Mapeamento geológico das Folhas SB 22-X-D-II-4-NO e SB 22-XD-II-4-NE

Abstract

The basic geological mapping on Folha Marabá (SB 22-X-D) aims to contribute to the region’s geology and to ascertain the reliability of the bibliographical data available to this date. Furthermore, it aims to propose a lithostratigraphic map of the studied area and to build an urban risk/planning map up the flood plains of the Tocantins and Araguaia rivers at the surroundings of the municipality of Esperantina – TO. Drainage maps, relief/drainage lineaments, homological zones, photo geological/geological maps and profiles using SRTM (software ARCGIS 9.3) images were made applying Soares & Fiori principles and fieldwork. Six homologous zones and two stratigraphic units were individualized. Zone I has an altimetry range between 105 – 120m, presents low roughness, it’s characterized by stratified oligo-miocenic sandstones, siltstones and mudstones from Barreiras formation belonging to Mocajuba sub-basin. Zone II presents an altimetry range between 100 – 105m and zones III, IV, V and VI belong to the same altimetric limit, between 95 to 100m, with its roughness ranging from moderate to high, they represent the quaternary semi-consolidated sediments of the Tocantins and Araguaia rivers’ flood plains. Zones I, II, III, V and VI possess dendritic drainage, however, zone IV presents an anastomosed drainage. The relief and drainage lineaments presents preferential directions NE-SW and, subordinately, NW-SE. The Tocantins and Araguaia rivers’ flood plains probably originated from tectonic events related to block caving, as the older plains are located on the farthest portion of the rails of the main channels of the Tocantins and Araguaia rivers. Besides that, the meeting point of the rivers, which forms the Bico do Papagaio, may be influencing, through sedimentary supply, different homologous zones in the same altimetric range. From the base to the top, stratified lithified sandstone from Parnaíba basin, sandstone/siltstone/mudstone from Barreiras formation of Mocajuba sub-basin and unconsolidated sediments from Tocantins-Araguaia hydrographic basin represents the stratigraphic piling. It’s suggested that the urban expansion of the municipality of Esperantina – TO and Bom Jesus do Tocantins – PA and São Pedro da Água Branca-MA neighbor municipalities are to be delimitated on the area corresponding to the homologous zones I and II, which are distant from the current flood areas, relative to the homolohous zones III, IV and V. This way, the population would be away from possible accidents of natural origins and of anthropic actions occasioned by urban planning problems, like floods, which are common in the Tocantins and Araguaia’s high river flow periods.