Cretaceous Radiolarian Biostratigraphy of the Urakawa and Obira Areas, Hokkaido
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概要
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The biostratigraphic distribution of Cretaceous Radiolaria in the Urakawa and Obira areas, situated in the meridional zone of Hokkaido, Japan, has been investigated and the stratigraphic range of each selected radiolarian species is determined. Employing eight radiolarian biohorizons set up on the basis of the first and last occurrences of a given species, a sequence of middle to upper Cretaceous (probably upper Albian to lowermost Campanian) strata is biostratigraphically divided into eight zones; one of which is subdivided into two subzones. These zones are named, in upward sequence, as follows : The Holocryptocanium barbui-Thanarla conica Zone, Diacanthocapsa euqanea - Thanarla elegantissima Zone, Eusyringium spinosum Zone, Dictyomitra formosa Zone (subdivided into the Eucyrtidium? matsumotoi and Archaeospongoprunum bipartitum Subzones), Squinabollum fossilis Zone, Archaeospongoprunum triplum Zone, Orbiculiforma quadrata Zone and Sponqostaurus (?) hokkaidoensis Zone. By means of the above-mentioned zones, the Urakawa sequence has been correlated with the Obira sequence. In addition, interregional correlations, that is, correlations of the proposed zones with those of previous authors (Riedel and Sanfilippo, 1974; Foreman, 1975, 1977; Dumitrica, 1975; Pessagno, 1976) are attempted. As a result of this correlation, it is confirmed that the Radiolaria is one of the most useful clues for interregional correlation of Cretaceous sediments. Additionally, comparisons of the present radiolarian zonation with those of other fossil groups (inocerami and foraminifera) are also attempted in the studied areas. It is realized that the assigned ages for Cretaceous deposits by means of zonations of different fossil groups are considerably close to one another. Ninety-six species are discriminated with the aid of both an optical and scanning electron microscopes in the present study. Of which 13 species are new to science. The chapter on systematic paleontology gives references for the hitherto known species and the description for new and indeterminate species.
- 東北大学の論文
- 1982-03-30