The exact stratigraphic position of the Cretaceous-Tertiary boundary in Alberta is controversial because of limited continental faunal and floral evidence. Twenty six K-Ar dates obtained from Alberta bentonites, together with eleven previously obtained, place the time boundary at 63±1 million years. There is no significant break in the depositional record at the Cretaceous-Paleocene boundary in central Alberta. Sanidine from bentonites gives more reliable dates than co-genetic biotite. Biotite when leached gives a date which is too young. K₂O/Rb₂O ratios in biotite suggest three stratigraphic groups of bentonite beds which may represent three periods of volcanic activity during continuous uppermost Cretaceous-Paleocene continental deposition. [The Kneehills Tuff (66 m.y.), bentonites in diachronous coal beds of the Cretaceous-Tertiary boundary (63-60 m.y.), and younger Paleocene bentonites (approximately 55 m.y.)]. No significant variation either in chemical composition or mineral constituents is apparent between 10 Cretaceous and 8 Paleocene analysed bentonites from near the Cretaceous-Tertiary boundary.

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