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Devonian Alberta
Alberta lay close to the equator during the Devonian Epoch and was mostly
covered by alternately expanding and receding seas. The resulting rocks were largely
limestones with some shales. In the Williston Basin (see map below) extensive reefs
were developed. Arid conditions and restricted circulation in reef-enclosed basins
resulted in deposition of impressive thicknesses of gypsum and salt. The reefs
provided permeable structures into which petroleum migrated, resulting in the rich oil
deposits in what we now call the Western Sedimentary Basin.
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