12.1 Rift Basins
ited prior to the onset of sea floor spreading. Their
changing thickness reflects a basin with nonuniform,
locally rapid subsidence.
Rifting in the Gulf of Suez started in the early
Miocene. This part ofthe Red Sea is an example of a
rift basin which, apart from a very short initial fluvial
and lacustrine phase, was inundated by the sea
throughout its history (Schütz 1994). Since the beginning of the Miocene, the central parts of this basin
have subsided 6-7 km, and the uplift of the rift shoulders amounts to 2-3 km.
The Afar depression between the southernrnost Red Sea
and Ethiopia, at the northem end of the East African rift
(cf Fig. 12.3a), is a very interesting exarnple ofthe propagation of rifting from the Gulf of Aden into this area, the
breakup of thinned continental crust, and the opening of a
new ocean basin (Manighetti et al. 1998).
Rio Grande rift. This large, segmented rift system
of North America extends over a distance of about
1100 km from Colorado via New Mexico to western
Texas (Fig. 12.3c). It evolved since the late
o ligocene between the craton on the east and the
Colorado Plateau on the west which underwent a
c10ckwise rotation of 1.5°. As a result, the extension
of the rift system increased from north to south from
about 10% to 30-50% (Chapin and Cather 1994).
The rift system displays several phases of increased
tectonic and volcanic activity (e.g. Keller and Cather
1994; Cather et al. 1994; Mack and Seager 1995).
The earlier phase is characterized by rhyolitic and
basaltic/andesitic volcanism, the products of which
were sufficient, at least in parts of the rift, to bury the
developing fault block topography. Later, block uplifts and complementary basins deve1oped, and older
basin fills were disrupted by normal faults. Intensified subsidence led to topographic c10sure and playa
deposits which were later overlain by alluvial fans
and ultimately by the axial river system of the Rio
Grande (Fig. 12.3d). Basaltic volcanism was reactivated in the MiocenelPliocene during a further major
pulse of extension. Several transfer (or accommodatiOI~) zones of the rift acted as preferred sites of volcamsm.
Upper Rhine Graben. The Rhine graben in central
Europe, along the border between France and Germany, was regarded in the past as an example for a
c1assical rift basin generated by pure shear and characterized by distinct rift shoulders (Fig. 12.5a,b).
...
Fig. 12.4. Simplified facies models ofhalf-graben fill
under continental (a,d) and coastal-marine conditions
(b,c,e). The tectonic structure of the basins may be
more eomplicated, and more synsedimentary faults
are common. Lakes and the axial river tend to shift
toward the boundary fault. e Half-graben morphol551
However, this rift system is also affected by left-Iateral strike-slip motion and an asymmetric detachment
zone at a depth of about 15 km (Meier and Eisbacher
1991). The zone of maximum subsidence migrated
from south to north (Fig. 12.5d, subsidence curves
are shown in Fig. 8. 12b). The simplified sections
(Fig. 12.5c,d) demonstrate the vertical and lateral
variations in the facies and thicknesses of the stratigraphic units present in this basin whieh may be regarded is an example of the complexity of rift basin
sediments.
The Upper Rhine graben is part of a wider extended structure, whieh is re1ated to the deve10pment
of the Alpine orogen and its northern foredeep
(Sissingh 1998, see below).
The Rhine graben is well explored by numerous drill holes
(summaries by Roll 1979; Pflug 1982; Geyer and Gwinner
1986; Plein 1993). Rifting began in the early Eocene and
continued to the present. The vertical section (Fig. 12.Sc)
reflects numerous changes in the depositional environment.
Greenish to reddish marls, lacustrine limestones and
dolomites, and various evaporites including potash salts
characterize the more arid playa lake and lagoonal intervals. Discontinuous bituminous shales are probably associated with more humid lake periods, but mayaiso have accumulated during times of marine ingressions, which are
normally recorded by gray marls and fossil-bearing sandy
limestones and sands near the basin margin. The upper part
of the section contains some layers of brown coal, indicating a general tendency towards a more humid climate. Volcanic activity during the Oligocene and Miocene was moderate and characterized by ashes of alkaline and bimodal
mafic-felsic composition. With the onset of longitudinal
drainage by the Rhine River, fluvial deposits accumulated
in the entire graben. As a result of continuing differential
subsidence, the youngest deposits show significant variations in thickness along strike .
Other Examples. Other young rift zones inc1ude the
north-trending central European Cenozoie rift system
crossing the continent from the Mediterranean to the
North Sea. It developed on cold, rigid erust and is
represented by the Rhöne-Bresse system and the Upper Rhine graben which splits at its northern end into
two branches, the Lower Rhine graben and the
Hessian depression or Leine graben (e.g. Sissingh
1998). The Oligoeene-Miocene, northeast-trending
rift structures in southwestern Europe formed on
more he<.ted erust and are affeeted by widespread
calcalkaline volcanism (Bois 1993). They appear to
be associated with the opening of the Tethys Oeean
and the boundary between the European-Iberian and
Afriean-Apulian phites .
ogy in shallow-marine carbonate environment may be
modified by reef buildups. and abundant reef detritus
on both sides. (After Leeder and Gawthorpe 1987).
f Redistribution of older rift-graben sediments due to
fault migration, uplift and rotation of internal blocks
ited prior to the onset of sea floor spreading. Their
changing thickness reflects a basin with nonuniform,
locally rapid subsidence.
