Planktonic Foraminiferal Biostratigraphy of the Takaku and Taga Groups in the Joban Coal Field, Northeast Honshu, Japan

概要

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To settle long-standing debatable stratigraphic questions concerning the Neogene Takaku and Taga Groups distributed in the Joban coal-field, litho- and microbiostratigraphical investigations were undertaken. Since these groups are distributed in separate areas due to fault system, chronostratigraphic relations of their constituent formations have for long remained unsolved. Planktonic foraminiferal assemblages from the Takaku and Taga Groups comprise the following five biofacies; Takaku, Takahagi, Kohama-I, Kohama-II and Tenpisan. The Takaku biofacies is recognized in the Numanouchi and Shimotakaku Formations of the Takaku Group and ranges in age from late Early Miocene to early Middle Miocene. The Takahagi, Kohama-I, Kohama-II and Tenpisan biofacies are all recognized in the Taga Group : the former two are of Middle to Late Miocene and the latter two the Pliocene. This investigation reveals that the Takaku and Taga Groups are of different ages; the former is older than the latter. Deposition of the Taga Group has been considerably long lasting, ranging from middle Middle Miocene to Late Pliocene; and from geographical viewpoints, strata composing the Taga Group in the southern part are generally older than those in the northern part.
東北大学の論文
1980-03-31