Discovery of mid-Cretaceous ammonoids from the Aridagawa area, Wakayama, southwest Japan

Abstract

Mid-Cretaceous ammonoid assemblages are newly identified from four localities in the Aridagawa area, Wakayama, southwest Japan. They consist of Middle to Upper Albian ammonoids such as Desmoceras (Pseudouhligella) dawsoni shikokuense, Puzosia subcorbarica, Mojsisoviczia sp., Oxytropidoceras sp., Mortoniceras sp., etc., and Mantelliceras japonicum, which indicates the Lower Cenomanian stage. The Albian ammonoids were found for the first time from the Chichibu Belt of Kii Peninsula. The discovery of these ammonoids indicates a considerably wide distribution of the mid-Cretaceous deposits in the Aridagawa area, and the necessity of a large revision of the previous stratigraphic division of the Cretaceous strata in the area. The mid-Cretaceous deposits in the Aridagawa area and their abundant molluscan fossils are important for reconstruction of the mid-Cretaceous paleoenvironment and tectonics in the eastern margin of Asia.