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Lopez-Gamundi, Oscar, and Roberto Barragan, 2012, Structural framework of Lower Cretaceous half grabens in the presalt section of the southeastern continental margin of Brazil, in D. Gao, ed., Tectonics and sedimentation: Implications for petroleum systems: AAPG Memoir 100, p.143158.


Copyright copy2012 by The American Association of Petroleum Geologists.

Structural Framework of Lower Cretaceous Half Grabens in the Presalt Section of the Southeastern Continental Margin of Brazil

Oscar Lopez-Gamundi,1 Roberto Barragan2

1CampC Energy, Carrera 4 72-35, Bogota, Columbia (e-mail: [email protected])
2Hess Exploration Malaysia, 207 Jalan Tun Razak, 5400, Kuala Lumpur, Malaysia (e-mail: [email protected])


We thank the management of Hess for authorizing the publication of this contribution. The discussions with Hess colleagues Thomas Melgaard and Willy Barreda provided insight into the details of the presalt geology of offshore Brazil. The publication of depth seismic reflection data was kindly authorized by TGS-NOPEC Geophysical Company. Time seismic reflection data are courtesy of Petroleum Geo-Services (PGS). Ian Clark and an anonymous reviewer provided peer reviews that helped improve the quality and presentation of the paper.


Recently acquired and processed prestack depth-migrated seismic data have helped to identify the key elements of the asymmetric Lower Cretaceous half grabens in the presalt, synrift-to-postrift transitional (sag) section of the Greater Campos Basin (Santos, Campos, and Espirito Santo basins), offshore Brazil. Evidence of such a structural configuration is provided by seismic reflection geometries, such as fanning (strongly divergent internal configuration) on fault borders, thinning (convergent internal configuration), and onlap onto flexural margins. Moreover, compaction synclines over basement footwall cutoff points have been identified. In poorly imaged areas, the termination of the divergent seismic configuration can be used to place the master fault of the half graben. Differential compaction at half-graben border fault margins caused by the contrasting nature of rift-fills and adjacent basement highs is postulated to have been a critical factor for the creation of counterregional dips necessary to form structural four-way closures at the sag level. Although the sag sequence extends beyond the underlying rift fill, commonly onlapping or draping over the basement, the key risk in these types of traps is the possibility that the overlying salt layer may rest directly on the basement. Fault-plane reflections indicate the predominance of planar fault-plane geometries. This is consistent with the absence of rollover anticlines or hanging-wall antiforms, which are a direct function of nonplanar listric faults. The final configuration of the traps may also be modified by important basin-scale factors (i.e., uplift resulting from magmatic underplating in the Santos Basin).

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