equifinality of basal ice facies from an antarctic cold based glacier threedebris bearingicefacieswererecognizedatthebaseofsuessglacier a cold basedglacierdamminga lakeintaylorvalley southvictoria land antarctica these faciesaretermed amber ice solidfacies and basal stratifiedfacies thispaper uses stable isotope composition dd and d 18 o gas content and gas composition co 2 o2 and n2 to develop an understanding of the processes responsible for the formation of these facies the basal iceischaracterizedbya strikingdifferencein icepropertiesbetweentheinnermostend of a 25m long tunnel dug 200m upstream fromthe glacier front and the front itself at the glacier front co isotopic data plot along a well defined freezing slope s 5 6 whereas insidethetunnel the isotopic data offset fromthefreezing slope and fromthe local meteoric water line which has a slope of 8 2 co 2 concentrations rise from a minimum of about 1000ppmv inthetunnelto about 220000ppmvatthe front takentogether these character istics strongly suggest an increasing contribution of liquidwater inthe formation of basal ice towards the glacier terminus we therefore conclude that visually similar basal ice facies can have differentorigins

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

influence of secular variation of the geomagnetic field on production rates of in situ produced cosmogenic nuclides abstract scaling factors are presented that allow a full description of the cosmic ray flux modulation during secular variation of the geomagnetic field these scaling factors are analogous to those determined in a similar work dunai t j earth planet sci lett 2000 176 157 169 that were accurate for field strengths equivalent to present day field strength but cannot accommodate field strength variations strategies to derive the relevant geomagnetic field parameters are discussed and are tested with existing production rate calibrations for 3 he a production rate of 103 4 2 atoms g olivine yr sea level and for zero cutoff rigidity was derived from calibration sites from hawaii western usa and canary islands covering the time range of 2 281 kyr

glaciohydraulic supercooling in iceland we present evidence of glaciohydraulic supercooling under jokulhlaup and ablation dominated conditions from two temperate icelandic glaciers observations show that freezing of sediment laden meltwater leads to intraglacial debris entrainment during normal and extreme hydrologic regimes intraglacial frazil ice propagation under normal ablation dominated conditions can trap copious volumes of sediment which forms anomalously thick sections of debris rich ice glaciohydraulic supercooling plays an important role in intraglacial debris entrainment and should be given more attention in models of basal ice development extreme jokulhlaup conditions can result in significant intraglacial sediment accretion by supercooling which may explain the concentration of englacial sediments deposited in heinrich layers in the north atlantic during the last glaciation

long term fluvial archives in hungary response of the danube and tisza rivers to tectonic movements and climatic changes during the quaternary a review and new synthesis abstract the paper discusses the quaternary evolution of the danube and tisza rivers and their main tributaries in the context of evolution of the entire pannonian basin which is europe s largest intramontane basin within the alp carpathian orogen the palaeo drainage reconstruction of the pannonian basin for the pre quaternary period is outlined in connection with the gradual regression of lake pannon since the late miocene deltas of rivers that entered the basin from the northwest and northeast were gradually transformed into extended alluvial plains thus the earliest possible ancestor of the danube coming southeastwards from the alps could be as old as late miocene by the pliocene the whole lake pannon was infilled the former extensional basin formation was replaced by a compresional stress field which resulted in an uplift of the marginal flanks and late stage subsidence anomalies the increasing relief led to the formation of the quaternary drainage pattern the actively subsiding young basins were filled by fluvial sediments transported by the danube and tisza river systems from the uplifting mountains between the subsiding regions of the little and great plains the danube has formed an antecedent valley with terrace staircases between the uplifting sections of the transdanubian range and the north midmountains the formation of the terraces is attributed to periodic climate changes during the pleistocene combined with differences in the uplift rate the paper gives a complex overview of the classical chronology of the six terraces based on various data sources mostly dating of loess paleosol sequences travertines aeolian sand and tephra strata overlying the fluvial sediments complemented by scattered vertebrate faunal data and archaeological evidence directly from the terrace sediments the quaternary drainage pattern evolution of the great plain with a strong tectonic control is discussed in detail rivers originating from the uplifting marginal areas were drawn towards the subsiding depressions which served as local base level changes in subsidence rates in space and time throughout the quaternary resulted in the evolution of a complex drainage pattern a special emphasis is placed on the late pleistocene holocene development of the middle tisza region and the koros basin where the berettyo koros rivers form an eastern tributary system of the tisza river a comparative evaluation of these two areas is especially relevant as they provide insights into large scale late pleistocene avulsion of the tisza river osl dating complemented with inferred transport directions determined from heavy mineral analysis of fluvial sediments in the koros basin has revealed an ancient large meandering river system that can be identified with the palaeo tisza which was flowing along a tectonically controlled depression during the late pleniglacial successions in the middle tisza region have allowed differentiation between the older channels of the palaeo bodrog river and the sajo hernad alluvial fan and the younger meander belts of the new course of the tisza in the tisza system changes in river style braided to various scales of meandering show correspondence to millennial scale climate changes of the last 25 ka while in the koros basin the effects of tectonics are overprinted onto the regional climatic signals

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

evidence for two zones of debris entrainment beneath the greenland ice sheet investigation of the ice debris and stable isotope characteristics of basal ice exposed at the margin of the greenland ice sheet provides a means of testing and refining models of ice sheet erosion and deposition the basal ice exposed at the ice sheet margin gives evidence of the processes operating at the bed at different locations which can be used to constrain theoretical models predicting varying basal conditions1 2 improved understanding of the effects of isotope fractionation in hydrogen and oxygen caused by freezing processes at the bed which modify the isotope characteristics of the basal ice layers enables us to report evidence of two separate zones of debris entrainment beneath the ice sheet

long term fluvial incision rates and postglacial river relaxation time in the french western alps from 10be dating of alluvial terraces with assessment of inheritance soil development and wind ablation effects studying river long profile development as a response to tectonic and climatic controls requires reliable age dating of paleo profile remnants preserved as river terraces cosmic ray exposure cre dating often represents the only method available to date river terraces but the interpretation of cosmogenic nuclide concentrations is complicated by pre depositional inheritance and post depositional disturbance of the terrace deposits through pedogenesis and surface inflation or deflation here we use cosmogenic 10be measurements to date alluvial terraces in the french western alps in order to estimate river incision rates and to infer river response to climatic fluctuations and tectonic forcing we assess inheritance by constructing 10be concentration vs pebble depth profiles and use a monte carlo technique to estimate terrace ages we find that inheritance is negligible on all terraces enabling us to date terraces as young as 5 ky terraces that predate the last glaciation experienced intense pedogenesis and wind ablation which led to significant scatter in the 10be concentrations of surface samples we assess these effects using a model of 10be ingrowth and show that the oldest cre ages of surface clasts are close to the probable terrace age we study two catchments which have undergone varying degrees of glacial disruption the buech river experienced variations in runoff and sediment flux during the last glaciation as well as occasional ice dammings of its outlet its upper terraces record incision rates averaged over 190 ky of 0 8 mm yr consistent with denudation rates estimated in the surrounding areas and suggesting long term stability of river incision rates climatic forcing is well documented for the drac river which was repeatedly dammed by glaciers during cold periods its postglacial incision history was triggered by an 800 m drop in base level following ice dam disappearance long profile development by knickpoint propagation explains the time lag of 2 5 ky between this base level drop and terrace abandonment upstream as well as subsequent peak incision rates of 6 cm yr followed by a gradual decrease in incision rates the present knickpoint location 55 km upstream from the glacial damming site enables us to calculate a fluvial response time of 15 20 ky controlled by knickpoint propagation rates of several meters per year within the drac river

late glacial and holocene 10be production rates for western norway we present a new regional calibration of the 10be production rate from two well dated surfaces insouthern norway a rock avalanche with 14c dated wood and a precisely dated younger dryas moraine c

