Reconstructing the incision of the Lancang River (Upper Mekong) in southeastern Tibet below its prominent knickzone using fluvial terraces and transient tributary profiles

Abstract The Lancang River (Upper Mekong) is a key large river in Asia with a prominent knickzone over 500 km distance (27.5-30.7°N), as it descends the southeastern margin of the Tibetan Plateau. To explore the role of tectonics in regulating the river downcutting at regional and local scales, we reconstructed the rate and spatial pattern of incision within and below the knickzone. We combined the investigation of fluvial terraces with tributary river profile analysis for a 300-km reach near Yunlong below the knickzone (25-27.5°N). We conducted field mapping and dating of strath terraces at the heights of 60-380 m above the trunk river. The overlying terrace deposits comprise fluvial conglomerates and overbank sands as well as tributary alluvial fan conglomerates. K-feldspar post-infrared infrared stimulated luminescence (pIR-IRSL) dating results suggest terrace formation during the Middle Pleistocene and the incision rate varying at