Gravity Flow Research Articles

Characteristics, genetic mechanism, and hydrocarbon accumulation of Cambrian gravity flow in the eastern Gucheng area, Tarim Basin, China

The platform margins of Gucheng and Luoxi in the Cambrian are developed on both sides of the eastern Tarim Basin. Based on the analysis of cores, thin sections, and seismic data of Luoxi platform margin slope areas, we systematically studied the formation condition, reservoir characteristics, and favourable accumulation factors of gravity flow. The types of gravity flow include debris flow, high‐density flow, and low‐density flow, and the high‐density flow reservoir is better. Hydrothermal fluids have an active effect on reservoir reconstruction. Six‐phase reefs are developed in the platform margin, and the lithology of the reservoir is algal framework dolomite and granular dolomite. Multi‐phase reefs form an inclined slope. The 3D seismic and geochemical data show that the platform margin reefs have karst unconformity characteristics. The platform margin slope has the requirements of geomorphology and reservoir source, and the total area of slope gravity flow is 5854 km2. The gravity flow in the Gucheng platform margin slope is near the Cheerchen fault zone, and tectonic movement forms the nose‐like structure. The gravity flow is between the source rocks of the Xidashan Formation and the Heituwa Formation. Hydrocarbon generation and caprock are both favourable for hydrocarbon accumulation. Multi‐phase events of hydrothermal fluids are favourable to the reservoir and hydrocarbon charging. Gravity flow is important for oil and gas exploration in the Tarim Basin.

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.

Highstand sublacustrine fans: The role of a sudden increase in sediment supply

AbstractContrary to widely used traditional sequence‐stratigraphic models, highstand sublacustrine fans developed in the deep‐water environment in the middle of the third member of the Eocene Shahejie Formation (Es3z, 42–40.5 Ma), Dongying Sag. Using four cores and 3D seismic data, we describe the sequence stratigraphy frameworks, sediment characteristics, depositional elements, and depositional model of the Liangjialou highstand sublacustrine fan. The Es3z is a complete third‐order sequence stratigraphic, bounded by T4 at the top and T6 at the base. Between T4 and T6, there is the maximum flooding surface (MFS) distributed from proximal to distal of the system in the third‐order stratigraphic sequence. Therefore, the Liangjialou Fan at the top of the Es3z, between MFS and T4, is a typical highstand sublacustrine fan as determined from seismic data. This highstand sublacustrine fan is characterised by gravel to fine‐grained sand, abundant amalgamation surfaces, and crude stratifications common in coarse‐grained structureless‐ to normal‐ graded sandstones. Climbing ripples and thin laminae rich in plant debris are common in inverse‐then normal‐graded sandstones. Channel‐levee, channel‐lobe transition zone, and lobes developed in this highstand sublacustrine fan, with clear internal progradation stacking patterns caused by hyperpycnal flow. The sudden increase in sediment supply in an accommodation decrease situation and the narrow shelf width are the primary controlling factors for forming highstand sublacustrine fans. In the late stage of the highstand systems tract, gravity‐flow deposits caused by hyperpycnal flow are developed from another new point source to form this highstand sublacustrine fan. Hyperpycnal flow in lacustrine basins can transport coarse‐grained sediments with the help of strong flood energy and steep slopes. Gravity flow deposits in lacustrine basins are not confined by sequence stratigraphy frameworks, and many additional areas of sand caused by hyperpycnal flow could be found in lacustrine basins.

