Pub Date : 2025-05-05DOI: 10.1016/j.orggeochem.2025.105013
Francien Peterse , Klaas G.J. Nierop , Nicole J. Bale , Sarah J. Feakins , Chan-Mao Chen
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a suite of membrane lipids that are widely used as empirical proxies for past temperature and pH. Although the stereochemistry of their glycerol moiety suggests that they are produced by bacteria, the exact producers and the biosynthetic pathway of brGDGTs remain unclear. Here we report the occurrence of tetraester and mixed ester/ether membrane-spanning lipids with a backbone consisting of iso-diabolic acid (iso-DA) containing up to two additional methyl groups in high-elevation (>1900 masl), acidic (pH < 4.5) mineral soils from Nepal and Rwanda. These compounds are presumed intermediate products during brGDGT synthesis but had not been detected in cultures or the environment before. Interestingly, while acid hydrolysis of the GDGT fraction releases iso-DA in the soil from Nepal, monoalkyl glycerol ethers with iso-C15 and iso-C17 chains are released in the soil from Rwanda. Although speculative, these results could support both current hypotheses that brGDGT synthesis can occur via tail-to-tail condensation of two iso-C15 fatty acids to form iso-DA, as well as through the reduction of diesters to diethers and subsequent carbon–carbon linking as shown to occur during the synthesis of archaeal GDGTs.
{"title":"Occurrence of tetraester and mixed ether/ester-bound iso-diabolic acid membrane-spanning lipids in acidic, high-elevation mineral soils","authors":"Francien Peterse , Klaas G.J. Nierop , Nicole J. Bale , Sarah J. Feakins , Chan-Mao Chen","doi":"10.1016/j.orggeochem.2025.105013","DOIUrl":"10.1016/j.orggeochem.2025.105013","url":null,"abstract":"<div><div>Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a suite of membrane lipids that are widely used as empirical proxies for past temperature and pH. Although the stereochemistry of their glycerol moiety suggests that they are produced by bacteria, the exact producers and the biosynthetic pathway of brGDGTs remain unclear. Here we report the occurrence of tetraester and mixed ester/ether membrane-spanning lipids with a backbone consisting of <em>iso</em>-diabolic acid (<em>iso</em>-DA) containing up to two additional methyl groups in high-elevation (>1900 masl), acidic (pH < 4.5) mineral soils from Nepal and Rwanda. These compounds are presumed intermediate products during brGDGT synthesis but had not been detected in cultures or the environment before. Interestingly, while acid hydrolysis of the GDGT fraction releases <em>iso</em>-DA in the soil from Nepal, monoalkyl glycerol ethers with <em>iso</em>-C<sub>15</sub> and <em>iso</em>-C<sub>17</sub> chains are released in the soil from Rwanda. Although speculative, these results could support both current hypotheses that brGDGT synthesis can occur via tail-to-tail condensation of two <em>iso</em>-C<sub>15</sub> fatty acids to form <em>iso</em>-DA, as well as through the reduction of diesters to diethers and subsequent carbon–carbon linking as shown to occur during the synthesis of archaeal GDGTs.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105013"},"PeriodicalIF":2.6,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071340","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 : 2025-05-03DOI: 10.1016/j.orggeochem.2025.105012
Yang Qin , Chiyang Liu , Junfeng Zhao , Faqi He , Wei Zhang , Lihua Yang , Nan Du , Deyong Shao
The Hangjinqi gas field, a vital tight sandstone gas field on the northern Ordos Basin margin, exhibits a debatable gas origin and accumulation mechanism. Integrating geochemical analyses with gas field data for basin-wide comparisons allows us to resolve the origin of the reservoired gas. Results reveal that the Upper Paleozoic coal-measure source rocks in the Hangjinqi area share similar characteristics with those in other Upper Paleozoic gas fields, where coal seams constitute the primary effective source rocks. However, they exhibit limited hydrocarbon-generating potential coupled with low thermal maturity. Natural gas has a broad range of dryness coefficient values. The carbon-hydrogen isotopes mostly exhibit a positive carbon-hydrogen isotope series, yet 40% of the samples display ethane and propane carbon-hydrogen isotope reversals. The C5-7 and C7 light hydrocarbons are dominated by isoalkanes and methylcyclohexane, respectively. The natural gas data follow the aromatic curve in the cross-plot of the heptane and isoheptane values. The natural gas in the Hangjinqi field is typical coal-derived gas, which is derived primarily from the Carboniferous-Permian transitional facies of humic organic matter, similar to Daniudi and other gas fields. Notably, the natural gas in the Hangjinqi gas field has undergone migration and dissipation (mainly including escape and loss). The Hangjinqi gas field presents an apparent contradiction between low maturity source rocks and high maturity natural gas. Its methane carbon isotope values significantly exceed those of the Daniudi gas field but align closely with those of the Sulige and Wushenqi gas fields, which are mature-type gas fields. Natural gas migration-dissipation is not the controlling factor in regional isotopic signatures. Therefore, approximately 40–76 % of the natural gas in the Hangjinqi gas field is exogenous gas. Moreover, these exogenous gases are derived primarily from the Sulige-Wushenqi gas field to its south, indicating strong genetic affinity. Overall, most Upper Paleozoic gas fields in the Ordos Basin have short migration distances, whereas the Hangjinqi gas field represents mixtures of locally generated hydrocarbons with gases migrating longer distances.
