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

确定自由氧（O2）何时首次出现在地球大气中，以及O2水平如何随后积累，波动和稳定在能够支持动物生命的水平，激励了研究人员几十年。解决这些问题的一个关键策略是研究古陆地岩石的氧化还原敏感元素地球化学，如古土壤（化石“土壤”）和红层，它们与古陆地表面和大气直接接触。红层是含铁（III）氧化物的硅质沉积岩，在许多情况下，是由土壤或地表沃茨中的铁（II）在沉积过程中氧化形成的。红层第一次出现在古元古代，是在大约24.5亿年前（Ga）开始的地球大氧化事件（GOE）之后。然而，使用最先进的地球化学技术对红层进行了大量研究，这些技术可以提供有关其形成机制的定量信息，评估氧化还原敏感的痕量金属（例如，Cr、V、Mo、U）被Fe（III）氧化物清除，并确定红层可能受到沉积后成岩作用和变质作用的影响。 这项研究将提供红层的第一次详细调查，将结构和矿物学数据与主要元素，高精度超微量元素和Cr稳定同位素地球化学相结合。这项研究的核心将是对地球上最古老的红层的首次深入研究，这些红层保存在加利福尼亚州。2.45-2.32 Ga休伦超群（安大略），但通过对较年轻的红层（三叠纪，下芬迪群，新斯科舍省/新玩法）和现代河流沉积物（纽芬兰，哥斯达黎加）的研究，将获得补充性见解。散装岩石地球化学将被用来约束沉积物和沉积岩的物源岩性和河流过程基线特征，并将使用一个连续的铁提取策略，以针对铁（三）-氧化物的地球化学特征。研究战略的结构，以评估，首次，什么古氧化还原代理信息可以建立从红层的地球化学，以及这些数据如何适应更广泛的框架，地球的氧化还原演化。这一策略可以为地球大气O2演变的关键阶段提供新的线索。这项研究也与红层矿床有关（例如，U，Cu）和火星表面的氧化。该研究将为众多学生提供深入的多学科培训，为他们在广泛的地球科学领域从事有影响力的职业做好准备。该研究计划将产生高影响力的科学贡献（出版物和会议演讲），并将发展成为一个广泛的全球合作网络，这将促进加拿大和MUN作为地球科学研究中心的发展。

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.