Abstract

Fusulinaceans are abundant throughout the lower Missourian (Kasimovian) interval in the type area of the Nansen Formation in the Canadian Arctic Archipelago, and two fusulinacean assemblages can be distinguished. The lower Protriticites sp. A assemblage includes Protriticites sp. A, P. sp. B, Pseudofusulinella usvae (Dutkevich) and P. pulchra (Rauser-Chernousova and Beljaev). The upper Eowaeringella placitasensis assemblage contains Eowaeringella placitasensis Stewart, E. ardmorensis (Thompson, Verville and Lokke), E. sp. cf. E. zimmermani Stewart, E. sp. A, E. sp. B, E. sp. C and Pseudofusulinella sp. A. Both assemblages are of early Missourian age and may correlate with the Protriticites pseudomontiparus-Obsoletes obsoletes zone of lowermost Kasimovian in the Pechora Pre-Urals on the basis of the co-occurrence of Eowaeringella, Pseudofusulinella usvae (Dutkevich) and P. pulchra (Rauser-Chernousova and Beljaev). The Middle/Upper Pennsylvanian boundary in the type Nansen is placed at the base of the Protriticites sp. A assemblage, which is 1.5 m below the Eowaeringella placitasensis assemblage. We think that the Protriticites sp. A assemblage corresponds to the interval between the Eowaeringella zone and the base of the Desmoinesian/Missourian boundary in the Midcontinent. Further, it probably corresponds to the Protriticites pseudomontiparus-Obsoletes obsoletes zone outside of the U.S.A., and accordingly, the Moscovian/Kasimovian and Desmoinesian/Missourian boundaries are more or less coincident in the Nansen.