| 南海神狐海域沉积物自生黄铁矿和石膏S同位素特征及对甲烷渗漏强度的示踪 |
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| 引用本文： | 张美,陆红锋,管红香,刘丽华,邬黛黛,吴能友.南海神狐海域沉积物自生黄铁矿和石膏S同位素特征及对甲烷渗漏强度的示踪[J].海洋学报(英文版),2018,37(7):20-27. |
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| 作者姓名： | 张美 陆红锋 管红香 刘丽华 邬黛黛 吴能友 |
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| 作者单位： | 中国科学院天然气水合物重点实验室, 中国科学院广州能源研究所, 510640, 广州,广州海洋地质调查局, 510760, 广州,中国科学院天然气水合物重点实验室, 中国科学院广州能源研究所, 510640, 广州;海洋国家实验室海洋矿产资源评价与探测技术功能实验室, 266071, 青岛,中国科学院天然气水合物重点实验室, 中国科学院广州能源研究所, 510640, 广州,中国科学院天然气水合物重点实验室, 中国科学院广州能源研究所, 510640, 广州,海洋国家实验室海洋矿产资源评价与探测技术功能实验室, 266071, 青岛;国土资源部天然气水合物重点实验室, 青岛海洋地质研究所, 266071, 青岛 |
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| 基金项目： | The Qingdao National Laboratory for Marine Science and Technology under contract No. QNLM2016ORP0210; the National Natural Science Foundation of China under contract Nos 41306061, 41473080 and 41376076; the Scientific Cooperative Project by China National Petroleum Corporation and Chinese Academic of Sciences under contract No. 2015A- 4813. |
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| 摘 要： | The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane(AOM) coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor(cmbsf) in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values(δ~(34) S) of pyrite vary greatly(from –46.6‰ to –12.3‰ V-CDT) and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction(OSR) and is influenced by AOM with depth.The relative high abundance and δ~(34) S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone(SMTZ).The sulfur isotopic composition of gypsum(from–25‰ to –20.7‰) is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO_2,iron(Ⅲ) and oxygen driven by the SMTZ location shift to great depths.The δ~(34) S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage.
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| 关 键 词： | 管状黄铁矿 自生石膏 S同位素 甲烷渗漏 南海北部 |
| 收稿时间： | 2017/7/24 0:00:00 |
Methane seepage intensities traced by sulfur isotopes of pyrite and gypsum in sediment from the Shenhu area, South China Sea |
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| ZHANG Mei,LU Hongfeng,GUAN Hongxiang,LIU Lihu,WU Daidai and WU Nengyou.Methane seepage intensities traced by sulfur isotopes of pyrite and gypsum in sediment from the Shenhu area, South China Sea[J].Acta Oceanologica Sinica,2018,37(7):20-27. |
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| Authors: | ZHANG Mei LU Hongfeng GUAN Hongxiang LIU Lihu WU Daidai and WU Nengyou |
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| Institution: | 1.Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion,Chinese Academy of Sciences,Guangzhou,China;2.Guangzhou Marine Geological Survey,Guangzhou,China;3.Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao,China;4.Key Laboratory of Gas Hydrate, Qingdao Institute of Marine Geology,Ministry of Land and Resources,Qingdao,China |
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| Abstract: | The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments. Anaerobic oxidation of methane (AOM) coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment, including pyrite and gypsum. Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor (cmbsf) in the entire core sediment of HS328 from the northern South China Sea. Most pyrites are tubes consisting of framboidal cores and outer crusts. Gypsum aggregates occur as rosettes and spheroids consisting of plates. Some of them grow over pyrite, indicating that gypsum precipitation postdates pyrite formation. The sulfur isotopic values (δ34S) of pyrite vary greatly (from–46.6‰ to–12.3‰ V-CDT) and increase with depth. Thus, the pyrite in the shallow sediments resulted from organoclastic sulfate reduction (OSR) and is influenced by AOM with depth. The relative high abundance and δ34S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone (SMTZ). The sulfur isotopic composition of gypsum (from–25‰ to–20.7‰) is much lower than that of the seawater sulfate, indicating the existence of a 34S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR. Pyrite oxidation is controlled by ambient electron acceptors such as MnO2, iron (III) and oxygen driven by the SMTZ location shift to great depths. The δ34S values of gypsum at greater depth are lower than those of the associated pyrite, revealing downward diffusion of 34S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate. These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral, which will be favor to the formation of gypsum. Overall, the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities, and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage. |
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| Keywords: | pyrite tube authigenic gypsum sulfur isotopes methane seepage northern South China Sea |
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