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The northern continental margin of the South China Sea (SCS) is an important component of deep‐water circulation, providing excellent conditions for studying bottom currents in a marginal sea. Seismic data were employed to discern the sedimentary patterns prevalent in the deep‐water continental slope sediments on the northern continental margin of the SCS, encompassing gravity flow, contourite and mixed depositional systems. The contourite depositional system includes various types of deposits (such as separated mounded drifts, patch or channel‐related drifts, deformed sheeted drifts, composite drifts, bottom current sediment waves, plastered contourite drifts) and various morphologic erosional features eroded by the bottom current (such as moats, non‐depositional surfaces, troughs and scarps). These contourite features are related to the continental slope's morphology and its sources. The Dongsha slope exhibits distinctive characteristics marked by intense bottom current erosion and deposition, featuring separated mounded drifts and deformed sheeted drifts along its lower slope. The lower slope of the Pearl River showcases a spectrum of bottom current‐induced features, including sediment wave fields, erosion fields and contourite drifts. The southern flank of the Shenhu slope is characterised by a bottom current erosion field, a non‐depositional surface, a sediment wave field and isolated mounded drifts. On the Yingqiong slope, the contourite drifts are limited to its southern flank where gravity flow action is absent, and the complex geomorphology interacts with the bottom current, forming a complex contourite depositional system. The results of this study serve as a foundational framework for further global research on bottom current circulation and hydrodynamics. [ABSTRACT FROM AUTHOR]

The study is dedicated to geological interpretation of high-resolution seismoacoustic data acquired in the Central Atlantic during cruise 60 of the R/V Akademik Ioffe. Seismic facies of abyssal plane deposits, contourites, gravitites, and sediment waves have been identified based on specific characteristics of the seismic structure of the upper sediment cover. Geological interpretation was conducted considering the results of lithological studies of sediment cores collected during research cruises of the Shirshov Institute of Oceanology, Russian Academy of Sciences, as well as deep-sea drilling data. The role of gravity-driven processes in the formation of near-surface deposits is most significant in the region adjacent to the continental margin of South America. In the entire study area, bottom currents are considered as one of the main agents of sediment cover formation, responsible both for the deposition of contourite drifts and stratified hemipelagic sediments. [ABSTRACT FROM AUTHOR]

Mixed turbidite–contourite depositional systems result from interactions between down‐slope turbidity currents and along‐slope bottom currents, comprising excellent records of past oceanographic currents. Modern and ancient systems have been widely documented along the continental margins of the Atlantic Ocean. Yet, few examples have so far been identified on the North‐west African continental margin, limiting understanding of the sedimentary and palaeoceanographic evolution in this area. This work uses two‐dimensional seismic reflection profiles to report, for the first time, the presence of three giant sediment mounds beneath the headwall region of the Sahara Slide Complex. The sediment mounds are elongated and separated by two broad canyons, showing a north‐west/south‐east orientation that is roughly perpendicular to the continental margin. These mounds are 24 to 37 km long and 12 to 17 km wide, reaching a maximum height of ca 1000 m. Numerous slide scarps are observed within and along the flanks of the mounds, hinting at the occurrence of submarine landslides during their development. Based on their geometries, external shapes, internal seismic architecture and stratigraphic stacking patterns, it is proposed that these sediment mounds comprise down‐slope elongated mounded drifts formed in a mixed turbidite–contourite system during four evolutionary stages: onset, growth, maintenance and burial. The significance of this work is that it demonstrates the gradual transition from a turbidite system to a full mixed turbidite–contourite system to be associated, in the study area, with the establishment of strong ocean currents along north‐west Africa. [ABSTRACT FROM AUTHOR]

This paper provides information on the integrated geological and geophysical investigations of the fracture zones of the Tropical Atlantic (cruise 65 of the RV Akademik Ioffe), as well as on the geomagnetic survey, passing observations of wind-generated waves, and quantitative distribution of cetaceans and flying fish in the North Atlantic (cruises 64 and 65 of the RV Akademik Ioffe) in October–December 2023. The preliminary scientific results are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The morphological evolution of two mud depocenters in the southwestern Baltic Sea is investigated by comparison of numerical model results to geological and oceanographic data. The pathways of dense currents during episodic dense-water inflows from the North Sea are shown to correspond to current pathways inferred from contouritic depositional geometries in the flow-confining channels within the study area. A favorable comparison of model results to published current speed observations shows that the mesoscale dynamics of individual inflow events are reproduced by the model, indicating that external forcing and basin geometry rather than internal dynamics control the mesoscale dynamics of inflow events. The bottom current directions during inflows show high stability in the flow-confining channels and explain the contouritic depositional geometries. Asymmetric depositional features in the channels are qualitatively reproduced in the model. Bottom currents are less stable in areas without contouritic features, possibly resulting in an overall diffusive effect on sediment distribution in those areas. In a simulation of resuspension by bottom-contacting fishing gear, inter-basin sediment transport is increased by 4–30%, depending on the area, compared to the case of natural hydrodynamic resuspension. The model predicts an increased winnowing of the finest sediment fraction due to bottom trawling, leading to an overall coarsening-to-fining trend in the direction of net sediment transport. The results show that rather than hemi-pelagic background sedimentation, episodic events with high bottom current velocities as well as bottom-trawling induced resuspension are responsible for the present-day and future morphological configuration of the mud depocenters in the southwestern Baltic Sea.

