摘要
野外观察发现 ,陕西西安地区的第三层古土壤是由 3层构成的复合古土壤。通过对长安双竹村剖面及蓝田段家坡剖面的地层结构、磁化率、颗粒成分以及有机质含量的分析 ,可以把形成第三层古土壤的中更新世时段 (330～ 2 72 ka B.P.)分为 6个温湿、冷干阶段 ,构成为 3个气候变化旋回。
From observing in field, the author has found the third paleosol in Xi'an region that developed in middle pleistocene, consists of 3 paleosol layers and 2 loess beds, which is different from S\-3 of Lanzhou profile and of Baicaoyuan profile. In Xian region, Shuangzhucun section lies to the southern of Xi'an city and Duanjiapo section lies to the eastern of Xi'an city. Firstly, stratigraphic structure was studied, from top to bottom the structure units are S\-\{3-1\}, L\-\{x-1\}, S\-\{3-2\}, L\-\{x-2\}, S\-\{3-3\}, L\-\{x-3\}. Secondly, the samples gathered from Shuangzhucun section (or Duanjiapo section ) was analyzed in laboratory; magnetic susceptibility, TOC and granulometric composition were studied, and the results are as following:\;(1) The maximum magnetic susceptibility value (296 SI) of S\-3 in Shuangzhucun section and the average value are all more than those of S\-0, S\-1 in other sections, for example, Qishan profile and Fufeng profile. The results show that the soil developing of the third paleosol in this area is stronger than that in others. On the curve of magnetic susceptibility of S\-3, there are 3 peak values corresponding to paleosols and 2 valley values corresponding to loess beds. In the meantime, the fact that the magnetic susceptibility value of the loess(141 SI) is far more than Malan loess shows that the loess layer between paleosols isn't pure loess parent material in Duanjiapo section; the magnetic susceptibility values of the top paleosol and the bottom paleosol appear two peaks, and the middle paleosol is not same as these.\;(2) From the result of TOC analyzing to Shuangzhucun section, it is found that the contents of TOC of paleosol and loess are all lower (<0.8%), but it still appears clearly peak and valley alternating: the peak of wave corresponds to paleosol(>0.5%) and the valley corresponds to loess (<0\^5%).\;(3) Analyzing to granulometric composition of S\-3 from Shuangzhucun loess section shows that the composition of paleosol is distinctively differentiated from that of loess layers. Every group of grain size, \%M\-d\% and \%S\-o\% appear distinctively changed in loess layer, and these changes are corresponding to quickly accumulation of loess at that time.\;According to the characters of stratigraphic structure, magnetic susceptibility, TOC and granulometric composition described above, as well as ancient temperature and rainfall that is recovered based on the curve of magnetic susceptibility, the period of time (330~272 ka B.P.) when the third paleosol formed may be divided into 6 stages of warm humid and cold arid climatic changes. The 6 stages show 3 climatic cycles: cycle I, include L\-\{x-3\}, S\-\{3-3\}; cycle Ⅱ, include L\-\{x-2\}, S\-\{3-2\}; cycle Ⅲ, L\-\{x-1\}, S\-\{3-1\}. The climatic character was cold and arid when L\-\{x-3\}, L\-\{x-2\}, L\-\{x-1\} were accumulating; when S\-\{3-3\}, the climate was subtropic warm humid; S\-\{3-2\}, the semi humid climate of warm temperate zone; and S\-\{3-1\}, the humid climate of warm temperate zone.
出处
《中国沙漠》
CSCD
北大核心
2000年第1期9-13,共5页
Journal of Desert Research
基金
国土资源部九.五重点科技项目!( 95 0 110 4)研究成果
IGCP379组成部分
关键词
颗粒成分
有机质
西安地区
古气候
the third layer paleosol
particle composition
TOC
climatic cycles
Xian region
