12.4 Intracontinental Sag Basins
ted in Fig. 12.17e) and eharaeterized by inereasing hiatuses
from south to north. The reason for this asymmetry in the
stratigraphicehart is that the southem end ofthe basin was
situated closer to a rift zone eonneeted with the sea and
emerged later than the northem part of the basin which was
filled with sediment more rapidly. Tbe rift-stage sediments
of the Illinois basin are siliciclastics; the post-rift sediments
contain roughly 50% dolomites and limestones, 25% sandstones, and 25% siltstones and shales.
Due to their long lifetimes, most of the intracontinental basins experienced significant changes in
their paleolatitudes and climate. Many ofthem record
changes from arid to humid conditions (reflected by
evaporites and coals). Lacustrine and restricted marine phases led to the formation of black shales;
reefs, prograding coastal and fluvial sands created
source rocks. Some of the early Paleozoic sediment
fills reflect the evolution of land plants and rockforming marine organisms from the Proterozoic era
to Phanerozoic times. Several basins in the southem
hernisphere contain tillites of the Permo-Carboniferous and older glacial periods. The high contribution
of late Jurassic/early Cretaceous basaltic rocks in the
filling of the Parana basin in South America, which
is related to the opening of the South Atlantic, is a
sirnilar phenomenon is the hot spot of Iceland and
East Greenland mentioned above.
Climate contrasts are particularly pronounced during the
existence of Pangea from the middle Carboniferous to the
middle Jurassie. The center of the Permo-Carboniferous
glaciation moved from South America via South Afriea,
Fig. 12.17. a Global distribution of intracontinental
sag basins (overview). Main zones of Atlantic-type
continental margin basins and zones of basins associated with plate convergence (Mesozoic-Cenozoic
mega-sutures) are indicated for comparison. b Principal features of two- and three-cycle sag basins. (Af577
India and Antaretica to Australia. At the same time, peat
fonned in low latitudes and evaporites in higher latitudes
ofthe northem hemisphere (e.g. Francis 1994). A long-distance high-resolution stratigraphie correlation of basins on
the northem hemisphere was proposed by Ross and Ross
(1995) for the Perrnian. An improved numerical time scale
for the Perrnian and Triassie
has shown, for example, that the average duration of eaeh
Zechstein evaporite cycle was about 1 Ma (Menning 1995).
Tbe sedimentary fill of some basins may exemplify the
wide range in the depositional environments of sag basins:
Western Siberian basin. Tbis huge basin is known for
its rieh hydrocarbon reserves. It accumulated mainly continental and volcaniclastic deposits during its first cycle. Tbe
Jurassie is rich in coal-bearing strata and bituminous
shallow-marine shales. In total, 7-8 km of sediment were
deposited in the central part and 10-12 km in the northem
and northeastem part ofthe basin (Khain 1994).
Michigan basin, North America. This basin collected
sediments from the Cambrian to the Jurassie, and then
again in the Quatemary, but it also experienced periods of
erosion and sediment starvation (Fisher et al. 1988). After
an initial stage of continental and shaIlow-marine deposition, the basin displays two upper Silurian, 600 m thick
evaporite-carbonate cycles, which are replaced along the
margins by reefs and skeletal shoals, while on the slopes
and in deeper water pinnacle reefs occur (Schreiber
1988b).
Murzuk and Kufra basins, North Africa. Tbe fiIls of
these basins are only 2 to 3 km thick and consist predominantly of fluvial deposits (Nubian sandstone ), which were
transported in northerly directions (SeIley 1985a). In the
late Cretaceous and early Tertiary, the basins were flooded
bythe sea.
ter Kingston et al. 1983). c Mega-sequences separated by major unconformities, Illinois basin, USA,
simplified, post-Permian development not shown.
d Subsidence history of Illinois basin. (a,c,d After
Leighton and Kolata 1990)
ted in Fig. 12.17e) and eharaeterized by inereasing hiatuses
from south to north. The reason for this asymmetry in the
stratigraphicehart is that the southem end ofthe basin was
situated closer to a rift zone eonneeted with the sea and
emerged later than the northem part of the basin which was
filled with sediment more rapidly. Tbe rift-stage sediments
of the Illinois basin are siliciclastics; the post-rift sediments
contain roughly 50% dolomites and limestones, 25% sandstones, and 25% siltstones and shales.
Due to their long lifetimes, most of the intracontinental basins experienced significant changes in
their paleolatitudes and climate. Many ofthem record
changes from arid to humid conditions (reflected by
evaporites and coals). Lacustrine and restricted marine phases led to the formation of black shales;
reefs, prograding coastal and fluvial sands created
source rocks. Some of the early Paleozoic sediment
fills reflect the evolution of land plants and rockforming marine organisms from the Proterozoic era
to Phanerozoic times. Several basins in the southem
hernisphere contain tillites of the Permo-Carboniferous and older glacial periods. The high contribution
of late Jurassic/early Cretaceous basaltic rocks in the
filling of the Parana basin in South America, which
is related to the opening of the South Atlantic, is a
sirnilar phenomenon is the hot spot of Iceland and
East Greenland mentioned above.
Climate contrasts are particularly pronounced during the
existence of Pangea from the middle Carboniferous to the
middle Jurassie. The center of the Permo-Carboniferous
glaciation moved from South America via South Afriea,
Fig. 12.17. a Global distribution of intracontinental
sag basins (overview). Main zones of Atlantic-type
continental margin basins and zones of basins associated with plate convergence (Mesozoic-Cenozoic
mega-sutures) are indicated for comparison. b Principal features of two- and three-cycle sag basins. (Af577
India and Antaretica to Australia. At the same time, peat
fonned in low latitudes and evaporites in higher latitudes
ofthe northem hemisphere (e.g. Francis 1994). A long-distance high-resolution stratigraphie correlation of basins on
the northem hemisphere was proposed by Ross and Ross
(1995) for the Perrnian. An improved numerical time scale
for the Perrnian and Triassie
has shown, for example, that the average duration of eaeh
Zechstein evaporite cycle was about 1 Ma (Menning 1995).
Tbe sedimentary fill of some basins may exemplify the
wide range in the depositional environments of sag basins:
Western Siberian basin. Tbis huge basin is known for
its rieh hydrocarbon reserves. It accumulated mainly continental and volcaniclastic deposits during its first cycle. Tbe
Jurassie is rich in coal-bearing strata and bituminous
shallow-marine shales. In total, 7-8 km of sediment were
deposited in the central part and 10-12 km in the northem
and northeastem part ofthe basin (Khain 1994).
Michigan basin, North America. This basin collected
sediments from the Cambrian to the Jurassie, and then
again in the Quatemary, but it also experienced periods of
erosion and sediment starvation (Fisher et al. 1988). After
an initial stage of continental and shaIlow-marine deposition, the basin displays two upper Silurian, 600 m thick
evaporite-carbonate cycles, which are replaced along the
margins by reefs and skeletal shoals, while on the slopes
and in deeper water pinnacle reefs occur (Schreiber
1988b).
Murzuk and Kufra basins, North Africa. Tbe fiIls of
these basins are only 2 to 3 km thick and consist predominantly of fluvial deposits (Nubian sandstone ), which were
transported in northerly directions (SeIley 1985a). In the
late Cretaceous and early Tertiary, the basins were flooded
bythe sea.
ter Kingston et al. 1983). c Mega-sequences separated by major unconformities, Illinois basin, USA,
simplified, post-Permian development not shown.
d Subsidence history of Illinois basin. (a,c,d After
Leighton and Kolata 1990)