The evolution of marine gateways and sea straits exerts major control on bottom current depositional systems. A well‐known interval in geological history characterized by frequent changes in marine connectivity is the Messinian Salinity Crisis (5.97 to 5.33 Ma) when the Mediterranean allegedly experienced major (>1 km) sea‐level drawdown followed by a catastrophic marine replenishment at the base of the Zanclean. Controversy exists around the timing and mode of this event as unambiguous flood deposits have so far never been drilled or recognized in outcrops. In the Sicilian Caltanissetta Basin (Italy), the Messinian/Zanclean boundary is directly underlain by the Arenazzolo Formation. This 5 to 7 m thick sandy sedimentary interval may reveal a genetic link with the abrupt refilling of the Mediterranean, but at present a detailed study to understand its origin is lacking. In this work, the Arenazzolo Formation at Eraclea Minoa has been studied by a multi‐method approach, employing detailed facies description, grain‐size analyses, petrographic analyses and palaeocurrent analyses. Palaeogeographical reconstructions and facies associations show that the Arenazzolo Formation sands were deposited on the northern flank of the Gela thrust front by persistent bottom currents, flowing parallel to the regional slope physiography, during a transgression. It is hypothesized that these currents are associated with the active circulation of surface and intermediate water masses coeval with a terminal Messinian flood, when basin margins overtopped and a reconnection between western and eastern Mediterranean was created. The Arenazzolo Formation is a unique example of a contouritic deposit formed by bottom currents that establish during the reconnection of major isolated water bodies. [ABSTRACT FROM AUTHOR]

This paper provides information on the integrated geophysical, sedimentological, and hydrophysical investigations, passing meteorological and biological observations in the Eastern Tropical Atlantic during the cruise 63 of the R/V Akademik Ioffe in October–December 2022. The preliminary scientific results are discussed. [ABSTRACT FROM AUTHOR]

The Ioffe Drift, located in the western South Atlantic to the north-east to the Vema Channel, was discovered on cruise 32 of the R/V Akademik Ioffe in 2010. Analysis of the seismoacoustic, biostratigraphic, lithological, grain-size, geochemical, and X-ray fluorescence data made it possible to estimate the Pleistocene age of the upper part of the drift, as well as to confirm the contourite genesis of the sediments. Quantitative analyses of benthic foraminiferal assemblages were carried out in sediment core AI-2436 (26°51.6′ S, 34°01.40′ W, 3800 m water depth) collected near the drift summit. The results made it possible to reconstruct relative changes in the organic matter flux to the seafloor, its periodicity, and bottom current intensity, as well as to suggest the interplay of deep-water masses during the Pleistocene. Visual evaluation of benthic foraminiferal tests identified three groups of damage of presumably variable genesis. The first group includes damage possibly resulting from impacts of particles transported by bottom currents. The second group consists of damage that occurred due to movement of tests by strong bottom currents. The third group contains deformations caused by dissolution in the carbonate-corrosive bottom-water environment. Thus, the specific features of tests in combination with commonly used methods may potentially serve as a supporting technique for contourite diagnostics. However, this method demands a development of application criteria and should be verified on reliable material. [ABSTRACT FROM AUTHOR]

• Direct in-situ evidence of mechanisms generating transverse flows across contourite moat and drift systems. • Observations were conducted in deep marine (South China Sea) and lacustrine (Lake Champlain) environments. • Bottom Ekman transport causes drift-ward deflection of near-bottom currents. • These findings are applicable to any rotating planet or moon with substantial liquid water. Despite six decades of investigation into deepwater sedimentary systems, the mechanisms that generate transverse flows to transfer sediments across contourite channel (moat) and drift systems have remained unclear. Here we present the direct evidence of driving mechanisms from in situ observations of contourite systems, both deep marine (South China Sea) and lacustrine (Lake Champlain) environments. In these Northern Hemisphere locations, bottom Ekman transport (arising from the combined effects of the Coriolis force and bottom friction) drove leftward deflection of near-bottom currents (relative to the direction of the frictionless main flow above), resulting in transverse flows across the contourite moat–drift systems. In the Southern Hemisphere, current deflection would be to the right. These findings are relevant to any rotating planet or moon that harbors substantial liquid water, where these processes could produce bottom current (contourite) features — invaluable archives of past changes in oceanic circulation and climate, on Earth and elsewhere. One-Sentence Summary: In situ observations show that bottom Ekman transport can result in transverse flows across contourite moat–drift systems. [ABSTRACT FROM AUTHOR]

Red Sea Deep Water is presently slow-moving, but was this true of the earlier Plio-Pleistocene (PP)? In seismic reflection records, the PP deposits are distorted by halokinetic deformation of their underlying Miocene evaporites. However, if reflections are flattened to a prominent reflector representing the top of the Miocene, they reveal mounded deposits within the earlier PP along both sides of the sea. Off Egypt, a plastered drift occurs along a salt wall. In the central Red Sea, they are mounded drifts. Seismic reflections from these deposits change shape gradually upwards to the modern seabed, which is commonly flatter, suggesting a gradual change in depositional conditions. To explain their origins, we appeal to other evidence. DSDP cores from the Late Pleistocene contain the rigid aragonite cements formed by restricted conditions, but not the lower and middle PP. Furthermore, mid-PP sedimentary δ18O values are similar to global ocean δ18O for that time, not enhanced as expected from excess evaporation. These data suggest that there was a greater exchange of Red Sea waters with the Indian Ocean during the mid-PP. That exchange may have allowed waters densified by evaporation in shallow regions of the northern Red Sea to flow south vigorously (the mounds would then be contourites). Alternatively, as the Pliocene seabed was shallower, wind-driven eddies may have affected more of the water column. Overall, the results indicate for the first time that deep circulation was stronger in the earlier PP compared with the present day. That circulation needs to be considered when evaluating organism dispersions across the Red Sea, regional climate, and influence of Red Sea Outflow Water on Indian Ocean Intermediate Water. During the Pliocene (about 3–5 million years ago), temperatures on Earth's surface were similar to those predicted in some models of Earth's future climate. This has led to researchers becoming interested in studying geological evidence of conditions during the Pliocene as a clue to Earth's future. In detail, however, the comparison may not be exact. In our article, we describe mounds of sediment that were originally formed on the bed of the Red Sea in the Pliocene. They appear similar to snow drifts, and like snow drifts, may have formed under steady currents. Sea water becomes dense with evaporation (making it more saline). At the present day, dense water created in the Gulf of Suez cascades down into the deep Red Sea as a slow current. Perhaps such movements were more vigorous in the Pliocene, helped by the water escaping through a deeper barrier in the south into the Indian Ocean? Alternatively, these mounds were formed by giant eddies, such as those on the surface of the modern Red Sea, which are moved by strong winds. In either case, the deep waters of the Pliocene Pliocene Red Sea were more vigorously moving compared to the quiescent deep waters of the modern-day. [Display omitted] • Seismic reflection images reveal mounded lower Plio-Pleistocene sediments. • Their geometries are similar to contourites, suggesting vigorous circulation. • Alternatively, these deposits may be results of wind-driven eddies. [ABSTRACT FROM AUTHOR]

