sandwave migration in monterey submarine canyon central california abstract repeated high resolution multibeam bathymetric surveys from 2002 through 2006 at the head of the monterey submarine canyon reveal a sandwave field along the canyon axis between 20 and 250 m water depth these sandwaves range in wavelength from 20 to 70 m and 1 to 3 m in height a quantitative measure was devised to determine the direction of sandwave migration based on the asymmetry of their profiles despite appreciable spatial variation the sandwaves were found to migrate in a predominantly down canyon direction regardless of season and tidal phases a yearlong adcp measurement at 250 m water depth showed that intermittent internal tidal oscillations dominated the high speed canyon currents 50 80 cm s which are not correlated with the spring neap tidal cycle observed currents of 50 cm s or higher were predominantly down canyon applying a simple empirical model flows of such magnitudes were shown to be able to generate sandwaves of a size similar to the observed ones

bedload sediment transport dynamics in a macrotidal embayment and implications for export to the southern great barrier reef shelf abstract keppel bay is a macrotidal embayment on a tectonically stable tropical coast which links the fitzroy river with the great barrier reef continental shelf estuaries and deltas act as conduits between catchments and inner shelf environments therefore understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral reefs that are potentially vulnerable to enhanced river sediment loads furthermore the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries particularly in turbid episodic systems such as the fitzroy river and keppel bay our sedimentological analysis of seabed samples shear stress modelling and three dimensional acoustic imaging reveals that keppel bay is a mixed wave and tide dominated estuarine system areas of sediment starvation and shoreward transport characterise the offshore zone whereas a complex of both active and relict tidal sand ridges and associated subaqueous dunes dominate the relatively protected southern keppel bay transport within this region is highly dynamic and variable with ebb dominated sediment transport through tidal channels into the outer bay where there is a switch to wave dominated shoreward transport ultimately bedload sediments appear to be reworked back inshore and to the north and are gradually infilling the bedrock defined embayment our characterisation of the keppel bay system provides a detailed example of the physiography of the seaward portion of a tide dominated system and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography

determination of trapping pressure and temperature of petroleum inclusions using pvt simulation software a case study of lower ordovician carbonates from the lunnan low uplift tarim basin abstract we report a case study carried out on lower ordovician reservoir carbonates of the lunnan low uplift tarim basin to determine trapping pressures and temperatures of petroleum inclusions from the intersection of isochores of coeval petroleum and aqueous fluid inclusions using pvt sim software there are four types of petroleum inclusions from this sequence their trapping pressures and temperatures are type i 80 105 c 199 230 bar type ii 135 145 c 235 250 bar type iii 155 165 c 344 360 bar and type iv 220 252 c 345 390 bar respectively which are consistently higher than their homogenization temperature and saturation pressures by about 5 15 c and 25 70 bar to confirm the reliability of the pvt simulation approach fluid inclusions were synthesized in calcite under controlled temperature and pressure conditions and studied using the same methods the calculated trapping pressure and temperature of the synthetic petroleum inclusions closely match the actual pressure and temperature applied in the experiment by reference to the burial and geothermal history of the tarim host rocks it was inferred that types i ii and iii petroleum inclusions represent fluids associated with three distinct phases of petroleum emplacement in the lower ordovician strata of this area occurring during late silurian to early devonian cretaceous to early tertiary and late tertiary respectively type iv petroleum inclusions occur only in some fine calcite veins from few samples and are believed to be related to an anomalous thermal event in this area on the basis of the trapping pressures and trapping temperatures of the petroleum inclusions three main phases of the petroleum filling of the lower ordovician reservoirs can be delineated phase i and phase iii petroleum events were related to petroleum migration and accumulation from the lunnan low uplift or nearby area the petroleum of the phase ii petroleum event appears to have originated from middle and upper ordovician source rocks in the northern slope area of the manjiaer depression with a long distance migration

morphodynamics and seismostratigraphy of a deep hole at tidal channel confluence the sedimentary circulation pattern at a deep hole at a tidal channel junction in an estuary environment is examined using morphosedimentological and seismostratigraphic data the bottom and sub bottom acoustic information side scan sonar and 3 5 khz profiler obtained at a tidal channel confluence in bahia blanca estuary argentina evidences the depositional and erosive features bed load sediment transport pathways and morphological evolution of the depression this important depression in the confluence zone of the channels is characterised by the presence of steep scour faces 14 at the mouth of both channels and gentle slopes 1 5 opposite to them bed load sediment transport analysis reveals a differential circulation pattern of sand on both sides of the hole which is associated with the different sediment availability in each channel the side scan sonar information therefore indicates that there is no available sand in one of the channels whereas the other channel is characterised by the presence of a large amount of sediment coming from its inner area deposition therefore occurs on the side where sediment is mobilised as bed load by the ebb current dominance and on the face developed downstream in the latter a part from the sediment is deflected inward by the tidal flood currents which produce the deposition of sediment on the gentle side the rest of the sediment is exported from the system by ebb currents in contrast erosion occurs on the opposite side of the hole and at the mouth of each channel and it is manifested by the outcrop of old sedimentary strata the seismostratigraphic information collected in this study indicates that the depression was originally a fully erosive morphological feature a descriptive model of the morphological evolution at a channel confluence is presented in this study

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

variations in sediment wave dimensions across the tidally dominated irish sea nw europe abstract new high resolution multibeam echosounder data have been collected in the irish sea in the last decade sediment waves oriented transverse to tidal flow dominate many parts of the irish sea and exhibit an almost continuous spectrum of heights and spacings sediment wave growth remains poorly quantified and from the irish sea swath bathymetry data many bedform dimensions have been measured and examined statistically a strong positive power correlation between sediment wave height and spacing was observed s 0 0692 0 8020 n 935 r 0 853 while height and spacing only weakly vary with water depth to assess the main factors influencing sediment wave height and spacing deviations from the typical hydrodynamically analogue sediment wave geometry in equilibrium are qualitatively and semi quantitatively investigated in the irish sea in conjunction with seabed characteristics coarser sediment generally forms larger sediment waves while suppressed sediment growth is found likely due to the limitations in mobile sediment supply and inefficiency of very coarse bedload transport

