Behavior of Marine Sulfate in the Early Paleozoic: Extending the Trace Sulfate Proxy

智力价值：在过去的十年里，对全球碳和硫循环的详细研究增加了我们对生物圈氧合作用的理解。地球的渐进式氧化作用？S生物圈在有机质埋藏的驱动下，导致了与光解质量无关的S同位素比值的均一化，随后海洋硫酸盐浓度增加，海洋硫的氧化还原循环增强。其中许多进展依赖于新的分析能力的发展，如34S/32S和33S/32S的同时测量，或使用不同的地球化学替代方法，如碳酸盐伴生硫酸盐的S同位素分析，或CAS。特别是，CAS数据集的提供导致了一些建模工作，以寻求更好地了解硫循环动力学及其与海洋碳同位素记录的联系。这些模型中最复杂的是利用一个随时间变化的同位素变化方程，其中S(或C-)同位素变化的速率不仅反映了输入和输出通量，而且还反映了海洋储层的大小，这起到了缓冲同位素变化速率的作用。不幸的是，对这一不断增长的CAS记录以及C-S联系的解释在前寒武纪受到以下因素的限制：(1)我们对代表大部分保存下来的地层记录的受限盆地和陆表海环境中CAS同位素组成的潜在变异性了解相对较差，(2)在其他方面研究得很好的序列的地质年代学控制通常较差，(3)C和S储集层大小的极端差异，这影响了同位素记录的敏感性，从而限制了它们的解释。然而，目前的数据表明，到前寒武纪结束时，海相碳酸盐和硫酸盐储集层的规模达到了应该优化各自同位素体系中保存的信息的规模。为了更好地了解CAS在沉积体系中的行为以及C和S系统之间的联系，我们对阿根廷前寒武纪和西纽芬兰的晚寒武世和中晚奥陶世地层进行了综合野外、地球化学和年代学研究。这些地点(1)保存了开阔的海洋序列，限制了其同位素记录的局部叠加；(2)代表了对于理解从元古界向显生界过渡过程中C-S同位素旋回演化至关重要的时间间隔；(3)提供了机会来确定中国科学院S同位素记录及其随时间变化的模拟是否能够区分可能由海洋环流驱动的海洋氧合作用的小尺度变化和相关的营养限制旋回。最后，阿根廷部分的大量膨润土为解释C-S记录提供了独特的机会，并在高分辨率年代学的背景下限制了拟议的建模。广泛影响：该项目旨在通过扩大田纳西大学碳酸盐野外和地球化学研究的广度，并让来自不同教育水平的学生参与科学研究过程，在促进教学、培训和学习的同时促进发现。该项目支持一名女性博士生，并将通过为至少两名学生提供研究机会，延续PIS让本科生参与研究的强大历史(5年内9次，导致5本同行评议的出版物)。最后，该项目将通过实地研究和阿根廷博士生费尔南多·戈麦斯在美国的地球化学培训来支持国际科学合作。除了这项提议所支持的更广泛的影响外，P.I.目前也是NSF资助的GK-12项目的参与者，该项目旨在加强TN农村中学的地球科学教育。国际和平协会已经将最初的野外考察季节作为探索地质时代的案例研究，目前正在利用这一项目培训当地科学教师Jay Bachman，教授地质科学中使用的岩石学和地球化学技术。国际和平研究所希望在整个项目期间继续开展此类活动。此外，地质年代学和地球化学分析的结果将增加EARTHIME倡议，为地球历史建立一个详细、综合的时间尺度。

Intellectual Merit: In the last decade, detailed investigation of the global carbon and sulfur cycles has increased our understanding of biospheric oxygenation. Progressive oxygenation of the Earth?s biosphere, driven by burial of organic matter, is interpreted to have resulted in the homogenization of photolytic mass-independent S-isotope ratios, followed by an increase in marine sulfate concentration and the enhanced redox cycling of marine sulfur. Many of these advances have relied on the development of new analytical capabilities, such as the simultaneous measurement of 34S/32S and 33S/32S, or the use of different geochemical proxies, such as the S-isotope analysis of carbonate-associated sulfate, or CAS. Availability of a CAS dataset, in particular, has resulted in a number of modeling efforts that seek to better understand sulfur cycle dynamics and its linkages with the marine C-isotope record. The most sophisticated of these models utilizes a time-dependent equation for isotopic change wherein the rate of S-(or C-) isotope change reflect not only the input and output fluxes, but also marine reservoir size, which acts to buffer the rate of isotopic change. Unfortunately, interpretation of this growing CAS record, and thus C-S linkages, is limited in the Precambrian by (1) our relatively poor understanding of potential variability of CAS isotopic compositions in restricted basins and epeiric sea environments that represent much of the preserved stratigraphic record, (2) the typically poor geochronologic control of otherwise well-studied successions, and (3) the extreme differences in the size of both C and S reservoirs, which affects the sensitivity of isotopic records and therefore limits their interpretation. Current data suggests, however, that by the end of the Precambrian, marine carbon and sulfate reservoirs reached sizes that should optimize the information preserved in their respective isotopic systems.In order to better understand the behavior of CAS in sedimentary systems and the linkages between C and S systems, we propose an integrated field, geochemical, and geochronological study of Late Cambrian and Mid-Late Ordovician strata of the Argentine Precordillera and Western Newfoundland. These localities (1) preserve open marine successions that should limit local overprinting of their isotopic records, (2) represent time intervals critical to understanding the evolution of C-S isotopic cycles in the transition from the Proterozoic to Phanerozoic worlds, (3) provide the opportunity to determine if S-isotope records from CAS and their timedependent modeling can distinguish small-scale changes in marine oxygenation potentially driven by oceanographic circulation and related cycles of nutrient limitation. Finally, numerous bentonites within the Argentine section provide the unique opportunity to interpret C-S records and constrain proposed modeling within the context of a high-resolution chronology.Broader Impacts: This project aims to advance discovery while promoting teaching, training, and learning by expanding the breadth of carbonate-based field and geochemical research at the University of Tennessee and involving students from differing educational levels in the process of scientific inquiry. The project supports one female Ph.D. student, and will continue the PIs strong history of involving undergraduates in research (9 in 5 years, leading to 5 peer-reviewed publications) by providing research opportunities for at least two students. Finally, the project will support international scientific collaboration through field research and U.S.-based geochemical training of Argentinian Ph.D. student Fernando Gomez. In addition to broader impacts supported by this proposal, the P.I. is a current participant in an NSF-funded GK-12 project aimed enhancing earth science education in rural TN middle schools. The PI has already used the initial field season as a case-study in exploring geologic time, and is currently using this project to train a local science teacher, Jay Bachman, on petrographic and geochemical techniques used in the geosciences. The PI expects to continue such activities through the duration of the project. Furthermore, results of geochronological and geochemical analysis will add to the EARTHIME initiative of creating a detailed, integrated time-scale for Earth history.