Rare earth elements in cold seep carbonates from the southwestern Dongsha area,northern South China Sea |
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| Affiliation: | 1. MLR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China;2. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;3. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;1. Geological Survey of Norway, 7491 Trondheim, Norway;2. CAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, UiT The Arctic University of Norway, 9037 Tromsø, Norway;3. Institute of Geology, Tallinn University of Technology, 19086 Tallinn, Estonia;4. Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia;5. British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom;6. Earth and Space Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany;7. Department of Geosciences, Swedish Museum of Natural History, PO Box 50 007, SE-10405 Stockholm, Sweden;8. Lundin Norway AS, Oslo, Norway;1. CAS Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;3. Department of Geodynamics and Sedimentology, Center for Earth Sciences, University of Vienna, 1090 Vienna, Austria;4. Coastal Studies Institute, Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA;5. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The circulation of methane-rich fluids at cold seeps often leads to the precipitation of seep carbonates close to the seafloor along continental margins, which can be used as records of past fluid seepage. Rare earth element (REE) concentrations in seep carbonates have been used to trace fluid sources and provide information on associated biogeochemical processes at cold seeps. The REE concentrations of a series of carbonates collected from cold seeps in the southwestern Dongsha area of the northern South China Sea are analyzed in this study. The total REE contents (ΣREE) of the seep carbonates analyzed show a wide variation from 17 ppm to 523 ppm with an average ΣREE value of 54 ppm, which are higher than the typical marine carbonate values of ∼28 ppm commonly reported and also higher than those of the carbonates from other cold seep areas. A positive correlation between Fe–Mn content and ΣREE was observed. These results suggest that the seep carbonates of this study were primarily controlled by the methane-derived fluid from which they precipitated. The Fe-rich dolomite and siderite, which are the main components of the carbonates, are responsible for the enrichment of the REE. A slight positive Ce anomaly observed in the shale-normalized REE patterns of the studied seep carbonates suggests that they formed in anoxic conditions, and the correlations between Ce/Ce* and LaN/SmN, Ce/Ce* and DyN/SmN, Ce/Ce* and ΣREE further reveal that the REE characteristics of most seep carbonate samples preserve the original redox conditions in which they precipitated and late diagenesis has had little effect on the REE. However, the REE characteristics of sub-samples DS2-2B, DS1-6A and DS1-7A are very different from those of the other sub-samples, indicating a greater impact of late diagenesis and post-oxidation favored REE enrichment. |
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| Keywords: | Rare earth element (REE) Cold seep carbonate Redox condition Northern South China sea |
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