Use of rubidium to date loess and paleosols of the Louchan sequence, central China

Rb concentrations, analyzed at 20-cm intervals from the Luochuan sequence of loess and paleosols, are sensitive to the loess-paleosol alternation controlled by monsoon climate. Because it is geochemically immobile, Rb can be well preserved in the loess-paleosol sequence after deposition, and its concentration depends mainly on properties of the winter monsoon-blown dust and on intensity of the summer monsoon-induced pedogenesis. A curvilinear relation has been developed between the measured Rb-concentration and the apparent sedimentation rate for the last glacial-interglacial cycle. This relation provides a time scale that corresponds well with the presently accepted ages for paleomagnetic reversals of Brunhes/Matuyama and Jaramillo events. With allowance for reduced Rb concentrations caused by early Pleistocene climate, the Rb-based time scale is also consistent with the boundary ages of other major paleomagnetic reversals of the past 2.58 myr. (C) 2000 University of Washington.