黄土地层中的CaCO_3与环境

CaCO_3 and Sedimentary Environment of Loess Strata

本文根据大量观察分析,对黄土地层中的CaCO_3含量、存在形式、淀积深度进行了研究,并进行了分类。结果表明,不仅CaCO_3含量能够反映气候变化,而且其存在形式和淀积深度同样能反映气候变化;其淀积深度很少受时间影响,比含量更能可靠地用于气候研究。

CaCO3 content, existing form and illuvial depth in loess strata are studied in this paper. In order to make clear the relation between CaCO3 content and climate, the author firstly classify CaCO3 into five types and their relation with climate are discussed as follows. (1) High fragmental CaCO3 content indicates weak leaching and arid climate, low content indicates intense leaching and humid climate. (2) Illuvial CaCO3 is secondary CaCO3 that formed by leaching and illuviating, and the content of secondary CaCO3 is higher than 5%. The illuvial CaCO3 is riot realiable for reconstructing the climate, but generally, low content represents humid climate and high content arid climate. However, dense accumulation of CaCO3 may indicates humid climate. (3) Contemporaneous remnant CaCO3 is the residu al of leaching that occured during the development of soil, the content of CaCO3 is less than 5% and the less the content is , the more humid the climate. (4) Deuterogenic residual CaCO3 (with the content less than 5%) is the remant of leaching that look place during the development of the overlying soil, the abandance of CaCO3 is low and can not reflect the climate of the soil strata growth. (5) Evaporated CaCO3 was the precipitates that deposited at the top layer of soil during the intensive evaporate process, and its content represented the desert climate with a mean annual rainfall less than 100mm. Loess and palaeosoil containing thin film and stain but not concretions was developed under the climate i with mean annual rainfall less than 450mm, (continued on page 54)