Abstract
Planktonic foraminiferal biostratigraphy has been used as one of the popular tools for correlating marine strata, especially in the tropical to subtropical region. However, it is difficult to correlate marine strata in and around Japan with those of the tropical to subtropical zones because of the sporadical occurrences of tropical to subtropical species. Only few biohorizons available for Japanese Miocene strata have been reported. A planktonic foraminiferal biostratigraphy for Japanese marine strata based on age-diagnostic species of middle latitudes is prerequisite to be established.The middle to upper Miocene Arakawa Group distributed in the Karasuyama area, central Japan yields abundant marine microfossils and is intercalated by many tuff layers. A planktonic foraminiferal biostratigraphy was examined from the upper part of the Kobana through the Ogane Formations of the Arakawa Group, which has been dated to yield K-Ar dates of 12.6 to 11.3 Ma.The studied sequence is correlated with the planktonic foraminiferal zones N. 12 to N. 14 of Blow (1969). Eleven planktonic foraminiferal biohorizons were recognized and a numerical age for each biohorizon is applied on the basis of those K-Ar dates. Diachroneities are suggested on some of these biohorizons based on a correlation between this section and other sections in Japan.
