sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

discontinuity surfaces clinoforms and facies architecture in a wave dominated shoreface shelf parasequence abstract detailed outcrop analysis of a wave dominated shoreface shelf parasequence exposed in the book cliffs utah reveals minor stratigraphic discontinuities which define clinoforms two types of discontinuity are recognized each with a distinctive lithologic character and geometry nondepositional discontinuities are marked by an abrupt decrease in the thickness and amalgamation of storm generated event beds and are interpreted to record hiatuses in sedimentation these discontinuities define clinoforms with a concave upward geometry that dip gently 0 02 0 58 over distances of 800 6000 m down depositional dip erosional discontinuities are marked by an abrupt increase in event bed amalgamation grain size and sand content and are interpreted as enhanced storm wave scours these discontinuities define more steeply dipping 0 22 0 95 concave upward clinoforms that extend over 100 1600 m down depositional dip and 500 1500 m along depositional strike the distribution and amalgamation of minor stratigraphic discontinuities defines linear zones of distinctive facies architecture that are oriented parallel to the paleoshoreline trend using the simple assumption that the shoreface shelf equilibrium profile remained approximately constant for each type of discontinuity throughout shoreface migration the bruun rule intra parasequence facies architecture can be speculatively interpreted in terms of shoreline trajectory which reflects the balance between sediment supply and accommodation the resulting interpretations support the notion that shoreline trajectory exerts a strong control on intra parasequence facies architecture and preservation of the shoreface shelf profile

distribution and mass of tephra fall deposits from volcanic eruptions of sakurajima volcano based on posteruption surveys we estimate the total mass of ash fall deposits for individual eruptions of sakurajima volcano southwest japan based on distribution maps of the tephra fallout five ash sampling campaigns were performed between 2011 and 2015 during which time sakurajima continued to emit ash from frequent vulcanian explosions during each survey between 29 and 53 ash samplers were installed in a zone 2 2 43 km downwind of the source crater total masses of erupted tephra were estimated using several empirical methods based on the relationship between the area surrounded by a given isopleth and the thickness of ash fall within each isopleth we obtained 70 40 520 t 4 7 10 8 2 7 10 5 km3 dre as the minimum estimated mass of erupted materials for each eruption period the minimum erupted mass of tephra produced during the recorded events was calculated as being 890 5140 t 5 9 10 7 3 6 10 6 km3 dre this calculation was based on the total mass of tephra collected during any one eruptive period and the number of eruptions during that period these values may thus also include the contribution of continuous weak ash emissions before and after prominent eruptions we analyzed the meteorological effects on ash fall distribution patterns and concluded that the width of distribution area of an ash fall is strongly controlled by the near ground wind speed the direction of the isopleth axis for larger masses is affected by the local wind direction at ground level furthermore the wind direction influences the direction of the isopleth axes more at higher altitude while a second maximum of ash fall can appear the influence of rain might only affect the finer particles in distal areas

mis 3 to mis 1 temporal and lgm spatial variability in arctic ocean sea ice cover reconstruction from biomarkers using the sea ice proxy ip25 and phytoplankton derived biomarkers brassicasterol and dinosterol arctic sea ice conditions were reconstructed for marine isotope stage mis 3 to 1 with special emphasis on the last glacial maximum lgm in sediment cores from the northern barents sea continental margin across the central arctic ocean to the southern mendeleev ridge our results suggest more extensive sea ice cover than present day during latter part of mis 3 increasing sea ice growth during mis 2 and decreased sea ice cover during the last deglacial the summer ice edge remained north of the barents sea even during extremely cold i e last glacial maximum lgm as well as warm periods i e bolling allerod during the lgm the western svalbard margin and the northern barents sea margin areas were characterized by high concentrations of both ip25 and phytoplankton biomarkers interpreted as a productive ice edge situation caused by the inflow of warm atlantic water in contrast the lgm central arctic ocean north of 84 n was covered by thick permanent sea ice throughout the year with rare break up indicated by zero or near zero biomarker concentrations the spring summer sea ice margin significantly extended southwards to the laptev sea shelf southern lomonosov ridge and southern mendeleev ridge during the lgm our proxy reconstructions are very consistent with published model results based on the north atlantic arctic ocean sea ice model naosim

geometry distribution and fill of erosional scours in a heterolithic distal lower shoreface sandstone reservoir analogue grassy member blackhawk formation book cliffs utah usa

arctic palaeo river discharge and environmental change evidence from the holocene kara sea sedimentary record abstract in this paper we summarize data on terrigenous sediment supply in the kara sea and its accumulation and spatial and temporal variability during holocene times sedimentological organic geochemical and micropaleontological proxies determined in surface sediments allow to characterize the modern riverine terrigenous sediment input ams 14c dated sediment cores from the ob and yenisei estuaries and the adjacent inner kara sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes the variability of sediment fluxes during holocene times is related to the post glacial sea level rise and changes in river discharge and coastal erosion input whereas during the late middle holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries huge amounts of sediments accumulated on the kara sea shelf farther north during the early holocene before about 9 cal kyr bp the maximum accumulation at that time is related to the lowered sea level increased coastal erosion and increased river discharge based on sediment thickness charts echograph profiles and sediment core data we estimate an average holocene 0 11 cal kyr bp annual accumulation of 194 106 t yr 1 of total sediment for the whole kara sea based on late holocene modern sediment accumulation in the estuaries probably 12 106 t yr 1 of riverine suspended matter i e about 30 of the input may escape the marginal filter on a geological time scale and is transported onto the open kara sea shelf the high resolution magnetic susceptibility record of a yenisei core suggests a short term variability in siberian climate and river discharge on a frequency of 300 700 yr this variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the high northern latitudes over the last decades such as the nao ao pattern a major decrease in ms values starting near 2 5 cal kyr bp being more pronounced during the last about 2 cal kyr bp correlates with a cooling trend over greenland as indicated in the gisp 2 ice core extended sea ice cover in the north atlantic and advances of glaciers in western norway our still preliminary interpretation of the ms variability has to be proven by further ms records from additional cores as well as other high resolution multi proxy arctic climate records

shelf construction in a foreland basin storm beds shelf sandbodies and shelf slope depositional sequences in the upper cretaceous mesaverde group book cliffs utah the upper cretaceous campanian kenilworth member of the blackhawk formation mesaverde group is part of a series of strand plain sandstones that intertongue with and overstep the shelfal shales of the western interior basin of north america analysis of this section at a combination of small sedimentological and large stratigraphical scales reveals the dynamics of progradation of a shelf slope sequence into a subsiding foreland basin four major lithofacies are present in the upper mancos and kenilworth beds of the book cliffs a lag sandstone and channel fill shale lithofacies constitutes the thin basal transgressive sequence which rests on a marine erosion surface it was deposited in an outer shelf environment shale interbedded sandstone and shale and amalgamated sandstone lithofacies were deposited over the transgressive lag sandstone lithofacies as a wave dominated delta and its flanking strand plains prograded seaward analysis of grain size and primary structures in kenilworth beds indicates that there are four basic strata types which combine to build the observed lithofacies the fine to very fine grained graded strata of the interbedded facies are tempestites deposited out of suspension by alongshelf storm flows geostrophic flows there is no need to call on cross shelf turbidity currents density underflows to explain their presence very fine to fine grained hummocky strata are likewise suspension deposits created by waning storm flows but were deposited under conditions of more intense wave agitation on the middle shoreface cross strata sets in this region are bed load deposits that accumulated on the upper shore face in the surf zone lag strata are multi event bed load deposits that are the product of prolonged storm winnowing they occur on transgressive surfaces while the graded beds are tempestites in the strict sense all four classes of strata are storm deposits the distribution of strata types and their palaeocurrent orientations suggests a model of the kenilworth transport system driven by downwelling coastal storm flows and probably by a northeasterly alongshore pressure gradient the stratification patterns shift systematically from upper shoreface to lower shoreface and inner shelf lithofacies partly because of a reduction in fluid power expenditure with increasing water depth but also because of progressive sorting which resulted in a decrease in grain size in the sediment load delivered to successive downstream environments the kenilworth member and an isolated outlier the hatch mesa lentil constitute a delta prodelta shelf depositional system their rhythmically bedded lenticular sandstone and shale successions are a prodelta shelf facies and may be prodelta plume deposits major upper cretaceous sandstone tongues in the book cliffs are underlain by erosional surfaces like that beneath the blackhawk formation which extend for many tens of kilometres into the mancos shale these surfaces are the boundaries of upper cretaceous depositional sequences the sequences are large scale genetic stratigraphic units they result from the arranging of facies into depositional systems the depositional systems are in turn stacked in repeating arrays which constitute the depositional sequences the anatomy of these foreland basin sequences differs

