burial and degradation of organic carbon in louisiana shelf slope sediments abstract the primary focus of this paper is to better understand carbon burial on the louisiana continental margin using spatial scales that covered various shelf depositional areas far field and near field sediment and organic carbon inputs relative to river mouth proximity and covering a variety of sedimentation rates box cores samples were collected in july 2003 cores were collected along two depositional transects extending westward and southward from the southwest pass sw pass a key difference between the two transects sampled in this study was the greater occurrence of mobile muds derived from spillover from shallower regions along the westward 50 m isobaths the dominant mechanism for mixing in the surface active zone saz on the inner louisiana shelf was due to physical not biological forces burial efficiencies for organic carbon 57 2 91 5 and total nitrogen 44 2 86 9 ranged widely across all shelf stations lower burial efficiencies for bulk organic carbon total nitrogen and pigment biomarkers were associated with mobile muds west of southwest pass chlorophyll a concentrations were significantly higher than pheopigments at depth at the mississippi river and southwest pass stations making up 40 4 and 77 4 of total pigment concentrations in the saz and 46 2 and 63 2 in the accumulation zone az respectively these results are in agreement with earlier plant pigment studies which showed that a large fraction of the phytodetritus delivered to the inner shelf was derived from coastal and river diatoms the amount of lignin preserved with depth decreased with increasing residence time in the saz and diagenetic zone dz along the canyon transect but not along the western transect trends for lignin concentration followed previously identified surface sediment trends indicating overall lower burial of refractory terrestrial material at depth with greater distance offshore

the importance of bioturbation to continental slope sediment structure and benthic processes off cape hatteras north carolina abstract even though the continental slope off cape hatteras has sediment accumulation rates on the order of 1 cm year large areas of soft sediment are intensively reworked by infaunal organisms primary sedimentary structures have been completely replaced with biogenic structures surface sedimentary structures are dominated by the bioturbational activities of a deep burrowing infauna to at least 30 cm the layer actively mixed by the benthos as evidenced by sediment profile and x ray images is estimated to range from 5 to 20 cm with the residence time for particles within the surface mixed layer ranging from about 4 5 to 18 years the biological mixing parameter g ranges from 0 4 to 5 5 which indicates moderate to strong biological mixing relative to accumulation and strata formation bioturbation contributes to the dynamic forces affecting the surface sediments by decreasing compaction of sediment layers and dilating sediment fabrics by sediment mixing and introducing large water filled burrows and voids to subsurface sediments the sediment profile images captured numerous subsurface feeding voids and worms in the process of making deep burrows many of which extended below the 5 to 10 cm average depth of the apparent color redoxpotential discontinuity layer high rates of accumulation of organic rich sediment lead to high standing stocks of benthos and intensive feeding burrowing activity that result in organic rich stratagraphic sequences that are thoroughly mixed cape hatteras is a apparent focusing point for the transport of shallow water sediments to the deep sea sediments across other areas of the continental slope just 100 s of kilometers south of cape hatteras are not as thoroughly mixed or biologically active

the impact of hurricane diana on the north carolina continental shelf abstract intense storms including hurricanes are believed to have an important impact upon the biota and sediment cover on the continental shelf hurricane diana crossed onslow bay north carolina during september 1984 and provided an opportunity to examine its effect on the sea floor an area in the bay transited by the hurricane had been surveyed previously by side scan sonar 3 5 khz echosounding and underwater television we re surveyed the area in november 1984 with the same techniques and collected box cores for sedimentary structure analysis the post hurricane survey yielded no unequivocal evidence of hurricane impact on the sea floor and surprisingly showed an abundance of seemingly delicate benthic organisms thriving on the impacted area sedimentary structures in the box cores included rip up clasts and cross laminations that are indicative of a dynamic sedimentary environment but they could have formed during non hurricane storm conditions the lack of a dramatic signature on the sea floor from hurricane diana is attributed to the low sediment influx and frequent occurrence of intense storms on the north carolina shelf these factors result in an armored depositional environment that shows little response to the passage of each successive storm

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

heavy metals in a contaminated australian estuary dispersion and accumulation trend very high concentrations of zn pb cu and cd occur in the muddy bottom sediments of lake macquarie a saline coastal lagoon in southeastern australia the trace metals emanate from industrial sources especially a lead zinc smelter at the northern end of the lake individual metal concentrations decrease progressively away from the source area but at differing rates zn is most mobile and cd appears to be deposited first they approach natural background levels in the southern part of the lake mn shows a reverse trend but ni co ag and fe rarely rise above background levels shallow cores in the lake bed penetrated a metal enriched surface zone 15 35 cm thick underlain by uncontaminated sediments with natural background metal concentrations sedimentation rates determined from radiocarbon ages on shells in the cores mainly range between 0 15 and 0 5 mm yr 1 over the 85 years since industrialization commenced less than 5 cm of mud has accumulated on the lake bed bioturbation is invoked to account for the depth to which the sediment has been enriched in heavy metals

storm surge versus turbidite origin of the coniacian to santonian sediments in the eastern part of the bohemian cretaceous basin a flyschoid facies occurs in the b ezno formation coniacian up to santonian of the eastern marginal part of the bohemian cretaceous basin according tojerzykiewicz 1970 1971 this facies is of deep water turbidite origin he based his interpretation on the study of sedimentary structures new palaeogeographic reconstruction of lithofacies relations investigation of deep drillings and detailed sedimentological analysis however allowed new results concerning the sedimentary environments and depositional mechanism of this facies according to the new model presented here this flyschoid facies was deposited in a shallow marine environment clayey sedimentation was the natural response to normal environmental conditions whereas sandstone intercalations reflect anomalous conditions during heavy storms during these events sands were transported basinwards up to distances of 25 km with normal bottom currents as well as turbidity currents acted as transporting mechanisms this flyschoid facies corresponds to other examples of clayey sequences with sandy storm layers

characterisation of collapsing loess by seismic dilatometer abstract structural collapse and sudden volume changes represent a major geotechnical issue particularly in loess soils there are different criteria for assessing collapse potential based on laboratory test results which require the collection of undisturbed samples from test pits this can be a complicated and costly procedure often financially unjustified for smaller projects this paper presents the results of seismic dilatometer tests sdmt performed at a single location in a loess soil in belgrade in addition to the results of single oedometer collapse tests performed on high quality samples from test pits after comparing laboratory test results it was possible to determine that in samples collected from boreholes dry unit weight is approximately 20 higher than in block samples taken from test pits while moisture content is between 1 and 4 higher unit weight estimated from dmt is on average 15 higher than the unit weight obtained from block samples the constrained modulus mdmt determined by dmt are highly compatible with oedometer modulus eoed obtained from samples at natural moisture content this paper presents two possible ways of identifying collapsing loess based on intermediate dmt parameters and the ratio of g0 mdmt the tests results indicate that if the ratio between the material index id and the horizontal stress index kd is greater than 5 the danger of collapse is imminent simultaneous observation of the changes of id and kd with depth on a semi log graph in the same scale is recommended in this way the relative distance between them may be clearly noticed the larger the distance becomes the greater the risk of collapse in the collapsing loess ratio g0 mdmt is found to be higher than 21 for kd less than 0 6 while in non collapsing loess g0 mdmt is less than 21 for higher values of kd in terms of dmt loess is considered as underconsolidated soil which is one of the most common definitions of loess

some thoughts on fine grained sediment transport and deposition abstract fine sediments are receiving greater emphasis due to economic significance as source rocks for petroleum the often nearly continuous record of depositional histories and the volumetric importance in the geologic record distribution of these particulates is driven primarily by ocean circulation deposition is primarily controlled by planktic biologic filtering aggregation and reworking early diagenesis is controlled by bacterial processes with consequent changes in bulk and chemical properties most fine particulates are initially deposited in the continental margins and then move to deep ocean floors by mass wasting and high concentration flows stability of these fine deposits even on slopes of gentle gradient is controlled primarily by water content which in turn is a function of sedimentation rate and texture of the supply mass transport can occur in a variety of forms from slow creep to catastrophic failures of large scale a sequence of morphologies can result from the various forms of movement most of the fine grained stratigraphic record urgently needs reevaluation and restudy models of paleogeographic reconstructions on a large scale need to include the results of physical and biological oceanographers since the older simpler scenarios of locations of zones of high bioproductivity and of the patterns of major ocean currents have been greatly modified in recent years biological oceanographers have contributed models for contemporary upwelling systems that have changed the thinking of paleobiologists and biostratigraphers working with biogenically dominated fine sedimentary rocks

the use of radon 222 as a tracer of sediment irrigation and mixing on the washington continental shelf abstract observations of the natural radioisotope rn 222 were used in conjunction with radiochemical biological and sedimentological techniques to investigate the irrigation and mixing of sediment at three sites about 90 m water depth along the washington continental shelf the rn 222 deficit difference between observed and predicted concentrations within the seabed was greatest near the columbia river during the summer molecular diffusion at most locations and times could account for only a portion of the deficit irrigation and mixing of the seabed explain the remainder biological mixing bioturbation and physical irrigation wave and tidal pumping have relatively little effect on the rn 222 deficit physical mixing erosion and deposition has a significant effect soon after a major erosion event storm however no such event occurred prior to the observations the conclusion is that biological irrigation and molecular diffusion are the primary causes of the rn 222 deficit and that biological irrigation is responsible for the observed spatial and temporal variations in the deficit therefore biological irrigation is greatest near the columbia river during the summer the spatial increase of irrigation near the columbia is probably due to a relatively large population of tube dwelling filter feeding polychaetes the temporal increases of irrigation during the summer is probably due to annual growth cycles of the benthic community and is not due to water temperature changes

sample disturbance effects in silt abstractthis paper presents results of testing good quality piston tube samples and parallel block samples from three silt sites in ireland and norway theoretical work and laboratory strain damage

depositional processes on an ancient and modern muddy shelf northern california the modern eel river shelf and analogous pleistocene rio dell formation in northern california provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence and thereby enables further understanding of muddy shelf processes the modern shelf is the site of accumulation of a thick deposit of holocene mud both large scale sediment distribution patterns and small scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation even on a high energy storm dominated coast the major factors in preservation of this flood signature are the cohesive behaviour of fine grained sediments and episodically rapid rates of sediment input the rio dell formation includes approximately 400 m of mostly fine grained shelf deposits that accumulated offshore from a palaeo eel river mouth the shelf sediments comprise four depositional sequences sequence 1 records progradation from outer to inner shelf depths facies trends closely resemble across shelf trends on the modern shelf suggesting that processes were similar detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf muddy facies of the rio dell sequence are characterized by bioturbated clayey silts interbedded with event layers of several types clay rich silt layers are interpreted as flood deposits and physically stratified coarse silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms sediment transport calculations and consideration of grain size distributions of bioturbated sediments which form the bulk of the rio dell sequence suggest that these sediments are the result of biological homogenization of the fine grained flood deposits and of the coarser grained storm deposits the results of this study in general indicate that fine grained shelf deposits do preserve a distinguishable if subtle record of depositional processes

mechanical behavior of silty soils of the venice lagoon as a function of their grading characteristics the main feature of the shallowest quaternary basin of the well renowned historic city of venice italy and its surrounding lagoon is the presence apparently without any regular trend in depth and site of a predominant silt fraction this is always combined with clay and or sand forming a chaotic and erratic interbedding of different sediments whose mineralogy is however variable in a relatively narrow range due to a unique geological origin and a common depositional environment after a brief description of the basic soil indexes of the venice lagoon soil the present study based on a comprehensive geotechnical laboratory investigation describes the range of variation of the most relevant time independent geotechnical properties moreover a new grain size index combining the geometrical characteristics of the particle distribution is introduced it is shown that the soil response at large and very small strains can be related to this grain size index which appears to be able to include the in

late quaternary linkage of sedimentary records to three astronomical rhythms and the asian monsoon inferred from a coastal borehole in the south bohai sea china abstract the bohai sea was formed by subsidence during the cenozoic some 2000 3000 m of fluvial lacustrine and marine sediments has been deposited in this basin previous studies focused mainly on the transgression history with little examination of orbital variation in relation to other areas within the asian monsoon domain here we present the late quaternary results of a new borehole in the south bohai sea optically stimulated luminescence and radiocarbon dating which provide concordant age estimates were employed to generate an initial chronology for the borehole after refining the chronology through astronomical tuning the results showed that 1 the grain size variation represents asian monsoon intensity which was dominated by both solar insolation major and global ice volume minor forcing 2 the magnetic susceptibility indicates river incision processes which were sensitive to orbital tilt with influence from solar insolation 3 the vegetation coverage responded to global ice volume coupled obliquity changes and that 4 neither external nor internal factors could dominate the paleoenvironmental evolution on orbital timescales in an independent way and they are both integrated in a complex pattern we conclude that three different astronomical rhythms have affected coastal evolution and that the sedimentary records in the south bohai sea china result from the nonlinear interaction and the complex response to driving processes

new model for the emplacement bioturbation and preservation of fine scaled sedimentary strata we present a new quantitative model for the formation and preservation of sedimentary fabric based on interacting sedimentation and bioturbation the model is one dimensional and is forced by fluctuation of the sedimentation rate which affects deposition of sediment possessing primary depositional fabric primary fabric is modified by bioturbation which is represented as a depth limited reaction term model output includes depth in seabed and preservation quotient a measure of relative preservation of primary versus biogenic fabric at each depth the required parameters sedimentation rate and bioturbation rate can be derived from studies of seabed processes model output can be compared directly to observations of both modern and ancient sedimentary strata

chemical evidence of differential particle dispersal in the southern washington coastal environment aliphatic hydrocarbons cupric oxide oxidation products of lignin and polycyclic aromatic hydrocarbons pah were analyzed by capillary gas chromatography in sediments from the southern washington continental shelf and slope the concentration of diploptene relative to plantwax n alkanes increased systematically in surface sediments with distance offshore along east west transects of the study area and remained constant in surface sediments along the midshelf silt deposit analogous trends were also observed for the concentration of cinnamyl phenols relative to vanillyl phenols and total methylphenanthrenes relative to phenanthrene these changes in sedimentary composition are evidence that diploptene from some terrestrial source lignin characteristic of non woody vascular plant tissue and a fossil organic material contained within weathered rock debris disperse across the washington continental shelf and slope in geographic patterns distinct from that for other river derived chemically related materials the compositional variations are explained by the particulate associations of the land derived chemicals and differential hydraulic dispersion of their respective carrier particles after discharge at the mouth of the columbia river

analysis and interpretation of piezocone data on the silty soils of the venetian lagoon treporti test site this paper reports the main results of an extensive piezocone testing campaign performed over the last years at the treporti test site venice italy within a long lasting and comprehensive research project aimed at developing a reliable geotechnical model of the heterogeneous and highly stratified venetian lagoon basin the project included the construction of a full scale vertical walled cylindrical test bank together with a detailed monitoring system of surface settlements pore water pressures subsoil strains and stresses beneath the loaded area the analysis of the large amount of data thus available referring to different phases of the loading history confirms the great potential of piezocone as an in situ testing technique especially for stratigraphic profiling of the predominantly silty subsoil of the venetian lagoon but at the same time reveals some limitations of widely used empirical correlations for the relevant soil characterization with special reference to compressibility and conso

sediment distribution patterns on the galicia minho continental shelf abstract a sedimentological and bathymetric study of the minho galicia shelf shows a strong contrast between a southern shelf region with a thin partially relict cover of sands and gravel and a northern region where fine grained sediments predominate this contrast is explained through differences in the sediment supply the oceanographic environment storms and ocean currents and the morphology of the shelf which results from its underlying tectonic framework most sediment is supplied to the galicia minho shelf by river discharges onto the minho shelf particularly that from the douro river in the northern part of the shelf the galician rias act as sediment traps rather than sediment suppliers the bulk of the sediment washes out of the rivers during episodic storm events while most of the coarse sediments remain deposited close to the coast the fine grained material is exported to the outer areas of the shelf subsequently coarse sediments close to the coast are transported southwards by the littoral drift whereas the fine grained material is frequently resuspended through the action of the large swells who influence reaches deep into the water this frequent resuspension has a long term sorting effect on the sediments furthermore resuspended sediments on the middle and outer regions of the shelf are transported northwards by a poleward flowing bottom current as a consequence of the differential transport of coarse sediments to the south and of the fine grained sediments to the north the outer reaches of the minho shelf are relatively poor in recent sediments in many areas relict sediments as well as features associated with ancient coastlines and river mouths still appear as seabed features in contrast the northern regions of the shelf are covered by a thin veneer of fine grained material that smooth other most of these fossil features the fine grained sediment fractions mostly very fine sands to coarse silts are deposited in two large mud patches the douro and the galicia mud patches which are situated at water depths of around 100 120 m these two mud patches are both controlled by the local hydrodynamics and morphology the beiral de viana to the west of the douro mud patch is a plateau up to 20 m high lying parallel to the shelf break and is a morphological expression of an underlying horst system this plateau acts as a barrier that prevents the drift of some of the fine grained material to the west out over the shelf break and the continental slope the galicia mud patch is situated on the eastern part of the galician shelf to the north of the douro mud patch it is situated near the extension of the porto tomar fault which results in the shelf being usually steep in this region down to a depth of about 100 m west of this area the slope is much more gentle northward transport of the sediment is strongly reduced by the e w trending outcrops of plutonic and metamorphic rocks

large scale coastal change in the columbia river littoral cell an overview abstract this overview introduces large scale coastal change in the columbia river littoral cell crlc covering 165 km of the southwest washington and northwest oregon coasts the littoral cell is made up of wide low sloping dissipative beaches broad coastal dunes and barrier plains three large estuaries and is bounded by rocky headlands the beaches and inner shelf are composed of fine grained sand from the columbia river and are exposed to a high energy winter wave climate throughout the holocene the crlc has undergone large fluctuations in shoreline change trends responding to a variety of coastal change drivers including changing rates of sea level rise infrequent yet catastrophic co seismic subsidence events a large regional sediment supply inter annual climatic fluctuations el nino cycles seasonally varying wave climate and numerous anthropogenic influences human influences on the crlc include construction of over 200 dams in the columbia river drainage basin dredging of navigation channels removing sand to upland sites and offshore deep water sites and construction of large inlet jetties at the entrances to the columbia river and grays harbor the construction of these massive entrance jetties at the end of the 19th century has been the dominant driver of coastal change through most of the littoral cell over the last hundred years presently some beaches in the littoral cell are eroding in response to nearshore sediment deficits resulting from a ebb jets of the confined entrances pushing the previously large shallow ebb tidal deltas offshore into deeper water and b waves dispersing the nearshore delta flanks initially onshore and then alongshore away from the jetties this overview describes 1 the motivation for developing a system wide understanding of sediment dynamics in the littoral cell at multiple time and space scales 2 the formation and approach of the southwest washington coastal erosion study and 3 an introduction to the papers in this special issue

