Marine and Petroleum Geology最新文献

{"title":"Genesis and geological significance of dolomite in shales of the first member of the cretaceous Qingshankou Formation, central depression, Songliao Basin, China","authors":"Min Yan ,&nbsp;Jinglan Luo ,&nbsp;Zihui Feng ,&nbsp;Hongmei Shao ,&nbsp;Danting Luo ,&nbsp;Bo Gao ,&nbsp;Jiping Wang ,&nbsp;Yongchao Wang","doi":"10.1016/j.marpetgeo.2025.107564","DOIUrl":"10.1016/j.marpetgeo.2025.107564","url":null,"abstract":"<div><div>This study presents the first nano-, micro-, and macro-scale analyses of dolomite minerals of varying maturity (all references to maturity in this study pertain to the maturity of organic matter) sampled from the first member of the Cretaceous Qingshankou Formation in the central depression of the Songliao Basin, China. Mineralogical, petrological, isotope and elemental analyses were combined to elucidate the pore fluid evolution and dolomite diagenesis, as well as their implications for the shale organic matter and reservoir space. Three types of authigenic dolomites are identified. The precipitation of authigenic dolomite during the early diagenesis to the mesodiagenesis followed the sequence of anhedral dolomite in low-maturity dolomitic shale (Ro: 0.58–0.70 %) → rhombic ankerite formed overgrowths on anhedral dolomite in medium-maturity dolomitic shale (Ro: 0.78–1.29 %) → saddle-shaped ankerite in crack in high-maturity dolomitic shale (Ro: 1.34–1.70 %); this was accompanied by the transition of pore fluid from seawater to organic fluid, and subsequently to high-temperature hydrothermal fluid. During the early diagenesis to the A₁ stage of mesodiagenesis, the methanogenic archaea in seawater induced the precipitation of anhedral dolomite, which prevented interparticle pore destruction during compaction and preserved the micropores in low-maturity dolomitic shales. During the A₂ stage of mesodiagenesis, the cementation of rhombic ankerite decreased the effective porosity, and consumed organic carbon as the carbon framework in the medium-maturity dolomitic shales. In the hydrocarbon expulsion environment, the dissolution of rhombic ankerite by organic acids promoted the development of micro-nano-scale dissolution pores and increased the effective porosity, which facilitated the expulsion of hydrocarbons from the medium-maturity dolomitic shales. During the B stage of mesodiagenesis, although the high-temperature hydrothermal fluid led to the occlusion of cracks by the cementation of saddle-shaped ankerite, the heat source provided by hydrothermal fluids and/or burial promotes the pyrolysis of organic matter and the development of organic pores, which increased the effective porosity and the expulsion of hydrocarbons in the high-maturity dolomitic shales. Therefore, the low-maturity dolomitic shales exhibit higher effective porosity and higher total organic carbon (TOC) content compared to medium- and high-maturity dolomitic shales. This study expands the high-quality shale from the traditionally organic pore region in higher-maturity conditions to the inorganic pore region with the enrichment of organic matter in lower maturity conditions, which is crucial for developing the hydrocarbon exploration field of shale.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107564"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144654701","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":"Isotopic equilibrium constraints on CO2 dissolution and carbon isotopic reversal in a thermogenic coalbed gas system associated with the Zhuzang syncline, Guizhou, China","authors":"Xiangrui Chen ,&nbsp;Yunpeng Wang ,&nbsp;Mingxin Tao ,&nbsp;Zheng Zhou ,&nbsp;Meng Wei","doi":"10.1016/j.marpetgeo.2025.107554","DOIUrl":"10.1016/j.marpetgeo.2025.107554","url":null,"abstract":"<div><div>Natural gas is a vital energy resource. The isotopic composition of natural gas plays a critical role in understanding its origin, thermal maturity, and secondary alteration. Both kinetic and equilibrium isotopic fractionations have been observed in various natural gas systems. However, the dominant mechanism (either equilibrium or kinetic) that controls the isotopic compositions of the primary natural gas is still unclear. Coalbed gas (CBG), formed and stored in situ coalbeds, is an ideal natural gas for studying this key issue. We collected CBG and coproduced water samples from the Zhuzang syncline in China. This study shows that the CBG is an over-mature thermogenic gas formed