Abstract

During 200 million years of Paleozoic history, north-facing bodies of preflysch, flysch, and shallow-water clastics with a cumulative thickness of over 30,000 feet (10 km) prograded and were thrust northward over the subsiding Arkoma shelf to form the present Ouachita mountains. The simplest and at present most likely driving mechanism is imbrication in the upper plate of a south-dipping subduction zone, with a cumulative dislocation many times greater than the present juxtaposition and tectonic deformation of the clastic bodies in the frontal, central and southern Ouachitas would imply. In this view, the Ouachitas represent the suture in which lapetus or another late Precambrian to Paleozoic ocean were consumed. Sedimentation rates on the Arkoma shelf reflect the opening of this ocean by sea-floor spreading; boulder beds in the Ouachita complex reflect details of its closing, potentially useful in tracking the rates of subduction. Other details, such as the quiescence implied by the Devonian/Mississippian cherts, are not fully explained by present plate models, probably because the latter are too local in scope.