Mississippian (geology)

Mississippian
358.9 ± 0.4 – 323.2 ± 0.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Map of Earth as it appeared 340 million years ago during the Mississippian, Viséan stage[citation needed]
Chronology
−360 — – −355 — – −350 — – −345 — – −340 — – −335 — – −330 — – −325 — – −320 — – −315 — – −310 — – −305 — – −300 — – Paleozoic Devonian Carboniferous Permian Mississippian Pennsylvanian Early Middle Late Early Mid Late Tournaisian Viséan Serpukhovian Bashkirian Moscovian Kasimovian Gzhelian     ← Carboniferous Rainforest Collapse ← Mazon Creek Fossils ← End of Romer's Gap ← Start of Romer's Gap Subdivision of the Carboniferous according to the ICS, as of 2021.[1] Vertical axis scale: millions of years ago
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Subperiod
Time span formality	Formal
Lower boundary definition	FAD of the Conodont Siphonodella sulcata (discovered to have biostratigraphic issues as of 2006)[2]
Lower boundary GSSP	La Serre, Montagne Noire, France 43°33′20″N 3°21′26″E / 43.5555°N 3.3573°E / 43.5555; 3.3573
Lower GSSP ratified	1990[3]
Upper boundary definition	FAD of the Conodont Declinognathodus nodiliferus
Upper boundary GSSP	Arrow Canyon, Nevada, United States 36°44′00″N 114°46′40″W / 36.7333°N 114.7778°W / 36.7333; -114.7778
Upper GSSP ratified	1996[4]

The Mississippian (/ˌmɪsɪˈsɪpi.ən/ miss-ə-SIP-ee-ən,^[5] 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 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 Valley.

The Mississippian was a period of marine transgression in the Northern Hemisphere: the sea level was so high that only the Fennoscandian Shield and the Laurentian Shield were dry land. The cratons were surrounded by extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas.^[6]

In North America, where the interval consists primarily of marine limestones, 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.^[7]

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.