The upper Horseshoe Canyon Formation in the Red Deer area is studied to determine successive depositional environments and to relate these environments to the development of Carbon and Thompson coals. It is intended that these objectives contribute to sedimentological models which aid coal exploration and exploitation.
Four informal lithologic units were recognized. In stratigraphic order, these are the lower and upper fine units, consisting mainly of siltstones with minor shales and fine grained sandstones, and an overlying coal-bearing sequence, the Carbon and Thompson coal zones, consisting of coarser grained sandstones, coals, siltstones and shales. It is suggested that the name Whitemud Formation be abandoned, at least in the subsurface, and the rocks be included with the Horseshoe Canyon Formation. Evidence favours a lacustrine origin for the older fine grained dominated unit. The succeeding coal-bearing sequence accumulated in a meandering fluvial system, with the coarser clastics (sand size and greater) representing active channel fill, the finer clastics (very fine grained sands, silts and clays) representing inactive channel fill and overbank deposits and the coals representing back-levee, channel fill and flood basin swamps, developing parallel to the paleo-channels. Within each coal-bearing zone, there are pronounced northwest-southeast alternating bands, typically 4 to 7 miles (6.4 to 11.3 km) wide, of preferred coal and sandstone development which relate to the spatial distribution of the above mentioned paleo-environments. This result agrees with previous findings, notably work on the provenance of Upper Cretaceous sands, in indicating paleo-drainage from the northwest.
Carbon and Thompson coals are low in percent sulfur (0.35 to 0.61 percent) and variable in ash content and non-coal partings. Coal resources are 6.640 x 109 tn (6.029 x 109 t) for the Carbon and 3.205 x 109 tn (2.910 x 109 t) for the Thompson for all coal seams at least 2 ft (0.6 m) thick, and 3.200 x 109 tn (2.906 x 109 t) for the Carbon and 1.100 x 109 tn (9.988 x 108 t) for the Thompson for all coal seams at least 2 ft (0.6 m) thick and with a cumulative thickness in excess of 6 ft (1.8 m).
Exploration for thick Carbon and Thompson coal seams should be concentrated within the northwest-southeast trends of thicker coal accumulation. As the regional dip is to the west, exploitation of seams in the western portion of the study area should be limited to underground mining and/or in situ gasification because of the large overburden thickness. Near-surface Carbon and Thompson coal seams, in the eastern portion of the study area, may be exploitable by strip mining methods.
Nurkowski, J.R. (1980): Geology and coal resources of the upper part of the Horseshoe Canyon Formation, Red Deer area, Alberta; Alberta Research Council, ARC/AGS Open File Report 1980-10, 40 p.