Marine and Petroleum Geology最新文献

{"title":"Sedimentology and diagenetic evolution of the Upper Permian Khuff Formation in Saudi Arabia. New perspectives from biostratigraphy, U/Pb geochronology and fluid inclusions","authors":"M. Deville de Periere ,&nbsp;X. Mangenot ,&nbsp;V. Dyja-Person ,&nbsp;A. Aldhubaib","doi":"10.1016/j.marpetgeo.2025.107462","DOIUrl":"10.1016/j.marpetgeo.2025.107462","url":null,"abstract":"<div><div>The Upper Permian section of the Khuff Formation is characterized by mud-dominated facies interpreted as lagoonal to peritidal sediments, interbedded with coated grain, grain-rich deposits suggesting lagoonal to high-energy shoal environments. The diagenetic overprint encompasses early dolomitization, dissolution, and burial diagenetic products such as dolomite cements and at least one phase of anhydrite. For the first time in the Khuff Formation of the Arabian Platform, <em>in-situ</em> LA-ICP-MS chronometry using U/Pb age dating has been performed in one well of the Rub al Khali Basin in order to refine the absolute timing of the various cement phases. The early dolomitization is interpreted as a very early replacive event resulting from hypersaline fluids, but is affected by recrystallization during the Middle Triassic (average 244.3 ± 7 Ma). Dolomite cements include a Guadalupian to base Lopingian phase (D1 – 265.5 ± 8 Ma) and a saddle dolomite (D2) dated from the Lower Jurassic (193.5 ± 15.7Ma). Fluid inclusion measurements in the latter indicate minimal precipitation temperatures of around 150 °C from rather medium salinity fluids, probably related to Lower Jurassic faulting. This study also shows the absence of calcite cements and of thermochemical sulfate reduction (TSR), usually present in the Khuff Formation at the platform-scale. The combined biostratigraphy assessment and U/Pb chronometry performed in this study suggest the section directly overlying the Middle Anhydrite to be slightly older than initially thought, and the transgression on top of the Middle Anhydrite marker extending into the Capitanian. Results also suggest that faults might have been active during the burial history allowing hydrothermal brines to percolate through studied interval.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107462"},"PeriodicalIF":3.7,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143942886","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":"Causal-Graph Lithology Classifier: Synergizing causal inference with graph neural networks for high-accuracy rock classification in well logging","authors":"Youzhuang Sun ,&nbsp;Shanchen Pang ,&nbsp;Zhihan Qiu ,&nbsp;Hengxiao Li ,&nbsp;Sibo Qiao","doi":"10.1016/j.marpetgeo.2025.107452","DOIUrl":"10.1016/j.marpetgeo.2025.107452","url":null,"abstract":"<div><div>Lithology classification is a vital task in geological exploration and plays a crucial role in the exploration and development of oil and gas resources. Traditional lithology classification methods often rely on empirical models or statistical approaches. While these methods have achieved some success, they frequently encounter issues such as low classification accuracy and poor model generalization when dealing with complex geological data. With advancements in deep learning technology, machine learning-based lithology classification methods have gradually been adopted. However, these methods often overlook the causal relationships between different lithologies and their impact on classification results. This paper proposes an innovative lithology classification method—the Causal-Graph Lithology Classifier (CG-Litho), which combines Graph Neural Networks (GNNs) and causal inference to effectively enhance classification accuracy and interpretability. Initially, the geological data is represented as a graph structure, where the data from each well is treated as a node, and the geological similarity or geographical relationship between wells is represented as edges. Utilizing GNNs, the model can propagate information across nodes to capture the spatial and geological feature interrelationships between different well locations. To further improve the model's performance, this paper introduces causal inference. By analyzing the causal impact of various geological features on lithology classification results through causal intervention, the model avoids correlation issues that cannot be explained by traditional methods. This GNN-based model, integrated with causal inference, not only identifies the complex interrelationships between lithologies but also effectively reduces the impact of data noise on classification results. Experimental results demonstrate that the proposed Causal-Graph Lithology Classifier excels in multiple practical application scenarios, significantly improving classification accuracy compared to traditional machine learning and deep learning models. Particularly, when handling well data with complex geological backgrounds, the model provides more stable and reliable prediction results. Additionally, the model's causal intervention mechanism offers geologists enhanced interpretability, helping them understand the causal relationships between variables and optimize exploration decisions. This study provides a new approach to lithology classification by integrating spatial information and causal inference through causal graph neural networks, enabling more efficient and interpretable lithology predictions. This method not only holds broad application prospects in geological exploration but also offers valuable insights for causal inference and graph learning problems in other fields.