morphology and maintenance of steep dunes near dune asymmetry transitional areas on the shallow shelf beibu gulf northwest south china sea abstract symmetrical dunes can be found in areas where dune asymmetry changes sense but in areas where dunes are not expected to be moving the development and maintenance of symmetrical dunes are poorly understood in the southeastern beibu gulf we have identified five typical dune asymmetry transitions at the depths of shallower than 50 m basing on the latest bathymetric data those regions are separated into two classes according to their different shapes and locations sand transport directions are deduced by dune migrations between surveys simulated regional currents and sand size trends the two classes of the regions are found to experience opposing net sand transports from the north and south around the asymmetry transitions the dunes have impressive steep sections relatively symmetrical shapes and almost straight crests they have a general height length h l relation h 0 0575 l1 0836 r2 0 834 which is steeper than dunes in other seas some of the dunes have extraordinary large heights exceeding a quarter of water depth which is attributed to the preserved sand body bidirectional sand accretion erosion in troughs and absence of significant erosion on crests the steepness and straight crests of dunes adapt to the nearly symmetrical or weak asymmetrical reversing currents which induce flow separations and reversals on both flanks of the dunes it also suggests that dunes develop differently under sufficient and limited sand supply dunes will gradually grow in size when being continually supplied with sand however if sand supply is restricted dunes may separate or turn into more isolated individuals to sustain the h l relation the h l relation of dunes can be maintained during either growth or separation overall the nearly symmetrical or weak asymmetrical reversing currents maintain the steep shapes of dunes while variations in sand supply affect their sizes to work out the detailed transports of sediment future observations of flow structures and related models of such two sided steep dunes are still required

morphology and dynamics of large subtidal dunes in bahia blanca estuary argentina abstract the purpose of this paper is to carry out a detailed analysis of subtidal dune morphology and temporal variability and to estimate dune migration rate to improve knowledge of this topic and so enhance the existing data on different marine environments in the world and especially in south america where this information is limited two swath bathymetry surveys were conducted across a dune field in the bahia blanca estuary argentina morphometric parameters and migration rate according to the dune type were analyzed the field is composed of large dunes exhibiting two morphological configurations which are differentiated into sinuous and barchan dunes the dunes studied are the largest of the estuary with heights and wavelengths greater than 5 m and 130 m respectively the crests of the large dunes are arranged with an orientation perpendicular to the axis of the channel from geometrical analysis of the parameters the dunes show a weakly positive correlation between dune height and wavelength as too between dune height and water depth no clear relationship was observed between maximum height and wavelength parameters with water depth across the estuary the bedforms migrate in the ebb direction with mean rate of 43 m year 1 comparison of our results with previous data shows that during three decades the western boundary of dune field has been displaced 900 m towards the outer estuary however the dune field configuration and distribution of diverse types of bedform appear to be relatively stable

organic inclusions in salt part 2 oil gas and ammonium in inclusions from the gabon margin abstract organic inclusions have been found in a salt diapir south of port gentil in the north subbasin of the gabon margin two main types of organic inclusions are described type 1 gas rich ch4 and co2 oil inclusions located in recrystallized halite associated with a complex mineral daughter paragenesis anhydrite quartz k feldspar dolomite ammonium sylvite and carnallite 1 and 2 5 molar nh4cl respectively the oil is essentially aliphatic with some aromatic content the composition being characteristic of mature oil the different methane c2 ratios in the gas and oil phases indicate an internal pressure close to 200 bars which is compatible with hydrostatic pressure at sampling depth homogenization temperatures of two phase hydrocarbon inclusions inside dolomite daughter crystals have been measured th 113 c type 2 organic inclusions are located in healed fracture planes in recrystallized halite and contain aliphatic oil the brine content is high and no gases have been detected different alkane compositions occur in different fracture planes type 2 inclusions correspond to injections of mature oil into halite fracture systems at low temperature 60 c comparisons between fluid inclusions in halite occurring in the bresse area france and in the north subbasin of the gabon margin help one to follow carbon and nitrogen cycles from diagenesis to catagenesis the organic inclusions hosted in salt rocks reflect the geochemical reactions that have occurred in the salt over time

hydrocarbon alteration in the bituminous salt of the klodawa salt dome central poland abstract the so called bituminous salts occurring in the klodawa dome located in central poland differ from the surrounding salts by their colour change from light to dark brown this colour is associated with an extremely large amount of hydrocarbon mainly located in the inclusions the presence of numerous fluid inclusions has been documented in previous petrologic studies distinguishing seven main types of fluid inclusion assemblages fia in terms of size shape as well as the ratio of filling material however four types of inclusions were selected in the current investigations according to their unusual optical behaviour raman micro spectroscopy a modern non destructive method was used for investigating a single inclusion being a part of fia presented in this paper raman spectra revealed a unique pattern of bands characterizing the content of the inclusions the hydrocarbons show a very complex character reflected in the appearance of a strong fluorescence background a well marked heterogeneity characterized the inclusions by diversity in the intensity of the background and in the pattern of the bands characterizing the presence of certain components one can distinguish the presence of carbonaceous matter showing the different degrees of order the depth profile and the analysis of the various points of the inclusions indicate that the carbonaceous matter is not evenly distributed in the inclusions but forms a thin disorganized film on their walls this film was also found in sites where the inclusions are filled with brine the certain characteristics associated with the presence of the incipient phase transformation of the organic matter or slightly transformed organic matter and the lack of light hydrocarbons as well as a number of petrologic features of inclusions indicate that these salt rocks have been subdivided into thermal transformations accompanied by the recrystallization of the halite and the escape of the more volatile compounds such as methane ethane etc

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

spatially varying environmental properties controlling observed sand wave morphology sand wave morphology and dynamics on continental shelves vary substantially and we hypothesize that these spatial variations depend on local bed properties and hydrodynamic characteristics to date process based modeling studies have not been able to simulate realistic equilibrium sand wave heights and empirical studies are mostly limited to case studies in order to explain the spatial variation in the morphology of equilibrium sand waves on continental shelves with processes and local bed conditions a large scale investigation is required in this paper we use high resolution multibeam echo soundings hydrodynamic models and databases and sedimentary data for the analysis of respectively sand wave shape characteristics and the comparison to hydrodynamic and sedimentary characteristics for the netherlands continental shelf the results are quantified lengths heights and asymmetry of all sand waves in the dutch part of the north sea furthermore we show that the mode of sediment transport bed load or suspended is a dominant factor in explaining sand wavelength height and asymmetry full results of shape characteristics of all sand waves on the netherlands continental shelf together with the tidal velocity water depth surface wave height and median grain size are provided in a repository with this paper http doi org 10 4121 uuid 0d7e016d 2182 46ea bc19 cdfda5c20308 these results are highly valuable for applied offshore engineering projects and to modelers for validating their morphodynamic model results