Dynamics of co-current gas–liquid film flow through a slippery channel

We consider a thin liquid film in a wide inclined channel being driven by gravity and co-current turbulent gas flow. The bottom plate with which the liquid is in contact with is taken to be slippery, and we impose the classic Navier slip condition at this substrate. Such a setting finds application in technological processes as well as nature (e.g., distillation, absorption, and cooling devices). The gas–liquid problem can be decoupled by making certain reasonable assumptions. Under these assumptions, we solve the gas problem to obtain the tangential and normal stresses acting at the wavy gas–liquid interface for arbitrary waviness. In modeling the liquid layer dynamics, we make use of the stresses computed in the gas problem as inputs to the interface boundary conditions. We develop the long-wave model and the weighted-integral boundary layer (WIBL) model to describe the thin film dynamics. We perform a linear stability of these reduced order models to scrutinize the effect of wall slip, liquid flow rate, and the gas shear on the stability of the flat film solution. It is found that the wall slip promotes the instability of the flat interface. Furthermore, we compute solitary wave solutions of the WIBL model by implementing Keller's pseudo-arc length algorithm on a periodic domain. We observe that the wave speed as well as the wave amplitude are attenuated on incrementing the liquid slip at the substrate. We corroborate these findings with the time-dependent computations of the nonlinear WIBL model.

Residual rocky forms in the landscape of the Outer Carpathians (Silesian Beskid Mts, Poland) – geotourist and sedimentological case study

This study investigated residual landforms developed within of the flysch bedrock in the Outer Western Carpathians as sandstone-to-conglomeratic tors. The studied relic rocky forms are locally exposed on the valley slopes in the top and plateau parts of the Silesian Beskid Mts. The cognitive values of such relic landforms, especially in the context of their morphogenetic traits and shaping of their macro- and microrelief, are well known and described. In contrast to epigenetic processes, the sedimentological aspect of the origin of such siliciclastic rocky deposits is still subject to different approaches in terms of terminology and interpretation. Thus, the aim of this study is to describe the conditions of environmental settings and character of the sediment transport and deposition processes from gravity flows, and to present a depositional system model for such a variety of flysch deposits. This study also attempts to present geotourist and geoeducational attractiveness of the tors against the background of regional geodiversity, geoheritage, and geoprotection. The results yielded a synthetic morpho-litho-sedimentological and geotouristic specification of the rocky forms analysed. The residual rocky landforms are polygenic geomorphological elements developed as a consequence of multistage and different scale of morph-forming activity operating on the basis of litho-sedimentological and tectonic assumptions under the influence of denudation processes.

Residual rocky forms in the landscape of the Outer Carpathians (Silesian Beskid Mts, Poland) - geotourist and sedimentological case study

This study investigated residual landforms developed within of the flysch bedrock in the Outer Western Carpathians as sandstone-to-conglomeratic tors. The studied relic rocky forms are locally exposed on the valley slopes in the top and plateau parts of the Silesian Beskid Mts. The cognitive values of such relic landforms, especially in the context of their morphogenetic traits and shaping of their macro- and microrelief, are well known and described. In contrast to epigenetic processes, the sedimentological aspect of the origin of such siliciclastic rocky deposits is still subject to different approaches in terms of terminology and interpretation. Thus, the aim of this study is to describe the conditions of environmental settings and character of the sediment transport and deposition processes from gravity flows, and to present a depositional system model for such a variety of flysch deposits. This study also attempts to present geotourist and geoeducational attractiveness of the tors against the background of regional geodiversity, geoheritage, and geoprotection. The results yielded a synthetic morpho-litho-sedimentological and geotouristic specification of the rocky forms analysed. The residual rocky landforms are polygenic geomorphological elements developed as a consequence of multistage and different scale of morph-forming activity operating on the basis of litho-sedimentological and tectonic assumptions under the influence of denudation processes.

Origin and driving mechanisms of marine litter in the shelf-incised Motril, Carchuna, and Calahonda canyons (northern Alboran Sea)

