The equivalent dose of different grain size quartz fractions from lakeshore sediments in the arid region of north China

Abstract

Equivalent dose ( D e) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different relationships between D e values and grain sizes of these five samples. The first relationship is that the D e values obtained from various grain sizes are in agreement within 1 delta errors. The second relationship is that D e values are similar to each other for fractions between 125 and 300 μm, while the D e value of the 63–90 μm fraction is 40∼55% smaller than others. For example, the D e values obtained for sample #3 are 20.15 ± 1.19 Gy, 19.80 ± 0.83 Gy and 20.93 ± 1.06 Gy for fractions of 90–125, 125–150 and 250–300 μm respectively, but are 10.79 ± 0.84 Gy for the 63–90 μm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (<90 μm) intruded after the dominant sedimentation. Comparison of OSL ages from different grain size fractions of sample #2 with a radiocarbon age from the same lithologic layer supports that fractions coarser than 125 μm yield more reliable burial ages, while the fraction finer than 90 μm yields underestimated ages for some lakeshore sediments from this arid region.