In recent decades, contourites—as sediments deposited or reworked by bottom currents— have begun to be considered important targets for deep-sea petroleum exploration and exploitation. The incidence of bioturbation, a common feature in contourite deposits, on petrophysical properties has never been approached in detail, however. Here, detailed comparative analysis of the impact of ichnological features on contourite rock properties is initiated through the application of different techniques: (a) X-ray micro-computed tomography (Micro-CT), (b) mercury intrusion porosimetry, and (c) analysis of impregnated thin sections. These three techniques were employed to study two types of contourite deposits, namely clastic (Miocene Morocco) and calcareous ones (Eocene–Miocene Cyprus). The results evidence the suitability of a multi-technique approach. Particular strengths and weaknesses may be encountered for each method depending on the type of material, the ichnological features, and the particular objectives. Trace fossils analysed in calcareous contourites show a neutral effect. In contrast, the burrow lining of Macaronichnus in the clastic contourites has a positive incidence on porosity. The appearance of this ichnotaxa could invigorate the reservoir capacity of bioturbated contourite deposits. Thus, we suggest that detailed analyses must be conducted focusing on ichnological features other than the ones traditionally considered. Still, this is a preliminary effort, and more detailed studies are needed to support the obtained results, and eventually extrapolate them to further contourite deposits. [ABSTRACT FROM AUTHOR]

High fluvial input combined with specific topographic and oceanographic settings in the Caspian Sea create favorable conditions for contourite deposition. For the first time in its middle portion, contourite deposits have been observed in high-resolution seismic profiles. Various types of contourite drifts and mixed depositional systems have been revealed on the lower slope and in the adjacent basin, some of which are accompanied by sediment wave fields. The deposition of contourites or turbidites and their lateral distribution is controlled by sea-floor topography and oceanographic processes, as well as the modern activity of gravity flows downslope on the western Caucasian slope and in the channel system on the Mangyshlak Sill. The contourite drifts and sediment wave fields form several contourite depositional systems, which seem to merge in the Caspian contourite depositional complex. This occurs near the foot of slopes of the Derbent Basin and is related to the counterclockwise circum-Caspian current in the Middle Caspian Sea. The fact that the Caspian Sea is the largest lake in the world makes this region a significant area for research into the "lake contourites" issue. The Caspian Sea is an important oil-producing area, and sedimentary processes related to the contourite and turbidite can be a source of potential geohazards in the construction and exploitation of underwater engineering structures [ABSTRACT FROM AUTHOR]

Grain size is an important textural property of sediments and is widely used in paleoenvironmental studies as a means to infer changes in the sedimentary environment. However, grain size parameters are not always easy to interpret without a full understanding of the factors that influence grain size. Here, we measure grain size in sediment cores from the Bering slope and the Umnak Plateau, and review the effectiveness of different grain size parameters as proxies for sediment transport, current strength, and primary productivity, during a past warm interval (Marine Isotope Stage 11, 424-374 ka). In general, sediments in the Bering Sea are hemipelagic, making them ideal deposits for paleoenvironmental reconstructions, but there is strong evidence in the grain size distribution for contourite deposits between ~408-400 ka at the slope sites, suggesting a change in bottom current transport at this time. We show that the grain size of coarse (>150 µm) terrigenous sediment can be used effectively as a proxy for ice rafting, although it is not possible to distinguish between iceberg and sea ice rafting processes, based on grain size alone. We find that the mean grain size of bulk sediments can be used to infer changes in productivity on glacial-interglacial timescales, but the size and preservation of diatom valves also exert a control on mean grain size. Lastly, we show that the mean size of sortable silt (10-63 µm) is not a valid proxy for bottom current strength in the Bering Sea, because the input of ice-rafted silt confounds the sortable silt signal. [ABSTRACT FROM AUTHOR]

In many modern deep‐water slope environments, deposits formed by bottom currents (contourites) are rather common. However, reports on ancient contourites in deep‐water environments are scarce and most of them remain contentious. Based on the study of high‐resolution sedimentological, sedimentary geological and magnetic fabric characteristics, this study presents the key evidence of bottom current activity in the Middle Ordovician Kelimoli Formation from the western margin of the North China craton, and reconstructs the deep‐sea circulation pattern and the direction of deep‐water bottom currents in the middle and low latitudes during the Middle Ordovician. Six typical carbonate microfacies are identified in the Kelimoli Formation, which can be grouped into three sedimentary facies types related to the main interpreted depositional processes (bottom current, undifferentiated bottom current and hemipelagic settling, and hemipelagic settling). The evidence of bottom current deposits are five‐fold. Firstly, it is possible to observe a variety of traction current structures, which mainly represent bed‐load‐dominated transport of sediments. Secondly, there are multi‐scale inverse grading and bi‐grading, as well as inversely‐graded and normally‐graded sedimentary sequences, which reflect the periodic change of bottom current activity. Thirdly, gradual or sharp contact boundaries and small internal erosional surfaces indicate omission surfaces caused by the oscillating variation of bottom current velocity. Fourthly, the continuous rhythmic change of sedimentary fabrics on the microscopic scale reflects sustained, waxing and waning current intensities. Fifthly, the anisotropy of magnetic susceptibility reveals the microscopic fabric characteristics of imbricated magnetic grains, which represent the continuous action of directional current, and the restored palaeocurrent direction indicates that the current is mainly parallel to the slope strike. After the palaeo‐north correction of the North China craton clockwise rotation of 120° to 150° since the Ordovician, anisotropy of magnetic susceptibility shows that the direction of bottom current in the study area is towards the north‐east/east. Therefore, it is speculated that there was a clockwise deep‐water circulation in the middle and low latitudes of the southern hemisphere during the Ordovician. This study not only provides sedimentological evidence for the Ordovician bottom current activity, but also contributes to a better understanding of the Ordovician palaeoceanographical environment, especially the Middle Ordovician deep‐sea circulation pattern. [ABSTRACT FROM AUTHOR]

