styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

intra and extrabasinal controls on fluvial deposition in the miocene indo gangetic foreland basin northern pakistan the miocene siwalik group upsection the chinji nagri and dhok pathan formations in northern pakistan records evolving fluvial systems within the himalayan foreland basin sedimentological variations are evaluated with respect to local regional and global controls on fluvial deposition and basin filling thick 5 m to tens of metres sandstones are composed of channel bar and fill deposits of low sinuosity meandering and braided rivers which formed large low gradient sediment fans or megafans river flow was dominantly toward the south east the proportion of thick sandstones varies in all siwalik sections on three scales and reflects similar variations in palaeochannel size and grain size 1 small scale variations are generally tens of metres thick and reflect the alternation of thick sandstones channel belt deposits and mudstone dominated strata overbank deposits through the section 2 medium scale variations are roughly one hundred to a few hundreds of metres thick and primarily correspond to changes in channel deposit thickness but also to the degree of superposition of channel deposits and or to changes in the number of channel belt deposits per unit of section and 3 large scale variations formation scale are greater than one km thick and primarily correspond to changes in channel deposit thickness time scales of small medium and large scale variations appear to be on the order of 104 105 and 106 years respectively the chinji nagri transition is characterized by increases in channel deposit proportion sandstone thickness palaeochannel size and discharge mean grain size of sandstones and sediment accumulation rates and a decrease in avulsion period the nagri dhok pathan transition is characterized by decreases in channel deposit proportion sandstone thickness palaeochannel size and discharge mean grain size of sandstones and avulsion period and a further increase in sediment accumulation rates formation boundaries across the potwar plateau decrease in age toward the west the chinji nagri transition ranges in age from 10 9 12 7 ma and the nagri dhok pathan transition ranges in age from 9 3 10 1 ma small scale variations are attributable to repeated river avulsions triggered by autocyclic processes and or mountain front tectonism e g faulting earthquakes medium scale variations are attributable to local changes in the position of large sediment fans also triggered by autocyclic processes and or mountain front tectonism the chinji nagri transition records the diversion or establishment possibly due to river piracy of a larger river system in the area river diversion or piracy probably took place within the mountain belt and is attributable to increasing and spatially variable mountain belt uplift rates and possibly the development of associated mountain front deformational structures the nagri dhok pathan transition records the diversion of the larger river system out of the area and the establishment of a smaller river system this diversion is attributable to progressively increasing rates of mountain belt uplift and basin subsidence the regional palaeoclimate throughout the time interval studied was apparently constant and eustatic sea level changes apparently had no effect on deposition in the area

seafloor undulation pattern on the adriatic shelf and comparison to deep water sediment waves abstract on the adriatic shelf a large field of seafloor and subsurface undulations typically 300 m wide 2 5 m high and several km long parallel to the bathymetric contour affects the progradational clinoforms of the late holocene prodelta wedge above a regional downlap surface that shows evidence of deformation and fluid escape the undulations are associated with mud reliefs that occur farther seaward in elongated swarms perpendicular to the regional slope and to the crests of the undulations a quantitative measurement of key morphobathymetric parameters such as wavelength height asymmetry and wave form indexes was performed on 13 selected seismic reflection profiles perpendicular to the undulations these measurements are determined with respect to water depth or downslope distance from the shallowest undulation the results highlight substantial differences from deep water sediment waves these differences include 1 most undulations show a staircase morphology with sub horizontal upslope limbs of 100 300 m delimited seaward by sharp edges and steep downslope limbs 2 landward or upslope dipping limbs do not develop 3 there is no consistent downslope decrease in wavelength or amplitude as opposed to most cases of sediment waves related to overflowing turbidity currents 4 there is a consistent downslope loss in crest continuity approaching areas where mud reliefs and sediment deformation are evident at the seafloor 5 many of the undulations show differences in angle of climb and in some cases a single undulation at the seafloor results from the burial and merger of more undulations in the underlying section these differences compared to bottom current or turbidity current sediment waves are augmented by the observation that the adriatic shallow water undulations are also typically associated with gas charged sediment fluid escape sediment deformation and localised failure planes it is therefore suggested that seafloor undulations evolved in response to sediment deformation and were successively amplified by differential deposition from bottom currents crossing an irregular seafloor in general we feel that case by case solutions should be found to explain the origin and evolution of seafloor wavy features based on the geologic stratigraphic setting the recognition of possible weak layers and the co existence of a variety of other deformation geometries that may occur within or adjacent to the field of wavy features the adriatic example can reinforce recent suggestions that besides purely depositional bedforms there exist also wave like deformation structures and multi process sediment waves faugeres et al 2002 multi process generated sediment waves on the landes plateau bay of biscay north atlantic marine geology 182 279 302

a major late devonian early carboniferous hercynian thermotectonic event at the nw margin of the arabian nubian shield evidence from zircon fission track dating zircon fission track zft ages of 17 precambrian samples from deep boreholes and outcrops in southern israel and sinai fall within the range 328 373 ma late devonian early carboniferous single zircon grain age distributions are unimodal with a high chi square probability the age data indicate total resetting of the zft clocks but only partial resetting of coexisting sphenes constraining the temperatures attained to about 225 50 c followed by relatively rapid regional cooling at the times indicated in the study area the lower paleozoic section presently overlying precambrian rocks is limited to cambrian strata up to 300 m thick further stratigraphic evidence for sub carboniferous erosion is preserved only in sw sinai to the east in southern jordan a 2 2 5 km thick lower paleozoic succession is reported despite the lack of stratigraphic evidence in the study area the zft data 1 strongly suggest that an equivalent or thicker section also existed 2 constrain the timing of the erosion to late devonian early carboniferous hercynian and 3 indicate that thermal gradients may have reached 50 c km prior to the uplift erosion event regional stratigraphic evidence indicates that the late devonian early carboniferous event was confined to a relatively narrow belt extending from the gulf of suez area to the vicinity of ne syria and se turkey

particle transport in the bari canyon southern adriatic sea to define the sediment transport pathways along the southern adriatic shelf and slope two oceanographic cruises were carried out in the southern adriatic in july 2004 and in march april 2005 to study the role of the bari canyon system on sediment dispersal three moorings including sediment traps and current meters have been deployed near the bottom at depths of 600 m for one year march 2004 march 2005 two moorings were deployed within the canyon station b in the northern branch and station c in the southern branch and one on the adjacent open slope north of the canyon system station a total mass fluxes tmfs measured by sediment traps were always higher in the canyon than on the adjacent slope the highest values were measured at station c average 8 07 g m 2 d 1 roughly double those of station b 3 07 g m 2 d 1 and the lowest outside the canyon at station a 1 69 g m 2 d 1 the highest tmf were recorded in spring 2004 a period characterized by the lowest water temperatures and the highest current speeds up to 72 cm 1 which were associated with the highest across slope current component along the canyon axes the simultaneous variations of fluxes occurring at the three stations imply that similar processes are active along the entire southern adriatic margin and that they are amplified inside the canyon in spring a vein of southward flowing north adriatic dense water naddw was observed along the adriatic shelf this was related to an enhanced across slope current component which was responsible for the higher particle fluxes both on the open slope and at the canyon stations these data suggest that the bari canyon is an efficient conduit for sediment from the adriatic continental shelf to the deep basin downcore profiles of 210 pb in sediments collected below the traps have been used to estimate sediment mass accumulation rates mars on a century scale on the open slope the annual trap flux recorded in 2004 2005 was lower than mar on the contrary in the bari canyon the annual trap flux was higher than mar indicating that the lateral advection of particles becomes predominant and that a fraction of the particles intercepted by sediment traps was only in transit through the canyon 2007 elsevier b v all rights reserved

temporal variations in the cooling and denudation history of the hunza plutonic complex karakoram batholith revealed by 40ar 39ar thermochronology the 40ar 39ar thermochronology of the late cretaceous hunza plutonic complex reveals an episodic cooling and denudation history for this regional scale pluton the 40ar 39ar analyses of biotites from a vertical relief section of 3200 m reveal a pulse of rapid cooling at 20 ma in the interval of 110 27 ma age elevation distributions suggest denudation rates of the order of 0 02 0 003 mm yr at 20 ma denudation rates increased significantly to 2 7 0 7 mm yr then returned to much slower rates until 12 ma a second pulse of rapid cooling beginning at 12 ma is revealed by inverse numerical modeling of multidiffusion domain alkali feldspars from a vertical section of 1700 m decreasing in elevation these samples record the onset of rapid cooling at 12 9 and 7 ma respectively all of the alkali feldspars record a period of nearly isothermal conditions prior to the onset of rapid cooling when rates increased to 30 c m y assuming a geothermal gradient of 30 c km these cooling rates translate into denudation rates of 1 0 mm yr apatite fission track analysis indicates denudation rates of 0 7 0 1 mm yr over the interval of 6 6 ma to 2 4 ma in agreement with the alkali feldspar data these data suggest denudation of 2 9 0 4 km since the plio pleistocene together the alkali feldspar and apatite data indicate that a minimum of 10 km of overburden has been removed since the mid late miocene an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 95tc02424 temporal variations in the cooling and denudation history of the hunza plutonic complex karakoram batholith revealed by 40ar 39ar thermochronology m a krol p k zeitler g poupeau and a pecher diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

geomorphic interpretation of low temperature thermochronologic data insights from two dimensional thermal modeling 1 low temperature thermochronologic data are useful for estimating mountain erosion rates because late stage cooling in mountain ranges often reflects exhumation via geomorphic erosion processes traditional interpretations of thermochronologic data assume steady uniform erosion conditions often violated in real mountain ranges here i examine whether unsteady or nonuniform erosion histories are detectable in patterns of erosion rate estimates made by traditional means to do so i numerically model the subsurface temperature field in a two dimensional section of earth s crust under various illustrative geomorphic scenarios i generate simulated cooling ages within two isotopic systems apatite fission track ft and u th he he at two landscape locations ridge tops and valley bottoms from these ages i make field estimates of erosion rates using the commonly employed elevation dependence and mineral pair methods calculations show that if errors on erosion rate estimates are kept small by replicate or transect sampling many unsteady or nonuniform erosional histories do produce distinctive patterns of erosion rate estimates for example temporally increasing erosion rates produce poor agreement between erosion rate estimates made with a single method while decreasing erosion rate produces good agreement between estimates made with a single method nonuniform erosion that decreases relief can produce erroneously high erosion rate estimates based on the elevation dependence method but also accurate and relatively precise mineral pair based estimates a history of decreasing relief can be distinguished from one of steady uniform erosion by 1 close agreement between mineral pair estimates and poor agreement between elevation dependence estimates and 2 the magnitude of the difference between ft and he ages the insights gleaned from these analyses can guide forward modeling of topographic and thermal evolution

