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}
Pub Date : 2025-06-27DOI: 10.1016/j.orggeochem.2025.105045
Guangli Wang , Ying Xu , Yang Yang , Zhirong Zhang , Yuhong Liao
Catalytic hydropyrolysis (HyPy) is an effective method for the release of covalently bound biomarkers from geo-macromolecules (e.g., kerogen or asphaltenes). It is particularly valuable for samples that lack geochemical proxies resulting from extensive maturation or secondary alteration. In this study, HyPy was carried out on asphaltene fractions isolated from crude oils collected from 10 reservoirs of various depths in the Panyu lower uplift in the central Pearl River Mouth Basin, South China Sea. Significant quantities of biomarkers and polycyclic aromatic hydrocarbons (PAHs) were released, and their molecular and isotopic compositions were obtained. The results suggest that these bound compounds were not affected by secondary alteration processes, such as biodegradation in shallow reservoirs or water washing in deeper ones. The δ13C values of the HyPy products were 1.2 ‰–2.2 ‰ more enriched than those of the original bulk oils, and are inconsistent with traditional δ13C patterns (the asphaltene fraction generally has the most enriched δ13C value among petroleum fractions). These reservoirs, therefore, may represent a composite petroleum system involving contributions from multiple source rocks rather than a single source as previously interpreted. This hypothesis is also supported by the molecular and biomarker signatures of the products, which showed elevated proportions of C11–C16n-alkanes and C19 tricyclic terpanes, and a marked dominance of 24-ethylcholestanes (ranging from 52 % to 79 % of total steranes), significantly exceeding the C27 and C28 homologues. A substantial input of organic matter from vascular plants, much higher than that of the presumed source rocks of the Eocene Wenchang Formation, was found. Therefore, the earlier petroleum charges to the Panyu lower uplift may be associated with the Eocene–Oligocene Enping Formation interbedded with coaly source rock intervals. In contrast, the maltenes of the oil samples were rich in 4-methylsteranes, dinosteranes, and triaromatic dinosteroids, as well as minor oleananes, which closely resemble the biomarker signatures of lacustrine source rocks from the Eocene Wenchang Formation. These findings support a dual contribution to the petroleum reservoirs across the Panyu lower uplift, where the major oils concerned with the coaly source rocks of the Enping Formation and the lacustrine shale source rocks of the Wenchang Formation were likely responsible for potential large hydrocarbon accumulations.
{"title":"Multiple sources of petroleum in the Panyu lower uplift evidenced by catalytic hydropyrolysis of petroleum asphaltenes","authors":"Guangli Wang , Ying Xu , Yang Yang , Zhirong Zhang , Yuhong Liao","doi":"10.1016/j.orggeochem.2025.105045","DOIUrl":"10.1016/j.orggeochem.2025.105045","url":null,"abstract":"<div><div>Catalytic hydropyrolysis (HyPy) is an effective method for the release of covalently bound biomarkers from geo-macromolecules (e.g., kerogen or asphaltenes). It is particularly valuable for samples that lack geochemical proxies resulting from extensive maturation or secondary alteration. In this study, HyPy was carried out on asphaltene fractions isolated from crude oils collected from 10 reservoirs of various depths in the Panyu lower uplift in the central Pearl River Mouth Basin, South China Sea. Significant quantities of biomarkers and polycyclic aromatic hydrocarbons (PAHs) were released, and their molecular and isotopic compositions were obtained. The results suggest that these bound compounds were not affected by secondary alteration processes, such as biodegradation in shallow reservoirs or water washing in deeper ones. The δ<sup>13</sup>C values of the HyPy products were 1.2 ‰–2.2 ‰ more enriched than those of the original bulk oils, and are inconsistent with traditional δ<sup>13</sup>C patterns (the asphaltene fraction generally has the most enriched δ<sup>13</sup>C value among petroleum fractions). These reservoirs, therefore, may represent a composite petroleum system involving contributions from multiple source rocks rather than a single source as previously interpreted. This hypothesis is also supported by the molecular and biomarker signatures of the products, which showed elevated proportions of C<sub>11</sub>–C<sub>16</sub> <em>n</em>-alkanes and C<sub>19</sub> tricyclic terpanes, and a marked dominance of 24-ethylcholestanes (ranging from 52 % to 79 % of total steranes), significantly exceeding the C<sub>27</sub> and C<sub>28</sub> homologues. A substantial input of organic matter from vascular plants, much higher than that of the presumed source rocks of the Eocene Wenchang Formation, was found. Therefore, the earlier petroleum charges to the Panyu lower uplift may be associated with the Eocene–Oligocene Enping Formation interbedded with coaly source rock intervals. In contrast, the maltenes of the oil samples were rich in 4-methylsteranes, dinosteranes, and triaromatic dinosteroids, as well as minor oleananes, which closely resemble the biomarker signatures of lacustrine source rocks from the Eocene Wenchang Formation. These findings support a dual contribution to the petroleum reservoirs across the Panyu lower uplift, where the major oils concerned with the coaly source rocks of the Enping Formation and the lacustrine shale source rocks of the Wenchang Formation were likely responsible for potential large hydrocarbon accumulations.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105045"},"PeriodicalIF":2.6,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144489968","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 : 2025-06-26DOI: 10.1016/j.orggeochem.2025.105046
