sediment dynamics over sand ridges on a tideless mid outer continental shelf abstract a sand ridge field with crests oriented ne sw 52 located between 55 and 85 m water depth on the valencia continental shelf spain was mapped with multibeam swath bathymetry and characterized with seismic profiling and sediment sampling boundary layer hydrodynamic measurements conducted over a sand ridge at 66 m depth show evidence of wave and current sediment resuspension during a major storm event with a three year recurrence period from the measured intrawave sediment concentration profiles it is shown that the suspended sediment time evolution is related not only to mean currents but also to the wave field the near bottom shear stress generated during storm conditions reached around 1 n m2 and was able to resuspend and transport sandy and muddy sediments for more than 32 h the total suspended sediment transport in a layer of 1 m above the bottom was around 4000 kg per meter width and directed 160 it is argued that these sand ridges were developed in a shallow environment and there is no evidence of present day ridge migration or morphological degradation it is hypothesized that sediment dynamics affecting sand ridges during storms favors the maintenance of their morphology

sandy contourite drift in the late miocene rifian corridor morocco reconstruction of depositional environments in a foreland basin seaway abstract the rifian corridor was a seaway between the atlantic ocean and the mediterranean sea during the late miocene the seaway progressively closed leading to the messinian salinity crisis in the mediterranean sea despite the key palaeogeographic importance of the rifian corridor patterns of sediment transport within the seaway have not been thoroughly studied in this study we investigated the upper miocene sedimentation and bottom current pathways in the south rifian corridor the planktic and benthic foraminifera of the upper tortonian and lower messinian successions allow us to constrain the age and palaeo environment of deposition encased in silty marls deposited at 150 300 m depth there are i 5 to 50 m thick mainly clastic sandstone bodies with unidirectional cross bedding and ii 50 cm thick mainly clastic tabular sandstone beds with bioturbation mottled silt lack of clear base or top and bi gradational sequences furthermore seismic facies representing elongated mounded drifts and associated moat are present at the western mouth of the seaway we interpret these facies as contourites the products of a westward sedimentary drift in the south rifian corridor the contourites are found only on the northern margin of the seaway thus suggesting a geostrophic current flowing westward along slope and then northward this geostrophic current may have been modulated by tides by comparing these fossil examples with the modern gulf of cadiz we interpret these current dominated deposits as evidence of late miocene mediterranean overflow into the atlantic ocean through the rifian corridor this overflow may have affected late miocene ocean circulation and climate and the overflow deposits may represent one of the first examples of mainly clastic contourites exposed on land

genesis and evolution of a mid shelf storm built sand ridge new jersey continental shelf u s a abstract sand ridges form discrete parts of a modern surficial veneer on many continental shelves worldwide yet are seldom cited as analogs for isolated marine sand bodies found in outcrop or the subsurface one reason may be that a comprehensive explanation for the evolution of modern mid shelf sand ridges has proven elusive new information most notably high resolution seismic data collected on modern sand ridges in adjacent areas by other workers has led to this reevaluation of a largely unpublished but extensive vibracore dataset from a mid shelf sand ridge off new jersey usa the presence of dipping reflections within other ridges is particularly notable on new high resolution seismic data but has yet to be confirmed in these other ridges by extensive coring reexamining the original well preserved vibracore peels from the mid shelf sand ridge sampled in the 1980s reveals that these internal reflections could be associated with burrowed low density mud beds new cross sections constructed with 20 vibracores suggest that the dipping internal reflections are accretionary surfaces associated with episodic ridge migration to the east and south radiocarbon dating indicates that the mid shelf sand ridge has migrated episodically over the last 5 ka and movement probably continues today during major storms this documented migration continues well after transgressive ravinement approximately 9 10 ka contradicting existing views that mid shelf ridges become moribund sometime after detachment from the shoreline the morphology migration history and internal sedimentary character suggest that the ridges are acting much like primary bedforms although these sand bodies are much larger in scale 5 to 8 m height or thickness than typical subaqueous dunes observed on modern storm dominated shelves

dimensions of the atlantic mediterranean connection that caused the messinian salinity crisis abstract what kind of gateway is needed to cause a salinity crisis although several reconstructions of possible atlantic mediterranean gateways are proposed for the late miocene so far the gateway that must have existed before the desiccation of the mediterranean during the messinian is unknown this study uses the theory of hydraulic control combined with the effect of bottom friction in order to find out to first order the geometrical dimensions of the connection that existed during the primary lower gypsum stage 5 97 5 61 ma of the messinian salinity crisis 5 97 5 33 ma the connecting strait is assumed to behave in a similar way as existing straits such as the strait of gibraltar or the bosphorus a salinity crisis in an enclosed basin results when its connection to the open ocean is highly restricted a strait needs to be relatively shallow narrow and or long in order to result in exchange fluxes that are of around 25 or less of the exchange at the strait of gibraltar today considering the evaporite deposits together with global sea level variations we estimate the cross section of a strait responsible of the msc to have a minimum depth of 30 45 m and a maximum width of 0 7 2 km for lengths in the range up to 500 km these dimensions are consistent with only a few of the miocene corridors identified the calculations are extended to explore the implications for sedimentary structures on the corridor floor

distinguishing depositional environments in shallow water mixed bio siliciclastic deposits on the basis of the degree of heterolithic segregation gelasian southern italy abstract a new sedimentological technique has been tested in gelasian cross stratified bio siliciclastic deposits cropping out in southern italy lucanian apennine to disentangle paleoenvironmental and model reconstructions for shallow water mixed sediments the proposed method suggests the use of the bioclastic siliciclastic ratio bls and the segregation index s i to evaluate the percentage of the dominant elastic component in a mixed deposit and in order to estimate the degree of the heterolithic segregation between bioclastic and siliciclastic particles the principle of this method is based on the experimental evidence that bioclasts and quartz grains reveal a different physical behavior if entrained by a hydraulic flow of a given energy thus a different internal texture of bioclastic and terrigenous particles in the same sedimentary deposit is regarded as the result of the variation in the energy of a number of hydrodynamic processes that characterize shallow marine settings including waves currents and tides the studied mixed sediments subdivided into facies associations exhibit stratigraphic shoaling upward successions recording repeated transitions from offshore to shoreface environments these trends are documented through the vertical variations in the degree of heterolithic segregation between mixed clastic particles quantified by using the s i introduced in the present study the assessment of the degree of heterolithic segregation is thus proposed as a proxy to distinguish depositional environments related to different water depths in shallow water mixed systems

plutonium radiocesium and radiocobalt in sediments of the hudson river estuary abstract anthropogenic radionuclides have reached the hudson estuary as global fallout from nuclear weapons testing and through local releases from commercial nuclear reactors significant activities of 238 pu and 239 240 pu fallout derived 134 cs and 60 co reactor released and 137 cs derived from both sources have accumulated in the sediments throughout the estuary with the primary zone of accumulation near the downstream end of the system in new york harbor the estuary appears to have trapped nearly all of the 239 240 pu delivered as fallout and consequently ocean dumping of dredged harbor sediment is currently the primary means for the net transport of these nuclides to coastal waters in contrast only 10 30 of the 137 cs 134 cs and 60 co delivered to the estuary have been retained on the fine particles which accumulate at a rapid rate in the harbor the primary factors which have governed the distribution of anthropogenic radionuclides in hudson sediments are 1 spread of fine particles labeled with both fallout and reactor nuclides throughout the axis of the estuary 2 differences in timing of the peak fallout years 1962 1964 and years of maximum reactor releases 1971 1972 3 large variations in sediment accumulation rates ranging from a few millimeters per year or less to many tens of centimeters per year 4 appreciable desorption of 137 cs and 134 cs from particles at higher salinities and 5 possible enhanced desorption of 60 co at higher salinities relative to 134 cs and 137 cs which may be associated with the release of reduced manganese from the harbor sediments

new bedform phase diagrams and discriminant functions for formative conditions of bedforms in open channel flows understanding of the formative conditions of fluvial bedforms is significant for both river management and geological studies diagrams showing bedform stability conditions have been widely used for the analyses of sedimentary structures however the use of discriminants to determine the boundaries of different bedforms regimes has not yet been explored in this study we use discriminant functions to describe formative conditions for a range of fluvial bedforms in a 3d dimensionless parametric space we do this by means of discriminant analysis using the mahalanobis distance we analyzed 3793 available laboratory and field data and used these to produce new bedform phase diagrams these diagrams employ three dimensionless parameters representing properties of flow hydraulics and sediment particles as their axes the discriminant functions for bedform regimes proposed herein are quadratic functions of three dimensionless parameters and are expressed as curved surfaces in 3d space these empirical functions can be used to estimate paleoflow velocities from sedimentary structures as an example of the reconstruction of hydraulic conditions we calculated the paleoflow velocity of the 2011 tohoku oki tsunami backwash flow from the sedimentary structures of the tsunami deposit in so doing we successfully reconstructed reasonable values of the paleoflow velocities

flow separation and shear stress over angle of repose bed forms a numerical investigation large asymmetric bed forms commonly develop in rivers the turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers this paper uses the delft3d modeling system to investigate the effects of bed form geometry and forcing conditions on flow separation length and associated turbulence and bed form shear stress over angle of repose 30 lee side angle bed forms the model was validated with lab measurements that showed sufficient agreement to be used for a systematic analysis the influence of flow velocity bed roughness relative height bed form height water depth and aspect ratio bed form height length on the variations of the normalized length of the flow separation zone the extent of the wake region where the turbulent kinetic energy tke was more than 70 of the maximum tke the average tke within the wake region and the form shear stress were investigated form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region extent of the wake region extent of water body above the bed form and the average tke within the wake region the results add to understanding of the hydrodynamics of bed forms and may be used for the development of better parameterizations of small scale processes for application in large scale studies

giant sand waves on the taiwan banks southern taiwan strait distribution morphometric relationships and hydrologic influence factors in a tide dominated environment abstract giant sand waves heights 10 m are widely developed on the taiwan banks the distribution pattern morphotypes and morphometric relationships of which have not yet been fully clarified based on multi beam bathymetric swath data covering 780 line km of survey track giant sand waves with heights up to 22 5 m and wavelengths up to 2115 m have been recorded the relationship between height h and wavelength l of the complete data set follows the regression trend of hmean 0 0625 l0 8152 r 0 94 which is in good general agreement with a previously determined average global trend of hmean 0 0677 l0 8098 this global trend did not include any data from the china seas the giant sand waves have been grouped into four morphotypes namely double crested symmetric symmetric asymmetric and asymmetric forms the individual bedform morphotypes and their spatial distribution were investigated in relation to water depth textural characteristics of the sediment and the hydrodynamic conditions recorded by several 25 hour repeated ship based current observations the relationship between mean water depth d and mean sand wave height h and mean wavelength l on the taiwan banks are hmean 0 29d r 0 35 and lmean 36d r 0 42 respectively with increasing water depth the shape of the sand wave becomes gentler it is found that the coarser sediment median grain size of 0 51 0 54 mm and stronger flow in the present study may contribute to the larger h d and l d ratios at the given water depths than other sand wave fields and flows of varying from equal to unequal northerly and southerly components correspond with sand waves from symmetrical to asymmetrical forms a decrease in velocity and a veering in direction of flows have been observed over the giant sand waves indicating the interaction between large bedforms and the near bed water layer in the study area