Introduction and methodsMarine litter density, distribution and potential sources, and the impact on canyon seafloor habitats were investigated in the Motril, Carchuna and Calahonda canyons, located along the northern margin of the Alboran Sea. During the ALSSOMAR-S2S oceanographic survey carried out in 2019, canyon floor imagery was collected by a Remotely Operated Vehicle along 5 km in the Motril Canyon, 10 km in the Carchuna Canyon, and 3 km in Calahonda Canyon, together with 41 surficial sediment samples. Additionally, coastal uses, maritime traffic and fishing activity data were analyzed. A 50 m resolution multibeam bathymetry served as base map.ResultsIn the Motril and Calahonda canyons, the density of marine litter was low and the material was dispersed, very degraded and partially buried. In contrast, the Carchuna Canyon contained a greater amount and variety of litter. The Carchuna Canyon thalweg exhibited a density of marine litter up to 8.66 items·100 m-1, and litter hotspots with a density of up to 42 items·m2 are found along the upper reaches of the canyon thalweg.DiscussionLow litter abundances found in the studied canyons most likely reflect low population densities and the absence of direct connections with streams in the nearby coasts. The high shelf incision of the Carchuna Canyon and its proximity to the coastline favor littoral sediment remobilization and capture as well as the formation of gravity flows that transport the marine litter along the thalweg toward the distal termination of the channel. Litter hotspots are favored by the canyon morphology and the occurrence of rocky outcrops. Most debris is of coastal origin and related to beach occupation and agricultural practices in the adjacent coastal plain. A third origin was represented by fishing gear in the study area. Fishing activity may be producing an impact through physical damage to the skeletons of the colonial scleractinians located in the walls of the Carchuna Canyon. In contrast, the Motril and Calahonda canyons can be considered passive systems that have mainly acted as depositional sinks in the recent past, as evidenced by buried marine litter.

Does sand promote or hinder the mobility of cohesive sediment gravity flows?

ABSTRACTSediment gravity flows exhibit a large range of flow behaviours, making their flow dynamics hard to predict and the resulting deposits a challenge to interpret. Cohesive sediment gravity flows containing clay are particularly complex, as their behaviour is controlled by the balance of turbulent and cohesive forces. A first set of laboratory lock‐exchange experiments investigated the effect of adding 25% very fine sand by volume to high‐density cohesive sediment gravity flows with strongly suppressed turbulence. This caused these mixed clay–sand flows to become more cohesive, have shorter runout distances, and have lower head velocities than the original pure‐clay flows, despite the increase in density difference and the non‐cohesive properties of the sand. Yield stress measurements confirmed that adding the non‐cohesive very fine sand increases the cohesive strength of dense clay suspensions. This higher cohesive strength outcompetes the enhanced density difference and reduces the flow mobility. A second set of experiments across a larger range of clay concentrations showed that, for low‐density cohesive sediment gravity flows dominated by turbulent mixing, the addition of 25% very fine sand increased the head velocities because of the enhanced density difference and weak cohesive forces. Thus, the addition of very fine sand may increase or decrease the mobility of cohesive sediment gravity flows, depending on the initial type of flow and the balance between turbulent and cohesive forces. In the natural environment, this study proposes that very fine sand can only increase the cohesive strength and reduce the flow mobility of cohesive sediment gravity flows that have a sufficiently strong matrix strength to fully support the sand particles. The contribution of very fine sand to the cohesive strength of high‐density cohesive sediment gravity flows may have important implications for flow transformation on submarine fans, especially in distal regions where transient–turbulent, cohesive flows are particularly common.

UNDERWATER CANYONS OF THE SOUTHWESTERN OUTSKIRTS OF SOUTHERN BAIKAL AS PRESUMABLE TRANSITERS OF TECHNOGENIC MATERIALS TO THE ABYSSAL SURFACE

Numerous publications by domestic and foreign authors deal with a significant role of underwater canyons in transit of loose material from the littoral to the abyssal surfaces of the seas. Lake Baikal fully corresponds in its hydrodynamic and bathymetric parameters to sea water basins, and the Baikal canyons are similar in their morphological and morphometric factors to sea canyons. A digital elevation model of the southwest underwater tip of the lake, generated based on a large array of bathymetric data, allowed identifying clearly defined valleys of the Shamanka and Slyudyanka canyons. The data obtained during the study of the canyon-valley area, carried out using special geophysical measuring instruments – Kongsberg EM710S multibeam echosounder and Knudsen CHIRP 3260 profilograph, – and analysis of the published materials showed a rather high degree of confindness of coarse debris to the canyon valleys and alluvial fans which implies their significant role in sediment transit. It has been shown that high seismicity of the Baikal basin and active wave conditions give rise to the formation of movable loose sediment masses and to the occurrence of gravity flows in the canyon valleys. Climate changes over the last decades contribute also to permafrost decomposition in the Baikal basin and to new-sediment transport into the lake. It is implied that an intensive development of the coastline leads to the coastal accumulation of a large amount of industrial and municipal contaminants which can move through the canyons to different distances into the lake water area. To date, there is no definite answer to the question about an actual role of underwater canyons in the transit of technogenic wastes to the abyssal lake surface. This requires organized large-scale specialized fieldwork with the use of high-precision geological-geophysical measuring instruments, and systematic sampling and thorough analysis of the bottom material.

