Marine Paleobathymetry and Paleotopography of the Hokuroku District during the Time of the Kuroko Deposition, Based on Foraminiferal Assemblages

Abstract

The marine paleobathymetry and paleotopography of the Kuroko deposits are reconstructed, based on foraminiferal assemblages occurring in bore holes of the Hokuroku district, Akita Prefecture, Northeast Japan.
Judging from the fossil planktonic foraminiferal assemblages, Hokuroku district was predominated by a subtropical water mass during the time of. the Kuroko deposition. Correlating the benthonic foraminiferal assemblage of the Hokuroku district with those of present-day subtropical Kuroshio area, the paleobathymetry of the Kuroko deposits is inferred to range from 500 to 2, 500 meters. Reconstructed submarine topography indicates the existence of a ditch-like depression at that time.
Arenaceous foraminiferal assemblages distributed in the Hokuroku district may have inhabited in an extraordinary acid water condition which was caused by the dissolution of volcanic gas supplied from the sea bottom.
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