Application of morphometric techniques for the delimitation of Borborema Highlands, northeast of Brazil, eastern escarpment from drainage knick-points

Abstract

This article seeks to contribute to the understanding of the dynamics and evolution of landforms, on a regional scale, from the application of morphometric indexes and structural analyzes, in the eastern portion of the Borborema Highlands, Northeast Brazil. The aim of this analysis is to minimize the subjectivities of the classifications and morphological hierarchies in the region in question. We sought to relate the morphology of the eastern sector of Borborema Highlands and the drainages that flow into the Atlantic, thus obtaining a morphometric indicator that would establish, in a quantitative fashion, how this relationship presents itself in the geomorphological landscape, in addition to proposing numerical and morphological thresholds that permitted the delimitation of the Highlands eastern escarpment. For that, the SL/K index was applied, based on HACK (1973) original propositions, subsequently adapted by Seeber and Gornitz (1983), in order to identify sectors of major regional gradient breaks. The Hypsometric Integral values were also obtained in search for correlations between drainage erosion capacity and regional flexural and tectonic influences. Distance measurements between anomalous sectors and base levels on the coast were added. The indexes were applied to the main watersheds that drain the eastern escarpment of the Borborema Highlands: Paraíba (PBW), Goiana (GOW), Capibaribe (CAW), Ipojuca (IPW), Sirinhaém (SIW), Una (UNW) and Mundaú (MUW). It was observed that the sectors identified as regional breaks on relief levels are found at different elevations, varying between 150m and 275m, instead of 200m as traditionally designated by regional literature. It was also observed that on the Transversal Zone, between Patos and Pernambuco lineaments, only one major regional gradient break occurs, whereas to the south of the Pernambuco Shear Zone more than one regional breaks were found, indicating a predominantly flexural influence in the first context and a more brittle in the second. As for the Hypsometric Integral, it was observed that the relationship commonly made between its values and evolutionary stages in the Davisian sense was not found.