AAPG Annual Convention and Exhibition

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New Insight Into the Seismic Architecture of the Pre-Salt Upper Sag Carbonate Depositional System, Brazil


The presentation investigates the seismic stratigraphic architecture of the uppermost pre-salt carbonate sag sequence (Aptian) in Brazil using 3D seismic and publicly available well data. Examples from an isolated carbonate platform on the São Paulo Plateau in the Santos Basin and a land-attached carbonate platform in the Campos Basin will be illustrated throughout the talk. Reservoir rocks comprise laminated boundstone, grainstone and ‘coquina’ facies. Published 2D seismic observations describe a flat parallel-layered package that is concordant with the base of the salt and passively infilling and draping an angular unconformity. In fact, in 3D, the reflection configuration of the uppermost sag sequence reveals the occurrence of broad carbonate platforms (1000's km2, up to 450 m thick) that display two types of margins that commonly developed over the edge of structural highs. 1) A prograding platform margin with dipping clinoforms (4-6°) that is similar to the classic rimmed/barrier profile. This type of margin is constructive and has, in plan view, an arcuate shape protruding basinwards. 2) An apparent aggrading to backstepping escarpment margin type that seems to be the result of the detachment of an evaporitic sequence that was once passing laterally into carbonate facies. In plan view, these margins are more linear and indented by scours (from the salt detachments). The three-dimensional architecture of the sag carbonate depositional system suggests a complex paleogeography.