dynamic implications of discontinuous recrystallization in cold basal ice taylor glacier antarctica crystallographic investigations have been conducted of cold 17 c debris bearing ice from the base of an antarctic outlet glacier taylor glacier the 4 m thick sequence studied has been retrieved from a 20 m long tunnel dug from the glacier snout and has been analyzed with an automatic ice fabric analyzer aifa the top and bottom of the sequence consists of clean meteoric ice englacial facies whereas alternating debris rich and clean bubbly ice layers are found in the middle part stratified facies ice from the englacial facies displays a polygonal texture and a strong c axis clustering toward the vertical denoting recrystallization through subgrain rotation sgr in contrast clean ice from the stratified facies shows sgr fabrics which are delimited at the contact with debris rich layers by large interlocking grains organized in ribbons these two distinct textures within the stratified facies are associated with looser c axis patterns at the scale of single thin sections which is interpreted as resulting from migration recrystallization mr the change from sgr to mr trends marks a clear increase in grain boundary and nucleation kinetics hence the term discontinuous recrystallization and may be associated with strain localization at rheological interfaces during basal ice genesis analogies with bottom ice from deep polar ice sheets where temperature is commonly higher than at the studied site are highlighted two recrystallization scenarios are proposed accounting for the development of both types of fabrics it is shown that by controlling the repartition of stress and strain energy within basal ice the rheology of debris bearing ice layers plays a decisive role in recrystallization dynamics at structural interfaces we also demonstrate how the same recrystallization regimes may occur in cold glaciers and temperate ice sheets provided that strain accumulation has been high enough in the former this challenges the common belief that migration fabrics observed in bottom ice from deep ice sheets are exclusive to warm stagnant annealed ice copyright 2008 by the american geophysical union

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice ii theory simple theory supports field observations lawson and others 1998 that subglacial water flow out of overdeepenings can cause accretion of layered debris bearing ice to the bases of glaciers the large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths if that flow ascends a sufficiently steep slope out of an overdeepening the water will supercool as the pressure melting point rises and basal ice accretion will occur diurnal occasional or annual fluctuations in water discharge will cause variations in accretion rate debris content of accreted ice or subsequent diagenesis producing layers under appropriate conditions net accretion of debris bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget

two facies interpretation of the basal layer of the greenland ice sheet contributes to a unified model of basal ice formation two exposures of basal ice in alaska and greenland which have previously provided the basis for contrasting models of basal ice development are in fact directly comparable reinterpretation of previous field descriptions combined with new structural and sedimentological data from west greenland facilitates a simple unification of previous models of basal ice development and a common terminology for the field description of basal ice sequences the stratigraphy of the basal ice sequence at any site indicates the subglacial conditions and processes operating up glacier of that site presented here are interpretations of the major sequence types

former dynamic behaviour of a cold based valley glacier on svalbard revealed by basal ice and structural glaciology investigations large numbers of small valley glaciers on svalbard were thicker and more extensive during the little ice age lia demonstrated by prominent ice cored moraines up to several kilometres beyond present day margins the majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds indicating they are likely to have undergone a thermal transition from a polythermal to a cold based regime we present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of tellbreen a small cold based valley glacier in central spitsbergen based on its basal sequence and glaciological structures within the basal sequence the underlying matrix supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer this is overlain by debris poor dispersed facies ice interpreted to have formed through strain induced metamorphism of englacial ice the sequential development of structures includes arcuate fracture traces interpreted as shear planes formed in a compressive transpressive stress regime and fracture traces interpreted as healed extensional crevasses the formation of these sediment ice facies and structures is indicative of dynamic warm based flow most likely during the lia when the glacier was significantly thicker

local erosion rates versus active tectonics cosmic ray exposure modelling in provence south east france over the past decade in situ produced cosmogenic nuclides have revolutionised the study of landscape evolution in particular numerous studies have demonstrated that in active tectonic settings cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long term deformation rates in western european countries erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates in this study we present the results of a depth profiling technique applied to alluvial terraces located along the rhone and the moyenne durance rivers the expected decrease with depth of the measured 10be concentrations has been modelled using a 2 inversion method in order to constrain the exposure history of the alluvial sediments the results suggest that 1 over the quaternary the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m myr in southeastern france and 2 providing a fairly good bracketing of the exposure age the modelled abandonment age of alluvial terraces affected by the moyenne durance fault allows estimating incision rates comparing the alluvial terrace elevations with topographic river profiles and a minimum vertical slip rate value of roughly 0 02 mm yr for the southern segment of the moyenne durance fault

basal ice microbiology at the margin of the greenland ice sheet basal ice at the margin of the greenland ice sheet was studied with respect to its physical characteristics and microbiological community the basal ice contained high concentrations of dissolved ferrous fe and must therefore be anoxic oxygen consumption experiments indicate that 50 of the oxidation was due to biological activity while the rest could be attributed to chemical processes most likely weathering reactions with ferrous fe at least six different fe containing mineral sources were detected in basal ice together with potential bioavailable fe nanoparticles an active denitrifier population was identified due to formation of 30 n dinitrogen gas after amendment of anoxic sediment slurries with 15 n no3 sulfate reduction could not be detected the solid ice facies contained an abundant 10 8 cells cm 3 and complex microbial community that harbored representatives of at least eight major phyla within the domain bacteria the clone library was dominated by members of the subdivision of proteobacteria of which the largest proportion was affiliated to the genus rhodoferax that comprises facultative aerobic iron reducers the second most abundant phylum was bacteroidetes the solid ice facies had many physical similarities with the overlying debris rich banded ice facies indicating that they formed by similar subglacial processes and harbor similar microbial communities this study extends our knowledge of life in subglacial environments such as beneath ice sheets genbank accession numbers hm439882 hm439950 hq144215 hq144221

river incision and terrace formation in the late cenozoic of europe abstract late cenozoic environmental changes which affected european rivers are reviewed focusing especially on those of mid pleistocene times c 1 2 0 8 ma or around mis 22 and thereafter these involved dominating but fluctuating cold climate periglacial conditions shorter but major episodes of glaciation and brief interglacials there were also related sea level and tectonic responses the known history of european rivers in this period is individually varied but is predominantly marked by multiple stages of episodic incision the form of which changed in style at around the mid pleistocene transition it is suggested that the nature of climatic oscillations the dating of incision episodes and the processes that achieve this incision are as yet insufficiently understood fluvial process studies suggest that the onset of incision may broadly relate to changes in slope discharge sediment load and calibre and bedrock erodibility and these may all have been transformed as the direct or indirect result of mid pleistocene climatic changes common properties of basal sediments on strath terraces suggest that it was during the extended but variable cold stage episodes that both valley deepening and lateral widening occurred and that climatic change was the principal driver of episodic deep valley incision

alpine tectonics of the pannonian basin the neogene evolution of the pannonian basin is fairly well understood in terms of back arc extension behind the carpathian thrust fold belt this middle miocene holocene basin however is superimposed on an earlier middle eocene early miocene basin traditionally called the paleogene basin of hungary although the paleogene stratigraphy of the basin is well known its structural evolution is not clear however a transtensional origin is assumed analogous to the overlying pannonian basin the existing data set on the paleogene basin can be integrated easily into a compressional basin model other intra carpathian paleogene basins such as the transylvanian and slovenian basins are now considered to be flexural in origin systematic interpretation of reflection seismic data shows that these tertiary basins are superimposed on a cretaceous alpine thrust fold belt the internal geometry of this belt in the basement of the pannonian basin indicates a close relationship to the surrounding mountain belts alps carpathians and dinarides whereas the neogene pannonian basin is in a mature stage of exploration the underlying paleogene flexural basins are much less explored furthermore the cretaceous thrust fold belts should be regarded as frontier areas for future oil and gas exploration efforts

debris entrainment and landform genesis during tidewater glacier surges the englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed the subsequent melt out of debris rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity we investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice englacial structures and ridge networks exposed at the margins of tunabreen a tidewater surge type glacier in svalbard the basal ice facies display clear evidence for brittle and ductile tectonic deformation resulting in overall thickening of the basal ice sequence the formation of debris poor dispersed facies ice is the result of strain induced metamorphism of meteoric ice near the bed debris rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults reoriented crevasse squeezes and preexisting fractures these structures are observed to melt out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff ridge networks are also located at the terrestrial margins of tunabreen neighboring von postbreen and in a submarine position within tempelfjorden analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris rich englacial structures this in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges

climate and related controls on interglacial fluvial sedimentation in lowland britain lewin john gibbard p l 2002 climate and related controls on interglacial fluvial sedimentation in lowland britain sedimentary geology 151 3 4 pp 187 210 rae2008

a quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment 1 we have constructed a numerical model of basal ice formation for glacier ice in contact with subglacial sediment the model predicts four different ice facies whose formation is controlled by availability of subglacial water to satisfy the basal freeze on rate clean or clotted facies may result from congelation or frazil ice growth occurring when supercooled meltwater separates ice base from substrate or if a groundwater source can supply water to the ice base at a velocity equal to the freezing rate laminated facies develops when the supply of subglacial water is sufficiently constrained for cryostatic suction to raise the subglacial effective stress above a threshold for intrusion of ice into sediment by regelation debris laminas 1 mm are entrained by short periodic regelation events of a few hours separated by longer periods days to months of congelation further meltwater limitation produces a massive dirty ice facies due to stacking of debris laminas the model predicts growth of solid dirty ice facies when the bed is meltwater depleted with fast freezing 5 mm yr 1 causing enhanced erosion 30 mm yr 1 we find that basal ice facies and sediment entrainment are controlled mainly by the ratio of freezing rate to water supply rate the predicted ice facies compare favorably with borehole camera imagery of the basal ice layer in kamb ice stream west antarctica facies variability in this layer suggests complex hydrologic history for the west antarctic ice sheet with significant changes occurring over a period of several thousand years

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

application of borehole optical televiewing to investigating the 3 d structure of glaciers implications for the formation of longitudinal debris ridges midre lovenbreen svalbard digital optical televiewing optv of hot water drilled boreholes is evaluated as a technique for the investigation of englacial ice and debris structures on the basis of six boreholes drilled in the terminus region of midre lovenbreen svalbard the resulting optv logs successfully reveal several visually distinctive englacial ice properties and deformation structures e g oblique englacial fractures imaged here for the first time combining these optv logs with surface mapping has resulted in the identification of eight separate structural elements several of which can be interpolated onto 3 d grids at a node spacing of 1 m vertically and 10 m horizontally basally derived englacial sediment layers are also found to be intercalated with primary stratification elevated into near vertical planes around a central fold axis by large scale lateral folding the analysis also allows supraglacial longitudinal debris ridges to be subclassified into two types a previously described type i form which are the exposed fold axes of large scale lateral folds and a new type ii form experiencing secondary deformation by small scale horizontal folding in association with vertical displacements across arcuate shear planes in response to longitudinally compressive stresses near the glacier terminus although using boreholes to investigate glacier structure is limited e g by parallelism with vertical planes applying optv to multiple boreholes at midre lovenbreen has successfully revealed a range of 3 d structural elements at high spatial resolution as such interpolating between multiple optv logs overcomes many of the problems associated with interpretations made solely on the basis of surface based structural mapping and combining the two techniques represents a powerful glaciological tool

a note of caution on the use of boulders for exposure dating of depositional surfaces abstract exposure dating of boulders has been widely applied to determine the age of depositional surfaces under the assumption that the pre depositional nuclide component in most boulders is negligible here we present a case study on fluvial terraces at the active mountain front of the eastern andes where this assumption is clearly invalid because sandstone boulders n 13 from terraces at two sites contain a highly variable inherited 10be component and have apparent 10be ages that exceed the age of the respective surface by up to 90 ka likewise boulders from active stream channels n 5 contain a substantial inherited 10be component equivalent to 5 48 ka of exposure the age of the fluvial terraces is well determined by two approaches that allow to correct for the pre depositional nuclide component 10be dating of amalgamated pebbles and 10be depth profiles on sand samples at site 1 three terraces have 10be ages of 3 5 ka t2 11 13 ka t3 and 16 20 ka t4 which are consistent with the terrace stratigraphy the age of terrace t3 is confirmed by a calibrated 14 c age of 12 61 0 20 ka bp obtained from a wood sample at site 2 terrace t3 has a 10be age of 13 16 ka the average inherited 10be concentration of sand grains determined from depth profiles and stream sediments is small and equivalent to 1 3 ka of exposure in contrast the mean inheritance of pebbles and boulders is higher and equivalent to exposure times of 10 ka and 30 ka respectively these differences in the pre depositional nuclide component are related to the different provenance and transport history of sand pebbles and boulders the sand is derived from rapidly eroding miocene sediments exposed near the mountain front whereas the pebbles and boulders originate from triassic sandstones in the internal part of the fold and thrust belt on their way to the mountain front boulders and pebbles were temporarily stored and irradiated in alluvial fans that are currently reworked as sediment deposition in intramontane basins and their subsequent excavation is common in the andes and other fold and thrust belts the presence of pre depositional nuclide components should be evaluated when applying exposure dating at active mountain fronts

middle pleistocene to holocene fluvial terrace development and uplift driven valley incision in the se carpathians romania abstract this study reveals that in the se carpathians terrace development and fluvial incision during the middle pleistocene holocene are predominantly controlled by tectonic uplift as shown by terrace distributions and uplift amounts and rates the work focuses on a transect from the internal nappes and brasov intramontane basin western domain to the external nappes and focsani foredeep basin eastern domain new infrared stimulated luminescence ages were obtained and minimum terrace formation ages were determined to derive fluvial incision rates and thereby to constrain tectonic uplift in the eastern domain non uniform terrace distributions in adjacent sub parallel more active punta and less active usi a rivers and an eastward migrated fluvial incision from the orogen to the foredeep basin indicate tectonic uplift as dominant control on terrace development strath terraces in the western and eastern domains indicate repeated events of vertical fluvial incision and lateral erosion during the early middle pleistocene and late middle pleistocene holocene respectively these events imply successive recurrent disturbances of equilibrium conditions due to pulses of increased tectonic uplift fill terraces in the western domain show that initial aggradation periods were followed by uplift driven vertical incision during the late middle late pleistocene as fill terraces show a wide spread development climatic change and complex response cannot be excluded as contributing factors synchronous to terrace development loess deposition periods during the late middle late pleistocene and latest pleistocene and intercalated episodes of palaeosol formation during the late pleistocene imply comparable climatic conditions across the se carpathians dominant strath terraces of the eastern domain indicate stronger fluvial incision 240 m since the late middle pleistocene whereas older strath and younger dominant fill terraces of the western domain designate a lower amount 90 m since the early middle pleistocene middle pleistocene holocene fluvial incision rates document higher tectonic uplift in the external nappes and lower towards the western intramontane and eastern foredeep basins

low frequency variability of the scottish coastal current induced by along shore pressure gradients abstract mean currents over much of the continental shelf west of scotland have a northward component low frequency currents measured close to the west coast of scotland in 1983 and 1984 show a mean northward flow but indicate that it is highly variable over time scales corresponding to the passage of weather systems it is shown that coastal along shore pressure gradients are an essential part of the description of the along shore dynamics northward pressure gradient and current pulses are associated with depressions passing to the north of britain whilst less frequent southward pulses are the response to smaller depressions tracking further south across the british isles part of the observed northward mean flow in the region may thus result from a pumping effect arising from the passage of successive depressions to the north of britain

terminal zone glacial sediment transfer at a temperate overdeepened glacier system continuity of sediment transfer through glacial systems is essential to maintain subglacial bedrock erosion yet transfer at temperate glaciers with overdeepened beds where subglacial fluvial sediment transport should be greatly limited by adverse slopes remains poorly understood complex multiple transfer processes in temperate overdeepened systems has been indicated by the presence of large frontal moraine systems supraglacial debris of mixed transport origin thick basal ice sequences and englacial thrusts and eskers at svinafellsjokull thrusts comprising decimetre thick debris rich bands of stratified facies ice of basal origin with a coarser size distribution and higher clast content than that observed in basal ice layers contribute substantially to the transfer of subglacial material in the terminal zone entrainment and transfer of material occurs by simple shear along the upper surface of bands and by strain induced deformation of stratified and firnified glacier ice below thrust material includes rounded and well rounded clasts that are also striated indicating that fluvial bedload is deposited as subglacial channels approach the overdeepening and then entrained along thrusts substantial transfer also occurs within basal ice with facies type and debris content dependent on the hydrological connectedness of the adverse slope a process model of transfer at glaciers with terminal overdeepenings is proposed in which the geometry of the overdeepening influences spatial patterns of ice deformation hydrology and basal ice formation we conclude that the significance of thrusting in maintaining sediment transfer continuity has likely been overlooked by glacier sediment budgets and glacial landscape evolution studies

