Geochemical properties of some soils developed on basalt rocks of North-West Iran

Soil genesis and evolution studies are based on well understanding of geochemical processes involved in pedogenic processes and formation of soil. Parent materials are main factors controlling soil properties in arid and semiarid regions. In this study, physicochemical and geochemical properties of 6 selected soil profiles developed on basalt rocks along arid (Eshtehard), semiarid (Qazvin) and semihumid (Roodbar) climosequence representing three different climatic zones were investigated. The total content of Si, Al, Fe, K, Mg, Ca, Na, Mn, P, Zn, Cl, Cu, Pb, Mo and Cd of all soil horizons were compared to parent rocks to reveal the role geochemical composition of rock on total concentrations of these elements in soil. Enrichment/depletion patterns of elements were assessed using Ti as reference element. The studied elements exhibited different enrichment/depletion patterns. In soils of arid region, the role of parent material and lithogenic properties in concentration of elements were greater than other areas and the content of these elements due to lower weathering and leaching were closer to the parent rock. While, in more humid climates pedogenic processes were more intensive and enrichment/depletion patterns of elements showed states that are more progressive. Distribution of some studied elements such as magnesium, calcium, iron and copper were significantly affected by soil forming process and the parent material affected some other elements such as sodium, aluminum, silicon, phosphorus, chlorine, manganese, molybdenum, cadmium and lead. In general, part of the difference in the concentrations of elements can be related to their chemical nature and the mobility of some elements, and some part to rapid weathering of parent materials affected by bioclimatological changes.