quaternary stratigraphy of the buried valleys of the lower red deer river alberta canada the quaternary fills of the buried valleys of southern alberta and saskatchewan have provided a wealth of information for the reconstruction of the glacial interglacial record of the western plains of canada and this paper reports on the previously unstudied stratigraphy of the buried calgary valley and its former tributaries in the lower red deer river area we attempt to differentiate empress group sediments which potentially relate to pre glacial interglacial interstadial and post glacial lake and river deposition using sedimentology stratigraphy and palaeoecology twenty nine stratigraphical logs indicate that empress group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the calgary valley located 15 km to the north of dinosaur provincial park radiocarbon dates of 52 4 ka 27 4 ka and 42 4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid wisconsinan in age however outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials interstadials and that older even pre glacial sediments could have survived subglacial channels recognisable on air photographs largely coincide with buried valley positions due to the preferential excavation of the quaternary sediment by meltwater and are filled with post glacial lake sediment from which a radiocarbon date of 16 ka bp was obtained pre glacial and glacial post glacial empress group sediments are lithologically indistinct but cover a large time span in southern alberta

quaternary events in the elkwater lake area of southeastern alberta new data necessitate revisions in the quaternary chronology of the elkwater lake area relicts of post middle miocene preglacial erosion surfaces descend to the north and south from the middle miocene depositional surface on the cypress hills plateau both sets of surfaces are marked by oxidized weathering zones locally culminating in relicts of preglacial paleosols both surfaces are overlain by a loess replete with cryogenic imprints deposition of this loess with cryogenic imprints shortly predates arrival of the green lake glacier at its terminus the green lake end moraine marks the maximum extent of laurentide ice in this area features previously attributed to the older elkwater glacier can be explained with reference to proglacial meltwater action associated with the green lake glacier the concept of elkwater drift is no longer valid younger loesses called upper loess mantle nonglaciated terrain and the green lake end moraine and began accumulating just before glacier peak tephra was deposited

constraints on the preservation of diamict facies melt out tills at the margins of stagnant glaciers abstract this paper reviews the formation and preservation of diamict facies melt out till generated in situ by the downwasting of stagnant ice at the margins of continental glaciers melt out tills are commonly envisaged as being the product of the top supraglacial or bottom subglacial melt of stagnant debris rich glacier ice but such deposits are relatively uncommon in modern glacier environments where they are thin laterally discontinuous and have a low preservation potential theoretical considerations of the distribution of englacial debris in continental ice sheets show that only the glacier margin is likely to contain the necessary volumes of englacial debris for melt out to be a significant diamict forming process however the application of thaw consolidation theory to the formation of such deposits shows that substantial porewater pressures and self sediment deformations can be induced during melt out especially in matrix rich debris the classic melt out mechanism widely invoked in the literature since 1875 and involving passive in situ aggregation from thawing englacial debris can be seen to operate under restricted conditions diamict facies produced by melt out are likely to form spatially disjunct and laterally discontinuous elements within complex and ice marginal stratigraphics the melt out process is not a mechanism whereby regionally extensive diamiet ite units can be deposited across glaciated basins

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

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

late wisconsin ice flow history in the buffalo head hills kimberlite field north central alberta ice flow of the last glaciation in the buffalo head hills kimberlite field of northern alberta is reconstructed from landform interpretations and clast orientations for the purpose of aiding kimberlite exploration in the region the paucity of bedrock outcrop and the absence of preserved striae and other erosional ice flow indicators on the soft cretaceous marine sediments inhibit detailed interpretations on glacial flow chronology poorly developed bedrock drumlins on the buffalo head hills and erosional ice flow indicators preserved on the kimberlite outcrops indicate southwestward ice flow during the maximum extent of ice during the last glaciation during the deglaciation of northern alberta later phases of ice flow were controlled by lobes of surging ice which surged into proglacial lakes west of the buffalo head hills the maximum phase of southwest flow was followed by southeastward ice movement of the peace river ice lobe similarly east of the buffalo head hills the maximum phase of ice flow was superceded by a south southwest ice advance of the wasbasca ice lobe

geologic and topographic controls on fast flow in the laurentide and cordilleran ice sheets ice streams are fast flowing arteries which play a vital role in the dynamics and mass balance of present day ice sheets although not fully understood fast flow dynamics are intimately coupled with geologic topographic thermal and hydrologic conditions of the underlying bed these are difficult observables beneath contemporary ice sheets hindering elucidation of the processes which govern ice streaxn behavior for past ice sheets the problem is antithetic geologic evidence of former ice streams exists but spatim and temporal histories are uncertain however detailed knowledge of bed geology and topography is available in many places we take advantage of this information to compile terrain characteristics relevant to fast flow dynamics in the laurentide and cordilleran ice sheets using seed points where fast flowing wisconsinan ice has been geologically inferred discriminant analysis of a suite of north american geologic and topographic properties yields a concise measure of ice bed coupling strength our analysis suggests that the interior plains and continental shelf regions of north america have low basal coupling relative to areas of variable relief or exposed bedrock in the cordillera and on the canadian shield we conclude that the interior plains and continental shelves are both topographically and geologically predisposed to large scale basal flows i e ice streaxns or surge lobes this result holds independent of whether the mechanism of fast flow is sediment deformation or decoupled sliding over the bed

evolution of late glacial ice marginal lakes on the northwestern canadian shield and their influence on the location of the dubawnt lake palaeo ice stream abstract during deglaciation of the north american laurentide ice sheet large proglacial lakes developed in positions where proglacial drainage was impeded by the ice margin for some of these lakes it is known that subsequent drainage had an abrupt and widespread impact on north atlantic ocean circulation and climate but less is known about the impact that the lakes exerted on ice sheet dynamics this paper reports palaeogeographic reconstructions of the evolution of proglacial lakes during deglaciation across the northwestern canadian shield covering an area in excess of 1 000 000 km2 as the ice sheet retreated some 600 km the interactions between proglacial lakes and ice sheet flow are explored with a particular emphasis on whether the disposition of lakes may have influenced the location of the dubawnt lake ice stream this ice stream falls outside the existing paradigm for ice streams in the laurentide ice sheet because it did not operate over fined grained till or lie in a topographic trough ice margin positions and a digital elevation model are utilised to predict the geometry and depth of proglacial lakes impounded at the margin at 30 km increments during deglaciation palaeogeographic reconstructions match well with previous independent estimates of lake coverage inferred from field evidence and results suggest that the development of a deep lake in the thelon drainage basin may have been influential in initiating the ice stream by inducing calving drawing down ice and triggering fast ice flow this is the only location alongside this sector of the ice sheet where large 3000 km2 deep lakes 120 m are impounded for a significant length of time and exactly matches the location of the ice stream it is speculated that the commencement of calving at the ice sheet margin may have taken the system beyond a threshold and was sufficient to trigger rapid motion but that once initiated calving processes and losses were insignificant to the functioning of the ice stream it is thus concluded that proglacial lakes are likely to have been an important control on ice sheet dynamics during deglaciation of the laurentide ice sheet

subglacial drainage eskers and deforming beds beneath the laurentide and eurasian ice sheets glaciological theory predicts that the subglacial drainage network at the base of gently sloping ice sheets resting on deforming sediment should consist of many wide shallow probably braided canals distributed along the ice sediment interface rather than an arborescent network of relatively few large tunnels as would develop over a rigid substrate a corollary prediction examined here is that eskers which form in large subglacial tunnels should be rare where subglacial bed deformation occurred but they may be relatively common where the bed was rigid bed deformation would be most likely where subglacial till was relatively continuous fine grained and of low permeability that is in regions where till is derived primarily from underlying sedimentary bedrock but unlikely where discontinuous coarse grained high permeability till was derived from underlying crystalline bedrock the observed distribution of eskers in areas covered by the laurentide and eurasian british scandinavian and barents sea ice sheets during the last glaciation shows that most eskers occur over crystalline bedrock overlain by discontinuous high permeability till but are rare or absent over sedimentary bedrock overlain by fine grained low permeability till thus matching reasonably well our prediction glaciological theory and geologic evidence indicate that esker systems on a subcontinental scale are time transgressive sedimentological evidence for a canal drainage system appears to be present in fine grained tills where eskers are largely absent

