Revised ages of late Holocene tephras in Beppu Bay, central Kyushu, southwest Japan

Abstract

In this study, we revised eruptive ages, especially the Aso and Yufu volcanoes, central Kyushu, by analyzing a sediment core of southwestern Beppu Bay, southwest Japan, where undisturbed sediments are continuously deposited in a dysoxic basin. We identified two ash-fall layers in the sequence covering the last ca. 3000 years by using the refractive index of volcanic glasses and other parameters. These layers were likely correlated with N2 ash of the Aso volcano and Yufu-dake 1 ash (Yf1) of the Yufu volcano on the basis of the refractive indices of volcanic glasses, heavy mineral compositions, special distribution, and facies. According to high precision age models, the eruptive ages (68.2% probability range) of these tephras were 1470–1490 and 2010–2100 cal yr BP, respectively, and concordant with reported ages of previous research. These precise ages of tephras improve linking or dating in the various environments, and contribute to investigation of environmental changes or sedimentary process from source to sink.