RECOGNIZING AND INTERPRETING A CRETACEOUS-AGED CHANNEL-BELT AVULSION IN THE WESTERN INTERIOR SEAWAY: PALEOENVIRONMENTAL IMPLICATIONS FOR THE MCMURRAY FORMATION

A world-class archive of fluvial-deltaic deposition can be found within deposits of the Early Cretaceous McMurray Formation in the southeast Athabasca Oil Sands Region (AOSR) Alberta, Canada. Uniquely-dense wireline well log and drill core data allows for the investigation of the stratigraphic and spatial distributions of ancient channelized systems, resulting in maps of considerable scale (>11,000 km²). The youngest and best-preserved of these systems in the McMurray Formation is interpreted to contain the deposits of an ancient channel-belt that experienced a regional avulsion. Avulsion mechanics, as understood from previous studies of modern or geologically-recent rivers, can be interpreted within this ancient system and used to help reconstruct the evolutionary history of this river. This has implications for paleoenvironmental interpretations, including a possible recognition of the effects of the backwater length in a large, shallow Early Cretaceous fluvial-deltaic system. The deposits featured in this study can help provide insight into the geologic history of the Western Interior Seaway, the preservation potential of large-scale fluvial features in the stratigraphic record, and their use in the reconstruction of ancient river systems.