Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea
Deep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl− concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the southwestern Xisha...
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2014-06-01
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| Online Access: | http://www.mdpi.com/1996-1073/7/6/3886 |
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| author | Min Luo Linying Chen Hongpeng Tong Wen Yan Duofu Chen |
| author_facet | Min Luo Linying Chen Hongpeng Tong Wen Yan Duofu Chen |
| author_sort | Min Luo |
| collection | DOAJ |
| description | Deep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl− concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the southwestern Xisha Uplift, northern South China Sea (SCS). Pore water collected from a gravity-core inside of a mega-pockmark exhibits a downward Cl− concentration decrease concomitant with an increase in δ18O value at the interval of 5.7–6.7 mbsf. Concentrations of Cl−, Na+, and K+ mainly cluster along the seawater freshening line without distinct Na+ enrichment and K+ depletion. Thus, we infer that the pore water anomalies of Cl− concentrations and δ18O values are attributed to gas hydrate dissociation instead of clay mineral dehydration. Moreover, the lower δ18O values of sulfate in the target core (C14) than those in the reference core (C9) may be associated with the equilibrium oxygen fractionation during sulfate reduction between sulfate and the relatively 18O-depleted ambient water resulting from gas hydrate formation. The gas hydrate contents are estimated to be 6%–10% and 7%–15%, respectively, according to the offset of Cl− concentrations and δ18O values from the baselines. This pockmark field in southwestern Xisha Uplift is likely to be a good prospective area for the occurrence of gas hydrate in shallow sediments. |
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| id | doaj.art-40bda74d095e4755ad7b9509da9c826a |
| institution | Directory Open Access Journal |
| issn | 1996-1073 |
| language | English |
| last_indexed | 2024-04-13T08:03:17Z |
| publishDate | 2014-06-01 |
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| series | Energies |
| spelling | doaj.art-40bda74d095e4755ad7b9509da9c826a2022-12-22T02:55:14ZengMDPI AGEnergies1996-10732014-06-01763886389910.3390/en7063886en7063886Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China SeaMin Luo0Linying Chen1Hongpeng Tong2Wen Yan3Duofu Chen4Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, ChinaKey Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, ChinaKey Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, ChinaDeep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl− concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the southwestern Xisha Uplift, northern South China Sea (SCS). Pore water collected from a gravity-core inside of a mega-pockmark exhibits a downward Cl− concentration decrease concomitant with an increase in δ18O value at the interval of 5.7–6.7 mbsf. Concentrations of Cl−, Na+, and K+ mainly cluster along the seawater freshening line without distinct Na+ enrichment and K+ depletion. Thus, we infer that the pore water anomalies of Cl− concentrations and δ18O values are attributed to gas hydrate dissociation instead of clay mineral dehydration. Moreover, the lower δ18O values of sulfate in the target core (C14) than those in the reference core (C9) may be associated with the equilibrium oxygen fractionation during sulfate reduction between sulfate and the relatively 18O-depleted ambient water resulting from gas hydrate formation. The gas hydrate contents are estimated to be 6%–10% and 7%–15%, respectively, according to the offset of Cl− concentrations and δ18O values from the baselines. This pockmark field in southwestern Xisha Uplift is likely to be a good prospective area for the occurrence of gas hydrate in shallow sediments.http://www.mdpi.com/1996-1073/7/6/3886gas hydratepore waterchlorideδ18Osouthwestern Xisha Uplift |
| spellingShingle | Min Luo Linying Chen Hongpeng Tong Wen Yan Duofu Chen Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea Energies gas hydrate pore water chloride δ18O southwestern Xisha Uplift |
| title | Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea |
| title_full | Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea |
| title_fullStr | Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea |
| title_full_unstemmed | Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea |
| title_short | Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea |
| title_sort | gas hydrate occurrence inferred from dissolved cl concentrations and δ18o values of pore water and dissolved sulfate in the shallow sediments of the pockmark field in southwestern xisha uplift northern south china sea |
| topic | gas hydrate pore water chloride δ18O southwestern Xisha Uplift |
| url | http://www.mdpi.com/1996-1073/7/6/3886 |
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