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Whereas the effects of high-order relative sea level change (3rd-order and higher) on the formation and architecture of submarine fan systems are relatively well established, a lack of large-scale spatial and temporal data has resulted in the impacts of low-order relative sea level change (i.e. , 2nd-order) eluding characterization. With the aim of revealing the impacts of 2nd-order relative sea level, this study applied regional-scale seismic geomorphology to examine 142 Miocene-aged (21–8.2 Ma) submarine fans in the Baiyun Sag of the Pearl River Mouth Basin (China), integrating a large 3D seismic volume (6000 km2), well logs and core data. By extracting seismic attributes calibrated to well data, architectural elements were interpreted, statistically correlated, and their evolution through time was assessed. The results were as follows: (1) architectural elements of submarine channels and lobes, as well as associated highstand deltas, shelf-margin deltas and incised valleys, were identified based on their seismic geomorphological features and location, revealing that submarine channels shift paleo-seaward from incised valleys and feed lobes; (2) there is a positive correlation between average width of submarine channels and average area of lobes, as well as between the average width of incised valleys and average width of submarine channels; (3) the size of architectural elements is inversely related to proportion of sand; and most importantly, (4) the size variation of architectural elements coincides with changes in 2nd-order relative sea level. Results also indicate that rapid tectonic subsidence played an important control on the size and sandiness of deep-water architectural elements. The findings of this study may inform reconstruction of submarine fan systems and prediction of their petroleum reservoir potential in other systems globally. • Submarine fan architectural elements were identified. • Two positive correlations between the architectural elements were revealed. • Second-order relative sea level had controlled the sizes and lithology of architectural elements. [ABSTRACT FROM AUTHOR]

The gas hydrate stability zone (GHSZ) is defined by pressure-temperature-salinity (pTS) constraints of natural gas hydrate (GH) system. It refers to a depth interval which usually extends several hundred meters into the sediment column at sufficient water depths. The lower boundary of the GHSZ often coincides in seismic reflection data with a bottom simulating reflector (BSR), which indicates the transition between the underlying free gas and the overlying no-free gas zone at the thermodynamic stability boundary. The GHSZ in geological systems is dynamic and can shift in response to sedimentation processes and/or changes in environmental conditions such as bottom water temperatures, hydrostatic pressure, and water salinity. The appearance of multiple BSRs has been interpreted as remnants of former GHSZ shifts which have persisted over geological timescales. In this study, we numerically simulate the sedimentation-driven development of multiple stacked BSRs in the Danube deep-sea fan in the Black Sea. We show that in this dynamic sediment depositional regime sufficient amounts of residual gas remain trapped in the former GHSZ, given sufficiently high initial gas hydrate saturations, so that paleo-BSRs could persist over long time scales (∼ 300 kyr). In particular, the formation and persistence of multiple BSRs in the Danube Delta is controlled by the sequence of sedimentation events of the levees induced by sea-level change. The kinetics of methane phase transitions between gas hydrate, dissolved methane, and free gas plays a key role in the coexistence, location and timing of the multiple BSRs. Thus, For a given permeability, distinct multiple BSRs appear only for a narrow range of GH formation (10 − 14 < k f mol / m 2 Pa s ≤ 10 − 12) and dissociation rates (10 − 16 < k d mol / m 2 Pa s < 10 − 14). • This study simulates the sedimentation-driven development of multiple stacked BSRs in the Danube paleo-delta, Black Sea. • Multiple BSR formation in Black Sea is controlled by the sequence of sedimentation events of levees due to sea-level changes. • Kinetics of phase transitions plays a key role in the coexistence, location, and timing of the multiple BSRs. • Development of multiple BSRs is possible only under a narrow range of parameters, unique for the Danube delta setting. [ABSTRACT FROM AUTHOR]

Sediments deposited on the eastern continental shelf of India are studied for texture, mineralogy and their major, trace, and rare earth elemental composition in lithogenic fraction. The objective of this study was to identify the sources, and evaluate the factors affecting the erosion and weathering in the catchment area and dispersal and deposition of sediments over the shelf region. Here, we present an extensive dataset covering the entire eastern continental shelf of India from the Ganges-Brahmaputra (G-B) basin in the north including the shelf off major peninsular Indian river basins of Mahanadi, Godavari, and Krishna up to the Kaveri basin in the southern tip. Textural and geochemical studies have shown that the lithology of the source rocks plays an important role in governing the chemistry and mineralogy of the sediments. The results show that the G-B shelf sediments are primarily derived from the Higher Himalaya Crystalline sequence (HHCS) and the Tethyan sedimentary series (TSS) exposed along the peaks and drainage divide of the Himalayas. Mahanadi shelf sediments are mainly derived from the felsic rocks belonging to Precambrian metamorphic formations of the Eastern Ghats, limestones, sandstones, and shales of the Gondwanas and recent deltaic alluvium deposits, whereas the Krishna-Godavari (K-G) sediments find a part of their source in the Deccan Basalts. The shelf sediments off River Kaveri are derived from a mixture of peninsular granitic gneisses, tonalite-trondjhemite gneisses, and charnockites. The sediment geochemistry has also allowed us in assessing the weathering patterns in the source areas. The sediments have undergone a moderate degree of weathering. Weathering intensities were found to have varied with the source area lithology. The least square regression of the geochemical data allowed us to estimate the relative contribution of each of these sources and their geographic extent. Unlike the massive offshore deposition and formation of a major Fan system (the Bengal fan), the fluvial sediment dispersal of the mighty Himalayan Rivers on the continental shelf is significant only at the G-B mouth and their contribution reduces to <50% at about 18oN. The sediment dispersal from the Godavari River is seen to extend on either side of the mouth of the river which is attributed to the reversing East India Coastal Current (EICC), which plays an important role, in the sediment transport along the central and south-central part of the east coast of India. The influence of the Mahanadi, Krishna, and Kaveri River sediments is however confined to a small area near their mouths and has a limited geographic extent of influence in the shelf region. • Entire eastern continental shelf of India is geochemically mapped, hithero not done • A distinct provinciality in geochemistry commensurate with source rock lithology is witnessed. • Geographic spread of each contributory source is estimated using mixing calculations • Reversing monsoon currents with season seem to control the sediment dispersal in the area. • Unlike the large geographic spread into deep-sea, spread of G--B derived sediments on the shelf is limited to narrow extent [ABSTRACT FROM AUTHOR]

Submarine fans are the largest sediment accumulations on Earth and are key to study the sediment-transfer zone between terrestrial source area and deep-sea depositional sink. They provide information of past climate, tectonics, carbon global inventory, and can be prolific hosts for oil/gas resources. In this paper, we present, for the first time, an analysis of the entire Magdalena Submarine Fan (MSF), from the shelf break to the distal domain, based on ~224,000 km2 of multibeam bathymetry, as well as backscatter, subbottom profiler and regional/local seismic reflection data recently acquired in southwestern Caribbean Sea. The aim is to describe in detail the MSF morphology and depositional architecture, propose a fan segmentation landform assemblage, and determine its extent within the deep basin. Three fan segments are identified: upper, middle and lower fans. The upper fan extends from the coastline to a depth of ~3000 m. Its eastern sector is characterized by a canyon system off the present-day mouth of the Magdalena River, through which most of the sediments are transported downslope to be deposited in intra-slope basins bounded by structural highs of the South Caribbean Deformed Belt. The western upper fan is characterized by distinct channel-levee complexes that are partially removed by mass transport complexes that originated near the continental shelf edge. The upper to middle fan transition is marked by a decrease in regional gradient from 1° to about 0.3° and local relief, a change from large, irregular sediment waves to more regular waves that slowly decrease in amplitude downslope, and the appearance of erosional megascours. The middle fan bedform assemblage evidences the presence of a channel-lobe transition zone in this sector of the MSF, separating well-defined, upper fan channels from lower fan depositional lobes. The middle to lower fan transition occurs between ~3800 and ~3950 m and is defined by a further decrease in gradient and by a change from sediment waves to planar parallel-bedded reflectors on subbottom profiles. The lower fan extends to a maximum depth of ~4250 m and is characterized by an almost flat seabed (slope of 0.05°), interrupted by a few isolated bathymetric highs and low-relief channels (<5 m deep). The entire area of the lower fan is interpreted as an area of turbidity current deposition, with relatively sandy sediments in the south and west giving way to muddier sediments in the northeast, which could correspond to distal fan lobes. The identification of four regional seismic facies related to MSF sedimentation allowed us to constrain the fan extent in the southwestern sector of the Caribbean. Distally, within the Colombia Basin the fan terminates against areas of elevated seafloor (Kogi-Coyaima and Quimbaya seamounts, Aruzi and Ticuna hills, and Beata Ridge), which have acted as barriers to sedimentation. Nevertheless, it was determined that the MSF extends beyond the Colombia Basin and locally reaches the Lower Nicaraguan Rise. In this new scenario, we established that the MSF is much more extensive than previously recognized, with an area of ~237,000 km2, which puts it among the World's largest submarine fans. • The morpho-structure of the entire Magdalena Submarine Fan (MSF) is presented • Upper, middle and lower fan segments are proposed from diverse landform assemblages • Channel-levee complexes partially removed by extensive MTCs defines the upper fan • Middle fan, with sediment waves and megascours, is defined as sediment bypass area • Evidence of turbidity current sedimentation, with probable lobes, in the lower fan [ABSTRACT FROM AUTHOR]

