Large ammonoid shellbed and huge calcareous concretion bed in shallow-marine fine sandstone of the lower Coniacian Ashizawa Formation, Futaba Group, Northeast Japan

Omori, H., Ando, H., Muramiya, Y., Utagawa, F., Kuma, R., & Yoshida, H. (2023). Large ammonoid shellbed and huge calcareous concretion bed in shallow-marine fine sandstone of the lower Coniacian Ashizawa Formation, Futaba Group, Northeast Japan. The Journal of the Geological Society of Japan, 129(1), 105–124. https://doi.org/10.5575/geosoc.2022.0049