Newly discovered Late Cretaceous molluscan fossils and inferred K/T boundary in the Nemuro Group, eastern Hokkaido, northern Japan

Abstract

Pachydiscus flexuosus, Tetragonites popetensis, Spheonoceramus hetonaianus, and other molluscan fossils are newly discovered from the Senpohshi, Hamanaka and middle Akkeshi formations, Nemuro Group, eastern Hokkaido, Japan. They are stage index fossils of Lower Maastrichtian. According to calcareous nannofossil biostratigraphy suggesting that the upper Akkeshi Formation is Paleocene in age, the K/T boundary in the Nemuro Group is possibly intercalated between the middle and upper Akkeshi Formation.