Controle litoestrutural no desenvolvimento de marmitas no leito rochoso do rio Carnaúba, Seridó Geoparque Mundial da Unesco, NE do Brasil

Abstract

Granitic forms resulting from turbulent flow, with hydraulic vortices, characterize the rocky bed of the lower course of the Carnaúba River, in a geosite of the Seridó Geopark, in the Seridó Oriental microregion, Northeast Brazil. These forms constitute a variety of types of potholes that individually represent various stages of evolution, in addition to reflecting the variation in the erosive potential of river flow throughout the Quaternary. In this work it was demonstrated that the efficiency of hydraulic vortices is associated with discontinuity structures and the mineralogical composition of granite facies, with abrasive erosion being responsible for sculpting potholes, with different dimensions and geometries. The incipient potholes gradually deepen and increase in diameter into cylindrical shapes as the vertical turbulent flow increases, then evolving into sigmoidal shapes. The lateral potholes, larger in depth than in width, represent a destructive phase of evolution. From a bibliographical review, fieldwork (quantification and measurements of the potholes), high-resolution photogrammetry and morphostructural analysis of the generated cartographic products, it was possible to establish a correlation between the preferential orientation of the potholes and the direction of the planes of weakness, as well as the classification of potholes by morphometric parameters