discriminating between subglacial and proglacial lake sediments an example from the danischer wohld peninsula northern germany subglacial lakes are common features of contemporary ice masses however they are rarely identified in the geological record this is due to the difficulty in discriminating between subglacial and proglacial lake sediments a proglacial origin is typically preferred as the simplest explanation we hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the danischer wohld peninsula northern germany which have been interpreted to record both proglacial and subglacial sedimentation we identify two major phases of ice activity and associated lake formation during the late weichselian glaciation 1 proglacial lake formation at 23 ka in front of the advancing baltic ice stream this lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent 2 retreat of ice back into the baltic basin at 19 ka and formation of a proglacial lake that persisted for 4 ka we suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka this is based on the presence of aggrading sediment deposits characterised by stratified laminated diamictons and interbedded tabular to channelized sorted sediments the juxtaposition of relatively undeformed waterlain sediment and subglacial till absence of glaciotectonic thrusting and folding or of fining coarsening successions and the geomorphic association with tunnel valleys to the south of the study area the style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments the luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems

coarse grained sediment gravity flow facies in a large supraglacial lake near williams lake in the central interior of british columbia the fraser river exposes long sections of late pleistocene glaciolacustrine sediments selectively preserved within a bedrock trough the dominant facies types are thick normally graded gravels and sands that occupy steeply dipping multistorey channels up to 300 m wide and several tens of metres deep channels appear to have been simultaneously cut and filled by high density turbidity currents in a glacial lake floored by stagnant ice fining upward sediment gravity flow sequences up to 50 m thick may be the product of quasi continuous surging turbidity flows triggered by catastrophic meltwater discharges into the trough or retrogressive failure of ice cored sediments large scale post depositional deformation structures such as synclinal folds normal faults sedimentary dyke swarms and dewatering structures record gravitational foundering of sediment and pore water expulsion caused by the melt of underlying glacier ice melting of buried ice masses along the floor of the trough appears to have controlled the flow paths of turbidity currents by producing sub basins within the overlying sediment pile an idealized model of supraglacial lacustrine sedimentation is developed that may be applicable to other glaciated areas with similar bedrock topography

the signature of strain magnitude in tills associated with the vistula ice stream of the scandinavian ice sheet central poland abstract at oborki in central poland we examined a 3 m thick late weichselian basal till deposited by the vistula ice stream a multi proxy approach involving a study of grain size grain roundness crushing index petrographic composition till fabric and till micromorphology in a closely sampled vertical profile was applied to decipher till formation and ice movement mechanisms the till consists of a succession of four texturally and structurally different units generated by a combination of processes related to effective stresses exerted on the bed by active ice deformation intergranular advection clast ploughing and localized basal decoupling played important roles during till formation micromorphological analysis reveals that the most common s matrix microstructures are grain lineations grain stacks turbate structures till pellets and crushed grains microshears dominate whereas plasmic fabric is not well developed we use grain roundness crushing indices and microshear geometry to determine subglacial strain magnitude in the till matrix microfabric and macrofabric s 1 eigenvalues together with i l indexes indicate low shear strains in the order of 10 10 2 strain estimates vary depending on the particle sizes used suggesting a plastic mode of till deformation all proxies studied suggest complex and temporally variable subglacial conditions under the marginal part of the vistula ice stream probably caused by changes in till rheology related to fluctuating porewater pressures fast ice flow was facilitated by a combination of bed deformation and enhanced basal sliding on a thin water layer our results may also be representative for other terrestrially based pleistocene ice streams moving over soft beds