bedforms and bed material transport pathways in the changjiang yangtze estuary abstract bed features were mapped using a thermal depth recorder and a side scan sonar in the changjiang yangtze estuary and flows were observed and bed surface materials were sampled to investigate bed material transport pathways distinct scales and dimensions of dunes were observed in terms of the classification scheme of ashley ashley g m 1990 classification of large scale sub aqueous bedforms a new look at an old problem journal of sedimentary research 61 160 172 forming a dune set in the flood season large dunes occurred predominately in the surveyed area of the estuarine zone and two dimensional dunes predominated in the dry season while three dimensional dunes prevailed in the flood season sharp lee sides of dunes have low angles indicating a significant suspended load transport for the bedform migration and the majority of them face down estuary reflecting the controlling process by the ebb current the bed material migrations in terms of relative maximum gross transport show a satisfactory agreement with the sonar mapping in the dry season the relative maximum gross transport as an independent estimator of migration direction can be used to effectively determine the bed material transport directions in the changjiang estuary

giant dune morphologies and dynamics in a deep continental shelf environment example of the banc du four western brittany france the aim of this paper is to improve the knowledge of spatio temporal variability of very large to giant dunes in deep tide dominated environment their growth mechanisms and dynamic evolution still remain in debate and constitute a significant scientific challenge in regard to difficulties to achieve accurate measures of migrations this motivated the realization of three recent swath bathymetry surveys across the wide dune field of the banc du four located offshore the western brittany the banc du four field is composed of more than 500 large dunes exhibiting a great diversity of morphologies ranging from 2d to 3d shapes and reaching the largest sizes of such sedimentary structure ever described wavelength over 1000 m and height over 30 m the analysis of the entire ensemble of dune parameters offers the opportunity to discuss the relative influence of forcings and the validity of the equations predicting the bedform geometry in shallow waters our results show a good height spacing power law correlation but do not strike the usual statistical regression observed in previous studies the steeper positive slope of the equation and the outstanding values of the height parameter reveal the complexity of local hydrodynamic regime interacting with bed load transport and sediment supply no clear relationship has been observed between asymmetry and size parameters water depth can not be considered as a major factor controlling the size of dunes otherwise the vertical sedimentary variation suggests the action of storm waves on dune crests and the horizontal migration rates of dunes in the eastern field of the banc du four were found to range from 3 to 20 m yr 1 such velocities were only mentioned before by van landeghem et al 2012 on deep continental shelves 70 m deep and attest of the still present morphodynamical equilibrium of the large dunes furthermore as was previously found for similar dunes in the irish sea no power law relationship between dune migration rates and dune size can be deduced similarly no strong correlation is established between migration rates and the degree of asymmetry nevertheless the dune asymmetry can be used to predict the migration direction as for dimension parameters the evolution asymmetry depends on the study area and migration rates more precisely when the crest lines of dunes form straight lines and their migration rates remain below 8 10 m yr 1 the degree of dune asymmetry increases with the migration rate this trend is reversed for the dunes with higher migration velocities and crests which are sinuous these results relativize the migratory predictions based on punctual geometrical observations

modification to the hardisty equation regarding the relationship between sediment transport rate and particle size bagnold type bed load equations are widely used for the determination of sediment transport rate in marine environments the accuracy of these equations depends upon the definition of the coefficient k 1 in the equations which is a function of particle size hardisty 1983 has attempted to establish the relationship between k 1 and particle size but there is an error in his analytical result our reanalysis of the original flume data results in new formulae for the coefficient furthermore we found that the k 1 values should be derived using u 1 and u 1cr data the use of the vertical mean velocity in flumes to replace u 1 will lead to considerably higher k 1 values and overestimation of sediment transport rates

dunlin group sequence stratigraphy in the northern north sea a model for cook sandstone deposition the dunlin group in the northern north sea consisting of the johansen amundsen burton cook and drake formations of late sinemurian toarcian age hosts important hydrocarbon reservoirs in the cook formation sandstones the johansen formation is associated with a relative fall of sea level and is interpreted to be a large sandstone delta confined within a broad incised valley at the base of the group during a later stage of relative sea level rise the finer grained amundsen and burton formations were deposited the overlying cook formation consists of four sandstone tongues each of which is characterized by a lower zone of sharp based upward coarsening thinly bedded shoreface sandstones and siltstones reflecting forced regression during falling relative sea level and an erosively based upper zone of thin tidal flat and thick deltaic estuarine sandstones reflecting lowstand incision as well as initial progradation and subsequent transgressive backfill of estuaries during relative sea level rise the drake formation shales were deposited during continued relative sea level rise several types of erosional surfaces are recognized within the studied succession 1 sequence boundaries occur at the base of the johansen formation and within the cook formation and represent the bottoms of incised valleys that truncate the underlying copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received may 4 1995 revised manuscript received march 27 1996 final acceptance september 12 1996 2department of geology paleontology university of zagreb 10000 zagreb croatia 3department of geology geophysics university of wyoming laramie wyoming 82071 this paper was part of the sequence stratigraphy research project at the university of bergen norway and is a product of studies on the architecture of lower jurassic shelf sandstones of the northern north sea the work was sponsored by statoil through a vista fellowship awarded to t marjanac and this support is gratefully acknowledged we are grateful to d mellere and l m falt for discussion and encouragement during the work we also thank else lien for drafting the sections and jane ellingsen for reprographs constructive criticism from d nummedal j webb and k t biddle on the final version of the manuscript is much appreciated

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

an assessment and calibration of formulations for bagnold s bedload equation abstract bagnold s bedload equation in the form q u ucr 3 has frequently been employed to predict sediment mass transport rates in tidal flows and to assist with the interpretation of ancient tidal deposits however physical considerations suggest that the form q u2 u2cr u is more correct this latter formulation is therefore calibrated with experimental data and the coefficient of proportionality is shown to be strongly dependent on the sediment grain size

use of swath bathymetry in the investigation of sand dune geometry and migration around a near shore banner tidal sandbank banner tidal sandbanks in the bristol channel have been repeatedly surveyed with a multibeam sonar to study the geometry and migration patterns of superimposed dunes the data presented in this paper constitute one of the first studies concerned with sediment transport around a banner sandbank helwick sands in the bristol channel using repeated swathbathymetry the data reveal that the dunes maintain their shapes over a period of 11 months and that they migrate in opposite directions on the alternate sides of the bank curiously dunes connect over the crest of the bank despite opposing sediment transport directions on the flanks dune height increases with water depth as found in similar environments we suggest how the morphology of the dunes results from the complex interaction between surface waves and tidal currents that occurs within the proximity of the headland 1995 furthermore repeated full bathymetric coverage of sub tidal sedimentary structures using swath sonar technology will provide information of their dynamics and threedimensional characteristics which are of interest for the understanding of coastal and shelf sedimentary transport this paper describes the morphology and dynamical characteristics of sand dunes at the eastern end of the helwick sandbank lying near a headland in the bristol channel fig 1 the analysis is based on two sets of swathbathymetry data collected on 26 september 2001 and 20 august 2002 the main objective of this paper is to demonstrate the potential for tracking dune migration and dune geometry changes from repeated bathymetric multibeam surveys this paper is therefore intended to a describe the morphological characteristics of the dunes and their spatiotemporal evolution b estimate dune migration rate and from that infer sediment transport flux and c relate these data to the work elsewhere of sediment transport around sandbanks and their maintenance in describing the sand dunes in this paper we follow the terminology developed by ashley 1990

