中国黄土磁化率与第四纪古气候研究

STUDY ON MAGNETIC SUSCEPTIBILITY OF LOESS AND QUTERNARY CLIMATE IN CHINA

本文以实验数据证明,黄土磁化率的高低与其经历的风化或土壤化强度密切相关,风化程度决定了磁铁矿的生成最及其颗粒的细小程度,从而决定了磁化率的高低。因此,与土壤化程度密切相关的中国黄土地层记录了第四纪古气候变化。

Loess stratigraphy in China consists of many loess and palaeosol layers overlaped each other, It is a direct product of palaeoclimate effect and records a variation of Quaternary climate. A lot of data confirms that the magnetic susceptibility value of the stratigraphy is correlated well to weathering (or pedogenic )degree of loess and palaeosol, indicating that palaeoclimate record of the loess/ palaeosols can be delineated by the susceptibility of loess on the central loess plateau, such as along Xifeng loess profile. Magnetic minerals and their grain size were studied by using method of rock magnetism. It shows that: (1) maghemite commonly exists. in loess and palaeosol; (2) pedogenic development is proportional to the content of magnetic minerals (magnetite mainly) formed in the pedogenesis, but inverse proportional to their grain sizes, while the content and grain size play a critical role in the susceptibility value of loess / palaeosols. These results suggust that palaeoclimatic warm-wet degree determines the content and grain size of magnetite (and maghemite ) formed in pedogenic processes, which decides susceptibility values of the loess and palaeosol. Therefore, the susceptibility of loess China in reflects the variation of Quaternary climate.