| SUN Tiantian,WU Daidai,YANG Fei,LIU Lihua,CHEN Xuegang,YE Ying. 2019. Sedimentary geochemical proxies for methane seepage at Site C14 in the Qiongdongnan Basin in the northern South China Sea. Acta Oceanologica Sinica, 38(7):84－95 |
| Sedimentary geochemical proxies for methane seepage at Site C14 in the Qiongdongnan Basin in the northern South China Sea |
| 南海北部琼东南盆地冷泉区表层沉积物微量元素的分析及其对甲烷渗漏的指示 |
| Received:May 08, 2018 |
| DOI：10.1007/s13131-019-1460-6 |
| Key words:Qiongdongnan Basin trace elements stable isotope values anaerobic oxidation of methane methane activity |
| 中文关键词: 琼东南盆地 微量元素 铬还原性硫化物(CRS) 硫同位素值 甲烷厌氧氧化作用(AOM) 甲烷渗漏 |
| 基金项目:The Program of Institution of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences under contract No. ISEE2018YB03; the Special Project for Marine Economy Development of Guangdong Province under contract No. GDME-2018D002; the Evaluation and Detection Technology Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology under contract No. KC201703; the Youth Innovation Promotion Association CAS under contract No. 201432. |
| Author Name | Affiliation | E-mail | | SUN Tiantian | Ocean College of Zhejiang University, Zhoushan 316021, China
Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China | | | WU Daidai | Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
Evaluation and Detection Technology Laboratory of Marine Mineral Resources, Pilot National Laboratory for Marine Sciences and Technology (Qingdao), Qingdao 266071, China | wudd@ms.giec.ac.cn | | YANG Fei | Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China | | | LIU Lihua | Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China | | | CHEN Xuegang | Ocean College of Zhejiang University, Zhoushan 316021, China | | | YE Ying | Ocean College of Zhejiang University, Zhoushan 316021, China | |
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| Abstract: |
| Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events. In this work, the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained. The results confirmed that, sulfate at 0-247 cm below sea floor (Unit I) is mainly consumed by organic matter sulfate reduction (OSR), while sulfate at 247-655 cm (Unit Ⅱ) is consumed by both the OSR and the anaerobic oxidation of methane (AOM). In addition, the bottom sediment layer is affected by weak methane seepage. The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles. The responses of trace elements, including Co/Al, Ni/Al, Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events. Based on the results, it is speculated that the depositional conditions of Unit Ⅱ changed with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions, and finally to suboxic conditions due to methane fluid leakage. The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S. This was probably due to weak methane leakage, which caused the slower upward diffusion and the effect of early diagenesis on the samples. It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters. |
| 中文摘要: |
| 近年研究表明，甲烷渗漏影响下的沉积物地球化学特征可用于重建过去的甲烷渗漏事件。本文做了南海北部琼东南盆地冷泉区C14站位柱状沉积物样品的Sr/Ca与Mg/Ca比值相关图和硫酸盐浓度剖面分析。研究结果表明，硫酸盐在海底0-247 cm （层段I）主要由有机质驱动的硫酸盐还原反应（OSR：organic matter sulfate reduction）所消耗，而在247-655 cm （层段Ⅱ）硫酸盐则由OSR和甲烷厌氧氧化作用（AOM：anaerobic oxidation of methane）驱动的硫酸盐还原反应消耗为主。此外，沉积柱底部受到微弱的甲烷渗漏的影响。Mo和U的富集系数也展现相似的变化趋势。微量元素（包括Co/Al，Ni/Al，Cr/Al和Zn/Al比值）对甲烷渗漏有很好的响应，被广泛用于重建沉积条件和甲烷渗漏事件。基于本文微量元素的结果，推测层段Ⅱ的沉积条件随深度增加从介于硫化和氧化环境之间到局部缺氧环境的变化，并且最终由于甲烷流体渗漏而变为次氧化环境。在早期成岩环境中，AOM产生的铬还原硫化物的稳定同位素值和OSR形成的硫化物的稳定硫同位素值严重亏损34S。这可能是由于甲烷泄漏较弱，导致向上扩散的甲烷流速较慢以及早期成岩作用对样品的影响。最后，提出要综合考虑沉积环境和成岩作用对这些化学参数的影响。 |
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