glaciotectonic deformations in the jammerbugt and glaciodynamic development in the eastern north sea the quaternary geology in the eastern part of the north sea is characterized by large scale glaciotectonic complexes the northernmost complex is the jammerbugt glaciotectonic complex here addressed which occupies an area of more than 300 km2 it was recently recognized during an investigation of conventional seismic profiles located about 10 km offshore the west coast of northern denmark the deformed bedrock includes the main part of the cretaceous chalk group in the north sea in the northern part of the complex the detachment surface is situated in lower cretaceous greensand about 400 m below sea level in the central part of the complex the thrusting ramps the strong reflectors at the base of the chalk group and the detachment surface continues in the lower part of the upper cretaceous chalk in the tectonic depression north of the complex marine and glaciomarine deposits represent the eemian early weichselian skaerumhede group indicating a saalian age of the glaciotectonic deformation the balancing of the thrust fault structures shows that the thrust sheets in the tailing end of the complex had their source in the skagerrak sea the hole caused by displacement contributed to formation of the skagerrak depression i e early stage of the norwegian trench

fluid pressure controlled soft bed deformation sequence beneath the surging breiðamerkurjokull iceland little ice age abstract the general subject of this paper is subglacial deformation beneath brei amerkurjokull a surging icelandic glacier more specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation during little ice age maximum the two outcrops studied north jokulsarlon n jk and brennhola alda ba were located at 2550 m and 550 m respectively from the front of the brei amerkurjokull sedimentological analysis at the forefield of the glacier shows thick coarse glaciofluvial deposits interbedded with thin fine grained shallow lacustrine swamp deposits overlain by a deformed till unit at n jk ba outcrop shows fine grained shallow lacustrine swamp deposits overlain by a deformed till unit the sequence of deformation events from one outcrop to the other is similar first major thrust planes which were rooted in shallow lacustrine swamp deposits developed by glacially induced simple shear next the thrusts were folded indicating the deformation of hydroplastic sediment assisted by moderate fluid pressure then clastic dyke swarms crosscut the sedimentary succession proving that fluid overpressure caused hydrofracturing associated with fluidisation finally as water escaped from the glacier bed fluid pressure dropped and normal faulting occurred in brittle state subglacial sediments fluid pressure variations are related to glacier dynamics they control the deformation sequence by modifying subglacial rheological behaviour and the nature of the subglacial tectonism

intrusion of basalt into frozen sediments and generation of coherent margined volcaniclastic dikes cmvds coherent margined volcaniclastic dikes cmvds are described for the first time from askja dyngjufjoll iceland these dikes display continuous coherent glassy margins 5 cm thick and have a variety of clastic interiors comprising vitric tephra pillow and pillow fragment bearing lapilli tuffs cmvds are interpreted to form when basaltic dikes interact with subglacial ice cemented volcaniclastic sediments formation requires chilling of dike margins drainage of the dike interior and flooding of the cavity by meltwater followed by non explosive mingling of magma clastics and water evidence for ice cementation includes minimal interaction with the host 3 mm peperite local pillowed dike margins and the preservation of continuous glassy coherent margins along the edge of a drained dike cavity cmvds should be present at other volcanic centers with ice cemented sediments including the martian cryosphere

book review glacial deposits in north east europe jurgen ehlers stefan kozarksi and phillip gibbard eds publisher a a balkema rotterdam 1995 ix 626 pp 92 00 isbn 90 5410 189 x

clastic dykes in over consolidated tills evidence for subglacial hydrofracturing at killiney bay eastern ireland abstract a swarm of vertical gravel filled dykes up to 6 m high and several decimetres wide cut through an over consolidated till at killiney bay the dykes are rooted in a gravel layer and many display plumes of clastic debris ejected into the overlying sediments burst out structures such features have not previously been described these clastic dykes are interpreted as the infillings of hydrofractures which formed when water pressures in the basal gravel layer exceeded the overburden pressure and tensile shear strength of the capping till the burst out structures extend up to 7 m from the tops of the dykes and provide strong evidence for forceful upward flow evidence suggests that the hydrofractures formed subglacially probably during a minor re advance their presence in late devensian 26 13 ka bp tills with an irish sea provenance irish sea till may have important implications for the subglacial hydrology of the last irish sea ice sheet these hydrofractures cannot form in unconsolidated glacimarine sediment and their presence precludes a glacimarine origin for these deposits they greatly affect the geotechnical properties of irish sea tills in particular providing very permeable routes through otherwise impermeable layers with important consequences in situations elsewhere in the irish sea basin where they have been used as aquicludes in landfill and low level nuclear waste disposal sites

the morphology structural evolution and significance of push moraines abstract push moraines glaciotectonic ice marginal moraines have a restricted distribution at modern glacier margins and consequently are of potential value in reconstructing pleistocene ice sheets providing data both on former glaciodynamics and on the palaeoenvironment of the glacial foreland to the wider earth science community push moraines are of interest as analogues for thin skin tectonics within orogenic belts this paper reviews the morphology structural geology formation and significance of push moraines the morphological and structural characteristics of small seasonal push moraines through to large multi crested examples produced by sustained glacier advances are reported before the primary controls on push moraine formation are examined these controls include the nature of the applied glacial stress field the presence and properties of decollement horizons and the shear strength and rheology of the glacial foreland a conceptual model of push moraine formation is introduced in which the range of observed morphological and structural forms are viewed within a matrix defined by the main variables which control their formation the absence of consensus over which of these variables is of greatest importance currently limits the significance of push moraines in palaeoglaciological research as a consequence this review emphasises the need for future research in order to realise the true potential of push moraine in the reconstruction of pleistocene environments

