tidally modulated occurrence of megaripples in a saturated surf zone 1 an abstracted model for saturated surf zone megaripple occurrence based on the hypothesis that megaripples form and persist unless flow conditions change too rapidly or the bed passes through the swash zone correctly predicts the bed state presence or absence of megaripples for 73 of measurements over 1 year at scripps beach more than seven standard deviations above the agreement between a random model and the measurements transitions between bed states are predicted within 1 5 hours for 54 of measurements compared with 6 agreement for a random model the model is forced with a record of water depth over the beach h from offshore tide measurements and inferred changes in bed elevation assuming that changes in flow conditions and depth are determined by tide level alone in a saturated surf zone model parameter values are estimated independent of model results megaripple formation time t 2 5 hours maximum rms depth change over time t hrms 0 1 m and minimum depth averaged over time t below which megaripples are smoothed hsw 0 3 m allowing model parameters to vary increases agreement between measurements and model predictions to a maximum 82 for parameter values t 3 hours hrms 0 05 m and hsw 0 1 m neither bed state nor bed state transitions are correlated with offshore wave conditions

coarse grained deep water sedimentation along a border fault margin of lake malawi africa seismic stratigraphic analysis lake malawi africa serves as an important modern analog for understanding depositional processes in an active rift setting this paper explores the depositional processes and stacking patterns of coarse grained facies across a large fan delta and associated sub lacustrine fan system offshore of the south rukuru river using single channel seismic data coupled with deep water vibracores and gravity cores a companion paper wells et al 1999 discusses the details of the depositional processes of the system inferred from core data using 2900 km of single channel seismic data eight genetic facies were defined based on seismic reflection character external geometry accompanying core data and location within the modern geomorphic system five sand dominated facies include 1 mouth of canyon fan facies 2 progradational fan delta facies 3 channel fill facies 4 canyon fill facies and 5 basin plain fill facies these facies occur as surficial deposits in water depths of more than 600 m suggesting that coarse grained sedimentation characterizes certain localities in even the deepest parts of lake malawi climatically driven lake level changes influenced the internal character of these facies their thickness and to some extent their location within the south rukuru study area however climate was generally subordinate to tectonism in controlling the temporal and spatial distribution of the facies tectonic controls can be categorized as 1 orientation of the first order border fault and intrabasinal faults 2 syndepositional footwall uplift and rotation and 3 temporal changes in the rate and location of maximum subsidence these controls affect the location and stacking of the mouth of canyon fans and the presence and orientation of sub lacustrine canyons and the zone of maximum sediment accumulation and depositional gradients

trace element signatures of chilean upwelling sediments at 36 s abstract with this contribution we continue the discussion on trace element te cycling in chilean upwelling sediments from within and below the oxygen minimum zone omz boning et al 2005 marine geology 220 1 21 low authigenic i e non lithogenic contents of te ag cd mo re and se were interpreted to result from the distinct seasonality in productivity induced organic flux bottom water oxygenation as well as dilution by terrigenous matter while all sediments were reducing enough to become depleted in mn highest enrichments in mo cd and re occur in sediments in contact with the omz here for a meaningful discussion total contents of as bi co cr cu ni pb sb tl v u and zn were corrected for the lithogenic background by determining te al ratios from local river samples the latter showed significantly lower te al ratios than average shale crust or andesite which are classically used for background correction hence the precise assessment of the lithogenic te contribution for the calculation of authigenic te contents allows to examine the source sink relationship of individual authigenic te for chilean sediments four te groups may be distinguished i mo re u and sb likely originate from sea water and accumulate via diffusive supply across the swi ii cd cr cu ni and zn require biologically induced pre concentration within biogenic material iii ag as se tl and v show an intermediate behaviour and iv bi and pb are contributed by anthropogenic activity highest enrichments in ni cu u as and v occur in sediments in contact with the omz the distinct depletion in co along with mn indicates the overall reducing but non sulfidic character of the chilean omz the degree of sedimentary sulfate reduction seems to be the most important control on chilean and peruvian near coastal enrichment of cd mo and u

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

basement structure and its influence on the structural configuration of the northern north sea rift the northern north sea rift basin developed on a heterogeneous crust comprising structures inherited from the caledonian orogeny and devonian post orogenic extension integrating two dimensional regional seismic reflection data and information from basement wells we investigate the pre rift structural configuration in the northern north sea rift three seismic facies have been defined below the base rift surface 1 relatively low amplitude and low frequency reflections interpreted as pre caledonian metasediments caledonian nappes and or devonian clastic sediments 2 packages of high amplitude dipping reflections 500 ms thick interpreted as basement shear zones and 3 medium amplitude and high frequency reflections interpreted as less sheared crystalline basement of proterozoic and paleozoic caledonian origin some zones of seismic facies 2 can be linked to onshore devonian shear zones whereas others are restricted to the offshore rift area interpreted offshore shear zones dip s ese and wnw in contrast to w to nw dipping shear zones onshore w norway our results indicate that devonian strain and ductile deformation was distributed throughout the caledonian orogenic belt from central south norway to the shetland platform most of the devonian basins related to this extension are however removed by erosion during subsequent exhumation basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters e g in the stord and east shetland basins pre rift structures with present day dips 15 were reactivated although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction

vertical mercury distributions in the oceans the vertical distribution of mercury hg was determined at coastal and open ocean sites in the northwest atlantic and pacific oceans reliable and diagnostic hg distributions were obtained permitting major processes governing the marine biogeochemistry of hg to be identified the northwest atlantic near bermuda showed surface water hg concentrations near 4 pm a maximum of 10 pm within the main thermocline and concentrations less than or equal to surface water values below the depth of the maximum the maximum appears to result from lateral transport of hg enriched waters from higher latitudes in the central north pacific surface waters to 940 m were slightly elevated 1 9 0 7 pm compared to deeper waters 1 4 0 4 pm but no thermocline hg maximum was observed at similar depths hg concentrations near bermuda were elevated compared to the central north pacific ocean this inter ocean pattern results from a combination of enhanced supply of hg to the northwest atlantic by rainfall and scavenging removal along deep water circulation pathways an upper water column hg maximum was also observed at a slope water station in the northwest atlantic and in the tasman sea we hypothesize that the source of this hg comes from diagenetic reactions in oxic margin sediments releasing dissolved hg to overlying water in contrast a broad minimum 1 5 0 2 pm in the vertical distribution was observed in the coastal waters off peru which coincided with the intense oxygen minimum zone in the water column removal of dissolved hg from solution during contact with highly anoxic shelf and slope sediments is proposed as the mechanism for producing this unique profile geochemical steady state box modeling arguments predict a relatively short 350 years mean residence time for hg in the oceans demonstrating the reactive nature of hg in seawater and precluding significant involvement in nutrient type recycling mercury s distributional features and reactive nature suggest that interaction of hg with settling particulate matter and margin sediments play important roles in regulating oceanic hg concentrations oceanic hg distributions are governed by an external cycling process in which water column distributions reflect a rapid competition between the magnitude of the input source and the intensity of the water column removal process in this regard hg shares many distributional features with other elements such as pb and bi which have very short oceanic residence times

