channel-like features. This sequence was deposited under a mostly compressional
regime, flexural subsidence remains, and generated secondary accommodation.
The Messinian features the superposition of two main sub-units in the Alboran
Sea: (1) a lower unit made up of marine sandy turbidites interbedded with carbonates
and volcaniclastic layers; and (2) an upper unit made up of gypsum and anhydrite
embedded in clays, linked to the Messinian Salinity Crisis deposits. Indeed, the
continuous compressional regime closed marine corridors linking the Mediterranean
Sea to the Atlantic Ocean during the Messinian and led to the drying up (desiccation)
of the Mediterranean Sea. While the Messinian deposits containing remnants of
evaporites have never been mapped, borehole records tend to show they are relatively thin in the basin and seem to have eroded before the reflooding of the whole
basin close to the Pliocene.
In general terms, post-Tortonian (~8 Ma) tectonics can be understood as a
contractive reorganization affecting the Alboran Domain and modifying the architecture of Miocene basins and margins (Comas et al. 1992) as well as the local
dimensions of sub-basins, favoring uplift of the Alboran Ridge and structural highs,
while deforming by folding and faulting the sedimentary record (e.g., Estrada et al.
1997; Ammar et al. 2007; Vázquez 2001; Marín Lechado et al. 2007; Ballesteros
et al. 2008; Martínez-García et al. 2011, 2013, 2017; Gómez de la Peña et al. 2018;
d’Acremont et al. 2020).
5.6 The Opening of the Strait of Gibraltar
The Messinian Salinity Crisis (MSC) ended in the latest Miocene, when the isolated
(or very restricted) the Mediterranean Sea became reconnected to world ocean
currents through the Strait of Gibraltar. Initial models of the MSC establish that
the Mediterranean Sea was progressively restricted from the Atlantic Ocean as the
Gibraltar Arch shifted to the west and the African plate to the north, resulting in the
closure of the Mediterranean-Atlantic gateways. However, a key question has
remained unexplained: the thickness of salt accumulated in the deep basins would
have required intermittent sea water inputs.
Over the past decades some authors have postulated that during the MSC, the
Mediterranean was still connected to the Atlantic Ocean through the Strait of
Gibraltar. Thus the deep desiccated basin model (Hsü et al. 1973) was replaced by
one entailing stratified dense brines upon a deep non-desiccated basin under a
normal sea level (Roveri et al. 2014). No direct proof supports a permanent Gibraltar
gateway throughout the MSC, leaving its existence as an open question. Unclear as
well is the contribution of the Paratethys Sea to the MSC salt precipitation.
The Alboran Basin proves key area to understand how the opening of the Strait of
Gibraltar occurred. Detailed analysis of the Alboran Basin stratigraphy, by means of
a dense net of seismic profiles correlated with commercial and scientific wells,
indicates that the Strait of Gibraltar formed at the end of the MSC, in the transition
to the Zanclean period, as a result of an unprecedented catastrophic event—the
5 A Geological History for the Alboran Sea Region
135
regime, flexural subsidence remains, and generated secondary accommodation.
The Messinian features the superposition of two main sub-units in the Alboran
Sea: (1) a lower unit made up of marine sandy turbidites interbedded with carbonates
and volcaniclastic layers; and (2) an upper unit made up of gypsum and anhydrite
embedded in clays, linked to the Messinian Salinity Crisis deposits. Indeed, the
continuous compressional regime closed marine corridors linking the Mediterranean
Sea to the Atlantic Ocean during the Messinian and led to the drying up (desiccation)
of the Mediterranean Sea. While the Messinian deposits containing remnants of
evaporites have never been mapped, borehole records tend to show they are relatively thin in the basin and seem to have eroded before the reflooding of the whole
basin close to the Pliocene.
In general terms, post-Tortonian (~8 Ma) tectonics can be understood as a
contractive reorganization affecting the Alboran Domain and modifying the architecture of Miocene basins and margins (Comas et al. 1992) as well as the local
dimensions of sub-basins, favoring uplift of the Alboran Ridge and structural highs,
while deforming by folding and faulting the sedimentary record (e.g., Estrada et al.
1997; Ammar et al. 2007; Vázquez 2001; Marín Lechado et al. 2007; Ballesteros
et al. 2008; Martínez-García et al. 2011, 2013, 2017; Gómez de la Peña et al. 2018;
d’Acremont et al. 2020).
5.6 The Opening of the Strait of Gibraltar
The Messinian Salinity Crisis (MSC) ended in the latest Miocene, when the isolated
(or very restricted) the Mediterranean Sea became reconnected to world ocean
currents through the Strait of Gibraltar. Initial models of the MSC establish that
the Mediterranean Sea was progressively restricted from the Atlantic Ocean as the
Gibraltar Arch shifted to the west and the African plate to the north, resulting in the
closure of the Mediterranean-Atlantic gateways. However, a key question has
remained unexplained: the thickness of salt accumulated in the deep basins would
have required intermittent sea water inputs.
Over the past decades some authors have postulated that during the MSC, the
Mediterranean was still connected to the Atlantic Ocean through the Strait of
Gibraltar. Thus the deep desiccated basin model (Hsü et al. 1973) was replaced by
one entailing stratified dense brines upon a deep non-desiccated basin under a
normal sea level (Roveri et al. 2014). No direct proof supports a permanent Gibraltar
gateway throughout the MSC, leaving its existence as an open question. Unclear as
well is the contribution of the Paratethys Sea to the MSC salt precipitation.
The Alboran Basin proves key area to understand how the opening of the Strait of
Gibraltar occurred. Detailed analysis of the Alboran Basin stratigraphy, by means of
a dense net of seismic profiles correlated with commercial and scientific wells,
indicates that the Strait of Gibraltar formed at the end of the MSC, in the transition
to the Zanclean period, as a result of an unprecedented catastrophic event—the
5 A Geological History for the Alboran Sea Region
135