groundwater flow beneath ice sheets part ii its impact on glacier tectonic structures and moraine formation abstract meltwater flowing as groundwater from beneath the margin of an ice sheet determines the distribution of sub surface heads and effective pressures a subglacial groundwater flow model is used together with an ice sheet loading model to compute the magnitudes and directions of the principal effective stresses in the subsurface from which the distribution of different types of sub surface failure in the subglacial and proglacial zones are deduced zones of hydrofracturing shear fracture and pervasive shear failure are distinguished beneath the ice sheet divide area intact rocks of high tensile strength may fail hydrofracturing and liquefaction are two coupled processes which lead to the formation of upward filled and downward filled sediment dykes and till wedges quicksand conditions are developed where strong vertical seepage pressures occur producing sediment diapirism it is suggested that subglacial permeability magnitude may be the product of a self organising process certain types of moraine extrusion moraines are suggested to be a consequence of upward movement and surface extrusion of sediment driven by rising groundwater it is suggested that groundwater over pressure associated with narrow proglacial permafrost plates are conductive to the formation of large push moraines and that many large ancient and modern examples are produced in this setting

sedimentary and structural evolution of a pleistocene small scale push moraine in eastern poland new insight into paleoenvironmental conditions at the margin of an advancing ice lobe abstract recent studies of push moraines have focused on the interplay between the dynamics of ice margins and the environmental variables of the foreland into which they advance these studies showed that the spatial distribution geometry and style of the glaciotectonic deformation of push moraines are controlled by ice induced stresses the strain rate the rheology of the deposits and hydraulic conductivity in this work we provide new insight into this interplay at a small spatio temporal scale specifically the ancient glacial system of the liwiec ice lobe within the younger saalian ice sheet in eastern poland the paleoenvironmental variables that are analysed here refer to the dynamics of the hydrological processes that affected the patterns and sediment deposition rate on the terminoglacial fan and the resulting mechanical stratigraphy and hydraulic conductivity of the foreland we document the progradational sequence of the fan deposits that developed as a result of the ice lobe thickening and the steepening of its stationary front the sedimentary features of the fan the lithology of its basement and the hydraulic conductivity of the foreland strongly influenced the geometry and kinematics of fold growth during the advance of the ice lobe the predominance of flexural slip and the development of fractures including fold accommodation faults were interpreted to be an effect of buckle folding due to horizontal shortening induced by ice advance the partial overriding of the push moraine by the ice lobe and thus the submarginal conditions for deformation were inferred from the significant hinge migration and internal deformation of the strata under undrained conditions in one of the folds the synfolding deposition pattern of the fan growth strata allowed us to suggest that the push moraine was probably formed by a sustained advance rather than surge

3d basin modelling of the hammerfest basin southwestern barents sea a quantitative assessment of petroleum generation migration and leakage abstract 3d basin modelling of the hammerfest basin southwestern barents sea was performed in order to address the masses of petroleum generated accumulated and lost during the evolution of the basin calibration of the model based on observed maturity vitrinite reflectance and present day temperatures took into account 1 two main erosion episodes an oligocene miocene event due to tectonic uplift and a plio pleistocene glacial erosion event and 2 variable heat flow from late palaeozoic to cenozoic the maturity levels of the main source rocks kobbe snadd and hekkingen formations were reconstructed and show that the highest maturities have been reached in the western and northwestern margin of the basin the beginning of petroleum generation in the kobbe snadd and hekkingen source rocks has been predicted to occur during late triassic early cretaceous and late cretaceous respectively our model reproduces satisfactorily the distribution of the main oil and gas fields and discoveries that have been found in the study area our results indicate that two events of hydrocarbons redistribution occurred in the basin the first event resulted in the main oil redistribution episode which took place during the oligocene miocene associated with tectonic uplift and gas expansion and the second was related to the main gas leakage events that occurred during the pliocene pleistocene glacialinterglacial cycles in general and the episodes of glacial retreat in particular glacial loading and unloading cycles resulted in overpressure fluctuations in the subsurface reservoirs modelling results indicate that during these episodes a portion at least 0 247 gt of thermogenic gas leaked from the main sto formation reservoirs reached the sediment interface and was released to the surface in the hammerfest basin

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

introduction to the hydrogeochemical investigations within the international stripa project abstract the international stripa project 1980 1990 has sponsored hydrogeochemical investigations at several subsurface drillholes in the granitic portion of an abandoned iron ore mine central sweden the purpose has been to advance our understanding of geochemical processes in crystalline bedrock that may affect the safety assessment of high level radioactive waste repositories more than a dozen investigators have collected close to a thousand water and gas samples for chemical and isotopic analyses to develop concepts for the behavior of solutes in a granitic repository environment the stripa granite is highly radioactive and has provided an exceptional opportunity to study the behavior of natural radionuclides especially subsurface production extensive microfracturing low permeability with isolated fracture zones of high permeability unusual water chemistry and a typical granitic mineral assemblage with thin veins and fracture coatings of calcite chlorite seriate epidote and quartz characterize the site preliminary groundwater flow modeling indicates that the mine has perturbed the flow environment to a depth of about 3 km and may have induced deep groundwaters to flow into the mine

