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

sedimentary architecture and 3d ground penetrating radar analysis of gravelly meandering river deposits neckar valley sw germany sedimentological outcrop analysis and sub surface ground penetrating radar gpr surveys are combined to characterize the three dimensional sedimentary architecture of quaternary coarse grained fluvial deposits in the neckar valley sw germany two units characterized by different architectural styles are distinguished within the upper part of the gravel body separated by an erosional unconformity i a lower unit dominated by trough shaped depositional elements with erosional concave up bounding surfaces that are filled by cross bedded sets of mainly openwork and filled framework gravel and ii an upper unit characterized by gently inclined sheets of massive and openwork gravels with thin sandy interlayers that show lateral accretion on a lower erosional unconformity the former is interpreted as confluence scour pool elements formed in a multi channel possibly braided river system the latter as extensive point bar deposits formed by the lateral migration of a meandering river channel the lateral accretion elements are locally cut by chute channels mainly filled by gravels rich in fines and by fine grained abandoned channel fills the lateral accretion elements are associated with gravel dune deposits characterized by steeply inclined cross beds of alternating open and filled framework gravel floodplain fines with a cutbank and point bar morphology cover the gravel deposits the gpr images revealing the three dimensional geometries of the depositional elements and their stacking patterns confirm a change in sedimentary style between the two stratigraphic units the change occurred at the onset of the holocene as indicated by 14 c dating of wood fragments and is related to a re organization of the fluvial system that probably was driven by climatic changes the integration of sedimentological and gpr results highlights the heterogeneity of the fluvial deposits a factor that is important for modelling groundwater flow in valley fill aquifers

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

towards realistic aquifer models three dimensional georadar surveys of quaternary gravel deltas singen basin sw germany abstract understanding sedimentary heterogeneities has nowadays become crucial for sophisticated aquifer management the methods used so far for aquifer characterization e g pump test coring analysis cannot provide the needed resolution for a sufficient prediction of the subsurface properties e g sudicky 1986 this calls for the application of the outcrop analogue approach to aquifers e g macfarlan et al 1994 aigner 1995 in this project we used georadar ground penetrating radar or gpr to acquire the subsurface information for high resolution three dimensional images and radar facies mapping of glaciolacustrine delta sediments in the singen basin sw germany a three dimensional reconstruction of sedimentary heterogeneities for a detailed aquifer characterisation becomes possible by combining gpr profiling and outcrop information a case study is presented showing a complex three dimensional architecture of a quaternary gravel body consisting of the following three types of architectural elements 1 glaciolacustrine delta foresets 2 erosional surfaces with scour pool fills and 3 horizontal glaciofluvial gravel sheets although this seems a relatively simple architectural inventory the three dimensional georadar profiling shows considerable internal heterogeneities the radar data are interpreted following the seismic stratigraphic approach i e the delineation of radar facies types and of radar sequences the three dimensional heterogeneities are visualized by means of time slices 3 d block or chair diagrams or series of radar facies maps

dynamics of bedload transport in turkey brook a coarse grained alluvial channel automatic and continuously recording samplers are deployed in a hertfordshire gravel bed stream to show that bedload transport is related to stream power the pattern is similar to that already established for north american channels but because the record is so detailed it is possible to identify the cause of the considerable scatter that is normal in such relationships a major factor is the occurrence of rhythmic pulses in bedload discharge that are not matched by similar fluctuations in hydraulic variables it is suggested that these pulses reflect downstream differences in the concentration of mobile particles in a slow moving traction carpet and that they may be likened to kinematic waves the record also reveals that the threshold of sediment transport always presumed hithero to be associated with incipient motion is related to the cessation of bedload transport in a river flood indeed the mean value of stream power at the finish of bedload transport is only 20 percent of that prevailing at the moment of incipient sediment motion because of this there is an inevitably poor correlation between actual bedload transport rates and those predicted by bedload equations which rely upon a single traction threshold these new data show that the general inverse relationship between bedload discharge and water depth grain size ratio proposed by bagnold 1977 1980 is not universal transport efficiency for this gravel bed stream is typically 0 05 per cent of available stream power which compares with 1 6 per cent for a river moving both gravel and sand and 5 per cent for another channel where bedload is composed predominantly of sand sized particles it is argued that coarse and fine grained alluvial channels may need to be considered separately by allowing for differences in traction threshold at the beginning and end of bedload events and by averaging bedload discharge flood by flood in order to smooth out the effect of pulses it is possible to achieve a reasonably good prediction of average bedload transport rate in terms of stream power