trace metal signatures of eastern mediterranean sapropels abstract sapropel samples of pliocene to pleistocene age recovered during odp leg 160 from sites 964 ionian basin 969 mediterranean ridge 966 967 top and northern slope of the eratosthenes seamount south of cyprus and 968 cyprus margin were analysed for major and trace elements eastern mediterranean sapropels are characterized by high organic carbon and sulphur contents and by significant enrichments in several redox sensitive and or sulphide forming trace metals bi cd co cr cu mo ni re sb tl u v enrichment factors relative to average shale are comparable to those found in ctbe black shales the re content is extremely high in the sapropels studied with maximum values up to 1000 ng g re mo ratios averaging 2 7 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to an anoxic water column during sapropel formation additionally enhanced ba concentrations in the sapropels support the assumption that bioproductivity was also high during these episodes trace metal signatures of sapropels originating from different drill sites on a transect across the eastern mediterranean are not only influenced by water depth but also by their location in the eastern mediterranean metal enrichments seem to be higher at the western sites compared with the eastern sites this probably reflects a change in the circulation pattern during periods of sapropel formation pliocene sapropels exhibit elevated trace metal contents in comparison with pleistocene examples therefore different palaeoceanographic conditions may have developed during the pleistocene compared with the pliocene altering palaeoceanography was probably controlled by climatic change which may be related to the onset of glaciation of the northern hemisphere decreasing summer precipitation throughout the late pliocene and the pleistocene may also have influenced sapropel deposition

geochemical signatures of the namibian diatom belt perennial upwelling and intermittent anoxia 1 a gravity core from the nambian diatom belt 83 m water depth was analyzed for major al ca fe k mg p si ti and minor elements ag as ba bi cd co cr cu mn mo ni rb re se sr tl u v zn zr as well as c and s the major element geochemistry is dominated by the contribution of biogenic phases opal and minor amounts of carbonate and phosphate whereas terrigenous components of eolian and fluvial origin form only a minor admixture of 15 examination of the fe s c relationship reveals a completion of pyritization close to the sediment seawater interface higher than average shale fe al ratios reflect the presence of highly reactive iron oxides in terrigenous source material from the namibian desert and suggest little loss of fe within the omz the low total fe content likely represents an important factor responsible for sporadic h2s eruptions the upwelling system off namibia may be regarded as an intermediate system combining high productivity typical for upwelling areas with the sporadic presence of h2s in the water column by examining the source sink relationship of individual trace metals two different trends are discernible mo re and u accumulate following seawater availability whereas ag cd cu ni tl and zn require a biological preconcentration step trace metals like as ba cr se and v show an intermediate behavior metal enrichment is favored by high interstitial water sulfide concentrations close to the sediment seawater interface leading to slightly elevated co contents as opposed to extremely low mn al ratios reflecting the overall reducing character of the namibian system maximum contents of cu ni and zn are significantly lower than those reported previously this may in part be related to the absence of fecal material and a stronger dilution by biosiliceous material at this location compared to the seaward flank of the diatom belt

bismuth in the atlantic and north pacific a natural analogue to plutonium and lead abstract bismuth has been analysed on samples from a vertical section from california to vertex iv north of hawaii from a profile in the western sargasso sea and from an extensive suite of surface stations in the north and south atlantic taken together with data from samples of bermuda rain and from the mississippi amazon and the orinoco and its tributaries a general outline of the processes controlling the bi distribution in the ocean can be worked out the dominant source in the open ocean is aeolian with the fluvial inputs being very small most of the aeolian input is probably derived from volcanoes an anthropogenic flux may be important in the northwest atlantic bismuth is scavenged in the mixed layer and regenerated at shallow depth to give a distribution in the northwest pacific similar to that of 239 240 pu and anthropogenic pb below 2 km the values are extremely low in the range 20 50 fm lower than the coexisting levels for 232 th the residence time of the element in the water column is sufficiently short that there are large concentration decreases between the deep waters of the atlantic and pacific in the latter ocean the element appears to reflect essentially one dimensional processes

depositional and halokinetic sequence stratigraphy of the neoproterozoic wonoka formation adjacent to patawarta allochthonous salt sheet central flinders ranges south australia parts of two third order neoproterozoic marinoan depositional sequences are documented in the wilpena group wonoka formation and bonney sandstone at patawarta diapir located in the central flinders ranges south australia these sequences represent an overall regressive succession transitioning upwards from outer to middle wave dominated shelf deposits to a tidally dominated barrier bar to coastal plain the lower middle upper limestone and green mudstone informal members of the wonoka formation comprise the highstand systems tract of the lower sequence the sequence boundary is at the top of the wonoka green mudstone member and is overlain by the lowstand systems tract of the upper sequence which includes the lower dolomite sandstone and upper dolomite beds of the patsy hill member of the bonney sandstone the upper sequence transgressive systems tract comprises thebonneysandstone theseunitscompriseonecompletetaperedcompositehalokineticsequence chs the lower halokinetic sequence boundary is associated with the maximum flooding surface of the lower depositional sequence and the upper halokinetic sequence boundary is interpreted as the transgressive surface of the overlying depositional sequence where an angular truncation of up to 908is documented the majority of our knowledge of salt tectonic processes is derived from the analysis of subsurface datasetsfromoffshorepetroleum bearingsaltbasins such as the gulf of mexico brazil west africa and

210po and210pb distributions in the central and eastern indian ocean abstract disequilibrium between 210 po and 210 pb and between 210 pb and 226 ra has been mapped in the eastern and central indian ocean based on stations from legs 3 and 4 of the geosecs indian ocean expedition 210 po 210 pb activity ratios are less than 1 0 in the surface mixed layer and indicate a residence time for po of 0 6 years 210 po and 210 pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100 500 m where po may be returned to solution after removal from the surface water and in samples taken near the bottom at a few stations 210 pb excesses relative to 226 ra are observed in the surface water but these excesses are not as pronounced as in the north pacific and north atlantic the difference is attributable to a lower flux of 210 pb from the atmosphere to the indian ocean below the main thermocline 210 pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom departures from this pattern are especially evident at stations taken in the bay of bengal where 210 pb 226 ra activity ratios as low as 0 16 are observed and near the mid indian ridge the data suggest that removal of 210 pb at oceanic boundaries coupled with eddy diffusion along isopycnals can explain gradients in 210 pb near the boundary application of a simple model including isopycnal diffusion chemical removal production and radioactive decay produces fits the observed 210 pb 226 ra gradients for eddy diffusion coeffients of 10 7 cm 2 s high productivity in surface waters of the bay of bengal makes this region a sink for reactive nuclides in the northern indian ocean

volatile fluxes from volcanoes volatile fluxes from mid ocean ridge mor and subaerial volcanism have been estimated or re evaluated using several natural tracers 3he 210po so2 and chemical ratios of volatile species in lavas and volcanic gases these estimates confirm the net predominance of anthropogenic fluxes over volcanic fluxes for co2 so2 and trace metals they also suggest that while most of the volatiles transferred during mor volcanism come from the mantle volatiles stored at the surface of the earth supply an appreciable fraction of subaerial fluxes and can be the dominant source for some of them the surface inventory of volatile species cannot result from steady state degassing with constant rate and needs much greater fluxes in the past or other volatile supply processes this inventory is the result of several of the following processes capture of the solar nebula and its subsequent partial escape impact degassing of accreting bodies and from archean to present mantle degasssing through volcanism and associated phenomena with recycling into the mantle through subduction

oil source rock correlation in the north viking graben abstract based on evaluation of geochemical properties of nearly 100 oils from the north viking graben we have identified three hydrocarbon populations one population is derived from marine shales of the draupne fm one from marine shales of the heather fm that are rich in land plant detritus and one from a mixture of the two while the draupne fm is the dominant source rock the heather fm lower callovian is an important source on the northern horda platform furthermore on the northern horda platform heather fm shales play a major role in controlling migration oil from the draupne fm migrates only into upper jurassic reservoirs as no large titled fault blocks permit juxtaposition of draupne fm and brent gp sands and the heather fm shales are thick and extensive oil from the heather fm migrates into both upper and middle jurassic reservoirs variations in properties of the hydrocarbons in the north viking graben petroleum system are due to a complex interplay of organic source maturity migration pressure distribution and biodegradation integration of geochemical and geological data on a regional scale has enhanced our ability to evaluate prospects in this important hydrocarbon system

