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  • Thumbnail for Fluvial landscapes of the Cretaceous: Insights integrating stable isotope geochemistry, sedimentology and taphonomy
    Fluvial landscapes of the Cretaceous: Insights integrating stable isotope geochemistry, sedimentology and taphonomy by Evans, Erica Sarah Janecke

    This project is focused on the study of climate, hydrology, and surface processes of western North America during the late Cretaceous (~75 million years ago) in what is now southern Utah. The goal of this project is to describe in detail the hydrology of fluvial systems associated with the deposition of the Kaiparowits Formation. Differences in stable isotope ratios of gar ganoine, pedogenic carbonate, and enamel from hadrosaur and crocodile teeth, in conjunction with previously published bivalve data, indicate there are three main parts to the fluvial system: 1) FS1—large anastomosing rivers draining upland areas 2) FS2—lakes subject to episodic flooding and 3) FS3—smaller streams draining the foreland basin.  Furthermore, it is possible to infer mixing of water between these sources, in particular the mixing of FS1 and FS3 waters to form FS2 water, presumably during seasonal flooding events that were analogous to processes taking place in modern-day Tonle Sap Lake in central Cambodia. The organic content of sediment, carbon isotope ratios of paleosol carbonate, and the carbon isotope ratios of hadrosaur dentine and enamel from different sites all indicate that soils along the margin of the FS2 lakes were characterized by episodic flooding and saturation, with those closer to the margin being saturated for a longer period of time, compared to more distal localities.  Furthermore, hadrosaurs that ate vegetation located closer to the lake margin have teeth with high carbon isotope ratios, consistent with the existence of closed canopy forests in these localities.  Thus, variations in the hydrology of these fluvial systems appears to have played an important role in determining the distribution of plants over Kaiparowits landscapes, with closed canopy forests perhaps accounting for the large diversity in herbivorous dinosaurs observed in southern Utah during the late Cretaceous.