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

3 d sedimentary architecture of a quaternary gravel delta sw germany implications for hydrostratigraphy abstract this paper investigates a quaternary gilbert type gravel delta that was formed in an ice marginal environment at the end of the last glacial period outcrop sediment core and ground penetrating radar gpr studies reveal the sedimentary facies and depositional architecture of the delta that comprises three major units 1 a 2 5 m thick gravelly topset with an erosional base formed by accretion of bedload sheets in a braided river 2 an up to 40 m thick steeply inclined 13 35 foreset dominated by gravelly lithofacies being the product of cohesionless debris flows and debris falls as well as gravity slides while sandy lithofacies was deposited by traction currents and 3 a 10 20 m thick sandy bottomset comprising low density turbidites syn to postdepositional deformation of parts of the bottomset deposits largely resulted from rapid deposition of overlying gravels and differential loading of the prograding foreset beds the development of the delta was most likely controlled by a high sediment supply and lake level fluctuations the overall coarsening upward succession reflects delta progradation and aggradation into a glaciolacustrine environment outcrop sedimentology served as a direct analogue in order to characterise the three dimensional sedimentary and hydraulic architecture of the nearby gravel delta aquifer applying a multidisciplinary approach sedimentological geophysical and hydrogeological data were integrated within the 3 d modelling package gocad earth decision sciences to develop high resolution 3 d aquifer models

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

a pseudo genetic model of coarse braided river deposits a new method is proposed to produce three dimensional facies models of braided river aquifers based on analog data the algorithm consists of two steps the first step involves building the main geological units the production of the principal inner structures of the aquifer is achieved by stacking multiple point statistics simulations of successive topographies thus mimicking the major successive flooding events responsible for the erosion and deposition of sediments the second step of the algorithm consists of generating fine scale heterogeneity within the main geological units these smaller scale structures are generated by mimicking the trough filling process occurring in braided rivers the imitation of the physical processes relies on the local topography and on a local approximation of the flow this produces realistic cross stratified sediments comparable to what can be observed in outcrops the three main input parameters of the algorithm offer control over the proportions the continuity and the dimensions of the deposits calibration of these parameters does not require invasive field measurements and can rely partly on analog data

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

semiautomated georadar data acquisition in three dimensions under favorable conditions georadar techniques can provide vivid images of the shallow subsurface 10 50 m although the significant advantages of 3 d georadar surveying strategies are well documented they generally require much greater expenditures than traditional 2 d approaches we introduce an efficient semiautomated 3 d georadar acquisition and processing scheme that does not jeopardize data quality a standard georadar acquisition unit is integrated with an innovative self tracking laser theodolite with automatic target recognition capabilities georadar and coordinate data are recorded simultaneously as the georadar antennae are transported steadily across a survey area while tracking a target prism mounted between the antennae the theodolite provides real time coordinate information with high accuracy in all directions at 1 m s moderate walking speed the coordinates are determined to better than 0 04 m and at 3 m s they are better than 0 07 m subsequent to acquisition semiautomati

origin of cross stratal layering in fluvial conglomerates devonian malbaie formation gaspe quebec planar cross bedded conglomerates in proximal braid plain deposits of the devonian malbaie formation of eastem gaspe quebec display a distinctive cyclic layering of three facies conglomerate with sand matrix a matrix free conglomerate in which the voids are filled by spany white calcite cement c and coarse sandstone b the sequence was previously interpreted as abc but is here reinterpreted as acb b forms cross strataparallel layers facies a and c together make up the gravel layers with c passing down foreset into a across a matrix cement interface which dips at low angles in the same direction as the foreset the sequence results from migration of gravel sand bed forms across bar tops with deposition of gravel at bar margins as foresets and infiltration of sand into the gravel fabric from blackflow currents induced by flow separation at the foreset crests infiltration proceeds until the framework voids are plugged by granules and coarser sand grains after which sand and granules may continue to accumulate on the plugged surface to form a discrete layer occasional peaks on the matrix open framework interface record sites of more effective infiltration elongate peaks strike parallel or downdip possibly reflect organisation of the sand load into npples across the foreset at the time of its infiltration or they may reflect regular variation in grain size or packing and hence ingress potential of the framework partial sequences in which one or another of the layers is missing apparently result from variation in the efficiency of sand transport up the foreset coupled with variation in the efficacy and timing of framework plugging or variable sorting in bar top bed forms

