modelling of the evolution of ground waters in a granite system at low temperature the stripa ground waters sweden abstract from chemical data collected by nordstrom and his colleagues on stripa ground waterswe have tried to model the evolution of the chemical composition of a ground water in a granitic system at low temperature the existence of two end member ground water compositions made it possible first to test the conventional model of a geothermal system according to which an overall equilibrium between the waters and a given mineral assemblage can be defined and then to show that such a model could be extended to low temperatures 10 c conversely if we know the mineral assemblage the equilibration temperature and the charge of the mobile ions in this case cl the composition of the solution is entirely fixed in our model of the stripa ground waters the existence of two end member ground water compositions can be explained by an evolution from a kaolinite albite laumontite equilibrium to a prehnite albite laumontite equilibium the latter requiring less al than the former we have also emphasized the importance of the cl ion concentrions ofof the ground waters because they cab be considered as indicators of the degree of reaction progress between rock and water thus determining the degree of equilibration of the system

thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

assemblages of submarine landforms produced by tidewater glaciers in svalbard 1 high resolution swath bathymetry from the marine margins of several svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging these landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity swath images comprise an assemblage of superimposed landforms allowing reconstruction of relative age of deposition 1 large transverse ridges interpreted as recessional moraines overridden by a subsequent ice advance 2 a series of curvilinear streamlined bedforms orientated parallel to former ice flow interpreted as lineations formed subglacially during rapid advance 3 large terminal ridges marking the farthest extent of ice at the last advance with flow lobes immediately beyond interpreted as submarine debris flows 4 a series of interconnected rhombohedral ridges interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed probably formed during immediate post surge stagnation and 5 a series of fairly evenly spaced small transverse ridges interpreted as push moraines produced annually at tidewater glacier termini during retreat a simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations we also show that megascale glacial lineations can form not only beneath large ice streams but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds

solute transport in formations of very low permeability profiles of stable isotope and dissolved noble gas contents of pore water in the opalinus clay mont terri switzerland pore water profiles of water stable isotope and dissolved noble gas content have been determined across the opalinus clay and adjacent formations at the rock laboratory at mont terri we have found enhanced helium contents up to 4he 1 10 4 cubic centimeters at standard pressure and temperature per gram of pore water and argon isotope ratios 40ar 36ar ratios up to 334 due to accumulation of 4he and 40ar produced in situ the helium profile was found to be in steady state with respect to in situ production and diffusive loss into the adjacent limestones where groundwater circulates from this profile a representative mean value of the apparent diffusion coefficient for helium in the pore water of the whole formation was derived for the first time to be da 3 5 10 11 m2 s 1 which is more than two orders of magnitude lower than the diffusion coefficient d0 in free water the stable isotope profile however indicates a component of fossil marine pore water which has not yet been replaced by molecular diffusion of meteoric water from the adjacent limestone and shale formations over the past 10 million years

late cenozoic geological development of the south voring margin mid norway abstract late cenozoic seismic stratigraphy of the voring continental margin has been studied in detail with emphasis on the geological development of the naust formation deposited during the last 3 million years the kai formation 15 3 ma comprises mainly biogenic ooze deposited in the more and voring basins in naust time there was a marked increase in supply of sediments from the inner shelf areas and the western part of the scandinavian mountain range and glaciers expanded to the shelf and reached the shelf edge several times during the last 1 5 2 million years during early to mid naust time the shelf was widened by westerly prograding sediment units but for a long period the shallowest part of the helland hansen arch hha formed a barrier preventing glacially derived debris from being distributed farther west west of the hha mainly stratified marine and glacimarine sediments were deposited a substantial part of these sediments were transported by the north flowing norwegian atlantic current which redistributed suspended particles from ice streams rivers coastal erosion and seabed winnowing after burial of the crest of the hha at c 0 5 ma glacial debris and slide deposits were also deposited west of this high in the north massive units of glacial debris were distributed beyond the crest of the hha also in mid naust time thinning westwards and interfingering with fine grained sediments on the lower slope the sklinnadjupet slide inferred to be c 250 000 years old corresponds in age with an earlier huge slide in the storegga area an elongated area of uneven seabed topography previously interpreted as diapirs vigrid diapirs on the slope west of the hha is shown to be formed by ooze eruption from the crest of the arch and submarine sliding

glacial morphology and sediment formation in the mertz trough east antarctica abstract the nathaniel b palmer 01 01 cruise produced a seabeam map showing unprecedented detail of the bathymetry in the mertz trough of east antarctica in addition seismic reflection surveys and sediment core collection were completed in the region the morphology of the mertz trough is combined with core data to interpret the sequence of events that occurred in this area since the last glacial maximum these complementary data indicate that an ice sheet once covered the mertz trough which deposited diamicton and formed mega scale glacial lineations during glacial maximal conditions and grounding line wedges during recession an erosional feature caused by subglacial meltwater breaching at least one of the grounding line deposits is also recognized along with a fan of sediment deposited seaward of the breach sediment cores from the mertz trough consist of two distinct units the diamicton deposited subglacially and a diatom mud and ooze deposited after the ice retreated the latter unit has been preferentially deposited in deeper areas of the trough as a hemipelagic drape and shows that a change in the nature of the diatom unit occurred about 3300 14c yr bp

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

groundwater surface waters interactions at slope and catchment scales implications for landsliding in clay rich slopes understanding water infiltration and transfer in soft clay shales slopes is an important scientific issue especially for landsliding geochemical investigations are carried out at the super sauze and draix laval landslides both developed in the callovo oxfordian black marls with the objective to define the origin of the groundwater in situ investigations soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems at super sauze the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations or at the landslide basement through a fault network such external origin of water is not observed at the local scale of the draix laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows hydrogeological conceptual models are proposed emphasizing the role of the interactions between local slope and regional catchment flow systems the observations suggest that this situation is a common case in the alpine area expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

regional fluid characterisation and modelling of water rock equilibria in the boom clay formation and in the rupelian aquifer at mol belgium abstract interstitial water from the boom clay formation around the hades high activity disposal experimental site an underground research facility belonging to the nuclear research centre sck cen at mol dessel belgium underground research facility at mol belgium and waters sampled at different locations in the rupelian aquifer underlying the clay formation have been studied the boom clay is a tertiary mudrock containing about 55 clay and the rupelian aquifer is located in a silty layer special care was taken to adapt or improve measurement sampling conservation and analysis methods to get a reliable regional and local database for the purpose of testing a general model describing the regulation and acquisition of the composition of these fluids the isotopic and chemical composition of the waters allows them to be assigned to a common origin namely mixing between a marine endmember and the clay interstitial water followed by reequilibration with the host rock through dissolution precipitation reactions involving identified secondary minerals oxidation reduction state and trace element behavior are also discussed and the limits of the model are outlined

