STRATIGRAPHY AND AGE-CALIBRATED δ13C RECORD FROM THE BYLOT SUPERGROUP, BAFFIN ISLAND: EVOLUTION OF SURFACE-OCEAN CHEMISTRY IN LATE MESOPROTEROZOIC

The late Mesoproterozoic was a period of gradual oxygen expansion in shallow marine environments. The Borden Basin, northern Baffin Island (Arctic Canada), is filled by well-preserved strata of the ~6km-thick Bylot Supergroup. Carbonates are predominant within the middle Bylot Supergroup, which is constrained by new radiometric ages to be ca. 1050 Ma. The Iqqittuq Formation records the transition from a siliciclastic margin to a NW-deepening carbonate ramp. This ramp evolved into a rimmed platform with the overlying Angmaat Formation representing the rim and restricted inner platform and the Nanisivik Formation to the NW representing the equivalent deep basin. The contact with the overlying Victor Bay Formation records reactivation of the basin. The Victor Bay Formation represents a carbonate ramp dominated by shales, rhythmites and floatstone (debrites) in the outer-ramp, limestones rich in molar-tooth structures in the mid-ramp, and by microbiolaminated limestones in the inner-ramp. Generation of accommodation space during this time allowed to build-up large deep-water stromatolitic reefs transitioning from the outer-ramp to the mid-ramp.

Carbon isotopic data for several late Mesoproterozoic successions in Arctic Canada have been used to evaluate regional correlation. Building upon these previous chemostratigraphic studies, we present a high-resolution δ¹³C_carb record from a platform transect spanning the calcareous middle Bylot Supergroup. Consistent with prior studies, these new data reveal reproducible fluctuations in δ¹³C_carb between -2‰ and +4‰, similar to patterns seen in late Mesoproterozoic successions globally. This geochronologically calibrated high-resolution carbon stable isotope profile will help refine correlations of late Mesoproterozoic strata across Arctic Canada and formerly contiguous continents, such as Siberia. Further, it will help constrain biogeochemical evolution and the geological time scale spanning the Mesoproterozoic–Neoproterozoic transition.