Collaborative Research: Experimentally Evaluating the Relationship between Cation Ordering and Oxygen and Clumped Isotope Fractionation in Dolomite

合作研究：实验评估白云石中阳离子有序性与氧和团簇同位素分馏之间的关系

• 批准号: 2118660
• 负责人: Ian Winkelstern
• 金额: $ 5.06万
• 依托单位: Grand Valley State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2118660&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimentally; Evaluating; Relationship

Magnesium-bearing carbonate minerals, such as calcite and dolomite, are ubiquitous in marine settings and represent an extremely valuable, deep-time record of Earth's past. Subsurface reservoirs comprised of these minerals can also host vast resources that are key to the economic activity and vitality of the country. To effectively and efficiently develop these economic resources, and to use these minerals as viable paleoenvironmental records, it is vital to understand their geologic history. To do this geoscientists often use geochemical proxies to constrain past environmental conditions. This fundamental research uses laboratory experiments to constrain how oxygen isotope compositions, an important geochemical proxy in dolomite and calcite, are impacted by an often overlooked mineralogical parameter called cation ordering. The results of this study will allow geoscientists to both improve their understanding of the natural environments in which dolomite forms on Earth's surface and potentially increase the fidelity of dolomite and other carbonate minerals as a geochemical archive of Earth history. The use of dolomite as a paleoenvironmental and diagenetic proxy is inhibited by uncertainty in published oxygen isotope water-mineral fractionation values. It is hypothesized here that much of this uncertainty can be attributed to water-mineral fractionation differences between different types of Ca-Mg-carbonate minerals (e.g., very high-Mg calcite, poorly-ordered dolomite and well-ordered dolomite) that have been collectively called ‘dolomite’ in the literature. This hypothesis is rooted in empirical data from the rock record and the laboratory that indicate that these various Ca-Mg-carbonate minerals form in sequence during dolomitization by different crystal growth mechanisms, which leads to vastly different Mg-Ca compositions, Mg-Ca cation ordering, crystalline microstructures, and potentially oxygen isotopic compositions. To test this hypothesis, well-controlled, high-temperature dolomitization experiments will be used where fluid and mineral δ18O will be measured through the sequential mineral transitions from very high-Mg calcite to poorly-ordered dolomite to well-ordered dolomite. How isotopic fractionation varies between these Ca-Mg-carbonate minerals, and the degree to which δ18O values are inherited from each precursor phase, will be assessed. The clumped isotopic composition of each dolomite phase will be measured and used to investigate whether cation ordering affects the clumped isotope acid digestion fractionation factor, another value for which published estimates differ greatly. This research aims to understand the relationship between cation ordering and δ18O in dolomite through well-constrained laboratory experiments. The isotopic framework developed in this project will enable more precise application of dolomite δ18O and 47 measurements in a wide variety of studies. These results will have the potential to enhance the use of stable and clumped isotope proxies in sedimentological studies of natural dolomites, and will allow for better interpretations of the diagenetic conditions of dolomitization. The results may also permit the use of shallow marine dolomites as more robust paleoclimate archives.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

含镁的碳酸盐矿物质（例如钙和白云岩）在海洋环境中无处不在，代表了地球过去极为有价值的深度记录。由这些矿物质组成的地下储备还可以托管大量资源，这是该国经济活动和活力的关键。为了有效有效地发展这些经济资源，并将这些矿物作为可行的古环境记录，了解其地质历史至关重要。进行这种地球科学家经常使用地球化学代理来限制过去的环境条件。这项基本研究使用实验室实验来限制氧同位素组成是如何受到经常被忽略的矿物参数（称为阳离子排序）的影响的重要地球化学代理。这项研究的结果将使地球科学家既能够提高对地球表面形成白云岩形成的自然环境的理解，又可能提高白云岩和其他碳酸盐矿物的忠诚度，作为地球历史的地球化学档案。在已发表的氧同位素水矿物分馏值中，不确定性抑制了白云岩作为古环境和成岩代理的使用。这里假设这种不确定性可以归因于不同类型的CA-MG-碳酸盐矿物质之间的水矿物矿物分馏差异（例如，非常高的钙钙，有序的白云石和井井有条的白云石）在文献中被共同称为“黑白石”。这一假设源于岩石记录和实验室的经验数据，表明通过不同的晶体生长机制，这些各种CA-MG-碳酸盐矿物质会顺序形成，从而导致MG-CA组成，MG-CA阳离子序列，晶体微观结构，潜在的氧气组合和潜在的氧气组合。为了检验这一假设，将使用良好控制的高温白云油化实验，如果将通过从非常高的钙钙到订购良好的白云石到有序的白云石的顺序矿物质过渡，将测量流体和矿物Δ18O。将从每个前体阶段进行评估。将测量每个白云岩相的簇同位素组成，并用于研究阳离子排序是否影响聚类的同位素酸消化分级因子，这是另一个值的估计值不同。这项研究旨在通过良好约束的实验室实验来了解白云岩中阳离子排序与Δ18O之间的关系。该项目中开发的同位素框架将使白云岩Δ18O和47种测量在各种研究中更精确地应用。这些结果将有可能增强天然白云岩的沉积学研究中稳定和簇的同位素代理的使用，并可以更好地解释对白云岩的成岩系条件。结果还可以允许使用浅海洋白云岩作为更强大的古气候档案。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛的影响评估标准通过评估来支持的。