Sedimentary characteristics of the Early and Middle Holocene loess in Tongchuan area and their implications for paleoclimate

The grain size of the loess and palaeosol in the Tongchuan section was studied as the main subject of this paper. Combining the magnetic susceptibility data, we analyzed the paleoclimate changes during the period from 11.4 to 1.5 kaBP. It is revealed that: (1) The loess-palaeosol deposits in the profile of Tongchuan are silt dominated (69.78%) over clay (28.35%) and sand (1.87%). (2) Silt and sand are higher in loess but lower in paleosol, while the values of clay particles and magnetization were lower in loess but higher in paleosol layers. (3) The variation trend of the clay (＜4 μm), silt (4～63 μm) and magnetic susceptibility index have good correspondence to the loess-palaeosol alternation and the cold and dry climatic events between 11.4～1.5 kaBP. Based upon it the climate change in this area can be divided into four stages. In the period of 11.4～10.2 kaBP, the climate was very dry and cold; in the period of 10.2～9.1 kaBP, temperature gradually increased, and the climate was slightly warm and dry; during the period of 9.1～4.4 kaBP, the climate was warm and humid; while in the period of 4.4～1.5 kaBP, climate gradually turned to cold and dry.