A micromorphological study of ferruginous and calcitic nodules and concretions of different soils characteristic of the principal terrace levels of the Guadalquivir Valley has been presented. The ferruginous nodules and concretions vary in size from 0.02 to 6.0 mm. in diameter and are composed of clastic mineral particles and fine ferruginous reddish brown clay material. The larger concretions, which form units that are easily separated from the soi1, can be classified into three types: (a) those with regular distribution of the coarse mineral grains; (b) those whose surface is covered with a ferruginous clay crust and whose coarse particles are primarily at the center and (c) mixed concretions having characteristics of both types representing different phases in the growth of the concretion. In smaller ferruginous pedological features the rounded form disappears. These concretions and nodules are related to processes of oxidation- and reduction common in the soils studied. Finally the principal forms and distribution of nodules and calcitic concretions and their probable origins are noted and discussed in relation to field evidence and ana1ytical and microscopic data.

9 páginas.-- 7 imágenes de fotografías.--18 referencias.-- Comunicación presentada en el Congreso Soil microscopy : proceedings of the fourth International Working Meeting on Soil Micromorphology, Ontario, Canada, 27th -31st August, 1973

Peer reviewed