Turbidite Research Articles

Transport of ‘Nama’‐type biota in sediment gravity and combined flows: Implications for terminal Ediacaran palaeoecology

ABSTRACTThe lower Nama Group in southern Namibia contains trace fossils and soft‐bodied and biomineralized macro‐organisms from the terminal Ediacaran Period (ca 550 to 539 Ma), offering insights into early metazoan evolution. Interpretation of the fossilized Nama Group organisms as being preserved in, or very close to, the environments in which they originally lived has yielded insights into organism feeding habits, reproduction and life histories. Sedimentological evidence presented here reveals that typical ‘Nama‐type’ Ediacaran macro‐fossils (Cloudina, Ernietta, Pteridinium and Rangea) in the Dabis and Zaris formations of the Witputz Sub‐basin seldom preserve organisms in life position in their original palaeoenvironments. Both soft‐bodied and biomineralizing organisms were transported in sediment gravity flows (debris flows, turbidity flows and transitional debris flow‐turbidity flow ‘hybrid’ event beds) or combined flow (hummocky cross‐strata) to their terminal environment of deposition in shoreface and offshore shelf settings. Transport has placed studied beds and their associated macro‐organisms in depositional settings detached from the original life habitat, with macro‐organisms sourced from shallower‐water, up‐slope environments. Integrated sedimentological and palaeontological data indicate that the Nama Group may not provide a high‐fidelity record of original Nama ecosystems. Individual macro‐organisms are clasts within beds, and can be horizontal, imbricated or chaotic in orientation. Transport can blend different communities at various scales (bed, outcrop and basin), complicating interpretations of life habitats, species interactions and taxon‐specific ecology, such as feeding behaviour and life position of organisms. Recognition of organism transport also impacts datasets used for comparing global Ediacaran fossil assemblages, with implications for tracking spatial and temporal patterns in early animal evolution.

3D stochastic simulation of a deep-water turbidite system: An example from the Los Molles Formation, southern region of the Neuquén Basin, Argentina

A recurring challenge in geological modeling is bridging the gap between different scales. For example, difficulties arise when connecting outcrop data through production to exploration scale models. An object-based stochastic simulation was performed using outcrop data from the Arroyo La Jardinera area in the southern region of the Neuquén Basin, Argentina. This simulation involved four depositional sequences in a vertical succession that includes turbidites and associated deep marine facies. The aims of this study are (a) to determine the best geological model consistent with field and aerial image data; (b) to validate the application of object modeling to determine facies distribution; (c) to evaluate uncertainties from models based on scarce data. The studied interval covers a transgressive (J1) to regressive succession (J21, J22, and J23) of basin plain to slope depositional settings, featuring sandy and gravelly turbidite channels, turbidite lobes and interlobes, lobe fringes, and muddy slope and basin plain. Each depositional sequence model was constructed using specific input parameters for architectural elements, with lithological proportions based on sedimentary logs. The J1 sequence includes basin plain, lobe fringe, and minor lobe deposits; J21 features turbidite lobes, fringes, and subordinate channels; J22 accommodates turbidite channels scoured into muddy slope facies; and J23 encompasses gravelly and sandy turbidite channels carved on muddy slope facies. The geostatistical modeling of outcrop data has allowed building a quantitative sedimentological model useful for understanding subsurface facies heterogeneity in both exploration (vertical) and production (horizontal) scales.

Recent ice‐contact delta formation in front of Pio XI glacier controls sedimentary processes in Eyre Fjord, Patagonia

AbstractPio XI Glacier (49°S) is the largest and one of the very few advancing glaciers in Patagonia. Satellite data indicate that the main glacier terminus transitioned from calving to land‐based around 2010, effectively resulting in the formation of an ice‐contact delta at the head of Eyre Fjord. Here, we investigate how this ice‐contact delta formation affected sediment transport processes in Eyre Fjord. Sediment cores and seismic profiles collected along the fjord provide evidence for a relatively abrupt increase in the number and magnitude of turbidity currents, coeval with the formation of the ice‐contact delta. This observation is supported by modern summer hydrographic observations and bathymetric data. We posit that the ice‐contact delta formation resulted in sediment input being concentrated at specific subaerial locations across the fjord head, which favoured the development of plume‐triggered turbidity currents. This suggests that a sudden increase in turbidite thickness in fjord sediment records could represent ice‐contact delta development at fjord heads.

