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Paleosol Evolution and Environmental Change on the Northeastern Margins of the Qinghai-Xizang (Tibetan) Plateau Since 150,000 Years
Xiao-Min FANG, Dept. of Geography, Lanzhou Univ., Lanzhou, Gansu, P.R.China
The Northeastern margin of the Qinghai-Xizang (QingZang) Plateau links the western Loess Plateau and the inland arid area of China, where there are a large dust input rate and the thickets loess in the world. Further, the uplift of the QingZang Plateau, together with its landform effect, causes the frequent interaction of the byflowing westerlies, plateau monsoon, winter monsoon, Southwest monsoon, and East Asia monsoon in this area and thus the environment is highly sensitive to global and regional climate changes. These two advantageous conditions from the unique high-resolution loess climatic record and the most complete paleosol sequence since the last interglacial in the world. In the last interglacial, 6 layers of paleosols were developed; in the Malan loess, 4 layers; and in the Holocene loess, 3-4 layers.
The systematic multi-approach absolute age determinations, soil micromorphology and physical-chemical analysis of these paleosols demonstrate that the pedogenic features and types of the paleosols alter very greatly since 150,000 years. The general evolution trend of the paleosols in different sites in same although some discrepancy in pedogenic type exists among them. The typical proxy paleosol evolution order is that calcic drab soils by the Chinese soil classification system (roughly equivalent to luvisols or cambisols by FAOUN soil classification system) in the last interglacial, weak paleosols of light chernozem in property in the last glacial, and Heilusols, Kastanozems or sierozems (calcisols) in Holocene, indicating the climate turned acceleratively into dry. In space, there is a small differences between the pedogenic degree of paleosols in the east and west parts of the marginal area in the last interglacial, which are generally calcic drab soils, and the nearer the inner (here referring to the source area of the Yellow River) of the QingZang Plateau, the stronger the pedogenic degree seems; whereas the very large difference between the pedogenic degree of paleosols in those two parts in Holocene and at present, which shows the paleosols in the west part evolved into desert soils or alpine meadow or steppe soils and those in the east part turned into steppe sierozems and Heilusols. Such paleosol evolution in time and space demonstrates that since the last interglacial the northeastern margin of the QingZang Plateau has undergone great uplift and further suggest a similar great uplift happened in the Himalayas in the south which hereinafter causes a decisive stop for the direct northern moving of moist Southwest monsoon and thus the northeastern margin of the QingZang Plateau to dry fast, especially in west part.
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