Print this pageOrigin of linear Viking reservoirs in Alberta, Canada
BURTON, JAMIE, and ROGER G. WALKER
The Late Albian Viking Formation in the Joffre-Mikwan-Fenn area of Alberta contains a series of narrow linear sandbodies. They are encased in mudstones with a marine to brackish trace fauna. The overall Joffre-Mikwan-Fenn trend is absolutely straight, at least 180 km long and 20 km wide. Contrasting interpretations place the linear sandbodies (1) in a linear restricted valley/embayment trending NW-SE open to the sea in the SE, or (2) in a NW-SE trending shoreline-to-open-marine setting with the sea to the NE. In the study area, the Viking contains four extensive erosional bounding discontinuities (BD) interpreted as transgressive surfaces of erosion. The second surface at Joffre (BD2) has an asymmetrical trough-like morphology with respect to horizontal log markers, suggesting a valley/embayment that strikes NW-SE. However, the gentle, landward-dipping side would become horizontal if log markers were given an original dip into the basin of about 1:375' (0.150), leaving a steeper incision facing seaward. This incision is interpreted as a shoreface profile that formed during a pause in overall transgression. At Joffre, local supply of coarse sediment mantled this shoreface, temporarily stopping the transgression, whereas alongstrike at Fenn, with no sediment supply, the transgression continued southwestward forming a flatter, more extensive surface. In this transgressive shoreface interpretation, with open marine conditions to the NE and no confining geometric elements to the NE, there is no suggestion of an enclosed embayment. The two interpretations have very different implications with respect to (1) alongstrike reservoir homogeneity, and (2) overall Viking paleogeography and history of relative sea level fluctuation.