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The distinction between turbidites, contourites and hemipelagites in modern and ancient deep-water systems has long been a matter of controversy. This is partly because the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap. In addition, the three facies types commonly occur within interbedded sequences of continental margin deposits. The nature of these end-member processes and their physical parameters are becoming much better known and are summarised here briefly. Good progress has also been made over the past decade in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics are summarised here in terms of standard facies models and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. A three-scale approach to distinction for all deep-water facies types should be attempted wherever possible, including large-scale (oceanographic and tectonic setting), regional-scale (architecture and association) and small-scale (sediment facies) observations.

Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we show that Holocene fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the contourite drifts are due to high rates of sedimentation. Over the past 50 million years, sedimentation rates at the studied contourite drift sites have overall increased, coincident with decreasing atmospheric CO2 and a cooling global climate. Our work suggests that a ramp‐up of the bottom‐current carbon pump has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the overall global cooling after the Eocene Thermal Maximum. Plain Language Summary Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we examine data from modern contourite drifts (large‐scale, alongslope‐trending bottom‐current deposits) across the globe and show modern fluxes of organic carbon into the drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1 to 2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the drifts are due to high rates of sedimentation in these deepwater environments, which are driven primarily by vigorous bottom currents—in other words, by a bottom‐current pump that is highly efficient at burying organic carbon. Our work suggests that a ramp‐up of the bottom‐current carbon pump, attributable to progressive intensification of global ocean circulation over the past 50 million years, has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the global cooling after the Eocene Thermal Maximum. Sedimentary records of past organic carbon fluxes in contourite drifts over geologic time could well prove useful in informing predictions of future climate. Key Points Modern fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1 The fluxes into the drifts are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones Over the past 50 million years, the bottom‐current pump has accelerated removal of carbon from the oceanic water

Significant gas discoveries have been made in the southern offshore basin of Tanzania continental margin while no gas accumulation has been found in the northern part of the basin. This study was aimed at finding out the reasons behind absence of gas discoveries in the northern offshore Tanzania continental margin despite the presence of potential gas flow indicators. 2D seismic interpretation and well logs analysis allowed assessment of depositional architectural elements and structural features across the basin. These aspects revealed architectural variations that have been used to account for the current non-discovery status in the northern part of the basin. Results of this work have shown that basin topography, influence of tectonics, sediment supply and depositional and post-depositional processes varied significantly over the whole offshore Tanzania during the Cretaceous-Holocene period. For example, the available 2D seismic profiles show that the Quaternary extensional tectonics created a N-S to NE-SW trending fault controlled sub-basin in the northern part of the study area, but similar feature could not be seen in the southern part of the basin. The variations of key factors controlling sedimentary development also caused dissimilarities in deposit types and dominance of sandy and muddy successions. The northern part of the study area is dominated by complex channel-levee systems containing sandstone bodies while the southern part contains hybrid turbidite-contourite (HTC) deposits and their respective thick drift successions that are stepping southward onto the HTCs. Deposit types play important role in accumulation of hydrocarbons. The HTCs for example contain clean sandstones with high net-to-gross ratio, and may be used to explaining why the existing commercial gas discoveries are found in the southern offshore Tanzania and not in the northern part of the basin.

