marine controlled source electromagnetics with geothermal purposes central gulf of california mexico abstract we acquired and interpreted data from two controlled source electromagnetic profiles in the gulf of california off the coast of santa rosalia baja california sur mexico this area is interesting from the geothermal point of view due to its proximity to the guaymas basin the la reforma caldera and the las tres virgenes volcano the first with intense submarine hydrothermal manifestations and the final one with a geothermal field in production the survey consisted of the deployment of 10 ocean bottom electromagnetic receivers distributed along two 14 km long profiles these sensors recorded the two horizontal components of the electric and magnetic fields the source consisted of a horizontal 200 m electric dipole towed behind the vessel the processed data were inverted to estimate the subsurface distribution of electrical resistivity using a finite element two dimensional multi frequency program resulting in adequate fits between observed and calculated data to estimate how well the models are constrained by the data sensitivity tests were applied to the models the tests were based on the jacobian matrix and a perturbation analysis of selected features of the model they show that the model in its central part is well constrained by the data down to a depth of about 2 5 km with the perturbation approach 16 resistivity features out of the 19 tested turned out to be well constrained by the data the estimated resistivity distribution was compared with the information obtained from other geophysical methods bathymetry gravity and 2d multi channel seismic reflection resulting in reasonably good correlations between them for the first profile we find a remarkable similarity with the current conceptual models proposed in the literature for a volcanic geothermal system where an altered conductive clay cap overlays another with higher electrical resistivity the second profile shows agreements with anomalies detected with echo sounder bathymetry suggesting the existence of hydrothermal manifestations

facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

contourite erosive features caused by the mediterranean outflow water in the gulf of cadiz quaternary tectonic and oceanographic implications abstract contourite depositional systems have been the focus of much recent research but still relatively little is known about contourite erosive features and their associated processes based on multibeam bathymetry side scan imagery and different resolution seismic records a detailed description and classification of the major erosive submarine valley features of the contourite depositional system of the gulf of cadiz middle slope is presented for the first time four types of erosive features have been differentiated including contourite moats contourite channels marginal valleys and large isolated furrows and interpreted in terms of their tectonic and oceanographic implications during the quaternary the study of the distribution and characteristics of erosive features is essential to better understand the present and past interaction of the mediterranean outflow water mow with the middle slope seafloor and allows us to propose a new and more precise scheme for the mow circulation patterns this scheme includes a main along slope circulation responsible for the excavation of the contourite moat and channels and a secondary down slope circulation responsible for the erosion of marginal valleys and isolated furrows three evolutionary stages have been observed in the development of the erosive system during the quaternary that can be related to changes in the distribution and splitting of the mow as a consequence of the segmentation of the ne sw diapiric ridges by neotectonic effects 1 early pleistocene to mid pleistocene linear diapiric ridges 2 mid pleistocene to late pleistocene diapiric reactivation and 3 late pleistocene to holocene main recent phase of diapiric ridges segmentation and rotation this study provides important regional clues for establishing the evolution of the erosive features in relation with neotectonic effects and represents a good example of the potential of erosive features as evidences for the reconstruction of the paleoceanography and recent tectonic changes

description of a contourite depositional system on the demerara plateau results from geophysical data and sediment cores the demerara plateau belonging to the passive transform margin of french guiana was investigated during the iguanes cruise in 2013 the objectives of the cruise were to explore the poorly known surficial sedimentary column overlying thick mass transport deposits as well as to understand the factors controlling recent sedimentation the presence of numerous bedforms at the seafloor was observed thanks to newly acquired iguanes bathymetric high resolution seismic and chirp data while sediment cores allowed the characterization of the deposits covering the mass transport deposits modern oceanographic conditions were determined in situ using mooring monitoring over a 10 month period our data indicate the presence of a contourite depositional system along the demerara plateau most likely related to bottom current activity of the north atlantic deep water nadw however at the regional scale large longitudinal waves parallel the nadw flow their shape and orientation seem to be inherited from interactions between bottom currents and paleomorphologies expressed at the top of mass transport deposits their evolution is possibly driven by the intensity of bottom current activity that might have changed over time overall this work presents an integrated approach combining seismic and sedimentological evidence to study the processes at the origin of contourite formation in the demerara plateau other regional factors such as local slope values and slope instability also control sedimentation

