Landscape evolution of the Salamanca watershed, Araripe Plateau: Insights from a river channel morphological classification

The drainage network of the Brazilian semi-arid responds directly to the complexity of the geomorphic background and surface processes. In this regional context, the Araripe Plateau, a table-like landform that reaches up of 950 m in elevation, stands out as a peculiar physiographic setting. The present work proposes an analysis of the Plateau?s fluvial system based on channel morphology descriptive criteria, in relation to their morphostratigraphic scenarios. The research sought to explore river typologies, dominant surface processes and geomorphic changes in the drainage system throughout the Holocene. Seven fluvial styles have been identified in the Salamanca River watershed, expressing lithological controls of the underlying sedimentary rocks, morphotectonic influence, variability in rainfall input, as well as changes in land use. Headwaters? channels cut through the sandstone of the structural summit surface and the unconsolidated sedimentary infills of topographic hollows along the escarpment base. On the hillslopes, downstream of the escarpment, the incised meandering river style with occasional pocket plains attest to shifts in patterns of fluvial dissection due to changes in base level. In the peripheral depression (Vale do Cariri), at an average elevation of 400 m, the arroyo and floodout river styles prevail, displaying a sequence of incised and non-incised river stretches, reflecting the operation of recent cutand-fill processes mostly controlled by the interannual rainfall variability. Cut-and-fill processes operating within the channels have prevailed all through the Holocene, as suggested by morphostratigraphical evidence, alternating overall valley bottom filling episodes with river entrenching periods (paleo-connectivity). Base level change during the upper Holocene did not result in comprehensive sediment delivery to the channel networks, as attested by remaining discontinuous pocket plains and fluvial terraces.