l
Plate- Tectonic Setting of Alluvial Basins
11.4.4 Basins Formed Along Strike-Slip Faults
As shown by Miall ( 1990, Table 9.6), strike-slip faults
occur in a variety of plate-tectonic settings. Of
concern here are those which constitute intracontinental plate-boundary transform faults and the
boundaries of divergent plate margins. In both settings, basins with significant nonmarine fills occur.
Plate boundaries undergoing oblique convergence
may also undergo strike-slip displacement, with the
offset typically localized along the axis of the
magmatic arc. The Sunda Arc of Sumatra offers an
example of this, and the forearc and backarc basins
of this area show the influence of wrench tectonics,
as described by Hamilton (1979) and Hutchison
(1989). Another important class of strike-slip-faultbounded basin is that which occurs as a result of
escape tectonics in the hinterland regions adjacent
to continental sutures. These basins are discussed in
Sect. 11.4.5.2.
Following the work of Luyendyk and Hornafius
(1987), Ingersoll (1988) proposed the definition of a
class of transrotational basins developed by block
rotation around vertical axes within strike-slip fault
zones. Such rotation causes thrust faulting where
blocks overlap and basins where blocks are rotated
apart. Luyendyk and Hornafius (1987) demonstrated that many Neogene basins in southern California are of this type.
It is important to realize that strike-slip motion
may, in fact, be a superficial representation of deep
crustal processes that show quite different structural
style. For example, the construction of the
Carpathian Mountains during the Neogene involved
differential movement of nappes along flat thrust
faults. These nappes, which moved at different
times, are separated in places by steep faults, which
show a history . of strike-slip movement where
the nappes were displaced relative to each other.
The Vienna Basin is a pull-apart basin that was created in this way (Royden 1985). Conversely, it has
now been shown that the Hornelen Basin of the
Norwegian Caledonides, long cited as a classic example of a strike-slip basin (e.g., see Steel and
Gloppen 1980) is soled by a low-angle extensional
detachment surface. This surface is scoop shaped.
Where the edges of the scoop reach the surface,
extensional movement shows a strike-slip motion
relative to adjacent undisturbed strata (Hossack
1984; Seranne and Segnret 1987). May et al. (1993)
have demonstrated that the San Gabriel fault,
bounding the Ridge Basin, is also a low-angle detachment fault.
393
11.4.4.1 Basins Associated
with Intracontinental Transform Faults
The San Andreas fault system in California and the
Alpine fault of New Zealand are the best-known
intracontinental transform faults, and much of our
knowledge of fault tectonics and basin style is derived from studies in these areas.
Ridge Basin, near Los Angeles, is a well-exposed
example of a basin developed by supracrustal loading in a transpressional setting, and excellent studies
by Crowell (l974b), Link and Osborne (1978),
Crowell and Link (1982), and Link (1984) have
turned it into a classic of its kind. The basin was
active during Miocene and Pliocene time, when the
San Gabriel Fault was the master fault (it is now
inactive). Salton Trough, at the head of the Gulf of
California, is an example of a pull-apart basin. It was
initiated during the Miocene and is still active, so it
has not been uplifted and dissected for our examination as has the Ridge Basin. Volcanism, heat flow
data, and tectonism in the Salton Trough suggest
that it is an incipient spreading center (Crowell
1974a) and may eventually open fully to expose new
oceanic crust, as in the Gulf of California. This would
accord with what appears to be a pattern of oblique
spreading in the area (a "leaky transform"). Based
on several Californian basins, Crowell (1974b) proposed a general model of pull-apart structure and
stratigraphy as shown in Fig. I 1.56.
