predicting the morphodynamic response of silt laden rivers to water and sediment release from reservoirs lower yellow river china the high sediment load of the yellow river results in rapid infilling of its reservoirs when sediment is not regularly flushed simultaneously the downstream reaches of the yellow river experience extremely high siltation rates which are reduced when sediment is retained in its reservoirs to minimize siltation in the reservoirs and the downstream river bed water and sediment are released from the reservoir in a controlled way through flushing experiments in this paper we analyze the effect of such a flushing event on the downstream river bed through data analysis and numerical modeling sedimentation may be minimized by relating the amount of sediment released from the reservoir to the sediment available for release through operational monitoring and by releasing relatively clear water after turbid water despite this flushing of sediment the reservoir will eventually fill up and more sediment released again into the lower yellow river the change in discharge magnitude and frequency brought about by the reservoir will then probably result in increased siltation rates in the lower yellow river compared to the predam situation

which triggers produce the most erosive frequent and longest runout turbidity currents on deltas subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet and it is important to understand how they are linked offshore from river mouths previously it was thought that slope failures or direct plunging of river flood water hyperpycnal flow dominated the triggering of turbidity currents on delta fronts here we re analyse the most detailed time lapse monitoring yet of a submerged delta comprising 93 surveys of the squamish delta in british columbia canada we show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes rather than landslides or hyperpycnal flows turbidity currents triggered by settling plumes occur frequently run out as far as landslide triggered events and cause the greatest changes to delta and lobe morphology for the first time we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

chute channel dynamics in large sand bed meandering rivers meander bends of many large sand bed meandering rivers are partitioned by chute channels that convey permanent flow and co exist with the mainstem for decades as a first step toward understanding the dynamics and morphodynamic implications of these bifurcate meander bends this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics regression models developed for the strickland river papua new guinea the lower paraguay river paraguay argentina and the beni river bolivia revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate the rate at which a bend elongates in a direction perpendicular to the valley axis trend image analyses of all rivers and field observations from the strickland suggest that the majority of chute channels form during scroll slough development rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank resulting in widely spaced scrolls with intervening sloughs that are positively aligned with primary over bar flow the rivers plot in order of increasing chute activity on an empirical meandering braided pattern continuum defined by potential specific stream power pv and bedload calibre d50 increasing stream power is considered to result in higher bend extension rates with implications for chute initiation in addition chute stability is shown to depend on river sediment load relative to flow discharge qs q such that while the beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power the formation of stable chute channels is suppressed by the high sediment load this tendency is consistent with previous experimental studies and results in a planform that is transitional between single thread meandering and braided copyright 2011 john wiley sons ltd

mechanics of dual mode dilative failure in subaqueous sediment deposits abstract we introduce dual mode dilative failure with flume experiments dual mode dilative failure combines slow and steady release of sediments by breaching with periodic sliding which rapidly releases an internally coherent wedge of sediments it occurs in dilative sandy deposits this periodic slope failure results from cyclic evolution of the excess pore pressure in the deposit sliding generates large transient negative excess pore pressure that strengthens the deposit and allows breaching to occur during breaching negative excess pore pressure dissipates the deposit weakens and ultimately sliding occurs once again we show that the sliding frequency is proportional to the coefficient of consolidation we find that thicker deposits are more susceptible to dual mode dilative failure discovery of dual mode dilative failure provides a new mechanism to consider when interpreting the sedimentary deposits linked to submarine slope failures

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

incipient motion of riverbank sediments with outflow seepage based on a force analysis an expression is derived to describe the critical shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters outflow seepage and physical and mechanical properties of sediments parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage slope angle and flow direction on the critical shields number the results show that the critical shields number decreases with an increase in the hydraulic gradient where bank collapse is concerned the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface at a certain value of hydraulic gradient the critical shields number decreases with increasing slope angle open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward

hyperconcentrated sand water mixture flows over erodible bed field surveys and experiments in a tilting flume on hyperconcentrated sand water mixture swm flows were conducted at slopes slightly smaller than the equilibrium slope a rapid development of sand bars propagating upstream was observed these bars consist of an almost horizontal terrace with subcritical flow a steep lee side slope with supercritical flow and a hydraulic jump between subsequent bars the erosion processes on the bar are limited by the high sand concentrations and flow velocities on the steep slopes as a result the erosion rate is more moderate than predicted by the pickup functions used in classical sediment transport theory a simple one dimensional model is presented to study the behavior of triangular schematized bars from an analysis of the equations it is concluded that an increase in erosion rate requires an increase in bed slope to maintain equilibrium flow conditions finally simulations with the model are compared with observations in the field and in the tilting flume t

location and probability of shoal margin collapses in a sandy estuary channel bank failure collapses of shoal margins and beaches due to flow slides have been recorded in dutch estuaries for the past 200 years but have hardly been recognized elsewhere current predictions lack forecasting capabilities because they were validated and calibrated for historic data of cross sections in specific systems allowing local hindcast rather than location and probability forecasting the objectives of this study are to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are such that we can predict their occurrence we identified shoal margin collapses generally completely submerged from bathymetry data by analyzing dems of difference dod of the western scheldt for the period 1959 2015 we used the bathymetry data to determine the conditions for occurrence specifically to obtain slope height and angle and applied these variables in a shoal margin collapse predictor we found 299 collapses along 300 km of shoal margin boundaries over 56 years meaning more than 5 collapses occur on average per year the average shoal margin collapse body is well approximated by a 1 3 ellipsoid shape covers on average an area of 34 000 m2 and has an average volume of 100 000 m3 shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross section of the entire estuary and occur most frequently where lateral shoal margin displacement is low a receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well we conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the western scheldt and likely locations are at laterally relatively stable shoal margins this provides hypotheses aiding the recognition of these features in sandy estuaries worldwide

