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}
Pub Date : 2025-04-11DOI: 10.1016/j.orggeochem.2025.104992
Jun Shi , Hua Wang , Huajun Gan , Zhao-Wen Zhan , Yun Li , Wenmin Jiang
The effect of pressure on the oil stability in reservoirs, particularly in deep to ultra-deep strata, is a topic of significant interest. A series of crude oil cracking experiments were conducted in closed gold-tube pyrolysis systems under compressible and incompressible conditions without added water to quantitatively investigate this phenomenon. Crude oil samples with a thermal maturity of 0.74% Ro were heated from 354 ℃ to 600 ℃ at rates of 2 ℃/h and 20 ℃/h. Constant confining pressures of 50 MPa and 100 MPa were maintained throughout the experiments. Additionally, experiments were conducted at programmed temperatures corresponding to thermal maturities of 1.0% EasyRo (380 ℃), 1.5% EasyRo (420 ℃), and 2.1% EasyRo (454 ℃), with heating rates of 2 ℃/h, and under two variable fluid pressures of approximately 50 MPa (ranging from 0 to >50 MPa) and approximately 100 MPa (ranging from 0 to >100 MPa). The results indicate that confining pressure has a marginal impact on the hydrocarbons generation and cracking. Whereas, the fluid pressure initially promotes cracking reactions and subsequently exerts a retardation effect. This was demonstrated by the variations in alkane yields (methane, C2–C5, C6–C12, and C13+ hydrocarbons). A kinetic analysis shows that the temperatures required for 51% and 62.5% conversion levels of liquid hydrocarbons vary marginally (by 1–5 ℃). This indicates that from a chemical kinetics perspective, pressure has a marginal impact on oil stability compared with temperature. This study introduces a novel approach to investigate the effects of pressure on oil stability and to elucidate the complex dynamics process of hydrocarbon reactions under varying pressure conditions in deep-ultra-deep reservoirs.
{"title":"Investigating pressure effects on oil stability in deep-buried strata via chemical kinetics","authors":"Jun Shi , Hua Wang , Huajun Gan , Zhao-Wen Zhan , Yun Li , Wenmin Jiang","doi":"10.1016/j.orggeochem.2025.104992","DOIUrl":"10.1016/j.orggeochem.2025.104992","url":null,"abstract":"<div><div>The effect of pressure on the oil stability in reservoirs, particularly in deep to ultra-deep strata, is a topic of significant interest. A series of crude oil cracking experiments were conducted in closed gold-tube pyrolysis systems under compressible and incompressible conditions without added water to quantitatively investigate this phenomenon. Crude oil samples with a thermal maturity of 0.74% <em>R</em>o were heated from 354 ℃ to 600 ℃ at rates of 2 ℃/h and 20 ℃/h. Constant confining pressures of 50 MPa and 100 MPa were maintained throughout the experiments. Additionally, experiments were conducted at programmed temperatures corresponding to thermal maturities of 1.0% EasyRo (380 ℃), 1.5% EasyRo (420 ℃), and 2.1% EasyRo (454 ℃), with heating rates of 2 ℃/h, and under two variable fluid pressures of approximately 50 MPa (ranging from 0 to >50 MPa) and approximately 100 MPa (ranging from 0 to >100 MPa). The results indicate that confining pressure has a marginal impact on the hydrocarbons generation and cracking. Whereas, the fluid pressure initially promotes cracking reactions and subsequently exerts a retardation effect. This was demonstrated by the variations in alkane yields (methane, C<sub>2</sub>–C<sub>5</sub>, C<sub>6</sub>–C<sub>12</sub>, and C<sub>13+</sub> hydrocarbons). A kinetic analysis shows that the temperatures required for 51% and 62.5% conversion levels of liquid hydrocarbons vary marginally (by 1–5 ℃). This indicates that from a chemical kinetics perspective, pressure has a marginal impact on oil stability compared with temperature. This study introduces a novel approach to investigate the effects of pressure on oil stability and to elucidate the complex dynamics process of hydrocarbon reactions under varying pressure conditions in deep-ultra-deep reservoirs.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104992"},"PeriodicalIF":2.6,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143820581","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 : 2025-04-07DOI: 10.1016/j.orggeochem.2025.104944
Yili Mao , Ke Du , Xiaofeng Xia , Zhiwei Gao , Qilin Xiao , Quan Shi , Yongge Sun
Benzothiophenes (BTs) and dibenzothiophenes (DBTs) are an important organic sulfur compounds (OSCs) in crude oils, primarily as proxies for thermal maturity and secondary alteration, though their biological sources and depositional environments remain debated. Compound-specific stable carbon isotopic measurements could provide new insights into their origins. In this study, we employed improved methylation/demethylation reactions for selective separation of thiophenic and sulfidic compounds from crude oils to measure the stable carbon isotopic compositions of individual BTs and DBTs. Experiments with model compounds show no significant isotopic fractionation of BTs and DBTs through entire procedure, while small fractionation occurs for sulfidic compounds. Pre-removal of alkanes and additional purification by alumina column chromatography effectively reduced co-elution interference, enhancing the accuracy of isotopic measurements. To demonstrate the method’s applicability, two crude oils from Chinese petroliferous basins were analyzed, integrating δ34S values of individual DBTs. In the low maturity, non-biodegraded lacustrine oil, the DBTs exhibit highly 13C-depleted values (av., −35.2 ‰) compared to oil fractions and non-sulfurized individual organic compounds. With the exception of 1-methyldibenzothiophene (−29.1 ‰), the BTs are enriched in 13C relative to DBTs by up to ∼5.5 ‰, suggesting the distinct organic sources. In the biodegraded marine oil, although a small discrepancy in δ13C values (∼1 ‰) remains, similar δ13C values of oil components indicate a shared source, as shown by δ13C values of pristane (–33.0 ‰) and phytane (–33.7 ‰). δ34S values of individual DBTs (21–23 ‰) suggest a common source for organic sulfur given its moderate maturity (equivalent vitrinite reflectance of ∼0.9 %Requ). While OSCs formation in oils from the Tarim Basin is attributed to the incorporation of TSR-H2S into labile compounds in biodegraded oils, we propose that OSCs in these oils form mainly from sulfur re-incorporation, followed by cyclization and/or aromatization into functionalized aromatic and alkyl cyclohexane compounds at the early stage of diagenesis. This leads to similar carbon and sulfur signatures in BTs and DBTs. Therefore, successful carbon isotope measurements of individual BTs and DBTs could provide new insights into their sources and formation pathways, and application limitations. Future studies on samples from diverse geological settings could further demonstrate the methods potentials.
{"title":"Determining carbon isotopic compositions of benzothiophenes and dibenzothiophenes in crude oils and potential geochemical implications","authors":"Yili Mao , Ke Du , Xiaofeng Xia , Zhiwei Gao , Qilin Xiao , Quan Shi , Yongge Sun","doi":"10.1016/j.orggeochem.2025.104944","DOIUrl":"10.1016/j.orggeochem.2025.104944","url":null,"abstract":"<div><div>Benzothiophenes (BTs) and dibenzothiophenes (DBTs) are an important organic sulfur compounds (OSCs) in crude oils, primarily as proxies for thermal maturity and secondary alteration, though their biological sources and depositional environments remain debated. Compound-specific stable carbon isotopic measurements could provide new insights into their origins. In this study, we employed improved methylation/demethylation reactions for selective separation of thiophenic and sulfidic compounds from crude oils to measure the stable carbon isotopic compositions of individual BTs and DBTs. Experiments with model compounds show no significant isotopic fractionation of BTs and DBTs through entire procedure, while small fractionation occurs for sulfidic compounds. Pre-removal of alkanes and additional purification by alumina column chromatography effectively reduced co-elution interference, enhancing the accuracy of isotopic measurements. To demonstrate the method’s applicability, two crude oils from Chinese petroliferous basins were analyzed, integrating δ<sup>34</sup>S values of individual DBTs. In the low maturity, non-biodegraded lacustrine oil, the DBTs exhibit highly <sup>13</sup>C-depleted values (av., −35.2 ‰) compared to oil fractions and non-sulfurized individual organic compounds. With the exception of 1-methyldibenzothiophene (−29.1 ‰), the BTs are enriched in <sup>13</sup>C relative to DBTs by up to ∼5.5 ‰, suggesting the distinct organic sources. In the biodegraded marine oil, although a small discrepancy in δ<sup>13</sup>C values (∼1 ‰) remains, similar δ<sup>13</sup>C values of oil components indicate a shared source, as shown by δ<sup>13</sup>C values of pristane (–33.0 ‰) and phytane (–33.7 ‰). δ<sup>34</sup>S values of individual DBTs (21–23 ‰) suggest a common source for organic sulfur given its moderate maturity (equivalent vitrinite reflectance of ∼0.9 %<em>R<sub>equ</sub></em>). While OSCs formation in oils from the Tarim Basin is attributed to the incorporation of TSR-H<sub>2</sub>S into labile compounds in biodegraded oils, we propose that OSCs in these oils form mainly from sulfur re-incorporation, followed by cyclization and/or aromatization into functionalized aromatic and alkyl cyclohexane compounds at the early stage of diagenesis. This leads to similar carbon and sulfur signatures in BTs and DBTs. Therefore, successful carbon isotope measurements of individual BTs and DBTs could provide new insights into their sources and formation pathways, and application limitations. Future studies on samples from diverse geological settings could further demonstrate the methods potentials.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104944"},"PeriodicalIF":2.6,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143785552","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号