--> Restorations of the Santos Basin, Brazil: Basement Fault Activity from Rifting to Passive Margin, Sanders, Carlo; Sciamanna, Simone; Serrano, Ana, #90100 (2009)

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Restorations of the Santos Basin, Brazil: Basement Fault Activity from Rifting to Passive Margin

Sanders, Carlo1
 Sciamanna, Simone1
 Serrano, Ana2

1Exploration, Repsol Brasil, Rio de Janeiro, Brazil.
2
Statoil-Hydro
Brazil, Rio de Janeiro, Brazil.

The
Santos basin in Brazil consists of a passive margin setting underlain by thick Aptian salt deposits and an Early Cretaceous rift basin that is home to some of the worlds largest recent oil discoveries. Because the tectonic history of the basin is still subject to debate, we restored three regional sections based on 2D and 3D seismic data spanning the entire width of the Santos Basin. The restorations are integrated with sediment decompaction and flexural isostasy to control paleo-topography, accommodation space and timing and location of main tectonic events. Specific methods were used to identify basement fault activity. The results are presented in a tectonic history of the basin.

Early Cretaceous rifting caused only modest upper crustal stretching (B=1.2). Individual rift faults initially show phases of pulsating rift activity, but activity gradually decreases and concentrates along a few faults at the end of the rifting. Faulting is still widespread during the so-called “sag” phase (Early Aptian), defining local paleo-topography and the depositional environment for the carbonates of the giant “pre-salt” petroleum reservoirs.

Basement fault activity concentrates in a few zones during the following Aptian salt deposition, and causes sub basins with substantial thickness variations. The “end of rifting” is thus not a uniform event, neither in time nor space. A few basement faults are still active during the Albian carbonate deposition, forming topography above the salt, and suggest that part of the “Albian gap” can be explained as a non-deposition feature. It forms an alternative to the popular rafting concept that displays some mechanical and regional improbabilities.

During the early passive margin phase, sediment deposition is limited to the near shore and bounded by a salt high at the base of the slope that gradually progrades towards the east until it is halted by a basement buttress.

During the Santonian, renewed basement (re-)activation takes place along a few major faults causing tilting and sliding above the salt. This coincides with large influx of coarse clastic deposits in the basin and widespread volcanism. Younger sediments finally progradate over the buttress towards the East and initiate local mini basins and salt diapirs. These salt structures remain in place above their respective basement “roots”.

Periodical basement activity is observed until present day and ultimately controlled much of the overall tectonic framework of the basin.

AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil