Organic Geochemical Records Of Paleoclimate Evolution Since Late Pleistocene In Eastern Yinchuan Basin

The eastern Yinchuan basin is located at the junction of monsoon and nonmonsoon,arid and semi-arid,loess and desert,loess plateau and Inner Mongolia plateau,which is very sensitive to climate change.The climate change in this area,especially since Pleistocene,can be analyzed by high resolution interpretation of various indicators in loess sediments.Based on the systematic collection of data from the late Pleistocene in Yinchuan basin,the natural section was selected for high-density sampling after field exploration,and environmental substitution indexes such as organic carbon,nitrogen and lipids were selected for testing and analysis.Besides,three chronologic samples at the appropriate horizon were selected for photoluminescence dating test.By analyzing the data and reading relevant geological data and literature,and combining the relevant studies of predecessors,the following conclusions and understandings can be obtained:(1)The lower content of total organic carbon and total nitrogen in the ice gully section is mainly controlled by the influence of soil overlying vegetation,indicating that the main sources of organic carbon and nitrogen are terrestrial herbaceous plants and lower aquatic plants,in line with that of composition of GDGTs.(2)According to the synchronous analysis of multiple indicators,the eastern Yinchuan basin has experienced synchronous changes in climate from warm to wet,cold to dry since the late Pleistocene,presenting a transition from warm to dry--warm to wet--cold to wet--warm to wet.(3)Comparison analysis indicated that the paleoclimate evolution since late Pleistocene in the study area was in line with those of surrounding areas.But more drought events occurred in the eastern Yinchuan basin.This should be influenced by the westerly circulation and east Asian monsoon simultaneously due to the unique location at the edge of the desert,which resulted in more frequent and complex climate change in thestudy area than other areas at the same time.