morphodynamic response of sand waves in the taiwan shoal to a passing tropical storm abstract data from three repeated multi beam echo sounder surveys of pre storm post storm and one year after the storm were used to study the response of sand waves in the taiwan shoal to the tropical storm talim the measurements showed significant decreases in wave height of giant sand waves between post storm and pre storm and moderate increases in one year period after the storm the maximum decrease in wave height is more than 2 m and the averaged decrease is 1 2 m along the measured profile the linear regression analysis shows an increasing trend of wave height changes from northwest to southeast along the profile the uneven evolution pattern was possibly caused by the asymmetry of the currents induced by the cyclone winds the analysis based on the morlet wavelet function showed that the storm smeared out small scale sand waves and eroded the giant sand wave crests and recovery of bedforms after the storm two dimensional features of storm effects were analyzed using the imagery of a digital terrain model processed in a 2d survey area for pre storm post storm and one year after the storm the analysis revealed sand wave migration processes during the storm and the growing back feature of the eroded wave crests after the storm

the oligocene succession in the eastern north sea basin development and depositional systems the oligocene sedimentary succession in the eastern north sea is revised and re interpreted by applying new state of the art reflection seismic data integrated with new bio and sr stratigraphy data from three key wells in the study area the oligocene succession in the eastern north sea is divided into four transgressive regressive t r sequences characterized by non accretional and or aggradational transgressive systems tracts and prograding regressive systems tracts detailed studies of three wells including biostratigraphy and sr analysis constrain the age relationships between the t r sequences internal clinoform geometry indicates that the sediments were sourced from the present southern norwegian mainland to the north of the depositional area the direction of progradation shifted from being se directed in the earliest rupelian early oligocene to s and sw directed during chattian time late oligocene rapid basin subsidence is indicated by the development of non accretionary transgressive systems tracts with subsequent progradation into water depths of hundreds of metres the creation of accommodation space was out of phase relative to eustatic sea level changes and mainly controlled by regional scale differential vertical movements where uplift and exposure of landmasses of the hinterland southern norway occurred concurrently with basin subsidence halokinesis had an intra basinal influence on the main sediment transport direction but probably did not contribute much in creation of accommodation space

abstract massive bed forms mega furrows on the continental rise at the base of the sigsbee escarpment northwest gulf of mexico abstract some of the largest deep water sedimentary bed forms ever found in the world oceans were recently discovered along the base of the sigsbee escarpment in the northwest gulf of mexico deep tow high resolution geophysical surveys on the continental rise south of the sigsbee escarpment have revealed the existence of mega furrows 10 m deep and 30 m wide spaced 100 m apart that occupy an area on the continental rise 20 to 40 km wide a single furrow within a field of furrows in the green knoll diapir area can be traced over a distance of 150 km the furrows are located at the base of the sigsbee escarpment from 90 to 93 west longitude from north of green knoll to the area just west of bryant canyon the presence of furrows longitudinal bed forms suggests that unidirectional bottom currents up to 100 cm sec may exist at the base of the escarpment the furrows are inferred to be formed by helical secondary circulation allen 1968 produced sedimentary furrows in the lab and found a hierarchy of bed forms ranging from uniform furrows at low flow conditions to meandering furrows and flute casts at the highest flow conditions all the conditions described by allen are present in the area due south of bryant canyon on the continental rise in terms of hazards relating to deepwater hydrocarbon exploration and production the formation of mega furrows demonstrates the existence of previously undocumented high velocity currents at the base of the escarpment end of record last page 410

morphology of submarine barchans and sediment transport in barchans fields off the dongfang coast in beibu gulf submarine barchans in three new regions were described using new high resolution multibeam bathymetric data off the dongfang coast in beibu gulf currents seismic profiles of horns surface sediments and comparative surveys in 2007 and 2009 were obtained to study barchan mobility and sand transport in the barchan fields the submarine barchans occur at depths of 15 25 m reaching up to 551 9 m in horn length and 8 6 m in height most barchans have asymmetrical horns and display wider plane shapes than subaerial barchans for the same length and height the morphology of barchans exhibits regional variations that are mainly controlled by finite water depth daily reverse currents sand supply changes and interaction of dunes barchan asymmetries internal bedding inclinations and grain size changes are in agreement with the dominant current directions results show that submarine barchans migrated 5 43 m in two years 2007 2009 through comparison of bathymetric data because of the marginally cohesive fine sediment composition and long distance from contemporary sediment sources it is believed that barchans in region c are not of modern origin however these bedforms can be also affected by high energy flow regimes collisions limit barchan widths and provide efficient transport paths between barchans on their horns large sand supply through the horns increases the barchan heights and also changes their shapes some small dunes are identified that are moving away from the barchans field in 2007 and have departed from the host barchans in 2009 these small barchans were probably caused by the separation of the faster moving horn tails from the host barchans when extreme situations happen the mechanism gives a new explanation for sand loss and size determination of submarine barchans c 2014 elsevier b v all rights reserved

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

sand wave fields beneath the loop current gulf of mexico reworking of fan sands extensive fields of large barchan like sand waves and longitudinal sand ribbons have been mapped by deep towed seamarc ia sidescan sonar on part of the middle and lower mississippi fan that lies in about 3200 m of water the area is beneath the strongly flowing loop current the bedforms have not been adequately sampled but probably consist of winnowed siliciclastic foraminiferal sands the size about 200 m from wingtip to wingtip and shape of the large barchans is consistent with a previously observed peak current speed of 30 cm s measured 25 m above the seabed the types of small scale bedforms and the scoured surfaces of chemical crusts seen on nearby bottom photographs indicate that near bed currents in excess of 30 cm s may sometimes occur at the time of the survey the sand transport direction was to the northwest in the opposite direction to the loop current but consistent with there being a deep boundary current along the foot of the florida escarpment some reworking of the underlying sandy turbidites and debris flow deposits is apparent on the sidescan sonar records reworking by deep sea currents resulting in erosion and in deposits characterised by coarsening upwards structures and cross bedding is a process that has been proposed for sand found in cores in shallower parts of the gulf of mexico this process is more widespread than hitherto supposed

gold and sulphide minerals in tertiary quartz pebble conglomerate gold placers southland new zealand abstract auriferous quartz pebble conglomerates qpc formed during tertiary sedimentary recycling in the waimumu district southland new zealand these sediments contain fine grained gold of detrital origin with abundant surface textures and gold forms associated with authigenic gold remobilisation most authigenic gold contains no detectable silver and occurs as overgrowths on detrital au ag and au ag hg alloys that contain up to 13 wt ag and 9 wt hg fine grained au ag and au ag hg alloys are compositionally heterogeneous exhibiting both well defined silver depleted and silver enriched rims rare coarse au ag alloy is intergrown with quartz and is homogenous discrete grains of authigenic porous sheet like gold occur in carbonaceous mudstone within a qpc sequence some qpc contain abundant sulphide minerals some of these sulphides pyrite and arsenopyrite are of long distance detrital origin presumably from the otago schist whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin derived from the erosion of qpc and underlying tertiary sediments there has also been authigenic deposition of sulphide minerals in the qpc themselves these diagenetic sulphides include framboidal and anhedral marcasite and framboidal and euhedral pyrite sulphur isotope data for the sulphide minerals range from 45 to 18 relative to vcdt sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from 9 to 1 and are most likely derived from the otago schist to the north both framboidal and anhedral marcasite have lower values both the gold and diagenetic sulphides from the belle brook qpc are compositionally similar to gold and sulphides from archaean qpc porous sheet like authigenic gold is morphologically similar to gold associated with carbonaceous material in the witwatersrand in addition southland marcasite textures resemble the rounded and banded pyrite in witwatersrand qpc placers there is abundant evidence from these tertiary qpc in southern new zealand for sedimentary transport of sulphide minerals and post depositional sulphide mineralisation in the surficial environment despite an oxygen rich atmosphere these young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers many of these textures are similar to those commonly ascribed to metamorphic processes in archaean auriferous qpc

the morphology of barchan shaped sand banks from western torres strait northern australia abstract large barchan shaped sand deposits have been observed in the north west of torres strait these deposits share characteristics of both subaerial barchan dunes and subaqueous sand banks a study of satellite imagery indicate that the deposits migrate in the direction indicated by their horns 10 15 m west per year and that sediment is shed from their horns features that are characteristic of barchan dunes however the orientations of sand dunes superimposed upon the sand banks indicate the presence of mutually evasive channels and circulation of sediment around the sand bank a characteristic of subaqueous sand banks the presence of mutually evasive channels is the criteria used to categorise the deposits as sand banks barchan forms are known to exist in regions with limited sediment supply and unidirectional current or wind regimes in the torres strait both these criteria are met previous work has demonstrated the presence of a net westward current through the torres strait that is driven by the southeast trade winds the relatively high displacement of the wind driven currents during the trade wind season relative to the monsoon appears to provide the necessary unidirectional regime to form barchans the low and typically eastwards displacement of the residual monsoon season current appears to have a negligible affect on the barchan form while seasonal wind driven currents appear to maintain the barchan shape of the sand banks tidal currents actively maintain mutually evasive channels observed by variations in dune orientation on the sand banks a sediment starved environment combined with bedload transport attributed to both wind driven and tidal currents is concluded to create a unique hydrodynamic environment where sand banks can attain a barchan form

