Study On Glacial Heritage Of Pingdingshan,Hexigten Banner,Inner Mogolia

The Pingdingshan area,located in Hexigten Banner,Inner Mongolia,with a coordinate of 43°4?46.74?N and 117°51?5.76?E,develops a large number of glacial heritages including ancient cirques,U-shaped valleys,horns,arêtes,etc.These large-scale and multiple-type heritages are mainly glacial erosion landforms.The numerous cirques are fully developed and well preserved.In the trough valley under the Nantai cirques group of Pingdingshan,we found obvious layered accumulation body,which is of complex composition with alternating layers of gravel and soil.Base on the detailed field investigation,this thesis conducted systematic research on the glacial heritages in Pingdingshan area by analyzing the topographic characteristics,cirques data,cause of the gravel accumulation body,and the Scanning Electron Microscope(SEM)of the quartz grain.The Optically Stimulated Luminescence(OSL)dating method is also used to discuss the development phase and formation age of the glacier in Pingdingshan.The main progresses of this thesis are as follows:1.Cirques are mainly distributed at the elevation of 1250 m and 1300 m.The measured 107 groups data of cirques length,width and height show that,the cirques at the elevation of 1250 m have larger scale and had endured strong erosion in the later stage.While the cirques at the elevation of 1300 m show obvious different shape.The flat indexes of the cirques range from 1.7 to 5.0,suggesting glacial origin.2.The four accumulation bodies in the study area all have the feature that one soil layer sandwiched between two gravel layers.The grain size distribution curves have characteristics of multimodal.The peak values vary in two ranges,from-2? to-1? and from 3? to 4?.Grain size frequency cumulative distribution curves show gentle convex arc on the whole.The standard deviation of the grain size ranges from1.5 to 2.5,with the skewness and kurtosis at about 0.The quartz grains surface of the accumulation bodies can be observed conchoidal fractures,striations,adhering particles,and a few hitting pits.Compared the grain size parameters of the study area with those of the three lateral moraine samples of the North Pole,we found that the two have very high similarity.All of the four accumulation bodies are glaciation genesis,but suffered from different intensity modification in later stage.3.The age of the gravel layer at the bottom of NO.1 accumulation body is66.46±6.72 ka,and the age of the gravel layer from the top of NO.4 accumulation body is 44.07±4.98 ka,corresponding respectively the early stage of last glacial period in MIS4 and the cold period in MIS3.This feature suggests that the glacier in the study area is simultaneous with that in other highly studied areas.4.The study area has experienced two phases glaciation.The first period,the cirque at elevation of 1250 m and accumulation body at the bottom developed at the time of 66.46±6.72 ka;The second period,the cirque at elevation of 1300 m and accumulation body at the top developed at the time of 44.07±4.98 ka.The first phase glaciation had endured stronger modification in later stage than the second phase,and preserved more complete.