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

braided fluvial sedimentation in the lower paleozoic cape basin south africa abstract lower paleozoic braided stream deposits from the piekenier formation in the cape province south africa provide information on lateral and vertical facies variability in an alluvial plain complex influenced by a moderate to high runoff four braided stream facies are recognized on the basis of distinct lithologies and assemblages of sedimentary structures a lower facies dominated by upward fining conglomerate to sandstone and mudstone channel fill sequences is interpreted as a middle to lower alluvial plain deposit with significant suspended load sedimentation in areas of moderate to low gradients these deposits are succeeded by longitudinal conglomerate bars which are attributed to middle to upper alluvial plain sedimentation with steeper gradients this facies is in turn overlain by braid bar complexes of large scale transverse to linguoid dunes consisting of coarse grained pebbly sandstones with conglomerate lenses these bar complexes are compared with environments of the recent platte river they represent a middle to lower alluvial plain facies with moderate gradients and no significant suspended load sedimentation or vegetation to stabilize channels these bar complexes interfinger basinward with plane bedded medium to coarse grained sandstones interpreted as sheet flood deposits over the distal portions of an alluvial plain with low gradients and lacking fine grained detritus or vegetation

hierarchical dynamic stratigraphy in various quaternary gravel deposits rhine glacier area sw germany implications for hydrostratigraphy the approach of dynamic stratigraphy aims to understand genetic processes that form stratigraphic units in a hierarchy of spatial and temporal scales this approach was used to investigate quaternary gravel deposits in terms of their sedimentology and in order to characterize the various sedimentary units in terms of their hydrogeological properties facies analysis within 62 gravel pits laboratory permeability measurements of field samples and geophysical surveys 3 d georadar 2 d seismic reflection led to the detection and classification of sedimentary heterogeneity according to the following six scales whereby each scale can be translated into defined hydrostratigraphic units 1 particles and pores micro scale that reflect depositional and diagenetic fluid dynamics as well as source material behaviour e g grain size roundness lithological composition this was found to be important for the hydrogeochemistry of groundwater in gravel aquifers e g higher sorption capacity of carbon rich limestone particles for organic pollutants 2 strata meso scale contain the recognition of sorting fabric texture and stratinomic features which can give an indication of transport and depositional dynamics five major lithofacies groups for example were distinguished within fluvial gravel bed deposits their variable hydraulic properties led to their subdivision into 12 hydrofacies types they form the smallest mappable hydrostratigraphic units which may result in either preferred pathways for fluid flow or flow barriers 3 depositional elements macro scale enable reconstruction of sedimentary geomorphic elements and their dynamics within a depositional system e g gravel bed braided river systems are dominated by gravel sheet gravel dunes and scour pool depositional elements hydrostratigraphically the architecture of depositional elements influences the hydraulic connectivity and local permeability structure distribution within an aquifer body five types of depositional elements in fluvial gravel bed deposits were distinguished and their geometries dimensions quantified 4 facies bodies mega scale composed of a stack of depositional elements and strata recording distinct environmental systems and their dynamics e g a coarse grained prograding delta system hydrostratigraphically facies bodies represent major compartments of an aquifer six major types of meltwater controlled facies bodies were identified in the study area 5 genetic sequences mega scale reflect the shifts of depositional environments caused by allocyclic changes e g glacial advance recorded by a coarsening upward sequence or autocyclic changes of landscape shaping events these sequences may form separate hydrostratigraphic units or aquifer storeys 6 basin fill giga scale comprising the lateral and vertical stacking of facies bodies and genetic sequences controlled by either long term glacier dynamics or short term flood events the regional distribution of permeable gravel units and for example less permeable diamicts builds the larger scale hydrostratigraphy

facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions an example from the quaternary poplar fan north western china

volcanic settings and their reservoir potential an outcrop analog study on the miocene tepoztlan formation central mexico abstract the reservoir potential of volcanic and associated sedimentary rocks is less documented in regard to groundwater resources and oil and gas storage compared to siliciclastic and carbonate systems outcrop analog studies within a volcanic setting enable to identify spatio temporal architectural elements and geometric features of different rock units and their petrophysical properties such as porosity and permeability which are important information for reservoir characterization despite the wide distribution of volcanic rocks in mexico their reservoir potential has been little studied in the past in the valley of mexico situated 4000 m above the neogene volcanic rocks groundwater is a matter of major importance as more than 20 million people and 42 of the industrial capacity of the mexican nation depend on it for most of their water supply here we present porosity and permeability data of 108 rock samples representing five different lithofacies types of the miocene tepoztlan formation this 800 m thick formation mainly consists of pyroclastic rocks mass flow and fluvial deposits and is part of the southern transmexican volcanic belt cropping out south of the valley of mexico and within the two states of morelos and mexico state porosities range from 1 4 to 56 7 average porosity is 24 8 generally permeabilities are low to median 0 2 933 3 md with an average permeability of 88 5 md the lavas are characterized by the highest porosity values followed by tuffs conglomerates sandstones and tuffaceous breccias on the contrary the highest permeabilities can be found in the conglomerates followed by tuffs tuffaceous breccias sandstones and lavas the knowledge of these petrophysical rock properties provides important information on the reservoir potential of volcanic settings to be integrated to 3d subsurface models

