Organic Geochemistry最新文献

{"title":"A search for biomarker evidence of an intermittent deep-sea hypersaline anoxic basin in the eastern Mediterranean during the Early Pliocene","authors":"","doi":"10.1016/j.orggeochem.2024.104827","DOIUrl":"10.1016/j.orggeochem.2024.104827","url":null,"abstract":"<div><p>Deep-sea hypersaline anoxic basins (DHABs) are extreme environments harbouring unique microbial assemblages. They have, however, rarely been identified in the geological record. Here, we investigate the potential use of organic biomarkers to detect former DHAB presence in the eastern Mediterranean during the Early Pliocene. Our findings suggest challenges in identifying DHABs in the geological record using biomarker records; this is due to pelagic organic matter overprinting the DHAB signals.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"196 ","pages":"Article 104827"},"PeriodicalIF":2.6,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0146638024000925/pdfft?md5=da6c16b99e11ceaf991ed4e4d9ed180b&pid=1-s2.0-S0146638024000925-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141410302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fossil steroid acids can arise from microbial alteration of steranes","authors":"Can Xie,&nbsp;Gangtian Zhu,&nbsp;Yuguang Hou,&nbsp;Zhiliang He","doi":"10.1016/j.orggeochem.2024.104816","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104816","url":null,"abstract":"<div><p>Steroid acids are unique molecular fossils composed of a steroid carbon skeleton linked to a carboxyl group. These biomarkers contain special geological and biological clues in their structures. However, the origin of steroid acids remains a subject of debate, and there is a lack of direct evidence in previous studies. Here, we present experimental evidence for the origin of steroid acids. The origin of steroid acids during biodegradation in crude oil was observed for the first time. Molecular structures of these steroid acids reveal that they arose from steranes via bacterial oxidation of sidechain terminal methyl groups. Our results suggest that microbial activities indeed contribute to the formation of carboxyl groups on the eukaryotic steroid skeletons, and we believe steroid acids are a promising biomarker for both geomicrobial processes and ancient eukaryotic life in the rock record.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"194 ","pages":"Article 104816"},"PeriodicalIF":3.0,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141322505","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":"New practical biodegradation proxies based on heteroatom compounds revealed by ESI (−) FT-ICR MS","authors":"Shuo Deng ,&nbsp;Sumei Li ,&nbsp;Xiaoyan Li","doi":"10.1016/j.orggeochem.2024.104815","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104815","url":null,"abstract":"<div><p>High-resolution mass spectrometry can be utilized to select specific proxies for the quantitative assessment of crude oil biodegradation degree, offering higher accuracy and convenience compared to conventional GC-MS methods. However, the current evaluation proxies are invalid for severely biodegraded crude oil. In this study, freshwater and saltwater lacustrine crude oils from the Liaohe Western Depression (Bohai Bay Basin) with varying degrees of degradation, were characterized using negative ion electrospray ionization [ESI (−)] Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results show that seven heteroatom classes were identified including N₁, N₁O₁, N₁O₂, O₁, O₂, O₃ and O₄. Certain differences exist in the abundance of heteroatom compounds in the nondegraded crude oils from the two origins, but both are dominated by N₁. The relative abundance of O₂ class species significantly increases, while the relative abundance of O₁ and N₁ class species decreases with an increase in the degree of biodegradation, reflecting the increase in the content of acid compounds as biodegradation products. O₂ class species become the predominant compound in the severe degradation stage. Biodegradation results in the enrichment of compounds with greater condensation, while the abundance of highly alkyl-substituted compounds decreases. The nitrogen-containing compound pairing proxies (DBE_12,13,15/DBE_9∼11-N₁) can be employed to assess the degree of biodegradation in crude oil