Middle and late Permian foraminifers from the Chichibu Belt, Takachiho Area, Kyushu, Japan: implications for faunal events

Abstract

The middle and late Permian to Triassic sequence of carbonate rocks in the Takachiho area, central Kyushu, Japan, originated as a Panthalassan seamount and formed parts of far-traveled accreted terranes. This succession is divided into the Permian Guadalupian Iwato and Lopingian Mitai formations, and the Triassic Kamura Formation. The Iwato Formation is further into three zones, the Neoschwagerina, Yabeina higoensis, and Neoendothyra permica zones in ascending order; the Mitai Formation includes the Nanlingella suzukii Zone. Biotic turnovers are recorded twice in the Iwato and Mitai formations. The first and more remarkable biotic event is the total disappearance of fusulines at the top of the Yabeina higoensis Zone. The Neoendothyra permica Zone is characterized by black fine-grained micritic limestones having only sparse non-fusuline foraminifers. The second biotic event is the first appearance of Wuchiapingian fusulines by which the Nanlingella suzukii Zone is defined. The Capitanian–Wuchiapingian boundary is drawn between the Neoendothyra permica and Nanlingella suzukii zones. Above this boundary both the numbers of individual foraminifers and diversity of species gradually increase. The turnovers recorded in the Takachiho area were the result of late Capitanian–Wuchiapingian environmental changes which were sufficient to cause the disappearance of large, multi-chambered fusulines and allow the new appearance of an ‘ultimate’ Paleozoic foraminiferal assemblage. Ten species of foraminifers, including Yabeina higoensis and Yabeina Columbiana, are described.