558
stages of both aborted rifts (without crustal separation) and fully developed rifts (followed by sea floor
spreading) lasted from about ~50 Ma to more than
200Ma.
Along the margins of the Atlantic and other ocean
basins resulting from the breakup of Pangea, the synrift sediments are mostly of Triassie to Jurassie age;
some are older and/or younger. They consist predominantly of fluvial sediments (often red beds), lake
deposits, evaporites, and some shallow-marine sediments of variable thickness and lirnited extent. Volcanic material may be present in large quantities. Paleozoic and Tertiary syn-rift sediment successions of
passive continental margins are commonly characterized by fluvial, lacustrine, and. shallow-marine sequences. Uplift and erosion of the rift shoulders at
passive margins mayaiso affect former shelf sediments and lead in the basin to offlapping
(prograding) stratal patterns. When the rift shoulders
are largely eroded and subsidence of the shelf continues due to crustal cooling, the associated sediments
begin to onlap (Van BaIen et al. 1995).
In the post-rift phase of the Atlantic, subsidence
continued at a slowing rate. Decreasing siliciclastic
sediment supply led to a fining-upward trend and a
shift from hernipelagic to pelagic deposits. The shelf
sediments of the post-breakup, mature ocean phase in
the late Cretaceous and Tertiary were dominated by
pelagic carbonates or silty clays. The major factors
now controlling marine sediments were long-term
climatic change, faunal evolution, oceanic
thermohaline eirculation, variations in the carbonate
produetion, and eustatie sea-Ievel variations.
Other Rifted Continental Margins
A eomplex tectonic and stratigraphie history sirnilar
to that ofthe North Atlantic is also known from other
passive eontinental margins. They show repeated
regional rifting episodes and possibly more than one
phase of breakup, for example the Campos basin of
Brazil and the Gabon basin of West Africa (Edwards
and Santogrossi 1990). In northwestern Australia
Fig. 12.9. a Position of Ieeland hot spot (circle; mantle plume) after the onset of sea-floor spreading in
the North Atlantie (magnetie line M 23) and voleanic
margin along East Greenland. Ds, Davis Strait; VP,
V 0ring Plateau; RB, Ratton Bank. (After White
1989). b Physiographie elements of the NorwegianGreenland Sea, generalized. Note the variable width
of the eontinental margin (shelt), continental platform of the Barents shelf, submarine plateaus, and
rift structures along the eastern margin. (After
Birkenmajer 1981; for more details see Eldholm et
al. 1989). c Conjugate margins in the North Atlantie
during the late Jurassie (magnetic line M-25) and
major Mesozoic-Cenozoie marginal basins. (Jansa
Chapter 12 Basin Evolution and Sediments
several deposWonal wedges were built out into the
evolving marginal basin (Boote and Kirk 1989).
Rifting between South Africa and South America
started as early as in the Permo-Carboniferous, i.e.
160 Ma prior to the onset of drifting and formation
of the South Atlantic ocean. The orientation of Triassie eontinental rifts (obliquely to the axis of the
South Atlantie) was still dictated by crustal structures
older than the Atlantic rift zone (a kind of orogenie
eollapse), whereas the younger rift zones (since the
rniddle Jurassie) followed the Atlantic trend (Fig.
12.ge; Uliana et al. 1989; Tankard et al. 1995). The
long his tory of the South Atlantic rift zone basin is
reflected by three mega-sequences, separated by unconforrnities and interrupted by extensive flood basalts in the Triassie, Jurassie and early Cretaceous.
The Permo-Carboniferous Karoo supergroup in Namibia is
characterized by glacial, fluvial, lacustrine and deltaic sediments. Continental Triassie and Jurassie sediments with
intercalated flood basalts reflect thermal uplift of the rift
shoulder and a permanently overfilled rift basin. Volcanic
activity continued in the lower Cretaceous when the South
Atlantic progressively opened from south to north
(Stollhofen 1999; see also Clemson et al. 1997).
The pre-drift separation of Madagascar from East Africa
also took place during a long time span from the early
Permian to the middle Jurassie (Wopfuer 1993; Hankel
1994). Here, the evolution ofthe rifted margin was affected
by middle Triassie uplift and erosion subdiving the basin
fills into an intracratonic Karoo unit and a "pericratonic"
transitional unit. The sea invaded this area several times.
and Wiedmann 1982). d Conjugate basins in the
South Atlantic (cf. Fig. 12.1 c). Basin arrangement is
asymmetrie, and the sediment thicknesses increase
from west to east (Gabon basin). The depoeenters
and major faults of the Tucano basin change their
positions and post-rift sediments are rnissing, while
the offshore Sergipe-Alagoas basin experienced significant post-rift subsidence (After Karner et al.
1992). e Change in the orientation of rifts in southernmost South America and South Africa from the
Triassie (northwest, related to older orogenie belts)
to the Middle Jurassie (north to northeast, opening of
the Atlantic). (After Uliana et al. 1989)
stages of both aborted rifts (without crustal separation) and fully developed rifts (followed by sea floor
spreading) lasted from about ~50 Ma to more than
200Ma.
