60
WALLACE H. FULLER
2. Origin
Salts that accumulate in solid form in desert soils may come from several
sources: (1) weathered products of parent material, (2) marine deposits
such as saline shales, (3) atmospheric transport of sea salt, (4) rainwater
salts from certain terrestrial sources (dust) brought into the atmosphere
by wind action, (5) fossil salt (marine inundations) which are of more
local importance, and (6) transient dust that deposits during calms, are
leached by rain, and are blown away again. Not all of these sources are
expected to be operative in every desert and no single set of conditions
is operative to satisfy the nature and extent of accumulations in all soils.
3. Distribution
Certain saline and sodic soils contain sufficient accumulations of salts
to place them in special intrazonal great soil groups of the Solonchak and
Solonetz. The soluble salts that accumulate in these soils come from a variety of sources. Solonchak soils have been referred to as "white" alkali
soils and Solonetz as "black" alkali soils. Solubilization of soil organic matter by sodium gives the salt crust of Solonetz a dark color, thus the name,
"black" alkali.
In Central Asia, Rozanov (1951) describes a network of migrations
to account for both the nature and extent of accumulations of salts in
desert soils depending on geomorphological conditions. Solution-deposition-resolution-redeposition takes place for each salt depending on its
solubility constant and the geomorphical condition. Thus carbonates may
precipitate out first, followed by gypsum and other sulfates, followed by
chlorides. In the United States the cation solubilities of calcium, magnesium, sodium, and potassium salts are stressed the same way the anions
are stressed in the Russian system.
An example of salt-deposition pattern is a more vertical distribution
given by Hunt (1960) for salt pans in Death Valley, California. Chlorides
appear in the center of the pan at the place where ground water evaporates: sulfates surround the chlorides and form beneath them; carbonates
surround the sulfates and form below them. Salt surfaces appear most commonly in depressions on valley floors and play as with boisons. They
present variable surfaces described as white powdery, black crusty, smooth
films, flaky, and rough and jagged (Hunt, 1966). Unfortunately for the
taxonomist, salt patterns are not always this simple. Relic salt depositions;
the changing topography, climate, and distribution; the amount and the
composition of rivers and streams flowing through; and the periodic flooding will alter any natural and simplified salt accumulation trend. Polynov
(1935) considered the flat desert regions of the sierozem zone as a vast
WALLACE H. FULLER
2. Origin
Salts that accumulate in solid form in desert soils may come from several
sources: (1) weathered products of parent material, (2) marine deposits
such as saline shales, (3) atmospheric transport of sea salt, (4) rainwater
salts from certain terrestrial sources (dust) brought into the atmosphere
by wind action, (5) fossil salt (marine inundations) which are of more
local importance, and (6) transient dust that deposits during calms, are
leached by rain, and are blown away again. Not all of these sources are
expected to be operative in every desert and no single set of conditions
is operative to satisfy the nature and extent of accumulations in all soils.
3. Distribution
Certain saline and sodic soils contain sufficient accumulations of salts
to place them in special intrazonal great soil groups of the Solonchak and
Solonetz. The soluble salts that accumulate in these soils come from a variety of sources. Solonchak soils have been referred to as "white" alkali
soils and Solonetz as "black" alkali soils. Solubilization of soil organic matter by sodium gives the salt crust of Solonetz a dark color, thus the name,
"black" alkali.
In Central Asia, Rozanov (1951) describes a network of migrations
to account for both the nature and extent of accumulations of salts in
desert soils depending on geomorphological conditions. Solution-deposition-resolution-redeposition takes place for each salt depending on its
solubility constant and the geomorphical condition. Thus carbonates may
precipitate out first, followed by gypsum and other sulfates, followed by
chlorides. In the United States the cation solubilities of calcium, magnesium, sodium, and potassium salts are stressed the same way the anions
are stressed in the Russian system.
An example of salt-deposition pattern is a more vertical distribution
given by Hunt (1960) for salt pans in Death Valley, California. Chlorides
appear in the center of the pan at the place where ground water evaporates: sulfates surround the chlorides and form beneath them; carbonates
surround the sulfates and form below them. Salt surfaces appear most commonly in depressions on valley floors and play as with boisons. They
present variable surfaces described as white powdery, black crusty, smooth
films, flaky, and rough and jagged (Hunt, 1966). Unfortunately for the
taxonomist, salt patterns are not always this simple. Relic salt depositions;
the changing topography, climate, and distribution; the amount and the
composition of rivers and streams flowing through; and the periodic flooding will alter any natural and simplified salt accumulation trend. Polynov
(1935) considered the flat desert regions of the sierozem zone as a vast