Submarine Channel Systems Research Articles

Sedimentary Characteristics and Evolution of the Late Miocene to Quaternary Tributary Channels in the Head of Bounty Channel, New Zealand

The Bounty Channel is a large-scale submarine channel system located in the eastern continental margin of New Zealand. Extending along the axis of the Bounty Trough, the channel system comprises three main tributaries (C1–C3) at its head, which merge downstream into a trunk channel leading to a terminal submarine fan. In this study, we use high-quality two-dimensional multichannel seismic data to investigate the formation and evolution of tributary channels C1 and C2. Four types of seismic facies are identified in the tributary channels: fill-type, mounded divergent, wavy, and subparallel facies. These seismic facies are correspondingly interpreted as topographic depression or channel fills, levees, sediment waves, and hemipelagic deposits. The Late Miocene tributary channels were developed above a pre-existing NE–SW-oriented depression. The Pliocene to Quaternary tributary channels are characterized by preferential development of higher levees on their left hand, and the presence of sediment waves on the lower levees of their right-hand, signaling an effect of the Coriolis force. The formation and evolution of the tributaries are primarily linked to regional tectonics, including increased convergence rate between the Pacific and Australian plates along the Alpine Fault in the Late Miocene and enhanced uplift and erosion at the Southern Alps during the Pliocene.

Interpreting environments of deposition from facies analysis of outcrop versus seismic reflection data: A cautionary tale from the Mount Messenger Formation, Taranaki Basin (New Zealand)

The lower part of the Mount Messenger Formation, which crops out along the North Taranaki coast (North Island, New Zealand), is widely regarded to display classic examples of exhumed basin floor fan strata. This interpretation is supported by numerous publications on the sedimentary facies and depositional environments inferred for these strata, which are exposed in coastal cliff exposures about 20 m high with limited lateral extent. Consequently, for almost three decades, this succession has served as an analogue and training ground for geoscientists investigating the features of basin floor fan deposits and their reservoir characteristics. Here, we bring together seismic stratigraphy and seismic geomorphology of 2D and 3D seismic reflection datasets, as well as photogrammetric models based on images collected using uncrewed aerial vehicle (UAV) drones from selected locations along the outcrop belt to challenge this paradigm. We analyzed seismic reflection data in an area immediately offshore and down-dip of the strata exposed in the coastal outcrop and found no objective criteria for submarine fan depositional elements based on accepted seismic stratigraphic criteria. Furthermore, mapping of seismic reflectors revealed large submarine channel systems (up to 3 km wide and up to 200 m deep) within the lower part of the Mount Messenger Formation. Submarine channel depositional elements (less than 250 m wide and 25 m thick) are also observed to incise through the outcrops, but they are generally below seismic resolution. In the context of the regional geology, we conclude that the lower Mount Messenger Formation accumulated as continental slope sediments cross-cut by channels rather than as basin floor fans. This study issues a cautionary tale about applying facies analysis to outcrop with limited 3D exposure to interpret sedimentary environments. The spatial distribution of facies and architectural elements viewed in seismic data are invaluable for testing the veracity of facies interpretations.

Morphological and architectural evolution of submarine channels: An example from the world's largest submarine fan in the Bay of Bengal

