Early Paleocene plant community and paleoclimate reconstruction of the Nacimiento Formation from the San Juan Basin, New Mexico.

Following the major extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Earth experienced a trend of long-term warming, punctuated by several short-term ‘hyperthermal’ events with associated carbon isotopic excursions in the early Paleogene. The early Paleocene climate record and the plant community response to the K-Pg extinctions and during and after hyperthermal events has been well studied in the northern Great Plains of North America but relatively little is known about the floral and climatic record at lower latitudes. The lack of data from terrestrial southern North American basins and from the middle Paleocene across North America limits our understanding of how Paleocene plant communities evolved and responded to climate change in the past and make it impossible to fully characterize regional patterns. This in turn inhibits our ability to understand how modern plant communities will respond to the unprecedented climate change the Earth is currently experiencing. The San Juan Basin in northwestern New Mexico and southern Colorado represents an ideal stratigraphic record for expanding our knowledge on plant community recovery and response to climate change, because unlike other basins in North America, the San Juan Basin preserves a remarkable, nearly continuous, record of both fossil floras and mammalian turnover that spans the early and middle Paleocene. Additionally, the early Paleocene floral record collected from the Nacimiento Formation in the San Juan Basin has been well characterized and documents a flora that is considerably more diverse than the contemporaneous floras in North America.