黄土高原晚上新世红粘土粒度的空间变化

Spatial Variation of Grain Size of the Late Pliocene ‘Red Clay’, Chinese Loess Plateau

对黄土高原由北到南 6个地点的晚上新世红粘土样品进行了常规粒度测量和化学提取的石英样的粒度测量。红粘土全样和石英样的平均粒径由偏北到南逐渐变细 ,粗颗粒含量也逐渐减少 ,表明红粘土可能是由偏北低空风而不是高空风搬运而来的。 3 .6～ 2 .6MaBP红粘土粒度与其上覆风成黄土粒度的空间变化具有可比性 。

The Tertiary ‘Red Clay’ deposit in Chinese Loess Plateau has attracted considerable research interests in recent years as it may provide the information of paleoclimate in Northern China. The evidences from sedimentology, geochemistry, geomorphology and field survey indicate that the ‘Red Clay’ may be of eolain origin, the same as the overlying loess. However, it is controversial on which wind system transported the deposit. In this paper, the grain size of bulk samples and chemically isolated quartzes from ‘Red Clay’ of the late Pliocene are investigated. The samples were taken from six locations spanning 550 km from the north to the south in the Loess Plateau. The results show that, the mean sizes of both bulk and quartz samples decease southwards, so does the coarse faction content (>42 μm% and >30 μm%). Moreover, the ‘Red Clay’ samples include a great deal of particles more than 20 μm, which was proved to be transported only by subaerial wind. These, therefore, suggest that it is mainly the northern subaerial wind rather than the supernal wind that transported the dust of ‘Red Clay’. The spatial distribution of ‘Red Clay’ is comparable to that of overlying eolian loess, which proves the ‘Red Clay’ may be formed in a little bit dry environment, but it is not so dry as to the environment the loess deposited.