本州北部,津軽盆地の鮮新世--更新世貝形虫〔英文〕
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This paper presents palaeoecological and systematic studies of ostracodes from the Plio-Pleistocene Daishaka Formation in the northeastern part of the Tsugaru Basin, North Honshu, Japan. Based on the analysis of molluscan fossils, most sediments of the Daishaka Formation are thought to be deposited in the sublittoral zone. Ostracodes from the Daishaka Formation are also mostly sublittoral sand inhabitants and are grouped into two assemblages -the upper and lower sublittoral sand assemblages. The ostracode species consist mainly of two different species groups as regards their geographical distribution. One group is composed of fossil and Recent species reported from Japan and its adjacent seas, and the other group includes species living in the cold, shallow-water area of the North Pacific, the North Atlantic and the Arctic Sea, associated with species related to these cold water forms. The ostracode fauna from the Daishaka Formation is peculiar in its richness of these circumpolar species when compared with other late Cenozoic faunas in Japan.One hundred and fifty two species of ostracodes have been identified. Among them, twenty-two species are described as new; they are, Pectocythere daishakaensis, Cluthia japonica, Paijenborchella hanaii, P. tsurugasakensis, Normanicythere japonica, Urocythereis? abei, U.? posterocostata, Ambostracon kitanipponica, Patagonacythere robusta, Finmarchinella (Finmarchinella) rectangulata, F. (Barentsovia) daishakaensis, Cornucoguimba alata, Acanthocythereis tsurugasakensis, Murrayina japonica, Buntonia hayamii, Robertsonites hanaii, R. tsugaruana, Semicytherura? daishakaensis, Cytheropteron yajimai, C. tsugaruense, Kangarina yamaguchii, and Loxoconcha (Loxoconcha) ozawai. One species, Robertsonites reticuliforma (Ishizaki. 1966), is redescribed. The following seven genera are reported for the first time from Japan : Cluthia (Leptocytheridae), Elofsonella, Normanicythere, Patagonacythere (Hemicytheridae), Murrayina, Celtia (Trachyleberididae) and Typholocythere (Cytheruridae).
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