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"180 ","pages":"Article 107452"},"PeriodicalIF":3.7,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144146701","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":"Noble gas constraint of CO2 source and connectivity in a CO2-rich gas reservoir, offshore Angola","authors":"Stuart M.V. Gilfillan ,&nbsp;James A. Scott ,&nbsp;Honggang Zhou ,&nbsp;Magali Pujol","doi":"10.1016/j.marpetgeo.2025.107460","DOIUrl":"10.1016/j.marpetgeo.2025.107460","url":null,"abstract":"<div><div>Subsalt prospects in the South Atlantic margin contain potential hydrocarbon plays as exemplified by significant discoveries on the Brazilian margin. On the conjugate east side of the South Atlantic Ocean, pre-salt sections of the offshore Kwanza Basin, Angola also contain potentially economic reservoirs. Here we report the results of an exploration well which encountered gas containing high portions of CO₂ (82–84 mol%) and CH₄ (14.2–16.6 mol%) from offshore Angola. Using bulk gas, stable carbon isotopes and noble gas compositions of gas samples collected via downhole sampling of the exploration well, we constrain the source and connectivity of the CO₂-rich gas reservoir. Measured CO₂/³He ratios indicate that the CO₂ is primarily mantle-derived, with the samples from the deepest portion of the reservoir exhibiting evidence of CO₂ loss, most probably due to CO₂ dissolution into the groundwater. Using neon isotopes, we show that noble gas measurements constrain that the CO₂ has a Mid-Ocean Ridge Basalt (MORB) source, related to the rifting of the Atlantic margin at approximately 110 Ma. We additionally identify that a recently outlined methodology utilising noble gases can be applied to show a disconnection between the two upper and lower sections of the reservoir encountered in the well. This corroborates the evidence of disconnection provided from the δ¹³C gas fraction (C1 to C5) and provides further verification of the use of noble gases to determine static vertical connectivity within a hydrocarbon prospect.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107460"},"PeriodicalIF":3.7,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143942887","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":"Why does widespread submarine creep occur on the low-gradient continental slope of the northern South China Sea?","authors":"Weijian Gao ,&nbsp;Wei Li ,&nbsp;Tiago M. Alves ,&nbsp;Song Jing ,&nbsp;Wenhuan Zhan","doi":"10.1016/j.marpetgeo.2025.107453","DOIUrl":"10.1016/j.marpetgeo.2025.107453","url":null,"abstract":"<div><div>Submarine creep concerns the slow, post- or syn-depositional gravity-driven motion of continental slope strata, and may evolve into submarine landslides that are large enough to cause catastrophic tsunamis. However, compared to other slope instability features, the factors controlling submarine creep are still poorly understood. By using bathymetric data, high-quality seismic profiles and attribute maps, this study investigates the factors contributing to submarine creep on the gentle (∼1°) continental slope of the northern South China Sea. Our results demonstrate that the presence of contourite drifts was a preconditioning factor for the development of creeping strata in the study area. Fluids accumulated at the base of a broad glide plane generated the overpressure required to initiate sediment creep. Remnant strata and slide blocks reduced the seal competence of a mass-transport deposit (MTD), forming high-permeability zones in which deep-seated faults propagated towards the surface. Faults within high-permeability zones provided long-term pathways for upward-migrating fluids, enabling it to weaken the stability of shallow strata. Subsequent long-term migration and accumulation of fluids within the moat adjacent to the MTD's high-permeability zone promoted the retrogressive propagation of the upslope glide plane. A combination of all these processes ultimately resulted in the development of a vast area of submarine creep during the Quaternary. Similar processes to these documented in South China Sea explain the onset of submarine creep phenomena on continental margins across the world.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"180 ","pages":"Article 107453"},"PeriodicalIF":3.7,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144107365","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":"Integrated analysis of the gas hydrate petroleum system in the western South Korea Plateau (WSKP), East Sea (Sea of Japan)","authors":"Kyoung-Jin Kim ,&nbsp;Bo-Yeon Yi ,&nbsp;Dong-Geun Yoo","doi":"10.1016/j.marpetgeo.2025.107459","DOIUrl":"10.1016/j.marpetgeo.2025.107459","url":null,"abstract":"<div><div>This study provides the first comprehensive definition of the late Neogene to Quaternary deepwater fan system and gas hydrate (GH) petroleum system in the western South Korea Plateau (WSKP). An integrated geological and geophysical approach was employed to evaluate reservoir, source, and preservation potentials, establishing the WSKP as a promising target for GH exploration. The late Neogene to Quaternary deepwater fan system comprises submarine canyons, slope channel systems, and lobe complexes, with Lobe 1 and Lobe 2 identified as high-potential reservoirs. These lobe deposits demonstrated favorable reservoir properties, including maximum