Description and Correlation of the Nagate Tephra Found in the Terrace Deposits at the Southern Foot of Asan Range in Tokushima Prefecture, Southwestern Japan

Abstract

We discovered a tephra in the terrace deposits at the southern foot of Asan Range in Tokushima Prefecture, southwestern Japan, and named it the Nagate tephra. The Nagate tephra is brown to gray-white in color and is composed of sand-and silt-sized grains that include many phenocrysts. The Nagate tephra is compared with Aso-4 tephra in terms of petrography, refractive index of volcanic glass, and chemical composition of pyroxene.
Aso-4 tephra erupted 70 to 90ka BP. The terrace which contains Nagate tephra was completed at the end of the last interglacial stage. The Nagate tephra is important in clarifying the active time of the Median Tectonic Line in the late Pleistocene.