Sediment Lobes Research Articles

Discovery of the Messinian Eratosthenes Canyon in the deep Levant Basin

The Messinian Salinity Crisis (MSC) was a major disruptive event in Earth's history involving all Earth's systems - hydrosphere, biosphere, lithosphere, and atmosphere. Approximately six million years ago, the entire Mediterranean Sea turned into a hypersaline basin when the Gibraltar gateway to the Atlantic Ocean narrowed and evaporation exceeded fresh water input. Consequently, marine fauna died and massive deposition of salt on the seafloor had led to the formation of the world's youngest salt giant.A fundamental observation related to this enigmatic period is a remarkable erosional surface, associated with 100 s-of-m deep canyons that were incised across the Mediterranean's continental margins during the crisis. Such canyons across the Levant margins were described in the 1970s and, later, in the 2000s they were shown to be the gateway for shallow, sinuous, submarine channels that continued towards deeper parts of the basin. Though it could have been assumed that these channels end as terminal sedimentary lobes in the Levant Basin, we show here that they contributed to a much wider sedimentary system in the Eastern Mediterranean Sea: farther west, they merge into a nearly 500-m-deep and ∼ 10-km-wide canyon, which we name after the nearby Eratosthenes Seamount. This remarkable canyon was excavated at the beginning of the MSC prior to salt deposition. We suggest that incision took place during Stage 1 of the MSC, but we cannot rule out faster incision (10s of ky) at the end of Stage 1 (∼5.60 Ma), or at its very beginning (∼5.97 Ma).Regardless of its exact age, we show that the Eratosthenes Canyon was excavated subaqueously and suggest that incision was caused by gravity currents, such as sediment-laden turbidites and/or dense brines. We argue that the increased salinity at the beginning of the crisis and a possibly limited sea level fall - whose amplitude should be investigated - had triggered these gravity currents, destabilizing the continental margin and carving the seabed wherever it was steep enough.

Barform deposits of the Carolyn Shoemaker formation, Gale crater, Mars

ABSTRACT The early environmental history of Mars is encoded in the planet's record of sedimentary rocks. Since 2012, the Curiosity rover has been ascending Mount Sharp, Gale crater's central mound, making detailed observations of sedimentary strata exposed there. The primary depositional setting represented by the rocks examined thus far has been a perennial lake, represented by the mudstones and sandstone lenses of the Murray formation. Here, we report on the sedimentology of outcrops examined in the Carolyn Shoemaker formation, which sits stratigraphically above the Murray formation. We interpret strata exposed in the Glasgow and Mercou members of the Carolyn Shoemaker formation to represent river bars in ancient alluvial and shoreline settings based on sedimentary structures, stratal geometries measured from photogrammetric data, and erosional morphology. The transition from a lacustrine to a fluvial depositional setting records the aggradation and progradation of coastal rivers into what was previously the extent of the Gale lake system. This may have occurred due to the shrinking of the lake over time due to climate-driven changes in the basin water balance, or local three-dimensionality in shoreline evolution, such as the formation of a new sedimentary lobe following a channel switch.

River avulsions and megafan development triggered by high recurrent explosive volcanism

Megafans are ever-evolving landforms and sedimentary bodies produced by rivers that regularly change their courses through avulsions, in which the processes that cause the avulsions and their rates are tightly linked to the formation and evolution of the fans. The commonly cited condition required for the formation of megafans is a highly variable climate setting (monsoonal) which results in variable discharge and sediment transport capacity. However, some megafans occur in tropical settings in rivers with lower discharge variability but high sediment loads due to input from volcanic or tectonically active sources. We examine the Santa Clara Megafan (Costa Rica) to establish a model of explosive volcanism-driven megafan evolution, an alternative model to the climate-driven one. Studying chronological, archaeological, historical and remote sensing data we infer that major avulsions and shifts in the main rivers of this megafan are temporally and spatially correlated to strong eruptions (VEI ≥ 3). Furthermore, a period of ca. 1700 years with few changes in the fluvial system of the eastern sector of the megafan coincides with a low volcanic activity in its source area (i.e. Turrialba Volcano). The megafan avulsion rate was estimated as ∼1 major avulsion per century in the last five centuries, when four strong eruptions (∼0.8 eruptions/century) took place. These shifts in the rivers in response to the volcanic activity produced the activation or abandonment of megafan sedimentary lobes at a secular pace. The record of these changes will support future archaeological studies and lahar hazard assessments. Furthermore, the Santa Clara Megafan provides a model to explain the formation of megafans on Earth or on other planets through non-climatic processes.

