High local variability in elevation of the Oldman-Dinosaur Park Formation contact revealed by digital outcrop reconstruction, and implications for dinosaur biostratigraphy of the Late Cretaceous (Campanian) Belly River Group of Alberta, Canada

The Late Cretaceous (Campanian) Belly River Group of Dinosaur Provincial Park (DPP), Alberta, Canada, combines the world's most complete dinosaur chronofauna with precise and accurate absolute age constraints obtained from ashfall deposits. However, the time-averaging of individual fossil quarries caused by their preservation in fluvio-deltaic depositional environments implies significant uncertainties on their relative age and by extension on our knowledge of local palaeodiversity patterns. The biostratigraphic position of a multigeneric bonebed at a transitional period between successive dinosaur assemblage zones, combined with its proximity to an exposure of the Oldman-Dinosaur Park Formation (OF-DPF) contact, provides an ideal study system for such an investigation. Images acquired with an unmanned aerial vehicle (UAV) were aligned by structure-from-motion (SfM) photogrammetry to construct a 3-D digital outcrop model (DOM), a digital elevation model (DEM), and an orthomosaic of the 0.446 km(2) area surrounding the bonebed. The first key result is that the absolute elevation of the OF-DPF contact varies by similar to 12 m locally, which causes hitherto underestimated uncertainties on any fossil locality's stratigraphic height relative to it. Moreover, we find that the lower DPF has the potential to be locally subdivided into at least three successive channel cut-and-fill rhythms, some of which are promising candidate marker beds for a more expansive correlation of DPP's fossil heritage. This study shows how rapidly developing UAV-based geological mapping methods contribute to exploring stratigraphic successions in other fossil-rich regions on a larger scale than what is currently possible from ground-based surveys alone.