Climatic environment changes during the last interglacial-glacial cycle in Zhifu loess section: Revealed by grain-size end-member algorithm

The last interglacial-glacial Zhifu loess section on the northern Shandong Peninsula is mainly composed of sandy loess、loess and palaeosol. Grain-size analysis suggest that silty sand dominate the loess (74.95%), followed by the clay (10.05%) and very fine sand (9.57%). In terms of mean grain size, paleosoil is finer than sandy loess with loess in between. End-member algorithm is used in the study of grain size composition of the Zhifu section. Four clustering end members (CEM) are recognized. Based on the clustering end member frequency curves and optical stimulated luminescence dating results, it is concluded that CEM1 and CEM2 represent the strong summer monsoon and warm summer climate respectively during the MIS5e, MIS5c and MIS5a periods; CEM3 represents the environment during the MIS5d and MIS5b periods with intensified winter monsoon and relatively cold climate; while the CEM4 represents the extremely strong winter monsoon environment during the MIS4 period. These fluctuations show a strong coherence with the magnetic susceptibility of the Loess Plateau and intensity of the winter monsoon indicated by the content of grains >32μm in the Xifeng loess section, as well as the transgression/regression events along the Bohai Bay recorded by benthic foraminifera.