<国立科博専報>青森県下北半島の鮮新 : 更新世貝形虫群集(予報)
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概要
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Uppermost 40 meters of the Hamada Formation yields abundant ostracods with very high species diversity. Most of the ostracod species are derived from tidal zone to lower sublittoral, and from rocky to sand and mud bottom habitats. Dominant members include constituents of the Omma-Manganjian fauna such as Schizocythere okhotskensis, Cytheropteron sawanense, Semicytherura subundata, S. henryhowei, Howeina camptocytheroidea, Finmarchinella spp., Palmenella limicola, Cytherre uranipponica, Loxocythere inflata, Urocythereis? gorokuensis, Ambossracon? kitanipponica, Patagonacythere robusta, Elofsonella coninna, Hemicythere spp., Robertsonites spp., Acanthocythereis dunelmensis, and Buffmicythere howei. The lower half of the sequence is dominated by cold water species, whereas in the upper half of the sequence cold temperate species of cold water origin become more abundant. Among these species is the characteristic warm water species Cythere omotenipponica which appears in sample C18. The boundary between the lower and upper sequences seems to be around the horizon of sample C20. Among these mixed assembleges of ostracods, two seemingly autochthonous ostracod associations with very low species diversity are detectable. One appears in the middle of the sequence (C22 and C24) and is characterized by the occurrence of Acanthocythereis tsurugasakensis, suggesting a deep (200-300m) water environment. The other appears at the top of the sequence (C4C, C4D and C4E) and characterized by the association of Neomonoceratina tsurugasakensis and Palmenella limicola, suggesting a muddy inner bay environment and retreating sea. Correlation of upper horizons between the Daishaka Formation and the Hamada Formation is suggestible based on combined ostracod occurrence and characteristics of intercalated tuff beds. Stratigraphic correlation and environmental analysis based on the ostracod assemblages cannot be further refined. An approach based on analysis of speciation of a certain species group seems to be far more useful even for these applied purposes.
- 国立科学博物館の論文
- 1987-12-01
著者
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