Pub Date : 2025-08-26DOI: 10.1016/j.orggeochem.2025.105058
Bei Liu , Maria Mastalerz , Juergen Schieber , David Bish
Clay minerals possess large surface areas and have long been thought to contribute to organic matter (OM) enrichment in black shales through the adsorption of OM in clay mineral interlayers. In this study, we review OM types and their modes of occurrence in fresh muddy sediments and their lithified counterparts, black shales, as well as the potential role of clay-OM interactions during black shale deposition. Solid OM (tens of nanometer- to hundreds of micrometer-scale particles) is the dominant form of OM in fresh muddy sediments and black shales and is too large to be accommodated in the interlayer region (<5 nm) of smectite and interstratified illite/smectite. For this reason alone, it is implausible that an interlayer adsorption mechanism would be responsible for bulk organic carbon preservation in black shales. OM and clay minerals in nature are instead physically associated via the formation of floccules and aggregates, which serve to retard the microbial degradation of OM. The association of OM and clay minerals argues for a reevaluation of the impact of clay minerals on organic carbon preservation in the sedimentary systems and the global carbon cycle.
{"title":"Organic matter enrichment in black shales: How important are clay minerals?","authors":"Bei Liu , Maria Mastalerz , Juergen Schieber , David Bish","doi":"10.1016/j.orggeochem.2025.105058","DOIUrl":"10.1016/j.orggeochem.2025.105058","url":null,"abstract":"<div><div>Clay minerals possess large surface areas and have long been thought to contribute to organic matter (OM) enrichment in black shales through the adsorption of OM in clay mineral interlayers. In this study, we review OM types and their modes of occurrence in fresh muddy sediments and their lithified counterparts, black shales, as well as the potential role of clay-OM interactions during black shale deposition. Solid OM (tens of nanometer- to hundreds of micrometer-scale particles) is the dominant form of OM in fresh muddy sediments and black shales and is too large to be accommodated in the interlayer region (<5 nm) of smectite and interstratified illite/smectite. For this reason alone, it is implausible that an interlayer adsorption mechanism would be responsible for bulk organic carbon preservation in black shales. OM and clay minerals in nature are instead physically associated via the formation of floccules and aggregates, which serve to retard the microbial degradation of OM. The association of OM and clay minerals argues for a reevaluation of the impact of clay minerals on organic carbon preservation in the sedimentary systems and the global carbon cycle.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105058"},"PeriodicalIF":2.5,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218389","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-20DOI: 10.1016/j.orggeochem.2025.105057
Constantin Sandu , Khaled Arouri , Poorna Srinivasan , Estefania Endara Arguello , Assad H. Ghazwani , Ibrahim Atwah
Carbazoles are nitrogen-based aromatic compounds generated from kerogen alongside main oil components and were used in many studies to constrain long migration distances and filling sequences of reservoirs. These compounds have great potential to be used in constraining migration in basin models due to their tendency to selectively change their composition along the migration path. To simulate their generation, a set of kinetic parameters are desired for compound characterization within the basin simulators. This study investigates the generation of carbazoles in Type II-S source rocks through hydrous pyrolysis experiments performed between 275–360 °C, and estimates the kinetic parameters based on the measured composition of pyrolysis products in both expelled and extracted fractions. Up to 870 ppm carbazole concentration was observed in extracted fluids with an average of 27 ppm and up to 70 ppm in expelled fluids but with a much lower average of 3 ppm. Comparing the carbazole yields in the extracted and expelled fractions leads to the conclusion that the bitumen fraction likely represents a primary step in producing carbazoles within the source rock. The kinetic parameters, in the form of activation energy varied between 40 and 70 kcal/mol for the generation process and 50–300 kcal/mol for degradation. Numeric simulations, using the kinetic parameters determined and a generic thermal history for the Arabian Basin, show a differential evolution of each compound that leads to a variation of composition in generated fluids. When compared with field measurements, the modeled composition can be an invaluable tool to constrain petroleum system models.