{"title":"Unravelling the origin of gas in tight sandstones of the Hangjinqi gas field, Ordos Basin, China: New insights from natural gas geochemistry data","authors":"Yang Qin , Chiyang Liu , Junfeng Zhao , Faqi He , Wei Zhang , Lihua Yang , Nan Du , Deyong Shao","doi":"10.1016/j.orggeochem.2025.105012","DOIUrl":"10.1016/j.orggeochem.2025.105012","url":null,"abstract":"<div><div>The Hangjinqi gas field, a vital tight sandstone gas field on the northern Ordos Basin margin, exhibits a debatable gas origin and accumulation mechanism. Integrating geochemical analyses with gas field data for basin-wide comparisons allows us to resolve the origin of the reservoired gas. Results reveal that the Upper Paleozoic coal-measure source rocks in the Hangjinqi area share similar characteristics with those in other Upper Paleozoic gas fields, where coal seams constitute the primary effective source rocks. However, they exhibit limited hydrocarbon-generating potential coupled with low thermal maturity. Natural gas has a broad range of dryness coefficient values. The carbon-hydrogen isotopes mostly exhibit a positive carbon-hydrogen isotope series, yet 40% of the samples display ethane and propane carbon-hydrogen isotope reversals. The C<sub>5-7</sub> and C<sub>7</sub> light hydrocarbons are dominated by isoalkanes and methylcyclohexane, respectively. The natural gas data follow the aromatic curve in the cross-plot of the heptane and isoheptane values. The natural gas in the Hangjinqi field is typical coal-derived gas, which is derived primarily from the Carboniferous-Permian transitional facies of humic organic matter, similar to Daniudi and other gas fields. Notably, the natural gas in the Hangjinqi gas field has undergone migration and dissipation (mainly including escape and loss). The Hangjinqi gas field presents an apparent contradiction between low maturity source rocks and high maturity natural gas. Its methane carbon isotope values significantly exceed those of the Daniudi gas field but align closely with those of the Sulige and Wushenqi gas fields, which are mature-type gas fields. Natural gas migration-dissipation is not the controlling factor in regional isotopic signatures. Therefore, approximately 40–76 % of the natural gas in the Hangjinqi gas field is exogenous gas. Moreover, these exogenous gases are derived primarily from the Sulige-Wushenqi gas field to its south, indicating strong genetic affinity. Overall, most Upper Paleozoic gas fields in the Ordos Basin have short migration distances, whereas the Hangjinqi gas field represents mixtures of locally generated hydrocarbons with gases migrating longer distances.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105012"},"PeriodicalIF":2.6,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899459","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 : 2025-05-01DOI: 10.1016/j.orggeochem.2025.105009
Yin Fu , Zuodong Wang , Ting Zhang , Wenjun Wang , Yongli Wang , Wang Zhang , Xiaobin Li , Zhiyong Wang
The Permian Lucaogou Formation shales are world-class source rocks with diverse biological, environmental, and economic properties. Considerable attention has been given to depositional environmental controls on organic matter enrichment. Here, we present a systematic organic and inorganic geochemical analysis of fresh core samples taken from the Lucaogou Formation in the Malu 1 well, located in the Santanghu Basin. The organic matter source of Lucaogou shale is dominated by prokaryotic organisms. γ- and β-carotanes are present in high abundance; lower carbon number carotenoids are also detected. Based on the distribution of n-alkanes, terpanes, and steranes, it is believed that γ-carotane and β-carotane mainly originate from bacteria. Low-carbon carotenoid-derived alkanes could result from the thermal decomposition products of γ-carotane and β-carotane. The minor input of terrigenous clastic material brought elemental nutrients that likely enhanced biotic productivity. Based on organic and inorganic data, the depositional environment can be defined by two stages (I and II). The contribution of green algae increases from Stage I to Stage II. The Stage I organic matter enrichment is controlled by the state of preservation, and the Stage II organic matter is interpreted to be controlled by biotic productivity. The depositional environment and the productivity of the lake have changed synergistically, together controlling the enrichment of organic matter in the Lucaogou shales.
