中国黄土中古土壤的发生学研究

应用形态学、微形态学、化学和矿物学研究了中国黄土中古土壤的发生学性状和成土过程。离石黄土(中更新世)中古土壤为发育程度(碳酸盐淋溶和粘化)不同的褐土型土壤。马兰黄土(晚更新世)中为生草过程强和粘化过程稍弱的灰褐土型土壤。全新世黄土中为碳酸盐淋溶和粘化过程均弱的弱度发育的碳酸盐灰褐土型土壤。午城黄土(早更新世)中可能是棕褐土。本文还探讨了黄土中古土壤在时间和空间上的演替和分类问题。

ON THE PEDOLOGIC GENESIS OF PALEOSOLS IN LOESS OF CHINA

The approach of genetical pedology is applied to elaborate the genetical characteristics, processes and classifications of the paleosols in loess deposited during Quaternary period. Fourteen layers of paleosols were buried in Lishi Loess accumulation (Middle Pleistocene). It has been argued that with the paleoclimatic fluctuations, specifically the increase of temperature and precipitation, these forming processes of the paleosols were proceeding in xero-forest and brushgrass zones where loess depositions were extremely weak or even stopped then. Soil morphological,micromorphological, chemical and mineralogical studies have revealed the existence of distinct humic-argillic, strong argillic and calcic horizons in these paleosols. Furthermore, humic horizons are 50 to 70 cm thick and humus content reduces regularly with depth. Argillic horizons are dark brown or reddish brown.Moreover, clayey loam texture and angular block structure are popular. There is humic ferric-argillan on the ped and pore surface. Aggregates of clay minerals are abundant while micas and feldspars were strongly weathered. Illites are dominant though other clay minerals, such as montmorillonites, vermiculites and kaolinites, also exist. Under neutral and weak alkaline conditions, carbonates were eluviated and precipitated. Aluminosilicates were weathered which caused desilicification and activation of ferric-alumino sesquioxides, and produced secondary clay minerals and enriched secondary clay minerals and ferric-alumino sesquioxides in argillic horizons. Typical cinnamon soils are formed in this way. However, these paleosols are actually cinnamon soils in different stages of development. In Malan Loess (Upper Pleistocene), one to three layers of paleosols exist which were gray cinnamon soil with strong humus accumulations and weak argillic processes. One or two of paleosols have been identified in Holocene Loess. Both carbonate eluviations and argillic processes were weak in these relatively new calcaric gray cinnamon soil. No typical well developed paleosols have been found so far though more than ten calcic horizons and weathered layers do exist in Wucheng Loess (Lower Pleistocene). Studies of pollens, animal fossils and calcic horizons imply the possible occurrence of favourable conditions for soil genesis during Early Pleistocene. Therefore, it may be reasonable to postulate that some brown cinnamon soils existed in the oldest loess and later were truncated. Cinnamon soil is one transitional type of soil between brown forest soil and chernozem. To the north of the cinnamon soil region, a gray-cinnamon soil zone lies between it and the chernozem soil region. To the south and southeast, the cinnamon soil region is delimited from the brown forest soil region roughly with a transitional zone where brown-cinnamon soils dominate. Brown-cinnamon soil, orthic cinnamon soil, gray-cinnamon soil and weakly developed calcaric gray-cinnamon soil occur temporarily from Early Pleistocene to Holocene and spatially from north to south. These paleosols in loess are referred to today's cinnamon soils and are further divided into orthic cinnamonic soil, gray-cinnamon soil and browncinnamon soil. In the terms of different developing stages, these subgroups are subdivided into haplic luvic and calcic families (genus).