International Journal of Coal Geology最新文献

{"title":"The modes of occurrence, distribution and enrichment of critical raw materials (Ga, Sr, Zr and Ba) within coal discards of the Witbank Coalfield, South Africa","authors":"X. Nkwamza,&nbsp;N. Malumbazo","doi":"10.1016/j.coal.2025.104870","DOIUrl":"10.1016/j.coal.2025.104870","url":null,"abstract":"<div><div>Coal mineralogy and trace element composition provide vital insights into the geological coal formation processes, depositional environments, and potential resource valorization. However, there is limited knowledge and understanding of the geochemical and mineralogical composition of coal discards from the Witbank Coalfield. Thus, the coal discards remain underexplored, limiting effective management and future utilization strategies. To address this gap, this study investigates the occurrence, distribution and enrichment of CRMs within Permian coal discards of the Witbank Coalfield. An integrated suite of analytical techniques such as TGA, Bomb calorimeter, FTIR, XRD, TIMA, SEM-EDS, XRF and ICP-MS was utilized to determine the dominant mineral assemblages and trace elemental enrichments. Results revealed quartz and kaolinite as the principal minerals, with subordinate carbonate and sulfide phases introduced through diagenetic and hydrothermal processes. The coal discards were enriched in trace elements such as Ga, Sr, Zr and Ba. Ga was associated with kaolinite and organic matter, Sr and Ba predominantly occurred in barite, and Zr was hosted primarily in detrital zircon grains. Their spatial variability reflects depositional and diagenetic controls. Geochemical proxies, such as Sr/Ba and TiO₂/Al₂O₃ ratios, indicate freshwater depositional conditions influenced by volcanic ash input and post-depositional alteration. These findings enhanced the understanding of the geochemical cycling within coal discards, their mineralogical stability, and potential environmental implications. Furthermore, the presence of acid-neutralizing minerals supports the potential use of these coal discards in mitigating acid mine drainage, while the enriched CRMs highlight opportunities for sustainable resource recovery.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104870"},"PeriodicalIF":5.7,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144989494","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of temperature on coal maceral dissolution and matrix alteration during NaClO stimulation: Insights from microscopy and Micro-CT","authors":"Sen Yang ,&nbsp;Zhentao Li ,&nbsp;Joan Esterle ,&nbsp;Karen M. Steel","doi":"10.1016/j.coal.2025.104868","DOIUrl":"10.1016/j.coal.2025.104868","url":null,"abstract":"<div><div>Oxidant stimulation has emerged as a promising supplementary approach to enhance gas recovery from coal seams, targeting coal organic matter more directly than acid stimulation, which affects mineral components. However, the reactivity of different coal maceral subtypes to oxidants, particularly under reservoir conditions, remains poorly understood. In this study, sodium hypochlorite (NaClO) was used to investigate the maceral-specific reactivity and matrix alteration of bituminous coal samples from the Bowen Basin, Australia, under varying temperature conditions. Microscopic and Micro-CT analyses revealed that higher temperatures significantly enhanced maceral dissolution. The observed reactivity followed the order: semifusinite &gt; vitrinite &gt; fusinite, with collodetrinite within vitrinite displaying notably higher reactivity than collotelinite. These divergences should be ascribed to the differences in aromaticity, functional group composition, and pore structure. Micro-CT results revealed maceral-dependent dissolution depths, ranging from 300 to 500 μm for semifusinite, ∼100 μm for fusinite, and 50–150 μm for vitrinite bands. As a fine-grained heterogeneous host to telovitrinite macerals and other detrital components, coal matrix exhibited strong alteration in directional dependence, with significantly enhanced pore and fracture development along the horizontal (bedding plane) direction. At 60 °C, the reaction depth reached up to 850 μm, accompanied by substantial pore enlargement, particularly within the 30–50 μm range. Mixed maceral zones showed deeper reaction fronts than vitrinite-rich areas, emphasizing the influence of maceral heterogeneity on oxidant penetration. This study highlights that both maceral composition and bedding structure critically govern the extent, directionality, and effectiveness of oxidant-induced matrix alteration. These findings provide important insights into optimizing oxidant stimulation strategies for improved gas recovery in heterogeneous coal reservoirs.