The directions of carbonate translocation through the soil may be vertical - either descending or ascending - and lateral or inclined.
The translocation of carbonates by descending vertical movement is a result of the progressive infiltration of water from atmospheric precipitation which dissolves the carbonates in the upper horizons of the soil and deposits them in the lower horizons producing precipitation of these salts, generally because of a decrease in water content or dissolved CO2. In order for this mechanism to take place, certain hydric conditions are necessary, such as circulation of sufficient water to carry the carbonates to deeper zones, but not so intense as to eliminate the carbonates from the soil, and additionally, either the presence of carbonates in the upper horizons (either received directly or through the action of the wind), or the release of Ca++ in sufficient quantities as a result of the weathering of primary minerals. This mechanism is the one which is most widely referred to in pedological studies and accounts for the classical distribution of the carbonates in the profile (i.e. superficial horizons totally decarbonated and deep horizons with carbonate accumulations).
The ascending vertical translocation model is explained by the existence of a water table rich in bicarbonates, a capillary ascent being caused by the action of evaporation and suction by plant roots. As the water evaporates or is absorbed by the vegetation, a consequent precipitation of the carbonates occurs.
Lastly, calcic horizons are often observed in the lower parts of the relief of limestone areas, generally in zones where there is a break in the slopes. This is explained by the existence of important flows of bicarbonate solutions migrating downhill, As they become more concentrated and the permeability of the soils diminishes in the depressions, the corresponding accumulation of carbonates is produced.
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