ABSTRACT: Devonian Carbonate Sequence Evolution of Western Canada

Jack Wendte, P. K. Wong, I. D. Muir, J. Weissenberger, M. G. Gilhooly, F. A. Stoakes

Carbonate sequence stratigraphy as postulated by Exxon is based on the premise that eustatic changes in sea level are the major control over stratal patterns and distribution of lithofacies. Our combined studies on the Middle and Upper Devonian of the Western Canada sedimentary basin provide a basis for testing this assumption.

These strata occur in five major sequences: (1) Elk Point, (2) Beaverhill Lake, (3) Woodbend, (4) Winterburn, and (5) Wabamun. Each sequence reflects a major transgressive-regressive mega-cycle of sedimentation lasting up to a few million years. Each mega- or first-order cycle records the widespread inundation of Devonian seas onto the craton (transgressive phase) and their gradual withdrawal (regressive phase). The transgressive lower part is characterized by backstepping platform and reefal carbonates. The upper regressive part is characterized by forestepping carbonate platforms and basin-filling shales and limestones.

Although the vertical succession of facies is in a gross sense consistent with the Exxon carbonate systems tract model, three fundamental differences exist. First, the vertical succession of facies patterns varies according to basin position and prevailing wind direction. Second, variations in the vertical succession of facies patterns occur on a local scale in response to varying energy conditions and circulation direction. Third, platform evolution may change from a backstepping to a forestepping style without a pronounced intermediate upstepping phase.

Our results indicate that comprehensive models predicting carbonate facies distributions must consider environmental controls as well as fluctuations in relative sea level.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990