GENESIS AND RESEARCH SIGNIFICANCE OF THE PLINTHITIC HORIZON
网纹红土的成因及其研究意义

Plinthitic horizon in mid-lower reaches of the Yangtze River in China is an index bed of Middle Pleistocene, which, developed commonly in the lower parts of the alluvium, eluvium, cliff debris or diluvium.It has irregulat plinthitic textures with red alternating in grey. white, yellow and brown.The red color and the nets of the plinthitic horizon are not original. but a result of a long-term leaehing and weathering under the conditions of humid and warm climate during middle Pleis-tocene.The results of chemical complete analysis and clay mineral analysis suggest that the leaching degree of plinthitic horizon is very similar to red soil but a little weaker than that of laterite, the clay mineral components of red clay and white clay are the same, while the iron content of them is dif ferent. Theref ore, the plinthitic horizon is resulted from the reduction and migration of three-valance iron.The distribution of the plinthitic horizon is strictly controlled by the fossil landform and altitude.The much more humid and warmer climate at that time.the flat topography as well as the frequent movement of the groundwater are absolutely necessary conditions to form the plinthitic horizon.The research on it has two specific meanings.First, the fact that the plinthitic horizon has experienced stronger shift since it formed, will provide valuable informations for the amplitude and character of the tectogenesis in South China since Middle Pleistocene.Second, the plinthitic horizon can not be developed in the precipitous hilly areas like - Lushan Mountains, this is also a very good evidence for solving the problem whether or not some glaciations have taken place in East China during the Quaterary period.