Pub Date : 2025-06-28DOI: 10.1016/j.coal.2025.104833
Zhenyu Xu , Xiaomei Wang , Fan Deng , Xingxing Guo , Yuxuan Han , Ke Sheng , Yuanhe Mu , Qin Yang
As the promising critical metal elements in coal, rare earth elements and yttrium (REY) can occur in minerals or complex with organic matter. Some differences have been observed in the modes of occurrence of REY in coals with different ranks, which raises interesting questions on their variation characteristic and mechanism during complex coalification. In this study, the modes of occurrence of REY and organic structure characteristics in bituminous coals with different ranks from the Hedong Coalfield are investigated. The sequential chemical extraction procedure shows that REY mainly remain in the residue in the low-rank bituminous coals and display an increasing total leaching rate as vitrinite reflectance increases. While in the high-rank bituminous coals, REY are dominated by HCl-leachable and residual phases. These results demonstrate that organic matter is the dominant carrier of REY in the low-rank bituminous coals. While in the high-rank bituminous coals, REY predominantly associate with phosphates and organic matter, indicating a gradual transformation from organic to mineral forms during coalification. Fourier Transform infrared (FTIR) spectroscopy experiments have found that the peak areas of most oxygenated functional groups are negatively correlated with vitrinite reflectance. In comparison to other functional groups, the content of phenolic group (Ar-OH) displays a strong positive correlation with the proportion of residual REY in the sequential chemical extraction experiment. This indicates that Ar-OH probably serves as the dominant organic binding site of REY during coalification. The loss of organic binding sites during coalification may result in the gradual decline of the proportion of organic-bound REY. Meanwhile, some REY released from these binding sites probably form authigenic minerals, leading to the higher proportion of mineral-associated forms of REY in the high-rank bituminous coals.
{"title":"Modes of occurrence of rare earth elements and yttrium in bituminous coals with different ranks from the Hedong Coalfield, northern China","authors":"Zhenyu Xu , Xiaomei Wang , Fan Deng , Xingxing Guo , Yuxuan Han , Ke Sheng , Yuanhe Mu , Qin Yang","doi":"10.1016/j.coal.2025.104833","DOIUrl":"10.1016/j.coal.2025.104833","url":null,"abstract":"<div><div>As the promising critical metal elements in coal, rare earth elements and yttrium (REY) can occur in minerals or complex with organic matter. Some differences have been observed in the modes of occurrence of REY in coals with different ranks, which raises interesting questions on their variation characteristic and mechanism during complex coalification. In this study, the modes of occurrence of REY and organic structure characteristics in bituminous coals with different ranks from the Hedong Coalfield are investigated. The sequential chemical extraction procedure shows that REY mainly remain in the residue in the low-rank bituminous coals and display an increasing total leaching rate as vitrinite reflectance increases. While in the high-rank bituminous coals, REY are dominated by HCl-leachable and residual phases. These results demonstrate that organic matter is the dominant carrier of REY in the low-rank bituminous coals. While in the high-rank bituminous coals, REY predominantly associate with phosphates and organic matter, indicating a gradual transformation from organic to mineral forms during coalification. Fourier Transform infrared (FTIR) spectroscopy experiments have found that the peak areas of most oxygenated functional groups are negatively correlated with vitrinite reflectance. In comparison to other functional groups, the content of phenolic group (Ar-OH) displays a strong positive correlation with the proportion of residual REY in the sequential chemical extraction experiment. This indicates that Ar-OH probably serves as the dominant organic binding site of REY during coalification. The loss of organic binding sites during coalification may result in the gradual decline of the proportion of organic-bound REY. Meanwhile, some REY released from these binding sites probably form authigenic minerals, leading to the higher proportion of mineral-associated forms of REY in the high-rank bituminous coals.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104833"},"PeriodicalIF":5.6,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144515584","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}
Pub Date : 2025-06-27DOI: 10.1016/j.coal.2025.104832
Søren B. Nielsen, Oskar Hagelskjær, Hamed Sanei
Thermal maturity assessment in sedimentary basins often relies on thermal indicators of varying quality and sensitivity, frequently available in an uneven distribution across wells. To improve interpretative reliability and reduce the influence of local statistical variability, we apply a joint inversion approach to thermal maturity data from three wells situated in contrasting geological settings. One well, Aars-1, located in the Danish Basin of the eastern North Sea, is constrained by high-quality data including present-day temperature, vitrinite reflectance (VRo), red-to-green (R/G) fluorescence quotients, and apatite fission track (AFT) ages. The other two wells, from the northwestern Black Sea Basin, contain VRo and R/G data but lack temperature and AFT records.
All wells contribute to constraining a kinetic model for the R/G quotient and the thermal evolutiuon of the Black Sea wells. The resulting models yield predicted present-day bottom hole temperatures of approximately 100 °C at 4000 m depth, consistent with values from independent studies in the region. The thermal immaturity of the Black Sea wells is attributed to low background heat flow and high sedimentation rates. In the immature to early mature maturity window, a linear relationship is established between VRo and R/G, described by the equation: VRo = 1.3239 × R/G – 0.2352, valid within the calibration range of 0.43 < R/G < 0.73 and 0.33 < VRo < 0.73. Based on this relationship, the previously reported VRo discontinuities at the base of the Black Sea wells are likely artefactual.
