Development of a High-Resolution Stromatolite Facies Model: Environmental Impacts at the Dawn of Oxygenation

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Development of a High-Resolution Stromatolite Facies Model: Environmental Impacts at the Dawn of OxygenationRussell ShapiroCalifornia State University, Chico StateThe Paleoproterozoic iron-bearing formations of the Animikie Basin host some of the best-preserved microfossils and diverse stromatolites from a time when the Earth was switching from anoxic to euxinic oceans. This interval, known as the "Great Oxidation Event," is an increasingly important research area for paleobiologists, geochemists, and economic geologists. However, important questions still exist as to the paleoenvironmental setting of the stromatolitic deposits, limiting the understanding of the complex interplay between oceanic conditions and the localized bacterial ecosystems. This proposal addresses how stromatolites vary in space in response to changing oceanographic and environmental conditions by applying powerful 3-D modeling software (Petrel v.2010) to an extraordinary collection of proprietary drill core. Specifically, this proposal addresses: (1) To what extent can the stromatolites be used to delineate shoreline geomorphology, enhancing paleoenvironmental reconstructions? and (2) What is the role of taphonomy in both stromatolite and microfossil preservation?Four major stromatolite types are found in roughly two, meter-scale horizons throughout the Animikie Basin, though not necessarily as continuous horizons. Mapping of open taconite mine walls (now flooded) demonstrated that macrostructural variability appears at scales of 10 to 100 meters. The stromatolites are biogenic and formed under normal marine conditions, above the chemocline, in suboxic waters. Based on this work, it is believed that the macrostructural forms of stromatolites, together with the sparse but well-preserved microfossil record, can be integrated with the sedimentologic and stratigraphic data to develop a model of stromatolite biofaces that will help to constrain the unique oceanographic variability in this critical interval of Earth history. The proposed research project will address stromatolite variation and the paleoenvironmental tectonic implications at a spatial resolution that has not been achieved in previous studies of this interval.Broader Impacts. The results of this project will be valuable to researchers studying paleontological and biogeochemical patterns in other pre-Cambrian basins during the "Great Oxidation Event." The dissemination plan calls for the development of a series of YouTube short films that will open up the dynamic and complex world of microbial-sediment interactions of the early oxygenated Earth to a broad audience. The research will provide critical primary research experience for several undergraduate students at a primarily undergraduate institution. The teaching methods of the PI will be enhanced with a greater understanding of this critical interval and opportunities for project-based learning which form an integral component of his pedagogy.