Evaporites

Rocks formed by the evaporation of water are called evaporites - gypsum, anhydrite, halite (common salt). This evaporation may occur in either shallow basins on land or in the sea. Material (salts) is eroded from land surfaces and is then carried to the sea by rivers. When seawater evaporates, the salts precipitate and settle to the bottom. The less-soluble compounds (those that dissolve less readily in water) are deposited first. Calcium sulfate (the compound that forms gypsum and anhydrite) is the first to be deposited. Sodium chloride (halite compound) is next in the order of solubility. Sea formed evaporates are generally thicker and are more widespread - most Kansas evaporates were formed in this manner.

Kansas evaporites were deposited in the Permian sea which was a shallow arm of the ocean that was shut off from the main body of water by some barrier, perhaps land areas in Oklahoma and Texas. With the rate of evaporation greater than the combined inflow of water from the ocean and rainfall, the salts of the ocean water became more concentrated thus producing the evaporite deposit. Occasionally more water from the ocean came into the Kansas sea and this in turn was evaporated, adding to the thickness of the evaporites. These evaporites were later buried by other deposits of Permian and younger ages of rocks.

Some of the Kansas evaporites were formed (and are still being formed) on land. Areas in northeastern Stafford County and near Jamestown in Cloud County form small salt (halite) flats. These are formed by groundwater erosion of gypsum and halite into a solution and then being redeposited at or near the top of the ground surface. Gypsum deposited in this way looks like dark granular earth and is called gypsite or "gypsum dirt".