Contribució al coneixement dels sòls fersialítics del sud de Lió (França)


  • Jaume Bech i Borràs


The macromorphological and physicochemical characteristics of fersialitic soils from the Corbas plain and from the Saint Symphorien d'Ozon, Villete de Vienne and Pont Eveque depressions (Lyon-Vienne area), are explained, indicating their relict nature.
Profiles, one from the «fersialitic with calcic reserve. group located on a fluvioglacial terrace probably dating from the fini-Wurmian period, and two from the «fersialitic» without calcic reserve,, group on moraines which show signs of cryoturbation, and of an older pedogenesis, Riss-Wurm or perhaps Mindel-Riss, are presented.
The first one shows a pH of between 7 and 7,2, a saturation level greater than 65 % and a clay illuviation index of more than 1/1,4. But from the iron illuviation index and the lower level of saturation -V- in the horizon B3 (50,3), it would perhaps be necessary to consider this soil as being a stage between the fersialitics with calcic reserve and those without it. From its colour it should perhaps be placed between the brown and the red fersialitics.
The second profile corresponds to a reddish brown acid fersialitic soil (pH less than 5), only slighthly illuviated and devoid of calcic reserve. Judging by the pH it belongs to the IX/22 group (CPCS, 1967) but from the clay illuviation index which is greater than 1/1,4 it resembles the IX/21 group. Thus, it seems like a IX/22-IX/21 slightly illuviated fersialitic intergrade.
The third profile described, a red acid fersialitic soil without calcic reserve, would also be taxonomically better classified as being between IX/21 and IX/22, due partly to the pH value and the dose of iron liberation in the horizon B, and partly to the exceedingly high values of the saturation complex as well as the clay illuviation index which is greater than 1/1,4.