Soils developed in diapiric environment in Mediterranean area: sector north of the Iberian Peninsula

This work gathers together the study of five soil pedons developed grounds in diapiric formation found in the North of Spain. Three of them formed on igneous volcanic materials (ophites) and two of them formed on sedimentary materials (clay and gypsum) of the Triasic Keuper, in a Mediterranean climate. Initially the morphological, physical, chemical, and mineralogical properties of the soils were evaluated. The results obtained indicate that there are two types of soils. The profiles derived from ophitic materials were characterized by thick and obscure A horizons, with fine granular structure on the surface and a high content of organic carbon (C). Its texture was coarse with clay proportions less than or equal to 15%. The base saturation on the cationic exchange complex is higher than 50% and the levels of pH in sodium fluoride (NaF) were lower than 10, a condition indicative of andic materials. The phosphate (PO(4)) retention in no case was higher than 26% which corroborates the scarcity of amorphic compounds. The biotite is the predominant mineral the clay fractions in the soils, inherited from the original material and not as a pedogenic product. The developed profiles on sediments of the Keuper have not been affected by the volcanic deposits. Their attributes show the influence of the original material: they are of a clearer color with loamy to fine textures. The cationic exchange complex is saturated in levels higher than 100%. In some cases, there is a strong increase in the content of exchangeable sodium (Na(+)) as a consequence of the associated salts in diapiric formations. Apparently, the accumulation of calcium carbonate (CaCO(3)) in these surfaces is more dependent on eolic contributions of nearby calcareous materials than on the mineral alteration in situ. The phyllosilicates 2:1 of the clay fraction are much more abundant in respect to the previous group of soils, the chlorite being the most common mineral in clay. It is to be noted the absence of biotite as a mineral in the mica group. The low rainfall < 650 mm together with the nature of the original materials make the pedogenic processes happen with little intensity, bringing about under-developed soils that represent the first stages of the present evolution. The profiles derived from volcanic materials (ophites) are Haploxerolls with different subgroups owing to not having cambic horizons or showing lithic contact. The Xerorthents have formed in clay materials of the Keuper. When the conductivity in the saturation extract was stronger than 2 dS m(-1) to 25 degrees C, they were classified as Torriothents.