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Enhanced sedimentation at glacial margins can produce submarine megaslides (>10,000 km3). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Slope failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). With accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was triggered by a major sediment influx at the onset of the MPT, when glacial‐interglacial cycles shifted from 41 to 100 Kyr. The absence of repeat megaslides may reflect a changing balance between seismic strengthening and sediment flux, where later sedimentation driven by cross‐shelf ice streams results in thin, fluidized, non‐cohesive slides. Continued accretion of the Surveyor Fan and megaslide also reduces critical wedge taper, further inhibiting major failure. Plain Language Summary: Sediment flux at glacial margins can produce submarine slides >10,000 km3 in size (megaslides). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). Due to accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, but with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was caused by the initial major sediment flux at the onset of the MPT, and that afterward only fluidized, thin, and non‐cohesive slides occurred. This is due to changing balance between seismic strengthening and sediment flux, and accretion of the Surveyor Fan and megaslide which reduces the critical wedge taper inhibiting major failure. Key Points: World's Fifth largest mapped megaslide documented beneath Surveyor Fan Gulf of AlaskaTiming of slope failure linked to onset of mid‐Pleistocene glacial intensificationAbsence of later failures due to changing balance of sediment flux/seismic strengthening and negative feedbacks from critical wedge processes [ABSTRACT FROM AUTHOR]

Tectonics play a significant role in shaping the morphology of submarine canyons, which form essential links in source-to-sink (S2S) systems. It is difficult, however, to investigate the resulting morphodynamics over the long term. For this purpose, we propose a novel experimental approach that can generate submarine canyons and hanging-wall fans on continuously evolving active faults. We utilize morphometric analysis and morphodynamic models to understand the response of these systems to fault slip rate (Vr) and inflow discharge (Q). Our research reveals several key findings. Firstly, the fault slip rate controls the merging speed of submarine canyons and hanging-wall fans, which in turn affects their quantity and spacing. Additionally, the long profile shapes of submarine canyons and hanging-wall fans can be decoupled into a gravity-dominated breaching process and an underflow-dominated diffusion process, which can be described using a constant-slope relationship and a morphodynamic diffusion model, respectively. Furthermore, both experimental and simulated submarine canyon–hanging-wall fan long profiles exhibit strong self-similarity, indicating that the long profiles are scale independent. The Hack's scaling relationship established through morphometric analyses serves as an important link between different scales in S2S systems, bridging laboratory-scale data to field-scale data and submarine-to-terrestrial relationships. Lastly, for deep-water sedimentary systems, we propose an empirical formula to estimate fan volume using canyon length, and the data from 26 worldwide S2S systems utilized for comparison show a strong agreement. Our geomorphic experiments provide a novel perspective for better understanding of the influence of tectonics on deep-water sedimentary processes. The scaling relationships and empirical formulas we have established aim to assist in estimating volume information that is difficult to obtain during long-term landscape evolution processes. [ABSTRACT FROM AUTHOR]

Continental margins that exhibit high terrigenous input are generally located near deltas that are capable of transporting large quantities of sediments into the basin. However, in rare cases, high terrigenous sedimentation occurs in regions deprived of major riverine systems where the sedimentary pathway is enigmatic. One such case is the Neogene of the Pelotas Basin of Brazil and Uruguay, adjacent to the La Plata River mouth. Since the Miocene, anomalous sedimentation formed a giant progradational wedge, the Rio Grande Cone, one of the largest submarine fan-like features on Earth. To understand the Neogene evolution of the margin and the origins of the Rio Grande Cone, here we present a seismic-stratigraphic framework based on well-logs and 2D seismic data. Three depositional environments are identified: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand deposits on the mud-dominated shelf; (2) on the slope, sediment instability resulted in structural deformation and multiple phases of mass transport deposition and (3) on the lower slope and basin floor, large contourite drifts formed by sediment reworking. We classify the Rio Grande Cone as a megaslide complex, due to its depositional and structural setting. Local deltaic systems were active on the shelf in the Neogene, but the limited size of their paleo-drainage systems in comparison to the volume of sedimentation in the margin suggests that an additional sedimentary pathway existed. In this sense, the demise of an epicontinental sea over the La Plata Basin during the Neogene likely enabled the input of large volumes of fine sediments into the margin, via the La Plata plume water. We suggest that the desiccation of this epicontinental sea and the intensification of ocean currents since the middle Miocene explains the anomalous Neogene terrigenous influx into the SW Atlantic margin. [ABSTRACT FROM AUTHOR]

This study provides a sedimentological, stratigraphic and palaeocurrent investigation of Upper Eocene to Lower Oligocene deep-sea fan deposits found in the central part of the Pindos foreland basin in western Greece. According to facies analysis, the examined succession at Amfilochia area has 13 sedimentary facies and 10 facies and sub-facies associations. Depositional elements include abyssal plain pelagics, outer fan, inner fan, and slope deposits. Outer fan sediments are classified as lobe-axis, lobe-off-axis, lobe-fringe, and distant lobe-fringe deposits, while inner fan sediments are classified as channel-fill, crevasse-splay, internal and external levee deposits. The stratigraphic study shows an upward shift from abyssal plain pelagics to outer, inner fan, and finally slope deposits, implying submarine fan system progradation and progressive infilling of a deep-water sediment depocentre. The sediments were deposited in the foredeep of the Pindos foreland system and correspond to the system's underfilled stage, when sedimentation was unable to exceed the accommodation provided by lithospheric flexure. They point to deposition near the onset of the Pindos orogen, after the closure of the Pindos basin because of the collision of the Apulian with the Pelagonian microplate during the Cretaceous-Palaeogene period. Palaeocurrent data from sole marks show bipolar directions associated with two distinct spreading sub-marine fan deposits. As a result, the study region was split into Upper (major SE-direction flow) and Lower (major NW-direction flow) parts, indicating that axial flows were predominant during sediment deposition. However, as the deposition of the elements continued, the progradation of both systems constrained the space accommodation because of the increased basin sediment supply and forced an increase in the degree of basin confinement that changed the compensational to aggradational stacking pattern. The goals of this research are to develop an updated facies model for these deep-sea fans as well as a robust correlation framework for the various stratigraphic units in the central Pindos foreland basin. This research also connects the stratigraphic development of deep-sea fan deposits to the evolutionary phases of the Pindos foreland system, providing fresh insights into the palaeogeographic circumstances in the Pindos foreland basin. [ABSTRACT FROM AUTHOR]

This investigation documents that the Rugged Terrain Unit, the Stimson formation, and the Greenheugh sandstone were deposited in a 1200 m-deep lake that formed after the emergence of Mt. Sharp in Gale crater, Mars, nearly 4 billion years ago. In fact, the Curiosity rover traversed on a surface that once was the bottom of this lake and systematically examined the strata that were deposited in its deepest waters on the crater floor to layers that formed along its shoreline on Mt. Sharp. This provided a rare opportunity to document the evolution of one aqueous episode from its inception to its desiccation and to determine the warming mechanism that caused it. Deep water lacustrine siltstones directly overlie conglomerates that were deposited by mega floods on the crater floor. This indicates that the inception phase of the lake was sudden and took place when flood waters poured into the crater. The lake expanded quickly and its shoreline moved up the slope of Mt. Sharp during the lake-level rise phase and deposited a layer of sandstone with large cross beds under the influence of powerful storm waves. The lake-level highstand phase was dominated by strong bottom currents that transported sediments downhill and deposited one of the most distinctive sedimentological features in Gale crater: a layer of sandstone with a 3 km-long field of meter-high subaqueous antidunes (the Washboard) on Mt. Sharp. Bottom current continued downhill and deposited sandstone and siltstone on the foothills of Mt. Sharp and on the crater floor, respectively. The lake-level fall phase caused major erosion of lacustrine strata that resulted in their patchy distribution on Mt. Sharp. Eroded sediments were then transported to deep waters by gravity flows and were re-deposited as conglomerate and sandstone in subaqueous channels and in debris flow fans. The desiccation phase took place in calm waters of the lake. The aqueous episode we investigated was vigorous but short-lived. Its characteristics as determined by our sedimentological study matches those predicted by an asteroid impact. This suggests that the heat generated by an impact transformed Mars into a warm, wet, and turbulent planet. It resulted in planet-wide torrential rain, giant floods on land, powerful storms in the atmosphere, and strong waves in lakes. The absence of age dates prevents the determination of how long the lake existed. Speculative rates of lake-level change suggest that the lake could have lasted for a period ranging from 16 to 240 Ky. [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]

