TheOuachita orogeny was amountain-building event that resulted in thefolding andfaulting ofstrata currently exposed in theOuachita Mountains. The more extensive Ouachita system extends from the current range inArkansas andOklahoma southeast to theBlack Warrior Basin inAlabama and to the southwest through theLlano,Marathon, andSolitario uplifts inTexas on intoCoahuila andChihuahua inMexico.[1]
The region during the earlyPaleozoic lay off the coast of the southern portion ofLaurentia, in what is now the southern United States. Laurentia straddled theequator at the time and theRheic Ocean was to the south of Laurentia. Through theOrdovician,Silurian,Devonian, and earlyCarboniferous, marine sedimentation left extensive deposits ofblack shale, quartzosesandstone, andchert beds. During theMississippian, aflysch sequence with dark shales andgraywackes was deposited. Lenses of silicictuff exist as evidence of limitedvolcanism.[1] These later sediments were formed over asubduction zone which formed along southern Laurentia.
South America approached Laurentia as the intervening oceanic crust was subducted. The collision of South American and Laurentian continental crust compressed and uplifted the region to form the Ouachita Mountains. During thePennsylvanian andPermian, river systems draining westward from the Ouachita Mountains deposited sediments in north-central Texas and Oklahoma, which are now exposed at the surface. The Ouachita Mountains were extensively eroded between thePermian and theJurassic, and much of the Ouachita system was subsequently buried beneathMesozoic andCenozoic sediments to the southeast and southwest. The structures there have only been revealed through deep drilling in petroleum exploration.[1]
