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Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary systemanalysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems. The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins. [ABSTRACT FROM AUTHOR]

Large rivers are characterized by large water discharges, high suspended sediment fluxes and low slope, and typically display multiple channels that are separated by large complex bars. The most common channel style found in these rivers is characterized by the alternating presence of single and multiple channel threads. Mid‐channel compound bars separate a main deeper channel from shallower secondary channels, leading to low‐order braiding and low to moderate sinuosity. Despite the importance of this type of river for global terrestrial sediment transport and the interpretation of ancient fluvial successions, integrated depositional models for large multi‐channel rivers are still not fully developed. This paper interprets the channel morphodynamics and depositional architecture of such large rivers by investigating the distinctive features of their laterally‐accreting mid‐channel bars in the Solimões–Amazonas River. This is achieved by examination of temporal series of satellite images, quantification of bedforms using multibeam echosounding surveys, analysis of shallow seismic and ground penetrating radar surveys of selected areas, and on‐site field observations and sample collections. Such mid‐channel bars produce directional variability in planform scroll bar accretion of up to 180°. As these bars – and their associated channels – evolve, they become progressively shallower, due to the bifurcation of the two channels and the resultant partitioning of discharge that leads to a gradual reduction in transport capacity within the outer channel. The preserved successions of this process in the alluvial plain are characterized by fining‐upward trends, with larger cross‐strata sets at mid‐depths and internal erosional surfaces marking distinct cycles of bar development with potentially differing palaeocurrent trends. The new depositional models proposed for these mid‐channel bars and channels constitute a basis for the recognition of large multi‐channel river deposits in the ancient rock record. [ABSTRACT FROM AUTHOR]

Autogenic feedbacks can produce large‐scale, organized stratigraphic patterns in alluvial fans, but autogenic depositional signatures of specific upstream boundary conditions remain challenging to interpret. Here, a combination of theory, experiment and field application is used to explore how autogenic lithofacies changes can be interpreted as stratigraphic indicators of upstream boundary conditions. Six experiments were conducted to test the effects of sediment supply and water discharge rates on autogenic advance and retreat of the lithofacies boundary (grain‐size transition) in an alluvial fan with two dominant grain sizes. Migration of the grain‐size transition caused a short‐term zigzag pattern in the grain‐size transition position in the dip‐directional deposit section. For each experiment, time‐lapse images and laser topographic scans of the fan surface and stratigraphic cross‐sections of the final deposits were used to quantify characteristic timescales of autogenic processes. Timescales for fan‐margin migration, surface wet‐fraction change and grain‐size transition migration generally shorten as sediment supply rate increases and water discharge rate decreases. Increasing the sediment supply rate shortens the duration of the fluvial sediment storage and release cycle, producing higher frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge tends to widen channels and lengthens the duration of the fluvial sediment storage and release cycle, constructing lower frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge also enables more sediment to transport further downstream during release events, leading to higher magnitude zigzags in the grain‐size transition trajectory. These relationships between upstream boundary conditions and the grain‐size transition trajectory demonstrate how autogenic stratigraphic signals could be used as a tool to infer relative changes in boundary conditions. [ABSTRACT FROM AUTHOR]

The lower limits of petrophysical properties for an effective reservoir are among the key parameters for assessing hydrocarbon reserves and are therefore directly related to hydrocarbon exploration and development strategies. However, the lower limits for marine sandstone gas reservoirs are still not clear and the impact factors also remain to be discussed. This study analysed the lower petrophysical property limits of an effective sandstone reservoir in the Qiongdongnan Basin using porosity, permeability and gas testing. The results showed that the lower porosity and permeability limits of effective reservoirs developed in the deltas are 8.9% and 1.2 × 10−3 μm2, respectively, and 11.3% and 4.0 × 10−3 μm2 in the submarine canyons and fans, respectively. Sedimentary facies, sediment transport distance, grain size and burial depth of sandstone significantly influence the lower physical property limits. The lower porosity and permeability limits increase with the increase in sediment transport distance as well as the decrease in sandstone grain size and burial depth. Sediment sources and sedimentary facies determine whether sandstone can become an effective reservoir in the Qiongdongnan Basin. Specifically, the sediment source dramatically influences the petrophysical properties of sandstone. The sandstone sourced from the Red River has higher porosity and permeability, followed by the sandstone sourced from the Hainan Uplift, and the sandstone sourced from the palaeo-uplift within the basin has the lowest porosity and permeability. The feldspar dissolution by CO2 and organic acid is the primary formation mechanism of the effective reservoir in the Lingshui Formation, whereas the dissolution of glauconite is more common in the sandstone reservoirs of the Sanya and Meishan formations. [ABSTRACT FROM AUTHOR]

The presented work deals with the numerical modeling of intense bedload-transport processes at confluences of mountain rivers and steep tributaries. Steep tributaries are characterized by having high transport capacities which supply large amounts of sediments to the confluence zone, where due to the sudden change in slope and the local hydraulic conditions, intense deposition can occur. The objectives of this study are to understand the potential applications and limitations of 2D numerical simulations for modeling these processes. The calibration of the applied 2D numerical model (BASEMENT, Basic Simulation Environment, v2.8) is based on comparing high-density point clouds of the confluence morphology at the end of flume experimental runs with numerical results. The calibrated numerical model is then used to test different discharge ratios and to investigate depositional patterns and mechanisms. The results show that key morphological features such as the confluence fan, the bank-attached bar and the scour hole can be accurately reproduced, showing that 2D numerical simulations are a valuable tool for modeling the complex interactions between morphodynamics and hydraulics at river confluences. Additionally, it is shown that the confluence morphology of steep tributaries and mountain rivers is strongly influenced by the sediment concentration in the tributary channel and the discharge in the main channel. [ABSTRACT FROM AUTHOR]

The deposits of the upper Neoproterozoic Zerrissene Group of central‐western Namibia represent a large siliciclastic deep‐water depositional system that showcases the intricacies of facies and architectural relationships from bed‐scale to fan‐system‐scale. The lack of vegetation in the Namib Desert and regular east–west repetition of folded stratigraphy (reflecting ca 50% tectonic shortening) provides quasi‐three‐dimensional exposure over a current area of approximately 2700 square kilometres. The Brak River Formation, the middle sand‐rich unit of the Zerrissene Group, consists of nearly 600 m of strata exposed in multiple parallel continuous outcrops up to ca 10 km in length and oriented obliquely to depositional dip. Ten stratigraphic sections are correlated ca 32 km (ca 64 km restored) across the basin and offer exposure comparable in scale to modern submarine fans. Six sedimentary facies are identified and grouped into four facies associations that represent axial‐to‐marginal portions of deep‐water lobes in an unconfined submarine fan system. Spatial facies patterns, regional thickness variations, and palaeocurrents indicate that Brak River Formation sediments were transported primarily from the north to south–south‐west through a trough‐like basin, and deposited within an unconfined basin plain at the junction of the Adamastor and Khomas oceans. The unique outcrop exposure and extent permits the documentation of system‐scale architecture and basin configuration of the Brak River submarine fan system. A transition from the sand‐rich lower Brak River Formation to more intercalated mudstone‐dominated intervals in the middle and upper Brak River Formation is interpreted to record a change from aggradational to compensational stacking of lobe deposits. This records the evolution of a large submarine fan as it filled the subtle seafloor topography and became less confined at the system‐scale. The documentation of these deep‐water deposits from centimetre‐scale to basin‐scale provides a new model for a system with extensive long‐distance transport of sand‐rich sediment gravity flows to submarine lobes without apparent channelization. [ABSTRACT FROM AUTHOR]

Subaquatic channels, situated in lakes, fjords, submarine canyons and on deep-sea fan systems, exhibit diverse morphometric characteristics controlled by sediment transport processes, particularly turbidity currents. These processes play a significant role in transporting sediment, organic carbon, nutrients, and pollutants and pose hazards to critical infrastructure. This study examines a balanced set of subaquatic channels across various settings, sizes, and locations, employing novel data harmonization techniques to address biases toward larger channels. The analysis reveals consistent scaling relationships, particularly the dominant role of bankfull width, influencing bankfull depth, cross-sectional area, wavelength, and amplitude. The aspect ratio (width-to-depth) emerges as a significant parameter, reflecting a necessary channel compactness to maintain turbidity currents. Meandering development reveals relations between width, wavelength, and amplitude, with a preference for specific ratios. Meandering is most pronounced at channel beginnings, transitioning to straighter forms downstream, potentially influenced by flow dynamics and flow confinement. The study broadens the understanding of subaquatic channel evolution, emphasizing the importance of bankfull width and providing insights applicable across settings and scales. [ABSTRACT FROM AUTHOR]

