Grain Size Evidence of Multiple Origins of Red Clays in the Jinhua-Quzhou Basin, South China

Six typical red clay profiles were sampled from Tangxi (TX), Langyaz (LYZ), South Shangshanwen (SSW), Xianqiao (XQ), Qijian (QJ) and Huhaitang (HHT) of Jinhua-Quzhou Basin, Zhejiang Province of China to evaluate the characteristics of grain size composition, distribution and parameters of red clays and to reveal the origin of red clays and interpret possible implications for paleoclimate in subtropical China. The results showed that red clays in TX, LYZ and SSW were fine and uniform, with no > 2 mm gravels and little > 63 μm fraction. They had a high content of 10–50 μm fraction, so-called “basic dust fraction”, and showed unimodal distributions, which were very comparable to those of the Xiashu Loess in southeastern China and the loess in North China. All these features reflected marked aeolian characteristics of the red clays in these areas. Red clays in XQ and QJ were much coarser than those in TX, LYZ and SSW, with high contents of > 63 μm fraction and even containing > 2 mm gravels in some layers. The grain size distribution patterns showed significantly progressive trends from the lower profile to the upmost layer and could not be compared with those of the loess in North China or the Xiashu Loess, implying they might be derived from underlying parent rocks and had some inherited properties from bedrock. Red clays in HHT had high contents of > 63 μm fraction and contain many > 2 mm gravels in each layer. The grain size frequency curves showed multiple-peaks and some abrupt variations were also observed on the profile, revealing its alluvial or diluvial origin in HHT. The multiple origins of red clays reflected the diversity and complexity of the Quaternary environment in South China. It can be concluded that grain size is an effective proxy indicator for the origin of most deposits.