Geologic Factors Affecting Land Development at Fort McMurray, Alberta

The near-surface geologic deposits in the Fort McMurray area can be subdivided into bedrock and unconsolidated surficial deposits. Bedrock outcrops include the Beaverhill Lake limestones, the McMurray oil sands, and the Clearwater Formation which consists of the Clearwater shale and the Wabiskaw glauconitic sandstone. Surficial deposits are comprised of gravelly till, outwash sand and gravel, colluvium, glaciolacustrine and recent lacustrine silts and clays and alluvium along stream valleys.

A survey of the geologic factors affecting land development indicated that many of the deposits are susceptible to erosion, slumping and landslides. The Clearwater Formation and surficial deposits are subject to gullying by surface water runoff when vegetative cover is absent. Undercutting on the inside of stream meanders contributes to bank erosion and instability. The Clearwater shales which are overconsolidated clay shales are prone to massive slumping and landslides on steep slopes in the area.

The following recommendations are made concerning land development in the area:

1. Vegetative cover should be left undisturbed to curtail gullying; if vegetation is removed it should be replaced as quickly as possible.

2. Developers should avoid areas where active stream undercutting is occurring.

3. Developments should not be placed on or near steep slopes composed of Clearwater shale because of their susceptibility to slumping and landslides.

4. The highlands above the stream valleys are suitable for development in terms of erosion hazards and slope stability.

However, before any development occurs additional information pertaining to groundwater conditions, sulphate content of soils, mineral resources, suitability of sites for solid waste disposal and geotechnical properties of the various deposits would be essential to assess properly all geologic factors that may affect land development in the area.