morphology and composition of submarine barchan dunes on the scotian shelf canadian atlantic margin abstract submarine barchan dunes have been mapped on browns bank scotian shelf using multibeam sonar bathymetry and backscatter strength the morphology of subaerial barchans has been studied for almost a century but the advent of multibeam sonar technology now enables a quantitative investigation of their submarine counterparts the browns bank submarine barchans occur at a depth of 60 70 m and are crescentic in planform reaching almost 700 m in horn width and 5 m in height the barchans are convex to the se with steep lee faces to the nw indicating a dominant nw flowing current the barchans overlie a widespread gravel lag covered elsewhere with little or no sand obstacle marks emanate from the lee faces of the barchans and represent a lack of sand deposition and exposure of gravel lag on the sea floor the browns bank submarine barchan sediment texture is gravelly sand or sandy gravel and is primarily composed of subrounded to well rounded quartz grains the allometric relationship between submarine barchan slip face height and distance between horns is markedly different from that of subaerial barchans for the same dune height barchan horn width is about ten times greater in the marine environment the superimposition of megaripples on the stoss slopes of the submarine barchans suggests that the barchans are active and therefore represent an engineering risk to sea floor infrastructure current observations and models indicate that seasonal mean current strength is less than the critical velocity required for barchan migration however the barchans may be active under higher velocity storm induced currents repetitive multibeam sonar mapping is required to detect if barchan migration is occurring over longer time scales

abyssal current character determined from sediment bedforms on the nova scotian continental rise abstract bottom photographs across the nova scotian continental rise show effects of an intense bottom current at 4800 5000 m that decreases in strength upslope to tranquil near bottom conditions at 3200 4000 m apparently weak currents are present above 3200 m long term geologically significant flow parallels the bathymetric contours toward the southwest but significant short term variability in direction is indicated by orientations of small scale bedforms the western boundary undercurrent documented elsewhere along the continental margin at depths less than 4000 m has relatively little effect in modifying the sea floor on the nova scotian rise but the deep currents 4000 m have a significant effect repeated photography of small seafloor areas suggests that many bedforms especially those of smaller scale are constructed and destroyed by strong variably directed current events benthic storms on time scales of 3 6 months or less thus a significant part of the geologic response of the seabed to currents may be event controlled on time scales not very different from those in coastal environments

ground truthing 6 5 khz side scan sonographs what are we really imaging a 1000 km2 area on the distal lobe of monterey fan shows a digitate pattern of juxtaposed high and low backscatter on gloria side scan sonographs this area was investigated using stereo photography high resolution seismic profiles and measurements of physical properties of cores to quantitatively evaluate the causes of backscatter from the 6 5 khz side scan sonar stereo photography and bottom video were used to determine that the sediment water interface typically has a bed roughness less than 10 cm over the entire ground truth area consequently bed roughness is not a significant contributor to the sonar backscatter vertical incidence 3 5 khz profiles reveal that high backscatter areas allow less penetration and have slightly more relief than low backscatter areas closely spaced measurements of p wave velocity density and grain size made on transponder navigated cores are used to investigate the geoacoustic properties of the sediment with the aid of a numerical model the model results demonstrate that the sediment water interface is in most cases acoustically transparent to the sonar energy and that most or all of the energy is refracted into the sediment to depths of at least a few meters rather than scattered from the surface the variability of the dominant lithofacies sands with minor silty clays or silty clay with minor sands accounts for a regional correlation with backscatter when viewed over hundreds to thousands of square kilometers but at the detailed scale of hundreds to a few square meters we have not yet been able to identify a correlation of backscatter intensity with the angle of incidence surface lithology measured acoustic impedance or attenuation however there is a qualitative but unexpected correlation with lithostratigraphic variability in this area thick up to 50 cm sand deposits with thin interbeds of silty clay correlate with lower backscatter than do silty clay deposits with thin interbeds of sand this suggests that volume inhomogeneities and complex constructive and destructive interferences caused by the subsurface volume inhomogeneities within the top few meters of the sediment ultimately modulate the intensity of backscatter the ground truthing effort was further complicated by trying to compare the very large sonar footprint of a pixel 70 000 m2 relative to the area of an individual core 0 006 m2 bottom photograph 5 m2 or seismic profile although 6 5 khz sonographs appear easy to interpret in a conventional and simplistic manner caution should be used when interpreting lithofacies from backscatter intensities