The Middle Jurassic–Early Cretaceous evolution of the Neuquén Basin is traditionally attributed to a long phase of thermal subsidence. However, recent works have challenged this model. In view of this, we study the Late Jurassic Tordillo Formation, a non‐marine depositional unit that marks a shift to regional regression across the basin. Previous studies propose different causes for this regression, including the growth of the magmatic arc in the west, uplift in the south or extension in the north. We studied the Tordillo Formation in sections located at an intermediate position in the Neuquén Basin, in order to understand the tectonic processes active during sedimentation. We present evidence of normal faulting within the Tordillo Formation and the base of the overlying Vaca Muerta Formation. Some of these faults can be attributed as syndepositional. We characterize the Tordillo Formation as part of a distal fan‐playa lake depositional system with a contemporaneous western magmatic arc as the main source of sediment. When compared to the Late Triassic–Early Jurassic NE to NNE‐oriented rifting, which marks the opening of the Neuquén Basin, the Late Jurassic extension shows a switch in stress orientation; the latter is orthogonal to the north‐trending subduction zone. We interpret this change as a renewed phase of back‐arc extension induced by slab rollback along with minor distributed intraplate extension prior to opening of the South Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Hemipelagites are widespread fine‐grained sediments found from shelf margin to deep‐water environments, and they are considered to have been formed as background sedimentation by vertical settling and slow lateral advection of clastic and biogenic fine‐grained particles. Downflow variation in hemipelagic sedimentation, however, is not yet clearly understood, and was investigated in the lower Pleistocene Kiwada and Takamizo formations in the Kazusa forearc basin on the Boso Peninsula, Japan. Mapping of three tephra key beds enabled detailed correlation of two hemipelagite beds over a distance of ca 30 km from shelf‐margin to basin‐plain environments. The sedimentation rates decreased gradually in the downslope direction, but increased locally in response to turbidite sedimentation. This downslope variation indicates that hemipelagic sedimentation is not necessarily constant and varies in response to progradation and retrogradation of deep‐water depositional systems, as well as additional input of fine‐grained sediments from turbidity currents. In contrast, the grain size, magnetic susceptibility, clay‐mineral composition, total organic carbon contents relative to total nitrogen contents (carbon/nitrogen), and δ13C values of organic carbon do not exhibit distinct downslope variation. This downslope consistency indicates that hemipelagites document temporal perturbations of geological and palaeoclimatic conditions in hinterlands, regardless of spatial and temporal variations in deep‐water depositional environments. The concentrations of total organic carbon, total nitrogen and five biomarkers were lower values in turbiditic mudstones and hemipelagites that formed above a turbidite bed than in those of the other hemipelagites. This variation suggests that an additional supply of fine‐grained sediments from turbidity currents likely diluted the organic matter in the hemipelagites. In addition, hemipelagites for which deposition was affected by turbidity currents exhibit slightly lower δ13C values, and may also document an additional contribution of terrestrial organic matter from turbidity currents. [ABSTRACT FROM AUTHOR]

Coarse‐grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin, China. The insufficient understanding of their sedimentary processes, depositional patterns, and controlling factors restricts efficient exploration and development. Coarse‐grained subaqueous fans in the Yong'an area, Dongying Depression, are investigated in this study. These fans include nearshore subaqueous fans, and sublacustrine fans, and their sedimentary processes, depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology. Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence. Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction. While the topography was gentle, sublacustrine fans did not develop. During the late weak tectonic activity stage, late sublacustrine fans developed with multiple stages superimposed. Frequent fault activity and related earthquakes steepened the basin margin, and the boundary fault slopes were 25.9°–34°. During the early–middle deposition stage, hyperpycnal flows triggered by outburst floods developed. During the late deposition stage, with weak tectonic activity, seasonal floods triggered hyperpycnal flows, and hybrid event beds developed distally. [ABSTRACT FROM AUTHOR]

Alluvial fans are found across a range of climates and are built from a combination of fluvial and debris flow processes. Correct identification of process is critical to reconstructing the climate and water histories of alluvial fans on Earth and Mars. Theory and data from subaerial Earth fans are often used to estimate paleoflow discharges and sediment fluxes for martian fans; however, most terrestrial work has been conducted on fans that are in hot, dry climates with runoff sourced from rainfall. This differs from the prevailing interpretation that martian fans were sourced from snowmelt under warming periglacial conditions. To characterize processes and rates of periglacial fan formation, we conducted a field-based study of the Black Mountain alluvial fan in the Aklavik Range, Canada. We observed active fluvial bedload transport as well as several small debris flows that had initiated from ice-filled gullies. Following a runoff event of ~0.005 mm/hr to ~0.2 mm/hr across the fan, we estimated sediment fluxes of ~0.04 m3/hr. Under bankfull conditions, we estimated runoff rates between ~0.01 mm/hr to ~14 mm/hr and corresponding sediment fluxes of ~0.3 m3/hr to ~550 m3/hr. This suggests that moderate flow events, well below the maximum runoff production rates suggested for Mars, are capable of entraining and transporting appreciable amounts of sediment by fluvial processes. However, sedimentological and geomorphological observations suggest that ~67% of the fan was deposited fluvially; the remainder was deposited by mass flows. Our results emphasize the need to take care in interpreting martian sedimentary processes and climate from fan surface morphology alone. [ABSTRACT FROM AUTHOR]

Submarine depressions are common features on the eastern Bahamian seafloor but the genesis of the deepest ones (>4000 m in water depth) is not well understood. We conducted a morphometric analysis and compared them to a worldwide database of rounded depressions, whatever their genesis is. The deep Bahamian depressions are large elongated structures, among the largest on Earth, with a width greater than 1000 m and a depth sometimes greater than 200 m. They extend at the toe of the Blake Bahama Escarpment (BBE), one of the tallest escarpments on Earth. Some of them align parallel to the BBE. Other depressions align along large submarine canyon axes. When aligned along canyon axes, the depressions closest to the canyon head are flanked by a topographic high interpreted as a slope-break deposit, i.e., sediment deposited after flow expansion following a hydraulic jump. Turbidity currents in the carbonate canyon system are not permanent processes, but are rather triggered during sea-level highstands when the carbonate platform is flooded. In addition, some depressions are not located in canyon axes. Consequently, the size and location of the depressions are not likely explained by a simple plunge pool mechanical erosion. Rather, our data suggest that all depressions could be initiated by giant karstic dissolution structures (dolines or sinkholes). Under interpretation, those located in canyon axes are sporadically refreshed by carbonate-laden turbidity currents. The height of the outsized chutes marking the crossing of the BBE by the canyon mouth generates a hydraulic jump allowing sediment deposition toward the bottom of the depression. Large depressions observed at this location in the Bahamas were the result of an initial dissolution phase related to retreat of the BBE and the more recent sediment-laden flow activity. The depressions orientated along canyon axes facilitated the regressive erosion that formed the canyons. At present, the depressions located at canyon mouths act as regular plunge pools. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of water level oscillation and sediment supply volume on shallow‐water delta development by means of a flume experiment. The experiment simulated the natural water level by dividing a cycle of sediment period into four parts: the draught period, the flood period (FP), the interflood period in a falling limb (IPF) and the interflood period in a rising limb (IPR). During the FP, flooding broke former channels and a large amount of sediments were evenly unloaded at the surface of lobes. Erosion often appeared at the beginning of the IPF and was dominant at low stand. Most sediments were concentrated in incised valleys and unloaded at the channel mouth to form a new lobe during the falling limb. Erosional channels and lobes were broken at the IPR. Sediments homogeneously covered the surface of lobes and few new lobes appeared during the period. Different sediment supplies influenced the characteristics of incised valley and channel style. Low sediment supply to the delta was strongly influenced by water level change, while high sediment supply was mainly affected by fluvial processes. Based on the flow sand content of water, channels can be classified into four types: (a) narrow and deep multiple channels, (b) narrow and shallow branch channels, (c) broad and shallow main channels, and (d) broad and deep stable channels. Their width‐to‐depth ratios are 1.1–3.5, 5.1–12.9, 7.3–20.2, 2.6–4.6, respectively. Most mouth bars were initially formed but then broken by water level oscillation and channel bifurcation. The preserved mouth bars were well preserved at the far end of lobes, where they entered the low‐energy environment. [ABSTRACT FROM AUTHOR]