Idealized facies of bottom current deposits (contourites) have been established for fine‐grained contourite drifts in modern deep‐marine sedimentary environments. Their equivalent facies in the ancient record however are only scarcely recognized due to the weathered nature of most fine‐grained deposits in outcrop. Facies related to the erosional elements (i.e. contourite channels) of contourite depositional systems have not yet been properly established and related deposits in outcrop appear non‐existent. To better understand the sedimentary facies and facies sequences of contourites, the upper Miocene contourite depositional systems of the South Rifian Corridor (Morocco) is investigated. This contourite depositional system formed by the dense palaeo‐Mediterranean Outflow Water. Foraminifera assemblages were used for age‐constraints (7.51 to 7.35 Ma) and to determine the continental slope depositional domains. Nine sedimentary facies have been recognized based on lithology, grain‐size, sedimentary structures and biogenic structures. These facies were subsequently grouped into five facies associations related to the main interpreted depositional processes (hemipelagic settling, contour currents and gravity flows). The vertical sedimentary facies succession records the tectonically induced, southward migration of the contourite depositional systems and the intermittent behaviour of the palaeo‐Mediterranean Outflow Water, which is mainly driven by precession and millennial‐scale climate variations. Tides substantially modulated the palaeo‐Mediterranean Outflow Water on a sub‐annual scale. This work shows exceptional examples of muddy and sandy contourite deposits in outcrop by which a facies distribution model from the proximal continental slope, the contourite channel to its adjacent contourite drift, is proposed. This model serves as a reference for contourite recognition both in modern environments and the ancient record. Furthermore, by establishing the hydrodynamics of overflow behaviour a framework is provided that improves process‐based interpretation of deep‐water bottom current deposits. [ABSTRACT FROM AUTHOR]

Abstract Subducted sediment plays a key role in modulating pore pressure and seismic behavior at subduction zones. We investigated the seismic character of incoming sediments to test how sediment and basement variations relate to the along‐strike changes within the accretionary prism and plate boundary conditions at the Nankai Trough. High‐resolution seismic data reveal for the first time the presence of countourite mounded drifts in the Shikoku Basin. These features have probably introduced permeability heterogeneities into an otherwise homogenous mud‐dominant unit. Additionally, we found that normal faults in this unit are more extensive than previously documented, which probably enhances along‐strike fluid transport. The wedge taper is more correlative with the thickness of the mud‐dominant facies than the turbidite thickness. This may be due to the permeability heterogeneities associated with contourite deposits and normal faults, or due to the absence of thick turbidite deposits. Turbidite deposits can either aid the drainage of the margin where they are not confined by basement topography, or contribute to high pore fluid pressures where they are confined by less permeable mudstone or basement topography. When confined turbidite deposits and contourite mounded drifts are subducted, they may contribute to localized compartments of excess pore pressure which provide the necessary conditions for slow slip behavior. We determined that along‐strike variations in seismic behavior are likely related to the subducting basement topographic and sediment characteristics, which vary on a local (

Subducted sediment plays a key role in modulating pore pressure and seismic behavior at subduction zones. We investigated the seismic character of incoming sediments to test how sediment and basement variations relate to the along‐strike changes within the accretionary prism and plate boundary conditions at the Nankai Trough. High‐resolution seismic data reveal for the first time the presence of countourite mounded drifts in the Shikoku Basin. These features have probably introduced permeability heterogeneities into an otherwise homogenous mud‐dominant unit. Additionally, we found that normal faults in this unit are more extensive than previously documented, which probably enhances along‐strike fluid transport. The wedge taper is more correlative with the thickness of the mud‐dominant facies than the turbidite thickness. This may be due to the permeability heterogeneities associated with contourite deposits and normal faults, or due to the absence of thick turbidite deposits. Turbidite deposits can either aid the drainage of the margin where they are not confined by basement topography, or contribute to high pore fluid pressures where they are confined by less permeable mudstone or basement topography. When confined turbidite deposits and contourite mounded drifts are subducted, they may contribute to localized compartments of excess pore pressure which provide the necessary conditions for slow slip behavior. We determined that along‐strike variations in seismic behavior are likely related to the subducting basement topographic and sediment characteristics, which vary on a local (<10 km) scale. Plain Language Summary: Subduction zone faults, such as those off the coast of southwest Japan, have been shown to slip at a range of speeds. The ruptures range from typical earthquakes, which occur within seconds or minutes, to slow earthquakes, which can rupture over the course of days or weeks. The sediment characteristics of the incoming plate play a key role in determining the type of slip behavior along a margin. When sediments are subducted, they are compressed and expel the fluid trapped in the sediment. If the fluid is unable to escape, the fluid pressure builds up, and can reduce the strength of the plate boundary fault. The type of sediment, as well as whether it has been faulted or modified by the ocean currents, can control how well fluid can escape. The sediment characteristics and corresponding plate boundary strength vary greatly on a sub‐10 km scale. Slow earthquakes in our study area are co‐located with subducted seamounts. We suggest that this is because the sediments commonly deposited on the sides of large seamounts are conducive to forming high pore fluid pressures upon subduction. This result in a locally weaker plate boundary fault, which may be a necessary condition for slow earthquakes. Key Points: High‐resolution seismic reflection data reveal for the first time asymmetrical contourite mounded drifts in the Shikoku BasinBasement topography and paleocurrents influenced the location of turbidite and contourite deposits, as well as how well sealed the deposits areContourites, turbidites, and normal faults result in localized heterogeneities in the hydrogeologic properties of the subducting sediment [ABSTRACT FROM AUTHOR]

