Study On Magnetic Characteristics Of Jingyuan Loess Section Since MIS5

The quaternary loess sediments are widely distributed, continuous sedimentary, which are very sensitive to the evolution of the ancient climate and global environmental change incident. Because of that the quaternary loess sediments in the quaternary palaeoenvironment study have very important significance. In this dissertation, the section we studying is located in the west of Liu Pan Mountain, in Jingyuan basin. This area’s geographical location is special and its climate pattern is unique. Past studying on Jingyuan loess section showed its magnetic susceptibility not only has the common version with Chinese Loess Plateau(CLP) but also has its own vary characteristics. Based on studying of magnetic characteristics of Jingyuan loess sediments, this dissertation also analyzes the particle size, carbonate, organic and many other environmental indicators. Through analyzing the correlation of each index and contacting them, it discusses the environmental significance of the magnetic characteristics of Jingyuan section and provides scientific basis for revealing environment and climate evolution process in northwestern of the CLP since MIS5. This dissertation includes several main results below:The mainly magnetic minerals in Jingyuan loess sediments are ferrimagnetic magnetite. There is also a small quantity of incomplete not entirely antiferromagnetic minerals. Magnetic minerals’ particles mainly are fine PSD and MD particles. Due to the pedogenesis in paleosol layer, it generates a certain amount of SP and SD particles. These small magnetic mineral grains made obvious contributions to magnetic susceptibility changes in paleosol layer. In Jingyuan loess deposits, correlation between carbonate content and magnetic characteristics is weak. In Holocene paleosol layer, carbonate had been obviously leached, it showed a great influence on magnetic susceptibility. Organic content tightly linked with the magnetism parameters changes, especially with the ferrimagnetic minerals. That may be indicate that due to the presence of organic, in paleosol generated a large amount of secondary ferrous magnetic minerals, which influenced the magnetic characteristics of sediments.The main drive factors of Jingyuan section’s magnetic susceptibility changes consistent with that of the CLP, which is under the effect of pedogenesis generating small magnetic minerals made a dramatic rise in the magnetic susceptibility. The other parameters of Jingyuan region show that this area’s heat and moisture conditions are not good as that in central and southeastern of the CLP, which lead to a result that paleosol development degrees in Jingyuan is much lower than other areas’. This dissertation points out that in Holocene paleosol development period, Jingyuan region’s climate is highly affected by the summer monsoon. In the last glaciation, it is cold and dry in Jingyuan. In the last interglacial period, the magnetism curves indicated three times summer monsoon obvious enhancement. But compared to low magnetism parameters variation in S0, in this layer, the grain size of magnetic minerals tended to change first and the secondary ferrous magnetic minerals were generated secondly, shows that although in the last interglacial period summer monsoon significantly enhanced for three times, but heat and moisture conditions still not as good as the Holocene period.