{"title":"A saline lacustrine depositional environment enhances organic matter enrichment in the Permian Lucaogou shales","authors":"Yin Fu , Zuodong Wang , Ting Zhang , Wenjun Wang , Yongli Wang , Wang Zhang , Xiaobin Li , Zhiyong Wang","doi":"10.1016/j.orggeochem.2025.105009","DOIUrl":"10.1016/j.orggeochem.2025.105009","url":null,"abstract":"<div><div>The Permian Lucaogou Formation shales are world-class source rocks with diverse biological, environmental, and economic properties. Considerable attention has been given to depositional environmental controls on organic matter enrichment. Here, we present a systematic organic and inorganic geochemical analysis of fresh core samples taken from the Lucaogou Formation in the Malu 1 well, located in the Santanghu Basin. The organic matter source of Lucaogou shale is dominated by prokaryotic organisms. γ- and β-carotanes are present in high abundance; lower carbon number carotenoids are also detected. Based on the distribution of <em>n</em>-alkanes, terpanes, and steranes, it is believed that γ-carotane and β-carotane mainly originate from bacteria. Low-carbon carotenoid-derived alkanes could result from the thermal decomposition products of γ-carotane and β-carotane. The minor input of terrigenous clastic material brought elemental nutrients that likely enhanced biotic productivity. Based on organic and inorganic data, the depositional environment can be defined by two stages (I and II). The contribution of green algae increases from Stage I to Stage II. The Stage I organic matter enrichment is controlled by the state of preservation, and the Stage II organic matter is interpreted to be controlled by biotic productivity. The depositional environment and the productivity of the lake have changed synergistically, together controlling the enrichment of organic matter in the Lucaogou shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105009"},"PeriodicalIF":2.6,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143890857","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 : 2025-04-29DOI: 10.1016/j.orggeochem.2025.104991
Biqing Zhu , Quanyou Liu , Huiyuan Xu , Dongya Zhu , Jingbin Wang , Xiaoqi Wu , Pengpeng Li , Yongqi Ruan
The Lower Cambrian organic-rich mudstones preserve extensive records of microbial life, potentially contributing to the ‘Cambrian explosion’ (∼540 to 520 Ma) and the formation of ancient petroleum resources. However, the link of organic δ13C variations to microbial communities in the Lower Cambrian Formation within the Tarim Craton, part of the Central Asian Orogenic Belt, remains incompletely understood. Here, we conducted a comprehensive biomarker and δ13C analysis of mudstone extracts. The prevalence of eukaryotic organisms relative to prokaryotes, together with increased primary productivity, results in substantial 12C enrichment in organic matter, with the converse relationship being equally valid. The Lower Cambrian mudstones formed in more reducing yet confined stratified environments. The presence of cholestane, ergostane, stigmasterane, and 4-methylsterane (e.g., dinosterane) indicates the occurrence of red algae, prasinophytes, green algae, and dinoflagellates, respectively. Notably, the predominance of ergosterane and stigmasterane over cholestane suggests a greater contribution from green algae over red algae. The even-carbon preference across the C14-C20 range is indicative of limited contributions from Gloeocapsomorpha prisca. The presence of 3β-methylhopane, 7-+8-monomethylheptadecane and 2α-methylhopane points to contributions from methanotrophs and cyanobacteria. Since methanotrophs are active in an oxygen- and sulfate-depleted environment, we speculate that 13C-rich organic matter with a high value of 3-methylhopane index (3-MHI) may be deposited in waters with expanded anoxic zones and a scarcity of photoautotrophic sulfur bacteria (e.g., Chlorobiaceae and Chromatiaceae). This study highlights the constraints of microbial communities on organic δ13C variations and enhances our understanding of the evolution of ecology and primary productivity during the Precambrian-Cambrian transition.
{"title":"Microbial communities constrain the organic δ13C variations in the Lower Cambrian mudstones","authors":"Biqing Zhu , Quanyou Liu , Huiyuan Xu , Dongya Zhu , Jingbin Wang , Xiaoqi Wu , Pengpeng Li , Yongqi Ruan","doi":"10.1016/j.orggeochem.2025.104991","DOIUrl":"10.1016/j.orggeochem.2025.104991","url":null,"abstract":"<div><div>The Lower Cambrian organic-rich mudstones preserve extensive records of microbial life, potentially contributing to the ‘Cambrian explosion’ (∼540 to 520 Ma) and the formation of ancient petroleum resources. However, the link of organic δ<sup>13</sup>C variations to microbial communities in the Lower Cambrian Formation within the Tarim Craton, part of the Central Asian Orogenic Belt, remains incompletely understood. Here, we conducted a comprehensive biomarker and δ<sup>13</sup>C analysis of mudstone extracts. The prevalence of eukaryotic organisms relative to prokaryotes, together with increased primary productivity, results in substantial <sup>12</sup>C enrichment in organic matter, with the converse relationship being equally valid. The Lower Cambrian mudstones formed in more reducing yet confined stratified environments. The presence of cholestane, ergostane, stigmasterane, and 4-methylsterane (e.g., dinosterane) indicates the occurrence of red algae, prasinophytes, green algae, and dinoflagellates, respectively. Notably, the predominance of ergosterane and stigmasterane over cholestane suggests a greater contribution from green algae over red algae. The even-carbon preference across the C<sub>14</sub>-C<sub>20</sub> range is indicative of limited contributions from <em>Gloeocapsomorpha prisca</em>. The presence of 3β-methylhopane, 7-+8-monomethylheptadecane and 2α-methylhopane points to contributions from methanotrophs and cyanobacteria. Since methanotrophs are active in an oxygen- and sulfate-depleted environment, we speculate that <sup>13</sup>C-rich organic matter with a high value of 3-methylhopane index (3-MHI) may be deposited in waters with expanded anoxic zones and a scarcity of photoautotrophic sulfur bacteria (e.g., <em>Chlorobiaceae</em> and <em>Chromatiaceae</em>). This study highlights the constraints of microbial communities on organic δ<sup>13</sup>C variations and enhances our understanding of the evolution of ecology and primary productivity during the Precambrian-Cambrian transition.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104991"},"PeriodicalIF":2.6,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143882916","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 : 2025-04-29DOI: 10.1016/j.orggeochem.2025.105007
Huiyuan Xu , Jian Ma , Kai Mangelsdorf
The aim of this special issue is to highlight the contributions of early-career scientists in the field of organic geochemistry, showcasing their innovative ideas, state-of-the-art research methods, and novel findings. By covering a wide range of topics, from petroleum geochemistry to palaeoenvironmental reconstruction, this issue seeks to advance our understanding of the Earth system through molecular fingerprint and isotopic geochemistry. Interdisciplinary studies that bridge geological, ecological, and environmental processes are particularly encouraged, reinforcing the role of organic geochemistry as a critical tool in modern Earth sciences.
