Marine and Petroleum Geology最新文献

{"title":"Oceanic redox variations during the Cambrian Age 2–3 in the Yangtze Block of South China: Evidence from pyrite-based proxies","authors":"Fangliang Fu ,&nbsp;Caineng Zou ,&nbsp;Zhengfu Zhao ,&nbsp;Songqi Pan ,&nbsp;Wei Wang ,&nbsp;Cui Luo ,&nbsp;Ganlin Hua ,&nbsp;Guanwen Lu ,&nbsp;Ming Yuan ,&nbsp;Jia Yin ,&nbsp;Zhenhua Jing","doi":"10.1016/j.marpetgeo.2025.107438","DOIUrl":"10.1016/j.marpetgeo.2025.107438","url":null,"abstract":"<div><div>The early Cambrian marks a pivotal period in metazoan evolution and ocean oxygenation through Earth's history, with sedimentary sequences in the Yangtze Block of South China preserving key records about biological and environmental evolution. Although previous studies have focused on redox conditions in shelf, slope, and basin environments, their controls on pyrite sulfur isotope (δ³⁴S_py) variations, and the influence of redox dynamics on biological activity within intraplatform basin remain unclear. This study presents results including diagnostic fossils, pyrite morphology, iron speciations, and δ³⁴S_py from the shales of the early Cambrian Qiongzhusi Formation in well W207, which is located in an intraplatform basin of the Yantze Block. These data are integrated with previous datasets from eight sections spanning shelf, slope, and basin environments. Our results indicate that during the transgression at the Cambrian Age 2–3 boundary (∼524–520 Ma), mid-depth euxinic waters on the slope expanded into the intraplatform basin, as supported by most samples with Fe_HR/Fe_T &gt; 0.38, Fe_py/Fe_HR &gt; 0.7, high Mo_EF/U_EF ratio (mean 5.2) and small sizes of framboidal pyrite (6.41 ± 0.70 μm). In contrast, in the early Cambrian Age 3 (∼520–517 Ma), these geochemical proxies collectively suggest widespread shelf oxygenation, coinciding with occurrence of abundant animal fossils in the strata. The seawater oxygenation probably facilitated metazoan diversification during the Cambrian explosion within the intraplatform basin. Deep-water oxygenation together with emerging bioturbations on the shelf shifted the oxic-anoxic redox interface from bottom water into sediments, promoting the formation of pyrite with heavy δ³⁴S_py values within seidments. Therefore, a spatial δ³⁴S_py gradient is observed during early Cambrian Age 3, with higher δ³⁴S_py values from the shallow shelf (more oxygen-rich) and deep basin (isotopically heavier sulfate in seawater) than those from middle-depth slope. The findings provide new insights into the redox landscape and its impact on biogeochemical cycling and metazoan evolution in the Yangtze Block during the early Cambrian.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107438"},"PeriodicalIF":3.7,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143906525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cyclic organic matter accumulation in a plateau salinized lacustrine basin: Major controls and hydrocarbon significance","authors":"Peng Pang ,&nbsp;Di Xiao ,&nbsp;Kunyu Wu ,&nbsp;Songtao Wu ,&nbsp;Haoting Xing ,&nbsp;Ying Xiong ,&nbsp;Rui Liu ,&nbsp;Xiucheng Tan","doi":"10.1016/j.marpetgeo.2025.107435","DOIUrl":"10.1016/j.marpetgeo.2025.107435","url":null,"abstract":"<div><div>Exploring the sedimentary process and organic matter enrichment mechanism of plateau saline lake basin holds unique theoretical research and practical production significance for the paleoenvironment restoration and hydrocarbon exploration in the plateau. This study aims to analyze the high-frequency sedimentary evolution and organic matter enrichment mechanism of the mixed deposits from the Eocene Lower Ganchaigou Formation (LGCG) in the Qaidam Basin on the Tibet Plateau, by means of petrology, mineralogy, and organic-inorganic geochemistry. Lithological characteristics indicated the high-frequency sedimentary sequences (&lt;10m) of the LGCG which are identified by a single cycle with four lithofacies from bottom to top: massive sandstones, laminated silty shales, laminated limestones, and bedded dolomites. Bulk organic geochemistry data showed the periodic variations of organic matter contents in the high-frequency sedimentary cycles. Organic matter predominantly occurs in dark gray laminated