Turbidity currents commonly bypass sediment in submarine channels on the continental slope, and deposit sediment lobes farther down-dip on the flat and unconfined abyssal plain. Seafloor and outcrop data have shown that the transition from bypass to deposition usually occurs over complex zones referred to as channel–lobe transition zones (CLTZs). Recognition of these zones in cores and outcrop remains challenging due to a lack of characteristic sedimentary facies and structures. This paper focuses on Unit E of the Permian Fort Brown Formation in the Karoo Basin, South Africa, in the Slagtersfontein outcrop complex, which has previously been interpreted as a CLTZ. This study integrates thin-section micrographs, sedimentary facies, bed-set and stratigraphic architecture, and palaeoflow directions to achieve a multiscale analysis of CLTZ features. A novel process-based facies scheme is developed to evaluate deposits in terms of the depositional or erosional tendencies of the flows that formed them. This scheme allows bypass to be distinguished from depositional zones by the spatial distribution of certain sediment facies. Areas of net sediment bypass were predominantly marked by erosive sediment facies and a larger variability in palaeoflow direction while depositional areas showed a lower variability in palaeoflow directions. Metre-scale structures in the bypass-dominated area reveal seafloor erosion and scour formation. Field relations suggest the presence of a ∼500 m long mega-scour in the CLTZ. The characteristic structures documented here are applicable for identifying CLTZs in sparse datasets such as outcrops with limited palaeogeographical context and sediment cores obtained from subsurface systems. [ABSTRACT FROM AUTHOR]

This study integrates provenance and statistical data, along with published sedimentological results, applied on the Lower Oligocene submarine‐fan deposits in Pindos foreland basin. Twelve outcrops were analysed using conglomerate clast composition, petrographic and statistical analysis and this integration suggests that the studied deposits were sourced by the Pindos Orogen. Conglomerate clast composition analysis suggests that the studied deposits contain mainly limestone clasts, followed by sandstone and chert clasts. This conclusion is further supported by the petrographic and cathodoluminescence analyses that have been conducted on the conglomerate matrix and, additionally, suggest the influence of a low‐grade metamorphic source. Potential source rock candidates in the Pindos Orogen that provided the detritus in the succession are represented by the Mesozoic carbonates (limestone and chert), the Cenozoic transitional (mixed carbonate and siliciclastic) and the Cenozoic clastic submarine‐fan deposits (sandstone). The rock units of Pelagonian zone likely represent the low‐grade metamorphic source rock. The principal component and cluster analysis of clast lithologies suggest the existence of three compositional clusters, with the first one being controlled by black chert clasts, the second one by sandstone clasts and the third one by limestone and red chert clasts. The upward increase of chert and lithic fragment abundances is ascribed to the progressive unroofing of the Pindos orogenic source regions. This study utilizes the Pindos foreland basin as an example to unravel the contribution of orogenic processes on sedimentary provenance of the adjacent pro‐foreland basins. Furthermore, this study highlights the advantage of implementing a multi‐faceted approach, including statistical treatment in sedimentary provenance. [ABSTRACT FROM AUTHOR]

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins. • Mixed siliciclastic-carbonate-tuffaceous deposits were preserved in the rift Luxi sag. • Moderate siliciclastic influx and volcanic eruption provide the material for mixed deposits. • Tractional currents and gravity flows are favorable for formation of mixed sedimentation. • Relatively high paleosalinity and rising lake-level are benefit for carbonate production. • Three stages of depositional models of mixed sedimentation in a rift sag were proposed. [ABSTRACT FROM AUTHOR]

Holocene inner shelf mud wedges are important paleoenvironmental archives because they typically contain continuous and extensive sedimentary sequences that can document past changes in sedimentary processes at very high temporal resolution. Here we investigate the fine-scale, seismic patterns of the Late Holocene Adriatic Mud Wedge (AMW), along the western Adriatic margin, to understand the processes of river-sea interactions and their effects on sediments distribution. While analyzing high-resolution seismic reflection profiles, we documented variations in the architectural stratal stacking patterns of the AMW, largely related to short-term fluctuations in sediment supply during the last sea level high (ca. 6000 years BP). Analysis of high-resolution seismic profiles revealed that the AMW consists of five clinothems (referred to here as "seismic units" SU1 to SU5) that were roughly dated by calibration with the continuous recovery well PRAD2-4. Each seismic unit is bounded by minor floodplains (H1 to H5), reflecting periods of relative sediment starvation at the margin. Our analysis provides an interpretative tool to differentiate the fluvial contribution of marine remodeling processes during the AMW evolution on millennium to centennial timescales. In addition, small-scale geomorphic features such as erosion surfaces, small distributary channels and terminal lobes were identified to provide information on heterogeneities that may impact an unconventional fine-grained delta reservoir, both in terms of continuity and overall hydrocarbon potential. • We document the Late Holocene evolution of the AMW between Conero Promontory and Gargano Promontory. • The first internal subdivision of the AMW at the intra-clinothem scale for almost its entire extent is presented and analyzed. • Evidence of short-lived phases of advancing and retreat of the AMW at the intra-clinothem scale have been observed. • The competition between sediments from rivers and the redistribution by oceanographic processes sees a progressive increase of the latter over time. • New evidence has enlightened the presence of small-scale, shallow water distributary channels across the AMW. [ABSTRACT FROM AUTHOR]

Submarine fans play a crucial role in understanding deep-sea sedimentary processes, establishing source-to-sink linkages, and identifying deep-water hydrocarbon reservoirs. Various types of submarine fans have been documented. Here we present findings on the Guangya submarine fan in the Southwest subbasin (SWSB) of the South China Sea (SCS), by analyzing multibeam bathymetric and two-dimensional multichannel seismic data. Bathymetric data reveal that the Guangya fan, covering an area of ~22,500 km2, comprises seven leveed channels, leading to a large composite lobe off the channel mouths. Different from typical submarine fans, the Guangya fan exhibits an elongated shape, extending longitudinally from the shelf edge through the slope to the abyssal plain, while laterally confined within a trough-like morphology in the southwestern tip of the SWSB and beyond. Lacking a typical feeding canyon, the fan appears to be self-fed by the leveed channels that serve as the primary depositional element. In contrast to the radial channel pattern in typical fans, the channels within the Guangya fan form a unique braid to dendritic pattern, genetically linked to channel merging and intersecting effects. Long wavelength and low wave height cyclic steps are identified, highlighting the occurrence of energetic supercritical turbidity currents. Seismic stratigraphic analysis shows that the Guangya fan primarily consists of high-amplitude reflections, indicating its coarser-grained or sandy turbidite-dominated nature. The fan has been evolved since the Pliocene, and mainly comprises depositional elements including channel fills, levees, lobes, and mass transport deposits. The specific tectonic context at the convergence of the conjugate margins, bounding the funnel-shaped SWSB, significantly influences the development of the Guangya fan. The Guangya fan could be originated from a shelf-edge staging area predominantly fed by the Mekong River during sea-level lowstands. • We report a unique elongated channelized submarine fan in the South China Sea. • The fan extends from the shelf edge to the abyssal plain. • The fan appears to be self-fed by dendritic submarine channels. • Tectonics plays a key role in the development of the fan. [ABSTRACT FROM AUTHOR]

• Geological and cosmogenic data from Corsica reveal two-stage river capture events. • Clast lithologies demonstrate a progressive reduction of the Paleo-Ostriconi basin. • River capture led to the formation of a large Pliocene-Quaternary submarine fan. • Focused erosion can affect sites of former river capture after millions of years. • Corsica is still adapting to the disequilibrium caused by uplift of Alpine Corsica. Quantitative analysis of fluvial topography and sediment yield changes are often independently used to detect major river capture events and episodes of drainage reorganization. Here we use a unique set of geological and in situ 10Be cosmogenic data from Corsica, Western Mediterranean, to provide evidence of major river capture events affecting the former Paleo-Ostriconi river catchment during the Pliocene, and to illustrate how the landscape of Corsica is still reacting to the disequilibrium caused by the late Miocene uplift of Alpine Corsica. We found that ∼1280 km2 of basin area originally draining towards the Ligurian Sea were abruptly connected to the Tyrrhenian Sea by the capturing Tavignano and Golo rivers, which led to the formation of a large Pliocene-Quaternary submarine fan offshore the Tyrrhenian coast. The increased sediment yield towards the Tyrrhenian margin after river capture in the Pliocene was three times greater than the average sediment yield in the same source-to-sink system during the Holocene (410±100 t·km−2· a −1 vs ∼131±8 t·km−2· a −1) and greater magnitude than any subsequent peaks in sediment yield during late Pleistocene glaciations. 10Be-derived denudation rates reveal that focused erosion still affects retreating knickpoints near the sites of former river capture in central Corsica, suggesting persistence of landscape disequilibrium for several millions of years. Our results demonstrate the potentially large impact of river capture on the stratigraphic record and highlight the importance of full consideration of landscape response times to onshore disturbances for any reliable interpretation of the offshore sedimentary archive. [Display omitted] [ABSTRACT FROM AUTHOR]

