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Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined 210Pb measurements from 409 cores, AMS14C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 106 t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 106 t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 106 t/a) compared to the deep-water basin (∼16.5–20.1 × 106 t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas. • Distribution of modern sedimentation rates in the South China Sea was illustrated at the basin scale. • The sediment budget and mass balance from a source–to–sink perspective was constructed. • Comparison of sedimentation rates and sediment budgets of the South China Sea and east China seas was conducted. [ABSTRACT FROM AUTHOR]

Submarine canyons are the key structures of the transitional area between the deep ocean floor and continental shelf known as the continental slope. They are important submarine features with high ecological, economic, and scientific value. With continual improvements to global and regional marine bathymetry products, digital bathymetric analysis (DBA) techniques must evolve to support ongoing marine geological research and to advance international bathymetric feature catalogs and mapping products. This study aims to further advance the delineation of submarine canyons and associated sea channels using DBA and the recent open-access GEBCO_2019 global bathymetry grid with 15 arc-second resolution, for a small study region in the southern Celtic Sea. A modified semi-automated delineation method is presented based on combining hydrological network analysis and the topographic position index (TPI), a commonly used parameter available in conventional digital terrain analysis toolsets. For the case-study area of interest, 96 submarine canyons were identified, with higher morphological detail than the previous ETOPO1 and SRTM30_PLUS based studies, which identified 81 and 52 submarine canyons, respectively for the same area of interest. The improvements include an increased number of vertices and limbs per canyon, increased positional precision for canyon starting points and endpoints, and the ability to identify associated sea channels. The results also highlight the importance of pre-processing and parameter localization to effectively exploit higher-resolution bathymetric data, which should also improve scale adaptability for application in different types of continental margins and with high-resolution bathymetry products. Future studies will benefit from the TPI-based identification process proposed in this study to identify submarine canyons and channels on other continental slopes, and to delineate different types of linear depressions from high-resolution digital bathymetry. • A method for extracting submarine canyons and associated sea channels from ocean bathymetry is presented. • The scale-adaptive, TPI-weighted flow accumulation method is adaptable to different types of continental margins. • New global bathymetry is used to extract features with the highest level of details to-date for a case-study region. • The method has potential to be used to map submarine canyons and associated sea channels globally. [ABSTRACT FROM AUTHOR]

The sedimentary record of the western South African continental shelf is condensed compared to the continental slope and contains erosional unconformities, owing to periods of non-deposition, eustatic sea-level fluctuations, episodic uplift and intensified continental aridity. Despite this, the sedimentary record of the continental shelf provides important information on the depositional history and palaeoenvironmental evolution of the region. A core retrieved from the western shelf of South Africa was analysed for its sedimentary composition, lithological variation, foraminiferal content and its relation to the palaeoenvironment of the region. Four depositional facies were identified along the core, namely quartzitic sand, sandy mud, and glauco-phosphatic sand and a glauco-phosphatic gravel. The basal facies consisting of quartzitic sand is interpreted to have been deposited between 15.90 and 14.60 Ma, corresponding to the timing of the Mid-Miocene Climatic Optimum (MMCO). The highly quartzitic nature of the sediments indicate a high terrestrial influence from fluvial sources. The overlying sandy mud facies was deposited between 14.60 and 13.90 Ma based on planktic foraminiferal biostratigraphy. Foraminiferal analyses of these two facies that were deposited in the Langhian stage of the middle Miocene point to subtropical sea surface conditions and mesotrophic benthic environments. Sea level was noticeably higher during the MMCO and part of the cooling period following the MMCO. An erosional surface that spans 10.77 Myr, equal to the late Miocene (13.90 Ma) to early Pliocene (3.13 Ma), marks the boundary between the two Langhian facies and the overlying two Pleistocene facies, consisting of coarser grained glauco-phosphatic gravelly sand units. The Pleistocene environment on the shelf is interpreted to contrast with the Langhian environment, where cooler, shallower conditions and a more eutrophic benthic environment was prevalent, during a time that Benguela upwelling intensified with higher frequency and higher amplitude sea level fluctuations. Palaeobathymetric interpretations indicate that middle Miocene sea-level in the region were up to 77 m higher than present day and 101 m lower in the Pleistocene, in-line with previous global studies. Glauco-phosphatic content that increase up-core also marks the shallowing of the environment under high productivity conditions. • Core stratigraphy reveal a sedimentary record from the middle Miocene to Pleistocene. • Highly quartzitic nature of sediments reveal terrestrial influence. • Glauco-phosphatic content increases up-core supporting shoaling of environment. • Middle Miocene palaeoenvironment interpreted to be warm subtropical and mesotrophic. • Pleistocene palaeoenvironment reflects high upwelling conditions in cooler waters and a eutrophic benthic environment. [ABSTRACT FROM AUTHOR]

Since the discovery of >570 methane flares on the northern U.S. Atlantic margin between Cape Hatteras and Georges Bank in the last decade, the acquisition of thousands of kilometers of additional water column imaging data has provided greater coverage at water depths between the outer continental shelf and the lower continental slope. The additional high-resolution data reveal >1400 gas flares, but the removal of probable duplicates from the combined database of new flares and those recognized in 2014 yields ∼1139 unique sites. Most of these sites occur in clusters of 5 or more seeps, leaving about 275 unique locations (including 47 clusters) for seepage along the margin. As a function of depth, seep distribution is heavily skewed toward the upper continental slope at water depths shallower than 400 m on the southern New England margin and ∼ 550 m in the Mid-Atlantic Bight, with additional seeps clustered at ∼1100 m and just deeper than ∼1400 m in both sectors. Despite little ongoing tectonic deformation or active faulting on this passive margin, a variety of processes driven from below the seafloor (e.g., migration of fluids along faults or through permeable strata, seepage above diapirs or other pre-existing structures) and from above (e.g., erosion, sapping, unroofing) contribute to the development of seeps in different settings along the margin. In addition, the prevalence of seeps on promontories overlooking shelf-breaking canyons may be directly related to the three-dimensional nature of the hydrate stability zone in these locations. As a function of depth, the parts of the slope at the contemporary landward limit of gas hydrate stability are devoid of seeps, and the upper slope zones with the most concentrated seepage were not within the gas hydrate stability zone even during the Last Glacial Maximum. Thus, if the large number of upper slope seeps is at least partially sourced in gas hydrate degradation, the gas emitted at these seeps must have migrated there from greater depths on the continental slope. • The number of known cold seep sites on the U.S. Atlantic margin has now doubled. • Seeps and clusters are found at ∼275 locations, mostly north of Cape Hatteras. • Most seeps are shallower than the landward limit of gas hydrate stability. • Faulting, erosion, unroofing, and hydrologic sapping dominate seep evolution. • Complex hydrate distribution leads to promontory seeps next to shelf-break canyons. [ABSTRACT FROM AUTHOR]

Sulfate reduction is a commonly reported process in a variety of continental margin settings that affects the carbon (C), sulfur (S), and iron (Fe) marine sedimentary cycles. However, sulfate reduction in unstable environment (turbidite deposition) is easily ignored, which results in a lack of understanding of the C, S, and Fe biogeochemical cycle. Therefore, to elucidate the role of turbidite sedimentation in the global C, S, and Fe biogeochemical cycle, total organic carbon (TOC), total sulfur (TS), iron speciation, pyrite contents, and sulfur isotopic composition in sediments (CL94) on the South China Sea continental slope were analyzed, along with sediment grain sizes, calcium carbonate (CaCO 3) content, and K/Al and Ti/Al ratios. Based on petrographic characteristics, grain size parameters, and element geochemistry (K/Al and Ti/Al ratio), it was concluded that the mid-section (322–350 cm) of Site CL94 is a turbidite layer. Compared with normal sedimentary environment, δ34S CRS (−39.7 ‰ on average) exhibits a high value in turbidite layer, which could be related to the high deposition rate and relatively closed environment caused by the turbidity current deposition. Furthermore, in situ deposition is virtually entirely unaffected by external influences, and this is the primary source of sulfide and reactive iron in the relatively closed environment. Thus, pyrite concentration in the turbidity layer fluctuates in conjunction with variations in sulfide and active iron. Moreover, the identification and data extraction of methane seeps were further complicated by the fact that the TS/TOC ratio and δ34S CRS features induced by the turbidity current were extremely similar to those of sediments around methane seeps. The examination of pyrite sulfur isotopic composition and TS/TOC ratios for detecting methane seepage requires further investigation. • The abnormal δ34S CRS in the mid-section is related to relatively closed environment caused by turbidity current. • The TS/TOC ratio and δ34S CRS in turbidity deposits are very similar to those of methane seepage. • Turbidity current plays an important role in the C, S and Fe biogeochemical cycle. [ABSTRACT FROM AUTHOR]

Here we present the mass and carbonate annual fluxes, collected by two sediment traps at 1000 m depth, located on the western and southern deep-water region of the Gulf of Mexico (GM), and compare them with the total mass and carbonate accumulation rates (CAR) from 46 sediment cores retrieved from continental slopes and the abyssal plain of the southern Gulf of Mexico (sGM). CaCO 3 fluxes in the sediment traps located close to 1000 m water depth, range between 15.1 and 22.4 g m−2 yr−1, these values fall on the high-end range of the mean fluxes reported for the global ocean (9–22 g m−2 yr−1). The carbonate fluxes from the water column are remarkably close to the CAR in the lower slope and abyssal sediments of the southern GM, implying that dissolution processes of biogenic carbonate in the sediments below 1000 m are negligible in the sGM. The spatial patterns of CARs in the sediments are mainly linked with surface productivity of calcareous organisms and export to depth over the continental slope and abyssal plain regions, with mean values of 15.7 ± 5.7 g m−2 yr−1 (0.15 ± 0.06 mol m−2 yr−1). However, there are some large areas over the abyssal plain to the north of the Campeche escarpment showing enhanced CAR values most likely as a result from two processes, lateral input from the Yucatan carbonate shelf region and massive collapse events originating at the Campeche escarpment and deposited to the north of the Yucatan Platform. These processes can account for an additional increase in carbonate mass accumulation by approximately 8 g m−2 yr−1 in this area, showing a decreasing gradient towards the N of the escarpment. Lateral transport by turbidity currents of carbonate platform sediments along submarine canyons and probably episodic gravity flows further aid to explain the localized higher carbonate mass accumulation (> 20 g m−2 yr−1) observed at the foot of the continental slopes to the west and south of the southern GM. We estimate total carbonate accumulation estimates for the entire Gulf of Mexico, from the upper slope to the abyssal plain (1000–3750 m), considering the northern deep-water region reported by Giering et al., 2018 , of 0.09 to 0.12 Tmol/yr accounts for 0.8 to 1.8% of all carbonate sedimentation in the ocean below 1000 m. Taking into considerations its small areal extent of <0.3% of the global ocean the GM carbonate accumulation accounts for a factor of 3 to 6 its areal importance, implying that changes in the production and export of carbonate in the GM due to surface ocean warming and acidification processes in this inland sea will have a sensible effect in the global carbon cycle. • Carbonate accumulation rates in the Gulf of Mexico sediments are very similar to sediment traps carbonate fluxes. • Pelagic export of calcareous organisms is the main origin of carbonate in deep-sea sediments of the GoM locally enriched by resedimentation processes. • Carbonate accumulation in the continental margin and abyssal plane of the GM is a factor of 3 to 6 its areal importance of the global ocean. [ABSTRACT FROM AUTHOR]

