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data collected on modern sand ridges in adjacent areas by other workers has led to this reevaluation of a largely unpublished but extensive vibracore dataset from a mid shelf sand ridge off new jersey usa the presence of dipping reflections within other ridges is particularly notable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

acoustic backscatter measurements from littoral seabeds at shallow grazing angles at 4 and 8 khz direct measurement of acoustic scattering from the seabed at shallow grazing angles and low kilohertz frequencies presents a considerable challenge in littoral waters specifically returns from the air water interface typically contaminate the signals of interest to address this issue drdc atlantic has developed a sea going research system for measuring acoustic scatter from the seabed in shallow water environs the system known as the wideband sonar wbs consists of a parametric array transmitter and a superdirective receiver in this paper backscatter measurements obtained with the wbs at two sandy shallow water sites off north america s atlantic coast are presented data were collected at 4 and 8 khz at grazing angles from 3 15 the backscattering strength is similar at both sites and below about 8 it appears to be independent of frequency within the statistical accuracy of the data the measurements show reasonable agreement with model estimates of backscatter from sandy sediments a smal

stratigraphy and genesis of a modern shoreface attached sand ridge peahala ridge new jersey abstract we investigated the genesis and evolution of peahala ridge a modern shoreface attached sand ridge 1 km 6 km in size and 4 7 m in bathymetric relief through an integrated sedimentologic and stratigraphic study involving vibracoring box coring grab samples high resolution seismic paleontology radiocarbon dating and oceanographic measurements near surface strata of peahala ridge include six important stratigraphic units modern shoreface upper ridge sand lower ridge sand swale inlet fill middle holocene back barrier and late pleistocene strandplain radiocarbon dating and determination of the stratigraphic relationships indicates that peahala ridge formed initially from an ebb tidal delta associated with a tidal inlet so thwestward migration of the inlet channel a vector resultant of landward coastal retreat and southerly longshore drift cut and then filled the swale separating peahala ridge from long beach island following inlet closure peahala ridge developed its present form as a shoreface attached shoreline oblique bathymetric feature hydrodynamic processes have played a major role in evolution of the ridge including considerable growth and accretion this combination of long term eustatic and short term hydrodynamic factors is the best explanation for the present morphology and internal stratigraphy of peahala ridge

sand ridges off sarasota florida a complex facies boundary on a low energy inner shelf environment abstract the innermost shelf off sarasota florida was mapped using sidescan sonar imagery seismic reflection profiles surface sediment samples and short cores to define the transition between an onshore siliciclastic sand province and an offshore carbonate province and to identify the processes controlling the distribution of these distinctive facies the transition between these facies is abrupt and closely tied to the morphology of the inner shelf a series of low relief nearly shore normal ridges characterize the inner shelf stratigraphically the ridges are separated from the underlying pleistocene and tertiary carbonate strata by the holocene ravinement surface while surficial sediment is fine to very fine siliciclastic sand on the southeastern sides of the ridges and shell hash covers their northwestern sides the cores of these holocene deposits are a mixture of both of these facies along the southeastern edges of the ridges the facies boundary coincides with the discontinuity that separates the ridge deposits from the underlying strata the transition from siliciclastic to carbonate sediment on the northwestern sides of the ridges is equally abrupt but it falls along the crests of the ridges rather than at their edges here the facies transition lies within the holocene deposit and appears to be the result of sediment reworking by modern processes this facies distribution primarily appears to result from south flowing currents generated during winter storms that winnow the fine siliciclastic sediment from the troughs and steeper northwestern sides of the ridges a coarse shell lag is left armoring the steeper northwestern sides of the ridges and the fine sediment is deposited on the gentler southeastern sides of the ridges this pronounced partitioning of the surficial sediment appears to be the result of the siliciclastic sand being winnowed and transported by these currents while the carbonate shell hash falls below the threshold of sediment movement and is left as a lag the resulting facies boundaries on this low energy sediment starved inner continental shelf are of two origins which both are tied to the remarkably subtle ridge morphology along the southeastern sides of the ridges the facies boundary coincides with a stratigraphic discontinuity that separates holocene from the older deposits while the transition along the northwestern sides of the ridges is within the holocene deposit and is the result of sediment redistribution by modern processes

stratigraphic variability due to uncertainty in model boundary conditions a case study of the new jersey shelf over the last 40 000 years abstract prediction of stratigraphy by numerical sedimentary models is influenced by a series of geological boundary conditions paleo bathymetry sediment supply sea level ocean storm climate and tectonics these boundary conditions evolve non linearly over time and have considerable uncertainty this study explores the impact of the uncertainty of complex boundary conditions on stratigraphic prediction two numerical models are sequentially run the climate driven hydrological model hydrotrend generates a time series of discharge and sediment load at the river mouth which then feed into the process based stratigraphic model sedflux 2d sedflux disperses sediment in the fluvio marine domain the bedload fluxes drive floodplain and mouthbar deposition while suspended sediment is dispersed in the ocean through hypopycnal plumes seafloor sediment is reworked by ocean storms failures and subsequent transport as sediment gravity flows sedflux records the thickness of the deposited sediment and the grain size preserved over time along a longitudinal profile one base case simulation and 20 sensitivity tests of the new jersey shallow margin over the last 40 000 yr serve to explore the impact of uncertain boundary conditions initially the shelf is exposed and arctic conditions prevail in the drainage area paleo temperature and precipitation estimates differ significantly between different community climate system model realizations impacting river sediment flux predictions subsequently high sediment supply from the rivers draining the melting laurentide ice sheet has a dominant impact on the shelf stratigraphy drainage basin characteristics are strongly controlled by the hard to define details of the laurentide ice sheet dynamics over the last 10 000 yr the shelf becomes sediment starved and storm dominated but the paleo storm conditions are uncertain and thus require a wide range of values shallow seismic data have been used to validate the large scale deposited thicknesses of the sedflux prediction the base case sedflux prediction for the sedimentary architecture of the new jersey shelf is consistent with the acoustically observed distribution of major sediment wedges due to the strong forcing of the relatively well constrained sea level changes the range in thickness predictions over the sensitivity tests is well within the lateral variations reconstructed from the observed seismic data sedflux predictions and a data set of 654 seafloor samples taken on the new jersey shelf between 50 and 150 m water depth shows a subtle fining towards deeper water sedflux systematically overpredicts the component of fine sediments at the seafloor likely because the model does not predict shell hash paleo storm climate is found to have a high uncertainty and strongly impacts the predicted grain size distributions we advocate a modeling approach which couples a series of sensitivity experiments to a predicted base case experiment in that way the stratigraphic variability caused by uncertainty in the boundary conditions is evident for later users

