東北地方の非海成鮮新 : 更新統の層序と対比 [in Japanese] Stratigraphy and Correlation of the non-marine Pliocene-Pleistocene in Northeast Honshu, Japan [in Japanese]
Access this Article
Search this Article
In the Northeast Honshu, many inland basins are distributed in a parallel direetion with the island arc. The Pliocene-Pleistocene of these basins are generally characterized by the existence of non-marine sedmients containing the considerable amount of volcanic products. In the Aizu Basin, one of the inland basin of the southern part of the Northeast Honshu, the Uppermost Miocene and Pliocene-Pleistocene Yamato Group is widely developed. Its total thickness attains more than 1000 meters, and it consists mainly of terrestrial sediments such as poorly consolidated fluvial and lacustrine deposits containing the volcanic products and lignite seams. The Yamato Group is subdivided in to the Fujitoge, Izumi, Nanaorezaka and Todera Formations, in aseending order. Eaeh of these formations has yielded abundant plant fossils. By the detailed examination of the stratigraphic distribution of characteristic species, eight floral assemblage zones have been established. Paleomagnetic studies of these formations and radiometric datings of some volcanic products were also performed. Four magneto zones were discriminated in the Yamato Group, and the correlation of these magneto zones with the standard polarity time scale was attempted. AZ-B reversed polarity zone which coincides with the Nanaorezaka and the upper half of Izumi Formation is correlated with the Matuyama reversed chron, and AZ-A normal polarity zone which is coincident with the Todera Formation is also correlated with the Brunhes normal chron. On the other hand, the Fukushima Basin has been developed along the middle course of the Abukuma River. The Lower Pleistocene Shimizumachi Formation and the Middle Pleistocene Takada Formation are distributed in the hilly lands along the southern and northwestern margins of the basin, respectively. These formations are unconformable with the underlying Neogene system and its basement rocks. The plant fossil assemblage of the Shimizumachi Formation is correlative with the Ootezawa flora from the lower part of Nanaorezaka Formation. The reversed polarity zone of the formation is therefore correlated with the later half of Matuyama chron. On the basis of the combined magneto- and biostratigraphic studies, the correlation of the Pliocene-Pleistocene of these inland basins including the Shinjo Basin have been made. In the correlation between the paleomagnetic polarity chrons and the Pliocene-Pleistocene series of these basins, the Olduvai subzone have been recognized in the Nanaorezaka Formation of the Aizu Basin, in the Shimizumachi Formation of the Fukushima Basin and the Dokuzawa Formation of the Shinjo Basin.
地質学論集 (30), 39-50, 1988