{"title":"Generation of carbazoles in Type II-S source rocks: Experimental analysis for kinetic parameters estimation","authors":"Constantin Sandu , Khaled Arouri , Poorna Srinivasan , Estefania Endara Arguello , Assad H. Ghazwani , Ibrahim Atwah","doi":"10.1016/j.orggeochem.2025.105057","DOIUrl":"10.1016/j.orggeochem.2025.105057","url":null,"abstract":"<div><div>Carbazoles are nitrogen-based aromatic compounds generated from kerogen alongside main oil components and were used in many studies to constrain long migration distances and filling sequences of reservoirs. These compounds have great potential to be used in constraining migration in basin models due to their tendency to selectively change their composition along the migration path. To simulate their generation, a set of kinetic parameters are desired for compound characterization within the basin simulators. This study investigates the generation of carbazoles in Type II-S source rocks through hydrous pyrolysis experiments performed between 275–360 °C, and estimates the kinetic parameters based on the measured composition of pyrolysis products in both expelled and extracted fractions. Up to 870 ppm carbazole concentration was observed in extracted fluids with an average of 27 ppm and up to 70 ppm in expelled fluids but with a much lower average of 3 ppm. Comparing the carbazole yields in the extracted and expelled fractions leads to the conclusion that the bitumen fraction likely represents a primary step in producing carbazoles within the source rock. The kinetic parameters, in the form of activation energy varied between 40 and 70 kcal/mol for the generation process and 50–300 kcal/mol for degradation. Numeric simulations, using the kinetic parameters determined and a generic thermal history for the Arabian Basin, show a differential evolution of each compound that leads to a variation of composition in generated fluids. When compared with field measurements, the modeled composition can be an invaluable tool to constrain petroleum system models.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105057"},"PeriodicalIF":2.5,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144923053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-20DOI: 10.1016/j.orggeochem.2025.105053
Shangli Liu , Haifeng Gai , Xinyue Shi , Peng Cheng , Tengfei Li , Qin Zhou , Sui Ji , Hui Tian
Total organic carbon (TOC) content is a crucial indicator in shale oil exploration due to its close correlation with shale oil content. However, the proportion of movable oil significantly decreases in high-TOC shales. Herein, eight marine shale samples from the same well, with TOC contents ranging from 1.86 % to 13.78 % and vitrinite reflectance values of 0.8–0.9 %, were analyzed to investigate the effect of TOC content on the occurrence and distribution of retained oils. Sequential extraction with various solvent mixtures revealed that extractable organic matter (EOM), as extracted by n-hexane/toluene (9:1v/v), primarily comprises saturated and aromatic hydrocarbons, which are chemically similar to the oils released by Rock-Eval pyrolysis before 300 °C (S1 peak). Therefore, the EOM is an effective way to evaluate the free oil content in shales. By contrast, the EOMs extracted by dichloromethane/methanol (93:7 v/v) and tetrahydrofuran/acetone/methanol (50:25:25 v/v/v) are mainly composed of resins and asphaltenes that correspond to the oils released during Rock-Eval pyrolysis above 300 °C, indicating their predominant occurrence as adsorbed oil. After sequential extraction, the specific surface area and pore volume of shale samples increase by an average 369 % and 254 %, respectively. Pore structure analysis reveals that organic matter (OM) content significantly affects the occurrence space of retained oil. In the case of early oil window maturity, excessive OM can lead to a low free oil ratio, low storage space, high adsorption capacity, and high threshold pore diameter of movable oil, indicating that excessive OM is unfavorable for the enrichment of movable oil. Therefore, there may be an upper TOC limit for shale oil sweet spots. For our samples, the free oil content significantly decreases when TOC exceeds 10 wt%. This threshold may vary for different shales depending on thermal maturity, kerogen type, and pore structure. Shale dominated by Type I/II kerogen typically exhibit a lower optimal TOC threshold at the main oil generation stage (Cf. Type III kerogen), further emphasizing the importance of identifying these thresholds during exploration.
