Marine and Petroleum Geology最新文献

{"title":"Maceral-specific evolution of molecular structure and porosity from the early oil to dry gas window in black shales","authors":"Yingzhu Wang ,&nbsp;Jianfa Wu ,&nbsp;Qing Luo ,&nbsp;Jinyou Zhang ,&nbsp;Zhuoheng Chen ,&nbsp;Jijin Yang","doi":"10.1016/j.marpetgeo.2025.107609","DOIUrl":"10.1016/j.marpetgeo.2025.107609","url":null,"abstract":"<div><div>The chemical composition and structural evolution of organic matter (OM) controls pore development in shale reservoirs, but their intrinsic relationship during thermal maturation remains insufficiently understood. This study integrates light microscopy, scanning electron microscopy (SEM), and Raman spectroscopy to investigate microscale variations in petrological features, molecular structures, and pore characteristics across diverse maceral types in the Upper Devonian Duvernay shales, spanning a thermal maturity range of 0.5 %–3.0 % reflectance (<em>R</em>_<em>o</em>) in the West Canada Sedimentary Basin. Results show that alginite and solid bitumen undergo more pronounced compositional transformation with thermal maturation than inertinite and vitrinite, as reflected in broad ranges of Raman spectral parameters. While inertinite consistently displays the highest aromaticity, vitrinite shows a similar aromaticity with pore-filling solid bitumen after <em>R</em>_<em>o</em> &gt;1.0 %. The divergent evolutionary pathways among diverse OM macerals are attributed to the differences in biological origin and hydrocarbon generation kinetics. OM-hosted pores mainly develop in solid bitumen after the late oil window, coincident with a sharp increase in both OM aromaticity and oil expulsion. Moreover, pore-filling solid bitumen shows a higher apparent transformation ratio (15 %–25 %) and larger mean pore size (40–45 nm) than alginite-derived solid bitumen, likely due to chromatographic fractionation. Throughout the gas window, pore-filling solid bitumen accounts for &gt;90 % of the total OM-hosted porosity. Those findings advance our understanding of pore generation and evolution mechanisms across maceral types, and provide a chemical framework for predicting shale reservoir quality over a range of thermal maturities.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107609"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145154765","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 and controls on shale oil enrichment of bedding-parallel fractures in the Chang 73 lacustrine shales, Yanchang Formation, Ordos Basin","authors":"Zilong Li ,&nbsp;Kelai Xi ,&nbsp;Yingchang Cao ,&nbsp;Yifan Zhang ,&nbsp;Xiaobing Niu ,&nbsp;Xiujuan Wang ,&nbsp;Wenzhong Ma ,&nbsp;Yuan You ,&nbsp;Yuxuan Wang ,&nbsp;Guanghui Yuan","doi":"10.1016/j.marpetgeo.2025.107590","DOIUrl":"10.1016/j.marpetgeo.2025.107590","url":null,"abstract":"<div><div>As the main fracture type of lacustrine shales, bedding-parallel fractures (BPFs) play a key controlling role in diagenetic mass transfer as well as hydrocarbon migration and accumulation. To reveal the origin of BPFs and their controls on shale oil enrichment, this study integrates core, thin section, scanning electron microscopy (SEM) observations, and fluid inclusion analysis, focusing on the BPFs of the lacustrine shales of the Chang 7₃ sub-member, Yanchang Formation, Ordos Basin. The results show that the variations in mineral composition, arrangement, and size on both sides of the laminae interface induce significant mechanical anisotropy, which become the essential geological prerequisite for the generation and extension of BPFs along the laminae interface. Furthermore, influenced by the mineral planar fabrics, BPFs can also develop within the laminae. Compared with laminated shale, massive mudstone does not show significant BPFs development characteristics due to the lack of lamina fabric. As a consequence of disequilibrium compaction, the vertical seepage force gradient caused by hydrocarbon generation overpressure periodically breaks through the pressure threshold of the closed shale system, resulting in the episodic opening of weak interfaces, thereby constituting the major formation mechanism of BPFs. In addition, the tectonic compression effect near the basin margin can also promote the development of BPFs to a certain extent. In different lithofacies of shales, the differences in the development characteristics and degree of BPFs are mainly caused by the variations in laminae attributes including laminae combination, linear density, and average thickness. High total organic carbon (TOC) content is conducive to increasing hydrocarbon generation overpressure. However, excessive TOC content reduces the compressive strength of rocks and has an adverse effect on the development of BPFs. The analysis of shale oil production indicates that, compared with non-bedding-parallel fractures (NBPFs), BPFs play a dominant role in the enrichment of shale oil and can significantly increase the daily oil production of individual wells. These findings provide a theoretical basis for revealing the origin, development pattern of BPFs and their influence on fluid activity in lacustrine shales.