International Journal of Coal Geology最新文献

{"title":"Raman spectroscopy of electrostatically isolated organic matter for thermal maturity assessment: A case study on the Mowry Shale","authors":"Tarek Ismail,&nbsp;Soheil Saraji","doi":"10.1016/j.coal.2025.104910","DOIUrl":"10.1016/j.coal.2025.104910","url":null,"abstract":"<div><div>Organic Matter (OM) thermal maturity plays a critical role in hydrocarbon generation within unconventional systems, controlling the transformation of kerogen to oil, and from oil to gas/condensate, thereby defining the fluid type in place. Reliable maturity evaluation underpins resource assessment, sweet-spot mapping, landing-zone selection, and calibration across geochemical, petrographic, and spectroscopic proxies. This study evaluates the thermal maturity of the Mowry Shale in the Powder River Basin using pyrolysis, vitrinite reflectance, and Raman spectroscopy, with emphasis on the impact of sample preparation. Three sample preparation approaches (powdered rock, polished kerogen concentrates, and electrostatically isolated organic-matter) were tested and compared. The novel electrostatic isolation technique separates organic matter from the surrounding mineral matrix, effectively exposing and concentrating it for analysis and substantially improving Raman spectral quality by reducing background noise and mineral interference. Raman parameters derived from electrostatically isolated OM showed a strong correlation between Raman Band Separation (RBS) and VRo-equivalent (R² = 0.85). This approach facilitates rapid and reliable OM identification with reduced preparation compared to conventional methods; however, its broader applicability to other formations needs further investigation. Furthermore, organic petrography provided a formation-specific calibration between Vitrinite Reflectance (VRo) and thermal maturity (Tmax), which enabled extension of VRo equivalency across the full dataset (39 samples) despite direct VRo measurements being available for only 16 samples.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"312 ","pages":"Article 104910"},"PeriodicalIF":5.7,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145531595","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":"Evaluation of lanthanides and yttrium in Chinese coal: Content, distribution, and recovery priority","authors":"Yunfei Li ,&nbsp;Chuncai Zhou ,&nbsp;Chen Li ,&nbsp;Feng Wang ,&nbsp;Shuheng Hu ,&nbsp;Wentao Wu ,&nbsp;Guijian Liu","doi":"10.1016/j.coal.2025.104901","DOIUrl":"10.1016/j.coal.2025.104901","url":null,"abstract":"<div><div>The rapid expansion of the new energy industry has resulted in a significant shift in the demand structure for specific lanthanides and yttrium (REY) and an overall increase in demand, thereby accelerating the depletion of conventional sources and driving the exploration of unconventional sources such as coal-based resources. This study established a comprehensive database of REY in Chinese coal, calculated the average REY content across the nation and various provinces using recoverable reserves, and classified recovery priorities accordingly. The results indicate that the average REY content in Chinese coal is 127.8 ppm, with significant regional variations: the highest contents are found in Shanxi, Qinghai, and the southwestern provinces. Coal-forming ages also influence REY resources potential, with late Carboniferous-early Permian (C₂-P₁) exhibiting the highest levels, followed by a gradual decline over ages until a minor rebound in the Paleogene to Neogene (E-N). Additionally, REY in coal exhibits both inorganic and organic affinities, with phosphorus-containing substances having the most substantial impact. Given the high potential for REY recovery and the considerable content of high supply risk rare earth elements (Pr, Nd, Gd, Tb, Dy, and Y in this work) in Guangxi and Chongqing, these regions are categorized as extremely high-priority areas.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"312 ","pages":"Article 104901"},"PeriodicalIF":5.7,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145491993","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":"Enrichment characteristics, volatilization properties, speciation transformation, and environmental implications of trace elements during coal combustion from Huaibei Coalfield, Anhui, China","authors":"Mengfei Lu,&nbsp;Ruijia Liu,&nbsp;Minglian Shen,&nbsp;Guijian Liu,&nbsp;Hao Hu,&nbsp;Zongfan Xie,&nbsp;Zhen Yue","doi":"10.1016/j.coal.2025.104911","DOIUrl":"10.1016/j.coal.2025.104911","url":null,"abstract":"<div><div>The behavior of trace elements (TEs) during coal combustion is highly temperature-dependent, presenting a dual challenge of environmental risk and resource potential. However, the strategic utilization and effective pollution control of coal ash are hindered by insufficient understanding of how combustion temperature differentially governs the fate of critical and harmful