International Journal of Coal Geology最新文献

{"title":"Investigating coalbed gas productivity response from hydrogeochemical and microbial perspectives: A case study of the Liulin block, eastern Ordos Basin, China","authors":"Yueguo Li ,&nbsp;Haijiao Fu ,&nbsp;Xianbo Su ,&nbsp;Detian Yan ,&nbsp;Gang Wang ,&nbsp;Shuguang Yang ,&nbsp;Xing Chen ,&nbsp;Jianzhang Liu ,&nbsp;Jintao Kong","doi":"10.1016/j.coal.2025.104817","DOIUrl":"10.1016/j.coal.2025.104817","url":null,"abstract":"<div><div>The benefits of coalbed gas (CBG) development are directly affected by the production capacity level. Previous studies of CBG productivity response have mainly focused on the hydrogeochemical characteristics of produced water, and paid less attention to the correlation between microbial communities and productivity. This study focuses on nine CBG wells in the Liulin Block of the eastern Ordos Basin, systematically analyzing the CBG genesis, as well as the relationships between hydrogeochemical parameters, microbial community characteristics and CBG productivity. The results show that the CBG in Liulin Block is a mixture of secondary biogenic gas and thermogenic gas, and the proportion of biogenic methane is 48.0 % to 49.7 %. The total dissolved solids (TDS) content is positively correlated with the average daily production of CBG, and the concentration of HCO₃⁻ is negatively correlated with the average daily gas production. The concentration of elemental Sn in the produced water is significantly correlated with average daily gas production. Positive δ¹³C_DIC values indicate the occurrence of microbial methanogenesis. Analysis of the microbial community shows that the bacterial community exhibits significant functional diversity, with <em>Hydrogenophaga</em> having the highest relative abundance and a positive correlation with average daily production of CBG. The archaeal community is dominated by methanogenic archaea. From the perspective of community diversity, the Operational Taxonomic Units (OTU) number, Chao1 and Ace indexes of the archaeal community show a positive correlation with average daily gas production. This study provides a novel perspective for research on microbial indicators of CBG production.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104817"},"PeriodicalIF":5.6,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212711","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":"Editorial of the special issue: The 2023 joint 74th ICCP and 39th TSOP meeting: Organic petrology in the energy transition era: Challenges ahead","authors":"Stavros Kalaitzidis,&nbsp;Kimon Christanis","doi":"10.1016/j.coal.2025.104811","DOIUrl":"10.1016/j.coal.2025.104811","url":null,"abstract":"","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104811"},"PeriodicalIF":5.6,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144237512","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":"Li concentration and isotopes in kaolinite and organic of coals determined by secondary ion mass spectrometry","authors":"Jia Song ,&nbsp;Beilei Sun ,&nbsp;Sandra Rodrigues ,&nbsp;Chao Liu ,&nbsp;Zhanming Guo ,&nbsp;David French","doi":"10.1016/j.coal.2025.104815","DOIUrl":"10.1016/j.coal.2025.104815","url":null,"abstract":"<div><div>Lithium (Li) enrichment in coal has attracted significant attention due to its economic potential and complex geochemical behavior during coal formation. This study investigates the concentration and isotopic composition of Li in kaolinite and organic matter from three high-Li coals from North China using Secondary Ion Mass Spectrometry (SIMS), complemented by TESCAN Integrated Mineral Analyzer (TIMA), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transform-Infrared Spectroscopy (FTIR), and Confocal Raman Microscopy (Raman). Results reveal that kaolinite is the primary host of Li, with concentrations exceeding 1516 μg/g. Lithium isotopic compositions (δ⁷Li) in kaolinite from high-rank coals exhibit narrow ranges, suggesting Li isotopic homogenization as a result of the elevated paleotemperature. In contrast, δ⁷Li values in lower-rank coals show greater variability, influenced by pore fluids and depth-dependent fractionation processes. Organic material, characterized by lower lithium concentrations (mostly &lt;100 μg/g) and highly variable δ⁷Li values, exhibits a heavier lithium isotopic composition in high-rank coal compared to δ⁷Li values in low-rank coal. These findings highlight the role of kaolinite in this isotopic fractionation. and emphasize the role of kaolinite as a major Li carrier. This study provides critical insights into Li enrichment mechanisms and isotopic fractionation during coalification, contributing to a better understanding of Li sources and mobility in coal-bearing strata.