We have studied the rock magnetic characteristics of 31 multicores and 7 gravity cores from deep-sea sediments of the distal Amazon Fan and Demerara Abyssal Plain. This study has permitted us to delineate the space/time pattern of Holocene physical sedimentation along the northeastern margin of South America associated with the Amazon River sediment plume. The rock magnetic variability is correlatable over the entire study region. This degree of correlation has permitted us to develop a composite picture of Holocene rock magnetic (and overall physical clastic) sedimentation. 26 radiocarbon dates have been combined with the rock magnetic correlations to provide a composite Holocene chronostratigraphy for that variability. We have built isopach maps of overall sedimentation for three windows in the Holocene (3000, 4500, and 7000 calendar years BP). The overall sedimentation in the center of our region is ~5 cm/kyr. But, sedimentation rates are faster closer to the coastline and associated with the distal clastic flux from the Amazon Plume. There is a secondary high in sediment accumulation under the North Brazil Current retroflection. Our maps suggest that the retroflection has been active at the millennial scale for at least the last 7000 years. We estimate that the mid-Holocene (~4.5–9000 calendar years BP) pattern of sedimentation was distinctly different from that of the last few thousand years. The clastic sediments were ~25% reduced in concentration (with the biogenic sediments similarly increased by ~25%), they were finer–grained, and significantly less rich in ferric iron phases (hematite/goethite). We think these three covarying clastic parameters are due to an interval of reduced clastic flux from the Amazon River Plume with a reduced proportion of Amazon Basin sediments (as opposed to Andes-derived sediments). We hypothesize this was due to significantly drier Amazon Basin environmental conditions during that time interval. [ABSTRACT FROM AUTHOR]

Earthquakes, tsunamis and gravity flows are common processes offshore Eastern Sicily and pose a significant hazard to coastal communities and infrastructure. The 1908 Messina earthquake and tsunami resulted in >60,000 casualties. It caused a large turbidity current, which broke the Malta-Zante telegraph cable. Yet, this gravity flow remains poorly characterised in terms of its route and flow behaviour. A comprehensive analysis of multibeam echosounder data, sub-bottom profiles, and sediment cores has been carried out to improve our understanding about gravity flow activity within conduit systems of the western Ionian Basin to reconstruct the characteristics of the 1908 sediment flow (e.g., erosion, velocity, source region). Three main canyon-channel systems can be distinguished within the study area. The easternmost system (C3) appears to be the most active in terms of sediment transport. There are numerous erosional and depositional bedforms, including large-scale scours (>100 m-long), turbidite sediment waves and channel wall collapses that are not overprinted by younger events. The other two canyon-channel systems (C1, C2) do not show many bedforms indicative of repeated and recent gravity flow activity. Indeed, the transport of the majority of sediment discharged into the western system (C1) is limited to <25 km downslope from the continental slope, while the central system (C2) facilitates sediment deposition from gravity flows. C3 is, thus, suggested to have been the main passageway of the 1908 sediment flow. It also leads directly to two of three cable break locations. The most likely source areas for the gravity flow are north-eastern Sicily and southern Calabria. Bedforms indicate a flow thickness of >170 m along the upper channel portion of C3 and > 140 m along its lower portion close to the cable breaks. An average flow velocity of 5.6 to 6.3 ms−1 is reconstructed, given the timing of the breaks and length of the canyon-channel system. The flow may have locally decelerated and accelerated while bypassing morphologic highs and knickpoints. These new findings significantly improve our understanding of the 1908 gravity flow (e.g., passageways, depositional/erosional behaviour, thickness, velocity) and provide important insights into gravity flow events in general, especially those with a large run-out. This knowledge is needed to assess potential hazards associated with these events. • the western Ionian Basin shows three distinct canyon-channel systems. • >140 m-thick gravity flow along main passageway in the east; velocity 5–6 m s−2. • numerous erosional and depositional bedforms (e.g., scours, sediment waves). • north-eastern Sicily and southern Calabria are potential source areas. • main failure likely offshore between San Leo and Bocale (southern Calabria). [ABSTRACT FROM AUTHOR]

Four decades of studies on pristine Baffin Island fjords are summarized with respect to sediment redistribution processes and resulting deposits. Sediment fill in these fjords occurred during the Holocene epoch, when deglacial and postglacial processes led to sandy-mud basin fills. The sand component mostly enters the fjord basins from fjordhead sandurs and their shoreline chute failures, triggering the release of yearly turbidity currents. These currents can travel long distances, often within leveed channels, leaving behind a seafloor of migrating cyclic steps that eventually transform into unconfined sediment waves. Channelized cyclic steps migrate upstream at up to tens of meters per year whereas unconfined finer-grained sediment waves migrate at much lower rates. Moored instruments and sediment traps in two fjords show turbidity currents to occur mostly in June through August when meltwater supply from glaciers is at a maximum. Not surprisingly, moored instruments were dragged downslope by turbidity current impact, suggesting high-concentration of suspended sediment within a thin near-bed layer. In rarer cases, large debris flows form even larger and longer submarine channels that carry sediment for tens of kilometers into the deep basin. These slide-generated debris flows can reorganize the basin floor as a sediment conduit for follow-on turbidity currents across thousands of years. Whereas sand is transferred to the deeper basin by turbidity currents, mud accumulates on the steep sidewall slopes and in the deep basin. Where mud accumulates on steep (≥13°) margins, many sidewall failures occur. Notably, right-hand margins contain a thicker sediment package and are affected by more sidewall failures than the left-hand side, primarily due to the Coriolis effect on increasing sediment accumulation rates. Of the many sidewall slope failures documented in Baffin Island fiords, iceberg collision with the seafloor is the only triggering mechanism directly observed. The association between subaerial debris flow fans and margin failures indicates that rock avalanches and subaerial debris flows also play a key role in triggering sidewall failures. The active seismic zone along Baffin Bay, likely initiated the rare but large deep-seated landslides observed in the sedimentary record. Baffin Island fjords are incredibly dynamic coastal environments with an ability to annually redistribute large masses of submarine sediment. • Sandur shorelines prograde slowly due to an average of ±65 shoreline chute failures generated every year per delta. • Turbidity currents create channelized cyclic steps, unconstrained cyclic step fields and sediment wave fields. • Fjord-margin sediment failures are common, where slopes exceed 13° and may be triggered by icebergs. • Massive failures, perhaps earthquake-related, reorganize seafloor transport along large submarine channels. • Within-layer sediment deformation is common where permeability between sediment layers is large. [ABSTRACT FROM AUTHOR]

