reconstructing the dynamics of the north west european pleistocene ice sheets abstract the flow lines of the north west european pleistocene ice sheets can be reconstructed with the aid of fabric measurements and glaciotectonic investigations from this there is evidence for a more extensive saalian glaciation of the north sea area than previously assumed with regard to the weichselian different glaciological models can be tested against the field evidence deformable bed and instantaneous glaciation may be partially responsible for the observed phenomena however while at the end of the weichselian there was fast moving ice largely following the course of the baltic sea depression during the weichselian maximum conventional radial ice flow as envisaged by hughes et al 1981 was dominant directional evidence suggests that fast moving baltic ice was present during the late stages of the older and younger saalian glaciations however possibly as a result of isostatic effects it occupied a more southerly position than during the weichselian

seismic stratigraphy of waterton lake a sediment starved glaciated basin in the rocky mountains of alberta canada and montana usa abstract upper and middle waterton lakes fill a glacially scoured bedrock basin in a large 614 km2 watershed in the eastern front ranges of the rocky mountains of southern alberta canada and northern montana u s a the stratigraphic infill of the lake has been imaged with 123 km of single channel fm sonar chirp reflection profiles offshore sonar data are combined with more than 2 5 km of multi channel land based seismic reflection profiles collected from a large fan delta three seismic stratigraphic successions sss i to iii are identified in waterton lake resting on a prominent basal reflector bedrock that reaches a maximum depth of about 250 m below lake level high standing rock steps reigels divide the lake into sub basins that can be mapped using lake floor reflection coefficients a lowermost transparent to poorly stratified seismic succession sss i up to 30 m thick is present locally between bedrock highs and has high seismic velocities 1750 2100 m s typical of compact till or outwash a second stratigraphic succession sss ii up to 50 m thick occurs throughout the lake basin and is characterised by continuous closely spaced reflectors typical of repetitively bedded and rhythmically laminated silts and clays most likely deposited by underflows from fan deltas paleo depositional surfaces identify likely source areas during deglaciation intervals of acoustically transparent seismic facies up to 5 m thick are present within sss ii at the northern end of upper waterton lake sss ii has a hummocky surface underlain by collapse structures and chaotic facies recording the melt of buried ice sediment collapse may have triggered downslope mass flows and may account for massive facies in sss ii a thin holocene succession sss iii

glacial tunnel valleys in the eastern goldfields of western australia cut below the late paleozoic pilbara ice sheet abstract open cut gold mines near kalgoorlie in the eastern goldfields region of western australia expose a late paleozoic carboniferous permian network of glacially eroded valleys filled with tillite and shale valleys are incised into archean and proterozoic strata of the low relief western australian shield and buried by tertiary and quaternary strata subsurface data identify a poorly integrated network of narrow 200 m wide deeply incised 80 m and steep sided channels that connect broader sub basins up to 3 km wide lowermost infill strata within valleys consist of bouldery diamictites containing abundant striated clasts of far travelled lithologies and are identified as tillites deposited by a late paleozoic ice sheet pilbara ice sheet that covered the west australian shield tillites are blanketed by shales containing early permian palynomorphs the form and sedimentary infill of the buried valley network is comparable to subglacially cut tunnel valleys that formed below the wet based margins of pleistocene continental ice sheets and a similar origin is proposed for those at kalgoorlie the significance of this finding is that hitherto little was known of the late paleozoic gondwanan ice sheet that grew on the western australian shield and which contributed substantial volumes of sediment to adjacent sedimentary basins the preservation of a relict late paleozoic glacial topography near kalgoorlie indicates that post permian erosion of the region was minimal and cannot be reconciled with denudation models which propose uniform post permian uplift and deep stripping across the shield

origins of the ice contact stratified ridges eskers of ireland abstract an extensive system of ridged landforms composed of ice contact stratified sediment was deposited in the central lowland of ireland during the most recent deglaciation 18 000 bp the ridges have been interpreted by others as deposits of an ice sheet drainage system i e eskers and as such have been used with other data to reconstruct the deglacial history the traditional deglaciation model shows systematic retreat of ice from south to north our study which involves an analysis of the ridged landforms using lithofacies sedimentary structures and paleocurrent data in conjunction with the geomorphology indicates that the pattern and nature of the ridges are not compatible with this model and support a new model of deglaciation warren 1991 in which the esker system fo med in an interlobate area during the simultaneous shrinking of two main glacial outflow centers an extensive lake system developed in the lowland between the two outflow centers ridges formed both perpendicular and parallel to ice margins involved both active and stagnating ice are both continuous and segmented beaded and were deposited in subaqueous and subaerial environments almost all of the ridges are associated with lacustrine sediments ice contact ridges are polygenetic and a genetic classification is proposed those that formed perpendicular to the ice margin are termed eskers those that formed parallel are termed moraines distinction between esker types continuous or beaded subglacial tunnel fills fluvial ice channel fills and subaqueous fans and moraine types s baqueous or subaerial is crucial to a reconstruction of the mode and pattern of deglaciation in the central irish lowlands

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

the origin of deep buried channels of elsterian age in northwest germany buried channels cut to a depth of over 100m into the underlying substratum of north germany are almost exclusively of elsterian age evaluation of geophysical well logs in the hamburg area for the first time allows the construction of detailed longitudinal and transverse profiles it can be shown that an apparently chaotic infill known from borehole records in some cases is actually a regular sedimentary sequence fining from proximal to distal channel formation seems to have been the result of catastrophic meltwater release in the marginal parts of the ice sheet the channel infill reflects these episodic outbursts of meltwater during deglaciation the channel remnants became infilled with fine sediments the channels ceased to exist as morphologically detectable forms at the end of the holsteinian stage

a new early cambrian konservat lagerstatte expands the occurrence of burgess shale type deposits on the yangtze platform abstract we report the fandian biota a new konservat lagerstatte from the cambrian stage 3 yuxiansi and jiulaodong formations in sichuan south china with close faunal links to the chengjiang biota in yunnan the biodiversity of the fandian biota includes total group euarthropods radiodonts bivalved forms acercostracans trilobites non biomineralized trilobitomorphs armoured lobopodians palaeoscolecids pedunculate brachiopods hyoliths chancelloriids sponges and filamentous algae benthic dwellers dominate the fossil community e g trilobitomorphs brachiopods sponges with rare instances of nektonic radiodonts bivalved euarthropods and infaunal palaeoscolecids organisms the fandian biota contains soft bodied taxa that were only known from chengjiang and xiaoshiba until now namely primicaris acercostracan xandarella non trilobite trilobitomorph and mafangscolex palaeoscolecid expanding the distribution of these previously endemic taxa beyond yunnan to the northern yangtze platform during the cambrian stage 3 our findings provide a more comprehensive understanding of early cambrian biodiversity that inhabited the yangtze platform over a substantially greater palaeobiogeographic distribution than previously considered