depositional model in subglacial cavities killiney bay ireland interactions between sedimentation deformation and glacial dynamics subglacial meltwater drainage and sedimentary processes play a major role in ice sheet dynamic but there is a lack of study of subglacial environment because modern ice sheet beds remain inaccessible previous authors already intended to provide diagnostic criterion and recent investigations suggest that fluid pressure variations are a key factor in subglacial environment this paper investigated the late devensian sedimentary record in order to describe subglacial sedimentological facies associations and deformation features related to fluid overpressures we used an integrated approach based on stratigraphy sedimentology and deformations styles to demonstrate a subglacial depositional model the studied interval is composed of stratified gravel and sand interbedded with diamicton and boulder pavement deposited in depressions formed by irregularity of the upper surface of diamicton deformation structures include convolutes dykes and normal micro faulting dykes show different dip directions from vertical oblique to subhorizontal from which both directions of shortening and extension can be determined vertical dykes are formed under pure shear strain related to ice weight only oblique dykes imply both ice bed coupling and simple shear strain between ice and substrate induced by flowing ice related to progressively increasing meltwater drainage intensity horizontal dykes are formed when minimum strain is vertical and therefore the overpressure exceeds the weight of overburden they are associated with high meltwater drainage intensity and ice bed uncoupling and refer to hydrofracturing overall depositional and deformation sequence also illustrates the increasing intensity of meltwater drainage in small cavity as high energy channelised deposits and in large cavities where subaqueous fan are deposited under hydraulic jump conditions moreover large cavities represent lee side cavities formed by fast flowing ice over an obstacle hydrofracturing is likely to occur when a dense fluid potentially associated with catastrophic drainage of an upstream cavity enters the low pressure confined environment of a downstream cavity and is injected under pressure in the soft substrate the studied glacial sequence represents a regional pattern probably related to an allocyclic control on sedimentation linked to long term glacial dynamics rather than local depositional conditions based on these results we provided a synthetic model linking depositional and deformation processes during ice sheet growth and decay but also valid at different timescales from annual to seasonal scale

micromorphology and petrography of late weichselian glaciolacustrine varves in southeastern sweden abstract the purpose of this investigation is to describe and interpret the sedimentology and petrography of late weichselian varves in southeastern sweden in order to determine their nature and origin it is focused on the microscopic evidence for glaciolacustrine varve sedimentation in the baltic ice lake and the possibilities of making a detailed facies classification of the sediments in an area with an established varve chronology the material examined was cores taken from five representative localities in an area below the highest shoreline of the baltic ice lake in the provinces of skane and blekinge i e below an altitude of 55 65 m the investigations included chemical analyses xrd microscopy polarized and sem edx investigations of the summer and winter layers of the varves the results of the chemical clay mineralogy xrd and microscopic examinations of the bedrock and mineral fragments indicate that the material in the different facies of the varved clay is mainly produced by moderate alteration and erosion from the local bedrock of predominantly granitoid rocks and of residual kaoline deposits it is possible to distinguish microscopic evidence of four varve types differing in texture depending on the water depth and how close to the ice the different facies were deposited i e if they were deposited proximally distally or extramarginally in relation to the ice margin it is also possible to relate these differences to changes in the palaeoclimate during the deglaciation of the area in the bolling and older dryas chronozones

progressive proglacial to subglacial deformation and syntectonic sedimentation at the margins of the mid pleistocene british ice sheet evidence from north norfolk uk abstract detailed analysis and interpretation of the stratigraphy and structures developed within polydeformed sediments exposed in the coastal section between west runton and sheringham eastern england has allowed the characterisation of the glacitectonic signature associated with the advance of a major mid pleistocene anglian ice sheet the sequence of pre glacial deposits and glacial sediments laid down during earlier southerly directed ice advances d1 d2 is deformed and disrupted by an ice advance from the west southwest that marks a major change in ice flow dynamics in northern east anglia the simplest interpretation of this deformation event d3 is in terms of a progressive proglacial to subglacial deformation model proglacial deformation occurred in advance of the ice margin and was dominated by thrusting positive topographic features which developed above the propagating thrusts controlled sediment dispersal patterns within outwash sandur leading to the formation of small sub basins between these morainic ridges the accretion of the wedge shaped proglacial thrust moraines to the main push moraine formed at the margin of the advancing glacier may have temporarily stalled forward motion of the ice thrusting and large scale folding associated with ice marginal deformation led to the stacking of material excavated from further up ice onto the stoss side of these accreted thrust related moraines that allowed the glacier to override the obstruction subglacial deformation was highly variable in its style and intensity ranging from heterogeneous folding and thrusting through to more pervasive ductile shearing associated with the formation of a subglacial shear zone the thickness and complexity of this shear zone increases up ice where it is characterised by a thick glacitectonic melange the pore water content of the deforming sediments controlled the pattern of deformation within the shear zone however an increase in the efficiency of the drainage system towards the front of the glacier would have led to a rapid thinning of this water enhanced zone of ductile shear evidence from north norfolk suggests that zones of preferential pore water flow within the glacier bed are a major controlling factor on the location of the subglacial shear zone consequently the bulk of the forward motion of the glacier may not be accommodated by shearing within the sediments immediately below its base but occur at a deeper level within the deforming bed

