新潟県北部に発達する中新世岩船層の底棲有孔虫化石について

抄録

This paper reports on the benthonic smaller foraminifera from the Iwaf une formation, Miocene Daishima stage, in northern part of the Niigata oil fields. The Daishima stage smaller foraminifera is hardly studied in Japan.
The benthonic smaller foraminifera occurs only the dark gray shale facies of the lowest Iwafune formation. It is consisted of three faunas as follows: arenaceous, calcareous and mixed faunas. Among them the first one is the main fauna of this formation.
The foraminiferal species of these fauna is similar to that of the Nishikurosawa-lower Funakawa fauna, middle Miocene, in the oil fields of Japan; the characteristic species which indicates the definite horizon of the Daishima stage, is not to be found.
The calcareous fauna is rather similar to that of the recent lower neritic-bathyal zones in the warm water. The arenaceous fauna and the lithofacies of the lowest Iwafune formation show that most of this area was under stagnant condition in the Daishima stage.