UPPERMOST PERMIAN CONODONTS AND THE PERMIAN-TRIASSIC BOUNDARY IN THE WESTERN CANADA SEDIMENTARY BASIN

The Permian-Triassic boundary interval was considered to be absent in many areas of the world, including western Canada, because of the unco nformity associated with a global eustatic fall. This boundary is best recognized in strata of the paleo-Tethys Sea and, in particular, sout hern China, where the boundary will likely be defined. Age assignments discussed in this paper are based upon the assumption that the bounda ry will be defined by the first appearance of Hindeodus parvus. Biostr atigraphic work presented herein indicate that the Permian-Triassic bo undary interval is represented in western Canada within the basal blac k shale of the Sulphur Mountain, Montney and Grayling formations which were previously correlated exclusively with the Triassic. Uppermost P ermian faunas have probably not been previously documented in the stud y area because the significance of considerable condensation within th e basal parts of these formations was not recognized. The best section is at Opal Creek in Kananaskis Country where the Permian-Triassic bou ndary is identified at 1.5 metres above the top of the Ranger Canyon F ormation. This suggests that a global eustatic fall, related essential ly to the amalgamation of Pangea, occurred during a protracted Late Pe rmian 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 pyriti c, lack bioturbation and current structures and have no benthic fossil s. This anoxic episode may have been a contributing factor toward the Late Permian extinction event, the largest in geologic history, althou gh extinctions largely occurred earlier in western Canada, since spong e spicules are the only Upper Permian macrofossils in the area. Conodo nts, which were minimally affected by this extinction, provide valuabl e 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 localiti es and possibly as young as Dienerian at Meiosin Mountain. This diachr oneity can be attributed to the duration of the transgression, as well as paleotopography on the transgressed surface. New exploration insig hts may result from detailed correlation of Upper Permian and Lower Tr iassic conodont biozones and sequences/parasequences in the area.