gallocanta karst polje and piedra river valley

Transcription

SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY
GALLOCANTA KARST POLJE AND PIEDRA RIVER
VALLEY
F.J. Gracia and J. Benavente
FIELD TRIP GUIDE -
B4
SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY
GALLOCANTA KARST POLJE AND PIEDRA RIVER VALLEY
F.-Javier Gracia and J. Benavente
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Dpto. Geología, Facultad de Ciencias del Mar y Ambientales; Universidad de Cádiz; Campus del río San Pedro, 11510
Puerto Real, Spain
E-mail: [email protected]; Phone: 956016168; Fax: 956016797
1. Geomorphological evolution of the Iberian Range
The Iberian Range, with a dominant NW-SE structural and topographic grain, is one of the main
mountain belts of the Iberian Peninsula. It stretches for about 400 km from its northwestern end in
the Sierra de la Demanda up to the Mediterranean Sea, and reaches 200 km in width (Fig. 1). The
topography is dominated by planation surfaces commonly about 1000 m above sea level, and the
highest mountains reach more than 2000 m in elevation. Hydrographically the Iberian Range
forms an important fluvial divide in the Iberian Peninsula, separating rivers flowing to the Ebro
Basin (Mediterranean drainage) from those flowing to the Duero and Tajo basins (Atlantic
drainage). The climate is relatively dry and characterised by hot summers and cold winters.
From the geotectonic point of view, the Iberian Range constitutes an intraplate alpine orogen
produced by the tectonic inversion of Mesozoic sedimentary basins as a consequence of the
convergence and collision between the Iberian, Euroasiatic and African plates. The rocks that
crop out in this mountain belt record two large tectosedimentary cycles: the Variscan (Hercynian)
and the Alpine cycles. The Variscan cycle is represented by rocks ranging from Precambrian to
Permian in age, largely made up of siliciclastic sediments. The relatively scarce outcrops of these
materials generally occur associated to alpine compressional structures (folds and thrusts) and
uplifted neotectonic blocks. The Alpine cycle, developed from the Upper Permian till the LowerMiddle Miocene, is divided into two major stages: the sedimentary stage (Triassic – Cretaceous)
and the orogenic stage (late Cretaceous to Lower-Middle Miocene), during which a new
compressional regime caused the tectonic inversion of the sedimentary basins and the deformation
of the Mesozoic and synorogenic Tertiary sequences (Sopeña et al., 2004).
Two major sedimentary cycles took place during the sedimentary stage. An initial rifting phase
favoured deposition in diverse sedimentary environments (shallow marine, transitional and
continental). The subsequent post-rifting subsidence phase covered the Jurassic and Cretaceous
periods and was characterised by thick and extensive carbonate sequences formed in shallow
marine platforms (Sopeña et al., 2004). These carbonate formations at present constitute the most
important outcrops and have played a decisive role in the geomorphological configuration of the
mountain belt. The folded Mesozoic carbonate rocks are commonly truncated by extensive
planation surfaces that give a plateau-like appearance to large areas of the Iberian Range.
The orogenic stage started by the beginning of the Tertiary, when the tectonic regime switched
from extensional to compressional. During this stage, several continental basins with synorogenic
sedimentation were formed within the Iberian Range. The contractional architecture of the orogen
is largely controlled by the superposition of structural levels with different rheology. The
basement includes Palaeozoic to Middle Triassic sediments with a dominantly brittle behaviour,
while the more ductile cover is made up of Jurassic to Palaeogene sediments. Both units are
separated by a regional detachment level formed by the Upper Triassic shales and evaporites
(Keuper facies).
Gallocanta karst polje and Piedra river valley
During the Lower-Middle Miocene the tectonic regime changed gradually from compressional to
extensional, resulting in the generation of grabens (Fig. 1) superimposed to the previous structures
(postorogenic rifting). Although in the central sector of the Iberian Range extensional tectonics
has been active from the Middle Miocene up to the present day, two main episodes of
deformation can be differentiated. The first extensional episode started in the Lower-Middle
Miocene and generated the two largest intramontane basins of the Iberian Range; the Calatayud
Graben and the Teruel Graben, both about 100 km long (Fig. 1). Both internally drained grabens
were filled by alluvial fans distally related to lacustrine environments with carbonate and
evaporite deposition. Sedimentation under endorheic conditions in these depressions finished
during Pliocene times. By the end of this episode great part of the Range was dominated by flat
planation surfaces developed on folded pre-Neogene sediments.
Stop 1: Calatayud and Daroca grabens
From this point (Port of Santed) we can see a panoramic view of the Calatayud Graben and its
Neogene sedimentary sequence. We are located upon a remnant of the most extensive Neogene
planation surface, called the Main Planation Surface of the Iberian Range, which records a period
of relative tectonic quiescence (Peña et al., 1984; Gutiérrez and Gracia, 1997). Although this
erosional surface is not considered to represent an isochron, its age has been locally constrained
on the basis of its topographic connection with the top of Pliocene limestone units in Calatayud
and Teruel grabens (Gracia, 1990; Gutiérrez, 1998). This surface and the uppermost Pliocene
calcareous sediments of these grabens have been widely used as markers of the neotectonic
deformations subsequent to their formation (Peña et al., 1984; Gutiérrez and Gracia, 1997).
The second extensional episode began in the Upper Pliocene and produced some of the most
outstanding morphotectonic features of the central Iberian Range (Peña et al., 1984; Gutiérrez and
Gracia, 1997). Extensional block tectonics reactivated Calatayud and Teruel grabens locally
tilting and faulting Pliocene formations, and generated new half-grabens located to the west of the
previously existing Neogene grabens. These include from North to South (Fig. 1): Munébrega
Half-graben (Gutiérrez, 1998), Daroca Half-graben (Gracia, 1990), Gallocanta Polje-Graben
(Gracia et al., 2002) and Jiloca Polje-Graben (Gracia et al., 2003). These Plio-Quaternary
morphostructures are controlled by NW-SE faults. Extensional neotectonics is still active in some
of the grabens as reveal the normal faults that affect Quaternary deposits and landforms
(Moissenet, 1983; Gracia, 1990; Gutiérrez, 1998). This is the case of the Daroca Half-Graben,
that can be seen from this panoramic view: the half-graben was inset in the Neogene sedimentary
sequence and mesa relieves of the Calatayud Graben, and was afterwards captured by the Jiloca
River.