fine grained versus coarse grained wave ripples generated experimentally under large scale oscillatory flow abstract wave ripples were generated in a wave tunnel under large scale oscillatory flow orbital diameter 1 4 5 m using two different grain sizes very fine sand and coarse sand the geometry of bed configurations that were produced varied strongly as a function of grain size small anorbital ripples wavelengths 10 cm heights 5 cm these results support the hypothesis advanced by leckie 1988 that large waves generate markedly different stratigraphic signatures in fine grained and coarse grained sediment

paleoenvironmental analysis of the ichnogenus zoophycos in the lower devonian tempestite sediments of the longmenshan area sichuan china abstract the trace fossil zoophycos is characteristic of the lower devonian in the longmenshan area of southeastern china three distinct storm generated or induced types of sedimentary sequences bearing zoophycos have been identified in shallow marine deposits of the bailiuping formation and the yangmaba formation the type a deposit is composed of siltstones with shell concentrations and wave ripples and small zoophycos at the top the type b deposit is characterized by fine graded sandstone with long wavelength hummocky cross stratification and black gray mudstone as well as the largest and densest zoophycos at the top the type c deposit has graded bioclastic limestone with short wavelength hummocky cross stratification muddy wackestone and large zoophycos at the top based on the features of the types of zoophycos the distribution zone of the zoophycos ichnogenus that preserved in tempestite sequence was built between the fair weather wave base and storm wave base in the lower devonian this research suggests that the distribution patterns of zoophycos formed in storm induced deposits may not provide significant clues for the estimation of relative water depths the hydrodynamic conditions and sedimentation rate are two important environmental factors of the development of the zoophycos in the lower devonian shallow marine deposits where it was mainly affected by storms between the fair weather and storm wave bases the abundance of zoophycos at the top of locally frequent storm deposits could indicate a fairly opportunistic behavior and they were formed in the early hst deposit which had a relatively stable environment with low energy and higher sedimentation rate

the pleistocene and holocene records of the mazarron basin se spain abstract here we reconstructed the evolution of the mazarron basin during the pleistocene and holocene in this regard we studied 9 cores with the aim to 1 define a chronological framework 2 obtain data on the palaeoenvironment and 3 establish the relationship with recent tectonics a total of 158 samples were recovered for amino acid racemization aar dating 4 for radiocarbon dating 14c and 332 for sedimentological and palaeontological determination and 110 for determination of the mineralogical content these approaches allowed us to elucidate the evolutionary phases of the palaeo landscape of the mazarron basin a fault controlled graben affected by diverse faults mainly those of las moreras and rella the ages of the records and the facies correlation indicate that las moreras fault controlled sedimentation during marine isotope stage mis 7 whereas the rella fault was strongly active during the middle holocene during mis7 a brackish lagoon developed in the western area overlying alluvial fan deposits later the area was uplifted thereby becoming exposed to erosion the activity of the rella fault allowed sedimentation in the western part of the mazarron basin during the middle holocene while in the upper holocene sedimentation occurred in the eastern part the holocene transgression was reflected in a temporarily floodable marsh in the hinterland with changing salinity conditions from brackish to euhaline waters along the sea front the marine influence was evident but not dominant thus the mazarron basin during the holocene was brackish to highly euhaline with variable biological diversity linked to a narrow and probably discontinuous communication with the sea with restricted circulation and long flushing times which was reflected by the significant presence of halite the record ended with recent alluvial anthropic sediments

industrial mercury in combination with natural pb210 as time dependent tracers of sedimentation and mercury removal from haifa bay israel the input rate of a particle reactive pollutant mercury from a chloralkali plant which was known in detail was used in combination with pb210 to determine the sedimentation and mixing rates in several locations in the area of a factory outfall sediment profiles were modelled using a numerical solution to the diagenetic equation the calculated sedimentation rate of 0 5 cm year 1 was close to values based on estimates of regional sand transport surface mixing rates of 7 8 cm2 year 1 with an exponential decrease with depth are similar to rates estimated in other near shore areas an atmospheric flux of excess pb210 to the area of 0 41 dpm cm 2 year 1 was estimated from the inventory in the sediment from two nearby fishponds the model predicted that despite the input of 0 5 cm year 1 of clean sand into the area the level of mercury in surface sediments would remain 0 3 ppm above background precontamination levels for more than 50 years after input controls were introduced due to particle mixing unlike most previous studies on the discharge of mercury into the near shore environment this receiving area is one of relatively coarse sandy sediment and particle poor oceanic water the majority of the mercury in the sediment was not attached to fine grained particles only 10 of the mercury supplied in the effluent was found in the sediments within a 150 km2area adjacent to the outfall it was hypothesized that there were insufficient fine grained particles to remove dissolved mercury from the water column thus the principal pathway of even particle reactive pollutants to the biosphere in this coastal area may be via the planktonic food chain with the benthic food web being important only locally

linking taphonomy to community level abundance insights into compositional fidelity of the upper triassic shell concentrations eastern alps abstract although actualistic live dead comparisons lead to robust estimates of fidelity of modern death assemblages quantitative evaluation of fidelity of fossil assemblage remains uncertain in this paper effects of storm reworking on compositional fidelity of the upper triassic shell concentrations eastern alps austria are evaluated an exploratory approach is based on comparison of reworked and non reworked assemblages in ordination analyses non reworked assemblages of one or more communities provide a baseline for evaluation of fidelity of reworked assemblages in siliciclastic rich intervals of the kossen formation shell concentrations are represented by 1 packstones with small shallow infaunal bivalves 2 floatstones and pavements with large semi infaunal bivalves and 3 bioclastic marlstones in carbonate rich intervals bioclastic floatstones with bivalves and brachiopods occur analyzing all shell concentrations eight sample groups sharing similar species composition are discriminated limited effect of storm reworking on composition of shell concentrations is indicated by 1 a general persistence of six sample groups when only non reworked assemblages are analyzed 2 similarity in composition between reworked and non reworked assemblages within sample groups and 3 compositional segregation between non reworked assemblages of distinctive sample groups mostly without any reworked assemblages of intermediate composition depth related variations in dead shell production shell destruction and body size governed preservation and distribution of the shell concentrations along onshore offshore gradient in the kossen basin first at times when environmental conditions were unfavorable for shell producers coupled with high background shell destruction rates limestone beds formed during storm events were shell poor second less common shell concentrations in upper than in lower parts of siliciclastic intervals can be related to higher environmental stress in shallower habitats third the difference between shell concentrations dominated by small and large bivalves is driven by between habitat differences in body size and is not due to a differential sorting of small and large shells combining community analysis based on species abundances with taphonomic analysis can thus be helpful in tracking fidelity of fossil assemblages

quantification of tsunami induced flows on a mediterranean carbonate ramp reveals catastrophic evolution cool water carbonates are the dominant limestones in the mediterranean basin since the early pliocene their deposition typically resulted in ramp morphologies due to high rates of resedimentation several such fossil carbonate ramps are characterised by a bimodal facies stacking pattern where background deposition of subaqueous dune and or tempestite deposits is repeatedly interrupted by anomalously thick sedimentary units dominated by backset stratification formed by supercritical flows a multitude of exceptional triggers e g storms floods tsunamis have been invoked to explain the origin of these supercritical flows which in the absence of a quantitative analysis remains speculative as yet here for the first time the catastrophic evolution of one such mediterranean carbonate ramp on favignana island italy is quantified by combining 87sr 86sr dating outcrop based palaeoflow reconstructions and hydraulic calculations we demonstrate that rare tsunami induced flows occurring on average once every 14 to 35 kyr lasting a few hours only deposited the anomalously thick backset bedded units that form half of the sedimentary record in between such events cumulative two years of storm induced flows deposited the remaining half of the succession by the stacking of subaqueous dunes the two to four orders of magnitude difference in average recurrence period between the two flow types and their associated sedimentation rates emphasises the genetic differences between the two styles of deposition in terms of sediment transport the studied carbonate ramp was inactive for at least 99 of the time with gradual progradation during decennial to centennial storm activity carbonate ramp evolution attained a catastrophic signature by the contribution of rare tsunamis producing short lived high energy sediment gravity flows

morphology of submarine barchans and sediment transport in barchans fields off the dongfang coast in beibu gulf submarine barchans in three new regions were described using new high resolution multibeam bathymetric data off the dongfang coast in beibu gulf currents seismic profiles of horns surface sediments and comparative surveys in 2007 and 2009 were obtained to study barchan mobility and sand transport in the barchan fields the submarine barchans occur at depths of 15 25 m reaching up to 551 9 m in horn length and 8 6 m in height most barchans have asymmetrical horns and display wider plane shapes than subaerial barchans for the same length and height the morphology of barchans exhibits regional variations that are mainly controlled by finite water depth daily reverse currents sand supply changes and interaction of dunes barchan asymmetries internal bedding inclinations and grain size changes are in agreement with the dominant current directions results show that submarine barchans migrated 5 43 m in two years 2007 2009 through comparison of bathymetric data because of the marginally cohesive fine sediment composition and long distance from contemporary sediment sources it is believed that barchans in region c are not of modern origin however these bedforms can be also affected by high energy flow regimes collisions limit barchan widths and provide efficient transport paths between barchans on their horns large sand supply through the horns increases the barchan heights and also changes their shapes some small dunes are identified that are moving away from the barchans field in 2007 and have departed from the host barchans in 2009 these small barchans were probably caused by the separation of the faster moving horn tails from the host barchans when extreme situations happen the mechanism gives a new explanation for sand loss and size determination of submarine barchans c 2014 elsevier b v all rights reserved

integrated ground based hyperspectral imaging and geochemical study of the eagle ford group in west texas abstract this study used ground based hyperspectral imaging to map an outcrop of the eagle ford group in west texas the eagle ford group consists of alternating layers of mudstone wackestone grainstone packstone facies and volcanic ash deposits with high total organic content deposited during the cenomanian turonian time period it is one of the few unconventional source rock and reservoirs that have surface representations ground based hyperspectral imaging scanned an outcrop and hand samples at close ranges with very fine spatial resolution centimeter to sub millimeter spectral absorption modeling of clay minerals and calcite with the modified gaussian model mgm allowed quantification of variations of mineral abundances petrographic analysis confirmed mineral identifications and shed light on sedimentary textures and major element geochemistry supported the mineral quantification mineral quantification resulted in mapping of mudstone wackestone grainstone packstone facies and bentonites volcanic ash beds the lack of spatial associations between the grainstones and bentonites on the outcrop calls into question the hypothesis that the primary productivity is controlled by iron availability from volcanic ash beds enrichment of molybdenum mo and uranium u indicated unrestricted marine paleo hydrogeology and anoxic to euxinic paleo redox bottom water conditions hyperspectral remote sensing data also helped in creating a virtual outcrop model with detailed mineralogical compositions and provided reservoir analog to extract compositional and geo mechanical characteristics and variations the utilization of these new techniques in geo statistical analysis provides a workflow for employing remote sensing in resource exploration and exploitation

critical bed shear stress and threshold of motion of maerl biogenic gravel abstract a determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility rate of erosion and deposition in conservation management the critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free living maerl beds in three contrasting environments open marine intertidal and beach in galway bay west of ireland the bed shear stress was determined using two methods law of the wall and turbulent kinetic energy in a rotating annular flume and in a linear flume the velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed the critical shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand the critical shields parameters for the maerl particles from all three environments fall below the shields curve along with a previously reported correlation between maerl grain shape and settling velocity these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter the intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment in samples with a high percentage of maerl and low percentage of siliciclastic sand the lower density lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment at velocities 10 cm s 1 higher than the threshold velocity of grain motion rarely documented subaqueous maerl dunes formed in the annular flume

spatially varying environmental properties controlling observed sand wave morphology sand wave morphology and dynamics on continental shelves vary substantially and we hypothesize that these spatial variations depend on local bed properties and hydrodynamic characteristics to date process based modeling studies have not been able to simulate realistic equilibrium sand wave heights and empirical studies are mostly limited to case studies in order to explain the spatial variation in the morphology of equilibrium sand waves on continental shelves with processes and local bed conditions a large scale investigation is required in this paper we use high resolution multibeam echo soundings hydrodynamic models and databases and sedimentary data for the analysis of respectively sand wave shape characteristics and the comparison to hydrodynamic and sedimentary characteristics for the netherlands continental shelf the results are quantified lengths heights and asymmetry of all sand waves in the dutch part of the north sea furthermore we show that the mode of sediment transport bed load or suspended is a dominant factor in explaining sand wavelength height and asymmetry full results of shape characteristics of all sand waves on the netherlands continental shelf together with the tidal velocity water depth surface wave height and median grain size are provided in a repository with this paper http doi org 10 4121 uuid 0d7e016d 2182 46ea bc19 cdfda5c20308 these results are highly valuable for applied offshore engineering projects and to modelers for validating their morphodynamic model results