facies architecture and sequence stratigraphy in glacially influenced basins basic problems and water level glacier input point controls with an example from the quaternary of ontario canada abstract sequence architecture is controlled by two fundamental factors the water level relative to the depositional surface which controls accommodation space and the points or areas of sediment injection which control how this space is filled in relative water level accommodation space and injection points normally vary together and various genetic terms are used to define systems tracts but in glacially influenced basins accommodation space is controlled not only by water level but also by the glacier injection points are similarly dually controlled by water level and by the terminus of the glacier during high lake levels the injection point of the glacier may be underwater at the base of the slope genetic terms like highstand and lowstand therefore are meaningless in successions controlled by sediment input points which are independent of water levels and accommodation space distinct water level and glacier input point systems can occur side by side the water level system controlled by lake level or sea level the glacier input point system controlled by the position of the subaqueous glacier front and both can form juxtaposed systems passing laterally into each other a bewildering and incompatible terminology is needed if the terms of genetic sequence stratigraphy are used for both water level and glacier input point systems because the sedimentary injection points and sequence boundaries of the two systems fluctuate out of phase with one another sequences developed by movement of the glacier are completely independent of those controlled by water levels if genetic sequence stratigraphy is applied to a basin with both lake level and glacier input point systems then each needs separate genetic terminologies to describe them which leads only to confusion however descriptive sequence stratigraphy allostratigraphy can be readily applied to successions like the quaternary of lake ontario we therefore suggest that genetic sequence terms be discarded and simpler allostratigraphic terminology used in glacially influenced basins

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills

stratigraphic architecture and infill history of a deglaciated bedrock valley based on georadar seismic profiling and drilling the sediment fill of a silled bedrock valley in western norway has been investigated with respect to stratigraphy and infill history using a combination of mapping georadar seismic profiling and drilling a small outlet glacier occupies the head of the valley that displays a stepwise down valley profile and terminates in a lake at 29 m above sea level the valley is surrounded by high steep bedrock slopes and is characterized by a series of filled basins each limited by sills of bedrock or moraine accumulations till glacial outwash and or rockslide deposits fill in the lower half of the two larger basins fan delta deposits fringed by the deposits of alluvial fans and colluvial cones dominate the upper fill of most basins fan delta deposits interfinger downstream with lake sediments in the larger basins and fluvial deposits comprise the top fill the overall infill pattern was controlled by deglaciation as well as basin size and shape an overall decreasing sediment supply following deglaciation is shown in the fill of a larger basin down valley whereas a recently increasing sediment supply during glacier growth is reflected primarily in an upstream basin only the lowermost basin was exposed to a sea level drop from 75 m above sea level to the present lake level associated with incision and river migration this observation is in contrast to the basins above marine influence where incision has been limited due to fixed downstream sills resulting in insignificant erosion except for some fan head entrenchment it follows that the fills of these small valley basins display progradational and aggradational trends of deposition and paraglacial reworking has been limited additionally the study demonstrates that georadar profiling combined with other methods is very useful for comprehensive investigation of valley basins

seven glacial cycles in the middle late pleistocene of northwest europe geomorphic evidence from buried tunnel valleys the deep ocean marine isotope record and the antarctic and greenland ice caps record numerous glacial and interglacial cycles since the middle pleistocene and yet evidence for similar numbers of ice sheet advances over the continent and shallow shelves of northwest europe is absent here we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the north sea basin between ca 500 and 40 ka consistent with that predicted by proxy records of glacial and interglacial climate change over 180 subglacial tunnel valleys that incise into pleistocene sediments in the north sea basin were mapped over 60 000 km 2 of three dimensional seismic reflection data using a subset of these data we identified seven separate episodes of subglacial erosion that can be correlated regionally in the uk sector of the central north sea the characteristics of the valley morphologies orientations and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice sheet advance and retreat cycle stratigraphic data suggest that the tunnel valleys formed significantly later than the brunhes matuyama reversal event at 780 ka and before the last glacial maximum marine isotope stage mis 2 21 ka these results imply a more complicated glacial history for northwest europe and more glaciations than the three glaciation model traditionally interpreted from the terrestrial record for the past 500 k y our data provide the most complete documentary evidence for repeated advance and retreat of the northwest european ice sheets since the middle pleistocene and for the first time indicate that terrestrial ice sheet advances in the north sea can be matched in number with the cold events recorded in oceanic and or ice core proxies of climate change over the past 500 k y

comment on m sarnthein h e stremme and a mangini the holstein interglaciation time stratigraphic position and correlation to stable isotope stratigraphy of deep sea sediments

the pleistocene of schoningen germany a complex tunnel valley fill revealed from 3d subsurface modelling and shear wave seismics abstract the pleistocene deposits of schoningen represent an outstanding geological and archaeological archive where an up to 45 m thick middle to late pleistocene succession has been preserved and unique artefacts from the lower palaeolithic have been discovered the preservation of such a thick and complete glacial interglacial succession is very rare in the geological record and requires a specific depositional setting we will present a new depositional model for the pleistocene succession of schoningen integrating outcrop data borehole data and high resolution shear wave seismics a total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture all collected sedimentological and geophysical data sets were integrated into a high resolution 3d geological model gocad for reconstructing the spatial distribution of facies associations and the large scale depositional architecture the spatial distribution of the artefacts will be discussed with respect to the depositional environment the elsterian and holsteinian deposits are restricted to a nnw sse trending elongated trough which is deeply incised into unconsolidated lignite bearing palaeogene deposits the geometry of this erosional structure points to a tunnel valley origin that was incised below the elsterian ice sheet the basal tunnel valley fill consists of cross stratified pebbly sand and gravel overlain by till after deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition during the subsequent holsteinian interglacial mis 9 a lake formed within this depocentre and lacustrine sediments accumulated this interglacial succession consists of peat organic rich silt and fine grained sand interpreted as lake bottom and deltaic sediments fed by surface run off shed from the elm ridge the lacustrine deposition was controlled by repeated lake level fluctuations in the range of 1 6 m leading to the formation of laterally stacked delta systems these lake level changes were probably triggered by climate causing variations of precipitation and surface run off during the late saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits the sedimentary facies and depositional architecture point to a shallow water delta subsequently the meltwater deposits were overlain by till the deposition of the middle pleistocene sediments within an elsterian tunnel valley explains the unique preservation of the sedimentary succession of schoningen the long lived interglacial lake provided an attractive site for animals and early humans ambushing them artefacts mainly became embedded on the delta plain which rapidly was transgressed during lake level rise and artefacts were thus preserved

