Paper No. 3
Presentation Time: 1:30 PM
PENNSYLVANIAN-EARLY PERMIAN PALEOENVIRONMENTAL TRENDS AND EVENTS ALONG NW PANGEA INDICATE CONTEMPORANEOUS GLOBAL RISE IN PCO2 AND TEMPERATURE
The Pennsylvanian-Early Permian succession of the Sverdrup Basin, Arctic Canada, which formed ~20-25oN along NW Pangea, provides evidence for a coeval global rise in pCO2 and temperature. Warm-water shallow conditions leading to extensive photozoan carbonates prevailed until the mid Sakmarian, reflecting an open connection with the Tethys Ocean via to the Uralian gateway. Upwelling from Panthalassa also brought cooler water onto the outer shelf, as evidenced by phosphate-rich heterozoan carbonates indicative of a relatively shallow thermocline. By Gzhelian time, tangential ooids of aragonite origin, pervasively developed before, ceased to exist in high-energy environments, as inorganic aragonite precipitation could no longer take place, the first manifestation of a shift from an aragonite sea to a calcite sea forced by pCO2 increase. This was followed by a proliferation of calcareous algae; by Late Asselian most grains in shallow settings became coated by oncoid-forming algae. This further suggests higher pCO2 and warmer conditions, which is also indicated by the incursion of Tethys-derived fusulinids. Meanwhile, cool-water heterozoan biota expanded into the outer shelf, indicating shoaling of the thermocline and increased upwelling from Panthalassa, possibly also as a result of global warming. Cyclothems became thicker during the Early Sakmarian during a major global transgression, recording the thawing of Gondwana glaciers. By then, a very shallow thermocline had developed with mid-shelf high-energy heterozoan carbonates passing into photozoan carbonates, suggesting further upwelling from Panthalassa. The mid to Late Sakmarian marks the end of cyclothymic sedimentation and a complete shift from photozoan to heterozoan biota. The Uralian gateway was then closed off, which led to the destruction of the thermocline and the establishment of shallow to deep, cool-water conditions all along western Pangea in spite of warmer conditions globally. This is also when biogenic chert started to impinge upon the shelf, a phenomenon associated with ocean acidification, the ultimate manifestation of the global pCO2 increase. By Artinskian time, a shallow lysocline prevented carbonates to form on the outer shelf, dissolving most carbonate material transported offshore from proximal cool-water factories.