891. FOSSIL OSTRACODE ASSEMBLAGES FROM THE PLIOCENE SASAOKA FORMATION, AKITA CITY, JAPAN : WITH REFERENCE TO SEDIMENTOLOGICAL ASPECTS

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  • 891. 秋田市笹岡層産貝形虫化石群集 : 堆積学的側面との関連性
  • 秋田市笹岡層産貝形虫化石群集--堆積学的側面との関連性〔英文〕
  • アキタシ ササオカソウサン カイケイチュウ カセキ グンシュウ タイセキガクテ

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Two hundred sixteen species of fossil ostracodes coming under 71 genera are recognized in the Pliocene Sasaoka Formation distributed in the eastern part of Akita City, northeast Japan. In general, cryophilic species which either live today in Japan or have been reported from the Plio-Pleistocene of that region are predominant in each sample, with subordinate amounts of such circumpolar species as Acanthocythereis dunelmensis (Sars), Hemicythere emerginata (Sars), Elofsonella concinna (Jones) and Palmenella limicola (Norman). In addition to such cold water species, warm water species inhabiting sea areas under the influence of the Kuroshio current are contained in each sample, running up to a few percent of the total. Q-mode cluster analysis of ostracode occurrence data brings out four clusters of samples (A, B, C and D). The results from grain size analysis of sediments containing fossil ostracodes are compared with the size of ostracode valves, the ratio of left to right valves, the ratio of adult to total valves, species diversity and equitability, with intention of understanding these four clusters. In general, physical agents had a great influence upon the distribution of fossil ostracode assemblages in the Sasaoka Formation, thus the depositional environment is to be assessed not only on the ecological side of ostracodes but also on the sedimentological side.

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