624
rine sediments of this basin include red beds and show a
surprisingly slow sedimentation rate.
Saar-Nahe basin, southwestern Germany and northeastern France (Fig. 12.39a). This is one of the largest (about
150 km long and 40 km wide) intramontane basins of the
European Variscan orogen (see overview by Franke et al.
1995; Schönenberg und Neugebauer 1997) and it may represent many other basins of this type and age. It is located
at the transform boundary between the Rheno-Hercynian
zone in the north and the Mid-German Crystalline High in
the south and contains Permo-Carboniferous non-marine,
coal-bearing strata (Fig. 12.39b). The partially exhumed
basin fill is weIl explored; its structure is stilI a matter of
debate (Henk 1993; Schäfer and Korsch 1998; Stollhofen
1998). The basin displays several major tectono-sedimentary units: a late orogenic transpressive proto-rift phase, a
non-volcanic and volcanic syn-rift phase with 35% extension (?, probably caused by gravitational orogenic collapse)
and rapid subsidence since the Westphalian, and a post-rift
phase with decreasing subsidence. The half-graben basin
probably developed on a southward-dipping detachment
zone. The cumulative sediment thickness reaches up to 10
km, but in fact it does not exceed a maximum of 6.5 km at
one locality because the depocenter migrated from southwest to northeast. Later, the basin fill experienced some
compression and was slightly folded.
The so-called proto-rift phase contains the deposits of
meandering rivers, lakes, and limnic tropical coal
(Westphalian) which has been mined for many years. In the
Stephanian, the sediments reflect subtropical conditions
and coal formation declined. In the Permian (Rotliegend),
arid conditions led to the development of playas, alluvial
fans, braided rivers and eolian dunes. The main sediment
transport directions changed two times during this evolution, i.e. from southwest to northeast and back to southwest. The syn-rift phases were characterized by synsedimentary tectonic activity creating longitudinal normal
faults and numerous transtensional transfer faults running
perpendicular to the basin trend. These structures and extensive intrusive and extrusive magrnatism (including
pyroclastic flows, ash falls, and the formation of acidic
domes) generated topographic barriers and dams acting as
boundaries between small subbasins. The locally enhanced
relief initiated intrabasinal erosion, mass flow deposits and
sediment redeposition; small depressions were rapidly
filled with siliciclastic and/or volcaniclastic sediments, basaltic lavas, or they were occupied by lakes. Rivers adjusted their courses to the changing topography; spatially
restricted areas became sediment-starved and could accumulate peat and biogenic limestones.
Grand Sillon Houiller, France. Another striking
intramontane structure of the Variscan massifs in Europe is
Fig. 12.40. a Lateral extrusion of Indoehina and formation of major basins in South China and Indoehina
as a result of India-Asia collision in the Himalayas.
Note offset of Mesozoie eontinental basins with red
beds along Red River fault; other features such as the
offset of metamorphic rocks and the uplift of older
granitie belts are not shown. (Compiled from Leloup
et al. 1995; Laeassin et al. 1997). b,c Cartoon and
main structures of lateral extrusion in the Eastem
Alps and assoeiated basin formation. (After
Ratschbacher et al. 1991; Frisch et al. 1998, simplified). d Oblique eollision of the North Ameriean and
Chapter 12 Basin Evolution and Sediments
the so-called coal channel in the Massif Central. It cuts the
total massif from south to north at a length of 300 km and
continues below the sediments of the Paris basin (Fig.
12.39a). Along this line, caused by sinistral strike-slip motion (~70 km displacement) and some extension, several
narrow coal-bearing basins evolved in the upper Carboniferous and collected additional sediments in the Permian
and Triassic. The sediments of these basins also experienced later deformation and segmentation. The Aumance
basin in the northern part of this structure accumulated
fluvial and lacustrine sediments of Stephanian to Autunian
age (Courel et al. 1998), separated by an angular
disconformity. The Permian coal seams are concentrated
along the eastern part of the basin which received less
clastic material than the western side where fluvial deposits
alternate with mass flow deposits indicating ongoing tectonic activity (extension and basin-internal fragrnentation).