Role of Organic Matter Present in the Water Column on Turbidity Flows

Turbidity flows are known to be affected by the density difference between sediment plumes and the surrounding water. However, besides density, other factors could lead to changes in flow propagation. Such a factor is the presence of suspended organic matter. Recently, it was found that flocculation does occur within plumes upon release of a sediment/organic matter mixture in a lock exchange flume. In the present study, mineral sediment (illite clay) was released into the outflow compartment containing water and synthetic organic matter (polyacrylamide flocculant). Even though the density of water was barely affected by the presence of flocculant, flow head velocity was observed to be larger in the presence of flocculant than without. Samples taken at different positions in the flume indicated that flocs were created during the small current propagation time (about 30–60 s) and that their sizes were larger with higher flocculant dosage. The size of flocs depended on their positions in the flow: flocs sampled in the body part of the flow were larger than the ones sampled at the bottom. All these properties are discussed as a function of sediment–flocculant interactions.

New insights on gravity flow dynamics during submarine canyon flushing events

Millions of tons of material are flushed through submarine canyons during infrequent high-magnitude events, transporting coastal sediment to the deep ocean. However, observations related to individual canyon flushing events are challenging due to the destructive nature and infrequency of flushing events. The impacts of one of the largest gravity flows in the past decade were documented in Kaikōura Canyon, Aotearoa−New Zealand, where >1 km3 of sediment was mobilized by the 2016 CE Kaikōura earthquake (Mw 7.8). We present new high-resolution (<1 m) multibeam data collected with an autonomous underwater vehicle (AUV) along the Kaikōura Canyon axis, together with side-scan sonar and seafloor video imagery. These data sets reveal a wide range of erosional and depositional features that were not previously identified. Eroded bedrock and deep erosional structures are found in the upper canyon, including linear grooves, and rockfall debris (>5-m-diameter boulders). This erosional area transitions downcanyon to coarse-grained depositional bedforms, including cyclic steps and gravel waves (average wavelengths of 250 m and wave heights of ∼20 m), covering the mid- and lower canyon. Our observations provide high-resolution field-based evidence of (1) flow transformation, from a debris flow to a high-density turbidity current; and (2) variations of flow dynamics within turbidity currents both across- and downcanyon, during an infrequent, high-energy canyon flushing event. This research offers new insights into the processes that create and shape nearshore bedrock-incising submarine canyons.

Formation mechanism and oil-bearing properties of gravity flow sand body of Chang 63 sub-member of Yanchang Formation in Huaqing area, Ordos Basin

Abstract Gravity flow sand body is an important reservoir for deep water deposition. The in-depth study of its formation mechanism and oil enrichment law can provide important guidance for oil and gas exploration in deep water areas. In this article, taking the deep-water gravity flow sand body of the Triassic Chang 63 sub-member in the Huaqing area as an example, the identification characteristics, formation mechanism, and oil-bearing characteristics of the gravity flow sand body are systematically discussed. The results show that sandy debris flow, turbidite flow, and mixed event flow present different superposition combination modes on vertical gravity flow deposition. The lithofacies of the gravity flow sandstone complex are mainly affected by lake level fluctuation, provenance supply, and hydrodynamic conditions. According to the formation conditions, sedimentary types. and distribution characteristics of deep water gravity flow sand bodies, a three-dimensional sedimentary mode of deep water gravity flow sand bodies is established. It is found that the physical and oil-bearing properties of the sandy debris flow sand body are better than those of the turbidity flow sand body. The reason is that the proportion of debris in the sand body of sandy debris flow is high, and the content of debris particles is generally greater than 70% according to the statistics of thin sections, which is conducive to the formation of pores. Second, sandy debris flow belongs to block transport, and the mixing of lithology is not sufficient in the process of block flow transport, so some pores will be preserved. Finally, gravity flows, which are dense at the beginning, become less dense later as detrital sediments unload, allowing them to be transported to distant regions. Therefore, the monolayer thickness of the sandy debris flow sand body is large (generally greater than 0.5 m), and the particle size of the debris ranges from 0.03 to 0.3 mm. Finally, the physical and oil-bearing properties of the sandy clastic flow sand body are better than those of the turbidity flow sand body.