the origin and preservation of a major hurricane event bed in the northern gulf of mexico hurricane camille 1969 cores collected from mississippi sound in the gulf of mexico were studied using 210 pbxs and 137 cs geochronology x radiography granulometry and a multi sensor core logger our results indicate the presence of a widespread sandy event layer that we attribute to hurricane camille 1969 an initial thickness of more than 10 cm is estimated from the cores which is large compared to the time averaged apparent accumulation rate of 0 29 0 47 cm y 31 physical and biological post depositional processes have reworked the sandy layer producing a regional discontinuity and localized truncation and resulting in an imperfect and biased record of sedimentary processes during the storm the oceanographic and sedimentological processes that would have produced an event bed during hurricane camille are simulated using a series of numerical models i e 1 a parametric cyclone wind model 2 the swan third generation wave model 3 the adcirc 2d finite element hydrodynamic model and 4 a wave current bottom boundary layer model that is coupled to transport and bed conservation equations trans98 the simulated bed ranges from 5 cm to over 100 cm within a tidal channel near the barrier islands seaward of the islands the bed is more than 10 cm in thickness with local variability the magnitude and local variability of the storm bed thickness are consistent with the observed stratigraphy and geochronology on both the landward and seaward sides of the barriers 2002 elsevier science b v all rights reserved

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

a simple model of flow sediment organism interaction abstract previous models of organism sediment interaction have been limited primarily to eddy diffusion type mixing while such models are useful in interpreting some stratigraphic records they cannot be expected to provide mechanistic insights into the diversity of interactions among sedimentary processes organism activities and boundary layer flows to provide a more general formulation capable of dealing with all three types of processes in concert a simple discrete time markov model is generated this version of the model deals explicitly only with particulate and not liquid phases the initial formulation is a two compartment ergodic model of deposit feeding particle selection by deposit feeders results in incorporation of the selected particles into fecal pellets and fecal pellet disaggregation completes the cycle particles which are more strongly selected or which are incorporated into more robust pellets thus spend more time and reach higher relative concentration in the fecal pellet compartment the next level of complexity is achieved by adding burial from the free sediment non fecal pellet compartment this model predicts that particles which are more strongly selected or incorporated into more robust fecal pellets will have greater residence times in surficial sediments both pellets and free sediments before they become part of the stratigraphic record and will therefore achieve higher concentrations in surficial sediments than will less preferred particles the full flow sediment organism system is reached by adding the potential for lateral advection of particles the probability of such advection is allowed to differ between pellets and free sediments increasing selection and robustness of fecal pellets then can either increase or decrease relative concentration and residence time of a given particle type in surficial sediments the model thus provides a means of explaining differences in stratigraphic patterns among materials deposited simultaneously it also suggests that deposit feeder selection may increase the average age i e time since initial deposition of surficial sediments by maintaining preferred particle types near the surface selection may likewise control the texture of surficial sediments in a manner which is easily confused with purely physical sorting parameters which require careful measurement in testing these simple predictions are selectivity by deposit feeders probability of selection rate of fecal pellet breakdown under realistically simulated conditions probability of pelletal disaggregation differential erodibilities of pellets versus free sediments relative probabilities of lateral advection and rates of burial of free sediments versus pelletized sediments probabilities of burial

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin abstract mudstone dominated shallow marine rocks of the kaskapau formation were deposited on a low gradient ramp that spanned the foredeep of the western canada foreland basin during the late cenomanian to middle turonian organic clay rich and silt rich mudstone accumulated on the flank of the forebulge 200 km from the western shoreline within this mudstone a large proportion of the clay minerals are organized into silt and very fine sand size aggregate grains these aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts the latter along with siliceous silt grains form wave and combined flow ripples graded beds scour fills and ripple tail lamination where sand size sediment comprising detrital siliceous calcareous bioclastic or phosphatic grains is present it is molded into combined flow ripples hcs gutter casts and lags thus all sediment grades indicate storm wave and current reworking of the sea floor at a distance of 200 km offshore the common occurrence of clay minerals in the form of aggregate grains organized into combined flow ripples and parallel lamination implies advective transport of clay minerals as bedload driven by combined flows across a very low gradient ramp on the distal part of this ramp latest cenomanian rocks include thin tongues of sw prograding quartz rich sandstone that was derived from an emergent forebulge this source was drowned during the early turonian eustatic rise when the sediment abruptly changed to organic rich mudstone dominated by clay mineral aggregates this compositional change was mainly a response to a sudden increase in distance to detrital sources in the west rather than a dramatic increase in water depth throughout much of early to middle turonian time the sea floor in the forebulge region lay above effective storm wave base for silt estimated at 70 m at sea level lowstands wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier upward sequences lags are interpreted to correspond to falling stage lowstand and early transgressive systems tract deposits on the western margin of the basin previous studies may have substantially overestimated water depth for organic and clay rich calcareous mudstones in the western interior seaway