during the Yanshanian orogeny. The CH₄-C₂H₆-CO₂ system was likely near carbon isotope equilibrium during the CBG formation. However, later alterations, such as meteoric water recharge, CO₂ dissolution, and CBG recovery led to obvious isotopic disequilibrium of the CH₄-C₂H₆-CO₂-DIC (dissolved inorganic carbon) system. Carbon isotope reversals (δ¹³C_CH4 &gt; δ¹³C_C2H6) were observed in the CBG samples, resulting from decreasing δ¹³C_C2H6 values after CBG formation. Based on isotopic equilibrium, the δ¹³C values of the primary ethane were estimated. Some hypotheses often used to explain isotope reversals in natural gas cannot explain the isotope reversals of the CBG samples. We propose that the CBG recovery process led to more negative δ¹³C_C2H6 and thus δ¹³C_CH4 &gt; δ¹³C_C2H6. Model-estimated 53–99 % CO₂ generated during thermogenic or microbial CBG formation has dissolved into coalbed water to become DIC. Hence, dissolution trapping is an important mechanism for CO₂ storage in coalbeds over geological timescales. This study implies that isotopic equilibrium fractionation plays a vital role in understanding the primary geochemical composition and secondary alteration of CBG.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107554"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144614855","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":"Genesis and geological significance of pyrite in the Ordovician carbonate-evaporative strata of central Ordos Basin, China","authors":"Lianqi Jia ,&nbsp;Biao Qin ,&nbsp;Chenlu Ma ,&nbsp;Ruining Zheng ,&nbsp;Jie Zhang","doi":"10.1016/j.marpetgeo.2025.107586","DOIUrl":"10.1016/j.marpetgeo.2025.107586","url":null,"abstract":"<div><div>Deep burial carbonate-evaporative strata (4000–10000m) have significant exploration potential for gas-rich petroliferous basins. However, high temperature and thermal evolution destroy most hydrocarbon related organic geochemical parameters used to analyze the alteration of oil and gas reservoirs. This study is the first systematic attempt to assess hydrocarbon alteration and cracking based on generational evolution and geochemistry of pyrite. Pyrites in the subsalt carbonate of Ordovician Majiagou Formation of central Ordos Basin are formed in four stages (Py1, Py2, Py3 and Py4). The mineral morphology and geochemical characteristics indicate that Py1 was formed from microbial sulfate reduction. Py2, Py3 and Py4 are derived from thermochemical sulfate reduction (TSR). This is supported by coexistence between pyrite and other TSR products (calcite, bitumen and elemental sulfur), reaction condition and rich TSR reactants (hydrocarbon and sulfate). TSR occurs in a closed system, proved by increasing δ³⁴S values from Py2 to Py4 (6.2 ‰–73.9 ‰) and unusually high δ³⁴S values of residual vein anhydrite (36.2 ‰–44.8 ‰) in the reservoir. TSR pyrites (Py2, Py3 and Py4) have relatively high concentrations of transition metal elements, which is consistent with worldwide oil. Significantly decreasing trace element concentrations from Py2 to Py4 and from core to rim are attributed to TSR reactant transformation from oil to wet gas. Py2, Py3 and Py4 probably correspond to oil-dominated TSR, TSR-induced oil cracking and wet gas-dominated TSR respectively. Therefore, TSR pyrite is a potentially effective mineral to the evolution of deep burial gas reservoirs.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107586"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145044504","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":"Turbidite sands filling accommodation associated with supra-mass transport deposit topography: Outcrop examples from Western Argentina","authors":"Victoria Valdez Buso ,&nbsp;Luke Fairweather ,&nbsp;Ben Kneller ,&nbsp;Juan Pablo Milana ,&nbsp;Fernando Farias Vesely","doi":"10.1016/j.marpetgeo.2025.107567","DOIUrl":"10.1016/j.marpetgeo.2025.107567","url":null,"abstract":"<div><div>Mass transport deposits (MTDs) generate topographic relief on their upper surfaces. The scale and geometry of the topographic features, and the interconnectivity of their sediment fill plays a crucial role in defining the characteristics of associated turbidite reservoirs. Turbidite sands may be ponded in isolated depocenters created by supra-MTD topography. The spacing and maximum thickness of ponded and isolated or tortuously interconnected sands are controlled by the dominant topographic wavelength and amplitude on the surface topography. Once the