Geochemical characteristics of the ancient weathered crust derived from red beds in Sichuan basin |
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| Authors: | Tang Shijia Luo Youfang |
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| Institution: | (1) Institute of Soil Science, Chengdu Branch, Academia Sinica, China |
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| Abstract: | The ancient weathered crust studied occurs on the razed surfaces of various physiographic periods at different altitudes in
the Sichuan red basin. A typical profile of the ancient weathered crust can be divided into three weathered belts from the
surface to the basement: the clastic clay belt (Belt I), the clastic breccia-clastic clay belt (Belt II), and the clastic
breccia belt (Belt III). These belts are different in clay mineral composition, reflecting varying degrees of chemical weathering.
Wide variations are recognized in the abundance of chemical elements in the profile of th ancient weathered crust. In comparison
with the underlying purple parent rocks, Fe2O3 > A12O3 > TiO2 > SiO2 are relatively concentrated in the ancient weathered crust, while CaO>P2O5>MnO>Na2O>MgO>K2O are relatively depleted due to leaching in order of Belt I > II > III.
The extent of chemical weathering in the ancient weathered crust in the Sichuan red basin is closely related to the time of
formation of the razed surface. For this reason, the contents of A12O3 and Fe2O3 or their concentration values, and the leaching amounts of CaO, MgO, K2O, Na2O, and P2O5 are higher in the ancient weathered crust at high altitudes than those at low altitudes. |
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