Submarine fan sediments are essential archives for understanding the interaction between continental weathering and climate change, but decoding multiple geological and environmental factors in such highly dynamic sedimentary environments is challenging. Here we present a high-resolution magnetic mineral record spanning the past ∼40 ka from the central Bengal Fan. Comprehensive rock magnetic and electron microscopic analyses are conducted to understand the origins of different magnetic mineral components in response to sedimentary and paleoclimate processes. Detrital magnetite and titanomagnetite are the dominant magnetic minerals in Bengal Fan sediments, whose abundance and grain size are primarily controlled by eustatic sea-level change. Increased Himalaya terrestrial input during Heinrich events is documented during sea-level low stand, but magnetic mineral variations and climate events are decoupled due to enhanced Indian hemipelagic sediment input since the last deglaciation sea-level rise. In addition, we identify an enriched biogenic magnetite layer near the Fe-redox boundary in the studied Bengal Fan sediment core, possibly related to relatively mild post-depositional diagenesis. Massive detrital inputs in the submarine fan sediments dilute the contribution of biogenic magnetite to the bulk magnetic record. Our results contribute to an integrated source-to-sink understanding of magnetic mineral components in continental margin submarine fans, which helps to construct multi-proxy Quaternary paleoclimate and paleogeography records in typical submarine fan deposits. • Direct recognition of detrital/biogenic magnetic minerals in Bengal Fan sediments. • Sea-level controls variations of detrital magnetic mineral component. • Stadial terrestrial input was enhanced during sea-level low stand. • Increased hemipelagic sediments at sea-level high stand reduce climate sensitivity. • Thriving biogenic magnetite near diagenetic Fe-redox boundary. [ABSTRACT FROM AUTHOR]

Quaternary deposits of the Midyan coast of Saudi Arabia include coral-bearing limestones interbedded with sheet-flow siliciclastic sands and gravels, interpreted as braid-delta fan deposits. The limestones and their contained faunas provide evidence of periodic local stabilization of gravel surfaces and effective starvation of siliciclastic supply. Some indicate growth and deposition in waters a metre or so deep whereas others were substantially deeper. An additional group reflects initial deposition in shallow waters with resedimentation downslope by storm or other 'delta-front' processes. The surfaces of the fans provided morphological and environmental analogues to fore- and back-reef situations in which corals, calcareous coralline algae, molluscs, and echinoderms flourished, but in this area did not form independent reefs. The dominant controls on the changes from siliciclastic- to carbonate-dominated deposition were not transitional, and primarily related to channel and fan-lobe migration rather than tectonic or eustatic sea level changes. Similar variations in the distribution of siliciclastic sediments may control carbonate occurrence in other mixed sequences. • This short paper is concerned with the interrelationships between carbonate and siliciclastic deposits during the Pleistocene. • Contrary to popular views that these are mutually exclusive, results show that they were deposited simultaneously in the same general area. • The carbonates include deposits formed both in very shallow water and on relatively deep slopes. • The wide spread of previously published age dates supports the view of deposition at different times separated topographically. [ABSTRACT FROM AUTHOR]

Using a suite of ultra-high resolution geophysical tools, remote operated vehicle dives, legacy cores, and isolated grab samples, we demonstrate at a regional shelf scale, the influence of antecedent geology (basement topography, shelf gradient and submerged shoreline features) on the evolving transgressive shelf stratigraphy of a subaqueous delta. The unconsolidated uppermost delta occurs as isolated remnants scattered across the low-gradient shelf. Seismic data reveal across-shelf heterogeneity in bedrock elevation, with prominent bedrock highs and depressions and several well-preserved aeolianite palaeo-shoreline complexes at water depths of −100, −60 and − 40 m. Analysis of bathymetric and seismic data demonstrates that these pre-existing shoreline complexes exert an overarching control on the distribution patterns of i) deltaic sediments, where they abut the landward flank of the shoreline form, acting as a barrier to seaward dispersal, and ii) shoreface sediments which remain sequestered on the mid-shelf on the seaward flank of the shoreline complex, hampering the landward translation of the shoreface in step with rising sea levels. Moreover, sediment distribution/accumulation is further constrained where elevated portions of the basement topography provide little to no accommodation, and act as zones of sediment bypass, and adjacent basement depressions accommodate sediment to seaward. The gentle antecedent slope, coupled with the gentle shoreline trajectory mediated transgressive erosion directly to landward. This is reinforced where local inflections in the wave ravinement profile form due to the presence of palaeo-shoreline complexes, aiding in the ultimate preservation of these submerged delta facets in the palaeo-shoreline lee. This study shows that low antecedent gradients, and palaeo-shoreline features, lead to development of transgressive coastal profiles that are predisposed to delta overstepping. The pre-existing basement topography and palaeo-shorelines constrain the positioning and morphology of the delta. We suggest that antecedent conditioning has partitioned accommodation for delta accumulation and moderated wave ravinement associated with transgression since the Last Glacial Maximum (LGM). The geological framework has acted as a recurring primary control on the geomorphic evolution of the submarine delta and shelf. • Seismic stratigraphy of the Thukela continental shelf • Reveal several submerged deltaic depocenters and shorelines • Show bedrock highs control depocenter positioning and preservation • Delta morphology and stratigraphy influenced by palaeo-shorelines • Palaeo-shorelines restrict ability for shoreface to migrate with rising sea level [ABSTRACT FROM AUTHOR]

A set of 2D high resolution seismic lines was acquired near the Kerch Peninsula during R/V Meteor Cruise M72/3 in March/April 2007 to the Eastern Black Sea. The high resolution seismic data were used for analysis of seismic facies and seismic sequences to gain insight into the sedimentary evolution of the study area. Seven seismic facies types were identified and six seismic units could be mapped. Based on seismic line interpretation, isopach and seismic facies distribution maps, a chronostratigraphic framework could be established for the study area. The study reveals that the sediment deposits were influenced by syndepositional tectonic movements, sea level and climate. During the late Miocene and the early Pliocene, possible slope fan deposits developed. At the boundary between the Miocene and Pliocene, the Messinian erosional truncation surface was observed. After the Messinian sea level fall, accompanied by a major transgressional phase during the Pliocene, the Paleo-Don and Kuban Rivers delivered a large terrigenous input to the Black Sea from the uplifted Crimean Mountains. This formed thick submarine fan deposits near the mouth of Kerch Strait during the late Pliocene. Facies variations within the seismic units are related to the sea-level and climate curves, and are reflected by grain size variations in the sediments and the shift of the river mouth. During the Quaternary, hemipelagic sediments interbedded with coarse-grained fluvial sediments developed in the study area, along with slumps, river channels and fan deposits. • A seismostratigraphic framework was established for late Miocene to Recent times in the Kerch seep area. • Lithological-Paleogeographic maps around Kerch seep area are created. • Sedimentary environment evolution process of the area around the Kerch seep is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Turbidity currents, and other types of underwater sediment density flow, are arguably the most important flow process for moving sediment across our planet. Direct monitoring provides the most reliable information on the varied ways in which these flows are triggered, and thus forms the basis for this contribution. Recent advances in flow monitoring make this contribution timely, although monitoring is biased towards more frequent flow types. Submarine deltas fed by bedload dominated rivers can be very active with tens of events each year. Larger events are generated by delta-lip failures, whilst smaller events can be associated with motion of up-slope migrating bedforms. River-fed submarine canyons are flushed every few years by powerful long run-out flows. Flows in river-fed delta and canyon systems tend to occur during months of elevated river discharge. However, many flows do not coincide with flood peaks, or occur where rivers do not reach hyperpycnal concentrations, and are most likely triggered by failure of rapidly deposited sediment. Plunging of hyperpycnal river floodwater commonly triggers dilute and slow moving flows in lakes and reservoirs, and has been shown to produce mm-thick fine-grained deposits. It is proposed here that such thin and fine deposits are typical of flows triggered by hyperpycnal river floods, rather than thicker sand layers with traction structure or displaying inverse-to-normal grading. Oceanographic canyons are detached from river mouths and fed by oceanographic processes (wave and tide resuspension, longshore drift, etc.). Most events in these canyons are associated with large wave heights. Up-slope migrating crescentic bedforms are seen, similar to those observed in river-fed deltas. Oceanographic processes tend to infill canyons, which are flushed episodically by much more powerful flows, inferred to result from slope failure. This filling and flushing model is less applicable to river-fed canyons in which flushing events are much more frequent. Oceanographic canyons may result from rapid sea level rise that detaches river mouths from canyon heads, and they can remain active during sea level highstands. Deep-water basin plains are often dominated by infrequent but very large flows triggered by failure of the continental slope. Recurrence intervals of these flows appear almost random, and only weakly (if at all) correlated with sea level change. Turbidites can potentially provide a valuable long-term record of major earthquakes, but widespread slope failure is the only reliable criteria for inferring seismic triggering. However, not all major earthquakes trigger widespread slope failure, so that the record is incomplete in some locations. [Copyright &y& Elsevier]