transport and accumulation of river derived sediment on the washington continental shelf usa the combined results of many physical oceanographic geochemical and geological investigations provide a coherent picture of the sedimentology of the washington continental shelf the major source of modern sediment is the columbia river sediment on the shelf is transported by bottom currents resulting from surface wind stress and gravity waves which occur as individual storm or wave events lasting one to several days primarily during the winter months field measurements of the sediment response to wind and wave generated bottom currents suggest that the modern sediment is transported as suspended load and disperses primarily northward parallel to the isobaths and is associated with a well developed mid shelf silt deposit smaller quantities of sediment are transported seaward over the shelf edge and into the numerous submarine canyons that incise the shelf analysis of available wave data suggests that thresholds of sediment motion were exceeded on the order of 22 16 and 1 5 of the time annually on the inner central and outer shelf respectively bottom current measurements suggest that threshold conditions were exceeded 13 and 6 of the time annually on the inner and central shelf respectively measurements of accumulation rates using 210 pb geochronology show that about 67 of the annual sediment discharge from the columbia river is being deposited in the mid shelf silt deposit 6 is being deposited over the shelf edge on the open slope and 11 is accumulating in the four major submarine canyons

seabed dynamics of the inner amazon continental shelf temporal and spatial variability of surficial strata the continental shelf southeast and northwest of the amazon river mouth is overlain by a sediment layer of about a meter in thickness characterized by 210pb profiles consisting of one or more segments with nearly uniform excess activity uniform 210pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments however biological activity is minimal in this area hence this surficial layer sl is a result either of physical reworking of the sediments or of rapid possibly episodic deposition of sediment factors controlling the formation of the sl were examined during the amasseds project between august 1989 and october 1991 primarily using 210pb t1 2 22 3 yr activity profiles and x radiography the thickness and character of the sl were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions e g discharge stage wind stress one of these stations was reoccupied during semidiurnal and fortnightly periods additionally replicate sediment cores were obtained at stations in order to assess small scale spatial variability of geochemical and sedimentological characteristics in the seabed the sl thicknesses in replicate sediment cores obtained at each site were found to vary within 5 cm normalized thickness of the sl decreased by an average of 17 cm between august 1989 and february 1990 a period of increasing wind stress during falling to rising river discharge the sl thickness subsequently increased slightly 8 cm from february to may 1990 and increased again 27 cm between may 1990 and october 1991 the maximum sl thicknesses were observed in october a period of low wind stress and minimal river input suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge variations in sl thickness are reflected by changes in suspended sediment mostly as fluid muds as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when sl thickness is at a minimum although a significant sl was present during all of the sampling periods changes in the character of 210pb profiles at two of the stations suggest that substantial perhaps complete removal and redeposition of the sl occurred some time between february and may preserved strata i e below the sl is characterized by greater evidence of bioturbation and increased sand content but otherwise is similar to that of the sl long term preservation of strata is thought to occur through episodic suspension and redeposition of the sl with net accumulation of decimeter thick hiatus bounded layers

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

re evaluation of coquinoid sandstone depositional model upper jurassic of central wyoming and south central montana the most extensive jurassic marine transgression in north america reached its maximum limits during the oxfordian age at this time siliciclastic sediments were being brought into the north american seaway from an uplifted zone to the west within this setting complexes of sand ridges and coquinoid sands layers were deposited coquinoid sandstones appear to fill erosional scours and were interpreted as channel fills re evaluation of these features in the light of recently discovered attributes of modern shelf sediments and processes has produced a revised model of coquinoid sand deposition in this setting coquinoid sandstones which fill channel like scours in the oxfordian upper jurassic rocks of central wyoming and south central montana appear to have formed through the migration of sand waves across the crests of inner shelf sand ridges during periods of storm and tidal flow erosion in the zone of flow reattachment in the troughs between sand waves resulted in the development of shell lags migration of these scour zones as the sand waves advanced resulted in the deposition of sheet like coquinoid sandstone bodies sand waves crossing the ridge crest tended to migrate more slowly and to be overstepped by later sand waves sand wave troughs thus buried have channel like geometries with apparent epsilon bedding

