Triassic Spray River Group in outcrop at Elliott Peak in Clearwater County, Alberta

This report provides a summary of the fieldwork that was completed by the Alberta Geological Survey near the hamlet of Nordegg during the summer of 2019. Triassic strata have been studied extensively in Willmore Wilderness Park, Jasper National Park, Banff National Park, and Peter Lougheed Provincial Park, but rarely have strata that occur between the north and south outcrop belts been studied and formally published in the literature. This study of outcrop in Clearwater County focuses on identifying the boundaries of the Spray River Group, which is equivalent to the Montney, Doig, Halfway, and Charlie Lake formations in the subsurface of Alberta. The Spray River Group is subdivided into the Lower and Middle Triassic Sulphur Mountain Formation and the Upper Triassic Whitehorse Formation. These units were studied at a well-exposed outcrop along a ridge below Elliott Peak on Sentinel Mountain. In the study area, the Sulphur Mountain Formation consists of four formally defined members (Phroso Siltstone, Vega Siltstone, Whistler, and Llama) of mixed siliciclastic-carbonate rocks. The overlying Whitehorse Formation consists of the Starlight Evaporite Member, which is composed of mixed siliciclastic-carbonate to carbonate-dominated rocks as well as interstratified evaporites. A low-resolution stratigraphic column along the ridge of Elliot Peak is provided, with the major boundaries that separate the members marked. Samples were collected at 5 m intervals for future geochemical and sedimentological analyses, which will facilitate future regional correlations to outcrop belts and subsurface units.