elements. Combining combustion experiments with thermodynamic simulations, this study systematically investigated the impact of temperature (400–1100 °C) on the enrichment, volatilization, and speciation transformation of selected critical (Li, V, Ga, Ge, Zr, and Mo) and harmful elements (Cr, Ni, Cu, Zn, Cd, and Pb) in Huaibei coal, and evaluated their distinct environmental implications. The results show that the elements Li, Ga, Zr and Pb are all slightly enriched or enriched in five coal samples, and their contents in coal ashes are on average more than twice those in raw coals, and up to more than four times. The decomposition of organic matter is completed at 500/600 °C, and kaolinite-quartz-muscovite in the raw coal transform into mullite-quartz in coal ash. Trace elements are mainly stabilized as sulfate (Li, V, Cr, Ni, Cu, Zn, Cd, and Pb) at low temperatures, and partially volatilized as gaseous hydroxides (Li, Ga, Mo, Cr, Ni, Cu, Zn, and Cd) with increasing temperatures, or exist as metal oxides in coal ash (Li, V, Ga, Ge, Zr, Cr, Cu, Zn, and Pb). Principal component analysis (PCA) reveals differential responses of TEs to progressive temperature increases. The generally lower volatility of critical elements compared to harmful elements in coal ash leads to their higher retention, highlighting their potential for resource recovery and the consequent positive environmental benefits. However, the presence of harmful elements in ash also causes tangible negative environmental effects, primarily manifested as increased potential ecological risks with increasing temperatures. Cadmium is identified as the dominant risk contributor capable of reaching high risk levels at elevated temperatures. This study provides scientific basis for the harmless utilization of coal ash resources through temperature regulation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"312 ","pages":"Article 104911"},"PeriodicalIF":5.7,"publicationDate":"2025-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145560220","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":"The environmental legacy of industrial coal combustion: tracing inorganic and organic contaminants in soils","authors":"Joana Ribeiro ,&nbsp;Mónica Ribeiro ,&nbsp;Laura Góis ,&nbsp;José Erbolato Filho ,&nbsp;Magdalena Misz-Kennan ,&nbsp;Monika Fabiańska","doi":"10.1016/j.coal.2025.104896","DOIUrl":"10.1016/j.coal.2025.104896","url":null,"abstract":"<div><div>As the world deal with the global climate and energy crises and energy transition, studies related to coal are still needed because, despite de phasing out of coal, the recognition of the environmental legacy left by fossil fuels is important to identify the influence of its use in the carbon cycle and to meet the main commitments of the European Green Deal. This study aims to identify the fingerprint in soil left by the past activity of Sines thermal power plant (S-TPP, Portugal), which lasted for decades. The multi-analytical approach (petrographic and geochemical techniques) used in the analysis of soil collected in the area surrounding the S-TPP allowed identification and quantification of inorganic and organic contaminants, their source, and allow the understanding of changes in the physic-chemical characteristics of soil induced by the contamination. The results reveal differentiated spatial distribution of changes and contaminants in soils, which are more intense in the south area, attributed to incorporation of contaminants through mobilization and dispersion influenced by predominant winds regime of the region. The incorporation of particles of coal and fly ash in soil enhances the concentration of some potentially toxic elements (As, Ba, Co, Cr, Ni, Se, U, V) beyond national reference values for healthy soil. The contaminants in soil also influence soil granulometric composition, alkalinity, electrical conductivity, total organic carbon and total sulphur. The sources of contaminants in soil are the fly ash and gaseous emission from smoke stacks and coal and fly ash particles mobilized during storage, handling and landfilling operations.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"311 ","pages":"Article 104896"},"PeriodicalIF":5.7,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383525","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":"Constraining rutile provenance in Nb-rich coal-bearing strata: An approach integrating trace element geochemistry and machine learning","authors":"Huidi Hao ,&nbsp;Bo Jiu ,&nbsp;Wenhui Huang ,&nbsp;Zhaoguo Wang ,&nbsp;Binchao Qin ,&nbsp;Linghao Huang","doi":"10.1016/j.coal.2025.104898","DOIUrl":"10.1016/j.coal.2025.104898","url":null,"abstract":"<div><div>Titanium oxides (predominantly rutile) constitute critical reservoirs of niobium within coal-bearing strata, yet their provenance discrimination remains methodologically challenging. This study establishes a robust rutile provenance discrimination framework for Nb-rich sequences (coal, tonstein, mudstone) in