Palynologic study of the Akkeshi and Tokotan Formations of the Nemuro Group, eastern Hokkaido

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The author has carried out the palynological study of the Akkeshi and Tokotan Formations of the Nemuro Group which is distributed in the coastal regions between Kushiro and Nemuro and consists of Campanian, Maastrichtian, and Danian marine sediments. He has collected 48 samples from the Hamanaka-Oborogawa, Akkeshi, and Tokotan Formations and discriminated 311 palynomorphs which are composed of 121 spores, 55 gymnospermous pollen, and 135 angiospermous pollen, excepting phytomicroplankton. He describes and illustrates minutely these spores and pollen grains in this paper and discusses on the Cretaceous/Tertiary boundary problem from the palynologic angle. The following forms are new : Biretisporites triangulatus n. sp., B. yoshimotoi n. sp., Pterisisporites hokkaidoensis n. sp., P. ochiishiensis n. sp., P. rotundus n. sp., P. verrucatus n. sp., Punctatisporites minor n. sp., Retitriletes borealis n. sp., R. nemuroensis n. sp., R. triangulatus n. sp., Saxosporis minor n. sp., Triplanosporites quadrangulatus n. sp., Undulatisporites subtriangulatus n. sp., Extrapunctatosporis micropunctatus n. sp., Laevigatosporites bellulus n. sp., L. convexus n. sp., L. tenuis n. sp., L. uedae n. sp., Latosporites subrotundus n. sp., Alisporites hokkaidoensis n. sp., Cupressacites ochiishiwanensis n. sp., Cycadopites laevis n. sp., Ephedripites (Ephedripites) angustus n. sp., E. (E.) robustus n. sp., Piceapollis minutus n. sp., Rossipollis minor n. sp., Aguilapollenites nemuroensis n. sp., Pentapollenites minus n. sp., Periscarioipollis rarus n. sp., Subtriporopollenites minor n. sp., Tricolpites hokkaidoanus n. sp., T. intrabaculatus n. sp., Tricolpopollenites akkeshiensis n. sp., T. oblongus n. sp., T. punctatus n. sp., T. rotundulus n. sp., and Triporopollenites suzukii n. sp. Moreover, new combinations are proposed: Baculatisporites cf. dubius Burger n. comb., B. wellmanii Couper n. comb., Cicatricosisporites minutaestriatus Bolkhovitina n. comb., and Murospora circulata Weyland & Krieger n. comb. Among the trilete spores,Baculatisporites (Osmundaceae ), Biretisporites, Deltoidospora, Leiotriletes (Schizaeaceae etc.), Monoleiotriletes, Pterisisporites (Pteridaceae), Retitriletes (Lycopodiaceae), Stereisporites (Sphagnaceae), and Triplanosporites (Schizaeaceae) appear predominantly. Among the monolete spores, Extrapunctatosporis (Athyriaceae) and Leavigatosporites (Polypodiaceae) occur abundantly. Of the gymnospermous pollen grains the following grains occur frequently: Cupressacites (Cupressaceae), Cycadopites (Cycadaceae), Ephedripites (Ephedraceae), Inaperturopollenites (Taxodiaceae etc.), Phyllocladidites (Phyllocladus), Pityosporites (Pinaceae), and Psophosphaera (Larix or Pseudotsuga). The angiospermous pollen assemblages include the Aguilapollenites (Triprojectacites) pollen group, oculata pollen grains, and some other pollen grains which are very important for age determination. In conclusion these pollen grains and a number of spores from the Akkeshi and Tokotan Formations indicate consistently Maastrichtian time, notwithstanding in the Tokotan Formation angiospermous pollen grains increase more in number and kind than in the Akkeshi Formation and the grains of the Aquilapollenites (Triprojectacites) pollen group decrease conversely. After all, the author could find no evidence supporting Danian time from the palynologic standpoint, whereas nannofossils of the uppermost Akkeshi Formation and the Tokotan Formation indicate the middle to late Danian time.
〔長崎大学教養部〕の論文

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高橋清
長崎大学名誉教授(元教養部長)

Palynologic study of the Akkeshi and Tokotan Formations of the Nemuro Group, eastern Hokkaido

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