4
J.N. Kellogg and W.U. Mohriak
tos and Campos basins are crossed by a major NW-trending lineament that
extends along the Jean Charcot seamounts, and advances onland towards
the Cabo Frio region (Souza et al. 1993).
The southeastern segment of the Brazilian margin (Fig. 1) is characterized by several E-W inflections of the coastline along Rio de Janeiro
State. This province (Cabo Frio region between the Campos and Santos
basins) is characterized by the deflection of the pre-Aptian hinge line from
the more general NE trend, and by widespread post-rift volcanic activity
(Mohriak et al.1995). The offshore and onland alkaline plugs are align,ed in
an E-W direction, from Po
A major tectonic feature in the eastern Brazilian Margin is the Vit6riaTrindade Ridge, anE-W lineament probably associated with a hot-spot
(Fig. 1). There are several submarine seamounts adjacent to the Abrolhos
Volcanic Complex, and towards the abyssal plain, volcanic islands may
reach the seafloor (e.g, Trindade and Martin Vaz Islands). Other volcanic
seamounts are aligned along E-Wand NW-SE directions, off Bahia, Sergipe, and Ala go as states. The southern portions of the Espirito Santo and the
Cumuruxatiba basins correspond to reentrants of the bathymetry (concavities from sea to land), approximately westward from the prolongation of
the volcanic features in the oceanic crust. Dating (K-Ar) of the Abrolhos
and Royal Charlotte volcanic complexes indicates that they contain mainly
Tertiary basaltic rocks, which intruded into the continental platform and
extruded above previously deposited sedimentary rocks, masking the possible occurrence of salt layers above the rift.
Northeastern Brazil is characterized by one large onshore rift (Reconcavo-Tucano-Jatoba Rift System), which failed to develop a thermal phase of
subsidence, and by the elongated Jacuipe and Sergipe-Alagoas basins,
which correspond to rifts that evolved as continental margin sedimentary
basins (Ojeda 1982; Matos 1992). The platform in the northeastern margin
is characterized by an abrupt shelf-break and by a continental-oceanic
crust boundary very close to the shelf-edge (Mohriak et al. 1998).
2.2 Structural and Stratigraphic Evolution
The tectonic evolution of the basins can be divided into pre-rift, rift,
protoceanic and continental margin phases (Asmus and Ponte 1973; Ponte
and Asmus 1978). Stratigraphic divisions, which take tectonic phases into
account, establish four megasequences (pre-rift, continental, transitional,
and marine) that are normally separated by erosional unconformities. The
J.N. Kellogg and W.U. Mohriak
tos and Campos basins are crossed by a major NW-trending lineament that
extends along the Jean Charcot seamounts, and advances onland towards
the Cabo Frio region (Souza et al. 1993).
The southeastern segment of the Brazilian margin (Fig. 1) is characterized by several E-W inflections of the coastline along Rio de Janeiro
State. This province (Cabo Frio region between the Campos and Santos
basins) is characterized by the deflection of the pre-Aptian hinge line from
the more general NE trend, and by widespread post-rift volcanic activity
(Mohriak et al.1995). The offshore and onland alkaline plugs are align,ed in
an E-W direction, from Po
A major tectonic feature in the eastern Brazilian Margin is the Vit6riaTrindade Ridge, anE-W lineament probably associated with a hot-spot
(Fig. 1). There are several submarine seamounts adjacent to the Abrolhos
Volcanic Complex, and towards the abyssal plain, volcanic islands may
reach the seafloor (e.g, Trindade and Martin Vaz Islands). Other volcanic
seamounts are aligned along E-Wand NW-SE directions, off Bahia, Sergipe, and Ala go as states. The southern portions of the Espirito Santo and the
Cumuruxatiba basins correspond to reentrants of the bathymetry (concavities from sea to land), approximately westward from the prolongation of
the volcanic features in the oceanic crust. Dating (K-Ar) of the Abrolhos
and Royal Charlotte volcanic complexes indicates that they contain mainly
Tertiary basaltic rocks, which intruded into the continental platform and
extruded above previously deposited sedimentary rocks, masking the possible occurrence of salt layers above the rift.
Northeastern Brazil is characterized by one large onshore rift (Reconcavo-Tucano-Jatoba Rift System), which failed to develop a thermal phase of
subsidence, and by the elongated Jacuipe and Sergipe-Alagoas basins,
which correspond to rifts that evolved as continental margin sedimentary
basins (Ojeda 1982; Matos 1992). The platform in the northeastern margin
is characterized by an abrupt shelf-break and by a continental-oceanic
crust boundary very close to the shelf-edge (Mohriak et al. 1998).
2.2 Structural and Stratigraphic Evolution
The tectonic evolution of the basins can be divided into pre-rift, rift,
protoceanic and continental margin phases (Asmus and Ponte 1973; Ponte
and Asmus 1978). Stratigraphic divisions, which take tectonic phases into
account, establish four megasequences (pre-rift, continental, transitional,
and marine) that are normally separated by erosional unconformities. The