The late Miocene and Pliocene climate in East Asia as recorded by grain size and magnetic susceptibility of the Red Clay deposits (Chinese Loess Plateau)

Grain-size characteristics of the aeolian Red Clay sediment series in China demonstrate the existence of warm-cool alternations during the late Miocene and Pliocene. From the dissimilarity between the temporal patterns of grain size and magnetic susceptibility it is inferred that the finest grain-size fraction in the Red Clay (clay and very fine silt) is transported by the wind, as is the case of the coarser (silty) component. Relatively cool climatic conditions are indicated by increased loess supply (represented by the silty component) from the NW, caused by a stronger winter monsoon, as in the overlying Quaternary system. It is striking that at the same time the amounts of clay also increased, probably due to transportation by intensified westerly circulation. Relatively warm periods are characterized by opposite grain-size properties. These warm-cool alternations on the Asian continent, dated by palaeomagnetic analyses, correlate well with already established changes in sea level and ice sheet volumes up to similar to6 Ma. In addition, time series analysis of the grain-size signal points to an orbitally forced climatic cyclicity (precession, eccentricity and (weak) obliquity). (C) 2003 Elsevier B.V. All rights reserved.