tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

buried late quaternary channel systems in the danish north sea genesis and geological evolution abstract the danish north sea has been subject to extensive seismic surveying both 2d and 3d during the past four decades the 3d seismic data from the area has mainly been used for hydrocarbon exploration but in the last decade it has also been utilized for investigating the quaternary sediments and especially buried incised valleys the erosional and depositional processes involved in forming such valleys are important in paleolandscape reconstruction but are often difficult to determine since sediment deposited by flowing water displays ambiguous geometric structures in this study we combine the analysis of infill geometries from high resolution 2d seismic data with plan view morphology analysis from 3d seismic data and lithological data from borehole reports in order to constrain the origin of buried channels in the danish north sea this data integration makes differentiations of a subaerial vs subglacial origin more robust the study focusses on analyzing a proglacial to fluvial channel system which was initiated as a subglacial tunnel valley system during the last glacial maximum and subsequently evolved as a fluvial system after deglaciation the channel system was active in a marsh environment during a period of subaerial exposure in the late weichselian to early holocene during the holocene transgression the system was gradually flooded leaving estuarine tidal deposits in the underfilled channels once the area was completely flooded the channel system was buried under marine sands

antarctic cryogenic sediments biotic and inorganic facies of ice shelf and marine based ice sheet environments abstract cryogenic sediments defined as marine deposits that form in association with ice icebergs sea ice ice shelves or marine based ice sheets are widespread in high latitude regions existing models for cryogenic depositional processes are of limited utility because of 1 lack of direct observational data 2 reliance on older land exposed sections from which inferential conclusions have been drawn 3 employment of inadequate glaciologic and oceanographic concepts and 4 failure to incorporate adequately information on the biotic content of these deposits as a first step toward developing a synthetic model for cryogenic deposition we relate glaciologic sedimentologic and biotic processes of the modern ice shelf and marine based ice sheet environments using data from antarctic continental shelves the principal deposit beneath grounded marine based ice sheets is lodgement till which often contains reworked and fragmented fossil material this till is identical in all important sedimentologic respects with terrestrial lodgement deposits marine lodgement tills commonly form geographically extensive sheets which are restricted to continental shelf sites and which may be differentiated from other cryogenic deposits by their high degree of compaction and reworked fossils waterlain till may form beneath grounded ice in areas where debris melting out of the glacier sole falls through a thin water layer up to a few m between the ice and its bed waterlain till usually lacks fossil material unless the source material for the subglacial debris is fossiliferous and is less compact than lodgement till deposition beneath large polar ice shelves e g ross filchner ronne is largely restricted to a zone probably km in width near the grounding line in this zone a complex of primary and secondary cryogenic deposits including waterlain till ice shelf rafted detritus isrd flow till slumps etc is likely to interfinger processes controlling this deposition include local basal conditions of the ice sheet and ice shelf freezing or melting presence or absence of subglacial outflow marine currents and tidal action sediment supply long and short term grounding line movement sea floor topography and water depth deposition of isrd is limited elsewhere beneath these large ice shelves because high surface accumulation rates cause downward particle paths for ice and debris thus most debris is released soon after passing the grounding line biotic activity beneath ice shelves declines rapidly in diversity and abundance between the calving margin and grounding line deposition rates seaward of the calving margin are much higher than beneath the large ice shelves here icebergs derived from outlet glaciers and ice streams that terminate directly in the sea may carry significant loads of subglacial englacial or superglacial debris which is released by a variety of mechanisms as the icebergs melt this ice rafted detritus mixes with biotic material from planktonic organisms as it falls through the water column to form compound ibrd if currents are present in the water column or at the seafloor sorting may occur to form residual ibrd on shallow banks grounded icebergs carrying subglacial debris may melt in situ forming iceberg till and iceberg ploughing of sediment may form iceberg turbate both these deposits may be difficult to distinguish from lodgement till but both are restricted to areas with modern water depths less than 450 m

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

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

deep electrical resistivity tomography for the prospection of low to medium enthalpy geothermal resources summary the growth of the geothermal industry sector requires innovative methods to reduce explo ration costs whilst minimizing uncertainty during subsurface exploration until now geoelec trical prospection had to trade between logistically complex cabled technologies reaching a few hundreds meters deep versus shallow reaching prospecting methods commonly used in hydro geophysical studies we present a recent technology for geoelectrical prospection and show how geoelectrical methods may allow the investigation of medium enthalpy geothermal resources until about 1 km depth the use of the new acquisition system which is made of a distributed set of independent electrical potential recorders enabled us to tackle logistics and noise data issues typical of urbanized areas we acquired a 4 5 km long 2 d geoelectrical survey in an industrial area to investigate the subsurface structure of a sedimentary sequence that was the target of a 700 m geothermal exploration well geo 01 satigny in the greater geneva basin western switzerland to show the reliability of this new method we compared the acquired resistivity data against reflection seismic and gravimetric data and well logs the processed resistivity model is consistent with the interpretation of the active seismic data and density variations computed from the inversion of the residual bouguer anomaly the combination of the resistivity and gravity models suggest the presence of a low resistivity and low density body crossing mesozoic geological units up to palaeogene neogene units that can be used for medium enthalpy geothermal exploitation our work points out how new geoelectrical methods may be used to identify thermal groundwater at depth this new cost efficient technology may become an effective and reliable exploration method for the imaging of shallow geothermal resources

seismic stratigraphy of shuswap lake british columbia canada abstract shuswap lake is a glacially overdeepened fiord lake located in the shuswap highlands of southern british columbia canada and consists of two sub basins each nearly 60 km long and up to 3 km wide single channel seismic reflection data collected along 218 km of track line identifies a tripartite infill stratigraphy up to 800 m thick preserved in bedrock basins eroded as much as 298 m below sea level a similar tripartite stratigraphy is exposed in nearby outcrops along the valley of the south thompson river and allows interpretation of age and depositional settings for the infill identified on seismic records in shuswap lake the lowermost seismic stratigraphic sequence sssi up to 407 m thick shows chaotic seismic facies with large scale diffractions and fills axial parts of v shaped bedrock basins outcrop data suggest that this sequence consists of subaqueously deposited ice contact silts sands and gravels deposited in a deep 1 km ice frontal lake during late wisconsin deglaciation ca 10 ka the overlying seismic stratigraphic sequence sssii up to 403 m thick shows continuous high frequency seismic facies that pass down basin into transparent reflection free facies high frequency facies are interpreted as rhythmically deposited silts and sands deposited by underflows varves such facies are well exposed along the south thompson river valley transparent distal facies likely record uninterrupted settling from suspended sediment transported down basin by interflow or overflow plumes and similar deposits are reported as currently forming in nearby kamloops lake a relatively thin deposition of very thick late glacial stratigraphic successions and an absence of older pre late wisconsin strata appears to be a characteristic shared by other narrow glacially overdeepened valleys and basins in central british columbia this may be the result of scour by subglacial meltwaters and sediment focussing during deglaciation of fiord like valleys occupied by deep ice frontal lakes and rapidly retreating ice margins

