Correlation of the Izaku Pyroclastic Flow Deposit in Kagoshima Prefecture with tuff bed intercalated in the Miyazaki Group : the eruption age of the Izaku-Hisamine tephra based on integrated stratigraphy of the Miyazaki Group and it significance

Abstract

The Izaku Pyroclastic-Flow Deposit in Kagoshima Prefecture was found to be correlated with the Hisamine Tuff(HST-4 tuff bed) in the upper part of the Miyazaki Group, on the basis of their petrographic features and paleomagnetism. The HST-4 tuff bed is a co-ignimbrite ash-fall deposit along with the Izaku pyroclastic flow eruption because it mainly consists of bubble wall type glass shards. Therefore, we propose to call these deposits the Izaku-Hisamine Tephra. Magneto- and planktic foraminiferal bio-stratigraphy of the upper part of the Miyazaki Group revealed that the HST-4 tuff bed occurs at the lowest part of a reversed MMR-B magnetic zone corresponding to Chron 2An.2 r of geomagnetic polarity time scale. Therefore, the eruption age of the Izaku Pyroclastic Flow is estimated to be 3.3 Ma.