12.3 Mega-Rifting and Mesozoic Sediments in Europe
573
carbonate production in keeping pace with the subsidence of the continental margins.
Germanie facies province. The fully marine facies in
the Alpine-Mediterranean Triassic was replaced by
predominantly continental clastic sediments in the
Gerrnanic facies province, i.e., on the western and
northwestern Tethyan shelves and in the
intracontinental basins of central and western Europe
(Fig. 12.16a; e.g., Schröder 1982). During the Permian, red beds, evaporites, and volcanics were deposited in narrow intramontane troughs of the former
Variscan fold belt. With the onset of the Triassic the
relief was largely peneplained, but differential subsidence (20 to 50 mlMa) of wide basins and uplift of
large blocks continued. The total thickness of the
Triassic sequence in the Germanic facies frequently
ranges from 800 to 2000 m, but is less adjacent to the
uplifted massifs. The thickness of the carbonates accumulated on the Tethyan shelves is much greater.
The term Triassic is derived from these regions, because its
sequence can be subdivided into three distinctly different
subunits(Fig.12.l6c):
(1) The lower Triassic continental Buntsandstein clastics.
The basins were filled by alluvial fans and extended red
sands tones and claystones, which accumulated in braided
and meandering fluvial systems (Tietze 1982; Mader 1985;
Perez-Arlucea and Sopena 1986). Locally, playa sediments
with evaporites were deposited. Fluvial cycles and
paleosols with silcrete and pedogenic carbonate reflect
short-term climatic variations and changes in the drainage
systems.
(2) Middle Triassic marine Muschelkalk carbonates and
evaporites. The marine environment in Central Europe is
associated with a long-term eustatic sea-level rise allowing
the Tethys Ocean to enter this area through two graben
systems, one to the east of the Bohemian massif and the
other between the Bohemian massif and Massif Central in
France (Fig. l2.l6a). To the north the basin was connected
with the Arctic Ocean by a seaway between Greenland and
Fennosarmatia. Warm and comparatively arid climate favored the production ofbiogenic carbonate and the precipitation of sulfate and halite. The carbonates show distinct
lateral facies changes ranging from open marine ramp settings to marginal banks and protected, hypersaline backbank regions (Aigner 1985). Mud flats and channels indicate moderate tidal activity (Schwarz 1975). Long-term
trends were superimposed by sea-level changes (Röhl
1990).
...
Fig. 12.16. Triassic to Jurassic riftlsag basin (megarift) evolution in Central Europe, overview. a,b
Paleotectonic and paleogeographic situation during
the middle Triassic (a Muschelkalk) and late Jurassic
(b). Abbrevations for land masses (massifs): AM
Armorican; BM Bohemian; EH Ebro High; IBM
Iberian; IM Irish; LBM London-Brabant; RM
Rhenish. (Simplified from Ziegler 1988). c Greatly
generalized Permian to lower Cretaceous sedimen(3) Upper Triassic continental beds 0/ the Keuper Group.
Most of the time huge playa lakes occupied the cemtral
parts of the basins in which red and greenish clayey marls
altemating with thin carbonate beds and some sabkha-type
evaporites accumulated, interrupted by short-term marine
ingressions. Massive, red silty clays in the uppermost part
of the sequence containing irregular layers of pedogenic
carbonate nodules are interpreted as fossil clay dunes (Sect.
2.3.3). Throughout this development, the neighboring
highlands shed sand and gravel into the basin from various
sources, but mostly from Fennosarmatia southward.
Basin fills similar to those in the central European area are
present, for example, in the Aquitaine basin, the Bay of
Biscay rift, the Paris basin, and the Celtic Sea basin (cf.
Fig. 12.l6a). These basins as well as the Gibraltar and Atlas rifts were affected by Tethyan transgressions (Ziegler
1988). In most of these basins, the Triassic sequences are
characterized by red beds and evaporites, Muschelkalktype shallow-marine carbonates, and Keuper-type playa
lake/continental deposits. In Spain, for example, the Triassic sequence is quite similar to that in Central Europe
(Garcia-Mondejar et al. 1986).
Jurassie. During the Rhaetian and early Jurassic, the
pre-existing rift systems remained active, and differential subsidence in central and western Europe continued. This development led, in combination with
long-term rising sea level, to a long-Iasting seaway
between the Tethys and Arctic Oceans (Fig. 12.l6b;
Ziegler 1988). Ocean spreading in the Tethys
prograded westward and connected the Tethys with
the evolving central Atlantic.
In Rhaetian time, the sea again invaded the central European basin and established normal marine, epicontinental
conditions until the end of the Jurassic and, in smaller areas, throughout the Cretaceous and part of the Tertiary.
Due to the influence of both the mixing of colder Arctic
water with warmer Tethys water and the increasingly humid and cooler climate, the sediments of the lower and
middle Jurassic are predominantly shales with minor contributions of fine sand and carbonate (Fig. l2.l6c). Sealevel oscillations led to widespread submarine erosional
unconformities characterized by reworked limestone and
siderite concretions, re.deposited iron ooids, and some layers containing glauconite and phosphorite.
The marked Hettangian and Toarcian transgressions
favored the formation of relatively thin, but extensive black
shale horizons. With the onset· of increasing biogenic carbonate production in the upper Jurassic, possibly associated with a trend towards a warmer climate, marls, limestones, and reefal carbonates were deposited .
tary succession in· relation to long-term sea level
changes and climatic trends. (Based on Wurster
1968; Krömmelbein 1986; Anderton et al. 1979;
Schröder 1982; Geyer and Gwinner 1986; Haq et al.
1987; Schwarzbach 1974; Frakes 1979). Note that
long-term trends are superimposed with shorter variations in climate and sea level, generating various
cyclic phenomena. See text for further explanation
573
carbonate production in keeping pace with the subsidence of the continental margins.