nd and pb isotope variability in the indus river system implications for sediment provenance and crustal heterogeneity in the western himalaya abstract the indus river system is the only major drainage system in the western himalaya and erodes not only the high himalaya but also topographically high regions within and north of the indus suture zone most notably the karakoram ion microprobe analysis of pb isotopes in detrital k feldspar grains taken from the tributaries of the indus together with bulk nd isotope analysis of those same sediments is here used to identify distinct sediment source regions these span the very radiogenic nanga parbat and associated lesser himalaya the relatively radiogenic intermediate high himalaya the unradiogenic ladakh and kohistan batholiths and intermediate values in the hindu kush karakoram and lhasa block the range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis k feldspars from the ladakh and kohistan batholiths are less radiogenic than the laterally equivalent gangdese granite of tibet interpreted to reflect the preferential recycling of accreted oceanic arc units within the western transhimalaya prior to india asia collision similarly the zanskar high himalaya are less radiogenic than their equivalents in nepal isotope values from pleistocene indus fan sediment are compatible with a dominant source in the karakoram with additional important contributions from the arc batholiths and high himalaya reflecting both the area and modern rates of tectonic uplift within the drainage basin in contrast radiogenic grains are common in the lower reaches of the modern indus river possibly as a result of the damming of the main river channel where it reaches the foreland

stable drainage pattern and variable exhumation in the western himalaya since the middle miocene abstractsedimentary records in peripheral basins of mountain belts record changes in erosion dynamics and drainage network reorganization but it is often difficult to discriminate between these different controls geochemical provenance data on paleo indus deposits from the western himalayan foreland provide constraints on the possible variation of the position of the drainage divide between the indus and ganges river systems here we present geochemical trace element and hf nd isotopic and thermochronological detrital zircon fission track dzft analyses of modern indus and miocene siwalik sediments from northern pakistan and compare these with published data on the indus fan available bedrock isotopic data are used to define three end member sediment sources himalaya karakorum and the kohistan ladakh arc and to calculate the contribution of each of these sources to the foreland basin and indus fan our results indicate that since the miocene the contribution of the himalayan rivers reaching th

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

sand waves on an epicontinental shelf northern bering sea abstract sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges 20 km 5 km 10 m high lying in an open marine setting in the northern bering sea the sand wave area which lies west of seward peninsula and southeast of bering strait is exposed to the strong continuous flow of coastal water northward toward bering strait a hierarchy of three sizes of superimposed bedforms all facing northward was observed in successive cruises in 1976 and 1977 large sand waves height 2 m spacing 200 m have smaller sand waves height 1 m spacing 20 m lying at a small oblique angle on their stoss slopes the smaller sand waves in turn have linguoid ripples on their stoss slopes repeated studies of the sand wave fields were made both years with high resolution seismic reflection profiles side scan sonographs underwater photographs current meter stations vibracores and suspended sediment samplers comparison of seismic and side scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year further documenting modification to the bottom by sediment transport during calm sea conditions in 1977 underwater video and camera observations showed formation and active migration of linguoid and straight crested current ripples current speeds 1 m above the bottom were between 20 and 30 cm s maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water many cross stratified sand bodies in the geologic record are interpreted as having formed in a tidal or storm dominated setting this study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open marine setting

a sequence stratigraphic model for reservoir sand body distribution in the lower permian shanxi formation in the ordos basin northern china abstract the lower permian shanxi formation is the main gas bearing stratigraphic unit in the northeastern ordos basin china based on an integrated investigation of well logs seismic data cores and outcrops the lower member of the shanxi formation has been subdivided into three third order sequences from base to top namely sq1 sq2 and sq3 the three sequences consist primarily of stacked lowstand systems tracts with little deposition of transgressive systems tracts and or highstand systems tracts detailed sedimentological and stratigraphic analyses indicated that the entire sequence is characterized by a regional transgression with incised valleys and channel fills marking the bases of each retro gradational sequence and swamp or inter channel bay mudstone and coal deposits capping each sequence the three sequences retracted source ward sequentially from the sandstone dominated sq1 to the mudstone dominated sq3 the spatial and temporal distributions of the reservoir sandstones was primarily controlled by retro gradational stacking patterns channel sand bodies formed during the lowstand systems tracts of sq1 sq2 and sq3 are excellent reservoirs which form excellent reservoir cap rock assemblages with the overlying fine grained sediments the unique sequence stacking patterns control the accumulation of hydrocarbons the reservoir quality of the sq1 sq2 and sq3 sequences become worse gradually from base to top within each sequence channel or incised valley fill of the lowstand systems tracts remain potential good expiration targets

relationships between right lateral shear along the karakoram fault and metamorphism magmatism exhumation and uplift evidence from the k2 gasherbrum pangong ranges north pakistan and ladakh the karakoram fault is a major nw se aligned dextral strike slip fault that has accommodated minor extrusion of thickened tibetan crust since the mid miocene controversy exists as to whether the fault is lithospheric in scale resulting in synkinematic metamorphism and granite melting or whether it is an upper crustal fault cutting through earlier metamorphic and granitic rocks structural metamorphic and geochronological data from the karakoram fault show that 1 metamorphism and granite genesis occurred prior to strike slip shearing meaning that u pb zircon and monazite ages from deformed granites cannot be used as proxies for dating strike slip shearing only as a maximum age constraint on initiation of ductile shearing 2 sheared miocene leucogranites along the fault are equivalent to the baltoro granite batholith offset 40 150 km along the fault and show a strain gradient from high ductile strain to undeformed away from the fault 3 40 ar 39 ar and fission track ages of k2 orthogneisses and gasherbrum diorite show that rocks adjacent to the fault cooled during cretaceous to mid tertiary time and were not reset during shearing indicating that shear heating was not important 4 the gasherbrum diorite adjacent to the fault has never been at depths greater than 6 km since the early cretaceous and less than 3 km of material has been eroded off since then we conclude that the karakoram fault has had no significant influence on regional metamorphism or melting at least at levels exposed today and is restricted to the upper middle crust

zircon fission track ages from the gasherbrum diorite karakoram range northern pakistan the gasherbrum peaks in the himalaya of pakistan reach elevations of 8000 m the relief between the peaks and the adjacent valley baltoro glacier is in excess of 3000 m eight samples of the early cretaceous gasherbrum diorite at elevations between 4880 and 7165 m on gasherbrum iv were collected for fission track dating zircon fission track ages from the gasherbrum diorite vary from early cretaceous to middle tertiary in age there is no consistent pattern between age and elevation the cretaceous ages indicate that these rocks were never deeply buried i e heated to temperatures in excess of 175 c to reset the zircons during cenozoic time these results also indicate that the uplift of this part of the himalaya has been either very rapid and recent or very slow since early cretaceous time this latter possibility is not consistent with the high relief at gasherbrum and what is known about regional tectonics gasherbrum iv zircons currently at approximately 4880 m have never been at depths greater than 6 km and less than 3 km of material has been removed from the top of the range by erosion since the early cretaceous rapid uplift has occurred very recently and erosion rates have notmore been able to keep pace with this uplift less

norwegian sea overflow through the faroe shetland gateway as documented by its bedforms we have used seabed information from three deep tow side scan sonar surveys in order to trace the high energy current core of norwegian sea overflow water nsow from the faroe shetland channel fsc through the faroe bank channel fbc towards the southern flank of the iceland faroe ridge a hierarchy of bedform types was used for estimating maximum mean near bottom current speed which has been compared with results from current meter measurements we conclude that in the fsc maximum mean nsow near bottom flow speed at some sites may occasionally approach or even exceed 1 0 m s both seabed data and oceanographic information indicate that the current core is concentrated along the faroes slope at the 500 600 m depth stratum with a change of the large scale channel topography towards the southern extremity of the faroe plateau where the fsc turns west towards the fbc the slope current core gradually descends towards basin depth along the wyville thomson ridge 1100 1200 m water depth maximum mean nsow near bottom current speed decreases slightly towards the west as the high speed current core runs upslope the ridge at the entrance to the narrow channel between faroe bank and the faroe plateau funnelling results in a renewed current acceleration at basin depth seabed evidence shows that further west in the fbc the nsow high speed current core is detached from the channel floor over larger areas from the fbc outlet most of the overflow waters continue as a high energy contour current concentrated along the southern flank of the iceland faroe ridge between 600 and 1000 m water depth

petroleum accumulation and leakage in a deeply buried carbonate reservoir nispero field mexico abstract the filling history of the nispero deeply buried lower cretaceous carbonate reservoir below 4000 m from the south part of gulf of mexico was studied using a combination of data from petrography stable isotopes and fluid inclusions and compared with a one dimensional burial model to derive timing a combination of techniques such as microthermometry confocal laser scanning microscopy clsm and raman microspectroscopy have been used to characterize the different fluid inclusion assemblages and discriminate between the reequilibrated and the preserved fluid inclusions the nispero reservoir is composed of a fractured finely crystalline replacement dolostone a first generation of fractures is filled by a non planar dolomite cement and a second generation by a planar e dolomite cement and a blocky sparite the reservoir is lastly stylolitised dolomite has 13c values between 0 9 and 4 0 pdb and 18o values between 4 5 and 10 8 pdb calcite has 13c values between 3 8 and 4 4 pdb and 18o values between 4 9 and 5 5 pdb these values suggest that the calcite represents a change in water composition and that dolomite and calcite cements do not precipitate from petroleum derived fluids however geological fluids are trapped as aqueous and oil inclusions in the calcite cements three petroleum aqueous inclusion assemblages were identified pseudo primary brown oil paired with brine inclusions and pseudo primary yellow oil paired with low salinity water inclusions distributed in local concentrations and secondary colourless oil paired with low salinity aqueous inclusions distributed in healed microfractures the burial model calibrated with bottom hole temperatures has been calculated using petromod 1d to generate the rock pt history under hydrostatic and lithostatic regimes reconstructed temperatures of initial trapping of fluid inclusion and calculated temperatures from 18o measured in dolomite and calcite cements are in good agreement data suggests that the reservoir was being filled at 97 c 315 bar by heavy black oils accompanied by high salinity water during the miocene period 11 6 m y the maximum estimated pressure of 700 bar at 130 c is reconstructed by petroleum inclusions trapping black oil and associated low salinity aqueous inclusions these pt conditions were reached during the pliocene 3 2m y present day reservoir conditions of 145 c and 500 bar are recorded by reequilibration of most of the fluid inclusions of the two assemblages and correspond to hydrostatic pressure the drop of pressure from 700 bar to 500 bar may be an explanation for the late stylolitisation

