Organic Geochemistry最新文献

{"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 ,&nbsp;S. Kusch ,&nbsp;S. Berg ,&nbsp;E.C. Hopmans ,&nbsp;M.T.J. van der Meer ,&nbsp;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 (&lt;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.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105011"},"PeriodicalIF":2.6,"publicationDate":"2025-08-01","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}

{"title":"A saline lacustrine depositional environment enhances organic matter enrichment in the Permian Lucaogou shales","authors":"Yin Fu ,&nbsp;Zuodong Wang ,&nbsp;Ting Zhang ,&nbsp;Wenjun Wang ,&nbsp;Yongli Wang ,&nbsp;Wang Zhang ,&nbsp;Xiaobin Li ,&nbsp;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":"2025-08-01","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}

{"title":"Diatom-derived highly branched isoprenoids are diverse and widespread in lakes","authors":"Aaron F. Diefendorf ,&nbsp;Watts L. Dietrich ,&nbsp;Hans Naake ,&nbsp;Megan C. Corcoran ,&nbsp;Andrew J. Kmetz ,&nbsp;Thomas V. Lowell ,&nbsp;Michael D. Schenk ,&nbsp;Gregory C. Wiles ,&nbsp;Mark A. Wilson","doi":"10.1016/j.orggeochem.2025.104993","DOIUrl":"10.1016/j.orggeochem.2025.104993","url":null,"abstract":"<div><div>Diatom-derived highly branched isoprenoid lipids (HBIs) are found extensively in marine sediments, but to date are only reported in a few lacustrine sediments. To expand on prior lake studies, we collected lake surface sediment samples, water samples, and filtered photic zone water from 50 lakes from the Great Plains to the northeastern United States. Samples were collected in May and June and a few sites were revisited in September and October. Studied lakes vary in climate, water chemistry (e.g., pH, salinity, alkalinity), size, and trophic states. They also vary in their diatom species compositions with 344 diatom taxa reported. We characterized HBI assemblages in each lake and found 11 different HBI compounds including one C_20:0 HBI, five C_20:1 HBI isomers, C_21:0 HBI, C_25:2 HBI, two C_25:3 HBIs, and C_25:4 HBI. C_20:0 HBI was present in all but two lakes and was often the most abundant HBI present. HBIs were also detected in nearly all the water filter samples indicating they are produced in the photic zone. C_20:0 HBI was present in all freshwater lakes, but not present or at very low concentration in the highest salinity lakes, which were dominated by C_21:0 HBI and C₂₅ HBIs. Many of the lakes were dominated by diatom genera and species that are not known to be HBI-producing genera, suggesting there are unrecognized HBI-producing diatom taxa. This inventory, illustrating the widespread presence and diversity of HBIs from lakes across large differences in water chemistries and climate, further suggests that HBIs may be useful diatom biomarkers for paleoclimate applications.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104993"},"PeriodicalIF":2.6,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143879109","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}

{"title":"Investigating pressure effects on oil stability in deep-buried strata via chemical kinetics","authors":"Jun Shi ,&nbsp;Hua Wang ,&nbsp;Huajun Gan ,&nbsp;Zhao-Wen Zhan ,&nbsp;Yun Li ,&nbsp;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 &gt;50 MPa) and approximately 100 MPa (ranging from 0 to &gt;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.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104992"},"PeriodicalIF":2.6,"publicationDate":"2025-07-01","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}

{"title":"Microbial communities constrain the organic δ13C variations in the Lower Cambrian mudstones","authors":"Biqing Zhu ,&nbsp;Quanyou Liu ,&nbsp;Huiyuan Xu ,&nbsp;Dongya Zhu ,&nbsp;Jingbin Wang ,&nbsp;Xiaoqi Wu ,&nbsp;Pengpeng Li ,&nbsp;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 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 <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 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., <em>Chlorobiaceae</em> and <em>Chromatiaceae</em>). 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.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104991"},"PeriodicalIF":2.6,"publicationDate":"2025-07-01","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}

{"title":"Introduction to Xplorer, Hybrid and Early-Career Virtual Special Issue","authors":"Huiyuan Xu ,&nbsp;Jian Ma ,&nbsp;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":"2025-07-01","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}

{"title":"Thermal stability of freshwater fern Azolla biomarkers as assessed by hydrous pyrolysis","authors":"Klaas G.J. Nierop ,&nbsp;Merel Mijs ,&nbsp;Rolande Dekker ,&nbsp;Michael D. Lewan ,&nbsp;Eveline N. Speelman ,&nbsp;Jan W. de Leeuw ,&nbsp;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":"2025-07-01","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}

{"title":"Determining carbon isotopic compositions of benzothiophenes and dibenzothiophenes in crude oils and potential geochemical implications","authors":"Yili Mao ,&nbsp;Ke Du ,&nbsp;Xiaofeng Xia ,&nbsp;Zhiwei Gao ,&nbsp;Qilin Xiao ,&nbsp;Quan Shi ,&nbsp;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 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 %<em>R_equ</em>). 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.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"205 ","pages":"Article 104944"},"PeriodicalIF":2.6,"publicationDate":"2025-07-01","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}

{"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 ,&nbsp;Susu Wang ,&nbsp;Wanglu Jia ,&nbsp;Yongge Sun ,&nbsp;Lian Jiang ,&nbsp;Jian Chen ,&nbsp;Ping’an Peng","doi":"10.1016/j.orggeochem.2025.104997","DOIUrl":"10.1016/j.orggeochem.2025.104997","url":null,"abstract":"&lt;div&gt;&lt;div&gt;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-&lt;em&gt;n&lt;/em&gt;-alkyl-benzenes. Although they have been studied separately for many years, recent studies have elucidated complicated co-elution of trimethyl-isoprenoid-benzenes and trimethyl-&lt;em&gt;n&lt;/em&gt;-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&lt;sub&gt;15&lt;/sub&gt;), and trimethyl-&lt;em&gt;n&lt;/em&gt;-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&lt;sub&gt;40&lt;/sub&gt; 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":"2025-07-01","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}

{"title":"Biodegradation sequence of coal organic matter and mechanism of biomethane formation in secondary biogenic gas accumulation areas","authors":"Yiliang Hu ,&nbsp;Yuan Bao ,&nbsp;Jiahao Meng ,&nbsp;Dan Li ,&nbsp;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 &gt; sterane &gt; 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":"2025-07-01","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}