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104868"},"PeriodicalIF":5.7,"publicationDate":"2025-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144895538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineralogy and elemental geochemistry of Pennsylvanian high-sulfur coals in the Huanghebei Coalfield, Shandong, Northern China: Implications for the enrichment and controlling factors of U","authors":"Bofei Zhang ,&nbsp;Wenfeng Wang ,&nbsp;Qingfeng Lu ,&nbsp;Wenlong Wang ,&nbsp;Xiaozhen Teng ,&nbsp;Long Chen","doi":"10.1016/j.coal.2025.104867","DOIUrl":"10.1016/j.coal.2025.104867","url":null,"abstract":"<div><div>Uranium enrichment in coal is of great significance for understanding metallogenic processes and assessing resource potential. Numerous studies have investigated the geochemical behavior and modes of occurrence of U in super-high-organic‑sulfur coals from Southern China. However, the Huanghebei Coalfield in Shandong, a major high‑sulfur coal-bearing region in North China, yet remains largely unidentified. This study investigates the U enrichment and controlling factors of the Pennsylvanian No.11 coal from Huanghebei Coalfield, Shandong, Northern China. Uranium is enriched in the No. 11 coal (up to 89.3 μg/g), where U, Mo, and V are exclusively concentrated in the topmost coal bench underlying the limestone roof. The enrichment of critical elements, including U, Mo, and V, is attributed to infiltration of marine water from the overlying strata during the early diagenetic stage. Uranium in the coal shows both organic and inorganic associations. Notably, a small portion of U occurs in uraninite, which is more easily reduced and precipitated under anoxic conditions. The relationships of Al₂O₃ vs. TiO₂, Al₂O₃/TiO₂-Nb/Yb and the REY distribution patterns indicate that the sediment-source rocks of the No. 11 coal were the North Qinling Orogenic Belt. The predominant minerals identified in the No. 11 coal are NH₄-illite, calcite, quartz, pyrite, bassanite and kaolinite, with minor amounts of dolomite and siderite. The modes of occurrence of NH₄-illite, kaolinite, calcite, pyrite, and quartz, as well as fluorapatite, indicate that the No. 11 coal was likely influenced by multi-stage injection of hydrothermal fluids. Authigenic NH₄-illite is relatively high abundant, probably formed by the interaction of kaolinite with nitrogen released from organic matter during metamorphism induced by igneous intrusion. The δ¹³C_VPDB and δ¹⁸O_VPDB values of epigenetic carbonates in the coals indicate that the carbon and oxygen in the carbonates are primarily derived from hydrothermal fluid activities. The No. 11 coal has potential for resource development and utilization as raw material for U and deserves further attention.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104867"},"PeriodicalIF":5.7,"publicationDate":"2025-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144903083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Implications of element enrichment in paralic coals from the Carboniferous in England","authors":"D.A. Spears","doi":"10.1016/j.coal.2025.104865","DOIUrl":"10.1016/j.coal.2025.104865","url":null,"abstract":"<div><div>The enrichment of trace elements in coals is of significant economic importance because of the growing demand for the critical elements. Several enrichment processes have been identified and in this paper the role of palaeosalinity is evaluated using published data from the East Pennine Coalfield (UK). The coal and associated mudrocks for which comprehensive ICP- AES and ICP-MS analyses are available is the Parkgate Coal. This is a high volatile bituminous coal of Upper Carboniferous (Pennsylvanian) age with a variable S content mainly due to pyritic S (Total S = 2.34 ± 1.83 %, Pyritic S = 1.17 ± 1.79 %).