chirp 2 7 khz echo characters of the south korea plateau east sea styles of mass movement and sediment gravity flow abstract the south korea plateau is a complex of ridges seamount chains troughs and a basin detailed analysis of 12 019 line km chirp 2 7 khz subbottom profiles from the south korea plateau and the eastern continental slope of korea reveals a distinctive zonal distribution of echo types depending systematically on seafloor morphology pelagites hemipelagites type i 2 and basement highs type iii 1 prevail on the ridge summits seamount chains and the upper to middle part of the eastern continental slope of korea and are commonly bounded downslope by creeps type iii 3 and slides slumps type iv 1 that occur extensively over the entire slope areas of the ridges seamount chains and eastern continental slope the mass movement deposits change downslope to debrites and turbidites types ii iii 2 iv 2 and iv 3 in the troughs and onnuri basin suggesting successive downslope evolution from slide and slump to debris flow and turbidity current the voluminous creeps slides and slumps over the entire slope areas of the plateau and eastern continental slope deeper than 300 m in water depth were most likely generated by frequent seismic shakings

on the baroclinic structure of the brazil current intermediate western boundary current system at 22 23 s 1 the baroclinic structure of the brazil current bc intermediate western boundary current iwbc at 22 23 s was investigated a reanalysis of the pioneer velocity profile measurements of the transcobra experiment evans and signorini 1985 revealed that the bc iwbc system is about 75 80 baroclinic mapped velocity structure showed flow reversal at about 450 m an iwbc thickness of 1200 m and core velocities exceeding 0 30 m s 1 total baroclinic transports for bc southwestwards and iwbc northeastwards were 5 6 4 2 sv and 3 6 4 1 sv respectively the strong baroclinic character of the bc iwbc system and the lack of direct velocity observations in the area yielded us to propose the use of the cross shelf version of the princeton ocean model to generate absolute baroclinic velocities from hydrographic data these velocities presented a similar reversal depth and the transports of about 6 7 sv for both bc iwbc were also comparable to values reported in the literature

sedimentological characteristics and depositional processes of sediment gravity flows in rift basins the palaeogene dongying and shahejie formations bohai bay basin china abstract sediment gravity flow deposits are common particularly in sandy formations but their origin has been a matter of debate and there is no consensus about the classification of such deposits however sediment gravity flow sandstones are economically important and have the potential to meet a growing demand in oil and gas exploration so there is a drive to better understand them this study focuses on sediment gravity flow deposits identified from well cores in palaeogene deposits from the liaodong bay depression in bohai bay basin china we classify the sediment gravity flow deposits into eight lithofacies using lithological characteristics grain size and sedimentary structures and interpret the associated depositional processes based on the scale spatial distribution and contact relationships of sediment gravity flow deposits we defined six types of lithofacies associations las that reflect transformation processes and depositional morphology la1 unconfined proximal breccia deposits la2 confined channel deposits la3 braided channel lobe deposits la4 unconfined lobe deposits la5 distal sheet deposits and la6 non channelized sheet deposits finally we established three depositional models that reflect the sedimentological characteristics and depositional processes of sediment gravity flow deposits 1 slope apron gravel rich depositional model which involves cohesive debris flows deposited as la1 and dilute turbidity currents deposited as la5 2 non channelized surge like turbidity current depositional model which mainly comprises sandy slumping suspended load dominated turbidity currents and dilute turbidity currents deposited as la5 and la6 and 3 channelized subaqueous fan depositional model which consists of non cohesive bedload dominated turbidity currents suspended load dominated turbidity currents and dilute turbidity currents deposited as la2 la5 originating from sustained extrabasinal turbidity currents hyperpycnal flow the depositional models may be applicable to oil and gas exploration and production from sediment gravity flow systems in similar lacustrine depositional environments elsewhere

transformation of debris flows into turbidity currents mechanisms inferred from laboratory experiments three sets of lock exchange experiments were run to look at the generation of turbidity currents from debris flows the flows ranged from reasonably dilute 4 volumetric concentration to dense 40 volumetric concentration with cohesive non cohesive and mixed cohesive non cohesive sediment concentration was measured at one height using an ultrasonic high concentration meter velocity was measured using ultrasonic doppler velocimetry profiling at 10 different heights in each run the resulting flows range from plug flows to well mixed flows comparison of the concentration profiles velocity time height plots and vertical profiles of downstream velocity and root mean square velocity showed several different transformation mechanisms depending on the concentration and composition of the flow transformation took place through one or more of the following processes erosion of material from the dense mass breaking apart of the dense underflow breaking of internal waves and turbulent mixing the extent of transformation depends on the viscosity and density of the flow initially very dense and viscous flows experience minor transformation only at the surface resulting in a dilute turbidity current flows that are initially not so dense and viscous are churned up entirely undergoing the different transformation processes for these flows transformation processes work throughout the entire flow not just at the surface transformation of the less dense flows is efficient with all or most material ending up in the resulting turbidity current

