The Age Of Paleo-landslide-dammed Lake In Dadu River

Large amount of dammed lakes have come up in the eastern margin of the Qinghai-Tibet Plateau due to its unique geographical location and tectonic geomorphic environment.A typical example is the ancient landslide barrier lake in Dapu River Valley.Barrier lakes is one of the remarkable extreme surface processes,which often causes catastrophic consequences.The study of the ancient barrier lake contributes to the understanding of the risk of regional blockage.In this paper,we study Shiguangdong and Jiajun landslide dammed lake at the upstream and the midstream of Dadu River in the eastern margin of the Tibetan Plateau.In March 2015,in the process of field work along the Banks of the dadu river we selected lake facies sedimentary profile,22 samples were collected.several profiles were chosen and the method of Single Aliquot Regeneration(SAR)combined with Standard Growth Curve(SGC)was adopted to study the Optically Stimulated Luminescence(OSL)dating of twelve lacustrine samples,which were collected from these profiles in Shiguangdong and Jiajun.We conducted experiment conditions for choose the suitable Test conditions for dating,Before the OSL dating experiments.Therefore,the OSL method and its test conditions are feasible and reliable for th e dredging of the lake sediments in Dadu River Basin.First,the main reason of the formation of the ancient barrier lake in Dadu River Basin is revealed.On this basis,we discussed the relationship between the ancient landslide barrier lake and the earthquake and climate and the main cause of the formation of the ancient landslide barrier lake.Then,the control effect of dam on river topography is analyzed according to the geological evidence of two ancient landslides.In this paper,the main conclusions of our study are as follows:(1)In this paper,the sediments of the two ancient landslides are mainly composed of silty clay and fine sand in Shigangdong and Jiajun,and the quartz particles extracted from the laboratory are medium grains(38 ~ 63?m).(2)Before and after the OSL test,the preheat plateau and dose recovery test were carried out to determine and select the appropriate experimental conditions.The suitable preheat temperature of the two samples of the lacustrine sediments were 260 ? and 220 ? in Shigangdong and Jiajun.Dose recovery text results show that the OSL data of this paper are reliable.(3)According to the results of OSL and the combination of previous studies,the results show that the ancient landslide dam lake is about 3.0 ka and ends at 1.6 ka.At least the Jiajun ancient landslide dam lake has been formed about at 9 Ka(Early-Holocene).Combined with previous studies for the ages of the ancient lake in East Tibetan plateau,The ages of thepaleo-dammed lake have been concentrated in the Late-Pleistocene,fewer occurred in the Holocene.(4)By analyzing the seismic and climatic conditions of the research area,explore the formation causes of the ancient landslide dam lake in this area,go further concluded that the research area qualified with the seismic condition which could induce the ancient landslide,thus there maintain the possibility that the ancient landslide could be triggered by an earthquake.(5)By researching the features of ancient barrier dams in Shigangdong and Jiajun,discuss the barrier dams' transformation effects of the watercourse,as well as the dammed lakes' impacts for longitudinal profile of the channel.