Cold seeps spread worldwide along the continental margins, which are closely related to the exploration of gas hydrates. Cold-seep carbonates have been reported to record the nature of seepage, including fluid source, sedimentary environment, and variation of seepage activity. We investigated the morphology, mineralogy, element compositions, and carbon and oxygen isotopes of 15 cold-seep carbonates collected from the Shenhu area, and compared them with 2 carbonates from the Haima cold seep, the South China Sea (SCS), to promote our knowledge of cold-seep system in SCS. Most of the Shenhu carbonates exhibit crust morphology, and some are in the form of chimneys and blocks. Their absolute (20％–65％) and relative carbonate mineral contents (mainly aragonite and calcite, with minor samples containing dolomite) vary significantly, indicating the multi-stage methane leakage in our study area. Some samples show a slight negative Ce anomaly, suggesting either the mixing of seawater or variation of the redox condition during the precipitation; the co-occurrence of strongly enriched U and Mo demonstrates anoxic condition during precipitation. The mixed genetic methane source was interpreted by δ 13 C of the Shenhu carbonates to range from -22.34‰ to -59.30‰ Vienna PeeDee Belemnite (VPDB), and the slight 18 O-enrichment imprinted on the carbonates suggests the possible influence from hydrate dissociation. The Haima carbonates, with biogenic methane as the main gas source, were presumably formed in a stronger fluid flux by compared with our Shenhu samples.

Chongmin CHEN;Lifeng ZHONG;Zhifeng WAN;Chiyu CHENG;Wei ZHOU;Xing XU

School of Marine Sciences,Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering,Sun Yat-sen University,Zhuhai 519000,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519000,China;MLR Key Laboratory of Marine Mineral Resources,Guangzhou Marine Geological Survey,Ministry of Natural Resources,Guangzhou 510075,China

海洋湖沼学报（英文版）

[1]Chongmin CHEN;Lifeng ZHONG;Zhifeng WAN;Chiyu CHENG;Wei ZHOU;Xing XU-.Geochemical characteristics of cold-seep carbonates in Shenhu area, South China Sea)[J].海洋湖沼学报（英文版）,2022(03):969-985

Haima,PeeDee,Belemnite,VPDB

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