conditions for formation of massive turbiditic sandstones by primary depositional processes it can be shown from bedform stability diagrams that each turbidity current regardless of whether its density is low or high or whether its history is simple e g surging flow or complex e g sustained flow should pass through a final waning phase in which flow conditions are prone to bedform development yet many thick deep marine sandstones of supposed turbidity current origin are totally devoid of tractional structures such as plane parallel lamination and ripple cross lamination tdure a mathematical model for the calculation of duration of sediment deposition from high density turbidity currents hdtcs is used to show that the absence of bouma tb and tc divisions cannot be explained by rapid temporal flow deceleration only the model calculations imply that discernible tractional structures are formed even at residence times within the upper stage plane bed and ripple stability regimes of several seconds and several tens of seconds respectively therefore other explanations have to be sought for the absence of lamination in turbiditic massive sandstones these include incompatible grain size post depositional removal or obstruction of lamination by bioturbation and liquefaction and erosion of laminated divisions followed by rapid burial

break up of the atlantic deep western boundary current into eddies at 8 s the existence in the ocean of deep western boundary currents which connect the high latitude regions where deep water is formed with upwelling regions as part of the global ocean circulation was postulated more than 40 years ago1 these ocean currents have been found adjacent to the continental slopes of all ocean basins and have core depths between 1 500 and 4 000 m in the atlantic ocean the deep western boundary current is estimated to carry 10 40 times 106 m3 s 1 of water2 3 4 5 transporting north atlantic deep water from the overflow regions between greenland and scotland and from the labrador sea into the south atlantic and the antarctic circumpolar current here we present direct velocity and water mass observations obtained in the period 2000 to 2003 as well as results from a numerical ocean circulation model showing that the atlantic deep western boundary current breaks up at 8 s southward of this latitude the transport of north atlantic deep water into the south atlantic ocean is accomplished by migrating eddies rather than by a continuous flow our model simulation indicates that the deep western boundary current breaks up into eddies at the present intensity of meridional overturning circulation for weaker overturning continuation as a stable laminar boundary flow seems possible

petroleum generation and charge history of the northern dongying depression bohai bay basin china insight from integrated fluid inclusion analysis and basin modelling abstract the petroleum generation and charge history of the northern dongying depression bohai bay basin was investigated using an integrated fluid inclusion analysis workflow and geohistory modelling one and two dimensional basin modelling was performed to unravel the oil generation history of the eocene shahejie formation es3 and es4 source rocks based on the reconstruction of the burial thermal and maturity history calibration of the model with thermal maturity and borehole temperature data using a rift basin heat flow model indicates that the upper interval of the es4 source rocks began to generate oil at around 35 ma reached a maturity level of 0 7 ro at 31 30 ma and a peak hydrocarbon generation at 24 23 ma the lower interval of the es3 source rocks began to generate oil at around 33 32 ma and reached a maturity of 0 7 ro at about 27 26 ma oil generation from the lower es3 and upper es4 source rocks occurred in three phases with the first phase from approximately 30 20 ma the second phase from approximately 20 5 ma and the third phase from 5 ma to the present day the first and third phases were the two predominant phases of intense oil generation samples from the es3 and es4 reservoir intervals in 12 wells at depth intervals between 2677 7 m and 4323 0 m were investigated using an integrated fluid inclusion workflow including petrography fluorescence spectroscopy and microthermometry to determine the petroleum charge history in the northern dongying depression abundant oil inclusions with a range of fluorescence colours from near yellow to near blue were observed and were interpreted to represent two episodes of hydrocarbon charge based on the fluid inclusion petrography fluorescence spectroscopy and microthermometry data two episodes of oil charge were determined at 24 20 ma and 4 3 ma respectively with the second episode being the predominant period for the oil accumulation in the northern dongying depression the oil charge occurred during or immediately after the modelled intense oil generation and coincided with a regional uplift and a rapid subsidence suggesting that the hydrocarbon migration from the already overpressured source rocks may have been triggered by the regional uplift and rapid subsidence the expelled oil was then charged to the already established traps in the northern dongying depression the proximal locations of the reservoirs to the generative kitchens and the short oil migration distance facilitate the intimate relationship between oil generation migration and accumulation

vertical structure energetics and dynamics of the brazil current system at 22 s 28 s 1 we use four current meter moorings and quasi synoptic hydrographic observations in conjunction with a one dimensional quasi geostrophic linear stability model to investigate downstream changes in the brazil current bc system between 22 s and 28 s the data set depict the downstream thickening of the bc its vertical extension increases from 350 m at 22 7 s to 850 m at 27 9 s most of this deepening occurs between 25 5 s and 27 9 s and is linked to the bifurcation of the south equatorial current at intermediate depths santos bifurcation which adds the antarctic intermediate water flow to the bc geostrophic estimates suggest that the bc transport is increased by at least 4 3 sv 70 to the south of that bifurcation moreover the santos bifurcation is associated with a substantial increase in the barotropic component of the bc system on average the water column average kinetic energy ike is 70 baroclinic to the north and 54 barotropic to the south of the bifurcation additionally the bc shows conspicuous mesoscale activity off southeast brazil the water column average eddy kinetic energy accounts for 30 60 of the ike instabilities of the mean flow may give rise to these mesoscale fluctuations indeed the linear stability analysis suggests that the bc system is baroclinically unstable between 22 s and 28 s in particular the model predicts southwestward propagating fastest growing waves 190 km from 25 5 s to 27 9 s and quasi standing most unstable modes 230 km at 22 7 s these modes have vertical structures roughly consistent with the observed eddy field

