Shallow-marine origin for Ordovician rocks of the Ouachita Mountains, Arkansas

Sedimentary structures and textures of the Ordovician Crystal Mountain and Blakely Formations, Arkansas, suggest that the widely accepted deep-water origin of these formations may be sedimentologically untenable. Sandstone beds of these formations are herein interpreted to be sublittoral sheet sandstones, deposited in a shallow-marine shelf association. Interbedded conglomerates resulted from debris flows activated by rifting along fault scarps. The Ordovician Ouachita trough is reinterpreted as a shallow basin underlain by granitic crust. The Crystal Mountain and Blakely Formations were deposited close to the shoreline of a continental area (Llanoria) that lay to the south or southwest of the present Ouachita Mountains.