Rb and Sr geochemical characterization of the Chinese Loess stratigraphy and its implications for palaeomonsoon climate

Concentrations and distributions of Rb and Sr in loess and palaeosol sample s from the Luochuan profile have been studied, in grain-size fractions and chemical forms. Results show that Rb is quite rich in the fraction of less than 2 mu m, and exits only in the residual phase, while Sr is distributed in sand and silt fractions, occurring in the residual and carbonate phases. Therefore, variations of the concentrations of Rb and Sr in loess and pala eosols are closely related not only to dustfall compositions depending on w inter monsoon wind strength but also to summer monsoon-induced pedogenic in tensity. This indicates that variations of Rb/Sr ratio in Chinese loess seq uences represent cyclic alternations of East Asian summer and winter monsoo n climates on the orbital time-scale. Variations in Sr concentrations along the sequence bear a high similarity to the oxygen isotope record of the de ep sea sediments over the past 2.5 Ma, whereas variations in Rb concentrati ons are in good agreement with the record of magnetic susceptibility determ ined with the duplicated samples from the same profile. This suggests that (1) the high-latitude ice volume is responsible for East Asian monsoon vari ations and (2) the signal of magnetic susceptibility depends dominantly on pedogenesis in Chinese loess sequences.