stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

ventifacts and wind abraded rock features in the taylor valley antarctica abstract an area north of lake fryxell in the taylor valley antarctica was surveyed to determine the frequency of occurrence of rocks that show strong evidence of wind abrasion and ventifaction which is defined here as rocks having well developed faceting to define their relative abundance in this area of the ice free mcmurdo dry valley system and to provide an indication of the role of wind as a geomorphic agent in this area the orientation of abrasion caused features facets keels and grooves with respect to the present day wind regime is also described rocks were examined on five linear transects ranging from 300 to 510 m in length a total of 1324 rocks were examined on average 60 of all rocks exhibited distinct wind abrasion features with polish being the most common feature and polished rocks were distributed equally between survey lines suggesting abrasion was ubiquitous in the study area approximately 4 of the rocks had distinct facets and or keels and fine grained ultramafic peridotite type rocks produced the most finely featured forms i e sharp facet edges and keels a larger percentage 12 5 had grooves grooves were typically associated with a tabular form of mafic diabase type igneous rock the distribution of faceted ventifacts and grooved rocks was not uniform for the five transects suggesting that the distribution mechanism for the surface rocks and the source areas determined to a large extent what form of ventifact could be produced at a location the orientation of the grooves and dip directions of the facets indicates the direction of the abrasive winds had a strong westerly component which coincides with the modern wind regime of winter katabatic flows that move down valley toward the ross sea the orientation of the facets and grooves suggests that the rate of formation of the ventifacts proceeds at a pace greater than other surficial processes e g down slope soil movement cryoturbation which should tend to remove trends in the facet and groove orientations or that the down slope movement of the surface is approximately perpendicular to the wind allowing preservation of the alignment

rapid deposition of sand and gravel mixtures downstream of a negative step the role of matrix infilling and particle overpassing in the process of bar front accretion an experimental flow channel was used to investigate the rapid deposition of sand and gravel mixtures downstream of a negative step hydraulic processes give rise to the quasi simultaneous accumulation of openwork gravels matrix filled contact framework and dilated framework gravels the resultant structure is analogous to a bar front in gravel bed streams flow conditions were non uniform but steady in time whereas open and closed gravel fabrics are usually interpreted as representing deposition from unsteady flows for example a varying discharge regime consideration of the percentage of sand in the deposits indicated that in terms of packing the sediments may be considered as a simple binary mixture with partial framework dilation occurring with sand percentages in excess of c 32 despite dilation for sand percentages less than 50 structural stability of the foreset gravels was maintained so that the bar front exhibited a distinct brinkpoint and a planar slip face at the angle of initial yield which made an angular contact with the base of the flume for sand percentages in excess of 80 individual gravel clasts were completely supported by sand the original structural stability was lost so that the bar front eroded by reverse currents assumed a tangential contact with the flume base below the angle of initial yield the brinkpoint was rounded and indistinct in addition to altering the bar front slope increasing the quantity of sand in the bed sediments had a major influence on the dip of gravel particles on the foresets in all experimental runs a surface sand seal with openwork gravels beneath developed upstream of the brinkpoint the mechanics of sand seal formation require further investigation however an overpassing mechanism was noted to be very important in sorting gravel particles rolling over the brinkpoint a published mathematical model describing the overpassing mechanism was found to be appropriate to the present experimental observations

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

formation and character of an ancient 19 m ice cover and underlying trapped brine in an ice sealed east antarctic lake abstract lake vida one of the largest lakes in the mcmurdo dry valleys of antarctica was previously believed to be shallow 10 m and frozen to its bed year round new ice core analysis and temperature data show that beneath 19 m of ice is a water column composed of a nacl brine with a salinity seven times that of seawater that remains liquid below 10 c the ice cover thickens at both its base and surface sealing concentrated brine beneath the ice cover is stabilized by a negative feedback between ice growth and the freezing point depression of the brine the ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2 800 14c years b p suggesting that the brine has been isolated from the atmosphere for as long to our knowledge lake vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end member lacustrine ecosystem on earth

