Depositional and Architectural Models for the Development of the Lower to Middle Albian Carbonate Succession, Campos Basin-Brazil
Wayne R. Wright1, Mark Tomasso1, Charles Kerans2, Marilia V. Sant' Anna3, Elizabeth Machado3, Fabio Costa3, and Alfredo Arau'jo3
1Bureau of Economic Geology, Jackson School of Geosciences-University of Texas at Austin, Austin, TX
2Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX
3Petrobras E&P-EXP, Rio de Janeiro, Brazil
The Albian carbonate play of the Campos Basin is an active exploration target with early success. A new geologic framework was developed for the 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. This Albian carbonate model is decidedly more complex than those previous implying a continuous ramp segmented and translated post-depositionally by halokinesis.
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