the formation of sedimentary mountain rock on continents and in seas located in arid regions where the annual rate of evaporation is greater than the amount of atmospheric precipitation. Arid lithogenesis is counterposed to humid lithogenesis. The concept of arid lithogenesis was introduced by N. M. Strakhov in 1956.
On dry land, regions of arid lithogenesis include deserts, semideserts, and dry steppes with their inland waters. They are characterized by a combination of high temperatures and a negative balance of moisture. Areas of continental arid lithogenesis predominate over areas of arid seas.
The composition of continental formations is characterized by terrigenous sediments poor in quartz, considerable enrichment by carbonaceous material, and intensive dust deposits (loess formation). Multicolored, brightly pigmented, sometimes saline deposits and layers of clay enriched by various magnesium silicates, meerschaum, or palygorskite are extremely typical.
Accumulations of copper, lead, and zinc ores occur in regions of arid lithogenesis, but deposits of sedimentary iron, aluminum, and manganese ores are not found.
Despite the paucity of native water resources in regions of arid lithogenesis, there is a fairly large number of seas, lakes, and other bodies of water from precipitation, and water may enter the arid basins from humid regions. All the lakes and seas in regions of arid lithogenesis gradually become salinized in the process of their development, as a result of which the role of organisms in the formation of sediment sharply decreases, and the processes of physical and chemical sedimentation are intensified. The least soluble carbonates of calcium and magnesium are precipitated from the water first; then they are joined by the sulfates gypsum and anhydrite and, under conditions of very high salinity, sodium chloride and the calcium-magnesium salts. Huge halogenic layers that serve as a source of many useful minerals are formed.
REFERENCEStrakhov, N. M. Tipy litogeneza i ikh evoliutsiia ν istorii Zemli. Moscow, 1963.
V. P. PETROV