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Trace elements in sedimentary rocks are highly sensitive to palaeoaquatic environmental changes in a sedimentary environment, making them an effective means for studying the paleoclimate and paleoenvironment during the deposition of sediments. The trace elements and major elements of mudstone cores sampled in the Binnan Oilfield in China were tested by inductively coupled plasma mass spectrometry (ICP–MS). Strontium (Sr), barium (Ba), vanadium (V), nickel (Ni) and boron (B), which are all sensitive to the sedimentary environment, were selected as discriminant indicators, and the sedimentary environment of the Shahejie Formation in the Binnan Oilfield was studied by combining with sedimentary indicators. The results show that the equivalent B content and the Sr/Ba ratio discriminate the research area for salt water and freshwater sedimentary environments. The V/(V + Ni) ratio is between 0.65 and 0.81, meaning that this area has a highly reductive sedimentary stratum. The trend of the Rb/Sr curve indicates that the paleoclimate of the Shahejie Formation changed from dry to humid and then back to dry.

Due to the limitations of analytical methodologies, the geochemical significance of C 5 alkylated benzenes has largely been overlooked. Thirty-four light oils and condensates were collected from the Tarim Basin and Beibuwan Basin for analysis using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS). The concentrations of twelve C 5 alkylated benzenes exhibit distinct distribution patterns in light oils and condensates originating from varying sedimentary environments and organic matter sources. The concentrations of 1-E-3,4,5-TMB, 1-E-2,3,4-TMB, and 1-E-2,4,5-TMB are likely influenced by the source of organic matter, whereas those of 1-E-2,4,6-TMB, 1-E-2,3,5-TMB, and 1,2,3,4,5-PMB are potentially governed by the sedimentary environment. Based on the differential sensitivity of C 5 alkylated benzenes to sedimentary environments and organic matter sources, the l-ethyl (E)-2,4,6-trimethylbenzene (TMB)/1-E-2,3,6-TMB (C5-R1) and 1-E-2,4,6-TMB/1-E-3,4,5-TMB (C5-R2) have been proposed as geochemical indicators for distinguishing the sedimentary environments and organic matter sources of crude oils from their respective source rocks. Oils derived from their respective source rocks that formed in oxic/disyoxic sedimentary environments are characterized by relatively high C5-R1 values (greater than 0.5), while those formed under reduced sedimentary conditions exhibit relatively low C5-R1 values (less than 0.5). Oils originating from terrestrial higher plants are characterized by relatively high C5-R2 values (greater than 1.0), whereas those derived from a mixed input of lower aquatic organisms and terrestrial higher plants display relatively low C5-R2 values (less than 1.0). The C5-R1 and C5-R2 ratios are likely to remain unaffected or only minimally influenced by secondary alteration processes (evaporative fractionation, biodegradation, and thermal maturity). The C5-R1 and C5-R2 ratios can serve as supplementary parameters for identifying sedimentary environments and organic matter sources, particularly in light oils and condensates where conventional biomarkers are significantly depleted.

This study integrates ichnological and sedimentological data to interpret depositional environments of the carbonate sediments of the Tirgan Formation (Lower Cretaceous) in the eastern Kopet-Dagh Basin, north-east Iran. Lithofacies analysis shows that these sediments were deposited in inner ramp, middle ramp and offshore (outer ramp) environments. Five ichnoassemblages are identified in the sediments that consist of Thalassinoides, Thalassinoides–Rhizocorallium, Planolites–Rhizocorallium, Arenicolites–Diplocraterion, and Arenicolites. Th, Th-Rh and Pl-Rh with low diversity and abundance of the trace fossils formed during waning phase of storms in a predominantly medium to high-energy hydrodynamic regime. High sedimentation rate and mobile substrate condition featuring a shallow-marine setting. Ar–Di ichnoassemblage, consisting of horizontal and vertical traces of deposit and suspension feeders, respectively, portray two different phases. A predominantly high energy phase with instable substrate is displayed by the vertical traces, while a minor omission phase, associated with a decrease in sedimentation rate or non-deposition, is indicated by the horizontal structures. Arenicolites ichnoassemblage with low bioturbation index and low ichnodiversity is related to a semi-sheltered area of lagoon environments with periodically marine water circulation. The study of the ichnological attributes in the studied successions indicates the presence of a shallowing up-ward trend in the storm‒tide-dominated ramp sequence. Ichnoassemblage development is largely controlled by depositional and ecological conditions, e.g., the stability of substrate, hydrodynamic regime (wave and tide), and food abundance, which altogether control the substrate colonization. Based on an integrated ichnological and sedimentological approach, we characterize the depositional environment, deciphering allogenic and autogenic environmental controls on the trace fossil distribution on a passive margin depositional setting.

