Climate Change Recorded in a Lacustrine Stratum in the Ordos Plateau during the Period of 5.8～4.5 Cal kaB.P.

With a view of deriving desertification(aeolian action) information from the Mu Us Desert,a sensitive region to climate change,in this paper the volumetric particle size distribution of five modern desert sand samples and 30 profile samples,collected from the Ordos Plateau and the front of low terrace of the Pojianghaizi Lake,is studied.The results show that the grain size characteristics of the samples at depths of 290~210 cm,190~160 cm,153.5~123.5 cm and 50~40 cm at the Pojianghaizi profile are significantly similar to that of modern desert sand,which reveals that the sediment at these depths is the paleo-desert sand(aeolian sand).Moreover,it is observed that there are 3 layers of lacustrain sediment embedded in the Pojianghaizi profile.The analyzed results of the radiocarbon dating,grain size,TOC and CaCO3 reveal that there was a sediment sequence ranging from 5.8 Cal kaB.P.to 4.5 Cal kaB.P.: before 5 749 Cal aB.P.,the overlaying aeolian sand layer reveals that an intensive aeolian action occurred under dry-cold climate due to the strong winter monsoon,and it is followed by a thin layer of lacustrine sediment,which reveals that a short episode of desert retreating and lake enlargement occurred;an aeolian sedimentation occurred during the period from 5 749 to 5 370 Cal aB.P.,which reveals that the desert expanded again;the period from 5 370 to 4 895 Cal aB.P.was characterized by a lacustrine sedimentation with a main composition of clay and silt,indicating the catchment of the Pojianghaizi Lake experienced a significant increase of precipitation;after the aeolian sedimentation with a thickness of 50 cm during the period from 4 895 and 4 580 Cal aB.P.,a short period of lacustrain sedimentation occurred.