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

tertiary fluvial gravels and evolution of the western canadian prairie landscape abstract the early tertiary of western canada and northern united states was marked by a change from compressional to extensional tectonics the result was regional uplift and magmatic events the uplift resulted in a major unconformity and deposition of extensive regional sheets of gravel and sand of which only isolated remnants remain these units are the eocene to miocene cypress hills formation the miocene wood mountain formation miocene flaxville formation and preglacial souris river gravels all four stratigraphic units consist of gravel and sand with lesser amounts of clay the formations were largely deposited as laterally continuous sheets of braided river gravels with some occurrences of meandering river sedimentation the sediment was deposited several hundred kilometres downstream of their source areas paleocurrent data for the cypress hills and wood mountain formations indicate that regional paleoslope dipped towards the north northeast the modern prairie landscape of western canada began to evolve with the deposition of these gravels during the eocene with creation of a basin wide unconformity followed by deposition of an extensive braidplain system that was subsequently uplifted incised and molded into its present form

postglacial geomorphic development of the dinosaur provincial park badlands alberta experimental studies concerning current geomorphic processes and erosion rates in the badlands of dinosaur provincial park alberta have not explained the unusual extent of badland development or prominent nonstructural near horizontal surfaces that occur in the park two of these surfaces result from spillway development associated with wisconsin deglaciation and the extent of badland development is associated with major spillway concentration and exposure of highly erodible cretaceous strata a third surface is associated with erosion caused by locally generated runoff all surfaces are blanketed with aeolian sands and silts deposited around 5500 bp which profoundly affected the hydrology of the area and water and sediment discharge from the badlands to the red deer river subsequent stripping of the aeolian cover by streams along with piping and tunnel erosion has reexposed vulnerable cretaceous strata and restored the high erosion rates now observed in these badlands

palynological analysis of the late early pleistocene sediments from queque cave in guangxi south china abstract palynomorphs extracted from the sediments in queque cave of the late early pleistocene in chongzuo guangxi zhuang autonomous region were investigated to reconstruct the paleoenvironment in the study area while the sediments are pollen poor they are sufficiently productive to carry out a paleoenvironmental analysis the source vegetation reflected by the palynomorphs from the unfossiliferous layer was temperate to warm temperate deciduous and evergreen broadleaved forest while it was warm temperate to subtropical deciduous and evergreen broadleaved forest from the mammalian horizons climatic parameters obtained using the coexistence approach indicate that the unfossiliferous layer mat 11 3 15 4 c map 601 1 1076 1 mm was cooler and drier than that from the mammal bearing layers mat 12 6 18 6 c map 784 7 1523 1 mm

phased occupation and retreat of the last british irish ice sheet in the southern north sea geomorphic and seismostratigraphic evidence of a dynamic ice lobe along the terrestrial margin of the southern north sea previous studies of the mis 2 glaciation impacting eastern britain have played a significant role in the development of principles relating to ice sheet dynamics e g deformable beds and the practice of reconstructing the style timing and spatial configuration of palaeo ice sheets these detailed terrestrially based findings have however relied on observations made from only the outer edges of the former ice mass as the north sea lobe nsl of the british irish ice sheet biis occupied an area that is now almost entirely submarine c 21 15 ka compounded by the fact that marine acquired data have been primarily of insufficient quality and density the configuration and behaviour of the last biis in the southern north sea remains surprisingly poorly constrained this paper presents analysis of a new integrated set of extensive seabed geomorphological and seismo stratigraphic observations that both advances the principles developed previously onshore e g multiple advance and retreat cycles and provides a more detailed and accurate reconstruction of the biis at its southern most extent in the north sea a new bathymetry compilation of the region reveals a series of broad sedimentary wedges and associated moraines that represent several terminal positions of the nsl these former still stand ice margins 1 4 are also found to relate to newly identified architectural patterns shallow stacked sedimentary wedges in the region s seismic stratigraphy previously mapped singularly as the bolders bank formation with ground truthing constraint provided by sediment cores these wedges are interpreted as sub marginal till wedges formed by complex subglacial accretionary processes that resulted in till thickening towards the former ice sheet margins the newly sub divided shallow seismic stratigraphy at least five units also provides an indication of the relative event chronology of the nsl while there is a general record of south to north retreat seismic data also indicate episodes of ice sheet re advance suggestive of an oscillating margin e g mis 2 maximum not related to first incursion of ice into region demonstrating further landform interdependence geographically grouped sets of tunnel valleys are shown to be genetically related to these individual ice margins providing clear insight into how meltwater drainage was organised at the evolving termini of this dynamic ice lobe the newly reconstructed offshore ice margins are found to be well correlated with previously observed terrestrial limits in lincolnshire and e yorkshire holderness e g mis 2 maximum and withernsea till this reconstruction will hopefully provide a useful framework for studies targeting the climatic mass balance and external glaciological factors i e fennoscandian ice sheet that influenced late stage advance and deglaciation important for accurately characterising both modern and palaeo ice sheets

observing artificially induced strain implications for subglacial deformation by analysing a series of four successive thin sections from a ceramic clay that was subjected to uniaxial compression we were able to monitor the development of microstructures in a fine grained sediment the artificially induced microstructures such as unidirectional clay reorientations and linear and circular grain arrangements are identical to features that have been observed in thin sections of subglacially deformed tills and therefore may be used as representative analogues we argue that the structures reflecting slip planar shear displacements as well as rotational movements can be explained by assuming a coulomb plastic response to imposed shear we conclude that sediments subjected to subglacial deformation behave as coulomb materials at least during the final stages of the deformation the present study bridges the gap between field studies experimental studies and theoretical modelling the microscopic observations assist in visualising inferred subglacial processes and facilitate up and downscaling between diverse methodological approaches copyright 2003 john wiley sons ltd

till stratigraphy and sedimentology at the margins of terrestrially terminating ice streams case study of the western canadian prairies and high plains complex glacigenic sediment sequences arranged in large arcuate assemblages and demarcating the lobate termini of fast ice flow corridors in western canada represent the terrestrial equivalents of the trough mouth fans of the marine palaeo ice stream record intensive sedimentological and stratigraphic investigations at a regional scale are employed in the interpretation of thick units or sequences of diamicton and two depositional scenarios are proposed first glacier marginal till thickening and the stacking of till wedges takes place in areas where an ice stream margin was stationary for short periods of time stacks of subglacial traction tills potentially record annual sub marginal incremental thickening at ice stream margins especially in areas where densely spaced recessional push moraines appear to record seasonal climatic forcing second proglacial lake and valley infilling with glacilacustrine rhythmites and mass flow diamictons is associated with the advection of sub marginal till into preglacial bedrock depressions and records ice stream marginal oscillations and debris influx into discontinuous proglacial lakes which act as subaqueous sediment sinks for materials that would otherwise have been used to construct sub marginal till wedges and moraines glacial overriding modifies the deposits produced in both scenarios through deformation and the dislocation and entrainment of bedrock and sediment rafts at the margins of bedrock valley walls resulting in the widespread development of glacitectonites and megablocks the occurrence of the thickest deposits as preglacial valley fills may be significant in groundwater siphoning away from subglacial deforming layers and the promotion of sticky spots