17β-Estradiol (E2) is a novel micro-pollutant that is widely distributed in aquatic sediments and has a universal toxicological effect on aquatic organisms. However, its ecological impact on aquatic microorganisms is not yet clear. In this study, we designed a simulation system for oligotrophic water deposition in the laboratory, analyzed the impact of different concentrations of E2 pollution on the carbon metabolism activity (carbon gas emission rate) of water microorganisms. Based on high-throughput sequencing results, we revealed the impact of E2 pollution on the community structure succession and metabolic function of bacteria, archaea, and methanogens in the simulated system, explored the impact mechanism of E2 pollution on microbial carbon metabolism in water bodies. Our results suggested that E2 significantly impacts the bacterial and archaeal community rather than the methanogen community, thereby indirectly inhibiting methane production. The achievements will bridge the theoretical gap between estrogen metabolism and carbon metabolism in sedimentary environments and contribute to enriching the ecological toxicology theory of steroid estrogen.

Lacustrine fine-grained sedimentary rocks in the Dongying Sag of the Bohai Bay Basin in China exhibit significant potential for hydrocarbon exploration. This study investigates the lithofacies types and sedimentary evolution of the Paleogene Shahejie Formation’s lower third member (Es3l) and upper fourth member (Es4u), integrating petrological and geochemical analyses to explore the relationship between lithofacies characteristics and sedimentary environments. The results show that the fine-grained sedimentary rocks in the study area can be classified into 18 lithofacies, with seven principal ones, including organic-rich laminated carbonate fine-grained mixed sedimentary rock lithofacies and organic-rich laminated limestone lithofacies. In conjunction with analyses of vertical changes in geochemical proxies such as paleoclimate (e.g., CIA, Na/Al), paleoproductivity (e.g., Ba), paleosalinity (e.g., Sr/Ba), paleo-redox conditions (e.g., V/Sc, V/V + Ni), and terrigenous detrital influx (e.g., Al, Ti), five stages are delineated from bottom to top. These stages demonstrate a general transition from an arid to humid paleoclimate, a steady increase in paleoproductivity, a gradual decrease in paleosalinity, an overall reducing water body environment, and an increasing trend of terrestrial detrital input. This study demonstrates that the abundance of organic matter is primarily influenced by paleoproductivity and paleo-redox conditions. The variations in rock components are predominantly influenced by paleoclimate, and sedimentary structures are affected by the depth of the lake basin. Special depositional events, such as storm events in Stage II, have significantly impacted the abundance of organic matter, rock components, and sedimentary structures by disturbing the water column and disrupting the reducing conditions at the lake bottom. The present study offers crucial insights into the genesis mechanisms of continental lacustrine fine-grained sedimentary rocks, facilitates the prediction of lithofacies distribution, and advances the exploration of China’s shale oil resources in lacustrine environments.