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

what sets the size of current ripples water flowing over sand in fluvial and marine settings often results in the formation of current ripples found in modern and ancient deposits on earth and mars ripple stratification records flow directions and fluid properties that are crucial to interpreting sedimentary records despite decades of observations of current ripples there is no universal scaling relation to predict their size or to distinguish them from dunes here we use dimensional analysis and a new data compilation to develop a scaling relation that collapses data for equilibrium wavelengths of ripples forming under unidirectional flows results show that ripples are larger with more viscous fluids coarser grains smaller bed shear stresses and smaller specific gravity of sediment the scaling relation also segregates ripples from dunes highlighting a narrow regime of transitional bedforms that have morphologic properties and sediment transport conditions that overlap with both ripples and dunes our analysis shows that previous absolute size based definitions of ripples and dunes only hold for certain conditions such as water flows transporting siliciclastic grains on earth the new theory allows estimates of ripple sizes in foreign fluids and on other planets including meter scale ripples in methane flows on titan or in viscous brines on mars

sticky stuff redefining bedform prediction in modern and ancient environments the dimensions and dynamics of subaqueous bedforms are well known for cohesionless sediments however the effect of physical cohesion imparted by cohesive clay within mixed sand mud substrates has not been examined despite its recognized influence on sediment stability here we present a series of controlled laboratory experiments to establish the influence of substrate clay content on subaqueous bedform dynamics within mixtures of sand and clay exposed to unidirectional flow the results show that bedform dimensions and steepness decrease linearly with clay content and comparison with existing predictors of bedform dimensions established within cohesionless sediments reveals significant over prediction of bedform size for all but the lowermost clay contents examined the profound effect substrate clay content has on bedform dimensions has a number of important implications for interpretation in a range of modern and ancient environments including reduced roughness and bedform heights in estuarine systems and the often cited lack of large dune cross sets in turbidites the results therefore offer a step change in our understanding of bedform formation and dynamics in these and many other sedimentary environments

depositional environment and organic matter accumulation of lower jurassic nonmarine fine grained deposits in the yuanba area sichuan basin sw china abstract this study investigated the lithological sedimentological and geochemical characteristics of lower jurassic strata ziliujing formation in the sichuan basin to identify the lithofacies and understand the depositional environments and differences in organic matter accumulation of these nonmarine fine grained sediments based on mineralogy and petrology rock types were recognized with mudstones siltstones and limestones being the most common rock types sedimentary structures biota and well log data were used to define and characterize 17 lithofacies and the following five facies associations of the fine grained sediments 1 delta front 2 clastic lakeshore 3 clastic shallow lake 4 clastic semi deep lake and 5 carbonate lake the content of total organic carbon ranges between 0 04 and 3 84 with an average of 0 74 the organic matter primarily consists of type kerogen major processes inferred from the lithofacies analyses include suspension biogenic and storm deposition on the basis of facies associations redox climate and salinity conditions biotic productivity and terrigenous input a total of six depositional environments are proposed i high productivity low oxygen swamp ii low oxygen semi deep lake iii high oxygen semi deep lake iv high oxygen shallow lake v deep water low oxygen semi deep lake and vi high salinity low oxygen shallow lake the nonmarine environments changed frequently unlike more stable environments the development of bivalves in the shallow lake is suggested to be related to high salinity caused by dry climate together with limited terrigenous input organic rich nonmarine fine grained sediments in the ziliujing formation formed in swamp and semi deep lake with settings under reducing conditions in a humid climate with relatively high terrigenous input results of the study may help us to understand the deposition of nonmarine organic rich fine grained lower jurassic sediments in southwest china

monitoring underwater nourishments using multibeam bathymetric and backscatter time series natural and man induced coastal erosion endanger life and environment in coastal areas worldwide for sedimentary barrier coasts beach and underwater nourishments are an efficient coastal protection strategy to optimize nourishments and to understand their impact on the marine environment monitoring strategies are required in this study we investigate the potential of multibeam echosounder mbes data providing both bathymetry and backscatter bs for monitoring the evolution of the nourished sediment and morphodynamics over time a time series of seven mbes measurements as well as two sets of box cores vibrocores and seismic data were acquired of a channel side nourishment near the wadden sea island ameland the netherlands between april 2017 and may 2019 in general a high confidence of the acoustic reliability of the bs time series measurements is demonstrated the unsupervised bayesian classification method supported by ground truthing is employed to produce a time series of sediment maps revealing sediments ranging from sandy mud to sand with varying amounts of shell fragments based on the sediment maps the nourished sediment could be distinguished from the natural sediment within one year the shell rich pre nourishment seabed is recreated by washing out finer sediments which are deposited towards the main tidal channel using the seismic data and vibrocores the shell rich pre nourishment seabed could be identified in the subsurface after being buried by the nourishments supporting the general findings furthermore a rapid development of steep bedforms with increasing sediment sorting is observed in parts of the nourished areas this study shows that high resolution sediment maps obtained from a time series of mbes bs together with bathymetry reveal morphodynamic and sedimentary processes of nourishment evolution and can advance underwater nourishment strategies

detrital clay grain coats in estuarine clastic deposits origin and spatial distribution within a modern sedimentary system the gironde estuary south west france

a new phase diagram for combined flow bedforms abstract combined flows which involve a combination of unidirectional and wave induced oscillatory flow are omnipresent in coastal and lacustrine environments despite the extensive progress made in understanding the bedforms generated by such flows in past studies there still remains a wide range of unexplored flow conditions where the bedform geometry and hence consequent sedimentary structures have not been explored especially for strong unidirectional flows greater than 0 30 m s 1 and intermediate oscillation periods between 2 and 8 seconds to address this gap in our knowledge the stability of bedforms in a 0 25 mm diameter sand bed was studied under pure unidirectional pure oscillatory and combined flow conditions with oscillation periods of 4 5 and 6 s the maximum orbital velocity uo was varied from 0 00 to 1 00 m s 1 while the unidirectional component uu was varied from 0 to 0 50 m s 1 the experimental data collected under unidirectional flows stronger than 0 30 m s 1 allows expansion of current understanding of the bed configurations for current dominated combined flows where the phase boundary between combined flow bedforms and current ripples was uncertain under these flow conditions ten distinctive bedform states can be recognized no motion nm 2d symmetric ripples 2d sr 3d symmetric ripples 3d sr 3d symmetric dunes 3d sr 3d asymmetric ripples 3d ar 3d quasi asymmetric ripples 3d qar 3d asymmetric dunes 3d ad 3d current ripples 3d cr 3d current dunes 3d cd and upper stage plane bed uspb each of these bedform stages is described quantified and characterized in dimensional phase diagrams a complete re evaluation of the nomenclature for combined flow bedforms is proposed which includes their planform and cross sectional geometry in order to better represent the bed morphologies this new nomenclature also unifies past research on bedforms in both unidirectional and oscillatory flows and thus presents a new synopsis of bedforms developed under such flows one of the main changes proposed that allows integration with the nomenclature used in unidirectional flows is the reclassification of large ripples as dunes furthermore the introduction of the planform and cross sectional geometries as properties by which to classify bedforms leads to the definition of a stable phase space for two dimensional symmetrical ripples and three dimensional quasi asymmetrical ripples these new data and analysis allow proposition of a new unified phase diagram for combined flows

sedimentary characteristics and interactions among volcanic terrigenous and marine processes in the late permian kuishan member eastern block of the north china craton abstract understanding the variability of depositional environment and depositional processes of the late permian kuishan member north china craton is crucial for unraveling the evolution of sedimentary basin and epicontinental sea in shandong tectonic domain the kuishan member in the eastern block of the north china craton formed in association with general regression of an epicontinental sea is composed of abundant volcanic deposits and nearshore sedimentary deposits three lithofacies assemblages together with eleven lithofacies are identified in the study area including volcanic deposits of the turbidity lithofacies assemblage epiclastic deposits of the nearshore lithofacies assemblage and mixed volcaniclastic and epiclastic sedimentary deposits of the terrestrial lithofacies assemblage these alternating volcanic epiclastic lithofacies assemblages illustrate the depositional environments induced by volcanic activities and nearshore wave influence syn eruptive lithofacies in the shallow water area were formed by high density turbidity currents and ash fall into water introduced by rising sea levels and high rainfall due to volcanic eruptions to the north whereas thin bedded shallow marine silty mud developed in the distal area inter eruptive lithofacies were represented by tuffaceous mudstone deposited in an exposed and oxidized setting due to falling sea level whereas epiclastic nearshore deposits accumulated by wave or current flow regimes paleocurrent measurements show that the predominant regression direction changes from uniform southwest to divergent southwest and southeast during volcanic inter eruptive periods the kuishan succession therefore can be regarded as a volcano related sequence in which the input of volcaniclastic and epiclastic deposits were significantly modulated by controls of volcanism with frequently changing coastline position of the epicontinental sea and alternating depositional environments

genesis and environmental significance of upper cretaceous shell concentrations from the cauvery basin southern india abstract upper cretaceous shallow marine calcarenites of the upper campanian maastrichtian kallankurichchi formation from the cauvery basin of southeastern india are rich in shell concentrations dominated by large bivalves with minor admixtures of brachiopods bryozoans and larger foraminifera rarely these concentrations occur as lenses or pavements but usually as beds 10 to 200 cm thick depending on the dominant skeletal elements five types of shell concentrations can be distinguished isognomon pycnodonte ceratostreon inoceramid platyceramus cataceramus and polyspecific concentrations these shell concentrations occur in various preservational states which reflect the gradual mixing and mechanical destruction of former communities analysis of the taphonomic signatures of their components and of the biofabric suggests that storm induced waves and currents reduced sediment input the settling behaviour of taxa and a high rate of production of biogenic hardparts were responsible in varying degrees for the formation of the various shell concentrations accordingly they can be classified as storm wave proximal tempestite and primary biogenic concentrations the shell concentrations formed below fair weather wave base in shallow subtropical low stress environments

