Loesses as a result of evolution of the water-rock system under weak water exchange

摘要

Analysis of the natural abundance ofloesses showed that they occur in the same zones as sodic waters, namely, forest-steppe, steppe and mountain-steppe landscapes with a weak water exchange (subsurface runoffis ＜0.3 l/s.km2). Thermodynamic calculation of the sodic-water-rock equilibrium evidences that the waters are always in equilibrium with montmorillonite, hydromica, kaolinite, and calcite but are in nonequilibrium with endogenous aluminosilicates. Therefore, in alkaline media sodic waters permanently (though slowly) dissolve terrigenous sediments and form clays and calcite, i.e., a complex of secondary deposits called loesses. The conclusion has been drawn that loesses and sodic waters are paragenetic products of the same geologic process running at the particular stage of evolution of the water-rock system. This stage is to be called sodic or sodic-loess.