Additional Contributor:
F.H. Trollope - Calgary
The Carboniferous System of the southern and central parts of the Western Canada Sedimentary Basin (WCSB) is represented by a thick succession deposited on the downwarped and downfaulted western margin of the ancestral North American plate and the central to western cratonic platform (Figs. 14.1 - 14.4). These deposits, which are divided here into three main map units, are preserved in a region that includes much of the eastern Cordillera and southern to western parts of the Interior Platform (Fig. 14.3), extending from southwestern Manitoba into southwestern District of Mackenzie.
The succession comprises two main lithofacies associations. The lower association generally thickens southwestward or basinward and is dominated by shale, spiculite and bedded chert of basin to slope origin. Upward and northeastward, the lower array passes into an upper association of platform and ramp carbonates and sandstone-dominated siliciclastic facies that were deposited in slope to continental settings. Both associations consist of numerous formations, many of which are separated by regional disconformities.
Relatively thin intervals of Upper Devonian strata occurring in the Bakken, Exshaw, Banff and Besa River formations, which span the Devonian/Carboniferous boundary (Fig. 14.2), are mapped and discussed with the Carboniferous. The Devonian strata are included because they are widely separated from underlying Famennian strata by disconformities, and are lithologically indistinguishable from overlying Carboniferous facies that occur in these formations.
Subaerial erosion during the latest Carboniferous, Permian, and subsequent periods removed much of the Carboniferous succession, particularly on the northern Interior Platform and the region west of the Rocky Mountain Front Ranges. Where the Carboniferous remains, it is generally unconformably overlain by either Permian or Mesozoic strata.
The Carboniferous of the WCSB contains substantial accumulations of conventional oil and gas, ranking third in recoverable reserves after the Devonian and Cretaceous (Podruski et al., 1988; Hay, this volume, Chapter 32). Approximately 14 percent (365 x 106 m3, 2295 million barrels) of the proven conventional oil reserves of the Western Canada Sedimentary Basin occur in the Carboniferous, and 16 percent (580 x 109 m3, 20.5 TCF) of the marketable conventional natural gas reserves. Sulphur extracted from sour gas is of significant economic importance, as is limestone, used principally for manufacture of Portland cement and lime. In addition, potentially economic coal seams are present in upper Viséan deltaic deposits of the Mattson Formation in southwestern District of Mackenzie.
Geological studies on the Carboniferous of the WCSB date back to 1887 (McConnell). The current lithostratigraphic nomenclature and the depositional origins of major lithofacies have been established by numerous geologists including: Douglas (1958), Edie (1958), Macauley (1958), McCabe (1959), Halbertsma (1959), Christopher (1961), Scott (1964), Macqueen and Bamber (1968), Macqueen et al. (1972), Fuzesy (1960), Bamber and Mamet (1978), Chatellier (1988), Richards (1989a), O'Connell (1990), Barclay et al. (1990), and Savoy (1992). Regional stratigraphic syntheses were presented by Macauley et al. (1964), Douglas et al. (1970), Bamber et al. (1984), Henderson (1989), Richards (1989b), and Richardset al. (in press).
The biostratigraphy of the Carboniferous in the WCSB is established for several fossil groups (Fig. 14.2). Zonations are available for conodonts (Baxter and von Bitter, 1984; Higgins et al., 1991), foraminifers (Mamet and Skipp, 1970; Mamet, 1976; Mamet and Bamber, 1979; Mamet et al., 1986), corals (Sando and Bamber, 1985); ostracodes (Crasquin, 1984), and brachiopods (Nelson, 1961; Carter, 1987). International correlations have been established mainly by utilizing foraminifers and conodonts.
The concept of the Tournaisian Series used in this chapter (Fig. 14.2) differs substantially from that used in many recent papers about the Carboniferous of the WCSB. The Tournaisian Series was formerly divided into three parts (Tn1, Tn2 and Tn3), and its base was placed in the Upper Devonian (see Richards, 1989a, p. 3).Conil et al. (1976) formally restricted the type Tournaisian ofEurope to make its base coincide with the Devonian/Carboniferous boundary. They also divided the Tournaisian into two parts, referred to as TI (= Hastarian Stage) and TII (= Ivorian Stage). These revisions, recently accepted by most European stratigraphers (see Paproth et al. 1983), are used here.
Last modified: August 13, 2008
