Geochemical distribution and background values of some minor and trace elements in Iraqi soils and recent sediments

Abstract EN

The analysis of about 21000 soil and recent sediments samples collected by Iraq Geological Survey in the seventies and eighties of the last century from the Western and Southern deserts and from the Mesopotamia plain analysed for some minor and trace elements (P2O5, K2O, Al2O3, Fe2O3, TiO2, SO3, Cu, Pb, Zn, U, Cr, Ni and V) are statistically treated in this study to extract natural background values for these terrains which represent about 70% of Iraq area.

The results are compared with soil analysis in other areas in Iraq of various physiographic, climatic and source rocks conditions, as well as with reported range values for the soil of the world.

Natural (geogenic) background range values are presented in two ways: the first involved all analytical results including natural anomalous values and the second after removing values above the statistically calculated threshold.

The concentration range values for the desert and Mesopotamia are comparable to those reported for world soil with some exceptions.

Higher upper range values are noticed for Cr, Ni and V, but the median values are within the world range.

The results also indicate significant influence on the background values by various factors including source rocks and pedogenic processes controlling soil development and maturity such as climate, vegetation, and drainage.

The distribution of the elements analysed varies between normal and log-normal, higher concentration outlayers are noticed in most trace elements distribution patterns as well as in SO3 distributions.

The distribution of minor elements (TiO2, Al2O3, Fe2O3, K2O and P2O5) is largely controlled by parent rocks.

Some trace elements are also related to source rocks, especially U, Cr and Ni.

Sulfate is enriched by authigenic processes.

This study clearly emphasizes the impact of various soil-forming processes, parent rocks, physiography and climate on the geogenic background range of the analysed elements.

It also suggests that local environmental studies to demonstrate pollution cases should consider comparison with backgrounds of the uncontaminated soil related to the same physiographic terrain instead of making conclusions based on comparison with world averages for soil, shale or Earth crust.