McMurray-Wabiskaw Identity Crisis in the Oil Sands of Northeastern Alberta, Canada

Corinne Bagdan¹, Mike Ranger², and Ken Weaving^1
1 Husky Energy, Calgary, AB
² Mike Ranger Consulting, Chestermere, AB

The stratigraphic contact of the base of the Clearwater Formation (Wabiskaw Member) with the underlying McMurray Formation has become a focus of controversy. Differing opinions on the position of the contact have implications for depositional models, with relevance beyond just the academic.

The McMurray type section crops out along the Athabasca River in the Ft. McMurray area. That outcrop becomes increasing argillaceous, weathered and recessive towards the top, masking upper contacts. Nearby, the type well drilled 1953 has older logs and core that are not to modern standards and resolution.

The Wabiskaw type locality lies in the subsurface and is located in the far southwest of Athabasca where its facies are atypical of the majority of the deposit including the outcrop. These facies changes, combined with confusing original definitions, fuel the debate.

Wabiskaw sands are defined by the presence of glauconite pellets and greater than 10% chert. A very dark, blue-gray shale interval that is often present at the contact is contentious, some assigning it to Wabiskaw, others to McMurray. The color of the shale has been attributed to the presence of glauconite, but mineralogical analysis proves this incorrect. In the subsurface these dark shales seem to cut across facies, including ichnofacies, suggesting they are not facies controlled, but perhaps result from a change in basin chemistry. To further complicate the issue, wave ravinement surfaces, transgressive surfaces of erosion, flooding surfaces, Glossifungites horizons and possible unconformities are commonly interpreted in this succession.

Stratigraphic priority based on the type localities, in addition to modern concepts in sedimentology, ichnology and sequence stratigraphy, must be considered in this challenging debate.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005