Blowouts are integral features of coastal dune fields. Their presence enhances both geomorphological and ecological diversity and enables the movement of sand by wind. Their role as a 'transport corridor' may be, however, considered negative from a coastal management perspective in heavily touristic areas, where the existence of blowouts close to the foredune can enhance the loss of sediment from the beach. This paper investigated the relationship between airflow dynamics and patterns of sediment transport from the beach to established dunes through a trough blowout located on the foredune. Seven three-cup anemometers were used to measure wind speed and direction over a 24 h sampling period at a frequency of 1 min under onshore (parallel to the blowout axis) medium and high wind speeds (max of 17.9 ms−1). To measure sediment transport, a total of 12 vertical sand traps were located at three positions along the length of the deflation basin. The results indicated that small amounts of sediments went into the blowout from the beach and that the highest rates of sediment remobilization took place within the deflation basin. These results highlight two processes: (a) flow channelization induced by the blowout topography caused an increase in wind speed and sediment transport toward the depositional lobe, and (b) the presence of embryo dunes and herbaceous vegetation at the beach–blowout boundary effectively reduced the amount of sediment transport from the beach to the landform. The results confirmed the significant role that vegetation plays in controlling sediment movement and conserving the beach–dune system. [ABSTRACT FROM AUTHOR]

Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]

Streams convey coarse-clastic sediments towards coasts, where interactions with deltaic and coastal processes determine their resultant sedimentology and geomorphology. Extracting hydroclimatic signals from such environments is a desired goal, and therefore studies commonly rely on interpreting available paleoclimatic proxy data, but the direct linking of depositional and geomorphic processes with the hydroclimate remains obscure. This is a consequence of the challenge of linking processes that are often studied separately and span across large spatial and temporal scales, including synoptic-scale hydroclimatic forcing, streamflows, water body hydrodynamics, fluvial and coastal sediment transport, and sedimentation. Here, we explore this chain of connected processes in the unique setting of the Dead Sea basin, where present-day hydroclimatology is closely tied with geomorphic evolution and sediment transport of streams and coasts that rapidly respond to lake-level fall. We use a 5-year (2018–2022) rich dataset of (i) high-resolution synoptic-scale circulation patterns, (ii) continuous wind-wave and rain–flood records, and (iii) storm-scale fluvial and coastal sediment transport of "smart" and marked boulders. We show the significance of Mediterranean cyclones in the concurrent activation of fluvial (floods) and coastal (wind waves) sediment conveyors. These synoptic-scale patterns drive the westerlies necessary for (i) delivering the moisture across the Judean desert, which is transformed into floods, and at the same time, (ii) the coeval, topographically funneled winds that turn into surface southerlies (>10 m s -1) along the Dead Sea rift valley. During winter, these mesoscale southerlies generate 10–30 high-amplitude, northward-propagating storm waves, with <4 m wave heights. Such waves transport cobbles for hundreds of meters alongshore, northward and away from the supplying channel mouths. Four to nine times per winter the rainfall generated by these atmospheric patterns is capable of generating floods that reach the stream mouths, delivering poorly sorted, coarse gravel. This usually occurs during the decay of the associated storm waves. This gravel is dispersed alongshore by waves during subsequent storms. As storm waves dominate and are >5 times more frequent than flash floods, coarse-clastic beach berms and fan deltas are deposited preferentially north of the delivering channel mouths. This asymmetric depositional architecture, controlled by the regional hydroclimatology, is identified for both the modern and late Pleistocene coast and delta environments, implying that the dominance of present-day Mediterranean cyclones also persisted in the region during the late Pleistocene when Lake Lisan occupied the basin. [ABSTRACT FROM AUTHOR]

Tectonic activity occurred during the depositional period of the Enping Formation in the southern Baiyun Sag in the Pearl River Mouth Basin, with a series of synsedimentary faults and a set of large fan delta reservoir bodies developing. There is no data from drilling, cores, etc. for this area, so this paper applies three‐dimensional seismic data to study the structural style of the steep slope zone, the seismic facies characteristics of fan deltas, and the source‐sink system and sedimentary model of the Enping Formation. The control action of tectonic activity on fan deltaic sedimentary systems is studied by combining interpretation of fault systems, dissection of structural styles, seismic reflection structure, seismic facies geometry, and seismic attribute analysis, together with theoretical analysis of the source‐sink deposition process. The Baiyun Sag has experienced tectonic activity since the Eocene, and a series of synsedimentary faults are developed in the southern steep slope zone. Under the common control of multiple large synsedimentary faults, a large ancient gully formed in the steep slope zone in the south, which gradually widened from south to north. The uplift area in the southern part of the sag was exposed for a long time during the deposition of the Enping Formation and consequently suffered weathering and erosion. The resulting sediments were transported through a system of provenance channels composed of slopes and an ancient gully to the depression area, where they were deposited and eventually converged to form a large fan delta. The fan delta presents the overall characteristics of NS strong wedge reflection and EW strong domal reflection—thick in the middle part and thin in the wings. It displays a lobe‐shaped distribution on the plane, with the fan root pointing to the south slope. According to differences in reflection intensity from bottom to top, it can be subdivided into three stages of progradational sedimentary bodies—the southern uplift and denudation zone, the large ancient gully, and the fan delta—which together constitute a complete source‐sink system. This represents a sedimentary model of progradational fan delta under the overall joint control of the restricted ancient gully and syndepositional faults. [ABSTRACT FROM AUTHOR]

Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross‐laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning‐energy flows, and that the parallel‐laminated units are deposited under transport conditions corresponding to upper plane bed at the dune–antidune transition. Thus, transport conditions that are more intense than those at the dune–antidune transition should deposit massive units. This study presents experimental, open‐channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non‐dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0·4. For values of the Shields number smaller than 0·4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel‐laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune–antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes. [ABSTRACT FROM AUTHOR]

The intensity of turbidite sedimentation over long timescales is driven by sea-level change, tectonically driven rock uplift and climatically modulated sediment delivery rates. This study focuses on understanding the effect of sea-level fluctuations and climatic variability on grain-size variations. The grain size and environmental magnetic parameters of Arabian Sea sediments have been documented using 203 samples, spanning the last 200 ka, obtained from International Ocean Discovery Program (IODP) Site U1457. Grain-size end-member modelling suggests that between ~200 and 130 ka there was an increase in the coarse silt fraction caused by sediment transport following reworking of the Indus Fan and development of deep-sea canyons. The sediment size and enhanced magnetic susceptibility indicate a dominant flux of terrestrial sediments. Sedimentation in the distal Indus Fan at c. 200–130 ka was driven by a drop in sea level that lowered the base level in the Indus and Narmada river systems. The low sea-stand caused incision in the Indus delta, canyons and fan area, which resulted in the transportation of coarser sediment at the drilling site. Magnetic susceptibility and other associated magnetic parameters suggest a large fraction of the sediment was supplied by the Narmada River during ~200–130 ka. Since ~130 ka, clay-dominated sedimentation is attributed to the rise in sea level due to warm and wet climate. [ABSTRACT FROM AUTHOR]

Drilling and coring during IODP Expedition 362 in the eastern Indian Ocean encountered probably the largest wood fragment ever recovered in scientific ocean drilling. The wood is Late Miocene in age and buried beneath ∼800 m of siliciclastic mud and sand of the Bengal–Nicobar Fan. The wood is well preserved. Possible origins include the hinterland to the north, with sediment transported as part of the submarine fan sedimentary processes, or the Sunda subduction zone to the east, potentially as a megathrust tsunami deposit. [ABSTRACT FROM AUTHOR]

Deep‐water deposits in marine basins have recently received considerable research attention. However, the controls of sediment transported to deep‐lacustrine environments are comparatively understudied. In this study, we utilize field‐based outcrop data to investigate the variability of sediment distribution and its controlling factors in the Lower Cretaceous synrift Xiguayuan Formation in the Luanping Basin. Two fan‐delta systems with variability dominate the measured outcrop sections. At the lithological scale, the ratio of conglomerate to strata in the Xiyuan fan‐delta system is 87%, and the average thickness of individual coarse‐grained layers is ~1 m; the corresponding values in the Caoying fan‐delta system are 52% and 0.4 m. In addition, sand‐rich gravity‐flow deposits are developed in front of the Xiyuan fan delta, whereas mud‐rich mass transport deposits (i.e., sliding block and slumping debris) are found in front of the Caoying fan delta. At the stratigraphical scale, a delta succession in the Xiyuan section characterized by sand‐rich facies from proximal to distal parts is developed in a relatively steep slope setting. In the Caoying section, however, a delta succession characterized by sand‐rich facies in the proximal to middle parts is found in addition to a mud‐rich distal part developed in a gentle slope setting. Differential sediment supply resulted in significant variation in the sediment distribution pattern. In particular, the grain size of the fan‐delta front controls that of the deep‐lacustrine gravity‐flow deposits fed by them. This study highlights the variability of sediment supply and their control on sediment partitioning in continental rift and marine basins. [ABSTRACT FROM AUTHOR]

