Effects of feldspar contamination on equivalent dose and the shape of growth curve for OSL of silt-sized quartz extracted from Chinese loess

This study examines the effects of feldspar contamination of different extent (by fluorosilicic acid etching for different time periods and mixing pure quartz with different percentage of un-etched grains) on blue-light stimulated luminescence (BLSL) of quartz (38-63 mu m) for Chinese loess. In particular, the D-e values and the shape of growth curves will be examined. The results show that: (1) The D-e determined using feldspar in Chinese loess is obviously underestimated, and infra-red stimulated luminescence (IRSL) has a greater underestimation than BLSL. For aliquots with no fluorosilicic acid etching, an IRSL D-e underestimation of similar to 30% is observed for a sample with an expected age of similar to 22 ka, similar to 19% underestimation for BLSL, and similar to 10% for post-IR BLSL. For quartz BLSL, the contamination of feldspar, which has not dissolved by fluorosilicic acid etching, will inevitably lead to age underestimation. We suggest that the IR-checking should be performed for every single aliquot. An aliquot should be excluded from the final D-e calculation if obvious IRSL signal was observed. (2) For the sample under examination blue LED stimulation can reset both IRSL and BLSL signals of feldspars, while IR stimulation cannot reset the BLSL of feldspars. (3) For multiple-mineral aliquot the growth curve shape of the post-IR BLSL is different from that of the IRSL, and within 25 Gy it is identical to that of the pure quartz BLSL. The contamination of feldspars in quartz will change the shape of a growth curve for quartz BLSL.