SOIL DEVELOPMENT INDEXES OF SOILS DEVELOPED ON FLUVIAL TERRACES (PENARANDA-DE-BRACAMONTE, SALAMANCA, SPAIN)

We have determined both morphological and analytical soil profile and horizon development indices for seven fluvial terrace soils of Holocen e to Middle Pleistocene age in relation to the sandy gravel parent mat erial. The relationship between age of fluvial terrace soils and morph ological and chemical indices of horizons and their depth indicates tw o main trends: (i) as soil age increases, index values tend to increas e throughout the chronosequence; (ii) the degree of differentiation be tween the horizons of each soil becomes progressively more evident. In the Holocene soils the rate of soil formation is rapid, decreasing in soils of Late Pleistocene age. At some 100,000 years, soils reach a s tate of maturity. Finally, in Middle Pleistocene soils (300,000 to 600 ,000 years old), evolution of these Palexeralfs is even slower. Morpho logical and analytical indices in all these soils undergo continuous c hanges throughout the chronosequence without seeming to reach a steady state.