Identifying and classifying lithologies is crucial for characterizing the potential of unconventional oil and gas resources. However, lithological complexity and frequent facies changes in marine–continental transitional shale systems present significant challenges in identifying and interpreting reservoir lithology. This paper focuses on the marine–continental transitional shale systems on the eastern margin of the Ordos Basin. According to the logging curves, core observations, and thin section analysis of eight cored wells, the reservoir lithology was classified into six basic types. Based on these, conventional logging curves were used as input to train machine learning models, including extreme gradient boosting (XGBoost), back propagation neural network (BPNN), support vector machine (SVM), random forest (RF), naïve Bayes (NB), and fully connected neural network (FCNN). To improve prediction accuracy, the acoustic (AC), compensated neutron (CNL), and density (DEN) logging curves that reflect changes in porosity were selected for superimposed reconstruction calculations, and new parameters (Φ1 and Φ2) were introduced to optimize the existing model. The study found that the accuracy, recall, precision, and F1-scores of the six classification models were all greater than 0.5, with the XGBoost model exhibiting the best overall performance, followed by the RF, FCNN, SVM, BPNN, and NB models. All original models performed well for limestone and sandstone but not for carbonaceous shale, black shale, and silty shale. With the introduction of new parameters, the revised models showed significant improvements in all evaluation metrics, with values exceeding 0.9. Among them, the XGBoost-R model performed the best overall, accurately identifying limestone and sandstone and achieving over 96

Enhanced silicate weathering has been traditionally considered a dominant mechanism for atmospheric carbon dioxide (CO2) drawdown, acting as a negative feedback on climate warming over geological time scales. In contrast, weathering of rock organic carbon (OCpetro) may constitute a positive climate feedback, with enhanced OCpetro oxidation amplifying warming by releasing CO2 to the atmosphere and oceans. However, the influence of CO2 emissions from oxidative weathering on ancient climate events is unclear. Here, we use rhenium isotopes to investigate the role of OCpetro weathering in modulating the global carbon cycle during the Hirnantian glaciation. These data indicate that the weathering intensity of sedimentary rocks was reduced during the glaciation, an observation that is consistent with lower CO2 emissions from the reduced oxidative weathering of OCpetro during this critical interval. Our findings highlight the likely contribution of OCpetro weathering to Earth's carbon cycle and its role in modulating climate during critical periods of Earth's history.

The Ordovician-Silurian (O-S) transition was marked by widespread deposition of organic-rich shales worldwide. However, the mechanism of organic matter accumulation remains debated. Previous studies mainly focus on primary productivity versus preservation conditions. Here, we emphasize the mechanisms driving accumulation of the extraordinarily high organic matter (EHOM) with total organic carbon (TOC) content over 3.0 wt%. In this study, the Wufeng-Lungmachi shale formations of two sections across the O-S transition on the northern margin of the Yangtze Shelf, South China, were investigated for TOC, elemental geochemistry, petrology of barite and pyrite concretions, and pyrite sulfur isotopes. Our results reveal two step-wise increases of TOC content identified as two episodes of EHOM accumulation. The first episode of EHOM enrichment in the Upper Ordovician was likely triggered by increased nutrient input from hydrothermal activity related to volcanism and probably upwelling events. The second episode, marked by large-scale EHOM enrichment in the Lower Silurian, was driven by large nutrient supply from enhanced continental weathering following the Hirnantian deglaciation and from enhanced phosphorus recycling under widespread ocean euxinia. These findings suggest that geological events acted as the primary triggers for the EHOM enrichment, and could sustain EHOM accu mulation over longer time scales by affecting environmental factors.