A summary seismostratigraphic description of the Nansen Basin sedimentary cover was compiled using data from the Norwegian sector of the Eurasian Basin and data interpretation from the Russian Arktika-2011 project. It was found that sea level fluctuations had a significant impact on sedimentation processes in the Arctic basin. Erosion processes on the shelf and slope were developed during regression phases. In the deep-water part, these processes were accompanied by the formation of fan systems, contourites, and slump bodies in both Neogene–Quaternary and older seismic sequences in the Nansen Basin. They are confined to the modern outer fan distinguished in the bottom topography in both young and older seismic sequences. The sedimentary infill was transported through the Franz Victoria and St. Anna troughs, which already existed at the beginning of the Eurasian Basin opening. The distal parts of the fans form extended sedimentary bodies in the basin with a loss of coherence and acoustic blanking of the seismic record. The contourites are distinguished in all sections near the continental foothill, and slump bodies occur on the slope near the shelf edge. Miocene–Pliocene sequences contain gravity flow sediments located more than 100 km away from the modern fan boundary. The sedimentary infill of the Nansen Basin was regulated both by the intensity of sediment influx and by changes in the hydrological regime of the basin associated with the periods of its isolation from the World Ocean and transition to a single water circulation system. The accumulation of contourite sediments began in the Miocene. They are developed near continental foothills together with fan lobes, and it is not possible to separate these sedimentary body types. The sharpest sea level fall at the Pliocene–Quaternary boundary resulted in the intense sediment input and the formation of spacious zones of coherence loss in the distal fan parts of the basin. The occurrence and spatial distribution of contourite and gravity flow deposits in the basin correlate with sea level fluctuations in antiphase with intense erosion on the Barents Sea shelf, which also depend on vertical movements in the basin surrounding (Svalbard and Franz-Joseph Land archipelagos). Seismic profiles without superimposed interpretation are given in the electronic supplementary materials. [ABSTRACT FROM AUTHOR]

The sediments of the Pleistocene-Holocene marine sequences of the Rio Grande Cone (RGC) (offshore Pelotas Basin, southernmost Brazilian Margin) are dominantly composed by muddy facies with thin interspersed sandy layers containing abundant very fine-to coarse green grains, heavy minerals assemblage, shards and planktonic foraminifera. These components contribute for a better understanding of the RGC filling during the Pleistocene-Holocene. However, the aim of this work was focused in the radiometric dating of the green grains as tool for provenance studies in marine sedimentary sequences. Based on Electron Microprobe, Scanning Electron Microprobe, Transmission Electron Microprobe and optical analysis the green grains occur as: (01) yellowish-green grains with smooth surfaces, low K 2 O and moderate Fe 2 O 3 contents, (02) pale green grains with surfaces slightly fractured with moderate K 2 O and Fe 2 O 3 contents, and (03) dark green grains characterised by fractured (cracked) surfaces and high of K 2 O and Fe 2 O 3 contents. These characteristics classified them as glauconitic minerals ranging from glauconitic smectite to glauconitic mica (glauconite) indicating the first (nascent) and intermediate (slightly-evolved and evolved) stages of the glauconitization process. K–Ar radiometric dating indicated ages from 33.2 ± 0.99 to 6.69 ± 0.54 Ma corresponding from Rupelian Stage (Oligocene) to Messinian Stage (Miocene) to these grains. Considering these glauconitic grains within a Quaternary sequence, an allochthonous (detrital) origin was attributed whose probable source areas were older sedimentary sequences exposed on the seafloor along fold-and-thrust belts related to the gravitational collapse of the RGC depocentre. After eroded the glauconitic minerals probably were distributed by countourite currents and deposited within the Quaternary deposits of the RGC. • K–Ar radiometric dating of glauconitic minerals to improve the knowledgment of deep-marine sedimentation processes. • The K–Ar ages obtained from the glauconitic minerals can explain the deposition of the Rio Grande Cone. • The radiometric results cleary show that the K–Ar in glauconites is a reliable technique to stratigraphic studies. [ABSTRACT FROM AUTHOR]

The silty top parts of graded turbidites of the Late Ordovician Pingliang Formation, which accumulated along the southern margin of the Ordos Basin (central China), have been reworked by contour currents. The reworking of the turbidites can be proven on the basis of paleocurrent directions in individual layers: the ripple-cross-bedded sandy divisions of some turbidites show transport directions consistently into the downslope direction (consistent with the direction of other gravity flows), but in the upper, silty fine-grained division they show another direction, viz. alongslope (consistent with the direction that a contour current must have taken at the same time). Both directions are roughly perpendicular to each other. Moreover, the sediment of the reworked turbidites is better sorted and has better rounded grains than the non-reworked turbidites.