polycyclic aromatic hydrocarbon distribution within lower hudson river estuarine sediments physical mixing vs sediment geochemistry abstract sediments and porewaters from two cores one from the east river new york and one from newark bay new jersey were sampled for polycyclic aromatic hydrocarbons pahs and other geochemical markers including 210 pb specific activities despite what appears to be similar sources of pahs to sediments within each core as inferred by ratios of alkylated to non alkylated pahs and pah isomer ratios sediments and associated pahs have undergone distinctly different depositional processes at each site sediments from the core in the east river appear to have been subject to intense physically driven resuspension resulting in selective depletion of low molecular weight pahs within the core presumably due to processes such as enhanced desorption and scouring of particle surfaces although sediment pah concentrations were higher in the east river core compared to the newark bay core porewaters were depleted of the majority of pahs analysed in the east river core relative to the newark bay core precluding quantifying sediment porewater pah distribution coefficients in this core sedimentary variables such as c n ratio particle surface area and sedimentary soot carbon were not related to organic carbon normalized pah distribution coefficients k oc obs rather in the core from the newark bay site k oc obs were influenced by sediment mixing and porewater dissolved organic carbon doc results indicate that in urban coastal areas the physical factors influencing time scales of sediment resuspension and deposition may be of primary importance over particle geochemistry in determining whether pahs will likely equilibrate between sediments and pore waters

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

a geochemical study of long chain n aldehydes in washington coastal sediments a series of n aldehydes c20 to c32 with strong even to odd carbon preference was identified in the mixture of solvent extractable lipids isolated from various washington coastal sediments a limited survey of the lipid composition of surface waxes of foliage and cuticular waxes of pollen from several major plant species indigenous to the pacific northwest revealed that similar series of n aldehydes are intrinsic to regional vegetation debris from such plants discharged at the mouth of the columbia river represents a preformed source of the n aldehyde series accumulating in sediments from the washington coastal region although the evidence suggests n aldehydes are largely introduced erosionally to this region as a chemical component of land derived debris and are not formed in situ in the coastal sediments further study is warranted to establish the postdepositional stability of this series of compounds relative to other lipids of higher plantwax origin despite but few literature reports of the occurrence of these geochemicals long chain n aldehydes are very likely common in many sediments from environments that receive an input of detrital organic matter from higher plants

towards a sediment budget for the santa cruz shelf a conceptual model is presented for the northern monterey bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine grained sediment introduced into monterey bay the principal sources of the fine sediment are the three rivers that enter monterey bay the san lorenzo pajaro and salinas rivers accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion and also are high relative to other documented mud accumulations of the west coast continental shelves

sediment mixing and accumulation rates in the sulu and south china seas implications for organic carbon preservation in deep sea environments abstract recent rates of carbon burial in two deep sea basins the sulu and south china seas are contrasted to determine factors influencing organic carbon preservation in deep sea sediments the sulu sea is an oxygen deficient warm water basin whereas the adjacent south china sea is more typical of open ocean conditions high resolution sea bed profiles of 14c reveal that accumulation rates for the sulu sea are 2 3 times higher than the south china sea at any given water depth e g 1 3 g cm 2 kyr 1 versus 4 3 g cm 1 kyr 1 respectively at 3000 m higher accumulation rates for the sulu sea are attributed to higher terrigenous input and better carbonate preservation in the warmer bottom waters benthic mixing rates determined using 210pb geochronology generally are lower in the sulu sea 0 004 0 254 cm2 yr 1 as compared with the south china sea 0 17 1 57 cm2 yr 1 especially at the 3000 m and 4000 m sites in the sulu sea where benthic mixing is negligible despite the higher bottom water oxygen levels in the south china sea organic carbon concentration profiles are strikingly similar for the two basins at any given water depth with similar concentration profiles higher accumulation rates in the sulu sea result in equivalently higher carbon preservation rates as primary production is thought to be similar for both basins if anything slightly higher for the south china sea the production rate can not explain the observed differences in carbon preservation in addition benthic mixing rates apparently do not play a major role in carbon preservation as extremely low rates at the deeper sulu sea would predict relatively low carbon preservation contrary to our observations we conclude that sediment accumulation rate is the dominant control on carbon preservation in this area of the western equatorial pacific

