Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 520, Issue -, Pages 141-152Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2019.05.023
Keywords
Belcher Group; Paleoproterozoic; Orosirian; carbon cycle; Cyanobacteria; Nuna
Categories
Funding
- NSERC PGS-D
- National Geographic
- American Philosophical Society Lewis and Clark Fund
- Northern Scientific Training Program
- McGill University GREAT
- Geological Society of America
- Mineralogical Association of Canada
- Stanford University
- Alfred P. Sloan Foundation
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The Orosirian Period (2050-1800 Ma) of the Paleoproterozoic Era represents an interval between the Great Oxidation Event and Lomagundi-Jatuli Excursion, and the apparent environmental stability of the late Paleoproterozoic to mid-Mesoproterozoic (1800-1300 Ma). Here, we present stratigraphic data, carbon isotope chemostratigraphy, element abundances, and U-Pb zircon depositional ages from the Belcher Group in subarctic Canada, providing an unparallelled global reference section for the Orosirian Period. U-Pb dates of 2018.5 +/- 1.0 Ma and 2015.4 +/- 1.8 Ma for two tuffs in the Kasegalik Formation (lowest Belcher Group) provide the first robust age constraints for Earth's earliest unambiguous cyanobacterial fossil, Eoentophysalis belcherensis. A tuffaceous shale similar to 4 km stratigraphically higher, at the contact of the Flaherty and Omarolluk formations (1854.2 +/- 1.6 Ma), provides an age for foreland basin development associated with the collision of the Superior and Hearne cratons. Carbonate carbon isotope data show smooth fluctuations ranging from -2.3 to +3.6 parts per thousand, reaching a maximum near ca. 1.88 Ga. This trend toward heavier carbon isotope values is interpreted as the result of global orogenesis during Nuna assembly that elevated nutrient supply and sedimentation rates, leading to an increase in the proportion of organic carbon burial relative to carbonate carbon burial. (C) 2019 Elsevier B.V. All rights reserved.
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