Paleoenvironmental and paleogeographical consideration on the Akasaka Limestone, Gifu Prefecture, Japan

Abstract

The present work deals with carbonate petrofacics and interpretation of paleodepositional environments of carbonate rocks represented in the successive fusuline biozones of the Permian Akasaka Limestone of Japan. The study shows that the carbonate rocks of the Akasaka Limestone would have been developed in an open marine shelf in reladon with sea level oscillations giving rise to two shallowing-upward sequences. On the other hand, a new idealized paleogeographic model is proposed on the basis of dissimilarities in faunal composition and species diversity gradient between the Akasaka Limestone and Akiyoshi Limestone. It is concluded that the two limestone buildups situated at different paleo-latitudes would have been conveyed to the Asian continent being diagonally accross the latitudes, rather than parallel, so that they would have passed the tropical zone at different times and, as a result, different timings of species diversity and opposite species diversity gradients would have been evoked between the two coeval faunas of the buildups.