TERRESTRIAL RECORD OF EOCENE THERMAL MAXIMUM 2 (ETM2) FROM THE SAN JUAN BASIN, NEW MEXICO, USA

The early Eocene is characterized by a series of abrupt carbon cycle perturbations and hyperthermal events which are excellent deep-time analogs to modern anthropogenic climate change. In some localities, these hyperthermal events are linked widespread changes in terrestrial environments such as increased continental runoff driven by intensification of the hydrologic cycle, overall opening of terrestrial landscapes, and changes in faunal and floral communities. Eocene Thermal Maximum 2 (ETM2), approximately 54.0 Ma, was the second largest early Eocene hypothermal event and is associated with an ~3-5 °C increase in global temperatures and ~-3‰ δ¹³C isotope excursion; however, terrestrial records of ETM2 are rare in western North America and limited to mid-high latitudes. The San Juan Basin, located in northwestern New Mexico, preserves an extensive but understudied series of early Eocene fluvial deposits from southern North America. Here we present an early Eocene terrestrial paleoclimate and sedimentological record from the San José Formation in the San Juan Basin, New Mexico.

Samples were collected from two lithostratigraphic sections from lower San José Formation the southeast San Juan Basin. Magnetostratigraphy and mammalian biostratigraphy constrain deposition to the early-middle Wasatchian North American Land Mammal Age during magnetochrons 24r to 23r (~56.0 to 52.5 Ma) including the C24r-24n.3n reversal (53.9 Ma) which immediately follows the ETM2 hyperthermal event. Clumped isotope paleothermometry (Δ₄₇) from pedogenic carbonates indicate overall warm temperatures with a rapid ~4-7 °C increase in temperature immediately preceding the C24r-C24n.3n reversal that is associated with a negative δ¹³C isotopic excursion. Mean annual precipitation estimates derived from paleosol bulk geochemistry indicate a coeval decrease in MAP >500 mm/yr. These paleoclimatic changes are contemporaneous with widespread amalgamated channel bodies, increased paleosol drainage, and the first appearance of mammalian taxa more adapted to an open habitat. These results suggest ETM2 is preserved in the San Juan Basin and will help expand our knowledge of early Eocene mid-low latitude terrestrial environmental response to hyperthermal events.