limestones, followed by the laminated silty shales, with the lowest contents in the bedded dolomites and massive sandstones. Inorganic geochemical proxies implied the cyclical changes of paleowater properties, paleoproductivity and sedimentation rate in the vertical profile that conformed to the high-frequency sedimentary sequences. Correlation analysis revealed that the enrichment of organic matter in the plateau saline lake is mainly related to high paleoproductivity and low sedimentation rate (&gt;5 cm/ka), and anoxic and low-salinity water conditions also promote the preservation of organic matter. Distinct from typical saline lake basins, the LGCG in the Qaidam Basin, a plateau saline lake, is characterized by lower organic matter abundance and higher hydrocarbon generation efficiency, due to reduced biological productivity and terrigenous input.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107435"},"PeriodicalIF":3.7,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143902384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depositional environments of the organic-rich shales from the Lower Cretaceous Dalazi Formation in the Yanji and Luozigou Basins of Northeast China","authors":"Xiangdong Zhao ,&nbsp;Wei Wang ,&nbsp;Hanlin Liu ,&nbsp;Yongliang Hu ,&nbsp;Xianye Zhao ,&nbsp;Chenran Song ,&nbsp;Chengguo Guan ,&nbsp;Daran Zheng ,&nbsp;Haichun Zhang","doi":"10.1016/j.marpetgeo.2025.107437","DOIUrl":"10.1016/j.marpetgeo.2025.107437","url":null,"abstract":"<div><div>The organic-rich shales from the Lower Cretaceous Dalazi Formation in northeastern China are well known for their rich terrestrial fossils and significant hydrocarbon potential. However, the exact depositional environments of these shales remain unclear. Here, integrated geochemical proxies, including iron speciation (Fe_HR/Fe_T, Fe_py/Fe_HR), pyrite sulfur isotopes (δ³⁴S_py), and major- and trace-element enrichments were carried out on these organic-rich shales from the Zhixin section of the Yanji Basin and the Beigou section of the Luozigou Basin in Northeast China. This study aims to provide insights into the contemporaneous continental chemical weathering intensities accompanied with the lake redox conditions during the deposition of the Dalazi Formation shales. Low chemical index of alteration (CIA) values were detected in the shales, indicating low weathered continental environments during the depositional period of the shales. The reduced water availability under dry climate evidenced by plant fossils likely contributes to limiting the intensity of chemical weathering with low CIA values.</div><div>All samples exhibit Fe_HR/Fe_T ratios &gt;0.38 and Fe_py/Fe_HR ratios far below 0.7, displaying the water column characterized by anoxic ferruginous conditions with limited HS⁻ availability during the shale deposition. The reconstruction of redox condition is consistent with the observations of the low pyrite contents, minimal well-formed framboidal pyrite crystals and covariation patterns of Mo_EF and U_EF in the shales. With low CIA values, the less continental input to the lake probably gives rise to the anoxic ferruginous deep-water conditions via limiting sulfate availability, which is consistently supported by high δ³⁴S_py values (12.2 ± 9.6 ‰), low pyrite contents, and the remarkable negative correlation between the CIA and δ³⁴S_py values. Considering the high content of organic matter up to 6.38 wt% and abundant fossil collections in the shales, this finding highlights the beneficial role of a sustained and stable anoxic ferruginous environment for preserving organic matter and carbonaceous fossils in the Dalazi Formation.