The geochronology of the Pliocene-Pleistocene deposits in the Aizu Basin, which are represented by the Izumi and Nana-orizaka Formations in ascending order, is presented from the stratigraphical, palaeomagnetical and palaeobotanical view points.
Three major normal and reversed polarity sequences are confirmed by the palaeomagnetic data. The polarity sequences are correlated with the Brunhes normal, the Matsuyama reversed and the Gauss normal epochs proposed by Cox and Dalrymple (1967). Five short polarity events are also recognized, and they are correlated with the Jaramillo normal, the Gilsa normal, the Olduvai normal, the Kaena reversed and the Mammoth reversed events.
The floras from the Pliocene deposits contain the extinct species such as Metasequoia japonica, Pseudolarix kaempferi, Juglans megacinerea and Pterocarya paliurus. The floras from the early Pleistocene deposits during the age represented by the Olduvai event contain the subalpine species such as Picea maximowiczii and P. jezoensis in addition to the extinct species mentioned above. While, the floras from the early Pleistocene deposits during the age represented by the Jaramillo event are dominated by the subalpine species such as Pinus koraiensis, Picea maximowiczii, P. jezoensis and Abies veitchii, but do not contain the extinct or exotic species. Moreover, the floras dominated by the subalpine species are found again in the middle horizon of the upper part of the Nana-orizaka Formation deposited during the Brunhes normal epoch.