Shi Qian , Huan Yang , Jie Wu , Shucheng Xie , Qinmian Xu
Branched glycerol monoalkyl glycerol tetraethers (brGMGTs, or H-brGDGTs), lipids that occur widely in anoxic sediments of peatlands, lakes, and oceans, have been proposed as new tools for paleotemperature reconstructions in lakes and peatlands. However, their reliability has not been widely assessed, particularly in sediment cores. Here, we report the H-brGDGT distributions in the Xiong'an (XA) 3 sediment core from North China, spanning 5.5 million years (Ma), to evaluate their reliability as a terrestrial paleothermometer. Seven major H-brGDGTs are consistently abundant throughout the sediment core. Their isomerization index (IRH) values, characteristic of river and lake environments, suggest H-brGDGTs were predominantly produced in situ with negligible soil input. Their abundances and distributions are strongly related to a widely used paleothermometer, MBT′5ME (methylation index of branched tetraethers for 5-methylated branched GDGTs), likely indicating their temperature dependence. An H-brGDGT-based temperature proxy, H-MBT′, which includes only the H-1020c and H-1034b isomers, was found to track temperature in both published modern peat/lake H-brGDGT data set and the XA3 sediment core. H-MBT′ reconstructed temperature trend is consistent with the brGDGT temperature record in the sediment core as well as global climate signals, revealing stable warmth during 5.5–2.6 Ma, abrupt cooling at ∼2.6 Ma coinciding with the onset of Northern Hemisphere Glaciation (NHG), and oscillating decline during 2.2–0 Ma. Our results validate H-brGDGTs as a potential paleothermometer in aquatic systems but highlight the need for the selection of proper H-brGDGT-based temperature proxies and environment-specific calibrations to refine accuracy.
{"title":"Assessing the reliability of H-brGDGTs as terrestrial paleothermometers in Plio-Pleistocene fluvio-lacustrine deposits from Northern China","authors":"Shi Qian , Huan Yang , Jie Wu , Shucheng Xie , Qinmian Xu","doi":"10.1016/j.orggeochem.2025.105046","DOIUrl":"10.1016/j.orggeochem.2025.105046","url":null,"abstract":"<div><div>Branched glycerol monoalkyl glycerol tetraethers (brGMGTs, or H-brGDGTs), lipids that occur widely in anoxic sediments of peatlands, lakes, and oceans, have been proposed as new tools for paleotemperature reconstructions in lakes and peatlands. However, their reliability has not been widely assessed, particularly in sediment cores. Here, we report the H-brGDGT distributions in the Xiong'an (XA) 3 sediment core from North China, spanning 5.5 million years (Ma), to evaluate their reliability as a terrestrial paleothermometer. Seven major H-brGDGTs are consistently abundant throughout the sediment core. Their isomerization index (IR<sub>H</sub>) values, characteristic of river and lake environments, suggest H-brGDGTs were predominantly produced <em>in situ</em> with negligible soil input. Their abundances and distributions are strongly related to a widely used paleothermometer, MBT′<sub>5ME</sub> (methylation index of branched tetraethers for 5-methylated branched GDGTs), likely indicating their temperature dependence. An H-brGDGT-based temperature proxy, H-MBT′, which includes only the H-1020c and H-1034b isomers, was found to track temperature in both published modern peat/lake H-brGDGT data set and the XA3 sediment core. H-MBT′ reconstructed temperature trend is consistent with the brGDGT temperature record in the sediment core as well as global climate signals, revealing stable warmth during 5.5–2.6 Ma, abrupt cooling at ∼2.6 Ma coinciding with the onset of Northern Hemisphere Glaciation (NHG), and oscillating decline during 2.2–0 Ma. Our results validate H-brGDGTs as a potential paleothermometer in aquatic systems but highlight the need for the selection of proper H-brGDGT-based temperature proxies and environment-specific calibrations to refine accuracy.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105046"},"PeriodicalIF":2.6,"publicationDate":"2025-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579680","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 : 2025-06-23DOI: 10.1016/j.orggeochem.2025.105044
Rongzhen Qiao, Meijun Li, Donglin Zhang, Hong Xiao
