626
ily, Malta, Tunisia) and the eastern Mediterranean
(the Hellenic and Cyprian arc; Reuther et al. 1993).
In the context of this book, the sedimentary basins
resulting from continental extrusion are of primary
interest. Here, a few examples are briefly described.
Southwestern China and Indochina. These basins inc1ude
the Malay basin, the Gulf of Thailand basins, the Mekong
delta basins, and a number of smaller grabens and halfgrabens (Fig. 12.40a; e.g. Tapponier and Molnar 1977;
Leloup et al. 1995; Laeassin et al. 1997). Most ofthe thiek
infillings of these basins (eommonly several km up to > I 0
km) eonsist of non-marine sediments. The basins loeated
below the Gulf of Thailand and in the area of the Mekong
delta have also aeeumulated young marine sediments.
Eastern Alps. Several intra-Alpine small eiongate basins resulted from eontinental extrusion (Fig. 12.40b,e;
Ratschbacher et al. 1991; Frisch et al. 1998). In earlier
publieations (e.g. Tollmann 1985), these basins are referred
to as intramontane basins. Their infillings largely eorrespond with those of intramontane basins (see above). The
Klagenfurt basin at the southern boundary of the extruded
ernstal wedge asymmetrie in cross seetion, strongly sheared
and overthrust from the south (Nemes et al. 1997). The
Styrian basin and the Pannonian basin in Hungary are also
affeeted by eontinental extrusion (cf. Seet. 7.4).
Cayman trough, Caribbean Sea. The 1100 km long
Cayman trough and the smaller Yueatan trough in the Caribbean Sea are puH-apart basins whieh developed in
transtensional strike-slip zones within oeeanie ernst in assoeiation with plate eollision (Fig. 12.40d, cf. Seet. 12.8.3).
These transform zones originated from oblique eollision
between the Caribbean plate with the island are of the
Greater AntilIes (inc1uding Cuba) and the North Ameriean
plate in the eariy Eoeene. The Caribbean plate first moved
northward, but after eollision with Florida and the Bahama
platform, it was foreed to rotate cloekwise and to move
eastward towards the "free spaee" of the Atlantie oeean.
Here the subduetion zone of the Lesser AntilIes led to the
eonsumption of Atlantie oeeanie erust, whereas erustal
slivers of the Carribbean plate to the north of the Cayman
trough were extruded to the west (see Gordon et al. 1997;
Mann 1997).
12.7.4 Pannonian-Type Basins
General Aspects
Relatively large, intramontane basins related to adjacent collision belts and subduction zones have been
referred to as Pannonian-type basins (cf. Sect. 1.2).
Such basins are underlain by thinned continental
crost, and they may originate from former retroarc
basins which have experienced extension behind
fold-thrust belts rnigrating away from the basin towards the foreland. This mechanism has been described as subduction rollback (Royden 1993).
Several authors have shed some doubt on the usefulness of the Pannonian basin as a model basin for
the interpretation of other intramontane basins. In
fact, the structural history of such basins, including
Chapter 12 Basin Evolution and Sediments
the Pannonian basin, is complex and still a matter of
debate. Recently, the impact of continental escape
(see above), caused by continental collision in nearby
orogenic belts, has been pointed out as an important
factor in modifying the structure and evolution of
such basins.
Pannonian-type basins should more accurately be
addressed as "basin systems" because they consist of
several smaller individual basins separated by relatively shallow basement blocks. This structural pattern results from the combined retroarc and escape
tectonic setting. The diachronous development of the
subbasins originates from two processes:
- Subsidence of subbasins located near the thrust belt
begins earlier and at a more rapid rate than that in the
central part of the entire basin system. Hence, the
subbasins adjacent to the surrounding mountain belts
contain thick, fault-bounded sediments which were
deposited during the extensional phase (syn-extensional sediment~). They are covered by thin postextensional strata (cf. Fig. 12.41e,f).
- In contrast, subbasins located far from the thrust
belt in more central parts of the basin exhibit only
thin fault-bounded syn-extensional sequences which
in turn are overlain by thick, flat lying, unfaulted
post-extensional sediments. Post-extensional subsidence is enabled by both crustal cooling and wrench
faulting.
The tectonic processes may be accompanied by
calcalkaline and alkali basaltic volcanism. The highest nearby mountain ranges act as principal sediment
sources, but major rivers draining large areas outside
the basin (such as the early Danube River in central
Europe) mayaiso playa significant role. The basins
and their smaller subbasins are successively filled
with sediments delivered by these rivers. A general
trend in basin filling is:
- During an early stage. Continental sediments or
marine transgressive beds followed by shallow-marine shales and marls with sandy intercalations.
- Intermediate stage. Relatively deep-marine sediments in the subbasins, resulting from rapid subsidence and insufficient sediment buildup to keep pace
with subsidence.
- Later stages. The basins shallow and may pass to
brackish, lacustrine, and finally fluvial environments.
The Pannonian basin
Structural Evolution
The prototype of these basins is the Pannonian basin
of Hungary and its neighboring countries. It lies
within the Alpine mountain belts of east-central Eu-
ily, Malta, Tunisia) and the eastern Mediterranean
(the Hellenic and Cyprian arc; Reuther et al. 1993).