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107437"},"PeriodicalIF":3.7,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The relationship between physical property evolution and reservoir formation in volcanic rock reservoirs: The Huoshiling Formation, Dehui Fault Depression, southern Songliao Basin","authors":"Liang Liu ,&nbsp;Jijun Li ,&nbsp;Tianhong Yang ,&nbsp;Libin Song ,&nbsp;Kexin Jia ,&nbsp;Lili Li ,&nbsp;Weiwei Qu ,&nbsp;Jun Jiang ,&nbsp;Shikai Ni ,&nbsp;Chenghong Luo","doi":"10.1016/j.marpetgeo.2025.107446","DOIUrl":"10.1016/j.marpetgeo.2025.107446","url":null,"abstract":"<div><div>The Huoshiling Formation in the Dehui Fault Depression has emerged as a significant target for tight oil and gas exploration in volcanic rock reservoirs. This research investigates the tight gas reservoirs of the Huoshiling Formation through a combination of core observation, thin-section analysis, image recognition, and thermal simulation experiments. The study explores diagenetic processes, the factors influencing reservoir physical properties, and the development of a coupling of reservoir physical property evolution and oil and gas accumulation. Three primary types of diagenesis in the Huoshiling Formation have been identified. Detailed diagenetic evolution sequences are established through thin-section observation and analyses of authigenic minerals, pore types, and diagenetic mineral contact relationships, complemented by carbon and oxygen isotope analysis. An innovative technique integrating cast thin-section scanning and large-field stitching, and image recognition is developed to quantitatively assess the impact of various diagenetic processes on reservoir properties. Reconstructing burial, thermal, and hydrocarbon generation histories and integrating fluid inclusion homogenization temperatures, reveals the peak periods of gas and oil generation. A porosity evolution history map was constructed using the diagenetic evolution sequence, computational image analysis, and back-stripping inversion methods. This analysis elucidates the relationship between the evolution of reservoir physical properties and hydrocarbon accumulation timing in the Huoshiling Formation.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107446"},"PeriodicalIF":3.7,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143906526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shale fracture prediction using integrated seismic methods","authors":"Zhiyuan Sun ,&nbsp;Shouyu Xu ,&nbsp;Cunfei Ma ,&nbsp;Tao Li ,&nbsp;Jiachang Zhang ,&nbsp;Fancheng Zeng","doi":"10.1016/j.marpetgeo.2025.107439","DOIUrl":"10.1016/j.marpetgeo.2025.107439","url":null,"abstract":"<div><div>A casing deformation incident occurred in the Longmaxi Formation during shale gas production at Platform H1 in the southern Sichuan Z215 well block. Based on the monitoring and analysis of microseismic signals, preliminary analysis suggests the hydration of NW-trending fractures generated by hydraulic fracturing. The deeper shale layers of the Longmaxi Formation (3500 m) are complicated to interpret seismically because they are poorly resolvable with weak fracture responses, such that traditional seismic attributes cannot effectively recognize microfaults and microfractures. This has hampered additional production in the Z215 well block. To enhance seismic resolution and accurately describe fracture distribution in this area, we applied an integrated approach combining seismic forward modeling, spectral decomposition, 3D U-Net convolutional neural networks, ant colony algorithm, seismic inversion, and microseismic signal monitoring for comprehensive fracture prediction. Fracture prediction from this method demonstrates high consistency with microseismic data and shows a fault-fracture network that is governed by NE-trending major faults and limited NW-trending fractures. Casing deformation at Platform H1 was associated with composite deformation comprising NE-trending major faults, EW-trending minor faults, and NW-trending fractures. This study shows that the integrated method proposed in this paper can predict fractures in the Z215 well block reliably; this may be a reference for shale fracture prediction in other regions.