Abstract
The Upper Pliocene Nakatsu Group along the Sagami River, in Sagamihara and Atsugi Cities and Aikawa Town in Kanagawa Prefecture, has been mainly studied by some palaeontologists as part of their research on molluscan fossils. The Nakatsu Group has been lithologically divided into the Kosawa, Kanzawa, Shimizu, Otsuka, and Shiota Formations in ascending order. The Otsuka and Shiota Formations intercalate many tephra layers; however, detailed stratigraphic study using these tephra layers has never been done. The Mk 19 tephra layer, interbedded in the Otsuka Formation, is composed of Ta, Tb type glass shards, plagioclase, quartz, garnet, amphibole, biotite, and opaque minerals. The garnet is an almandine-spessartine solid solution. The combination of Mk 19 and the Mk 20, abundant in quartz, is useful for correlation in this region.
