632
ins can be seen from Fig. 12.42e. Here, the length of
the basin, i.e., the amount of strike-slip displacement
represented by the overlap of the master faults, is
plotted versus maximum sediment thickness of the
basin. Short basins have a comparatively shallow
basin floor, while long pull-aparts tend to be very
deep and display one or two depocenters on newly
formed oceanic crust. Known basin depths range
from a few hundred meters up to 7-10 km (Dead Sea,
Los Angeles basin, and some troughs in the
Pannonian basin).
The general principles in the evolution of pull-apart basins
are discussed, e.g., by Ballance and Reading (1980), Reading (1980), Mann et al. (1983), Hempton and Dunne
(1984), Biddle and Christie-Blick (1985), Ben-Avraham
and Zoback (1992).
12.8.2 Sediments of Pull-Apart Basins
In their early stage of evolution, the rapidly subsiding
basins tend to be filled by lake or sea water, as long
as rivers or other sediment transporting systems are
not yet adjusted to the newly formed morphologie
depression. Later, modified or newly developed
drainage systems of rivers or submarine canyons can
funnel larger volumes of sediment into the pullaparts and enable them to keep pace with or overcome subsidence. Mean sedimentation rates of
known basin fills are very high ranging from 0.5 to 4
mlka.
Another characteristic feature of many pull-aparts
is their asymmetrie basin fill displayed in both longitudinal and lateral sections. The basin margin
bounded by a strike-slip fault is usually characterized
by a steep fault scarp of high relief, while the opposite side is more irregular and morphologically less
pronounced. Hence, lateral cross sections mostly
show deep downfaulting on the side of the dominant
fault and less subsidence on the opposite side along
the subordinate fault system (Fig. 12.43a,b).
Several of the modern examples on land (e.g., the Dead
Sea, the Death Valley in California, the Erzincan Basin in
Turkey) showarelief ranging from 2000 to ~4000 m on
the strike-slip bounded side. Pull-apart basins below the
sea display similar morphological features (e.g., the troughs
ofthe Californian borderland, see below).
Continental pull-apart basins are frequently filled
with fluvial and lake deposits, but these facies have a
limited lateral extent (Fig. 12.43b). These two facies
associations can create cyclic basin fills when a kind
of balance between sediment supply and basin subsidence exists. Then moderate tectonic pulses (e.g. episodic strike-slip and subsidence) or climate change
from humid to semiarid can repeatedly shift the
depositional system from lacustrine to braidplain faChapter 12 Basin Evolution and Sediments
eies and vice versa (e.g. Plint and Browne 1994). If
an asymmetrie basin is fed predominantly from its
sides, the deeply downfaulted, high-relief side of the
basin commonly displays marginal sediments consisting of locally derived coarse-grained alluvial fans
and debris flows. By contrast, the opposite, subordinate margin is characterized by a wider zone of finer
materials of alluvial plains built up by gentler
streams. The remaining, more central part of the basin tends to be filled with deltaic sediments and various lake deposits depending on the climate of the
region. Pull-aparts in humid climates may accumulate
some black shales and peat. External drainage in
conjunction with an open lake system or a throughflowing river may be replaced in more arid climate
by an internal drainage system dropping its total dissolved and suspended load in the basin (cf. Sect.
12.1.3, Fig. 12.4).
If a pull-apart basin is fed from one end by a river
sufficiently competent to keep it filled all the time, a
depositional architecture similar to that shown in Fig.
12.43a may result. In this case, the depocenter migrates away from the direction of the strike-slip motion, and the sediments young upstream as shown by
the dip of the strata. Hence, the thickness of the dipping strata may turn out to be greater than the true
basin depth. However, if a major river enters the basin from the opposite end, the depocenter tends to
migrate downstream.
Strike-slip motion and particularly transtension is
frequently accompanied by voleanism of variable
nature including silicic and intermediate magmas.
Hence, volcaniclastic sediments often contribute to
the fillings of pull-apart basins.
Marine pull-apart basins evolve along continental
margins or on subsided continental blocks. Here, deposition may begin with comparatively deep-marine
facies, including mass flows and turbidites. As the
basins enlarge their drainage area and become increasingly filled, their depositional environment
passes to shallow-marine and finally continental conditions.
Basins far away from efficient sediment sources form special troughs which are considerably deeper than the neighboring sea floor. These basins tend to remain underfilled
for considerable time spans. Their sedimentary facies may
include pelagic sediments and deposits of submarine fans
and gravity mass movements. Such basins exist in the Gulf
of Aden, the Red Sea, and the Gulf of California (cf. Sect.
