Abstract

The Permian-Triassic boundary interval was considered to be absent in many areas of the world, including western Canada, because of the unconformity associated with a global eustatic fall. This boundary is best recognized in strata of the paleo-Tethys Sea and, in particular, southern China, where the boundary will likely be defined. Age assignments discussed in this paper are based upon the assumption that the boundary will be defined by the first appearance of Hindeodus parvus. Biostratigraphic work presented herein indicate that the Permian-Triassic boundary interval is represented in western Canada within the basal black shale of the Sulphur Mountain, Montney and Grayling formations which were previously correlated exclusively with the Triassic. Uppermost Permian faunas have probably not been previously documented in the study area because the significance of considerable condensation within the basal parts of these formations was not recognized. The best section is at Opal Creek in Kananaskis Country where the Permian-Triassic boundary is identified at 1.5 metres above the top of the Ranger Canyon Formation. This suggests that a global eustatic fall, related essentially to the amalgamation of Pangea, occurred during a protracted Late Permian interval and that the subsequent transgression began during the latest Permian and continued into the Triassic. An anoxic depositional site is suggested for these basal shales as they are typically pyritic, lack bioturbation and current structures and have no benthic fossils. This anoxic episode may have been a contributing factor toward the Late Permian extinction event, the largest in geologic history, although extinctions largely occurred earlier in western Canada, since sponge spicules are the only Upper Permian macrofossils in the area. Conodonts, which were minimally affected by this extinction, provide valuable indices for high-resolution sequence biostratigraphic correlation in this interval. The age of the basal shales varies across the region; they are Changhsingian at Opal Creek, Griesbachian at several localities and possibly as young as Dienerian at Meiosin Mountain. This diachroneity can be attributed to the duration of the transgression, as well as paleotopography on the transgressed surface. New exploration insights may result from detailed correlation of Upper Permian and Lower Triassic conodont biozones and sequences/parasequences in the area.

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