Erosion Patterns and Sediment Suply From The Sul-Rio-Grandense Shield, Brazil
Event - XVIII Reunión Argentina de Sedimentología
Abstract
Landscape evolution models (LEMs) provide estimations of erosion magnitudes and sediment transport to adjacent sedimentary basins. Using such models, these processes are simulated to unveil patterns in topography adjustments and approximate the amount of sediment produced in a source area. Under the Stream Power Erosion Law, a range of diverse erodibility resulting from different lithological and structural frameworks shapes landscapes and consequently produces varied bulk volumes of sediments. Therefore, we propose to outline the heterogeneities in erodibility on the Sul-Rio-Grandese Shield (SRGS) in Southern Brazil, as it is a major component for the shield landscape evolution and sediment production to the Pelotas Basin. In the SRGS, crystalline basement rocks under four major river systems (Camaquã, Turuçu, Piratini, and Jaguarão Rivers) were studied for their contrast in each lithological and structural context. Field measurements of rock strength using a Schmidt hammer were made and combined with extracted data from digital elevation models on river channel steepness to highlight the contrast in rock erodibility. The measured data shows rocks of greater resistance with hardness values up to 80, contrasting with weaker rocks of lower values around 45 and 50. Additionally, the data was applied to a landscape evolution model to simulate and calculate the amount of sediment produced by each river system. The results show patterns of mature erosion stages where faulted igneous and metamorphic rocks have lower rock strength compared to early stages in non-faulted igneous and metamorphic rocks with high hardness values. Longitudinal profiles and erosion maps show the topographic evolution within each basin and the migration of drainage divides within the studied area. Moreover, the erosion migration also generates knickpoints due to differences in rock resistance, emphasizing different stages of denudation. The simulation of each drainage basin's evolution shows major contrasts in sediment production that correlate with the erodibility of underlying rocks. The dynamic nature of the drainage systems, influenced by erosion through different rock types and their structural configuration within the area, has important implications for understanding the generation and evolutionary behavior of fluvial erosion and sediment production. Furthermore, it provides valuable insights into interpreting the geomorphology and downstream sediment supply to the Pelotas Basin.
