Stratigraphic cross sections illustrate lithology, facies, general thickness changes, and rock units of the Mississippian strata which are known in the subsurface in the Peace River area.
Mississippian sedimentary rocks were truncated to the northeast and east by post-Mississippian pre-Permo-Pennsylvanian erosion. Erosion occurred in three additional periods in the more easterly and northerly parts of the area—in pre-Triassic, pre-Jurassic, and pre-Cretaceous time. More than 3,000 feet of sedimentary rocks remain in the thickest known section and represent all the Mississippian units recognized in surface sections of the Rocky Mountains. More than 1,000 feet of strata present in the British Columbia subsurface have been eroded in the Peace River area of Alberta.
Several of the formations of the central plains and foothills are recognizable. The Exshaw of the Sturgeon Lake district is a shale-siltstone-limestone sequence which grades northward to shale. The Banff formation, which at the south is a carbonate unit overlain by a clastic zone, thickens to the north where a shale facies is present. Similarly the Pekisko of the northern part of the Peace River area is a dark shale, in contrast to the bioclastic limestone facies throughout the rest of Alberta. The Shunda is composed of a series of bioclastic limestones and gray shales over the entire area.
A new formation name, the Debolt, is here proposed for a sequence of rocks divided by a thin clastic zone into a 300-foot lower unit of fragmental limestones, probably correlative with the Turner Valley of southern Alberta, and a 5oo-foot unit of dolostones with evaporites, possibly equivalent to the Mount Head. Amerada Crown “G” F 23-11 has been chosen as the type well section of the Debolt.
Above the Debolt is a series of clastics with some carbonates and evaporites considered to be correlative with the Tunnel Mountain. These beds are assigned to the Stoddart, a new formation proposed by Rutgers.
The Pekisko, Shunda, and lower Debolt comprise Laudon’s Dessa Dawn of the Wapiti Lake surface sections.
The “Permo-Pennsylvanian” beds, indefinite as to age, are composed of light-colored chert, dense dolostones, and quartz-chert sandstones. Considerable erosion of the Stoddart and Debolt indicates a major unconformity and time lapse before deposition of the “Permo-Pennsylvanian” over the Mississippian.