</div><div>Supporting information on the mineralogy of this and other major coals comes from XRD analyses. Although there is an extensive geochemical data base on coals and mudrocks from this Coalfield, most of the analyses were made using XRF with a restricted suite of trace elements (13). Comprehensive analyses of marine shales are not available for this coalfield and to evaluate the marine influence use is made of analyses of samples from the Netherlands. These samples are of comparable age and from the same extensive depositional area. Enrichment values calculated for the Parkgate Coal based on detrital trace elements in the mudrocks show that the chalcophile elements are enriched and pyrite is the major host for many of them. Other elements are enriched including Ge and Be and there is an organic association, possibly reflecting an original plant origin. The importance of a seawater control is demonstrated by close similarities in the enrichment values between the coals and marine shales. Use could be made of the enrichment values determined in this work to identify a seawater influence in coals elsewhere. Elements not enriched, and for which other controls operated, are Ga, Li, Zr and Nb. Although not confirmed for the UK coals the REE are probably in the same category. Alternatives to the control of seawater on the element enrichments in the studied coals are considered and rejected as having little or no effect.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104865"},"PeriodicalIF":5.7,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144895537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Degradation of organic matter by radioactive radiation in black shales: An overlooked modification of organic molecular structures","authors":"Leibo Bian ,&nbsp;Zhe Zhao ,&nbsp;Xiaomei Wang ,&nbsp;Hamed Sanei ,&nbsp;Anthony Chappaz ,&nbsp;Jin Dong ,&nbsp;Zhongtian Dong ,&nbsp;Linfeng Xie ,&nbsp;Niels H. Schovsbo ,&nbsp;Fariborz Goodarzi ,&nbsp;Shuichang Zhang ,&nbsp;Wenzhi Zhao","doi":"10.1016/j.coal.2025.104864","DOIUrl":"10.1016/j.coal.2025.104864","url":null,"abstract":"<div><div>Natural radioactive radiation emitted by uranium (U) in sedimentary basins continuously transforms organic matter and thus its degrading impact overprints the burial-related thermal maturation process. However, the systematic pathway for irradiated alteration of sedimentary organic matter and its influence remain poorly understood. This omission hinders a comprehensive understanding of organic matter evolution after burial. Our study investigated the artificially and naturally irradiated alteration of organic matter in the U- and organic-rich Cambro-Ordovician Alum Shale of Northern Europe and Triassic Chang 7–3 shale in the Ordos Basin of China. After exposure of samples to a Co-60 source, radiation accelerated the conversion of bitumen to natural gas with a lower gas dryness (C₁/C_1–5 &lt; 0.8), while kerogen is converted to natural gas with a higher gas dryness (&gt;0.8). Moreover, enhanced radiation dose facilitates the transformation from resins and asphaltenes to aromatics and leads to enrichments of carbon-13 isotope, when the radiation dose reaches the thresholds of approximately 100 and 2000 kGy, respectively. Natural radiation exposure in the Chang 7–3 shales, identified by spatial distribution and affiliated phases of U, may have influenced bitumen structures through accelerating transformation of macro- to micro-organic compounds and generation of wet gas that could have enhanced hydrocarbon mobility. Moreover, an addition to the standard model for organic matter burial and transformation is proposed with integration of natural radiation exposure. Based on the calculated Proterozoic-Phanerozoic radiation dose in sedimentary rocks, we hypothesize that the radioactive processes might have consistently modified the characteristics of retained bitumen in uranium-enriched shales, thereby affecting carbon cycle on Earth's surface environments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104864"},"PeriodicalIF":5.7,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144867138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics of different types of soluble organic matter in low- to middle-rank coals: Implications for tar generation and migration during tar-rich coal pyrolysis","authors":"Ruihui Zheng ,&nbsp;Yuan Bao ,&nbsp;Jiajun Li ,&nbsp;Jiao Xue ,&nbsp;Xuan Yuan ,&nbsp;Kuan