STABLE ISOTOPE PALEOECOLOGY AND PALEOCLIMATOLOGY OF THE PLEISTOCENE SILVER CREEK JUNCTION FOSSIL FAUNA (NORTHERN UTAH, USA)

Silver Creek Junction, located approximately 5 km north of Park City, Utah, is a Pleistocene fossil site that has yielded remains from 25 mammal taxa. Carbon-14 dating of an unidentified bone from the deposit indicates an age of 42,907 ± 518 years BP. To reconstruct the site’s paleoclimate, paleoenvironment, and the paleoecology of its fauna, we sampled teeth of various taxa for stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope analysis. Specifically, we sampled enamel from ten Bison teeth, six Equus teeth, one Antilocapra americana tooth, and four Mammuthus teeth, as well as dentine from three Megatherium teeth. Enamel was prioritized because its stable isotope composition is thought to be resistant to diagenetic alteration. Samples were collected serially at various distances from the occlusal surface to capture both seasonal variability and mean paleoenvironmental conditions. The total number of samples yielded by this approach is 132 for Bison, 144 for Equus, 15 for Antilocapra, 80 for Mammuthus, and 63 for Megatherium.

The δ¹³C values of mammals’ teeth primarily reflect the proportion of C₃ vs. C₄ plants in the diet, and, in pure C₃ ecosystems, also provide insights into vegetation openness and mean annual precipitation. The δ¹⁸O values in water-dependent taxa reflect meteoric water composition, which correlates with mean annual temperature, while those from drought-tolerant taxa capture aridity. By integrating δ¹³C and δ¹⁸O data across taxa with different water dependencies, we aim to reconstruct a detailed picture of the site's paleoclimate and paleoenvironment as well as of the ecological adaptations of its fauna, contributing valuable information to our understanding of this late Pleistocene ecosystem.