IDENTIFICATION OF PEDOGENIC CARBONATE MINERALS USING STABLE CARBON AND OXYGEN ISOTOPES, X-RAY DIFFRACTION AND SEM ANALYSES

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Abstract
A Cca and Ck horizon of an Orthic Regosol in Alberta were investigated using 13C/12C and 18O/16O isotope ratios, X-ray diffraction and the scanning electron microscope as a possible basis for differentiating pedogenic and lithogenic carbonate minerals Using the stable carbon-isotope method, the abundance of newly-formed pedogenic carbonate minerals in bulk soil samples of the Cca and Ck horizon was estimated to be 48 and 33% respectively. The δ18O values of carbonate minerals in bulk soil samples of the Cca and Ck horizon were −13.1 and −12.0‰, respectively. The presence of Mg-bearing pedogenic calcite in the sand and fine silt (2–10 μm) fractions of the Cca horizon were associated with soluble Mg2+/Ca2+ ratios of about two. Pedogenic carbonate minerals were visible as tiny equidimensional crystals about 0.1–0.6 μm in diameter, and as surface coatings on the sand-size, primary carbonate minerals in both horizons. These results may have a practical application in the use of ca and k suffixes in horizon designation. Key words: Pedogenic carbonate minerals, stable isotopes, Mg-bearing calcite, surface morphology

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