The change from endorheic to exorheic conditions in the Neogene and Plio-Quaternary structural
depressions took place progressively through the capture of the basins by headward erosion of the
external drainage network. In this sense, the trajectory of some of the main rivers is adapted to the
grabens, whereas the Jalón River crosses transversally the Calatayud Graben (Fig. 1). Once each
basin was captured, the new drainage network started to incise the endorheic infill of the grabens
developing stepped sequences of alluvial levels (pediments and terraces). The capture process has
not completely finished yet. Some sectors of the Jiloca Polje-Graben remain endorheic and the
Gallocanta Polje-Graben still constitutes a lacustrine basin (Fig. 1).
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Figure 1. Geological sketch showing the distribution of the Neogene and Plio-Quaternary grabens in the central sector of
the Iberian Range (modified from Gracia et al., 2003).
2. Gallocanta Polje and lake
2.1. General geological and geomorphological features
This closed topographic basin has a catchment area of 550 km2, with an elongated shape NE-SW
oriented. It is framed by mountain ranges: Sierra de Santa Cruz-Valdelacasa to the NE (up to
1400 m high), and Sierra de Caldereros to the SW (1443 m). The Gallocanta Basin has persisted
as a closed basin until present due to its relatively high altitude (around 1000 m) and includes
more than 20 lakes of variable size. The Gallocanta saline lake, covering about 14 km2, is the
largest one of the Iberian Range and shows an elongated outline parallel to the Santa Cruz
mountain front. La Zaida fresh water lake, with some 3 km2, is located 3 km to the NW and shows
a round plan form (Fig. 2). The basin constitutes an altiplano with the NW and SE borders subject
to the headward erosion of the Piedra and Jiloca fluvial systems respectively. The zone has a
semiarid climate with a mean annual precipitation of 450 mm and an average annual temperature
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of about 10ºC. The depression is dominated by winds blowing from the NW, channelled along the
topographic through.
Figure 2. Geological map of the Gallocanta Basin. 1: Palaeozoic and Lower Triassic siliceous sediments, 2: Upper Triassic
clays and evaporites (Keuper), 3: Carbonate Mesozoic sediments, 4: Palaeogene, 5: Neogene, 6: Quaternary (Gracia et al.,
2002).
The ranges bordering the depression are composed of Palaeozoic and Lower Triassic siliceous
units and form fault-controlled mountain fronts. The Sierra de Valdelacasa is made up of an
alternating sequence of Cambrian-Ordovician quartzites and slates forming a monocline dipping
to the SW. The Sierra de Caldereros is formed by folded Ordovician and Permo-Triassic
sediments. These mountain ranges flank an extensive fault-bounded outcrop of deformed
Mesozoic sediments. Upper Triassic shales and evaporites (Keuper) form the impervious
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substratum of the Gallocanta Lake. The rest of the Mesozoic units are represented by Jurassic and
Upper Cretaceous carbonate rocks. The alpine deformational structures show a prevalent NW-SE
trend. Locally, the carbonate Mesozoic sediments are unconformably overlied by Tertiary detrital
sediments which fill two small synclinal troughs. Other minor disperse outliers of Neogene
sediments of probable Late Pliocene age form isolated platforms and are interpreted as proximal
and mid fan facies (Olmo et al., 1983a).
Quaternary forms and deposits are mainly represented by pediments and lacustrine sediments.
The former develop at the foot of the most important mountain fronts and are only thinly mantled
with alluvial cover. The mechanical erosion of the north-eastern quartzitic range produced a
sequence of three pediment levels, inset and stepped towards the depression bottom. The
lacustrine sediments appear surrounding Gallocanta Lake forming a system of stepped lacustrine
terraces. Under the lake a very thin sequence of lacustrine sediments has also been identified by
drilling.
Several remains of the Middle Miocene planation surface can be identified in the mountain ranges
bordering the depression, at an altitude between 1340 and 1360 m. This surface truncates both
Mesozoic carbonates and Palaeozoic quartzites, showing equivalent heights at both margins of the
depression. Towards the West, this surface connects in altitude with an erosional unconformity of
Middle Miocene age at a nearby small Tertiary trough (Gracia, 1990). Two other stepped levels of
Neogene planation surfaces appear in the western sector of Gallocanta Basin, gently inclined to
the North. These stepped planation surfaces form a piedmontreppen (according to terminology of
Penck, 1924), elaborated during the post-orogenic stage of the Iberian Range, from the Upper
Miocene to the Pliocene (Gutiérrez and Gracia, 1997).
A different set of planated surfaces solely developed on carbonate Mesozoic outcrops can be
recognised. These surfaces, inset in relation to the Neogene planation surfaces, are stepped
towards the Gallocanta and La Zaida lakes and show a concentric distribution around them (Fig.
3). They correspond to karstic corrosion planation surfaces with dolines and abundant karren
locally covered by residual clays.
Figure 3. Geomorphological map of Gallocanta Polje. 1: Residual relief, 2: Neogene planation surfaces, 3: Tertiary
sediments, 4: Corrosion surface C1, 5: Corrosion surface C2, 6: Corrosion surface C3, 7: Pediment G3, 8: Corrosion surface
C4, 9: Pediment G4, 10: Hanging and/or captured polje bottom, 11: Present polje bottom, 12: Alluvial fan, 13: Swallow
hole (ponor), 14: Dominant topographic slope. The A-B trace indicates cross section represented in Figure 4. Letters
represent villages (Gracia et al., 2002).