post glacial filling of a semi enclosed basin the arguin basin mauritania semi enclosed basins are not very common features in the world and are most frequently the result of tectonic movements studies of their filling are usually based on the micropaleontological analyses of sediment cores torgersen et al 1988 reeves et al 2007 or seismic analyses lykousis et al 2007 cagatay et al 2009 van daele et al 2011 the morphology of semi enclosed basins is generally simple and bowl shaped and their edges are marked by one or more sills their depths range from a few dozen to several thousand meters semi enclosed basins are however present in some regions in the world the semi enclosed basin of the golfe d arguin northwest africa is present on a wide shallow shelf bordering the sahara desert in a stable tectonic context its sedimentary filling took place during the end of the post glacial transgression the current knowledge on sedimentary filling of semi enclosed basins is rather limited and inadequate to fully understand the processes at play three campaigns have allowed the creation of the first morpho bathymetric map of the golfe d arguin shedding new light on its large scale morphology a series of rocky shoals banc d arguin interrupted by two sills in the north and south divides the shelf into two parts the inner and outer the inner part of the golfe d arguin called the arguin basin forms a shallow semi enclosed depression the basin is situated on the stable west african margin and the lack of any vertical tectonic movement provides an ideal situation for studying the progradation regression variations and the sediment depositional conditions caused by the post glacial sea level changes based on the analysis of very high resolution seismic data seven units were identified the sedimentary sequence of deposition of the arguin basin was interpreted in relation to the bedrock morphology the sea level rise and the climatic changes their chronology was established in comparison to the regional sea level curve basin physiography and unit distribution the arguin basin is interpreted as a land locked freshwater lake during the post glacial sea level rise corresponding to wet climatic conditions the inner part was flooded ca 8 7 ka bp when the sea level reached the sills the filling then corresponded to a marine estuarine environment the climatic aridification and the sea level stabilization from 6 5 ka bp onwards allowed the deposition of the last units which are composed of aeolian sand combined with a significant marine biogenic carbonate fraction bedrock morphology plays a major role in determining the depositional sequence architecture it controls the available accommodation space and in conjunction with climate changes influences the environmental processes that shape the deposit geometry

anatomy of shelf deltas at the edge of a prograding eocene shelf margin spitsbergen although shelf edge deltas are well imaged seismic features of holocene and pleistocene shelf margins documented outcrop analogues of these important sand prone reservoirs are rare the facies and stratigraphic architecture of an outcropping shelf edge delta system in the eocene battfjellet formation spitsbergen is presented here as well as the implications of this delta system for the generation of sand prone shelf margin clinoforms the shelf edge deltas of the battfjellet formation on litledalsfjellet and hogsnyta produced a 3 5 15 km shelf edge attached slope apron 70 m of sandstones proximally tapering to zero on the lower slope the slope apron consists of distributary channel and mouth bar deposits in its shelf edge reaches passing downslope to slope channels chutes that fed turbiditic lobes and spillover sheets in the transgressive phase of the slope apron estuaries developed at the shelf edge and these also produced minor lobes on the slope the short headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf and the shelf edge position of the discharging deltas made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin the abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane parallel laminae within turbidite beds in the slope channels and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals the examined shelf edge to slope system now preserved mainly below the shelf break and dominated by sediment gravity flow deposits has a threefold stratigraphic architecture a lower progradational part in which the clinoforms have a slight downward directed trajectory a thin aggradational zone and an upper part in which clinoforms backstep up onto the shelf edge a greatly increased density of erosional channels and chutes marks the regressive to transgressive turnaround within the slope apron and this zone becomes an angular unconformity up near the shelf edge this unconformity with both subaerial and subaqueous components is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level the studied shelf margin clinoforms accreted mostly during falling stage sea level below the shelf edge but the outer shelf later became estuarine as sea level became re established above the shelf edge

grain size control of large compound flow transverse bedforms in a tidal inlet of the danish wadden sea abstract flow transverse bedforms were recorded along a 2 km reach of the northernmost tidal inlet of the danish wadden sea the bed of the inlet channel is covered with large to very large compound dunes and superimposed medium sized dunes composed of medium to coarse sands the mean grain size of the bed material along the centre line of the inlet throat decreases from 0 56 mm in the inner part to 0 3 mm in the outer part both dune populations are essentially two dimensional with straight to slightly curved crest lines the ebb current is very similar in magnitude along the entire channel axis whereas the flood current is of similar magnitude in the inner half but reaches only about half of the maximum ebb current velocity in the outer section sediment transport occurs during both the ebb and flood periods the latter being less vigorous and of shorter duration as a result the inlet as a whole is ebb dominated dominant ebb current 1 01 m s 1 dominant flood current 0 79 m s 1 in agreement with the tidal dynamics a net ebb oriented bedform migration rate of 32 m yr 1 was determined from the survey data the large to very large dunes display distinct flood caps during the flooding tide whereas the medium sized dunes reverse their direction during each tide the downstream dimensional evolution of the large dunes is complex switching from initial growth to progressive decline followed by renewed growth in length but progressive decline in height this latter degradational phase begins in the middle of the survey reach and continues seawards until the large forms disappear completely at the same time the outer channel section becomes dominated by medium sized dunes which grow in size with decreasing grain size surprisingly there is no correlation between dune dimensions and water depth as would be expected at such shallow depths the complex evolution of dune dimensions as a function of grain size is discussed in terms of recent tidal bedform stability theory it is clear however that more site specific observations are required to fully explain the phenomenon

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

fluid inclusions and pvtx modelling examples from the garn formation in well 6507 2 2 haltenbanken mid norway abstract fluid inclusions study and multi techniques quantitative analyses have been coupled to reconstitute pvtx conditions of aqueous and petroleum fluid entrapment of a local haltenbanken area well 6507 2 2 from the garn formation unusual low temperature behaviour showing the liquid portion separating into two liquids has been described this behaviour is typical of a gas condensate volatile mixture with high methane content and heavy alkanes the variable liquid vapour ratio compositions and morphologies of all petroleum inclusions can be interpreted as a result of a combination of heterogeneous trapping and necking down thus all petroleum inclusions can be related to a single petroleum source three main episodes of fluid entrapment can be distinguished the first one corresponds to the water trapped within detrital quartz microfractures at around 50 c and 50 bar the second to the petroleum fluid arrival in the biphase field of a critical system around 100 120 c and 190 230 bar the third one to the main trapping of present day petroleum inclusions during the recrystallisation of quartz cements around 110 160 c and 230 280 bar within the last few million years of a short and relatively rapid burial