contour current accumulation off the vema channel mouth southern brazil basin pattern of a contourite fan abstract in the southern part of the brazil basin 3 5 khz echosounding reveals the existence of a cone shaped sedimentary accumulation 4480 m depth this sediment body is interpreted as deposited by the antarctic bottom water currents aabw at the downstream exit of deep valleys cutting through the rio grande rise it is located between two major channels that prolonged northeastward the valleys into the brazil basin the vema channel in the southeast and the sao paulo abyssal gap in the northwest as a consequence most of the aabw flow is channelized in two branches deposition of the current transported particles occurs below the shear zone which takes place between the two branches the quaternary sediments consist of silty clayey muddy contourites associated with manganiferous deposits the accumulation is built by lateral migration of secondary channels and by lateral construction of lobes between the two major channels which are both well stabilized on account of a morphotectonic control on their location the entire sediment body progrades upward and downstream toward the northeast on the basis of morphological seismic and lithological arguments we would like to propose the name of contourite fan for such a contour current controlled accumulation

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

magnetic reversal frequency and apparent polar wander of the siberian platform in the earliest palaeozoic inferred from the khorbusuonka river section northeastern siberia summary marly limestones that crop out along the khorbusuonka river northeastern siberian platform define a well dated lower and middle cambrian sequence which was sampled for magnetostratigraphy in the upper part of the section from the uppermost lower cambrian toyonian stage to the middle cambrian amgan and mayan stages thermal demagnetization isolates two magnetic components carried either by magnetite haematite or both the first is parallel to the recent geomagnetic field at the site and is removed in the low to middle temperature range the second component is isolated at higher temperatures and has dual magnetic polarities this component yields a positive but partial since we consider only two sites fold test with other middle cambrian data previously obtained from the distant kulumbe river section and was probably acquired during sedimentation or at an early stage of diagenesis it records a very high magnetic reversal frequency of at least six to eight reversals per myr during the entire middle cambrian assuming a 10 myr duration for this epoch a much more complex palaeomagnetic behaviour is observed within the upper tommotian lower atdabanian lower cambrian part of the khorbusuonka section demagnetization diagrams show large overlaps between magnetic components which prevents the isolation of a clear magnetic component at high temperatures analysis of these overlaps is however consistent with the existence of an ill determined primary magnetic direction for the lower cambrian which is very different from that isolated in the middle cambrian although still in need of further confirmation the possibility that a large drift in siberian apparent polar wander occurred over a rather short time during the lower cambrian appears to be supported by our data

contourite drift molded by deep mediterranean outflow since its inception in early pliocene time the deep mediterranean outflow has eroded and sculptured the southern iberian margin the 50 km long 300 m thick faro drift constructed by this powerful bottom current has been the subject of detailed study sandy silty and muddy contourite facies can be clearly characterized and a distinctive vertical arrangement or sequence of these facies can be related to hydrodynamic fluctuation these results are important for the identification of ancient contourites the reconstruction of paleocirculation patterns and documentation of the effects of quaternary climates on the mediterranean outflow

internal structure of a contourite drift generated by the antarctic circumpolar current 1 we describe the internal structure and stratigraphy of a well imaged contourite drift from the southern ocean this drift which we have named the south falkland slope drift lies on the northern flank of the falkland trough due south of the falkland islands drifts which occur directly in the path of the antarctic circumpolar current acc downstream of the drake passage gateway are of considerable paleoceanographic significance since their detailed stratigraphic record will help to constrain the history of the acc we have reprocessed a grid of seismic reflection profiles generously provided by westerngeco ltd in order to enhance imaging of the south falkland slope drift and of drift deposits within the trough the resultant high quality images enable us to map the internal architecture of these drifts in unprecedented detail by combining seismic stratigraphic mapping with measured sedimentation rates from nearby boreholes we have inferred ages of the principal mappable horizons with minor adjustments to sedimentation rates through time we can show that these ages correspond to significant southern ocean events we propose that the south falkland slope drift initiated at 24 5 20 5 ma in accordance with some but not all published estimates of acc establishment a highly reflective horizon with an estimated age of 14 5 ma corresponds to growth of the east antarctic ice sheet which led to a period of significant global cooling a similarly bright reflective horizon with an estimated age of 9 ma is thought to be related to a reorganization of bottom current flow which just predated establishment of grounded ice sheets on the antarctic peninsular shelf finally a prominent early pliocene unconformity at 4 5 ma may be linked with the onset of major northern hemisphere glaciation or with antarctic ice sheet expansion we conclude that this well imaged drift is an important and largely continuous stratigraphic record of acc activity and suggest that it would be an excellent drilling target

