Response of grain-size components of loess-paleosol sequence to Quaternary climate in the Southern Loess Plateau, China

A new, thick, and complete loess-paleosol sequence is a good response to climate changes. In this paper, the distribution and parameters of grain size in the Xiushidu (XSD) sequence in the southern Loess Plateau were systematically investigated. A comparative analysis of the sediment granularity with different areas was also conducted. The results show that the XSD sequence is primarily constituted by coarse silt (52.18%), clay (21.71%), and fine silt (20.27%), and the contents of colloidal particles (3.63%) and fine sand (2.21%) are relatively small. The contents of 1 similar to 5 mu m and < 5 mu m show a slight increase from S(9)to S-5, while the contents are clear downward from L(5)to L-0, indicating that the climate is gradually getting colder after S-5. Grain-size distribution curves show a bimodal pattern for loess/paleosol. The grain-size component and peak pattern illustrate that dust materials were not only transported by wind but also experienced pedogenesis. Moreover, the changes of grain-size indicatorM(z)values indicate climatic instability. Comparing with the Beglitsa, Oitak (AYTK), Lanzhou (LZ), Pengyang (PY), Luochuan (LC), and XSD sequences, we can infer that the XSD sequence not only has experienced the strong pedogenesis and the warm and humid climate but also has influenced by the Himalayas, the Tibetan Plateau, the QM, and the LPM. These analyses help to clarify the climatic and environmental context of loess-paleosol sequence deposition phases and regional environmental evolutions.