topography is filled to the saddles (the lowest point between adjacent topographic lows), the sand body forms a continuous sheet peppered with lacunae (‘holes’) marking the emergent heights (‘nunataks’). This is illustrated by confined turbidites over a 200-m thick MTD at Cerro Bola, Western Argentina. Field data differentiate ponded turbidites into a) Underfilled section; an isolated and laterally variable sand interval, confined by short-wavelength (tens to hundreds of meters) topography. Correlation of thicker beds suggests that larger flows were able to over-run at least the saddles in the topography, with only a small portion of the flow being captured in each low. b) Overfilled section; consists of a laterally continuous sand interval that covers the short-wavelength topography while progressively onlapping longer-wavelength (km-scale) features. Depositional facies may help to differentiate the confined/ponded stages, where local topography is still emergent, and thus to indicate the overall connectivity.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107567"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144704831","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":"Genesis and developmental pattern of Middle Permian dolomite in Northwestern Sichuan, China","authors":"Zhidian Xi ,&nbsp;Fei Huo ,&nbsp;Huachuan Jiang ,&nbsp;Xingzhi Wang ,&nbsp;Huiwen Huang ,&nbsp;Yuhan Huang ,&nbsp;Yi Hu ,&nbsp;Xueyan Wu ,&nbsp;Yang Li ,&nbsp;Wenli Xu ,&nbsp;Anqing Chen","doi":"10.1016/j.marpetgeo.2025.107555","DOIUrl":"10.1016/j.marpetgeo.2025.107555","url":null,"abstract":"<div><div>The formation of large-scale dolomite reservoirs in the Middle Permian of Northwest Sichuan shares a good temporal correlation with the occurrence of major events in the Emeishan Large Igneous Province (ELIP). However, because the dolomitized fluids, the timing of dolomitization and the genesis mechanism of the dolomites are not comprehensively understood, its developmental pattern requires further analysis. This paper identified the diagenetic fluids of different types of dolomites via petrological characteristics of dolomites, carbon and oxygen isotopes, strontium isotopes, and other geochemical data, as well as fluid inclusions and laser U-Pb isotope dating. The dolomite genesis model related to the dynamical formation mechanism of the ELIP was also reconstructed. The Middle Permian dolomites in Northwest Sichuan are divided into matrix dolomite (Md) and cement dolomites (Cd). Importantly, the matrix dolomites include very finely to finely crystalline matrix dolomite (Md1), finely to medium crystalline matrix dolomite (Md2), and medium to coarsely crystalline matrix dolomite (Md3). The dolomites were primarily modified by three phases of dolomitizing fluids. The Md1 phase yields a U-Pb age of 262 ± 9.2 Ma, consistent with the host stratigraphic age, and exhibits ⁸⁷Sr/⁸⁶Sr ratios matching Permian seawater values. These features indicate Md1 formed dominantly through penecontemporaneous seawater reflux dolomitization. In contrast, the Md2 phase shows a U-Pb age of 261.3 ± 7.4 Ma—also stratigraphically consistent—but contains later-stage subsurface cements with a distinct U-Pb age of 245.7 ± 1.9 Ma. This significant age offset demonstrates that Md2 resulted from overprinting by multiple dolomitizing fluid phases. These fluids were mainly formed owing to the temperature difference between the warming stratigraphic water and the cold seawater in the ELIP under the geothermal warming effect. The cold seawater on the slope creates a fluid potential energy difference, generating lateral open circulation and causing thermal convection. Furthermore, Md3 and Cd have negatively skewed δ¹⁸O values, along with higher Th and Eu/Eu∗ values, suggesting that the diagenetic fluids were substantially shallow buried strata water, which resembled Permian seawater. They were mostly produced under the higher geothermal temperatures during the ELIP active period, which generated a substantial fluid potential energy difference, and were driven by a more rapid thermal convection cycle. This study quantitatively constrains the timing of dolomitization using laser U-Pb isotope dating, aiming to give a reliable and valuable reference for the impact of tectonic activities on dolomite genesis caused by the Large Igneous Province.