Iron Minerals in Soils on Red-Earth Deposits in the Cis-Ural Region

摘要

In soils developed from the red-earth deposits in the Cis-Ural region (Perm oblast), hematite does not ensure the theoretically possible redness due to the concealing effect of rivaling pigments, i.e., humus in the upper horizons and Fe(II) in the gleyed horizons. The soil color depends on the minimal (spring) values of the hydrogen partial pressure index rHmin rather than on the average value of this index rHav. The hematite content decreases in the gleyed and humus horizons (despite the absence ofthe morphological features of gley in the latter due to the concealing effect of humus). The gley horizons are heterogeneous with respect to the state of iron. Upon the maximum wetting in the gley horizons of the mucky-humus gley soil, hematite is beingreduced to Fe(II), which is proved by the low values of rHmin (<19). In a less humified dark humus gley soil, the values of rHmin exceed 19, which points to the inherited gley features in this soil. In the mucky-humus gley soil, an inverse dependence between the magnetic susceptibility % and EHmin is observed upon EHmin <320 mV. In this case, the degree of reduction of the highly magnetic iron oxides rises from 0.3 to 1.0 due to a decreasing portion of maghemite yFe2O3 and an increasing portion of magnetite Fe_3O_4.