Whitemud and Battle Formations, Kneehills Tuff Zone, a Stratigraphic Marker

The "Kneehills Tuff zone" comprises the white-weathering clays and argillaceous sands of the Whitemud Formation together with the overlying purplish-grey weathering, dark grey to black, clay and shale of the Battle Formation. In the Red Deer River - Bow River region the "Kneehills Tuff zone " divides the Edmonton Group into two parts and in the Oldman River region it separates the St. Mary River Formation from the overlying Willow Creek Formation. The Battle Formation contains in its upper part a distinctive, thin, light greyweathering, silicified, volcanic ash bed called the Knee hills Tuff. Laboratory investigation has shown that the mineralogy of the Kneehills Tuff bed is that of a volcanic ash that was silicified prior to any appreciable chemical alteration and that samples from all localities studied are almost identical. The Battle Formation is composed, mainly, of decomposed volcanic ash with some added detritus, and samples are similar from all localities studied. Mineralogical differences exist between the Whitemud Formation in southeastern Alberta and the same formation in western Alberta, the most significant being the relative proportions of the various clay minerals in the rocks. The predominant clay mineral in the Whitemucl Formation of southeastern Alberta is kaolin whereas that in samples from the west side of the Sweetgrass Arch is montmorillonite. The white colour of the rock where weathered, is due to the large proportion of clay minerals present . The development of the relatively large kaolin content in the Whitemucl Formation has been attributed to the subaerial weathering of potassium feldspar; a process that required a period of time during which temperatures were fairly moderate and uniform and when little detritus was being added by streams. The overlying Battle shale consists largely of decomposed volcanic ash. The original ash is thought to have been deposited by wind in an extensive body of shallow water free from much wave and current action. The small percentage of detrital material in this tmit suggests that at this time, also, little sediment was being transported by the streams. The Kneehills Tuff bed, wherever it occurs, represents contemporaneous deposition of wind-transported volcanic ash and, thus, the bee\ can be used as a time marker. For this reason, and because the combination of the Whitemud and Battle formations is unique, the "Knee hills Tuff zone" is considered to be a most valuable stratigraphic marker for surface geological mapping. The "zone" can, also, be recognized on electric logs of wells drilled for oil and gas throughout most of the western part of the southern Alberta Plains . It is, therefore, an important stratigraphic datum for subsurface correlation within the Upper Cretaceous, 11011- marine sediments.