56
WALLACE H. FULLER
this way may be quite productive, even when the loess deposit is as shallow
as 15 cm. The maximum salinity of gypsum saturation water is about 30.5
mEq/liter at 24°C, well within the limit for growing many economic agricultural crops. A knowledge of the gypsum content of alkali soils (sodic)
is important since gypsum is used as an inexpensive amendment to supply
calcium for replacement of sodium in the improvement of the physical condition of soils.
Some gypsiferous soils have developed in sedimentary deposits containing gypsum. The Purgatory Series (Calciorthid) in the Southwest United
States is such a soil. Gypsum is found throughout as crystals and as white
patches on the surface. Although this is a productive agricultural soil,
maximum productivity is not achieved, more because of the unusually high
clay content in the B horizon than the gypsum.
2. Origin
The origin of gypsum accumulations in the eluvial horizon still is not
settled, although many suggestions appear in the literature. According to
Rozanov (1951), who has made an extensive study of the available data,
gypsum formation depends on the sulfur content of the parent rock rather
than on differences of hydrothermic regime in desert areas. Another widespread hypothesis assumes that gypsum is a relic and that it would have
existed already in the parent rock, though in a diffuse form. During
weathering processes, soils formed with gypsum stratified at certain depths,
depending on the local conditions at the time of formation. Rozanov
(1951) considers gypseous-eluvial accumulations resulting from primary
calcium sulfate (parent rock), concentrated by weathering, to be merely
a particular case. He suggests a general process consisting of gypsum formation by the oxidation of sulfurous compounds by sulfur bacteria.
The paucity of gypsum in the Gobi Desert is used to strengthen the
suggestion that, gypsum accumulations in the weathering crust of deserts,
are chiefly due to the pétrographie composition of the weathered rock.
The most abundant parent rocks in the Gobi and Eastern Betpak-Dala
are igneous and metamorphic, which are notably poor in sulfur and sulfur
compounds and thus are quite unable to give rise to appreciable accumulations of gypsum.
3. Distribution
It is further pointed out that gypsum accumulations and/or crusts are
widespread in areas of the North African Desert, in the desert belt of
Australia, and in the Egyptian Desert, where soils have developed over
sulfur-containing material of sedimentary parent rock, limestone, and rocks
of the Eocene age.
WALLACE H. FULLER
this way may be quite productive, even when the loess deposit is as shallow
as 15 cm. The maximum salinity of gypsum saturation water is about 30.5
mEq/liter at 24°C, well within the limit for growing many economic agricultural crops. A knowledge of the gypsum content of alkali soils (sodic)
is important since gypsum is used as an inexpensive amendment to supply
calcium for replacement of sodium in the improvement of the physical condition of soils.
Some gypsiferous soils have developed in sedimentary deposits containing gypsum. The Purgatory Series (Calciorthid) in the Southwest United
States is such a soil. Gypsum is found throughout as crystals and as white
patches on the surface. Although this is a productive agricultural soil,
maximum productivity is not achieved, more because of the unusually high
clay content in the B horizon than the gypsum.
2. Origin
The origin of gypsum accumulations in the eluvial horizon still is not
settled, although many suggestions appear in the literature. According to
Rozanov (1951), who has made an extensive study of the available data,
gypsum formation depends on the sulfur content of the parent rock rather
than on differences of hydrothermic regime in desert areas. Another widespread hypothesis assumes that gypsum is a relic and that it would have
existed already in the parent rock, though in a diffuse form. During
weathering processes, soils formed with gypsum stratified at certain depths,
depending on the local conditions at the time of formation. Rozanov
(1951) considers gypseous-eluvial accumulations resulting from primary
calcium sulfate (parent rock), concentrated by weathering, to be merely
a particular case. He suggests a general process consisting of gypsum formation by the oxidation of sulfurous compounds by sulfur bacteria.
The paucity of gypsum in the Gobi Desert is used to strengthen the
suggestion that, gypsum accumulations in the weathering crust of deserts,
are chiefly due to the pétrographie composition of the weathered rock.
The most abundant parent rocks in the Gobi and Eastern Betpak-Dala
are igneous and metamorphic, which are notably poor in sulfur and sulfur
compounds and thus are quite unable to give rise to appreciable accumulations of gypsum.
3. Distribution
It is further pointed out that gypsum accumulations and/or crusts are
widespread in areas of the North African Desert, in the desert belt of
Australia, and in the Egyptian Desert, where soils have developed over
sulfur-containing material of sedimentary parent rock, limestone, and rocks
of the Eocene age.