models regarding the formation of glacial sediments in Britain. This has seen a change from a belief in the marine origin for the drifts by 19th century workers, through various types of land-based origin, and, in the late 1980s, back to a glaciomarine origin for some of the glacial sediments. Howse (1864) was an early believer in the importance of terrestrial ice-sheets and their erosive power, through his work in north-east England. Goodchild (1875, 1887), working in Edenside, stressed the complexity of the glacial deposits and considered that practically all of the glacial sediments in this area formed sub-glacially, or englacially, during the melting of a stagnant ice sheet. Mackintosh (1877) developed a tripartite succession for the glacial deposits in north-west England, where a lower and an upper boulder clay was separated by a middle sand. His model invoked deposition by glacial ice from the Lake District for the lower boulder clay, followed by deposition of the middle sand and the upper boulder clay by floating coastal ice. Traditionally, however, these sequences were interpreted as the product of multiple glaciations. Ice that advanced to form the lower boulder clay then retreated, deposited the sand and gravel, before readvancing to form the upper boulder clay. In contrast, Binney (1848) advocated a monoglacial view where he maintained that the glacial successions were complex and that sand and boulder clay lithologies could replace each other within any given sequence at random. Nevertheless the rigid tripartite framework involving bi-glaciation proposed by Hull (1864) gained the ascendency (
The modern interpretation of tripartite drift sequences in northern England developed from the ideas of Boulton (1967, 1968, 1970, 1972) in Spitsbergen and subsequently in North Wales (1977), by Worsley (1967a, 1970, 1985) and G.S.P. Thomas (1989) in the Cheshire–Shropshire lowlands, and by the development of the supraglacial land-system model (Boulton and Paul, 1976; Eyles, 1983; and Paul, 1983). Hence the majority of glaciogenic sequences in northern England are now associated with the growth and decay of a single ice sheet (Evans and Arthurton, 1973). However, in the Solway lowlands, the Carlisle Plain and in coastal west and south Cumbria the sequence is regarded as more complex. Here an upper till has been recognized that was deposited by a late readvance of Scottish ice (Trotter, 1922, 1929; Trotter et al., 1937; Huddart, 1970, 1971a, b, 1972, 1977, 1991, 1994). Huddart (1970, 1991, 1994, 1997) recognized an associated series of pro-glacial depositional environments, including pro-glacial lake and sandur. However, this till has also been interpreted as a glaciomarine mud drape, produced by the flocculation of clay from meltwater plumes discharging from calving, tidewater glaciers during the deglaciation of the Irish Sea basin (Eyles and McCabe, 1989, 1991). Despite having been dismissed as largely illusory by Evans and Arthurton (1973), Pennington (1978) and Thomas (1985b), the readvance concept has gained renewed support by the recognition of pro-glacial glaciotectonic deformation in west Cumbria during the Nirex investigations (e.g. Knight et al., 1997; Wingfield et al. 1997; Akhurst et al. 1997; Browne et al., 1997, Merritt and Auton, 2000), which was first recognized by Huddart (1970): There is still some discussion as to the number of readvances of the Irish Sea basin ice sheet and their impact on the stratigraphy and landforms. The 'Gosforth Oscillation' (Trotter et al., 1937; Akhurst et al., 1997; Browne et al., 1997), the Low Furness Readvance (Huddart et al., 1977), the Kirkham moraine of Gresswell (1967), discussed in Longworth (1985), the Delamere moraine and the Bar Hill–Ellesmere–Wrexham moraine have all had their supporters as indicators of a readvance of the ice sheet during the deglaciation from the maximum Devensian ice limit.
The extent of the Late Devensian ice sheet
Initial recession of the Irish Sea lobe is thought to have been rapid, and by 18 000 years BP the ice margin lay across the Isle of Man, although the 14C dates used in this supposition generally are thought to be too old because of the hardwater effect. It seems much more likely that the date is closer to 14 500 years BP (see McCabe et al., 1998). Ice cover over Wales was dominated by a local ice cap that coalesced to the west and north with Irish Sea ice. Ice advanced across the Cheshire and Shropshire lowlands as far as the Wolverhampton area (Morgan, A.V., 1973; Bowen et al., 1986; Worsley, 1991b). A more northerly end-moraine complex (the Wrexham–Ellesmere–Whitchurch moraine), believed by Boulton and Worsley (1965) to mark the maximum extent of the ice sheet in the Cheshire–Shropshire Plain, is now generally accepted to be the expression of a series of prolonged stillstands along this line (Thomas, G.S.P., 1989). The form of the Wrexham–Ellesmere–Whitchurch end-moraine complex indicates that the ice front was bilobate at this point, where it was divided by the Mid-Cheshire Ridge (Boulton and Worsley, 1965). Early workers recognized that the last ice sheet flowed out of the Irish Sea Basin in a NNW–SSE direction (Mackintosh, 1879; Morton, 1860, 1870) and this regional pattern of ice flow is now firmly established (Gresswell, 1964; Thomas, G.S.P, 1985a, 1989; Glasser and Hambrey, 1998). The eastern margin of Irish Sea ice penetration into the Cheshire–Shropshire area pushed against but did not cover the Pennines (Johnson, 1985b).
There are few precise dates for ice recession across central England, but there is evidence that parts of Yorkshire were ice-free by 17 000 years BP (Gascoyne et al., 1983). Apart from perhaps local residual ice in the Cumbrian mountains, the main ice sheet appears to have been positioned north of the Scottish border by around 15 000 years BR Cumbria itself was ice-free by 13 500 years BP (Gale, 1985) and all of Wales was probably ice-free at this time also (Haynes et al., 1977; Musk, 1985). For example, a date for organic sediment in a kettlehole sequence at Glanllynnau dated to 14 468 years BP indicates that west Wales was ice-free by this time. In eastern England Late Devensian ice advanced across Holderness, through eastern Lincolnshire, as far as the northern edge of Norfolk (Suggate and West, 1959; Straw, 1969). There also is evidence that this ice advanced rapidly, possibly during a surge-type event, into the southern North Sea (Boulton et al., 1985; Long, A.J. et al., 1988; Eyles et al., 1994; Evans et al., 1995). This advance was not sustained and ice had receded from the offshore area soon after 18 000 years BP (Lambeck, 1993b).
