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 loesspaleosol 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.