Identification of three Early Pleistocene tephras in and around the west part of the Musashino Upland, Tokyo, Northeast Japan

In and around the west part of the Musashino Upland, southwest of the Kanto Tectonic Basin, Ob4b-4 (1.62 Ma), Ob4b-1 (1.63 Ma), and Ob3 (1.71-1.78 Ma) tephras in the Kazusa Group, early Quaternary strata, were identified by using characteristic properties such as chemical composition of volcanic glass shards and titanomagnetite, and refractive indices of glass shards, hornblende, cummingtonite, and orthopyroxene. Changes in altitudes of Ob4b-1 identified in four cores and at three outcrops together with those by previous studies indicate geological structure of the Kazusa Group, revealing a gentle northeastward sloping with a gradient of 15/1000 and a prominent discontinuity of the strata along the Tachikawa Fault Zone

Identification of Early Pleistocene tephras in the Fuchu core, Musashino Uplands, Tokyo

Three widespread Early Pleistocene tephras were identified in a sediment core drilled at Fuchu in the central part of the Musashino Uplands of the West Kanto Plain, the central Japanese Islands. Characteristic properties such as geochemical composition and refractive indices of glass shards correlate these unknown tephras to three well-characterized tephras formed by calderaforming eruptions. Ebs-Fkd (1.70 Ma), Nyg (1.75 Ma) and Sgn-Kd44 (2.0-1.8 Ma) tephras, all inthe Kazusa Group, early Quaternary strata, are compared to Fuchu core samples and other boring cores from the Musashino Uplands area. Changes in altitudes of those tephras found in other cores under the upland reveal changes to the Kazusa Group’s sedimentary environment and landform at the time of the tephra’s deposition