Mineralogical analysis as a means for distinguishing levels in a red soil chronosequence

Three red soils and a brown soil developed on the three distinct levels of the fluviglacial terraces in the interfluvial. area between the beds of the rivers Aragon and Aragon Subordan (Pyrenean range, France-Spain) were stud ied. This terrace system features ubiquitous red soil topping the upper 60 m terrace and brown soil on the intermediate (20 m) and lower terrace (2-3 m). However, the most salient feature of the studied area, an explanation f or which was sought in this work, is the presence of red soils in the two s ub-levels that form the 20 m terrace. For this purpose, and also with a vie w to characterizing the soils, material from the different levels studied w as subject to textural analysis using three different dispersal methods (wa ter, Sodium hexametaphosphate, and previous removal of iron oxides), In thi s way, the clay/silt ratio and naturally dispersed clay (NDClay) were deter mined (the latter as the clay-H2O/clay-hexam ratio). The heavy and light fr actions of sand were examined under a petrographic microscope and a scannin g electron microscope (SEM) and the results were subjected to an analysis o f variance. The interpretation of these results, in addition to the presenc e of pseudomorphic pyrites and other iron forms, and on the interpretation of analytical data, the red soils in the two sub-levels of the 20 m terrace were transported from a neighboring zone.