Evaporitic conditions in the Michigan Basin commenced in Late Ordovician time and continued into the Early Devonian. Five major evaporite (anhydrite/halite) cycles in the Silurian Salina Group (termed “A-1,” “A-2,” “B,” “D,” and “F”) can be recognized. They are further subdivided into two or more cycles of evaporite deposition by intercalations of less soluble members. Only the lowermost Salina evaporite produced a sylvinite deposit. The water surface was enlarged in subsequent evaporite cycles, which did not go beyond halite saturation, suggesting an enlargement of the water supply. Additional seawater came from the Kokomo Sea in Indiana; continental waters likely also...