The identification of the fall-units of the Tokyo pumice bed by chemical composition of ferromagnetic minerals.

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.