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The Gallocanta Depression was traditionally considered to be a neotectonic graben generated by
the supposed recent activity of the NE border fault (Olmo et al., 1983a & b; Hernández et al.,
1983). However, in contrast to some nearby sectors of the Iberian Range, the altitudinal
distribution of Neogene planation surfaces in the zone reveals that it is not affected by any
substantial deformation. The younger corrosion planation surfaces are not inclined towards the
mountain front, but always towards the depression bottom. The Valdelacasa mountain front does
not show geomorphological characteristics indicative of recent tectonic activity. No
geomorphological anomalies have been recognised in the drainage network crossing the front and
the pediment heads give way to rock-cut surfaces bevelling the Valdelacasa Fault and the
Mesozoic units in both the hanging wall and the foot wall (Fig. 4). Boreholes drilled near the lake
shore indicate that the sedimentary fill under the lake has a very limited thickness (< 2 m) and is
formed by fine lacustrine sediments underlain by red clays (terra rossa), which overlay the
Triassic evaporitic bedrock. None of the boreholes indicate the presence of coarse-grained
deposits commonly found in piedmonts linked to tectonically active mountain fronts. Finally, no
historical seismic activity has been recorded in the Gallocanta Depression. All these data
demonstrate that the Gallocanta basin was not originated by recent tectonic activity. Instead, its
geomorphological characteristics indicate a karstic origin by corrosion of Mesozoic carbonate
rocks.
2.2. Polje origin and evolution
The polje is limited to the NE by a hydrogeological barrier formed by the faulted contact between
the carbonate Mesozoic sediments and the siliceous Palaeozoic rocks of Sierra Santa CruzValdelacasa mountain ridge. Only the western sector of the polje is incised by the Piedra River,
which flows towards the North until reaching the Jalón River near Calatayud. According to
Sweeting (1972) and Gams (1978) classifications, it correspond to a border-polje or a semi-polje.
The origin of the polje probably was related to the second extensive episode of the Iberian Range,
in the Upper Pliocene. During this tectonic pulse, the Neogene planation surfaces probably
suffered a subtle tilting, generating a gentle topographic depression linked to Valdelacasa Fault
(Fig. 4). This tectonically-induced base level would have controlled the direction of the runoff and
underground water flows favouring the formation of the polje in this linear sector. In any case,
there is no geomorphological or sedimentary evidence to prove this hypothetical neotectonic
deformation. The initial structurally controlled karstic depression was restricted by the outcrops of
Pliocene detrital deposits (Figs. 2 and 3).
Four planation corrosion levels have been identified sourrounding the centre of the depression (C1
to C4, Fig. 3), inset in relation to the most recent Neogene planation surface. Their heights
progressively decrease from 1140 m (C1) to 1050 m (C4). The present polje floor and Gallocanta
lake shore appear at about 1000 m. During the development of the third corrosion surface (C3) the
polje was divided into several minor depressions in the western sector, disconnected from the
main polje bottom (Fig. 3). Most of these minor karstic depressions are currently drained by the
Piedra River, although there are some other closed depressions whose floors are slightly deeper
than the C3 corrosion surface (like the Campo Zamora, Fig. 4). The corrosion surface C4 occurs
mainly in the surroundings of Gallocanta and La Zaida lakes and is locally covered by
accumulations of residual red clays up to several meters thick.
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Figure 4. Geological cross section of the Gallocanta Polje (see location in Figure 3). 1: Palaeozoic quartzites and slates, 2:
Lower Triassic sandstones (Buntsandstein), 3: Middle Triassic dolomites (Muschelkalk), 4: Upper Triassic clays and
evaporites (Keuper), 5: Jurassic limestones, 6: Cretaceous limestones, 7: Miocene sands, 8: Pliocene conglomerates, 9:
Polje bottoms, S1: Middle Miocene planation surface, C2, C3 and C4: Planation corrosion surfaces, G4: Pediment (Gracia et
al., 2002).
The deepening of the polje bottom and the development of stepped corrosion surfaces was
controlled by the relative lowering of the local water table (Ford and Williams, 1989). Due to the
low hydraulic gradient, a water table located close to the polje bottom favours horizontal
dissolution as opposed to vertical dissolution. Under these circumstances corrosion planation and
corrosion pedimentation (lateral solutional undercutting, lateral corrosion or rim corrosion;
Roglic, 1940, Sweeting, 1972, Jakucs, 1985) leads to the generation of a flat bottom and its
progressive widening. The presence of abundant stripped covered karren in the corrosion surfaces
suggests that the solutional processes operated beneath a thin veneer of drift material, a process
called cryptocorrosion (Nicod, 1976, Fabre and Nicod, 1982). The water table decline with
respect to the polje bottom involves a drop in the base level for corrosion planation. The water
table lowering favours vertical dissolution and the deepening of the polje bottom until it reaches
the epiphreatic zone. The alternation of periods dominated by bottom deepening and periods of
planation and enlargement of the polje bottom controlled by the local water table position,
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resulted in the four stepped corrosion surfaces in the Gallocanta Polje. The deepening stages of
the polje bottom also involved the generation of three stepped levels of mantled pediments in
Santa Cruz-Valdelacasa piedmont (Fig. 3). Additionally, the stream headward erosion favoured
the progressive piracy of some small poljes located close to the lake, while others were captured
by the Piedra River and its tributaries.
Regardless of the water table relative position, the vertical deepening of the polje bottoms is
restricted by the impervious Triassic shales and evaporites underlying the carbonate rocks. Once
the polje floors get close to the impermeable rocks, stable lacustrine systems can develop on their
bottoms. The existence of corrosion surfaces between La Zaida and Gallocanta (Fig. 5) indicates
that the karstic depression was never occupied by a single lake. These lakes were formed in
previously individualised polje bottoms, once their floors reached the impervious Triassic bedrock
through corrosional lowering. The generation of Gallocanta and La Zaida lakes must be
temporarily linked to the interruption of the polje deepening, probably in the Upper Pleistocene.