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

flow switching and large scale deposition by ice streams draining former ice sheets fast flowing ice streams are responsible for the bulk of mass transfer through large ice sheets we use extensive three dimensional seismic data from the western norwegian margin to explain how a several hundred kilometer long ice stream has undergone major switching in flow direction from one glaciation to the next the direction of ice flow is inferred from the pattern of buildup of thousands of cubic kilometers of glacier derived debris and observations of large scale streamlined landforms on former subglacial beds we demonstrate that ice streams can undergo major changes in flow direction through modification of their large scale topographic setting whereas ice stream switching in modern ice sheets has been regarded mainly as a reflection of internal changes in ice sheet dynamics switching over successive 100 k y glacial cycles may in this case be a response to the effects of continuing sediment deposition and the large scale development of ice influenced continental margins

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

subglacial bedforms reveal complex basal regime in a zone of paleo ice stream convergence amundsen sea embayment west antarctica the flow of ice streams which account for most discharge from large ice sheets is controlled by processes operating at the ice stream bed data from modern ice stream beds are difficult to obtain but where ice advanced onto continental shelves during glacial periods extensive areas of the former bed can be imaged using modern swath sonar tools we present new multibeam swath bathymetry data analyzed alongside sparse preexisting data from the amundsen sea embayment the compilation is the most extensive continuous area of multi beam data coverage yet obtained on the inner continental shelf of antarctica the data reveal streamlined subglacial bedforms that define a zone of paleo ice stream convergence but in contrast to previous models do not show a simple downflow progression of bedform types along paleo ice stream troughs we interpret high spatial variability of bedforms as indicating a complex mechanical and hydrodynamic regime at the former ice stream beds consistent with observations from some modern ice streams we conclude that care must be taken when using bedforms to infer paleo ice stream velocities

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

high resolution quantitative seismic imaging of a strike slip fault with small vertical offset in clay rocks from underground galleries experimental platform of tournemire france imaging tectonic faults with small vertical offsets in argilittes clay rock using geophysical methods is challenging in the context of deep radioactive waste disposals the presence of such faults has to be assessed since they can modify the rock confining properties in the tournemire experimental platform tep france fault zones with small vertical offsets and complex shape have been identified from underground works however 3d high resolution surface seismic methods have shown limitations in this context that led us to consider the detection and characterization of the faults directly from underground works we investigate here the potential of seismic full waveform inversion fwi applied in a transmission configuration to image the clay rock medium in a horizontal plane between galleries and compare it with first arrival traveltime tomography fatt our objective is to characterize seismic velocities of a block of argilittes crossed by a subvertical fault zone with a small vertical offset the specific measurement configuration allows us to neglect the influence of the galleries on the wave propagation and to simplify the problem by considering a 2d isotropic horizontal imaging domain our fwi scheme relies on a robust adaptation of early arrival waveform tomography the results obtained with fatt and fwi are in accordance and both correlate with the geological observations from the gallery walls and boreholes we show that even though various simplifications are done in the inversion scheme and only a part of the data is used fwi allows to get higher resolution images than fatt and is especially less sensitive to the incomplete illumination as it uses also diffracted energy the results provided in this study highlight the complexity of the fault zone showing a complex interaction of the main fault system with a secondary system composed of decimetric fractures associated with the presence of water

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

influence of redox conditions on iodide migration through a deep clay formation toarcian argillaceous rock tournemire france abstract with a half life of 15 7 ma a high mobility and the potential to accumulate in the biosphere 129 i is considered in safety assessment calculations for radioactive waste repositories to be one of the main contributors to the radiological dose several authors have reported that at low concentration i is weakly retained on argillaceous rocks this process is not yet well understood and different hypotheses have been put forward as to whether reactive phases or experimental artifacts e g pyrite oxidation could be the reason for the retention of i observed at low concentration the aim of this study was to investigate the effect on i mobility of i the redox conditions and ii the amount of pyrite and natural organic matter nom contents of the rock these questions were addressed by performing batch sorption through diffusion and out diffusion experiments on rock samples of toarcian argillaceous rock from tournemire aveyron france one of the challenges faced during this study was to distinguish actual transport properties from experimental artifacts a especially elaborate experimental set up allowed limiting the i oxidation of both argillaceous rock and i and ii carbonate precipitation a comparison of the batch sorption results obtained for two toarcian clay specimens that differed in their amount of pyrite and nom allowed relating i sorption to pyrite oxidation however no evidence was found to associate the i behavior to the nom amounts while the through diffusion experiments showed a very slight sorption distribution ratio r d 0 016 ml g 1 for the lowest i concentration under oxic conditions the out diffusion tests performed after the through diffusion experiments on the same cells showed significant sorption under both oxic and anoxic conditions resulting in r d ranging from 0 02 ml g 1 to 1 25 ml g 1 the range of r d values was higher for the upstream reservoir under oxic conditions the discrepancies observed between the through diffusion and the out diffusion experiments suggest a kinetic control of the i uptake by argillaceous rocks under oxic and anoxic conditions

push moraines and glacier contact fans in marine and terrestrial environments the local climatic regime and the mass balance state are important determinants of the dynamics of terrestrial and marine glacier fronts which in turn determine the sediments and landforms produced at the glacier front many modern glaciers undergoing overall retreat in areas of maritime climate produce winter push moraines during a late winter readvance followed by a summer retreat whilst in more continental regions no significant winter readvance occurs and annual push moraines are absent the frontal dynamics which lead to these changes are analysed and the form structure sequence and field relations of both terrestrial and marine push moraines are described from iceland spitsbergen and baffin island long term changes in mass balance leading to major glacier advances or readvances also generate large push moraines in terrestrial environments push moraine formation is accompanied by uplift rejuvenation and down cutting of outwash systems whose sediments become closely associated with glaciotectonic structures which permit pre syn and post tectonic sequences to be identified the development of ice marginal fan moraine complexes is modelled as a function of the relative magnitude of two parameters the velocity of ice movement and the calving rate a high ice velocity just exceeded by the calving rate gives closely spaced push moraines and confluent ice marginal fans a high velocity far exceeded by the calving rate produces closely spaced moraines but separate ice marginal fans a low ice velocity in combination with a high calving rate results in well separated and feebly developed push moraines while a low ice velocity and a low calving rate produces feeble push moraines and coalescent fans

cenozoic margin development and erosion of the barents sea core evidence from southwest of bjornoya abstract five stratigraphic boreholes at the western barents sea margin reveal an evolution from a palaeocene normal shelf setting to a complex late cenozoic offshore marginal marine system influenced by mass flows and finally a glacially influenced shelf environment palaeocene epeiric sea sedimentation was sourced by erosion at the stappen high earliest eocene extension associated with volcanism was followed by rapid subsidence of the vestbakken volcanic province which became filled by sediments from an uplifted stappen high by the middle eocene siliciclastic shelf sediments were deposited and the infill had reached a balance with subsidence tectonic movements at this time may have caused local uplift which restricted the ventilation of local basins west of the stappen high but marine conditions existed in the area until early oligocene times when subaerial exposure was caused by tectonic uplift and probably also a fall in eustatic sea level pronounced oligocene and pliocene unconformities reflect major events of uplift and erosion at the margin and abundant fossil reworking indicates erosion of the uplifted cretaceous and tertiary strata the oligocene erosion had its associated depocentre to the south and west of the study area and was less important regionally than the pliocene pleistocene phase the pliocene uplift first led to local erosion along the margin subsequent subsidence may initially have had a thermal component this was followed by extensive downwarping under the load of largescale deposition sourced by regional erosion in the barents shelf region an eocene volcanic phase was probably related to the initiation of seafloor spreading isotopically dated volcaniclastic intervals in one of the cores give evidence of a late pliocene volcanic phase this event was associated with local tectonic movements which may be part of a regional uplift in the western northwestern part of the barents sea glaciations caused by the neogene climatic deterioration became enhanced by uplift and this led to extensive regional glacial erosion the main depocentre was offset to the south by ice flow curving around the uplifted area

