In the Interior Plains, the Lower to Middle Devonian clastics, redbeds, evaporites and carbonates of the Elk Point Group (Fig. 10.1) overlie Precambrian or lower Paleozoic rocks with an erosional unconformity that has up to 1400 m of relief. The sediments and evaporites accumulated in paleotopographic basins separated by highlands. Tathlina Highland, Western Alberta Ridge and Peace River Highland (Fig. 10.2) remained emergent during the Middle Devonian.
Lower and lower Middle Devonian strata are present in the southern Mackenzie Mountains (NWT) and extend eastward into the subsurface of the northern plains. They accumulated in Root Basin and Willow Lake Embayment (Fig. 10.2). Here the Lower Elk Point subgroup (Fig. 10.1) reaches a thickness of more than 1000 m. Equivalent beds in the southern plains attain a maximum thickness of 358 m.
The strata of the Upper Elk Point subgroup conformably overlie the lower subgroup and accumulated in the Willow Lake and Elk Point embayments. They attain a thickness of more than 340 m in the northern plains and 215 m in the southern plains.
The Elk Point strata are discontinuously exposed along the northeastern margin of the Western Canada Sedimentary Basin in southeastern Manitoba, western Saskatchewan, northeastern Alberta and the southeastern part of the District of Mackenzie. They are also exposed in the Cordilleran Orogen to the west.
There are many reports available that deal with the economically important Lower and Middle Devonian rocks of Western Canada. The Pine Point lead-zinc deposits in the District of Mackenzie, Northwest Territories were described by Campbell (1967), Skall (1977), Kyle (1981), Rhodes et al. (1984) and Krebs and Macqueen (1984); the lead-zinc deposits in northeastern British Columbia were discussed by Taylor et al. (1975).
The salt deposits in the subsurface of the Interior Plains were mapped by Hamilton (1971) and Meijer Drees (1986); the potash deposits in southern Saskatchewan by Holter (1969). Some of the oil pools in the Rainbow Lake field of northern Albera were described by Hriskevich (1968), Langton and Chin (1968) and Frydl (1989); the Zama Lake reservoir rocks were described by McCamus and Griffith (1967). Collins and Lake (1989) discussed the Sierra gas field of northeastern British Columbia. The reservoir rocks of the Pointed Mountain, Kotaneelee and Beaver River gas fields of northeastern British Columbia and the District of Mackenzie were described by Snowdon (1977) and Morrow et al. (1986). Those of the Tableland oil field in southeastern Saskatchewan were discussed by Martindale and MacDonald (1989). The reservoir rocks of the Mitsue and Nipisi oil fields in central Alberta were described by Kramers and Lerbekmo (1967), Shawa (1969) and Alcock and Benteau (1976).
Regional studies on the Elk Point strata include the compilations of Grayston et al. (1964), Belyea and Norris (1962), Law (1955, 1971), Douglas et al. (1970), Belyea (1971) and Meijer Drees (1990). The Elk Point strata along the northeastern outcrop edge in the District of Mackenzie, Alberta, Saskatchewan and Manitoba were described by Douglas and Norris (1960a), Norris (1963, 1965), Norris et al. (1982), and Vopni and Lerbekmo (1972). Those exposed in the Rocky Mountains of Alberta and northeastern British Columbia and the Mackenzie Mountains of the Yukon and Northwest Territories were described by Norford (1981), Taylor and Mackenzie (1970), Morrow (1978), Morrow and Cook (1987), and Douglas and Norris (1960b, 1961, 1963).
The lower part of the Elk Point succession onlaps an irregular surface of considerable relief. In the interior plains of the District of Mackenzie the succession unconformably overlies Ordovician and Silurian carbonates; in northern Alberta it overlies Precambrian igneous and metamorphic rocks; in southern Alberta it overlies Cambrian clastics and carbonates. In southern Saskatchewan, the pre-Devonian surface consists again of Ordovician and Silurian carbonates. The absence of lower Paleozoic strata in the Northern Alberta sub-basin suggests that this region was deeply eroded before the onset of Devonian deposition.
The formations in the upper part of the Elk Point Group are widely distributed and outline an ancient embayment (the Elk Point Embayment) that extended southeastward from northeastern British Columbia and the District of Mackenzie into the Williston Basin of southern Saskatchewan, Manitoba and North Dakota. The smaller embayment in southwestern British Columbia (the Golden Embayment) is separated from the Elk Point Embayment by the Western Alberta Ridge in southwestern Alberta (Fig. 10.2).
The upper boundary of the Elk Point Group is a relatively flat surface; consequently the Elk Point isopachs (Fig. 10.3) clearly indicate the outline of the paleotopographic basins and the amount of paleotopographic relief. In the area southwest of the Devonian outcrop belt that parallels the Canadian Shield, the orientation of the isopachs changes. Here, salt was leached from the Elk Point succession, resulting in a collapse of the upper surface.
Last modified: August 11, 2008