The effect of bioturbation on rocks’ flow-media properties (e.g., porosity and permeability) and its impact on reservoir quality has been previously documented. However, the occurrence of ichnological features and their impact on rock properties in contourite deposits, a facies of economic interest, is poorly known. The study evaluates the effects of bioturbation on different types of contourite facies, particularly dominantly calcareous contourites and sandy clastic contourites, using mercury intrusion porosimetry. Porosity (total, intraparticle and interparticle) is characterized in selected samples, comparing the host rock with the infills of the trace fossils; Macaronichnus, Parahaentzschelinia and Scolicia from El Adergha and Kirmta sections in Morocco, and Chondrites, Planolites and Thalassinoides from Petra Tou Romiou, Agios Konstantinos, and Kalavassos outcrops in Cyprus. The obtained data reveal variance between porosities according to different types of contourite facies and trace fossils. Total porosity shows similar values for the host sediment in clastic and calcarenitic contourites, but interparticle porosity is nearly absent in calcarenitic contourites, where intraparticle porosity is almost exclusive. This is owing to the abundance of foraminifera chambers that increase intraparticle primary porosity. Regarding the ichnotaxa, higher total porosity values were obtained from the infilling material of Parahaentzschelinia, Scolicia and Macaronichnus, which could be related with the redistribution of grains by trace makers during feeding activity. Considering the impact of bioturbation on reservoir quality, there are significant differences between clastic and calcareous contourites. In the clastic contourites, bioturbation increases in the total porosity, particularly interparticle porosity, suggesting a positive impact for the reservoir properties of the studied units. However, in calcarenitic and muddy chalk contouritic facies, bioturbation has a minor effect on porosity and no predictable influence on the flow-media characteristics.

High fluvial input combined with specific topographic and oceanographic settings in the Caspian Sea create favorable conditions for contourite deposition. For the first time in its middle portion, contourite deposits have been observed in high-resolution seismic profiles. Various types of contourite drifts and mixed depositional systems have been revealed on the lower slope and in the adjacent basin, some of which are accompanied by sediment wave fields. The deposition of contourites or turbidites and their lateral distribution is controlled by sea-floor topography and oceanographic processes, as well as the modern activity of gravity flows downslope on the western Caucasian slope and in the channel system on the Mangyshlak Sill. The contourite drifts and sediment wave fields form several contourite depositional systems, which seem to merge in the Caspian contourite depositional complex. This occurs near the foot of slopes of the Derbent Basin and is related to the counterclockwise circum-Caspian current in the Middle Caspian Sea. The fact that the Caspian Sea is the largest lake in the world makes this region a significant area for research into the “lake contourites” issue. The Caspian Sea is an important oil-producing area, and sedimentary processes related to the contourite and turbidite can be a source of potential geohazards in the construction and exploitation of underwater engineering structures

Despite numerous efforts to properly differentiate between contourites and other deep‐water deposits in cores and outcrops, reliable diagnostic criteria are still lacking. The co‐occurrence of downslope and along‐slope sedimentary processes makes it particularly difficult to differentiate these relatively homogeneous deposits. The main aim of this paper is to identify differences in deep‐water sediments based on Principal Component Analysis of grain size and geochemistry, sedimentary facies, and reinforced by microfacies and ichnofacies. The sediments studied were obtained from two International Ocean Drilling Program Expedition 339 sites in mounded and sheeted drifts in the Gulf of Cadiz. The statistical approach led to the discernment of hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine‐grained turbidites and debrites over a range of depositional and physiographic elements. These elements are linked to contourite drifts, the drift‐channel transition, the contourite channel and distal upper slope. When bottom currents or gravity‐driven flows are not the dominant depositional process, marine productivity and continental input settling forms the main depositional mechanism in deep‐water environments. This is reflected by a high variability of the first principal component in hemipelagic deposits. The stacked principal component variability of these deposits evidences that the contourite drift and the adjacent contourite channel were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. This interrelation questions the paradigm that a drift is made up solely of muddy sediments. The interrelation of sedimentary processes is a consequence of the precession‐driven changes in the intensity of the Mediterranean Outflow Water related to Mediterranean climate variability, which are punctuated by millennial‐scale variability. Associated vertical and lateral shifts of the Mediterranean Outflow Water, and therefore of its interface with the East North Atlantic Central Water, controlled sediment input and favoured turbulent sediment transport in the middle slope. During the interglacial precession maxima/insolation minima, a more vigorous upper core of the Mediterranean Outflow Water and the enhanced impact of the East North Atlantic Central Water – Mediterranean Outflow Water interface allowed for the development of the sandier contourite deposits. [ABSTRACT FROM AUTHOR]

The effect of bioturbation on rocks' flow-media properties (e.g., porosity and permeability) and its impact on reservoir quality has been previously documented. However, the occurrence of ichnological features and their impact on rock properties in contourite deposits, a facies of economic interest, is poorly known. The study evaluates the effects of bioturbation on different types of contourite facies, particularly dominantly calcareous contourites and sandy clastic contourites, using mercury intrusion porosimetry. Porosity (total, intraparticle and interparticle) is characterized in selected samples, comparing the host rock with the infills of the trace fossils; Macaronichnus, Parahaentzschelinia and Scolicia from El Adergha and Kirmta sections in Morocco, and Chondrites, Planolites and Thalassinoides from Petra Tou Romiou, Agios Konstantinos, and Kalavassos outcrops in Cyprus. The obtained data reveal variance between porosities according to different types of contourite facies and trace fossils. Total porosity shows similar values for the host sediment in clastic and calcarenitic contourites, but interparticle porosity is nearly absent in calcarenitic contourites, where intraparticle porosity is almost exclusive. This is owing to the abundance of foraminifera chambers that increase intraparticle primary porosity. Regarding the ichnotaxa, higher total porosity values were obtained from the infilling material of Parahaentzschelinia, Scolicia and Macaronichnus, which could be related with the redistribution of grains by trace makers during feeding activity. Considering the impact of bioturbation on reservoir quality, there are significant differences between clastic and calcareous contourites. In the clastic contourites, bioturbation increases in the total porosity, particularly interparticle porosity, suggesting a positive impact for the reservoir properties of the studied units. However, in calcarenitic and muddy chalk contouritic facies, bioturbation has a minor effect on porosity and no predictable influence on the flow-media characteristics. [ABSTRACT FROM AUTHOR]