This study demonstrates the value of combining independent thermal indicators across multiple wells and depositional settings. The approach enhances the robustness of thermal history reconstructions and offers a practical framework for evaluating relative heat flow and maturity in basins with incomplete or uneven datasets. Particularly, the R/G quotient, derived from autochthonous alginite deposited within the basin, is less affected by transport-related degradation than VRo and may offer a more representative measure of in-place thermal maturity, particularly in high-sedimentation environments.
{"title":"Relationship between vitrinite reflectance, fluoresence red/green quotients, apatite fission tracks and temperature by joint inversion of three wells","authors":"Søren B. Nielsen, Oskar Hagelskjær, Hamed Sanei","doi":"10.1016/j.coal.2025.104832","DOIUrl":"10.1016/j.coal.2025.104832","url":null,"abstract":"<div><div>Thermal maturity assessment in sedimentary basins often relies on thermal indicators of varying quality and sensitivity, frequently available in an uneven distribution across wells. To improve interpretative reliability and reduce the influence of local statistical variability, we apply a joint inversion approach to thermal maturity data from three wells situated in contrasting geological settings. One well, Aars-1, located in the Danish Basin of the eastern North Sea, is constrained by high-quality data including present-day temperature, vitrinite reflectance (VRo), red-to-green (R/G) fluorescence quotients, and apatite fission track (AFT) ages. The other two wells, from the northwestern Black Sea Basin, contain VRo and R/G data but lack temperature and AFT records.</div><div>All wells contribute to constraining a kinetic model for the R/G quotient and the thermal evolutiuon of the Black Sea wells. The resulting models yield predicted present-day bottom hole temperatures of approximately 100 °C at 4000 m depth, consistent with values from independent studies in the region. The thermal immaturity of the Black Sea wells is attributed to low background heat flow and high sedimentation rates. In the immature to early mature maturity window, a linear relationship is established between VRo and R/G, described by the equation: VRo = 1.3239 × R/G – 0.2352, valid within the calibration range of 0.43 < R/G < 0.73 and 0.33 < VRo < 0.73. Based on this relationship, the previously reported VRo discontinuities at the base of the Black Sea wells are likely artefactual.</div><div>This study demonstrates the value of combining independent thermal indicators across multiple wells and depositional settings. The approach enhances the robustness of thermal history reconstructions and offers a practical framework for evaluating relative heat flow and maturity in basins with incomplete or uneven datasets. Particularly, the R/G quotient, derived from autochthonous alginite deposited within the basin, is less affected by transport-related degradation than VRo and may offer a more representative measure of in-place thermal maturity, particularly in high-sedimentation environments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104832"},"PeriodicalIF":5.6,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144515591","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}
Pub Date : 2025-06-25DOI: 10.1016/j.coal.2025.104827
Rongbin Yang , Qingyong Luo , Jiapeng Wu , Qixiang Huang , Man Lu , Wenxin Hu , Dandan Wang , Zhengyu Chen , Jinqi Qiao
Continental hypersaline lacustrine basins constitute critical repositories of unconventional shale oil resources, often hosting source rocks with primary exploration value. The hydrocarbon generation potential and organic matter accumulation within the Qianjiang Formation of Jianghan Basin, however, remain elucidated inadequately. This study targets the third member of the Qianjiang Formation (Eq3) through systematic analysis of dolomitic shale sequences from the QYP1 directional well in Qianjiang Depression. A comprehensive analytical approach is employed, integrating programmed open-system pyrolysis, major and trace element geochemistry, biomarker analysis, and organic petrology. The multidisciplinary framework is utilized to evaluate sediment provenance, organic matter supply, paleoenvironmental reconstruction (including paleoclimate, redox condition, and paleosalinity) during the Eq3 depositional period, and the thermal maturity of organic matter. Based on these influencing factors, the hydrocarbon generation potential and organic matter enrichment model for source rocks of the Eq3 interval are assessed.
