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

通过生物体（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揭示地球上生命的进化。此外，这些矿物可用于重建形成环境中的环境条件。白云岩是地质记录中普遍存在的矿物，也是重要的油气储集岩。因此，陨石可以是重建和理解整个地球历史上环境变化的令人难以置信的档案，特别是揭示了地球和其他行星上生物体的进化。 然而，钙钛矿发生在许多不同的沉积和/或成岩环境中，很难使用目前可用的矿物学或地球化学工具精确确定形成机制。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。如果能够明确地识别地质记录中与生物体（微生物-微生物）相关的微生物，将消除其中一些复杂性，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，微生物参与形成的方解石诱导独特的签名，可用作“生物标志物”，并使识别微生物方解石的地质记录。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中沉淀的微生物白云石样品以及目前在海洋泻湖和湖泊环境中形成的微生物白云石样品来测试这一假设。本研究的主要目的是探讨白云岩中Ca、Mg和Sr稳定同位素的应用，以阐明白云岩的形成机制。为了实现这一目标，该研究将首先分析一套白云石样品（以及它们通过实验沉淀的溶液），以识别独特的特征。这将通过对现代泻湖和湖泊环境中最近形成（或目前正在形成）的白云石以及其他相关矿物、外聚合物物质和沉淀流体的分析来补充。还将分析地球表面氧气水平增加的两个主要时间间隔内的古玄武岩。结合岩相学和地层学信息，地球化学指纹将能够识别微生物白云岩。将使用电感耦合等离子体发射光谱法（ICP-OES）分析溶解样品和色谱分离溶液的主要和痕量元素组成。将通过多收集器电感耦合等离子体质谱（MC-ICP-MS）和热电离质谱（TIMS）测定稳定同位素组成。将对固体样品进行岩相学和可视化分析（显微镜、SEM、TEM），还将收集C和O同位素（IRMS）数据的矿物学（XRD）。该奖项反映了NSF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.