Geochemical Fingerprinting of Bentonites Resolves Stratigraphic Uncertainties: Implications for Dinosaur Faunal Turnover, Dinosaur Park Formation, Alberta, Canada

The Campanian aged Dinosaur Park Formation (DPF) outcrops predominantly in Dinosaur Provincial Park (DPP), Alberta, Canada and is a UNESCO World Heritage site designated for producing some of the highest abundance and diversity of dinosaur fossils globally. The DPF represents a foreland basin coastal plain environment and is comprised of fluvial sandstones and floodplain mudstones of variable thickness and lateral continuity. This variability has prevented identification and use of distinct stratigraphic markers, hampering stratigraphic correlation throughout DPP. A lack of a stratigraphic framework within the DPF contributes to uncertainty for placement of dated bentonites, proposed dinosaur biostratigraphic zones, and the timelines of faunal turnover events. To address these issues, geochemical fingerprinting techniques were used on seven previously dated bentonite beds in the DPF at DPP. Bentonites are ideal for stratigraphic correlation as the ash layers they were derived from were rapidly laid down in a widespread area during short lived volcanic eruptions. However, bentonites in the DPF are often difficult to distinguish by outcrop appearance. Fingerprinting was done using whole rock geochemistry from unprocessed samples as well as microprobe geochemistry of individual phenocrysts including biotite, feldspars, volcanic glass, and zircons. Additionally, phenocryst ratios within each sample were counted and combined with geochemical data for further characterization. Our results show that the bentonites fingerprinted here have distinguishable differences geochemically and physically, allowing for relatively cost effective and simple and identification parameters that can assist in establishing a stratigraphic framework to inform biostratigraphic correlations for the DPF in DPP.