A comprehensive dataset is collated in a study on sediment transport, timing and basin physiography during the Early Cretaceous Period in the Boreal Basin (Barents Sea), one of the world's largest and longest active epicontinental basins. Long-wavelength tectonic tilt related to the Early Cretaceous High Arctic Large Igneous Province (HALIP) set up a fluvial system that developed from a sediment source area in the NW, which flowed SE across the Svalbard archipelago, terminating in a low-accommodation shallow sea within the Bjarmeland Platform area of the present-day Barents Sea. The basin deepened to the SE with a ramp-like basin floor with gentle dip. Seismic data show sedimentary lobes with internal clinoform geometry that advanced from the NW. These lobes interfingered with, and were overlain by, another younger depositional system with similar lobes sourced from the NE. The integrated data allow mapping of architectural patterns that provide information on basin physiography and control factors on source-to-sink transport and depositional patterns within the giant epicontinental basin. The results highlight how low-gradient, low-accommodation sediment transport and deposition has taken place along proximal to distal profiles for several hundred kilometres, in response to subtle changes in base level and by intra-basinal highs and troughs. Long-distance correlation along depositional dip is therefore possible, but should be treated with caution to avoid misidentification of timelines for diachronous surfaces. [ABSTRACT FROM AUTHOR]

Alluvial fans at tributary junctions modulate sediment flux through river networks, by buffering the mainstem channel from disturbance in the tributaries. Buffering occurs through the storage (and release) of sediment in fans. Here, we use an extensive historic dataset to characterise the ways in which fan buffering can change as sediment supply varies. In New Zealand's East Coast region, sediment supply and fluvial transport are prolific by global standards. We reconstruct how tributary‐junction fans in this region have responded to sediment generated by deforestation and extreme storms. The dynamics of five fans along the Tapuaeroa River are examined for the period 1939–2015. In response to major sediment loading, fans aggraded by up to 12 m and prograded by up to 170 m. Net sediment accumulation ranged from near zero to 1.5×106 m3. Fan size, gradient, sediment storage and buffering were influenced by both upstream and downstream controls. Key upstream (tributary) influences were sediment supply and stream power; downstream (mainstem) influences included distal confinement and, importantly, the nature of fan interaction with the mainstem, which aggraded by up to 6 m. The fans' ability to buffer the Tapuaeroa River from change in the tributaries was largely governed by this downstream interaction: as the mainstem aggraded, it increasingly curtailed fan progradation, thus limiting buffering. Previous studies of tributary‐junction fans have related fan morphometry to basin characteristics. However, we find that fan slope and area can vary considerably at decadal, annual or even monthly timescales. Consequently, we suggest that such studies could benefit by examining regional histories of disturbance. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multibeam bathymetry, coupled with seismic reflection profiles and sediment cores, was collected to understand the sediment process mechanisms for active onshore-offshore sediment transfer system from coastal erosion to nearshore transfer of sediment into a submarine channel and fan system. Savary Island in the northern Salish Sea of British Columbia, Canada, emerged immediately after deglaciation and became exposed to winter storms that began a continual modification of the island. Subsequent to coastal erosion, sediments are moved from the south side of the island, by strong tidal currents and longshore drift, to the island's north side. The mobilized sands are then entrained into and swept down submarine channels during gravity flows, likely a response to enhanced hydrodynamic tidal flow. Downslope progradation within the channels is primarily a result of downslope migrating submarine dunes that transfer sand to small submarine fans. Further transport beyond the channels into the deeper basin occurs via turbidity flows that have been active throughout the late Holocene. The prospect for Savary Island is grim, as this sediment transfer system will likely continue until the island disappears altogether. [ABSTRACT FROM AUTHOR]

Marine and terrestrial material deposited together in Integrated Ocean Discovery Program Expedition 354 cores in the Bay of Bengal offer the opportunity to link the evolution of monsoonal climate and tectonic erosional history. We test the utility of foraminiferal climate reconstructions in this active depositional environment in which turbidity currents transport material to Expedition 354 sites and may mix foraminiferal shells from higher up on the Bengal Fan with local shells. Mg/Ca and δ18O in ~80 modern (<1 kyr) individual Trilobatus sacculifer specimens reconstruct seasonal sea surface temperature (SST) and sea surface salinity (SSS) at three locations: lower fan Expedition 354 Site U1454 near the modern active channel and more likely to be influenced by turbidity currents, lower fan Expedition 354 Site U1449 far from channel activity, and Site 342KL on the continental slope. Because the lower Bengal Fan locations have less seasonally variable SST and SSS than conditions closer to the continental slope, we can determine if foraminiferal populations are local or have been transported from a distal source. Mg/Ca and δ18O from Site U1449 are not likely to be affected by turbidity currents and reflect local conditions. In contrast, Mg/Ca and δ18O from Site U1454 show strong evidence that foraminifera from the active channel record a mixture of local conditions and distal conditions recorded at higher latitudes. Our results suggest that foraminifera can be used to reconstruct SST and δ18O in this complex depositional environment, but caution must be taken when the downcore lithology indicates turbidites and possible sediment transport. Key Points: Mg/Ca and δ18O measured in planktonic foraminifera record sea surface conditions in the Bay of BengalWe present evidence that foraminifera shells have been transported with turbidity currents from the northern to southern Bay of BengalFar away from influence of turbidites foraminifera faithfully reconstruct SST and δ18O of seawater in this complex depositional environment [ABSTRACT FROM AUTHOR]

The depositional record of intermontane basins provides a valuable archive of the temporal evolution of orogenic belts; their common isolated nature may, however, hinder the efficient usage of standard approaches to constrain the age of a basin fill. In this paper the authigenic 10Be/9Be dating method is employed and tested to construct an age model of the existence and regression of Lake Turiec, which appeared during the Late Miocene in the intermontane Turiec Basin, Central Western Carpathians (Central Europe). The initial authigenic 10Be/9Be ratio, essential for the dating method, was analyzed on five sites of the Pleistocene-Holocene age, and back-calculation of the paleo-initial ratio was performed using lacustrine succession dated by magnetostratigraphy. Noteworthy, the initial ratio appears to be affected mainly by (post)depositional settings, and not by different provenance of the analyzed sediment. The sedimentological analysis of the Upper Miocene outcrops allowed the definition of the facies associations of an alluvial fan, a braided river, a fan delta and an open lake. The distribution of facies associations in the basin fill implies an increase in sediment supply to accommodation rate ratio due to the replacement of the open lake environment by the interconnected alluvial fan-braided river-fan delta system. Authigenic 10Be/9Be dating yielded ages of the lacustrine succession reaching ∼10.7–7.8 Ma, while the age of the fan delta succession, considered as the timing of the regression, was established to ∼6.7 Ma. The deposition of alluvial fans dominated the basin after the regression of the lake, possibly up to ∼4.0 Ma. The abrupt increase in sediment supply to the accommodation ratio at ∼6.7 Ma was caused by the uplift of the Malá Fatra Mts. at the western margin of the Turiec Basin, which had previously formed a moderate topography. The timing of this process generally coincides with the overall decrease in accommodation rates in the region due to the inversion of the Pannonian Basin System. The endorheic character of the basin before ∼6.7 Ma prevented the transport of the sediment denudated from the recently most uplifted parts of the Western Carpathians and carried towards the Pannonian Basin System, while the present-day source-to-sink system could only be formed later. This implies a low sediment supply and restricted denudation rate not only from the morphostructures surrounding the basin, but also from the Tatra Mts. and Nízke Tatry Mts. during the period ∼10.7–6.7 Ma. The research supports the suitability of intermontane basins for authigenic 10Be/9Be dating in a setting of high accommodation rates and limited redeposition of older muddy sediment. However, a special attention has to be paid to the depositional settings during determination of initial 10Be/9Be ratios. • Authigenic 10Be/9Be dating resolve history of a long-lived isolated late Miocene lake. • Initial 10Be/9Be affected by (post-)depositional settings, effect of provenance unnoticed. • Lake Turiec existed between ∼10.7–6.7 Ma, then filled by a fan delta-braided river-alluvial fan depositional system. • Regression due to increased sediment supply from mountains uplifting after ∼7 Ma. • Termination of endorheic character and establishment of the Váh River catchment followed. [ABSTRACT FROM AUTHOR]