{"title":"Controls of organic matter content on shale oil occurrence and distribution: Insights from retained oil composition and pore structure in marine shales","authors":"Shangli Liu , Haifeng Gai , Xinyue Shi , Peng Cheng , Tengfei Li , Qin Zhou , Sui Ji , Hui Tian","doi":"10.1016/j.orggeochem.2025.105053","DOIUrl":"10.1016/j.orggeochem.2025.105053","url":null,"abstract":"<div><div>Total organic carbon (TOC) content is a crucial indicator in shale oil exploration due to its close correlation with shale oil content. However, the proportion of movable oil significantly decreases in high-TOC shales. Herein, eight marine shale samples from the same well, with TOC contents ranging from 1.86 % to 13.78 % and vitrinite reflectance values of 0.8–0.9 %, were analyzed to investigate the effect of TOC content on the occurrence and distribution of retained oils. Sequential extraction with various solvent mixtures revealed that extractable organic matter (EOM), as extracted by <em>n</em>-hexane/toluene (9:1v/v), primarily comprises saturated and aromatic hydrocarbons, which are chemically similar to the oils released by Rock-Eval pyrolysis before 300 °C (S<sub>1</sub> peak). Therefore, the EOM is an effective way to evaluate the free oil content in shales. By contrast, the EOMs extracted by dichloromethane/methanol (93:7 v/v) and tetrahydrofuran/acetone/methanol (50:25:25 v/v/v) are mainly composed of resins and asphaltenes that correspond to the oils released during Rock-Eval pyrolysis above 300 °C, indicating their predominant occurrence as adsorbed oil. After sequential extraction, the specific surface area and pore volume of shale samples increase by an average 369 % and 254 %, respectively. Pore structure analysis reveals that organic matter (OM) content significantly affects the occurrence space of retained oil. In the case of early oil window maturity, excessive OM can lead to a low free oil ratio, low storage space, high adsorption capacity, and high threshold pore diameter of movable oil, indicating that excessive OM is unfavorable for the enrichment of movable oil. Therefore, there may be an upper TOC limit for shale oil sweet spots. For our samples, the free oil content significantly decreases when TOC exceeds 10 wt%. This threshold may vary for different shales depending on thermal maturity, kerogen type, and pore structure. Shale dominated by Type I/II kerogen typically exhibit a lower optimal TOC threshold at the main oil generation stage (Cf. Type III kerogen), further emphasizing the importance of identifying these thresholds during exploration.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105053"},"PeriodicalIF":2.5,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144880327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-18DOI: 10.1016/j.orggeochem.2025.105056
Simon T. Belt , Lukas Smik , Katrine Husum , Jochen Knies
Two tri-unsaturated and isomeric (E/Z) highly branched isoprenoid (HBI) diatom lipid biomarkers were quantified in 228 water column samples collected from the English Channel, West Svalbard (Arctic), the Scotia Sea (Southern Ocean) and East Antarctica. We found that the relative amounts of the two HBIs correlate well with water temperatures taken at the time of sampling. Based on these findings and some other HBI data reported previously, we suggest that the proportion of the HBI E-isomer (termed EZ25) may serve as a new proxy for palaeo sea surface temperatures, including in the polar regions. Next steps will involve determination of EZ25 in surface and downcore sediments to ascertain whether the temperature response described herein translates well to the geological record.
对采集自英吉利海峡、西斯瓦尔巴群岛（北极）、斯科舍海（南大洋）和东南极洲的228个水柱样品进行了两种三不饱和异构（E/Z）高支化类异戊二烯（HBI）硅藻脂类生物标志物的定量分析。我们发现，两种hbi的相对量与采样时的水温有很好的相关性。基于这些发现和先前报道的其他一些HBI数据，我们认为HBI e -异构体的比例（称为EZ25）可能作为古海面温度的新代表，包括在极地地区。下一步将包括测定地表和核心沉积物中的EZ25，以确定本文描述的温度响应是否能很好地转化为地质记录。
{"title":"A potential new sea surface temperature proxy based on isomeric highly branched isoprenoid lipid biomarkers: EZ25","authors":"Simon T. Belt , Lukas Smik , Katrine Husum , Jochen Knies","doi":"10.1016/j.orggeochem.2025.105056","DOIUrl":"10.1016/j.orggeochem.2025.105056","url":null,"abstract":"<div><div>Two tri-unsaturated and isomeric (<em>E</em>/<em>Z</em>) highly branched isoprenoid (HBI) diatom lipid biomarkers were quantified in 228 water column samples collected from the English Channel, West Svalbard (Arctic), the Scotia Sea (Southern Ocean) and East Antarctica. We found that the relative amounts of the two HBIs correlate well with water temperatures taken at the time of sampling. Based on these findings and some other HBI data reported previously, we suggest that the proportion of the HBI <em>E</em>-isomer (termed EZ<sub>25</sub>) may serve as a new proxy for palaeo sea surface temperatures, including in the polar regions. Next steps will involve determination of EZ<sub>25</sub> in surface and downcore sediments to ascertain whether the temperature response described herein translates well to the geological record.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105056"},"PeriodicalIF":2.5,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-05DOI: 10.1016/j.orggeochem.2025.105054
