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Abstract

This work describes the interaction between tectonic and stratigraphic/sedimentary processes during deposition of the huge deep-water systems containing sandstones reservoirs in the Campos basin (offshore Brazil). These sandstones established a major oil province with about 10 billion barrels of proven recoverable hydrocarbons. An integrated approach, including quantitative petrography, facies architecture, sequence stratigraphy, and tectonic-structural analysis indicates a complex evolution, rather than the previous scenario of gravitational salt tectonics and eustatic base level fluctuations that implies the lowstand paradigm for deep-water sandstones. The marine phase of deposition in the Campos Basin was far from a steady-state, passive margin model.

In general, the main deep-water sand depocenters in the divergent margin phase of the Campos basin were controlled by basement reactivations that triggered successive episodes of salt tectonics, which in turn controlled sand distribution and facies architecture. The first event caused the complete destruction of the Albian carbonate shelf and the formation of a mega-slope during the Late Cretaceous. As a consequence, the main deep-water sand systems show an increase in petrographical immaturity, which corresponds to tectonic reactivation of the basement as they systematically filled and spilled out of depocenters created by basement highs in the offshore Campos basin. The magmatism and dynamic uplift caused by movement of the basin above a thermal anomaly in the mantle are indicated by the anomalously high volcanic contributions in deep-water sandstones, particularly during the Maastrichtian.

Tectonic, magmatic, and structural (upstream) controls on deep-water systems were subdued after the Eocene. Since the late Oligocene, when the shelf was fully reestablished, the classic lowstand systems tract approach predicts quite well the prevalent eustatic processes controlling (downstream control) deposition of deep-water sandstones in the Campos Basin.

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