use of ground penetrating radar for 3 d sedimentological characterization of clastic reservoir analogs clastic reservoir analogs based on 2 d outcrop studies provide valuable definitions of geometric and petrophysical heterogeneities at interwell scales integration of 3 d ground penetrating radar gpr surveys with sedimentological and stratigraphic data provides information on the internal heterogeneities of sedimentary sequences at scales that allow dissection of the 3 d anatomy of clastic depositional systems two 3 d gpr data volumes were acquired in the ferron sandstone of east central utah the data show prominent lenticular features a variety of lithologies and structural elements such as channels and shale drapes that match well with those seen at the same stratigraphic levels in adjacent cliff faces

using two and three dimensional georadar methods to characterize glaciofluvial architecture abstract the threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport to characterize these heterogeneities we have conducted extensive two dimensional 2 d and three dimensional 3 d ground penetrating radar gpr or georadar surveys in two quarries within the rhine valley of northeastern switzerland the quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum wurm stage glaciation after the surveys the terrace walls beneath the two study sites were photographed as they were being excavated by combining information extracted from the 2 and 3 d georadar images with the outcrop photographs it was possible to correlate georadar facies with the various glaciofluvial architectural elements the dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions architectural elements were generally elongated parallel to the mean flow directions of the ancient river system variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction time slices showed structural trends not evident on 2 d georadar images and photographs data interpretation was quicker more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone

lake hoare antarctica sedimentation through a thick perennial ice cover lake hoare in the dry valleys of antarctica is covered with a perennial ice cover more than 3 m thick yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom rough topography on the ice covering the lake surface traps sand that is transported by the wind in late summer vertical conduits form by melting and fracturing making the ice permeable to both liquid water and gases cross sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits this is the primary sedimentation mechanism in the lake sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m this conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1 5 m despite the close spacing of the cores the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate apparently sand descends into the lake from discrete highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time in some locations on the lake bottom distinctive sand mounds have been formed by this process they are primary sedimentary structures and appear unique to the perennially ice covered lacustrine environment in some locations they are tens of centimetres high and gently rounded with stable slopes in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose a simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria eukaryotic algae and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites

3 d ground penetrating radar applied to fracture imaging in gneiss three dimensional ground penetrating radar georadar techniques suitable for geological engineering applications have been developed and tested initial experiments were conducted on the floor of a quarry in southern switzerland from which ornamental gneissic rock is extracted during a brief two day period constant offset georadar data were recorded over a 650m2 area with a grid cell size of 0 1 m 0 2 m georadar velocities were estimated from the results of expanding spread surveys all georadar data and associated geometry files were recorded automatically in seismic industry formats the experimental georadar data set was processed image enhanced and interpreted using 3 d seismic reflection software operating on a workstation arbitrary vertical sections time slices 3 d images and animated movies in which the observer travels through the entire data volume were constructed from the resultant migrated georadar data semi automatic tracking routines allowed continuous subhorizontal reflectio

sedimentation in ice covered lake hoare antarctica the sedimentation mechanisms that occur in ice covered lake hoare antarctica are examined to determine how sediment enters the lake and how the sedimentation pattern affects blue green algal growth at the lake bottom the 3 m thick ice cover contains pebbly sand as much as 2 m below the surface sediment with similar texture and mineralogy is found at the lake bottom this evidence together with the lack of sediment in the inflowing stream and the markedly different texture of sediment from the other terrains around the lake suggest that most of the sediment at the lake bottom comes in through the ice cover sand grains intermittently migrate through porous ice on the surface water filled vertical gas channels penetrating two thirds of the ice cover and possibly through cracks in the ice that act as conduits the algae at the lake bottom are able to survive in part because sediment that comes through the ice cover does not obliterate them

