HOW HOT DID IT GET? UPDATING ESTIMATES OF TEMPERATURE CHANGE DURING EARLY EOCENE HYPERTHERMAL EVENTS IN THE BIGHORN BASIN, WY

The Early Eocene was the warmest time of the Cenozoic, and was characterized by rapid global warming events, termed hyperthermals, that (~10,000 years) increased temperatures rapidly (~10,000 years or less) above the already warm climate of the time. Often studied as a potential analog for modern global warming, significantly more is known about the temperature response during these events from the perspective of marine records than terrestrial records. The Bighorn Basin in Wyoming preserves the best characterized record of three of these hyperthermals: the Paleocene-Eocene Thermal Maximum (PETM), ETM2 and H2.

To better understand the temperature response in the Bighorn Basin during ETM2 and H2, we generated a clumped isotope temperature (T(Δ₄₇)) record for paleosol carbonate nodules, at a ~15 kyr sample resolution, from ETM2 and H2. This record suggested the magnitude of temperature change for these two events was similar to each other and large (~8-9°C). However, these data were all generated before the current use of community accepted standards with defined values, and a new T(Δ₄₇) calibration that is anchored to these values. For example, differences in temperature (up to 10°C) and magnitudes of temperature change were found, depending on which calibrations were used and the Δ₄₇ values of the samples. To bring these data into alignment with this new reference frame, we analyzed a subset of this high-resolution dataset to create a dataset-specific correction scheme; standards run at with the original dataset do not have known values in the new reference frame. We will discuss the effects of this update on the magnitudes of terrestrial temperature for these events, a few unusual fabrics in the petrography of the samples, the necessity of additional cleaning to produce reliable analyses, and how these records compare to their marine equivalents. We will also compare these data to a preliminary high-resolution temperature record developed for the PETM in the Bighorn Basin.