geostrophic sand ridge dune fields and associated bedforms from the northern kwazulu natal shelf south east africa subaqueous dunes are formed on the kwazulu natal outer shelf due to sediment transport by the agulhas current geostrophic current these dunes occur within two dune fields at depths of 35 to 70 m the net sediment transport direction is south but short period reversals form northward migrating bedforms the dune fields are physically bounded by late pleistocene beachrock and aeolianite ledges a bedform hierarchy has been recognized in the dune fields comprising a system of three generations of climbing bedforms the outer dunefield has given rise to a sand ridge h 12 m l 4 km w 1 1 km and an 8 lee slope whereas the inner dune fields have achieved large scale dune status bedload parting zones within the dune fields occur where the sediment transport direction switches from north to south due to reversals in the geostrophic flow these zones occur at depths of 60 47 and 45 m an interpretative stratigraphic model is presented on what such geostrophite deposits would look like in the ancient sedimentary record

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

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

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

sediment flux in the modern indus river inferred from the trace element composition of detrital amphibole grains abstract the drainage basin of the modern indus river is composed of tectonic blocks that include oceanic arc units in the indus suture reworked components of the indian plate and various parts of the former southern margin of eurasia against which india collided we investigate how these source units contribute to the modern bedload of the indus river using the major and trace element composition of single detrital amphibole grains sediments from rivers eroding restricted drainage areas were analyzed to characterize the major potential source units samples taken at various localities downstream in the main indus river allow the evolving provenance to be assessed when coupled with existing bulk sediment nd isotope data a basic mass balance for the river can be constructed the rapidly exhuming southern karakoram metamorphic complex is the dominant sediment source to the deep sea indus fan although the nanga parbat massif located adjacent to the river s course is also rapidly exhuming this is not an important source of sediment probably because of its small area and the tectonic mechanism for its exhumation the trace element composition of detrital amphibole grains can be a useful provenance indicator especially in the identification of dominant sources in a complex mixed sediment environment trace element ratios nb zr and ba y were identified as being especially useful in discriminating detrital amphibole grains from various sources

late holocene climate variability in the adriatic sea central mediterranean planktic and benthic foraminifera assemblages from a set of sediment cores collected on the adriatic shelf and the southern adriatic deep basin provide compelling evidence of submillennial scale environmental changes during the last 6000 years repeated peaks in globigerinoides sacculifer represent warm dry intervals including the mediaeval warm period the roman age the late bronze age and the copper age the last occurrence lo of g sacculifer 550 years bp approximates the base of the little ice age lia significant turnovers in the structure of the water column reflect changes in the rate of formation and depth of flow of the north adriatic dense water naddw and the levantine intermediate water liw about 7500 years bp the benthic oxygen isotope records mark the timing when the naddw formation intensified on the slope and shifted to its modern route about 5500 years bp when sea level reached its modern high stand oxygen isotope records of intermediate planktic dwellers indicate a northward intrusion of the liw on the slope the oscillating isotope trends during the last five millennia document a discontinuous invasion of liw into the central adriatic possibly reflecting short term climate changes with weakened liw production during colder and wetter intervals

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

insights into the evolution of the hindu kush kohistan karakoram from modern river sand detrital geo and thermochronological studies the hindu kush kohistan karakoram region is critical to understanding the long term accretion history of the south asian margin pre and post india asia collision and the impact of these collisions on the development of high topography however knowledge about this region remains incomplete due to sparse studies here we present a study comprising detrital zircon u pb geochronology detrital muscovite 40ar 39ar thermochronology and numerical modeling on 40ar 39ar dates the study identifies zircon u pb age peaks at 200 ma 110 130 ma 60 80 ma and 28 40 ma supporting the polyphase collisions and crustal growth in the south asian margin modeling study reveals fast cooling erosion at 115 129 ma 69 71 ma 27 35 ma and 8 ma which are synchronous with collision related crustal growth indicating the significant impact of accretion both prior to and post india asia collision this study along with studies in eastern karakoram reveals along strike variations in erosion and exhumation with young since late miocene intense erosion focusing on the east central karakoram we suggest that this east west spatial variation in exhumation may have been associated with more intense crustal shortening and thus the greater crustal thickness topographic relief and altitude observed in the eastern compared to western karakoram

remagnetization in bituminous limestones of the neoproterozoic araras group amazon craton hydrocarbon maturation burial diagenesis or both 1 neoproterozoic carbonates of the araras group exhibit two distinct magnetic components across the same carbonate succession in a cross section between the amazon craton and the paraguay fold belt pink dolostones of the mirassol d oeste formation carry a dual polarity primary component whereas black bituminous limestones of the guia formation yield a secondary postfolding component magnetic signatures of the guia limestones such as high anhysteretic remanence magnetization saturation isothermal remanence magnetization ratios high frequency dependent magnetic susceptibility and contradictory lowrie fuller and cisowski tests are typical of remagnetized carbonates unblocking temperatures suggest that the stable high temperature remanence is carried by both pyrrhotite and magnetite for which an authigenic origin is suggested by scanning electron microscope observations the different magnetic properties noted between dolostones with or without bitumen and between dolostones and limestones in the same metamorphic conditions lead to the hypothesis that the amount of hydrocarbon as well as the lithology influence nucleation of authigenic magnetic minerals in these rocks presence of magnetite pseudoframboids and euhedral iron sulphide crystals occurring in fracture and voids are in favor of a chemical remanence crm the presence of pyrrhotite as one of the main carriers of crm in these rocks and its association with bitumen in fractures is probably related to an epigenetic enrichment of sulfur due to hydrocarbon seepage however hydrocarbon maturation solely could not explain the differences of the magnetic mineralogy observed in the craton and the fold belt enhanced magnetite formation in the thrust and fold belt is interpreted to be the result of higher temperatures leading to stronger diagenesis of clay minerals

february 2003 marine atmospheric conditions and the bora over the northern adriatic 1 a winter oceanographic field experiment provided an opportunity to examine the atmospheric marine conditions over the northern adriatic mean february winds are from a northeasterly direction over most of the adriatic and a more northerly direction along the western coast wind speeds are fastest in jets over the ne coast during bora events and weakest in the mid northwestern adriatic diurnal air temperature cycles are smallest on the ne coast and largest in the midwestern adriatic the maximum sea air difference is 10 c on the eastern coast and near zero on the midwestern adriatic boras are northeasterly from wind events that sweep off croatia and slovenia bringing slightly colder and drier air over the northern adriatic the main bora season is december to march winter 2002 2003 was normal for bora events synoptic scale temporal variations are correlated over the northern adriatic fastest bora winds and highest wind stress over the northern adriatic is concentrated in four topographically controlled jets the strongest is the senj jet while the trieste jet extends across the entire northern adriatic between each two jets is a weak wind zone the greatest mean net heat loss is in bora jets in the ne adriatic where it was 438 w m 2 and is weakest in the midwestern northern adriatic where it was near zero wind stress is concentrated over the ne half of adriatic in four bora jets while wind stress is weak in the nw adriatic there is significant variation in wind stress mean and standard deviation structure over the northern adriatic with each bora event

dense water bottom currents in the southern adriatic sea in spring 2012 abstract in february 2012 a severe cold spell in the european region triggered a massive production of very dense water on the northern mediterranean sea shelves the spreading phase of the newly formed dense water was extensively studied in the adriatic sea by means of 2 ship surveys and 5 moorings fully equipped to monitor the flow of the bottom layer for the adriatic sea opposite to the gulf of lions the area of cascading is far from the source area and this implies substantial modifications adjustments and dilution of the source water mass along its path with a spreading phase lasting several months indeed all the moorings detected events although weaker than in the preceding months until june 2012 the surveys detected 2 branches of naddw on the shelf the first branch not denser than 29 7 kg m3 and the second branch not denser than 29 5 kg m3 despite the extremely dense water generated in the northern adriatic during events of dense water flow moorings recorded temperatures generally between 12 5 and 13 c seldom less temperatures along the shelf break also did not fall below 13 c at depths greater than 400 m turbulent mixing therefore heavily modified the cascading plumes which left the shelf with thicknesses between 10 and 30 m mooring data in the lowermost 100 mab suggest that the thickness of the cascading layer increased by several tens of meters downslope as a consequence of entrainment detraining frictional layers as well as locations of active cascading were identified mostly by isolated casts highlighting the submesoscale domain of the downsloping plumes the use of ladcp data allowed identification of very energetic bottom flow 40 50 cm s in many locations with otherwise little signature in tracers not previously observed the bari canyon system bcs was so far recognized as a hot spot for cascading in the southern adriatic however during the 2012 event this is not the only preferred site for cascading significant dense flow was detected in other locations the northernmost mooring site closer to the inception of the cascading process in particular showed active cascading and several dynamical differences from the bcs denser water with thinner boundary layer events organized in multiple pulses with sub inertial periodicity and with very short duration 12 h to 1 day that is generally not seen in other locations

