Geological Atlas of the Western Canada Sedimentary Basin - Chapter 26

Chapter 26
Quaternary Geology of the Western Plains

Authors:
M.M. Fenton - Alberta Geological Survey, Edmonton
B.T. Schreiner - Saskatchewan Research Council, Saskatoon
E. Nielsen - Manitoba Energy and Mines, Winnipeg
J.G. Pawlowicz - Alberta Geological Survey, Edmonton

Introduction

This chapter focuses primarily on the Quaternary-age sediment in the area bounded by the Canadian Shield in the northeast, the disturbed belt in the west, the 49th parallel in the south, and the 60th parallel in the north (Fig. 26.1). However, because the regional isopach map encompasses all the unconsolidated sediment above the bedrock, including stratified sediment between the lowermost till and the bedrock, some older sediment of Late Tertiary age is also incorporated. This is particularly true in the deeper portions of preglacial valleys. This preglacial sediment is discussed in the section illustrating the subregional relations.

Previous Work

Investigation of the Quaternary sediments of Western Canada began with the early expeditions to the region during the 1800s. Early publications include Dawson (1875, 1885, 1898), Dawson and McConnell (1895), McConnell (1885), and Tyrrell (1887). Recent papers include those by Klassen (1989), Fenton (1984), Fulton et al. (1984), and Fullerton and Colton (1986, this paper focuses on Montana). Works by Klassen (1989), Dyke and Prest (1987) and Prest (1984) provide additional information on the Late Wisconsinan and Holocene history of the area.

Geological Framework

The Quaternary sediments of the Interior Plains were deposited on nearly flat-lying sedimentary rocks consisting largely of a narrow belt of Paleozoic carbonates subcropping along the edge of the Shield, poorly consolidated sandstones of Late Cretaceous and Early Tertiary age subcropping along its western margin, and Cretaceous shales in the central area (Green, 1972; Whitaker and Pearson, 1972; Manitoba Mineral Resources Division, 1979).

The Quaternary sediment covering the Interior Platform is of glacial, fluvial, lacustrine, aeolian and organic origin. The majority of the sediment is till (glacial diamicton), with lacustrine sediment the next most abundant. The sediment deposited directly by the glaciers consists primarily of till. One of the most noticeable properties of this sediment is the presence of clasts of Precambrian and Paleozoic bedrock that have been glacially transported from the east and north. The till can be subdivided into a number of units or facies (see for example Proudfoot, 1985, and Mougeot, 1991). The sediment deposited beyond the glaciers and during the nonglacial intervals is predominantly stratified material of lacustrine and fluvial origin, ranging from gravel to clay (Teller and Clayton, 1983).

The tills are generally massive and therefore form aquitards. The stratified units form aquifers where coarse grained and aquitards where fine grained. Overall, the Quaternary stratigraphy consists of a series of till aquitards confining aquifers composed of comparatively coarse-grained stratified sediment. In areas of thick sediment, these aquifers are a major source of groundwater. The Quaternary sediments also provide a major portion of the aggregate and fill used in the plains.

The Interior Plains comprise a variety of terrain types of which about 70 percent are of glacial origin and 20 percent lacustrine origin. The glacial terrain can again be divided into a number of terrain types, all of which can be recognized on airphotos. Each type is characterized by certain sediments (Prest, 1970; Clayton et al., 1980; Mougeot, 1991).