hummocky cross stratification and megaripples a geological double standard abstract hummocky cross stratification in ancient sedimentary deposits is considered to be diagnostic of inner shelf storm deposits the geometry of the cross strata sets implies a low relief oval bedform of a few meters spacing orientation is poorly defined or random hummocky cross strata sets have been attributed to the action of strong storm wave surges megaripples of 2 5 m spacing are typical responses of the inner atlantic shelf of north america to storm flows side scan sonar records have shown that megaripples on the inner shelf are commonly hummocky oval to circular in plan view and lack asymmetry box cores and vibracores reveal gently inclined to horizontal lamination as the characteristic primary structure the megaripples am produced by combined flow storm currents these are alongcoast geostrophic flows with a mean flow component of 20 60 cm sec 1 a high frequency wave orbital current of similar or weaker intensity is present but its role in megaripple formation is subordinate to that of the mean flow the high velocity coastal margin of the flow is often jetlike and downwelling in nature and is characterize by a down current decrease in sand flux and rapid deposition of sand the bottom boundary layer of such flows is characterized by dense sediment suspensions 40 60 mgl 1 and is highly turbulent due to the interaction of the mean flow and wave orbital current components eddy diffusivity up to 200 cm2 sect at 40 cm above the bed sand transport in this coastal boundary zone is obliquely offshore but neither the density of the sediment suspension nor storm surge ebb appear to be important driving forces it is difficult to account for either modern hummocky megaripples or ancient hummocky cross stratification as responses to purely oscillatory flows combined flow currents are the typical response of mostmodern shelves and epicontinental seas to storms and presumably were so in the past hummocky cross stratified beds are generally too thick 20 80 cm to be accounted for by in situ resuspension they are more likely to have been despoited by combined flow currents in areas where these currents were experiencing a downstream velocity decrease and sediment deposition throughout much of the storm s duration evidence for strong scour in swales between hummocks and the smoothly rounded surface of the hummocks suggests a transitionlike bed regime measurements on the atlantic shelf likewi e suggest a transitionlike regime whose boundary layer is characterized by lower velocity than the transitional regime of unidirectional flow in flumes but more intense turbulence and a higher suspended sand concentration the lack of normal cross bedding in bothmodern and ancient hummocky bedforms indicates that these features did not migrate this characteristic may be a consequence of the complex trajectories followed by near bottom water particles in response to combined flow currents

combined flow processes and sedimentary structures on the shoreface of the wave dominated grande riviere de la baleine delta abstract shoreface sediments exposed in raised deltaic deposits along the hudson bay coast are characterized by a thick succession of predominantly parallel laminated and small scale cross laminated fine sand ripple forms where preserved include both combined flow and wave ripple geometries hummocky cross stratification is present in lower parts of the section similar facies have been found in cores from the present day shoreface measurements of waves currents and suspended sediment concentrations in 10 m water depth conducted over a 15 day period in the fall of 1999 captured four different meteorological periods these included an intense four day storm which sustained significant wave heights over 3 m for 15 hours and a storm surge of over 1 m height fair weather conditions produce weak alongshore tidal flows but oscillatory motions generated by small local waves predominate during storms orbital motions dominate the flow but a strong inertial flow generated by wind forcing is also present comparison with a published combined flow bedform stability diagram suggests that the predominant bedforms at 10 m depth would be small 2 d wave dominated ripples and small weakly asymmetrical 3 d ripples under fair weather conditions and large 3 d ripples and upper plane bed under storm wave conditions the predominantly interbedded parallel laminated and small scale cross laminated facies is therefore interpreted to be characteristic of the upper shoreface where the seabed experiences intense oscillatory motions under all storms and even some fair weather conditions combined flow ripples would form during storm events because of the stronger wind driven mean residual current hummocky cross stratification forms in deeper water during storms where the ratio of maximum orbital velocity to mean residual current velocity remains for longer periods in the large 3 d ripple field during the waning phase of storms a numerical bed predictor model using the 15 day data set as input also suggests bimodal conditions fluctuating between wave ripples and upper plane bed at 10 m water depth this model further indicates that combined flow ripples would form rarely but tends to underestimate the threshold of sediment suspension

origin of giant wave ripples in snowball earth cap carbonate the most extreme climate transitions in earth history are recorded by the juxtaposition of neoproterozoic glacial deposits with overlying cap carbonate beds some of the most remarkable sedimentary structures within these beds are sharp crested trochoidal bedforms with regular spacing of as much as several meters that are often interpreted as giant wave ripples formed under extreme wave conditions in a nonuniform postglacial climate here we evaluate this hypothesis using a new bedform stability diagram for symmetric oscillatory fl ows that indicates that the fi rst order control on the formation of trochoidal rather than hummocky bedforms is sediment size not wave climate new measurements of bedform wavelengths and particle sizes from the ca 635 ma nuccaleena formation australia indicate that the giant ripples are generally composed of coarse to very coarse sand most are within the trochoidal bedform stability phase space for normal wave climates moreover numerical simulations of flover fi xed bedforms show that symmetric trochoidal ripples with a nearly vertical angle of climb may be produced over long time periods with variable wave climates in conjunction with rapid seabed cementation these data reveal that rather than extreme wave conditions the giant wave ripples are a consequence of the unusual mode of carbonate precipitation during a global carbon cycle perturbation unprecedented in earth history

clastic domains of sandstones in central eastern venezuela trinidad and barbados heavy mineral and tectonic constraints on provenance and palaeogeography current models for the tectonic evolution of northeastern south america invoke a palaeogene phase of inter american convergence followed by diachronous dextral oblique collision with the caribbean plate becoming strongly transcurrent in the late miocene heavy mineral analysis of cretaceous to pleistocene rocks from eastern venezuela barbados and trinidad allow us to define six primary clastic domains refine our palaeogeographic maps and relate them to distinct stages of tectonic development 1 cretaceous passive margin of northern south america 2 palaeogene clastics related to the dynamics of the proto caribbean inversion zone before collision with the caribbean plate 3 late eocene oligocene southward transgressive clastic sediments fringing the caribbean foredeep during initial collision 4 oligocene middle miocene axial fill of the caribbean foredeep 5 late eocene middle miocene northern proximal sedimentary fringe of the caribbean thrustfront and 6 late miocene recent deltaic sediments flowing parallel to the orogen during its post collisional mainly transcurrent stage domain 1 3 sediments are highly mature comprising primary guayana shield derived sediment or recycled sediment of shield origin eroded from regional palaeogene unconformities in trinidad palinspastic restoration of neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east reflecting progradation from the maturin basin into central trinidad across the nw se trending bohordal marginal offset distorted by about 70 km of dextral shear through trinidad there is no mineralogical indication of a northern or northwestern erosional sediment source until oligocene onset of domain 4 sedimentation paleocene middle eocene rocks of the scotland formation sandstones in barbados do show an immature orogenic signature in contrast to venezuela trinidad domain 2 sediments this requires 1 at least a bathymetric difference if not a tectonic barrier between them and 2 that the barbados deep water depocentre was within turbidite transport distance of the early palaeogene orogenic source areas of western venezuela and or colombia domains 4 6 from late oligocene show a strong direct or recycled influence of caribbean orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south the delay in the appearance of common caribbean detritus in the east relative to the paleocene and eocene appearance of caribbean influenced sands in the west reflects the diachronous eastward migration of caribbean foredeep subsidence and sedimentation as a response to eastward younging collision of the caribbean plate and the south american margin

storm influences on a tidal sandbank s surface middelkerke bank southern north sea the results are presented of two types of pre storm and post storm surveys carried out on the middelkerke bank southern north sea the first type of survey was planned to detect detailed morphological changes in two selected areas of the bank totalling 3 km2 for the survey in these shallow waters to be completed in a fast and accurate way use was made of a special hovercraft based hydrographic system the other type of survey concerned grab samplings covering the sandbank in order to study spatial variations in surficial grain size the pre storm and post storm morphological surveys showed that small and medium dunes disappear under stormy conditions a 5 m westerly displacement of most of the large and very large dunes has been interpreted as the result of bedform migration under normal fair weather locally dominant ebb flow the lowering of the large dunes crests by up to 1 2 m is considered an effect of the storms the accretion of the lower part of the northwestern flank is attributed to the deposition of sand derived from shallow parts of the sandbank during storms the grain size surveys showed that especially the central and northern parts of the sandbank were affected by grain size changes the northwestern flank showing a clear coarsening and the landward southeastern flank a fining with respect to the fair weather situation it is put forward that the waves approaching from the north cause an extra winnowing on the exposed flank of the bank on the southeastern flank of the bank which is better protected against the wave action fine particles are then deposited

observations of time dependent bedform transformation in combined wave current flows although combined wave current flows in the nearshore coastal zone are common there are few observations of bedform response and inherent geometric scaling in combined flows our effort presents observations of bedform dynamics that were strongly influenced by waves currents and combined wave current flow at two sampling locations separated by 60 m in the cross shore observations were collected in 2014 at the sand engine mega nourishment on the delfland coast of the netherlands the bedforms had wavelengths ranging from 14 cm to over 2 m and transformed shape and orientation within at times as little as 20 min and up to 6 hr the dynamic set of observations was used to evaluate a fully unsteady description of changes in the bedform growth with the sediment transport continuity equation exner equation relating changes in bedform volume to bedload sediment transport analysis shows that bedform volume was a function of the integrated transport rate over the bedform development time period the bedform development time period time lag of bedform growth adjustment is important for estimating changes in bedform volume results show that this continuity principle held for wave current and combined wave current generated bedforms

