This chapter deals with Middle Cambrian, Upper Cambrian and Lower Ordovician rocks (Sauk II and III sequences of Sloss, 1963) of the Western Canada Sedimentary Basin (WCSB).
The interval is particularly well exposed in the front and main ranges of the Southern Rocky Mountains, where alternating units of carbonates and siliciclastics attain thicknesses greater than 3500 m. The mountain sections are generally underlain by Lower Cambrian clastics and overlain by Middle Ordovician and Middle Devonian limestones and clastics, and carbonates of Late Devonian age.
The interval is widely developed in the subsurface of the foothills and plains as far north as about 54°N latitude in Alberta and Saskatchewan, and extends into southwestern Manitoba (Fig. 8.1). The sediments in the plains are dominantly siliciclastic and lie unconformably on crystalline Precambrian rocks of the Canadian Shield. The sequence locally reaches thicknesses of more than 500 m in the subsurface but is deeply eroded at the sub-Devonian unconformity in central and northern Alberta and in northern Saskatchewan. The sequence pinches out in eastern Saskatchewan below overstepping Middle Ordovician strata.
A small remnant of strata, interpreted as Middle Cambrian, occurs in the Hay River Embayment, north of the Peace-Athabasca Arch. These strata are probably contiguous with the Cambrian and Ordovician sections of northeastern British Columbia. However, some believe that these rocks are of Middle and Early Devonian age.
The present synthesis describes the general lithology and distribution of Cambrian and Lower Ordovician strata in the subsurface of the Western Canada Sedimentary Basin, and correlates these strata with coeval formations in the Rocky Mountains.
The main original contributions of this chapter lie in the eight regional cross sections that pass through the basin (Figs. 8.8 to 8.15) and the four regional maps (Figs. 8.19 to 8.22). The remaining material draws heavily from the published and private writings of many scientists, here extensively abstracted and paraphrased. Particular reliance is placed on the excellent work of J.D. Aitken for information on the Cambrian in the mountains and on the subsurface work of H. van Hees and D.C. Pugh. Lower Paleozoic rocks north and west of the Hay River Embayment, or in the areas west of the Main Ranges are not dealt with here. Interested readers are directed to Aitken (in press b) and North (1964).
Last modified: August 7, 2008