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

evolution of buntsandstein fluvial sedimentation in the northwest iberian ranges central spain abstract the buntsandstein sediments in central spain permian and triassic are mainly continental redbeds that form the base of a sequence that passes up into siliciclastic and carbonate tidal sediments the muschelkalk facies buntsandstein sedimentation began with conglomeratic and sandy fluvial facies whose detailed sedimentological analysis is the main subject of this work massive sheets are the most important conglomerate facies they were formed by deposition as longitudinal bars channel fill conglomerates are the second most important facies lateral accretion deposits also occur in the conglomerates they evolved from longitudinal bars because of decreasing flow or because the bars had reached a certain height sandstones are composed of eleven different facies large linguoid or transverse bars were the main bedforms in this environment these bedforms may be related downstream to large oblique troughs developed when the tabular bedform grew to a certain size or when a tabular bedform reached another one that acted as an obstacle compound and composite compound bars consisting of large sets of trough cross bedding with scoured wavy bases are al o recognized in the sandstone facies two major cycles occur in the complete conglomerate sequence which correspond to different physiographic models the lower cycle was mainly formed by channels and bars that were smaller than those in the upper cycle the upper cycle is more extensive than the lower one and has characteristics that indicate a higher stability paleocurrents for both cycles have a north northeasterly trend the vertical evolution of these sediments is clearly related to the different fault systems that controlled their distribution the paleogeography of the sandstone facies together with paleocurrents perpendicular to the conglomerate paleoccurents indicate deposition from a separate dispersal system that extensively overlies the previous one this unit which can be followed extensively over most of the iberian ranges and even outside the iberian ranges represents the growth of a fluvial braidplain over a large area of iberia during the lower triassic

a numerical three dimensional conditioned unconditioned stochastic facies type model applied to a remediation well system in this study a three dimensional stochastic facies based aquifer model was developed the model can be used to numerically simulate flow and solute transport in heterogeneous groundwater aquifers the stochastic generation process can be conditioned by using available facies information in one vertical plane or two orthogonal vertical ones in this study the information was obtained from a facies interpretation of a vertical georadar profile in a natural gravel formation in switzerland in the domain outside the known profile unconditioned lenses and layers were generated at random according to statistical information on coherent sedimentary structures based on observations in adjacent gravel pits jussel et al 1994a the method was applied to a single extraction well designed to capture an initially block shaped contaminant plume a total of 80 conditioned and unconditioned synthetic aquifers was generated the flow and transport simulations were performed using a finite element flow model and a random walk transport model the results are presented as the ensemble of integral solute mass recovery curves of single realizations one would expect conditioning to reduce the bandwidth of the recovery curves representing the uncertainty but the results show that the bandwidth even increased this effect was attributed to a discrepancy in the mean volumetric fraction of the different facies types in the conditioned and the unconditioned cases moreover a simulation using a homogeneous model with constant equivalent flow and transport parameters overestimated the remediation efficiency the influence of a linear reversible equilibrium sorption on the remediation well efficiency was taken into account by an uncorrelated random field of the retardation factor based on values from the literature however the impact of the variability in hydraulic conductivity clearly exceeded the effect of the variability in the retardation factor

structures and textures in triassic braided stream conglomerates bunter pebble beds in the sherwood sandstone group north staffordshire england in the northern parts of the needwood and stafford eccleshall basins england the pebble beds of the sherwood sandstone group contain thick successions of texturally mature fluvial pebble cobble conglomerates which are organized into either horizontal or cross stratified sets the horizontally lying sets generally coarser grained and more poorly sorted than the cross bedded sets are usually disorganized and either matrix or clast supported although thin lenses of well sorted occasionally openwork units interpreted as falling stage phenomena are often present the cross stratified conglomerates have foresets exhibiting remarkable textural organization with a coarse bimodal sometimes matrix supported part grading upwards or being abruptly overlain by a finer well sorted occasionally openwork part and finally capped by sandstone these rhythmic textural changes are attributed partly to an avalanche process at high stage and partly to falling stage conditions the most common types of vertical association are thick successions of horizontally bedded conglomerates up to 20 m and sequences of an upwards coarsening nature 2 12 m in which cross stratified sets are overlain by flat lying sets the environment of deposition of the gravels is interpreted as one in which water depths at high stage were greater than depths in most modern braided stream plains proglacial or alluvial fan but shallower than depths associated with the pleistocene catastrophic floods from which texturally mature giant gravel bars have been recorded recent braided streams with relatively confined channels and considerable bar channel relief are better analogues in particular medial or mid channel bars with a two tier structure subaqueous and partly emergent portions may explain the upward coarsening sequences in which horizontally lying conglomerates overlie cross stratified conglomerates the thicker sequences of horizontally stratified conglomerates represent proximal longitudinal bar deposits sheets of pebbly sandstone and argillaceous sandstone lying between the conglomerates and commonly occurring towards the top of the succession largely represent deposition from sandwaves and dunes finer interbedded argillaceous sandstones siltstones and mudstones are interpreted as overbank and waning flood deposits basin forming tectonism of increasing intensity probably caused the initial coarsening upwards of the lower part of the succession whilst more stable tectonic conditions and decreasing relief on the margins of the basins and in the areas of provenance in the midlands and the hercynides account for the upwards fining of the upper part of the succession