short term dynamics and maintenance processes of headland associated sandbanks shambles bank english channel uk abstract the short term over a spring tidal cycle dynamics of a headland associated sandbank shambles bank english channel are investigated by means of field measurements synchronous data using an acoustic doppler current profiler adcp and repeated side scan sonar imagery and two dimensional 2d hydrodynamic and sediment transport models the dynamics of the bank are described in terms of along and cross bank velocity components sand transport pathways and bedform asymmetries the results showed the occurrence of a net bedload convergent zone along the crest of the bank as a result of anti clockwise veering of sediment transport towards the crest this transport pattern is suggested to be the result of the dynamic interplay between two distinct tidally related processes acting over the sandbank during each phase of the tidal cycle a the formation and different stages of a transient tidal eddy that drives bedload movement during the flood phase of the tide and b the bottom friction induced by the presence of the sandbank that governs the bedload transport dynamics during the ebb phase of the tidal cycle

patterns of bottom current flow deduced from dune asymmetries over the gulf of cadiz shelf southwest spain abstract the analysis of dune like morphologies on the gulf of cadiz continental shelf using high resolution seismic reflection profiles and sediment samples reveals a well defined distribution pattern controlled by the area s hydrodynamics these bedforms are considered to be modern features from the holocene and therefore they provide information about the bottom circulatory patterns established over the continental shelf most of the submarine dunes have been identified over a shallow physiographic feature named the barbate high the current flows that generate the bedform fields can be attributed to a complex interaction of several hydrodynamic agents in which the process of current direction reversal related to the tidal cycle in the straits of gibraltar seems to be involved eastward oriented submarine dunes located on the onshore zones of the inner shelf are generated by the atlantic inflow which over these shallow zones is mainly orientated towards the east during high tide conditions in the straits of gibraltar bedforms oriented westwards and west northwestwards in the offshore zones indicate that a previously undescribed flow occurs on the gulf of cadiz continental shelf this flow is attributed to the influence of ebb tidal currents which move preferentially towards the west over these zones as a result of this complex bottom flow pattern a clockwise sand transport pattern over the barbate high is established

q model building using one way wave equation migration q analysis part 2 3d field data test in part one of this paper we presented an inversion based method wave equation migration q analysis to estimate the quality factor q model for seismic attenuation to demonstrate the feasibility of this method we applied this method to a 3d seismic dataset acquired in the north sea attenuation problems caused by a shallow gas and a shallow channel are observed in this field this study aims at characterizing these attenuation anomalies these attenuation anomalies are correlated with low interval velocities the provided velocity model does not accurately reflect the low velocity anomalies therefore we first applied wave equation migration velocity analysis to update the provided velocity model the updated velocity shows low velocity regions around the gas and channel features the subsurface angle gathers migrated using the updated velocity model are flatter and the events in the migrated images after velocity updating are more coherent then we applied wave equation migration q analysis to inv

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

a total load algorithm for sand transport by fast steady currents a simple algorithm for total load sand flux is proposed which is suitable for application to high energy environments where fast currents promote significant sand suspension the algorithm is a power relationship constrained by a threshold condition q k u1 u1t u1t nwhereqis total sand flux u1andu1tare mean current velocity and threshold current velocity 1 m above the bed respectively andkis an appropriate entrainment function the algorithm has been calibrated for sands mean grain diameter 190 930 m over a range of mean current velocities 0 2 1 5 ms 1 using the extensive experimental data set of guyet al 1966 prof papers u s geology survey 462 96 it is shown thatkandnare dependent on mean grain diameter they can be determined from appropriate calibration curves the exponentnvaries from 4 increasing with decreasing grain diameter as transport by suspension becomes increasingly important napproaches a minimum constant value for coarser sands as bed load transport becomes dominant there is evidence that the exponentndecreases with increasing current velocity in the case of fine sands moved by fast currents the entrainment functionkdecreases with decreasing grain diameter as bed roughness and entrainment efficiency decrease and approaches a minimum constant value for fine sands the algorithm reproduces flume sand transport rates more reliably than the previous formulations of gaddet al 1978 journal of sedimentary petrology 48 239 252 and hardisty 1983 journal of sedimentary petrology 53 1007 1010 which ignore suspension and use erroneous calibration coefficients

types of internal structure and external morphology of submarine dunes under the influence of tide and wind driven processes dover strait northern france abstract the expression of tide and wind driven processes in the internal architecture and external morphology of very large submarine dunes is investigated at a dune field located in the central part of the dover strait southern north sea current measurements and sediment transport calculations enable quantification of the dominant tide and wind driven processes and very high resolution seismic recordings are used to analyse internal structure and external morphology of dunes in the study area moderate to storm winds induce temporary currents that can lead to the reversal of sediment transport direction and induced erosive processes on the seabed dune master bedding consists of extended erosive surfaces with 9 11 slopes that bound storm generated sets of cross beds 1 5 4 85 m thick 2 65 m on average three types of architectures are observed within the dune field and occasionally within single dunes these types which display a strong linkage between internal structure and external morphology consist of 1 asymmetric dunes with cosets which dip in the direction of the marked external asymmetry of the dunes 2 dunes with a complex external morphology composed of mega herringbone structures each displaying an opposing progradation direction and 3 dunes with a symmetric megaripple bedding unit at their summit the diversity of the internal architecture and external morphology results from the variable combinations of tide and wind driven processes occurring in the study area the asymmetry of tidal peak current velocity and the relative strength of wind driven currents are the parameters that have the most important influence on dune architecture asymmetric dunes with cosets result from a strong asymmetry in tidal peak current velocity which is reversed only slightly during storms dunes with mega herringbone structures and dunes with symmetric megaripple units at their summit are observed in areas where the asymmetry of the tidal peak current velocity is negligible allowing reversal of the sediment transport and dune migration directions each time moderate winds blow the latter architectural type is specific to sand rich areas the different dune architecture types display strong geometrical similarities to structures observed in dunes from other shelf environments where driving processes are different this implies that a study based only on a geometric description of internal structures will not enable the reconstitution of ancient depositional environments a better discriminant criteria seems to be the thickness of the second order sets of cross beds which is correlated with specific hydro sedimentary processes dune height also probably has an important influence on the thickness of second order sets of cross beds as dune height and set thickness display a clear relationship in the present study