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

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

magnitudes and source areas of large prehistoric northern alpine earthquakes revealed by slope failures in lakes we identify evidence for three large paleo earthquakes in central switzerland with moment magnitudes m 6 5 7 0 significantly exceeding historically known values these earthquakes occurred during the past 15 k y and were strong enough to simultaneously affect a large region that includes the present day major cities of lucerne and zurich we reconstruct the chronology magnitudes and epicenters of these prehistoric earthquakes using temporal and spatial correlation of multiple subaqueous landslide deposits in lake zurich and lake lucerne through high resolution seismic surveys radiocarbon dated sediment cores and spatial calculations using an empirical seismic attenuation model our data indicate ongoing alpine deformation that generated and could potentially generate destructive events in heavily populated regions that have been unaccustomed to seismic activity during historic time

diatoms of the mcmurdo ice shelf antarctica implications for sediment and biotic reworking abstract in the course of investigations of the origin of the mcmurdo ice shelf mis we analyzed diatoms in 59 sediment samples collected from its upper surface fragments of centric marine species most of which occur in the ross sea today were found in all samples but identifiable marine taxa dominated the total diatom flora in only two samples in contrast non marine diatoms are abundant and diverse in most mis samples these non marine species probably live in the numerous melt ponds which are distributed widely over the shelf surface during the warmest few weeks of each austral summer non marine diatoms are clustered in four assemblages which are probably related in a complex way to geographic position on the ice shelf sediment age local geochemical variations and seasonal blooms the presence of marine diatoms in mis sediments is consistent with isotopic evidence that the mis consists of frozen seawater and with debenham s hypothesis that transport of marine macrofossils to its surface is accomplished by freezing on at the base and upward movement through the shelf caused by surface melting the combined marine and non marine diatom floras of the mis suggest a new mechanism to explain mixed diatom floras and sediments observed in antarctic cores these composite floras and sediments may be introduced or reintroduced to the marine environment during austral summers by melt water streaming off the front of the mis or through crevasses additionally icebergs calved from the mis release theie load of mixed biota and sediment when they melt these observations may pertain to oher present and former antarctic ice shelves that are characterized by surface ablation and basal freezing

the seismic stratigraphy of okanagan lake british columbia a record of rapid deglaciation in a deep fiord lake basin this paper presents the first detailed data regarding the newly discovered deep infill of okanagan lake okanagan lake 50 00 n 119 30 w is 120 km long 3 5 km wide and occupies a glacially overdeepened bedrock basin in the southern interior of british columbia this basin and other elongate lakes of the region e g shuswap kootenay kalamalka canim and mahood lakes mark the site of westward flowing ice streams within successive cordilleran ice sheets an air gun seismic survey of okanagan lake shows that the bedrock floor is nearly 650 m below sea level more than 2000 m below the rim of the surrounding plateau the maximum thickness of pleistocene sediment in okanagan lake basin approaches 800 m forty six seismic reflection traverses and an axial profile show a relatively simple stratigraphy composed of three seismic sequences argued to be no older than the last glacial cycle 30 ka a discontinuous basal unit sequence i characterized by large scale diffractions and up to 460 m thick infills the narrow v shaped bedrock floor of the basin and is interpreted as a boulder gravel deposited by subglacial meltwaters overlying seismic sequence ii is composed of two sub sequences sub sequence iia is a chaotic to massive facies up to 736 m thick lakeshore exposures close to where this unit reaches lake level show deformed and chaotically bedded glaciolacustrine silts containing gravel lens and large ice rafted boulders the surface topography of this sub sequence is irregular and in general mimics the form of the underlying bedrock as a result of compaction this sequence passes laterally into stratified facies sub sequence iib at the northern end of the basin seismic sequence ii appears to record rapid ice proximal dumping of glaciolacustrine silt as the okanagan glacier backwasted upvalley in a deep lake a thin 60 m max laminated seismic sequence iii drapes the hummocky surface of sequence ii and represents postglacial sedimentation from fan deltas the extreme thickness of sequences i and ii in okanagan lake reflects the focussing of large volumes of meltwater and sediment into the basin during deglaciation pre existing sediments that pre date the last glacial cycle appear to have been completely eroded glaciological conditions during sedimentation may have been similar to marine based outlet glaciers calving in deep water in fiord basins in contrast to marine settings where ice bergs are free to disperse large volumes of dead ice were trapped within the basin structural evidence for sedimentation around dead ice blocks has been previously used to argue that the cordilleran ice sheet downwasted in situ we emphasize in contrast the trapping of dead ice left behind by rapidly calving lake based outlet glaciers

deglacial history of glacial lake windermere uk implications for the central british and irish ice sheet in the uk a combination of outcrop mapping satellite digital elevation models high resolution marine geophysical data and a range of dating techniques have constrained the maximum limit and overall retreat behaviour of the british and irish ice sheet biis the changing styles of deglaciation have been most extensively studied in the west and north western sectors of the biis primarily using offshore geophysical surveys the surviving record in the southern terrestrial sector is fragmentary permitting only large scale tens of kilometres and longer timescale c 1 ka reconstructions of ice margin movement with limited information on deglacial processes here we present a high resolution study of the retreat behaviour for a section of the southern ice margin from windermere in the the lake district using high resolution 2d multi channel seismic mcs data processed using prestack depth migration by combining the seismic stratigraphy with landform morphologies extant cores and seismic velocity measurements we are able to distinguish between over consolidated till recessional moraines de geer moraines flowed till ice front fan supra en glacial melt out till and subsequent glaciolacustrine lacustrine sedimentation the results reveal a complex and active valley glacier withdrawal from windermere that changed character between basins and produced two small localised areas of ice stagnation and downwasting this study indicates that similar active ice margin retreats probably took place in other valleys of the lake district during the late devensian deglaciation rather than the previously held view of rapid ice stagnation and downwasting when combined with the regional terrestrial record this supports a model of early ice loss in terrestrial england compared to other parts of the united kingdom

