Research On The Changes Of Paleoclimate Environment In Hunshandake Sandland Since The Cenozoic

Great tracts of land are covered by desert or sandy land in the arid and semiarid region,The strong surface processes in the arid and semiarid region may not only increase the risk of natural disasters,but also affect the production and livelihood of local people,and even affect the climate in the Northern hemisphere and larger spatial areas through dust transmission.The study of climate change history in the arid and semiarid region is a critical global problem with broad impact and and difficulties to deal with.It has attracted widespread attention from the intermational community.The response to climate change in the arid and semiarid region has become one of the important measures for win-win international cooperation.The deposition rate and erosion rate of sediments in desert or sandy area are fast.It can be compared with loess in space.In the study of climate change,it have become a typical dust accumulation for interpreting paleoclimatic evolution history in the arid and semiarid region.Otindag sandy land is one of the four major sandy lands in China.It is an important component of the mid-latitude temperate inland in the arid and semiarid region.It is located in the east-central part of the Inner Mongolia plateau.Located at the edge of the East Asian monsoon area,the study area has become an ecologically fragile area which is very sensitive to the climatic and environmental evolution.It is an ideal place to study the climate change in the arid and semiarid areas of China and even the Northern Hemisphere.The predecessors have carried out a series of in-depth paleoclimatic studies on aeolian sand-sandy paleosol sequences,lacustrine sedimentary and loess-paleosol sequences in Otindag sandy land at a relatively short time scale.However,the current research on the paleoclimate of Otindag sandy land mainly focuses on the last interglacial period,the research before which have rarely been reported.Multiple periods of volcanism have occurred in Otindag sandy land since the Cenozoic.Basalt interbeded with lacustrine sand,silt,clay deposits formed by multiple volcanic activities is widely developed in the area.In view of the fact that basalt can obtain a more accurate K-Ar age,combining the K-Ar age of basalt of upper and lower layers of various sedimentary layers,stratigraphic chronological framework with a longer time scale can be established.Based on extensive scientific investigation and systematic sampling work in Otindag sandy land,this paper selects four representative profiles for the analysis of K-Ar chronology and substitute index of environment.It also summarizes data of previous studies using basalt as dating carrier in the study area.The depositional time frame is based on existing optically stimulated luminescence dates(OSL),paleomagnetism dates and K-Ar age of basalt.This paper restores the process of climate change in Otindag sandy land since Cenozoic based on the analysis of sedimentary facies and climatic proxies in order to supplement the research on Cenozoic climate change.Moreover,the evolution mechanism of the paleoclimate change is preliminarily exploreed.It is found that the climate in the study area was generally humid during Paleogene,but there were still several dry and wet fluctuations.The climate conditions in the Middle Eocene and Late Eocene were relatively dry.During the Miocene period,the climate experienced a process from warm and dry to warm and wet,and then gradually changed to cold and dry.In the Pliocene,the climate was warm and humid as a whole.The relatively humid climate lasted until the middle Pleistocene,and in the late Pleistocene,the climate changed to drought.The climatic environment has been characterized by frequent changes in dry and wet conditions since the Holocene.The study indicates that the climatic and environmental changes in the study area were influenced by the global climatic variations and the growth of Tibetan Plateau in the early and middle stages of the Cenozoic.Climate changes in sandy land have been affected by changes in global ice volume and the uplift of the Tibetan Plateau,and it is a regional response to the periodic fluctuation of global ice amount since the Late Cenozoic.