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107439"},"PeriodicalIF":3.7,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899981","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine learning-based sweet spot prediction for lacuscrine shale oil in the Weixinan Sag, Beibu Gulf Basin, China","authors":"Ruoxin Huang ,&nbsp;Yifan Li ,&nbsp;Zhiqian Gao ,&nbsp;Caiwei Fan ,&nbsp;Junjun You ,&nbsp;Ruisi Li ,&nbsp;Chengkun Deng ,&nbsp;Guocui Li","doi":"10.1016/j.marpetgeo.2025.107436","DOIUrl":"10.1016/j.marpetgeo.2025.107436","url":null,"abstract":"<div><div>This study aims to overcome challenges related to sparse well distribution, pronounced lithological heterogeneity, and limited core data in offshore lacustrine shale oil reservoirs through the development of an integrated evaluation framework that enables quantitative prediction and spatial mapping of sweet spots. Conventional well logs, nuclear magnetic resonance (NMR) data, geochemical analyses, and laboratory measurements are integrated to construct a grading system for four key properties—reservoir quality, oil-bearing property, mobility, and fracability—with threshold values determined by statistical distributions. To address sample scarcity, a Generative Adversarial Network (GAN) is applied for data augmentation, while Recursive Feature Elimination with Cross-Validation (RFECV) is employed for optimal feature selection. Considering the complex, nonlinear, and anisotropic nature of shale reservoirs, a Generalized Regression Neural Network (GRNN) is constructed, with its smoothing parameter globally optimized using the Sparrow Search Algorithm (SSA), resulting in high predictive accuracy (R² &gt; 0.8). Furthermore, the study establishes a coupling relationship between lithofacies assemblages and the four properties. This integrated approach supports spatial prediction of both individual parameters and the comprehensive sweet spot evaluation index. The results indicate that laminated (LSA) and interbedded (ISA) shales exhibit distinct sweet spot characteristics (porosity &gt;6 %, clay content &lt;25 %, and OSI &gt;100) with high-potential zones primarily located in the central W1, southeastern W2, and central W3 regions. This methodology offers a reliable technical framework for quantitative assessment and development planning of offshore lacustrine shale oil resources under data-constrained conditions.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107436"},"PeriodicalIF":3.7,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into shale pore structure and microscopic fluid occurrence characteristics in the Paleogene Funing Formation, Subei Basin, China","authors":"Weizheng Gao ,&nbsp;Pengfei Zhang ,&nbsp;Junjie Wang ,&nbsp;Nengwu Zhou ,&nbsp;Yajie Yin ,&nbsp;Guohui Chen ,&nbsp;Wenbiao Li ,&nbsp;Han Wu ,&nbsp;Chao Liu ,&nbsp;Shuangfang Lu","doi":"10.1016/j.marpetgeo.2025.107434","DOIUrl":"10.1016/j.marpetgeo.2025.107434","url":null,"abstract":"<div><div>Microscopic pore structure and mineral composition play a critical role in controlling the distribution and occurrence of shale fluids. This study examines shale samples from the Paleogene Funing Formation in the Gaoyou Sag of the Subei Basin using an integrated approach, including nuclear magnetic resonance (NMR) T₂ and T₁–T₂ tests, Rock-Eval, scanning electron microscopy (SEM), and low-temperature nitrogen adsorption/desorption (LTNA/D) analyses. This study focuses on the influence of organic matter, mineral composition, and pore structure on the occurrence and distribution of fluids. Results indicate that the pore types primarily consist of intergranular and grain-edge pores amidst quartz and calcite, with secondary contributions from intragranular pores associated with clay minerals. The NMR T₂ spectra are dominated by p2 (1–30 ms) and p1 (&lt;1 ms) peaks, corresponding to mesopores (100–1000 nm), micro- and minipores (&lt;100 nm), respectively. The NMR T₁–T₂ technique effectively quantifies pore fluid distributions and contents in both the as-received (AR) and water-oil restoration (WOR) states. The loss of original pore oil is mainly due to the migration of movable oil. The abundance of organic matter in shale affects its oil content, with excessive organic matter accumulation tending to restrict shale oil mobility. Pore fluid distribution is predominantly determined by pore structure. Capillary-bound water and adsorbed oil primarily occur in micro- and minipores, while the presence of pore water further influences the spatial distribution of adsorbed oil. Conversely, capillary-bound oil is primarily concentrated in mesopores, whereas movable oil is mostly stored in macropores (&gt;1000 nm). Mineral contents in different lithologies exert a significant influence on the distribution of shale oil and water contents. Clay-rich shale typically exhibits higher amounts of capillary-bound water. Felsic-argillaceous mixed (FAM) shales, show that an increase in quartz content further enhances the occurrence and mobility of shale oil, while higher calcite content has the opposite effect. Conversely, in argillaceous-calcareous mixed (ACM) shales, which are dominated by calcite, higher calcite content is associated with larger accumulations of free oil. These findings may provide valuable insights into the mechanisms of shale oil enrichment and offer practical guidance for identifying sweet spots in the Gaoyou Sag, Subei Basin.