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

seismic and bathymetric evidence for four different episodes of iceberg scouring on the new jersey outer shelf possible correlation to heinrich events abstract re analysis of dense chirp seismic surveys on the outer new jersey shelf reveals two sets of shallowly buried incisions the incisions are linear to slightly sinuous oriented ne sw and exhibit cross cutting relationships we interpret both sets as paleo iceberg scours one set cuts into the r horizon a regional unconformity that formed 45 40 ka and which was subsequently buried by the finer grained outer shelf sediment wedge osw the second set is part of an erose boundary between a layered lower unit of the osw and an upper more transparent unit the erose boundary scours are deeper and have steeper slopes than the r horizon scours the latter often exhibit bermed edges whereas the former do not these differences in cross sectional morphology are likely determined by the material properties of the sediments being scoured sand at the r horizon and clay at the erose boundary the orientation of both sets of scours is consistent with previously recognized iceberg scours in stratigraphically younger seafloor on the outer new jersey shelf in 110 150 m water depths located 40 km to the northeast we argue that heinrich events recurring periods of massive iceberg flux into the north atlantic represent the most likely times for transporting icebergs to these latitudes based on stratigraphic relationships a recently published ambient sea level curve and radiocarbon age constraints we attribute the r horizon scours to heinrich event h4 37 cal ka the erose boundary scours to h3 30 cal ka and the seafloor scours to h2 23 cal ka and or h1 17 cal ka facies changes immediately following the r horizon and erose boundary scours may be related to heinrich event forced climate changes perhaps the onset of interstadial conditions and associated melt water pulses floods these pulses floods repeatedly carried fine grained rock flour produced by widespread glacial erosion to the new jersey shelf

sediment transport in the new york bight north american atlantic shelf vincent c e swift d j p and hillard b 1981 sediment transport in the new york bight north american atlantic shelf mar geol 42 369 398 aanderaa current meter data collected during the course of noaa s new york bight project are sufficiently extensive in time 135000 observation hours and space 41 stations to permit an estimate of the sediment transport in this area the analysis is based on mean flow observations the role of wave oscillatory currents in resuspending sediment is considered but not explicitly included in the sediment transport calculations an estimate of the potential sediment transport rate qb at each station for three different threshold velocities uth 12 16 and 20 cm s 1 were made using a bagnoldtype transport equation qb const uc uth 3 for uc uth qb 0 for uc uth where uc is the mean current speed comparison was made between the results from this simple equation and other bedload and suspended load transport rates which include wave data for a limited subset of the bight data this comparison indicates that the bagnold results are reasonable for the along isobath transport estimates but are not reliable for the cross isobath transport in the cross isobath direction waves appear to play a dominant role in determining the transport rate the comparison also indicates that the bagnold approach tends to overestimate transport in deep water in shallow water resuspension of sand and rotor pumping of current meters both may become important and sediment transport calculations may not be accurate fine sediment suspended transport is approximately double the potential bedload transport for fine sand 0 02 cm but does not dominate the total transport as is believed to occur on the washington shelf smith and hopkins 1972 the data show that the new york bight is a storm dominated shelf with the general southwestward drift of water 6 cm s 1 modulated by more intense storm induced flows the transport calculations indicate that the bulk of sediment transport occurs during the winter months when wind stress is at a maximum and the water column is well mixed two major transport provinces are present a the hudson shelf valley and b the rest of the shelf the shelf valley acts as a sink and a barrier to the continuity of the mainly southwestward transport of sediment 104 g cm 1 yr 1 along the shelf within the valley the potential transport of material is of the order of l05 g cm 1 yr 1 along the valley axis progressive vector transport paths for fine sediment indicate that removal of sediment out of the ends of the valley can occur rapidly however consider ation of the finesediment budget for the whole hudson shelf valley and of the attenua tion of wave activity with depth show that these results are not inconsistent with the presence of high mud concentrations in the valley up valley sediment rates predominate during the period for which data are available

kerogen chemical structure and source organisms in a cenomanian organic rich black shale central italy indications for an important role of the sorptive protection pathway abstract the bonarelli horizon is an important cenomanian turonian black shale in the umbria marche appenines of central italy it appears as the final term of a cyclic deposition of ca 40 thinner laminated clayey or siliceous organic rich levels the kerogen of the cenomanian clayey black level located 12 m below the bonarelli termed nn 8c was examined via microscopic spectroscopic and pyrolytic methods the chemical structure of this kerogen is based on a network of long aliphatic chains linked via ether bridges however in addition to the classical normal chains nn 8c comprises c40 chains with a lycopane skeleton such chains have only been previously reported in kerogen pyrolysates of two samples derived from the microalga botryococcus braunii however any contribution of b braunii can be ruled out in the case of nn 8c kerogen since it is nanoscopically amorphous based on 13c values of their pyrolysis products a common algal origin is demonstrated for the above two types of chains and hence there is a major algal input to this kerogen however some incorporation of bacterial lipids and a low contribution of higher plant material are indicated by the nature of some pyrolysis products although a large contribution of pyrite is noted in the nn 8c sample thus revealing an intense sulphate reducing activity no significant sulphur incorporation took place in the organic matter accordingly the vulcanization pathway is not implicated in the formation of nn 8c kerogen the selective preservation and the degradation recondensation pathways were possibly involved but they are unlikely to have played a major role in fact the sorptive protection process favoured by the clayey nature of the mineral matrix was probably the main pathway implicated in the formation of nn 8c kerogen and this process may have provided an efficient protection to various diagenetically sensitive constituents especially lipids

strataform overview of its design and synthesis of its results abstract the strata formed on continental margins record the history of both marine and terrestrial events occurring on earth the strataform program was created to develop a better understanding of relationships between these events and margin stratigraphy in order to obtain the maximum information from strata they are being examined simultaneously on various temporal and spatial scales and their formation is being studied where events and accumulation are known to be active the general objectives of strataform are to add geological perspective to studies of sedimentary processes to constrain stratigraphic interpretations better and to develop numerical models relating processes and stratigraphy this research is being undertaken on margins off northern california and new jersey which provide unique opportunities for investigation of short term and long term stratigraphy respectively this volume and paper focus upon studies undertaken off northern california north of cape mendocino this area is tectonically active with a coastal mountain range narrow shelf and input of sediment primarily from the eel river recent estimates indicate that 1 to 3 10 7 t yr of mud silt and clay are supplied to the continental shelf sand accumulates on the inner shelf 70 reaches the continental slope or deeper during the previous lowstand of sea level sediment discharge was 25 greater and probably led to hyperpycnal debris and other flows transporting sediment down the slope on the eel shelf flood and storm events combine to create normally stratified fine grained layers with basal sand and much terrestrial organic debris these layers are modified through time but some can be buried and preserved subsurface flood layers seem to impact observations of acoustic backscatter on the middle shelf and subsurface fluids gas freshwater affect electromagnetic measurements on the inner shelf budgets of eel river mud accumulation for the past century indicate 20 trapped on the adjacent shelf and 20 on the upper slope 150 600 m the remaining 60 is dispersed to more distal locations over holocene time scales eel river sediment has built a small sandy subaqueous delta and a subtle bulge of muddy sediment on the middle shelf north of the river gullies have been eroded on the open slope during lowstands of sea level and have accreted upward during highstands a massive failure has formed the humboldt slide due to earthquake activity and unstable substrates possibly from excess pore pressures and gas the tectonic setting has impacted margin stratigraphy from small scales fluid expulsion pockmarks to large scales spatial variation of late cenozoic sedimentation the broad dispersal of eel sediment demonstrates the three dimensional character of the resulting stratigraphy including the large scale clinoform structure developed on the shelf upper slope the rollover point topset foreset boundary for this feature is the shelf break i e below sea level which is important information for stratigraphic interpretations of sea level change