geological and oceanographic perspectives on event bed formation during hurricane katrina 1 storm deposits in ancient shelf sediments typically form thick sequences of interbedded sand and mud deposited during shoreline regression whereas modern shelf sediments are generally thin veneers deposited during shoreline transgression in this paper we present a preliminary comparison between ancient and modern storm beds deposited in these disparate contexts hurricane katrina deposited a storm bed on the louisiana shelf with a maximum observed thickness of 0 58 m which thinned to approximately 0 1 m at 200 km west of landfall this thickness is similar to event beds observed in both ancient and modern sediments using data for tropical cyclone landfalls in the gulf of mexico we estimate the return time for a storm of this size to be 40 50 years in this region this estimated frequency for deposition of storm beds is useful in evaluating ancient storm sequences that were deposited during similar climatic conditions

field investigation of bedform morphodynamics under combined flow abstract fieldwork was conducted at the red cliff sandbar located in the upper humber estuary in order to investigate bedform dynamics under different hydrodynamic conditions related to combinations in tidal and wave generated currents a fixed mooring was deployed to obtain current flow and wave properties across the sand bar site at both spring and neap tidal flows and during conditions of high wind generated waves a terrestrial laser scanner was used to scan the sandbar during low water across the various forcing conditions acquiring detailed information of ripple geometries under spring tide and calm wave conditions two dimensional asymmetrical ripples with straight crest lines were generated on the sandbar surveys were also conducted during strong winds prior to high wind waves two dimensional symmetrical and washed out ripples were observed during spring and neap tidal conditions respectively the lengths of these ripples were almost the same as those generated under current only conditions but their heights were relatively smaller after the strong wind periods 2d current induced ripples were replaced by flatbed conditions and 2d symmetrical wash out ripples which indicates wave induced bed shear stress is enhanced by the presence of a tidal current most pertinently our study reveals discrepancies between field observations and existing predictions of bed configurations that are largely based on laboratory investigations this is likely due to a larger grain size distribution in field conditions and due to turbulence dampening by high concentrations of suspended clay particles the study thus highlights a need to extend a range of field investigations that explore the current deficiencies in our abilities to predict bedforms and bedform dynamics in estuarine systems

sediment transport patterns in the san francisco bay coastal system from cross validation of bedform asymmetry and modeled residual flux abstract the morphology of 45 000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the san francisco bay estuary and adjacent outer coast the spatially averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport additionally the region wide ebb oriented asymmetry of 5 suggests net seaward directed transport within the estuarine coastal system with significant seaward asymmetry at the mouth of san francisco bay 11 through the northern reaches of the bay 7 8 and among the largest bedforms 21 for 50 m this general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary particularly along clearly defined seaward transport pathways will limit the supply of sand to chronically eroding open coast beaches the bedform asymmetry measurements significantly agree up to 76 with modeled annual residual transport directions derived from a hydrodynamically calibrated numerical model and the orientation of adjacent flow sculpted seafloor features such as mega flute structures providing a comprehensive validation of the technique the methods described in this paper to determine well defined cross validated sediment transport pathways can be applied to estuarine coastal systems globally where bedforms are present the results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply related impacts

sand waves on an epicontinental shelf northern bering sea abstract sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges 20 km 5 km 10 m high lying in an open marine setting in the northern bering sea the sand wave area which lies west of seward peninsula and southeast of bering strait is exposed to the strong continuous flow of coastal water northward toward bering strait a hierarchy of three sizes of superimposed bedforms all facing northward was observed in successive cruises in 1976 and 1977 large sand waves height 2 m spacing 200 m have smaller sand waves height 1 m spacing 20 m lying at a small oblique angle on their stoss slopes the smaller sand waves in turn have linguoid ripples on their stoss slopes repeated studies of the sand wave fields were made both years with high resolution seismic reflection profiles side scan sonographs underwater photographs current meter stations vibracores and suspended sediment samplers comparison of seismic and side scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year further documenting modification to the bottom by sediment transport during calm sea conditions in 1977 underwater video and camera observations showed formation and active migration of linguoid and straight crested current ripples current speeds 1 m above the bottom were between 20 and 30 cm s maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water many cross stratified sand bodies in the geologic record are interpreted as having formed in a tidal or storm dominated setting this study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open marine setting

structure and tectonics of the upper cenozoic puerto rico virgin islands carbonate platform as determined from seismic reflection studies the puerto rico virgin islands carbonate platform was deposited over an area of 18 000 km2 from early oligocene to holocene on top of an inactive and subsiding cretaceous earliest oligocene island arc regional single channel and multichannel seismic reflection lines presented in this study provide the first information on the regional stratigraphy and structure of this platform that has previously been known mainly from onshore stratigraphic sections of a relatively small 2250 km2 portion of the platform exposed by late neogene tectonic uplift along the north coast of puerto rico seismic reflection lines are used to map the thickness of the carbonate platform strata and to correlate this thickness with onshore outcrop and well data from northern and southern puerto rico st croix u s virgin islands and the saba bank limestone thickness variations from a little over 2 km to almost zero are used to subdivide the puerto rico virgin islands platform into five distinct carbonate provinces 1 north puerto rico area including the onshore exposures 2 virgin islands area 3 st croix and saba bank area 4 south puerto rico area and 5 mona passage area carbonate thickness and structural information from each area are used to test five previously proposed models for the deformation and vertical movements of the platform the most prominent feature of the platform in the puerto rico virgin islands area is a large east west trending arch the northern limb of this arch exhibits a smoother more uniform dip than the steeper more abruptly faulted southern limb the core of the arch is responsible for the exposure of arc basement rocks on puerto rico the origin of this arch which occurs over a 300 km wide area is best explained by north south shortening and arching caused by interaction at depth of subducted slabs of the north america and caribbean plates other important evidence for this model can be found in the benioff zones observed in the earthquake profiles loading of the caribbean plate results in downward flexing of the north america plate and causes the 4 km subsidence of the carbonate platform north of puerto rico

a note on megaripples in the surf zone evidence for their relation to steady flow dunes megaripples in the combined flow environment of the nearshore are proposed to behave like dunes or large ripples in rivers tidal estuaries and deserts their profile basically is symmetric and thus significantly different from the traditional asymmetric triangular features observed in steady flows similarly their planform often exhibits little directionality unlike crescentic or lunate steady flow dunes that point in the downstream direction these characteristics are the result of complex combined flows in the nearshore including oscillatory flows wave skewness and steady currents undertow rips and alongshore flows recent observations of megaripples in the nearshore suggest that they occur frequently however they are rarely considered in studies of flow resistance or sediment transport in addition megaripples are thought to be the source of hummocky cross stratification in sedimentary sequences and are generally attributed to storm waves on inner continental shelves however observations show that they also exist inside the surf zone and under lower energy conditions a better understanding of their dynamics and thus their occurrence and characteristics would improve the understanding of nearshore wave and circulation dynamics sediment transport large scale morphodynamics and the resulting sedimentary sequences it is hypothesized that megaripples in the nearshore are dynamically similar to steady flow features which are observed in rivers estuaries and deserts and have been studied in much more detail

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

catastrophic extinction of caribbean rudist bivalves at the cretaceous tertiary boundary strontium isotope ratios 87 sr 86 sr in pristine low mg calcite of shells of rudist bivalves from the titanosarcolites limestones exposed in the central maldon and marchmont inliers of jamaica indicate that species rich rudist coral associations persisted into the latest maastrichtian 66 65 ma this finding contradicts the currently accepted hypothesis of stepwise extinction of rudist bivalves in the middle maastrichtian and argues for a catastrophic impact related demise of caribbean cretaceous reefal ecosystems at the cretaceous tertiary boundary

vertical variation of oxygen isotope in bay of bengal and its relationships with water masses 1 we present here for the first time comprehensive depth specific near surface to 1800 m oxygen isotope 18o data set of 175 water samples collected from 22 different locations in the bay of bengal bob during july august 2009 and december january 2012 2013 the study is aimed to constrain the water mass parameters using oxygen isotope and salinity four water masses are identified on the basis of temperature salinity relationship a bay of bengal water bobw 0 50 m b mixed zone mz 60 120 m c indonesian throughflow itf 200 500 m and d indian ocean deep water idw 600 1800 m our study shows 1 18o salinity correlation slope 0 15 0 01 intercept 4 58 0 24 r2 0 89 n 54 for the bobw is found to be consistent with surface bob water reported earlier 2 relatively lower correlation r2 0 24 n 47 in underlying mixed zone suggesting mixing of various water masses 3 significant linear correlation between 18o and salinity in idw r2 0 70 indicating depleted less saline water from southern hemisphere spread up to 18 n and 4 vertical profiles at various sampling locations showing a continuous enrichment of 18o 0 6 0 8 within top 60 100 m irrespective of their proximity to coastline in conjunction with a sharp decrease in 14c data below the same depth zone 60 100 m as reported earlier we suggest the 18o value reaches to its acme at a zone of mixing between younger bobw and relatively older itf this preliminary study indicates oxygen isotope and salinity together can be used to identify different water masses in the bob

