Discovery of Aira-Tn ash in the Oga Peninsula, Akita Prefecture, northeast Honshu, Japan

Abstract

A thin volcanic ash intercalation was found in a 0.2 to 1.4 m thick peat layer in the basal part of the sedimentary layer, provisionally named the Hakoi Formation, unconformably overlying the Katanishi Formation; this formation yielded warm, near-shore marine and brackish water fauna and flora and has been correlated with the Last Interglaciation in the glaciated regions. The carbon-14 age of fossil wood from a horizon slightly above the ash is 15 470 yr BP. These characteristics indicate that the ash is Aira-Tn ash, ejected from the Aira Caldera, southern Kyushu, the most prominent marker tephra of the Late Pleistocene in Japan. The pollen assemblage of the peat indicates a cold climate during the time of deposition of the ash. -from English summary