There are two contrasting views concerning ice thickness during the Last Glacial Maximum, exemplified by the 'maximum' and 'minimum' ice-sheet reconstructions of Boulton et al. (1977, 1985)
Mitchell and Clark (1994) reviewed the evidence upon which reconstructions of the Late Devensian ice sheet are based. Surprisingly little is known about detailed flow directions and dynamics of this ice sheet. Reconstructions of the entire ice sheet (Boulton et al.,1985; Bowen, 1991) are highly generalized. Regional reconstructions of the ice sheet in northern England (
Heinrich (H) events are the regularly occurring periods of iceberg production identified in North Atlantic Ocean sediments during the past 100 000 years (Heinrich, 1988; Andrews et al., 1998). Each Heinrich event is associated with an increase in ice-rafted debris in the North Atlantic and these events have been proposed as the trigger for major climatic changes in the North Atlantic region (Broecker, 1994). Recent studies of Greenland ice cores and North Atlantic sediment cores also suggest that the last deglacial cycle (c. 21 000–13 000 years BP) was interrupted by a series of millennial-scale climate shifts (Dansgaard et al., 1993; Bond and Lotti, 1995). These climate shifts punctuated the overall recession of the mid-latitude ice sheets and seem to be climate-driven, because discharges involve more than one ice sheet (Clark et al., 1995; Bond and Lotti, 1995). McCabe (1996) first attempted to link episodes of fast ice flow ('drumlinization) in Britain to these millennial-scale discharge events. His work suggested that individual phases of drumlinization are correlated with the climate-driven circum-North Atlantic climate events. Subsequently, McCabe et al. (1998) identified a period of rapid bed reorganization beneath the last British ice sheet around 14 000 years BP, younger than was envisaged previously. This phase of fast ice flow involved overprinting and drumlinization of earlier transverse landforms by ice streams that fed into the Irish Sea to form tidewater calving fronts. McCabe et al. (1998) correlated this event with other evidence from around the North Atlantic area that suggests there was a widespread climatic event around this time. They consider this to be evidence that the British ice sheet participated in Heinrich I event
Very little is known about the basal thermal regime of the Late Devensian ice sheet in northern England. No detailed calculations of ice-sheet basal thermal regime have been attempted as they have for the Late Devensian ice sheet in parts of Scotland (Gordon, 1979; Glasser, 1995). At its maximum extent, Boulton et al. (1977) considered the last ice sheet to have a frozen bed in its interior with a temperate margin, but provided little data on a regional scale. Clearly this thermal regime is not compatible with much of the geomorphological evidence for fast ice flow (Mitchell, 1994). Equally, little is known about how the basal thermal regime of the ice sheet changed during growth and decay. It is probable that the plateau ice fields that existed at times in areas such as the Lake District were predominantly cold-based (Rea et al., 1998). G.S.P. Thomas (1989) also suggested a shift in the basal thermal regime during the Devensian ice retreat to account for cold-based supraglacial sedimentation in the south Cheshire–Shropshire lowlands and temperate-based ice in the north Cheshire–Lancashire area.
The most comprehensive models of the last British ice sheet are those of Andersen (1981), Boulton et al. (1977) and Boulton et al. (1985)
Quantitative studies have shown that an average depth of rock and sediment 34–62 m has been removed from the British landscape by glacial erosion (Glasser and Hall, 1997), rising to 125–155 m if erosion of sediment on the continental shelf is included (Clayton, 1996, 1997). Thus rates of glacial erosion locally may exceed those of non-glacial processes, although of course there is a wide regional variation in intensity. Clayton (1974) attempted to classify the British landscape according to the intensity of modification of the landscape by glacial erosion
Although clasts of exotic origin can be found in most glaciogenic sediments throughout northern England, it is the large, isolated examples, often occurring as erratic trains, that have commanded most attention. Erratic trains have been widely used to indicate both local and regional ice movements across the area
Landforms of glacial erosion in the uplands are confined mainly to the Lake District and northern Pennines, although there are outlying features in areas such as the Cheviot Hills. Depending on definition, the Lake District hosts up to 158 cirques (Marr, 1916; Hay, 1934; Manley, 1959; Temple, 1965; Clough, 1977; Sissons, 1980; Evans, 1987; Evans and Cox, 1995; Rea et al., 1998). Many of these cirques supported small glaciers during the Loch Lomond Stadial (Younger Dryas), and during other previous episodes of marginal glaciation. Well-developed cirques are rare outside the Lake District, although cirque-like features and sites favourable for glacier growth exist in several locations in the western Pennines (Rowell and Turner, 1952; Manley, 1959; Mitchell, 1991b, d, 1996; Wilson and Clark, 1995) and in the Peak District (Johnson et al., 1990). Farther east, in the Cheviot Hills, two ill-defined cirques are cut into the western flank of the massif at Hen Hole and Bizzle (Clapperton, 1970). Much of the work on these features is purely descriptive in nature and the age of the cirques and their relationship to ice-sheet erosion in this area remains unknown.
A related group of features are the glacial troughs excavated during periods of ice discharge from the mountain areas. Linton (1957) examined the valley patterns in the Lake District and concluded that the valleys containing lakes form a radial drainage pattern. He concluded that the lake-containing valleys were the sites of very active ice dispersal and represented glacially scoured rock basins. This is difficult to reconcile with later models that consider the Lake District to be surrounded by vigorous ice masses in the Irish Sea and the lowlands to the east (Mitchell, 1994). Clapperton (1970) also has discussed the cross-profiles and morphology of valleys in the Cheviot Hills and concluded that the Lambden, Goldscleugh, Bellyside, Bizzle and College valleys were created and enlarged by glacier ice originating from catchment areas on the Cheviots. Glacial troughs, although not developed to the same extent, may also be present in the Yorkshire Dales, for example at Chapel-le-Dale (Waltham et al., 1997).