the Ordos Basin through integrated machine learning and rutile trace element geochemistry. Comprehensive analyses via laser Raman spectroscopy (LRS), electron probe microanalysis (EPMA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) demonstrate that: LRS identifies rutile as the dominant Ti-phase with minor anatase; trace element mapping reveals V-Nb-Zr-Cr enrichment in coal-hosted rutile versus Si-V-Fe-Nb enrichment in tonstein/mudstone rutile. Geochemical discriminant diagrams show most datapoints within metamorphic fields, with minor magmatic/mineralized signatures; Zr-in-rutile thermometry further confirms the Khondalite Belt (KB) and northern Trans-North China Orogen (TNCO) as primary provenances. Machine learning processing of trace element datasets (Si, Fe, Ti, Cr, Nb, Ta, Zr) using an optimized Random Forest (RF) model identifies the eastern KB and northern TNCO as core source domains. This research not only provides new provenance constraints for critical metal enrichment mechanisms in coal measures but also establishes a transferable machine learning-geochemistry methodology for multi-source tracing in sedimentary basins, offering practical implications for strategic mineral exploration.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"311 ","pages":"Article 104898"},"PeriodicalIF":5.7,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145441783","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":"Abundances of elements in global coals","authors":"Shifeng Dai ,&nbsp;James C. Hower ,&nbsp;Robert B. Finkelman ,&nbsp;Marina P. Ketris ,&nbsp;Yakov E. Yudovich ,&nbsp;Yutang Zhang ,&nbsp;Jingjing Liu ,&nbsp;Changqiu Zhao ,&nbsp;Na Xu ,&nbsp;Ian T. Graham ,&nbsp;David French ,&nbsp;Yu Liu ,&nbsp;Ruiwen Yan ,&nbsp;Zhengfu Zhao","doi":"10.1016/j.coal.2025.104899","DOIUrl":"10.1016/j.coal.2025.104899","url":null,"abstract":"<div><div>The abundance of elements in coal is important not only because it provides a solid scientific and practical foundation for various geochemical comparisons, but also because it helps address broader questions in Earth Sciences. In this study, data on major and trace elements in global coals comprising hundreds of thousands of coal samples were compiled from peer-reviewed journal articles, books, various databases, dissertations, and technical reports. These data formed the basis for estimating element abundances in global coals presented in this study. All collected data were rigorously screened for reliability, and any records with questionable quality were excluded from the analysis. Boxplot analysis was then applied to estimate element abundances, and median values of ash yields and different forms of sulfur in global coals. The results primarily include the minimum and maximum values within the normal range; the median (the 50^th percentile, representing the average abundance); and outliers for all global coals, low-rank coals, and medium- to high-rank coals. Additionally, these statistical parameters are also provided for coals from different major coal-forming periods (including Pennsylvanian (Late Carboniferous) and Early Permian, Late Permian, Late Triassic, Early and Middle Jurassic, Late Jurassic and Early Cretaceous, and Paleogene and Neogene), and Chinese coals and U.S coals.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"311 ","pages":"Article 104899"},"PeriodicalIF":5.7,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462071","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":"Organic matter accumulation in Barremian marine black shales of the Qiangtang Basin, China","authors":"Shengqiang Zeng ,&nbsp;Jian Wang ,&nbsp;Xiugen Fu ,&nbsp;Wei Sun ,&nbsp;Wangzhong Zhan","doi":"10.1016/j.coal.2025.104887","DOIUrl":"10.1016/j.coal.2025.104887","url":null,"abstract":"<div><div>Barremian organic-rich black shales are significant source rocks in the eastern Tethyan Qiangtang Basin. Based on petrological, inorganic and organic geochemistry analyses, the black shales are divided into three units from bottom to top. Unit 1 micritic limestones exhibit high total organic carbon (TOC) contents and Type II₂ kerogen, indicating a mixture of marine microalgae and land plants. Unit 2 black shales show the highest TOC contents, predominantly Type II₁ kerogen suggesting marine microalgal source. In contrast, Unit 3 marls have relatively low TOC contents, Type II₂ kerogen, indicating mixed terrestrial and marine OM sources. The black shales show a low organic maturity, and the hydrocarbon generation potential of the black shale and micritic limestone samples is substantially higher than that of the marl samples. Palaeoredox proxies indicate that Unit 1 deposited under dysoxic-anoxic conditions, and Unit 2 formed under anoxic-euxinic conditions, while Unit 3 deposited under oxic-suboxic conditions. Primary productivity proxies reflect high productivity in Units 1 and 2, and low productivity in Unit 3. Rb/K and total sulfur/TOC ratios suggest