NATURE AND BEHAVIOR OF MONTMORILLONITE IN AN ACID INLAND MARINE SHALE FROM EAST CENTRAL SASKATCHEWAN

The mineralogy and chemistry of an acid clayey Cretaceous marine shale outcropping near Arborfield in east central Saskatchewan were studied. pH values as low as 3. 6 and levels of exchangeable Aluminum of up to 28 cmol( plus ). kg** minus **1 were recorded in this material. Clay separates of the shale were monomineralic, consisting of highly crystalline smectite (montmorillonite). Ion activity product values, calculated from saturation extract composition data, indicated that the montmorillonite is stable despite the intense acidity of the shale. The high pH values (up to 8. 5) which were observed in the upper soil horizons overlying the shale are due to the incorporation, by glacial action, of calcareous till into the shale. This till was apparently the source of the mica, kaolinite, and quartz present along with the montmorillonite in clays isolated from the upper horizons.