Northern England contains arguably some of the finest glaciokarst in the British Isles (Waltham et al., 1997). These areas are characterized by limestone pavements and scars formed on the tops and edges of the outcrops of more resistant limestone beds. Post-glacial solutional features, such as karren, fret the upper surfaces of the limestone pavements and commonly there is little post-glacial soil development. Deep gorges formed by glacial meltwater also are common. Outstanding examples of this type of landscape can be found in the Yorkshire Dales (Goldie, 1973, 1981; Waltham and Tillotson, 1989), with less extensive tracts of glaciokarst in Lancashire and Cumbria (Goldie, 1996). These areas of limestone pavement are important both geologically and biologically (Ward and Evans, 1976).
Although descriptions of glaciokarst are numerous in textbooks on geomorphology (e.g. Sweeting, 1972; Jennings, 1985; Trudgill, 1985), the subject has- been surprisingly neglected in modern research literature. Most accounts of these areas talk generally about the effects of 'glacial scouring', 'glacial plucking' and of vast areas 'scraped clean by glaciers'. Descriptions are primarily qualitative and quantitative process studies are rare. There is seldom any consideration of the wider ramifications of these statements, such as the implications for the spatial variation in ice-sheet thermal regime or the glaciological conditions required to initiate widespread erosion beneath an ice sheet overlying porous bedrock. There does appear, however, to be a positive correlation between areas of the British Isles affected by Pleistocene glaciation and the location of pavements (Piggott, 1965; Williams, 1966; Clayton, 1981).
Alternative theories argue that limestone pavements are largely exhumed palaeokarst surfaces that developed beneath former soil covers and were merely exposed by glacial erosion (Vincent, 1995; Vanstone, 1998). Pavement formation therefore would be controlled by the location of palaeokarst surfaces formed during Dinantian marine transgression and recession (Ramsbottom, 1973, 1977; Wright, 1982; Adams and Horbury, 1989). Limestone pavements are therefore not exclusively Quaternary features but owe many of their attributes to the cyclic nature of Dinantian shelf sedimentation, displaying rejuvenated palaeokarstic forms (Vincent, 1995). These competing theories concerning the formation of limestone pavements remain speculative and largely untested, although clearly they have important implications for the nature and efficiency of Quaternary glacial erosion.
Meltwater behaviour beneath modern glaciers is poorly understood, so it is not surprising that the picture of meltwater flow beneath Quaternary ice masses also is incomplete. Clues to these patterns of meltwater behaviour in the Quaternary record are given by the existence of glacial meltwater channels, normally recognized by their abrupt inception and termination and lack of a significant modern catchment, and by accumulations of glaciofluvial sediment. Meltwater channels are probably one of the most-mapped glacial geomorphological features, yet their glaciological implications are rarely explored fully or fully utilized in ice-sheet reconstruction. Meltwater channels occur as isolated examples, such as Newtondale, or as part of an integrated network of channels recording ice-sheet recession, such as those that are incised into the flanks of the Pennines at Ludworth Intake (Johnson, 1965a), and Humbleton Hill in the Cheviot Hills (Clapperton, 1971b).
One of the most contentious debates in the British Quaternary concerns the origin of 'over spill' meltwater channels related to the ice-dammed lakes identified by Kendall (1902) and others in northern England. Kendall's 'overspill' theory was eventually challenged by Sissons (1958a, 1960b, 1961), who demonstrated that many of the meltwater channels identified as overspills were in fact subglacial in origin. Drawing on a growing body of literature from Scandinavia that stressed ice-sheet stagnation during recession, Sissons argued that glaciers need not decay actively and that ice need not provide an impermeable barrier to drainage. In a series of papers on the former ice-dammed lakes of the Scottish Highlands (Sissons, 1977, 1978, 1979a, 1982) he went on to establish more rigorous criteria for the recognition of ice-dammed lakes in the Pleistocene record. These criteria include the need for unequivocal evidence of former shorelines linked to overflow or drainage routes, deltas and lacustrine sediments. Gregory (1962a, b) described the landforms of deglaciation in Eskdale and noted numerous lines of evidence in this area to support Sissons' theory of ice stagnation. Gregory (1962b, 1965) disputed Kendall's claims that Newtondale is an overspill channel through his study of the glacial lakes of Eskdale, to the north of the Newtondale channel. His work showed that much of the meltwater in fact drained sub-glacially to the north-east. Gregory (1965) noted that of the four lines of evidence used by Kendall to support the existence of a pro-glacial lake (overflow channels, lacustrine deposits, deltas and lake shorelines) there was little of this evidence to support the existence of a pro-glacial lake in Eskdale. This led Gregory to propose that although Newtondale is undoubtedly a meltwater channel, it is unlikely that it was created purely by overflow of an Eskdale–Kildale glacier lake during the Devensian. Support for this theory comes from the gravel spread at the southern end of the channel. Catt (1977c) suggests that the size of this gravel spread is anomalously small and it is too fine-grained to have resulted from the high discharge required to cut a channel the size of Newtondale. Catt (1977c) therefore argued that although Newtondale may have been used by meltwater during the Late Devensian, it was probably cut in a pre-Devensian glaciation. There is, however, no lithostratigraphical or chronostratigraphical evidence to prove this theory.
Since the 1960s, descriptions and interpretations of other meltwater-channel systems in northern England have confirmed that channels can form in a variety of ways and that a number of different meltwater landforms exist (Clapperton, 1968; 1970, 1971a, b; Russell, 1995; Sambrook Smith and Glasser, 1998; Glasser and Hambrey, 1998; Glasser and Sambrook Smith, 1999). This work has been supplemented by descriptions of glacial lakes and meltwater channels in the modern glacial environment. There is evidence that some of the criteria suggested by Sissons may be too rigid because the record of former ice-dammed lakes depends to a great extent on the nature and topographical setting of the lake. For example, ice-dammed lakes that occupy supraglacial positions are entirely capable of producing large spillways of the type originally envisaged by Kendall without leaving significant shorelines, or deltaic or lacustrine sediments (Bennett et al., 1998).
