ASSESSING THE AUTHENTICITY OF STABLE ISOTOPE COMPOSITIONS IN VERTEBRATE SKELETAL REMAINS: IMPLICATIONS FOR PALEOCLIMATIC INTERPRETATION OF THE UPPER CRETACEOUS KAIPAROWITS FORMATION, SOUTHERN UTAH

The Upper Cretaceous (Campanian) Kaiparowits Formation is an unusually thick (860m) fluvial deposit that crops out near the Grand Staircase Escalante National Monument. Although the Kaiparowits Formation preserves the most one of the complete fossil record of the Upper Cretaceous North America, the paleoclimate of the Kaiparowits Formation is not well studied. Stable isotope proxies are invaluable tool for answering such question. However, the authenticity of the isotope composition need to be investigated because isotope composition can be diagenetically altered. The objective of this study is two-fold; (1) to study the diagenetic alteration of the stable isotope composition of the skeletal remains in the Kaiparowits Formation, and (2) to interpret paleoclimate of the Kaiparowits Formation using authentic isotope data. Crocodiles, turtles and hadrosaurs were selected because of their abundance and broad stratigraphic range. Fossil samples are loaned from the Natural History Museum of Utah (UNHM). Fossil localities these samples were revisited during the summer 2015 field season to document lithology, measure sections and collect rock samples. The stable isotope compositions of bone/tooth structural carbonate and phosphate were analyzed at the University of Arkansas Stable Isotope Laboratory. Bone and turtle shell fragments exhibit preserved microstructures such as osteon, and pores are filled with carbonate cement. There is no statistical difference between the isotopic composition of bones from the different taxa, potentially suggesting diagenetic alteration (mean turtle δ¹³C = -7.66‰ SMOW, δ¹⁸O = 20.94‰ SMOW; mean hadrosaur δ¹³C = -7.28‰ SMOW, δ¹⁸O = 20.81‰ SMOW). However, further investigation is necessary for such investigation. Additional data including petrography, carbonate and phosphate oxygen isotope data will be added to this data set to confirm diagenesis or trends in the isotopic composition between taxa and stratigraphy.