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，这种矿物还可以用来重建形成环境中的环境条件。白云石是地质记录中普遍存在的矿物，也是重要的油气储集岩。因此，白云岩可以成为重建和了解整个地球历史上环境变化的令人难以置信的档案，并特别揭示地球和其他星球上生物的进化。然而，白云石赋存于许多不同的沉积和/或成岩环境中，利用目前可用的矿物学或地球化学工具很难准确确定形成机制。这限制了这种矿物在地球生物学、石油研究和低温地球化学研究中的应用，并使其复杂化。能够明确地识别与地质记录中的活体生物(微生物-白云岩)有关的白云岩，将消除其中的一些复杂性，并允许对沉积环境进行更直接的解释。在这项研究中，研究人员假设微生物参与了白云岩的形成，产生了独特的特征，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。研究人员将使用在不同温度和生长条件下在受控实验室实验下沉淀的微生物白云石样品和目前在海相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。这项研究的主要目的是研究白云岩中钙、镁和锶稳定同位素的用途，以揭示白云岩的形成机制。为了达到这一目标，该研究将首先分析一套白云石样品(以及它们通过实验沉淀出来的溶液)，以确定独特的签名。这将得到最近(或目前正在形成)现代泻湖和湖泊环境中形成的白云石以及其他伴生矿物、外聚物质和降水流体的分析的补充。还将分析两个主要时间段的古白云岩，当时地球表面的氧气水平增加。结合岩石学和地层学信息，地球化学指纹将使微生物-白云岩的识别成为可能。溶解的样品和色层分离的溶液将使用电感耦合等离子体光学发射光谱(ICP-OES)分析常量和微量元素组成。稳定的同位素组成将用多收集器电感耦合等离子体质谱(MC-ICPMS)和热电离质谱(TIMS)进行测定。将对固体样品进行岩相学分析，并收集C和O同位素(IRMS)的可视化(显微镜、扫描电子显微镜、透射电子显微镜)、矿物学(X射线衍射)数据。研究团队拥有所需的经验和手段。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.