thicknesses of 15–38 m and 11–28 m, respectively, high lateral continuity, and elevated net-to-gross ratios. Source potential was attributed to two tectonostratigraphic units (MS2 and MS3), which exhibited high total organic carbon (&gt;1.0 wt %) and hydrogen index values (&gt;200 mgHC/gTOC) for bioigenic gas generation. Organic-rich claystones deposited under hemipelagic conditions served as effective source rocks. The biogenic gas window (20–60 °C) was observed at depths of 250–750 ms below the seafloor, corresponding to MS2 and MS3 intervals. Fault systems facilitated efficient gas migration, enabling upward transport from source rocks in MS2 and MS3 to reservoirs in MS4. Preservation potential was corroborated by seismic indicators such as bottom simulating reflectors, seismic attribute anomalies, and amplitude versus offset responses. This study offers a framework for understanding the GH petroleum system in the WSKP, advancing knowledge on depositional systems and GH accumulation. The findings contribute to understanding GH systems in back-arc basins and provide a foundation for future exploration.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"180 ","pages":"Article 107459"},"PeriodicalIF":3.7,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144068804","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":"Methane clumped isotopes of shallow gas hydrates in the Haima cold seeps, South China Sea: Implications for marine carbon cycling and sequestration","authors":"Haodong Chen ,&nbsp;Jing Zhao ,&nbsp;Qianyong Liang ,&nbsp;Jiacheng Li ,&nbsp;Junxi Feng ,&nbsp;Xi Xiao ,&nbsp;Zongheng Chen ,&nbsp;Yun Li ,&nbsp;Yongqiang Xiong","doi":"10.1016/j.marpetgeo.2025.107449","DOIUrl":"10.1016/j.marpetgeo.2025.107449","url":null,"abstract":"<div><div>Determining the methane sources and sinks of natural gas hydrates is pivotal to understanding carbon cycling over geological history. However, methane sources in natural gas hydrates remains poorly understood. In this study, we collected samples of hydrate-bound gas and pore fluid from shallow sediments in the Haima cold seeps of the Qiongdongnan Basin, South China Sea, and conducted various geochemical analyses to identify the sources and sinks of methane in this area. Particularly, methane clumped isotopes, an emerging method for tracing methane sources and sinks, were applied. Our results indicate that thermogenic methane accounts for 47.3 % of the shallow gas hydrates in the seeps, microbial methane being the rest. Furthermore, the data of headspace gas and pore water indicate the trace of anaerobic oxidation of methane (AOM) in the methane captured in shallow gas hydrates. By comparing our results with published datasets for deep gas hydrates, we refined the generation and accumulation span of biogenic methane as the Pliocene to Quaternary. Findings from this study highlight the contributions from different sources to hydrate-bound gas in the Qiongdongnan Basin and the coupled relationship between shallow gas hydrate formation, and deep oil and gas reservoirs. Our work advances the understanding of methane gas depletion and carbon sequestration in shallow sediments associated with cold seeps, and enhances the knowledge basis for the future exploitation of natural gas hydrates.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"180 ","pages":"Article 107449"},"PeriodicalIF":3.7,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144068889","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":"Estimating gas hydrate saturation in sediments using geophysical methods","authors":"Linsen Zhan,&nbsp;Wenjiu Cai,&nbsp;Haotian Liu,&nbsp;Ran Yang,&nbsp;Shiyuan Shi,&nbsp;Hailong Lu","doi":"10.1016/j.marpetgeo.2025.107458","DOIUrl":"10.1016/j.marpetgeo.2025.107458","url":null,"abstract":"<div><div>Quantifying the presence of gas hydrates within sediments is essential for accurately assessing their resource potential and effectively exploiting gas hydrate-bearing sediments (GHBS). Common geophysical methods for determining gas hydrate saturation include well-logging, seismic reflection, and controlled-source electromagnetic (CSEM) surveys, which detect changes in the electrical and acoustic properties of sediments. However, different methods can yield varying saturation estimates even within the same area, and the applicability of these techniques has not been fully explored. This review examines the typical anomalies associated with gas hydrate presence in seismic, well-logging, and CSEM surveys, assessing the underlying principles, strengths, and limitations of each of these geophysical methods. Case studies and method comparisons illustrate the application of these techniques across various geological settings, emphasizing the complex interplay between hydrate saturation, sediment properties, and measurement frequencies. Characterizing GHBS using geophysical methods remains challenging due to the oversimplification of rock physical models for natural gas hydrate systems, as well as the discrepancies between pore-scale distribution and larger scales of geophysical measurement tools. To address these issues, advanced rock physics models that integrate resistivity and elastic properties – while accounting for the coexistence of gas hydrates and free gas, as well as anisotropic sediment behavior – are essential for improving the accuracy of saturation estimates. Additionally, resolving scale-related discrepancies through advanced upscaling techniques and integrated multi-disciplinary datasets is critical for reliably extrapolating localized hydrate saturations to reservoir-scale resource evaluations.