geomorphology and sedimentology of surging glaciers a land systems approach the identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice sheet dynamics and for reconstructing ice sheets and climate no single landform or diagnostic criterion has yet been found with which to identify surging glaciers a surging glacier land system model is constructed using observations and measurements from contemporary surging glacier snouts in iceland svalbard u s a and canada for differentiating ancient surging margins from other non surging palaeoglaciers this integrates the suite of landforms sediments and stratigraphy produced at surging glacier margins landforms produced during surging include thrust moraines concertina eskers and subglacial crevasse squeeze ridges sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds which display severe glaciotectonic contortion and faulting hummocky moraine comprising interbedded stratified sediments and mass flow diamictons has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ an example of the application of the land system model is presented for east central alberta canada a surging palaeo ice stream is identified within this part of the southwestern laurentide ice sheet where thrust block moraines crevasse squeeze ridges flutings hummocky moraine and glaciotectonized sediments are juxtaposed

styles of till deposition at the margin of the last glacial maximum north sea lobe of the british irish ice sheet an assessment based on geochemical properties of glacigenic deposits in eastern england the geochemical composition of last glacial maximum lgm tills and glacitectonites in east yorkshire and lincolnshire was analysed to assess vertical changes in their geochemical signature with respect to the current regional stratigraphic division and generic models of till deposition results fail to precisely differentiate the traditional basement skipsea and withernsea till types instead there is often more variability within these till types than between them the geochemical signatures are also laterally discontinuous and are often repeated vertically at a number of sites suggesting that the till sequences are composed of a number of lithologically distinct rafts which have been tectonically stacked or elevated to higher levels in the sediment pile at dimlington the production of a glacitectonically folded and stacked moraine is proposed as a mechanism to explain the remarkably thick sequence of withernsea till and the repetitions in geochemical composition we argue that the changes in till matrix geochemistry are related to changes in the dominance of ice lobes of different provenance which reworked pre existing quaternary sediments excavated local bedrock and progressively mixed these sediments with more far travelled material from further north the most significant implication of these findings is that the current lgm till stratigraphy of east yorkshire and lincolnshire is too simplified and therefore does not recognise the sedimentary and structural complexity produced by repeated onshore possibly surging flow by a dynamic north sea lobe at the eastern margin of the british irish ice sheet

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

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

depositional and tectonic setting of the miocene wood mountain formation southern saskatchewan coarse gravels of the miocene wood mountain formation that cap the wood mountain upland in southern saskatchewan are an erosional remant of a much more expansive sheet of gravel and sand the formation consists of gravel and sand deposited as a thin sheet on a regional planation surface that extends approximately along strike for at least 160 km this sheet with a maximum thickness of 31 m is the deposit of low sinuosity braided river channels that flowed to the north northeast the wood mountain formation represents an initial episode of erosion followed by low accommodation deposition where the net aggradation rate was likely low the sediments of the wood mountain formation are associated with change in tectonic style in western north america from one of compression to one of extension the gravels were deposited above a regional erosion surface associated with isostatic uplift of the central montana uplift

a multi technique study of the glacial stratigraphy of co clare and co kerry southwest ireland a multi technique approach has been adopted in a study of the lithostratigraphy of glacial deposits in southwestern ireland including clast lithological analysis fine sand geochemistry low frequency mass specific susceptibility and fine sand calcium carbonate equivalent content a revised lithostratigraphical scheme is suggested for the quaternary glacial deposits of the region together with a simple strategy that may be adopted for stratigraphical studies in other regions of southern ireland it appears that geochemical determinations via inductively coupled plasma atomic absorption spectrometry are particularly useful in characterising and discriminating between till units within local stratigraphical studies and may be used to inform the applicability of other utilitarian techniques for use on a regional scale copyright 2002 john wiley sons ltd

on the interpretation of subglacial till fabric abstract the modal distribution of stone long axis fabrics and their respective eigenvalues can be used to infer the genesis of subglacial till in this paper we offer a two axis diagram that compares fabric modality to fabric isotropy s3 s1 and addresses the problem of eigenvectors falling between the modes of some well developed till fabrics with low eigenvalues our simple five fold scheme of modality categories includes 1 unimodal clusters 2 spread unimodal 3 bimodal clusters 4 spread bimodal and 5 polymodal to girdle like fabrics and requires the analyst to study equal area lower hemisphere schmidt plots of the fabric data after assigning the fabric to a morality category isotropy is calculated and both results are plotted on the graph whic helps to separate two main fields of subglacial till 1 lodgement and subglacial meltout tills and 2 deformation fill on the basis of selected published fabrics from tills at modern glaciers as well as our own pleistocene till data lodgement and subglacial meltout tills tend to have unimodal or bimodal fabrics in contrast deformation tills and tills that experienced multiple processes tend to have polymodal to girdle like fabrics some overlap occurs between fields be cause of the complex nature of till formation i e because pure end member till facies are rare and most tills are hybrids we strongly recommend that schmidt plots be visually analyzed and used in conjunction with eigenvalues when studying till however fabric data alone is not enough multiple criteria including structural lithologic and stone morphologic data from the till must also be considered before drawing conclusions on till genesis furthermore if eigenvectors fall between fabric modes then they cannot be used to indicate former ice movement directions finally our new modality isotropy diagram may have wider applications

flow pattern evolution of the laurentide and cordilleran ice sheets across west central alberta canada implications for ice sheet growth retreat and dynamics during the last glacial cycle this paper presents a reconstruction of the geometry dynamics and flow pattern of the laurentide and cordilleran ice sheets along the albertan portion of the eastern canadian rocky mountains during the last glaciation sediment landform associations relating to the evolution of these ice sheets document their initial convergence and mutual deflection across west central alberta the continued advance of laurentide ice locally displaced cordilleran ice westward into the front ranges and deflected trunk ice emerging from the athabasca river valley south eastwards along the foothills these convergent flow patterns remained major features in the regional geometry of both ice sheets throughout the last glacial maximum the onset of deglaciation was characterized by the northward retreat of the laurentide ice sheet which progressively unblocked valleys along the mountain front the configuration of buttress removal initiated the lateglacial expansion and sequential drawdown of the eastern cordilleran ice sheet along fast flowing outlet glaciers subsequent regional retreat of laurentide and cordilleran ice was associated with the development of large proglacial lakes which amplified deglaciation by destabilizing the margins of both ice sheets triggering extensive readvances due to periodic changes in water level associated with the opening and closing of outlets by ice margin fluctuations

