The Late Quaternary Palaeolake Evolution And Environmental Changes In Baotou Basin

Baotou Basin is located in central and western of Inner Mongolia, it's part of the Hetao Basin. Since the late Pleistocene, the geomorphic environment in the study area had experienced lake extension and shrinkage. Deposits were mainly altered from lake deposits into fluvial deposits,which shows that the changes of the environment were considerable. The paper selects Baotou Basin WanShuiQuan profile as the research object, dated the collected lake sediment samples collected by the C-14 dating techniques, rebuilded baotou basin ancient lake change and environmental change history of MIS3 stage, and discussed climate change of Baotou Basin rhythm and driving mechanism.Through study and analysis, the main conclusions are as follow:Baotou Basin WanShuiQuan profile lake sediment dating data shows, in the late quaternary 50-30 Ka B.P., there were two lake developments and one lake recession event.1,60-50 Ka B.P.lake extending phaseDuring 60-50 Ka B.P.period, Baotou Basin accumulated dark gray silty clay, which rich in organic matter, constituted the typical thick lacustrine strata. The lacustrine strata development is the important evidence of existence of Baotou Basin ancient lake; the dark gray silty clay reveals the wet climate at that time. The age of the top layer is about 50 Ka B.P., combined with the age of the shorelines at margin of the Loop basin, concluded that the deep-water ancient lake developed in Baotou Basin during 60-50 Ka B.P. period, corresponded with MIS3 stage of the Late Pleistocene. 2,50-37 Ka B.P. rivers developing phaseDespite the lack of dating materials of this layer, the age of upper clay of the sediment is 37.952±0.827 Ka B.P., so the age of this sedimentary layer is 50-37 Ka B.P.. The main accumulations of this layer are yellow gravel stratum, grinding roundness is better, sand is evener, interbedded with gravels and pebbles, which is the typical sedimentary characteristics, indicating a severe recession in the ancient lake, the lake shrinked and the river developed. This phase corresponded with the MIS3b stage.3,37-30 Ka BP the lake re-developing phaseThe top and bottom age of the layer are 37.952±0.827 Ka B.P.and 30.429±0.358 Ka B.P.. During this stage, the formation was mainly composed of light gray sandy clay, and the clay was subtle parallel bedding, which is the lacustrine sedimentary characteristics. Lake re-developed at this stage, light gray sandy clay sedimentary reflected the humid climate. the sedimentary strata are MIS3a stage Material. In late MIS3 stage the section strata characteristics showed the re-development of the ancient lake basin. Combined with existing research, there might be a continuity ancient lake occurred in Baotou Basin, the area may be smaller than the ancient lake in the early MIS3.The measured results of Baotou Basin WanShuiQuan lake sediment profiles of three periods shows that the MIS3 period development of ancient lake may be related to wet climate, river development period was corresponded with dry climate. Lake environment evolution of Baotou Basin shows, ancient lake evolution may not only influenced by regional climate factors, but also are likely to be influenced by regional water system, tectonic movement, the Yellow River evolution (Inner Mongolia section) and so on, which need further study.