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内容記述 |
The sample employed in this study is a piece of blue-grayish mudstone, dredged by the Hakusan-Maru on September 7, 1970, from the northwestern slope of the Yamato-tai (about 1600m in depth), in the Sea of Japan (Lat. 39°30.3' N, Long. 134°38.5' E). Various kinds of plant micro fossils such as pollen, spores, diatoms, silicoflagellates, dinoflagellates and acritarchs are found in the maceration-residua. Of them, well preserved diatoms and dinoflagellates are dominant. More than twenty species belonging to eleven genera of Dinoflagellata are identified, namely Achomosphaera hyperacantha, A. sp. a, Spiniferites bulloidea, S.mirabilis, S.ramosus, ?Cannosphaeropsis sp. b, Leptodinium sp. a, Lingulodinium machaerophorum, Operculodinium centrocarpum, Hystrichokolpoma rigaudae, Areoligera sp., Thalassiphora sp., and Tuberculodinium vancampoae. The dinoflagellate assemblage is relatively similar to those of the upper Miocene Nakayama and the lower Pliocene Kawachi formations distributing in Sado Island of Niigata Prefecture. And so this assemblage is considered to be Miocene in age. Pollen grains are also abundant, and somewhat ill-preserved. Coniferous pollen such as Abies and Pinus are extremely dominant, followed by Tsuga, Taxodiaceae and Quercus. Less common palynomorphs are Juglans, Carya, Alnus, Betula, Carpinus, Zelkova, Tilia and Liquidambar (?). Carya and Liquidambar are exotic genera, and considered to be Tertiary elements in Japan. The presence of limnetic freshwater species like Nelumbo and Nymphoides (?) is remarkable. Other NAP, i. e. Artemisia, Chenopodium and Compositae are present in very low percentages. |
NUE20_2_63-70.pdf (610.8 kB)