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C dating of the oldest lacustrine sediments in Gallocanta Lake, obtained from boreholes, gave an
age of 12.230 yr BP (Burjachs et al., 1996). Swallow holes or ponors in Gallocanta and La Zaida
lakes collect the flow of some channels incised in the polje bottom (Fig. 5), indicating a certain
present karstic functionality.
Figure 5. Geomorphological map of Gallocanta Lake (Gracia et al., 2002). 1: Structural scarp, 2: Neogene clastic
deposits, 3: Corrosion surface C3, 4: Corrosion surface C4, 5: Pediment G4, 6: Lacustrine terrace T4, 7: Lacustrine terrace
T5, 8: Lacustrine terrace T6, 9: Mantled pediment, 10: Alluvial fan, 11: Covered slope, 12: Flat bottomed valley, 13:
Lacustrine floodplain, 14: Scarp in Quaternary deposits, 15: Doline, 16: Swallow hole (ponor), 17: Village.
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2.2. Gallocanta Lake: General characteristics and coastal dynamics
Gallocanta Lake has a NW-SE elongated shape, with 7.7 km length and 2.8 km of maximum
width. The lake has a maximum depth of 2.5 m (reached in 1917; Rodó et al., 2002), although
during dry periods it becomes completely desiccated. This is a saline lake where water salinity
oscillates between 100 and 1000 times the salinity of the fresh meteoric water entering the lake
(Comín et al., 1990). Salts in the lake waters are entirely supplied by underground flow from the
underlying Triassic evaporites. The sediments covering the centre of the lake consist of carbonate
and sulphate muds. During dry periods the shore zone is covered by a thin and discontinuous salt
crust.
Stop 2: Gallocanta Lake
From this point, at Gallocanta village, we have a wide view of the Gallocanta Lake and
surrounding areas. Correlation between mantled pediment levels and corrosion surfaces (C2, C3
and C4) is based on their altimetrical connection (Figs. 4 and 5). Three levels of lacustrine
depositional terraces border the lake. The top surface of the oldest terrace (T4), 8 m above the high
water level of the lake, altimetrically connects to the corrosion surface C4 and pediment level P4
(Fig. 5); all these surfaces can be considered as broadly isochronous. The lacustrine deposit of this
high terrace level is made up of several gravel sequences. The next terrace levels (T5 and T6) are
located 3-4 and 1-1.5 m respectively above the high water lake level. These lower terraces are
composed of clay and silt sediments deposited under low energy depositional environments.
During Holocene and historical times the Gallocanta Lake has undergone a progressive
segmentation due to the growth of paired and cuspate littoral spit bars (Fig. 5), a common process
in elongated lakes oriented parallel to the dominant wind direction (Zenkovich, 1967). Three
segmentation phases can be deduced from the distribution of lacustrine terraces (Fig. 5). The first
one, coeval with terrace level T4, gave place to the individualisation of a small lake, La Lagunica,
separated from the main lacustrine body by a long and strait gravel spit. This lake was artificially
desiccated in the 1950’s. A second segmentation phase started during the generation of terrace T6,
producing the isolation of a marsh area in the SE lake border. Finally, another segmentation is
currently being produced, by the growth of two oppossed spit bars in the northern sector (named
“Los Picos”, the peaks). These bars divide the lake into two lacustrine bodies (the northern
rounded one and the main central body), which are still connected due to the strong currents
existing in the narrow strait separating both cuspate beaches.
Coastal dynamics in Gallocanta Lake is very active (Gracia, 1995). Meteorological data indicate
that persistent winds of regional extent can often reach speeds of up to 100 km/h in Gallocanta
basin, due to its height and orientation. This wind produces waves that propagate to the SE
affecting both lake shores. Figure 6a shows the distribution of the maximum effective fetch for
wind-driven waves in the lake. The southeastern part of the central body records the maximum
wave energy, which produces a piling up of water and lateral return currents. By this process, the
lake elongates perpendicular to the prevailing wind. An amount of about 400 m retreat has been
produced during recent times in the eastern end of the central lake body. As a consequence, a
quite straight downwind shore, with an almost N-S direction, has been formed (Figure 6b). This
wave erosion affects terrace level T6 by undercutting a vertical cliff.
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Figure 6. Wave dynamics in Gallocanta Lake (Gracia, 1995). a) Distribution of maximum effective fetch (in metres) for
NW prevailing winds; dark zones represent islands.
Figure 6 (cont.): b) Wave front propagation in the lake, deduced from aerial photographs and field observations; arrows
represent longshore currents; dashed arrows indicate supposed backflow currents. Several coastal features related to wave
action have been also represented, like microcliff zones (dark shadow zones) and littoral spits.
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As waves travel more slowly in shallower waters due to depth reduction and the increased effect
of bottom friction, wave fronts are refracted and delayed near the shore. This effect (Figure 6b)
generates longshore currents along the central body coast, moving southeastwards. The currents
erode, transport and accumulate debris as shoreline bars and spits. There is an important
development of littoral forms along the SW shore, with spits that almost enclose small lagoons
(Figure 7a), cuspate and recurved spits (Figure 7b), as well as barrier islands, submerged bars and
small deltas. The greater development of shoreline sedimentary forms in the SW shore is related
to the more important rivers arriving to this side of the central lake body. Lake level fluctuations
directly affect all these features. A water level rise is commonly accompanied by coastal flooding,
shoreline erosion (beach and cliff retreat), or even landward shifting of nearshore bars due to the
increase in effective fetch and, consequently, in wave energy. During dry periods water level
lowering produces coastal emergence, which leaves behind abandoned coastal forms of variable
nature (spits, nearshore bars and small lagoons) that are incorporated to the present coastal
floodplain (Fig. 5); the final effects are similar to a coastal progradation.
From an environmental point of view, Gallocanta Lake is the greatest ephemeral saline lake in
Europe, and probably one of the best preserved. In 1972 it was declared as Zone of Controlled
Hunting, in 1984 as National Hunting Refuge and in 1995 as Wild Life Refuge of International
Interest. Since 1988 Gallocanta Lake has been included in the list of humid zones with
international importance (Ramsar Convention). It has also been considered as Zone of Special
Protection by the European Directive for Preservation of Wild Bird Fauna. The lake constitutes an
extraordinary important place for European migratory birds. From all the numerous species
identified yearly, the most important and representative one is the crane (Grus grus), which can
be present every winter in an average number higher than 25.000 individuals (62.000 in 1997).
