The Barreirinhas Basin is an ideal location to study shale-dominated gravity-driven thrusting systems because of the limited areal extent of the deformed areas compared to other areas in the world. Regional seismic reflection profiles across the Barreirinhas Basin on the Brazilian Equatorial margin show two major deepwater fold and thrust belts linked landward to extensional fault systems. Thrust faults are interpreted to be products of shortening caused by gravity driven extension on the continental margin that involve rocks of both the shelf and the slope. Results show two main deformation events during the Cretaceous (between ca. 89 and 84 Ma) and several episodes during the Later Cenozoic (ca. 55–0 Ma). All events were characterized by displacement along a detachment fault linking a landward system of normal faults to a basinward system of folds and thrust faults. The Cretaceous deformation involved a <1.5-km-thick sequence deformed in a 30-km-wide set of listric normal faults (an extensional domain) on the outer continental shelf and upper slope. Those normal listric faults merge seaward into a bed-parallel detachment surface forming a 30-km-wide translational domain and a 30-km-wide zone of imbricate thrust faults (a compressional domain) at the toe of the slope. The Cenozoic structural system involves a thick (over 4 km) sedimentary sequence of Turonian to Miocene age, which cross-cuts the preexisting Cretaceous deformed sequence. The Cretaceous and Cenozoic deformational events formed two discrete bowl-shaped fault systems that are linked at different stratigraphic levels. Plots of displacement versus time show normal and thrust-fault movements during the same time intervals, confirming the link between extension on the continental shelf and compression on the slope. Deformation increased dramatically during the past 10 m.y., with movement on all earlier and some newly formed faults. The increased deformation coincided with tectonic paleogeographic and topographic changes in northern South America during the Late Miocene that led to an increase in sediment supply to the Barreirinhas Basin.
- Received 25 March 2012.
- Revision received 21 August 2012.
- Accepted 5 September 2012.
- © Geological Society of America