correlating biodegradation to magnetization in oil bearing sedimentary rocks abstract a relationship between hydrocarbons and their magnetic signatures has previously been alluded to but this is the first study to combine extensive geochemical and magnetic data of hydrocarbon associated samples we report a detailed study that identifies a connection between magnetic mineralogy and oil biodegradation within oil bearing sedimentary units from colombia canada indonesia and the uk geochemical data reveal that all the oil samples are derived from mature type ii kerogens deposited in oxygen poor environments biodegradation is evident to some extent in all samples and leads to a decrease in oil quality through the bacterially mediated conversion of aliphatic hydrocarbons to polar constituents the percentage of oil components and the biodegradation state of the samples were compared to the magnetic susceptibility and magnetic mineralogy a distinct decrease in magnetic susceptibility is correlated to decreasing oil quality and the amount of extractable organic matter present further magnetic characterization revealed that the high quality oils are dominated by pseudo single domain grains of magnetite and the lower quality oils by larger pseudo single domain to multidomain grains of magnetite and hematite hence with decreasing oil quality there is a progressive dominance of multidomain magnetite as well as the appearance of hematite it is concluded that biodegradation is a dual process firstly aliphatic hydrocarbons are removed thereby reducing oil quality and secondly magnetic signatures are both created and destroyed this complex relationship may explain why controversy has plagued previous attempts to resolve the connection between magnetics and hydrocarbon deposits these findings reinforce the importance of bacteria within petroleum systems as well as providing a platform for the use of magnetization as a possible exploration tool to identify subsurface reservoirs and a novel proxy of hydrocarbon migration

pleistocene forced regressions and tidal sand ridges in the east china sea abstract tidal sand ridges are common features on modern shelves but only few examples of such preserved sand bodies are described in pleistocene deposits in the stratigraphic record some sand bodies encased in shales previously interpreted as sand ridges have been reinterpreted as shoreface deposits more than 5000 km of high resolution seismic data from the east china sea correlated to geotechnical boreholes and shallow cores demonstrate the potential of sand ridge preservation and allow reconstruction of the depositional history of pleistocene fourth order 100 kyr depositional sequences a high subsidence rate of about 300 m myr allows the preservation of three elementary sedimentary facies constitutive of a motif which was repeated during glacio eustatic cycles they consist of 1 regressive marine prodeltaic prograding wedges 2 estuarine and continental deltaic facies and 3 transgressive sand ridges similar in shape and orientation to modern sand ridges major discontinuities traceable over the entire outer continental shelf along distances of hundreds of kilometers are transgressive and regressive surfaces of marine erosion whereas sequence boundaries formed by fluvial erosion are difficult to identify on this low gradient shelf because of the asymmetry of the pleistocene glacio eustatic cycles most of the preserved sedimentary record with the exception of sand ridges corresponds to forced regressive deposits deposits that formed during a seaward shift of the shoreline due to relative sea level lowering

transgressive sand ridges on the mid shelf of the southern sea of korea korea strait formation and development in high energy environments abstract the mid shelf of the southern sea of korea korea strait is covered by a series of shore parallel sand ridges up to 63 km long 3 9 km wide and 22 m thick the ridges are a moribund type but show well organized dipping strata indicating appreciable progradation the submerged paleo channel system the paleo seomjin river associated with the sand ridge field suggests that the ridges primarily originated from river mouth sandy shoals which subsequently developed into shore parallel linear sand bodies in high energy environments the combined effect of coastal tidal and longshore and offshore ocean currents was possibly responsible for shore parallel sediment transport and growth of the ridges 14c dates core lithology and sea level data suggest that the sand ridges mainly formed and developed during the middle period of the postglacial transgression they are postulated to have developed sequentially from offshore to onshore in response to sea level rise during that time very slow sea level rise and high sediment supply through the paleo channel system probably provided favorable conditions for forming the sand ridges the ridges became inactive during the late transgression period as a result of a substantial reduction of wave and current strength and remained on the mid shelf

remagnetization of the rush springs formation cement oklahoma implications for dating hydrocarbon migration and aeromagnetic exploration the permian rush springs formation above the cement anticline in oklahoma contains a late permian early triassic chemical remanent magnetization crm that is interpreted to reside in authigenic magnetite the crm is found in bleached carbonate cemented sandstones that were altered by hydrocarbons and contain authigenic magnetite the magnetite presumably precipitated in the late permian early triassic as a result of chemical conditions created by hydrocarbons or associated fluids that migrated from underlying reservoir units red sandstones around cement that were not altered by hydrocarbons contain a permian crm that resides in hematite the red and bleached sandstones have similar magnetization intensities and susceptibilities this raises questions about the use of aeromagnetic surveys in hydrocarbon exploration

shoshonitic and ultrapotassic post collisional dykes from northern karakorum sinkiang china abstract high k calc alkaline shoshonitic and ultrapotassic post collisional dykes of neogene age have been found in the remote and little known region of northern karakorum located around the shaksgam valley north of the k2 gasherbrum range china the dykes derive from more or less comparable basic magma s and display rather unusual petrographic and geochemical characters with respect to the other k rich rocks the geochemical data are consistent with derivation of the basic magma s from small degrees of partial melting of garnet lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the indian plate beneath karakorum the spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene phlogopite plagioclase garnet amphibole followed by the precipitation of abundant alkali feldspar amphibole apatite quartz additionally assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz plagioclase xenocrysts and by the occasional presence of granitic xenoliths an apparent connection exists between magmatism and tectonism in the complex karakorum fault zone kfz it is suggested that during the neogene the strike slip kfz and some adjacent post metamorphic faults transiently behaved as extensional fault systems down to deep levels triggering ascent and emplacement of the k rich magma the subsequent re activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper baltoro glacier and k2 gasherbrum range relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the shaksgam valley area

a geological transect from kun lun to karakorum sinkiang china the western termination of the tibetan plateau preliminary note a geological geophysical expedition ev k2 cnr 1988 visited the area from west kun lun to karakorum k2 gasherbrum seven tectonic units including sedimentary magmatic and metamorphic rocks were distinguished in this area the northernmost are suggested to belong to the kun lun and qiangtang microplates the sedimentary sequence of shaksgam is proved to extend from the permian to the jurassic with carboniferous and cretaceous ages more doubtful this sequence shows intermediate affinities between the karakorum and the qiangtang the two southernmost units belong to the karakorum microplate the karakorum fault zone comprises a complex pattern of faults and thrusts with brittle deformation and uplifting of granitoid bodies

crustal structure interpreted from magnetic anomalies this review discusses publications during the last quadrennium 1987 1990 that used aeromagnetic data marine magnetic data satellite magnetic data and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies the publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies particularly in deep crustal magnetization exploration for hydrocarbons and inversion of marine magnetic anomalies interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard

reduced magnetization produced by increased methane flux at a gas hydrate vent abstract magnetic susceptibility measurements on near surface sediment cores from the north cascadia accretionary sedimentary prism show that seismic blanking or wipe out zones in the upper few hundred metres of sediments are associated with a prominent low magnetic susceptibility signature seismic blanking and low magnetization are both attributed to high upward methane flux within a vent zone as evidenced by the presence of massive gas hydrate within the cores sedimentological analysis of these cores also reveals the presence of authigenic pyrite within the areas of magnetic susceptibility lows this phenomenon is suspected to be produced by the reducing environment associated with the high upward methane flux and increased bacterial activity within the topmost sediments resulting in diagenesis of highly magnetic detrital minerals such as magnetite into nearly non magnetic pyrite these low magnetic susceptibility zones may produce magnetic anomalies with a magnitude of 10 35 nt near the seafloor such anomalies might be detected using high resolution near bottom magnetometers to provide a means of mapping zones of methane venting

stratigraphic framework of sediment starved sand ridges on a mixed siliciclastic carbonate inner shelf west central florida abstract seismic reflection profiles and vibracores have revealed that an inner shelf sand ridge field has developed over the past few thousand years situated on an elevated broad bedrock terrace this terrace extends seaward of a major headland associated with the modern barrier island coastline of west central florida the overall geologic setting is a low energy sediment starved mixed siliciclastic carbonate inner continental shelf supporting a thin sedimentary veneer this veneer is arranged in a series of subparallel shore oblique and to a minor extent shore parallel sand ridges seven major facies are present beneath the ridges including a basal neogene limestone gravel facies and a blue green clay facies indicative of dominantly authigenic sedimentation a major sequence boundary separates these older units from holocene age organic rich mud facies marsh which grades upward into a muddy sand facies lagoon or shallow open shelf seagrass meadows cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies ravinement or sudden termination of seagrass meadows the shelly sand facies grades upward to a mixed siliciclastic carbonate facies which forms the sand ridges themselves this mixed siliciclastic carbonate facies differs from the sediment on the beach and shoreface suggesting insignificant sediment exchange between the offshore ridges and the modern coastline additionally the lack of early holocene pre ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively radiocarbon dating has indicated that these sand ridges can form relatively quickly 1 3 ka on relatively low energy inner shelves once open marine conditions are available and that frequent high energy storm dominated conditions are not necessarily required we suggest that the two inner shelf depositional models presented open shelf vs migrating barrier island may have co existed spatially and or temporally to explain the distribution of facies and vertical facies contacts

the reshaping of the south west adriatic margin by cascading of dense shelf waters abstract the south west adriatic margin sam includes a steep and morphologically complex continental slope stretching about 600 km from the pelagosa sill to the otranto strait the margin is clearly dissected by submarine slides active fault systems e g the gondola deformation belt numerous shallowly incised and relatively straight canyons located south of bari canyon and a variety of large scale erosional and depositional features this area is seasonally impacted by dense shelf water forming in the north adriatic through wind forced winter cooling moving south along the western side of the basin and cascading across the south adriatic slope the area has been investigated through multibeam surveys integrated by high resolution seismic stratigraphic data resolving glacial and post glacial deposits this paper gives a detailed and comprehensive description of the sam seafloor morphology to document how the process of dense shelf water cascading concurs to a thorough restyling of the submarine landscape by interacting with the pre existing and markedly differentiated morphologies and sediment distribution we focus on depositional and erosional features such as giant sediment drifts down to 1200 m water depth muddy and sandy sediment waves comet marks against pre existing slide blocks furrow fields against steep slopes large scours at the shelf edge and large erosional moats adjacent to major morphological barriers the analysis of the bedform orientation and spatial distribution indicates that the downslope cascading bottom currents dominantly directed to the se encounter a straight upper slope oriented north south in the north and progressively more east west proceeding to the south as the slope orientation becomes more e w it also appears more dissected by small scale canyons active during glacial times in the latter area therefore the dense shelf waters follow a slope parallel direction almost perpendicular to the pre existing slope canyons as a consequence erosional furrows develop perpendicular to the canyon flanks and some of the canyon heads become disconnected from the main canyon downslope

