Middle Eocene initiation of the large East Asia Paleoriver

The formation of large rivers is controlled by both deep-Earth and surface processes. The drainage system that existed along the East Asian margin before the present-day drainage pattern is poorly understood. The basin-and-swell physiography of the East Asian margin was thought to have hindered the formation of large rivers during the early Cenozoic. To reveal drainage reorganizations, we combined regional geological constraints with provenance analysis of the East China Sea Shelf Basin (ECSB). For the first time, we applied coupled zircon and rutile U-Pb chronology to the ECSB, which is a crucial place for tracing river evolution along the East Asian margin. Our results, coupled with data from the literature, document a major regional provenance change in the middle Eocene. Before this change, the zircon age spectra showed only a single peak at ca. 110 Ma, indicating that the sediments were derived solely from proximal sources. After the change, the spectra began to show multiple peaks. These multiple peaks indicate a much larger drainage basin, incorporating several different detrital sources, some of which were located far inland. Detrital rutile shows a dominant age peak at ca. 220 Ma, indicating that most detritus was derived from the southeastern North China Block and Sulu-Dabie orogen. Both the zircon and rutile age spectra indicate that the Korean Peninsula became a main source area following the late Eocene. Coinciding with the major provenance change documented in the ECSB, fluvial sediments filled up the Subei−South Yellow Sea Basin, at which time it became a bypass area for a newly formed, large, southward-flowing axial river, which we term the East Asia Paleoriver. Such tectono-sedimentary evolution was strictly related to rift-basin formation and geodynamic processes driven by Izanagi-Pacific Ridge subduction. The East Asia Paleoriver, sourced from the southeastern North China Block and Sulu-Dabie orogen, and debouching into the ECSB, was established along the East Asian margin in the middle Eocene, expanded in the late Eocene to include the Korean Peninsula, and existed until the middle Miocene. Our findings shed new light on the evolving landscape in East Asia and show how basin and provenance analysis can be combined to reconstruct paleodrainage patterns.