Map 328

Map 328

MAP 328

Bedrock Topography of Zama Lake Area, Alberta (NTS 84L)

The bedrock topography map shows the elevation of the bedrock surface. In general, the bedrock topography controls the surface topography in the map area. Rainbow Ridge, Bassett Hill and the Chinchaga Plain are generally underlain by bedrock highs. Rainbow Ridge and other westerly trending bedrock ridges parallel the regional ice flow (Paulen et al., 2005a and 2005b; Plouffe et al., 2004; Smith et al., 2005) suggesting modification by glacial erosion. Major buried valleys lie within the Fort Nelson Lowland and the Rainbow Lake Plain. The elevation of the bedrock rises to >700 m asl in the uplands, similar to the land surface. The elevations in the lowest parts of the buried valleys differ markedly from the land surface in that they are as low as 25 m asl compared to a minimum ground surface elevation of 335 m asl. Two major northwesterly trending buried valleys that extend into British Columbia are the Rainbow Valley in the south and the Zama Valley in the north. A deeply incised depression located within the Zama Valley in Township 110, Range 3, west of the 6th Meridian has eroded through the entire Cretaceous bedrock sequence, including gas-bearing sandstones of the Bluesky Formation, and into the Devonian Wabamun Group limestone down to an elevation of 25 m asl. Buried valleys are one factor that may contribute to the presence of shallow gas within drift, which is known to occur in the Zama Valley within Township 110, Range 3, west of the 6th Meridian, and elsewhere in the Zama Lake region.