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

the sklinnadjupet slide and its relation to the elsterian glaciation on the mid norwegian margin abstract the sklinnadjupet slide scar is a large buried feature on the continental slope southeast of the voring plateau the mass flow occurred ca 250 000 years ago on a slope angle of ca 0 5 and removed glacial debris from the up to 350 m thick naust s sequence on the upper slope this part of the mid norwegian margin appears to have been fairly stable throughout the last 2 8 million years naust s represents the third last glacial unit in the skjoldryggen region and was deposited during the elsterian ca 400 200 ka bp during this glaciation a wide depression was formed on the continental shelf between haltenbanken and traenabanken with the strongest glacial erosion in the west trending sklinnadjupet palaeo trough this trough leads directly towards the deep 90 km wide slide scar indicating that a local depocentre was formed here before the mass flow occurred the shallowest crest of the helland hansen arch is located below the southern part of the slide scar and two large craters were formed on the surface of this anticlinal structure our model suggests that the deposition of glacial sediments above the helland hansen arch caused high excess pore pressures along the shallowest crest of this structure and formed a high pore pressure gradient towards the sea floor on its western flank an earthquake possibly triggered the initial slide where the slope was steepest west of the crest most of the slide scar was already formed when the slide finally eroded into the anticline high excess fluid pressure subsequently mobilised the diatomaceous oozes in the helland hansen arch and formed the craters much of this material flowed down slope without being totally disintegrated and was deposited as levee ridges and mounds above slide deposits from the first phase of the mass flow they have previously been wrongly interpreted as diapirs

quantitative study of geochemical processes in the dogger aquifer paris basin france the quantification of geochemical reactions in hydrothermal aquifers requires an exhaustive approach because of their interdependence all chemical elements likely to have a quantitative influence on dissolution or precipitation reactions have to be taken into account geochemical constraints the number of which equals the number of the chemical elements were determined with the help of chemical analyses of the solution in the case study of the dogger aquifer paris basin france 12 elements are taken into account al c cl ca f h k mg na o s si three constraints apply to water activity neutrality and conservation of chloride in aqueous solutions the determination of the remaining constraints was based on saturation indices stability diagrams of minerals and partial pressure of carbon dioxide pco2 the present day solutions are at equilibrium with respect to nine minerals albite anhydrite chalcedony calcite dolomite fluorite kaolinite k feldspar and illite or chlorite thus it was demonstrated that the composition of these solutions including computed pco2 is only a function of temperature and chloride content moreover it was possible to test the validity of the geochemical system by computing its speciation and comparing these theoretical results with actual chemical analyses ph and concentrations finally geochemical simulations were used in predicting what quantities would be dissolved or precipitated as either the temperature or the chlorinity varied although the rock is predominantly calcareous these quantities could not be determined if the influence of the aluminosilicates were neglected this chemical component approach with which one can pose and solve rigorously the chemical equilibrium problem constitutes a prerequisite for the quantitative study of geochemical processes related to fluid flow

geochemical characterization and modelling of the toarcian domerian porewater at the tournemire underground research laboratory abstract for safety evaluation of hazardous waste repositories in clay rocks a thorough assessment of porewater chemistry and water rock interactions is required however this objective is a challenging task due to the low hydraulic conductivity and water content of such rocks which subsequently renders porewater sampling difficult without inducing perturbations for this reason an indirect approach was developed to determine porewater composition of clay rocks by a geochemical model of water rock interaction using some properties of the rock and the solution the goal of this paper is to obtain the porewater composition of the toarcian domerian argillaceous formation at tournemire south of france for which a reliable model is still lacking the following work presents a comprehensive characterization of the geochemical system of the tournemire clay rock including mineralogy petrology mobile anions cation exchange properties accessible porosity and co 2 partial pressure perturbation corrections from fracture water sampling were also computed these water were found in sealed fractures beaucaire et al 2008 and their radiocarbon apparent age is estimated at 20 ka their age together with their equilibrium situation allow considering these fracture waters as representative of the formation porewater the model developed to calculate the tournemire porewater composition is essentially based on cation exchange by a multi site approach but equilibrium with some mineral phases calcite quartz and pyrite is also considered different exchange sites of different affinities towards cations are used which proportions are given by the mineralogy exchange on illite is performed with a three sites model while one site is considered for smectite phases multi site model results are compared with corrected fracture water data and two other models a model only based on mineral equilibrium and a model using cation exchange on one global site the best results were obtained with the models that take into account cation exchange and particularly with the multi site model the interest in considering a model with exchange sites of different affinities is particularly obvious for a satisfactory representation of the k content in solution a dependence of k content to the amount of high affinity sites was observed leading to an improvement of its simulation when uncertainty on mineralogical data is considered once validated the multi site model was applied at different levels of the tournemire argillaceous formation to obtain a profile of the porewater composition

antarctic ice streams a review an ice stream is a part of an inland ice sheet that flows rapidly through the surrounding ice the distinction between an ice sheet and an outlet glacier is clear in principle but muddy in practice many antarctic glaciers are intermediate in character the ross ice streams which flow through the west antarctic inland ice into the ross ice shelf are distinct in character differing even from other ice streams in the marine ice sheet of west antarctica their surface elevation profiles are low their bed slopes are low and smooth and their driving stresses diminish monotonically downglacier in transverse profile they are broader in relation to ice thickness and exhibit shallower subglacial troughs than other ice streams many models for the fast sliding of glaciers have been applied to the ross ice streams most have included in some form a reduction in basal drag resulting from a lesser effective than glaciostatic pressure at the bed most models are only semi physical at best so need to be tuned by fitting to assumed parameters at some place or places in the real ice sheet the recent discovery of a very small effective pressure beneath one ice stream consequently has led to some gross errors in the velocities predicted by the models the difficulty may be resolved if it is true as recent experiments suggest that ice stream b and by extrapolation other ross ice streams as well slide on a deforming bed that absorbs most or all of the differential motion between the ice and the bedrock

