A TERMINAL MESOPROTEROZOIC RECORD OF ENVIRONMENTAL AND BIOLOGICAL DISRUPTION TO THE BORING BILLION FROM THE BYLOT SUPERGROUP, ARCTIC CANADA (Invited Presentation)

It has long been argued that following the Great Oxidation Event, Huronian snowball glaciation, and Lomagundi and Shunga carbon isotope excursions between 2500 and 1800 Ma, Earth experienced one billion years of environmental and biologic stability. However, mounting evidence is reshaping this fundamental assumption about the latter portion of this interval (i.e. 1200 to 800 Ma). The Bylot Supergroup in Arctic Canada was deposited within the epicratonic Borden Basin on Baffin and Bylot islands, Nunavut and records dynamic interactions between tectonics, biology, and the environment commencing by 1050 Ma. New geochemical data indicate that the Borden Basin fluctuated between lacustrine, restricted and open marine conditions throughout its depositional history. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) of marine limestone capture an increase from 0.705 to 0.706 that coincide with peak Grenville orogenesis, suggesting that the amalgamation of Rodinia influenced global silicate weathering and the delivery of nutrients to the ocean in the terminal Mesoproterozoic Era. Diverse carbonate facies from the middle Bylot Uluksan Group preserve reproducible and age-calibrated fluctuations in δ¹³C that mark the onset of increased variability in the carbon isotopic composition of seawater after a prolonged interval of values ~+0‰. Previous workers have also interpreted S and Cr isotopic data from Uluksan Group evaporites and carbonates to record expansion of the marine sulfate reservoir and atmospheric oxygenation, respectively. Diverse microfossil assemblages have been recovered from the Bylot Supergroup, including the oldest unambiguous crown-group eukaryote, the red alga Bangiomorpha pubescens. New microfossil data demonstrate co-variation between eukaryotic diversity and both the degree of marine influence and redox conditions. Additionally, some eukaryotic taxa that had previously been documented only in mid-Tonian strata, were recovered from the Bylot Supergroup, extending their temporal range by >200 Myrs. Together, these findings from the Bylot Supergroup demonstrate that the chronometrically defined Mesoproterozoic-Neoproterozoic boundary may represent a meaningful transition in the context of Earth history.