Reconstructing sedimentary processes in a Permian channel–lobe transition zone: an outcrop study in the Karoo Basin, South Africa

AbstractTurbidity 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.

Modeling long-term delta dynamics reveals persistent geometric river avulsion locations

River deltas grow through repeated stacking of sedimentary lobes, the location and size of which are determined by channel avulsions (relatively sudden changes in river course). We use a model coupling fluvial and coastal processes to explore avulsion dynamics under a range of wave energies and sea-level-rise rates and find that the primary control on avulsion location and delta lobe size in our model is the critical superelevation ratio (SER), the amount of channel aggradation relative to the surrounding floodplain that is required to trigger an avulsion. The preferred avulsion location arises because of geometric constraints – a preferential avulsion node occurs at the break in floodplain slope that develops as the river progrades and/or sea level rises. This concavity develops in our model because the river profile aggrades and erodes via linear diffusion, whereas the diffusion of the floodplain topography is limited to episodic crevasse splays. These results are in contrast to recent modeling work, which was motivated by laboratory experiments and assumes a union between river channel and floodplain aggradation rates, and where avulsion nodes are driven by backwater hydrodynamics. The preferred avulsion length in our model scales well with laboratory, field, and model results without including hydrodynamic backwater effects. This work suggests an alternative mechanism to explain avulsion locations on deltas where floodplain topography aggrades and/or diffuses more slowly than the river channel profile, and it points to the need to elucidate river channel and floodplain connectivity over large space and time scales, and how the connectivity varies from one type of delta to another.

Sedimentary architecture of the undeformed Lower Miocene Görendağı Submarine Fan deposits from Neo-Tethys Ocean (Eastern Anatolia-Turkey): Tectonic control on preservation of fan morphology

Submarine fan deposits which constitute the remnants of Neo-Tethys are widely observed throughout the Bitlis–Zagros Suture Belt. Most of these deposits are located in the Arabian-Eurasian collision zone and have been intensively deformed due to ongoing tectonic activity. In this study, the depositional characteristics and preservation processes of the undeformed, Lower Miocene Görendağı Submarine Fan deposits, associated with this zone, are studied with respect to their sedimentological and structural features. These deposits display feeder or distributary channels, overbank, and lobe sediments and classical Bouma Ta–d divisions. They are subdivided into inner, middle, and outer fan, according to sedimentological and morphological properties. Sand-rich submarine fan deposits have 39 m thickness and approximately 2 km of lateral extension.The submarine fan body is bounded to the north and the south by two reverse faults, namely the Özyurt and Göktepe faults. These faults formed an accommodation space where the fan was deposited and also caused the deepening of the basin. The position and activity of these oppositely inclined reverse faults, which form a triangular zone, are the main reason for preservation of the original fan morphology in the Görendağı Submarine Fan. Our results indicate that the Görendağı Submarine Fan represents one of the last sequences deposited before the closure of the southern branch of the Neo-Tethys Ocean and also the most well-preserved.

