The Formation And Evolution Of The Hobq Desert In Late Quaternary Of Hetao Area,inner Mongolia

Hobq Desert is located in the north of east-western uplift zone of the Ordos Plateau and on the transitional slope which is from Ordos Plateau to Hetao Plain.The south terrain of the Hobq Desert is lower than the north side,and is surrounded by the Yellow River from the west,north and east direction.The southern of Hobq Desert is a structural platform,the middle of it is an aeolian dune,and northern of it is floodplain.The Hobq Desert is the marginal location under the effect of modern Asian Summer Monsoon,where can be categorized as a transitional area from semiarid to arid.The ecological environment is fragile in the Hobq Desert,where is sensitive to the responses of climate changes.The evolutionary process of Hobq desert is an epitome of environmental changes in Hetao-Erdos region.The surface of Hobq Desert develops desert-facies aeolian sediments,formed by aeolian sediments like dune,inter-dune and sand sheet.By obtaining the records of geological information from the quaternary sediment in the sandy-cover area,we could discover the procedure of formation and development of the Hobq Desert,form the stratigraphic framework,and provide evidences of reconstructing the evolution of regional environment.With the help of remote-sensing images,radar scanning we could restore the ancient wind-directiom and process of desertification by combining the type of dune,the maturity of development,wind direction and the data of meteorology.That is the Hobq Desert northwest wind dominated low wind environment,do not support the long-distance transportation,the aeolian systems are near source deposition.To determine the source of the aeolian sand,after exposing the aeolian sand on surface by using slot drill and impact drill,we utilized the analysis of sediments like granularity analysis and scanning electron microscope,OSL and 14 C constrain,we obtained the sediments sequences of the alluvial system of underlying river and the lacustrine system,identifying that the ancient channel of Yellow River was hidden in the underlying of Hobq,and caused “in-situ sand accumulation” on the dried channel forced by wind,that is,the Yellow River provide the dominant source of material forthe Hobq Desert.The small range of gravel desert developed in the northern of Hobq,which belongs to re-deflation facies of deposit,is actually the bottomset of dune exposed by wind,and this proved again the existence of “in-situ sand accumulation”.Through the indication from varies climate proxies,we discuss the paleoclimate background and how it influence the evolution of the Hobq Desert.Controlled by the deep positive concealed faults,the alluvial system of underlying northern of desert is constructed by braided river of Yellow River and floodplain sediments,in which the small range of gravel desert developed in the northern of Hobq belongs to re-deflation facies of deposit.Date back to 16-11 ka,in the process of the shrinkage of paleolake,the ancient Yellow River passed and eroded the layer of lacustrine sediments,accumulating gravel and fine sand on the bottom of paleolake as the basis of sand source.The middle of Holocene dated back to 4.1 ka ago,the low-lying areas of Hobq and dune accumulated initially.Late Holocene was dated back to 1.44 ka ago,when the ability of aeolian-sand activation became stronger,the Hodq area gradually formed the landscape of desert.