origin of anomalous tertiary subsidence adjacent to north atlantic continental margins abstract at the beginning of the tertiary the northern north atlantic continental margins were characterized by voluminous igneous activity caused by continental rifting in the presence of the iceland hot spot many of the mesozoic sedimentary basins close to these margins have been permanently uplifted by igneous underplating and remain close to or above sea level at the present day however a significant number of other basins underwent rapid subsidence at the same time sometimes by as much as 3 km of sediment loaded subsidence in 15 20 ma several hypotheses attempting to explain the cause of this tertiary subsidence have been proposed the observational data are summarized here and then each hypothesis is considered in turn it is argued that many of these are implausible one possible alternative explanation links early tertiary subsidence uplift and magmatism if basaltic melts are trapped within the lithosphere it is possible to produce either uplift or subsidence depending on the density of the trapped melt at depths greater than 50 km melts will solidify rapidly in the garnet stability field to form primary eclogite which is dense enough to cause subsidence while satisfying the constraints of long wavelength airy isostasy unfortunately such an hypothesis is difficult to test the simplest explanation for tertiary subsidence is still a minor episode of lithospheric stretching although to date there is only limited evidence for sufficient tertiary normal faulting further work must be carried out before this simple and testable hypothesis can be confidently rejected

test of sediment initial motion theories using irregular wave field data sediment initial motion theories predict the flow conditions that coincide with onset of sediment motion but usually the most that can be determined from burst sampled field data is whether or not sediment was in motion furthermore initial motion theories are usually based on regular wave laboratory data with little or no guidance given on how such theories are to be transferred to the real world of irregular waves a field dataset obtained from the zone of wave shoaling beyond the surfzone is used to compare the performance of three initial motion theories in a way that takes explicit account of wave irregularity and the limitations of burst sampling the dataset comprises video images of the seabed and measurements of waves currents and suspended sediment the initial motion theories tested were komar miller s 1975 j sedim petrol 45 362 367 wave orbital speed theory a wave stress theory and a wave plus current stress theory fourteen transitions from no sediment motion to sediment motion were observed but not all of those represented a challenging test of theory using the criterion that the best theory is the one that minimizes errors in classifying bursts as no sediment motion or sediment in motion komar miller s 1975 theory was found to perform the best when waves were characterized by significant wave height and mean spectral period both of which can be estimated directly from pressure data alone komar and miller s theory was better at predicting the onset of extended transport events which occurred during confused seas rather than the transition back to moribund seabed under clean swell at the end of such events the conclusion regarding best theory is dependent on the choice of scales used to characterize wave motion the way forward therefore is to standardize and define terms precisely

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

bedform geometry on a barred sandy shore abstract an instrumented sled was used to repeatedly measure nearshore profiles and bedform height length and asymmetry on a double barred beach at mangawhai northland new zealand the 6 week experiment measured cross shore profiles at 30 m intervals to 12 m water depth and 500 m alongshore bedform response to changing wave conditions that included both fairweather swell and storm waves was sampled bedform geometry is closely tied to large scale morphology with alternating bands of flat bed and lunate megaripples lmr 0 3 m 2 9 m on the longshore bars a transition in bedform morphology occurs on the seaward face of the outer bar with symmetrical vortex ripples 0 04 m 0 7 m replaced by lmr within the transition zone increases relative to so that increases onshore with a shift to increasingly 3 dimensional forms bedforms reconfigured to the fairweather swell 2 weeks after a storm at the start of the experiment this was shown by a substantial reduction in longshore and cross shore variability in average bedform size and steepness wave measurements made on the ripple field seaward of the longshore bars at 5 2 and 6 9 m mean sea level msl indicate that sand mobilisation was episodic under fairweather swell skin friction shields parameter w 0 35 by comparison w 2 under storm waves indicates that the entire nearshore bed was active at least to 6 9 m msl this is consistent with the presence of lmr on storm deposits to 6 m msl lunate megaripples dominate bed roughness when parameterised by 2 they persist seaward of the longshore bars for weeks after storms because substantial sand transport is required to reconfigure the bed to fairweather conditions the natural variability in bedform geometry will need to be accounted for if realistic morphodynamic models are to be realised

oblique rifting and sequential faulting in the jurassic development of the northern north sea abstract jurassic structural development of the northern north sea has characteristics of oblique rifting this is interpreted to result from an obliquity between jurassic nw se to wnw ese directed extension and a preexisting n s trending zone of deformation related to permo triassic rifting and thinning of the crust the zone of maximum jurassic extension i e the viking and sogn grabens defines a narrow 25 40 km depression which trends diagonally nne ssw across a broader 130 150 km permo triassic basin the jurassic rift zone consists of a system of ene chelon rift segments with changing symmetry along strike bounded by faults oblique to the overall graben envelope sequential jurassic fault development as well as the interference between n s and ne sw striking faults are explained within the context of oblique rifting the early late bajocian oxfordian rift stage was dominated by reactivation of n s striking major faults whereas a number of coeval but smaller faults have a ne sw orientation ne sw striking faults show increasing importance during the jurassic stretching phase and major faults defining this orientation accommodated most of the kimmeridgian volgian extension faults striking nesw are observed to cross cut earlier n s trending faults they interfere with n s trending faults to define faultblocks with rhombohedral shape and they are associated with partial collapse of crestal areas of n s oriented fault blocks to form structural terraces

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

depositional architecture of a wave dominated clastic shoreline pilmatue member argentina linking dynamics and stratigraphic record of bar trough systems abstract bar trough morphologies are a dominant feature of modern wave dominated clastic shorelines despite these barred configurations being widely described from modern systems there is still some uncertainties associated with their interpretation in the ancient record there is a lack of detailed outcrop based studies describing the facies distribution and architecture within bar trough systems which causes a disparity between observations of modern processes and the subsequent preserved rock record this work presents a detailed characterization and interpretation of the sedimentary record of a bar trough setting this was achieved through the analysis of nearshore i e upper shoreface and foreshore deposits within a parasequence in the lower cretaceous pilmatue member of the agrio formation neuquen basin argentina a high resolution facies and architectural analysis was developed combining detailed sedimentary logs with the mapping of bounding and internal surfaces within the nearshore deposits the facies analysis suggests that trough and planar cross bedded facies are remnants of dunes in the upper shoreface due to a strong influence of longshore currents while planar laminated facies would be the result of swash processes in the foreshore additionally the presence of a well defined surf diastem the persistent low angle obliquity of palaeocurrents and the preservation of concave upward stratigraphic surfaces led to the interpretation of those deposits as representing the production of a bar trough configuration with longshore currents distributing large amounts of sediment along the shore this analysis allowed us to reconstruct the dominant processes for sediment transport and deposition within these barred nearshore settings and to identify different key architectural surfaces for the upper shoreface and foreshore deposits the architectural analysis of such surfaces led to define four different orders of hierarchy which respond to depositional and erosional processes operating at different scales the comparison between different resulting architectures of wave dominated barred shoreline offers the possibility to improve in the palaeoenvironmental reconstructions for ancient or recent successions the proposed model for bar trough clastic shoreline successions relates an absence of bar related deposits to major storms and shoreline erosional processes this conceptual model offers a new interpretation for explaining the mid scale evolution of bar trough settings and the relationship between the modern and ancient record