{"title":"Introduction to Xplorer, Hybrid and Early-Career Virtual Special Issue","authors":"Huiyuan Xu , Jian Ma , Kai Mangelsdorf","doi":"10.1016/j.orggeochem.2025.105007","DOIUrl":"10.1016/j.orggeochem.2025.105007","url":null,"abstract":"<div><div>The aim of this special issue is to highlight the contributions of early-career scientists in the field of organic geochemistry, showcasing their innovative ideas, state-of-the-art research methods, and novel findings. By covering a wide range of topics, from petroleum geochemistry to palaeoenvironmental reconstruction, this issue seeks to advance our understanding of the Earth system through molecular fingerprint and isotopic geochemistry. Interdisciplinary studies that bridge geological, ecological, and environmental processes are particularly encouraged, reinforcing the role of organic geochemistry as a critical tool in modern Earth sciences.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 105007"},"PeriodicalIF":2.6,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143882863","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 : 2025-04-24DOI: 10.1016/j.orggeochem.2025.104996
Yiliang Hu , Yuan Bao , Jiahao Meng , Dan Li , Ruihui Zheng
Laboratory biodegradation experiments of organic matter (OM) in coal provide a theoretical foundation for comprehending the formation of secondary biogenic gas (SBG). However, limited research has been conducted on the microbial degradation extent and sequence of OM degradation experienced by underground coal seams throughout geological history. This study analyzes underground coal samples from the typical SBG accumulation areas in the Ordos Basin to investigate the origin and composition of OM in coal as well as their contributions to SBG formation. The findings indicate that terrigenous input is the primary source of OM in coal in these regions, which has undergone varying degrees of biodegradation. Notably, there are significant differences in the degree of biodegradation between saturated and aromatic hydrocarbons. Saturated hydrocarbons show PM grade 4–5 degradation while aromatics demonstrate PM grade 5–7 degradation. Aromatics display a higher susceptibility to biodegradation compared to saturated hydrocarbons, which differs significantly from crude oil. The degradation susceptibility sequence for saturated hydrocarbons is as follows: n-alkane > sterane > hopane. The biodegradation susceptibility of aromatic hydrocarbons depends on both the number of aromatic rings and alkyl-substituents; those with fewer rings and alkyl-substituents degrade more rapidly. Biodegradation of OM in coal plays a crucial role in SBG generation; however, a high degree of OM biodegradation does not necessarily correlate with greater accumulation of SBG due to other factors such as tectonic fractures and hydrogeological conditions that affect its preservation.
{"title":"Biodegradation sequence of coal organic matter and mechanism of biomethane formation in secondary biogenic gas accumulation areas","authors":"Yiliang Hu , Yuan Bao , Jiahao Meng , Dan Li , Ruihui Zheng","doi":"10.1016/j.orggeochem.2025.104996","DOIUrl":"10.1016/j.orggeochem.2025.104996","url":null,"abstract":"<div><div>Laboratory biodegradation experiments of organic matter (OM) in coal provide a theoretical foundation for comprehending the formation of secondary biogenic gas (SBG). However, limited research has been conducted on the microbial degradation extent and sequence of OM degradation experienced by underground coal seams throughout geological history. This study analyzes underground coal samples from the typical SBG accumulation areas in the Ordos Basin to investigate the origin and composition of OM in coal as well as their contributions to SBG formation. The findings indicate that terrigenous input is the primary source of OM in coal in these regions, which has undergone varying degrees of biodegradation. Notably, there are significant differences in the degree of biodegradation between saturated and aromatic hydrocarbons. Saturated hydrocarbons show PM grade 4–5 degradation while aromatics demonstrate PM grade 5–7 degradation. Aromatics display a higher susceptibility to biodegradation compared to saturated hydrocarbons, which differs significantly from crude oil. The degradation susceptibility sequence for saturated hydrocarbons is as follows: <em>n</em>-alkane > sterane > hopane. The biodegradation susceptibility of aromatic hydrocarbons depends on both the number of aromatic rings and alkyl-substituents; those with fewer rings and alkyl-substituents degrade more rapidly. Biodegradation of OM in coal plays a crucial role in SBG generation; however, a high degree of OM biodegradation does not necessarily correlate with greater accumulation of SBG due to other factors such as tectonic fractures and hydrogeological conditions that affect its preservation.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104996"},"PeriodicalIF":2.6,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143868299","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 : 2025-04-19DOI: 10.1016/j.orggeochem.2025.105011
Z.R. van Kemenade , S. Kusch , S. Berg , E.C. Hopmans , M.T.J. van der Meer , D. Rush
