Pergamon zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. Geodynomics Vol. 20, No. 4, 515-539, 1995 pp. zyxwvutsrqponm 0264- 3707(95)00024- O Copyright @ 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0264-3707/95 $9.50 + 0.00 DEEP SEISMIC REFLECTION PROFILING OF SEDIMENTARY BASINS OFFSHORE BRAZIL: GEOLOGICAL OBJECTIVES AND PRELIMINARY RESULTS IN THE SERGIPE BASIN WEBSTER UEIPASS MOHRIAK,’ JO& HENRIQUE LIRA RABELO,’ RENATO DARROS DE MATO!? and MOZART C. DE BARROS’ ’ Petrbleo Brasileiro S.A., Departamento de Explora@o, SUTEX, Divisio de Tecnologia de Interpreta+o, Av. Chile, 65, s. 1305, 20.031-170 Rio de Janeiro, RJ, Brazil, ‘Petr6leo Brasileiro S.A., Departamento de Explora@o, DENEST, DivisHo Regional de Interpretaqio Explorat&ia, Aracajri, SE, Brazil (Received 29 December 1994; accepted in revised form 29 M ay 1995) Abstract-The first deep seismic reflection profiles offshore Brazil were acquired in Campos Basin and processed to 10 s TWT in 1984. Starting in 1989, Petrob& acquired an extensive data set of deep seismic profiles using special acquisition equipment capable of effectively penetrating through the sedimentary layers and imaging the whole crustal architecture. These deep (18 s TWT) seismic reflection profiles extend across the Atlantic-type marginal basins, from the platform to the deep- water province, presently considered frontier regions for petroleum exploration. This work addresses the geological objectives of a deep seismic profile in the Sergipe Basin and discusses the results obtained by integrating regional seismic, gravity and magnetic data. When combined, these data provide evidence that deep seismic reflectors observed in the Sergipe Basin are related to intracrustal-upper mantle structures rather than sedimentary features. The deep seismic reflection profile in the Sergipe Basin also suggests that, rather than a non-volcanic passive margin, the deep- water extension of this basin is marked by several magmatic structures, including thick wedges of seaward-dipping reflectors and volcanic plugs. These magmatic features are associated with basin- forming processes resulting from lithospheric extension during the breakup of Gondwana in the Early Cretaceous and subsequent emplacement of oceanic crust. These results are compared to the crustal scale structures observed in the Campos Basin, in the southeastern margin of Brazil. The interpretation of the deep structure of these basins indicates that final separation between the South American and African plates formed passive margins characterized by different patterns of crustal attenuation underlying the rift blocks. SEISMIC REFLECTION PROFILING, INTRODUCTION The geological interpretation of sedimentary basins offshore Brazil advanced immensely in the late 1970s and early ’80s with the aquisition, processing and interpretation of regional seismic profiles in the deep-water region of the South Atlantic. These petroleum exploration programs led to the discovery of the giant oil fields in the Campos Basin (Barros, 1980; Guardado et al., 1989; Mohriak zyxwvutsrqp et al., 1990b). However, the deeper portions of several sedimentary basins were 515