SEDIMENTOLOGY FROM AFAR: USING A UAV TO ACCESS A STEEP ROADCUT

The Ordovician Juniata Formation is exposed as a roadcut along US Route 322 in Potters Mills, Pennsylvania. Interpretations of the depositional environment here have historically varied from fluvial to shallow marine. However, more recent interpretations suggest that it likely represents a transition from shallow marine to fluvial setting. Recent road construction (2015-2020) has removed vegetation and exposed fresh surfaces on this existing roadcut, and allowed for a reevaluation of the sedimentology and stratigraphy of this outcrop.

The Potters Mills exposure is expressed within a second-order syncline. Inclined bedding at the northern and southern fringes of the exposure allow easy access for stratigraphic description. However, despite nearly 500 meters of laterally exposed rock face, access to the youngest strata in the section is limited as the beds lie flat and stack vertically over 12 meters above grade. Within this vertical section there are repeated packages of fining-upward successions, where closer inspection is needed to determine the nature and environment of deposition.

We attempt to solve this problem of access with the use of a Mavic 2 Enterprise Advance unmanned aerial vehicle (UAV) equipped with a high-resolution camera system capable of capturing 48 megapixel images on a ½ inch CMOS Sensor. We use this UAV to capture and analyze high-resolution photographs for both qualitative and quantitative data of these bedding surfaces. Qualitative data includes identifying and describing sedimentary structures, including evidence of cross bedding, trace fossils, and soft-sediment deformation. Quantitative data includes measurements of bed thickness and number of these beds. These data can be used to recognize depositional patterns by conducting stacking pattern analysis, similar to fluvial aggradation cycles, this can provide insight into base level trends at the time of deposition. This ultimately provides insight as to the depositional environment and aids in discerning a terrestrial from a marginal marine setting.

Photogrammetry by UAV allows us to obtain both quantitative and qualitative information that would otherwise remain tantalizingly just out of reach for study. It is the hope that by accessing this new information a more definitive depositional history of this location will emerge.