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107434"},"PeriodicalIF":3.7,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143895005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural geometry and evolution of the eastern Yuqi strike-slip faults in the Tabei Uplift, Tarim Basin (NW China)","authors":"Zhendong Wang ,&nbsp;Shang Deng ,&nbsp;Qinqi Xu ,&nbsp;Yong Zhang ,&nbsp;Huadong Wei ,&nbsp;Wei Huang ,&nbsp;Bin Wang","doi":"10.1016/j.marpetgeo.2025.107430","DOIUrl":"10.1016/j.marpetgeo.2025.107430","url":null,"abstract":"<div><div>The strike-slip fault system in the eastern Yuqi area of the Caohu Sag, distinct from the conjugate strike-slip fault systems in the Halahatang Sag, provides a valuable case study for understanding the genetic variations among strike-slip faults across different locations within the Tabei Uplift. This system in the eastern Yuqi area comprises ENE-, NE-, N–S-, and E–W-oriented strike-slip faults. The development of the ENE- and NE-oriented faults was primarily influenced by the paleostructure, specifically the structural slope-break zone. The evolution of these fault sets can be divided into three main stages: (1) In the Late Ordovician, initial uplift occurred in the Akekule Uplift and the northern Caohu Sag, leading to the development of the western Akekule Uplift as a paleostructural high. Conjugate faults formed in the western Akekule Uplift, constrained by the rigid Yakela Fault-convex. (2) During the Silurian to Early Devonian, northward compression and subsequent extrusion along the Akekumu Fault resulted in the formation of a series of ENE- and NE-oriented sinistral strike-slip faults in the western Yuqi area, at the leading edge of the Akekumu Fault. Simultaneously, the structural slope-break zone began to develop in the eastern Yuqi area, controlling the formation and orientation of the NE- and ENE-oriented faults. (3) In the Permian, increased N–S-trending regional compression, driven by the closure of the South Tianshan Ocean, led to the formation of the reverse fault RF-ENE1 and an upward-steepening interlayer reverse fault (RF-CAO2). NE-oriented strike-slip faults, such as Fault YQ13, were reactivated, and NS-oriented strike-slip faults, including Fault YQD and Fault Lungudong, potentially experienced sinistral strike-slip movement.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107430"},"PeriodicalIF":3.7,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphology and in-situ sulfur isotope characteristics of pyrite across the Ordovician-Silurian boundary marine shale in South China: Indicative significance for sedimentary environment","authors":"Shichao Ji ,&nbsp;Chao Liang ,&nbsp;Yu Han ,&nbsp;Qing Tang ,&nbsp;Yingchang Cao ,&nbsp;Keyu Liu ,&nbsp;Jing Wu ,&nbsp;Haoran Xie ,&nbsp;Fanglu Chen","doi":"10.1016/j.marpetgeo.2025.107431","DOIUrl":"10.1016/j.marpetgeo.2025.107431","url":null,"abstract":"<div><div>Pyrite plays a crucial role in the sulfur cycle, mirroring changes in global and local redox conditions within sedimentary environments across geological records. The grain size of framboidal pyrite effectively indicates the redox state of the sedimentary water column, while its sulfur isotope characteristics provide insights into early diagenetic history. However, variations in water column hydrodynamics can diminish the reliability of framboidal pyrite grain size distribution as an indicator of redox conditions. Bulk pyrite sulfur isotope measurements are often affected by later diagenetic processes. This study aims to investigate the impact of hydrodynamic conditions on framboidal pyrite grain size and to reconstruct the redox