Abstract: Drilling for gas hydrates at the northern continental margin of the South China Sea (SCS) provides a unique insight into the formation of the gas hydrate system in fine-grained sediments, even though most high concentrations of hydrates are found in coarse sediments. Detailed studies of 3D seismic data from a deepwater basin (Baiyun Depression) of this region reveal the presence of overpressured fluid flow, mostly manifested in gas chimneys. Gas chimneys are commonly characterized by disrupted reflections (DR), dim amplitude anomalies (DA), and enhanced reflections (ER) on conventional seismic profiles. Gas chimneys are also characterized by chaotic, low-continuity and low-frequency on instantaneous frequency and instantaneous amplitude profiles. Gas hydrates and a prominent BSR were discovered in the region of gas chimney occurrence. Logging data and sample analyses from drill holes over the chimney structures indicate close relationships between active fluid flow and the formation and accumulation of gas hydrates. Our results document that gas chimneys consisting of a connected network of fractures provide a passageway along which fluids ascend beneath the gas hydrate stability zone (GHSZ) for hydrate formation in fine-grained sediments of the northern South China Sea. Fluids accumulate in uppermost part of the slope where they are trapped beneath the prograding submarine delta sequence, which is not permeable enough for fluids to migrate through. Gas-charged fluids may originate from deep-seated hydrocarbon reservoirs, which are indicated by the molecular and isotopic signatures of gases in gas hydrates occurrence zone. We suppose that the fractures extend into the GHSZ, creating a space for hydrate condensation in the fine-grained sediments of the slope. Gas chimneys may account for the overpressured fluid activity and, most likely, the gas hydrate enrichment in the northern SCS. [Copyright &y& Elsevier]

Abstract: A large number of pockmarks have been identified in the Rosetta Region of the Western Nile Deep Sea Fan. Co-located high resolution 2D and Chirp datasets have been used to identify seabed and buried pockmarks which are interpreted to span the Holocene to Pleistocene period. The pockmarks range in size and stratigraphic position from large buried pockmarks to small unit seabed pockmarks. Clusters of small unit pockmarks are stratigraphically positioned above the centre of large buried Pleistocene pockmarks and are used to infer: 1) rejuvenation of the larger pockmark conduit once burial has occurred, and 2) a change in the frequency and magnitude of pockmark formation events. [Copyright &y& Elsevier]

Abstract: Fluid escape structures on the Nile Deep Sea Fan were investigated during the MEDIFLUX MIMES expedition in 2004. Mud volcanoes, pockmarks and authigenic carbonate structures were surveyed for the first time with a high-resolution deep-towed 75kHz sidescan sonar and a 2–8kHz Chirp sediment echosounder. In combination with existing multibeam bathymetry and detailed seafloor in situ geological observations, these new data allowed detailed seep analyses. About 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data at water depths from 770 to 1700m. These gas flares coincide at the seabed with 1) the centres of the mud volcanoes where mud is also extruded, 2) the borders of the mud volcanoes where the emitted gases contribute to the precipitation of authigenic carbonates, and 3) to the edges of broad sheets of authigenic carbonates. Subsurface sediments are commonly disturbed by ascending fluids throughout the delta, with an abundance of seep-related carbonate structures on the seafloor. The feeder channels below mud volcanoes, similar to the gas conduits below the widespread carbonate crust structures and pockmarks, are relatively narrow and, for the vast majority of them, do not exceed a few metres in diameter. The seeps on the Nile Deep Sea Fan clearly follow lineations on the seafloor that we can relate to faults. [ABSTRACT FROM AUTHOR]

Abstract: An approach combining interpretation of seismic reflection data with analysis of core lithology, especially analysis of the depositional ages of turbidites, showed that depositional patterns in the deep-sea basin of the eastern Kumano Trough, which is a forearc basin along an active convergent plate margin, were different during sea-level lowstand, slow transgressive, rapid transgressive, and highstand stages. During the lowstand and early transgressive stages, turbidites were deposited on the deep-sea basin floor where they formed a submarine fan composed of terrigenous sediments supplied by rivers via a submarine canyon. Subsequent coastline retreat and bay development during the rapid transgression stage caused a decrease in the amount of coarse-grained terrigenous sediments reaching the basin floor. However, turbidites were still deposited within the submarine canyon during the rapid transgressive and highstand stages. These deposits contain shelf sediments that have been reworked by tidal currents and storms, and sediments from slope failures caused by submarine earthquakes, but they do not contain the terrigenous sediments that are characteristic of the turbidites of the lowstand and slow transgression stages. [Copyright &y& Elsevier]

Abstract: Different types of seep carbonates were recovered from the ‘Kouilou pockmarks’ on the Congo deep-sea fan in approximately 3100m water depth. The carbonate aggregates are represented by pyritiferous nodules, crusts and slabs, tubes, and filled molds. The latter are interpreted to represent casts of former burrows of bivalves and holothurians. The nodules consisting of high-Mg-calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs. Nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic ANME-1 group, whereas aragonitic crusts resulted from the activity of archaea of the ANME-2 cluster. Evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates, showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules. Formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts, probably reflecting higher porosities of the host sediment during carbonate formation. This finding is supported by lower δ 18O values of crusts, agreeing with precipitation from pore waters similar in composition to seawater. The aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate-rich pore waters similar to seawater. Moreover, the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that ANME-1 archaea tend to occur deeper in the sediment than members of the ANME-2 group. Methane represents the predominant carbon source of all carbonates (δ 13C values as low as −58.9‰ V-PDB) and the encrusted archaeal biomarkers (δ 13C values as low as −140‰ V-PDB). Oxygen isotope values of some nodular carbonates, ranging from +3.9 to +5.1‰ V-PDB, are too high for precipitation in equilibrium with seawater, probably reflecting the destabilization of gas hydrates, which are particularly abundant at the Kouilou pockmarks. [Copyright &y& Elsevier]

Abstract: Deep-water sedimentation is currently a major focus of both academic research and industrial interest. Recent studies have emphasized the fundamental influence of seafloor topography on the growth and morphology of deep-sea fans. In topographically complex slopes, the development of turbidite systems is strongly controlled by pre-existing bounding slopes. The aim of this work is to study the effect of basin confinement on the Caprera deep-sea fan (CDF), the main turbidite system of the Olbia intraslope basin (OIB) located in the eastern Sardinian margin (Central Tyrrhenian Sea). The OIB is the northernmost intraslope basin of the margin, bound seaward by the Etruschi and Baronie seamounts, and landward by the Sardinian continental slope. The OIB is completely filled and sediments can spill toward the lower Tavolara basin (TB) through a system of bypass canyons located in a saddle between the two seamounts. The CDF has been imaged by high-resolution swath-bathymetric dataset acquired by the ISMAR of Bologna during the cruises TIR96 and TIR99. The multibeam data have been integrated with seismic lines in order to understand the shape, the morphology and internal organization of the CDF. The CDF faces a wide shelf sector and as a consequence canyons are presumably stranded from river supply during high stands of sea level. At the base of slope the CDF consists of a wide leveed channel. The increasing channel flank relief moving downfan, the presence of knickpoints, erosional remnants, chutes scouring the levees and erosional terraces show that the Caprera channel, at the present day, is out of grade. In addition, erosional processes also act beyond the channel mouth, where distal erosional channels are present, and in the basin plain, that is scoured by a broad shallow valley. The bypass of sediments, from the completely filled OIB to the lower TB, has promoted the lowering of the ultimate base level for sediment gravity flows which is considered the cause of the disruption of the equilibrium profile of the CDF. However, the seismic data show that, in the CDF phases of deposition also alternate with the mainly erosional ones. These are interpreted to reflect the variability in flow volume during different sea level stands. The depositional style of the CDF does not conform to simple deep-sea fan models, and emphasizes that seafloor topography is a prime control on turbidite system development also in tectonically inactive margins. [Copyright &y& Elsevier]

