POST-IR IRSL DATING OF K-FELDSPAR FROM LAST INTERGLACIAL MARINE TERRACE DEPOSITS ON THE KAMIKITA COASTAL PLAIN, NORTHEASTERN JAPAN

To establish a suitable luminescence dating protocol for marine terrace deposits in Japan, we tested the applicability of K-feldspar post-infrared (IR) infrared stimulated luminescence (IRSL) (pIRIR) dating using a marine isotope stage (MIS) 5e terrace deposit from the Kamikita coastal plain (NE Japan), where independent age control from a tephra is available. One of the most commonly used pIRIR signals, measured at 290 degrees C with the first IR stimulation temperature at 50 degrees C (pIRIR(50/290)), faded with a mean g(2days) value of 1.94 +/- 0.19%/decade. In contrast, the pIRIR signal with a higher first IR stimulation temperature of 200 degrees C (pIRIR(200/290)) had a much lower fading rate (g(2days) = 0.16 +/- 0.49%/decade). The average fading-uncorrected and -corrected pIRIR(200/290) ages of MIS 5e subtidal sediments obtained from two sampling sites were 126 +/- 3 ka and 132 +/- 2 ka, which is in good agreement with the independent age control. We conclude that is it is now possible to use pIRIR protocol to estimate the ages of not only marine terraces formed during MIS 5 substages (5a, 5c) but also of older marine terraces, for which age evidence is limited.