Pliocene–Pleistocene glacimarine shelf to slope processes in the south‐western Barents Sea

AbstractThe glacimarine shelf‐edge is a complex depositional environment in which the interplay between accommodation and glaciation has played an important role in influencing sediment deposition and margin architecture. It can be challenging to unravel the history of basin infill in these areas, particularly where landforms are deeply buried. This study presents an integrated workflow for deciphering the architecture and evolution of erosional and depositional elements in a crucial location of the south‐western Barents Sea margin, with a focus on the comparatively poorly understood processes and patterns of glacimarine sedimentation that occurred during the Pliocene and Early Pleistocene. Wellbore interpretations of lithology are combined with the analysis of seismic facies, geomorphology and attributes using merged 3D seismic reflection data to investigate the morphology and development of buried landforms and depositional features on the outer‐shelf, shelf edge and upper‐slope. The Pliocene (preglacial) slope system is dominated by upper‐slope channels, upper‐slope channels with associated sediment lobes, and mass‐transport deposits. The first appearance of mega‐scale glacial lineations in the study area is close to the onset of the Pleistocene (around 2.58 Ma), suggesting that an ice stream reached the palaeo‐shelf edge during the earliest Pleistocene. The prevalence of upper‐slope channels and mass‐transport deposits throughout the Pleistocene stratigraphy shows that the basinwards transfer of sediment took place mainly by evacuation of sediment through relatively linear channels combined with mass‐movement events. The results presented in this study have implications for understanding the glacial history of the south‐western Barents Sea and sedimentary processes on glacimarine shelf edges more generally.

Applying Directional Filters to Satellite Imagery for the Assessment of Tropical Cyclone Impacts on Atoll Islands

Volto, N. and Duvat, V.K.E., 2020. Applying directional filters to satellite imagery for the assessment of tropical cyclone impacts on Atoll Islands. Journal of Coastal Research, 36(4), 732–740. Coconut Creek (Florida), ISSN 0749-0208.This paper highlights the major insights provided by directional filters using ENVI® software for detecting and mapping cyclone-generated accretional features and analyzing postcyclone sediment reworking. It relies on the study of the impacts of category 5 tropical cyclone Fantala (April 2016) on Farquhar Atoll, Seychelles Islands. Using directional filters first allowed the detecting and mapping of terrestrial (sediment sheets, sediment lobes) and intertidal (shingle and rubble tongues, sediment sheets, sandbars) depositional features. It also helped with highlighting spatial-temporal variations in the postcyclone reorganization of reef flat deposits. One year after the cyclone, along the rectilinear shoreline of elongate islands (i.e. North Island and South Island), massive reef-to-island sediment transfer had already caused the dismantling of cyclone-generated features and beach readjustment; however, in places, newly formed cyclone features exhibited limited dismantling. In contrast, at the island tips, the reworking of postcyclone sediment deposits was still ongoing, explaining still rather limited beach readjustment. The results advocate for the use of remote sensing techniques that complement fieldwork and multidate shoreline change assessment to promote more comprehensive analyses of tropical cyclones' impacts.

Origin and timing of past hillslope activity in the hyper-arid core of the Atacama Desert – The formation of fine sediment lobes along the Chuculay Fault System, Northern Chile

Abstract Hillslopes represent areas of predominant denudation and constitute the transition and trajectory to floodplains; they play a crucial role in understanding the long-term landscape evolution of desert environments. However, although hillslope processes are known to be very slow or even stagnant in (hyper-) arid environments, process mechanisms under the virtual absence of water are poorly understood, and process rates are essentially unknown. Based on irrigation experiments, different monitoring techniques including drone-based high-resolution digital elevation models, geomorphological, stratigraphical, geochronological (OSL), sedimentological and geochemical investigations, as well as μCT scans of sediment cores, this contribution presents detailed insights into the chronostratigraphy of tongue-shaped, 50 m-long and 30 m-wide fine sediment lobes located along a 10–30° steep thrust-related slope east of the Salar Grande (Atacama, Chile). Irrigation experiments were performed to gain insights into precipitation thresholds for surface runoff and hillslope dynamics. Although artificial rainfall intensities were ~46 mm/h, infiltration was 100%, and the experiments did not initiate surface runoff or (detectable) slope material displacements. In addition, a distinct stratigraphic pattern with buried paleo-surfaces and paleo-biological surface crusts suggests increased hillslope activity during the late Pleistocene, potentially driven by changes of (fog-induced) humidity, salt-related shrink and swell processes, or paleo-seismic activity. While a variety of geo-bio-archives document periods of increased precipitation in the Andean parts of the Atacama Desert throughout the Quaternary, evidence for contemporaneous paleoclimatic changes from areas disconnected to Andean precipitation fluctuations (i.e., the Coastal Cordillera) is scarce. In this regard, the investigated landforms potentially represent one of only few sediment records recording paleoclimatic changes in the central desert, independent from Andean rainfall.