The Sines Contourite Drift (SCD) is a plastered drift with terraced-like morphology, formed by the Mediterranean Outflow Water (MOW) that emplaced in the Alentejo Margin, SW Iberia. The high (~ 27 cm/kyr) and variable sedimentation rates experienced since the Pleistocene resulted in low consolidation, and the development of excess pore pressure, which, associated with the seismicity in SW Iberia, offer significant conditions for slope instability in the SCD’s Late Pleistocene-Holocene muddy-contourite and hemipelagic sediments. Therefore, it is crucial to assess the susceptibility of the area to submarine landslide hazards. Slope instability is assessed both under static and transient conditions, based on the sediment mechanical properties, obtained through drained and undrained triaxial tests performed on sediment samples of three gravity cores (CO14-GC-2B, CO14-GC-3B, and CO14-GC-7B), respectively, retrieved at 1208-, 1280-, and 1425-m water depth (mwd). Those properties consist of internal friction angle ( ϕ ′ ), with average values ranging between 28.5° and 35.1°; sediment unit weight ( γ ) that ranges from 16.9 to 18.1 kN/m 3 ; and undrained shear strength ( S u ), ranging between 5.81 and 6.50 kPa. Cohesion ( c ′ ) values are incipient and thus considered as 1 kPa in the modeling under static conditions. The analysis also accounts for the peak ground acceleration (PGA), determined according to the magnitude of seismicity recorded in the area. The SCD is prone to slope instability and collapse, especially in gradients > 5°, due to the sediment’s low consolidation, strength, and permeability. Seismicity greatly reduces the factor of safety (FS), promoting slope instability.

Contourite drifts were found for the first time on the SW Kara Sea shelf based on the analysis of bathymetry and seismoacoustic data obtained in the cruises 41 (2019) and 49 (2020) of R/V Akademik Nikolai Strakhov . These drifts are confined to a narrow NS depression with a depth of 240 m. They are separated from underlying sediments by the basal unconformity caused by the bottom current formed in the marine environment after melting of the Barents–Kara ice sheet during the Late Pleistocene–Holocene time. Hydrological measurements carried out in the cruise 89-1 (2022) of R/V Akademik Mstislav Keldysh made it possible to reveal the bottom current with a measured velocity of up to 10 cm/s.

Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26–25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial–interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25 Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions.

A widespread area of seafloor depressions ‐ circular, arcuate to elongated‐shaped ‐ has been found along the Northern Haitian coast, at water depths between 600 and 2,000 m. Characterized by wavelengths spanning several hundred meters and heights of tens of meters, these depressions are linked with a series of narrow ridges boasting varied morphologies. Our analysis integrating multichannel seismic reflection, high‐resolution bathymetry data, and sedimentological and geochemical evaluations of surface sediment cores indicates that present‐day seafloor morphology results from the interaction of slope bottom currents with the seafloor. The analyzed sediment cores exhibit hemipelagites, silty and sandy contourites, fine‐grained turbidites and reworked sand layers, implying sedimentation in a contourite drift system. This is further corroborated by seismic reflection data depicting wavy reflectors and aggradational stacking features typical of contourite drifts. Seafloor depressions are likely erosional features formed on the top of a contourite drift formed by the interaction of bottom currents with an irregular seafloor morphology. The seafloor equilibrium was initially disturbed by mass‐wasting events. Subsequently, the quasi‐steady flow of along‐slope bottom currents influenced sedimentary distribution and controlled the morphology of the seafloor depressions‐constant re‐shaping through erosion on their flanks. The resulting rough seafloor could have facilitated the destabilization of bottom currents and the development of erosive eddies responsible for the current morphology of the seafloor depressions. This study highlights the interplay between sedimentary processes (accumulation and compaction) and bottom currents, showing how their combined effects influence slope sedimentation and seafloor geomorphology, forming unique erosional features. Plain Language Summary Between 600 and 2,000 m of water depth, the seafloor of the northern Haiti margin presents a field of sub‐vertical to elongated depressions. Scientific investigations dealing with the nature of the seafloor material and subsurface structure revealed that such peculiar seafloor morphologies are not related to fluid escape features but to the interplay between sedimentary processes and water masses currents. A submarine landslide triggered in the past has likely created a rough seafloor resulting in the destabilization of currents linked to the deep water masses, enhancing seafloor erosion and deposition. Key Points A widespread area of seafloor depressions has been found along the Northern Haitian coast in water depths between 600 and 2,000 m The depressions are erosional features formed by the interaction of bottom currents with irregular seafloor The Windward Passage allows interactions among several currents

