Abstract
The Miocene Yagii Formation of the Matsuyama Group in Saitama Prefecture, central Japan, is rich in plant macrofossils, and is thus important in the reconstruction of the palaeovegetation of the Miocene period. We carried out fission-track (FT) dating of zircon crystals extracted from two tuff beds in the Yagii Formation to provide a chronological framework for palaeoecological analyses. The lowermost Y-1 tuff of the Yagii Formation gave an FT age of 9.1±0.7 Ma, and the uppermost Y-9 tuff yielded an FT age of 9.6±1.3 Ma. These data suggest that the age of the Yagii Formation is Late Miocene. The age of the Yagii flora is nearest to that of the Upper Itahana flora of Gunma Prefecture, Kanto District. Both floras indicate similar lowland palaeovegetation; however, the floras are different in that the Upper Itahana flora indicates mountain slope vegetation, whereas this is not the case for the Yagii flora.
