MacEachern, James

The Lower Cretaceous McMurray Formation is interpreted as a brackish-water, tidally influenced estuarine complex. The study area encompasses Townships 90-95, Ranges 10-14W4 in northeast Alberta. Facies analysis of 41 cored wells led to the identification and differentiation of large- and small-scale lateral accretion IHS associated with tidal-fluvial channels. Five sedimentary facies are assembled into four recurring facies associations to characterize these channel systems. Sedimentological and ichnological characteristics point to elevated physico-chemical stress in most large-scale channel successions, interpreted to be the consequence of carrying the bulk of the fluvial discharge through these trunk channel systems. By contrast, small-scale channels display less evidence of physico-chemical stress indicating they carried little fluvial flow. Abandoned channel deposits likewise show reduced paleoenvironmental stress. This study suggests that the deposits of small-scale channels and abandoned channels are the most suitable for assessing the degree of marine influence in the study area.