Deformation, Metamorphism, and Mineralization in Gypsum-Anhydrite Cap Rock

Marine evaporites

“…Some of the depths given for natural deposits are: up to 1,000 feet, Lower Fars evaporites, Iran (Strong, 1937); 1,037 feet, Zechstein evaporites, Cerebos no. 21 boring, northern England (Dunham, 1948); 1,230 feet, Louisiana (Newland, 1921); and rarely below 1,183 feet, gypsum, Sulphur Salt Dome, Louisiana (Goldman, 1952). The exceptional records of gypsum at considerably greater depth (for example, 2,467 feet in Hayton boring, no them England [Dunham, 1948]) may perhaps result from alteration of borehole cores during or after the drilling.…”

“…Pseudomorphs after early gypsum have also been recorded from the German Zechstein (Borchert and Baier, 1953). Gypsum has replaced anhydrite in bulk in many places (for example, Hammerschmidt, 1883;Sherlock and Hollingworth, 1938;Goldman, 1952). Considerable amounts of sulfur have occasionally been formed at the expense of calcium sulfates (for example, see Goldman, 1952).…”

“…Many complex replacements in the cap zones of salt domes have been described (for example, by Goldman, 1952). Especially noteworthy are the removal of chlorides in solution and the accumulation of insoluble residues, especially anhydrite, to form a Y44 DATA OF GEOCHEMISTRY cap; the replacement of anhydrite by gypsum; and the replacement of sulfates by carbonates.…”

Anhydrite deposits of the United States and characteristics of anhydrite important for storage of radioactive wastes

“…Much of the data that follow on the nature and origin of cap rock are based on the report by Walker (1974). Additional general studies focusing on cap rock include those of Goldman (1933Goldman ( , 1952, Taylor (1937Taylor ( , 1938, and Murray (1966Murray ( , 1968. Because of several unique characteristics and economically important associations of petroleum, native sulfur, and salt, salt domes of the Gulf Coast basin have…”

“…The theory most widely accepted on the o'rigin of cap rock is that it represents a residue of anhydrite and other insoluble minerals that accumulate at the upper surface as the salt dome rises through water-bearing sediments and is dissolved (Goldman, 1933;Taylor, 1937Taylor, , 1938Murray, 1966Murray, , 1968). The anhydrite crystals, which make up about 99 percent of the water-insoluble residue in a dome salt (Gera, 1972;Walker, 1974), are then recrystallized and compacted to form a massive cap rock; this may locally be hydrated to form gypsum.…”