proglacial lakes character behaviour and geological importance proglacial lakes are ubiquitous within the quaternary record and can provide exceptional breadth and depth of palaeoenvironmental information present deglaciation is increasing the number and size of proglacial lakes around the world this study provides a synthesis of knowledge on proglacial lake character and behaviour and critically evaluates the importance of proglacial lakes from a geological perspective we show how ice marginal or ice contact lakes and other distal proglacial lakes can be distinguished from each other by geomorphological sedimentological chemical and biological characteristics the key controls on proglacial lake geomorphology and sedimentology are outlined and discussed proglacial lakes can exacerbate mountain glacier and ice sheet margin ablation via mechanical and thermal stresses but very large lakes can moderate summer air temperatures and relatively retard summer ice ablation proglacial lakes interrupt meltwater flux and are very efficient sediment traps hydrological routing and consequent geomorphological activity can be radically modified by sudden drainage of proglacial lakes and resultant glacial lake outburst floods exceptionally large proglacial lake drainages affected global ocean circulation and global climate during the quaternary overall analyses of proglacial lakes can provide a valuable insight into i patterns character and behaviour of mountain glaciers ice sheets and glaciations and ii the impacts of past present and future deglaciation

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

small to medium sized glacitectonic structures in till and in its substratum and their comparison with mass movement structures abstract ductile and brittle deformation structures have been observed in till of various origins particularly in subglacial till and flowtill and in the substratum beneath subglacial till although some of the glacitectonic structures have been claimed to be palimpsest structures from debris rich glacier ice such a preservation is not proven to be very common however deformation structures are found in megablocks and other clasts that occur in melt out till and in deformation till most glacitectonic deformation structures are formed in the substratum or in the already deposited subglacial till by an actively moving glacier for instance recumbent folds shears boudins thrusts hook folds diapirs tension fractures till wedges fissility glacitectonic breccia conjugate sets of fractures structures similar to those reported from subglacial primary till and its substratum occur also in flowtill and other mass movement deposits but deformations are less common in the substratum beneath them the orientation of the deformations in flowtill is unrelated to the direction of glacial movement the shapes of some shears and folds are different in flowtill when compared with those in subglacial till and its substratum still the flow and shear structures alone are not sufficient to distinguish certain varieties of till fir instance subglacial primary till from flowtill but they are useful as local directional indicators of stress and as genetic criteria in combination with other features particularly with directional glacial erosion marks and fabric

a critical assessment of subglacial mega floods a case study of glacial sediments and landforms in south central alberta canada the existing subglacial megaflood explanation of glacial sediment deposition and landform production in south central alberta relies upon four sets of observations and associated interpretations 1 a subglacial genesis for all glacilacustrine sediments lying stratigraphically below a local melt out till or ice stagnation facies 2 a melt out genesis for the ice stagnation facies 3 a syn depositional status for the glacitectonic disturbance visible in most exposures due to periodic ice bed re coupling and 4 a subglacial megaflood origin for a truncation surface and clast lag that occurs at the top of the sedimentary exposures and the carving of hummocky terrain and flutes in the area we provide alternative interpretations of the sediment landform assemblages of the area and demonstrate that alternative simpler interpretations of the evidence can be proposed specifically we propose 1 a proglacial rather than subglacial origin of glacilacustrine sediments 2 a glacilacustrine origin for the melt out till and its subsequent glacitectonic disturbance by minor glacier readvances 3 postdepositional rather than syn depositional glacitectonic disturbance due to a significant advance by glacier ice after the accumulation of a thick sequence of glacilacustrine sediments 4 that some linear chains of hummocks are the morphological expression of glacitectonic folding and thrusting 5 that the use of the truncation surfaces to propose a subglacial fluvial origin for hummocky moraine is flawed logic because they do not constitute the tops of hummocks but rather occur on the interfluves that separate the numerous small coulees incised into the valley sides during postglacial time truncation surfaces and clast lags occur locally on the beds of spillway tracts and can be explained as the products of erosion by subaerial spillway water the mega flood explanation of flutings and hummocky moraine in the region is also questioned because these landforms record a regional ice flow imprint of mis aligned and cross cutting flow sets terminating at series of inset and locally cross cutting and lobate transverse ridges moraines these landform associations preclude a subglacial flood origin for the flutings and demonstrate that the transverse ridges are more appropriately interpreted as recessional push moraines the similarity of the glacial landforms of this region to the active temperate glacial landsystem produced by historical glacier recession in modern glacierized catchments where sheetfloods have not been influential in subglacial landform production allows us to apply a modern analogue to landscape interpretation that does not include subglacial sheetflooding