Along the margins of the Atlantic and other ocean
basins resulting from the breakup of Pangea, the synrift sediments are mostly of Triassie to Jurassie age;
some are older and/or younger. They consist predominantly of fluvial sediments (often red beds), lake
deposits, evaporites, and some shallow-marine sediments of variable thickness and lirnited extent. Volcanic material may be present in large quantities. Paleozoic and Tertiary syn-rift sediment successions of
passive continental margins are commonly characterized by fluvial, lacustrine, and. shallow-marine sequences. Uplift and erosion of the rift shoulders at
passive margins mayaiso affect former shelf sediments and lead in the basin to offlapping
(prograding) stratal patterns. When the rift shoulders
are largely eroded and subsidence of the shelf continues due to crustal cooling, the associated sediments
begin to onlap (Van BaIen et al. 1995).
In the post-rift phase of the Atlantic, subsidence
continued at a slowing rate. Decreasing siliciclastic
sediment supply led to a fining-upward trend and a
shift from hernipelagic to pelagic deposits. The shelf
sediments of the post-breakup, mature ocean phase in
the late Cretaceous and Tertiary were dominated by
pelagic carbonates or silty clays. The major factors
now controlling marine sediments were long-term
climatic change, faunal evolution, oceanic
thermohaline eirculation, variations in the carbonate
produetion, and eustatie sea-Ievel variations.
Other Rifted Continental Margins
A eomplex tectonic and stratigraphie history sirnilar
to that ofthe North Atlantic is also known from other
passive eontinental margins. They show repeated
regional rifting episodes and possibly more than one
phase of breakup, for example the Campos basin of
Brazil and the Gabon basin of West Africa (Edwards
and Santogrossi 1990). In northwestern Australia
Fig. 12.9. a Position of Ieeland hot spot (circle; mantle plume) after the onset of sea-floor spreading in
the North Atlantie (magnetie line M 23) and voleanic
margin along East Greenland. Ds, Davis Strait; VP,
V 0ring Plateau; RB, Ratton Bank. (After White
1989). b Physiographie elements of the NorwegianGreenland Sea, generalized. Note the variable width
of the eontinental margin (shelt), continental platform of the Barents shelf, submarine plateaus, and
rift structures along the eastern margin. (After
Birkenmajer 1981; for more details see Eldholm et
al. 1989). c Conjugate margins in the North Atlantie
during the late Jurassie (magnetic line M-25) and
major Mesozoic-Cenozoie marginal basins. (Jansa
Chapter 12 Basin Evolution and Sediments
several deposWonal wedges were built out into the
evolving marginal basin (Boote and Kirk 1989).
Rifting between South Africa and South America
started as early as in the Permo-Carboniferous, i.e.
160 Ma prior to the onset of drifting and formation
of the South Atlantic ocean. The orientation of Triassie eontinental rifts (obliquely to the axis of the
South Atlantie) was still dictated by crustal structures
older than the Atlantic rift zone (a kind of orogenie
eollapse), whereas the younger rift zones (since the
rniddle Jurassie) followed the Atlantic trend (Fig.
12.ge; Uliana et al. 1989; Tankard et al. 1995). The
long his tory of the South Atlantic rift zone basin is
reflected by three mega-sequences, separated by unconforrnities and interrupted by extensive flood basalts in the Triassie, Jurassie and early Cretaceous.
The Permo-Carboniferous Karoo supergroup in Namibia is
characterized by glacial, fluvial, lacustrine and deltaic sediments. Continental Triassie and Jurassie sediments with
intercalated flood basalts reflect thermal uplift of the rift
shoulder and a permanently overfilled rift basin. Volcanic
activity continued in the lower Cretaceous when the South
Atlantic progressively opened from south to north
(Stollhofen 1999; see also Clemson et al. 1997).
The pre-drift separation of Madagascar from East Africa
also took place during a long time span from the early
Permian to the middle Jurassie (Wopfuer 1993; Hankel
1994). Here, the evolution ofthe rifted margin was affected
by middle Triassie uplift and erosion subdiving the basin
fills into an intracratonic Karoo unit and a "pericratonic"
transitional unit. The sea invaded this area several times.
and Wiedmann 1982). d Conjugate basins in the
South Atlantic (cf. Fig. 12.1 c). Basin arrangement is
asymmetrie, and the sediment thicknesses increase
from west to east (Gabon basin). The depoeenters
and major faults of the Tucano basin change their
positions and post-rift sediments are rnissing, while
the offshore Sergipe-Alagoas basin experienced significant post-rift subsidence (After Karner et al.
1992). e Change in the orientation of rifts in southernmost South America and South Africa from the
Triassie (northwest, related to older orogenie belts)
to the Middle Jurassie (north to northeast, opening of
the Atlantic). (After Uliana et al. 1989)