environmental context of pleistocene peopling of the central urals abstract the broader territory of the urals has principal significance for elucidating the historical processes and environmental contexts of the pleistocene expansion of people from the south eastern parts of europe into west siberia and the northern russian arctic regions interaction of past climate change and the regional topographic modelling triggered by neotectonic activity reflected by pronounced natural transformations attest to the complexity of the quaternary development in the central urals affecting timing and intensity of the earliest human occupation of this territory the initial peopling of the western fore ural area is associated with the early palaeolithic dispersal into the marginal east european plain probably during some climatically favourable middle pleistocene interglacials the chusoaya river valley transecting the central ural mountain range was one of the main geographic corridors for the subsequent middle and upper palaeolithic migrations into the eastern trans ural regions of west siberia a long term behavioural adjustment to cold periglacial habitats is linked to progressive cultural and biological evolution during the late pleistocene the north central trans urals upper palaeolithic complex in the sosva river basin with open occupation sites based on mammoth fauna exploitation indicates adaptation to sub polar tundra steppe environments of the west siberian plain during the last glacial stage geoarchaeological records provide further insights into the timing and ecology conditions of the pleistocene colonisation of north central eurasia the present study summarises the current evidence on trajectories of the pleistocene environmental development in the broader central urals still a marginally investigated geographical area of eurasia

origin of shore normal channels from the shoreface of sable island canada a suite of modern shore normal channels was discovered on the southern shoreface of sable island canada repetitive multibeam and sidescan surveys of these features as well as box coring and sampling showed that the depressions were perennial features of the shoreface they occurred in fine and medium sand and were most abundant in depths less than 20 m they were up to 1 m deep and 50 m wide increased in size seawards and generally followed the seabed slope the channels dominated the inner shoreface becoming wider and deeper seawards to depths in excess of 40 m there is a continuum of scales in width and depth of these channels the smallest of which are equated with gutters preserved in the geological record the internal structure of the shoreface sediments where the gutters are found is characterised by normally graded tempestites composed of cut and fill structures overlying an erosion surface thus the environmental setting internal structure and scale are similar to ancient counterparts gutters have been interpreted to result from downwelling over palaeo shorefaces during ancient storms myrow 1992b the composition of gutter infill as well as the stability evolution associated bedforms and hydrodynamic conditions under which they formed were examined to verify genetic interpretations of the ancient counterparts the multi sensor benthic lander ralph was deployed within a field of shore normal channels for 17 days during late winter 1998 ralph burst sampled flow at hourly intervals whilst imaging the seabed resulting sequential imagery revealed the genesis of a group of five gutters during storm spin down that was coincident with the formation of large scale wave ripples this was followed by infilling of the gutters and wave ripple destruction within 20 hours by longshore sand transport the gutters were located within and parallel to a larger channel 50 m wide and 0 50 m deep they were formed by coastal set up and subsequent downwelling that was triggered by the rotation of storm winds from seawards onshore wind to landwards offshore wind the gutters formed within 2 to 3 hours during spin down of a winter storm under live bed conditions of sand transport wave height and mean tidal flows were well below those of the storm peak and so they were not directly responsible for creating the gutters the mechanism we propose for the evolution of gutters supports the geological interpretations that is a storm driven downwelling event as described by swift and niedoroda 1985 however the downwelling event appeared to take place suddenly rapid acceleration in flow briefly few hours duration and within narrow corridors guided by wider and deeper channels of the shoreface high turbidity during the time of gutter formation leads us to believe that the phenomenon of inner shelf turbidity currents as suggested by walker 1985 exists and may be instrumental in channel formation

the last glaciation of earth size and volume of ice sheets abstract the volume and size of the late glacial ice sheets in the northern hemisphere has been estimated based on geomorphic and chronostratigraphic data limited glacial extents during the late glacial maximum characterized both arctic canada and northern eurasia in contrast to the presence of the large laurentide scandinavian and devensian ice sheets to the south glacial maxima were not synchronous throughout the northern hemisphere for example the novaya zemlya ice sheet reached its maximum extent ca 39 000 bp approximately 20 000 years earlier than the maximum extent of the contiguous scandinavian ice sheet western and central siberia and the chukhui peninsula were marked by limited glaciation during the last glacial maximum although pre sartanian events were more extensive mountain glaciation in northeast asia was similarly restricted during the last glacial maximum spatial and dynamic characteristics of the last glaciation developed in response to climatic factors the establishment and strength of high pressure systems over siberia limited precipitation and glacier formation throughout northeastern eurasia

a parametric and comparative study of different tephra fallout models abstract we perform a parametric and comparative study on three different tephra dispersal models fall3d hazmap and tephra applied to two different scenarios expected for etna volcano these scenarios are similar to the recent 2002 03 and 1990 etna eruptions and correspond respectively to a weak and to a strong plume eruption for each model and scenario we perform a parametric study on several inputs in order to quantify how a variation on a given input parameter i e an uncertainty on the model input affects the results of the model the study considers topographic effects different description for the eruption column column height influence different fits for terminal velocities of particles the effect of particle shape and finally the variation of the modal grain size model differences are quantified by means of a normalized distance that indicates how close in average the results from two different simulations are we also compare predictions from different models to determine under which circumstances the use of a more elaborated model is justified results from our parametric study show that output of the models can be strongly sensitive to the uncertainties and assumptions on input parameters such as mainly mass eruption rate column height distribution of the mass along the column bulk grain size distribution this highlights that for optimal forecasts is urgent to improve the description of these parameters and of some important physical processes like fragmentation and eruption column dynamics further differences between models are often lower than those due to the uncertainties of input parameters although they become more high in simulating weak plumes thus the choice of the model mainly depends on the kind of application such as the need to simulate the evolution of volcanic clouds in the atmosphere finally the use of both a semi analytical hazmap and a fully computational fall3d model for inverting field data of the 2001 etna eruption showed that the best fit parameters are similar for both models and are consistent with values obtained using independent techniques

the extent of the barents kara ice sheet during the last glacial maximum it has been a long standing discussion whether the barents kara ice sheet expanded onto mainland russia during the last glacial maximum lgm in this paper we describe many well dated by conventional and ams 14 c methods and optically stimulated luminescence sedimentary sequences in the controversial area of northern russia the sequences discussed are not covered by till and yet all predate the lgm the deposits consist mostly of aeolian or lacustrine easily deformable soft silt and fine sand two sites feature frozen mammoth carcasses and three sites contain palaeolithic artefacts and mammalian bones we emphasise that these formations show no sign of having been overridden by an ice sheet at several sites deposition of aeolian sediments and formation of ice wedges took place during the lgm time span these observations present unambiguous proof that the barents kara ice sheet did not cover mainland russia during lgm with a possible exception for the northern tip of the taimyr peninsula r 2001 elsevier science ltd all rights reserved

grace gravity observations constrain weichselian ice thickness in the barents sea the barents sea is subject to ongoing postglacial uplift since the melting of the weichselian ice sheet that covered it the regional ice sheet thickness history is not well known because there is only data at the periphery due to the locations of franz joseph land svalbard and novaya zemlya surrounding this paleo ice sheet we show that the linear trend in the gravity rate derived from a decade of observations from the gravity recovery and climate experiment grace satellite mission can constrain the volume of the ice sheet after correcting for current ice melt hydrology and far field gravitational effects regional ice loading models based on new geologically inferred ice margin chronologies show a significantly better fit to the grace data than that of ice 5g the regional ice models contain less ice in the barents sea than present in ice 5g 5 6 3 m equivalent sea level versus 8 5 m which increases the ongoing difficulty in closing the global sea level budget at the last glacial maximum

peatlands of the western siberian lowlands current knowledge on zonation carbon content and late quaternary history the western siberian lowlands wsl are the world s largest high latitude wetland and possess over 900 000 km 2 of peatlands the peatlands of the wsl are of major importance to high latitude hydrology carbon storage and environmental history analysis of the existing russian data suggests that the mean depth of peat accumulation in the wsl is 256 cm and the total amount of carbon stored there may exceed 53 836 million metric tons a synthesis of published and unpublished radiocarbon dates indicates that the peatlands first developed at the end of the last glacial with a rapid phase of initiation between 11 000 and 10 000 cal yr bp initiation slowed after 8000 cal yr bp and reached a nadir at 4000 cal yr bp there has been renewed initiation particularly south of 621n following 4000 cal yr bp the initial development of peatlands in the wsl corresponds with the warming at the close of the pleistocene cooling after 4000 cal yr bp has likely led to increased permafrost and increased peatland development particularly in central and southern regions cold and dry conditions in the far north may have inhibited peatland formation in the late holocene r 2002 elsevier science ltd all rights reserved

