Assessment and Calibration of the Great Oxidation Event in sedimentary strata of the Paleoproterozoic Huronian Supergroup

古元古代休伦超群沉积地层大氧化事件的评价与标定

• 批准号: RGPIN-2017-06372
• 负责人: Rainbird, Robert
• 金额: $ 4.66万
• 依托单位: Carleton University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751175
• 关键词: Assessment; Calibration; Great; Oxidation; Event

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.

目的：该项目将重点研究约25 - 22亿年前的沉积岩，即休伦超群，它在安大略休伦湖以北的广阔地区非常突出。休伦被认为是地球上保存最完好和最具代表性的继承，但我们对其绝对年龄，地层和沉积环境的了解有限。我的研究的主要目的是：1）确定地球大气成分从缺乏自由氧到含有自由氧的根本转变的性质和时间（大氧化事件或GOE），并确定这种转变是一个单一的，不可逆的事件或振荡过程发生在10秒或100秒的数百万年; 2）描述和解释跨越GOE时间间隔的沉积岩的沉积环境，并确定它们是否记录了这种大气转换; 3）确定休伦超群的年龄和物源，作为评估沉积路径和盆地发展构造模型的一种手段-休伦盆地中记录的构造变化是否与GOE有关？科学方法：该提案寻求资金支持2博士，3硕士和几个本科生谁将：1）地图的分布和第一次出现的沉积层，表明自由大气氧，（如陆地红层和海洋硫酸盐矿床）; 2）测量和对比以前未研究的地层剖面，并检查采矿业和档案岩心; 3）收集地质年代学标本，以便：a）直接测定火山灰层地层单位的年代; B）测定与岩浆活动和金属富集有关的沉积后流体循环事件的年代; c）测定锆石砂颗粒的年代，以确定其物源，从而评价休伦盆地的构造历史。地球化学将包括分析沉积黄铁矿和可能的硫酸盐的S同位素，以评估以前的大气氧水平。该研究将通过将经典沉积学与尖端地质年代学和地球化学技术相结合，评估休伦超群GOE的拟议地球化学证据是否真正反映了从无氧到氧化气氛的转变，这一组合在世界上任何地方都从未被应用于这一关键时间间隔。通过将这些结果与基于我们对同一地层间隔的地球化学和同位素分析得出的结论进行比较，我们将评估GOE在地质上是瞬时的还是长期的振荡演化。 通过这种方法，我们可以更有信心地理解海洋和大气的氧化还原结构何时以及为什么随着时间的推移而变化，并对地球上生命的早期进化产生明显的影响。