Abstract: Continental margins in regions influenced by temperate ice sheets experience climate-dependent changes in sedimentary processes. A new stratigraphy is presented for Ocean Drilling Program Hole 888B, from the Nitinat Fan, on the Vancouver Margin, in which we examine the relationship between fluctuations in glacial-sourced sediment delivered to the continental shelf and turbidite character and frequency. Glacial/interglacial episodes are determined based on: (1) core lithology, where sandy/coarse-grained sediment and fine-grained clay/silty clay represents glacial and interglacial intervals, respectively; (2) δ 18O of planktonic foraminifera G. bulloides, in which higher values indicate warmer sea surface temperatures and lower global ice volume; (3) magnetic susceptibility, in which higher values indicate coarser grain sizes deposited during glacials; and (4) ratios of sinistral N. pachyderma to dextral N. incompta, in which higher proportions of N. pachyderma are a sign of cooler sea surface temperatures. Finally, using radiocarbon 14C dates, specific Marine Isotope Stages (MIS) within the top 240 m of core are assigned: MIS 2–4 (2–118 mbsf), MIS 5 (118–157 mbsf), and MIS 6 (213–240 mbsf). Using this chronology, sedimentation rates for the Nitinat Fan were greater (187 cm/kyr) during glacial MIS 2–4 than interglacial MIS 5 (69 cm/kyr). Additionally, during glacial MIS 2–4 thicker turbidites (upwards of ~150 cm) were deposited relatively frequently (~75 year periodicity) compared with those from MIS 5, which are relatively thin (up to 27 cm) and deposited more rarely (~130 year periodicity). These results indicate that turbidite frequency and thickness are linked to climate through ice sheet extent, since transport of glacimarine sediment to the continental slope promotes turbidity currents that are responsible for the most significant amount of offshore sedimentation. This study shows that geological processes influencing turbidite deposition can fluctuate over time and may not necessarily be represented by ongoing processes within the modern depositional setting. [Copyright &y& Elsevier]

Abstract: This paper reports the first “in situ” seafloor observations of fluid escape structures in a fault-controlled caldera-type depression of about 8 km diameter, named the Menes caldera, in the Eastern Mediterranean sea off Egypt (western province of the Nile Deep Sea Fan). A detailed analysis of seven Nautile dives, performed during the Nautinil cruise in 2003, focused on determining the nature, origin, importance, mechanisms and environmental impacts of the fluid escape processes from the geological observations. Seafloor maps, constructed from direct visual observations and video records made from the submersible, and sampling results, for three mud volcanoes of the caldera, Cheops, Chephren and Mykerinos show differences in activity but many common characteristics. The three volcanoes show a crater-like depression. The study reveals a strong contrast between Mykerinos, where no seepage activity was found, and the craters of Cheops and Chephren, where an intense activity of brine seepage was discovered. On Cheops, a dome of dark grey mud raises slightly above the brine surface in the central part of the brine lake, and shows numerous circular vents of 1–2 m diameter that become gradually colonized by microbial mats. Chephren hosts a deep (>200 m) and warm (45 °C) brine lake. Alternations of areas void of or covered with microbial mats at the surface of the Chephren brine lake indicate large surface disturbances that may result from the occurrence of several active vents at the bottom of the lake. A special feature at Chephren is a brine overflow at the western edge of the crater, also indicative of the very high activity of brine seepage. The Nautinil observations indicate that the Menes caldera in the Eastern Mediterranean is a highly active site of brine seepage. Growth faults rooted in pre-Messinian sediment layers provide pathways for warm fluids to escape pressurized source levels below the Messinian salt. [Copyright &y& Elsevier]

Abstract: We investigated lipid biomarkers in three depth-intervals of a methane-derived carbonate crust collected from a pockmark in the Nile Deep-Sea fan sampled during the Nautinil cruise of the R/V l''Atalante. A diverse set of 13C-depleted archaeal and bacterial lipids were detected along this crust with δ 13C values as low as −118‰. This provides evidence that anaerobic oxidation of methane was the main process that induced the formation of this carbonate crust. Archaeal lipid biomarker distributions revealed the presence of archaea belonging both to the ANME-1 and ANME-2 phylogenetic clusters, with the former predominating. The distribution and compound specific δ 13C values of AOM-derived lipid biomarkers showed no significant variations with depth. These results infer that the archaeal community structure and thus the local seepage environment remained relatively stable during the 5000 kyr period of the carbonate crust precipitation. [Copyright &y& Elsevier]

Abstract: We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼1 km2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of ‘fossil’ carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope. [Copyright &y& Elsevier]

Abstract: The Zambezi deep-sea fan, the largest of its kind along the east African continental margin, is poorly studied to date, despite its potential to record marine and terrestrial climate signals in the southwest Indian Ocean. Therefore, gravity core GeoB 9309-1, retrieved from 1219 m water depth, was investigated for various geophysical (magnetic susceptibility, porosity, colour reflectance) and geochemical (pore water and sediment geochemistry, Fe and P speciation) properties. Onboard and onshore data documented a sulphate/methane transition (SMT) zone at ~450–530 cm sediment depth, where the simultaneous consumption of pore water sulphate and methane liberates hydrogen sulphide and bi-carbonate into the pore space. This leads to characteristic changes in the sediment and pore water chemistry, as the reduction of primary Fe (oxyhydr)oxides, the precipitation of Fe sulphides, and the mobilization of Fe (oxyhydr)oxide-bound P. These chemical processes also lead to a marked decrease in magnetic susceptibility. Below the SMT, we find a reduction of porosity, possibly due to pore space cementation by authigenic minerals. Formation of the observed geochemical, magnetic and mineralogical patterns requires a fixation of the SMT at this distinct sediment depth for a considerable time—which we calculated to be ~10000 years assuming steady-state conditions—following a period of rapid upward migration towards this interval. We postulate that the worldwide sea-level rise at the last glacial/interglacial transition (~10000 years B.P.) most probably caused the fixation of the SMT at its present position, through drastically reduced sediment delivery to the deep-sea fan. In addition, we report an internal redistribution of P occurring around the SMT, closely linked to the (de)coupling of sedimentary Fe and P, and leaving a characteristic pattern in the solid P record. By phosphate re-adsorption onto Fe (oxyhydr)oxides above, and formation of authigenic P minerals (e.g. vivianite) below the SMT, deep-sea fan deposits may potentially act as long-term sinks for P. [Copyright &y& Elsevier]

Seismic reflection data from drifting ice stations and an icebreaker survey document the presence of a submarine fan along the east flank of the Lomonosov Ridge in the Amundsen Basin, Arctic Ocean. The fan extends from a source area at the North Greenland and Canadian Arctic continental margin to the North Pole. The fan probably developed in response to the combined effect of increased glacial sediment input during the Plio–Pleistocene and topographically confined transport of glacial debris in the deep sea passage between Lincoln Sea margin and the southern end of the Lomonosov Ridge. [Copyright &y& Elsevier]

Fast-flowing ice streams drain huge basins within modern ice sheets and are a mechanism for rapid iceberg production and mass loss. Some ice streams are known to be unstable, and to switch between fast flow and stagnation. Numerical ice-sheet models and geophysical observations of large-scale streamlined glacial landforms and large glacier-derived sedimentary fans along high-latitude continental margins indicate the presence of ice streams in Quaternary ice sheets. High-resolution AMS dated sedimentary records from an inter-fan area on the Svalbard continental margin yield evidence on the timing of initiation of fast glacier flow during a glacial cycle of ice-sheet growth and decay. Sedimentation rates and iceberg-rafted debris influx show that debris delivery to the Svalbard margin was relatively high during the period of Late Weichselian ice-sheet growth from about 30 000–18 000 yr BP. Both parameters fell dramatically in inter-fan areas when full-glacial conditions, with ice at the continental shelf edge, were established at about 18 000 yr BP. This shift is interpreted to mark the initiation of a fast-flowing ice stream, the convergence of flow from the surrounding ice sheet into this ice stream, and the consequent slowing of ice flow and sediment delivery to the inter-fan area beyond the ice-stream margins. This provides a constraint on the timing of ice-stream initiation during the cycle of ice-sheet growth and decay. [Copyright &y& Elsevier]

