vary between hundreds of m and a few km in length and <6 km in width. Contourite
channels are represented by the U-shaped structural corridors of Al-Hoceima Valley,
formed between the aligned Xauen Bank and Frances Pagès seamounts and the
Moroccan margin, and of the Alboran Trough, which could be considered a deepgateway connecting the east and west basins. They are a few km wide and up to tens
of km long. The scarps represent the along slope boundaries of terraces. They are
narrow (<16 km wide) and steep (2
–11
) escarpments, hundreds of km long, which
play a major role in shaping the transition between the physiographic provinces, the
shelf-break-upper slope being the most proximal, and the transition from the Iberian
slope to the base of slope and the West African slope to the basins, the most distal
(Fig. 6.6b). Erosive contouritic features are generally easily recognisable due to the
truncation of the underlying deposits, hyperbolic, and prolonged facies with high
acoustic reflectivity.
On top of the large slope plastered drifts and sheeted drifts, contourite mixed
terraces extend, producing flat areas <30 km wide on the Iberian and African slopes,
where the truncation of reflectors against the seafloor is easily recognisable in the
proximal sectors. Three terraces have been mapped, T1 and T2 on the Spanish
margin and T3 on the Moroccan margin (Figs. 6.6 and 6.9a).
6.5.2.5 Mass-Movement Features
The term ‘mass-movement’ used here refers to a general term by Locat and Lee
(2000) that defines sediment movement driven by gravity rather than by interstitial
fluid motion and comprises a great variety of sedimentary instabilities, from slides to
turbidity currents. The main evidence for mapping recent features resulting from
mass-movements in the Alboran Sea is the following: the disappearance of deposits,
deformation and/or loss of the sedimentary structure, and associations of genetically
related features. Based on these criteria three main sedimentary systems comprise
these mass-movement features: turbidite systems, lone valleys, and landslides
(Fig. 6.6a).
Turbidite systems are one of the most significant clastic accumulations in deepsea areas of the margins and adjacent basins (Normark et al. 1993). Turbidite
systems are formed by various architectural elements, including canyons, main
and distributary channels, overbanks/levees, and lobes (Mutti and Normark 1991).
In the Alboran Sea, these systems interrupt the lateral continuity of contourites and
have only been mapped on the Spanish margin and Alboran Ridge (Fig. 6.6a).
Eleven turbidite systems have been defined, with variable dimensions (length/
width: 7.7 Â 7 km to 123 Â 25 km), exhibiting two main types of sedimentary
models: submarine fans (La Linea, Guadiaro, Baños, Torrenueva, Fuengirola,
Sacratif, Almería on the Iberian margin; Al-Borani and Piedra Escuela on the
southern face of the Alboran Ridge), and submarine ramps Salobreña and
Calahonda) types on the Iberian margin (Fig. 6.10). The submarine fan model
comprises a U- or V-shaped feeder canyon, generally with axial incisions at the
base (i.e. talwegs), that crosses the continental slope and evolves into a main, leveed
176
G. Ercilla et al.
channels are represented by the U-shaped structural corridors of Al-Hoceima Valley,
formed between the aligned Xauen Bank and Frances Pagès seamounts and the
Moroccan margin, and of the Alboran Trough, which could be considered a deepgateway connecting the east and west basins. They are a few km wide and up to tens
of km long. The scarps represent the along slope boundaries of terraces. They are
narrow (<16 km wide) and steep (2
–11
) escarpments, hundreds of km long, which
play a major role in shaping the transition between the physiographic provinces, the
shelf-break-upper slope being the most proximal, and the transition from the Iberian
slope to the base of slope and the West African slope to the basins, the most distal
(Fig. 6.6b). Erosive contouritic features are generally easily recognisable due to the
truncation of the underlying deposits, hyperbolic, and prolonged facies with high
acoustic reflectivity.
On top of the large slope plastered drifts and sheeted drifts, contourite mixed
terraces extend, producing flat areas <30 km wide on the Iberian and African slopes,
where the truncation of reflectors against the seafloor is easily recognisable in the
proximal sectors. Three terraces have been mapped, T1 and T2 on the Spanish
margin and T3 on the Moroccan margin (Figs. 6.6 and 6.9a).
6.5.2.5 Mass-Movement Features
The term ‘mass-movement’ used here refers to a general term by Locat and Lee
(2000) that defines sediment movement driven by gravity rather than by interstitial
fluid motion and comprises a great variety of sedimentary instabilities, from slides to
turbidity currents. The main evidence for mapping recent features resulting from
mass-movements in the Alboran Sea is the following: the disappearance of deposits,
deformation and/or loss of the sedimentary structure, and associations of genetically
related features. Based on these criteria three main sedimentary systems comprise
these mass-movement features: turbidite systems, lone valleys, and landslides
(Fig. 6.6a).
Turbidite systems are one of the most significant clastic accumulations in deepsea areas of the margins and adjacent basins (Normark et al. 1993). Turbidite
systems are formed by various architectural elements, including canyons, main
and distributary channels, overbanks/levees, and lobes (Mutti and Normark 1991).
In the Alboran Sea, these systems interrupt the lateral continuity of contourites and
have only been mapped on the Spanish margin and Alboran Ridge (Fig. 6.6a).
Eleven turbidite systems have been defined, with variable dimensions (length/
width: 7.7 Â 7 km to 123 Â 25 km), exhibiting two main types of sedimentary
models: submarine fans (La Linea, Guadiaro, Baños, Torrenueva, Fuengirola,
Sacratif, Almería on the Iberian margin; Al-Borani and Piedra Escuela on the
southern face of the Alboran Ridge), and submarine ramps Salobreña and
Calahonda) types on the Iberian margin (Fig. 6.10). The submarine fan model
comprises a U- or V-shaped feeder canyon, generally with axial incisions at the
base (i.e. talwegs), that crosses the continental slope and evolves into a main, leveed
176
G. Ercilla et al.