The glacial origin of carbonates in the calcic and petrocalcic horizons of the soils developed on glacial deposits in the southern Alborz Mountain slope

The dissolution of carbon dioxide in water is one of the sources of soil carbonates, which have an inverse relationship with water temperature. The origin of soil-forming carbonates formed in glacial sediments, and the effect of glacial processes on their formation were investigated. This study was conducted in the year 2021 in Alborz province, and eight profiles located in Karaj and Hashtgerd regions with glacial-alluvial parent materials were described and sampled. Physical and chemical characteristics, including soil texture before and after the removal of carbonates by the hydrometer method, pH, and EC in saturated extract, organic carbon by the Walkley-Black method, Calcium Carbonate Equivalent (CCE) measured by the calcimetric method in 27 samples were determined. Cation Exchange Capacity (CEC) measured by the ammonium acetate method. Soil description and classification were performed based on the American classification system. A micromorphological study of undisturbed samples, before and after the removal of carbonates, was carried out following their impregnation with polyester resin, cutting, sawing, mounting on glass slides, and reducing the thickness to about 30 microns. Imaging was done with a polarizing microscope, and the analysis and interpretation of the results were carried out according to the guide for the analysis of thin sections. The results showed that the petrocalcic horizons formed on glacial tills and moraines are the result of the long-term infiltration of cold water rich in dissolved carbonates into the soil. This model of the formation of secondary carbonates in the soil is different from other models that mainly consider the origin of carbonates to be the dissolution and recrystallization of primary carbonates or the biological respiration of roots and living organisms.