Other also important species include the pochard (Aythya ferina) with 80.000 individuals, or the
coot (Fulica atra), with 40.000 individuals (Sampietro, 2002). Every year the number of wild
birds recorded in the lake exceeds the 80% of the total European population in all these species. In
recent years a Visitors Centre was built in the southern border of the lake, where interactive
activities let people learn about the main ecosystems of the zone, flora and fauna, the most
relevant wintering birds, their aspect, noise, behaviour, etc. A Museum of Wild Birds can be also
visited at Gallocanta village.
2.3. Late Quaternary evolution of Gallocanta Lake
The sediments of the lake bottom were studied by several authors by means of boreholes drilled in
the central sector of the lacustrine basin. The sedimentary substratum under the lake sediments
(Roc, 2003) is represented by a continuous level of residual red clays (terra rossa) with some sand
and pebble lens associated to ephemeral streams. Sediments overlying the red clays are less than 2
m thick and are composed of fine grained clastic facies and carbonate muds, which reflect
alternating desiccation and flooding periods. Pérez et al. (2002) and Roc (2003) made a detailed
sedimentological study and elaborated a facies map for the present lake sediments.
Some controversy still exists about the precise age of the lacustrine sediments underlying the lake
and their palaeoenvironmental evolution. Davis (1994) sampled and dated the upper 20 cm and
inferred an age of 1500 AD for the upper 15 cm. Burjachs et al. (1996) made radiocarbon dating
on pollen samples taken at the base of the lacustrine sequence (0,95 m depth) and at a mid point
(0,60 m), obtaining ages of 12,230 yr BP for the former and 840 yr BP for the latter. Other dating
helped them to reconstruct historical climatic fluctuations, like the Medieval Warm Period and the
Little Ice Age. Rodó et al. (1997) applied AMS radiocarbon dating on organic matter found in a
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mud level at 1.7 m depth, obtaining an age of 32,650 ± 480 yr BP. Schütt (2000) studied the upper
95 cm of the sedimentary record and differentiated three main units: a lower one deposited under
arid conditions, an intermediate one related to sub-humid environments and a later one that
reflected an increase in aridity. Rodó et al. (2002) analysed the geochemistry of the upper 40 cm
and after several age determinations inferred several drought and humid episodes from 1889 until
present. Finally, Roc (2003) applied several dating techniques for different samples taken in the
upper 80 cm and obtained about 2 AD for the oldest sediments and 1837 AD for a sample taken at
20 cm depth.
a
b
Figure 7. Aerial photographs showing a) the development of a straight spit and an almost enclosed bay and b) several
recurved spits at the western and southern shore of Gallocanta Lake, respectively (vertical photos taken during a high
water period, 1978).
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Stop 3: Quaternary coastal lacustrine deposits of Gallocanta lake
At the southern edge of Gallocanta Lake we can see good sections of the ancient terrace level T4
on several gravel-exploitation pits. These fronts show a 4 m thick deposit formed by two units
(Figure 8): an upper one of 0,5 – 1 m, formed by fluvial-torrential gravels associated to a recent
mantled pediment, and a lower one of 3 m which is the proper lacustrine deposit, with laminated
gravels and sands. This deposit can be supposed to be coeval with the deepest lacustrine
sediments recognised in the boreholes (dated as late Upper Pleistocene). Genetically this
depositional terrace level was formed during the first segmentation phase and separates the small
“La Lagunica” lake from the Gallocanta Lake. The sedimentological characteristics of the
sections help to understand the sedimentary processes prevailing on the lake shore during these
early stages. The deposit is organised into sets of fine gravels to coarse-medium sands with cross
stratification structures. Two alternating types of sets can be differentiated (Figure 8): one with
onshore dipping planar cross-stratification and foreset dip angles of 30-35º landwards, and a
second one with low-angle lakeward-dipping (about 10-15º) and low-angle onlapping
relationships. The first type can be interpreted as the result of the onshore migration of linear
megaripples, representing a landward migration of bar systems. Sometimes the sets culminate
with aeolian levels of very fine sorted rubificated sands, indicative of emersion. Sets of the second
type can be interpreted as accretionary beach face sequences during progradation and the
lakeward-dipping bedding surfaces would represent erosional truncations produced by storm
action.
Figure 8. Cross section of lacustrine terrace T4 deposits in the SE border of Gallocanta Lake (Gracia, 1995).
The general characteristics of the deposit represent alternating episodes of high and low energy
levels in a nearshore environment. The two types of sets alternate vertically and horizontally and
show the typical geometric and sedimentological characters of the classic ridge & runnel
sequences described for wave-dominated beaches, both marine and lacustrine (Hart and Plint,
1989). The lakeward dipping sets represent high energy situations, with partial erosion of
previous bars. A high energy level would be related to a climatic change (stronger winds
generating longer and higher waves), or to a higher water level (increasing the effective fetch of
the ancient lake), or to both at the same time. The alternating disposition of bars and beach sets
can be interpreted as the result of wave energy and/or lake level fluctuations, and then at least four
general climatic and/or hydrological oscillations can be deduced during the genesis of this
deposit. These data help to estimate the relative size of the ancient Gallocanta Lake. The
maximum water depth probably reached about 10 m, deduced from the relative height of this
terrace level plus the maximum thickness of the lacustrine deposits under the lake. During the
13
Upper Pleistocene the lake possibly occupied about 50 km2, with a maximum effective length of
10 km, responsible for the generation of 1 m thick bars.