micromorphological evidence for polyphase deformation of glaciolacustrine sediments from strathspey scotland a combination of field investigation and micromorphological analysis has been applied to polydeformed late devensian rhythmites and glacigenic diamicton exposed in strathspey scotland this provided information on the geometry kinematics and relative ages of ductile and brittle structures and records a complex subglacial deformation history the deformation is interpreted as resulting from a single progressive event associated with over riding of proglacial lake sediments by wet based ice the earliest deformation d1 resulted from compaction loading pure shear and imposed a bedding parallel s1 fabric throughout the rhythmites s1 was subsequently deformed by kink bands and minor ductile shearing during d2 a later d3 event characterized by soft sediment deformation and fluidization of matrix poor sands was accompanied by an increase in pore water pressure this lead to hydrofracturing of the rhythmites the most intense deformation d4 which resulted from simple shear was partitioned into the upper part of the sequence it produced folding thrusting and brittle microfaulting in response to nnw directed ice push these findings indicate that in general subglacial deformation is not homogeneous and can extend to depths of 3 m below the presumed ice sediment interface

antarctic marine gravity field from high density satellite altimetry summary closely spaced satellite altimeter profiles 5 km collected during the geosat geodetic mission geosat gm and those planned for the extended ers 1 mission are easily converted to grids of vertical gravity gradient and gravity anomaly as profile spacing decreases it becomes increasingly difficult to perform a crossover adjustment on the original geoid height profiles without introducing large cross track gradients if one is only interested in the horizontal and vertical derivatives of the gravitational potential however adjustment of the profile is unnecessary the long wavelength radial orbit error is suppressed well below the noise level of the altimeter by simply taking the along track derivative of each profile ascending and descending slope profiles are then interpolated onto separate uniform grids these two grids are summed and differenced to form comparable grids of east and north vertical deflection using laplace s equation the vertical gravity gradient is calculated directly from the vertical deflection grids fourier analysis is required to construct gravity anomalies from the two vertical deflection grids these techniques are applied to high density 2 km profile spacing geosat gm profiles in antarctic waters 60 s to 72 s gridding and interpolation are performed using the method of projection onto convex sets where the smoothness criteria corresponds to upward continuation through 4 km of ocean the resultant gravity grids have resolution and accuracy comparable to shipboard gravity profiles after adjustment of a dc shift in the shipboard gravity profiles 5 mgal the rms difference between the ship and satellite gravity is 5 5 mgal many interesting and previously uncharted features are apparent in these new gravity maps including a propagating rift wake and a large leaky transform along the pacific antarctic rise

the paleoclimatic significance of deformation structures in neoproterozoic successions abstract this paper reviews the different types of soft sediment deformation structures that can form in glacial and non glacial settings and explores the potential use of these structures in resolving long standing debates in paleoenvironmental reconstructions of neoproterozoic glacigenic successions soft sediment deformation structures are created when compressional gravitational or shear stress is applied to unlithified sediments during or shortly after deposition in subglacial or ice marginal glacial settings shear and compressional stress imparted by ice moving on top of a deformable substrate or advancing ice buldozing unlithified ice marginal sediments can result in a wide range of folding faulting and shear structures in glaciofluvial or stagnant ice marginal setting gravitational collapse and remobilization of sediments associated with the melting of buried ice can result in normal faulting and broad folding in glaciolacustrine or glaciomarine settings compressional shear and gravitational types of deformation structures can occur as a result of grounding ice or icebergs rapid sedimentation and reworking downslope associated with high sedimentation rates in non glacial settings similar deformation structures can form as a result of slope instability and reworking of sediments downslope rapid sedimentation seismic shaking wave induced shearing or loading in this context two case studies are presented to demonstrate the type of paleoenvironmental information that an analysis of deformation structures can provide in the first case study analysis of deformation in the port askaig formation scotland reveals a distinctive stratigraphic distribution of deformation structures the types of deformation observed together with their recurrence over several 100s of meters and their basinal context are used to infer a seismic origin for the deformation which in turn suggests a significant tectonic control on sedimentation atop a record of ice margin fluctuations in a glaciomarine setting in the second example analysis of deformation in the smalfjord formation northern norway provides strong evidence for deformation by active ice overriding glaciofluvial deposits the types of deformation in this example together with its complexity scale and associated facies provide the strongest case for ice marginal deformation in sum analysis of deformation structures together with analysis of structural geology stratigraphy facies and facies associations can provide additional constraints on paleoenvironmental conditions at the time of deposition which can help us refine or test paleoenvironmental models proposed for this critical time period in earth history

mechanisms of englacial conduit formation and their implications for subglacial recharge abstract ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by shreve 1972 movement of water in glaciers journal of glaciology 11 62 205 214 the shreve model is based on three main assumptions 1 englacial drainage is in steady state 2 englacial water will flow along the steepest hydraulic gradient within the glacier and 3 pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls the shreve model has been widely adopted as a fundamental component of englacial drainage theory there is no evidence however that the model provides a realistic picture of actual glacial drainage systems to evaluate shreve s theory we used speleological techniques to directly survey englacial conduits we mapped a total of 8 25 km of passage in 27 distinct englacial conduits in temperate polythermal cold based and debris covered glaciers between 2005 and 2008 new information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176 m using speleological techniques in all cases englacial drainage systems consisted of a single unbranching conduit englacial conduit morphologies were found to be intimately linked to the orientation of a glacier s principal stresses or the presence of pre existing lines of high hydraulic conductivity if a sufficient supply of water is available hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive on unfractured glacier surfaces relatively shallow subhorizontal conduits with migrating nickpoints form by cut and closure provided channel incision is significantly faster than surface lowering conduits can also form along permeable debris filled crevasse traces that connect supraglacial lake basins of different potential our results suggest that shreve type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect or are advected through zones of acceleration

howe lake a hydrodynamic blowout structure howe lake formerly called goudie lake is an unusual feature of southeast saskatchewan almost perfectly circular diameter 295 m it is much deeper 26 m than almost any other prairie lake i