buried iceberg ploughmarks in the early quaternary sediments of the central north sea a two million year record of glacial influence from 3d seismic data abstract buried linear to curvilinear depressions interpreted as iceberg ploughmarks were identified through most of the 2 ma long and about 700 m thick early quaternary sedimentary record in two 3d seismic cubes from the central north sea basin 56 58 n 2 3 e the mean width of 402 features measured at 6 time slices in cube c08 was between 49 and 63 m and mean length was 2 5 to 3 7 km mapping the

a physicochemical characterisation and geochemical modelling approach for determining porewater chemistries in argillaceous rocks abstract argillaceous sediments are being investigated in many countries as potential host rock formations for the disposal of high level radioactive waste quantification of the water chemistry in such formation is often difficult because the groundwater flow rates are so low that reliable samples for chemical analysis cannot be obtained a physicochemical characterisation procedure for rock samples combined with geochemical modelling is described which allows porewater composition to be determined in low porosity permeability clay rich systems the methodology was applied to core samples of opalinus clay within the framework of an international investigation being carried out at mt terri canton jura switzerland

groundwater characterisation and modelling of water rock interaction in an argillaceous formation tournemire france abstract chemical na k mg ca cl so 4 hco 3 si al fe mn toc and isotopic 18 o h 2 o 2 h h 2 o 3 h h 2 o 14 c dic 13 c dic 34 s so 4 18 o so 4 data were obtained on groundwater collected from fractures inside the consolidated argillaceous formation of tournemire aveyron and from the aquifers surrounding this formation because of the very low transmissivity of such fractures 10 10 m 2 s 1 specific devices were developed for limiting out gassing and air contamination of groundwater during the sampling two modelling approaches are proposed to account for the chemical evolution of fracture groundwater from na cl hco 3 to na so 4 type the first one is based on mineral equilibria only and the second one also takes into account the ion exchange reactions the two modelling approaches are able to reproduce k concentrations and they led to an almost constant p co 2 10 2 6 atm which only depends on equilibrium with the calcite dolomite kaolinite quartz assemblage the modelling of na ca 2 and hco 3 behaviours is improved by taking the ion exchange reactions into account in some boreholes the time evolution of the chemical composition of fluids was greatly influenced by so 4 reduction combined with oxidation of dissolved organic c the isotopic composition of aqueous so 4 in fracture groundwater confirms that so 4 reduction processes have occurred since the drilling of these boreholes but also previously during the natural evolution of groundwater these redox reactions constitute a source of aqueous inorganic c that has to be considered in the computation of groundwater ages with 14 c for the studied fracture groundwaters the maximum age estimates range from 17 to 29 ka this shows that fractures may induce relatively fast groundwater flow compared to the very long migration times that are calculated by only considering diffusive transport in the rock microporosity

an extensive and dynamic ice sheet on the west greenland shelf during the last glacial cycle considerable uncertainty surrounds the extent and timing of the advance and retreat of the greenland ice sheet gis on the continental shelf bordering baffin bay during the last glacial cycle here we use marine geophysical and geological data to show that fast flowing ice sheet outlets including the ancestral jakobshavn isbrae expanded several hundred kilometers to the shelf edge during the last glaciation ca 20 ka retreat of these outlets was asynchronous initial retreat from the shelf edge was underway by 14 880 calibrated cal yr b p in uummannaq trough radiocarbon dates from the adjacent disko trough and adjoining trough mouth fan imply later deglaciation of jakobshavn isbrae and significantly an extensive readvance and rapid retreat of this outlet during the younger dryas stadial yd this is notable because it is the first evidence of a major advance of the gis during the yd on the west greenland shelf although the short duration suggests that it may have been out of phase with yd temperatures

desaturation and structure relationships around drifts excavated in the well compacted tournemire s argillite aveyron france this study aimed to explore the relationships between the extension of rock desaturation and the excavation damaged zone edz subsequent to the excavation of a century old tunnel and of recent drifts 1996 and 2003 at the tournemire underground research laboratory url located in the aveyron county south of the massif central france the other objective of this work was to assess the impact of desaturation on the hydraulic head profile measured around the tunnel one section was selected per drift two boreholes were drilled for each section one parallel and one inclined 45 with respect to the bedding for each borehole we performed on site drill core mapping petrophysical measurements pneumatic and hydraulic tests by means of a modular mini packer system mmps results indicate that the edz around drifts is mainly a combination of unloading joints mimicking the drift shape and of desaturation cracks parallel to the bedding the edz extension around the tunnel is twice to three times that of the drifts of 1996 and 2003 and is essentially composed of unloading joints resulting from the mechanical response of the rock the masonery covering the tunnel walls is assumed to have protected the rock from seasonal variations of air humidity thus limiting without excluding the formation of desaturation cracks the edz extension deduced from core mapping is in agreement with that deduced from pneumatic tests with permeabilities several orders of magnitude greater than in the undisturbed zone degrees of saturation for the three sections range between 0 9 and 1 in the edz area and reach 1 in the undamaged zone the head profile deduced from measurements recorded since 2002 indicates the occurrence of an excavation disturbed zone edz of about 40 m around the tunnel this edz is likely due to the existence of sub atmospheric water pressures clearly seen in the first meter around the tunnel we have tried to quantify the impact of the tunnel since its excavation on saturation degree and on hydraulic heads the simulation was performed by considering as a first approach the absence of fracturing in the edz a constant suction of 3300 m deduced from the mean annual values of relative humidity and temperature measured in the tunnel atmosphere since 2002 was applied at the tunnel wall the degrees of saturation simulated around the tunnel are underestimated in the edz area and consistent to experimental data in the unfractured zone the modelling of hydraulic heads is overestimated in the horizontal direction and is in the domain of experimental values in the vertical direction but the lack of intermediate data cannot enable us to conclude on this consistency this study demonstrated the role played by fracturing on the distribution of petrophysical parameters and of heads around drifts and the century old tunnel it has also demonstrated the necessity of coupling mechanic and hydraulic calculations by considering capillary forces

neogene and quaternary depositional environments on the norwegian continental margin 62 n 68 n abstract 2d multichannel seismic and mini sleeve gun profiles reveal that an up to 1 5 s twt thick sedimentary succession has been deposited on the norwegian continental margin 62 n 68 n during neogene and quaternary well defined miocene depocentres have evolved both in the north sea fan region and along the flanks of structural highs in the voring basin miocene sediments are on the other hand mainly absent within the storegga slide scar seismic facies analyses show that these deposits locally are characterised by a mounded and or migration aggradation pattern which we relate to a current influenced depositional environment hence the early neogene sediments on the norwegian continental margin are classified as contourites the contourites have most likely been deposited in connection with the establishment of a deep water exchange in the norwegian greenland sea due to the opening of the fram strait and subsidence of the greenland scotland ridge at about 2 5 ma a significant change in this depositional environment took place down slope sedimentary processes became now more important and throughout the late plio pleistocene sediments were mainly sourced from the norwegian mainland and the adjacent continental shelf causing depocentres to evolve along the shelf edge