landscape evolution and ice sheet behaviour in a semi arid polar environment james ross island ne antarctic peninsula this study of landscape evolution presents both new modern and palaeo process landform data and analyses the behaviour of the antarctic peninsula ice sheet through the last glacial maximum lgm the holocene and to the present day six sediment landform assemblages are described and interpreted for ulu peninsula james ross island ne antarctic peninsula 1 the glacier ice and snow assemblage 2 the glacigenic assemblage which relates to lgm sediments and comprises both erratic poor and erratic rich drift deposited by cold based and wet based ice and ice streams respectively 3 the boulder train assemblage deposited during a mid holocene glacier readvance 4 the ice cored moraine assemblage found in front of small cirque glaciers 5 the paraglacial assemblage including scree pebble boulder lags and littoral and fluvial processes and 6 the periglacial assemblage including rock glaciers protalus ramparts blockfields solifluction lobes and extensive patterned ground the interplay between glacial paraglacial and periglacial processes in this semi arid polar environment is important in understanding polygenetic landforms crucially cold based ice was capable of sediment and landform genesis and modification this landsystem model can aid the interpretation of past environments but also provides new data to aid the reconstruction of the last ice sheet to overrun james ross island

the geography of basal ice and its relationship to glaciohydraulic supercooling svinafellsjokull southeast iceland abstract glaciohydraulic supercooling is potentially an important mechanism of basal ice formation with significant implications for quaternary science but remains controversial some studies cite similarities between basal ice and the ice forming at vents of upwelling supercooled subglacial water as evidence that where supercooling occurs it dominates basal ice formation other studies find no evidence linking supercooling to basal ice even at glaciers where supercooling occurs questioning the supposed genetic link between basal ice and vent ice at svinafellsjokull southeast iceland we compare the physical characteristics and geographical distribution of stratified basal ice with the characteristics and distribution of phenomena such as upwellings and anchor ice terraces associated with supercooling two physically and geographically distinct basal ice populations emerge one occurs only where there is evidence for glaciohydraulic supercooling and has physical characteristics consistent with an origin by supercooling the other is ubiquitous even at locations where there is no evidence for supercooling and has characteristics consistent with non supercooling modes of origin we suggest that glaciohydraulic supercooling does not account for all of the basal ice at svinafellsjokull and that other mechanisms of basal ice formation are also significant

early pleistocene incision of the san juan river utah dated with 26al and 10be cosmogenic 26al and 10be in alluvial gravel on a strath 150 m above the san juan river utah reveal a depositional age of batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document 1 36 0 20 0 15 end document ma this gravel is correlative with a series of terraces that grade to glen canyon on the colorado river indicating a similar age for incision there the calculated incision rate 110 14 m m y is somewhat slower than that of the colorado river in the eastern grand canyon and suggests active steepening of the colorado river the cosmogenic nuclides also indicate rapid erosion in the sediment source area and are consistent with alluviation due to enhanced pleistocene erosion in the san juan mountains

deformation properties of subfreezing glacier ice role of crystal size chemical impurities and rock particles inferred from in situ measurements to improve understanding of the deformation properties of subfreezing polycrystalline glacier ice and in particular the role of crystal size chemical impurities and rock particle impurities we analyze in situ strain rates of the basal layers of meserve glacier antarctica strain rates were monitored on the walls of a subglacial tunnel where down flow shear stress is relatively uniform and ice properties were measured texture fabric and impurity content we propose a simple empirical model describing strain rate variations due to variations in crystal size and impurity content and we use all relevant meserve data to constrain model parameters we conclude that there is a direct dependence of strain rate on crystal size which reflects an important role for a grain size sensitive deformation mechanism such as grain boundary sliding or diffusion chemical impurities are found to enhance the grain size sensitive deformation and are found to be an important control on strain rate variations in the very impure ices of meserve glacier however the per molar sensitivity of strain rate to chemical impurity content is shown to be very low such that in the ice age ices of the greenland ice sheet there is probably an immeasurable contribution of chemical impurities to strain rate enhancement though we cannot exclude chemical enhancements as high as 1 3 there our analyses detect no direct rheologic effect of rock particles in the meserve ices which suggests that rock content is not directly responsible for the low viscosity of dirty basal layers

thermodynamics of basal freeze on predicting basal and subglacial signatures of stopped ice streams and interstream ridges we have constructed a numerical model that simulates the response of subglacial sediments to basal freeze on the model is set up to emulate the basal zone of drilling sites in the ross sea sector of thewest antarctic ice sheet we treatbasal freeze on atanice sedimentinterfaceasathermodynamicprocessthatcouplestheflowofwater heat and solutes inunfrozensubglacial sedimentsunderlyinga freezingicebase thecouplingof these flows occurs through the clapeyron equation which specifies the dependence of the basal freezing melting temperature on ice pressure water pressure solute concentration and surface tension effects thermally driven water flow is induced when an ice base becomes supercooled below the pressure melting point because ice water surface tension inhibits ice growth in small pore spaces of fine grained subglacial sediments our model results show that basal freeze on is capable of inducing considerable changes in the basal zone of both ice streams and interstream ridges these changes are associated with specific signatures that compare with borehole observations and geophysical surveys water pres sure levels are reduced and thick layers of debris laden basal ice develop these basal ice layers andunderlying sedimentscontain a distinct isotopic signal the predicted stable iso tope ratios reflect rayleigh type isotopic fractionation whose significance increases with increasing freezing rates supercooling of the ice base induces also measurable changes in the ice temperature profile of the glacier till porosity represents another quantity whose evolution is influenced strongly by basal freeze on in particular measurements of vertical porositydistributionbeneathstoppedicestreamscouldbeusedtoback calculatethetiming of the onsetof basal freezing our modelresults show thatthebasal zoneof ice streams and interstream ridges responds sensitively to changes inbasal melting freezing rates this sen sitivity may allow reconstruction of past conditions beneath ice streams and interstream ridges from measurements made on basal ice samples and subglacial sediment samples our model resultsalso indicate thatmeltwater from fast flowing ice streams may be driven towardsthe freezing icebase of interstream ridges

late holocene changes in character and behaviour of land terminating glaciers on james ross island antarctica virtually no information is available on the response of land terminating antarctic peninsula glaciers to climate change on a centennial timescale this paper analyses the topography geomorphology and sedimentology of prominent moraines on james ross island antarctica to determine geometric changes and to interpret glacier behaviour the moraines are very likely due to a late holocene phase of advance and featured 1 shearing and thrusting within the snout 2 shearing and deformation of basal sediment 3 more supraglacial debris than at present and 4 short distances of sediment transport retreat of 100m and thinning of 15 20m has produced a loss of 0 1km3 of ice the pattern of surface lowering is asymmetric these geometrical changes are suggested most simply to be due to a net negative mass balance caused by a drier climate comparisons of the moraines with the current glaciological surface structure of the glaciers permits speculation of a transition from a polythermal to a cold based thermal regime small land terminating glaciers in the northern antarctic peninsula region could be cooling despite a warming climate

a borehole camera system for imaging the deep interior of ice sheets the design and first deployment is described for the jet propulsion laboratory california institute oftechnology ice borehole camera system for acquisition of down looking and side looking images in a borehole made by a hot water drill the objective of the system is to acquire images in support of studies of the basal dynamics and thermodynamics of west antarctic ice streams a few sample images obtained during the 2000 01 antarctic field season are shown from the basal layers of ice stream c