the northern sector of the last british ice sheet maximum extent and demise abstract strongly divided opinion has led to competing apparently contradictory views on the timing extent flow configuration and decay mechanism of the last british ice sheet we review the existing literature and reconcile some of these differences using remarkable new sea bed imagery this bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last british and fennoscandian ice sheets critically it also allows a viable pattern of ice sheet disintegration to be proposed for the first time covering the continental shelf around the northern united kingdom extensive echosounder data reveals striking geomorphic evidence in the form of tunnel valleys and moraines relating to the former british and fennoscandian ice sheets the pattern of tunnel valleys in the northern north sea basin and the presence of large moraines on the west shetland shelf coupled with stratigraphic evidence from the witch ground basin all suggest that at its maximum extent a grounded ice sheet flowed from se to nw across the northern north sea basin terminating at the continental shelf edge the zone of confluence between the british and much larger fennoscandian ice sheets was probably across the northern orkney islands with fast flowing ice in the fair isle channel focusing sediment delivery to the rona and foula wedges this period of maximum confluent glaciation c 30 25 ka bp was followed by a remarkable period of large scale ice sheet re organisation we present evidence suggesting that as sea level rose a large marine embayment opened in the northern north sea basin as far south as the witch ground basin forcing the two ice sheets to decouple rapidly along a north south axis east of shetland as a result both ice sheets rapidly adjusted to new quasi stable margin positions forming a second distinct set of moraines c 24 18 ka bp the lobate overprinted morphology of these moraines on the mid shelf west of orkney and shetland indicates that the re organisation of the british ice sheet was extremely dynamic probably dominated by a series of internally forced readvances critically much of the ice in the low lying north sea basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels final stage deglaciation was marked by near shore ice streaming and increasing topographic control on ice flow direction punctuated retreat of the british ice sheet continued until c 16 ka bp when following the north atlantic iceberg discharge event heinrich 1 ice was situated at the present day coastline in nw scotland

the holstein interglaciation time stratigraphic position and correlation to stable isotope stratigraphy of deep sea sediments marine molluscan shells from para type and other loclities of the holsteinian interglaciation were dated by thu and the electron spin resonance esr method to more than 350 000 and 370 000 yr b p beyond the limit of thu dating the high age estimate is corroborated by a kar age of 420 000 yr b p determined from volcanic ash near the base of the ariendorf paleosol in the middle rhine valley believed to be a pedostratigraphic equivalent of the holsteinian shells from the herzeele marine unit iii an equivalent of the wacken domnitz warm stage in northern france and subsequent to the holsteinian revealed ages between 300 000 and 350 000 yr b p a correlation of these two warm stages with marine oxygen isotope stages 11 and 9 on the specmap and cartune time scales is suggested from the benthic oxygen isotope record one may infer that no exceptionally high global sea level rise corresponds to the large transgressions of the holstein sea in northern germany therefore a significant proportion of the transgression was probably the result of an unusually large local glacial isostatic depression caused by the extreme buildup of ice during the preceding elster glaciation stage 12 according to the deep sea record it lasted approximately 50 longer than the subsequent cold stage 10 the outstanding soil formation with braunlehm and the well developed thermal optimum of the holsteinian are tentatively related to a phase of minimum sea ice cover in the norwegian greenland sea as deduced from long benthic carbon isotope records from the central atlantic

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

facies architecture within a regional glaciolacustrine basin copper river alaska abstract this paper defines the principal architectural elements present within the pleistocene glaciolacustrine basin fill of the copper river basin in alaska the copper river drains an intermontane basin via a single deeply incised trench through the chugach mountains to the gulf of alaska this trench was blocked by ice during the last glacial cycle and a large ice dammed lake referred to as lake atna filled much of the copper basin facies analysis within the basin floor allows a series of associations to be defined consistent with the basinward transport of sediment deposited along calving ice margins and at the basin edge basinward transport involves a continuum of gravity driven processes including slumping cohesive debris flow hyperconcentrated concentrated density flows and turbidity currents this basinward transport results in the deposition of a series of subaqueous fans of which two main types are recognised 1 large stratified basin floor fans which extend over at least 5 km and are exposed in the basin centre these fans are composed of multiple lobes incised by large mega channels giving fan architectures that are dominated by horizontal strata and large cross cutting channel fills individual lobes and channel fills consist of combinations of diamict derived from iceberg rainout and the ice marginal release of subglacial sediment multiple units of fining upward gravels which grade vertically into parallel laminated and rippled fine sands and silts deposited by a range of density flows and currents derived from the subaqueous discharge of meltwater and rhythmites grading vertically into diamicts deposited from a range of sediment density flows re mobilising sediment deposited by either iceberg rainout or the ice marginal release of sediment 2 small complex proximal fans which extend over less than 2 km and are exposed in the southern part of the basin these fans are composed of coalescing and prograding lobes of diamict and gravel deposited both directly by subaqueous meltwater and from sediment density flows these lobes are cross cut by a range of sand and gravel filled troughs and channels cut by subaqueous outwash and either overlie or are overlain by horizontal sheets of gravel and diamict deposited from a range of sediment density flows the fans are therefore characterised by a complex and laterally variable facies architecture water depth proglacial topography stability of meltwater portals and sediment supply may all be important in determining the type of subaqueous fan present at any one location we suggest that the copper river basin fill is dominated by packages of sediment containing multiple subaqueous fans with individual fans separated by units of diamict each sediment package is in turn separated from the next by a palaeo landsurface shaped by interstadial interglacial fluvial processes and by volcanic debris flows