stages of evolution of a toarcian compacted claystone around galleries excavated between 1 and 124 years ago by the study of noble gases dissolved in pore water at the tournemire underground research laboratory france abstract the purpose of this work is to study the diffusion properties in an argillaceous formation and how these properties change after the excavation of galleries over a long period the tournemire underground research laboratory url located in aveyron france offers the unique opportunity to investigate different stages of the evolution of the so called excavation damaged zone edz over a period of about 124 a four horizontal boreholes parallel to the bedding and one vertical borehole were drilled in order to study diffusion transport in the edz in both directions in galleries excavated 124 13 6 and 1 a ago respectively noble gases dissolved in the pore water of 47 core samples were extracted in order to establish precise depth profiles mainly produced in situ by decay of u and th radiogenic he accumulates in the pore water of rocks and escapes toward the gallery allowing a characterization of the diffusive transport in the edz and its evolution with time for the oldest gallery 1882 1888 core mapping reveals an edz well developed with fractures up to a depth of 1 8 m in this zone all radiogenic he has been lost and at the same time heavy noble gases are trapped in the rock with an enrichment of xe relative to kr and of kr relative to ar from 1 8 m he concentration increases with depth to reach a plateau at about 3 5 m corresponding to a concentration normally found in the unaltered zone considering diffusive transport of the radiogenic he to the edz model calculations allowed proposing transport properties in the unfractured and undisturbed zone uz with a pore diffusion coefficient dp of 1 10 10 m 2 s deduced from the best fit curve to experimental data and a mean porosity of 0 1 obtained form petrophysical measurements the most recent gallery 2008 did not show any evidence of edz at depths greater than 7 5 cm a fracture located around 0 75 m possibly of tectonic origin induced large advection and diffusion losses of he on both sides in the next 50 cm excesses of ar kr and xe are found suggesting diffusion of air from the gallery associated with he losses the 6 a old gallery is clearly influenced by fractures of tectonic origin increasing the edz thickness of 0 7 m up to a damaged zone of 1 8 m based on the he concentration profile the 13 a old gallery 1996 has a net edz of 1 2 m larger than the 0 7 m deduced from the structural analysis by core mapping followed by a disturbed zone of up to 3 5 m that could represent an intermediate stage before the development of fractures in the edz the vertical borehole drilled in the same gallery shows a less extensive damaged zone 1 4 m and allows the determination of a dp of 3 10 11 m 2 s taking into account the anisotropy relative to the stratification plane the rare gas analysis has therefore enabled confirmation and better description of the net time dependent evolution of the edz around drifts in the argillaceous tournemire site no obvious edz for the 1 a gallery 2008 1 2 m width for the 13 a old gallery 1996 and 2 m width for the century old tunnel the occurrence of a disturbed and unfractured zone dz around the 13 a old gallery undetected by structural studies and geophysical methods clearly demonstrates the power of radiogenic he in assessing the transport properties around drifts excavated at different ages in compacted clay rocks

coupled hydrogeochemical modelling using kirmat to assess water rock interaction in a saline aquifer in central eastern tunisia abstract to quantify water rock interactions and forecast their spatiotemporal evolution in the shallow aquifer of sidi el hani located in central eastern tunisia the numerical code kirmat was used based on available geological mineralogical thermodynamic kinetic and hydrodynamic data the model was built and calibrated on two transects of the aquifer oriented along the flow lines of groundwater the numerical results show that the interactions between water and rock are responsible for groundwater salinity which is strongly dominated by chlorides sodium and sulphates the variations of dissolved species in space and time are the result of halite dissolution anhydrite and gypsum dissolution and precipitation calcite dissolution and dolomite precipitation the precipitation of dolomite can locally induce a reduction in permeability and further enhance an increase in leaching because the residence time between rock and water will be amplified three numerical sensitivity studies have been conducted to evaluate the influence of water rock interactions on groundwater salinization the study highlights the finding that the modelled fate of dissolved species in the unconfined aquifer is rather sensitive to the darcy velocity but not very sensitive to the initial volume fractions of minerals in the two transects and the composition of groundwater injected at the upstream boundary

identification and preservation of landforms diagnostic of past ice sheet activity on continental shelves from three dimensional seismic evidence ice ages have occurred a number of times in earth9s history and are important in understanding changes in long term climate however it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes e g debris flows diagnostic large scale glacial landforms produced beneath ice sheets and preserved on continental shelves after deglaciation can establish a glacial origin three dimensional seismic evidence from the 2 7 ma naust formation norwegian margin illustrates several glacial landforms that are also commonly occurring features on modern high latitude shelves 1 streamlined mega scale lineations produced by fast flowing ice streams 2 ploughmarks formed by iceberg keels and 3 regularly spaced transverse ridges or push moraines formed during ice retreat we have found for example buried ice keel ploughmarks on a paleoshelf dating to ca 2 ma norwegian margin seismic stratigraphy data show that ice advanced and retreated many times and some paleoshelf surfaces were preserved such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments

three dimensional seismic data from the barents sea margin reveal evidence of past ice streams and their dynamics three dimensional seismic data from the southern flank of the outer bear island trough at the western barents sea margin show former ice stream activity the interpretation of such activity is based on megascale lineations and long chains of megablocks and rafts buried in thick till units between glacially eroded horizons in several units the sediment blocks and rafts are aligned in chains up to 2 km wide and 50 km long individual megablocks have an areal extent of up to 2 2 km 2 and their internal structure is well preserved providing information about the processes involved in their incorporation into the ice subsequent detachment and partial disintegration previous discussions of sub ice stream processes have focused on ductile deformation of weak sediments and molding of subglacial landforms this work also demonstrates the importance of brittle sediment deformation in these settings adding to the understanding of ice streams as agents of glacial erosion transport and sedimentation

diffusion as the main process for mass transport in very low water content argillites 2 fluid flow and mass transport modeling 1 on the basis of chloride concentrations of pore water in the tournemire massif part 1 a conceptual model for mass transport in argillites by diffusion is proposed from this conceptual model and current knowledge of the geological history of the massif one dimensional numerical simulations are formulated for chloride transport in tournemire massif over the past 53 ma good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is the main process for mass transport in the massif this model is also tested using deuterium contents of pore water applying variable concentrations to meteoric water circulating in system boundary layers based on the thermal dependency of its isotopic composition these simulations reveal the likely important role of lithologic heterogeneities such as fractures in the horizontal distribution of tracer concentrations