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

glacial landsystems of the southwest laurentide ice sheet modern icelandic analogues landform assemblages and associated stratigraphy sedimentology and structure are used in the reconstruction of palaeo ice sheet dynamics in alberta western canada interpretations are based upon the modern analogues from four outlet glaciers at the margins of vatnajokull and myrdalsjokull iceland in the area between lloydminster and lac la biche central alberta an extensive landform assemblage of megaflutings crevasse squeeze ridges and thrust block moraine arcs document the former surging of part of the margin of the laurentide ice sheet during later stages of recession this landform assemblage including numerous exposures of glacitectonised bedrock and quaternary sediments is comparable to the landsystem of the surging glaciers eyjabakkajokull and bruarjokull in iceland near high river southern alberta the former existence of an ice lobe characterised by active recession is recorded by closely spaced low amplitude recessional push moraines that drape tunnel valleys these are comparable in form and pattern to annual push moraines and fluted till surfaces produced by breidamerkurjokull and sandfellsjokull iceland and also include rimmed depressions produced by the escape of artesian water during ice marginal pushing this study provides interpretations of the regional glacial geomorphology of alberta based upon comparisons of form and stratigraphy with modern glacial analogues and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features implications for ice dynamics and regional till stratigraphies are discussed copyright 1999 john wiley sons ltd

on subglacial stone pavements in till four pavements from central and western canada display uneven pavement surfaces abundant tilted and inverted stones reversed lee ends fine crossing striae in various directions weak striae around curves worn facets distributed evenly on rounded stones and till fabric girdles collectively inconsistent with the popular concept of stones firmly held in till being abraded by overriding ice based on these data new models are offered that involve stone rotation in viscously deforming till to produce deformation pavements in the specific model increased pore water pressure under moving ice locally mobilizes previously formed lodgment and or erosional pavements into deformation pavements in the more general model stones released from the sole of a wet based glacier rotate interact and settle into a viscous suspension zone in deforming till according to velocity density and viscosity gradients stone axes and striae settle into various orientations following dewatering and till stiffening conceptu

till deposition by glacier submarginal incremental thickening macro and micro scale sedimentological analyses of recently deposited tills and complex push squeeze moraines on the forelands of icelandic glaciers and in a stacked till sequence at the former younger dryas margin of the loch lomond glacier lobe in scotland are used to assess the depositional processes involved in glacier submarginal emplacement of sediment where subglacial meltwater is unable to flush out subglacial sediment or construct thick debris rich basal ice by cumulative freeze on processes glacier submarginal processes are dictated by seasonal cycles of refreezing and melt out of tills advected from up ice by a combination of lodgement deformation and ice keel and clast ploughing although individual till layers may display typical a and b horizon deformation characteristics the spatially and temporally variable mosaic of subglacial processes will overprint sedimentary and structural signatures on till sequences to the extent that they would be almost impossible to classify genetically in the ancient sediment record at the macro scale icelandic tills display moderately strong clast fabrics that conform to the ice flow directions documented by surface flutings very strong fabrics typify unequivocally lodged clasts despite previous interpretations of these tills as subglacial deforming layers micro morphological analysis reveals that shearing played only a partial role in the emplacement of till matrixes and water escape and sediment flowage features are widespread a model of submarginal incremental thickening is presented as an explanation of these data involving till slab emplacement over several seasonal cycles each cycle involves 1 late summer subglacial lodgement bedrock and sediment plucking subglacial deformation and ice keel ploughing 2 early winter freeze on of subglacial sediment to the thin outer snout 3 late winter readvance and failure along a decollement plane within the till resulting in the carriage of till onto the proximal side of the previous year s push moraine 4 early summer melt out of the till slab initiating porewater migration water escape and sediment flow and extrusion repeated reworking of the thin end of submarginal till wedges produces overprinted strain signatures and clast pavements

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes

large scale reorganization and sedimentation of terrestrial ice streams during late wisconsinan laurentide ice sheet deglaciation glacial geomorphological mapping of shuttle radar topography mission srtm data from the western canadian prairies demonstrates that during the last late wisconsinan deglaciation of the laurentide ice sheet terrestrial ice streams underwent a major reorganization of their flow configuration this reorganization involved a 90 shift in flow direction and was accompanied by a corresponding increase in the influence of topography on streaming flow ice streams included both topographically confined and pure ice streams that flowed independent of topography streaming flow is recorded by suites of highly elongate 60 km long subglacial bedforms bounded sharply at their lateral margins by prominent moraines initial streaming flow was unconfined by topography but was replaced progressively and crosscut by younger topographically confined flows flow reorganization is inferred to have been caused by temporal and spatial variations in the interaction between frozen and thawed bed conditions with thinning and shutdown of one ice stream ultimately triggering initiation of others this highlights the role of internal glaciodynamically driven reorganization in triggering streaming flow within large ice sheets and shows that large scale flow reorganization can occur over the time scale of a single deglaciation in terrestrial ice streams

hummocky moraine sedimentary record of stagnant laurentide ice sheet lobes resting on soft beds abstract over large areas of the western interior plains of north america hummocky moraine hm formed at the margins of laurentide ice sheet lis lobes that flowed upslope against topographic highs current depositional models argue that hm was deposited supraglacially from stagnant debris rich ice disintegration moraine across southern alberta canada map and outcrop data show that hm is composed of fine grained till as much as 25 m thick containing rafts of soft glaciotectonized bedrock and sediment chaotic non oriented hm commonly passes downslope into weakly oriented hummocks washboard moraine that are transitional to drumlins in topographic lows the same subsurface stratigraphy and till facies is present throughout these landforms and others such as doughnut like rim ridges flat topped moraine plateaux and linear disintegration ridges are identified as belonging to subglacially deposited soft bed terrain this terrain is the record of ice lobes moving over deformation till derived from weakly lithified bentonite rich shale drumlins record continued active ice flow in topographic lows during deglaciation whereas hm was produced below the outer stagnant margins of ice lobes by gravitational loading pressing of remnant dead ice blocks into wet plastic till intervening zones of washboard moraine mark the former boundary of active and stagnant ice and show hybrid drumlins whose streamlined form has been altered by subglacial pressing humdrums below dead ice the presence of hummocky moraine over a very large area of interior north america provides additional support for glaciological models of a soft bedded laurentide ice sheet

glacial sediments and landforms of holderness eastern england a glacial depositional model for the north sea lobe of the british irish ice sheet abstract borehole records and exposures at coastal cliffs and inland quarries around holderness are used in a critical assessment of the glacial depositional environments that operated at the margin of the north sea lobe of the british irish ice sheet at the last glacial maximum four lithofacies associations lfa are recognized in the area lfas 1 and 4 are laminated to massive diamictons traditionally called the skipsea and withernsea tills members and display deformation structures indicative of stress from the ne attenuated rafts of soft bedrock lithologies ice bed separation canal fill features and pseudo stratification and clast macrofabric data predominantly indicate deformation only to low strains they are interpreted as subaqueous deposits subsequently deformed by glacier ice to create end products that lie on the glacitectonite continuum localized increases in strain signature are equated with the development of shear zones between onshore thickening wedges of deformed pre existing lake sediment lfa 2 comprises cross bedded clinoforms locally steepening into foresets at the core of linear hummocks along the central spine of holderness lfa 2a and rhythmically laminated silts and sands with dropstones lfa 2b these sediments are interpreted as coalescent glacilacustrine subaqueous outwash fans fining distally to lake bottom rhythmites and varves ice contact deposition is evident in compressional folding faulting and hydrofracture filling due to ice overriding and extensional faulting associated with localized ice melt out depressions produced by folding or sagging provided the accommodation space for the later deposition of lfa 2 and 3 through syntectonic sedimentation lfa 3 comprises flat lying beds of well to poorly sorted cross stratified sands and gravels interpreted as proximal proglacial braided outwash deposits laid down largely in ribbon sandar defined by the topography of abandoned ice contact glacilacustrine depo centres well developed ice wedge pseudomorphs in lfa 3 record permafrost conditions during ice sheet marginal recession indicating that north sea lobe oscillations may have been non climatic or surge related a depositional model is proposed in which advance and retreat phase tills glacitectonites and associated ice contact lake sediments are the geological imprint of a single glaciation the initial advance of the north sea lobe is recorded by a westerly thinning advance till lfa 1 later lfa 1 and 4 retreat tills are strictly glacitectonites and are thicker depositional units because later ice readvances encroached upon and cannibalized more substantial sequences of deglacial lake sediment and subaqueous ice contact fans lfa 2 similar regional till architectures will be manifest wherever the palaeogeography resulted in the onshore flow of ice and the concomitant production of glacitectonites from glacial lake sediments

