Latest Neogene-Quaternary seismic stratigraphy and post-opening tectonic history on the southwest margin of the Ulleung Basin, East Sea

Sequence analysis of 2D seismic profiles and sediment data from the southwestern margin of Ulleung Basin reveals that the latest Neogene-Quaternary deposits comprise five depositional sequences (DS1–DS5), separated by erosional unconformities (H1–H5). The lower two sequences (DS1 and DS2), correlated with the Miocene strata, are acoustically characterized by hummocky and chaotic seismic facies, and were significantly deformed with several faults and folds. During the late Miocene, distinct geologic structures, including the Ulsan Structure (US), Dolgorae Thrust Belt (DTB), and Gorae Structure (GS) were also developed sequentially, which were closely related to formation of lower two sequences. However, the upper three sequences (DS3–DS5), belonging to the Plio-Quaternary strata, is acoustically characterized by well-stratified and prograding reflection configurations, and remained relatively undeformed. The tectonic movement related to the regional structures (US, DTB, and GS) was almost stopped since the Pliocene, whereas the part of the GS has been uplifted until the present. These results indicated that sedimentation for the upper three sequence since the Pliocene was mainly influenced by periodically repeated sea-level changes rather than tectonic activity.