Palynostratigraphic Study of the Nemuro Group.

点击翻译按钮获取中文摘要

In 1989, Takahashi and Ueda collected 48 samples from the Hamanaka-Oborogawa, Akkeshi, and Tokotan Formations of the Nemuro Group in eastern Hokkaido and Takahashi examined 565 palynomorphs from 7 samples of the Akkeshi Formation around Akkeshi Bay, 768 palynomorphs from 9 samples of the Akkeshi and Tokotan Formations around Ochiishi Bay, and 36 sporomorphs from 3 samples of the Akkeshi Formation along the seaside of Choboshi. According the previous biostratigraphic data on foraminiferida, ammonoids, inoceramids nannofossils etc., the Akkeshi Formation is of Maastrichtian age the Tokotan Formation is of Danian age. Both the Akkeshi and Tokotan Formations yield many pollen grains of Triprojectacites pollen group, Callistopollenites, Wodehouseia etc. Which are a good indicator of Maastrichtian time. Microfloral change between the Akkeshi and Tokotan Formations is not so large. In 1990, Takahashi collected 11 samples of the Tokotan Formation at Konbumori, Nemuro city, examined 746 palynom … More orphs from 9 samples of it, and discriminated 176 species. This Tokotan palynoflora is compared with that of the Tokotan Formation at Ochiishi and of Maastrichtian age, too. Regarding the Kiritappu Formation which consists of predominant conglomerate beds and only some mudstone beds distributed restrictied, Takahashi found 105 palynomorphs from 4 samples at Kiritappu and 267 palynomorphs from 4 samples from Yururi Island. As a whole, he examined 137 species. The Kiritappu Formation yield 52 common species to both the Tokotan and Akkeshi Formations. Most of these common species appear for very long time. The largest essential difference of the palynomorph assemblage of the Kiritappu Formation is that Auilapollenites, Callistopollenites, Wodehousiea etc. Which appear restrictedly only in the Maastrichtian don't occur and pollen grains of the Magnoliaceae appear newly. Accordingly, it may be reasonable that the Cretaceous (Maastrichtian) /Tertiary (Danian) boundary is drawn between the Tokotan and Kiritappu Formations. Less