Paleoclimatic evolution of Xingkai Lake Plain from late Middle Pleistocene to mid-late Late Pleistocene

Optically Stimulated Luminescence(OSL) dating and palynological analysis were conducted on Quaternary borehole sediments in Mishan area of Xingkai Lake Plain. The results indicate that the 54.40 m thick sedimentary sequence in this area is well-preserved with stable deposition, dating back to approximately 162.0 ka and representing the sedimentary strata since the late Middle Pleistocene. Based on the characteristics of the spore-pollen assemblages in the borehole, four palynological assemblage zones were identified from the bottom upward: Zone Ⅰ(open forest-steppe vegetation), Zone Ⅱ (pine-birch steppe vegetation), Zone Ⅲ (pine-elm steppe vegetation), and Zone Ⅳ (coniferous forest-steppe vegetation). The overall vegetation assemblage is interpreted as a savanna-like environment. Integrating the variations in these spore-pollen assemblages, the climatic evolution since the late Middle Pleistocene in the study area were reconstructed. The Xingkai Lake region underwent a shift from cold and dry conditions in the late Middle Pleistocene to warm and humid conditions in the early Late Pleistocene, then to cold and dry climate in the early-middle Late Pleistocene, and again to warm and humid conditions in the mid-late Late Pleistocene. The spore-pollen evolutionary pattern in the area is similar to the vegetation evolution pattern observed in Sanjiang Plain. This study provides data support for understanding the environmental evolution of Xingkai Lake Plain and offers fundamental data for elucidating the climate evolution patterns in East Asia since the late Middle Pleistocene.