TERMINATION OF A PRODUCTIVE UPWELLING SYSTEM IN EASTERN PANTHALASSA AT THE P-T BOUNDARY: EVIDENCE FROM OPAL CREEK, AB

While the end-Permian extinction in the marine realm is well known from the Tethys Ocean, it remains little studied in the vast Panthalassic basin. Opal Creek, in Alberta, is biostratigraphically defined as a continuous Permian-Triassic Boundary (PTB) section representing deep outer shelf deposition along the Panthalassic western margin of Pangaea. Significant organic carbon and nitrogen isotope excursions precede the extinction of the only remaining dominant benthic organisms (siliceous glass sponges). Geochemical comparison with underlying Guadalupian (Middle Permian) age rocks suggests that the latest Permian at Opal Creek represents the shutdown of a productive cold-water upwelling ecosystem with a mid-water column oxygen minimum and the transition to a warm and less vigorously circulating system with a bottom-water oxygen minimum. A decrease in the photosynthetic fractionation effect following a latest Permian marine transgression along western Pangaea is attributed to increased productivity in the photic zone, with the corresponding spike in δ¹⁵N representing denitrification in a mid-water oxygen minimum. Enrichments in productivity- and redox-sensitive trace elements suggest a productivity spike due to the synergistic effects of warming and residual upwelling, with euxinic conditions generated by biological oxygen demand in the mid-water column. Unlike many Tethyan sections, there is no sharp disturbance of inorganic carbon isotopes associated with the Permian-Triassic Boundary, highlighting the need for a global approach when studying the Permian-Triassic transition.