Tolus breccias ond ropid
focies chonqes bosinword
smoll lhrtJsl ploles
braided right- �lip wne
right-slip fotJII conlinu�s on
to sol.llheost
comp!n
corner
morg•n· folds,
result of convergence
between boundary
righl·slip /oults
Fig. 11.56. A general model for pull-apart basins. (Crowell
!974b)
Plate- Tectonic Setting of Alluvial Basins
11.4.4 Basins Formed Along Strike-Slip Faults
As shown by Miall ( 1990, Table 9.6), strike-slip faults
occur in a variety of plate-tectonic settings. Of
concern here are those which constitute intracontinental plate-boundary transform faults and the
boundaries of divergent plate margins. In both settings, basins with significant nonmarine fills occur.
Plate boundaries undergoing oblique convergence
may also undergo strike-slip displacement, with the
offset typically localized along the axis of the
magmatic arc. The Sunda Arc of Sumatra offers an
example of this, and the forearc and backarc basins
of this area show the influence of wrench tectonics,
as described by Hamilton (1979) and Hutchison
(1989). Another important class of strike-slip-faultbounded basin is that which occurs as a result of
escape tectonics in the hinterland regions adjacent
to continental sutures. These basins are discussed in
Sect. 11.4.5.2.
Following the work of Luyendyk and Hornafius
(1987), Ingersoll (1988) proposed the definition of a
class of transrotational basins developed by block
rotation around vertical axes within strike-slip fault
zones. Such rotation causes thrust faulting where
blocks overlap and basins where blocks are rotated
apart. Luyendyk and Hornafius (1987) demonstrated that many Neogene basins in southern California are of this type.
It is important to realize that strike-slip motion
may, in fact, be a superficial representation of deep
crustal processes that show quite different structural
style. For example, the construction of the
Carpathian Mountains during the Neogene involved
differential movement of nappes along flat thrust
faults. These nappes, which moved at different
times, are separated in places by steep faults, which
show a history . of strike-slip movement where
the nappes were displaced relative to each other.
The Vienna Basin is a pull-apart basin that was created in this way (Royden 1985). Conversely, it has
now been shown that the Hornelen Basin of the
Norwegian Caledonides, long cited as a classic example of a strike-slip basin (e.g., see Steel and
Gloppen 1980) is soled by a low-angle extensional
detachment surface. This surface is scoop shaped.
Where the edges of the scoop reach the surface,
extensional movement shows a strike-slip motion
relative to adjacent undisturbed strata (Hossack
1984; Seranne and Segnret 1987). May et al. (1993)
have demonstrated that the San Gabriel fault,
bounding the Ridge Basin, is also a low-angle detachment fault.
393
11.4.4.1 Basins Associated
with Intracontinental Transform Faults
The San Andreas fault system in California and the
Alpine fault of New Zealand are the best-known
intracontinental transform faults, and much of our
knowledge of fault tectonics and basin style is derived from studies in these areas.
Ridge Basin, near Los Angeles, is a well-exposed
example of a basin developed by supracrustal loading in a transpressional setting, and excellent studies
by Crowell (l974b), Link and Osborne (1978),
Crowell and Link (1982), and Link (1984) have
turned it into a classic of its kind. The basin was
active during Miocene and Pliocene time, when the
San Gabriel Fault was the master fault (it is now
inactive). Salton Trough, at the head of the Gulf of
California, is an example of a pull-apart basin. It was
initiated during the Miocene and is still active, so it
has not been uplifted and dissected for our examination as has the Ridge Basin. Volcanism, heat flow
data, and tectonism in the Salton Trough suggest
that it is an incipient spreading center (Crowell
1974a) and may eventually open fully to expose new
oceanic crust, as in the Gulf of California. This would
accord with what appears to be a pattern of oblique
spreading in the area (a "leaky transform"). Based
on several Californian basins, Crowell (1974b) proposed a general model of pull-apart structure and
stratigraphy as shown in Fig. I 1.56.
Tolus breccias ond ropid
focies chonqes bosinword
smoll lhrtJsl ploles
braided right- �lip wne
right-slip fotJII conlinu�s on
to sol.llheost
comp!n
corner
morg•n· folds,
result of convergence
between boundary
righl·slip /oults
Fig. 11.56. A general model for pull-apart basins. (Crowell
!974b)