Intrabasin drainage divide asymmetry and associated stream capture in four Appalachian lithotectonic provinces

Drainage reorganization by stream capture is fundamentally associated with asymmetric drainage divides that separate fluvial networks with systematically different valley elevations. While stream captures along passive margin escarpment-type asymmetric divides have received significant attention in post-orogenic settings, the distribution and evolution of asymmetric intrabasinal divides remain poorly understood. Inspection of Appalachian topography reveals numerous small-scale asymmetric divides and minor "escarpments" between river networks that share a common near-field base level or very closely spaced outlets to external base level. Many of these divides migrate and decay through discrete stream capture events, even in dendritic networks of the Appalachian Plateau, which lack the rectilinear geometry known to favor efficient capture. Other small asymmetric divides show no evidence of capture despite having appropriate relief and fluvial network geometry. As the physical scale of these minor divides precludes control by tectonic or climatic forcing, the effect of small-scale lithologic variations on stream profile shape and knickpoint recession is the likely driving force behind the development of asymmetry. These localized lithologic effects may complicate the use of algorithms based on channel network position to identify smaller unstable divides within the landscape. The distribution of asymmetric divide systems throughout all Appalachian lithotectonic provinces suggests internal, lithologically forced disequilibrium is a pervasive and significant aspect of post-orogenic topographic decay.