The Bengal Fan, as the largest submarine fan in the world, receives a large amount of sediments discharged from the Himalayas through the Ganges-Brahmaputra (G-B) river system. However, previous studies of this system seldom focused on the role of channels, which are widely developed in the Bengal Fan, in sediment transportation over the last glacial cycle. Here, we discuss the coupled sedimentary archive in two gravity cores along the Active Channel in the Bengal Fan. Our findings are based on grain size, clay minerals, and Sr and Nd isotope compositions of these two sediment cores. End-member modeling of grain-size data reveals that the intermediate end-member represents the flux of distal fluvial particles from the G-B river system, the fine end-member denotes regional sediment supply of weathered volcanic materials, especially from the eastern Indian Peninsula, and the coarse end-member probably reflects nearby terrigenous input, aeolian input and/or volcanic glass. Sediment provenance analysis based on clay minerals, and Sr and Nd isotopes confirmed sediment supply from the G-B river system which was characterized by high illite percentage, high 87Sr/86Sr ratios and low ε Nd values, especially during five stages (50–45 ka, 42–37 ka, 31–28.5 ka, 24–20 ka and 14–9 ka). During these stages, heavy fine-grained sediment supply from the G-B river system was discharged into the study area under the influence of climate change rather than sea-level fluctuation, additionally emphasizing the importance of channels in the sediment transport process. Moreover, we find a significant alteration of sediment sources at ∼26 ka, which may be related to conversion of the deep-water currents in the Bay of Bengal. • There is staged sediment supply from the G-B Rivers into the Bay of Bengal. • Heavy sediment supply of the G-B Rivers was affected by climate change. • The channels developed on the Bengal Fan are important in the sediment transport process. • Sediment source change at ∼26 ka may be related to conversion of deep-water currents. [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]

Up to date, most in-situ studies and observations of turbidity currents were conducted in submarine canyons that are either, large, shelf incising or adjacent to big perennial rivers, or a combination of these features. Little if any observations have been made in the numerous, small submarine canyons (<20 km) that are confined to the continental slope and located far offshore smaller and often ephemeral streams, which are far more common globally. In this study, measurements were collected from October 2019 until June 2020 in Bat-Galim Canyon, a small (5 km long) submarine canyon located offshore Haifa, Israel, in the Eastern Levantine Basin (southeastern Mediterranean) where only minor, ephemeral streams reach the sea. This was performed using two similar mooring stations, positioned at depths of 350 and 710-meter along the canyon, which carried an array of measuring instruments, set between 2 and 50 meters above the canyon thalweg. Our data shows that the small Bat-Galim canyon is an active conduit for significant sediment transport to the deep-sea, much of it via turbidity currents that flow down the canyon during winter storms. The characteristic values of the turbidity currents in the Bat-Galim canyon were similar to those reported in much bigger submarine canyons. In addition, we observed temperature inversions during these events, wherein the sediment-laden warm surface water plunged and flowed underneath the colder, and otherwise denser, canyon water. This temperature inversion may lead to sediment lofting and upward convection through the water column for hundreds of meters, once sediment settling relieves the warm water of some of its ballast. These unique findings highlight the need to investigate the importance of small submarine canyons on continental slopes worldwide as water and sediment conduits to the deep-sea, even in dryer regions, and the impact of temperature inversions by turbidity currents on various water column processes. • First time-series measurements within a submarine canyon in the Levantine Basin. • Turbidity currents observed in the small (5km long) and confined to the slope canyon. • Similar traits of turbidity currents and sediment transport in this and much larger, shelf-incising canyons. • These winter events caused temperature inversions in the water column. [ABSTRACT FROM AUTHOR]

The present and paleo-drainage networks, depositional surfaces, fault throw, slope of the downthrown fault blocks, soil properties, sediment characteristics and published optically stimulated luminescence (OSL) ages are used to define the role of tectonics and climate in the growth of forty-five terminal fans (TFs) in the Indo-Gangetic foreland basin. Twenty-three TFs show a single exposed surface throughout, suggesting no or imperceptible breaks in sedimentation during their formation. In contrast, twenty-two TFs show multiple growth surfaces, separated by soil profiles and erosional surfaces. The available optically stimulated luminescence (OSL) dates of these depositional surfaces suggest different phases of TF growth. Tectonically triggered surface faulting altered accommodation space, slope of the substrate, and sediment supply and initiated new TF depositional cycles. The tectonically stable periods, in contrast, did not form TFs, despite the favourable humid climate conditions. Instead, the dry and humid climatic regimes, when combined with frequent surface faulting, produced and remobilized sediments more quickly, promoting TF growth. The humid climate TFs are spatially extensive (average area = 2000 km2), with clay horizons interspersed between sand facies. The dry climates TFs are smaller (average area = 1370 km2), with intervening calcrete horizons and surface salt-efflorescence. Low precipitation and inadequate sediment supply hampered the growth of these dry climate TFs. Despite a considerable period of surface exposure, the surfaces of dry climate TFs lack a well-developed soil profile. The upper Ganga Plain provides more accommodation space across the faults than the middle Ganga Plain. Accommodation space and substrate slope have little effect on TF area unless climatically triggered sediment remobilization occurs. For a given accommodation space and substrate slope, steeper sloping TFs occupy less area than lower sloping ones. Faults with throws of <5 m and substrate slopes of <2° do not form TFs; instead sediment wedges are formed across fault slope breaks. The TFs in the upper Ganga Plain show more growth surfaces than the middle Ganga Plain. The older growth surfaces are either progressively arranged across the direction of channel shift or occur as inliers in between the younger alluvium. Well-developed distributaries on the older TFs disperse sediment more readily, rather than accumulating it in proximal fan regions. However, the younger TFs, with relatively less-developed distributary channel networks, vertically stack sediments in their proximal part and occasionally transport sediment as sheet floods to their distal end regions. The combined geomorphic response of TFs to tectonic events and climatic fluctuations is, therefore, simultaneous for TF growth and stabilization. • Ganga Plain terminal fans (TF) form at topographic slope breaks away from mountains. • TF growth mechanism investigated using remote sensing and field investigations. • Ganga Plain TFs develop as a result of tectonic-climatic interactions. • Tectonics provides overall accommodation space for TF building. • Climate then controls TF growth (humid periods) and inactivity (drier periods). [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]

Deep sea channel systems are recognized in most submarine fans worldwide as well as in the geological record. The Indus Fan is the second largest modern submarine fan, having a well-developed active canyon and deep sea channel system. Previous studies from the upper Indus Fan have reported several active channel systems. In the present study, deep sea channel systems were identified within the middle Indus Fan using high resolution multibeam bathymetric data. Prominent morphological features within the survey block include the Raman Seamount and Laxmi Ridge. The origin of the newly discovered channels in the middle fan has been inferred using medium resolution satellite bathymetry data. Interpretation of new data shows that the highly sinuous deep sea channel systems also extend to the east of Laxmi Ridge, as well as to the west of Laxmi Ridge, as previously reported. A decrease in sinuosity southward can be attributed to the morphological constraints imposed by the elevated features. These findings have significance in determining the pathways for active sediment transport systems, as well as their source characterization. The geometry suggests a series of punctuated avulsion events leading to the present array of disconnected channels. Such channels have affected the Laxmi Basin since the Pliocene and are responsible for reworking older fan sediments, resulting in loss of the original erosional signature supplied from the river mouth. This implies that distal fan sediments have experienced significant signal shredding and may not represent the erosion and weathering conditions within the onshore basin at the time of sedimentation. [ABSTRACT FROM AUTHOR]

