Grosmont Formation Outcrops (T108-R6W5) at Vermilion Chutes, Peace River, North-Central Alberta (NTS 84J/07)

This report describes outcrops of the Mikkwa and Grosmont formations that are exposed at Vermilion Chutes on the Peace River. The outcrop at the Mikkwa Formation exposed at the lower Vermilion Chutes is considered equivalent to the Grosmont Formation based on the

- similar lithology and paleontology to the Grosmont Formation in the subsurface,

- lack of a mappable Mikkwa Formation unit in the subsurface, and

- prior correlation of the Mikkwa Formation with the Grosmont Formation.

The lower Vermilion Chutes outcrop is mostly undolomitized and contains both reef and non-reef facies, representing shallow-water patch reef and lagoonal paleoenvironments within the Grosmont carbonate platform.

At the upper Vermilion Chutes, the Grosmont Formation outcrop is bitumen stained and pervasively dolomitized, containing vugs originating from moulds of corals and stromatoporoids. Downstream from the Vermilion Chutes, at a locality called Grosmont Flat, is a flat-lying outcrop similar in lithology to that of the upper Vermilion Chutes, but it contains circular, dish-shaped erosional structures up to 10 m in diameter.