The best section representing the Eocene/Oligocene boundary in Japan.

Kunio Kaiho, H. Okada, Y. Takayanagi

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


The best section containing the Eocene/Oligocene boundary in Japan is a composite section exposed along the course of Kumanosawa and Yubari River in the Yubari area, central Hokkaido. The Kumanosawa section represents the upper portion of the Poronai Formation whereas the Yubari River section comprises the top level of the Poronai Formation and the conformably overlying Momijiyama Formation. The upper portion of the Poronai Formation exposed along this combined section measures 480 m in thickness and consists principally of dark-gray massive siltstone intercalated with 5 cm to 10 m thick sandy tuff layers with scattered calcareous concretions. Isthmolithus recurvus occurs in the upper part of the Poronai Fm., indicating the I. recurvus subzone (CP15b) of the latest Eocene and possibly part of subzone CP16a of the earliest Oligocene (Coccolithus subdistichus). The Momijiyama Fm. is barren of nannofossils. -from Authors

Original languageEnglish
Pages (from-to)159-160
Number of pages2
JournalUnknown Journal
Publication statusPublished - 1986 Jan 1
Externally publishedYes

ASJC Scopus subject areas

  • Environmental Science(all)
  • Earth and Planetary Sciences(all)


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