EARLY PERMIAN GLOBAL WARMING LED TO COOL-WATER HETEROZOAN CARBONATE SEDIMENTATION ALONG NW PANGEA

In the Sverdrup Basin, Arctic Canada, Bashkirian (Pennsylvanian) to Asselian (Lower Permian) heterozoan (bryozoan, echinoderm, brachiopod) wackestone and packstone occur in the lower part of glacio-eustatic cycles, representing low-energy sedimentation in a cool-water outer shelf setting. These carbonates pass upward and landward into shallow, warm photozoan carbonates (phylloid and dasycladacean algae, Palaeoaplysina, small foraminifers and fusulinaceans, colonial rugose corals, ooids, oncoids, submarine cement, etc.) indicative of shallow-water, high-energy packstone–grainstone deposition in a mid- to inner-shelf setting. These conditions persisted for about 28 Myrs. Yet over a short time span in the Early Sakmarian (less than 0.5 Myr), significantly cooler-water conditions were established in the Sverdrup Basin. This led to the significant retreat of photozoan carbonates to the most proximal areas, while heterozoan carbonates expanded landward and shoaled within wave base. Paleolatitudes (25-30^o N) and climate indicators show warm, subtropical conditions continue to prevail at that time suggesting oceanic cooling was caused by upwelling from the Panthalassic Ocean to the west, also shown by an increase in syn-sedimentary phosphate. The Sakmarian cooling is problematic because it occurs more than 15 Myr prior to closure of the Uralian seaway, which is responsible for the post-Artinskian disappearance of photozoan carbonates along NW Pangea. Cooling is contemporaneous with rapid global warming, as shown by the thawing of Gondwana glaciers and paleoclimatic proxies indicating very high pCO₂ in the atmosphere. Based on modern comparisons with global warming-induced upwelling along the western margin of North America, we suggest the Early Sakmarian introduction of cool-water and establishment of a very shallow thermocline in the Sverdrup Basin was caused by an increase in the frequency, volume and depth of upwelling along the western margin of Pangea in response to global warming and accompanying northward migration of upwelling-forcing high pressure summer cells over northern Panthalassa. Warm-water conditions continue to prevail above the thermocline up until the Late Artinskian as shown by conodont biota, nearshore warm-water photozoan carbonates and basin marginal evaporites.