Refining the understanding of Earth's oxygenation through the paleo-redox geochemistry of redbeds

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Establishing when free oxygen (O2) first appeared in Earth's atmosphere and how levels of O2 subsequently accumulated, fluctuated, and stabilised at levels capable of supporting animal life have motivated researchers for decades. A key strategy to unravel these issues is to investigate the redox-sensitive element geochemistry of ancient terrestrial rocks, such as paleosols (fossil “soils”) and redbeds, which formed in direct contact with the paleo-land surface and atmosphere. Redbeds are siliciclastic sedimentary rocks bearing Fe(III)-oxides that, in many cases, formed from the oxidation of Fe(II) in soils or surface waters during their deposition. Redbeds appeared for the first time only in the Paleoproterozoic, following the onset of Earth's Great Oxidation Event (GOE) that began approximately 2.45 billion years ago (Ga). However, redbeds are vastly understudied using state-of-the-art geochemical techniques that could provide quantitative information on their formation mechanisms, evaluate whether redox-sensitive trace metals (e.g., Cr, V, Mo, U) were scavenged by the Fe(III)-oxides, and establish how redbeds may have been influenced by post-depositional diagenesis and metamorphism.******This research will provide the first detailed investigation of redbeds that integrates textural and mineralogical data with major element, high-precision ultra-trace element, and Cr stable isotope geochemistry. The heart of the research will be the first in-depth study of Earth's oldest redbeds, which are preserved in the ca. 2.45-2.32 Ga Huronian Supergroup (Ontario), but complementary insight will come through the study of younger redbeds (Triassic, Lower Fundy Group, Nova Scotia/New Brunswick) and modern river sediments (Newfoundland, Costa Rica). Bulk rock geochemistry will be used to constrain the provenance lithology and fluvial process baseline characteristics of the sediments and sedimentary rocks, and a sequential Fe extraction strategy will be used to target the geochemical characteristics of the Fe(III)-oxides. The research strategy is structured to evaluate, for the first time, what paleo-redox proxy information can be established from the geochemistry of redbeds and how these data fit into the wider framework of Earth's redox evolution. This strategy could shed new light on Earth's critical stages of atmospheric O2 evolution. The research is also relevant to redbed-hosted deposits (e.g., U, Cu) and the oxidation of the Martian surface. The research will provide in-depth, multi-disciplinary training to numerous students, preparing them for impactful careers in a wide range of Earth science sectors. The research program will produce high-impact scientific contributions (publications and conference presentations) and is structured to evolve into an extensive network of global collaborations that will foster the growth of Canada and MUN as an Earth Science research hub.****** **** **** **** ****