Prydz Bay is located at the terminus of one of the largest marine-terminating glacial systems of East Antarctica. Consequently, its sedimentary record may hold information on the response of marine biogeochemical cycling to changes in Antarctic palaeoceanography and palaeoclimate. Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) offer great potential for tracing such changes, as these membrane lipids have been linked to distinct biogeochemical processes and environmental niches. Here, we present the BHP and GDGT inventory of a Holocene sediment record, recovered from a marine basin in eastern Prydz Bay. BHP and GDGT lipidomics were complemented with (organic) geochemical tools to reconstruct palaeoenvironmental conditions. GDGT-based indices suggest terrestrial organic matter influx was insignificant. Our results show elevated nucleoside-BHPs in early Holocene sediments from ∼9.1 to 10.7 cal ka BP. Their presence is interpreted to reflect autochthonous production under hypoxic-anoxic water column conditions, as inferred from BHT-x ratios of ≥0.2. The record is characterized by a large diversity of rare and novel unsaturated BHPs and BHP isomers. Their occurrence is potentially related to homeoviscous adaptations of the membranes of predominantly aerobic bacteria to cold conditions (i.e., reconstructed sea surface temperatures are −2.4 to −0.8 °C based on ). Increased abundance and diversity of these BHPs between ∼5.5–7.5 and ∼8.9–9.8 cal ka BP is likely associated with an oxygenation of the basin at this time. During the late Holocene (<3.0 cal ka BP), the water column experienced photic zone euxinia, high rates of nitrogen loss and methanogenesis, as indicated by the presence of isorenieratene, enriched δ15N values and high GDGT-0/cren ratios, respectively. BHPs in these sediments likely derive from two different ecological niches: i) the uppermost oxygenated to suboxic waters where aerobic methane oxidation occurred and ii) the deeper sulfidic waters. More reducing conditions in the late Holocene coincide with increased brGDGT cyclization and methylation, and is proposed to indicate a shift in the source bacterial niche from sediments to the water column. This study shows that GDGT and BHP distributions can be linked to distinct redox regime shifts within the basin, which appear regulated by changes in sea level and sea ice in Prydz Bay. Our findings highlight the potential use of these lipids as tracers for biogeochemical cycling in marine polar regions.
Prydz湾位于东南极洲最大的海洋冰川系统之一的终点。因此，其沉积记录可能包含海洋生物地球化学循环对南极古海洋和古气候变化的响应信息。细菌藿烷多元醇（BHPs）和甘油二烷基甘油四醚（GDGTs）为追踪这些变化提供了巨大的潜力，因为这些膜脂与不同的生物地球化学过程和环境生态位有关。在这里，我们介绍了从Prydz湾东部海相盆地恢复的全新世沉积物记录的BHP和GDGT清单。将BHP和GDGT脂质组学与（有机）地球化学工具相结合，重建古环境条件。基于gdgt的指标提示陆源有机质流入不显著。我们的研究结果表明，在全新世早期沉积物中，核苷- bhps在~ 9.1 ~ 10.7 cal ka BP之间升高。根据BHT-x比值≥0.2，它们的存在被解释为反映了缺氧-缺氧水柱条件下的本地生产。记录的特点是大量的多样性罕见和新颖的不饱和必和必拓和必和必拓异构体。它们的出现可能与主要好氧细菌的膜对寒冷条件的自粘适应有关（即，基于TEX86OH重建的海面温度为−2.4至−0.8°C）。这些BHPs的丰度和多样性在~ 5.5-7.5和~ 8.9-9.8 cal ka BP之间增加，可能与此时盆地的氧化作用有关。在全新世晚期（3.0 cal ka BP），水柱经历了光区缺氧、高氮损失率和甲烷生成，分别表现为异硫氰酸的存在、丰富的δ15N值和高GDGT-0/cren比值。这些沉积物中的BHPs可能来自两个不同的生态位：i)发生好氧甲烷氧化的最上层含氧到缺氧的水域和ii)较深的硫化物水域。全新世晚期更多的还原条件与brGDGT环化和甲基化的增加相吻合，表明源细菌生态位从沉积物向水柱转移。研究表明，GDGT和BHP分布可能与盆地内明显的氧化还原状态变化有关，这种变化似乎受Prydz湾海平面和海冰变化的调节。我们的发现强调了这些脂质作为海洋极地生物地球化学循环示踪剂的潜在用途。
{"title":"Bacteriohopanepolyols and glycerol dialkyl glycerol tetraethers record Holocene redox regime shifts in a marine inlet in eastern Prydz Bay, Antarctica","authors":"Z.R. van Kemenade , S. Kusch , S. Berg , E.C. Hopmans , M.T.J. van der Meer , D. Rush","doi":"10.1016/j.orggeochem.2025.105011","DOIUrl":"10.1016/j.orggeochem.2025.105011","url":null,"abstract":"<div><div>Prydz Bay is located at the terminus of one of the largest marine-terminating glacial systems of East Antarctica. Consequently, its sedimentary record may hold information on the response of marine biogeochemical cycling to changes in Antarctic palaeoceanography and palaeoclimate. Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) offer great potential for tracing such changes, as these membrane lipids have been linked to distinct biogeochemical processes and environmental niches. Here, we present the BHP and GDGT inventory of a Holocene sediment record, recovered from a marine basin in eastern Prydz Bay. BHP and GDGT lipidomics were complemented with (organic) geochemical tools to reconstruct palaeoenvironmental conditions. GDGT-based indices suggest terrestrial organic matter influx was insignificant. Our results show elevated nucleoside-BHPs in early Holocene sediments from ∼9.1 to 10.7 cal ka BP. Their presence is interpreted to reflect autochthonous production under hypoxic-anoxic water column conditions, as inferred from BHT-<em>x</em> ratios of ≥0.2. The record is characterized by a large diversity of rare and novel unsaturated BHPs and BHP isomers. Their occurrence is potentially related to homeoviscous adaptations of the membranes of predominantly aerobic bacteria to cold conditions (i.e., reconstructed sea surface temperatures are −2.4 to −0.8 °C based on <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span>). Increased abundance and diversity of these BHPs between ∼5.5–7.5 and ∼8.9–9.8 cal ka BP is likely associated with an oxygenation of the basin at this time. During the late Holocene (<3.0 cal ka BP), the water column experienced photic zone euxinia, high rates of nitrogen loss and methanogenesis, as indicated by the presence of isorenieratene, enriched δ<sup>15</sup>N values and high GDGT-0/cren ratios, respectively. BHPs in these sediments likely derive from two different ecological niches: i) the uppermost oxygenated to suboxic waters where aerobic methane oxidation occurred and ii) the deeper sulfidic waters. More reducing conditions in the late Holocene coincide with increased brGDGT cyclization and methylation, and is proposed to indicate a shift in the source bacterial niche from sediments to the water column. This study shows that GDGT and BHP distributions can be linked to distinct redox regime shifts within the basin, which appear regulated by changes in sea level and sea ice in Prydz Bay. Our findings highlight the potential use of these lipids as tracers for biogeochemical cycling in marine polar regions.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105011"},"PeriodicalIF":2.6,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143912012","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 : 2025-04-19DOI: 10.1016/j.orggeochem.2025.105010
