| 南海北部琼东南盆地浅表层沉积物的地球化学特征及对沉积环境的指示* |
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| 引用本文： | 孙甜甜,邬黛黛,潘梦迪,杨飞,吴能友,陈雪刚,刘丽华.南海北部琼东南盆地浅表层沉积物的地球化学特征及对沉积环境的指示*[J].热带海洋学报,2018,37(4):70-80. |
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| 作者姓名： | 孙甜甜 邬黛黛 潘梦迪 杨飞 吴能友 陈雪刚 刘丽华 |
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| 作者单位： | 1. 浙江大学海洋学院, 浙江 舟山 3160212. 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, 广东 广州 5106403. 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, 山东 青岛 2660714. 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, 山东 青岛 266071 |
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| 基金项目： | 国家自然科学基金项目(41273022);中国石油-中国科学院科技合作项目(2015A-4813);中国科学院青年创新促进会项目(2014321);青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室开放基金(KC201703) |
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| 摘 要： | 南海北部琼东南盆地海底存在着巨型麻坑, 现有研究多认为其形成主要与海底流体渗漏有关。目前对琼东南盆地深海沉积物地球化学特征及麻坑区的生物地球化学过程等尚不清楚。文章选取南海北部琼东南盆地C14、C19两个站位岩心样品, 进行了总硫(TS)、总碳(TC)、总有机碳(TOC)、铬还原性硫化物(CRS)及其δ34SCRS值测试, 并结合总氮/总碳(TN/TOC)比值和已发表的孔隙水中SO42-浓度等进行了地球化学特征分析。研究表明: C14站位以3.91m bsf (below seafloor)为界, 上下分别存在有机质参与的硫酸盐还原反应(OSR)和甲烷厌氧氧化作用(AOM)驱动的硫酸盐还原反应(SR); 3.91m bsf以上的部位沉积物的TS、TC含量均低于3.91m bsf以下部位, 且沉积物孔隙水中SO42-浓度由3.91m bsf以上的缓慢凹型减少变成3.91m bsf以下的线性减少, 说明该处成为沉积物中地球化学特征分界的明显标志; 在3.91m bsf以下, 受到甲烷渗漏的影响。C19站位沉积物中TS与TC含量由浅到深逐渐增加, 但与TN/TOC比值变化呈现几乎相反趋势, 即整个岩心以OSR为主, 并呈现出有机质早期成岩阶段的沉积现象。C14和C19两个站位柱状沉积物的δ34SCRS值变化范围分别为-50.2‰~-46.9‰和-50.1‰~-42.0‰ (V-CDT标准), 均显示出了较为偏负的硫同位素值, 表明研究区主要的生物化学过程是在相对开放体系下硫酸盐还原作用的结果, 综合说明该研究区麻坑的甲烷流体已经喷发, 目前可能处于衰退期, 甚至已经不活跃, 该结果与前人的认识基本一致。
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| 关 键 词： | 铬还原性硫化物 硫同位素值 甲烷厌氧氧化作用 硫酸盐还原反应 麻坑 琼东南盆地 |
| 收稿时间： | 2017-08-29 |
| 修稿时间： | 2017-10-10 |
Geochemical characteristics of surface sediments in the Southern Qiongdongnan Basin of the northern South China Sea and its implication for sedimentary environment* |
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| Tiantian SUN,Daidai WU,Mengdi PAN,Fei YANG,Nengyou WU,Xuegang CHENG,Lihua LIU.Geochemical characteristics of surface sediments in the Southern Qiongdongnan Basin of the northern South China Sea and its implication for sedimentary environment*[J].Journal of Tropical Oceanography,2018,37(4):70-80. |
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| Authors: | Tiantian SUN Daidai WU Mengdi PAN Fei YANG Nengyou WU Xuegang CHENG Lihua LIU |
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| Institution: | 1. Ocean College of Zhejiang University, Zhoushan 316021, China2. Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China3. Evaluation and Detection Technology Laboratory of Marine Mineral Resources, Qingdao National Laboratory for Marine Sciences and Technology, Qingdao 266071, China4. Key Laboratory of Gas Hydrate, Ministry of Land and Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China |
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| Abstract: | The seabed pockmark is widely found in the Qiongdongnan Basin in the northern slope of the South China Sea. The formation of pockmark is mainly regarded as related to the seabed fluid seepage in recent studies. However, it is still unclear what the geochemical characteristics of the seabed sediment are and what corresponding activities of the pockmark are. Two sediment cores of C14 and C19 from the Southern Qiongdongnan Basin were recovered and investigated in this study. Here, we examine the contents of total sulfur (TS), total carbon (TC) and total organic carbon (TOC) contents as well as chromium reducible sulfur (CRS) content and its stable isotopes (δ34SCRS) values. Combined with the ratio of total nitrogen to total organic carbon (TN/TOC) and reduced sulfate content in pore water, we analyze the geochemical characteristics. The results suggest that there are two types of sulfate reduction reaction (SR) at the C14 site - the anoxygenous oxidation of organic matter controlled SR (OSR) at the depth of 0~3.91 meters below seafloor (m bsf) and the anaerobic oxidation of methane (AOM) derived SR at the depth of 3.91~7.55 m bsf, and the depth of 3.91 m bsf is the boundary of the two types of reaction of SR. The contents of TS and TC below 3.91 m bsf are higher than those above 3.91 m bsf, and the concentration of sulfate in pore water below 3.91 m bsf decreases linearly with depth, Therefore, the depth of 3.91 m bsf is a significant indicator for geochemical characteristics in sediment core. Moreover, the SR below 3.91 m bsf is controlled by the seepage of methane-bearing fluid. The contents of TS and TC at the C19 site increase with depth. However, the variation of TN/TOC ratios is almost contrary to the patterns of TS and TC contents, that is, because OSR is the main SR type of the whole sediment core at the C19 site and the organic matter is revealed to be deposited in early diagenetic stage. The δ34SCRS values from cores C14 and C19 are -50.2‰~-46.9‰ and -50.1‰~-42.0‰, respectively. The negative δ34SCRS values suggest that the major biogeochemical process is the result of sulfate reduction in a relatively open system. Therefore, the methane-bearing fluid for the pockmark in the Qiongdongnan Basin had leaked and the pockmark is now seemingly in a weak seepage stage and/or even to be inactive. |
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| Keywords: | chromium reducible sulfur (CRS) stable isotopes anaerobic oxidation of methane (AOM) sulfate reduction (SR) pockmark Qiongdongnan Basin |
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