2019 Volume 125 Issue 4 Pages 307-322
Clastic rocks in the Hida Gaien Belt, located in the Hongo area, Takayama City, Gifu Prefecture, central Japan, are subdivided into the Moribu and newly proposed Douden formations. The Moribu Formation is lithologically subdivided into three parts: a lower part consisting of mudstone intercalated with sandstone and limestone; a middle part characterized by massive, thickly bedded sandstone; and an upper part composed of alternating beds of sandstone and mudstone. The Jurassic Douden Formation consists mainly of alternating beds of sandstone, mudstone, and conglomerate.
We present new U-Pb detrital zircon ages from the sandstone beds. The youngest detrital zircon age peaks from the lower-middle and upper parts of the Moribu Formation yield detrital zircon ages of ca. 263-256 Ma and ca. 250 Ma, respectively, indicating that their maximum depositional age is middle-late Permian. The depositional age of the upper part may extend into the Early Triassic. The Douden Formation probably accumulated during the Early Jurassic, based on the youngest detrital zircon age peaks of ca. 186 Ma and 181 Ma from sandstones in the lower and upper parts, respectively. The sandstones contain abundant volcanic fragments. It is therefore probable that the zircon U-Pb ages correspond to the depositional age.
The Douden Formation can be correlated with the upper part of the Jyogodani and Kitamatadani formations in the Lower Jurassic Kuruma Group, Inugadake area, and also with the upper part of the Gamaharadani Formation, Kotakigawa area. The lithofacies and zircon age distribution in the Douden Formation are similar to those of the Jyogodani and Gamaharadani formations.