Sediment gravity flow frequency offshore central California diminished significantly following the Last Glacial Maximum

A high-resolution multibeam survey from a portion of the San Simeon Channel (offshore Morro Bay, California) captured a zone of recurring troughs and ridges adjacent to prominent submarine meander bends. Through an integrated study using surveying data, sediment core analysis, radiocarbon dating, and stable isotope measurements, we hypothesize that turbidity current event frequency was higher during the late Pleistocene than at present conditions. We speculate that the rise in sea-level following the Last Glacial Maximum sequestered sedimentation largely to the shelf during the Holocene. This work suggests that the occurrence of sediment gravity flows in this region, particularly away from any submarine channels, is appreciably lower than at times of continental shelf subaerial exposure.

Drying Liquid Coatings with an Evaporation Mask: Theory and Experiments.

We report a study of the spatially varying thickness of dried films of polymer solutions resulting from a nonuniform evaporation flux. The controlled heterogeneity of the evaporation flux is imposed by placing a solid mask above the evaporating film spread on a solid substrate. At the end of drying, a depression has formed under the mask, together with overthicknesses extending from the edge of the mask and over distances that may be larger than its size. By considering the flows induced in a vertically homogeneous film, we obtain analytical solutions for the thickness profiles during drying using a linear approximation in the limits of either gravity or capillarity-driven flows. We demonstrate that gravity can play a role in the deformations of the films, even if their initial thicknesses are 1 order of magnitude smaller than the capillary length. In addition, we examine two possible reference states for the linear approximation, i.e., far from the mask in the film of decreasing thickness and increasing viscosity, or under the mask where no evaporation occurs. We further compare these results with experimental ones obtained by drying thin films of polymer solutions under a mask. Both the extent and amplitude of the thickness heterogeneities of the dry film are quantitatively predicted by the linear analysis for a reference state under the mask. Our results therefore provide new insight on the patterns resulting from evaporation masks and can be generalized to minimize thickness heterogeneities in any situation in which the evaporation flux is nonuniform.

Microfacies and reservoir characteristics of the lacustrine deepwater gravity flows of the Chang 7 in the Southwestern Ordos Basin, China

Microfacies and reservoir characteristics of the lacustrine deepwater gravity flows of the Chang 7 in the Southwestern Ordos Basin, China

A new insight on sedimentary facies of the Miocene to Pliocene Agbada Formation, offshore Niger Delta Basin, Nigeria

The Niger Delta Basin contains rich oil and gas resources and has always been a focus for oil and gas exploration. Further research on the sequence stratigraphy and sedimentary facies is particularly significant in hydrocarbon exploration. In this study, the sequence stratigraphic structure and sedimentary facies of the Miocene and Pliocene Agbada Formation in the southeastern part of the Niger Delta were studied based on the integrated investigation of coring, well logging, seismic and geological data. The results show that: (1) One Type 1 and three Type 2 sequence boundaries are identified in the Agbada Formation. Based on the identified sequence boundaries, the Agbada Formation can be divided into three third order sequences SQ1, SQ2 and SQ3, which are well-developed, isochronal and traceable in this area.(2) The Agbada Formation in the study area was consisted of delta front, gravity flow channel and turbidite fan deposits.The latter two appeared at the bottom of SQ3 and SQ1, respectively. Moreover, the delta-gravity flow accumulation development model in the study area was established. (3) The main factors affecting the formation of gravity flow included sufficient sediment supply and specific triggering mechanism, which both induced the failure of delta front/slope and the consequent debris flows/turbidity currents. The discovery of gravity flow might be of great significance for further hydrocarbon exploration.

