Late Cenozoic erosion pattern of the eastern margin of the Sichuan Basin: Implications for the drainage evolution of the Yangtze River

Evolution of the drainage network of the Yangtze River plays an important role in landscape evolution across East Asia during the Cenozoic. The mountains on the eastern margin of the Sichuan Basin form a drainage divide between the tributary rivers of the modern Upper and Middle Yangtze, and the erosion history of these mountains has major implications for the evolution of the Yangtze River. Linear inversion of long profiles of two Yangtze tributaries draining the area allows us to estimate their incision processes, and reveals contrasting erosion patterns between the west and east sides of the mountain belt. Along the Wu River, which drains into the Sichuan Basin, higher incision rates are focused on lower channels near the river's outlet on the Upper Yangtze. In contrast, within the catchment of the Yuan River, which drains into the Jianghan Basin of the Middle Yangtze, the inverted fluvial erosion rate is distributed relatively uniform in space. We calibrate the inferred incision history using previously published cosmogenic ¹⁰Be-derived basin-averaged erosion rates, and the results show that the contrasting erosion patterns between the two rivers emerged since the early Miocene (~21–16 Ma). At this time, the incision rates of the lower Wu River started to increase from ~0.04 km/Ma towards the Quaternary average at ~0.07 km/Ma, while the rates of the Yuan River remained low (<0.04 km/Ma). By comparing our results with erosion histories of the eastern Sichuan Basin and Three Gorges, we suggest that during the early Miocene, connection between the Sichuan and Jianghan Basins through the Three Gorges led to additional lowering of the local base level in the Sichuan Basin, which triggered an acceleration in incision rates of the Upper Yangtze tributaries draining into the basin.