High-resolution 2D and 3D seismic data are used to investigate the morphology, internal architecture and origin of widespread seafloor undulations in the eastern area of a submarine canyon system, northern South China Sea. The seafloor undulations reveal similar seafloor morphologies, and three different types (Types A, B and C) can be classified based on their relative locations and internal seismic characters. Types A and B are observed in the canyon areas, whereas Type C occurs in the canyon heads. Seismic reflections within Types A and C are continuous and have an upslope migrating trend, while Type B seafloor undulations are separated by listric faults. Our analysis reveals the origins of these three different types of seafloor undulations. Type A seafloor undulations are sediment waves formed by turbidity currents flowing through the submarine canyons. Gravity-driven submarine creep resulted in the formation of Type B seafloor undulations. Type C undulations are sediment waves generated by internal waves interacting with the continental slope. Our results provide information about the origin of widespread seafloor undulations in other submarine canyon systems. It is also of great significance to future risk assessments, as the study area now is one of the most active regions for hydrocarbon exploration in SE Asia. • Widespread seafloor undulations are identified on the South China Sea margin. • Three types of seafloor undulations show different morphology and internal character. • Different processes are responsible for the generation of the seafloor undulations. • Correctly identifying their origin is important for future geohazard assessments. [ABSTRACT FROM AUTHOR]

Abstract Based upon 3-D seismic reflection data, published drill core studies, oceanographic observations and numerical modelling, this study identifies a small scale contourite depositional system that is locally confined by canyons, slope failures, erosional terraces and erosional slopes on the Jianfeng slope, northern South China Sea (~1500 to ~2300 m water depth). Possible oceanic driving mechanisms for the spatial heterogeneity in sedimentation and erosion within the Quaternary deposits in this complex slope system are investigated. Numerical simulations show that the quasi-steady South China Sea deep water circulation, which affects the study area, is characterised by low velocities (maximum 4 cm/s), with a slight modulation by tides (±1 cm/s). This quasi-steady deep-water thermohaline circulation is able to keep sediment particles in suspension, rather than to erode seafloor sediment. The bottom hydrodynamic regime becomes energetic when mesoscale eddies (horizontal scale of 10 to 100 km) approach. Our modelling study indicates that both surface and bottom mesoscale eddies are essential to account for the spatial heterogeneity in sedimentation pattern along the northern South China Sea continental slope. According to simulation, the eddy front contains the highest flow velocity over a mesoscale eddy cycle (45 days), exceeding the threshold for resuspension of unconsolidated sediment (15 cm/s). As a consequence massive resuspension is produced at various sites, and redistributed by sub-mesoscale (horizontal scale of 1 to 10 km) circulations originated from an eddy-topography interaction. In contrast to the surrounding areas, which are subject to erosional forcing for a relatively long part (>7% of an eddy cycle), both the locally-confined drift and a further upstream large elongated-mounded drift experience little erosion (<2.5% of an eddy cycle), and serve as depositional centres for sediment from remote areas and erosion from adjacent areas. Our study demonstrates a promising new perspective for bridging the scales between short-term sediment dynamics and long-term sedimentation through a comparison of modelled scenarios between normal conditions and energetic events. Highlights • Depositional features of a complex deep-water sedimentary system are investigated. • Modelled contourite deposition and sedimentary structures are compared. • The SCS deep thermohaline circulations are insufficient to remobilise sediments. • Contourite deposition is controlled by the interaction of eddies and topography. [ABSTRACT FROM AUTHOR]

Abstract The NW Iberian continental margin is characterised by a complex morphology and by a sedimentary system which was highly dynamic over glacial to interglacial times. The sedimentary history of the continental slope was strongly influenced by the interaction of bottom currents with topographic highs of structural origin leading to the accumulation of several sediment drifts. A combined analysis of gravity cores from different water depth with hydroacoustic data reveals the vertical behaviour of the upper Mediterranean Outflow Water (MOW) core after the Last Glacial Maximum (LGM). A coarser grained interval during Deglacial and early Holocene times (17.2 to 9.9 cal ka BP) points to an increase in bottom current strength. This increase in velocity was probably related to oceanic density fronts, which migrated through the 300 m thick transition zone between the underlying Labrador Sea Water and the overlying MOW. Radiocarbon dates timed the current strengthening to 17.2 cal ka BP, and a following weakening of the bottom current to 13.3 cal ka BP at 1965 m water depth and to 9.9 cal ka BP at 1885 m water depth. The depth-dependent current weakening suggests an upward shifting of the transition zone by 80 m that was related either to an overall shallowing of MOW or a vertical contraction of this water mass. The upward movement happened over a time interval of approximately 3.4 thousand years. In addition sediment core analysis reveals significant lateral heterogeneities within cm to dm thick sediment layers in the contourite drift. These heterogeneities suggest a need of a detailed core coverage across current-influenced deposits for palaeoceanographic studies to minimize misinterpretations. Highlights • A contourite drift records bottom current strengthening during deglacial times. • The sedimentary succession documents an upward shift of the Mediterranean Outflow Water 16 during the late deglacial times. • The upward shift of the Mediterranean Outflow Water lower boundary by 80 m occurred after 13.3 cal ka BP over about 3,4 ka. • The Si/Al element ratio provides a semi-quantitative proxy for grain size variations at the NW 20 Iberian margin. • Contourite drift investigated represents internal lateral heterogeneous sediment pattern. [ABSTRACT FROM AUTHOR]

Considerable effort has been made to link submarine slope failures to changes in local and global-scale environmental conditions, in order to assess landslide hazard probability. Here we provide the first radiocarbon dates of hemipelagic sediment overlying mass transport deposits and inferred failure surfaces of the Currituck Slide Complex (CSC), a prominent landslide scar on the U.S. mid-Atlantic continental slope. The dates, taken from both the upper and lower scars of the complex, constrain the age of the last major failure event to 13,835 and 16,020 years BP. Time correlation of the hemipelagic sediments across the landslide scar and proximal deposit suggests a single failure of both the upper and lower parts of this 160 km3 volume. A higher rate of sediment supply from the periglacial Appalachian Mountains and from glacial melt-water pulses, with an exposed continental shelf at that time, may have enlarged a shelf-edge delta at the site of the CSC, which may have facilitated or triggered failure. A smaller landslide at the southern edge of the complex with a less well-defined geomorphologic footprint is dated at 5500 BP and possibly represents the reshaping of the seafloor around the CSC triggered by low-frequency earthquakes on the nearby continental margin. • New, detailed shallow subsurface stratigraphy for the Currituck Landslide (Currituck Slide Complex). • First absolute dating-backed age for the last major failure of the Currituck Landslide Complex (13,835 and 16,020 years BP). • Potential failure preconditioning and trigger links to local response to global climate shifts. • Small, younger landslide event dated at around 5500 years BP. [ABSTRACT FROM AUTHOR]

This paper explains the current seafloor morphology and processes that affect the formation and evolution of three mud volcanoes and one mud volcano/mud diapir complex in the deepest sector of the Spanish margin of the Gulf of Cádiz. The present study provides novel results and interpretations based on an extensive multidisciplinary data set. New high resolution bathymetric and backscatter data from multibeam echosounders enabled a detailed geomorphological analysis aimed at identifying diverse seafloor features in the different edifices studied and their adjacent bottoms. These features are mainly related to fluid escape (e.g., mud volcanoes, mud flows and depressions), gravitational (e.g., slide deposits and scars), and tectonic (e.g., faults and uplifted antiforms) processes. Very high-resolution parametric profiles and single channel seismic reflection profiles were interpreted for further analysis of the internal structures, demonstrating their important interplay with diapiric processes. Box-corer and gravity-corer have been used to identify different sediment types that have been correlated with backscatter values. The dominant benthic species associated with fluid venting and also with different types of substrates (hard and soft) were characterized using submarine images obtained with an underwater camera deep-towed sled. The benthic species observed were contrasted, and added to those collected with beam trawl and box-corer for characterisation of the benthic and demersal communities. Different geological and biological indicators have been used as proxies of the interaction of these features with the geological processes (such as fluid-escape-related, gravitational, or structural) to characterise the environmental conditions that determine the geomorphology, substrates, habitats and their associated biota. Multivariate analyses combining faunistic and environmental data resulted in the presence of 3 main faunistic assemblages linked to different levels of fluid venting and the importance of depth and variables linked to fluid venting processes (e.g. mud breccia, Methane-derived authigenic carbonates) in the distribution of these assemblages. A conceptual model has been proposed to explain the actual seafloor morphology and the different processes that affect the formation and evolution of the fluid venting submarine structures studied. • New high resolution bathymetric model of fluid venting structures. • Proposal of geo-bio proxies to assess the fluid flow activity in seepages areas. • Proposed conceptual model for fluid venting structures. • This work draws attention to the importance of multidisciplinary studies. [ABSTRACT FROM AUTHOR]

Sediment cores from the south-eastern Nordic Seas simultaneously archive the variability of the Fennoscandian Ice Sheet (FIS), the British-Irish Ice Sheet (BIIS) and the regional oceanic conditions. This study aims to contribute to our understanding of the marine-based section of the FIS and the BIIS between 35,000 and 15,000 years BP, by using cores MD99-2283, MD99-2284 and MD99-2289, retrieved along the upper continental slope between the Faroe-Shetland Channel and the Vøring Plateau. For this, we present a revised, radiocarbon based, Bayesian modelled chronological framework and a compilation of new and published sedimentological, geochemical and micro-paleontological datasets. Our results show a possibly first Weichselian FIS/BIIS confluence at ca. 25,500 years BP in the central North Sea, which buttressed the BIIS to the East, potentially leading to a northwards BIIS deflection via the Shetlands. The Norwegian Channel Ice Stream (NCIS) most likely only reached the shelf edge after 23,300 ± 500 years BP, possibly for the first time during the Weichselian. The NCIS onset directly preceded a pronounced influx of warm Atlantic water to the northern North Sea margin possibly implying forcing through ocean melt. We find a highly variable NCIS, with three ~ 1400 yearlong episodes of increased ice rafted debris flux interrupted by ~ 600 yearlong minima. When compared to other sides of the European Ice Sheet, these episodes appear to correlate well, suggesting a common forcing mechanism. In conclusion, our data supports recent suggestions that the last glacial stage of the BIIS was more extensive in the central North Sea and the confluence later than previously thought. [ABSTRACT FROM AUTHOR]

