ELSEVIER Earth and Planetary Science Letters 161 (1998) 135–143 Wind-blown origin of the Pliocene red clay formation in the central Loess Plateau, China Z.L. Ding a,b,Ł , J.M. Sun a , T.S. Liu a , R.X. Zhu c , S.L. Yang a , B. Guo c a Institute of Geology, Chinese Academy of Sciences, Beijing 100029, China b State Key Laboratory of Loess and Quaternary Geology, Xian 710054, China c Institute of Geophysics, Chinese Academy of Sciences, Beijing 100101, China Received 17 March 1998; revised version received 20 June 1998; accepted 26 June 1998 Abstract In order to determine the depositional processes of the Pliocene red clay formation deposited directly beneath the Plio–Pleistocene loess in the Chinese Loess Plateau, four red clay sections spanning over 400 km are studied. Grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction (>63 μm) being negligible, and that all the curves indicating changes in different grain size parameters have a similar pattern. The grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4–8 μm. The REE patterns of 28 samples from the Jiaxian red clay section are all characterized by LREE enrichments, relatively flat HREE and slight negative Eu anomaly, being similar to those of eolian loess and the average upper continental crust. These lines of evidence point to a wind-blown origin of the red clay deposits. Accumulation of the loess–soil sequences in the Chinese Loess Plateau during the past 2.6 Ma can be therefore regarded as the continuation of the Pliocene atmospheric dust deposition. Observations of spatial grain size changes in the Loess Plateau suggest that the eolian red clay might be transported mainly by the westerlies, differing significantly from the overlying loess that was transported essentially by the East-Asia winter monsoonal winds.  1998 Elsevier Science B.V. All rights reserved. Keywords: Loess Plateau; China; wind transport; sediments; Pliocene; magnetostratigraphy 1. Introduction Wind-blown loess deposits are widely distributed in the Loess Plateau of north-central China, covering an area of about 440,000 km 2 [1,2]. In the central and southern parts of the plateau, loess sequences have a thickness ranging from about 130 to 180 m, and consist of over 30 loess–soil couplets [3–7]. Complete loess–soil sequences are generally under- Ł Corresponding author. Fax: C86 10 6491 9140; E-mail: dingzl@midwest.com.cn lain by reddish clay–silt sediments known as the red clay formation. The contact between the so-called ‘earthy’ red clay formation and the eolian loess is found to occur about at the Matuyama=Gauss mag- netic chron boundary [3,5,8–13]. In the past two decades or so abundant information about various aspects of the loess has been obtained, but little at- tention has been paid to the red clay formation. As the Neogene climate history such as the initiation and development of the East Asia monsoon system might be learned from the red clay, a full investigation of the formation is needed, particularly regarding its 0012-821X/98/$19.00  1998 Elsevier Science B.V. All rights reserved. PII S0012-821X(98)00145-9