Liu","doi":"10.1016/j.coal.2025.104863","DOIUrl":"10.1016/j.coal.2025.104863","url":null,"abstract":"<div><div>Soluble organic matter (SOM) in low- to middle-rank coal can be categorized into free (FSOM), mineral-associated (MSOM) and chemical-associated (CSOM) states. However, the characteristics of these different types of SOM remain poorly understood in tar-rich coal research, primarily due to the long-standing perception of coal as a conventional gas source rock. This paper investigates the geochemical characteristics of different types of SOM and the molecular structure characteristics of their residues after successive treatments, discusses the influence of organic matter maturity and tar yield on these characteristics, and clarifies the generation and migration mechanisms of pyrolysis tar. Nine low- to middle-rank coals with different maturity and tar yield collected from the Ordos Basin underwent successive treatments to obtained FSOM, MSOM and CSOM. Comparison of organic characteristics reveals: (1) SOM content follows the order of FSOM&gt; CSOM&gt; MSOM. The FSOM and MSOM are primarily composed of aromatics, while asphaltenes are the main components of the CSOM. (2) SOM polarity follows the order of CSOM&gt; MSOM&gt; FSOM, the polarity of FSOM and MSOM is influenced by both organic matter maturity and tar yield, while the polarity of CSOM is primarily affected by matter origin. (3) SOM maturity shows the order of CSOM&gt; MSOM&gt; FSOM, the geochemical characteristics of SOM are influenced by both organic matter maturity and tar yield. Comparison of molecular structure characteristics reveals: (1) Oxygen functional group content gradually increases across all SOM fractions, while aliphatic functional group content gradually decreases across all SOM fractions. (2) Molecular structure is influenced by both organic matter maturity and tar yield. Comprehensive comparison of the organic geochemistry and molecular structure characteristics reveals: (1) Group composition of CSOM is significantly affected by aromatic and hydroxyl functional groups. (2) FSOM and MSOM primarily contribute to the free hydrocarbons during tar-rich coal pyrolysis. (3) Migration pathway of pyrolysis tar follows the order of silicate minerals, carbonate minerals, pores and expulsion. These differences provide new insights into the understanding of pyrolysis tar generation and migration mechanisms.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104863"},"PeriodicalIF":5.7,"publicationDate":"2025-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144867137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Understanding coalbed gas distribution from longwall mining: Geochemical and isotopic approach","authors":"Yaroslav Bezyk ,&nbsp;Dawid Szurgacz ,&nbsp;Dariusz Strąpoć ,&nbsp;Magdalena Misz-Kennan ,&nbsp;Monika J. Fabiańska ,&nbsp;Ewa Szram ,&nbsp;Łukasz Kruszewski ,&nbsp;Miroslaw Zimnoch ,&nbsp;Jarosław Nęcki ,&nbsp;Izabela Sówka ,&nbsp;Tomasz Kowalski ,&nbsp;Carina van der Veen ,&nbsp;Thomas Röckmann ,&nbsp;Maciej Górka","doi":"10.1016/j.coal.2025.104859","DOIUrl":"10.1016/j.coal.2025.104859","url":null,"abstract":"<div><div>Coalbed methane plays a critical role in both energy resource potential and environmental and mine safety strategies. Despite much research has been done on coalbed gas origin, the combined effects of coal maturity, gas migration processes, and mine ventilation in an active mining environment are still not fully understood. This study combined molecular and stable carbon and hydrogen isotope analyses of coalbed gases collected along the longwall coal face during the early and final stages of operation, with petrographic and geochemical characteristics of freshly mined coal from the Upper Silesian Coal Basin, Poland. Complementary organic petrography and biomarker analysis performed on freshly mined coal revealed that the vitrinite-rich bituminous coal is at peak oil-window maturity. Gas composition from a borehole in the coal seam indicated methane as the dominant component (up to 87 %), with contributions from carbon dioxide (up to 2.3 %) and lower amounts (0.1–1.5 %) of heavier hydrocarbons (C₂ − C₆). Heterocyclic species of sulfur (thiophene) and nitrogen (pyridine), chlorinated (1,2-DCE) compounds, oxygen-bearing organic gases (acetic acid), dimethyl sulfide (DMS), and some portion of ortho-cresol, tetrahydrofuran, formaldehyde, and cumene tracers were also found in the complex gas mixtures from the borehole.