Facies variations in gravelly cyclic steps deposited from turbidity currents: Miocene fan delta front deposits compared with a modern active fan delta, central Japan

AbstractGravelly cyclic steps formed by turbidity currents have recently been widely recognised in the geological record. However, the comparison between modern and ancient gravelly cyclic steps remains challenging. In this study, the facies variations of gravelly cyclic steps deposited from turbidity currents in an outcrop of Miocene fan delta front deposits in central Japan are compared with the geomorphic evolution of analogous cyclic steps on the active fan delta front in modern geological systems. These cyclic steps share common characteristics in setting, grain size and dimensions, allowing direct comparison between ancient and modern examples. Repeat bathymetric surveys of the modern Kurobe River fan delta have revealed various types of upslope migrating bedforms interpreted as cyclic steps. Most of these are short‐lived due to erosion of thalwegs by powerful surge‐type turbidity currents triggered by slope failures or burial of thalwegs by deposition, possibly from river‐fed hyperpycnal flows. Such erosion and burial events occur annually on the fan delta front, resulting in compensational cycles. Sedimentary facies of the Miocene fan delta front deposits include conglomerate with a gently upslope dipping erosional base, backset‐stratified sandstone and foreset‐stratified sandstone, which are interpreted as deposits of hydraulic jumps in high‐density turbidity currents in scours on the stoss sides of cyclic steps. Parallel‐stratified conglomerate sandstone is an additional component. Although previous facies models of gravelly cyclic steps have focussed on deposits on stoss sides, a comparison of modern and ancient examples suggests that facies on the lee sides could be parallel‐stratified conglomerate sandstone and undulating bedforms, reflecting supercritical flow conditions. The present study also suggests that hyperpycnal and surge‐type high‐density turbidity currents may deposit different types of facies and play different roles in the construction and destruction of cyclic steps. The present study has significant implications for facies models of gravelly cyclic steps.

Modeling the Tilt of Bend‐Traversing Turbidity Currents: Implications for Sinuous Submarine Channel Development

AbstractThe controls on the development of submarine channel sinuosity are contested: slope gradient and Coriolis forcing have both been recognized as key governing factors: gradient via an inverse relationship (low sinuosity at high slope and vice versa), and Coriolis forcing through its effect on sedimentation patterns (reducing lateral bend migration, and hence sinuosity development, at high latitudes and/or in large channels). Using theoretical models to calculate the bulk properties of channelized turbidity currents, this study investigates the joint role of the Coriolis force and parameters including channel size, downchannel slope and turbidity current properties in the development of submarine channel sinuosity. Model validation is undertaken through the comparison of the calculated turbidity current tilting against the measured tilting of channel levees in the Northwest Atlantic Mid‐Ocean Channel; this approach is then used to evaluate the controls on channel sinuosity in nine other modern seafloor channels. The results indicate that the Coriolis force only becomes significant when the size of the channel, the slope gradient and flow conditions are within appropriate ranges instead of solely being dependent on latitude. Thus, thick and dense (≥1% bulk sediment concentration) flows traveling within steep‐gradient, small‐scale channels were shown to be relatively less susceptible to flow modification by Coriolis forcing even at high latitudes. On the other hand, thin and dilute (≪1% bulk sediment concentration) flows in shallow‐gradient, large‐scale channels showed susceptibility to Coriolis forcing at all latitudes. These results offer new insights into submarine channel evolution and intra‐channel sedimentation patterns.