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107590"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145010435","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":"Unraveling the parameters controlling diagenetic evolution in relatively shallow-buried, syn-tectonic ramp limestones (Upper Cretaceous), United Arab Emirates","authors":"Mohammad Alsuwaidi ,&nbsp;Howri Mansurbeg ,&nbsp;Abdullah H. Awdal ,&nbsp;Salahadin Shahrokhi ,&nbsp;Ali M. Al-Tameemi ,&nbsp;Filippo Casali ,&nbsp;Mohammed Y. Ali ,&nbsp;Luiz Fernando De Ros ,&nbsp;Ibrahim Q. Mohammed ,&nbsp;Hamed Gamaleldien ,&nbsp;Sadoon Morad","doi":"10.1016/j.marpetgeo.2025.107607","DOIUrl":"10.1016/j.marpetgeo.2025.107607","url":null,"abstract":"<div><div>This study utilizes petrographic, geochemical, and fluid-inclusion microthermometric analyses to unravel the controls on the distribution of diagenetic alterations of shallow-buried Upper Cretaceous syn-tectonic, foreland, ramp limestones of the United Arab Emirates. The diagenetic alterations are linked to porewater evolution during the tectonic evolution of the basin, as well as to the depositional facies and sequence stratigraphy. Limited improvement of reservoir quality was promoted by dissolution of allochems and formation of moldic pores. Porosity reductionensued mostly from: (i) cementation by meteoric waters and by hot basinal/hydrothermal brines with wide ranges of δ¹⁸O_V-PDB (−6.3 ‰ to −3.2 ‰) and precipitation temperatures (T_h ≈ 65–125 °C; salinity ≈ 16–22 wt% NaCl eq), and (ii) mechanical compaction of ductile peloids formed by micritization of allochems. Micritization, notably prevalent in the transgressive lagoon and upper ramp slope packstones, as well as in the regressive shoal grainstones below marine-flooding surfaces, led to the development of abundant microporosity. Porosity was preserved in some of the grainstones by partial calcite cementation (rims, as well as scattered equant crystals and syntaxial overgrowths), which supported the framework against mechanical compaction. Dissolution of aragonitic allochems and concomitant cementation by equant calcite was prevalent in regressive shoal grainstones during repeated episodes of subaerial exposure and meteoric-water incursion as a consequence of the syn-tectonic deposition. The δ¹³C_V-PDB (−11.6 ‰ to +13.2 ‰; mostly −2‰ to +2 ‰) suggests derivation from marine porewaters and/or dissolution of the host limestones and, in some cases, from methanogenesis of organic matter and methane oxidation. The lack of systematic differences in porosity and permeability between the limestones from the crest and the flanks of the field is attributed to the accomplishment of most diagenetic alterations before oil emplacement.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107607"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145094867","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":"Inconsistencies in organosulfur compounds during natural and artificial maturation","authors":"Poorna Srinivasan ,&nbsp;Constantin Sandu ,&nbsp;Estefania M. Endara Arguello ,&nbsp;Ibrahim Atwah","doi":"10.1016/j.marpetgeo.2025.107541","DOIUrl":"10.1016/j.marpetgeo.2025.107541","url":null,"abstract":"<div><div>Hydrous pyrolysis techniques are valuable for understanding and quantifying petroleum yield, thermal maturity, compositional variations, and kinetics across different kerogen types. Such data is essential for basin modeling and well planning. Previous studies have shown that sulfur-rich Type II-S kerogen generates hydrocarbons at lower temperatures due to its lower activation energy, resulting in early cracking. Consequently, organosulfur presents a challenge in numerous basins worldwide, as sulfur-rich source rocks from various regions must be examined closely to accurately predict hydrocarbon generation in each basin. Additional factors, such as total organic carbon content and mineralogy, also influence the timing and yield of oil generation. Methyldibenzothiophene isomers have proven to be reliable maturity indicators in sulfur-rich source rocks, often providing more accurate maturity predictions than biomarkers at higher maturity levels. However, few studies have closely examined the compositional and isomeric changes of alkylated methyldibenzothiophene compounds under hydrous pyrolysis conditions. In this study, hydrous pyrolysis experiments were conducted on three sulfur-rich source rocks and one sulfur-rich crude oil at temperatures between 275 and 360 °C to monitor and quantify changes in alkylated MDBT compounds as well as other aromatic hydrocarbons. The results were compared to four naturally matured Type II-S source rocks, spanning the immature to condensate windows, to evaluate the effects of hydrous pyrolysis on aromatic compounds. Significant differences in thermal maturity parameters were observed in the kerogen, bitumen, and expelled oil. While the increase in the 4-MDBT/1-MDBT ('MDR') ratio provided consistent thermal maturity estimates in natural samples, the hydrous pyrolysis experiments revealed that these geochemical markers are inconsistent under artificial thermal conditions, potentially due to additional sulfur species forming in the reactor, buffering reactions in the closed system reactor, the limited temperature range of the experiments, or other matrix-controlled interactions that are found in nature but are not occurring in the reactor. In contrast, aromatic biomarkers such as triaromatic steroids showed a positive increase in their isomer ratios relative to the experimental run temperature. The chemical differences between these organosulfur-rich samples (e.g., TOC, hydrogen index, mineralogy) suggest that the original source material—not solely the sulfur content—plays a critical role in the kinetics of alkylated dibenzothiophene compounds.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107541"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144654697","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":"SynSection: Sedimentology-driven data generation for deep learning applications in carbonates petrography","authors":"Axel Ransinangue ,&nbsp;Richard Labourdette ,&nbsp;Erwann Houzay ,&nbsp;Sebastien Guillon ,&nbsp;Raphael Bourillot ,&nbsp;Emmanuel Dujoncquoy ,&nbsp;Nesrine Chehata","doi":"10.1016/j.marpetgeo.2025.107490","DOIUrl":"10.1016/j.marpetgeo.2025.107490","url":null,"abstract":"<div><div>The analysis of carbonate rocks through petrographic methods has long posed significant challenges in geological sciences, particularly regarding the systematic description and quantification of thin sections. Recent developments in artificial intelligence have suggested promising avenues for automation; however, the field remains constrained by limited training data availability, as manual annotation requires considerable time investment and can result in variable interpretations. This study addresses these challenges by introducing SynSection, a method for generating synthetic pairs of carbonate thin section images with corresponding labels for both classification and segmentation tasks. This approach has been carefully designed to incorporate sedimentological heuristics, ensuring the geological validity of generated samples through the integration of three primary components: 2D grain packing, groundmass generation using texture synthesis, and image blending for image composition. The advantage of this methodology lies in its ability to exponentially expand a limited set of manually labeled images, thereby reducing the resources required for dataset creation while maintaining consistency in annotation. The method was evaluated through the generation of 100,000 synthetic image-annotation pairs, implementing a transfer learning strategy in which models were initially trained on synthetic data before being fine-tuned on real thin section images. This approach demonstrated significant improvements in both classification and segmentation tasks compared to conventional training methods that rely solely on limited real data. In classification tasks, the transfer learning strategy enhanced performance metrics by 7.2%, achieving a top accuracy score of 94.9%. The impact of the method was particularly notable in segmentation tasks, where the binary grain segmentation model achieved an Intersection over Union (IoU) of 77.2% and a point counting determination score of 93.2%. The multiclass segmentation achieved a mean Intersection over Union (mIoU) of 55.3% and a point counting score of 89.6%, reflecting the inherent complexity of grain type differentiation. These results, which are consistent with medical imaging applications, demonstrate the method’s potential to optimize carbonate thin section analysis by reducing time allocated to descriptive tasks. The approach generates diverse training data that maintains geological validity, establishing a quantitative framework for automated petrographic analysis that aligns with standardized classification criteria and expert-defined features.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107490"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144828743","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 dissolution mechanism of calcite and its impact on CO2 sequestration in deep-water sandstone during CO2 flooding: A case study in the Chang 7 member, Ordos Basin, China","authors":"Wei Wang ,&nbsp;Xiaolei Zhang ,&nbsp;ChaoJie Mao ,&nbsp;Zhilei Hao ,&nbsp;Zhengzhong Liang ,&nbsp;Dao Wei Wang ,&nbsp;Yushuang Zhu","doi":"10.1016/j.marpetgeo.2025.107566","DOIUrl":"10.1016/j.marpetgeo.2025.107566","url":null,"abstract":"<div><div>Robust and innovative strategies to reduce carbon emissions to address the growing threat of global climate change. Deep-water tight sandstone, with calcite as its primary cementing material, can be an essential reservoir for CO₂ sequestration. However, the microscopic dissolution mechanism of calcite is still poorly understood and can significantly impact the effectiveness of geological CO₂ storage. We investigated the dissolution behaviours of calcite in deep-water tight sandstone and its volume changes on CO₂ during CO₂ flooding. We used a novel 3D, micrometric-scale reactive-transport model, where the distribution and geometric characteristics of calcite were