Cretaceous radiolarian biostratigraphy in the yezo group, Hokkaido, Northeast Japan

Hiromichi Koyasu, Hiroshi Nishi, Reishi Takashima, Noritoshi Suzuki

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


An Aptian-Santonian radiolarian biostratigraphy was established in the Cretaceous marine sequences of the Yezo Group, Northeast Japan. Radiolarian fauna in the Yezo Group showed great diversity with 159 nassellarian and 8 spumellarian species identified in the studied sections. Based on the stratigraphic distributions of these species, 10 bioevents can be used to define the following 11 radiolarian zones in ascending order: Pseudocrolanium puga Interval Zone, Pseudodictyomitra lanceloti Interval Zone, Pseudodictyomitra lodogaensis Interval Zone, Dictyomitra communis Partial-Range Zone, Crolanium sachalinicum Interval Zone, Pseudodictyomitra pseudomacrocephala Interval Zone, Pseudodictyomitra nakasekoi Interval Zone, Dictyomitra densicostata Interval Zone, Crucella cachensis Interval Zone, Dictyomitra. formosa Interval Zone and Amphipternis sp. B Interval Zone. In addition, we identified 6 radiolarian bioevents that are useful for global correlation, and 8 bioevents that are correlative between Japan and Tethyan sections. The studied sections were analyzed for planktic foraminiferal and carbon isotope stratigraphies so that the exact stratigraphic positions of the stage boundaries could be determined in our radiolarian biostratigraphic scheme: the Albian/Cenomanian boundary occurs at the upper part of the P. pseudomacrocephala Zone, while the Cenomanian/Turonian boundary (CAE 2) occur at the top of the D. densicostata Zone. The Turonian/ Coniacian and Coniacian/Santonian boundaries place at the base and middle of the Amphipternis sp. B Zone, respectively. Although the exact horizon of the Aptian/Albian boundary in the Yezo Group is not well identified, it may be placed at the middle of the P. lanceloti Zone.

Original languageEnglish
Pages (from-to)297-319
Number of pages23
JournalNewsletters on Stratigraphy
Issue number3
Publication statusPublished - 2019 Jun


  • Cretaceous
  • Northwest Pacific
  • Radiolarian biostratigraphy
  • Yezo Group

ASJC Scopus subject areas

  • Geology
  • Stratigraphy


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