Vertical variations in planar lamination of marine shale: Elucidating hydrodynamic changes during the Ordovician–Silurian transition on the Upper Yangtze Block

The hydrodynamics and their evolution on the Upper Yangtze Block during the Ordovician–Silurian transition period remain unclear. The present study is an assessment of how regional and global events may have influenced the hydrodynamic evolution based on a planar lamination investigation of the shales from the Upper Yangtze Block. Analyses of large thin sections and argon-ion polished thin sections using field emission-scanning electron microscopy (FE-SEM) showed that there are four types of planar lamination, namely, silty graded planar lamination (SGPL), silt–clay graded planar lamination (SCGPL), silt–clay interlaminated planar lamination (SCIPL), and paper-like planar lamination (PPL). SGPL is formed by turbidity current with a flow speed less than 15 cm/s. SCGPL is formed by turbidity currents with a flow speed less than 15 cm/s for normal grading type and 15–25 cm/s for alternating grading type. SCIPL has a continuum of sparsely spaced type, closely spaced type, and alternating type, which is formed by bottom current with an increasing flow speed from 15 to 25 cm/s to above 25 cm/s. PPL can be divided into normal grading and composite grading types. The former is formed by vertical settling, while the latter is formed by bottom current with a flow speed of 5–15 cm/s. Vertically, types of planar lamination varied from SGPL to PPL and then SCIPL manifesting the waxing and waning of flow speed with a positive excursion at graptolite biozone Metabolograptus extraordinarius (WF4) and a negative excursion at graptolite biozone Persculptograptuspersculptus (LM1). The sudden decrease in flow speed across Linxiang and graptolite biozone Paraorthograptuspacificus (WF3) and the subsequent progressive increase from graptolite biozone Akidograptus ascensus (LM2) to graptolite biozone Demirastrites triangulatus (LM6) and to graptolite biozone Stimulograptus sedgwickii (LM8) during deposition of the Ordovician–Silurian transition succession on the Upper Yangtze Block were linked to the bulge uplift, the rapid subsidence, and the relaxation controlled by the Kwangsian orogeny. In contrast, the positive excursion at WF4 and the negative excursion at LM1 were strongly controlled by the Hirnantian Glaciation and global warming, respectively.

Geomorphic processes within the La Gomera-Tenerife Channel (Canary Islands): Decoding the interaction of bottom currents with seabed topography

The La Gomera-Tenerife Channel is a narrow passage between La Gomera and Tenerife Islands, i.e., two volcanic edifices of the Canary Archipelago (Atlantic Ocean). A geophysical study was conducted to identify the main geomorphic processes affecting the seabed and their interplay. In particular, submetric resolution bathymetric and side scan sonar backscatter data were collected in the southern sector of the Channel, down to 1200 m water depth. Their integrated analysis revealed a complex seabed morphology and a variety of morpho-sedimentary features, resulting from three main geomorphic processes: submarine volcanic activity, mass wasting (e.g., turbidity currents, small landslides and exotic blocks emplaced by a massive landslide event), and bottom currents activity. Bottom currents strongly reshaped the seabed into bedforms, confined drifts and moats. Although the flanks of volcanic islands are typically dominated by mass wasting and volcanic features, our results indicate that bottom current activity can be predominant in confined settings and around topographic features due to modification of flow patterns and enhancement of current flows.This study is the first to document volcanic, mass wasting and bottom current features within the La Gomera-Tenerife Channel. Furthermore, it provides insights on: i) morpho-sedimentary reconstructions of narrow passages between volcanic islands; ii) interplay among different geomorphic processes; iii) oceanographic reconstructions. The variety of geomorphic processes shaping the La Gomera-Tenerife Channel makes this area significant for high-resolution studies. Moreover, it provides new insights on poorly known processes, such as: the interaction of bottom currents with complex topography and bottom current morpho-dynamic in curved moats.

Petrophysical evaluation of the turbidite channels in Kafr Elsheikh Formation using wireline logging, West El-Burullus gas field, Offshore Nile Delta, Egypt

Petrophysical evaluation of the turbidite channels in Kafr Elsheikh Formation using wireline logging, West El-Burullus gas field, Offshore Nile Delta, Egypt

Flow and depositional response of turbidity currents to complex canyon topographies: A numerical simulation perspective

