| ZHANG Mei,LU Hongfeng,GUAN Hongxiang,LIU Lihua,WU Daidai,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 |
| 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 |
| Methane seepage intensities traced by sulfur isotopes of pyrite and gypsum in sediment from the Shenhu area, South China Sea |
| 投稿时间：2017-07-24 |
| DOI：10.1007/s13131-018-1241-1 |
| 中文关键词: 管状黄铁矿 自生石膏 S同位素 甲烷渗漏 南海北部 |
| 英文关键词:pyrite tube authigenic gypsum sulfur isotopes methane seepage northern South China Sea |
| 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. |
| 作者 | 单位 | E-mail | | 张美 | 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 | zhangmei@ms.giec.ac.cn | | 陆红锋 | 广州海洋地质调查局, 510760, 广州 | | | 管红香 | 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 | | | 刘丽华 | 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 | | | 邬黛黛 | 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 | | | 吴能友 | 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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| 中文摘要: |
| 南海北部陆坡具有沉积速率高，有机质丰富等天然气水合物赋存的有利条件，该区域还发现有大量的甲烷渗漏。甲烷厌氧氧化（AOM）和硫酸盐还原共同作用导致自生矿物（黄铁矿，石膏）在沉积物中富集。在南海北部的HS328站位，大量的黄铁矿和石膏富集在667-850 cmbsf层位，产出的黄铁矿呈管状，由草莓球核和外壳组成；石膏主要由板状组成，呈玫瑰花状和球状集合体，部分石膏包裹着黄铁矿，说明石膏形成于黄铁矿之后。黄铁矿的δ34S值变化较大（-46.6‰~-12.3‰ V-CDT），且随深度的增加而增大，说明浅部黄铁矿由有机质驱动硫酸盐还原作用（OSR）形成，AOM的影响随深度增加。在沉积物580~810cmbsf层位，相对高含量黄铁矿及其S同位素值说明这个层位是古硫酸盐-甲烷转换带（Paleo-SMTZ）。石膏S同位素值（-25‰~-20.7‰）比海水硫酸盐的S同位素值要低，说明亏损的S源可能来源OSR形成黄铁矿的氧化，这个反应由硫酸盐-甲烷转换带（SMTZ）变深而引起周围环境中电子接收体如MnO2,Fe3+和O2等对黄铁矿的氧化。深部石膏的S同位素值（δ34S）比同层位黄铁矿的S同位素值低，也同样反映了深部石膏的S源来自上部海水和OSR成因黄铁矿的氧化，这些硫酸盐还会导致碳酸盐矿物的溶解和Ca2+的增加，有利于石膏的形成。总之，黄铁矿和石膏的矿物学特点和S同位素组成可以用于指示渗漏强度导致氧化还原条件的变化，黄铁矿和石膏可以用作记录甲烷渗漏强度变化。 |
| 英文摘要: |
| 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 (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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