Yangtze offshore,China: highly laminated sediments from the transition zone between subaqueous delta and the continental shelf |
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| Institution: | 1. State Key Laboratory for Estuarine and Coastal Research Institute, East China Normal University, Shanghai, 200062, China;2. IGG, Geological Survey of Japan, AIST, Higashi 1-1-1, Tsukuba, Ibaraki 306-8567, Japan;3. Department of Environmental Science and Technology, Meijo University, Shiogamaguchi 1-501, Tempaku, Nagoya 468-8502, Japan;4. Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan |
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| Abstract: | This study examines the deposition of highly laminated muddy sediment in vibrocores recovered from a depth of 40–55 m of water and located 120 km east of the Yangtze River mouth. X-radiographs show numerous sharp-based sedimentary rhythmics with nearly parallel and undulated laminations, interbedded with silty lenses and interbeds. The laminated sediment varies from clayey silt to silty clay. AMS radiocarbon dates on well-preserved bivalves are primarily younger than 5500 y BP, indicating the formation of the laminated sediment under the present sea-level conditions. Macro- and microfossils in the sediments are consistent with the modern offshore sedimentary setting. The laminated sediment originated from the Yangtze estuary, but the sedimentation processes were not deltaic. The highly laminated sediment that lies below the normal wave base of 10 m was deposited on the seaward margin of the Yangtze subaqueous delta, closely associated with submarine tidal and storm-generated currents. |
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