Petrographic and chemical studies were made of samples of Kneehills Tuff from various outcrop localities in Alberta, between Cypress Hills in the south and Whitecourt in the north. The length and breadth of zircon crystals in each sample were determined and size-frequency curves constructed. A comparative study was made of samples and separates from late Cretaceous or early Tertiary tuff beds exposed in the Foothills area and a sample of rhyolite associated with the Boulder batholith in Montana.

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Results of the investigations showed the Kneehills Tuff to be uniform in texture, mineralogy and chemical composition over a wide area and almost identical to the upper tuff lenses above the Kneehills zone in the Drumheller area. It is suggested that the pyroclastic material for these tuff beds was derived from a late effusive phase of the Boulder batholith. Tuff beds of late Cretaceous or early Tertiary age exposed in the Foothills area were not the principal concern of this study, but in the few comparisons made, they do not appear to be directly related to the Kneehills type.

Radioactive dating of the zircon from the Kneehills Tuff by the lead-alpha method yielded an age of 53 million years. By the radiation damage method, the age is 110 ± 50 million years.

The potassium-argon age of feldspar from a bentonitic ash bed in the Ardley coal seam above the Kneehills Tuff is 52 million years, a figure in good agreement with lead-alpha, lead-isotope and potassium-argon ages for the Cretaceous-Tertiary boundary.

Individual tuff lenses in the Kneehills zone appear to be wind carried material from separate explosive outbursts at the source. The areal extent of each lens was controlled by late Cretaceous topography and meteorological conditions at the time of vulcanism. The original ash was apparently deposited in fresh water basins and altered diagenetically.

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