A Stratigraphically Resolved Sulfur Isotope Record of the Oxygenation of Earth's Atmosphere and its Correlation with C, Fe, and Mo Geochemical Cycles in the Early Paleoproterozo

Andrey Bekkerhal-0545484发现了2.47 Ga前黄铁矿和重晶石中硫同位素的非质量相关分馏（Farquhar等人，2000），可能与无氧大气中的光化学过程有关（Farquhar等人，2001年）提供了一个新的代理大气氧化还原状态。现有的数据表明，最古老的古元古代冰川作用，限制在2.45和2.32 Ga之间，之前的大气氧的上升。冰川作用之后的氧化过程可能是从富含甲烷的太古代大气的温室条件到含氧、甲烷贫乏的寒冷条件的转变。然而，一个明显的地层和时间的差距之间仍然存在最年轻的沉积黄铁矿与一个明确的非质量依赖的信号在S同位素形成于2.47 Ga和冰前黄铁矿没有非质量依赖的信号。我们建议测量一个高分辨率的地层记录的地球氧化的硫同位素分馏的基础上，填补差距与S同位素数据沉积黄铁矿页岩夹层内的带状铁的形成中，西澳大利亚州布罗克曼超层序的上部。Brockman超层序的中上部沉积于2463.5 ~ 2449.3Ma之间，是2.48- 2.45Ga地幔柱爆发事件晚期的产物。我们的初步数据表明，在这些单位缺乏非质量依赖分馏。如果得到证实，这些数据将（1）将大气氧的上升间隔括为20 Ma：（2）提供数据来模拟大气氧的上升是逐渐的还是突然的;以及（3）允许地层控制氧化作用与构造岩浆事件的关系，气候变化以及大气和海洋化学成分和碳地球化学循环的其他变化。我们将记录钻探岩心DDH WW 1和DD 98 SGP 001，由西澳大利亚地质调查局和皮尔巴拉钢铁公司储存，分别测量了高分辨率的地层S同位素记录，并对钻井取心页岩有机质中的C同位素进行了支持性分析。S-和C-同位素分析将在地球物理实验室进行。将把表征良好的岩心样品的等分试样分发给我们的合作者Olivier Rouxel（WHOI）、Tim里昂和克林特Scott（UCR）、Ariel Anbar（ASU）和Eirik Krogstad（GSU）进行协调分析，以获得大气氧气上升的独立证据。O. Rouxel将分析页岩中沉积黄铁矿的铁同位素，带状铁地层中的氧化铁矿物和大块页岩样品，以评估铁循环对古元古代早期海洋氧化还原状态变化的响应。T.里昂和他的博士学位学生C.Scott将测量氧化还原敏感元素（Mo、Re和U）的含量、C和S的浓度以及Fe的形态，以了解在陆地氧化风化作用的影响下，海水成分是如何变化的。A. Anbar将分析Mo同位素和E。Krogstad将分析页岩中的U和Pb同位素以及REE，以约束大气和海洋的氧化还原状态。要求提供资金，以支持岩心记录和从澳大利亚岩心储存库中提取样本，分析硫同位素和同位素，并向我们的同事分发样本。更广泛的影响：该项目将通过来自CIW，UCR，ASU，GSU和西澳大学的博士后，研究生和本科生的参与以及美国和澳大利亚几个机构在地质子学科之间的合作来促进培训和学习。这些结果将有利于科学教育，因为大气中氧气上升的问题已经引起了公众的注意（例如Kerr，2005），不仅将作为对大气中氧气上升的现有假设的一阶检验，而且还将为新的或改进的理论的发展提供框架。我们的共同努力不仅将为侧重于大气和海洋的氧化还原状态的多学科研究树立榜样，而且还将为大气氧开始上升的时间间隔提供对大气和海洋氧化还原状态的定性和定量约束。

Andrey BekkerEAR-0545484The discovery of non-mass dependent fractionation of sulfur isotopes in pre-2.47 Ga pyrite and barite (Farquhar et al., 2000), plausibly related to photochemical processes in an oxygen-free atmosphere (Farquhar et al., 2001) provided a new proxy for the atmospheric redox state. Available data suggest that the oldest Paleoproterozoic glaciation, constrained between 2.45 and 2.32 Ga, was preceded by the rise of atmospheric oxygen. The succession of oxygenation followed by glaciation might track a shift from the greenhouse conditions of a methane-rich, Archean atmosphere to the chill of oxygenated, methane-poor conditions. Yet, an apparent stratigraphic and temporal gap remains between the youngest sedimentary pyrites with a clear non-mass dependent signal in S isotopes formed at 2.47 Ga and pre-glacial pyrites with no non-mass dependent signal. We propose to measure a high resolution stratigraphic record ofEarths oxygenation based on sulfur isotope fractionations to fill the gap with S isotope data forsedimentary pyrites from shales interlayered with banded iron formations within the middle and upper parts of the Brockman Supersequence, Western Australia. The middle and upper parts of the Brockman Supersequence were deposited between 2463 5 Ma and 2449 3 Ma during the late stage of a 2.48-2.45 Ga mantle plume breakout event. Our preliminary data indicate a lack