raft tectonics the effects of residual topography below a salt de collement abstract some natural examples of thin skinned extensional structures resulting from gravitational gliding on passive margins which display complex listric growth fault patterns are not just controlled by the slope direction examples from the gulf of guinea are presented it is proposed that the inherited topography of the underlying basement can control the initiation of faults oblique to the gliding direction we carried out a series of small scale physical models in order to investigate the effects of residual topography beneath a de collement on faulting in the overlying rafted sedimentary cover the experimental results sustain the hypothesis of structural inheritance and their implications are discussed in the light of natural examples from the gulf of guinea

antarctic bottom and lower circumpolar deep water circulation in the eastern indian ocean 1 net northward transport below n 28 1 kg m 3 3200 m into the perth basin of between 4 4 and 5 8 sv is estimated from a year long current meter mooring array between the broken and naturaliste plateaus northward transport of between 2 0 and 2 5 sv of antarctic bottom water n 28 2 kg m 3 that must upwell within the southern region of the perth basin results in an area averaged diapycnal velocity and diffusivity of w 2 5 3 1 10 6 m s 1 and 13 15 10 4 m2 s 1 respectively diffusivity estimates for the perth basin are several times larger than area averaged mixing estimates for the abyssal subtropical south atlantic and pacific oceans however the dissipation of turbulent kinetic energy required to maintain the abyssal mixing in the perth basin e o 10 9 w kg 1 is similar to that required in the south atlantic ocean the area averaged diffusivity in the perth basin does not require unreasonable energy dissipation rates as this ocean basin is only weakly stratified the abyssal diffusivity of the perth basin results from intense mixing at the basin boundary and in the basin interior over rough topography the complex bathymetry and low abyssal stratification suggests that the indian ocean for a given energy dissipation may support a larger meridional overturning circulation than other subtropical basins

an improved method for reconstructing the stratigraphy and bathymetry of continental margins application to the cenozoic tectonic and sedimentary history of the congo margin a number of techniques such as backstripping and forward modeling have been previously used to reconstruct the tectonic sedimentary and thermal history at passive margins still these techniques are generally inaccurate in places such as the west african margin where the stratigraphic record is disrupted by continuous faulting of the sediment pile caused by salt tectonics and by erosional unconformities the ability to reconstruct the stratigraphy salt thickness and water depth along profiles of these types of margins is important for determining the factors controlling the geological history of the margin and the evolution of hydrocarbon systems to reconstruct the stratigraphy paleowater depths and salt flowage on a profile across the congo margin we combined backstripping and palinspastic reconstruction this enabled us to restore the faulting and salt flowage and simultaneously to take into account the isostatic response of the lithosphere to sediment loading and unloading this method allowed us to estimate the paleowater depth as well as the stratigraphy and the geometry of the sedimentary section on the profile through time the determination of the regional isostatic response of the lithosphere is performed with the use of a new model to estimate the flexural rigidity of continental lithosphere to demonstrate this method we perform the cenozoic reconstruction of the congo margin the results yield a coherent geological history of the margin from the eocene to the present in the eocene the margin was a carbonate ramp with a deep seated shelf break 600 m during the eocene oligocene transition intermediate water depth oceanic currents triggered submarine erosion of the eocene slope and shelf from the miocene to the present we observe a large increase in the input of terrigenous clastic sediments as a result the shelf prograded 40 km across the eocene ramp as the clastic sediments prograded across the margin into the deep basin faulting of the sediment pile and salt withdrawal caused the formation of grabens in places where salt swells had previously formed finally the reconstruction suggests that the congo margin was uplifted by at least 330 m between the late oligocene and the middle miocene

hydrocarbon plumbing systems of salt minibasins offshore angola revealed by three dimensional seismic analysis analysis of three dimensional seismic data from the lower congo basin offshore angola reveals numerous fluid flow features in the miocene to holocene succession and the potential for large shielded traps underneath basinward overhanging salt structures the fluid flow evidence includes present day sea floor pockmarks clustered above salt structures pliocene pleistocene stacked paleopockmarks and miocene pockmark fields other fluid flow features include high amplitude cylindrical pipe structures 60 to 300 m 197 984 ft wide and 25 to 300 m 82 984 ft high within lower and middle miocene strata thick 150 m 492 ft high reflectivity zones within the pliocene succession associated with bottom simulating reflections and subvertical low amplitude chimneys originating from the deeper section 1 km 0 6 mi beneath the sea floor the miocene pockmark fields occur at a specific horizon suggesting a regional fluid expulsion event at ca 12 ma and the miocene fluid flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs the pliocene pleistocene fluid flow regime was dominated by short distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water the present day fluid flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer scale salt flank controlled migration the study emphasizes the use of seismically imaged fluid flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time involving several fluid types and flow regimes depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers traps and seals

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part i detailed study of one oil seeping site abstract we report the geophysical characterisation of natural oil seep sites through a combination of sea surface evidence of oil leakage from spatial imagery with a large collection of seafloor and subsurface geophysical data this paper provides a detailed characterisation of one selected active seep site and identifies possible specific feature of oil seep sites the oil seep is a complex shaped feature on the seafloor consisting of a cluster of heterometric pockmarks inside a main depression area and peripheral metre scale seafloor mounds a strong deformation related to salt tectonics controls the location of the seafloor source by fracturing the overburden the associated thermal anomaly induces a vertical modification position of the base of the gas hydrate stability zone bghsz that is used as a fluid migration route towards the crest of the diapir the combination of local depressions and seafloor amplitude anomalies linked with vertical high amplitude pipes rooted on the bghsz suggests a focused fluid flow towards the seafloor in peripheral areas the seafloor mounds are linked by shallow faults to buried high amplitude patches on sub bottom profiler sections the combination of restricted size seafloor mounds with a progressive deepening of the high amplitude from the seafloor suggests a substantial decrease of the hydrocarbon flow towards peripheral areas the proximity of actively oil supplying seafloor depressions and seafloor mounds shows that the hydrocarbon flow rapidly decreases laterally the thermogenic seep site is affected by two consistent and sub parallel reflections with negative polarity the first is interpreted as the methane related bghsz the second could correspond to the base of a thermogenic bghsz produced by a mixture of heavier gas the seafloor roughness and double bsr appear to be specific features of oil seep sites the geophysical features revealed at a localised study area will be extrapolated towards a larger province for relevance validation

early oligocene stratigraphic turnover on the west africa continental margin a signature of the tertiary greenhouse to icehouse transition the post rift stratigraphy on the west african margin is characterized by aggradation of a carbonate ramp during late cretaceous to eocene epochs and progradation of a terrigenous wedge from oligocene to the present such first order structure has been attributed in the past to geodynamic forcing however comparison of the stratigraphic record of the margin with eustasy 18o and 87sr 86sr curves shows a close temporal relationship with the tertiary climate cooling an increase of continental weathering and a long term lowering of sea level we suggest that the transition from low amplitude high frequency sea level changes during the greenhouse period to high amplitude high frequency sea level changes during the icehouse period may account for i the switch from an aggrading carbonate ramp to a prograding clastic wedge and ii the enhanced continental weathering and increased terrigenous influx to the margin

thermo chronological approach to reservoir diagenesis in the offshore angola basin a fluid inclusion 40 ar 39 ar and k ar investigation 1 microthermometric analyses of fluid inclusions and geochronological surveys of authigenic silicates in neocomian sandstones and albian dolomitic reservoirs from the offshore angola basin have allowed determination of the age and the physical chemical conditions for fluid migration in a late diagenetic stage the 40 ar 39 ar laser probe dating of adularia overgrowths from the albian reservoirs shows that the trapping of primary aqueous and oil inclusions occurred during the early miocene 25 6 or 3 2 ma the k ar age of authigenic illites from the neocomian sandstones is slightly younger 19 or 1 ma and the crystallization of regular illite smectite mixed layers is related to a previous eocene to paleocene diagenetic stage 51 58 ma there appears to have bee both a regional and vertical variation in the salinity of aqueous fluids during the miocene the fluid inclusion trapping temperatures were estimated by correcting the homogenization temperatures of aqueous fluids assuming that pressures during the miocene were close to the present reservoir pressures and by intersecting the isochores of aqueous and oil inclusions assuming they were trapped at strictly similar pressure and temperature conditions the fluid inclusion temperatures are consistent with those derived from the tetrahedral aluminum content aliv of authigenic chlorites 168 206 degrees c in the albian reservoirs at depths between 2350 and 3580 m and 175 237 degrees c in the neocomian sandstones at depths between 2770 and 4470 m in both reservoir formations miocene tempe atures were higher than the present ones and related either to deeper burial or higher geothermal gradient

on the response of southern hemisphere subpolar gyres to climate change in coupled climate models 1 we investigate the responses of the southern hemisphere subpolar gyres to projected climate changes over the 21st century by coupled model intercomparison project phase 3 and 5 models under increased greenhouse gas forcing the southern hemisphere westerly winds consistently become intensified resulting in increased cyclonic wind forcing in the subpolar region in these models under such wind forcing changes it is a robust feature that there are consistent increases in the westward flow close to the coast of antarctica with strong implications to the mass balance of the antarctic ice shelves and ice sheets however there are large discrepancies in the responses of the gyre axes and overall gyre strengths some models show equatorward expansions of the southern gyre limbs resulting in consistent and large gyre strength increases while some other models show poleward contractions of the gyres and generally small and less consistent gyre strength changes these uncertainties are primarily a result of the uncertain simulations of eddy driven circulations in the antarctic circumpolar current the associated buoyancy forcing changes play a secondary role in driving these oceanic responses this study reveals that there are large uncertainties in the projections of the subpolar circulation in the current generation of coupled climate models although cmip5 models have considerably smaller inter model spreads in the present day and projected gyre strengths to predict the subpolar circulation changes future improved modelling studies need to particularly reduce the uncertainties in the projections of the westerly jet and to reduce the uncertainties in the eddy driven circulation responses to wind forcing changes

