2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 10
Presentation Time: 1:30 PM-5:30 PM


LAST, William M. and GINN, Fawn M., Geological Sciences, University of Manitoba, 125 Dysart Road, Winnipeg, MB R3T 2N2, Canada, wm_last@umanitoba.ca

The Great Plains region of western Canada contains a large number of saline lakes. Although most of these salt lakes today are Na -SO4 dominated, some show high proportions of Mg, Ca and HCO3, and many have abundant carbonate minerals in their Holocene stratigraphic records. Despite the inherent difficulty in distinguishing between detrital components derived from weathering versus those carbonates originating from within the basin by inorganic and biological processes, there are a number of lakes in which endogenic and authigenic carbonates are common.

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.