AUTHIGENIC DOLOMITE IN A SALINE SOIL IN ALBERTA, CANADA

The formation of dolomite is poorly understood and highly controversia l, since well-ordered dolomite has never been synthesized under earth surface conditions and natural occurrences of modern dolomite have bee n reported only rarely from restricted sedimentary environments. It is generally accepted that dolomite does not form in soils. This study i nvestigates the characteristics and origin of dolomite in a sulfatic s aline soil in east-central Alberta, Canada, in which dolomite makes up more than half of the <2-mu m fraction. X-ray diffraction analysis sh ows that the dolomite is stoichiometric and ordered, with only slight deviations in unit cell parameters relative to ideal dolomite. The cla y-sized dolomite is enriched in O-18 and depleted in C-13 relative to detrital dolomite and dolomite present in larger size fractions, and h as a radiocarbon age ranging from 1270 to 5270 yr before present, clea rly indicating an authigenic origin. The very small dolomite particle size and differences in isotope content from coexisting calcite sugges ts that the dolomite formed by direct precipitation in the soil rather than by dolomitization of a preexisting calcite.