Pollen Stratigraphical Study of the Uonuma Group

Abstract

In the present article the authors intended to make clear the geologic age of the Chuetsu and Uonuma Groups, through the studies on the stratigraphy and the pollen floral change of these two groups. The results obtained are summerized below.1) The geology of the Chuetsu and Uonuma Groups in the western area of Tokamachi city is shown in Fig. 1.2) The results of the pollen analysis are shown in Figs. 2 and 3. The prosperity and decline of Taxodiaceae are well shown in these figures, and the floral zonation in Fig. 4 is established based on the occurrence of Taxodiaceae.3) The curve of the paleo-temperature in Fig. 4 was drawn upon the ecological data of the pollen assemblages.4) In Fig. 5, the Uonuma Group is compared with the Osaka Group which shows the most representative Quarternary succession in Japan, mainly based on the pollen floral change.5) The occurrence of the genera of Taxodiaceae is very characteristic: namely they change from (1) inferiority of Metasequoia, to (2) flourish of Metasequoia, to (3) inferiority of Metasequoia with Cryptomeria, to (4) flourish of Cryptomeria ascendingly. This phenomenon is samely seen in the Osaka Goup.6) The disappearance of the Tertiary elements and the appearance of the Quarternary elements in the Uonuma Group are earlier than in the Osaka Group.7) If we permit the presumption that the horizon of so-called Olduvai normal events is the boundary of Plio-Pleistocene, the boundary concerned in the Uonuma Group may be in the neighbourhood of Mf-3.