field observations of bedforms and sediment transport thresholds of fine sand under combined waves and currents abstract seabed video images and s4 wave current meter data collected during the build up of a moderate storm on the scotian shelf are analysed for bedform development and sediment transport threshold of fine sand under combined waves and currents as the storm built up the following sequence of bedforms was observed 1 relict wave dominant ripples with worm tubes and animal tracks during the preceding fairweather period 2 irregular sinuous asymmetrical current dominant and intermediate wave current ripples under bedload transport 3 regular nearly straight or sinuous asymmetrical to slightly asymmetrical wave dominant ripples under saltation suspension 4 upper plane bed under sheet flow conditions 5 small crest reversing transitory ripples at the peak of the storm and 6 large scale lunate megaripples which developed when the storm decayed these data also show that only single sets of asymmetrical intermediate wave current ripples will form when waves and currents are co linear the development of the crest reversing transitory ripples indicates a high energy transition stage under quasi sheet flow conditions a direct comparison of the skin friction combined shear velocity and the critical shear velocities for bedload suspension and sheet flow transport under estimated the onset of these sediment transport modes as the presence of ripples causes the shear stress to increase from ripple trough to ripple crest the ripple enhanced skin friction shear velocity must be used to determine properly the initiation of bedload transport at high transport stages the boundary layer dynamics is controlled mainly by the thickness of the bedload transport layer thus a transport related bedload shear velocity predicted based upon the sum of the grain roughness and bedload roughness has to be compared against the conventional threshold criterion to properly define the onset of suspension and sheet flow transport modes

morphological characteristics of the basque continental shelf bay of biscay northern spain their implications for integrated coastal zone management this contribution integrates and analyzes data from high resolution multibeam seismic profiles bathymetric lidar and surficial sediment data for the geomorphological seascapes characterisation and process description of the basque inner and middle continental shelf northern spain from the data obtained the basque shelf is characterised by a heterogeneous seafloor where on a small spatial scale different morphologies and sedimentary processes can be observed tectonic activity and sea level changes together with present processes of sediment supply and climatic conditions have a critical influence on the present configuration of the continental shelf and the distribution of seafloor types on the basis of all of the datasets seafloor classification bedform analysis long term sea level change induced seafloor features and anthropogenic features over the seafloor are described as a result three distinct zones have been identified for the basque shelf related to the main geomorphological features and seascapes as summarised below i a western part with a northwestern orientation which coincides with the prevailing wave direction this zone is characterised by a predominantly rocky substrate except within the mouth of the nervion estuary where sandy sediments appear to infill a paleo channel ii a central part which is oriented towards the northeast and receives less wave energy within this zone a sedimentary seabed is predominant sorted bedforms are well developed and can be detected in water depths in excess of 90 m iii an eastern zone which is characterised by sedimentary seafloor and shore terraces here a flat rocky seafloor is covered by a thin layer of sediments throughout the study area the bathymetry and sedimentary features of the shoreface and inner shelf are controlled mainly by climatic conditions coastal dynamics and the underlying geological framework the integration of these data sets together with their interpretation is a valuable source of information for integrated coastal zone management iczm and constitutes a useful tool for implementing various european directives

comparison between predicted and observed sand waves and sand banks in the north sea for the first time a prediction model of regular morphological patterns on the seabed was tested against observations of sand wave and sand bank occurrence in the entire north sea the model which originates from first physical principles predicts this occurrence via two dimensionless parameters on the basis of the water depth the tidal velocity amplitude the level of zero intercept above the seabed z0 and a viscosity variation parameter alt epsilon the latter two quantities were varied in a number of predictions for the entire north sea whereas for the first two local values were used the range of realistic values of alt epsilon and z0 was large enough to let these two parameters distinguish between the possible combinations of bed forms as is shown in the shallower southern bight of the north sea the results were more sensitive to variations in z0 than in alt epsilon a slightly more detailed approach focused on sand waves only in the southern north sea and estimated local values for z0 using depth information quantification of the results showed that the model was able to predict the contours of the sand wave patches but it could not account for the absence of the bed features within this area the type of bed deposit partly explains the smaller scale variation the work confirms the validity of the theoretical bed form prediction model and verifies the hypothesis that the large scale seabed features are formed as free instabilities of tide topography interactions

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

sedimentological effects and palaeoecological implications of the tube building polychaete lanice conchilega pallas the tube building polychaete lanice conchilega forms intertidal mounds in association with macroalgae this assemblage produces structures that can record tidal and seasonal cycles in the stratigraphic record they mark low tide levels because the assemblage occurs below neap low tide and many of the structures form when water drains off the assemblage mounds are created by disturbance of the sediment surface around aggregations of the assemblage and accumulation of sediments within the aggregations the initial aggregations may be relict patches of adult worms new clumps of juveniles or both juvenile worms and drift algae easily settle and survive in high density patches whereas predators and waves more readily disturb low density patches algae and tubes extend through accumulated sediment and create a new higher surface through this interactive process the high density patches increase height rapidly while the low density patches erode regardless of density when the initial distribution is regular the surface remains flat rising evenly or eroding evenly accumulation and erosion increases during spring tides and decreases during neap tides mound development also follows a seasonal pattern the recruitment of juvenile worms in spring facilitates algal settlement and initiates mound buildup the rate of tube building and algal growth increases in early summer as the erosive forces of storms decline this leads to the greatest development of mounds in late summer just before the macroalgae begin to die the loss of algae coincides with autumnal storms and causes catastrophic erosion of the mounds into relict patches of dormant tube worms patches of tubes that survive the winter enhance spring recruitment and renewal of mound development the shape of the mounds is often obscured during burial and preservation because of this it may be difficult to distinguish the original form of ancient mounds without contemporaneous cementing organisms but cycles of deposition and erosion are recorded in lanice tubes and other biogenic structures these structures can be used in conjunction with physical structures to define tidal height seasonality or current regime in general however the presence of tube aggregations per se is not diagnostic of a specific hydraulic environment

pliocene lower pleistocene shallow water mixed siliciclastics and carbonates yanigua and los haitises formations in eastern hispaniola dominican republic the virtually unfolded sedimentary cover of the cordilleras central and oriental in the eastern dominican republic eastern hispaniola tropical north atlantic largely consists of pliocene to early pleistocene mixed siliciclastics and carbonates these deposits have been grouped into two laterally interfingering mapping units the yanigua and los haitises formations the former mainly siliciclastics comprises marl marly limestone and minor conglomerate sandstone lignite and carbonaceous clay and crops out closest to the basement the los haitises formation mainly consists of limestone and intercalating beds of marly limestone and marl lithological mapping at the 1 50 000 scale and facies analysis of twelve measured sections and of additional fourteen outcrops suggest that these deposits mainly formed on a shallow water marine platform fringing the precursor reliefs of the cordillera oriental and the southeastern end of the cordillera central only a limited proportion of sediment formed in floodplains and marshes marl and marly limestone dominated the inner platform sediments terrigenous mud decreased away from the emergent basement and carbonate sedimentation dominated the more external platform corals molluscs echinoids foraminifers bryozoans coralline algae and halimeda are the main components with varying amounts of carbonate mud the platform was generally a low energy environment with seagrass patches in the inner platform corals grew as isolated colonies or as small patch reefs dominated by porites in marly and bioclastic substrates branching corals stylophora and acropora grew in extensive carpets in more distal areas at least in the last stage of its development early pleistocene the platform was rimmed by a reef barrier similar to the holocene caribbean barrier reefs with acropora gr palmata a cervicornis porites montastrea siderastrea and diploria as the main reef builders

a 3 d ground penetrating radar and wavelet transform analysis of the morphology of shoreface deposits in the upper cretaceous ferron sandstone member utah wavelengths of hummocky cross stratified hcs beds a common sedimentary feature of storm dominated shorefaces are documented for the first time using measurements in three dimensional 3 d ground penetrating radar gpr data for a well developed upper cretaceous lower shoreface succession at dry wash in the ferron sandstone member utah the shallow marine sequence consists of upward thickening hcs sand beds alternating with interstorm deposits the thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles weakly coarsening upward mud to very fine grained sand fair weather background deposits suggest a slow progradation of deposition with no significant change in environment the gpr interpretation mapped three conformable high continuity high amplitude reflections throughout the 3 d gpr data volume the interpreted radar surfaces rss are well correlated with tops of hcs sand beds and thus paleotopographic surfaces the associated radar units rus have a uniform thickness on average 0 8 m 2 6 ft the rus and the adjacent outcrop observations suggest that the shoreface sandstone at the dry wash site has a simple layered internal architecture the hummocky swaley surfaces generally dip westerly as a product of postdepositional structural alterations that are mostly in the shoreline direction and contain variable size structurally undulating rounded features a 2 d continuous wavelet transform analysis is applied to the detrended rss producing a multiresolution image decomposition of the gpr surfaces surface features with a wavelength range of 1 7 m 3 23 ft are in good agreement with the observations on modern hummocky shallow marine seabeds quantitative measurements indicate that the hummocky surfaces at the dry wash site are dominated by uniformly distributed circular to elongate bed forms with maximum correlation at 1 5 3 5 m 4 9 11 4 ft wavelength and that the deltaic sedimentary layers were simultaneously deformed by the middle campanian compressional stress of the sevier orogeny transmitted from the northwest quantitative information on the subseismic scale surface geometry of the hcs beds is expected to result in more refined reservoir models in addition the connectivity of units indicated by the scale of the morphology can be an indirect indicator of unit correlation and permeability paths

