642
evolution in the Triassic and Jurassic as a backarc basin
behind an oceanic island arc of the eastern Pacific
(Schamel 1991; see also Pindell and Tabbutt 1995; Colletta
et al. 1997). After the elosure of this basin, a pericratonic
trough developed which accumulated thick marine limestones and shales in the Cretaceous and early Tertiary.
These sediments acted later as hydrocarbon source rocks.
In the middle and late Tertiary, the basin fillings were incorporated into the east-vergent thrust sheets of the young
Andean orogeny which led to uplift and the formation of
the Central and Eastern Cordilleras. The complex structural
evolution of the Andes is still not fully resolved (e.g.
Roeder and Chamberlain 1995; Kley 1998). During this
period the Magdalena basin represented the inner part of a
retroarc basin or foredeep which collected shallow-marine
shales and molasse-type sandstones. At present, the former
basin is subdivided into an array of intramontane "successor" basins.
South-east basin, France. The largest basin in France
is located between the western Alps and the Massif Central
(cf. Fig. l2.39a). It developed on relatively mobile continental crust since the Triassic and displays a complex history (Dubois and Delfaud 1998) which was largely controlled by the evolution of the Tethys, the Alpine orogeny,
and the western Mediterranean. After Triassic rifting and a
phase of elastic and evaporite sedimentation, further rifting
and block-faulting, related to the opening of the Tethys
ocean (Liguro-Piemont segment), led to a first basin fragmentation and the accumulation of marine shales and limestones of variable thicknesses in the Jurassic and Cretaceous. As a result of the opening of the Atlantic ocean
(Gulf of Gascony) and the collision of Iberia with Europe,
the basin was deformed and emerged. Toward the evolving
orogen of the Alps, parts of the South-East basin represented a passive margin basin which was later overridden
in the east by Alpine thrust sheets and transformed into a
foreland basin. The southern part of the basin was affected
by proto-Mediterranean Tertiary rifting (Liguro-Provenyal
rift between the Provence and the islands of Corsica and
Sardinia) and the subsequent opening of the western Mediterranean (Fig. 12.39a). East-west directed extension in
central Europe and more north-south directed extension
along the Mediterranean coast created several subbasins of
differing strike (Hippolyte et al. 1993). The subbasins subsided rapidly in Oligocene and Neogene times, particularly
those elose to the Alps. The maximum sediment thicknesses in these basins range from 10 to 15 km.
Chapter 12 Basin Evolution and Sediments
12.9.4 Sediment Preservation Potential of
Various Basin Settings
The preservation of sediment fills of some age depends to a large degree on the basin type, its syndepositional tectonic setting, and its post-depositional
structural evolution. Some of the examples of this
chapter demonstrate this relationship (see also Sect.
11.7).
It is evident that mountain belts resulting from continental collision and uplift cannot preserve their entire sedimentary history. Only the sediments of deep
intramontane basins, of deep-seated thrust sheets, and
those of overthrust and deeply subsided forelands are
well protected against long-term erosion. More distal
foreland sediments tend to be eroded earlier due to
uplift of the foreland plate.
Old fold-and-!hrnst belts have comrnonly lost most
of their sedimentary cover including moderately metamorphosed rocks. Pelagic oceanic sediments and
deep-sea trench sediments which undergo subduction
can survive only partially in accretionary prisms.
Here, they are strongly deformed, metamorphosed,
and sooner or later also subjected to erosion.
This is the reason why the oceanic sediments of
periods older than the Mesozoic are largely gone or
obscured by accretion and metamorphism. Below the
present-day oceans, the oldest oceanic ernst with oceanic sediments is Jurassie in age. It is found only in
marginal regions, whereas most existing deep-sea sediments and their underlying ernst are younger.
The sediments of remnant and foreare basins, incorporated into thrust sheets, may escape from erosion
for some time, particularly so if they lose in elevation
by gravitational collapse of highly uplifted regions of
an orogen, as e.g. in the Alps and the Himalayas (cf.
Sects. 12.5 and 12.7.3). The sediments of oceanic
backare basins comrnonly have a limited life time because these basins tend to be closed. Retroarc basins
on continental ernst which experience overthrusting
and are transformed into foredeeps offer better
chances of sediment preservation.
A good chance of being preserved have the sediments of intracontinental rift and sag basins as weH as
sediments deposited on passive continental margins.