Submarine mass movements may have profound effects on the morphology and stratigraphic architecture of continental margins. Furthermore, they can represent a threat to human life and infrastructures, and also have implications for hydrocarbon exploration/production. In polar regions, they are one of the predominant sedimentary processes on the continental slope. Exploration seismology has been widely employed to study mass-transport deposits (landslides, glacigenic debris flows, mass flows, etc.), which are usually characterized by chaotic reflections. In this study, we analyse a seismic profile acquired in the southern part of the Storfjorden trough mouth fan (NW Barents Sea margin), showing the presence of two submarine mass-transport deposits (MTDs). A giant MTD (PLS-1) is located on the lower continental slope at 2.6–3 km depth, while a more recent MTD (PLS-2) occurs at 1.9–2.4 km depth. Velocity and attenuation seismic tomography, seismic attributes analyses and rock-physics models reveal distinct petrophysical properties for PLS-1 and PLS-2. Despite the known influence of burial depth(s), fluid flow content, and compaction on the internal character of MTDs, the two deposits studied here, in fact, show distinct petrophysical characteristics that reflect lithological variations - more than to any other control. These results suggest different source areas for the two MTDs. The inferred coarser sediment in PLS-1 indicates provenance from areas with abundant glacigenic debris flows, (such as the Bjørnøya Trough-Mouth Fan). Conversely, the finer, relatively fluid-rich sediments of PLS-2 that underwent little translation could have an origin in the area between trough-mouth fans. Here, slow-moving ice resulted in a relatively scarce release of subglacial debris at the shelf edge and the continental slope was subject to enhanced erosion and degradation with a comparatively higher production of relatively fine-grained turbidite flows. [ABSTRACT FROM AUTHOR]

New marine-geophysical data were analyzed to investigate the sedimentary processes operating on the continental slope north of Nordaustlandet, Svalbard. Kvitøya Trough terminates in a trough-mouth fan (TMF) on the slope, whereas Albertini Trough incises the shelf edge and a TMF is notably absent. Instead, the continental slope beyond Albertini Trough is dominated by thick, acoustically stratified units likely formed by down-slope and along-slope sedimentological processes combined. The morphological and sedimentological differences between Albertini and Kvitøya troughs may partly be due to the larger dimensions of Kvitøya Trough and its associated glacial catchment area relative to Albertini, suggesting that the transport of a larger volume of glacigenic sediments potentially was a contributing factor in building Kvitøya TMF. By contrast, the downfaulted bedrock below outer Albertini Trough provided larger accommodation space for glacigenic sediments which accumulated in an outer-shelf basin, highlighting the importance of the structural-geological setting in TMF development. Debris-flow deposits and/or channel-levee deposits on the lower continental slope and rise off Kvitøya Trough indicate bypassing of glacigenic sediments from the shelf to the deep ocean, a process that is likely a result of locally steep slope gradients (< 9°). The volume of the Kvitøya TMF is smaller than TMFs along the western Svalbard margin, which may be linked to the more erosion-resistant bedrock of the northern margin and/or the comparatively small drainage basin of Kvitøya Trough compared to drainage basins of ice streams that drained westwards from Barents Sea. In addition, the Kvitøya TMF is incised by gullies indicating that they formed after Last Glacial Maximum (LGM) while larger tributary canyons flanking the Kvitøya TMF likely have developed during a longer time span. High seafloor backscatter values in the tributary canyons and gullies are interpreted as coarse-grained deposits that lead down-slope to debris-flow deposits, suggesting an origin for the tributary canyons and gullies through incision by gravity flows of sediment-laden meltwater during and/or after deglaciation. [ABSTRACT FROM AUTHOR]

Large sediment waves have been observed over the Gulf of Roses (GoR) continental slope (NW Mediterranean), developed between ~200 and ~400 m water depth. Geometric parameters computed from the acquired swath bathymetry revealed mean wave lengths of ~2000 m, and maximum wave heights of ~60 m. Single-channel reflection seismic profiles provided information on the sediment wave internal structure and the Quaternary stratigraphic architecture of the GoR outer shelf and slope. Seven main seismic units could be identified, with continuous development of sediment waves over the outer continental shelf and upper slope, showing differences in wave height and length. The seismic units are differentiated by erosional surfaces that can be followed from the outer shelf down the slope, and which have been correlated with Pleistocene eustatic oscillations. Sediment cores were collected over the sediment wave crests and troughs, and grain size distribution and sediment accumulation rates were analysed. Results show a dominant fraction of fine sediments, allowing classifying the observed bedforms as mud waves. Calculated sediment accumulation rates ranged between 0.08 and 0.18 cm/y, with no clear sedimentation pattern (e.g. differential sediment deposition rates) observed between wave crests and troughs. Nevertheless, the presence of thick surface mixed layers and the increase of the sand fraction in the upper sections of the cores indicate that the surface sediments are affected by bottom trawling activities, since the area is highly impacted by this human activity. The sediment waves observed over the GoR slope are most likely to be formed by bottom currents generated by overflows of dense water originated in the Gulf of Lions shelf, which cascade downslope in an oblique angle with respect the main bathymetric contours. This study offers new insights on the role of dense shelf water cascading processes and associated off-shelf sediment transport reshaping the morphology of the open-slope regions. [ABSTRACT FROM AUTHOR]

Okinawa Trough is a transitional zone between the shallow shelf and the deep ocean, which is covered by a large number of terrigenous materials, recording sea-level fluctuations, tectonic activities, and source-sink during the late Quaternary. Based on grain size and trace element analysis of Core S01–10 from the western continental slope area of central Okinawa Trough, high-resolution paleoenvironment records since 14 ka had been obtained. There is a significant positive correlation between the ratio data of Nb, Th, Sc and REE elements of Core S01–10, which reflects the composition characteristics of terrigenous materials. We use REEs and their discrimination plot of Gd/Yb-Yb and La/Yb-Gd/Yb to conclude that the terrigenous materials mainly came from the Yellow River during 14,000–11,500 a. Moreover, grain size parameters and the provenance discriminant function (DF) show that the transportation of terrigenous materials substance from the main rivers in Chinese Mainland (the Yellow and Yangtze Rivers) to the western slope of central Okinawa Trough is affected by the East Asian winter monsoon. This is mainly manifested in two major stages. During 14,000–11,500 a, these indicators fluctuate on the whole, but in the mass, they indicate a strong East Asian winter monsoon stage, which also leads to the formation and enhancement of the low-temperature underflow, leading to the Yellow River as the dominant source. During 11,500–1920 a, these indicators fluctuated more frequently, reflecting the strengthening/weakening of the East Asian winter monsoon in a shorter period. The tendency of East Asian winter monsoon analyzed by using grain size parameters and DF is consistent with the Ti content of Lake Huguang Maar on the whole, which also verifies the feasibility of the results from the side. Overall, the contribution of substance from the relevant source areas is different in different periods, but Paleo-Huanghe remains the main source. According to the study, the analysis of grain size parameters and trace element in the western slope of central Okinawa Trough can indicate changes of provenance, sea level rising and falling and winter monsoon in this area since 14 ka, which is helpful to explore and reconstruct the sediment provenance and Paleoenvironment evolution in this area since the late Pleistocene. • Based on AMS14C ages, grain size and trace elements, high-resolution paleoenvironment records since 14 ka had been obtained. • The terrigenous materials mainly came from the Yellow River between 14,000–11,500 a. • The terrigenous materials to the western slope of central OT is mainly affected by the East Asian winter monsoon. [ABSTRACT FROM AUTHOR]

Offshore freshened groundwater (OFG) has been documented in many continental margins worldwide. OFG systems are dynamic, expanding and contracting with falling and rise sea-levels. OFG has long been thought to be an important geomorphic agent in continental margins, either via active discharge at the seafloor, which can erode depressions, or the generation of excess pore pressure, which can deform sediments and cause slope failure. It has also been proposed that OFG flow can drive the loss of sediment shear strength via salt leaching, when seawater in pores is replaced by freshwater. Here, we measure changes in the geotechnical properties of seafloor clayey silt due to salt leaching using flushing experiments, and assess the implications of these changes on the stability of siliciclastic continental margins with 2D limit equilibrium modelling. We document a ∼ 50% decrease in undrained cohesive strength of seafloor sediment after flushing, as well as a decrease in its shear strength, bulk density, and moisture content, which is similar to that reported for subaerial quick clays undergoing salt leaching. When applied to a theoretical submarine domain 300 m wide by 100 m high, we estimate that salt leaching can trigger slope failure when the thickness of the flushed layer is >3.5 m or when the slope gradient is >3°. Such conditions are primarily satisfied on the continental slope or the shallow seafloor close to the shoreline. Salt leaching by OFG flow merits consideration as a potential mechanism destablising submarine sedimentary slopes. • Role of salt leaching in seafloor stability is assessed via experiments and models. • Undrained cohesive strength of clayey silt subjected to leaching decreased by 50%. • Failure occurs when flushed layer is >3.5 m thick and slope gradient is >3°. [ABSTRACT FROM AUTHOR]

Submarine landslides are widely recognised around the Northeast Atlantic margin, some of which forming vast slide complexes. On the mid-Norwegian margin, the Storegga Slide complex has been active since the early Pleistocene, first as a regional event (Slide W) at 1.7 Ma, and later culminating in the Storegga Slide sensu stricto at 8.2 ka. By interpreting high-quality seismic data, this work investigates slope instability styles, and their geneses, on the northwest flank of the Storegga Slide complex. Seismic and borehole data prove: i) the presence of two new landslides formed prior to Slide W, ii) that mass-transport complexes occurred during the evacuation of sediment oozes, iii) the existence of a series of cracks on the seafloor, denoting modern slope instability. Fluid accumulation in glacial-marine deposits was a primary factor promoting early instability; fluid pipes increase in number below the oldest landslide deposits, with most pipes terminating at their glide planes. Furthermore, mathematical models show that vertically stacked intervals with weak layers, and older landslide deposits, are able to promote further instability. This work thus suggests episodic fluid flow as the primary factor promoting long-term instability near the Storegga Slide complex. As a corollary, we reveal the stability of the continental slope to still be precarious, at present, on the northwest flank of the Storegga Slide. • Two submarine landslides preceded the first regional slide in the Storegga area. • Multiple MTCs are observed to complement the development of ooze evacuation structures. • Episodic fluid flow is suggested the primary factor promoting long-term instability. • Seafloor cracks indicate a currently unstable upper continental slope near Storegga. [ABSTRACT FROM AUTHOR]

