Analysis of passive margins by balancing cross sections: theoretical discussion and application to the Campos Basin

Abstract

The understanding of the relation between salt tectonics and sedimentation represents an important step in the investigation of many sections of passive margin. The mapping of the sedimentary facies that make up the depositional sequences affected by halokinesis, associated with the description of the tectonic structures and the quantification of the deforming processes, constitute a new way ofunderstanding the evolution of these regions, presently showing great exploration interest. Within this context the palinspastic restoration of transverse geological sections constitutes an adequate tool for the resolution of these problems. The restoration technique has as its objective to test the geometrical confidence leveI of an interpreted tectonic-stratigraphic section and to determine palinspastic surfaces. The method consists in recognizing the registered deformation in the geological section, verifying if there is mess balance and coherence between the interpreted and restored sections. The procedure requires the application of computer software based on specific algorithms in order to a/low complex graphical transformations. During the analytical process the layers are decompated, and the fault blocks are treated as modules which must be.retrodeformed to the prévious depositional situation defined by the interpreter. Restoration of three geological sections are described in the Campos Basin, in the eastern coast of Brazil, whose original sections were interpreted from we/ls and seismic sections depth converted. During the analysis, the RECON 2.0 (Lana and Bender, 1992) balancing program was used, which is based on interactive graphical transformations that represent geological processes, including translation, rotation, and simple shear of faulted blocks.