the tectonic evolution of the south atlantic from late jurassic to present an improved tectonic database for the south atlantic has been compiled by combining magnetic anomaly geosat altimetry and onshore geologic data we used this database to obtain a revised plate kinematic model starting with a new fit reconstruction for the continents around the south atlantic we present a high resolution isochron map from chron m4 to present fit reconstructions of south america and africa that require rigid continental plates result in substantial misfits either in the southern south atlantic or in the equatorial atlantic to achieve a fit without gaps we assume a combination of complex rift and strike slip movements 1 along the south american parana chacos basin deformation zone 2 within marginal basins in south america salado colorado basin and 3 along the benue trough niger rift system in africa these faults are presumed to have been active before or during the breakup of the continents our model describes a successive unzipping of rift zones starting in the southern south atlantic between 150 ma tithonian and approximately 130 ma hauterivian rifting propagated to 38 s causing tectonic movements within the colorado and salado basins subsequently between 130 ma and chron m4 126 5 ma the tip of the south atlantic rift moved to 28 s resulting in intracontinental deformation along the parana chacos basin deformation zone between chron m4 and chron mo 118 7 ma rifting propagated into the benue trough and niger rift inducing rift and strike slip motion after chron mo the equatorial atlantic began to open while rifting and strike slip motion still occurred in the benue trough and niger rift since chron 34 84 ma the opening of the south atlantic is characterized by simple divergence of two rigid continental plates

cold seeps at the salt front in the lower congo basin ii the impact of spatial and temporal evolution of salt tectonics on hydrocarbon seepage abstract this study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front i e the seaward boundary of salt induced deformation in the lower congo basin lcb seafloor topography backscatter data and tv sled observations indicate active fluid seepage from the seafloor directly at the salt front whereas suspected seepage sites appear to be inactive at a distance of 10 km landward of the deformation front high resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region the unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt tectonic deformation facilitates seafloor seepage at the salt front bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area onlap structures associated with fan deposits which were formed after the onset of salt tectonic deformation represent potential traps for gas which may hinder gas migration towards seafloor seeps faults related to the thrusting of salt bodies seawards also disrupt along strata gas migration pathways additionally the development of an effective gas hydrate seal after the cessation of active salt induced uplift and the near surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt tectonic deformation this process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects congo fan deposits on the abyssal plain these observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting

vertical evolution of fluid venting structures in relation to gas flux in the neogene quaternary of the lower congo basin offshore angola abstract the processes preceding the genesis of pockmarks and their subsequent evolution has been rarely studied since pockmarks were discovered in 1970 a high resolution 3 d seismic survey from the continental slope of the lower congo basin allows us to study in detail the structures that developed before the formation of pockmarks as well as their subsequent geometric evolution this paper aims at reporting new type of fluid related structures that relate to pockmarks the objective of this research is to understand 1 the evolution of these structures and their genetic relationship with pockmarks and 2 how their morphologies may be influenced by changes in venting intensity over time pockmark and chimney structures in this survey are hosted within late miocene to quaternary hemipelagites above clastic reservoirs in a petroliferous basin they are all associated with positive high amplitude anomalies phaas on seismic data phaas are interpreted from their dramatically higher acoustic impedance relative to the background sedimentary values of the host units and by their association with seismic pull up effects from their planform and cross sectional geometry phaas are primarily interpreted as being due to the development of methane related carbonates but they may be associated with gas hydrates in one or two examples methanogenic carbonates form either by authigenic accumulation or by anaerobic methane oxidation amo once upwardly migrating methane enters the sulfate methane transition zone smtz typically within the first few tens of meters below the seabed therefore vertical accumulations of phaas are interpreted to reflect the temporal evolution of methane flux migrating upward to reach the paleo seabed or smtz timing of local scale fluid leakage can therefore be diagnosed by analyzing phaas at seep locations that occur in association with pockmark chimney structures a conceptual model for the evolution of different fluid venting structures is proposed here and is based on the analysis of venting structures that we expressed by 3 d seismic reflections in this model the main features are linked into a process based sequence culminating in the infill and termination of the pockmarks as fluid venting sites our model summarizes different rhythms of venting which are expressed by different types of phaas along with venting structures linear phaas and conduits inferred slow seeps they can be succeeded by sub circular phaas and shallow depressions which inferred slow to moderate seeps then the seep can become either a fast vent and terminated into a pockmark crater or it can become less active and be sealed afterwards subsurface sediment fluidizations and remobilizations are likely to happen in the last case and are probably caused by hydrate dissociations

thin skinned extensional tectonics on a salt detachment northern kwanza basin angola abstract thin skinned extension on a salt detachment of a style known as raft tectonics characterizes deformation of the late aptian to recent section in the northern kwanza basin angola large rafts and intervening grabens are interpreted to have developed as a result of gravity gliding increased dip and gravity spreading asymmetrical loading of a sedimentary wedge major raft movement occurred primarily from the middle tertiary but some deformation appears to have started as early as late cenomanian or early turonian times individual grabens measure up to 70 km in length 15 km in width and nearly 3 km in depth and show switching polarities in the sense of thickening of the tertiary sedimentary infill graben geometries were controlled by syndepositional extension and the local availability of salt from the data examined which includes both seismic and well data the grabens appear to become younger from east to west reflecting basinward progression of the deformation as the age relationships could be related to insufficient sampling of strata deposited in complex sedimentation patterns they may have no relevance to the timing of the deformation the diachronous deformation is therefore speculative extension in the northern kwanza basin is estimated at 60 the outermost raft is translated 55 km westwards in addition to the extensional structures compressional folds thrust faults and salt structures mark the toe of the gravity gliding and spreading system all of the rafts lie within the african portion of the aptian salt basin on rifted continental crust and they are generally unrelated to structures below the salt biostratigraphy and lithostratigraphy indicate that the grabens formed on the shelf and upper slope from the middle eocene associated compressional features developed near the slope rise the unusual expression of raft tectonics is attributed to a combination of 1 the presence of a salt layer 2 a stable basement configuration that allowed quiescent accumulation of the raft sequence and 3 an increase in basin dip and sediment supply

perturbation of polygonal fault propagation by buried pockmarks and the implications for the development of polygonal fault systems abstract evidence is presented that constrains the earliest part of the growth history of a polygonal fault tier using high resolution 3d seismic data from the west african margin we document the interaction between a shallow buried wedge shaped polygonal fault tier and pockmarks located at the base of the fault tier strongly curved patterns of perturbed polygonal faults are mapped in the shallowest portions of a tier overlying a series of pockmark craters these perturbed patterns differ markedly from the background polygonal pattern developed away from areas of pockmark influence perturbation is attributed to local stress effects relating to residual topography of the underlying pockmarks by analysing the thickness variations of mapped layers within the polygonally faulted tier we demonstrate that any residual topography was most likely healed after approximately one third of the total tier thickness was deposited hence the nucleation of the polygonal faults into their perturbed propagation trajectories must have been established within the first 100 150 m of burial from these observations of early nucleation in the basal third of a tier we propose a new model of polygonal fault growth in which individual faults nucleate near the base of a tier at an early stage of burial and then propagate preferentially upwards with basal tips restricted by an underlying mechanically competent unit the base of the tier continued growth then shifts the locus of displacement such that final displacement distributions are more axio symmetrically disposed with respect to the base and top of the tier

early cretaceous rifts of western and central africa an overview abstract the structure and evolution of early cretaceous rift basins in western and central africa are described two stages of rift development and fracturing have been identified 1 from neocomian to early aptian roughly e w and nw trending troughs upper benue n cameroon s chad sudan etc opened in response to a submeridian extensional regime in central africa while in western africa the n s trending transsaharian fault zone acted as a sinistral wrench 2 from middle aptian to late albian large northwest trending troughs e niger sudan sirte etc opened in response to a northeast extensional regime while the central african fault zone from benue to sudan exhibited strike slip movements generating pull apart basins these rift and fracture systems delimit three large blocks within the african plate a western block an arabian nubian block and an austral block the arabian nubian block tends to separate from the two other blocks migrating towards the north during the first stage of basin development and then towards the ne during the second stage the opening of the atlantic ocean was the dominant driving force for the western and austral blocks while the arabian nubian block probably moved in response to the opening of the indian ocean and to the evolution of the tethyan margin

stratigraphic record of translation down ramps in a passive margin salt detachment abstract ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps on passive margins movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp this growth syncline gradually moves seaward down and then off the monocline as if on a conveyor belt this shift creates accommodation space for a new isopach thick to form just landward of the older one repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin kinematic forward models and restored cross sections from the kwanza basin angola show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors 1 the relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines 2 bathymetric scarps above basement ramps can create spectacular seaward dipping onlap surfaces 30 km long downdip adjoining ramps generate stacked interfering onlap surfaces 3 salt diapirs or anticlines are commonly shortened at the top of the ramp especially where this coincides with the base of the continental slope diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side this buffering can have a major control on the entire gravity spreading system containing the diapirs

contraction induced by block rotation above salt angolan margin gravity spreading above salt at passive margins is the major mode of deformation of post salt sediments whereas this process generally creates a structural zoning extensional upslope and contractional downslope discrepancies can however arise for example evidence of contractional deformation occurs in the extensional domain of the angolan margin to the south of the congo delta fan slope parallel seismic lines show grabens rollover and extensional diapirs conversely strike parallel seismic lines present inversion of early grabens apparently related to a regional scale decrease in sedimentary thickness away from the congo delta as the spreading rate and the characteristic spacing of structures are direct functions of sedimentary loading one can expect structural changes along strike due to sedimentary thickness variations this hypothesis was tested using spreading type experiments of brittle ductile models lying on top of an inclined rigid substratum the experiments simulate the progradation of a synkinematic sedimentary cover above salt with a lateral variation of sedimentation rate the models show that the spreading rate was higher in the thicker part early grabens initiated perpendicular to the slope direction where sedimentation rate was high they kept their orientation during spreading and formed purely extensional synsedimentary structures grabens rollovers and diapirs where sedimentation rate was low blocks separated by grabens rotated in a domino type fashion but this domain continued to extend in a slope parallel direction strike slip between blocks was entirely localised within the early grabens which inverted and formed anticlines structures obtained in experiments are directly comparable to those in seismic lines of the angolan margin in both the angolan margin examples and the laboratory experiments block rotation is interpreted as slope parallel strike slip shear zones due to lateral variations in spreading rate

