Regional distribution of the Loess-like Red Clay in Subtropical China and its Paleoclimatic implications

摘要

Grain-size and geochemical characteristics of 18 Quaternary Red Clay (QRC) profiles in the lower and middle reaches of the Yangtze River between 25 °N - 31°N in subtropical China were studied. The results showed that the QRC, distributed along the Yangtze River between 29°N - 31°N, shares the loess-like characteristics with the Xiashu Loess, which may originate from aeolian dust deposits. The QRC, mainly distributed between 28°N - 29°N, however, is in double-part structure: The upper part alsoshows the loesslike characteristics; the lower part indicates alluvial features. The loess-like QRC is mainly distributed along the Yangtze River, but gradually declines southwards and is rarely seen to the south of 28° N. The existence of the loess-like QRC is strong evidence for the occurrence of heavy dustfalls in the modern red-soil areas in subtropical China during the Quaternary glacial periods. The loess-like QRC is located approximately 3° latitude south of the Xiashu Loess, implying that theloess/red clay boundary in the Yangtze Valley had frequently oscillated with the alternations between glacial and interglacial climates during the Quaternary period. This leads to multiple or overlapped soil parent materials in the region. Soil properties are not totally determined by modern climate. The possible influence of paleoclimate on soil genesis should also be considered.