Meltwater channels also are important to the historical development of ideas, other than those related to ice-dammed lakes. For example, in County Durham, Anderson (1939, 1940) described a series of meltwater channels and glaciofluvial deposits graded to a height of 190 feet (119 m) OD and postulated that this represented the height of the Late-glacial sea level. Peel (1949, 1956) described 'up and down' channels in Northumberland at Beldon Cleugh and East Dipton and suggested for the first time a possible subglacial (as opposed to subaerial lake overflow) origin for the channels. This theme was later developed by Sissons in a series of papers (Sissons, 1958a, 1960b, 1961) and used in particular to explain the formation of many of the meltwater channels of the Tyne Gap area (Sissons, 1958b). The tunnel valleys of Merseyside described by Gresswell (1964) and Howell (1973) are likely to have formed by sub-glacial meltwater erosion, perhaps modifying the effects of large-scale glacial erosion in the lowlands.
There is a wide variety of glaciofluvial landforms and sediments in northern England, associated with several types of topographical and environmental locations:
Evidence for the advancing Scottish Readvance ice front came from the former gravel pit described in Huddart (1970, 1991) and Huddart and Tooley (1972). Here there was an increasing grain size, an increase in gravel unit thickness, a decrease in grain roundness and change in bedform from distal to more proximal sandur environments up-section. All the palaeocurrent and lithological evidence indicated deposition from the west to north-west, as compared with an ice-flow direction to the south-west indicated by the drumlinized terrain to the east (
In the only major col in the Penrith Sandstone escarpment between Beacon Hill and Barrock Fell are a series of glaciofluvial landforms
Two major depositional levels have been noted in the Eden valley at 129 m and 99 m OD, although higher, lower and intermediate stages are known. At Baronwood there is a complex delta with three superimposed sequences of topsets, foresets and bottomsets
The Brampton kame belt is a major glaciofluvial tract from Boothby in the north-east to Little Salkeld in the Eden valley (
This lateral facies model had a downstream component, and at Whin Hill imbricate gravel bars and large-scale channelling developed in a proximal zone near to the meltwater source and was found in the upper part of the succession. The environment envisaged for this type of ridge accumulation is illustrated in
The Petteril valley shows evidence of sedimentation associated with a stagnant ice-sheet. At Carrow Hill there is a flat-topped hill (
The stratigraphy suggests the following depositional stages (
Outside Cumbria, Shaw (1972a) described ice-contact glaciofluvial ridges north-west of Ironbridge Gorge, where he produced evidence for sediment accumulation during ice-stagnation. At Mousecroft Lane upstanding ridges, faults and lateral kettleholes showed that sediment accumulated in ice-walled channels, with unidirectional palaeocurrents and marginal till flows from the ice into the channel. At this location the final melting of 'Irish Sea' ice allowed invasion by Welsh ice and the subsidence consequent on the final melting involved the sediments of this advance. At Venus Bank a low-sinuosity stream channel deposit showed large thicknesses of high-flow-regime horizontal stratification, in which vertical accumulation predominated over lateral accumulation. At Ryton downstream sequences form proximal gravel bars, through an area of dunes into a distal zone of plane bed with scouring. The Ryton fluvial systems were characterized by a relatively straight channel, non-uniform flow and alternations of high and low flow conditions. The downstream migration of the facies was considered to have been responsible for the production of upward-coarsening sequences. All three of these successions – at Mousecroft Lane, Venus Bank and Ryton – described in detail by Shaw (1972a) belonged to an integrated drainage system, since their palaeocurrents are parallel to those at Norton Farm, Dorrington and Buildwas, and follow the major valleys. Occasional delta sequences, as in the lower part of the Venus Bank stratigraphy and at Buildwas, were thought to be built out into ice-marginal lakes during downwasting of stagnant ice.
Late Devensian glaciogenic processes have created considerable thicknesses of till in the coastal lowlands and valleys of Northern England. Hughes et al. (1998) describe over 70 m of glacial deposits in boreholes at Foxhouse South opencast site, midway between Maryport and Cockermouth, Cumbria. Smith and Francis (1967) note the existence of glacial till 92 m thick near Sedgefield in County Durham. Descriptions of these tills generally follow the tripartite model of Hull (1864), using the middle sands as stratigraphical markers. The so-called 'middle' horizons are often restricted and repeated and early reservations were expressed about their regional significance (Reade, 1883b; Barrow, 1888; Travis, 1913). Lewis (1894) had also described the 'middle' horizons as the result of subglacial stream deposition. In opencast sites in Cumbria, away from the coastal areas, there is evidence for upper tills, sand and gravel and laminated clays (Hughes et al., 1998) (see
In the Vale of York the single Late Devensian till is a reddish-brown clay with abundant erratics of Magnesian Limestone and Triassic Sandstones, as well as Lake District, Carboniferous and Lower Palaeozoic rocks. Towards the Pennines, where Yorkshire Dales ice fed into the Vale of York, the till is greyer and rich in Carboniferous Limestone, sandstone and chert erratics (Lovell, 1982). This single till contrasts with the multiple tills in parts of Cleveland, where three tills occur south of Hartlepool (James, 1982) and four at Rockcliffe Scar (Francis, 1970). In Holderness there are multiple tills, which recently have been described and interpreted by Eyles et al. (1994) and Evans et al. (1995) in terms of deformation tills deposited during glacial events shortly after 18 000 years BP. McCabe et al. (1998), however, have suggested a major ice readvance about 14 700–14 000 years BP (see Dimlington site report, this chapter).
In the Lancashire Plain, Longworth (1985) provided evidence of the unrepresentative nature of an extensive tripartite sequence from borehole data for the M55 motorway. Similar complex glaciogenic sequences with multiple tills have been noted in Cumbria (Huddart, 1970, 1981c, 1983) and from borehole logs along the M62 in east Lancashire (Johnson, 1985b). In the Cheshire–Shropshire lowlands, although the tripartite interpretative model had been supported by the [British] Geological Survey (e.g. Poole and Whiteman, 1961), it became apparent that the Stockport Formation embraced a complex Late Devensian glaciogenic sequence (Worsley, 1967a, b, 1985).