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107555"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633914","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":"Kinetics of thermochemical sulfate reduction based on pyrolysis gold-tube experiments on lacustrine oil: Implications for H2S prediction in Brazilian pre-salt reservoirs","authors":"Igor V.A.F. Souza ,&nbsp;Yongchun Tang ,&nbsp;Le Lu ,&nbsp;Alexandre A. Ferreira ,&nbsp;Geoffrey S. Ellis ,&nbsp;Rut A. Díaz ,&nbsp;Luiz Felipe Carvalho Coutinho ,&nbsp;Ana Luiza S. Albuquerque","doi":"10.1016/j.marpetgeo.2025.107600","DOIUrl":"10.1016/j.marpetgeo.2025.107600","url":null,"abstract":"<div><div>The Pre-salt section in the Santos Basin area is one of the largest oil discoveries in the world during the last 20 years. The reservoir fluid in this area contains non-hydrocarbon gases (CO₂ and H₂S) that can negatively impact the economic prospects of the field. Previous studies have indicated that the main H₂S generation process in Pre-salt reservoirs is thermochemical sulfate reduction (TSR). However, a more comprehensive understanding of these occurrences is required, particularly considering the reservoir temperatures (less than 120 °C) and the variations in δ³⁴S H₂S values. Moreover, there is currently no published research addressing the kinetic behavior of TSR in lacustrine oils. To better understand the origin of these non-hydrocarbon gases, TSR experiments with gold tubes were carried out to obtain information about the fluid changes, kinetic behavior, identification of fluid proxies, and to create a fluid composition model to predict H₂S in exploratory areas. With increasing extent of TSR reaction, the experimentally generated gases show the following patterns: i) Large generation of non-hydrocarbon gases with CO₂ being predominant; ii) The progressive increase in gas dryness (C₁/ΣC_1-5) ultimately reaching 99.9 % by the end of the experiments; iii) The carbon isotopic composition (δ¹³C) trending toward heavier values for C₁-C₃ and CO₂; and iv) The sulfur isotopic composition of H₂S approaches the δ³⁴S of sulfate. Additionally, the TSR process reduced the liquid mass by as much as 50 %, mainly focused on the gasoline range fraction (C₆-C₁₄), indicating the suitability for hydrocarbon oxidation. A large amount of residual hydrocarbons was observed at the end of each experiment, reaching 33 % of the original mass under the most extensive TSR conditions. The parameters for the TSR kinetics were: i) pre-exponential factor (<em>Af</em>) of 4.8x10¹³ s⁻¹, ii) unimodal activation energy (<em>Ea</em>) in 53 kcal/mol, iii) total potential of 767 mg H₂S/g oil. These kinetic parameters were tested in one geological scenario derived from the regional petroleum system model and compared with previous kinetic models from the literature. Two types of TSR reactions (with and without initiators/catalysts) were identified by the model predictions. The model generated with the kinetic parameters proposed by this work predicted a gas composition the closest to that observed in the modeled well. The developed kinetic model can be an important tool for better H₂S prediction in exploratory areas of the Pre-salt Santos Basin.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107600"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145094968","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":"Sedimentary characteristics and fault-controlled depositional models of gravity flows in the Eocene Shahejie formation, Bohai Bay Basin, China: Insights for hydrocarbon exploration in rifted lacustrine basins","authors":"Jie Geng ,&nbsp;Renchao Yang ,&nbsp;Aiping Fan ,&nbsp;Nils Lenhardt ,&nbsp;Liang Dong ,&nbsp;Yang Li","doi":"10.1016/j.marpetgeo.2025.107601","DOIUrl":"10.1016/j.marpetgeo.2025.107601","url":null,"abstract":"<div><div>Sediment gravity flows are critical sediment transport mechanisms in deepwater environments and play a key role in hydrocarbon accumulation. The well-developed sediment gravity flow deposits of the Shahejie Formation are major oil-bearing units in the Dongying Depression (Bohai Bay Basin, eastern China), yet the types of sediment gravity flow deposits and their controlling factors remain debated. This study introduces a novel step-fault-controlled framework in the lower section of the third member of the Eocene Shahejie Formation (ES3L sub-member) that goes beyond traditional models by highlighting the finer-scale structural influences on sediment distribution. The research discusses sedimentary characteristics, lithofacies types, facies distribution, and depositional