2021 Volume 60 Issue 2 Pages 27-41
Feldspar optically stimulated luminescence (OSL) dating was applied to the channel sediment in an abandoned river valley around a cutoff spur formed by the Totsukawa River in the Kii Mountains, southwestern Japan. The depositional age of the channel sediment was not determined because the dated feldspar grains were likely to be incompletely bleached to various degrees, and most of the grains attained saturation in OSL signals. However, the depositional age was constrained to be younger than 280 ka based on the characteristic saturation dose of the dose response curve measured from “unsaturated” feldspar grains. The river-incision rate calculated from the constrained depositional age was consistent with the denudation rates estimated from sediment yields in catchments. This result indicates that, even if the determining depositional age of the sediment is difficult due to the insufficient bleaching, constraining that age may be possible by using the characteristic saturation dose of the dose response curve measured from unsaturated feldspar grains.
