Tectonic Influence on Deposition and Erosion in a Ramp Setting: Upper Cretaceous Cardium Formation, Alberta Foreland Basin

Abstract

This paper presents the results of a combined outcrop and subsurface investigation of the Upper Cretaceous Cardium Formation in northwestern Alberta and adjacent British Columbia, Canada. More than 100 measured core and outcrop sections combined with more than 1100 well logs were used to examine stratigraphic relationships in an area of over 45,000 km2. The Cardium consists of stacked regressive-transgressive cycles deposited during shoreline progradation along the western margin of a foreland basin occupied by the Western Interior seaway. In general, these cycles consist of shoaling upward successions (highstand systems tracts composed of shoreface sandstones and conglomerates and heterolithic offshore deposits) capped by transgressive erosion surfaces. Linear incised lowstand coarse-grained shoreface deposits are present at some stratigraphic levels. A single, thick (locally more than 20 m thick in the study area) nonmarine wedge that overlies shoreface sandstones is interpreted to represent deposition during rising sea level rather than accumulation behind a prograding strandline. Preservation of the incised lowstand shoreface deposits is associated with topographic breaks. In places, trends of isopachs, facies transitions, erosional bevels on transgressive erosion surfaces, synsedimentary faults, and modern production trends can be directly superimposed and closely correspond to basement structural trends. This suggests that basement structures were being remobilized during Cardium deposition, possibly in response to thrusting in the orogen c belt.