Convergent tectonics and glaciomarine sedimentary processes in the northern Gulf of Alaska have produced a variety of troughs, canyons, channels, gullies, and other drainage related features over a range of spatial scales. To evaluate the effects of glaciomarine and fault processes on observed drainage morphology we measured regional drainage feature cross-profile shape characteristics across the area. Our results show overlap between U-shaped feature cross-profile locations, ice sheet extents, and instability zones on the shallow shelf and slope that were previously inferred by observations of potential mass-movement structures such as slumps, slides, and debris flows. U-shaped profiles were also observed in areas of recent slope progradation such as the flank of the proximal deep-sea Surveyor Fan. We used principal component analysis (PCA) and geographically weighted regression (GWR) to relate drainage cross-profile morphology to proxy variables for ice sheets, faults, and instability zones. This method enables quantitative evaluation of the effects on cross-profile shape explainable by each variable as indicated by the magnitude, distribution, and variation of parameter coefficients both at the local and regional scale. Our multiple variable GWR model can explain most of the regional variability in cross-profile shape with the contribution of each parameter varying throughout the study area. Parameters associated with ice sheet extent have the strongest overall relationship with drainage shape, while the distance from an instability zone is the strongest local relationship. The fault proxy parameter shows relatively strong correlations with cross-profile shape near the Transition Fault, and the narrowest zone of morphologic influence overall. • U-shaped features often correspond with ice sheet extents or zones of instability. • Faults, ice sheets, and instability zones can mostly explain cross-profile shape. • Ice sheet extents had the overall strongest relationship with cross-profile shape. • More focused shape influence for fault zones, and a broader influence for ice sheets. [ABSTRACT FROM AUTHOR]

The relative impacts of autogenic and allogenic controls on the architectural evolution of deep-sea fans are not well constrained, mainly because of the difficulty in evaluating the role of each control on any specific stratigraphic pattern. This study presents four-dimensional (4D) forward stratigraphic modelling of the Late Quaternary Congo Axial Fan, which provides new insights on forcing factors of sedimentation over time. This modelling is based on a geological model describing successive sedimentary progradational/retrogradational cycles in the Congo turbidite system during the last 38 kyr. Analyses of geophysical and marine core data have suggested that the architectural cycles were controlled by changes in fluvial sediment discharge in relation to arid and humid periods in the Congo River watershed. The aims of this study were to simulate the architectural evolution of the Late Quaternary Congo Axial Fan from 210 ka to the present and investigate the factors controlling sedimentation using DionisosFlow™, a process-based stratigraphic forward modelling software. For this objective, several scenarios were tested to simulate the role of autogenic and climate forcings based on proxies recorded in marine sediments. The modelling results confirmed that climatic variations of sediment and water discharge succeeded in reproducing the timing, position, and sediment volume of basin-scale progradational/retrogradational cycles. The best-fit simulations particularly emphasise the role of continental vegetation cover expansion, governed by the precession-driven West African monsoon, on the sediment flux to the deep-marine environment. This vegetation/climate coupling acts directly on the transport capacity of flow over time by controlling the magnitude of river runoff and the timing of sediment production, storage, and transfer from the continent to the ocean. Thus, our results confirm the utility of stratigraphic forward models in constraining "source-to-sink" models for the architectural evolution of submarine fans. • First 4D stratigraphic forward modelling of the Quaternary Congo Fan (DionisosFlow™). • Test of autogenic and climate forcings using continental and marine proxies. • Relative impact of sediment/water discharge and sand fraction on turbidite geometry. • Role of climate-vegetation coupling on the sediment transfer from land to turbidites. [ABSTRACT FROM AUTHOR]

The present work simulated a hypothetical 4D delta-canyon-fan depositional system using stratigraphic forward modelling (SFM) to: 1) investigate the differences and linkages of the sea-level control on the evolution of each sub-environment; 2) explain the evolution under the constraints of sea-level change from the perspective of channel activities. The SFM approach LECODE applied in this study combines an open-channel flow approach with a non-uniform sediment transport algorithm, with former to simulate water dynamics of turbidity currents and river flows and latter to simulate the transportation, deposition, and erosion of sediments. The input data is calibrated via sensitivity analysis and survey of analogue records. The results are compared with three sets of actual seismic data as verification. After introducing the general characteristics of the model, this study compares the influence of sea-level change on the delta, canyon, and fan, respectively, by analysing stratigraphic framework, the architecture of channel-levee complex, channel distribution and migration, sedimentation/erosion rate, and peak velocity. Moreover, a higher sediment supply case and a lower sediment supply case are compared to test the situation when sediment supply is less dominant. Finally, the influence of sea-level change on channel migration is discussed and the system evolution, especially the canyon evolution, is explained from the view of channel activities. The results show that sea-level control will be weakened from the delta to the fan via the canyon along with sediment transport. With higher sediment supply, the weakening is stronger. With lower sediment supply, the whole system is more sensitive to the sea-level change and this sensitivity lasts longer. The channel migration is more influenced by local topography, even adjacent topography, rather than sea-level change. The inner bank erosion near the canyon head is directly related to the shelf morphology. The translation and asymmetrical distribution of turbidity channels result in the translation and asymmetrical erosion of canyon bends. The insights extracted from this study could discriminate sea-level control on submarine canyon and fan instead of regarding them as an entirety of ultimate sink in source-to-sink research. Also, the integrated investigation with both qualified perspectives and quantified data could refine sequence stratigraphic concepts and provide a prototype for hydrocarbon exploration on high-sediment-supply river-fed delta-canyon-fan systems. • A delta-canyon-fan model using process-based stratigraphic forward approach. • Control of sea-level change weakens from canyon to fan. • High sediment supply strengthens the weakening effect of sea-level change control. • Local bathymetry dominate channel migration rather than sea-level change. • Evolution curves of deposition and current velocity against sea-level change. [ABSTRACT FROM AUTHOR]

The continental slope and rise seaward of the Totten Glacier and the Sabrina Coast, East Antarctica features continental margin depositional systems with high sediment input and consistent along-slope current activity. Understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain. Geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad-scale topography and oceanography. The study area contains two areas with distinct geomorphology. Canyons in the eastern part of the area have concave thalwegs, are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles. Ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment. They can be thought of as giant levee deposits. The ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east. The major canyon in the western part of the area is unusual in having a convex thalweg; it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge. The western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the Totten Glacier. This contrasts with interpretations of similar ridges described from other parts of Antarctica which emphasise sediment input from canyons immediately up-current. The overall geomorphology of the Sabrina Coast slope is part of a continuum of mixed contourite-turbidite systems identified on glaciated margins. • The slope and rise off the Totten Glacier feature sediment ridges between submarine canyons. • Sediment ridges in the east are formed from turbidity currents flowing in adjacent canyons and a pelagic component. • In the west, larger ridges are formed from widespread hemipelagic and contouritic sedimentation. • The western ridges are separated by a submarine canyon with a convex thalweg mostly sourced from the ridge flanks. [ABSTRACT FROM AUTHOR]

Based upon new seismic reflection data, this study reveals the development of a complex sedimentary system on the lower-slope terrace off Maputo on the southern Mozambique margin. The deep-water sedimentary system clearly shows the interaction of downslope and alongslope processes. Downslope features include: a pronounced canyon, slope creep, submarine slides, and multi-stage mass-transport deposits. Alongslope features include: contourite drifts and sediment waves, erosional moats, valleys, erosive surfaces and a distinctive contourite terrace. We show an evolution through time as follows: (1) restricted marine sedimentation during the Early Cretaceous after the initial break-up, with slope progradational clinoforms and hemipelagite drape developed; (2) open marine sedimentation characterized by the onset of alongslope sedimentary processes during the Late Cretaceous and development of a contourite depositional system; (3) downslope gravity processes dominated sedimentation during the Paleocene-Eocene, including development of a canyon and submarine fan; and (4) an alongslope contourite depositional system was re-established on the lower slope in the Middle Miocene, while turbidites (from a northern source) covered the Mozambique Basin. The Mozambique Fracture Zone marks a distinct and steep slope seaward of the contourite terrace, and has significantly influenced both contourite and turbidite deposition. Our study provides new insights into the onset and evolution of bottom current control on margin sedimentation, the interaction of downslope and alongslope processes and how these processes have jointly sculpted this part of the southern Mozambique margin. • Depositional features of a complex deep-water sedimentary system are investigated. • Late Cretaceous onset of current-controlled deposition. • Downslope-alongslope interaction in constructing the continental margin. • The Mozambique Fracture Zone significantly influenced contourite and turbidite deposition. [ABSTRACT FROM AUTHOR]

