UPLIFT OF FORELAND INTRACRATONIC PLATEAUS DUE TO EROSION OF ADJACENT FOLD-THRUST BELTS: A CASE STUDY OF THE OZARK PLATEAU

Most plateaus occur in active orogenic belts—but not all do. The Ozark Plateau and the Appalachian Plateau of the eastern United States fringe the foreland side of tectonically inactive and deeply eroded Paleozoic fold-and-thrust belts of the Appalachian-Ouachita orogen. In these foreland intracratonic plateaus (FIPs), sub-horizontal beds of marine cratonic platform and overlying foreland-basin strata currently sit 0.5 to 1.2 km above sea level. Significantly, the fold-thrust belts that once shed sediments into these forelands now have average elevations that are lower than their former foreland basins. Why do FIPs, and their associated topographic inversion, develop? To address this question, we built a numerical model with the Landlab platform to simulate how topography evolves as foreland lithosphere flexes upward in response to unloading from post-tectonic erosion. The model assumes that the deformed, tilted, cleaved, and fractured clay-rich strata of the fold-thrust belt have less resistance to erosion than do flat-lying foreland strata of carbonates and sandstone. We used characteristics of the Ozark Plateau and Ouachita fold-thrust belt as a case study to test this model. Our results demonstrate that isostatic uplift due to erosion, given reasonable differences in resistance to erosion between the fold-thrust belt and the foreland, can generate the observed topographic inversion in the absence of dynamic forcing. Our model can explain the presence of the Ozark Plateau, and may provide insight into uplift of the high portions in the Appalachian Plateau (e.g., the Catskill Mountains of New York and the Deep Valleys Province of Pennsylvania).