Shallow ground waters and the formation of carbonate soils in southeast Bulgaria – a study in progress

Carbonate soils and indurate calcrete horizons are common in southeast Bulgaria. The carbonate accumulations are of variety of micro-structural and textural types. The calcrete usually forms lens or disk-like bodies on flat hills. The carbonate soils are observed on top of porous sediments but not on crystalline rocks. In the study area, where calcrete is common, the pH value of the agricultural land is usually above 7.5 and the surface, shallow ground and deep ground water is saturated with respect to calcium carbonate. Chemical analyses of indurate calcrete horizons, carbonate soils, rain water and ground water from southeast Bulgaria are commented in the text. It appears that competing processes of leaching and reprecipitation from waters oversaturated with respect to CaCO₃ are responsible for formation of transitional compounds - calcrete precursors, which further are transformed to calcrete. Because the rain water’s acidity and ground water’s degree of over-saturation, with respect to CaCO₃, vary with the season, it appears that seasonal variations in the water composition and the temperature control the net balance of soil carbonates.