informed by section casting and cathode luminescence images. We found that the calcite particles adjacent to each other in deep-water tight sandstone form numerous micrometer-scale calcite aggregates. During CO₂ flooding, the dissolution rates of calcite particles vary since solute migration limits the overall dissolution rate. Calcite aggregates react as single particles, with the external surface continuously dissolving and the internal surface maintaining balance. The dissolution products of the calcite aggregates accumulate in the formation water, inhibiting the dissolution of the surrounding calcite and thereby reducing the overall dissolution rate of the deep-water tight sandstone calcite. Large volumes of calcite initially dissolve rapidly, then gradually slow down. This affects the CO₂ sequestration efficiency and migration patterns. These findings provide vital insights into the physical properties and geomechanical integrity during CO₂ storage in deep-water tight sandstone and have long-term storage security and environmental protection implications.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107566"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144704893","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":"Trace and rare earth element signatures in microcrystalline aragonite as indicators of oil vs. methane seepage","authors":"Yuedong Sun ,&nbsp;Shanggui Gong ,&nbsp;Jörn Peckmann ,&nbsp;Fang Chen ,&nbsp;Yao Guan ,&nbsp;Dong Feng","doi":"10.1016/j.marpetgeo.2025.107534","DOIUrl":"10.1016/j.marpetgeo.2025.107534","url":null,"abstract":"<div><div>Oil seeps are important hydrocarbon sources to the ocean and sustain diverse chemosynthesis-based ecosystems. Distinguishing oil- from methane-dominated seeps in the geological record is crucial for reconstructing the evolution of chemosynthetic communities, yet remains challenging. Authigenic carbonates precipitating at seeps offer a valuable archive of the composition of seep fluid. While previous work has focused on fibrous aragonite cement, the geochemical potential of volumetrically dominant microcrystalline analog remains underexplored. Here, we present a comprehensive study of the petrography and stable isotope as well as element composition of oil-derived seep carbonates from the northern Gulf of Mexico (sites GC232, GC185), compared to methane-derived seep carbonates from the northern Gulf of Mexico (site AT340) and the South China Sea (site GMGS2-08). All studied samples are dominated by microcrystalline aragonite. Carbon isotope data (average δ¹³C = −20.9 ± 4.5 ‰; VPDB) and the presence of oil residues agree with crude oil degradation as the main carbon source of the oil-seep carbonate. Compared to methane-seep carbonates, oil-seep carbonates exhibit higher rare earth elements (REE) contents, slight light-REE enrichment, and elevated contents of uranium (U), molybdenum (Mo), zinc (Zn), and cobalt (Co), signatures linked to microbial oil oxidation. These element patterns preserved in microcrystalline aragonite offer a novel proxy for identifying oil seepage in the rock record, particularly in cases where fibrous cement is absent.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107534"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579701","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":"Constraining self-sourcing stratigraphic plays in North Sumatra: Integration of basin-petroleum system and stratigraphic forward modeling","authors":"Qi Adlan ,&nbsp;Barry M. Hartono ,&nbsp;Harya D. Nugraha ,&nbsp;Adhipa Herlambang ,&nbsp;Waleed AlGharbi ,&nbsp;Eriko Sabra","doi":"10.1016/j.marpetgeo.2025.107611","DOIUrl":"10.1016/j.marpetgeo.2025.107611","url":null,"abstract":"<div><div>Stratigraphic traps are typically identified and delineated using 3D seismic analysis or by integrating well data. These plays involve greater exploration uncertainty than conventional traps, especially in regions where multiple petroleum systems coexist. A notable example is the self-sourcing stratigraphic trap, where hydrocarbons migrate laterally within coeval rock formations. This challenge is particularly significant in frontier areas lacking 3D seismic data and with limited well data. Therefore, developing a reliable methodology is essential to accurately identify potential stratigraphic trap zones while effectively accounting for the complex interactions within petroleum systems.</div><div>This study integrates stratigraphic forward modeling (SFM) and basin and petroleum system modeling (BPSM) to better constrain self-sourcing stratigraphic traps. The North Sumatra Basin was selected as the study area because it features a complex petroleum system involving three source rocks and various trapping mechanisms, including stratigraphic traps from the Middle Miocene. The systematic approach demonstrated in this study involves four key stages: (1) assessing geochemical evidence, (2) using SFM to delineate trap zones, (3) simulating organic matter distribution, and (4) applying BPSM to evaluate source rock maturation and hydrocarbon expulsion. This systematic approach provides a cost-effective framework for early-stage hydrocarbon exploration, helping geoscientists de-risk prospects before committing to high-cost data acquisition like 3D seismic surveys. It is particularly suited for evaluating stratigraphic traps associated with self-sourcing plays and has potential applications in unconventional resource exploration, including shale gas. Regionally, this research provides the first geochemical evidence of oil mixing in the area and presents conclusive insights into the four active petroleum system plays, potentially redefining exploration strategies in the region.