Seismic stratigraphy and depositional history of stacked cut-and-fill structures in the Ulleung Basin, East Sea (Japan Sea)

Multichannel seismic reflection profiles and well data were used to reveal the generation and evolution of stacked cut-and-fill structures (CF) and their depositional products in the Ulleung Basin, East Sea. The CFs in a syn-compressional megasequence show discontinuous, low-amplitude, chaotic, and transparent reflections. On the basis of stratigraphic position, 30 CFs are observed in three depositional sequences (DS8-DS10) in the southwestern shelf margin of the basin. They range from 0.5 to 8.8 km in width and 58 to 453 m in thickness. At the same stratigraphic interval of the basin proper, the depositional products consist mostly of discontinuous chaotic reflections. Seismic characteristics, spatial distribution, dimension, and high gamma ray responses suggest the CFs were originated by submarine canyons. During the period of DS8, small CFs were formed locally in the shelf margin, where little influenced by the deformation of the thrust-fold (Dolgorae Thrust Belt). Extensive and numerous CFs in DS9 occurred 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. In conclusion, this study suggests that variation in compressional tectonic movements and sediment supply, related to the back-arc closure of the East Sea, mainly controlled the evolution of the CFs and their depositional products rather than eustasy.