Fernie Formation and Minnes Group (Jurassic and lowermost Cretaceous), northern Rocky Mountain Foothills, Alberta and British Columbia

Abstract

The Fernie Formation and Minnes Group represent infilling of a marine trough, grading from mid-basin to alluvial plain deposits. This report establishes a regional stratigraphic framework, outlines the correlations and facies, and documents the ages of rocks ranging from earliest Jurassic (Hettangian) to Early Cretaceous (Late Valanginian). The lower and upper boundaries are defined by regional unconformities. The Jurassic-Cretaceous boundary lies within beds transitional between the Fernie Formation and the Minnes Group. The Fernie Formation of this region, consisting of marine sediments, is not strictly comparable with the Fernie sequence of the southern and central Foothills. An unconformity within the formation truncates Middle and Lower Jurassic strata. The Minnes Group consists of marine and nonmarine sediments, including quartzose and cherty sandstone, siltstone, conglomerate, shale, and coal- bearing beds. In the northern half of the area, the Minnes Group is divided into four formations (in ascending order): Monteith, Beattie Peaks, Monach and Bickford. In the southern half, equivalent beds are included in the Monteith and Gorman Creek formations. Partly equivalent beds are assigned to the Nikanassin Formation of the northern Alberta Foothills. Marine cycles within these Late Jurassic and Early Cretaceous rocks record a complex interaction of tectonic and sea- level processes, and the initial development of a foredeep on the eastern side of the Cordilleran Orogen. Clastic sediments were derived from a cratonic and Cordilleran source. The Fernie and Minnes rocks form potential source and reservoir rocks for hydrocarbons. The Minnes Group has produced limited amounts of natural gas and has been explored to a limited extent for coal.