We use newly available, extensive two- and three-dimensional seismic datasets in the Vøring Plateau sector of the mid-Norwegan continental margin to investigate the architecture and evolution of Quaternary contourite drifts in the Norwegian Sea. The drifts typically comprise tens of cubic kilometres of sediment, often intercalated between lenses of glacigenic debris flows, and demonstrate migrating depositional centres along the upper and middle slope sectors of the mid-Norwegian margin through the last ~2.7 M.yr. By contrast, the contourite deposited in the southern Vøring Plateau area is anomalously large covering an area of ~17,000 km2 and comprising over 720 km3 of sediment. Correlation of internal drift surfaces with well-dated sediment cores shows that the massive, up to 280 m thick drift contains two major units that were deposited over the last two glacial-interglacial cycles, yielding extremely high sedimentation rates, comparable to those sourced directly from erosive meltwater-rich glaciers and fast-flowing ice streams. A revised evolutionary drift model provides an end-member example of how a combination of rapid glacially-derived sediment delivery and its subsequent transport and deposition by along-slope processes may exert considerable influence on continental margin morphology over geologically short timescales. • The Quaternary evolution of contouritic sedimentation on the mid6 Norwegian continental margin has been examined using extensive 3D and 2D seismic data. • Seven individual buried contourite drifts have been mapped on the Vøring Plateau sector of the Norwegian Sea. • Contourites reported here typically comprise tens of cubic kilometres of sediment and demonstrate migrating depositional centres along the upper and middle slope sectors of the mid-Norwegian margin through the last ~2.7 Ma. • By contrast, the contourite deposited during the last 250,000 years in the southern Vøring Plateau area is anomalously large, covering an area of ~17,000 km2 and comprising over 720 km3 15 of sediment. • A revised drift evolution developed here provides an end-member example of how a combination of rapid glacially-derived sediment delivery and its subsequent transport and deposition by along-slope processes may exert considerable influence on continental margin morphology even over geologically short timescales. • Due to its thickness, the large contourite drift on the southern Vøring Plateau contains an exceptionally high-resolution record of the Late Quaternary palaeoceanography and palaeoglaciology, and may constitute an excellent target for future scientific drilling. [ABSTRACT FROM AUTHOR]

Time-series bathymetric data acquired from 1967 to 2011 are used to evaluate the morphological evolution of the continental shelf and upper continental slope off the city of Nice (SE France, Ligurian Sea). Mapping in water depths of 0–300 m was undertaken to identify the changing morphology of landslide scars and their erosive chutes. Quantitative Digital Terrain Model (DTM) comparisons reveal areas of erosion and deposition over intervals of 5–8 years. Sediment remobilization events on the upper slope (above depths of 200 m) are frequent and significant; landslide scars with volumes > 25,000 m 3 can occur with frequencies of < 8 years. Shelf break retreat toward the coastline can reach 60 m over 7–8 years where the continental shelf is wider (> 200 m). Periods of quiescence (1980–1990 and 2006–2011) are seen to alternate with periods when rapid retrogressive failure increase sediment volumes eroded from the upper slope-shelf transition by an order of magnitude (1999–2006). Temporal variations in landslide activity were correlated to several potential triggering factors that individually would not induce failures, including earthquake activity, rapid deposition of fine-grained sediments on a steep slope, and rainfall leading to fresh groundwater circulation below the shelf. This 4D bathymetric study suggests that over the last 50 years the most important factor triggering landslides offshore Nice is overpressure due to freshwater outflows. [ABSTRACT FROM AUTHOR]

Possible driving mechanisms of sediment dynamics in a contourite drift–moat–obstacle system on the continental slope off the NW Iberian Peninsula are investigated in this study based on a statistical analysis of an 18-month long mooring record in combination with a 3-dimensional process-based numerical modelling. Analysis of the mooring data indicates that the modern hydrodynamic regime in the study area is non-linear, with a significant impact of internal tides and a non-negligible influence by the Earth's rotation. A consistent counteraction between barotropic and baroclinic tidal currents, mainly at M 2 frequency, results in a weak bottom flow that rarely exceeds the threshold velocity for resuspension of sandy silts in the system. This observation explains a Late Holocene hemipelagic (vertical settling) deposition of a fine-grained (8–10 μm) sediment surface layer over the entire drift as well as inside the moat. In order to unravel possible driving forces for active sediment remobilization during the Deglacial/Early Holocene interval between 17,000 and 4000 cal yr BP that is consistent with the sedimentary record, different oceanographic scenarios were designed for a numerical study. Simulation results demonstrate that pulse-like oceanic density fronts and associated km-scale eddies, which originate from instability in the transition zone of two water masses (Labrador Sea Water, Mediterranean Outflow Water), being aided by tidal and geostrophic currents and locally strengthened by topography, are the most reasonable mechanisms inducing contouritic sediment transport and deposition that are observed in the sediment-core transect. These density fronts are of subordinate impact for the modern contourite drift which is bathed by Labrador Sea Water nowadays. However, a vertical downward migration or expansion of the overlying Mediterranean Outflow Water by ~ 300 m between 17,000 and 4000 cal yr BP would facilitate a generation of significant density fronts at the depth of the contourite drift. This MOW migration is believed to leave imprints on other contourite systems located at similar depth in the region. [ABSTRACT FROM AUTHOR]

Several fields of large-scale sediment waves have been observed along the Gulf of Valencia continental margin (NW Mediterranean). The largest sediment waves develop on the continental slope, extending from 250 to 850 m water depth, with wavelengths ranging between 500 m and 1000 m and wave heights from ~ 2 m to ~ 50 m. On the lower part of the slope, sediment waves are quasi-stationary “vertically accreting”, becoming up-slope migrating towards the mid- and upper part of the slope. A second group of sediment waves have developed over the outer continental shelf, with wavelengths of 400 to 800 m and heights of 2 to 4 m, also displaying an up-slope migrating pattern. Multi-channel seismic lines crossing the continental margin show that the sediment waves over the continental slope region have been continuously developed on the foreset region of the prograding margin clinoform. Several units of sediment waves have been identified in the sedimentary record, evolving in accordance with the margin progradation. Detailed analysis of single-channel (sparker) seismic profiles revealed the presence of several sediment depositional subunits over the outer continental shelf, some of them with successive development of sediment waves being truncated by erosive surfaces, likely related to Quaternary eustatic sea-level oscillations. These erosional surfaces can be followed downslope into paraconformable strata of the sediment waves on the continental slope, where constant bedform growth is observed, without being affected by sea level changes. Based on geophysical data, the thickness of the sediment waves mapped units show that the largest sediment waves (in wave ratio, length and height) develop where sediment deposition rates are the highest, coinciding with the upper part of the continental slope (foreset clinoforms), confined by the presence of structural highs. The development of these sediment waves has been previously explained by the interaction of internal waves over the continental slope. Because sediment waves are preserved in the sedimentary record since the Lower/Pliocene, internal waves activity could have been present in this part of the margin shortly after the Zanclean reflooding of the Mediterranean Basin, following the Messinian desiccation event ~ 5.6 My ago. Deep water hydrodynamic conditions were re-established at that time, modulating sediment transport and deposition over the continental slope and outer continental shelf. [ABSTRACT FROM AUTHOR]

Over the recent years, two research fields addressing continental slope sedimentary systems have gained significant momentum: contourites and cold-water coral mounds. Being both related to intense bottom currents and being both dependent on sediment supply, they share some commonalities resulting in their widespread co-occurrence. However, as cold-water coral mounds predominantly occur in shallow to intermediate water depths, this co-occurrence is restricted to these depth levels. For both systems, the available knowledge is derived basically from North Atlantic Ocean settings, indicating the potential to discover such systems hidden in the other ocean basins (as well as still hidden in the Atlantic). Contourites and cold-water coral mounds have the capability of providing high-resolution palaeo-environmental records, although with often differing temporal ranges and/or temporal resolutions. Applying the concept of a joint exploitation of sedimentary records obtained from mounds and contourites offers the unique possibility of analysing contourite and mound development as well as the related palaeo-environmental settings much more comprehensively than done when only considering one of these archives. Thus, after two decades of intense research, providing significant knowledge about contourites and cold-water coral mounds from the North Atlantic, new ideas and concepts may arise from a close collaboration of scientists working in these two fields. [ABSTRACT FROM AUTHOR]

The seabed morphology, type of sediments, and dominant benthic species on eleven mud volcanoes and diapirs located on the northern sector of the Gulf of Cádiz continental slope have been studied. The morphological characteristics were grouped as: (i) fluid-escape-related features, (ii) bottom current features, (iii) mass movement features, (iv) tectonic features and (v) biogenic-related features. The dominant benthic species associated with fluid escape, hard substrates or soft bottoms, have also been mapped. A bottom current velocity analysis allowed, the morphological features to be correlated with the benthic habitats and the different sedimentary and oceanographic characteristics. The major factors controlling these features and the benthic habitats are mud flows and fluid-escape-related processes, as well as the interaction of deep water masses with the seafloor topography. Mud volcano eruptions give rise to mud flows and/or aqueous fluid seepage. These processes sustain chemosynthesis-based communities, closely associated with fluid seepage. Large depressions in the nearby area are influenced by collapse-related phenomena, where active fluid escape and the erosive effect of bottom currents have been identified. When the extrusion activity of the mud volcano is low and the seepage is diffuse, authigenic carbonates form within the edifice sediments. The bottom current sweeps the seafloor from the SE to the NW. When the velocity is moderate, sedimentary contourite processes take place on both sides of the edifices. At high velocities, the authigenic carbonates may be exhumed and colonised by species associated with hard substrates. Small carbonate mounds are found at the summits of some volcanoes and diapirs. Living corals have been found on the tops of the shallowest mud volcanoes, revealing different oceanographic conditions and strong bottom currents that favour the availability of nutrients and organic particles. The edifices affected by very high current velocities are located in the channels where erosive processes dominate. [ABSTRACT FROM AUTHOR]