Results demonstrate that the organic-rich sediments of the Eq3 shales in the Qianjiang Depression exhibit exceptional hydrocarbon potential, qualifying as prime targets for shale oil exploration. Key characteristics include elevated total organic carbon (TOC), elevated S1 + S2 values, and superior hydrogen index (HI). Primary source of organic matter is attributed to saline lacustrine algae, as evidenced by a strong linear correlation between liptinite and TOC content and high proportion of lamalginite. The analyzed organic matter exhibits thermal maturity levels ranging from immature to low-mature level. Organic matter enrichment in these evaporative lacustrine source rocks is controlled by a combination of factors, including paleoclimate, sediment supply, organic matter sources, and depositional conditions. Paleoclimate reconstructions indicate that the Eq3 interval was deposited under cold and arid conditions, with low Ga/Rb, SiO2 and high K2O/Al2O3, Al2O3 + K2O + Na2O, accompanied by weak chemical weathering with minimal sediment recycling. Depositional environment demonstrates strongly reducing conditions and exceptional organic matter preservation, as indicated by low Pr/Ph ratios, exceptionally high Gamm/C30 (βα + αβ) hopane indices, rominent extended tricyclic terpanes ratios (ETR) and widespread pyrite occurrence. Elevated gammacerane, β-carotane content, along with high Sr/Ba, B/Ga and DBT/P radios, suggest high paleosalinity. Water column stratification further enhanced paleoproductivity and provided optimal conditions for organic matter preservation. Hydrocarbon-generating organic matter is predominantly derived from aquatic alga
{"title":"Hydrocarbon generation potential and organic carbon enrichment in evaporitic lacustrine source rocks from the Qianjiang Formation, Jianghan Basin (Central China): An integrated geochemical-petrological investigation","authors":"Rongbin Yang , Qingyong Luo , Jiapeng Wu , Qixiang Huang , Man Lu , Wenxin Hu , Dandan Wang , Zhengyu Chen , Jinqi Qiao","doi":"10.1016/j.coal.2025.104827","DOIUrl":"10.1016/j.coal.2025.104827","url":null,"abstract":"<div><div>Continental hypersaline lacustrine basins constitute critical repositories of unconventional shale oil resources, often hosting source rocks with primary exploration value. The hydrocarbon generation potential and organic matter accumulation within the Qianjiang Formation of Jianghan Basin, however, remain elucidated inadequately. This study targets the third member of the Qianjiang Formation (Eq<sup>3</sup>) through systematic analysis of dolomitic shale sequences from the QYP1 directional well in Qianjiang Depression. A comprehensive analytical approach is employed, integrating programmed open-system pyrolysis, major and trace element geochemistry, biomarker analysis, and organic petrology. The multidisciplinary framework is utilized to evaluate sediment provenance, organic matter supply, paleoenvironmental reconstruction (including paleoclimate, redox condition, and paleosalinity) during the Eq<sup>3</sup> depositional period, and the thermal maturity of organic matter. Based on these influencing factors, the hydrocarbon generation potential and organic matter enrichment model for source rocks of the Eq<sup>3</sup> interval are assessed.</div><div>Results demonstrate that the organic-rich sediments of the Eq<sup>3</sup> shales in the Qianjiang Depression exhibit exceptional hydrocarbon potential, qualifying as prime targets for shale oil exploration. Key characteristics include elevated total organic carbon (TOC), elevated S<sub>1</sub> + S<sub>2</sub> values, and superior hydrogen index (HI). Primary source of organic matter is attributed to saline lacustrine algae, as evidenced by a strong linear correlation between liptinite and TOC content and high proportion of lamalginite. The analyzed organic matter exhibits thermal maturity levels ranging from immature to low-mature level. Organic matter enrichment in these evaporative lacustrine source rocks is controlled by a combination of factors, including paleoclimate, sediment supply, organic matter sources, and depositional conditions. Paleoclimate reconstructions indicate that the Eq<sup>3</sup> interval was deposited under cold and arid conditions, with low Ga/Rb, SiO<sub>2</sub> and high K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub> + K<sub>2</sub>O + Na<sub>2</sub>O, accompanied by weak chemical weathering with minimal sediment recycling. Depositional environment demonstrates strongly reducing conditions and exceptional organic matter preservation, as indicated by low Pr/Ph ratios, exceptionally high Gamm/C<sub>30</sub> (βα + αβ) hopane indices, rominent extended tricyclic terpanes ratios (ETR) and widespread pyrite occurrence. Elevated gammacerane, <em>β</em>-carotane content, along with high Sr/Ba, B/Ga and DBT/P radios, suggest high paleosalinity. Water column stratification further enhanced paleoproductivity and provided optimal conditions for organic matter preservation. Hydrocarbon-generating organic matter is predominantly derived from aquatic alga","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104827"},"PeriodicalIF":5.6,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144511107","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}
In the Elephant Game Reserve (EGR) in Mozambiquan Maputaland, several small peatlands have been developed between dunes. The aim of the study is to determine the peat-forming conditions and elucidate the evolution of the peatlands. Herbaceous vegetation (reeds and sedges) thrive on the surface of the mires. Fifty-five organic and inorganic samples were picked up from nine manually-retrieved cores up to 4.4 m deep, across several locations in the EGR. The maximum thickness of the organic sediments is 2.5 m. The determinations performed included proximate and ultimate analyses, pH and electrical Conductivity (eC) measurements, organic-petrography examination, as well as mineralogical and geochemical analyses applying X-ray diffraction and X-ray fluorescence spectrometry, respectively. The peat samples display ash yields between 10.1 and 46.8 % (on dry basis), sulphur content up to 8.9 % (db), pH and eC values from 2-7.3 and 142–2360 μS/cm, respectively. Quartz, K-feldspars and pyrite are the major minerals contained in peat; accordingly, silica is the major element with iron, aluminum, calcium and magnesium being minors. The maceral composition of peat reveals the predominance of the huminite group (57.6–78.6 vol%, on mineral matter-free basis), followed by inertinite (13.8–38.2 vol%) and liptinite (<9.6 vol%). The prevalence of the detrohuminite subgroup, particularly of attrinite, along with inertodetrinite, points to intense mechanical decomposition of the plant remains and periodical lowering of the local watertable with subsequent fires, during which the mire surface was exposed to oxidation. Overall, peat accumulation took place under rheo- to mesotrophic conditions.
