Ages and grain-size characteristics of Dashu sediment section in Hanyuan County,Sichuan Province

The results of OSL dating of five lacusteine deposit samples from one 11.2m thick profile,Dashu Village in Hanyuan County,show that they have been deposited since the Mid-Pleistocene to Late-Pleistocene.There were three types in the frequency curve of sedimentology,including a-type with two peaks,b-type with three peaks and c-type with three peaks and a thick tail,showing six modes of 1-2Φ、3-4Φ、4-5Φ、5-6.5Φ、6.5-8Φ、10-11Φ respectively in each layers,and presented significant trends in the mode changes.The a-type reflected characteristics of deep water sediments,and the rest two types indicated a shallow water in the offshore lake.The suspended sediments are mainly composed of better sorting silt with the median of 18.12μm.Significantly positive correlations are between clay and fine silt,silt.The median size is positive correlated with sand,but negative correlation with clay.The profile from the bottom upwards can be divided into eight sedimentary stages,constituting three depositional cycles from fine to coarse grains and suggesting the different hydrodynamic conditions.