Abstract

This paper suggests the Ouachita Mountains of Arkansas constitute a large, broadly arched nappe or perhaps a series of nappes. Near Benton, large areas of strata are overturned, and fabric diagrams of bedding, cleavage and axial planes attest to isoclinal recumbent folding. From southwest to northeast, all planar elements rotate from horizontal to northeast-dipping attitudes. The Little Rock structural salient is composed of a strongly digitate upper limb. Recumbent folds occur as far west as Mt. Ida, Arkansas, where a thrust, fronting the north edge of the Crystal Mountains, overrides them.

Flanking the northeast edge of the Ouachitas is a major glide plane from which the Carboniferous sediments detached and accumulated as a series of orogenetic landslides. The combined plunging action of the nappes and slides drove the thrust faults of the foreland. Flattening in the decollement zone accounts for some of the displacement of the thrust faults, which root north of the Benton-Broken Bow uplift.

Thrust faults south of the uplift are attributed to back limb shears on the upper limb of the nappe or perhaps they constitute the foreland of another nappe buried beneath the Coastal Plain.

Two alternate tectonic models are suggested, One, that the core of the Ouachitas is an infrastructure carrying and folding a suprastructure composed of Carboniferous sediments. Two, that basement uplift caused northward sliding of the lower Paleozoic strata and in turn, sliding of the Carboniferous sediments off the lower Paleozoics.