high resolution morphobathymetric analysis and evolution of capbreton submarine canyon head southeast bay of biscay french atlantic coast over the last decade using descriptive and numerical modeling abstract in this study the capbreton canyon head just off the coast is investigated using high resolution multibeam bathymetry datasets sediment samples and numerical modeling the hr bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon the analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore hydrodynamic modeling a coupled wave flow model shows that for high energy waves the rotational nature of surf zone circulation reverses and wave induced currents have the potential to transport large quantities of nearshore sands toward the canyon head all these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift over the 15 years of observation 1998 2013 time lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking in terms of hazards despite this strong activity the position of the canyon head and the profile of its longitudinal slope remained stable and appear as a comforting factor however the activity of unusual lateral erosions needs to be monitored

resedimentation of cold pumiceous ignimbrite into water facies transformations simulated in flume experiments deposits and transport processes resulting from the resedimentation of cold unconsolidated ignimbrite into water were simulated by flume experiments the ignimbrite sample used was poorly sorted 2 4 3 fine ash rich 2000 kg m 3 and pumice 500 to ca 1300 kg m 3 as a result of the binding forces of the ash matrix the experiments involved resedimentation from a steep front onto the floor with or without an initial ramp of the water filled tank under both still and wave generated conditions larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action the mass of the collapse and proportion of pore space water strongly influenced the style of resedimentation and the deposits initial collapse events were from the top of the steep front and fell onto the floor the largest densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break in slope fine ash was transported in dilute turbidity currents and coarse unsaturated pumice clasts floated off moderate collapse events generated high density turbidity currents trapping pumice in the flow causing them to saturate these low density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit large collapse events slumped producing poorly sorted mounds similar in texture to the original starting material as the matrix of the ignimbrite sample became saturated with water moderate and large collapse events generated debrisflows and slurries that deposited massive poorly sorted deposits furthermore once more gentle slopes were established between the sample and deposit small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low relief ash channels the experiments show that excluding large collapse events and debrisflows resedimenting ignimbrite in water is effective at segregating low density pumice clasts from dense lithic clasts and fine ash experiments using fine ash poor ignimbrite and well sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches the grainflow deposits had textures similar to the fines poor starting material

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

sediment pick up functions experimental research has been performed to determine the sediment pick up by a uniform flow without initial sediment load a sediment lift was designed by which the sediment particles were moved upwards at a constant rate through a circular opening in the flume bottom five types of bed material sand have been used with d d5 d0 values in the range 130 1500 m the mean flow velocities were in the range 9 5 1 0 m s the experimental results have been used to derive an empirical pick up function the results have also been used to evaluate several existing pick up functions finally the proposed empirical pick up function has been applied to predict the bed load and suspended load transport in the latter application the proposed function has been used as a bed boundary condition in a mathematical model for suspended sediment transport

reproduction of estuarine bathymetry by means of a process based model western scheldt case study the netherlands abstract the current study aims to investigate the processes governing the evolution of major morphological features in alluvial estuaries as well as their morphodynamic interaction with the geometry by means of a 3d morphodynamic process based numerical model delft3d the main hypothesis is that channel shoal patterns evolve through the interaction between tidal movement the available sediments and the tidal basins geometry once such a system is not disturbed too much by extreme events stable morphological patterns will emerge that compare well with observed features starting from a flat bed and imposing the western scheldt geometry model results show two distinct time scales i e channel shoal pattern formation within decades and a slow longitudinal profile development continuing for centuries the developing channel shoal patterns reflect major morphological features observed in the western scheldt estuary using the 1998 bathymetry as a reference we applied different indicators and techniques to evaluate the model performance over time namely visual comparison hypsometries brier skill score bss mean basin depth and longitudinal profiles sensitivity analysis shows that trends in development are similar for different model parameter settings like introducing salt fresh water density differences or variations in sediment grain size and sediment transport formulation varying river discharge and including non erodible layers dredging and dumping activities and 3d hydrodynamics led to occasional improvements the geometry is an important governing factor for pattern development applying an erodible geometry reveals a timescale for geometric adaptation that is much longer than the pattern development timescale within the basin model runs including highly schematized extreme conditions suggest that extreme events play a limited role the main conclusion of the study is that the interaction between tidal forcing and basin geometry plays a major role in the development of morphological features in an alluvial tidal basin such as the western scheldt a process based model taking into account these major forcing mechanisms can predict such features with significant skill the bathymetries generated in this study may form the basis for further studies considering for example the impact of sea level rise on estuarine morphodynamic development or a rapid assessment of estuarine bathymetry in the absence of measured data

the importance of breaching as a mechanism of subaqueous slope failure in fine sand large bank failures comprising up to 10 6 m 3 of sediment are common features along steep channel banks in estuaries and large rivers that consist of clean fine sands and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall steeper than the angle of repose instead of the voluminous surging plastic sediment water flow or hyperconcentrated density flow sensu mulder alexander 2001 generated by liquefaction this type of failure known as breaching by dredging companies and hydraulic engineers produces a sustained quasi steady turbidity current to date sedimentologists have not recognized the process of breaching as such in this paper it is suggested that breaching may be the origin of many thick massive sand layers known from ancient deposits from various environments notably in some turbidite successions possible differences in the sedimentary structure of the deposits produced by breach failures vs liquefaction slope failures liquefaction flow slides can be deduced from a knowledge of the sediment transport processes initiated by the failure a field study is presented on some poorly structured beds in the eocene vlierzele sands in belgium which are supposed to have originated from liquefaction failures but are reinterpreted to be the products of breaching it is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure liquefaction flow slide failure or local erosion by river or tidal channel flow at the initial stage of the failure event

