秦岭凤州黄土研究

RESEARCH FOR THE LOESS IN FENGZHOU, QINLING MOUNTAIN

凤州黄土剖面是秦岭具代表性的黄土剖面．磁性地层研究结果表明，秦岭黄土是在2．48Ma前开始堆积的。凤州黄土剖面的地层结构、物质成分及磁化率曲线反映出秦岭近2．5Ma来的古气候变化至少发生过33次冷干──湿热旋回，这种变化与深海氧同位素曲线完全可以对比．

In the Qinling Mountain, loess is mainly distributed over the mountainous basin and the higher valley terraces, where the disintegration is weaker. The Yangjiashan loess section,Fengzhou, Shaanxi Province (34°00′N and 106°39′E) is one of the typical loess sections in the Qinling mountain. It has a total thickness of 82m, and contains 33 layers of paleosol. At the base of the loess there is Neogene red clay. This section is made up of Brunhes normal polarity zone and Matuyama reversal polarity zone. The Matuyama-Brunhes polarity boundary (B/M) is located in the loess layer L8; Jaramillo, Olduvai and Reunion normal polarity subzone were discovered from the section. The Gauss-Matuyama boundary (M/Ga),situated in the basal part of loess section, corresponds to the loess/red clay boundary. Therefore, we can make the conclusion that the Qinling loess began from 2. 48 Ma B. P., which corresponds to the early loess formation age of the loess plateu of China.In the Qinling mountain, the particle size of loess is pedominently less than 0. 25mm,with the content of silt (0. 01 - 0. 05mm) over 48%. The composition of the Qinling loess basically resembles that of the loess in the Loess Plateau, indicating that original materials of both of them were mainly transported by the wind from desert regions of Northwest China.Basing on the stratigraphic structure, the material composition and magnetic susceptibility of the Fengzhou loess section, the climatic changes in the Qinling mountain during the last 2. 5Ma can be divided into sixty six cold-dryand warm-humid stages, or equivalent to thirty three climatic cycles. The above climatic cycles can be correlated with a deep sea oxygen isotope (δ18O) curve.