Deep‐water stratigraphic successions from syn‐ to post‐rift stages are an archive of evolving physiographic configurations, and can record axial and transverse sedimentary sources. The healing of topography decreases the influence of syn‐rift structures on sedimentation patterns and transport processes over time, which leads to a long‐term transition from dominantly axial to transverse dispersal patterns. The Halten and Dønna terraces, offshore mid‐Norway, comprise a series of rift‐related sub‐basins established during the Jurassic, which were infilled with sediments during the Cretaceous. The Cretaceous Lysing Formation developed as slope‐ and basin‐floor fans within a series of weakly confined post‐rift sub‐basins with some shallow marine deposits interpreted on the basin margins. A deep‐water setting is supported by seismic interpretation, and bed type and architectural element analysis in all cored and uncored wells in the area. We document that an axial submarine fan system was active throughout the post‐rift stage due to subtle inherited topography from syn‐rift structures, which interacted with locally sourced transverse sediment sources. This led to a complicated stratigraphic architecture, with lobe fringe deposits of the axial fan system juxtaposed with channel‐fills and channel‐lobe transition zone deposits of transverse systems. The refined palaeogeographic reconstruction of the Lysing Formation illustrates how subtle topography can impact sediment routing patterns many millions of years after the end of rifting and can be used for palaeoenvironmental interpretations in other post‐rift settings. [ABSTRACT FROM AUTHOR]

Recent advances in clastic and carbonate sedimentology have seen a resurgence of interest in the dynamics of bedform development under supercritical flow conditions, that is under unidirectional currents at Froude numbers ( I Fr i ) values higher than unity. Enhanced climate seasonality in the region during the Early Eocene Climatic Optimum triggered sediment-laden, ephemeral fluvial discharge events that are recorded in stratal signatures of transcritical to supercritical flow stages in proximal to medial subaqueous portions of lake-margin deltas, where greater accommodation allowed for better preservation potential. This dual-flow model of relatively infrequent cyclic-step development and more common antidunal aggradation draping the cyclic-step morphology sheds new light on the dynamics of glaciofluvial delta slopes and on the interpretation of spatial facies transitions in subaqueous supercritical-flow deposits. A modern environmental analogue for the Eocene deposits of Utah and their (palaeo)climatic implications is documented by Tan & Plink-Björklund (2021), who discuss the sedimentology of dry river-bed deposits and its inferred relationships to the architecture of subsurface deposits in a linked fluvial to shallow-lacustrine clastic system from Lake Daihai, Inner Mongolia (northern China), combining observations from shallow trenched and ground-penetrating radar. [Extracted from the article]

Research on the depositional record of submarine fans and related turbidite systems has highlighted the importance of channel, lobe and levée–overbank architectural elements as fundamental building blocks. However, many of the characteristics and processes of deposits left by flows traversing those fans remain elusive, because flows seem to be able to go unconfined for long distances. Offshore southern California (USA), the La Jolla Canyon decreases in relief to become an approximately U‐shaped channel across the basin floor of the San Diego Trough. The La Jolla Channel gradually loses confinement and transitions to a network of scours, some of which align to form incipient channels, and fields of bedforms. High‐resolution seafloor topography, CHIRP seismic‐reflection data, sediment cores and hydrodynamic flow analysis are used to explore these features. The focus is on two regions of bedforms: (i) a field of net‐depositional, concentric bedforms across the eastern levée–overbank upstream from the terminus of the La Jolla Channel; and (ii) a linear train of more erosional bedforms approximating an incipient channel adjacent to the present mouth of the La Jolla Channel. These bedforms are interpreted to be among a class of upper‐flow‐regime bedforms called cyclic steps, which were formed by densimetric Froude supercritical turbidity currents that spilled out of the present La Jolla Channel. The high‐resolution data for the La Jolla Fan provide valuable insights into the characteristics of supercritical bedforms likely common to distal submarine fans, as well as on sedimentary processes likely important for submarine fan growth into sedimentary basins. In particular, the pattern of evolution of the La Jolla Fan suggests that cyclic steps with wavelengths on the order of tens of metres to a few hundreds of metres could be fundamentally important for the evolution of the distal submarine fans with relatively low‐relief main channels. [ABSTRACT FROM AUTHOR]

Martian gullies are surface features, typically composed of an alcove, a channel and a depositional apron. They have been extensively studied since their first observations in the 2000s and were initially attributed to the action of liquid water. Later studies highlighted that their activity is spatially and temporally correlated with the seasonal presence of surface CO 2 ice, suggesting a link between seasonal frost and gully activity. However, the exact mechanisms leading to gully formation are still under debate. Establishing whether or not gullies are formed by liquid water has important implications for Mars recent climate and habitability. Here, we study the evolution of seasonal frost and its connection to gully activity in Sisyphi Cavi, located in the southern circumpolar region (68°S - 74°S; 345°E − 5°E). The high latitude of this site allows for detailed temporal monitoring, owing to the high frequency imaging by spacecraft in polar orbits, largely unavailable for other martian gullies, hence this site has the potential to reveal new insights on gullies in general. In particular, we used repeat images from MRO HiRISE (Mars Reconnaissance Orbiter, High Resolution Imaging Science Experiment) and TGO CaSSIS (Trace Gas Orbiter, Colour and Stereo Surface Imaging System). Our findings show that the general timing and characteristics of the defrosting patterns in Sisyphi Cavi follow seasonal patterns that are consistent from year to year. The timing of the start of defrosting and its temporal evolution are controlled by the overall orientation of the host hillslope, with equator-facing slopes defrosting before pole-facing ones and the steepest pole-facing slopes defrosting last. Gully alcoves defrost before channels and aprons located on the same hillslope independent of the orientation of the hillslope likely because the aprons have a lower thermal inertia than the alcoves that counteracts the orientation effect, which on pole-facing slopes would mean the alcoves should defrost last. We observe the presence of seasonal and ephemeral dark spots and flows which are interpreted to be a result of sediment deposition on top of the seasonal ice deposits, triggered by basal sublimation. Our observations suggest that the appearance of dark spots and dark flows can be spatially correlated with surface roughness, including presence of boulders, contrasts in material types, irregular lobes/levees and braiding caused by gully activity, and therefore could be used to help detect recently active gullies on Mars in areas with seasonal frost without the need of repeat imaging. Finally, we propose that presently observed gully activity in Sisyphi Cavi is driven by defrosted material flowing on to a frosted apron. We infer that the presence of a frosted apron could be common precursor for this type gully activity. We note that this activity only involves the mobilisation of loose materials and we have not observed any erosion of the wall rock present in Sisyphi Cavi. [Display omitted] • We perform detailed monitoring of gullies and seasonal frosts in Sisyphi Cavi. • Gully alcoves defrost before their aprons even on pole-facing slopes. • Early alcove defrosting is likely related to their higher thermal inertia. • Frosted aprons are common on Mars and could be a precursor to gully activity. • Dark spots/flows found on rough terrain may highlight recently active gullies. [ABSTRACT FROM AUTHOR]

