EARLY PLIOCENE TERRESTRIAL TEMPERATURE ESTIMATES FROM THE VALLEY AND RIDGE OF NORTHEASTERN TENNESSEE: STABLE ISOTOPE ANALYSES OF ALLIGATORS, TORTOISES, TURTLES AND FISH FROM THE GRAY FOSSIL SITE

Global CO2 levels have reached 419 ppm and are expected to be greater than 600 ppm by the end of the century. Because these levels are unprecedented in the historic record, geological archives have become important tools to explore scenarios of ecological adaptation and resilience. The Gray Fossil Site (GFS) in northeastern Tennessee is an early Pliocene (4.7-4.9 Ma) lagerstatte with an abundant and diverse vertebrate fauna. Alligator enamel, turtle and fish bones from the GFS were analyzed using Fourier Transform Infrared Spectroscopy (FTIR) and stable isotope analyses. Although the PO4 portion of these samples has been microbially altered during diagenesis, the δ¹⁸O of structural carbonate (CO3) in bone and tooth enamel provides temperature estimates for this unique depositional environment. Groundwater temperature estimates derived from GFS fish remains average 15.6° C, warmer than the local modern baseline (14.2° C). The average growing season temperature estimated from turtle and alligator δ¹⁸O is 20.2° C. However, species-specific basking and dispersal behaviors are likely drivers of broad variability in estimates from terrestrial reptiles.