history across the Ordovician-Silurian boundary. To achieve this, we examined the morphology, grain size distribution of pyrite, total organic carbon, trace element abundances in the Wufeng (Ordovician)-Longmaxi (Silurian) formation in South China. The results indicate that enhanced hydrodynamic conditions driven by upwelling led to a significant increase in the average grain size of framboidal pyrite formed in reducing environments, as well as greater grain size variability. We also conducted in situ sulfur isotope analyses on two framboidal pyrite grains from the top of the Wufeng Formation and the base of the Longmaxi Formation. A response model was developed to illustrate the relationship between grain-scale δ³⁴S_pyr distribution and sea-level fluctuations. Ultimately, the redox evolution across the Ordovician-Silurian boundary in the Weiyuan area was reconstructed into five stages: (1) The upper Wufeng Formation experienced intensifying reducing conditions, culminating in euxinia at the top. (2) Oxidizing conditions briefly prevailed at the base of the Longmaxi Formation. (3) Oxygen levels in the sedimentary waters of the lower Longmaxi Formation decreased, stabilizing in a prolonged dysoxic-euxinic state. (4) The middle-lower Longmaxi Formation saw a gradual increase in the oxidative state of the sedimentary waters, transitioning to an oxic environment. (5) The middle Longmaxi Formation's sedimentary waters sustained a long-term dysoxic-oxic state.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107431"},"PeriodicalIF":3.7,"publicationDate":"2025-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143891114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Origin of the Cenozoic faults in the “B” structure of the central inversion belt in the northern part of the Xihu Sag, East China Sea Basin","authors":"Anqi Tian ,&nbsp;Chenglin Liu ,&nbsp;Chuangxin Liu ,&nbsp;Daowu Huang ,&nbsp;Hongliang Huo ,&nbsp;Binbin Liu ,&nbsp;Hongyan Gao ,&nbsp;Ziyie Tian","doi":"10.1016/j.marpetgeo.2025.107429","DOIUrl":"10.1016/j.marpetgeo.2025.107429","url":null,"abstract":"<div><div>The periodic activation of faults in the inversion belt facilitates hydrocarbon migration and accumulation while also potentially destabilizing pre-existing reservoirs, affecting long-term hydrocarbon stability. Based on 3D seismic data, and employing maximum likelihood attributes and time-slice-assisted analysis methods, this study systematically analyzes the fault geometry and relative motion characteristics, following the principle of corresponding points along cross-sections. The analysis of the fault's three-dimensional spatial evolution shows that the faults in the study area exhibit deep “rootless flower” and middle-to shallow-layer “flower-like” structural patterns. The deep-seated faults trend NE-NEE, with strike-slip movement changing from right-lateral to left-lateral. Middle-to shallow-layer faults are predominantly near E-W normal faults, with left-lateral strike-slip movements, forming Riedel R′ shear faults due to intense late compressional and rotational actions. The shallow faults show the strongest strike-slip activity, with the maximum slip displacement in the core reaching 820 m. These faults have undergone four main deformation stages: early Eocene extensional faulting, late Eocene positive inversion and strike-slip, Oligocene inherited strike-slip, and intense late Miocene strike-slip inversion. The phase-specific fault activity is primarily influenced by a combination of far-field tectonic processes, including the subduction retreat and rotation of the Pacific Plate, back-arc extension, remote effects from the India-Eurasia plate collision, and the migration and rotation of the Philippine Plate. Through an in-depth analysis of the fault evolution process, a more refined predictive model for the formation and evolution of hydrocarbon reservoirs has been established, providing crucial tectonic context and theoretical support for oil and gas exploration and development.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"178 ","pages":"Article 107429"},"PeriodicalIF":3.7,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143879255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}