| Abstract | Triassic rocks in the southern Canadian Rockey Mountains comprise the Spray River Group, which is divided into the lower Sulphur Mountain Formation and the upper Whitehorse Formation. The Sulphur
Mountain Formation consists of grey to rusty brown weathering siltstones, sandstones, silty limestones, dolomites, and shales that comprise, in ascending order, the Phroso Siltstone, the Vega Siltstone, the whistler, and the Llama Members. In the
eastern Front Ranges and subsurface of the Foothills between Athabasca and Bow Rivers, the Vega Siltstone Member is characterized by a light grey to buff-weathering dolomite lentil herein named the Mackenzie Dolomite. The Whitehorse Formation
consists of pale-weathering, variegated dolomites, limestones, sandstones, siltstones, and intraformational and/or
solution breccias, which are, throughout most of the region, divided into the Starlight Evaporite and Winnifred Members. In the
Athabasca-Bow River region, the Starlight Evaporite Member contains a resistant light grey to buff-weathering sandstone lentil, herein named the Olympus Sandstone. Petrographic examination of Sulphur Mountain and Whitehorse strata indicates a
composition of detrital quartz, orthoclase, microcline, and plagioclase feldspar, cellophane, layered silicates such as muscovite, clay, and clay-like minerals, opaque and accessory minerals such as pyrite, hematite, zircon, tourmaline, rutile,
apatite and organic carbonaceous matter. Dolomite and calcite form significant concentrations, occurring as cement and matrix in the siltstones of the Sulphur Mountain Formation, and as well rounded detrital grains, ooliths, pellets, clasts, and
skeletal fragments in both the Sulphur Mountain and Whitehorse Formations. Gypsum occurs sparingly. The limited mineral variety and concentration suggest that the rock components were derived from a source area of low relief, consisting of
pre-existing sediments. Studies of HCl insoluble residues from the Sulphur Mountain Formation indicate a decrease in carbonate concentration toward the presumed source of detrital sediments in the east and northeast. Analyses of sedimentary
directional structures in the overlying Whitehorse Formation suggest formation probably by longshore currents from the west and northwest. Sediments of the Sulphur Mountain Formation were deposited mainly in a shallow-water neritic environment, which
in some regions probably formed part of a series of coalescing delta complexes, along the eastern margin of the Cordilleran Geosyncline. Sediments of the Whitehorse Formation are postulated to have been deposited in an arid to semi-arid, shallow
water, intertidal or lagoonal environment. |