Stratigraphy and sedimentary basin developments of the Tetori Group in its main area, central Japan

Late Mesozoic nonmarine deposits are distributed widely on the eastern Asian continent and bear various kind of fossils such as dinosaurs, amphibians, reptiles, fishes, mammals, bivalves, gastropods, insects, ostracods, conchostracans, terrestrial plants and others. Biostratigraphic resolution of these non-marine species as chronological indices is a moot problem which, to be answered adequately, requires thorough paleoecological and paleoenvironmental analysis. The Tetori Group is one of the main late Mesozoic terrestrial deposits in East Asia, and bears common taxa in the area. Hitherto, regional formation names of the Tetori Group were given separately for sequences in the Shokawa, Oshirakawa, Shiramine and Takinamigawa areas of the greater Mount Hakusan region that is a main area of exposure for the group. Based on geological correlation among these areas, the group consists of a coherent stratigraphic section throughout the whole area. Therefore, the group is divided into seven formations, the Ushimaru. Mitarai, Otaniyama, Kuwajima/Okurodani, Amagodani, Okura and Bessandani in ascending order. The geological map of the area is then revised to show the distribution of these formations. This means the discussion and evaluation of zoo and phyto fossil assemblages as chronological and ecological are indices are possible in the corrected stratigraphic framework. Thus, the westward-shifting of the Tetori basin is much more easily interpreted by thickness and paleoenvironmental analysis of the Tetori Group sequences.