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

ice dammed lakes and rerouting of the drainage of northern eurasia during the last glaciation during the quaternary period ice sheets centred over the barents and kara seas expanded several times onto mainland russia and blocked northflowing rivers such as the yenissei ob pechora and mezen large ice dammed lakes with reversed outlets e g toward the caspian sea formed south of these ice sheets some lakes are reconstructed from shorelines and lacustrine sediments others mainly from ice sheet configuration ice dammed lakes considerably larger than any lake on earth today are reconstructed for the periods 90 80 and 60 50 ka the ages are based on numerous optically stimulated luminescence osl dates during the global last glacial maximum lgm about 20 ka the barents kara ice sheet was too small to block these eastern rivers although in contrast to the 90 80 and 60 50 ka maxima the scandinavian ice sheet grew large enough to divert rivers and meltwater across the drainage divide from the baltic basin to the river volga and that way to the caspian sea climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet the final drainage of the best mapped lake is modelled and it is concluded that it probably emptied within few months we predict that this catastrophic outburst had considerable impact on sea ice formation in the arctic ocean and on the climate of a much larger area c 2003 elsevier ltd all rights reserved less

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

quaternary science 2007 a 50 year retrospective this paper reviews 50 years of progress in understanding the recent history of the earth as contained within the stratigraphical record of the quaternary it describes some of the major technological and methodological advances that have occurred in quaternary geochronology examines the impressive range of palaeoenvironmental evidence that has been assembled from terrestrial marine and cryospheric archives assesses the progress that has been made towards an understanding of quaternary climatic variability discusses the development of numerical modelling as a basis for explaining and predicting climatic and environmental change and outlines the present status of the quaternary in relation to the geological time scale the review concludes with a consideration of the global quaternary community and the challenge for the future

three empirical methods for the calculation of distal volume of tephra fall deposits abstract three empirical methods for the calculation of distal tephra fall volumes are presented and tested the three methods allow calculation of approximate distal tephra fall volumes under different conditions and abundances of field data all methods use proximal data to extrapolate the distal situation they are based on i shape and dispersal axis of proximal isopachs method of ellipses ii break in slope distance on log t vs a diagram where one distal isopach is available method of a ip with one distal isopach and iii distal thinning rate and break in slope distance on log t vs a diagram method of k 1 vs a ip the application of the three methods to published data of 23 32 eruptions in which it is possible to define at least two segments on the log t vs a diagram yields different results the method of ellipses yields good results if the thickness of reconstructed distal isopachs is greater than about 1 cm whereas the method of a ip with one distal isopach is more accurate if the distal isopach has a thickness below the half thickness at the break in slope distance t t ip the method of distal thinning rate k 1 vs break in slope distance a ip allows calculation of distal thinning rate and break in slope distance from only proximal data in this case calculated distal volumes approximate the actual one only if the deposits have a proximal volume total volume ratio greater than 0 7 otherwise they must be considered as minimum values to be added to the proximal volumes an empirical correlation between proximal thinning rate k and column height h t 7 6 k 0 47 r 0 90 is also presented column heights calculated in this way are within 20 of the observed published values in 94 of the examined cases

minimum volume of a tephra fallout deposit estimated from a single isopach a simple method is presented to calculate the minimum volume of an exponentially thinning fall deposit for which only one isopach is available this method exploits the fact that the product of the area enclosed within an isopach a and its thickness t reaches a maximum value ta max for a certain isopach it is shown that the minimum volume is vmin 3 69ta which is equal to the actual volume when ta ta max calculation of vmin for 327 isopachs from 74 fallout deposits shows that it is often just a bit lower than the volume calculated from all the available isopachs it is therefore proposed that vmin provides a useful minimum volume estimate for fallout deposits for which only one isopach is available

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

a late holocene palaeoenvironmental snapshot of the angamma delta lake megachad at the end of the african humid period abstract during the african humid period ahp there was a large increase in the area of lakes and wetlands lake megachad one of several huge lakes underwent dramatic fluctuations during the ahp prior to regression in the mid holocene however the timing and nature of ahp termination has been disputed we present evidence from sediments of the angamma delta from the northern end of the palaeolake for lake megachad lake level fluctuations at the end of the ahp delta slope deposits were deposited around 7000 cal bp at the height of the ahp overlying bioclastic sediments from 4300 to 4800 cal bp at an elevation of 285 290 m lie below the palaeolake highstand 339 m but close to the elevation of the bahr el ghazal sill which divided the lake s two sub basins ostracod 18o values indicate that the waters of the northern sub basin were evaporated to levels similar to modern lake chad palaeoecological evidence suggests that the lake was perennial and evaporative enrichment is attributed to restricted circulation of lake waters as the sill emerged the age and elevation of the bioclastic sediment coupled with published lake level reconstructions suggest a complex lake level history with a major regression at the end of the ahp followed by a short lived lake level rise and then a further regression this new evidence for changes in lake level provides support for other geological records and some modelling experiments that suggest rapid fluctuations in hydroclimate at the end of the ahp

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

significance of pot and gutter casts in a middle triassic carbonate platform betic cordillera southern spain pot casts and gutter casts are described for the first time in the lower part of the majanillos formation a middle triassic carbonate unit located in the external zones of the betic cordillera southern spain their identification as well as their relation to tempestites enables the better interpretation of the depositional environments and the shoreline to offshore facies transition on the anisian muddy carbonate ramp of the southern iberian massif the majanillos formation contains three members which become progressively more marly towards the top well preserved pot and gutter casts and thin intercalations of calcarenite which are interpreted as tempestites are abundant in the lowest member above the pot and gutter casts thicker calcarenite beds which locally contain hummocky cross stratification predominate bioturbated nodular limestones are prevalent at the top of the member the remaining succession which records a long term triassic transgressive cycle consists mostly of fine grained limestones deposited in very shallow marine environments calcarenitic sediments only accumulated within potholes and gutters in the nearshore they developed during storms when strong currents transported sediment to the outer shelf where it was deposited as tempestite beds pot and gutter casts characterize sedimentation in the bypass zone it is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry it is proposed that gutter casts display a trend of increasing width thickness ratios towards the outer shelf the identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments