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

in absurdum long term predictions and nuclear waste handling abstract careful use of scientific knowledge allows predictions into the future when the time units for our predictions increases to hundreds of thousands of years we have extended our abilities in absurdum this is true for long term safety statements regarding the handling of our high level nuclear waste the fennoscandian shield has been claimed to offer exceptionally stable bedrock conditions over immense time periods we only need to go back to the last deglacial phase some 10 000 years ago to have a totally different situation from that of today at that time sweden was characterized by exceptionally high seismic activity both in amplitude and frequency these conditions like a number of related phenomena will be repeated at future ice ages in such an environment there can be no safe repository in the bedrock in the absence of true long term safety we can only recommend the utilization of the dry rock deposit drd method where the waste is stored in the bedrock under dry conditions under constant control and monitoring accessible for maintenance and possible future methods of rendering the waste harmless and even removal

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

the deforming bed characteristics of a stratified till assemblage in north east anglia uk investigating controls on sediment rheology and strain signatures the glacial coastal exposures of north norfolk are a type site for subglacial glaciotectonic deforming bed sediments this investigation of the lower stratified diamict within the north sea drift at west runton reveals two distinct lamina types type 1 laminae are the product of primary extensional glaciotectonism with ductile intergranular pervasive shear predominating over brittle shear type 2 laminae also exhibit structures that can be attributed to ductile intergranular pervasive shear and brittle shear but the lateral continuity of type 2 laminae and the presence of dropstone like structures supports a primary subaqueous origin with secondary subglacial deformation when coupled with micromorphological analysis these findings show that ductile viscous creep mechanisms control sedimentary architecture and that shear stratification in particular has the potential to affect the rheological properties of the sediment pile and the hydraulic routing of basal water ultimately influencing critical effective pressure fluctuations and the thresholds controlling the subglacial drainage system

a review of metal transfer mechanisms through transported cover with emphasis on the vadose zone within the australian regolith abstract there is a growing trend to try to make surface geochemistry effective for exploring areas of transported cover using sensitive techniques such as partial extractions of soil and gas analysis however these techniques have had mixed success in delineating buried ore bodies because the particular mechanisms and their effectiveness in transferring ore related metals upwards through transported cover are poorly understood this precludes discriminating null results a potentially ineffective technique from negative results no mineralization a review of mechanisms capable of transferring metals through barren transported cover to the surface identified those well documented and others not well studied but nonetheless promising the mechanisms are classified according to two main processes phreatic process involving groundwater flow convection dilatancy bubbles diffusion and electromigration and vadose processes involving capillary migration gaseous transport and biological transfer microbial metabolism affects the kinetics of many hydrochemical processes especially sulfide oxidation and other redox transfers and also impacts negatively and positively on the generation of gases throughout the entire cover sequence phreatic mechanisms require groundwater to transfer solutes and are most effective these have the most predictive capability where there are shallow water tables in the australian landscape groundwater occurs commonly more than 5 m below surface except in lower discharge landform sites and therefore other mechanisms biological capillary gaseous are necessary to transfer metals up from the water table thus much of the emphasis in this paper is on vadose processes an integrated approach is necessary combining different mechanisms with the nature and evolution of the transported cover and climatic settings regions and landforms of highly weathered transported cover with current or past water tables residing within the cover and long standing vegetation will favor combined mechanisms such as electrochemical plant uptake capillarity and bioturbation fresh relatively unweathered and thick 30 m transported cover may prove the most unlikely to develop surface geochemical anomalies gas e g co 2 h 2 s mechanisms may work provided that sufficient gases are generated from the oxidation of ore to produce a surface signature

the athabasca fluting field alberta canada implications for the formation of large scale fluting erosional lineations abstract current drumlin and fluting hypotheses centred on processes of formation erosion and deposition by subglacial deformation accretion by lodgement glacial erosion and meltwater erosion and deposition rarely receive comprehensive field testing this paper documents the morphology internal structure and landscape associations of the athabasca fluting field alberta and discusses how well these characteristics are explained by postulated fluting forming processes fluting hypotheses are comprehensively tested by this approach and their rejection or acceptance are firmly based on field observation and knowledge of processes using multiple criteria fluting is shown to be erosional and not to be a product of pervasive subglacial deformation or accretion by lodgement morphology landscape associations bed truncation plus glaciofluvial lags and gravel on fluting ridges are inferred to support erosion by meltwater intact primary bedding synsedimentary faults and injection structures very close to the landsurface showing no sign of shear deformation are used to reject erosion by subglacial deformation fluting is shown to be closely associated with tunnel channels and indicates that these channels were overtopped by broad floods that formed the fluting field and eroded anabranching tracts over the length of the alberta plains prior to fluting formation sequences with melt out and lodgement till conduit sediment and boulder lags record net deposition over an extended time period diapirism prior to fluting formation marks a period of extreme pressure gradients which are related to bed separation following fluting formation there was only minimal landscape modification dominated by glaciofluvial and glaciolacustrine deposition not glacial processes this progression is presented as evidence for two very different glacial regimes separated by a short period with diapirism and extensive landscape modification by meltwater erosion we note that the study area was glaciated only once during the late wisconsinian and it follows that glacial sedimentation and landscape modification were confirmed to this single glacial episode

merging diverse data sets to reveal anomalies in the earth s gravitational field gravity measurements determined from shipboard surveys are based on direct detection of the local gravitational field whereas those measured using satellite data are determined using altimetry measurements of the sea surface topography the satellite based gravity determinations use repeated measurements of the sea surface topography along erm profiles enabling estimates of along track precision and resolution to be made shipboard based gravity measurements are limited to single observations methods for merging these two diverse sets of gravity data have been developed based on a stochastic approach using kriging this stochastic approach appears to provide a generally applicable method of estimation particularly in regions of variable spacing between measurement points