Devika Varma , Yord W. Yedema , Francien Peterse , Gert-Jan Reichart , Jaap S. Sinninghe Damsté , Stefan Schouten
<div><div>Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) and hydroxylated isoGDGTs (OH-isoGDGTs) are widespread in marine, lacustrine, and terrestrial environments and serve as paleoenvironmental proxies. Several indices based on their distributions, such as <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> (based on isoGDGTs), <span><math><mtext>RI-OH</mtext></math></span>, <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span> (both based on OH-isoGDGTs), <span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span> and <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> (both based on isoGDGTs and OH-isoGDGTs), have been utilized as sea water temperature proxies. Although terrestrial organic matter (OM) input of isoGDGTs may affect the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> in coastal marine settings, relatively little is known on its consequences for OH-isoGDGT distributions and related proxies. Here, we studied the distributions of OH-isoGDGTs in soils, rivers, and coastal marine settings at three locations: the Kara Sea, the Iberian margin, and the northern Gulf of Mexico, receiving terrestrial OM through the Yenisei, the Tagus and the Mississippi Rivers, respectively. In general, we observe higher relative abundances of OH-isoGDGTs (<span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span>) in coastal marine environments compared to soils and rivers from the same area. Comparison of OH-isoGDGT distributions shows that, in particular, the abundance of OH-isoGDGT with one cyclopentane moiety relative to total OH-isoGDGTs was lower in terrestrial settings. In general, the <span><math><mtext>RI-OH</mtext></math></span> was higher in terrestrial settings, while such a consistent offset was not observed for <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span>. The <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index, exhibits a distinct difference between terrestrial and marine settings, similar to the pattern observed for the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span>. This similarity is primarily attributed to the relatively minor influence of terrestrial OH-isoGDGTs compared to regular isoGDGTs in the <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index. Despite these differences, only the coastal sediments of the Kara Sea showed indications of a potential bias of OH-isoGDGTs-based proxies caused by terrestrial OM input. However, these distributional variations may also be caused by the large salinity gradient in the Kara Sea, since it has bee
{"title":"Impact of terrestrial organic matter input on distributions of hydroxylated isoprenoidal GDGTs in marine sediments: Implications for OH-isoGDGT-based temperature proxies","authors":"Devika Varma , Yord W. Yedema , Francien Peterse , Gert-Jan Reichart , Jaap S. Sinninghe Damsté , Stefan Schouten","doi":"10.1016/j.orggeochem.2025.105010","DOIUrl":"10.1016/j.orggeochem.2025.105010","url":null,"abstract":"<div><div>Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) and hydroxylated isoGDGTs (OH-isoGDGTs) are widespread in marine, lacustrine, and terrestrial environments and serve as paleoenvironmental proxies. Several indices based on their distributions, such as <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> (based on isoGDGTs), <span><math><mtext>RI-OH</mtext></math></span>, <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span> (both based on OH-isoGDGTs), <span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span> and <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> (both based on isoGDGTs and OH-isoGDGTs), have been utilized as sea water temperature proxies. Although terrestrial organic matter (OM) input of isoGDGTs may affect the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> in coastal marine settings, relatively little is known on its consequences for OH-isoGDGT distributions and related proxies. Here, we studied the distributions of OH-isoGDGTs in soils, rivers, and coastal marine settings at three locations: the Kara Sea, the Iberian margin, and the northern Gulf of Mexico, receiving terrestrial OM through the Yenisei, the Tagus and the Mississippi Rivers, respectively. In general, we observe higher relative abundances of OH-isoGDGTs (<span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span>) in coastal marine environments compared to soils and rivers from the same area. Comparison of OH-isoGDGT distributions shows that, in particular, the abundance of OH-isoGDGT with one cyclopentane moiety relative to total OH-isoGDGTs was lower in terrestrial settings. In general, the <span><math><mtext>RI-OH</mtext></math></span> was higher in terrestrial settings, while such a consistent offset was not observed for <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span>. The <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index, exhibits a distinct difference between terrestrial and marine settings, similar to the pattern observed for the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span>. This similarity is primarily attributed to the relatively minor influence of terrestrial OH-isoGDGTs compared to regular isoGDGTs in the <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index. Despite these differences, only the coastal sediments of the Kara Sea showed indications of a potential bias of OH-isoGDGTs-based proxies caused by terrestrial OM input. However, these distributional variations may also be caused by the large salinity gradient in the Kara Sea, since it has bee","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105010"},"PeriodicalIF":2.6,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143917858","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 : 2025-04-19DOI: 10.1016/j.orggeochem.2025.105008
Klaas G.J. Nierop , Merel Mijs , Rolande Dekker , Michael D. Lewan , Eveline N. Speelman , Jan W. de Leeuw , Gert-Jan Reichart
The freshwater fern Azolla produces a unique series of ω20-hydroxy and ω9,ω10-dihydroxy lipids. These compounds were also detected in Eocene sediments (∼48.5 Ma) characterized by the occurrence of fossil remains of Azolla and are thought to be prime markers for the past occurrence of Azolla implying that they could serve as palaeo-environmental indicators of freshwater conditions. However, the suitability of these Azolla biomarkers for application to more mature sediments is unknown. In this study, Azolla caroliniana specimens were heated using hydrous pyrolysis at temperatures ranging from 220 to 365 °C for 72 h to examine the stability and degradation of the Azolla biomarkers during simulated diagenesis. Initially all ω20-hydroxy and ω9,ω10-dihydroxy lipids are converted to their ketone analogues. At 260 °C n-alkanes are formed. ω20-Hydroxy and ω9,ω10-dihydroxy lipids are degraded between 260 and 280 °C. At 300 °C, only ω20-keto-1-ols, ω20-keto fatty acids and ω20-ketones, along with their ω9 and ω10 analogues, remain to preserve their ω20, ω9 and ω10 functionalities, while at 320 °C and higher only the ω20-, ω9, and ω10-ketones were observed. At higher temperatures the proportions of n-alkanes became dominating. The high thermal stability of the ω20, ω9/ω10 functionality shows that it has a relatively high preservation potential. Hence, it may potentially be a robust source indicator of the depositional environment of Azolla-derived organic carbon reflecting freshwater or brackish surface waters.
{"title":"Thermal stability of freshwater fern Azolla biomarkers as assessed by hydrous pyrolysis","authors":"Klaas G.J. Nierop , Merel Mijs , Rolande Dekker , Michael D. Lewan , Eveline N. Speelman , Jan W. de Leeuw , Gert-Jan Reichart","doi":"10.1016/j.orggeochem.2025.105008","DOIUrl":"10.1016/j.orggeochem.2025.105008","url":null,"abstract":"<div><div>The freshwater fern <em>Azolla</em> produces a unique series of ω20-hydroxy and ω9,ω10-dihydroxy lipids. These compounds were also detected in Eocene sediments (∼48.5 Ma) characterized by the occurrence of fossil remains of <em>Azolla</em> and are thought to be prime markers for the past occurrence of <em>Azolla</em> implying that they could serve as palaeo-environmental indicators of freshwater conditions. However, the suitability of these <em>Azolla</em> biomarkers for application to more mature sediments is unknown. In this study, <em>Azolla caroliniana</em> specimens were heated using hydrous pyrolysis at temperatures ranging from 220 to 365 °C for 72 h to examine the stability and degradation of the <em>Azolla</em> biomarkers during simulated diagenesis. Initially all ω20-hydroxy and ω9,ω10-dihydroxy lipids are converted to their ketone analogues. At 260 °C <em>n</em>-alkanes are formed. ω20-Hydroxy and ω9,ω10-dihydroxy lipids are degraded between 260 and 280 °C. At 300 °C, only ω20-keto-1-ols, ω20-keto fatty acids and ω20-ketones, along with their ω9 and ω10 analogues, remain to preserve their ω20, ω9 and ω10 functionalities, while at 320 °C and higher only the ω20-, ω9, and ω10-ketones were observed. At higher temperatures the proportions of <em>n</em>-alkanes became dominating. The high thermal stability of the ω20, ω9/ω10 functionality shows that it has a relatively high preservation potential. Hence, it may potentially be a robust source indicator of the depositional environment of <em>Azolla</em>-derived organic carbon reflecting freshwater or brackish surface waters.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 105008"},"PeriodicalIF":2.6,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143874720","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 : 2025-04-14DOI: 10.1016/j.orggeochem.2025.104997
Mingyue Tao , Susu Wang , Wanglu Jia , Yongge Sun , Lian Jiang , Jian Chen , Ping’an Peng
Trimethyl-alkylbenzenes in oil are an important class of molecular marker for determining biological sources, source rock depositional environment and maturity. They can be classified into three major types based on the type of side chain, including trimethyl-isoprenoid-, trimethyl-isohexyl-, and trimethyl-n-alkyl-benzenes. Although they have been studied separately for many years, recent studies have elucidated complicated co-elution of trimethyl-isoprenoid-benzenes and trimethyl-n-alkyl-benzenes on commonly used chromatographic columns. Moreover, simultaneous detections of these three types of trimethyl-alkylbenzenes were rarely reported. Reservoir bitumens, widely distributed along the northwestern margin of the Sichuan Basin, exhibit maturity characteristics that provide crucial insights for regional petroleum exploration in this ancient, giant petroliferous basin. So far, there has been no report on detection of