origin evolution and dynamic context of a neoglacial lateral frontal moraine at austre lovenbreen svalbard moraines marking the neoglacial limits in svalbard are commonly ice cored investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics this paper examines the composition of the lateral frontal moraine associated with the neoglacial limit at austre lovenbreen and assesses the likely geomorphological evolution the moraine was investigated using ground penetrating radar gpr with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003 multiple up glacier dipping reflectors and syncline structures are found in the gpr surveys the reflectors are most clearly defined in lateral positions where the moraine is substantially composed of ice the frontal area of the moraine is dominantly composed of debris the core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression the long term preservation potential of the ice dominated lateral moraine is negligible whereas the preservation of the debris dominated frontal moraine is high a glacier surface bulge identified on the 1936 aerial imagery provides evidence that austre lovenbreen has previously displayed surge activity although it is highly unlikely to do so in the near future in its current state this research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics

the extent and chronology of cenozoic global glaciation abstract the quaternary is synonymous with extensive glaciation of earth s mid and high latitudes although there were local precursors significant glaciation began in the latest eocene ca 35 ma in eastern antarctica it was followed by glaciation in mountain areas through the miocene in alaska greenland iceland and patagonia later in the pliocene e g in the bolivian andes and possibly in tasmania and in the earliest pleistocene e g in the alps new zealand iceland and greenland today evidence from both the land and the ocean floors demonstrates that the major continental glaciations outside the polar regions rather than occurring throughout the 2 6 ma of the quaternary were markedly restricted to the last 1 ma 800 ka or less marine isotope stage mis 22 ca 870 880 ka included the first of the major worldwide events with substantial ice volumes that typify the later pleistocene glaciations i e mis 16 12 10 6 4 2

permafrost or seasonal frost a review of paleoclimate proxies of the last glacial cycle in the east central european lowlands abstract our critical revision of the sedimentological characteristics and genetic interpretation of relict periglacial soil deformation features cryoturbations and sand wedges suggests that the continuous permafrost zone did not necessarily reached the lowland areas of the pannonian basin as suggested by previous studies the discontinuous permafrost zone most probably penetrated the north western part of the study area for a certain period but most of the lowlands might have been affected only by sporadic isolated permafrost and or deep seasonal frost the re evaluated climate conditions implied by the periglacial soil structures and other proxies for a periglacial environment of the area do not constrain such a narrow zone of extremely low mean annual air temperature maat and mean annual precipitation map the compilation of the climate thresholds suggested by the observed and revised interpretation cryoturbation features and thermal contraction cracks with other paleoclimate proxies converge on 0 2 c maat and 300 490 mm map on the lowland areas of the pannonian basin during the coldest phase of the last glacial these values indicate a temperature drop of 10 2 c and a precipitation decrease of 30 50 relative to modern conditions

luminescence dating of the stratzing loess profile austria testing the potential of an elevated temperature post ir irsl protocol abstract feldspar infrared stimulated luminescence irsl signals saturate at 2000 gy i e 500 700 ka assuming a dose rate of 3 4 gy ka typical for loess and it is therefore theoretically possible to date middle pleistocene loess however the accuracy of age estimates is hampered by anomalous fading which leads to significant age underestimation fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses as the growth curve approaches saturation recent studies have identified a post ir irsl signal that shows less fading and is thus less dependent on accurate fading corrections this study builds upon these investigations and applies a post ir irsl sar dating protocol to polymineral fine grain samples of the loess palaeosol sequence in stratzing lower austria after a preheat at 320 c 60 s and an ir bleach at 50 c 200 s irsl was measured at 290 c for 200 s the same set of conditions were used to measure the response to a test dose recycling ratios recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation although finite residual doses of up to 20 gy are observed for the oldest samples the natural signal is in or close to saturation indicating that fading is negligible in nature this observation is inconsistent with the measured laboratory fading rates of 1 1 5 decade and needs further investigation

basal glacier ice and massive ground ice different scientists same science whilst glaciologists and permafrost researchers investigate ice bodies using similar techniques there has been surprisingly little collaboration between the two communities this paper examines the potential benefits of interdisciplinary research into the formation of basal ice beneath glaciers and the origin of massive ice in glaciated permafrost regions active collaboration in these areas has already improved our understanding of the formation of basal ice beneath cold based glaciers the critical role played by basal freezing in controlling the dynamic behaviour of stagnating ice streams and the significance of glacier permafrost interactions at the margins of pleistocene ice sheets however in order to promote future collaboration certain obstacles need to be overcome the contrasting ice classification schemes employed by glaciologists and permafrost scientists for example need to be unified in order to allow detailed comparisons of ice rich sequences in both environments this could in turn enable exciting research advances most notably by facilitating the identification of preserved remnants of pleistocene ice sheets within permafrost regions that provide a potentially invaluable and currently largely untapped source of palaeoglaciological information

uranium series dating of travertine from suttő implications for reconstruction of environmental change in hungary abstract terrestrial carbonate formations such as travertines speleothems and lake sediments are important archives of terrestrial climate forcing at the sutt section in hungary a complex succession of travertine is covered by a loess palaeosol sequence both are high resolution terrestrial archives of climate and environment change uranium series 230th u dating was carried out to set up a more reliable chronological frame for the travertine as the growth of travertine is very complex pore cements may cause serious problems for precise dating the state of alteration of primary spar and micrite was characterised by microscopic cathodoluminescence and microprobe analyses the travertine from sutt showed homogeneous phases of primary calcite minor micropores and rare pore cements the carbon isotopic composition indicates that the source of carbon was a mixture of atmospheric and soil derived co2 calculated water temperatures based on oxygen isotope data range from 22 c to 31 c an attempt to provide an independent relative dating approach by palaeomagnetic techniques failed 230th u ages were determined applying an isochron approach using the leachate leachate method as the travertine deposits have a dense structure the bulk sampling method was successfully applied in determining uranium series ages with much higher precision than former studies with alpha spectrometry travertines from sutt yielded mid pleistocene ages ranging from the antepenultimate glacial to the penultimate interglacial 310 240 ka these results are in agreement with those from optically stimulated luminescence osl dating and amino acid racemisation aar dating of the overlying sediment indicating at least an mis 7 age for the travertine

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

cosmocalc an excel add in for cosmogenic nuclide calculations as dating methods using terrestrial cosmogenic nuclides tcn become more popular the need arises for a general purpose and easy to use data reduction software the cosmocalc excel add in calculates tcn production rate scaling factors using lal stone dunai and desilets methods topographic snow and self shielding factors and exposure ages erosion rates and burial ages and visualizes the results on banana style plots it uses an internally consistent tcn production equation that is based on the quadruple exponential approach of granger and smith 2000 cosmocalc was designed to be as user friendly as possible although the user interface is extremely simple the program is also very flexible and nearly all default parameter values can be changed to facilitate the comparison of different scaling factors a set of converter tools is provided allowing the user to easily convert cut off rigidities to magnetic inclinations elevations to atmospheric depths and so forth because it is important to use a consistent set of scaling factors for the sample measurements and the production rate calibration sites cosmocalc defines the production rates implicitly as a function of the original tcn concentrations of the calibration site the program is best suited for be 10 al 26 he 3 and ne 21 calculations although basic functionality for cl 36 and c 14 is also provided cosmocalc can be downloaded along with a set of test data from http cosmocalc googlepages com

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

quantification of quaternary vertical movements in the central pannonian basin a review of chronologic data along the danube river hungary abstract this study aims at a new quantification of neotectonic deformation of the central part of the pannonian basin we use terrace levels and associated travertine as well as speleothem data along the danube river to quantify its incision rate and thus estimate the amount and rate of uplift at the axis of the hungarian mountain range hmr several terrace levels and other geomorphic features along the danube river are indicative for quaternary uplift of the axial part of the emerging hungarian mountain range while the correlative terraces are at considerable height at the axis of the hmr the terraces are gradually dipping below the basin fill of the adjacent lowlands the correlation of the terrace segments is difficult because of their poor preservation small size and variable height the geomorphologic horizons indicate gradual incision of the river throughout the quaternary during simultaneous deformation however no reliable chronological data have been available so far to quantify landscape forming processes such as uplift incision or erosion rates a reconsideration of existing published data for three consecutive segments of the danube valley yields incision rates between 0 14 and 0 41 mm year for the last 360 ky with the highest value for the area of the danube bend accordingly the middle to late quaternary uplift rate of the axial zone of the hmr exceeded significantly that of the marginal areas these rates represent an approximation as some quantitative data are still controversial our results suggest that formation of the danube terraces is result of river incision triggered by the uplift of the hmr and modified by periodic climate changes

