Abstract
A Late Cretaceous heteromorph ammonoid : Polyptychoceras sp. cf P. haradanum and an assemblage of fossil spores and pollen were newly discovered from a floated block along the Neohigashidani River in Neo village, Gifu Prefecture, central Japan. The block consists of dark gray mudstone, and contains a part of well-preserved Polyptychoceras shell, and pollen and spores assemblage. The fossil assemblage suggests Santonian to Early Campanian age. The mudstone block might have been derived from the Akeshidani Rhyolites (Okumino acid Igneous Complex). However, the known age of the complex, which is assigned to OK-2 (68-60 Ma), is much younger than the age suggested by the ammonoid. Alternatively, the block might have been derived from an nuknown Upper Cretaceous deposits, or from a clast in the Akeshidani Rhyolites although both hypotheses have yet been substantiated. Taking the new discovery of Santonian to Early Campanian ammonoid fossil into consideration, further research is needed to clarify the geologic history of the Mino Belt.
