ABSTRACT

An accumulation of residual materials occurs at the Palaeozoic erosion surface in west-central Saskatchewan, mainly where Mississippian Madison Group limestones subcrop beneath the Cretaceous Blairmore Formation. This accumulation, known as the Residual Zone, is discontinuous and highly irregular in thickness and distribution. It comprises an unstratified, heterogeneous assemblage of minerals, characterized by abundant chert fragments. Examination of mechanical logs and drill cuttings has revealed evidence that rocks of this lithology not only overlie, but also occupy former caverns in, the Madison sediments from which they were derived.

Petroleum exploration of the Residual Zone has been mostly in the Alsask-Hoosier area adjoining the Alberta boundary. Oil has been produced from the Residual Zone at four localities in this area; vuggy oil-stained chert is widespread. One well has produced over 168,000 barrels of oil to the end of 1970. The residual sediments remain untested in large areas.