Migrating incision wave and the bottom-up drainage integration of the upper Yangtze River on the Tibetan Plateau before Pliocene times

The evolution of the upper Yangtze River (UYR) is intricately tied to the developing topography shaped by the uplift of the southeastern Tibetan Plateau and the evolution of the Asian Monsoon. Diverse processes governing drainage evolution have given rise to varying perspectives on the formation age of the UYR. This study undertakes a comprehensive analysis, based on linear river-profile inversions of 43 catchments draining into the UYR, to reconstruct the spatial and temporal patterns of fluvial incision history as chronicled by river knickpoint migration. The results reveal that the initiation epochs of knickpoints migration in tributaries span from 10 Ma to 3 Ma, and exhibit a decreasing trend as one moves upstream along the main channel. The main knickpoint in the trunk, a consequence of intensified uplift in the southeastern Tibetan Plateau during the middle Miocene, migrated headward via a bottom-up integration process at a calculated rate of 118–274 km/Myr. This migratory knickpoint and headward erosion in the drainage played a pivotal role in integrating watersheds and expanding the UYR's influence onto the inner Tibetan Plateau, a process that was largely complete prior to the start of the Pliocene.