The fringe of fine‐grained deep‐marine systems often exhibits complex sedimentary facies and facies associations, because the presence of clay promotes the development of transient turbulent flows with complex depositional properties. Relatively little is known about the variation of current‐induced sedimentary structures found within these facies. This study provides the first comprehensive description and interpretation of mixed sandstone–mudstone bedforms observed in the fringe of the mud‐rich submarine fan that makes up the Aberystwyth Grits Group and Borth Mudstone Formation (Wales, UK). Using textural and structural descriptions, 158 bedforms in sediment gravity flow deposits were characterized into three main types: 'classic' sandy current ripples, large current ripples and low‐amplitude bed‐waves. The sandy current ripples comprise clean sandstone, with average heights and lengths of 11 mm and 141 mm, respectively. The large current ripples are composed of mixed sandstone–mudstone and possess greater dimensions than the sandy current ripples, with an average height of 19 mm and an average length of 274 mm. The low‐amplitude bed‐waves are long thin bedforms composed commonly of mixed sandstone–mudstone, with an average height and length of 10 mm and 354 mm, respectively. The large current ripples and low‐amplitude bed‐waves are strikingly similar to experimental bedforms produced under decelerating mixed sand–mud flows and are interpreted to form beneath transitional flows with enhanced and attenuated near‐bed turbulence, respectively. From the fringe to the distal fringe of the fan, the dominant bedform type changed from sandy current ripples, via large current ripples, to low‐amplitude bed‐waves, suggesting that the flows changed from turbulent to increasingly turbulence‐modulated. It is proposed that the flow Reynolds number reduced, reflecting this flow transformation, from a combination of constant or decreasing flow height, flow deceleration from sediment deposition, and increasing flow viscosity due to the shear‐thinning nature of clay‐rich suspensions. Large current ripples and low‐amplitude bed‐waves are likely to be common in the fringe of other submarine fans. The presence and spatial trends in mixed sand–mud bedform types may be an important tool in interpreting fan fringe environments. [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]

Well‐exposed, vertically dipping, glacially polished outcrops of the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera include basin‐floor deposits of the Upper Kaza Group overlain by slope channel complexes of the Isaac Formation. Within the 2·5 km thick Kaza and Isaac succession is an up to 360 m thick interval composed of diverse deep‐water stratal elements including scour and interscour deposits, distributary channels, fine‐grained turbidites, terminal splays, mass‐transport deposits, erosional and levéed channels and avulsion splays, which collectively were formed during the development of an ancient passive‐margin channel‐lobe system. The proportion and vertical and lateral arrangement of stratal elements reveal three distinct complexes. The lower complex, consisting mostly of distributary channels and small and large scours, is interpreted to represent the detachment of lobes from an upflow levéed channel, wherein a well‐developed channel‐lobe transition zone was formed by efficient, siliciclastic flows during a period of sustained transport bypass and limited deposition coincident with the onset of falling relative sea level. The middle, comparatively thicker and more sandstone‐rich complex, comprises distributary channel fills, fine‐grained turbidites and lesser terminal splays that are interspersed with small scours, capped by a slope levéed channel filled with coarser‐grained siliciclastic sediment. The abundance of basin‐floor elements suggests negligible separation between the levéed channel and lobe, and therefore a poorly‐developed channel‐lobe transition zone, resulting from inefficient, siliciclastic‐rich depositional flows that became dominant during lowstand and/or ensuing transgression. The stratal makeup of the upper complex resembles the lower detached complex, suggesting a return to efficient flows, and an abrupt change to mixed carbonate–siliciclastic sediments associated with highstand conditions. Accordingly, the stratigraphic architecture and stacking pattern of the Kaza–Isaac interval, which relate to the formation of multiple channel‐lobe transition zones, were controlled by temporal changes in sediment supply and flow characteristics during the long‐term progradation of the Laurentian continental margin. [ABSTRACT FROM AUTHOR]

Hyperpycnites are extrabasinal turbidites related to hyperpycnal flows which form during river floods. Compared to intrabasinal turbidite systems in deep marine or lacustrine settings, hyperpycnites in shallow lakes settings are not understood. In this work, we studied the typical sedimentary characteristics of shallow lacustrine hyperpycnal flow deposits in outcrops of the Luanping Basin, Northeast China. Based on the sedimentary architecture and analysis of the facies associations in these outcrops, the hyperpycnites can be classified into the following three types: (a) bedload‐dominated erosional channel deposits, (b) bedload‐ and suspended‐load‐dominated channel‐to‐lobe transitional deposits, and (c) suspended‐load‐dominated lobe deposits. The erosional channels in proximal locations are filled by mud clasts, parallel‐laminated sandstones, massive sandstones, cross‐bedded sandstones, massive siltstones, and mudstones. The channel‐to‐lobe transitional deposits in a middle location are composed of parallel‐laminated sandstones, cross‐bedded sandstones, mud clasts near internal erosional surfaces, ripple cross‐bedded sandstones, massive siltstones, and mudstones. The lobe deposits in distal locations are composed of ripple cross‐bedded sandstones, massive siltstones, and mudstones. The sedimentary process of the shallow lacustrine hyperpycnal flows shows obvious response to periodic flood energy fluctuations. Gentle slope, small capacity of flood discharges and semiarid paleoclimate may be the possible reason for the observed sedimentary architecture of the shallow lacustrine hyperpycnal flow deposits. Therefore, this study offers new insights into the sedimentology of shallow lacustrine deposits in rift basins. [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]

A timely and updated review of the Late Paleogene deep marine sedimentary successions is vital for a better understanding of the historical advances in sedimentology and stratigraphic evolution of West Sabah. The main objective of the study is to discuss the facies characteristics and depositional environment of the Late Paleogene rock formations. In addition, the stratigraphic aspects of the Paleogene interval will also be discussed. The Oligocene Temburong Formation exposed in several localities of West Sabah had been field researched with varying depositional processes and facies analysis. Moreover, the distribution of submarine fan, the observed variety of deep marine sediments associated with various sedimentary processes and the source of sediments of the co-eval West Crocker Formation were also investigated with contorted layers of mass transport deposits (MTD) reported first time in the formation. The upper and lower stratigraphic contacts of Late Paleogene formations, the age of individual rock formations and use of the term "Crocker Formation" in the literature are discussed with numerous unconformities and their stratigraphic positions in the Paleogene interval have been incorporated to understand the historical development of the Paleogene stratigraphy of the West Sabah. Owing to degrading tropical climate of the area, there are limitations and constraints on field-based research where the older outcrops are altered with housing development and dense vegetative cover. This review outlined the scientific developments and highlighted the ambiguities associated with stratigraphic placement of the Temburong and Crocker formations that still needed to be resolved to get an upgraded depiction of the Late Paleogene sediments of West Sabah. [ABSTRACT FROM AUTHOR]

Seismic‐reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as "layer cake" or "ramp" stratigraphy because the topset‐foreset‐bottomset clinoforms are not well exposed. Regional 2‐D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin‐floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres‐wide outcrops. The studied margin‐scale clinoforms are not representing a continental‐margin but a deepwater shelf margin that built out in a back‐arc basin. Lajas‐Los Molles clinoforms have been outcrop‐mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf‐edge rollover zone is occasionally occupied by a 40–50‐m‐thick coarse‐grained shelf‐edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf‐edge deltas contains tidal sandbodies. Shelf‐edge deltas transition downslope into turbidite‐ and debris flow‐filled channels that penetrate down the mud‐prone Los Molles slope. At the base‐of‐slope, some 300m below the shelf edge, there are basin‐floor fan deposits (>200 m thick) composed of sandy submarine‐fan lobes separated by muddy abandonment intervals. The large‐scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment. [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]

Shelf‐margin clinothem successions can archive process interactions at the shelf to slope transition, and their architecture provides constraints on the interplay of factors that control basin‐margin evolution. However, detailed textural analysis and facies distributions from shelf to slope transitions remain poorly documented. This study uses quantitative grain‐size and sorting data from coeval shelf and slope deposits of a single clinothem that crops out along a 5 km long, dip‐parallel transect of the Eocene Sobrarbe Deltaic Complex (Ainsa Basin, south‐central Pyrenees, Spain). Systematic sampling of sandstone beds tied to measured sections has captured vertical and basinward changes in sedimentary texture and facies distributions at an intra‐clinothem scale. Two types of hyperpycnal flow‐related slope deposits, both rich in mica and terrestrial organic matter, are differentiated according to grain size, sorting and bed geometry: (i) sustained hyperpycnal flow deposits, which are physically linked to coarse channelized sediments in the shelf setting and which deposit sand down the complete slope profile; (ii) episodic hyperpycnal flow deposits, which are disconnected from, and incise into, shelf sands and which are associated with sediment bypass of the proximal slope and coarse‐grained sand deposition on the medial and distal slope. Both types of hyperpycnites are interbedded with relatively homogenous, organic‐free and mica‐free, well‐sorted, very fine‐grained sandstones, which are interpreted to be remobilized from wave‐dominated shelf environments; these wave‐dominated deposits are found only on the proximal and medial slope. Coarse‐grained sediment bypass into the deeper‐water slope settings is therefore dominated by episodic hyperpycnal flows, whilst sustained hyperpycnal flows and turbidity currents remobilizing wave‐dominated shelf deposits are responsible for the full range of grain sizes in the proximal and medial slope, thus facilitating clinoform progradation. This novel dataset highlights previously undocumented intra‐clinothem variability related to updip changes in the shelf process‐regime, which is therefore a key factor controlling downdip architecture and resulting sedimentary texture. [ABSTRACT FROM AUTHOR]

