Geocaching - The Official Global GPS Cache Hunt Site

When you drive on an icy road, eat a potato chip or wear a pair of leather shoes, you may be using one of Michigan’s least known natural resources---salt. During the Paleozoic Era, beginning about 600 million years ago and ending about 230 million years ago, seawater invaded the Michigan Basin(an area about 80,000 sq. miles) at least six times. As the seas receded and evaporated, rock and mineral deposits such as halite (rock salt), gypsum (calcium sulfate with water), liquid brines, petroleum, lime, clay, sandstone and coal were left behind.

During the early decades of the 20th century, Michigan led the nation in salt production. Michigan is a leading producer of many natural salines---underground waters rich in chlorides, calcium, magnesium, sodium and, in lesser amounts, potassium, bromine and iodine. Salt under Michigan has created fortunes, towns and manufacturing centers. Michigan ranks first in the United States in the production of calcium chloride (salt) and in gypsum, fourth in cement and sand and gravel, and is a large producer of crushed stone for a variety of purposes. These minerals are found in the sedimentary rocks of the Michigan Basin or in the extensive glacial deposits. Salt is obtained from beds of rock salt (the Salina Formation is but one) over 1,100 ft below the surface in Detroit and from natural and artificial brines of dissolved salt that are pumped to the surface in Midland, Manistee, Muskegon, Wayne, and St. Clair Counties. The salt layers were laid down as evaporite deposits in the seas of the middle Paleozoic era---in the Mississippian, Devonian, and Silurian periods. Indians took salt from the same springs and sometimes used it as an item of trade with neighboring tribes. Some of the earliest white settlements were begun at brine springs in the southeastern part of the state. (Brine is water saturated with common salt.) Salt was so important to early pioneers that during the winter of 1836-37 in Branch County a 20-pound venison ham could be traded for a fist-sized lump of salt. Used mainly as a preservative, salt was essential for survival on the Michigan frontier.

From the top to the base of the image is about a meter. Note that the salt occurs in distinct beds, or layers. This layering is due to the fact that the salt was depoisted layer-by-layer in an evaporation basin. The darker layers are still salt, but contain some admixtures of silt and clay (i.e., the water was muddier then).

Evaporite deposits (gypsum and rock salt, or halite) formed in the Michigan basin when waters flowed into the basin, and then evaporated, depositing the salts. This is referred to as the "Salt Cycle".