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

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

inversion of three dimensional wide angle seismic data from the southwestern canadian cordillera seismic refraction wide angle reflection data were recorded on a triangular array in southwestern british columbia centered on the boundary between the coast belt to the southwest and the intermontane belt to the northeast the experiment part of the lithoprobe southern cordillera transect enabled determination of the three dimensional 3 d velocity structure of the crust and upper mantle an algorithm for the inversion of wide angle seismic data to determine 3 d velocity structure and depth to reflecting interfaces is developed the algorithm is based on existing procedures for the inversion and forward modeling of first arrival travel times and forward modeling of reflection travel times including 1 forward modeling using a 3 d finite difference algorithm and 2 a simple velocity model parameterization for the inversion which eliminates the need to solve a large system of equations the existing procedure is extended to allow 1 the inversion of reflection times to solve for depth to a reflecting interface and or velocity structure 2 the inversion of first arrival travel times to solve for depth to a refracting interface and 3 layer stripping application of the algorithm to southern cordillera data uses pg to constrain upper crustal velocity structure pmp to constrain lower crustal velocity structure and depth to moho and pn to constrain upper mantle velocities and depth to moho the 3 d velocity model for the southwestern canadian cordillera is characterized by 1 significant lateral velocity variations at all depths that do not in general correlate with surface geological features or gravity data 2 a relatively high velocity middle and lower crust in the southwestern part of the study area which correlates with a strong relative gravity high and outlines the eastern extent of lower wrangellia an accreted terrane forming the insular belt to the west 3 a narrow zone of slower velocity in the lower crust and change in crustal thickness associated with the fraser fault system lending additional support to the view that it is a crustal penetrating fault 4 an average upper mantle velocity of 7 85 km s and 5 a depth to moho of 33 36 km in the intermontane belt and 36 38 km throughout most of the coast belt decreasing in the west to 33 km near the insular coast contact horizontal velocity structure slices and an interpreted cross section based on these and other results show the complexity of crustal structure in the region

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

the depositional history of an esker near ottawa canada the 10 km long stittsville ridge trending parallel to the last direction of ice advance into the ottawa area is here classified as an esker the sediments of the ridge are interpreted as subaqueous outwash deposited from a subglacial or englacial meltwater conduit emptying into an inlet in the late wisconsin glacier front the ridge formed by the coalescence of subaqueous outwash fans as the ice retreated northward sedimentological variation along the ridge is attributed to a change in the morphology of the inlet as the ice front retreated from an initially narrow symmetrical shape to a broader and increasingly asymmetrical form