pleistocene tectonics inferred from fluvial terraces of the northern upper rhine graben germany abstract this study of fluvial terraces of the river rhine and tributaries aims to search for indications of pleistocene tectonic activity the study area includes the northern upper rhine graben urg the mainz basin and the adjacent rhenish massif with the middle rhine valley high rates of quaternary surface processes large amount of human modifications relatively slow tectonic deformation and presently low intra plate seismic activity characterize this area therefore the records of relatively slow tectonic deformation are less well preserved and thus difficult to detect this study uses the relative position of fluvial terraces to determine the more local effects of fault movements on the terraces and to evaluate their displacement rates and patterns the research is based on a review of previous terrace studies and new terrace mapping from the eastern mainz basin and the bordering urg using topographic map interpretations and field observations this newly mapped sequence of terrace surfaces can be correlated to other terraces in the vicinity on the basis of relative height levels terrace correlation between the western mainz basin and middle rhine valley relies on a single chronostratigraphic unit mosbach sands and additional relative height correlations this is the first study to present a continuous correlation of terraces from the western margin of the urg to the rhenish massif and enables the study of the transition from the subsiding graben to the uplifted rhenish massif by means of a longitudinal profile which ranges from the urg to the rhenish massif the influence of individual fault movements on the terrace levels and the large scale regional uplift is demonstrated it is evident from the profile that the uplift of early to middle pleistocene terraces increases northwards towards the rhenish massif the uplift was diachronic with a significant pulse occurring first in the northern urg lower pleistocene and later in the rhenish massif middle pleistocene the largest vertical displacements are recorded for the boundary fault separating the mainz basin and the rhenish massif hunsruck taunus boundary fault and for faults bounding the northeastern mainz basin the motions and displacement rates calculated for individual faults indicate deformation rates in the order of 0 01 0 08 mm year at this stage the calculation of displacement rates depends mostly on a single dated stratigraphic unit additional dating of terrace deposits is urgently needed to better constrain the temporal development of the terrace sequence and the impact of tectonic movements

evolution of subglacial overdeepenings in response to sediment redistribution and glaciohydraulic supercooling received 16 august 2012 revised 18 december 2012 accepted 15 january 2013 1 glaciers erode bedrock rapidly but evacuation of sediments requires efficient subglacial drainage networks if glaciers erode more rapidly than evacuation proceeds a protective subglacial till layer can form to armor the bed where glaciers cross overdeepenings local closed depressions the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow here we present results of a dynamic distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season we use steady state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings numerical results from a modified form of the spring hutter equations show behaviors that cannot be inferred from either local or steady state calculations in general opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling drainage efficiency strongly affects erosion and deposition rates results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs this progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling we discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets

sedimentary signatures of basal ice formation and their preservation in ice marginal sediments reconstruction of subglacial processes from sedimentological evidence is central to our understanding of glaciological conditions beneath former ice masses at svinafellsjokull southeast iceland we assess the extent to which two different processes of basal ice formation regelation and glaciohydraulic supercooling can be identified from ice marginal sediments our results indicate that the sedimentary characteristics of deposits produced by these two processes can be distinguished from one another and that it may be possible to recognise evidence of these processes in quaternary sediments and to reconstruct their spatial pervasiveness sediments derived from the melting of regelation basal ice have i a massive structure ii a sediment matrix 0 to 10 dominated by coarse sand and iii a higher proportion of angular clasts than supercool basal ice and associated sediments sediments derived from supercool basal ice i can be either massive or layered ii tend to have a silt dominated matrix and iii contain a slightly higher proportion of rounded and well rounded clasts than regelation basal ice and sediments previous studies indicate that the dominance of silt within supercool basal ice may be unique to this process and hence supercooling should leave a readily recognisable signature in the sedimentary record our results from svinafellsjokull lend support to that idea although we suggest that further work is required to assess whether silt dominance is a process signature diagnostic of supercooling and in particular the extent to which subglacial sediment supply determines the sedimentary character of basal ice facies and associated sediments

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

phases of compression during the evolution of the pannonian basin and its bearing on hydrocarbon exploration abstract progress in understanding the structural evolution of the pannonian basin is reported this has been driven by the application of seismic stratigraphy constrained by magnetostratigraphic data and the recent release of a great amount of hydrocarbon exploration data this has led to a redefinition and better understanding of the syn rift period and style of rifting in addition a complex structural evolution history during the post rift phase has been recognized two compressive events are defined one in the early stage and another in the late stage of evolution the importance of these findings for hydrocarbon exploration includes an improved knowledge of the timing of trap formations and a possible explanation for remarkably variable reservoir pressures in pools of the great hungarian plain

tectonic implications of the gps velocity field in the northern adriatic region 1 continuous and episodic gps observations between 1991 and 2004 show that adria moves independently of both stable eurasia and nubia adria moves nne at 3 4 5 mm yr increasing from n to s relative to eurasia and may be fragmenting along the gargano dubrovnik seismic zone the observed 2 3 mm yr of n s adria eurasia convergence is taken up by contraction across a narrow 70 km zone in the eastern alps and concomitant extrusion of the alpine north pannonian unit the adria central dinarides boundary is a broader collisional zone with intense 1 1 5 mm yr shortening near shore and 2 mm yr spread across the dinarides the remaining 1 2 mm yr motion e of the alps and ne of the dinarides is absorbed by the inverted contracting pannonian basin leaving no significant deformation above 0 5 mm yr in the western and northern carpathians and european platform

ice crystal properties of amber ice and strain enhancement at the base of cold antarctic glaciers to improve our understanding of the deformation properties of cold based polar glaciers we examine here some of the factors leading to the localization of strain within the amber ice facies we present a crystallographic case study of amber ice a fine grained bubbly ice containing a relatively high impurity content sampled at the base of two antarctic glaciers the crystal fabrics and textures of amber ice were computed by application of a recently developed automated method to date it was tedious and awkward to determine amber ice facies accurately because of the sub millimetric crystal size and relatively high debris content of this facies the authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis our investigations reveal highly homogeneous crystallographic properties for the studied amber ice the ice crystals are mainly polygonal equant and sub millimetric and show a strong lattice preferred orientation these properties beside the relatively high impurity content are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers

magnetic fabrics in the basal ice of a surge type glacier 1 anisotropy of magnetic susceptibility ams has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments here we present results from debris rich basal glacier ice to examine deformation associated with glacier motion basal ice samples were collected from tunabreen a polythermal surge type glacier in svalbard the magnetic fabrics recorded show strong correlation with structures within the ice such as sheath folds and macroscopic stretching lineations thermomagnetic low temperature susceptibility varying field susceptibility and isothermal remanent magnetism acquisition experiments reveal that the debris rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier an up glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation the results suggest that ams can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed

is a periglacial biota responsible for enhanced dielectric response in basal ice from the greenland ice core project ice core a detailed dielectric profiling dep conductivity profile measured in the 6 m of the basal silty ice sequence from the greenland ice core project grip ice core summit central greenland is presented and compared to previous multi parametric studies dep conductivities span the whole glacial interglacial range observed higher up in the grip core 9 25 s m 1 values in the bottom meter of the sequence reach the level of some of the highest peaks from holocene volcanic layers in the core 33 s m 1 on a steady increase of the values down the sequence are superimposed large fluctuations inphase with other variables measured in the core such as 18o debris content or gas compositions in co2 and ch4 analysis of the type and strength of intercorrelations shows that the controlling variable for the dep signal must be closely related to the gas content and composition of the ice plausible candidates for this causality link are investigated enhancing of the conductivity by co2 and ch4 encaged in the ice lattice as gas hydrates is ruled out since these are nonpolar clathrates of structure i known as having negligible impact on the orientational stability of the water molecules under ac currents nh4 is proposed as the best candidate since it has been shown to enhance dep conductivities by introducing bjerrum defects in the ice lattice and since it could have been initially present partly as gaseous nh3 in the ice this proposition is supported by the nh4 profile in the basal ice sequence using calibration curves from higher up in the core it is shown that is in fact fully explained by intracrystalline conductivity of pure ice solely disrupted by ammonium impurities in the ice lattice the origin of the nh4 signal is discussed in the light of organic acid profiles formate acetate and oxalate it appears that the most likely source is local degradation of biological residues which supports the hypothesis that part of the basal ice was formed locally in the absence of the present day ice sheet

ice formation in subglacial lake vostok central antarctica abstract the investigation of chemical and isotopic properties in the lake ice from the vostok ice core gives clues to the mechanisms involved in ice formation within the lake a small lake water salinity can be reasonably deduced from the chemical data possible implications for the water circulation of lake vostok are developed the characteristics of the isotopic composition of the lake ice indicate that ice formation in lake vostok occurred by frazil ice crystal generation due to supercooling as a consequence of rising waters and a possible contrast in water salinity subsequent consolidation of the developed loose ice crystals results in the accretion of ice to the ceiling of the lake

