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The Mississippian ( ), also known as Lower Carboniferous or Early Carboniferous, is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronology units, the stratum that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi Valley.
The Mississippian was a period of marine transgression in the Northern Hemisphere: the sea level was so high that only the Baltic Shield and the Canadian Shield were dry land. The were surrounded by extensive delta systems and , and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas.Cesare Emiliani, Planet Earth: Cosmology, Geology, and the Evolution of Life and Environment 1992 496.
In North America, where the interval consists primarily of marine , it is treated as a geologic period between the Devonian and the Pennsylvanian. During the Mississippian an important phase of orogeny occurred in the Appalachian Mountains. The USGS geologic time scale shows its relation to other periods. USGS Timescale
In Europe, the Mississippian and Pennsylvanian are grouped together as the Carboniferous system, and traditionally referred to as the Upper Carboniferous and Lower Carboniferous instead.
The lower two come from European stratigraphy, the top from Russian stratigraphy. Besides Europe and Russia, there are many local subdivisions that are used as alternatives for the international timescale. In the North American system, the Mississippian is subdivided into four stages:
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