Structural Restorations of the Camamu-Almada Passive Margin, Northeastern Brazil: Timing of Movement, Anomalous Uplift, and Thick Sedimentation

Authors: Sean Romito (presenter), Ana Krueger, Paul Mann, University of Houston

The Camamu and Almada passive margin off the northeastern coast of Brazil covers an area of 22,000 km2 and is conjugate to the Gabon basin, offshore western Africa. The margin includes: 1) unrifted Precambrian metamorphic continental crust (40 km-thick); 2) proximal and necked thin (20 km-thick) to ultra-thin (5 km-thick) continental crust; 3) distal undetermined transitional crust (4 to 6 km-thick); and 4) Aptian and younger oceanic crust (6 to 8 km-thick). Fission track studies onshore have shown three periods of post-rift (post-Aptian) uplift during the late Cretaceous, Eocene, and Miocene, but little work has been done in the offshore. We investigate the overall tectonic evolution of both the Camamu and Almada basins by structurally restoring two Kirkchhoff PSDM seismic lines recorded to a depth of 40 km.In both the Camamu and the Almada, a 50 km-wide marginal rift developed throughout the Berrasian to Aptian continental breakup between South America and Africa that localized up to 7 km of pre- and syn-rift sedimentation. Crustal extension on both continental and transitional crust occurred through large-offset, basinward-stepping normal faults. Complex, large salt-withdrawal minibasins, up to 2.5 km-thick, formed immediately following evaporitic deposition, pushing the salt basinward into salt pillows and diapirs. A large, Eocene unconformity eroded down to late-rift Aptian sedimentation and matches the largest uplift event quantified onshore. These results are significant in that they quantify the tectonic history of a triple junction with an atypical rift history of both transtension and transpression throughout the rifting process, and are key in understanding the timing of hydrocarbon migration, trapping mechanisms, and basin modeling.

Bio:

Sean Romito, University of Houston

Sean earned a BSc in Geology from the University of Texas at Dallas, and currently is a PhD candidate and research assistant at the University of Houston, where he develops large-scale tectonic research within the Caribbean plate and the Brazilian passive margin.

He has experience as intern on prospect generation within onshore US basins; field work as a wellsite geologist in the Permian; and intern on geologic risk within the Texas panhandle.

Sean is a member of AAPG and HGS.