Marker Tephra Layers Indicating the Lowest Part of the Quaternary System Found in the Moroyama Hills and Kawajima Core, Western Kanto Plain, Central Japan

Abstract

 Vitric tephra layers named Ushinosawa tephra from the Moroyama Hills in the western Kanto Plain, and KJT-380.5 tephra and KJT-384.15 tephra from the 600 m-long Kawajima core in the central part of Kanto Plain are described. Magnetic polarities suggest these tephra layers are intercalated at the lowest part of the Matuyama choronozone. Ushinosawa and KJT-380.5 tephra layers are characterized by low K₂O concentration in volcanic glass, and can be correlated with Reiho tephra of the Tokai Group in Suzuka City, Mie Prefecture. KJT-384.15 tephra is characterized by a high K₂O concentration in volcanic glass and can be correlated with newly described Onbebashi 1 and 2 tephras of the Tokai Group. These tephra layers can be considered to be wide spread marker tephras. This is the first report on widespread marker tephras just above the Gauss–Matuyama boundary in Japan. These marker tephra layers are expected to be a valuable key bed for exploring the Neogene–Quaternary boundary in various parts of Japan in the future.