ABSTRACT

The curvilinear reef trends of the Middle to Late Devonian of the Alberta Basin, such as the Rimbey-Meadowbrook trend, are, in addition to hosting prolific hydrocarbon reservoirs, some of the most enigmatic structures in the basin. The reason why the Alberta Basin underwent rapid evolution from a nearly featureless carbonate shelf to a mosaic of reefs and basinal sediments remains unknown. The recently documented anisotropic nature of the basement suggests that some basement weaknesses may have been susceptible to reactivation. Basement control of reef structures has been a long-held hypothesis, although the recognition of a mechanical rationale for the linkage between basement and cover has been a neglected element of the "basement-control" model.

In-plane stresses are gaining wide recognition for their potential significance in controlling sea level fluctuations and contributing to subsidence patterns in basins. A variety of processes may contribute to in-plane stress levels, including short-wavelength contributions from tectonic activity at plate margins and long wavelength contributions from the position of lithospheric plates with respect to geoid anomalies. The Late Devonian was a time when the North American continent was influenced by unusually high in-plane compressive stresses related to the presence of orogenic belts along its margin, and its position in a pre-Pangean geoid low. It is proposed here that anomalously high in-plane compressive stresses during the Middle to Late Devonian may have exceeded the yield stress of basement structures, leading to reactivation of basement weaknesses and thereby fragmenting the Alberta shelf into a complex of reefs and interreef areas.

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