sedimentary growth pattern on the northern argentine slope the impact of north atlantic deep water on southern hemisphere slope architecture large sedimentary deposits consisting of several major contourite drifts were studied by means of high resolution multichannel seismic data at the middle slope along the northern argentina continental margin to determine their evolutionary stages as well as to identify and assess the possible impact of northern source deep water nsdw on the slope architecture the imaged contouritic sediments allow decoding on the regional paleo oceanographic setting of the last 32 ma earliest contouritic sedimentation can be observed close to the eocene oligocene boundary based on an aggradational stacking pattern with a complex and wavy seismic facies pointing toward a hydrodynamically turbulent flow pattern this facies is most likely related to the opening of the drake passage associated with global cooling and a strengthening of surface intermediate and deep ocean currents in the southern ocean during the middle miocene plastered drift sequences with an aggradational reflection pattern were deposited their depositional style indicates weak non turbulent current conditions which are interpreted to be related to a vertical shift of water mass interfaces caused by the first formation of nsdw during the mid miocene climatic optimum on top the formation of plastered drift sequences led to the modern extent of the ewing terrace which was probably controlled by the continuous strengthening and thickening of nsdw until the final closure of the central american seaway cas during the pliocene and quaternary after the complete closure of the cas and under the influence of the full force of the nsdw mounded plastered drift sequences are built upon the ewing terrace generating the modern slope morphology therefore we suggest that deep water production in the northern hemisphere plays a significant role by controlling the shape of the continental slopes in the southwestern south atlantic since the middle miocene highlights slope of northern argentine continental margin is current controlled since 32 ma variability of northern source deep water nsdw controls sedimentary processes sedimentary processes are susceptible to changes of the brazil malvinas confluence impact of nsdw on slope processes is underestimated in the southern hemisphere

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

high resolution stratigraphy of the mediterranean outflow contourite system in the gulf of cadiz during the late pleistocene the impact of heinrich events abstract a detailed high resolution stratigraphic analysis of the mediterranean outflow contourite system at the continental slope of the gulf of cadiz has been carried out through the correlation between a dense network of seismic reflection profiles sparker airgun 3 75 khz and parametric echosounder topas calypso giant piston and standard gravity cores from such correlation we determine a stacking pattern constituted by four main seismic units a d that are internally structured into ten subunits each subunit shows a single sequence formed by transparent seismic facies at the base to smooth parallel reflectors of moderate to high amplitude facies at the top being well correlated in the cores with a coarsening upward sequence the latest pleistocene holocene deposits form glacial interglacial depositional sequences related to cycles with a frequency range below the milankovitch band that corresponds to millennial timescale climatic changes such as dansgaard oeschger 1 5 ka and bond cycles 10 15 ka oxygen isotope records of planktonic foraminifera and the occurrence of ice rafted debris ird in the most recent contourite subunits show clear evidence of the influence of the north atlantic climatic conditions especially the climatic heinrich events h in the slope sedimentation of the gulf of cadiz and then in the circulation of the mediterranean outflow water mow the coarser contourite deposits are mostly associated with the last glacial maximum younger dryas and heinrich events on the central area of the middle slope during globally cooler conditions the mow was denser so that it was more active in deeper areas than today on the other hand during warm periods the mow became less dense favoring an increased intensity of the mow on the distal area of the upper slope therefore spatial and vertical fluctuations of the mow contourite system are strongly affected by global climate and oceanographic changes being clearly influenced by iceberg discharges and probably also by the resumption of thermohaline circulation in the north atlantic ocean during ice melting periods

