Geological and environmental implications of the evaporite karst in Spain

Environ Geol (2008) 53:951–965 959
there is conflict between the preservation of this exceptional
natural heritage and the open-cast mining of gypsum.
One of the quarries, currently under exploitation, is considered
the second largest gypsum quarry in the world. The
impacts caused by this economic activity include alteration
of the natural landscape, destruction of exokarstic and
endokarstic landforms (Fig. 3d), and negative changes in
the surface and underground hydrology (Pulido-Bosch
et al. 2004).
Calatayud Neogene Graben (Iberian Range)
The most evident manifestation of subjacent karstification
of evaporites in Calatayud Graben, both in Calatayud and
in Barrachina areas, are the subsidence phenomena recorded
in the overlying sediments: Neogene sedimentary
units of the basin fill and Quaternary alluvial deposits. To
the southeast of Calatayud city there are two areas covering
4.4 and 12 km 2 where the supra-evaporitic carbonate and
detrital units have subsided more than 200 m due to interstratal
karstification of the halite- and glauberite- bearing
evaporites (Fig. 3e). The strongly deformed collapse sediments,
foundered within the subhorizontal evaporites, show
numerous brittle and ductile deformations with a very
chaotic arrangement (Gutiérrez 1996). In Barrachina area,
Tertiary sediments underlain by evaporites also show
abundant dissolution-induced gravitational deformations.
In Calatayud area, terrace deposits of the Jalón and Jiloca
Rivers shows thickenings in excess of 100 m, superimposed
terrace units, and numerous deformations related to the
development of dissolution-induced basins and paleosinkholes.
The magnitude and spatial distribution of the
thickenings identified in different terrace levels indicate
that synsedimentary subsidence has diminished and
migrated in a downstream direction through time (Gutiérrez
1996). In nearby Barrachina village, the terrace deposits of
the Pancrudo River also show thickenings, superimposed
units, and sagging and collapse paleosinkholes (Fig. 3a).
Current subsidence activity in Calatayud area has a clear
influence on the dynamics of the fluvial systems and causes
numerous damages to buildings and infrastructures. The
Jalón River floodplain shows diffuse-edged and swampy
subsidence depressions up to 1 km long that locally control
the trajectory and sinuosity of the river channel. Collapse
sinkholes are particularly frequent in the vicinity of irrigation
ditches and canals. The initially projected trace of
the Madrid-Barcelona motorway (E-90) was changed to
avoid a sinkhole-prone area. A 12 km long stretch of the
highly vulnerable Madrid–Zaragoza high-speed railway
has been built on soft and water-saturated floodplain alluvium
underlain by karstified evaporites. The city of Calatayud
is located at the foot of a gypsum escarpment on an
alluvial fan and the Jalón River floodplain. Most of the
historical buildings of Calatayud, declared Historical
Monuments in 1967, are severely damaged by subsidence.
Integrated analysis of the spatial distribution of subsidence
damage, and the characterization of underlying sediments,
indicate that subsidence in Calatayud is primarily due to
karstification of the evaporitic bedrock and hydrocompaction
of the gypsiferous silts of the alluvial fan deposits
(Gutiérrez 1998a; Gutiérrez and Cooper 2002). In
November 2003, the structure of a five-storey building with
pad foundations was seriously damaged by a catastrophic
collapse sinkhole that resulted from upward propagation of
a cavity more than 600 m 3 in volume. The building was
finally demolished and the direct losses caused by this
single subsidence event have been estimated at 4.8 million
euros (Gutiérrez et al. 2004b). Frequent rock-falls and
rock-topples derived from the gypsum escarpment restrict
urban development and cause frequent road cuts and
damage to buildings. In 1988, one person was killed by a
rock-fall and several buildings have been destroyed by
slope movements (Fig. 3c).
Teruel Neogene Graben (Iberian Range)
The dissolution-induced subsidence phenomena have affected
alluvial deposits of the Alfambra fluvial system in
different sectors of the Teruel Graben. In the northern
sector (Villalba Alta-Escorihuela), the suballuvial karstification
of the Orrios Gypsum has given rise to thickenings
in terrace and pediment deposits, and paleosinkholes with
synsedimentary deformations that host palustrine facies
(Moissenet 1989). Downstream, in the area where the Alfambra
River crosses the Tortajada Gypsum (Cuevas
Labradas-Tortajada), deposits of the terrace levels situated
at 75, 60–55, and 44–38 m above the river channel, reach
45, 60, and 40 m in thickness, respectively. The main
thickening affects the 60–55 m terrace, filling a dissolution
trough 3.2 km long in the western margin of the valley
(Gutiérrez 1998a, b). The most spectacular paleosinkholes
are found in an artificial railway cut located in Villalba
Baja village. Deformed alluvium in this exposure shows
gravel pockets interpreted as liquefaction-fluidization
structures induced by catastrophic collapse processes
(Gutiérrez 1998a, b). Several active sinkholes associated
with old subsidence structures have been detected at this
site, suggesting that the distribution of paleosinkholes can
be used for the spatial prediction of sinkholes (Gutiérrez
1998a, 2004). North of Teruel city, a Middle Pleistocene
terrace of the Alfambra River, located at 60–50 m above
the river channel, reaches more than 55 m in thickness.
Synsedimentary subsidence recorded by these deposits may
be related to the combined effect of karstification of the
underlying Triassic evaporites and neotectonic activity
(Gutiérrez 1998a).
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