climate controlled glacial erosion in the unconsolidated sediments of northwestern europe based on a genetic model for tunnel valley formation the development of large erosive subglacial forms in unconsolidated sediments is generally attributed to the eroding power of subglacial meltwater flowing under high pressure conditions most explanations however differ in the source of meltwater and the speed at which it erodes the subglacial bed based on the geometry of deep tunnel valleys and glacial basins in northwestern europe a reconstruction of subglacial hydrological conditions during the development of subglacial depressions is made it is demonstrated that the flow of subglacial meltwater in subglacial channels under high glaciostatic pressures is only capable of eroding large volumes of sediment as long as there is imminent glaciohydrological instability for the thick aquifers in northwestern europe this instability is achieved when large quantities of supraglacial meltwater are available furthermore a theoretical definition is given for maximum depression depth to be reached by subglacial erosion it is shown that this maximum depth is strongly related to average air temperatures during deglaciation and that glacier bed lowering is to be expected during any final phase of glaciations the theoretical framework presented enables a tentative comparison between large scale glacial morphology of different glaciations in northwestern europe

sedimentation in glacial environments and the identification of tills and tillites in ancient sedimentary sequences abstract tills and tillites are defined and subdivided into primary tills comprising lodgement tills melt out tills and sublimation tills and secondary tills comprising flow tills and deformation tills they are defined on the basis of their mode of deposition which endows them with their distinctive properties another category of till that of supra till is defined on the basis of its debris source derived supraglacially from valley sides and nunataks which gives these tills a coarse grained character the processes of till deposition and of outwash sedimentation are associated in several recurrent combinations which allow the definition of three principal glacial sediment associations and land systems which define the character of the sequences within which tills tend to occur the criteria which allow tills of different genesis to be identified and to be distinguished from non till diamictons are reviewed there are several features which are uniquely characteristic of till but unfortunately these are few it has been found generally necessary to employ an array of characteristics which though not individually unique to till when taken together can be strong evidence for particular till types the recognition of several typical and repetitive facies sequences which form in the major glacial sedimentary environments can also be important indicators of till genesis

late pleistocene stratigraphy and implications for deglaciation and subglacial processes of the flathead lobe of the cordilleran ice sheet flathead valley montana usa abstract the flathead lobe of the cordilleran ice sheet advanced and retreated across the flathead valley a 90 km long by 15 25 km wide basin the glacier terminated at the southern end of the flathead valley during its last glacial maximum i used geologic mapping sedimentologic study and mapping from 3300 descriptive water well logs to define the stratigraphy of glacial and post glacial deposits in the flathead valley and to infer subglacial processes and retreat rates units in the 30 200 m thick stratigraphic sequence include deep sand and gravel proglacial alluvium diamicton till locally gravelly silt and clay coarse grained subaqueous deposits at recessional moraines and glaciolacustrine deposits and surficial sand and gravel outwash and holocene stream deposits a nearly continuous till overlies alluvium and is in turn directly overlain by glaciolacustrine deposits glaciolacustrine shoreline indicators at altitudes of 940 958 m show that the flathead lobe receded as a proglacial lake expanded in that range of altitudes this lake the ancestral flathead lake was impounded behind bedrock that was downcut 60 78 m since the late pleistocene glaciolacustrine deposits are as much as 180 m thick in discontinuous troughs that locally cut through till to alluvium and bedrock the troughs are mostly 1 5 km in width 6 25 km in length sinuous in plan view and undulatory in longitudinal profile the troughs extend below the elevation of flathead lake and have been below local base level since glaciation these characteristics point to incision by meltwater hydrostatically pressurized beneath the flathead lobe in subglacial tunnel channels sand and gravel at the trough bases and part of the glaciolacustrine fill in the troughs are subglacial deposits tunnel channels that terminate at recessional moraines suggest excavation occurred sporadically during deglaciation the distribution of glaciolacustrine silts indicates that the flathead lobe retreated and the ancestral flathead lake expanded by 87 km before the lake outlet stream could downcut its dam by 500 m year 1

high resolution seismic and resistivity profiling of a buried quaternary subglacial valley northern alberta canada high resolution seismic and resistivity profiles were acquired to assist in the delineation of a buried quaternary subglacial valley the existence of which was first discovered by drilling one aspect of this valley is the glacial sediments that host substantial methane at shallow depths 50 m or less geophysical well logs indicate that the glacial sediments in this area generally have lower compressional wave speeds v p 10 m than adjacent undisturbed cretaceous age rocks which have v p 2200 m s and r 300 m valley the reflection profile reveals a complex series of events consistent with heterogeneous deposition one major reflection dips eastward across the valley the reflection character changes abruptly on either side of this event with dipping clinoform reflections beneath and nearly horizontal reflections above these may be related to changes in deposition processes beneath a retreating ice sheet as has been suggested by earlier workers the buried valley s basal reflections are complex and possibly reflect glaciotectonic deformation or block plucking the near surface methane gas is within but at the edge of the valley the methane gas saturated zone displays anomalously high resistivities both in the well logs and in resistivity tomography

tunnel valleys current knowledge and future perspectives tunnel valleys are elongated incisions that are commonly interpreted as being the result of erosional processes by subglacial meltwater occurring under continental ice sheets the abundance size and the primarily coarse grained infill of these features have made tunnel valleys important hydrocarbon and groundwater reservoirs although numerous tunnel valleys have been described over the last century their formation and infill remain poorly understood this review summarizes and discusses the current knowledge of tunnel valleys providing an overview of the observations around the world morphological aspects that separate tunnel valleys from other landforms are discussed as well as the wide variety of sedimentary environments found to contribute to the infilling of these features the depth of the incision and the character of ice retreat significantly determine the final infill architecture the formational hypotheses proposed in the literature are assessed to test their wider applicability to all other tunnel valleys in order to find a generic model that helps in the prediction of the morphology and infilling of both pleistocene and pre pleistocene age a quasi steady state model with small meltwater outbursts that erode tunnel valleys near the ice margin seems compatible with most of the known valleys other proposed models require specific geographical or climatic conditions

