摘要
本文在黄土地层中首次确定了更新世三个时期的风化壳,并根据粘土矿物X-射线衍射、薄片观察、孢粉分析鉴定和CaCO_3淀积深度资料,对风化壳类型和形成条件进行了研究。
By field investigation in the Guanzhong Plain, the fact that there are three periods of weathering crusts in the loess have been ascertained for the first time by the author. They consist of the 1st, 4th and 5th reddish-brown paleosols and the weathered broken loess below them. The 2nd and 3rd paleosols which have begun to change toward crust of weathering have preliminary characteristics of the section of weathering crust. The crusts of weathering in loess, 4—8 m in thickness, are distributed mainly in the southeastern part of the Loess Plateau.On the basis of X-ray diffraction data of the samples from clayized layers of the paleosols, the clay minerals in the upper part of the crust of weathering are mainly hydromica, chlorite and ver niculite and a small amount of montmoriIlonite and kaolinite. Therefore, the crusts of weathering in loess are mainly of hydromica montmorillonite type.The optically oriented clays of the lst and 4th paleosoils make up 10—20％ and 30—40％ respectively and are charcterized by containing spore-pollen assem blage of mixed forest of the coniferous and decidous broadleaf trees in the southern part of the warm temperate zone, and the depth of the CaCO_3 deposition is the same as that of the soils on the northern margin of the north subtropic zone. The optically oriented clay of the 5th paleosol makes up about 50％, containing the spore-pollen assemblage of the trees grouing in the north subtropic zone, and the depth of CaCO_3 deposition is the same as that of subtropic soils. The above data indicate that the crust of weathering consisting of the lst paleosol and the broken loess below it was developed under the moist climate of the south temperate zone; the crust of weathering consisting of the 4th paleosol and the broken loess below it was developed under the moist climate of the south temperate zone or near the north subtropic zone; the crust of weathering consisting of the 5th paleosol and the broken loess below it was developed under the moist climate of the north subtrpic zone.The occurrence of the crust of weathering in loess indicates that the weathering crust developing in the loosen and fine-grained soils can be formed in a short period of time. This is becuse the loosen and fine-grained soil is easy to weather. The vertical joints that are well developed in broken loess layers were produced by weathering rather than the constraction of soils or structural action. The surface of the crusts of weathering in lcess are flat and no signs of erosion of the weathering crust have been found, which proves that the erosion of the loess on the Loess tableland and terraces was much weaker during the warm and moist period of the Quaternary than during the modern period.
出处
《地质论评》
CAS
CSCD
北大核心
1991年第2期117-124,共8页
Geological Review
基金
国家自然科学基金
中国科学院西安黄土与第四纪地质开放研究实验室资助的课题。课题名称:黄土高原第四纪环境和黄土湿陷性研究(项目编号:84040030)。
