An Accumulative Pedogenic Process in Chinese Loess Plateau.
Xue-feng Hu, Dept of Environmental Science and Engineering, Shanghai Univ, No. 149 Yanchang Road, Shanghai, 200072, China
The dust fall in Chinese Loess Plateau is continual in the whole Quaternary period. In the glacial periods, when cold and dry winter monsoon dominated, the dust fluxes were higher, resulting in the sparse vegetation and weak pedogenesis. In contrast, in the interglacial periods, the pedogenesis became intensive due to the warm and humid climate. However, even in the most optimum time of the interglacial periods, the winter monsoon had not totally vanished and the dust deposition not intermitted either. The pedogenic processes in Chinese Loess Plateau were thus always accompanied by the dust accumulation. In fact, the pedogenesis was just synchronized with the dust deposition. In the glacial climate, the typical loess was formed as the dust deposition rate was higher than the pedogenic rate; while in the interglacial climate, the paleosols were developed as the pedogenic rate was higher than the deposition. However, the distinction between the loess and paleosols is only relatively correct. As a matter of fact, the loess is only a weakly developed paleosol; and the paleosol is only a loess significantly affected by the weathering and pedogenesis. The pedogenic horizons of the paleosols in Chinese Loess Plateau are often uniform and 3-5 metres thick. The paleosols often show some multi-pedogenic properties, such as the co-existence of secondary CaCO3 and optical directional clay. These features are the specific evidence for the synchronization between the pedogenesis and loess deposition. Affected by this special process, the real parent materials of the paleosols were not the underlain loess, but the dust materials unintermittedly added into the profiles. Hence, strictly speacking, the paleosols had no pedogenic relationships with the underlain loess. Because the soil profiles were constantly thickened during the pedogenic processes, each micro-layer of the paleosol profiles had ever been the topsoil (A horizon), and then subsoil (B horizon). Therefore, the functional division of pedogenic horizons in the paleosols is meaningless. Because of the constant addition of the dust rich in CaCO3 and easily weathered minerals, the weathering degree of the paleosols had always been buffered. Thus, in Chinese Loess Plateau, even the most developed paleosols are less weathered than the brown soils (Luvisols) in China. The author proposes to classify this unusual pedogenic process as a new pedogenic one, and to nominate it as an accumulative pedogenesis.