Abstract
The Plio-Pleistocene strata in Japan is typified by the marine Kazusa group in Kanto district and the aqueous Osaka group in Kinki district. On these groups, numerous studies of stratigraphy, paleontology, paleomaganetism, and so on, were reported, and the Plio-Pleistocene boundary was discussed from several view points. The pollen flora of the Kazusa group along the Yoro river was investigated by the writer and the results are summerized as follows. 1) There are two steps in the disappearance of the Pinus trifolia flora; a) Keteleeria and Pseudolarix? become extinct at the middle part of the Umegase formation (between U6 and U10), and b) Metasequoia and Picea A, at the middle of the Kokumoto formation. 2) By the sequence of the disappearance of the Pinus trifolis flora and the pollen composition, the Kazusa group is divided into six zones. 3) The correlation of the pollen zone of the Kazusa group and the Plio-Pleistocene flora in Kinki district may be shown as follows; Zone 1...Pinus trifolia flora and Transitional flora 1 Lower half of Zone 2...Transitional flora 2 Upper half of zone 2 and Zone 3...Metasequoia flora Zone 4 ...Paliurus nipponicus flora and 4) The Plio-Pleistocene boundary, as defined in the Osaka group, should be drown between U6 and U10.
