Jac Plain Shallow Drill Core Clay Mineral Environmental Significance

The characteristics of clay mineral such as sedimentary differentiation, composition and assemblage and crystallinity have recorded the information of environmental change during the processes of clay minerals formation.And the study of clay meinerals in China is majored in the area of loess, rivers, ocean and so on. However, the study is very little in Jianghuai Plain where is the typical regions of monsoon and the translation zone of the ocean and the land of the east of China.The paper researched the YZ bore in the middle of Jianghuai plain. After analysising the parameters of clay minerals in the sediments, it disscussed the environment significance of clay minerals in this aera and reconstructed the progress of the climate-variations-pattern since the last Deglaciation in monsoon area of east China through integrating the parameters of clay minerals with indicators analysis of the geochemistry ,physical and the age sequence , which were established by AMS¹⁴C. In the meanwhile, it also discussed the climate change-driven mechanism of Holocene though the proxy sequence analysis which we got. And the results were following:Firstly, the deposits was made of four kinds of clay minerals and little feldspar and clastic quartz. The dominate clay mineral was illite in the relative clay mineral content, and the average was 68.98%. The second was chlorite which was from 6.67 to 22.26%, and the average was 14.93%; And the others in order were kaolinite which was form 5.76 to 13.81% with 9.91% averagely, while the montmorillonite was from 1.99 to 14.45% with 6.17% averagely. The type of clay minerals composition was illte-chlorite-kaolinite-montmorillonite, which was similer to the composition of clay minerals of the sediment in China's Yangtze River. And the Kübler index which was from 0.31△2θto 0.46△2θwas higher than the loess and ancient soil of China's inland. The scope of crystallinity of illite was lower too.The chemical index range of illite is from 0.25 to 0.81 with 0.56 averagely, most of which were above 0.5. Illite was high, which all showed that the clay minerals had undergone a stronger weathering. Kaolinite showed a positive correlation with chlorite, but was negatively correlated with illite.Secendly, the composition of clay minerals was affected by many factors , sush as the source, the ancient climate, the deposition phase, water power, organic matter content, redox conditions and so on. Kaolinite, which was negatively correlated with illite, indicated that the weather was worm and wet. While chlorite, showed a positive correlation with kaolinite, which might not indicated the dry and cold weather. The form of chlorite was correlation with the weather of study area and environment of the lake wchich was formed during the sediment process.The third was that it was well compared with the records of the K/I of YZ bore lithology, Rb/Sr, Md, CaCO₃, TOC and so on, which indicated the change of climate, and had restored the process of climate change of Jianghuai Plain since the last Deglaciation from 14.6 to 13.1kaBP as the warm climate of the last Deglaciation and form 13.1 to 11. 8kaBP YD time as the Climate deteriorating, low-drought and from 11.8 to 9.3kaBP as the warming up for the early Holocene period and form 9.3 to 4.0kaBP as the Holocene warm period, the ratio of temperature and humidity was well and from 4.0 to 2.3kaBP as a small cold period of late Holocene. Moreover, it was similar to the climate of modern time from 2.2ka.The fourth was that the cycles of 508a, 242a,136a and 123a were got out by doing power spectrum analysis of YZ bore in Holocene period. It constrats well with the circle which had been out from Rb/Sr and MD. Further more, this paper confirmed that there was a fluctuant cycle with millennium-century scale since the Holocene in the Jianghuai plain. Theses results indicated that climate changes in Jianghuai plain were probaly mainly driven by solar activity and influenced by the ocean.