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

microstratigraphic and multi analytical evidence for advanced neanderthal pyrotechnology at abric romani capellades spain abstract the complexity of social behaviour by neanderthal communities is consolidated by illustrating the sophistication of fire linked activities in their home based contexts this was achieved by relating the microfacies analysis of cultural deposits to combustion structures at the abric romani capellades spain the geometry and nature of cultural microfacies from a selection of hearths and their surrounding empty areas were characterized in thin sections the related bulk fraction from the distinctive individual microstrata was extracted water sieved and examined under the binocular microscope the selective micro sampling was performed from the collection of undisturbed blocks in combustion structures of layer j 1995 excavation the procedure was applied to combustion structures from the lower layer o 2009 excavation the integrated micromorphological observation and binocular sorting allowed identification of a similar assemblage of components that are closely linked to distinctive anthropic microfacies individual grains were characterized by esem edax x ray diffraction and raman spectrometry x ray fluorescence analysis was performed on the host matrix the specific association of remarkable components cultural microfacies is identical for the combustion structures of layers o and j the four groups components identified comprise carbonaceous polymorphs allochthonous mineral clasts organo phosphatic compounds and native metals the phase association of organic and mineral phases allowed recognition of a common natural precursor rich in hydrocarbon species and metallic compounds that were probably extracted from a miocene source microscale analysis in thin sections linked the combustion microfacies to the transformation contexts of the metal rich carbonaceous precursors heat resistant polymers and graphitic components associated with wood ash are suggested to trace pyrolitic residues from flaming combustion the intimate mixing of the metal rich carbonaceous polymorphs to finely crushed heated bones allowed identification of pyrogenic transformations of the fossil fuel with fresh biomass analysis at microscale in thin sections linked the processed by products to finely prepared and meticulously consolidated surfaces showing distinctive colours yellow brown blue green red white and black the repeated surface preparation and their exceptional preservation at microscales illustrate the great concern of neanderthal occupants for maintaining the long term memory of their carefully designed home space the recognition of advanced pyrotechnology by using fossil fuels for lighting firing spatial design colouring in the combustion structures of abric romani incites speculation on the exceptional social status of this home based camp site further development of the microfacies multi analytical analysis should more deeply penetrate the social sophistication of neanderthal communities

identification and numerical modelling of hydrocarbon leakage in the lower congo basin implications on the genesis of km wide seafloor mounded structures abstract we present a combined approach of interpretation of 2d seismic reflection data and numerical modelling of hydrocarbon generation and migration across the southern slope of the lower congo basin in order to investigate the factors controlling timing and distribution of hydrocarbon leakage in this area we identified three main families of past and present day leakage features 1 mid upper miocene seismic chimneys concentrated basinwards and ending up on buried pockmarks 2 plio pleistocene chimneys rather clustered to the east of the study area and ending up in seafloor pockmarks and 3 fewer scattered chimneys identified within the miocene sequences ending up in shallow enhanced reflectors flat spots stratigraphic and structural elements seem to control the distribution of these features at least two major events of leakage occurred during the middle late miocene and intermittently during the pliocene present external factors as sediment supply are associated to the miocene leakage event whilst internal structural elements probably triggered the pliocene to present day leakage a major seabed morphological feature represented by a margin paralleled belt of more than 1 km wide mounds was identified above growth faults to the east of the study area data constrained 2d hc generation and migration modelling suggests a genetic link between these structures and vertical migration leakage of thermogenic methane sourced from either currently mature oligo miocene source rocks or secondary cracking and further expulsion from over mature upper cretaceous source rocks hence the mounds are likely to represent a lineation of methane derived carbonate build ups despite the natural limitations of a 2d migration model when combined and calibrated with observations from seismic data it can be used as a valid tool to assess petroleum migration routes in sedimentary basins to the best of our knowledge this is the first integrated approach combining both seismic observations and numerical modelling carried out in the angola basin

flexural response of passive margins to deep sea erosion and slope retreat implications for relative sea level change we suggest that the magnitude of the early late oligocene eustatic fall as predicted from sequence stratigraphy has been overestimated because of flexural rebound along margins that was induced by late eocene to early oligocene erosional unloading the unloading of sediments from a continental margin during periods of deep sea erosion and slope retreat will be accompanied by some form of flexural rebound the magnitude and form of this rebound are controlled by 1 the amount of sediment removed from the margin and 2 the strength of the lithosphere at the time of sediment removal along margins with narrow continental shelves this rebound will induce a relative sea level fall resulting in a basinward shift in the shoreline and the predicted systems tracts will be similar to those expected for a eustatic fall in contrast rebound along wide continental shelves will not alter the position of the shoreline even though a relative sea level fall may be recorded across the outer shelf deep sea drilling and seismic reflection data from many margins support the interpretation of a late eocene to early oligocene 38 34 ma deep sea erosional event best developed along the continental slope and rise seismic reflection and drilling data also document a prominent canyon cutting event across the shelf during the early late oligocene 32 29 ma this event has been interpreted in terms of a large eustatic fall 150 m nevertheless there appears to be a correlation between late eocene to early oligocene deep sea erosion and the development or at least enhancement of unconformities across the shelf during the early late oligocene

direct observations of the current structure east of the bahamas quasisynoptic absolute velocity sections were obtained in the western north atlantic to the east of the bahamas on five cruises from 1992 to 1994 showing complex spatial and temporal variability of the currents throughout the water column lowered acoustic doppler current profilers were used on all cruises for comparison an acoustically tracked free fall profiler was used on the august 1992 and june 1993 cruises where simultaneous profiles from both methods are available depth averaged differences are less than 0 01 m s 1 in the ensemble mean and standard deviation though small the mean difference appears to be statistically non zero for one of the two doppler profilers used no cause has been found the individual velocity sections show a banded structure of currents in the offshore direction with strong baroclinic and depth averaged components extending over the full sampling domain two sections show a picture of the southward flowing deep western boundary current dwbc differing from previous observations during august 1992 and june 1993 the mean dwbc core was located more than 100 km offshore in observations prior to 1990 it was usually near 50 km offshore net southward transport below 800 m integrated from the coast to 400 km offshore varied from 15 to 50 sv with a mean of about 40 sv 1 sv 1 106 m s 1 our mean is consistent with previous estimates our sections add new evidence that the transport is highly variable to at least 400 km offshore

neogene sedimentation history of the congo fan abstract high resolution seismic reflection data were interpreted to develop a model for the neogene sedimentation in the congo fan area identification of two reflectors representing marine isotope stages 6 and 12 allows a distinction between the early and the late quaternary a single sediment source system during the late paleogene early neogene gradually changes into a two sediment source system in the late neogene since the late quaternary the congo river has been the prevailing sediment source the evolving benguela current further modified the system and led to a high biogenic productivity evidence for gas in the sediments can be found in the whole area of investigation additionally indications for a tectonic control of the congo canyon have been found in the distribution of sedimentary units and unit thicknesses

sources and transport of the deep western boundary current east of the kerguelen plateau east of the kerguelen plateau a deep western boundary current in the australian antarctic basin brings cold dense waters north from the margins of antarctica geostrophic velocities referenced to acoustic doppler cur rent proler data both shipboard and lowered suggest the flow is unidirectional throughout the water column with es timated northwestward transport below potential temper ature 1 co f 28 7x1 0 6 m 3 s 1 and 49 9x1 0 6 m 3 s 1 respectively hydrographic and acoustic doppler current proler data show that the deep boundary current is sup plied by northward flow emerging from the confluence of westward flow along the antarctic continental slope and eastward flow of weddell basin waters through the princess elizabeth trough to the south of the kerguelen plateau 1 0 to 0 5 0 2 1 1 3 1 4 61 7 8 42 5 0 5 to 0 0 2 0 0 3 3 2 8 41 9 14 52 3 0 0 to 0 5 8 1 3 6 1 4 15 03 2 26 04 4 1 0 to 0 5 10 3 2 2 7 7 28 06 7 48 99 4

neogene quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of ne brazil we investigate the role of reactivation of precambrian basement fabric in the tectono sedimentary and geomorphological evolution of the paraiba basin continental margin of northeastern brazil during the cretaceous neogene and quaternary this basin represents part of the last bridge between south america and africa before the last breakup stage of the south atlantic rifting in the early cretaceous the paraiba basin infill is composed of siliciclastic and carbonate cretaceous units as well as aeolian fluvial and marine quaternary units we used shuttle radar imagery aeromagnetic wellbore and field data the reduced to the pole magnetic map rtp indicates the continuity of the steeply dipping precambrian basement shear zones beneath the paraiba basin the combined analysis of surface and subsurface data shows that ne sw and e w striking shear zones were subjected to brittle reactivation in the aptian middle albian during the basin opening and again in the neogene quaternary forming a system of horsts and grabens along the basin some of these structures such as the e w oriented pernambuco shear zone present modern day seismicity n s and mainly nw se striking transfer faults cut across aptian middle albian to neogene quaternary strata these four main fault directions control main river channels and alluvial valleys up to 2 km wide topographic breaks up to 50 m were created by late reactivation of rift faults which mark the boundary between horsts and grabens along the basin in addition structural data evidence syn tectonic faulting with vertical offsets up to 80 m in the cretaceous and up to 70 m in the neogene quaternary we conclude that shear zones across the study area are long lived structures that have behaved as weakness zones their neotectonic brittle reactivation has controlled sediment deposition and landform development which continued through the neogene quaternary

raft tectonics the effects of basal slope angle and sedimentation rate on progressive extension abstract in the gulf of guinea the upper cretaceous tertiary sedimentary cover has undergone gravity gliding above an aptian salt layer for various basal slope angles from 0 to 4 gliding started during albian time and evolved up to the present with variable sedimentation rates faulting patterns are seen to vary in particular as a function of the basal slope angle and the syn kinematic sedimentation rates a series of laboratory experiments on small scale models is used to study the effects of the two parameters mentioned above models are composed of two layer slabs with newtonian silicone putty at the base to represent a basal salt decollement and dry sand on top to represent the sedimentary overburden models are allowed to deform under their own weight for various basal slope angles ranging from 0 to 5 with two different syn kinematic sedimentation rates it is shown that the basal slope angle controls the location of faulting in the overburden within a single downslope deformation domain for values smaller than 2 and within two domains lying downslope and upslope for higher values of the width of the deformation domains also varies as a function of overburden faulting always starts with syn kinematic grabens which evolve into symmetric or asymmetric grabens or into tilted blocks bounded by listric normal faults while synthetic listric normal faults characterize the downslope deformation domains both synthetic and antithetic listric normal faults can occur in the upslope deformation domain ductile deformation within the basal decollement layers results from variable combinations of pure shear and simple shear interaction of ductile deformation in the ductile decollement layer with faulting in the overburden locally produces complex and heterogeneous strain patterns notably within salt rollers finally increasing rates of syn kinematic sedimentation are seen to increase the rate of downslope displacement and to enhance and favour the development of listric normal faults