Over 25 mounds have been identified in the Corsica Channel (Mediterranean Sea) through multibeam bathymetric mapping at depth of 400–430 m, with dimensions ranging from 70 to 330 m, achieving maximum heights of 25 m. Two mounds have been explored in detail using a remotely operated vehicle, revealing thick coral growth with a predominance of the branching scleractinian Madrepora oculata as main frame builder and subordinate Desmophyllum pertusum. The solitary scleractinians Desmophyllum dianthus and Javania cailleti add to the biodiversity here, which accounts for at least 50 macro- and megabenthic species. In consideration of the remarkable surface (ca. 5.3 km2) covered by living corals, their density and healthy appearance, and discontinuity with other major cold-water coral (CWC) occurrences in the Mediterranean Sea, we propose that this area represents a distinct CWC province in a sector already known for the presence of pre-modern CWC mounds. Noticeably, well-developed contourite drift systems occur in the Corsica Channel, lending support to their strict spatial link with coral establishment at depth. The ecosystemic value of the new CWC province calls for proper conservation measures to ensure their present Good Environmental Status.

Interbedded contourites, turbidites and pelagites are commonplace in many deep‐water slope environments. However, the distinction between these different facies remains a source of controversy. This detailed study of calcareous contourites and associated deep‐marine facies from an Eocene–Miocene sedimentary succession on Cyprus clearly documents the diagnostic value of microfacies in this debate. In particular, the variability of archetypical bi‐gradational contourite sequences and their internal subdivision (bedding, layering and lamination) are explored. Contourites can be distinguished from turbidites, pelagites and hemipelagites by means of carbonate microfacies in combination with bed‐scale characteristics. Particle composition provides valuable information on sediment provenance. Depositional texture, determined by the ratio between carbonate mud and bioclasts, is crucial for identifying bi‐gradational sequences in both muddy and sandy contourites, and normally‐graded sequences in turbidite beds. Equally important are the type and preservation of traction structures, as well as the temporality and impact of bioturbation. Shell fragmentation under conditions of increased hydrodynamic agitation (textural inversion) is recognized as a carbonate‐specific feature of bioclastic sandy contourites. [ABSTRACT FROM AUTHOR]

Research into the contourite deposits in the Upper Meishan Formation of the southern Qiongdongnan Basin in South China Sea is weak; their characteristics, distribution and original geological conditions are not clear. Using geological and geophysical methods including seismic and drilling data, based on seismic reflection characteristics, geometrical configuration description, and wave impedance inversion, two types of contourite deposits are recognized. Contourite deposits have blurred boundaries between each deposit and disordered internal seismic reflections; They are mound‐shaped only in transverse section, and banded in the longitudinal direction. Type I contourite deposits are conical, with medium‐high amplitude, low‐continuity, low‐frequency mound‐shaped seismic facies, and subparallel‐chaotic reflections internally. These deposits are conical with sharp tops, the canal between mounds is V‐shaped and deep. The western wing is gentle and the eastern wing is steep, with the slope toe mostly between 10° and 20°, and width height ratio about 1–2. Type II contourite deposits are flat, exhibiting medium‐amplitude, medium‐continuity, low‐frequency mound‐shaped seismic facies, with subparallel weak reflections internally. Their mounds are flat with gently arced tops, with shallow canals between. The slope toe is between 5° and 10°, with a width height ratio of about 2–5. The wave impedance value of these contourite deposits is 4.6 kg/m3×m/s to 6.8 kg/m3×m/s, about 5.8 kg/m3×m/s on average, which is presumed to represent marly‐calcareous clastic sediments. The contourite deposits mainly develop beneath the slope break at the margin of the fault‐controlled platform in the Southern Uplift zone of the basin. In plane view, they are distributed approaching a west‐to‐east direction, and in section, lie in low‐lying areas near the faults at fault‐controlled terraces of the Southern Uplift zone, with a paleo‐current direction nearly west‐to‐east. The paleotectonic setting of the gentle monoclinic platform was favorable for the development of such contourite deposits. The intensification of the Mid‐Miocene deepest bottom current gave rise to the contourite‐forming currents around the Southern Uplift zone in the northern South China Sea, which flow from Hainan Island to the Xisha Trough in a nearly west‐to‐east direction leading to the contourite deposits developing in the late Mid‐Miocene transgressive environment, with multiple slow sea‐level fall cycles. [ABSTRACT FROM AUTHOR]

Ichnological analysis at the Pakhna Formation (Miocene, Cyprus) reveals, for the first time, the presence of graphoglyptid structures. The Pakhna Formation is dominated by pelagic/hemipelagic sediments, together with contourite, reworked turbidite and turbidite facies. Thus, a complex interaction between pelagic, bottom-current and gravitational sedimentation is envisaged. The discernment of facies is sometimes difficult, based principally on stratigraphic and microfacies features. The record of Helminthorhaphe as a component of the graphoglytid group supports the presence of turbidites, facilitating their differentiation from the other facies. Nereites ichnofacies, punctuating a dominant/background Zoophycos ichnofacies, would reflect changes in paleoenvironmental conditions. This record offers significant perspectives to advance in the study of bottom-current and gravitational processes through outcrop examples. [ABSTRACT FROM AUTHOR]

Morphology of the Rio Grande Rise and the acoustic structure of different types of deposits in its uppermost sedimentary cover were discussed based on high-resolution seismoacoustic profiling of cruises #32 (2010) and #52 (2016) of R/V Akademik Ioffe. Slopes of the Rio Grande Rise are composed mainly of landslide deposits and gravitites, but contourite sedimentation is possible on its southern slope. Contourite sedimentary waves and, probably, small drifts are identified in the Cruzeiro do Sul Trough at the top of the Rio Grande Rise. Mixed gravitite–contourite sedimentary systems seem to be located at the foot of northern and southern slopes. The downslope density flows and the Antarctic Bottom Water (AABW) contourite current are responsible for the formation of these features. [ABSTRACT FROM AUTHOR]