control of alongshore oriented sand spits on the dynamics of a wave dominated coastal system holocene deposits northern gulf of lions france article the maguelone shore extends along the northern coast of the gulf of lions west of the rhone delta and east of high gradient coastal streams that have provided most of the clastic sediments to the gulf of lions margin since the early miocene this 10 km wide area is constituted by a small coastal watershed 15 km long in low lying carbonate hills a kilometre wide marsh a sandy beach barrier and a shoreface experiencing local low sedimentation rates this onshore offshore transition zone is a key area to understand the relationships between erosion by pass deposition and preservation processes unlike the neighbouring rhone deposits that display numerous thick deltaic sequences related to a continuous sediment flux the maguelone shore exhibits peculiar sedimentary bodies the analysis of about 250 km of new vhr seismic profiles acquired over the study area 9 short cores and outcrops data allowed us to determine the three dimensional high resolution geometry of the coastal system tracts from quaternary to present day this revealed dominant denudation processes in the upstream catchments associated with the formation of incised valleys during quaternary lowstands in addition this study investigates the erosion and deposition mechanisms controlled by littoral hydrodynamics that have been taken place on this shore since the last transgression in particular metre high and hundreds of metre long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is discussed the maguelone shore can be used as an experimental study for onshore offshore dynamics under the influence of microtidal wave current hydrodynamics and very low river derived sediment flux during a eustatic cycle geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea level changes and is successfully analysed with 2d sequence stratigraphy cross shore models it is observed that in areas like the maguelone shore traditional sequence stratigraphy methods might not be fully relevant and need to integrate alongshore hydrodynamical processes

neogene depositional processes on the texas louisiana continental slope revealed by high resolution seismic studies systematic interpretation of high resolution seismic profiles 3 5 10 khz echograms and 100 hz air gun from the continental slope and rise of offshore texas and louisiana from the shelf break across the highly deformed zone of salt diapirs folds and intraslope basins to water depths greater than 3 500 m seaward of the sigsbee escarpment reveals the geometries scales distributions and depositional processes of deep water deposits in this region the 3 5 10 khz data indicate that redistribution of sediment by mass transport processes a ubiquitous and a wide spectrum of slumps slide blocks and debris flows are observed from small isolated deposits in intraslope basins to large complex deposits covering hundreds of kilometers the reflection character echo character of many intraslope basin and canyon floors indicates sand rich deposits however aggradational leveed channel systems characteristic of deep sea fans are not observed in the steep walled intraslope basins in contrast some large submarine fan channel levee complexes do extend seaward from the mouths of these large canyons and basins at the base of the sigsbee escarpment to form one or more large deep sea fans on the continental rise apparently large quantities of terrigenous sediments can be transported by turbidity flows through the intricate network of rugged intraslope basins and canyonsmore to feed these fans evidence of sediment redistribution by bottom currents contour currents is also observed in the form of sediment waves and drift deposits across a large area of the continental rise seaward of the southeastern base of the sigsbee escarpment less

deep currents in the gulf of mexico abstract direct current measurements using moored arrays have been made below 1000 m in the eastern central and western gulf of mexico basin the major low frequency velocity fluctuations in the lower 1000 to 2000 m of the water column in the three regions have the characteristics of topographic rossby waves trws spectral peaks are observed at periods of about 25 days and 40 to 100 days motions are highly coherent with depth variances increase toward the bottom despite the very weak stratification of the deep waters of the gulf wave lengths are about 150 250 km and phase propagation is offshore with energy propagation westward a group velocity of about 9 km day 1 could be directly estimated from significantly coherent signals between eastern and western arrays this value is consistent with estimates derived from the dispersion relation and is higher than the westward translation speed of 3 to 6 km day 1 of the large anticyclonic eddies shed from the loop current it appears that a major source of

