从古土壤看北京环境变迁

古土壤是在古自然环境条件下形的土壤，西胡林黄土剖面位于北京低山丘陵区，埋藏有七层古土壤，根据形态和微形态特征，可以划分出碳酸盐型古土壤、普通褐土型古土壤，淋溶褐土型古土壤和棕壤型古土壤。其地球化学特征和土壤学特性的研究表明，各古土壤类型之间和发生层之间存在着显著差异，通过古城磁测年和地层对比，确定古土壤的年龄。在研究古土壤性状的基础上，配合孢粉分析，可以勾画出北京低山丘陵区的环境变迁，北京地区自50万年前至1万前，交替经历了14次温湿、冷干的气候变化。

RESEARCH ON THE VARIANCE OF ENVIRONMENT IN BEIJING BY PALEOSOLS

There are some types of the paleosols in the hilly regions of Beijing. The seven layers of the paleosols is embedded in the loess section of Xihulin, which located in the second terrace of qshuihe River. According to the character of configuration and microconfiguration, the paleosols may be divided into the brown earth, carbonate drab soil, drab soil and leached drab soil. The research of its geo-chemical characteristics of elements revealed that there are marked differences for contents of CaO, Na₂OAl₂O₃, Fe₂O₃, SiO₂ and etc, among the paleosols and between the paleosols and the genetic units, the similar conclusion is observed from the research of the soil magnetic character. By means of comparing with other loess section, paleomagnetic studies and spore-pollen analysis, age is ensured. The different types of paleosols are formed during varied geologic period and are largely attributable to bia-climatic conditions, therefore paleosols indicated that the bio-climate had undergone 14 times replacement from warm to cold in the region of Beijing, as well North China, from 500 thousand to 10 thousand ago.