Evaluation of a Highstand Clastic Wedge: The Jurassic Aklavik Formation, Northwest Territories

Carly Barnett¹, Richard Evoy², and S. George Pemberton^3
1 EnCana Corporation, Calgary, AB
² Petro-Canada, Calgary, AB
³ University of Alberta, Edmonton, AB

The southeastern basin-margin of the Brooks-Mackenzie Basin includes strata of the Jurassic Aklavik Formation, the upper-most unit of the Bug Creek Group. These rocks are found in the subsurface in the southwestern region of the Mackenzie Delta, Northwest Territories, and in outcrop to the west in the Richardson Mountains.

Facies identified from outcrop suggest the presence of two different systems tracts. The more typical facies represent highstand conditions, suggesting deposition of a prograding wave-dominated delta and associated shorefaces. A second facies association, suggestive of transgressive conditions, represents drowning and re-activation of the shoreface and deltaic deposits. Supporting this interpretation, a Glossifungites surface was identified, delineating a transgressive surface of erosion.

Previous work on the Aklavik Formation focused on the shoreface model. The principal facies in the study area agree with this idea, specifically suggesting deposition took place within a wave-dominated, but heavily storm-influenced, shoreface setting. Only in certain outcrop localities was a deltaic influence recognized. These deltaic sediments tend to exhibit higher visible porosity and permeability than the well-sorted, highly cemented shoreface sands, signifying that the better reservoir may be associated with these sediments.

The identification of the deltaic facies, and the correct interpretation within the related facies association, changes the overall interpreted depositional environment for the Aklavik Formation. This new model affects the subsurface mapping of this formation, and therefore increases the predictive power of potential reservoirs in the subsurface.

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