The present work maps and studies the continental slope off the southeastern Mediterranean Israeli coast. Bathymetric grids with 15–50 m/pixel resolution were used to map over four hundred submarine landslides and numerous fault scarps exposed on the sea floor. Landslide scars are found at water depth ranging between 130 m and 1000 m, where slopes exceed a critical gradient of about 4°–5°. Landslide surface areas range from 0.0024 km 2 to 91 km 2 , where the observed size distribution has a peak (roll over) showing that the most probable landslide area is 1.6 × 10 − 2 km 2 . In general landslides in the north of the studied area are smaller and occur at shallower depth than the southern ones. Landslides show a hierarchical pattern, resulting from sequential, retrograding, slope-failure events and are also observed to interact with a group of faults oriented sub-parallel to the coast. These faults are a result of salt tectonic related extension, their scarps forming elongated step-like morphological features rupturing the surface of the continental slope, as well as the deeper sea floor. The morphology of the landslides as well as their cross cutting relation with the faults scarps, suggest that these landslide are recent, apparently younger than 50,000 years. The triggering mechanism is not clear yet, though several conditions which are known to promote slope instability prevail in the studied area: submarine slope gradients are close to the inferred critical slope angle; continuous sedimentation increases the load on the slope; active salt tectonic results in an overall extension and surface rupturing by normal faults; the studied area is merely 100 km away from seismogenic zones; and finally, apparent existence of gas close to the surface. Hence, it is suggested that submarine slope failure events in the studied area are also possible in the future. [ABSTRACT FROM AUTHOR]

The offshore Niger Delta provides a spectacular example of gravity collapse tectonics, but the timing of shale mobilisation remains poorly understood. Here we present new information from the western Niger Delta, based on a detailed interpretation of a 3D seismic volume, calibrated with biostratigraphic data from exploration wells. The study area is underlain by mobile shales containing thrust-fold anticlines, overlain by >5 km thick Late Eocene to present succession of folded and faulted sediments with fluid migration features. Sedimentation rates estimated at one deep well increased during two phases, more than doubling during the Late Eocene to Serravallian (39.5–12.5 Ma), and by up to ten times during the Tortonian (9.5 Ma) to present. Thinning and onlapping geometries within the lowermost, Late Eocene-Burdigalian (39.5–18.5 Ma) interval are interpreted to record syn -depositional deformation. This indicates that shale tectonics in the offshore western Niger Delta initiated early in the evolution of the region, supporting previous interpretations that the active compressional zone of the Niger Delta was in the present continental slope before prograding to the outer-fold-thrust belt in the Pliocene. Stratal thinning above the crests of thrust-fold anticlines in the northeast and southwest of the study area suggests that shale tectonics persisted throughout the Neogene and Quaternary. A chaotic column that rises to seafloor from the crest of thrust-fold anticline, interfingering with the stratified succession is interpreted as a mud volcano edifice that has been active since at least the Burdigalian. This supports early shale mobilisation in response to generation of overpressure and also the fact that mud volcano system once formed, may act as conduits for pressure release throughout the history of a gravity-driven collapse system. The spatial association of seafloor mud volcanoes and pockmarks with deeper thrust-fold anticlines and normal faults suggests fluid migration from depth. In contrast, pockmarks overlying mass-transport deposits and submarine channels suggest fluid-flow from dewatering of more recent sediments. Our findings provide new insights into the Cenozoic tectono-stratigraphic evolution of the offshore western Niger Delta and the relation of shale mobility to fluid migration and escape during continental margin collapse. • Shale tectonics in the offshore Niger Delta initiated early in the evolution of the system in the Late Eocene/Early Miocene • Buckle folds within the Late Eocene-Burdigalian interval record the onset of shortening and gravity-driven deformation • Mud volcano systems once formed may act as conduits for pressure release throughout the history of a gravity collapse system • Increased sedimentation during the Late Eocene-Burdigalian facilitated overpressure development and shale mobilisation • Mud volcanoes and pockmarks above thrust-fold anticlines and deep faults record deep fluid-flow. Pockmarks above MTDs and submarine channels record shallow fluid-flow [ABSTRACT FROM AUTHOR]

The pattern of sediment dispersal and the location of sediment depocentres on continental margins can be very complex in both space and time. We aim at investigating how significantly external and internal factors, such as river runoff, bottom current and sliding can deviate the sediment dispersal from a simplistic fully sea-level controlled spreading. In this study we examined the sedimentation at two transects across the Mozambique-Zambezi slope between 17°20S-20°S, where multibeam bathymetry, sub-bottom profiler data and sediment cores were acquired. The period investigated spans the last 40 cal ka BP with a focus on the contrast between the last glacial (lowstand) and the Holocene (highstand) periods. Results show contrasting patterns of sediment dispersal, deposition and preservation. Sea level fluctuation remains the main forcing and most of the sediment from the Zambezi River settled on the inner shelf since the last sea level rise. However, we found that two major depocentres have developed on the upper slope during the Holocene consequent to the interaction of bottom currents with seabed morphologies at the shelf edge and at the upper slope. Early Holocene sliding in the north-east and in the south-west upper slope is a secondary but yet major factor of sediment transfer to the deep domain. Identified preconditioning factors for sliding on the slope are related to lowstand sediment loading and fluid circulation on the upper slope, and erosion at the base of slope of a plastered drift. Triggering must be related to margin wide mechanisms such as changes in hydrostatic pressure and reorganisation of sediment dispersal, subsequent to the post-glacial sea level rise, or maybe a period of regional seismicity. Climatic conditions in the Zambezi River watershed during the Bolling-Allerod and Younger Dryas periods are recorded and imprinted on the upper slope in the form of a detrital rich layer and a prominent slope-wide high-amplitude reflector. All over the continental slope, plastering of sediment deposits by bottom currents is pervasive and shows a morphological continuum from erosional scours at the base of slope to sediment waves on the upper slope and a possible interaction between along and across slope transport processes. We conclude that, in addition to sea level, the interplay of external and internal factors such as oceanic circulation and sliding, together with margin morphology, lead to the development of unexpected depocentres on the continental slopes. Thus, the study of modern marine analogues is crucial to avoid misleading interpretation of fossil deposits in terms of paleo sea level and more generally of paleo-environmental conditions. • Early Holocene sliding occurred in contrasting morphological and sedimentary settings • Expanded Holocene deposits on the upper slope related to interaction between bottom current and the morphology of the margin and of the seabed • Continuum of sediment undulations ranging from scours to sediment waves from base of slope to upper slope • Sedimentation contrast between Bolling-Allerod/Younger Dryas and Early Holocene periods visible as a high amplitude reflector [ABSTRACT FROM AUTHOR]

The Gulf of Cadiz Contourite Depositional System (GCCS) developed due to the interaction of the Mediterranean Outflow Water (MOW) with the middle continental slope of the SW Iberian continental margin. The GCCS evolved in a complex tectonic setting within the foreland of the Betic Orogeny and near the Nubia-Eurasia plate boundary. This study used tectonostratigraphic analysis of an extensive 2D multichannel seismic reflection dataset to investigate how inherited basin configuration and tectonic activity controlled sedimentary stacking pattern and evolution of the GCCS. Three regional tectonostratigraphic units (U1 - U3) were recognised in the margin. The younger seismic unit U3 corresponds to the Miocene-Quaternary foreland basin system where the contourite system is generated. Seismic analysis also detected the dextral strike-slip Gil Eanes Fault Zone (described herein for the first time), the Cadiz Fault, the Albufeira-Guadalquivir-Doñana Basement High and several diapiric structures. Integrated analysis of seismic profiles showing these tectonic structures with thickness and earthquake distribution maps suggest four tectono-sedimentary domains. The distinct characteristics shown by contourite features in the different domains, depends at broad-scale on the tectonic-control of the accommodation space (i.e., subsidence or uplift) and at local-scale on the presence of structural highs and fault-related depressions. Both influence bottom-current circulation and thus the evolution of the contourite deposits through the late Miocene and Quaternary. Three main stages have been recognised in the Gulf of Cadiz evolution: 1) the region was the western continuation of the Betic Corridor until the final re-opening of the Strait of Gibraltar (8–5.3 Ma). In this stage there is a predominance of turbidites or hemipelagic deposits, dependant on tectonic activity; 2) with the final re-opening of the Mediterranean-Atlantic connection there is the onset of the Pliocene- Quaternary contourite depositional system (5.3–2.0 Ma). Short-term changes in sedimentation during this stage, from contourite to turbidite deposits, indicate periods of increased tectonic activity; and 3) after the onset of the transpressive tectonic regime in the area (from 2.0 Ma), sedimentation became more homogeneous suggesting stable conditions (decrease of tectonic activity) with dominant contourite deposition. This work highlights the remarkable influence of structural features and tectonic events in controlling the seafloor relief and in turn in influenced the local oceanic circulation processes that controlling the morphology and sedimentary evolution of contourite systems. • Identified four tectono-stratigraphic domains bound by lithospheric structures • Three tectono-sedimentary evolutionary stages were recognised in the Gulf of Cadiz • A new structure was identified in this study, the strike-slip Gil Eanes Fault Zone • Inherited topography and structural features influenced contourite development • Local bottom-current circulation regulated by tectonic-related seafloor relief [ABSTRACT FROM AUTHOR]

The Demerara plateau, located offshore French Guiana and Suriname, is part of a passive transform continental margin particularly prone to develop slope instabilities, probably in relation to the presence of a free distal border along its steep continental slope. Slope failure occurred at different periods (Cretaceous to Neogene) and shows an overall retrogressive evolution through time. Upslope these failure headscarp, an enigmatic regional Mio-Pliocene unconformity has been discovered through the interpretation of new academic and industrial datasets. The aim of this work is to describe and understand the origin of this surface. Our analysis shows that this unconformity is made of a series of valleys that cross-cut sedimentary strata. Each one of these valleys has a short lateral extent and is closed along two perpendicular directions, which suggests that it could correspond to a highly meandering system, or to some sub-circular depressions. The infill of these features is equivalent to the regional stratigraphic strata found outside the structures, but in a subdued position. This seems to imply that the structures have originated by a local loss of sediments at their base or by sliding processes. Furthermore, these depressions intersect each other through time, while migrating progressively downslope. We discuss a series of hypotheses that try to explain the onset and evolution of these depressions forming the Mio-Pliocene unconformity (Canyons? Slope failures? Contourite moats? Hydrate pockmarks?). Having established that these structures are depressions formed by collapse, and have many similarities with structures recently described in the literature as pockmarks associated with gas hydrate dissolution, we favor this hypothesis. We propose that these hydrate pockmarks form with a mass failure that was triggered by fluid-overpressure development at the base of the hydrate stability zone. [ABSTRACT FROM AUTHOR]