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104815"},"PeriodicalIF":5.6,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144184395","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":"Component identification of solid biomass fuels using reflected light microscopy: Interlaboratory study 2","authors":"Agnieszka Drobniak ,&nbsp;Maria Mastalerz ,&nbsp;Zbigniew Jelonek ,&nbsp;Iwona Jelonek ,&nbsp;Menandro N. Acda ,&nbsp;Tushar Adsul ,&nbsp;Neža Malenšek Andolšek ,&nbsp;Lorenzo Animali ,&nbsp;Omid H. Ardakani ,&nbsp;Telma Ataide ,&nbsp;Demberelsuren Batbold ,&nbsp;Mohd Younus Bhat ,&nbsp;Tara Congo ,&nbsp;Bryon S. Donohoe ,&nbsp;Olugbenga A. Ehinola ,&nbsp;Deolinda Flores ,&nbsp;Carolina Fonseca ,&nbsp;Santanu Ghosh ,&nbsp;Paula Gonçalves ,&nbsp;Paul C. Hackley ,&nbsp;Konrad Ziemianin","doi":"10.1016/j.coal.2025.104814","DOIUrl":"10.1016/j.coal.2025.104814","url":null,"abstract":"<div><div>As nations transition toward sustainable energy systems, biomass has become a vital component of global energy portfolios. Derived from organic materials such as wood, agricultural residues, forestry byproducts, and organic waste, biomass is a renewable energy source with significant environmental and economic benefits. Responsible biomass energy production can improve waste management, reduce emissions of greenhouse gases, and mitigate environmental pollution. However, as the diversity of biomass-derived fuels increases, robust quality assessment methods are essential to ensure their efficiency, safety, and minimal environmental impact.</div><div>Reflected light microscopy (RLM) is one such technique with the potential to complement conventional physico-chemical analyses by enabling a rapid identification of material constituents and impurities. To refine this methodology and evaluate the reproducibility of solid biomass component identification using RLM, an interlaboratory study (ILS) was conducted. The study involved the recognition of 58 components across 45 photomicrographs, with the participation of 65 scientists and students from 25 countries.</div><div>The participants faced high difficulty identifying some of the marked components, and as a result, the percentage of correct answers ranged from 19.0 % to 98.3 %, with an average correct identification rate of 62.7 %. The most challenging aspects of the identification process included distinguishing between woody and non-woody (agro) biomass, accurately identifying petroleum-derived materials, and differentiating agro biomass from inorganic matter.</div><div>The results suggest that while RLM is an important tool for characterizing solid biomass, further development of methodology guidelines and training are necessary to enhance its effectiveness. Future research should prioritize preparing detailed, image-rich, microscopic morphological descriptions of biomass fuel components, which could improve the accuracy and reliability of using RLM in biomass fuel characterization.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104814"},"PeriodicalIF":5.6,"publicationDate":"2025-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144212712","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 petrography and geochemistry of the Lower-Carboniferous coals from the Ekibastuz Basin, Kazakhstan","authors":"Majid Safaei-Farouji ,&nbsp;David Misch ,&nbsp;Reinhard F. Sachsenhofer ,&nbsp;Johannes Weitz ,&nbsp;Ivan Kojic ,&nbsp;Ksenija Stojanović ,&nbsp;Serik Tursyngaliyev ,&nbsp;Medet Junussov ,&nbsp;Milovan Fustic","doi":"10.1016/j.coal.2025.104813","DOIUrl":"10.1016/j.coal.2025.104813","url":null,"abstract":"<div><div>The Bogatyr Komin open-pit mine in the Ekibastuz Basin, located in north-east Kazakhstan, is one of the largest coal mines in the world. It is based on three Lower Carboniferous seams (from bottom to top: seams 3, 2, and 1), which together form a 150 m thick, uniform seam complex. At the study site on the western basin edge, the seams dip steeply. Organic petrological and geochemical investigations have been performed to determine the maturity and depositional environment of these exceptionally thick seams.</div><div>Vitrinite reflectance (0.8–1.1 %Rr) classifies the coal as high-volatile bituminous A coal, which is also supported by Tmax values and maturity-related biomarker ratios. Vitrinite reflectance patterns prove pre-deformational coalification and a relatively high paleo-heat flow, likely caused by magmatic activity.</div><div>High ash yields and relatively low sulfur contents indicate that the coal accumulated in low-lying mires without marine influence. The input of detrital minerals decreased during peat accumulation. Relatively high concentrations of sulfur-bearing aromatic compounds, particularly in the lower part of seam 3, may reflect volcanic activity, which is also evidenced by the presence of distinct ash layers (“kaolinitic beds”) and kaolinite in coal samples.</div><div>Thick wood-forming plants were rare in the peat-forming vegetation. However, samples from seams 1 and 3 contain higher concentrations of aromatic compounds derived from lignin-bearing arborescent cordiaite-conifer-pteridosperm vegetation. Enhanced bacterial activity during deposition of the upper part of seam 2 and seam 1 is indicated by elevated hopane concentrations.