The Chang 7 Member of the Yanchang Formation in the Ordos Basin consists predominantly of airfall and water-borne tuff along with tuffaceous shale, which exhibit considerable hydrocarbon potential, yet their thermal evolution and hydrocarbon generation behaviors remain inadequately studied. As an emerging unconventional exploration target, this interval was investigated through systematic thermal simulation experiments utilizing a novel programmable dual-pressure constant-flow system, which enables precise control of fluid pressure and automated monitoring of hydrocarbon generation and expulsion processes under semi-open/semi-closed conditions. The study focuses on low-maturity, organic-rich massive tuff and laminated tuffaceous shale from Well Z40, revealing that although all samples are sedimentary in origin, the airfall tuffs are rich in vitric pyroclasts—including accretionary pellets (AP1)—while water-borne tuffs are dominated by feldspar crystal pyroclasts. Key findings demonstrate that massive tuff displays markedly higher hydrocarbon expulsion efficiency compared to laminated tuffaceous shale, with an earlier onset of expulsion and contributions derived from both kerogen cracking and heavy oil components. Thermal evolution analysis further indicates that massive tuff attains higher organic maturity under identical conditions. In laminated shale, expulsion efficiency correlates increases with TOC content, reflecting the role of organic matter in pore development and fluid connectivity. The superior expulsion performance of massive tuff is attributed to its higher volcanic glass content, low clay abundance, and dispersed organic matter distribution, which create highly efficient migration pathways. In contrast, laminated tuffaceous shale exhibits stratified organic matter closely associated with clay minerals, requiring higher thermal maturity (Ro > 0.6%) and elevated TOC to form an interconnected organic network that facilitates efficient expulsion. This study highlights that variations in pore structure, organic matter distribution, and thermal maturity represent the primary controls on differential expulsion efficiency between organic-rich tuff and tuffaceous shale in the Chang 7 Member, providing crucial insights for the exploration and development of shale oil in volcanic-lacustrine basins.

Graptolites were abundant and cosmopolitan zooplankton in Early Paleozoic oceans, but a prominent change in species occurred across the Late Ordovician mass extinction. We use ocean redox, iron isotope (δ56Fe), and phosphorus phase partitioning records from shelf and deep-ocean settings to evaluate the drivers behind this major reshaping of the pelagic marine ecosystem. A marked decrease in mesopelagic graptolites coincided with a stepwise negative δ56Fe shift on the shelf, driven by partial seawater Fe drawdown resulting from episodic intensification of mid-depth euxinia. Subsequently, a positive δ56Fe shift in both deep-ocean and shelf sediments reflects extensive seawater Fe removal during the development of more widespread euxinia. This led to enhanced sedimentary phosphorus recycling from sediments, which ultimately fueled the radiation of epipelagic graptolites. Thus, wide-scale changes in Fe cycling, linking the global oceanic redox state to phosphorus cycling, were ultimately responsible for the initial demise and subsequent radiation of select graptolite species.

Shale lithofacies are of vital importance to the assessment of shale gas resources and development potential. The lithofacies classification is generally based on petrological and geochemical tests. However, due to the limited samples and economic costs, lithofacies prediction based on logging data has become a trend. In this study, lithofacies were classified using TOC, XRD, and thin-section identification (TSI) analyses of marine-continental transitional shale samples from the Benxi Formation in the Hengshan-Wubu area, Ordos Basin. A hybrid predictive model integrating the back-propagation (BP) neural network and conventional log-interpretation methods was subsequently developed. Based on the predicted lithofacies from logging data, both vertical and planar distribution patterns were characterized, and favorable shale gas intervals (sweet spots) were identified. The TOC tests show that TOC values of the shale in the Jinci Member range from 0.15% to 19.1%, with an average of 3.50%. The XRD tests show that the Jinci Member shale is rich in clay minerals, ranging from 5.1% to 95.7% (avg. 54.2%), followed by quartz, which varies from 1.1% to 65.6% (avg. 30.5%). The test results reveal that shale lithofacies in the study area are predominantly composed of argillaceous shale, with organic-rich shales mainly occurring within the argillaceous and mixed shale categories. Among all samples, organic-rich siliceous argillaceous shale is the most abundant, accounting for 20.0%, followed by organic-rich mixed shale (18.6%) and organic-poor siliceous argillaceous shale (15.7%). Characterized by high TOC content and abundant brittle minerals, the organic-rich siliceous argillaceous and mixed shales are favorable types of lithofacies. Prediction results show that organic-rich lithofacies are vertically concentrated in intervals between Coal Seams No. 8 and No. 9 and in the lower part of Coal Seam No. 9 within the Jinci Member, defining the vertical sweet spots. Laterally, favorable areas are mainly distributed in the northwestern and western parts of the study area. These findings provide a valuable reference for target selection in shale gas exploration within the Carboniferous-Permian marine-continental transitional shales of the Ordos Basin.

