Provenance of the Hayang Group (Early Cretaceous) in the Yeongyang Subbasin, SE Korea and its bearing on the Cretaceous palaeogeography of SW Japan

The Lower Cretaceous Hayang Group in the Yeongyang Subbasin, SE Korea, was deposited in a forearc basin formed by the subduction of the Palaeo-Pacific (Izanagi) Plate underneath the East Asian continent. It is characterized by an alternating sequence of reddish sandstones and mudstones deposited in fluvial plain environments. Sandstone compositions upsequence reveal that the tectonic regimes of source terrains evolved successively from basement uplift to recycled orogen, to magmatic arc, and back to recycled orogen. Characteristically, sandstones contain abundant plagioclases but rare K-feldspars, except for sandstones derived from basement sources. Sandstones derived from recycled orogens are rich in sedimentary rock fragments, especially chert fragments, which contain radiolarian faunas similar to those of the Jurassic accretionary complex located in Southwest Japan. Minor continental arc volcanism contributed volcanic materials to the basin during the middle stage of the basin filling. During the deposition of the Hayang Group strike-slip fault movements were active due to the oblique subduction of the Izanagi Plate and caused strong pulsed uplift of the trench slope break areas, resulting in supply of accretionary complex-derived sediments. Considering a direct drainage connection between the uplifted accretionary complex in Southwest Japan and the Yeongyang Subbasin, current Cretaceous palaeogeographic reconstructions of the East Asian continental margin need to be reconsidered and it is suggested that the collage of tectonic blocks in Southwest Japan assembled in post-Early Cretaceous time.