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

目标：该项目将专注于被称为胡伦超群的~25亿-22亿年前的沉积岩，这些沉积岩在安大略省休伦湖以北的广阔地区非常暴露。胡罗尼亚人被认为是地球上这个时代保存最完好、最具代表性的继承者之一，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)描述地球大气组成从缺乏自由氧到~2.4 Ga处含有自由氧的根本转变(大氧化事件或GOE)的性质和时间，并确定这种转变是一个单一的不可逆事件，还是发生在10s或100s百万年之间的振荡过程；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变；3)确定胡伦超群的年龄和物源，作为评估盆地发展的沉积路径和构造模式的一种手段--胡伦盆地记录的构造变化能否与GOE联系起来？科学方法：该提案寻求资金支持2名博士、3名硕士和几名本科生，他们将：1)绘制指示自由大气氧的沉积层的分布和第一次出现的地图(例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钻芯；以及；3)收集地质年代学标本，以：a)直接测定火山灰地层单位的年龄；b)测定与岩浆作用和金属富集有关的沉积后流体循环事件；c)测定锆石砂粒的年龄，以确定其来源，以评价胡伦盆地的构造史。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，以评估以前的大气含氧量水平。影响：这项研究将结合经典沉积学和尖端的地质年代学和地球化学技术，评估拟议的胡隆超群中的GOE的地球化学证据是否真的反映了从无氧大气到氧化大气的转变，这一组合在世界任何地方都是前所未有的。通过将这些结果与我们基于同一地层段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是地质上的瞬时演化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会随着时间的推移而发生变化，从而对地球上早期生命的演化产生明显的影响。

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.