evidence for rapid sedimentation in a tunnel channel oak ridges moraine southern ontario canada abstract in south central ontario a late wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of lake ontario the tunnel channels are locally infilled and the unconformity buried by sediment of the oak ridges moraine based on seismic reflection profiling and drillcore the tunnel channels are known to continue beneath the moraine detailed sedimentological analysis of 300 m of continuous core from two drillholes located 7 km apart in subparallel tunnel channels identified three facies the gravel facies is 17 m thick and occurs in only one of the cores it directly overlies the unconformity and may include a number of upward fining units seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi horizontal gravel layers bed load sheets deposited from fluidal flows along the deep channel axis the graded massive sand facies up to 37 m thick is the most common facies and consists of silty medium sand with minor coarse sand strata are reverse graded normal graded or massive with isolated silt intraclasts and evidence locally for dewatering this facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump or major channel confluence the third facies consists of medium scale and small scale cross stratified sand medium scale cross stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies small scale cross stratified sand is progressively more common upward in core medium and small scale cross stratified sands was deposited respectively by subaqueous dunes and ripples formed in dilute fluid flows the complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel deposition followed closely and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment which in turn resulted in extremely high rates of sedimentation immediately downflow such depositional conditions support the notion that tunnel channels in the study area formed and or served as conduits for subglacial jokulhlaup discharges and that the laurentide ice sheet most probably did not generally drain by steady state processes but instead by short lived catastrophic events

tunnel valley formation in northwest germany geology mechanisms of formation and subglacial bed conditions for the bornhoved tunnel valley the bornhoved tunnel valley consists of a relatively broad elongated depression filled primarily with tills and a narrow channel in the axial part filled with outwash glaciolacustrine sediments and tills the tunnel valley is at least 13 km long 222 m deep bottom at 191 m b s l and extends parallel to the axis of a peripheral sink between two permian salt diapirs in the substratum it is suggested that the initiation of the tunnel valley was controlled by a differential response of the bed materials to ice overriding on top of and between the salt structures the bornhoved tunnel valley is a polygenetic feature that resulted from different erosional processes throughout all three main glaciations in northern germany during the elsterian glaciation glaciotectonic squeezing occurred to be later replaced by subglacial meltwater erosion during the ice retreat and the holsteinian interglacial the valley was filled with fine grained glaciolacustrine and marine sediments which were subsequently removed and redeposited further down ice as a 200 m thick glaciotectonic melange by the first saalian advance the second saalian advance caused only minor changes and the tunnel valley was reactivated as a subglacial channel during the weichselian glaciation it is suggested that at the time of the first weichselian ice advance a large subglacial water reservoir developed in the area of the baltic sea basin and caused a rapid surge like ice movement as the ice sheet advanced out of the baltic sea basin drainage of the water reservoir was prevented by the ice toe overriding the permafrost on the saalian highlands during the ice retreat frozen ground was left beyond the ice margin and subglacial meltwater catastrophically drained through the tunnel valley with a discharge roughly estimated at about 3 75 103 m3 s it seems possible that drainage of the subglacial water collector through the bornhoved tunnel valley and other similar channels south of the baltic sea led to increased ice sheet basal friction and was one reason for successively smaller extents of the subsequent weichselian advances evidence against pervasively deforming bed materials in the vicinity of the bornhoved tunnel valley in the weichselian glaciation indicates that the valley served as an efficient drainage path for porewater from the subglacial sediments

time transgressive tunnel valley formation indicated by infill sediment structure north sea the role of glaciohydraulic supercooling structure and lithology of the infill sediments from 16 subglacial buried tunnel valleys of pleistocene age in the north sea were analyzed using 3d seismic data and geophysical log data from five hydrocarbon exploration wells the infill sediments are characterized by three seismic facies facies i the volumetrically most important and structurally most distinct is composed of clinoform reflections downlapping axially up valley up ice facies ii is composed of near horizontal continuous and well layered reflections onlapping the clinoform reflections and the valley walls and facies iii is composed of clinoform reflections downlapping axially down valley down ice a model of formation of this sediment architecture is proposed in which valley incision and infill are causally linked it is proposed that facies i is related to glaciohydraulic supercooling of subglacial meltwater in the distal parts of tunnel valleys the valleys formed time transgressively during ice retreat whereby sediment eroded further up ice was re deposited along adverse subglacial slopes of the valleys close to the ice margin the formation of facies ii and iii is related to the deposition in proglacial basins during final deglaciation copyright 2008 john wiley sons ltd

description and esr dating of the holsteinian interglaciation abstract the classical region of the holsteinian interglacial is in the vicinity of hamburg and the lower elbe it is defined on the basis of pollen and is clearly distinguishable from the eemian interglacial hallik 1960 muller 1974 the holsteinian interglacial is represented by a sequence of sediments up to 100 m in thickness these consist of limnic fluvial and marine beds and show a transgression up to the height of present sea level twenty seven molluscs from holsteinian deposits were used for esr dating the ages show that the holsteinian may be correlated with stage 7 of the deep sea record v28 238 shackleton and opdyke 1973

on the formation of the tunnel valleys of the southern laurentide ice sheet abstract catastrophic releases of meltwater produced by basal melting and stored for decades in subglacial reservoirs at high pressure may have been responsible for eroding the broad deep tunnel valleys that are common along the margins of some lobes of the southern laurentide ice sheet we surmise that these releases began when the high water pressure was transmitted to the margin through the substrate the water pressure in the substrate at the margin would then have been significantly above the overburden pressure leading to sapping failure headward erosion of a conduit in the substrate piping could then tap the stored water resulting in the outburst in some situations development of a siphon may have lowered the reservoir below its overflow level thus tapping additional water following the flood the seal could have reformed and the reservoir refilled setting up conditions for another outburst order of magnitude calculations suggest that once emptied a subglacial reservoir could refill in a matter of decades the amount of water released during several outbursts appears to be sufficient to erode a tunnel valley we think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier as reservoirs would then have been larger and more common and the seal more robust and more likely to reform after an outburst

