HIGH-PRECISION U-PB CA-TIMS GEOCHRONOLOGY FOR CORRELATION OF UPPER CAMPANIAN CONTINENTAL FAUNAS ACROSS THE WESTERN INTERIOR BASIN: AN UPDATE ON THE KAIPAROWITS FORMATION, SOUTHERN UTAH

The upper Campanian of Laramidia preserves one of the most widespread and voluminous records of continental vertebrate fossils, including dinosaurs, in the world. Ongoing investigations are focused on the development of a high-resolution U-Pb CA-TIMS based chronostratigraphic framework for select upper Campanian strata across the Western Interior Basin. To date, we have focused on three key study areas, which include the Dinosaur Park Formation in Alberta, the Judith River/Two Medicine clastic wedge in Montana, and the Kaiparowits Formation in southern Utah. Acquisition of new U-Pb ages for interstratified bentonites from Alberta to Utah permits previously inaccessible levels of precision for correlating coeval fossils and strata, and facilitates investigation of basin-scale ecologic, evolutionary, and taphonomic patterns across an extensive continental ecosystem. Here we present refined correlations between these three latitudinally distant formations, with a focus on new results from the Kaiparowits Formation. This new suite of dated Kaiparowits bentonites, includes samples from remote outcrop areas, which allows for improved intraformational correlations between key fossil localities. Among the more interesting results of this work is the identification of a number of statistically indistinguishable ages on bentonites from the Dinosaur Park and Kaiparowits formations.

We applied a novel, multifaceted approach for fingerprinting bentonites for tephrostratigraphic correlation by analysing glass (or melt) inclusions trapped in zircon crystals. The melt inclusion were analysed for bulk chemical compositions via electron microprobe and Lu-Hf ratios via LA-MC-ICPMS. As these inclusions essentially represent samples of parent magma, they can be used to test whether or not ash beds originated from a single volcanic event and hence to inform on the tectonic setting and source of volcanism. This approach holds great promise for determining the source(s) of volcanic ash in the basin, and for correlation of strata and fossil localities. Preliminary results suggest that coeval ash beds from Alberta and Utah are geochemically distinct and likely of different sources.