Southern Oklahoma Aulacogen

Southern Oklahoma Aulacogen Stratigraphic range: Early to mid Cambrian
An outline of the Aulacogen
Area	Approximately 42,500 sq mi (110,000 km2)
Location
Coordinates	35°00′N 99°18′W / 35°N 99.3°W / 35; -99.3.
Country	United States

The Southern Oklahoma Aulacogen  (ah-lah-coh-jin)  is a failed rift, or failed rift arm (aulacogen), of the triple junction that became the Iapetus Ocean spreading ridges. It is a significant geological feature in the Western and Southern United States. It formed sometime in the early to mid Cambrian Period and spans the Wichita Mountains, Taovayan Valley, Anadarko Basin, and Hardeman Basin in Southwestern Oklahoma. The Southern Oklahoma Aulacogen is primarily composed of basaltic dikes, gabbros, and units of granitic rock.

The Southern Oklahoma Aulacogen extends roughly 500 miles long (805 km) by ~80–90 miles wide (129–145 km). The two remaining continental plate boundary arms of the triple junction from which the Southern Oklahoma aulacogen formed became spreading zones for the spreading of the Iapetus Ocean during the breakup of the supercontinent, Rodinia, estimated to have occurred in the Cryogenian Period, approximately 750 million years ago. These arms closed in the Pennsylvanian Period (~323.2–298.9 Ma) and formed part of the Ouachita orogenic belt. The Southern Oklahoma Aulacogen is estimated to contain over 250,000 km³ of igneous rock. The aulacogen is inverted: rather than extending across the surface it penetrates into the North American craton, and is aligned with the northern edge of a deeply buried Proterozoic basin of uncertain origin which may have formed through igneous layering or deposition. The aulacogen terminates on contact with the Ouachita orogenic belt. The Southern Oklahoma Aulacogen is associated with a widespread anomalous area in which seismic waves travel more slowly. A common comparison is drawn from this aulacogen to the Dniepr-Donets Aulacogen in Baltica because both are significant intracratonic rifts.