Abstract

Deposits of the Cardium Formation at Pembina are characterized by an upward-coarsening interval, commencing at the base with black, bioturbated shale and study siltstone that incorporates increasing amounts of very fine and fine sand. Bioturbation also characterizes this interval, although it drops off very quickly toward the top, where distinctly bedded sandstones and shales dominate. Chert conglomerates cap the sequence.

The thickness and distribution of lithofacies that comprise this upward-coarsening interval are extremely variable across the field. Rapid vertical variability is a common characteristic in core samples. Correlations of closely spaced cores indicate clearly that lithofacies are also characterized by a rapid lateral change. Complex patterns of sedimentation and scour define the upper high-energy part of the sequence. This arrangement is controlled by input of sediment into the area, scour of pre-existing deposits, and subsequent resedimentation. The results of these processes can be observed in outcrops where, in addition to hummocky cross-stratification, large scours, rib and furrow structures, and boulder conglomerates of surrounding lithologies are evident.

Field wide maps of the top surface of the reservoir display a ridge-and-swale topography formed by accumulations of conglomerate and scouring processes, respectively. Ridges measure approximately 13 to 18 km in length and 3 to 8 km in width. The contact between the conglomerate and underlying sandstone is similarly controlled by scour. This surface exhibits a subdued ridge-and-swale topography. Ridges on this surface measure approximately 9 to 17 km in length and 2 to 6 km in width.