Foraminifera of the Eocene Shitakara Formation in eastern Hokkaido, with the designation of neotype specimens of Yoshida (1957)

Abstract

Forty-three species belonging to thirty-seven genera of benthic foraminifera were differentiated from the Eocene Shitakara Formation in the eastern part of the Kushiro Coalfield, eastern Hokkaido. The foraminiferal assemblages show upward transgression from the inner to outer sublittoral condition. They contain abundant agglutinated and calcareous hyaline benthic species, including Labrospira crassiformis, Haplophragmoides subamakusaensis, and Cribroelphidium sorachiense, indicating similarity to the Eocene fauna in central Hokkaido. Two planktonic species Chiloguembelina ototara and Tenuitella insolita also indicate a late Eocene age. Neotype specimens of Cyclammina pacifica var. kushiroensis, Nonion kushiroense, and Nonion sorachiense var. konbumoriense described by Yoshida (1957) have been designated as replacements for holotype specimens that were lost in a fire in May 1965. A taxonomical reexamination based on the neotypes and topotypes indicates that Cyclammina pacifica var. kushiroensis is a distinct species, whereas Nonion kushiroense and Nonion sorachiense var. konbumoriense are junior synonyms of Cribroelphidium sorachiense (Asano 1954). All foraminiferal taxa are illustrated with taxonomical notes.