沖縄本島勝連半島沖の島々に分布する知念層および琉球層群の層序

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  • Stratigraphy of the Chinen Formation and the Ryukyu Group on islands off Katsuren Peninsula, Okinawa-jima, Ryukyu Islands, Japan.
  • オキナワ ホントウカツレン ハントウオキ ノ シマジマ ニ ブンプ スル チ ネンソウ オヨビ リュウキュウソウグン ノ ソウ ジョ

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The Pleistocene Ryukyu Group composed of reef complex deposits crops out on six islands off Katsuren Peninsula, Okinawa-jima, Ryukyu Islands, southwestern Japan. It conformably overlies Plio-Pleistocene sandy limestone and calcareous mudstone of the Chinen Formation containing abundant bioclasts and rests unconformably on Pliocene siltstone of the Shimajiri Group. We propose a major revision of the previous stratigraphic scheme for the Ryukyu Group and provide a formal stratigraphic description. The Ryukyu Group comprises the Yokatsu and Minatogawa Formations, in ascending order, on these islands. The Yokatsu Formation constitutes the main body of the group exceeding 30m in thickness and is exposed at elevations up to 125m. It is divisible into five units. Each unit comprises coral limestone and overlying rhodolith, Cycloclypeus-Operculina, and detrital limestones, showing a deepening-upward sequence. The Minatogawa Formation rests unconformably on the Yokatsu Formation, reaches 30m in thickness, and consists of well-sorted detrital and coral limestones that are thought to have been deposited in a shallow lagoon (moat);its surface exposure is confined to the areas at elevations less than ca. 40m in Ikei-jima and Tsuken-jima. Geologic ages of the limestones on these islands are unknown at this time.

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  • 地質学雑誌

    地質学雑誌 108 (5), 318-335, 2002

    一般社団法人 日本地質学会

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