Rethinking on sedimentary sequence and geochronological framework of Core NTCJ1 in the Sheyang estuary of Northern Jiangsu, East China

The Sheyang estuary is located in the muddy coast of Northern Jiangsu, East China, in the transition zone between the eroded coast of the abandoned Yellow River delta in Northern Jiangsu and the silted coast in central Jiangsu, which is characterized by the alternation of erosion and siltation as a node of modern coastal geomorphic evolution, as well as one of the key areas of geo-interactions between the old Yellow River and old Changjiang River during the Late Quaternary. To investigate deeply the Late Quaternary sedimentary sequence models of the coasts and continental shelves under the interactions among different large rivers, the sedimentary sequence and geochronology of 22.00 m-long Core NTCJ1 drilled at the Sheyang estuary were recently re-studied in lithology, grain size, ostracods, foraminifera, clay minerals, elemental geochemistry, and ESR dating, and the results were compared with those of other adjacent cores and shallow seismic profiles. The new results show that: (1) Core NTCJ1 recorded the sedimentary environment evolution since Marine Isotope Stage 5 (MIS 5), the first continental facies layer formed from MIS 4 to MIS 2 may be missing, the MIS 1 marine facies layer overlain directly the MIS 5 marine facies layer, and the second continental facies layer formed in MIS 6 has not been drilled yet; (2) The middle-upper part of Core NTCJ1 sediments (0～17.95 m) are characterized by fine grain size, mainly silty, and dark yellow in color, and obvious reversal graded bedding, which could be interpreted as the abandoned Yellow River deltaic deposits formed between AD 1128 and 1855 with a progradational sequence, and may contain a small amount of the Holocene coastal-shallow marine deposits at the bottom, but it is difficult to identify them yet. The lower part sediments (17.95～22.00 m) are characterized by coarse grain size, mainly fine sandy, and dark grey in color; they had not been drilled through and could be explained as a channel-fill deposit in the MIS 5 tidal estuary and were obviously influenced by the old Yellow River.