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

a late pleistocene time series of bottom current speed in the vema channel abstract a coarsening of the mean particle size of the carbonate free silt fraction from sea floor samples below 4000 m in the vema channel has been used to separate high velocity antarctic bottom water aabw from the overlying slower north atlantic deep water nadw a time series of fluctuations in bottom current speed within the modern aabw nadw transition zone was examined by determining the particle size distribution of sediments from eight gravity cores with a high resolution stratigraphy for the past 250 kyrs the bottom current paleospeed was inferred from a correlation of particle size in seafloor samples with mean current speed from nearby current meters the mean bottom current speed at depths comparable to modern aabw was highest 7 10 cm s during interglacial to glacial transitions corresponding to the oxygen isotopic stage 6 7 and 4 5 boundaries and at present the mean bottom current speed at depths comparable to modern nadw was nearly uniform for most of the past 250 kyrs except during glacial oxygen isotopic stage 2 when the speed dropped to 2 cm s or one half of the present speed the application of the calibrated particle size method to examine bottom current paleospeed allows testing of paleoceanographic models which rely on assumptions or inferences of changes in bottom water production rate during the late pleistocene paleoclimatic fluctuations

seismic patterns of a muddy contourite fan vema channel south brazilian basin and a sandy distal turbidite deep sea fan cap ferret system bay of biscay a comparison abstract the aim of this paper is to discriminate the depositional facies geometries and mechanisms of deposition of contouritic fans from those of turbidite distal fans with a view to provide better resolution of reservoir prediction two examples are analysed the vema contouritic drift in the south brazilian basin and the cap ferret turbiditic fan in the bay of biscaye the vema contourite fan is a neogene mud rich accumulation 200 400 m thick fed by antarctic bottom water bottom currents and located downstream of the rio grande rise it forms one single mound fan shaped body in between two major channels and where the main part of the deep circulation is funnelled into as a result of the morphological and hydrological background the comourite drift progrades mostly downstream the accumulation was built as several depositional units channel levee systems bounded by widespread discontinuities showing erosional patterns this resulted from episodes of strong and or unstable current activity producing the discontinuities alternating with periods of relatively weak and stable currents and major deposition the pliocene quaternary cap ferret distal deep sea fan is a thick 500 m sand rich turbiditic accumulation fed directly by an uplifting mountain range the accumulation is developed downstream of a main turbiditic feeder channel and the volume of sediment involved is much higher than for the vema contourite fan it shows a complex network of shallow channels and low relief levees which merge downstream into thin sandy sheet like deposits several depositional units are stacked vertically each unit is built by the lateral migration of a channel levee system the stacking pattern of the successive units is prograding towards the basin the presence of major discontinuities cutting throughout a whole accumulation and the fairly irregular geometry of the channel levee deposits absence of any obvious migrating trend appear to be the most distinctive features of a contourite fan on the other hand the lateral migration of the channel level geometries and the presence of erosional surfaces of limited extent and restricted to the channels are the main diagnostic features of a distal turbidite fan otherwise the seismo facies are fairly similar in both sedimentary bodies

