Inoceramid bivalves from the Ashizawa Formation of the Futaba Group (Upper Cretaceous) in the Iwaki area, Fukushima Prefecture, Northeast Japan and their geological implications: especially the Turonian-Coniacian stage boundary

Abstract

The Ashizawa Formation of the Futaba Group in the Iwaki area, northeast Japan, is considered to be early to middle Coniacian in age. Three inoceramid species, Mytiloides incertus (Jimbo, 1894), Cremnoceramus waltersdorfensis waltersdorfensis (Andert, 1911), and “Cremnoceramus rotundatus” (sensu Matsumoto and Noda, 1985), have been newly discovered in this formation. These fossils are indicative of a late Turonian age, and thus deposition of the Futaba Group probably started earlier than previously thought.