In particular the fillings of early rift basins tend to
become deeply buried. This is also trne to some degree of post-rift sediments on slowly subsiding continental ernst. Passive margin sediments affected by
overthrusting are better preserved than sediments associated with intracontinental overthrusting. The latter
tend to become rapidly eroded due to high uplift.
evolution in the Triassic and Jurassic as a backarc basin
behind an oceanic island arc of the eastern Pacific
(Schamel 1991; see also Pindell and Tabbutt 1995; Colletta
et al. 1997). After the elosure of this basin, a pericratonic
trough developed which accumulated thick marine limestones and shales in the Cretaceous and early Tertiary.
These sediments acted later as hydrocarbon source rocks.
In the middle and late Tertiary, the basin fillings were incorporated into the east-vergent thrust sheets of the young
Andean orogeny which led to uplift and the formation of
the Central and Eastern Cordilleras. The complex structural
evolution of the Andes is still not fully resolved (e.g.
Roeder and Chamberlain 1995; Kley 1998). During this
period the Magdalena basin represented the inner part of a
retroarc basin or foredeep which collected shallow-marine
shales and molasse-type sandstones. At present, the former
basin is subdivided into an array of intramontane "successor" basins.
South-east basin, France. The largest basin in France
is located between the western Alps and the Massif Central
(cf. Fig. l2.39a). It developed on relatively mobile continental crust since the Triassic and displays a complex history (Dubois and Delfaud 1998) which was largely controlled by the evolution of the Tethys, the Alpine orogeny,
and the western Mediterranean. After Triassic rifting and a
phase of elastic and evaporite sedimentation, further rifting
and block-faulting, related to the opening of the Tethys
ocean (Liguro-Piemont segment), led to a first basin fragmentation and the accumulation of marine shales and limestones of variable thicknesses in the Jurassic and Cretaceous. As a result of the opening of the Atlantic ocean
(Gulf of Gascony) and the collision of Iberia with Europe,
the basin was deformed and emerged. Toward the evolving
orogen of the Alps, parts of the South-East basin represented a passive margin basin which was later overridden
in the east by Alpine thrust sheets and transformed into a
foreland basin. The southern part of the basin was affected
by proto-Mediterranean Tertiary rifting (Liguro-Provenyal
rift between the Provence and the islands of Corsica and
Sardinia) and the subsequent opening of the western Mediterranean (Fig. 12.39a). East-west directed extension in
central Europe and more north-south directed extension
along the Mediterranean coast created several subbasins of
differing strike (Hippolyte et al. 1993). The subbasins subsided rapidly in Oligocene and Neogene times, particularly
those elose to the Alps. The maximum sediment thicknesses in these basins range from 10 to 15 km.
Chapter 12 Basin Evolution and Sediments
12.9.4 Sediment Preservation Potential of
Various Basin Settings
The preservation of sediment fills of some age depends to a large degree on the basin type, its syndepositional tectonic setting, and its post-depositional
structural evolution. Some of the examples of this
chapter demonstrate this relationship (see also Sect.
11.7).
It is evident that mountain belts resulting from continental collision and uplift cannot preserve their entire sedimentary history. Only the sediments of deep
intramontane basins, of deep-seated thrust sheets, and
those of overthrust and deeply subsided forelands are
well protected against long-term erosion. More distal
foreland sediments tend to be eroded earlier due to
uplift of the foreland plate.
Old fold-and-!hrnst belts have comrnonly lost most
of their sedimentary cover including moderately metamorphosed rocks. Pelagic oceanic sediments and
deep-sea trench sediments which undergo subduction
can survive only partially in accretionary prisms.
Here, they are strongly deformed, metamorphosed,
and sooner or later also subjected to erosion.
This is the reason why the oceanic sediments of
periods older than the Mesozoic are largely gone or
obscured by accretion and metamorphism. Below the
present-day oceans, the oldest oceanic ernst with oceanic sediments is Jurassie in age. It is found only in
marginal regions, whereas most existing deep-sea sediments and their underlying ernst are younger.
The sediments of remnant and foreare basins, incorporated into thrust sheets, may escape from erosion
for some time, particularly so if they lose in elevation
by gravitational collapse of highly uplifted regions of
an orogen, as e.g. in the Alps and the Himalayas (cf.
Sects. 12.5 and 12.7.3). The sediments of oceanic
backare basins comrnonly have a limited life time because these basins tend to be closed. Retroarc basins
on continental ernst which experience overthrusting
and are transformed into foredeeps offer better
chances of sediment preservation.
A good chance of being preserved have the sediments of intracontinental rift and sag basins as weH as
sediments deposited on passive continental margins.
In particular the fillings of early rift basins tend to
become deeply buried. This is also trne to some degree of post-rift sediments on slowly subsiding continental ernst. Passive margin sediments affected by
overthrusting are better preserved than sediments associated with intracontinental overthrusting. The latter
tend to become rapidly eroded due to high uplift.