ISOTOPIC VARIATION IN AQUATIC GASTROPODS FROM THE CONTINENTAL LATE CRETACEOUS KAIPAROWITS FORMATION, SOUTHERN UTAH, U.S.A

Marine base level exerts a fundamental control on continental sedimentary architecture, affecting the vertical and lateral deposition of sediments along the coastal plain. In the Late Cretaceous Kaiparowits Formation of southern Utah, coastal plain and alluvial deposition is recorded in a continuous 2 myr section, with abundant and well-preserved continental fossils, of which mollusks are the dominant fauna. Previously, the effects of changes in base level were investigated through studies on diversity using populations of inland mollusks living in fluvial and pond facies. Recent isotopic work in the formation has demonstrated that pedogenic carbonates and unionoid bivalves are sensitive to changes in paleoclimatic conditions and alluvial depositional processes. In this study, we build on this previous work using carbon and oxygen stable isotopes in aragonite shell from aquatic gastropods in pond and river deposits. Analysis of 67 gastropod shells from 3 species indicate similar carbon and oxygen values to unionoid bivalves in the basin, and show no evidence for differential fractionation by species suggesting vital effect is minimal. Pond gastropods have increased δ¹⁸O values up section, which corresponds to a highstand systems tract that supported greater pond longevity. This relationship, and those we continue to explore, suggest that aquatic gastropods are valuable geochemical archives with the potential to expand our understanding of basin scale processes on the flora and fauna living in the Western Interior Basin.