--> Salt Tectonics in Central-North Part of the Santos Basin, Brazil, Corrêa, Fernando S.; Chang, Hung K.; Letouzey, Jean, #90100 (2009)

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Salt Tectonics in Central-North Part of the Santos Basin, Brazil

Corrêa, Fernando S.1
 Chang, Hung K.1
 Letouzey, Jean2

1Applied geology, São Paulo State University, Rio Claro, Brazil.
2
Geology-Geochemistry-Geophysics, Institut Français du Petróle,
Rueil-Malmaison, France.

The Santos Basin is a typical passive margin basin encompassing a rift sequence with volcanic, continental siliciclastic and carbonate deposits, followed by thick evaporites marking the transition to the marine drift sequence. This includes Albian carbonates and transgressive-regressive siliciclastic systems with a large Senonian prograding wedge. This study focused on the north-central part of the basin, investigating the geometry and evolution of pre/post salt structures from the shallow to distal portion of the margin. A large SW-NE post-salt antithetic fault system, the Cabo Frio Fault Zone (CFFZ), carries up to 60km displacement on a single fault, resulting from gravity gliding on the salt. This is bounded by two N20-30W trending basement fault systems affecting the base of the salt. Analogue modelling and balanced cross sections were used to investigate the parameters controlling the observed fault systems. Model results suggest that initial salt thickness variations, sediment progradation from the margin, and thermal/loading subsidence, determined the observed gliding pattern. Initial salt thickness seems to have been affected by N20-30W fault systems. The Albian carbonate sequence shows small synthetic and antithetic faults in the proximal part of the margin, resulting in small salt rollers and occasional rafts. During the Senonian, the thick prograding/aggrading sequence caused withdrawal of the underlying salt and salt inflation at the toe of the prograding wedge. This resulted in the antithetic behavior of the CFFZ. Meanwhile, an important synthetic fault system developed in the north, accommodating all regional extension until Paleocene times. Convergent and divergent gliding resulted in a post-salt transfer zone, whose main characteristic is the abrupt change in structural style. The post-salt structural style in the central area enables hydrocarbon accumulation in stratigraphic traps near to progradational onlaps above the Albian Gap and/or eventual turbidites that overtook the mini-basins in front of Cabo Frio Fault Zone. Other typical plays are structural traps associated with anticlines formed by diapirs, such as the Mexilhão field. In the northern area, despite the fact that diapir-associated anticlines are an attractive scenario, the main oil discoveries occur in stratigraphic traps located in turbidite reservoirs above salt diapirs which contain heavy crude oil.

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