Contourite porosity, grain size and reservoir characteristics

Acknowledgements Many people are to thank for the collection and release of the data used in this study. In particular, we thank the captain, officers and crew, and the scientific and technical shipboard parties of the different IODP expeditions utilised. We each thank our respective institutes for their ongoing support. Xiaohang Yu acknowledges financial support from the National Natural Science Foundation of China (No. 41976067).Peer reviewedPostprin

Morphostructure and tectono-sedimentary control of a mixed contourite-turbidite system in a transpressive margin : Gulf of Cadiz, SW Iberia

A comprehensive analysis has been carried out of morphological features, morphometric characterisation and structural attributes of the northern Gulf of Cadiz slope, offshore Spain and Portugal. This study used an extensive database including high-resolution bathymetric mapping, 2D seismic reflection profiles and sediment cores recovered during IODP Expedition 339 in order to document the nature of a transpressive continental margin. The principal features include faults, channels, diapirs, fluid-escape features (pockmarks, mud volcanoes, mud mounds, chimneys), mass-transport deposits (slides, slumps, debrites), and erosionaldepositional forms (scarps, scours and sediment waves). A complete new morpho-sedimentary map of the region has been constructed, and a novel morphometric analysis carried out. This study shows that tectonism exerts the strongest control on sedimentation. Most structural features are aligned NE-SW, others are orientated E-W and NW-SE, and geomorphological features show parallel alignment. These morpho-tectonic features affect the physiography of the sea floor and hence hydrodynamics of currents. Diapiric ridges and large faults affect the seafloor gradient. Channels in the study area evolved, avulsed and changed direction in response to their interaction with geomorphological structures and current action. Furthermore, tectonism resulted in significant differences in the geomorphological characteristics and morphometrics (drainage density, basin shape, and stream numbers) between the northern and the southern half of the study area. This is linked to the presence of a large accretionary wedge complex in the south, resulting from large-scale plate tectonic interaction. The north-westwards advancement of the AWC, in addition to transpressive tectonism, is responsible for the number and dimension of morphological features in the south of the study area. The northern Gulf of Cadiz margin can be referred to as a mixed depositional system having a varied sedimentary assemblage including contourites, turbidites, bottom-current reworked turbidites, debrites, mass transport deposits, hemipelagites and pelagites. The different facies are, in part, spatially and temporally separated, and in part, closely interbedded. Contourites are the dominant facies in the Quaternary, with turbidites and associated downslope facies most evident in the older Pliocene-Miocene succession. Grainsize statistical analysis (over 1200 turbidite and over 600 contourite samples), together with mineralogical study, reveal distinctive features of standard turbidites and contourites, whereas reworked turbidites have some similarities to both. Bi-variate plots of grainsize statistical data help distinguish between turbidites and contourites. Especially valuable are the mean size vs skewness and the coarsest percentile vs median (CM) cross plots

