Climate and soil moisture environment during develop-ment of the fifth palaeosol in Guanzhong Plain  

作　　者：ZHAO JingBo GU Jing DU Juan 

机构地区：[1]College of Tourism and Environment Sciences,Shaanxi Normal University,Xi’an 710062,China [2]State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710075,China

出　　处：《Science China Earth Sciences》2008年第5期665-676,共12页中国科学（地球科学英文版）

基　　金：the National Natural Science Foundation of China (Grant No. 40672108);State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (Grant No. SKLLQ0605)

摘　　要：Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordi- nary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argil- lans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual pre- cipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordinary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argillans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual precipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.

关 键 词：Guanzhong PLAIN the FIFTH PALAEOSOL WEATHERING characteristics paleo-gravity water paleo-moisture content soil EVAPORATION 

分 类 号：P532[天文地球—古生物学与地层学]