quaternary geology of the duck hawk bluffs southwest banks island arctic canada a re investigation of a critical terrestrial type locality for glacial and interglacial events bordering the arctic ocean duck hawk bluffs southwest banks island is a primary section 8 km long and 60 m high in the western canadian arctic archipelago exposing a long record of quaternary sedimentation adjacent to the arctic ocean a reinvestigation of duck hawk bluffs demonstrates that it is a previously unrecognized thrust block moraine emplaced from the northeast by laurentide ice previous stratigraphic models of duck hawk bluffs reported a basal unit of preglacial fluvial sand and gravel beaufort fm forested arctic overlain by a succession of three glaciations and at least two interglacials our observations dismiss the occurrence of preglacial sediments and amalgamate the entire record into three glacial intervals and one prominent interglacial the first glacigenic sedimentation is recorded by an ice contact sandur containing redeposited allochthonous organics previously assigned to the beaufort fm this is overlain by fine grained sediments with ice wedge pseudomorphs and well preserved bryophyte assemblages corresponding to an interglacial environment similar to modern the second glacial interval is recorded by ice proximal mass flows and marine rhythmites that were glacitectonized when laurentide ice overrode the site from amundsen gulf to the south sediments of this interval have been reported to be magnetically reversed 780 ka the third interval of glacigenic sedimentation includes glacifluvial sand and gravel recording the arrival of laurentide ice that overrode the site from the northeast island interior depositing a glacitectonite and constructing the thrust block moraine that comprises duck hawk bluffs sediments of this interval have been reported to be magnetically normal 780 ka the glacitectonite contains a highly deformed melange of pre existing sediments that were previously assigned to several formally named marine and interglacial deposits resting in an undeformed sequence in contrast the tectonism associated with the thrust block moraine imparted pervasive deformation throughout all underlying units highlighted by a previously unrecognized raft of cretaceous bedrock during this advance laurentide ice from the interior of banks island coalesced with an ice stream in amundsen gulf depositing the interlobate sachs moraine that contains shells as young as 24 cal ka bp late wisconsinan during deglaciation meltwater emanating from these separating ice lobes deposited outwash that extended to deglacial marine limit 11 m asl along the west coast of banks island our new stratigraphic synthesis fundamentally revises and simplifies the record of past quaternary environments preserved on southwest banks island which serves as a key terrestrial archive for palaeoenvironmental change

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

paleocurrent direction measurements in a volcanic setting by means of anisotropy of magnetic susceptibility a case study from the lower miocene tepoztlan formation transmexican volcanic belt central mexico sources of ancient volcanic rocks are often unknown if they are either eroded and or covered by younger deposits this problem as well as the provenance of reworked volcaniclastic fluvial and mass flow deposits can be partially solved by the application of anisotropy of the magnetic susceptibility ams for massive and poorly sorted volcaniclastic rocks in particular this may be the only way of finding reliable transport directions and therefore allowing for paleogeographic reconstructions here we present a data set of 428 ams measurements and 249 measurements of sedimentary paleocurrent indicators from the miocene tepoztlan formation at the southern edge of the transmexican volcanic belt central mexico the highest degree of reliability of ams measurements is gained for data from lava samples and the lowest from mass flows sedimentary structures in sandstones and conglomerates such as trough cross stratification asymmetric ripple marks and the shape of scours and channels could be used to calibrate the results from ams data and to prove their reliability ams data on fluvial deposits point to a drainage system with a w e flow direction indicating an outflow of the river system into the ancient gulf of mexico