• The maximum possible intrusion length is derived for turbidity current intrusion. • A method is developed for predicting flow and sediment transport rates. • Correlation between relative intrusion length and intensity is discovered. • Predictions agree well with laboratory and field measurements. Turbidity current intrusion often occurs in canals, approach channels and tributary areas of large reservoirs, causing sedimentation problems in these environments. Many models and semi-empirical equations have been proposed to calculate flow and sediment transport rates for turbidity current intrusion, under an assumption that the current front can keep propagating freely in the channel before dying out, but the effect of the finite length of closed-end channels has rarely been considered. A self-similar solution to the vertical two-dimensional model for turbidity currents is used to obtain the equation of the maximum possible length for the intrusion of turbidity currents. The maximum possible length is then used to modify an existing discharge equation for turbidity current intrusion in long channels and establish a more general calculation method that can be applied for intrusion in closed end channels. Data from two existing flume experiments are used to calibrate the derived equation of sediment transport rate for turbidity current intrusion. Field measurements obtained from several tributary mouths in the Xiaolangdi Reservoir are also used to calibrate the derived intrusion discharge equation. The agreement between predictions and observations, as well as the comparison between the proposed calculation method and the one before modification, demonstrate that the intrusion discharge is not only determined by the depth of turbid water and sediment concentration at the inlet of the tributary channel, but also influenced by the ratio of the real intrusion length to the maximum possible intrusion length. [ABSTRACT FROM AUTHOR]

Submarine canyons are prevalent in the world's oceans and are instrumental in transporting sediment from coastal regions to deep-sea fans. Conventional sediment parameters such as mean grain size, sorting, and provenance have typically been used to characterize these deposits, but they provide little information on sediment source or the delivery processes involved. Fortunately, transported along with the mineral grains are the remains of organisms living within the sediment. Biological constituents have unique environmental signatures that are more precise proxies for source areas than are mineral grains alone. They may be used to identify a single biofacies deposit (SBD) due to local sediment transport or a displaced, multiple biofacies deposit (MBD) resulting from staged sediment transport or a full-canyon flushing event. This Ascension-Monterey Canyon system study demonstrates that by using the biological constituents in marine deposits, the source areas and transport mechanisms may be identified. The 19,000 year record of core S3-15G captured hemipelagic mud interspersed with individual turbidites of sand and silt transported to the core site at lower bathyal depths (3491 m). The relative abundance of displaced benthic foraminifera was found to correlate positively with grain size, with 75% of the fauna being displaced in the cross-bedded turbiditic sand (Tc) units, 39% in the laminated turbiditic sand (Td) units, and 15% in the turbiditic mud (Tet) units. Nineteen samples were SBDs representing local canyon wall sloughing, bioerosion, or hemipelagic deposition at or near the core site. Sixty-five were MBDs, 31 of which were turbiditic sands originating in the estuarine to inner shelf, outer shelf, upper slope, or upper middle slope, and the remaining 34 were turbiditic muds with displacement initiated in the estuarine to inner shelf, outer shelf, and the upper slope. Commonly, the biological remains of several biofacies characterize these MBDs, reflecting staged sediment transport with storage occurring behind slumps that act as barriers to movement until finally released. Sediment bypassing, typically of the deeper biofacies, and full-canyon flushing, were also evident. Identifying and interpreting the distribution of allochthonous biological sediment constituents in marine deposits is a powerful tool in the investigation of sediment transport that can be applied to other submarine canyon systems. [ABSTRACT FROM AUTHOR]

• First monitoring of sediment transfer in submarine channel from source to sink. • River input and lobe aggradation approximately balances over decadal timescales. • Most turbidity currents deposit within the proximal part of the channel. • Infrequent large flows flush the channel; transporting sediment onto the lobe. • Flushing events can occur without obvious triggers, and can be internally generated. Submarine channels are the primary conduits for land-derived material, including organic carbon, pollutants, and nutrients, into the deep-sea. The flows (turbidity currents) that traverse these systems can pose hazards to seafloor infrastructure such as cables and pipelines. Here we use a novel combination of repeat seafloor surveys and turbidity current monitoring along a 50 km-long submarine channel in Bute Inlet, British Columbia, and discharge measurements from the main feeding river. These source-to-sink observations provide the most detailed information yet on magnitude-frequency-distance relationships for turbidity currents, and the spatial-temporal patterns of sediment transport within a submarine channel-lobe system. This analysis provides new insights into mass redistribution, and particle residence times in submarine channels, as well as where particles are eventually buried and how that is recorded in the deposits. We observe stepwise sediment transport down the channel, with turbidity currents becoming progressively less frequent with distance. Most flows dissipate and deposit within the proximal (< 11 km) part of the system, whilst longer run-out flows then pick up this sediment, 'shuffling' it further downstream along the channel. This shuffling occurs mainly through upstream migration of knickpoints, which can generate sediment bypass along the channel over timescales of 10–100 yrs. Infrequent large events flush the channel and ultimately transport sediment onto the lobe. These flushing events can occur without obvious triggers, and thus might be internally generated. We then present the first ever sediment budget analysis of an entire submarine channel system, which shows that the river input and lobe aggradation can approximately balance over decadal timescales. We conclude by discussing the implication of this sediment shuffling for seafloor geohazards and particle burial. [ABSTRACT FROM AUTHOR]

Abstract: Subaqueous sediment density flows are one of the volumetrically most important processes for moving sediment across our planet, and form the largest sediment accumulations on Earth (submarine fans). They are also arguably the most sparely monitored major sediment transport processes on our planet. Significant advances have been made in documenting their timing and triggers, especially within submarine canyons and delta-fronts, and freshwater lakes and reservoirs, but the sediment concentration of flows that run out beyond the continental slope has never been measured directly. This limited amount of monitoring data contrasts sharply with other major types of sediment flow, such as river systems, and ensure that understanding submarine sediment density flows remains a major challenge for Earth science. The available monitoring data define a series of flow types whose character and deposits differ significantly. Large (>100km3) failures on the continental slope can generate fast-moving (up to 19m/s) flows that reach the deep ocean, and deposit thick layers of sand across submarine fans. Even small volume (0.008km3) canyon head failures can sometimes generate channelised flows that travel at >5m/s for several hundred kilometres. A single event off SE Taiwan shows that river floods can generate powerful flows that reach the deep ocean, in this case triggered by failure of recently deposited sediment in the canyon head. Direct monitoring evidence of powerful oceanic flows produced by plunging hyperpycnal flood water is lacking, although this process has produced shorter and weaker oceanic flows. Numerous flows can occur each year on river-fed delta fronts, where they can generate up-slope migrating crescentic bedforms. These flows tend to occur during the flood season, but are not necessarily associated with individual flood discharge peaks, suggesting that they are often triggered by delta-front slope failures. Powerful flows occur several times each year in canyons fed by sand from the shelf, associated with strong wave action. These flows can also generate up-slope migrating crescentic bedforms that most likely originate due to retrogressive breaching associated with a dense near-bed layer of sediment. Expanded dilute flows that are supercritical and fully turbulent are also triggered by wave action in canyons. Sediment density flows in lakes and reservoirs generated by plunging river flood water have been monitored in much greater detail. They are typically very dilute (<0.01vol.% sediment) and travel at <50cm/s, and are prone to generating interflows within the density stratified freshwater. A key objective for future work is to develop measurement techniques for seeing through overlying dilute clouds of sediment, to determine whether dense near-bed layers are present. There is also a need to combine monitoring of flows with detailed analyses of flow deposits, in order to understand how flows are recorded in the rock record. Finally, a source-to-sink approach is needed because the character of submarine flows can change significantly along their flow path. [Copyright &y& Elsevier]

The article focuses on evidence of the course reversal of the Fraser River in British Columbia, Canada during the Pleistocene Epoch. Geochronological analysis of volcanic dams in the Dog Creek region of the Fraser River suggests a reversal of drainage and sediment transport. Topics include glaciofluvial erosion, the formation of the submarine Nitinat Fan, and uplift of the Coast Mountain range.

