Characteristics of Tephras Interbedded with the Holocene Sediments on the Sanriku Coast, Northeast Japan

Abstract

 Tephras interbedded with Holocene sediments in coastal lowlands along the Sanriku Coast, northeast Japan are described, and well-known widespread and local tephras are correlated based on morphology, refractive index, and chemical composition of volcanic glass shards, stratigraphy, and radiocarbon age. As a result, tephras that are correlated with Towada-a (To-a), Towada-Chuseri (To-Cu), Kikai-Akahoya (K-Ah), Oguni pumice, Towada-Nambu (To-Nb), and Hijiori-Obanazawa (Hj-O) are identified. In particular, To-Cu is distributed throughout the study area and is recognized to be a useful key tephra. In addition, To-a and Oguni pumice were discovered for the first time on the Sanriku Coast. The results suggest that the morphologies and the refractive indexes of volcanic glasses are useful and important for distinguishing tephras and correlating with widespread and local tephras on the Sanriku Coast.