supergene manganese ore records 75 myr long campanian to pleistocene geodynamic evolution and weathering history of the central african great lakes region tectonics drives climate assists abstract the southeastern part of the democratic republic of the congo locally hosts proterozoic manganese deposits the deposits of kisenge kamata are the most significant but manganese ores are also known to occur at kasekelesa former katanga province and mwene ditu former kasai province for the present study cryptomelane rich samples from these two localities were dated using the 40ar 39ar step heating method with a co2 laser probe the ages obtained are within a range of c 77 myr to c 2 myr cryptomelane formation took place at c 76 4 ma c 59 6 ma c 45 ma c 35 ma c 23 8 ma c 15 4 ma and c 13 3 ma at kasekelesa and it occurred at c 35 ma c 22 4 ma c 15 ma c 5 5 7 2 ma c 3 6 ma and c 2 1 2 3 ma at mwene ditu the campanian age c 76 4 ma recorded at kasekelesa is the oldest 40ar 39ar age that has up to now been recorded for mn ores from africa it documents the formation of oxidized ore along a campanian or older erosion surface which could be part of the african erosion surface the complete age record suggests that continent wide tectonics accounts for most of the recognized supergene ore formation episodes controlled by vertical lithospheric movements that are ultimately responsible for alternating stages of landscape stability and erosion tectonics is thus regarded as the first order control for secondary ore formation in central africa over the last 80 myr climate is a second order control because sufficient water supply is needed for supergene enrichment whereby climatic conditions are recognized to have been favourable during some relatively cold late mesozoic and paleogene periods as well as during some humid and warm neogene stages

cold seeps at the salt front in the lower congo basin i current methane accumulation and active seepage abstract active high intensity gas seepage is documented for the first time at the seaward edge of the salt occurrence in the southern lower congo basin microbial methane release from the seafloor occurs on the crests of two 800 m high ridges formed by fault propagation folding intense uplift is documented since the end of the miocene by distinct onlapping reflections on the landward flank of these ridges a paleo pockmark structure suggests an onset of seepage coincident with this deformation period high resolution seismic imaging reveals methane migration along strata from oligocene miocene fan deposits towards the ridge crests where large gas accumulations form beneath a discontinuous bottom simulating reflection bsr detailed mapping revealed that free gas and gas hydrate occurrences below and above the base of the gas hydrate stability zone are closely linked to sedimentary strata in the flanks of topographic ridges gas transport through the gas hydrate stability zone originates from the shallowest area of the bsr directly beneath the seafloor seep sites suggesting pressure controlled venting these sites represent the most seaward salt related gas seepage features documented in the area and illustrate the initiation of long lasting seepage at the front of an area of compressional tectonics at a passive continental margin

tectonostratigraphic development in the eastern lower congo basin offshore angola west africa abstract as in all aptian salt basins off western africa the post rift evolution of the lower congo basin offshore angola was greatly influenced by raft tectonics we suggest that rafting in the lower congo basin took place during relatively short periods 7 10 ma characterized by high strain rates separated by longer periods 15 35 ma characterized by low strain rates the high strain rate periods are dated as aptian late cretaceous late eocene late oligocene and late miocene recent with respect to the tertiary development we have obtained a positive correlation between sedimentary thickness and cumulative stretching suggesting sedimentary loading as an important driving mechanism for raft tectonics during the tertiary two different types of depocentres developed these are i broad first order depocentres governed by regional subsidence and ii narrower elongated second order depocentres governed by growth on active faults within the study area the depocentres seem to have migrated from the west towards the east

bone needle fragment in lgm from the shizitan site china archaeological evidence and experimental study an eyed bone needle fragment found in shizitan 29 site shanxi province dated to ca 23 26 ka cal bp is one of the early needles with a precise stratigraphic context and date among the open air palaeolithic sites in north china although the needle was found broken based on microwear observation and experiments in making and using bone needles we conclude that it had been used for sewing further archaeological evidence including a sandstone needle shaping stone drilling tools perforated ornaments and microscopic evidence of thread support the presence of a bone needle at the shizitan 29 site it was the same type as the bone needles used in siberia during the late pleistocene and the use of needles at shizitan was one of the strategies for making warm clothes to adapt to the coming of the last glacial maximum lgm 24 000 18 000 cal bp

dynamic interactions between the gulf of guinea passive margin and the congo river drainage basin 2 isostasy and uplift 1 the gulf of guinea continental margin is paralleled by a coastal relief that isolates the congo drainage basin and can play a subsequent role in interactions between margin deposits and continental denudation migration of depocenters from the ogooe and kwanza rivers to the congo fan in the oligocene low present day sediment delivery or pleistocene submarine channels instabilities are possible evidences for this interaction in order to test this hypothesis we examine successively margin isostasy regional uplift erosional unloading and flexural bulge created by sediment loads satellite free air gravity and two dimensional thermomechanical modeling including depth of necking are used to determine the structure of continental margin and strength conditions for two selected sections across south gabon and congo fan both verify similar conditions for extension geometry depth of necking 10 20 km and strength equivalent elastic thickness of 20 30 km differences in observed gravity are explained mainly by differences in sediment volumes regional uplift during miocene of at least 450 m is attributed for both continent and margin as evidenced by the elevated base level of the congo drainage basin and the uplift of shelf break and coastal plains topography corrected for regional uplift valley erosion below relics surfaces and corresponding erosion unloading has been determined as a proxy of oligocene topography it shows a typical rift shoulder topography isolating congo drainage basin from margin in such conditions small amplitude flexural uplift related to sediment loads can possibly have negative feedbacks for both oligocene and present time

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part ii a regional validation abstract the lower congo basin is known to discharge a substantial volume of oil towards the sea surface from more than one hundred seafloor seep sites distributed throughout the deep province of the lower congo basin a large geochemical coring survey confirmed the presence of oil on the seabed the combination with the seismic data considerably improved the identification of the origin of the oil slicks on the seabed multiple specific geophysical characteristics of thermogenic hydrocarbon seep sites were highlighted in a previous detailed analysis of seismic datasets this study aims to test the characteristics previously identified at regional scale the active discharge zone is limited to the distal province of the basin it is characterised by strong compression shortening due to the sliding of the post salt super sequence resulting in numerous salt diapirs that control the location of seafloor oil seep sites the paper describes the bathymetric reflectivity amplitude and sub bottom profiler characteristics of a group of thermogenic seep sites they correspond essentially to submarine mounds or pockmarks of complex and irregular shape surrounded by hummocky mounds active oil pockmarks are systematically associated with positive amplitude anomalies on the seabed and are linked to vertical high amplitude columns rooted in the seismic reflector and associated with the base of the gas hydrate stability zone the sub bottom profiler data shows that the hummocky mounds are connected by a network of faults to high amplitude bodies buried under a consistent sediment thickness based on the definition of specific geophysical features seafloor mounds complex shape and irregular pockmarks positive anomalies of seafloor amplitude high amplitude vertical pipes we identified a series of potential oil seep sites at basin scale the mounds are particularly recognizable using the seismic curvature attribute we have identified 2946 individual hummocks that are grouped in 50 zones with a density of 35 240 per km2 they are believed to be associated with asphalt storage on the seafloor and related to the biodegradation of heavy oils during hydrocarbon dysmigration through the sedimentary pile unusual double bsrs occur over the study area these are also a specific feature of thermogenic seep sites barely half of the potential sites identified on the seismic datasets are associated with recurrent oil slicks at the sea surface the proportion of remaining anomalies may be associated with inactive seep sites over the period of satellite based monitoring or gas dominated seep sites

palaeoecology of neanderthals during dansgaard oeschger cycles in northeastern iberia abric romani from regional to global scale abstract the sequence from abric romani has provided several palaeoecological studies this paper presents a synthesis of the results yielded by palynology including the data from the entire non excavated deposits and the data obtained through the study of large mammals micromammals herpetofauna and anthracology from the excavated layers the palaeobotanical studies show that the sequence is mainly related to pine forests and near or within these dominant forests there were smaller plant formations and or secondary species with a mediterranean and or atlantic character nevertheless continuous forest did not dominate the entire region the fauna occupying the territory indicate open spaces in which seasonal grasslands proliferated dry assemblages in sunny areas and humid ones in mountain shadows the non excavated archaeological layers correspond to mis 4 initially characterized by temperate and humid conditions and thereafter cool and humid until hs 6 and mis 3 afterwards at the beginning of the mis 3 the dansgaard oeschger cycles 1500 yr rapid and abrupt climatic changes occurred during the deposition of the archaeological levels o n m l k and j later these events were interrupted by a cold and dry phase between ca 49 and 47 ka bp which affected levels ja i and h culminating with hs 5 finally this cold episode was followed by the hengelo interstadial or do 12 characterized by a temperate and humid climate identified in levels e and d

a seismic reconnaissance survey of the northern congo fan abstract to study the time varying influence of the congo river and the benguela current on the deposition at the angola continental margin a high resolution reflection seismic survey was carried out on the northern congo fan four seismostratigraphic units have been defined for the upper 800 m 1000 ms twt of the data the units record different depositional environments ranging from pre establishment of the congo river drainage system to the influence of the benguela current an indication of a general change in the turbidite system is provided by a shift in channel distribution and a relocation of the depocentre of coarse material the ascent of salt is recorded up to the pliocene gas that has migrated out of lower cretaceous shales and that was produced from large quantities of organic matter in the younger sediments can be found on the flanks and on top of the salt domes in a few places this gas even ascends to the ocean floor along structural pathways through the topmost unit

warming and freshening in the abyssal southeastern indian ocean abstract warming and freshening of abyssal waters in the eastern indian ocean between 1994 95 and 2007 are quantified using data from two closely sampled high quality occupations of a hydrographic section extending from antarctica northward to the equator these changes are limited to abyssal waters in the princess elizabeth trough and the australian antarctic basin with little abyssal change evident north of the southeast indian ridge as in previous studies significant cooling and freshening is observed in the bottom potential temperature salinity relations in these two southern basins in addition analysis on pressure surfaces shows abyssal warming of about 0 05 c and freshening of about 0 01 practical salinity scale 1978 pss 78 in the princess elizabeth trough and warming of 0 1 c with freshening of about 0 005 in the abyssal australian antarctic basin these 12 yr differences are statistically significant from zero at 95 confidence intervals over the bottom few to several hundred decibars of t

