Abstract

The stratigraphic nomenclature of the Frasnian Fairholme Group is complicated by unresolved sedimentological and diagenetic problems. Solutions are proposed on the basis of facies analysis and condont data from transects across the Cline Channel. The latter is a northeast-southwest trending basinal feature which separates the Fairholme and Southesk-Cairn carbonate complexes.

The use of black chert in defining the Flume Member is questioned. The Cairn Formation-Peechee Member contact is diachronous, related to facies and diagenetic changes, while the Grotto and Arcs Members are facies equivalents. The porous, light colored platform margins at Hummingbird, Cripple Creek and Wapiabi Gap were initially “drowned” by deeper water coralline dolomites, not basinal shales. This coralline facies migrated landward during successive rises in sea level.

Two major sedimentary sequences, controlled by eustatic rises in sea level are identified, along with numerous smaller depositional cycles. The first eustatic rise in sea level began in the Lower asymmetricus Zone. By the Upper asymmetricus Zone, Perdrix Formation shales had onlapped the lower Cairn Formation platform on both sides of the Cline Channel. Buildup and backstepping of platform margins continued to the end of the A. triangularis Zone. The second major eustatic cycle began in the Lower gigas Zone and coincided with the beginning of Mt. Hawk Formation shale deposition. This unit represents the greatest extent of basinal deposition during the Frasnian.

A biostratigraphy for the Frasnian carbonate complexes is defined by conodonts, particularly of onlapping basinal units.