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

智力优势：在过去的十年中，对全球碳和硫循环的详细调查增加了我们对生物圈氧化的理解。地球逐渐氧化？的生物圈，由埋藏的有机质驱动，被解释为导致了光解质量无关的S-同位素比的均匀化，其次是海洋硫酸盐浓度的增加和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34 S/32 S和33 S/32 S的同时测量，或使用不同的地球化学代用指标，如碳酸盐相关硫酸盐的S同位素分析，或CAS。特别是，CAS数据集的可用性导致了一些建模工作，旨在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利用了同位素变化的时间依赖方程，其中S-（或C-）同位素变化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率的作用。不幸的是，在前寒武纪，对这种不断增长的CAS记录的解释，以及由此产生的C-S联系，受到以下因素的限制：（1）我们对代表大部分保存的地层记录的有限盆地和陆表海环境中CAS同位素组成的潜在变化的理解相对较差，（2）对其他研究充分的层序的典型地质年代学控制较差，（3）C、S储层规模的极大差异，影响了同位素记录的灵敏度，从而限制了对它们的解释。然而，目前的数据表明，到前寒武纪末，海洋碳和硫酸盐储层达到了应该优化保存在各自同位素系统中的信息的大小。为了更好地了解CAS在沉积系统中的行为以及C和S系统之间的联系，我们提出了一个综合领域，地球化学，阿根廷前科迪勒拉和纽芬兰西部晚寒武世和中晚奥陶世地层的年代学研究。这些地点（1）保存了开阔的海洋序列，这应该限制其同位素记录的局部重叠，（2）代表了理解从元古宙到中生代世界过渡中C-S同位素循环演化的关键时间间隔，（3）提供机会，以确定来自CAS的S同位素记录及其随时间变化的建模是否可以区分小-海洋环流和相关的营养限制循环可能导致海洋氧合的规模变化。最后，阿根廷剖面内的大量辉长岩为解释C-S记录和在高分辨率年表的背景下约束拟议的建模提供了独特的机会。该项目旨在推进发现，同时促进教学，培训，通过扩大碳酸盐的广度来学习在田纳西大学进行实地和地球化学研究，并让不同教育水平的学生参与科学探究过程。该项目资助一名女博士。学生，并将继续参与研究的本科生（9在5年内，导致5同行评议的出版物）通过提供至少两名学生的研究机会的PI强大的历史。最后，该项目将通过实地研究和美国-基于阿根廷博士的地球化学培训。学生费尔南多·戈麦斯。除了这一建议所支持的更广泛的影响外，P.I.是NSF资助的GK-12项目的当前参与者，该项目旨在加强TN农村中学的地球科学教育。PI已经将最初的野外季节作为探索地质年代的案例研究，目前正在利用这个项目培训当地的科学教师Jay Bachman，教授地球科学中使用的岩相学和地球化学技术。PI希望在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有助于EARTHIME倡议，为地球历史建立一个详细的、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.