the vertical partition of oceanic horizontal kinetic energy to produce an interpretation of the surface kinetic energy as measured by altimeters a survey is made of the vertical structure of kinetic energy profiles in a large number of globally distributed long current meter records although the data are geographically confined primarily to a latitude band in the north pacific to the north atlantic and to a few moorings in the south atlantic the results show generally speaking that most regions are dominated by the barotropic and first baroclinic modes because of the near surface intensification of baroclinic modes altimeters primarily reflect the first baroclinic mode and thus the motion of the main thermocline there is good quantitative agreement with a few exceptions with estimates of the surface kinetic energy obtained from the topex poseidon altimeter and from vertical extrapolations to the surface of the mooring profiles these results are consistent with previous suggestions that barotropic models have little skill in depicting variability as seen in the altimeter data an eof analysis is shown to produce fictitious mode coupling unless the dynamical modes have very different energy levels

ancient lacustrine hyperpycnites a depositional model from a case study in the rayoso formation cretaceous of west central argentina abstract hyperpycnal flows originate when sediment laden fluvial discharges enter standing lower density water because of their excess density the flows plunge near the river mouth and continue to travel basinward as a quasi steady and fully turbulent underflow the related deposits are hyperpycnites and constitute a particular type of turbidite with poorly known facies and facies tracts although hyperpycnal flows seem to be quite common in present times their occurrence in fossil strata is poorly documented this paper addresses the characteristics and depositional processes of shallow lacustrine sandy hyperpycnites on the basis of the field analysis of well exposed lower cretaceous strata rayoso formation in the neuquen basin of west central argentina the rayoso formation is composed of clastic and minor evaporitic red beds up to 1200 m thick deposited in a shallow perennial lake of variable salinity affected by long lived hyperpycnal flows main clastic facies are composed of fine grained sandstones with climbing ripples and plane beds other common sandstone facies include massive beds and low angle cross stratification most sandstone facies are related to traction plus fallout processes and often show a vertical fluctuation between sedimentary facies originated under different traction plus fallout conditions within single beds these fluctuations are interpreted to be evidence of deposition from flow fluctuations in sustained hyperpycnal flows most beds internally show the existence of three depositional phases acceleration ap erosion plus bypass ep and deceleration dp which record the complete evolution of a single long lived hyperpycnal flow at a fixed point additionally the depositional evolution of a single long lived hyperpycnal flow with distance records initially the progressive basinward migration of the ap and ep phases and finally an overall deposition under the dp phase both in proximal and distal areas this evolution provides an adequate explanation for the basinward extension of channelized features and for the occurrence of fine grained sandstones with climbing ripples both in proximal and distal positions within the same hyperpycnal system consequently facies analysis derived from application of the bouma sequence is not valid for deposits of quasi steady hyperpycnal flows

onset of submarine debris flow deposition far from original giant landslide submarine landslides can generate sediment laden flows whose scale is impressive individual flow deposits have been mapped that extend for 1 500 km offshore from northwest africa these are the longest run out sediment density flow deposits yet documented on earth this contribution analyses one of these deposits which contains ten times the mass of sediment transported annually by all of the world s rivers understanding how this type of submarine flow evolves is a significant problem because they are extremely difficult to monitor directly previous work has shown how progressive disintegration of landslide blocks can generate debris flow the deposit of which extends downslope from the original landslide we provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide encased within deposits of a more dilute flow type called turbidity current very little sediment was deposited across the intervening large expanse of sea floor where the flow was locally very erosive sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea floor gradient from 0 05 degrees to 0 01 degrees this debris flow was probably generated by flow transformation from the decelerating turbidity current the alternative is that non channelized debris flow left almost no trace of its passage across one hundred kilometres of flat 0 2 degrees to 0 05 degrees sea floor our work shows that initially well mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

shelf break upwelling driven by brazil current cyclonic meanders analysis of hydrographic data and results of numerical modeling show the occurrence of upwelling associated with the cyclonic meanders of the brazil current in the region known as the southeast brazil bight or santos bight the temperature and salinity distributions collected during summer and winter confirm the idea that meander induced shelf break upwelling plays an important role in the pumping of south atlantic central water from the slope region onto the continental shelf

