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 in the early Paleogene. While the early Paleocene climate record and plant community response to the K-Pg extinctions and hyperthermal events has been well studied in the northern Great Plains of North America, relatively little is known about the floral and climatic record at lower latitudes. The lack of data limits our understanding of how Paleocene plant communities evolved and responded to climate change in the past and makes it impossible to fully characterize regional patterns. The San Juan Basin (SJB) in northwestern New Mexico represents an ideal stratigraphic record for expanding our knowledge on plant community recovery and response to climate change. Unlike other basins in North America, the SJB 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 SJB has been well characterized and documents a flora that is considerably more diverse than the contemporaneous floras in North America.

Here we report data from five census localities collected from the upper Nacimiento (~64 – 62 Ma) and compare these floras to the lower Nacimiento Formation floral record. Preliminary identifications of morphotypes and diversity analyses indicate that the upper Nacimiento Formation floras are markedly different in morphotype composition and document a lower species richness than older floras collected from the SJB. Additionally, paleoclimate reconstructions based on the floras indicate a relatively warm and wet climate, with some evidence for a possible cooling trend up section. This pattern of a decrease in species richness and cooling from the early into the middle Paleocene mirrors similar trends seen in the Northern Great Plains, suggesting it may be a regionally significant event. Additional analyses focused on the diversity and paleoecology of the Nacimiento Formation plant community will be investigated to compare floras from across North American to assess regional plant community response temporally through the early and middle Paleocene.