The generation of a new lacustrine terrace level at a lower height was a response to an important
reduction of the lake extension and water level lowering, mainly due to climatic aridification
during Holocene times. Minor-order climatic fluctuations during the Late Quaternary probably
produced alternation of bar/beach deposits and constituted terrace-building sequences. High-order
climatic fluctuations, progressively evolving towards more arid conditions, would suppose an
absolute water level lowering capable of creating a new lower terrace level. Nevertheless, karstic
subsidence affecting the underlying evaporites could have also played an important role in the
lake bottom lowering (Gracia, 1995).
2.4. Hydrology and hydrogeology of Gallocanta lacustrine basin
Climatically the Gallocanta Basin shows a semiarid regime and the lake extension varies
considerably between decades, yearly or seasonally. Although the maximum lake extension has
not varied significantly since Roman Times, important water level oscillations occurred
historically, from a complete desiccation to more than 2 m depth. Comín et al. (1990) correlated
water level and precipitation changes for the 1990’s decade, concluding a lag between lake level
and rainfall of 0.3 – 2.4 years. After a detailed study of lake level variations since 1910 to the
present, Rodó et al. (1997) concluded that the hydrological regime of Gallocanta Lake presents a
clear positive correlation with the ENSO (El Niño – Southern Oscillation), while no relationship
is found when compared with the NAO (North Atlantic Oscillation).
None of the lacustrine terrace deposits include any salt level. Salts are only present in the upper
centimeters of the boreholes made in the lake bottom sediments (Pérez et al., 2002). These data
suggest a quite recent moment at which this lake became saline. Historical documents (Campillo,
1915) indicate that by 1457 the Aragonian King allowed the exploitation of salts accumulated in
the lake. Other later documents describe different permissions made for salt extraction, up to the
late XIX Century. The youngest moment by which the lake still contained fresh water can be
estimated after data obtained by Burjachs et al. (1996), already cited (840 yr BP, dated by
radiocarbon on a non-saline sample taken at about 0.6 m depth under the lake bottom). Hence, if
this dating is correct, it seems that the lake waters became saline in a short period of time,
between XII and XV centuries. The explanation for such a rapid process could be related to an
episode of karstic subsidence on the underlying Triassic evaporites with the subsequent
outcropping of underground saline waters. Indeed, a continuous vertical scarp of about 0.5 m
surrounds the northern lake body affecting very recent forms and deposits (Fig. 5). Close to this
northern lake body a group of saline springs (“Los Ojos”) constitute the main supply of salt water
to Gallocanta Lake (Fig. 9). Today the Gallocanta Lake waters present a salt content that varies
significantly, between 15 and more than 200 g/l, depending on the lake water volume. During
desiccation periods water salinity progressively increases, producing subsequent chemical
precipitation of carbonates, sulphates and sodium and potassium chlorides.
14
Salt water spring
Fresh water spring
Well
Drilling
Piezometric flow
Resurgence
Zaida
lake
Los Ojos
Gallocanta
lake
Figure 9. Hydrogeological map of Gallocanta Basin (piezometric lines obtained from Fenero, 1988).
Hydrologically, the Gallocanta Lake receives surficial and underground waters flows. After a
hydrological study between 1941 and 1991, García and Arqued (2000) concluded that the average
rainfall supply is about 131 hm3/year, from which 117.7 hm3/year are evapotranspirated and 3.8
hm3/year correspond to overland flow. The groundwater flow from the aeration zone to the lake
(Fig. 9) represents about 5 hm3/year and the average recharge is 4.3 hm3/year. Total water
resources of Gallocanta Lake are estimated in 12.8 hm3/year. However, these values do not take
into account water losses and gains related to karstic processes. A quite evident ponor-estavelle
can be identified to the East of Las Cuerlas village and is connected to the lake by a shallow
channel which drains the water outflow during periods of reversed flow (Fig. 5). Additionally, a
karstic resurgence between La Zaida and Gallocanta lakes indicates the underground
communication between both water bodies (Fig. 9).
15
Stop 4: La Zaida fresh-water lake
The fresh water lacustrine basin of La Zaida has a maximum depth of 1 m and a subcircular
geometry. This smaller lake has an evident karstic origin on Lower Jurassic to Upper Cretaceous
carbonates, which outcrop in its S and SW margins forming a continuous vertical scarp. The lake
receives an overflow water supply of about 7.5 hm3/year. However, after an agreement between
farmers from Gallocanta and Used villages in the XVI century, the hydrological regime of the
lake was modified by a dam that regulates its overland water supply. When the lake dries out
completely, the dam is closed and the flow is diverted to Gallocanta Lake, while the dry bottom of
La Zaida Lake is cultivated. The following year the dam is again opened. There exists an evident
hydrogeological connection between La Zaida and Gallocanta lakes. A swallow hole can be seen
during low-water periods in the southern margin of La Zaida Lake (Fig. 5). During high-level
periods, water infiltrates into the ponor and circulates as underground flow through the geological
contact between the Jurassic carbonates and the Triassic clays and evaporites (Fig. 10).
Groundwater finally crops out in a karstic resurgence, inset in the youngest corrosion surface and
located between both lakes (Fig. 9). The resurgence forms a small subsidence depression from
which an episodic gully drains the fresh outflowing water to Gallocanta Lake.
Figure 10. Geological cross section between La Zaida and Gallocanta lakes. 1: Upper Triassic clays and
evaporites (Keuper), 2: Jurassic limestones, 3: Lower Cretaceous sands and clays, 4: Upper Cretaceous
limestones, 5: Recent lacustrine deposits, 6: Resurgence. Arrows indicate ponor location and underground water
flow paths. C2, C3 and C4: corrosion surfaces.
