4.3 Modern Examples, Sedimentary History
and homogeneous, bioturbated sediments. It is pos sible that the latter seetions eorrespond with low sealevel stands.
4.3.3 The Red Sea and Gulf of Aden
Tectonic Setting
The teetonie and sedimentary histories of the Gulf of
Aden and Red Sea are closely related. However,
basin-generating proeesses and marine deposition
eommeneed earlier in the Gulf of Aden than in the
Red Sea and first prograded from east to west and
then, i.e. in the Red Sea, from south to north.
The teetonie evolution of these basins, partieularly that of
the Red Sea, is diseussed in numerous artieles (e.g.
Coehran 1981 and 1983a; Le Piehon and Coehran 1988;
Makris and Henke 1992; Beydoun and Sikander 1992; Bott
et al. 1992; Bosworth 1994). Publieations on the pre-rift
and Neogene sedimentary history of these basins inelude
Cronan et al. (1974), Stoffers and Kühn (1974), Miller and
Barakat (1988), Montenat et al. (1988), Hughes and
Beydoun (1992).
The Gulf of Aden opened in the late Middle
Oligoeene along a transform fault with dextral motion aeeompanied and followed by extension. Its
present-day teetonie setting, displaying in its eenter
many small, deeply subsided pull-apart basins, resembles that of the younger Gulf of California, but
the Gulf of Aden has beeome wider due to substantial sea-floor spreading. However, the evolution of its
western portion, including the Afar region, is younger than the eastern part. Basin-forming proeesses
reaehed the southern Red Sea in the late Oligoeene
and the eentral and· northern Red Sea in the early
Mioeene. Following the teetonie evolution, syn-rift
marine sediments first inundated the eastern Gulf of
Aden, before they were deposited in the southern and
northern Red Sea.
The Red Sea is a young, narrow oeean basin in a
transitional mode from rifting to drifting (Fig. 4.6a,
ef. Seets. 12.1 and 12.2). Its teetonie evolution is
more eomplex than previously assumed. Here, the
Afriean and Arabian plates were also separated initially by a transform fault (with sinistral strike-slip
motion), before lateral extension beeame the dominant proeess. This is doeumented by some small pullapart basins with oeeanie erust along the diseontinuous northern axial trough. Seisrnie reeords aeross the
northern and eentral part of the Red Sea show that
the basin is asymmetrie with some oeeanie crust on
the western side and stretehed eontinental erust on
the eastern Arabian side.
In the northern Red Sea, rifting generated a wide
"main trough" on top of thinned, intensively faulted
eontinental erust (Fig. 4.6b) eharaeterized by tilted
177
bloeks and horst and graben struetures. The period of
extension and dike injeetion lasted for about 20 Ma
and affeeted an area of 100 to 160 km in width.
In contrast to the northern Red Sea still being in
the rifting stage, the rniddle and more southern part
of the basin experieneed drifting sinee ~4 Ma. Here,
the main trough is biseeted by a deep axial trough,
formed by sea floor spreading. To the north and
south of this region, the axial trough is represented
by aseries of deeps, alternating with shallower
intertrough zones.
Pre-Rift and Syn-Rift Sediments with Evaporites
Prior to transform motions and rifting, both the Gulf
of Aden and the Red Sea were lowlands or topographie depressions whieh allowed the deposition of
eontinental and shallow-marine sediments. In the
Gulf of Aden area, Jurassie to Eoeene marine sediments cover wide areas. In the Red Sea, marine sediments seem to be ineompletely present (in the south
sinee the Jurassie; in the north sinee the Upper Cretaeeous.
During early rifting, eontinental, eoastal, and
shallow-marine sediments of mostly normal salinity
were deposited in the Gulf of Aden and Red Sea. In
addition, some evaporites and dolomites formed during short intervals.
The subsequent period (middle to late Mioeene) is
eharaeterized by limes tone deposition in the eastern
Gulf of Aden and gypsumJanhydrite in its western
part. In the Red Sea, thiek evaporites including halite
aeeumulated (see also Seet. 6.4.3) partially in
shallow-water and coastal sabkha environments, but
probably also in deeper water of the rapidly subsiding basin. The evaporites reaeh thieknesses of more
than 1000 m in the northern part and up to 3000 or
4000 m in the eentral and southern parts of the basin.
During its "salinity erisis", the Red Sea was probably
eonneeted with the Mediterranean Sea and closed at
its southeastern end. Later, the Strait of Bab al
Mandab opened and eonneeted the Red Sea with the
Gulf of Aden and the Indian Oeean.
The evaporites probably formed prior to the generation of
the axial trough, i.e., on thinned eontinental erust.
Evaporites found in the axial trough are interpreted by subsequent salt flow from the flanks of the rnain trough into
the axial trough (Girdler and Whitmarsh 1974). In the eentral Red Sea (DSDP Site 227), the drilled upper seetion of
the evaporites eontains, besides halite, several intervals of
anhydrite, dark shales, and dolomites, whieh c1early indieate .that evaporite deposition oeeurred diseontinuously.
