(Platt et al. 2013) who suggest rapid subsidence at the WAB initiation. The lower
Miocene deposits are found overlying a basement composed of metamorphic units
related to the Alpujarride-Sebtide Complex (Comas et al. 1999), or to the
Malaguide-Ghomaride Complex (Do Couto et al. 2016). The origin of subsidence
responsible for the deposition and fast burial of the sediments (causing
undercompaction) can be found in the extreme thinning of the crust associated
with the extensional detachments described onshore in the Beticas-Rif system.
The Middle Miocene (Langhian—Serravallian) witnesses the deposition of two
sub-units: (1) a lower unit made of clays, interbedded silty to sandy clays, and basal
coarse-grained sandstone, the unit displaying typical features of undercompaction
with abnormal overpressures; and (2) an upper unit consisting of well-graded sandsilt-clay turbidites and turbiditic muds interbedded with volcanogenic layers. The
lower Langhian unit, presenting signs of overpressure, was deposited in syn-rift
settings as in the lower Miocene. However, at the end of the Burdigalian, the
extensional setting of the Alboran Domain changes from regional N-S extension to
widespread E-W extension. Such a transition triggered a moderate subsidence step in
the WAB and adjacent basins. During the Serravallian, E-W extension proceeded
westward, leading to the exhumation of E-W elongated metamorphic domes inland,
thereby triggering the onset of subsidence in the southeastern Betics. This modification of the lithospheric configuration largely affected the WAB, which recorded
the onset of a strong subsidence phase, signaled by an up to 3 km-thick Serravallian
sequence (Do Couto et al. 2016).
The geometry of the Serravallian sequences, exhibiting overall landward to
basinward onlap geometry, indicates that the WAB underwent relatively homogeneous yet intense subsidence (“sag basin”) during part of its evolution. This period
coincides with high volcanic activity in the Alboran Sea, recorded in the thick
volcaniclastic series. Subsidence evaluation indicates two successive Langhian and
Serravallian subsidence pulses (e.g., Comas et al. 1999) leading to the deposition of
deep sea turbiditic fans. Elsewhere in the Alboran Sea, the Serravallian is also
present in the SAB, marking the deepest deposits (Martínez-García et al. 2017).
The sag basin geometry is indicative of subsidence along a relative thermal cooling
period of the crust (White and McKenzie 1989). Besides, subsidence was accompanied by flexural basement tilting, both to the southeast in the norther margin and to
the northwest in the southern one (Vázquez 2001; Soto et al. 2010; Do Couto et al.
2016). These processes favor a slope tectonics of overpressured shales caused a
downslope migration, which also resulted in secondary basin subsidence (Soto et al.
2010).
The Upper Miocene (Tortonian-Messinian) is a key period in the WAB. It
encompasses the transition from a regional tectonic extensional setting to a compressive regime. The lower Tortonian is marked by the deposition of graded sandsilt-clay turbidites interbedded with a few volcanogenic layers. The widespread
spatial distribution and rather isopach character of this stratigraphic sequence indicate the end of the mostly extensional period. Its topmost surface is nowadays folded
and partly eroded. Above, the upper Tortonian comprises sandstone intervals, with
claystones and silty clay beds, also corresponding to turbidite facies with some
134
J.-T. Vázquez et al.
Miocene deposits are found overlying a basement composed of metamorphic units
related to the Alpujarride-Sebtide Complex (Comas et al. 1999), or to the
Malaguide-Ghomaride Complex (Do Couto et al. 2016). The origin of subsidence
responsible for the deposition and fast burial of the sediments (causing
undercompaction) can be found in the extreme thinning of the crust associated
with the extensional detachments described onshore in the Beticas-Rif system.
The Middle Miocene (Langhian—Serravallian) witnesses the deposition of two
sub-units: (1) a lower unit made of clays, interbedded silty to sandy clays, and basal
coarse-grained sandstone, the unit displaying typical features of undercompaction
with abnormal overpressures; and (2) an upper unit consisting of well-graded sandsilt-clay turbidites and turbiditic muds interbedded with volcanogenic layers. The
lower Langhian unit, presenting signs of overpressure, was deposited in syn-rift
settings as in the lower Miocene. However, at the end of the Burdigalian, the
extensional setting of the Alboran Domain changes from regional N-S extension to
widespread E-W extension. Such a transition triggered a moderate subsidence step in
the WAB and adjacent basins. During the Serravallian, E-W extension proceeded
westward, leading to the exhumation of E-W elongated metamorphic domes inland,
thereby triggering the onset of subsidence in the southeastern Betics. This modification of the lithospheric configuration largely affected the WAB, which recorded
the onset of a strong subsidence phase, signaled by an up to 3 km-thick Serravallian
sequence (Do Couto et al. 2016).
The geometry of the Serravallian sequences, exhibiting overall landward to
basinward onlap geometry, indicates that the WAB underwent relatively homogeneous yet intense subsidence (“sag basin”) during part of its evolution. This period
coincides with high volcanic activity in the Alboran Sea, recorded in the thick
volcaniclastic series. Subsidence evaluation indicates two successive Langhian and
Serravallian subsidence pulses (e.g., Comas et al. 1999) leading to the deposition of
deep sea turbiditic fans. Elsewhere in the Alboran Sea, the Serravallian is also
present in the SAB, marking the deepest deposits (Martínez-García et al. 2017).
The sag basin geometry is indicative of subsidence along a relative thermal cooling
period of the crust (White and McKenzie 1989). Besides, subsidence was accompanied by flexural basement tilting, both to the southeast in the norther margin and to
the northwest in the southern one (Vázquez 2001; Soto et al. 2010; Do Couto et al.
2016). These processes favor a slope tectonics of overpressured shales caused a
downslope migration, which also resulted in secondary basin subsidence (Soto et al.
2010).
The Upper Miocene (Tortonian-Messinian) is a key period in the WAB. It
encompasses the transition from a regional tectonic extensional setting to a compressive regime. The lower Tortonian is marked by the deposition of graded sandsilt-clay turbidites interbedded with a few volcanogenic layers. The widespread
spatial distribution and rather isopach character of this stratigraphic sequence indicate the end of the mostly extensional period. Its topmost surface is nowadays folded
and partly eroded. Above, the upper Tortonian comprises sandstone intervals, with
claystones and silty clay beds, also corresponding to turbidite facies with some
134
J.-T. Vázquez et al.