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

a review on the applications of image logs in structural analysis and sedimentary characterization abstract image logs provide important information on lithology sedimentary textures paleoflow directions fractures and in situ stress analysis lacking of criteria used for establishing the image log facies limits the applications of image logs in sedimentary reservoir interpretation this paper provides a thoroughgoing review focusing on the recent applications of borehole image logs for sedimentological and structural description and interpretation and aims to establish image log facies which can provide guidelines in sedimentary reservoir interpretation this paper firstly summarizes the principles and basic characteristics of various imaging logging tools and then briefly introduces the pre processing workflow of the image log data then the generated images are used for depth and orientation shifts of cores by calibrating individual sedimentary and structural features descriptive and concise image log facies are established based on combinations of image textures including dip type dip pattern and color scheme and the characteristics as well as physical criteria for each individual image facies are summarized the established image log facies are then interpreted in terms of structural and sedimentological features such as lithology sedimentary structures vugs fractures and faults the image log facies and its stacking patterns are then used to interpret the lithofacies associations by calibrating with cores and conventional logs natural fractures and induced fractures are recognized by image logs and the principles of breakouts and drilling induced fractures for in situ stress analysis are reviewed then the applications of image logs in investigation of fracture attitudes and states as well as in computation of fracture parameters are summarized the procedures to evaluate fracture effectiveness through image logs are discussed at last the application of image logs for structural dip analysis is reviewed and image logs are used for recognizing faults fracture sets and attitudes of stratum through the dip patterns the basic procedures for paleocurrent reconstruction which includes dip picking of cross beddings structural dip determination and structural dip removal are reviewed then the paleocurrent directions of the lower cretaceous bashijiqike formation in the kuqa depression were reconstructed which could help further understanding of the depositional systems this review will help extend the utility of image logs in interpreting small to large scale sedimentary and structural features and bridges the gaps between well log analysis and sedimentary and structural interpretation

architectural styles and sedimentology of the fluvial lower beaufort group karoo basin south africa abstract the permo triassic beaufort group comprises in excess of 3000 m of sandstone and mudstone rich fluvial deposits that vary both laterally and vertically in abundance architecture and clustering styles the lower 1370 m has been studied in detail detailed stratigraphic logging and photographic interpretation have been carried out on river cliffs and hillside sections and sedimentary structures have been mapped by close inspection of clean outcrops seven fluvial architectural styles have been identified encompassing sand body and sand body cluster scales 1 flat topped sheets dominated by lateral accretion 2 concave up topped sheets dominated by lateral accretion 3 heterolithic ribbons dominated by lateral accretion 4 flat topped ribbons with attached splays dominated by downstream accretion 5 unconfined moderately amalgamated concave up topped complexes 6 unconfined strongly amalgamated sheet complexes and 7 valley confined strongly amalgamated ribbon complexes the internal architecture of each indicates mixed lateral and downstream accretion modes on several scales with local variability lateral accretion deposits differ from typically published facies models in that trough cross bedding is rare possibly the result of an inability to generate dunes due to the dominant very fine sandstone grain size the observed architecture and sedimentary structures are the product of 1 a semiarid climate producing fluvial and debris flows and cementation of sediment packages at the surface which exerts a strong control on the magnitude of channel scour the nature of channel fill and compaction history 2 local variability in subsidence rate causing variation in the vertical spacing of channel belts channel slope and plan form and variation in preservation of topographically higher features e g levees 3 relative position in a fluvial megafan influencing suspended load to bedload partitioning from proximal to distal locations and formation of channel belt complexes and 4 relative sea level changes causing incised valley formation and fill only in the most distal parts of the system

the fluvial and lacustrine sedimentary systems and stratigraphic correlation in the upper triassic xujiahe formation in sichuan basin china the calcarenites and siliciclastic sandstones in the upper triassic xujiahe formation are key targets of the unconventional gas exploration in sichuan basin to resolve the long debated stratigraphic correlation of the interfingering lithostratigraphic members between the different exploration blocks a facies classification scheme integrating sedimentary structures in borehole images bhi and lithology from wireline logs is calibrated in the cored wells and extrapolated into the noncored wells three major sedimentary systems are recognized in xujiahe by mapping the facies trends and paleocurrent directions in the coarse grained sediments one system may dominate over the others at different times and or locations in the foreland basin in response to the orogenic movements in the surrounding mountains the longmen shan in the northwest of the study area is the main source provenance for the carbonate conglomerates and calcarenites meanwhile the systems in the northeast and southeast deposited the sandstone wedges alternating lacustrine swamp and fluvial sediments are penetrated in both proximal and distal areas in the basin although there is no indication of a basinwide lake in the xujiahe period abundant sandy shale breccia conglomerates containing large shale breccias plant materials and contorted shale blocks in association with thick foreset bedded sandstones suggest subaqueous gravity flows possibly because of the collapse of a multistoried delta front characterization of these dynamic sedimentary systems through multidisciplinary interpretation of the seismic data cores bhi and wireline logs is not only fundamental to the sedimentary analysis but also the exploration strategy in the areas with optimal juxtaposition of reservoir sandstones and coaly source rocks

the influence of radon diffusion on the 210pb distribution in sediments a mathematical model is presented which describes the distribution of radon 222 in sediments having a constant or variable depth distribution of radium 226 the model is extended to the distribution of lead 210 taking into account the mobility of radon the precursor of 210pb within the sediment column the 210pb model is compared at constant radium activity with the conventional approach which disregards the radon diffusion when estimating sedimentation rates by the 210pb method the ratio between apparent and real sedimentation rate s s expressed as a function of three dimensionless parameters demonstrates the importance of the radon diffusion effect this effect is particularly important for sediments with small initial excess 210pb activity small sedimentation rate large radon diffusivity or a combination of these factors applied to lake geneva the sedimentation is estimated to be larger by 30 50 than the original value by krishnaswami et al 1971 in sediments which are mixed at the surface physical mixing or bioturbation the 210pb activity in the mixed layer is diminished compared to that in the settling sediment material robbins et al 1977 and radon diffusion makes the activity difference even larger especially for low initial excess 210pb activity small sedimentation rate and large mixing intensity this result may be of importance for the balance of 210pb in an aquatic system if the calculations are based on activities measured in the sediment

bedforms controlled by residual current vortices in a subtropical estuarine tidal channel abstract the objective of the present work was to analyze the bottom morphology the genesis of the bedforms and the patterns of current and sediment transport of the internal portion of the south mouth in paranagua bay parana brazil this region was used as a laboratory field to study the geomorphology of a dune field on a tide channel with features of flood delta in the inner portion and ebb delta in the direction of the continental shelf a sediment hydrodynamic model was used to calculate the direction and magnitude of the sediment transport and the residual current flows a map of apparent roughness was used in the numerical model obtained through the soundings of a sidescan sonar starfish sonar and estimated from the classification of the dune field so it is possible to obtain simulations with higher correspondence with reality it was observed two vortices of residual circulations near the shores of pontal do sul and ilha do mel with directions towards the continental shelf the residual circulation vortex is responsible for the triangular shape of the large dunes near the pontal do sul margin in the flood the sediment material is conducted inward forming small ripples and accumulating sediment material on large dunes during the ebb these ripples are supposedly destroyed and attached to the large dunes or to the water column on the other hand the bedforms of saco do limoeiro are formed due to the effects of the tide when entering the mouth and the confinement of the water mass in the region until the next moment of padding

radionuclide dating of recent sediment and the validation of pollen environment reconstruction in a small watershed reservoir in southeastern china abstract a 76 cm sediment core was collected from the huangdong reservoir southeastern china the radionuclides 137 cs and 210 pb and sediment grain size analysis were applied to establish the chronology and modern sedimentation rates the chronology established by the 137 cs time markers was consistent with the constant flux constant sedimentation cfcs model and the known time of dam construction 1960 ad recognized from the curve of sediment grain size at the depth of 54 cm the results show that the sedimentation rate of the huangdong reservoir is relatively high implying that soil erosion and water loss were strong the sedimentation rate before the construction of the reservoir was approximately 1 5 cm a which belongs to the fluvial flooding deposit the rate decreased to approximately 1 0 cm a during the reservoir deposition since 1960s pollen and micro charcoal analysis were performed to test the reliability of pollen based environment reconstruction including vegetation cover deforestation planting and fire disasters the results of pollen and micro charcoal indicated that the herbs primarily gramineae ferns such as dicranopteris and several trees mainly pinus varied following chorography or historical records we discovered that the most important indicators for local forest cover changes are pollen concentration and the ap nap value ratio of arboreal pollen to non arboreal pollen human impact on forests is manifested by a sharp decrease in pollen percentage of trees and absolute pollen concentration forest fire events were recorded by the peaks of charcoal concentration and the c p value ratio of charcoal concentration to pollen concentration for example the massive deforestation and intensive fires during the great leap forward movement and the cultural revolution are reflected by pollen and micro charcoal spectra this work testifies that radionuclide use as a dating method is applicable in southern china and the 137 cs method has demonstrated its reliability in the small reservoir setting in spite of low absolute values the environmental proxies such as grain size pollen and charcoal are sufficiently sensitive to reveal local ecosystem changes caused by natural disasters or human activity

a unified model for bedform development and equilibrium under unidirectional oscillatory and combined flows the development of bedforms under unidirectional oscillatory and combined flows results from temporal changes in sediment transport flow and morphological response in such flows the bedform characteristics for example height wavelength and shape change over time from their initiation to equilibrium with the imposed conditions even if the flow conditions remain unchanged these variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record hence understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record this article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional purely oscillatory and combined flow conditions which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples the present results yield a unified model for bedform development and equilibrium under unidirectional oscillatory and combined flows the experimental results show that the processes of bedform genesis and growth are common to all types of flows and can be characterized into four stages i incipient bedforms ii growing bedforms iii stabilizing bedforms and iv fully developed bedforms furthermore the development path of bedform growth exhibits the same general trend for different flow types for example unidirectional oscillatory and combined flows bedform size for example small versus large ripples bedform shape for example symmetrical or rounded bedform planform geometry for example two dimensional versus three dimensional flow velocities and sediment grain sizes the equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition

lacustrine sediment chronology defined by 137cs 210pb and 14c and the hydrological evolution of lake ailike during 1901 2013 northern xinjiang china abstract dating lake sediments in arid and semi arid zones by using 137cs and excessive 210pb 210pbex methods is challenging because of the irregular climatic variations and anthropogenic effects here we try to establish the reliable geochronology of the lacustrine core drilled from lake ailike northern xinjiang of china by using 137cs and 210pbex dating methods and improve our understanding of the principal factors that affect the dating results the results indicate that it is important to normalize the 137cs activities by particle size and organic matter in order to diminish their enrichment effects on 137cs activities and thus help us to obtain the accurate 137cs ages the performance of the sediment isotope tomography sit model is better than the other 210pbex derived models the erosion process results in the failure of the commonly used constant rate of supply crs model as well as the low values of the sedimentation rate the 137cs inventory and the post 1963 mean annual flux of 210pbex in ailike core furthermore based on the sit model chronology we further clarify the lake evolution history of the past century and assess the anthropogenic impacts on lake ailike the hydrology of lake ailike was mainly controlled by natural climate before 1960 ce whereas it was completely controlled by intensive human activities after 1960 ce this study supports that the 210pbex based sit model appears to be an adequate method for deriving ages in the lacustrine systems with strong hydrological variability

