The Cardium Formation, exposed along the Rocky Mountain Foothills and present beneath the Alberta Plains, comprises a terrigenous, muddy, sandy, and conglomeratic clastic wedge that accumulated during the Turonian and Coniacian stages of the Late Cretaceous along the western margin of the Alberta Foreland Basin. This clastic wedge is a complex lithostratigraphic interval that contains multiple disconformities, paraconformities and diastems of variable regional extent. The formation is encased in a thick succession of black mudstones, the Blackstone/Kaskapau formations below and the Wapiabi/Muskiki formations above. All these formations comprise a sedimentary assemblage assigned throughout Alberta and British Columbia to the Smoky, Alberta, La Biche and Colorado groups.
In plan view the formation is arranged in an arcuate strip, approximately 1000 km long, that swings through a 90 degree arc from Waterton Lakes National Park and Canada-U.S. border, past Grande Prairie, Alberta and beyond to Dawson Creek, British Columbia (Fig. 23.1). In the foothills, the formation has been brought to the surface by multiple, juxtaposed, east verging thrusts. In the plains it is confined to the subsurface within allochthonous and autochthonous intervals of the Colorado/ Alberta/Smoky/La Biche groups. The clastic wedge projects approximately 200 km into the basin's interior from the British Columbia-Alberta boundary, is 150 m thick in foothills exposures, thins in the subsurface of the plains to less than 50 m, and becomes indistinct along its easternmost terminus, melding into the mudstones (Fig. 23.2). The formation's dominant rock types are mudstone and sandstone, with small but important conglomerate fractions.
The Cardium Formation is of significant geological interest for two principal reasons: 1) it represents a complex stratotectonic pulse that alternated between sandy and muddy stages during the period of maximum inundation of the Mesozoic North American foreland basin, and 2) it possesses a colossal hydrocarbon storage capacity, manifest in a series of stratigraphic traps, the largest of which is the supergiant Pembina Field (Fig. 23.2) (Nielsen and Porter, 1984; Krause et al., 1987a, b).
Sedimentological responses identified within the formation indicate that accumulation took place in muddy and sandy inner and outer shelf, shoreface, lagoonal, tidal, estuarine and coastal plain settings. The deposits alternated between coarse- and fine-grained stages that were controlled by both autocyclic and allocyclic processes, such as delta avulsion, compaction-driven subsidence, tectonically-driven subsidence, tectonically-controlled sediment sources, and tectonic and eustatically controlled changes in sea level. These processes contributed to the development of a complex sedimentary mosaic containing varied and abundant stratigraphic traps and reservoirs. Hydrocarbons stored in these reservoirs appear to have been derived from neighboring rocks, and are typically light and sweet (Deroo et al., 1977; Creaney and Allan, 1992). Reservoirs have been found at depths ranging between 1200 and 2700 m.
Literature on the Cardium Formation and its hydrocarbon reservoirs is considerable, exceeding 400 references (see Krause et al., 1987a; Leggitt et al., 1992). This literature comprises an array of geological and engineering studies published in academic and trade journals, oil company submissions to Alberta's Energy Resources Conservation Board, Geological Survey of Canada reports and maps, and university theses and technical memoranda.
Engineering. The formation has been described in a variety of engineering studies. The following are of regional stratigraphic interest: Groeneveld (1964), Gillund (1969), Alpay (1972), Chakravorty et al. (1978), McLeod (1978), Purvis and Bober (1979), Krause and Collins (1984) (see Krause et al., 1987a, b for other references).
Geophysics. Geophysical studies considered here are of regional stratigraphic interest. These studies have established characteristic seismic reflection signatures for the formation, in the search for stratigraphic traps and the description of triangle zones; namely, those by Wren (1984), Slatt et al. (1987), Chappell (1989), MacKay (1991) and Nazar (1992).
Mineralogy and Diagenesis. Information on the diagenesis and mineralogy of the formation is sparse. Notable studies include Sinha (1970), Machemer (1984), Krause et al. (1987b), Staley (1987), Machemer and Hutcheon (1988) and Selim et al. (1990).
Paleontology. There are not many paleontological studies of the Cardium Formation and it has only been studied systematically in the past decade: Pemberton and Frey (1984) - trace fossils; Sweet and McIntyre (1988) - palynomorphs; Heise (1987) - palynomorphs; Vossler and Pemberton (1988) - trace fossils; Hall et al. (1991) - ammonites.
Sedimentology. Contributions to our present understanding of the Cardium Formation since the advent of modern sedimentological practices have been many. They include Berven (1966), Michaelis and Dixon (1969), Swagor et al. (1976), Griffith (1981), Wright and Walker (1981), Krause (1982), Walker (1983a, b, c; 1984; 1985), Krause and Nelson (1984, 1991), Krause et al. (1987b, in press), Plint and Walker (1987), Plint et al. (1987), Plint (1988), Bergman and Walker (1987), Walker and Eyles (1988, 1991), Leggitt et al. (1990), Joiner (1991), Keith (1985, 1991), Pattison and Walker (1992), and Deutsch (1992).
Stratigraphy. Extensive stratigraphic studies of the Cardium Formation in the subsurface and in outcrop, by the oil industry and the Geological Survey of Canada, followed the discovery of the supergiant Pembina oilfield in 1953 (Michaelis, 1957; Nielsen, 1957; Stott, 1963, 1967). More recently, regional characteristics of the formation have been discussed by Duke (1985) and Plint et al. (1988). Stratigraphic schemes for the subsurface and correlations to outcrop have been presented by Michaelis (1957), Swagor (1975), Krause and Nelson (1984), Plint et al. (1986, 1988), Hall et al. (in press).
As outlined in Figures 23.3a and 23.3b, three schemes for subdividing the formation into members are presently in use. Two classifications are lithostratigraphic, one proposed for outcrops by Stott (1963, 1967) and one designed for the subsurface by Krause and Nelson (1984). A third scheme is an informal allostratigraphic classification proposed by Plint et al. (1986, 1987, 1988). Significantly, this latter classification correlates outcrop with subsurface strata, but discards all previous proposals. Recently, Deutsch (1992) and Deutsch and Krause (1990) have shown that the Ram and Moosehound members of Stott (1963) can be extended to the subsurface, thus casting doubt on the need to eliminate previous work and confirming Stott's (1967) correlations into the subsurface (see also the Stratigraphy discussion below). Other previous and formally established stratigraphic intervals are also correlatable between outcrop and subsurface, but their stratigraphic characterization is presently under review.
Structure. Structural analysis of the formation has proceeded from a dual perspective: 1) mesoscale examination of the distribution and orientation of fractures in outcrop, notably by Muecke and Charlesworth (1966) and Barton (1983), and in the subsurface by McLeod (1978) and Bell and Gough (1981); and 2) macro- and mega-scale studies of outcrops in the foothills and subsurface of the plains, where the Cardium Formation can be used as a marker horizon. These studies have focused on geological mapping and on geometric characterization of imbricate and east-verging thrusts, horses and duplexes, and triangle zone thrusts and passive roof duplexes; e.g., Martin (1956), Irish (1965), Bally et al. (1966), Ollerenshaw (1966, 1968a,b, 1970, 1972a,b, 1974, 1976a,b, 1978), Teal (1983), MacKay (1991), Skuce et al. (1992).
Last modified: August 20, 2008