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

late pleistocene debris flow deposits in large glacial lakes in british columbia and alaska the movement of late wisconsin 30 000 b p ice sheet lobes counter to the direction of regional drainage ponded large lakes up to 5000 km2 in both the upper fraser river valley in british columbia and the cooper river valley in alaska along the fraser river near quesnel glaciolacustrine sediment gravity flow complexes contain thick up to 10 m and laterally extensive up to 3 km diamict units containing large rafts of poorly lithified tertiary rocks diamicts offlap and thin away from tertiary bedrock highs and were emplaced by subaqueous debris flows these flows probably evolved from slumps and slides associated with the downslope failure of unstable tertiary bedrock slopes triggered by rising lake levels a process akin to first filling slope failures around the margins of man made lakes in alaska along the copper river valley massive and stratified diamicts were also deposited by debris flows and are interbedded with thin bedded turbidites poorly sorted gravels and normally graded diamicts debris flow deposits show basal grooves internal compressional structures and rafted clasts that protrude from bed tops flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock observations in both british columbia and alaska stress the significance of sediment gravity flow processes acting to deposit glacial sedimentary successions in large ice contact lake basins

time transgressive tunnel valley infill revealed by a three dimensional sedimentary model hamburg north west germany deep elongated incisions often referred to as tunnel valleys are among the most characteristic landforms of formerly glaciated terrains it is commonly thought that tunnel valleys were formed by meltwater flowing underneath large ice sheets the sedimentary infill of these features is often highly intricate and therefore difficult to predict this study intends to improve the comprehension of the sedimentology and to establish a conceptual model of tunnel valley infill which can be used as a predictive tool to this end the densely sampled pleistocene tunnel valleys in hamburg north west germany were investigated using a dataset of 1057 deep wells containing lithological and geophysical data the stratigraphic correlations and the resulting three dimensional lithological model were used to assess the spatial lithological distributions and sedimentary architecture the sedimentary succession filling the hamburg area tunnel valleys can be subdivided into three distinct units which are distinguished by their inferred depositional proximity to the ice margin the overall trend of the succession shows a progressive decrease in transport energy and glacial influence through time the rate of glacial recession appears to have been an important control on the sedimentary architecture of the tunnel valley fill during periods of stagnation thick ice proximal deposits accumulated at the ice margin while during rapid recession only a thin veneer of such coarse grained sediments was deposited ice distal and non glaciogenic deposits i e lacustrine marine and terrestrial fill the remaining part of the incision the infill architecture suggests formation and subsequent infill of the tunnel valleys at the outer margin of the elsterian ice sheet during its punctuated northwards recession the proposed model shows how the history of ice sheet recession determines the position of coarse grained depocentres while the post glacial history controls the deposition of fines through a progressive infill of remnant depressions

dynamics of marine glacier termini read from moraine architecture allostratigraphic mapping of the internal facies architecture of marine moraines reveals the development history of ice contact sedimentary systems the new method for a high resolution analysis of the dynamic stratigraphy of moraines provides important information on the ice front behavior glacier dynamics and regional climatic conditions based on a series of case studies of the moraines of temperate glaciers in norway an allostratigraphic model is suggested as a conceptual guide for the field analysis of ice contact deposits based on outcrop sections as well as seismic or ground penetrating radar profiles

an attempt at correlation between the velay pollen sequence and the middle pleistocene stratigraphy from central europe abstract long continuous lacustrine sequences constitute on the continent a precious tool for coupling the long term continental environmental changes with deep sea and ice core records using the count from the top method moreover they can contribute to long distance correlation on the continent itself and thus help to classify discontinuous sedimentary records palynostratigraphical correlation is proposed here between the velay long sequence and the late middle pleistocene series from central europe with special attention to temperate episodes the similarities between the praclaux and the holsteinian interglacial suggest that they are both contemporaneous with marine isotopic stage mis 11 even if absolute dates are still divergent the evidence of two major warm periods with an interglacial type of vegetation between the holsteinian and the eemian is confirmed by the velay record

aminostratigraphy of european marine interglacial deposits molluscan fossils collected from shallow water marine sediment across nw europe and nearby arctic regions have been analysed for the extent of isoleucine epimerization dl ratio in indigenous protein residues the dl ratios confirm that essentially all classical eemian sites from nw europe are of the same age and are correlative with the type locality near amersfoort in the netherlands shells from interglacial marine sediment beneath the type weichselian till in poland also correlate with the type eemian site dl ratios in holsteinian marine shells 0 29 are substantially higher than in their eemian counterparts 0 17 late cromerian shells yield even higher ratios 0 46 dl ratios in late glacial shells 0 06 and middle weichselian shells 0 09 permit differentiation from modern 0 01 and last interglacial material based on the position of the matuyama brunhes boundary and the differences in dl ratios the eemian must correlate with isotope substage 5e whereas the holsteinian is most likely substage 7c possibly stage 9 but certainly younger than stage 11 intra saalian warm periods may be terrestrial equivalents of the younger substages of stage 7 extensive pre eemian marine sediments along the sw coast of denmark previously correlated with the holsteinian are shown to be of late cromerian age the underlying till there is the first widespread evidence of a pre elsterian till in nw europe dl ratios in molluscs from last interglacial sites along the arctic coast of the ussr the arctic islands and eastern greenland are substantially lower than in their european counterparts due to their low thermal histories the combined mid and high latitude data are used to develop a predictive model for the expected dl ratio in any of several moderate epimerization rate taxa for last interglacial sites with mean temperatures between 20 and 15 c not all sites could be unambiguously assigned to an established interglacial the fjosanger norway and margareteberg sweden sites previously thought to be eemian yield dl ratios higher than in secure nearby eemian material it is yet unresolved whether these are aberrant sites or if they predate the last interglacial in situ shoreline deposits encountered in borings in sw belgium and in exposures on the belgium coastal plain contain molluscs that yield dl ratios intermediate between secure eemian and late weichselian ratios raising the possibility that a late stage 5 high sea level event attained near modern levels in the southern north sea basin resolution of these uncertainties is the focus of future work

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

numerical 230th u dating and a palynological review of the holsteinian hoxnian interglacial abstract earth scientists increasingly consider the holsteinian interglacial and mis 11 as synonyms despite the limited number of numerical dates and ambiguous stratigraphic and palynological correlation with the numerical marine isotope timescale hence we present new tims 230th u dates from two fen peat layers of the holsteinian reference site at bossel in northern germany and re evaluate published numerical data from two sites with hoxnian deposits in england a new method for the calculation of methodically controlled minimum 230th u ages mcma was developed the synopsis of the 230th u dates allows a correlation of both the holsteinian and hoxnian interglacials to mis 9 this correlation is supported by supplementary 230th u dates of fen peat from several pre eemian but non holsteinian sites in germany there is palynological evidence for a reliable correlation between precisely investigated and numerically dated holsteinian deposits in poland germany england sw ireland and france an apparently contradictory palynological correlation from the french central massif is discussed

