Micromorphology, submicroscopy and microprobe study of carbonate pedofeatures in a Vertisol gilgai soil complex, South Russia

Carbonate nodules and soft masses were studied in a gilgai soil complex in the North Caucasus, South Russia. Microrelief with an amplitude about 30 cm resulted in a wetter environment with stronger leaching in the microlow and a drier pedoenvironment with carbonate accumulation in the microhigh. Various macroforms of carbonate nodules and soft masses were identified in soil pits and sampled for micromorphology, scanning electron microscopy (SEM), and microprobe analyses to better characterize them and elucidate their pedogenesis. Common and unique attributes were described for carbonate pedofeatures depending on loci in gilgai soil complex. The most probable hypothesis for their formation is as follows. Nodules represent early pedogenic products that were initiated before gilgai formation. Modern hydrology resulted in variability of dissolution/recrystallization of the nodules along the gilgai microtopography. The variability in degree of impregnation, aggregation into pellets, and presence of hard nodular cores reflects several generations of soft masses.