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

contemporary genesis of sand ridges in a tideless erosional shoreface abstract a sand ridge field located over a retreating deltaic lobe in the ebro delta nw mediterranean is characterized using three sets of co located multibeam bathymetric data acquired in 2004 2013 and 2015 measurements of near bottom currents high resolution seismic profiles and aerial photographs the aim of this study is to illustrate the processes and timing involved in the initial stages of sand ridge development the sand ridge field extends from the 5 to 15 m isobaths and the ridges have maximum heights and wavelengths of 2 5 and 400 m respectively they have straight crests that are arranged obliquely to the shoreline and are composed of fine sand in general the sand ridges are symmetric although asymmetries with the lee side of the ridge facing to the se and to the nw are also present the genesis of the sand ridge field is closely related to the contemporary evolution of the ebro river mouth the change of the main river channel in the 1940s led to progressive abandonment of the former river mouth and to severe coastal retreatment 37 m yr 1 making large amounts of sediment available for ridge formation the persistent mistral winds nw induce near bottom currents flowing towards the se which are able to rework and transport sandy sediments the sand ridges are currently active with mean se migration rates of 10 m yr 1 most likely in pulses when high speed currents occur wave storm events induce reverse flows e se which reshape the ridges to symmetric or opposite asymmetry geometries the bedform morphologies the oblique arrangement with respect to the shoreline the angle between the strongest current and the crestlines and the sediment grain size match well with those of shoreface connected attached sand ridges and particularly with the initial stages of sand ridge development on storm dominated continental shelves sediment availability shoreline retreat relatively strong near bottom currents induced by winds seafloor irregularities and relative sea level rise on the ebro delta combine to provide a suitable transgressive environment for sand ridge development time scales related to sand ridges are usually of hundreds thousands of years but here it is demonstrated that the genesis of sand ridges can take place within a few decades the studied bedforms are unlikely to persist in the absence of rapid sea level rise leading to sediment scarcity and wave and current reworking

biogeochemistry of lipids in surface sediments of the peru upwelling area at 15 s abstract organic carbon lycopane a monoene of 2 6 10 trimethyl 7 3 methyl butyl dodecane c37 alkenones and 20 5 and 22 6 polyunsaturated fatty acid concentrations in two box cores from the peru continental margin area at 15 s in 90 and 268 m water depth have depth profiles that are synchronous and appear to indicate an historical record of fluctuating higher productivity lower productivity enso periods the u37k ratio calculated using c37 2 and c37 3 alkenones in the 268 m water depth core in the center of the upwelling zone varies with depth in the core in a manner consistent with the u37k functioning as an historical recorder of euphotic zone temperature concentrations and cpi for n alkanes c25 c31 are reported for both cores a c27 anthrasteroid has been identified and quantified in the 268 m water depth core

paleogeographic setting and depositional architecture of a sand dominated shelf depositional system miocene utsira formation north sea basin abstract the middle late miocene utsira sandstone of the north sea basin contains a fully preserved regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca 8 myr the sediment dispersal system was defined by 1 sediment input through a prograding strandplain platform coast to shelf bypass and regional basin centered transport and deposition within an elongate seaway 2 a high energy marine regime 3 very low rates of sediment supply and accumulation in the accommodation dominated seaway 4 high sediment reworking ratio and consequent abundance of autochthonous sediment 5 regional along strike sediment transport and 6 local to subregional landward sediment transport shelf systems were primarily nourished by sediment reworked from the shetland strandplain which prograded eastward into the central viking trough the viking strait lay between the constructional platform and the nondepositional horda platform southward longshore transport on the high energy shoreface and shallow shelf platform constructed the mounded south viking shelf shoal southward building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system low angle sigmoid clinoforms with downstepping aggradational tops are distinctive architectures of the strike fed sand bodies the combination of strong marine currents and slow but continual sand supply from the shetland strandplain created regional sandy shelf depositional systems that individually covered 3500 to 6000 sq km of basin floor defining elements of the shelf shoal systems include their location within the basin axis mounded morphology stratal architecture and construction by amalgamated marine sand facies

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

seabed characterization on the new jersey middle and outer shelf correlatability and spatial variability of seafloor sediment properties abstract nearly 100 collocated grab samples and in situ 65 khz acoustic measurements were collected on the new jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data and more recently with chirp seismic reflection profiling eighteen short cores were also collected and probed for resistivity based porosity measurements the combined data set provides a basis for empirically exploring the relationship among the remotely sensed data such as backscatter and reflection coefficients and directly measured seabed properties such as grain size distribution velocity attenuation and porosity we also investigate the spatial variability of these properties through semi variogram analysis to facilitate acoustic modeling of natural environmental variability grain size distributions on the new jersey shelf are commonly multi modal leading us to separately characterize coarse 4 mm fine

a mechanism for the formation and maintenance of shore oblique sand ridges on storm dominated shelves a remarkable set of shore oblique sand ridges occupies the inner portion of the storm dominated middle atlantic and south atlantic bights off the east coast of the united states of america a mechanism for present day formation and growth of these distinctive geological features follows from a linearized analysis of the stability of alongshore periodic topographical perturbations based on a depth averaged fluid dynamical model with a simple representation of sediment transport the analysis indicates exponential growth of shore oblique features as a result of offshore deflection of storm driven alongshore flows at ridge crests which leads to a convergence of sediment flux because the effective carrying capacity decreases with increasing distance offshore the analysis indicates a set of conditions required for ridge growth model solutions for topography under conditions favorable for ridge growth are strikingly similar to the observed sand ridges

tidal induced large scale regular bed form patterns in a three dimensional shallow water model the three dimensional model presented in this paper is used to study how tidal currents form wave like bottom patterns inclusion of vertical flow structure turns out to be necessary to describe the formation or absence of all known large scale regular bottom features the tide and topography are treated as a coupled system and the potential free instabilities in this system are investigated a linear stability analysis is used to study the dynamics of bed forms this yields information on the role of physical mechanisms such information cannot be obtained by direct numerical nonlinear simulation the basic state represents a horizontal elliptical flow veering in vertical direction over a flat bottom it is shown that in such a system modes can grow which have characteristics of both tidal sand banks and sand waves the model predictions are compared with observations and show good agreement