Lower Cretaceous Barents Sea strata: epicontinental basin configuration, timing, correlation and depositional dynamics

AbstractA 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.

Deep-seated focused fluid migration as indicator for hydrocarbon leads in the East Shetland Platform, North Sea Province

Abstract Hydrocarbon exploration in the North Sea Basin has revealed a multitude of focused fluid conduits, which manifest in seismic data as pipe or chimney structures that in some instances are connected to underlying hydrocarbon reservoirs. 3D seismic data from the eastern margin of the East Shetland Platform reveal the presence of more than 450 focused fluid conduits. Most of these initiate at the Base Tertiary Unconformity and cross-cut the overlying sediments. The focused fluid conduits correlate with intra-platform basin structures beneath the Base Tertiary Unconformity and with permeable sediment lobes, channels and deltaic units in the overlying Paleocene to Eocene successions, which include known hydrocarbon reservoirs (e.g. Bressay, Bentley, Skipper or Piper). Clusters of pipes associated with other channels and deltaic units may indicate the presence of additional prospects at the eastern margin of the East Shetland Platform. Our study highlights the potential of using seismically imaged focused fluid system analyses in hydrocarbon exploration in platform areas on both sides of the Viking Graben and other frontier areas as they reveal the presence of working hydrocarbon charge pathways.

Geomorphic evolution of the Malta Escarpment and implications for the Messinian evaporative drawdown in the eastern Mediterranean Sea

Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97–5.33Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSCbase-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i)canyon erosion by submarine gravity flows, with the most recent activity taking place <2600cal. years BP; (ii) deposition by bottom currents across the entire depth range of the Malta Escarpment; (iii) tectonic deformation in the southern Malta Escarpment in association with a wrench zone; (iv) widespread, small-scale sedimentary slope failures preconditioned by oversteepening and loss of support due to canyon erosion, and triggered by earthquakes. We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800–2000m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation predominantly occurred before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes.

A diverted submarine channel of Early Cretaceous age revealed by high-resolution seismic data, SW Barents Sea

Abstract Mud-rich prograding sediment lobes make for most of the Barremian – Albian stratigraphic record in the SW Barents Sea. Submarine canyons and channels potentially represent key components of sediment transport from shelf to basin floor but geological evidences are lacking. We present high-resolution seismic data and scrutinize an elongated, ∼150-km long bright seismic amplitude and resistive anomaly located alongslope of a NW-sourced Barremian delta in the SW Barents Sea. Seismic interpretation is performed on a comprehensive database comprising 3D/2D high-resolution P-Cable and conventional seismic data, tied to three exploration wells to provide age-control on key horizons. Our results highlight that the elongated geophysical anomaly originates from a soft layer deposited over a harder, erosional surface. The erosive morphology displays three narrow, V-shaped incisions to the NE of the Hoop area which develop into a single, ∼6 km-wide, U-shaped channel towards the transition to the Fingerdjupet Subbasin. The geological feature is named Ceres and interpreted as a submarine channel carved in Aptian, a period of marked sea level rise and sediment starvation in the Hoop area. An evolutionary model of a diverted submarine channel is proposed where a flooded delta lobe acted as a topographic barrier, funneling bottom currents and thereby carving an alongslope, possibly contouritic channel. This is the first documented case of a submarine channel pathway – delta lobe interaction on the Norwegian continental shelf. To account for the geophysical expression of Ceres, two competing explanations are discussed: (1) hydrocarbon-bearing sands, and (2) organic-rich source rock. Both scenarios have important implications for petroleum prospectivity: a faulted stratigraphic trap holding large volumes of hydrocarbons or alternatively the channel-controlled distribution of mature Aptian source rock in the SW Barents Sea.