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

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

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

processes controlling the dynamics of compound sand waves in the north sea netherlands the understanding of the morphodynamics of harmonic bed forms on the seabed is essential for modeling marine sediment transport and coastal morphologic development previous research has mainly focused on the type and distribution of bed forms but areally extensive data and time series of seabed features are scarce multibeam and side scan sonar data from four expeditions reveal the contrasts between a coastal site with asymmetric and flattened three dimensional 3 d compound sand waves on a shoreface connected ridge and an offshore site with asymmetric and sharp crested 2 d compound sand waves migration rates of the coastal sand waves are 6 5 20 m yr 1 while migration rates of the offshore sand waves are 3 6 to 10 m yr 1 this contrasting morphology and dynamic behavior of compound sand waves at the two north sea sites is explained by differences in the relative importance of tidal currents and wave activity near the bed these new field data provide parameters and boundary conditions for sand transport models while the empirically derived behavior of sand waves may be used to validate sand transport and sand wave models 2005

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

observations of bedform migration and bedload sediment transport in combined wave current flows bedload transport is an important mechanism for sediment flux in the nearshore yet few studies examine the relationship between bedform evolution and net sediment transport our work contributes concurrent observations of bedform mobility and bedload transport in response to wave dominant current dominant and combined wave current flows in the nearshore bedload sediment flux from migrating bedforms during combined wave current conditions accounted for at least 20 more bedload transport when compared with wave dominant flows and at least 80 more than current dominant flows bedforms were observed to transport the most sediment during periods with strong currents with high energy skewed waves and while bedform orientation and transport direction were aligned regardless of flow type bedform migration rates were directly proportional to the total kinetic energy contained in the flow field eleven bedload transport models formulated to be used in combined flows both shear and energetics based were compared with sediment flux estimated from measured bedform migration an energetics based sediment transport model was most representative for our data

caribbean chronostratigraphy refined with u pb dating of a miocene coral an exceptionally well preserved aragonitic coral of the extinct species goniopora hilli was collected from late cenozoic sedimentary deposits in the dominican republic and dated using u pb techniques nine coralline subsamples yielded a 238 u 206 pb 207 pb 206 pb three dimensional 3 d inverse linear concordia age of 5 52 0 15 2 ma which when coupled with 87 sr 86 sr ratios obtained from the same coral allows for tighter constraints on temporal variability of marine species diversity prior to closure of the central american seaway the recognition that pre quaternary aragonitic corals can be suitable for u pb dating creates new possibilities for refining the chronologies of late cenozoic marine sedimentary sequences

strontium isotope stratigraphy of upper cretaceous rudist bivalves biozones evolutionary patterns and sea level change calibrated to numerical ages abstract numerical ages derived from strontium isotope stratigraphy of 81 late turonian maastrichtian rudist localities from the caribbean to oman are used to establish stratigraphical ranges of readily identifiable taxa of rudist bivalves hippuritida based on these ranges seven biozones for the turonian maastrichtian of the central eastern mediterranean tethys and three biozones for the mid campanian maastrichtian of the arabian plate are established most of these are interval zones each based on the first stratigraphical appearance of the nominal taxon micro evolutionary patterns such as phyletic size increase have been demonstrated for some of the nominal species as well as a trend of stratigraphical range expansion from the turonian to the maastrichtian implications of the geochronology of late cretaceous carbonate platforms for the biostratigraphy of other benthic fossils are briefly discussed three significant gaps in the stratigraphical distribution of rudist localities in the lower middle and uppermost campanian respectively correlate with other records of sea level change indicating that they correspond to major eustatic sea level falls only a limited number of rudist taxa is evaluated here but the early and latest campanian sea level falls correspond to faunal turnover and extinction of characteristic associations of late cretaceous hippuritida the final extinction of the hippuritida at the cretaceous paleogene boundary is evaluated based on the available numerical ages of eighteen late maastrichtian localities eighteen genera are recorded at the six youngest localities which thus have a species richness similar to older late cretaceous localities while the ultimate cause for extinction of the hippuritida must be evaluated on time scales beyond the resolution of strontium isotope stratigraphy the data set evaluated provides some insight into the pattern of their demise which is considered to be the result of a high degree of endemism indicating limited exchange between increasingly isolated populations this isolation was possibly related to the gradual decrease in the areal extent of maastrichtian carbonate platforms due to a long term cooling trend and local tectonics that affected carbonate platform growth in the regions studied

horizontal and vertical sediment sorting in tidal sand waves modeling the finite amplitude stage the bed of coastal seas displays a large number of rhythmic bed features of which sand waves are relevant to study from an engineering perspective sediments tend to be well sorted over these bed forms which is so far poorly understood in terms of modeling of finite amplitude sand waves using delft3d we employ bed stratigraphy and consider four different grain size classes which are normally distributed on the phi scale the standard deviation sortedness is then varied whereas the geometric mean grain size is kept constant the results show that typically the crests of sand waves are coarser than the troughs residual flow causes net sedimentation on the lee side of the crest and consequently the general sorting pattern is distorted since larger grains experience a larger settling velocity they are deposited on the upper lee slope whereas the smaller grains are found on the lower lee slope due to sand wave migration also the internal structure of the sand wave is revealed which follows the same sedimentation pattern as the lee slope surface these results qualitatively agree with sorting patterns observed offshore the sorting processes lead to longer wavelengths and lower wave heights as a function of standard deviation this relates to the dampening effect of suspended sediment transport for fine grains finally it appears that the modeled wave heights fall in the same range as observations in the north sea these results are valuable for e g predicting the morphological response after engineering activities and determining suitable aggregates for sand extraction

video transects reveal that tidal sand waves affect the spatial distribution of benthic organisms and sand ripples the sandy seabed of shallow coastal shelf seas displays morphological patterns of various dimensions the seabed also harbors a rich ecosystem increasing pressure from human induced disturbances necessitates further study on drivers of benthic community distributions over morphological patterns moreover a greater understanding of the sand ripple distribution over tidal sand waves may improve morphological model predictions here we analyzed the biotic abundance and ripple morphology in sand wave troughs and crests using video transects we found that both the epibenthos and endobenthos are significantly more abundant in sand wave troughs where ripples are less abundant and more irregularly shaped finally we show that camera systems are relatively quick and effective tools to study biotic spatial patterns in relation to seabed morphology

internal waves vs surface storm waves a review on the origin of hummocky cross stratification hummocky cross stratification hcs is considered a diagnos tic structure of surface storm activity at the shoreface offshore transition however the origin of hcs is still debated laboratory experiments have not yet reproduced it and direct observations on the continental shelves do not exist most hydrodynamic interpretations invoke pure oscilla tory flows unidirectional dominated combined flows and oscillatory dominated flows but they all share the assump tion of hcs to reflect the combined action of surface storm waves and related currents within this context of uncertain ties internal waves gravity waves propagating along the pycnocline provide an alternative mechanism to explain the origin of hcs internal waves breaking on the shelf create episodic high turbulence events and induce upslope and downslope currents as well as oscillatory flows at the depth where the pycnocline intersects the sea floor in this scenario both the oscillatory and the unidirectional components needed for hcs to form are not necessarily linked to surface storm waves but can occur at various depth as far and near there is a pycnocline where internal waves can form

linking the morphology and ecology of subtidal soft bottom marine benthic habitats a novel multiscale approach high resolution surveying techniques of subtidal soft bottom seafloor habitats show higher small scale variation in topography and sediment type than previously thought but the ecological relevance of this variation remains unclear in addition high resolution surveys of benthic fauna show a large spatial variability in community composition but this has yet poorly been linked to seafloor morphology and sediment composition for instance on soft bottom coastal shelves hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre scale mega ripples to sand waves and kilometre scale linear sandbanks this multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats we therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry multibeam backscatter classification video surveying of epibenthos and box core samples of sediment and macrobenthos in a study on the brown bank a sandbank in the southern north sea we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys acoustic and video data characterised the seafloor surface and subsurface and macrobenthos communities were found to be structured by both sandbank and sand wave topography we found indications that acoustic techniques can be used to determine the location of epibenthic reefs the multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling

age and paleogeographical origin of dominican amber the age and depositional history of dominican amber bearing deposits have not been well constrained resinites of different ages exist in hispaniola but all of the main amberiferous deposits in the dominican republic including those famous for yielding biological inclusions were formed in a single sedimentary basin during the late early miocene through early middle miocene 15 to 20 million years ago according to available biostratigraphic and paleogeographic data there is little evidence for extensive reworking or redeposition in either time or space the brevity of the depositional interval less than 5 million years provides a temporal benchmark that can be used to calibrate rates of molecular evolution in amber taxa

