Optically stimulated luminescence dating of Late Pleistocene tephric loess intercalated with Towada tephra layers in northeastern Japan

摘要

To investigate the pre-50 ka eruption history of Towada volcano, northeastern Japan, optically stimulated luminescence (OSL) dating was applied to fine-grained quartz extracted from Late Pleistocene tephric loess intercalated with Towada tephra layers in a sediment core from the Kamikita Plain. The bulk OSL signal was found to be unsuitable for dating, because the medium and slow-1 components were thermally unstable. After a deconvolution of the bulk OSL signal to extract the fast component, the equivalent dose was estimated by using the single-aliquot regenerative-dose protocol. The OSL ages obtained for the tephric loess were generally in agreement with the stratigraphic sequence in the interval from 2.10 to 7.45 m depth, where they ranged from 156 +/- 12 ka to 49 +/- 3 ka, in ascending order. We calculated the ages of CP, SP, RP, and KbP tephras by interpolating OSL ages; these are 111 +/- 6 ka, 89 +/- 6 ka, 61 +/- 4 ka, and 58 +/- 4 ka, respectively; these ages are broadly concordant with previous estimates. The age of the RP tephra is of particular importance because its eruption marked the beginning of the caldera-forming stage of Towada volcano. Our results show that this eruption occurred about 20 ka younger than previously thought (ca. 80 ka). Our results demonstrate that OSL dating of quartz grains in tephric loess can be used to estimate the ages of intercalated tephra layers and contribute to our understanding of the eruption histories of volcanoes. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.