We present the results of an integrated geomorphological and seismo-stratigraphic study based on high resolution marine data acquired in the north-western Sicilian continental margin. We document for the first time five contourite drifts (marked as EM1a, EM2b, EM2, EM3a, and EM3b), located in the continental slope at depths between ca. 400 and 1500 m. EM1a,b have been interpreted as elongated mounded drifts. EM1a,b are ca. 3 km long, 1.3 km wide, and have a maximum thickness of 36 m in their center that thins northwards, while EM1b is smaller with a thickness up to 24 m. They are internally characterized by mounded seismic packages dominated by continuous and parallel reflectors. EM2 is located in the upper slope at a depth of ca. 1470 m, and it is ca. 9.3 km long, more than 3.9 km wide, and has a maximum thickness of ca. 65 m. It consists of an internal aggradational stacking pattern with elongated mounded packages of continuous, moderate to high amplitude seismic reflectors. EM2 is internally composed by a mix of contourite deposits (Holocene) interbedded with turbiditic and/or mass flow deposits. EM1a,b and EM2 are deposited at the top of an erosional truncation aged at 11.5 ka, so they mostly formed during the Holocene. EM3a,b are ca. 16 km long, more than 6.7 km wide, and have a thickness up to 350 m. Both EM2 and EM3a,b have been interpreted as sheeted drift due to their morphology and seismic features. The spatial distribution of the contourite drifts suggests that the drifts are likely generated by the interaction of the LIW, and deep Tyrrhenian water (TDW) on the seafloor, playing an important role in the shaping this continental margin since the late Pleistocene-Holocene. The results may help to understand the deep oceanic processes affecting the north-western Sicilian continental margin.

The Ioffe Drift located in the Antarctic Bottom Water pathway from the Vema Channel to the Brazil Basin provides a suitable site to study past variations in bottom contour currents and their contribution to erosion and accumulation of deep-sea sediments. Our previous study of the reference core AI-2436 from the drift summit (Ivanova et al., 2016a) documented the stratigraphic sequence of the uppermost part of the sedimentary cover ranging from the recent through upper Pliocene, the reduced thickness and/or absence of biostratigraphic zones, and the occurrence of several hiatuses. Here, we provide the multi-proxy biostratigraphic, magnetic susceptibility (MS), color reflectance and X-ray fluorescence (XRF) data in the sediment cores AI-3318 from the summit and AI-3316 from the NE slope of the Ioffe Drift. The new data report numerous long- and short-term stratigraphic gaps over the last ~3 Ma. An interval of specific high-amplitude peaks representing abrupt changes in volume MS and XRF variability is identified from 2.51/2.59 to ~1.9 Ma which can likely serve as a regional stratigraphic benchmark in the future studies of deep-sea contourites. The correlation of three sediment records from the drift suggests that the most pronounced series of hiatuses, associated with enhanced AABW flow intensity occurred from 1.6 to ~0.81 Ma (i.e. roughly, during the Mid-Pleistocene Transition), and from 2.51/2.59 to ~1.9 Ma (i.e. covers the onset of the modern-type deep-water circulation in the South Atlantic (Turnau and Ledbetter (1989)). Comparison of the studied sediment records with DSDP Site 516 reveals reduced thickness of all recovered biostratigraphic zones and more often occurrence of hiatuses in the Ioffe Drift than on the Rio Grande Rise suggesting more vigorous contour currents in the former area. • First multi-proxy records documenting hiatuses from the Ioffe Drift. • The interval of abrupt changes is inferred from 1.9 to 2.51/2.59 Ma. • Report reduced thickness of all recovered biostratigraphic zones. • Links hiatuses on the Ioffe Drift with the AABW flow intensity. • Provides biostratigraphic correlation between Ioffe Drift and Rio Grande Rise. [ABSTRACT FROM AUTHOR]

The discovery of the super-giant Coral and Mamba gas fields in the offshore of Northern Mozambique provides a unique insight into the architecture of a new deep-water play-type. High-quality seismic and extensive well data from both fields shows that very clean (clay matrix-poor) sandstone reservoirs, with thickness >100 m and extended over tens of km can be formed by the syndepositional interaction of down-slope high-density turbulent gravity flows and across-slope bottom currents. This is recorded by: i) the marked asymmetry of submarine channels and lateral stacking in which top-of-fan seismic reflectors show a lateral transition from high to low amplitude response from axis to off-axis locations; ii) the occurrence of laterally-deviated lobe deposits, sediment waves and channel-associated drifts in the inferred bottom current direction; iii) the presence of very clean sandstones forming the bulk of the fan units and the consistent lack of interbedded fine-grained facies; iv) the occurrence of fine-grained and thin-bedded facies adjacent to the main fan axes, which are characterized by repeated transitions between ripples and parallel-laminated sandstones, mud-drapes, shale clasts and bi-directional cross-laminae in the same bed, indicating intense traction and velocity pulsations. This association forms a mixed depositional system, in which only the basal and coarse-grained part of the turbidity current load is deposited and preserved in the axial part of the system, whilst all the finer-grained sediments are pirated from the turbulent cloud by laterally flowing bottom currents and deposited in the adjacent sediment drifts. The inferred process results in exceptionally high quality reservoirs whose architectural and facies models were confirmed by the appraisal campaign and production well tests and incorporated into the reservoir model. The results of this study indicate a significant exploration potential in similar geological settings and the definition of a potential new play type, that could lead to the reinterpretation of existing deep-water datasets. • First insight of the Area 4 in northern Mozambique and the Coral Field. • New deep-water play-type: very thick, clean and extensive reservoir sandstones. • Deposits formed by syndepositional interaction of bottom currents and gravity flows. • High quality dataset composed of well logs, cores and 3D seismic. • A facies tract related to deposits affected by bottom currents is proposed. [ABSTRACT FROM AUTHOR]