The characteristics and evolution of different types of channel-complex sets (CCSs) have long attracted attention from both academia and the oil industry. 3D seismic data from the world's largest submarine fan in the Bay of Bengal allow the exploration of morphology, architecture, and evolution of a Pleistocene submarine channel system from inception to abandonment. Four types of architectural elements are recognized, including feeder and distributary channel-complex set (CCS), levees, bend cutoffs, and incised and unincised crevasse splays. Three types of CCSs are recognized: (1) erosional non-leveed CCSs with the lowest values of channel width (W), thickness (T), and cross-sectional area (Ca) (mean values of W = 153 m, T = 20 m, and Ca = 2613 m2); (2) graded CCSs with the highest values of W, T and Ca (mean values of W = 745 m, T = 89 m, and Ca = 49183 m2); (3) aggradational leveed CCSs with intermediate values of W, T and Ca (mean values of W = 476 m, T = 56 m, and Ca = 21968 m2). Graded CCSs and aggradational leveed CCSs have overbank levees, crevasse splays and bend cutoffs, whereas erosional non-leveed CCSs lack these features. Such architectural difference in overbank deposits suggests a channel evolution pattern of initial incision (erosional non-leveed CCSs) and then aggradation (graded and aggradational leveed CCSs), resulting in a pattern of incision-to-aggradation channel evolution. An increase-then-decrease in channel morphometrics (represented by W, T, and Ca) from erosional non-leveed CCSs with the lowest mean values of W, T, and Ca, to graded CCSs with the highest mean values of W, T, and Ca, and finally to aggradational leveed CCSs with the intermediate mean values of W, T, and Ca suggest that the incision-to-aggradation channel evolution is related to waxing-then-waning energy cyclicity. Submarine channel turbidity flows during the waxing energy phase became progressively more energetic and increasingly more erosional, producing erosional non-leveed CCSs. Instead, submarine channel turbidity flows during the waning energy phase were more diluted and increasingly more depositional, thereby producing aggradational leveed CCSs. The phase of peak environmental energy was most likely accompanied by most energetic turbidity currents, resulting in graded CCSs. Results and observations from the current study contribute to a better understanding of architectural complexity and evolution of submarine channels.

Flow dynamics and sedimentation at a turbidity channel confluence in the Yinggehai basin, northwestern South China sea

Submarine channel systems transport vast amounts of terrestrial sediment into the deep sea via turbidity currents, however, there is a paucity of research detailing their dynamics, especially regarding the issue of how flows transport sediment and deposit at channel bends and channel junctions. From the analysis of core data, a high-resolution 3D seismic dataset, and local topography, a 3D numerical model is used to simulate the evolution of turbidity currents containing multiple size classes of sediments in the Late Miocene submarine channels in the Yinggehai Basin, northwestern South China Sea. The model solves the Reynolds-averaged Navier–Stokes (RANS) equations, the mass conservation equation, and the Exner equation for bed evolution caused by sediment entrainment and deposition. The results for the tendency of the total volumetric concentration of sediment in the turbidity current and bed thickness distribution reasonably match the infilled thickness of the channel interpreted from seismic data. The turbidity current in submarine channels is limited by the sloping topography and the channel geometry. Geochemical results show that, during the Late Miocene, sediments were derived from mixed sources. The simulation result accurately reveals the scope and magnitude of sediment contributions from each provenance. The confluence zone of the two channels (W and E) receives coarse-grained thick-bedded sediments via E channel flow transport showing a homogeneous distribution, a good hydrocarbon reservoir. This study improves our understanding of the processes of turbidity currents and their depositional characteristics within submarine channels, the reconstruction of their depositional environment, flow structures, spatial partitioning of sediment, and reservoir distributions within sinuous channels.

Lateral and temporal variations of a multi-phase coarse-grained submarine slope channel system, Upper Cretaceous Cerro Toro Formation, southern Chile