The Middle-Upper Permian marine shale formations in the middle Yangtze region are an important replacement field for shale gas exploration and development in China, with great resource potential. However, their reservoir development is complex. Based on previous studies, this study systematically summarizes the reservoir characteristics and research progress of three sets of shale formations from the Middle-Upper Permian: Gufeng, Wujiaping, and Dalong Formations in the middle Yangtze region. The results show that: (1) All three sets of shale formations are characterized by high total organic carbon (TOC) contents, moderate thermal maturity, and well-developed nanopores, exhibiting favorable reservoir quality. Among them, the Gufeng Formation shale exhibits the highest TOC content, with kerogen dominated by Type I. The Wujiaping and Dalong Formations show relatively lower TOC contents, and their kerogen is mainly Type II. In terms of lithofacies, the Gufeng and Dalong Formations are dominated by siliceous shale, whereas the Wujiaping Formation exhibits complex lithofacies and significant heterogeneity due to variable depositional environments. In terms of pore structure, the Gufeng Formation shale displays a wide pore-size range, with development from the nanoscale to the microscale, whereas the Wujiaping and Dalong Formation shales are dominated by micropores and mesopores. (2) The three sets of shale reservoirs are complex, characterized by diverse lithofacies, multiple pore types, and strong multi-scale heterogeneity. (3) Overall research on the Middle-Upper Permian marine shale reservoirs in the middle Yangtze region remains relatively limited. Therefore, it is recommended to carry out quantitative reservoir characterization through integrated multi-scale analysis of outcrops, cores, and experiments, promote interdisciplinary collaboration, introduce techniques such as artificial intelligence and big data analysis, establish a comprehensive shale reservoir evaluation system tailored to the geological characteristics of this region, and conduct graded optimization and evaluation of “sweet spot” intervals and areas, thereby providing solid theoretical support and decision-making guidance for large-scale exploration and effective development of Middle-Upper Permian marine shale gas in the middle Yangtze region.

Liquid hydrocarbons (LHCs) derived from humic organic matter (HOM) exhibit high potential for late-stage gas generation through recombination reactions. The biomarker composition and isotopic geochemical signatures of these LHCs can provide insights into the origin, maturity, and depositional environment of organic matter. Semi-open system thermal simulation experiments were performed on typical low-maturity humic source rocks from the Ordos Basin. The resulting LHCs were quantitatively characterized, followed by separation into compound-grouped fractions and subsequent analysis by GC–MS and stable carbon and hydrogen isotopic measurements. Based on the yield characteristics of LHCs, the applicability of biomarker parameters in HOM is systematically assessed, and the carbon and hydrogen isotopic fractionation mechanisms of alkanes are explored. The results demonstrate that: (1) LHCs are generated throughout the entire pyrolysis process of HOM, with the C15+ resins and asphaltenes fraction accounting for a relatively high proportion. The n-alkanes in HOM are dominated by short- to medium-chain homologues. Within the maturity range covered by pyrolysis experiments, the δ13C values of compound-grouped fractions are heavier than −27‰; those of n-alkanes are heavier than −29‰, and the corresponding δD values are lighter than −140‰, (2) the distribution of n-alkanes, relative content composition of steranes, and carbon isotopic compositions of polar fractions collectively indicate that the organic matter was predominantly derived from terrestrial C3 plants. Isoprenoid alkane ratios and the gammacerane index suggest that the source rock was deposited in a dysoxic freshwater environment, and terpane parameters exhibit a favorable correlation with thermal maturity across the oil-generation window, and (3) the kinetic isotope effect (KIE), along with cracking of polar compounds and C15+ aromatic hydrocarbons, causes the average δ13C values of n-alkanes to initially increase and subsequently decrease. Throughout thermal maturation, aromatic moieties and unsaturated cross-linked structures in HOM undergo hydrogen isotopic exchange with D-depleted formation water. Cracking via active free-radical reactions further amplifies this isotopic exchange, yielding n-alkanes with lighter average δD values. The distinct linear distribution patterns between δ13C and δD values of n-alkanes can be utilized to discriminate mixed-source oils and provide preliminary maturity assessment. This study enhances the understanding of the geochemical characteristics of LHCs derived from HOM and provides a scientific basis for the evaluation of hydrocarbon generation potential, gas-source correlation, and maturity in humic source rocks.