gulf stream meanders observations on propagation and growth we present a new method for continuously tracking the location of the gulf stream using a moored array of inverted echo sounders time series of lateral displacements of the front shown accurate to 8 km have been collected along three sections spaced 100 150 and 200 km downstream ne of cape hatteras north carolina for a period of 12 months these records are highly coherent at all periodicities longer than 4 days from the observed phase lags a dispersion relationship is presented for the meanders as the period and wavelength t h increase from 4 days 180 km to 30 days 600 km the phase speed decreases smoothly from 40 to 20 km d the meanders exhibited rapid growth at periods longer than 4 days doubling in variance in each 50 km step downstream this downstream growth is most appropriately described by a spatial e folding scale k 400 km for t x 14 days 400 km from an array of seven inverted echo sounders ies and three deep current meters deployed 100 to 200 km northeast of cape hatteras in 2000 4000 m water this array continu ously monitored the path of the gulf stream and the deep currents under it on four deployment and recovery cruises to the area expendable bathythermograph traces xbt and hydrographic data were collected to survey the temperature and density structure along the stream path and on sections normal to it after a brief review of earlier studies on meanders this paper presents a discussion of the measurement techniques using ies in the gulf stream we show by direct compari sons with traditional measurement methods that 1 each ies produces a continuous record of the thermocline depth here taken to be the 15oc isotherm for subsequent comparison with standard methods of determining the position of the north wall of the stream with accuracy of 20 m in a range of variation of 800 m and 2 the array of ies s paired across the stream produces continuous estimates of the stream position with 8 km accuracy the results from the three ies sections located 100 150 and 200 km downstream of cape hatteras show very high coherence throughout the array with rapid 20 to 40 km d l translation of the meanders downstream accompanied by rapid growth of the lateral displacements doubling in variance with each 50 km step downstream in a companion paper w e johns and d r watts manuscript in preparation 1982 we discuss the current meter records and the relationship of the deep currents to gulf stream meanders 1981 they have wavelengths of 150 200 km and propagate downstream at rates of approximately 30 40 km d downstream of cape hatteras the envelope of meandering broadens greatly to 200 300 km figure 1 and the stream can shift through more than its own width in the early shipboard surveys fuglister and worthington 1951 fuglis ter 1963 the path of the stream south of nova scotia was dominated by long wavelength 400 km large amplitude meanders those which were studied in detail were found to be quasi stationary and were characterized by a slowly evolving baroclinic field indicating temporal growth far ther upstream near 72ow however significant eastward propagation was observed one meander crest moved at a rate of approximately 17 km d for 3 days fuglister and worthington 1951 hansen 1970 later conducted monthly path surveys between 75 o and 55ow for 1 year with weekly surveys over a 2 month period using a towed thermistor he found meanders on appreciably shorter scales with wave lengths ranging from 200 to 400 km mean downstream propagation rates of 5 10 cm s and spatial growth rates of 2 x 10 3 km were estimated by constructing lines of constant phase between features on successive path se quences the rapid evolution between monthly paths how ever produced considerable ambiguity in identifying and tracking events weekly paths evolved more continuously and were apparently not aliased by higher frequency wave number phenomena

impact of synsedimentary metre scale normal fault scarps on sediment gravity flow dynamics an example from the gres d annot formation se france abstract synsedimentary faults result in the direct interaction between tectonic and sedimentary processes at similar spatio temporal scales sedimentological analysis of sediment laden gravity flows in the northern part of the gres d annot formation sanguiniere sub basin col de la moutiere tete ronde has revealed the presence of fault scarps of metre scale height these synsedimentary fault scarps were sufficient to disturb the sediment gravity flow dynamics resulting in i a strong variation of the erosive behaviour of a concentrated flow and ii the transformation of a strongly stratified laminar hyperconcentrated flow into a turbulent flow in short distance less than 500 m these disturbances develop without the flows being deviated by the fault scarps but produce great facies heterogeneity the least homogeneous facies mixing sand and clay being localized on the upstream obstacle side the most homogeneous massive sand downstream

energetics of eddy mean flow interactions in the brazil current between 20 s and 36 s the energetics of eddy mean flow interactions in the brazil current bc between 20 s and 36 s are investigated in nineteen transects perpendicular to the 200 m isobath ten years 2000 2009 of output data from the hybrid coordinate ocean model hycom ncoda reanalysis with a spatial resolution of 1 12 5 and five day averages are used the mean kinetic energy mke and eddy kinetic energy eke fields presented the same subsurface spatial pattern but with reduced values the eke increases southward with high values along the bc path and the offshore portion of the jet the values of the barotropic conversion term btc are highest in the surface layers and decreased with depth whereas the values of the baroclinic conversion term bcc and the vertical eddy heat flux vehf are highest in the subsurface despite the vertical thickening of the bc the highest energy conversion rates are confined to the upper 700 m of the water column the energetic analysis showed that the current features mixed instability processes the vertical weighted mean of the btc and bcc presented an oscillatory pattern related to the bathymetry the eddy field accelerates the time mean flow upstream and downstream of bathymetric features and drains energy from the time mean flow over the features the bc is baroclinically unstable south of 28 s and the highest energy conversion rates occur in cabo de sao tome cabo frio and the cone do rio grande

coarse grained submarine fan and slope apron deposits in a cretaceous back arc basin antarctica the cretaceous of west james ross island antarctica represents the proximal fill of a late mesozoic back arc basin that was probably initiated by oblique extension during the early development of the weddell sea the succession records sedimentation in two contrasting depositional systems a laterally persistent slope apron flanking the faulted basin margin interrupted both spatially and temporally by coarse grained submarine fans slope apron deposits are dominated by thinly interbedded turbiditic sandstones and mudstones mudstone association interspersed with non channelized chaotic boulder beds intraformational slump sheets and isolated exotic blocks representing a spectrum of mass flow processes from debris flow to submarine gliding localized sand rich sequences sandstone breccia association represent sandy debris lobes at the mouths of active slope chutes the submarine fan sediments conglomerate association are typified by coarse conglomerates and pebbly sandstones interpreted as the deposits of high density turbidity currents and non cohesive debris flows three assemblages are recognized and are suggested to represent components of the inner channelled zone of coarse grained submarine fans from major fan channels through ephemeral marginal channels or terraces to levee or interchannel environments the occurrence of both slope apron and submarine fan depositional systems during the early and mid cretaceous is attributed to localized input of coarse arc derived sediment along a tectonically active basin margin periods of extensive fan development were probably linked to regional tectonic uplift and rejuvenation of the arc source region cyclicity within individual fan sequences is attributed to migration or switching of fan channels or canyons slope apron sedimentation was controlled largely by intrabasinal tectonics local unconformities and packets of amalgamated slide sheets and debris flow deposits probably reflect episodic movement on basin margin faults differential subsidence across the basin margin anchored the basin slope for at least 20 myr and precluded basinward progradation of shallow marine environments