The coal seams are overlain by lacustrine black shales and
later by continental strata containing dolomitic and reddish
beds.
12.7.3 Basins Resulting from Continental
Extrusion
Continental or tectonic extrusion (escape) as a result
of plate eollision has been reeently observed within
and adjaeent to several large orogenie belts. The
most spectular example is the extrusion of Indoehina
caused by the indentation of the Indian plate into
Asia in the Himalayas. Part of the shortening of the
eolliding eontinental erust was transformed into lateral extrusion of neighboring erustal fragments. This
proeess led to several long-extended strike-slip
zones, e.g. the Red River shear zone along the northem boundary of Indoehina, ~ 1 000 km long with
~ 700 km sinistral displacement. Other examples include the Eastem Alps, the northem Hungarian plain,
Turkey and the Aegean Sea (see below), the Caribbean Sea and the Bismarek Sea in the southwestem
Paeifie (Mann 1997).
A phenomenon related to continental extrusion is
the formation of transfer zones in regions where
erusts of irregular shape, thiekness and density eollide. This leads to ehanges in the angle of downbending of the lower plate and a segmentation of the
eollision zone and adjaeent basins. Examples have
been deseribed from the central Mediterranean (Sie•
Caribbean plates, westward direeted eontinental extrusion, and formation of the Cayman trough and
Yueatan trough (post-middle Mioeene stage). (After
Gordon et al. 1997, modified). e Neogene extension
and graben formation in the Aegean Sea eaused by
northward subduetion of the Afriean plate and westward eseape of Turkey along the North Anatolian
trans form fault. In the northemmost part of the
Aegean Sea and in Greeee, a southwestward dipping
detachment fault exists whieh has initiated small
halfgrabens. (Based on Dinter and Royden 1993;
Cohen et al. 1995, simplified)
rine sediments of this basin include red beds and show a
surprisingly slow sedimentation rate.
Saar-Nahe basin, southwestern Germany and northeastern France (Fig. 12.39a). This is one of the largest (about
150 km long and 40 km wide) intramontane basins of the
European Variscan orogen (see overview by Franke et al.
1995; Schönenberg und Neugebauer 1997) and it may represent many other basins of this type and age. It is located
at the transform boundary between the Rheno-Hercynian
zone in the north and the Mid-German Crystalline High in
the south and contains Permo-Carboniferous non-marine,
coal-bearing strata (Fig. 12.39b). The partially exhumed
basin fill is weIl explored; its structure is stilI a matter of
debate (Henk 1993; Schäfer and Korsch 1998; Stollhofen
1998). The basin displays several major tectono-sedimentary units: a late orogenic transpressive proto-rift phase, a
non-volcanic and volcanic syn-rift phase with 35% extension (?, probably caused by gravitational orogenic collapse)
and rapid subsidence since the Westphalian, and a post-rift
phase with decreasing subsidence. The half-graben basin
probably developed on a southward-dipping detachment
zone. The cumulative sediment thickness reaches up to 10
km, but in fact it does not exceed a maximum of 6.5 km at
one locality because the depocenter migrated from southwest to northeast. Later, the basin fill experienced some
compression and was slightly folded.
The so-called proto-rift phase contains the deposits of
meandering rivers, lakes, and limnic tropical coal
(Westphalian) which has been mined for many years. In the
Stephanian, the sediments reflect subtropical conditions
and coal formation declined. In the Permian (Rotliegend),
arid conditions led to the development of playas, alluvial
fans, braided rivers and eolian dunes. The main sediment
transport directions changed two times during this evolution, i.e. from southwest to northeast and back to southwest. The syn-rift phases were characterized by synsedimentary tectonic activity creating longitudinal normal
faults and numerous transtensional transfer faults running
perpendicular to the basin trend. These structures and extensive intrusive and extrusive magrnatism (including
pyroclastic flows, ash falls, and the formation of acidic
domes) generated topographic barriers and dams acting as
boundaries between small subbasins. The locally enhanced
relief initiated intrabasinal erosion, mass flow deposits and
sediment redeposition; small depressions were rapidly
filled with siliciclastic and/or volcaniclastic sediments, basaltic lavas, or they were occupied by lakes. Rivers adjusted their courses to the changing topography; spatially
restricted areas became sediment-starved and could accumulate peat and biogenic limestones.