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

sedimentary facies changes and climatic tectonic controls in a foreland basin the urumqi river tian shan northwest china abstract a sedimentological study was conducted on an interbedded fine gravel and silt succession up to 70 m thick at cangfang gou in northern chaiwopu basin tian shan nw china the succession informally termed urumqi gravel is part of the gravelly basin infill that commenced around 1 87 ma bp in the early pleistocene its upper boundary determined by a magnetostratigraphical study is slightly above the brunhes matuyama b m at 780 ka bp detailed facies analysis indicates that the river underwent multiple cyclic changes from a bed load dominated braided to a suspension load dominated sinuous regime the latter probably adopted a single thread meandering pattern confined within its course and was predominated by overbank accretion of fines without development of distinct point bars the river probably represents the proto urumqi river it appears that the cyclic sequences are climatically controlled their preservation in the succession is largely attributed to the continued aggradation resulted from the subsidence of the chaiwopu basin in the early pleistocene

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

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

controls on synorogenic alluvial fan architecture beartooth conglomerate palaeocene wyoming and montana late palaeocene uplift of the beartooth range in northwestern wyoming and southwestern montana generated the beartooth conglomerate along the eastern and northeastern flanks of the range systematic unroofing sequences and intraformational unconformities folds and faults in the conglomerate attest to deposition during uplift along the eastern flank at least three ancient alluvial fan systems and a braidplain system can be distinguished on the bases of petrofacies and lithofacies the two southern fans consist of 700 m of sedimentary clast conglomerate and subordinate sandstone dominated by hyperconcentratedflow and stream flow facies the next fan to the north is dominated by plutonic and metamorphic clasts and contains abundant mud matrix supported debris flow facies as well as stream flow facies the northernmost depositional system consists of arkosic channellized fluvial conglomerate and sandstone overbank mudstone and crevasse splay sandstone units palaeocurrent data indicate eastward dispersal away from the beartooth range outstanding exposure of the beartooth conglomerate allows facies to be mapped on lateral photographic mosaics a seven fold hierarchy of bounding surfaces and enclosed lithosomes exists in the beartooth conglomerate first through fourth order surfaces are analogous to first through fourth order surfaces that recently have been documented in sandy fluvial facies with one exception sediment gravity flows are bounded by first order surfaces fifth order surfaces are either erosional e g lateral migration of fanhead trench or accretionary e g aggradation of fan surface during backfilling of trench and construction of lobes on lower fan during entrenchment on upper fan some fifth order surfaces coincide with intraformational angular unconformities and are thus the result of long term fanhead entrenchment following uplift of the upper part of the fan sixth order surfaces bound individual fan packages that are several hundred metres thick and 10 km2 in area the enclosed sixth order lithosomes are distinguishable in terms of petrofacies and lithofacies a single seventh order surface bounds the entire beartooth conglomerate lower order lithosomes are produced by intrinsic processes of fan construction fifth order lithosomes can be attributed to both extrinsic and intrinsic controls sixth and seventh order lithosomes are generated by extrinsic controls

radar architecture and evolution of channel bars in wandering gravel bed rivers fraser and squamish rivers british columbia canada abstract the alluvial architecture and evolution of two kilometer scale compound bars in the wandering gravel bed fraser and squamish rivers british columbia canada are described integrating ground penetrating radar bathymetry and aerial photographs enables the internal architecture to be linked to the evolution of the gravelly barforms over the previous 50 years these linkages reveal the sedimentary mechanisms that formed the various architectural packages within compound bars and unit bars growth of compound bars is controlled by the accretion of unit bars onto discrete segments along their gravelly edges the attachment of unit bars deflects the thalweg to impinge on and erode specific portions of bars and channel banks bar growth leads to the stabilization of bars vegetation colonization of bar interiors and island formation it is the formation of islands along with channel avulsions that maintains channel division in wandering rivers seven styles of gravelly deposition are imaged in the alluvial architecture vertical accretion deposits formed from the deposition of gravelly bedload sheets are the most common strata a moderate abundance of slipface deposits preserves high relief bar margins lateral accretion dominates point bar deposits downstream accretion deposits govern some phases of down bar growth partial and complete channel fill and chute fill deposits are eroded into underlying sediments as are scour and fill deposits upstream accretion deposits are uncommon a depositional model of gravelly channel bars in the two rivers is presented and reveals that the architecture is made up of depositional styles similar to those observed in braiding river successions although the sedimentary packages are preserved in different proportions differences in braiding river and wandering river sedimentology largely reflect the relatively frequent migration of channels and bars in braiding rivers which preserve high proportions of channel fill and chute fill and confluence scour and fill deposits conversely the moderately stable island and channel network in wandering rivers limits channel shifting and consequently preserves a low number of channel fills moderate proportions of slipface strata and coherent patterns of sand deposition along bar tops provide evidence of comparatively uniform flow patterns in independent channel segments divided by islands these patterns of bar sedimentation and channel shifting preserved in the alluvial architecture appear to be signature characteristics of wandering rivers the occurrence of similar architecture in both the fraser and squamish rivers suggests that the model likely applies to most wandering gravel bed rivers