off shelf fluxes across the southern adriatic margin factors controlling dense water driven transport phenomena abstract the northern adriatic sea is a basin where dense shelf waters form during winters if the following favorable conditions are attained high salinities mainly related to low river water discharge po river in primis during fall season and strong heat fluxes induced by cold and dry bora wind events blowing from north east extremely favorable conditions to northern adriatic dense waters naddw formation characterized winter 2012 when following several months of low po river runoff a strong event of cold air outbreak cao occurred from the end of january until mid february consequently the mean temperature of northern adriatic waters dropped to about 6 c and exceptional densities potential density anomaly locally exceeding 30 0 kg m 3 were reached the production and spreading mechanisms of dense water in the adriatic sea have been modeled by means of the coawst coupled ocean atmosphere wave sediment transport modeling system the model builds upon a high resolution 1 km spaced horizontal grid fully 3 d primitive equations hydrodynamic model coupled with a phase averaged wave model and sediment routines and is driven by simulated atmospheric forcings the dataset used to assess model outputs relies on the measurements acquired during the dedicated field campaigns operation dense water a set of two rapid response cruises carried out in southern adriatic during winter 2012 and by five mooring arrays deployed in the southern adriatic margin sam that allowed the continuous acquisition of temperature salinity currents and suspended matter samples results from the integrated data model approach suggest that the naddw propagates along the shelf to the southern basin following both a shallower vein and a deeper stream with a process characterized by a strong variability mean value of 0 31 sv with peaks rapidly growing in the first weeks after the cao up to 2 19 sv additionally coawst capability to couple different numerical models allowed to disentangle the relative importance of aspects on dense water generation mixing and spreading demonstrating how coupled runs can lead to volumes up to 50 larger with respect to uncoupled simulations additional light is shed on the transport pathways off the shelf and on possible sediment transport phenomena in the area in this benefiting from an unprecedented spatial resolution and a new bathymetry reflecting very high resolution data acquired via multi beam techniques although dense water propagation appears as a relatively large scale process involving the whole western side of the sam topographic local discontinuities and seabed slopes appear crucial in triggering descent and governing flow patterns the presence of suspended sediment along the water column despite not significantly influencing the overall fluxes across sections is responsible of pulling part of the veins towards deeper zones

a model for sand ridges on the shelf effect of tidal and steady currents the dynamics of sand ridges as observed on the innershelves and midshelves of various coastal seas are investigated within the framework of an idealized model these seabed undulations include shoreface connected sand ridges and tidal sand banks the new aspects in this study are the explicit incorporation of both steady and tidal currents a shelf with a sloping bottom and a statistical approach to describe the sediment transport during storms linear in the current and fair weather conditions cubic in the current the present model is used to gain understanding of the different ridge characteristics in different geographical regions this is done by analyzing the initial growth of small bottom perturbations which evolve on a basic state describing a longshore uniform flow over a reference topography it is found that basically five different bottom modes can be excited shoreface connected sand ridges coriolis ridges friction induced bars trapped tidal ridges and tidal sand banks their growth which is due to different physical mechanisms strongly depends on the weather climate and the geometrical characteristics of the shelf

continental shelf drift deposit indicates non steady state antarctic bottom water production in the holocene a late quaternary current lain sediment drift deposit over 30 m in thickness has been discovered on the continental shelf of east antarctica in an 850 m deep glacial trough off george vth land radiocarbon dating indicates that a period of rapid deposition on the drift averaging 290 cm kyr occurred in the mid holocene between about 3000 and 5000 yr before present slower rates of around 10 cm kyr during the past 0 3000 yr and from 5000 to about 13000 yr bp coincides with deposition of bioturbated ice rafted debris ird rich sandy mud under an energetic bottom current regime in contrast the mid holocene 3000 5000 yr bp sediments are fine grained laminated to cross laminated with minimal ird content and are contemporaneous with a period of warmer marine conditions with less sea ice production this pattern suggests that bottom currents were weaker than present day in the mid holocene and that the rate of dense bottom water production was reduced at that time this scenario is consistent with the hypothesis of non steady state rates of antarctic bottom water production through the holocene as recently proposed by broecker and his colleagues

sand bodies at the shelf edge in the gulf of lions western mediterranean deglacial history and modern processes abstract the outer continental shelf of the gulf of lions is covered by thick mainly regressive sand deposits a combination of seismic sedimentological and geochronological methods allows us to demonstrate that a veneer of transgressive sand bodies few m to less than 1 m thick reworks these deposits they take the form of sand ridges and transverse dunes that formed at different periods in fact the low gradient outer shelf of the gulf of lions displays a complete record of deglacial history including not only transgressive deposits that formed during sea level rise but also bedforms that still evolve under episodic high energy events that occur under more highstand conditions core lithology 14 c dates and regional sea level curve suggest that the formation of the sand ridges was favoured during a period of deceleration of sea level rise such as during the younger dryas event the dunes are part of a mobile carpet here u160 the deposition of this marine sand veneer is possibly related to the interplay between different factors that trigger the turning on off for bottom currents sand deposition transport on the outer shelf in fact the sands appear to have been reworked intermittently due to high energy conditions in shallow water depth currents wave regime and wind driven circulation as well as they form current ridges superimposed to the transgressive deposits in the westernmost part of the studied area at the bourcart canyon s head

tectonometamorphic evolution of the central karakorum baltistan northern pakistan abstract new structural and metamorphic data from the chogo lungma glacier area and basha valley enlighten the polyphased tectonometamorphic evolution of the metamorphic complex of karakorum a pre to early d1 event is defined by a metamorphic cleavage in the core of some zoned garnet and staurolite porphyroblasts the main tectonometamorphic event d1 is characterized by n110 e south vergent isoclinal folds associated with a metamorphic axial plane cleavage formed in a predominantly flattening regime of deformation it corresponds to a grt bt mu ky peak metamorphism m1 620 730 c and 7 5 11 kbar the d2 tectonometamorphic event corresponds to the development of several conical domes elongated striking n110 e to n140 e the s2 cleavage is seldom individualized as it usually corresponds to a reworking of s1 in some areas late evolution of d2 doming deformation is marked by a crenulation petrologically d2 is characterized by shearing and boudinage of m1 minerals and by development of sillimanite it corresponds to a decompressional evolution 7 5 down to 4 kbar with only slight changes in temperature a late event corresponds to large undulations and open folds which affect the d2 crenulation we propose here a model of vertical plus dextral extrusion of the middle crust to explain the dome structures in karakorum the steep pattern of the metamorphic p t path implies rapid exhumation rates and suggests that the different phases could be part of a continuum of deformation preliminary results by 40 ar 39 ar method give young cooling ages

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

fission track thermochronology of the wind river range wyoming evidence for timing and magnitude of laramide exhumation fission track analysis of wind river range basement rocks provides information about the timing magnitude and cooling that occurred in response to laramide uplift eighty samples were collected from precambrian rock along six traverses in the northern central and southern parts of the range over 5 km of elevation apatite fission track ages and track length data suggest that the range did not have a uniform thermal history during late mesozoic and cenozoic time zircon fission track ages are precambrian implying that these rocks have not been at temperatures higher than 200 c 9 10 km burial depth since precambrian time apatite ages from the northeastern and southwestern flanks of the range suggesst that cooling may have initiated in the wind river range by about 85 ma but was definitely occurring by 75 ma data from the green river lakes area and fremont peak in the northern part of the range indicate that cooling was occurring by 62 ma and was most rapid between 60 and 57 ma apparent rates of exhumation vary from 94 m m y to 246 m m y in this part of the range the central part of the range records this same period of rapid cooling but structural and topographic relief are not as great ages from the southern part of the range suggest that uplift and erosion may have been initiated earlier there but continued at much slower rates 34 m m y over a longer period of time than in the north samples from a drill hole in the central wind river range have apatite ages ranging from 37 ma to 86 ma and suggest a significant cooling event at approximately 42 ma involving nearly 2 km of the rock column timing magnitudes and apparent rates of exhumation have varied spatially in the wind river range

the impact of cascading currents on the bari canyon system sw adriatic margin central mediterranean abstract the bari canyon system bcs is a peculiar erosional depositional feature characterised by two main almost parallel conduits emanating from a broad crescent shaped upper slope region when viewed in cross sections parallel to the margin bcs appears markedly asymmetric with a right hand southern side that is higher and steeper about 800 m in relief and more than 30 steep the left hand side of the canyon is instead much smoother as a consequence bottom currents flowing along the slope from the north enter the canyon and interact with its complex topography leading to preferential deposition on the up current side of pre existing morphological relief where mass failure deposits generate morphologic relief outside the canyon sediment is preferentially deposited up current n ward bcs includes three main ew oriented sediment conduits canyon c to the south channel b in the central area and moat a in the north channel b shows a well developed levee deposit on its right hand side and appears markedly straight and erosional on the upper slope the deepest portion of channel b is substantially abandoned and draped but still shows a subdued thickening of the draped unit north and up current of pre existing morphologic relief confirming the impact of along slope flowing currents canyon c is flanked by erosional walls all the way to the basin floor where deep sea furrows develop with a nw se orientation today dense water formation in the adriatic is seasonally modulated and displays a significant variability on inter decadal scales dense water formation during glacial intervals was likely different from the modern because most of the north adriatic shelf was subaerially exposed and the deep water mixing in the south was likely reduced as suggested by paleoceanographic reconstructions the growth patterns of bcs since the lgm are characterised by concurrent erosion of the upper portion of channel b and of the lower portion of canyon c it is possible that flows through the straight narrow and steep upper segment of channel b spill over its right hand levee in ca 600 m water depth where the relief of levee b on the channel floor is minimal and enter canyon c where substantial erosion takes place in this view the upper portion of canyon c where hard grounds and corals are encountered is flushed by currents characterised by reduced turbidity while the lower part of canyon c collects additional flows from upper channel b

