Horseshoe Canyon - Bearpaw Transition and Correlation of Associated Coal Zones across the Alberta Plains

The Horseshoe Canyon Formation contains about 40% of the total coalbed methane gas resources of the Upper Cretaceous-Tertiary succession, of which about 58% are hosted by the Drumheller and the Basal coal zones. This study correlates the Horseshoe Canyon-Bearpaw transition and associated coal zones across central and southern Alberta Plains and examines outcrops and associated subsurface strata of the Horseshoe Canyon Formation in the Edmonton area.

Three Bearpaw marine tongues are interfingered with the Lower and Middle Horseshoe Canyon Formation. The Lower and Middle Bearpaw marine tongues consist of two distinctive marine regressive (coarsening-up) sequences, whereas the Upper Bearpaw Marine Tongue consists of only one. At least five major flooding surfaces are present in the Horseshoe Canyon-Bearpaw transitional zone, each of which marks a marine transgression followed by a marine regression. Amongst the flooding surfaces, the First Flooding Surface can be traced to west-central Alberta.

The gradual regional shifting of facies between the Bearpaw marine tongues and Horseshoe Canyon nonmarine deposits were controlled by relative fluctuations of sea level, which were controlled by global eustasy and regional tectonics. In contrast, frequent facies changes at particular locations may have been controlled by basement discontinuities.

Ten coal seams are developed in the Edmonton area. Seams #1, #2 and #3 are correlated with the Basal Coal Zone in the Drumheller area. Seams #4, #5 and #6 in the Edmonton area are correlated with the Lower Drumheller Coal Zone in the Drumheller area. Seams #7 and #8 in the Edmonton area are most likely equivalent to those in the Upper Drumheller Coal Zone in the Drumheller area. Seams #9 and #10 appear to be correlative to the Daly/Weaver Coal Zone.

In the Edmonton area, coal seams are mainly of sub-bituminous rank and highly fractured. Strike of the face cleats is N40-450E (perpendicular to the Rocky Mountain Thrust Belt) and strike of the butt cleats is N50 degrees to 45n degrees W, roughly perpendicular to the face cleats.