Microfacies types and distribution of epicontinental shale: A case study of the Wufeng–Longmaxi shale in southern Sichuan Basin, China

For black shales, laminae and bedding are hard to identify, grain size is difficult to measure, and trace fossils do not exist. Taking the Ordovician Wufeng – Silurian Longmaxi shale in southern Sichuan Basin, China, as an example, the types, characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections, argon-ion polishing field emission-scanning electron microscopy (FE-SEM), and kerogen microscopy. The epicontinental sea develops delta, tidal flat and shelf facies, with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies, the calcareous and clayey flats under intertidal flat facies, the calcareous and clayey shelfs under shallow shelf facies, the deep slope, deep plain and deep depression under deep shelf facies, and the overflow under gravity flow facies. Basinward, silty lamina decreases and clayey lamina increases, the grain size changes from coarse silt to fine mud, the silica content increases from about 20% to above 55%, the carbonate and clay minerals content decreases from above 40% to around 10%, and the kerogen type changes from type II2 to type II1 and type I. Provenance and topography dominate the types and distribution of shale microfacies. The underwater distributary channel, interdistributary bay, clayey flat, clayey shelf, and overflow microfacies are developed in areas with sufficient sediment supply. The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply. The deep shelf shale area is divided into deep slope, deep plain, and deep depression microfacies as a result of three breaks. The formation of epicontinental shale with different microfacies is closely related to the tectonic setting, paleoclimate, and sea level rise. The relatively active tectonic setting increases the supply of terrigenous clasts, forming muddy water fine-grained sediment. The warm and humid paleoclimate is conducive to the enrichment of organic matter. The rapid sea level rise is helpful to the widespread black shale.

Algorithm for Appropriate Design of Hydroelectric Turbines as Replacements for Pressure Reduction Valves in Water Distribution Systems

Gravity flow water distribution systems (WDSs) are used to permit water flow from an input point of highest elevation (source) to the terminal points of a system (consumers). In such WDSs, typically, there is no need for external power to maintain the flow due to the typical high gradients that exist. However, those gradients cause high water velocity and pressure to some network areas that could potentially lead to pipes bursting. Currently, the only means to regulate pressure within allowable range are Pressure Reduction Valves (PRVs). They are installed at various locations, but they cannot utilize the existing hydropower potential in terms of electrical energy production. This paper provides a methodology for hydro-turbines dimensioning, so that they mimic PRV operation in terms of pressure regulation while producing power efficiently. This includes an algorithmic process within which the proper turbine design and performance prediction are initially determined, and then, via an interconnection between EPANET and MATLAB, the hydraulic behavior of their operation within the water network is modeled and simulated. The methodology has been tested with simulations of a typical urban WDS. The results indicate that the produced turbine geometries mimic PRV action at the respective locations with more than 1% accuracy during 70% of the time (2% maximum error), while producing electric energy with hydraulic efficiency over 60%.

The behavior of lemon-based thickened fluids submitted to the IDDSI flow test as a strategy for dysphagia treatment

Dysphagia is a health condition that causes swallowing difficulty, which may be treated by many techniques. Feeding modified foods should be a usual protocol for these individuals, as it will rarely be a diet of choice but a diet necessary to maintain a safe oral intake of nutrients. All people who suffer from changes in swallowing have difficulty in oral feeding, which compromises their nutritional status, mainly due to dehydration. Thickening of fluids is a well-established management strategy for oropharyngeal dysphagia. Thus, this research aimed to evaluate commercial lemon-based beverages (juices and flavored waters) with the addition of thickeners through the gravity flow test, according to the protocol established by the International Dysphagia Diet Standardization Initiative (IDDSI). Eight commercial beverage samples, categorized as flavored carbonated water (L01, L02, L03, L04), isotonic beverage (L05), liquid soft drink (L06) and powdered soft drink (L07 and L08), in addition to two thickeners based on xanthan gum were used. A 10 mL slide-tip syringe with a barrel length of 61.5 mm was employed for the flow test. thickening agents to lemon-based beverages caused substantial changes in their rheological properties. Differences between samples and treatments were observed according to the type and amount of thickener. Samples L05 and L08 showed 8.55 and 8.05 mL retention in the syringe, respectively, classifying them as moderately thickened liquids, while the others samples were classified as slightly thickened liquids. The ideal treatment for the dysphagic patient aims to ensure a safe intake and a correct nutritional and water supply, in addition to the consequent improvement of the patient’s general clinical condition. According to their nutritional profile, the inclusion of these beverages may be interesting in increasing some micronutrients such as sodium, potassium, calcium, phosphorus and magnesium. The flow properties of lemon-based beverages can be a good option for patients with dysphagia when improved using low amounts of thickening agents to suit their diets.

A discrete element modelling of gravity flow in sublevel caving considering the shape and size distribution of particles

ABSTRACT One of the most significant challenges for cave mining methods is dilution, a process which is generally controlled by the gravity flow of caved materials. In this study, the discrete element method (DEM) was used to investigate the effects of changing the porosity of blasted ring material and caved waste rocks and of changing the ring inclination on material flow in a sublevel cave (SLC) mine. Yade software was used to simulate two-dimensional gravity flow in a longitudinal section of the sublevel while taking into consideration the shape and size distribution of the flowing rock particles. Four simulations were generated with different porosities, and the material flow in the models was compared to each other. The results demonstrate that when ring porosity is increased, dilution decreases, and the height of the extraction zone grows longitudinally. Also, a lower porosity of the blasted ore material in the ring can cause early dilution entry and expansion of the extraction zone towards the caved waste.. Finally, the effect of ring inclination on the material flow and dilution was investigated. The results of these simulations show an increased dilution as the ring inclination increases and a change in the shape of the extraction zone.

Effect of Dam Emplacement and Water Level Changes on Sublacustrine Geomorphology and Recent Sedimentation in Jackson Lake, Grand Teton National Park (Wyoming, United States)

Dam installation on a deep hydrologically open lake provides the experimental framework necessary to study the influence of outlet engineering and changing base levels on limnogeological processes. Here, high-resolution seismic reflection profiles, sediment cores, and historical water level elevation datasets were employed to assess the recent depositional history of Jackson Lake, a dammed glacial lake located adjacent to the Teton fault in western Wyoming (USA). Prograding clinoforms imaged in the shallow stratigraphy indicate a recent lake-wide episode of delta abandonment. Submerged ∼11–12 m below the lake surface, these Gilbert-type paleo-deltas represent extensive submerged coarse-grained deposits along the axial and lateral margins of Jackson Lake that resulted from shoreline transgression following dam construction in the early 20th century. Other paleo-lake margin environments, including delta plain, shoreline, and glacial (drumlins, moraines) landforms were likewise inundated following dam installation, and now form prominent features on the lake floor. In deepwater, a detailed chronology was established using137Cs,210Pb, and reservoir-corrected14C for a sediment core that spans ∼1654–2019 Common Era (CE). Dam emplacement (1908–1916 CE) correlates with a nearly five-fold acceleration in accumulation rates and a depositional shift towards carbonaceous sediments. Interbedded organic-rich black diatomaceous oozes and tan silts track changes in reservoir water level elevation, which oscillated in response to regional climate and downstream water needs between 1908 and 2019 CE. Chemostratigraphic patterns of carbon, phosphorus, and sulfur are consistent with a change in nutrient status and productivity, controlled initially by transgression-driven flooding of supralittoral soils and vegetation, and subsequently with water level changes. A thin gravity flow deposit punctuates the deepwater strata and provides a benchmark for turbidite characterization driven by hydroclimate change. Because the Teton fault is a major seismic hazard, end-member characterization of turbidites is a critical first step for accurate discrimination of mass transport deposits controlled by earthquakes in more ancient Jackson Lake strata. Results from this study illustrate the influence of dam installation on sublacustrine geomorphology and sedimentation, which has implications for lake management and ecosystem services. Further, this study demonstrates that Jackson Lake contains an expanded, untapped sedimentary archive recording environmental changes in the American West.

