Post-rift geomorphological evolution of a passive continental margin (Paraíba region, northeastern Brazil): Insights from river profile and drainage divide analysis

Abstract

The post-rift erosional history of elevated passive continental margins (EPCMs) has been considered of low-rate tectonics across many regions worldwide. However, research in the northeastern Brazilian passive continental margin suggests variations in the post-rift tectonic styles, timing and rates. This is especially the case of the Paraíba region, where there are reports of uplift affecting Quaternary strata. However, transient fluvial features potentially developed during this event remain to be investigated. In this study, we document transient responses of a fluvial landscape promoted by variations in Quaternary tectonic uplift in the Paraíba region, where outcrops are scarce. The aim was to trace the Quaternary post-rift geomorphological evolution and the mechanisms of development of the northeastern Brazilian margin. A digital elevation model (DEM) was utilised to provide long river profiles based on the χ approach, normalized channel steepness index (ksn), and drainage divide analysis. The results indicated non-linear χ-profiles, migration of knickpoints upstream along the river profiles, and incised channels in elevated areas close to the inner margin plateau. In addition, there were cross divide differences in topographic metrics, with divide movements following a high elevation, chevron-shaped plateau. These transient fluvial features were mostly recorded over lithologies of relatively similar strength, in or near pre-existing basement structures. Thus, they were attributed to a topographic rejuvenation due to variations in tectonic uplift during the Late Quaternary. This tectonic geomorphological interpretation supports previous studies that the late development of the eastern South American EPCM was marked by a period of locally increased tectonics, potentially driven by far-field compressive stresses concentrated along main shear zones.