Departmental Bulletin Paper Re-examination of previous correlation of distal Ks5 Tephra and proximal Oda pyroclastic flow deposits in South Kyushu, SW Japan

Nishizawa, Fumikatsu  ,  Suzuki, Takehiko

(51)  , pp.83 - 91 , 2016 , Department of Geography, Tokyo Metropolitan University
Two pyroclastic flow deposits named Nabekura (Nb) and Oda (Oda) Pyroclastic Flow Deposits in ascending order, in the southern Kyushu Island, SW Japan, are intercalated in the Kokubu Group distributed around the northern coastal area of the Kagoshima Bay. The purpose of this study is to reveal their differences in petrographic properties such as glass chemistry and refractive indices of volcanic glass shards, hornblende, and orthopyroxene. Nb and Oda are evidently distinguished by refractive indices of orthopyroxene and variation in the chemical composition of glass shards. We re-examined the proposed correlation of Oda with Ks5 (Boso Peninsula, Central Japan) by previous studies, comparing other two distal tephras petrographically similar to Ks5. It is concluded that Oda is not correlated to Ks5, OgA, and Hg-7.

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