The Morrissey and Mist Mountain Formations -- Newly Defined Lithostratigraphic Units of the Jura-Cretaceous Kootenay Group, Alberta and British Columbia

Abstract

ABSTRACT Recent work in the Rocky Mountain Foothills and Front Ranges of southwestern Alberta and southeastern British Columbia has demonstrated that the economically important coal-bearing strata between the Jurassic Fernie Formation and the Lower Cretaceous Blairmore Group can be subdivided into three formations, which in ascending order are Morrissey (new), Mist Mountain (new), and Elk. Accordingly, it is proposed to elevate the former Kootenay Formation to group status, and at the same time re-establish the original definition and recognition of the Kootenay by including some older sandstone strata which have been transferred by previous workers into the Fernie Formation. The type section of the Morrissey Formation is on Morrissey Ridge, Elk River valley, British Columbia. This formation comprises a coarsening-upward sequence of massive, cliff-forming sandstone ranging in measured thickness from 20 m near Moose Mountain to a maximum of 80 m near Mist Mountain and Highwood Pass, southwestern Alberta. The formation can be subdivided into two members, the Weary Ridge (new), and the overlying Moose Mountain. The Weary Ridge Member, with designated type section on Weary Ridge in the upper Elk River valley of southeastern British Columbia, comprises an orange-brown to brownish-grey weathering, very fine to coarse-grained sandstone up to 55 m thick. The Moose Mountain Member, with type locality at Moose Mountain, Alberta, in contrast comprises a medium-grey weathering, fine- to coarse-grained, better-indurated and more massive sandstone, up to 36 m thick. The Mist Mountain Formation, stratigraphically equivalent to either the combined Adanac, Hillcrest and Mutz Members, or the Coal-Bearing member of the former Kootenay Formation, is proposed for an interbedded sequence of sandstone, siltstone, mudstone, shale and thin to thick seams of bituminous to semianthracite coal, up to 665 m thick. Exposures on a western spur of Mist Mountain near Highwood Pass in southwestern Alberta have been selected as the type section. The long-recognized Elk Formation extends geographically beyond the Fernie area, to other areas of southeastern British Columbia and southwestern Alberta. It comprises an interbedded succession of sandstone, siltstone, mudstone, shale and, locally, thick beds of chert pebble conglomerate and thin seams of high-volatile bituminous coal. A supplemental reference section is suggested for the formation on Morrissey Ridge south of Fernie, British Columbia. The Kootenay Group conformably overlies Upper Jurassic strata of the Fernie Formation and in most areas is disconformably overlain by Lower Cretaceous strata of the Blairmore Group. Near Fernie, Highwood Pass and Canmore, the Elk is possibly conformably overlain by the Pocaterra Creek Member of the Cadomin Formation (Blairmore Group). The Kootenay Group grades laterally into strata of the Nikanassin Formation in the vicinity of the North Saskatchewan River.