observations of sand waves megaripples and hummocks in the dutch coastal area and their relation to currents and combined flow conditions 1 this paper aims to investigate the distribution and stability of large scale bed forms in response to storm and fair weather conditions in a shallow marine environment multibeam and side scan sonar data off the dutch coast median grain size 0 25 0 35 mm were collected to monitor sand waves 100 800 m and superimposed megaripples 1 40 m through multiple storm and fair weather events box cores were used to observe the vertical bed structure and grain size in the dutch coastal area two dimensional 2 d megaripples x 1 15 m are the dominant bed forms in current dominated 0 4 m s tidal flow regimes with oscillatory flows 0 4 m s undulating bed topography of mound like 3 d bed forms 20 40 m is observed immediately after storms these bed forms are covered by smaller 3 d megaripples which are related to sets of low angle converging laminae in box cores interpreted as hummocky cross stratification hcs the sand waves form compound bed forms of sets of 2 d and 3 d megaripples the morphology of the sand waves is a function of the general wind wave climate of the marine environmental setting with flat topped 3 d sand waves occurring in shallow wave dominated settings and 2 d sand waves occurring in the tide dominated environment farther offshore copyright 2005 by the american geophysical union

isostatic thermal and flexural models of the subsidence of the north coast of puerto rico published seismic reflection records show that the north coast of puerto rico subsided in three stages each dominated by different physical mechanisms in the late mid eocene to mid oligocene tensional thinning of hot island arc crust and sediment loading caused uniform subsidence of 1 to 2 km during the oligocene and miocene the area sank uniformly almost 2 km because of sediment loading and thermal contraction from the previous stage of magmatism in the pliocene flexural isostasy led to mild uplift on land and over 4 km of sinking along the south side of the puerto rico trench the flexure was driven mainly by tectonic erosion of island arc crust by the newly underthrust north american plate

palaeogeographical changes in response to glacial interglacial cycles as recorded in middle and late pleistocene seismic stratigraphy southern north sea offshore stratigraphic records from the north sea contain information to reconstruct palaeo ice sheet extent and understand sedimentary processes and landscape response to pleistocene glacial interglacial cycles we document three major middle to late pleistocene stratigraphic packages over a 401 km2 area norfolk vanguard boreas offshore wind farm offshore east anglia uk through the integration of 2d seismic borehole and cone penetration test data the lowermost unit is predominantly fluviatile yarmouth roads formation marine isotope stage mis 19 13 including three northward draining valleys the middle unit swarte bank formation records the southernmost extent of tunnel valley fills in this area of the north sea providing evidence for subglacial conditions most likely during the anglian stage mis 12 glaciation the yarmouth roads and swarte bank deposits are truncated and overlain by low energy estuarine silts and clays brown bank formation mis 5d 4 smaller scale features including dune scale bedforms and abrupt changes in cone penetration test parameters provide evidence for episodic changes in relative sea level within mis 5 the landscape evolution recorded in deposits of mis 19 5 are strongly related to glacial interglacial cycles although a distinctive aspect of this low relief ice marginal setting are opposing sediment transport directions under contrasting sedimentary process regimes

fluvio lagoonal sedimentary sequences in leyre delta and arcachon bay and holocene sea level variations along the aquitaine coast france abstract along the aquitaine coast bay of biscay france scarcity of recent coastal deposits corresponding to post holocene sea level variations is a direct consequence of the strong erosional processes observed in this coastal zone the general transgressive trend may be due to various geodynamic events such as contemporary sea level rise or regional subsidence related to tectonic or isostatic post glacial adjustments of this southern part of the european plate this paper is a discussion of new data about sedimentary sequences described in recent deposits infilling the mesotidal arcachon bay and its inner fluvial delta of the leyre river enlighted by geophysical and geomorphological information on the geodynamic evolution of the central part of the aquitaine basin the conclusion is that the transgressive trend of this coast is related to both subsidence and sea level elevation

strontium isotopes and miocene sequence stratigraphy across the northeast florida platform abstract a preliminary assessment of miocene sea level fluctuations is presented based on the integration of sr derived ages and sequence stratigraphic concepts applied to subsamples of 12 cores that transect the hawthorn group on the northeast florida platform the hawthorn group section includes phosphorite nodules peloids and crusts as well as dolosilt and dolostone nodules and beds formed during early burial diagenesis of organic rich sediments deposited during periods of intensified and persistent upwelling associated with rising and maximum sea level the 87sr 86sr composition of phosphorite and dolomite is used to determine the age of in place phosphorite crusts and dolostone beds condensed sections and reworked phosphorite and dolostone sand and gravel unconformities and transgressive surfaces regional correlation of unconformities and condensed sections provides the basis for a sequence stratigraphic framework from which the age and relative amplitude of sea level fluctuations are constructed seven depositional sequences are identified from the data depositional sequences correspond to local sea level fluctuations with maximum water depths at approximately 25 24 21 20 19 18 17 15 14 12 11 9 and 8 6 ma greatest water depth apparently occurred at 17 15 ma

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

multibeam backscatter as a tool for sea floor characterization and identification of oil spills in the galicia bank this study is focused on the potential of using the multibeam acoustic backscatter both for sea floor characterization of the galicia bank and for identification of sea bottom oil spills an extended multibeam data set was acquired during the rg 1 and rg 2 surveys aboard rv hesperides in 2003 for the geological and geophysical characterization of the galicia bank where the oil tanker prestige wreck is located 3 d images have been made by integrating bathymetry and backscatter data multibeam data have been additionally supported by gravity core information in order to correlate sea floor acoustic backscatter with the surficial sediments and their physical properties the major factors that seem to control the zonation of the backscatter intensity images are i the type of the sedimentary processes gravitational turbiditic hemipelagic which control at the same time the grain size distribution and ii the sea bottom morphologies such as basement outcrops however there are some backscatter halos that cannot be explained by these processes in the backscatter maps the bow and stern of the prestige wreck are clearly marked by a high backscatter intensity anomaly whose existence is discussed

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

bottom topography and roughness variations as triggering mechanisms to the formation of sorted bedforms 1 a new model is presented that addresses the occurrence of sorted bedforms on inner shelves of coastal seas these features consist of alternating bands of coarse and fine grains with small topographic undulations we show that inherent feedbacks between alongshore currents sea waves bottom topography and roughness variations result in the emergence of morphological patterns similar to the observed bed features we find that two modes are amplified which display different characteristics yielding a possible explanation to the diversity exhibited by sorted bedforms in the field the results illustrate that both roughness variations and bottom topography influence the generation of sorted bedforms

strontium isotope stratigraphy for oligocene miocene carbonate systems in puerto rico and the dominican republic implications for caribbean processes affecting depositional history abstract87sr 86sr derived mean ages from low mg calcite kuphus incrassatus and ostrea haitensis bivalves provide an updated and refined chronostratigraphy for selected oligocene miocene carbonate and siliciclastic units in puerto rico and the dominican republic results indicate ages of middle to late oligocene for the san sebastian formation ca 29 78 26 51 ma the lares limestone ca 26 51 24 73 ma and the montebello member ca 27 30 24 10 ma middle miocene to the early part of the late miocene for the cibao formation ca 12 17 ma the aguada los puertos limestone ca 14 67 11 14 ma and the aymamon limestone ca 10 98 ma in northern puerto rico as well as for the ponce limestone ca 14 97 9 84 ma in southern puerto rico and the yanigua los haitises formations ca 15 75 12 58 ma in northeastern dominican republic and late miocene for the cercado formation ca 6 31 5 88 ma in northwestern dominican republic these results show some significant modifications to previous chronostrati

bed load transport on the shoreface by currents and waves tide driven bed load transport is an important portion of the net annual sediment transport rate in many shoreface and shelf environments however bed load transport under waves cannot be measured in the field and bed load transport by currents without waves is barely measurable even in spring tidal conditions there is consequently a strong lack of field data and validated models the present field site was on the shoreface and inner shelf at 2 to 8 5 km offshore the central dutch coast far outside the surfzone where tidal currents flow parallel to the coast bed load transports were carefully measured with a calibrated sampler in spring tidal conditions without waves at a water depth of 13 18 m with fine and medium sands the near bed flow was measured over nearly a year and used for integration to annual transport rates an empirical bed load model was derived which predicts bed load transports that are a factor of n5 smaller than predicted by existing models however they agree with laboratory data of sand and gravel transport in currents near incipient motion the damped transport rates may have been caused by cohesion of sediment or turbulence damping due to mud or biological activity the annual bed load transport rate was calculated using a probability density function pdf derived from the near bed current and orbital velocity data which represented the current and wave climate well when compared to 30 years of data from a nearby wave station the effect of wave stirring was included in the transport calculations the net bed load transport rate is a few m 2 year this is much less than predicted in an earlier model study which is partly due to different bed load models but also due to the difference in velocity pdf the annual transport rate is very sensitive to the probability of the largest current velocities