accumulation of fine grained material in a danish tidal area abstract the exchange of fine grained material m between the north sea and the tidal area of gradyb in the danish wadden sea has been determined by means of the 210 pb dating method the amount of fine grained material accumulating in the area 169 km 2 has been calculated to be 142 10 3 t yr 1 of this approximately 85 is derived from the north sea 5 6 from rivers 4 from internal coastal erosion and another 5 6 from the combined effect of waste atmospheric deposition and net primary production these results have been verified through a budget for excess 210 pb it is demonstrated that fine sediments from the north sea are sorted before accumulating in the wadden sea with the result that the deposited material contains more coarse silt and less clay than is found in the source material from the north sea the relation between accumulated fine grained material and the volume of exchanged water is found to be in the same order of magnitude in gradyb as in jadebusen and dollard this relation is suggested to be a characterising parameter of the sedimentation in tidal areas

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

can dispersive pressure cause inverse grading in grain flows discussion the concept of dispersive pressure was originally proposed by bagnold 1954 who showed experimentally that sheared granular material develops a dispersive pressure that is proportional to the shear stress and the particle concentration legros 2002 presented a theoretical analysis suggesting that dispersive pressure cannot account for the inverse grading commonly observed in grain flows modified grain flows or traction carpets contrary to what has been accepted for decades by many sedimentologists he pointed out that if the dispersive pressure in a sheared granular mass increases and exceeds the applied normal stress or static pressure the net upward force acting upon the bed causes it to expand as has in fact been observed in experiments bed expansion immediately causes a decrease in particle concentration and consequently in dispersive pressure until the latter balances the static pressure and expansion stops if the dispersive pressure becomes less than the static pressure the net downward force acting upon the granular bed causes compaction thus increasing the particle concentration and dispersive pressure this is an important concept enhancing our understanding of an as yet poorly understood process however legros 2002 went further to state that the dispersive pressure must always equal the applied normal shear stress at every level emphasis mine through the shearing granular bed this implies that the whole sheared bed is in constant equilibrium which is probably not the case in this discussion a modified process is proposed that accounts for the bipartite traction carpet structure proposed by sohn 1997 traction carpets are moving layers of highly concentrated bedload material developed beneath and driven by an overlying turbulent flow dzulynski and sanders 1962 sohn 1997 on the basis of numerical analyses computer simulations field measurements and experimental studies bagnold 1955 1963 hanes and bowen 1985 wan

lagrangian observations in the intermediate western boundary current of the south atlantic abstract subsurface float measurements at 800 m depth carried out from 1994 to 2003 in the brazil basin are used to characterise the equatorward intermediate western boundary current iwbc and its connections to the ocean interior transversally the boundary flow is less than 100 km wide and most intense at 10 20 km from the 800 m isobath its average velocities range from 0 1 ms 1 to 0 3 ms 1 depending on latitude with individual daily values as high as 0 7 ms 1 the flow meridional extent exhibits 3 contrasted domains i from 27 s to the vitoria trindade ridge at 20 30 s the boundary flow intensifies northward along a relatively smooth topography a counter current adjacent to it on its seaward side feeds it with intermediate water from the northern limb of the subtropical gyre ii at latitudes 20 15 s characterised by a very irregular topography the iwbc becomes weaker with even no real proof of its presence at 18 15 s an intense mesoscale variability prevails there which apparently takes over from the boundary flow to ensure the northward transport of water to 15 s where the iwbc re forms iii north of this latitude the boundary flow increases again to 10 s along smooth isobaths then decreases when encountering a rougher topography and the zonal jets of the equatorial current system a counter current present from 5 s to 14 s partly fed from the boundary flow contributes to its drainage the iwbc shows two main input locations at 27 23 s and 15 12 s in the southern parts of the two latitudinal domains of smooth topography where the northward current increases output locations coincide with major capes in the continental slope geometry at 20 s and 18 s the southeastern and northeastern corners of the abrolhos bank at 8 s near the recife plateau and at 5 s near cape sao roque

on the steadiness and instability of the intermediate western boundary current between 24 and 18 s abstractthe intermediate western boundary current iwbc transports antarctic intermediate water across the vitoria trindade ridge vtr a seamount chain at 20 s off brazil recent studies sugges

downscaling of the global hadgem2 es results to model the future and present day ocean conditions of the southeastern brazilian continental shelf changes in the regional hydrodynamics of the region of the south atlantic near the east coast of brazil were evaluated from the beginning to the end of the century the analysis was based on the anomalies from two downscaling experiments using the hadgem2 es outputs for the historical and rcp4 5 runs from the coupled model inter comparison project phase 5 the anomalies between the experiments were collected in a system of two nested grids with 1 3 circ and 1 12 circ horizontal resolutions a northward displacement of the brazil current bc a southward bc transport intensification and a 1 44 circ c increase of the mean values of sea surface temperatures were observed the sea level rise slr was projected up until 2100 across the study area and the spatial variations were shown to have an average on slr rate of 7 30 mm year 1 for those regions close to the coast these results highlight the importance of studying climate change and applying methods to enable the evaluation of its effects on coastal zones especially for regions with few existing studies such as the brazilian continental shelf area