vertex manganese transport through oxygen minima abstract manganese transport through a well developed oxygen minimum was studied off central mexico 18 n 108 w in october november 1981 as part of the vertex vertical transport and exchange research program refractory leachable and dissolved mn fractions associated with particulates caught in traps set at eight depths 120 1950 m were analyzed particles entering the oxygen minimum had relatively large mn loads however as the particulates sank further into the minimum total mn fluxes steadily decreased from 190 nmol m 2 day 1 at 120 m to 36 nmol m 2 day 1 at 400 m manganese fluxes then steadily increased in the remaining 800 1950 m reaching rates of up to 230 nmol m 2 day 1 at 1950 m manganese concentrations were also measured in the water column dissolved mn levels 1 were consistently observed within the 150 600 m depth interval in contrast suspended particulate leachable mn amounts were especially low at those depths and never exceeded 0 04 nmol kg 1 the combined water column and particle trap data clearly indicate that mn is released from particles as they sink through the oxygen minimum rate of change estimates based on trap flux data yield regeneration rates of up to 0 44 nmol kg 1 yr 1 in the upper oxygen minimum 120 200 m however only 30 of the dissolved mn in the oxygen minimum appears to be from sinking particulate regeneration the other 70 probably results from continental slope release horizontal transport processes dissolved mn scavenges back onto particles as oxygen levels begin to increase with depth scavenging rates ranging from 0 03 to 0 09 nmol kg 1 yr 1 were observed at depths from 700 to 1950 m these scavenging rates result in mn residence times of 16 19 years and scavenging rate constants on the order of 0 057 yr 1 manganese removal via scavenging on sinking particles below the oxygen minimum is balanced by mn released along continental boundaries and transported horizontally via advective diffusive processes manganese appears to be very weakly associated with particulates nevertheless the amounts of mn involved with sinking biogenic particles are large and the resulting fluxes are on the same order of magnitude as those necessary to explain the excess mn accumulating on the sea floor the overall behavior of mn observed in this and other studies strongly suggests some type of equilibrium occurring between dissolved and particulate phases this equilibrium appears to shift in direct or indirect response to dissolved oxygen levels

autogenic controls on hybrid bed distribution in submarine lobe complexes abstract hybrid beds the deposits of sediment gravity flows that show evidence for more than one flow regime turbulent transitional and or laminar have been recognized as important components of submarine lobe deposits a wide range of hybrid bed types have been documented however quantitative analysis of the stratigraphic and geographic distribution of these enigmatic bed types is rare here extensive exposures integrated with research borehole data from unit a of the laingsburg formation and fan 4 of the skoorsteenberg formation ecca group south africa provide the opportunity to examine geographical and stratigraphic patterns over a range of hierarchical scales for this purpose 23 000 individual beds have been evaluated for deposit type and bed thickness on average hybrid beds make up data from unit a laingsburg formation show hybrid beds are less common in the basal a 1 and top a 6 subunits compared to a 2 a 5 in both core data sets the bases and tops of some lobe complexes a 2 a 3 and a 5 7 are observed to be slightly enriched in hybrid beds whereas others a 5 1 a 5 5 and a 6 1 show no hybrid beds in their bases which does not conform to expected allogenically driven distributions that predict more hybrid beds during the initiation of lobe complexes instead the occurrence and distribution of hybrid beds in lobe complexes are interpreted to be controlled by autogenic processes including flow transformation processes on the basin floor meaning enrichment in frontal lobe fringe settings therefore the 1d distribution of hybrid beds in lobe complexes reflects the dominant stacking pattern of lobes within a lobe complex with enrichment at the base and top of lobe complexes due to overall progradational to retrogradational stacking patterns individual lobes show a wide range of hybrid bed distributions due to stacking patterns of the component lobe elements these findings highlight the importance of autogenic processes rather than allogenic controls in the distribution of hybrid beds which has implications for reservoir evaluation and the assessment of lobe stacking patterns in 1d core data sets

control of rift obliquity on the evolution and segmentation of the main ethiopian rift the main ethiopian rift has evolved in two stages with successive activation of differently oriented fault systems analogue modelling of the earth s lithosphere demonstrates that such a rift evolution requires neither magma weakening nor a change in plate kinematics the main ethiopian rift is an active rift in the break up stage and it marks the incipient boundary between the nubia and somalia plates1 rifting started with the activation of large boundary faults and diffuse volcanism followed by focused magmatism and faulting in the rift floor along step like segments oblique to the rift axis that now act as a protoridge for future seafloor spreading2 this concentration of volcano tectonic activity has been thought to be either magma assisted2 3 or controlled by a change in rift kinematics with a late oblique rifting phase that would have caused the development of the step like fault segments that focused magma upwelling4 5 geodetic6 7 seismic8 and stress field9 data confirm current oblique rifting kinematics but plate kinematics models do not predict a change in nubia somalia motion in the past 11 million years10 here i use lithospheric scale analogue models of oblique rifting to analyse the development of the main ethiopian rift i find that neither magma weakening nor a change in plate kinematics are required to simulate a two phase evolution with successive activation of differently oriented fault systems i conclude that rift evolution and segmentation are controlled by rift obliquity independent of magmatic processes

a marine late jurassic syn rift succession in the lusitanian basin western portugal tectonic significance of stratigraphic signature abstract in the lusitanian basin which is located along the western iberian margin rapid subsidence in the oxfordian tithonian resulted from extension related to the opening of the north atlantic in the santa cruz area located in the western part of the lusitanian basin the kimmeridgian syn rift marine abadia formation and the overlying alluvial kimmeridgian tithonian praia da amoreira member of the lourinha formation were deposited in the middle part of the hangingwall dip slope of a larger half graben that constitutes the turcifal subbasin the marine part of the succession consists of base of slope and lower slope mudstones and sandy turbidites middle slope mudstones upper slope to shelfal shoreline mudstones and sandstones and fan deltaic deposits two intermediate scale fining to coarsening fucu units are present in the marine strata the lower fucu unit represents a normal base of slope lower slope to upper slope shoaling upward succession the unit reflects the progradation of a hangingwall shelfal ramp and infilling of an inherited rift bathymetry during a period of relative tectonic quiescence the upper fucu unit represents an intermediate scale deepening shoaling upward or backstepping forestepping sequence which is related to a single rift event the backstepping segment was deposited during a period of increasing basinal subsidence and basin floor tilt rates the early syn rotational stage it consists of submarine channel fill incised into slumped upper slope sediments and adjacent overbank deposits the backstepping segment terminates with a clay prone marine interval with abundant soft sediment deformation features which represent a period of maximum sea level stand during the rotational climax the overlying forestepping segment consists of a shoaling upward slope to fan deltaic succession which terminates with alluvial deposits it represents an interval with decreasing basinal subsidence and basin floor tilt rates and renewed overbalance of sediment supply which led to a regression during the late syn rotational stage in medial reaches of the hangingwall dip slope periods of increasing to decreasing rift activity are recorded by a backstepping forestepping package or a threefold sandstone mudstone sandstone lithosome motif the formation of smaller scale units superimposed on the intermediate scale fucu syn rotational motif were controlled predominantly by minor fault controlled subsidence events or higher frequency faulting events

