Cenozoic sedimentary records from the eastern offshore of China reveal the Eocene birth of the Yangtze River

The Yangtze River, which links the Tibetan Plateau to the eastern offshore of China, is one of the most important sediment routing systems in East Asia. However, the timing of its establishment has remained controversial. This study examines new and published zircon U-Pb geochronology data from eastern offshore basins (the East China Sea Shelf Basin and South Yellow Sea Basin) and major rivers in East Asia, establishing new constraints on the timing of full integration of the Yangtze River. We report detrital zircon U-Pb ages (n = 664) from Paleogene strata in the East China Sea Shelf Basin, the primary sink for the river during the Cenozoic. Detrital zircons from the Eocene to early Oligocene Pinghu Formation range from 34.9 ± 0.7 to 2800 ± 42 Ma, with 100–250 Ma and 1700–2100 Ma age clusters, and small Paleozoic, Neoproterozoic, and Paleoproterozoic-Archean peaks. A similar age range (33 ± 0.4 to 2842 ± 43 Ma) and nearly identical peaks are documented for the Oligocene Huagang Formation. The maximum depositional age, based on the youngest single grains in our samples, is 34.9 ± 0.7 Ma for Pinghu Formation and 33 ± 0.4 Ma for Huagang Formation. Statistical comparison of the new U-Pb ages with published data from sands collected in major segments of the modern Yangtze River and its estuary demonstrate similar provenance, but with larger contributions of 700–1000 Ma and 1700–2100 Ma zircons, sourced from the Songpan-Garze terrane. Additionally, the new data suggest that both the East China Sea Shelf Basin and the South Yellow Sea Basin retain young (<80 Ma) zircons, likely sourced from the Jinshajiang segment of the Yangtze River. The youngest of these zircons are ∼37-33 Ma and only occur in sands from the upper reaches of the modern river. The high degree of similarity between the eastern offshore samples and the modern Yangtze system suggests the river and source-to-sink system were established by the late Eocene, and may point to topographic adjustments in the Qiangtang portion of the Tibetan Plateau as a driver of drainage expansion and integration.