interactions among adriatic continental margin morphology deep circulation and bedform patterns abstract within the mediterranean region the adriatic basin is one of the key sites for the formation and spreading of dense shelf water once formed in the northern shallow region as a response to strong wintry cold air outbreaks dense water masses move southeastwards as bottom hugging gravity currents eventually reaching the south adriatic continental margin a fraction of the dense water mass is thus intercepted by the shelf break whence it flows down the continental slope driven by its negative buoyancy and interacting with ambient water and seafloor topography this process generates a wide variety of dynamics and morphological features such as erosional moats furrows giant comet marks sediment drifts and sediment waves in this study we merge the outcomes of a state of the art wave ocean coupled numerical model with the geological evidence from the analysis of southern adriatic bedform patterns the model was run to reproduce an exceptional cold event that occurred in winter 2012 and benefits from a high resolution bottom topography produced from data collected during recent bathymetric surveys model results allow the identification of flow pathways along and across the continental shelf and slope with particular emphasis on the role of large scale margin geometry in controlling morphodynamic processes and its implications in terms of resolution requirements for modelling purposes although modelled overall water fluxes and basin renewal ratios are mostly controlled by regional circulation and large scale morphology local topographic features and singularities appear crucial in triggering concentrating and modulating bottom currents dynamics and sediment transport towards the south adriatic pit as well as enhancing mixing and entrainment of ambient water as long as this degree of information is provided within the bathymetric constraint modelled hydrodynamic pathways in the study case are consistent with observed bedform morphology and their spatial pattern for different zones in the continental slope temporal variability of the flows has been investigated permitting to disentangle the relative contribution of dense water cascading and background circulation at the basin and sub basin scale in controlling bedform dynamics this study gives a first quantitative insight on the hydrodynamic mechanisms responsible for south adriatic margin reshaping suggesting a modelling approach to the interpretation of the high resolution bathymetric and stratigraphic data made available by recent survey technologies

a contourite depositional system along the uruguayan continental margin sedimentary oceanographic and paleoceanographic implications abstract for the first time a multidisciplinary approach to evaluate the influence of bottom currents in the uruguayan continental margin is presented bathymetric data and multichannel 2d and 3d seismic reflection profiles were used to construct a morphosedimentary map to interpret and decode sedimentary and oceanographic processes along the uruguayan continental margin based on these results an extensive contourite depositional system on the margin is described which contains an impressive array of large erosive depositional drifts and mixed terrace features which have been generated primarily by the near bottom flows associated with water masses of antarctic and subantarctic origin from the eocene oligocene boundary up to present time the long term influence of water masses from higher southern latitudes in combination with down slope sedimentary processes have strongly controlled the overall margin morphology most of the features described here were formed during the middle late miocene epoch due to paleoceanographic shifts that include the arrival of antarctic intermediate water along the margin which in combination with deeper antarctic bottom water are fundamental in the margin evolution in combination with quaternary climatic and eustatic changes in sea level fluctuations of the brazil malvinas confluence influenced subsequently glacial and interglacial stages as recognized in sedimentary features defined here these paleoceanographic changes controlled the sedimentary stacking pattern and the locations of high amplitude reflections along the contourite terraces which could be associated with sandy deposits a more detailed understanding of the margin will improve interpretations of variations in the south atlantic subtropical gyre and further constrain general climatic and ocean circulation models

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

anatomy of a compound delta from the post glacial transgressive record in the adriatic sea abstract on the mediterranean continental shelves the post glacial transgressive succession is a complex picture composed of seaward progradations related to sea level stillstands and or increased sediment supply to the coasts and minor flooding surfaces associated with phases of enhanced rates of sea level rise among late pleistocene examples major mid shelf progradations have been related to the short term climatic reversal of the younger dryas event a period during which the combination of increased sediment supply from rivers and reduced rates of sea level rise promoted the formation of progradations up to tens meter thick while the documentation of coastal and subaqueous progradations recording the younger dryas interval is widely reported in literature the model of compound progradation within transgressive deposits has not yet been proposed here we present the documentation of a deltaic system where both delta front sands and related fine grained subaqueous progradations prodeltaic to shallow marine have been preserved the paleo gargano compound delta pgcd formed offshore the modern gargano promontory southern adriatic sea and is composed of a coastal coarse grained delta of reduced thickness and a muddy subaqueous clinoform up to 30 m thick the pgcd probably the first worldwide documentation of a compound delta within the transgressive record provides the opportunity to investigate the processes controlling the formation of a compound delta system during an overall sea level rise and the factors that allowed its preservation the finding of the pgcd provides the opportunity for a comparison with modern worldwide compound systems

diagenetic alteration of permian strata at oil fields of south central oklahoma usa abstract many oil fields in south central oklahoma including cement velma carter knox and eola have a chimney of altered rock within slightly deformed permian red beds the chimneys occur above and within the oil reservoirs where the chimneys crop out the altered rock is commonly well exposed the alteration consists chiefly of removal of haematite from sand grains cementation of sandstone by pyrite marcasite calcite and dolomite and at the cement field replacement of a bed of gypsum by calcite the total volume of these late diagenetic minerals is vast many hundreds of millions of tons the diagenetic alteration of red beds occurred when crude oil and abundant natural gas migrated vertically from major anticlines in pennsylvanian and older strata into the gently folded gypsum bearing permian red beds during cementation the rush springs sandstone in the cement field had a high porosity 40 50 which suggests that here alteration occurred before substantial burial in the red beds anaerobic bacteria mediated the oxidation of ch 4 and possibly alkanes within crude oil to co 2 and simultaneously reduction of so 4 4 anions to h 2 s the cementation resulted when carbonate species reacted with ca 2 and mg 2 and the bleaching resulted when sulphide species reacted with fe 3 and fe 2 the evidence for the bacterially mediated alteration is the anomalously low isotopic values for carbon and sulphur carbonate minerals have 13 c values as low as 39 2 0 and most values are less than 15 0 o sulphide minerals have 32 s values as low as 37 9 and most values are less than 8 5 0

causes and spatial distribution of anomalous magnetization in hydrocarbon seepage environments in diagenetic environments containing hydrocarbons the most important magnetic minerals formed appear to be magnetite and pyrrhotite whereas the most important magnetic mineral dissolved or replaced is hematite hence hydrocarbon seepage and migration may result in positive absent or negative anomalous magnetization magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending on the amounts of magnetite and pyrrhotite formed relative to the amounts of hematite destroyed where anomalous magnetization is formed by hydrocarbon seepage the magnetic contrasts are located in relatively reducing geochemical plumes such plumes are located above leaking subsurface hydrocarbon accumulations if buoyancy is the predominant driving force for hydrocarbons commonly however migration of the escaping hydrocarbons is dominated by advection hydrocarbon seepage therefore may be vertical or may have any direction other than vertical depending on the position of the leaking hydrocarbon accumulation in the prevailing flow system and on the distribution of high permeability pathways such as carrier beds and faults in these cases magnetic contrasts are deflected or displaced and they are not likely to be vertically above the hydrocarbon source anomalous magnetization magnetic contrasts has been documented from some hydrocarbon seepage environments and can be used for hydrocarbon exploration in association with other surface exploration methods similar magnetic contrasts should also be detectable in core and could be used for evaluation of subsurface proximity to hydrocarbon traps the magnitude and spatial distribution of such magnetic contrasts whether at the surface or in the subsurface depend on geochemical microbial geophysical sedimentologic and hydrogeologic processes these factors must be taken into consideration in aeromagnetic and ground based prospecting for hydrocarbons in particular the use of anomalous magnetization as an exploration tool should always be accompanied by a hydrogeologic study the results of this study suggest that magnetic contrasts could also be used in environmental studies for example to detect hydrocarbons leaking from storage tanks or waste disposal sites on the other hand magnetic contrasts may be generated also by natural and anthropogenic processes that have no genetic relationships to hydrocarbons consequently anomalous magnetization may or may not be genetically related to natural or anthropogenic hydrocarbon accumulations

metamorphic evidence for an inverted crustal section with constraints on the main karakorum thrust baltistan northern pakistan abstract the shyok suture zone separates rocks in the asian plate from rocks in the kohistan ladakh island arc in baltistan this suture has been reactivated by the late break back main karakorum thrust mkt the p t histories of metamorphic rocks both north and south of the mkt have been determined in an effort to place constraints on the tectonic history of this zone the terranes north and south of the mkt have different unrelated metamorphic histories rocks from the kohistan ladakh island arc south of the mkt have undergone a static low p 2 4 kbar c 500 c thermal metamorphism the p t paths and metamorphic textures of these rocks are consistent with metamorphism due to emplacement of plutonic rocks into the island arc this metamorphism pre dates folding and deformation of these rocks rocks in the karakorum metamorphic complex north of the mkt have experienced a complex deformational and metamorphic history prograde metamorphic isograds have been deformed by subsequent south verging folding and by gneiss dome emplacement however decompression metamorphic reactions occurred during nappe emplacement higher pressure rocks are associated with higher level nappes creating an inverted pressure metamorphic sequence 8 9 kbar rocks over 5 6 kbar rocks there is little variation in temperature with structural level 550 625 c these two different terranes have been juxtaposed after metamorphism by the late south directed mkt

high resolution mapping of bora winds in the northern adriatic sea using synthetic aperture radar 1 the adriatic sea is regularly subjected to strong bora wind events from the northeast during winter the events have a strong effect on the oceanography in the adriatic driving basin scale gyres that determine the transport of biogeochemical material and extracting large amounts of heat the bora is known to have multiple surface wind jets linked to the surrounding orography and have been the focus of many studies but it has not been possible to describe the detailed spatial structure of these jets by in situ observations using high resolution spaceborne radarsat 1 synthetic aperture radar sar images collected during an active bora period 23 january 16 february 2003 we created a series of high resolution 300 m maps of the wind field the obtained winds show reasonable agreement with several in situ wind observations with an rms wind speed error of 3 6 m s slightly higher than the 2 3 m s errors reported in previous studies these sar images reveal the spatial structure of the bora wind in unprecedented detail showing several new features in the senj region of croatia several images show rhythmic structure with wavelengths of 2 3 km that may reflect bora pulsation seen at fixed locations by previous investigators along the italian coast several images show a wide 20 30 km band of northwesterly winds that abruptly change to the northeasterly bora winds further offshore meteorological model results suggest that these northwesterly winds are consistent with those of a barrier jet forming along the italian apennine mountain chain

