Characteristics And Geological Significance Of The Late Pleistocene Lacustrine Sediments In Diexi,Sichuan

The Wenchuan earthquake occurred in the middle of the Longmenshan tectonic belt on the eastern edge of the Tibetan Plateau.The huge earthquake caused great damage to the densely populated area of Wenchuan and Maoxian,and tens of thousands of people were killed or injured in the earthquake.Therefore,more and more attention has been paid to the study of paleoearthquakes in this region.However,due to the special landforms in the eastern edge of the Tibetan Plateau,the traditional paleoearthquakes research methods are difficult to be used in this region,and more and more attention has been paid to lacustrine sedimentation methods.The Upper of Minjiang river in the eastern margin of the Tibetan Plateau is not only an important ecological service area in China,but also a tectonically active area.In this paper,we study the provenance of Diexi museum lake sedimentary profile record of 9.45 m.Through the study of sediment grain size and quartz surface microstructure,the correlation of the tectonic activity and lacustrine sediments in the study area are discussed in this paper,a preliminary understanding to the structure activity relationship with the ancient lacustrine sediments was built,and we have a preliminary understanding of the different group of the source of the lacustrine sediments.The following conclusions are drawn:(1)According to EMA of grain size data,the grains are divided into two parts with a particle size of 20 ?m as the boundary,they are the fine particle component with a peak value of 10?m and particle size <20 ?m and the particle size >20 ?m with a peak value of 56 ?m.(2)It was found that most of the grains were aeolian by calculating the Y value with the Sahu discrimination.And the frequency curve shows a single peak of about 10 ?m and double peaks of about 10 ?m and 100 ?m.The component <20 ?m may be the background dust of stable deposition.(3)According to the c-m figure,with the deposit of the distal sediment,there were also some sediments affected by other sedimentary mechanisms are deposited.(4)The surface microstructure of quartz is characterized by low-relief,cleavage,conchoidal fractures,adhering particles,and less chemical features.(5)The wide occurrence of cleavage,adhering particles and small number of fractures on the surface of the quartz indicates that the generation of these quartzs may be related to the frequent local earthquakes.Dust storms,loose deposits,and landslides provide a source of lacustrine sediments that are transported by the wind and deposited in the lake.