Authigenic Dolomite in a Saline Soil in Alberta, Canada

Abstract The formation of dolomite is poorly understood and highly controversial, since well‐ordered dolomite has never been synthesized under earth surface conditions and natural occurrences of modern dolomite have been reported only rarely from restricted sedimentary environments. It is generally accepted that dolomite does not form in soils. This study investigates the characteristics and origin of dolomite in a sulfatic saline soil in east‐central Alberta, Canada, in which dolomite makes up more than half of the <2‐µm fraction. X‐ray diffraction analysis shows that the dolomite is stoichiometric and ordered, with only slight deviations in unit cell parameters relative to ideal dolomite. The clay‐sized dolomite is enriched in 18 O and depleted in 13 C relative to detrital dolomite and dolomite present in larger size fractions, and has a radiocarbon age ranging from 1270 to 5270 yr before present, clearly indicating an authigenic origin. The very small dolomite particle size and differences in isotope content from coexisting calcite suggests that the dolomite formed by direct precipitation in the soil rather than by dolomitization of a preexisting calcite.