Sediment critical shear stress and geotechnical properties along the modern Yellow River Delta, China

ABSTRACTA geological engineering study was undertaken to determine the spatial distribution of sediment critical shear stress in the modern Yellow River Delta and to determine the influence of sediment erodibility on sediment erosion and microtopography formation. The critical shear stress was tested using a cohesive sediment meter for sediments along lines running perpendicular to the coast in different sedimentary lobes of the delta, where the geotechnical properties of sediments were also determined. The results demonstrate that significant differences in critical shear stress exist among high, middle, and low tidal flats, which are influenced by biodisturbation in the different sedimentary lobes. Regional characteristics of the modern Yellow River Delta show that critical shear stress levels are the lowest in the northern area (0.11–0.4 Pa), are the highest in the eastern area (2.8–4.55 Pa), and are significantly heterogeneous in the northeastern area. The critical shear stress is found to be more nonuniform and levels of antierosion strength are relatively lower than values found for other estuarine deltas around the world.

Aliphatic hydrocarbons and triterpenes of the Congo deep-sea fan

Hydrocarbons were analyzed in sediments from the Congo River deep-sea fan, from the Congo River, and in sinking particles collected by sediment traps 40m above the sediment. Studied sites encompassed three lobes of decreasing age of formation along the canyon: sites A, F and C and a another lobe system, disconnected from the active channel since 4 ka, Site E. Terrestrial long-chain odd n-alkanes were dominant in all sediments of the lobe system. Unsaturated terpenoids sourced by higher plants, such as gammacerene, lupene, ursene and oleanene, were also detected. At site C, characterized by high accumulation rates (10–20cmyr−1), the organic matter spends less time in the oxic layer than at other sites and high phytadiene concentrations 10–17μggOC−1) evidenced recent terrestrial and phytoplanktonic remains reworked in anaerobic conditions. In these sediments, organic carbon-normalized concentrations of terrestrial alkanes and terpenoids were several fold higher than in the lobe sediments with lower accumulation rates (sites A and F), arguing for a more rapid degradation of terrestrial hydrocarbons than bulk organic carbon in the first steps of pre-diagenesis. Ample variations in the contributions of biomarkers from higher plants, ferns, bacteria and angiosperms, indicate an heterogeneous contribution of the soil and vegetation detritus delivered to the Congo lobe sediments. Lower concentrations in terrestrial hydrocarbons at site E, 45km away from the active canyon, indicated that river particles are still admixed to the dominant marine organic matter. Diploptene and hop-7(21)-ene have a dual origin, from terrestrial and marine microorganisms. Scatter in their relationship to gammacerene argues for a contribution of marine microorganisms, in addition to soils-sourced microorganisms. The close distribution patterns of diploptene, hop-21-ene, hop-7(21)ene and neohop-13(18)-ene is in line with the hypothesis of sequential clay-catalyzed isomerisation of bacterial hopenes. Terrestrial biomarker accumulation fluxes at site C are one order of magnitude higher than vertical pelagic flux, demonstrating the magnitude of the inputs delivered through turbiditic transport in the submarine canyon. Crude oil contamination was evidenced at the disconnected site E (UCM, C21 to C26 tricyclic diterpanes, CPI) and, in smaller amounts, in some sediments from sites A and C. It may be related to marine crude oil extraction and transport. A short-chain mode of alkanes with an even predominance is evidenced in sediments of the lobe complex and likely sources, crude oil, microorganisms and ferns, are discussed.

