Salt as a mineral is called halite. The chemical composition of halite is NaCl, or sodium chloride, which is the same as common table salt.
"Although all water bodies on the surface and in aquifers contain dissolved salts, the water must evaporate into the atmosphere for the minerals to precipitate. For this to happen, the water body must enter a restricted environment where water input into this environment remains below the net rate of evaporation. This is usually an arid environment with a small basin fed by a limited input of water. When evaporation occurs, the remaining water is enriched in salts, and they precipitate when the water becomes supersaturated." (from Evaporite - Wikipedia.htm) Evaporation of about 80 feet of sea water is required to produce a foot of salt. Salt deposits found in Kansas are as shown below.
"The Hutchinson Salt Member covers about 37,000 square miles in the subsurface of central and south-central Kansas, reaching a maximum thickness of more than 500 feet under Clark, Comanche, and Barber counties. About 80 percent of the rock in the Hutchinson Salt Member is salt (much of the rest is shale), more salt and fewer impurities than most salt beds. Thick salt layers also occur in western and southwestern Kansas in the Ninnescah Shale, Blaine Formation, and the Flower-pot Shale. Most of these salt beds, which have never been mined, are much deeper below the surface than the eastern edge of the Hutchinson Salt Member, where mining occurs", (from "Salt in Kansas"Kansas Geological Survey, Public Information Circular (PIC) 21) since the formations gently dip to the west-northwest at approximately 20 feet per mile.
"The eastern edge of the Hutchinson Salt Member is actively being eroded, or dissolved, by contact with ground water. This area, where the salt is closest to the surface, is known as the dissolution front. Because salt is so easily dissolved in water, outcrops at the surface are not present in Kansas." (illustration from KGS--Hutchinson Response--General Geology.htm)
"The Michigan Basin is one of the greatest areas of rock salt and other evaporites like gypsum in the world, and these sediments have been the basis of major chemical and plasterboard industries in Michigan. This basin was bounded on the northwest by the Wisconsin Arch and on the southeast by the Cincinnati Arch. Also the Kankakee Arch developed across northeastern Illinois, forming two separate basins. Although it did not form a land barrier, it greatly restricted circulation of sea waters within the Michigan Basin.
The rate of subsidence within the Michigan Basin then increased markedly, and a series of coral reefs developed along the Kankakee Arch and in the shallow waters along the western and southern margins of the basin. Some of these reefs can be seen today on the south side of Chicago, and I-94 crosses over a giant quarry into one of them. Assuming that these reefs formed in an environment similar to modern reefs, we can infer something about the Great Lakes area during this time. All modern reefs grow on a shallow bottom, no deeper than the depth of light penetration, generally about 200 feet (60 m). Furthermore, coral reefs are restricted to tropical regions where water temperatures are consistently above 77oF. Thus, the presence of extensive reefs around the Michigan Basin suggests a shallow tropical or sub-tropical environment. Well preserved fossils in most of these ancient reefs substantiate this assumption. Outward from the reefs, in the deeper water, muds rich in CaCO3 accumulated on the floor of the vast shallow seas, generally producing thinly bedded dolomite that contains few fossils. But the genial climates came to an end.
The close of the period was a long time of aridity in which the seas became so salty that living creatures swam to a more suitable home. The conditions were roughly analogous to the present-day Mediterranean Sea where water from the Atlantic flows in over the rather shallow restriction at the Straits of Gibraltar. The arid climate in the region evaporates the sea water and concentrates the salt. The heavier, highly saline water sinks to the bottom and cannot escape and therefore tends to accumulate. Great salt beds (named the Salina Salt Beds) were deposited in the basin. In the central part of the basin 2300 feet of alternating salt, shale, and limestone beds have been penetrated in the Salina, with 1600 feet of rock salt. The rock salt bowl becomes thinner towards its rim. Most gypsum units are less than 20 feet in thickness. Contrast that with the over 400 feet of halite in the basin. These deposits are buried up to 1250 feet below the present surface.
The extensive development of offshore carbonate rocks and an absence of sandstones and shales suggests that no land mass was present in the Great Lakes area while these deposits were being formed." (from geo.msu.edu/geogmich/evaporite.html 8 Feb 2009.)
The very presence of bedded salt in the geologic record is evidence that it was not deposited during a WET "global flood" year (371 days). Salt dissolves in water, it doesn’t deposit out of water unless the water is saturated with salt. And when it is saturated with salt, no vertebrate life can live in those waters. So, why do we find huge salt beds in the middle of the sedimentary rock formations, which are very widespread and in some locations stacked one above another as discussed above? How did this happen in the midst of the biggest water event in history—the Noachian flood? Obviously it didn't !! And as per Genesis 1:2 "Thus the heavens and the earth were finished, and all the host of them." (ESV) it is obvious that many of these salt formations are pre-Flood !! And thus covered to varied depths by other materials.