Submarine canyons are prominent features on continental margins, acting as major conduits for sediment transport primarily through turbidity currents. Understanding how these currents interact with complex canyon topographies is crucial for deciphering the canyon system evolution, yet challenging due to limited field observations. Focusing on a group of slope-confined canyons within the Pearl River Mouth Basin, northern South China Sea, this study integrates multibeam bathymetry, core analysis, and process-based Computational Fluid Dynamics (CFD) modeling to investigate the influence of realistic canyon topography on turbidity current dynamics and resulting sediment deposition. Analysis of core samples revealed a potential turbidite layer characterized by silts and sandy silts. Using these sediment information and bathymetric data, we conducted a series of three-dimensional CFD simulations. Our findings highlight the significant variability in turbidity current characteristics, particularly flow velocity and sediment concentration, within the canyon groups. This variability is primarily controlled by canyon head depth, the width-to-relief ratio, and slope gradients. Notably, the simulations revealed unique flow structures not typically observed in experimental settings, including unidirectional flows, small-scale helical flows, stacked and mixed flow cells, and flow separation and convergence across inter-canyon ridges. Our CFD simulations also revealed a distinct near-wall pattern of linear deposition of coarse-grained sediments, which is similar to the observed bathymetric changes between 2009 and 2017. Based on the consistent results, we propose a conceptual model wherein differential erosion, driven by oceanographic processes, plays a key role in shaping the observed linear depositional patterns.

How is particulate organic carbon transported through the river-fed submarine Congo Canyon to the deep sea?

Abstract. The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial organic carbon to the deep sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the submarine Congo Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ∼7 % of the dissolved and particulate organic carbon from the world's rivers. However, sediment and particulate organic carbon transport mechanisms that operate in the Congo Canyon and submarine canyons more globally are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps, and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the submarine Congo Canyon to the deep sea. We show that particulate organic carbon transport in the canyon axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 m s−1) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 m s−1) turbidity currents occur for 35 % of the time during monitoring periods and transport particulate organic carbon with mud and sand at an estimated transit flux that is more than 3 to 6 times the flux induced by tides. Organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo submarine fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally.

MAMCL: Multi-attributes Masking Contrastive Learning for explainable seismic facies analysis

Seismic facies analysis is crucial in hydrocarbon exploration and development. Traditional machine learning approaches typically require manual selection of attributes and lack interpretability analysis. We propose an interpretable framework, multi-attribute masking contrastive learning (MAMCL), designed to adaptively select, explore and aggregate seismic attributes for seismic facies analysis. The MAMCL framework includes a depthwise CNN module for feature extraction and an iTransformer module for feature aggregation. Based on the assumption that different attributes computed on the same seismic sample imply common information associated with the same geologic facies, we formulate an unsupervised strategy of contrastive learning to pre-train the MAMCL framework for refining the attributes. This pre-training method encourages the network to extract and integrate highly correlated attribute features by enhancing the expression of commonalities within the same sample, and implicitly increase the distance between features of different categories by differentiating the expressions of different samples. Ultimately, these refined features only need to be input into a simple clustering algorithm, such as K-Means, to achieve seismic facies classification. MAMCL requires no labels or manual selection of attributes and can utilize the self-attention mechanism of iTransformer to compute adaptive attribute weights, facilitating interpretability analysis. We applied MAMCL framework to both unlogged turbidite channel systems in Canterbury Basin, New Zealand, and logged Chengdao area in Bohai Bay Basin, China, achieving reliable classification results and providing interpretability analysis.

From flood to turbidity current: combined models to simulate continent to ocean sediment transport in the Var system, France