The tectono-thermal evolution of the eastern Ordos Basin since the Permian has been systematically reconstructed using multiple geothermometers, including zircon (U-Th)/He, apatite fission track, apatite (U-Th)/He, and vitrinite reflectance data. The study provides insights into the burial, denudation, and maturity history of the basin. The tectono-thermal evolution is divided into four main stages: rapid burial during the Permian-Triassic, fluctuating burial during the Jurassic, rapid subsidence in the Early Cretaceous, and continuous uplift since the Late Cretaceous. Temperature evolution reflects continuous warming from the Permian to Early Cretaceous and a cooling phase from the Late Cretaceous to the Cenozoic. The Early Cretaceous heat flow peak, ranging from 90 to 95 mW/m2, was most pronounced in the western North China Craton, with values progressively declining towards the east. Shale gas accumulation in the Shanxi Formation of the Daning-Jixian area has been influenced by the basin's thermal history, with gas content correlating with apatite helium ages (AHe). The primary favorable zone for shale gas is defined within the range of 1,100-1,300 m below sea level at the base of the Shanxi Formation. This study further identifies two optimized zones based on tectono-thermal factors, including sediment provenance uniformity, greater burial depth, and shorter periods of intense uplift. These zones indicate areas where gas accumulation is enhanced by deeper burial and less extensive uplift, minimizing gas loss. This research provides a detailed understanding of the tectono-thermal evolution of the eastern Ordos Basin, shedding light on the mechanisms controlling shale gas enrichment and offering a foundation for future resource exploration in the region.

Aromatic hydrocarbons (AHc), as major constituents of coal and petroleum systems, are widely used as geochemical proxies for depositional environment, organic matter source, and thermal maturity. In this study, semi-open pyrolysis experiments were conducted on low-maturity humic organic matter (HOM) from the Ordos Basin. After fractionation of the liquid products, the aromatic fractions of retained oil (ReO) and expelled oil (ExO) were analyzed by gas chromatography–mass spectrometry (GC–MS), and 145 aromatic compounds from 16 homologous series were identified. Naphthalene, phenanthrene, dibenzothiophene (DBT), and pyrene series were selected to evaluate maturity parameters and to examine molecular processes relevant to late-stage gas generation. The results indicate that: (1) these aromatic series generally exhibit a unimodal abundance pattern during HOM maturation, with an initial increase followed by a decline, and the phenanthrene series remains dominant; (2) alkyl aromatic parameters can record thermal maturity within a defined window (Meas-Ro approximately 0.85–1.42%), among which alkyl phenanthrene parameters show the highest sensitivity, consistent with observations from sapropelic organic matter (SOM) and coal; and (3) the aromatic-rich framework of HOM favors the formation of thermally stable pyrobitumen and may provide methyl-derived methane during late-stage gas generation. At Meas-Ro values above 1.42%, the abundances of naphthalene and phenanthrene decrease markedly, suggesting consumption during high-maturity transformation, although the contributions of non-hydrocarbons and asphaltenes require further investigation. This study supports the application of aromatic maturity parameters in humic-derived liquid hydrocarbons and provides new constraints on late-stage gas generation from HOM. The findings provide a geochemical basis for evaluating the gas-generation potential of coal-bearing source rocks and may contribute to the exploration of deep and ultra-deep coal-derived gas accumulations.

