Sedimentary Sequence and Age of Core NTCJ1 in the Sheyang Estuary, Western South Yellow Sea: A Re-Interpretation

Abstract

The Sheyang estuary is located on the northern Jiangsu muddy coast, in the western South Yellow Sea, and in the transition area between the eroded coast of the abandoned Yellow River delta and the silted coast of the central Jiangsu. This area is also one of the key areas of interactions between the paleo-Yellow River and paleo-Changjiang River during the late Quaternary. In order to investigate deeply the late Quaternary sedimentary sequence models of coasts and continental shelves under the interactions of the above two large rivers, the sedimentary sequence and age of the core NTCJ1 drilled at the Sheyang estuary were re-examined and re-interpreted recently, based on the existing data on lithology, grain size, ostracods, foraminifera, clay minerals, geochemical elements, and Electron Spin Resonance (ESR) dating, together with other adjacent key cores and shallow seismic profiles. The three new perspectives were summarized as follows: Firstly, the 22.00 m-long core NTCJ1 recorded the evolution of the sedimentary environments since Marine Isotope Stage 5 (MIS 5), and the first continental facies layer formed in MIS 4-2 is supposed to be missing; therefore, the MIS 1 marine facies layer directly overlays on the MIS 5 marine facies layer. Furthermore, the second continental facies layer formed in MIS 6 and/or the stage of the relatively low sea-level of MIS 5 has not been drilled yet. Secondarily, the middle-upper part of the NTCJ1 core sediments (0.00–17.95 m) are characterized by a finer grain, with a predominantly silty texture and dark yellow tone, and from bottom to top it shows a change from fine to coarse and then to fine in grain size, which could be substantially interpreted as the abandoned Yellow River deltaic deposits mainly formed in 1128–1855 CE, and may contain a small amount of Holocene coastal-shallow marine deposits at the bottom; however, it is difficult to identify them currently. Thirdly, the lower part of the NTCJ1 core sediments (17.95–22.00 m) have not yet been drilled through and are characterized by a coarser grain, with a predominantly fine sandy texture and dark grey tone, which could be interpreted as a delta front deposit in the MIS 5 tidal estuary and were obviously influenced by the paleo-Yellow River.

Characteristics and Environmental Indications of Grain Size and Magnetic Susceptibility of the Late Quaternary Sediments from the Xiyang Tidal Channel, Western South Yellow Sea

“…Meanwhile, the contents of carbonate minerals in eight samples above the drilling depth of 16.14 m showed an obvious increase, indicating the enhanced impact of the paleo-Yellow River-derived sediments [33]. The core NTCJ1 in the Sheyang estuary also recorded a delta front deposit in the MIS 5 tidal estuary, which was obviously influenced by the paleo-Yellow River [55]. Accordingly, during this period, the Changjiang River probably migrated southward and gradually moved away from the study area.…”