</div><div>The exceptional thickness of the coal complex indicates a geodynamic setting with high subsidence rates.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104813"},"PeriodicalIF":5.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144170243","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":"Solid bitumen formation and resulting differential porosity development in the Mesoproterozoic Xiamaling shale during artificial thermal maturation","authors":"Ji Chen ,&nbsp;Jingwen Zheng ,&nbsp;Daxiang He ,&nbsp;Peng Cheng ,&nbsp;Qin Zhou ,&nbsp;Tengfei Li ,&nbsp;Haifeng Gai","doi":"10.1016/j.coal.2025.104812","DOIUrl":"10.1016/j.coal.2025.104812","url":null,"abstract":"<div><div>Solid bitumen constitutes a predominant organic component in thermally mature source rocks, yet its role in shale reservoirs remains poorly constrained. This study integrated hydrocarbon expulsion simulation via sequential solvent extraction with isothermal pyrolysis experiments conducted on an early mature bituminite-rich shale sample from the Mesoproterozoic Xiamaling Formation in North China. Organic petrography and gas adsorption were applied to characterize the solid bitumen and pore structure in pyrolysis residues, respectively. The primary objective was to advance the understanding of the solid bitumen formation and its influence on the porosity development of shales within the dry gas window. Quantitative petrographic evidence confirms that the composition of retained extractable organic matter exerts fundamental control over the yield and properties of solid bitumen. Notably, the polar fraction (e.g., asphaltene component) exhibits superior solid bitumen-generating capacity, indicating that expulsion-driven compositional fractionation of residual hydrocarbons serves as the primary determinant of intraformational solid bitumen heterogeneity. Furthermore, empirical data demonstrate an inverse relationship between solid bitumen content and porosity development of shales across the investigated maturity spectrum (vitrinite reflectance 1.02 %–3.62 %), manifested through depressed specific surface area and diminished pore volume metrics. Our findings suggest that provenance-controlled variations in solid bitumen occurrence and subsequent pore architecture may induce complex reservoir quality modifications, potentially accounting for divergent porosity trends observed in natural shale systems. While this investigation provides fundamental insights into organo-petrophysical relationships, the general applicability of these conclusions warrants further validation through subsequent research.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104812"},"PeriodicalIF":5.6,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144170242","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":"Multiproxy-based evidence of wildfire occurrence in the Lower Permian coal-bearing Rio Bonito Formation, Paraná Basin, Brazil","authors":"M.M. Bicca ,&nbsp;W. Kalkreuth ,&nbsp;T.F. Silva ,&nbsp;M. Guerra-Sommer ,&nbsp;I. Degani-Schmidt ,&nbsp;C.M. Felix ,&nbsp;D.R. Boardman ,&nbsp;P.A. Souza","doi":"10.1016/j.coal.2025.104810","DOIUrl":"10.1016/j.coal.2025.104810","url":null,"abstract":"<div><div>Coals from southern Brazil are preserved in the Lower Permian postglacial Rio Bonito Formation of the Paraná Basin. Previous studies on the Candiota Coalfield have shown intervals with significant accumulations of inertinite macerals in the Banco Louco and S9 coal seams. Aiming to understand the causes of these anomalous inertinite accumulations, this study analyzed coal samples from the anomalous inertinite-rich interval and underlying carbonaceous siltites from the top of the Candiota Coal Superior (CCS), Banco Louco (BL), S9, and overlying S8 seams (post-anomalous) obtained from two borehole cores. The samples were analyzed using organic petrology, SEM, palynology, and biomarker (PAH) techniques. The results indicate that inertinite macerals accumulated in the paleoswamp in alternating small cycles, with general inertinite enrichment (fusinite, semifusinite, and inertodetrinite) towards the top of each coal seam analyzed. Macrocharcoal was present in all coal seams as charred wood, leaf fragments, and one reproductive structure. The peak of the inertinite-rich interval occurs at the S9 seam with the dominance of microcharcoal dispersed in fine-grained sediments and completely black palynomorphs, suggesting a significant wildfire event affecting the interval. Inertinite reflectance measurements indicated the predominance of ground and surface fire events with the rare occurrence of crown fires. Combustion of organic matter is also marked by the dominant presence of 3–5 ring PAHs and local occurrence of 6-ring PAHs (including coronene). The peatland flora was mainly composed of hygrophilous lycopsids and filicopsids, with subordinate elements represented by sphenopsids, mesophilous glossopterids, and meso-xerophilous conifers. The frequent oscillations in the vegetation