Geochemical Characteristics of Loess from Northeast of Poyang Lake since Last Glacial and Its Provenance Implications

Key words: 
• Northeast Poyang Lake /
• Xiashu loess /
• D-D transection /
• geochemical characteristics /
• sand-loess system

Abstract: The sandy hill sand and loess deposits constitute the regional sand-loess system,which are widely distributed in the middle reach of Yangtze River especially in the Poyang Lake area since the last interglacial. A transect named D-D transect was set from north to south along with the winter monsoon direction. The <20 mm grains extracted from bulk sample on the basis of wet-sieve methods were used to measure major and trace element abundances by XRF. Our results reveal that: (1)The content of major element has a systemic change from north to south.The changes are most pronounced within the range of 5 to 20 km away from the Yangtze River,and then level off. SrO,Na₂O,CaO,K₂O,MnO,CaO are of negative logarithmic function changes, SiO₂,ZrO₂,Al₂O₃,TiO₂ and CIA are of positive logarithmic function changes ; The profiles of D-D transect seem to have a similar source displayed by the scatter diagrams of ZrO₂/Al₂O₃ vs. ZrO₂/TiO₂, TiO₂/Al₂O₃vs. TiO₂/ZrO₂, K₂O/Al₂O₃vs. ZrO₂/TiO₂, K₂O/TiO₂vs. ZrO₂/Al₂O₃,SrO/TiO₂vs. SrO/Al₂O₃,Base/ZrO₂vs. Base/TiO₂,ect. These characteristics further reveals that all of the profiles in D-D transect belong to the same aeolian deposits system. (2) The stable elemental compositions of the D-D transect are similar to the WN loess, Xiashu loess, and sediment of flood land of the Yangtze River, these results reveal that aeolian deposits and the Yangtze River sediment have a rich source and over-commixing. Therefore, it is suggested that the factors on chemical composition of clastic sediment should be fully studied when geochemistry methods are used to analyze the province and depositional setting, and multiple methods can be synthetically used and the study on regional geology should be paid more attention.