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

a numerical investigation of ice lobe permafrost interaction around the southern laurentide ice sheet permafrost existed around and under marginal parts of the southern laurentide ice sheet during the last glacial maximum the presence of permafrost was important in determining the extent form and dynamics of ice lobes and the landforms they produced because of influences on resistance to basal motion and subglacial hydrology we develop a two dimensional time dependent model of permafrost and glacier ice dynamics along a flowline to examine i the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology and ii the influence of permafrost on ice motion and surface profile the model is applied to the green bay lobe which terminated near madison wisconsin during the last glacial maximum simulations of ice advance over permafrost indicate that the bed upstream of the ice sheet margin was frozen for 60 200 km at the glacial maximum permafrost remained for centuries to a few thousand years under advancing ice and penetrated sufficiently deep tens of meters into the underlying aquifer that drainage of basal meltwater became inefficient likely resulting in water storage beneath the glacier our results highlight the influence of permafrost on subglacial conditions even though uncertainties in boundary conditions such as climate exist

glacier permafrost interactions processes products and glaciological implications abstract glaciers and permafrost represent key components of the global cryosphere widely held assumptions that 1 they are largely mutually exclusive and 2 glaciers resting on permafrost are slow moving and geomorphologically ineffectual have meant that glacier permafrost interactions have been given little attention within the research literature recent research however has demonstrated that such interactions are likely to have been more extensive than previously thought particularly during periods of ice sheet growth when glaciers would have advanced over pre existing permafrost work in both modern and ancient environments has revealed that subglacial processes such as basal sliding and subglacial sediment deformation can remain active at temperatures below the pressure melting point due to the persistence of premelted liquid water consequently cold based glaciers resting on permafrost are potentially more dynamic than previously thought and are capable of creating subglacial features typically viewed as only forming beneath warm based ice in addition the active coupling of cold based ice with ice marginal permafrost means such ice masses are capable of deforming sediments and occasionally bedrock to depths of tens or even hundreds of meters and are commonly associated with the development of a range of distinctive ice marginal landforms including push or thrust moraines and hummocky or controlled moraines this reflects the influence of permafrost on the entrainment of debris rich basal ice as well as the hydraulic transmissivity of the groundwater system and the associated porewater pressures within the substrate this review considers the key characteristics of permafrost and its formation likely extent and rheological behaviour within glacial environments traditional conceptions regarding the motion and landscape impact of cold based glaciers resting on permafrost are considered before their re examination in light of recent work demonstrating the operation of basal processes at sub freezing temperatures the implications for our understanding of the dynamics of glaciers and ice sheets as well as landforms and sedimentary sequences indicative of glacier permafrost interactions are explored and exemplified with reference to modern and ancient glacial environments gaps in our existing knowledge are identified and profitable areas for future research suggested

recent tectonic activity of the gafsa fault through morphometric analysis southern atlas of tunisia abstract this article focuses on the neotectonics of the southern atlas of tunisia based on morphometric analyses five major relevant morphometric parameters were processed and analyzed residual topography hypsometric index drainage anomalies maximum vertical curvature and terrain roughness and compared to the structural and tectonics of the study area these are relevant to describe the topographic changes and therefore suggest possible neotectonic activity the analysis of these morphometric indices reveals that two structures in the study area jebels ben younes and bou ramli are distinguished by a specific morphometric footprint high residual topography high hypsometric integral value of some watersheds hi 0 6 high frequency of drainage anomalies high maximum vertical curvature and high roughness index the correlation of these geomorphic indices with the structural pattern of the study area confirms the neotectonic reactivation dating from the quaternary and the dextral strike slip component of the gafsa fault the major tectonic feature in the southern atlas of tunisia thus the morphometric analysis of the digital elevation model and the drainage network provide a more accurate insight into the morphodynamics of the study area

tensile and shear fracturing in predominantly compressive stress fields a review abstract many rock engineering geologic problems can be better solved if the genesis of rock fractures rock joints is understood this paper concentrates on tensile fractures and shear fractures created in predominately compressive stress fields such fractures prevail in many areas stress based and fracture mechanics based concepts are introduced they are used to show how tensile fractures are created how shear fractures can be produced through coalescence of tensile fractures and how shear fractures and tensile fractures can be created simultaneously which of these mechanisms acts depends on the particular combination of stress field and material properties laboratory experiments and observations in nature obtained from an extensive literature review strongly support the theoretical predictions they also show that actual fracture patterns are often produced by a combination of mechanisms acting simultaneously or in sequence the better understanding of fracture genesis which should result from this paper is not only interesting by itself but is useful when interpreting exploration results

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

a complex subglacial clastic dyke swarm solheimajokull southern iceland abstract a complex network of clastic dykes dissects loosely consolidated holocene sediments along the east flank of the proglacial braid plain of solheimajokull southern iceland the dykes comprise downward bifurcating intrusions up to 0 5 m thick and several metres in length and are intruded into glaciogenic deposits sandy gravel gravelly sand interlaminated silt and sand and diamicton the dykes were sourced from a clast poor sandy diamicton interpreted as a subglacial till and were intruded downwards beneath solheimajokull glacier during a previous phase of advance as the glacier advanced southwards it loaded the sediment column resulting in the intrusion of dykes with a consistent south southwest dip with rare northward dipping examples the dyke fills are characterised by laminated sediment with laminae oriented parallel to the dyke margins and comprise interlaminated clay silty clay silt sand sandy gravel and diamicton in some dykes high concentrations of pebble to boulder sized clasts occur in association with rotated pods of the laminated sediment the laminae are thought to have evolved by a slow long lived intrusion process that involved the repeated fracture and expansion of the host sediments followed by viscous smearing on of subglacial material onto the dyke walls rather than rapid injection of fluidised sediment

