ABSTRACT

The nonmarine Lower Cretaceous Blairmore Group of the southern Alberta Foothills can be divided into three formational units, tentatively designated here as the Lower, Middle, and Upper Blairmore Formations. The Lower Blairmore comprises a succession of quartzose sandstones and varicolored shales with a fossiliferous limestone member at the top. The Middle Blairmore is composed of feldspathic sandstones and shales largely derived from volcanic detritus. The Upper Blairmore comprises a succession of siliceous sandstones and varicolored shales that in southwestern Alberta grades up into tuffs and agglomerates of the Crowsnest Volcanic Member.

The Upper Blairmore Formation is present only in the southern Alberta Foothills, but lithologic equivalents of the Lower and Middle Blairmore Formations can be recognized throughout the Plains and Foothills regions of central Alberta. Foraminifera of Middle Albian age, described from the Clearwater and Loon River Formations of the northern Plains, are present in the basal beds of the Middle Blairmore in the central Foothills and in beds of the Mannville Group in the central Plaints, beneath continental beds containing a typical non-dicotyledonous Blairmore flora.

Thus, the Lower Blairmore of the southern Foothills is correlative with the lower Luscar and Gething Formations of the central and northern Foothills, and the Ellerslie and McMurray Formations of the central and northern Plains. The Middle Blairmore of the southern Foothills is correlative with the upper Luscar and Mountain Park Formations of the central Foothills, and the Upper Mannville, Clearwater-Grand Rapids, and Spirit River-Peace River Formations of the central and northern Plains. However dicotyledonous remains are not present in Blairmore-equivalent beds of the central Foothills and central and northern Plains, and it is inferred that strata equivalent to the Upper Blairmore Formation of the southern Foothills and the Commotion Formation of the northern Foothills are absent in these areas through non-deposition or erosion.