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

sedimentary and hydraulic characterization of a heterogeneous glaciofluvial deposit application to the modeling of unsaturated flow abstract flows in the unsaturated zones of alluvial deposits are often poorly understood at the scale of structures such as stormwater infiltration basins the heterogeneous nature of the sediment inherent to this type of formation can lead to preferential flows the difficulty of quantifying them lies in obtaining hydrodynamic parameters representative of the soil structure in situ when the latter is inaccessible this study proposes a method of estimating the hydrodynamic parameters of the lithofacies composing a glaciofluvial deposit east lyon france and their integration in a 2d flow model to model flow in the unsaturated zone the approach developed comprises a sedimentological study based on the miall code carried out to determine the analogy between the lithofacies of the study site and those of two glaciofluvial reference sites currently in the process of formation chamonix france breidamerkurjokull iceland thereby permitting easy access to all the lithofacies identified on the study site the water retention and hydraulic conductivity curves were obtained on the reference sites by using beerkan type infiltration tests for finely textured materials completed by the arya and paris model and data from the literature for coarser materials thus hydrofacies corresponding to all the lithofacies were characterized these hydrofacies were used to model a drainage phase on the study site at the scale of a trench 13 50 m long 2 50 m deep the model highlighted the importance of the role played by the spatial distribution of hydrofacies on flows with a pronounced capillary barrier effect of the very coarse lithofacies and a sand lens leading to funneled flows by assuming that there is a direct link between the sedimentary lithological heterogeneity and the unsaturated hydrodynamic properties of the materials composing its different structures it was possible to perform a detailed hydrodynamic characterization of the unsaturated zone that could then be used to model flows and in particular highlight preferential flows

quantitative characterization of architecture elements and their response to base level change in a sandy braided fluvial system at a mountain front abstract the rockcave member of the yungang formation middle jurassic in the datong basin china is a multistory sandstone that is interpreted as a sandy braided fluvial deposit based on grain size lithofacies and architectural elements the depositional setting was the mountain front of the datong basin which was tens of kilometers from the shoreline of a lacustrine basin during the middle jurassic the concept of base level is used to analyze the architectural elements of the braided system obtained from photographic mosaics and high resolution measurement of six outcrop sections from yungang rock cave grain size lithology and bounding surfaces together with scale and dimension parameters of the sedimentary structures in various architectural elements were used to quantitatively characterize each group of architectural elements and stratigraphic units width thickness values of trough crossbeds were found to be a fundamental component of the hydrodynamic regimes during base level rise the braided fluvial system developed large scale channel units bar units and overbank fills the relatively high proportion of bar units and overbank fills reflect processes operating during positive accommodation however during base level fall there are a high proportion of small scale channel units that reflect incision dominated processes such as channels with low w t values for trough crossbeds and less common overbank fines

architectural analysis of fluvial sequences in the northwestern part of kyongsang basin early cretaceous se korea abstract the northwestern part of kyongsang basin early cretaceous largely comprises interbedded sandstones and mudstones of fluvial depositional environments with local basin margin conglomeratic deposits of alluvial fan systems these non marine successions are divided into 5 successive stratigraphic units each of which is unique in facies assemblages and architecture of sandstone bodies one stratigraphic unit sinpyong anpyong unit is documented in this paper with detailed architectural analysis of sandstone bodies the deposits of the sinpyong anpyong unit are divided into three major components thick sandstone thin sandstone and mudstone dominated bodies the thick sandstone bodies 2 47 m thick comprise stacked element groups bounded by laterally persistent erosional surfaces probably representing superposition of channel belts within individual element groups elements are laterally superposed indicating growth and superposition of bars and movement of associated channels the thickness of bar deposits and dip angles of laterally inclined strata suggest that channels were a few to 10 m in depth and 9 m to several tens of meters in width paleocurrent data indicate southward or southeastward draining channel systems the thin sandstone bodies generally the thick sandstone bodies formed in major channels and channel belts are characterized by lateral superposition of numerous bar and channel deposits limited extent of individual lateral accretion sets and the presence of mid channel bar deposits suggesting deposition in braided rivers detailed reconstruction of bars and channels reveals a range of processes including growth coalescence and erosion of bars and migration switching and filling of channels lateral accretion of bars and the associated channel migration might have been principal processes in the sinpyong anpyong river systems bars were commonly coalesced by lateral superposition forming large bar complexes