Deep-Sea Bottom Currents: Their Nature and Distribution

The oceans are stratified into distinct layers with different physical and chemical properties. One of the principal divisions is between theupper warm-water sphere and the deep cold-water sphere, separated by the thermocline. The thermocline is the zone of marked temperaturechange from about 200 to 1000 m water depth. For physical oceanographers, deep-sea bottom currents are generally defined as the flow ofwater masses in the cold-water sphere beneath the base of the thermocline (Zenk, 2008).There are at least three different bottom current types that can be recognized as operating in deep water settings (Shanmugam, 2008;Rebesco et al., 2014; Esentia et al., 2018) including: (a) wind-driven bottom currents, (b) thermohaline bottom currents, and (c) deepwatertidal bottom currents, both barotropic and baroclinic. Bottom currents are also affected by intermittent processes, such as giant eddies,benthic storms, flow cascading, and tsunamis. All of these currents and processes are capable of affecting seafloor sediment through theirerosion, transport and deposition.Early work by the German physical oceanographer Wüst (1933) initially proposed that bottom currents driven by thermohalinecirculation might be sufficiently strong to influence sediment flux in the deep ocean basins. But his work was largely ignored until the early1960s when Bruce Heezen of Woods Hole Oceanographic Institute took up the challenge from a marine geological perspective. In their nowseminal paper of 1966, Heezen, et al. demonstrated the very significant effects of contour following bottom currents or contour currentsin shaping sedimentation on the deep continental rise off eastern North America. The deposits of these semipermanent alongslope currentssoon became known as contourites, clearly distinguishing them from the deposits of downslope event processes known as turbidites. Theensuing decade saw a profusion of research on contourites and bottom currents in and beneath the present-day oceans, and the demarcationof slope-parallel, elongate, mounded sediment bodies made up largely of contourites that became known as contourite drifts (Hollister andHeezen, 1972; McCave and Tucholke, 1986).For the most part, physical oceanographers have worked independently of geologists on the nature and variability of bottom currents,so that much integration is still required between these disciplines. Important contributions that to some extent bridge this divide havecome from the HEBBLE project on the Nova Scotian Rise (Hollister and McCave, 1984), work along the Brazilian continental margin(Viana et al., 1998), and an extensive program of research in the Gulf of Cadiz, culminating in IODP Expedition 339 (Stow et al., 2013;Hernandez-Molina et al. 2014). Prior to this latest mission, the international deep-sea drilling program in its various guises (DSDP, IPOD,ODP, IODP) has contributed enormously to contourite research—the paleoceanographic context and study of oceanic gateways remainprimary targets at present. A topical synthesis of ocean currents can be found in Stow (2017).This contribution in the Encyclopedia of Ocean Sciences is one of three on deep-sea bottom currents and their deposits. The focushere is on the nature and variability of bottom currents, based largely on physical oceanographers’ observations of modern oceans, theirwater mass structure and patterns of circulation. The other two contributions outline the contourite drifts, erosion surfaces and bedformmorphology caused by bottom current interaction with the seafloor, and the nature of bottom current deposits, known as contourites

Deep-Sea Bottom Currents: Their Nature and Distribution

The oceans are stratified into distinct layers with different physical and chemical properties. One of the principal divisions is between theupper warm-water sphere and the deep cold-water sphere, separated by the thermocline. The thermocline is the zone of marked temperaturechange from about 200 to 1000 m water depth. For physical oceanographers, deep-sea bottom currents are generally defined as the flow ofwater masses in the cold-water sphere beneath the base of the thermocline (Zenk, 2008).There are at least three different bottom current types that can be recognized as operating in deep water settings (Shanmugam, 2008;Rebesco et al., 2014; Esentia et al., 2018) including: (a) wind-driven bottom currents, (b) thermohaline bottom currents, and (c) deepwatertidal bottom currents, both barotropic and baroclinic. Bottom currents are also affected by intermittent processes, such as giant eddies,benthic storms, flow cascading, and tsunamis. All of these currents and processes are capable of affecting seafloor sediment through theirerosion, transport and deposition.Early work by the German physical oceanographer Wüst (1933) initially proposed that bottom currents driven by thermohalinecirculation might be sufficiently strong to influence sediment flux in the deep ocean basins. But his work was largely ignored until the early1960s when Bruce Heezen of Woods Hole Oceanographic Institute took up the challenge from a marine geological perspective. In their nowseminal paper of 1966, Heezen, et al. demonstrated the very significant effects of contour following bottom currents or contour currentsin shaping sedimentation on the deep continental rise off eastern North America. The deposits of these semipermanent alongslope currentssoon became known as contourites, clearly distinguishing them from the deposits of downslope event processes known as turbidites. Theensuing decade saw a profusion of research on contourites and bottom currents in and beneath the present-day oceans, and the demarcationof slope-parallel, elongate, mounded sediment bodies made up largely of contourites that became known as contourite drifts (Hollister andHeezen, 1972; McCave and Tucholke, 1986).For the most part, physical oceanographers have worked independently of geologists on the nature and variability of bottom currents,so that much integration is still required between these disciplines. Important contributions that to some extent bridge this divide havecome from the HEBBLE project on the Nova Scotian Rise (Hollister and McCave, 1984), work along the Brazilian continental margin(Viana et al., 1998), and an extensive program of research in the Gulf of Cadiz, culminating in IODP Expedition 339 (Stow et al., 2013;Hernandez-Molina et al. 2014). Prior to this latest mission, the international deep-sea drilling program in its various guises (DSDP, IPOD,ODP, IODP) has contributed enormously to contourite research—the paleoceanographic context and study of oceanic gateways remainprimary targets at present. A topical synthesis of ocean currents can be found in Stow (2017).This contribution in the Encyclopedia of Ocean Sciences is one of three on deep-sea bottom currents and their deposits. The focushere is on the nature and variability of bottom currents, based largely on physical oceanographers’ observations of modern oceans, theirwater mass structure and patterns of circulation. The other two contributions outline the contourite drifts, erosion surfaces and bedformmorphology caused by bottom current interaction with the seafloor, and the nature of bottom current deposits, known as contourites

