Base Level and Lithologic Control of Drainage Reorganization in the Sierra de las Planchadas, NW Argentina

Abstract

AbstractPlanform drainage reorganization in catchments is a common response to changes in boundary conditions. Rivers reorganize through two predominant mechanisms: discrete stream capture events and progressive divide migration. Using general geomorphic observations, flow azimuth analysis, χ anomalies, local headwater relief, and the normalized steepness index (ksn), we examine drainage reorganization, its potential controls, and the response timescales for drainages in the Sierra de las Planchadas, NW Argentina. We additionally expand on the comparison of trunk and tributary ksn values as a potential tool for recognizing drainage reorganization. We identify three significant patterns of reorganization: (1) the migration of the main drainage divide (MDD) toward the hinterland, (2) capture of longitudinal drainages by transverse reaches, and (3) shrinking foreland catchments that will result in changes to basin outlet spacing. We determine that the migration of the MDD is due to local base level differences between the major range‐bounding basins, while more local patterns, such as the capture of longitudinal drainages, are the result of the distribution of erosionally resistant lithologies. We additionally assess the response timescales required for topologic changes to the drainage network, such as divide migration; we conclude that, as suggested by modeling studies, they are longer than the timescale required for channel profile adjustment.