Implications of the discovery of rapidly deposited lacustrine sediments in the Suwalong reach of the upper Jinsha River, SE Tibetan Plateau

A large amount of lacustrine sediments was found in the Suwalong reach, which is located upstream of the Jinsha River at the southeastern margin of the Tibetan Plateau. The study area belongs to the alpine valleys, with arid and semiarid climate. The appearance of lacustrine sediments indicates that river-blocking events had occurred in this reach and formed stable dammed lakes. By optically stimulated luminescence (OSL) dating, the burial time of lacustrine sediments was analysed, and the time sequence of river blocking and dam breaking in this reach was obtained. According to the burial time and thickness of lacustrine sediments, the deposition rate of sediments was obtained, and the maximum deposition rate is 170.5 mm/a, indicating that the provenance was abundant during the formation of lacustrine sediments. The results of grain size and SEM analysis show that the lacustrine sediments were mainly transported into lakes by wind, and the results of major element analysis also indicate that lacustrine sediments did not come from local areas. Combined with the above experimental results, we come to the conclusion that during the river-blocking period, the tectonic activities in the Suwalong reach and its vicinity were very active, triggered numerous landslides and rockfalls, and produced abundant silt particles. These silt particles were transported into the dammed lake of the Suwalong reach by wind.