MIDDLE DEVONIAN SALT FORMATIONS AND THEIR BROMIDE CONTENT, ELK POINT AREA, ALBERTA

Abstract

The Prairie Evaporite formation, or First Salt, of the Elk Point area contains three types of halite: chevron, clear, and brown. The chevron halite is thought to be primary and to have grown upwards from the Devonian sea floor. The origin of the clear and brown varieties is not known. Where these types occur together, the clear halite has a tendency to contain more bromide than either chevron halite or brown halite. The total range for bromide in halite from the Prairie Evaporite is from 0.004 to 0.02 weight percent (wt.%).The Cold Lake and Lotsberg formations, the lower two salts, consist of clear halite which is so low in bromide (0.0004 wt.%) that it could not have crystallized from sea water, neither could this halite have crystallized from sea water previously saturated by dissolving halite. It is probable that the lower two salts resulted from solution of halite in fresh water, with subsequent crystallization. Solution may have occurred during discharge of meteoric groundwater, while the basin was structurally low, subsequent surface evaporation having promoted crystallization. In this way, salt could have been recycled without removal from the area. Alternatively, surface runoff, and downward movement of surface runoff, may have been important in the recycling of halite.Groundwater in Devonian formations of central Alberta, and spring waters from Devonian formations in Manitoba, are saline and relatively high in bromide (0.001–0.10 wt.% Br). The bromide content cannot be explained simply by solution of halite in meteoric waters. Either these brines are modified remnants of seawater, or else there is some undefined source of bromine causing enrichment.