Luke M. Brosnan , Stephen F. Poropat , Madison Tripp , Sebastian Stanley , Peter Hopper , Xiao Sun , William D.A. Rickard , Antônio Á.F. Saraiva , Renan A.M. Bantim , Juliana M. Sayão , Alexander W.A. Kellner , Kliti Grice
Paraloid® resins, particularly Paraloid® B-72, are widely used in palaeontological preparation to stabilise fossils. However, their presence may interfere with organic geochemical analyses. To evaluate this, standard biomarker extraction protocols were applied to pure Paraloid® B-72, to a fossil bone previously treated with the resin, and to commercial grade acetone commonly used as its solvent. The resin was mobilised by dichloromethane-containing solvent mixtures during extraction and fractionation. Despite this, saturated and aromatic biomarkers were successfully isolated since the polyacrylate resin is insoluble in non-polar solvents. Paraloid® B-72 predominately eluted into the aromatic and polar fractions, but did not significantly impact saturated biomarker profiles. Insoluble residues isolated from these fractions analysed by flash pyrolysis–gas chromatography–mass spectrometry revealed compounds mainly from the resin. Microwave assisted solvent extraction appears to effectively separate Paraloid® B-72 from fossils, as no resin-derived monomers were detected in the extracted fossil pyrolysate. This suggests that the insoluble organic fraction of resin-stabilised fossils can be reliably studied using biomarker techniques with minimal interference. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) analysis produced abundant organic fragments from Paraloid® B-72, but mapping specific oxygen-bearing peaks associated with the resin may allow researchers to distinguish regions containing indigenous organics from those contaminated by the consolidant. These findings indicate that, with appropriate analytical approaches, both soluble and insoluble organic fractions of Paraloid®-treated fossils can yield valid biomarker data, enabling chemical analysis of specimens previously deemed unsuitable due to conservation treatments.
{"title":"Can useful biomarker information be obtained from museum fossil specimens treated with Paraloid® B-72 acrylic resin?","authors":"Luke M. Brosnan , Stephen F. Poropat , Madison Tripp , Sebastian Stanley , Peter Hopper , Xiao Sun , William D.A. Rickard , Antônio Á.F. Saraiva , Renan A.M. Bantim , Juliana M. Sayão , Alexander W.A. Kellner , Kliti Grice","doi":"10.1016/j.orggeochem.2025.105054","DOIUrl":"10.1016/j.orggeochem.2025.105054","url":null,"abstract":"<div><div>Paraloid® resins, particularly Paraloid® B-72, are widely used in palaeontological preparation to stabilise fossils. However, their presence may interfere with organic geochemical analyses. To evaluate this, standard biomarker extraction protocols were applied to pure Paraloid® B-72, to a fossil bone previously treated with the resin, and to commercial grade acetone commonly used as its solvent. The resin was mobilised by dichloromethane-containing solvent mixtures during extraction and fractionation. Despite this, saturated and aromatic biomarkers were successfully isolated since the polyacrylate resin is insoluble in non-polar solvents. Paraloid® B-72 predominately eluted into the aromatic and polar fractions, but did not significantly impact saturated biomarker profiles. Insoluble residues isolated from these fractions analysed by flash pyrolysis–gas chromatography–mass spectrometry revealed compounds mainly from the resin. Microwave assisted solvent extraction appears to effectively separate Paraloid® B-72 from fossils, as no resin-derived monomers were detected in the extracted fossil pyrolysate. This suggests that the insoluble organic fraction of resin-stabilised fossils can be reliably studied using biomarker techniques with minimal interference. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) analysis produced abundant organic fragments from Paraloid® B-72, but mapping specific oxygen-bearing peaks associated with the resin may allow researchers to distinguish regions containing indigenous organics from those contaminated by the consolidant. These findings indicate that, with appropriate analytical approaches, both soluble and insoluble organic fractions of Paraloid®-treated fossils can yield valid biomarker data, enabling chemical analysis of specimens previously deemed unsuitable due to conservation treatments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105054"},"PeriodicalIF":2.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144842815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-31DOI: 10.1016/j.orggeochem.2025.105047