In most of the upland regions of northern England, such as the Cheviot Hills, Pennines and Lake District, till distribution is patchy and variable both in lithology and in thickness. Most of the tills are considered to be Late Devensian in age. This is based on the relative lack of dissection and shallow, poorly developed soils. Lateral variation in the upland tills, resulting from bedrock lithology differences and local ice-movement directions, makes correlation between areas difficult (Catt, 1991a).
It is clear that a complex sediment distribution results from glaciogenic processes. The glacial land-systems approach is a means of classifying and mapping sediment sequences and landforms on the basis of their characteristic topography, subsurface conditions and sediments (Boulton and Paul, 1976; Boulton and Eyles, 1979; Eyles, 1983; Paul and Little, 1991). The value of such a land-systems approach is its ability to produce a large-scale geomorphological zonation
The maximum geographical limits of the Late Devensian ice sheet
The stages in deglaciation in the western margin of the Cheshire–Shropshire lowland are discussed in detail in G.S.P. Thomas (1989). In stage A (
Worsley (1970) interpreted the Delamere moraine to the north as a 'sand plain' (Davis, 1890) built out into a lake, and descriptions are provided in Earp and Taylor (1986). Along the northern margins the sequence of ice oscillations was probably complex and sections within this zone often reveal multiple till sequences, as at Sandiway, where the tills were interpreted as flow tills (Thompson and Worsley, 1966).
Farther north through the Fylde there is a discontinuous multiple ridge called the 'Kirkham moraine', which Gresswell (1967) thought was a terminal position linked with the Bride moraine in the Isle of Man. Longworth (1985) casts doubt on this interpretation, however, and invokes a supraglacial origin for its formation. In Cumbria, readvances created a moraine line associated with the Low Furness Readvance and the Gosforth Oscillation/Scottish Readvance moraine along the Black Combe coastal plain and north along the coastal zone as far as the St Bees moraine.
On the east coast, the maximum limit across the Humber estuary is marked by morainic ridges east of Winteringham and Winterton and across the Ancholme Valley at Winterton Holmes (Gaunt, 1981). In the Vale of York the maximum limit is south of the York and Escrick moraines but these landforms mark a stabilized ice-front position. Lacustrine laminated clay and sands overlap up the morainic slopes (Dakyns et al., 1886; Gaunt, 1970a) and the borehole evidence indicates that the laminated clay continues northwards under the moraine. This confirms the belief that the moraine was deposited into Lake Humber.
In the Yorkshire Pennines a series of terminal moraines is found in each of the major valleys (Raistrick, 1926, 1927). There is evidence for six halt stages in the valleys of the Aire and Wharfe, but not all these stages are seen in the more northern valleys owing to later separation from the Vale of York glacier. Many of these moraines dammed-up elongated lakes in the valleys upstream and now form flat sections of the valley floor as they were filled up by laminated clays and silts (Raistrick and Woodhead, 1930; Arthur-ton et al., 1988). Moraines also formed in the Lake District during valley glacier recession (Gresswell, 1962; Wilson, 1977; Sissons, 1980; Clark and Wilson, 1994). Marr (1916) and Rais-trick (1925) both considered that the Rosthwaite and Thornythwaite moraines resulted from a stillstand of valley glaciers during the general recession, whereas Hay (1944) and Wilson (1977) suggested that the moraines were the result of a readvance of the valley glaciers.
The Late Devensian deglaciation of the Irish Sea basin has been explained in terms of glaciomarineprocesses and environments caused by rapid ingress of the sea into a glacio-isostatically depressed basin (Eyles and Eyles, 1984; McCabe, 1987; Eyles and McCabe, 1989, 1991). This led to high relative sea level, instability of the ice sheet and rapid calving
The glaciomarine account of Irish Sea basin deglaciation begins with a rise of global sea level associated with the start of a phase of worldwide ice recession. Rising seas impinged on the southern front of the Irish Sea ice sheet. Embayments in the front of the ice shelf focused iceberg calving and concentrated the rapid southward movement of ice from the main ice mass in the basin. As sea level rose still further the marine ice-margin retreated north, stabilizing temporarily at grounding lines. The waning land-based ice around the basin produced abundant meltwater, much of which flowed at the base of land ice, so easing ice movement and reinforcing the drawdown effect of iceberg calving at the ice front. Drumlin swarms were produced under fast moving land-ice, with some reworking of glacial sediments and incorporation of material that meltwater had carried beneath the ice. Subglacial tunnel valleys were incised, particularly along the main valleys. Thick beds of marine sediments were deposited in areas where tidewater ice margins were stationary for sufficiently long intervals and morainal banks built up from debris released at the ice front. Many flat upper surfaces of sand and gravel now well above sea level have been interpreted as deltas formed where major meltwater channels at ice fronts reached the sea. Thin mud drapes were ascribed to suspension settling of fine glacial debris in the sea. At some sites around the Irish Sea basin in-situ, rather than derived and reworked, marine fossils have been recorded and demonstrate the enclosing sediments to be glaciomarine.