pleistocene recharge to midcontinent basins effects on salinity structure and microbial gas generation the hydrogeochemistry of saline meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history chemical evolution of basinal brines and physical stability of saline formation waters during episodes of freshwater recharge this is especially germane for interior cratonic basins such as the michigan and illinois basins although there are large differences in formation water salinity and hydrostratigraphy in these basins both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the pleistocene exploration for unconventional microbial gas deposits which began in the upper devonian age antrim shale at the northern margin of the michigan basin has recently extended into the age equivalent new albany shale of the neighboring illinois basin providing access to heretofore unavailable fluid samples these reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry new formation water and gas samples were obtained from devonian mississippian strata in the illinois basin these included exploration wells in the new albany shale an organic rich black shale of upper devonian age and formation waters from over and underlying regional aquifer systems siluro devonian and mississippian age the hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the illinois basin critically influenced fluid migration into the new albany shale the new albany shale formation water chemistry indicates significant invasion of meteoric water with d values as low as 46 05 into the shale the carbon stable isotope system 13c values as high as 29 4 coupled with 18o d and alkalinity of formation waters alkalinity 24 08 meq kg identifies the presence of microbial gas associated with meteoric recharge regional geochemical patterns identify the underlying siluro devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured new albany shale reservoirs recharge from overlying mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the new albany shale recharge of dilute waters cl 1000 mm into the siluro devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern illinois basin margin taken together with salinity and stable isotope patterns in age equivalent michigan basin formation waters they suggest a regional impact of recharge of 18o and d depleted fluids related to pleistocene glaciation devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane this recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity given the relatively quiet tectonic history and subdued current topography in the midcontinent region it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale hosted gas deposits

structural architecture and glacitectonic evolution of the mud buttes cupola hill complex southern alberta canada this paper presents the results of a detailed multidisciplinary study of the deformed bedrock and overlying quaternary sediments exposed at the mud buttes in southern alberta canada this large arcuate cupola hill is composed of intensely folded and thrust sandstones siltstones and mudstones of the cretaceous belly river group glacitectonism responsible for the development of this internally complex landform occurred at the margin of the newly defined prospect valley lobe of the laurentide ice sheet analysis of the deformation structures reveals that construction of this landform occurred in response to at least two phases of south directed ice sheet advance separated by a period of retreat the first phase led to the formation of a forward propagating imbricate thrust stack leading to polyphase deformation of the belly river group d1 thrusting led to the detachment of thrust bound slices of bedrock which were accreted to the base of the developing imbricate stack this process resulted in the structurally higher and older thrust slices being progressively back rotated tilted accompanied by d2 thrusting and folding further thrusting during d3 was restricted to the core of the mud buttes as the deforming sequence accommodated further compression imposed by the advancing ice minor oscillations of the ice margin led to localised brittle ductile shearing d4 of the bedrock immediately adjacent to the ice contact part of the thrust stack the second phase of ice advance led to the accretion of a relatively simple thrust and folded sequence seen the northern side of mud buttes the resulting composite thrust moraine was subsequently overridden by ice advancing from the nnw to form a dome like cupola hill this readvance of the prospect valley lobe led to the formation of a thin carapace of quaternary sediments mantling the mud buttes which include glacitectonite till and an organic rich clay silt palaeosol

coeval brittle and ductile deformation beneath the late wisconsinan puget lobe washington state usa late wisconsinan glacial sediments exposed on whidbey island and camano island puget sound washington state usa were deposited in a proglacial shallow marine outwash environment during northward retreat of the puget lobe of the cordilleran ice sheet sediments mainly comprise massive and cross bedded sand and gravels and rhythmically bedded clay and silt fine sand couplets interbedded with diamictons that were deposited by a range of mass flows of different viscosities although sediment stratigraphy and ice advance retreat patterns are well established for the puget lobe brittle and ductile deformation structures within and separating these sediment units are less well understood these structures record the nature of ice bed interactions taking place in subglacial and proglacial environments this study examines evidence for these processes and environments key deformation structures identified include open to overturned folds normal and reverse faults clastic dikes and hydrofractures and passive loading structures evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes sediment rheology and sediment system responses to changes in strain caused by ice bed interactions

penecontemporaneous non tectonic brecciation of unconsolidated silts and muds abstract at several localities sediments have been found which partly or completely consist of angular fragments from the geological context it is clear that the fine grained parent material was broken up after deposition this cannot be explained by endogenic forces so that sedimentary and diagenetic penecontemporaneous processes must be the cause occurrences from poland and the netherlands are described together with an analysis of the brecciation processes these breccias are the result of pressure which may have been cryostatic or caused by bioturbation flowage of liquified material or similar processes