</div><div>Isotopic data of methane in the examined longwall coal face averaged at −48.1 ± 0.7 ‰ for δ¹³C and − 192.1 ± 7.1 ‰ for δ²H and coal maturity vitrinite reflectance at 0.75 ± 0.02 %. These molecular and isotopic coalbed gas data implied a thermogenic origin of the coalbed methane, with fingerprints of biodegradation in thermogenic system. Slightly depleted isotope values from the borehole under examination (δ¹³C: −50.9 ± 0.2 ‰ and δ²H: −194.2 ± 2.8 ‰) suggested the presence of free gas stored in the coal fractures. Spatial variations in gas composition and isotopic shifts across the longwall panel were found to be driven by ventilating airflow supplied to the working face. Isotope alteration along airflow path from main- to tailgate entries emphasized the influence of secondary processes, such as desorption and diffusion. Preferential loss of isotopically light ¹²CH₄ molecules, especially at gas accumulation zones (tailgate), aligns with findings from laboratory desorption experiment on successively crushed coal samples. In contrast, less systematic δ²H-CH₄ patterns under active mining reflected the combined effects of gas mixing, site-specific conditions, and parameters of coal mine operations.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104859"},"PeriodicalIF":5.7,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144780412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CBM enrichment mechanisms in the Southern Qinshui Basin: A synergistic role of tectonic-lithological-hydrodynamic coupling","authors":"Xiaoxiao Sun ,&nbsp;Hui Wang ,&nbsp;Fengfeng Du ,&nbsp;Yanbin Yao ,&nbsp;Dameng Liu ,&nbsp;Zhong Liu","doi":"10.1016/j.coal.2025.104861","DOIUrl":"10.1016/j.coal.2025.104861","url":null,"abstract":"<div><div>The Qinshui Basin is renowned for its thick, laterally extensive coal seams, high thermal maturity, and significant coalbed methane (CBM) potential. However, reservoir heterogeneity resulting from multi-stage tectonic activity leads to pronounced variability in CBM enrichment, posing challenges for efficient development. This study examines the influence of individual and coupled tectonic, roof–floor lithological, and hydrodynamic factors on CBM accumulation in the southern Qinshui Basin, using seismic data, well logs, and gas content analysis. Four distinct CBM enrichment models are identified from north to south: in shallow seams, atmospheric precipitation-driven groundwater recharge, coupled with anticlinal structures, controls the spatial distribution of gas; with increasing burial depth, reduced groundwater mobility and improved roof–floor sealing shift the dominant control from hydrodynamic to lithological factors; in structural slope zones, gas enrichment is governed by the coupling of nose structure and hydrodynamic sealing; In fault-dominated areas, gas migration along faults and the sealing capacity of fault zones are the primary controls. These findings provide a scientific basis for optimizing CBM exploration and development in geologically complex basins.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104861"},"PeriodicalIF":5.7,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144766729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics of pre- and syn-rift sequences in the central Gulf of Suez: Implications for hydrocarbon generation and paleoenvironment","authors":"Moataz El-Shafeiy ,&nbsp;Thomas Gentzis ,&nbsp;Ismail A. Hussein ,&nbsp;Dina Hamdy","doi":"10.1016/j.coal.2025.104850","DOIUrl":"10.1016/j.coal.2025.104850","url":null,"abstract":"<div><div>The October sub-basin is one of the largest oil fields in Egypt, situated within the central Gulf of Suez petroleum province. Four wells were studied to investigate the petroleum system using integrated geochemical and petrographic techniques. This gives valuable information on the source rock potentialities, which may help in new hydrocarbon discoveries in the October sub-basin. Organic-rich pre-rift (Late Cretaceous-Eocene) and syn-rift (early-middle Miocene) sequences were analyzed for TOC, Rock-Eval pyrolysis, vitrinite reflectance (R_o%), and lipid biomarkers. 