Claim CD301:

Evaporites can precipitate from unsaturated brines; they can form without evaporation (H. M. Morris 1974). A mechanism is sketched by J. D. Morris (2002):

Many now think the salt was extruded in superheated, supersaturated salt brines from deep in the earth along faults. Once encountering the cold ocean waters, the hot brines could no longer sustain the high concentrations of salt, which rapidly precipitated out of solution, free of impurities and marine organisms.

Source:

Response:

1. Most evaporite deposits are not associated with evidence of hydrothermal activity. The huge amount of energy needed to deposit kilometers of salt in a few weeks should have left obvious evidence, such as heat-altered rocks or evidence of magma. Typical hydrothermal deposits such as iron and manganese are not often found associated with evaporites. Sea-floor basalts are a common site of hydrothermal activity, and other hydrothermal deposits are found there, but salt deposits are never found associated with them.
   
   
2. Hydrothermal systems operating today are not depositing any salt, much less the thick, laterally extensive layers we find in the sedimentary record. In fact, hydrothermal solutions contain less sodium and chlorine than normal sea water (Open University Team 1989, 100).
   
   
3. Evaporites are observed forming today in basins with no significant outflow; the water that flows in evaporates and leaves behind layers of dissolved salts. Ancient evaporites are also found in sedimentary context, and they are often associated with other evidence of being open to the air, such as footprints, dessication cracks and occasional raindrop impressions. None of these structures are consistent with an underwater hydrothermal environment.
   
   Evaporites are also found in sabkha environments, where crystals or nodules of salt grow within fine-grained sediments as saline groundwater (usually from a nearby ocean) is drawn upward by evaporation. As the water evaporates at the surface, salt nodules grow, often forming a chicken-wire pattern. Some sabkha evaporites grow into gypsum rosettes, huge crystals resembling flowers. These features also are known from ancient evaporites. They also are inconsistent with hydrothermal deposition.

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