brackish environment in Units 1 and 2 and brackish or seawater condition in Unit 3. Hydrothermal activity during Unit 2 black shale deposition provided essential nutrients for phytoplankton in the photic zone, leading to high OM production. Upwelling/restriction proxies imply deposition under moderately restricted conditions for Unit 1, strongly restricted conditions for Unit 2, and upwelling/weakly restricted conditions for Unit 3. Palynological analysis indicates a warm, semi-humid to humid temperate climate during deposition of Units 1 and 2, contrasting with a hot, arid to semi-arid climate during Unit 3 marl deposition. OM accumulation of Unit 1 micritic limestone was primarily controlled by stratified dysoxic-anoxic conditions, high primary productivity, warm humid/semi-humid climate, and moderate watermass restriction. For Unit 2 black shale, the main controlling factors were stratified anoxic-euxinic environment, warm humid temperate climate, strongly restricted water condition, and intermittent strong hydrothermal activity. During Unit 3 marl deposition, low primary productivity, an oxygen-rich water environment leading to OM degradation, combined with a hot arid/semi-arid climate, resulted in organic-lean deposition.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"311 ","pages":"Article 104887"},"PeriodicalIF":5.7,"publicationDate":"2025-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145289880","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":"Quantifying inertinite carbon in biochar","authors":"Hamed Sanei ,&nbsp;Małgorzata Wojtaszek-Kalaitzidi ,&nbsp;Niels Hemmingsen Schovsbo ,&nbsp;Rasmus Stenshøj ,&nbsp;Zhiheng Zhou ,&nbsp;Hans-Peter Schmidt ,&nbsp;Nikolas Hagemann ,&nbsp;David Chiaramonti ,&nbsp;Tryfonas Kiaitsis ,&nbsp;Arka Rudra ,&nbsp;Anna J. Lehner ,&nbsp;Robert W. Brown ,&nbsp;Sophie Gill ,&nbsp;Erica Dorr ,&nbsp;Stavros Kalaitzidis ,&nbsp;Fariborz Goodarzi ,&nbsp;Henrik Ingermann Petersen","doi":"10.1016/j.coal.2025.104886","DOIUrl":"10.1016/j.coal.2025.104886","url":null,"abstract":"<div><div>The carbon dioxide removal (CDR) potential of biochar is determined by the long-term stability of its biogenic carbon, derived from atmospheric CO₂ fixed by photosynthesis and stabilized in solid form. This stability (carbon permanence) is commonly assessed using decay models to evaluate resistance to re-emission as greenhouse gases. However, these models are limited, as they focus primarily on short-term degradation of labile carbon fractions and are not suited to project the behavior of the highly recalcitrant component of biochar over extended timescales.</div><div>Inertinite represents highly aromatized and condensed carbon structures that are geochemically stable over millennia. This paper builds upon the Inertinite Benchmarking (<em>IBR</em>_<em>o</em><em>2</em>) methodology, directly quantifying the stable carbon fraction in biochar rather than relying on modeling. The method combines thermochemical analysis and incident-light microscopy to measure the reactive (labile) component and solid carbonized macerals, respectively. Random reflectance analysis (<em>R</em>_<em>o</em>) provides a representative distribution of carbonization states, with <em>R</em>_<em>o</em> values &gt;2.0 % defining the inertinite fraction after discounting reactive organic carbon. The <em>R</em>_<em>o</em> distribution is processed using kernel density estimation (KDE) and numerical integration to classify inertinite carbon with precision and statistical robustness.</div><div>As CDR crediting can be linked to measured inertinite content, statistical validity is essential. A Monte Carlo simulation model evaluates uncertainties from sampling frequency and production variability. Results show that increased sampling reduces uncertainty and lowers the conservative safety margin needed for potential errors. This framework supports a justified safety margin applied to reported inertinite carbon and corresponding CDR values, enabling conservative and robust crediting.</div><div>By combining direct quantification of inertinite carbon with probabilistic modeling of uncertainty, the <em>IBR</em>_<em>o</em><em>2</em> method offers a transparent and rigorous framework for assessing biochar permanence, aligned with emerging international certification and national inventory methodologies.