The Uplift of the Ozark and Appalachian Foreland Cratonic Plateaus, USA

Stephen Marshak, University of Illinois Urbana-Champaign
Alison Anders, University of Illinois Urbana-Champaign
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Abstract

The Ozark Plateau and the Appalachian Plateau—unlike the Tibet Plateau and the Altiplano—do not lie within Cenozoic orogens. Rather, they both are located on the foreland side of the tectonically inactive Late Paleozoic Appalachian-Ouachita fold-and-thrust belts. In each of these foreland cratonic plateaus, sub-horizontal beds of marine Paleozoic strata currently crop out 0.5-1.2 km above sea level, indicating that the uplift post-dated the cessation of late Paleozoic orogeny. Significantly, in both examples, the fold-thrust belts that once shed sediment into the areas that are now foreland cratonic plateaus have since been deeply eroded. In fact, the average elevations of the fold-thrust belts are less than the average elevation of their former forelands, and the boundary between the flat-lying strata of the foreland and the valley-and-ridge province left by the erosion of the fold-thrust belt is an abrupt escarpment.
What caused the topographic inversion that produced the Ozark and Appalachian foreland cratonic plateaus? We suggested (Anders et al., 2022) that they are a consequence of flexural rebound of the foreland in response to erosion of the tectonically thickened and deformed crust of Paleozoic fold-thrust belts. Specifically, loading caused by emplacement the thrust stack had flexurally bent down the foreland's lithosphere by the end of the Paleozoic. Once deformation stopped, the orogen eroded more rapidly and more deeply than did the foreland for two reasons: (1) deformed rocks of the orogen contained more planes of weakness (fractures and cleavage) than did the flat-lying strata of the foreland; and (2) thrusting during formation of the fold-thrust belt emplaced slices of weak argillaceous rock.
To test our hypothesis, we simulated the landscape evolution of the Ozark Plateau using the Landlab platform. Our model results illustrate that the distribution of isostatic uplift due to differences in erosion resistance between the fold-thrust belt and the foreland can generate the Ozark Plateau in the absence of dynamic forcing. Initial modeling suggests, however, that the highest areas of the Appalachian Plateau—the Catskill Mountains region of eastern New York and the Deep Valleys physiographic province of central Pennsylvania—might not be a consequence solely of flexural rebound, for the modeled width of the predicted uplifted area is less than the observed width of the plateau. This discrepancy suggests that, in the case of the Appalachian Plateau, dynamic processes, such as those discussed by Gernon et al. (2025), may play a role in post-Jurassic uplift.

Session

Large-scale tectonics