Abstract
We re-examined upper Mesozoic deposits around the border between Gifu and Toyama prefectures, central Japan, to resolve controversy regarding their stratigraphy. The deposits are divided into the Tetori Group and the overlaying the Jinzu Group (new lithostratigraphic unit). The Tetori Group includes marine deposits bearing Jurassic ammonites, whereas the Jinzu Group consists of terrestrial deposits. The Tetori Group is divided into the Magawa Formation and the conformably overlying Arimine and its stratigraphic equivalent, the Kiritani Formtion. The Jinzu Group, from bottom to top, is divided into the Ioridanitoge, Inotani and Shiroiwagawa Formations. The geological map of the area is revised to show the distribution of these six formations. The Tetori Group is assigned an age of Callovian to early Kimmeridgian based on ammonites, and the Inotani Formation of Jinzu Group is assigned an age of Aptian to Albian based on zircon-fission track dating with best-fit peak ages of 102.6 (−6.1, +6.5) , 111.6 (−6.2, +6.6), 112.5 (−11.0, +11.7) and 121.0 (−12.1, +11.7) . The Jinzu Group in the Jinzu Section in the eastern part of its distribution, is suggested to be Aptian and Albian, but the Tetori Group in the Hakusan Section in the western part of its distribution is suggested to be Bathonian to Barremian. Therefore, the Jinzu and Tetori Groups were probably deposited at different times.