composition were potentially related to climate changes and related environmental conditions, varying from hygrophilous to meso-hygrophilous and mesophilous, indicating that the vegetation composition adapted to environmental/climate changes as recognized by the alteration in the pollen-spore-producing flora towards the top of BL seam and their expansion in the overlying seams at the top of the anomalous interval. In the middle of the S9 seam, the completely dark palynomorphs and phytoclasts, plus a high abundance of pyrogenic biomarkers including 6-ring PAHs, point to significant fire events linked to the peak of the inertinite-rich interval during drier, warming intervals, which contributed to modifying the paleoecological patterns of the peatland. The paleo-wildfires of the Asselian age (ca. 298 Ma) Candiota Coalfield are the oldest record of wildfires in peat-forming environments of southern Brazil, being coeval with a warming period at the end of the Late Paleozoic Ice Age in Western Gondwana.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104810"},"PeriodicalIF":5.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144069774","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":"Selective trace element uptake in iron sulfides during burial metamorphism of coal: Insights from the coal-bearing Socka Beds, Northeastern Slovenia","authors":"Aleš Šoster ,&nbsp;Viktor Bertrandsson Erlandsson ,&nbsp;Stephen Ajuaba ,&nbsp;Nastja Rogan Šmuc","doi":"10.1016/j.coal.2025.104805","DOIUrl":"10.1016/j.coal.2025.104805","url":null,"abstract":"<div><div>The coal-bearing basal section of the Late Eocene Socka Beds in northeastern Slovenia exhibits iron sulfide mineralization associated with coal. Detailed petrographic analyses have identified five distinct textural and geochemical varieties of pyrite and marcasite. Geochemical analyses reveal that pyrite is notably enriched in Cu, Zn, and Mo, while marcasite shows enrichment in Co, Ni, As, Se, and Sb. Geochemical proxies suggest that marcasite formed under relatively higher temperatures, significantly more reducing conditions, and lower pH compared to pyrite, a distinction that is reflected in their contrasting geochemical signatures. Pyrite incorporates trace elements linked to seawater incursions, while marcasite contains trace elements associated with the progressive degradation of organic matter and the release of organically-bound trace elements. This study demonstrates that iron sulfide speciation is not confined to a single precipitation phase but involves multiple generations of minerals that reflect shifts in physicochemical conditions over time. Additionally, it demonstrates that the incorporation of trace elements is primarily governed by the availability of metals and fluid chemistry, rather than by mineral-specific selective sequestration. These findings offer new insights into the physicochemical pathways that govern sulfide formation in coal-forming environments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104805"},"PeriodicalIF":5.6,"publicationDate":"2025-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143942438","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":"Mitigation of geothermal energy drilling risks in the presence of hydrocarbons: A basin scale approach applied to the eastern Swiss Plateau area (Schlattingen-1, Herdern-1 and St. Gallen-GT-1 geothermal transect)","authors":"S. Omodeo-Salé ,&nbsp;T. Cassola ,&nbsp;A. Moscariello","doi":"10.1016/j.coal.2025.104806","DOIUrl":"10.1016/j.coal.2025.104806","url":null,"abstract":"<div><div>Geothermal exploration can be complicated by the presence of hydrocarbons in the subsurface. This is a well-known issue in Switzerland, where geothermal projects were affected by the consequences of an unexpected finding of hydrocarbons during drilling operations. This was the case of the Schlattingen-1 well in 2011 and the St. Gallen-GT-1 well in 2013, both located in the north-eastern part of the Swiss Plateau. To confidently predict the potential of hydrocarbon occurrence in the subsurface, a 2D basin and petroleum system modelling (BPSM) was performed along a regional geological section of the eastern sector of the Swiss Plateau, including the Schlattingen-1, Herdern-1 and St. Gallen-GT-1 wells.</div><div>The BPSM reconstructs the temperature history of the basin by considering the geodynamic, structural and stratigraphic evolution of the basin. The modelling results were calibrated with present-day borehole temperature, porosity and vitrinite reflectance data. To calculate the hydrocarbon generation and accumulation potential in the studied area, the source rocks were geochemically and petrographically characterized. In the southern part of the section, gas accumulations are predicted by the model at the top of the Permo-Carboniferous graben, just beneath the St. Gallen GT-1 well. In the northern part, around the Schlattingen-1 and Herdern-1 well sites, the model indicates the migration and accumulation of hydrocarbons within the Mesozoic units. Migration to the uppermost Molasse units also occurs along faults, thrust planes and permeable units, when present.