La Distribució dels carbonats en els sòls de la Depressió Central Catalana

Resum

Soils from different calcareous substrates are studied in order to search the evolution of the carbonate fraction. There is a close relationship between soil-type and lithologic material.
From hard limestones, red-brown (fersiallitic) soils are formed. In general they have lost the carbonates almost completely but, in some cases, they have secondary lime in different forms. These accumulations of calcium carbonate are associated with an increase in the carbonate content of the finer fractions, clay and fine silt.
On calcareous sandstones, completely carbonate-leached red-brown soils coexist with carbonatic ones, in the same ecological conditions. In the latter, as in soils formed from calcarenite substrate, carbonates concentrate in the sand fractions. The total amount of carbonates in the profile depends on its content in the parent material but, in any case, the carbonate leaching rate is high: 40-50 %.
On calcareous clays and calcilutites, the soils are highly calcareous, mainly in the silt fraction, and they have the lower carbonate leaching rate, about 10 %.
Soils from gypsic materials have lost most of the gypsum and thus the carbonate is relatively concentrated.
Two general types of soils with respect to carbonate evolution are distinguished: a) Carbonate-leached soils, mostly occurring in fissures in the rock layers, which are postulated to be relicts. b) Calcareous soils, in which carbonates are mainly removed from the top horizons and from the finer granulometric fractions. The dynamics of these soils is supposedly in agreement with the current climatic conditions.
The overall evolution of the soils in the studied area is characterized by the presence of calcium carbonate, which comes either from an incomplete carbonate leaching of the calcareous substrates, from carbonate deposition of previously leached red soils or from the relative accumulation of carbonates in soils from gypsipherous materials.