the shallow and deep western boundary circulation of the south atlantic at 5 11 s repeated shipboard observation sections across the boundary flow off northeastern brazil as well as acoustic doppler current profiler adcp and current meter records from a moored boundary array deployed during 2000 04 near 11 s are analyzed here for both the northward warm water flow by the north brazil undercurrent nbuc above approximately 1100 m and the southward flow of north atlantic deep water nadw underneath at 5 s the mean from nine sections yields an nbuc transport of 26 5 3 7 sv sv 106 m3 s 1 along the boundary at 11 s the mean nbuc transport from five sections is 25 4 7 4 sv confirming that the nbuc is already well developed at 11 s at both latitudes a persistent offshore southward recirculation between 200 and 1100 m depth reduces the net northward warm water flow through the 5 s section west of 31 5 w to 22 1 5 3 sv and through the 11 s section to 21 7 4 1 sv west of 32 0 w the 4 yr long nbuc transport time series from 11 s yields a seasonal cycle of 2 5 sv amplitude with its northward maximum in july interannual nbuc transport variations are small varying only by 1 2 sv during the four years with no detectable trend the southward flow of nadw within the deep western boundary current at 5 s is 25 5 8 3 sv with an offshore northward recirculation yielding a nine section mean of 20 3 10 1 sv west of 31 5 w for antarctic bottom water a net northward flow of 4 4 3 0 sv is determined at 5 s for the 11 s section the moored array data show a pronounced energy maximum at 60 70 day period in the nadw depth range which was identified in related work as deep eddies translating southward along the boundary based on a kinematic eddy model fit to the first half of the moored time series the mean nadw transfer by the deep eddies at 11 s was estimated to be about 17 sv given the large interannual variability of the deep near boundary transport time series which ranged from 14 to 24 sv the 11 s mean was considered to be not distinguishable from the mean at 5 s

hyperpycnites deposited 700 km away from river mouths in the central japan sea abstract relatively little is known about the characteristics of deposits and potential runout distances of hyperpycnal currents this study describes and discusses evidence of sediment deposition from sustained long duration quasi steady turbidity currents in the distal part of the toyama deep sea channel which extends ca 700 km from river mouths in the central japan sea the study is based on gravity cores and airgun seismic reflection profiles obtained from the channel distal reaches the silty turbidite beds of the channel s terminal fan show rhythmic layering that indicates sustained turbidity currents with distinct flow strength fluctuations some of the rhythmite beds show a fining upward internal trend net flow strength waning whereas others show an upward coarsening net flow strength waxing followed by fining seismic reflection profiles from the channel levees show large bedforms of climbing dune type attributed to the spillover of thick sustained turbidity currents the deposition of the terminal fan rhythmites and accretionary levee bedforms is attributed to turbidity currents generated by hyperpycnal river effluent a quantitative assessment of sediment concentrations in the coastal rivers indicates that their effluents could become hyperpycnal nearly every year or during every major seasonal flood the density of a river generated underflow would increase by the entrainment of saline water and seafloor sediment on the steep slope of the toyama bay resulting in robust long runout turbidity currents the estimated flow velocities of these currents were around 0 3 m s and their recurrence period for the last 1000 years was of the order of 70 years the estimated duration of hyperpycnal flows required for the deposition of rhythmite beds 700 km away from the river mouth is of the order of several days to 3 4 weeks the study provides new insights into the recognition and classification of hyperpycnites in distal zones of deep marine turbiditic systems

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

response of unconfined turbidity current to normal fault topography turbidity currents descending the slopes of deep water extensional basins or passive continental margins commonly encounter normal fault escarpments but such large magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory this study uses advanced computational fluid dynamics numerical simulations to monitor the response of large natural scale unconfined turbidity currents 100 m thick and 2000 m wide at the inlet gate to normal fault topography with a maximum relief of nearly 300 m for comparative purposes the turbidity current is first released on a non faulted pristine slope of 1 5 simulation model 1 the expanding and waxing flow bypasses the slope without recognizable deposition within the vertical resolution limit of 2 m similar flow is then released towards the tip model 2 and towards the centre model 3 of a normal fault escarpment in both of these latter models the sand carried by flow tends to be entrapped in four distinct depozones an upslope near gate zone of flow abrupt expansion and self regulation a flow transverse zone at the fault footwall edge a flow transverse zone at the immediate hangingwall and a similar transverse zone near the crest of the hangingwall counter slope where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow the near bottom reverse flow appears to be generated on a counter slope of 1 1 increased to 2 by deposition the kelvin helmholtz interface instability plays an important role by causing three dimensional fluctuations in the flow velocity magnitude and sediment concentration the thick deposits of large single surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows the study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope fan conceptual models when it comes to the spatial prediction of main sand depozones this article is protected by copyright all rights reserved

the intermediate depth circulation of the western south atlantic the subsurface oceanic circulation is an important part of the earth climate system subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances occasionally supplemented by current meter measurements neutrally buoyant floats however now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western south atlantic here our combined data set provides unprecedented observations and quantification of key flow patterns such as the subtropical gyre return flow 12 sv 1 sverdrup 10 6 m 3 s 1 its bifurcation near the santos plateau and the resulting continuous narrow and swift northward intermediate western boundary current 4 sv this northward flowing water passes through complex equatorial flows and finally enters into the north atlantic

