The Geologic Development of Inland Basins in the Southern Part of the Tohoku District, Japan

In the southern part of the Tohoku District, there are many developing inland basins, which are various in scale, such as the Aizu, Inawashiro, Fukushima, Koriyama, Tajima, Tsugawa and Nozawa Basins. The generation of inland basins began at the late Miocene, and most of them appeared as a result of the formation of mountain area by the upwarping movement during late to latest Miocene. Most of them continued to exist from the latest Miocene through Pliocene, though the sedimentary areas were reduced, and they changed into hills or mountains with the uplifting movement by late Pliocene except the basin area of Aizu. At the beginning of early Pleistocene, many of the basins, which had been reduced or had once disappeared by the uplifting movement, were some what enlarged or revived again. They are represented by the palaeo-inland basins which were formed in the present basin areas such as Aizu, Fukushima, Koriyama, Tajima, Nozawa and Tsugawa. These palaeo-inland basins were uplifted and turned into hills at middle Pleistocene. However, the Aizu Basinis the only one remaining as a sedimentary basin. The Fukushima Basin has started once again as a sedimentary basin during middle Pleistocene. Both the Koriyama and the Inawashiro Basin had been buried during middle Pleistocene and early half of late Pleistocene, but changed to the terrains where the formation of terraces progressed during the late half of late Pleistocene and Holocene. Other smaller basins, such as the Tajima, Nozawa and Tsugawa Basins, consist of the assemblage of terrace surfaces formed during middle to late Pleistocene and Holocene: Among the palaeo-inland basins, which had appeared during latest Miocene, numerous ones changed to hills or mountains and disappeared step by step, and the survivors have come to be limited in scale, with the uplifting movements of the Ou-Backbone Mountain Range and the Echigo Mountain Range. Since middle Pleistocene, the only two inland basin s, the Aizu and Fukushima Basin, have survived as a sedimentary basin.