Abstract

Rapid facies changes associated with reef development occur in the Devonian Winterburn and Woodbend sediments of the Drumheller area. To indicate the facies relationships, the “Limy” and “Dolomitic” sediments are divided into several informal rock types. The “Dolomitic” sediments are classified according to their interpreted original or undolomitized rock types.

The Cooking Lake formation, composed of predominantly pelletoidal and fragmental limestones, forms the base of reef development in portions of the Southern Alberta Reef Complex. A line of organic shoals is indicated in the Cooking Lake, six to eight miles in front of the Reef Complex.

The Duvernay formation is closely associated with reef development. It is composed predominantly of reef detritus close to the Reef Complex and contains incipient reef developments in a lime mud facies beyond the detrital zone.

The Ireton formation is a lime mud facies with tongues of fragmental carbonate. The upper portion of the Ireton is dolomitic and contains a dark organic dolomite band which becomes the main constituent of the Ireton interval over the Reef Complex.

The Southern Alberta Reef Complex, an informal term used to designate the Woodbend carbonates of the southern portion of the study area, is composed of fragmental carbonate and reefoid beds. Organic material predominates in a band approximately 3 miles wide along the reef front.

The Nisku interval contains shoals of light organic dolomite with associated fossil fragmental dolomites and pelletoidal dolomites separated by intershoal areas of dark dolomitic muds and bedded dark organic dolomites.

The depositional environment of the sediments indicates a period of almost continuous reef growth modified by cycles of emergence and submergence. The emergence or lowering of the sea level is associated with erosion of the reef while the submergence was probably a period of rapid growth.