4.3). The large Cayman trough in the Caribbean Sea has a
mean depth of 5 km below sea level and contains a sediment cover of significant thickness (:; 1000 m) only in its
eastern part.
ins can be seen from Fig. 12.42e. Here, the length of
the basin, i.e., the amount of strike-slip displacement
represented by the overlap of the master faults, is
plotted versus maximum sediment thickness of the
basin. Short basins have a comparatively shallow
basin floor, while long pull-aparts tend to be very
deep and display one or two depocenters on newly
formed oceanic crust. Known basin depths range
from a few hundred meters up to 7-10 km (Dead Sea,
Los Angeles basin, and some troughs in the
Pannonian basin).
The general principles in the evolution of pull-apart basins
are discussed, e.g., by Ballance and Reading (1980), Reading (1980), Mann et al. (1983), Hempton and Dunne
(1984), Biddle and Christie-Blick (1985), Ben-Avraham
and Zoback (1992).
12.8.2 Sediments of Pull-Apart Basins
In their early stage of evolution, the rapidly subsiding
basins tend to be filled by lake or sea water, as long
as rivers or other sediment transporting systems are
not yet adjusted to the newly formed morphologie
depression. Later, modified or newly developed
drainage systems of rivers or submarine canyons can
funnel larger volumes of sediment into the pullaparts and enable them to keep pace with or overcome subsidence. Mean sedimentation rates of
known basin fills are very high ranging from 0.5 to 4
mlka.
Another characteristic feature of many pull-aparts
is their asymmetrie basin fill displayed in both longitudinal and lateral sections. The basin margin
bounded by a strike-slip fault is usually characterized
by a steep fault scarp of high relief, while the opposite side is more irregular and morphologically less
pronounced. Hence, lateral cross sections mostly
show deep downfaulting on the side of the dominant
fault and less subsidence on the opposite side along
the subordinate fault system (Fig. 12.43a,b).
Several of the modern examples on land (e.g., the Dead
Sea, the Death Valley in California, the Erzincan Basin in
Turkey) showarelief ranging from 2000 to ~4000 m on
the strike-slip bounded side. Pull-apart basins below the
sea display similar morphological features (e.g., the troughs
ofthe Californian borderland, see below).
Continental pull-apart basins are frequently filled
with fluvial and lake deposits, but these facies have a
limited lateral extent (Fig. 12.43b). These two facies
associations can create cyclic basin fills when a kind
of balance between sediment supply and basin subsidence exists. Then moderate tectonic pulses (e.g. episodic strike-slip and subsidence) or climate change
from humid to semiarid can repeatedly shift the
depositional system from lacustrine to braidplain faChapter 12 Basin Evolution and Sediments
eies and vice versa (e.g. Plint and Browne 1994). If
an asymmetrie basin is fed predominantly from its
sides, the deeply downfaulted, high-relief side of the
basin commonly displays marginal sediments consisting of locally derived coarse-grained alluvial fans
and debris flows. By contrast, the opposite, subordinate margin is characterized by a wider zone of finer
materials of alluvial plains built up by gentler
streams. The remaining, more central part of the basin tends to be filled with deltaic sediments and various lake deposits depending on the climate of the
region. Pull-aparts in humid climates may accumulate
some black shales and peat. External drainage in
conjunction with an open lake system or a throughflowing river may be replaced in more arid climate
by an internal drainage system dropping its total dissolved and suspended load in the basin (cf. Sect.
12.1.3, Fig. 12.4).
If a pull-apart basin is fed from one end by a river
sufficiently competent to keep it filled all the time, a
depositional architecture similar to that shown in Fig.
12.43a may result. In this case, the depocenter migrates away from the direction of the strike-slip motion, and the sediments young upstream as shown by
the dip of the strata. Hence, the thickness of the dipping strata may turn out to be greater than the true
basin depth. However, if a major river enters the basin from the opposite end, the depocenter tends to
migrate downstream.
Strike-slip motion and particularly transtension is
frequently accompanied by voleanism of variable
nature including silicic and intermediate magmas.
Hence, volcaniclastic sediments often contribute to
the fillings of pull-apart basins.
Marine pull-apart basins evolve along continental
margins or on subsided continental blocks. Here, deposition may begin with comparatively deep-marine
facies, including mass flows and turbidites. As the
basins enlarge their drainage area and become increasingly filled, their depositional environment
passes to shallow-marine and finally continental conditions.
Basins far away from efficient sediment sources form special troughs which are considerably deeper than the neighboring sea floor. These basins tend to remain underfilled
for considerable time spans. Their sedimentary facies may
include pelagic sediments and deposits of submarine fans
and gravity mass movements. Such basins exist in the Gulf
of Aden, the Red Sea, and the Gulf of California (cf. Sect.
4.3). The large Cayman trough in the Caribbean Sea has a
mean depth of 5 km below sea level and contains a sediment cover of significant thickness (:; 1000 m) only in its
eastern part.