{"title":"The evolution of interdunal peat-forming environments in the Maputaland coastal plain, Mozambique","authors":"Marios Panagiotis Chrysochos , Stavros Kalaitzidis , Mussa Achimo , Lopo Vasconcelos , Chrysoula Chrysakopoulou , Kimon Christanis","doi":"10.1016/j.coal.2025.104828","DOIUrl":"10.1016/j.coal.2025.104828","url":null,"abstract":"<div><div>In the Elephant Game Reserve (EGR) in Mozambiquan Maputaland, several small peatlands have been developed between dunes. The aim of the study is to determine the peat-forming conditions and elucidate the evolution of the peatlands. Herbaceous vegetation (reeds and sedges) thrive on the surface of the mires. Fifty-five organic and inorganic samples were picked up from nine manually-retrieved cores up to 4.4 m deep, across several locations in the EGR. The maximum thickness of the organic sediments is 2.5 m. The determinations performed included proximate and ultimate analyses, pH and electrical Conductivity (eC) measurements, organic-petrography examination, as well as mineralogical and geochemical analyses applying X-ray diffraction and X-ray fluorescence spectrometry, respectively. The peat samples display ash yields between 10.1 and 46.8 % (on dry basis), sulphur content up to 8.9 % (db), pH and eC values from 2-7.3 and 142–2360 μS/cm, respectively. Quartz, K-feldspars and pyrite are the major minerals contained in peat; accordingly, silica is the major element with iron, aluminum, calcium and magnesium being minors. The maceral composition of peat reveals the predominance of the huminite group (57.6–78.6 vol%, on mineral matter-free basis), followed by inertinite (13.8–38.2 vol%) and liptinite (<9.6 vol%). The prevalence of the detrohuminite subgroup, particularly of attrinite, along with inertodetrinite, points to intense mechanical decomposition of the plant remains and periodical lowering of the local watertable with subsequent fires, during which the mire surface was exposed to oxidation. Overall, peat accumulation took place under rheo- to mesotrophic conditions.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104828"},"PeriodicalIF":5.6,"publicationDate":"2025-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144513683","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}
Pub Date : 2025-06-18DOI: 10.1016/j.coal.2025.104829
Christopher R. Fielding , Stephen McLoughlin , Chris Mays , Allen P. Tevyaw , Tracy D. Frank
The upper Permian Newcastle Coal Measures (NCM) host world-class coal resources in coastal New South Wales, Australia. They formed close to the foredeep axis of a developing retroarc foreland basin associated with the Hunter-Bowen contractional event. In addition to the typical coal-bearing lithological suite of mudrocks, heteroliths, sandstones, and coals (with several beds of volcanic ash), the NCM preserve numerous, linear bodies of conglomerate up to 100 m thick and 20 km wide that are anomalous in the context of paralic coal-bearing successions worldwide. Four facies associations are recognized: A) linear bodies of conglomerate, gravelly sandstone and sandstone, interpreted as the deposits of major coastal plain channels, B) interbedded mudrocks and sandstones, interpreted as the product of coastal plain floodplains and floodbasins, C) coals and coaly mudrocks, interpreted as the product of coastal plain mires, and D) massive and bedded tuffs, interpreted as the product of pyroclastic falls and flows from nearby stratovolcanoes. Despite having formed on a coastal plain during a time of known sea-level changes, no depositional sequences can be recognized in the NCM, due to high rates of accommodation and sediment supply. The repeated co-occurrence of southward-trending major channel belts across the Newcastle coalfield is attributed to the area being located in the axial foredeep of the basin. A new palaeogeographic reconstruction is proposed in which the northern Sydney Basin, in the late Permian, extended further northwards across what is now the southern New England Orogen, and the north-south-elongate basin was drained by continental scale, basin-axial river systems that carried significant volumes of gravel.