Steranes and terpanes, as key biomarkers in oils and source rock extracts, provide valuable information about their biological origins, depositional environment, and thermal maturity. The distribution patterns of steranes and terpanes in ultra-deep oil reservoirs within the Shuntuoguole low uplift are complex. The intensity of hydrothermal activity and the influence of sulfur ions were assessed based on the conversion of “Biphenyl–Dibenzothiophene–Phenanthrene” series compounds. The results reveal that the southern sections of F5, F12, and F4 exhibit relatively strong hydrothermal activity (F number: No. number fault zone). The southern sections of F5, F1, and F4 are more significantly impacted by sulfur ion activity under the hydrothermal action. Studies indicate that sterane and terpene concentrations decrease due to sulfur ion activity under the hydrothermal action. Tricyclic terpanes, cholestanes, C31-35 homohopanes, C30 hopane, C29 diahopane, and pregnane exhibit low stability under the influence of sulfur ion activity in the hydrothermal action. Notably, although tricyclic terpanes, cholestanes, and pregnane show low stability, they are not preferentially depleted. Combined analysis of the relative Gibbs free energies of C30 diahopane and C30 hopane showed that sulfur ions do not promote pyrolysis by altering the degradation pathways of steranes and terpanes. Instead, sulfur ions likely lower the pyrolysis threshold by reducing the activation energy, preserving the relative stability of steranes and terpanes. This study advances the understanding of organic–inorganic interactions in hydrothermal systems.
{"title":"Sulfur ions reduce the activation energy of steranes and terpanes under hydrothermal action","authors":"Rongzhen Qiao, Meijun Li, Donglin Zhang, Hong Xiao","doi":"10.1016/j.orggeochem.2025.105044","DOIUrl":"10.1016/j.orggeochem.2025.105044","url":null,"abstract":"<div><div>Steranes and terpanes, as key biomarkers in oils and source rock extracts, provide valuable information about their biological origins, depositional environment, and thermal maturity. The distribution patterns of steranes and terpanes in ultra-deep oil reservoirs within the Shuntuoguole low uplift are complex. The intensity of hydrothermal activity and the influence of sulfur ions were assessed based on the conversion of “Biphenyl–Dibenzothiophene–Phenanthrene” series compounds. The results reveal that the southern sections of F5, F12, and F4 exhibit relatively strong hydrothermal activity (F number: No. number fault zone). The southern sections of F5, F1, and F4 are more significantly impacted by sulfur ion activity under the hydrothermal action. Studies indicate that sterane and terpene concentrations decrease due to sulfur ion activity under the hydrothermal action. Tricyclic terpanes, cholestanes, C<sub>31-35</sub> homohopanes, C<sub>30</sub> hopane, C<sub>29</sub> diahopane, and pregnane exhibit low stability under the influence of sulfur ion activity in the hydrothermal action. Notably, although tricyclic terpanes, cholestanes, and pregnane show low stability, they are not preferentially depleted. Combined analysis of the relative Gibbs free energies of C<sub>30</sub> diahopane and C<sub>30</sub> hopane showed that sulfur ions do not promote pyrolysis by altering the degradation pathways of steranes and terpanes. Instead, sulfur ions likely lower the pyrolysis threshold by reducing the activation energy, preserving the relative stability of steranes and terpanes. This study advances the understanding of organic–inorganic interactions in hydrothermal systems.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105044"},"PeriodicalIF":2.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144338788","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 : 2025-05-27DOI: 10.1016/j.orggeochem.2025.105026
Keith F. O’Connor , Melissa A. Berke , Cindy De Jonge , Ellen C. Hopmans , Lori A. Ziolkowski , Darci Rush
Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS2) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS2 analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R2 = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.
{"title":"Occurrence of nucleoside-bacteriohopanepolyol in high latitude soils: evidence of environmental controls on bacterial lipid membrane distributions","authors":"Keith F. O’Connor , Melissa A. Berke , Cindy De Jonge , Ellen C. Hopmans , Lori A. Ziolkowski , Darci Rush","doi":"10.1016/j.orggeochem.2025.105026","DOIUrl":"10.1016/j.orggeochem.2025.105026","url":null,"abstract":"<div><div>Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS<sup>2</sup>) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS<sup>2</sup> analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R<sup>2</sup> = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105026"},"PeriodicalIF":2.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272111","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 : 2025-05-24DOI: 10.1016/j.orggeochem.2025.105025
Georg Scheeder, Christian Ostertag-Henning, Martin Blumenberg
Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of n-alkylated benzenes and toluenes, the phytanyl toluene (and −benzene) is often abundant. In the present study, n-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C22-C24meta-substituted n-alkyl (combined in the ratio as “n”) to phytanyl (“iso”) toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to n-alkyl toluenes systematically decreases with maturity and therefore the “n/(n + iso)” toluene index increases. The relative change is due to both the processes of catalytic formation of n-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the “n/(n + iso)” toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.
{"title":"Abundance of phytanyl and n-alkyl toluenes in petroleum from the Lower Saxony Basin (Germany) provides information on maturity, palaeosettings and sources","authors":"Georg Scheeder, Christian Ostertag-Henning, Martin Blumenberg","doi":"10.1016/j.orggeochem.2025.105025","DOIUrl":"10.1016/j.orggeochem.2025.105025","url":null,"abstract":"<div><div>Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of <em>n</em>-alkylated benzenes and toluenes, the phytanyl toluene (and −benzene) is often abundant. In the present study, <em>n</em>-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C<sub>22</sub>-C<sub>24</sub> <em>meta</em>-substituted <em>n</em>-alkyl (combined in the ratio as “<em>n</em>”) to phytanyl (“<em>iso</em>”) toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to <em>n</em>-alkyl toluenes systematically decreases with maturity and therefore the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index increases. The relative change is due to both the processes of catalytic formation of <em>n</em>-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105025"},"PeriodicalIF":2.6,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123964","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 : 2025-05-21DOI: 10.1016/j.orggeochem.2025.105014
Xiaoyong Yang , Youjun Tang , Peng Sun , Yiming Hu , Haifeng Yang , Feilong Wang
Aryl isoprenoids (AIs), a series of aromatic carotenoid derivatives, have served as significant biomarkers for paleoecology reconstructions. However, the effect of biodegradation on AIs remains unclear to date. Here, a confirmed family of progressively biodegraded oils from the Miaoxi Depression, Bohai Bay Basin was analyzed to investigate the fate of these compounds during severe biodegradation under natural conditions. Two pseudohomologous series with carbon numbers ranging from 13 to 31 and 40 were identified as 2,3,6- and 2,3,4-AIs in the reference oil. The concentrations of total AIs showed a gradual decline with increasing biodegradation but AIs survive in the most severely biodegraded oil (with a PM rank of 8 and an M-MN2 of 983) in this study. The differential proximity of adjacent methyl groups on the benzene ring may result in 2,3,4-AIs being more resistant to biodegradation compared to 2,3,6-AIs. No preferential biodegradation of individual AIs is proceeded systematically by carbon number, which may result from competition of two biodegradation pathways and favor of specific microbial communities. Moreover, the AIs-bearing proxies, including aryl isoprenoid ratio (AIR) and concentrations of total AIs, 2,3,6-AIs and 2,3,4-AIs, exhibit a significant decrease with increasing microbial alteration. Therefore, these proxies must be employed with caution to reconstruct photic-zone euxinia (PZE) for crude oils with potential microbial degradation.
{"title":"Aryl isoprenoids in severe biodegradation oils from the Miaoxi Depression, Bohai Bay Basin","authors":"Xiaoyong Yang , Youjun Tang , Peng Sun , Yiming Hu , Haifeng Yang , Feilong Wang","doi":"10.1016/j.orggeochem.2025.105014","DOIUrl":"10.1016/j.orggeochem.2025.105014","url":null,"abstract":"<div><div>Aryl isoprenoids (AIs), a series of aromatic carotenoid derivatives, have served as significant biomarkers for paleoecology reconstructions. However, the effect of biodegradation on AIs remains unclear to date. Here, a confirmed family of progressively biodegraded oils from the Miaoxi Depression, Bohai Bay Basin was analyzed to investigate the fate of these compounds during severe biodegradation under natural conditions. Two pseudohomologous series with carbon numbers ranging from 13 to 31 and 40 were identified as 2,3,6- and 2,3,4-AIs in the reference oil. The concentrations of total AIs showed a gradual decline with increasing biodegradation but AIs survive in the most severely biodegraded oil (with a PM rank of 8 and an M-MN2 of 983) in this study. The differential proximity of adjacent methyl groups on the benzene ring may result in 2,3,4-AIs being more resistant to biodegradation compared to 2,3,6-AIs. No preferential biodegradation of individual AIs is proceeded systematically by carbon number, which may result from competition of two biodegradation pathways and favor of specific microbial communities. Moreover, the AIs-bearing proxies, including aryl isoprenoid ratio (AIR) and concentrations of total AIs, 2,3,6-AIs and 2,3,4-AIs, exhibit a significant decrease with increasing microbial alteration. Therefore, these proxies must be employed with caution to reconstruct photic-zone euxinia (PZE) for crude oils with potential microbial degradation.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105014"},"PeriodicalIF":2.6,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144105273","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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