Pleistocene Eolian Sediments Characteristics And Its Geological Significance In Fengzhen Basin,Inner Mongolia

Fengzhen City is located in the south-central Inner Mongolia Autonomous Region.Its terrain is high in the north and low in the south and Yunmen Mountain in the east,Kouquan Mountain in the south,Matou Mountain in the west,Baiyacha Mountain in the north,southern side is connected to the Datong Basin through the Yu River.It is a small basin in the Fengzhen area.Because the Matou Mountain in the west and the Baiyao Mountain in the north are mainly Cenozoic basalts,and a set of Pleistocene lacustrine strata are deposited in the basin,this basin is defined as the Quaternary Fengzhen Basin.The northern part of the Quaternary Fengzhen Basin is the Inner Mongolia Plateau,the southwest is the Loess Plateau,and the southeast is the Taihang Mountains.Because of its special geographical location,Fengzhen become the northern margin of Quaternary eolian sediments.There are thick eolian sediments in the basin.These deposits are continuous and there are natural carriers of climatic change records.Therefore,this paper selects the eolian sediments of the basin as the research object.New OSL dating,particle size analysis and sporopollen analysis were used to study on these eolian sediments.It shows that this stratum developed in the late Pleistocene,which considered to be an eolian deposit and lake facies,,and the formation era can be compared with the Malan loess.Based on the statistics of sporopollen types and quantities,the sporopollen percentages were drawn.Combining with lithological descriptions and OSL dating data,the climates of Fengzhen from Qp2 to Qh were divided into four periods: Phase Overall,savanna is the main vegetation landscape in the Fengzhen area.Both vegetation types and statistical results can be compared with other sections of Datong region.It reflects that the climate became drier and colder in fluctuation gradually.Based on the regional stratigraphic comparison and Neotectonic movement,it is considered that basement of the basins is composed of Proterozoic metamorphic rocks and Oligocene,Miocene and Pliocene deposits and volcanic rocks.During the Pliocene period,the vast area of Xiwuqi-Jining Datong-Hohhot was basically within the same elevation range,and at that time the climate was hot and humid,and a set of red lacustrine strata was deposited.After entering the Quaternary,affected by the neotectonic movement,the above-mentioned vast areas have different elevations,and the elevations generally decrease from north to south in the northeast direction,forming the current geomorphological features and the climate tends to be cold and dry.Gradually reduce the salinization and eventually dry up.