Deep-Sea Bottom Currents: Their Nature and Distribution

The oceans are stratified into distinct layers with different physical and chemical properties. One of the principal divisions is between theupper warm-water sphere and the deep cold-water sphere, separated by the thermocline. The thermocline is the zone of marked temperaturechange from about 200 to 1000 m water depth. For physical oceanographers, deep-sea bottom currents are generally defined as the flow ofwater masses in the cold-water sphere beneath the base of the thermocline (Zenk, 2008).There are at least three different bottom current types that can be recognized as operating in deep water settings (Shanmugam, 2008;Rebesco et al., 2014; Esentia et al., 2018) including: (a) wind-driven bottom currents, (b) thermohaline bottom currents, and (c) deepwatertidal bottom currents, both barotropic and baroclinic. Bottom currents are also affected by intermittent processes, such as giant eddies,benthic storms, flow cascading, and tsunamis. All of these currents and processes are capable of affecting seafloor sediment through theirerosion, transport and deposition.Early work by the German physical oceanographer Wüst (1933) initially proposed that bottom currents driven by thermohalinecirculation might be sufficiently strong to influence sediment flux in the deep ocean basins. But his work was largely ignored until the early1960s when Bruce Heezen of Woods Hole Oceanographic Institute took up the challenge from a marine geological perspective. In their nowseminal paper of 1966, Heezen, et al. demonstrated the very significant effects of contour following bottom currents or contour currentsin shaping sedimentation on the deep continental rise off eastern North America. The deposits of these semipermanent alongslope currentssoon became known as contourites, clearly distinguishing them from the deposits of downslope event processes known as turbidites. Theensuing decade saw a profusion of research on contourites and bottom currents in and beneath the present-day oceans, and the demarcationof slope-parallel, elongate, mounded sediment bodies made up largely of contourites that became known as contourite drifts (Hollister andHeezen, 1972; McCave and Tucholke, 1986).For the most part, physical oceanographers have worked independently of geologists on the nature and variability of bottom currents,so that much integration is still required between these disciplines. Important contributions that to some extent bridge this divide havecome from the HEBBLE project on the Nova Scotian Rise (Hollister and McCave, 1984), work along the Brazilian continental margin(Viana et al., 1998), and an extensive program of research in the Gulf of Cadiz, culminating in IODP Expedition 339 (Stow et al., 2013;Hernandez-Molina et al. 2014). Prior to this latest mission, the international deep-sea drilling program in its various guises (DSDP, IPOD,ODP, IODP) has contributed enormously to contourite research—the paleoceanographic context and study of oceanic gateways remainprimary targets at present. A topical synthesis of ocean currents can be found in Stow (2017).This contribution in the Encyclopedia of Ocean Sciences is one of three on deep-sea bottom currents and their deposits. The focushere is on the nature and variability of bottom currents, based largely on physical oceanographers’ observations of modern oceans, theirwater mass structure and patterns of circulation. The other two contributions outline the contourite drifts, erosion surfaces and bedformmorphology caused by bottom current interaction with the seafloor, and the nature of bottom current deposits, known as contourites