Rates of dust deposition between 50 ka and 20 ka revealed by OSL dating at Yuanbao on the Chinese Loess Plateau

A new chronology has been constructed for an 18-m section of Malan Loess at Yuanbao, near Linxia, on the western edge of the Chinese Loess Plateau. The chronology has been obtained using the optically stimulated luminescence signal from coarse silt-sized grains of quartz extracted from eighteen samples collected at approximately 1-m intervals down the section. In the upper 9 m, the dust deposition rate was 1.11 m/ka, covering the time period from 26.1 ± 1.9 ka to 17.5 ± 1.2 ka and there is no evidence of hiatus at this scale of analysis. At greater depths, the average rate of dust deposition is lower, although there was a short period of higher deposition between 37 ka and 34 ka. No large breaks (> 5 ka) in deposition were deduced from the OSL ages for the lower part of the loess section dating from 51.2 ± 4.6 ka to 30.0 ± 2.5 ka. The age of the boundary at 9.1 m, between the more uniformly deposited upper loess and the lower loess is compared to the age of the transition in the marine record between Marine Isotope Stages 3 and 2. The chronological information at Yuanbao is also used to challenge the previous use at this section of an age model based on changes in grain size.