Description and Interpretation of Coarsening-Upward Cycles in the McMurray Formation, Northeastern Alberta: Preliminary Results

The McMurray Formation in the Athabasca bitumen accumulation region of northeastern Alberta exhibits some of the most complex lithofacies variations within the Western Canada Sedimentary Basin. Refinements to depositional models are necessary, and a greater comprehension of internal stratigraphic architecture of the formation is required. Such an improvement in understanding of the stratigraphic framework of the McMurray Formation could aid in the determination of occurrence and distribution of reservoir facies at both a lease and reservoir scale. This information could ultimately improve cost savings regarding the drilling strategy associated with various subsurface SAGD projects. A new sequence stratigraphic framework for the McMurray Formation was proposed by Ranger (1994). He identified a number of laterally correlatable sequences. We focus on some of the sedimentological details associated with these sequences and try to develop environmental interpretations based on core examination from Townships 79 and 80, Range 7W4. A series of stacked coarsening-upward cycles (representing the highstand systems tract of sequences) has been identified within the Lower Cretaceous McMurray Formation of northeastern Alberta. These coarsening-upward cycles are interpreted to represent progradation of mixed wave/fluvial-influenced bayhead deltas into a partially-closed, brackish inland seaway. INTRODUCTION Until recently, the internal stratigraphic architecture of the McMurray Formation had been poorly understood. Some researchers, however, (e.g.; Nelson and Glaister, 1978; Ranger, 1994; Ranger and Pemberton, 1997) have successfully commenced to unravel the stratigraphic complexity of the McMurray Formation through the recognition of some geologically significant and correlatable stratigraphic surfaces. These surfaces comprise argillaceous units that can be correlated for several sections and bound cleaning/coarsening-upward cycles. Such coarsening-upward cycles in the McMurray Formation have rarely been documented in current literature, and yet are not uncommon in wells or cores. It is of paramount importance that the genesis of these coarseningupward cycles be fully comprehended, and their genetic relationship to the more typical channel facies of the McMurray Formation be understood (Ranger et. al., 1994; Ranger and Pemberton,