Residual Dose of K-Feldspar post-IR Irsl of Beach-Shoreface Sands at Kujukuri, Eastern Japan

Abstract

Abstract We assessed the residual dose of K-feldspar grains from modern and Holocene beach–shoreface sands at Kujukuri, eastern Japan. Samples from the modern foreshore and shoreface (to 34 m depth) show residual doses <0.2 Gy for infrared-stimulated luminescence (IR)50 measured during post-IR infrared-stimulated luminescence (pIRIR)50/150, equivalent to potential burial age overestimation of only several decades for given dose rates. Residual doses of 1–3 Gy are retained by pIRIR50/150, equivalent to 400–1,300 years; pIRIR50/290 residual doses are up to 30 Gy, suggesting possible overestimation by >10,000 years. Residual doses of Holocene sands were also assessed by comparison with radiocarbon ages, revealing consistent results with modern sands. The pIRIR50/290 results show no pronounced correlation of residual dose with water depth, except for a few samples from <5 m depth with residual doses several tens of per cent lower than those of deeper sands, suggesting that most samples were not fully bleached and that sustained subaerial sunlight bleaching diminishes the difficult-to-bleach component. Compared to the uncertainties associated with other factors, such as the fading correction, the residual doses of IR50 and pIRIR50/150 are negligible for samples older than late and early Holocene, respectively. In contrast, the residual dose of pIRIR50/290 may lead to critical age overestimation of Late Pleistocene deposits if the residual dose is not properly corrected.