Interregional lithostratigraphy and biostratigraphy of the Pleistocene Setana Formation, southwestern Hokkaido, Japan.

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  • 西南北海道瀬棚層の広域的岩相層序区分と生層序年代
  • セイナン ホッカイドウ セタナソウ ノ コウイキテキ ガンソウソウジョ クブン ト セイソウジョ ネンダイ

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Litho- and biostratigraphical studies have been carried out on the Pleistocene Setana Formation distributed in the Oshima Peninsula, southwestern Hokkaido. The Setana Formation is redefined and subdivided into the following six members ; Hanaishi Conglomerate, Chinkobe Sandstone, Hatakenosawa Conglomerate, Natsuji Conglomerate, Nakasato Conglomerate, and Soebetsu Sandstone. The Hanaishi Conglomerate, Natsuji Conglomerate, and Nakasato Conglomerate Members are correlated with the lower part of the Setana Formation, and the Chinkobe Sandstone, Hatakenosawa Conglomerate, and Soebetsu Sandstone to the upper part. These members yield planktonic foraminifera and calcareous nannofossils, and the fossils indicate that the lower and upper part of the Setana Formations were deposited about 1.2 to 1.0 Ma and about 1.0 to 0.6 Ma, respectively. The lower Setana Formation was deposited in shallow sea where cold-water dominated, whereas the upper part was formed in a deeper and expanded sea in which warm-water intruded periodically under the glacial eustatic sea-level controls. Biostratigraphical study reveals that the Setana Formation can be correlated with the Daishaka Formation, upper part of the Kitaura Formation, the Haizume Formation, and middle to upper parts of the Omma Formation in the Japan Sea side of the Honshu Island, as well as to the Tomikawa Formation in southwestern Hokkaido.


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