The study of the Cenozoic deposits of the Bragantine Region has been limited by the scarcity of good outcrops. In order to make available a greater volume of data regarding these deposits, we have carried out a subsurface investigation using ground-penetrating radar (GPR), with the objective of providing a description of the facies characteristics, interpreted from electromagnetic data, stratigraphic correlation and visualization of the spatial distribution of the deposits. The GPR equipment is based on sending electromagnetic waves that register the lithological variations according to physical-chemical properties. In this study, a 200 Mhz monostatic antenna was used, collecting radar profiles in continuous mode and at a constant walking speed. The results obtained by the interpretation and correlation of the radar sections led to the recognition of three stratigraphic units at Praia do Atalaia, named A, B and C, which correlate tentatively, from bottom to top, with the Pirabas, Barreiras and Post Barrier Formations respectively. The 3D correlation of the radar sections showed that unit A consists mainly of mound reflections, and that its thickness is increasing (up to 5m) towards the coastline. Unit B, predominantly with chaotic reflections, is the thickest (up to 10 m), occurring throughout the study area. Unit C, also of wide areal distribution, has a variety of reflections, including parallel, progradational, channel, and chaotic patterns. The 3D visualization also assisted in recognizing reflections attributed to deformational features, such as large folds and faults, which were attributed to tectonic factors. These features are more abundant in the A unit, decreasing in intensity in the B unit, and almost absent in the C unit. Based on these data, it is concluded that GPR represents an efficient tool in the recording of Cenozoic deposits of the Bragantine Zone, providing a 3D visualization of its strata, as well as enabling the detection of tectonic events, which become progressively less intense in younger deposits.
|