sensitivity of last glacial maximum climate to sea ice conditions in the nordic seas published reconstructions of last glacial maximum lgm sea surface temperatures and sea ice extent differ significantly we here test the sensitivity of simulated north atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments an atmospheric general circulation model has been used to perform two simulations of the lgm and a modern day control simulation standard climap reconstructions of sea ice and sea surface temperatures have been used for the first simulation and a set of new reconstructions in the nordic seas northern atlantic have been used for the second experiment the new reconstruction is based on 158 core samples and represents ice free conditions during summer in the nordic seas with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well the simulated glacial climate is globally 5 7 k colder than modern day with the largest changes at mid and high latitudes due to more intense hadley circulation the precipitation at lower latitudes has increased in the simulations of the lgm relative to the simulation with the standard climap reconstructions reduction of the sea ice in the north atlantic gives positive local responses in temperature precipitation and reduction of the sea level pressure only very weak signatures of the wintertime icelandic low occur when the standard climap sea surface temperature reconstruction is used as the lower boundary condition in lgm with reduced sea ice conditions in the nordic seas the icelandic low becomes more intense and closer to its present structure this indicates that thermal forcing is an important factor in determining the strength and position of the icelandic low the arctic oscillation is the most dominant large scale variability feature on the northern hemisphere in modern day winter climate in the simulation of the lgm with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the north atlantic reduction of the north atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter the synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the lgm are used a closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter the trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced seasonally open waters in the nordic seas in the new reconstruction apparently act as a moisture source consistent with the current understanding of the rapid growth of the fennoscandian and barents ice sheets during the lgm the signal from the intensified thermal forcing in the north atlantic in boreal winter is carried zonally by upper tropospheric waves and thus generates non local responses to the changed sea ice cover

ice sheets and sea level of the last glacial maximum this paper outlines the general issues regarding ice sheets and sea level of the last glacial maximum lgm which formed the basis of an epilog project workshop papers in this special issue of quaternary science reviews provide a comprehensive assessment of these issues from the perspective of geological reconstructions of ice sheet extent records of sea level change ice sheet modelling geophysical models of glacial isostatic adjustment and geochemical proxies of ice volume this new assessment has substantially narrowed the uncertainties in the total changes in ice sheets and sea level and their proxies suggesting a net decrease in eustatic sea level at the lgm ranging from 120 to 135 m r 2001 elsevier science ltd all rights reserved

dynamic versus flexural controls of late cretaceous western interior basin usa the united states cretaceous western interior basin has long been considered a foreland basin driven by the sevier thrust and associated basin sediment loads however flexural studies demonstrate that this effect exists only within a narrow band in front of the thrust belt most of the basin appears to be due to mantle flow induced dynamic subsidence associated with farallon plate subduction here we show how the components of evolving long wavelength dynamic subsidence and flexural subsidence created the accommodation space and controlled the stratigraphy across the western united states based on a correlated stratigraphic section across central utah and colorado these backstripped subsidence data reveal the dynamic topography driven nature of the western interior basin the results seem to support that the depocenters track the trough of dynamic subsidence with ca 18 myr cycles through time and space and the stratigraphic patterns of large scale progradation eastward migration of depocenter and regional clinoform like downlap are related with the dynamic subsidence interpretation of these data also provides more insights into the repeated ca 2 to 6 myr cycles of thrust induced subsidence in front of the thrust belt which control the local eastward progradation of the sand bodies from the thrust belt the dynamic flexural subsidence and eustatic sea level changes interacted and controlled the timing and distribution of unconformities our work shows how the stratigraphy precisely records the timing patterns and position of dynamic versus flexural subsidences and that combination of such data leads to important geophysical discoveries and supplies strict constraints for geodynamic modeling

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

constraints on sst estimates for the northern north atlantic nordic seas during the lgm abstract a map of estimated calcification temperatures of the planktic foraminifer neogloboquadrina pachyderma sinistral tnps for the nordic seas and the northern north atlantic for the last glacial maximum was produced from oxygen isotopes with support of mg ca ratios to arrive at the reconstruction several constraints concerning the plausible salinity and 18 o fields were employed the reconstruction indicates inflow of temperate waters in a wedge along the eastern border of the nordic seas and at least seasonally ice free waters the reconstruction from oxygen isotopes shows similarities with mg ca based paleotemperatures in the southern and southeastern sector while unrealistically high mg ca values in the central nordic seas prevent the application of the method in this area the oxygen isotope based reconstruction shows some agreement with temperature reconstructions based on the modern analogue technique but with somewhat lower temperatures and a stronger internal gradient inside the nordic seas all told our results suggest a much more ice free and dynamic high latitude ocean than the climap reconstruction

morphodynamic evolution of kongsfjorden krossfjorden svalbard during the late weichselian and holocene we present a combination of fjord bathymetry and shallow seismic data from kongsfjorden and krossfjorden svalbard to characterize and analyse change in the fjord coastal environment physiography and the glaciosedimentary processes since the last glacial maximum swath bathymetry reveals a series of several styles of landform frequently superimposed upon each other permitting the reconstruction of the relative timings of deposition of each landform with the oldest successively overlain and cross cut by younger landforms and erosional processes large transverse ridges interpreted as recessional moraines are overlain by streamlined lineations formed subglacially during a subsequent ice advance a complex of recessional morainal ridges occurring within the central fjord are incised by glacial lineations and meltwater channels from younger glacial events

middle weichselian environments on western yamal peninsula kara sea based on pollen records pollen data from two sections from a coastal cliff on the western yamal peninsula 69 43 27vn 66 48 80ve document the environmental history during the karginsky middle weichselian interstadial low pollen concentrations high amounts of redeposited pollen and relatively high presence of artemisia pollen characterize sediments deposited at about 33 000 14 c yr b p grass sedge plant associations with few other herbs occupied the area during the late karginsky interstadial artemisia pollen may indicate rather xerophytic vegetation and disturbed soils in the area the dominance of redeposited pollen reflects scarce disturbed vegetation cover and low pollen productivity the climate was relatively cold and dry sediments dated to 32 400 14 c yr b p contain fewer redeposited pollen and concentration of non redeposited pollen is significantly higher pollen contents indicate the dominance of tundra like grass sedge vegetation and more humid conditions pollen records dated between 30 100 and 25 100 14 c yr b p also reflect scarce tundra like vegetation during this interval the presence of betula nana and salix pollen may reflect limited presence of shrub communities this suggests that the climate was somewhat warmer during the latter part of the interstadial however generally the pollen records show that harsh environmental conditions prevailed on the yamal peninsula during the karginsky interstadial

modeling the marine extent of northern hemisphere ice sheets during the last glacial cycle mechanisms which determine time dependent changes of the marine ice margin in dynamic ice sheet models are important but poorly understood here we derive an empirical formulation for changes in the marine extent when modeling the northern hemisphere ice sheets over the last glacial cycle in a three dimensional thermo mechanically coupled ice sheet model we assume that the strongest control on changes in marine extent is ice calving and that the variable most crucial to calving is water depth the empirical marine extent relationship is tuned so that the major marine retreat history of the north american and eurasian ice sheets are modeled accurately in time and space we find that this empirical treatment based on water depth is sufficient to reproduce the observations and discuss the implications for the physics of marine margin changes and the dynamics of the northern hemisphere ice sheets since the last glacial maximum

the ice hill an example of retarded deglaciation in siberia abstract the geological structure of one of the southernmost sites of thick ice beds in the yenisei valley near the arctic circle is discussed the erosion contacts of the foliated and contorted ice abundance of glacial debris and the position between the basal till and ablation cover indicate a glacial origin for the ice layer the ice occurs in the cores of arcuate accretion ridges built of ablation materials the overlying sequence consists of a series of diamicton flows alternating with lacustrine and outwash sediments laterally the ice rock complex changes into thick lacustrine rhythmites underlain by basal tills the ice containing hummocky terrain is often lower than the adjacent lacustrine plain therefore inversion of ice controlled topography is suggested several stages of glaciokarst development are supposed to have occurred after an eastward moving ice lobe stagnated more than 50 ka bp the main depositional events are associated with the middle weichselian draining of ice dammed lake igarka and with early holocene topographic inversion the holocene warming apparently caused diapiric deformation of the buried ice probably because of the density and thickness differences between the ice and the overburden the long history of burial and preservation of the remnants of basal glacier ice was controlled by pleistocene permafrost landscape evolution in northern siberia is governed by such retarded deglaciation in contrast with atlantic environments the thick ablation sequence may be described in terms of a spitsbergen model but the siberian basal tills because of their position within the permafrost must be regarded as exfoliated layers of debris rich ice according to shantzer lavrushin s model the occurrence of buried glacier ice and the mode of distribution of the permafrost shows the relict nature of the latter in areas of modern and former retarded deglaciation intermittent diamicton flows are supposed to mark episodes of climatic amelioration like the pleistocene and holocene diamictons with driftwood at the ice hill such warm diamictons may account for some early holocene and similar puzzling interglacial ice advances