Several coarse grained metasediment units with preserved primary sedimentary structures were investigated within and in the surroundings of the Penninic Tauern Window. In its NE part - the central area of the study, breccias and conglomerates form elongated lenses a few kilometres in length, composed of multiple layers separated by erosional boundaries. Most of the breccias and conglomerates are matrix-supported, but a few are clast-supported. They were mainly deposited by debris flows and to a lesser extent by high-concentration turbidity currents. Various coarse-grained to fine-grained, thick- to thin-bedded turbiditic sandstones occur west of the breccias. They are interpreted as turbidity current deposits. Some layers are contorted, probably due to syn-sedimentary slumping. The entire organization of the bedforms implies that the coarse-grained sediments represent mainly fault controlled slopea-prons and the more fine-grained sandstones submarine fans, respectively. Black shales and mudstones that separate the breccias, conglomerates and sandstones are regarded as slope and/or base-of-slope to hemipelagic sediments. Additionally, observations from other areas e.g. Penken, Tarntal and Radstadt Mountains, show breccias and conglomerates formed as slope-aprons. Breccias from Richbergkogel display features of both slope-apron and submarine fan. Large elongate blocks of dolomite and limestone cropping out along the northern and southern margins of the Tauern Window were derived mainly from units to the south containing Triassic carbonate platform sediments and represent olistoliths. Our findings suggest that the slope-aprons and the submarine fans were related to the development of the southern margin of the Penninic Ocean and reflect its diachronous opening lasting from Middle Jurassic to Early Cretaceous. Moreover, the mass transport deposits from the Matrei Zone indicate the beginning of the ocean closure which is supposed to have taken place in the late Early Cretaceous. [ABSTRACT FROM AUTHOR]

Abstract: The source and transport mechanisms of land-derived Okinawa Trough sediments were studied using the field data of temperature, salinity and turbidity in the East China Seas. The results suggest that there are two primary sediments sources from the Chinese Mainland to the Okinawa Trough: one is the Old Huanghe River submarine delta, and the other is the Changjiang River sediments, which are distributed at the Changjiang River estuary and the off-coast of Zhejiang and Fujian provinces. It is difficult for the Huanghe River suspended sediments to arrive in the Okinawa Trough via the new estuary. Although the Taiwan warm current blocks the seaward terrigenous transportation to a certain extent, part of the coastal suspended sediments are transported to the outer shelf. Suspended particulate matter is unable to get through the barrier of the Kuroshio Current under normal conditions. However, episodic events, such as winter storms, internal-tidal waves and turbidity flows, are capable of transporting suspended particulate matter into the Okinawa Trough. The super typhoon “Ewiniar” induced strong waves and influenced the thermocline depth and suspended sediment concentration of the East China Seas. The typhoon-induced waves pushed the thermocline depth down to around 40m and caused the resuspension of large volumes of sediments in its path. In the other East China Seas regions, the typhoon-induced swells deepened the thermocline depth by about 5m and increased suspended sediment concentrations. The typhoon effect on suspended sediment concentration of the East China Seas disappeared within 2 weeks. [Copyright &y& Elsevier]

Fan deltas grow largely through repeated cycles of lobe construction and channel erosion during the period of channelized flow. Although previous studies suggest that variable flood discharge may play a key role in strong erosion and related fully confined main channel formation in fan deltas, analog experiments with constant discharge and sediment supply showed that strong erosional events were cyclic. Understanding erosion cycles is important for land management and flood hazard mitigation. Here, we present flume experiments to investigate the mechanism and controlling factors of fully confined main channel-related erosion under constant discharge conditions. The results reveal that: (1) fully confined main channel-related erosion is triggered by turbulence within stratified fluid in hydraulic jump process. When the topography difference of the fan delta is sufficiently small, the flow direction changed from steeper flanks to the centerline. The flow velocity along centerline increase due to weak viscosity and steep slope of fan delta, changing the subcritical flow to supercritical flow. Supercritical flow transports sediment to the shoreline and is resisted by the standing body of water in the basin, causing the decrease of flow velocity accompanied by hydraulic jump. The turbulence formed in hydraulic jump process triggers the formation of scour hole which erodes the fan delta. (2) Input conditions control the range of the critical slope and frequency of erosion cycles. The critical slope is inversely related to the slope of the discharge and grain size of sediments, whereas it is directly related to the sediment/water ratio. The frequency of erosion cycles is directly related to the slope of substrate layer, discharge and sediment/water ratio. (3) The fan delta evolves under the interaction between the deposition process and topography. Moreover, dynamic equilibrium of experiments including main channel-related erosions and autogenic slope adjustments can be found in natural fan deltas. [ABSTRACT FROM AUTHOR]

The planform geometry of submarine channels commonly exhibits a spatio-temporal stability generally not observed in fluvial channels. As such, submarine channels tend to lack the meander loop cutoffs and frequent avulsion history typical of fluvial channels. Fluvial sinuosity develops through inner-bend deposition and outer-bend erosion. Inner-bend deposits have also been recognized in submarine channels, from subsurface and seafl oor images and from ancient channel outcrops, and have been demonstrated within physical models. However, outer-bend sediment accumulations are a feature thought to be unique to submarine channels. We report on physical experiments on channelized, subaqueous, particle-driven turbidity currents that demonstrate that channel-fill architecture relates directly to the degree of flow bypass, in turn largely determined by the degree of confinement. In general, weakly bypassing fl ows deposit at the outer bend, whereas strongly bypassing flows deposit at the inner bend. Therefore flows within aggradational channel systems whose axes are bypass dominated may preferentially deposit at the inner bend, ultimately having the effect of increasing channel sinuosity through time; this is an evolution pattern commonly observed in seismic images. Once developed, the apparent spatio-temporal longevity of sinuosity within many systems may be explained by the passage of turbidity currents of varying magnitude (and consequently bypass potential) depositing preferentially at either the inner or outer bank of the channel, maintaining a quasi-stable morphological equilibrium. Fluvial channels do not have the ability to reduce or maintain their sinuosity in this way, which plausibly explains why they tend to develop cutoffs at higher rates than subaqueous channels. [ABSTRACT FROM AUTHOR]

Contrary to widely used sequence-stratigraphic models, lowstand fans are only part of the turbidite depositional record; our analysis reveals that a comparable volume of coarse-grained sediment has been deposited in California borderland deep-water basins regardless of sea level. Sedimentation rates and periods of active sediment transport have been determined for deep-water canyon-channel systems contributing to the southeastern Gulf of Santa Catalina and San Diego Trough since 40 ka using an extensive grid of high-resolution and deep-penetration seismic-reflection data. A regional seismic-reflection horizon (40 ka) has been correlated across the study area using radiocarbon age dates from the Mohole borehole and U.S. Geological Survey piston cores. This study focused on the submarine fans fed by the Oceanside, Carlsbad, and La Jolla Canyons, all of which head within the length of the Oceanside littoral cell. The Oceanside Canyon-channel system was active from 45 to 13 ka, and the Carlsbad system was active from 50 (or earlier) to 10 ka. The La Jolla system was active over two periods, from 50 (or earlier) to 40 ka, and from 13 ka to the present. One or more of these canyon-channel systems have been active regardless of sea level. During sea-level fluctuation, shelf width between the canyon head and the littoral zone is the primary control on canyonchannel system activity. Highstand fan deposition occurs when a majority of the sediment within the Oceanside littoral cell is intercepted by one of the canyon heads, currently La Jolla Canyon. Since 40 ka, the sedimentation rate on the La Jolla highstand fan has been >2 times the combined rates on the Oceanside and Carlsbad lowstand fans. [ABSTRACT FROM AUTHOR]

Abstract: Sinuous deep-water channels display a wide range of geometries and internal architectures. Most modern examples have been documented from large passive-margin fans, supplied by major rivers carrying huge volumes of dominantly fine-grained sediments, e.g. Amazon, Mississippi, Zaire, Bengal, Indus, Rhône and Nile Fans. However, similar examples have also been documented from tectonically active margins, e.g. Magdalena Fan. In most cases, modern sinuous channels comprise the core element of laterally extensive channel–levee systems that often aggrade significantly above a low-gradient (0.1–0.5°) fan surface; individual channels may extend downslope for 100s of kilometres. Typically, channels are subject to frequent avulsions, with only one channel active at any given time. Present highstand conditions have ensured that activity in many modern sinuous channels is much reduced due to the disconnect between fluvial feeder system and canyon head, and some have even been heavily modified or destroyed by major mass-transport deposits. Exceptions include Zaire Fan, where recent activity has provided useful insights into flow processes. The majority of detailed studies relating to sinuous channels in the subsurface originate from offshore west Africa, where channels typically occur within incisional (confined) slope–channel complexes and often represent the latter stages of channel complex fill. Both dominantly aggradational and laterally migrating styles are recognised, while modern seafloor channels in this region display a similar incisional character, e.g. Cap Timiris Canyon. Morphologic expression of sinuosity is harder to recognise at outcrop, but there are an increasing number of documented examples of lateral accretion deposits, representing point-bar growth, that are currently thought to be diagnostic of sinuous channel forms. Sinuous channel lateral migration, and point-bar growth, appears to be driven by sustained flow of fluvial-sourced (probably hyperpycnal) low-density turbidity currents, although there does appear to be variation in energy conditions, with some outcrop examples showing switches in erosive and depositional phases of activity. Previous studies have frequently focussed on the obvious gross planform morphologic similarities between fluvial and deep-water sinuous channels, e.g. nature of sinuosity, presence of point bars and cut-off loops. However, we suggest here that the differences between submarine and river channels are of greater significance, in terms of geometry, flow processes, migration style and deposit character. Sinuous deep-water channels typically form initially by a moderate amount of incision followed by rapid initial bend growth (associated with bypass of sediment). Channels that show significant aggradation then reach a point where there is a near cessation of planform movement (ossification), and growth is dominated by vertical aggradation. A new process model is proposed for this developmental sequence that synthesises observations and experiments that were previously paradoxical. [Copyright &y& Elsevier]