migration and internal architecture of marine dunes in the eastern english channel over 14 and 56 year intervals the influence of tides and decennial storms submarine dune dynamics are controlled by tidal currents and wind forces according to the relative in uence of these forces and the nature of dune sediment different bedform behaviors can be observed the footprint of the different hydrodynamic agents is recorded into the internal architecture of dunes this paper is concerned with bedforms that compose the thick sediment wedge located in the eastern english channel off the bay of somme this sedimentary archive constitutes an interesting feature to achieve a better understanding of seabed sediment dynamics and its timeline building stages the dynamics of large submarine dunes which are organized in elds are studied thanks to bathymetric and seismic data over the periods 1937 1993 and 1993 2007 dune morphology presents low lee and stoss side slopes on average 8 and 3 respectively and dune migration rate is not very high dune movements are in the direction of residual tidal currents i e toward the east with mean migration rates around 0 8 to 5 0 25 m yr 1 and up to 6 6 0 7 m yr 1 respectively at multi decennial and decennial time scales the dune internal archi tecture is complex with superimposed eastward prograding units displaying locally opposite progradation second order discon tinuities dip of 0 5 4 perpendicular to dune crests constitute dune master bedding by counting the number of second order re ectors between 1937 1993 and 1993 2007 the formation periodicity of these bounding surfaces is estimated to range from 4 to 18 years these time intervals coincide with the long term tidal cyclicities and also with the inter annual to decennial variability of storm activity in northern europe two theories were made to interpret the dune internal structures the second order surfaces are interpreted either as the depositional surfaces corresponding to the marks of weak energy periods weak tidal and storm action or as erosive surfaces due to an opposite direction of dune migration provoked temporarily by exceptional storms from the northeast

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

long term morphodynamic evolution and the equilibrium mechanism of a flood channel in the yangtze estuary china the stability of flood channels has attracted considerable attention because of their complicated interactions with the prevailing hydrodynamics and importance in ship navigation this research examines long term morphodynamic evolution in the yangtze estuary from 1861 to 2002 and the equilibrium mechanism of the xinqiao channel in the yangtze estuary by digitizing 15 selected maritime charts and calculating the volume of the channel although the total period of channel development is much longer than the historical data used in this paper three stages are identified during the study period the first embryonic stage 66 years the second formation stage 33 years and the third equilibrium stage 45 years variations in coastline location channel volume and hydrodynamics in the channel during the three stages indicate that the channel equilibrium was reached and maintained when the channel direction was aligned with the direction of offshore tidal wave propagation variations in river and sediment discharges affect erosion and deposition in the channel and thus channel geometry however future reduction in sediment supply by 10 33 due to the ongoing river engineering projects would increase the volume of the xinqiao channel only by 1 3 it seems unlikely that the above change in sediment discharge will disrupt the equilibrium of the xinqiao channel

combined use of confocal laser scanning microscopyand pvt simulation for estimating the composition andphysical properties of petroleum in fluid inclusions we present a method to determine the composition and pvt properties of petroleum inindividual petroleum fluid inclusions confocal laser scanning microscopy is used to generatethree dimensional images of single petroleum inclusions because liquid petroleum fluorescesunder the laser the images readily distinguish the liquid and vapour within the inclusion and canbe used to determine the inclusions volumetric liquid vapour ratio using pvt modellingsoftware the liquid vapour ratio is used along with the homogenisation temperature to determinethe bulk composition phase envelope isochore and a range of physical properties of the includedpetroleum this is done using an iterative series of pvt calculations which match twoparameters 1 the molar volume of the petroleum at room and homogenisation temperatures 2 the liquid vapour ratio of the inclusion at room temperature key uncertainties in the methodare explored including the accuracy with which the liquid vapour ratio can be determined thecomposition of the titrant gas used in the iterative procedure and the composition of thepetroleum chosen to model the physical properties of the included petroleum data from coevalinclusions suggest that the saturation pressure gas oil ratio viscosity molar volume densityand surface tension of included petroleum are determined with a precision of a few percent confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratoryunder carefully controlled pvtx conditions however it is likely that the physical properties ofincluded petroleums are more accurately modelled by fluids which are genetically related tothem if proven to be accurate the method will provide a routine method for determiningpalaeopressure in petroleum systems finally we present data from a central north sea examplewhich are geologically realistic and which for the first time record the evolution of fluid pressureand petroleum composition in a petroleum reservoir

individual characterization of petroleum fluid inclusions composition and p t trapping conditions by microthermometry and confocal laser scanning microscopy inferences from applied thermodynamics of oils abstract this paper proposes a new method to characterize individual oil bearing fluid inclusions it uses both the homogenisation temperatures measured by microthermometry and the degree of gas bubble filling measured by confocal laser scanning microscopy in conjunction with thermodynamic modelling for describing liquid gas phase transitions and the volumetric behaviour of hydrocarbon mixtures it is associated with a two parameter compositional model that describes the wide range of compositions of petroleums we show that this method can give 1 useful estimations of the compositions and pressure temperature entrapment conditions of oils in fluid inclusions and 2 insights into the various processes that have affected these fluids either before entrapment liquid gas unmixing gas leaching mixing etc or after leakage etc

on bagnold s sediment transport equation in tidal marine environments and the practical definition of bedload bagnold s sediment transport equation has proved to be important in studying tidal marine environments this paper discusses three problems concerning bagnold s transport equation and its practical application 1bagnold s suspended load transport equation and the total load transport equation with are incorrect from the viewpoint of energy conservation in these equations the energy loss due to bedload transport has been counted twice the correct form should be for suspended load transport and for total load transport with 2the commonly used bagnold s transport coefficient k varies as a non linear function of the dimensionless excess shear stress which can be represented best by the power law where the coefficient a and exponent b depend on sediment grain size d the empirical values of a and b for fine to medium grained sands are determined using guy et al s 1966 flume experiment data 3the sediment transport rates predicted from this equation are compared with bedform migration measurements in the flume and the field this comparison shows that the sediment transport rates measured from bedform migrations are higher than the predicted bedload transport rates but comparable to the calculated total load bedload plus intermittent suspended load transport rates this indicates that bedform migration involves both bedload and intermittent suspended load transport as a logical conclusion bedform migration data should be compared with bagnold s total load transport equation rather than with his bedload transport equation in this respect the term bed material might be more appropriate than the term bedload for estimating sediment transport rate from bedform migration data the sediment transport rates predicted from this modified bagnold transport equation are in good agreement with field measurements of bedform migration rates in four individual tidal marine environments which cover a wide range of sediment grain size flow velocity and bedform conditions ranging from small ripples megaripples to sandwaves