Grand Sillon Houiller, France. Another striking
intramontane structure of the Variscan massifs in Europe is
Fig. 12.40. a Lateral extrusion of Indoehina and formation of major basins in South China and Indoehina
as a result of India-Asia collision in the Himalayas.
Note offset of Mesozoie eontinental basins with red
beds along Red River fault; other features such as the
offset of metamorphic rocks and the uplift of older
granitie belts are not shown. (Compiled from Leloup
et al. 1995; Laeassin et al. 1997). b,c Cartoon and
main structures of lateral extrusion in the Eastem
Alps and assoeiated basin formation. (After
Ratschbacher et al. 1991; Frisch et al. 1998, simplified). d Oblique eollision of the North Ameriean and
Chapter 12 Basin Evolution and Sediments
the so-called coal channel in the Massif Central. It cuts the
total massif from south to north at a length of 300 km and
continues below the sediments of the Paris basin (Fig.
12.39a). Along this line, caused by sinistral strike-slip motion (~70 km displacement) and some extension, several
narrow coal-bearing basins evolved in the upper Carboniferous and collected additional sediments in the Permian
and Triassic. The sediments of these basins also experienced later deformation and segmentation. The Aumance
basin in the northern part of this structure accumulated
fluvial and lacustrine sediments of Stephanian to Autunian
age (Courel et al. 1998), separated by an angular
disconformity. The Permian coal seams are concentrated
along the eastern part of the basin which received less
clastic material than the western side where fluvial deposits
alternate with mass flow deposits indicating ongoing tectonic activity (extension and basin-internal fragrnentation).
The coal seams are overlain by lacustrine black shales and
later by continental strata containing dolomitic and reddish
beds.
12.7.3 Basins Resulting from Continental
Extrusion
Continental or tectonic extrusion (escape) as a result
of plate eollision has been reeently observed within
and adjaeent to several large orogenie belts. The
most spectular example is the extrusion of Indoehina
caused by the indentation of the Indian plate into
Asia in the Himalayas. Part of the shortening of the
eolliding eontinental erust was transformed into lateral extrusion of neighboring erustal fragments. This
proeess led to several long-extended strike-slip
zones, e.g. the Red River shear zone along the northem boundary of Indoehina, ~ 1 000 km long with
~ 700 km sinistral displacement. Other examples include the Eastem Alps, the northem Hungarian plain,
Turkey and the Aegean Sea (see below), the Caribbean Sea and the Bismarek Sea in the southwestem
Paeifie (Mann 1997).
A phenomenon related to continental extrusion is
the formation of transfer zones in regions where
erusts of irregular shape, thiekness and density eollide. This leads to ehanges in the angle of downbending of the lower plate and a segmentation of the
eollision zone and adjaeent basins. Examples have
been deseribed from the central Mediterranean (Sie•
Caribbean plates, westward direeted eontinental extrusion, and formation of the Cayman trough and
Yueatan trough (post-middle Mioeene stage). (After
Gordon et al. 1997, modified). e Neogene extension
and graben formation in the Aegean Sea eaused by
northward subduetion of the Afriean plate and westward eseape of Turkey along the North Anatolian
trans form fault. In the northemmost part of the
Aegean Sea and in Greeee, a southwestward dipping
detachment fault exists whieh has initiated small
halfgrabens. (Based on Dinter and Royden 1993;
Cohen et al. 1995, simplified)