Multichannel seismic reflection profiles and well data were analyzed to unravel the origin and depositional history of stacked cut-and-fill structures (CF) in the southwestern margin of the Ulleung Basin, East Sea. The CFs in a syn-compressional megasequence are characterized by discontinuous, low-amplitude, chaotic, and transparent seismic reflections. They display both U-shaped and V-shaped morphologies along their lengths. The CFs are thickest and widest at the shelf edge and taper both landward and basinward. Based on the stratigraphic position, the CFs are found in three depositional sequences (DS8–DS10). Thirty CFs have been identified that range from 0.5 to 8.8 km in width and 58 to 453 m in thickness (assuming a 2000 m/s seismic velocity of the sediments). The larger and numerous CFs occurred in the middle depositional sequence. Seismic characteristics, spatial distribution, hundred-meter-scale incisions, and high gamma-ray responses indicate that the CFs were caused by submarine canyons. During the period of DS8, small CFs were formed locally on the shelf margin, and were little influenced by the deformation of the thrust-fold (Dolgorae Thrust Belt). Extensive and numerous CFs in DS9 developed in the oversteepened shelf margin, where uplift of both the thrust-fold and anticline (Gorae V structure) occurred simultaneously, and where a large volume of sediment was supplied. During the period of DS10, a general decreasing pattern in the occurrence and dimensions of the CFs resulted from waning tectonic activity of the thrust-fold that reduced sediment supply. Consequently, this study suggests that variation in contractional tectonic activity and sediment supply, associated with the back-arc closure of the East Sea, mainly controlled the evolution of the CFs rather than eustasy.

Integrating seismic interpretation facilitates the discernment of tectonostratigraphic evolution in the eastern Korean continental margin, East Sea. The sedimentary succession of this margin is divided into three major seismic units based on distinct unconformities. These unconformities and their associated seismic characteristics indicate that the eastern Korean continental margin has experienced four evolutionary stages through extensional and subsequent two‐phase tectonic inversions. Early Miocene back‐arc opening of the East Sea triggered the extension of NNW–SSE and N–S trending rifts, resulting in non‐marine to deep‐marine deposition of typical rift‐related linked sedimentological systems in the eastern Korean continental margin. In the early Late Miocene, changes in plate motion and the subduction mode of the Japanese island (NW–SE compression) caused the positive inversion of extensional fault‐bounded half‐grabens in the eastern Korean continental margin, and the Hupo Basin was likely created by the regional flexural response. During this depositional period, hemipelagic sedimentation accompanied by episodic gravity‐controlled slope failures was predominant in the deep‐water environment. The subsidence of the Hupo Basin was enhanced by crustal shortening (E–W compression) that was induced by subduction initiation at the western margin of the Ulleung Basin during the late Early Pliocene (ca. 3.8 Ma). At that time, sedimentary environment gradually became shallower with time and coarse‐grained terrigenous input into the Hupo Basin began so that shallow‐ to deep‐marine sedimentation occurred. In the Quaternary period, the uplift of the Hupo Bank and coeval subsidence of the Hupo Basin were maintained by continued compressive neotectonics. The shallow‐ to deep‐marine deposition continued, but greater quantities of coarse‐grained terrestrial sediment were transported into the Hupo Basin due to combined effects on tectonics and eustasy. Based on the tectonostratigraphic reconstruction developed in this study, we propose that the Hupo Basin is likely a Late Miocene–Quaternary compression‐related basin induced by crustal or thrust loading.

Mass-transport deposits (MTDs) and submarine fan complexes are the results of gravity-induced sedimentary flows occurring mainly in deep-water environments (Bouma,