a late cretaceous mixed turbidite contourite system along the uruguayan margin sedimentary and palaeoceanographic implications abstract the late cretaceous is a critical period in the evolution of the south atlantic significant changes in the tectonic configuration of continental landmasses and marine basins during this time lead to major shifts in the sedimentary and oceanographic regimes using a combination of 2d and 3d seismic data with well data from the uruguayan margin this work provides a new highly detailed description of the late cretaceous sedimentary evolution of the margin and its regional and global palaeoceanographic implications the polonio drift system pds occupies the middle to lower slope of the uruguayan margin the pds is characterised by four channel drifts which propagate obliquely 120 170 from the palaeoslope and exhibit over 800 m of local relief relative to the surrounding seafloor seismic interpretation identified four seismic units su 1 su 4 separated by five major discontinuities r 1 r 5 these record the onset albian upper turonian 113 89 8 ma growth coniacian upper maastrichtian 89 8 66 ma and burial paleocene 66 56 ma phases for the pds during the onset stage down slope processes dominate but three major shifts in the sedimentary stacking pattern occur these coincide with palaeoceanographic changes in the south atlantic during the cenomanian turonian 100 5 89 9 ma campanian maastrichtian 83 6 66 ma and paleocene 66 56 ma following the opening of the falkland malvinas agulhas seaway fas the subsidence of the walvis ridge and the opening of the vema channel bottom current influence first occurs during the growth stage coniacian campanian when mounded deposits shift from aggradational and slightly progradational towards the n su 2 to clear lateral migration towards the s su 3 this sedimentary pattern indicates a regional palaeoceanographic shift in bottom current flow from northerly to a subsequent southerly direction bottom currents do not appear to have actively eroded sediment although they apparently had the potential to pirate and entrain fine grained material from turbidity plumes which build on underlying bathymetric features such as basement horsts and channel levees these produce large mounded morphologies adjacent to channels drift growth ceases following the termination of shelf progradation r 4 enabling sluggish bottom currents contributed to a homogeneous sedimentary drape bottom currents intensify in the beginning of the paleocene forming contourite depositional systems with well developed contourite terrace along the middle slope further research can elucidate the nature and mechanics of turbidite contourites interactions along continental margins this work offers new insights for the implications and consequences of the interaction of turbidites and contourites which can improve the characterisation of deep water deposits and understanding palaeoceanographic interpretations

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

sensitivity of east asian monsoon climate to the uplift of the tibetan plateau abstract using the cola center for ocean land atmosphere studies general circulation model a series of numerical experiments were conducted to examine the impact of uplift of the tibetan plateau on the evolution of the monsoon climate in east asia an attempt was made to isolate the effect of the plateau uplift from the changes in other forcing mechanisms we examined the spatial and temporal variation patterns of a variety of climatic variables and indices including monsoon intensity sea level pressure surface and upper air winds temperature at different levels precipitation air humidity and soil moisture our results suggest that the evolution of the east asia monsoon may be more sensitive to the uplift of the tibetan plateau than that of the south asia monsoon moreover the effect of the plateau uplift on the east asia winter monsoon is more significant than that on the summer monsoon in the northern part of east asia north china the formation of the monsoon climate is marked mainly by the establishment of the northerly winds in winter or the winter monsoon system corresponding to the uplift of the plateau when the height reaches approximately 50 of its current elevation on the other hand the establishment of the monsoon climate in the southern part of east asia the yangtze river valley and the area south of it may be much earlier than that in the northern part

sediment drifts and contourites on the continental margin off northwest britain abstract seismic reflection profiles and short cores from the continental margin off northwest britain have revealed a variety of sediment drift styles and contourite deposits preserved in the northeast rockall trough and faeroe shetland channel the sediment drifts include 1 distinctly mounded elongate drifts both single and multi crested 2 broad sheeted drift forms varying from gently domed to flat lying and 3 isolated patch drifts including moat related drifts fields of sediment waves are locally developed in association with the elongate and gently domed broad sheeted drifts the contrasting styles of the sediment drifts most probably reflect the interaction between a variable bottom current regime and the complex bathymetry of the continental margin the bulk of the mounded gently domed drifts occur in the northeast rockall trough whereas the flat lying sheet form deposits occur in the faeroe shetland channel a much narrower basin which appears to have been an area more of sediment export than drift accumulation patch drifts are present in both basins in the northeast rockall trough the along strike variation from single to multi crested elongate drifts may be a response to bottom current changes influenced by developing drift topography muddy silty muddy and sandy contourites have been recovered in sediment cores from the uppermost parts of the drift sequences on the basis of their glaciomarine origin these mid to high latitude contourites can be referred to collectively as glacigenic contourites both partial and complete contourite sequences are preserved the former consist largely of sandy mid only and top only contourites sandy contourites by their coarse grained nature and their formation under strongest bottom current flows are the most likely to be preserved in the rock record however the very large scale of sediment drifts should be borne in mind with regard to the recognition of fossil contourites in ancient successions