{"title":"Fluvial architectural style and stacking patterns in a high-accommodation coal-bearing succession: the upper Permian Newcastle Coal Measures, eastern Australia","authors":"Christopher R. Fielding , Stephen McLoughlin , Chris Mays , Allen P. Tevyaw , Tracy D. Frank","doi":"10.1016/j.coal.2025.104829","DOIUrl":"10.1016/j.coal.2025.104829","url":null,"abstract":"<div><div>The upper Permian Newcastle Coal Measures (NCM) host world-class coal resources in coastal New South Wales, Australia. They formed close to the foredeep axis of a developing retroarc foreland basin associated with the Hunter-Bowen contractional event. In addition to the typical coal-bearing lithological suite of mudrocks, heteroliths, sandstones, and coals (with several beds of volcanic ash), the NCM preserve numerous, linear bodies of conglomerate up to 100 m thick and 20 km wide that are anomalous in the context of paralic coal-bearing successions worldwide. Four facies associations are recognized: A) linear bodies of conglomerate, gravelly sandstone and sandstone, interpreted as the deposits of major coastal plain channels, B) interbedded mudrocks and sandstones, interpreted as the product of coastal plain floodplains and floodbasins, C) coals and coaly mudrocks, interpreted as the product of coastal plain mires, and D) massive and bedded tuffs, interpreted as the product of pyroclastic falls and flows from nearby stratovolcanoes. Despite having formed on a coastal plain during a time of known sea-level changes, no depositional sequences can be recognized in the NCM, due to high rates of accommodation and sediment supply. The repeated co-occurrence of southward-trending major channel belts across the Newcastle coalfield is attributed to the area being located in the axial foredeep of the basin. A new palaeogeographic reconstruction is proposed in which the northern Sydney Basin, in the late Permian, extended further northwards across what is now the southern New England Orogen, and the north-south-elongate basin was drained by continental scale, basin-axial river systems that carried significant volumes of gravel.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104829"},"PeriodicalIF":5.6,"publicationDate":"2025-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337817","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}
Pub Date : 2025-06-18DOI: 10.1016/j.coal.2025.104830
M. Waliczek, A. Zakrzewski, G. Machowski, G. Ząbek
This study presents the results of microscopic and geochemical analyses of the Menilite Formation from the Polish part of the Outer Carpathians. Twelve Oligocene shales from the Central Carpathian Synclinorium of the Silesian Nappe were examined to evaluate the petrological characterization of the solid bitumen and other organic matter (OM), identify the hydrocarbon evidence in the analyzed samples, and to understand the hydrocarbon generation in low thermal maturity rocks. The OM dispersed in the analyzed Menilite Formation is mainly represented by alginite and bituminite-rich, oil-prone kerogen. The reflectance measurements of vitrinite (VRo %), solid bitumen (BRo %), and the values of the maturity biomarker parameter indicator revealed that the analyzed samples contain immature to early mature organic matter in terms of hydrocarbon generation. Three types of solid bitumen (SB) were noticed: dark brown, almost black in reflected white light with a scratchy or granular surface bitumen (GR), as well as two types of homogenous SB. One reflected shades of brown-orange when observed under UV light, while the other was a non-fluorescent, lighter gray in reflected white light. Solid bitumen appears in samples where the reflectance of vitrinite is equal to at least 0.43 % VRo and has the ability to reflect light from 0.26 to 0.32 % BRo. A strong correlation was found between lighter homogenous solid bitumen reflectance with vitrinite reflectance, CPI 25–31, and dinosterane distribution. The lack of a broad interrelation between geochemical parameters and vitrinite reflectance values was linked with different kerogen mixtures within the analyzed strata. Higher content of bacterial Type II kerogen prompted the generation of early-mature hydrocarbons, while higher input of Type I and/or III kerogen leads to a decrease in the scale of the phenomenon of early-mature hydrocarbons. In Menilite shales, the hydrocarbons are generated in the forms of oil droplets and oil exudates.
{"title":"Evidence of solid bitumen and hydrocarbons in low thermal maturity Menilite shales from the Polish part of the Outer Carpathians","authors":"M. Waliczek, A. Zakrzewski, G. Machowski, G. Ząbek","doi":"10.1016/j.coal.2025.104830","DOIUrl":"10.1016/j.coal.2025.104830","url":null,"abstract":"<div><div>This study presents the results of microscopic and geochemical analyses of the Menilite Formation from the Polish part of the Outer Carpathians. Twelve Oligocene shales from the Central Carpathian Synclinorium of the Silesian Nappe were examined to evaluate the petrological characterization of the solid bitumen and other organic matter (OM), identify the hydrocarbon evidence in the analyzed samples, and to understand the hydrocarbon generation in low thermal maturity rocks. The OM dispersed in the analyzed Menilite Formation is mainly represented by alginite and bituminite-rich, oil-prone kerogen. The reflectance measurements of vitrinite (VR<sub>o</sub> %), solid bitumen (BR<sub>o</sub> %), and the values of the maturity biomarker parameter indicator revealed that the analyzed samples contain immature to early mature organic matter in terms of hydrocarbon generation. Three types of solid bitumen (SB) were noticed: dark brown, almost black in reflected white light with a scratchy or granular surface bitumen (GR), as well as two types of homogenous SB. One reflected shades of brown-orange when observed under UV light, while the other was a non-fluorescent, lighter gray in reflected white light. Solid bitumen appears in samples where the reflectance of vitrinite is equal to at least 0.43 % VR<sub>o</sub> and has the ability to reflect light from 0.26 to 0.32 % BR<sub>o</sub>. A strong correlation was found between lighter homogenous solid bitumen reflectance with vitrinite reflectance, CPI 25–31, and dinosterane distribution. The lack of a broad interrelation between geochemical parameters and vitrinite reflectance values was linked with different kerogen mixtures within the analyzed strata. Higher content of bacterial Type II kerogen prompted the generation of early-mature hydrocarbons, while higher input of Type I and/or III kerogen leads to a decrease in the scale of the phenomenon of early-mature hydrocarbons. In Menilite shales, the hydrocarbons are generated in the forms of oil droplets and oil exudates.