Seismic stratigraphy and depositional history in the SW margin of the Ulleung Basin, East Sea

Interpretion of the 2D seismic data set revealed the depositional history and structural forming processes in the southwestern margin of the Ulleung Basin, East Sea. Based on the seismic facies and sediment succession with various unique structures in the study area, they were divided into five depositional sequences (DS1 to DS5), separated by erosional unconformities (H1–H5). The lower two depositional sequences (DS1-DS2) show deformed succession with faults and folds, whereas the upper three depositional sequences (DS3-DS5) indicate non-deformed succession. DS1 and DS2, regarded as the late Miocene strata, comprise hummocky and chaotic seismic facies. During the late Miocene, the Dolgorae Thrust Belt (DTB) and Gorae Structure (GS) were created sequentially and are strongly associated with the creation of the DS1 and DS2. On the other hand, the upper three sequences (DS3–DS5), which are part of the Plio-Quaternary strata, are acoustically distinguished by reflection configurations that are both well-stratified and progressive. Since the Pliocene, the tectonic movement associated with the regional structures (US, DTB, and GS) has been nearly stopped. On the other hand, a portion of the GS has been developed until now. As a result of these findings, it was determined that DS1 and DS2 were mainly controlled by tectonic activity. The sedimentation of the upper three sequences (DS3-DS5) after the Pliocene was driven primarily by periodic and repeated sea-level changes rather than by tectonic activity.