the role of erosion by fish in shaping topography around hudson submarine canyon abstract an 800 km2 area of rough topography around the head of hudson canyon off the eastern united states is attributed to erosion by tilefish lopholatilus chamaeleonticeps and associated species of crustaceans the rough topography has a relief of 1 10 m occurs in water depths of 120 500 m and has been cut into a semilithified silty clay substrate since the onset of the holocene transgression commercial fishing activity indicates that a large population of tilefish which dig burrows in the sea floor occupy the area of the rough topography average tilefish burrows are 1 6 m in diameter and 1 7 m in depth they have a clustered not uniform distribution and their average density is 2 500 per km2 the close match of areas of rough topography and high til fish populations the active burrowing of the sea floor and the clustered distribution of the burrows suggest that the hummocky topography in this area may be the result of continuous erosion by tilefish and associated crustaceans during the holocene an erosion rate of 13 cm per 1 000 years is necessary to create this topography during the past 13 000 years and 18 cm per 1 000 years if as is more likely based on the depths at which tilefish presently are found the erosion started 9 000 years ago

modification of the quaternary stratigraphic framework of the inner continental shelf by holocene marine transgression an example offshore of fire island new york abstract the inner continental shelf off fire island new york was mapped in 2011 using interferometric sonar and high resolution chirp seismic reflection systems the area mapped is approximately 50 km long by 8 km wide extending from moriches inlet to fire island inlet in water depths ranging from 8 to 32 m the morphology of this inner continental shelf region and modern sediment distribution patterns are determined by erosion of pleistocene glaciofluvial sediments during the ongoing holocene marine transgression much of the shelf is thus an actively forming ravinement surface remnants of a pleistocene outwash lobe define a submerged headland offshore of central fire island east of the submerged headland relatively older pleistocene outwash is exposed over much of the inner continental shelf and covered by asymmetric sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment erosion of the eastern flank of the submerged pleistocene headland over the last 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface attached ridges offshore of western fire island west of the submerged headland erosion of pleistocene outwash continues in troughs between the sand ridges resulting in modification of the lower shoreface comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of 1000 m westward since formation comparison of modern sediment thickness mapped in 1996 1997 and 2011 allows speculation that the nearshore shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges

relict iceberg keel marks on the new jersey outer shelf southern hudson apron swath sonar bathymetry reveals sinuous furrows 400 m wide kilometers long and 4 m deep inscribed in semilithified clays on the southern hudson apron we interpret these as keel marks created by floating icebergs detached from the retreating laurentide ice sheet since ca 25 ka keel mark orientations suggest two phases of iceberg rafting these phases could correlate with heinrich meltwater events h2 and h1 ca 25 and 17 ka bracketing the late wisconsinan glacial maximum ca 22 ka during holocene transgression some keel marks were reworked and reformed into oblique ridges where older sandier sediments crop out at the seafloor relict glacial features on the new jersey outer shelf provide a tie between the timing of laurentide glacial retreat and the evolution of shallow stratigraphy on this mid latitude shelf during the last global sea level cycle ca 120 ka to present

shoreface ravinement evolution tracked by repeat geophysical surveys following hurricane ike bolivar peninsula texas 2008 2013 we have investigated the impact of hurricane ike on the shoreface of the bolivar peninsula texas using three nearsurface marine geophysical surveys during a five year span following the storm which made landfall in september of 2008 multibeam bathymetry sidescan backscatter and chirp subbottom reflection data were collected during each survey the first survey in november 2008 discovered the presence of an erosional landward facing scarp across a broad of the barrier spit shoreface at approximately 3 5 m water depth the erosion incised into a shallow reflection horizon interpreted as the holocene shoreface ravinement exposing lag deposits that were truncated at the scarp and forming a thin high backscatter anomaly up to 1 0 m of material was excavated shoreward of the scarp including up to 0 5 m of shoreface sand above the shoreface ravinement and another 0 5 m of indeterminate

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

pleistocene climatic history reflected in planktonic foraminifera from odp site 1073 leg 174a new jersey margin nw atlantic ocean abstract abundance records of planktonic foraminifera 150 m from the upper 520 m of odp site 1073 hole 1073a leg 174a 639 m water depth have been integrated with specmap derived isotope stratigraphy percentage of calcium carbonate and coarse sediment fraction data in order to investigate the pleistocene climatic history of the new jersey margin six planktonic taxonomic groups dominate the foraminiferal assemblage at site 1073 neogloboquadrina pachyderma d mean 33 8 turborotalita quinqueloba 18 5 n pachyderma s 18 4 globigerina bulloides group 11 4 globorotalia inflata group 9 4 and globigerinita glutinata 4 1 based on the distributions of these six foraminiferal groups the pleistocene section can be divided into three paleoclimatic intervals interval i intermediate corresponds to the quaternary sediments from sequence boundary pp1 to the seafloor 79 5 0 mbsf emiliania huxleyi acme 85 ka at 72 mbsf interval ii warm occurs between sequence boundaries pp3 and pp1 325 79 5 mbsf last occurrence of pseudoemiliania lacunosa 460 ka at 330 mbsf and interval iii coldest occurs between sequence boundaries pp4 and pp3 520 325 mbsf calcareous nannofossils and dinocysts in proximity to pp4 indicate that the sedimentary record for 0 9 1 7 ma is either missing altogether or highly condensed within the basal few meters of the section neogloboquadrina pachyderma d displays eight peaks of abundance which correlate for the most part with depleted 18o values increases in calcium carbonate percentages low coarse fraction percentages increased planktonic fragmentation greater dissolution and low n pachyderma s abundances these intervals are interpreted as representing warmer interglacial conditions neogloboquadrina pachyderma s displays seven peaks of abundance which correlate for the most part with 18o increases decreases in calcium carbonate percentages increases in coarse fraction percentages and low n pachyderma d abundances these intervals are interpreted as representing cooler glacial conditions in interval iii a faunal response to relative changes in sea surface temperature is reflected by abundance peaks in neogloboquadrina pachyderma d followed by turborotalita quinqueloba and then n pachyderma s proceeding from warmest to coolest respectively this tripartite response is consistent with the oxygen isotope record and although not as clear also occurs in intervals i and ii six peaks peak intervals of globigerina bulloides abundance are closely matched by peaks in globigerinita glutinata and occur within oxygen isotope stage ois 2 latter part 3 4 5 8 9 13 14 and 15 we speculate that these intervals reflect increased upwelling and nutrient levels during both glacials and interglacials eight peak intervals of globorotalia inflata show a general inverse correlation with g bulloides and may reflect lowered nutrient and warmer surface waters

late quaternary sedimentation on the outer and middle new jersey continental shelf result of two local deglaciations high resolution seismic profiles show two prominent late quaternary sediment wedges on the outer and middle new jersey continental shelf an extensive wedge along the outermost shelf and upper slope up to 50 m thick appears to have been deposited on the hudson apron during an early melting of the late wisconsin laurentide ice sheet subsequent southward transport of this sediment occurred during sea level regression still stand and transgression a mid shelf sediment wedge which forms the fortune shore probably was deposited during a second melt event 11 to 12 ka as sea level was transgressing over the shelf

