Grain-size characteristics and origin of Longjie silt layer in the Yuanmou area,Yunnan,China

Chronostratigraphy and sedimentology study of Longjie section where silt layers are well preserved in Yuanmou area of Yunnan province. Approximate thickness of this section is 40.6m, the 14C dating result from where 10.9m away from the top is 26305±1152 a BP,which indicates that the silt layer belongs to Late Pleistocene. By grain-size analyzing,Longjie silt layer is mainly composed by silt, medium size is 15.28μm, and the frequency curve displays a distinct doule-peak feature barely without any crude tailings. Compared to the grain-size distribution and parameter of Daihai lake sediment, Xifeng yellow earth and Xuancheng fluvial sediments, grain-size feature of Longjie silt layer is generally the same with that of Daihai lake deposit, while is quite distinct from yellow earth and fluvial sediments, this indicates that Longjie silt layer is lacustrine deposit under relatively low hydrodynamic force.