the stratigraphic and sedimentological significance of late devensian ice sheet surging in holderness yorkshire u k amino acid analyses of marine mollusc valves show that the basement till of holderness yorkshire is of late devensian age ca 20 000 bp and not pre ipswichian 125 000 bp as is traditionally supposed together with the overlying skipsea and withernsea tills the basement till is argued to be a deformation till resulting from the repeated onshore surging of late devensian ice over a muddy sea floor and the subglacial transport attenuation and mixing of marine sediment silts on the surface of the basement till yielding 14c dates of 18 500 and 18 240 bp have been regarded as minimum ages for late devensian glaciation in eastern england e g the dimlington stadial of rose 1985 1989 the amino acid data presented here indicates that the maximum of the late devensian glaciation in eastern england occurred earlier sedimentological interpretation of the late devensian tills of holderness as glacially reworked marine sediments supports previous glaciological models of the british ice sheet involving surging of ice lobes along the coast of eastern england the basement skipsea and withernsea tills are separated by shallow marine sediments and may be representative of deformable bed till facies deposited below pleistocene ice sheets moving over soft fine grained sediments

the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

origin of an esker like ridge erosion or channel fill sedimentology of the monington esker in southwest wales abstract a ridge of stratified gravel and sand near cardigan in southwest wales has previously been interpreted as an esker its sedimentology is exposed in sand pits and consists of cross bedded gravel and sand incised into a complex of climbing ripple cross laminated sand interbedded with silt and clay the succession records the progradation of fluvial channels across a former lake floor there is no clear sedimentological evidence that the sediments were deposited in an ice contact setting and therefore the feature should not be called an esker the interpretation favoured here is that the ridge is an erosional remnant either of a formerly more extensive outwash plain or of a kame terrace deposited when the adjacent valley was filled with dead ice recognition of an esker needs to be based on sedimentology and regional setting as well as on geomorphology

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

geological survey of canada s contributions to understanding the composition of glacial sediments drift compositional studies were initiated at the geological survey of canada gsc in the mid 1960 s in projects that drew heavily on the technology and approaches developed in fennoscandia over the previous century as this research progressed and expanded in the 1970 s its fennoscandian character diminished and like the geochemical exploration research program that it closely paralleled drift prospecting began to acquire a distinctly canadian character imposed by the geographical and logistical constraints of climate and asymmetric population distribution gsc research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering because glacial sediments are generated largely by crushing and abrasion their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness this s

ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec abstract outcrops bearing stained striated facets indicative of north northeastward moving ice truncated by unstained striated facets indicative of various younger flows occur in the caniapiscau area of north central quebec this is the first report of differential staining of striated facets in the region we propose that the staining occurred in an ice free interval of probable interglacial age this early ice flow probably occurred during ice retreat toward the quebec highlands ice flow and glacial transport data from the southern hudson bay and james bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an early wisconsinan glacier in the quebec highlands the northern part of this flow was diverted northwestward through hudson bay and the southern part southwestward across james bay following a progressive counterclockwise rotation of flow a zone of intersection zi of two major glacier bedform systems often referred to as the horseshoe shaped labrador ice divide represents the head of a large northward convergent ice flow system that extended to ungava bay and beyond the ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of caniaspiscau reservoir we propose that this capture event correlates with the gold cove advance in ungava bay and on baffin island at about 9900 14c yr bp it is the largest advance of quebec labrador ice yet proposed for the region this correlation is based on the relative ice flow chronology accommodation of glacial lakes naskaupi and mclean in the deglaciation sequence the constraints placed on last glacial maximum lgm ice configuration by the postglacial uplift pattern and events in the deep sea record therefore the ungava ice flow pattern is not a relict pre wisconsinan glacial landscape as recently proposed

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

valley asymmetry evidence for periglacial activity in the central north sea present day open valleys with distinct asymmetric profiles have been studied from the central north sea the bulk of the valleys exhibit steep north facing and shallow south facing slopes this asymmetry is ascribed to preferential slumping of the south facing slope under periglacial climatic conditions exceptions to the regional asymmetric trend are probably the result of more localized factors such as fluvial and microclimatic processes and the effects of local geology the recognition of this type of within valley asymmetry associated with slumping in buried valleys within the quaternary sequence may be indicative of former periglacial activity

