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

Key words: 
• Pliocene /
• &lsquo /
• Red Ciay' /
• grain size

Abstract: The Tertiary‘Rcd Clay' deposit in Chincsc Loess Plateau has attracted considerable research interests in recent wars as it may provide the information of palcoclimatc in Northern China. The evidences from sedimentology, geochemistry, gcomorphology and field survcv indicate that the‘Rcd Clay' may he of colain origin the same as the overlying loess.Howcver, it is controversial on which wind svstcm transported the deposit. In this paper the grain size of hulk samples and chcmicallv isolated quartzes from‘Rcd 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 hulk and quartz samples decease southwards so does the coarse-faction content(>42μm % and>30μm%).Moreover the‘Rcd Clay' samples include a great deal of particles more than 20μm,which was proved to he transported onlv by suhacrial wind.These therefore suggest that it is mainly the northern suhacrial wind rather than the supernal wind that transported the dust of‘Rcd Clay'.The spatial distribution of‘Rcd Clav' is comparable to that of overlying colian locss} which proves the‘Rcd Clay' may he formed in a little hit dry environment but it is not so dry as to the environment the loess deposited.