Stable Isotope Chemostratigraphy Across the Conformable Permian-Triassic Boundary at Opal Creek, Alberta

Geoffrey H. Garrison¹, Peter D. Ward¹, and Charles Henderson^2
1 University of Washington, Seattle, WA
² University of Calgary, Calgary, AB

Sedimentary stable isotope measurements are consistent with earlier biostratigraphic conclusions that the contact between the Late Permian Ranger Canyon and Early Triassic Sulphur Mountain Formations is conformable in southwest Alberta, as opposed to an erosional unconformity as was traditionally believed. Furthermore, δ¹³C stratigraphy supports the proper placement of the Permian-Triassic boundary 1.5 m up from the base of and within the Sulphur Mountain Formation, not at the basal contact. Thus, the Opal Creek Permian-Triassic boundary (PTB) section appears to be the southernmost section in the northeast Panthalassic ocean region to have continuous deposition across the PTB, and thus provides new biogeographic and paleobiological information about the P/T extinction. The Opal Creek δ¹³C data record has similar structure to other sections (e.g., Meishan) confirming the global scale of carbon cycle perturbations prior to the PTB; Opal Creek δ¹³C show the typical negative excursion just prior to the earliest Triassic deposits. However, fossil records from Opal Creek to the Canadian arctic indicate protracted extinctions during the Late Permian beginning well before any changes in the carbon record. Thus, these data indicate that the end-Permian mass extinction was not due to a singular short term event (e.g. impact). Whatever perturbed the carbon record, however, may have been the final blow.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005