glaciotectonism and landsliding in little sandhill creek alberta abstract slope failure and gully erosion along little sandhill creek a tributary of the red deer river alberta canada has exposed large stratigraphic sections in which the effects of glaciotectonism and landsliding are clearly revealed six main units are identified ranging from a deposit of coarse fluvial sands through various glacial diamictons and gravels and sands to postglacial fluvial and lacustrine pond and aeolian sediments incision by little sandhill creek since late wisconsinan deglaciation ca 12 500 b p resulted in periodic landslides culminating in the main slope failure which occurred post ca 5400 b p the slide was reactivated by irrigation water return flow from the adjacent prairie surface

cosmogenic 36cl dating of the foothills erratics train alberta canada the foothills erratics train of alberta was carried into place during coalescence between montane glaciers and the laurentide ice sheet its age has been controversial late wisconsinan and pre wisconsinan ages have been assigned to it cosmogenic 36 cl exposure dating was carried out on erratics over a 130 km segment of the erratics train seven of eight age determinations support emplacement during the late wisconsinan glaciation these ages eliminate the possibility of an ice free corridor during the last glacial maximum they are also consistent with the hypothesis that the laurentide ice sheet was the most extensive of all pleistocene continental ice sheets in western canada

an updated radiocarbon based ice margin chronology for the last deglaciation of the north american ice sheet complex abstract the north american ice sheet complex naisc consisting of the laurentide cordilleran and innuitian ice sheets was the largest ice mass to repeatedly grow and decay in the northern hemisphere during the quaternary understanding its pattern of retreat following the last glacial maximum is critical for studying many facets of the late quaternary including ice sheet behaviour the evolution of holocene landscapes sea level atmospheric circulation and the peopling of the americas currently the most up to date and authoritative margin chronology for the entire ice sheet complex is featured in two publications geological survey of canada open file 1574 dyke et al 2003 quaternary glaciations extent and chronology part ii dyke 2004 these often cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka all ages in uncalibrated radiocarbon years using a combination of geomorphology stratigraphy and radiocarbon dating however by virtue of being over 15 years old the ice margin chronology requires updating to reflect new work and important revisions this paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies we also update the original radiocarbon dataset from the 2003 2004 papers with 1541 new ages to reflect work up to and including 2018 a major revision is made to the 18 ka ice margin where banks and eglinton islands once considered to be glacial refugia are now shown to be fully glaciated our updated 18 ka ice sheet increased in areal extent from 17 81 to 18 37 million km2 which is an increase of 3 1 in spatial coverage of the naisc at that time elsewhere we also summarize region by region significant changes to the deglaciation sequence this paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of dyke et al 2003 and dyke 2004 where new information is lacking this is a pragmatic solution to satisfy the needs of a quaternary research community that requires up to date knowledge of the pattern of ice margin recession of what was once the world s largest ice mass the 36 updated isochrones are available in pdf and shapefile format together with a spreadsheet of the expanded radiocarbon dataset n 5195 ages and estimates of uncertainty for each interval

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

subglacial lake mcgregor south central alberta canada abstract it is proposed that a lake here named subglacial lake mcgregor existed beneath the laurentide ice sheet at or near the last glacial maximum the lake resided in the ancient buried mcgregor and tee pee preglacial valleys which are now mostly filled with glacigenic deposits the greatest thickness of sediment in the valleys is in the form of chaotically deposited lake beds that were laid down in a subaqueous environment by a number of process gravity flow water transport and suspension settling topographic sedimentary and stratigraphic evidence point to a subglacial not a proglacial origin for the beds during the early stages of lake existence ice movement was significant as there are numerous sets of shear planes in the sedimentary beds this indicates that the lake filled lake sedimentation and drained shearing of the beds by overlying ice when ice contacted the bed often thus early in its history the lake s was were ephemeral during the later stages of lake existence the lake was relatively stable with no rapid draining or influx of sediment gradual drainage of the lake resulted in lowering of the ice onto the lake beds resulting in subglacial till deposition drainage was not a single continuous event rather it was characterized by multiple phases of near total drainage till deposition followed by water accumulation lake sedimentation water accumulation events became successively less significant reflected by thinning of lake beds and thickening of till beds higher in the stratigraphic sequence since subglacial lake sedimentation appears to be restricted to the subglacial valleys it is suggested that the valleys acted as a large scale interconnected cavity system that both stored and transported water it is also suggested that these acted as the main routes of water flow beneath the laurentide ice sheet

reconstructing the confluence zone between laurentide and cordilleran ice sheets along the rocky mountain foothills south west alberta landform mapping near the athabasca valley was fundamental to determining whether the late wisconsinan laurentide and cordilleran ice sheets lis cis coalesced in this paper we examine the detailed landform record using new lidar digital elevation and hillshade models of the area of confluence and eventual desuturing of these ice sheets this work reveals an earlier more extensive cordilleran advance before coalescence with the lis when the ice sheets coalesced the flow pattern was dominated by ice flow along the mountain front with cordilleran ice flowing out of major trunk valleys but laurentide ice flowing into the foothills up smaller valleys this flow pattern implies that when the ice sheets coalesced the cis was already waning or at least was not at its maximum deglaciation was interrupted by several re advances probably related to the destabilizing effect of proglacial lakes along the ice margin

subglacial conditions under the last ice sheet in northwest germany ice bed separation and enhanced basal sliding abstract theoretical reconstruction of ice thickness during the weichselian glaciation in a portion of northwest germany yields maximum thicknesses of about 280 m some 50 km into the ice sheet from the margin this corresponds to averaged driving stress at the glacier bed in the order of 17 kpa the increase in ice thickness away from the margin was non uniform caused by undulations in pre existing topography steady state subglacial water pressure heads were high up in the ice sheet reaching the flotation point in places hydraulic lifting of the ice sheet probably occurred causing non deforming bed conditions where transformation of basal shear stresses to soft subglacial sediments was prevented by a water film thin stringers of undeformed sorted sediments occurring in tills are attributed to basal meltwater washing during phases of ice bed separation the basal water film was over 5 mm thick using a quantitative approach coupled with field data we demonstrate that neither internal ice deformation nor bed deformation contributed much to the ice motion instead the rapid movement of the weichselian ice sheet was caused by basal sliding with ploughing the ice sheet was probably characterized by an unstable behaviour

landform and sediment imprints of fast glacier flow in the southwest laurentide ice sheet evidence for former fast glacier flow ice streaming in the southwest laurentide ice sheet is identified on the basis of regional glacial geomorphology and sedimentology highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream preliminary mapping from a digital elevation model of alberta identifies corridors of smoothed topography and corridor parallel streamlined landforms megaflutes to mega lineations that display high levels of spatial coherency ridges that lie transverse to the dominant streamlining patterns are interpreted as a series of minor recessional push moraines b thrust block moraines or composite ridges hill hole pairs constructed during readvances surges and c overridden moraines cupola hills apparently of thrust origin together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms localised cross cutting and or misalignment of flow sets indicates temporal separation and the overprinting of ice streams lobes the fast flow tracks are separated by areas of interlobate or inter stream terrain in which moraines have been constructed at the margins of neighbouring competing ice streams outlet glaciers this inter stream terrain was covered by more sluggish non streaming ice during full glacial conditions thin tills at the centres of the fast flow corridors in many places unconformably overlying stratified sediments suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams outlet glaciers is consistent with subglacial deformation theory in this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory sometimes with fast flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally the occurrence of minor push moraines and flutings and associated landforms because of their similarity to modern active temperate glacial landsystems are interpreted as indicative of ice lobe marginal oscillations possibly in response to seasonal climatic forcing in locations where meltwater was more effectively drained from the glacier bed further north the occurrence of surging glacier landsystems suggests that persistent fast glacier flow gave way to more transitory surging possibly in response to the decreasing size of ice reservoir areas in dispersal centres and also locally facilitated by ice bed decoupling and drawdown initiated by the development of ice dammed lakes copyright 2008 john wiley sons ltd

