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  • Thumbnail for Major and trace element geochemistry of pedogenic carbonates as a proxy for climate change during the ETM2 and H2 hyperthermal events in the Bighorn Basin, WY
    Major and trace element geochemistry of pedogenic carbonates as a proxy for climate change during the ETM2 and H2 hyperthermal events in the Bighorn Basin, WY by Hopper, Elizabeth Ann

    A series of rapid global warming events, triggered by the release of CO2, occurred at ~55.5 Ma. These events are called hyperthermals, and they have garnered a great deal of attention as probable analogs for present-day CO2 increase and climate change. The best known hyperthermal event is the PETM, which was followed by two smaller events called ETM2 and H2. Pedogenic carbonate nodules from the Bighorn Basin in Wyoming provide the first terrestrial records of ETM2 and H2. Since pedogenic carbonates precipitate out of the groundwater, the major and trace element composition of these nodules can be used as a proxy for groundwater conditions during ETM2 and H2. The ratios Na/K, Na/Al, K/Al and Mg/Al were used as weathering indicators. Boron was used as a proxy for pH, and Phosphorus was used as a proxy for plant activity. The redox sensitive elements Fe, Cu, Se, V, U Zn, and Ni were considered as proxies for soil saturation. Comparison of pre hyperthermal to mid hyperthermal groundwater chemistry indicates that (1) Weathering intensity and sedimentation rates decreased during ETM2 and H2 (2) soil and groundwater became more acidic during ETM2 and H2 (3) The acidification was primarily driven by increases in plant activity during ETM2 and (4) Average rainfall decreased during ETM2, but the hyperthermal was characterized by wet and dry cycles.