sediment waves on the south china sea slope off southwestern taiwan implications for the intrusion of the northern pacific deep water into the south china sea abstract using an integrated multi beam bathymetry high resolution seismic profile piston core and ams 14 c dating data set the current study identified two sediment wave fields fields 1 and 2 on the south china sea slope off southwestern taiwan field 1 is located in the lower slope and sediment waves within it are overall oriented perpendicular to the direction of down slope gravity flows and canyon axis geometries morphology and internal seismic reflection configurations suggest that the sediment waves in field 1 underwent significant up slope migration field 2 in contrast is located more basinward on the continental rise instead of having asymmetrical morphology and discontinuous reflections as observed in field 1 the sediment waves in field 2 show more symmetrical morphology and continuous reflections that can be traced from one wave to another suggesting that vertical aggradation is more active and predominant than up slope migration three sediment wave evolution stages stage 1 through stage 3 are identified in both field 1 and field 2 during stage 1 the sediment waves are built upon a regional unconformity that separates the underlying mass transport complexes from the overlying sediment waves in both of these two fields there is progressive development of the sediment waves and increase in wave dimensions from the oldest stage 1 to the youngest stage 3 even though up slope migration is dominant in field 1 whereas vertical aggradation is predominant in field 2 throughout these three stages the integrated data and the depositional model show that the upper slope of the study area is strongly dissected and eroded by down slope gravity flows the net result of strong erosion is that significant amounts of sediment are transported further basinward into the lower slope by gravity flows and or turbidity currents the interactions of these currents with bottom contour currents induced by the intrusion of the northern pacific deep water into the south china sea and preexisting wavy topography in the lower slope result in the up slope migrating sediment waves in field 1 and the contourites as observed from cores ts01 and ts02 further basinward on the continental rise turbidity currents are waned and diluted whereas along slope bottom contour currents are vigorous and most likely dominate over the diluted turbidity currents resulting in the vertically aggraded sediment waves in field 2 the results from this study also provide the further evidence for the intrusion of the northern pacific deep water into the south china sea and suggest that this intrusion has probably existed and been capable of affecting sedimentation in south china sea at least since quaternary

a proposed new type of arsenian pyrite composition nanostructure and geological significance this report describes a new form of arsenian pyrite called as3 pyrite in which as substitutes for fe fe as s2 in contrast to the more common form of arsenian pyrite as1 pyrite in which as1 substitutes for s fe as s 2 as3 pyrite has been observed as colloformic overgrowths on as free pyrite in a hydrothermal gold deposit at yanacocha peru xps analyses of the as3 pyrite confirm that as is present largely as as3 empa analyses show that as3 pyrite incorporates up to 3 05 at of as and 0 53 at 0 1 at 0 27 at 0 22 at 0 08 at and 0 04 at of pb au cu zn ni and co respectively incorporation of as3 in the pyrite could be written like as3 y au 1 y 2 fe2 where au and vacancy help to maintain the excess charge hrtem observations reveal a sharp boundary between as free pyrite and the first overgrowth of as3 pyrite 20 40 nm thick and co linear lattice fringes indicating epitaxial growth of as3 pyrite on as free pyrite overgrowths of as3 pyrite onto as free pyrite can be divided into three groups on the basis of crystal size 8 20 nm 100 300 nm and 400 900 nm and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals the yanacocha deposit in which as3 pyrite was found formed under relatively oxidizing conditions in which the dominant form of dissolved as in the stability field of pyrite is as3 in contrast reducing conditions are typical of most environments that host as1 pyrite as3 pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments including high sulfidation epithermal deposits and shallow groundwater systems where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of as3 and toxic heavy metals in oxidizing natural systems

