SIMS Analysis of Carbonate-Associated Sulfate: Toward Building a d34S Record of Individual Carbonate Grains and Fossils

碳酸盐相关硫酸盐的 SIMS 分析：建立单个碳酸盐颗粒和化石的 d34S 记录

• 批准号: 0951509
• 负责人: David Fike
• 金额: $ 15.12万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-15 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0951509&HistoricalAwards=false
• 关键词: SIMS; Analysis; Carbonate; Associated; Sulfate

Sulfur isotope ratios (δ34S) have become one of the most useful geobiological tools for probing sedimentary rocks with regard to: the evolution of the sulfur cycle, the first appearance and subsequent rise(s) (and falls) of atmospheric oxygen, and the redox balance of buried sedimentary phases (pyrites vs. sulfates). Moving beyond evaporite-based studies, the increasing application of carbonate-associated sulfate (CAS) has enabled us to fill in the temporal record of seawater sulfate (δ34SSW) over much of Earth history. When compiled, however, these data yield several surprises, often recording high-frequency stratigraphic variation in δ34SCAS and large differences in δ34SCAS between spatially distant but coeval sections, which are inferred to reflect conditions of low (~mM) marine sulfate concentrations for much of the Ediacaran and early Paleozoic. As a bulk-rock proxy, δ34SCAS can be influenced by the complex histories that ancient sediments often have experienced, combining detrital, pelagic, benthic, diagenetic, and metamorphic components. Deciphering the multiple origins of sulfate within carbonate minerals is critical to extract meaningful information from δ34SCAS about the depositional and diagenetic environment. This project will develop a method to analyze δ34SCAS using secondary ion mass spectrometry (SIMS) to investigate the variability of δ34SCAS between multiple co-existing phases, including analysis of individual grains and fossils, at a scale (~10μm) previously unobtainable. Preliminary δ34SCAS data have been collected on a Cameca 7f Geo to demonstrate the feasibility of this method. With proper development, this approach can dramatically improve our ability to a primary seawater sulfate δ34S curve through time (e.g., from unaltered brachiopods), much the same way that micro-drilling and analysis of δ13Ccarb, δ18Ocarb, and 87Sr/86Sr from individual well-preserved fossils advanced our understanding of the evolution of these biogeochemical proxies over the Phanerozoic. The ability to extract precise (sub-permil precision) δ34SCAS data from individual grains or fossils would allow us to robustly document spatial variations in marine δ34S (e.g., between benthic and pelagic organisms, or from basin to basin), without the uncertainties associated with complex bulk-rock proxies. By developing a new analytical tool (SIMS analysis of δ34SCAS) that can be widely applied to geobiological questions throughout Earth history, this project will open up a new field of microanalytical work that can be fruitfully explored by many researchers for decades to come. Analysis of δ34SCAS by SIMS will be a central component of undergraduate, graduate, and post-graduate research in the PIs lab, providing them with research experience using cutting-edge analytical tools and techniques. The PI?s course ?Methods in Biogeochemistry? currently has a section on SIMS applications with hands-on instrument use, to which this technique could profitably be added.

硫同位素比（δ 34 S）已成为探测沉积岩的最有用的地球生物学工具之一，涉及：硫循环的演化、大气氧的首次出现和随后的上升（和福尔斯）以及埋藏沉积相（黄铁矿与硫酸盐）的氧化还原平衡。除了基于碳酸盐的研究之外，碳酸盐相关硫酸盐（CAS）的应用越来越多，使我们能够填补地球历史上大部分时间的海水硫酸盐（#948; 34 SSW）的时间记录。 然而，当编译时，这些数据产生了几个惊喜，经常记录δ 34 SCAS中的高频地层变化和δ 34 SCAS之间的空间距离，但同时代的部分，推断反映了低（毫米）海洋硫酸盐浓度的条件下，埃迪卡拉纪和早古生代。 作为散装岩石代理，δ 34 SCAS可能受到古代沉积物通常经历的复杂历史的影响，包括碎屑、远洋、底栖、成岩和变质成分。 解读碳酸盐矿物中硫酸盐的多重来源对于从#948; 34 SCAS中提取有关沉积和成岩环境的有意义的信息至关重要。该项目将开发一种使用二次离子质谱（西姆斯）分析#948; 34 SCAS的方法，以研究#948; 34 SCAS在多个共存相之间的变化，包括分析单个颗粒和化石，在以前无法获得的尺度（~10 #956;m）。在Cameca 7 f Geo上收集了初步的#948; 34 SCAS数据，以证明该方法的可行性。通过适当的开发，这种方法可以大大提高我们对初级海水硫酸盐34 S随时间变化曲线的能力（例如，来自未改变的腕足动物），与δ 13 Ccarb，δ 18 Ocarb和87 Sr/86 Sr比值的变化，进一步加深了我们对这些地球化学指标在中生代演化的认识。从单个颗粒或化石中提取精确（亚permil精度）#948; 34 SCAS数据的能力将使我们能够稳健地记录海洋#948; 34 S的空间变化（例如，海底生物和大洋生物之间或从盆地到盆地之间的差异），而没有与复杂的大块岩石代用指标有关的不确定性。通过开发新的分析工具（δ 34 SCAS）可以广泛应用于整个地球历史的地球生物学问题，该项目将开辟一个新的微观分析工作领域，许多研究人员可以在未来几十年内卓有成效地探索。分析δ西姆斯的34 SCAS将成为PI实验室的本科生，研究生和研究生研究的核心组成部分，为他们提供使用尖端分析工具和技术的研究经验。私家侦探？怎么走？生物地球化学方法目前有一个关于西姆斯应用程序与动手仪器使用的部分，这种技术可以有益地添加到其中。