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

drainage beneath ice sheets groundwater channel coupling and the origin of esker systems from former ice sheets abstract the nature of the drainage system beneath ice sheets is crucial to their dynamic behaviour but remains problematic an experimentally based theory of coupling between groundwater and major channel systems is applied to the esker systems in the area occupied the last ice sheet in europe which we regard as a fossil imprint of major longitudinal drainage channels we conclude that the large scale distribution and spacing of major eskers is consistent with the theory of groundwater control in which esker spacing is partly controlled by the transmissivity of the bed it is concluded that esker patterns reflect the large scale organisation of the subglacial drainage pattern in which channel development is coupled to groundwater flow and to the ice sheet s dynamic regime the theory is then used to deduce basal meltwater recharge rates and their spatial variability from esker spacing in an area in which the ice sheet was actively streaming during its final retreat patterns of palaeo groundwater flow and head distribution and the seasonally varying magnitude of discharge from stream tunnels at the retreating ice sheet margin major channel esker systems appear to have been stable at least over several hundred of years during the retreat of the ice sheet although major dynamic events are demonstrably associated with major shifts in the hydraulic regime modelling suggests that glaciation can stimulate deep groundwater circulation cells that are spatially linked to channel locations with groundwater flow predominantly transverse to ice flow that the circulation pattern has the potential to create large scale anomalies in groundwater chemistry and that the spacing of channels will change through the glacial cycle influencing water pressures in stream tunnels subglacial hydraulic gradients and effective pressure if the latter is reduced sufficiently it could trigger enhanced bed deformation thus coupling drainage to ice sheet movement it suggests the possibility of distinctive phases of sediment deformation and drumlin mobilisation during a glacial cycle

sedimentation in a deep glacier fed lake lake tekapo new zealand surface sediments cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in lake tekapo sedimentation is dominated by the godley river which forms an extensive delta in the northern third of the lake delta growth accounts for 55 of annual sediment deposition in winter sandy muds are deposited at the top of the delta slope where they may move under gravity as a surficial slide oversteepening of the upper slope also generates deep seated failures the entire 20 km2 of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment down the delta slope sedimentation rates decrease surface sediments get finer and varves become better developed in the lake basin sediments are parallel bedded varves which contain typical winter summer annual cycles as well as minor non annual flood varves annual varve thickness and semi annual varve frequency are determined by variations in the discharge of the godley river sedimentation in the basin accounts for 40 of the budget and sedimentation rates decrease with distance from the delta except at the distal end of the basin where turbid underflows are stopped by the rising lake floor beyond the basin sedimentation rates decrease abruptly coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore the remaining 5 of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement which occasionally slumps to the basin floor

sedimentary facies and depositional architecture of ice contact glaciomarine systems abstract the characteristics of ice contact glaciomarine systems are reviewed based on a range of weichselian and holocene examples from the fjordal basins in norway and svalbard these depositional systems occur as large morphological ridges end moraines including push moraines which are coarse grained and show large scale foreset bedding the paper addresses some of the major problems with regard to the recognition classification and stratigraphic analysis of these systems the ice proximal glaciomarine systems are classified here into three categories 1 ice contact submarine fans 2 ice contact deltas and 3 glaciofluvial deltas this classification integrates morphological and sedimentological criteria and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common non glacial deltaic systems the emphasis is on the criteria for the recognition of the ice contact glaciomarine systems i e ice contact fans and ice contact deltas and their discrimination from common gilbert type deltas and fan deltas the review further focuses on ice contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations it is shown that both the periods of ice front stability and changes in the ice front position as well as the magnitude and rate of those changes are all recorded in the ice contact depositional system the sedimentary record further reflects glacio isostatic sea level changes and local palaeogeography a new conceptual model is suggested which places these ice contact glaciomarine systems in a dynamic stratigraphic context the model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework and is meant to be a guide for the analysis of the sedimentary record of ice contact systems

deep circulation of groundwater in overpressured subglacial aquifers and its geological consequences abstract it is generally assumed that meltwater from the base of ice sheets is discharged in a relatively thin subglacial zone whereas this may be true for ice sheets resting on impermeable beds many ice sheets such as the glacial period ice sheets of north america and europe flowed over extensive aquifers a theory is developed which suggests that high rates of meltwater discharge into these aquifers would have completely reorganised their flow fields producing intergrated patterns of glacially pressurised flow controlled by the continental scale form of the ice sheet surface rather than the small scale topographic basins which determine modern aquifer extent the theory is applied to the aquifers which underlay the saalian ice sheet in the netherlands where it is shown that potential gradients and groundwater flow velocities would have developed which were two orders of magnitude greater than modern values and that the dominant flow vectors would have been normal to those of the modern flow thus glacial interglacial cycling in areas which have suffered periodic glaciation during the late cenozoic may have experienced alternating phases of greater and lesser flow energy it represents another example of climatically driven cyclical change in the earth under highly energised glacial conditions potential gradients much larger than modern values may have produced many common features of sediment disruption such as diapirs liquifaction structures and pipes and forms such as glacial doughnuts and pock marks which have hitherto been explained by other processes deep and penetrative flushing of aquifers by glacial meltwater may have left a distinctive geochemical signal in them which may be used to test the theory gases such as methane generated at shallow depth may have been trapped beneath the glacial cap rock and may also have played an important role in these processes

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

large scale channel fill structures in late ordovician glacial deposits in mauritania western sahara abstract late ordovician siliciclastic glacial and related deposits on the north gondwana continental shelf comprise striking incised features referred to as large scale channel fill structures these are described from exposures and aerial photographs in two areas adrar and hodh in mauritania the channel fill structures are up to several kilometres in length and several hundred metres wide they are slightly sinuous narrow sandstone bodies deeply incised into the late ordovician glacial drift and the cambro ordovician bedrock palaeogeographical reconstructions indicate that these structures were located in the ice marginal zone they are preferentially oriented parallel to palaeo ice flow directions sedimentary facies analysis reveals three vertically stacked architectural units infilling a u shaped erosional basal unconformity unit 1 is thin and made up of conglomeratic sandstones of various origins comprising debris flows deltaic like progradational foresets and trough cross stratified sands in adrar architectural unit 2 shows sheet like evenly laminated fine to medium grained well sorted sandstones characteristic of a high energy marine environment in contrast in the hodh area unit 2 displays vertically stacked successions of coarse grained sandstones that indicate high discharge sediment laden flows these are interpreted as meltwater sediments in both adrar and hodh architectural unit 3 is made up of gravelly coarse grained trough cross stratified sandstone emplaced in a braided low sinuosity fluvial environment the three stage infilling history and the palaeogeographic location combined with size and shape criteria make it possible to compare the channel fill structures with pleistocene tunnel valleys found in areas of low relief in cool temperate and low arctic zones such features are incised by high pressure subglacial meltwater and later infilled by proglacial to postglacial deposits based on this comparison architectural unit 1 represents subglacial or proglacial outwash high sediment discharge in unit 2 took place in a proglacial environment in the hodh area while an isostatically downwarped shelf was responsible for a marine incursion in the adrar channels and deposits in unit 3 are fluvial postglacial sediments identification of preserved channel fill structures may be useful in reconstructing late ordovician ice sheet dynamics