classification of sedimentary furrows and a model for furrow initiation and evolution sedimentary furrows are longitudinal bed forms which form in fine grained cohesive sediments of the deep sea floor as well as in similar sediments in estuaries and in large lakes deep sea furrows have been observed where bottom currents often flow in one direction at 5 to 20 cm sec currents are much stronger greater than 50 cm sec in furrowed estuarine environments but sediment accumulation rates are higher a review of furrows studied in a variety of locations and environments suggests that these bed forms fall into two broad morphological classes those developed in muddy cohesive sediments tend to have steep walls and flat floors while those developed in carbonate rich cohesive sediments are broad and have gently sloping walls at abyssal depths furrows can often be detected by their distinctive echo patterns on 3 5 khz echo sounders a series of similar evenly spaced hyperbolic echoes which often have their apices tangent to the sea floor however different furrow cross sections may generate distinctive hyperbolic echo patterns a model for furrow initiation and development in muddy cohesive sediments suggests that furrows develop in depositional environments swept by recurring directionally stable and episodically strong currents furrows are initiated when secondary circulations in the boundary layer align coarse generally light debris in sand ribbon like bed forms as the coarse light sediments move along the sea floor they abrade small longitudinal troughs into the muds the grooves may fill in during intervals between strong current events if sedimentation rates are too high once a furrow is established on the sea floor further development may be controlled by the balance between sediment deposition and erosion where deposition occurs continuously and erosion occurs only episodically during brief periods of increased current strength narrow furrows width 1 5 to 1 15 of spacing appear to develop where deposition exceeds erosion whereas wide furrows width 1 2 of spacing develop where erosion exceeds or equals deposition dissolution may play an important role in the formation and evolution of furrows in carbonate rich cohesive sediments secondary circulation patterns over established furrows may be strongly controlled by bed form topography

hummocky cross stratification is not produced purely under progressive gravity waves hummocky cross stratification is a type of bedding in sedimentary rocks caused by the draping of sand around low steepness three dimensional bedforms this distinctive form of stratification has been thought to be diagnostic of the former action of storm waves and hence its occurrence has been used to reconstruct ancient palaeogeographies and marine processes here i examine theoretical and empirical aspects of hummocky cross stratification pertaining to its origin and argue that the notion that it was produced purely under progressive storm waves is incompatible with observed hummock spacings and possible values of the ratio a under waves a is the amplitude of oscillation near the bed and is the bedform spacing my view is supported by recent observations on naturally occurring hummocky megaripples from the sea floor of the inner atlantic shelf of north america

the postglacial pleistocene of the northern russian mainland abstract the paper summarizes the results of recent studies of late pleistocene postglacial geological events which occurred in the flatlands of northern russia stretching from the timan ridge to the laptev sea coast the available sedimentary record includes thawed and perennially frozen subaerial sediments and in places lacustrine and fluvial formations hundreds of geochronometric measurements by radiocarbon and luminescence techniques place this record within the time span of 50 11 ka bp which confirms an early mid weichselian age of the underlying glacial complex first established by the queen programme the spectrum of proxies includes sedimentary facies pollen data plant macrofossils oxygen isotope values megafauna remains insect assemblages traces of dna paleosols and permafrost properties together they indicate a continental progressively deteriorating climate with very cold winters and warmer than present summers through the second half of the late pleistocene minor climatic fluctuations are largely due to slightly changing humidity during mis 3 these changes are more pronounced in periglacial european russia in the vicinity of the barents kara ice sheet where the mid weichselian biotic maximum contrasts with conditions in the late weichselian polar desert in siberia the periglacial environments were more stable and beneficial for biota inspite of the increased continentality the recent data accumulated by various researchers are incompatible with the conventional correlation of the karginsky interglacial strata of siberia with mis 3 or any part of the european pleniglacial

determining the channel sinuosity of ancient fluvial systems from paleocurrent data abstract the classification of modern river channels is based primarily on their sinuosity values which can be determined directly from aerial photographs ancient channel systems are seldom sufficiently exposed to allow direct measurement of thalweg and valley lengths but paleocurrent directions can be used to calculate fairly accurate sinuosity values aerial photographs of four modern meander belts were studied to determine the relationship between local current directions within the meander belts and the actual sinuosity of the active river channels a value of 3 2 times the standard deviation gave the best approximation of the operational channel range resulting in a close correspondence between calculated and actual sinuosity values this method can therefore be used to estimate the s nuosity of ancient fluvial systems

creating virtual 3 d outcrop because of the high precision of present day gps and reflectorless laser technology geologic information and remotely sensed data i e seismic and gpr grids wells can be positioned accurately in 3 d and reconstructed as a virtual image hence we have developed the virtual outcrop for applications that require knowledge about the 3 d spatial arrangements of rock types

flow units connectivity and reservoir characterization in a wave dominated deltaic reservoir meren reservoir nigeria the meren e 01 agbada formation middle miocene reservoir offshore nigeria consists of a lower progradational shoreface succession terminated by a minor sequence boundary overlain by a progradational and retrogradational shoreface succession deposition occurred in a wave dominated delta front as indicated by the presence in core of hummocky cross beds slumped units and turbidites eight flooding surfaces were correlated and isopach maps sandstone quality trend maps and mudstone quality trend maps were constructed for each parasequence this work revealed a complex reservoir architecture characterized by shoreface clinoforms and a history of progradation and retrogradation cycles three different three dimensional geological characterizations of the e 01 reservoir were built a geostatistical model that used only well data a more geologically complex facies based model that used the sandstone quality trend maps in addition to well data and the most geologically complex sequence stratigraphic model that used mudstone quality trend maps in addition to the above data the three models were analyzed in terms of sandstone continuity and connectivity to hypothetical injector and producer wells only the sequence stratigraphic model predicted significant vertical compartmentalization through tortuosity generated by flooding surface mudstones waterflood fluid flow simulation of a downdip sector of the geologic models predicts similar recovery for the three models but a significantly different distribution of unswept oil only the sequence stratigraphic model identified parasequences with abundant unswept oil that are large enough to be economic infill prospects history matched full field fluid flow simulations verify both the reservoir compartments predicted by the sequence stratigraphic model and infill targets

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

geomorphological and sequence stratigraphic variability in wave dominated shoreface shelf parasequences physical stratigraphy within shoreface shelf parasequences contains a detailed but virtually unstudied record of shallow marine processes over a range of historical and geological timescales using high quality outcrop data sets it is possible to reconstruct ancient shoreface shelf morphology from clinoform surfaces and to track the evolving morphology of the ancient shoreface shelf our results suggest that shoreface shelf morphology varied considerably in response to processes that operate over a range of timescales 1 individual clinoform surfaces form as a result of enhanced wave scour and or sediment starvation which may be driven by minor fluctuations in relative sea level sediment supply and or wave climate over short timescales 10 1 10 3 years these external controls cannot be distinguished in vertical facies successions but may potentially be differentiated by the resulting clinoform geometries 2 clinoform geometry and distribution changes systematically within a single parasequence reflecting the cycle in sea level and or sediment supply that produced the parasequence 10 2 10 5 years these changes record steepening of the shoreface shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation modern shorefaces are not representative of this stratigraphic variability 3 clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shore face progradation 10 5 10 8 years these controls determine the external dimensions of the parasequence

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

simulation of fast flow features of the fennoscandian ice sheet during the last glacial maximum in order to reconstruct the palaeoglaciation in fennoscandia and north ern asia during the late weichselian ice age phase simulations with the dynamic and thermodynamic ice sheet model sicopolis are carried out our focus is on the last glacialmaximum lgm around20 kyr bp climateforcingisbasedonmeanannualsur face temperature and precipitation derived from present data and palaeoclimatic model ling intercomparison project pmip ukmo21results for the lgm these distributions areinterpolatedvia aglacial indexdefinedby thegreenlandicecoreproject grip d 18 o record the extent of the scandinavian and the barents ice sheets is reproduced in good agreement with the quaternary environments of the eurasian north queen recon struction but the kara sea and taymyr peninsula areas are excessively glaciated the fast flow regions derived from the simulations which are generally connected to regions with a temperate base and temperate ice above are compared to hypothesized palaeo ice stream locations especially in the norwegian channel and the baltic area in the norwegian channel temperate basal conditions with temperate ice above prevail and favour fast flow in the baltic area ice sheet advance is generally accompanied by slow ice velocities 5200ma 1 some temporary fast flow features occur due to transitional temperate base conditions and higher velocities arise in retreat phases

