Sediment features and provenance analysis of the late Mesozoic-early Cenozoic strata of the Ryukyu Islands: Implications for palaeogeography of East China Sea

Strata from the Ryukyu Islands provide an important source of data for the study of the provenance patterns, sedimentary and tectonic evolution of the East China Sea Shelf Basin (ECSSB). This research uses petrologic, mineralogical and geochronological analysis to investigate the Upper Cretaceous-Miocene strata of the central and southern Ryukyu Islands. The results show that both these locations experienced a shift in their sediment provenance and characteristics over time. In central Ryukyu, the Upper Cretaceous sediments show multiple peaks for zircon ages from the Mesozoic to the Archean. However, the Eocene sediments indicate a single source, because the zircon ages have a narrow distribution focused on 110 Ma, during the Late Yanshanian orogeny. This probably indicates that the provenance shifted, from mixed deposition of near-source Permian-Early Jurassic basement and long-distance transportation of old material from the North China Block and Korea in the Late Cretaceous, to limited near-source in situ deposition in the Eocene. This change could be the result of blocking of sediment transport, by an uplift that developed at the edge of the continental margin. In southern Ryukyu, the Eocene sedimentary rock was mainly from Mesozoic sources, while the Miocene sedimentary rock has multiple peaks for zircon ages. These areas may have experienced a single provenance source of Mesozoic island arc magmatic rocks in the Eocene, and then received more Proterozoic and Archean continental crustal material from the South China Block to the west and ECSSB to the north. This change indicates an expansion of the provenance area, due to the post-rifting subsidence after the expansion of south ECSSB and South China Sea.