325 m thick platform reef complex.

Abstract ref. 1594:
The MacKenzie, or northwestern, margin of the Frasnian (Late Devonian) Southesk-Cairn carbonate platform is exposed along the McConnell thrust (Laramide) approximately 45 km east of Jasper, Alberta. Exposure is approximately perpendicular to the platform margin providing an excellent example of bank-to-basin depositional style at the Cairn (Lower Leduc), Peechee (Upper Leduc), Grotto-Arcs (Nisku), and Ronde (Blue Ridge-Graminia) stratigraphic levels. The Southesk-Cairn carbonate complex initiated on a regionally extensive shallow-marine platform of the Flume Formation (latest Givetian to earliest Frasnian). The Flume platform overlies a relatively flat pre-Devonian surface and represents an overall deepening-upward sequence. Local evidence suggests that depositionally produced relief (i.e., stacked biostromes) within the Flume, played a fundamental role in the subsequent localization of the Southesk-Cairn platform margin in the Mount MacKenzie area during Cairn time. The Cairn margin has a transgressive, wedge-shaped profile. It is primarily composed of skeletal grainstones and represents a ramp-style bank-to-basin transition. The Cairn platform phase ended with a brief, but pronounced backstepping event. In contrast, the Peechee margin has a well developed stromatoporoid reef-margin facies, a broad back-reef sand apron and a relatively steeply dipping (about 10 degree ) foreslope facies. The combination of starved sedimentation in the adjacent basin and rapid aggradation of the Peechee reef-margin environment produced up to 200 m of platform-to-basin relief. The Grotto-Arcs strata represent a reef-rimmed margin that developed approximately 3 km bankward of the Peechee margin. The Arcs comprises reef and restricted platform-interior facies, whereas the Grotto represents a distally steepened ramp facies. Black, anoxic sediments of the Perdrix Formation were deposited adjacent to the northern margin of the Southesk-Cairn carbonate platform and represent a starved basin which developed during Cairn through Peechee and possibly Grotto time according to conodont data. The slow sedimentation rate of the Perdrix strata was replaced by an episode of very rapid basin infill by Mount Hawk sediments. Platform to basin relief was reduced and nearly filled next to the MacKenzie margin during the late Grotto and during a pre-Ronde sub-aerial exposure event. The Ronde margin initiated more than 4 km basinward of the underlying Arcs and then prograded an additional 2 km over lower Mount Hawk strata. It was a reef-rimmed margin with a moderately dipping foreslope facies characterized by a prominent slope buildup and an orange siltstone unit which separates it from the lower Mount Hawk Formation. A comparison with other outcropping platform-margins indicates that several factors in addition to regional sea level fluctuations influenced the development of these Late Devonian buildups.