the differences in morphological development between the intertidal flats of the eastern and western scheldt human interventions have a large impact on estuarine morphology the intertidal flats in the eastern scheldt and western scheldt estuaries the netherlands have faced substantial morphological changes over the past decades these changes are thought to be caused by human interventions such as the construction of the storm surge barrier in the mouth of the eastern scheldt and the deepening of the navigation channels of the western scheldt this paper analyses several datasets and numerical simulations of hydrodynamics providing an overview of the various morphological characteristics of the intertidal flats in the two estuaries over time and space apart from the volume area and average height of these areas also the integral steepness of each flat is quantified based on its full geometry the analyses focus on the intertidal flats surrounded by water which allows for a robust comparison between the different flats the intertidal flats in the western scheldt appear to be substantially steeper compared to those in the eastern scheldt the data indicates that a larger average height of a flat is related to a larger steepness despite variations in the evolution of the different flats distinct characteristics of both estuaries are observed an opposed trend is identified over time the flats in the western scheldt have mainly increased in height whereas the flats in the eastern scheldt have lowered after the completion of the storm surge barrier this opposing development is associated with differences in tidal flow velocities in the estuaries which are the result of human interventions

how heterogeneity in the shear dilation of a deposit controls the mechanics of breaching slope failure breaching is a type of retrogressive submarine slope failure associated with pore pressure drops in both space and time and this drop strengthens the failing deposit breaching is characterized by a near vertical failure surface that retreats with a relatively constant velocity on the order of a millimeter per second breaching is controlled by interactions between shear dilation generated pore pressure drops and pore pressure dissipation through intergranular fluid flow laboratory measurements show that shear dilation in a deposit increases with increasing effective stress ratio between the major principal effective stress and the minor principal effective stress as well as decreasing confining stress we present a two dimensional numerical model that indicates how effective stress ratio and confining stress produce spatially varying dilation affecting the mechanics of breaching experimental results show that dilation in a breaching deposit increases with proximity to the failure surface as a result the maximum magnitude of pore pressure drop is very close to the failure surface the numerical model confirms that the sediment release is dominated by pore pressure dissipation through intergranular fluid flow in the horizontal direction this allows the erosion rate to be treated as a constant in the vertical direction numerical model results also show that because dilation decreases with increasing vertical depth the deposit becomes less stable with depth suggesting a potential upper limit for the thickness of the deposit undergoing breaching

tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore la jolla southern california chirp seismic and swath bathymetry data acquired offshore la jolla california provide an unprecedented three dimensional view of the la jolla and scripps submarine canyons shore parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons these shore parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea level fluctuations based on stratal geometry and acoustic character we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences an acoustically laminated estuarine unit deposited during early transgression an infilling or healing phase unit formed during the transgression and an upper transparent unit beneath the transgressive surface steeply dipping reflectors with several dip reversals record faulting and folding along the la jolla margin scripps canyon is located at the crest of an antiform where the rocks are fractured and more susceptible to erosion la jolla canyon is located along the northern strand of the rose canyon fault zone which separates cretaceous lithified rocks to the south from poorly cemented eocene sands and gravels to the north isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation for example the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the holocene sea level rise the distribution of the infilling unit is controlled by pre existing relief that records tectonic deformation and erosional processes the thickness and distribution of the upper transparent unit are controlled by long wavelength tectonically induced relief on the transgressive surface and hydrodynamics

effects of shoal margin collapses on the morphodynamics of a sandy estuary shoal margin collapses of several million cubic meters have occurred in the western scheldt estuary the netherlands on average five times a year over the last decades while these collapses involve significant volumes of material their effect on the channel shoal morphology is unknown we hypothesize that collapses dynamicize the channel shoal interactions which could impact the ecological functioning flood safety and navigation in the estuary the objective is to investigate how locations probability type and volume of shoal margin collapse affect the channel shoal dynamics we implemented an empirically validated parameterization for shoal margin collapses and tested its effect on simulated estuary morphological development in a delft3d schematization of the western scheldt three sets of scenarios were analyzed for near field and far field effects on flow pattern and channel shoal morphology 1 an observed shoal margin collapse of 2014 2 initial large collapses on 10 locations and 3 continuous collapses predicted by our novel probabilistic model over a time span of decades results show that a single shoal margin collapse only affects the local dynamics in the longitudinal flow direction and dampen out within a year for typical volumes whereas larger disturbances that reach the seaward or landward sill at tidal channel junctions grow the direction of the strongest tidally averaged flow determined the redistribution of the collapsed sediment we conclude that adding the process of shoal margin collapses increases the channel shoal interactions and that in intensively dredged estuaries shoal margins oversteepen amplifying the number of collapses but because of dredging the natural morphological response is interrupted

large scale experiments on breaching flow slides and the associated turbidity current breaching flow slides are accompanied by the generation of turbidity currents measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface as well as for the validation of numerical models however there are insufficient data available detailing the velocity distribution or sediment concentration in these currents this paper presents experimental results of unique large scale physical model experiments on breaching flow slides conducted at the water lab of delft university of technology the netherlands the model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand we performed a series of novel experiments in which various non vertical initial slope angles were tested providing the first quantitative data for such initial conditions measurements of flow thickness velocities and sediment concentrations are obtained providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology the experimental results reveal that the breaching generated turbidity currents are self accelerating and that they dominate the problem of breaching flow slides we evaluated the theoretical expression for the erosion velocity in the case of pure beaching where the turbidity current has no influence on the erosion and it overestimated the observed erosion the analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope until a certain threshold leading to the steepening of the breach face and thus the occurrence of surficial slides