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

paleomagnetic evidence for late miocene counterclockwise rotation of north coast carbonate sequence puerto rico a paleomagnetic study of the essentially undeformed middle tertiary carbonate sequence along the north coast of puerto rico reveals statistically significant pre pliocene discordance of characteristic component directions against those expected from cratonic north america for much of the section despite generally weak to moderately weak magnetic intensities confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization intrasite bipolarity and or the reproducibility of measurements the mean geographic direction for the upper oligocene to middle miocene strata is 335 2 degree 32 9 degree and the corrected mean paleomagnetic pole is 207 6 degree 66 5 degree n 3 alpha 95 4 3 degree this suggests a counter clockwise ccw block rotation of puerto rico and its microplate of 24 5 degrees plus minus 5 8 degrees during the late miocene using a width of 250 km for the northern caribbean plate boundary zone ncpbz between the north american plate and caribbean plate the mean left lateral displacement implied is 1 8 to 2 4 cm yr which agrees fairly well with published relative motion rates for the two plates average rotation rate for 50 ma to 20 ma was 0 7 degree my but perhaps as great as 4 degree my in the miocene resolution of mean paleolatitude indicates northward motion of a degree or lessmore during the period of rotation causes of this short lived rotation may include 1 tectonic escape from the inhibiting presence of the bahama banks and beata ridge during eastward motion of puerto rico along the sinistral transpressive puerto rico trench and muertos trough fault systems or 2 changes in relative plate motions of the caribbean and north american plate during the late miocene less

on the behaviour of tidal current directions due to the presence of submarine sand waves abstract side scan sonar records reveal that the crestlines of megaripples in the troughs as well as on both sides of the slopes of sand waves form an angle with the crestline of the sand waves itself the existence of such an angle between the crestline of megaripples and sand waves indicates that changes of the tidal current direction across sand waves can be expected direct evidence that such tidal current direction changes occur above sand waves is derived from measurements of the air sea interaction drift buoy asib system at the sea surface and from side scan sonar records of the sea bed both systems were operated from on board research vessels during two c star field experiments in the hoek van holland study area off the dutch coast in april 1996 and in april 1997 measurements performed by electrical resistance wires on board the asib system indicate that variations of the short and moderate wave direction and the wave directional spread are associated with changes of the tidal current direction at the sea surface according to the results of the measurements derived from the asib system and the side scan sonar records it can be summarised that the variation of the direction of short and moderate period water waves as well as changes of the tidal current speed and direction across large sand waves must be considered for correct modelling of the wave current interaction mechanism

global dominance of coralline red algal facies a response to miocene oceanographic events rhodoliths free living coralline red algae can thrive under a wide range of temperatures reduced light and increased nutrient levels and often form a distinct so called rhodalgal lithofacies that is an important component of cenozoic shallow water carbonates global distributions illustrate that from the late early to early late miocene burdigalian early tortonian rhodalgal facies reached peak abundances and commonly replaced coral reef environments accompanied by a decline in other carbonate producing phototrophs we argue that the dominance of red algae over coral reefs was triggered in the burdigalian by enhanced trophic resources associated with a global increase in productivity as evidenced by a long term shift toward higher carbon isotope values rhodalgal lithofacies expanded further in the middle miocene when strengthened thermal gradients associated with the establishment of the east antarctic ice sheet led to enhanced upwelling while climate change generated increased weathering rates introducing land derived nutrients into the oceans globally cooler temperatures following a climatic optimum in the early middle miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs the global shift in nearshore shallow water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow water carbonate facies as indicators of past oceanographic conditions

grain sorting effects on the formation of tidal sand waves a model is developed to investigate the process which leads to the formation of sand waves in shallow tidal seas characterized by a heterogeneous sea bed composition the main goal of the analysis is the evaluation of the effects that a graded sediment has on the formation of the bottom forms and the investigation of the sorting process induced by the growth of the bottom forms the analysis is based on the study of the stability of the flat bed configuration i e small amplitude perturbations are added to the flat bottom and a linear analysis of their time development is made for an oscillatory tidal current dominated by one tidal constituent the results show that the graded sediment can stabilize or destabilize the flat bottom configuration with respect to the uniform sediment case depending on the standard deviation sigma of the grain size distribution and on the ratio r over cap between the horizontal tidal excursion and the water depth for moderate values of r over cap i e values just larger than the critical value for which the sediment is moved and sand waves appear the presence of a sand mixture stabilizes the flat bed on the other hand for large values or r over cap the mixture has a destabilizing effect in both cases the effect that a sand mixture has on the stability of the flat bed configuration is relatively small moreover for moderate values of r over cap the fine fraction of the mixture tends to pile up at the crests of the bottom forms while the coarse fraction moves towards the troughs for large values or r over cap the grain size distribution depends on the value of sigma the results are physically interpreted and provide a possible explanation of the apparently conflicting field observations of the grain size distribution along the sand wave profile carried out in the north sea

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

stable isotopic signature of southern ocean deep water co2 ventilation the link between atmospheric co2 level and ventilation state of the deep ocean is poorly understood due to the lack of coherent observations on the partitioning of carbon between atmosphere and ocean in this southern ocean study we have classified the southern ocean into different zones based on its hydrological features and have binned the variability in latitudinal air co2 concentration and its isotopic ratios together with air co2 we analysed the surface water for the isotopic ratios in dissolved inorganic carbon dic using the binary mixing approach on the isotopic ratio of atmospheric co2 and its concentration we identified the delta c 13 value of source co2 the isotopic composition of source co2 was around 9 22 0 26 parts per thousand for the year 2011 and 2012 while a composition of 13 49 4 07 parts per thousand was registered for the year 2013 we used the delta c 13 of dic to predict the co2 composition in air under equilibrium and compared our estimates with actual observations we suggest that the degeneration of the dic in presence of warm water in the region was the factor responsible for adding the co2 to the atmosphere above the place of observation coincides with the zone of high wind speed which promotes the process of co2 exsolution from sea water c 2015 elsevier ltd all rights reserved

the distribution of macrozoobenthos in the southern north sea in relation to meso scale bedforms this study investigates the distribution of macrozoobenthos in relation to meso scale bedforms in the southern north sea three sites on the dutch continental shelf were sampled that are representative of large areas of the north sea and show diverse morphological settings these sites are i part of a shoreface connected ridge ii the lower part of a concave shoreface and iii a sandwave area within these sites two or three different morphological units were distinguished sampling was undertaken in two seasons for two consecutive years the species composition was analysed for differences in benthic assemblage within sites based on the meso scale morphology and between sites and seasons in addition the benthic assemblage was correlated to water depth median grain size d50 and sorting d60 d10 results show that significant differences in the benthic assemblage can be found related to meso scale bedforms but macro scale morphological setting and seasonal effects are more important 2006 elsevier ltd all rights reserved

the quebradillas limestone miocene pliocene northern puerto rico and tectonics of the northeastern caribbean margin the uppermost formation of the limestone belt of northern puerto rico is herein redesignated the quebradillas limestone a type section is established within the original type locality north of the town of quebradillas as here redefined the quebradillas limestone consists of a limestone sequence overlying the uppermost amphistegina algal limestone of the aymamon limestone along highway 2 north of the town of quebradillas the formation consists of three types of limestone biomicrite which form the basis for subdividing the formation into three members the lower member consists of globigerine biomicrite and is 16 m thick in many areas the lower member contains thin beds of oyster shells and shell fragments inter bedded within marl both the matrix of the oyster bearing beds and the marl are rich in planktonic foraminifers the middle member is essentially operculinoides biomicrite and is slightly amphistegina algal biomicrite and its thickness is estimated to be 44 4 m the threefold subdivision has been recognized throughout the outcrop belt of the formation from the west coast of the island eastward to barceloneta it probably applies to the easternmost outcrops as well the quebradillas aymamon boundary is an erosional unconformity between the two formations the globigerine limestone of the lower member of the quebradillas fills solution cavities in the uppermost aymamon and in places the upper aymamon shows marked relief most of the quebradillas is pliocene in age although part of the lower member may be latest miocene the quebradillas limestone is a regressive sequence the lower member represents a lower neritic to upper bathyal environment the middle member an outer shelf environment and the upper member a forereef subtidal and intertidal beach environment the upper member is veneered by what appears to be a paleosol which in turn is overlain by quaternary eolianite marginal marine and marine deposits the quebradillas is not limited to only the onshore coastal area of the island but extends northward into the puerto rico trench above a water depth of 5 000 m the quebradillas covers an area of at least 4 000 km 2 on the southern slope of the trench and the total area could be as much as 9 000 km 2 seismic and dredge sample data suggest that the quebradillas consists of the same facies offshore as in both outcrop and one well onshore the presence of widespread quebradillas in the puerto rico trench has important tectonic implications for regional studies of both the puerto rico trench and the northern caribbean region