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107458"},"PeriodicalIF":3.7,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143936290","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":"Integrated 3D forward stratigraphic and basin modeling of the Santos Basin, offshore Brazil: Implications of sedimentary depositional facies and CO2 migration for silicification of continental carbonate reservoirs","authors":"Alina-Berenice Christ ,&nbsp;Marie-Christine Cacas-Stentz ,&nbsp;Nathalie Collard ,&nbsp;Fadi Henri Nader ,&nbsp;Elisabeth Bemer ,&nbsp;Rodrigo Brandão Bunevich ,&nbsp;João Paulo Borges Gomes ,&nbsp;Olinto Gomes de Souza Jr. ,&nbsp;Maria Anna Abreu de Almeida dos Reis","doi":"10.1016/j.marpetgeo.2025.107455","DOIUrl":"10.1016/j.marpetgeo.2025.107455","url":null,"abstract":"<div><div>Silicification plays an important role in the quality of pre-salt reservoirs, resulting in significant heterogeneities that are difficult to predict. A better understanding of the distribution of silicified pre-salt reservoirs at the basin scale helps in mapping such heterogeneities and further optimizing responsible hydrocarbon exploration and production. Here we investigate a scenario involving the interaction of an internal silica source from Mg-rich clay (sedimentary depositional facies) and CO₂-rich fluid upwelling along deep-rooted faults. These are some of the main controlling factors of silicification, as confirmed with conceptual and numerical geochemical modeling. We present a new modeling workflow integrating forward stratigraphic modeling (FSM), basin/thermal modeling, quantitative chemical modeling, and map-based analysis to derive silicification probability maps of the Barra Velha Formation in the Santos Basin (Brazil). FSM simulates, with a process-based approach, the sediment distribution in the Barra Velha Formation including Mg-rich clay. Basin/thermal modeling simulates the rock-fluid systems evolution, CO₂ migration, accumulation, and concentration in the formation. Geochemical modeling provides Mg-clay transformation ratios depending on Mg-clay content of rock matrix and CO₂ concentration. Combining all elements together enables calculation of basin scale silicification probability maps across the study area. Highest probability of silicification is found above uplifted areas known to include Mg-rich clay, intense faulting, and trapping structures.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"180 ","pages":"Article 107455"},"PeriodicalIF":3.7,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144068805","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":"Widespread shallow-marine anoxia in Late Ordovician epicratonic seas of eastern Laurentia: Evidence from lithological and geochemical proxies","authors":"Dan Atasiei ,&nbsp;Jisuo Jin ,&nbsp;Karem Azmy ,&nbsp;Cameron J. Tsujita ,&nbsp;Frank Brunton","doi":"10.1016/j.marpetgeo.2025.107454","DOIUrl":"10.1016/j.marpetgeo.2025.107454","url":null,"abstract":"<div><div>The Late Ordovician experienced dramatic episodes of globally widespread accumulation of organic-rich marine sediments as represented by black shales and their carbonate equivalents, often associated with ocean anoxia. During the mid-Katian, a widespread lithofacies of black, laminated, organic-rich marlstones, referred to as BLORMs (new term) in eastern Laurentia, contain abundant benthic shelly fossils, such as brachiopods and large trilobites that are incompatible with anoxic water conditions previously suggested for the facies. Here, we present lithological, paleontological, and geochemical data to demonstrate that the BLORM facies accumulated in shallow epicratonic seas under predominantly suboxic conditions punctuated by frequent intervals of anoxia. Organic-rich laminae were the result of frequent eutrophication events associated with nutrient enrichment from weathering inputs enhanced by Taconic orogenic phases, and cool-water upwelling from the Appalachian Foreland Basin. The transitions from the normal-marine limestone of the Cobourg Formation to the Collingwood BLORM facies, and then to clay shale of the Blue Mountain Formation in southern Ontario represented oceanographic signals or changes resulting in widespread shallow-marine anoxia and a regional collapse of the carbonate factory in eastern Laurentia. The drastic increase in clay influx and decrease in TOC contents in the clay shale of the middle-upper Blue Mountain Formation mark the end of BLORM depositional conditions. The variations in the weathering (Rb/Sr, Al/Ti, ∑REE), redox (Cr, V, Mo, U, Th/U) and primary productivity (TOC, δ¹⁵N, Zn, P) proxies reflect the fluctuations of sea level and the influence of the Taconic orogenic pulses on siliciclastic inputs into the marine environment. The TOC, δ¹⁵N and P_org profiles show distinct shifts that peak at a stratigraphic level correlated with the base of the Blue Mountain Formation and a significant increase in siliciclastic inputs as reflected by the climbing Rb/Sr, Al/Ti and ∑REE profiles, which is consistent with sedimentological evidence.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"179 ","pages":"Article 107454"},"PeriodicalIF":3.7,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932006","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":"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}