636
high that the underlying pull-apart basins and their spreading troughs are filled up (Fig. 12.44e; Fuis and Kohler
1984; Einseie 1986) and no longer have a topographie expression. The Pliocene to Quaternary infilling ofthe Imperial Valley depression is 5 to 6 km thiek and begins with an
approximately 1000 m thiek shallow-marine to braekish
sequenee overlain by very thick, mainly laeustrine and fluvial deposits (Quinn and Cronin 1984). Their basement,
eonsisting of rift-stage ernst and newly formed oeeanie
ernst, is depressed under the high sediment load. Magma of
basaltie to aeidie eomposition rarely extrudes at the surfaee
of the alluvial plain.
This sediment volume/space estimate and further
evaluations utilizing other assumptions indicate that
Gulf of Califomia-type spreading troughs can be
maintained under very high sedimentation rates if the
12.8.5 Summary (Pu li-Apart Basins)
- Pure strike-slip motions and trans tension along
trans form faults create narrow pull-apart basins
of variable length (often several tens to hundreds of kilometers) in continental and oceanic
settings.
- The floor of long basins tends to subside deeper
than that of short basins. Long basins may develop oceanic spreading troughs with the intrusion of basaltic magma.
- Rapid strike-slip causes extremely fast subsidence and thus often an early, short phase of
basin deepening. Later subsidence is driven
mainly by the increasing sediment load.
Continental pull-aparts commonly collect alluvial fans, fluvial and lacustrine deposits. These
basin fills are mostly asymmetrie in both longitudinal and cross sections.
Chapter 12 Basin Evolution and Sediments
rate of strike-slip and crustal accretion is also high.
In this case, the basaltic magma rarely extrudes on
the sea floor, but rather generates a sill-sediment
complex of several hundreds of meters in thickness
between sheeted dikes (oceanic layer 2) and the sediment cover (layer 1, cf. Sect. 13.8.3). In contrast, low
sedimentation rates in conjunction with normal
spreading rates (l to 10 crn/a) lead to very thin sediment covers on top of newly accreted crust.
Penninian (Valais) trough of the Alps. The Mesozoie
northern Penninian trough may represent an aneient exampie of a tee tonic setting, depositional environment
(Bündnerschiefer), and intrusion ofbasaltic magma similar
to the modern Gulf of California (Kelts 1981).
Displaced fanlsource relationships, the migration of depocenters parallel to the master
faults, and special tectonic . features provide
evidence for strike-slip motion.
The sedimentation rates, sediment thicknesses
(in limited areas), and structural complexities
of pull-aparts are often greater than those of
rift basins.
The life span of pull-apart basins is commonly
short (a few millions of years).- Pull-apart basins can be interesting targets for hydrocarbon
exploration in spite of their limited size. Rapid
subsidence and burial of source rocks favor the
preservation and maturation of organic matter
(cf. Sect. 10.3.3).
high that the underlying pull-apart basins and their spreading troughs are filled up (Fig. 12.44e; Fuis and Kohler
1984; Einseie 1986) and no longer have a topographie expression. The Pliocene to Quaternary infilling ofthe Imperial Valley depression is 5 to 6 km thiek and begins with an
approximately 1000 m thiek shallow-marine to braekish
sequenee overlain by very thick, mainly laeustrine and fluvial deposits (Quinn and Cronin 1984). Their basement,
eonsisting of rift-stage ernst and newly formed oeeanie
ernst, is depressed under the high sediment load. Magma of
basaltie to aeidie eomposition rarely extrudes at the surfaee
of the alluvial plain.
This sediment volume/space estimate and further
evaluations utilizing other assumptions indicate that
Gulf of Califomia-type spreading troughs can be
maintained under very high sedimentation rates if the
12.8.5 Summary (Pu li-Apart Basins)
- Pure strike-slip motions and trans tension along
trans form faults create narrow pull-apart basins
of variable length (often several tens to hundreds of kilometers) in continental and oceanic
settings.
- The floor of long basins tends to subside deeper
than that of short basins. Long basins may develop oceanic spreading troughs with the intrusion of basaltic magma.
- Rapid strike-slip causes extremely fast subsidence and thus often an early, short phase of
basin deepening. Later subsidence is driven
mainly by the increasing sediment load.
Continental pull-aparts commonly collect alluvial fans, fluvial and lacustrine deposits. These
basin fills are mostly asymmetrie in both longitudinal and cross sections.
Chapter 12 Basin Evolution and Sediments
rate of strike-slip and crustal accretion is also high.
In this case, the basaltic magma rarely extrudes on
the sea floor, but rather generates a sill-sediment
complex of several hundreds of meters in thickness
between sheeted dikes (oceanic layer 2) and the sediment cover (layer 1, cf. Sect. 13.8.3). In contrast, low
sedimentation rates in conjunction with normal
spreading rates (l to 10 crn/a) lead to very thin sediment covers on top of newly accreted crust.
Penninian (Valais) trough of the Alps. The Mesozoie
northern Penninian trough may represent an aneient exampie of a tee tonic setting, depositional environment
(Bündnerschiefer), and intrusion ofbasaltic magma similar
to the modern Gulf of California (Kelts 1981).
Displaced fanlsource relationships, the migration of depocenters parallel to the master
faults, and special tectonic . features provide
evidence for strike-slip motion.
The sedimentation rates, sediment thicknesses
(in limited areas), and structural complexities
of pull-aparts are often greater than those of
rift basins.
The life span of pull-apart basins is commonly
short (a few millions of years).- Pull-apart basins can be interesting targets for hydrocarbon
exploration in spite of their limited size. Rapid
subsidence and burial of source rocks favor the
preservation and maturation of organic matter
(cf. Sect. 10.3.3).