Pleistocene forced regressive deposits on the Korea Strait shelf influenced by tectonic and ocean currents

Abstract

We examined the architecture of Pleistocene sequences of the Korea Strait (KS) margin controlled by ocean currents and compressional tectonic regimes, using a dense grid of high-resolution single-channel seismic profiles and sediment cores. Along with uplifted strata featuring an erosional and/or non-depositional flat seabed in the northern shelf of the study area, three Middle-Upper Pleistocene sequences are characterized by forced regressive deposits recorded at 100-ka intervals covering one postglacial sequence across the shelf. The three forced regressions together comprise an offlapping stacking pattern, where the degree of erosion of the upper surface of the older sequence is greater than that of the younger sequence. The tectonic tilt involved in landward uplift and seaward subsidence across the shelf basin causes differential erosional rates among the forced regression deposits. The Upper Pleistocene forced regression deposits are preserved as a set of 20-ka clinoform wedges with aggradational to progradational stacking patterns, leading to a falling stage systems tract (FSST) during the stepwise fall in sea level, followed by a shelf edge-perched lowstand systems tract (LST) wedge during the Last Glacial Maximum (LGM). The northeast-facing Tsushima Current (TC) passing through the KS played an important role in allowing the fine sediments originating from the Nakdong River to form the FSST clinoform wedges and the LST oblique prograding delta lobe along the shelf break.