Late Neogene to Quaternary paleoenvironmental changes in the Akita area, Northeast Japan

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  • Sato Tokiyuki
    Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science Akita University
  • Sato Nobuaki
    Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science Akita University JX Nippon Oil & Gas Exploration Corporation
  • Yamasaki Makoto
    Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science Akita University
  • Ogawa Yuriko
    Institute of Applied Earth Sciences, Faculty of Engineering and Resource Science Akita University
  • Kaneko Mitsuyoshi
    JX Nippon Oil & Gas Exploration Corporation

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  • 石灰質ナンノ化石からみた秋田地域の新第三紀末～第四紀古環境変動
  • セッカイシツ ナンノ カセキ カラ ミタ アキタ チイキ ノ シン ダイサンキマツ~ダイシキ コ カンキョウ ヘンドウ

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We studied in detail the calcareous nannofossil biostratigraphy of the upper Pliocene to Quaternary sequences in the Osugozawa route of Gojome area, Aikawa and Komasugawa routes of the Oga peninsula, and two oil exploration wells of NKH-1 and 3 located in Honjo area, Akita Prefecture, Japan. The Pliocene/Pleistocene boundary redefined at the base of Gelasian Stage was identified in the lower part of the Sasaoka Formation in the Osugozawa route. The base of Calabrian stage, formerly considered as the Pliocene/Pleistocene boundary, was also identified in the lower part of the Kitaura Formation in the Oga Peninsula, based on magneto- and nannofossil bio-stratigraphy. Pliocene to Quaternary formations in the Akita area were correlated to those in the Japan Sea side area.<br>We also revealed the tectonic movements along the southern coast of Akita Prefecture on the basis of the nannofossils obtained from drill cuttings and the subsurface geology of the area. The results clarified that the Kita-Yuri thrust faults were active between 3.85 and 1.71 Ma. Paleodepth of western Akita Prefecture were also changed from bathyal to shallow marine environments in 2.75 Ma, a consequence of both fault activity and the climate crush associated with drastic latest Pliocene cooling.

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