3. Piedra River canyon, waterfalls and tuffa complex
3.1. Geomorphology of the Piedra River Valley
The Piedra River, with about 90 km length in a South-North direction, constitutes one of the most
important intramontane rivers of the central Iberian Range. Along its course the river crosses
zones with contrasted geomorphological characteristics that make the valley a very interesting
example of fluvio-karstic environment. Figure 11 shows a longitudinal section of the valley with
the distribution of different morphological sectors (A to E) and morphogenetic levels that help to
understand the geomorphological evolution of the valley. Several planation surfaces appear in this
region: a very high one developed above 1200 m height, that after regional correlation (see
section 2.1) can be considered as formed in the Middle Miocene. Two other stepped levels of
planation surfaces can be recognised, inclined to the North towards the Calatayud Graben. The
highest one corresponds with the Main Planation Surface of the Iberian Range, at about 1180 m,
and topographically connects to the North with the top of a lacustrine calcareous unit of the
16
Calatayud Graben considered as Late Miocene by Meléndez et al. (1982). The lower surface is
locally fossilised by Pliocene alluvial fans.
1400
1300
Middle Miocene planation surface
Main
Upper P
P
lanat
liocene
ion
planatio
n surfac Surface o
C1
e
f the
Iber
C2
ian
Ran
ge
Cimballa
1200
C3
1100
1000
900
0
8 km
800
900
1
Llumes
La Tranquera dam
700
2
3
600
800
0
2 km
700
q
Re
da
w
t
wa
ici
pr
Ca
s
ou
s
i
Ta
e’s
6
l
al
7
f
er
at
lw
r
Ho
7
ll
fa
er
ija
u
La
5
f
er
at
Jalón River
4
l
al
8
Nuévalos
9
Figure 11. Longitudinal profile of the Piedra River Valley. Pc: Late Miocene lacustrine limestone level of the Calatayud
Graben, C1, C2 and C3: Karstic corrosion surfaces of the Gallocanta Polje. Below: detailed distribution of waterfalls and
tufa terrace levels in the surroundings of the Monastery of Piedra.
Inset in the Neogene planation surfaces there appear several remains of karstic corrosion surfaces
C1, C2 and C3 of the Gallocanta Polje (Fig. 11, sectors A and B). The distribution of karstic
surfaces in this zone indicates the existence of a polje bottom roughly oriented NW-SE and
limited by terrigenous Tertiary deposits (Fig. 3). In this sectors no remain exists of the corrosion
surface C4 and the Piedra River directly incises the C3 surface. Probably, the episode of water
table lowering that produced the genesis of the C4 corrosion surface in the Gallocanta Polje, led to
the fluvial capture of this local polje bottom by a tributary of the Jalón River. Hence, the
Gallocanta Polje was divided into two sectors with very different evolution: the eastern one
continued as a polje until finally changing into a lacustrine basin, while the western one was
instead captured by the Jalón fluvial system (Piedra River), and from then on river incision
prevailed.
The Piedra River commences at Sierra de Caldereros piedmont (Fig. 2), where it crosses a wide
system of old alluvial fans (upper sector A in fig. 11), considered as Plio-Quaternary by Olmo et
al. (1983b). Although the fans may be probably younger, it seems that fluvial incision in this zone
has been very low during Quaternary times. Between Embid and Torralba (Fig. 2 and Fig. 11 –
sector B) the Piedra River excavates the bottom of the local polje existing on the NW zone of the
Gallocanta Depression. Along these 20 km the Piedra River develops a deep canyon with vertical
walls of about 70 m depth on gently folded Cretaceous limestones. At both sides of the canyon
17
several corrosion surfaces belonging to the former Gallocanta Polje can be identified, between
170 and 40 m above the Piedra River bed. The carbonate walls of the canyon show numerous
karst conduits exhumed by fluvial incision. Several collapse dolines and karstic springs also
appear along the bottom of the canyon, many of them still active at present. The canyon finishes
when the river passes through the Aldehuela Depression, a small Tertiary basin filled by more
erodible Oligocene clastic sediments (Fig. 2 and fig. 11 – sector C). As a consequence, the valley
widens and the river channel increases its gradient, giving rise to a significant decrease in the
river sinuosity.
North of the Aldehuela Depression, the Piedra River again cuts Mesozoic limestones, forming a
second canyon along 30 km excavated on Cretaceous and Jurassic carbonates (Fig. 11 – sector D).
In this zone the river develop several stepped levels of tufa deposits, both fossil and active, mostly
associated to prograding waterfalls. Finally, the lower valley sector (Fig. 11 – sector E) includes
the artificial La Tranquera dam, which starts at Nuévalos village and was constructed for
irrigation purposes. After the dam, the Piedra River significantly increases its gradient while
incising into Palaeozoic slates and schists until reaching the Jalón River.
Stop 5: Cimballa karstic spring
The Mesozoic units in sector B (Fig. 11) are gently folded, with a slight tilt towards the North. As
the Piedra River incises into these formations, older levels outcrop in the valley bottom. The
Jurassic limestones constitute the most important karstic aquifer of the region. At Cimballa village
the Piedra River bed reaches the Jurassic levels when crossing a NNW-SSE normal fault which
affects the Neogene planation surfaces and exerts an important morphostructural control on the
Piedra River (Fig. 2). At this favourable point an important karstic spring outcrops and supplies
about 30 hm3/year (Cascales et al., 1979), from which more than one third could be supplied by
the carbonate aquifer of the Gallocanta Polje (Roc, 2003). The spring adds carbonate-rich waters
to the Piedra River and gives rise to a spring tufa deposit formed by macrophyte reefs
(phytoherms) growing around the main outflowing points. The mixture of both fluvial and spring
waters produces carbonate precipitation and then tufa deposition begins in the Piedra River: a
longitudinal phytoherm develops on the river bed from this point to Llumes village (Fig. 11),
along more than 5 km.
Figure 12. Geomorphological map of the Piedra River valley in the Monastery of Piedra area. 1: Cuesta fronts on Triassic
and Jurassic limestones, 2: Upper Triassic clays and evaporites, 3: Cuesta fronts on Cretaceous carbonates, 4:
Anticline/syncline, 5: Platforms on Tertiary conglomerates, 6: Neogene planation surface, 7: Tufa terrace T1, 8: Tufa
terrace T2, 9: Tufa terrace T3, 10: Tufa terrace T4, 11: Tufa terrace T5, 12: Gravel fluvial terrace Tg5, 13: Tufa terrace T6,
14: Tufa terrace T7, 15: Gravel terrace Tg7, 16: Tufa terrace T8, 17: Gravel terrace Tg8, 18: Pediment level G8, 19: Tufa
terrace T9, 20: Gravel terrace Tg9, 21: Pediment level G9, 22: Alluvial fan, 23: Present fluvial valley bottom, 24: cascade.
