Journal of Marine Sciences ›› 2020, Vol. 38 ›› Issue (2): 16-25.DOI: 10.3969/j.issn.1001-909X.2020.02.003

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Formation of nodules on continental slopes in thenortheast of the South China Sea and itsimplications for cold seep

LU Yi1,2, CHU Fengyou*1,2, DONG Yanhui1,2, ZHU Zhimin1,2, ZHU Jihao1,2, LU Jianggu1,2   

  1. 1. Second Institute of Oceanography, MNR, Hangzhou 310012, China;
    2. Key Laboratory of Submarine Geosciences, MNR, Hangzhou 310012, China
  • Received:2020-01-06 Online:2020-06-15 Published:2020-11-13

Abstract: The polymetallic nodule samples were analyzed for their mineralogical and geochemical features, which were acquired on the northeastern slope of the South China Sea using the ROV named as Sea Dragon III. The results showed that the nodules in the study area were predominantly by rod-shaped with a two-layer structure. The outer layer of the polymetallic nodules was mineralogically and geochemically similar to hydrogenic nodules. While the inner layer was porously and composed of goethite with residual minor pyrite. Geochemically, the inner layer was characterized by high concentration of Fe and As but extremely low concentration of Mn, REE and other elements. The inner layer carbon isotopes ( δ13C ) of sample NH-2 was -30.91‰. The study presented that the early forming process of the nodules was related to the activities of cold seep, but the pyrite was oxidized following the extinction of cold seep. Under the influences of contour current in the area, the ferromanganese oxides continued to grow in the outer layer of the nodules.

Key words: cold seep, South China Sea, Dongsha, continental slopes

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