This study details sedimentary and compositional characteristics of the Middle to Late and Early Pleistocene calcareous clay units recovered from Site U1453 in the middle Bengal Fan. The sedimentary characteristics reveal that the calcareous clay units consist of calcareous hemipelagic muds and terrigenous hemiturbidite muds which represent intervening periods of hemipelagic sedimentation sensu stricto and a slow sedimentation from suspension clouds of low-concentration turbidity currents on the fan surface, otherwise dominated by sand and mud turbidites. Variations in compositions, such as organic and inorganic carbon contents and δ13C of bulk organic matters of the calcareous hemipelagic muds, indicate the glacial-interglacial climate forcing of carbonate dissolution, surface marine productivity, and sources of particulate organic matters in the middle Bengal Fan during the Middle to Late Pleistocene. The glacial-interglacial climate forcing on hemipelagic sedimentation seems to be much obscure during the Early Pleistocene because of dilution by terrigenous clay inputs. Grain-size distribution of bulk sediments suggests the presence of coarse foraminifer and finer nannofossil modes in the calcareous clay units and the size of dominant foraminifer species could have been finer in the Early Pleistocene. [ABSTRACT FROM AUTHOR]

Repeat multibeam bathymetric surveys conducted in 2004, 2005 and 2018 show that seven slope-confined canyons on the continental slope of the Pearl River Mouth Basin, South China Sea, were dominated by large volume, widespread erosion. Erosion volumes were up to 3.4 times greater than deposition volumes. Erosion-dominated areas of the canyons are up to 2.3 times greater than areas dominated by deposition. Average rates of erosion (ranging from 0.7 to 0.8 m/yr) were greater than average rates of deposition (ranging from 0.5 to 0.8 m/yr). In plan view, the erosion-dominated zones exhibit two characteristic shapes: (1) linear, found mainly in upper canyon reaches, distributed predominantly along canyon axes and at the base of eastern canyon walls, and; (2) blocky, found mainly in lower canyon reaches, widely distributed along the steep canyon walls and on lower-canyon interfluves. The deposition-dominated zones are scattered along canyon floors and walls. Seismic reflection data show lateral shifts of canyon fill deposits through time, indicative of longer-term eastward canyon migration. The linear erosion-dominated zones may be attributed to erosive turbidity currents triggered by energetic internal solitary waves shoaling on the shelf. The eastward canyon shifts were likely induced by rapid near-bed eastward currents generated mainly by westward propagating powerful internal solitary waves of depression. The widespread erosion in the deeper canyon areas and interfluves is likely a consequence of slope instabilities associated with the presence of gas hydrates. This study indicates that active sedimentary processes can occur in slope-confined canyons even during sea level highstands. Local, site-specific oceanographic and geological features (e.g., internal solitary waves, gas hydrates) can significantly increase sedimentary activity in and around submarine canyons. • Seven slope-confined canyons in the northern South China Sea were dominated by erosion, 2004–2018 • Ratios of erosion-dominated to deposition-dominated area in the canyons ranged from 1 to 2.3 • Ratios of eroded to deposited sediment volumes ranged from 1.2 to 3.4 • In the upper canyon reaches, internal solitary waves resulted in the triggering of turbidity currents. • In the lower reaches, gas hydrate activity likely caused submarine slope instabilities. [ABSTRACT FROM AUTHOR]

Sediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep‐water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high‐resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long‐wavelength crescentic shape, is interpreted as net‐erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net‐depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low‐density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast‐flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr′) decreases. Therefore, this study shows that both net‐erosional and net‐depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite–contourite system. [ABSTRACT FROM AUTHOR]

Rambatan Formation in the western part of North Serayu Basin, Brebes, Central Java, comprises generally flysch facies of turbidite sediments deposited in a deep marine environment. This formation is equivalent to Merawu Formation found in the eastern part of the basin and deposited in the environment of tidal flat to subtidal. The turbidite sediments were highly controlled by a rapid downward movement taking place continuously during Early to Late Miocene. The variation of the depositional environment has been the object of this research which aims to understand the sedimentation process of Rambatan Formation in this type locality with a modern turbidite approach. Rambatan Formation was deposited in N13-N19, as a deep marine sediment channel, turbidite, and deep marine tidal zone. The sedimentation was affected by gravity flow and bottom current. The sediments on N13-N14 were marked by turbidite sediments until Middle N17. The sediment supply increased on Middle N17, as a sediment filler on a channel marked by contourite mud layer (muddy slump) and debris flow, with sources from the north. The increase of sediment supply was followed by an environmental transformation from a deep marine channel into deep marine tidal area. In N19, the sediments were redeposited as turbidite sediment, starting with debris flow in Middle N18. [ABSTRACT FROM AUTHOR]

Channel-feeding fan deltas without any conglomerates have recently been discovered on the steep slope in the Albert basin at the northern end of the west branch of the East African Rift. However, the new deposition system's mechanics and patterns are unknown. To reveal the sedimentary process of the distinctive fan delta, we integrate forward stratigraphic modeling (FSM) technology with interpretations of the core, well logs, and 3D seismic data. Firstly, a reference FSM model is constructed to describe the evolution of the fan delta, taking into account initial bathymetry, source supply, lake level, and fluvial discharge as independent variables. Then, the Orthogonal Experimental Design (OED) is employed based on the uncertainty analysis of each independent factor to generate FSM multi-realizations for formation thickness and Net-to-Gross. Sensitivity analysis of Multi-FSM realizations reveal that source supply is the most influential variable affecting formation thickness and texture. Combined with the tectonic evolution of Albert Basin, the formation dip during the deposition period is much smaller than present. Multiple incised channels were formed in the provenance area, which became the primary source system of the fan delta, facilitating the sediments' transportation over a certain distance to produce well-developed cross-bedding sandstone. The channel-feeding fan delta has a narrower plain and wider front, and the principal sand body is high-quality distributary channel. The discovery of the channel-feeding fan delta without any gravel formed on the steep slope of the rift basin enriches the theory of deposition in rift basins. In addition, the application of FSM technology helps to improve the quantification of sedimentary processes. • Channel-feeding fan delta without any conglomerate deposited in the south steep zone of Albert Rift. • Source supply, initial bathymetry, transportation, and eustasy were used for the experimental design of FSM. • Sensitivity analysis indicates that sediment supply significantly influences the stratigraphic thickness and texture. • The channels-feeding fan delta has a limited fan delta plain and wider front with medium-coarse sands but few gravels. [ABSTRACT FROM AUTHOR]

We use new U-Pb detrital zircon (DZ) geochronology from the Pleistocene Amazon submarine fan (n = 1352 grains), integrated with onshore DZ age data, to propose a sedimentary model for sea level-modulated and hydroclimate-modulated sediment transfer in Earth's largest source-to-sink system. DZ ages from the modern Amazon River sediment display a progressive downstream dilution by older cratonic zircons, leading to the expectation of a submarine fan with high proportions of craton-derived sediment. Our new DZ age data from the submarine fan and mixture modeling suggest that higher proportions of sediment were supplied from the distant central Andes to the Amazon fan during the last two glacioeustatic lowstands, and thus the observed DZ age spectra of the modern lower Amazon River indicate a relative increase in craton-derived sediment during the Holocene. We interpret that during interglacials, when sea level was high and the submarine fan inactive, the lower Amazon River did not efficiently transfer sand-sized sediment to the margin and thus became enriched in craton-derived sediment. During sea-level lowstands, increased gradients and incision in the lower Amazon River due to base-level lowering resulted in enhanced connectivity and transfer of Andes-sourced zircons to the deep sea. These results are also consistent with interpreted patterns of Andean-Amazon hydroclimate anti-phasing (enhanced precipitation in the central Andes and increased aridity in the northern Amazon Basin) during the Last Glacial Maximum. Our results suggest that sand-sized sediment in the Amazon submarine fan records multi-millennial patterns of sea level and South American hydroclimate. [ABSTRACT FROM AUTHOR]