deformation styles as a key for interpreting glacial depositional environments lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation we propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation five styles are recognised pure shear p simple shear s compressional c vertical v and undeformed u these dictate the first letter of the codes the remaining letters conveying the evidence this information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed individual structures are not diagnostic of particular environments but the suite of structures their relative scale stratigraphical relationships and orientation relative to palaeoslopes and to palaeoice flow directions can be used to infer the environment in which they formed this scheme is applied at five sites in west wales the typical succession is interpreted as subglacial sediments overlain by meltout tills flow tills and sediment flows paraglacial redistribution of glacial sediments is widespread large scale compressional deformation is restricted to sites where glaciers readvanced large scale vertical deformation occurs where water was locally ponded near the ice margin there is no evidence for glaciomarine conditions copyright 2003 john wiley sons ltd

structure and sediment budget of yinggehai song hong basin south china sea implications for cenozoic tectonics and river basin reorganization in southeast asia the temporal link between offshore stratigraphy and onshore topography is of key importance for understanding the long term surface evolution of continental margins here we present a grid of regional high quality reflection seismic and well data to characterize the basin structure we identify fast subsidence of the basin basement and a lack of brittle faulting of the offshore red river fault in the yinggehai song hong basin since 5 5 ma despite dextral strike slip movement on the onshore red river fault we calculate the upper crustal whole crustal and whole lithospheric stretching factors for the yinggehai song hong basin which show that the overall extension observed in the upper crust is substantially less than that observed for the whole crust or whole lithosphere we suggest that fast basement subsidence after 5 5 ma may arise from crustal to lithospheric stretching by the regional dynamic lower crustal mantle flow originated by collision between india eurasia and indian oceanic subduction below the eurasian margin in addition we present a basin wide sediment budget in the yinggehai song hong basin to reconstruct the sedimentary flux from the red river drainage constrained by high resolution age and seismic stratigraphic data the sediment accumulation rates show a sharp increase at 5 5 ma which suggests enhanced onshore erosion rates despite a slowing of tectonic processes this high sediment supply filled the accommodation space produced by the fast subsidence since 5 5 ma our data further highlight two prominent sharp decreases of the sediment accumulation at 23 3 ma and 12 5 ma which could reflect a loss of drainage area following headwater capture from the paleo red river however the low accumulation rate at 12 5 ma also correlates with drier and therefore less erosive climatic conditions

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

3d seismic analysis of buried tunnel valleys in the central north sea tunnel valley fill sedimentary architecture fourteen overlapping 3d seismic reflection data sets originally acquired by the oil and gas industry were used to image and investigate complex networks of buried tunnel valleys in the uk sector of the central north sea more than 180 individual tunnel valleys were observed and mapped to horizontal resolutions of 12 50 m and vertical resolutions of 8 10 m the results presented here identify three recurring seismic facies that locally define stratigraphic organization from base to top of the buried tunnel valley fills i high amplitude disrupted units ii a unit containing gently dipping disrupted reflections or transparent facies and iii well layered continuous reflections a comparison to similar works in the region is used to infer tunnel valley infill during changing depositional conditions from high energy subglacial meltwater to quiet glaciolacustrine or glaciomarine environments

glaciomarine facies within subglacial tunnel valleys the sedimentary record of glacioisostatic downwarping in the irish sea basin coastal exposures of late pleistocene sediments deposited after 19 000 yr bp near dublin ireland provide a window into the infill of a subglacially cut tunnel valley exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi storey u shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head gravels are truncated by poorly sorted ice proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin the sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive poorly sorted gravel facies interpreted as subaqueous debris flow deposits gravel beds show local inverse and normal coarse tail graded facies recording the restricted development of turbulent flow sediment gravity flow deposits fill broad 2 km shallow 10 m and overlapping channels penetrative deformation structures e g dykes are common at the base of channels the same subglacially eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km2 of the western irish sea tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio isostatic downwarping below the last british ice sheet the facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves

microstructures in subglacial and proglacial sediments understanding faults folds and fabrics and the influence of water on the style of deformation abstract macroscopic field and micromorphological studies have been carried out on subglacially and proglacially deformed glacigenic sequences at a number of sites throughout scotland uk examination of microstructures folds faults hydrofractures plasmic fabrics aided understanding of the deformation histories preserved in the sediments but a similar range of structures were developed in both subglacial and proglacial settings discrimination between subglacial and proglacial deformation was only possible when micromorphological data was used in conjunction with larger scale field observations variations in lithology and water content were controlling factors influencing the style and apparent intensity of deformation recorded changes in pore water content and pressure during deformation can lead to liquefaction and hydrofracturing with early formed structures locally controlling the pattern of water escape liquefaction can also lead to homogenisation of the sediments and the destruction of earlier deformation structures even at relatively low strains beds or zones of liquefied sand and silt may form highly lubricated detachments within the sediment pile resulting in a marked reduction in the amount of shear transmitted to underlying units a multidisciplinary approach involving sedimentological geomorphological stratigraphical and structural field observations combined with micromorphological analysis is recommended to confidently unravel the glacitectonic history and depositional environment of most deformed glacigenic sedimentary sequences

the pre weichselian glaciations of north west europe abstract in north west europe no evidence has been found for glaciations older than the elsterian the elsterian seems to consist of at least two separate ice advances with a minor interval in between during the elsterian in the area south of the baltic sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity the channels were active until the late elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay during the saalian no comparative channels were being formed three different ice advances can be distinguished within the saalian the stratigraphical correlation of which is to be discussed no convincing evidence was found for any interglacial within the saalian sequence there are good reasons to assume that the ice advances were only separated from each other by minor ice free intervals