The applicability and reliability of K-feldspar pIRIR225 signal to dating Quaternary sediments

Among dating methods that can be applied to Quaternary sediments, quartz OSL (Optically Stimulated Luminescence) dating has been used in various environments because quartz, the target mineral for dating, are ubiquitous. Recently, for samples older than datable limit of quartz OSL dating (ca. similar to 10 ka), K-feldspar IRSL (InfraRed Stimulated Luminescence) signals are widely applied. In this paper, we aim to examine the bleaching characteristics of K-feldspar pIRIR(225) signal and the reliability of the K-feldspar pIRIR(225) age results. K-feldspar pIRIR(225) signals stimulated with solar simulator show slower bleaching than those of quartz OSL and K-feldspar IR50 signal. This indicates that the K-feldspar pIRIR(225) ages are likely to overestimate the depositional ages due to slow bleaching at deposition. K-feldspar pIRIR(225) dating performed on a modern flood deposit was, however, as low as 8.8 +/- 0.6 Gy. Although K-feldspar pIRIR(225) ages for five samples collected from terrestrial alluvial fan deposits vary from sample to sample, they are older than quartz OSL ages only by 5.5 +/- 2.9 ka on average. These results suggest that the K-feldspar pIRIR(225) signals may overestimate depositional ages due to slow bleaching. However, it is presumed that the effect is likely to be negligible for old samples, thus K-feldspar pIRIR(225) dating can be reliably applied to Quaternary sediments, particularly for those older than similar to 100 ka.