Organic Geochemistry最新文献

{"title":"Multiple sources of petroleum in the Panyu lower uplift evidenced by catalytic hydropyrolysis of petroleum asphaltenes","authors":"Guangli Wang ,&nbsp;Ying Xu ,&nbsp;Yang Yang ,&nbsp;Zhirong Zhang ,&nbsp;Yuhong Liao","doi":"10.1016/j.orggeochem.2025.105045","DOIUrl":"10.1016/j.orggeochem.2025.105045","url":null,"abstract":"<div><div>Catalytic hydropyrolysis (HyPy) is an effective method for the release of covalently bound biomarkers from geo-macromolecules (e.g., kerogen or asphaltenes). It is particularly valuable for samples that lack geochemical proxies resulting from extensive maturation or secondary alteration. In this study, HyPy was carried out on asphaltene fractions isolated from crude oils collected from 10 reservoirs of various depths in the Panyu lower uplift in the central Pearl River Mouth Basin, South China Sea. Significant quantities of biomarkers and polycyclic aromatic hydrocarbons (PAHs) were released, and their molecular and isotopic compositions were obtained. The results suggest that these bound compounds were not affected by secondary alteration processes, such as biodegradation in shallow reservoirs or water washing in deeper ones. The δ¹³C values of the HyPy products were 1.2 ‰–2.2 ‰ more enriched than those of the original bulk oils, and are inconsistent with traditional δ¹³C patterns (the asphaltene fraction generally has the most enriched δ¹³C value among petroleum fractions). These reservoirs, therefore, may represent a composite petroleum system involving contributions from multiple source rocks rather than a single source as previously interpreted. This hypothesis is also supported by the molecular and biomarker signatures of the products, which showed elevated proportions of C₁₁–C₁₆ <em>n</em>-alkanes and C₁₉ tricyclic terpanes, and a marked dominance of 24-ethylcholestanes (ranging from 52 % to 79 % of total steranes), significantly exceeding the C₂₇ and C₂₈ homologues. A substantial input of organic matter from vascular plants, much higher than that of the presumed source rocks of the Eocene Wenchang Formation, was found. Therefore, the earlier petroleum charges to the Panyu lower uplift may be associated with the Eocene–Oligocene Enping Formation interbedded with coaly source rock intervals. In contrast, the maltenes of the oil samples were rich in 4-methylsteranes, dinosteranes, and triaromatic dinosteroids, as well as minor oleananes, which closely resemble the biomarker signatures of lacustrine source rocks from the Eocene Wenchang Formation. These findings support a dual contribution to the petroleum reservoirs across the Panyu lower uplift, where the major oils concerned with the coaly source rocks of the Enping Formation and the lacustrine shale source rocks of the Wenchang Formation were likely responsible for potential large hydrocarbon accumulations.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105045"},"PeriodicalIF":2.6,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144489968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sulfur ions reduce the activation energy of steranes and terpanes under hydrothermal action","authors":"Rongzhen Qiao,&nbsp;Meijun Li,&nbsp;Donglin Zhang,&nbsp;Hong Xiao","doi":"10.1016/j.orggeochem.2025.105044","DOIUrl":"10.1016/j.orggeochem.2025.105044","url":null,"abstract":"<div><div>Steranes and terpanes, as key biomarkers in oils and source rock extracts, provide valuable information about their biological origins, depositional environment, and thermal maturity. The distribution patterns of steranes and terpanes in ultra-deep oil reservoirs within the Shuntuoguole low uplift are complex. The intensity of hydrothermal activity and the influence of sulfur ions were assessed based on the conversion of “Biphenyl–Dibenzothiophene–Phenanthrene” series compounds. The results reveal that the southern sections of F5, F12, and F4 exhibit relatively strong hydrothermal activity (F number: No. number fault zone). The southern sections of F5, F1, and F4 are more significantly impacted by sulfur ion activity under the hydrothermal action. Studies indicate that sterane and terpene concentrations decrease due to sulfur ion activity under the hydrothermal action. Tricyclic terpanes, cholestanes, C_31-35 homohopanes, C₃₀ hopane, C₂₉ diahopane, and pregnane exhibit low stability under the influence of sulfur ion activity in the hydrothermal action. Notably, although tricyclic terpanes, cholestanes, and pregnane show low stability, they are not preferentially depleted. Combined analysis of the relative Gibbs free energies of C₃₀ diahopane and C₃₀ hopane showed that sulfur ions do not promote pyrolysis by altering the degradation pathways of steranes and terpanes. Instead, sulfur ions likely lower the pyrolysis threshold by reducing the activation energy, preserving the relative stability of steranes and terpanes. This study advances the understanding of organic–inorganic interactions in hydrothermal systems.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105044"},"PeriodicalIF":2.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144338788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Occurrence of nucleoside-bacteriohopanepolyol in high latitude soils: evidence of environmental controls on bacterial lipid membrane distributions","authors":"Keith F. O’Connor ,&nbsp;Melissa A. Berke ,&nbsp;Cindy De Jonge ,&nbsp;Ellen C. Hopmans ,&nbsp;Lori A. Ziolkowski ,&nbsp;Darci Rush","doi":"10.1016/j.orggeochem.2025.105026","DOIUrl":"10.1016/j.orggeochem.2025.105026","url":null,"abstract":"<div><div>Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS²) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS² analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R² = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105026"},"PeriodicalIF":2.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Abundance of phytanyl and n-alkyl toluenes in petroleum from the Lower Saxony Basin (Germany) provides information on maturity, palaeosettings and sources","authors":"Georg Scheeder,&nbsp;Christian Ostertag-Henning,&nbsp;Martin Blumenberg","doi":"10.1016/j.orggeochem.2025.105025","DOIUrl":"10.1016/j.orggeochem.2025.105025","url":null,"abstract":"<div><div>Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of <em>n</em>-alkylated benzenes and toluenes, the phytanyl toluene (and −benzene) is often abundant. In the present study, <em>n</em>-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C₂₂-C₂₄ <em>meta</em>-substituted <em>n</em>-alkyl (combined in the ratio as “<em>n</em>”) to phytanyl (“<em>iso</em>”) toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to <em>n</em>-alkyl toluenes systematically decreases with maturity and therefore the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index increases. The relative change is due to both the processes of catalytic formation of <em>n</em>-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105025"},"PeriodicalIF":2.6,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123964","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aryl isoprenoids in severe biodegradation oils from the Miaoxi Depression, Bohai Bay Basin","authors":"Xiaoyong Yang ,&nbsp;Youjun Tang ,&nbsp;Peng Sun ,&nbsp;Yiming Hu ,&nbsp;Haifeng Yang ,&nbsp;Feilong Wang","doi":"10.1016/j.orggeochem.2025.105014","DOIUrl":"10.1016/j.orggeochem.2025.105014","url":null,"abstract":"<div><div>Aryl isoprenoids (AIs), a series of aromatic carotenoid derivatives, have served as significant biomarkers for paleoecology reconstructions. However, the effect of biodegradation on AIs remains unclear to date. Here, a confirmed family of progressively biodegraded oils from the Miaoxi Depression, Bohai Bay Basin was analyzed to investigate the fate of these compounds during severe biodegradation under natural conditions. Two pseudohomologous series with carbon numbers ranging from 13 to 31 and 40 were identified as 2,3,6- and 2,3,4-AIs in the reference oil. The concentrations of total AIs showed a gradual decline with increasing biodegradation but AIs survive in the most severely biodegraded oil (with a PM rank of 8 and an M-MN2 of 983) in this study. The differential proximity of adjacent methyl groups on the benzene ring may result in 2,3,4-AIs being more resistant to biodegradation compared to 2,3,6-AIs. No preferential biodegradation of individual AIs is proceeded systematically by carbon number, which may result from competition of two biodegradation pathways and favor of specific microbial communities. Moreover, the AIs-bearing proxies, including aryl isoprenoid ratio (AIR) and concentrations of total AIs, 2,3,6-AIs and 2,3,4-AIs, exhibit a significant decrease with increasing microbial alteration. Therefore, these proxies must be employed with caution to reconstruct photic-zone euxinia (PZE) for crude oils with potential microbial degradation.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105014"},"PeriodicalIF":2.6,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144105273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry Articles – April 2025","authors":"","doi":"10.1016/j.orggeochem.2025.105015","DOIUrl":"10.1016/j.orggeochem.2025.105015","url":null,"abstract":"","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105015"},"PeriodicalIF":2.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144211861","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":"Occurrence of tetraester and mixed ether/ester-bound iso-diabolic acid membrane-spanning lipids in acidic, high-elevation mineral soils","authors":"Francien Peterse ,&nbsp;Klaas G.J. Nierop ,&nbsp;Nicole J. Bale ,&nbsp;Sarah J. Feakins ,&nbsp;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 (&gt;1900 masl), acidic (pH &lt; 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>-C₁₅ and <em>iso</em>-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 <em>iso</em>-C₁₅ 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}

{"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 ,&nbsp;Chiyang Liu ,&nbsp;Junfeng Zhao ,&nbsp;Faqi He ,&nbsp;Wei Zhang ,&nbsp;Lihua Yang ,&nbsp;Nan Du ,&nbsp;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_5-7 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.</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}

{"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":"2025-05-01","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}

{"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":"2025-04-29","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}