moats, where the sediment motion velocities decay sharply, forming mounded,
separated, and confined drifts (e.g. Stow et al. 2008; Rebesco et al. 2014).
Reworking at regional scale mainly occurs on the upper continental slope of the
Iberian and African margins, where terraces have been mapped (Figs. 6.6 and 6.15).
The reworking happens where the interfaces of the AW with LMW and DMW touch
the continental slope seafloor. Turbulent motion characterises the interfaces due to
the presence of internal waves that alter flow velocity with oscillations of up to
0.4 m/s, producing vertical displacement of water (50 m) above and below the
mentioned interfaces (Fig. 6.15) (e.g. Sarnthein et al. 1982; Pomar et al. 2012;
Shanmugam 2013a, b; Chen et al. 2014; Ercilla et al. 2016). Currently, internal
waves are mostly formed within the Strait of Gibraltar (e.g. Armi and Farmer 1988;
Bruno et al. 2002), and above striking variations in relief, such as the shelf break
(e.g. Ercilla et al. 2016). The sediment cores have revealed the presence of wide
areas of coarse sediments, free from fine sediments, on the seafloor at the proximal
sites of the terrace (Fig. 6.14) (Ercilla et al. 1994), providing evidence for the action
of this important turbulent motion. The position of the Atlantic and Mediterranean
water mass interfaces would have varied during the past high frequency and high
amplitude glacio-eustatic changes in sea level, caused by the three variables of the
Earth’s orbit (eccentricity/obliquity/precession) (e.g. Ercilla et al. 1994; Chiocci
et al. 1997; Lobo et al. 2008). The horizontal displacements of interfaces during
the sea-level changes would have favoured the reworking of extensive areas of the
upper slope and enlargement of the terraces.
Additionally, the interplay between favourable bottom currents and climatic
conditions could have influenced the complex CM development in different phases,
possibly related to the last deglaciation (<5400 years) corresponding to the Late
Holocene, as suggested by Fink et al. (2013) for the EMP mounds.
Mass-Movement Processes
Mass-movement processes are responsible for the formation of both the turbidite
systems and the landslides. The morphology and deposits making up the architectural elements of turbidite systems indicate they are mainly formed by the action of
channelized turbidity currents and related flows (mass flows), i.e. downslope density
flows (Fig. 6.15). The U- and V-shapes of the canyons and related tributary gullies
suggest those flows have a significant erosive capacity (Fig. 6.10e). Their energy is
mainly related to sediment load characteristics and the relatively high seafloor
gradients that directly influence the gravitational force (e.g. Ercilla et al. 1998;
Pirmez et al. 2000; Ferry et al. 2005; McHargue et al. 2011). Sediment cores
recovered from canyon floors indicate that turbidity and mass flows transport a
great variety of grain sizes, from gravels to clay. Most of the canyons (except
Torrenueva and Baños) were formed during the Messinian salinity crisis (Estrada
et al. 2011; Ercilla et al. 2019), and their present-day morphosedimentary characteristics (Fig. 6.10a–e) are the result of gravitational flows that have been acting on
them since that time. Pliocene and Quaternary sedimentary studies suggest that
gravitational flows were active, eroding and enlarging the canyons, mainly during
the glacial periods, when the sea-level and continental sediment sources were closer
6 Seafloor Morphology and Processes in the Alboran Sea
191
separated, and confined drifts (e.g. Stow et al. 2008; Rebesco et al. 2014).
Reworking at regional scale mainly occurs on the upper continental slope of the
Iberian and African margins, where terraces have been mapped (Figs. 6.6 and 6.15).
The reworking happens where the interfaces of the AW with LMW and DMW touch
the continental slope seafloor. Turbulent motion characterises the interfaces due to
the presence of internal waves that alter flow velocity with oscillations of up to
0.4 m/s, producing vertical displacement of water (50 m) above and below the
mentioned interfaces (Fig. 6.15) (e.g. Sarnthein et al. 1982; Pomar et al. 2012;
Shanmugam 2013a, b; Chen et al. 2014; Ercilla et al. 2016). Currently, internal
waves are mostly formed within the Strait of Gibraltar (e.g. Armi and Farmer 1988;
Bruno et al. 2002), and above striking variations in relief, such as the shelf break
(e.g. Ercilla et al. 2016). The sediment cores have revealed the presence of wide
areas of coarse sediments, free from fine sediments, on the seafloor at the proximal
sites of the terrace (Fig. 6.14) (Ercilla et al. 1994), providing evidence for the action
of this important turbulent motion. The position of the Atlantic and Mediterranean
water mass interfaces would have varied during the past high frequency and high
amplitude glacio-eustatic changes in sea level, caused by the three variables of the
Earth’s orbit (eccentricity/obliquity/precession) (e.g. Ercilla et al. 1994; Chiocci
et al. 1997; Lobo et al. 2008). The horizontal displacements of interfaces during
the sea-level changes would have favoured the reworking of extensive areas of the
upper slope and enlargement of the terraces.
Additionally, the interplay between favourable bottom currents and climatic
conditions could have influenced the complex CM development in different phases,
possibly related to the last deglaciation (<5400 years) corresponding to the Late
Holocene, as suggested by Fink et al. (2013) for the EMP mounds.
Mass-Movement Processes
Mass-movement processes are responsible for the formation of both the turbidite
systems and the landslides. The morphology and deposits making up the architectural elements of turbidite systems indicate they are mainly formed by the action of
channelized turbidity currents and related flows (mass flows), i.e. downslope density
flows (Fig. 6.15). The U- and V-shapes of the canyons and related tributary gullies
suggest those flows have a significant erosive capacity (Fig. 6.10e). Their energy is
mainly related to sediment load characteristics and the relatively high seafloor
gradients that directly influence the gravitational force (e.g. Ercilla et al. 1998;
Pirmez et al. 2000; Ferry et al. 2005; McHargue et al. 2011). Sediment cores
recovered from canyon floors indicate that turbidity and mass flows transport a
great variety of grain sizes, from gravels to clay. Most of the canyons (except
Torrenueva and Baños) were formed during the Messinian salinity crisis (Estrada
et al. 2011; Ercilla et al. 2019), and their present-day morphosedimentary characteristics (Fig. 6.10a–e) are the result of gravitational flows that have been acting on
them since that time. Pliocene and Quaternary sedimentary studies suggest that
gravitational flows were active, eroding and enlarging the canyons, mainly during
the glacial periods, when the sea-level and continental sediment sources were closer
6 Seafloor Morphology and Processes in the Alboran Sea
191