how did thin submarine debris flows carry boulder sized intraclasts for remarkable distances across low gradients to the far reaches of the mississippi fan submarine density flows dominate sediment transport into many parts of the ocean and form submarine fans which are some of the largest sediment accumulations on earth previous studies often assumed that the distal fringes of submarine fans would be dominated by extensive sheet like deposits from dilute and expanded turbidity currents because only turbidity currents would transport large volumes of sediment for long distances across such low gradients deposits with a remarkable frondlike shape occur at the furthest fringe of the mississippi submarine fan understanding the emplacement process of these deposits is important because their frondlike shape suggests deposition from debris flows rather than turbidity currents previous analyses concluded that these deposits comprise a complex arrangement of thin interbedded turbidity current and debris flow deposits here we propose a different internal geometry for the frondlike deposits intervals previously described as in place turbidites are interpreted to be clasts within a single debrite interval that is 1 to 2 m thick this debrite interval is underlain by clean sand the debrite interval could have been emplaced by multiple debris flows or one event comprising multiple pulses clasts in the debrite interval are much bigger than previously thought including boulders with diameters that can exceed 50 cm we show that thin 2 m and extremely fluidal debris flows could have carried these boulders across gradients of only 0 06 to the fringes of one of the world s largest submarine fans without hydroplaning this long transport distance could occur if the density of the clasts was less than that of the surrounding debris flow emplacement of the basal clean sand layer appears closely linked to debris flow deposition because the clean sand layer pinches out in a location similar to that of the overlying debrite we therefore suggest that the basal clean sand most likely settled out from the overlying debris flows and that the clean sand is not a fore running turbidity current deposit shearing at the base of a mud rich debris flow would most likely produce a muddy basal sand interval rather than the clean sand that is observed this basal sand interval is therefore less likely to be a record of a lubricating layer with high pore fluid pressure on which the debris flows moved this study shows how thin and highly mobile debris flows can redistribute large volumes of sediment including bouldersized clasts long distances into the deep ocean across remarkably low gradients

sediment failures and flows in the gulf of cadiz eastern atlantic several types of sediment failures in the gulf of cadiz were observed using multibeam bathymetry acoustic imagery and high resolution seismic these instabilities are mainly sediment failures and flows their width and length vary from 1 to more than 10 km the failures are mainly related to high sedimentation rates particularly in places where the mediterranean outflow water mow spills over such as channel bends and the outer side of the giant contourite levee steep slopes are also a trigger for failure at the continental shelf slope transition on valley sides on canyon flanks and on the sides of bathymetric highs other mass movements are related to fluid escape mud volcanoes and earthquakes in areas where the mow flows along the seafloor the constant shearing and related erosion can add to the overall stresses the frequency of failures can be estimated using the deposits resulting of their distal transformations into turbidites

upper pleistocene turbidite sand beds and chaotic silt beds in the channelized distal outer fan lobes of the mississippi fan cores from a mississippi outer fan depositional lobe demonstrate that sublobes at the distal edge contain a complex local network of channelized turbidite beds of graded sand and debris flow beds of chaotic silt off lobe basin plains lack siliciclastic coarse grained beds the basin plain mud facies exhibit low acoustic backscatter on seamarc ia sidescan sonar images whereas high acoustic backscatter characteristic of the lobe sand and silt facies the depth of the first sand silt layer correlates with relative backscatter intensity and stratigraphic age of the distal sublobes i e shallowest sand highest backscatter and youngest sublobe the high proportion 50 of chaotic silt compared to graded sand in the distal outer fan sublobes may be related to the unstable muddy canyon wall source areas of the extensive mississippi delta fed basin slope a predominace of chaotic silt in cores or outcrops from outer fan lobes thus may predict similar settings for ancient fans

carapebus member eocene campos basin brazilian offshore an example of deep sea fan turbidites winnowed by bottom currents abstract the carapebus member eocene campos basin offshore end page 545 brazil consists of coarse grained turbidite sand bodies enclosed by pelitic deposits the turbidite sands represent a major oil reservoir in the brazilian offshore on the basis of core analysis e log correlation patterns and seismic data these sand bodies are interpreted as original deep sea fan sediments that were extensively winnowed by bottom currents indirect evidence for such an interpretation is given by the complete absence of thin bedded and fine grained turbidite sediments direct evidence is the highly burrowed fine grained and irregularly stratified bottom current deposits this complex depositional system was formed on a passive continental margin setting concurrently with an overall seaward progradation of clastics the correct understanding of such depositional odels seems to be of primary importance for the oil exploration of the atlantic margins end of article last page 546

geophysical evidence for widespread cenozoic bottom current activity from the continental margin of nova scotia canada abstract two dimensional and three dimensional multichannel seismic reflection data are utilized to examine previously unrecognized contourite depositional systems along the continental margin of nova scotia canada prior to this study these features were thought to be of limited extent in the study area the new data show that contourite drifts are widespread with greatest drift development during the late miocene to pliocene giant sediment waves form stacked aggrading sequences of bedforms and their development is linked to pre existing seafloor morphology small sediment drifts developed locally throughout the late paleogene and neogene either southwest and down current of seafloor obstacles or form channel fills major erosional pulses form regional seismic markers first along the continental rise in the early oligocene then along the continental slope during the late miocene and pliocene three dimensional seismic data show that erosion surfaces preserve along slope amplitude anomalies two dimensional low relief sediment waves and barchanoid bedforms the geophysical evidence implies that a northeast to southwest along slope bottom current influenced cenozoic depositional patterns throughout the study area