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104830"},"PeriodicalIF":5.6,"publicationDate":"2025-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144337816","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}
Pub Date : 2025-06-15DOI: 10.1016/j.coal.2025.104826
Kalyn J. Tew , Rona J. Donahoe , Ibrahim G. Okunlola
Historical and newly acquired data are used to model the spatial variability of rare earth elements (REE), Sc, Y, and Li concentrations in two coal ash impoundments. Samples were collected using a limited sampling scheme and modeled in ArcGIS Pro for total REYSc, Ce, La, Sc, Y, Nd, and Li using 3-dimensional empirical Bayesian Kriging (EBK 3D). Although a higher sample density was modeled at Site 1, the composition of the ash is more variable and randomly distributed throughout the impoundment, resulting in poorly constrained models. At Site 2, the models better represent the spatial distributions of REYSc, Ce, La, Nd, and Li within the coal ash, which vary systematically from east to west, as well as with depth. These results demonstrate that EBK 3D offers a distinct and effective approach for modeling elemental concentrations in coal ash impoundments with limited sampling. Unlike traditional interpolation methods, EBK 3D accounts for spatial uncertainty and variability in three dimensions. It is particularly useful when ash remains undisturbed, the coal source is consistent, or the coal source transitions gradually. This approach introduces a novel methodology for evaluating the resource potential of impounded coal ash as an unconventional feedstock for critical elements.
{"title":"Modeling the spatial distribution of REEs and Li within two coal ash impoundments","authors":"Kalyn J. Tew , Rona J. Donahoe , Ibrahim G. Okunlola","doi":"10.1016/j.coal.2025.104826","DOIUrl":"10.1016/j.coal.2025.104826","url":null,"abstract":"<div><div>Historical and newly acquired data are used to model the spatial variability of rare earth elements (REE), Sc, Y, and Li concentrations in two coal ash impoundments. Samples were collected using a limited sampling scheme and modeled in ArcGIS Pro for total REYSc, Ce, La, Sc, Y, Nd, and Li using 3-dimensional empirical Bayesian Kriging (EBK 3D). Although a higher sample density was modeled at Site 1, the composition of the ash is more variable and randomly distributed throughout the impoundment, resulting in poorly constrained models. At Site 2, the models better represent the spatial distributions of REYSc, Ce, La, Nd, and Li within the coal ash, which vary systematically from east to west, as well as with depth. These results demonstrate that EBK 3D offers a distinct and effective approach for modeling elemental concentrations in coal ash impoundments with limited sampling. Unlike traditional interpolation methods, EBK 3D accounts for spatial uncertainty and variability in three dimensions. It is particularly useful when ash remains undisturbed, the coal source is consistent, or the coal source transitions gradually. This approach introduces a novel methodology for evaluating the resource potential of impounded coal ash as an unconventional feedstock for critical elements.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104826"},"PeriodicalIF":5.6,"publicationDate":"2025-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144307327","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}
Pub Date : 2025-06-06DOI: 10.1016/j.coal.2025.104825
Katalin Sári , Mária Hámor-Vidó , Ernő Takács , Márton Bauer , Richard William McIntosh , Zoltán Püspöki
An intriguing problem of the Upper Miocene stratigraphy in the Pannonian Basin is the correlation of marginal lignite-bearing units to the thick siliciclastic succession in the basin centre; however, it is inevitable in the stratigraphic investigation of the Jászság Basin, necessitated by a regional scale hydrogeological study. An essential precondition of this investigation is integrating data from lignite and hydrocarbon research of very different scales. The Tiszapalkonya-1 long core traversing the lignite-bearing succession across 1300 m enabled this data integration, as (i) it was measured by wireline logs, (ii) its lignite samples were subjected to laboratory and coal petrological analyses and (iii) the logs can be correlated with seismic sections.
Three lignite-bearing units were identified in the section. According to lithological and organic petrological data, the lower represents mostly floodplain conditions with intermediate complex and marsh. The middle indicates a change from aquatic to unbalanced wet forest swamp, floodplain. In the upper unit more stable, balanced accumulation could develop. The density log proved to be a reliable proxy on the occurrence and ash content of peat-forming environments, and the lignite-bearing units occur as autonomous seismic facies based on their higher seismic amplitude. These enable the basin-scale tracking of the identified lignite-bearing units. A log-based multi-proxy time-series analysis revealed regular cycles in the succession but raised some necessity of re-consideration of the existing magnetostratigraphy of the section. The density log gained eminent cyclostratigraphic potential due to the sensitivity of the “coal window” to climate changes.