models based on core samples, well logs, and seismic data from the relay ramp of the Dongying Depression, offering important insights for hydrocarbon exploration strategies. The results indicate that the sediment gravity flows responsible for the deposition in the study area were mainly sandy debris flows, turbidity currents, and hyperpycnal flows. Debrite sandstone deposits are characterised by numerous floating mud clasts, often associated with soft-sediment deformation structures. Turbidite sandstones are characterised by load casts and normal grading. Hyperpycnites are characterised by couplets of inverse grading and normal grading, periodic changes in grain size, and abundant plant debris. The development of sediment gravity flows within the study area was controlled by step faults. As a result, a step-fault-controlled sedimentary model of sediment gravity flow deposition was developed with the following characteristics: 1) Delta front deposition prevailed on the upper step fault, with minor deposition from gravity flows; 2) hybrid deposition of sandy debris flows and turbidity currents took precedence on the middle step fault; and 3) hyperpycnites dominated on the lower step fault. This study investigates the impact of stair-step faults on the sedimentary facies of gravity flows, providing guidance for oil and gas exploration and development in rifted lacustrine basins worldwide.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107601"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145094965","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":"3D reconstruction of pore throat connectivity in Shale: An SAXS-MICP integrated framework","authors":"Linhao Zhang ,&nbsp;Shu Jiang ,&nbsp;Jiale Fu ,&nbsp;Fei Xie ,&nbsp;Zhile Han ,&nbsp;Zihao Li ,&nbsp;Mengdi Sun","doi":"10.1016/j.marpetgeo.2025.107584","DOIUrl":"10.1016/j.marpetgeo.2025.107584","url":null,"abstract":"<div><div>Digital rock technology enables simulation of reservoir dynamic response under coupled multi-physical fields, providing scientific basis for optimization of development schemes through virtual experiments. However, traditional CT technology shows significant limitations in processing low-porosity samples (&lt;5 %), with insufficient ability to accurately identify nano-scale throats, resulting in unrealistic isolated pore networks in reconstruction. Meanwhile, challenges remain in balancing resolution and field of view, as well as experimental cost and efficiency. To address these issues, this study innovatively introduces Small-Angle X-ray Scattering technology, leveraging its advantages of wide testing range, excellent sample representativeness, and ability to characterize closed pores. The research employs fast Gaussian random field method for 3D reconstruction, combines Delaunay triangulation and minimum spanning tree algorithms for network structure optimization, and integrates throat parameters obtained from mercury intrusion capillary pressure data. Finally, a low-porosity porous media model with realistic connectivity characteristics was successfully constructed, laying a solid foundation for detailed reservoir characterization and fluid transport mechanism research.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107584"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144892257","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":"New constraints on the nature and composition of the São Paulo Plateau, Santos Basin: Magmatic, continental or hybrid crust?","authors":"Michelle Cunha Graça ,&nbsp;Nick Kusznir ,&nbsp;Natasha Stanton ,&nbsp;Gianreto Manatschal ,&nbsp;Andres Mora","doi":"10.1016/j.marpetgeo.2025.107612","DOIUrl":"10.1016/j.marpetgeo.2025.107612","url":null,"abstract":"<div><div>The São Paulo Plateau (SPP), located in the Santos segment of the southeastern (SE) Brazilian margin underlying thick Cretaceous to Recent sediments, is an enigmatic feature with disputed crustal composition. Proposed crustal types include thinned continental crust, thick magmatic crust, and hybrid crust consisting of continental crust and magmatic addition. We use combined analysis of mainly geophysical datasets to investigate the crustal basement thickness and crustal type of the SPP, and the variation in timing of its rifting and magmatic addition. 