The Viking and Westgate Formations in Outcrop: Potential Analogs for Subsurface Reservoirs, Central Foothills, Alberta

Xavier Roca¹ and A. Guy Plint^2
1 University of Western Ontario, London, ON
² Department of Earth Sciences, University of Western Ontario, London, ON

The Late Albian Viking Formation, a marine-estuarine sand-prone succession interbedded between transgressive black shale units, is one of the major hydrocarbon reservoirs of the Alberta foreland basin. Although present throughout the subsurface in the Alberta plains and western Saskatchewan, Viking outcrops were not recognized in the adjacent western thrust-and-fold belt prior to 2000. Recently, 10 new outcrops of the Viking and Westgate Formations have been discovered in the central Foothills of Alberta between townships 37 and 39. In these localities, the Viking Formation consists of lower to upper shoreface hummocky and swaley cross-stratified sandstones and interbedded mudstones, that are everywhere erosively capped at the VE4 surface by a chert and quartzite conglomerate. An overlying conglomeratic unit reaches a maximum thickness of >7 m in Fall Creek, and is characterized by a locally steep erosive basal contact, horizontal bedding, accretion surfaces and alternating open and closed-work conglomerate. To the NW, the conglomeratic unit gradually thins out over 30 km, disappearing in Gap Creek, where paleosols capping shoreface successions are recognized. The inferred fluvial origin of the conglomerate (with possible marine reworking) and potential adjacent interfluve areas support its interpretation as the fill of a shallow paleovalley. The fact that this conglomeratic unit overlies VE4 implies that it represents a marginal facies of the Westgate Fm. If this is the case, the newly discovered outcrops could represent an analog for the paleovalleys previously identified in the subsurface of the Alberta plains, which represent some of the most prolific Viking pools.

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