EAGER - Testing a new approach to shed light on the dolomite problem - an investigation using the isotopes of Magnesium, Calcium and Strontium.

通过生物（生物矿物）的参与而形成并保存在地质记录中的矿物可以用来阐明地球上生命的进化。此外，这些矿物可以用来重建地层环境中的环境条件。白云岩是地质记录中普遍存在的矿物，也是重要的石油储集岩。因此，白云岩是重建和理解整个地球历史上的环境变化的不可思议的档案，特别是揭示了地球和其他行星上生物的进化。然而，白云岩出现在许多不同的沉积和/或成岩环境中，很难用现有的矿物学或地球化学工具精确地确定形成机制。这限制了这种矿物在地质生物学、石油研究和低温地球化学研究中的应用，并使其复杂化。如果能够明确地识别地质记录中与生物体（微生物白云岩）相关的白云岩，将消除这些复杂性，并允许对沉积环境进行更直接的解释。在这项研究中，研究者假设微生物参与白云岩的形成会产生独特的特征，这些特征可以用作“生物标记”，并能够在地质记录中识别微生物白云岩。研究者将使用在不同温度和生长条件下的受控实验室实验中沉淀的微生物白云岩样品和目前在海洋泻湖和湖泊环境中形成的微生物白云岩样品来验证这一假设。本研究的主要目的是研究Ca、Mg和Sr稳定同位素在白云岩中的应用，以揭示白云岩的形成机制。为了实现这一目标，该研究将首先分析一套白云岩样本（以及它们在实验中沉淀的溶液），以识别独特的特征。对现代泻湖和湖泊环境中最近形成（或目前正在形成）的白云岩以及其他伴生矿物、外聚合物物质和沉淀流体的分析将为这一研究提供补充。在地球表面氧含量增加的两个主要时间间隔，古代白云岩也将被分析。地球化学指纹图谱将与岩石学和地层学资料相结合，使微生物白云岩的鉴定成为可能。溶解样品和色谱分离溶液将使用电感耦合等离子体光学发射光谱（ICP-OES）分析主要和微量元素组成。稳定同位素组成将由多收集器-电感耦合等离子体质谱（MC-ICP-MS）和热电离体质谱（TIMS）测定。固体样品将分析岩石学和可视化（显微镜，扫描电镜，透射电镜），矿物学（XRD）为C和O同位素（IRMS）数据也将收集。研究小组有必要的经验和仪器。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Minerals which are formed through the involvement of organisms (biominerals) and are preserved in the geological record can be used to shed light on the evolution of life on Earth. Moreover, such minerals can be used to reconstruct environmental conditions in the environments of formation. Dolomite is a ubiquitous mineral in the geological record and an important petroleum reservoir rock. Accordingly, dolomites can be incredible archives for reconstructing and understanding environmental changes throughout Earth's history and specifically shed light on the evolution of organisms on Earth and in other planets. However, dolomites occur in many different sedimentary and/or diagenetic settings and it is hard to precisely determine formation mechanisms using currently available mineralogical or geochemical tools. This limits and complicates the utility of this mineral for geobiology, petroleum research, and low temperature geochemical studies. Being able to unequivocally identify dolomites that form in association with living organisms (microbial-dolomites) in the geological record would eliminate some of these complexities and allow for more straightforward interpretation of deposition environments. In this study the investigator hypothesizes that the involvement of microorganisms in the formation of dolomites induces unique signatures that could be used as "bio-markers" and enable identification of microbial-dolomites in the geological record. The investigator will test this hypothesis using microbial-dolomite samples that were precipitated under controlled laboratory experiments at different temperatures and growth conditions and microbial-dolomite samples forming at present in a marine-lagoon and a lake setting. The major goal of this proposed research is to investigate the utility of Ca, Mg and Sr stable isotopes in dolomite to shed light on the mechanisms of dolomite formation. To address this goal the research will first analyze a suite of dolomite samples (and the solutions from which they precipitated experimentally) to identify unique signatures. This will be complimented by the analysis of dolomite that formed recently (or is currently forming) in modern lagoon and lake environments along with other associated minerals, exopolymeric substances and precipitation fluids. Ancient dolomites across the two major time intervals when oxygen levels increased at the Earth surface will also be analyzed. Together with petrographic and stratigraphic information the geochemical fingerprinting will enable identification of microbial-dolomite. Dissolved samples and chromatographically separated solutions will be analyzed for major-and trace element compositions using inductively coupled plasma optical emission spectroscopy (ICP-OES). Stable isotope compositions will be determined by multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) and thermal ionization mass spectrometry (TIMS). Solid samples will be analyzed petrography and visualization (microscopy, SEM, TEM), mineralogy (XRD) for C and O isotope (IRMS) data will also be collected. The research team has the needed experience and instrumentation.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.