monitoring of natural oil seepage in the lower congo basin using sar observations abstract synthetic aperture radar sar is a spaceborne tool allowing near real time imagery over large ground footprints of areas hundreds of kilometres wide sar also allows persistent observations of the process of oil discharges benefiting from 1 day and night observations 2 independence of cloud cover and 3 high revisiting frequencies the interpretation of 82 sar scenes over the lower congo basin for the 1994 2012 period allowed the recognition of 1400 natural seepage slicks associated with 102 individual seep sites we acquired an additional sar data set with a short revisit time over a selected prolific area the data set consisted of 22 sar scenes acquired over a 10 day period meaning a maximum revisiting period of 12 h between subsequent sar acquisitions the short term approach shows that seepage slicks were detected with wind speeds between 1 5 and 6 5 m s 2 91 to 12 63 knots both long term and short term monitoring evidences that seepage events are intermittent with the occurrence rate of oil release ranging from 5 to 80 short term monitoring shows that the seepage pace is independent between seep sites suggesting contrasted controlling factors it also shows that the residence time of seepage slicks is systematically shorter than 12 h which is far below reported values understanding the seepage slick residence time is essential to provide an accurate estimation of the fluid flow and to compute the volumetric outflow the integration of in situ mooring points measuring the current velocity 10 m below the sea surface in addition to local wind field and slick length allowed us to more accurately estimate the residence time of oil slicks at the sea surface before vanishing the results show that the sea surface residence time of oil slicks is limited to a few hours with a median value of 3 h 15 min these new residence time estimations allowed us to propose a quantification of the regional oil output in the lower congo basin estimated at 4380 m3 year this area may therefore be considered as the world s third biggest oil supplying province from natural leakages

comparison of the rift and post rift architecture of conjugated salt and salt free basins offshore brazil and angola namibia south atlantic abstract this study presents a regional comparison between selected 2d seismic transects from large conjugated salt and salt free basins offshore southern brazil campos basin santos basin pelotas basin and southwest africa kwanza basin northern and southern namibe basin walvis basin tectonic stratigraphic interpretation of the main rift and post rift units free air gravity data and flexural isostatic backstripping were used for a comprehensive basin to basin documentation of key mechanisms controlling the present day differences in conjugated and neighbouring south atlantic basins a significant variation in the tectonic sedimentary architecture along strike at each margin and between the conjugated basins across the south atlantic reflects major differences in 1 the structural configuration of each margin segment at transitional phase between rifting and breakup as emphasized in the highly asymmetric settings of the large santos salt basin and the conjugated salt free southern namibe basin 2 the post breakup subsidence and uplift history of the respective margin segment which caused major differences for example between the campos and espirito santo basins and the conjugated northern namibe and kwanza basins 3 variations in the quantity and distribution of post breakup margin sediments which led to major differences in the subsidence history and the related present day basin architecture for example in the initially rather symmetric siliciclastic pelotas and walvis basins and 4 the deposition of aptian evaporites in the large rift and sag basin provinces north of the rio grande rise and walvis ridge highly contrasting the siliciclastic basins along the margin segments south of the ridges the resulting present day architecture of the basins can be generally classified as i moderately symmetric salt free and magma rich in the northern part of the southern segment i highly asymmetric salt bearing and magma poor vs salt free and magma rich in the southern part of the central segment and iii moderately symmetric to asymmetric salt rich and magma poor in the central part of the central segment of the south atlantic

role of subaerial volcanic rocks and mantle plumes in creation of south atlantic margins implications for salt tectonics and source rocks abstract seaward dipping reflectors sdrs represent flood basalts rapidly extruded during either rifting or initially subaerial sea floor spreading evaporites can form on this basaltic proto oceanic crust as in the afar triangle today evidence for sdrs in south atlantic deep water regions comes from proximity to the uniquely large parana etendeka volcanic province onshore the tristan and gough hot spots drilled volcanic rocks and seismic profiles showing sdr provinces more than 100 km wide as much as 7 km thick and thousands of kilometers long sdrs are clearest adjoining the aptian salt basins however we speculate that sdrs are also present but seismically obscured below the salt basins we argue that the conjugate aptian salt basins are post breakup not pre breakup they were separated from the start by a mid oceanic ridge distal salt accumulated on proto oceanic crust not rift basins this hypothesis is supported by seismic stratigraphy and structure magnetic anomalies plate reconstructions and hydrothermal potash evaporites an important implication for exploration is that thick basalts rather than rift age source rocks may underlie distal parts of the salt basins

the long term evolution of the congo deep sea fan a basin wide view of the interaction between a giant submarine fan and a mature passive margin zaiango project abstract we have integrated the relatively unknown distal domains of the lower congo basin where the main depocenters of the congo submarine fan are located with the better constrained successions on the shelf and upper slope through the analysis of thousands of km of 2d seismic reflection profiles off shore the congo angola passive margin the basin architecture is depicted by two ca 800 km long regional cross sections through the northern congo and southern angola margin a large unit deposited basinward of the aptian salt limit is likely to be the abyssal plain equivalent of the upper cretaceous carbonate shelf that characterized the first post rift deposits in west equatorial african margins a latest turonian shelf deepening event is recorded in the abyssal plain as a long period coniacian eocene of condensed sedimentation and basin starvation the onset of the giant tertiary congo deep sea fan in early oligocene following this event reactivates the abyssal plain as the main depocenter of the basin the time space partitioning of sedimentation within the deep sea fan results from the interplay among increasing sediment supply margin uplift rise of the angola salt ridge and canyon incision throughout the neogene oligocene early miocene turbidite sedimentation occurs mainly in nw se grabens and ponded inter diapir basins on the southern margin angola seaward tilting of the margin and downslope salt withdrawal activates the up building of the angola escarpment which leads to a northward congo shift of the transfer zones during late miocene around the miocene pliocene boundary the incision of the congo submarine canyon confines the turbidite flows and drives a general basinward progradation of the submarine fan into the abyssal plain the slope deposition is dominated by fine grained hemipelagic deposits ever since results from this work contribute to better understand the signature in the ultra deep deposits of processes acting on the continental margin as well as the basin wide sediment redistribution in areas of high river input

accelerated contribution of the paleo congo river to global seawater 87 sr 86 sr change following eocene oligocene collapse of the african surface

environmental reconstruction and dating of shizitan 29 shanxi province an early microblade site in north china global cooling during the last glacial maximum lgm posed significant challenges to peoples living in northern eurasia using micromorphology pollen and non pollen palynomorphs npp and faunal analyses this study reconstructs the local paleoenvironmental contexts of repeated ephemeral occupations at shizitan 29 in shanxi province north china across the lgm from ca 28 to 18 ka cal bp followed by a gap until a final occupation ca 13 5 ka cal bp among the significant finds at shizitan 29 are remains of 285 hearths and a rich lithic assemblage that contains the earliest radiocarbon dated evidence for microblades in china appearing first in layer 7 the environmental data show that the low mountains and tributary river valleys of the yellow river in the loess plateau provided abundant sources of water and food in spite of environmental fluctuations microblade producing groups repeatedly visiting this locality survived severe climate change by making use of fire selective herbivore hunting processing plant foods with grinding stones and symbolic ornamentation such as ostrich shell beads npp data also indicate the potential presence of flax and other fiber processing the shizitan 29 data demonstrate how humans adapted to challenging local conditions throughout the lgm allowing them to stay within this northerly region without migrating to warmer southern latitudes

frontal structure water masses and circulation in the crozet basin due to topographic steering by the crozet and kerguelen plateaus the antarctic circumpolar current acc core in the crozet basin area is shifted to its northernmost position in the southern ocean along the southern limb of the south indian subtropical gyre here the jet like current is embedded within a narrow band 26 5 kg m3 in the western half of the basin and heavier mode 26 7 kg m3 in its eastern half these different varieties of crozet basin mode water are closely correlated with the degree of exchange and mixing between subtropical and subantarctic waters along the dynamically active frontal zone the area north of the kerguelen plateau appears to be an important source of water mass modification antarctic intermediate water advected from the west also undergoes there significant modification by intrusions across the frontal zone of fresher oxygen richer colder subantarctic water energetic eddy activities observed along the frontal zone likely enhance such cross frontal exchange of water masses equatorward spreading of the modified thermocline water masses mode water antarctic intermediate water occurs as part of the anticyclonic circulation in the south indian subtropical gyre which is centered within the basin strong injection of north indian deep water into the acc south of amsterdam island is clearly evidenced for the first time this deep oxygen minimum water centered at about 3000 m can be traced to the east of madagascar from where it spreads southward through the eastern part of the crozet basin due to the influence of this water mass north atlantic deep water characteristics of the circumpolar deep water are significantly altered in kerguelen amsterdam passage our results indicate a cyclonic deep level circulation pattern in the crozet basin with a northward flow 9 sv of circumpolar deep water antarctic bottom water as a deep western boundary current and a partially compensating southward flow 3 sv of north indian deep water through the eastern part of the basin it is concluded that the crozet basin constitutes an important passage for the exchange of water masses between the southern ocean and the indian ocean

archaeological soil and pollen analysis of experimental floor deposits with special reference to butser ancient farm hampshire uk archaeological stratigraphies that may contain floors are often encountered for more than a decade soil micromorphologists working on archaeological sequences have benefited from having access to reference thin sections of ethnoarchaeological and experimental floors including those from the floors of iron age houses reconstructed by the late dr peter reynolds at butser ancient farm hampshire uk this paper reports upon experimental studies mainly carried out at butser during 1990 95 and their suggested application to microstratigraphic and microfacies analysis of occupation sites sampling at butser in 1990 was very much a rescue operation nevertheless fundamental differences in soil micromorphology were found between domestic house beaten floor deposits and those formed in a stable these differences were also reflected in the parallel study of pollen from these deposits with microchemical analyses helping to explain anomalous pollen preservation in the unsuitable soil at butser the limited bulk chemical study produced less clear results but when compared with findings from some roman and early medieval sites in london showed that the chemical trends hinted at butser are probably replicated in some ancient floors a preliminary interdisciplinary study of samples from the london guildhall clearly suggested the potential of such microstratigraphical and microfacies analyses and intimates at the potential of attaining rigorous consensus interpretations stable floor deposits are both organic and phosphate rich with homogeneous soil micromorphological and pollen characteristics beaten floors are much more mineralogenic and heterogeneous in terms of their microfabric and pollen that also indicate trampling in of a wide variety of allocthonous materials the last commonly responsible for raised magnetic susceptibility at archaeological sites these findings prove the worth of the ethnoarchaeological simulations carried out at the moel y gar stable and domestic pimperne house this microfacies approach is viewed as complementary to site reconstruction through macrofossil analysis of beetles and plant remains especially where sites are being investigated at the microstratigraphic level the phosphate content of stabling deposits may allow preservation of pollen in what may otherwise be deemed unsuitable material as demonstrated at butser