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104886"},"PeriodicalIF":5.7,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145267368","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":"Petrolographic characteristics of graphitic carbon in coal-based graphite: Implications for the applicability of reflectance","authors":"Jiuqing Li ,&nbsp;Yong Qin ,&nbsp;Jian Shen ,&nbsp;Yilin Chen ,&nbsp;Geng Li ,&nbsp;Peipei Zhu","doi":"10.1016/j.coal.2025.104884","DOIUrl":"10.1016/j.coal.2025.104884","url":null,"abstract":"<div><div>Coal-based graphite deposits developed in Lutang, Hunan Province, China, provide an opportunity to investigate the petrographic characteristics of graphitic carbon. Optical microscopy and microphotometry were employed to observe the morphology, microstructure, occurrence and reflectance of graphitic carbon and thus classify its type. The results indicated that the evolutionary stage of the coal-based graphite reached the semi-graphite to graphite phase, and five types of graphitic carbon, namely, matrix graphite, granular graphite, needle graphite, flake graphite and pyrolytic carbon, were identified. The maximum reflectances of different types of graphitic carbon vary, indicating a differential evolutionary stage. However, the bireflectance progressively increases through the sequence of needle graphite, pyrolytic carbon and flake graphite, reflecting enhanced structural ordering of basic structural units. In terms of their particle size and reflectance characteristics, granular graphite, needle graphite, pyrolytic carbon, and flake graphite exhibit phanerocrystalline structures, whereas matrix graphite belongs to the cryptocrystalline graphite category. Three primary mechanisms for the origin and formation of graphitic carbon were proposed: in situ solid-phase transformation, liquid-phase crystallization, and vapor-phase deposition. Flake graphite serves as the ideal material for measuring reflectance in coal-based graphite, with its reflectance value acting as an indicator of evolutionary maturity.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104884"},"PeriodicalIF":5.7,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155171","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":"The organic petrology of graptolites in sections parallel and perpendicular to the bedding: Implication for thermal maturity evaluation","authors":"Jin Wu ,&nbsp;Qingyong Luo ,&nbsp;Ningning Zhong ,&nbsp;Fariborz Goodarzi ,&nbsp;Yang Bai ,&nbsp;Václav Suchý ,&nbsp;Meijun Li ,&nbsp;Lipeng Yao ,&nbsp;Imran Khan ,&nbsp;Ye Zhang ,&nbsp;Haoran Wang ,&nbsp;Haixu Liu ,&nbsp;Yinghang Tang","doi":"10.1016/j.coal.2025.104883","DOIUrl":"10.1016/j.coal.2025.104883","url":null,"abstract":"<div><div>Graptolites are widely presented in the Ordovician–Silurian Wufeng–Longmaxi Formations and other Lower Paleozoic marine shales throughout the world, and their reflectance is regarded as an effective index for the thermal maturity assessment of the graptolite-bearing shales devoid of vitrinite. Graptolites display distinct optically biaxial features, and the optical characteristics and reflectance of graptolites reveal significant differences depending on orientation of respective graptolite fragments relative to the bedding planes. However, specific studies on these optical discrepancies remains limited, resulting in confusion and/or substantial errors in thermal maturity assessment of graptolite-bearing shales. In this study, the organic petrological method was employed to compare the optical characteristics of graptolites in sections parallel and perpendicular to the bedding. Graptolites and in-source solid bitumen (SB) are the dominant organic components in the Alum and Wufeng–Longmaxi graptolite-bearing shales, and the liptinites are only detected in low maturity samples. In the studied sediments, both non-granular and granular graptolites were identified in abundance, but non-granular graptolites, which exhibit higher reflectance and stronger anisotropy than granular graptolites, were the predominant species. The intense positive correlations between the mean random reflectance (GR_o) and true maximum reflectance (R_max) and bireflectance of non-granular graptolites indicate their increasing anisotropy with maturation. R_max values in sections parallel to the bedding are slightly lower than or equal to those in sections perpendicular to the bedding, and the mean maximum reflectance (<span><math><mover><mi>R</mi><mo>¯</mo></mover></math></span>_max), the intermediate reflectance (R_int), and bireflectance are lower than those in sections perpendicular to the bedding. GR_o values in sections parallel to the bedding display a strong positive correlation with GR_o in sections perpendicular to the bedding, and the former are higher than the latter. GR_o exhibits stronger positive correlations with R_max, <span><math><mover><mi>R</mi><mo>¯</mo></mover></math></span>_max, and bireflectance in sections perpendicular to the bedding than those in sections parallel to the bedding, revealing the stronger anisotropy of non-granular graptolites in sections perpendicular to the bedding. According to the reflectance discrepancies of non-granular graptolites in sections parallel and perpendicular to the bedding, several equivalent equations are proposed to evaluate the thermal maturity of Ordovician–Silurian graptolites-bearing sediments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104883"},"PeriodicalIF":5.7,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096990","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}