Contribuições para a interpretação da evolução geomorfológica do Baixo Jaguaribe/CE

Abstract

This work aims to propose an analysis of the elements responsible for the dynamics of the geomorphological evolution of the Low Jaguaribe Valley/CE. The present study starts from the structural processes that sustain the relief, comprising the phases of deposition and incision, formation of the valley and current evolution of the area. The evaluation of the crystalline basement, the morphology of the terraces, the relation between the canal and the escarpment of the Potiguar basin and the evolutionary marks from the paleochannel records are considered. The applied methodology is based on stratigraphic sections, in the total of 10 sections realized in the city of Russas / CE, application of multispectral index, as NDVI (Normalized Difference Vegetation Index) to evaluate the vegetation present in the paleochannels, basement profiles through well depths data and evaluation of the channel and escarpment morphology of the Potiguar basin. Based on the data obtained, the Jaguaribe valley shows irregularities in the basement, which may have influenced the implementation of the River valley. The results indicate that in the evolution of the Jaguaribe valley, the basement constituted a significant factor, as well as the climatic changes of the Cenozoic and the alterations of the base level that defined the episodes of deposition and incision in the area. On a regional scale, the geomorphology of the valley presents four phases: 1) formation of a planning surface with inselbergs, 2) deposition of the Potiguar basin in the Cretaceous, through the opening of the Atlantic Ocean, lateral retreat by circumundation and exhuming the granite inselbergs 3) deposition of the Barreiras and Faceira Formation, marked by the quaternary climatic changes, defined by the phases of deposition and incision and 4) current evolution marked by the direction of channel migration. Nowadays, the evolution of the channel follows east direction; the analysis indicate that through three elements one can observe that direction: 1) terraces to the west of the channel, constituting a geomorphological indicator of the direction of the migration of the drainage, 2) expressivity of paleochannels to the west of the current channel and 3) sense of layers trimming of the Potiguar basin, towards the rift, to the east. It intends to contribute to the regional geomorphology and to provide greater details of the active processes in the evolution of Low Jaguaribe Valley.