Avaliação do relevo da Serra da Canastra a partir da análise morfoscópica de sedimentos da bacia hidrográfica do Rio São Francisco da nascente ao entorno (MG)

Abstract

This research explores a laboratory technique also understood as a mineralogical prospecting method, invented by Powers in 1953, which employs three analyses of sediment shapes (Roundness, Sphericity, and Lithology), known as Sedimentary Morphoscopy. The materials were collected from the fluvial channel of the São Francisco River, located in the Serra da Canastra National Park, spanning three municipalities: São Roque de Minas, Piumhi, and Vargem Bonita, from its historical source to its confluence with the Samburá River. Sedimentary Morphoscopy is based on the observation and counting of the vertices belonging to the detrital body. Specifically, for the classification of roundness, attention is given to characteristics ranging from Very Angular (VA), Angular (A), Subangular (SA), Subrounded (SR), Rounded (R), to Very Rounded (VR). In this way, the erosive process occurs through the transport of these sediments, ultimately influencing sphericity, which is classified as high, medium, or low. Lithology plays a crucial role in this technical analysis for recognizing the geological type present at each sampling point within the study area. The objective of this study is to propose a Morphoscopic Index for use in fluvial sediments, based on interpolation using the Kriging method. Sampling point selection was conducted using data processing based on the Hydrologically Consistent Digital Terrain Model (DTM-HC) and, from this, generating results through the Hack Index using QGIS software. The results indicate a variation in the Morphoscopic Index between 0.38 and 0.17 for the 2.0 mm grain size class. This corresponds to the plausible classification of grain shape from the collection point downstream, where the more angular grains (less eroded) correspond to an index of 0.38, while the less angular (highly eroded) grains correspond to an index variation of 0.17. The sedimentary materials followed their normal flow path within the channel over a distance of 9.64 km, demonstrating that they traveled a relatively short distance to exhibit a high proportion of very rounded sediments in the Sedimentary Morphoscopy Index.