TIMING AND STRUCTURAL FRAMEWORK OF THE OZARKS UPLIFT

Previous investigators have characterized the southern margin of Laurentia as a product of Neoproterozoic rifting and development of a passive margin prior to docking of the Ouachita allochthon in the early Pennsylvanian. Although many investigators have suggested that the Ozarks were uplifted at that time, tectono-stratigraphic sequences record earlier uplift, consistent with down-warping of the Arkansas Novaculite foredeep and flexural epeirogenic uplift in the hinterland, which began during the middle Devonian and continued through the Mississippian, ultimately culminating in Pennsylvanian time. The sub-late Devonian and sub-Mississippian unconformities are prominent features that record uplift and denudation in the hinterland. Truncated folds and syn-tectonic sedimentation of chaotic beds, slumps, slide blocks, and syn-sedimentary folds are found in lower and middle Mississippian carbonates. Key lines of evidence for syn-tectonic movement come from stable-isotope profiles as well as the observation that displaced masses invariably are associated with downthrown fault blocks.

An array of fault orientations in the hinterland includes a dominant SE-NW trend in the eastern and central Ozarks and conjugate SW-NE faults in northeastern Oklahoma and northwestern Arkansas. Cox (2009) recognized that oblique collision of the Ouachita allochthon with the southern margin of Laurentia was manifest in a series of strike-slip and oblique faults with right-lateral transport on the SE-NW trend and left-lateral on SW-NE-trending faults. Most studies suggest that these are rooted on basement blocks, where supracrustal rocks are deformed as a result of lower structural movements. If the Ozarks constitute an oblique collisional setting, why are grabens (extensional features) so prevalent, along with folds, which are subparallel to the trends of major faults? We propose that fault linkages, relay ramps, a few thrust faults, bends, folds, and grabens between major fault zones indicate development of incipient positive and negative flower structures in this strike-slip-dominated terrain.