The Tectonic and Geological Environment of Coastal South America
5
pre-rift megasequence occurs only in the northeastern margin (both onshore and offshore) and is subdivided into Paleozoic and Jurassic supersequences. The marine megasequence may be divided into restricted and
open marine supersequences. The transitional megasequence is characterized by salt tectonics, which imparts one of the most important controls
on the evolution of all the sedimentary basins along the Eastern Brazilian
Margin, with the exception of the Pelotas Basin (Chang et al. 1992). The
sedimentary fill and structural styles of the basins along the Brazilian Margin are intrinsically related to basement-involved rift phases and basement-detached drift phases that were created during the separation of the
South American and African tectonic plates.
The rift phase in most Eastern Atlantic sedimentary basins is characterized by a mosaic of N-S or NE/SW down-stepping synthetic faults, sometimes interrupted by antithetic faults creating a network of half-grabens
with internal highs. E-W or NW-SE transfer fault systems accommodate
the different stretching rates between the basins. The drift phase started
when the stretching and rifting of the continental crust ceased and accretion of oceanic crust began. Salt movements, affecting the overlying rocks,
created a series of listric growth faults in the evacuation zones, intraslope
sub-basins surrounded by piercing salt domes, salt walls, and thrust faults.
The distribution of the salt along the Brazilian and African margins is very
irregular. Huge diapirs and salt walls (e. g., Santos and Campos offshore
Brazil, Kwanza and Gabon offshore Africa) characterize some basins
whereas others have much smaller quantities of evaporites (e. g., SergipeAlagoas in Brazil, Rio Muni and Douala in Africa). Lithospheric stretching
and rifting ceased in the Eastern Brazilian Margin with the onset of seafloor spreading in the early to middle Cretaceous (probably by late Aptian
-early Albian), but there are some indications (e.g., offsets at the base of
the Aptian salt and other younger reflectors) of localized reactivations of
basement-involved normal faults in the Sergipe-Alagoas and Jacuipe
basins up to late Cretaceous time. In these basins, the transition between
the continental and marine environments is characterized by recurrent
tectonic activity, with concomitant magmatic activity.
The drift phase is characterized by a shallow-water Albian to Cenomanian carbonate platform in most basins, and the Upper Cretaceous is characterized by a major transgression which culminates with drowning of these
platforms and predominance of bathyal environments (Chang et al. 1992;
Rangel et al. 1994).As a consequence of thermal subsidence and the initiation of oceanic spreading in the South Atlantic, bathymetric depths increased
progressively. The late Cretaceous/early Tertiary deepwater sedimentary
environments predominated in a number of basins (e.g., Campos Basin).
This time interval (Cenomanian to Paleocene) is characterized by predomi-
5
pre-rift megasequence occurs only in the northeastern margin (both onshore and offshore) and is subdivided into Paleozoic and Jurassic supersequences. The marine megasequence may be divided into restricted and
open marine supersequences. The transitional megasequence is characterized by salt tectonics, which imparts one of the most important controls
on the evolution of all the sedimentary basins along the Eastern Brazilian
Margin, with the exception of the Pelotas Basin (Chang et al. 1992). The
sedimentary fill and structural styles of the basins along the Brazilian Margin are intrinsically related to basement-involved rift phases and basement-detached drift phases that were created during the separation of the
South American and African tectonic plates.
The rift phase in most Eastern Atlantic sedimentary basins is characterized by a mosaic of N-S or NE/SW down-stepping synthetic faults, sometimes interrupted by antithetic faults creating a network of half-grabens
with internal highs. E-W or NW-SE transfer fault systems accommodate
the different stretching rates between the basins. The drift phase started
when the stretching and rifting of the continental crust ceased and accretion of oceanic crust began. Salt movements, affecting the overlying rocks,
created a series of listric growth faults in the evacuation zones, intraslope
sub-basins surrounded by piercing salt domes, salt walls, and thrust faults.
The distribution of the salt along the Brazilian and African margins is very
irregular. Huge diapirs and salt walls (e. g., Santos and Campos offshore
Brazil, Kwanza and Gabon offshore Africa) characterize some basins
whereas others have much smaller quantities of evaporites (e. g., SergipeAlagoas in Brazil, Rio Muni and Douala in Africa). Lithospheric stretching
and rifting ceased in the Eastern Brazilian Margin with the onset of seafloor spreading in the early to middle Cretaceous (probably by late Aptian
-early Albian), but there are some indications (e.g., offsets at the base of
the Aptian salt and other younger reflectors) of localized reactivations of
basement-involved normal faults in the Sergipe-Alagoas and Jacuipe
basins up to late Cretaceous time. In these basins, the transition between
the continental and marine environments is characterized by recurrent
tectonic activity, with concomitant magmatic activity.
The drift phase is characterized by a shallow-water Albian to Cenomanian carbonate platform in most basins, and the Upper Cretaceous is characterized by a major transgression which culminates with drowning of these
platforms and predominance of bathyal environments (Chang et al. 1992;
Rangel et al. 1994).As a consequence of thermal subsidence and the initiation of oceanic spreading in the South Atlantic, bathymetric depths increased
progressively. The late Cretaceous/early Tertiary deepwater sedimentary
environments predominated in a number of basins (e.g., Campos Basin).
This time interval (Cenomanian to Paleocene) is characterized by predomi-