After evaporite deposition, extension eontinued, accompanied by halokinetie struetures.
and homogeneous, bioturbated sediments. It is pos sible that the latter seetions eorrespond with low sealevel stands.
4.3.3 The Red Sea and Gulf of Aden
Tectonic Setting
The teetonie and sedimentary histories of the Gulf of
Aden and Red Sea are closely related. However,
basin-generating proeesses and marine deposition
eommeneed earlier in the Gulf of Aden than in the
Red Sea and first prograded from east to west and
then, i.e. in the Red Sea, from south to north.
The teetonie evolution of these basins, partieularly that of
the Red Sea, is diseussed in numerous artieles (e.g.
Coehran 1981 and 1983a; Le Piehon and Coehran 1988;
Makris and Henke 1992; Beydoun and Sikander 1992; Bott
et al. 1992; Bosworth 1994). Publieations on the pre-rift
and Neogene sedimentary history of these basins inelude
Cronan et al. (1974), Stoffers and Kühn (1974), Miller and
Barakat (1988), Montenat et al. (1988), Hughes and
Beydoun (1992).
The Gulf of Aden opened in the late Middle
Oligoeene along a transform fault with dextral motion aeeompanied and followed by extension. Its
present-day teetonie setting, displaying in its eenter
many small, deeply subsided pull-apart basins, resembles that of the younger Gulf of California, but
the Gulf of Aden has beeome wider due to substantial sea-floor spreading. However, the evolution of its
western portion, including the Afar region, is younger than the eastern part. Basin-forming proeesses
reaehed the southern Red Sea in the late Oligoeene
and the eentral and· northern Red Sea in the early
Mioeene. Following the teetonie evolution, syn-rift
marine sediments first inundated the eastern Gulf of
Aden, before they were deposited in the southern and
northern Red Sea.
The Red Sea is a young, narrow oeean basin in a
transitional mode from rifting to drifting (Fig. 4.6a,
ef. Seets. 12.1 and 12.2). Its teetonie evolution is
more eomplex than previously assumed. Here, the
Afriean and Arabian plates were also separated initially by a transform fault (with sinistral strike-slip
motion), before lateral extension beeame the dominant proeess. This is doeumented by some small pullapart basins with oeeanie erust along the diseontinuous northern axial trough. Seisrnie reeords aeross the
northern and eentral part of the Red Sea show that
the basin is asymmetrie with some oeeanie crust on
the western side and stretehed eontinental erust on
the eastern Arabian side.
In the northern Red Sea, rifting generated a wide
"main trough" on top of thinned, intensively faulted
eontinental erust (Fig. 4.6b) eharaeterized by tilted
177
bloeks and horst and graben struetures. The period of
extension and dike injeetion lasted for about 20 Ma
and affeeted an area of 100 to 160 km in width.
In contrast to the northern Red Sea still being in
the rifting stage, the rniddle and more southern part
of the basin experieneed drifting sinee ~4 Ma. Here,
the main trough is biseeted by a deep axial trough,
formed by sea floor spreading. To the north and
south of this region, the axial trough is represented
by aseries of deeps, alternating with shallower
intertrough zones.
Pre-Rift and Syn-Rift Sediments with Evaporites
Prior to transform motions and rifting, both the Gulf
of Aden and the Red Sea were lowlands or topographie depressions whieh allowed the deposition of
eontinental and shallow-marine sediments. In the
Gulf of Aden area, Jurassie to Eoeene marine sediments cover wide areas. In the Red Sea, marine sediments seem to be ineompletely present (in the south
sinee the Jurassie; in the north sinee the Upper Cretaeeous.
During early rifting, eontinental, eoastal, and
shallow-marine sediments of mostly normal salinity
were deposited in the Gulf of Aden and Red Sea. In
addition, some evaporites and dolomites formed during short intervals.
The subsequent period (middle to late Mioeene) is
eharaeterized by limes tone deposition in the eastern
Gulf of Aden and gypsumJanhydrite in its western
part. In the Red Sea, thiek evaporites including halite
aeeumulated (see also Seet. 6.4.3) partially in
shallow-water and coastal sabkha environments, but
probably also in deeper water of the rapidly subsiding basin. The evaporites reaeh thieknesses of more
than 1000 m in the northern part and up to 3000 or
4000 m in the eentral and southern parts of the basin.
During its "salinity erisis", the Red Sea was probably
eonneeted with the Mediterranean Sea and closed at
its southeastern end. Later, the Strait of Bab al
Mandab opened and eonneeted the Red Sea with the
Gulf of Aden and the Indian Oeean.
The evaporites probably formed prior to the generation of
the axial trough, i.e., on thinned eontinental erust.
Evaporites found in the axial trough are interpreted by subsequent salt flow from the flanks of the rnain trough into
the axial trough (Girdler and Whitmarsh 1974). In the eentral Red Sea (DSDP Site 227), the drilled upper seetion of
the evaporites eontains, besides halite, several intervals of
anhydrite, dark shales, and dolomites, whieh c1early indieate .that evaporite deposition oeeurred diseontinuously.
After evaporite deposition, extension eontinued, accompanied by halokinetie struetures.