Study on the evolution of sandy hills along Poyang Lake area for the last 100,000 years

Poyang Lake,which lies to the east of Mount Lushan in Jiangxi,is the biggest fresh water lake in China.It is also one of the abandoned lakes of the Yangtze River.As it is in the eastern monsoon area,it has a line vision in winter and a vast expanse in summer.Large areas of sandy hills appear around the Poyang Lake and the riverside of the Yangtze Rriver in the Hukou-Pengze section.They are well sorted and always come to 40 to 140 m high,looking like a desert in East China.Lots of scientists have done research in these sandy hills since the mid-20th century.They started with the formation and evolution of these sandy hills,and some of them analyzed the ancient climate change by the magnetic properties of sand samples.Shaling sandy hill in Xingzi which lies on the west shore of Poyang Lake is one of those sandy hills.After field investigation and collection of 26 sandy sediment samples in March 2005,we used sifter and laser granularity to measure their grain size.We also use 14C dating and thermoluminescence dating for three samples. Based on the field investigation of the landform and physiognomy,we classified these sandy sediments in Xingzi into seven different kinds and four periods of aeolian sandy hills.Those four aeolian sandy hills periods are 95 kaB.P.Old Red Dune,46 kaB.P.Red Dune,27kaB.P.～15kaB.P.Yellow Dune and 250 years Modern Dune.The other three kinds of sediments are secondary deposit on valley bottom,wind-erosion residual deposit on the lake shore and loose aeolian sediments on the Yellow Dune surface. As the wind power is the main driver of sand,the grain size of these aeolian sediments can show the wind power for the time when they deposited.We compared the grain size of the sand samples and come to the conclusion that wind power in these four periods can be arranged by Yellow Dune,Modern Dune,Red Dune,and Old Red Dune in a descending order.By comparson of the sediment series with the deep-sea oxygen isotope curve change,the Old Red Dune period of Poyang Lake is in the late Wurm glaciation(MIS5b),Red Dune period is in the middle Wurm glaciation(MIS3),Yellow Dune is in the last glacial maximum(MIS2),and Modern Dune is in the Little Ice Age.This result accords with the research result of sandy hills of this area by other scientists and can be compared with the global change in stade since the last interglacial stage and show the change of winter monsoon in Poyang Lake area.