Geological and environmental implications of the evaporite karst in Spain

Environ Geol (2008) 53:951–965 953
Marine Mesozoic and Tertiary evaporitic formations
The most widespread episodes of evaporitic sedimentation
took place during Triassic and lower Liassic times in
shallow-marine platform environments (lagoons, sabkhas)
affected by a rifting process (Ortí et al. 1996). Triassic
evaporites are made up of Ca-sulfate and halite units up to
400 m thick embedded in variegated marls and shales. This
formation occurs in numerous outcrops dispersed over the
Alpine orogens, locally forming diapiric structures (Fig. 1).
The lower Liassic evaporites (anhydrite zone), up to 800 m
thick, are composed of Ca-sulfates associated with dolomites
(Pérez-López et al. 1996). Borehole data reveal the
presence of several Jurassic and Upper Cretaceous anhydritic
units more than 100 m thick in some sectors of the
Iberian Peninsula. In the Iberian Range and in the Pyrenees
there are also gysiferous units deposited in transitional and
probably continental environments with a poorly constrained
late Cretaceous-Paleocene age (Garum facies).
Jurassic and Cretaceous Ca-sulfate units, with a limited
outcrop extent, are frequently represented close to, and at,
the ground surface by collapse breccias generated by interstratal
karstification of the evaporites and brecciation of
the associated carbonate rocks, forming the so-called carniolas
(Gutiérrez et al. 2001).
During the Paleogene, marine evaporitic sedimentation
was restricted to the southern foredeep of the Pyrenees,
where evaporite deposition took place during two regressive
phases: the Middle Eocene phase (Lutetian), and the
Upper Eocene phase (Priabonian). Evaporite deposition of
the first phase, confined to the eastern sector, is represented
by the Beuda Gypsum, composed of 100 m of anhydrite/
gypsum and minor halite deposits at depth (Ortí and Rosell
1997). The second phase developed in two sub basins,
probably linked in the initial stage to form a single sedimentary
trough, 300 km long, called the South Pyrenean
Potash Basin. These sediments are composed of Ca-sulfate
and halite with a substantial amount of K-Mg chlorides,
mainly sylvite and carnallite. The Cardona Saline Formation
(eastern subbasin), with 300 m of chlorides, remains in
the autochthonous zone of the Ebro Basin, whereas the
Guendulain Formation (western subbasin), up to 100 m
thick, has been incorporated into the allochthonous structural
units of the Pyrenees (Rosell and Pueyo 1997).
Neogene marine formations occur in the Penedés Basin
(Catalan Coastal Range) and in a large number of
intramontane basins of the eastern sector of the Betic
Cordillera. The internal basins of the Betic Cordillera
(Lorca, Fortuna, Guadalentín, Granada) host Tortonianearly
Messinian evaporitic sequences up to several hundred
meters thick made up of Ca-sulfate and halite that record a
transition from marine to continental conditions (Playà
et al. 2000). In the external basins of the Betic Cordillera
(Sorbas, Almería, Nijar-Carboneras, San Miguel de Salinas,
Palma de Mallorca), the marine evaporites, Upper
Messinian in age, are composed of 12–14 cyclic layers of
primary selenitic gypsum with a total thickness of 70–
130 m (Rosell et al. 1998).
Continental Tertiary evaporitic formations
Most of the main Spanish Tertiary basins contain extensive
and thick continental evaporitic formations. The Ebro Basin,
subsequent to the Priabonian potassic phase, evolved
into an endorheic condition giving way to the deposition of
extensive Ca-sulfate and halite lacustrine evaporitic formations
of Upper Eocene-early Oligocene age. These are
the Barbastro Gypsum and the Puente de la Reina Gypsum,
located in the central-eastern and the western sectors of the
basin, respectively. They reach 300–400 m in thickness
and crop out in the core of several salt anticlines (Salvany
1997). From the Middle Oligocene to the early Miocene,
two thick evaporitic formations were deposited in the
western sector of the Ebro Basin, the Falces and the Lerín
Formations. The tightly folded Falces Formation reaches
more than 1,000 m thick in the core of diapiric anticlines
and is made up of Ca-sulfate, glauberite, and halite. The
Lerín Formation, 500–1,000 m in thickness, is made up of
Ca-sulfate, glauberite, halite, and polyhalite (Salvany
1997). At the beginning of the Miocene, the basin depocenter
shifted to the central sector of the Ebro Basin, where
the Zaragoza Formation (upper Oligocene?-lower Miocene)
was deposited. This formation, 800 m thick, crops
out around Zaragoza city and includes, close to the surface,
halite and glauberite units more than 150 and 30 m thick,
respectively (Salvany et al. 2007). The youngest evaporitic
unit corresponds to the Cerezo Gypsum (Upper Miocene),
located in the Bureba corridor, which links the Ebro and
the Duero basins. This unit, about 200 m thick, bears Casulfates
and glauberite (Anadón 1990). In addition to these
formations deposited in central high-salinity lakes, the
Ebro Basin fill also contains several minor gypsum units
deposited in marginal lakes, like the Paleogene evaporites
associated to the Catalan Coastal Range and the Oligo-
Miocene units located along the Iberian margin of the basin
(Ortí 1997).
Evaporite sedimentation in the Tertiary Duero Basin is
recorded by a few Middle–Upper Miocene gypsum units
less than 100 m thick with a significant proportion of
insoluble sediments (Mediavilla et al. 1996). The Tertiary
Tajo Basin is composed of two subbasins: the western
sector or the Madrid Basin, and the eastern sector or the
Loranca Basin. During the Paleogene, evaporite deposition
was restricted to the Madrid Basin, represented by folded
Ca-sulfate units. This basin also contains an extensive
Miocene evaporitic succession constituted by two units: the
123