Optically Stimulated Luminescence Geochronology Of Sediments In Xuelongnang Palaeo-dammed Lake,Upper Reaches Of Jinsha River Valley

The southeastern margin of the Qinghai-Tibet Plateau is rich in geomorphological environment and active area of tectonic movement.The upper reaches of the Jinsha River are located in this area.There are many alpine mountains and valleys distributed here.The internal and external dynamic geological processes are strong,and the ancient and modern barrier lakes are well developed.The barrier lake is a special surface process formed during the development of geological history.It contains abundant environmental information.It is of great academic value to study the chronology of ancient barrier lake sediments for discussing the origin and evolution of ancient barrier lakes.Xuelongnang palaeo-dammed lake are located on the upper Jinsha River at the southeastern margin of the Tibetan Plateau.In this paper,we collected 20 OSL sampies from the lacustrine profiles of Xuelongnang palaeo-dammed lake and its adjacent area,and the equivalent dose(De)of each sample was measured by Single Aliquot Regeneration(SAR)dose method.Before the OSL dating experiments,We conducted experiment conditions for choose the suitable test conditions for dating.Make sure the OSL method and its test conditions are feasible and reliable for the Xuelongnang lacustrine sediments in upper Jinsha River.By analyzing the distribution law of the equivalent dose(De)value and calculating statistics of the chronological model,screening the samples with good retreat conditions,and obtaining the reliability of the equivalent dose obtained by the OSL dating method.Combined with previous studies and regional investigations on the dam-breaking deposits and lacustrine sediments of the Xuelongnang paleo-landslide in the upper reaches of the Jinsha River.Then discuss the formation and ending ages of the paleo-dammed lake and the geomorphological evolution of the area to study the significance of geological disasters and environmental evolution.In this paper,the main conclusions of our study are as follows:(1)According to the results of preheating plateau experiment,cyclic ratio statistics and optical luminescence characteristics of samples,it is concluded that the quartz Single Aliquot Regeneration(SAR)dose methodbased on photoluminescence dating technology is suitable for the dating of sediments in paleo-dammed lakes.(2)By analyzing the distribution characteristics of equivalent dose(De)of sediment samples,it is concluded that 14 of the 20 OSL samples are relatively good in sun retreat,while the other 6 samples are relatively poor in sun retreat.The equivalent dose(De)of the sediment samples calculated by mean method is reliable.(3)Based on the results of photoluminescence dating and the analysis of stratum contact,it is concluded that the formation age of Xuelongnang paleo-dammed lake is about 2.1 ka,and its extinction age is about 1.2 ka.The existence of the paleo-dammed lake for about 900 years indicates that the landslide-type barrier lake can persist on a centenary scale and has a long stability.