Mississippian

The Mississippian is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earliest/lowermost of two subperiods of the Carboniferous period lasting from roughly 359 to 318 Ma (million years ago). As with most other geochronologic units, the rock beds 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 River valley.

In North America, where the interval consists primarily of marine limestones, it was in the past treated as a full-fledged geologic period between the Devonian and the Pennsylvanian. In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous system, and sometimes called the Upper Carboniferous and Lower Carboniferous instead. During the Mississippian subperiod an important phase of orogeny occurred in the Appalachian Mountains.

Subdivisions

In the official geologic timescale, the Mississippian is subdivided into three stages:

* Tournaisian 359.2 ± 2.5 million years ago to 345.3 ± 2.1 million years ago
* Visean 345.3 ± 2.1 million years ago to 326.4 ± 1.6 million years ago
* Serpukhovian 326.4 ± 1.6 million years ago to 318.1 ± 1.3 million years ago

first two come from European stratigraphy, the last is 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:

* Kinderhookian (the lower two-thirds of the Tournaisian)
* Osagean (top of the Tournaisian and bottom of the Visean)
* Meramecian (middle Visean)
* Chesterian (top of the Visean plus the Serpukhovian)

External links

* The Carboniferous
* Geologic Time Periods

References

1. ^ Gradstein et al. (2004)