Geological Atlas of the Western Canada Sedimentary Basin - Chapter 28

Chapter 28
Geological History of the Peace River Arch

Author:
S.C. O'Connell - Alberta Geological Survey, Edmonton

Introduction

The Peace River Arch (PRA) is a large cratonic uplift in northwestern Alberta and northeastern British Columbia. It is one of only a few large-scale tectonic elements in the Western Canada Sedimentary Basin that has significantly disturbed the Phanerozoic cover of the craton. The structure has influenced the location of oil and gas accumulations in strata ranging from the Middle Devonian to the Upper Cretaceous, and has long been a focus of hydrocarbon exploration in the region.

The arch was discovered in 1949 (DeMille, 1958), and the first regional analysis of the feature was published in 1958 in a PRA Symposium issue of the Journal of the Alberta Society of Petroleum Geologists (vol. 6, no. 3). Regional syntheses of the PRA have since been published by Sikabonyi and Rodgers (1959), Cant (1988), and O'Connell et al. (1990). In addition, the origin of the PRA has been discussed by Burwash and Krupicka (1969, 1970), Stelck et al. (1978), Zelt (1989), and Stephenson et al. (1989).

The PRA is one of four major positive cratonic features that developed at the western edge of the North American craton, bordering the lower Paleozoic passive margin (Fig. 28.1). The PRA is the largest of these structures, and has the longest recorded history of tectonic activity. The West Alberta Arch paralleled the passive margin and formed a southern continuation of the PRA landmass until its burial during the Late Devonian (Frasnian)(Moore, 1989). The Tathlina High, which is parallel to the PRA, formed an uplifted area in northwest Alberta and the District of Mackenzie from the Cambrian until its burial in the Middle Devonian (Givetian) (van Hees, 1964; Moore, 1989). In southern Alberta the Sweetgrass Arch (Lorenz, 1982; Podruski, 1988) and Montania (Norris and Price, 1966) formed smaller cratonic uplifts from the Late Proterozoic onward.

Configuration of the Arch

The PRA is an east-northeasterly trending structure that has a total preserved length of approximately 750 km (see Burwash et al., this volume, Chapter 5). At its western end, near the Alberta/British Columbia boundary, the arch stands approximately 1,000 m above the regional elevation of the basement (Cant, 1988). The amplitude of the arch decreases eastward to between 400 and 500 m at the fifth meridian and several tens of metres at its eastern end, near the fourth meridian. Most of the maps referred to in this synthesis are derived from O'Connell et al. (1990) and extend from 54 to 58° latitude and from the fifth meridian (114°) to either the British Columbia/Alberta boundary, or to the Cordilleran outcrop in British Columbia (Fig. 28.2).

The PRA is an asymmetrical structure with a steeply dipping northern flank and a more gently dipping southern slope (Fig. 28.3; O'Connell et al., 1990; McMechan, 1990). An isopach from the top of the Devonian to the basement (Fig. 28.4) shows that total deposition immediately to the north of the arch was several hundred metres thicker than it was to the south. A structure contour map of the Precambrian surface (Fig. 28.5; Trotter, 1989) delineates the approximate structural boundaries of the arch. The zone of structural disturbance is approximately 140 km wide at the sixth meridian. O'Connell et al. (1990) proposed that the Arch is vertically offset along a north-south-trending line that may coincide with a basement shear zone (Fig.28.5).

Descriptions of PRA structures are presented by DeMille (1958), Lavoie (1958), Williams (1958), Sikabonyi and Rodgers (1959), Jones (1980), Cant (1988), Barclay et al. (1990), Dix (1990), and O'Connell et al. (1990), who all use well log and sedimentological data to identify fault locations and trends, as well as magnitudes and types of offset. There are no published descriptions of regionally significant PRA structures or structural trends based on the interpretation of reflection seismic data, although seismic studies of some local features are publicly available (e.g., Anderson et al., 1989).