Micromorphology of solonetzic horizons as related to environmental events in the Caspian Lowland |
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| Authors: | M Lebedeva M Gerasimova M Konyushkova |
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| Institution: | (1) Dokuchaev Soil Institute, Moscow, Russia |
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| Abstract: | Micromorphology of solonetz species with special attention to natric horizon was studied in microcatenas at the Dzhanybek
Research Station (northwestern Caspian Lowland). The solonetzic (natric) horizon is easily identified, and it occurs at varying
depths, which are the criteria for subdividing solonetzes into 4 species, namely, crusty, shallow, medium and deep. In this
sequence, the depth of humus-accumulative horizons increases, and the upper boundary of salinity manifestations goes down.
The following micromorphological features are assumed as typical for natric horizons: angular blocky microstructures with
partially accommodated aggregates having sharp boundaries and narrow plane-like packing voids; b-fabric speckled in the aggregates’
centers and monostriated at their peripheries merging into stress coatings; very few interpedal voids; organo-clay coatings;
humusenriched infillings; no calcite and gypsum pedofeatures. A complete set of “natric” features was found only in the crusty
solonetz; the shallow solonetz lacks only illuviation coatings, while the medium and deep species have several modifications
of fabric elements: blocky aggregates have a rounded shape and are penetrated by biogenic channels favoring their further
biogenic reworking; plant residues became more abundant and diverse, and blackened tissues occur; illuviation clay coatings
evolved into papules; stress coatings gave birth to striated bfabrics, thus maintaining a high plasma orientation.
The thin sections of natric horizons made 50 and 20 years ago were examined to study the influence of environmental changes
(increase in precipitation and rise of ground water table) on micropedofeatures. The following processes took place: (i) in
the topsoil: humus accumulation and biogenic structurization; (ii) in the natric horizon — re-arrangement of clay coatings
into micromass b-fabrics; and (iii) in the lower part of the natric horizon — development of pseudosand fabric, calcite and
gypsum formation. The trends revealed are in good agreement with the environmental events. |
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| Keywords: | Pedogenic trend natric horizon biogenic feature salt |
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