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2 Acta Geologica Polonica

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A revised inoceramid biozonation for the Upper Cretaceous based on high-resolution carbon isotope stratigraphy in northwestern Hokkaido, Japan

Hayakawa T., Hirano H.

Acta Geologica Polonica

2013

Vol. 63, no. 2

239--263

Biostratigraphic correlations of inoceramid bivalves between the North Pacific and Euramerican provinces have been difficult because the inoceramid biostratigraphy of the Japanese strata has been based on endemic species of the northwest Pacific. In this study, carbon stable isotope fluctuations of terrestrial organic matter are assembled for the Upper Cretaceous Yezo Group in the Haboro and Obira areas, Hokkaido, Japan, in order to revise the chronology of the inoceramid biozonation in Japan. The carbon isotope curves are correlated with those of marine carbonates in English and German sections with the aid of age-diagnostic taxa. According to the correlations of the carbon isotope curves, 11 isotope events are recognised in the sections studied. As a result of these correlations, the chronology of the inoceramid biozones of the Northwest Pacific has been considerably revised. The revised inoceramid biozones suggest that the timing of the origination and extinction of the inoceramids in the North Pacific biotic province is different from the stage/substage boundaries defined by inoceramids, as used in Europe and North America.

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

Kawabe F.

Acta Geologica Polonica

2003

Vol. 53, nr 2

81-91

An integrated planktonic foraminifer and ammonoid biostratigraphy for the Oyubari area, 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-occuring 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 (Pseudohligella) japonicum, regarded as a Cenomanian marker species in the North Pacific province, is of latest Albian age in the global biochronological scale.