NO CENOZOIC CONNECTIVITY BETWEEN UPPER YANGTZE RIVER AND RED RIVER

Reorganization and capture of the rivers draining the SE margin of Tibet has been a debate of significant contention over the last decade, particularly the question of whether the paleo-Yangtze and Red River were once linked. Studies have suggested reorganization occurred anywhere from the Eocene to Pliocene. However, while the majority of research has focused on when the reorganization occurred, a small but growing subset of work has begun to favor the idea that there was no ancient large river network in the Cenozoic along the SE Tibetan plateau. U/Pb zircon geochronology of 10 Cenozoic basins, Eocene to Pleistocene, all share high commonality despite extensive spatial variability and depositional environments. The provenance of Cenozoic detrital zircon samples is often compared against the Triassic turbidites of the Songpan Ganze Terrane. However, closer examination of the detrital zircon U/Pb ages of Mesozoic sediments over an area >8 million km² surrounding our basins, demonstrates a strikingly high similarity amongst one another. Populations from the Songpan Ganze Terrane, Qamdo Basin, Khorat Plateau, Kontum Massif, Qiangtang Terrane, Sukhothai, Khorat Plateau and Youjiang basin share indistinguishable age modes, and closely match much of our Cenozoic sediment, suggesting that these age modes are nondescript. All other U/Pb variability in Tertiary sediments can be explained by local derivation. Paleoflow measurements on imbricated clasts and cross-beds show strong variability in direction, often with northern flow and eastern flow but rarely the predicted southern flow necessary to satisfy the paleo-connection. Stratigraphic interpretations of the depositional environments of Cenozoic sediment range from alluvial fans, lacustrine– even eolian– but rarely resemble a large trunk stream. The large spacing between Cenozoic basins and restricted spatial extent also does not necessarily imply connectivity. This combination of non-unique U/Pb age populations, inconsistent flow in paleocurrent measurements, and non-suggestive stratigraphic interpretations point to the conclusion that there was no Tertiary connection between the Paleo-Yangtze and Paleo-Red Rivers.