sand bed roughness in the nearshore 1 measurements made using sonar altimeters mounted on an amphibious surveying vehicle are analyzed for root mean square rms bedform roughness observations for 22 days over a 500 m 700 m area are used to quantify the cross shore distribution of roughness and its variability large bedforms with amplitudes 5 50 cm occur frequently in shallow water 2 m water depth however the patchiness of these bedforms is also largest in shallow water this is likely owing to the spatial and temporal variability of the waves and currents of the sediment grain size distributions and of the large scale nearshore morphology large bedforms were observed to exist only for mobility numbers 150 above this threshold the rms roughness was 2 cm and the bed was interpreted to have transitioned to sheet flow conditions however the state of the bed e g large ripples small ripples flat bed was not predictable for mobility numbers between about 30 and 150 existing models for orbital ripples do not predict the observed large bedforms and have little predictive skill for these data

distribution and origin of hybrid beds in sand rich submarine fans of the tanqua depocentre karoo basin south africa abstract this study documents the stratigraphic and palaeogeographic distribution of hybrid event beds that comprise both debris flow cohesive and turbidity current non cohesive deposits this is the first study of such beds in a submarine fan system to combine outcrop and research borehole control and uses a dataset from the skoorsteenberg formation of the tanqua depocentre in the karoo basin south africa three types of 0 1 1 0 m thick hybrid beds are observed which have a basal weakly graded fine grained sandstone turbidite division overlain by a division of variable composition that can comprise 1 poorly sorted carbonaceous rich material supported by a mud rich and micaceous sand matrix 2 poorly sorted mudstone clasts in a mud rich sand silt matrix or 3 gravel grade rounded mudstone clasts in a well sorted mud poor sandstone matrix these upper divisions are interpreted respectively as 1 the deposit of a debris flow most likely derived from shelf edge collapse 2 the deposit of a debris flow most likely developed through flow transformation from turbidity current that eroded a muddy substrate and 3 from a turbidity current with mudstone clasts transported towards the rear of the flow all three hybrid bed types are found concentrated at the fringes of lobes that were deposited during fan initiation and growth the basinward stepping of successive lobes means that the hybrid beds are concentrated at the base of stratigraphic successions in medial and distal fan settings hybrid beds are absent in proximal fan positions and rare and thin in landward stepping lobes deposited during fan retreat this distribution is interpreted to reflect the enhanced amounts of erosion and availability of mud along the transport route during early lowstands of sea level therefore hybrid beds can be used to indicate a fan fringe setting infer lobe stacking patterns and have a sequence stratigraphic significance

mercury in surface waters of the open ocean mercury was determined in samples of surface seawater and rainfall from coastal and open ocean areas of the northwest atlantic and pacific oceans mercury concentrations in surface seawater and open ocean rainfall ranged from 0 5 to 11 pm and 6 to 130 pm respectively the pluvial flux of hg to the open ocean was estimated at 1 7 109 g yr using mean concentrations of hg in rainfall and annual rainfall volume estimates for the major ocean basins fluvial input while difficult to reliably assess was a less important about 0 18 109 g yr source of hg to the ocean the mean residence time of hg in the surface mixed layer to 75 m was calculated at 4 7 years which is similar to other very reactive elements such as al pb and bi surface seawater hg distributions are markedly influenced by atmospheric sources due to an elevated supply of hg to the northwest atlantic by rain higher hg values were observed in surface seawater in the northwest atlantic ocean 4 0 0 7 pm than at low latitudes in the central north pacific ocean 2 1 0 4 pm surface seawater hg concentrations between coastal new england and the sargasso sea do not show the large offshore concentration gradient typical of elements which have relatively large fluvial or coastal sources rather the hg distribution in this region was similar to that obtained for the atmospherically derived constituents pb and 210pb surface seawater hg measurements in the central pacific ocean along 160 w between 20 n and 20 s showed a depression 60 in the equatorial upwelling area which coincided with the transect region exhibiting low 234th 238u activity ratios this relationship implies that hg has enhanced scavenging and removal from surface seawater in biologically productive oceanic zones in contrast to the surface distribution in the northwest atlantic a pronounced on shore gradient in sea surface hg concentration was observed in the tasman sea this may have resulted from the upwelling of water high in hg content into the near coastal zone

dynamics of large and small scale bedforms on a macrotidal shoreface under shoaling and breaking waves abstract bedform dimensions bed position changes near bed velocities and suspended sand concentrations are analyzed from measurements at a single location on a macro tidal beach in the south west of england the study was conducted in 0 5 2 25 m water depth under both swell and wind generated storm waves with both weak and strong currents present bed positions and suspended sand concentrations were measured using the 3 transducers of a multi frequency acoustic backscatter sensor with 5 mm vertical resolution two distinct bed types based on wavelength were observed each with two or more subtypes possible i small scale bedforms 20 cm which include two dimensional 5 forms and three dimensional vortex 6 forms small scale forms were dominant under non breaking conditions while the large scale forms occurred under both non breaking and breaking waves the large scale forms dominate under breaking conditions both types but particularly low steepness forms were highly mobile with maximum horizontal migration rates of 5 cm min 1 large upto 15 cm and rapid upto 3 0 cm min 1 changes in vertical bed elevation were also observed in association with the development and migration of large scale forms large scale bedforms were also highly variable spatially often being interspersed with smaller scale forms under decaying flow regimes and with areas of flat bed under increasing regimes observations suggest these forms are present even under high energy surf zone conditions wave shields 1 models for predicting ripple dimensions did not perform well in this environment this lack of agreement reflects the complex hydrodynamic regimes associated with random grouped shoaling and breaking waves together with the presence of currents often at large angles to the waves as well as the rapid rates of change in the wave forcing associated with tidal cycle oscillations in this macrotidal environment suspended sediment concentrations and transport rates are particularly sensitive to the bedforms present and also to bed position changes associated with ripple migration estimates of transport rates are subject to potentially large errors upto 30 without compensation for bed elevation changes relative to sensor position

beryllium in the water column of the central north pacific the existence of the cosmogenic radioisotope of beryllium 10be t1 2 1 5 myr was first confirmed1 2 almost 25 yr ago subsequently merrill et al 3 worked out the sedimentary geochemistry of the stable isotope of the element 9be the geochronological potential of 10 be could not be exploited however because of its extremely low abundance global average production rate 1 08 atoms cm 2 min 1 4 and the difficulties associated with the analysis of the stable species 9be particularly in natural waters this situation is changing dramatically with the application of accelerator techniques to the detection of the radioisotope5 it thus becomes important to obtain a detailed understanding of the geochemistry of 9be since the potential use of the stable isotope for normalization purposes would significantly enhance the usefulness of the radioactive species in dating studies we report here the first detailed profile for 9be in the oceanic water column

spatial variability in depositional reservoir quality of deep water channel fill and lobe deposits abstract initial porosity and permeability in deep water systems are controlled by primary sedimentary texture and mineralogy therefore understanding the sedimentary processes that control changes in primary texture is critical for improved reservoir quality predictions a well constrained exhumed submarine lobe in the jaca basin and a submarine channel fill element in the ainsa basin northern spain were studied to characterize the depositional reservoir quality in axial to marginal fringe positions construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties and their relationship to reservoir quality distribution samples were analyzed in thin section to establish how depositional processes inferred from outcrop observations affect textural properties results show that high density turbidites are concentrated in lobe and channel axis positions and exhibit good depositional reservoir quality lobe off axis deposits contain high and low density turbidites and have moderate depositional reservoir quality conversely low density turbidites dominate lobe fringe and channel margin positions and have relatively poor depositional reservoir quality there is a sharp decrease in depositional reservoir quality between the lobe off axis and lobe fringe due to 1 an abrupt increase in matrix content 2 an abrupt decrease in sandstone amalgamation and 3 a decrease in grain size there is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to 1 an increase in total sandstone thickness and amalgamation 2 an increase in grain size 3 a decrease in matrix content rates of change of key properties are up to two orders of magnitude greater between channel fill sub environments compared to lobe sub environments spatial variability in properties of discrete architectural elements and rates of changes provides input to reservoir models during exploration appraisal and development phases of hydrocarbon fields

