The Study Of Sand-loess System In The Poyang Lake Region Since Late Interglacial

The sandy hill sand and loess are widely distributed in the middle reach ofYangtze River especially in Poyang Lake region since the last interglacial. Althoughmany achievements about those deposits have been obtained, there still have manyproblems for the future discussion. Firstly, the different between loess in middlereach Yangtze River and low reach Yangtze River was paid little attention. Secondly,the spatial relation between sandy hill sand and loess, which the deposit is located indownwind of sandy hill, was neglected too much before research. What’s more, thesource of southern loess still remains controversial.Based on the former study data and carefully filed study of theDingshang-Taiping region located in northeast of PoYang Lake was chose as ourstudy region. A transect along with winter monsoon direction was set and six sandyhill sections and loess sections were chose meanly and80sandy hill sand and loesssamples, which were used for the grain size and element test, were taken from thosesections. In order to contrast the grain size characteristics of lower reach YangtzeRiver loess with the middle reach of Yangtze River, we took52loess samples fromTaiShanXinchun and YangZhiJi near NanJing city. Based on the carefully grain sizeand element analyses and geomorphic feature in our study region, we conclude that（1） The D-D transects loess, which is obviously different from those of fluvialsediments but is same as the eolian sediments in other region, is eolian origin.（2） The major element of D-D loess such as P, Na, Ca, Mg, Mn, P were migratedand leached, while Ti, Fe were slightly richen. The migrate features of majorelements reveal that the D-D loess have finished the primary process of chemicalweathering characterized by leaching of Ca, Na and is undergoing the secondprocess characterized by leaching K, Si and enriching Al.（3） The D-D loess underwent moderate chemical weathering and ranked thefollowing order with other aeolian sediments: LuoChuan loess <NangjingZhengjiang loess, D-D loess <<AnHui Xuancheng red soil. The difference ofgeomorphic feature leaded to the intensity of chemical weathering of D-D loess isslightly higher than the loess of the lower reach Yangtze River.（4） Based on the immigration and leach rate, the major elements of D-D loessranked the following order: Ca>P>Na>Mg>Mn>K>Si>Al>Fe³⁺>Ti.（5） The characteristic of grain size and immobile element of sandy hill sand andloess indicates that the sandy hill sand and loess origin from the adjacent floodplainsto the north of Yangtze River. The sandy hill sand and loess was transported by the winter monsoon and was consisted a sand-loess system that is a response to thedesert-loess in North and is an indicator of region aridification and the strengthenedwinter monsoon activity during glacial period.