Geochemical Characteristics Of Elements And Environmental Evolution In The Northeastern Of The Tibetan Plateau Since The Holocene

The Holocene is an important period in the development of human civilization,which is closely related to modern humans.The research on the evolution of climate and environment during this period has become a hot spot in the study of paleo-environment.The northeastern of the Tibetan Plateau is located in the northwest edge of the Asian monsoon region.Under the common influence of monsoon circulation and westerly circulation,it is sensitive to climate change.The special geographical background makes it an ideal place to study regional and even global climatic and environmental evolution.However,due to the complex circulation patterns and special geographical background of the study area,the environmental conditions of different regions within the study area are quite different,combines with different climatic proxies and dating methods are different,make the climatic and environmental evolution of the northeastern Tibetan Plateau since the Holocene is still controversial.In view of this,this paper takes the aeolian sand-paleosol sequence of ZK profile in the northeastern of the Tibetan Plateau as the research object,analyzes the geochemical characteristics of elements in the profile and their environmental significance,combines with ¹⁴C dating method,the process of the environmental evolution in the northeastern of the Tibetan Plateau since Holocene has been reconstructed,which provides supplementary data for the previous studies.The results show that:（1）Among the major elements,the SiO₂,Na₂O/K₂O,Sa and Ki are higher in aeolian sand layer,indicating cold and dry climate;the Na₂O,CaO,MgO,K₂O,Al₂O₃,Fe₂O₃,TiO₂,CIA and W are higher in paleosol layer,indicating warm and humid climate.（2）The ratios of TiO₂/Al₂O₃,K₂O/Al₂O₃and Fe₂O₃/Al₂O₃in ZK profile are distributed in the closed range of loess-paleosol,aeolian sand,fluvial sediment and lacustrine sediment in Qaidam Basin,indicating that the weathered detritus in Qaidam Basin may provide rich provenance for the aeolian sand-paleosol sequence in ZK profile.（3）Among the trace elements,the Ba,P,Mn,Rb,Sr,Cu,Zn,V,Cr,Y,Sr/Cu,Cu/Mn,Zn/Mn and Sr/Ba are higher in paleosoil layer than that in aeolian sand layer,the high values indicate warm and wet climate,while the low values indicate cold and dry climate;the Rb/Sr is the opposite,the high value indicates cold and dry climate,while the low value indicates warm and wet climate.（4）Since the Holocene,the environment of the northeastern of the Tibetan Plateau has experienced a transition from warm-wet to cold-dry,which can be divided into a warm-wet period of 9.4～4.2 ka BP and a cold-dry period of 4.2～0 ka BP.Among them,there were sub-level climatic fluctuations in 6.6～6.2 ka BP,2.4～2.0 ka BP and 1.7～1.5ka BP.（5）Since the Holocene,there were eight cold events in the northeastern of the Tibetan Plateau,including 9.2 ka BP,8.2 ka BP,6.2 ka BP,5.3 ka BP,4.2 ka BP,2.8 ka BP,1.5 ka BP and 0.5 ka BP cold event.The 4.2 ka BP cold event was the strongest one in the Holocene.