Geological Atlas of the Western Canada Sedimentary Basin - Chapter 15

Chapter 15
Permian Strata of the Western Canada Sedimentary Basin

Authors:
C.M. Henderson - The University of Calgary, Calgary
B.C. Richards - Geological Survey of Canada, Calgary
J.E. Barclay - Geological Survey of Canada, Calgary

Introduction

Overview

Permian strata of the Western Canada Sedimentary Basin consist mainly of phosphatic marine siliciclastics and silty to sandy carbonates. They occur only in a narrow belt throughout most of the eastern Cordillera and, locally, on the Interior Platform in the Peace River and Liard River areas, owing to localization of deposition and truncation beneath several sub-Mesozoic unconformities. These strata, representing the lower Absaroka Sequence of Sloss (1963), were deposited mainly on the western margin of the ancestral North American plate in the pericratonic Ishbel Trough (Fig. 15.1), which extended from the 49th parallel to the ancestral Aklavik Arch in the northern Yukon (Henderson, 1989; Henderson et al., in press). Permian sediments were also deposited in the Peace River Embayment, a downwarped and downfaulted region of the Interior Platform that opened westward into the Ishbel Trough during the Permian (Naqvi, 1972; Henderson, 1989). Permian strata are generally thin but laterally persistent in the Western Canada Sedimentary Basin. The thin nature of the succession resulted from a combination of depositional condensation and erosion beneath several intra-Permian unconformities and eastward truncation beneath sub-Triassic to sub-Cretaceous subaerial unconformities.

Previous Work

The stratigraphic succession and current formational nomenclature for the Permian System in the Western Canada Sedimentary Basin has been established and described in numerous studies, particularly those of Beales (1950), McGugan and Rapson (1961, 1963a, 1963b), McGugan and Rapson-McGugan (1976), MacRae and McGugan (1977), McGugan and Spratt (1981), Scott (1964), Norris (1965) and McGugan (1984) for the southern Canadian Rocky Mountains, and Halbertsma (1959), Laudon and Chronic (1949), Naqvi (1972), Sikabonyi and Rodgers (1959), Bamber et al. (1968), and Bamber and Macqueen (1979) for the Peace River Embayment and northeastern British Columbia (see also summaries by Henderson, McGugan, Richards, and Bamber, in Glass (ed.), 1990). Regional lithostratigraphic syntheses have been prepared by McGugan et al. (1964), Douglas et al. (1970), Henderson (1989), and Henderson et al. (in press). Important biostratigraphic reports include Jansonius (1962), McGugan (1963, 1983), McGugan and May (1965), Logan and McGugan (1968), McGugan et al. (1968), Nassichuk (1969), Ross and Bamber (1978), McGugan and Rapson (1979), MacRae and McGugan (1977), Bamber and Copeland (1970), Henderson and McGugan (1986), and Henderson and Orchard (1991).

Geological Framework

The major tectonic elements in the Western Canada Sedimentary Basin during deposition of Permian sediments were the Ishbel Trough, the Peace River Embayment and the Interior Cratonic Platform (Fig. 15.1). The Ishbel Trough, named by Henderson et al. (in press; see also Henderson, 1989), developed on the downwarped and downfaulted ancestral western margin of the North American plate and resulted mainly from extension. The location of the western margin of the Ishbel Trough is not well established, but the axis of the western rim may be locally preserved in the Kootenay or Cariboo terranes (Struik and Orchard, 1985; Struik, 1986). The Cariboo Terrane is part of the Proterozoic to upper Paleozoic Cassiar Terrane, which lacks Permian strata and may have been subaerially exposed during the Permian. A marginal basin to the west of the Cariboo Terrane (Barkerville Terrane within the Kootenay Terrane: Monger and Price, 1979; Monger and Berg, 1987) was characterized by Permian volcanic and sedimentary deposits (Sugar Limestone). Western marginal basin deposits are also present in the Slide Mountain Terrane west of the Kootenay Terrane (Struik and Orchard, 1985). The eastern margin of the Ishbel Trough was a broad hinge-zone along the western margin of the Cratonic Platform (Fig. 15.1) and coincided approximately with that of the Carboniferous Prophet Trough (see Richards et al., this volume, Chapter 14; Richards, 1989). In northeastern British Columbia and southwestern District of Mackenzie the hinge line coincided with the Bovie Lake Fault (Figs. 15.1, 15.10), but generally the position of the eastern trough margin cannot be defined because of eastward sub-Mesozoic truncation of Permian strata. In the Peace River area, Permian sediments were also deposited east of the Ishbel Trough, on the western Interior Cratonic Platform in the Peace River Embayment (Douglas et al., 1970), a deeply downwarped and downfaulted part of the cratonic platform in northeastern British Columbia and northwestern Alberta. The Peace River Embayment resulted from rejuvenation of a Carboniferous embayment that occupied approximately the same area but differed significantly in terms of tectonic character (Richards et al., in press; Richards, 1989; Barclay et al., 1990; and Richards et al., this volume, Chapter 14). The extent of the embayment was, in part, controlled by the position of structures like the Beatton High and the Sukunka Uplift (Fig. 15.1; Richards et al., this volume, Chapter 14).