Contrasting Modern Turbidite Systems from the SE Brazil Margin

Cizia M. Hercos¹, Renato O. Kowsmann², Fernando Castro¹, Adriano R. Viana², Simone Schreiner¹, and Luis Claudio Machado^1
1E&P, Petrobras, Macaé, Brazil
²R&D Center/Cenpes/Pdexp, Petrobras, Rio de Janeiro, Brazil

Two canyon-fed modern turbidite systems of the contiguous Campos and Espirito Santo Basins (Almirante Camara and Watu systems) represent contrasting characteristics in terms of structural control, slope morphology and depositional architecture.

The Almirante Camara canyon is carved into a convex slope shaped by the underlying Late Miocene prograding wedge.

Downslope the turbidite system crosses a 130km-wide area deformed by salt tectonics. It is deeply entrenched in a salt-controlled trough, either bounded laterally by salt ridges or follows graben structures produced by diapiric crestal collapse. A 15km-wide lobe complex has developed halfway along its path where subdued salt relief and muddy debris-flow tongues have locally leveled the trough. Turbidite sediments in the trough and in the lobe complex consist of Late Pleistocene/Holocene coarse sands, similar to those of the present outer shelf. The system terminates on the continental rise where strong contour currents occur.

In contrast, the continental slope of Espirito Santo is concave and devoid of seafloor-modifying salt structures. Two mature canyon systems indent the shelf. Numerous gullies carve the steep upper slope between the canyons where a wedge of prodeltaic sediments was deposited. These gullies are filled with algal hash sourced by the outer shelf carbonate platform. The channels at the mouth of the two canyons merge into one channel on the lower continental slope. Coarse-grained sediments (coarse gravel to micaceous fine sand) infill the channels that display prominent levees containing fining-thinning upward sequences of thin-bedded very fine sands and silts composed of mica and terrestrial organic debris. Further downslope, frontal and lateral lobes with associated sediment waves are developed as channel relief and slope gradients diminish.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery