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

Abstract

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

Keywords

• erosion
• Indochina
• Tibet
• rivers
• provenance
• zircon