A regionally extensive Early Mississippian hiatus is recognized at the transition from preflysch to flysch rocks in the Ouachita system of the southern mid-continental United States. It is recognized only in sections where detailed biostratigraphic control exists, and it is coeval with a regional unconformity in the Ouachita foreland throughout parts of Texas, New Mexico, and Oklahoma. Widespread Early Mississippian erosion and nondeposition is attributed to a reconfiguration in basin geometry caused by the onset of Ouachita orogenic activity. Crustal flexure resulting from the impending collision would have initiated erosional processes throughout the foreland, while simultaneously altering bottom-current pathways in the basin and allowing for a prolonged period of sedimentary bypass. In the Late Mississippian, increased constriction may have eventually cut off transequatorial bottom-water circulation, allowing deposition to resume on the shelf and in the basin. An important tectonic implication of this study is that Ouachita deformation started in the Late Devonian to earliest Mississippian, at least 10 m.y. before the onset of flysch deposition.