Characteristics of quartz grains in the red clay of Tongling City and their environmental implications

Hot debate has been occurred for long concerning the origin and provenance of the vermicular red clay in South China. In this paper, transportation mechanism and provenance of the vermicular red clay were studied by means of grain size and surface textures of the quartz grains from the red clay in Tongling city in the south of Anhui province. The quartz grains from the Tongling section show some obvious characteristics of wind transportation. The grains are fine in general and gradually coarsen up from bottom to top. The vermicular red clay is dominated by silt (10～50 μm), ranging from 40.62% to 60.37%. The frequency curves of the quartz grains are essentially bimodal with a low hidden peak in the coarse fraction. And the frequency curves of different layers in the profile shows good consistency. Microscopic images of quartz grains show that they are, in fact, the mixture of rounded and poorly rounded grains. Some particles have obvious hydrodynamic effects remained on the surface, such as underwater polished surfaces, V-shaped pits, etc., some have obvious traces of wind action, such as dish-shaped pits, crescent-shaped pits, etc., while the others show some surface texture jointly formed by hydrodynamic and wind actions, suggesting a mixture of distant and nearby sources. The near-source sediments may come from the floodplain of surrounding rivers, where the hydrological characteristics are retained due to the short-distance of wind transport. The surface of the quartz particles at the bottom of the profile has obvious features of hydrogenic origin, and the aeolian features increase upwards. Finally, it is confirmed that the red vermicular clay in Tongling city is a kind of mixed deposits composed of the particles from near and distant wind sources, and the contribution of the materials of different sources depends upon the change of East Asian monsoon.