Eastern Section Meeting

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Refining the mapping of basement faults in SW Ontario–two points don't necessarily determine a fault line


The basement complex in southwestern Ontario is much more complex than is generally accepted. Regional maps show many faults that are rooted in the Precambrian. These faults were originally drawn in based upon limited well control or sporadic seismic lines. In the absence of more data, it is natural to “connect the dots” to determine the locations of faults. Integrating aeromagnetic data with seismic and well control is a cost-efficient way to improve geologic mapping of basement-rooted faults. Even regional aeromagnetic data that were acquired decades ago show much more variability in the basement than is generally accounted for in geologic maps. These data reveal local lithologic changes and structural features that are superimposed upon a regional basement fabric. Within the last few years, the ability to refine the interpretation of basement faults has progressed even further. A high-resolution aeromagnetic survey was acquired over a portion of the southwestern Ontario. Using better acquisition parameters and technology, this survey is a great improvement over the old regional one. This survey reveals an even greater number of high frequency anomalies in and at the surface of the Precambrian. Segmentation of basement faults can create lateral offsets and horst and graben blocks. In overlying rocks, these features can give rise to drag faults, structural draping, and controls for stratigraphic pinchouts that can have a significant impact on hydrocarbon entrapment. Several mapped faults including the Dover Fault, Electric Fault, Clearville Fault, and Dawn Fault will be shown to be much more complex than they are currently accepted to be.