Due to different sedimentary environments, the realistic formation always presents different electrical anisotropic characteristics. Multicomponent induction logging technology is an efficient method to solve complicated electrical anisotropy problems. However, because of the mathematical complexity, the investigation of unconventional electrical anisotropy in borehole geophysics is still insufficient. Additional situations, such as the classification of electrical anisotropy and the corresponding solution, need to be considered. For convenience, we introduce a universal algorithm to solve arbitrary electrical anisotropic problems. Uniaxial and biaxial anisotropic resistivity media are studied. In addition, the anisotropic dip and azimuth angles are used to further characterize the complex electrical anisotropy conditions. Numerical simulations confirm the robustness of the algorithm, and illustrate the tool responses under different electrical anisotropic situations. It can be concluded that anisotropic dip and azimuth can exert a great influence on triaxial induction logging responses. Some important phenomena can be observed; for example, critical borehole and critical anisotropic dip exist in the rotated uniaxial and biaxial media. Different monotonic rules can be found before and after these critical angles. Cross-coupling magnetic components, Hxy (Hyx) and Hyz (Hzy), are closely related to the anisotropic azimuth. The proposed algorithm can effectively overcome the deficiency of the traditional method and reduce the uncertainties in resistivity interpretation.

Numerous uncertainties persist regarding the differential enrichment mechanisms of shale gas reservoirs in southern China. This investigation systematically examines the sedimentary environments and reservoir characteristics of the Wufeng–Longmaxi formations in the Changning area of the Sichuan Basin, through the integration of comprehensive drilling data, core samples, and analytical measurements. Multivariate sedimentary proxies (including redox conditions, terrigenous detrital influx, basinal water restriction, paleoclimatic parameters, paleowater depth variations, and paleo-marine productivity) were employed to elucidate environmental controls on reservoir development. The research findings demonstrate that during the depositional period of the Wufeng Formation in the Changning area, the bottom water was characterized by suboxic to anoxic conditions under a warm-humid paleoclimate, with limited terrigenous detrital input and strong water column restriction throughout the interval. Within the Longmaxi Formation, the depositional environment evolved from intensely anoxic conditions in the LM1 through suboxic states in the LM3 interval, approaching toxic conditions by the LM2 depositional phase. Concurrently, the paleoclimate transitioned towards warmer and more humid conditions, accompanied by progressively intensified terrigenous input from the LM1-LM6, while maintaining semi-restricted water circulation. Both paleowater depth and paleoproductivity peaked from the Wufeng Formation to the LM1 interval, followed by gradual shallowing of water depth and declining productivity during the LM3–LM6 depositional phases. Comparative analysis of depositional environments and reservoir characteristics reveals that sedimentary conditions exert a controlling influence on multiple reservoir parameters, including shale mineral composition, organic matter enrichment, pore architecture, petrophysical properties (e.g., porosity, permeability), and gas-bearing potential.

To study the carbon burial rates in different sedimentary environments in Lianyungang coastal area since the Late Pleistocene, two deep boreholes of ZK1 and ZK2 were deployed to carry out measurements of sediment TOC (total organic carbon) and TN (total nitrogen) content, as well as AMS14C dating, and photoluminescence dating, soluble salts, foraminifera and particle size data, to analyse the spatial and temporal distribution characteristics of carbon burial, the sources of organic carbon and the main influential factors on carbon burial. The stratigraphic age was dated based on historical geology and sedimentary geology combined with dating data, and seven sedimentary units are classified: from bottom to top, tidal flat to nearshore coastal environment (U1, Qp31), river environment (U2, Qp32−1), river environment (U3, Qp32−2), river environment (U4, Qp32−3), coastal-shallow shelf environment (U6-1, Qh), coastal environment (U6-2, Qh), and coastal-tidal flat environment (U7, Qh). U1, U6, and U7 sedimentary units are good carbon sinks body. The average TOCBF (organic carbon burial rate) of the cohesive soil is 12.03–13.57 g m−2 a−1 for U1 cohesive soil, and the average TOCBF of the sandy soil is 2.72–7.85 g m−2 a−1. The average TOCBF of soft soil is 48.22–58.23 g m−2 a−1 for U6-2 soft soil. The average TOCBF of soft soil is 68.58–107.6 g m−2 a−1 for U7 soft soil. U2, U3 and U4 sedimentary units have low carbon sink capacity. The colour of the sediments of these three sedimentary units is mainly yellow, indicating an oxidative environment. It is assumed that most of the organic matter in the sediment was mineralised and decomposed shortly after deposition and that the amount of organic matter that could be preserved in the soil was less. The average TOCBF is between 0.68 and 2.01 g m−2 a−1. The TOCBF is mainly controlled by the sedimentation rate. The surface layer (0–20 cm) has high TOC, which is mainly due to the short burial time, during which some of the TOC has not been fully mineralised and decomposed, and the influence of human activities. The C/N (TOC/TN) is recommended for U6 sediments to analyse the source of organic matter, with C/N ranging from 5.32 to 7.42, presumably the source of sediment organic matter is mainly of marine origin. The C/N analysis of organic carbon sources is not recommended for terrestrial sediments. The conceptual model of TOC cycle in riverine and offshore sediments is summarised and refined.