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

architectural element analysis applied to glacial deposits internal geometry of a late pleistocene till sheet ontario canada deposits left by continental ice sheets are characterized by sedimentological complexity and stratigraphic heterogeneity but stratigraphic descriptions of such deposits and resulting first generation facies models are still based primarily on one or two dimensional borehole or outcrop data reconstruction of depositional environments hydrogeological investigations of pleistocene glacial deposits and hydrocarbon exploration in pre pleistocene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions architectural element analysis is used widely by sedimentologists for categorizing internal stratigraphic heterogeneity in sandstones particularly those of fluvial origin this paper demonstrates the first application of architectural element analysis to glacial deposits such as tills outcrop borehole and a broad range of subsurface geophysical data were collected from a thick 60 m till sheet present across an 80 km 2 study area near toronto canada the till sheet is not homogeneous but is composed of three distinct architectural elements and associated lithofacies viz diamict elements interbeds of subglaciofluvial sediments and glaciotectonically deformed zones application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacial processes below the laurentide ice sheet and creates a framework for understanding ground water and contaminant movement in underlying aquifers

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

glacial geomorphology of terrestrial terminating fast flow lobes ice stream margins in the southwest laurentide ice sheet glacial geomorphological mapping of southern alberta canada reveals landform assemblages that are diagnostic of terrestrial terminating ice streams fast flowing outlet glaciers with lobate snouts spatial variability in features that comprise the landform assemblages reflects changes in a palaeo ice stream activity switch on off and b snout basal thermal regimes associated with climate sensitive steady state flow palaeo ice stream tracks reveal distinct inset sequences of fan shaped flowsets indicative of receding lobate ice stream margins former ice lobe margins are demarcated by a major often glacially overridden transverse moraine ridges commonly comprising glacitectonically thrust bedrock and b minor closely spaced recessional push moraines and hummocky moraine arcs details of these landform types are well exhibited around the former southern margins of the central alberta ice stream where larger scale more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges mtr types 1 3 hummocky terrain ht types 1 3 flutings and meltwater channels spillways the mtr type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined the mtr type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts the mtr type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain the close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin where the ht type 3 hummocks represent former ice walled lake plains the ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern alberta are consistent with palaeoglaciological reconstructions proposed for other ice stream fast flow lobes of the southern laurentide ice sheet where alternate cold polythermal and temperate marginal conditions associated with climate sensitive steady state flow sequentially gave way to more dynamic streaming and surging activity

ribbed bedforms on palaeo ice stream beds resemble regular patterns of basal shear stress traction ribs inferred from modern ice streams rapidly flowing ice streams are an important mechanism through which ice sheets lose mass and much work has been focussed on elucidating the processes that increase or decrease their velocity recent work using standard inverse methods has inferred previously unrecognised regular patterns of high basal shear stress sticky spots 200 kpa beneath a number of ice streams in antarctica and greenland termed traction ribs they appear at a scale intermediate between smaller ribbed moraines and much larger mega ribs observed on palaeo ice sheet beds but it is unclear whether they have a topographic expression at the bed here we report observations of rib like bedforms from dems along palaeo ice stream beds in western canada that resemble both the pattern and dimensions of traction ribs their identification suggests that traction ribs may have a topographic expression that lies between and partly overlaps with ribbed moraines and much larger mega ribs these intermediate sized bedforms support the notion of a ribbed bedform continuum their formation remains conjectural but our observations from palaeo ice streams coupled with those from modern ice masses suggest they are related to wave like instabilities occurring in the coupled flow of ice and till and modulated by subglacial meltwater drainage their form and pattern may also involve glaciotectonism of subglacial sediments

ice thrust terrains and glaciotectonic settings in central alberta airphoto analyses geologic field mapping and study of borehole logs and surficial topographic maps in ice thrust terrains in central alberta suggest that all these techniques are needed to identify ice thrust terrains that may or may not have topographic expressions three geomorphological settings susceptible to glaciotectonic deformation are described as escarpment valley and plains settings the bedrock slopes in the escarpment setting ranged from 19 to 51 m km the bedrock slopes in the valley setting ranged from 23 to 32 m km and the valley was 8 5 km wide between crests and 4 km at the bottom the bedrock slopes of the plains setting ranged from 2 to 5 m km ice thrust features are found in topographic troughs in front of an ice sheet where water bodies were impounded these proglacial water bodies thawed the permafrost in front of the glacier the disintegration of proglacial permafrost decreased the resistance of subglacial strata to ice thrusting ice thrust features can be expected in areas wh

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

reversal of the regional scale flow system of the williston basin in response to pleistocene glaciation low 18o values of formation waters collapse structures related to salt dissolution hydrodynamic blowout structures and biodegradation of oils all suggest a significant influx of fresh water into the williston basin along the outcrop belt in southern and central manitoba during pleistocene glaciation the thickness of the continental ice sheet over manitoba would have provided sufficient potentiometric drive to reverse the regional scale flow system of the williston basin the dynamic nature of the flow system suggests that modern day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed

glacial and postglacial stratigraphy of dinosaur provincial park and surrounding plains southern alberta canada abstract thirty one stratigraphic logs from the dinosaur provincial park area reveal seven major lithofacies associations lfa s lfa 1 is a preglacial fluvial deposit recording deposition on a sandy braided floodplain this lfa fines upwards to lfa 2 a glacilacustrine deposit which records the first advance of laurentide glacier ice into the region erosional contacts between lfa s 1 and 2 and bedrock suggest that large expanses of badlands may have existed prior to glaciation lfa 3 is a grey till which together with glacitectonized bedrock records ice movement from the northeast lfa 4 represents supraglacially derived diamictons and outwash its oxidized colour indicates either a considerable period of subaerial weathering or groundwater activity and the deposit is tentatively assigned an interstadial or interglacial age a second glaciation is recorded by lfa 5 heterogeneous diamicton and lfa 6 homogeneous diamicton lfa 5 records a period of subglacial molding and then cavity filling by fluvial and debris flow deposits lfa 6 records lodgement and melt out of the same glacier ice after it had glacitectonically thrust large rafts of older lfa s the sequence of molding cavity fill tectonism melt out represents large scale decoupling of the glacier from its bed and later surges creating extensive deformation of the substrate melt out was interrupted in some places by remobilization caused by surges which continued throughout ice retreat lfa s 7a 7e record deposition in glacilacustrine fluvial pond and aeolian environments after deglaciation some previously reported and new radiocarbon dates on regional and local surface drainage are discussed with reference to fluvial incision and holocene climate all lfa s are tentatively correlated with stratigraphic sequences reported from adjacent areas of southern alberta and former regional glaciodynamics are assessed