a preliminary survey of relict shoreface attached sand ridges in western lake superior abstract high resolution multibeam and seismic reflection surveying in western lake superior near the outflow of the amnicon river wisconsin has shown that the nearshore lake floor appears to consist of till with no recent sediment cover this surface is partially obscured 3 km offshore by a series of low relief elongate sand ridges that are arranged in an en echelon pattern at an oblique angle to the present day shoreline they are extensively gullied suggesting that they are not presently active two sets of elongate features can be identified the features in first group group i are over 0 5 km wide rise 3 5 m above the surrounding lake floor and are over 2 km long the features belonging to the second set group ii are not as well developed and are typically smaller than those in group i group ii features are typically 0 2 0 3 km wide 0 4 1 6 km long and rise 1 3 m above the surrounding lake floor the most striking difference between the groups is the difference in their orientation with respect to the shoreline the group i features run ne sw while the group ii features are directed approximately n s the shoreline runs approximately ene wsw so the features in both cases open northeast the group i features are believed to be relict drowned shoreface attached sand ridges that formed when the lake level lay over 10 m below its present day level these sand ridges formed as the result of currents associated with strong northeasterly gales moving the abundant sediment eroded off the shore the smaller group ii features are believed to be sub aqueous sand dunes that developed transverse to bottom currents produced by the northeasterly gales no dates have been obtained for the sand ridges based upon their depth and the lake level history curve for lake superior we suggest that the ridges formed either 6500 6000 bp prior to the nipissing highstand

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

seismic geomorphology architecture and genesis of miocene shelf sand ridges in the pearl river mouth basin northern south china sea abstract multiple stages of large scale shelf sand ridges including the shoreface attached and the offshore types have developed in the miocene successions on the mid shelf region of the pear river mouth basin northern south china sea utilizing a high quality 3d seismic data set accompanying 2d seismic profiles and well logs the morphology architecture and genesis of these shelf sand ridges have been systematically investigated in this study the ridges are of very large scale with the largest one having a maximum height of 64 m a width of more than 20 km and a length of 37 km within the 3d survey area being mound shaped they also display obvious asymmetry character with the ridge crest preferentially located on the se side three main internal components including the ridge front central ridge and the ridge tail have been recognized through careful anatomy analysis of the two most well imaged ridges each displaying distinct expressions on seismic amplitudes and geometries in the plan view most of the shelf sand ridges are generally ne sw oriented and widening to the sw direction scouring features can also be clearly observed along the sw direction including scour depressions and linear sandy remnants on well logs the shelf sand ridges are represented by an overall coarsening upward pattern intervals with blocky sandstones are preferentially present on higher locations due to a differential winnowing process controlled by shelf topography plenty of evidence indicates that these ridges were primarily formed by the reworking of forced regressive or lowstand deltaic deposits under a persistent southwesterly flowing current during the subsequent transgression this very current is a composite one which is speculated to consist of winter oceanic current scsbk south china sea branch of kuroshio intrusion onto the shelf and internal waves propagating from the luzon strait tidal currents might have contributed to the se growth of the ridge in response to the reglaciation of antarctic ice sheet and the closure of pacific indian ocean seaway in the middle miocene the intensification of the north pacific western boundary current was considered to have potential links to the initiation of the shelf sand ridges at 12 ma the development of shelf ridges was terminated and replaced by rapid deltaic progradation at 5 5 ma

lithofacies distribution and sediment dynamics on a storm dominated shelf from combined photographic acoustic and sedimentological profiling methods bay of plenty new zealand abstract sediment dynamics on a storm dominated shelf western bay of plenty new zealand were mapped and analyzed using the newly developed multi sensor benthic profiler marum neridis iii an area of 60 km 7 km between 2 and 35 m water depth was surveyed with this bottom towed sled equipped with a high resolution camera for continuous close up seafloor photography and a ctd with connected turbidity sensor here we introduce our approach of using this multi parameter dataset combined with sidescan sonography and sedimentological analyses to create detailed lithofacies and bedform distribution maps and to derive regional sediment transport patterns for the assessment of sediment distribution photographs were classified and their spatial distribution mapped out according to associated acoustic backscatter from a sidescan sonar this provisional map was used to choose target locations for surficial sediment sampling and subsequent laboratory analysis of grain size distribution and mineralogical composition finally photographic granulometric and mineralogical facies were combined into a unified lithofacies map and corresponding stratigraphic model eight distinct types of lithofacies with seawards increasing grain size were discriminated and interpreted as reworked relict deposits overlain by post transgressional fluvial sediments the dominant transport processes in different water depths were identified based on type and orientation of bedforms as well as bottom water turbidity and lithofacies distribution observed bedforms include subaquatic dunes coarse sand ribbons and sorted bedforms of varying dimensions which were interpreted as being initially formed by erosion under fair weather conditions sediment is transported from the northwest towards the southeast by littoral drift during storm events a current from the southeast to the northweast is induced which is transporting sediment along the shore in up to 35 m water depth shorewards oriented cross shore transport is taking place in up to 60 m water depth and is likewise initiated by storm events our study demonstrates how benthic photographic profiling delivers comprehensive compositional structural and environmental information which compares well with results obtained by traditional probing methods but offers much higher spatial resolution while covering larger areas multi sensor benthic profiling enhances the interpretability of acoustic seafloor mapping techniques and is a rapid and economic approach to seabed and habitat mapping especially in muddy to sandy facies

buried paleo channels on the new jersey continental margin channel porosity structures from electromagnetic surveying abstract we report on a marine electromagnetic em survey across two portions of the new jersey continental margin that have been previously shown to contain buried paleo channels the em method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity r thought to represent a subaerially eroded surface exposed during the late wisconsinan glaciation channels that cut r are seen through increases in apparent porosity another seismically imaged channel sequence which lies within the outer shelf sediment wedge sequence above r does not have an electrical signature indicating that the sediments above and below the channel boundaries have similar physical properties

early agriculture and palaeoenvironmental history in the north of the iberian peninsula a multi proxy analysis of the monte areo mire asturias spain a multi proxy study pollen and npps geochemical composition and radiocarbon dating combined with principal components analysis was applied to a core sampled in the monte areo mire asturias n spain which covers the last 11 600 years cal bp both signals of holocene climate change and transformations by human activities were recorded the cooler stage of the early holocene the hypsithermal and the neoglaciation periods were indentified but later holocene abrupt climate changes seem not to have been recorded due to the particular evolution of the fen mire system and the impact of human activities on the local hydrology evidence for human activity included a first phase of pastoralism by 7300 cal bp and an extraordinary record of adoption and establishment of agriculture the first evidence of cereal pollen dated to approximately 6700 cal bp represents one of the earliest records of agriculture in northern spain contrary to previous studies which based on assumed biogeographical limitations proposed a late adoption of agriculture in the area our results indicate a rapid expansion of agriculture in northern spain from the eastern to the westernmost areas more in agreement with recent archaeobotanical investigations zapata et al 2004 zapata et al 2005 the research also indicates that climate and human activities interplayed to determine the evolution of the studied area and that a multi proxy approach applied to natural archives appropriately located in areas with evidence of past human occupation is a productive way to obtain circumstantial evidence of early human activity

