Foraminifera from the Kushiro Formation, Hokkaido
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概要
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The Kushiro formation is one of the typical lower Pleistocene formations in Hokkaido., The stratigraphy, paleontology, especially the molluscs and pollen, and the geological age of this formation have been already reported and discussed in detail (Y., Otuka, 1934; Y., Sasa, 1939)., Herein the writer reported the smaller Foraminifera derived from three foraminiferous beds of this formation, namely, the Harutori mud bed of the Basal member, the Harutori shell sand bed of the Lower sand member and the Tenneru shell bed of the Middle sand member., The sedimentary features of these beds are divided into two facies, viz., the mud facies of the Harutori mud bed which occurs as a "rhythmite", and the shell sand of the latter beds., The foraminiferal assemblages of these two facies are characterized by their own particular former., The environment of the mud facies is considered to be Euneritic to Mesoneritic fascia, and that of the sand facies to belongto the Tidal to Euneritic fascia., Comparing the assemblage of 'the Harutori slaell sand bed with that of the Tenneru shell bed, the former indicates a condition rather deeper than the latter., From a comparative study of the fossil foraminifetal assemblage of the Kushiro formation with that of the Recent one off Kushiro, the following features are recognized: 1) Species abundant and common to both assemblages are Nonion japonicum, Pseudononion Nonionella pulchella, Elphidium etigoense, Elphidium kusiroense, Buliminella elegantissima, Eponides frigidus, and Cibicides lobatulus., 2) Species characteristic in the Recent assemblage are Eggerella, advena, Flphidium incertum clavatum, Elphidiella, sibirica and Discorbis baccata, these are common species in Arctic waters., 3) Characteristic species of large frequency in the fossil assemblage of the Kusiro formation are Quinqueloculina costata, Quinqueloculina hasimotoi, Elphidium concinnum, Discopulvinulina bradyi, Dicopulvinulina, of., nitida, Discopulvinulina orbicularis and Cymbalopora bradyi; these are common warm water species whose distributions are restricted to the sea south of the southern end of Hokkaido., 4) The species can be classified into the following 5 groups, namely, species of world wide distribution, species endemic to the seas surrounding Japan, warm water species, cold water species, etc., The respective distributions are shown in Fig., 2., From the above stated reasons, the foraminiferal assemblages of the Kushiro formation are infered to have lived under influence of thermal conditions warmer than at present.,
- 一般社団法人 日本地質学会の論文
一般社団法人 日本地質学会 | 論文
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