estimating hydrogeological conditions over the last 120 ka an example from the sellafield area uk for a number of years united kingdom nirex limited investigated the suitability of the area around sellafield in nw england to assess its suitability to host a deep repository for intermediate level and some low level radioactive wastes resulting from britain9s nuclear programme the investigation programme collected a large amount of lithological hydrogeological and hydrochemical data from 18 boreholes up to 2000 m deep a potential route by which radionuclides may leave the repository and return to surface is the groundwater pathway it was recognized that the groundwater regime could be disturbed significantly by major climate changes particularly glacial interglacial cycles over the very long time scales considered in the assessment of the radiological safety of a repository available geological and hydrogeological data for the sellafield area are reviewed in the context of current thinking on glacial hydrogeology showing that disturbance of the hydrogeological regime is possible during glaciation and that there are significant uncertainties in determining the timing and magnitude of the effects caused by glaciation however the evidence available both from quaternary fracture filling minerals and from the chemistry of groundwater now present suggests that any disturbance to the deeper hydrogeological regime was relatively minor and that any subglacial recharge has been removed by the present flow regime there is a possibility that high hydraulic heads at depth in the low permeability basement rock considered as a host for the repository the borrowdale volcanic group of ordovician age beneath a cover of triassic sandstones may be residual

melt out till and ribbed moraine formation a case study from south sweden abstract hummocky moraine with dispersed agglomerations of ribbed moraine here named asnen type ribbed moraine forms a 20 40 km wide zone over smaland south sweden terminated to the north by a sharp boundary to streamlined terrain the hummocky ribbed moraine zone can be geomorphologically linked to the subaqueous goteborg moraine formed at an oscillation stand still phase during the deglaciation of the swedish west coast based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt out from stagnant debris rich ice with synsedimentary deposition of sorted sediments preferentially at a melting ice bed interface to accommodate for the geomorphological expression such an interpretation further implies that debris rich ice formed in an intermediate adfreezing zone between ice at the pressure melting point and a frontal frozen zone at deglaciation basal debris rich ice was stacked into transversally arranged zones controlled moraine forming ribbed moraine embryos the active phase of ridge formation the stacked sequences of debris rich ice eventually melted out beneath a stable and melt retarding supraglacial ablation complex to form the final moraine ridges the passive phase of ridge formation in areas with no stable supraglacial ablation complex the resulting landform after final de icing was a hummocky moraine landscape internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments intercalated with stream deposited sediments all resting on a platform of subglacial melt out till de icing of the zone now occupied by hummocky and ribbed moraine took a considerable time deglacial 14 c age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary and that it took another 200 300 yr for the stagnant ice zone to melt during the final formation of present day landforms

consolidation of sediments by glaciers relations between sediment geotechnics soft bed glacier dynamics and subglacial ground water flow a theory of subglacial consolidation is developed which shows how the meltwater flux beneath a glacier leaves a consolidation signature from which many important glacier dynamic properties can be inferred conditions under which water is discharged through channels or in a thin film at the ice bed interface or by ground water flow are discussed and it is concluded that glaciers flowing over aquifers of high transmissibility can induce deep circulation patterns quite different from non glacial circulation

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

tectonic fabric map of the ocean basins from satellite altimetry data abstract satellite altimetry data provide a new source of information on the bathymetry of the ocean floor the tectonic fabric of the oceans i e the arrangement of fracture zones ridges volcanic plateaus and trenches is revealed by changes in the horizontal gravity gradient as recorded by satellite altimetry measurements seasat and geosat altimetry data have been analyzed and a global map of the horizontal gravity gradient has been produced that can be used to identify a variety of marine tectonic features the uniformity of the satellite coverage provides greater resolution and continuity than maps based solely on ship track data this map is also the first global map to incorporate the results of the geosat mission and as a result new tectonic features are revealed at high southerly latitudes this map permits the extension of many tectonic features well beyond what was previously known for instance various fracture zones such as the ascension tasman and udintsev fracture zones can be extended much closer to adjacent coninental margins the tectonic fabric map also reveals many features that have not been previously mapped these features include extinct ridges minor fracture zone lineations and seamounts in several areas especially across aseismic plateaus or along the margins of the continents the map displays broad gravity anomalies whose origin may be related to basement structures

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

controlled moraines origins characteristics and palaeoglaciological implications abstract controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de icing and possess clear linearity due to the inheritance of the former pattern of debris rich folia in the parent ice linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt out as a result moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris rich ice was concentrated in frozen toe zones recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that a controlled moraine development can be ascribed to a specific process e g englacial thrusting or supercooling and b controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts e g ancient polythermal or supercooled snouts these assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris rich ice thickening mechanisms are seen to produce the same geomorphic features polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier permafrost interface end moraines lie on a process form continuum constrained by basal thermal regime the morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores but the final deposits landforms tend to consist of discontinuous transverse ridges with intervening hummocks preserving only a weak impression of the former englacial structure these are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice walled lake plains and lying down flow of streamlined landforms produced by warm based ice a variety of debris entrainment mechanisms can produce the same geomorphic signature spatial and temporal variability in process form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin

the role of meltwater in glacial processes abstract water plays a dominant role in many glacial processes and the erosional depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized at its maximum extent c 20 000 years ago the volume of the laurentide ice sheet was 33 106 km3 about the same as the volume of all ice present today on planet earth the bulk of this was released as water in little more than 10 000 years pulses of meltwater flowing to the atlantic ocean from large ice dammed lakes altered thermohaline circulation of the world s oceans and global climate one such discharge event via hudson bay at 8200 years bp released 160 000 km3 of water in 12 months global sea levels recovered from glacial maximum low stands reached at about 20 000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods rates as high as 4 m per hundred years meltwaters played a key role in lubricating ice sheet motion and thus areal abrasion across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the canadian shield the recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments till by sliding induced shearing and deformation of overpressured sediment and soft rock the transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates some workers credit catastrophic subglacial megafloods with the formation of drumlins and flutes on till surfaces subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins it has been estimated that less than 6 of the total volume of glaciclastic sediment produced during the pleistocene remains on land fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the glacial landscape in north america the recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long term equilibrium flow directions of basinal fluids with regard to pre pleistocene glacial record meltwaters moved enormous volumes of terrestrial glaciclastic sediment to marine basins and thus played a key role in preserving a record of glaciation a record otherwise almost entirely lost on land