post glacial persistence of turbiditic activity within the rhone deep sea turbidite system gulf of lions western mediterranean linking the outer shelf and the basin sedimentary records emplacement of post glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity on the continental rise of the gulf of lions western mediterranean an aseismic area we identified turbiditic beds deposited during the rising stage and highstand of sea level swath bathymetry sediment cores in situ cone penetrating tests cptu heavy mineral associations and radiocarbon dating determined the source composition distribution and age of the turbiditic beds turbidites are composed of homogeneous to positively graded silts to medium sand with quartz up to 90 shell debris and shelfal benthic faunas their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms their source is found in relict regressive sands at the outershelf their deposition occurred just after the onset of the post glacial sea level rise and the concomitant sediment starvation of the rhone deep sea turbiditic system until recently whilst canyons are fed with sand by strong seasonal hydro sedimentary dynamics on the outershelf the emplacement of post glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons our study revealed that this low energy aseismic margin undergoes significant transport of sand down to the base of slope during the sea level rise and the holocene highstand

reduced complexity probabilistic reconstruction of alluvial aquifer stratigraphy and application to sedimentary fans in northwestern india abstract generating a realistic model of subsurface stratigraphy that fits data from multiple well locations is a well established problem in the field of aquifer characterisation this is particularly critical for the alluvial fan hosted aquifers in northwestern india as they have some of the highest rates of groundwater extraction in the world and spatially limited subsurface observations the objective of this study is to develop a reduced complexity model that generates probabilistic estimates of aquifer body occurrence within a sedimentary fan based loosely on the northwestern indian aquifer system we propose a parsimonious inverse weighted random walk model that reconstructs potential channel belt pathways within a discrete depth range or slice by i connecting known aquifer locations with the fan apex ii filling adjacent cells with non aquifer material based on estimated channel body dimensions and iii random filling of the remaining cells until the model fraction of aquifer material is comparable to the bulk aquifer fraction observed from well data once filled individual depth slices can be stacked to produce a three dimensional representation of aquifer body geometry allowing informed inference and testable predictions about the configuration of aquifer units in the subsurface a receiver operating characteristic roc curve shows that the model performs better than fully random filling both in matching the locations of aquifer material in the subsurface and in reconstructing the geometry of relict channel bodies preserved on the fan surface the model differs from purely statistical empirical approaches by incorporating some geomorphic knowledge of fluvial channel belt geometry within the fan system in contrast to a fully process based approach the model is computationally fast and is easily refined as new subsurface data become available

flow slide prediction method influence of slope geometry a quasi two dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand the initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation the condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state i e a state in which the undrained response to any quick change in load however small it may be consists of a sudden large increase in pore pressure the metastability of any sand element is predicted as a function of its constitutive properties its location in the slope and the slope geometry the constitutive properties are derived from dry triaxial tests and basically describe the liquefiability brittleness of the sand the metastability criterion for a soil element in a slope is different from that under triaxial loading flow slides observed in large scale

comparison of source rock geochemistry of selected rocks from the schei point group and ringnes formation sverdrup basin arctic canada abstract organic rich from the schei point group middle to late triassic in age and the ringnes formation late jurassic from the sverdrup basin of the canadian arctic archipelago have been geochemically evaluated for source rock characterization most samples from the schei point group are organic rich 2 toc and are considered as immature to mature oil prone source rocks kerogen types i i ii iia and ii iia these kerogen types contain abundant aom1 aom2 and alginite tasmanales nostocopsis leiosphaeridia acritarch and dinoflagellate with variable amounts of vitrinite inertinite and exinite samples from the ringnes formation contain dominant vitrinite and inertinite with partially oxidized aom2 alginite and exinite forming mostly immature to mature condensate and gas prone source rocks kerogen type ii iii iib iii and a few ii iia schei point samples contain higher bitumen extract saturate hydrocarbons and saturate aromatic ratio than the ringnes samples triterpane and sterane dominant c 30 distribution patterns and stable carbon isotope of bitumen and kerogen suggest that the analyzed samples from the schei point group are at the onset of oil generation and contain a mixture of sapropelic algal and minor terrestrial humic organic matter sterane carbon number distributions in the ringnes formation also suggest a mixed algal and terrestrial organic matter type there are some variations in hopane carbon number distributions but these are apparently a function of thermal maturity rather than significant genetic differences among samples pyrolysis gas chromatography mass spectrometry of the two samples with similar maturity shows that the schei point sample generates three times more pyrolyzate than the ringnes sample both samples have a dominant aliphatic character although the ringnes sample contains phenol and an aromaticity that is higher than that of the schei point sample

regional maturity as determined by organic petrography and geochemistry of the schei point group triassic in the western sverdrup basin canadian arctic archipelago abstract maturity and source rock potential of organic rich beds in the triassic schei point group in the sverdrup basin arctic canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically i e rock eval and biomarker maturation parameters the samples evaluated belong to the eden bay member of the hoyle bay formation and contain a predominance of marine algal material in the form of tasmanales and dinoflagellates along with mixed terrestrial organics the rock matrix is dominantly carbonate with some shaly input indicating that the rocks were deposited in an iron poor highly euxinic environment with few exceptions there is good agreement between parameters determined using microscopy namely r o max and r gq and geochemical parameters t max hi dia c 27 dia c 27 reg c 27 steranes s s r c 29 steranes the ternary diagram showing the abundance of normalized c 27 c 28 and c 29 regular steranes indicates a mostly marine depositional environment for the schei point source rock this is confirmed by the abundance of marine fauna and flora in these samples analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the sverdrup basin this is due in part to the increase in overburden of sediments in the axis of the basin also the high thermal conductivity of salt has strongly influenced the maturity of schei point source rocks over the crest of the salt cored structures i e well hazen f 54 and the proximity of salt has enhanced maturation levels at well rock point j 43 the sections investigated were also considered to have an excellent gas potential due to their higher than average toc content