meteorological controls on sand transport and dune morphology in a polar desert victoria valley antarctica the hyperarid polar desert of the mcmurdo dry valleys contains an abundance of aeolian sedimentary deposits the largest in antarctica providing a unique setting for studying cold climate aeolian processes and dune morphology meteorological controls on sand transport and changes in dune morphology were monitored for 11 days in november december 2004 on a barchan dune in the victoria valley mcmurdo dry valleys sand transport in this environment was found to be influenced by 1 interparticle cohesion ice bonding 2 diurnal variations in the speed of thermally driven easterly valley winds due to reduced solar heating by night and 3 topographically modified foehn southwesterly winds the threshold entrainment velocity during easterly valleys winds was 5 3 m s at 0 4 m 0 21 m s warm dry and gusty foehn southwesterly winds were found to promote aeolian processes by dislodging surface sediments with dune morphology responding rapidly importantly no diurnal signal in sand transport was observed under these conditions when wind speed and sand transport occurred independently of solar heating measured changes in dune morphology indicate that the dune field of the victoria valley under current environmental conditions is in dynamic equilibrium with frequent up valley sand transport by thermally generated valley winds balanced by less frequent but greater magnitude down valley sand transport by moderate to strong foehn southwesterlies this results in little net movement of dunes and subsequent change in the position of the dune field accordingly we believe that regional scale shifts in climate that cause change in the synoptic circulation patterns of the ross sea region that affect the frequency of either the up valley easterlies or down valley foehn winds will result in a net change in the morphology of the victoria valley s dune field such change in circulation may become apparent early as change in the morphology of the victoria valley sand dunes we therefore suggest this site should be monitored as an indicator site for identifying change in regional weather and climate

architectural element analysis within the kayenta formation lower jurassic using ground probing radar and sedimentological profiling southwestern colorado abstract a well exposed outcrop in the kayenta formation lower jurassic in southwestern colorado was examined in order to delineate the stratigraphy in the subsurface and test the usefulness of ground probing radar gpr in three dimensional architectural studies two fluvial styles are present within the kayenta formation sandbodies within the lower third of the outcrop are characterized by parallel laminations that can be followed in the cliff face for well over 300 m these sandbodies are sheet like in appearance and represent high energy flood deposits that most likely resulted from episodic floods the remainder of the outcrop is characterized by concave up channel deposits with bank attached and mid channel macroforms their presence suggests a multiple channel river system the gpr data collected on the cliff top together with sedimentological data provided a partial three dimensional picture of the paleo river system within the kayenta formation the 3 d picture consists of stacked channel bar lenses approximately 50 m in diameter the gpr technique offers a very effective means of delineating the subsurface stratigraphy its high resolution capabilities easy mobility and rapid rate of data collection make it a useful tool its shallow penetration depth and limitation to low conductivity environments are its only drawbacks