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

the hudson shelf valley its role in shelf sediment transport abstract freeland g l stanley d j swift d j p and lambert d n 1981 the hudson shelf valley its role in shelf sediment transport mar geol 42 399 427 the hudson shelf valley was deeply incised by pleistocene lowstands of the sea during the holocene transgression fluvial estuarine and estuary mouth depositional environments were displaced landward and sedimentation in these environments partially filled the valley holocene sediment thickness in the seaward half of the valley is about the same as on the shelf to either side but in the landward half of the valley 22 m of sediment is present versus 5 10 m on the adjacent shelf sediment volume calculations in the upper shelf valley show that there is about three times the infill volume east of the thalweg as compared to the infill to the west this configuration indicates that the valley has served as a sediment trap and records the westward migration of the thalweg during the holocene most of the infill was the result of littoral drift which transported sand westward along the south shore of long island during the holocene transgression modern sediment transport as calculated from current meter observations and inferred from bedform observations is mainly south westward along the regional trend of the isobaths and across the shelf valley therefore infill on the eastern side of the shelf valley is continuing at present observations of the regional distribution of sediment types indicate that the asymmetrical valley fill is part of a pattern of bottom response to flow the former drainage divides on both sides of the shelf valley are surfaced by coarse lag deposits on slopes facing northeast into the direction from which the major storm flows come while the down current sides are mantled with fine sand

continental shelf morphology and stratigraphy offshore san onofre california the interplay between rates of eustatic change and sediment supply abstract new high resolution chirp seismic data acquired offshore san onofre southern california reveal that shelf sediment distribution and thickness are primarily controlled by eustatic sea level rise and sediment supply throughout the majority of the study region a prominent abrasion platform and associated shoreline cutoff are observed in the subsurface from 72 to 53 m below present sea level these erosional features appear to have formed between melt water pulse 1a and melt water pulse 1b when the rate of sea level rise was lower there are three distinct sedimentary units mapped above a regional angular unconformity interpreted to be the holocene transgressive surface in the seismic data unit i the deepest unit is interpreted as a lag deposit that infills a topographic low associated with an abrasion platform unit i thins seaward by downlap and pinches out landward against the shoreline cutoff unit ii is a mid shelf lag deposit formed from shallower eroded material and thins seaward by downlap and landward by onlap the youngest unit iii is interpreted to represent modern sediment deposition faults in the study area do not appear to offset the transgressive surface the newport inglewood rose canyon fault system is active in other regions to the south e g la jolla where it offsets the transgressive surface and creates seafloor relief several shoals observed along the transgressive surface could record minor deformation due to fault activity in the study area nevertheless our preferred interpretation is that the shoals are regions more resistant to erosion during marine transgression the cristianitos fault zone also causes a shoaling of the transgressive surface this may be from resistant antecedent topography due to an early phase of compression on the fault the cristianitos fault zone was previously defined as a down to the north normal fault but the folding and faulting architecture imaged in the chirp data are more consistent with a strike slip fault with a down to the northwest dip slip component a third area of shoaling is observed off of san mateo and san onofre creeks this shoaling has a constructional component and could be a relict delta or beach structure

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

bedforms of the canadian eastern seaboard a comparison with global occurrences this paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern canadian continental shelf in order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found and thereafter to relate the subsequent terminology to any diagnostic generic characteristic identifiable from the records sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples these latter features are identifiable adopting the classification of dalrymple et al 1978 which proves adequate for the acoustic differentiation of 2 d and 3 d types though we observed a greater coherence in bedform spacing of the 2 d types than reported hitherto sand ridges were adequately defined and recognised using the description of swift et al 1978 with respect to storm generated ridges and that of off 1963 and others with respect to tidal current ridges such ridges appear not to be uniquely described by ratios of their metrics the bedforms on the southeastern canadian continental shelf are abundant and wide spread virtually all types of bedforms recognisable on the u s shelf are present to the north the majority of these bedforms appear to be storm generated and are considered intermittently active many of the sand waves s s have no measureable relief though retaining their distinctive spatial geometry both active and moribund sand ridges were found of these ridges both tidal and storm generated types were identified the storm generated ridges were further broken down into shoreface connected ridges and offshore ridges a metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height length ratios provided the bedforms are active and fully developed there is some overlap between megaripples and small sand waves and indeed between 2 d and 3 d megaripples yet the distinction is good between sand waves and sand ridges even moribund types sand ribbons in general can be confused with moribund sand waves and megaripples a detailed morphological examination is required to distinguish each feature data from sand ridges of the eastern canadian shelf combined with data from similar features found globally shows that ridge heights tend to cluster into three distinctive modes these modes are at heights of 7 13 and 27 m the first mode is correlated with storm generated ridges the second with tidal current ridges and the third possibly with submerged barrier islands

stratigraphic analysis of a sediment pond within the new england mud patch new constraints from high resolution chirp acoustic reflection data abstract the new england mud patch nemp is an anomaly on the atlantic coast of north america this 13 000 km2 area located south of cape cod between the 60 m and 160 m isobaths is a region of active fine grained deposition on a shelf that is predominantly non depositional or erosional prior studies theorized that nemp sediments are derived from fines winnowed from georges bank transported westward by coastal currents and then settled in more quiescent conditions a chirp seismic reflection 2015 and coring 2016 survey of part of the nemp was conducted in support of a planned acoustic experiment for the office of naval research the survey focused on a 30 km e w by 8 km n s region between the 70 m and 85 m isobaths encompassing a sediment pond 12 m thick the dense 250 m survey lines allow a pseudo 3d stratigraphic interpretation the sediment pond occupies an embayment eroded into pre lgm substrate sediments perhaps by glacial outwash marine sands beneath the mud are organized into oblique sand ridge morphology the sense of obliquity morphologic asymmetry and internal dipping reflectors indicate that the sand ridges formed under east directed transport however as evidenced by westward prograding depocenters and onlap nemp deposition occurred under west directed transport consistent with modern shelf conditions the onset of fine grained deposition was therefore contemporaneous with a significant shift in the hydrologic regime muds deposited immediately above the sand ridges include a significant sand component whose modal grain size is identical to that of the sand ridges this admixture may indicate that during the early stages of mud deposition the tops of the sand ridges remained unburied and exposed to reworking episodic storm driven transport of sand to the muddy deposits may account for some of the sand component of nemp sediments

seafloor response to flow in a southern hemisphere sand ridge field argentine inner shelf abstract the inner continental shelf adjacent to buenos aires province argentina is characterized by a series of sand ridges averaging 4 7 m in relief and spaced about 2 7 km apart the ridges trend north south forming a 20 to 35 southward opening angle with the northeast southwest trending coast although the adjacent coast is of depositional strand plain origin it is presently undergoing erosional retreat and the formation of the ridges appears to be part of the retreat process seafloor grain size distributions and bedform arrays are responses to the same velocity field that has formed the ridges along transects normal to the ridges grain size variation is 90 out of phase with the topography the coarsest sediment is not at ridge crests or trough axes but instead occurs on the landward slope finest sands are on the seaward slope side scan sonar reveals bedforms aligned obliquely to both ridges and the coast these are inferred to be sand waves the grain size and bedform patterns suggest that the formative flows are northward currents with an offshore flow component near the bottom although flows observed during the study period were dominantly north to south the grain size gradients and bedform orientations are equivalent to those characteristic of the atlantic shelf of north america with a north south inversion the comparison suggests that inner shelf transport directions in response to wind events can be predicted from the regional geometry and climate of the shelf

