ABSTRACT

Samples of the Tokyo pumice bed were collected from 13 localities. Ferromagnetic minerals contained in the samples were all identified as titanomagnetite by X-ray diffraction method. TiO₂ and V₂O₃ contents of titanomagnetite provide information useful for identifying each fall-unit of the Tokyo pumice bed. The bed at the reference outcrop was divided in 10 fall-units on the basis of visual observation of stratified structure and chemical composition of titanomagnetite. The presence of two additional fall-units was also confirmed by comparative study of samples from different localities. The area covered by a given fall-unit was bounded by using TiO₂ content of titanomagnetite separated from each sample.