Sedimentary and tectonic origin of a transgressive surface of erosion: Viking Formation, Alberta, Canada

The upper Albian Viking Formation in the subsurface of Alberta contains at least four major erosional surfaces, or bounding discontinuities. The highest of these surfaces, Viking Erosion surface 4 (VE4), can be correlated basinwide. Several well log markers onlap the VE4 surface. They represent coarse to granule sandstones with extremely sharp bases. These tongues of sandstone can be traced up to 20 km basinward from their points of onlap and are interpreted as thin lower shoreface sandstones that formed during minor forced regressions superimposed on the overall transgression. The initial regression that immediately preceded VE4 implies a fall of relative sea level of at least 40 m, and a northeastward movement of the shoreline of at least 250 km. These two figures imply a basinward gradient of about 0.00016. -Author