Turbidity currents are a form of gravity-driven flow that occurs in subaqueous environments. These currents contain a low volumetric percentage of particles but are very important in transporting them from coastal to deep-marine environments. In the Var sediment routing system, southeastern France, there is a sedimentary record of turbidity currents formed by submarine landslides and flooding of the Var River. In 2006, there was continuous monitoring of the marine section that recorded four turbidity currents. To explore the connectivity between the terrestrial source and marine basin we linked two reduced complexity models of sediment transport and landscape change. The aim of the paper is to combine two models, one dedicated to the prediction of river water and sediment run-off, and the second dedicated to the transport, erosion, and sedimentation by a turbidity current. The landscape evolution model CAESAR-Lisflood was used to model discharge and sediment yield. The behaviour of turbidity currents was modelled with the cellular automata model CATS. From calibration of the two models against observations of discharge and suspended sediment in the Var River system, we find that in 2006, two rainfall events would have led to hyperpycnal turbidity currents. These two events match well with two of the four-recorded events. Focusing on the largest event we find that the source pulse of sediment from the terrestrial environment is short-lived, less than half a day, but contains a significant quantity of fine particles. The event transferred on the order of 105 m3 of suspended sediment from source to sink. This study demonstrates that hyperpycnal turbidity currents can be generated with concentrations as low as 2-6 kg/m3 at the Var River mouth far below the theoretical 40 kg/m3 threshold, suggesting active convective sedimentation in the surface plume and sea-water dilution at the flooding river mouth. A substantial amount of sediment (35% of the input volume) is directly transferred towards the deepest part of the system during a short-living hyperpycnal turbidity current. However, a considerable (65%) part remains in the surface as a hypopycnal plume feeding the hemipelagic sedimentation.

OpenFOAM-avalanche 2312: depth-integrated models beyond dense-flow avalanches

Abstract. Numerical simulations have become an important tool for the estimation and mitigation of gravitational mass flows, such as avalanches, landslides, pyroclastic flows, and turbidity currents. Depth integration stands as a pivotal concept in rendering numerical models applicable to real-world scenarios, as it provides the required efficiency and a streamlined workflow for geographic information systems. In recent years, a large number of flow models were developed following the idea of depth integration, thereby enlarging the applicability and reliability of this family of process models substantially. It has been previously shown that the finite area method of OpenFOAM® can be utilized to express and solve the basic depth-integrated models representing incompressible dense flows. In this article, previous work (Rauter et al., 2018) is extended beyond the dense-flow regime to account for suspended particle flows, such as turbidity currents and powder snow avalanches. A novel coupling mechanism is introduced to enhance the simulation capabilities for mixed-snow avalanches. Further, we will give an updated description of the revised computational framework, its integration into OpenFOAM, and interfaces to geographic information systems. This work aims to provide practitioners and scientists with an open-source tool that facilitates transparency and reproducibility and that can be easily applied to real-world scenarios. The tool can be used as a baseline for further developments and in particular allows for modular integration of customized process models.

Vertebrate taphonomy and taphofacies of the Capianga Member, Aliança Formation (Jurassic), Jatobá Basin, Brazil

In addition to the study of sedimentary facies, the reconstruction of paleoenvironments depends on a detailed understanding of the taphonomy of a fossil accumulation. The Capianga Member of the Aliança Formation (Middle to Late Jurassic of the Jatobá Basin, northeastern Brazil) reveals vertebrate fossil accumulations composed predominantly of disarticulated bone and osteoderms, scales, spines and isolated teeth from a lacustrine paleoenvironment. However, the taphonomic history of the accumulation has not yet been studied extensively. The present work aims to interpret taphonomic facies based on lithological data and the systematic collection of fossils from the Capianga Member of the Aliança Formation, located in the northeastern portion of the Jatobá Basin, mainly in the municipality of Ibimirim. Six lithofacies were identified: Fm – massive claystones, Fl – Shale laminated Lt – calcilutites, Lc – calcarenites, Gf – fibrous gypsum and Scl – calciferous sandstones. Two primary taphonomic classes were recognized, consisting essentially of disarticulated elements, including (1) incomplete, semi-complete, or rarely complete bioclasts (such as osteoderms and fish scales) and (2) small-sized, occasionally complete bioclasts (osteoderms and scales) that sometimes compose bonebeds. According to the vertebrate taphonomy characteristics, three taphofacies were identified, with the Taphofacies A and B occurring in calcarenites and the Taphofacies C in calcilutites. The interpretation of these taphofacies reveals a multi-episodic history of the lacustrine environment. The integrated model suggests that the genesis of the identified taphofacies is linked to the action of lowering the water level of the paleolake, as well as the agents responsible for transport and disarticulation. These agents are related to pre-burial sub-aerial exposure, the action of unidirectional turbidity currents in shallow waters, and the likely influence of storms.