contourite drift types and their distribution in the north and south atlantic ocean basins abstract patterns of sediment accumulation under the control of deep bottom currents depend on interacting factors intensity of the regional deep circulation morphology of the sea floor coriolis effects abundance of terrigenous and biogenic supplies subsequent turbidity of deep nepheloid layers and depth of the ccd based on many examples of bottom current deposits from the atlantic and from other oceans we recognise three major types of contourite accumulation 1 giant elongate drifts 2 contourite sheets and 3 channel related drifts they generally occur in distinct topographic settings and show different geometries facies and rates of deposition in the north atlantic strong bottom circulation an open basin system and high sediment supply have led to the construction of large elongate contourite drifts which have striking relief 200 1000 m above the surrounding sea floor and are composed of muddy contourites rich in calcareous pelagic material in the south atlantic strong bottom currents are often trapped in gyre like circulation patterns around topographically closed basins or are accelerated through deep narrow connecting passages the resulting deposits are mainly extensive contourite sheets covered by fields of large sediment waves and channel related drifts including contourite fans constructed at the downstream exit of deep passages

suspended particulate matter transport through the vema channel richardson m j biscaye p e gardner w d and hogg n g 1987 suspended particulate matter transport through the vema channel mar geol 77 171 184 sixteen month time series measurements of water velocity and light scattering were coupled with hydrographic and suspended particulate matter sections to determine the flux and the variability in flux of suspended particulate matter through the vema channel the northward flux of spm through the vema channel ranged from 3 to 10 5 104 g s 1 with a mean of 6 5 104 g s 1 the largest fluxes were measured in the deepest and eastern portions of the channel with maximum fluxes of suspended particulate matter at specific sites being roughly two to four times the mean flux some of the suspended particulate matter in the channel may be eroded from the channel itself by the swift currents or eddy like features however the known manganese encrustation and hard floor of the channel suggest that the deep channel floor is not a likely source of sediment a primary source of the suspended particulate matter in the channel may be the sediment drifts in the argentine basin with their associated high standing crops of resuspended particulate matter this resuspended material would then be transported by the antarctic bottom water into and through the vema channel into the brazil basin the northward flux of suspended particulate matter through the vema channel is presently a significant but not dominant influence on sedimentation in the brazil basin

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

flow processes and sedimentation in contourite channels on the northwestern south china sea margin a joint 3d seismic and oceanographic perspective abstract 3d seismic data from the northwestern south china sea margin coupled with the quantification of oceanographic processes and morphological results were used to infer three dimensional flow processes and in turn sedimentation in contourite channels contour currents resulting from the northern pacific deep water npdw ccs flowing through the bends of contourite channels around a topographic high lead to an imbalance in the transverse direction around the bend between three competing forces i e upslope directed coriolis forces versus downslope directed centrifugal and pressure gradient forces the interface deflection of npdw ccs by coriolis pressure gradient and centrifugal forces yields a helical flow cell consisting of upper return flows directed downslope and basal flows orientated upslope ekman boundary layers at the base and flow interface are also likely present leading to flows in the downslope direction the helical flow cell in the bulk of contour currents and ekman boundary layers constitute a coriolis force induced helical flow circulation which we suggest promoted asymmetric intra channel deposition i e downslope deposition versus upslope erosion forcing contourite channels to consistently migrate in an upslope direction such coriolis force induced helical flow circulation is evidenced by occurrence of volumetrically significant overbank deposits along downslope margins and by asymmetric channel cross sections with steepened channel walls and truncation terminations along upslope margins it exhibits subcritical flow conditions represented by internal froude numbers estimated as 0 04 to 0 19 and is sufficiently deep to spill out of the studied contourite channels yielding overbank deposits along downslope flanks of the contourite channels