Source and sink characteristics of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

The “source-conduit-sink” model is crucial for studying deep-water sedimentary systems along a continental margin. Using seismic data, bulk rare earth element compositions of sediments and zircon U-Pb age data, we examined the supply and deposition (i.e., the source and sink) of the sediments in the Central Canyon of the South China Sea. Five phases of secondary canyon fill are present in the Central Canyon. The natural levees developed at the head of phase 1 of the secondary canyon deposits indicate that the Central Canyon initially developed at 10.5Ma. The sediments in the Central Canyon were supplied by the Ledong submarine fan, and the provenance of the material in the Ledong submarine fan and Central Canyon was eastern Vietnam. Large amounts of sediments were transported through the Central Canyon to the Shuangfeng Basin and deposited during four phases of submarine fan development. Phases 1–3 of the Shuangfeng submarine fans are composed of deep-water branching channel and inter-channel sediments. Phase 4 of the Shuangfeng submarine fan consists of deep-water channel and lobe sediments. Tectonic events, including the broad uplift of the Tibetan Plateau and central-southern Vietnam during the late Miocene, reversal of the strike-slip Red River Fault, and rapid subsidence in the Qiongdongnan Basin at approximately 5.5Ma, provided favourable conditions for the growth of the Ledong submarine fan, Central Canyon and Shuangfeng submarine fan system.

Seismic responses and controlling factors of Miocene deepwater gravity-flow deposits in Block A, Lower Congo Basin

The Miocene deepwater gravity-flow sedimentary system in Block A of the southwestern part of the Lower Congo Basin was identified and interpreted using high-resolution 3-D seismic, drilling and logging data to reveal development characteristics and main controlling factors. Five types of deepwater gravity-flow sedimentary units have been identified in the Miocene section of Block A, including mass transport, deepwater channel, levee, abandoned channel and sedimentary lobe deposits. Each type of sedimentary unit has distinct external features, internal structures and lateral characteristics in seismic profiles. Mass transport deposits (MTDs) in particular correspond to chaotic low-amplitude reflections in contact with mutants on both sides. The cross section of deepwater channel deposits in the seismic profile is in U- or V-shape. The channel deposits change in ascending order from low-amplitude, poor-continuity, chaotic filling reflections at the bottom, to high-amplitude, moderate to poor continuity, chaotic or sub-parallel reflections in the middle section and to moderate-weak amplitude, good continuity, parallel or sub-parallel reflections in the upper section. The sedimentary lobes are laterally lobate, which corresponds to high-amplitude, good-continuity, moundy reflection signatures in the seismic profile. Due to sediment flux, faults, and inherited terrain, few mass transport deposits occur in the northeastern part of the study area. The front of MTDs is mainly composed of channel-levee complex deposits, while abandoned-channel and lobe-deposits are usually developed in high-curvature channel sections and the channel terminals, respectively. The distribution of deepwater channel, levee, abandoned channel and sedimentary lobe deposits is predominantly controlled by relative sea level fluctuations and to a lesser extent by tectonism and inherited terrain.

Vast amount of accommodation space controlled evolution of a continuous Pliocene–Pleistocene mixed cool-water carbonate-siliciclastic prograding wedge in the Bay of Oran (Western Mediterranean)

The Bay of Oran is part of the northern Algerian continental margin, located in the Western Mediterranean Sea between Europe and northern Africa. A regional terrace in ca. 320 m water depth described in earlier studies and a second deeper located one (∼1200 m water depth) provide an unusually vast amount of accommodation space for an observed prograding wedge. Seismo-stratigraphic interpretation of high-resolution reflection seismic data show different phases of mixed cool-water carbonate-siliciclastic deposition: (Ia) Initial aggradation with low dipping foreset deposition during early-Pliocene relative sea-level highstand. (Ib) Deposition transitions to progradation when aggradation reaches the base level. (IIa) Once progradation reaches the shelf break, terrace deposition is reduced to coarse fraction foreset deposits until it ceases entirely. (IIb) Finer sediments are bypassed and start to aggrade on the lower slope terrace until deposits reach the shelf terrace depth. (III) Due to accommodation space prolongation progradation recommences. Phase IIa and phase III deposits are separated by a hiatus. A drop in mean sea-level during the mid-Pleistocene will have caused the base level to fall below the upper strata, hence causing some reworking and redeposition. However, sea-level variations are not considered to be a main controlling factor of the depositional sequences. The evolution of this continuous Pliocene–Pleistocene mixed cool-water carbonate-siliciclastic prograding wedge is instead attributed to the controlling factor of this unusually vast amount of accommodation space. In closest proximity to the sea-floor, sparse recent sedimentation in form of 5–10 m thick sediment lobes can be observed in subbottom profiler data only. From a tectonic point of view, a prolongation of the Yusuf Fault into the survey area though expected by other authors could not be supported with the available dataset.

