Correlation of the Hakkoda–Kokumoto Tephra, a widespread Middle Pleistocene tephra erupted from the Hakkoda Caldera, northeast Japan |
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| Authors: | Takehiko Suzuki Dennis Eden Toru Danhara and Osamu Fujiwara |
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| Institution: | Department of Geography, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji, Tokyo 192-0397, Japan (email: );, Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand,;Kyoto Fission-Track Co., Ltd, 44-4 Minamitajiri-cho Omiya Kita-ku, Kyoto 603-8832, Japan and;Tono Geoscience Center, Japan Nuclear Cycle Development Institute, 959-31 Jorinji, Izumi-Cho, Toki 509-5102, Japan |
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| Abstract: | Abstract A Middle Pleistocene widespread tephra referred to here as Hakkoda–Kokumoto Tephra (Hkd–Ku) has been newly recognized. Hkd–Ku, derived from the Hakkoda Caldera located in northernmost Honshu Is. of northeast Japan, covers much of Honshu Is. At the type locality in the proximal area, Hkd–Ku comprises Plinian pumice deposits and an immediately overlying ignimbrite. The fine vitric ash nature of the distal ash‐fall deposits of Hkd–Ku suggests that they are coignimbrite ash‐fall deposits. Hkd–Ku was identified using a combination of refractive indices and chemical compositions of major, trace and rare earth elements of glass shards, heavy mineral content, refractive indices of orthopyroxene and paleomagnetic polarity. On the basis of these properties, Hkd–Ku was identified in Oga and Boso Peninsulas and Osaka Plain, 830 km southwest of the source. Stratigraphic positions in Boso Peninsula and Osaka Plain within marine sediments that have a reliable chronology based on oxygen‐isotope, and litho‐, bio‐, magneto‐ and tephrostratigraphy indicate that the age of Hkd–Ku is ca 760 ka, positioned in the transition between marine oxygen‐isotope stages 19.1 and 18.4. The widespread occurrence of Hkd–Ku providing a tie line between many different Pleistocene sections over a distance of 800 km is a key marker horizon in the early part of the Middle Pleistocene. This tephra gives a time control point of ca 760 ka to marine sediments in the Oga Peninsula – where no datum plane exists between the Brunhes–Matuyama chron boundary and oxygen‐isotope stage 12 – and to the volcanostratigraphy of the Hakkoda Caldera. The distribution of Hkd–Ku showing emplacement of coignimbrite ash‐fall deposits in the area 830 km southwest of the source emphasizes the upwind transport direction, relative to the prevailing westerly winds, typical of other coignimbrite ash‐fall deposits in the Japanese islands. |
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| Keywords: | coignimbrite ash-fall deposits Hakkoda Caldera Hakkoda–Kokumoto Tephra ignimbrite Middle Pleistocene northeast Japan widespread tephra |
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