Gravel-inlaid mud clasts as indicators of transport processes of subaqueous sediment gravity-flows

Much sedimentological research aims to understand the depositional processes by establishing the relationship between the transport processes of subaqueous sediment gravity flows (SSGFs) and the characteristics of their deposits. A distinctive type of gravel-inlaid mud clasts, which has been largely overlooked, is embedded with occasional granules or pebbles, and exhibits various angular shapes that are present in cores of SSGF deposits worldwide. SSGF deposits from four cored wells in the Liushagang Formation of the Weixi'nan depression, China, have been analyzed to explore the characteristics, distribution, and potential formation mechanisms of gravel-inlaid mud clasts, thereby revealing the transport processes of SSGFs. In the research area, SSGF deposits are dominated by gravelly high-density turbidites, sandy high-density turbidites, low-density turbidites, and hybrid event beds. Gravel-inlaid mud clasts are common in massive sandstones and bipartite or tripartite beds, exhibiting various distribution patterns. The erosional contact at the base of these beds, where coarse grains are partially embedded within the muddy substrate, indicates that gravel-inlaid mud clasts originate through processes of erosion and delamination. Their distribution from the lower to the upper part of massive sandstones and bipartite or tripartite beds suggests a floating process from base to top. The formation and distribution of gravel-inlaid mud clasts demonstrate the downflow transformation from high-density turbidity currents to low-strength debris flows, driven by the erosion of the underlying muddy substrate, ultimately resulting in the formation of hybrid event beds. The lofting of gravel-inlaid mud clasts increases the cohesion of the upper part of the high-density turbidity current, facilitating its transformation into a low-strength debris flow. Furthermore, the occurrence of gravel-inlaid mud clasts within massive sandstones clearly demonstrates that they are products of high-density turbidity currents rather than sandy debris flows. The identification of gravel-inlaid mud clasts and their distribution within deep-water deposits can be regarded as a reliable indicator for reconstructing SSGF transport processes from high-density turbidity currents to low-strength debris flows, ultimately transitioning into low-density turbidity currents.

Inception of Constructional Submarine Conduit by Asymmetry Generated by Turbidity Current

Submarine conduits are features responsible for transporting clastic debris from continents to the deep ocean. While the architecture of conduits has been extensively studied, the process of their inception remains unclear. This study highlights the possibility that some conduits are initiated by depositional processes involving turbidity currents. Here, we present the results of eight experiments where gravity currents were allowed to develop their own pathways. The simulation tank represented natural scales of continental shelves, slopes, and basins. The initial experiments involved sediment-laden flows with low density (1–10% in volume). In first experiment runs (Series I), sediment deposition occurred primarily on the shelf and slope, resulting in an asymmetric transverse profile. This asymmetry facilitated subsequent conservative currents (1034 to 1070 kg/m3 due to salt dissolution) flowing alongside during the second series, resulting in the formation of a constructive submarine conduit. This feature is analogous to gully formations observed in various locations. This study correlates these findings with gully-like features and proposes a model where non-confined density flows can evolve into confined flows through the construction of asymmetric topography. An evolutionary model is proposed to explain the mechanism, which potentially elucidates the formation of many submarine conduits.

Extreme erosion and bulking in a giant submarine gravity flow.

Sediment gravity flows are ubiquitous agents of transport, erosion, and deposition across Earth's surface, including terrestrial debris flows, snow avalanches, and submarine turbidity currents. Sediment gravity flows typically erode material along their path (bulking), which can dramatically increase their size, speed, and run-out distance. Hence, flow bulking is a first-order control on flow evolution and underpins predictive modeling approaches and geohazard assessments. Quantifying bulking in submarine systems is problematic because of their large-scale and inaccessible nature, complex stratigraphy, and poorly understood source areas. Here, we map the deposits and erosive destruction of a giant submarine gravity flow from source to sink. The small initial failure (~1.5 cubic kilometers) entrained over 100 times its starting volume, catastrophically evolving into a giant flow with a total volume of ~162 cubic kilometers and a run-out distance of ~2000 kilometers. Entrainment of mud was the critical fuel, which promoted run-away flow growth and extreme levels of erosion.