Sedimentary environment of a dammed lake buried in the modern riverbed of the Yalong River during the Last Glacial Maximum and its implication for fluvial geomorphic evolution

Abstract Along the eastern margin of the Qinghai–Tibet Plateau, there are frequent occurrences of strong tectonic movement and large-scale landslides. River blockages often occur in deep-cut river valleys, forming large-scale dammed lakes. In this study, a ~26.5 m thick lacustrine sedimentary profile that underlying the modern riverbed of the Yalong River is reported. Here, 14C dating results show that lacustrine deposition began at ~25 ka and continued till ~10 ka, mainly during the Last Glacial Maximum. Paleoclimatic indicators, such as particle size, magnetic susceptibility, and spore-pollen combination, were used to reconstruct the evolution process of the paleoenvironment in the study area, revealing that a paleo-flood event occurred at ~19 ka. The Tongzilin dammed lake contains an excellent record of the geomorphic evolution of the lower reaches of the Yalong River during the Last Glacial Maximum. Before 25 ka, the Yalong River experienced strong downcutting to form a deep valley, which created the space conditions for the formation of the dammed lake; from 25 to 10 ka, the dammed lake remained relatively stable, with dominating accumulation; and after 10 ka, the dammed lake broke and the river continued to downcut.