The development of Punta Stilo Swell (PSS), a submerged lobate-shaped promontory located in the Crotone-Spartivento Basin, is inferred to be closely linked to the Calabrian Arc kinematics since mid-Miocene onward. The latter consists of an alternation between long-term phases of subsidence related to forward migration of the Calabrian accretionary complex, and short-term compressional-transpressional phases, characterized by episodes of uplift and formation of regional unconformities, in a context of stopping or slowdown of Calabrian accretionary complex migration. In particular, the study area is supposed to have respectively experienced phases of compressional and extensional tectonics during late Messinian and early Pliocene, which likely produced a reactivation of inherited compressional and extensional structures. Late Pliocene/Pleistocene transtensional tectonics is documented along the offshore extension of the Soverato-Lamezia Fault Zone (SLFZ), in the N sector of the PSS. The resulting physiographic modifications associated with such compressional, extensional and transtensional tectonics is believed to have controlled the accumulation of the thick Plio-Pleistocene succession of the PSS. The northern continental slope is inferred to be the result of late Pliocene/Pleistocene transtensional tectonics occurred along the SLFZ, whereas the shelf break is considered the result of an early Pliocene extensional tectonics. The considerable steepness (>10°) of the southern and eastern continental slope of the PSS is associated with the late Messinian compressional tectonic activity and is marked by the occurrence of slope failure-associated events. • The PSS was generated from late Messinian to Pleistocene compressional, extensional and transtensional tectonics. • The tectonic evolution of the PSS is linked to the central Mediterranean geodynamics. • The present-day steepness of the slope setting is the expression of the late Messinian compressional tectonics. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to assess the control of faults of the rift and post-rift stages on the shelf morphology of the Potiguar Basin in northeastern Brazil. This aborted rift basin was generated during the opening of the Equatorial Atlantic in the Aptian. The offshore portion of the continental margin consists of a narrow (~ 40 km) and shallow (~ 70 m below present sea-level) continental shelf with a very steep continental slope (1:11). Our dataset encompasses gravity, bathymetric, shallow seismic and structural data. The results indicate that low sedimentation rates during the Quaternary period contributed to the identification of structural controls in pre-Holocene rocks. The key evidence for fault reactivation on the seafloor is the link between coastal and shelf features associated with pre-Cenozoic structures of the Potiguar Basin. During periods of low sea level, the incision of shelf valleys was readjusted longitudinally and transversally due to the structural controls. Shelf gradient breaks are associated with the occurrences of coplanar ESE--WNW-oriented faults, and uplifted and subsided areas occur in between these fault systems. The results indicate a strong correlation between the margin geometry, modern shelf surface, near-surface expression, and the rift-phase faults, which appear to be reactivated in concordance with the present-day margin stress field. We conclude that neotectonics has influenced both the sediment deposition and morphology of the NE Brazilian Equatorial margin during Quaternary times. [ABSTRACT FROM AUTHOR]

Abstract: Seabed data acquired from the southern Barents Sea continental margin offshore Norway reveal detailed morphology of large sandwave fields. Multibeam echosounder bathymetry and backscatter, shallow seismic, sediment samples and seabed video data collected by the MAREANO program have been used to describe and interpret the morphology, distribution and transport of the sandwaves. The bedforms lie on a slope dominated by relict glacial forms and muddy/sandy/gravelly sediments. Sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later. The contour-parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic Norwegian Atlantic Current (NwAC) demonstrate that the NNW-flowing oceanographic circulation is the primary driving current. The fields coincide with the depth range at which a transition between warm, saline and underlying cooler, less saline waters fluctuate across the seabed. Statistically rigorous measurements of height, width and various parameters of slope and symmetry confirm a tendency to downstream (NNW) sandwave migration but with significant exceptions. Anomalous bedform symmetry domains within the fields are tuned to meso-scale topography along (relict) glacial debris flow chutes, indicating current focusing. Upstream and upper slope-derived winnowed sand transport eroded from the glacial sediments is the supposed source. Sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers. Perpendicular cross-cutting of stoss face 3-D ripples by linear (2-D) ripples in the sandwave troughs and lee faces is evidence for non-synchronous, episodic current variations. Though deep Ekman transport and internal wave action are unproven here, these could explain chute-related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling, thus contributing to long-term maintenance of the sandwave field. [Copyright &y& Elsevier]

Abstract: Several relatively small and spatially-isolated landslides with low mobility characterize the geomorphology of the upper continental slope off the Vesterålen islands. Here, we present results from a multidisciplinary study that integrates swath bathymetry data, high-resolution seismic reflection profiles and a multitude of geological and geotechnical laboratory tests from a 12m long piston core in order to investigate the origin and hazard potential of these shallow landslides. Four of the landslides have their upper headwall around the 500m isobath, whereas the main escarpments of another four landslides lie around 700 to 800m. The slip planes of the translational landslides lie within laminated glacial marine clays, overlying a well-defined seismic horizon. These clays have a higher plasticity and water content compared to the surrounding soils (sandy clays), and they exhibit a modest strain-softening behaviour in triaxial tests. The interdisciplinary data set is used as input to various numerical analyses in order to assess the failure and triggering mechanisms for these landslides, as well as their hazard potential. Stability analyses, dynamic analyses and post-earthquake pore pressure dissipation modelling suggest that the margin is essentially stable and that it would require a large magnitude earthquake to trigger landslides. The resulting deformation and excess pore pressure generation occur primarily within the top 10m of the soil, and they become more pronounced towards the surface. Finally, the run-out distance of these landslides is limited and strongly depends on the volume of displaced material and the slope angle. Mobility analyses reveal that the acceleration phase lasts about 1min and that peak velocities may have reached up to 17m/s. Hence, the consequences of such flows during a time of active seabed exploitation or the impact with seabed infrastructure could be devastating. [Copyright &y& Elsevier]

Abstract: High-resolution swath-bathymetry data integrated with sub-bottom profiles and single-channel seismics reveal an 18km long, up to 1000m wide and 10–15m deep crack located approx. 4km upslope from a slide scar on the continental slope off northern Norway. This crack is formed by subsidence of the sea-floor sediments to a depth of 120m due to downslope movement of an ~80km2 large sediment slab that represents the final stage of retrogressive mass wasting in this area. From its morphological freshness, the crack this is inferred to have formed sometime during the last 13cal. ka BP. These findings add to our understanding of the origin of sea floor cracks on passive continental margins where explanations as slip of normal faults or gas expulsion from the dissociation of gas hydrates previously have been suggested for the formation of cracks in similar settings. [Copyright &y& Elsevier]

Nile derived siliciclastic sediments are the main source of sedimentation along the Levant continental margins of the Mediterranean Sea. These sediments are transported along the southeastern Mediterranean coast via well-documented longshore currents, mainly operating along the shelf. However, the cross shelf component of sediment transport, responsible for conveying sediments toward the upper slope, is less known. To better understand the cross-shelf vs. the longshore component of sediment transport we studied a ~6 m long piston core (DOR280) sampled on the upper continental slope (280 m water depth) and analyzed benthic foraminiferal assemblages and their shell taphonomy alongside the particle size distribution and mineralogy of bulk sediments, to document both the source and the transport mechanism of those upper continental-slope sediments. The radiocarbon dating at the core-base is ~650 Cal. Yrs BP, indicating an exceptionally high average sedimentation rate of ~800 cm/kyr. DOR280 consists of two alternating distinct sedimentary facies: (1) laminated (L) intervals up to ~40 cm thick each and showing a high ratio of allochthonous vs. autochthonous (allo/auto) benthic foraminiferal species and a high percentage of broken shells, indicating contribution of transported sediments originating from mid-shelf habitats; (2) non-laminated (NL) intervals up to ~200 cm thick each and showing a low allo/auto ratio and low percentages of broken shells, indicating mostly in-situ hemipelagic deposition. The L intervals are interpreted here as turbidites. The sedimentation rates calculated only for the NL intervals are still exceptionally high, thus excluding hemipelagic sedimentation as the sole mechanism for the NL deposition. Therefore, a contour bottom current transported component is suggested here as a source of the NL sedimentation. We conclude that a mixed contourite-turbidite system actively prevails along the upper continental slope of the Levant coast, offshore Israel. The mid-shelf to upper slope sediment transport is nearly continuous and presents occasional turbidite events of average decadal reoccurrence time. • A piston core from the upper continental slope offshore Israel is studied. • Upper slope sedimentation rates are found to be exceptionally high: 800 cm/Kyr. • Benthic foraminiferal assemblages and taphonomy indicate transported sediments. • A mixed contourite-turbidite system prevails along the studied continental slope. • Benthic foraminifera provide a robust tool for evaluating marine geo-hazards. [ABSTRACT FROM AUTHOR]

The continental margin of the Ross Sea has been consistently sensitive to the advance and retreat of the Ross Ice Sheet (RIS) between the interglacial and glacial periods. This study examines changes of the glaciomarine sedimentation on the continental slope and rise to the eastern side of Hillary Canyon in the central Ross Sea, using three gravity cores collected at increasing water depths. Besides older AMS 14C ages of bulk sediments, based on the analytical results, sediment lithology was divided into units A, B1, and B2, representing Holocene, deglacial, and glacial periods, respectively. The sedimentation rate decreased as the water depth increased, with a higher sedimentation rate in the deglacial period (unit B1) than the Holocene (unit A). Biological productivity proxies were significantly higher in glacial unit B2 than in interglacial unit A, with transitional values observed in deglacial unit B1. Biological productivity generally decreased in the Antarctic continental margin during the glacial period because of extensive sea ice coverage. The higher biogenic contents in unit B2 are primarily attributed to the increased transport of eroded and reworked shelf sediments that contained abundant biogenic components to the continental slope and rise beneath the advancing RIS. Thus, glacial sedimentation on the continental slope and rise of the central Ross Sea was generally governed by the activity of the RIS, which generated melt-water plumes and debris flows at the front of the grounding line, although the continental rise might have experienced seasonally open conditions and lateral effects due to the bottom current. • Glaciomarine sedimentation in the continental slope and rise of the Ross Sea • Higher geochemical and isotopic properties of the glacial and degalcial sediments • More supply of reworked shelf sediments by the glacial advance of Ross Ice Sheet • Role of Ross Ice Sheet on the sediment deposition in the central Ross Sea [ABSTRACT FROM AUTHOR]

