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The hadal zone, >6 km deep, remains one of the least understood ecosystems on Earth. We address bioturbational structures in sediment cores from depths exceeding 7.5 km, collected during the IODP Expedition 386 in the Japan Trench. Micro-CT imaging on 20 core sections allowed to identify biogenic sedimentary structures (incipient trace fossils) and their colonization successions within gravity flow deposits. Their frequency, and consequent changes in substrate consistency, oxygenation and organic matter delivery and remineralization controlled the endobenthic colonization. The gravity-flow beds show recurring bioturbation successions: The initial colonization is characterized by deposit-feeding structures such as Phycosiphon, Nereites and Artichnus generating typically 20 cm thick intensively bioturbated fabrics. The final colonization stage comprises slender spiral, lobate and deeply penetrating straight and ramifying burrow systems such as Gyrolithes, Pilichnus and Trichichnus , interpreted to include burrows of microbe farming and chemosymbiotic invertebrates. The main factor precluding colonization is soupy substrate. Organic matter degradation and post-event upward expansion of the anoxic zone drive the change from deposit feeding to microbe-dependent feeding strategies. To better understand bioturbation in the hadal zone, the authors here examine sediment cores collected from depths of more than 7.5 km. They characterise biogenic sedimentary structures, colonization patterns, and their relation to gravity flow events.

The First Member of the Cretaceous Qingshankou Formation (K2qn1) in the Gulong Sag, Songliao Basin, contains vast shale oil resources conventionally interpreted as deposits of suspension settling in a quiescent, anoxic deep-lacustrine environment. However, this static “deep-lake” model fails to account for the strong lithofacies heterogeneity and high-energy sedimentary records observed in recently acquired core data. This study reconstructs the sedimentary dynamics of the K2qn1 shale through high-resolution core description, thin-section petrography, and flow-loop hydrodynamic simulations. We identify abundant sedimentary structures diagnostic of high-energy combined flows, including Hummocky Cross-Stratification (HCS), Swaley Cross-Stratification (SCS), erosional scour surfaces, and large-scale tabular intraclasts (up to 40 mm). Hydrodynamic simulations, utilizing an “equivalent substitution” method, demonstrate that the Minimum Vertical Suspension Velocity (Vmf) required to transport these large intraclasts exceeds 1.0 m/s. This threshold is 1 to 5 orders of magnitude higher than theoretical values derived from classical settling equations, confirming that the paleolake bottom was frequently perturbed by high-velocity storm-driven currents. Consequently, we propose an “Intermittent High-Energy Deposition Model,” wherein background suspension settling was punctuated by episodic storm events. We argue that these high-energy events facilitated organic matter enrichment through a “Transport-Burial Pump” mechanism, which operated in concert with the chemical stratification associated with the Oceanic Anoxic Event 2 (OAE2) to enable rapid physical burial and sealing of organic matter. These findings challenge the traditional fine-grained sedimentological paradigm and suggest that storm-reworked intervals—characterized by enhanced brittleness and hydrodynamic winnowing—constitute the primary “sweet spots” for lacustrine shale oil exploration.

Microbially induced sedimentary structures (MISS) derive from the interaction between sediments and unicellular microorganisms and are of interest to the search for the earliest signs of life in ancient rocks, on Earth and on Mars. Here, we describe a type of MISS in the form of a polygonal structure characterised by a domed rim. Despite earlier suggestions of a biological origin, several aspects regarding their formation mechanism, the criteria to distinguish these structures from abiotic mud cracks, and their preservation potential in the geological record remain insufficiently constrained. To identify and define the distinctive features characterising this MISS, we have investigated the morphology and formation mechanism of polygonal microbial mats in two modern sabkha locations in Qatar. The sedimentological, mineralogical and geochemical analyses suggest that the studied polygons result from microbe‐mineral interactions causing the stabilisation of detrital minerals (e.g. quartz, feldspar) and precipitation of micrite comprised of calcite and high‐Mg calcite. The polygonal morphology is mainly the result of two co‐occurring mechanisms: shrinkage, as a result of desiccation and microbial growth. A ∼1.5 cm‐sized domed‐rim has been identified as the key morphological feature that is exclusively present in and that allows for the recognition of, the polygons that form in association with a growing microbial mat. In cross‐section, a domed‐rim is comprised of millimetre‐thick laminae showing angular relationships (e.g. overgrowth of older lamina sets) that, we argue, cannot be formed in the absence of growing biomass. Finally, through the study of a radiocarbon‐dated ancient sabkha outcrop, it is shown that domed‐rim microbial polygons can survive degradation and diagenesis, producing a mineral fossil structure that can potentially be preserved for billions of years.

While the internal structure of transgressive dunes is relatively well understood, little is known about that of climbing dunes. The Valdevaqueros dune, located 10 kilometers northwest of Tarifa (Cádiz), is considered one of the largest and most active transgressive dunes in Europe, as well as one of the main climbing dunes of the Iberian Peninsula. This study analyzes the internal structure of the Valdevaqueros dune using ground-penetrating radar (GPR) profiles. The results reveal a variety of sedimentary structures that reflect different wind intensities and directions. The findings highlight the significant role of topography in the development of these structures. These results contribute to expanding knowledge about climbing dunes, and particularly the dynamics of the Valdevaqueros dune.