the sedimentology and accretionary styles of an ancient gravel bed stream the budleigh salterton pebble beds lower triassic southwest england abstract three accretionary styles are present in the fluvial conglomerates and pebbly sandstones of the lower triassic budleigh salterton pebble beds bspb of east devon the lower portions of this 20 30 m sequence are dominated by extensive 50 m sheets or narrow lenses of planar cross bedded conglomerate sets 1 3 m thick these abruptly pass both downstream and laterally into horizontally bedded conglomerates cross bedded sandstones and muddy sandstones this accretionary style reflects deposition from linguoid shaped macroforms whose distal margins were bounded by slipfaces they accreted at anabranch confluences and as bank attached bars in relatively confined and channelised gravel bed streams lateral facies changes represent macroform evolution resulting from changing discharges or abandonment of a channel reach followed by accretion of a new macroform the upper portions of the bspb mainly comprise couplets of horizontally bedded conglomerate overlain by large scale trough cross bedded sandstone the conglomerate shows local channel macroform relief and lateral and downstream transitions into sets of gently dipping conglomerate this style of accretion represents deposition in less confined and less channelised fluvial systems by relatively low relief gravel macroforms and large sand dunes the third style recognised in the bspb is much more localised it consists of wedge like sets of large scale trough cross bedded conglomerate the sets are formed by erosion and subsequent fill of scours cut into a thick sandy substrate techniques of lateral profile analysis and hierarchical ordering of bounding surfaces can usefully be applied to some parts of the bspb this is important as the approach was originally developed for the deposits of sand bed streams however this approach is more difficult to apply to fluvial conglomerates because of the cryptic nature of some gravel stratification the appearance and character of some hierarchies of bounding surfaces may differ from their equivalents in fluvial sandstones

control on 234u 238u in lake water a study in the dry valleys of antarctica abstract the 234 u 238 u ratio in surface waters is generally higher than secular equilibrium due to nuclide recoil during alpha decay of 238 u the size of the deviation from secular equilibrium contains information about the environment in which the water is found this potential tool for environmental reconstruction has previously been studied in rivers groundwater and sediment pore water here we conduct a first assessment of the controls on 234 u 238 u in lakewaters thirty three waters from glacial melt streams and lakes of the mcmurdo dry valleys antarctica were analysed for u concentration and isotope ratio glacial melt has a low u concentration and a 234 u 238 u identical to seawater suggesting that u in antarctic ice is largely sourced from sea salt aerosols stream waters have higher u concentration 0 009 to 1 282 ppb and 234 u 238 u 1 280 to 1 832 due to chemical weathering of sediment in stream channels and 234 u recoil from this sediment average 234 u 238 u is 1 502 close to the average of observations from other surface waters worldwide the absence of groundwaters in the dry valleys indicates that reasonably high 234 u 238 u ratios do not require groundwater sources of u so care should be taken before using high 234 u 238 u as an indicator of groundwater inputs to stream waters lakewaters have u concentrations ranging from 0 027 to 46 ppb i e up to 14 times the seawater concentration and 234 u 238 u from 1 05 to 4 50 young lakes have 234 u 238 u which reflects the sources of u in one case lake joyce a 234 u 238 u lower than seawater may suggest u sourced from melting of old ice in which 234 u excess has partially decayed in older lakes 234 u 238 u is significantly higher than that in the inputs due to addition of recoil 234 u from sediments underlying the lake the size of the deviation from secular equilibrium can only be explained however if recoil from a large area of sediment is considered this is reasonable for the two lakes with particularly high 234 u 238 u bonney vanda which are both relicts of much larger lakes present during the last glacial period on the basis of this study the addition of recoil 234 u to lake water is expected to be a general feature and to cause a noticeable increase in 234 u 238 u for lakes with a u residence time of more than a few thousand years

braided rivers perspectives and problems progress towards a fuller understanding of the dynamics and deposits of braided rivers demands an interdisciplinary approach to a host of unresolved problems although many advances have been made within recent years in interpreting the mechanics of flow transport of sediment and sedimentary architecture of braided rivers many key issues remain to be addressed in particular several areas demand attention the mechanisms of braid bar initiation confluence diffluence dynamics the nature of sedimentary facies over a range of grain sizes and the influence of flow stage and aggradational regime upon the depositional architecture over a range of channel scales this paper focuses upon these issues and highlights several areas of fruitful future interdisciplinary collaboration 1993 the geological society

