ABSTRACT

The Carson Creek North reef complex occurs in the subsurface of west-central Alberta, with an area of about 24 sq mi and a maximum thickness of about 350 ft. The reef complex and the underlying reef platform form the Swan Hills Formation of the Beaverhill Lake Group of probable late Middle and early Upper Devonian age.

Structure maps, isopach maps, and cross-sections illustrate the atoll-like reef geometry and paleotopography. Stromatoporoids and algae were by far the most important reef organisms. Brachiopods, corals, and other fossils are common, but were not as important in governing reefal development. Many of the organisms, especially the stromatoporoids, appear to have been environmentally controlled, allowing the reef complex to be subdivided into 7 biotopes each having distinctive biosomes.

Integrated data allow the reef complex to be divided into 5 facies, 11 microfacies, and 32 rock types. Geomorphic localities envisaged for the rock types vary from deep quiet water to shallow turbulent water to subaerial.

The most important diagenetic features which have affected the reef-complex limestones are, biological diagenesis, cementation, lithification, neomorphism, solution and fracturing, compaction and development of authigenic accessory minerals. In general, however, post-depositional diagenesis has not greatly altered the original sedimentary features.

The geological history of the reef complex has been portrayed in 6 major stages of development: (1) Reef Platform Development -- mild transgression and deposition of a biostromal-type carbonate unit; (2) Biohermal Development -- more extensive transgression resulting in biohermal reef growth; (3) Green Shale Development -- major regression with subaerial erosion, solution of reefal carbonate and consequent accumulation of argillaceous insolubles; (4) Bank Development -- stability or mild transgression resulting in a calcarenite bank unit; (5) Reef Death -- regression and erosion of the reef resulting in termination of reef growth; (6) Waterways Development -- transgression and deepening of the water resulting in argillaceous non-reef sedimentation.