[Clay fraction mineralogy and pedogenesis in Val Chiavenna [Lombardy]]
2003
Bonifacio, E. | Fissore, C. (Turin Univ. (Italy). Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali) | Comolli, R. | Previtali, F. (Milan Univ. (Italy). Dipartimento di Scienze dell'Ambiente e del Territorio)
The joint influence of climate and vegetation may induce very different degrees of soil development in alpine areas. In this situation it is particularly interesting to follow the transformations occurring to layer silicates. The clay fraction is, in fact, not only a complex mixture of minerals both inherited from parent material and formed during the early stages of pedogenesis, but it also contains layer silicates that are the result of complex processes. The aim of this work was to follow the transformations occurring in the clay fraction in some soil profiles of the Val Chiavenna (Sondrio, Northern Italy), relating them to soil type and processes of soil formation. For this purpose, eleven profiles were selected and the clay fraction was separated and analyzed by X-ray diffraction. The complexity of clay fraction is clearly visible in the poorly developed soils of the highest elevation: together with minerals typical of this degree of development, such as illite and chlorite, kaolinite and smectite were also found, indicating the influence of allochthonous materials. More lower on the slope, in Podzols, pedogenetic processes induce chlorite dissolution in the eluvial horizon and formation of mixed layers through the profile. When pedogenesis has been interrupted, clay mineralogy allowed to differentiate between the horizons of the present soil and the buried ones. On alluvial fans the tranformations in the clay fraction are only the typical ones of early stages of soil development: partial loss of potassium from illites and beginning of chlorite dissolution
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