Micromorphology of calcitic features in highly calcareous soils of Fars Province, Southern Iran

The micromorphology of calcitic pedofeatures in highly calcareous arid and semiarid soils of the Fars Province, Southern Iran has been studied in order to determine their genesis and distribution in different climatic regions. Available soil moisture, soil temperature, soil texture, vegetation and availability of calcium carbonate are amongst the main factors determining the type and morphology of calcitic features. Size and frequency of microcrystalline calcite nodules and coatings increase from aridic to xeric, but decrease again towards the areas with a ustic moisture regime. Cytomorphic and acicular calcite are observed mainly in areas with an ustic moisture regime and a denser vegetative growth, but rarely in xeric areas. Layered pendents of calcite are common beneath coarser fragments, but are considered as relicts of a more humid paleoclimate. Calcite depletion pedofeatures are observed in xeric–mesic areas with higher available soil moisture. Ultraviolet (UV) violet (VL) and blue light (BL) fluorescence and cathodoluminescence (CL) studies proved to be useful in differentiating in this region pedogenic from geogenic calcite. All types of pedogenic calcite were UV and BL-fluorescent but didnʹt show CL, whereas, limestone fragments showed CL, but no UV–BL-fluorescence. The absence of CL in the studied pedogenic calcite samples is suggested to be related to the oxidative environment, hindering mobilisation of Mn++.