WAB underwent relatively homogeneous yet intense subsidence, interpreted as
being controlled by the pull of the dipping subducting lithosphere and relative
thermal cooling of the crust probably after the magmatic stages 1 and 2 (TorresRoldán et al. 1986; Duggen et al. 2004), thereby explaining the considerable
thickness (10 km) of the sedimentary infill (Do Couto et al. 2016). It is worth noting
that deep structures in the basement imaged by means of deep seismic reflection
profiles in the northern half of the Alboran Basin have been interpreted as extensional shear zones, associated with major extensional detachments in the Betic
Cordillera (Watts et al. 1993; Vázquez et al. 1995; Vegas et al. 1995; Comas et al.
1997). The Motril Basin (northern E-W elongated part of the WAB) exhibits a rather
different pattern, with an asymmetric geometry (Comas et al. 1999) comparable in
shape to the asymmetric intramontane basins described inland (e.g., Sorbas Basin,
Fig. 5.4), even though the total thickness of sedimentary rocks is far greater (<7 km).
While the southern branch of the WAB is strongly affected by late-Miocene-topresent compression that produces its inversion, folding, and uplifting to constitute
the Xauén and Francesc Pagés banks (d’Acremont et al. 2020; Lafosse et al. 2020).
The SAB and basins located to southeast differ from the WAB in that it lies above
a crustal domain pertaining to Africa (Estrada et al. 2018; Gómez de la Peña et al.
2018). The sedimentary record appears to be younger than that of cores drilled in the
WAB, starting in the middle Miocene (Serravallian) (Martínez-García et al. 2017).
The EAB is located above thinned continental and magmatic crust (Booth-Rea et al.
2007) and the sedimentary record start also in the middle Miocene in its western part
(Alvarez-Marrón 1999) but probably the initial age and the total thickness of the
sedimentary column increases towards the east, in the transition with the oceanic
crust of the Algero-Balearic basin (Comas et al. 1999; Booth-Rea et al. 2007).
According to recent studies, whereas the late-Miocene-to-present compression reorganizes the morphology of the Alboran sub-basins, deeply buried Miocene normal
faults demonstrate the widespread character of extensional tectonics around Alboran
at that period (Martínez-García et al. 2017).
The Lower Miocene (Aquitanian-Burdigalian) is marked by the sedimentation of
clays with interbedded sandy intervals above a basal pebbly sandstone in a syn-rift
setting. Well data point to undercompacted shales, nowadays presenting overpressure in boreholes. Together, the seismic facies and borehole lithologies indicate that
the lower Miocene consists of olistostromes containing polymictic rocks (olistoliths
and rock breccia) embedded in an undercompacted shale matrix. The spatial distribution of these units is highly heterogeneous, the thickest depocentres occupying the
center of the WAB (Do Couto et al. 2016), or Motril Basin (Comas et al. 1999), and
so far nowhere else. The lower Miocene undercompacted shales are involved in the
mud volcanic activity of the area (Sautkin et al. 2003; Gennari et al. 2013) and
likewise in the shale tectonics that affect the WAB (Chalouan et al. 1997; PérezBelzuz et al. 1997; Talukder et al. 2003; Soto et al. 2010). It is difficult to estimate a
paleobathymetry with respect to the sedimentary facies.
The undercompaction of shales in the lower Miocene series (Jurado and Comas
1992; Soto et al. 2010), the lack of late Oligocene sediments (Martínez del Olmo and
Comas 2008), and the metamorphic paths of basement units are cited by authors
5 A Geological History for the Alboran Sea Region
133
being controlled by the pull of the dipping subducting lithosphere and relative
thermal cooling of the crust probably after the magmatic stages 1 and 2 (TorresRoldán et al. 1986; Duggen et al. 2004), thereby explaining the considerable
thickness (10 km) of the sedimentary infill (Do Couto et al. 2016). It is worth noting
that deep structures in the basement imaged by means of deep seismic reflection
profiles in the northern half of the Alboran Basin have been interpreted as extensional shear zones, associated with major extensional detachments in the Betic
Cordillera (Watts et al. 1993; Vázquez et al. 1995; Vegas et al. 1995; Comas et al.
1997). The Motril Basin (northern E-W elongated part of the WAB) exhibits a rather
different pattern, with an asymmetric geometry (Comas et al. 1999) comparable in
shape to the asymmetric intramontane basins described inland (e.g., Sorbas Basin,
Fig. 5.4), even though the total thickness of sedimentary rocks is far greater (<7 km).
While the southern branch of the WAB is strongly affected by late-Miocene-topresent compression that produces its inversion, folding, and uplifting to constitute
the Xauén and Francesc Pagés banks (d’Acremont et al. 2020; Lafosse et al. 2020).
The SAB and basins located to southeast differ from the WAB in that it lies above
a crustal domain pertaining to Africa (Estrada et al. 2018; Gómez de la Peña et al.
2018). The sedimentary record appears to be younger than that of cores drilled in the
WAB, starting in the middle Miocene (Serravallian) (Martínez-García et al. 2017).
The EAB is located above thinned continental and magmatic crust (Booth-Rea et al.
2007) and the sedimentary record start also in the middle Miocene in its western part
(Alvarez-Marrón 1999) but probably the initial age and the total thickness of the
sedimentary column increases towards the east, in the transition with the oceanic
crust of the Algero-Balearic basin (Comas et al. 1999; Booth-Rea et al. 2007).
According to recent studies, whereas the late-Miocene-to-present compression reorganizes the morphology of the Alboran sub-basins, deeply buried Miocene normal
faults demonstrate the widespread character of extensional tectonics around Alboran
at that period (Martínez-García et al. 2017).
The Lower Miocene (Aquitanian-Burdigalian) is marked by the sedimentation of
clays with interbedded sandy intervals above a basal pebbly sandstone in a syn-rift
setting. Well data point to undercompacted shales, nowadays presenting overpressure in boreholes. Together, the seismic facies and borehole lithologies indicate that
the lower Miocene consists of olistostromes containing polymictic rocks (olistoliths
and rock breccia) embedded in an undercompacted shale matrix. The spatial distribution of these units is highly heterogeneous, the thickest depocentres occupying the
center of the WAB (Do Couto et al. 2016), or Motril Basin (Comas et al. 1999), and
so far nowhere else. The lower Miocene undercompacted shales are involved in the
mud volcanic activity of the area (Sautkin et al. 2003; Gennari et al. 2013) and
likewise in the shale tectonics that affect the WAB (Chalouan et al. 1997; PérezBelzuz et al. 1997; Talukder et al. 2003; Soto et al. 2010). It is difficult to estimate a
paleobathymetry with respect to the sedimentary facies.
The undercompaction of shales in the lower Miocene series (Jurado and Comas
1992; Soto et al. 2010), the lack of late Oligocene sediments (Martínez del Olmo and
Comas 2008), and the metamorphic paths of basement units are cited by authors
5 A Geological History for the Alboran Sea Region
133