lead concentrations in the northeast pacific evidence for global anthropogenic perturbations lead concentrations were determined by isotope dilution mass spectrometry in 34 surface and deep water samples collected in the northeast pacific between hawaii and california and off the california coast using a deep water sampler protected against fouling by contamination from the ship and hydrowire measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90 or more of the total lead is in a dissolved form lead concentrations are about 10 fold higher in surface and thermocline waters than in deep waters values drop as low as 1 ng kg 5 pmol kg below 3500 m depth lead profiles thus appear different compared to those of most trace metals which show enrichment in deep waters compared to surface concentrations lead concentrations in surface waters increase from 5 to 15 ng kg 25 to 75 pmol kg along a transect starting from a location 200 km off the california coast and continuing towards the center of the north pacific gyre this increase is congruent with that observed for 210 pb concentrations in the same waters sampled at the same time lead is supplied to the open north pacific largely from the atmosphere at a rate of about 60 ng cm 2 yr which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold this excess originates from emissions from smelters and combustion of leaded gasoline overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers vertical lead concentration profiles below the surface mixed layer are probably not in steady state there concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters based on an estimated 10 fold input and concentration increase since the mid eighteenth century in the surface mixed layer in the central northeast pacific it is calculated that the 10 ng kg average concentration between 100 and 900 m is 2 to 5 times larger and the 1 8 ng kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid eighteenth century profiles of lead concentrations in the north atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the north pacific because of the effects of greater industrial lead contamination while lead concentration profiles in the south pacific are expected to be shifted generally to lower values compared to the north pacific by about this same factor because of the effects of lesser industrial lead contamination

evidence of rift segmentation and controls of middle to late jurassic synrift deposition in the ryggsteinen ridge area northern north sea multiple episodes of rifting and preexisting structure reactivation may result in rift segmentation which is a fundamental factor in deformation variability and sediment dispersal to understand the structural framework and basin evolution in segmented rift systems this study addresses an integrated structural and stratigraphic analysis of the middle upper jurassic sequences in the northern north sea four major fault systems were active during the jurassic oblique rifting 1 east northeast striking synthetic shear faults along preexisting caledonian structures which developed into basin wide transfer fault zones and induced first order rift segmentation each rift segment shows independent deformation 2 north south striking reactivated permian triassic faults which uplifted the footwall developing major structural highs 3 southwest northeast striking normal faults and 4 northwest southeast striking antithetic shear oblique slip faults which caused internal deformation and induced second order rift segmentation within rift segments rift segmentation led to stepovers from the viking graben to the sogn graben the entry of regional drainages was determined by first order rift segmentation prior to segmentation bathonian callovian drainage shows a northeast southwest line source nature and facies changes are quite homogenous during the oxfordian kimmeridgian segmentation took place and modified the drainage system into a point source facies show a large spectrum of variability from shallow marine to deep water turbidites over short distances furthermore drainage routes were influenced by second order rift segmentation west directed drainages deflected toward the northwest by adapting to gradient surfaces established by oblique slip faults as such the structural and stratigraphic expressions in this study provide an example of synrift deposition controlled by different orders of rift segmentation

distribution of be al se and bi in the surface waters of the western north atlantic and caribbean abstract the mixed layer distributions of several trace elements have been determined along a detailed transect from rhode island to the panama canal when taken together with a new and existing profile data from the north atlantic and north pacific some general inferences emerge as to the processes controlling their concentrations in the surface waters the large enrichments in be observed in the upper waters of the north atlantic relative to the north pacific appear to be sustained mainly by fluvial inputs those of se are derived from atmospheric transport aluminium and bi also appear to have an aeolian source in the sargasso sea however in the tropical eastern pacific the al input may be fluvial on this cruise be al and the se species were analyzed on board ship within a few hours of collection the demonstration that this is feasible opens up the prospect of the application of large scale chemical hydrography to the study of the processes controlling the distribution and water column variability of trace elements in the oceans

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

the geochemical cycle of 9be a reconnaissance an initial survey has been made of the geochemistry of 9be in natural waters with a view to utilizing the isotope with the cosmogenic species 10be t1 2 1 5 m y in geochronological studies of sedimentary accumulation the mobility of9be in continental waters is a strong function of ph with acid streams ph 6 being strongly enriched as compared to alkaline carbonate rivers large scale scavenging of beryllium occurs in the estuaries of rivers containing more than about 200 pm of the element in alkaline systems of lower concentration the element appears to behave conservatively the net flux of beryllium to the ocean is estimated as that equivalent to an average effective river concentration of about 150 pm beryllium is strongly enriched in ridge crest hydrothermal solutions over ambient seawater the flux is approximately 70 of that from the continents the deep water concentrations of 9be vary by only 20 between the north atlantic and north pacific demonstrating that the chemical saltation produced by scavenging from the deep water column and release from the sediments predominates over simple advective concentration along flow lines isotopic homogenization of 10be and 9be is probably achieved in the ocean the situation in continental waters appears much less promising

processes of sedimentation on a lacustrine border fault margin interpretation of cores from lake malawi east africa large lakes are attractive research sites because they provide ideal spatial scales for understanding the complex relationships between facies distributions and processes of sedimentation in this paper we describe deepwater facies and associated environments of deposition based primarily on cores from the tectonically active south rukuru sublacustrine fan system of lake malawi east africa where river discharge is high offshore gradients are steep and gravity driven processes are common the coring program was tied to a simultaneous seismic investigation which is discussed in a companion paper soreghan et al 1999 all facies except the hemipelagic drape contain widespread evidence of gravity driven sedimentation processes with turbidity currents being responsible for most of the sediment transport and deposition multiple fining up turbidite units dominate the sandy facies of the canyons channels mouth of canyon fans and basin plain fill environments and thin distal turbidites are present in cores through most of the muddier facies angular gravel and coarse sand are common not only throughout the canyons of the sloping relay ramp region but also as far offshore as the main axial channel and its depocenter the basin plain fill facies turbidites range in thickness from 0 25 to 2 0 m are usually stacked and can be recognized by well defined bouma sequences a hemipelagic drape of highly laminated to structureless mud which forms an uneven blanket over much of the lake bottom is commonly interspersed with turbidites because lake levels can change rapidly as a result of climatic variations the rate of sediment mobilization is extremely fast relative to marine systems vertical excursions in lake level of 100 m over only a few hundred years may lessen the distinctions between highstand and lowstand deposits the border fault setting allows coarse sediment to be delivered to the steep offshore even during periods of lake high stand however during periods of falling and low lake level it is likely that downcutting and erosion of highstand deltas increase the magnitude and intensity of turbidite deposition in the mouth of canyon fan and in the basin plain fill environments

thermomechanical structure of european continental lithosphere constraints from rheological profiles and eet estimates summary the eet equivalent elastic thickness of the lithosphere is a measure of the integrated lithospheric strength it is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere we present a comparison of eet estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the european and eurasian continental lithosphere we discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for precambrian segments of europe s lithosphere variscan europe and the alpine collision belt this analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western europe and asian parts of eurasia the eet estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of eet derived from flexural studies of sedimentary basins forelands and orogenic belts these rheological profiles suggest weakening of the major parts of the european and eurasian continental lithosphere by decoupling of the crustal and upper mantle parts a comparison with the seismicity depth distribution for some selected sites suggests that the intra plate seismicity is essentially restricted to the upper crustal parts of europe s lithosphere providing additional support to the notion of the decoupled lithosphere the presence of intra plate stress fields can explain a significant part of the observed variations in eet estimates within individual thermotectonic age groups a comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of eet inferred from the rheological response of basins and orogens at more moderate levels of intra plate stress

