{"title":"Drimane-type sesquiterpanes as molecular tracers for thermal effects and geologic processes in sedimentary basins","authors":"Biqing Zhu , Quanyou Liu , Huiyuan Xu , Dongya Zhu , Weilong Peng , Xiaoqi Wu , Yongqi Ruan , Chi Zhang","doi":"10.1016/j.chemgeo.2025.122987","DOIUrl":null,"url":null,"abstract":"<div><div>Drimane-type sesquiterpanes exhibit exceptional thermal stability and ubiquity across organic-rich sedimentary systems, from hydrothermal vents to crude oils, positioning them as critical molecular intermediaries in biomarker transformation pathways. The systematic GC–MS analysis of multi-phase crude oils from the Tarim Basin's ultra-deep reservoirs (depth > 7 km, temperature > 140 °C) identifies thermally-controlled molecular transformations. Cheilanthanes, particularly C<sub>19</sub> ∼ C<sub>23</sub> homologues, exhibit greater thermal stability than hopanes. Drimane-type sesquiterpanes display source-dependent initial abundances and maturation-driven transformations: 4,4,8,8,9-pentamethyldecane (RD1) accumulates progressively, 4,4,8,9,9-pentamethyldecane (RD2) shows transient accumulation followed by depletion, while drimane (D) and homodrimane (HD) decline continuously. The transmethylation reaction under high thermal stress leads to RD1 enrichment, making it an ultra-stable end-member in the thermal maturation of C<sub>15</sub> drimane-type sesquiterpanes. Maturity indicators derived from trimethylnaphthalenes and methylphenanthrenes exhibit good correlations with thermal gradient, whereas dibenzothiophene-derived parameters demonstrate the weak correlation. In contrast, sesquiterpane-derived ratios display superior strong correlation with thermal gradient compared to aromatic hydrocarbon indices. The RD1/(RD1 + D + HD) ratio is proposed as an optimized molecular proxy for assessing thermal effects and phase behaviors in sedimentary basins. This study provides a potential tool for investigating the thermal effects of diverse geological processes, such as plate movement, earthquake slip, magmatic intrusion, and hydrothermal activity.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"693 ","pages":"Article 122987"},"PeriodicalIF":3.6000,"publicationDate":"2025-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemical Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0009254125003778","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Drimane-type sesquiterpanes exhibit exceptional thermal stability and ubiquity across organic-rich sedimentary systems, from hydrothermal vents to crude oils, positioning them as critical molecular intermediaries in biomarker transformation pathways. The systematic GC–MS analysis of multi-phase crude oils from the Tarim Basin's ultra-deep reservoirs (depth > 7 km, temperature > 140 °C) identifies thermally-controlled molecular transformations. Cheilanthanes, particularly C19 ∼ C23 homologues, exhibit greater thermal stability than hopanes. Drimane-type sesquiterpanes display source-dependent initial abundances and maturation-driven transformations: 4,4,8,8,9-pentamethyldecane (RD1) accumulates progressively, 4,4,8,9,9-pentamethyldecane (RD2) shows transient accumulation followed by depletion, while drimane (D) and homodrimane (HD) decline continuously. The transmethylation reaction under high thermal stress leads to RD1 enrichment, making it an ultra-stable end-member in the thermal maturation of C15 drimane-type sesquiterpanes. Maturity indicators derived from trimethylnaphthalenes and methylphenanthrenes exhibit good correlations with thermal gradient, whereas dibenzothiophene-derived parameters demonstrate the weak correlation. In contrast, sesquiterpane-derived ratios display superior strong correlation with thermal gradient compared to aromatic hydrocarbon indices. The RD1/(RD1 + D + HD) ratio is proposed as an optimized molecular proxy for assessing thermal effects and phase behaviors in sedimentary basins. This study provides a potential tool for investigating the thermal effects of diverse geological processes, such as plate movement, earthquake slip, magmatic intrusion, and hydrothermal activity.
期刊介绍:
Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry.
The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry.
Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry.
The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.