Research On The Formation Mechanism Of Reticulated Red Clay And Growth Of Reticulated Mottles

Reticulated red clay horizon is a unique strata, which usually develop in the red weathering crust widely distribute in southern China. It is called reticulated red clay because of the light reticulated mottles in the horizon, which sharp like net, tube or vermicular. Abundant studies have been made in the following aspects: material composition, distribution regularities, Era and environmental meaning. Though the researches have made lots of achievement, there are still some problems exists: 1) It is still unable to promote a theory which can explain the formation mechanism. 2) The study about the development of the reticulated mottles is not clarified, so is its environmental indicate meaning.Based on previous studies and several times of field work, we select four profiles along the middle and lower reaches of Yangtze River: Yue Yang profile(YY), Xi Saishan(XSS) profile in Huangshi, Wangjia Zhulin(JSW) profile in Jiujiang and Tu Tang(TT) profile in Pengze. Ten samples with different develop level were taken from the profiles. After separate the reticulated mottles and matrix apart, testing the grain size, major elements, trace elements, moisture content, p H, Eh, free iron and Fe3+/Fe2+. The results show that:1)The difference distribution of pore and moisture content in the reticulated red clay may be the internal mechanism of the reticulated mottles prime formation.2) In homogeneity fine grain size red clay, compare to the red matrix, the mottles contains less fine size clay, higher water content, lower p H(4.96-5.73) and Eh(297-338mv), indicate the acid reducing environment. While the matrix has lower water content because of the development of irony coating, so that the matrix lean to the oxidation environment with higher Eh(335-384mv)and p H(5.82-6.31).3) The acid reducing environment lead to the strong leaching of the transition metal elements like Fe、Mn、Co、Ni、Cr、V、Ti, the elements gathering in the matrix and develop the irony coating; which make the stable elements like Si O2 and Zr gathering in the mottles.4) Because of the development of irony coating in matrix and fine grain size particle decreasing in mottles, the pole rate increase in mottles and decrease in matrix, which enlarge the water content difference and accelerate the leaching-transfer and sediment-accumulation of the elements between matrix and mottles. This is a positive feedback process, as long as the soil alternative wet and dry, the water keep float in a certain period, this process which constantly support the develop of mottles. So that the reticulated red clay can be more mature.5)With more gathering of transition metal elements(mainly Fe), the matrix become redder while the mottles become lighter because of the losing of Fe and gathering of stable elements. Lead to the color difference between the mottles and matrix, indicate the sufficient ongoing of the leaching-transfer and sediment-accumulation process, the mottles will be more developed, so is the maturity of the mottle. The maturity of the reticulated mottles can be show by the color difference: △E=[(△a)2+(△b)2+(△L)2]1/2.Study shows that the alternative wet and dry environment in soil, as well as the warm and wet climate is the external mechanism of the reticulated mottles formation.The further study, by analyze plenty of the reticulated red clay horizon in southern China, shows that the alternative wet and dry climate characteristics in the subtropical monsoon region is the decent environment for the formation and development of the reticulated red clay in southern China. The reticulated red clay is pole soil. And it is still developing. The formation and development is a common soil environment phenomenon in monsoon area the reticulated mottle is soil new growth.This study has explained the internal and external condition for the formation of reticulated red clay in mechanism aspect. It solved many phenomenon that can’t be explain in former researches. Also, by explore the environmental indicating meaning of the reticulated mottles maturity, a new proxy is been provided to the reconstruction work of Quaternary climate in southern China.