咸阳市区晚更新世黄土微结构特征及其环境意义

The micro-structural characteristics of the Late Pleistocene loess and its environmental meaning in Xianyang City

目的揭示咸阳市区晚更新世黄土的微结构特征,探讨黄土微结构特征与其形成环境的关系,为区域环境提供科学依据。方法应用粒度分析和扫描电子显微镜对咸阳市区晚更新世黄土．古土壤系列的微结构进行分析研究。结果粒度小于0．005 mm的黏粒级含量在黄土与古土壤中差异最大,S1古土壤高达39．7％,而L1黄土仅24％;S1古土壤黏粒中大量铁质黏粒胶膜呈流胶状出现并有次生伊利石的产出,结构密实;L1黄土微骨架颗粒相互支架,黏粒胶结物含量较少,胶结程度差,土质疏松。结论咸阳市区晚更新世S1古土壤形成在湿热的森林环境,L1黄土形成于干冷的草原环境,S0黑垆土形成于凉湿气候环境。

Aim To reveal the micro-structural characteristic of the Late Pleistocene loess in Xianyang City and study the relationship between micro-structural characteristic and its formation environment and provide scientific basis for the district engineering construction and paleoenvironmental research. Methods The micro-structure and the grain constitution of the loess samples from different geography unit in Xianyang downtown area were analysed using scanning electron microscope and grain degree analysis. Results The differences of the grain size distribution between paleosols and loesses can be distinguished. Paleosols have higher clay-size grain（ 〈0. 005 mm in diameter = content than loess layers. Clay fraction content is 39.7% for S1 paleosol, but it,s 24% for L1 loess. Most iron clay coating showed flowing colloid and most illite clay in the clay-size grains of S1 paleosol. The microstructure is closer. There were lesser clay-size grains between supporting grain of the L1 loess. The microstructure is looser. Conclusion The formation environment of S1 paleosol at Xianyang area in the Late Pleistocene was hot and wet forest environment. But the formation environment of the L1 loess was cold and dry steppe environment. Heilu soil was formed at cool and humid environment.