dynamics of dilative slope failure breaching is a style of retrogressive subaqueous slope failure controlled by dilation and consequent pore pressure drop it has the potential to generate turbidity currents that build thick successions of turbidites we present pore pressure measurements made during breaching failure as well as a physical model that shows how the pore pressure field within the failing deposit is connected to the erosion rate associated with the failure surface we show that breaching can occur in any dilative granular material conditions for breaching could be common on the continental shelf making it an important mechanism in transferring sediment into the deep ocean a dynamic equilibrium exists between the slope failure and the pore pressure dissipation during breaching this equilibrium leads to a way to estimate the rate of sediment release from breaching using a simple material property the coefficient of consolidation contrary to previous work we find that the erosion rate is independent of the dilation of the deposit due to the coupling between erosion and pore pressure dissipation the equilibrium between the erosion and pore pressure dissipation decouples the steady state pore pressure field from the permeability of the deposit this is the first time this behavior has been recognized in sediment failures

lightning discharges produced by wind turbines new observations with a 3 d lightning mapping array and high speed video are presented and discussed the first set of observations shows that under certain thunderstorm conditions wind turbine blades can produce electric discharges at regular intervals of 3 s in relation to its rotation over periods of time that range from a few minutes up to hours this periodic effect has not been observed in static towers indicating that the effect of rotation is playing a critical role the repeated discharges can occur tens of kilometers away from electrically active thunderstorm areas and may or may not precede a fully developed upward lightning discharge from the turbine similar to rockets used for triggering lightning the fast movement of the blade tip plays an important role on the initiation of the discharge the movement of the rotor blades allows the tip to runaway from the generated corona charge the second observation is an uncommon upward downward flash triggered by a wind turbine in that flash a negative upward leader was initiated from a wind turbine without preceding lightning activity the flash produced a negative cloud to ground stroke several kilometers from the initiation point the third observation corresponds to a high speed video record showing simultaneous upward positive leaders from a group of wind turbines triggered by a preceding intracloud flash the fact that multiple leaders develop simultaneously indicates a poor shielding effect among them all these observations provide some special features on the initiation of lightning by nonstatic and complex tall structures

breaching related turbidites in fluvial and estuarine channels examples from outcrop and core and implications to reservoir models abstract an understanding of the paleoenvironment and the main sedimentary processes behind preserved deposits is crucial to correctly interpret and represent lithofacies and facies associations in geomodels that are used in the hydrocarbon industry particularly when a limited dataset of cores is available in this paper a fairly common facies association is discussed containing massive sands here defined as thick 0 5 m structureless sand beds devoid of primary sedimentary structures or with some faint lamination deposited by mass failures of channel banks in deep fluvial and estuarine channels amongst geologists it is generally accepted that liquefaction is the main trigger of large bank failures in sandy subaqueous slopes however evidence is mounting that for sand deposits a slow retrogressive failure mechanism of a steep subaqueous slope known as breaching is the dominant process a model of breaching induced turbidity current erosion and sedimentation is presented that explains the presence of sheet like massive sands and channel like massive sands and the sedimentary structures of the related deposits sheet like packages of spaced planar lamination that are found together with massive sand bodies in deposits of these environments are identified as proximal depositional elements of breach failure events the model acquired from sedimentary structures in deposits in the eocene estuarine vlierzele sands belgium is applied to outcrops of the dinantian fluvial fell sandstone england and cores of the tilje and nansen fms lower jurassic norwegian continental shelf the possible breach failure origin of some other massive sands described in literature from various ancient shallow water environments is discussed breach failure generated massive sands possibly also form in deep marine settings the potentially thick and homogeneous well sorted sand deposits bear good properties for hydrocarbon flow when found in such an environment however in case of deposition in an estuarine or fluvial channel these sand bodies are spatially constricted and careful facies interpretation is key to identifying this when constructing a static reservoir model this needs to be considered both for in place volume calculations as well as drainage strategies

spatial change of grading pattern of subaqueous flood deposits in lake shinji japan abstract we acquired three geo slicer cores along a longitudinal profile on the subaqueous portion of the hii river delta built since the 1630s in lake shinji western japan grading patterns of 26 individual sand beds in the cores vary spatially we interpret these sand beds as subaqueous flood deposits from their sedimentary structures the geomorphology of the delta lobe and the absence of hydrodynamic influences other than river floods entering the lake most sand beds at shallow depths 4 m below the water surface display triple stacks of inverse to normal grading single inverse to normal grading appears between 4 and 5 m depth and normal grading dominates in deeper beds inverse and normal grading could reflect the waxing and waning of the parent flow respectively we explain the occurrence of triple stacks of inverse to normal grading in shallower horizons and single inverse to normal grading in deeper horizons as consequences of lateral movement of the plunge point of flood plumes during the course of flood events spatially decelerating sediment laden river plumes steeply increase their velocity after they plunge beneath the water surface in depth limited proximal areas of a subaqueous delta back and forth translation of the plunge point over a fixed point due to the waxing and waning of river discharge leads to three cycles of waxing and waning of flow velocity and the resulting deposits at the fixed point would have triple stacks of inverse to normal grading in the distal parts of the delta velocity of fully plunged hyperpycnal flow increases and then decreases reflecting directly the waxing and waning of river discharge and the resulting deposits would be composed of single inversely to normally graded beds in the most distal parts the slower initial part of the hyperpycnal flow may be overtaken by the succeeding faster part to yield a monotonically waning flow at a fixed point this process may have resulted in sand beds with uniformly normal grading in lower distal horizons assuming that flood hydrographs for the hii river have not changed since the 17th century these findings mean that the momentum of river flow during floods propagates to the outflow differently at different distances from the river mouth our results show that in parts of the delta front slope the outflow of river floods accounts for the inverse to normal grading considered to be an important basis for identifying hyperpycnal flow turbidites however in other parts of this environment grading patterns of flood deposits do not necessary reflect the flood hydrograph overdependence on inverse to normal grading in identifying hyperpycnal flow deposits may lead to inaccurate estimations of their frequency in the sedimentary record on the other hand special care is needed for the reconstruction of paleo flood hydrographs using sedimentary records