first geomorphological record and glacial history of an inter ice stream ridge on the west antarctic continental shelf inter ice stream areas cover significant portions of antarctica s formerly glaciated shelves but have been largely neglected in past geological studies because of overprinting by iceberg scours here we present results of the first detailed survey of an inter ice stream ridge from the west antarctic continental shelf well preserved sub and proglacial bedforms on the seafloor of the ridge in the eastern amundsen sea embayment ase provide new insights into the flow dynamics of this sector of the west antarctic ice sheet wais during the last glacial cycle multibeam swath bathymetry and parasound acoustic sub bottom profiler data acquired across a mid shelf bank between the troughs of the pine island thwaites pitpis and cosgrove palaeo ice streams copis reveal large scale ribbed moraines hill hole pairs terminal moraines and crevasse squeeze ridges together these features form an assemblage of landforms that is entirely different from that in the adjacent ice stream troughs and appears to be unique in the context of previous studies of antarctic seafloor geomorphology from this assemblage the history of ice flow and retreat from the inter ice stream ridge is reconstructed the bedforms indicate that ice flow was significantly slower on the inter ice stream ridge than in the neighbouring troughs while terminal moraines record at least two re advances or stillstands of the ice sheet during deglaciation an extensive field of crevasse squeeze ridges indicates ice stagnation subsequent to re advancing ice which deposited the field of terminal moraines in the ne the presented data suggest that the ice flow behaviour on the inter ice stream ridge was substantially different from that in the adjacent troughs however newly obtained radiocarbon ages on two sediment cores recovered from the inter ice stream ridge suggest a similar timing in the deglaciation of both areas this information closes an important gap in the understanding of past wais behaviour in the eastern ase our newly documented bedforms will also serve as an important diagnostic tool in future studies for interpreting ice sheet histories in similar inter ice stream areas

till tongue stratigraphy seismostratigraphic studies on the scotian and mid norwegian continental shelves have led to the development of a conceptual model for glacial deposition and erosion by ice sheets in a marine environment till tongue model some of the terminal deposits of the marine ending glaciers are composed in part of acoustically incoherent wedge shaped bodies the wedges are thought to be part of a grounding line system associated with a floating terminus according to the model the sedimentary wedges are formed through the accumulation of glacial debris by subglacial processes proximal to the grounding line together with a penecontemporaneous proglacial contribution from sediment gravity flows sedimentation rates appear to be highest near and proximal to the grounding line that is within a grounding line zone ice proximal stratified glaciomarine sediment accumulates from plumes within the water column and rain out of ice rafted debris the glaciomarine sediment interfingers with the till tongues resulting from oscillations of the grounding line till tongues represent discrete stratigraphic units formed in both vertical and lateral successions marginal to massive till deposits major till tongues can be correlated regionally for hundreds of kilometers and thus can provide a basis for stratigraphic correlation on the mid norwegian shelf lateral and vertical successions of till tongues delineate several large scale till units which represent major advances and retreats of the ice that probably were of both stadial and glacial rank we refer to this type of succession as a till tongue stratigraphy it appears that till tongue formation is limited to intermediate water depths which range from 75 to 1 000 m present water depth but those formed in water depths 600 700 in may not be strictly subglacial in origin we speculate that processes leading to the development of till tongues possibly give rise to the formation of subglacial undermelt till together with thin flow tills near the grounding line it is also possible that another type of subglacial till embracing concepts inherent in the expression deforming basal tills as described by alley and others 1989 may contribute to the formation of till tongues boundaries between the major till units of the mid norwegian shelf are mainly depositional in the zone of maximum glaciation near the shelf edge and upper slope proximal to this zone of major deposition intraformational erosional processes dominate and give rise to smooth widespread time transgressive erosional surfaces erosion progressively increases in a proximal direction beveling the earlier glacial deposits and ultimately reaches and modifies the bedrock surface these regional surfaces are analogous to the ross sea unconformity which was also formed by glacial erosion morainic deposits within a till tongue stratigraphy are termed grounding zone moraines and are subdivided into advance and retreat varieties with linear tabular and hummocky attributes fields of small morainic ridges lift off moraines form in basinal areas during recession

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

intra crater activity aa block lava viscosity and flow dynamics arenal volcano costa rica abstract arenal volcano has exhibited an almost continuous effusion of lava since september 19th 1968 present intra crater activity is characterized by a relatively quiet rate of effusion accompanied by rhythmic pulsing of the lava due to degassing phenomena at the vent the main lava type is aa which is seldom associated with lava aplastada flattened lava this latter lava is formed within the zone of major activity and exhibits smooth slightly curved reddish brown oxidized surfaces which develop irregular cracks on cooling the genesis of this lava type is due to gas oxidation and rhythmic pulsing the additional stresses produced by the latter phenomenon combined with surface tension forces would hinder the formation of aa lava and generate flattened lava the dynamic development of lava flows can be explained in terms of three continuous cyclic phases early mature and collapsing a single flow can be divided into four structural units the upper part unit a the middle upper vesiculated part unit b the nucleus unit c and the fragmental base unit d rheologically these lavas behave like a bingham plastic characterized in the field by plug flow while the 1968 1973 lava flows are characterized by an advanced but incomplete transition from aa to block lava present flows generally undergo the entire process in this case the transition zone for a mature flow is located within the middle lower part of the volcanic cone reaching an approximate length of 300 m transition occurring during the mature phase has been investigated in detail it is related to the progressive brittle deformation of the middle upper part unit b fracturing takes place along the side of the plug where the shear strain is higher as well as within the central part where it is due to topographic discontinuities systematically reflected in the mechanical behavior of the rigid plug viscosities calculated on the basis of field measurements at 50 200 m from the crater give values of 108 poise these values are consistent with experimental results obtained in the range of extrusion temperatures 1100 1150 c and are in good agreement with experiments on suspension rheology in basalts for a similar temperature range and degree of crystallinity the high viscosity of arenal lavas can be explained in terms of their high crystallinity 70 80 lower extrusion temperatures and higher silica content in respect to basalts the existence of two interstitial immiscible melts also contributes to increase viscosity

