ИСТИНА

Typical Vertisols (WRB, 2015) are churning, heavy clay soils formed on parent material with a high proportion of swelling clays. They have deep wide cracks when dry, and occur in depressions and level to undulating areas, mainly in tropical, subtropical, semi-arid to subhumid and humid climates with an alternation of wet and dry seasons. Typical vegetation is savannah, grassland and/or woodland. They may have a gilgai microrelief. Vertisols are recognized by vertic horizon with wedge-shaped aggregates and slickensides starting ≤ 100 cm from the soil surface. The aim of our research is to evaluate the extreme environments for Vertisol formation i.e. the full range of possible climate (MAAT and MAP), vegetation, geomorphology, parent material and time, where they occur. We also aimed to estimate the change of leading soil forming factor and its impact on shrink-swell process and formation of vertic features in the extreme cases, and to find the special attributes, characteristic for each extreme case. Most Vertisols occur in semi-arid tropics with MAP 500–1000 mm/yr. Meanwhile they are known in extremely dry (50 mm) or wet (3000 mm) climates. The MAAT in Vertisols areas is generally in between of 15-26 оС. But they occur in areas with MAAT 30 оС, and have been recently found in Siberia with MAAT –4.2 оС. Typically Vertisols are montmorillonitic. At the same time kaolinite (in Australia, Hawaii, Cambodia, Salvador, Sudan), illite (Australia, Bulgary) and polymineral (Trinidad) Vertisols also occur. Gilgai indicating strongest shrinking, swelling and shearing vary in lateral size from 3-4 up to 20 m, have amplitude from 5-30 up to 100 cm, and a range of forms. The most common gilgai are rounded. Tank, melon-hole, wavy, lattice, dendritic gilgai also occur. Extremal gilgai in Australia having an amplitude > 240 m and wavelength ~120 m was named giant. The age of Vertisols is known from < 100 yrs to ~2.5 billion yrs. Extreme Vertisols (i.e. formed in atypical environment or having atypical attributes) may be the result of various combinations of texture, mineralogy, geomorphology, and hydrothermic conditions. On the other hand, extreme Vertisols can be associated with the history of soils and landscapes development being in fact relic soils (exhumed or non-buried paleosol), or initial Vertisols started to shrink/swell due to climatic changes (drying, wetting, warming) or at a next appropriate stage of the climatic cycle.