Abstract

Pliocene/Pleistocene boundary and paleoceanographic significance of the upper Miyazaki Group, southern Kyusyu, Southwest Japan, based on calcareous nannofossils and planktic foraminiferal assemblages

The journal of the geological society of Japan, 118, 109-116, 2012.
Chiyonobu Shun, Morimoto Jumpei, Torii Masayuki, Oda Motoyoshi

The Plio-Pleistocene succession is exposed along the Nagatani river (NGT route) in northern Miyazak region, southern Kyushu, on the Pacific side of southwestern Japan. The NGT section is prominent sequence, which the upper Takanabe Formation of the uppermost part of the Miyazaki Group, to clarify the paleoceanographic condition based on the faunal compositions of calcareous nannofossil and planktic foraminifera. We especially focused on two genera Discoaster and Reticulofenestra, and Coccolithus pelagicus in calcareous nannofossils and Globigerinoides ruber, Globigerinoides quadrilobatus, Globigerinoides sacculifer, and Neogloboquadrina incompta in planktic foraminifera as proxies of paleoceanography. These changes in relative abundance of these floral and faunal compositions suggest that the paleoceanographic condition at Miyazaki area shifted from the stratified surface water mass (Kuroshio current) during late Pliocene to upwelling condition (cold-water mass) during early Pleistocene via a transitional phase just after the last occurrence biohorizon of genus Discoaster.