Mississippian Subsystem

The Mississippian Subperiod, the initial division of the Carboniferous Period, spanned from 358.9 to 323.2 million years ago. It is primarily characterized by extensive shallow-water limestone deposits found across continental interiors, particularly in the Northern Hemisphere. These limestones are notable for their composition, shifting from calcite-dominated grains to aragonite-dominated ones, reflecting changes in seawater chemistry due to decreased seafloor spreading. During this time, sea levels began a cyclical retreat from continental interiors, culminating in a global lowstand at the boundary between the Mississippian and Pennsylvanian periods. The Mississippian also marks the near extinction of armored fishes that were prevalent in the preceding Devonian Period. The formations of this period are well-documented in regions like the Mississippi Valley in the United States, as well as in parts of Europe.12