浮遊性有孔虫による北海道の古第三系の地質年代 : 堆積間隙と海水準変動との関係

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タイトル別名
  • Geologic ages of the Paleogene of Hokkaido, Japan based upon planktonic foraminifera : The relationship between the hiatuses and sea-level movements
  • フユウセイ ユウコウチュウ ニ ヨル ホッカイドウ ノ コ ダイ3ケイ ノ

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抄録

Fifteen species and subspecies of planktonic foraminifera, many of which were not previously reported from the Paleogene of Hokkaido, are identified from Eocene and Oligocene formations in the Ishikari, Kushiro and Tempoku regions of Hokkaido, Japan. Planktonic foraminifera from the middle part of the Poronai Formation in the Ishikari region establish a Late Eocene age. The upper part of the Poronai Formation in the Ishikari region and the lower part of the Utsunai Formation in the Tempoku region are considered to lie within an Upper Eocene to Lower Oligocene interval based on planktonic foraminifera. In the Kushiro region, Subbotina frontosa (Subbotina) from the top of the Kawaruppu Formation and K-Ar age obtained from a coarse tuff in the middle Kawaruppu Formation indicate an Early Eocene to early-Middle Eocene age for the upper part of the formation. The joint occurrence in the Kamicharo Formation of Globorotalia opima opima Bolli and such species as Globigerina ciperoensis Bolli and Globigerinita juvenilis (Bolli) enables assignment of the fauna to the middle Oligocene G. opima opima zone of Bolli (1957). Combining these age assignments and other age data, two hiatuses spanning a considerable time period are recognized. In the Kushiro region, most of the Middle Eocene is absent and Upper Oligocene to Lower Miocene sequences are not represented in most of Hokkaido. The beginnings of these two hiatuses are closely coincidental with the two major global sea level falls which are recognized in Eocene and Oligocene intervals on the basis of recently established sea-level fluctuations along the passive margin of the world. Subsidence along the eastern margin of the Eurasian plate which resulted from an abrupt change in the direction of the movement of the Pacific plate is inferred to be one factor responsible for the creation of the "Paleo-Poronai Sea" (newly proposed name).

収録刊行物

  • 化石

    化石 34 (0), 41-49, 1983

    日本古生物学会

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