RECONSTRUCTING THE PCO2 AND CLIMATE RECORD OF THE LATE EARLY PALEOCENE IN THE SAN JUAN BASIN, NEW MEXICO

Following the K-Pg boundary, the connection between climate and pCO₂ has proven to be difficult to interpret due to multiple perturbations in the global carbon cycles. In particular, the Deccan Traps volcanism (~66.25-65Ma), the Chicxulub bolide impact, and multiple carbon isotope excursions (e.g., the Latest Danian event at ~62 Ma), deeply confounds our understanding of the Earth system responses in pCO₂ record and temperature record during the Early Paleocene. Additionally, relatively little is known about the pCO₂ levels and terrestrial paleoclimate during the late Early Paleocene, from 64 to 62 Ma, further limiting our ability to deconvolve the relationship between climate and pCO_2. The San Juan Basin (SJB), located in northwestern New Mexico, preserves an almost continuous sequence of fossil-rich deposits in the early Paleocene, making it an ideal place to reconstruct the paleoclimate and pCO₂ using palaeobotanical approaches.

Here we expand the early and middle Early Paleocene pCO₂ and terrestrial paleoecological record using fossil leaves we collected from the upper Nacimiento formation (64-62 Ma) in the SJB. The pCO₂ reconstructions use a leaf gas exchange model developed for leaves within the Platanaceae family, and canopy structure is reconstructed using the established relationship between sunlight and the undulation index (UI) of leave pavement cells. These data combined with the paleoclimate record generated from fossil leaf based estimates from the SJB allow us to assess how pCO₂ levels fluctuated during the early Paleocene, and how it affected plant communities in the Early Paleocene.