ABSTRACTUnderstanding variations in the sedimentary processes and resulting stratigraphic architecture in submarine channel systems is essential for characterizing sediment bypass and sedimentary facies distribution on submarine slopes. In the Santonian to Campanian Cerro Toro Formation, southern Chile, a coarse-grained slope system, informally known as the Lago Sofia Member, developed in a structurally controlled environment, with complex and poorly established relationships with the surrounding mud-rich heterolithic deposits.A detailed architectural analysis of the most continuous and best-exposed channel system in the Lago Sofia Member, the Paine C channel system, provides insights on lateral facies transitions from channel axis to margin, stacked in a multi-phase sequence of events marked by abrupt changes in facies, facies associations, and architecture.The Paine C channel system is incised into siltstones and claystones interbedded with thin-bedded very fine sandstones, interpreted to be either channel-related overbank or unrelated background deposits. The coarse-grained deposits are divided into a lower conglomeratic unit and an upper sand-rich unit. The lower conglomeratic unit can be further subdivided into three phases: 1) highly depositional and/or aggradational, dominated by thick and laterally continuous beds of clast- to matrix-supported conglomerate, herein named transitional event deposits; 2) an intermediate phase, including deposits similar to those dominant in phase 1 but also containing abundant clast-supported conglomerates and lenticular sandstones; and 3) a bypass-dominated phase, which records an architectural change into a highly amalgamated ca. 45-m-thick package composed purely of lenticular clast-supported conglomerates with local lenticular sandstones. Between the conglomeratic phases, a meter-scale package composed of interbedded thin- to medium-bedded sandstone and mudstone deposits is interpreted to drape the entire channel, indicating periods of weaker gravity flows running down the channel, with no evidence of bedload transport.The upper sand-rich unit is divided into lower amalgamated and upper non-amalgamated phases, and represents a rapid architectural change interpreted to record an overall waning of the system. The sandstone unit laps out onto a mass-transport complex which is interpreted to have been triggered initially at the same time as major architectural change from conglomerates to sandstones.While mindful of the fact that each system is a complete analogue only for itself, we propose a new depositional model for coarse-grained submarine channel systems, in which particular characteristics can provide significant insights into architectural heterogeneity and facies transitions in channelized systems, allowing substantial improvement in subsurface facies prediction for fluid reservoirs.

The Sediment Budget Estimator (SBE): A process model for the stochastic estimation of fluxes and budgets of sediment through submarine channel systems

AbstractTurbidity currents transport vast amounts of sediment through submarine channels onto deep-marine basin-floor fans. There is a lack of quantitative tools for the reconstruction of the sediment budget of these systems. The aim of this paper is to construct a simple and user-friendly model that can estimate turbidity-current structure and sediment budget based on observable submarine-channel dimensions and general characteristics of the system of interest. The requirements for the model were defined in the spirit of the source-to-sink perspective of sediment volume modeling: a simple, quantitative model that reflects natural variability and can be applied to ancient systems with sparse data availability. The model uses the input conditions to parameterize analytical formulations for the velocity and concentration profiles of turbidity currents. Channel cross section and temporal punctuation of turbidity-current activity in the channel are used to estimate sediment flux and sediment budget. The inherent uncertainties of geological sediment-budget estimates motivate a stochastic approach, which results in histograms of sediment-budget estimations, rather than discrete values. The model is validated against small-scale experimental turbidity currents and the 1929 Grand Banks turbidity current. The model performs within acceptable margins of error for sediment-flux predictions at these smallest and largest scales of turbidity currents possible on Earth. Finally, the model is applied to reconstruct the sediment budget related to Cretaceous slope-channel deposits (Tres Pasos Formation, Chile). The results give insight into the likely highly stratified concentration profile and the flow velocity of the Cretaceous turbidity currents that formed the deposits. They also yield estimates of the typical volume of sediment transported through the channels while they were active. These volumes are demonstrated to vary greatly depending on the geologic interpretation of the relation between observable deposit geometries and the dimensions of the flows that formed them. Finally, the shape of the probability density functions of predicted sediment budgets is shown to depend on the geological (un)certainty ranges. Correct geological interpretations of deep marine deposits are therefore indispensable for quantifications of sediment budgets in deep marine systems.

Late Messinian submarine channel systems in the Levant Basin: Challenging the desiccation scenario

Abstract The question of whether the Mediterranean Sea desiccated during the Messinian salinity crisis (MSC) has been strongly debated for decades. In the Levant Basin, this debate was recently reignited in relation to the latest stage of the crisis after cessation of salt deposition. The desiccation supporters argue that salt truncation—and its subsequent burial by a latest Messinian, clastic-rich evaporitic unit—occurred subaerially on a desiccated seafloor. However, we show that this latest Messinian unit contains a dense net of channels with meanders, levees, and overspill deposits and is very similar to the turbidite channels observed on the modern seafloor. The aggradation characteristics of these buried channels (levee height, channel depth, and channel-floodplain coupling) indicate a marine rather than fluvial origin. Our conclusion adds to the findings of a previous study that salt truncation occurred in deep waters by dissolution. In a wider perspective, we suggest that the flush of clastics into the basin during the last stage of the MSC indicates a combination of wet climate and sea-level rise that started before the Zanclean (earliest Pliocene).

Evolution of submarine channel morphology in intra-slope mini-basins: 3D-seismic interpretation from offshore Niger delta

The morphological characteristics of a submarine channel system, within buried intra-slope mini-basins in the offshore Niger Delta have been investigated on 3D seismic data. The studied submarine channel named Amaku Channel Levee System (ACLS) initiated after avulsion of a feeder channel called Amaku Major System (AMS). The ACLS runs across three folds (A, B, and C), related to mobile shale deformation, being underlain by mass transport complexes (MTCs), lobes, and levees. From three defined channel reaches (upper, middle, and lower reaches), we have used seismic facies description, channel architecture characterization and quantitative analyses to decipher the spatial and temporal evolution of the channel levee system. Our results reveal that the western channel margin was controlled by structural barriers associated with mobile shale deformation, while the eastern channel margin was influenced by depositional barriers linked to levees and mass transport complexes (MTCs). We argue that the depositional barriers are in some cases more efficient than the structural barriers in controlling channel pathways, since pre-channel sediments confine the channel elements and divert them against positive reliefs. Seismic observations show that channels migrate from folds to structural lows causing flow stripping processes. Downstream variations of morphological parameters (such as sinuosity, width, and levee width), indicate that pre-existing deposits prevented these basin-ward migrations, driving straightening and narrowing of the channel system. This study reveals that submarine channels can undergo dramatic morphological and stratigraphic changes in structurally complex areas because of the configuration of sidewall reliefs, which is controlled, in turn, by the interplay between structural deformation and pre-channel deposition.

The formation and development of avulsions and splays of submarine channel systems: Insights from 3D seismic data from the northeastern Bengal Fan

Avulsions and splays of submarine channels are important autogenic responses affecting sediment distribution in deep-water areas; however, their formation and development are still not well understood. Using high-resolution 3D seismic data and spectral decomposition red–green–blue (RGB) color blends, two seismically well-imaged submarine channel systems (SCS1 and SCS2) on the northeastern Bengal Fan are used to document the formation and development of avulsions and splays. The results suggest that avulsions occur mainly during the early evolution stage of submarine channel systems. SCS1 and SCS2 are respectively accompanied by one and four avulsions and accordingly produce two and five independent submarine channels. During this early phase, these channels collectively incise into the underlying stratigraphy but lack levee deposits. Splays, in contrast, develop consistently during the late evolution stage of the submarine channel systems. Three crevasse splays and three overbank splays develop on the overbank areas of SCS1 and SCS2. During that late stage, channel and levee deposits build over the site of former erosion, thus forming the aggradational phase of channel evolution. Crevasse and overbank splays are two different types of splays observed on this part of the Bengal Fan. The former are created by flow breaching of the adjacent levees, producing large-scale elongated shapes; they are related to relatively stable sediment gravity flows, a high-degree of channel instability, and steep levee topography. Overbank splays, however, are created by flow overtopping adjacent levees and produce small-scale, fan-like shapes; they are related to gradually-weaking sediment gravity flows, a low-degree channel unstability, and gentle levee topography.

Seismic geomorphology of a Late Cretaceous submarine channel system in the Kribi/Campo sub-basin, offshore Cameroon

In this study, a 3D seismic reflection dataset and well-log data were integrated to investigate the geometry and internal configuration of a submarine channel system within the Late Cretaceous interval of the deep-water Kribi-Campo sub-basin, offshore Cameroon. This interval is characterized by a well-developed submarine channel system consisting of an early and a late-stage channel. Morphologically, the submarine channel system has a northeast-southwest trend and is U-shaped in cross-section with a length of 56 km within the study area. The early-stage channel has a relatively straight morphology and varies in width and depth from 3 to 5 km and 89–197 m, respectively. However, the late stage of the channel is characterized by a narrower (1–3 km) and shallower (41–103 m) incision, with sinuous morphology carved into the early channel infill. The changing interaction of differential local tectonic, relative sea level, source sediment supply and change in slope gradient are the major control on the geometry and internal characteristics of the submarine channel system. At local scale, basin tectonics is associated with the development of a structural high, controlling submarine channel morphology and depositional patterns in these filled ponded basins. The filling of the channel system coincided with the long-term Maastrichtian relative sea level rise, punctuated by higher order falls in relative sea level. Sand appears to have been fed to the channel system by the palaeo-Sanaga and palaeo-Nyong Rivers, with sand rich aprons developed were these rivers crossed into the study area. The early-stage of the submarine channel is dominated by coarse-grained sediments in the southwest and fine-grained sediments in the northeast, while the late-stage channel is mainly filled with fine-grained sediments. The presence of coarse-grained sediments occurring within the submarine channel axis downstream represents a potential for hydrocarbon reservoirs. The 3D seismic geomorphological analysis of this ancient submarine channel system along the western African margin, as presented in this study, has broad implications in the understanding of the distribution of deep-water sediments with potential for hydrocarbon exploration in the region.

Provenance constraints for the evolution of a multibranch submarine channel system across the Ledong gas field, eastern margin of the Yinggehai Basin

Provenance identification and evolving process restoration for submarine sedimentary systems are crucial for understanding the deposition process of gravity flows and for future evaluations of oil and gas reservoirs. This paper targets a newly discovered late Miocene multibranch submarine channel developed in the Ledong gas field, eastern margin of the Yinggehai Basin, South China Sea. The natural gas sweet spot, Ledong block, located in the intersection area of the channel's three branches, was systematically studied via zircon U–Pb dating, heavy minerals, seismic and well logging approaches, and structure analysis to obtain information about the characteristics of provenance and the process of sedimentation. Detrital zircon U–Pb age distribution and heavy mineral assemblage results indicate that the channel shares similar geochronological signatures of sediment from the rivers in western Hainan Island. The seismic interpretation suggests that the East Branch bifurcates at the intersection area, meeting the North Branch in the northwest and extending southeast to form the South Branch. Active fault movement during the early Miocene provides negative topography for the formation of the gravity flow channel, while the later sea level fall facilitates the transport and deposition of the river sediments. This study finally reconstructs a time series-based sedimentary model to better illustrate the channel evolution process. The development of channel reservoirs in the southeast Yinggehai Basin could be mainly constrained by the fault's activation as well as the Hainan sediment supply. The findings reveal the major provenance constraints for the evolution of a multibranch submarine channel system across the Ledong gas field and are of great significance for future natural gas resource exploration.

Fill, flush or shuffle: How is sediment carried through submarine channels to build lobes?

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

Sedimentary features and filling process of the Miocene gravity-driven deposits in Ledong area, Yinggehai Basin, South China Sea

The shallow marine channels and fans in the Yinggehai Basin have huge hydrocarbon exploration potential. The depositional features and filling processes of the submarine channel and fan system during 10.5–7.2 ma were studied based on seismic data, cores, well curves, and lab data. (1) Five depositional elements were recognized in the channel system, including PSC, MSC, DSC, levee, and abandonment fill, and the deposits show the typical sedimentary structure of debris flow. The filling process of the channel system was divided into three stages based on deposits supply intensity. The stages were made up of several filling units, and each unit possessed at least one complete channelized depositional succession. (2) The fan system was developed under the large-scale “U” shaped feeding canyon, and its filling process was divided into two stages, the shape and distribution were controlled by shelf break and syn-sedimentary faults in the early stage, and was influenced by the localized changes of paleogeomorphology in late stage. The influence factors for the development of gravity-driven systems were summarized into two levels: regional depositional environment changes and localized distinctive geologic settings. The former one controlled the development of shallow water gravity-driven deposits in the whole basin, mainly including rapid falling of sea-level, moderate subsidence rate, and stable deposits supply. The latter one controlled the morphology and distribution of depositional elements in gravity-driven systems. The pre-existing banded low terrain induced by blind faults controlled the shape of the confined channel, and variable faulting intensity in different segments of the syn-sedimentary fault and localized paleogeomorphology changes influenced the distribution of channels and inner fan in the fan system. The study of deposition features, internal architecture, and controlling factors may provide a reference for further exploration in this area and a deeper understanding of gravity-driven processes in shallow marine.

