THE PARENT MATERIALS OF OLTENIA SOILS

Abstract

The parent material of the soils are a mixture of many minerals in different alteration stages. These minerals are dependent on the mineralogical and geochemical nature of eruptive and lithologic sources, the mineral particle sizes, their alteration degree and the solubilization of some elements during the repeated remouving and sedimentation before the formation of actual parent material.  In addition the large variation of texture, chemical and mineralogical composition are accentuated by pedological processes which produce a organic matter bioaccumulation in the upper horizons, a preferential leaching of some elements and a colloid translocation to the depth. Therefore it is difficult to estimate the geochimical distribution of some elements in a certain areal especially when the parent material of a soil profile results by successive sedimentations. In order to estimate the contribution of parent material at soil composition and properties a group of Oltenia soil samples from main types and all horizons were selected. 309 soil samples were selected from all horizons of Oltenia soils and from the main soil types (chernozem, phaeozem, luvisol, arenosol, vertisol, fluvisol, leptosol). The cation correlations with the clay content show the more the correlations have a higher coefficient the more the cations are included in the same structure. The bioaccumulation of potassium in the surface horizons determine the fixation of potassium in micaceous structures and take part to the transformation smectite↔illite. The particle size, ordering in broken surface and in internal structure are in a great part inherited from the parent material. The potassium content in illite-like minerals of Oltenia soils has as average 5.41% K2O and a variation range of 3.22 - 7.12% K2O. In order to estimate these analytical data of parent material were investigated by means of soil chemical composition and the element distributions which display their forms in soil. The unimodal distribution of natrium, calcium and magnesium is due especially to their mobility as salts and another analysed elements may be in many forms, namely in lattice of minerals, in clay-humico-sesquioxde plasma or chelated by organic matter.