Experimental results presented here quantify how the thickness of turbidity currents affects the evolution of an aggrading subaqueous channel. Ten sediment-laden currents with identical initial conditions were released into a tank to determine how depositional flows interact with and modify a pre-existing channel form. Deposition was always greatest on the channel floor, systematically reducing channel depth and causing the ratio of initial current thickness to channel depth to increase with each flow. The ratio of longitudinal to lateral current velocity decreased exponentially with increasing relative current thickness. This change in lateral spreading demarcated regimes of channelized, quasi-channelized, and unconfined flow. Channelized currents have thicknesses that are less than 1.3 times local channel depth; unconfined currents are greater than five times channel depth; and quasi-channelized currents occur in between. The unconfined cases were consistent with prior experiments and theory defining the flow field for nonchannelized turbidity currents. Sedimentation patterns for even the thickest currents were influenced by subdued channel topography. [ABSTRACT FROM AUTHOR]

The Monterey East system is formed by large-scale sediment waves deposited as a result of flows stripped from the deeply incised Monterey fan valley (Monterey Channel) at the apex of the Shepard Meander. The system is dissected by a linear series of steps that take the form of scour-shaped depressions ranging from 3·5 to 4·5 km in width, 3 to 6 km in length and from 80 to 200 m in depth. These giant scours are aligned downstream from a breech in the levee on the southern side of the Shepard Meander. The floor of the breech is only 150 m above the floor of the Monterey fan valley but more than 100 m below the levee crests resulting in significant flow stripping. Numerical modeling suggests that the steps in the Monterey East system were created by Froude-supercritical turbidity currents stripped from the main flow in the Monterey channel itself. Froude-supercritical flow over an erodible bed can be subject to an instability that gives rise to the formation of cyclic steps, i.e. trains of upstream-migrating steps bounded upstream and downstream by hydraulic jumps in the flow above them. The flow that creates these steps may be net-erosional or net-depositional. In the former case it gives rise to trains of scours such as those in the Monterey East system, and in the latter case it gives rise to the familiar trains of upstream-migrating sediment waves commonly seen on submarine levees. The Monterey East system provides a unique opportunity to introduce the concept of cyclic steps in the submarine environment to study processes that might result in channel initiation on modern submarine fans. [ABSTRACT FROM AUTHOR]

How well do deep-sea sedimentary archives track erosion in upland sources, driven by climatic change or tectonic forcing? Located on the western edge of South Asian monsoon influence, the Indus River system is particularly sensitive to variations in monsoon rainfall and thus provides a unique opportunity to estimate the nature of sedimentary signal propagation (i.e., recognizable pulses of sediment) through a large river basin under different climatic conditions. In this review we examine the impact that changing monsoon rainfall has had on NW Himalayan landscapes and its foreland since the middle Miocene. Rates of erosion are linked to summer monsoon rains over tectonic timescales but patterns of erosion are more explicitly linked to tectonically-driven rock uplift. Positive feedback between rock uplift and orographic precipitation drives increased erosion and transport from the Lesser Himalaya since the Miocene. After 2 Ma, erosion increasingly shifts to the Inner Lesser Himalaya. As defined multiproxy evidence, strong monsoon rainfall intervals broadly result in increased erosion and faster sediment transport together with increased chemical weathering, although the latter is further linked with global temperature and to the magnitude of sediment recycling within the routing system. We estimate that during the Holocene, most sediment (67–89% of the total ~6000 km3 or 16.3 x 1012 t) delivered to the ocean was sourced either from direct bedrock erosion through channel incision linked to higher discharge or from remobilized, recycled glacial sediment initially deposited during the Last Glacial Maximum (LGM). Post-LGM sediment is primarily stored within the delta plain and shelf clinoform systems. Over the last 14 kyr, average mass delivery rates (936–1404 Mt/y) are much higher than pre-damming estimates (pre-1940s; 250–300 Mt/y). To reconcile observations with pre-damming estimates, high sediment supply rates, probably during strong monsoon intervals over the early Holocene, are required. Long-term rates were high (182-273 Mt/y) during a middle Miocene strong monsoon interval. Quaternary Indus submarine fan sedimentation is limited to sea-level lowstands, at which times shelf and delta sediment is eroded and reworked into deep water. As a result, and for at least the past 2–3 m.y., most sediment delivered to the Indus submarine fan was initially eroded from bedrock during strong summer monsoon intervals but deposited into the fan under weak monsoon intervals. During the most recent sea level lowstand, only ~24% of sediment deposited in the fan was derived from synchronous onshore bedrock erosion, with the remaining accounted for by recycled terrace, floodplain, and shelf clinoform system sediment. Variations in monsoon intensity over the last glacial cycle strongly impact the locus of onshore erosion, with increased relative Himalayan bedrock erosion during times of strong, wet monsoon intervals and increased Karakoram bedrock erosion during drier glacial intervals. [ABSTRACT FROM AUTHOR]

This study provides a detailed sedimentological, stratigraphic and depositional model for the lower Whakataki Formation. The fine-grained nature of the turbidite successions and common T bcde successions suggests deposition associated with medial to distal submarine fan deposits. However, the textural and compositional immaturity, combined with a high carbonaceous and carbonate content of the clastic sediments indicates a proximal detrital input. In the examined section of the lower Whakataki Formation the sedimentology and facies associations identified that the turbidite successions were deposited as dilute low-density turbidity currents that transported sediment down-slope, overflowing or bypassing upper- and mid-trench-slope basins into a structurally confined lower trench-slope basin. Flows entering the structurally confined basin were deflected to the north-northeast, producing palaeo-flow along the axis of the basin and represent deposition in the early stages of trench-slope basin development. Here, we provide a depositional model for a lower (immature) trench-slope basin and highlight that the application of the 'classical' submarine-fan model to all fine-grained turbidite deposits is not always appropriate. [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]

This study synthesizes 15 years (2001–2016) of detailed multibeam hydrographic mapping covering the entire 26,500 km2 of the Israeli Exclusive Economic Zone (EEZ). Multibeam data were collected on-board three research vessels across the continental shelf, slope, and the deep Levant basin; between water depths of about 15 m to 2100 m. Single-channel 3.5 kHz seismic reflection chirp profiles were collected simultaneously with the multibeam surveys in selected parts of the area. The new data enabled the first comprehensive quantitative seafloor morphological analysis of the slope and deep basin. Using GIS techniques on the high-resolution multibeam data, we analyze the spatial distribution and quantitatively describe the seafloor morphologies in detail. High-resolution chirp seismic profiles demonstrate the underlying shallow structure. Results indicate that the seabed comprises five main morphologies: folds, faults, sediment waves, deepwater channels, and sediment fan lobes. Quantitative morphological analysis and seismic data interpretation were used to derive field relations between these morphologies, which along with previously collected multi-channel seismic reflection data, suggest that a concentric fold geometry formed around the Nile outlet during the late Pliocene to early Pleistocene, as part of a general thin-skin radial salt-tectonic deformation above the Messinian mobile unit. This radial motion was accompanied by displacement along NNE-trending strike-slip faults in the basin, and an extensional component across E-W trending strike-slip faults along the Levant margin. While some of these displacements continue to deform the modern seabed (across Area A), others are covered by a wedge of Quaternary deposits, mainly in the northeastern part of the basin (Area B). Areas A and B also differ in grain size distribution, as indicated by backscatter analysis of the multibeam data. These observations divide the Israeli EEZ into two distinct areas: (Area A) Nile derived siliciclastic sediments transported directly into the deep basin via confined (forming meandering channels and overbank deposits) and unconfined flows (forming fans and lobes). The wedge consisting of Area B was fed by erosion products of the Nile outlet that were transported northwards along the continental shelf by seafloor currents of the Levant Jet System, and glided down the northern Levant continental slope as turbidity currents. This supply built at least seven sequences of Quaternary sediment waves that form upslope migrating cyclic steps. The complete data coverage and quantitative morphological analysis presented here introduce new spatial and temporal constraints that call for a reexamination of previous seabed sampling locations not accounting for detailed bathymetry, and to augment future seabed sampling efforts, understanding the sediment supply paths across the basin, and the geomorphological footprint of salt tectonics processes. Image 1 • New Multibeam bathymetry coverage of entire Israeli EEZ. • GIS quantitative seafloor geomorphology analysis. • Comprehensive representation and analyses of all morphological elements in the basin. • Field relations and Quaternary development of Eastern Mediterranean seafloor. • Two main sediment transport mechanisms into basin. [ABSTRACT FROM AUTHOR]

Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θ sht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γ mfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins. • Alternation of two different growth styles of lacustrine clinothems is identified. • Strongly aggradational clinothems suggest increased deep-water sediment delivery. • Strongly progradational clinothems suggest limited deep-water sediment delivery. • Climate-cycle controls clinothem patterns and associated deep-water processes. [ABSTRACT FROM AUTHOR]

• We present a morphometric and mass balance analysis of Martian valleys and fans. • Two different types of fan-shaped deposits are defined. • Type I fans: might have mainly deposited in subaerial conditions. • Type II fans: likely formed by typical deltaic sedimentation. Fan deposits located at the mouths of Martian valleys have been interpreted as indicators of wet conditions during Mars history. However, the processes, time and amount of water needed to carve the valleys and form the fans are still debated. Here we present a detailed morphometric and mass balance analysis of valleys and fan-shaped deposits using high resolution topography, which provides new insights into past depositional environments. Based on morphometric and volumetric measurements, we found that several Martian fans previously interpreted as deltas can be categorized into two main types. Type I fans are more numerous, relatively well preserved, are associated with smaller and less mature drainage networks and were deposited on steeper gradients. The balance between eroded and deposited materials indicates that this set of fans might have been formed mainly in subaerial settings by depositional processes other than typical deltaic sedimentation (e.g. alluvial, glacial, mass-wasting in general), since a significant loss of sediment during deposition did not occur (we obtained a volume ratio of eroded vs. deposited materials of approximately 1). Therefore, we propose that the identified Type I fans were not deposited in prevailing subaqueous deltaic settings, but mainly in subaerial conditions with perhaps sporadic presence of ephemeral bodies of standing water within the basins. In contrast, Type II fans are less abundant, highly eroded, were deposited on flatter areas and formed downstream of more mature drainage networks with longer, deeper and wider valleys. The mass balance for this set of fans clearly shows that considerable amounts of sediment were not retained in the fans, implying large offshore transport of sediment during their formation (eroded vs. deposited volume ratios between 3 and 10 are probable). This evidence supports a fluvio-deltaic origin for this class of fans, indicating the existence of paleolakes over substantial periods of time. Based on the collected morphometric measurements and mass balance modeling we conclude that only a small percentage of the fans (Type II fans correspond to ∼ 1 / 3 of the sampled areas) are consistent with the occurrence of favorable and durable conditions for life, i.e. long-lived integrated fluvial, deltaic and lacustrine environments. Whereas, the majority of fans might have been formed in subaerial settings with significant contributions of alternative processes besides fluvial transport and deposition thus not necessarily requiring the occurrence of extended epochs of clement climatic conditions. [ABSTRACT FROM AUTHOR]

Seabed sediment flows called turbidity currents form some of the largest sediment accumulations, deepest canyons and longest channel systems on Earth. Only rivers transport comparable sediment volumes over such large areas; but there are far fewer measurements from turbidity currents, ensuring they are much more poorly understood. Turbidity currents differ fundamentally from rivers, as turbidity currents are driven by the sediment that they suspend. Fast turbidity currents can pick up sediment, and self-accelerate (ignite); whilst slow flows deposit sediment and dissipate. Self-acceleration cannot continue indefinitely, and flows might reach a near-uniform state (autosuspension). Here we show how turbidity currents evolve using the first detailed measurements from multiple locations along their pathway, which come from Monterey Canyon offshore California. All flows initially ignite. Typically, initially-faster flows then achieve near-uniform velocities (autosuspension), whilst slower flows dissipate. Fractional increases in initial velocity favour much longer runout, and a new model explains this bifurcating behaviour. However, the only flow during less-stormy summer months is anomalous as it self-accelerated, which is perhaps due to erosion of surficial-mud layer mid-canyon. Turbidity current evolution is therefore highly sensitive to both initial velocities and seabed character. Summarising model for turbidity current behaviour in submarine canyons underlain by loose sand. Small increases in initial velocity cause major differences in subsequent flow velocities and runout distance, causing divergence in flow behaviour (purple, dark blue and light blue lines). However, flows can sometimes self-accelerate and ignite within the mid-canyon (green dotted line), due to changes in substrate strength and erodibility. There is a threshold initial transit velocity (red line) above which turbidity currents can autosuspend (purple line). • Turbidity currents form the largest sediment deposits and deepest canyons on Earth. • First detailed measurements from many sites along a turbidity current pathway. • Flow behaviour diverges; small increases in initial speed lead to longer runout. • After initial acceleration, fast flows reach a near-uniform state of autosuspension. • The only flow in summer is anomalous, perhaps due to erosion of surficial-mud layer. [ABSTRACT FROM AUTHOR]

• The main provenances of surface sediments in the lower Bengal Fan are the Himalayas and the Indian river systems. • The average contribution of the Himalayas is 55% and that of the Indian river system is 45%. • Contributions from the Himalayas gradually decreases from southeast to northwest, while the opposite trend occurred for the Indian river systems. • The material supply from the two provenances is dominated by different monsoonal currents. The Bengal Fan, the largest submarine fan in the world, receives a large amount of terrestrial material from the Himalayas and the Indian Peninsula, making it an ideal area for studying land-sea interactions in different time scales. Using the major and trace element compositions of 98 surface sediment samples from the lower Bengal Fan, we identified the provenances of the sediments, calculated the relative contributions of each provenance, and further assessed their controlling factors. The statistic results of the major and trace elements confirm that terrigenous materials comprise the majority on the sediment and that the study area can be divided into three depositional provinces. The main sources of sediments are the Himalayas and Indian river systems, which can be distinguished in the Fe/Al-K/Al scatter diagram. Based on calculation results of a two end-member mixing model, the relative contributions of the Himalayas and the Indian rivers are 55% and 45%, respectively. However, the spatial distributions of sediments from these two sources in the three provinces exhibit a large variation. The Himalayan contributions decrease from 63% in province I (southeast part of the study area) to 53% in province II (central part of the study area) and 45% in province III (northwest part of the study area). Correspondingly, the contributions of Indian rivers increase from province I through province III. During the high sea levels of modern time, seasonal monsoonal currents play a key role in controlling the sediments transport from South Asia continent to the lower fan. [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]

In the southern Central Andes of Argentina, between 34° and 41°S, the Neuquén Group records Upper Cretaceous nonmarine deposits that provide direct evidence of synorogenic sedimentation associated with the development of an early foreland basin. The configuration of this basin and its relation to the Malargüe fold and thrust belt are analyzed in this article using sedimentological analyses, U-Pb dating of detrital zircons and seismic and surface structural data. The remnant wedge-top depozone preserved in the Argentinian Andean slope exposes sedimentological information that indicates that braided fluvial systems, which may have formed part of broader fluvial fans, transported and deposited the sediments from an extensive relief area located in the present western Andean slope to the Chilean Coastal Range zones. The eastern border of this depositional system was defined by a basement uplift, interpreted either as a forebulge or an incipient broken foreland system, from where gravel-sandy braided river systems fed the foredeep depozone transporting and depositing sediments from the exposed cratonic area in the east. Consequently, an initial underfilled foreland basin was configured. The evolution of this early basin and the areas of sediment supply were controlled by the eastern expansion of the Malargüe fold and thrust belt, through the development of thick-skinned anticlines, which progressively fragmented the wedge-top zone. The evidence collected suggests that the Late Cretaceous uplift was a major tectonic event that exposed the entire Mesozoic column of the Neuquén basin up to the Permian-Triassic basement, which implies more than 2,500 m of denudation at that time. U-Pb determinations yielded a maximum depositional age of ca. 91 ± 2 Ma (Late Turonian), which suggests either non-deposition or cannibalization of a sedimentary interval of ca. 10 My at 36°S, when compared to the age of the basal sections of the Neuquén Group at other latitudes. Unlabelled Image • The Neuquén Group was initially deposited in an underfilled foreland basin. • Western deposits correspond to the wedge top of an evolving fold and thrust belt. • Detrital components partly come from mountain systems located on the Chilean Andes. • The Neuquén Group registers an unroofing sequence next to the sierra Azul anticline. • Late Cretaceous uplift exposed the entire Mesozoic column of the Neuquén basin. [ABSTRACT FROM AUTHOR]