application of till pebble lithology to the differentiation of glacial lobes in southern alberta variations in the pebble composition of surface till in southern alberta indicate the presence of three contemporaneous lobes in the last continental glacier the ice lobe domains have similar pebble associations and differ only in the frequency of occurrence of rock constituents a large part of the percentage variability within each domain is caused by irregular entrainment of locally derived stones which dilutes pebble contents and results in a lithology substantially different from the provenance composition the study has shown that the regional trends are preserved and can be recognized in the locally modified lithologies but the latter have to be isolated and evaluated differently from the regular provenance lithologies the common diluting agent in the area is fluvial gravel that is widespread on erosional bedrock surfaces and in preglacial valleys because the gravel is generally coarse pebble fractions of larger size are more affected by local dilution than are successively finer fractions q

terrestrial ice streams a view from the lobe abstract the glacial landforms of minnesota are interpreted as the products of the lobate extensions of ice streams that issued from various ice sheds within the laurentide ice sheet low relief till plains trough shaped lowlands boulder pavements and streamlined forms make up the subglacial landsystem in minnesota that is interpreted as having been formed by streaming ice extremely uniform tills are created subglacially in a way that remains somewhat mysterious at the ice margins thrust moraines and hummocky stagnation topography are more common than single crested simple moraines if the ice lobes had repeated advances subglacial drainage features are obscure up ice but are present down ice in the form of tunnel valleys eskers spooner hills and associated ice marginal fans ice streaming may occur when basal shear stress is lowered as a result of high subglacial water pressure subglacial conditions that allow the retention of water will allow an ice lobe to extend far beyond the ice sheet as long as the ice shed also supports the advance by supplying adequate ice even with adequate ice flux however the advance of an ice lobe may be terminated at least temporarily if the subglacial water is drained through tunnel valleys or perhaps a permeable substrate thrust moraines and ice stagnation topography will result from sudden drainage although climate change is ultimately responsible for the accumulation of ice in the laurentide ice sheet the asynchronous advances and retreats of the ice lobes in the mid continent are strongly overprinted by the internal dynamics of individual ice streams as well as the interaction of ice sheds which obscure the climate signal

rhythmic till sedimentation evidence for repeated hydraulic lifting of a stagnant ice mass the youngest sedimentary facies exposed in erosional hummocky terrain in south central alberta canada is composed of alternating beds of massive silty clay diamicton and sorted sand and or silt diamicton beds are similar in thickness 5 20 cm both laterally and vertically within the sequence and sedimentary structures and consistent clast orientations support a subglacial origin for both the diamicton and the sorted sediment alternation between diamicton and sorted strata document rhythmic sedimentary sequences deposition of melt out till followed by current deposition laterally extensive sorted beds indicate that the currents responsible for sand and silt deposition must have flowed as a sheet this flow was shallow no more than 20 cm indicated by scours below boulders that were suspended from the base of glacial ice sheet flow requires that the water was stored beneath the ice prior to drainage consequently some of the diamicton may have been deposited by rain out through the shallow stored water and hence each diamicton bed may represent a combination of direct melt out onto the bed and rain out through the water column inferred cycles of water accumulation and drainage may have been annual

glacially streamlined hard and soft beds of the paleo ontario ice stream in southern ontario and new york state abstract an extensive tract of glacially streamlined terrain across a large part of southern ontario canada is recognized as the footprint of the paleo ontario ice stream ois within the easternmost great lakes sector of the last laurentide ice sheet the upstream part is a drumlinized and megagrooved hard bed underlain by cambro ordovician carbonates and sandstones subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base recorded by sporadic spreads of hummocky rubble moraine downstream the hard bed passes underneath a streamlined soft bed of till cored drift drumlins and megaridges of the classic peterborough and new york state drumlin fields the boundary between the two bed types is a 10 km wide mixed bed of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin spatial variation in the geomorphology of 2500 drift drumlins indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins a large moraine system may mark the final collapse and melt of the ice stream accompanying abrupt flow switching of its margin

stratigraphy and sedimentology of devensian dimlington stadial glacial deposits east yorkshire england the stratigraphy and sedimentology of the glacial deposits exposed along the coast of east yorkshire are reviewed critical sections at filey brigg barmston and skipsea are examined to reassess the stratigraphy of devensian dimlington stadial glacial deposits in the light of recent developments in glacial sedimentology sedimentary and glaciotectonic structures studied in the field and by using scanning electron microscopy are emphasised two hypotheses are considered for the genesis of the interbedded diamictons and stratified sediments the first involves the deposition of lodgement till and or deformation till followed by meltout till which was overridden to produce more deformation till reflecting periods of ice stagnation punctuated by glacier thickening the second hypothesis which is favoured on the basis of field evidence and micromorphology involves the vertical accretion of a deforming till layer associated with cavity channel or tunnel valley fills beneath active ice at barmston the upper part of the diamicton contains elongate pendant structures containing gravels indicating that the diamicton was saturated and able to flow the diamictons therefore represent a complex sequence of tills deposited and deformed by active ice during the dimlington stadial previously published stratigraphical schemes involving classifications of multiple tills in east yorkshire should be simplified and it is more appropriate to assign these to a single formation the skipsea till formation rhythmic glaciolacustrine and proglacial glaciofluvial sediments overlie the tills at barmston and skipsea these were deposited in sag basins during deglaciation as the tills settled and deformed under thickening sediment and as buried ice melted out extensive sands and gravels cap the succession and were deposited on a sandur during the later stages of deglaciation

sedimentology of coastal deposits in the seychelles islands evidence of the indian ocean tsunami 2004 the seychelles an archipelago in the indian ocean at a distance of 4 500 5 000 km from the west coast of sumatra were severely affected by the december 26 2004 tsunami with wave heights up to 4 m since the tsunami history of small islands often remains unclear due to a young historical record it is important to study the geological traces of high energy events preserved along their coasts we conducted a survey of the impact of the 2004 indian ocean tsunami on the inner seychelles islands in detail we studied onshore tsunami deposits in the mangrove forest at old turtle pond in the curieuse marine national park on the east coast of curieuse island it is thus protected from anthropogenic interference towards the sea it was shielded until the tsunami in 2004 by a 500 m long and 1 5 m high causeway which was set up in 1909 as a sediment trap and assuring a low energetic hydrodynamic environment for the protection of the mangroves the causeway was destroyed by the 2004 indian ocean tsunami the tsunami caused a change of habitat by the sedimentation of sand lobes in the mangrove forest the dark organic rich mangrove soil 1 9 was covered by bimodal fine to medium carbonate sand 1 7 2 2 containing coarser carbonate shell fragments and debris intertidal sediments and the mangrove soil acted as sources of the lobe deposits the sand sheet deposited by the tsunami is organized into different lobes they extend landwards to different inundation distances as a function of the morphology of the onshore area the maximum extent of 180 m from the shoreline indicates the minimum inundation distance to the tsunami the top parts of the sand lobes cover the pneumatophores of the mangroves there is no landward fining trend along the sand lobes and normal grading of the deposits is rare occurring only in 1 of 7 sites the sand lobe deposits also lack sedimentary structures on the surface of the sand lobes numerous mostly fragmented shells of bivalves and molluscs were distributed up to 150 m from the coastline intact bivalve shells were mostly found positioned with the convex side upwards on small ledges of a granitic body at 130 150 m from the shore mostly fragmented and gravel sized shells were deposited at different elevations up to 4 m above sea level this implies a run up height of at least 4 m above sea level up to 150 m from the present shoreline