ground penetrating radar characterization and porosity evolution of an upper pleistocene oolite capped depositional cycle red bays northwest andros island great bahama bank abstract linkages among surface sediments depositional processes geomorphic forms stratigraphic architecture and pore distribution in bahamian sand bodies and oolite capped depositional successions have been characterized in recent studies an understanding of how these parameters especially porosity are preserved or modified in the eogenetic environment is essential in bridging the gap between modern and ancient analogs two complementary 3d 200 mhz and 400 mhz ground penetrating radar surveys and three shallow cores reveal that the uppermost part of the upper pleistocene marine isotope stage 5e lucayan formation at red bays andros island great bahama bank comprises a single 6 m thick upward shallowing parasequence six radar packages p1 p6 bounded by radar surfaces s1 s6 have been identified in the two 3d radar volumes the stratigraphic succession indicates development of a burrowed backshoal lagoon during early flooding of the bank top followed by deposition of flood tide driven low angle sheet sands and sigmoidal subaqueous dune deposits as the shelf margin sand shoal moved bankward as a function of continued sea level rise constructional accommodation on the front of the prograding subaqueous dune in the northwest part of the survey area and erosional accommodation created by downcutting of a shallow tidal channel into the upper part of the subaqueous dune depositional unit in the northeast part of the study area were filled with peloid and ooid dominated carbonate sands as sea level stabilized the uppermost radar package is a thin 0 15 to 0 55 m partially calichified carbonate sand sheet that mantles the entire survey site and that reflects late highstand and fall of sea level exposure of the studied interval to meteoric vadose diagenesis over the past 100 000 years has resulted in partial stabilization of the largely aragonitic precursor sediment through selective partial dissolution of aragonitic grains mainly ooid cortical layers peloids and mollusk shells accompanied by precipitation of patchily distributed low magnesium calcite cement core data demonstrate a relationship between stratigraphically controlled sedimentological attributes diagenesis and pore distribution three distinctive zones of porosity were present upon deposition a lower zone of relatively high interparticle porosity 21 3 to 33 2 in the medial part of p1 a low porosity zone

extraction of sandy bedforms features through geodesic morphometry abstract state of art echosounders reveal fine scale details of mobile sandy bedforms which are commonly found on continental shelfs at present their dynamics are still far from being completely understood these bedforms are a serious threat to navigation security anthropic structures and activities placing emphasis on research breakthroughs bedform geometries and their dynamics are closely linked therefore one approach is to develop semi automatic tools aiming at extracting their structural features from bathymetric datasets current approaches mimic manual processes or rely on morphological simplification of bedforms the 1d and 2d approaches cannot address the wide ranges of both types and complexities of bedforms in contrast this work attempts to follow a 3d global semi automatic approach based on a bathymetric tin the currently extracted primitives are the salient ridge and valley lines of the sand structures i e waves and mega ripples the main difficulty is eliminating the ripples that are found to heavily overprint any observations to this end an anisotropic filter that is able to discard these structures while still enhancing the wave ridges is proposed the second part of the work addresses the semi automatic interactive extraction and 3d augmented display of the main lines structures the proposed protocol also allows geoscientists to interactively insert topological constraints

sedimentology and sequence stratigraphy of early syn rift tidal sediments the nukhul formation suez rift egypt abstract facies and tectono stratigraphic models for the tidally influenced miocene nukhul formation are presented based on outcrop data from hammam faraun fault block suez rift egypt deposits of the nukhul formation are attributed to two linked depositional settings offshore to shoreface and estuary settings and were deposited during initial stages of rifting in hanging wall depocenters of early formed propagating fault segments the offshore to shoreface deposits consist of variably bioturbated mudstones that pass gradationally upward to bioturbated bioclastic sandstones the more landward estuary deposits can be separated into a tripartite division of estuary mouth estuary funnel with bayhead delta and upper estuary channel deposits estuarine processes generated a complex intercalation of lithologies with both gradational and sharp facies transitions in the estuary deposits tidal ravinement surfaces are typically characterized by mudstones of the estuary funnel association below passing abruptly up to erosionally based estuary mouth sandstones maximum flooding surfaces are expressed by an abrupt erosional contact separating estuary mouth sandstones below and estuary funnel mudstones above stratigraphic development was strongly influenced by the evolving early rift structure depocenters were narrow 2 5 km wide and elongate 10 km long parallel to the strike of normal fault segments the shoreface shoal prevented wave energy in the estuary and increased the relative influence of tidal currents the elongate fault controlled geometry of the depocenters confined the bayhead delta and further enhanced tidal influence stratal geometry reflects deformation associated with low relief growth folds and surface breaking faults that together formed part of an evolving fault array this basin configuration and associated nukhul stratigraphy is markedly different to tectono stratigraphic models for crustal scale tilted fault blocks that are applicable from late stages of rifting

the geochemistry of plutonium in fresh and marine water environments abstract the chemical behaviour of plutonium in the hydrosphere is a subject of both great practical and intrinsic importance the production and eventual disposal of pu and other artificial radionuclides dictates that this be the case the main objective of this paper is to provide a synthesis and critical examination of currently published data and interpretations on the geochemistry of pu in natural waters and sediments where appropriate an attempt is made to reinterpret published data with the aim of establishing the relationships between geochemical and biological processes and the distribution concentration and speciation of pu particular attention is paid to the question of the potential for the chemical remobilization of pu from the solid to the aqueous phase approximately one third of the text deals with freshwaters mostly lakes while two thirds discusses the estuarine coastal and open ocean environments

recent lake sedimentation in the middle and lower yangtze basin inferred from 137 cs and 210 pb measurements abstract the reduction of water storage capacity in the lakes of the yangtze basin was an important factor for the disastrous 1998 flooding this study attempted to quantify sedimentation and its role in the water storage reduction in the middle and lower reaches of the yangtze basin using the radionuclide of caesium 137 137cs and lead 210 210pb as tracers sixteen cores were taken from eight lakes including the two largest lakes in the region poyanghu and dongtinghu the two dating techniques were used in combination to quantify recent sediment accumulation rates and their changes over the last few decades the 137cs and 210pb measurements indicated higher sedimentation rates for dongtinghu which were consistent with observed severe reduction of water storage capacity the inferred sedimentation rates for the remaining lakes were lower and did not reflect the perceived rate of severe soil erosion upstream or the substantial water storage reduction the low sedimentation rates inferred for most lakes tentatively suggest that sediment deposition was not the primary reason for the observed reduction in water storage capacity nevertheless a clear increasing trend in sedimentation rates has been documented for most of the studied lakes over the past few decades sedimentation and its role in water storage reduction require further study due to the many problems associated with its quantification such as the post depositional redistribution of sediments and water exchanges between the yangtze river and the studied lakes

mixed siliciclastic carbonate evaporite sedimentation in an arid eolian landscape the khor al adaid tide dominated coastal embayment qatar abstract the khor al adaid embayment of southern qatar represents a unique shallow water mixed siliciclastic carbonate coastal depositional system that developed in a hyper arid climatic setting over the past 6000 years the embayment which was formed during the flandrian transgression as a result of flooding across a partially fault controlled incised fluvial drainage is supplied by quartz rich sands delivered by wind blown dunes migrating southward across the surface of qatar these offshore migrating eolian derived sediments are being redistributed by tidal currents in an otherwise low energy coastal zone where in situ formation of carbonate mud and a low diversity skeletal assemblage is ongoing within salinity restricted environments three depositional sectors are delineated 1 an energetic linear fault controlled entrance channel into which the eolian dunes spill directly 2 a relatively deep up to 20 m outer lagoon interpreted to represent a flooded karst collapse structure and 3 a sprawling low energy shallow physical oceanographic modeling integrating multi seasonal current meter and tidal gage measurements demonstrates tidal current flow velocities are relatively high in both the entrance channel and at the constricted entrance to the inner lagoon associated flow expansion into less confined areas results in deposition of the eolian derived sands as flood tidal deltas one in the outer and two in the inner lagoon a weakly developed ebb tidal delta occurs where the entrance channel debouches into the arabian gulf flood tide dominance is also apparent in entrance channel deposits where sand accumulates in seaward terminating ebb barbs along the margins of the flood dominant thalweg such flood tide dominance of the thalweg is unusual and likely reflects the absence of river discharge evidence of significant inverse estuarine circulation seaward flow of a brine along the embayment floor is mostly absent in spite of the landward increase of salinity where concentrations reach more than double normal seawater salinity in the inner lagoon modeling results show that seaward flowing brines formed in the inner lagoon are trapped in the relatively deep outer lagoon and that mixing by tidal currents in the energetic entrance channel precludes the formation of vertical density gradients there because siliciclastic mud is essentially absent and most of the sediment forming the deltas consists of sand upper intertidal deltaic deposits that would normally consist of mud are absent resulting in the flood tide deltas having a pronounced lobate geometry similar to that of fluvial deltas formed predominantly of sand away from tidal deltas low energy lagoons are floored by carbonate mud of local production with minor gypsum precipitating in the inner lagoon wind generated waves only locally influence sedimentation forming complex nearshore bars along some lagoonal shorelines the overall landward increase in salinity is accompanied by a decrease in the diversity of benthic fauna and their skeletal remains a fairly diverse faunal assemblage is observed in the entrance channel near the arabian gulf including colonial corals whereas the inner lagoon assemblage is dominated gastropods belonging to pirenella cingulata the remnants of large eolian dunes are preserved in the low energy setting of the inner lagoon segmenting the waterbody and locally increasing restriction the sedimentology of the arid zone coastal khor al adaid embayment may serve as an analogue for environmental settings that were perhaps more commonplace in arid zones of flooded continents during greenhouse times

recent subsidence and northeast tilting of the nile delta egypt abstract sediment borings collected in the nile delta of egypt many of them radiocarbon dated indicate that the entire northern sector of this major depositional center in the eastern mediterranean is presently subsiding mapping of the base of the holocene deltaic facies which is dated at about 8000 6500 yrs b p reveals that differential lowering of the northern delta plain is preferentially accentuated toward the northeast long term subsidence rates at or near the coast averaged for the mid to upper holocene range from about 0 1 to 0 25 cm yr between alexandria and the north central delta margin rates increase markedly eastward to a maximum of about 0 5 cm yr in the port said manzala lagoon region and this rapid lowering explains the presence of thick marine delta lobe sequences of holocene age in cores in the northeastern delta in contrast only reworked remnants of holocene marine delta lobe deposits of the earlier river nile branches which once flowed to the north and northwest are preserved seaward of the present north delta coast subsidence has induced marked environmental changes particularly with respect to coastal erosion and salt water incursion the asymmetric pattern of saline ground water here attributed in part to the northeast tilt of the delta plain has serious implications for agricultural development in this intensely cultivated region