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

types of submarine fan lobes models and implications different lobe models imply significantly different reservoir geometries thus one must apply the proper lobe model to ancient fan sequences braided suprafan lobes are characterized by stacked channel sand bodies with good lateral and vertical communication and they constitute excellent reservoir facies depositional lobes composed of sheet like sand bodies with good lateral and moderate vertical communication exhibit properties of good reservoir facies fanlobes which refer to meandering channels and associated levee facies of large mud rich submarine fans such as the mississippi fan are characterized by offset stacked sand bodies with poor lateral and vertical communication these lenticular sands have the potential to be moderately good reservoir facies ponded obes which represent mud rich slump facies of slope environments comprise poor reservoir facies because of low sand content and poor sand body connectivity furthermore the presence of contorted mud layers in ponded lobes is expected to hinder fluid flow external mounded reflections in seismic profiles often are interpreted as lobes however there are no definite seismic criteria to delineate mud rich lobes from sand rich lobes

geomorphological and sequence stratigraphic variability in wave dominated shoreface shelf parasequences physical stratigraphy within shoreface shelf parasequences contains a detailed but virtually unstudied record of shallow marine processes over a range of historical and geological timescales using high quality outcrop data sets it is possible to reconstruct ancient shoreface shelf morphology from clinoform surfaces and to track the evolving morphology of the ancient shoreface shelf our results suggest that shoreface shelf morphology varied considerably in response to processes that operate over a range of timescales 1 individual clinoform surfaces form as a result of enhanced wave scour and or sediment starvation which may be driven by minor fluctuations in relative sea level sediment supply and or wave climate over short timescales 10 1 10 3 years these external controls cannot be distinguished in vertical facies successions but may potentially be differentiated by the resulting clinoform geometries 2 clinoform geometry and distribution changes systematically within a single parasequence reflecting the cycle in sea level and or sediment supply that produced the parasequence 10 2 10 5 years these changes record steepening of the shoreface shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation modern shorefaces are not representative of this stratigraphic variability 3 clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shore face progradation 10 5 10 8 years these controls determine the external dimensions of the parasequence

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

observed and predicted bed forms and their effect on suspended sand concentrations abstract in this paper we study the effect of bed forms on suspended sand concentrations and we compare three existing bed form predictors to field and laboratory measurements over a wide range of conditions and propose a new predictor that better collapses the measured bed form dimensions we apply the different bed form predictors to estimate the suspended sediment concentration distributions based on the 1d advection diffusion equation and the bed form enhanced shear stress which includes the flow contraction effect according to nielsen coast eng 10 1986 23 predictions of suspended sand concentration improve when including a bed form predictor interestingly it does not make much difference which bed form predictor is implemented but more whether a bed form predictor is implemented however the choice of a particular bed form predictor is more important when the bed form effect in the sand transport model is based a roughness length scale k s and thus on 2 instead of where k s is nikuradse s equivalent roughness length scale is the bed form height and is the bed form length this is the case in the van rijn van rijn l c 2000 general view on sand transport by currents and waves data analysis and engineering modelling for uniform and graded sand transpor 2000 and crosmor 2000 models z2899 20 z2099 30 z 2824 30 wl delft hydraulics delft the netherlands sand transport model for example we discuss the effect of so called long wave ripples on the suspended sand concentrations

small scale morphology across the surf zone small scale 5 m horizontal length nearshore morphologic height variations were measured by combining crab surveys with bed elevations acquired with a 1 mhz sonic altimeter mounted on the crab during the october phase of the duck94 experiment bedform plan views were recorded simultaneously using a 500 khz side scan sonar mounted on the crab waves and currents were measured at the same time significant temporal and spatial variations in the small scale morphology were measured in response to changing waves and currents during the 2 weeks examined three cases are examined in detail 1 mild waves and weak longshore currents resulting in wave ripples throughout the study area 2 storm waves with strong longshore currents resulting in lunate and straight crested mega ripples in the trough of the barred beach and 3 narrow band normally incident waves with a strong rip current resulting in a planar bed except in the throat of the rip where mega ripples were measured wavenumber spectra of the bed were generally broad indicating newly formed ripples coexisted with residual ripples from the past to form complex multi scaled ripple patterns

depth and configuration of the crystalline basement in the viking graben area northern north sea the depth of the crystalline basement in the viking graben area has been mapped the dominant structural feature in the study area is a n s trending zone approximately 150 km wide containing a variety of structures graben basins and structural highs and named the northern north sea rift zone the viking graben is only one structural element though a major one in this zone the following depth ranges appear to apply a on platforms basement shelves and major structural highs 1 3 km b in basins 7 9 km maximum depth c in graben 8 10 km maximum depth

magnitude of lead flux to the atmosphere from volcanoes pb s tl s and bi s ratios were measured in eruptive and fumarolic volcanic gases and indexed to the global flux of volcanic s to characterize approximate global volcanic emissions of these three metals to the atmosphere which are about 1200 tons pb yr 600 tons tl yr and 4000 tons bi yr this volcanic pb input is similar to the magnitude of natural soil dust pb input which is about 1400 tons pb yr during the holocene interglacial both are negligible compared to annual industrial inputs of 300 000 tons pb yr which maintain the present tropospheric reservoir of pb however polar ice records indicate that thousands of years ago the atmospheric pb reservoir was only 1 of its present size which means that volcanic pb was the source of about half the pb in the atmosphere during preindustrial holocene times

suspended sediment reference concentration under waves field observations and critical analysis of two predictive models two commonly adopted but fundamentally different approaches for predicting time averaged suspended sediment reference concentration cref under waves are tested against field measurements and compared with each other the first model relates cref to the cube of the non dimensional skin friction whereas the second model adopts a more complex function of excess skin friction incorporating the empirical constant 0 the dataset is from the zone of wave shoaling seaward of an open coast surfzone and includes measurements of waves currents suspended sediment and bedforms estimates of cref are derived from acoustic backscatter data and the seabed and suspension process are described from video footage when waves were energetic the bed was deformed into large hummocks during less energetic conditions the bed was rippled the time averaged concentration profiles over the ripples were consistent with settling flux balanced by pure gradient diffusion and a sediment diffusivity that is constant with elevation above the bed cref in that case is shown to apply at z 0 where z is the elevation above the bed over the hummocks there was a sheet flow at the base of the suspension and cref is shown to apply at z 1 cm the concentration profiles over the hummocks implied sediment diffusivity that varied linearly with elevation within 10 cm of the bed and constant sediment diffusivity above that level for both rippled and hummocky beds 0 derived from the field data was found to be sensitive to the value assumed for critical stress for initiation of sediment motion which could explain the range of values reported in the literature for 0 0 was also found to vary in a complex way with skin friction which suggests that the reference concentration model based on excess skin friction is not correctly formulated nevertheless two functions for 0 one applying to rippled beds and the other to hummocky beds were contrived to make the model fit the data the model based on non dimensional skin friction was found to be a good predictor of cref when a correction was made for flow contraction over ripples the correction was not required for the hummocky bed where sediment was being entrained in a thin sheet flow layer the model based on non dimensional skin friction correctly portrayed the relationship between flow and sediment response without contrivance and therefore should be the favoured approach in predicting reference concentration