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

young uplift in the non glaciated parts of the eastern alps abstract we report the first incision rates derived from burial ages of cave sediments from the mur river catchment at the eastern margin of the eastern alps at the transition zone between the alpine orogen and the pannonian basin this river passes through the paleozoic of graz a region of karstifiable rocks called the central styrian karst this river dissects the study area in a north south direction and has left behind an abundance of caves these caves can be grouped into several distinct levels according to their elevation above the present fluvial base level age estimates of abandoned cave levels are constrained by dating fluvial sediments washed into caves during the waning stages of speleogenesis with the terrestrial cosmogenic nuclide method these ages and the elevations of the cave levels relative to the current valley floor are used to infer a very complex history of 4 million years of water table position influenced by the entrenchment and aggradation of the mur river we observe rather low rates of bedrock incision over the last 4 ma in the order of 0 1 mm y with an e folding decrease in this trend to lower rates at younger times we relate this incision history to a tectonic setting where an increase of drainage area of the mur river due to stream piracy in late miocene to pliocene times is linked to surface uplift the later decrease in valley lowering rates is attributed to the rise of the base level related to aggradation of sediments within the valley sediment transport through the valley from the upstream section of the mur river limited the erosional potential of the river to a transport limited state at the later stages of the incision history

a first attempt to date the original deckenschotter of penck and bruckner with cosmogenic nuclides abstract in the classical area of alpine quaternary stratigraphy bavaria germany a succession of four gravel spreads that are separated from each other by valley incision was recognized by penck and bruckner 1909 die alpen im eiszeitalter tauchnitz leipzig 1199p the two older gravel terraces attributed to glaciations named gunzian and mindelian have so far not been dated recent advances in the use of cosmogenic nuclides allow the burial age determination of sediments the method uses the different decay of the two nuclides 26al and 10be to date the time since a deposit was shielded from further radiation a depth profile makes it possible to model ages for surface sediments that are not shielded completely this paper discusses the various constraints that must be addressed in order to date surface sediments and it presents the ages obtained 2 35 ma for gunzian 0 68 ma for mindelian these dates are in good agreement with measurements of tectonic displacement and development of catchments the results confirm that the burial age determination method is basically feasible for such terraces

investigating the penultimate and last glacial cycles of the suttő loess section hungary using luminescence dating high resolution grain size and magnetic susceptibility data the loess paleosol record at sutt provides an excellent high resolution archive of climate and environmental changes loess deposits with a thickness of 20 m cover the travertine at sutt in the northern part of hungary next to the right bank of the danube river the loess sequence is intercalated with two greyish stratified horizons three brownish steppe like soils and a pedocomplex including a reddish brown paleosol covered by a chernozem like paleosol detailed infrared stimulated luminescence irsl dating was carried out revealing more or less continuous sedimentation from marine isotope stage mis 6 mis 2 sedimentological and paleomagnetic investigations have been performed to provide a high resolution study of the sutt loess paleosol sequence in order to reconstruct the paleoclimate and environmental changes during the penultimate and last glacial cycles grain size and magnetic susceptibility ms records of the sutt profile basically show similar patterns to those of other european loess sections however small differences are traced at sutt including more intensive deposition of coarser grained materials during mis 6 4 the loess record at sutt has a transitional position within the european loess belt as its sediment was deposited under an intermediate climate between the loess successions from the southern carpathian basin which accumulated under drier climate and the loess sequences from western europe which developed under wetter climate during the middle and late pleniglacial

stable isotope δd δ18o relationships of ice facies and glaciological structures within the mid latitude maritime fox glacier new zealand relationships between stable isotopes d o ice facies and glacier structures have hitherto gone untested in the mid latitude maritime glaciers of the southern hemisphere here we present d o values as part of a broader study of the structural glaciology of fox glacier new zealand we analyzed 94 samples of d o from a range of ice facies to investigate whether isotopes have potential for structural glaciological studies of a rapidly deforming glacier the d o measurements were aided by structural mapping and imagery from terminus time lapse cameras the current retreat phase was preceded by an advance of 1 km between 1984 and 2009 with the isotopic sampling and analysis undertaken at the end of that advance 2010 11 stable isotopes from debris bearing shear planes near the terminus interpreted as thrust faults are isotopically enriched compared with the surrounding ice when plotted on co isotopic diagrams d o ice sampled from the shear planes appears to show a subtle but distinctive isotopic signal compared with the surrounding clean ice on the lower glacier hence stable isotopes d o have potential within the structural glaciology field but larger sample numbers than reported here may be required to establish isotopic contrasts between a broad range of ice facies and glacier structures

revisiting the loess palaeosol sequence in paks hungary a post ir irsl based chronology for the young loess series in hungary many loess palaeosol sequences have been found to be discontinuous in order to allow for correlations with other quaternary records reliable chronologies are needed we therefore apply post ir infrared ir stimulated luminescence post ir irsl pirir290 dating to the uppermost 20 m of the loess sequence at paks the pirir290 ages are compared with blue quartz osl ages to test for potential age overestimation due to poor signal re setting and the observed good agreement is taken to imply that the more difficult to bleach pirir290 signal was reset prior to deposition our pirir290 based chronology reveals that most of the late pleistocene loess was deposited during marine isotope stage mis 3 and during the last glacial maximum lgm this is in disagreement with formerly published ages the discrepancy can most likely be explained by anomalous fading resulting in an age underestimate this conclusion is supported by our uncorrected standard irsl ages we further confirm that the basaharc double soil complex can be correlated with mis 7 the underlying loess and soils cannot be dated accurately because the pirir290 signal approaches saturation

basal ice sequences in antarctic ice stream exposure of past hydrologic conditions and a principal mode of sediment transfer 1 the brightness distribution of sequentially extracted borehole camera imagery shows two distinct sequences of basal ice in kamb ice stream the upper sequence 7 3 m comprises clear ice and layers with dispersed and stratified debris the lower sequence 8 2 m consists of accretion ice with alternating layers of stratified and solid debris the two sequences have volumetric debris contents of about 5 and 20 respectively we infer that the upper sequence formed in a tributary where subglacial meltwater was abundant and that the lower sequence formed on the siple coast plain where basal freezing currently dominates the basal thermal regime the basal ice layer contains the equivalent of 2 1 0 4 m of frozen sediment the high volume of sediment is a result of debris rich layers interpreted to have formed by accretion in the stagnant phase of ice stream on off cycles fast ice streaming punctuated by entrainment of debris during stagnation episodes is consistent with inferred past flow of adjacent ice streams and geologic features in the ross sea our results show that sediment wedges near grounding lines may form by melt out of basal ice debris this is different from previous studies where it was assumed that sediment transfer occurs through sediment deformation within layers of subglacial till cumulative freezing in recurring ice stream cycles shows that entrainment of sediment by basal freeze on is an important erosion mechanism and that high sediment fluxes can occur when ice streams override coulomb plastic substrates

tectonic and climatic control on terrace formation coupling in situ produced 10be depth profiles and luminescence approach danube river hungary central europe abstract the terrace sequence of the hungarian part of the danube valley preserves a record of varying tectonic uplift rates along the river course and throughout several climate stages to establish the chronology of formation of these terraces two different dating methods were used on alluvial terraces exposure age dating using in situ produced cosmogenic 10 be and luminescence dating using monte carlo approach to model the denudation rate corrected exposure ages in situ produced cosmogenic 10 be samples originated from vertical depth profiles enabled the determination of both the exposure time and the denudation rate post ir irsl measurements were carried out on k feldspar samples to obtain the ages of sedimentation the highest terrace horizon remnants of the study area provided a best estimate erosion corrected minimum 10 be exposure age of 700 ka we propose that the abandonment of the highest terrace of the hungarian danube valley was triggered by the combined effect of the beginning tectonic uplift and the onset of major continental glaciations of quaternary age around mis 22 for the lower terraces it was possible to reveal close correlation with mis stages using irsl ages the new chronology enabled the distinction of tiib 90 ka mis 5b c and tiiia 140 ka mis 6 in the study area surface denudation rates were well constrained by the cosmogenic 10 be depth profiles between 5 8 m ma and 10 0 m ma for all terraces the calculated maximum incision rates of the danube relevant for the above determined 700 ka time span were increasing from west

