Most part of geologists still believe that salt rocks as halite NaCl, anhydrite CaSO4, gypsum CaSO4·2H2O, sylvite KCl, tachyhydrite CaMg2Cl6·12H2O, carnallite KMgCl3·6H2O, among others would be formed intrinsically by evaporation processes of shallow saline waters at surface environments and thus would configure sequences formed by the so-called "evaporites" which would be a class of chemical sedimentary rocks. The paradigm of the model related to formation of evaporites dates since 1849 by Italian chemist Usiglio and after proposals by Bischof and Ochsenius, respectively in 1854 and 1877 based on previous ideas would take place through the model of restriction by a barrier (Barrier Model) of saline water bodies where the salt to precipitate and form layers according to its solubility, concentration and evaporation rates that are influenced by topography and arid climates.
Would be traditional evaporite model the only real explanation for the genesis of salt deposits? The traditional evaporite model is, however, not the only way of explaining all the salts appearing on Earth today. Thus, a group of Norwegian scientists have, over the past decade developed the new Hydrothermal Salt Theory (Hovland et al., 2006). Unlike the traditional model, this theory is more physically and chemically consistent, and over time, may take over parts of the current view. The new theory is not only valid on Earth, but also on planet Mars, where probably there are salt domes and salt deposits (Hovland et al., 2009)
It is noteworthy that there is no rock-forming minerals in the crust of the Earth with high content of chlorine or abundance to justify the occurrence of huge deposits of salt halite (NaCl). It makes sense then think that salt would not be derived primarily only from the dissolution of surface rocks. By the other hand, salt usually occurs associated with volcanic environments and hydrothermal systems as mud volcanism, for instance. There are many examples in the world, in marine, estuarine and continental environments and also a wider range of altitudes.
Good example of non-marine salt association is the salt of the Salar de Uyuni, in Bolivia. This occurrence is situated over 3,650 m altitude in the Andes, wide more than 100 km in area about 3,000 square miles. The salar is surrounded by several volcanic buildings. Another example is the Danakil Depression, in Ethiopia, Eritrea and the salts that occur in the Afar Triangle in Djibouti, where there is also intense volcanism. White Sands National Monument, in New Mexico, USA is another good example of salt related to volcanism. In this place there are spetacular dunes, not sand dunes, but gypsum dunes and the Carrizozo Malpais lava flow, over 70 km long, occurs closely towards north of White Sands. There also many similar occurences in the world.
Hydrothermal Salt Theory offers plausible explanation on the origin and evolution for the end-members of these salt sequences, but the dogmas of geology, as the principle of actualism, are still very influential and difficult paradigm shift to an unconventional theory. This is due the difficult of most part of geologists still do not have comprehension of physical, chemical laws and mass balance of natural processes because they still remaining prisoner with their reasoning in context of restricted "a priori" theories.
Indeed, understanding the whole process - from the origin to the formation of salt deposits is not simple, since the elements and compounds have high chemical reactivity with many changes. Maybe Hydrothermal Salt Theory is the great light to the knowledge of salt rocks formation and evaporites are only extrinsic processes of salt rework at surface shallow environments.
Why are the oceans salty? That is a question that even children always ask and geologists and scientists still do not get an apropriated answer, obviously because they do not have enough understanding about what is salt and its origin but the Hydrothermal Salt Theory is probably a right way to answer that and other many questions about salt and its real origin.
The traditional evaporite model could explains only certain situations after salt formed originally by hydrothermal systems reach to surface and reworked at this enviroment by normal evaporation processes. On the other hand, Hydrothermal Salt Theory also explain existence of deep-water salt sequences.
Hovland, M., Rueslåtten, H., Johnsen, H.K., Kvamme, B., Kutznetsova, T., 2006. Salt formation associated with sub-surface boiling and supercritical water. Marine and Petroleum Geology 23, 855-869.
Hovland, M., Rueslåtten, H., ,Johnsen, H.K., Fichler, C., 2009.(Abstract) Hydrothermal evaporites - from the Conrad Deep, via Dallol, to Elysium Planitia. International Association of Sedimentologists (IAS) Annual meeting, Alghero, Sardinia, Book of Abstracts.