Abstract
Most of the present Japanese micropaleontologists consider that the Orbulina surface of Japan lies within the Lower Miocene Saigo Formation of the Kakegawa region. However, it is reascertained by the writer that Orbulina appears first in the unconformably overlying Upper Miocene Sagara Group. The Orbulina surface of this region should be placed in the stratigraphic break between the Saigo and Sagara. In the Takasaki region, the writer finds that Orbulina first occurs in the uppermost part of the Fukushima Formation (Globigerinatella insueta Zone).
Based on the revision of the previous planktonic foraminiferal zones of the Takasaki region, the writer gives some remarks on the zonation of the Lower-Middle Miocene of Japan as follows: (1) the main part of the type section of SAITO's Globorotalia fohsi barisanensis Zone is included in the Globigerinatella insueta Zone and its uppermost part in the Globorotalia fohsi peripheroronda Zone, (2) SAITO's Globorotalia fohsi fohsi (sensu BOLLI) Zone is correlated with the interval from the Globorotalia fohsi fohsi Zone to Globorotalia fohsi robusta Zone of the tropical region (Zones N.10 to N.12), (3) the writer here proposes the Globorotalia mayeri Zone above this zone.