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

stable isotopes in the basal silty ice preserved in the greenland ice sheet at summit environmental implications modelling ice sheet behaviour in the context of climatic changes depends on initial and boundary conditions which can be better defined by studying the composition of basal ice this study deals with basal ice reached by deep drilling at summit in central greenland grip core the isotopic composition of this ice indicates that ice formed at the ground surface in the absence of the ice sheet largely contributed to its formation the basal silty ice is a remnant of a growing stage of the ice sheet possibly the original build up

origin and significance of dispersed facies basal ice svinafellsjokull iceland dispersed facies basal ice massive i e structureless ice with dispersed debris aggregates is present at the margins of many glaciers and as a product of internal glacial processes has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment the origin of dispersed facies is poorly understood with several hypotheses having been advanced for its formation and there is disagreement as to whether it is largely a sedimentary or a tectonic feature we test these established hypotheses at the temperate glacier svinafellsjokull iceland and find that none fully account for dispersed facies characteristics at this location instead dispersed facies physical sedimentological and stable isotope d 18 o dd character istics favour a predominantly tectonic origin that we suggest comprises the regelation and strain induced metamorphism of debris rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation including the preservation of dispersed facies despite the relatively low sediment content of dispersed facies 1 6 by volume its thickness up to 25 m and ubiquity at svinafellsjokull results in a significant contribution to annual sediment discharge 1635 3270 m 3 a 1 that is 6 5 times that contributed by debris rich stratified facies basal ice

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

quantification of fluvial incision in the duero basin nw iberia from longitudinal profile analysis and terrestrial cosmogenic nuclide concentrations the duero basin is one of the largest cenozoic basins in iberia and contains a relatively well preserved sedimentary infill the top of the sedimentary sequence crops out at elevations up to 900 m above sea level the present day basin drains to the atlantic ocean via the duero river through the arribes gorge but during the cenozoic the basin experienced a long endorheic period marked by the formation of evaporites the time the basin opened to the atlantic ocean and the formation of the modern duero river drainage system remains poorly constrained in this study we quantify the spatial distribution of river incision within bedrock and sedimentary units by comparing the nearly relict higher reaches with the lower deeply incised reaches of the tributary system results show an abrupt increase in stream incision westward reaching a minimum bedrock incision depth of 600 m in the arribes gorge using cosmogenic 10be and 21ne data we estimate exposure ages for erosion surfaces at various levels in the incised duero river the cosmogenic nuclide dataset suggests that the final 2 300 m of fluvial incision in the arribes gorge occurred at a rate of 2 3 mm yr over the last 100 ka

basal ice facies a review and unifying approach abstract over the past 30 years numerous basal ice facies have been identified named and classified however the resulting facies descriptions and names are inconsistent and no single scheme encompasses all of the different ice types that exist at different ice masses in this paper we review and critique existing basal ice facies names descriptions and classification schemes and propose a new non genetic approach that has the capacity to name and describe all basal ice types we define six fundamental basal cryofacies and a further 12 composite cryofacies which can all be defined on the basis of a cursory evaluation of debris disposition and concentration more detailed cryofacies description is based on characterizing three sets of ice properties that can also be estimated visually in the field a the thickness of the basal ice facies and its constituent sub layers b the concentration and texture of debris included within any or all of those layers and c the concentration and size of bubbles included within any or all of those layers we also propose a shorthand method for the presentation of this descriptive information here codes for the layer thicknesses are presented as standard text and codes for the included debris characteristics and included bubble characteristics are presented as superscripts and subscripts respectively sub layers are characterized similarly but within a nested sequence of brackets we evaluate the effectiveness of these two schemes by using them to rename and reclassify several existing basal ice facies results indicate that the schemes are robust and that they provide a coherent non genetic framework for the effective naming and description of basal cryofacies

deformation of debris ice mixtures mixtures of rock debris and ice are common in high latitude and high altitude environments and are thought to be widespread elsewhere in our solar system in the form of permafrost soils glaciers and rock glaciers these debris ice mixtures are often not static but slide and creep generating many of the landforms and landscapes associated with the cryosphere in this review a broad range of field observations theory and experimental work relevant to the mechanical interactions between ice and rock debris are evaluated with emphasis on the temperature and stress regimes common in terrestrial surface and near surface environments the first order variables governing the deformation of debris ice mixtures in these environments are debris concentration particle size temperature solute concentration salinity and stress a key observation from prior studies consistent with expectations is that debris ice mixtures are usually more resistant to deformation at low temperatures than their pure end member components however at temperatures closer to melting the growth of unfrozen water films at ice particle interfaces begins to reduce the strengthening effect and can even lead to profound weakening using existing quantitative relationships from theoretical and experimental work in permafrost engineering ice mechanics and glaciology combined with theory adapted from metallurgy and materials science a simple constitutive framework is assembled that is capable of capturing most of the observed dynamics this framework highlights the competition between the role of debris in impeding ice creep and the mitigating effects of unfrozen water at debris ice interfaces

climate and material controls on periglacial soil processes toward improving periglacial climate indicators one of the distinguished efforts of a l washburn was to reconstruct mean annual air temperature using periglacial features as climate indicators this paper reviews existing periglacial indicators and proposes a strategy to improve their thermal resolution based on recent periglacial process studies with a focus on solifluction and thermal contraction cracking and associated landforms structures landforms resulting from solifluction reflect both the depth subjected to freeze thaw and the thickness of frost susceptible soils the thickness of a solifluction structure can be used to infer the dominant freeze thaw regime and minimum seasonal frost depth ice wedge pseudomorphs have limited potential as a climate indicator because 1 they mainly reflect extreme winter temperatures 2 their thermal thresholds depend on the host material and 3 they need to be distinguished from frost wedges of other origin produced under different thermal and or material conditions monitoring studies of currently active ice wedges suggest that ice wedge cracking requires a combination of low temperature and large temperature gradients in the frozen active layer further field monitoring of periglacial processes and their controlling factors under various climate conditions and in various materials are needed however to improve the resolution of periglacial paleoclimate indicators

dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

plio quaternary uplift of the iberian chain central eastern spain from landscape evolution experiments and river profile modeling abstract the iberian chain central eastern spain is characterized by a dome shaped topography with poorly incised and relatively flat landscape in its interior at an elevation of 1300 m a recent regional tectonic event started during or after the late pliocene inducing deep valley incision on the flanks of the iberian chain the rate and timing of this deformation as well as the magnitude of the uplift induced erosion processes still lack a quantitative validation we used 3d signum and 1 d river profile numerical models to investigate the landscape evolution of the iberian chain from the late pliocene to the present and to study the response of topography and rivers to tectonically induced base level lowering our model results are supported by geological geomorphological and geochronological data the results of the signum experiments show that the iberian chain topography has experienced regional uplift since ca 3 ma with rates between 0 25 and 0 55 mm y 1 in response to this uplift rivers have incised at an average long term incision rate of about 0 22 mm y 1 and have progressively captured drainage areas from the chain interior to further validate the results of landscape evolution modeling we use a 1 d river incision model to explore the incision history of several rivers draining the iberian chain the results constrain the range of values of bedrock erodibility from 5 8 10 5 to 5 0 10 4 m 0 4 y 1 and predict long term incision rates similar to those from the signum experiments