Basin deformation history deduced from shelf break and growth strata in the southern Ulleung Basin, East Sea (Japan Sea)

Previous studies about tectonic events in the Ulleung Basin have been performed using diverse methods, but the deformation history of the Ulleung Basin is still controversial. In the Ulleung Basin, the Dolgorae and Gorae I structures were formed by basin deformation I (northwest-southeast compression) and the Gorae V structure was formed by basin deformation II (east-west compression). Since the quality of seismic data of the Dolgorae structures is not good, it is more difficult to reveal the basin deformation history through structural analysis of the seismic data. Thus, we traced the change in paleo-shelf breaks and studied provenance using image logs as indirect tectonic evidence and analyzed the growth strata of the Dolgorae and Gorae structures using seismic data for analyzing basin deformation. The shape of the paleo-shelf break has changed from linear to curved shape since 12.5 Ma, and the progradation rate of the paleo-shelf break was the fastest during 10.6–12.5 Ma. Before 12.5 Ma, sediments were supplied in the southwest direction, but after 12.5 Ma, they were supplied in the southeast direction originated from uplifted Dolgorae thrust fault zone. This evidence imply that basin deformation occurred in 12.5 Ma. During basin deformation I, the Gorae I structure was formed later than the Dolgorae structures due to the propagation of compression, and during basin deformation II, the Gorae V structure was formed from 5.33 Ma based on analysis of growth strata.