2023 Volume 132 Issue 6 Pages 483-503
Two previously described tephras are correlated with tephra layers at several areas in the Kanto Plain, including the Sayama Hills, beneath the Musashino Uplands and the Tama Hills in western part of the plain, the Choshi district, the Boso Peninsula, and the northern part of the Miura Peninsula, defining them as SYG-Kd29 and Ob3-Kd31B. The eruption ages for SYG-Kd29 and Ob3-Kd31B are precisely determined from a chronological framework composed of biostratigraphy, magneto-stratigraphy, and oxygen isotope stratigraphy, with estimations of 1.634 Ma (around the peak of MIS 57) and 1.664 Ma (transition from MIS 59 to 58), respectively. Major and minor elemental compositions of volcanic glass shards suggest the source volcano of SYG-Kd29 is located in the northern Honshu to Hokkaido area. On the other hand, major elemental compositions of volcanic glass shards in Ob3-Kd31B suggest that its source is located in the central Japanese Islands or the Izu-Bonin Arc. The paleogeography of the southern part of the Kanto Plain around the deposit of SYG-Kd29 is as follows: alternating shallow marine and fluvial environments caused by glacial eustasy in and around the westernmost part of the Musashino Uplands and the Sayama Hills, oceanic and bathyal environment in the central part of the Tama Hills and the northern part of the Miura Peninsula with a depth of > 200 m, and abyssal environment from the Choshi district to the Boso Peninsula with a depth of > 1,500 m.
