PALEOCLIMATIC INVESTIGATION OF THE KAIPAROWITS FORMATION, SOUTH-CENTRAL UTAH USING STABLE ISOTOPE PROXIES

The Upper Cretaceous (Campanian) Kaiparowits Formation preserves one of the most complete fossil record of the Cretaceous North America. The Kaiparowits fossil record exhibit unique paleoecology including elevated biodiversity and endemic taxa. In an effort to study the interaction between the physical environment and ecosystem, paleoclimate was investigated via isotope compositions of the fossil bone/teeth structural carbonate. The fossil isotopic compositions were compared to the diagenetic carbonate cement in order to investigate the diagenetic alteration. Crocodile, turtle and hadrosaur fossils were selected for this study because of their abundance and broad stratigraphic range. Fossil samples were loaned from the Natural History Museum of Utah (UNHM), and rock samples were collected at the fossil localities provided by UNHM during the field seasons of 2015 and 2016. Rock samples include sandstone, mudrock, and limestone nodule. The average δ¹³C(VPDB) of hadrosaur teeth, crocodile teeth, and turtle shell are -6.28‰, -7.68‰, and -7.60‰ respectively, which reflect the taxonomic dietary difference. Hadrosaur tooth δ¹³C also exhibit 2.10‰ depletion toward upsection, suggesting increasing humidity during the deposition of the Kaiparowits Formation. The average δ¹⁸O(VSMOW) of hadrosaur teeth, crocodile teeth, and turtle shell are 21.96‰, 21.44‰, and 20.94‰ respectively, and δ¹⁸O of all taxa exhibit slight enrichment (0.90-1.02‰) toward upsection. The average δ¹³C of sandstone, mudrock and limestone nodule are -4.38‰, -2.01‰ and -7.23‰ respectively, reflecting the carbonate cements precipitated from different diagenetic fluid. The δ¹³C of rock samples also exhibit depletion toward upsection. The average δ¹⁸O of sandstone, mudrock and limestone nodule are 18.71‰, 21.98‰, and 21.16‰ with no discernible enrichment/depletion trend, suggesting δ¹⁸O of fossil structural carbonate may preserve biogenic signals. Our results are compatible with lithostratigraphic studies.