Geomorphology and Geochemistry of a Gypsum Karst near Canal Flats, British Colombia

A thick series of gypsum beds occurs in the Burnais and Harrogate Formations (Middle Devonian) and crops out in a belt 60 miles (100 km) long in the Kootenay Ranges, British Columbia. Landforms of an associated till-mantied gypsum karst were studied in the valleys of the Lussier River and Coyote Creek, southeast of Canal Flats. Karst features in the area include collapse sinkholes (some of which are ponded), springs and related ponors, caves, tufa deposits, geological organs, and solution breccias. Collapse sinkholes, the most common features, are discussed in detail, and it is shown that their origin can be much more complex than is generally recognized.Thirty-nine water samples from different hydrological situations in the two valleys were analyzed for solute concentration. Stepwise linear discriminant function analysis of the data revealed five distinct classes of water with calcium concentration, temperature, and the degree of saturation with respect to gypsum as the principal distinguishing variables. The results suggest that modern groundwater flow in the area is mainly through carbonate rather than the sulfate strata. Particular springs of high sulfate content indicate the proximity of the base of the gypsum. Hydrological and geochemical evidence suggests that sinkholes develop preferentially near the upper and lower contacts of the gypsum subcrop. The use of these indicators for mapping drift-mantled gypsum deposits is discussed.