breaching in fine sands and the generation of sustained turbidity currents in submarine canyons natural moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume because of this shear dilatancy negative pore pressures are generated in the bed in cases of low permeability these negative pressures are released relatively slowly which retards the maximum rate of erosion this effect is incorporated in a new analytically derived pick up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes sometimes more than 5 m high in fine non cohesive sands this process termed breaching in the field of sediment dredging may produce large failures in sand bars or river banks the analytical function that describes the breaching process in fine sand is incorporated in a one dimensional steady state numerical model of turbidity currents describing the spatial development of flow this model is applied to simulate a large flushing event in scripps submarine canyon pacific coast of california breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps predicted velocities are compared with values measured during a flushing event implications for the interpretation of deep water massive sands are discussed

erosion velocity of large grains subjected to a high uniform flow velocity abstractthere is limited knowledge on the erosion rates of large grains the available erosion models of granular material at large flow velocities are only validated up to a median particle diamet

underwater sand bed erosion and internal jump formation by travelling plane jets theory and experiments are used to investigate the water and sediment motion induced along a sea bed by travelling plane jets steadily moving jets are considered and represent an idealization of the tools mounted on ships and remotely operated vehicles rovs for injection dredging and trenching the jet induced turbulent currents simultaneously suspend sand from the bed and entrain water from the ambient to describe these processes a shallow flow theory is proposed in which the turbulent current is assumed stratified into sediment laden and sediment free sublayers the equations are written in curvilinear coordinates attached to the co evolving bed profile a sharp interface description is then adopted to account rigorously for mass and momentum exchanges between the bed current and ambient including their effects on the balance of mechanical energy travelling wave solutions are obtained in which the jet induced current scours a trench of permanent form in a frame of reference moving with the jetting tool depending on the operating parameters it is found that the sediment laden current may remain supercritical throughout the trench or be forced to undergo an internal hydraulic jump these predictions are confirmed by laboratory experiments for flows with or without jump in which the current remains attached to the bed bottom profiles computed by the theory compare favourably with imaging measurements

geometry and topology of estuary and braided river channel networks automatically extracted from topographic data automatic extraction of channel networks from topography in systems with multiple interconnected channels like braided rivers and estuaries remains a major challenge in hydrology and geomorphology representing channelized systems as networks provides a mathematical framework for analyzing transport and geomorphology in this paper we introduce a mathematically rigorous methodology and software for extracting channel network topology and geometry from digital elevation models dems and analyze such channel networks in estuaries and braided rivers channels are represented as network links while channel confluences and bifurcations are represented as network nodes we analyze and compare dems from the field and those generated by numerical modeling we use a metric called the volume parameter that characterizes the volume of deposited material separating channels to quantify the volume of reworkable sediment deposited between links which is a measure for the spatial scale associated with each network link scale asymmetry is observed in most links downstream of bifurcations indicating geometric asymmetry and bifurcation stability the length of links relative to system size scales with volume parameter value to the power of 0 24 0 35 while the number of links decreases and does not exhibit power law behavior link depth distributions indicate that the estuaries studied tend to organize around a deep main channel that exists at the largest scale while braided rivers have channel depths that are more evenly distributed across scales the methods and results presented establish a benchmark for quantifying the topology and geometry of multichannel networks from dems with a new automatic extraction tool

non uniform across shelf variations in thickness grain size and frequency of turbidites in a transgressive outer shelf the middle pleistocene kakinokidai formation boso peninsula japan abstract across shelf variations in thickness grain size and frequency of sandstone beds in a transgressive outer shelf succession were investigated from the middle pleistocene ca 0 7 ma kakinokidai formation on the boso peninsula japan the transgressive deposits are generally muddy and contain slumps and slump scars the intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge complex deposits in the southwestern upslope area during storm events mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed by bed correlation of the outer shelf sandstone beds although overall thickness grain size and frequency of sandstone beds decrease in the downslope direction some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits these sandstone beds subsequently thicken and fine and finally thin out in the farther downslope area in addition to the local thinning of sandstone beds the frequency of sandstone beds first decreases and then increases in the farther offshore direction from this evidence we concluded that these non uniform patterns of across outer shelf variations in thickness grain size and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer shelf floor these physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds compared with the bed shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand stage shelf systems

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

tectonic evolution geomorphology and influence of bottom currents along a large submarine canyon system the sao vicente canyon sw iberian margin abstract a multi scale dataset consisting of multi beam echo sounder 2d multi channel seismic and sidescan sonar tobi data allows us to identify a large variety of morphologies originating from sedimentary and tectonic processes along the sao vicente canyon svc which is the largest submarine canyon developed in the external part of the gulf of cadiz the svc is located in one of the most seismogenic areas of western europe the convergence between the eurasian and african plates has controlled the formation and evolution of the canyon the svc is tectonically controlled by three main thrust faults the marques de pombal fault the sao vicente fault and the horseshoe fault no major rivers feed sediment to the canyon head but the main sediment source is related to the dismantling of canyon flanks and the mow mediterranean overflow water this current contributes sediments by two different processes a conturites deposition at the head and flanks of the svc that periodically fail into the canyon and b the coarser grained and denser sediment of the mow might be trapped at the head of the canyon and could develops into hyperpycnal flows the svc is characterized by retrogressive erosion being submarine landslide deposits and scars the main seafloor morphologies the tectonic and stratigraphic interpretation of seismic profiles indicate that the svc is a clear example of a diachronous and segmented canyon developed since the late miocene in an area of present day active plate tectonics this study investigates the interaction between active tectonics the dynamics of submarine canyons and the resulting geomorphologies

