Abstract
Planktonic foraminiferal biostratigraphy is established for the late Pliocene Kuwae Formation exposed along the Tainai River, Kitakanbara district, Niigata Prefecture, central Japan. The Orbulina universa/Globorotalia ikebei Zone(PF 6) and the Neogloboquadrina pachyderma(dextral)/Globorotalia orientalis Zone(PF 7) of Maiya(1978) are recognized in the Kuwae Formation. In addition, No. 3 Globorotalia inflata bed which is characterized by the abundant occurrence of G. inflata group(G. orientalis and G. inflata praeinflata) is identified in the Kuwae Formation. The probable base of the No. 3 G. inflata bed which defines the base of the Nishiyama Stage lies between the FO(first occurrence) of Neodenticula koizumii(diatom, 3.5Ma) and RI(rapid increase) of N koizumii(3.0-3.1Ma), and is dated at about 3.4Ma by interpolation. However, it needs more data of planktonic foraminiferal analysis to confirm the base of the No. 3 G. inflata bed. Globorotalia inflata group occurs intermittently in the Kuwae Formation, suggesting intermittent inflow of relatively warm current into the Sea of Japan during late Pliocene. Systematic code numbers(PF 1-PF 9) are given to the zones of the late Cenozoic planktonic foraminiferal zonation of Maiya(1978).
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