Abstract
Diatom and calcareous nannofossil biostratigraphy was established for the PlioceneKuwae Formation along the Natsui stratigraphic section, Tainai River, Kitakanbara area in NiigataPrefecture, central Japan. Three useful diatom biohorizons, the FO (first occurrence) ofNeodenticula koizumii; RI (rapid increase) of N. koizumii and LO (last occurrence) of Neodenticulakamtschatica along with calcareous nannofossil datum A defined by Sato and Kameo (1996) wereidentified in the formation, which established a precise chronologic framework of the Natsuisection. Fresh water diatom fossils and reworked Miocene diatom valves occurred throughoutthe section and the proportion of these taxa fluctuates in a frequency of several tens ofthousands years. Sporadic occurrences of warm water diatoms such as Hemidiscus cuneiformis, Nitzschia reinholdii and Rhizosolenia bergonii were recognized at several horizons. Among these, theoccurrence at the horizon just above the FO of N. koizumii was found both in the present sectionand in the Yabuta Formation in the Himi area, which suggests its probable correlation.
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