Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications
The lower and middle Carboniferous shale sequences are one of the important potential hydrocarbon source rocks in the piedmont of the southwestern Tarim Basin, China (PSTB). Rock samples were collected from the lower and middle Carboniferous formations on the Kushanhe, Altash, and Aitegou outcrops i...
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| author | Xueyou Tan Zhushi Ge Suyang Cai Qilin Xiao |
| author_facet | Xueyou Tan Zhushi Ge Suyang Cai Qilin Xiao |
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| description | The lower and middle Carboniferous shale sequences are one of the important potential hydrocarbon source rocks in the piedmont of the southwestern Tarim Basin, China (PSTB). Rock samples were collected from the lower and middle Carboniferous formations on the Kushanhe, Altash, and Aitegou outcrops in the PSTB with the intention of mapping the hydrocarbon molecules within these shale sources and disclosing the relevant geochemical implications. The ratios of Pr/Ph < 1.0 and DBT/P < 0.4 and the enrichment of C<sub>23</sub> tricyclic terpanoid indicate that the Carboniferous shale sources were deposited in a reducing and sulfate-poor marine setting with the contribution of terrestrial freshwater. Marine aquatic algae act as the major contributor, resulting in the formation of Type II<sub>1</sub> kerogen. The Carboniferous shale sequences contain abundant diamondoids with 2–4 cages with the predominance of methyldiamantanes, dimethyldiamantanes, and methyltriamantanes. Quantitative extended diamondoid analysis indicates the occurrence of carbonate-rich and carbonate-poor organic facies in the PSTB. Compared to the carbonate-poor facies, the carbonate-rich facies is relatively depleted in C<sub>27</sub> diasteranes and rich in gammacerane, C<sub>27</sub> regular steranes, and alkylated triamantanes. This indicates that it was deposited in the more salty and stratified water column but with less input of land higher plants. The clay catalysis effects are assumed to be responsible for the discrepancy in steranes and diamondoids. The Carboniferous shale sequences also contain abundant polycyclic aromatic hydrocarbons with 2–5 rings with the predominance of C<sub>0–1</sub>-phenanthrenes, chrysenes, and benzofluoranthenes. Thermal maturity parameters associated with polycyclic aromatic hydrocarbons and diamondoids suggest that the Carboniferous shale sources have arrived at the late mature to highly mature stage. This study provides the detailed molecular fingerprints of the lower and middle Carboniferous shale source sequences and explores the underlying geochemical implications. This should be helpful for oil–oil and oil–source correlations and hence petroleum exploration activity in the PSTB. |
| format | Article |
| id | doaj-art-fd4231d31de54bcf985de40c2d94ffa4 |
| institution | OA Journals |
| issn | 1996-1073 |
| language | English |
| publishDate | 2025-05-01 |
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| spelling | doaj-art-fd4231d31de54bcf985de40c2d94ffa42025-08-20T02:33:11ZengMDPI AGEnergies1996-10732025-05-011811273710.3390/en18112737Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical ImplicationsXueyou Tan0Zhushi Ge1Suyang Cai2Qilin Xiao3Key Laboratory of Exploration Technologies for Oil and Gas Resources, Yangtze University, Ministry of Education, Wuhan 430100, ChinaKey Laboratory of Exploration Technologies for Oil and Gas Resources, Yangtze University, Ministry of Education, Wuhan 430100, ChinaKey Laboratory of Exploration Technologies for Oil and Gas Resources, Yangtze University, Ministry of Education, Wuhan 430100, ChinaKey Laboratory of Exploration Technologies for Oil and Gas Resources, Yangtze University, Ministry of Education, Wuhan 430100, ChinaThe lower and middle Carboniferous shale sequences are one of the important potential hydrocarbon source rocks in the piedmont of the southwestern Tarim Basin, China (PSTB). Rock samples were collected from the lower and middle Carboniferous formations on the Kushanhe, Altash, and Aitegou outcrops in the PSTB with the intention of mapping the hydrocarbon molecules within these shale sources and disclosing the relevant geochemical implications. The ratios of Pr/Ph < 1.0 and DBT/P < 0.4 and the enrichment of C<sub>23</sub> tricyclic terpanoid indicate that the Carboniferous shale sources were deposited in a reducing and sulfate-poor marine setting with the contribution of terrestrial freshwater. Marine aquatic algae act as the major contributor, resulting in the formation of Type II<sub>1</sub> kerogen. The Carboniferous shale sequences contain abundant diamondoids with 2–4 cages with the predominance of methyldiamantanes, dimethyldiamantanes, and methyltriamantanes. Quantitative extended diamondoid analysis indicates the occurrence of carbonate-rich and carbonate-poor organic facies in the PSTB. Compared to the carbonate-poor facies, the carbonate-rich facies is relatively depleted in C<sub>27</sub> diasteranes and rich in gammacerane, C<sub>27</sub> regular steranes, and alkylated triamantanes. This indicates that it was deposited in the more salty and stratified water column but with less input of land higher plants. The clay catalysis effects are assumed to be responsible for the discrepancy in steranes and diamondoids. The Carboniferous shale sequences also contain abundant polycyclic aromatic hydrocarbons with 2–5 rings with the predominance of C<sub>0–1</sub>-phenanthrenes, chrysenes, and benzofluoranthenes. Thermal maturity parameters associated with polycyclic aromatic hydrocarbons and diamondoids suggest that the Carboniferous shale sources have arrived at the late mature to highly mature stage. This study provides the detailed molecular fingerprints of the lower and middle Carboniferous shale source sequences and explores the underlying geochemical implications. This should be helpful for oil–oil and oil–source correlations and hence petroleum exploration activity in the PSTB.https://www.mdpi.com/1996-1073/18/11/2737Tarim Basincarboniferous source rockterpanesdiamondoidsorganic facies |
| spellingShingle | Xueyou Tan Zhushi Ge Suyang Cai Qilin Xiao Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications Energies Tarim Basin carboniferous source rock terpanes diamondoids organic facies |
| title | Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications |
| title_full | Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications |
| title_fullStr | Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications |
| title_full_unstemmed | Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications |
| title_short | Molecular Compositions of Hydrocarbons Within the Lower and Middle Carboniferous Shale Sequences from the Outcrops in the Piedmont of Southwestern Tarim Basin and the Possible Geochemical Implications |
| title_sort | molecular compositions of hydrocarbons within the lower and middle carboniferous shale sequences from the outcrops in the piedmont of southwestern tarim basin and the possible geochemical implications |
| topic | Tarim Basin carboniferous source rock terpanes diamondoids organic facies |
| url | https://www.mdpi.com/1996-1073/18/11/2737 |
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