gas hydrate and free gas petroleum system in 3d seismic data offshore angola abstractevidence of gas hydrate and free gas occurrences in a 3d seismic volume from the west central coastal province of the congo fan offshore angola illustrates all the components of a complete petroleum system analysis and interpretation are based on the information in attributes calculated from three 3d time migrated common angle seismic volumes the attributes include seismic amplitude spectral components dip magnitude amplitude variation with angle and instantaneous frequency the source is organic rich muds associated with late cretaceous to early tertiary channels the migration paths are along growth faults and the traps are partly defined by the gas hydrate stability zone for the gas hydrate partly by the bottom simulating reflector for the subhydrate free gas and partly by faults for both the spatial distribution of free gas is further supported by the associated seismic bright spots and also by the attenuation of high frequencies of p waves that traverse the gas saturated zo

evidence of a large upper cretaceous depocentre across the continent ocean boundary of the congo angola basin implications for palaeo drainage and potential ultra deep source rocks abstract the analysis of 2d deep seismic reflection profiles across the slope and abyssal plain of the angola oceanic basin reveals the existence of a significant and formerly unknown depocentre beneath the giant cenozoic congo deep sea fan between 7000 m and 9000 m depth deposited directly onto the aptian oceanic crust the unit which is up to 2 5 km thick and extends for more than 200 km basinwards of the continent ocean boundary is probably aged albian turonian its radial fan shaped depocentre is centred on the present day congo river outlet and contains at least 0 2 mio km 3 of sediments these observations and the results from flexural modelling indicate that 1 the location of the congo river s outlet has remained fairly stable since the late cretaceous and 2 the basal unit was indeed sourced by a palaeo congo river probably located nearby the present day one thus the atlantic sedimentary system related to the exoreism of the congo river is much older than previously thought thermal modelling indicates that the maturation history of this upper cretaceous deposits is highly influenced by the interaction between the initial high heat flow of the young oceanic crust and further increase in sediment supply due to the progradation of the overlying tertiary deep sea fan during the miocene hence despite low present day heat flow values should the unit have source rock potential its basal section may be currently generating hydrocarbons all in all the results from our models also suggest that the interplay between an initially high heat flow and the further high sediment supply in areas of major river input may be a key factor for the thermal maturation of potential source rocks deposited onto a present day cold oceanic crust

source rock characteristics and compositional kinetic models of cretaceous organic rich black shales offshore southwestern africa abstract the source rock potential of cretaceous organic rich whole rock samples from deep sea drilling project dsdp wells offshore southwestern africa was investigated using bulk and quantitative pyrolysis techniques the sample material was taken from organic rich intervals of aptian albian and turonian aged core samples from dsdp site 364 offshore angola dsdp well 530a north of the walvis ridge offshore namibia and dsdp well 361 offshore south africa the analytical program included toc rock eval pyrolysis gc bulk kinetics and micro scale sealed vessel pyrolysis mssv experiments the results were used to determine differences in the source rock petroleum type organofacies petroleum composition gas oil ratio gor and pressure volume temperature pvt behavior of hydrocarbons generated from these black shales for petroleum system modeling purposes the investigated aptian and albian organic rich shales proved to contain excellent quality marine kerogens the highest source rock potential was identified in sapropelic shales in dsdp well 364 containing very homogeneous type ii and organic sulfur rich type iis kerogen they generate p n a low wax oils and low gor sulfur rich oils whereas type iii kerogen rich silty sandstones of dsdp well 361 show a potential for gas condensate generation bulk kinetic experiments on these samples indicate that the organic sulfur contents influence kerogen transformation rates type iis kerogen being the least stable south of the walvis ridge the turonian contains predominantly a type iii kerogen north of the walvis ridge the turonian black shales contain type ii kerogen and have the potential to generate p n a low and high wax oils the latter with a high gor at high maturity our results provide the first compositional kinetic description of cretaceous organic rich black shales and demonstrate the excellent source rock potential especially of the aptian aged source rock that has been recognized in a number of the south atlantic offshore basins

the dakhleh glass product of an impact airburst or cratering event in the western desert of egypt impact cratering is a ubiquitous geological process on the terrestrial planets meteorite impact craters are the most visible product of impact events but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time in this contribution we report on an unusual impact glass the dakhleh glass dg which is distributed over an area of 400 km 2 of the dakhleh oasis egypt this region preserves a rich history of habitation stretching back to over 400 000 years before the emergence of homo sapiens we report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the dg formed during an impact event the wide distribution and large size of dg specimens up to 50 cm across the chemistry e g cao and al2o3 contents up to 25 and 18 wt respectively the presence of lechatelierite and burnt sediments and the inclusion of clasts and spherules in the dg is inconsistent with known terrestrial processes of glass formation the age and other textural characteristics rule out a human origin instead we draw upon recent numerical modeling of airbursts to suggest that the properties of dg coupled with the absence of a confirmed crater can best be explained by melting of surficial sediments as a result of a large airburst event we suggest that glass produced by such events should therefore be more common in the rock record than impact craters assuming that the glass formed in a suitable preserving environment

dynamic interactions between the gulf of guinea passive margin and the congo river drainage basin 1 morphology and mass balance 1 a sediment budget between the congo river drainage basin and the western african margin in the gulf of guinea is proposed on the basis of published and unpublished offshore tertiary isopach maps and onshore digital elevation analysis the overall denudation of that area may be as high as 3 5 106 km3 with a maximum of 10 coming from mesozoic and cenozoic covers the southern part of the congo river basin related to uplift of the south african and kalahari shields appears as the most immature from the morphologic standpoint but provides one third of the present day sediment production it represents a maximum denudation of 150 000 km3 on the easternmost part east african rift drainage basins show a more mature relief and a maximum denudation of 270 000 km3 which can increase to 570 000 km3 if the congo drainage basin had extended up to the east branch of the rift these values are confidently established from the existence of remnant geological surfaces and can explain the volume of tertiary sediment in the gulf of guinea during upper cretaceous the most important accumulations of sediments correspond to the ogooe and kwanza fans which shows that the organization of continental drainage was different as was potential source of sediments in the northern part of the present day congo river drainage basin there was a compressional episode during santonian that may have caused significant relief and erosion along a benue chad axis

rapid south atlantic spreading changes and coeval vertical motion in surrounding continents evidence for temporal changes of pressure driven upper mantle flow the south atlantic region displays 1 a topographic gradient across the basin with africa elevated relative to south america 2 a bimodal spreading history with fast spreading rates in late cretaceous and eo oligocene and 3 episodic regional uplift events in the adjacent continents concentrated in late cretaceous and oligocene here we show that these observations can be linked by dynamic processes within earth s mantle through temporal changes in asthenosphere flow beneath the region the topographic gradient implies westward pressure driven mantle flow beneath the basin while the rapid spreading rate changes on order 10 million years require significant decoupling of regional plate motion from the large scale mantle buoyancy distribution through a mechanically weak asthenosphere andean topographic growth in late miocene can explain the most recent south atlantic spreading velocity reduction arising from increased plate boundary forcing associated with the newly elevated topography but this mechanism is unlikely to explain the late cretaceous tertiary spreading variations as changes in andean paleoelevation at the time are small we propose an unsteady pressure driven flow component in the asthenosphere beneath the south atlantic region to explain the late cretaceous tertiary spreading rate variations temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions we find that this prediction from our models agrees with geologic and geophysical observations of the south atlantic region including episodes of passive margin uplift regional basin reactivation and magmatic activity

reconnaissance study of the ancient zaire congo deep sea fan zaiango project analysis of more than 19 000 km of multichannel seismic reflection data from the zaiango project covering the zaire deep sea fan allowed us to identify the oceanic crust and five seismostratigraphic units on the basin floor and abyssal plain in the absence of a direct stratigraphic tie the time frame is provided by long distance correlations a stratigraphic model for the evolution of the zaire deep sea fan is proposed a widespread major regional unconformity representing probably the eocene oligocene transition marks a drastic change of sedimentation pattern in the basin floor a pelagic aggradational sequence albian eocene overlying the oceanic crust gives way to an onlapping prograding sequence of turbidite deposits oligocene recent this change marks the onset of the ancient zaire deep sea fan triggered by the climatic change related to the greenhouse icehouse shift at the eocene oligocene transition which was responsible for a drastic increase in continental erosion and terrigenous sedimentary supply to the margin the volume of the fan is at least 0 7 mkm 3 much broader and thicker than formerly assumed a short lived episode of rapid facies progradation

importance of the eastern indian ocean for the abyssal pacific 1 the role of the eastern indian ocean in controlling the abyssal circulation in the pacific is examined using a 1 1 world ocean model thanks to the improvement of bottom topography and the incorporation of a bottom boundary layer model the bottom water formation off the adelie coast is produced this bottom water is not only the source of the abyssal water in the eastern indian but also has a great influence on the whole abyssal pacific the lower part of circumpolar deep water cdw which enters the abyssal pacific passing through south of new zealand changes its property through mixing with this bottom water flowing underneath cdw in the australian antarctic basin and the south australia basin the tracer experiments show that the water ventilated off the adelie coast occupies about 20 of the abyssal pacific whereas north atlantic deep water nadw occupies about 50 the weddell sea bottom water about 20 and the ross sea bottom water about 10 the flux of the ventilated water estimated by the tracer experiments is 17 1 sv for nadw 6 3 sv from the weddell sea 6 2 sv from off the adelie coast and 3 5 sv from ross sea in this model the total flux of 33 1 sv is not far from the estimate from observations though it may overestimate by 1 4 sv this does not directly indicate that the real world ocean should have the large amount of the bottom water sources in the pacific indian sector however the model offers a picture of the water properties consistent with the observation

architecture and depositional pattern of the quaternary deep sea fan of the amazon abstract the quaternary deep sea fan of the amazon is composed of four superimposed lens shaped channel levee complexes covering most of the fan surface and controlled by allocyclic processes high amplitude sea level variations of recent glacial cycles induced river fed turbiditic currents that discharged directly into the submarine canyon during low sea level in contrast individual channel levee systems and associated terminal lobes are governed by two distinct autocyclic processes 1 an initial phase of avulsion and adjustment with unconfined sand deposition high amplitude reflection packets and 2 down fan progressive aggradation progradation of a graded channel levee lobe system when a new equilibrium profile is reached during the latter phase the system acts as a particularly efficient sand cleaning and separating factory that is responsible for the high reservoir potential of such turbidites