{"title":"Obituary for Prof. Dr. Dietrich Welte (1935–2025)","authors":"","doi":"10.1016/j.orggeochem.2025.105047","DOIUrl":"10.1016/j.orggeochem.2025.105047","url":null,"abstract":"","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"209 ","pages":"Article 105047"},"PeriodicalIF":2.5,"publicationDate":"2025-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145061217","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-30DOI: 10.1016/j.orggeochem.2025.105052
Bin Cheng , Guocong Sun , An Xie , Jie Sun , Xinxin Bo , Xin Tian
The identification of secondary alteration processes in Jurassic reservoirs of the Turpan Depression and the contribution of petroleum from Permian sources remains largely unexplored. This study, based on geochemical analyses of representative oil and condensate samples, systematically integrates carbon isotope data, biomarkers, C5-C7 light hydrocarbon, and diamondoids compositions to identify secondary alterations and assess the contribution of hydrocarbons derived from Permian source rocks. The results reveal that the Jurassic oil reservoirs of wells Y7 and Qt1 have undergone extensive biodegradation, followed by subsequent oil mixing processes with slight to moderate biodegraded oils and fresh, unaltered oils, respectively. Evaporative fractionation is frequently observed in the Jurassic reservoirs, although the degree of its occurrence varies considerably. Reservoirs in the Shengbei sub-sag experienced more intense alteration compared to those in other sub-sags, with the Sb3 and Sb5 reservoirs exhibiting the highest degrees of alteration. Thermal maturity evaluations, based on saturated, aromatic, and light hydrocarbons, reveal that most samples range from peak to late oil-generation stages. Some light oils and condensates have progressed toward the condensate/wet gas stage because of higher maturity charging events. Correlation analysis indicates the coexistence of three end-member oil and condensate families within the Jurassic reservoirs, those generated from Jurassic coal-measure source rocks, those derived from Jurassic Qiketai source rocks, and those originating from Middle Permian source rocks, further suggesting that the Permian-origin hydrocarbons have made a substantial contribution to the Jurassic reservoirs in some regions, despite being generated at varying thermal maturity stages. Overall, the Jurassic oil reservoirs in the Turpan Depression have undergone multiple secondary alteration processes and experienced complex charging events from both Jurassic and Permian source rocks, resulting in a highly complicated hydrocarbon accumulation mechanisms.
{"title":"Secondary alteration and probable sources of oils and condensates in Jurassic reservoirs of the Turpan Depression, Turpan-Hami Basin, NW China","authors":"Bin Cheng , Guocong Sun , An Xie , Jie Sun , Xinxin Bo , Xin Tian","doi":"10.1016/j.orggeochem.2025.105052","DOIUrl":"10.1016/j.orggeochem.2025.105052","url":null,"abstract":"<div><div>The identification of secondary alteration processes in Jurassic reservoirs of the Turpan Depression and the contribution of petroleum from Permian sources remains largely unexplored. This study, based on geochemical analyses of representative oil and condensate samples, systematically integrates carbon isotope data, biomarkers, C<sub>5</sub>-C<sub>7</sub> light hydrocarbon, and diamondoids compositions to identify secondary alterations and assess the contribution of hydrocarbons derived from Permian source rocks. The results reveal that the Jurassic oil reservoirs of wells Y7 and Qt1 have undergone extensive biodegradation, followed by subsequent oil mixing processes with slight to moderate biodegraded oils and fresh, unaltered oils, respectively. Evaporative fractionation is frequently observed in the Jurassic reservoirs, although the degree of its occurrence varies considerably. Reservoirs in the Shengbei sub-sag experienced more intense alteration compared to those in other sub-sags, with the Sb3 and Sb5 reservoirs exhibiting the highest degrees of alteration. Thermal maturity evaluations, based on saturated, aromatic, and light hydrocarbons, reveal that most samples range from peak to late oil-generation stages. Some light oils and condensates have progressed toward the condensate/wet gas stage because of higher maturity charging events. Correlation analysis indicates the coexistence of three end-member oil and condensate families within the Jurassic reservoirs, those generated from Jurassic coal-measure source rocks, those derived from Jurassic Qiketai source rocks, and those originating from Middle Permian source rocks, further suggesting that the Permian-origin hydrocarbons have made a substantial contribution to the Jurassic reservoirs in some regions, despite being generated at varying thermal maturity stages. Overall, the Jurassic oil reservoirs in the Turpan Depression have undergone multiple secondary alteration processes and experienced complex charging events from both Jurassic and Permian source rocks, resulting in a highly complicated hydrocarbon accumulation mechanisms.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105052"},"PeriodicalIF":2.5,"publicationDate":"2025-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144724532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-23DOI: 10.1016/j.orggeochem.2025.105049
Ziao Geng , Meijun Li , Shuichang Zhang , Shengbao Shi , Wenqiang Wang , Lei Zhu , Tiantian Li , Jianfeng Zhang
This study analyzes the δ13C values of various polycyclic aromatic compounds (PACs), including dibenzofuran, and methyldibenzofurans in two sets of coals from the Junggar and Ordos basins in NW China. The results reveal that the δ13C values of individual PACs are primarily influenced by the source of degraded organic matter rather than thermal maturity. The significant differences in δ13C values (−11.7 ‰) between dibenzofuran (DBF) and its methylated homologues (MDBFs) imply different sources. DBF is primarily derived from higher plants, while MDBFs have multiple sources from both lichens and higher plants. However, the δ13C values of DBF and MDBF in predominantly pyrogenic samples are relatively similar. This is due to two factors: (1) The kinetic isotope effect leads to preferential demethylation of 12C-enriched MDBF isomers, and the residual MDBFs are consequently enriched in 13C isotopes. The DBF produced by this process is enriched in 12C isotope, leading to depletion of δ13C for DBF in the combustion products. (2) Greater higher plant than lichen inputs result in higher δ13C values of MDBFs also potentially causes lower δ13C values in DBF. These two factors combine to produce similar δ13C values for DBF and MDBFs in samples heavily affected by wildfires.
{"title":"Geochemical implications of the carbon isotope compositions of individual polycyclic aromatic compounds in coals from the Junggar and Ordos basins, NW China","authors":"Ziao Geng , Meijun Li , Shuichang Zhang , Shengbao Shi , Wenqiang Wang , Lei Zhu , Tiantian Li , Jianfeng Zhang","doi":"10.1016/j.orggeochem.2025.105049","DOIUrl":"10.1016/j.orggeochem.2025.105049","url":null,"abstract":"<div><div>This study analyzes the δ<sup>13</sup>C values of various polycyclic aromatic compounds (PACs), including dibenzofuran, and methyldibenzofurans in two sets of coals from the Junggar and Ordos basins in NW China. The results reveal that the δ<sup>13</sup>C values of individual PACs are primarily influenced by the source of degraded organic matter rather than thermal maturity. The significant differences in δ<sup>13</sup>C values (−11.7 ‰) between dibenzofuran (DBF) and its methylated homologues (MDBFs) imply different sources. DBF is primarily derived from higher plants, while MDBFs have multiple sources from both lichens and higher plants. However, the δ<sup>13</sup>C values of DBF and MDBF in predominantly pyrogenic samples are relatively similar. This is due to two factors: (1) The kinetic isotope effect leads to preferential demethylation of <sup>12</sup>C-enriched MDBF isomers, and the residual MDBFs are consequently enriched in <sup>13</sup>C isotopes. The DBF produced by this process is enriched in <sup>12</sup>C isotope, leading to depletion of δ<sup>13</sup>C for DBF in the combustion products. (2) Greater higher plant than lichen inputs result in higher δ<sup>13</sup>C values of MDBFs also potentially causes lower δ<sup>13</sup>C values in DBF. These two factors combine to produce similar δ<sup>13</sup>C values for DBF and MDBFs in samples heavily affected by wildfires.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105049"},"PeriodicalIF":2.6,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144687102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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