Tectonostratigraphic evolution of the Hupo Basin in the western margin of the Ulleung back-arc basin, the East Sea

The tectonostratigraphic evolution in the western margin of the Ulleung back-arc basin was reconstructed based on the seismic reflection data. According to our stratigraphic and structural analysis, the study area developed via four tectonostratigraphic stages, one extensional and two subsequent tectonic inversions. Together with the back-arc opening of the East Sea, most fault-controlled depocenters (e.g., half-grabens) were formed mainly in the western margin of the Ulleung Basin during the Early–early Late Miocene. This syn-extensional sedimentation occurred in non-marine to deep-marine environments analogous to typical rift-related linked depositional systems. During the early Late Miocene, the Ulleung back-arc basin had changed entirely into a compressive regime (NW–SE compression). Under the inversion tectonics, NNE–SSW and N–S trending extensional faults were mainly reactivated as reverse faults. The Hupo Basin was likely created by the regional flexural response to the crustal or thrust loading. As the formation of the Hupo Basin began, hemipelagic sedimentation accompanied by episodic gravity-controlled slope failures prevailed in the deep-water environment. Since the late Early Pliocene, the subsidence of the Hupo Basin was enhanced by the crustal shortening. The sedimentary condition became shallower gradually upward and coarse-grained terrigenous input into the Hupo Basin began, leading to deposition in shallow- to deep-marine environments. During the Quaternary, although the tectonic activity was subdued, the Hupo Fault was reactivated as a reverse fault, maintaining the uplift of the Hupo Bank and coeval flexural subsidence of the Hupo Basin. During this depositional period, shallow- to deep-marine deposition continued but a greater quantity of coarse-grained terrestrial sediments was transported into the Hupo Basin. The Quaternary depositional systems are likely the result of the interplay between tectonics and eustasy.