Effects of drainage captures in the retreat of Serra do Mar: an analyze using the combination of numerical models and cosmogenic isotopes

Both internal and external Earth’s dynamics are constantly changing the landscapes and one of the most influent external components are the fluvial processes, altering the relief through erosion and fluvial deposition, as well as through its respective drainage network’s reorganization. The drainage basins dynamics seeks to achieve a balance between tectonic uplift and river erosion. The use of parameter Chi (χ) allows a comparison of basins in different scales, erosion and uplift rates, making it possible to determinate its steady or transient state and comprehends the dynamics de divisor migration of basins. Although the great advances have been reached in last decades, there are still many questions without answer. For the accomplishment of this study, two areas in the Serra do Mar of São Paulo and Paraná were chosen due to the presence of important river captures, which generated significant reorganizations in the drainage network. Furthermore, cosmogenic isotopes (¹⁰Be) data from existent literature in Serra do Mar of Paraná allows the estimation of the denudation rate of these basins in the long term. In this study, these rates are analyzed combined with values of Chi, verifying the influence of the captured rivers, which contribute to the understanding of landscape evolution. This study uses the Digital Elevation Model (DEM) SRTM 30m. The DEM data were treated in ArcGIS and analyzed in MATLAB, where oceanic and continental basins were selected, considering sea level as the base level. The analysis was made through functions of Topographic Analysis Kit (TAK), integrated to TopoToolBox, to generate longitudinal and elevation-Chi profiles and Chi maps plotted with knickpoints data and, for the Paraná basins, the product obtained were simultaneously analyzed with ¹⁰Be data. From the analysis of these data, was possible to notice the ocean basins are capturing the continental basins and, therefore, that these basins are in a transient state, which means that their divisor is migrating towards higher Chi values, thus, towards the interior of the continent. In Paraná basins, the retreating areas of the Serra do Mar escarpment directly related to places of high erosion rates on the oceanic slope. These results, although preliminary, attest the potential of analysis methods used, proving the influence of river captures in the disruption of the steady state between adjacent drainage basins located on the oceanic and continental slopes, as well as their influence on the differentiated retreat in the Serra do Mar escarpment.