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

seismic facies and regional architecture of the oak ridges moraine area southern ontario analysis of over 50 line kilometres of land based shallow seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac

bathymetric distribution of fossil foraminifera within marine sediment cores from the eastern part of lutzow holm bay east antarctica and its paleoceanographic implications abstract faunal analysis of fossil foraminifera from marine gravity and piston cores collected by the japanese antarctic research expeditions 1981 and 1992 is used to estimate the impact of the latest quaternary paleoceanography on coastal environments of the eastern part of lutzow holm bay east antarctica accelerator mass spectrometry ams carbon 14 ages produced from sedimentary organic carbon were less than 16 ka non corrected detailed correlation among submarine cores and holocene elevated marine deposits exposed on the eastern shore of the embayment is difficult due to the indefinite reservoir correction value for marine organic matter and to upward increasing abnormal ages for some cores a local carbonate dissolution level can be delineated around the present depth of 300 400 m or shallower in the eastern part of lutzow holm bay during the holocene based on distributional trends of arenaceous calcareous benthic and planktonic foraminifera recognized within a depth less than 600 m downcore recovery of calcareous foraminifera containing bulimina aculeata from two cores obtained in a drowned glacial trough deeper than 600 m situated far beyond the dissolution depth of caco3 indicates the incursion of warm high nutrient and caco3 saturated circumpolar deep water cdw from the offshore area along the trough toward the southeastern coast of lutzow holm bay during the holocene the intrusion of cdw impacted on the marine environments of the southeastern coast thereby contributing to peripheral retreat of the ice sheet as well as increasing calcareous benthic foraminiferal productivity along the southeastern coast of lutzow holm bay

seismic facies of glacial deposits from marine and lacustrine environments seismic facies analysis is the interpretation of sedimentary processes and depositional environments from seismic reflection data the technique was primarily developed by the hydrocarbon industry as a predictive indicator of lithology it involves the description and geological interpretation of a number of seismic reflection parameters of which configuration character and external form are the most commonly analysed parameters in recent years the concept of seismic facies analysis has been increasingly used in high resolution seismic reflection studies of late cenozoic marineand lacustrine glacigenic sequences in support of non antarctic resource and development studies e g minerals hydrocarbons fish pipelines etc and high latitude environmental surveys such studies are key to the proper oversight and utilisation of the offshore environments and to understanding the processes associated with the growth and decay of ice sheets as examples the petroleum industry has long had problems drilling on northern glaciated shelves due in part to sub seabed boulder horizons and gas hydrates but also with icebergs furrowing the seabed and impacting on sea floor installations artificial islands constructed as ice protected drilling plat

expansion and retreat of the jura ice sheet france during the last glacial maximum in continental environments while there is no uninterrupted record of glaciation glacier activity can be reconstructed from the nature and geometry of sediments trapped by lake filling examination of the combe d ain lake filling provides insight into the history of the jura mountains during the last glacial maximum lgm from the evidence of outcrops borehole cores and seismic reflection profiles of the lake filling we show that glaciation was marked by three stages of stabilization then recessional moraines marked five episodes of stabilization in the course of glacial retreat comparison with b 18 o data from ice cores of greenland makes possible to date the last glacial maximum at 25 500 22 000 cal bc and

holocene foraminiferal assemblages from firth of tay antarctic peninsula paleoclimate implications abstract the 77 m sediment core from firth of tay provides complete record of glacial retreat and holocene climate change on the weddell sea side of the antarctic peninsula that began 9400 yr bp benthic foraminiferal data indicate significant environmental changes as recorded at 600 m water depth at the drill site three foraminiferal assemblages fas globocassidulina spp fursenkoina fusiformis fa miliammina arenacea fa and paratrochammina bartrami portatrochammina antarctica fa reflect increasingly glacier distal conditions they started with most glacier proximal conditions that lasted until 8800 yr bp which is indicated by cribroelphidium cf webbi and continued with elevated input of coarse glacial sediment until 7750 yr bp the mid holocene climatic optimum between 7750 and 6000 yr bp appears to be the time of highest primary production which led to higher corrosiveness of bottom waters and biased species composition of the m arenacea fa it was terminated by minor cooling the neoglacial that took place after 3500 yr bp is marked by an increase in p bartrami and p antarctica the major constituents of the p bartrami p antarctica fa this fa became periodically dominant after 900 yr bp indicating increasingly glacier distal conditions due to cooling coinciding with increasing aridity rising altitude of the glacial equilibrium line and less glacial influence on marine biota episodic high abundances of a fourth foraminiferal assemblage globocassidulina biora fa that occurs practically throughout the core is difficult to interpret explicitly although there are some concerns if g biora fa represents in situ fauna it appears to be an opportunistic fauna that dominated during periods of more glacial sediment input and sediment remobilization leading to better carbonate preservation

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

recent glacial history and rapid ice stream retreat in the amundsen sea microfossil analyses of core top samples from 20 sites in the eastern and southern amundsen sea delimit three biotic provinces which are related in part to the activity of a large ice stream and modern sea ice distribution in recent sediments on the outer shelf planktonic and calcareous benthic foraminifera are abundant but diatoms are rare here low diatom abundances in sediments despite high abundances in the overlying sea ice are attributed to nondeposition caused by ocean currents pine island bay sediments are almost barren of microfossils even though diatoms are abundant in overlying surface waters we attribute this discrepancy to deposition of exclusively non organic sediments beneath a former extension of the floating terminus of pine island glacier which probably retreated from this area during the last century the polynya which occupies this area during present day summers is probably so recent a feature that little or no biogenic sediment has accumulated recent sediments in the eastern margin province between pine island bay and the outer shelf contain abundant diatoms and arenaceous foraminifera high diatom abundances here probably record the presence of the amundsen sea polynya during the last few millennia the presence of a compact diamicton beneath recent sediments on the outer shelf and in the eastern margin province suggests that grounded ice formerly occupied the amundsen sea shelf with ice streams in deep elongated troughs these ice streams may have retreated up to 200 km during the holocene

