Biogeochemical factors in the formation of terra rossa in the southern crimea

Abstract

The micromorphology and the chemical and mineralogical composition of oolitic limestones and those of calcareous breccia of the southern Crimea at different stages of weathering and conversion to terra rossa were studied. Experiments were carried out to model the processes of leaching and oxidation of oolitic limestones as well as experiments on microbiological reduction of iron hydroxides in terra rossa. It has been ascertained that terrigenous aluminosilicate material and ferric sulphides dispersed in oolitic limestones are the original components for the formation of terra rossa in the southern Crimea. The oxidation of sulphides and the concentration of iron hydroxides proceed with the active participation of iron bacteria (and possibly sulphur bacteria) inhabiting the zone of weathering. Sulphuric acid resulting from the oxidation of sulphides facilitates the dissolution of limestone and the release of the aluminosilicate material included in it. The accumulation of red clay material is due to limestone weathering in situ and to the red-coloured deluvium of limestones supplied from the upper mountain slopes. The absence of definite restrictions of terra rossa to certain climatic conditions and, at the same time, its local occurrences within one climatic region appear to be related to the distribution of limestone facies containing iron sulphides.