Friday, 14 July 2006

Reticulate Red Clay with Aeolian Origin in Southern China and Its Paleo-environmental Implications.

Xue-feng Hu, Dept of Environmental Science and Engineering, Shanghai Univ, No. 149 Yanchang Rd, Shanghai, 200072, China

The red clay and red crust are widespread in southern China. With acid or strongly acid reaction, low base saturation (BS) and strongly weathered desili-allitic properties, they are widely believed to be the outcome of long-term humid and warm climate in the Quaternary period. Owing to the appearance of net-like structures with red stripes alternating with white ones in the middle and lower parts of red clay profiles, this red clay is also called reticulate red clay. The reticulate red clay in Xuancheng, Anhui Provine and Jiujiang, Jiangxi Province, southern China, was studied. Grain-size distribution of the original and quartz samples of the reticulate red clay and the REE distribution patterns imply their aeolian origin. The further study indicated the reticulate red clay distributed in the region between 28~31 N altitude in the lower and middle reaches of the Yangtze River originates from aeolian deposit; while that to the south of the region often contains much coarse grains, apparently showing alluvial or diluvial characteristics. The appearance of the reticulate red clay with aeolian origin indicates the large-scale dust fall had once occurred in the current red soil areas of the Yangtze River Valley in the Quaternary glacial periods, when winter monsoons were strengthened and dust invaded southern China. Further study on the regional distribution of the reticulate red clay with aeolian origin will be conducive to revealing the southern border of the large-scale dust fall in China during the Quaternary glacial periods. The reticulate red clay with aeolian origin has double climatic implications: Its aeolian origin reflects a dry and cold glacial climate; but its acid and desili-allitic properties reveal it had experienced a hot and humid interglacial climate. The author supposes the original material of this red clay had been an aeolian deposit at least before the last interglacial period, and then it suffered strong weathering and formed acid and allitic properties in subsequent interglacial climate. Owing to the multi-cycli changes of climate in Quaternary period, one pedogenic process mighty be influenced by several different climates, resulting in the different climatic impressions in the same soil or sediment. The existence of the strongly weathered red clay with aeolian origin in southern China is a good example for multi-pedogenic processes.

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