LATERAL STRATIGRAPHIC RELATIONSHIPS OF FLUVIAL OUTCROPS AND FOSSILIFEROUS ZONES AROUND THE K-PG BOUNDARY IN MONTANA FOX HILLS, HELL CREEK, AND FORT UNION FORMATIONS USING PHOTOGRAMMETRY

Large-scale 3D models of fluvial outcrops through the Upper Cretaceous to Paleocene Fox Hills, Hell Creek, and Fort Union formations in Montana can improve our ability to correlate stratigraphic intervals across large areas in complex terrain, help us identify potential new sites for fossil collection, and allow us to assess fossil distribution (hence patterns of preservation and paleoecology) with respect to deep time geomorphology. Each of these outcomes will allow us to better understand the critical interval up to, and across the end-Cretaceous extinction.

To build these 3D models, over 18,000 high resolution images were collected from six localities using an Unmanned Aerial Vehicle (UAV – DJI Phantom 4). 3D photogrammetric modeling was used to generate ultra-high-resolution digital elevation models of the surveyed outcrops from the UAV and ground-based digital images using Agisoft Photoscan software. Mapping field and photographic sedimentologic interpretations on to the 3D outcrop model and orthomosaic images allows for the interpretation of both the depositional settings and geometries of facies in time and space at each locality. By projecting surfaces through the 3D model, we can identify correlative fluvial units (e.g., paleosols, channel belts, avulsion units) across rough terrain.

This approach allows the gathering of detailed sedimentologic and stratigraphic information from remote areas and in terrain which is difficult to navigate or study in any other way. It is cost effective and time efficient, allowing for detailed study of large areas. This study will allow us to better understand and define the lateral paleo-geomorphologic relationships of fluvial systems and how these change with time. It will also aid with the identification of additional target localities for fossil prospecting, and will help build a greatly improved understanding of the Upper Cretaceous and Paleocene geomorphology and paleoecology of the Williston Basin.