DEM-based morphotectonic analysis of a passive continental margin of South America: northern Paraíba Basin, NE Brazil

• Autor(a) principal: Fabio Corrêa Alves
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações do INPE
• Texto Completo: http://urlib.net/sid.inpe.br/mtc-m21c/2021/03.04.13.54

The evolution of the relief in several areas of northeastern Brazil has been increasingly related to tectonics. This is the case of the central and southern sectors of the Paraíba Basin, where basin inversion has been suggested by an abundance of faults and folds in Miocene and late Pleistocene deposits displaying domic relief. A previous geomorphological investigation revealed a similar relief in Quaternary deposits to the north in this basin. However, rock exposures in this sector are scarce, making it difficult to carry out a detailed geological investigation to verify whether the domic relief was also due to basin inversion. This work aimed to investigate if qualitative and quantitative analyses of digital elevation model (DEM) data can explain if the dome at the northern sector of the Paraíba Basin is related to the tectonic inversion in the Late Quaternary. This development used the 1 arc-second DEM of the Shuttle Radar Topography Mission (SRTM) as data source for different applications. The morphological analysis of the domic reliefs was based on drainage networks, swath topographic profiles and geomorphic indices, analysis of drainage divides, as well as detection and study of knickpoints. A methodology for geological discrimination of sedimentary units was developed through geomorphometric regionalization and revealed that the slope, elevation, hypsometric integral, topographic coherence, and valley depth were the most suitable variables to discriminate Miocene from Quaternary units. This method resulted satisfactory overall (80.6 %) and by class accuracies (Post-Barreiras terrain: producers accuracies = 83% and users accuracies = 90.7 %). The morphological analysis of the domic reliefs revealed radial to recurved trellis patterns; tilted and asymmetric sub-basins; and anomalous river profiles. The analysis of drainage divide indicated some mobile segments with direction towards a high-elevation, chevron-shaped plateau related to lithological control by differences in bedrock erodibility. Although this was the cause of some knickpoints detected in the study area, river profiles with slope-break knickpoints, and steep channels with high incision and elevation values recorded mostly on homogeneous lithology were more likely related to tectonics. Statistical analysis suggested that the lowest knickpoints in each river were formed during a single tectonic event not older than the Miocene. The geomorphometric evidence of tectonic control, added to the domic relief, suggested that the northern Paraíba Basin might have also been affected by the basin inversion that produced the folding of correlated strata in the central and southern sectors of the Paraíba Basin. This event is correlated with the Andean Quechuan tectonic phase. Therefore, the most likely is that a pulse of rock upwarping could have triggered the lowering of river base levels and the propagation of knickpoints upstream river profiles, probably due to intraplate compression by the combined pushes of the Mid-Atlantic Ridge (towards the W) and the Andes (towards the E), as suggested for other areas in NE Brazil. These results corroborate the proposal that the passive margin of the South American plate remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous.