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The distinction between turbidites, contourites and hemipelagites in modern and ancient deep-water systems has long been a matter of controversy. This is partly because the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap. In addition, the three facies types commonly occur within interbedded sequences of continental margin deposits. The nature of these end-member processes and their physical parameters are becoming much better known and are summarised here briefly. Good progress has also been made over the past decade in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics are summarised here in terms of standard facies models and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. A three-scale approach to distinction for all deep-water facies types should be attempted wherever possible, including large-scale (oceanographic and tectonic setting), regional-scale (architecture and association) and small-scale (sediment facies) observations.

Turbidites on active margins represent key archives of great earthquakes, yet turbidity currents triggered by non‐seismic events complicate paleoearthquake records and influence geochemical budgets. Sediment cores collected from highstand‐detached Astoria Canyon address whether non‐seismic turbidity currents are preserved in canyon stratigraphy. Detailed analysis of a core indicates fluvial origin of turbidites based on sedimentology, geochronology, and organic matter composition. Turbidites are ∼15 cm thick, graded, and laminated. Turbidite 210Pb activity is low, and depositional ages align with major Columbia River floods. Turbidite organic matter is terrestrial and modern (−26‰ δ13Corg, 18 C:N, ∼6 mg lignin per 100 mg OC). These deposits provide the first direct evidence of modern non‐seismic turbidite deposition in northern Cascadia, with implications including that highstand stratigraphy preserves non‐seismic events, turbidite composition reflects sediment source, and turbidite deposition represents a significant component of sediment and carbon accumulation.

Turbidite palaeoseismology has produced arguably the most comprehensive multimillennial scale records of subduction-zone earthquakes but is underpinned by techniques that are vigorously debated in earthquake science. Resolving this argument requires new direct observations that test the approach’s essential assumptions. Here we present measurements from turbidites triggered by the 2016 M w 7.8 Kaikōura earthquake in New Zealand, one of the most well-instrumented earthquakes in history. This natural experiment provides an ideal test for turbidite palaeoseismology because fault source, ground motions and turbidite deposition in discrete canyons are well-resolved by analysis of sediment cores combined with physics-based ground-motion modelling. We find that the Kaikōura earthquake triggered flows in ten consecutive canyon–distributary systems along a 200 km segment of the Hikurangi subduction margin where long-period (>2 s) peak ground velocities exceeded turbidity-current-triggering thresholds between 16–25 cm s −1 . Comparison between ground motions and turbidite deposition confirm that there is a predictable relationship between earthquake source, ground motions and deposition of coseismic turbidites. We demonstrate that the patterns of triggering and resultant turbidite character may preserve evidence of fault-rupture direction along with the radiating patterns and amplification of earthquake ground motions. Marine turbidite deposition is confirmed to relate to earthquake ground motions by an analysis of turbidite deposits and simulations of ground motions from the 2016 Kaikōura earthquake.

The Chengjiang biota provides critical insights into metazoan diversification during the Cambrian Explosion, preserved at multiple localities with varying fossil abundances across the Chengjiang Bay. This work reports new B/Ga and B/K data from three drill cores near fossil localities, to evaluate salinity influences on ecological distribution of the biota. The results document a pronounced B/Ga and B/K decline at the biota's basal horizon, alongside a southwestward‐increasing B/Ga gradient from <6 to ∼13. These findings suggest significant freshwater influx into the Chengjiang Bay and the Chengjiang biota was deposited under a temporally decreasing salinity context. Enhanced freshwater input likely promoted turbiditic deposition of the event beds preserving the Chengjiang biota. Crucially, our data demonstrate a southwestward‐increasing salinity gradient in the Chengjiang Bay that governed ecological distribution of the Chengjiang Biota, with brackish waters suppressing marine animal development in the northeast, whereas stable marine conditions sustained elevated biodiversity in the southwest.

Significant gas discoveries have been made in the southern offshore basin of Tanzania continental margin while no gas accumulation has been found in the northern part of the basin. This study was aimed at finding out the reasons behind absence of gas discoveries in the northern offshore Tanzania continental margin despite the presence of potential gas flow indicators. 2D seismic interpretation and well logs analysis allowed assessment of depositional architectural elements and structural features across the basin. These aspects revealed architectural variations that have been used to account for the current non-discovery status in the northern part of the basin. Results of this work have shown that basin topography, influence of tectonics, sediment supply and depositional and post-depositional processes varied significantly over the whole offshore Tanzania during the Cretaceous-Holocene period. For example, the available 2D seismic profiles show that the Quaternary extensional tectonics created a N-S to NE-SW trending fault controlled sub-basin in the northern part of the study area, but similar feature could not be seen in the southern part of the basin. The variations of key factors controlling sedimentary development also caused dissimilarities in deposit types and dominance of sandy and muddy successions. The northern part of the study area is dominated by complex channel-levee systems containing sandstone bodies while the southern part contains hybrid turbidite-contourite (HTC) deposits and their respective thick drift successions that are stepping southward onto the HTCs. Deposit types play important role in accumulation of hydrocarbons. The HTCs for example contain clean sandstones with high net-to-gross ratio, and may be used to explaining why the existing commercial gas discoveries are found in the southern offshore Tanzania and not in the northern part of the basin.

High amounts of Chattian-Langhian orogenic magmatism have generated volcaniclastic deposits that are interbedded within the penecontemporaneous sedimentary marine successions in several central-western peri-Mediterranean chains. These deposits are widespread in at least 41 units of different basins located in different geotectonic provinces: (1) the Africa-Adria continental margins (external units), (2) the basinal units resting on oceanic or thinned continental crust of the different branches of the western Tethys, (3) the European Margin (external units), and (4) the Western Sardinia zone (Sardinia Trough units). The emplacement of volcaniclastic material in marine basins was controlled by gravity flows (mainly turbidites; epiclastites) and fallout (pyroclastites). A third type comprises volcaniclastic grains mixed with marine deposits (mixed pyroclastic-epiclastic). Calc-alkaline magmatic activity is characterized by a medium- to high-potassium andesite-dacite-rhyolite suite and is linked to complex geodynamic processes that affected the central-western Mediterranean area in the ∼26 to 15 My range. The space/time distribution of volcaniclastites, together with a paleogeographic reconstructions, provide keys and constraints for a better reconstruction of some geodynamic events. Previous models of the central-western Mediterranean area were examined to compare their compatibility with main paleotectonic and paleogeographic constraints presented by the main results of the study. Despite the complexity of the topic, a preliminary evolutionary model based on the distribution of volcaniclastites and active volcanic systems is proposed.

The Forties Sandstone Member is an important deep-water reservoir in the Central North Sea. The role of depositional characteristics, grain-coating clays, and diagenesis in controlling the reservoir quality of the sandstones is poorly understood. The main aim of the study is to understand the role of depositional characteristics, grain-coating and pore-filling clays, and diagenesis in controlling the reservoir quality evolution of turbidite-channel sandstones. The study employed a multi-disciplinary technique involving thin section petrography and scanning electron microscopy (SEM) to investigate the impact of grain size, clay matrix content, mode of occurrence of grain-coating chlorite and illite, and their impact in arresting quartz cementation and overall reservoir quality in the sandstones. Results of our study reveal that porosity evolution in the sandstones has been influenced by both primary depositional characteristics and diagenesis. Sandstones with coarser grain size and lower pore-filling clay content have the best reservoir porosity (up to 28%) compared to those with finer grain size and higher pore-filling clay content. Quartz cement volume decreases with increasing clay-coating coverage. Clay coating coverage of >40% is effective in arresting quartz cementation. Total clay volume of as low as 10% could have a deleterious impact on reservoir quality. The Forties Sandstone Member could potentially be a suitable candidate for physical and mineralogical storage of CO2. However, because of its high proportion (>20%) of chemically unstable minerals (feldspar, carbonates, and clays), their dissolution due to CO2 injection and storage could potentially increase reservoir permeability by an order of magnitude, thereby affecting the geomechanical and tensile strength of the sandstones. Therefore, an experimental study investigating the amount of CO2 to be injected (and at what pressure) is required to maintain and preserve borehole integrity. The findings of our study can be applied in other reservoirs with similar depositional environments to improve their reservoir quality prediction.

Apatite inclusions hosted by zircon offer a means to probe the magmatic history of granitic rocks and better constrain the volatile budgets of crystallising granitic melts. Building on recently developed F–Cl–OH partitioning models for apatite and coexisting melt, we outline an approach for estimating the melt concentrations of F and Cl from the composition of apatite inclusions in zircon, constrained by Ti-in-zircon crystallisation temperatures. The melts in equilibrium with apatite inclusions in zircon for the ‘I-type’ Jindabyne, Why Worry and Cobargo granitic suites of the Lachlan Orogen (eastern Australia), have Cl concentrations of 20–2880 ppm and F concentrations of 65–575 ppm. Variations in melt Cl and F concentrations between the granitic suites is attributed to differences in source compositions, specifically the relative contribution of F-rich turbiditic sediments and Cl-rich juvenile arc magmas. Within individual granitic suites, the calculated melt F and Cl concentrations decrease with magmatic differentiation and falling melt temperatures, and this appears to reflect the partitioning of Cl and F into biotite and hornblende, and into exsolving aqueous fluids. This study demonstrates that apatite-melt exchange coefficients for F, Cl and OH can be applied to apatite inclusions in zircon to quantify the F and Cl content of the melt, without additional context from the host rock samples.

Manned submersible dives in the northwest South China Sea encountered substantial amounts of plastic litter accumulated at the base of scours along the floor of a submarine canyon, which may associate with the depositional behaviors of turbidity currents. In this study, we conduct numerical simulations using field‐scale bathymetry to investigate the relationship between the canyon floor morphology, flow processes, and the locations and sizes of the plastic litter piles. The consistent deposition pattern caused by the numerical turbidity currents with different input parameters indicate that morphology of the canyon may exert a dominant influence on turbidite deposition. This is attributed to a significant reduction in shear velocity as simulated turbidity currents flowing through the scours on the canyon floor. Spatial correspondence between deposits of turbidity currents and plastic litter accumulation suggests that suspended sediments and plastic may undergo simultaneous dynamic processes during the transportation of turbidity currents. Plain Language Summary The issue of marine plastic litter has attracted wide attention, particularly in terms of its transportation mechanisms and locations of accumulation on the ocean floor. Turbidity currents are subaqueous sediment‐gravity flows that can transport large amounts of sediment, nutrients and pollutants into the deep sea, yet there is sparse research on the dynamics of plastic litter transport under the control of turbidity currents, and its accumulation in the deep sea. Here, we present a series of numerical simulations of turbidity currents in a submarine canyon with various input parameters, when combined with observational data on topography and plastic litter distribution, confirm that turbidity currents constitute a plausible mechanism for the transport of plastic litter and for its accumulation in response to changes in flow associated with scours. In addition, we find that the concavity of the scours is also necessary for plastic litter accumulation, since it induces significant fluctuations in the shear velocity and the corresponding depositional process. Key Points Numerical simulations were applied to investigate turbidity currents as a cause for plastic litter accumulations in a submarine canyon The simulated turbidite deposits and observed plastic litter accumulations exhibit a strong spatial correspondence The morphology of the canyon floor may exert dominant influence on the plastic litter accumulations in submarine canyons

Turbidity currents transport vast amounts of sediment, carbon, and heat along submarine channels, yet their overspill onto channel‐levees and abyssal mixing remain poorly constrained due to lack of direct observations. Ocean‐bottom seismometers (OBS) deployed on the Congo Canyon–Channel levees captured the structure and turbulence of overspill during an exceptionally large canyon‐flushing event in 2020. Overspill persisted for 3 weeks and comprised numerous short (20‐min to 2‐hr) pulses focused at outer bends. Spectra during overspill show well‐resolved turbulence inertial subranges, yielding event‐average dissipation rates of 10−6–10−5 m2 s−3, comparable to energetic internal‐tide breaking. Abyssal overspill can therefore be long‐lasting and highly pulsed, providing an episodic but locally important source of deep‐ocean mixing. This new view of levee overspill has important implications for building levees and the interpretation of ancient turbidites. Individual levee deposits may be formed incrementally by many pulses of dilute and fine‐grained flow from a single turbidity current.