Kinematics of the Barreirinhas Basin Deep-water Fold and Thrust Belt, Brazilian Equatorial Margin
Structural Geologist, HRT America
Deepwater fold and thrust belts linked to gravity-driven shelfal extension characterize large sectors of the Brazilian Equatorial margin. The Barreirinhas Basin is dominated by two brief deformation events during the Cretaceous (ca. 89 and 84 Ma) and episodic deformation in the Cenozoic (ca. 55–0 Ma). Both systems are linked landward to extensional fault systems.
Cretaceous deformation involved a < 1.5-km-thick sequence. A 30-km-wide zone of listric normal faults on the continental shelf and upper slope merges seaward into a bed-parallel detachment surface forming a 30-km-wide translational domain, in turn linked to a 30-km-wide zone of imbricate thrust faults at the toe of slope.
The Cenozoic fault system cuts through over 4 km of Cretaceous and Cenozoic bedding and Cretaceous structures, forming bowl-shaped "mega-slumps" 35 km in down-dip extent. Extensional faulting propagated landward so that the location of the shelf break migrated landward. Thrust faults simultaneously raised the elevation of the lower slope; the interaction maintained the slope gradient below 5 degrees. Finite fault motion rates demonstrate that fault motion for shortening and extension operated in tandem, with extension on the shelf directly accommodated by shortening at the toe of slope.
Strain increased dramatically during the last 10 m.y, coincident with increased sedimentation supply to the basin, suggesting that rapid sedimentation is likely the driving mechanism for deformation. Understanding the complex interaction of source rock burial rate, strain style and rate, and timing of hydrocarbon expulsion is critical to successful exploration.
AAPG Search and Discovery Article #90203 © AAPG Geoscience Technology Workshop, Trinidad and Tobago Deep Horizon and Deep Water Frontier Exploration in Latin America and the Caribbean, March 9-11, 2014, Port of Spain, Trinidad