aeolian control on the deposition of high altitude lacustrine basins in the middle east the case of lake neor nw iran abstract lake neor is the largest lacustrine basin in the high mountains of the middle east at 2500 m altitude in the alborz belt this lake of holocene age is a shallow fresh water body of glacial origin with ca 4 km 2 surface area and a 40 km 2 drainage area its sedimentary sequence comprised of peat and gyttja consists of 10 m infill which is fairly thick for such a lake autochthonous organic matter is limited in and around the lake except for small areas at the northern and southern ends inorganic constituents of the infill sediment include a significant amount of fine grained calcite dolomite and mica particles that are exotic to the catchment they do not occur in the source rocks as the drainage area of the lake is composed of only andesites and trachyandesites of eocene age in addition the uppermost part of the infill includes abundant fine grained charcoal particles derived from large forest fires perhaps derived as far as the mediterranean region as shown by the present meteorological records the sediment of lake neor is under aeolian control during dust storms this is leading to a considerable amount of deposition air borne particles the infill of some lakes particularly those in highlands may have contain an important aeolian component and thus they cannot be used directly for the interpretation of the evolution of the palaeogeography without taking into consideration the role of dust storms on deposition

transport modeling in heterogeneous aquifers 1 statistical description and numerical generation of gravel deposits transport of solutes in groundwater is decisively influenced by the heterogeneity of the aquifer the goal of the present work is the numerical generation of synthetic heterogeneous aquifer models based on a statistical description of heterogeneities in gravel aquifers large unweathered outcrops in several gravel pits in northeastern switzerland were investigated in this context on the basis of sedimentological observations it was possible to specify distinct sedimentary structures appearing as lenses or layers all structures have been identified in each of the investigated outcrops by inspecting and analyzing photographs of the outcrops it was possible to estimate the probability density functions pdf of the geometrical attributes of the sedimentary structures disturbed and undisturbed samples were taken from these structures to estimate the pdf of their hydraulic properties that is the hydraulic conductivity and the porosity the information obtained is used to generate distinct numerical realizations by unconditional stochastic simulation of synthetic aquifers having the same statistical properties with respect to hydraulic conductivity and porosity as the investigated deposits

aquifer architecture analysis using ground penetrating radar triassic and quaternary examples s germany applying the concept of analogue studies long used in reservoir characterization outcrop analogues in two aquifer units of southern germany have been investigated upper triassic keuper alluvial sandstones stubensandstein and quaternary glaciofluvial gravels architectural element analysis of the outcrops is combined with ground penetrating radar profiles derived a few meters behind the outcrop walls such calibration is used to better understand the three dimensional sedimentary architecture many sedimentary units at the same time represent hydraulic flow units and are characterized by specific radar signatures this approach leads to promising results not only in unconsolidated aquifers but also in fully consolidated sedimentary rocks our studies will lead to a database with which more realistic predictions of the hydraulic behaviour of sedimentary aquifers systems needed for numerical hydrogeological simulations will be possible

trapping of aeolian sediments and build up of the ice cover of a dry based antarctic lake among the perennially frozen lakes of the dry valleys of south victoria land antarctica some are dry based i e frozen to the bottom one of these is studied here by a multiparametric investigation isotopic composition in da nd 18 o ions gas and ice texture analyses a sediment layer about 10 cm thick appearing at a depth of 3 5m is also studied by grain size x ray diffraction and scanning electron microscope analyses the information retrieved indicates that this ice block lake results from a build up in two steps and explains how aeolian sediments were included as a layer into the ice copyright 2002 john wiley sons ltd