geochemistry of precambrian carbonates iv early paleoproterozoic 2 25 0 25 ga seawater in an effort to narrow down the first and second order variations in isotopic composition of the early paleoproterozoic 2 25 0 25 ga seawater we report a comprehensive study of mineralogy chemistry and isotopic composition of the malmani dolomite transvaal supergroup south africa duck creek dolomite wyloo group australia and bruce limestone member of the espanola formation huronian supergroup canada based on trace element data their diagenetic rank increases in the order duck creek bruce malmani the interpolation of alteration trends to best values yields an estimate of 0 70550 for 87sr86sr comparable to our previously published value of 0 70496 for 13c the measured range of 0 1 5 pdb is similar to that observed for phanerozoic marine carbonates in contrast the best 18o value for dolostones is 5 pdb depleted in 18o relative to phanerozoic counterparts but comparable to the estimates obtained by similar approach for archean facies the isotope geochemistry and mineralogy of bruce limestone member is consistent with the proposition that the sequence may have been deposited in a lacustrine environment possibly related to the recession of the brace glaciers if such interpretation proves unacceptable from a sedimentological standpoint the origin of the unusual isotopic signatures must be sought despite the above trace element interpretation in as yet unspecified post depositional alteration phenomena in contrast to phanerozoic carbonates the early paleoproterozoic as well as the previously described archean counterparts are enriched in mn and fe

strain partitioning and fault slip rates in the northeastern caribbean from gps measurements 1 gps data collected in the dominican republic from 1994 to 2001 show that oblique convergence between the north american and caribbean plates is partitioned between 5 2 2 mm yr 1 of dip slip reverse motion on the north hispaniola thrust approximately n s and 12 8 2 5 mm yr 1 and 9 0 9 0 mm yr 1 of approximately e w left lateral strike slip motion on the septentrional and enriquillo faults 95 confidence the agreement between gps and paleoseimological slip rates on the septentrional fault together with the 770 960 years since the last major earthquake and the 800 1200 years maximum repeat time of major earthquakes may indicate that the septentrional fault is currently in the late phase of its rupture cycle

linking the oxygen isotope record of late neogene eustasy to sequence stratigraphic patterns along the bahamas margin results from a paleoceanographic study of odp leg 166 site 1006 sediments abstract during odp leg 166 the recovery of cores from a transect of drill sites across the bahamas margin from marginal to deep basin environments was an essential requirement for the study of the response of the sedimentary systems to sea level changes a detailed biostratigraphy based on planktonic foraminifera was performed on odp hole 1006a for an accurate stratigraphic control the investigated late middle miocene early pliocene sequence spans the interval from about 12 5 ma biozone n12 to approximately 4 5 ma biozone n19 several bioevents calibrated with the time scale of berggren et al 1995a b were identified the odp site 1006 benthic oxygen isotope stratigraphy can be correlated to the corresponding deep water benthic oxygen isotope curve from odp site 846 in the eastern equatorial pacific shackleton et al 1995 proc odp sci res 138 337 356 which was orbitally tuned for the entire pliocene into the latest miocene at 6 0 ma the approximate stratigraphic match of the isotopic signals from both records between 4 5 and 6 0 ma implies that the paleoceanographic signal from the bahamas is not simply a record of regional variations but indeed represents glacio eustatic fluctuations the odp site 1006 oxygen and carbon isotope record based on benthic and planktonic foraminifera was used to define paleoceanographic changes on the margin which could be tied to lithostratigraphic events on the bahamas carbonate platform using seismic sequence stratigraphy the oxygen isotope values show a general cooling trend from the middle to late miocene which was interrupted by a significant trend towards warmer sea surface temperatures sst and associated sea level rise with decreased ice volume during the latest miocene this trend reached a maximum coincident with the miocene pliocene boundary an abrupt cooling in the early pliocene then followed the warming which continued into the earliest pliocene the late miocene paleoceanographic evolution along the bahamas margin can be observed in the odp site 1006 13c values which support other evidence for the beginning of the closure of the panama gateway at 8 ma followed by a reduced intermediate water supply of water from the pacific into the caribbean at about 5 ma a general correlation of lower sedimentation rates with the major seismic sequence boundaries ssbs was observed additionally the ssbs are associated with transitions towards more positive oxygen isotope excursions this observed correspondence implies that the presence of a ssb representing a density impedance contrast in the sedimentary sequence may reflect changes in the character of the deposited sediment during highstands versus those during lowstands however not all of the recorded oxygen isotope excursions correspond to ssbs the absence of a ssb in association with an oxygen isotope excursion indicates that not all oxygen isotope sea level events impact the carbonate margin to the same extent or maybe even represent equivalent sea level fluctuations thus it can be tentatively concluded that ssbs produced on carbonate margins do record sea level fluctuations but not every sea level fluctuation is represented by a ssb in the sequence stratigraphic record

connections among ice runoff and atmospheric forcing in the beaufort gyre during sheba thin ice and freshening of the arctic ocean surface in the beaufort sea led to speculation that perennial sea ice was disappearing mcphee et al 1998 since 1987 we have collected salinity 18o and ba profiles near the initial sheba site and in 1997 we ran a section out to sheba resolving fresh water into runoff and ice melt we found a large background of mackenzie river water with exceptional amounts in 1997 explaining much of the freshening at sheba ice melt went through a dramatic 4 6 m jump in the early 1990s coinciding with the atmospheric pressure field and sea ice circulation becoming more cyclonic the increase in sea ice melt appears to be a thermal and mechanical response to a circulation regime shift should atmospheric circulation revert to the more anticyclonic mode ice conditions can also be expected to revert although not necessarily to previous conditions

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

late neogene chronology and sequence stratigraphy of mixed carbonate siliciclastic deposits of the cibao basin dominican republic a stratigraphic study of late miocene pliocene mixed carbonate and siliciclastic sediment upper part of the yaque group was conducted in northern hispaniola to refine the chronostratigraphy of uplifted nearshore marine sequences in the cibao basin classic late neogene sections in these sequences include a spectacularly preserved faunal record for the northern caribbean refined ages of the cercado formation 6 6 6 0 ma the gurabo formation ca 5 8 4 0 ma and the mao formation 3 9 3 5 ma allow correlation to regional and global sea level events each of the three formations corresponds to one depositional sequence composed of mixtures at different proportions of skeletal debris mostly coral and mud size silt siliciclastic sediment distinct stratal geometries and lithofacies individualize the three formations each separated by pebble conglomerates the cercado formation depositional sequence consists of prograding inner shelf siliciclastic sands and patch reefs the basal transgressive unit of the gurabo formation is made of seaward prograding low angle clinothems of bedded and burrowed siliciclastic sand with molluscs and free living corals the upper gurabo unit consists of massive middle shelf clinothems of silt with bedded reef debris and in situ branching coral thickets these clinothems grade basinward into massive deeper water silt deposits at the shelf edge and basin slopes the mao formation sequence records the transition from lowstand fluvial deltaic facies to transgressive and highstand marine clinothems made mostly of coral debris in a silt matrix in the mao formation outcrops the coral silt clinothems can be divided into at least 10 high frequency cycles 40 k y based on lithofacies channelized and slumped coarse siliciclastic sand gravel and nonmarine alluvium cap the sequence likely associated with lowered sea level starting at ca 3 3 ma and perhaps the onset of regional uplift the major lithologic and sequence geometry changes in the cibao basin correlate with trends in the oxygen isotope ice volume proxy and likely reflect deposition responding to major periods of marine transgression and highstand an especially prominent feature is the major deepening and margin back step near the miocene pliocene boundary continuing in the early pliocene which resulted in the deposition of the gurabo formation transgression and sea level highstand in the late early pliocene 3 9 3 5 ma produced distinctive margin progradation primarily by coral debris this progradation event was synchronous with progradation in the nearby western great bahama bank the different stratal configurations of the three sequences can be attributed to a combination of factors including 1 shelf morphology and location on the shelf 2 paleoceanographic conditions such as warm sea surface temperatures and reduced upwelling which controlled coral productivity and reef geometry and 3 the influx of siliciclastic mud from the adjacent mountains

three phase tectonic evolution of the northern margin of puerto rico as inferred from an integration of seismic reflection well and outcrop data abstract integration of seismic reflection well and outcrop data from the oligocene pliocene puerto rico virgin islands platform prvi platform north of puerto rico indicates that three major tectonic phases characterize this seismically active region within the north america caribbean plate boundary zone tectonic phase 1 cretaceous to eocene formation and sedimentary infilling from a southern source area into a forearc basin formed between down to the north normal faults near the present day coast of puerto rico and an outer arc ridge near the present day shelf break tectonic phase 1 concluded the last volcanic arc activity in puerto rico produced by the subduction of oceanic crust of the north america plate beneath the caribbean arc system formation of the outer arc high defining the northern limit of this elongate basin may have been related to the accretion of off scraped sedimentary rocks beneath the northern margin of puerto rico in a manner similar to that observed in active arcs the end of tectonic phase 1 is related to initial collision between the caribbean arc and the bahama carbonate platform tectonic phase 2 oligocene to pliocene formation of a 1600 m thick northward thickening prvi platform predominately formed by carbonate rocks this phase started with a period of non deposition and erosion resulting in an latest eocene oligocene unconformity the base of the prvi platform is formed by a 400 m thick middle to late oligocene basal siliciclastic sequence that prograded northward across the forearc basin depositional thicknesses of sedimentary layers deposited during phase 2 are controlled by two large arches the nnw trending guajataca arch appears to have formed as the result of tectonic activity in the mona passage area the northeast trending san juan arch cannot be related to any adjacent structure or plate boundary feature onlap relations between carbonate rocks of the platform and both arches suggest that the arches were most active in the period from middle oligocene to early miocene rocks deposited during tectonic phase 2 are surprisingly devoid of faults and folds given their central position within the north america caribbean strike slip plate boundary zone that is known from regional studies to have been active throughout the deposition of the platform rocks tectonic phase 3 pliocene to holocene northward tilting of the prvi platform submerged the northern edge of the platform to a depth of 4 km and elevated the southern edge of the platform to several hundred meters above sea level on puerto rico northward tilting of this area occurred on the northern limb of a large arch or anticline formed parallel to the long axis of the island of puerto rico and its shelf areas the arch formed in response to a post pliocene convergence between the north america and caribbean plates