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

non glacial paleoenvironments and the extent of weichselian ice sheets on severnaya zemlya russian high arctic abstract the extent of the barents kara sea ice sheet northern europe and russia during the last glacial maximum lgm in marine isotope stage mis 2 is controversial especially along the southern and northeastern russian high arctic margins we conducted a multi disciplinary study of various organic and mineral fractions obtaining chronologies with 14 c and luminescence dating methods on a 10 5 m long core from changeable lake 4 km from the vavilov ice cap on severnaya zemlya the numeric ages indicate that the last glaciation at this site occurred during or prior to mis 5d 4 early middle weichselian deglaciation was followed by a marine transgression which affected the changeable lake basin after the regression the basin dried up in late middle weichselian time ca 25 40 ka reworked marine sediments were deposited in a saline water body during the late weichselian mis 2 the basin was not affected by glaciation and lacustrine sediments were formed which reflect cold and arid climate conditions during the termination of the pleistocene and into the holocene warmer and wetter climate conditions than before led to a higher sediment input thus our chronology demonstrates that the northeastern margin of the lgm barents kara sea ice sheet did not reach the changeable lake basin this result supports a modest model of the lgm ice sheet in northern europe determined from numeric ice sheet modelling and geological investigations

mechanisms for forming discontinuity surfaces within shoreface shelf parasequences sea level sediment supply or wave regime abstract a 2d process response model was used to evaluate potential mechanisms involved in the formation of small scale stratigraphic variability that is observed within progradational wave dominated shoreface shelf parasequences model experiments which are based on scenarios that consist of a 25 ky progradational phase suggest that discontinuity surfaces form when either sediment supply or sea level fall rapidly or when wave height regime increases over relatively short time periods 102 104 y during coastal progradation in these cases mean deposition rate near the lower shoreface drops which combined with coastal progradation results in a discontinuity surface both observed and simulated discontinuity surfaces form predominantly in lower shoreface deposits and bound meter scale stratigraphic cycles simulations show that wave regime variability affects the shoreface shelf to a much greater depth than minor sea level change therefore facies shifts along wave climate induced bounding surfaces occur over wider reaches of the shoreface shelf system than sea level induced facies shifts high frequency variability in sediment supply rate results in the formation of discontinuity surfaces across which there are no distinct facies shifts

pot and gutter casts from the chapel island formation southeast newfoundland abstract member 2 of the chapel island formation of southeast newfoundland contains a diverse suite of erosional structures known as pot and gutter casts these are particularly abundant in a lithofacies deposited in a nearshore zone characterized by erosion and sediment bypass during storm emplacement of sands the steep to overhanging walls of both pot and gutter casts imply rapid filling during the same storm events that created these depressions erosion is thought to have taken place under strong offshore directed unidirectional flow storm surge or other relaxation flow as with many sandstone tempestites the initial stages of the storm events were dominated by strong and in this case highly erosive unidirectional flow and the latter stages by oscillatory flow as evidenced by wave diagnostic lamination in the sandy infills pot casts have geometries and soles indicating vortex flow similar to that which forms potholes in bedrock in glaciated regions gutter casts that lead into potholes do so at their edge a requirement for generating rotary currents within the depression pot casts are commonly tilted relative to paleohorizontal and their direction of plunge is either upcurrent or downcurrent variation in geometry of the erosional structures from the chapel island formation and from erosional structures in general can be accounted for by the following substrate type diagenetic history of substrate and flow parameters such as pattern of water motion velocity and intermittency of flow

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

chemical and bacteriological analysis of soil from the middle and late weichselian from western spitsbergen arctic abstract this paper discusses temporal variability in the biogeochemical properties of the deeper permafrost soils of western spitsbergen arctic that dates back up to the middle weichselian period 44 8 ka bp results indicate that during the mid of the last interstadial 37 ka bp the chemical and biological properties of the soils were different from the stadial period that followed trace element concentration during the period remained low electrical conductivity along with k mg na so 4 2 cl and hco 3 content of the soils during this period was high mineralizable nitrogen organic carbon biomass nitrogen and total bacterial counts were also high these observations concurrently lead to a conclusion that the soils of western spitsbergen during the interstadial period were under marine influence the culturability of bacterial cells was low which increased later with the onset of the stadial

changes in the flow of atlantic water into the arctic ocean since the last deglaciation evidence from the northern svalbard continental margin 80 n 1 the svalbard archipelago is located in the high arctic 76 80 n within the northernmost reach of the west spitsbergen current which is the continuation of the north atlantic current in this specific setting close to the polar front even small variations in the current system are expected to give large and distinct signals in paleoceanographic parameters thus the svalbard area is ideal for monitoring the past history of the inflow of atlantic water to the arctic ocean we have studied sediment core np94 51 taken outside the mouth of the hinlopen strait on the northern svalbard shelf the paleoceanographic development of the last deglaciation and the holocene has been reconstructed using benthic and planktonic foraminifera oxygen isotopes and ice rafted detritus the results show that the first strong subsurface inflow of atlantic water to the arctic ocean after the last glacial maximum commenced at 12 6 14c kyr b p circa 15 000 calendar cal years b p during the bolling allerod interstadial during the younger dryas polar conditions prevailed at the surface with extensive sea ice cover and the inflow of atlantic derived water was generally diminished the inflow of more saline but still cold atlantic water was relatively strong during the early holocene and caused intensified seasonal biological productivity the atlantic water inflow declined gradually during the mid holocene between 4500 and 1100 cal years b p the inflow was very weak and the bottom waters over the northern svalbard margin were cold and of lower salinity during the last 1000 years climatic conditions improved such that the subsurface inflow of atlantic derived water increased however the surface waters were still cold

late quaternary stratigraphy of western yamal peninsula russia new constraints on the configuration of the eurasian ice sheet ice sheet reconstructions for the last glacial maximum in northern eurasia range from nearly complete coverage by a contiguous marine based ice sheet to large unglaciated areas stratigraphic records from yamal peninsula russia provide new insight on the eastern limit of the eurasian ice sheet in the kara sea radiocarbon and infrared stimulated luminescence ages from coastal cliff sections date the emplacement of the kara diamicton as older than ca 40 ka reflecting regional glaciation ice wedge growth peat accumulation and eolian and fluvial deposition characterized the past 40 k y and do not support coverage of yamal peninsula by an ice sheet or proximity to a glacier margin thus the late weichselian eurasian ice sheet was largely confined to barents sea and its global sea level contribution is reduced to 7 m of sea level equivalent

the svalbard barents sea ice sheet historical current and future perspectives abstract the history of research on the late quaternary svalbard barents sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years since the onset of scientific research there in the early 19th century svalbard has been a natural laboratory where ideas and concepts have been tested and played an important but rarely acknowledged role in the break through of the ice age theory in the 1870 s the history of how the scientific perception of the svalbard barents sea ice sheet developed in the mid 20th century also tells a story of how a combination of fairly scattered and often contradictory observational data and through both deductive and inductive reasoning could outline a major ice sheet that had left but few tangible fingerprints since the 1980 s with increased terrestrial stratigraphical data ever more marine geological evidence and better chronological control of glacial events our perception of the svalbard barents sea ice sheet has changed the first reconstructions depicted it as a static concentric single domed ice sheet with ice flowing from an ice divide over the central northern barents sea that expanded and declined in response to large scale late quaternary climate fluctuations and which was more or less in tune with other major northern hemisphere ice sheets we now increasingly perceive it as a very dynamic multidomed ice sheet controlled by climate fluctuations relative sea level change as well as subglacial topography substrate properties and basal temperature in this respect the svalbard barents sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine based ice sheets build up and decay