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

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

geoacoustic inversion of ambient noise a simple method the vertical directionality of ambient noise is strongly influenced by seabed reflections therefore potentially geoacoustic parameters can be inferred by inversion of the noise in this approach using vertical array measurements the reflection loss is found directly by comparing the upward with the downward going noise theory suggests that this simple ratio is in fact the power reflection coefficient potentially a function of angle and frequency modeling and parameter searching are minimized and the method does not require a detailed knowledge of the noise source distribution the approach can handle stratified environments and is believed to tolerate range dependence experimental data from five sites four in the mediterranean one on the new jersey shelf are described most of the mediterranean sites had temporally varying noise directionality yet yielded the same reflection properties as one would hope one site was visited in conditions of very low surface noise this paper concentrates on an experimental demonstration of the feasibility of the method and data quality issues rather than automatic search techniques for geoacoustic parameters

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

range dependent waveguide scattering model calibrated for bottom reverberation in a continental shelf environment an analytic model is developed for scattering from random inhomogeneities in range dependent ocean waveguides using the rayleigh born approximation to green s theorem the expected scattered intensity depends on statistical moments of fractional changes in compressibility and density which scatter as monopoles and dipoles respectively and the coherence volume of the inhomogeneities the model is calibrated for ocean bottom scattering using data acquired by instantaneous wide area ocean acoustic waveguide remote sensing oawrs and geophysical surveys of the onr geoclutter program the scattering strength of the seafloor on the new jersey shelf a typical continental shelf environment is found to depend on wave number k medium coherence volume vc and seabed depth penetration factor fp following a 10log10 fpvck4 dependence a computationally efficient numerical approach is developed to rapidly compute bottom reverberation over wide areas using the parabolic equation by exploiting correlation between

seismic geomorphology of buried channel systems on the new jersey outer shelf assessing past environmental conditions abstract quantitative geomorphologic analysis of shallowly buried dendritic channel systems on the new jersey shelf provides estimates of paleo hydrologic parameters needed to link channel morphology to the former hydrodynamic setting these channels observed in 1 4 khz deep towed chirp seismic data formed presumably as fluvial systems when the shelf was exposed during the last glacial maximum lgm the presumed fluvial origin of these channels is supported by their incision into underlying pleistocene strata a chaotic seismic fill unit at their bases which may be indicative of non marine gravel lag and measured stream junction angles that are consistent with a riverine origin the channels would also have been subjected to estuarine tidal environments during ensuing sea level rise we employ empirically derived hydraulic equations for modern rivers and estuaries to estimate paleo discharges velocities and maximum shear stresses using the preserved and interpolated paleo channel geometries as a guide generally trunk main channels have box like symmetric cross sections with width depth ratios of 100 whereas smaller tributary channels have more v shaped asymmetric cross sections with width depth ratios of 40 70 the high width depth ratios along with low sinuosities 1 1 and slopes

mean and tidal currents in baltimore canyon the mean and tidal current fields within baltimore canyon and on the shelf and slope around it were observed with instrumented moorings at 12 sites currents on the shelf are similar to those observed elsewhere over the northeastern u s outer shelf with mean flow southwestward at 10 to 15 cm s 1 parallel to the shelf break tidal current velocity in the direction of the major axis of the m2 ellipse over the shelf is about 9 cm s 1 currents within the canyon are complex mean flow near the bottom along the canyon axis is downcanyon at 5 cm s at a depth of 275 m but upcanyon at 7 cm s 1 at 600 m depth and negligible at depths of 1000 m and 1500 m at 50 m above the bottom mean flow at each of these sites is less than it is at 6 m above the bottom the m2 tidal currents in the canyon tend to be aligned with topography and have velocities ranging up to 22 cm s 1 maximum instantaneous current speeds were found near the bottom in the canyon axis with a peak speed for the entire survey of 106 cm s 1 near the bottom at the 275 m level

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

high resolution organic record of bridge creek deposition northwest new mexico abstract organic and inorganic geochemical data are presented and interpreted for a high resolution sample set from the uppermost portion of a transgressive systems tract condensed interval spanning the cenomanian turonian boundary at red wash northwest new mexico source potential toc rock eval yields thermal maturity vr elemental ca th and u in whole rock and molecular n alkanes steranes terpanes data are presented for a 64 sample 12 4 m composite section of limestones marlstones and shales of the bridge creek member of the greenhorn formation vertical sampling resolutions of 1 spl 19 cm spatial and 1 spl 33 ka temporal are used to monitor the progress of the transgression from the uppermost cenomanian up to the beginning of the highstand systems tract the section is thermally immature and maturity fluctuations are absent indicating that organic parameters are a function of organic matter production and preservation including diagenesis the rhythmic lithologic fluctuation within the bridge creek is not reflected in the source potential elemental or molecular data which show either no obvious pattern e g carbonate content toc or a unidirectional trend toward development of anoxia upsection e g hydrogen index sterane distributions homohopane index the distribution of the triaromatic steroid hydrocarbons c 20 21 26 28 according to side chain length also varies significantly despite the absence of maturity differences all of the unidirectional trends in the data are interpreted as related to either productivity differences e g sterane hopane ratios and changes in the relative concentration of r c 28 and r c 30 desmethylsteranes or the development of anoxia in the lower water column e g decreases in the diasterane regular sterane ratio increases in the homohopane index westward movement of the paleoshoreline during bridge creek time is also monitored by upsection decreasing th u ratios at red wash