of non-mass dependent fractionation in these units. If confirmed, these data will (1) bracket the rise of atmospheric oxygen to an interval of 20 Ma; (2) provide data to model whether the rise of atmospheric oxygen was gradual or abrupt; and (3) allow a stratigraphic control on the relationship of oxygenation to tectonomagmatic events, climatic changes and other changes in chemical composition of the atmosphere and ocean and C biogeochemical cycle.We will log drill cores DDH WW1 and DD98SGP001, stored by the Geological Survey of Western Australia and Pilbara Iron Co., respectively, measure a high resolution, stratigraphic S isotope record, and carry out supporting analyses of C isotopes in organic matter in drill core shales. S- and C-isotope analyses will be made at the Geophysical Laboratory. Aliquots of well-characterized drill core samples will be distributed for coordinated analyses to our collaborators Olivier Rouxel (WHOI), Tim Lyons and Clint Scott (UCR), Ariel Anbar (ASU), and Eirik Krogstad (GSU) to obtain independent evidence for the rise of atmospheric oxygen. O. Rouxel will analyze Fe isotopes of sedimentary pyrites from shales, Fe oxide minerals in banded iron formations and bulk shale samples to evaluate the response of the Fe cycle to changes in the oceans redox state in the Early Paleoproterozoic. T. Lyons and his Ph.D. student C.Scott will measure the content of redox-sensitive elements (Mo, Re, and U), C and S concentrations, and Fe speciation to understand how seawater composition changed under the impact of the advent of oxidative terrestrial weathering. A. Anbar will analyze Mo isotopes and E. Krogstad will analyze U and Pb isotopes and REE in shales to constrain redox state of the atmosphere and ocean. Funds are requested to support core logging and sample retrieval from Australian drill core repositories, analysis for S- and Cisotopes, and distribution of samples to our colleagues. No direct support of our colleagues research is requested.Broader Impact: The project will promote training and learning through involvement ofpostdoctoral, graduate, and undergraduate students from CIW, UCR, ASU, GSU, and University of Western Australia and collaboration between several institutions in US and Australia across geological sub-disciplines. The results will benefit science education because the question of the rise of atmospheric oxygen has already captured public attention (e.g. Kerr, 2005) and will serve not only as a first order test of existing hypotheses for the rise of atmospheric oxygen but also will provide a framework for the development of new or refined theories. Our combined efforts will not only set an example for multidisciplinary studies focused on the redox state of the atmosphere and ocean but, also, will provide qualitative and quantitative constraints on the redox state of the atmosphere and ocean for the time interval when atmospheric oxygen started to rise.