Aplicação dos métodos geofísicos elétrico e eletromagnético na determinação de unidades sedimentares costeiras tropicais em Bragança, Nordeste do Pará

Abstract

This thesis shows the application of geophysical methodology on several deposition environments of the Planície Costeira Bragantina (Bragantina Coastal Plain), which are being studied in the Mangrove Dynamics and Management (MADAM) Project. The aim of the work was to test geophysics on coastal deposition environment to help the geological understanding of the recent stratigraphic evolution of the Bragantina Coastal Plain. Geophysical measurements were carried out on several morpho-stratigraphic geological units using: (a) the conventional dc resistivity method, through Schlumberger vertical sounding, and (b) the slingram horizontal loop electromagnetic method, with measurements taken for eight frequencies. Vertical electric soundings allowed to know the resistivity distribution in subsurface. The resistivity models could be correlated to geology, but the results were not satisfactory for the depth of investigation as a result of the environment high condutivity. The electromagmetic method was easier and quicker to apply than the resistivity method. Electromagnetic data were analized in profiles and in electromagnetic soudings. The data allowed to stablish geological contacts and geophysical signatures for the coastal deposits of the area.