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

mid pleistocene thin skinned glaciotectonic thrusting of the aberdeen ground formation central graben region central north sea this paper presents the results of a high resolution 2d seismic survey of mid pleistocene glaciogenic sediments in the central graben region of the central north sea sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid pleistocene ice sheet the total observed length of the thrust stacked section is approximately 5 6 km comprising a series of discrete thrust slices which range in length from 700 m the basal detachment of the thrust complex occurs at a depth of ca 220 m below the sea bed within the upper aberdeen ground formation a thin skinned glaciotectonic model involving proglacial to ice marginal glaciotectonic thrusting followed by post tectonic deposition is proposed initial ice advance led to the over pressurizing of groundwater within a laterally extensive sand sheet in the upper aberdeen ground formation promoting the formation of a major decollement surface at the base of the developing thrust stack over pressurization of the groundwater system is thought to have occurred in response to rapid ice advance suggesting that the development of large scale thrust complexes may be associated with surge type behaviour the proposed model evidences complex dynamics of mid pleistocene ice sheets within the central north sea

subglacial deformation and water pressure cycles as a key for understanding ice stream dynamics evidence from the late ordovician succession of the djado basin niger subglacial deformation is crucial to reconstructing glacier dynamics sediments associated with the late ordovician ice sheet in the djado basin niger exhibit detailed structures of the subglacial shear zone three main types of subglacial shear zones ssz are discriminated the lowermost ssz developed on sandstones displays riedel macrostructures and cataclastic microstructures these resulted from brittle deformation associated with strong glacier bed coupling and low pore water pressure where they developed on a clay rich bed the overlying ssz display s c to s c fabrics sheath folds and dewatering structures these features indicate high ductile shear strain and water overpressure on fine grained sand beds the ssz exhibit homogenized sand units with sand stringers interpreted as fluidized sliding beds the succession of subglacial deformation processes depends on fluid pressure behavior in relation to subglacial sediment permeability fluid overpressure allows subglacial sediment shear strength and ice bed coupling to be lowered leading to ice streaming

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

hydrogeological implications of glacial landscape evolution at skeiðararsandur se iceland abstract patterns of groundwater recharge and flow in present day and palaeo glacial environments are governed by both geomorphology and subsurface sedimentology this paper assesses the hydrogeological implications of glacial landscape evolution and develops a conceptual model of glacial landscape evolution and hydrogeological interaction the ice marginal zone of skei ararsandur se iceland was selected as a case study of a temperate actively receding glacier landsystem that is affected by both surging behaviour and periodic glacier outburst floods jokulhlaups the groundwater table elevation was measured approximately every 2 5 days throughout two six week summer field seasons in 2000 and 2001 and once in march 2001 using a network of shallow piezometers and hydraulic conductivity was calculated based on grain size distribution analysis of sampled aquifer materials the hydraulic conductivity of the near surface aquifer at the study site spans three orders of magnitude and is highest and most varied in areas inundated by the november 1996 jokulhlaup the shallow water table in the study area responds dynamically to precipitation events with the greatest fluctuation in an enclosed moraine lake basin with a perched aquifer underlain by ice and in a zone of outwash fans proximal to the ice margin the seasonal decline in water table is greatest at the ice margin reflecting the reduced winter recharge from the stagnant ice zone landsystems with morainic relief are associated with localised moraine precipitation fed groundwater systems these localised groundwater systems are superimposed on the intermediate regional scale groundwater systems that discharge further down sandur and offshore and are dominated by the gently sloping geomorphologically uniform outwash plain groundwater fed lakes formed in depressions from ice blocks deposited during jokulhlaups may provide important ecological niches the investigations at this site demonstrate that glacial outburst floods and glacier margin fluctuations produce a suite of sediments landforms and environments that affect the hydrogeological system

the origin and glaciodynamic significance of sandstone ridge networks from the hirnantian glaciation of the djado basin niger the djado basin niger was located beneath the inner part of the late ordovician ice sheet the felar felar formation consists mainly of glaciomarine deposits associated with the major ice sheet recession within the glaciation and is bounded by two glacial unconformities structures corresponding to sandstone ridges are found within the felar felar formation sandstone ridges are several metres high about 10 m wide and hundreds of metres long these structures are organized in extensive anastomosed to subpolygonal networks the association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub glacial conditions for their origin sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the felar felar formation by sub glacial turbulent and pressurized meltwater then subglacial cavities were infilled with sand derived from glacial abrasion sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo ice sheet

aligned glaciotectonic rafts on the central barents sea seafloor revealing extensive glacitectonic erosion during the last deglaciation 1 erosion rates on glaciated continental shelves are remarkably high especially within ice stream troughs although glaciotectonic erosion may have considerably contributed to enhanced glacial erosion of these landscapes entrainment mechanisms of glaciotectonically emplaced megablocks and rafts remain little understood here we report a northeast southwest trending chain of over 1300 glacial rafts observed on the seafloor in bjornoyrenna a paleo ice stream trough with particularly high erosion rates the landform assemblage adjacent to the glacial rafts includes streamlined bedforms and crevasse squeeze ridges and may represent a lateral shear zone where a paleo ice stream met cold stagnant ice during the last deglaciation individual glacial rafts along the chain are up to 30 m high tend to be elongated with lengths and widths on the order of tens of meters and are oriented from northeast southwest to north south the north southern rearrangement of rafts may reflect a compressional strain regime along the ice stream margin