Submarine canyons are the principal conduit for turbidity currents transporting sediment to the deep sea. This study examines the interplay between ice-margin conditions and the style of turbidity currents during deglaciation from 19 to 11 ka. We investigated 7 cores from Halibut Canyon, located seaward of a small ice stream draining the Newfoundland Ice Dome. Cores were X-radiographed for sedimentary structures, sediment provenance was assessed from X-ray fluorescence geochemistry, and age was determined by AMS C-14 dating. High resolution seismic profiles and cores show three phases of canyon evolution: (1) Canyon erosion by plunging hyperpycnal meltwater from shelf-edge ice at maximum ice extent. (2) During deglaciation, active deposition of an inner levee by turbidity currents, adjacent to an erosional talweg system, recorded in cores from the Younger Dryas (12 ka) to before H1 (16.5 ka). (3) Passive canyon fill during the Holocene by the alongslope Labrador Current, with only minor down-canyon sediment supply. In the active canyon depositional phase, turbidity currents were of variable size, reaching thicknesses >390 m at 40 km down canyon. Numbers of sand beds and mean grain size decrease down canyon, which is inferred to result from rapid entrainment of ambient seawater on the steep gradient and a downflow thinning of the lower part of the current with fine sand in suspension. Silt becomes increasingly segregated from muds downcanyon as a result of floc break-up and re-formation. The processes inferred from Halibut Canyon are representative of other canyons on formerly glaciated margins. • 3 ice-margin canyon evolution phases: erosion, active deposition, passive deposition • Core record from before H1 (16.5 ka) through Younger Dryas (12 ka) to Holocene • Sediment sources tracked by X-ray fluorescence; Holocene from Labrador Current • Currents form by plume fallout from meltwater flowing from ice margin on the shelf • Flows accelerate, entrain water, and thicken, but the sandy base thins down-canyon [ABSTRACT FROM AUTHOR]

Over the past ten years, a huge amount of source-to-sink studies have aimed to unravel the tectonic, climatic and other processes that shape the landscape from mountains to the deep ocean. Interestingly, these studies have been mainly dedicated to siliciclastic or mixed systems, for which the connection between drainage basins, continental shelves, slope and basin environments are often well constrained. Here we present a study focusing on a source-to-sink study dedicated to a pure carbonate system, located in the SW Indian Ocean (Glorieuses archipelago). Extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition, the lateral variability, and volumes of neritic sands deposited on the platform top. Additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge, corresponding to the export of carbonate sediments from the platform top toward the platform edge, under the influence of dominant currents and wind-driven processes. High-resolution seismic, bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel-levee complexes and turbiditic lobes, which have accumulated on the seafloor on top of a 250 m-thick sedimentary basin at 2000–3400 m water depth. Our study points out that carbonate sands and aragonitic mud produced on the platform top during the Holocene have been shed to the adjacent basin. We also demonstrate that this routing system was active at least throughout the last three glacial/interglacial cycles. This study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms: 1 - it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin; 2 - it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity; 3 - a first estimate of a carbonate source-to-sink system is proposed, demonstrating that 0,57 km3 of sediments have been produced during the Holocene, 0,3 km3 being presently stored on the platform, and the remaining having been exported to the deep basin. • First study to propose a carbonate source-to-sink budget, from platform top to adjacent basin. • Neritic sands produced on platform top are mainly stored along the leeward platform edge. • Carbonate sediments are exported in the basin through channel-levee complexes. • This carbonate routine systems was active during past glacial/interglacial cycles. [ABSTRACT FROM AUTHOR]

The Capbreton submarine canyon is a striking feature of the south-east of the Bay of Biscay. This canyon forms a deep incision through the continental shelf and slope, and displays remarkable structures linked to its present-day hydrosedimentary activity. Its head has been disconnected from the Adour River since 1310 CE, but remains close enough to the coast to be supplied with sediment by longshore drift. Gravity processes in the canyon body are abundantly described and documented, but activity in the head and the fan of the canyon is poorly constrained. Furthermore, many questions remain regarding the details of processes affecting the head, the body and the fan of the Capbreton canyon. In this work, we address the paucity of documentation concerning (1) the temporal evolution of sediment transfer between the head and the deep reaches of the canyon, and (2) the interaction between gravity processes and the morphology of the canyon floor, including both shaping and feedback mechanisms. This study is based on the analysis and comparison of eight multibeam bathymetric surveys acquired in the upper part of the Capbreton canyon between 1998 and 2018, in depths ranging 10–320 m below sea level. This rare time series exposes the morphological evolution of this outstanding dynamic area over the last 20 years. Our work shows that much of the changes are located in the canyon floor and head. Following a period characterized by a unique flat floor thalweg, the canyon was affected by an incision with low lateral terraces which resulted in a narrow axial thalweg. The deepening of the narrow thalweg was induced by retrogressive erosion according to the presence of upstream-migrating knickpoints, while low elevation residual terraces formed as the canyon reached a local equilibrium profile. The flat thalweg observed in 1998 is likely a result of a partial filling of the canyon thalweg by a substantial emptying of the canyon head and significant mass transfer to the proximal part of the canyon. A flat floor thalweg was not observed again in the remaining of our time series (since 2010), suggesting a possible quieter working mode of the canyon. We also propose the first accurate volume quantification of sediment displacement on the canyon floor. Our findings underline the alternation of filling and erosive periods in the canyon axis and an unexpected continuous sediment deposition in the canyon head during the last 20 years. • Rare time series allows the morphologic follow-up of an active canyon. • 20-years comparison underlines alternating filling and erosive periods. • Erosion processes are highlighted by fast upstream-migrating knickpoints. [ABSTRACT FROM AUTHOR]

We use >10,000 km of high-resolution seismic-reflection data together with multibeam bathymetry to document complex and highly variable post-Last Glacial Maximum (LGM) sediment distribution and thickness in the coastal zone (~10 m isobath to 5.6 km offshore) along a ~800 km section of central California's transform continental margin. Sediment thickness ranges from 0 (seafloor bedrock) to 64 m with a mean of 8.7 m. We delineate 25 coastal zone "sediment domains," and group them based on common geomorphology and sediment occurrence. Thickest sediment occurs in "mountain front" and "large river" domains, which comprise 14.5% and 7.9% of the coastal zone and contain 30.1% and 18.2% of coastal zone sediment, respectively. In contrast, "small river" domains and "sediment-poor shelf" domains comprise 50.7% and 15.7% of the coastal zone and contain 18.4% and 12.7% of its sediment. The distribution and thickness of post-LGM sediment in the coastal zone is controlled by a combination of tectonics, sediment supply, and eustasy. Sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts, more slowly uplifting marine terraces, and fault-bounded headlands and alluvial-estuarine troughs. Sediment supply is maximized along steep, landslide-prone, mountain fronts and at the mouths of large watersheds, and minimized along lower-relief, terraced coastal landscape drained by smaller rivers and creeks. In the offshore coastal zone, tectonics generates local uplifts and basins, and influences shelf width and gradient as well as the locations of some shelf-incised submarine canyons. Sea-level rise raises base level, drowns estuaries, creates accommodation space on the shelf (amount based on gradient), and isolates the heads of many submarine canyons at or near the shelfbreak. Comparison of shelf sediment volumes with estimates of "unaltered" watershed sediment supply reveals that a relatively small proportion of post-LGM sediment supply is preserved on the shelf offshore of some of the largest rivers. Sediments deposited in shoreline and shelf environments have limited preservation potential, and the most complete long-term geologic record of the post-LGM transgression and highstand is likely represented in slope and submarine fan deposits. • We document sediment distribution along ~800 km of California's transform margin. • Thickest sediment occurs offshore of large rivers and steep mountain fronts. • More than half of coastal zone is "sediment-poor" shelf. • Sediment distribution controlled by mix of tectonics, sediment supply, and eustasy. [ABSTRACT FROM AUTHOR]

Linosa Island represents the emergent tip of a mostly submarine, much wider volcanic edifice, with at least 96% of its areal extent lying below sea level. Marine geological surveys carried out in 2016 and 2017 allowed to reconstruct the submarine portions of Linosa and to characterize the main volcanic features, providing new, unexpected insights on the evolution of this little-explored volcanic complex. In particular, the submarine setting of the NW offshore is represented by a ~10-km long volcanic belt punctuated by a number of small eruptive cones, appearing more recent with respect to the assumed Mid/Late-Quaternary age of volcanism on the island. This evidence suggests that the growth of the volcanic edifice has likely been more complex than that claimed on the base of subaerial volcanism only, and supports a north-westward migration of the activity over time. The submarine southern flank of the volcanic edifice is also characterized by eccentric eruptive cones, but mostly without evidences of recent activity. The main processes responsible for the growth and evolution of Linosa volcano and their possible relative chronology are discussed in the framework of what previously known on the base of the limited subaerial portions, with implications on the potential hazard of the volcanic edifice (considered as not-active in recent times). Similarity with the Pantelleria volcano, located in the NW Sicily Channel, are also evidenced, especially for what regards the distribution and morphometric characteristics of eruptive cones occurring in the submarine portions of both islands. • The new bathymetry of Linosa allows updating the knowledge on this volcanic edifice. • Its growth appears to be more complex than claimed on the base of subaerial volcanism only. • The regional, NW-SE directed structural control is evident in the submarine setting. • Similarities with the submarine portions of Pantelleria Island have been evidenced. • The submarine evidences of volcanic activity have implications on the potential hazard evaluation. [ABSTRACT FROM AUTHOR]