formation evolution and present day activity of offshore sand ridges on a narrow tideless continental shelf with limited sediment supply abstract an integrated approach combining swath bathymetry high resolution seismic reflection and seabed sediment sampling was performed to characterize a field of sand ridges on the murcia continental shelf in the western mediterranean sea the aim of this work was to improve knowledge about the formation evolution and present day dynamics of these bedforms on a narrow tideless continental shelf receiving little sediment input sand ridges are observed on the middle shelf at water depths ranging between 58 and 78 m the sand ridges are 1 5 to 3 m high and show a predominant e w orientation oblique to the present day shoreline smaller scale subaqueous dunes 0 3 1 3 m high appear superimposed on the sand ridges and beyond the ridge field the subaqueous dunes show a nw se orientation and asymmetric profiles with the lee side facing southwest the comparison of two bathymetric surveys 10 years apart revealed that the subaqueous dunes are migrating towards the southwest at very low rates 3 m yr 1 internally both sand ridges and dunes display southwestward dipping oblique reflections indicating long term migration in that direction the morphology architecture and distribution of the murcia sand ridges suggest that they were formed in a shallow water environment during the holocene transgression and were later detached from the coast due to the subsequent sea level rise the shallow architecture of the sand ridges reveals the presence of small mound like features within the sand ridges most probably associated with coastal deposits which could have served as a precursor for the development of the sand ridges the preservation of these deposits within the sand ridges evidences limited offshore ridge migration at present active subaqueous dunes superimposed on the sand ridges suggest that they may play a significant role in the ridge evolution at a regional scale the comparison of the murcia sand ridges with those described in the western mediterranean allows us to propose a gradation from partially evolved to fully evolved sand ridges with increasing water depth

a unified model of ripples and dunes in water and planetary environments subaqueous and aeolian bedforms are ubiquitous on earth and other planetary environments however it is still unclear which hydrodynamic mechanisms lead to the observed variety of morphologies of self organized natural patterns such as ripples dunes or compound bedforms here we present simulations with a coupled hydrodynamic and sediment transport model that resolve the initial and mature stages of subaqueous and aeolian bedform evolution in the limit of large flow thickness we identify two types of bedforms consistent with subaqueous ripples and dunes and separated by a gap in wavelength this gap is explained in terms of an anomalous hydrodynamic response in the structure of the inner boundary layer that leads to a shift of the position of the maximum shear stress from upstream to downstream of the crest this anomaly gradually disappears when the bed becomes hydrodynamically rough by also considering the effect of the spatial relaxation of sediment transport we provide a new unifying framework to compare ripples and dunes in planetary environments to their terrestrial counterparts terrestrial and planetary subaqueous and aeolian ripples and dunes can be compared in a unified framework according to simulations with a hydrodynamic and sediment transport model

genetic processes and environmental significance of lower devonian brachiopod shell concentrations in longmenshan area sichuan china abstract the distinctive features of the lower devonian rocks of the longmenshan area in southwestern china are brachiopod shell concentrations especially in the bailiuping ganxi and xiejiawan formations where brachiopod shell concentrations occur widely throughout depending on the dominant skeletal elements six types of shell concentrations can be distinguished protochonete acrospirifer howellella orientospirifer polyspecific shell and polyspecific fragments concentrations according to the shell features taphonomic signature host sediments and their relationships four genetic models of the various shell concentrations are described in this paper the genetic processes and distributions along an onshore offshore area were clarified on the base of taphonomic analysis pavements of opportunistic species of protochonetes are autochthonous assemblages living in quieter deeper more offshore waters near the maximum storm wave base the pavements are the result of reduced sedimentation the substrate was silty and water saturated with variable turbidity soupy mud transport by high energy processes is interpreted as the final formation process of polyspecific fragments concentrations with most extensive scope from intertidal zone to the maximum storm wave base the acrospirifer howellella and orientospirifer concentrations have been stirred by storm wave action and quickly buried after short transport tempestite model they are most easily preserved around the average storm wave base the polyspecific shell concentrations which include large bivalves are autochthonous assemblages living in shallow and relatively quieter water near shore environments autochthonous assemblages of the opportunist protochonetes bailiupingensis occurring in the bailiuping formation of the longmenshan area not only record of storm events but are also important features to identify and correlate the bailiuping formation in the field

reworking and discontinuities in holocene sedimentation in the nile delta documentation from amino acid racemization and stable isotopes in mollusk shells abstract the late holocene sedimentary history of the northwestern edge of the nile delta is reconstructed from amino acid racemization radiocarbon and stable isotope analysis of a series of bivalve shells from a core taken at the edge of lake maryut near alexandria amino acid racemization confirmed by radiocarbon and stable isotope analysis indicates that in many parts of the core mixed age mollusk assemblages are present dating of the time of sediment accumulation at various levels in the core is therefore based on the age of the youngest shells which are identified by amino acid racemization analysis lowest d l values ams radiocarbon analysis is used to determine the ages of the shells except for the most recent sediments last 100 yr for which aspartic acid racemization provides more precise ages amino acid racemization analysis of 59 shells from 21 levels in the 4 8 m holocene sequence in the core enabled identification of a large hiatus holocene sedimentation started at ca 2400 bc apparently corresponding to a westward shift of the course of the canopic nile distributary which lies to the east deposition continued at a rate of 1 4 mm per year ceasing at ca 550 bc at which time the canopic nile shifted eastward again and subsequently became defunct a marine connection during this period is indicated by stable isotope values of shells sediment accumulation began again only at the end of the 19th century when a series of irrigation canals was connected to the lake maryut basin stable isotope values indicate a strong freshwater influence deposition has continued to the present at a very high rate 19 mm per year due to supply of sediments by agricultural activity the relative ease with which racemization analyses can be carried out permits detailed analysis of core chronostratigraphy leading to more accurate reconstruction of core chronology hiatuses can be pinpointed and documented and age mixtures can be identified with appropriate individual shells being selected for ams radiocarbon analysis aspartic acid racemization analysis permits dating of samples from the last several hundred years a period for which radiocarbon analyses provide poor precision

do subglacial bedforms comprise a size and shape continuum understanding the evolution of the ice bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created however the formation of the suite of landforms generated at this boundary subglacial bedforms is a contentious issue that is yet to be fully resolved bedforms formed in aeolian fluvial and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes for subglacial bedforms a size and shape continuum has been hypothesised yet it has not been fully tested here we analyse the largest data set of subglacial bedform size and shape measurements ever collated 96 900 bedforms our results show that flutes form a distinct population of narrow bedforms however no clear distinction was found between drumlins and megascale glacial lineations msgls which form a continuum of subglacial lineations a continuum of subglacial ribs also exists with no clear size or shape distinctions indicating separate populations furthermore an underreported class of bedform with no clear orientation to ice flow quasi circular bedforms overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two potentially merging these three bedform types into a larger continuum

dunes and alternate bars in tidal channels a simple idealized model is proposed to predict the appearance of alternate bottom forms in tidal channels the model is based on the linear stability analysis of the flat seabed driven by tidal currents the hydrodynamics is described by means of the full three dimensional continuity and reynolds equations to quantify turbulent stresses the boussinesq assumption is introduced and an algebraic model is used for the eddy viscosity the morphodynamics is described by the exner equation and a simple sediment transport predictor when applied to tidal channels the model predicts the appearance of alternate bottom forms if the channel width is larger than a critical value this finding agrees with previous analyses however the results obtained show the existence of two different modes close to the conditions of incipient sediment motion or when the suspended load is intense the model suggests the appearance of an alternate sequence of shoals and pools the first mode characterized by a wavelength which might be comparable with the horizontal excursion of the tide however under such circumstances to provide accurate quantitative results the model should be extended to include the effects of the local acceleration and of the possible variations of the depth and width of the channel which are neglected in the analysis in all the other conditions the model predicts the appearance of a second mode presently termed tidal alternate bars this mode is geometrically similar to the first mode i e it is characterized by depositional and erosional areas which are found in an alternate arrangement but it has significantly shorter wavelengths in this case the wavelength of the bedforms scales with the water depth the physical mechanism generating tidal alternate bars appears to be the same as that generating tidal dunes and it cannot be described by means of a depth averaged approach

video observations of bed form morphodynamics in a meander bend a new optical remote sensing technique for estimating water depth from an oblique camera view is described the water surface and the bed were imaged simultaneously to create time dependent maps of the water surface velocities and the bed elevations that can be used to validate numerical models at high spatial and temporal resolution the technique was applied in a sandy meander bend at the university of minnesota saint anthony falls laboratory outdoor streamlab the root mean square differences between optical estimates of the bed and in situ observations ranged between 0 01 and 0 03 m mean bed form wavelength was 0 73 m and mean crest height was 0 07 m but both varied with distance around the meander bend bed form classification varied with distance downstream and sinuosity of bed forms varied with local radius of curvature bed form roughness scaled similarly to other natural riverine environments although wavelength and height magnitude and variability were larger than predicted by empirical formulations for straight reaches bed form translation rate varied between 1 and 5 mm s 1 estimates of velocity from particle image velocimetry piv on the water surface were 10 higher than in situ observations collected 0 05 m below the water surface using the piv observations to drive simple equations for bed load sediment flux we explained up to 72 of the observed variance in downstream sediment flux the new methodology described here provides nonintrusive high spatial and temporal resolution measurements of both the bed and the flow

spectral behavior of gravel dunes abstract spectral behavior of gravel dunes formed under different flow discharges is analyzed with an attempt to verify the 3 spectral law that has been confirmed extensively for sand dunes a schematic spectrum of gravel dunes is proposed based on the spectral analysis as well as results from the literature the results of spectral analysis show a significant deviation from the 3 spectral law for gravel dunes and the magnitude of deviation correlates with flow discharge possible explanations for the deviation from the 3 spectral law being associated with kinetic and geometrical characteristics have been explored to investigate the kinetic characteristics of gravel dunes a wavelet based method that calculates the celerity of dunes based on a pair of elevational time series is quantitatively tested our results suggest that 1 the kinetic explanation based on the relationship between dune celerity and dune length cannot fully explain the spectral behavior of gravel dunes 2 the geometrical explanation based on the self similarity hypothesis is confirmed by the relationship between dune length and dune height and 3 the development of gravel sheets accounts for the differences in kinetic and geometrical characteristics between gravel dunes and sand dunes

taphofacies models for epeiric sea environments middle paleozoic examples abstract skeletonized organic remains display various modes of occurrence which may be used to better understand the sedimentary dynamics of strata within which they occur aspects of skeleton biostratinomy and early diagenesis are distributed nonrandomly within the stratigraphic record and therefore are useful in discriminating taphonomic facies for purposes of taphonomic comparisons skeletonized marine taxa are reduced to five generally defined types massive arborescent univalved bivalved and multielement different skeletal types display different attributes which reflect specific responses to physical chemical and or biological processes the taphonomic properties of disarticulation reorientation and sorting fragmentation corrosion and abrasion skeletal dissolution and early diagenesis display patterns which are predictable with respect to a variety of inter related physico chemical parameters these can be quantified through indices which evaluate relative frequencies of occurrence sedimentary events alter the temporal and spatial homogeneity of processes which generate background taphofacies and superimpose event related properties thereby generating composite taphofacies such events produce taphonomic signature which in themselves correspond to specific environmental conditions i e water depth and event intensity indeed background and event related processes interact to generate complex but nonetheless diagnostic facies attributes useful in reconstructing paleoenvironments the comparison of standard indices among beds should allow the recognition of stratigraphic patterns and facilitate the diagnosis of systematic gradients among taphonomic properties deductively derived taphofacies models corroborated by empirical data from paleozoic strata illustrate the distribution of taphonomic properties with respect to environmental energy turbulence background sedimentation rate and sediment oxygenation these parameters also indirectly influence other less obvious factors including bioturbation and sediment chemistry trends in the distribution of taphonomic properties taphonomic gradients permit us to map otherwise unrecognized trends in these environmental parameters across a hypothetical onshore offshore transect within a generalized epeiric sea setting taphofacies models provide the quantifiable basis by which evolution of taphofacies may be gauged and then related to biotic and abiotic phenomena moreover taphofacies models evaluate the preservability of skeletal remains in different environmental settings and therefore provide information important in paleoecological studies