The combination of oceanographic processes and a negligible fluvial terrestrial sediment contribution makes the Santos Basin margin (southwestern Brazil) a unique environment for studying thew morphological imprint of bottom currents on the seafloor morphology. We divide the seafloor into four domains: outer shelf, upper, middle, and lower slope, based on an analysis of sub-bottom Chirp profiles, multichannel seismic data, hydrographic data, numerical simulation outputs, and a seismic-derived bathymetry map. A clinoform at the outer shelf and upper slope, topped by erosional morphologies, developed below the SW-flowing Brazil Current (BC). At the bottom of the upper slope, a rugged and mounded surface around 600 mbsl coincides with the current flow reversal to the underlying NE-flowing Intermediate Western Boundary Current (IWBC). The smooth middle slope exhibits sheeted contourites interrupted by occasional channel-and-mound complexes. From the middle slope base, salt tectonics becomes a major player in setting the seafloor morphology. The slope-parallel Santos Channel develops above a subsurface diapir and the Cabo Frio Fault. The latter divides between the landward gap in subsurface Albian salt and the basinward rich diapir realm. Hence, the lower slope is reworked by the SW-flowing Deep Western Boundary Current (DWBC); however, salt tectonics dictates its morphology. Our study consists of a unique example for studying the morpho-sedimentary imprint of a counter-current flowing on the continental slope and also for exploring the interaction between bottom flows with a suite of endogenic processes, such as salt tectonics, fluid flows, and mass movements. • Acoustic recognition of contourites generated by opposite flows. • Outer shelf and upper slope dominated by the Brazil Current. • A smooth surface represents the boundary between Brazil Current and Intermediate Western Boundary Current. • Steep middle slope molded by channel-and-mound features. • Santos channel and drift not in equilibrium with present-day hydrodynamics. [ABSTRACT FROM AUTHOR]

Combining high-resolution bathymetry and 2-D seismic data with 3-D hydrodynamic numerical simulation results to identify Quaternary plastered contourite drifts in the South China Sea northern margin (i.e., the Jianfeng and Yitong slopes), this study aims to disentangle the impacts of bottom currents associated with the intermediate and deep water masses. Upslope parts of plastered drifts (~1000–1200 mwd) are smooth and gentle (up to 1°) surfaces, which can also be classified as contourite terraces. They are characterised by non-deposition and sheeted deposition that indicate dominant flow conditions capable of transporting sediments. The responsible hydrodynamic forcing here is the anticyclonic South China Sea Intermediate Water currents, which flow eastward with a mean velocity of 2–3 cm/s. These are sporadically enhanced and can exceed 6 cm/s during high-energy intermittent events such as deep-reaching eddies. The central parts of the plastered drifts, located seaward of the terraces, present a subtle mounded morphology (1°–2°, ~1200–1500 mwd) partly perturbated by wavy bedforms. The downslope parts of the plastered drifts feature step-forming slides/slumps with steep slope gradients (1°–5°, ~1500–2000 mwd). According to our simulation results, the depth range of the plastered drifts overlaps the transition zone between the intermediate and deep water masses, wherein the simulated mean current velocity is 0–2 cm/s with variable directions, suggesting its deposition-favourable environment. Steep (>2°) slopes beneath the plastered drifts (below ~2000 mwd) present along-slope truncations, including contourite channels and moats that indicate enforced currents capable of erosion. Responsible hydrodynamic forcing is the cyclonic South China Sea Deep Water currents, which flow westward with a mean velocity of 3–5 cm/s and exceed 15 cm/s during high-energy intermittent events. The results of this study show a clear link between bottom currents' behaviours (e.g., mean flow condition and variability) and contouritic depositional patterns, which suggest that continental slopes can be effectively shaped by large-scale ocean circulations through the topography-current interaction. The weakest hydrodynamic condition and highest sediment accumulation rate, occurring in the ~800 m thick transition domain between two water masses in the study area, facilitate the development of plastered drifts at the seaward side of contourite terraces. The outcomes of our study may have broad implications for understanding the relationship between processes and products in continental margins. • Linkage between contourite morphology and oceanic forcing in northern SCS is elucidated. • Terraced plastered drifts develop in response to hydrodynamics of water mass interface. • Modelled contouritic erosion and deposition agree with seismic stratigraphic structures. • Contourites are shaped by low and high-frequency currents that interact with topography. [ABSTRACT FROM AUTHOR]

Submarine canyons are observed along both passive and active continental margins, but the factors controlling their complex morphology are still poorly understood. Here, we use high-resolution multibeam bathymetric and 2D seismic data to investigate an area of the northwest South China Sea in which 48 submarine canyons are identified. These previously unstudied submarine canyons incise the continental shelf, being located at a water depth between 200 m and 2200 m. Canyon morphology varies from southwest to northeast, namely in what their length and incision depth are concerned. We therefore divide these canyons into four main types: a) Types A, B and C showing a predominant NW-SE direction, and b) Type D canyons striking to the north. By analysing their internal architectures, we propose that submarine canyons along the northwest South China Sea margin were initiated in the Late Miocene by retrogressive slope failure in response to the gradual build-up of sediment on the continental slope. Differences in sediment supply and fault activity are recognised here as the main factors controlling the morphology of the investigated submarine canyons. In addition, recurrent mass-transport deposits (MTDs) fed sediment from the northwest South China Sea margin into the study area, accelerating the filling of the Central Canyon system, a giant submarine canyon located to the south of the investigated continental slope. The discovery of gas fields (LS22–1, LS17–2) and a gas hydrate drilling zone (GMGS5) in the Central Canyon system proves that MTDs comprise good reservoir intervals. Our results contribute to a better understanding of the origin and development of submarine canyons and highlight the role of sediment supply and tectonic events in controlling canyon morphology. • Forty-eight (48) submarine canyons are investigated in the northwest South China Sea. • Submarine canyons were initiated by retrogressive slope failure in the Late Miocene. • Sediment supply and fault activity control submarine-canyon morphology. [ABSTRACT FROM AUTHOR]

Repeat multibeam mapping of two slope-confined canyons on the northwest Australian margin provides new understanding of the processes that are active in shaping these environments. The Cape Range and Cloates canyons initiate on the mid to lower continental slope but are now known to be connected to the shelf via small channels and gullies. Both canyons have areas of steep walls, with evidence of slides, and large depressions on the canyon floors. These canyons were first mapped systematically with multibeam sonar in 2008 and were remapped in 2020 during a biodiversity survey that also collected high-resolution imagery and biological samples. Comparison of seabed features between these two time periods indicates active sliding, minor headwall retreat and continued excavation of deep depressions on the canyon floor. Significantly, intact blades of displaced seagrass imaged at various depths up to 4200 m throughout both canyons indicates that material sourced from the adjacent continental shelf is being transported through these canyon systems. Turbidity currents are actively modifying canyon walls and floor depressions, while also providing a sediment source that has resulted in minor accretion on the canyon floor. Sedimentation likely regulates benthic communities in these canyons, with imagery showing highest densities of sessile invertebrates in habitats protected from sedimentation (e.g. rock overhangs, cliff edges). Since steep canyon habitats are rare within these canyons, and support high benthic abundance, they likely represent biologically significant areas of the Gascoyne Marine Park. Repeat mapping provides an understanding of the dynamics of these canyons and a context for assessing and monitoring the stability of the seabed habitats within this marine reserve. • Repeat mapping of slope-confined submarine canyons reveals active sedimentary processes on a passive continental margin. • Both canyons contain evidence for active sliding, minor headwall retreat and continued excavation of deep floor depressions. • Intact displaced seagrass blades indicate channelling of material from the continental shelf through these canyon systems. • Sessile invertebrates have highest densities in rare habitats protected from sedimentation, such as on rock overhangs. [ABSTRACT FROM AUTHOR]

The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions. • A detailed analysis of Pleistocene sediments from IODP Expedition 374 Site U1525 • Three main intervals of deposition between: 2.4 Ma–1.4 Ma, 1.4 Ma–0.8 Ma and < 0.8 Ma • Depositional context for the Hillary Canyon and the Ross Sea trough-mouth fan • Sandy, foraminifera-bearing interval at ~1.18 Ma suggests ice sheet collapse • Ice grounded at shelf edge more often after 1 Ma, TMF prograded over Site U1525 [ABSTRACT FROM AUTHOR]

Abstract: Five quantitatively distinct gully types are identified on the Antarctic continental margin from swath bathymetric data of over 1100 individual features. The gullies differ in terms of length, width, depth, width/depth ratio, cross-sectional shape, branching order, sinuosity and spatial density. Quantitative analysis suggests that Antarctic gully morphology varies with local slope character (i.e. slope geometry, gradient), regional factors (i.e. location of cross-shelf troughs, trough mouth fans, subglacial meltwater production rates, drainage basin size), sediment yield and ice-sheet history. In keeping with interpretations of previous researchers, most gullies are probably formed by hyperpycnal flows of sediment-laden subglacial meltwater released from beneath ice-sheets grounded at the continental shelf edge during glacial maxima. The limited down-slope extent of gullies on the western Antarctic Peninsula is explained by the steep gradient and slope geometry at the mouth of Marguerite Trough, which cause flows to accelerate and entrain seawater more quickly, resulting in a reduction of the negative buoyancy effect of the sediment load. Due to pressure gradients at the ice-sheet bed caused by variations in ice thickness inside and outside palaeo-ice stream troughs, subglacial meltwater flow was generally focussed towards trough margins. This has resulted in gullies with larger cross-sectional areas and higher sinuosities at the trough margins. A unique style of gullying is observed off one part of the western Antarctic Peninsula, corresponding to an area in which the ice-sheet grounding line is not thought to have reached the shelf edge during the Last Glacial Maximum. We interpret the features in this area as the cumulative result of slope processes that operated over a long period of time in the absence of hyperpycnal meltwater flows. [Copyright &y& Elsevier]