under conditions of similar maturity. As the degree of biodegradation increases, the content of 2 ∼ 5-cyclic naphthenic acids increase, while the content of acyclic acids with weaker resistance to degradation decreases. The ratio of acyclic acids to 2 ∼ 5-cyclic naphthenic acids (Modified A/C Ratio 2) can effectively assess the biodegradation level of crude oils ranging from nondegraded to severe degradation. The O₂/(N₁ + O₁) Ratio reflects the formation of acids during the biodegradation process and exhibits a robust positive correlation with crude oil density and degradation degree. The new proxies provide higher precision and broader applicability compared to conventional methods, enabling quantitative evaluation of biodegradation levels. The application of ESI FT-ICR MS technology holds significant importance in the assessment of heavy oil and the exploration of its genetic mechanisms.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"194 ","pages":"Article 104815"},"PeriodicalIF":3.0,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141313506","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":"Generation of abnormal distributions of inter- and intramolecular δ13C compositions in hydrocarbons from gold tube pyrolysis of an Australian torbanite","authors":"Zhirong Zhang ,&nbsp;Caiming Zhang ,&nbsp;Yan’e Chen ,&nbsp;John K. Volkman ,&nbsp;Yongge Sun","doi":"10.1016/j.orggeochem.2024.104813","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104813","url":null,"abstract":"<div><p>Abnormal stable carbon isotopic (δ¹³C) compositions, deviating from the conventional order of δ¹³C₁ &lt; δ¹³C₂ &lt; δ¹³C₃, are frequently observed in natural gas reservoirs. For thermogenic gas, these anomalies, such as δ¹³C₁ &lt; δ¹³C₃ &lt; δ¹³C₂ or δ¹³C₁ &gt; δ¹³C₂ &gt; δ¹³C₃, have multiple formation mechanisms including gas mixing in conventional systems and desorption processes of gaseous hydrocarbons in unconventional shale gas systems due to their inconsistency with Rayleigh fractionation processes. Considering distinct reaction pathways (e.g., C₁ polymerized to C₂), these aberrant δ¹³C signatures are often construed as intrinsic hallmarks of extensively evolved natural gas. However, on the basis of gas generation simulation, not all findings exhibit abnormal δ¹³C values, hinting at multifaceted and intricate mechanisms governing the isotopic fractionation of alkane gas components. This study conducted gold tube pyrolysis of an Australian torbanite, revealing four distinct types of δ¹³C anomalies in hydrocarbon classes. Polycyclic aromatic hydrocarbons (PAHs) exhibited δ¹³C values more negative than co-occurring <em>n</em>-alkanes. δ¹³C₃ displayed a negative trend shift from EasyRo = 3.5 %, resulting in a partially δ¹³C-reversed gas (δ¹³C₁ &lt; δ¹³C₃ &lt; δ₁₃C₂) formed at EasyRo ≈ 4.1 %. Moreover, intramolecular δ¹³C₃ (both terminal and central carbons, termed δ¹³Ca and δ¹³Cb, respectively) reversed alongside the overall δ¹³C₃ trend. Additionally, the evolution of site preference in δ¹³C₃ (termed ‰SP = δ¹³Ca – δ¹³Cb) transitioned from progressively negative to positive. The results of this study demonstrate that the potential conversion between saturated hydrocarbons, aromatic hydrocarbons, and alkane gases is at least partially responsible for δ¹³C anomalies, but also that gaseous hydrocarbons formed from other fractions at high maturity cannot be ruled out, such as kerogen and pyrobitumen.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"194 ","pages":"Article 104813"},"PeriodicalIF":3.0,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141302940","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 2024","authors":"","doi":"10.1016/j.orggeochem.2024.104796","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104796","url":null,"abstract":"","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"193 ","pages":"Article 104796"},"PeriodicalIF":3.0,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141324733","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":"The stable sulfur isotope and abundance fluxes of reduced inorganic sulfur and organic sulfur phases recorded in the Permian-Triassic transition of the Meishan type section","authors":"","doi":"10.1016/j.orggeochem.2024.104808","DOIUrl":"10.1016/j.orggeochem.2024.104808","url":null,"abstract":"&lt;div&gt;&lt;p&gt;Sulfur