</div><div>The main uncertainties of the modelling results include: i) distribution and characteristics of faults; ii) thickness and hydrocarbon potential of the source rocks; iii) lithological and petrophysical properties of potential reservoir and seal units; iv) calibration data with big ranges and not uniformly measured. To refine the assumptions and enhance the understanding of the basin's evolution, further data should be collected and existing data reanalysed. Building risk analysis and probabilistic models would also help to plan drilling mitigation measures aimed at reducing these uncertainties. The workflow presented in this study can be highly valuable to geothermal projects. It allows more effective planning of the drilling procedure, thus reducing the operational risks and contributing to the overall project success.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104806"},"PeriodicalIF":5.6,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143947696","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":"Palaeoenvironmental reconstruction of the coal-forming conditions during Oligocene in Niger Delta, Southern Nigeria: Implications for organic matter preservation and hydrocarbons potential","authors":"J.E. Ogala ,&nbsp;K. Perleros ,&nbsp;E. Kyriazaki ,&nbsp;M. Angelopoulos ,&nbsp;O.I. Ejeh ,&nbsp;M. Wojtaszek-Kalaitzidi ,&nbsp;S. Kalaitzidis ,&nbsp;K. Christanis","doi":"10.1016/j.coal.2025.104807","DOIUrl":"10.1016/j.coal.2025.104807","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Twenty eight (7 coal, 12 organic-rich and 9 inorganic) cutting samples obtained from six boreholes drilled over a &lt;em&gt;c&lt;/em&gt;. 60-km&lt;sup&gt;2&lt;/sup&gt;-large area in the alluvial plain of Niger River between Obomkpa and Issele-Azagba, southern Nigeria, were examined and evaluated by means of coal-petrography, mineralogical (XRD) and geochemical (CHNS, Rock Eval, XRF) analyses. This study aimed to provide an initial assessment of the palaeoenvironmental conditions during the Oligocene-Miocene peat accumulation.&lt;/div&gt;&lt;div&gt;As the samples were received a long time after sampling, moisture could not be determined. The ash and the volatile matter yields of the samples vary from 19.9 to 88.5 wt% (db) and 63.5–67.9 wt% (daf), respectively. Huminite is the dominant maceral group ranging from 60.6 to 90.6 vol% (on mineral matter-free basis), with detrohuminite being the major sub-group. The inertinite content is very low (&lt;1.5 %), whereas liptinite macerals are frequent to quite enriched (8.8–37.9 %) with alginite and liptodetrinite being the most common. The mean random huminite reflectance of all the coal samples varies between 0.32 % and 0.39 %.&lt;/div&gt;&lt;div&gt;As mainly sandstones, intercalated with siltstones and claystones are the main sedimentary rocks deposited in the Niger-River alluvial plain, the inorganic part of all the studied coaly and carbonaceous samples consists primarily of quartz and kaolinite, whereas goethite, mixed clay layers (illite-montmorillonite), anatase and gypsum occur in minor amounts. Accordingly, SiO&lt;sub&gt;2&lt;/sub&gt; and Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; display values ranging from 9 to 58 % and up to 23 wt%, respectively, while Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; up to 12 wt% and TiO&lt;sub&gt;2&lt;/sub&gt; up to 2 wt%.&lt;/div&gt;&lt;div&gt;Palaeoenvironmental geochemical proxies indicate a mixed source area for the siliciclastic facies, with significant recycling and weathering, deposited under a pure freshwater regime. The carbonaceous layers seem to have been deposited in a relative semi-arid climate, while the palaeomires were established under a more humid regime, promoting anaerobic conditions, which is in agreement with the observed very low inertinite content. Facies diagrammes based on the maceral contents were applied to reconstruct the environmental conditions in the palaeomires. According to the TPI &lt;em&gt;vs.&lt;/em&gt; GI diagramme, the peat-forming vegetation was mostly herbaceous yielding low TPI and medium GI values, and the conditions were fluvial-limnotelmatic. The GWI &lt;em&gt;vs.&lt;/em&gt; VI diagramme points to herbaceous vegetation on the palaeomire surface and mesotrophic water conditions with intense mineral matter influx from palaeo-Niger River. The area received frequent rainfall along with river flooding; thus, peat remained water-logged. Within the several hundred metres thick alluvial sediments, only short periods of limnotelmatic conditions prevailed in the area, yielding coal beds less than 17 m thick. The small number of the available cores distribut","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"306 ","pages":"Article 104807"},"PeriodicalIF":5.6,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143942439","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}