Discussion Of Provenance And Environmental Evolution Of Loess Records At Otindag Sandy Land Margin

Use OSL(Optically Stimulated Luminescence)dating and sedimentary characteristics to confirm Jingpeng profile which at Otindag Sandy Land margin is a loess deposition during the last glacial.Previous work in this region is attention on Holocene,and lack of the last glacial loess research data,so this research can complement the data during the last glacial.According to geochemistry,particle size and magnetic susceptibility,in combination with chronological supports of OSL dates,the climate change in this region during the last glacial is reconstructed,and the instability of the last glacial climate is revealed,the Otindag Sandy Land and Horqin sandy land expansion and contraction history is reconstructed too.And last,we use Sr-Nd isotopes system to make a preliminary discussion on the loess sediment sources in the study area:1.OSL dating revealed deposits of Jingpeng profile is a loess deposits during 66.7-14.5 ka B.P.2.By analyze of constant elements,microelement and rare earth elements geochemical features of Jingpeng profile,we suggests that elementary composition of this region are similar to the Loess Plateau,other loess depositions region.3.Use OSL dating to create chronostratigraphic framework and combined with geochemistry,particle size,magnetic susceptibility characteristics,we reconstructed the last glacial climate history in the study region: 66.7 to 60.9 ka B.P.,the climate is mainly cold-dry,corresponding MIS4;60.9 to 43.5 ka B.P.,the climate is warm-humid,corresponding MIS3 c,the stage can be divided into two relatively warm-humid phases and a weak warm-humid phase;43.5 to 28.9 ka B.P.,the climate is cold-dry,corresponding MIS3b;28.9 to 23.6 ka B.P.,the climate is warm-humid,corresponding MIS3a;23.6 to 14.5 ka B.P.,the climate is cold-dry,corresponding MIS2.During the last glacial maximum,the response to climate in the study region is far less than the Loess Plateau.4.The loess depositions of Jingpeng profile recorded six times climate fast cooling events which response to Heinrich events during the last glacial,occurred in 15.5ka B.P.,22 ka B.P.,29.5 ka B.P.,39 ka B.P.,47.9 ka B.P.and 62.5 ka B.P..These cooling things revealed Jingpeng profile has recorded the climate instability during the last glacial.5.Many times expansion and contraction occurred in Otindag Sandy Land and Horqin Sandy Land during the last glacial.The two sandy lands are mainly active dunes in MIS4,MIS3 c and MIS3 b,while in the MIS3 a and MIS2 periods,mainly in the semi-fixed dunes.6.The characteristics of Sr-Nd isotope revealed the source regions are Otindag Sandy Land,Horqin Sandy Land and the northern of Alxa Desert,and revealed the study region is affected by westerly wind.At the same time,the Nd isotopic composition can not only indicate the source region,but also has some directive significance to the expansion and contraction of the desert and the change of the East Asian monsoon intensity.