are antarctic peninsula ice sheet grounding events manifest in sedimentary cycles on the adjacent continental rise the direct record of late miocene early pliocene antarctic peninsula ice sheet expansions from a previously published seismostratigraphic study of the outer shelf at ocean drilling program site 1097 is compared to the glacial history we deduced from published proxy evidence within coeval sections on the adjacent continental rise the proxies are sedimentary structures laminated vs massive bioturbated facies and clay minerals predominantly smectite and chlorite contents from ocean drilling program site 1095 located on the distal part of a large drift the comparison shows that more sedimentary cycles are evident on the continental rise for three of the four diatom biozones we considered this indicates that the continental rise sedimentology may indeed be related to local or regional paleoenvironmental variability including antarctic peninsula ice sheet grounding events on the adjacent outer continental shelf if correct this would be a promising result because unlike the outer continental shelf sequences drilled thus far the continental rise record is relatively continuous and can be dated using paleomagnetic and biostratigraphic data however our study also shows that no objective criteria provide direct linkages between the glacial history we deduced from the two continental rise proxies and that previously derived from the continental shelf seismic stratigraphy furthermore the two sedimentologic proxies on the continental rise do not always provide a consistent picture of glacial history when compared against each other

a pliocene mixed contourite turbidite system offshore the algarve margin gulf of cadiz seismic response margin evolution and reservoir implications abstract a buried mixed contourite turbidite system has been identified in the pliocene succession of the algarve basin in the northern gulf of cadiz this margin is currently dominated by the mediterranean outflow water and associated contourite deposition analysis of seismic data along with careful geographical and oceanographic reconstructions of the margin show the gradual move from a turbidite dominated towards a contourite dominated margin and the subsequent birth of an impressive elongate mounded contourite drift system the faro albufeira drifts the contourite drift can be distinguished from down slope turbiditic and mass transport deposits based on the acoustic character distribution analysis and through careful margin reconstruction in the earliest pliocene seismic unit p1 has been interpreted as a dominant down slope most likely turbidite system sourced mainly from the northeast there is clear evidence of contourite reworking at seismic unit p2 where upslope progradation and a sheeted morphology are observed high amplitude reflections are thought to be a result of more vigorous bottom currents in the early upper pliocene that were capable to redistributing coarser sediments however in the northeast of the study area a thick sequence of chaotic seismic facies has been interpreted as mass transport deposits sourced from the north indicate that the bottom currents were unable to dominate over the entire margin due to high down slope clastic influx semi transparent seismic unit p3 indicates that the upper pliocene initially experienced a reduction in bottom current intensity however upslope progradation shows that a mixed system was maintained above the base quaternary discontinuity ca 2 6 ma highly erosive discontinuities and high amplitude seismic reflections are evidence of pronounced intensification of the mediterranean outflow water and a move to a fully contourite dominated slope mixed turbidite contourite systems such as the one identified in the algarve basin could provide impressive petroleum potential where downslope clastics are winnowed and reworked by bottom water currents to leave good reservoir properties here we present a conceptual model for sheeted drifts as hydrocarbon reservoirs in the subsurface

geomorphology of ona basin southwestern scotia sea antarctica decoding the spatial variability of bottom current pathways abstract ona basin the westernmost oceanic basin in the southern scotia sea is affected by the opposite flows of circumpolar deep water cdw and weddell sea deep water wsdw thus it represents a key location for exploring seafloor morphologies influenced by bottom currents the present study aims to capture the spatial arrangement of recent subsurface contourite features assuming a latitudinal influence of water masses and the interactions between along and downslope processes in order to contribute to the knowledge of regional deepwater flow pathways and to the sedimentary model of small sediment starved oceanic basins to this end the investigation combines an interpretation of multibeam bathymetry and parametric echo sounder seismic data complemented with hydrological data the distribution of morpho sedimentary features in ona basin reveals two major domains the southern margin of the basin can be regarded as a mixed hybrid system containing abundant sediment drifts with channels and contourite moats and a lateral continuity interrupted by downslope morphologies in contrast the northern abyssal setting comprises relatively homogeneous large sheeted drifts with superimposed sediment waves mounded drifts and several scattered erosive features likely reflecting the more distinct influence of deepwater contourite processes our work demonstrates that tectonic features in the southern basin control the interaction between deepwater along and downslope processes as the westward flow of the wsdw is deflected channelized and intensified along its westward route in the northern region the study indicates an overall clockwise rotation of the wsdw flow with the spatial and vertical variability of cdw and wsdw affecting the distribution of bottom current features around seamounts and or structural highs the results underscore the importance of sloping interphases in the water mass vertical structure the degree of basin confinement and the influence of local bathymetric elevations in sedimentation models of small sediment starved oceanic basins