Gradually, the retreating ice margins and the advancing seas reached coastal Cumbria, the Solway Firth and Galloway, areas that were still incompletely recovered from glacio-isostatic crustal depression. High relative sea levels of 152 m OD were inferred for supposed marine deltas in Wasdale and Eskdale. In Dumfriesshire raised deltas were noted at Dumfries (50 m) and Dalton (70 m), but as part of a reassessment of the glaciofluvial sedimentology of the Nith and Annan basins, Huddart (1999) considered there to be no evidence of raised delta sequences. The glaciomarine explanation of deglaciation in the Cumbrian lowlands requires land-based ice moving generally westward to marine termini in the vicinity of the present coast and marine incursions. It considers that the glaciomarine landforms were contemporary, or near contemporary, with drumlin formation under mobile land ice. It proposes that the Cumbrian land-based drumlin-forming ice streams terminated at marine margins now onshore, for example, in Low Furness and north of Maryport, as evidenced by morainal banks and raised deltas
The glaciomarine interpretation requires evidence for deposition in marine environments at sites categorized as morainal banks and marine deltas. It depends on adequate evidence for contemporary ice margins at those sites and for ice cover landward of them. Evidence of late incursions of ice from the north-west and west on to the lowlands directly opposes the glaciomarine hypothesis. Ice readvance models place ice on the 'wrong' side of morainal banks and deltas (that is to the west) for the glaciomarineinterpretation. It is noteworthy that in direct juxtaposition to their comment that the Scottish Readvance proposition relies on identification of high-level lacustrine deltas, Eyles and McCabe (1989) stated 'sedimentological and microfaunal evidence indicate that the deltas [their high-level glaciomarine deltas] record local marine limits', but they presented no sedimentological or microfaunal evidence from the Cumbrian sites. The failure to report marine fossils from supposed glaciomarine Cumbrian sediments is of major significance, especially as these fossils are not uncommon at other sites on the fringes of the Irish Sea, especially on the Irish coast (e.g. McCabe et al., 1990; Haynes et al., 1995). Huddart and Clark (1994) concluded that the interpretations of Eyles and McCabe (1989) have not been substantiated in Cumbria and that they have incorporated landforms and sediments from Cumbria into their model without full regard for the detailed sedimentological, palaeocurrent and lithological evidence available that suggests an alternative explanation for these glaciogenic deposits.
It is not suggested that there were no marine ice margins associated with the Late Devensian deglaciation in parts of the Irish Sea basin, but each area and sequence must be interpreted on the basis of the evidence it provides. For example, in offshore Cumbria there appears to be some evidence for glaciomarine events from an offshore seismo-stratigraphical framework and associated Nirex boreholes. The framework has been established using seismically distinctive sequences, which are bounded top and bottom by unconformities, and their correlative conformities (Eaton and Williams, 1993; Eaton, 1996; Huddart, 1997). Six major seismically distinctive sedimentary sequences (1–6 in
There is thus some evidence here for giaciomarine conditions in the Irish Sea basin and it is how to relate contemporary relative sea levels with the deglaciation of the Dimlington Stadial ice sheet where most controversy still lies. The integration of the Nirex data with preexisting data from the Lake District and Irish Sea basin has allowed a tentative model of the build up and decay of this ice sheet to be suggested as a series of cartoon sketch maps (Akhurst et al., 1997; Huddart, 1997; Merritt and Auton, 1997a, b, 2000; Thorne et al., 1997). These are illus trated in
Currently the consensus view is that the model of Eyles and McCabe (1989) cannot be accepted for many areas of the Irish Sea basin fringes and certainly not in Cumbria but that in the basin itself there seems to be evidence for glaciomarine sediments and that the deglaciation might have been accompanied by a tidewater margin. McCarron (2001) reviewed critically the lines of evidence on which the glaciomarinehypothesis rests (sedimentology, deformation structures, delta deposits, marine fauna, amino-acid ratios and radiocarbon dates). The sedimentological interpretation of many Irish Sea basin sections has been challenged, it is argued that subglacial sediments are common rather than rare and there is widespread evidence of glaciotectonism, as at St.Bees. Any delta deposits are the result of local ponding or occur where glaciers from different sources are uncoupled. They do not record past sea levels and the ad hoc theory of 'piano-key tectonics' is not required to explain the irregular pattern of altitudes. The cold water foraminifera interpreted as in situ he regarded as reworked from older Irish Sea sediments. Amino-acid age estimates used in support of the glaciomarine model he regarded as unreliable. However, radiocarbon dates from distinctive foraminiferal assemblages in north-east Ireland show that glaciomarine sediments do occur above present sea level, but they are restricted to low altitudes in the northwest of the basin.
As the sediment distribution and stratigraphical sequence is not that well known in the basin the sequences of retreat phases and readvances that undoubtedly took place and the time frame involved remain controversial. However, if the interpretation of McCabe (1996) and McCabe et al. (1998) for five major millennial time-scale oscillations in northern Britain is correct, despite the fact that their suggested marginal limits in Cumbria are considered incorrect, it is relatively easy to fit some of the readvances documented for Cumbria into this framework in a general sense. The readvance(s) is post-drumlin formation because it cuts across the drumlin field in the Solway lowlands, west Cumbria and Furness, and there is the possibility that it could be correlated with the last major incursion of ice from south-western Scotland on to the Northern Ireland lowlands, i.e. the Ballykelly oscillation (McCabe, 1996). This could not have occurred when deep water was present in the North Channel and must record a lowstand in relative sea level. A similar climatically controlled readvance could account for the late pro-glacial and glaciotectonized, readvance terrestrial-sequences in Cumbria, shown schematically in
McCabe et al. (1998) and McCabe and Clark (1998) concluded that both the St Bees Moraine and the Bride Moraine on the Isle of Man formed at the maximum extent of the Kinard Point stadial readvance. Merritt and Auton (2000), however, although tempted to correlate the Scottish Readvance (sensu Huddart 1970, 1991) with this readvance, drew attention to the fact that McCabe et al.'s (1998) model showed far more ice present at that time in north-west Cumbria than envisaged by Huddart (1970, 1991). Merritt and Auton (2000) suggested that their model fitted more closely with that of the Gosforth Oscillation, which involved synchronous readvances from Wasdale and the Irish Sea basin, together with drumlinization in northwest Cumbria. However, they recognized that if this correlation is made then there is little time available for a subsequent Scottish Readvance after 14 000 years BP. Hence they suggested that the Gosforth Oscillation might correlate with the Belderg Readvance recognized in western Ireland at c. 17 000 years BP (McCabe, 1996) or even the Dimlington Advance on the Yorkshire coast after 18 500 years BP
In north-east England there is further controversy, because Eyles et al. (1994) have speculated on the role of fine-sediment trapping in extensive pro-glacial marine or freshwater bodies in promoting the southward extension of ice lobes along the east coast of England as they overran deformable sediment and surged. Teasdale and Hughes (1999) also suggest the possibility that marine influences were close, both in time and space, to the eastern coastal ice lobes. For example, the Dogger Bank Formation in the North Sea, which is thought to be the distal equivalent of the Bolders Bank Formation (clay-rich, Devensian, lodgement tills) (Balson and Jeffery, 1991), contains a dinoflagellate flora indicating shallow, open marine waters.
