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.