the separation of the yucatan current from the campeche bank and the intrusion of the loop current into the gulf of mexico data collected in the eastern gulf of mexico during 1974 1975 and 1976 show that the penetration of the loop current into the gulf is strongly correlated with the location of the yucatan current on the campeche bank the loop does not penetrate far into the gulf when the yucatan current separates from the bank in the vicinity of the catoche tongue i e the eastern campeche bank deep loop penetrations are correlated with separations farther west on the bank the angle of the yucatan current at separation is also correlated with the location of separation i e smaller angles relative to due east are correlated with separations from farther east on the bank thus small angles at separation are correlated with shallow intrusions of the loop historical temperature data collected in the eastern gulf are reviewed and support these correlations simple conservation of potential vorticity considerations can explain the correlation between the angle at separation and the penetration of the loop

deformed barchans under alternating flows flume experiments and comparison with barchan dunes within proctor crater mars abstract it is generally considered that barchans isolated crescentic shaped dunes develop where wind is unidirectional and the available sand is insufficient to cover the entire dune field however bishop bishop m a 2001 seasonal variation of crescentic dune morphology and morphometry strzelecki simpson desert australia earth surface process and landforms 26 783 791 observed barchans that developed in areas where winds blow seasonally in opposite directions and described a peculiar deformation feature the rear slipface that is not found in ordinary barchans barchans under such bidirectional flows are poorly understood and it is necessary to study barchans that formed under many different flow conditions we conducted flume experiments to investigate the deformation of barchans under alternating water flow and observed new deformation features in addition to rear slipfaces we conclude that the deformation of barchans can be categorized into four types one of which shows morphologies similar to barchans within proctor crater mars the deformation type depends on the strength of the reverse flow relative to the forward flow and the absolute velocity of the forward flow comparison of our results with barchan dunes within proctor crater enable us to qualitatively estimate the wind strength and direction related to dune formation on mars these results are in agreement with those of fenton et al fenton l k toigo a d richardson m i 2005 aeolian processes in proctor crater on mars mesoscale modeling of dune forming winds journal of geophysical research 110 e6 e06005

sedimentary environment of the faroe shetland and faroe bank channels north east atlantic and the use of bedforms as indicators of bottom current velocity in the deep ocean in the northeast atlantic much of the deep cold water flow between the norwegian sea and the main north atlantic basin passes through the faroe shetland and faroe bank channels generating strong persistent bottom currents capable of eroding and transporting sediment up to and including gravel a large variety of sedimentary bedforms including scours furrows comet marks barchan dunes sand sheets and sediment drifts is documented using sidescan sonar images seismic profiles seabed photographs and sediment cores from the floor of the channel published information on current velocities associated with the various bedforms has been used to reconstruct the pattern of bottom currents acting on the channel floor the results broadly reflect the current pattern predicted on the basis of regional oceanographic observations but add considerable detail the internal consistency of the results suggests that the methods used are robust giving confidence in the fine detail of the observed bottom current structure bottom current velocities in the range 1ae0 m s 1 are indicated by the range of observed bedforms with the strongest currents associated with south west transport of norwegian sea deep water nsdw at water depths of 800 1200 m the main nsdw flow forms a relatively narrow core that follows the base of the faroes slope this core follows the 90 change in trend of the faroes slope at the junction between the faroe shetland and faroe bank channels the strongest currents within the nsdw core are found over the shallowest sill in the faroe shetland channel and in the narrowest part of the channel immediately downstream of the sill and are generated by topographic constriction of the flow eastward flow of deep water along the northern flank of the wyville thomson ridge suggests a complex current pattern with some recirculation of deep water within the deep faroe bank channel basin the observations suggest that coriolis force is the main agent controlling the westward deflection of the nsdwinto the faroe bank channel contradicting a previous suggestion that this was controlled by the topography of the wyville thomson ridge

