Depositional history of the subaqueous delta off the southeastern coast of Korea during the post-glacial period

Abstract

The distal mud deposit (DMD) of the Korea Strait Shelf, located along the southeastern coast of Korea and detached from the main sediment source, the mouth of the Nakdong River, is considered a subaqueous delta system. The complex spatiotemporal changes in the stratigraphic architecture of the DMD were reconstructed, based on combined seismic and sediment core data, according to the three stages of post-glacial sea-level rise. During the early transgressive stage (from ca. 19 to 10.9 ka), transgression occurred at a relatively deeper northern outer shelf of the DMD, where Unit A began to be deposited in an aggradational stratal stacking pattern. During the late transgressive stage (ca. 10.9 to 8 ka), further sea-level rise provided sufficient accommodation for DMD, but an insufficient sediment supply from the Nakdong River might have prevented sedimentation. At the highstand stage (ca. 8 ka to the present), the increased supply of suspended sediments from the Nakdong River coupled with the entrance of the Tsushima Warm Current through the Korea Strait may have enabled the along-shore lobate progradation of Unit B on the flat and wide southern shelf. After appoximately 2 ka, as Unit B proceeded into the narrow, steep northern shelf, it started to prograde in a shore-normal direction, controlled by a rapid downslope decrease in near-bed shear stress. Over the last 700 years, sediments have been actively deposited at the depocenter of the DMD by frequent storm surges during the summer season. The reconstructed depositional history of the DMD demonstrates the importance of the pre-existing shelf morphology, along-shore currents, and storm surges in offshore sediment transport for a subaqueous delta in a microtidal shelf with a relatively small riverine sediment load.