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 o f loess and paleosols, are sensitive to the loess-paleosol alternation cont rolled by monsoon climate. Because it is geochemically immobile, Rb can be well preserved in the loess-paleosol sequence after deposition, and its con centration depends mainly on properties of the winter monsoon-blown dust an d on intensity of the summer monsoon-induced pedogenesis. A curvilinear rel ation has been developed between the measured Rb-concentration and the appa rent sedimentation rate for the last glacial-interglacial cycle. This relat ion 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 c limate, the Rb-based time scale is also consistent with the boundary ages o f other major paleomagnetic reversals of the past 2.58 myr. (C) 2000 Univer sity of Washington.