This paper presents the results of seismostratigraphic interpretation of the Upper Cretaceous sedimentary succession preserved within two synclines flanking the Szamotuły diapir in northwestern Poland. This succession is characterized by a complex Santonian–Campanian internal geometry characteristic of contourites – that is, deposits formed by contour (bottom) currents. The aim of the present paper is to document these contourites using 2D seismic reflection profiles calibrated by the Obrzycko 1 well. The contourite drifts in the immediate vicinity of the Szamotuły structure exhibit elongated mounded shapes, with adjacent concave moats. At greater distances from the diapir, gradual aggradational patterns are observed. The formation of these Santonian– Campanian contourites was associated with growth of the Szamotuły diapir during regional compression and Polish Basin inversion. These contour currents and associated contourites formed an integral part of a regional axial depositional system developed within the flanks of the Mid-Polish Anticlinorium. Furthermore, this paper discusses the potential role of contourites as palaeomorphological indicators of palaeoslopes in varied geodynamics settings, such as inverting sedimentary basins, as opposed to the passive margins upon which they have been most commonly documented.

The evolution and resulting morphology of a contourite drift system in the SE Pacific oceanic basin is investigated in detail using seismic imaging and an age-calibrated borehole section. The Nazca Drift System covers an area of 204 500 km2 and stands above the abyssal basins of Peru and Chile. The drift is spread along the Nazca Ridge in water depths between 2090 and 5330 m. The Nazca Drift System was drilled at Ocean Drilling Program Site 1237. This deep-water drift overlies faulted oceanic crust and onlaps associated volcanic highs. Its thickness ranges from 104 to 375 m. The seismic sheet facies observed are associated with bottom current processes. The main lithologies are pelagic carbonates reflecting the distal position relative to South America and water depth above the carbonate compensation depth during Oligocene time. The Nazca Drift System developed under the influence of bottom currents sourced from the Circumpolar Deep Water and Pacific Central Water, and is the largest yet identified abyssal drift system of the Pacific Ocean, ranking third in all abyssal contourite drift systems globally. Subduction since late Miocene time and the excess of sediments and water associated with the Nazca Drift System may have contributed to the Andean orogeny and associated metallogenesis. The Nazca Drift System records the evolution in interactions between deep-sea currents and the eastward motion of the Nazca Plate through erosive surfaces and sediment remobilization.

This study entails the characterization of the depositional environment of the Hupo Basin shelf. By means of sedimentary structure analysis, grain size, textures, sediment color, as well as optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) ages, a sediment core (19ESDP-101, 120 m) has been interpreted to be the product of shallow-water contourites. The shallow-water (165 m) contourite deposits observed in the core are divided into seven sedimentary facies grouped into four facies associations (FA): FA1) contourite drift, FA2) contourite drift/channel transition, FA3) contourite channel/drift transition, and FA4) contourite channel. FA1 resulted from the interaction between hemipelagic fallout, low-density gravity flow, and sedimentation under low velocity bottom currents. Compared to FA1, both FA 2 and FA3 are indicative of higher velocity bottom currents, owing to their relative increase in grain size and the presence of subtle indicators of bed-load transport. FA 4 portrayed massive to slightly bedded sand, representing a contourite channel environment with high-energy conditions. Fluctuations in the bottom current activity, related to the intensification and deceleration of the North Korean Cold Current (NKCC), have caused fluctuations between contouritic and hemipelagic-dominated periods. The vertical sedimentary facies stacking patterns observed at the Hupo Basin site suggested that, over time, the depositional processes changed at the site where the core was optained. The facies association stacking pattern suggests the lateral migration of the contourite depositional system and continuous flow of the NKCC. Our findings and interpretations can serve as a much needed reference for shallow-water contourite recognition in modern environments. Moreover, our proposed model can be used to more accurately interpret shallow-water contourite deposits.