Dongyong Wang , Meijun Li , Jianfa Chen , Hong Xiao , Xianli Zou , Lu Yang , Haochen Chen , Huiqiang Qin
{"title":"The biological source and paleoenvironment implication of rare short-chain lanostanes in alkaline lacustrine sediments","authors":"Dongyong Wang , Meijun Li , Jianfa Chen , Hong Xiao , Xianli Zou , Lu Yang , Haochen Chen , Huiqiang Qin","doi":"10.1016/j.orggeochem.2023.104705","DOIUrl":null,"url":null,"abstract":"<div><p>Highly mature organic-rich source rocks in the Early Permian Fengcheng Formation, Mahu Sag, Junggar Basin, northwestern China, were deposited in an alkaline lacustrine environment. Analysis of extracts of eight core samples by gas chromatography–mass spectrometry detected a series of short-chain lanostanes (C<sub>23</sub>–C<sub>25</sub>) lanostanes. The relative abundance of short-chain lanostanes has a strong positive correlation with those of long chain (C<sub>30</sub>–C<sub>32</sub>) homologues, indicating a possible common biological origin and genesis. Compound specific isotopic analyses of phytane, steranes, hopanes and C<sub>30</sub> lanostane from the core extracts reflect input from primary photosynthetic producers including cyanobacteria. Abundant lamalginite was observed in the samples from the study area. A well-defined positive relationship is also evident between the relative abundance of lanostanes and the ratios of 7-+8-methyl heptadecanes/<em>C</em><sub>max</sub> and 2-methyl hopanes/C<sub>30</sub>-hopanes. Given that 7-+8-methyl heptadecanes and 2-methyl hopanes are considered to be diagnostic molecular biomarkers for organic matter derived from cyanobacteria, it is possible that cyanobacteria may serve as a possible biological precursor for lanostanes in the Fengcheng Formation. The influence of maturity on the lanostanes is considered to be minor, as no significant relationship is found between lanostanes and thermal maturity parameters, although this may be due to a limited maturity range of the samples. The co-existence of high contents of phytane, β-carotanes, and gammacerane, and their correlations in abundance with lanostanes, indicates a strongly reducing sedimentary environment.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"186 ","pages":"Article 104705"},"PeriodicalIF":2.6000,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Organic Geochemistry","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0146638023001511","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Highly mature organic-rich source rocks in the Early Permian Fengcheng Formation, Mahu Sag, Junggar Basin, northwestern China, were deposited in an alkaline lacustrine environment. Analysis of extracts of eight core samples by gas chromatography–mass spectrometry detected a series of short-chain lanostanes (C23–C25) lanostanes. The relative abundance of short-chain lanostanes has a strong positive correlation with those of long chain (C30–C32) homologues, indicating a possible common biological origin and genesis. Compound specific isotopic analyses of phytane, steranes, hopanes and C30 lanostane from the core extracts reflect input from primary photosynthetic producers including cyanobacteria. Abundant lamalginite was observed in the samples from the study area. A well-defined positive relationship is also evident between the relative abundance of lanostanes and the ratios of 7-+8-methyl heptadecanes/Cmax and 2-methyl hopanes/C30-hopanes. Given that 7-+8-methyl heptadecanes and 2-methyl hopanes are considered to be diagnostic molecular biomarkers for organic matter derived from cyanobacteria, it is possible that cyanobacteria may serve as a possible biological precursor for lanostanes in the Fengcheng Formation. The influence of maturity on the lanostanes is considered to be minor, as no significant relationship is found between lanostanes and thermal maturity parameters, although this may be due to a limited maturity range of the samples. The co-existence of high contents of phytane, β-carotanes, and gammacerane, and their correlations in abundance with lanostanes, indicates a strongly reducing sedimentary environment.
期刊介绍:
Organic Geochemistry serves as the only dedicated medium for the publication of peer-reviewed research on all phases of geochemistry in which organic compounds play a major role. The Editors welcome contributions covering a wide spectrum of subjects in the geosciences broadly based on organic chemistry (including molecular and isotopic geochemistry), and involving geology, biogeochemistry, environmental geochemistry, chemical oceanography and hydrology.
The scope of the journal includes research involving petroleum (including natural gas), coal, organic matter in the aqueous environment and recent sediments, organic-rich rocks and soils and the role of organics in the geochemical cycling of the elements.
Sedimentological, paleontological and organic petrographic studies will also be considered for publication, provided that they are geochemically oriented. Papers cover the full range of research activities in organic geochemistry, and include comprehensive review articles, technical communications, discussion/reply correspondence and short technical notes. Peer-reviews organised through three Chief Editors and a staff of Associate Editors, are conducted by well known, respected scientists from academia, government and industry. The journal also publishes reviews of books, announcements of important conferences and meetings and other matters of direct interest to the organic geochemical community.