Is There a Mid-Capitanian Extinction Event in Mid-High Paleolatitudes?

The Sverdrup Basin in the Canadian Arctic is an extraordinary geological laboratory filled with 13 km of Lower Carboniferous to Paleogene rocks that are exceptionally exposed in this cold desert. Warm-tropical photozoan carbonates quickly shifted to cool-temperate heterozoan (bryonoderm-extended) carbonates during the Sakmarian (Early Permian) in association with a Precaspian uplift event that closed the connection with the Tethys Ocean. The Middle Permian is dominated by cool-temperate bryonoderm assemblages in mixed siliciclastic-carbonate successions and the Upper Permian characterized by an impoverished heterozoan to hyalosponge assemblage in chert-rich facies. This pattern of oceanic cooling characterizes the margins across all of NW Pangea, whereas elsewhere the world was warming. It is within this context that the magnitude of mid-high paleolatitude extinction events are considered for the Capitanian and end-Permian. Event stratigraphy is a geological subdiscipline that identifies, studies, and correlates the sedimentary products of unpredictable, widespread, sudden, and often catastrophic physical and/or biologic events. A sudden low-latitude mid-Capitanian (~261-262Ma) extinction of fusulinaceans and calcareous algae has been identified in association with an Emeishan volcanic event and a large negative carbon isotopic excursion (CIE). Is this a global event? Some studies in Spitsbergen and Ellesmere Island (Sverdrup Basin) focused on short intervals and demonstrated significant levels of brachiopod extinction in the upper Kapp Starostin and Degerbols formations at approximately the same time as in low latitudes. Other studies considered a longer interval beginning with the Voringen Member (late Sakmarian; ~290.5Ma) in Spitsbergen at the base of the Kapp Starostin Formation, showing a longer term step-wise trend of brachiopod extinction, with the greatest turnover at the top of the Voringen. The differences in interpretation may relate to sampling, taxonomy, biostratigraphic dating, and resolution. Correlating Middle to Upper Permian rocks in the region is difficult because Jinogondolella and Clarkina are restricted or absent because of distinct provincialism, but conodonts still occur. In an unpublished study on brachiopods from the Assistance and Trold Fiord formations on Ellesmere Island (109 taxa; 50 used for biostratigraphy) diversity increased from lower Roadian (14) to upper Roadian (30), peaked in the lower Wordian (40), decreased in upper Wordian (24) to Capitanian (14) to lower Wuchiapingian (5), followed by apparent extinction. In fact, key taxa exhibit apparent extinction throughout much of the Permian in the Sverdrup Basin including trilobites (mid-Sakmarian), calcareous algae and colonial rugose corals (early Artinskian), fusulinaceans (late Artinskian), solitary rugose corals (mid-Wordian), brachiopods and bryozoans (Wuchiapingian), and sponges (mostly demosponges; latest Permian). There were no macrofossils present at the end of the Permian outside of sponges, soft-bodied bioturbators, and a couple of conodont species. Overall the pattern in the Sverdrup Basin is a long-term (~40Myrs) decrease in diversity that began with the closing of the Uralian Seaway. Long term trends in cooling, oxygen depletion, and acidification (lysocline shoaling) led to the progressive regional extirpation of taxa. Detailed studies have shown chemical perturbations, for example Hg-spikes, fly ash, and CIEs that may correlate with far-field events. But are these extinctions global events, if there is little to go extinct?