Persistent River Basin Disequilibrium in a Cratonic Landscape: Ozark Dome, USA

Abstract:

Quantitative research on landscape evolution has focused on tectonically active landscapes, leaving the pace and primary drivers of topographic change in tectonically quiescent environments, which make up the majority of Earth’s surface, poorly understood. We use topographic analysis and a characteristic metric of river basin geometry, χ, to test the hypothesis that river basin dynamics, including divide migration and stream capture, can cause transient pulses of incision and large gradients in erosion rate, which in turn influence the morphology of cratonic landscapes. In testing this hypothesis, we describe and interpret the disequilibrium observed in river networks draining a typical low-elevation cratonic landscape, the Ozark dome, USA and propose alternative mechanisms to climate and tectonics that generate and sustain large-scale landscape disequilibrium. The Ozark dome was uplifted in the fore-bulge of the Ouachita orogeny and lies south of the extent of glaciation and primarily north of eustatic sea-level changes. The Ozarks have not experienced significant tectonic activity since the late Paleozoic. Landscape response times predicted by stream-power river incision models would suggest that landscapes subjected to consistent, low rates of isostatic uplift should be close to steady state. Yet, rivers draining the Ozark dome appear to be in disequilibrium. Anomalous stream network topology, variable relief across the dome, cross-divide topographic asymmetry that corresponds with large cross-divide gradients in χ, and the prevalence of multiple flights of strath terraces suggest transient and non-uniform bedrock incision rates. Our results suggest that erosional competition between river basins drive much of the observed topographic asymmetry and the in-situ formation of high-elevation, low-relief surfaces on the Ozark dome. This implies that basin dynamics, rather than tectonics, lithology, or climate, may set the large-scale morphology of some cratonic landscapes.