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

anatomy of a subaqueous ice contact fan and delta complex middle pleistocene north west germany this paper presents a detailed analysis of the high resolution facies architecture of the middle pleistocene porta subaqueous ice contact fan and delta complex deposited on the northern margin of glacial lake weser northwest germany a total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture the field study was supplemented with a ground penetrating radar survey and a shear wave seismic survey all collected sedimentological and geophysical data were integrated into a high resolution three dimensional geological model for reconstructing the spatial distribution of facies associations the porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake bottom surface at the margin of a retreating ice lobe the northernmost fan complex is up to 55 m thick 6ae2 km wide and 6ae5 km long the incipient fan deposition is characterized by high energy flows of a plane wall jet very coarse grained highly scoured jet efflux deposits with an elongate plan shape indicate a high froude number probably 5 these jet efflux sediments are deposited in front of a large 3ae2 km long up to 1ae2 km wide and up to 25 m deep flute like scour indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence approximately five times the conduit diameter evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes deposited in front of 1ae 3t o 2ae5 km long flute like scours that are 0ae8 to 1 km wide and 7 to 20 m deep in response to continued aggradation small jets developed at the periphery of these bar like deposits and filled in the low areas adjacent to the original superelevated regions locally raising the depositional surface and characterized by large scale trough cross stratified sand and pebbly sand the incision of an up to 1ae2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event probably related to a lake outburst and lake level fall in the range of 40 to 60 m at the mouth of this channel highly scoured jet efflux deposits formed under hydraulic jump conditions during flow expansion subsequently gilbert type deltas formed on the truncated fan margin recording a second lake level drop in the range of 30 to 40 m these catastrophic lake level falls were probably caused by rapid ice lobe retreat controlled by the convex up bottom topography of the ice valley

woolly mammoth mammuthus primigenius blum and its environment in northern europe during the last glaciation abstract woolly mammoths were large herbivorous cold adapted mammals of the late pleistocene the diet and habitat requirements of the species set certain constraints on the palaeoenvironments it could occupy the relationship between the mammoth s shifting range and changing environments can be explored using independent data on ice sheet configuration temperature and vegetation provided the locality and age of the fossil remains can be validated here we present a comprehensive record of occurrence of the woolly mammoth in the circum baltic region of northern europe during the last glaciation based on a compilation of radiocarbon dated remains the record shows that the mammoth was widespread in northern and north eastern europe during marine isotope stage 3 mis 3 at 50 000 30 000 calibrated years ago 50 30 ka the presence of the species up to 65 n latitude supports the restriction of the scandinavian ice sheet sis during mis 3 the widest distribution range round 30 ka was followed by a decline that led to the disappearance of mammoths from the area during the maximum extent of the sis from 22 to 18 ka the woolly mammoth re colonized the baltic region and southern scandinavia after the onset of the late glacial deglaciation at 17 ka the late glacial record suggests a markedly fluctuating population changing its range in tune with the rapid environmental changes the last appearance of mammoth in our study region was in estonia during the younger dryas greenland stadial 1 gs1 at about 12 ka the two major periods of occurrence during mis 3 and the late glacial stadial suggest that mammoth had a wide tolerance of open to semi open tundra and steppe tundra habitats with intermediately cold climate whereas the 22 18 ka disappearance suggests a major southward and or eastward retreat in response to extremely cold glacial conditions near the sis margin the final regional extinction correlates with the re forestation during the rapid warming at the younger dryas holocene boundary

first radiocarbon dates on woolly mammoth mammuthus primigenius from northern germany a major gap in the radiocarbon chronology of woolly mammoth in europe results from an absence of dated records from the late weichselian moraine regions of the northern european lowlands in the past many fossil mammoth remains were discovered in the province of mecklen burg western pomerania in northeastern germany seven finds which were well preserved were radiocarbon dated by accelerator mass spectrometry the dates ranging from 44 8 to 23 9 14 ck a bp 50 28 cal ka bp can be correlated with marine isotope stage mis 3 of the late quaternary and indicate that mammoth was able to colonise this region during a period of rapid environmental changes the new radiocarbon evidence fits well into the known colonisation pattern of woolly mammoth and shows a continuous distribution in the late weichselian moraine areas of northern germany before the expansion of the scandinavian ice sheet copyright 2009 john wiley sons ltd

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

stability analysis of unsaturated soil slopes considering water air flow caused by rainfall infiltration abstract even though soil is a mixture of solids with voids that are filled by air and water most previous studies on rainfall infiltration and its influence on slope stability were based on a single phase water flow model by assuming that the pore air pressure was atmospheric the purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope water air two phase flow analyses were conducted to investigate the contribution of pore air pressure on infiltration by rainfall in order to study the infiltration behavior with respect to soil type flow analyses were performed with two types of soil under similar settings results obtained from the two phase infiltration analysis were then used as input to the stability analysis by the strength reduction method infiltration and stability analyses based on a single phase water flow model were also carried out which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope the results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone hence remarkable delaying effects on water flow were induced such water air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope