A Late Eocene‐Oligocene Through‐Flowing River Between the Upper Yangtze and South China Sea

We test the hypothesis of a major Paleogene river draining the SE Tibetan Plateau and thecentral modern Yangtze Basin that thenflowed south to the South China Sea. We test this model usingU‐Pb dated detrital zircon grains preserved in Paleogene sedimentary rocks in northern Vietnam and SWChina. We applied a series of statistical tests to compare the U‐Pb age spectra of the rocks in order tohighlight differences and similarities between them and with potential source bedrocks. Monte Carlo mixingmodels imply that erosion was dominantly derived from the Indochina and Songpan‐Garzê Blocks andto a lesser extent the Yangtze Craton. Some of the zircon populations indicate local erosion andsedimentation, but others show close similarity both within northern Vietnam, as well as more widely in theEocene Jianchuan, Paleocene‐Oligocene Simao, and Oligocene‐Miocene Yuanjiang basins of China. Thepresence of younger (<200 Ma) zircons from the Qamdo Block of Tibet is less easily explicable in terms ofrecycling by erosion of older sedimentary rocks and implies a regional drainage linking SE Tibet and theSouth China Sea in the Late Eocene‐Oligocene. Detrital zircons from offshore in the South China Seashowed initial local erosion, but with a connection to a river stretching to SE Tibet in the Late Oligocene. Achange from regional to local sources in the Early Miocene in the Yuanjiang Basin indicates the timing ofdisruption of the old drainage driven by regional plateau uplift.