Outcrop of the Middle Devonian Keg River Formation on the Firebag River, Northeastern Alberta (NTS 74E/11)

This report contains the description of an outcrop of the Middle Devonian Keg River Formation along the north bank of the Firebag River west of the Fort Chipewyan winter road bridge. Field descriptions were supplemented with the results of thin-section analyses carried out on six samples from the outcrop, providing additional information on composition, textures, and porosity of the rocks. The outcrop consists of a basal unfossiliferous dolostone containing no other defining features, a series of laminated and tabular-bedded dolostone beds originating from a lagoonal to intertidal paleoenvironment and a capping stromatoporoid-biostromal to -biohermal dolostone.

Post-depositional alteration processes interpreted from outcrop and thin-section observations include marine cementation, recrystallization, dolomitization, dissolution, fracturing, hydrocarbon migration, and late-stage calcite cementation. Dolomitization of the original limestone obscured, but did not completely obliterate original sedimentary structures. Observed porosity types include inter- and intraparticle, intercrystalline, and solution-enlarged porosity. Porosity values range between 10% and 46%, with the values of >20% found in dolomitized peloidal and fragmental grainstone and stromatoporoid bindstone in the biostromal to biohermal part of the outcrop.