the benthic boundary layer and sediment transport the major problems facing scientists studying marine boundary layer fluid mechanics in 1979 concerned the specific mechanismic operating in the regions of the top and the bottom of the boundary layer at the top the mechanisms of fluid escapement from the boundary layer and mixing into the ocean interior could only be postulated approximations of diffusivity across the top of the layer were being debated the values of which were more articles of faith than physically validated estimates cf armi 1979 garrett 1979 at the bottom the intermittent generation of stress cf gordon 1975 heathershaw and simpson 1979 was held responsible for the wide variability observed in the drag coefficient and the thickness of the viscous sub layer was claimed to be greater than that traditionally found from laboratory studies caldwell and chriss 1979

overconsolidation and stiffness of venice lagoon sands and silts from sdmt and cptu abstractthis study is part of an extensive research program carried out at the treporti test site venice italy where a cylindrical trial embankment was constructed and monitored from the beginning of its construction until complete removal 4 years later this paper concentrates mainly on the evaluation of overconsolidation and stiffness of the venice lagoon sands and silts the possibility of estimating the overconsolidation ratio ocr in sand by the combined use of seismic dilatometer sdmt tests and piezocone cptu tests is investigated a tentative correlation for estimating the ocr in sand from the ratio mdmt qt is constructed field compression curves have been back figured from 1 m field oedometer curves reconstructed from local vertical strains measured by a sliding deformeter under the embankment center the sdmt and cptu soundings performed before embankment application and postremoval have permitted analyzing how the ocr caused by the embankment was reflected by the before after sdmt and

internal tides as a major process in amazon continental shelf fine sediment transport abstract the description of hydrodynamics associated with the extensive reef system on the shelf break adjacent to the amazon river is still a challenge for ocean sciences despite the discharge of more than one billion tons of cohesive sediment per year the outer continental shelf of the world s largest river presents very low concentrations of suspended sediment near the bottom and an absence of modern fine sediment deposits nearly one hundred kilometers before the shelf break the offshore limit of the subaqueous delta consists of a sigmoidal clinoform standing between 40 and 70 m in depth a depositional feature that cannot be explained solely by estuarine like gravitational circulation this paper aims to test the hypothesis that internal tides have a major role in the control of offshore fine sediment transport for that we implement a set of tridimensional non hydrostatic and high resolution up to 2 m vertical and 2 km horizontal delft3d models the experiments showed that even disregarding river plume buoyancy wind drag superficial waves and ocean currents the exclusive interaction between barotropic tidal currents bathymetry and the stratification structure of the ocean is capable of generating asymmetrical current patterns compatible with modern deposition the maximum shelf slope and the relative depth between the outer shelf and the pycnocline represent the main factors influencing the generation and shoreward propagation of internal tides over time spring neap cycles are eventually capable of reverting cross shore subtidal transport tendencies while seasonal variability in ocean stratification modulates the intensity of baroclinic processes

mangrove expansion in the gulf of mexico with climate change implications for wetland health and resistance to rising sea levels abstract black mangroves avicennia spp are hypothesized to expand their latitudinal range with global climate change in the 21st century induced by a reduction in the frequency and severity of coastal freezes which are known to limit mangrove colony extent and individual tree size the gulf of mexico is a prime candidate for population expansion to occur because it is located at the northward limit of black mangrove habitat this may come at the expense of existing coastal saline wetlands that are dominantly spartina spp marsh grasses the present study was conducted to focus on the implications of a marsh to mangrove transition in gulf wetlands specifically 1 wetland resistance to accelerating eustatic sea level rise eslr rates 2 resistance to wave attack in large storms increased cyclonic storm frequency intensity is predicted with future climate warming and 3 organic carbon sequestration and wetland soil geochemistry field sites of adjacent and inter grown avicennia germinans mangrove and spartina marsh populations in similar geomorphological setting were selected in back barrier areas near port aransas and galveston tx elevation surveys in the more mature port aransas site indicate mangrove vegetated areas are 4 cm higher in elevation than surrounding marsh on an average regional scale and 1 2 cm higher at the individual mangrove scale 210pb and 137cs accumulation rates and loss on ignition data indicate that mineral trapping is 4 1 times higher and sediment organics are 1 7 times lower in mangroves at port aransas this additional mineral trapping does not differ in grain size character from marsh accumulation elevation change may also be effected by soil displacement of higher root volumes in mangrove cores port aransas porosities are lower in mangrove rooted horizons with a corresponding increase in sediment strength suggesting mangrove intervals are more resistant to wave induced erosion during storm events port aransas mangroves exhibit higher pore water redox potentials and salinities over entire core depths and depressed ph over rooted intervals suggesting a distinct diagenetic environment exists relative to marsh sites the rooting network which introduces oxygen into the sediment and focuses evapo transpiration and salt exclusion within this zone may prove advantageous when competing with grasses by elevating salinities to levels that are toxic for spartina trends observed in the more mature systems of port aransas are generally absent in galveston suggesting the youth and physically shorter stature of these systems means they have not yet established a unique sediment signature