late quaternary morphostratigraphy of lake st joseph southeastern canadian shield evolution from a semi enclosed glacimarine basin to a postglacial lake abstract this paper reports and describes multibeam echosounder subbottom profiler and sediment sampling data collected in lake st joseph southern quebec a formerly glacimarine sedimentary basin that has been glacio isostatically uplifted to form a small lake its study provides a unique opportunity for investigating changes in sedimentary environments from a glacial sea to a postglacial lake multibeam bathymetry allows the observation of two basins separated by a bathymetric ridge and of mass movement deposits in both basins high resolution seismic stratigraphy reveals the presence of seven seismic units these seven units relate to the advance and retreat of the laurentide ice sheet over the region following ice retreat transparent u3 and high amplitude reflection u4 units were deposited during the champlain sea invasion the transparent unit likely represents a rapidly retreating glacier which allowed the deposition of massive silt and clay whereas the high amplitude reflectors which are internally composed of transparent to chaotic lenses are interpreted as the result of a deceleration of ice retreat or a stabilization of the glacier and of glacio isostatic rebound overlying the champlain sea sediments a unit composed of smaller laminations u5 suggests that it was deposited during the marine to lacustrine transition in a paraglacial environment this is supported by its presence in the northern basin where the riviere aux pins mouth is located and its absence in the southern basin where no river is observed the bathymetric ridge between the two basins thus limited sediment transport following the complete retreat of the champlain sea organic rich sediments u7 were deposited in the lake in the northern basin the presence of the riviere aux pins allowed their deposition in the form of rhythmites whereas the absence of rivers in the southern basin resulted in the deposition of an acoustically transparent unit a mass movement u6 identified during the deposition of unit 7 occurred around 1250 ad and is interpreted as earthquake triggered

lake dwellers occupation gap in lake geneva france switzerland possibly explained by an earthquake mass movement tsunami event during early bronze age abstract high resolution seismic and sediment core data from the grand lac basin of lake geneva reveal traces of repeated slope instabilities with one main slide evolved mass flow minimum volume 0 13 km 3 that originated from the northern lateral slope of the lake near the city of lausanne radiocarbon dating of organic remains sampled from the top of the main deposit gives an age interval of 1865 1608 bc this date coincides with the age interval for a mass movement event described in the petit lac basin of lake geneva 1872 1622 bc because multiple mass movements took place at the same time in different parts of the lake we consider the most likely trigger mechanism to be a strong earthquake mw 6 that occurred in the period between 1872 and 1608 bc based on numerical simulations we show the major deposit near lausanne would have generated a tsunami with local wave heights of up to 6 m the combined effects of the earthquake and the following tsunami provide a possible explanation for a gap in lake dwellers occupation along the shores of lake geneva revealed by dendrochronological dating of two palafitte archaeological sites

high resolution seismic stratigraphy of late quaternary fill of lake annecy northwestern alps evolution from glacial to interglacial sedimentary processes abstract lake annecy is a peri alpine lake of glacial origin remnant of the last glaciation the lake basin accumulated over 150 m of sediment since the last glacial maximum a dense grid of high resolution seismic data acquired during a 1993 sparker survey revealed the glacial and post glacial sedimentary infill the depth and morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface this paper focuses on the interpretation of the high resolution seismic facies of the infilling sediments of the lake basin in correlation with the results of the annecy core the quality and density of the seismic data allow in this case detailed analysis of the seismic facies in their three dimensional organisation and permit reliable interpretation in terms of depositional process and palaeo environmental setting the study reveals that the geometry and seismic facies of the infilling deposits are controlled essentially by the basin morphology and the characteristics of the sediment supply the sediment supply to the lake changes throughout the deglaciation from subglacial drainage to proglacial meltwater streams to alluvial streams and finally to the present day interglacial condition where authigenic sedimentation prevails the depositional patterns change accordingly from chaotic outwash deposits and glacio lacustrine muds at the base over axially aggrading lacustrine fans prograding alluvial fan deltas at the lake margins to finally a drape of lacustrine chalk and marl the interpreted sedimentary environment and deduced character of the sediment source are used to reconstruct the changing palaeo environment in the catchment area

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

wurmian deglaciation of western lake geneva switzerland based on seismic stratigraphy abstract western lake geneva le petit lac was filled during the quaternary over a major erosion surface truncating the cemented folded and thrusted tertiary sediments of the foreland alpine basin the carving of the lake occurred during quaternary glaciations with ice originating from the rhone valley catchment basin flowing in two branches oriented sw and ne over the swiss plateau lake geneva is situated on the south western branch of this paleo ice cap for the first time a dense grid of high resolution seismic profiles airgun 5 inch3 airgun 1 inch3 and echosounder has imaged the whole quaternary sequence providing a paleoenvironmental interpretation and a detailed reconstruction of the rhone glacier retreat stages during glacial events that led to the formation of western lake geneva the quaternary sequence filling up the bedrock valley is exceptionally thick with up to 220 m of deposits and consists of glacial glacio lacustrine and lacustrine sediments fourteen seismic units have been defined units u1 u14 unit u1 represents the remnants of glacial deposits older than the last glacial cycle preserved in the deepest part of the lake and in secondary bedrock valleys unit u2 represents gravel and sands deposited by meltwater circulation at the bottom of the glacial valley unit u3 is a thick stratified unit marking the beginning of the deglaciation when the rhone glacier became thinner and buoyant and allowed the formation of a subglacial lake younger glacial units units u4 u5 u7 u9 u11 are acoustically chaotic sediments deposited subglacially under the water table undermelt tills while the glacier was thinning these glacial units are bounded by synform erosion surfaces corresponding to readvances of the glacier the transition from a glacial to a glacio lacustrine environment started with the appearance of a marginal esker fan system unit u6 esker formation was followed by a small advance retreat cycle leading to the deposition of unit u7 then the ice front receded and stratified sediments were deposited in a glacio lacustrine environment units u8 u10 and u12 this retreat was punctuated by two readvances coppet unit u9 and nyon unit u11 producing large push moraines and proglacial debris flows finally a lacustrine environment with a characteristic lake current pattern and mass movement deposits took place units u13 and u14 except for unit u1 the sedimentary sequence records the wurmian deglaciation in a fjord like environment occupied by a tidewater glacier with a steep calving ice front the presence of an esker fan system reveals the importance of subglacial meltwater flow in continental deglaciation push moraines and erosion surfaces below the glacier indicate at least 5 readvances during the deglaciation thus revealing that oscillations of ice front are the key process in deglaciation of perialpine fjord lakes the dating of these continental glacier fluctuations would allow correlation with oceanic and ice records and help to understand the climatic mechanisms between oceans and continents

