* Corresponding author. Tel.: #86-10-6200-8111; fax: #86-10- 6491-9140. E-mail address: dingzl@midwest.com.cn (Z.L. Ding). Quaternary Science Reviews 19 (2000) 547 } 558 Re-arrangement of atmospheric circulation at about 2.6 Ma over northern China: evidence from grain size records of loess-palaeosol and red clay sequences Z.L. Ding*, N.W. Rutter, J.M. Sun, S.L. Yang, T.S. Liu Institute of Geology, Chinese Academy of Sciences, P.O.Box 9825, Beijing 100029, People's Republic of China State Key Laboratory of Loess and Quaternary Geology, Xian 710054, People's Republic of China Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada T6G 2E3 Abstract Recent studies have shown that the red clay sequence underlying the Quaternary loess of the Chinese Loess Plateau is wind-blown in origin. Continuous atmospheric dust deposition in the past 7.0 Ma has been documented. To address the wind system that transported the Tertiary red clay, two north}south transects were studied in the Chinese Loess Plateau. One of the transects was designed to study spatial changes in grain size of the last glacial}interglacial loess records, and the other to observe particle changes of the Tertiary red clay underlying the Quaternary loess. The loess transect consists of nine sections, and the red clay transect of four sections. Analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the Late Pleistocene, which is consistent with the idea that the aeolian materials of the Quaternary in the Loess Plateau are transported by the northerly winter monsoonal winds. Grain size distribution of the red clay sequences, however, does not show such a change. From north to south along the red clay transect, the particle size distribution is almost identical in the four sections, suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material. It is suggested that the red clay may have been transported by the westerlies from the dust-source regions of northwestern China onto the Loess Plateau. A remarkable re-arrangement of atmospheric patterns at about 2.6 Ma, therefore, has been recorded by the red clay-loess shift. It is speculated that this re-arrangement of atmospheric patterns may have been caused by the onset of glaciation in the Northern Hemisphere.  2000 Elsevier Science Ltd. All rights reserved. 1. Introduction It has been convincingly demonstrated that the Quat- ernary loess-palaeosol sequence of the Chinese Loess Plateau is a valuable archive of regional climate history (Liu, 1985; Kukla et al., 1988; Kukla and An, 1989; Rutter et al., 1991; An et al., 1991a; Ding et al., 1993; Liu and Ding, 1993). In the middle and southern parts of the Loess Plateau, loess sections have a thickness ranging from about 130 to 180 m, and span an interval from 2.4}2.6 Ma to the Holocene (Heller and Liu, 1982, 1984; Liu, 1985; Rutter et al., 1990; Ding et al., 1992). Over 30 intercalated palaeosols have been recognized in the loess sequences (Kukla and An, 1989; Ding et al., 1993). A standard interpretation for the formation of the loess-soil sequence is that during glacial periods of the Pleistocene, high atmospheric dust in#ux was deposited onto the Loess Plateau under a climate dominated by winter monsoonal winds, whereas the dust in#ux was greatly reduced during interglacial periods, and soils were developed under an intensi"ed summer monsoonal climate (Liu, 1985; Li et al., 1988; Kukla and An, 1989; An et al., 1991a, b; Rutter and Ding, 1993). The alterna- tion of loess and soil units can thus be regarded as the product of the oscillatory monsoon system over East Asia. At many sites of the Loess Plateau, reddish clay-silt sized sediments of varying thickness are seen to underlie the oldest loess unit L33 (Ding et al., 1992). As the 0277-3791/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 3 7 9 1 ( 9 9 ) 0 0 0 1 7 - 7