The Central Foreland NATMAP Project is a multi-disciplinary project designed to investigate the nature of regional variations in Cordilleran bedrock stratigraphy, structural style, and surficial geology, with a goal to aid petroleum and mineral exploration. Two principal areas are under investigation; the Liard Basin region of the southern Northwest Territories and adjacent Yukon (NTS 95B and 95C); and in the south, the Rocky Mountains and Foothills of northeastern British Columbia (NTS 94G).

Location Map

The main objective of the surficial geology component is to map and explain the surficial materials and geomorphic features of the three map areas. This project will improve existing databases so that timely information can be provided to industry. Maps will locate accessible sources of aggregate necessary for economical construction of roadways, buildings, well sites, and pipelines. Maps of thickness and extent of surficial materials will abet the execution and interpretation of seismic surveys. Extensive glaciolacustrine sediment, thick shales, and poorly-indurated sandstone beds are unstable and can pose problems for development. An inventory of potential natural hazards including landslides, avalanches, and surface instability caused by permafrost will provide essential information.

Till samples will be analyzed for indicators of potential mineral resources of the area. This area lies in a former contact zone between continental (Laurentide) and Cordilleran ice masses; therefore, resolving the glacial history is essential for drift prospecting. Several mineral exploration companies have recently undertaken diamond exploration in areas adjacent to the map area.

The 2001 field season concentrated on the Fort Liard (95B) and La Biche River (95C) map areas. Access to 95B was by helicopter based in the Hamlet of Fort Liard and by zodiac on the Liard River (J. Bednarski). Fieldwork in (95C) was primarily by foot traverses from fly camps (R. Smith). In addition to the mapping work, Fisherman Lake was cored to address water quality issues brought up by the Hamlet of Fort Liard (R. Smith). A final field season will be conducted in these areas in the summer of 2002.

The Central Foreland study area in relation to the last glacial maximum in northwestern Canada, as reconstructed by Dyke and Prest (1987). Major ice-flow lines are shown by the arrows. The thick lines show probable ice divides. Granite erratics form the Canadian Shield have been found at the western border of 95C, indicating a more extensive Laurentide ice advance than previoulsly suggested.

Images

	Large glaciofluvial terraces along the Muskwa River in the Trutch map area (94G). The photo is looking downvalley to the east at Sleeping Chief Mountain (elev. 2022 m).
	The confluence of silt laden Liard River and the dark organic-rich Petitot River and the Hamlet of Fort Liard. Mount Coty, within the Liard Range, is due north across the Liard River (Fort Liard 95B).
	The Liard River flowing northward along the mountain front (95B).
	An unexpected summer snowstorm; 40 cm between June 22nd and June 23rd, 2001. Late-lying snowpacks can be found along east and north-facing slopes of the mountain ranges through early July. Summer temperatures, however, can exceed 30°C.
	Fisherman Lake, west of Ft. Liard (Pointed Mountain, a prominent natural gas site is seen at left (west of the lake). During an outreach session with residents in December 2000, concerns were raised by them about perceived changes in water quality of Fisherman Lake. Two sediment cores were taken from this lake in July 2001 in order to assess recent (<200 year) changes in lake chemistry.
	A large (>2 km long) block rotational slump and debris flow in poorly consolidated Tertiary sediment along the Beaver River (95C).
	A catastrophic landslide extending about 1.5 km into a tributary valley to the Halfway River, where thick sandstone overlies weak shale units. The photograph is looking to the southeast (94G).
	Looking northward from the Liard Range. The Liard River is flowing northward toward Nahanni Butte visible on the horizon (95B).
	Landslides below outcrops of Mattson and Flett formations flanking a small mountain south of Mount Flett, visible in the upper left (95B).
	A 12 m section through glaciolacustrine sediment along the Whitefish River. The lower half of this section is frozen, with several 10 cm thick segregated ice lenses running through it. Discontinuous permafrost is commonly associated with thick, silt-rich glaciolacustrine sediment along the river valleys, and in extensive till blankets in the southwest region of map 95C.
	Diatoms are a microscopic (5 to 200 µm) class of algae, possessing species-specific exoskeletons (valve) of biogenic silica (this photo shows Aneumastus tusculus (Ehr.)Mann & Stickle). Diatom analyses will be conducted on the sediment cores from Fisherman Lake in order to assess changes in lake water chemistry (pH, nutrients).
	Preliminary map of mass wasting distribution in the La Biche River (95C) map area. Mass wasting is very prominent along the Kotaneelee and La Biche ranges and reflects extensive, weakly indurated sandstone beds in the Mattson Formation, and extensive shale deposits in the synclinal basins between the ranges. Slumping of surficial material is associated with raised glaciolacustrine sediment along river valleys.

Selected References

Bednarski, J. 1999. Preliminary report on mapping surficial geology of Trutch (94G), northeastern British Columbia. Current Research 1999A, Geological Survey of Canada. p. 35-43.

Bednarski, J. M. 2000. Surficial geology Trutch, British Columbia. Open File 3885, Geological Survey of Canada, scale 1: 250 000.

Bednarski J. M. 2001. Drift composition and surficial geology of the Trutch map area (94G) northeastern British Columbia. Open File D3815, Geological Survey of Canada, CD-ROM.

Smith, I. R. 2000. Preliminary report on surficial geology investigations of La Biche River map area, southeast Yukon Territory. Current Research 2000-B3, Geological Survey of Canada, 9 p.

Authors: Jan Bednarski and Rod Smith