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Evolution of a Pre-, Syn- and Post-Halokinetic Lower to Middle Albian Carbonate Platform Succession, Campos Basin-Brazil

Wright, Wayne 1; Tomasso, Mark 4; Kerans, Charles 2; Sant'Anna, Marilia 3; Machado, Elizabeth C.3; Costa, Fabio O.3; Araujo, Alfredo D.3
1 Jackson School of Geosciences, Bureau of Economic Geology, University of Texas at Austin, Austin, TX.
2 Department of Geological Sciences, University of Texas at Austin, Austin, TX.
3 Petrobras E&P-EXP, Rio de Janeiro, Brazil.
4 Enhanced Oil Recovery Institute, Universiyt of Wyoming, Laramie, WY.

The Albian carbonate play of the South Atlantic is an active exploration target and proven production interval on both the South American and African margins. A new geologic framework was developed for the Campos Basin Albian carbonates using a 150 km by 60 km area with all the available data. A complicated evolution of the Albian platforms is noted with three locally developed platform margins forming during the global 2nd order Lower to Middle Albian transgression. The oldest rimmed-platform margin was situated at the paleo-shelf edge of the underlying sag-phase. This oldest platform margin was strongly controlled by the underlying rift geometry. During subsequent transgression, the Albian margin backstepped and the older platform margin aggraded. The second platform margin was sited on a more proximal high ~15 km landward. After development of the second platform, continued transgression produced up-dip progradational infill of the underfilled deep shelf. Both previous platform successions tie minimally to the youngest and thickest up-dip platform ~25 km further landward. All three successions were affected by halokinesis, but to very different extents. The second margin backbuilding phase displays only minor faulting and translation. The youngest up-dip platform actually formed during evaporite movement and contains both growth-related and passive carbonate fill. The listric faulting of this platform migrated updip resulting in growth-related packages that young updip, but are laterally discontinuous, i.e. isolated sub-platforms. This facies mosaic is encased and associated with aggradational and transgressive deposits associated with the overall backstepping and flooding of the platform. The Albian carbonate model utilizes a concurrently developed unified evaporite deposition and migration model. Evaporite deposition, subsequent movement and timing related to Albian carbonate deposition are all fundamentally linked and often related to the pre-salt basin morphology. Our multistage Albian platform model is distinctly more complex than previous models that imply a continuous ramp segmented and translated post-depositionally by halokinesis.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009