Abstract
We discuss the uppermost Cenozoic calcareous nannofossil biostratigraphy of two hot spring wells (Toshimaen and Tokyo-dome) located in central part of Tokyo. The lithology of the upper Pliocene to lower Pleistocene is mainly composed of silty sandstone to sandy siltstone, pumiceous tuff, and siltstone which are correlated to the Kazusa Group in the Boso Peninsula.
Calcareous nannofossil assemblages of the Tokyo-dome well are characterized by abundant occurrences of Reticulofenestra spp. (small form). Discoaster spp., which indicates the early to late Pliocene age, and the early Pliocene marker species Reticulofenestra pseudoumbilicus are found in the lower part of the section. Four early Pleistocene nannofossil datums between 1.73 Ma and 1.21 Ma are traceable to the lower part of the section. Nannofossil assemblages found in the Toshimaen well are dominated by the latest Pliocene to early Pleistocene species. Four Quaternary nannofossil datums which are recognized in the Tokyo-dome well are also detected in the lower part of the sequence. This indicates that the Quaternary sequences found in both wells clearly correlate to the lower Pleistocene Kiwada Formation of the Boso peninsula. The middle to upper Pleistocene marine sequence above the Kiwada Formation was not detected in these wells.
