福島県いわき市に分布する上部白亜系双葉層群足沢層産イノセラムス科二枚貝とその地質学的意義：特にチューロニアン/コニアシアン階境界付近について

抄録

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.