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[HQR05-03] Residual doses of modern beach-shelf feldspar sands at Kujukuri
Keywords:residual doses, Kujukuri, luminescence dating
Infrared Stimulated Luminescence (IRSL)and post-Infrared IRSL (pIRIR)from feldspar have slower bleaching rates than quartz OSL and are likely associated with residual doses related to incomplete sunlight bleaching. While residual doses lead to inaccuracy of age estimates, they potentially record valuable information of erosion, transport, and deposition processes of sediment particles. In this study, we estimated spatial variations of residual doses determined for modern beach to shelf feldspar sands on the Kujukuri coast. SAR protocols were applied to grains 180-250 µm in diameter and with densities of 2.53-2.58 g/cm3. IRSL prior to pIRIR was measured at 50°C and preheat was set at +30°C of measurement temperature of pIRIR.
The residual doses tended to increase with higher preheat temperature for IRSL and higher measurement temperature of pIRIR, reflecting the difference of bleaching rate. At a relatively low preheat (150°C), the IRSL was well bleached with a maximum residual dose of about 0.2 Gy. Residual doses of pIRIR150 and pIRIR225, pIRIR measured at 150°C and 225°C, respectively, were up to 0.8 Gy and 3 Gy, respectively, for beach samples. pIRIR290 residual doses varied from 8 to 14 Gy in the seabed to the foreshore range, while doses decreased toward the dunes on the more landward side to 7 Gy. This subaerial decrease is interpreted as a result of sunlight bleaching during wind transport. In some of the subaqueous samples, higher residual doses of pIRIR were observed near the sea cliff and in deeper water. Although measurements of more samples are needed, the preliminary results of this study indicate that the residual dose may provide information on the sand transport process on the Kujukuri coast.
The residual doses tended to increase with higher preheat temperature for IRSL and higher measurement temperature of pIRIR, reflecting the difference of bleaching rate. At a relatively low preheat (150°C), the IRSL was well bleached with a maximum residual dose of about 0.2 Gy. Residual doses of pIRIR150 and pIRIR225, pIRIR measured at 150°C and 225°C, respectively, were up to 0.8 Gy and 3 Gy, respectively, for beach samples. pIRIR290 residual doses varied from 8 to 14 Gy in the seabed to the foreshore range, while doses decreased toward the dunes on the more landward side to 7 Gy. This subaerial decrease is interpreted as a result of sunlight bleaching during wind transport. In some of the subaqueous samples, higher residual doses of pIRIR were observed near the sea cliff and in deeper water. Although measurements of more samples are needed, the preliminary results of this study indicate that the residual dose may provide information on the sand transport process on the Kujukuri coast.