Germanie facies province. The fully marine facies in
the Alpine-Mediterranean Triassic was replaced by
predominantly continental clastic sediments in the
Gerrnanic facies province, i.e., on the western and
northwestern Tethyan shelves and in the
intracontinental basins of central and western Europe
(Fig. 12.16a; e.g., Schröder 1982). During the Permian, red beds, evaporites, and volcanics were deposited in narrow intramontane troughs of the former
Variscan fold belt. With the onset of the Triassic the
relief was largely peneplained, but differential subsidence (20 to 50 mlMa) of wide basins and uplift of
large blocks continued. The total thickness of the
Triassic sequence in the Germanic facies frequently
ranges from 800 to 2000 m, but is less adjacent to the
uplifted massifs. The thickness of the carbonates accumulated on the Tethyan shelves is much greater.
The term Triassic is derived from these regions, because its
sequence can be subdivided into three distinctly different
subunits(Fig.12.l6c):
(1) The lower Triassic continental Buntsandstein clastics.
The basins were filled by alluvial fans and extended red
sands tones and claystones, which accumulated in braided
and meandering fluvial systems (Tietze 1982; Mader 1985;
Perez-Arlucea and Sopena 1986). Locally, playa sediments
with evaporites were deposited. Fluvial cycles and
paleosols with silcrete and pedogenic carbonate reflect
short-term climatic variations and changes in the drainage
systems.
(2) Middle Triassic marine Muschelkalk carbonates and
evaporites. The marine environment in Central Europe is
associated with a long-term eustatic sea-level rise allowing
the Tethys Ocean to enter this area through two graben
systems, one to the east of the Bohemian massif and the
other between the Bohemian massif and Massif Central in
France (Fig. l2.l6a). To the north the basin was connected
with the Arctic Ocean by a seaway between Greenland and
Fennosarmatia. Warm and comparatively arid climate favored the production ofbiogenic carbonate and the precipitation of sulfate and halite. The carbonates show distinct
lateral facies changes ranging from open marine ramp settings to marginal banks and protected, hypersaline backbank regions (Aigner 1985). Mud flats and channels indicate moderate tidal activity (Schwarz 1975). Long-term
trends were superimposed by sea-level changes (Röhl
1990).
...
Fig. 12.16. Triassic to Jurassic riftlsag basin (megarift) evolution in Central Europe, overview. a,b
Paleotectonic and paleogeographic situation during
the middle Triassic (a Muschelkalk) and late Jurassic
(b). Abbrevations for land masses (massifs): AM
Armorican; BM Bohemian; EH Ebro High; IBM
Iberian; IM Irish; LBM London-Brabant; RM
Rhenish. (Simplified from Ziegler 1988). c Greatly
generalized Permian to lower Cretaceous sedimen(3) Upper Triassic continental beds 0/ the Keuper Group.
Most of the time huge playa lakes occupied the cemtral
parts of the basins in which red and greenish clayey marls
altemating with thin carbonate beds and some sabkha-type
evaporites accumulated, interrupted by short-term marine
ingressions. Massive, red silty clays in the uppermost part
of the sequence containing irregular layers of pedogenic
carbonate nodules are interpreted as fossil clay dunes (Sect.
2.3.3). Throughout this development, the neighboring
highlands shed sand and gravel into the basin from various
sources, but mostly from Fennosarmatia southward.
Basin fills similar to those in the central European area are
present, for example, in the Aquitaine basin, the Bay of
Biscay rift, the Paris basin, and the Celtic Sea basin (cf.
Fig. 12.l6a). These basins as well as the Gibraltar and Atlas rifts were affected by Tethyan transgressions (Ziegler
1988). In most of these basins, the Triassic sequences are
characterized by red beds and evaporites, Muschelkalktype shallow-marine carbonates, and Keuper-type playa
lake/continental deposits. In Spain, for example, the Triassic sequence is quite similar to that in Central Europe
(Garcia-Mondejar et al. 1986).
Jurassie. During the Rhaetian and early Jurassic, the
pre-existing rift systems remained active, and differential subsidence in central and western Europe continued. This development led, in combination with
long-term rising sea level, to a long-Iasting seaway
between the Tethys and Arctic Oceans (Fig. 12.l6b;
Ziegler 1988). Ocean spreading in the Tethys
prograded westward and connected the Tethys with
the evolving central Atlantic.
In Rhaetian time, the sea again invaded the central European basin and established normal marine, epicontinental
conditions until the end of the Jurassic and, in smaller areas, throughout the Cretaceous and part of the Tertiary.
Due to the influence of both the mixing of colder Arctic
water with warmer Tethys water and the increasingly humid and cooler climate, the sediments of the lower and
middle Jurassic are predominantly shales with minor contributions of fine sand and carbonate (Fig. l2.l6c). Sealevel oscillations led to widespread submarine erosional
unconformities characterized by reworked limestone and
siderite concretions, re.deposited iron ooids, and some layers containing glauconite and phosphorite.
The marked Hettangian and Toarcian transgressions
favored the formation of relatively thin, but extensive black
shale horizons. With the onset· of increasing biogenic carbonate production in the upper Jurassic, possibly associated with a trend towards a warmer climate, marls, limestones, and reefal carbonates were deposited .
tary succession in· relation to long-term sea level
changes and climatic trends. (Based on Wurster
1968; Krömmelbein 1986; Anderton et al. 1979;
Schröder 1982; Geyer and Gwinner 1986; Haq et al.
1987; Schwarzbach 1974; Frakes 1979). Note that
long-term trends are superimposed with shorter variations in climate and sea level, generating various
cyclic phenomena. See text for further explanation