architecture of shoreface to deep water systems in segmented rift systems evidence from the southern margin of the sogn graben northern north sea the spatial distribution of syn rift deposits and temporal evolution of sandy gravity flows in the context of rift segmentation are poorly constrained based on conventional core description well log analysis and 3d seismic interpretation this study focuses on the upper jurassic successions in the southern margin of the sogn graben northern north sea thirteen facies associations are classified in order to discuss the architecture of shoreface gravity driven submarine fans and basin plain deposits on the scale of centimeters to meters in the eastern part of the study area gamma ray log stacking patterns suggest that northeast southwest oriented shoreface successions underwent progradational to retrogradational deposition during the oxfordian age lithological description of conventional cores indicates that large submarine fan system formed by debris flow dominated channels and turbidity flow dominated lobe complexes covers a broad 22 20 km depositional area the entry of regional drainages and the location of sandy gravity flow deposits were controlled by first order rift segmentation whereas the route of submarine canyon feeder system and the orientation of submarine fan lobes were determined by second order rift segmentation thus both first order and second order rift segmentation should be considered when determining the sedimentary facies and depositional architecture of sandy gravity flow deposits in individual rift segments

the marine geochemistry of dissolved gallium a comparison with dissolved aluminum abstract dissolved ga concentrations in the pacific ocean range from 2 to 30 picomolar they are low in surface waters 2 12 pm with a subsurface maximum at 150 300 m 6 17 pm a mid depth minimum from 500 to 1000 m 4 10 pm and increasing values with depth to a maximum in the bottom waters 12 30 pm the highest concentrations are in the central gyre with lower values toward the north and east where productivity and particle scavenging increase dissolved ga concentrations in the surface waters of the northwest atlantic are nearly an order of magnitude higher than in the central north pacific with higher values in the gulf stream than in the continental slope boundary region dissolved al concentrations in the high latitude north pacific are also lower than in the central gyre and are the lowest yet reported for this element the features are similar however to other dissolved al profiles a surface maximum 0 8 nmol kg a mid depth minimum 0 06 nmol kg and increasing concentrations toward the sediment water interface 0 4 nmol kg the vertical distributions and horizontal transects indicate three sources of dissolved ga to the oceans the surface distribution reflects an eolian source with no net fluvial input to the open ocean the subsurface maximum a feature not seen for north pacific dissolved al is attributed to vertical exchange processes the source for the deep waters of the north pacific is from a sediment surface remineralization process or a pore water flux scavenging removal throughout the water column is evident in the vertical profiles for both dissolved ga and al with intensified removal in the boundary regions where productivity and particle scavenging are at a maximum residence times of dissolved ga in surface waters are nearly an order of magnitude longer than the corresponding values for al

principal bed states during sandyduck97 occurrence spectral anisotropy and the bed state storm cycle 1 results are presented from 70 days of nearly continuous in situ acoustic imagery of the nearshore sandy seabed in 3 m mean water depth at two locations separated by 40 m cross shore distance the bottom sediments were 150 m median diameter sand with nearly identical size distributions at the two locations five principal bed states were observed irregular ripples cross ripples linear transition ripples lunate megaripples and flat bed the linear transition and flat bed states were the most frequent together accounting for 68 of the total time bed state occurrence was a strong function of incident wave energy each bed state occurring within a relatively narrow range of sea and swell energies during the 12 major storm events spanned by the record the bed response was characterized by a repeatable bed state storm cycle involving four of the five principal states lunate megaripples did not appear repeatedly and thus may be a special case with no obvious dependence of bed state occurrence on prior bed state or on third moment measures of wave nonlinearity radial spectra from the rotary acoustic images indicate pronounced differences in the anisotropy of spatial scales for the different bed states and exhibit onshore offshore differences which are likely related to ripple migration

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

supercritical and subcritical turbidity currents and their deposits a synthesis common facies models of turbidite deposits are based on idealized sequences of turbidite units which are assumed to reflect the depositional processes of a decelerating turbidity current we show how suites of turbidite units i e distinct turbidite facies associations that are easily described from core and outcrop may characterize the entire range of large scale dynamics of turbidity currents enabling estimates of their densimetric froude number fr subcritical versus supercritical and suspension fall out rate stratified versus nonstratified flows the linking of facies associations with large scale flow dynamics resolves process facies links that were hitherto unresolved by the common turbidite facies models

parallel lamination formed by high density turbidity currents experiments were conducted in order to investigate processes of sediment transport and deposition from sustained turbidity currents with initial volume fraction sediment concentration of 0 20 0 25 and 0 35 parallel lamination was formed at bed aggradation rates up to 4 mm s 1 and bedload layer sediment concentration up to 0 36 this observation contradicts the generally held assumption that parallel lamination forms only from low density flows and at low bed aggradation rates this misconception illustrates a poor understanding of threshold values of grain support mechanisms in the bedload layer the present results bring new insight into understanding sediment transport in the deep sea and interpreting the sedimentary record

trace metal signatures of jurassic cretaceous black shales from the norwegian shelf and the barents sea abstract black shale samples of jurassic to cretaceous age recovered during the norwegian shelf drilling program between 1987 and 1991 from sites 7430 10 u 01 barents sea 6814 04 u 02 norwegian shelf near the lofoten and 6307 07 u 02 norwegian shelf near trondheim were analyzed for major and trace elements these laminated black shales are characterized by high total organic carbon toc and total sulfur ts contents as well as by significant enrichments in several redox sensitive and or sulfide forming trace metals ag bi cd co cr cu mo ni re sb tl u v and zn enrichment factors relative to average shale are comparable to those found in cenomanian turonian boundary event ctbe black shales and mediterranean sapropels the re content is high in the studied black shales with maximum values up to 1221 ng g re mo ratios averaging 2 3 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to a dominantly anoxic and sulfidic water column during black shale formation interbeds with higher re mo ratios especially in high resolution sampled core sections point to brief periods of suboxic conditions additionally enhanced zn concentrations in the black shales from the barents sea support the assumption that hydrothermal activity was also high during black shale deposition trace metal signatures of black shales at different drill sites on a transect along the norwegian shelf are not only influenced by water depth but also by their location in the boreal realm metal enrichments are higher in the northern compared to the southern sites volgian tithonian 151 144 ma bp black shales exhibit elevated trace metal contents in comparison to their berriasian 144 137 ma bp counterparts this probably reflects a change in the circulation pattern during periods of black shale formation therefore different paleoceanographic conditions probably controlled by climatic change linked to the transgression of the paleo sealevel and the north atlantic opening may have developed from the volgian to the berriasian

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models

sedimentary facies and stratigraphy of a last interglacial coastal barrier in south brazil shoreline sedimentation during the last interglacial highstand on the rio grande do sul coastal plain southern brazil is represented by a sandy barrier that extends almost uninterrupted for hundreds of kilometers along the coast facies analyses of high quality exposures in several sandpits situated in the northern part of the coastal plain provided an opportunity to examine the stratigraphic nature of these deposits based on distinct assemblages of physical and biogenic sedimentary structures the vertical sequence of facies reveals a regressive prograded barrier with vegetated coastal dune sands overlying beach and shallow marine sediments progradation was probably promoted by abundant supplies of nearshore sand during the highstand and early fall of sea level forced regression associated with the last interglacial period around 125 ka as indicated by elevations of ophiomorpha burrows the maximum level reached by the sea was around 7 m above the present sea level paleocurrent data suggest that in the studied area shoreline orientation hydrodynamics and sediment transport during the last interglacial highstand were similar to present day conditions