The Ouachita orogeny was a mountain building event that resulted in the folding and faulting of strata currently exposed in the Ouachita Mountains. The more extensive Ouachita system extends from the current range in Arkansas and Oklahoma southeast to the Black Warrior Basin in Alabama and to the southwest through the Llano, Marathon, and Solitario uplifts in Texas on into Coahuila and Chihuahua in Mexico.
The region during the early Paleozoic lay off the coast of the southern portion of Laurentia, in what is now the southern United States. Laurentia straddled the equator at the time and the Rheic Ocean was to the south of Laurentia. Through the Ordovician, Silurian, Devonian, and early Carboniferous, marine sedimentation left extensive deposits of black shale, quartzose sandstone, and chert beds. During the Mississippian a flysch sequence with dark shales and graywackes was deposited. Lenses of silicic tuff exist as evidence of limited volcanism.
These later sediments were formed over a subduction zone which formed along southern Laurentia as South America approached to collide with it . The collision compressed and uplifted the region to form the Ouachita Mountains. The Ouachita Mountains were extensively eroded between the Permian and the Jurassic. Much of the Ouachita system was buried beneath Mesozoic and Cenozoic sediments to the southeast and southwest. The structures there have only been revealed through deep drilling in petroleum exploration.
- http://www.du.edu/~jcalvert/geol/ouach.htm The Ouachita System
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