d18O ANALYSIS OF THE CLAM CRASSATELLITES VADOSUS FROM THE LATE CRETACEOUS COON CREEK FORMATION
Preliminary lab analysis shows no significant linear correlation between carbon and oxygen isotopes, suggesting no measurable kinetic or vital fractionation effects and indicating no apparent diagenetic recrystallization of the clam shell; oxygen isotopes appear to have been in or near equilibrium with the clams' ambient water at the time of carbonate shell accretion. Environmental conditions such as temperature and salinity can thus be inferred from the oxygen isotope profiles of these mollusks.
Results of the analyses show oxygen isotopes oscillate in a roughly sinusoidal pattern around a median value of -1 in each shell, while amplitude of the oscillations varies slightly between shells. Values do not appear negative enough to suggest an environment near a freshwater source such as a bayhead or delta. In addition, the isotope profiles are not significantly different from values measured in roughly contemporaneous carbonates in open marine environments and other areas of the Western Interior Seaway. These intimations parallel previous paleoenvironment interpretations of a nearshore shelf environment based on paleofaunal assemblages, planktonic:benthic foraminifera ratios, and sediment analyses.