Abstract
Undated terrigenous strata distributed in northeastern Toyama Prefecture, central Japan, have been correlated with the Middle Jurassic to Lower Cretaceous Tetori Group, based solely on lithological criteria. Within the sequence in Toyama Prefecture, the Kurobishiyama Formation conformably overlies the Mizukamidani Formation, and the Uchiyama Formation unconformably overlies the Kurobishiyama Formation. The Shiritakayama and Uchiyama Formations, which are composed of different facies of the same age, are also conformably overlain by the Oyashirazu Formation.
The U-Pb ages of zircons in these strata and in dacite dikes intruding the strata constrain the depositional ages of the formations. Based on the youngest U-Pb age of detrital zircons from the Mizukamidani Formation of ca. 123 Ma, and the U-Pb ages of zircons from a dacite dike intruding the Mizukamidani and Kurobishiyama formations of ca. 109 Ma, the Mizukamidani and Kurobishiyama formations are considered to be of Aptian age (126.3-113.0 Ma). The Mizukamidani and Kurobishiyama Formations are correlated with the Nochino and Bessandani Formations, which are the uppermost horizons of the Tetori Group, western Hokuriku District. The Shiritakayama and Uchiyama Formations are younger than the Tetori Group, as the youngest detrital zircons in these strata yield U-Pb ages of ca. 110 Ma.