Evolution of sediment gravity flows in response to early Carboniferous subduction and closure of the West Junggar Basin, China

This study describes and characterises the spatial distribution and evolution of Carboniferous deep-water sediment gravity flows and their associated deposits in the West Junggar region of north-western China. It uses a combination of outcrop sections, cores and seismic profiles to define nine lithofacies associated with a different sediment gravity flow types, including turbidity currents, debris flows, hyperpycnal flows and supercritical flows. The subduction and closure of the remnant West Junggar Ocean basin demonstrated variable palaeogeographical characteristics and configurations during different periods of the Carboniferous. Fossil assemblages and zircon dating data indicate that the target strata have completely recorded the evolution of the Western Junggar remnant ocean in the Carboniferous. The basin evolution is divided into the stable ocean basin stage, the slow subduction and filling stage and the fast subduction and filling stage. Active faulting and varying slope gradients affected the occurrence and types of sediment gravity flows during each stage. Tectonic and seismic activities associated with subduction caused continental slope instabilities and basinward transport of sediment by gravity flows with active faults on the continental slope triggering sediment gravity flows. At the beginning of subduction, the ability of gravity flows to transport coarse debris was limited owing to the shallow gradient of the continental slope. Sediment transport via gravity flows was dominated by sandy debris flows, muddy debris flows, turbidity currents and less frequent flood-controll3ed hyperpycnal flows. As the basin entered the fast subduction and filling stage, the slope gradient steepened and the frequency of active thrust faulting increased, which triggered high-density turbidity currents and supercritical flows. Additionally, the warm and humid paleoclimate led to the development of hyperpycnal flows during the fast-filling stage. This study demonstrates the importance of understanding the character and distribution of sediment gravity flows and associated deposits, especially, the implications for the hydrocarbon industry.

Composition of fine‐grained sediment in the Hikurangi Trough: Evidence for intermingling among axial gravity flows, transverse gravity flows and margin‐parallel ocean currents

ABSTRACTThe International Ocean Discovery Program cored five sites during Expeditions 372 and 375 to investigate the Hikurangi margin, offshore Poverty Bay, North Island, New Zealand. Trench‐wedge deposits were recovered at Site U1520, and the frontal accretionary prism was cored at Site U1518. Based on X‐ray diffraction analyses of the clay‐sized fraction, illite and smectite are the dominant clay minerals. Compositional scatter is unusually large, and a well‐defined mixing trend is evident between illite‐rich and smectite‐rich end members. The proportion of smectite ranges from 9 to 59 wt.% at Site U1518 and from 12 to 62 wt.% at Site U1520. Nearby slope deposits at Sites U1517 and U1519 are more homogeneous, with consistently higher proportions of smectite. The East Cape Current is probably responsible for transporting smectite‐rich suspensions towards the south‐west from sources that include the Taupo Volcanic Zone. Illite‐rich muds require different sources and different routing paths to the trench. Some suspended sediment probably originated in the Waipaoa watershed on the North Island, entering the trench via Māhia Canyon. Other gravity flows probably started in Kaikōura Canyon or Cook Strait and moved towards the north‐east, down the trench's axial channel. The influence of turbidity currents on clay composition changes with water depth, as do the effects of reworking by contour currents and the role of passive hemipelagic settling. The broad continuum of clay compositions in the trench is enhanced by variable amounts of mixing among multiple ocean currents and fluctuating durations of suspension within a bottom nepheloid layer. That complexity deviates from the paradigm of turbidite‐dominated trench wedges. The margin's compositional diversity also complicates the goal of predicting or modelling three‐dimensional variations in frictional, geotechnical and hydrogeological properties. Those lithological properties are important because they affect slope stability along strike and changes in fault‐slip behaviour along the subduction interface.