planation surfaces as a record of mantle dynamics the case example of africa abstract there are two types of emerged relief on the earth high elevation areas mountain belts and rift shoulders in active tectonic settings and low elevation domains anorogenic plateaus and plains characteristic of the interior of the continents i e 70 of the earth emerged relief both plateaus and plains are characterized by large erosional surfaces called planation surfaces that display undulations with middle several tens of kilometres to very long several thousands of kilometres wavelengths i e characteristic of lithospheric and mantle deformations respectively our objective is here 1 to present a new method of characterization of the very long and long wavelength deformations using planation surfaces with an application to central africa and 2 to reconstruct the growth of the very long wavelength relief since 40 ma as a record of past mantle dynamics below central africa i the african relief results from two major types of planation surfaces etchplains weathering surfaces by laterites and pediplains pediments these planation surfaces are stepped along plateaus with different elevations this stepping of landforms records a local base level fall due to a local tectonic uplift ii central africa is an extensive etchplain type weathering surface called the african surface from the uppermost cretaceous 70 ma to the middle eocene 45 ma with a paroxysm around the early eocene climatic optimum restoration of this surface in central africa suggests very low elevation planation surfaces adjusted to the atlantic ocean and indian ocean with a divide located around the present day eastern branch of the east african rift iii the present day topography of central africa is younger than 40 30 ma and records very long wavelength deformations 1000 2000 km with 1 the growth of the cameroon dome and east african dome since 34 ma 2 the angola mountains since 15 12 ma increasing up to pleistocene times and 3 the uplift of the low elevation 300 m congo basin since 10 3 ma some long wavelength deformations several 100 km also occurred with 1 the low elevation central african rise since 34 ma and 2 the atlantic bulge since 20 16 ma these very long wavelength deformations record mantle dynamics with a sharp increase of mantle upwelling around 34 ma and an increase of the wavelength of the deformation and then of mantle convection around 10 3 ma

deep structure of the west african continental margin congo zaire angola between 5 s and 8 s from reflection refraction seismics and gravity data summary the deep structure of the west african continental margin between 5 s and 8 s was investigated using vertical reflection and wide angle reflection refraction techniques during the zaiango project a joint programme conducted in 2000 april by ifremer and totalfinaelf to penetrate below the salt layer a non conventional low frequency seismic source was used in the single bubble mode together with ocean bottom instruments hydrophones and seismometers and a 4 5 km long streamer that recorded multichannel seismic reflection mcs the data show that the continental crust thins abruptly over a lateral distance of less than 50 km from 30 km thick below the continental platform based on gravity data to less than 4 km thick below the lower congo basin that formed prior to the aptian salt deposition this subsalt sedimentary basin 180 km wide 4 km thick with velocities varying from 4 7 km s 1 to 5 8 km s 1 at the bottom is located between the foot of the continental slope and the oceanic domain it is underlain by crust of an intermediary or transitional type between continental crust and what can be recognized as oceanic crust in the transitional zone a crustal upper layer is present below the pre salt sedimentary basin 3 to 7 km thick with velocities increasing from 5 8 km s 1 at the top to 6 8 km s 1 at the bottom of the layer this layer appears to thin regularly from 6 7 km thick below the depocentre of the pre salt sedimentary basin to 3 4 km thick below the western termination of the basin below this upper crustal layer an anomalous velocity layer 7 2 to 7 8 km s 1 is documented below the eastern side of the basin where the crustal thinning is at a maximum the origin of this layer is unknown several arguments like rifting duration between 15 ma and 30 ma or the absence of seaward dipping reflectors precludes the hypothesis of underplated mantle material but other hypotheses such as serpentinized material or high grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks are plausible near the ocean termination of the basin the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles 7 11 and 14 having a dense ocean bottom seismometer hydrophone obs obh spacing on these profiles an anomalous velocity layer is present in the westernmost part of the transitional zone below the basement ridge and in the oceanic domain this layer absent on profile 3 may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

ocean circulation and frontal structure near the southern kerguelen plateau the physical context for the kerguelen axis ecosystem study oceanographic observations from ships floats and remote sensing are used to describe the ocean circulation and frontal structure from the southern kerguelen plateau to the antarctic margin the flow of the antarctic circumpolar current acc is largely zonal upstream of the kerguelen plateau the southern branch of the polar front and the northern branch of the southern acc front saccf are deflected to the north by the topography and cross the plateau through the fawn trough the southern branch of the saccf and the southern boundary of the acc pass to the south of banzare bank through the princess elizabeth trough these fronts turn sharply to the north on the eastern flank of the plateau then retroflect to the south before continuing eastward satellite altimetry and float trajectories suggest the acc regime to the east of the plateau is eddy rich and characterised by extensive meandering of the acc fronts in contrast to the low eddy energy and zonal flow observed west of the plateau the antarctic slope current flows west along the upper continental slope with hydrographic data indicating some of the flow turns offshore and feeds the southern boundary flow in the western boundary current flow over the plateau itself is relatively quiescent and floats in this region have a long residence time 1 year the regional circulation is closely associated with the distribution of biological productivity in surface waters as revealed in satellite measurements of ocean colour including high productivity in subpolar waters along the eastern edge of the plateau and over the antarctic continental shelf moderate productivity over the plateau and low productivity in acc waters in the fawn trough and north of the saccf

major controlling factors on hydrocarbon generation and leakage in south atlantic conjugate margins a comparative study of colorado orange campos and lower congo basins abstract we present a supra regional comparative study of the major internal and external factors controlling source rock sr maturation and hydrocarbon hc generation and leakage in two pairs of conjugate margins across the south atlantic the brazil campos basin angola lower congo basin margins located in the central segment and the argentina colorado basin south africa orange basin in the southern segment our approach is based on the analysis and integration of borehole data 1d numerical modeling 2d seismic reflection data and published reports coupling of modeling results sedimentation rate calculation and seal bypass system analysis reveal that 1 oil window is reached by syn rift srs in the southern segment during the early to late cretaceous when thermal subsidence is still active while in the central segment they reach it in late cretaceous neogene during a salt remobilization phase and 2 early hc generation from post rift srs in the southern segment and from all srs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates the latter seems to be associated with the andes uplift history for the western south atlantic basins campos and colorado and to a possibly climate driven response for the eastern south atlantic basins orange and lower congo additionally we observe that the effect of volcanism on sr maturation in the southern segment is very local the comparison of cretaceous mass transport deposit mtd episodes with hc peak of generation and paleo leakage indicators in the southern segment revealed the possible causal effect that hc generation and leakage have over mtd development interestingly paleogene leakage indicators which were identified in the argentina south africa conjugate margins occur contemporaneously to low sedimentation rate periods nonetheless present day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal failure events linked to eustatic sea level drops

30 000 year old wild flax fibers a unique finding of wild flax fibers from a series of upper paleolithic layers at dzudzuana cave located in the foothills of the caucasus georgia indicates that prehistoric hunter gatherers were making cords for hafting stone tools weaving baskets or sewing garments radiocarbon dates demonstrate that the cave was inhabited intermittently during several periods dated to 32 to 26 thousand years before the present kyr b p 23 to 19 kyr b p and 13 to 11 kyr b p spun dyed and knotted flax fibers are common apparently climatic fluctuations recorded in the cave s deposits did not affect the growth of the plants because a certain level of humidity was sustained

deep western boundary current and southern frontal systems of the antarctic circumpolar current southeast of the kerguelen plateau 1 the structures of the deep western boundary current and southern frontal systems of the antarctic circumpolar current acc southeast of the kerguelen plateau were investigated top to bottom hydrography was conducted around 58 s and two underway observations were made around 56 s and 61 s middepth floats were also used to describe the subsurface flow and temperature fields along the 58 s section a cold dome was located just off the plateau and northwestward and southeastward flows were found in its western and eastern sides the observed flow structure was highly barotropic the maximum volume transport of the bottom water was 22 sv equatorward including a possible cyclonic recirculation of 10 sv the transport of the deep recirculation can be explained by the potential vorticity homogenization in the closed isopachs formed by the bottom slope off the plateau and the overlying acc flowing southeastward through the fawn trough the spatial scale of the cold dome which showed a signature of the southern acc front was around 100 km at 58 s and the similar cold domes were also found around 56 s and 61 s along with a signature of the southern boundary of acc around 61 s the sharp excursion of the southern acc front was also confirmed by the middepth float trajectories and the distribution of temperature maximum this indicates the equatorward excursion up to 54 s with the warmer acc water just east of the southern frontal systems

northern boundary currents and adjacent recirculations off southwestern australia full depth hydrographic and velocity measurements along 115 e south of australia whp section i9s reveal an active northern boundary current regime within 200 300 km of the australian continental shelf and an offshore recirculation regime within the south australian basin in the upper ocean an oft described westward flowing northern boundary current the flinders current extends through the thermocline and the salinity minimum strata of antarctic intermediate water with an opposing eastward recirculation to its south the new data shows that beneath the flinders current an eastward flowing deep northern boundary current transports water of subtropical indian ocean origin supplied by southward deep flow along the western continental slope of australia in the perth basin between these northern boundary currents and the antarctic circumpolar current thermocline and deep geostrophic shears indicate weak recirculations eastward at thermocline levels and westward in the deep water lowered acoustic doppler current profiler data reveal stronger organized recirculations to both the flinders current and the deep northern boundary current with the westward deep recirculation exceeding the eastward transport of the deep northern boundary current and thus representing a net supply of deep water to the perth basin

strong export of antarctic bottom water east of the kerguelen plateau deep western boundary currents east of the antarctic peninsula and the kerguelen plateau are important pathways for transporting deep antarctic water masses to the global ocean an array of moored current meters used to quantify the water transport in this system reveals a flow that is stronger than any measured in a deep western boundary current at similar depths so far the primary paths for the transport of antarctic bottom water from the southern ocean into the global ocean are the deep western boundary currents east of the antarctic peninsula and the kerguelen plateau1 previous ship based observations documented distinct water properties and velocities associated with a deep western boundary current in the kerguelen region2 3 4 5 6 7 but the mean flow is as yet unconstrained here we report measurements from a coherent array of eight current meter moorings that reveal a narrow and intense equatorward flow extending throughout the water column just east of the kerguelen plateau velocities averaged over two years exceed 20 cm s 1 at depths of about 3 500 m the strongest mean deep western boundary current flow yet observed at similar depths we estimate the mean equatorward transport of water colder than 0 c at 12 3 1 2 106 m3 s 1 partially compensated by poleward flow we also estimate the net equatorward flow of water colder than 0 2 c at about 8 106 m3 s 1 substantially higher than the 1 9 106 m3 s 1 reported from the boundary current that carries dense water from the weddell sea into the atlantic ocean north of the falkland plateau8 we conclude that the kerguelen deep western boundary current is a significant pathway of the global ocean s deep overturning circulation

