Rethinking on shallow sedimentary sequence and its evolution of the Xiyang tidal channel in the Radial Sand Ridge Field, South Yellow Sea

Since the Late Quaternary, both the Yellow River and Changjiang River entered into the South Yellow Sea flowing through the middle Jiangsu coast. As a result, a series of sediments have been deposited in this area controlled by the river-sea interactions. The Radial Sand Ridge Field (RSRF) off the middle Jiangsu coast has been formed after the Holocene transgression. The Xiyang tidal channel in the northwestern RSRF is constrained by the tidal flat coast and tidal ridges. It is located in the transition zone between the northern Abandoned Yellow River delta and southern modern Changjiang River delta. Therefore, it becomes the important window area to reveal the sedimentary sequence formed in the coast and continental shelf under the active interactions between different large rivers during the Late Quaternary. As to the upper strata with the depth less than 60 m below the current mean sea-level in the Xiyang tidal channel, there are still different viewpoints on its sedimentary sequence, chronology framework and evolution, while the concerned studies are still pretty limited. Recently, the results of further Late Quaternary stratigraphic correlations and synthesis study on shallow seismic profiles showed that, (1) Due to disordered dating results and improper correlation of terrigenous stiff mud layers, the chronology framework of Xiyang upper strata built previously based on core 07SR01 and Y1 is incorrect, the main part of the upper strata including two sedimentary cycles are the Late Pleistocene deposits and the stiff mud layer of the Last Glacial Maximum is often missing due to the tidal scouring, the thickness of surficial Holocene sediments are generally less than 10 m in the submerged sand ridges, and extensively less than 5 m in other places, or even zero in some places; (2) The shallow seismic unit 3 (U3) only steadily located in the northwestern part of the Xiyang tidal channel indicates the southern margin of the old Yellow River delta developed during MIS 3, and the middle Jiangsu coast in which the Xiyang tidal channel is located was probably influenced deeply by the old Yellow River sediments since the Late Pleistocene, however it is still necessary to recover a new sedimentary core in the key position of northwestern part, plus further study and verification based on the new core and other acquired shallow seismic profiles and cores in the southeastern part should be done. Thus, this paper proposed the further study plan as follows, based on the 3D visualization of the seismic sequence framework, the spatial characteristics of the seismic units and main reflection interfaces would be extracted. Furthermore, combined with the sedimentology and chronology studies of the existing and designed cores, the reliable chronology framework would be set up expectedly, and the provenance from large rivers would be identified. Applying the sequence stratigraphy method, referencing the adjacent published core data, it is targeted to ascertain the shallow sedimentary sequence in the Xiyang tidal channel, and to reveal its evolution.