抄録
Recent fieldwork in the west part of Kobe City, Hyogo Prefecture, Japan resulted in the new discovery of augite-bearing mafic tuffs from the middle part of the Shirakawa Formation of the Kobe Group. A large amount of rhyolitic tuff has been well known except for three beds of mafic tuff in the Kobe Group. In the research area, the beds can be traced as a unit composed of three thin beds of ashfall origin with thickness of 15-16, 5-6 and 2-3cm and overly on paleosol. Each layer, furthermore, contains mineral fragments of augite and calcic plagioclase (An64-91). Its color is olive green and its fission-track age is determined as 32.8±2.0Ma. As a conclusion, these tuffs can be regarded as the most useful key bed in the Shirakawa Formation.