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

exhumation history of the west kunlun mountains northwestern tibet evidence for a long lived rejuvenated orogen abstract how and when the northwestern tibetan plateau originated and developed upon pre existing crustal and topographic features is not well understood to address this question we present an integrated analysis of detrital zircon u pb and fission track double dating of cenozoic synorogenic sediments from the kekeya and sanju sections in the southwestern tarim basin these data help establishing a new chronostratigraphic framework for the sanju section and confirm a recent revision of the chronostratigraphy at kekeya detrital zircon fission track ages present prominent triassic early jurassic 250 170 ma and early cretaceous 130 100 ma static age peaks and paleocene early miocene 60 21 ma to eocene late miocene 39 7 ma moving age peaks representing source exhumation triassic early jurassic static peak ages document unroofing of the kunlun terrane probably related to the subduction of paleotethys oceanic lithosphere in combination with the occurrence of synorogenic sediments on both flanks of the kunlun terrane these data suggest that an ancient west kunlun range had emerged above sea level by triassic early jurassic times early cretaceous fission track peak ages are interpreted to document exhumation related to thrusting along the tam karaul fault kinematically correlated to the main pamir thrust further west widespread middle late mesozoic crustal shortening and thickening likely enhanced the early mesozoic topography paleocene early eocene fission track peak ages are presumably partially reset limited regional exhumation indicates that the early cenozoic topographic and crustal pattern of the west kunlun may be largely preserved from the middle late mesozoic the main pamir tam karaul thrust belt could be a first order tectonic feature bounding the northwestern margin of the middle late mesozoic to early cenozoic tibetan plateau toward the tarim basin late oligocene early miocene steady exhumation at a rate of 0 9 km myr is likely related to initial thrusting of the tiklik fault and reactivation of the tam karaul thrust thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the west kunlun orogen at this time this episode of exhumation and uplift associated with magmatism across western tibet is compatible with a double sided lithospheric wedge model primarily driven by breakoff of the indian crustal slab accelerated exhumation of the mountain front at a rate of 1 1 km myr since 15 ma supports active compressional deformation at the margins of the northwestern tibetan plateau we thus propose that the west kunlun mountains are a long lived topographic unit dating back to triassic early jurassic times and have experienced middle late mesozoic to early cenozoic rejuvenation and late oligocene miocene expansion

late miocene to early pliocene tectonometamorphism and cooling in south central karakorum and indus tsangpo suture chogo lungma area ne pakistan abstract the chogo lungma glacier is located at the northeastern edge of the nanga parbat haramosh spur where the ladakh kohistan arc formations are laminated between the karakorum and high himalaya units in the karakorum metamorphic complex metamorphism of a pelitic and granitic protolith took place in two tectonometamorphic phases isoclinal folds 700 c 1 gpa were followed by doming 630 700 c 400 750 mpa in a compressional climax lemennicier et al 1996 one hornblende and two biotites associated to syntectonic magmatism with mantle affinities contemporaneous of doming give cooling ages between 3 0 and 7 7 ma a muscovite from an orthogneiss in the karakorum gives an age of 5 ma fast cooling 70 110 k ma has prevailed ever since two muscovites from a foliated intrusion emplaced on the thrust of the ladakh kohistan arc over the high himalaya crystallines have ages of 8 2 and 9 ma despite being collected in the same locality dating the thrust at just before 9 ma all this points to a coeval tectonometamorphism and thrusting in that area during the tortonian

observations on a bottom vein of dense water in the southern adriatic and ionian seas we discuss the motion and spreading of a bottom vein of very dense marine water which originates 29 4 in winter through cooling and evaporation processes resulting from the violet bora wind blowing over the shallow north adriatic sea into the deepest layers of the southern adriatic and ionian seas eastern mediterranean basin our analysis is focused on the peculiar physical processes that control this bottom flow we first describe the vein motion in the southern adriatic sea in which this current follows approximately the isobaths in partial accordance with the conservation of potential vorticity and the main mixing process of dense water with levantine intermediate water occurring in an offshore oriented canyon near bari this canyon causes a deepening and flattening of the original vein of dense water such that downstream the water can be observed only on the otranto sill at depths of 800 m with 29 25 the subsequent flow in the ionian sea follows approximately the 900 m isobath in the gulf of taranto and along the calabrian and east sicilian coasts in agreement with the results of smith s and killworth s theoretical models of steady motion of density driven currents over a regular slope in a rotating system for stratified fluids

sand wave migration predictor based on shape information 1 migration of offshore seabed waves which endangers the stability of pipelines and communication cables is hard to measure the migration rates are small compared to the measurement errors here sandwave migration rates are determined from the change in the crest position deduced from long time series of bathymetric echo sounding data the crests are identified as local extremes in a bathymetric profile after low pass filtering this approach is applied to both two dimensional data and to profiles along pipelines a consistent migration rate of several meters per year is found a strong correlation between the sandwave shape and the migration rate is translated in a migration predictor the predictor assumes that the sandwaves migrate in the direction of the steepest slope following a quadratic relation with the asymmetry furthermore it is included that longer waves travel faster but higher waves travel slower the predictor is calibrated against data from nine areas and validated using three additional areas an error analysis using markers shows that the error of the predictor is small compared to the noise in the individual crest position observations

influence of seabed slope and coriolis effects on the development of sandbanks near headlands the mechanism responsible for asymmetric sediment accretion around an idealized symmetrical headland is clearly the coriolis force what is not evident however is how the coriolis force manifests itself in the headland dynamics to promote asymmetric depositional patterns in this study patterns of scour and accretion topographic and advective vorticity bed load and suspended load transport pathways around a theoretical coastal headland are examined previous studies have emphasized the contribution of the coriolis force to a secondary flow mechanism tidal stirring this investigation provides evidence to suggest that secondary flow dynamics are not significant in sandbank generation associated with headlands it further demonstrates the direct contribution of the coriolis force in reinforcing inertial terms near headland scour and asymmetric accretion examination of the vorticity balance throughout the simulations reveals that high levels of slope induced topographic vorticity act in direct opposition to advective vorticity near a headland tip it is also demonstrated that the coriolis force manifests itself in the production of vorticity this has been used in the investigation as a means of detecting the sensitivity of the flow to the coriolis force in regimes where advective and topographic vorticity production is very similar flat bed cases it is found that bed evolution is more sensitive to the coriolis force in regimes where topographic vorticity clearly dominates the vorticity balance in seabed slope case the influence of the coriolis force becomes less important

late paleozoic remagnetization and its carrier in the trenton and black river carbonates from the michigan basin paleomagnetic study of subsurface samples of the upper ordovician trenton and black river limestones collected from six industrial wells in the southern part of the michigan basin yields a well clustered characteristic direction mean dec inc of 170 6 10 9 alpha 95 7 6 circ after rotation of random declinations by aligning a present day field overprint with geographic north the corresponding paleomagnetic pole at 52 4 n 111 0 e is similar to those of the remagnetized carbonates in ontario and new york state suggesting that the michigan formations were also remagnetized in the late paleozoic rock magnetic characterizations suggest that the characteristic magnetization is carried by single and pseudosingle domain magnetite grains very fine rounded single crystal magnetite grains believed to be products of chemical precipitation observed by scanning and scanning transmission electron microscope sem stem are inferred to be the carrier of the remagnetization paired carbon isotope analys

magnetic characterization of oil sands at osmington mills and mupe bay wessex basin uk this study combines magnetic experimentation and geochemical analysis on oil sands from osmington mills and mupe bay wessex basin uk to investigate the possibility of a relationship between hydrocarbons and magnetic mineralogy removal of hydrocarbons by chemical extraction was conducted to allow comparison of 1 oil sands and 2 cleaned sands detailed magnetic analysis including low temperature and high temperature experimentation revealed that all but one sample was dominated by siderite identified by the neel transition at 37 38 k as well as containing large grains of multidomain magnetite verwey transition 110 k and hematite morin transition 250 k scanning electron microscopy and energy dispersive x ray analysis confirmed the presence of iron oxides in particular framboids 500 nm 45 mm in diameter probably magnetite hysteresis parameters showed distinct grouping of oil sands compared to their clean counterparts and a negative linear regression in log space was observed r 1 4 0 7 between the percentage of extractable organic matter and magnetic susceptibility these results suggest a relationship exists between magnetic minerals and the alteration of oil due to biodegradation which is not yet fully understood possible mechanisms are suggested to be due to anaerobic bacteria or the transportation of the oil as it migrates through the host rock aeromagnetic surveys have established a general connection between magnetic anomalies and hydrocarbon accumulations on a regional scale but with a large degree of ambiguity e g donovan et al 1979 reynolds et al 1991 gay 1992 leblanc morris 1999 several major remagnetizations worldwide e g mccabe et al 1984 1987 elmore leach 1990 suk et al 1993 garner cioppa 2006 are associated with hydrocarbon provinces and anomalous aeromagnetic signals this is thought to be due to chemical alteration of minerals as fluids such as hydrocarbons migrate through the host rock but no definitive mechanism has been determined recent research by several groups has tried to identify the magnetic minerals themselves for hydrocarbon identification e g liu et al 1998 aldana et al 1999 diaz et al 2000 aldana costanzoalvarez 2003 ivakhnenko potter 2004 costanzo alvarez et al 2006 liu et al 2006 rijal et al 2010 aldana et al 2011 guzman et al 2011 rijal et al 2011 for example costanzo alvarez et al 2000 and liu et al 2006 conducted rock magnetic measurements on producing and nonproducing wells and identified anomalous values of magnetic susceptibility x at certain depth intervals within both oil producing and non producing wells characterized by a low coercivity mineral probably magnetite aldana et al 1999 categorized these anomalies into two types 1 fe rich spherical aggregates of authigenic origin as seen by scanning electron microscopy sem analysis only found in producing wells costanzo alvarez et al 2000 aldana costanzo alvarez 2003 and most likely magnetite and 2 characterized by magnetite and hematite but no association with spherical aggregates present in both non producing and producing wells costanzo alvarez et al 2000 aldana costanzo alvarez 2003 liu et al 2006 also found variances between oil producing and non oil producing layers using basic hysteresis parameters saturation remanence magnetization mrs saturation magnetization ms coercivity bc and remanent coercivity bcr the results showed that within an oil bearing layer its x ms and mrs values were between 24 and 36 times higher than the corresponding layer obtained from a dry well with maghemite siderite and pyrite contributing to the enhanced magnetic signature another study by ivakhnenko potter 2004 investigated the magnetic susceptibility of crude oils refined oil fractions and formation waters from sites worldwide it was found that all the fluids were diamagnetic but had distinct differences in magnetic susceptibility for example the crude oils were more negative than formation waters from the same location the physical and chemical properties of the oils appeared to correlate with the magnetic susceptibility such as gravity metal concentration density and api american petroleum index from elmore r d muxworthy a r aldana m m mena m eds 2012 remagnetization and chemical alteration of sedimentary rocks geological society london special publications 371 http dx doi org 10 1144 sp371 6 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics geological society london special publications published online june 27 2012 as doi 10 1144 sp371 6