1D basin models were built to assess hydrocarbon generation timing and remaining potential. This analysis provides valuable insights into source rocks characteristics, including quantity, quality, thermal maturity, and paleoenvironmental implications. Pre-rift strata show fair-very good organic richness, while syn-rift strata demonstrate poor-good organic richness. Pyrolysis shows that the NW wells predominantly contain Type III dispersed organic matter and organic petrography shows the presence of vitrinite in the form of collotelinite and collodetrinite) in both sequences. The same analysis also shows that the SE wells contain Type II-III and II kerogen while organic petrography shows the presence of dispersed liptinitic organic matter (e.g., telalginite, lamalginite, sporinite, liptodetrinite) and also low inertinite content. This indicates a greater marine organic matter input, which is also supported by biomarker data, with the latter suggesting low-oxygen conditions in the SE parts of the sub-basin. Pre-rift source rocks range from immature to the upper oil/wet gas window (R_o% of 0.50–1.35 % in the NW wells, 0.41–0.82 % in the SE wells), but mostly within the oil window. The NW wells show higher thermal maturity, particularly in well NO124–1, likely due to elevated geothermal gradients from rift-related Oligocene-Miocene igneous activity. As expected, syn-rift strata are immature or in the early oil window (R_o % 0.37–0.61 % in the NW, 0.36–0.61 % in the SE). Thermal maturity modeling indicates that pre-rift strata are effective source rocks entered the early oil window ∼20–15 Ma, earlier onset in the NW wells. Present-day pre-rift transformation ratios are higher in the NW (60–88 %) than in the SE (17–35 %) wells, suggesting greater remaining hydrocarbon generation potential in the SE region.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104850"},"PeriodicalIF":5.7,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144757945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentology and geochemistry of the Upper Permian Longtan and Dalong formations in the Lianyuan Sag, Xiangzhong Depression, South China: Implications for paleoclimate, provenance, tectonic setting, and organic matter accumulation","authors":"Zhongrui Wu ,&nbsp;Ralf Littke ,&nbsp;Shuo Qin ,&nbsp;Yahao Huang ,&nbsp;Sheng He ,&nbsp;Yaohui Xu ,&nbsp;Yan Liu ,&nbsp;Xiao Chen ,&nbsp;Kaiming Wang","doi":"10.1016/j.coal.2025.104849","DOIUrl":"10.1016/j.coal.2025.104849","url":null,"abstract":"<div><div>The organic-rich shales in the Upper Permian Longtan Formation (LF) and Dalong Formation (DF) are important hydrocarbon source rocks and have become key targets for shale gas exploration in the Yangtze area, South China. To investigate the provenance, tectonic setting, paleoenvironmental conditions, and mechanisms of organic matter (OM) accumulation, this study presents an integrated petrological and geochemical study of a continuously cored well in the Xiangzhong Depression, South China. The LF was deposited in marine–continental transitional facies under a hot and humid climate with intense chemical weathering. OM is predominantly terrigenous-derived, consisting mainly of vitrinite and inertinite. Multiple geochemical proxies, together with pyrite framboid analyses, suggest that oxic, brackish water conditions, low paleoproductivity, and a high influx of terrestrial material prevailed during the deposition of the LF. In contrast, the DF comprises fully marine sediments, reflecting a depositional setting influenced by a rapid sea-level rise and progressive climatic aridification. These changes resulted in a saline, anoxic water column with enhanced primary productivity and reduced weathering intensity. The relationships between total organic carbon (TOC) content and geochemical indicators suggest that paleoclimate and terrigenous influx are the dominant factors controlling the OM accumulation in the LF, whereas upwelling-induced high productivity was the dominant factor driving OM enrichment in the DF. This study provides a comprehensive dataset on the LF and DF, which exhibit markedly different depositional environments, and aims to address the gap in the evaluation of Permian shale gas potential in the Middle Yangtze region.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104849"},"PeriodicalIF":5.7,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}