A revised depositional setting for Halton sediments in the Oak Ridges Moraine area, Ontario

Outcrop and continuous core descriptions, high-resolution seismic profiling, and downhole geophysical data are integrated with detailed mapping to update sedimentary and stratigraphic frameworks for Halton sediment, a complex mud-rich lithofacies succession. Halton sediment has a gradational transition from underlying Oak Ridges Moraine (ORM) sediment and can abruptly overlie Newmarket Till. Halton strata thin and fine upwards from ORM sand and gravel to graded sand, silt, and clay rhythmites, with muddy diamicton and sand and gravel interbeds. These strata fill basin lows and drape ORM sediment lobes and Newmarket Till drumlins. These distinct sedimentary units are here informally referred to as Halton formation. Formal Halton Till is a proposed subunit of Halton formation, a clay-rich diamicton mapped from Niagara Peninsula to ORM and eastward. Halton Till has traditionally been inferred to represent a late, climatically induced readvance of grounded ice from Lake Ontario basin, which deposited drumlinized till. Halton sedimentary architecture and facies are interpreted as deposition in an ice-marginal or subglacial lake bounded by Niagara Escarpment, ORM, and grounding line oscillation of a semi-buoyant ice shelf or ice lid over Lake Ontario. Large volumes of transported mud are distal equivalents of ORM high-energy gravelly sand deposits to the east. Glaciolacustrine sedimentation is indicated by mud-rich texture and laminations. Clay–silt rhythmites, diamicton interbeds, and intraclasts indicate ponding, debris flow, and periodic ice loading. Halton depositional model may apply to other muddy diamictons in Great Lakes basins. Halton formation facies are not compatible with proposed grounded ice stream events in Lake Ontario basin.

Modern sediment characteristics and accumulation rates from the delta front to prodelta of the Yellow River (Huanghe)

Since 1976, the main channel of the Yellow River (Huanghe) has been on the east side of the delta complex, and the river has prograded a broad new delta lobe in Laizhou Bay of the Bohai Sea. In 2012, extensive bathymetric and high-resolution seismic profiles were conducted and sediment cores were collected off the new delta lobe. This study examined delta sedimentation and morphology along a profile across the modern subaqueous Yellow River delta and into Laizhou Bay, by analyzing sediment radionuclides (137Cs, 210Pb and 7Be), sedimentary structure, grain-size composition, organic carbon content, and morphological changes between 1976 and 2012. The change in the bathymetric profile, longitudinal to the river’s course, reveals subaqueous delta progradation during this period. The subbottom boundary between the new delta lobe sediment and the older seafloor sediment (before the 1976 course shift) was identified in terms of lithology and radionuclide distributions, and recognized as a downlap surface in the seismic record. The accumulation rate of the new delta lobe sediment is estimated to be 5–18.6 cm year–1 on the delta front slope, 2 cm year–1 at the toe of the slope, and 1–2 cm year–1 in the shelf areas of Laizhou Bay. Sediment facies also change offshore, from alternations of gray and brown sediment in the proximal area to gray bioturbated fine sediment in the distal area. Based on 7Be distribution, the shorter-term deposition rate was at least 20 cm year–1 in the delta front.