COLLABORATIVE RESEARCH: The Oxidation of Kerogen During Weathering

[804781] berner地球化学碳循环对地球大气（Po2, Pco2）在地质时间尺度上的演化具有重要影响。作为这个循环的一部分，沉积有机质（SOM）的氧化作用占维持Po2平衡所需总耗氧量的80%以上。然而，之前很少有人研究SOM氧化的途径、效率或速率，因此地球化学碳循环中的整个联系仍然不明确。有机质氧化为二氧化碳被认为是一个整体的、长期的风化过程，通常的表达式CH2O +O2CO2+H2O意味着作用于均质物质的单步反应。事实上，SOM是复杂且多相的，因此在转化为无机碳之前，氧化可能通过一系列尚未定义的中间产物和顺序氧化反应进行。因此，为了更好地理解SOM氧化过程，需要详细表征在SOM氧化的各个阶段获得的这些结构和成分。本研究拟通过对有机质分子结构发生改变的氧吸收和其他氧化/风化反应的表征，探讨黑色页岩有机质化学风化的途径、速率和效率。在富含有机碳的岩石上，已经沿着风化剖面收集了样本。选定的地层（格林河、伍德福德、新奥尔巴尼和蒙特利）代表了特定的矿物学和有机质类型。因此，本研究的结果将揭示渐进性风化SOM的序列，并表明岩性和有机质类型在确定该序列中可能发挥的作用。通过比较剖面之间的黄铁矿损失和检查已知年龄的剖面，可以限制SOM风化的速率。六个页岩剖面的初步结果表明，在风化过程中，总有机碳在3-5 m的距离上损失了70-90%。每条剖面表面都有少量但数量可观的残余有机质残留，表明有机质再矿化效率不完全。对风化剖面的进一步分析将确定有机质的元素、同位素和岩石学组成，以及页岩矿物学和诸如粒度和渗透率等物理数据。有机地球化学分析工具，特别是核磁共振，红外光谱，以及与气相色谱-质谱联用的闪蒸热解，将用于破译分子水平的结构特征，如碳骨架类型和含氧功能。14C年代测定法将用于区分受现代土壤碳污染的样品。通过研究SOM风化的速率、效率和途径，以及残余（放射性碳死亡）有机质向当代有机碳储层（土壤、湖泊和/或海洋沉积物）的供应，本研究将对地球科学的几个学科产生有价值的影响，包括化学海洋学、表面地球化学、地球化学循环模型、环境地球化学和第四纪地质学。该项目的合作性质以及所使用的分析工具、化学技术和数值方法的范围将为参与该项目的研究生和本科生提供坚实的经验和知识基础。SOM风化的研究（包括项目的发展和提案的准备）是研究生Steven Petsch博士论文研究的重要组成部分，将本科生纳入研究将提高他们的教育和研究。

9804781BernerThe geochemical carbon cycle exerts a major influence on the evolution of Earth's atmosphere (Po2, Pco2) over geologic time scales. As part of this cycle, oxidation of sedimentary organic matter [SOM] comprises more than 80% of the total oxygen consumption required to maintain an equable Po2. However, little prior effort has been made to examine the pathways, efficiency or rates of SOM oxidation, and thus an entire link in the geochemical carbon cycle remains poorly defined. Oxidation of organic matter to carbon dioxide is assumed to be the overall, long-term weathering process, with the common expression CH2O +O2CO2+H2O implying a single-step reaction acting on an homogeneous material. The reality is that SOM is complex and heterogeneous, so that oxidation likely proceeds through an as yet undefined series of intermediate products and sequential oxidation reactions prior to conversion to inorganic carbon. Thus, to better understand the process of SOM oxidation, detailed characterization of these structures and compositions obtained at various stages of SOM oxidation is required.This study proposes to investigate the pathways, rates and efficiency of the chemical weathering of organic matter contained in black shales by characterizing uptake of oxygen and other oxidation/weathering reactions, which alter the molecular structure of SOM. Samples have already been collected along weathering profiles developed on organic carbon-rich rocks. The selected formations (Green River, Woodford, New Albany, and Monterey) represent specific end-members of mineralogy and organic matter type. Thus, the results of this study will both reveal the sequence of progressively weathered SOM, and indicate the role that lithology and organic matter type may play in defining this sequence. The rate of SOM weathering will be constrained by comparing pyrite loss between profiles and by examining profiles of known age. Preliminary results from six shale profiles indicate between 70-90% loss of total organic carbon across a distance of 3-5 m during weathering. A small but significant mass of relict organic matter remains at the surface of each profile, implying incomplete SOM remineralization efficiency. Further analyses of the weathering profiles will determine elemental, isotopic and petrographic composition of the organic matter, along with shale mineralogy and physical data such as grain size and permeability. Organic geochemical analytical tools, specifically nuclear magnetic resonance, infrared spectroscopy, and flash pyrolysis in tandem with gas chromatography-mass spectrometry, will be used to decipher molecular level structural characteristics such as carbon skeleton types and oxygen-containing functionality. 14C age dating will be used to distinguish samples contaminated by modern soil carbon.By addressing the rate, efficiency and pathways of SOM weathering and supply of relict (radiocarbon dead) organic matter to contemporary organic carbon reservoirs (soils, lacustrine and/or marine sediments), this study will have a valuable impact on several disciplines of the Earth sciences including chemical oceanography, surficial geochemistry, geochemical cycle modeling, environmental geochemistry, and Quaternary geology. The collaborative nature of the project and the range of analytical tools, chemical techniques and numerical methods employed will generate a solid foundation of experience and knowledge for graduate students and undergraduates involved in this project. This study of SOM weathering (including development of the project and preparation of this proposal) comprises a crucial part of the Ph.D. thesis research for a graduate student, Steven Petsch, and the inclusion of undergraduates in the research will enhance both their education and the research.