the age of supergene manganese deposits in katanga and its implications for the neogene evolution of the african great lakes region abstract supergene manganese deposits commonly contain k rich mn oxides with tunnel structure such as cryptomelane which are suitable for radiometric dating using the 39ar 40ar method in africa mn deposits have been dated by this method for localities in western and southern parts of the continent whereas only some preliminary data are available for central africa here we present new 39ar 40ar ages for mn oxide samples of the kisenge deposit in southwestern katanga democratic republic of the congo the samples represent supergene mn oxide deposits that formed at the expense of primary paleoproterozoic rhodochrosite dominated carbonate ores main phases of mn oxide formation are dated at c 10 5 ma 3 6 ma and 2 6 ma for a core that crosses a mineralized interval the latter shows a decrease in age with increasing depth recording downward penetration of a weathering front surface samples of the kisenge deposits also record a c 19 2 ma phase as well as c 15 7 ma 14 2 ma and 13 6 ma phases the obtained ages correspond to distinct periods of paleosurface development and stability during the mio pliocene in katanga because katanga is a key area bordered to the north by the congo basin and to the east by the east african rift system these ages also provide constraints for the geodynamic evolution of the entire region for the mio pliocene the kisenge deposits record ages that are not systematically found elsewhere in africa although the 10 5 11 ma event corresponds to a roughly simultaneous event in the kalahari manganese field south africa the rest of the katanga paleosurface record differs somewhat from records for other parts of africa for which older eocene ages have been obtained this difference is most probably related to the specific regional geodynamic context uplift of the east african plateau with associated erosion and the opening of the east african rift system at c 25 ma are events whose effects in the study area interfere with those of processes responsible for the development of continent wide paleosurfaces

large scale circulation over and around the northern kerguelen plateau abstract the kerguelen plateau is known to constitute a major barrier to the eastward flowing antarctic circumpolar current however there is limited knowledge on the regional circulation due to sparse observations especially in the northern kerguelen plateau between the fawn trough and the kerguelen islands as part of the physical component of the multidisciplinary keops cruise systematic ctd measurements along three sw ne oriented sections were made on the latter plateau cutting through the annual phytoplankton bloom across the eastern flank of the plateau into deep water major hydrographic features and geostrophic velocities perpendicular to the sections were first documented from these in situ observations in order to interpret the results within the general circulation context and to trace the upstream pathways of the observed water masses we established a synthetic picture of the large scale circulation over and around the entire northern kerguelen plateau using the combination of new data from keops with historical hydrographic data together with all available information on mid depth and near surface velocities derived from autonomous floats surface drifting buoys and satellite altimetry this synthesis shows that the time mean geostrophic flow over the shallow platform is sluggish of the order of 3 5 cm s 1 with a general anticyclonic circulation roughly following the local bathymetry this weak flow is bordered to the east by relatively strong up to 18 cm s 1 northwestward flow along the eastern flank of the northern kerguelen plateau due to a northward bifurcation of cold antarctic waters of eastern enderby basin origin carried by the powerful fawn trough current we have shown the utmost importance of the general circulation for the spatial distribution of primary productivity in that the sluggish circulation over the complex shallow topography of the northern kerguelen plateau may precondition the recurrence of annual blooms in contrast to neighboring strong advective regimes without blooming in deep water

water mass and biogeochemical variability in the kerguelen sector of the southern ocean a machine learning approach for a mixing hot spot author s rosso isabella mazloff matthew r talley lynne d purkey sarah g freeman natalie m maze guillaume

bondi cave and the middle upper palaeolithic transition in western georgia south caucasus abstract the late pleistocene expansion of anatomically modern humans amhs into eurasia and the concurrent demise of the neanderthals appears to be a complex and regionally variable process the southern caucasus region with its rich cave sites has recently provided important results regarding this process in this paper we report on the results of fieldwork in bondi cave western georgia providing a new radiocarbon chronology stratigraphic observations analyses of lithic technology and provenance faunal and floral remains as well as paleoenvironmental data the cave includes middle palaeolithic ca 45 000 ka cal bp cultural horizons and a long upper palaeolithic sequence ca 40 000 27 000 cal bp from layer v to iv a modern human tooth was found in layer vb we estimate its age at 39 000 35 800 cal bp 95 4 based on the bayesian age model we built if the context of the tooth is reliable as we think it is this would make it the oldest morphologically modern human in the caucasus upper palaeolithic hunting of tur and bison as well as the collection of various plants including flax is attested mobile upper palaeolithic foragers inhabited the cave in generally cold and dry periods but a mosaic of environments including forests and meadows was nonetheless available to them the archaeological sequence of bondi and adjacent sites indicates a substantial time gap between the middle and upper palaeolithic occupations thus disproving neanderthal amh interaction in this area and lending support to a replacement scenario in the southern caucasus assuming of course that the early upper palaeolithic eup is related to the arrival of amhs

direct observations of the antarctic slope current transport at 113 e the antarctic slope current asc defined here as the region of westward flow along the continental slope off antarctica forms the southern limb of the subpolar gyres it regulates the exchange of water across the shelf break and provides a path for interbasin westward transport despite its significance the asc remains largely unobserved around most of the antarctic continent here we present direct velocity observations from a 17 month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths in the southeastern indian ocean near 113 e the observed time mean flow consists of a surface intensified jet associated with the antarctic slope front asf and a broader bottom intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope the time mean transport of the asc is 29 2 sv fluctuations in the transport are large typically exceeding the mean by a factor of 2 they are mainly due to changes in the northward extent of the current over the lower slope however seasonal changes in the wind also drive variations in the transport of the asf and the flow in the upper slope both mean and variability are largely barotropic thus invisible to traditional geostrophic methods this article is protected by copyright all rights reserved

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

structural evolution and sequence formation offshore south gabon during the tertiary abstract the present investigation of the tertiary succession offshore south gabon is based on seismic surveys of 1985 1989 vintage and wells covering the southern part of gabonese waters in general the tertiary basin off south gabon evolved during two structural stages during the paleocene and early middle eocene a trough like basin subsided slowly towards the west during this period there was a cyclic development of the succession which consists of up to four sequences mostly bounded by type 2 sequence boundaries the sequential changes were induced by eustatic sea level changes this pattern changed during the neogene when the evolution was characterized by continental crustal flexuring in early middle miocene times this resulted in strong subsidence of the western part of the basin and uplift of the eastern part consequently the eastern part was exposed to strong erosion and a thick middle miocene succession was deposited west of the shelf approximately the present day shelf especially on the slope the clinoformal and lens shaped middle late miocene succession which consists of four sequences bounded by type 1 sequence boundaries has been controlled by eustatic changes in sea level in addition to the overall subsidence pattern salt tectonics has modified the external and internal architecture of the sequences on a local scale canyon formation in connection with slumping results in the establishment of well developed fan systems on the lower part of the slope and on the basin floor area

overcoming pitfalls of vitrinite reflectance measurements in the assessment of thermal maturity the case history of the lower congo basin abstract vitrinite reflectance has been always considered the most reliable thermal maturity indicator in sedimentary basins nevertheless the reliability of vitrinite reflectance measurements can be affected by many external factors that change from basin to basin e g organic facies temperature and pressure conditions leading to wide uncertainties in thermal modelling calibration and thus in the evaluation of timing and amount of hydrocarbons generation we demonstrate that in case of vitrinite suppression and or retardation in siliciclastic successions the classical sweeney and burnham kinetics do not match the actual thermal evolution of the basin in these cases thermal evolution can be successfully modelled using a complementary approach based on smectite illitization kinetics or more appropriate kinetics e g presro tm and t p ro to evaluate the effect of pressure on organic matter maturation where pressure data are available this approach was applied in the lower congo basin where 32 cuttings from a 5 km deep well drilled in the upper oligocene miocene malembo formation have been analysed to derive organic and inorganic constraints to model the basin thermal evolution vitrinite and bitumen reflectance measurements show values between 0 3 and 1 0 along the well whilst the illite content of mixed layer i s ranges between 35 and 88 passing from r0 to r1 to r3 stacking order with increasing depth present day temperature distribution through the well indicates a geothermal gradient of about 40 c km and measured pressures show an overpressured interval between 3 and 4 km depth retardation and suppression phenomena affected vitrinite reflectance in this interval but did not influence smectite illitization the comparison between thermal maturity scenarios constrained by organic and inorganic thermal indicators shows differences in the calculation of the depth of the onset of hydrocarbon generation that is overestimated of about 500 m in the lower miocene interval when only suppressed retarded vitrinite reflectance values are used to calibrate models

isotopic interrogation of a suspected late eocene glaciation ephemeral polar glaciations during the middle to late eocene 48 34 ma have been proposed based on far field ice volume proxy records and near field glacigenic sediments although the scale timing and duration of these events are poorly constrained here we confirm the existence of a transient cool event within a new high resolution benthic foraminiferal 18o record at ocean drilling program odp site 738 kerguelen plateau southern ocean this event named the priabonian oxygen isotope maximum prom event lasted 140 kyr and is tentatively placed within magnetochron c17n 1n 37 3 ma based on the correlation to odp site 689 maud rise southern ocean a contemporaneous change in the provenance of sediments delivered to the kerguelen plateau occurs at the study site determined from the 63 m fraction of decarbonated and reductively leached sediment samples changes in the mixture of bottom waters based on fossil fish tooth nd were less pronounced and slower relative to the benthic 18o and terrigenous nd changes terrigenous sediment nd values rapidly shifted to less radiogenic signatures at the onset of the prom event indicating an abrupt change in provenance favoring ancient sources such as the paleoproterozoic east antarctic craton bottom water nd reached a minimum value during the prom event although the shift begins much earlier than the terrigenous nd excursion the origin of the abrupt change in terrigenous sediment provenance is compatible with a change in antarctic terrigenous sediment flux and or source as opposed to a reorganization of ocean currents a change in terrigenous flux and or source of antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in east antarctica during the early late eocene

flow processes and sedimentation in unidirectionally migrating deep water channels from a three dimensional seismic perspective three dimensional seismic data were used to infer how bottom currents control unidirectional channel migration bottom currents flowing towards the steep bank would deflect the upper part of sediment gravity flows at an orientation of 1 degrees to 11 degrees to the steep bank yielding a helical flow circulation consisting of a faster near surface flow towards the steep bank and a slower basal return flow towards the gentle bank this helical flow model is evidenced by the occurrence of bigger muddier suggested by low amplitude seismic reflections lateral accretion deposits and gentle channel wall with downlap terminations on the gentle bank and by smaller sandier indicated by high amplitude seismic reflectors channel fills and steep channel walls with truncation terminations on the steep bank this helical flow circulation promotes asymmetrical depositional patterns with dipping accretion sets restricted to the gentle bank which restricts the development of sinuosity and yields unidirectional channel migration these results aid in obtaining a complete picture of flow processes and sedimentation in submarine channels