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

eustatic and tectonic control on deposition and lateral variability of quaternary regressive sequences in the adriatic basin italy abstract during the late pleistocene sea level variations related to glacio eustatic cycles induced the deposition of four regressive sequences on the western continental shelf of the adriatic basin the four sequences are bounded by erosion surfaces that formed during sea level fall sub aerial exposure of the shelf and subsequent sea level rise and erosional reworking the sequences and the erosion surfaces at their top numbered 1 4 top down are correlated on distances in the order of 300 km in the central and south adriatic core control on deposits of the most recent depositional sequence sequence 1 suggests that each sequence records a fourth order ca 100 120 kyr cyclicity of sea level change within each depositional sequence progradational units representing highstand to forced regression are dominant whereas transgressive deposits are absent or reduced in both thickness and lateral extent sequences are thus referred to as regressive sequences deposition during sea level fall occurred on an overall subsiding shelf through the dispersal of fine grained sediment supplied from the adjacent alpine and apennine chains this resulted in stacked forced regression deposits thick enough to survive complete removal during subsequent phases of sub aerial and marine erosion erosion and or non deposition were enhanced only where tectonic uplift and morphological highs further reduced the remaining accommodation space resulting in local thickness reduction or in the non preservation of the regressive sequences at larger scale thickness variability and depocenter distribution north and south of the gargano promontory an uplifted block bisecting the adriatic foreland reflect differential deposition and preservation of regressive deposits as a function of contrasting tectonic setting and resulting physiography of the shelf and upper slope

sediment starved sand ridges on a mixed carbonate siliciclastic inner shelf off west central florida high resolution side scan mosaics sediment analyses and physical process data have revealed that the mixed carbonate siliciclastic inner shelf of west central florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms the sand ridges mostly oriented obliquely to the shoreline trend extend from 2 km to over 25 km offshore they show many similarities to their well known counterparts situated along the us atlantic margin in that both increase in relief with increasing water depth both are oriented obliquely to the coast and both respond to modern shelf dynamics there are significant differences in that the sand ridges on the west central florida shelf are smaller in all dimensions have a relatively high carbonate content and are separated by exposed rock surfaces they are also shoreface detached and are sediment starved thus stunting their development morphological details are highly distinctive and apparent in side scan imagery due to the high acoustic contrast the seafloor is active and not a relict system as indicated by 1 relatively young ams 14c dates 1600 yr bp from forams in the shallow subsurface 1 6 meters below seafloor 2 apparent shifts in sharply distinctive grayscale boundaries seen in time series side scan mosaics 3 maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation 4 sediment textural asymmetry indicative of selective transport across bedform topography 5 morphological asymmetry of sand ridges and 2d dunes and 6 current meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded although larger sand ridges are found along other portions of the west central florida inner shelf these smaller sand ridges are best developed seaward of a major coastal headland suggesting some genetic relationship the headland may focus and accelerate the n s reversing currents an elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf allowing them to be more easily influenced by currents and surface gravity waves tidal currents storm generated flows and seasonally developed flows are shore parallel and oriented obliquely to the nw se trending ridges indicating that they have developed as described by the huthnance model although inner shelf sand ridges have been extensively examined elsewhere this study is the first to describe them in a low energy sediment starved dominantly mixed siliciclastic carbonate sedimentary environment situated on a former limestone platform

spatial variation in exhumation rates across ladakh and the karakoram new apatite fission track data from the eastern karakoram nw india characterization of low temperature cooling histories and associated exhumation rates is critical for deciphering the recent evolution of orogenic regions however these may vary significantly over relatively short distances within orogens it is pertinent therefore to constrain cooling histories and hence exhumation rates across major tectonic boundaries we report the first apatite fission track ages from the karakoram fault zone in the eastern karakoram range which forms part of the western margin of the tibetan plateau ten samples from elevations of 3477 4875m have apatite fission track dates from 3 3 0 3 ma to 7 4 1 1ma the ages correspond to modeled average erosional exhumation rates of 0 67 0 27 0 18mm yr across the eastern karakoram the results are consistent with a trend northward from the indus suture zone across the ladakh terrane and into the karakoram in which tectonic uplift associated with crustal thickening increases toward the north raising elevation and promoting glaciation and generation of extreme relief as a result erosion and exhumation rates increase south to north present day precipitation on the other hand varies little within the study area and on a larger scale decreases southwest to northeast across this portion of the orogen the eastern karakoram results highlight the diverse patterns of exhumation driven by regional variations in tectonic response to collision along the western margin of tibet

dynamics of particles along the western margin of the southern adriatic processes involved in transferring particulate matter to the deep basin abstract the southern adriatic is an area of dense shelf water dsw cascading and open ocean convection the impact of dsw cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years in order to improve our knowledge on the interannual variability of the dsw cascading with the ultimate goal to understand timing of dsw formation and transport as well as the cascading process its variability in intensity and duration and the ultimate impact of the dense water on the deep sea in march 2009 we deployed an instrumented mooring in a field of sediment waves 860 m depth located down current to the bari canyon in march 2010 a second mooring was installed in the northern channel of the canyon winters 2009 2010 and 2011 were mild and particularly wet and the po river discharge remained relatively high throughout the whole winter hence we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the adriatic shelf by contrast in winter 2012 the north adriatic experienced a severe cold wave with ne bora winds and reduced fresh water input these weather conditions allowed the formation of extremely dense shelf water three additional moorings were quickly deployed during this cold event in the southern adriatic sea to investigate the spatial variability of particle and organic matter fluxes exiting from the adriatic continental shelf under the influence of a strong dsw cascading event slow near bottom currents never exceeding 40 cm s 1 were recorded between march 2009 and february 2012 water temperatures depicted minor negative shifts total mass fluxes tmfs were low annual avg 1 7 2 8 g m 2 d 1 and 0 3 0 6 g m 2 d 1 in the canyon and in the sediment wave field respectively and peak values 6 8 g m 2 d 1 but showed significant seasonal and interannual variability fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth mass flux peaks during the 2112 dsw cascading were up to 5 times higher than the peaks of previous years up to 18 70 g m 2 d 1 with a spatial variability mainly driven by the localized pathways of dsw cascading in the canyon near bottom currents exceeded 70 cm s 1 and temperature dropped to 12 2 c while current speeds were high also at 1200 m depth 60 cm s 1 in the moat surrounding the dauno seamount surprisingly mass flux peaks occurred from the 16th february to the 1st of march 3 4 weeks ahead of the usual dsw occurrence suggesting an early arrival of the dsw the deep dsw cascading was the main process driving the particle transfer across the southern adriatic margin during late winter spring 2012 mooring data showed a nw se gradient of temperature and kinetic energy from upslope to basin floor indicating slope transverse flow modulated by local obstruction caused by the rugged seafloor topography bari canyon is one of the sites of dsw flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials this approach allowed evaluation of additional mechanisms of particle transport e g open ocean convection storm driven downward transport shallow dense water cascading that are particularly relevant in years when the dsw formation is less vigorous and cascading processes are sluggish the small amplitude of total mass flux peaks the weak currents and the relatively high and constant temperatures recorded during 2009 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid water nepheloid layer triggered in turn by a shallow cascading of not particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy thus the intensity of dsw cascading shallow vs deep plays a first order control on the particulate fluxes through the western margin of the southern adriatic while storm induced sediment transport can occasionally be relevant too

impact of dense bottom water on a continental shelf an example from the sw adriatic margin abstract dense shelf waters have been recognised as a key factor in transporting sediment and organic matter across continental slopes however the effect of their circulation on continental shelves is still overlooked the adriatic sea is one of the areas in the mediterranean where dense shelf water forms and flows as a bottom hugging gravity current along the continental margin a fraction of this dense water passes beyond the shelf break and flows downslope through cascading while a large lighter and faster portion remains on the shelf with a principal vein flowing between 80 and 120 m water depth this paper presents the 3d shape internal architecture and sediment facies of a variety of large scale sedimentary features detected on the continental shelf and at the shelf edge between 50 and 300 m water depth these features include giant comet marks large flute shaped scours muddy sediment waves very large dunes with superimposed bedforms active and relict sand ridges and shelf edge contourites both erosional and depositional features show an overall internal geometry and orientation consistent with water masses flowing southward and are located where flows become accelerated by topographic constraints and deviated by the curvature of the shelf edge in this study the morphology and seismic stratigraphic structure of large scale bedforms are investigated in an effort to place constraints on bedform evolution and preservation especially as predictive tools for sand resource management and to bring new evidence of the interaction between unidirectional hydrodynamic processes and seafloor dynamics on the shelf