The strong heterogeneity of pores in marine–continental transitional shale reservoirs significantly restricts the efficient development of deep shale gas. Fractal dimension is a key parameter for effectively quantifying and characterizing the complexity of shale pore structure. The low-temperature CO2/N2 adsorption, high-pressure mercury intrusion, and nuclear magnetic resonance multi-scale characterization combined with fractal geometry theory were conducted to elucidate the mechanisms controlling fractal characteristics of macro-, meso-, micropores in this study. The multi-scale fractal dimension for each pore size range was determined using the thermodynamic model, the Menger sponge model, and the Frenkel–Halsey–Hill model, respectively. Multi-scale fractal analysis revealed micropore fractal dimension (DC) was governed by TOC and clay mineral interactions. Organic matter stacking reduced surface heterogeneity, whereas clay content exceeding 50

Black shale with extraordinarily high organic matter (EHOM) content is prevalent in the Chang 7 Member of the Middle Triassic Yanchang Formation, Ordos Basin. This interval shows significant potential for hydrocarbon generation; however, mechanisms for EHOM accumulation of these black shales remain highly debated. In order to reconstruct the depositional environment of the basin and investigate the mechanisms behind the EHOM enrichment, a comprehensive analysis encompassing elemental carbon and sulfur, major elements, mineral and microbiological fossils, and biomarkers was conducted on 45 shale samples of the Chang 7 Member from a well located in the north slope break belt of the basin. The results indicate that EHOM of these shales has evolved into the mature stage, with a notable potential for hydrocarbon generation. Their OM has mixed-source origins, primarily derived from algal matter, with a significant contribution from higher plants. During the deposition of the Chang 7 Member, the prevailing climate was warm and humid, with moderate weathering intensity and relatively low paleosalinity, fresh-brackish water depositional environment. In semi-deep to deep lake environments, the organic matter enrichment in the Chang 73 sub-member shale follows a medium-high palaeoproductivity and anoxic preservation model. During the Chang 72 depositional period, water depth decrease leads to the deterioration of preservation conditions, resulting in a significant reduction in the abundance of organic matter. During the deposition of the Chang 71 period, the increase in organic matter abundance is mainly attributed to the decrease of terrestrial debris dilution and medium-high paleoproductivity. The enrichment of EHOM is related to volcanic activity, in conjunction with a warm and humid climate, low salinity level, minor terrigenous detritus input, anoxic conditions, algal blooms, and an elevated paleoproductivity sedimentary environment.

Marine-continental transitional (MCT) shale gas is an important successor of unconventional natural gas resource in China. Based on integrated analyses of published data including outcrop investigation, exploration practice, drilling cores, and experimental testing, the recent progresses of both global and domestic shale gas development were systematically reviewed and compared, and we further examined the exploration progress and challenges of MCT shale gas in the Ordos Basin, Sichuan Basin, and their adjacent areas, and conducted a comprehensive discussion of the key geological conditions for the formation of shale gas and its resource potential, challenges, and counter measures. The results show that MCT shale in China is mainly developed within the Carboniferous–Permian strata (Benxi, Shanxi, and Longtan formations), dominated by lagoon, swamp, and tidal flat facies, and possesses favorable conditions for shale gas formation and development potential. They mainly include the generation and storage of shale gas as follows: (1) The organic-rich intervals are thick and widespread, dominated by Type III organic matter with high total organic carbon (TOC) content (⩾3.0

Organic matter (OM)-hosted pores are critical to controlling shale oil and gas adsorption in black shales. However, the specifics of pore structure evolution in OM during thermal maturation are not yet well understood. In this study, the shales of the early-mature and middle-mature Triassic Yanchang Formation of the Ordos Basin, late-mature Ordovician–Silurian Renheqiao Formation of the Baoshan Block, and over-mature Ordovician–Silurian Wufeng-Longmaxi Shale of the Sichuan Basin were investigated. Multiple techniques were utilized to investigate the evolution of OM type and pore structure characteristics during thermal maturation. OM in the early-mature Yanchang Formation shales is dominated by the oil-prone macerals bituminite and alginite. In comparison, OM in the late-mature Renheqiao Formation and over-mature Wufeng-Longmaxi Shale is dominated by solid bitumen and pyrobitumen, respectively. Organic pores are hosted by secondary OM, solid bitumen and pyrobitumen, and are best developed in the over-mature stage. The loss on ignition-corrected specific surface area (SSA) and pore volume of isolated OM increase with increasing thermal maturity, with the SSA and pore volume ranging from 5–10 m2/g and 0.02–0.05 cm3/g at vitrinite reflectance < 0.7% to 200–250 m2/g and 0.3–0.4 cm3/g at equivalent vitrinite reflectance 2.5–3.0%, respectively. OM in the oil window-maturity Yanchang Formation shales has a shale oil adsorption pore volume (pore size < 12 nm) of 0.0417 to 0.0784 cm3/g and can adsorb 46–87 mg oil/g TOC. This study underscores the necessity of a good understanding of OM type and thermal maturity in order to properly assess the oil and gas adsorption by OM in black shale strata.

