Upper Albian to Lower Cenomanian biostratigraphy in the Oyubari area, Hokkaido, Japan: toward a Cretaceous biochronology for the North Pacific

An integrated planktonic foraminifer and ammonoid biostratigraphy for the Oyubari area, Hokkaido, Japan, provides new insights into the late Albian to early Cenomanian biochronology of the North Pacific province. The following foraminifers extend Tethyan zonation to the Oyubari area: Biticinella breggiensis (lower Upper Albian), Rotalipora subticinensis - Rotalipora ticinensis (middle Upper Albian), Rotalipora appenninica (upper Upper Albian), and Rotalipora globotruncanoides (Lower Cenomanian) zones. Co-occurring age-indicative ammonoids such as Mortoniceras rostratum, Mariella bergeri, and Mantelliceras saxbii, are in accord with these foraminifer ages. The base of the Cenomanian stage in Hokkaido is recognized as the first occurrence of Rotalipora globotruncanoides, which is close to the horizon of the occurrence of Mantelliceras. The first occurrence of Desmoceras (Pseudouhligella) japonicum, regarded as a Cenomanian marker species in the North Pacific province, is of latest Albian age in the global biochronological scale.