Abstract: Rock samples dredged offshore the Pontine Archipelago (400–2000m water depth) were studied by palaeontological analyses of planktic foraminifera and endo-epilithozoan faunas colonising Fe–Mn crusts and by petrographic analyses of volcanic samples. Palaeontological and petrographic analyses have revealed a complex Plio-Pleistocene depositional history controlled by hemipelagic sedimentation and volcanic activity with episodic non-depositional phases. The sedimentary deposits are associated with ferromanganese hardgrounds, more or less colonised by endolithic and epilithozoan organisms. The presence of foraminifera typical of tropical and subtropical waters (such as Globigerinoides ruber, Globigerinoides trilobus, Pulleniatina obliquiloculata and Sphaeroidinella dehiscens) indicates that the micritic deposition occurred during warm climatic periods, whilst micrite cementation and hardground formation are here attributed to colder climates. The depositional processes recognised on the Pontine continental slope reveal a sediment-starved condition that locally resemble those of seamount environment. The slope sedimentation found in the Pontine Archipelago can be helpful in the interpretation of ancient deposits from seamounts and continental slope depositional environments, characterised by hardground and hiatuses. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: Submarine channels with meandering patterns and extensive levee complexes are commonly found on continental slopes and fans. Here, a three-dimensional numerical model is applied to conduct a systematic study of poorly-sorted depositional turbidity currents in sinuous submarine channels with different side slope and sinuosity. Multiple runs with the same inflow conditions are made to study deposition patterns inside the channel and levees. Not only many known facts, such as the spilling and stripping of turbidity currents at channel bends as well as the different pattern of deposition at the inner and outer banks of channel bends, are produced, but also some important new findings, such as: i) small river-like circulation near the bottom corner of outer bank co-exists with predominant lateral convection as secondary flow; ii) the levee on the outer bank of a channel bend apex of steeper lateral slope shows larger variation in grain size distribution than the thinner, more smooth levee on its opposite side; iii) the levees at bend inflections inherit the characteristics of the upstream levees at channel bend apexes; iv) the downstream cross-section that cuts both sinuous channel beds and banks is characterized by thicker channel bed deposits intersected by arch-shaped thinner on-bank deposits; v) the levee deposit displays an asymmetric wave pattern in the downstream direction, and the flow direction is from the short rising side to the long dropping side. The flow and sedimentation patterns summarized in this study may promote the understanding of physical processes of submarine turbidity currents and their depositions and assist in interpreting seismic, outcrop and/or borehole data for reconstruction of original depositional environment. [Copyright &y& Elsevier]

Abstract: This study presents an approach to the classification of submarine canyons on the Australian continental slope. There are many canyons around the Australian continental margin it provides an opportunity to undertake a characterisation and inventory of these potentially important assets. By establishing a shelf, break and foot of slope based on gradient, submarine catchments are defined based on a drainage network derived from across the continental shelf and slope. On completion of this classification, metrics are extracted for both the drainage network representing submarine canyons and the catchment morphology. The rationale for this research is to demonstrate the application of algorithms developed for drainage analysis. These algorithms have traditionally been applied in terrestrial environments for the automatic extraction of drainage networks and catchments from digital elevation models. This work is made possible by recent advances in deep-sea multibeam technology, so that the seafloor morphology can be mapped in higher definition. With the recent advances in data quality, these algorithms can be applied to an integrated and combined model of both elevation and bathymetric datasets to provide better insight into geomorphological features, including the relationships between subaqueous sedimentary canyons, channels and drainage system morphology. Drainage analysis provides a rapid automatic procedure to derive networks on the continental shelf and slope. Results show that by establishing a shelf break and foot of slope based on gradient, submarine catchments can be derived on the continental slope based on the drainage analysis. The Australian continental slope contains 257 shelf-incised catchments based on analysis of a bathymetric model mapped at a resolution of 250m. The drainage analysis demonstrates the capabilities of correctly predicting the layout of dendritic patterns leading to a better geological understanding. [Copyright &y& Elsevier]

Abstract: This study aims to present an overview of the seafloor morphology and shallow sedimentary structure of the Storfjorden and Kveithola Trough Mouth Fans (TMFs) on the northwestern Barents Sea continental margin. Data have been compiled from two International Polar Year (IPY) cruises (SVAIS, of the BIO Hespérides and EGLACOM of the R/V OGS-Explora) that yielded 15,340km2 of multi-beam bathymetry and 9500km of sub-bottom seismic profiles. In this area, the continental shelf edge defines three wide and subdued sedimentary lobes forming Storfjorden TMF, one single lobe on Kveithola TMF, and three inter-TMF areas on the continental slope. The two northernmost lobes of Storfjorden TMF (Lobes I and II) are composed by thick (up to 50m) sequences of glacially derived debris flow deposits interbedded with thin a few metres de-glacial and interglacial deposits. A network of upper slope gullies incises these debris flow deposits as a consequence of subglacial meltwater release at or near the shelf break. Gullies evolve into channels whose morphologic evidence disappears midslope, leaving place to a subdued chevron-like morphological pattern inherited by the preceeding glacial maximum debris flow deposits. A drastic change occurs on the continental slope of Storfjorden TMF Lobe III and Kveithola TMF, where are several translational submarine landslides mostly originated in the upper slope, the majority of which detach at the contact between Middle Weishelian glacigenic debris flows and the overlying acoustically laminated plumites. Dendritic canyon systems only develop in inter-TMF areas. The data suggest that TMF continental slope progradation depends on short-lived episodes of extreme sedimentation during glacial maxima and during the early deglaciation phase, and that an important controlling factor is the mechanism of ice stream retreat from the continental shelf edge. We suggest that the two northern Storfjorden sub-ice streams were composed of thicker and perhaps faster ice progressively draining a distal and larger ice source mainly located on Svalbard. Conversely, the southernmost Storfjorden sub-ice stream and the Kveithola ice stream were fed by a local, smaller marine-based ice dome grounded on Spitsbergenbanken. The ice dome persisted after the LGM, maintaining a local ice drainage system close to the shelf edge whose sedimentary evidence can be found on the continental slope of the southern lobe of Storfjorden TMF and Kveithola TMF. The high degree of lateral variability in the style of sedimentation on TMF slopes suggests that ice stream dynamics may vary considerably within the same glacial trough, and that such variability affects the long-term development of the architecture of TMFs. [Copyright &y& Elsevier]

Abstract: Large rivers on continental margins play an important role as interfaces between land and ocean sedimentation. In many cases the modes and history of sediment dispersal, and the final deposition of the impressive volumes of terrigenous matter in the deep ocean remain poorly constrained by detailed sedimentary observations. The Zambezi River, by far the largest river of southeast Africa, discharges into the narrow, funnel-shaped Mozambique Strait between Africa and Madagascar. Here, we study the distribution of lithic grain sizes and major bulk fractions of biogenic and abiogenic components in core tops and long sediment cores off the Zambezi River, spanning the past ~60,000years of the central and northern Mozambique continental margin. Due to the particular current regime, the modern Mozambique margin shows distinct sedimentation patterns not seen off most rivers of comparable size. Deposition is largely free of hiatuses, with high accumulation rates of fine-grained material, and only minor signs of erosion or sediment winnowing. Zambezi riverine detritus dominates the sedimentary facies between 20°S and 17°S from below the shelf break down to 2000m water depth. However, a considerable fraction at present high sea level is deposited not directly downstream the Zambezi River mouth, but is dispersed to the northeast by along-shore transport, opposite to the mean flow within the Mozambique Strait. As a consequence, downslope transport today is highly unfocused and a canyon system at the upper slope is only poorly developed. We suggest that most of the riverine matter leaves the continental shelf ~200km to the northeast of the present river mouth. Sediments took a more direct, chanellized path during the last glacial period of lowered sea level, which was confirmed by the reconstruction of Holocene and Late Glacial sedimentation rates in the area. In this regard, the Zambezi River–Margin sedimentary system stands for a margin with considerable temporal and spatial variabilities in downslope deposition on glacial-to-interglacial timescales. [Copyright &y& Elsevier]

Abstract: The continental slope of the northern Gulf of Mexico seaward of the Mississippi Delta is characterized by very rapid Quaternary sedimentation. Thick sequences of underconsolidated muds and mudstones are present, which are severely overpressured. In the Ursa Basin, Site U1322 of the Integrated Ocean Drilling Program (IODP) provided an excellent coring record of interleaved fine-grained turbidites and hemipelagic sediments, in part severely affected by submarine slumping and sliding after deposition. Cores were continuously sampled and analyzed for anisotropy of magnetic susceptibility (AMS), to elucidate the effects of different transport mechanisms and degree of settling and consolidation on magnetic fabric properties. Generally AMS ellipticity increases with depth irrespective of transport mode, due to loss of porosity. Samples from slumped mass transport deposits (MTD), however, have higher AMS if compared to immediately overlying non-slumped material. MTD samples dominantly show triaxial magnetic fabrics whereas those found in non-slumped sediments are much more oblate. Long axes of the fabric ellipsoid reflect the direction of eastward to southward suspension transport in samples not overprinted by sliding or slumping. Short ellipsoid axes in non-slumped material are vertical, and thus parallel to the axis of maximum uniaxial shortening. In the MTD samples, many short ellipsoid axes are inclined, reflecting an overprint of the uniaxial shortening by bed-parallel shearing induced by the slumping. Shear and MTD transport direction deduced from the fabrics is top-to-SE, downslope along the morphological axis of Ursa Basin. Generally we show that magnetic fabrics of muds and mudstones are sensitive recorders of sedimentary and tectonic processes, and can be used to reconstruct essential parts of basin history. [Copyright &y& Elsevier]

Abstract: The morphology and distribution of submarine landforms in Hinlopen Trough, Northern Svalbard margin, and the upper continental slope beyond, are investigated using swath-bathymetric data, together with side-scan sonar, acoustic profiler records and sediment cores. Sun-illuminated images reveal a number of landform assemblages on the sea floor of Hinlopen Trough and confirm that this depression was occupied by an ice stream during the Late Weichselian glaciation around 20ka before present. The geomorphology of the inner-shelf is characterised by bedrock drumlins and ice-sculpted bedrock. There is a middle-shelf transition from a rock bed to an unconsolidated sedimentary bed that contains highly-attenuated drumlins and megaflutes formed within a dark grey, matrix-supported diamict, interpreted as subglacial till. Outer-shelf landforms are mainly iceberg ploughmarks. The geomorphological imprint identified from Hinlopen Trough is similar to that of many former ice streams; the trough is dominated by elongate landforms orientated parallel to the inferred flow direction and is lacking in transverse features indicative of inter-ice stream locations. A characteristic down-flow progression in landform elongation is also observed, suggesting an increase in ice velocity across the continental shelf. The lack of grounding-zone features imaged from swath-bathymetric data implies that deglaciation was probably rapid within the trough. A large depositional fan exists on the upper continental slope beyond the trough, characterised by debris flow deposits relating to the down-slope transport of glacigenic sediment. Order of magnitude calculations of the volume of glacigenic sediment on the continental slope indicate that the ice stream provided high rates of debris delivery of around 5–7.5m/ka. This suggests that Hinlopen Trough ice stream represented a major route for the transfer of ice and debris to the Hinlopen Fan on the northern continental margin of Svalbard during the Late Weichselian glaciation. [Copyright &y& Elsevier]