Petrographic classifications of sand and sandstone proposed more than half a century ago are still in use, although they were formulated at a time when depositional and post-depositional sedimentary processes were poorly understood, and before the relationships between tectonics and sedimentation could be interpreted in modern plate-tectonic terms. As a consequence, too many scientific articles and technical reports are still encumbered with obsolete concepts, graphical tools, and ambiguous terminology that make sediment descriptions awkward and misleading. A renovation that treasures the legacy of the pioneers is required. The descriptive petrographic classification of sand and sandstone proposed in this paper is based on the quasi-universally used Gazzi-Dickinson point-counting method, and simply translates into words ternary compositions of quartz, feldspar, and lithic fragments without introducing any new names. The classic QFL plot is subdivided into 15 fields - labelled by adjectives introduced long ago by K.A.W. Crook and endorsed by W.R. Dickinson and more recently by G.J. Weltje - which reflect relative abundances of the three main framework components (provided they exceed 10%QFL). According to standard use, the less abundant component goes first, the more abundant last (e.g., litho-feldspatho-quartzose composition translates into Q > F > L > 10%QFL). For lithic-rich sand and sandstone, information on the prevailing rock fragment type can be added by an additional free adjective (e.g., metamorphiclastic, carbonaticlastic), as proposed long ago by R.V. Ingersoll. For lithic-poor feldspatho-quartzose and quartzose sand and sandstone, further formal subdivisions are proposed based on the Q/F ratio, thus reaching a total of 18 compositional fields overall. Modern sand known to be derived from different source rocks and found in major world's rivers, deserts, and deep-sea fans fits in the pigeonholes defined by the relative abundance of quartz, feldspar, and lithic fragments. The aim of this classification is to restore directness in sandstone petrology, and to avoid ambiguities generated in the past by making reference to badly defined archetypes, such as greywacke or arkose, thus confusing petrographic composition with subjective considerations about plate-tectonic setting, texture, hydraulic behaviour, mechanical durability, or chemical durability in the illusion that a classification could be genetic at the same time as descriptive. [ABSTRACT FROM AUTHOR]

The effects of changes in slope gradient on deposition processes and architecture have been investigated in different deep-sea systems both in modern and ancient environments. However, the impact of subtle gradient changes (< 0.3 ∘) on sedimentary processes along deep-sea fans still needs to be clarified. The Ogooue Fan, located in the northeastern part of the Gulf of Guinea, extends over more than 550 km westwards of the Gabonese shelf and passes through the Cameroon volcanic line. Here, we present the first study of acoustic data (multibeam echosounder and 3.5 kHz, very high-resolution seismic data) and piston cores covering the deep-sea part of this West African system. This study documents the architecture and sedimentary facies distribution along the fan. Detailed mapping of near-seafloor seismic-reflection data reveals the influence of subtle slope gradient changes (< 0.2 ∘) along the fan morphology. The overall system corresponds to a well-developed deep-sea fan, fed by the Ogooue River sedimentary load, with tributary canyons, distributary channel–levee complexes and lobe elements. However, variations in the slope gradient due to inherited salt-related structures and the presence of several seamounts, including volcanic islands, result in a topographically complex slope profile including several ramps and steps. In particular, turbidity currents derived from the Gabonese shelf deposit cross several interconnected intra-slope basins located on the low gradient segments of the margin (< 0.3 ∘). On a higher gradient segment of the slope (0.6 ∘), a large mid-system valley developed connecting an intermediate sedimentary basin to the more distal lobe area. Distribution and thickness of turbidite sands is highly variable along the system. However, turbidite sands are preferentially deposited on the floor of the channel and the most proximal depositional areas. Core description indicates that the upper parts of the turbidity flows, mainly composed of fine-grained sediments, are found in the most distal depocenters. [ABSTRACT FROM AUTHOR]

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

Abstract: The origin of the fourth member of the Eocene Shahejie Formation in the northern steep slopes of the Minfeng Sub‐sag, Dongying Sag, China, was investigated by integrating core studies and flume tank depositional simulations. A non‐channelized depositional model is proposed in this paper for nearshore subaqueous fans in steep fault‐controlled slopes of lacustrine rift basins. The deposits of nearshore subaqueous fans along the base of steep border‐fault slopes of rift basins are typically composed of deep‐water coarse‐grained sediment gravity‐flow deposits directly sourced from adjacent footwalls. Sedimentation processes of nearshore subaqueous fans respond to tectonic activities of boundary faults and to seasonal rainfall. During tectonically active stages, subaqueous debris flows triggered by episodic movements of border‐faults dominate the sedimentation. During tectonically quiescent stages, hyperpycnal flows generated by seasonal rainfall‐generated floods, normal discharges of mountain‐derived rivers and deep‐lacustrine suspension sedimentation are commonly present. The results of a series of flume tank depositional simulations show that the sediments deposited by subaqueous debris flows are wedge‐shaped and non‐channelized, whereas the sediments deposited by hyperpycnal flows generated by sporadic floods from seasonal rainfall are characterized by non‐channelized, coarse‐grained lobate depositional bodies which switch laterally because of compensation sedimentation of hyperpycanal flows. The hyperpycnal‐flow‐deposited non‐channelized lobate depositional bodies can be divided into a main body and lateral edges. The main body can be further subdivided into a proximal part, middle part and frontal part. Normal mountain‐derived river‐discharge‐deposited sediments are characterized by thin‐bedded, fine‐grained sandstones and siltstones with a limited distribution range. Normal mountain‐derived river‐discharge‐deposited sediments and deep‐lacustrine mudstones are commonly eroded in the area close to boundary faults. A nearshore subaqueous fan can be divided into three segments: inner fan, middle fan and outer fan. The inner fan is composed of debrites and the proximal part of the main body. The middle fan consists of the middle part of the main body and lateral edges, normal mountain‐derived river‐discharge‐deposited fine‐grained sediments and deep‐lacustrine mudstones. The outer fan comprises the frontal part of the main body, lateral edges, and deep‐lacustrine mudstones. Based on the non‐channelized depositional model for nearshore subaqueous fans, criteria for stratigraphic subdivision and correlation are discussed and applied. [ABSTRACT FROM AUTHOR]

Morphometric analysis of submarine fan systems, the largest sedimentary deposits on Earth, demonstrates scaling relationships between genetically related channels and lobeshaped bodies (LBs) deposited beyond the channel terminus, providing insight into the architectural development of these systems. Compiling dimensional data from depositional systems that cover a range of sediment supply characteristics, tectonic settings, and geographic locations enables investigation into global trends in depositional morphology. LBs have a consistent, scale-independent length-to-width ratio of ~2:1. The thickness-to-area ratios for LBs show multiple morphologic trends, likely driven by topographic confinement, with LBs getting proportionally thicker in relation to increasing confinement. Morphometric analysis of genetically related channel dimensions (width, relief, cross-section area) and LB dimensions (length, width, thickness, area, volume) reveals robust scaling relationships; most notably, channel width and cross-sectional area can be used to predict the volume and depositional area of related LBs. These relationships demonstrate that LBs proportionally scale to their concomitant channels, and thus to the volume of sediment supplied prior to an avulsion. While the dimensions of submarine fans scale to associated terrestrial catchments, the building blocks of submarine fans (i.e., channels and LBs) do not, suggesting a down-system decoupling (or lack of scaling) at LB deposition time scales. Applying these morphometric trends and scaling relationships as input parameters for source-to-sink and reservoir models can improve predictions of stratigraphic architecture, sediment partitioning, and sediment/ carbon flux in modern and ancient submarine fan systems. [ABSTRACT FROM AUTHOR]

