Plio-Quaternary seismic stratigraphy and geological structure of the Korea Strait shelf, Southeast Korea

Analysis of high-resolution seismic profiles from the SE continental shelf of Korea reveals that the shelf sequence consists of four sedimentary units, namely, Pliocene deposits (III), Lower Pleistocene deposits (IIB), Upper Pleistocene deposits (IIA), and Holocene deposits (I), which were mainly controlled by regional tectonic activity and sea-level fluctuations. Vertically, with the exception of unit I, the units form a series of superimposed prograding wedges that thicken seaward. A structural high, including several faults and folds, occurs north of Tsushima Island, extending northeastward to the Dolgorae Thrust Belt at the southern margin of the Ulleung Basin. In this study, we deduced that the deformed zone was formed due to compressional deformation associated with back-arc closure that occurred after the extension of the East Sea. Most of the faults and folds, oriented in NE–SW or NNE–SSW trends, mainly developed in the lower two units (III and IIB). The lower two units were also significantly deformed, whereas the two overlying units remained relatively undeformed. This indicated that, during the Pliocene and Lower Pleistocene (units III and IIB), sedimentation was mainly controlled by tectonic activities, whereas sedimentation after the Lower Pleistocene (units IIA and I) was mainly influenced by periodically repeated sea-level changes rather than tectonic controls.