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107611"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145154192","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":"Revisiting genetic affinities of Tertiary crude oils in the western Qaidam Basin: new insights from sulfurized biomarkers","authors":"Jian Ma ,&nbsp;Chaodong Wu ,&nbsp;Xingqian Cui","doi":"10.1016/j.marpetgeo.2025.107571","DOIUrl":"10.1016/j.marpetgeo.2025.107571","url":null,"abstract":"<div><div>Hydrocarbon biomarkers, diagnostic fossil molecules tied to specific organisms, are essential for classify crude oils and associated paleoenvironments. While previous studies on Tertiary crude oils and source rocks from the western Qaidam Basin emphasized uniform depositional environments, recent discoveries of Eocene marine incursions and H₂S-rich gas reservoirs complicate these interpretations. Organic sulfur compounds (OSCs) in Qaidam Tertiary crude oils, though unexplored, offer new insight into genetic affinities and depositional histories. However, the structural complexity of OSCs posts challenges for direct detection. Catalytic desulfurization, which release sulfurized biomarkers, provides an alternative approach to understanding OSCs and sulfurization mechanisms. Herein, sulfurized biomarkers from crude oils across the western Qaidam Basin were investigated using Raney nickel desulfurization. The new biomarker inventories after desulfurization exhibiting lower thermal maturity than their free hydrocarbon counterparts, indicating early sequestration of organic molecules via natural sulfurization. The exceptional abundance of desulfurized C₃₇ and C₃₈ alkanes likely originates from previously sulfurized C₃₇ and C₃₈ long-chain alkenones. Higher abundances of sulfurized homohopanes, gammacerane and carotenoids in the Qigequan and Gasikule Oilfields highlight distinctive anoxic and stratified environments in the westernmost Qaidam Basin. In contrast, anomalously over-matured signatures in the Yingzhong Oilfield reveal unusual thermal evolution. Overall, sulfurized biomarkers confirm compositional heterogeneities and genetic affinities among oilfields, providing primitive information that enhances oil-source rock correlations and paleoenvironment reconstruction. This study underscores the need to evaluate both free and sulfurized lipids to fully understand petroleum systems.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107571"},"PeriodicalIF":3.6,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144770843","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":"Pyrite morphologies in Bazhenov Formation source rocks: diversity, systematic classification, sulfur isotopic composition and insights into sedimentation and diagenesis processes","authors":"Alina Karamova,&nbsp;Tagir Karamov,&nbsp;Mikhail Spasennykh","doi":"10.1016/j.marpetgeo.2025.107535","DOIUrl":"10.1016/j.marpetgeo.2025.107535","url":null,"abstract":"<div><div>Pyrite is a common authigenic mineral in organic-rich source rocks, which is diverse in morphology and carries valuable genetic information about geological processes. This study proposes comprehensive genetic morphological classification of pyrite aggregates in organic-rich shales of the Bazhenov Formation – one of the world largest source rock located in the Western Siberia. Scanning electron microscopy was used to analyze over 530 samples from 17 wells, identifying various types of pyrite such as framboids (with corresponding subtypes based on orderliness of the internal structure, crystallographic shape of microcrystals, infilling of internal structure, and integrity), euhedral crystals, and pyrite pseudomorphosis. The obtained sulfur isotopic composition for framboidal pyrite, which turned out to be the lightest (δ³⁴S vary in the range from −55.38 ‰ to −26.02 ‰), is indicative of anoxic conditions on seafloor. Euhedral pyrite develops in diagenesis under limited sulfate supply, reflecting slow growth in pore-water depleted in ³²S (δ³⁴S values range from +15.05 ‰ to +26.49 ‰). Described morphological types cover the diversity of pyrite forms in other similar geological objects around the world, which allows pyrite to be used as a geochemical proxy for paleoenvironmental reconstructions and hydrocarbon exploration, enhancing understanding of sulfur cycle and basin evolution.</div></div>","PeriodicalId":18189,"journal":{"name":"Marine and Petroleum Geology","volume":"182 ","pages":"Article 107535"},"PeriodicalIF":3.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144588495","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}