Rifting in the Gulf of Suez started in the early
Miocene. This part ofthe Red Sea is an example of a
rift basin which, apart from a very short initial fluvial
and lacustrine phase, was inundated by the sea
throughout its history (Schütz 1994). Since the beginning of the Miocene, the central parts of this basin
have subsided 6-7 km, and the uplift of the rift shoulders amounts to 2-3 km.
The Afar depression between the southernrnost Red Sea
and Ethiopia, at the northem end of the East African rift
(cf Fig. 12.3a), is a very interesting exarnple ofthe propagation of rifting from the Gulf of Aden into this area, the
breakup of thinned continental crust, and the opening of a
new ocean basin (Manighetti et al. 1998).
Rio Grande rift. This large, segmented rift system
of North America extends over a distance of about
1100 km from Colorado via New Mexico to western
Texas (Fig. 12.3c). It evolved since the late
o ligocene between the craton on the east and the
Colorado Plateau on the west which underwent a
c10ckwise rotation of 1.5°. As a result, the extension
of the rift system increased from north to south from
about 10% to 30-50% (Chapin and Cather 1994).
The rift system displays several phases of increased
tectonic and volcanic activity (e.g. Keller and Cather
1994; Cather et al. 1994; Mack and Seager 1995).
The earlier phase is characterized by rhyolitic and
basaltic/andesitic volcanism, the products of which
were sufficient, at least in parts of the rift, to bury the
developing fault block topography. Later, block uplifts and complementary basins deve1oped, and older
basin fills were disrupted by normal faults. Intensified subsidence led to topographic c10sure and playa
deposits which were later overlain by alluvial fans
and ultimately by the axial river system of the Rio
Grande (Fig. 12.3d). Basaltic volcanism was reactivated in the MiocenelPliocene during a further major
pulse of extension. Several transfer (or accommodatiOI~) zones of the rift acted as preferred sites of volcamsm.
Upper Rhine Graben. The Rhine graben in central
Europe, along the border between France and Germany, was regarded in the past as an example for a
c1assical rift basin generated by pure shear and characterized by distinct rift shoulders (Fig. 12.5a,b).
...
Fig. 12.4. Simplified facies models ofhalf-graben fill
under continental (a,d) and coastal-marine conditions
(b,c,e). The tectonic structure of the basins may be
more eomplicated, and more synsedimentary faults
are common. Lakes and the axial river tend to shift
toward the boundary fault. e Half-graben morphol551
However, this rift system is also affected by left-Iateral strike-slip motion and an asymmetric detachment
zone at a depth of about 15 km (Meier and Eisbacher
1991). The zone of maximum subsidence migrated
from south to north (Fig. 12.5d, subsidence curves
are shown in Fig. 8. 12b). The simplified sections
(Fig. 12.5c,d) demonstrate the vertical and lateral
variations in the facies and thicknesses of the stratigraphic units present in this basin whieh may be regarded is an example of the complexity of rift basin
sediments.
The Upper Rhine graben is part of a wider extended structure, whieh is re1ated to the deve10pment
of the Alpine orogen and its northern foredeep
(Sissingh 1998, see below).
The Rhine graben is well explored by numerous drill holes
(summaries by Roll 1979; Pflug 1982; Geyer and Gwinner
1986; Plein 1993). Rifting began in the early Eocene and
continued to the present. The vertical section (Fig. 12.Sc)
reflects numerous changes in the depositional environment.
Greenish to reddish marls, lacustrine limestones and
dolomites, and various evaporites including potash salts
characterize the more arid playa lake and lagoonal intervals. Discontinuous bituminous shales are probably associated with more humid lake periods, but mayaiso have accumulated during times of marine ingressions, which are
normally recorded by gray marls and fossil-bearing sandy
limestones and sands near the basin margin. The upper part
of the section contains some layers of brown coal, indicating a general tendency towards a more humid climate. Volcanic activity during the Oligocene and Miocene was moderate and characterized by ashes of alkaline and bimodal
mafic-felsic composition. With the onset of longitudinal
drainage by the Rhine River, fluvial deposits accumulated
in the entire graben. As a result of continuing differential
subsidence, the youngest deposits show significant variations in thickness along strike .
Other Examples. Other young rift zones inc1ude the
north-trending central European Cenozoie rift system
crossing the continent from the Mediterranean to the
North Sea. It developed on cold, rigid erust and is
represented by the Rhöne-Bresse system and the Upper Rhine graben which splits at its northern end into
two branches, the Lower Rhine graben and the
Hessian depression or Leine graben (e.g. Sissingh
1998). The Oligoeene-Miocene, northeast-trending
rift structures in southwestern Europe formed on
more he<.ted erust and are affeeted by widespread
calcalkaline volcanism (Bois 1993). They appear to
be associated with the opening of the Tethys Oeean
and the boundary between the European-Iberian and
Afriean-Apulian phites .
ogy in shallow-marine carbonate environment may be
modified by reef buildups. and abundant reef detritus
on both sides. (After Leeder and Gawthorpe 1987).
f Redistribution of older rift-graben sediments due to
fault migration, uplift and rotation of internal blocks