Proximal–distal fall deposit correlation of VEI‐5 tephra (Towada‐Chuseri) from Towada volcano, northeast Japan

Abstract

ABSTRACTA tephra layer offers an isochronous surface in sediments, thus serving as a key bed and/or an age marker. Recent high‐resolution sediment research (e.g. varved sediments) has revealed optically invisible tephra fingerprints and provided high‐precision tephra ages. However, a tephra‐based correlation cannot succeed without detailed knowledge of the tephra characteristics in a proximal area to correlate with tephra in high‐resolution sediments in remote areas. Here we documented the detailed characteristics of Towada‐Chuseri (To‐Cu) tephra, which is associated with the Middle Holocene volcanic explosivity index 5 eruption of Towada volcano, northeast Japan. We used To‐Cu tephra samples to achieve the proximal–distal correlation of three members: Chuseri pumice (Cu), Kanegasawa pumice (Kn) and Utarube ash (Ut). These distal occurrences correlate with proximal To‐Cu tephra based on volcanic glass morphology and refractive index, as well as on major element composition of volcanic glass shards. Refractive indices allow the preliminary correlation of each member, and major element composition helps in distinguishing Ut from the other members. Glass morphology provides additional support. These correlations reveal that To‐Cu, especially Cu, covered central to northeast Japan while confirming that To‐Cu is the representative tephra in the Middle Holocene of the Tohoku region.