Middle Permian foraminifers of the Izuru and Nabeyama Formations in the Kuzu area, Tochigi Prefecture, Japan Part 1. Schwagerinid, neoschwagerinid, and verbeekinid fusulinoideans

Abstract

The Middle Permian Izuru and Nabeyama Formations in the Kuzu area, Tochigi Prefecture are composed of thick basaltic rocks and fossiliferous partly dolomitized limestone. Fusulinoidean biostratigraphy is first established in these two formations, and the stratigraphic distribution of the 30 species of fusulinoideans distinguished from 70 localities is shown. The Izuru and Nabeyama Formations are biostratigraphically subdivided into the lower Parafusulina nakamigawai, the middle Parafusulina yabei, and the upper Parafusulina tochigiensis zones. The first zone is correlated to the Parafusulina nakamigawai Zone of the basal part of the Akasaka Limestone. The middle part of the third zone corresponds to the upper part of the Neoschwagerina craticulifera Zone to the lower part of the Neoschwagerina margaritae Zone of the Akasaka Limestone based on the occurrence of Gifuella amicula. More precise correlation of the Parafusulina yabei and Parafusulina tochigiensis zones will be possible when biostratigraphic zonation by schwagerinids is made clear in relation to the stratigraphic range of neoschwagerinids in Middle Permian limestones of the Jurassic terrane of Japan. Seven species of Parafusulina including two new species, P. shimotsukensis and P. tochigiensis, and Pseudodoliolina ozawai and Gifuella gifuensis are described and discussed herein.