Surficial Geology of the McLennan Area, Alberta (NTS 83N/NE): Report to Complement Surficial Geology Map of the McLennan Area

The purpose of this investigation was to determine the distribution of surficial materials, Quaternary history and collect geochemistry and KIM samples. This report compliments the surficial geology map. The study area is west of the Lesser Slave Lake and a few kilometres north of High Prairie. The physiography includes the Heart River Upland (northwest) and the Peace River Lowlands (west and southeast). The Lowlands, below about 680 m, include Falher Plain (west), Bearhead Plain (west and southwest) and the High Prairie Plain (southast).

The Heart River Upland is a wooded terrain with abundant wetlands and includes a broad area of moraine in the north central part and hummocky to flat glaciolacustrine sediment covers much of the remainder. Major meltwater channels include a southwest trending channel occupied by the South Heart River and a second system, in the west, trending southeastward to form a major glaciofluvial delta on the north side of the South Heart channel. In places these sediments have been blown into dunes. The Peace River Lowland is an open, low relief, terrain extensively cultivated. Primary sediment cover is glaciolacustrine sediment, in places including rhythmites, deposited in Glacial Lake Peace (GLP) Topography is generally flat except where the melting of buried stagnant ice formed hummocky terrain.

There is evidence for three relatively stable lake stages of Glacial Lake Peace. A high level stage at about 680 to 670m, an intermediate level, about 640 to 630 m, and a last low stage at about 595 to 585 m. Lake sediment above 680 m may have been deposited, as local isolated lakes and/or in other areas during as an earlier and higher stage of GLP. Following drainage of this lake much of the High Prairie Plain was gradually covered by fluvial sediment from the South Heart River and smaller streams flowing northward from the southern highlands. A few landslides occurred in the bedrock exposed in the south flanks of the Heart River Uplands.

The Quaternary stratigraphy and glacial history is poorly understood with only a few deep exposures. A section along the South Heart channel exposes about 3 m of gravely sand over a very clay rich till. One site in the north central part exposes a massive gray brown till overlying a lighter olive brown till. These tills may correlate with the Sawn Lake till and underlying till recognised to the north in the Buffalo Head.