In the context of this book, the sedimentary basins
resulting from continental extrusion are of primary
interest. Here, a few examples are briefly described.
Southwestern China and Indochina. These basins inc1ude
the Malay basin, the Gulf of Thailand basins, the Mekong
delta basins, and a number of smaller grabens and halfgrabens (Fig. 12.40a; e.g. Tapponier and Molnar 1977;
Leloup et al. 1995; Laeassin et al. 1997). Most ofthe thiek
infillings of these basins (eommonly several km up to > I 0
km) eonsist of non-marine sediments. The basins loeated
below the Gulf of Thailand and in the area of the Mekong
delta have also aeeumulated young marine sediments.
Eastern Alps. Several intra-Alpine small eiongate basins resulted from eontinental extrusion (Fig. 12.40b,e;
Ratschbacher et al. 1991; Frisch et al. 1998). In earlier
publieations (e.g. Tollmann 1985), these basins are referred
to as intramontane basins. Their infillings largely eorrespond with those of intramontane basins (see above). The
Klagenfurt basin at the southern boundary of the extruded
ernstal wedge asymmetrie in cross seetion, strongly sheared
and overthrust from the south (Nemes et al. 1997). The
Styrian basin and the Pannonian basin in Hungary are also
affeeted by eontinental extrusion (cf. Seet. 7.4).
Cayman trough, Caribbean Sea. The 1100 km long
Cayman trough and the smaller Yueatan trough in the Caribbean Sea are puH-apart basins whieh developed in
transtensional strike-slip zones within oeeanie ernst in assoeiation with plate eollision (Fig. 12.40d, cf. Seet. 12.8.3).
These transform zones originated from oblique eollision
between the Caribbean plate with the island are of the
Greater AntilIes (inc1uding Cuba) and the North Ameriean
plate in the eariy Eoeene. The Caribbean plate first moved
northward, but after eollision with Florida and the Bahama
platform, it was foreed to rotate cloekwise and to move
eastward towards the "free spaee" of the Atlantie oeean.
Here the subduetion zone of the Lesser AntilIes led to the
eonsumption of Atlantie oeeanie erust, whereas erustal
slivers of the Carribbean plate to the north of the Cayman
trough were extruded to the west (see Gordon et al. 1997;
Mann 1997).
12.7.4 Pannonian-Type Basins
General Aspects
Relatively large, intramontane basins related to adjacent collision belts and subduction zones have been
referred to as Pannonian-type basins (cf. Sect. 1.2).
Such basins are underlain by thinned continental
crost, and they may originate from former retroarc
basins which have experienced extension behind
fold-thrust belts rnigrating away from the basin towards the foreland. This mechanism has been described as subduction rollback (Royden 1993).
Several authors have shed some doubt on the usefulness of the Pannonian basin as a model basin for
the interpretation of other intramontane basins. In
fact, the structural history of such basins, including
Chapter 12 Basin Evolution and Sediments
the Pannonian basin, is complex and still a matter of
debate. Recently, the impact of continental escape
(see above), caused by continental collision in nearby
orogenic belts, has been pointed out as an important
factor in modifying the structure and evolution of
such basins.
Pannonian-type basins should more accurately be
addressed as "basin systems" because they consist of
several smaller individual basins separated by relatively shallow basement blocks. This structural pattern results from the combined retroarc and escape
tectonic setting. The diachronous development of the
subbasins originates from two processes:
- Subsidence of subbasins located near the thrust belt
begins earlier and at a more rapid rate than that in the
central part of the entire basin system. Hence, the
subbasins adjacent to the surrounding mountain belts
contain thick, fault-bounded sediments which were
deposited during the extensional phase (syn-extensional sediment~). They are covered by thin postextensional strata (cf. Fig. 12.41e,f).
- In contrast, subbasins located far from the thrust
belt in more central parts of the basin exhibit only
thin fault-bounded syn-extensional sequences which
in turn are overlain by thick, flat lying, unfaulted
post-extensional sediments. Post-extensional subsidence is enabled by both crustal cooling and wrench
faulting.
The tectonic processes may be accompanied by
calcalkaline and alkali basaltic volcanism. The highest nearby mountain ranges act as principal sediment
sources, but major rivers draining large areas outside
the basin (such as the early Danube River in central
Europe) mayaiso playa significant role. The basins
and their smaller subbasins are successively filled
with sediments delivered by these rivers. A general
trend in basin filling is:
- During an early stage. Continental sediments or
marine transgressive beds followed by shallow-marine shales and marls with sandy intercalations.
- Intermediate stage. Relatively deep-marine sediments in the subbasins, resulting from rapid subsidence and insufficient sediment buildup to keep pace
with subsidence.
- Later stages. The basins shallow and may pass to
brackish, lacustrine, and finally fluvial environments.
The Pannonian basin
Structural Evolution
The prototype of these basins is the Pannonian basin
of Hungary and its neighboring countries. It lies
within the Alpine mountain belts of east-central Eu-