Supervolcano eruptions have played a major role in the evolution of life and environments on Earth. The Emeishan large igneous province (LIP) eruptive activity had been suggested to be the cause of the Guadalupian (Middle Permian) mass extinction event and the transition from icehouse to greenhouse climate in the Permian. However, the causal mechanism of the Emeishan LIP's impact on the environment and mass extinction is still unresolved. This study presents > 300 foraminiferal species, mercury (Hg) and carbon isotopic compositions, zircon U-Pb ages, biomarkers, and elemental data across the Guadalupian-Lopingian (G-L; i.e., middle-upper Permian) boundary of South China to investigate mass extinction and the evolution of the Emeishan LIP. A precise chronological framework across the G-L boundary is reconstructed using five U-Pb age data integrated with carbon isotopic stratigraphic correlations. A U-Pb age of 260.58 +/- 0.86 Ma determined using secondary ion mass spectrometry from a section of continuous deposition is suggested as a revised age for the G-L boundary. Organic carbon isotopic composition (delta C-13(org)) and Hg geochemistry data show three pulses of Emeishan LIP eruptive activity in the earliest Wordian, in the middle Capitanian, and at the G-L boundary, respectively. The second and third pulses of the Emeishan LIP eruptive activity in the middle Capitanian and at the G-L boundary, respectively, coincided with two stages of the Guadalupian mass extinction, demonstrating a causal link. The Emeishan LIP eruptive activity probably caused the Guadalupian mass extinction by triggering marine anoxia and global warming.

We conducted in-depth research on the hydrocarbon generation and expulsion characteristics of the Permian humic source rocks and the evolution of the reservoir gas content in the eastern margin of the Ordos Basin. Using low-mature shale from the Palougou section, thermal simulation experiments were conducted in a closed system. Rock-Eval pyrolysis, total organic carbon (TOC) analysis, vitrinite reflectance (EasyR(o)) analysis, and gas chromatography (GC) were performed on sample residues and products. Based on isothermal adsorption experiments combined with the hydrocarbon expulsion conceptual model, we established evolution models for thermogenic gas (G), gas-in-place (GIP), adsorbed gas (V-ad), and free gas (V-free). The results are as follows: (1) The hydrocarbon generation and expulsion stages can be divided into the immature (EasyR(o)<0.77%), oil generation (EasyR(o) = 0.77-1.54%), oil cracking (EasyR(o) = 1.54-2.51%), and secondary heavy hydrocarbon gas cracking stages (EasyR(o) = 2.51-3.61%). Based on aromatic and phenolic features, the humic source rocks have a significant late gas potential at EasyR(o)>1.99%; (2) The volume of G is 5.89-9.25 cm(3)/g. The V-ad is positively correlated with the pressure and TOC, and negatively with the temperature, ranging from 0.67 to 13.34 cm(3)/g. The hydrocarbon expulsion efficiency (eta(pg)) is 65.28-86.62%, and the GIP is 5.02-7.38 cm(3)/g. Furthermore, the hydrocarbon generation intensity (I-St) and expulsion intensity (I-Pt) are (0.42-8.62) & times; 10(8)/km(2) and (1.89-21.75) & times; 10(8) t/km(2), respectively. In the study area of Daning-Jixian, the amount of hydrocarbon generation (Q(St)) is 25.94 & times; 10(8) t and expulsion (Q(Pt)) is 9.17 & times; 10(11)t; (3) A key well Daji3-4 in the study area contains the strata from the Benxi Formation to the P(1)s(2)(2) member, and the main hydrocarbon generation center is located in the lower Shan(2)(3) layers, with the current free gas volume of 0.41 cm(3)/g. Rapid subsidence began at around 144 Ma during the Late Cretaceous, which increased the geothermal gradient, leading to increased maturity and a significant increase in gas content.