Northern England provides some of the classic glacio-lacustrine sequences in Britain. Many of these are linked to Kendall's (1902) pioneering work on ice-dammed lakes and the origin of meltwater channels (see 'Glacial meltwater erosion section', pp. 100–101). After Kendall's 'overspill' theory was challenged by Sissons (1958a, 1960b, 1961) very few ice-dammed lakes were recognized. Sissons' own work (1977, 1978, 1979a, 1982) on the classic ice-dammed lakes of the Scottish Highlands, established the criteria for unequivocal evidence: shorelines linked to overflow/drainage routes, deltas and lake sediments. Several examples are discussed below and in the site reports of Warren House Gill (Chapter 4), Holme St Cuthbert and Newtondale (this chapter). Most of the lakes are associated with ice movement from lowland areas against the topography, or retreat from such situations, and the larger examples are situated in extensive basins.
In Cumbria there is good evidence in the Carlisle plain for a lake dammed by retreating Late Devensian ice, which unlike the marginal zones of this "ice sheet, maintained an active ice front (Huddart, 1970, 1981c). A suite of deltas between 66 and 30 m above OD was built out by the proto-Eden and Irthing rivers. At the earliest stage (66–60 m OD) the lake was confined to the Irthing valley (with deltas around Irthington and in the lower Cam Beck valley) and at its maximum was only 5 km by 3 km. Great thicknesses of lake-bottom sediments have been exposed around Great Easby, between Castle Bank and Boothby Bank. At the latter site there is a sequence of nearshore silts and mudflows, whereas at Great Easby there are individual, 50-cm-thick, proximal varves with current structures, convolute lamination and then diamicton units (Huddart, 1970). The 54 m OD stage is recorded by deltas around the Cam Beck and around Wetheral. They indicate that the lake grew in size as the ice retreated. Below this the delta from Warwick Bridge to Aglionby indicates a lake level between 37 and 44 m OD and this stage is indicated by the flat surface on which Carlisle airport operates. Farther west a lake at 30 m OD is indicated by the Crosby Moor delta and that the delta now dissected by Collar Beck around Scotby Park and Rose Hill. The latter delta has been modified by an ice readvance that deposited a till on its slopes but did not overtop it (Huddart, 1971b).
No lower lake levels have been found to the west, but this must be because of the later readvance ice, which reworked the lake sediments. Lake-floor sediments have been found below an upper till at several locations in the Carlisle plain, east and north-east of Carlisle, for exam ple, sequences 9 m thick between Linstock and Drawdykes Castle. However, it is thought probable that these sediments were deposited in a pro-glacial lake dammed by the readvancing ice, and not the retreating earlier ice. Although there is this major delta sequence, there is only one possible drainage channel that connects the River Caldew valley to the misfit River Wampool by way of Caldew Mires, east of Dalston. The channel is over 300 m wide, is located between 30 and 39 m OD and is a larger valley than either the present day Caldew or Petteril. Huddart (1981c) considered that drainage from earlier stages of the lake was probably subglacial. Although the [British] Geological Survey interpreted these stages of Lake Carlisle as resulting from the retreat of the Scottish Readvance ice, it is considered that it was the retreat of the earlier Late Devensian ice that held up most of these lakes. This explains why the lake did not spread into the lower Petteril and Caldew valleys, because they were occupied by stagnating ice at the time of lake formation and during the readvance.
In south Cumbria the readvance stage(s) of the Late Devensian Irish Sea ice pro-glacially dammed lakes in the St Bees valley, the lower Eden valley, lower Wasdale and the Gosforth lowlands, Eskdale, the Black Combe coast and Whicham valleys. Here the ice was advancing against the regional drainage lines. In lower Wasdale the thickness of glacial sediments proved in borehole logs is over 80 m and most seems to be glacio-lacustrine in origin (Huddart, 1970, 1981c; Huddart and Tooley, 1972). Although most of the lakes postulated by Smith (1912, 1932) in lower Wasdale, Eskdale and Miterdale were based on supposed overflow channels, deltas and beaches, these have been re-interpreted by Smith (1967) and Huddart (1970) as a product of subglacial and ice-marginal processes, as there are examples of kame terraces in lower Wasdale and subglacially engorged eskers on the flanks of Corney Fell above the major submarginal or subglacial channel systems (Huddart and Tooley, 1972). However, there is evidence in the form of lake sediments and deltas in lower Wasdale and the Gosforth lowlands that lakes formed during one of the readvance stages.
In north-east England at the close of the Late Devensian, eastward-flowing meltwater from the western Scottish, Lake District and Pennines ice, which was stagnant in the valleys and downwasting, was dammed by active, advancing northern ice, so creating a series of ice-dammed lakes, the largest of which were Lake Wear (Raistrick, 1931b; Smith, 1994; Mills and Holliday, 1998; Hughes and Teasdale, 1999), which extended into the Team and Tyne valleys, and Lake Edder Acres (Catt, 1991a). Smith (1994) suggested that Lake Wear stood at different levels as outlets opened and closed between 132 and 43 m OD and, although the maximum lake level must have been above this height, most of the deposits are below 90 m OD. The glacio-lacustrine sediments deposited in this lake, between 5 and 55 m thick, were called the 'Tyne–Wear Complex' (Smith, 1994) and generally are interbedded laminated silty clays and clayey silts, with fine-grained sands and stony clays and some gravels. In Northumberland, Anderson (1939) identified sands and gravels in the valleys of the Aln, Coquet, Wansbeck and Blyth as deposited in a lake dammed by North Sea ice, with shorelines at 58 and 42 m OD and on the eastern flanks of the Cheviot Hills, Clapperton (1971b) noted extensive glacio-lacustrine deposits.
