The Yushu loess deposition in eastern Songnen Basin since the last glacial period and its environmental significance

Abstract：Magnetic susceptibility and grain-size distribution of the loess-river sand profile in eastern Songnen plain of northeastern China since the last glacial period were analyzed, and the paleo-environmental history of this region was investigated. The results demonstrate that： 1) the loess deposition of eastern Songnen plain occurred at least 46 ka B.P., i.e., at the last glacial period. There exist four modes of grain size distribution of sediments, which have been mixed with loess and river sand. The mode of river sand sediments (④) was dominant at 46 ka B.P., and the mode of loess dust (③) was dominant after 46 ka B.P. In the past 3000 years, the climate became drier and more deserts were activated in the eastern part of Songnen basin; 2) the loess dust of eastern Songnen basin mainly came from the Keerqin desert, the Songnen desert and other large deserts in northwest areas, and the Keerqin desert was extensively developed in the last glacial period; 3) there was a tectonic movement 40 ka B.P. in Songnen basin, and after this movement, loess dust was deposited in Yushu area with the development of the keerqin desert; 4) the climate evolution of northeastern China in Holocene can be divided into five stages, being respectively about 10000 a B.P., some 9000 a B.P., around 6000 a B.P., 4500 a B.P. and 2500 a B.P. in age.