pattern recognition of lidar data and sediment anisotropy advocate a polygenetic subglacial mass flow origin for the kemijarvi hummocky moraine field in northern finland abstract object based image analysis and supervised machine learning on a digital elevation model derived from airborne laser scanning data were conducted to assess the aggregate raw material potential over the kemijarvi hummocky moraine field in finnish lapland geomorphometric analysis revealed surface stoniness to be diagnostic of moraine hummocks it was utilized to detect true moraine hummocks from among the potential hummocks delineated using object based image analysis with logistic regression of curvature features derived from the digital elevation model area under the receiver operating characteristics curve auc 0 77 based on the electrical sedimentary anisotropy data the kemijarvi moraine is polygenetic such that the ridges are diagonally and erosionally fluted from sector 280 290 on their surfaces while the ridge cores are deposited from the nw from sector 310 340 the cores are composed of infill gravels and crudely stratified diamict sequences we consider the core of the kemijarvi hummocky moraine field to represent pre existing early weichselian subglacial ridges rather than being generated through monogenetic late weichselian compressional shearing and stacking frozen bed extension or bed ribbing instability mechanisms as presented for ribbed moraines that are transverse to ice flow recently evidence has been presented of multiple slip events earthquakes with moment magnitudes mw 6 7 7 0 up ice from kemijarvi we therefore propose that the genesis of the hummocks may be associated with past early weichselian fault instability within glacio isostatic adjustment s which was able to generate subglacial water bodies possibly lakes and saturated materials that were forced towards the se based on this new geomorphological evidence from mapping using a digital elevation model derived from airborne laser scanning data and azimuthal conductivity surveys combined with the reinterpretation of previously presented geophysics and sedimentological observations we suggest the kemijarvi hummocky moraine field to be reconsidered as the kemijarvi subglacial mass flow field which holds significant potential for construction aggregate materials

landform signature of the laurentide and cordilleran ice sheets across alberta during the last glaciation government geological survey maps and research publications have portrayed the distribution of glacial landforms associated with the advance and retreat of the laurentide and cordilleran ice sheets across alberta at a local regional and continental scale to date this information has not been systematically synthesized into a single compilation at a consistent scale although this original work provided valuable information to constrain reconstructions of former ice sheet extent configuration and flow geometry its derivation primarily from the interpretation of aerial photographs and the shuttle radar topography mission 90 m digital elevation model dem may result in methodological inconsistencies and spatial biases these biases together with challenges associated with geomorphic mapping in densely forested areas of western and northern alberta limit the usefulness of previous mapping when applied to inversion based ice sheet reconstructions which have specific input data demands recently ligh

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

subglacial recharge into the western canada sedimentary basin impact of pleistocene glaciation on basin hydrodynamics brine springs discharging from devonian carbonates of the western canada sedimentary basin have distinct water chemistry from brines in laterally equivalent units deeper in the basin stable isotope data suggest that the brine springs originated as pleistocene meltwater these waters are interpreted to originate as an influx of subglacial meltwater related to a reversal of the basin scale flow system caused by the overriding ice sheet esker distribution shows a notable relationship between shield and sedimentary rocks an integrated sedimentary basin ice sheet model supports the interpretation that high permeability carbonate units acted as preferential subglacial drains that in turn affected esker development the fluid flow history of the western canada sedimentary basin is characterized by back and forth movement through geological time in response to changing boundary conditions modern day flow systems may not then be indicative of historic movement of economic fluids through the basin

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

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

a gravel diamicton lag on the south albertan prairies canada evidence of bed armoring in early deglacial sheet flood spillway courses a clast supported massive diamicton to poorly sorted massive gravel gm dcm bed in the area around dinosaur provincial park southern alberta canada provides a means of identifying early deglacial flood courses this is especially useful where flood and spillway courses have very subtle geomorphic definition and are difficult to map from aerial photographs the gm dcm bed conformably overlies a brown late wisconsinan till and rarely overlies bedrock and lacustrine sediments the geographic distribution of the bed is restricted to flat to gently undulating prairie on either side of the red deer river where shallow floods and spillway melt waters were concentrated upon deglaciation the bed has also been observed along the banks of the south saskatchewan river at medicine hat 90 km to the south and is therefore regionally extensive because the gm dcm bed has none of the attributes of supraglacial sediment and possesses a clast fabric and sphericity very similar to those of underlying till it is interpreted as a winnowed gravel diamicton lag which was produced by low competence melt water floods along shallow depressions in the prairie surface after the drainage of local proglacial lakes after enough of the fine grained matrix of the late wisconsinan till was removed to create a lag

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

the cypress hills formation upper eocene to miocene a semi arid braidplain deposit resulting from intrusive uplift the upper eocene miocene cypress hills formation of the cypress hills plateau in southwestern saskatchewan and southeastern alberta is interpreted as a braidplain deposit the regional paleoslope dipped to the northeast and the east west distribution of outcrop exposes facies representing lateral variation across the slope of the braidplain overall the average clast size of the deposits decreases from west to east with western area sediments dominated by boulder sized gravels deposited on longitudinal bars the eastern outcrop area contains deposits of braided channels cut into and interbedded with finer interchannel material including lacustrine marlstones silcretes and debris flow deposits the latter commonly containing abundant fossils the gravels of the cypress hills formation are multicyclic they were originally derived from the western ranges of the rocky mountains during laramide orogenesis and later shed farther into the basin during rebound due to unloading of the laramide thrusts by

kinematic indicators in fault gouge tectonic analog for soft bedded ice sheets abstract polished slip planes resulting from basin and range detachment faulting of mid tertiary volcaniclastics are well exposed at lake pleasant arizona u s a slip planes show erosional features formed by abrasion below moving sheets of gouge coarse grained diamict during repeated faulting and shearing tectonically generated forms are identical to those found in glaciated terrains slip planes show rat tail ridges and grooves ridge in groove structures nail head striations and wear tracks a prominent morphological element consists of flute ridges up to 30 cm wide and at least 7 m long formed of gouge preserved in the lee of boulders projecting as obstacles above slip surfaces crescentic scours around the stoss side of such boulders record enhanced abrasion by streams of gouge debris clasts are striated and show shapes comparable to flat iron clasts produced by glacial abrasion kinematic indicators at lake pleasant are directly comparable in form to flutes and drumlins in glaciated terrains the data presented here not support a recent hypothesis arguing that glacial striations flutes and drumlins are the product of turbulent subglacial meltwater instead diamict produced along fault planes gouge by low grade shearing is directly comparable to diamict facies deformation till formed by pervasive shear at the base of soft bedded ice sheets both facies are tectonically generated cataclastites produced in low grade shear zones and display genetically related but differently scaled streamlined bedforms

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages

deformation till in the great lakes region implications for rapid flow along the south central margin of the laurentide ice sheet structural and lithologic data indicate that while deposited under actively moving ice considerable portions of three muddy calcareous subglacial tills in the great lakes region probably experienced some component of ductile deformation viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds unlithified sediment clasts mixed ostracode shells reversed stone lee ends girdle and transverse fabrics irregular stone pavements fine striae following stone curves and inconsistent stone striae and a axes deforming fine textured subglacial till is considered as a subhorizontal shear zone rheologically layered with associated structures in descending order ductile e g isoclinal folds brittle ductile e g fissility and brittle e g till wedges rheology would be controlled mainly by till pore water content matrix texture and stone content spatial and temporal superposition of rheologies and subglacial processes probably occur