FORMATION OF CALCIUM CARBONATE CONCRETIONS IN NATRIC HORIZONS OF ILLINOIS SOILS

Abstract

A mechanism for the formation of CaCO3 concretions was proposed. This mechanism was based on the premise that CaCO3 concretions formed after the development of the natric horizon. The process involved diffusion of Ca from Ca-rich zones below the sodium-affected zones up to the natric horizon and precipitation in response to the high pH values of the natric horizon.

Calculations of the solubility of calcite and albite as a function of pH, and calculations of Na levels required to give different exchangeable sodium percentages support the conclusion that formation of the concretions was subsequent to the formation of the natric horizon not before or during the inception of the natric horizon.