correlation of upper pleistocene sediments in northern west siberia abstract a geochronometric database comprising 121 optically stimulated luminescence and 59 radiocarbon dates plus u th date on peat from 24 key sections in northern west siberia is presented and discussed these data have been obtained during russian norwegian joint research for the past 15 years and are augmented by reports on radiocarbon dated mammoth carcasses in west siberia together they provide the basis for revising the regional stratigraphic scheme and for correlation to the european quaternary chronostratigraphy and marine oxygen isotope record the geochronologic correlation of sedimentary formations across west siberia involves classical stratotypes of fluvial shallow limnic and temperate marine sediments of the karginsky horizon ca 130 ka which was previously attributed to mis 3 the older kazantsevo marine formation is thus assigned a middle pleistocene age the uppermost glacial sedimentary complex containing glacial ice was deposited by shelf based ice sheets between ca 100 and 60 ka bp the postglacial pleistocene sediments are mostly ice bound loess like deposits and sink hole silts containing numerous mammoth carcasses that are radiocarbon dated to between ca 42 and 25 ka bp there are no traces of glacial activity on the siberian plains during mis 2 a period for which palaeoclimatic proxies suggest a cold and dry environment this synthesis indicates that the prior usage of the siberian correlation horizons of kazantsevo and karginsky as equivalents of the eemian and middle pleniglacial is stratigraphically invalid

review of methods of estimating rhyolitic tephra volumes applications to the taupo volcanic zone new zealand there have been at least 35 rhyolitic plinian eruptions in the last 50 kyr from 2 volcanic centres in taupo volcanic zone tvz new zealand to determine the total volume of erupted material calculation techniques are reviewed and further developed all involve extrapolation from isopach maps three methods assume an exponential decay of thickness with distance from source and a further two are based on the area enclosed by each isopach comparison of methods shows those based on area to be more accurate except the log log plot of area and thickness which requires excessive extrapolation a log volume vs thickness plot is considered superior because minimal extrapolation is needed for most tephras volumes calculated by the different methods are in reasonable agreement volumes previously calculated by the crystal concentration method are 2 3 times greater than those from the six methods used here total pumice fragmentation is probably not required for the liberation of crystals and this would decrease calculated volumes during the last 50 kyr magma has been erupted at a constant mean rate in the taupo volcanic zone a simple step function shows a strong relationship between deviations from the mean rate and either the next erupted volume or the time to the next eruption extrapolation of these step functions suggests future eruptions in less than 400 years for okataina and about 8000 years for taupo the volume of rhyolitic material erupted from tvz within the last 50 kyr is estimated at 360 km3 of tephra 350 km3 of ignimbrite and 55 km3 of extrusive equivalent to about 350 km3 of magma at an average rate of eruption of 7 km3 year at least 4200 km3 of rhyolitic magma has been erupted since the inception of tvz about 0 6 m y ago if back are spreading of tvz at 7 mm yr is compensated for by dyke intrusion into the upper 10 km of crust 8400 km3 of magma is required the total volume of magma generated by partial melting is estimated at 12 600 km3 removal of this melt would cause subsidence of 2 1 km the present depth to subvolcanic basement in tvz

advection of atlantic water to the western and northern svalbard shelf since 17 500 cal yr bp abstract the changes in flow and character of the warm atlantic water through the last 17 500 cal yr are reconstructed from the distribution of benthic foraminifera species planktonic and benthic foraminifera abundances stable oxygen isotopes and lithology in two cores from the western and northern shelf of svalbard the results show almost continuous presence of atlantic water at the shelf areas since 14 500 cal yr bp the bolling and allerod intervals stand out as periods of highest bottom waters temperatures the strong inflow of saline but chilled atlantic water during the early holocene was followed by cooling and freshening of the bottom waters during the mid and late holocene the two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of atlantic water recorded further south in the nordic seas the early holocene warming was not just an effect of higher solar insolation but was also due to increased heat flux from the stronger atlantic water inflow driven by wind force and or thermohaline circulation

submarine landforms and the reconstruction of fast flowing ice streams within a large quaternary ice sheet the 2500 km long norwegian svalbard margin 57 80 n morphological interpretation of regional and detailed bathymetric data sets on the 2500 km long norwegian shelf from the north sea 57 n to svalbard 80 n has revealed a dynamic ice flow pattern along the western marginof the scandinavian and barents svalbard ice sheets about 20 cross shelf troughs with megascale glacial lineations msgl elongate ridges and grooves oriented parallel to trough long axes are interpreted as former pathways for fast flowing ice streams studies of large scale margin morphology and seismic profiles have identified large submarine fans at the mouths of several major cross shelf troughs less dynamic ice probably existed on shallower banks the two largest paleo ice streams were the norwegian channel ice stream and bear island trough ice stream each 150 200 km wide at the mouth the lengths of individual msgl vary from hundreds of meters to several tens of kilometers and the distance between ridges varies from 0 1 to 3 km msgl amplitudes reach 15 m but are commonly 10 m the onset of msgl and hence fast ice flow is generally close to the outer coast at the border zone between crystalline rocks and softer sedimentary rocks transverse submarine ridges on various scales commonly parallel to the shelf edge reflect either the maximum ice sheet position or the recessional pattern of the ice sheet lateral ice stream moraines several tens of kilometers long have also been mapped along the sides of several cross shelf troughs identifying the border zone between fast ice flow and stagnant or slow flowing ice on intervening banks

pleistocene marine deposits in the coastal areas of kola peninsula russia abstract on the basis of field data datings from both electron spin resonance and optically stimulated luminescence and micro and macrofauna in addition to presence of diatoms three late pleistocene marine units have been identified in the coastal areas of the kola peninsula the stratigraphically lowest sequence is correlated to the ponoi beds and the boreal transgression attributed to the marine isotope stages mis 5e to 5d in the white sea depression and to mis 5e to 5c in the barents sea thermophilic fauna and diatoms indicate normal water salinity and a water temperature above zero the second marine unit referred as the strel na beds can be correlated with the early weischselian transgression termed the belomorian transgression with low water salinity and a water temperature similar or colder than the present times belomorian transgressions are reliably detected in the white sea and are not clearly found in the barents sea the results obtained from the sediments of the ponoi and strel na beds indicate a continuously existing marine reservoir from 130 to 80 70 ka ago entire mis 5 in the white sea depression the early middle weichselian barents kara ice sheet invasion and its recession might have caused the glacioeustatic middle weichselian mis 3 transgression and the third late pleistocene marine sequence has been deposited in the regressing shallow cold sea with less saline waters the results help in the understanding of the history of late quaternary ice sheets in north eurasia and provide evidence for the debatable early and middle weichselian marine events

orographic effects on the transport and deposition of volcanic ash a case study of mount sakurajima japan volcanic ash is a major atmospheric hazard that has a significant impact on local populations and international aviation the topography surrounding a volcano affects the transport and deposition of volcanic ash but these effects have not been studied in depth here we investigate orographic impacts on ash transport and deposition in the context of the sakurajima volcano in japan using the chemistry resolving version of the weather research and forecasting wrf model sakurajima is an ideal location for such a study because of the surrounding mountainous topography frequent eruptions and comprehensive observing network at sakurajima numerical experiments reveal that across the 2 8 grain size range the deposition of medium sized ash 3 5 is most readily affected by orographic flows the direct effects of resolving fine scale orographic phenomena are counteracting mountain induced atmospheric gravity waves can keep ash afloat while enhanced downslope winds in the lee of mountains up to 50 stronger can force the ash downwards gravity waves and downslope winds were seen to have an effect along the dispersal path in the vicinity of both the volcano as well as other mountains depending on the atmospheric conditions resolving these orographic effects means ash can be transported higher than the initial injection height especially for ash finer than 2 shortly after the eruption within 20 minutes and close to the vent within the first 10 km effectively modifying the input plume height used in an ash dispersal model an effect that should be taken into account when initialising simulations

