关键词: 黄土本质, 黄土化过程, 灰黄色古土壤, 环境

Abstract: There are soil macrostructure in loess, such as similar prismy sturcture, lumpy structure, grangular struc-ture, root holes, and microstructure, such as optically oriented clay film developed in stronger soil formationprocesses. Loess is rich in CaCOj, but it is mainly secondary and is the illuvial products formed by dissolving anddepositing of CaCO, and is a sign of illuvial layer of CaCO;. These characteristics show that loess experienced soilformation processes. The fossil animals, such as snail, and a lot of root holes also indicate that the loess formedin soil formation processes. The developmental process of loess was longer than of mellow soils, the reasons whyit didn 't change into red-brown paleosols were cold and arid climate and the features of the soil formation pro-cesses. The soil profile of loess is not clear, which results from continual dust deposition and CaCO illuviation. Loess developed mainly in steppe, desert-steppe and forest-steppe areas, the loess in different areas and of differ-ent characteristics is mainly Sierozems, Chestnut Soils, Brown Soils, Brown Desert Soils and Loessia Soils.
Soil formation mainly indudes weak dissolving, migrating and illuvating of CaCO, as well as weak biological action in desert-steppe. CaCOj exists in the form of powder and spots and CaSO 4 sometimes occurs in the areaswhere soil structure develps poorly and root holes and insect holes are a few. The obvious migrating and illuviat-ing of CaCOj and forming of biological structure are the dominant processes in which loess develops in steppe ar-eas. CaCOexists in the form of film and soil structure, such as granular structure and root holes, is obvious inthe areas. Besides notable migrating and illuvating of CaCOj as well as forming of biological of structure, claygrouting sometimes occurs in forest-steppe areas in the formation process of loess. CaCO nodules often occur, granular, lumpy, similar prismy sturcture and root holes developed well, and organic substance is high in con-tent and optically oriented clay film sometimes can be seen in the areas.
Grey-yellow loess that is the paleosol can be used as a mark in reconstructing paleoclimate. According to thealternation of loess and paleosol, the biological, soil and climatic changes since 2.5 Ma can be classified into 101 stages consistuting 51 cycles and sub-cycles.

Key words: essence of loess, processes forming loess, grey-yellow paleosols, environment