{"title":"Integrated stratigraphy of an upper miocene lignite-bearing succession based on wireline log, seismic and organic petrographic data in the Tiszapalkonya-1 core section, NE Hungary","authors":"Katalin Sári , Mária Hámor-Vidó , Ernő Takács , Márton Bauer , Richard William McIntosh , Zoltán Püspöki","doi":"10.1016/j.coal.2025.104825","DOIUrl":"10.1016/j.coal.2025.104825","url":null,"abstract":"<div><div>An intriguing problem of the Upper Miocene stratigraphy in the Pannonian Basin is the correlation of marginal lignite-bearing units to the thick siliciclastic succession in the basin centre; however, it is inevitable in the stratigraphic investigation of the Jászság Basin, necessitated by a regional scale hydrogeological study. An essential precondition of this investigation is integrating data from lignite and hydrocarbon research of very different scales. The Tiszapalkonya-1 long core traversing the lignite-bearing succession across 1300 m enabled this data integration, as (i) it was measured by wireline logs, (ii) its lignite samples were subjected to laboratory and coal petrological analyses and (iii) the logs can be correlated with seismic sections.</div><div>Three lignite-bearing units were identified in the section. According to lithological and organic petrological data, the lower represents mostly floodplain conditions with intermediate complex and marsh. The middle indicates a change from aquatic to unbalanced wet forest swamp, floodplain. In the upper unit more stable, balanced accumulation could develop. The density log proved to be a reliable proxy on the occurrence and ash content of peat-forming environments, and the lignite-bearing units occur as autonomous seismic facies based on their higher seismic amplitude. These enable the basin-scale tracking of the identified lignite-bearing units. A log-based multi-proxy time-series analysis revealed regular cycles in the succession but raised some necessity of re-consideration of the existing magnetostratigraphy of the section. The density log gained eminent cyclostratigraphic potential due to the sensitivity of the “coal window” to climate changes.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104825"},"PeriodicalIF":5.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144263080","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}
Pub Date : 2025-06-06DOI: 10.1016/j.coal.2025.104816
Rafał Morga , Roman Wrzalik
To date, the pore system of graptolite periderm in shales with thermal maturity at the transition phase from the oil to the gas window has been poorly researched and understood. It was also not clear whether the graptolite periderm develops secondary pores. Therefore, porosity, pore characteristics, and surface roughness of the graptolite periderm (graptolite reflectance GR = 1.30–1.83 %; vitrinite reflectance equivalent VRE = 1.11–1.50 %) in the Silurian shales of the Baltic Basin (northern Poland) were investigated by atomic force microscopy (AFM). The size of the 200 × 200 nm measurement area was chosen to allow observation of pores with diameters ≥1.4 nm. The graptolite periderm shows a very low porosity (0.16–0.28 %), which increases with increasing thermal maturity and decreases the mean equivalent pore diameter and surface roughness. With the onset of the gas window (at GR ≥ 1.58 %; VRE ≥ 1.31 %), limited secondary porosity develops, and percentage of pores <5 nm in size significantly increases. Elliptical or roundish micropores appear within the granular fragments, and sparse pores <5 nm in size emerge within the non-granular fabric. The ability of the graptolite periderm to generate gaseous hydrocarbons at the beginning of the gas window is poor. Granular type is more generative compared to non-granular type. The ratio between the two types of fabric is not significant for the overall source and reservoir potential of the host formation at the maturity level considered in this study. However, it can be important at higher maturities. Changes in the pore system and roughness parameters align with the alteration of the chemistry and microstructure of graptolite periderm. The development of secondary porosity can depend on thermal degradation of the graptolite periderm during and after burial.