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

facies analysis in the lower greensand using ground penetrating radar this paper presents the results of a ground penetrating radar survey in the woburn sands formation lower greensand group near leighton buzzard a total of almost 4 km of survey has been acquired to investigate the internal structure of the sands the radar survey achieved a resolution on the order of tens of centimetres with penetration up to 10 m and revealed a variety of horizontal dipping and curved reflectors the reflections are interpreted using seismic interpretation methodology two scales of unconformity defined radar sequences are described first order radar sequence boundaries can be identified at the termination of primary reflectors second order radar sequence boundaries can be identified at the terminations of both primary reflectors and first order surfaces first order radar sequence boundaries are interpreted as reactivation surfaces within bedforms which are produced by changes in bedform geometry in response to a change in hydraulic regime or superimposed bedforms second order surfaces are interpreted as the product of bedform migration reflection character and geometry are described and form the basis of a ground penetrating radar facies analysis nine different radar facies have been identified these are interpreted as large sets of planar cross stratification sets of trough cross stratification cosets of cross stratification tidal bundles clay drapes diagenetic concretions and possibly bioturbated sands a reconstruction of the bedforms suggests that they were formed by very large curved crested dunes these interpretations are checked against outcrop as the sands are excavated in working sand pits

sediment transport and bed morphology at river channel confluences river channel confluences form important morphological elements of every river system being points at which rapid changes in flow sediment discharge and hydraulic geometry must be accommodated this article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence bed morphology at channel confluences is characterized by three distinct elements avalanche faces at the mouth of each confluent channel a deep central scour and a bar within the separation zone formed at the downstream junction corner these elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels as confluence angle and discharge ratio increase the sediment contributions from the confluent channels are progressively segregated in their paths through the junction with sediment being transported around rather than through the centre of the confluence this segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence an increase in the scour depth a change in the orientation of the scour and an increase in the size of the separation zone bar field measurements closely replicate the flume simulation a model of sediment transport and bed morphology links these features to the fluid dynamics of these sites an understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record

the use of electrical resistivity tomograms as a parameterization for the hydraulic characterization of a contaminated aquifer abstract hydraulic characterization of a contaminated aquifer is an important step in depollution processes because its hydraulic parameters control the choice and efficiency of the depollution protocol to be adopted the characterization presented in this article uses a 3d electrical resistivity imagery to identify the spatial heterogeneities of a contaminated aquifer under tidal influence indeed we use a 3d resistivity model as a source of information to parameterize the reconstruction of the hydraulic conductivity in 3d by inverting a set of hydraulic data acquired on the 13 monitored wells in response to two pumping tests this parameterization relies on the identification of the main electro facies in the resistivity model in the saturated zone which will then be exploited in the hydraulic characterization to find their corresponding hydraulic conductivity values this strategy of parameterization permits to reduce the number of the hydraulic conductivity parameters to be identified to eight hydro facies with a stochastic algorithm called the adaptive metropolis algorithm the hydraulic responses associated with the pumping tests are obtained once the natural effect of the tide is removed the hydraulic conductivity model has permitted to highlight the main heterogeneities in the aquifer in which the hydraulic conductivity is ranging between 10 4 6 10 2 8 m s this range of variability reveals the permeable and smooth character of the aquifer in which the presence of coarse sand and flint blocks enhances its transmissivity these permeable zones are electrically identified by resistive anomalies in the 3d electrical resistivity imaging

particle over passing on depth limited gravel bars an experimental channel is used to examine the transport of mixed sand and gravel bedload over the crestal platform of hump back bars and along the top of planar gravel sheets hydraulic processes result in the simultaneous transport of cobbles and pebbles over a static closely packed bed consisting of like sized and finer particles for prescribed conditions flat upper stage plane sand beds develop over the crestal location with pebbles rolling easily over the sandy bed at the brinkpoint flow separation ensures effective segregation of the gravel from the sand over the slip face the deposition rate of the sand is insufficient to fill fully the interstices within the gravel foresets before rapid deposition of gravel further advances the bed form consequently distinctive vertical assemblages of open work and closed contact framework gravels could be generated as another bar migrates over and preserves the initial structure in respect to the observed mechanisms of sorting over the bars a mathematical expression is developed to explain the critical conditions allowing coarse particle mobility over planar sand or gravel beds under upper stage plane bed conditions on the crestal platform the model then is used to ascertain whether the depositional environment ascribed to certain facies in the bunter pebble beds described in a recent publication is appropriate given the distinctive facies assemblages generated in this experiment and the known hydrodynamic control of the particle segregation process