prediction of ignitive turbidity currents in scripps submarine canyon swift highly erosive continuous turbidity currents are known to be triggered in scripps submarine canyon during storms a relatively modest agitation due to edge waves can generate currents at least as swift as 1 9 m s 1 pantin 1979 and parker 1982 have described a mechanism by which a turbidity current can self accelerate by entraining sediment from the bed parker termed the mechanism ignition herein two models of steady spatially developing turbidity currents are developed and applied to scripps submarine canyon fairly specific predictions are obtained for the onset of ignitive acceleration and for the downstream development of the turbidity currents the results are in general agreement with available measurements in the same canyon it is speculated that ignitive turbidity currents constitute a major mechanism by which sand submarine canyons are eroded and by which sand is delivered to the abyssal plain

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

submarine canyons associated with alternating sediment starvation and shelf edge wedge development northern kwazulu natal continental margin south africa abstract multibeam bathymetry and high resolution boomer data reveal a shelf edge wedge embayed by numerous canyons on the currently sediment starved northern kwazulu natal continental margin submarine canyons in the southern portions of the study area may be differentiated from those in the north by the presence of an underlying erosive surface marked by palaeo depressions and a thinner shelf edge wedge canyons exhibit square interfluves in the mid slope slump and landslide failure surfaces in their walls and high amplitude chaotic reflectors interpreted as slump deposits infilling older thalwegs the shelf edge wedge architecture where it is embayed by canyons is progradational into the canyon axes and marked particularly in the north by block like features these are interpreted as syn depositional growth faults lenses comprising chaotic high amplitude reflector packages are common within the wedge and are interpreted as laterally discontinuous slump masses instability of the shelf edge wedge is considered the driving force for canyon inception initial failures generated downslope eroding sediment flows and submarine rills that evolved into their modern forms by retrogressive slumping when the rill walls became oversteepened continued delivery of sediment to the shelf edge wedge was contemporaneous with canyon widening and headward erosion mid slope canyon topography formed as the result of sandy turbidity currents that ignited downslope of these slump sources coupled with non aggradation of the adjoining interfluves differences in the thickness of the shelf edge wedge are the result of varying fluvial influences where larger rivers crossed the shelf during sea level lowstands the shelf edge wedge has been cannibalised this is more pronounced in areas with subsurface palaeo depressions that may have constrained the downslope eroding phase especially during lowstands where there were insignificant fluvial influences no subsurface depressions and a better preserved shelf edge wedge are apparent post dating the shelf edge wedge a protracted period of sediment starvation occurred halting canyon development and stunting more elaborate erosion patterns such as those of other margins

experiments on the pickup flux of sand at high flow velocities abstracttwo regimes can be distinguished for the pickup flux of sand at a shields parameter of less than about 0 5 corresponding with flow velocities of 0 5 1 m s the erosion process is dominated by the size and density of the grains grain by grain pickup at higher flow velocities the bulk properties of the sand bed start to influence the erosion process dilative behavior results in the inflow of water to the sand bed which reduces the pickup flux dilatancy reduced pickup because of the shearing of layers of sand a pickup function was recently developed for this regime incorporating the effect of bulk properties such as permeability and porosity on the pickup this function agrees well with data of previous erosion experiments in which the permeability and porosity of the sand bed were varied however these experiments just met the condition for dilatancy reduced pickup the flow velocity during these previous experiments was between 1 and 1 5 m s while the shields parameter varied bet

morphological evolution of a well constrained subaerial subaqueous source to sink system wabush lake since 1964 the iron ore company of canada has deposited iron tailings resulting from mining operations into wabush lake western labrador canada this activity has resulted in a continuous hyperpycnal flow flowing over the lake floor bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental iron ore company of canada plans to maintain safe disposal strategies of tailings into the lake here this dataset is used to study the evolution of different channels present in wabush lake and their link with knickpoints found at the head of most of these channels the channels show notable evolution from one survey to the next some knickpoints and channels may be followed throughout more than one survey the evolution of these knickpoints is the process responsible for the creation of erosional channels the context in which they appear as well as the evolution of some of the subaqueous channels is analysed cyclic steps and sediment waves are also found in the lake these rhythmic bedforms also created by the passage of turbidity currents are analysed sediment waves found in wabush lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment

evaluation of organic maturity and hydrocarbon source potential of the ringnes formation sverdrup basin arctic canada abstract organic rich shales are common in the ringens formation member an oxfordian kimmeridgian argillaceous unit which is widespread in the sverdrup basin of the canadian arctic archipelago the shales and siltstones of the ringnes are laminated to burrowed and are interpreted to have been deposited under sub oxic conditions in a mid to outer shelf setting the organic matter om which is up to 11 wt has relatively low h1 and oi values rock eval toc data organic petrography and the environment of deposition of the ringnes are interpreted to infer that the organic matter in basin margin samples is mainly of terrestrial origin with a variable but minor marine component in the axial region of the basin the om appears to be of a mixed marine and terrestrial origin and has been partially oxidized the high organic content is attributed to sedimentation rates high enough to bury the organic rich sediments before complete destruction by aerobic bacteria and benthic scavengers the organic content and hi values increase towards the axis of the basin the thermal maturity of the ringnes shales varies from immature on the basin margins to mature along the basin axis in the eastern and central portions of the basin however the ringnes shales are overmature at many localities due to the presence of diabase sills and dykes which were intruded in early cretaceous by contrast the maturity of the ringnes is anomalously low over the crests of large salt cored structures rock eval toc data and petrographic evidence indicate that the ringnes shales have potential to generate significant amounts of thermogenic gas at low levels of thermal maturity

