Reconstructing the depositional history of the terminal Mesoproterozoic Bylot basins of northeastern Laurentia

The Bylot basins, comprising the Borden (BB), Fury and Hecla (FHB), Thule (TB) and Aston-Hunting (AHB) basins record the evolution of present-day northeastern Canada and northwestern Greenland between ca. 1.3-1.0 Ga. The BB and AHB host the only known fossils of Bangiomorpha pubescens, a red alga that represents the oldest taxonomically resolved eukaryote discovered to date. Geochemical studies suggest that the BB was intermittently open to the ocean and restricted, potentially even lacustrine, highlighting the potential significance of freshwater environments for eukaryotic evolution. Recent radiometric dates anchor these findings in the geologic record and demonstrate that most sediment accumulation in these basins occurred hundreds of millions of years later than originally assumed ca. 1050 Ma. Deposition in the Bylot basins therefore overlaps with phases of the Grenville Orogeny, as supported by 87Sr/86Sr, which capture the effect of weathering of the Grenville Province. These data and interpretations are based mainly on studies in the BB, which has received the most attention out of the Bylot basins. In stark contrast, the FHB to the south, and the TB to the northeast, have received comparatively little attention, as the former is not as well exposed. As important interpretations emerge from work in the BB, ideas must be tested through renewed investigations in the other Bylot basins which are presumed to be geodynamically linked with the BB and provide greater regional context. This thesis strives to shed light on the FHB and TB through new mapping, stratigraphic logging, geochronology and paleoenvironmental reconstructions. Mapping campaigns to the FHB and TB update geologic maps and improve stratigraphic frameworks to strengthen correlations with strata of the BB. The age of the Fury and Hecla Group was assumed to be ca. 1.27 Ga based on the affinity of basal basalts to the Mackenzie Large Igneous Province, but this inference lacked geochronological evidence. We have generated the first depositional age constraint for the Fury and Hecla Group, a rhenium-osmium age of 1087 ± 6 Ma on black shales of the Agu Bay Formation. This age confirms that, like the BB, strata of the FHB were predominantly deposited after 1100 Ma, which implies a large depositional hiatus in the lower part of the stratigraphy. Whereas extension during the late Mesoproterozoic is often thought to have been isolated to the midcontinent, our results indicate that Mesoproterozoic extension in Laurentia was far more extensive than previously thought. Extension generated numerous cratonic basins on Laurentia, which host important microfossils key to understanding the early evolution of eukaryotes. To investigate the importance of these non-marine ecosystems for eukaryotic evolution, we test the B/Ga and Sr/Ga paleosalinity proxies on Proterozoic strata for the first time. We begin with the Arctic Bay Formation, which is thought to have been deposited in a restricted setting, and demonstrate that the B/Ga proxy reasonably predicts paleosalinity. We extend this to the FHB and TB where it indicates that deposition of shale rich successions predominantly occurred in brackish to lacustrine settings. Last, to better understand the co-evolution of the individual Bylot basins, we present the first unified tectonostratigraphic framework for the region, which identifies three broad phases of deposition that can be related to well-understood tectonic stresses on Laurentia

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