cycle fluxes implicated in the Permian-Triassic mass extinction have traditionally been studied by the sulfur phase abundances in sedimentary rocks and the stable sulfur isotopic value (δ&lt;sup&gt;34&lt;/sup&gt;S) of seawater sulfate inferred from mineral sulfate analyses. This information might be complemented by studies of the reduced inorganic sulfur and organic sulfur produced following bacterial sulfate reduction. To explore this potential the δ&lt;sup&gt;34&lt;/sup&gt;S and concentration analyses of total reduced inorganic sulfur (TRIS) and organic sulfur – separately in the forms of kerogen (Ker) and individual organosulfur compounds, specifically dibenzothiophenes (DBTs) – has been conducted on sediments across the Late Permian to Early Triassic marine type section of Meishan-1 (South China). The relatively steady δ&lt;sup&gt;34&lt;/sup&gt;S profiles (e.g., &lt; 5 ‰ variation) of all sulfur phases measured through much of the late Permian were indicative of a primary seawater sulfate control, but other biogeochemical modulators caused prominent δ&lt;sup&gt;34&lt;/sup&gt;S fluctuations of TRIS and DBT adjacent to the extinction event. The late Triassic δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;TRIS&lt;/sub&gt; profile of Meishan-1 displayed a notable &lt;sup&gt;34&lt;/sup&gt;S enrichment (+15 ‰ increase) in bed 22–24 sediments concomitant with lower δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;DBT&lt;/sub&gt; values (−7 ‰ decrease), whereas co-eval δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;KerS&lt;/sub&gt; values remained relatively constant. The contrasting δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;DBT&lt;/sub&gt; and δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;KerS&lt;/sub&gt; data suggests the dynamic behavior of specific diagenetic sulfurisation processes may be resolved by the δ&lt;sup&gt;34&lt;/sup&gt;S of discrete organic sulfur compounds (i.e., dibenzothiophenes, DBTs), but dissipated by the sulfurisation collective represented by the bulk kerogen fraction. The inverse isotopic trend observed between DBT and TRIS resulted in negative Δδ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;DBT-TRIS&lt;/sub&gt; values identifying an organic sulfurisation pathway(s) with an unusual preference over pyrite (FeS&lt;sub&gt;2&lt;/sub&gt;) for the lighter stable sulfur isotope. A redox control of the δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;DBTs&lt;/sub&gt; and δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;TRIS&lt;/sub&gt; deviations in the bed 22–24 extinction interval was confirmed by coincident variation in TRIS/(TRIS + KerS) and pyrite (Py) and highly reactive (HR) iron ratios (Fe&lt;sub&gt;Py&lt;/sub&gt;/Fe&lt;sub&gt;HR&lt;/sub&gt;). The iron (Fe) speciation data indicated a transition to ferruginous conditions, ruling out Fe&lt;sup&gt;2+&lt;/sup&gt; limitation as a factor in the bias against &lt;sup&gt;34&lt;/sup&gt;S evident in DBT formation. The &lt;sup&gt;34&lt;/sup&gt;S depletion of the DBTs promoted by the ferruginous setting may arise from the rapid and irreversible reaction of organic substrates with labile sulfur anions (e.g. HS&lt;sup&gt;-&lt;/sup&gt;) or be supported by an especially localised sediment–water depositional microenvironment. Our study highlights the potential of incorporating stable sulfur isotope analytics of reduced and organic sulfur phases, particularly of specific organic compounds, ","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"196 ","pages":"Article 104808"},"PeriodicalIF":2.6,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0146638024000731/pdfft?md5=9d326d93b611a1880f6b5891064fc7b0&pid=1-s2.0-S0146638024000731-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141281834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reconstructing the palaeoecology of a middle Permian alkaline lake using molecular fossils, case study of the Lucaogou Formation in the Junggar Basin, NW China","authors":"Wenjing Ding ,&nbsp;Dujie Hou ,&nbsp;Li Li ,&nbsp;Lian Jiang ,&nbsp;Ziming Zhang ,&nbsp;Yuhan Jiang ,&nbsp;Simon C. George","doi":"10.1016/j.orggeochem.2024.104791","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104791","url":null,"abstract":"<div><p>The lacustrine Lucaogou Formation was deposited during the middle Permian in the Junggar Basin, northwestern China. The depositional environment was an alkaline, brackish to saline lake. The biological diversity of the Lucaogou Formation was reconstructed using biologically informative molecules such as <em>n</em>-alkanes, steranes, and hopanes, and the δ¹³C composition of organic matter. C₃₀ 4α-methyl-24-ethylsterane, C₃₁ lanostane, and abundant C₃₀ − C₃₁ 3β-methylhopanes were detected in the organic matter, suggesting the presence of type Ⅰ aerobic methanotrophs including the Methylococcaceae. C₃₀ − C₃₁ 2α-methylhopanes and 7- and 8-methylheptadecanes are suggestive of the presence of cyanobacteria. Cyanobacteria and green algae are proposed to have made the dominant contribution to the organic matter. The presence of more ¹³C-enriched hopanoids in the lower unit compared to the upper unit of the Lucaogou Formation suggest a greater contribution of cyanobacteria to the organic matter in the lower unit. The high abundances of C₂₈ and C₂₉ steranes relative to C₂₇ steranes are likely due to green algae from the Chlorophyta, including the class Chlorophyceae. Dinosteranes that are diagnostic for dinoflagellates were not detected. The low concentrations of C₄₀ isorenieratane, renieratane, β-isorenieratane, renierapurpurane, and β-renierapurpurane that are indicative of photosynthetic green and purple sulfur bacteria indicate a minor contribution from Chlorobiaceae and Chromatiaceae to the organic matter. It is inferred that low to moderate amounts of ciliates grew at or below the relatively unstable chemocline in the lake. The presence of C₁₉-norisopimarane, 8β(H)-labdane, and 4β(H)-19-norisopimarane suggests the presence of coniferous plants growing around the lake, probably including Pinaceae, Araucariaceae, Cupressaceae.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"193 ","pages":"Article 104791"},"PeriodicalIF":3.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141241205","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":"Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa","authors":"A.J. Baxter ,&nbsp;F. Peterse ,&nbsp;D. Verschuren ,&nbsp;J.S. Sinninghe Damsté","doi":"10.1016/j.orggeochem.2024.104812","DOIUrl":"10.1016/j.orggeochem.2024.104812","url":null,"abstract":"<div><p>Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p <span><math><mrow><mo>&lt;</mo></mrow></math></span> 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"195 ","pages":"Article 104812"},"PeriodicalIF":2.6,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0146638024000779/pdfft?md5=a3a4873cc3f71b9b393f0ba399fd01b3&pid=1-s2.0-S0146638024000779-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141781946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study on the swelling of macromolecular geological organic matter with hydrocarbons and heteroatomic compounds","authors":"Tian Liang ,&nbsp;Xiao-Hui Lin ,&nbsp;Yan-Rong Zou ,&nbsp;Zhao-Wen Zhan ,&nbsp;Shuang Yu ,&nbsp;Chang-Chun Pan ,&nbsp;Ping’an Peng","doi":"10.1016/j.orggeochem.2024.104809","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104809","url":null,"abstract":"<div><p>In this study, we conducted swelling experiments on eleven macromolecular geological organic materials using five types of organic solvents. Our primary objective was to investigate the absorption capacity of different solid organic materials in organic fluids and analyze the influence of their chemical structures. The samples utilized in this research included solid bitumen, kerogen, and coal samples from various basins. The chemical structure of the samples was assessed using solid-state ¹³C nuclear magnetic resonance (NMR), while X-ray diffraction (XRD) was employed to monitor any detect the structural changes during the swelling process. Our findings reveal that macromolecular geological organic compounds demonstrate a preferential expulsion of saturated hydrocarbons, followed by polycyclic aromatic hydrocarbons, upon interaction with liquid organic matter. The sulfur-containing compounds in solid organic matter demonstrated higher solubility than hydrocarbon compounds, while the solubility of oxygen-containing compounds varied based on the structure of the aliphatic chain and the proportion of oxygen atoms. This research, introduces LA [= L_ac × A_ac] as a new parameter to assess the combination of aliphatic chain length [L_ac] and [A_ac] abundance in solid organic matter. Furthermore, XRD testing revealed that the chemical structure unit of heteroatom compounds in solid organic matter consists of amorphous carbon, primarily composed of aliphatic chains. In this study, we evaluated the retention capacity of various macromolecular geological organic matter for both hydrocarbons and heteroatomic compounds. Additionally, the extent of swelling was investigated, providing theoretical support to diverse fields including organic petrology, petroleum geology, coal geology, and organic geochemistry.