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Structural Geology of the Ouachita Mountains: Abstract
Nappes form the structural framework of the Quachita Mountains, Fabric studies and recent mapping reveal three structural subprovinces; a southern nappe largely in Ordovician shales; a northern nappe composed of Ordovician through Devonian strata; and an outer belt of orogenetic landslides and thrust faults in Carboniferous strata.
The southern nappe is broadly arched. Near Benton, Arkansas, on its thoroughly cleaved upper limb, axial surfaces of digitate isoclinal folds dip gently southward. Northeastward, across the axial surface of the nappe, sole marks, cross laminae, and graded beds indicate an overturned lower limb. All planar structures, bedding, cleavage, and axial planes, are flat-lying, although steepening northeast dips develop progressively northeastward. Still farther northeastward the axial surface of the nappe is recrossed, for the stratigraphic succession indicates a digitate upper limb.
A slide marks the lower limb of the northern nappe. From southwest to northeast it comprises an overturned lower limb, an axial zone, a strongly digitate upper limb, and, near Little Rock, a second slide. All structural elements dip northeastward. Southwest of this second slide, homogeneous macroscopic folding deformed the thoroughly cleaved lower Paleozoic strata. Northeast of the slide, however, orogenetic landsliding of Carboniferous rock off the nose of the northeastward-diving nappe formed a broad belt of chaotic deformation including antiformal and synformal overfolds. The plunging action of the gravity slides drove the thrust faults marking the northern edge of the Ouachita Mountains.
Acknowledgments and Associated Footnotes
1 University of Missouri, Columbia, Mo
Copyright © 2006 by the Tulsa Geological Society