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

selective glacial erosion on the norwegian passive margin glaciated passive margins display dramatic fjord coasts but also commonly retain plateau fragments inland it has been proposed recently that such elevated low relief surfaces on the norwegian margin are products of highly efficient and extensive glacial and periglacial erosion the glacial buzzsaw operating at equilibrium line altitudes elas we demonstrate here that glacial erosion has acted instead to dissect plateaus in western norway low relief surfaces are not generally spatially associated with cirques and do not correlate regionally with modern and last glacial maximum elas glacier dynamics require instead that glacial erosion is selective with low relief surfaces representing islands of limited pleistocene erosion deep glacial erosion of the coast and inner shelf has provided huge volumes of sediment 70 000 km3 largely resolving apparent mismatches 65 100 000 km3 between fjord and valley volumes and pliocene pleistocene sediment wedges offshore nonetheless as pleistocene glacial valleys and cirques are cut into preexisting mountain relief tectonics rather than isostatic compensation for glacial erosion have been the main driver for late cenozoic uplift on the norwegian passive margin

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

extreme sediment and ice discharge from marine based ice streams new evidence from the north sea a major problem for understanding the dynamics of ice streams has been a lack of precise data on ice streaming longevity and sediment transport efficacy here we present the first well constrained data on sediment flux from a paleoice stream this has been achieved by computing the volume of sediment deposited as debris flows on the fan located at the outlet of the norwegian channel ice stream and converting to a flux measurement by accounting for the duration of streaming in this episode between 20 and 19 ka during the last glacial stage in this period the ice stream delivered an average 1 1 gt of sediment per year equivalent to 8000 m 3 yr 1 per meter width of ice stream front the calculated flux is an order of magnitude higher than most previous estimates for other paleoice streams and is comparable to the present sediment flux from the world9s largest rivers the short period of debris flow deposition suggests that the norwegian channel ice stream underwent rapid on off switching with punctuated iceberg delivery to the north atlantic as a consequence

ice sheet grounding zone wedges gzws on high latitude continental margins abstract grounding zone wedges gzws are asymmetric sedimentary depocentres which form through the rapid accumulation of glacigenic debris along a line source at the grounding zone of marine terminating ice sheets during still stands in ice sheet retreat gzws form largely through the delivery of deforming subglacial sediments the presence of gzws in the geological record indicates an episodic style of ice retreat punctuated by still stands in grounding zone position moraine ridges and ice proximal fans may also build up at the grounding zone during still stands of the ice margin but these require either considerable vertical accommodation space or sediment derived from point sourced subglacial meltwater streams by contrast gzws form mainly where floating ice shelves constrain vertical accommodation space immediately beyond the grounding zone an inventory of gzws is compiled from available studies of bathymetric and acoustic data from high latitude continental margins the locations and dimensions of gzws from the arctic and antarctic alongside a synthesis of their key architectural and geomorphic characteristics are presented gzws are only observed within cross shelf troughs and major fjord systems which are the former locations of ice streams and fast flowing outlet glaciers typical high latitude gzws are less than 15 km in along flow direction and 15 to 100 m thick gzws possess a transparent to chaotic acoustic character which reflects the delivery of diamictic subglacial debris many gzws contain seaward dipping reflections which indicate sediment progradation and wedge growth through continued delivery of basal sediments gzw formation is inferred to require high rates of sediment delivery to a fast flowing ice margin that is relatively stable for probably decades to centuries although the long term stability of the grounding zone is controlled by ice sheet mass balance the precise location of any still stands is influenced strongly by the geometry of the continental shelf the majority of high latitude gzws occur at vertical or lateral pinning points which encourage grounding zone stabilisation through increasing basal and lateral drag and reducing mass flow across the grounding zone

gravity measurements and their variations before the 2008 wenchuan earthquake it was recognized 50 years ago that coseismic gravity changes take place during a large earthquake in the past 30 years there have been research efforts devoted to investigating possible associations between gravity variations and earthquakes in china before the wenchuan m w 7 9 earthquake a group of researchers at the second crust monitoring and application center of china earthquake administration noticed significant gravity changes in a region covering the well known south north earthquake belt in china and suggested in 2006 that the possibility for a major earthquake to occur near wenchuan in either 2007 or 2008 was high these researchers used gravity changes as the primary earthquake precursor to make the suggestion in this article we report the method used for repeated regional gravity survey the procedures for gravity survey data analysis and the characteristics of gravity variations before the wenchuan earthquake that ruptured on 12 may 2008 although gravity changes at a number of locations in the region surrounding wenchuan were significant more research is needed to investigate whether these gravity variations could be viewed as a precursor of the wenchuan earthquake uncertainties in the reported gravity variations include inevitable measurement errors related to ground gravity surveys covering a large region hydrologic effects on gravity and the effects of vertical crustal movements on gravity other limitations of the data are that the density of the gravity observation stations is coarse and that the time intervals of the surveys were two to three years long based on these observations we make several recommendations about data collection and data analysis procedures that would enhance future earthquake research using gravity monitoring data in china

deep sea floor evidence of past ice streams off the antarctic peninsula the past existence of a giant ice stream off the northern end of the antarctic peninsula is suggested by a convex upward elongated sediment body now at a mean water depth of 1000 m because of its morphological characteristics i e a set of parallel to subparallel ridges and grooves to 100 km long with an overall width of 25 km we call this depositional body a bundle structure we hypothesize that bundle structures form by accumulation of basal deformation till under their parent ice streams from its location size and overall characteristics the bundle structure described here constitutes the best preserved largest deepest and relatively low latitude evidence of giant ice streams that flowed offshore antarctica during glacial maxima bundle structures reveal the very dynamic behavior of ice caps in the northern antarctic peninsula during the last glacial maximum with catchment areas draining rapidly under marine based critical subglacial conditions bundle structures represent a new megascale streamlined glacial landform

a ploughing model for the origin of weak tills beneath ice streams a qualitative treatment abstract glaciological studies of west antarctic ice streams have shown that weak sub ice stream tills provide the basal lubrication that makes fast ice streaming possible under low driving stresses given the significant current interest in time dependent ice stream behavior there is a clear need for a conceptual model of weak sub ice stream tills that treats in a simple but physically correct way the coupling between evolution of till properties and ice stream dynamics as a possible alternative to the previous viscous bed model we propose a ploughing model that is consistent with the experimentally determined coulomb plastic rheology of sub ice stream till in the ploughing model the till is a several meters thick layer of sedimentary material that is disturbed and transported by ploughing that occurs during sliding of a bumpy ice base the thickness of the till layer is determined in the ploughing model by the amplitude of the largest roughness elements ice keels there is no direct proof for the existence of ice bumps and ice keels beneath the modern west antarctic ice streams but bedforms e g megalineations and bundle structures left behind by pleistocene ice streams strongly support our assumption that an ice stream base is irregular generation of new till material occurs when ice keels protrude through the existing till layer and erode the top of the sub till preglacial sediments based on a single tethered stake measurement of engelhardt and kamb j glaciol 44 1998 223 made at the upb camp ice stream b west antarctica fig 1 we estimate that the till flux due to sliding with ploughing is there 3 yr 1 per meter width to balance the estimated till flux in the upb area substrata erosion by ice keels would have to take place at a high but not unreasonable non dimensional rate of 4 assuming 1 contact area in the case of the west antarctic ice streams erosion of sub till materials by ice keels may be particularly fast and unimpeded because these ice streams are overriding unlithified preglacial tertiary sediments the most significant implication of the proposed ploughing model is that it permits treating basal resistance to ice motion as being velocity independent plastic till rheology while allowing subglacial transport of till as in the viscous bed model models of ice streams with a plastic bed exhibit a greater potential for unstable behavior than models of ice streams with viscous beds