influence of the kuroshio on mesoscale convective systems in the baiu frontal zone over the east china sea abstracttwo mesoscale convective events in the baiu frontal zone bfz were documented based on intensive atmospheric soundings and oceanic castings in the east china sea during may 2011 in addition to continuous surface meteorological observations satellite products and objective analyses these events occurred while the bfz was nearly stagnant and a mesolow was deepening in the zone near surface southerlies associated with the low level jet transported a warm humid air mass from south of the bfz enhanced evaporation which was mainly attributable to the high sea surface temperature of the kuroshio augmented the moisture content of the air mass and helped maintain a convectively unstable stratification in the lower troposphere around the bfz

distinctive characteristics of a streamflow dominated alluvial fan deposit sanghori area kyongsang basin early cretaceous southeastern korea abstract in the northwestern part of the non marine kyongsang basin early cretaceous conglomeratic deposits occur at intervals along the northern basin margin and grade basinward into interbedded sandstone and mudstone one of these conglomeratic deposits referred to as the sanghori deposit is 150 m thick and characterized by amalgamated sheets of conglomerate and sandstone facies assemblages 1 and 2 alternating with interbedded sandstone and purple siltstone facies assemblage 3 facies assemblage 1 comprises clast supported disorganized and organized sheet conglomerates interbedded with massive to stratified sandstones this assemblage is interpreted as the product of proximal gravel bed stream deposition facies assemblage 2 consists of trough and planar cross stratified and horizontally stratified sandstones it represents sandy braided stream deposits in which sand bars and dunes were common sedimentary facies and architecture of the coarse grained facies assemblages suggest that the gravel bed and sandy braided streams were wide and shallow and rapidly aggraded during flash floods facies assemblage 3 consists of interbedded purple siltstone and tabular sandstone which show evidence of weak pedogenic modification and bioturbation these characteristics are interpreted as the result of floodplain processes sediments were supplied from the north and dispersed radially forming a streamflow dominated alluvial fan system the sanghori alluvial system was most probably fed from a large drainage basin resulting in the predominance of streamflow deposits and rounded clasts the alternation of the gravel bed stream and floodplain deposits was due to autocyclic switching of active fan sectors under the conditions of relatively slow and steady basin subsidence

interpretation of drill core and georadar data of coarse gravel deposits abstract pollution in the shallow subsurface has led to an increasing need of understanding how to quantitatively characterize both the heterogeneity of gravel aquifers and the influence of heterogeneity on groundwater flow and solute transport models play an important role in decision making processes especially in the context of better characterizing and in forecasting the behavior of a given geological system the objective of the present paper is the derivation of a gradual lithofacies based interpretation of outcrop drill core and ground penetrating radar gpr or georadar data of different quality the presented method allows a probability estimation of drill core layer descriptions and radarfacies types representing defined sedimentary structure types the method includes a determination of initial structure type probabilities for grain size categories and combinations thereof described in drill core layer descriptions as well as a subsequent differentiation of these structure type probabilities in an iterative process considering additional information like main constituent quantity fraction and sorting of single grain size categories color chemical precipitation layer thickness and adjacent layer the radarfacies types are calibrated with drill cores located in the vicinity of georadar sections the calibration process consists of the assignment of the calculated structure type probabilities from the drill core layer descriptions to the corresponding radarfacies types considering the proportion in thickness between drill core layers and georadar structures the structure type probabilities can be given for points along boreholes and a grid with arbitrary mesh size along georadar sections the method is applied to field examples from the rhine wiese aquifer near basel in switzerland the resulting structure type probabilities can be used for conditioning stochastic simulations of geological models however the conditioned stochastic simulation of the rhine wiese aquifer is the topic of another paper the results show the importance of a detailed sedimentological analysis of outcrops and drill cores as well as its significance on the distinction of sedimentary structure types