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

the margin of the last barents kara ice sheet at markhida northern russia the markhida moraine is a broad zone of ice marginal landforms and deposits running e w across the pechora lowland in northern russia it was formed along the southern margin of an ice sheet advancing onto the coast from the kara sea previous researchers grosswald 1980 1983 1994a grosswald et al 1974 concluded that the moraine was formed during a readvance of the barents kara ice sheet after 9000 14c yr b p this conclusion was based on the occurrence of deformed lacustrine sediments dated 9000 to 10 000 14c yr b p between two presumed basal tills in the type section at markhida a reinvestigation of the section by the authors revealed only one basal till overlain by lacustrine sediments and diamictons yielding radiocarbon dates between 9000 and 10 000 14c yr b p luminescence dating from the sand underlying the till gave middle weichselian ages deformation structures and fabric in the sediments overlying the till solely reflect gravity driven processes not glaciotectonic deformation as claimed by previous investigators we conclude that most of these sediments were finally deposited during very slow retarded melting of a large body of buried glacier ice and the underlying permafrost thus the markhida moraine as an ice marginal feature was formed prior to 10 000 14c yr b p probably during the late weichselian but possibly as early as the middle weichselian

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

holocene environmental history recorded in lake lyadhej to sediments polar urals russia an 1180 cm long core recovered from lake lyadhej to 68 15 n 65 45 e 150 m a s l at the nw rim of the polar urals mountains reflects the holocene environmental history from ca 11 000 cal yr bp pollen assemblages from the diamicton ca 11 000 10 700 cal yr bp are dominated by pre quaternary spores and redeposited pinaceae pollen pointing to a high terrestrial input turbid and nutrient poor conditions existed in the lake ca 10 700 10 550 cal yr bp the chironomid inferred reconstructions suggest that mean july temperature increased rapidly from 10 0 to 11 8 c during this period sparse treeless vegetation dominated on the disturbed and denuded soils in the catchment area a distinct dominance of planktonic diatoms ca 10 500 8800 cal yr bp points to the lowest lake ice coverage the longest growing season and the highest bioproductivity during the lake history birch forest with some shrub alder grew around the lake reflecting the warmest climate conditions during the holocene mean july temperature was likely 11 13 c and annual precipitation 400 500 mm the period ca 8800 5500 cal yr bp is characterized by a gradual deterioration of environmental conditions in the lake and lake catchment the pollen and chironomid inferred temperatures reflect a warm period ca 6500 6000 cal bp with a mean july temperature at least 1 2 c higher than today birch forests disappeared from the lake vicinity after 6000 cal yr bp the vegetation in the lyadhej to region became similar to the modern one shrub betula nana salix and herb tundra have dominated the lake catchment since ca 5500 cal yr bp all proxies suggest rather harsh environmental conditions diatom assemblages reflect relatively short growing seasons and a longer persistence of lake ice ca 5500 2500 cal yr bp pollen based climate reconstructions suggest significant cooling between ca 5500 and 3500 cal yr bp with a mean july temperature 8 10 c and annual precipitation 300 400 mm the bioproductivity in the lake remained low after 2500 cal yr bp but biogeochemical proxies reflect a higher terrestrial influx changes in the diatom content may indicate warmer water temperatures and a reduced ice cover on the lake however chironomid based reconstructions reflect a period with minimal temperatures during the lake history

new constraints on the limits of the barents kara ice sheet during the last glacial maximum based on borehole stratigraphy from the pechora sea a new 14 c verified borehole stratigraphy provides the first age controlled reconstruction of the late quaternary glacial history of the pechora sea southeasternmost barents sea a complete glaciation of the pechora sea is confirmed for middle weichselian time prior to ca 35 40 ka composition of glacial erratics indicates that ice was moving from or across southernmost novaya zemlya and vaygach island after a brief interstadial period with normal marine conditions the pechora sea was affected by a drop in sea level and a drier climate subsequently the late weichselian barents kara ice sheet occupied the northwestern part of the pechora sea but did not reach the coast of the pechora lowland as previously believed these data provide a new constraint on the last glacial maximum lgm ice sheet limits in the eurasian arctic the inferred direction of the last glacial maximum ice movement in the pechora sea was from the northeast but with a stronger northern component than the penultimate glaciation the ice sheet retreated early ca 13 ka after which the shallow pechora sea was subjected to strong erosion during the postglacial sea level rise

new estimations of habitable land area and human population size at the last glacial maximum abstract the estimation of human population size during the pleistocene is complex and one which has been dealt with extensively in the literature however because many of these previous estimations are based in part on archaeological site distributions they are more a reflection of present day geography than of what the earth looked like in the past we address this issue by calculating an estimation of habitable land area during the last glacial maximum between 22 and 19 kya when sea level was 120 m lower than today using the polygon creation function in google earth we then subtract areas of land that were likely uninhabitable during the lgm either due to glacier cover extreme aridity elevation or areas at high latitudes from this the combined habitable land areas of eurasia africa and the australian landmass are estimated as 76 959 712 4 km 2 this estimation is then coupled with population density data for medium to large bodied carnivores and ethnographic population density data for hunter gatherers culled from the literature total human census population size in the old world during the last glacial maximum is estimated at 2 117 000 2 955 000 based on carnivore densities and 3 046 000 8 307 000 for hunter gatherer densities

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

geostrophic circulation or shallow marine turbidity currents the dilemma of paleoflow patterns in strom influenced prograding shoreline systems in ancient storm influenced prograding shoreline sequences sole marks mainly tool marks from hummocky crossstratified storm deposits are commonly oriented normal to paleoshoreline and the trend of paleobathymetric contours in the basin asymmetrical tool marks typically indicate flows directed offshore several workers have attributed their formation to storm generated shallow marine turbidity currents this interpretation conflicts with observations from modern shelves where storm driven circulation generally is geostrophically balanced and time averaged bottom currents approximately parallel bathymetric contours and the local shoreline the resolution of these apparently conflicting observations may lie in the realization that tool marks and many other small paleoflow indicators form almost instantly as the result of instantaneous flow conditions very near the bed beneath storm generated flows in the shallow ocean instantaneous and time averaged characteristics of the bottom boundary layer generally exhibit little similarity storm generated tool marks are formed by the movement of large tools within the thin less than 1 m inner boundary layer resulting from the superimposition of waves and currents the orientation of the peak instantaneous shear stress moving large tools under such combined flows mainly reflects wave orbital motions which typically are normal to shore the magnitude of stress is greatly increased in the offshore direction and decreased in the onshore direction by superimposition of a steady current with an offshore component of flow but the direction of stress is only slightly affected in ancient storm influenced sequences therefore shore normal tool marks generally were not formed by turbidity currents rather their orientation is best attributed to shoaling waves approaching the coast at a very high angle asymmetrical tool marks are directed offshore due to enhanced shear stress on the offshore stroke of waves superimposed on a geostrophic current with an offshore flow component tool marks do not reflect the time averaged bottom flow direction in fact they provide almost no information concerning steady bottom currents in contrast high angle cross beds formed in coarser sediment by the migration of dunes and sandwaves although relatively rare in offshore storm deposits generally reveal approximately shore parallel flows in ancient systems cross beds closely reflect the time averaged flow direction in the outer boundary layer of a geostrophic current for three reasons 1 the net transport direction for sand moving as bed load beneath a combined flow lies between the directions of peak instantaneous shear stress and time averaged shear stress 2 large ripples disrupt the thin inner boundary layer and 3 long time intervals relative to wave induced velocity oscillations are required to form large ripples

the last ice sheet of the kara sea terrestrial constraints on its age abstract the ice dispersal features on the siberian mainland unanimously indicate that the last ice domes were positioned on the kara sea shelf and adjacent coastal plains the age of the last glacial maximum evokes much controversy the problem may be solved by sorting out the available radiocarbon dates both statistically and using geological common sense over 200 finite radiocarbon dates have been analysed 77 of the entire population represent sediments overlying the topmost till including dating the most reliable organics such as mammoth remains the rest of the dates 23 have been obtained from the underlying sediments mostly on materials readily prone to redeposition and contamination such as driftwood and shells the last culmination of the shelf ice sheet must have occurred beyond the range of the conventional radiocarbon method and after the last warm water sea transgression correlative to the eemian the early weichselian age for the last kara sea ice sheet is also supported by the lack of proglacial lacustrine sediments with finite radiocarbon dates in periglacial west siberia