2D and 3D combined analysis of deep seismic reflection and gravity anomaly data has been used to determine Moho depth, crustal thickness and basement density variation. Flexural back-stripping has been used to map sediment-corrected residual depth anomaly (RDA). A combination of observations of crustal thickness from gravity inversion, magnetic anomalies reduced to the pole, basement density from gravity-seismic joint-inversion, and RDA have been used together to distinguish and identify crustal basement types. Using these approaches, we show the distribution and coexistence of continental, hybrid and magmatic crust, as well as possible exhumed mantle in the Santos Basin.</div><div>In addition, 2D and 3D post-breakup subsidence modelling consisting of flexural back-stripping, decompaction and reverse thermal subsidence modelling has been used to determine the palaeo-datum of base and top salt at the time of salt formation. This salt palaeo-datum modelling is used to distinguish syn-tectonic from post-tectonic salt and to investigate the contrasting consequences of magmatic versus thinned continental crust on the palaeo-bathymetry of Aptian salt deposition. We show that the distribution of post-tectonic salt primarily corresponds to that of continental crust thinned by widespread early Aptian rifting while syn-tectonic salt locations correspond to that of magmatic crust extended by late Aptian rifting.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107612"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145219119","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":"Reservoir space types, controlling factors, and evolution models of interbedded shale in the Jurassic Lianggaoshan Formation, Sichuan Basin","authors":"Yan Wu ,&nbsp;Min Wang ,&nbsp;Xuefeng Bai ,&nbsp;Xin Wang ,&nbsp;Yu Sun ,&nbsp;Youzhi Wang ,&nbsp;Xinyi Yang ,&nbsp;Liang Xu ,&nbsp;Tianyi Li","doi":"10.1016/j.marpetgeo.2025.107583","DOIUrl":"10.1016/j.marpetgeo.2025.107583","url":null,"abstract":"<div><div>The type, structure, and origin of shale pores, which serve as both storage spaces for hydrocarbon accumulation and percolation pathways, fundamentally determine reservoir quality and further influence sweet spot identification and production performance in shale oil reservoirs. The heterogeneous interlayers such as siltstone and silty mudstone developed in continental shale have greatly altered the pore structure, fluid storage state and percolation capacity of the reservoir, resulting in significant differences in its reservoir properties compared with shale. This study investigates lacustrine interbedded shale reservoirs through a comprehensive approach incorporating X-ray diffraction (XRD), thin-section petrography, field emission scanning electron microscopy (FE-SEM), low temperature nitrogen adsorption, and nuclear magnetic resonance (NMR) techniques. The results demonstrate that the reservoir properties of different shale lithofacies are generally better than those of fine siltstone lithofacies, especially the organic-rich laminated argillaceous shale (O-rLAS) lithofacies, which has the best reservoir properties. Organic matter (OM) - related pores (particularly organo-clay composite pores) and the interlayer fractures/intercrystalline pores of clay mineral constitute the primary contributors to the reservoir space. Thermal cracking of organic matter and clay mineral transformation enhance the storage capacity of shale lithofacies, whereas cementation is identified as the main factor responsible for the poor reservoir quality of fine siltstone lithofacies. The development of OM-related pores is jointly controlled by thermal maturity, total organic carbon (TOC), and OM type, as well as clay mineral content. The occurrence state of clay minerals with OM and clay mineral type predominantly influence the development of clay mineral interlayer pores. Dissolution pores are mainly affected by TOC and felsic mineral content, while felsic mineral content significantly impacts the development of intergranular pores and microfractures. This study enriches the theoretical understanding of diagenetic and reservoir-forming mechanisms in continental shale reservoirs. It provides critical geological basis and theoretical support for accurately identifying and evaluating the high-quality \"sweet spots\" of continental interbedded shale oil. These findings offer practical guidance for efficient exploration and development of such complex reservoirs.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107583"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144863176","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}