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

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

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

three dimensional sedimentary architecture of quaternary sand and gravel resources a case study of economic sedimentology sw germany quaternary sands and gravels form important yet often highly heterogeneous economic deposits detailed 3 d analysis of the sedimentary structure and stratigraphy of these deposits allows for an accurate estimation of exploitable material this paper presents a case study in sw germany reconstructing the 3 d distribution of glacial sediments based on a high resolution process orientated sedimentary facies classification and lithostratigraphy integrated within the geo modelling package gocad situated along the maximal ice extent of the rhine glacier during the last glaciation the study area is characterised by a morphologically prominent terminal moraine and its associated sandur which form the stratigraphically youngest sediments of a glacial basin partially exposed in two gravel pits these outcrops helped to reconstruct the complex sedimentary architecture of the northern part of the glacial basin the regional analysis is based on core data as well as geoelectric and geomagnetic surveys all data were integrated into km scale high resolution geological 3 d models depicting the large scale dynamics of multiple glacier advances and retreats during the early to late pleistocene these models allow quantifying the thickness and volume distribution of exploitable sandy gravel and help to evaluate the occurrence of non exploitable interbedded diamicton horizons the high quality and quantity of gravels particularly north of the terminal moraine classifies the investigated area as very prospective for raw materials exploitation in the future

climate and tectonic controls on pleistocene sequence development and river evolution in the southern vienna basin austria abstract the impact of climate and tectonism on sedimentation and lithofacies development is demonstrated for austria s largest pleistocene sedimentary basin situated within the vienna basin the coarse grained massive facies is associated with high energetic flood events reflecting a distinct seasonality effect of discharge during glacial times in contrast fine grained well stratified sediments mark periods of rather high discharge to sediment supply ratios during warmer periods preservation of depositional sequences was facilitated by subsidence rates of approx 0 5 1 mm a high subsidence rates in the basin preserve a relatively large record of sequences compared to fluvial terraces which reflect mainly sediments deposited during and shortly after glacials 14c and relative ages demonstrate the strong impact of oscillations in climate on fluvial stratigraphy covering times from the upper period of mis 3 to mis 1 abundant sediment supply and the associated increase in accumulation space as well as tectonic factors affect not only the sequence development but also the geomorphology of two mountain front alluvial fans which toe out into the mitterndorf basin high discharge to sediment supply ratios leads to fan incision and to abandonment of fan surfaces during phases of reduced sediment supply the effect of subsidence results in headcut erosion and if sufficient time is available may lead to complete through trenching abandoned fan surfaces are exposed to widespread soil formation which mark sequence boundaries to the following coarse grained massive facies reflecting high sediment supply to discharge ratios

sedimentology of the whiteclay gravel beds ogallala group in northwestern nebraska usa structurally controlled drainage promoted by early miocene uplift of the black hills dome abstract the newly recognized whiteclay gravel beds wgb of the miocene ogallala group crop out as a narrow discontinuous ribbon of sands and gravels in dawes and sheridan counties northwestern nebraska usa the wgb are exposed in a series of municipal gravel quarries and natural exposures that define a linear trench in underlying strata at least 20 m deep and up to 300 m wide with short southeast trending reaches separating generally longer east trending sections this gravel filled trench can be recognized from the nebraska south dakota border near whiteclay nebraska southeastward to east of gordon nebraska a distance of 30 km the outcrop belt of the wgb is coincident in location and trend with the whiteclay fault zone where exposed in quarries the walls of the trench are steep sided vertical or locally overhanging polished surfaces slickensides and parallel joint sets are common in the walls of the trench near whiteclay but uncommon in those to the east the narrow belt defined by this trench is filled by stratified gravel the wgb are interpreted to have formed in response to tectonic upheaval associated with uplift of the black hills of south dakota in early miocene times fault rupture topography facilitated formation of a steep sided canyon or valley up to 20 m deep being virtually straight with sharp bends at intervals of several km an alluvial channel belt developed in the floor of the valley filling the available accommodation space with coarse sand and gravel via aggradational stacking of the deposits of successive channels and channel belts channel belts were probably braided with individual channels up to 4 m deep and a few tens of metres wide the multi storey character of the deposit indicates multiple episodes of cutting and filling the coarse grain size of the fill suggests energetic discharge with frequent bankfull flows even though the system had a relatively low gradient 0 004 an abundance of reworked fossil debris is derived from several stratigraphic units clasts of which have been identified in the fill the presence of a contemporary merychippine horse and a primitive species of the oreodont brachycrus constrain formation of the wgb to a short interval within the early miocene c 17 5 ma the mammal fauna suggests that this stream was a valuable source of water while fragments of aquatic organisms such as turtles and fish indicate perennial discharge the wgb provides a crucial window into a pluvial period in the miocene that is largely unpreserved elsewhere in the basin facilitated in part by fault rupture topography