西黒沢階の上限について  [in Japanese] On the top of the Nishikurosawa Stage  [in Japanese]

The top of the Nishikurosawa Stage is defined by the top of the Denticulopsis hustedtii Zone (Crucidenticula nicobarica Zone) or the base of the Denticulopsis praedimorpha Zone of diatom zonation, the top of the Globorotalia peripheroacutal/Globorotalia miozea (s.l.) Zone (the lower part of N. 11 Zone) of planktonic foraminiferal zonation, the top of the Diphyes latiusculum Zone of dinoflagellate cyst, and the CN5a Zone of calcareous nannoplankton zonation. The boundary between the Nishikurosawa and Onnagawa Stages is represented by the boundary between sandstone and the alternation of diatomaceous mudstone and siliceous mudstone of the Nishikurosawa Formation and massive diatomaceous mudstone of the Onnagawa Formation at Nishikurosawa on the north coast of the Oga Peninsula, the boundary strato type.