{"title":"Nanoporosity of graptolite periderm by atomic force microscopy (AFM): A case study from the Baltic Basin, Poland","authors":"Rafał Morga , Roman Wrzalik","doi":"10.1016/j.coal.2025.104816","DOIUrl":"10.1016/j.coal.2025.104816","url":null,"abstract":"<div><div>To date, the pore system of graptolite periderm in shales with thermal maturity at the transition phase from the oil to the gas window has been poorly researched and understood. It was also not clear whether the graptolite periderm develops secondary pores. Therefore, porosity, pore characteristics, and surface roughness of the graptolite periderm (graptolite reflectance GR = 1.30–1.83 %; vitrinite reflectance equivalent VRE = 1.11–1.50 %) in the Silurian shales of the Baltic Basin (northern Poland) were investigated by atomic force microscopy (AFM). The size of the 200 × 200 nm measurement area was chosen to allow observation of pores with diameters ≥1.4 nm. The graptolite periderm shows a very low porosity (0.16–0.28 %), which increases with increasing thermal maturity and decreases the mean equivalent pore diameter and surface roughness. With the onset of the gas window (at GR ≥ 1.58 %; VRE ≥ 1.31 %), limited secondary porosity develops, and percentage of pores <5 nm in size significantly increases. Elliptical or roundish micropores appear within the granular fragments, and sparse pores <5 nm in size emerge within the non-granular fabric. The ability of the graptolite periderm to generate gaseous hydrocarbons at the beginning of the gas window is poor. Granular type is more generative compared to non-granular type. The ratio between the two types of fabric is not significant for the overall source and reservoir potential of the host formation at the maturity level considered in this study. However, it can be important at higher maturities. Changes in the pore system and roughness parameters align with the alteration of the chemistry and microstructure of graptolite periderm. The development of secondary porosity can depend on thermal degradation of the graptolite periderm during and after burial.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104816"},"PeriodicalIF":5.6,"publicationDate":"2025-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144243228","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}
Pub Date : 2025-06-03DOI: 10.1016/j.coal.2025.104818
Zhiheng Zhou, Hamed Sanei
Point counting is a widely used quantitative technique in microscopic analysis for estimating the volume percentage of target constituents within a sample. Its application in coal petrography has been standardized through international guidelines such as ISO 7404 and ASTM D2797/D2799, which were primarily developed for the analysis of carbonaceous materials such as coal and peat. These standards have governed sample preparation, maceral identification, and point counting procedures since the 1980s. However, modern applications of coal petrography point counting to dispersed organic matter (DOM), particularly in low-TOC samples, have revealed methodological incompatibilities. As a result, significant procedural modifications have been implemented across laboratories, but no universally adopted approach has been established.
To address these challenges, this study proposes and evaluates a point counting method for dispersed organic matter (DOM) using a 21-crosshair grid reticle. The method embeds 21 crosshairs within a 60-μm-diameter region (under 500× magnification) in the microscope system and requires counting at least 300 suitable microscopic fields where all crosshairs fall on sample particles. The use of 21-crosshair grid increases the probability of intersecting DOM in sample particles within pellets. This results in a 68 % reduction in analysis time (from 2.5 h to 1.0 h per sample) compared to when traditional coal petrography point counting is applied to DOM. Furthermore, the use of a denser grid in the 21-crosshair DOM point counting method improves measurement accuracy by more effectively capturing the areas of constituents within sample particles. By requiring the counting of at least 300 suitable microscopic fields, it generates a robust dataset of over 6300 points, achieving strong correlations (R2 > 0.80) between the volume percentage of maceral assemblage and TOC in case studies. The method has been validated in applications such as hydrocarbon potential assessment, solid bitumen characterization, thermal maturity analysis, and depositional environment reconstruction. This paper bridges the gap between traditional standards and modern analytical needs by proposing a standardized, efficient, and reliable method for DOM point counting.
{"title":"Maceral point counting for dispersed organic matter (DOM)","authors":"Zhiheng Zhou, Hamed Sanei","doi":"10.1016/j.coal.2025.104818","DOIUrl":"10.1016/j.coal.2025.104818","url":null,"abstract":"<div><div>Point counting is a widely used quantitative technique in microscopic analysis for estimating the volume percentage of target constituents within a sample. Its application in coal petrography has been standardized through international guidelines such as ISO 7404 and ASTM D2797/D2799, which were primarily developed for the analysis of carbonaceous materials such as coal and peat. These standards have governed sample preparation, maceral identification, and point counting procedures since the 1980s. However, modern applications of coal petrography point counting to dispersed organic matter (DOM), particularly in low-TOC samples, have revealed methodological incompatibilities. As a result, significant procedural modifications have been implemented across laboratories, but no universally adopted approach has been established.</div><div>To address these challenges, this study proposes and evaluates a point counting method for dispersed organic matter (DOM) using a 21-crosshair grid reticle. The method embeds 21 crosshairs within a 60-μm-diameter region (under 500× magnification) in the microscope system and requires counting at least 300 suitable microscopic fields where all crosshairs fall on sample particles. The use of 21-crosshair grid increases the probability of intersecting DOM in sample particles within pellets. This results in a 68 % reduction in analysis time (from 2.5 h to 1.0 h per sample) compared to when traditional coal petrography point counting is applied to DOM. Furthermore, the use of a denser grid in the 21-crosshair DOM point counting method improves measurement accuracy by more effectively capturing the areas of constituents within sample particles. By requiring the counting of at least 300 suitable microscopic fields, it generates a robust dataset of over 6300 points, achieving strong correlations (R<sup>2</sup> > 0.80) between the volume percentage of maceral assemblage and TOC in case studies. The method has been validated in applications such as hydrocarbon potential assessment, solid bitumen characterization, thermal maturity analysis, and depositional environment reconstruction. This paper bridges the gap between traditional standards and modern analytical needs by proposing a standardized, efficient, and reliable method for DOM point counting.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104818"},"PeriodicalIF":5.6,"publicationDate":"2025-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144221678","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}
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