Geochemical inheritance of soils that develop from volcanic rocks (Navarra, Western Pyrenees)

Study of soil geochemistry is important because it offers a means by which to define the background levels of heavy metals in soils, which is an essential first step in the analysis of soil pollution. Our study analysed how a volcanic rock parent material influences the geochemistry of the soil that develops from it, thus confirming that a geochemical imprint is left in soil. We studied seven soil profiles selected according to certain lithological criteria. Rock outcrops of a similar composition were identified, all of which were volcanic rocks that principally differed in their magmatic affinities; namely alkaline basalts and dykes, and tholeiitic ophites. Therefore, we analysed two soil profiles from basalts, one profile formed from doleritic dykes and four from ophites. The soils differ in their topographic setting, profile depth, degree of alteration of the parent material, and soil moisture regime for those from ophites. These features collectively led to the development of different soil types for which the geochemical features of the underlying rock were expressed within the soil chemistry. After determining the elemental compositions of the soils and applying multivariate statistical analyses, we were able to differentiate between soils developed from alkaline igneous rocks, and those formed from tholeiitic igneous rocks.