Coastal areas are essential for global ‘blue carbon’ burial, significantly impacting the global carbon cycle. To better understand the carbon burial capacity, impact factors, and response mechanisms of surface sediments in different coastline regions, this study investigated the surface sediments of the Spartina alterniflora vegetation, transition, and bare flat areas along Jiangsu coast in China. The results indicated significant changes in organic carbon (OC), inorganic carbon (IC), and various physicochemical property indicators between the three coastal environments. There were also significant differences in the important impact factors of OC and IC in each region. In areas of vegetation, OC and IC influenced each other, while nitrogen (N), clay, and sand were common impact factors. The pH only had a significant impact on OC. In the bare flat area, the important impact factors of OC and IC were identical: OC/IC, clay, salinity (SAL), and sand. However, the important impact factors of OC and IC in the transition area have undergone significant changes. The important impact factors of OC were N, total phosphorus (TP), total sulfur (TS), SAL, and sand. The partial least squares regression analysis results of IC were poor, and there were no important impact factors. This study refined the spatial distribution patterns and response mechanisms to the important impact factors of carbon in different coastal subregions, providing a basis for accurately evaluating the role of coastal wetlands in mitigating global climate change.

Organic matter (OM)-hosted pores play a crucial role in unconventional shale reservoirs, with their development influenced by OM type and thermal maturity across terrestrial, transitional, and marine deposits. In this study, a comparative analysis of porosity and pore structures is presented using organic petrographical, petrophysical, and mineralogical methods on organic-rich samples from diverse depositional environments. A pore evolution model for these sediments in different settings is proposed. Results show that kerogen particles in terrestrial shales at low and moderate thermal maturity (Dameigou Formation and Qingshankou Formation) are mostly nonporous. Transitional shales (Longtan Formation) contain vitrinite and inertinite, with only some inertinite exhibiting visible primary pores. In marine shales at higher maturity (late oil window; Dalong Formation), the interparticle pore space is occupied by solid bitumen, and secondary porosity is present at higher maturity, approaching the thermal gas generation stage. In over-mature marine shales (Wujiaping and Daye Formations), secondary pores are densely distributed within pyrobitumen. A negative correlation between organic carbon content and pore volume is observed in low-maturity lacustrine and transitional shales due to poorly developed kerogen-bound pores and interparticle pore occlusion by solid bitumen. However, over-mature marine shales exhibit a strong positive correlation due to extensive secondary porosity in pyrobitumen. Thus, pore evolution within OM is controlled by kerogen type and maturity. In oil-prone marine and lacustrine shales, secondary porosity in solid bitumen and pyrobitumen increases with thermal maturity. In contrast, terrestrial kerogen rarely forms solid bitumen and mainly develops micropores rather than mesopores at high maturity.