APPARENT DISEQUILIBRIUM OF CHANNEL PROFILES IN THE BUFFALO RIVER BASIN, AR

The Ozarks and Boston Mountain regions of Arkansas are a series of uplifted and dissected plateaus experiencing initial uplift contemporaneous with the Appalachians. Despite decades of study, the post-uplift history of the Ozarks region remains uncertain. Here we examine mechanisms responsible for the long-term persistence of the region. We also develop a statistical technique to analyze chi gradients for a large set of channels that cross the same lithologies. Chi analysis of the Buffalo River Basin, which straddles the Ozarks and Boston Mountains, reveals apparent disequilibrium in erosion rates among different parts of the basin. We examine lithologic controls on disequilibrium and find that chi gradient is greatest in the uppermost reaches of the basin, where a large interval of Pennsylvanian sandstone caps the ridges. Block detachment of the sandstone causes large boulders to be stranded in the upper tributaries, where stream power is likely too low to mobilize or effectively erode the boulders. Downstream of the sandstone caprock, the supply of sediment, predominately chert, to the trunk stream increases, and may cause a shift from detachment-limited to transport limited-conditions in the main channel.