图书馆知识库

Magnetic susceptibility, as a convenient and reproducible rock magnetic index, has been widely used in paleoclimatic reconstruction and has achieved great success in China Loess Plateau. The mechanism that pedogenesis intensity contributes to the magnetic susceptibility is generally accepted in China Loess Plateau. However, the magnetic susceptibility change mechanism in Xinjiang is still unclear, so that the paleoclimatic significance of magnetic susceptibility remains controversial. In this study, a typical loess section (Yangchang section) with accurate chronology from the southern margin of Tarim Basin was selected for rock magnetism and high resolution magnetic susceptibility study. Combined with the grain size characteristics, mineral components and elemental concentrations, the magnetic susceptibility change mechanism was discussed. The results show that the main magnetic-bearing mineral is coarse-grained magnetite with a small amount of hard magnetic minerals and paramagnetic minerals in the Yangchang loess sediments. According to the variation characteristics of magnetic-bearing minerals and magnetic susceptibility, the section can be further divided into two stages: Phase I (8.5 similar to 2.5 ka), the content of soft magnetic minerals are relatively high, and the magnetic susceptibility stays in relatively high value. Phase II (2.5 similar to 0.2 ka), hard magnetic minerals and paramagnetic minerals, represented by pyrite, increase, while the magnetic susceptibility decreases significantly. Correlation analysis and cross wavelet analysis results show that the change of magnetic susceptibility is consistent with that of coarse particles in phase I, suggesting a so-called "wind velocity theory" model control of magnetic susceptibility in this stage. While in phase II, besides the positive correlation between magnetic susceptibility and the contents of coarse grain, a strong negative correlation between the magnetic susceptibility and pedogenic proxy was also observed, indicating a combined effects of "wind velocity theory" and "reductive pedogenesis" processes on magnetic susceptibility change during phase II. This study provides valuable information on rock magnetic characteristics and magnetic susceptibility change in this area, and gives a new clue on further paleoclimatic reconstruction in Xinjiang and Central Asia based on magnetic susceptibility.