Multiple Sulfur Isotope Fractionations during Thermal Decomposition of and Thermochemical Sulfate Reduction by Natural Organic Compounds

天然有机化合物热分解和热化学硫酸还原过程中的多种硫同位素分馏

• 批准号: 1024550
• 负责人: Hiroshi Ohmoto
• 金额: $ 22.27万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1024550&HistoricalAwards=false
• 关键词: Multiple; Sulfur; Isotope; Fractionations; during

Intellectual merit: Anomalous isotope fractionations of sulfur (AIF-S) signatures preserved in pre-2.4 Ga sedimentary rocks have been used to drive the debate about when the Earth first had an oxygenated atmosphere. The mechanism for these sulfur isotope anomalies has been postulated to be produced by UV photolysis of volcanic SO2 gas in an anoxic atmosphere. Recent investigators, however, have recognized that the UV photolysis of SO2 by a broadband UV lamp, which closely simulates the UV spectra of sunlight, does not produce many of the AIF-S signatures in natural samples. The PI and colleagues reported the presence of distinct AIF-S signatures in the H2S and Cr-reducible sulfur species (probably disulfide) that were generated from relatively high temperature (150-200°C) reactions between crystals of amino acids and sodium sulfate in the presence of H2O, and suggested that thermochemical sulfate reduction (TSR) by organic matter in sediments might have produced some of the AIF-S signatures in pre-2.4 Ga sedimentary rocks (Watanabe et al., 2009). This discovery is significant, because, until this study, UV photolysis of SO2 was the only known cause for AIF-S. The TSR model was criticized by many researchers who claimed the process was not applicable to natural systems, in which the organic compounds are complex. Research proposed in this proposal will systematically investigate: (i) the multiple sulfur isotopic characteristics of the gaseous, liquid and solid products (e.g., H2S, Cr-reductive S, organic S compounds) and (ii) chemical characteristics (e.g., C/H/S/N ratios and compound ratios) of heavy hydrocarbon (oil) and light hydrocarbon (gas) that were generated during (a) thermal decomposition of, and (b) TSR by, the remnants of cyanobacteria and immature kerogen from the Eocene Green River Formation.The results would provide insight into (a) why AIF-S signatures are observed in both organic-rich, and some organic-poor rocks (e.g., BIFs and carbonates), (b) why AIF-S apparently disappeared in younger rocks; and (3) how the AIF-S record in sedimentary rocks can be linked to the environmental, chemical, and biological evolution of early Earth.Broader Impacts: The proposed project will a graduate student as a part of his Ph.D. thesis research and two undergraduate students (one per year) as a research assistants. The PI plans to participate in the WISE program: Women in the Sciences and Engineering Institute with a graduate researcher. Future students and young scientists will benefit from the new data and ideas generated from this project.

智力优点：保存在前2.4 Ga沉积岩中的异常硫同位素分馏（AIF-S）特征已被用于推动关于地球何时首次拥有含氧大气的争论。这些硫同位素异常的机制已被假定为在缺氧大气中的火山SO2气体的UV光解产生的。然而，最近的研究人员已经认识到，通过宽带紫外灯对SO2的紫外光分解（接近模拟太阳光的紫外光谱）不会在天然样品中产生许多AIF-S特征。PI及其同事报告了H2S和Cr可还原硫物质中存在不同的AIF-S特征（可能是二硫化物），产生于相对较高的温度（150-200°C）在H2O存在下氨基酸晶体和硫酸钠之间的反应，并建议沉积物中有机物的热化学硫酸盐还原（TSR）可能产生了一些前-2.4 Ga沉积岩（Watanabe等人，2009年）。这一发现意义重大，因为在这项研究之前，SO2的紫外光分解是AIF-S的唯一已知原因。TSR模型受到许多研究人员的批评，他们声称该过程不适用于有机化合物复杂的自然系统。本提案中提出的研究将系统地调查：（i）气体、液体和固体产品的多种硫同位素特征（例如，H2S、Cr-还原性S、有机S化合物）和（ii）化学特性（例如，通过对始新世绿色河组中的蓝藻残余物和未成熟干酪根的热分解和TSR反应过程中产生的重烃（油）和轻烃（气）的碳/氢/硫/氮比值和化合物比值）的分析，可以深入了解（a）为什么在富含有机质和一些有机质贫乏的岩石（例如，BIFs和碳酸盐），（B）为什么AIF-S在较年轻的岩石中明显消失;以及（3）沉积岩中的AIF-S记录如何与早期地球的环境，化学和生物进化联系起来。更广泛的影响：拟议的项目将作为他博士学位的一部分。论文研究和两名本科生（每年一名）作为研究助理。PI计划与一名研究生研究员一起参加WISE方案：科学和工程学院的妇女。未来的学生和年轻科学家将受益于该项目产生的新数据和想法。