episodes of tidally forced swale erosion on the inner shelf interspersed with millennial fluviodeltaic progradational interludes insights from northern bohai bay china abstract erosional swales are common features on the seafloor with vigorous bottom flow s on continental shelves with energetical tidal currents and limited river discharge the initiation and evolution of tidally induced erosional depressions and bedforms have been extensively discussed but little is known about the evolution of such features when interspersed with active deltaic progradation over millennial timescales a recent boomer seismic investigation revealed a swale erosional complex within and proximal to the subaqueous delta in northern bohai bay nbhb china providing us with an opportunity to investigate such features here using the same seismic dataset we analyze the morphology reflective characteristics and evolution of the erosional and depositional structures the erosional swale complex consists of two episodes of tidally induced incised channels within a northern progradational system nps located in the northernmost bohai bay and prograde to the southeast followed by an episode of extensive trough and bump formation negative and positive relief within the middle and northern nbhb which are also erosional features these features are all highly lineated oriented wnw ese we attribute their formation to the similarly oriented tidal flows in this region the multi episode evolution of the swale erosional complex is predominately associated with progradation of the nps whose lobes cap the pre existing erosional features and provide substrate for new erosion the trough and bump complex was subject to long term erosion and may represent an evolution from the previous linear tidally forced marine incisions the complex was subsequently buried in part by the step wise progradation of a southern progradational system sps developed within the southern 2 3 bohai bay and prograde to the north northeast in addition we also observed clusters of longitudinal bedforms with convex internal reflectors superimposed on the erosional remnant bumps coeval with the erosion dominated environment they are observable on both sandy and muddy substrates

a method for semi automated objective quantification of linear bedforms from multi scale digital elevation models the increasing availability of large detailed digital representations of the earth s surface demands the application of objective and quantitative analyses given recent advances in the understanding of the mechanisms of formation of linear bedform features from a range of environments objective measurement of their wavelength orientation crest and trough positions height and asymmetry is highly desirable these parameters are also of use when determining observation based parameters for use in many applications such as numerical modelling surface classification and sediment transport pathway analysis here we 1 adapt and extend extant techniques to provide a suite of semi automatic tools which calculate crest orientation wavelength height asymmetry direction and asymmetry ratios of bedforms and then 2 undertake sensitivity tests on synthetic data increasingly complex seabeds and a very large scale 39 000 km2 aeolian dune system the automated results arecompared with traditional manually derived measurements at each stage this new approach successfully analyses different types of topographic data from aeolian and marine environments from a range of sources with tens of millions of data points being processed in a semi automated and objective manner within minutes rather than hours or days the results from these analyses show there is significant variability in all measurable parameters in what might otherwise be considered uniform bedform fields for example the dunes of the rub al khali on the arabian peninsula are shown to exhibit deviations in dimensions from global trends morphological and dune asymmetry analysis of the rub al khali suggests parts of the sand sea may be adjusting to a changed wind regime from that during their formation 100 to 10 ka bp

the role of non uniform roughness in the formation of sand ribbons abstract sand ribbons typically are shallow water sedimentary features characterized as thin elongate bands of sand overlying a coarser lag sediment which is exposed between them the ribbons are oriented along the direction of the dominant current and are formed by a secondary circulation pattern that includes a small component of the boundary shear stress directed toward the center of the sand ribbons a perturbation expansion coupled with flume experiments indicates that this circulation pattern is linked to differences in the bottom roughness between the sand ribbons and the adjacent coarser strips the non uniform turbulence field arising from this roughness distribution drives a secondary helical flow the expansion indicates that there is a preferred ratio of sand ribbon spacing to water depth 4 1 for unstratified channel flow conditions the secondary flow pattern forces the downstream flow to readjust so that the boundary shear stress over the smooth sand strips is considerably smaller than the mean stress this serves to retard the movement of sand through such a system

forced regressive and lowstand hudson paleo delta system latest pliocene growth of the outer new jersey shelf abstract interpretation of the latest pleistocene stratigraphy of the outer new jersey shelf has evolved over the last three decades with addition of new geological and geophysical data during the last decade new results have described and interpreted various depositional elements within the latest pleistocene that overlie the regional reflector known as the r horizon on the basis of observations made from detailed mapping of the r horizon and the overlying sediment wedge s using high resolution shallow seismic chirp data acquired in several phases between 2001 and 2006 we revise the depositional model for the offlapping multi clinothem sediment wedge on the latest pleistocene outer new jersey shelf as strike elongated lobes of a falling stage wave influenced delta system fed by a pre lgm paleo hudson river channel s that probably reached the late pleistocene shelf edge off new jersey this sediment wedge is composed of a series of prograding and offlapping clinothems of varying thickness within our data which does not extend to the basinward termination of the wedge we seldom observe preserved topsets of these clinothems parts of the foresets of some clinothems are also not preserved particularly in the proximal part of the wedge the sediment wedge is elongated in strike direction nne ssw which suggests along strike sediment movement and possible redistribution of sediment in that direction by ambient shore parallel currents our data do not record any time equivalent fluvial channels at the proximal end of the sediment wedge though there are channel features that cap and cut down into several of the clinothems that make up the wedge farther seaward we suggest that this can be explained in two possible ways 1 relatively large spatial separation between the prograding front of the delta system and the delta plain topset deposits as is very common under a falling stage sea level condition and 2 lack of preservation of the stratigraphic record of the delta plain channels because of the likely vigorous falling stage erosion of topsets during the fall of sea level and possibly also during the subsequent transgressive ravinement and flooding after the lgm the clinothems within the sediment wedge show systematic variation in thickness indicating a northward shift of the main depocenter this shift might also be an indication of gradual northward migration of the principal fluvial feeder such a possibility is supported by previously reported late pleistocene paleo hudson channel deposits south of the modern hudson shelf valley

impact of dense bottom water on a continental shelf an example from the sw adriatic margin abstract dense shelf waters have been recognised as a key factor in transporting sediment and organic matter across continental slopes however the effect of their circulation on continental shelves is still overlooked the adriatic sea is one of the areas in the mediterranean where dense shelf water forms and flows as a bottom hugging gravity current along the continental margin a fraction of this dense water passes beyond the shelf break and flows downslope through cascading while a large lighter and faster portion remains on the shelf with a principal vein flowing between 80 and 120 m water depth this paper presents the 3d shape internal architecture and sediment facies of a variety of large scale sedimentary features detected on the continental shelf and at the shelf edge between 50 and 300 m water depth these features include giant comet marks large flute shaped scours muddy sediment waves very large dunes with superimposed bedforms active and relict sand ridges and shelf edge contourites both erosional and depositional features show an overall internal geometry and orientation consistent with water masses flowing southward and are located where flows become accelerated by topographic constraints and deviated by the curvature of the shelf edge in this study the morphology and seismic stratigraphic structure of large scale bedforms are investigated in an effort to place constraints on bedform evolution and preservation especially as predictive tools for sand resource management and to bring new evidence of the interaction between unidirectional hydrodynamic processes and seafloor dynamics on the shelf

evidence for a common scale o 0 1 m that controls seabed scattering and reverberation in shallow water analysis of the spectral content of long range reverberation yields two observations first there is a remarkably similar scale o 0 1 m between three diverse continental shelf regions this is surprising given the complexity and diversity of geologic processes second there is strong evidence that the scale is associated with heterogeneities within the sediment thus sediment volume scattering not interface scattering controls long range reverberation from a few hundred hertz to several kilohertz this is also unexpected given that at long ranges the vertical grazing angles are less than the critical angle and hence the penetration of the acoustic field into the sub bottom is expected to be modest the consistency of the scale o 0 1 m suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings neither the feature nor mechanism is known at this time