Farther down the east coast there is evidence of large ice-dammed lakes, resulting from eastern ice lobes blocking the Tees estuary area, in the form of laminated clays and shoreline sands (Agar, 1954; Beaumont, 1967); Lake Pickering (see Newtondale and Hole of Horcum GCR site report) and Lake Humber. Beaumont (1967) described an Upper Tees Clay up to 100 m OD, which had very few, small stones, was up to 6 m thick and had a weak or random fabric. He thought that in the early stages of ice advance into the Tees lowlands there was ponding of sub-aerial drainage in a lake. Lake Pickering was dammed at both its westerly and easterly ends by ice and overflowed into the Vale of York via the Kirkham Abbey Gorge in the Howardian Hills (Catt, 1977a). Lake Humber formed when the Humber Gap was blocked by ice in the east at first and subsequently by a plug of glacial moraine and by ice fronts in the Vale of York (Lewis, 1887a, b; Gaunt, 1974, 1981). The lake developed up to 33 m OD between the ice to the north, the Pennines to the west, Lincoln Edge to the south and the Yorkshire Wolds to the east. In high-level sand and gravel deposits associated with this lake, a bone fragment from Brantingham (Gaunt, 1974), either just below or within these deposits, was dated to 21 853 years BP. During deglaciation the lake extended north wards at a lower level between 10 and 4 m OD and up to 20 m of laminated clay was deposited. The lake drained until late in its history via the Lincoln Gap, and silting up was the most likely cause of the lake vanishing. A palaeosol on laminated clay at West Moor, near Doncaster has been 14C dated to 11 100 years BP (Gaunt et al., 1971), which provides a minimum age for the lake's disappearance. Gaunt (1981) suggested pro-glacial, supraglacial and marginal glacio-lacustrine origins for lakes in a more extensive precursor of Lake Humber. His argument was that the Peak District and Pennine valleys south of Leeds were ice free and hence glacial lakes may have existed, and there are laminated clays near Barnsley (Green et al., 1878), near Rothwell (Gilligan, 1918) and on top of Brayton Barff (Gaunt, 1981).
The concept of Lake Lapworth in the Cheshire–Shropshire lowlands was appraised carefully by Worsley (1975). He suggested that there was considerable support for its former presence and that very much more of the evidence is explained by accepting the lake hypothesis than by rejecting it. On the basis of shorelines, laminated sediments, overflow channels and the nature of the glaciofluvial morphology (see Aqualate Mere site report, this chapter), Dixon (in Whitehead et al., 1927) recognized Glacial Lake Newport and Wills (1924) recognized Glacial Lake Buildwas. On ice retreat these amalgamated to form the larger Lake Lapworth, which must have overflowed through the Ironbridge Gorge at some stage. Interest in Lake Lapworth was revived by Poole and Whiteman (1961), who extended the original definition of the lake to include a lake extending from Ironbridge as far north as Chorley in Lancashire. Although this concept remains extremely doubtful, Worsley (1970), in a review of Pleistocene events in the Cheshire–Shropshire lowlands, considered that the data available gave support to the glacial lake hypothesis, with the lake having the general dimensions of the classic Lake Lapworth. Shaw (1972a), however, stated that there was no evidence for a widespread lake during the retreat of the Irish Sea ice in Shropshire.
One of the most conspicuous, widespread and well-developed glacial depositional landforms, composed largely of till, are the subglacial drumlin fields, superimposed drumlins and drift tails, which largely are found in the lowlands of the region. Mitchell (1991a, b, 1994), however, describes drumlins up to 600 m in south-east Cumbria and neighbouring North Yorkshire. The main drumlin fields occur in the lower Tweed valley in Northumberland (Clapperton, 1970), in the Solway lowlands and along the coastal plain north-west of the Lake District (Huddart, 1970; King, 1976), in Edenside (Hollingworth, 1931), in the south-east Lake District around Kendal, through the Yorkshire Dales south of Settle, in the Ribble valley and the west Craven lowlands (Raistrick, 1933; Johnson, 1985b), in the southern Lake District valleys, across the Furness peninsula (Gresswell, 1962; Grieve and Hammersley, 1971; Huddart et al., 1977) and into north Lancashire (Longworth, 1985). It has been suggested by Johnson (1985b) that the Morecambe Bay–Furness–Southern Lake District drumlins are located where local relief helped impede the movement of ice southwards, and according to Boulton et al. (1977) this would cause the sliding velocity of the basal ice to decrease to a point to which lodgement tills would be deposited and moulded into drumlins by the ice. Such changes took place where the Cumbrian valley glaciers were coalescing into larger piedmont glacier ice-streams.
The origin of drumlins, summarized in Bennett and Glasser (1996) and Benn and Evans (1998), is controversial and has given rise to numerous models, hypotheses and explanations (Menzies, 1979a, b, 1989; Menzies and Rose, 1987a, b, 1989). Any theory must be able to produce a mechanism for drumlin forms, a mechanism for promoting the unstable amplification of relief and a mechanism for quenching the unstable amplification once drumlins have reached a critical size (Hindmarsh, 1999). The following mechanisms have been proposed:
Summary
Glacial events affecting northern England have left the strongest imprint on the landscape that we see today. During the Quaternary Period the area was glaciated numerous times and subjected to repeated cycles of ice-sheet growth and decay. The landform and sedimentary record contains evidence of both full ice-sheet (glacial) conditions and restricted ice-cap/cirque-glacier (stadial) events. Evidence for glaciation prior to the Late Devensian is fragmentary and most of the landforms and sediments date from this most recent glacial episode. Large quantities of rock and sediment were eroded from upland areas and transported to the lowland fringes of the ice sheets and to offshore depocentres. These changes in the landscape were accompanied by wholesale reorganization of the major drainage patterns. Palaeoglaciological reconstruction is still poorly constrained, and although parameters such as ice-sheet extent, thickness, flow patterns, thermal regime, and their change over time can be used to enhance our understanding of climate changes during the Quaternary Period, much of these data are still lacking. The GCR sites described in this chapter contribute to the resolution of the following key debates: