Subventions et des contributions :

Subvention ou bourse octroyée s'appliquant à plus d'un exercice financier. (2017-2018 à 2022-2023)

Objectives: The project will focus on ~2.5-2.2 billion-year-old sedimentary rocks known as the Huronian Supergroup, superbly exposed in the broad region north of Lake Huron, Ontario. The Huronian is recognized as one best preserved and most representative successions of this age anywhere on Earth, yet we have a limited understanding of its absolute age, stratigraphy and environment of deposition. The principal aims of my research are to: 1) To characterise the nature and timing of a fundamental changeover in the composition of Earth's atmosphere from one that lacked free oxygen to one that contained free oxygen (the Great Oxidation Event or GOE) at ~2.4 Ga and determine if this changeover was a single, irreversible event or an oscillatory process taking place over 10s or 100s of millions of years; 2) to describe and interpret the depositional environments of the sedimentary rocks that span the GOE time interval and determine whether they record this atmospheric changeover; 3) to determine the age and provenance of the Huronian Supergroup, as a means of evaluating sedimentation pathways and tectonic models of basin development - can tectonic changes recorded in the Huronian basins be linked with the GOE?

Scientific Approach: The proposal seeks funding for support of 2 PhD, 3 MSc and several undergraduate students who will: 1) map the distribution and first appearance of sedimentary layers that indicate free atmospheric oxygen, (e.g. terrestrial red-beds and marine sulphate deposits); 2) measure and correlate previously unstudied stratigraphic sections and examine mining industry and archival drill core, and; 3) collect geochronology specimens to: a) directly date of stratigraphic units from volcanic ash layers; b) date post-depositional fluid circulation events related to magmatism and enrichments of metals; c) date zircon sand grains to determine their provenance to evaluate the tectonic history of the Huronian basins. Geochemistry will include analysis of S isotopes of sedimentary pyrite and possibly sulphate to assess former levels of atmospheric oxygen.

Impact: The research will evaluate whether the proposed geochemical evidence of the GOE in the Huronian Supergroup truly reflects a transition from oxygen-free to oxidizing atmosphere, by combining classical sedimentology with cutting-edge geochronlogical and geochemical techniques, a combination that has never before been applied to this critical time interval anywhere in the world. By comparing these results with conclusions based on our geochemical and isotopic analyses of the same stratigraphic interval, we will evaluate whether the GOE was geologically instantaneous or a protracted, oscillatory evolution. With this approach, we can understand with much greater confidence when and why the redox structure of the ocean and atmosphere varied through time with its obvious consequences for early evolution of life on Earth.