Aeolian origin and palaeoclimatic implications of the 'Red Clay' (north China) as evidenced by grain-size distribution

The 'Red Clay' is an important deposit underlying the Quaternary loess-palaeosol sequence in the Chinese Loess Plateau, being regarded as an excellent record of palaeoclimate changes in the late Tertiary. Several properties of the 'Red Clay' have been measured previously in order to derive climatic information. However, the sedimentary processes involved and the origin of the materials remain controversial. Here we present results of grain-size analyses of the 'Red Clay' from four representative sites in the Chinese Loess Plateau. In particular their grain-size distribution is compared with that of typical Quaternary aeolian loess-palaeosol, as well as lacustrine and fluvial sediments. It appears from the sedimentological evidence that the major part of the 'Red Clay' is of aeolian origin. It is rather similar in some of its properties to the Quaternary loessic palaeosols. The dust forming the 'Red Clay' was transported by a wind system that was weaker than that involved in the accretion of the Quaternary loess. Furthermore, the 'Red Clay' sediment has been modified by post-depositional weathering.