The Mar del Plata (MdP) Canyon at the Argentine continental margin is incorporated into a major contourite depositional system, built by the incursion of southern-sourced water masses affecting the seafloor at different waters depths. The new sedimentological, morphological and hydro acoustic data provide novel insights into contour and turbidity current interactions in mid-slope (blind) canyons, which do not have a connection to the shelf or an onshore river system. Such canyons are capable to record climate-related ocean stratification changes, current variability, and slope stability. Three sediment cores were obtained along the MdP Canyon thalweg covering the last 20,000 years and compiled with two cores from the adjacent Ewing Terrace. Turbidity-current activity within the MdP Canyon was limited to the time interval from Last Glacial Maximum (LGM) to the late deglacial. During the LGM and early deglacial, turbidites reached both the proximal sector and the distal northern flank of the canyon. During the late deglacial only the proximal sector was characterized by turbidite deposition. Similarities in mineralogy and grain-size data indicate that the material transported by the turbidity currents originated from the mid-slope Ewing Terrace. Glacial turbidity-current activity was most probably favored by increased sediment supply along the Ewing Terrace from a shallowed and/or enhanced glacial Antarctic Intermediate Water (AAIW) nepheloid layer. These sediments were trapped by the MdP Canyon, in particular at the head area. During the late deglacial, a displacement or limited AAIW nepheloid layer resulted in less sediment transfer along the Ewing Terrace and immediate accumulation in the MdP Canyon head restricting turbidite deposition to the proximal sector of the canyon. In general, contourite-turbidite interactions provide valuable information on variations in thermohaline circulation such as AAIW distribution and current strength. • Thermohaline circulation induced turbidity-current activity. • Contour and turbidity current interaction restricted to late last glacial period. • Intermediate nepheloid layer sediment supply induces sediment instabilities. • Transformation of sediment flows into low-density turbidity currents. [ABSTRACT FROM AUTHOR]

Located on the northwestern margin of the South China Sea, the origin of asymmetrical shelf-slope clinoforms accumulated on the continental margin of the Qiongdongnan Basin since the late Miocene is ambiguous and it likely is the first case of oblique sediment transport and dispersal among the most studied mud-rich shelves of the world during Neogene to Recent sea-level changes. We calculate the paleo-sediment flux required to build the shelf-slope clinoforms based on 2-D seismic data, and the results are 3 to 17 time larger than the estimated paleo-sediment discharge from the proximal catchment area of Hainan Island. This large mismatch suggests that sediments on the shelf-edge of Qiongdongnan Basin were not only from Hainan Island but more likely from a larger drainage system. The strong (tens km) southward migration of the western portion of the Qiongdongnan shelf-edge break compared to the weak (1–2 km) shelf-edge progradation in the eastern portion, suggests that the Qiongdongnan shelf prism is highly asymmetric and is caused by a large sediment supply centered to the west, with most likely the Red River (Song Hong) as the sediment supply driver. The fine-grained lithology of the studied shelf margin sediments off Hainan Island, especially since the end Miocene, suggests that they were derived mainly from the Red River and were transported southeastward from the Gulf of Tonkin by shelf currents. We propose a model for asymmetric shelf-slope accretion of mud-rich shelves in which a significant part of the sediment-prism volume was obliquely dispersed across the subsiding shelf as fluid mud during highstand sea-levels. The model presented here describes oblique construction of shelf-slope clinoforms in a mud-rich system in response to variations in sediment dispersal and depocenter during multiple sea-level cycles. This model of long-term (~107 years), lateral asymmetric accretion contrasts with oblique sediment transport in other source-to-sink sedimentary systems around the world. • Sediments on the shelf edge of QDNB are higher than that coming off Hainan Island. • Red River derived sediments are obliquely transported to QDNB by shelfal currents. • More sediments delivered to western QDNB making asymmetric shelf-slope accretion. [ABSTRACT FROM AUTHOR]

The stratigraphy of the Tagus river ebb-tidal delta off Lisbon (Portugal) is investigated using high resolution multichannel seismic reflection profiles with the purpose of searching for sedimentary or erosive features associated with landslides. The Tagus delta is sub-divided in two prograding seismic units of 17 ky to 13 ky and 13 ky to Present based on the calibration of seismic lines using gravity and box-cores in the Tagus pro-delta. We report the existence of a buried landslide with 11 km of length, 3.5 km of width and a maximum thickness of 20 m that accounted for the collapse of half of the upper unit of the Tagus river delta front in Holocene times. The non-collapsed half of the delta front contains extensive shallow gas of still unknown origin and nature. An estimated age of ~8 ky BP for the Tagus delta landslide is proposed based on stratigraphic correlation. The trigger mechanisms of the newly identified Tagus landslide are discussed as well as of the several landslides also found in the lower delta unit. These findings present a first step towards a future assessment of the susceptibility of the nearby coastal areas and the off-shore infrastructures to hazards related to such large collapses. • Imaging a 8 kyear, 10km x 4 km, 20 m thick buried landslide in the Tagus River submarine delta, off Lisbon, Portugal • Widespread occurrence of gas in sediments of the Tagus River ebb-delta front, offshore Lisbon city, Portugal • Seismic stratigraphy of Late Pleistocene-Holocene, 17ky to present Tagus River ebb-delta and shelf. • The ~20 km Tagus delta front comprehends two non-overlapping areas of shallow gas and landslide. • What triggered the Tagus delta landslide: earthquake? Over pressured gas in sediments? Environmental conditions? Seismicity? [ABSTRACT FROM AUTHOR]

The seafloor of the Bay of Bengal is covered by thick sediment deposits that constitute the largest turbiditic system in the world. This system is fed primarily by the Ganges and Brahmaputra rivers, which drain the high Himalayan ranges. Sediment transfers from the delta to the deep-sea fan take place as turbidity currents in channel-levee systems. Previous studies have shown that, during high sea-level stand periods, the sediments were being mainly stored in the Ganges-Brahmaputra delta, and turbiditic transfer was occurring through active channels. Most of these channels are now inactive and sealed by hemipelagic deposits. However, the evolution of the inactive channels during the last sea-level variations has never been described in detail. Sedimentation in the currently active channel, the Active Valley, was particularly important during the last sea-level rise, which suggests a very good connection between the fluvial systems and the deep turbidite system at this time. During the MONOPOL cruise (2012), we retrieved a giant piston core (MD12-3412) near the currently inactive E4 channel. Previous studies have hypothesized that this channel is connected to the Swatch of No Ground canyon on the upper fan. The upper part of the core covers the last ~250 kyr. It reveals that, contrary to what is known about the Active Valley, the turbidite activity in E4 took place mainly during low sea-level phases (glacial stages), and stopped around 11.8 kyr cal BP. This different mode of activity suggests that (i) E4 was not abandoned but served as a secondary channel, and (ii) that the supply of turbidite material at the site of core MD12-3412 was not related to past changes in summer monsoon strength. Periods of activation of the E4 channel observed on core MD12-3412 were previously identified on the shelf area, by Hubscher and Spiess (2005), as thick Forced Regression System Tracts (FRST) after a displacement of deltaic edifices. High turbidites record on the deep basin are mainly synchronous with sea-level fall and rise conditions, but mostly during low sea-level periods. This could be explained by a residual connection between the coastal system and the E4 channel during sea level low stands. • A supposed inactive channel-levee since 125 kyr is investigated on the Bay of Bengal. • The channel is reactivated mainly during low sea level stages. • Channel activity does not seem linked with monsoons intensity but sea level variation. [ABSTRACT FROM AUTHOR]