geothermal mineral equilibria the dominant reaction determining the chemistry of fluids in a geothermal system of the new zealand type consists of the conversion of primary plagioclase by co2 to calcite and clays with log pco2 15 26 7850 t 273 2 temperature t in c subsequent reactions involving secondary minerals control relative co2 h2s contents the distribution of mineral phases throughout a geothermal system reflects the stepwise conversion of thermodynamically unstable primary phases through a series of intermediate metastable phases to a thermodynamically stable secondary assemblage the relative stabilities of these phases was evaluated on the basis of their solubilities the least soluble aluminiumsilicate representing the thermodynamically most stable phase under a given set of conditions observed assemblages of secondary minerals in geothermal systems represent indicators allowing mineral fluidinteraction conditions to be evaluated on the basis of multi component mineral stability diagrams

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

morphology sedimentary infill and depositional environments of the early quaternary north sea basin 56 62 n abstract the north sea basin has been subsiding during the quaternary and contains hundreds of metres of fill seismic surveys 170 000 km2 provide new evidence on early quaternary sedimentation from about 2 75 ma to around the brunhes matuyama boundary 0 78 ma we present an informal seismic stratigraphy for the early quaternary of the north sea and calculate sediment volumes for major units early quaternary sediment thickness is 1000 m in the northern basin and 700 m in the central basin total about 40 000 km3 northern north sea basin fill comprises several clinoform units prograding westward over 60 000 km2 architecture of the central basin also comprises clinoforms building from the southeast to the west an acoustically layered and mounded unit unit z was deposited remaining accommodation space was filled with fine grained sediments of two central basin units above these units an upper regional unconformity equivalent uru records a conformable surface with flat lying units that indicate stronger direct glacial influence than on the sediments below on the north sea plateau north of 59 n the upper regional unconformity uru is defined by a shift from westward to eastward dipping seismic reflectors recording a major change in sedimentation with the shetland platform becoming a significant source a model of early quaternary sediment delivery to the north sea shows sources from the scandinavian ice sheet and major european rivers clinoforms prograding west in the northern north sea basin representing glacigenic debris flows indicate an ice sheet on the western scandinavian margin in the central basin sediments are generally fine grained suggesting a distal fluvial or glacifluvial origin from european rivers ploughmarks also demonstrate that icebergs derived from an ice sheet to the north drifted into the central north sea basin by contrast sediments and glacial landforms above the uru provide evidence for the later presence of a grounded ice sheet

stable isotope contents of porewater in a claystone formation tournemire france assessment of the extraction technique and preliminary results abstract claystones are one of the types of geological formations that are considered for the isolation of radioactive wastes the study of water transfer through these rocks comes up against a lot of difficulties among them is the problem of extracting representative samples of interstitial water from indurated claystones with very low water contents usually less than 10 vol the vacuum distillation technique considered here for samples from the tournemire site toarcian argillite formation is one of the few usable techniques to extract water from this type of rock in order to perform stable isotope investigations on porewater tests have shown that the isotope water content is not only influenced by the yield of extraction and the temperature of distillation as already known but also by the rain size and the contact time between the crushed sample and the atmosphere this affects particularly 18 o data the first isotopic results on the tournemire claystones suggest a meteoric origin for its interstitial water data show a depletion in heavy isotopes with respect to present day meteoric water that could suggest a recharge under climatic conditions cooler than at present a clear link appears between the isotope contents of water and the structural context interstitial waters of rock samples taken in the fractured zone of the massif seem to have been affected by a secondary process evaporation or water rock exchange leading to the enrichment in heavy isotopes

constraining porewater chemistry in a 250m thick argillaceous rock sequence the geochemistry of an argillaceous rock sequence from a deep borehole in ne switzerland was investigated the focus was to constrain the porewater chemistry in low permeability jurassic rocks comprising the liassic the opalinus clay formation the brown dogger unit and the effingen member malm a multi method approach including mineralogical analysis aqueous and ni ethylenediamine extraction squeezing tests and pco2 measurements as well as geochemical modelling was applied for this purpose a consistent dataset was obtained with regard to the main solutes in the porewaters a fairly constant anionaccessible porosity of 50 of the total porosity was deduced for all analysed samples which displayed variable clay mineral contents sulphate concentrations were shown to be constrained by a sulphate bearing phase presumably by celestite or a sr ba sulphate application of a simple equilibrium model including cation exchange reactions calcite and celestite equilibrium showed good agreement with squeezing data indicating the suitability of the modelling approach to simulate porewater chemistry in the studied argillaceous rocks the modelling highlighted the importance of correct determination of the exchangeable cation population the analysis corroborates that squeezing of the studied rocks is a viable and efficient way to sample porewater

research on water rock soil interaction by dynamic tracing method for huangtupo landslide three gorges reservoir pr china as groundwater activity develops in a landslide system the water rock soil interaction increasingly influences the development of the landslide hazard in this paper huangtupo landsli de was chosen as the subject of our research which is located beside the three gorges reservoir and the deformation continued for a long time first based on a comprehensive field survey ten types of bad geological elements which probably induce the deformation were collected from different parts of landslide these include a soft rock layer the sliding soil a weak intercalation and the typical rock close to the slip zone then to trace the internal relationships among these samples the microstructure chemical composition of minerals the migration and evolution of clay minerals also the particle size distribution characteristics of all the samples were analyzed separately comparison of the result shows that the evolutionary paths are very obvious among these samples with the activities of water rock soil interaction the formation and evolution of main bad geological elements can be summarized afterwards the detailed mechanism of interaction is revealed by focusing on four samples which compose one of these three paths using additional data from physical and mechanical tests the study shows how water rock soil interaction affects the microstructure and weakens the mechanical properties of rock and soil the presented detailed research probes the water rock soil interaction mechanism specifically for huangtupo riverside landslide as a case study furthermore the applied multi sample dynamic tracing method is verified as a means to discover and illustrate the deformation mechanism of landslides

bimodal plio quaternary glacial erosion of fjords and low relief surfaces in scandinavia glacial landscapes exhibit both high and low relief land surfaces a comparison of fjord erosion and offshore deposition suggests that glacier erosion created both the dramatic fjords and high elevation low relief surfaces in western scandanavia