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"193 ","pages":"Article 104809"},"PeriodicalIF":3.0,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141241186","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":"Multiple isotopes (C-S-N-H) and bound biomarkers in asphaltenes: New constraints on the classification and genesis of reservoir bitumens from the northwestern Sichuan Basin, South China","authors":"Susu Wang ,&nbsp;Jian Chen ,&nbsp;Wanglu Jia ,&nbsp;Ping’an Peng","doi":"10.1016/j.orggeochem.2024.104807","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2024.104807","url":null,"abstract":"<div><p>Reservoir bitumens in the northwestern Sichuan basin are significant for elucidating the sources and charging history of oil and gas, given their widespread occurrence in multiple strata in the area and abundant biomarkers. The debate regarding the origin and genesis of these bitumens has persisted for a long time, due to severe biodegradation and the development of multiple sets of high maturity source rocks with few biomarkers for oil-source correlation. To resolve these questions, asphaltenes, which are more resistant to biodegradation than free hydrocarbons, were systematically analyzed with the bulk multi-isotopes (C-S-N-H), bound molecules and the carbon isotopic compositions of bound individual <em>n</em>-alkanes. These characteristics were then compared to those of bulk bitumen and free hydrocarbons, leading to three main conclusions. In most samples, relatively abundant 25-norhopanes and 17-nortricylic terpanes were identified along with <em>n</em>-alkanes in free hydrocarbons, suggesting at least two oil charging events. In the samples having free <em>n</em>-alkanes, the carbon isotopic compositions of asphaltene-bound <em>n</em>-alkanes closely resemble those of corresponding free <em>n</em>-alkanes. Moreover, the bulk C-S-N isotopic compositions of asphaltene also approach those of corresponding bulk bitumen. These results suggest that the source of the oil charges occuring at different times are mostly the same for an individual sample, though different bitumen samples may have distinct sources. Free hydrocarbons, including <em>n</em>-alkanes and biomarkers, may have been produced by the secondary cracking of asphaltenes. Second, the integration of bulk C-S-N isotopic compositions of the asphaltenes and bitumens has enabled the studied samples to be classified into four groups. Source facies is the primary control of the distinct isotopic compositions with other factors like biodegradation, thermal maturity and migration having only minor influence. In combination with biomarkers, the organic matter and sedimentary environment of source rocks could be characterized for each group. A careful comparison of the bulk C-S-N isotopic compositions of asphaltenes and bitumens with those previously reported for source rocks (organic C and S and bulk N isotopes) suggests the main source rocks in the Upper Ediacarian-Lower Cambrian Formations, supporting the conclusions of previous studies. Furthermore, those source rocks in much younger formations, such as the Middle Permian as well as the Middle Devonian Formations, may also have contributed significantly to the widespread reservoir bitumens in the region. These findings highlight the usefulness of bulk C-S-N isotopic composition of asphaltenes for distinguishing oils with complex genesis and large gas exploration potential of the Upper Paleozoic source rocks in the region.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"193 ","pages":"Article 104807"},"PeriodicalIF":3.0,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141241204","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}