COLLABORATIVE RESEARCH: The Oxidation of Kerogen During Weathering

合作研究：风化过程中干酪根的氧化

• 批准号: 9804781
• 负责人: Robert Berner
• 金额: $ 23.31万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-08-01 至 2001-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9804781&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Oxidation; Kerogen; During

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.

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。作为这一循环的一部分，沉积有机质[SOM]的氧化占维持稳定的PO2所需的总耗氧量的80%以上。然而，以前几乎没有努力研究土壤有机质氧化的途径、效率或速率，因此，地球化学碳循环中的整个环节仍然没有得到很好的界定。有机物质氧化成二氧化碳被认为是整体的、长期的风化过程，常见的表达式CH2O+O2CO2+H2O意味着作用于均质材料的一步反应。现实情况是，SOM是复杂和异质的，因此在转化为无机碳之前，氧化可能通过一系列尚未确定的中间产物和顺序的氧化反应进行。因此，为了更好地了解SOM氧化的过程，需要对SOM氧化的各个阶段获得的这些结构和组成进行详细的表征。本研究建议通过表征氧的吸收和其他氧化/风化反应来研究黑色页岩中有机质的化学风化途径、速率和效率，这些反应会改变SOM的分子结构。已经在有机富碳岩石上形成的风化剖面上收集了样品。选定的地层(格林河、伍德福德、新奥尔巴尼和蒙特利)代表了矿物学和有机质类型的特定端元。因此，这项研究的结果既将揭示逐步风化的有机质序列，也表明岩性和有机质类型在确定该序列中可能起到的作用。SOM的风化速率将通过比较剖面之间的黄铁矿损失和检查已知年龄的剖面来限制。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米的距离内损失了70%-90%。在每个剖面的表面仍有少量但数量可观的残留有机质，这意味着SOM再矿化效率不够高。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，以及页岩矿物学和物理数据，如粒度和渗透率。有机地球化学分析工具，特别是核磁共振、红外光谱和闪速热解与气相色谱-质谱联用，将用于破译分子级结构特征，如碳骨架类型和含氧官能团。14C测年将用于区分被现代土壤碳污染的样品。通过研究土壤有机质风化的速率、效率和途径以及残留(放射性碳死亡)有机质向当代有机碳库(土壤、湖泊和/或海洋沉积物)的供应，这项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、地表地球化学、地球化学循环模拟、环境地球化学和第四纪地质学。该项目的协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。这项关于SOM风化的研究(包括项目的开发和本提案的准备)是研究生Steven Petsch博士论文研究的关键部分，将本科生纳入研究将促进他们的教育和研究。