Sediment routing from the Red River to the Yinggehai Basin during late Oligocene: detrital zircon fingerprinting of basin-mountain coupling

The Red River, which flows through several tectonic blocks in Southeast Asia, is considered to have formed in response to the Cenozoic tectonic reorganization of the SE Tibetan plateau. This study present new detrital zircon U-Pb geochronological data from Oligocene samples in the Red River subaqueous delta to constrain sediment provenance and paleo-drainage evolution. The U-Pb age patterns indicate that whereas the Yangtze and Cathaysia Blocks served as primary sediment sources for the Yinggehai Basin in the Late Oligocene, the Qiangtang Block contributed substantial distal detritus to the basin system. Comparative analysis with existing detrital zircon records from the Yinggehai Basin shows a notable absence of the 562 Ma age peak in Lower Miocene strata, which was prominent in the underlying Oligocene deposits. This stratigraphic discrepancy suggests a significant drainage reorganization within the Red River system, resulting from the loss of Qiangtang Block catchment areas. Middle Miocene sediments exhibit diminished 797 Ma and 970 Ma zircon age peaks relative to underlying units. This indicates reduced sediment flux from both the Yangtze and Cathaysia blocks to the Yinggehai Basin and consequent contraction of the Paleo-Red River’s drainage network. The Middle Miocene detrital zircon age spectra show remarkable consistency with modern Red River sediments, which shows that the present-day Red River drainage configuration had almost been established by this period. This source-to-sink system investigation on the northwestern corner of the South China Sea provides critical constraints on the paleogeographic evolution and drainage development of the southeastern Tibetan Plateau since the Late Oligocene.