Lithostratigraphic Characterization of a Buried Bedrock Valley Using Airborne and Surface Geophysics

A helicopter-borne frequency-domain electromagnetic instrument was used to investigate the lithostratigraphic architecture of a buried bedrock valley near Elora, Ontario. The resulting airborne electrical resistivity model was evaluated against co-located high-resolution ground-based electrical resistivity, seismic refraction, and gravity surveys across two sections of the valley. Results were interpreted using published geological datasets including continuous core, geophysical logs, and an existing regional Quaternary geologic model. A comparison between the local geophysically-based model and the regional Quaternary model shows that an airborne electromagnetic survey can markedly improve characterization of bedrock valley morphology and Quaternary architecture. These results provide confidence in regional-scale interpretations of airborne electromagnetic data for the purpose of delineating lithostratigraphic boundaries. Such data would provide valuable insight into the placement of boreholes for additional and complementary characterization at the borehole scale, leading to delineation of hydrostratigraphic boundaries. In combination, these data will inform 3-D groundwater flow models.