We describe in detail the calcareous nannofossil biostratigraphy of the Miocene formations distributed in Hokuriku to northern Japan. Helicosphgaera ampliaperta which indicates NN4 zone in early Miocene, is found in the Turikake, Tanosawa, Sunakobuchi, Kurosedani, Higashi-Innai and Kokozura Formations. The boundary between NN4/NN5 Zone is also traceable to the lower part of the Higashibessho and in the Sunakobuchi Formations. Although the Formations correlated to NN4 Zone are widely found in the Japan Sea side area, Sphenolithus belemnos, early Miocene marker species of NN3, is not found in these area. This indicates that the oldest marine sediments found in the Japan Sea side area are correlated to the interval between 14.91Ma and 17.71Ma.
北陸～北日本に分布する中新統石灰質ナンノ化石層序
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