nature and classification of waterlain glaciogenic sediments exemplified by pleistocene late paleozoic and late precambrian deposits this study of waterlain glaciogenic sediments is designed to present both a review and new information on glaciogenic subaquatic deposits of differing age in a number of localities in north and south america and south africa the late paleozoic glaciogenic deposits of the parana basin in brazil and the karoo basin of south africa are singled out for special attention as they show a reasonably complete lateral sequence of terrestrial to off shore glaciogenic sedimentation although the environment of subaquatic glaciogenic sedimentation varies from one area to the next certain common elements are found which can be used to develop a generalized model for both glaciomarine and glaciolacustrine sedimentation for descriptive purposes the model is divided into two broad categories a shelf facies and a basinal facies the shelf facies is marked by massive diamicton ite which may be 200 m or more in thickness and which is frequently overlain by a complex of clastic sediments consisting primarily of gravity and fluid flows the basinal facies is marked by products of subaquatic slumps and more distal turbidites and glaciomarine sediments new terminology is introduced the massive diamicton ite which is diagnostic of the shelf facies probably represents deposition from the base of active ice in a subaquatic environment and is termed undermelt diamicton ite the gravity and fluid flows which are usually found overlying undermelt diamicton ite and in the basinal facies are subdivided into six categories glaciogenic subaquatic outwash glaciogenic suspension flow glaciogenic chaotic debris flow glaciogenic subaquatic debris flow glaciogenic slurry flow and glaciogenic turbidity flow the relative abundance of undermelt diamicton ite and the various types of gravity and fluid flows can be used to define inner shelf outer shelf inner basin and outer basin facies of glaciomarine sedimentation

pleistocene sediments beneath the ross ice shelf we report here the results of new micropalaeontological studies of sediments collected from beneath the ross ice shelf at risp site j9 82 22 s 168 38 w risp sediments hold the key to understanding the history of the west antarctic ice sheet dynamics of marine based ice sheets sedimentation processes that operate beneath ice shelves and perhaps the early glacial history of antarctica risp sediments were formerly assigned an age of late middle miocene on the basis of their diatom flora our diatom analyses do not support this age assignment diatoms in risp cores are of mixed ages ranging from miocene to late quaternary thus indicating that the sediments record a history of reworking the most recent of which could have occurred no earlier than late pleistocene these results support our previous work with ross sea sediments but throw considerable doubt on a recent hypothesis concerning miocene palaeogeographical evolution of the ross sea region

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

the record of historic earthquakes in lake sediments of central switzerland deformation structures in lake sediments in central switzerland can be attributed to strong historic earthquakes the type and spatial distribution of the deformation structures reflect the historically documented macroseismic intensities thus providing a useful calibration tool for paleoseismic investigations in prehistoric lake sediments the swiss historical earthquake catalogue shows four moderate to strong earthquakes with moment magnitudes of mw 5 7 to mw 6 9 and epicentral intensities of i0 vii to i0 ix that affected the area of central switzerland during the last 1000 years these are the 1964 alpnach 1774 altdorf 1601 unterwalden and 1356 basel earthquakes in order to understand the effect of these earthquakes on lacustrine sediments four lakes in central switzerland sarner see lungerer see baldegger see and seelisberg seeli were investigated using high resolution seismic data and sediment cores the sediments consist of organicand carbonate rich clayey to sandy silts that display fine bedding on the centimeter to millimeter scale the sediments are dated by historic climate and environmental records 137 cs activity and radiocarbon ages deformation structures occur within distinct zones and include large scale slumps and rockfalls as well as small scale features like disturbed and contorted lamination and liquefaction structures these deformations are attributed to three of the abovementioned earthquakes the spatial distribution of deformation structures in the different lakes clearly reflects the historical macroseismic dataset lake sediments are only affected if they are situated within an area that underwent groundshaking not smaller than intensity vi to vii we estimate earthquake size by relating the epicentral distance of the farthest liquefaction structure to earthquake magnitude this relationship is in agreement with earthquake size estimations based on the historical dataset d 2004 elsevier b v all rights reserved

signatures of late pleistocene fluvial incision in an alpine landscape uncertainty regarding the relative efficacy of fluvial and glacial erosion has hindered attempts to quantitatively analyse the pleistocene evolution of alpine landscapes here we show that the morphology of major tributaries of the rhone river switzerland is consistent with that predicted for a landscape shaped primarily by multiple phases of fluvial incision following a period of intense glacial erosion after the mid pleistocene transition 0 7 ma this is despite major ice sheets reoccupying the region during cold intervals since the mid pleistocene we use high resolution lidar data to identify a series of convex reaches within the long profiles of 18 tributary channels we propose these reaches represent knickpoints which developed as regional uplift raised tributary bedrock channels above the local fluvial baselevel during glacial intervals and migrated upstream as the fluvial system was re established during interglacial periods using a combination of integral long profile analysis and stream power modelling we find that the locations of 80 of knickpoints in our study region are consistent with that predicted for a fluvial origin while the mean residual error over 100 km of modelled channels is just 26 3 m breaks in cross valley profiles project toward the elevation of former end of interglacial channel elevations supporting our model results calculated long term uplift rates are within 15 of present day measurements while modelled rates of bedrock incision range from 1 mm yr for low gradient reaches between knickpoints to 6 10 mm yr close to retreating knickpoints typical of observed rates in alpine settings together our results reveal approximately 800 m of regional uplift river incision and hillslope erosion in the lower half of each tributary catchment since 0 7 ma