dynamics of nonmigrating mid channel bar and superimposed dunes in a sandy gravelly river loire river france abstract a field study was carried out to investigate the dynamics during floods of a nonmigrating mid channel bar of the loire river france forced by a riffle and renewed by fluvial management works interactions between the bar and superimposed dunes developed from an initial flat bed were analyzed during floods using frequent mono and multibeam echosoundings acoustic doppler profiler measurements and sediment grain size analysis when water left the bar terrestrial laser scanning and sediment sampling documented the effect of post flood sediment reworking during floods a significant bar front elongation spreading on margins and swelling was shown whereas a stable area no significant changes was present close to the riffle during low flows and falling limbs of floods intense sediment reworking on the top of the bar and lateral scouring occurred hydrological variations controlled the sediment supply in terms of phasing quantity and grain size delivered by surrounding channels during floods and thus superimposed dune development their development was also linked to the sediment availability armor layers riffle proximity their relatively constant height highlights a preferential adaptation on dune length during floods the role of each morphological forcing parameters riffle vs channel widening and curvature on the bar dynamics and evolution is stage dependent the shape dynamics and long term morphological evolution of the bar and of the river reach surrounding islands channel translation mainly depends on the presence of the natural riffle

palaeo environmental archive of groundwater surface water interaction zone the kebara wetlands carmel coast israel abstract the holocene sequence of the kebara wetlands a groundwater surface water interaction zone ecosystem was studied in a borehole core a retrieved from the eastern trough of the carmel coast of israel a multi proxy approach was used for environmental reconstruction and new ages were added for reassessment of the chronology the fauna mainly ostracods flora and palaeo salinity estimates indicate marginal wetland that experienced shrinkage and enlargement reflecting changing hydrological and climatic conditions new luminescence ages of sediments and radiocarbon dating of terrestrial seeds in the upper part of the sequence provide a more reliable and accurate chronology the lower part of the core between about 14 000 and about 7000 bp indicates mainly wetter conditions while the upper part dated to the last 7000 bp suggests drier conditions in general with a few wetter episodes the almost total disappearance of the fauna in the core after about 6000 bp is in agreement with regional climate records that document increasing aridity in the levant a comparison of modern 18o and 13c water and ostracod values from the timsah ponds the present remnants of the wetland with the values derived from ostracods in the drilling indicates that like today the past wetlands were fed mainly by the karstic carbonate rich yarkon taninnim mountain aquifer this paper emphasizes the importance of understanding the sources of the water feeding the wetlands for the re assessment of previous chronology that was based on total organic carbon toc 14c dating

fallout plutonium and natural radionuclides in annual bands of the coral montastrea annularis st croix u s virgin islands abstract we have investigated the banded coral montastrea annularis as a recorder of the history of fallout pu in surface seawater thirty annual growth bands representing growth during coral years 1951 1980 were subsampled from m annularis collected at st croix u s virgin islands coral years begin and end in late summer early autumn and are designated for the calendar year in which they end 239 240 pu was finite in coral years 1954 1980 and the coral pu record is very simply related to the fallout history of 90 sr peaks in coral pu in coral years 1959 and 1964 correspond to fallout peaks in 1959 and 1963 respectively peak broadening and time lags in the coral pu record as compared to the 90 sr fallout record are consistent with retention of fallout pu in surface seawater for about two years characteristic removal time during the period of major fallout and possibly longer thereafter the simplicity of the coral pu record and its close correspondence with fallout history suggest that 239 240 pu was incorporated into the coral skeleton with constant discrimination relative to ca the effects of speciation and oxidation state upon pu incorporation are presently unknown to aid the pu interpretation ca mg sr na and natural radionuclides 238 u 228 ra 232 th and 210 pb were also determined in the annual bands in small samples 0 5 g ca mg and na show correlated variations which could be due to seasonal variability in uptake the 238 u and 228 ra records were generally consistent with uptake at constant discrimination from surface water reservoirs of nearly constant concentration although one sample showed probable diagenetic addition of u 232 th was not detected with certainty this implies that terrigenous particles were not consistently entrapped within the coral skeleton interpretation of 210 pb was difficult because 226 ra was not measured montastrea annularis preserves a record of fallout pu to make this record useful it must be considered in the broadest possible geochemical context

validation of accumulation rates in teluk banten indonesia from commonly applied 210pb models using the 1883 krakatau tephra as time marker abstract teluk banten is a tropical shallow marine embayment on the north coast of java close to the krakatau volcanic complex the tsunami generated by the 1883 krakatau eruption resulted in the deposition of a tsunamite tephra layer on the bottom of teluk banten the krakatau event layer has been used as a time marker to validate 210 pb geochronological dating models this validation was performed to answer the question why should we believe excess 210 pb derived mass accumulation rates the commonly used models have therefore been applied to 210 pb activity profiles from 25 gravity cores models that have been validated are the constant flux and constant sedimentation cf cs with and without a surface mixed layer the constant initial concentration cic the constant rate of supply crs and the flux balance model after comparison of the mass accumulation rates mars of the different models with the mars obtained from the krakatau layer the following could be concluded firstly activity profiles without a surface mixed layer gave cf cs mars which were on average a factor 1 4 0 3 n 8 too high including a mixing rate of 0 5 0 4 cm 2 yr 1 into the model could explain this overestimation secondly for 210 pb activity profiles with a surface mixed layer the mars were in good comparison 1 0 0 3 n 12 with the mars derived from the krakatau event layer thirdly increased accumulation instead of reworking had to be the main cause of the comparatively thick upper layer of five cores with very high inventories fourthly assuming a variable accumulation rate and applying the cic model and crs model for these five cores the weighted average cic mars were in general more accurate than the crs mar finally the flux balance model which is not often used gave mars that were a factor 1 3 0 2 n 25 too high the advantage of this model is that it is independent of the profile shape the disadvantage is that a reliable and accurate initial activity over longer time scales has to be obtained

assessing decadal scale changes to a giant sand wave field in eastern long island sound three digital precision bathymetric data sets spanning 16 1 yr enabled a long term analysis of the geometric migration and volumetric changes to large bedforms in a 1 km2 region of eastern long island sound whereas a 1 yr study of sand wave mechanics during 1987 provided indirect evidence of long term southwestward transport this study adds a june 2003 data set and conclusively demonstrates a basinward southwestward progression of sand waves between 7 and 17 m in height in addition the modus operandi of sand wave migration during various temporal scales involves crestal flexing crestal rotation and differential migration along the crest a volumetric analysis suggests that the sand waves are in a waning phase of migration and early stage of preservation as sea level rises into the basin and flood dominant tidal currents decrease in strength

channel dynamics and geomorphic resilience in an ephemeral mediterranean river affected by gravel mining abstract gravel mining has been a widespread activity in ephemeral rivers worldwide whose long lasting hydrogeomorphological impacts preclude effective implementation of water and environmental policies this paper presents a gis based method for temporal assessment of morphosedimentary changes in relation to in channel gravel mining in a typical ephemeral mediterranean stream namely the rambla de la viuda eastern spain the aims of this work were to identify morphosedimentary changes and responses to human activities and floods quantify river degradations and analyze factors favoring fluvial recovery for further applications in other rivers aerial photographs and lidar topography data were studied to analyze geomorphic evolution over the past 70 years along a 7 5 km reach of an ephemeral gravel stream that has been mined intensively since the 1970s to evaluate changes in the riverbed we mapped comparable units applying morphological hydraulic and stability based on vegetation density and elevation criteria to 13 sets of aerial photographs taken from 1946 to 2012 a detailed spatiotemporal analysis of comparable units revealed a 50 reduction in the active section and a 20 increase in stable areas compared to the conditions observed prior to gravel mining instream mining was first observed in 1976 aerial photograph covering already up to 50 of the 1956 riverbed area river degradation since then was quantified by means of a lidar dtm and rtk gps measurements which revealed a 3 5 m incision that had started simultaneously with gravel mining climate and land use changes were present but the effects were completely masked by changes produced by instream gravel mining therefore river incision degradation was triggered by scarcity of sediment and lack of longitudinal sedimentary connection creating an unbalanced river system that is still adjusting to the present hydrosedimentary conditions

sediment transport of fine sand to fine gravel on transverse bed slopes in rotating annular flume experiments large scale morphology in particular meander bend depth bar dimensions and bifurcation dynamics are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream however existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes and in practice models are calibrated on measured morphology the objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near bed flow conditions with varying secondary flow intensity sediment sizes 0 17 4 mm sediment transport mode and bed state to test existing predictors we conducted over 200 experiments in a rotating annular flume with counterrotating floor which allows control of the secondary flow intensity separate from the streamwise flow velocity flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions we isolated separate effects of all important parameters on the transverse slope resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on shields number and strongly depend on bed state and sediment transport mode fitted functions are provided for application in morphodynamic modeling

headland associated banner banks generated during the last deglaciation near the strait of gibraltar gulf of cadiz sw spain the inception and evolution of large scale bedforms on the barbate platform gulf of cadiz sw iberian peninsula are investigated based on a detailed study of multibeam bathymetric data high resolution seismic profiles and tidal current simulations elongated rocky outcrops and several large scale bedforms classified as sand banks were identified on the platform barbate zahara el palmar el varadero and canos de meca banks the barbate and zahara banks exhibit the most complex internal stratigraphic architecture which comprises five seismic units the basal unit u1 is interpreted as incised valley infill and is overlain by nearshore bars u2 two high energy growth phases u3 and u4 that combine progradation and accretion form the present day external bank shape superimposed bedforms covered these banks under the modern hydrodynamic regime u5 the multiphase accretion and progradation of u3 and u4 in the zahara and barbate banks were closely linked to the presence of a palaeo headland termed here as palaeo cape trafalgar and strong tidal current eddies that resulted from the progressive flooding of the barbate platform during the last deglaciation this configuration was relatively stable while the rocky outcrops were exposed to sub aerial conditions forming a palaeo coast with coastal bluffs we suggest that during this period of coastal stabilization u3 and u4 grew as banner banks on either side of the palaeo cape trafalgar the present study proposes that the configuration of palaeo headland associated with palaeo banner banks zahara and barbate banks along each side of the palaeo cape trafalgar represents a transgressive analogue model of headland associated tidal bank systems developed in funnel shaped coastal systems terminating in narrow straits

sedimentary structures sorby and the last decade henry clifton sorby pioneered in the last century the description and especially the hydrodynamic interpretation of sedimentary structures together with their use as palaeocurrent indicators research completed since the last syntheses were published a decade ago shows that work along these lines continues to be necessary and relevant particularly as regards the physical explanation of structures and to present significant challenges and opportunities perhaps the most pressing needs are for a better understanding of 1 bedforms in gravels silts and carbonate sediments 2 tidal and especially sand wave bedding 3 hummocky and swaley cross stratification and 4 soft sediment and dewatering structures in turbidites many sedimentary structures present a little exploited opportunity to quantify process rates and define short time periods from the rock record

