Headward drainage basin expansion drives Miocene incision along the Yangtze River, China

Along the southeastern margin of the Tibetan Plateau, the onset of rapid fluvial incision during the Miocene is commonly attributed to growth of high topography. Recent recognition of lacustrine strata preserved atop interfluves, however, suggest that headward expansion of river networks drove migration of the topographic divide. Here, we explore the impact of this process on fluvial incision and sediment transport along the Yangtze River. Landscape evolution simulations using TopoToolbox (TTLEM and TVD-FVM) demonstrate that expansion of the Yangtze watershed into previously internally-drained basins since the Late Miocene could be responsible for 1-2 km of fluvial incision. The distribution of modern knickpoints and river profiles are consistent with this hypothesis. We suggest that increased erosive power associated with capture and basin integration drove accelerated incision and sediment transport during the Late Miocene. Progressive captures and integration of sub-basins could have driven punctuated episodes of rapid incision as drainage divides were progressively breached. Our results support the notion that the low-relief landscape atop the eastern Tibetan Plateau was elevated prior to Miocene time, and that basin integration and headward incision into this high-standing plateau drive rapid incision downstream of this former topographic divide.