microfossil distributions in modern amundsen sea sediments abstract acquisition of 20 piston cores from the amundsen sea continental shelf provides material for the first determinations of modern and paleo distributions of microfossils including planktonic and benthic foraminifera diatoms and radiolaria in this region microfossil analyses of filtered sea water and sea ice samples allow comparisons of the biocoenosis with the thanatocoenosis in the sediments in all three biotic provinces are distinguished 1 the outer shelf region north of thurston island is characterized by high abundances of planktonic and calcareous benthic foraminifera low diatom abundances in sediments here despite high abundances in the sea ice may reflect prevention of deposition by ocean currents 2 the southernmost province in pine island bay is marked by very low abundances of all microfossil groups possibly because the floating terminus of pine island glacier has retreated from this area only during the last 100 years in that case the polynya that exists today in this region during some austral summers is so recent a feature that little or no biogenic sediment has had an opportunity to accumulate beneath it 3 the eastern margin province situated between the pine island bay and outer margin provinces along the eastern coast of the amundsen sea is characterized by high abundances of diatoms and arenaceous benthic foraminifera which probably record the presence of the amundsen sea polynya in this area during the last 1000 to 2500 years dominance of the benthic fauna in this area by arenaceous foraminifera is a function of the great depth from which most cores in this area were retrieved 500 924 m below the ccd

subglacial emplacement of tills and meltwater deposits at the base of overdeepened bedrock troughs the sedimentary infill of subglacially eroded bedrock troughs in the alps are underexplored archives for the timing extent and character of pleistocene glaciations but may contain excellent records of the quaternary landscape evolution over several glacial interglacial cycles the onset of sedimentation in these bedrock troughs is often reflected by diamicts and gravels directly overlying bedrock in the deepest basin segments subglacial or proglacial depositional environments have been proposed for these coarse grained basal units but their characteristics and origin remain controversial this article presents results from drill cores that recovered a coarse grained basal unit in a major buried bedrock trough system in the lower glatt valley northern switzerland the excellent core recovery allowed a detailed study combining macroscopic microscopic and geochemical methods and gives unprecedented insights into the transition from erosion to deposition in overdeepened bedrock troughs these results show that the basal infill comprises diamicts interpreted as subglacial tills separated by thin sorted interbeds originating from subglacial cavity deposition the stacking may thus represent repeated switching between a coupled and decoupled ice bed interface indicating an ever transforming mosaic of subglacial bed conditions decoupling in response to high basal water pressures is probably promoted by the confined subglacial hydraulic conditions resulting from the bedrock acting as aquitard the narrow reverse sloping outlet and a large catchment area while stratigraphic and lithological evidence suggests that erosion and the onset of basal sedimentation occurred during the same glaciation different scenarios for the relative timing of infilling in relation to formation and glaciation of the bedrock trough are discussed overlying deltaic and glaciolacustrine sediments suggest deposition during subsequent deglaciation of the bedrock trough the basal sediment characteristics are in agreement with previous reports in hydrogeological and seismic exploration and suggest the occurrence of similar basal successions in other subglacially overdeepened basin in the alps and elsewhere

a subaquatic moraine complex in overdeepened lake thun switzerland unravelling the deglaciation history of the aare glacier abstract to investigate the history of the aare glacier and its overdeepened valley a high resolution multibeam bathymetric dataset and a 2d multi channel reflection seismic dataset were acquired on perialpine lake thun switzerland the overdeepened basin was formed by a combination of tectonically predefined weak zones and glacial erosion during several glacial cycles in the deepest region of the basin top of bedrock lies at 200 m below sea level implying more than 750 m of overdeepening with respect to the current fluvial base level i e lake level seismic stratigraphic analysis reveals the evolution of the basin and indicates a subaquatic moraine complex marked by high amplitude reflections below the outermost edge of a morphologically distinct platform in the southeastern part of the lake this stack of seven subaquatic terminal moraine crests was created by a fluctuating quasi stagnant grounded aare glacier during its overall recessional phase single packages of overridden moraine crests are seismically distuinguishable which show a transition downstream into prograding clinoforms with foresets at the ice distal slope the succession of subaquatic glacial sequences foresets and adjacent bottomsets represent one fifth of the entire sedimentary thickness exact time constraints concerning the deglacial history of the aare glacier are very sparse however existing 10be exposure ages from the accumulation area of the aare glacier and radiocarbon ages from a late glacial lake close to the outlet of lake thun indicate that the formation of the subaquatic moraine complex and the associated sedimentary infill must have occurred in less than 1000 years implying high sedimentation rates and rapid disintegration of the glacier these new data improve our comprehension of the landforms associated with the ice contact zone in water the facies architecture of the sub to proglacial units the related depositional processes and thus the retreat mechanisms of the aare glacier

the biogeography of major diatom taxa in southern ocean surface sediments 3 tropical subtropical species abstract this paper gives a modern circumscription of tropical subtropical diatoms regarding their relationship with sea surface temperatures sst and sea ice cover diatoms from 228 core top sediment samples collected from the southern ocean were studied to determine the geographic distribution of eight major diatom species taxa preserved in surface sediments generally located north of the subantarctic front the comparison of the relative contribution of diatom species with modern february sst and sea ice cover reveals species specific sedimentary distributions regulated both by water temperatures and sea ice conditions although selective preservation might have played some role their presence in surface and downcore sediments from the southern ocean are reliable indicators of high sst and poleward transport of waters from the tropical subtropical atlantic our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord

evidence for abundant subglacial meltwater beneath the paleo ice sheet in pine island bay antarctica marine geological and geophysical data collected from the continental shelf in pine island bay antarctica reveal a complex paleo subglacial drainage system controlled by bedrock topography and subglacial meltwater discharge significant amounts of freely flowing meltwater existed beneath former ice sheets in pine island bay subglacial drainage is characterized by descriptions of glacial landforms imaged on the sea floor and sedimentary deposits collected in piston cores bedrock geology is characterized using seismic data large scale landforms on the shelf include channels and cavities incised into impermeable crystalline bedrock there is a transition from randomly oriented channels on the inner shelf to a dendritic pattern of elongate channels on the middle shelf on the outer shelf a change in basal conditions occurs where sedimentary deposits bury crystalline bedrock no evidence for flowing meltwater exists on sedimentary substrates instead meltwater formed a the ice sediment contact was incorporated into the sediments contributing to development of a deforming lied which was sampled in piston cores characterization of subglacial meltwater processes that occurred in the past may aid in understanding the role meltwater plays in stability of the west antarctic ice sheet today

