Dynamic paleogeomorphic reconstruction revealing the incision process of the Three Gorges of the Yangtze River

Abstract

The Yangtze River is the largest river in Asia. It is an important geomorphological event in a united tectonics-climate-geomorphology system in Cenozoic era in China. The incision of the Three Gorges, which is located between the Sichuan and Jianghan basins, marked the formation of the modern Yangtze River. However, it is still controversial on the key scientific issue of "when the Three Gorges formed or was incised", due to the abundant geological data. The previous study usually focused on one factor affecting the river development, e.g., tectonic movements, sedimentology, paleoclimate and sea level changes, to conclude this key issue. Those key factors could be quantitatively combined into Badlands, a software that simulates the paleo-geomorphology. Take the area to the east of the "first bend" (Shek Kwu Town in Yunnan Province) of the Yangtze River as the study area, we used Badlands to reconstruct the geomorphology and river system evolution process since the Late Cretaceous (80Ma). Then the seismic data of Sichuan Basin and Jianghan Basin were used to test the reliability of our model results. The results revealed that the river flow direction in the Sichuan Basin was reversed to drain northwards due to the Late Eocene-Oligocene uplift in the eastern Tibet and the southwestern Upper Yangtze River. The Jianghan Basin had been in a low base level during the early Paleogene, controlled by the continental rifting environment in eastern China. The reversal of the drainage direction in the Sichuan Basin and the long-lasting low basal level in the Jianghan Basin eventually made the Three Gorges to be incised at the latest Oligocene. We proposed that the flow direction of the Upper Yangtze River was reversed and captured by the Middle Yangtze River is the incision mechanism of the Three Gorges.