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Grain-size Features of Red Earth in Mid-subtropics

ZHU Li-Dong~(1,2),YE Wei~2,ZHOU Shang-Zhe~3,LI Feng-Quan~2,YANG Li-Hui~2(1.College of Resource and Environment,Lanzhou University,Lanzhou,Gansu 730000;2.Zhejiang Normal University,Jinhua,Zhejiang,321004;3.Geography Department,South China Normal University,Guangzhou,Guangdong 510631)  
There are different opinions on origin problem of the red earth in the Pleistocene,namely diluvium,alluvium,aeolian,and so on.Based on the grain-size analysis of five representative sections from the mid-subtropics,deposit-environment of the red earth is discussed in this paper.The results show that:(1) Grain-size distributions of five red earth sections in mid-subtropics are very similar,which probably indicates aeolian characteristics from their parent materials and the weathering process.The average content of 463 μm particle group ranges from 48.12% to 68.89%,the one less than 4μm and the one over 63μm are respectively from 23.83% to 50.10% and less than 5%. Generally speaking,the grain-size frequency curves of the red earth show the double-peak mode—the 10-63μm paticle group is "the dominated mode",and the one less than 4μm is "the secondary mode" or "the dominated mode" of some samples.(2) The particle parameters are highly correlation,which suggests that the sedimental environment of brown-yellow unit,typical red clay unit and vermiculated red earth unit are similar.However,the probability accumulation curves of red earth could be divided into two types—three-segment pattern or five-segment pattern,which maybe show the more complicated sorting-environment.(3) Mean grain-size value and content of 4-63μm particle group of brown-yellow unit are larger than those of typical red clay unit and vermiculated red earth unit.
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