The Ordovician-Silurian transition represents a critical period marked by the formation of marine shale gas horizons within the South China Block. However, the mechanism for organic matter enrichment of Paleozoic marine shales in the western South China Block remain contentious, primarily due to insufficient understanding of paleogeomorphological evolution. In this paper, we describe the sedimentology of the Ordovician-Silurian succession composed of the Wufeng-Longmaxi Formation in the western South China Block and report new paleontological, and geochemical data for this succession to explore the relationship between basin paleogeomorphology and water mass environment. Nine graptolite zones are identified, spanning from the WF1 (Linxiang Formation) through WF2-WF4 (Wufeng Formation) to LM1-LM5 (Longmaxi Formation) in this well. Based on sedimentological and geochemical analyse results, three distinct stages of redox and paleoproductivity conditions in the water mass have been identified: (1) suboxic environments and low paleoproductivity in WF2-WF4; (2) euxinic and stagnant water conditions in LM1-LM3 accompanying with high paleoproductivity; and (3) anoxic water and low paleoproductivity in LM4-LM5. By integrating marine redox fluctuation, paleoproductivity conditions and regional hiatus (LM1-LM3) observed across multiple successions, we interpret thatthe western margin of the South China Block have been significantly affected by a collision between the South China Block and Yanbian terrane. The results of this study indicate that the accumulation of organic matter in the western margin of the South China Block was predominantly controlled by paleogeomorphology being caused by this collision event.

The Ordos Basin, characterized by its abundant transitional shale gas resources, plays a significant role in Chinese oil and gas exploration industry. However, the complex sedimentary environment and lithofacies combination of transitional shale make it highly challenging for reservoir quality evaluation. Acknowledging the rapid development of artificial intelligence, particularly the extensive use of machine learning in geology, this study proposes a new approach to assess the quality of transitional shale reservoirs through the utilization of the Random Forest algorithm (RF). Firstly, the lithology identification chart and reservoir quality evaluation standard were established using data and logging curves, and the relevant datasets were constructed. Four logging curves (Acoustic curve (AC), Compensated Neutron Log (CNL), Density curve (DEN), Gamma Ray (GR)), which serve as input variables to reflect reservoir characteristics, were carefully selected, while reservoir quality classification was used as the output results. Subsequently, the RF model was constructed and trained using this dataset. By analyzing the confusion matrix, it was observed that the RF model achieved an impressive accuracy level of approximately 90

Most of the global climate changes are closely associated with volcanic activity. However, the link between global cooling during the Ordovician-Silurian (O-S) transition and volcanism remains unclear due to limited constraints on large volcanic events before, during, and after the peak of the Hirnantian glaciation (PHG). Here, we present high-resolution mercury (Hg) concentrations and isotopes from South China across the O-S transition to assess volcanic activity and its contributions to climate changes. Anomalous Hg enrichments and volcanic-range Hg isotopes in samples above volcanic ash layers confirm the effectiveness of Hg as a tracer of volcanic events. Variations in Hg isotopes across the O-S transition reveal multiple Hg sources related to volcanic activity, that is, dominant volcanic Hg input during pre-PHG and post-PHG-2, deposition of volcanic-sourced atmospheric Hg(II) to seawater during PHG, and increased terrestrial Hg input from enhanced weathering during post-PHG-1. We propose that prolonged global cooling was driven by an albedo catastrophe caused by volcanic aerosols and sustained by reduced atmospheric CO2 levels due to enhanced organic carbon burial and weathering. This study highlights Hg as a tracer of volcanic activity and provides new evidence on the role of volcanism in driving climate changes across the O-S transition.