manzala lagoon nile delta egypt modern sediment accumulation based on radioactive tracers this study was undertaken to determine whether recent anthropogenic changes in the nile basin have affected the modern rate of sediment accumulation in the nile delta excess 210pb 137cs and 239 240pu were used to develop a sediment chronology for a core from central manzala lagoon the delta sector which has had the highest average rate of sediment accumulation during the holocene to about 0 7 cm year 1 excess 210pb was detected in the top 32 cm of the core yielding an accumulation rate of 1 2 cm year 1 higher than the mean rate for the holocene a high 137cs 239 240pu ratio requires a reactor source possibly chernobyl for these nuclides low concentrations of excess 210pb and weapons fallout nuclides precluded recognition of changes in sediment accumulation rate in manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the nile delta

dunes in the world s big rivers are characterized by low angle lee side slopes and a complex shape dunes form critical agents of bedload transport in all of the world s big rivers and constitute appreciable sources of bed roughness and flow resistance dunes also generate stratification that is the most common depositional feature of ancient riverine sediments however current models of dune dynamics and stratification are conditioned by bedform geometries observed in small rivers and laboratory experiments for these dunes the downstream lee side is often assumed to be simple in shape and sloping at the angle of repose here we show using a unique compilation of high resolution bathymetry from a range of large rivers that dunes are instead characterized predominantly by low angle lee side slopes 10 complex lee side shapes with the steepest portion near the base of the lee side slope and a height that is often only 10 of the local flow depth this radically different shape of river dunes demands that such geometries are incorporated into predictions of flow resistance water levels and flood risk and calls for rethinking of dune scaling relationships when reconstructing palaeoflow depths and a fundamental reappraisal of the character and origin of low angle cross stratification within interpretations of ancient alluvial sediments dunes in the world s big rivers are dominated by lee side slopes with angles of less than 10 according to a bedform analysis of high resolution bathymetric datasets

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

sedimentology clay mineralogy and palaeosols of the mid carnian pluvial episode in eastern spain insights into humidity and sea level variations this study examines rainfall variations of the mid carnian pluvial episode cpe based on the continental fluvial sedimentology palaeosol and clay mineralogy records of the stable meseta e spain in the formation examined manuel fm or k2 fm the cpe is represented by three regressive transgressive sequences r t or subunits k2 1 k2 2 and k2 3 from base to top each subunit broadly consists of a genetic stratigraphic sequence bearing well developed highstand lowstand and transgressive system tracts hst lst and tst hydromorphic features in the palaeosols suggest changes in the activity of both ground and surface waters the clay mineral assemblage is dominated by illite with a minor presence of kaolinite and traces of smectite in some samples after ruling out tectonism in the study area climate and eustatism emerge as the main allogenic controls in the sedimentary record differentiated sedimentary facies and architectural elements in the k2 2 subunit were likely controlled by both a more humid climate and source area while k2 1 and k2 3 were more related to base level changes and eustatic control the presence of more waterlogged pedotypes and of kaolinite and traces of smectite in the clay mineral assemblage of k2 2 also indicates increased humidity notwithstanding our data do not point to intense rainfall periods for the cpe in e spain

genetic significance of an albian conglomerate clastic wedge eastern carpathians romania abstract the impressive 2000 m thick conglomerates of the bucegi formation exposed in the southernmost part of the eastern carpathians were interpreted initially as large alluvial fans and later suggested to be deposited as deepwater submarine slope deposits however the routing system of the coarse sediment transfer from the source area to the deepwater slope source to sink analysis has not been explained and the mechanisms involved in the shelf sediment storage and bypass onto the slope have not been discussed the present research on the albian bucegi formation has provided the following new insights on their source to sink aspect 1 that the upper member of the bucegi formation with its frequent channelized and sheet like fine conglomerates and sandstones contrasts greatly with the middle and lower members of deepwater slope and basin floor origin the upper member is interpreted as fluvial and shallow marine deposits that were temporarily stored and reworked on a shelf albeit a narrow one bridging the area between the deforming hinterland and the deepwater slope deposits 2 the upper and middle members are genetically linked and developed through the basinward migration of a large scale hundreds of metres in amplitude clinoform with relative flat lying topsets and slightly steeper few degrees coarser grained slopes that built out to the south and southeast a configuration that is common along continental margins and also generally along all types of deepwater basin margins 3 the middle member contains a range of submarine sediment density flows that vary from high density mobile debris flows to lower density sandy turbidites the sediment textures sorted grain populations inherited from the shelf sorting factory can to some extent still be recognised in the slope stratigraphy and 4 the large 10 20 m diameter carbonate and metamorphic olistoliths that are ubiquitous on the shelf and to a lesser extent slope reflect the steep gradients and very active tectonic setting of the fractured and thrusted hinterland from which these outsized blocks were transported onto the adjacent shelf the now proposed narrow shelf platform of the albian bucegi basin margin thus functioned to temporarily store sands and gravels to distinctly sort some of this sediment and to eventually bypass both sorted and new flood generated unsorted materials onto the slope compared with other basin margins this albian bucegi margin was extremely coarse grained because of its proximity to the actively deforming mountain range to a fractured basement that produced more gravel than sand to the great sediment flux from steep short rivers and to the narrowness 10 20 km of the shelf

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

recent sedimentation and sediment accumulation rates of the ba lat prodelta red river vietnam abstract the ba lat river is the major distributary of the red river system in north vietnam to assess the recent to subrecent depositional processes in the ba lat prodelta a detailed sediment analysis was conducted bottom samples were collected during two field surveys one in the dry season winter and one in the wet season summer a steep frontal prodelta slope is characterized by very rapid sedimentation tens of cm per year of muddy sediments under influence of the turbid river plume beyond direct influence of the river plume the bottom slope decreases and bottom transport by the prevailing southward directed currents becomes important coarse grained tempestites alternate with the dominating muddy sediments downcore changes in the 234 th activities indicate that the subaqueous delta progrades to the southwest with erosion and reworking of older sediments occurring north of the present outlet the southwestward progradation is also encountered in the trend of 210 pb activities indicating that this process has continued for at least 100 years avulsion of the ba lat outlet in 1973 has led to a decrease in sedimentation rates north of the ba lat outlet

tidal bundle sequences in the jordan sandstone upper cambrian southeastern minnesota u s a evidence for tides along inboard shorelines of the sauk epicontinental sea abstract this study documents for the first time tidal bundling in a lower paleozoic sheet sandstone from the cratonic interior of north america providing insights into the hydrodynamics of ancient epicontinental seas the jordan sandstone upper cambrian in the upper mississippi valley contains large scale planar tabular cross sets with tidal bundle sequences which were analyzed in detail at an exceptional exposure tidal bundle sequences neap spring neap cycles were delineated by foreset thickening thinning patterns and composite shale drapes the latter of which represent accumulations of mud during the neap tides of neap spring neap tidal cycles fourier analysis of the bundle thickness data from the 26 measurable bundle sequences revealed cycles ranging from 15 to 34 bundles per sequence which suggests a semidiurnal or mixed tidal system along this part of the late cambrian shoreline we extend the tidal interpretation to widespread occurrences of the same facies in outcrops of lesser quality where the facies is recognizable but too few bundles are exposed for tidal cycles to be measured by doing so this study shows that tidally generated deposits have a significant geographic and temporal extent in upper cambrian strata of central mid continent north america the deposition and preservation of tidal facies was related to the intermittent development of shoreline embayments during transgressions the tidally dominated deposits filled ravined topographies that were repeatedly developed on the updip parts of the shoreface resulting coastal geomorphologies accompanied perhaps by larger scale changes in basinal conditions and or configuration led to changes in depositional conditions from wave dominated to tide dominated outcrops of the jordan sandstone tidal facies in the upper mississippi valley represent the farthest inboard recorded transmission of ocean generated tides in the laurentian epicontinental seas demonstrating that tidal currents were significant agents in the transport of sand along the far cratonic interior shorelines of cambrian north america the results of this study improve the facies level understanding of the genesis of sheet sandstones furthermore tidalites documented here occur in a specific position within a sequence stratigraphic architecture for the jordan sandstone this provides a framework to compare these ancient deposits and processes to younger e g carboniferous epicontinental systems where stratal and sediment dynamics are better documented

nile delta extreme case of sediment entrapment on a delta plain and consequent coastal land loss abstract accelerated erosion of egypt s nile delta coast during this century has generally been attributed to construction of two dams at aswan entrapment of sediment in lake nasser behind the high dam and effects of barrages and river control structures on river nile deposition below aswan also considered important are natural factors including delta subsidence rising sea level and strong coastal current processes this study proposes that more influential in controlling coastal land loss is the near complete entrapment of modern and reworked nile sediment on the nile delta plain sediment is primarily retained in an extremely dense network of irrigation and drain channels and also in wetlands in the northern delta the increased number of artificial canals more than 10 000 km of waterway is a response to egypt s drive to augment its much needed agricultural production by perennial irrigation the drastically reduced amount of sediment now reaching the sea discharged primarily from lagoon outlets and several canal mouths is removed by strong easterly directed coastal and innermost shelf currents the nile delta is an extreme example of a depocenter which has been completely altered by man from an active prograding delta to a locally eroding coastal plain

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

significance of molluscan shell beds in sequence stratigraphy an example from the lower cretaceous mannville group of canada1 detailed study of marine shales the ostracod zone within a cretaceous third order transgressive regressive sequence in the alberta foreland basin reveals a systematic association between shell beds and parasequence scale flooding surfaces including surfaces of maximum flooding the ostracod zone a subsurface lithostratigraphic unit known as the calcareous member in outcrop consists of 10 20 m of black shale and bioturbated sandstones with many thin fossiliferous limestones parasequences shallowing up cycles 2 3 m thick were delineated within this transgressive unit based on lithology sedimentary structures degree of bioturbation dinoflagellate diversity total organic carbon and carbon sulphur ratios many flooding surfaces are firmgrounds or hardgrounds shell rich limestones occur in three different positions relative to these flooding surfaces and each has a distinctive bioclastic fabric and origin i base of parasequence shell beds bops lie on or just above flooding surfaces in the deepest water part of a parasequence they are thin up to a few centimetres graded or amalgamated skeletal packstones wackestones composed of well sorted granular shell and are interpreted as hydraulic event concentrations of exotic shell debris ii top of parasequence shell beds tops are capped by flooding surfaces at the top shallowest water part of a parasequence they typically are several decimetres thick are physically amalgamated packstones grainstones or bioturbated wackestones and contain abundant whole as well as comminuted shells these are composite multiple event concentrations of local shells iii mid sequence shell beds rest on as well as are capped by firmgrounds or hardgrounds and are intercalated between parasequences in the deepest water part of the larger sequence they are laterally extensive lime mudstones a few decimetres thick with sparse shells in various states of dissolution recrystallization and replacement these beds are terrigenous starved hiatal concentrations and record maximum flooding within the ostracod zone offshore sections of the ostracod zone typically contain several starved mid sequence shell beds underscoring the difficulty of identifying a single maximum flooding surface within a third order sequence

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data