geology of the campanian m1 sandstone oil reservoir of eastern ecuador a delta system sourced from the amazon craton abstract the campanian m1 sandstone member of the napo formation is one of the main reservoirs of the capiron tiputini oil play system of the eastern part of the oriente basin of ecuador this study presents a geological model for this reservoir at the apaika and nenke oil fields included within the block 31 and the eden yuturi oil field operated by petroamazonas ep the geological characterization of the m1 sandstone is based on an integrated study which includes core description electric log analyses and seismic data interpretation the sedimentological descriptions from available cored sections show that m1 sandstone records a variety of fluvial to shallow marine processes including mass flow and delta front turbidity currents not previously documented the stratal stacking pattern interpreted from electric logs indicates that the succession reflects deltaic progradation rather than the backstepping pattern typically displayed by the underlying albian to santonian sediments of the napo formation seismic rms amplitude defines clinoform geometries with sigmoidal sand body architecture prograding from east to west correlation with neighboring regions in colombia suggest that the m1 sandstone was probably part of a large river dominated delta system sourced from the east during major campanian progradation the location of the source area of sediment was determined using u pb detrital zircon dating provenance ages are uniform within the m1 sandstone cluster in a population that ranges from 1 4 to 1 6 billion years these ages indicate that sands were derived mostly from erosion of the lithotectonic rio negro jurena province located to the northeast of the studied area detrital ages from the overlying maastrichtian tena formation include ages between 80 and 200 ma pointing to an important change in the source areas located in the eastern cordillera of ecuador the change in sediment supply from east to west recorded in the tena formation coincide with the initial episodes of the andean orogeny and may be driven by the collision of fragments of the caribbean large igneous province clip against the continental margin of northwestern south america

initiation of turbidity currents outcrop evidence for eocene hyperpycnal flow turbidites abstract the most widely used although not as widely documented explanation for initiation of turbidites is the conversion of catastrophic sediment failures into turbidites such instantaneous sediment failures generate short lived surge type flows that deposit turbidite beds described as bouma sequences in this communication we present data from the eocene central basin of spitsbergen that shows turbidite systems that are volumetrically dominated by thick ungraded and laminated sandy turbidite beds deposited by gradual aggradation from sustained flows sustained flows are long lived and more or less continuous they can be generated by a variety of mechanisms e g 1 instability during volcanic eruptions and the consequent remobilisation of unconsolidated material 2 seismically triggered subaerial sliding within the drainage 3 storm surges 4 retrogressive slope failure 5 breaching and 6 hyperpycnal flows our database shows that in the eocene central basin the sustained flows were generated by hyperpycnal flows i e by direct river effluent the hyperpycnal flow turbidites have been recognized on the basis of 1 physical connection between fluvial and turbidite channels at the shelf edge 2 abundance of thick turbidite sandstone beds 3 sand prone nature of the turbidite systems 4 downslope changes of individual thick sandy turbidite beds and their collapsed pinch out segments 5 great abundance of continental material leaves coal fragments in turbidite beds 6 low abundance of associated slumped or debris flow beds and 7 the occurrence of turbidites in systematically accreted shelf margins these features strongly suggest that hyperpycnal flow generated by direct river effluent deposited significant number of turbidite beds in the documented slope and basin floor turbidite successions we also argue that the hyperpycnal flows are preferentially fed into the deepwater slopes beyond the shelf edge during the falling stage and lowstand of relative sea level the turbidite beds were studied in the context of seismic scale 1 15 km dip oriented outcrops by measuring detailed vertical sections following individual beds and packages of beds downslope for distances over 5 km lateral mapping and helicopter taken photomosaics

direct measurements of western boundary currents off brazil between 20 s and 28 s current measurements from three moored arrays on the brazilian continental slope between 20 degrees s and 28 degrees s are investigated for the existence and strength of western boundary currents from near the surface down to the north atlantic deep water the brazil current is found to deepen southward from 100 m to more than 670 m and to strengthen its volume transport to 16 2 x 10 6 m 3 s antarctic intermediate water is transported in a well developed boundary current southward at 28 degrees s and northward north of cabo frio 24 degrees s this result supports earlier suggestions derived from the analysis of hydrographic data that antarctic intermediate water enters the brazil basin from the east and bifurcates as it meets the continental break off brazil north atlantic deep water is transported southward in a weakly developed boundary current that leads to lower estimates of volume transport than expected from earlier hydrographic data analysis

fault rate controls on carbonate gravity flow deposits of the liassic of central high atlas morocco the aim of this work is to describe and to explore linkages between fault activity and gravity related sedimentary deposits during the early rifting of a carbonate depositional system the study area located at the southern edge of central high atlas morocco hosts 900 m thick liassic gravity related sedimentary deposits preserved at the hanging wall of one of the possibly inherited reactivated hercynian faults tizi n firest fault this study documents gravity flow deposits constrained by a high resolution biostratigraphic framework ca 100 ka these gravity flow deposits evolve over time unstratified conglomerate beds are limited to the sinemurian and are preserved near the fault incomplete ungraded bouma sequence beds are preserved preferentially at the transition between the sinemurian and the carixian while complete graded bouma sequences are recorded during the carixian and domerian fine grained turbidite beds are observed dominantly during the domerian incomplete graded bouma sequences are observed all along the section our work suggests that fault activity over time associated to rifting has led to this diversity of gravity flow deposits fault activity plays a key role in the initiation of gravity flows but also influences the type of gravity flow deposits by controlling the amount of sediment available the sediment grain size the slope morphology and the basin deepening

