DOLOMITE IN SALINE LAKES OF THE NORTHERN GREAT PLAINS, WESTERN CANADA
Non-detrital dolomite occurs in at least ten lakes in the region. The dolomite is typically fine grained, poorly ordered, and non-stoichiometric. Both Ca-rich and Mg-rich varieties occur. It is most often found as part of a complex mixture with other endogenic carbonates and detrital clays, however in some lakes CaMg(CO3)2 also occurs in discrete beds and laminae. Aragonite, Mg-calcite, monohydrocalcite, and hydromagesite are often associated with the dolomite.
Although considerable effort has been made in the past several decades to understand the occurrence of Recent dolomite in non-marine settings, few generalizations can be made regarding its formation in these lakes. Dolomite is found in lakes having a wide spectrum of limnological and geochemical characteristics, from highly productive hypersaline playas to hyposaline perennial basins. The dolomite in Manito Lake shows clear evidence of biogenic origin and is most likely the product of a microbially-mediated pathway. In contrast, dolomite in Freefight, Waldsea, and Deadmoose lakes is most likely associated with sulfate reduction processes, whereas Manitoba and Chappice Lake dolomite is probably generated by mainly inorganic mechanisms.
The occurrence and composition of the dolomite in these lacustrine basins provide considerable insight into the evolution of the lake waters and the paleoenvironmental implications of these changes.