Stable carbon isotopes of carbonate pendants from Chernozemic soils of Saskatchewan, Canada

Abstract

Carbonate pendants are almost pure pedogenic carbonate that formed in an environment that may contain lithogenic carbonates. Pendants were sampled from three Chernozemic soils in Saskatchewan: a Calcareous Black soil of the Oxbow Association (C 3 vegetation dominant), an Orthic Dark Brown profile of the Biggar Association, and a transect of four Dark Brown soils of the Amulet Association (both with mixed C 3 and C 4 vegetation). All the soils were developed from glacial deposits which contain 10 to 20% CaCO 3. Pedogenic carbonate is composed of minute crystals in layered clusters about 0.5 to 4 μm in diameter. Lithogenic carbonate pebbles exhibit fine- and close-structured dolomite with large rhombohedral crystals. The δ 13C values of the carbonate pendants in the Oxbow soil reflect the range of the δ 13C values of the soil organic matter (−25.0 to −26.0‰), with a relatively consistent fractionation factor of +16.5‰. More positive δ 13C values (−4.0 to −6.9‰) from the Biggar soil are consistent with the more positive δ 13C value of the soil organic matter, as some of the organic matter is derived from blue grama, a C 4 grass with a δ 13C value of −16.0‰. More positive δ 13C values for the Bk horizons of upper location in the Orthic Dark Brown soils suggest a higher proportion of C 4 plants today than in the past.