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

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.