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

the morphodynamics and internal structure of intertidal fine gravel dunes hills flats severn estuary uk in the macrotidal severn estuary uk the dynamics of intertidal fine gravel dunes were investigated these dunes are migrating across a bedrock platform systematic observations were made of hydraulic climate geometry migration rates and internal sedimentary structures of the dunes during spring tides the ebb flow is dominant dunes grow in height and have ebb orientated geometry with bedrock floors in the troughs during neap tides a weak flood flow may dominate dunes then are flood orientated or symmetrical neap dune heights decrease and the eroded sediment is stored in the dune troughs where the bedrock becomes blanketed by muddy gravel during spring tides instantaneous bed shear stresses reach 8 n m 2 sufficient to disrupt a 9 mm gravel armour layer however a sustained bed shear stress of 4 n m 2 is required to initiate dune migration at which time the critical depth mean velocity is 1 m s 1 ebb and flood inequalities in the bed shear stress explain the changes in dune asymmetry and internal structures during flood tides the crests of the dunes reverse such that very mobile sedimentary caps overlie a more stable dune core because ebb tides dominate internal structures of the caps often are characterised by ebb orientated steep open work foresets developed by strong tidal currents and some lower angle crossbeds deposited as weaker currents degrade foresets the foresets forming the caps may be grouped into cosets tidal bundles and are separated from mud infused cores of crossbeds that lie below by reactivation and erosion surfaces blanketed by discontinuous mud drapes the cores often exhibit distinctive muddy toe sets that define the spacing of tidal cosets

fluid inclusion constraints on temperatures of petroleum migration from authigenic quartz in bitumen veins abstract solid bitumens in fracture systems commonly contain microscopic crystals of authigenic quartz which were precipitated coevally with the bitumen early in the paragenesis of the fracture fillings the quartz contains primary fluid inclusions both aqueous and hydrocarbon yielding homogenization temperatures particularly in the range 95 130 c indicating minimum temperatures of entrapment during petroleum migration volumes of up to 50 entrained quartz and a predominance of aqueous inclusions indicate that the petroleum fluid had a substantial aqueous component

morphology internal structure and reversal of asymmetry of large subtidal dunes in the entrance to gironde estuary france abstract the gironde is a macrotidal estuary characterized by important changes in tidal current velocity and river discharge two surveys were made in the lower estuary in june 1987 and october 1989 in an area with large dunes the symmetry of these dunes 1 5 6 7 m high changes from flood dominated in upstream areas to ebb dominated in downstream areas a transition zone consists of symmetrical dunes with a very low vertical form index the internal structure of the dunes revealed by seismic records shows a hierarchy of bounding surfaces related to fluctuations in movement speed and asymmetry of the dunes the lowest part of symmetrical dunes consists of ebb oriented reflectors while the upper part has flood oriented reflectors the same profile lines run in 1989 show that each large dune can be identified despite an upstream shift of the transition zone of about 1000 m comparison of seismic records shows that some lower reflectors are preserved between the two surveys and that the dunes moved downstream a mean distance of 30 m in 1989 the internal structure of symmetrical dunes was reversed with flood oriented reflectors in the lower part overlain by ebb oriented reflectors both seasonal changes in river discharge and fortnightly oscillations of the tidal range control the magnitude and orientation of the net bed load transport in the study area because the response time of the large dunes is longer than that of the superimposed small dunes the reversal of asymmetry of the large dunes requires a long period process while fortnightly oscillation or even semi iurnal reversal of the tidal current during spring tides could cause reversal of small dunes

residual transport model in correlation with sedimentary dynamics over an elongate tidal sandbar in the gironde estuary southwestern france abstract this study qualitatively describes by a multidisciplinary approach hydrodynamic and residual sediment transport over a sandbar in a macrotidal environment the sandbar is elongated and attached to a headland that is located in the gironde estuary southwestern france bathymetric surveys side scan sonar sonograms grain size trends of surficial sediment and 2dh numerical simulations of current patterns were used to define a conceptual model for the dynamics of this sandbar the sandbar is oriented anticlockwise with respect to the main flow the channel oriented bar face is ebb dominated whereas the opposite face is flood dominated resulting in a clockwise residual transport the line of sediment flux convergence corresponds to the crest of the bar the residual flow over the bar appears to originate from the regional estuarine flow the dominant process responsible for the maintenance of the sandbar seems to be the depth averaged main tidal flow rather than secondary circulation due to headlands or the interaction between the tidal flow and the seabed to generalize this regional conceptual model a qualitative comparison is made with the theories of sandbar dynamics due to tidal currents pingree and maddock 1979 zimmerman 1981 huthnance 1982 and others the seabed stability approach developed by huthnance 1982 seems to be the most reliable theory to explain the saint georges bank dynamics even though many natural factors are not taken into account

morphology and internal structure of sand shoals and sandbanks off the dorset coast english channel the morphology and internal structure of sand shoals and sandbanks around a coastal headland portland bill southern uk are described on the basis of sidescan sonar and high resolution seismic data sets morphological and architectural evidence combined with the spatial distribution and nature of the bedrock surface indicates that the evolution of these deposits especially the sandbanks may not only be hydrodynamically controlled but also morphologically controlled the internal structure of the sand shoals reveals a simple pattern of clinoforms dipping in the same direction as their steeper profile in contrast the internal structure of the sandbanks reveals that their lower seismic units consist of a sedimentary core interpreted as the remains of a lowstand deposit or an early stage of the bank development under different prevailing hydrodynamic conditions the present morphology of the sandbanks is represented by upper seismic units characterized by large scale sandwave foresets dipping at 6 8 the nature and morphology of the bedrock surface may also influence the development of sandbanks in some cases for example to the west of portland bill the morphology of the bedrock surface basal reflector restricts the development of the portland bank this information may explain the asymmetric evolution of sandbanks around portland bill

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

velocity inversion by differential semblance optimization differential semblance optimization dso is an approach to inversion of reflection seismograms which avoids the severe convergence difficulties associated with nonlinear least squares inversion the method exploits both moveout and amplitude characteristics of reflections we have implemented a version appropriate to plane wave p tau seismograms and layered constant density acoustic earth models theoretical and numerical analyses of this version of dso indicate that stable and reasonably accurate estimates of both velocity trend and reflectivity can be derived to test dso further we applied it to a marine data set from the gulf of mexico where the method produced results which compare favorably to well log information the method can be extended to incorporate laterally heterogeneous velocity models

long term evolution and internal architecture of a high energy banner ridge from seismic survey of banc du four western brittany france the recent completion of a coupled seismic and swath bathymetric survey conducted across the sand ridge system of the banc du four located on the atlantic continental shelf of brittany mer d iroise france provided new data for the study of the long term evolution of deep tidal sand ridges five seismic units are distinguished within the ridge separated by pronounced major bounding surfaces the basal unit is interpreted to be shoreface deposits forming the core of the ridge it is overlaid by a succession of marine sand dunes fields forming the upper units sandwave climbing which combines progradation and accretion is the major process controlling the growth of the ridge the elevation of the preserved dune foresets reaches values of about 20 30 m within the ridge the foresets indicate a combination of giant dunes characterized by numerous steep up to 20 clinoforms corresponding to a high energy depositional environment moreover the presence of scour pits linked to the 3d geometries of giant dunes allow the growth of bedforms migrating oblique to the orientation of giant dune crest lines all of the radiocarbon ages of the biogenic surficial deposits of the banc du four range from 10 036 to 2748 cal years b p and suggest the banc du four has grown during the last sea level rise the apparent absence of recent surface deposits could be caused by a change in benthic biogenic productivity or the non conservation of recent deposits in contrast the presence of relatively old sands at the top of the ridge could be explained by the reworking and leakage of the lower units that outcrop locally at the seabed across the ridge moreover the long term evolution of the ridge appears strongly controlled by the morphology of the igneous basement the multiphase accretion of the ridge is closely linked to the presence of a residual tidal current eddy consecutive with the progressive flooding of the coastal promontories and straits that structured the igneous basement therefore the banc du four should be thought of as a representative example of a large scale high energy banner bank

