Geological Atlas of the Western Canada Sedimentary Basin - Chapter 4

Chapter 4
Potential Fields and Basement Structure - Western Canada Sedimentary Basin

Authors:
G.M.Ross - Geological Survey of Canada, Calgary
J. Broome - Geological Survey of Canada, Ottawa
W. Miles - Geological Survey of Canada, Ottawa

Introduction

The Western Canada Sedimentary Basin (WCSB) rests on a foundation of continental crust and lithospheric mantle that makes up the buried extension of the Precambrian Canadian Shield. Geophysical data permit indirect examination of this lithosphere from two different perspectives. The first pertains to upper crustal (less than 15 km) structure and utilizes potential field data (aeromagnetic and gravity anomaly maps) to trace into the subsurface the variations in crustal structure that are apparent in the exposed shield. The second perspective pertains to the long-wavelength structure of the crust and mantle (filtered subsets of potential field data and deep seismic refraction and reflection studies) and hence addresses possible causitive mechanisms associated with basin formation and subsidence patterns. However, distinguishing Precambrian lithospheric features from those acquired during Phanerozoic basin formation is problematical (see Stephenson et al. 1989, and Ross, 1990).

The purpose of this chapter is to provide a brief overview of potential field data and their interpretation in the Western Canada Sedimentary Basin. More detailed discussions may be found in Ross et al. (1991; in press), Villeneuve et al. (1993) and Ross and Stephenson (1989). For a discussion of seismic refraction/reflection studies and electromagnetic-magnetotelluric studies the reader is referred to summary papers by Ross and Stephenson (1989), Sweeney et al. (1991) and Jones and Craven (1990), respectively.

A short review of the tectonic history of the exposed shield adjacent to the edge of the Phanerozoic strata precedes the presentation of potential field data and is intended to provide a context for the interpretation and inferred continuation of shield elements into the subsurface. An appreciation of the tectonic fabric and evolution of the shield is relevant to subsequent chapters that examine the sedimentary sequence. In particular, the degree to which basement structures may have controlled anomalous sedimentation, diagenetic and structural patterns in both the Western Canada Sedimentary Basin and the adjacent Cordillera is controversial.

As this Atlas goes to press, LITHOPROBE is embarking on a five-year program to examine the deep crustal structure of Alberta and its influence on the evolution of the sedimentary units. These studies may provide much-needed constraints on the role of basement structure in the evolution of the Western Canada Sedimentary Basin.