Systematic organization of thin-bedded turbidites in ancient deep-marine levees: Possible evidence of rhythmic pulsing in turbidity currents

ABSTRACT Deep-marine levees are areally extensive features that border submarine channel systems and act to confine throughgoing sediment gravity flows. Compared to the adjacent channel, where episodes of erosion and bypass are commonplace, levees are mostly depositional features that experience little erosion, and therefore high preservation potential of individual beds, and as a consequence are generally assumed to provide a nearly continuous depositional record of sediment transport events down deep-marine slopes. Nevertheless, despite their size, volumetric prominence, and interpretive significance in the deep-marine sedimentary record, levees have received much less research attention compared to the adjacent channels. Exceptionally well exposed levee deposits in the Neoproterozoic Windermere Supergroup are dominated by thin-bedded, upper-division turbidites that form sharply bounded bedsets typically comprising 2–10 beds with similar grain size, bed thickness, Tc and Td/e division thickness, number of sets of ripple cross-lamination per bed, and ripple height, width, and spacing; additionally, the lithological and dimensional characteristics of the component beds in a bedset change at similar rates and spatial position along depositional strike. Such similarity suggests that deposition of each bed in a bedset is not associated with separate flow events (i.e., turbidity current), but instead represent systematic and recurring pulses or surges during a single flow event with similar hydraulic and textural conditions as they overspilled the channel margin and spread over the levee. Additionally, pulses were of sufficiently low frequency to allow the accumulation of a Td/e layer at the top of each bed and at least partial consolidation of the underlying bed. Finally, studies that have monitored and evaluated the frequency of turbidity currents in modern deep-marine systems suggest that there are a smaller number of beds, and even fewer bedsets preserved in ancient levee deposits than flow events. This suggests that many flows do not travel far enough downslope, or are of insufficient height, to result in any significant deposition on the levee. The bulk of levee strata, therefore, is likely deposited by anomalously large, pulsing flows that deposit multiple beds, but occur only once every several hundred to even several thousand years.

Evolution of Deep-Water Sinuous Channel Offshore Cameroon, West Africa, Using 3D Seismic Data

Using newly acquired 3D seismic data, the deep-water sinuous channel has been discovered in the Miocene sequence on the continental margin of Cameroon, West Africa. The investigation is using high-resolution 3D seismic data, covering an area of 1500 km2, with the water depth ranging from 400 m - 2000 m. Two submarine channel systems have been documented in the northern part of the study area, the offset stacked channel and North-Northeast – Southwest channel. The offset stacked channel dimension is about 3 km wide, c. 20 km long and c. 500 ms TWT thick, extending from east to west. The evolution of this channel can be divided into three stages based on the changes in channel scale, geometry, and fill type. In the initial stage, the channel is characterized as symmetry ‘U’ shaped, bidirectional onlap, high amplitude reflections, inferring to high energy flow and sand-prone channel fill. In the following stages, the channel reduced the size and flow energy. North-Northeast – Southwest channel developed at the end of the Miocene. It is c. 3 km wide, 20 km long, 50 ms TWT thick, indicating a new sediment source for the study area. At the end of the Miocene, both channel systems show a high sinuously as an indicator of low energy flows. Uplift in the Late Miocene possibly leads to the compacted channel complex which is appeared in the anticline form, giving a great hydrocarbon trap potential for the study area.

Knickpoints and crescentic bedform interactions in submarine channels

AbstractSubmarine channels deliver globally important volumes of sediments, nutrients, contaminants and organic carbon into the deep sea. Knickpoints are significant topographic features found within numerous submarine channels, which most likely play an important role in channel evolution and the behaviour of the submarine sediment‐laden flows (turbidity currents) that traverse them. Although prior research has linked supercritical turbidity currents to the formation of both knickpoints and smaller crescentic bedforms, the relationship between flows and the dynamics of these seafloor features remains poorly constrained at field‐scale. This study investigates the distribution, variation and interaction of knickpoints and crescentic bedforms along the 44 km long submarine channel system in Bute Inlet, British Columbia. Wavelet analyses on a series of repeated bathymetric surveys reveal that the floor of the submarine channel is composed of a series of knickpoints that have superimposed, higher‐frequency, crescentic bedforms. Individual knickpoints are separated by hundreds to thousands of metres, with the smaller superimposed crescentic bedforms varying in wavelengths fromca16 m toca128 m through the channel system. Knickpoint migration is driven by the passage of frequent turbidity currents, and acts to redistribute and reorganize the crescentic bedforms. Direct measurements of turbidity currents indicate the seafloor reorganization caused by knickpoint migration can modify the flow field and, in turn, control the location and morphometry of crescentic bedforms. A transect of sediment cores obtained across one of the knickpoints show sand–mud laminations of deposits with higher aggradation rates in regions just downstream of the knickpoint. The interactions between flows, knickpoints and bedforms that are documented here are important because they likely dominate the character of preserved submarine channel‐bed deposits.

New statistical quantification of the impact of active deformation on the distribution of submarine channels

Submarine channel systems play a crucial role in governing the delivery of sediments and pollutants such as plastics from the shelf edge to deep water. Understanding their distribution in space and time is important for constraining the locus, magnitude, and characteristics of deep-water sedimentation and for predicting stratigraphic architectures and depositional facies. Using three-dimensional seismic reflection data covering the outer fold-and-thrust belt of the Niger Delta, we determined the pathways of Miocene to Pliocene channels that crossed, at 173 locations, 11 fold-thrust structures for which the temporal and spatial evolution of strain rates has been constrained over a period of 11 m.y. We use a statistical approach to quantify strain and shortening rate distributions recorded where channels have crossed structures compared to the fault array as a whole. Our results prove unambiguously that these distributions are different. The median strain rate where channels cross faults is &amp;lt;0.6%/m.y. (~40 m/m.y.), 2.5× lower than the median strain rate of active fault segments (1.5%/m.y.) with a marked reduction in the number of channel-fault crossings where fault strain rates are &amp;gt;1%/m.y. Our results quantify the sensitivity of submarine channels to active deformation at a population level for the first time and enable us to predict the temporal and spatial routing of submarine channels affected by structurally driven topography.

The Geomorphology of Submarine Channel Systems of the Northern Line Islands Ridge, Central Equatorial Pacific Ocean

More than 844,000 km² of the northern Line Islands Ridge mapped with multibeam bathymetry and backscatter provide unprecedented views of the geomorphology of this isolated area in the central equatorial Pacific Ocean. A compilation of all available multibeam data in the area reveals six extensive submarine dendritic channel systems that encompass a combined drainage area that exceeds 60,000 km². The channel systems occur in a predominately carbonate environment and are the longest calciclastic submarine channel systems mapped in the oceans to date. The channel systems occur in a carbonate-dominated region well above the carbonate compensation depth and have developed into the surface of basins that are surrounded by small guyots and seamounts that make up a discontinuous rim around the summit of the northern Line Island Ridge. The channels have mostly straight or gently curved well-developed tributaries and main reaches. Although the Line Island Ridge has been dated at 86 to 68 Ma old, the channels occur on the surface and are not buried by any significant sediment accumulations. Levees are very rare along the channel banks and no bathymetric expression of submarine fans was found where the channels exit onto the adjacent abyssal basins. There is sparse evidence of landslide deposits throughout the ridge although the flanks of the guyots exhibit numerous headwall scarps. The presence of plunge pools below the northwest escarpment, together with well-defined channels meters to hundreds of meters deep relative to the surrounding seafloor, suggests the channels might be relatively recent (perhaps late Neogene or even younger) features developed long after the ridge subsided more than a kilometer below sea level.

Dynamic accumulation of gas hydrates associated with the channel-levee system in the Shenhu area, northern South China Sea

Abstract Research on the formation and distribution of submarine channel systems and associated gas-bearing fluids is of great significance for gas hydrate exploration. Disseminated gas hydrates with high saturation up to 65% were recovered from a submarine ridge, equivalent to the levee of the channel–levee system in the Shenhu area, northern South China Sea. Sedimentary deposits in the submarine ridge were dominated by fine-grained silt and clay-rich silt; gas hydrates with relatively high saturation preferentially accumulated in coarser sediments with less clay content. Although abundant foraminifera fossils may have increased reservoir pore space, their presence was not a necessary condition for high-saturation hydrates. Higher levels of pyrite appeared in the reservoirs corresponding to high-saturation hydrates, which suggests that the reducing environment caused by sufficient methane provided adequate gas to form higher-saturation hydrates. Because of the migration of the channel–levee system, different channels formed their respective depositional systems composed of channel-filling, buried channel-filling, erosion grooves, and slumped turbidities. Relatively coarse-grained deposits were identified in the channel fillings and levees, and the accumulation of hydrates was affected by the lithological features of the sediments and their spatial coupling with the gas hydrate stability zone (GHSZ). GHSZ modeling based on in situ measurements indicated that erosion and sedimentation, as well as variations of the geothermal gradient, resulted in the upward/downward migration of bottom simulating reflectors (BSRs). On the erosion flank of the channel, the strata thinned, and rapid erosion was likely to destroy the shallower BSR, causing gas hydrate decomposition and methane release, and may have caused turbidite slumping and seepage, whereas the strata thickened on the deposition flank of the channel. The BSR in the channel–levee system would gradually move toward the new GHSZ, eventually forming a new BSR; parts of the BSR that formed under the original P–T conditions have remained, and double BSRs occurred in the seismic profile. The thermal fluid that moved upward through a gas chimney may also have caused the migration of the GHSZ, resulting in the emergence of double BSRs. During the lateral migration of the channel and the vertical migration of the gas-bearing fluid, there was a dynamic adjustment relationship between the GHSZ and the erosion–deposition process of the channel, resulting in the dynamic accumulation of hydrates in the Shenhu area. A model to demonstrate the relationship between channel migration and variation of the BSR was established, which is of great significance for understanding the formation and accumulation mechanisms of gas hydrates.

The evolution of submarine slope-channel systems: Timing of incision, bypass, and aggradation in Late Cretaceous Nanaimo Group channel-system strata, British Columbia, Canada

Abstract Submarine channel systems convey terrestrially derived detritus from shallow-marine environments to some of the largest sediment accumulations on Earth, submarine fans. The stratigraphic record of submarine slope channels includes heterogeneous, composite deposits that provide evidence for erosion, sediment bypass, and deposition. However, the timing and duration of these processes is poorly constrained over geologic time scales. We integrate geochronology with detailed stratigraphic characterization to temporally constrain the stratigraphic evolution recorded by horizontally to vertically aligned channel-fill stacking patterns in a Nanaimo Group channel system exposed on Hornby and Denman Islands, British Columbia, Canada. Twelve detrital zircon samples (n = 300/sample) were used to calculate maximum depositional ages, which identified a new age range for the succession from ca. 79 to 63 Ma. We document five phases of submarine-channel evolution over 16.0 ± 1.7 m.y. including: an initial phase dominated by incision, sediment bypass, and limited deposition (phase 1); followed by increasingly shorter and more rapid phases of deposition on the slope by laterally migrating (phase 2) and aggrading channels (phase 3); a long period of deep incision (phase 4); and a final rapid phase of vertical channel aggradation (phase 5). Our results suggest that ∼60% of the evolutionary history of the submarine channel system is captured in an incomplete, poorly preserved record of incision and sediment bypass, which makes up &amp;lt;20% of outcropping stratigraphy. Our findings are applicable to interpreting submarine channel-system evolution in ancient and modern settings worldwide and fundamentally important to understanding long-term sediment dispersal in the deep sea.