U.S.-France Collaborative Study of the Alteration of Ancient Stromatolites: New Insights through Coupled Petrology and Isotope Geochemistry

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a non-technical explanation Stromatolites, the macrofossil evidence of microbial activity, are an important biosignature in the search for life on early Earth and in extraterrestrial missions. Although it has become increasingly important to place value on organic biomarkers to define a record of past life, stromatolites remain the most readily visible microbial macrofossil. Yet, the taphonomic effect of diagenesis and metamorphism on stromatolites is poorly known, hampering their utility as a faithful recorder of past life.The project proposes to develop a new collaboration to describe and quantify the effects of contact and regional metamorphism and fluid-induced diagenetic changes on biogenic stromatolite beds of the 1,878 Ma Biwabik-Gunflint iron formations of the Lake Superior region. This target has been chosen because it offers a phenomenal natural laboratory setting that is accessible, samples can be carefully and accurately plotted in a three-dimensional framework, and the geologic history is complex and covers several divergent taphonomic pathways. The full study will be significant to researchers studying paleontological and biogeochemical patterns in other altered sediments both on early Earth and extraterrestrial targets. The research will provide critical primary research experience for two undergraduate students at a primarily undergraduate institution, enhancing their careers with opportunities not available at their host institution. The teaching methods of the PI will be enhanced with a greater understanding of coupled petrologic and geochemical information. Most critically, by creating a new collaboration, there will develop additional opportunities for interdisciplinary project-based learning which forms an integral component of the PI?s pedagogy.a technical description The focus of this CNIC proposal is to work in a world-class laboratory at the Université of Brest, France. During this visit, the new collaborative team will analyze samples for iron isotope and trace element geochemical proxies that will integrate with the PI?s extensive database on mineralogic and petrographic changes throughout the metamorphic gradient of a biogenic stromatolite layer. This specific collaboration will both complement and challenge previous research on the geochemical imprint of iron formations and the preservation of original geobiochemical signatures in ancient fossil deposits. The implications will be of major importance to researchers in fields as diverse as astrobiology, geochemistry, mineralogy, economic geology, and paleobiology.