a study of the dynamics of a marine sandwave the movement of the crest of a sandwave was studied using cross sectional profiles obtained from lines of sea bed reference stakes measurements were made over a six month period before and after flood and ebb tides in relation to both spring and neap tides and surface wave conditions additional observations were obtained on a daily basis over an equinoctial neap to spring to neap tidal period in conjunction with boundary layer flow measurements tracer experiments were conducted to study the dispersion of sediment from the sandwave crest the results showed that the sandwave was relatively stable at neap tides whilst at higher tidal ranges the crest position oscillated with successive flood and ebb tides net flank erosion occurred on the less steep upstream slope during the dominant ebb tide this together with increased deposition on the lee slope caused the crest to advance it was not possible to extrapolate sandwave migration over long periods as the tidal dynamic trends were interrupted by wind stress and surface wave activity high particle orbital velocities generated at the sea bed by storm waves caused major reductions in crestal heights calculated volumes of sediment eroded and accreted were used with boundary layer flow measurements to calculate threshold velocities for the movement of the sediment and sediment transport rates

oxygen isotope distribution at shallow to intermediate depths across different fronts of the southern ocean signatures of a warm core eddy abstract southern ocean an important component of the earth s climate system is changing in response to the anthropogenic climate change to understand better the dynamics of the southern ocean we documented oxygen isotopic variability and its relation to salinity especially at intermediate depths to 1000 m across different fronts at six stations in the southern ocean signatures of a warm core eddy extended from 40 to 44 s and 56 to 59 5 e it consisted of subtropical surface water stsw other water masses identified were the antarctic surface water aasw antarctic intermediate water aaiw and upper circumpolar deep water ucdw based on the salinity temperature and oxygen isotopic ratios the slope of the oxygen isotope salinity relationship indicates that the water in the warm core eddy was derived from a region dominated by evaporation precipitation while the water surrounding the eddy came from a region dominated by melting freezing the shoaling of aaiw up to water depth of 500 m was observed along the transect these new oxygen isotope data especially from the intermediate depths will also help fill existing gaps in the global seawater oxygen isotope dataset

introduction to special section on marine sand wave and river dune dynamics marine sand waves and river dunes are rhythmic patterns formed at the interface between a sandy bed and turbulent flows driven by tidal and river currents their origin development and dynamics are far from being fully understood to enhance the discussion on this topic we organized the international conference marine sand wave and river dune dynamics marid in april 2004 in enschede netherlands scientific papers that originated from the marid conference are presented in this special section this introduction places these papers in the context of recent progress

oxygen isotope and salinity variations in the indian sector of the southern ocean a combined study of stable oxygen isotopes i 18o and salinity of surface ocean waters collected from the southern indian ocean during the late austral summer and early fall 25th january to 1st april 2006 helped to trace atmospheric and oceanic processes near the equator a very clear signature of the domination of evaporation precipitation process was seen while a precipitation dominated zone was located between two evaporation dominated zones south of the equator the signature of the agulhas front af and the subtropical front stf recognizable by the sharp decrease in salinity and i 18o in the surface waters were identified at 41 s and 44 s in february during the return journey march these two fronts had merged and were located at 41 s south of 45 s the slope of the i 18o salinity relationship was close to zero while north of 62 s could have some precipitation evaporation effect south of 63 s was clearly dominated by freezing melting

neogene sedimentation and tectonics in the cibao basin and northern hispaniola an example of basin evolution near a strike slip dominated plate boundary sedimentologic analyses subsidence history interpretation and a new gravity survey are synthesized to interpret basin evolution in a region of large strike slip offsets and oblique crustal convergence within the northern caribbean plate boundary zone we investigate the mid miocene to mid pliocene yaque group which accumulated in the western cibao basin of northern hispaniola asymmetric subsidence of the cibao basin was accompanied by southward transgression and deposition of an upward fining succession from shallow marine or brackish water conglomerate through sub wavebase siltstone to deep water calcareous siltstone and uncommon interbedded sandstone bioclastic limestone is locally present and in most cases accumulated in a forereef location in early pliocene time ca 4 ma fine grained sediment deposition was briefly interrupted by widespread conglomerate accumulation however basin subsidence was uninterrupted and water depths continued to increase at this time basinal subsidence accelerat

inner shelf to lower shoreface hummocky sandstone bodies with evidence for geostrophic influenced combined flow lower cretaceous west greenland abstract hummocky sandstone bodies were deposited on the margin of an early cretaceous rift basin in an overall progradational inner shelf to lower shoreface unit excellent outcrops of this unit permitted a detailed study of sedimentary structures and paleocurrents in relation to sandstone geometries the sandstone bodies are lensoid and 0 5 4 m thick with lateral extensions from a few meters to more than 30 m laterally they pinch into thin sandstone sheets that continue for at least 130 m along the entire outcrop or swell within a distance of 20 30 m to form another sandstone lens the lower boundaries are sharp with local erosional relief up to 1 m hummocky cross stratification wave ripple cross lamination and low angle cross stratification are closely interbedded within the sandstone aminated mudstone beds 10 60 cm thick separate the sandstone bodies and are generally continuous over the entire length of the outcrop sedimentary structures in the sandstone bodies were produced by high energy wave generated oscillatory currents and unidirectional geostrophic currents vertical stratification successions from individual storm events reflect deposition during both increasing storm current velocity succeeded by waning storm deposits and more typically waning storm facies successions deposition of the unusual vertical successions was probably controlled by an episodically high sediment supply the local presence of the hummocky sandstone bodies on a regional scale was controlled by a paleogeographic setting where the bathymetric contours locally caused geostrophic cu rents to decelerate

late neogene planktonic foraminifera of the cibao valley northern dominican republic biostratigraphy and paleoceanography abstract an assemblage of planktonic foraminifera is described from 125 samples taken from the cercado gurabo and mao formations in the cibao valley northern dominican republic the primary objectives of this study are to establish a biochronologic model for the late neogene of the dominican republic and to examine sea surface conditions within the cibao basin during this interval the cercado formation is loosely confined to zones n17 and n18 7 0 5 9 ma the gurabo formation spans zones n18 and n19 5 9 4 5 ma the mao formation is placed in zone n19 4 5 3 6 ma changes in the relative abundances of indicator species are used to reconstruct sea surface conditions within the basin increasing relative abundances of globigerinoides sacculifer and globigerinoides ruber in conjunction with a decreasing relative abundance of globigerina bulloides suggests the onset of increasing sea surface temperature and salinity in conjunction with diminishing primary productivity at 6 0 ma abrupt increases in the relative abundances of g sacculifer and g ruber at 4 8 ma suggest a major increase in sea surface temperature and salinity in the early pliocene the most likely mechanism for these changes is isolation of the caribbean ocean through progressive restriction of pacific caribbean transfer via the central american seaway periods of high productivity associated with upwelling events are recorded in the upper cercado formation 6 1 ma and in the middle mao formation 4 2 ma by spikes in g bulloides and neogloboquadrina spp respectively the timing of major increases in sea surface salinity and temperature as well as decreasing productivity 4 8 ma and periods of upwelling 6 1and 4 2 ma in the cibao basin generally corroborate previously suggested caribbean oceanographic changes related to the uplift of panama changes in sea surface conditions depicted by paleobiogeographic distributions in the cibao basin suggest that shoaling along the isthmus of panama had implications in a shallow caribbean basin as early as 6 0 ma major paleobiologic changes between 4 8 and 4 2 ma likely represent the period of final closure of the cas and a nearly complete disconnection between pacific and caribbean water masses this study illustrates the use of planktonic foraminifera in establishing some paleoceanographic conditions salinity temperature productivity and upwelling within a shallow water basin outlining the connection between regional and localized oceanographic changes

the residence time of southern ocean surface waters and the 100 000 year ice age cycle from 1 25 million to 700 000 years ago the ice age cycle deepened and lengthened from 41 000 to 100 000 year periodicity a transition that remains unexplained using surface and bottom dwelling foraminifera from the antarctic zone of the southern ocean to reconstruct the deep to surface supply of water during the ice ages of the past 1 5 million years we found that a reduction in deep water supply and a concomitant freshening of the surface ocean coincided with the emergence of the high amplitude 100 000 year glacial cycle we propose that this slowing of deep to surface circulation i e a longer residence time for antarctic surface waters prolonged ice ages by allowing the antarctic halocline to strengthen which increased the resistance of the antarctic upper water column to orbitally paced drivers of carbon dioxide release