10" 



20° 



30° 



SALVADOR 



RIO DE JANEIRO 



PORTO ALEGRE 



Figure 14. — Lamonf-Doherty geophysical cruises on easfern 

 Brazil margin to IVlay 1974. Most coverage within 200 miles 

 of the coast was within last 3 years under I DOE Program. 



10° 



20° 



30° 



SALVADOR 



Salt Edge 



l ll l l l ll l l l l ll Basement Ridge 

 200-Meter Contour 



- PORTO ALEGRE 



35" 



Figure 15. — Boundary of Brazilian diapiric zone and salt 

 deposits. Basement ridge is southeast edge of Sao Paulo 

 plateau. 



Figure 16. — Paleogeographic features of South Atlantic sea 

 floor — Cape- Argentine Basin, Walvis Ridge/ Rio Grande 

 Rise, and Angola-Brazil Basin. 



the southwest and the Niger-Benue at the bight. Off the northern 

 bulge, where fluvial influx was lacking, the sedimentary blanket 

 is dominantly calcareous. Later stages of deposition are repre- 

 sented by cvaporites. Seismic reflection profiles indicate that the 

 Mesozoic-Cenozoic sediment blanket is thickest beneath the 

 outer continental shelf and upper slope. In various areas in- 

 creased sediment thicknesses have been observed and in some 

 instances these have been intruded by salt structures of possible 

 Triassic to Jurassic age. However, salt diapirs appear to be 

 restricted to coastal basins and their extensions on the inner 

 shelf. 



The major changes in the continental margins appear to be 

 related to sea level variations, orogenies in the Tertiary caused 

 by the convergence of the African and Iberian plates, and 

 changes in deep bottom-water circulation. Some coastal defor- 

 mation may have been caused by salt tectonics rather than 

 Tertiary orogenies. 



Southwest Atlantic Margin Bibliography 



Bryan, G. M., N. Kumar, and P. J. M. de Castro. 1972: The 

 North Brazilian ridge and the extension of Equatorial frac- 



33 



