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

几十年来，确定地球大气层中首次出现游离氧(O2)的时间，以及随后O2水平是如何积累、波动和稳定在能够维持动物生命的水平上的，一直激励着研究人员。解决这些问题的一个关键战略是研究与古陆地表面和大气直接接触形成的古土壤(化石“土壤”)和红层等古陆相岩石的氧化还原敏感元素地球化学。红层是含有Fe(III)氧化物的硅质碎屑沉积岩，在许多情况下，是在沉积过程中土壤或地表水中的Fe(II)氧化形成的。红床仅在大约24.5亿年前(GA)开始的地球大氧化事件(GOE)开始后，才在古元古代首次出现。然而，利用最先进的地球化学技术对红层进行了大量的研究，这些技术可以提供有关红层形成机制的定量信息，评估对氧化还原敏感的痕量金属(如铬、钒、钼、铀)是否被Fe(III)氧化物清除，并确定红层可能如何受到沉积后成岩和变质作用的影响。这项研究将首次对红层进行详细调查，将结构和矿物学数据与常量元素、高精度超痕量元素和铬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进行首次深入研究，这些红层保存在大约2.45-2.32Ga的胡伦超群(安大略省)中，但补充的见解将来自对较年轻的红层(三叠纪、下芬迪群、新斯科舍省/新不伦瑞克)和现代河流沉积物(哥斯达黎加纽芬兰)的研究。块状岩石地球化学将用于约束沉积物和沉积岩的物源岩性和河流过程基线特征，而顺序提铁策略将用于靶向Fe(III)氧化物的地球化学特征。该研究战略旨在首次评估从红层的地球化学中可以建立哪些古氧化还原替代信息，以及这些数据如何与地球氧化还原演化的更广泛框架相适应。这一战略可能会为地球大气氧气演化的关键阶段提供新的线索。这项研究也与红层矿床(如铀、铜)和火星表面的氧化有关。这项研究将为许多学生提供深入的、多学科的培训，为他们在广泛的地球科学部门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(出版物和会议报告)，其结构将演变为一个广泛的全球合作网络，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.