COLLABORATIVE RESEARCH: A combined phytolith-isotope geochemistry approach to paleo-vegetation reconstruction in Montana

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Collaborative Research: A combined phytolith-isotope geochemistry approach to Cenozoic paleo-vegetation reconstruction in MontanaNathan Shelton and Selena Smith, University of MichiganCarolyn Stroemberg, University of WashingtonGrasslands make up ~40% of Earth's terrestrial vegetation and provide humans with our staple foods (e.g., corn, rice, wheat). Exactly how ongoing anthropogenic climate change will impact grassland ecosystems and agricultural crop productivity is a crucial question, and addressing it requires knowledge of how these important biomes were assembled in the first place. Based on plant macrofossils, co-evolved mammals, stable isotopic data, fossil soils, and phytolith (plant silica) data, the scientific community knows that grassland ecosystems dispersed at an intercontinental geographic scale sometime during the mid-Cenozoic. However, because different proxies suggest different scenarios for the emergence of grasslands both in terms of gross spatial and temporal patterns (e.g., North America vs. Africa), the details of this profound ecological transition are less certain. In most areas, only one paleo-vegetation proxy has been applied, so very little is understood about potential sampling and taphonomic biases in different records that could affect vegetation interpretation. In addition, potentially important environmental heterogeneity remains undocumented. To resolve these issues, the PIs will use an interdisciplinary, multi-proxy approach to reconstructing the evolution of grasslands in Montana over the past ~40 Ma that can be compared directly with a paleoclimatic reconstruction based on paleosols. Specifically, the PIs will construct a long-term, high-resolution record of paleovegetation using phytoliths, pedogenic carbonates, and organic matter collected from paleosols (i.e., C isotopes to assess photosynthetic pathways). They will focus on three critical climatic transitions that are broadly believed to have significantly impacted the presence and abundance of grasses in North America, namely the Eocene-Oligocene transition (EOT), the Oligocene-Miocene transition (OMT), and the Middle-Late Miocene transition (MLMT).