Deep Seismic Survey of Brazilian Passive Basins: The Northern and Northeastern Regions.

This paper describes, in a preliminary form, the new, extensive program of deep seismic reflection lines using special acquisition equipment and processing to 18 s TWT (seconds, two-way travel time) using state-of-the art seismic procedures. This program started in 1989 and aims at comparing crustal structures of different basins along the continental margin of northern and northeastern Brazil, a region with contrasting styles of deformation. The rifting process that resulted in the break-up of Pangea originated both Atlantic-type passive margin basins and sheared passive margin basins, with different crustal geometries and subsidence patterns. The regional seismic lines will also help in the evaluation of geological features that are difficult to characterize using standard petroleum industry seismic surveys. Besides tectonic studies that will focus on the geological interpretation and understanding of basinforming processes, the program will also provide a more reliable visualization of rift-phase structures In the lower part of the sedimentary sequence, both in shallow and deep water regions, and the regional characterization of oceanIc fracture zones, intraplate magmatism and halokinetic/lutokinetic structures.