Surficial geology, Mega River, Alberta

Abstract

The Mega River map area (NTS 84M/SW) is located in northwest Alberta. The southern third of the map lies within the Fort Nelson Lowlands physiographic region, and comprises the generally flat, low-lying (360-545 metres above sea level (asl)) area that drains southwards into the Hay River drainage basin. The northern two-thirds of the map is situated within the Alberta Plateau physiographic region, and includes the conspicuous Bootis Hill, considered to be a bedrock remnant, that rises to 771 metres asl. The map area is blanketed by Boreal forest and extensive bogs and fens. Soils are generally poorly drained, commonly with shallow water tables, reflecting the high clay content of the tills and glacial lake sediments in which they have formed. Sporadic permafrost is present in the map area, as evidenced by shallow frozen sediments, and concentrations of thermokarst ponds. The main economic activity in the map area is natural gas extraction with a minor component of forestry and trapping. The surficial geology of the Mega River map area was interpreted from 1:60 000 scale black and white airphotos (Alberta Sustainable Resource Development, 1994). Aspects of the regional surficial geology were also interpreted from shuttle radar topography mission (SRTM) imagery (3-arc second). Fieldwork was conducted over a two week period in summer 2004. Till within the Mega River map area has a high clay content (10-40 %), reflecting glacial erosion and entrainment of shale-rich bedrock and reworking of advance-phase glaciolacustrine sediment. In some localities, a second thinner and distinctly sandier till (30-45% sand in the <2 mm size fraction of the matrix) overlies this basal clay-rich till. Fabrics in the two tills tend to be very similar, and contacts between them are often diffuse suggesting that it is a second facies relating to deposition of a greater component of more far travelled (Canadian Shield-derived) coarser englacial sediment, rather than a different trajectory of ice. Clast content of the regional till deposits tends to be very low, generally between 1 and 10%, and are dominantly Canadian Shield and locally derived shale and sandstone erratics. Till, dug from borrow pits, is the most abundantly used form of aggregate in the map area and is employed to build well pads and most petroleum development and access roads. There are no known gravel pits situated within the Mega River map area. Kame terraces identified along the eastern margin of Bootis Hill and in the Wally Lake area may represent potential granular aggregate resources. This map represents a product of the Shallow Gas and Diamond Opportunities in Northern Alberta and British Columbia project, conducted under the Northern Resources Development Program of the Geological Survey of Canada (Natural Resources Canada). The project involved the collaboration of the Alberta Geological Survey (Alberta Energy and Utilities Board), as part of their Alberta Mineral Strategy, Quaternary mapping initiative, and also the British Columbia Ministry of Energy, Mines and Petroleum Resources.