Mineralogical Characteristics Of Sediments And Its Palaeoclimatic Indications In The Karst Basin Of Weining, Guizhou Province

Mawo karst basin affected by both the southwest Indian monsoon and the southeast Pacific monsoon, it sensitively responsed to the climate,in Weining county,Guizhou province. The sediments in this basin record the evolution of the information environment, is a perfect place for paleoclimate research. Mineralogical and geochemical characteristics of the Mawo Karst Basin Sediments profile in Weining were investigated using X-ray diffraction(XRD),particle size analysis,drilling profiles major elements and trace element analysis,obtain the characteristic of geochemistry elements and mineralogical in the profiles of Mawo karst basin in Weining county, Guizhou province,We discussed sedimentary environmental change in the past about 40,000 years. The main conclusions can be summed up as follows.(1)The minral deposits of profile 4 mainly composed of clay minerals(38%~72%), calcite(0%~39%), quartz(10%~55%), feldspar(0%~3%) and other components. The clay mineral content is most and volatile, calcite content is higher at the gray lake layer, it may related with the layer of shell. Based on the total clay and calcite mineral content divided into(a-i) 9 layers.(2) Clay minerals composition is dominantly with illite-smectite mixed-layer mineral(30%~75%)and chlorite(10%~45%),second with kaolinite(5%~20%)and illite(10%),almost does not contain smectite. illite-smectite mixed-layer mineral and chlorite show the opposite trend. The crystallinity and chemical index of Illite are more sensitive than other indicators, they appear fluctuation at the bottom of profile.(3) Element geochemical study showed that, the vertical variation of Ti/A1,Zr,Rb showed obvious regularity in the profiles, are consistent with the color of profiles. High Ti/A1 ratios indicated warm and humid climate, low Ti/A1 ratios indicated cold and dry climate.(4) Zr/Rb and grain size were important indexs of climate. Low Zr/Rb ratios,more content of fine particles in basin sediments, are more likely to indicate chemical weathering strong,with high temperature and abundant rainfall. High Zr/Rbratios, more content of coarse particles in basin sediments, more likely to indicate dominated by physical weathering, chemical weathering relatively weak, with the lower temperatures, less rainfall climate.(5) Through comprehensive analysis by whole-samples mineral composition,clay mineral composition, element geochemical characteristics.There are four palaeoclimatic periods, three obvious cycles,and the first three stages,each contain two minor cycles in alternating temperature humidity.