Geological Atlas of the Western Canada Sedimentary Basin - Chapter 17

Chapter 17
Paleogeographic Evolution of the Western Canada Foreland Basin

Author:
D.G. Smith - Canadian Hunter Exploration Ltd., Calgary

Introduction

Over the years, several authors have attempted paleogeographic reconstructions of the foreland basin succession of the Western Canada Sedimentary Basin. Given the limited data available, particularly in earlier years, many are surprisingly accurate. Noteable contributions to our understanding of foreland basin paleogeography include those of Nelson (1970), Williams and Stelck (1975), Jackson (1984), Smith et al. (1984), and Stott (1984). The intent of this chapter is to build on these earlier efforts utilizing the vast database available to chapter authors, in concert with recent concepts of sequence stratigraphy. The product includes 14 paleogeographic maps of the major sandstone bearing units in the foreland basin succession and an accompanying brief geological description of each. It is hoped that this will provide the Atlas user with a geographic depiction of the major sandstone systems along with a basic understanding of environments of deposition, regressive or transgressive trends, and sediment dispersal patterns.

Understandably, there are limitations to this approach. In transgressive and regressive sequences, sandstones are diachronous from one area to another, presenting the problem of depicting sandstones of different ages on what would appear at first glance to be a chronostratigraphic map. In lieu of the nearly impossible task of constructing a myriad of chronostratigraphic slices for each formation, the author has chosen to depict most zones at their peak of regression or transgression, thus allowing the mapping of all sandstones and/or environments of deposition developed along the way. Unconformities and lowstand disconformities present another problem. With differential beveling from one area to another, sediments beneath the unconformity will be of different ages in different areas, even though they may be depicted on the same map. Consequently, all maps should be viewed with the understanding that they do not depict an instant in geological time, but rather demonstrate geological processes and patterns of deposition over the time period of the interval mapped.

The text accompanying each paleogeographic map includes a brief lithological description of the interval mapped and a short geological summary, including discussions on environments of deposition, patterns of coastal advance or retreat, tectonics, sediment dispersal patterns and the effect of sea-level fluctuations on the system.

Detailed analyses of the zones described in this chapter are presented in subsequent chapters by other authors. The reader is encouraged to consult these chapters for additional information.