solid bitumen bituminite and thermal maturity of the upper jurassic lower cretaceous chia gara formation kirkuk oil field zagros fold belt kurdistan iraq abstract the upper jurassic lower cretaceous chia gara formation a proven marine source rock characterised by predominance of amorphous organic matter aom is known from few outcrops in ne iraq and a number of exploration wells in the zagros fold belt this study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock forming minerals of the tithonian berriasian chia gara formation intersected by the kirkuk well k 109 drilled in the giant kirkuk oil field ne iraq the organic petrographic analyses including incident light microscopy and confocal laser scanning microscopy clsm were applied to carbonate source rocks with low to moderate organic carbon contents our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite i e tasmanites and leiospheridia liptodetrinite and vitrinite based on optical characteristics and clsm spectral fluorescence measurements examinations of bituminite point towards the presence of bituminite type iii the bituminite type iii encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and or with solid bitumen the qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples the photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0 19 and 0 43 sbrr and lambda max values extending from 515 nm to 590 nm respectively the corresponding results of the solid bitumen exhibit 1 a lack of a relationship with depth and 2 suggest its poor property as a reliable maturity indicator for the examined samples the presence of oil exudates oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase the performed thermal maturities assessments of dispersed organic matter point towards early mature to peak mature oil window with vitrinite reflectance values ranging between 0 52 vrr at 2801 m to 0 83 vrr at 3089 m depth mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies e g clear rimmed dolomite with localised intensive dolomitisation in the phyllosilicate rich matrix predominance of calcite and siderite is observed followed by zinc blende and pyrite the composition of organic matter in the examined chia gara formation with predominance of bituminite and solid bitumen makes the major marine source rock of iraq s cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index hi with only minor terrestrial input in addition the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by clsm during hydrocarbon prospecting

brazilian carbonate reservoir a successful seismic time lapse monitoring study brazilian carbonate reservoirs contain huge oil in place volumes and are likely to have an important economic impact in global oil industry such carbonate reservoirs both albian and aptian are located offshore in deep water which has an important role in development costs in siliciclastic plays it is standard practice to use time lapse 4d seismic to locate wells in unswept areas maximizing the recovery factor however in carbonate plays time lapse seismic monitoring remains challenging with few cases of success published around the world carbonates differ from siliciclastic rocks in many aspects with a varied chemical composition and complex pore connectivity carbonates bring on a large diversity of facies each one showing a specific seismic response moreover the usually high incompressibility of the carbonate matrix reduces sensitivity to pressure and saturation changes which are the main effects expected on a hydrocarbon field undergoing production considering both the economic relevance and the difficulties of using time lapse seismic to monitor carbonate reservoirs petrobras created a strategic program to face this challenge a time lapse seismic s4d study of an albian carbonate reservoir located in the campos basin offshore brazil three legacy data were available streamer 1987 streamer 2002 and ocean bottom cable 2010 extensive feasibility studies are performed as well as a meticulous prestack 4d

flow slides in the netherlands experience and engineering practice this paper deals with flow slide experience in the netherlands it gives an extensive survey of empirical field data concerning the geological characteristics of the region the profiles just before the flow slides and the damage that flow slides can cause the traditional dutch procedure for analyzing the flow slide potential of underwater sand slopes is described this is an engineering approach that is mainly based on the empirical field data together with geological surveys and soil investigations performed at the relevant site key words sand collapse flow slides liquefaction slope stability

sediment transport of fine sand to fine gravel on transverse bed slopes in rotating annular flume experiments large scale morphology in particular meander bend depth bar dimensions and bifurcation dynamics are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream however existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes and in practice models are calibrated on measured morphology the objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near bed flow conditions with varying secondary flow intensity sediment sizes 0 17 4 mm sediment transport mode and bed state to test existing predictors we conducted over 200 experiments in a rotating annular flume with counterrotating floor which allows control of the secondary flow intensity separate from the streamwise flow velocity flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions we isolated separate effects of all important parameters on the transverse slope resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on shields number and strongly depend on bed state and sediment transport mode fitted functions are provided for application in morphodynamic modeling

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

investigation of core data reliability to support time lapse interpretation in campos basin brazil quantitative interpretation of time lapse seismic data requires knowledge of saturation and pressure effects on seismic velocities although the former can usually be modeled adequately using the gassmann equation the latter is obtained mainly by laboratory measurements which can be affected by core damage we investigate the magnitude of this effect on compressional wave velocities by comparing laboratory experiments and log measurements we use gassmann fluid substitution to obtain low frequency saturated velocities from dry core measurements thus mitigating the dispersion effects taken at reservoir pressure the analysis is performed for an unusual densely cored well from which 43 cores were extracted over a 45 m thick turbidite reservoir these computed velocities show very good agreement with the sonic log measurements this confirms that for this particular region the effect of core damage on ultrasonic measurements is less than the measurement error consequently stress sensitivity of elast

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord head delta rivers and turbidity currents are the two most important sediment transport processes by volume on earth various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths including direct plunging of river discharge delta mouth bar flushing or slope failure caused by low tides and gas expansion earthquakes and rapid sedimentation during 2011 106 turbidity currents were monitored at squamish delta british columbia this enables statistical analysis of timing frequency and triggers the largest peaks in river discharge did not create hyperpycnal flows instead delayed delta lip failures occurred 8 11 h after flood peaks due to cumulative delta top sedimentation and tidally induced pore pressure changes elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta lip which is the most significant of all controls on flow timing in this setting