the coupled geochemistry of au and as in pyrite from hydrothermal ore deposits the ubiquity of au bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of au and as in this sulfide occurs under a wide range of physico chemical conditions despite significant advances in the last 20years fundamental factors controlling au and as ratios in pyrite from ore deposits remain poorly known here we explore these constraints using new and previously published empa la icp ms sims and pixe analyses of as and au in pyrite from carlin type au epithermal au porphyry cu cu au and orogenic au deposits volcanogenic massive sulfide vhms witwatersrand au iron oxide copper gold iocg and coal deposits pyrite included in the data compilation formed under temperatures from 30 to 600 c and in a wide variety of geological environments the pyrite au as data form a wedge shaped zone in compositional space and the fact that most data points plot below the solid solubility limit defined by reich et al 2005 indicate that au1 is the dominant form of au in arsenian pyrite and that au bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native au the analytical data also show that the solid solubility limit of au in arsenian pyrite defined by an au as ratio of 0 02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal chemical properties of pyrite and post depositional alteration compilation of au as concentrations and formation temperatures for pyrite indicates that au and as solubility in pyrite is retrograde au and as contents decrease as a function of increasing temperature from 200 to 500 c based on these results two major au as trends for au bearing arsenian pyrite from ore deposits are defined one trend is formed by pyrites from carlin type and orogenic au deposits where compositions are largely controlled by fluid rock interactions and or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids the second trend consists of pyrites from porphyry cu and epithermal au deposits which are characterised by compositions that preserve the au as signature of mineralizing magmatic hydrothermal fluids confirming the role of this sulfide in controlling metal ratios in ore systems

detrital pyrite in witwatersrand gold reefs x ray diffraction evidence and implications for atmospheric evolution pyrite is easily oxidized and therefore unambiguous evidence of detrital pyrite grains in metasediments is a significant constraint on when an oxygenated atmosphere developed compact rounded pyrite in the witwatersrand gold reefs of south africa has a detrital habit and is texturally equivalent to and spatially associated with detrital zircon and chromite x ray precession photography reveals that petrographically featureless as poor grains are untwinned single crystals of high diffraction quality this new evidence from crystallography is consistent with mechanically abraded pyrite from primary lode gold deposits and excludes an origin by replacement of a pre existing detrital phase further evidence of a detrital origin for the compact rounded pyrite is afforded by isolated grains of arsenian pyrite displaying truncated as rich growth bands the geographically extensive witwatersrand fluvial conglomerates evidently had a matrix of quartz and pyrite sand and pyritic mud in their unconsolidated state and thus the late archean atmosphere of earth was likely essentially anoxic

gold accumulation in the archaean witwatersrand basin south africa evidence from concentrically laminated pyrite abstract concentrically laminated pyrite is a relatively common although volumetrically minor component of auriferous conglomerates in the archaean ca 3 0 2 7 ga witwatersrand basin of south africa this type of pyrite contains high amounts several tens of ppm of au but the origin of the pyrite is debated and the timing of au deposition in these grains is not known in order to constrain the formation of pyrite we have studied concentrically laminated pyrite and other coexisting types of pyrite inclusion rich massive pyrite by analysing the contents and distribution of au and other trace elements by laser ablation icp ms the s and fe isotope composition by sims and the mineral inclusions by scanning electron microscope and laser raman spectroscopy trace element maps indicate that concentrically laminated pyrite is enriched in sb mn au ag tl cu mo mn and contains two types of gold finely dispersed au invisible gold with au ag 0 1 and likely of primary origin and au inclusions with au ag 10 of secondary origin the study of mineral inclusions revealed the presence of muscovite chlorite fine grained carbonaceous matter monazite ti oxides and quartz iron and multiple s isotopes suggest that concentrically laminated pyrite and inclusion rich pyrite were formed from two separate pools of s and fe with different isotope characteristics sulfur was derived from atmospheric s that had undergone mass independent isotope fractionation to form so 4 2 with negative 33 s that constituted concentrically laminated pyrite and elemental s with positive 33 s that formed inclusion rich pyrite iron pools were derived from partial oxidation of fe 2 so that concentrically laminated pyrite formed from a low 56 fe residual fe 2 average 0 2 and inclusion rich pyrite formed from a high 56 fe fe 3 pool average 2 7 biological activity may have been involved in the reduction of so 4 2 causing a wide spread of 34 s values 25 s reducing microorganisms as well as in the partial oxidation of fe 2 anaerobic photosynthetic fe reducers or photosynthetic o 2 producers and in the formation of pyrite from fe 3 dissimilatory fe reducers we propose that concurrent biogenically mediated pyrite formation and au trapping suggest that microbial activity was responsible for the accumulation of au and other trace elements e g sb mn ag tl cu mo mn which are commonly enriched in organic matter rich sediments