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

ice marginal depositional responses to readvance episodes in the late devensian deglaciation of the isle of man abstract remapping of the quaternary geology of the isle of man and consequent revision of the stratigraphic succession identifies three glacigenic formations each separated by a major unconformity the oldest formation the shellag represents an extensive ice advance beyond the island limits to the last glacial maximum lgm the overlying formation the orrisdale represents a major readvance episode during retreat from the lgm and is associated with the construction of the bride moraine and the deposition of extensive proglacial subaqeous sediment examination of the sedimentology and micropalaeontology of these sediments indicates that the water body was most likely lacustrine and not marine application of sequence stratigraphy to the overlying jurby formation identifies evidence for three further phases of readvance each off lapping one another into the margin of the lake basin via a complex system of ice contact subaqueous fans and outwash fan deltas the jurby formation is dated by organic sediments overlying it as older than 18 5 14 4 kyr bp and provides an ice marginal correlative for heinrich event 1 readvance limits identified 50 km to the west in eastern ireland

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

the trace fossil gyrophyllites in deep sea siliciclastic deposits of the istebna formation upper cretaceous palaeocene of the carpathians an example of biologically controlled distribution abstract gyrophyllites kwassizensis glocker occurs abundantly in deep sea density current siliciclastics of the istebna formation silesian nappe outer western carpathians poland slovakia and czech republic close to the cretaceous palaeogene boundary it is composed of petal shaped lobes radiating from a thin shaft forming rosettes on a few levels in the sediment the trace fossil is interpreted as a feeding structure produced by a soft body worm which actively filled the lobes with mud transported from the underlying layer probably in response to migration of redox boundary in a generally poorly oxygenated environment probably due to microbial decomposition of cellulose and other organic particles the mud from below was more nutritional than the more fresh mud from the sea floor the number of lobes in a rosette from 7 to 15 is referred to ontogenetic development of the tracemaker and indirectly to time of burrow occupation the number varies between localities and may indicate a more hospitable habitat in the areas where the number is higher g kwassizensis occurs only in a narrow stratigraphic interval after a significant drop of sedimentation rate caused by non eustatic reasons in facies conditions which are not unique during the long history late jurassic miocene of the external carpathian subbasins this suggests that facies control was less important for distribution of this trace fossil than some undetermined biological factors which enabled successful but incidental invasion of the tracemaker to deep sea floor of one of the subbasins the silesian basin

sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern celtic sea thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49 n in the celtic sea the northern samples facies a are clast rich overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas the southern samples facies b are distal glacimarine plastic silty clays containing abundant cold water microfaunas both these facies are correlated with the late devensian scilly till enabling a quantitative reconstruction of ice thicknesses grounding line sea level and shoreline elevations in the celtic sea at 19 000 years bp the ice advance terminated in marine waters towards the shelf edge break and is likely to have constituted a thin lobate surge over deformable marine sediments 1990 the geological society

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

amino acid evidence for devensian ice west gower south wales complete inundation of south wales by ice during the penultimate wolstonian glaciation has been widely suggested1 3 although it is generally agreed that the last glaciation was less extensive than the preceding one4 6 there has been controversy concerning its limits stemming mainly from the lack of clear geomorphological evidence and the dearth of datable material7 9 14c dates from the shelly till in pembrokeshire were first thought to indicate an extension of last glaciation ice into the area10 but serious doubts were subsequently raised about the reliability of finite dates on shells of this age range11 12 we present here results of amino acid analysis of shells from recently exposed till and from underlying raised beach remnants at broughton bay west gower total d allo l iso ratios from the raised beach are consistent with analyses on shells from comparative beach remnants elsewhere in south west britain7 13 15 shells of 21 identifiable littoral species extracted from the till suggest inshore marine conditions similar to those at present amino acid ratios from littorina spp provide firm evidence for the encroachment of devensian ice on to gower approximately to the limit suggested by bowen7 fig 1a

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism