Cold-Water Corals in Gas Hydrate Drilling Cores from the South China Sea: Occurrences, Geochemical Characteristics and Their Relationship to Methane Seepages
Cold-Water Corals in Gas Hydrate Drilling Cores from the South China Sea: Occurrences, Geochemical Characteristics and Their Relationship to Methane Seepages
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南海天然气水合物钻探岩心中的冷水珊瑚：产状、地球化学特征及其与甲烷渗漏的关系
DOI：
10.3390/min9120742
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发表时间：
2019-12-01
期刊：
影响因子：
2.5
通讯作者：
Cheng, Sihai
中科院分区：
文献类型：
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作者：
Deng, Yinan;Chen, Fang;Cheng, Sihai
冷水珊瑚(CWCS)常见于冷渗漏区。然而，流体渗流与化学武器的发展之间的关系尚不清楚。本文首次报道了南海中国海钻井岩心含天然气水合物沉积物中化学武器化石骨架的赋存状态、物种鉴定、矿物学、碳、氧同位素和元素组成。调查了三个位点(GMGS-08、GMGS-09B和GMGS-16)，但只在一个位点(GMGS-09B)发现了CWCS。有趣的是，CWCS在三个层位上被发现，它们都嵌入了自生碳酸盐。化石CWCS的3个属(Crispatotrochus sp.，Solenosmilia sp.)和Enallopsamia sp.)都被确认了。CWC碎片主要为文石。CWCS的增量C-13值介于-8.4‰到-0.6‰之间，显著高于伴生的渗漏碳酸盐的Delta C-13值(Delta C-13值平均为-55.6‰，n=19)，这表明CWCS的碳源不是甲烷。自生碳酸盐似乎为珊瑚的定居提供了底物。GMGS-09B站位的水深高点、适宜的水温和较强的底层水流可能是保持研究区域水煤浆生长的有利条件的关键。此外，铬、镍、铅、铀、钡、钍和锶等微量元素的高含量表明，CWCS受到可到达水-沉积物界面的强烈流体渗漏和相关微生物活动的影响。因此，同样明显的是，富油气渗漏区的CWCS不仅对流体排放对底水化学的影响提供了关键的约束，而且很可能是冷泉活动结束时间的非常精确的记录。
Cold-water corals (CWCs) are frequently found at cold seep areas. However, the relationship between fluid seepage and CWC development is not clear. Here, for the first time, we report the occurrences, species identification, mineralogy, carbon and oxygen isotopes, as well as elemental compositions of fossil CWC skeletons from gas-hydrate-bearing sediment in drilling cores from the South China Sea (SCS). Three sites (GMGS-08, GMGS-09B, and GMGS-16) were investigated but CWCs were only found at one site (GMGS-09B). Interestingly, the CWCs were found in three horizons and they were all embedded with authigenic carbonates. Three genera of fossil CWCs (Crispatotrochus sp., Solenosmilia sp. and Enallopsammia sp.) were identified. The CWC fragments are predominantly aragonite. The CWCs exhibit delta C-13 values between -8.4 parts per thousand and -0.6 parts per thousand that are significantly higher than delta C-13 values of the associated seep carbonates (delta C-13 values with an average of -55.6 parts per thousand, n = 19), which indicates a carbon source other than methane for the CWCs. It appears that authigenic carbonates provide a substratum for coral colonization. Bathymetric high points, appropriate water temperature and stronger bottom-water currents at site GMGS-09B might be crucial to keep conditions favorable for the growth of CWCs in the studied area. In addition, high trace-element concentrations of Cr, Ni, Pb, U, Ba, Th, and Sr suggest that the CWCs are influenced by strong fluid seepage that can reach the water-sediment interface, and associated microbial activity. Hence, it also becomes evident that CWCs in hydrocarbon-rich seepage areas not only provide a critical constraint on the impact of fluid emission on the bottom water chemistry, but also are likely to be very precise recorders of the end time of cold seep activity.