slump and debris flow dominated upper slope facies in the cretaceous of the norwegian and northern north seas 61 67 n implications for sand distribution a regional sedimentological study of cretaceous sequences in the mid norway region norwegian sea and in the agat region agat field area northern north sea reveals that these sequences were predominantly deposited in an upper continental slope environment by slumps and debris flows examination of nearly 500 m of core from 14 wells shows eight distinct lithofacies facies 1 contorted conglomerate and pebbly sandstone represents deposits of sandy slumps and debris flows possibly in a channel setting facies 2 contorted sandstone is the most widespread and is the product of sandy slumps and debris flows facies 3 contorted mudstone indicates deposition from muddy slumps and debris flows facies 4 rippled sandstone suggests bottom current reworking facies 5 gr ded sandstone represents turbidity current deposits and is very rare facies 6 laminated mudstone is a product of pelagic or hemipelagic deposition facies 7 cross bedded sandstone is indicative of tidal processes and facies 8 laminated sandstone represents delta front and shelf deposits these facies and their association suggest a shelf edge delta to upper slope environment of deposition existing core data document deltaic facies only in the mid norway region the proposed shelf edge delta and upper slope model has important implications for sand distribution 1 this model provides an alternative to the conventional submarine fan model previously applied to these sequences 2 although slump and debris flow emplaced sands are usually discontinuous and unpredictable highly amalgamated slump and debris flow sands may develop thick reservoirs 3 by using the eocene frigg formation as an analog it is predicted that externally mounded seismic facies in the study area may be composed of sandy slumps and debris flows

energy flux to a cyclonic eddy off cabo frio brazil abstract to evaluate the energy flux from the mean flow of south atlantic western boundary currents toward typical cabo frio eddies at brazilian southeast coast the southwestern atlantic circulation was simulated with the princeton ocean model throughout the study period the vertical profile of eddy available potential energy direction was monitored the results indicated that baroclinic instability eddies first appear in intermediate depths and then its signal propagates upward draining energy from the brazil current bc until it reaches the surface 30 days after its formation the depth of eddy formation is related to the vertical profile of the mean potential vorticity cross current gradient q s the beginning of the potential energy flux toward the perturbation and the origin of the eddy occurred at a similar depth and time the observed pattern suggests the following cycle 1 a well defined southwestward flowing bc in the beginning of the period with a baroclinically unstable profile o

depositional characteristics and reservoir potential of paleogene sediment gravity flow deposits on a faulted slope of the zhanhua sag bohai bay basin china abstract deep water sandstones related to sediment gravity flows are becoming an increasingly important exploration domain in continental rift basins in china however ambiguities remain regarding the initiation evolution and deposition of sediment gravity flows on faulted slopes where step faults are commonly developed to address the uncertainties related to these processes grain size analysis lithofacies analysis logging interpretation and seismic interpretation were employed to study paleogene sediment gravity flow deposits from well cores on a faulted slope in the zhanhua sag of the bohai bay basin twelve lithofacies related to sediment gravity flows were recognized and attributed to intrabasinal sediment gravity flows isgfs induced by slope failures and extrabasinal sediment gravity flows esgfs generated by floods active faults were important triggers for isgfs on the faulted slope in the zhanhua sag the fault activity rate had a prominent role in determining the volume of re transported sediments which further influenced the evolution of the resulting flows travelling across multiple faults downslope isgfs generally underwent considerable velocity losses with the result that almost all sediments were deposited in shallow water moreover unconsolidated isgf deposits could be transported again to generate sediment gravity flows obscuring the depositional characteristics of isgfs esgfs originated from rivers during floods and involved the transformation of cohesive into turbulent hyperpycnal flows in humid and warm climates active sag border faults favoured the generation of long lived esgfs these flows usually travelled along intra sag faults and therefore considerable volume of sediments could be transferred into deep water the resulting thick bedded hyperpycnites contributed substantially to the reservoirs of bonan oilfield meanwhile short lived esgfs usually generated in the regions where sag border faults were extinct they generally travelled down the faulted slope and deposited sediments in shallow water these features suggest that the initiation evolution and deposition of sediment gravity flows on the faulted slope are mainly controlled by faults and climate hyperpycnites can serve as excellent reservoirs for hydrocarbon accumulation and they are probably common in other sags of the bohai bay basin

experimental quasi steady density currents abstract hyperpycnal flows may be important mechanisms for transporting particles from continents to oceans given their frequency of generation at many modern river mouths their deposits are probably very common in the rock record although they are not frequently recorded in the literature these currents may last longer and be steadier than surge like turbidity flows and consequently their deposits are likely to be significantly different in this paper simple laboratory experiments are used to investigate how flows and deposits may vary the thickness of the experimental flows near the flow front varies with distance from the source depending on slope effluent discharge grain size and sorting runout distance varies with the proportion of fine grained sediment rather than with mean grain size flow front velocity varies with effluent discharge and sediment concentration and in a complex manner with mean grain size and sorting the variation of deposit mass with runout distance depends on proximal slope angle and the maximum mass per unit area approximating to bed thickness is inversely dependent on slope angle variation in initial suspended particle concentration results in deposits of similar shape but different volume although the total mass of the deposit depends on the discharge the maximum mass per unit area approximating to maximum bed thickness does not the distance over which particles are deposited increases and the deposit flattens as particles are deposited progressively further downstream at higher discharges perhaps relating to more efficient turbulent suspension at higher re more complete energy cascade in addition to longer horizontal component of settling trajectory at higher velocity the amplitude of mass variation depends on the grain size as with laboratory surges gladstone et al sedimentology 1998 833 844 the finer the sediment the more efficient is the sediment transport