Unconventional reservoirs have burst with a great force in the oil and gas worldwide production. Reefal limestone reservoir is one of them. The present study deals with the reefal carbonate Hammam Faraun Member in Al-Hamd oil field. This study focus on the interpretation of sedimentological and petrophysical data to show the effect of diagenetic processes on middle and lower Miocene reefal carbonate reservoirs in Al-Hamd oil field. Comprehensive petrophysical analysis for Hammam Faraun Member was performed using wireline logs and core data to determine the proper petrophysical parameters. Of the reservoir intervals. The analytical reservoir rock achieving the main reservoir parameters as shale content ( V sh ), effective porosity ( Ø eff ), water and hydrocarbon saturation ( S W and S hr ) as well as the net-pay thickness. The Formation Micro Imager (FMI) was also applied to detect the variation, types, and directions of the fracture systems that present in the lower and middle Miocene reefal limestone reservoir. Petrographic analysis was done, indicating the presence of a clear effect of diagenetic factors on the quality, productivity, and efficiency of the reefal limestone reservoirs behavior. The diagenetic factors include dolomitization, slicification, recrystallization, and solution process which affect greatly the petrophysical characteristics of the reefal carbonate Hammam Faraun reservoir in the study area. The core analyses were also used to detect the paleo environment, associated textural/ lithological and sedimentological characteristics to gain and understand the factors responsible for the productivity behavior of the reservoir in the Al-Hamd oil field. Rock facies have been divided as specific characteristics and were further described considering their color, texture, grain-size characteristics, and the depositional and biogenic sedimentary structures.

Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems, and then guide the oil and gas exploration. To do this we have undertaken a detailed investigation of the modern Great Halten River distributive fluvial system from the Sugan Lake Basin, Qinghai, China. Unmanned aerial vehicle (UAV) photography, satellite remote sensing data and elemental analysis were used to determine differences in the sedimentary characteristics of the distributive fluvial system. From the apex to the toe, the changes in the slope, river morphology, sedimentary characteristics and element content in different regions were determined and three facies belts: “proximal”, “medial” and “distal” were identified. We found that the sedimentary structure and elemental content characteristics of each facies differ greatly. We compare the large-scale evolution of rivers from braided to meandering rivers, and the fine description of sedimentary characteristics in combination with each observation, we strengthen our overall understanding of the modern DFS from macro to micro scale. At the same time, we summarize the sedimentation model of the Great Halten River DFS, and our study provides a reference for establishing the sedimentary model in continental petroliferous basins.

The sedimentary structure of tailings is of high significance to the engineering design and safety management of tailings dams. However, due to a lack of accurate measurement techniques for the flow field and hydrodynamic conditions of tailings reservoirs, it is challenging to study the complicated sedimentary structure of tailings dams from the perspective of fluid mechanics. This study focuses on developing a large-scale particle image velocimetry (LSPIV) system in a 20 m long and 2 m wide deposition model flume to measure the flow field characteristics during the ore-drawing process accurately. According to the surface flow field characteristics measured by LSPIV, the tailings in the flume can be divided into three zones, namely the fan-shaped zone, channel zone, and laminar flow zone. Then, a simple method for estimating the flow rate of the slurry was proposed using the surface velocities measured by LSPIV. The flow rate of iron tailings slurry in the flume displays a decreasing trend along the flow direction. The variation of the flow rate of tailings slurry can be described by an exponential function. After the deposition of tailings slurry, the sedimentary characteristics of tailings are investigated, and the distribution of iron tailings particles is discussed in combination with the flow field of the tailings slurry. The LSPIV system can be applied to further deposition model tests of different slurry concentrations, discharge flow rates, and tailings compositions to investigate the effects of these factors on the tailings flow and deposition.

The huge tsunami waves induced by the 2011 off the Pacific coast of Tohoku Earthquake severely affected shallow marine ecosystems along the Pacific coast of northeastern Japan. This study examined core samples using X-ray radiography, computed tomography scanning, and grain size analysis to identify temporal changes in the physical and biogenic sedimentary structures of seafloor deposits in Onagawa Bay, northeastern Japan, following the 2011 tsunami. Cores were sampled during research cruises in October 2012, December 2013, and April 2014. The seafloor sediments consisted of two lithological layers. The upper section (between the surface and a depth of 8 cm) was composed of muddy sediments deposited by normal depositional processes and/or the weakening tsunami currents. In contrast, the lower part of the cores (below a depth of 8 cm) consisted of tsunami-induced deposits, i.e., horizontally laminated sandy sediments generated by the strong currents associated with the 2011 tsunami. Sampling of these sediments in 2012 and 2013 showed burrows of up to 10 mm in diameter, but restricted to the upper mud layer. In contrast, in 2014, 20–40-mm-diameter mud-filled burrows were seen in both the upper mud and lower sand layers, indicating that recolonization of the seafloor sediment by large and deep-burrowing animals began within 3 years of the 2011 tsunami. The intense sediment mixing by large burrowing animals will homogenize the seafloor sediment and decrease the preservation potential of the tsunami deposits in this bay.

The paper firstly presents, two biogenic sedimentary structures (trace fossils) belonging to the ichnofamily Graphoglyptidae, represented by the ichnogenera Ubinia and Megagrapton from the middle member of the Sinaia Formation in the Prahova valley. The new ichnospecies Ubinia jipai is described. Advancing the hypothesis of the complex structure, of the Megagrapton-Ubinia type, it is not excluded that this morphological configuration represents an unknown ichnotaxon from the bottom of the deep Cretaceous seas.

Contourite drifts were found for the first time on the SW Kara Sea shelf based on the analysis of bathymetry and seismoacoustic data obtained in the cruises 41 (2019) and 49 (2020) of R/V Akademik Nikolai Strakhov . These drifts are confined to a narrow NS depression with a depth of 240 m. They are separated from underlying sediments by the basal unconformity caused by the bottom current formed in the marine environment after melting of the Barents–Kara ice sheet during the Late Pleistocene–Holocene time. Hydrological measurements carried out in the cruise 89-1 (2022) of R/V Akademik Mstislav Keldysh made it possible to reveal the bottom current with a measured velocity of up to 10 cm/s.