Abstract: The deposits of the Imlekin Formation of the Upper Pegtymel depression were formed in the southern margin of the Chukotka Terrane synchronously with accretion of the Kulpolney island arc to the Chukotka-Arctic Alaska microplate. The sedimentological structural features of the Upper Jurassic-Lower Cretaceous sections indicate their accumulation within various parts of submarine fans of a shallow marine basin. The submarine slump origin of the boulder-pebble (tillite-like) conglomerates is substantiated. The petrographic, geochemical, and geochronological methods identified two dominant provenances: Triassic clastic rocks and Volgian suprasubduction volcanic rocks. The Middle Volgian-Early Berriasian age of the Imlekin Formation is specified. The geodynamic model proposed explains the change of the sources and direction of the sediment transport in the Volgian. [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]

Submarine fans in tectonically active continental-slope basins are targets of petroleum exploration and production. These slope fans commonly comprise compensationally stacked sandy and muddy architectural elements, including mass-transport deposits, weakly confined to distributary channel-and-lobe deposits, and leveed-channel deposits. The lateral continuity and vertical connectivity of these architectural elements are important uncertainties in reservoir characterization that influence fluid-flow behavior during hydrocarbon production. Here, we use a simple forward stratigraphic model to simulate the stratigraphic patterns and illuminate the likely distribution of fine-scale, sub-seismic heterogeneity in a slope fan. We used published seismic-reflection horizons from the tectonically active Columbus basin, offshore Trinidad, to define the top and base of a Pleistocene submarine fan. We then simulated the stratigraphic evolution of the slope fan with a series of DionisosFlow™ forward stratigraphic models. All variables were kept constant during the simulations in order to test the hypothesis that the autogenic evolution of the surface topography alone, as a result of erosion and deposition, can produce compensational-stacking patterns common in submarine fans. A reference-case model is similar to the thickness trend of published isochron maps of the Trinidad slope fan. The reference-case model also produced patterns of compensational stacking. Varying the time step impacts the heterogeneity of the model. Shorter time steps are characterized by less sediment accumulation, which results in less sediment diversion during the subsequent time step, more gradual migration of channel deposits, shorter offset distances of depocenters, and shorter length-scale heterogeneity compared to longer time steps. Thus, a key characteristic of slope-fan deposits is autogenic compensational stacking, without any external forcing, which governs heterogeneity in these reservoirs. Furthermore, our results suggest that relatively simple diffusion-based models can produce realistic compensation patterns and future work will be focused on higher-resolution model calibration to seismic-reflection data and the influence of input variables on heterogeneity of channel-and-lobe deposits of slope fans. [ABSTRACT FROM AUTHOR]

Hybrid beds, the deposits of sediment gravity flows that show evidence for more than one flow regime (turbulent, transitional and/or laminar), have been recognized as important components of submarine lobe deposits. A wide range of hybrid bed types have been documented, however, quantitative analysis of the stratigraphic and geographic distribution of these enigmatic bed types is rare. Here, extensive exposures integrated with research borehole data from Unit A of the Laingsburg Formation and Fan 4 of the Skoorsteenberg Formation, Ecca Group, South Africa, provide the opportunity to examine geographical and stratigraphic patterns over a range of hierarchical scales. For this purpose, >23,000 individual beds have been evaluated for deposit type and bed thickness. On average, hybrid beds make up < 5% of all events and <10% of the cumulative thickness. Lobe complex 1 (LC1) of Fan 4,Skoorsteenberg Formation, preserves a prominent geographical trend of hybrid beds becoming more prevalent towards the frontal fringes of a lobe complex (up to 33.2% of beds), whereas their proportion in proximal and medial lobe complex settings is <10%. Data from Unit A, Laingsburg Formation, show hybrid beds are less common in the basal (A.1) and top (A.6) subunits compared to A.2-A.5 in both core data sets. The bases and tops of some lobe complexes (A.2, A.3 and A.5.7) are observed to be slightly enriched in hybrid beds, whereas others (A.5.1, A.5.5 and A.6.1) show no hybrid beds in their bases, which does not conform to expected allogenically-driven distributions that predict more hybrid beds during the initiation of lobe complexes. Instead, the occurrence and distribution of hybrid beds in lobe complexes are interpreted to be controlled by autogenic processes, including flow transformation processes on the basin-floor meaning enrichment in frontal lobe fringe settings. Therefore, the 1D distribution of hybrid beds in lobe complexes reflects the dominant stacking pattern of lobes within a lobe complex, with enrichment at the base and top of lobe complexes due to overall progradational to retrogradational stacking patterns. Individual lobes show a wide range of hybrid bed distributions, due to stacking patterns of the component lobe elements. These findings highlight the importance of autogenic processes rather than allogenic controls in the distribution of hybrid beds, which has implications for reservoir evaluation and the assessment of lobe stacking patterns in 1D core data sets. [ABSTRACT FROM AUTHOR]

Autogenic controls have significant influence on deep-water fans and depositional lobes morphology. In this work, we aim to investigate autogenic controls on the topography and geometry of deep-water fans. The influence of the sediment concentration of turbidity currents on deep-water fans morphology was also investigated. From the repeatability of 3D physical modeling of turbidity currents, two series of ten experiments were made, one of high-density turbidity currents (HDTC) and another of low-density turbidity currents (LDTC). All other input parameters (discharge, sediment volumetric concentration and grain size median) were kept constant. Each deposit was analyzed from qualitative and quantitative approaches and statistical analysis. In each experimental series, the variability of the morphological parameters (length, width, L/W ratio, centroid, area, topography) of the simulated deep-water fans was observed. Depositional evolution of the HDTC fans was more complex, showing four evolutionary steps and characterized by the self-channelizing of the turbidity current, while LDTC fans neither present self-channelizing, nor evolutionary steps. High disparities on the geometrical parameters of the fans, as characterized by the elevated relative standard deviation, suggest that autogenic controls induced a stochastic morphological behaviour on the simulated fans of the two experimental series. [ABSTRACT FROM AUTHOR]

The Zagórnik-Rzyki studied section includes the upper part of the Veřovice Fm and the lower part of the Lhoty Fm (Aptian–Albian), which are small fragments of the much thicker sedimentary succession of the Silesian Nappe (Polish Outer Carpathians). Logged section gives a good insight into the relatively proximal but muddy submarine fan environment with at least partially confined nature and widely distributed facies of heterolithic deposits and banded sandstone. Three distinguished facies associations represent a gradual lateral shift toward the depositional lobe flank in a relatively proximal setting, away from the main sediment distribution pathways. The studied heterolithic deposits show various internal sedimentary structures (muddy ripples, draped ripples, low-amplitude bed-waves, low-angle laminated bedforms, small lenticular bedforms and plane-parallel laminated mudstone) considered as a record of the dynamic of sedimentary processes on a submarine depositional lobe flank environment. Despite the predominance of finning upward grain size trends (wanning flow deposits), sedimentary structures in the heterolithic deposits may stack in a varied order, also forming coarsening upward trend (waxing flow deposits), bi-gradational trend (waxing to wanning flow deposits), and complex trends (deposits with multiple waxing to wanning flow pulses) indicating record of hyperpycnal flows. Lack of hybrid event beds despite the occurrence of transitional flow deposits is evidence that even in mud-dominated to mixed sand-mud submarine turbidite systems, the flow transformation from fully turbulent to cohesive laminar behaviour is incomplete in relatively proximal depositional environment. Instead, a variety of facies banded sandstone and heterolithic deposits may represent a significant fragment of the sedimentary record in the proximal depositional lobe flank setting. [ABSTRACT FROM AUTHOR]

The seismic stratigraphy, evolution and depositional framework of a sheared-passive margin, the Durban Basin, of South East Africa are described. Based on single-channel 2D seismic reflection data, six seismic units (A-F) are revealed, separated by major sequence boundaries. These are compared to well logs associated with the seismic data set. Internal seismic reflector geometries and sedimentology suggest a range of depositional regimes from syn-rift to upper slope and outer shelf. Nearshore and continental facies are not preserved, with episodic shelf and slope sedimentation related to periods of tectonic-induced base level fall. The sedimentary architecture shows a change from a structurally defined shelf (shearing phase), to shallow ramp and then terminal passive margin sedimentary shelf settings. Sedimentation occurred predominantly during normal regressive conditions with the basin dominated by the progradation of a constructional submarine delta (Tugela Cone) during sea-level lowstands (LST). The earlier phases of sedimentation are tectonic-controlled, however later stages appear to be linked to global eustatic changes. [ABSTRACT FROM AUTHOR]