environmental connotations of benthic foraminiferal assemblages from coastal west antarctica abstract this paper examines the variability in foraminiferal assemblages in surface samples from coastal settings along the northwestern antarctic peninsula as well as in the pine island bay area material comes from water depths ranging between 20 and 1257 m latitudes between 62 and 73 s and bottom water temperatures from 1 5 to 1 2 c the microfossil analysis within this broad geographical and environmental context provides a basis for paleo environmental studies environmental affinities of the assemblages were interpreted based on a wide array of ecological conditions including ctd data as well as on faunal indices and ecological affinities of the key taxa six foraminiferal assemblages are dominated by calcareous taxa among other factors they correspond to variable food supply terrigenous sedimentation and water mass properties another two assemblages are dominated by arenaceous foraminifera and reflect conditions corrosive to carbonate our findings indicate that preserved fossil assemblages in cores from these locations may not be accurate representations of living assemblages

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

erosion under climate and human pressures an alpine lake sediment perspective we review the scientific efforts over the last decades to reconstruct erosion from continuous alpine lake sediment records we focused both on methodological issues showing the growing importance of non destructive high resolution approaches xrf core scanner as well as progresses in the understanding of processes leading to the creation of an erosion signal in lakes we distinguish continuous records from event records both provide complementary information but need to be studied with different approaches continuous regionally relevant records proved to be particularly pertinent to document regional erosion patterns throughout the holocene in particular applying the source to sink approach event based approaches demonstrated and took advantage of the strong non linearity of sediment transport in high altitude catchment areas this led to flood frequency and intensity reconstructions highlighting the influence of climate change upon flood dynamics in the mountain the combination of different record types both in terms of location high vs low elevation sedimentology high vs low terrigenous contribution and significance local vs regional is one of the main outputs of this paper it allows the establishment of comprehensive histories of nw french alps erosion but also and consequently soil dynamics and hydrological patterns throughout the holocene we also discuss the influence of glacier dynamics one of the major agents of erosion in the alps a major feature is the growing human influence upon erosion at a local scale since at least the middle of the bronze age 3500 cal bp however and according to the regional record from lake bourget only few periods of rising erosion at local scales generated a regional record that can be discriminated from wetter climatic periods among them the period between 200 bce and 400 ad appeared to be marked by a generalised rise in human triggered erosion at local scales in the northern french alps this review highlights the importance of modern high resolution and interdisciplinary studies of lake sediments in order to better understand the complex relationships between humans climate and the earth system in general we strongly argue that regional integration of data is now required to move a step further such an integration is easier with cost and time effective methods as well as after a better definition of approaches and their limits this should lead to a stronger collaboration between paleo data producers and modellers in the near future

proglacial subaquatic outwash fan and delta sediments in push moraines indicators of subglacial meltwater activity abstract a significant proportion of the glaciofluvial sediments in the rehburg stage saalian glaciation push moraines in germany appears to be subaquatic in origin they form subaquatic fans deltas and lacustrine deposits composed mainly of reworked autochthonous sediments with only minor amounts of erratic mainly scandinavian material subaquatic sediments occur in three positions with respect to the push moraines 1 pre tectonic and early syn tectonic sediments incorporated in the push moraine and overlying preglacial sediments 2 syn tectonic sediments overlying angular unconformities and filling depressions between anticlinal ridges on top of the push moraine and 3 post tectonic sediments on the distal push moraine slopes this indicates that lakes existed prior to and during the advance of the scandinavian ice sheet onto the north german lowlands and also after formation of the push moraines and prior to their overriding the topsets are commonly overlain by a deformation till produced by subglacial shearing of these sediments the rehburg push moraines closely follow the northern margin of the hercynian highlands in germany blocking of the ice marginal drainage by advancing ice lobes produced vast lakes between the ice sheet and the northern slopes of these highlands both the sedimentology and the petrology of the sediments in the rehburg push moraines suggest that these subaquatic sediments are products of subglacial erosion beneath ice lobes or ice streams since the pre tectonic lakes formed at the ice margin the subaquatic fans and deltas were constructed from the mouths of subglacial tunnels thus it is proposed that these sediments are eskerine in origin a subglacial provenance is supported by the occurrence in some of these sediments of layers and lenses of a pure and uniform petrology intercalated with strata of a more mixed petrology these are interpreted as the products of meltwater tunnelling in the saturated sediments beneath the ice lobes which produced the push moraines

identification of erosional mechanisms during past glaciations based on a bedrock surface model of the central european alps the bedrock topography beneath the quaternary cover provides an important archive for the identification of erosional processes during past glaciations here we combined stratigraphic investigations of more than 40 000 boreholes with published data to generate a bedrock topography model for the entire plateau north of the swiss alps including the valleys within the mountain belt we compared the bedrock map with data about the pattern of the erosional resistance of alpine rocks to identify the controls of the lithologic architecture on the location of overdeepenings we additionally used the bedrock topography map as a basis to calculate the erosional potential of the alpine glaciers which was related to the thickness of the lgm ice we used these calculations to interpret how glaciers with support by subglacial meltwater under pressure might have shaped the bedrock topography of the alps we found that the erosional resistance of the bedrock lithology mainly explains where overdeepenings in the alpine valleys and the plateau occur in particular in the alpine valleys the locations of overdeepenings largely overlap with areas where the underlying bedrock has a low erosional resistance or where it was shattered by faults we also found that the assignment of two end member scenarios of erosion related to glacial abrasion plucking in the alpine valleys and dissection by subglacial meltwater in the plateau may be adequate to explain the pattern of overdeepenings in the alpine realm this most likely points to the topographic controls on glacial scouring in the alps the flow of lgm and previous glaciers were constrained by valley flanks while ice flow was mostly divergent on the plateau where valley borders are absent we suggest that these differences in landscape conditioning might have contributed to the contrasts in the formation of overdeepenings in the alpine valleys and the plateau