Type Locality:

California Standard Steen River 2-22-117-5W6M, in northwestern Alberta, between 1,588 and 1,669 m (5,210 and 5,475 ft).

Distribution:

The Keg River Formation extends from the Precambrian Shield east of the 4th Meridian to the Shekilie Barrier near the British Columbia and Northwest Territories borders, where it can no longer be distinguished from overlying Muskeg Formation equivalent dolomites. To the south the Keg River Formation onlaps the Peace River Arch and becomes the equivalent of the Winnipegosis Formation near the Saskatchewan border. The thickness of the Keg River Formation varies from 10 to 300 m (33 to 984 ft). The lower Keg River is between 20 and 30 m (66 and 98 ft) thick it cannot always be recognized as a separate member. The upper Keg River Formation has been recognized only in the Black Creek basin and other subbasins east of the 6th Meridian. It is generally between 10 and 30 m (33 and 98 ft) thick. The name "Rainbow Member", used only in the Rainbow subbasin is 60 to 260 m (197 to 853 ft) thick. The upper Keg River Reef Member can be recognized in the Zama and Bitscho sub-basins and varies in thickness from 50 to 105 m (164 to 344 ft).

Lithology:

The Keg River Formation, as defined by Law consists of grey and brown dolomite with poor intercrystalline or vuggy porosity, and brown, cryptocrystalline, slightly argillaceous and fossiliferous, dense wackestone limestone and minor dolomite in the lower 15 m (49 ft) of the type section. The lower Keg River Member consists of brown to dark grey-brown, slightly bituminous, argillaceous, cryptocrystalline, fossiliferous, dense limestones that were deposited on a moderately shallow marine shelf or platform. Locally part or all of the lower Keg River Member consists of dolomite with occasional poor vuggy porosity. Bituminous partings can be common. Crinoids, brachiopods, ostracodes, gastropods and tentaculitids make up from 10 to 20% of the framework. Thamnopora, Cystiphyllum, platy Alveolites, Syringopora and lamellar to irregular stromatoporoids can make up to 30% of the framework. Packstones and grainstones are rare. The upper Keg River Member consists of three units (Hriskevich, 1966): a lower carbonate usually consisting of dolomite, a middle bituminous limestone to bituminous shale unit, and an upper limestone unit. The lower carbonate unit is a carbonate bank deposit made up of microcrystalline to coarse bioclastic debris, with crinoid fragments making up to 30% of the framework. Packstones and grainstones with intermittent poor vuggy and intercrystalline porosity are common in this unit. Tentaculitids are frequently found in the middle unit. The upper unit is generally devoid of fossils. Thin beds with microcrystalline to very fine bioclastic debris occur in both the middle and upper unit. The Rainbow Member (Hriskevich, 1966) consists of reefal limestones or dolomites made up of boundstones, packstones and grainstones which have been subjected to diagenetic changes such as cementation, leaching, late stage dolomitization, fracturing, infixing with internal sediments, replacement by anhydrite and deposition of carbon in pores. Three stages of reef growth can be recognized in the Rainbow Member. A lower stage where corals, stromatoporoids, calcareous algae and minor crinoids, bryozoa and brachiopods formed patch reefs on a 14 m (46 ft) thick crinoid bank. Atoll, semi-atoll and pinnacle reef growth took place during the second stage. Broken up stromatoporoids, corals and calcareous algae formed a rim of well cemented rubble around the atoll reefs and a semi-rim in the pinnacle reefs. During the last stage stromatoporoids and corals became increasingly rare. Laminated beds of grainstones to packstones ale common in this stage. Porosity in the Rainbow Member ranges from poor to excellent. The amount of cementation, leaching and dolomitization that has taken place varies from one reef to another. Filling of the pores with carbon is common in many of the reefs in the middle 61 m (200 ft) of the Rainbow Member. The name "Upper Keg Reef Member" was proposed by McCamis and Griffith in the Zama subbasin for reefal limestones and dolomites that appear to be time equivalent to the lower two stages of the Rainbow Member. Fauna and lithofacies in the Rainbow Member and upper Ice River Reef facies show many similarities.

Relationship:

The Keg River Formation disconformably overlies the Chinchaga Formation. The Rainbow Member conformably overlies the lower Keg River Member and is conformably overlain by the Muskeg Formation in the Rainbow sub-basin. The upper Keg River Reef Member conformably overlies the lower Keg River Member and is unconformably overlain by the Zama Member of the Muskeg Formation. Lateral equivalents of the Keg River Formation are the Pine Point, Hume and Nahanni formations north and west of the Shekilie Barrier in the Northwest Territories and British Columbia. In eastern Alberta and Saskatchewan the Winnipegosis Formation is the lateral equivalent of the Keg River Formation. The upper part of the Keg River Formation and Rainbow Member may in part be time equivalent to the lower part of the Muskeg Formation. The upper Keg River Member is the time equivalent of at least the lowest stage of the Rainbow Member. The correlations between the upper two stages of the Rainbow Member and the upper Keg River Member and the lower Muskeg Formation are controversial. (Hriskevich, 1966; Langton and Chin, 1968; Barss et al., 1970; Bebout and Maiklem, 1973; Schmidt et al., 1977). The upper Keg Reef Member is the time equivalent of the upper Keg River Member.

History:

Hriskevich (1966) divided the Keg River Formation in the Rainbow sub-basin into three members: 1) The Lower Keg River Member, type section Banff Aquitaine Rainbow West 7-32-109-8W6M, between 2,018 and 2,064 m (6,622 and 6,772 ft); 2) Upper Keg River Member, type section Imperial et al. Black Creek 10-27-109-9W6M, between 2,018 and 2,064 m (6,622 and 6,672 ft); and 3) Rainbow Member, type section in 2-32-109-8W6M, between 1,788 and 2,018 m (5,866 and 6,622 ft). McCamis and Griffith (1967) divided the Keg River Formation in the Zama subbasin into two members, the lower Keg River Member, and the upper Keg River Reef Member. The type section of the upper Keg River Reef Member is in the B.A. H.B. Zama North 16-19-116-4W6M well, between 1,500 and 1,560 m (4,922 and 5,117 ft). McCamis and Griffith did not recognize the upper Keg River Member in the Zama subbasin.

Other Citations:

Barss, Copland and Ritchie, 1979; Bebout and Maiklem, 1973; Hriskevich, 1966, Langton and Chin, 1968; Law, 1955; McCamis and Griffith; Schmidt, McDonald and McIlreath, 1977.