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

organic inclusions in salt part 3 oil and gas inclusions in cambrian evaporite deposit from east siberia a contribution to the understanding of nitrogen generation in evaporites abstract halite in cambrian kcl deposits from the southern part of the siberian platform which have been thermally overprinted by dolerite intrusions commonly contains inclusions dominantly composed of co2 and less commonly host inclusions composed of hydrocarbons four types of hydrocarbon inclusions have been identified in samples taken from locations devoid of dolerite intrusions these are 1 monophase gaseous inclusions i e n2 ch4 or n2 ch4 2 aliphatic oil inclusions 3 two phase l1 l2 hydrocarbon brine inclusions and 4 n2 hydrocarbon inclusions the area where the n2 rich inclusions occur is associated with ammonium free k chlorides by comparing different types of k salt environments the origin of the nitrogen could be identified first ammonium ions are produced by deamination of organic matter and stored in k chlorides and thereafter n2 is released from nh4 k minerals by oxidation in zones rich in iron oxides and or by 40k radiolysis

a flume study on the development and equilibrium morphology of current ripples in very fine sand an empirical model is constructed for the development and equilibrium dimensions of small scale unidirectional bedforms in sand with a median grain size of 0 095 mm based on a series of steady flow experiments in a flume current ripples always attain a linguoid plan morphology with constant average height 13 1 mm and wavelength 115 7 mm provided that sufficient time is allowed for their formation the development pattern of these ripples on a flat bed is independent of flow velocity and involves four stages 1 incipient ripples 2 straight and sinuous ripples 3 non equilibrium linguoid ripples and 4 equilibrium linguoid ripples straight and sinuous ripples are non equilibrium bedforms at all flow velocities the time needed to reach equilibrium dimensions is related to the inverse power of flow velocity and ranges from several minutes to more than hundreds of hours at flow velocities where washed ripples are stable the equilibrium wavelength is similar to that of equilibrium linguoid ripples but the equilibrium height rapidly decreases from 13 1 mm to zero towards upper stage plane bed conditions the results of the flume experiments correspond reasonably well with those of previous studies provided that various complicating factors such as different experimental methods different sediment characteristics shallow flow depths and non equilibrium runs are accounted for

high resolution seafloor images in the gulf of cadiz iberian margin in the gulf of cadiz the hydrodynamic process acting on particle transport and deposition is a strong density driven bottom current caused by the outflow of the saline deep mediterranean water at the strait of gibraltar the mediterranean outflow water mow new high resolution acoustic data including em300 multibeam echo sounder deep towed acoustic system sar and very high resolution seismic completed by piston cores collected during the cadisar cruise allow to improve the understanding of the hydrodynamics of the mow in the eastern part of the gulf of cadiz interpretation of data corrects the previous model established in this area and allows for the first time the accurate characterization of various bedforms and erosive structures along the mow pathway and the precise identification of numerous gravity instabilities the interaction between the mow the seafloor morphology and the coriolis force is presently the driving force of the sedimentary distribution pattern observed on the gulf of cadiz continental slope

headland associated banner banks generated during the last deglaciation near the strait of gibraltar gulf of cadiz sw spain the inception and evolution of large scale bedforms on the barbate platform gulf of cadiz sw iberian peninsula are investigated based on a detailed study of multibeam bathymetric data high resolution seismic profiles and tidal current simulations elongated rocky outcrops and several large scale bedforms classified as sand banks were identified on the platform barbate zahara el palmar el varadero and canos de meca banks the barbate and zahara banks exhibit the most complex internal stratigraphic architecture which comprises five seismic units the basal unit u1 is interpreted as incised valley infill and is overlain by nearshore bars u2 two high energy growth phases u3 and u4 that combine progradation and accretion form the present day external bank shape superimposed bedforms covered these banks under the modern hydrodynamic regime u5 the multiphase accretion and progradation of u3 and u4 in the zahara and barbate banks were closely linked to the presence of a palaeo headland termed here as palaeo cape trafalgar and strong tidal current eddies that resulted from the progressive flooding of the barbate platform during the last deglaciation this configuration was relatively stable while the rocky outcrops were exposed to sub aerial conditions forming a palaeo coast with coastal bluffs we suggest that during this period of coastal stabilization u3 and u4 grew as banner banks on either side of the palaeo cape trafalgar the present study proposes that the configuration of palaeo headland associated with palaeo banner banks zahara and barbate banks along each side of the palaeo cape trafalgar represents a transgressive analogue model of headland associated tidal bank systems developed in funnel shaped coastal systems terminating in narrow straits

hummocky cross stratification and post vortex ripples length scales and hydraulic analysis duke 1987 argues that the structure reported by greenwood sherman 1986 as hummocky cross stratification from a shallow lacustrine environment is instead bedding formed by simple post vortex oscillation ripples his primary concern is with the length scale of the structures identified in box cores however using measured flow data it is shown here that existing models of bedform generation based upon wave orbital velocity orbital diameter and grain diameter do not support a simple post vortex ripple interpretation in particular the relative steepness of the structure refutes such an origin the structural characteristics of the lacustrine cores most closely match those associated with classic hummocky cross stratification and were produced under a combined oscillatory quasi steady flow field

macroturbulence generated by dunes fraser river canada abstract a selectable frequency acoustic profiler and electromagnetic current meter were deployed in the lower fraser river canada to examine large turbulent structures features were generated on the lower stoss sides of dunes and appeared at the surface tens of metres downstream as strong upwellings boils they were identified with acoustic clouds in the acoustic profile event recurrence periods measured from acoustic time series and from ejection events identified in the current meter record had similar two component frequency distributions but the acoustic values lacked the highest frequencies a comparison of measured periods with predictions from the strouhal law indicate that both dune amplitude and the internal boundary layer developed over the dunes are significant length scales associated with the generation of the macroturbulence our data give no support to the notion that boils develop from microturbulent bursts