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Open AccessArticle

Cold-Water Corals in Gas Hydrate Drilling Cores from the South China Sea: Occurrences, Geochemical Characteristics and Their Relationship to Methane Seepages

by Yinan Deng 1,2,3,†, Fang Chen 1,3,*, Niu Li 3,4,5,*,†, Meng Jin 4,6, Jun Cao 1,3, Hong Chen 1, Yang Zhou 1, Cong Wu 1, Chang Zhuang 1, Yi Zhao 1 and Sihai Cheng 1
1
MNR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China
2
Research Center for Earth System Science, Yunnan University, Kunming 650091, China
3
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
4
CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
5
Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences Guangzhou, Guangzhou 510301, China
6
University of Chinese Academy of Sciences, Beijing 100049, China
*
Authors to whom correspondence should be addressed.
Both authors should be regarded as joint first authors.
Minerals 2019, 9(12), 742; https://doi.org/10.3390/min9120742
Received: 1 November 2019 / Revised: 20 November 2019 / Accepted: 27 November 2019 / Published: 29 November 2019
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 δ13C values between −8.4‰ and −0.6‰ that are significantly higher than δ13C values of the associated seep carbonates (δ13C values with an average of −55.6‰, 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. View Full-Text
Keywords: cold water corals; methane seeps; carbon and oxygen isotope; authigenic carbonate; South China Sea cold water corals; methane seeps; carbon and oxygen isotope; authigenic carbonate; South China Sea
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MDPI and ACS Style

Deng, Y.; Chen, F.; Li, N.; Jin, M.; Cao, J.; Chen, H.; Zhou, Y.; Wu, C.; Zhuang, C.; Zhao, Y.; Cheng, S. Cold-Water Corals in Gas Hydrate Drilling Cores from the South China Sea: Occurrences, Geochemical Characteristics and Their Relationship to Methane Seepages. Minerals 2019, 9, 742.

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