Formation and evolution of a giant old deposit in the First Bend of the Yangtze River on the southeastern margin of the Qinghai-Tibet Plateau

Abstract

The formation of the First Bend of the Yangtze River is an important event in the fluvial geomorphological evolution on the southeastern margin of the Qinghai-Tibet Plateau. After the formation of the First Bend, the water system in the Jinsha River (Upper Yangtze River) changed, resulting in a key period shaping geomorphology in this area. A large number of deposits (e.g., avalanches, landslides and debris flows) formed in the valley. Analysis of these deposits enables an understanding of paleoenvironmental, paleoclimatic and paleotectonic characteristics. Remote sensing interpretation and on-site investigation have confirmed the existence of the Sangushui old deposit in the First Bend of the Yangtze River. To understand the formation and evolution of this deposit, the genetic mechanism of the deposit was analyzed using field research, topographic interpretation and dating, combined with paleoclimate and paleostructure data. Results show that the deposit was formed at around 33.5 ± 1.4 ka BP by moraine destruction caused by an earthquake with the synergistic action of climate. By using a 3D discrete element model based on terrain reconstruction, the dynamic process of the landslide was simulated. Simulation results indicate that the sliding process lasted 150 s and the speed of the main sliding body reached 72 m/s. A giant deposit about 3.6 km long, l.4 km wide and 105 m thick was formed during this process. Finally, the peak acceleration of the paleoearthquake that induced the landslide was obtained by seismic parameter inversion. In addition, the formation of the Sangushui old deposit and subsequent valley evolution is proposed, providing information for the formation of the First Bend of the Yangtze River.