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

硫同位素比值在以下方面已成为探测沉积岩的最有用的地质生物工具之一：硫循环的演化，大气氧的首次出现和随后上升(S)(和下降)，以及埋藏沉积相(黄铁矿和硫酸盐)的氧化还原平衡。除了以蒸发岩为基础的研究外，碳酸盐伴生硫酸盐(CAS)的日益应用使我们能够填补地球历史上大部分时间内海水硫酸盐的时间记录。然而，当汇编时，这些数据产生了几个令人惊讶的结果，经常记录到34SCA的高频地层变化，以及空间上遥远但同时代的剖面之间的巨大差异，这被推断为反映了埃迪卡拉纪和早古生代大部分地区海相硫酸盐浓度低(~mm)的条件。作为块状岩石的代表，34SCAS可能会受到古代沉积物经常经历的复杂历史的影响，这些历史结合了碎屑、远洋、海底、成岩和变质成分。破译碳酸盐矿物中硫酸盐的多重来源对于从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仪(SIMS)分析34SCAs的方法，以调查多个共存相之间的变异性，包括对单个颗粒和化石的分析，规模(~10；amp；956；m)以前无法获得。在Cameca 7f Geo上收集了初步的SCAS数据，以证明该方法的可行性。如果开发得当，这种方法可以极大地提高我们获得原生海水硫酸盐-34S曲线的能力(例如，来自未改变的腕足动物)，这与从保存完好的单个化石中对13Ccarb、18Ocarb和87Sr/86sr进行显微钻探和分析促进了我们对这些生物地球化学指标在显生界的演化的理解大致相同。从单个颗粒或化石中提取精确的(亚永久精度)数据的能力将使我们能够有力地记录海洋34S的空间变化(例如，底栖生物和远洋生物之间，或从一个盆地到另一个盆地)，而不会出现与复杂的块状岩石代理相关的不确定性。通过开发一种新的分析工具(SIMS分析)，可以广泛应用于整个地球历史上的地球生物学问题，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这一领域。SIMS对SCAS的分析将是PIS实验室本科生、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。皮？S课程？生物地球化学方法？目前有一个关于SIMS应用与实际操作仪器使用的部分，这项技术可以被有益地添加到其中。

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.