2
J.N. Kellogg and W.U. Mohriak
xatiba, Jequitinhonha, Camamu-Almada, Jacuipe, and Sergipe/Alagoas)
along continental margins. A shallow platform with Tertiary sediments
onlapping the Precambrian basement to the west, a deep rift trough filled
with Neocomian to Aptian sediments, and thinner rift sequences from the
slope towards the boundary between continental and oceanic crust characterize sedimentation along the continental margin (Mohriak et al.
1998). Salt tectonics is expressed by thin subhorizontallayers in the proximal regions near the boundary faults or hinge lines that correspond to the
western limits of the rift troughs. Towards the slope and deep waters, salt
and extensional tectonics affecting the overburden dominate the basin
architecture (Mohriak et al. 1995). Gravity-driven compressional tectonics
may be found towards the boundary between the continental and oceanic
crust (Demercian et al. 1993; Cobbold et al. 1995). The thermal phase of
subsidence may result in thick depocenters in some basins (e. g., Santos
and Espirito Santo Basin), whereas other basins are characterized by an
abrupt shelf-edge and by thin sequences overlying tilted rift blocks or
oceanic crust in deep water regions (e.g., Jacuipe Basin).
Physiographic features related to the tectonic framework of the South
Atlantic Ocean are ( 1) the spreading ridge between the South American
and the African continents, located closer to the coastline in the northern
basins of the South American Margin, and (2) segments of the South Atlantic Margin that are about perpendicular to the ridge (Fig. 1). Linear tectonic features are the Walvis Ridge in Africa, the Vito ria-Trindade Ridge in
the Eastern Brazilian Margin, and the Florian6polis Fracture Zone, northwest of the Rio Grande Rise. The continental platform is wide in the southern basins and in the northernmost provinces (in front of the Amazon
Cone), but is rather narrow in the northeastern margin.
Some major tectonic features in the Eastern Brazilian Margin include
the Rio Grande Rise south of the Florian6polis Lineament and the Sao
Paulo Plateau, which is characterized by a large salt diapir province. In the
deep water region, salt tectonics is responsible for mini-basins and evacuation troughs, expressed in the sea bottom as concave irregularities. Basinwards from the outer limit of the salt diapir province, several structures
with a circular outline correspond to volcanic plugs, such as the Almirante
Saldanha Seamount (Fig. 1). Bathymetric and potential field data are helpful to characterize volcanic features, such as the Rio Grande Rise and the
Rio Grande Fracture Zone, in the oceanic domain of the Pelotas Basin
(Gamboa and Rabinowitz 1981). The Florian6polis lineament (north of the
Rio Grande Rise and south of the Sao Paulo Plateau) is the western prolongation of the Rio Grande Fracture Zone. It is aligned in an E-W direction,
and is associated with several igneous plugs (Sao Paulo or Florian6polis
Ridge). The abyssal plain, the continental rise and the platform of the San-
J.N. Kellogg and W.U. Mohriak
xatiba, Jequitinhonha, Camamu-Almada, Jacuipe, and Sergipe/Alagoas)
along continental margins. A shallow platform with Tertiary sediments
onlapping the Precambrian basement to the west, a deep rift trough filled
with Neocomian to Aptian sediments, and thinner rift sequences from the
slope towards the boundary between continental and oceanic crust characterize sedimentation along the continental margin (Mohriak et al.
1998). Salt tectonics is expressed by thin subhorizontallayers in the proximal regions near the boundary faults or hinge lines that correspond to the
western limits of the rift troughs. Towards the slope and deep waters, salt
and extensional tectonics affecting the overburden dominate the basin
architecture (Mohriak et al. 1995). Gravity-driven compressional tectonics
may be found towards the boundary between the continental and oceanic
crust (Demercian et al. 1993; Cobbold et al. 1995). The thermal phase of
subsidence may result in thick depocenters in some basins (e. g., Santos
and Espirito Santo Basin), whereas other basins are characterized by an
abrupt shelf-edge and by thin sequences overlying tilted rift blocks or
oceanic crust in deep water regions (e.g., Jacuipe Basin).
Physiographic features related to the tectonic framework of the South
Atlantic Ocean are ( 1) the spreading ridge between the South American
and the African continents, located closer to the coastline in the northern
basins of the South American Margin, and (2) segments of the South Atlantic Margin that are about perpendicular to the ridge (Fig. 1). Linear tectonic features are the Walvis Ridge in Africa, the Vito ria-Trindade Ridge in
the Eastern Brazilian Margin, and the Florian6polis Fracture Zone, northwest of the Rio Grande Rise. The continental platform is wide in the southern basins and in the northernmost provinces (in front of the Amazon
Cone), but is rather narrow in the northeastern margin.
Some major tectonic features in the Eastern Brazilian Margin include
the Rio Grande Rise south of the Florian6polis Lineament and the Sao
Paulo Plateau, which is characterized by a large salt diapir province. In the
deep water region, salt tectonics is responsible for mini-basins and evacuation troughs, expressed in the sea bottom as concave irregularities. Basinwards from the outer limit of the salt diapir province, several structures
with a circular outline correspond to volcanic plugs, such as the Almirante
Saldanha Seamount (Fig. 1). Bathymetric and potential field data are helpful to characterize volcanic features, such as the Rio Grande Rise and the
Rio Grande Fracture Zone, in the oceanic domain of the Pelotas Basin
(Gamboa and Rabinowitz 1981). The Florian6polis lineament (north of the
Rio Grande Rise and south of the Sao Paulo Plateau) is the western prolongation of the Rio Grande Fracture Zone. It is aligned in an E-W direction,
and is associated with several igneous plugs (Sao Paulo or Florian6polis
Ridge). The abyssal plain, the continental rise and the platform of the San-