these compounds from these reservoir bitumens, which may have suffered from severe biodegradation resulting in challenges to the understanding of genesis of these bitumens. In this study, asphaltenes, which are resistant to biodegradation, were carefully examined and asphaltene-bound hydrocarbons were compared to free hydrocarbons for the distribution of trimethyl-alkylbenzenes. Three main conclusions were drawn. Firstly, three major types of trimethyl-alkylbenzenes were detected through comparisons with available standards and well-characterized oils. These are 2,3,6-trimethyl-aryl isoprenoids (2,3,6-TMIPBs), 2,3,6-trimethyl-isohexylbenzene (2,3,6-TMiHB, C15), and trimethyl-n-alkylbenzenes (TMnABs, mainly 2,4,5-/2,3,5-, 2,3,6-, 2,3,4-trimethyl series), which show significant differences in concentrations for both free and asphaltene-bound hydrocarbons. Secondly, four groups of reservoir bitumens having distinct isotopic compositions also show large differences in the distributions of 2,3,6-TMIPBs and 2,3,6-TMiHB, providing further constraints on both biological sources and depositional environments for their source rocks. For the major group mainly sourced from the upper Ediacaran to lower Cambrian source rocks, abundant 2,3,6-TMIPBs and isorenieratane were detected. This finding, combined with global distributions of multiple kinds of C40 aromatic carotenoids (isorenieratane, chlorobactane, okenane) in the upper Ediacaran to lower Cambrian source rocks and their generated oils, indicates that photic zone euxinia was prevalent in ancient oceans, which may be of great significance for biological evolution in this key geological period. Thirdly, the ratios of 2,3,6-TMIPBs and 2,3,6-TMiHB to TMnABs have suggested subtle differences in the maturity of free hydrocarbons and asphaltenes, which can be used to reveal complex genetic processes for these bitumens, including at least two oil charging phases, different degrees of secondary cracking of asphaltenes mainly from early charg
{"title":"Three major types of trimethyl-alkylbenzenes and significance for the genesis of reservoir bitumens from the northwestern Sichuan Basin, South China","authors":"Mingyue Tao , Susu Wang , Wanglu Jia , Yongge Sun , Lian Jiang , Jian Chen , Ping’an Peng","doi":"10.1016/j.orggeochem.2025.104997","DOIUrl":"10.1016/j.orggeochem.2025.104997","url":null,"abstract":"<div><div>Trimethyl-alkylbenzenes in oil are an important class of molecular marker for determining biological sources, source rock depositional environment and maturity. They can be classified into three major types based on the type of side chain, including trimethyl-isoprenoid-, trimethyl-isohexyl-, and trimethyl-<em>n</em>-alkyl-benzenes. Although they have been studied separately for many years, recent studies have elucidated complicated co-elution of trimethyl-isoprenoid-benzenes and trimethyl-<em>n</em>-alkyl-benzenes on commonly used chromatographic columns. Moreover, simultaneous detections of these three types of trimethyl-alkylbenzenes were rarely reported. Reservoir bitumens, widely distributed along the northwestern margin of the Sichuan Basin, exhibit maturity characteristics that provide crucial insights for regional petroleum exploration in this ancient, giant petroliferous basin. So far, there has been no report on detection of these compounds from these reservoir bitumens, which may have suffered from severe biodegradation resulting in challenges to the understanding of genesis of these bitumens. In this study, asphaltenes, which are resistant to biodegradation, were carefully examined and asphaltene-bound hydrocarbons were compared to free hydrocarbons for the distribution of trimethyl-alkylbenzenes. Three main conclusions were drawn. Firstly, three major types of trimethyl-alkylbenzenes were detected through comparisons with available standards and well-characterized oils. These are 2,3,6-trimethyl-aryl isoprenoids (2,3,6-TMIPBs), 2,3,6-trimethyl-isohexylbenzene (2,3,6-TMiHB, C<sub>15</sub>), and trimethyl-<em>n</em>-alkylbenzenes (TMnABs, mainly 2,4,5-/2,3,5-, 2,3,6-, 2,3,4-trimethyl series), which show significant differences in concentrations for both free and asphaltene-bound hydrocarbons. Secondly, four groups of reservoir bitumens having distinct isotopic compositions also show large differences in the distributions of 2,3,6-TMIPBs and 2,3,6-TMiHB, providing further constraints on both biological sources and depositional environments for their source rocks. For the major group mainly sourced from the upper Ediacaran to lower Cambrian source rocks, abundant 2,3,6-TMIPBs and isorenieratane were detected. This finding, combined with global distributions of multiple kinds of C<sub>40</sub> aromatic carotenoids (isorenieratane, chlorobactane, okenane) in the upper Ediacaran to lower Cambrian source rocks and their generated oils, indicates that photic zone euxinia was prevalent in ancient oceans, which may be of great significance for biological evolution in this key geological period. Thirdly, the ratios of 2,3,6-TMIPBs and 2,3,6-TMiHB to TMnABs have suggested subtle differences in the maturity of free hydrocarbons and asphaltenes, which can be used to reveal complex genetic processes for these bitumens, including at least two oil charging phases, different degrees of secondary cracking of asphaltenes mainly from early charg","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104997"},"PeriodicalIF":2.6,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143825393","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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