Stable Isotope Chemostratigraphy Across the Conformable Permian-Triassic Boundary at Opal Creek, Alberta
Geoffrey H. Garrison1, Peter D. Ward1, and Charles
Henderson2
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