large scale development of the mid norwegian margin during the last 3 million years abstract during the last c 2 7 my large quantities of glacially derived material were transported westwards from the norwegian mainland areas and inner shelf and deposited mainly as prograding sediment wedges into a basin of intermediate depth offshore mid norway the deposits are more than 1000 m thick in extensive areas and are defined as the naust formation in the haltenbanken traenabanken region the shelf edge migrated 100 150 km westwards the narrow more shelf was built out only in the order of 30 50 km mainly due to a steeper pre existing slope dipping towards a much deeper basin in this area the holocene storegga slide as well as older slides displaced slope sediments towards the deeper part of the basin in early naust time the most extensive progradation occurred in the northern area possibly due to the combined effect of land uplift and glaciations the importance of glaciations for the progradation of the more shelf and areas farther south increased through the pleistocene period the norwegian channel ice stream became very important during the last three glaciations and a thick succession of glacigenic debris flows was deposited on the north sea fan more than 400 m of sediments accumulated during the weichselian all the last three glaciations supplied glacial debris beyond the shelf edge the most extensive progradation in the north was in the skjoldryggen region particularly during the elsterian glaciation during ice free periods hemipelagic and contouritic sediments were deposited on the slope such sediments are most common in the storegga slide area where they hosted glide planes beneath the major slides

rates of sediment delivery from the fennoscandian ice sheet through an ice age sediment delivery rates through an entire ice age are investigated using seismic records of glacial erosion products from the fennoscandian ice sheet deposited offshore of mid norway in the 2 7 m y old naust formation volume 100 000 km 3 the mean sedimentation rate over the ice age is 0 24 m k y 1 with bedrock lowering of 520 m in the ice sheet catchment the mean sediment delivery is 2 3 times higher for the most recent 600 k y than for earlier naust sequences the hypothesis that glacial erosion is most rapid early in an ice age when there was presumably much weathered bedrock and preglacial sediment available is not accepted for our study area more important are changing ice sheet dimensions and dynamics varying intensity of individual glacial cycles and complex ice sheet dynamics in single deglaciations the mean rate of sediment delivery from ice sheets is an order of magnitude higher than from fluvial activity in the huge amazon and mississippi systems implying that ice is a very effective agent of long term denudation during cold periods of earth history

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

ice sheet dynamics through the quaternary on the mid norwegian continental margin inferred from 3d seismic data reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system but most detailed palaeo glaciological reconstructions have hitherto focused on the very recent history of ice sheets here we present a three dimensional 3d reconstruction of the changing nature of ice sheet derived sedimentary architecture through the quaternary ice age of almost 3 ma an extensive geophysical record documents a marine terminating calving fennoscandian ice sheet fis margin present periodically on the mid norwegian shelf since the beginning of the quaternary spatial and temporal variability of the fis is illustrated by the gradual development of fast flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time buried subglacial landforms reveal a complex and dynamic ice sheet with converging palaeo ice streams and several flow switching events that may reflect major changes in topography and basal thermal regime lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine terminating part of the fis this palaeo environmental examination of the fis provides a useful framework for ice sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume

14c dating of gorleben groundwater previous attempts to apply 14c for dating of groundwater in the gorleben aquifer system has given results with conflicting 3h and stable isotope data and hydrological estimates 14c model ages of 1 10 ka have been found for 3h containing recharge water up to 31 ka for groundwater with holocene stable isotope signatures and 6 10 ka for groundwater at 35 m depth in this paper it is shown that the reasons are assumption of to high 14c concentration in recharge groundwater and not correcting for the influence of 14c dilution by dissolved inorganic c dic from microbiologically mediated mineralization of organic components in deep sediments to overcome these difficulties a new approach is applied evaluating the site specific 14c source term including the influence of nuclear atmospheric testing and the already previously used overall dilution of dic closed system conditions are assumed and no isotopic fractionation is considered for most of the groundwaters the 14c ages achieved by the present method are in agreement with 3h stable isotopes and hydrological estimates it is shown that down to approximately 140 m depth no 14c decay can be detected situations are also discussed either where the 14c method is not applicable shallow peat bog like groundwater or does not yield reliable groundwater ages brines at 200 m depth

late cenozoic prograding wedges on the nw european continental margin their formation and relationship to tectonics and climate abstract during late pliocene to pleistocene times prominent prograding wedges were deposited along the continental margin of nw europe resulting in seaward shelf break migration of up to 150 km much of the sediment accumulation occurred marginal to the former mid to high latitude ice sheets the geographical distribution and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late pliocene to pleistocene climate deterioration and onset of major northern hemisphere glaciations the onset of wedge growth on the nw uk and irish margins was initiated at about 4 ma in response to tectonic tilting of the margin in that region however glacially derived sediments here comprise a significant proportion of the wedges especially since 0 44 ma for the faroe margin no detailed chronology is available however it may be inferred that onset of glacigenic wedge growth here did not post date that observed on the nw uk and irish margins offshore norway wedge growth has largely occurred since ca 2 7 ma in response to northern hemisphere glaciations also recording a major change in sediments transport routes at 0 8 1 1 ma reflecting larger fennoscandian ice sheets presently it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase in response to uplift in this area in the western barents sea an early phase of wedge growth was glacio fluvial in character off western spitsbergen the development was similar to that of the barents sea although the glacigenic wedge growth phase may have started somewhat earlier the wedges commonly display gently inclined seaward prograding clinoforms and transparent to chaotic internal acoustic facies sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that to various extents have been affected by bottom current action the clinoforms of these wedges vary in geometry from oblique to sigmoidal and they also show varying degrees of aggradation throughout their development the resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply sedimentary processes and accommodation space the latter being a function of tectonic movements and or loading induced subsidence as well as eustatic sea level fluctuations

what controls the location of ice streams ice streams influence ice sheet mass balance and stability but key aspects of their behaviour remain poorly understood this paper reviews and discusses one very important aspect what controls their location in an ice sheet seven potential controls on ice stream location are identified from the literature topographic focusing topographic steps macro scale bed roughness calving margins subglacial geology geothermal heat flux and subglacial meltwater routing for each control the theoretical basis for its link to rapid ice flow is introduced followed by discussion of the evidence of its influence on the location of both contemporary and palaeo ice streams based on this new synthesis topographic focusing subglacial geology meltwater routing and calving margins appear to be most commonly associated with fast ice flow it is clear that rather than a single control however there exist a number of potential controls of varying influence we propose a hierarchy of factors with those occurring at the top of the hierarchy exerting a stronger influence on ice stream location and where present beneath an ice sheet are very likely to be associated with fast flow those factors occurring lower down the hierarchy are less commonly associated with ice streaming but appear to be influential in the absence of more common controls in such a hierarchy topographic focusing in the presence of a calving margin is the primary control in the absence of this ice streams will preferentially occur in areas with favourable subglacial meltwater routing and subglacial geology in the absence of these bed roughness geothermal heat flux and topographic steps may promote ice streaming significantly the primary controls on a given ice stream location are likely to influence its spatial and temporal dynamics ice streams governed by the presence of meltwater routing and or calving processes might exhibit more variable behaviour because these controls can vary over relatively short time scales compared to controls that vary over longer time scales e g geothermal heat flux subglacial roughness geology and topography identifying the controls on ice stream location is therefore of paramount importance when understanding ice stream longevity and their past and future activity