M: Cistercian Monastery.
18
19
3.2. Tufa deposits and forms along the Piedra River Valley
Downstream from Cimballa, the Piedra River forms a continuous and sometimes spectacular
gorge until La Tranquera dam. Along this sector the river develops a series of cascades and
waterfalls, especially concentrated at two main places: La Requijada and Monastery of Piedra,
separated about 1.5 km (Fig. 11 below). A set of nine levels of stepped tufa terraces can be
distinguished in this sector and have been represented in figs. 11 and 12. At present, fluvial
carbonate precipitation is still very active, mainly in the form of prograding waterfalls. Three
kilometers before La Requijada place, at Llumes village the Piedra River crosses the base of the
Jurassic sequence. Groundwater from the underlying Upper Triassic evaporites supplies calcium
and produces additional carbonate precipitation due to the common ion effect. As a consequence,
a tufa barrage and a small cascade appear at this point (Fig. 11 below).
Stop 6: La Requijada waterfall
At La Requijada the Piedra River forms two small cascades and another important and spectacular
waterfall. Eight different tufa terrace levels can be distinguished in the zone. Their distribution
and heights indicate that probably the main waterfall was formed after the generation of level T4
and before the generation of terrace T5 (Fig. 11 below). This fluvial sector not only includes one
of the most time-persistent tufa environments of the Piedra Valley, but also probably the most
active one. Arenas et al. (2004) made a detailed sedimentological study of several fossil tufa
deposits from this point to the Monastery of Piedra zone. Although these authors only recognised
four main levels of tufa accumulation, they concluded that some of the most important tufa
deposits in the valley can be found at La Requijada sector, with near 50 m thickness. The
sequence is formed by several incision + aggradation episodes, which finally end on a prograding
barrage system that represents a river bed stabilisation episode at a certain height - the one that
defines the final tufa terrace level elevation.
Stop 7: The Piedra River Canyon at the Monastery of Piedra
At the old Virgin of La Blanca hermitage there is a good view point for watching the main tufa
terraces and morphologies around and downstream the Monastery of Piedra. Some of them
indicate ancient tufa accumulation processes today inactive. Arenas et al. (2004) identified several
fossil tufa deposits occupying a lateral valley (to the West of the Piedra River Valley) where no
presently active carbonate accumulation occurs. The distribution of tufa terrace levels in that
valley (Fig. 12) indicates that carbonate precipitation was active during a prolonged period of
time. From a chronological point of view, Arenas et al. (2004) dated by U/Th a sample from an
intermediate level (equivalent to T5 level of fig. 12) in this zone. The obtained age, between 105
and 85 ka, suggest a correspondence with isotopic stage 5, an Upper Pleistocene warm period
during which tufa deposition was very active in Spain (Durán, 1989).
The Piedra River canyon ends at Nuévalos village, where the last cascade and tufa barrage of the
valley develops at a quite narrow gorge. The village occupies several tufa terrace levels. At this
point the river enters in La Tranquera dam, also fed by the Ortiz River. Four gravel terrace levels
appear in the Ortiz River valley, which can be easily correlated with the middle and lower tufa
terrace levels of the Piedra River (Fig. 12). During the generation of the younger levels, vertical
incision prevailed in both valleys. However, headward erosion in the Piedra valley was blocked
by La Requijada – Monastery of Piedra tufa systems. Waterfall retreat/progradation processes not
only depend on base level fluctuations, but also on climate variations and vegetation activity. As a
consequence, the tufa complex prevented the upstream propagation of incision phases and during
20
Quaternary times the high and middle Piedra valley sectors (A – C in fig. 11) experienced little or
only moderate incision, especially if compared with the low valley sector (E in fig. 11).
Stop 8: Present tufa precipitation at the Monastery of Piedra Natural Park
On 1194 thirteen Cistercian monks founded the Monastery of Piedra as a request of King
Alphonse II of Aragon, who donated an old castle and the lands surrounding it in the place known
as “Piedra Vieja” (old stone), in the Piedra River canyon. After a governmental expropriation in
the middle XIX century the Monastery was finally acquired by the Muntadas family. Members of
this family discovered the Iris Cave (beneath the Horse’s Tail Waterfall) and transformed the zone
into a Park. Today the Muntadas inheritors preserve and manage the Park as a naturalistic and
cultural attraction that receives thousands of visitors every year. A brief visit to the old Cistercian
Monastery will let us observe different dependencies (cloister, chapterhouse, refectory, the old
abbey, etc.). It is worth to point out that the Monastery kitchen was the first place in Europe
where chocolate was cooked. The cultural visit will finish at the little Wine Museum, which
belongs to the famous Calatayud wine region.
Since the construction of the Park the river flow has been partly diverted at several points to form
artificial cascades, waterfalls and ponds. The average river discharge outgoing the Monastery is
1.22 m3/sec (about 38 hm3/year, Arenas et al., 2004) and the cascades and waterfalls constitute
one of the most spectacular examples of presently active tufa systems in Europe. The visit through
the Monastery of Piedra Natural Park includes the two most important natural cascades in this
sector of the Piedra River Valley, the Capricious Cascade (about 25 m high) and the Horse’s Tail
Waterfall (53 m high). The second one is a rapidly prograding cascade that has created a great
blind cave behind the tufa curtain (the Iris Cave), with spectacular stalactites hanging from the
cave ceiling. Another interesting feature is the fish farm, the first one installed in Spain (in 1867)
to breed salmonids and cyprinids, and today managed by the Aragón regional government to
repopulate other rivers and lakes with rainbow trouts. The visit finishes in the artificial Mirror
Lake, constructed on an abandoned meander of the Piedra River, in a zone subject to active mass
movements and rock falls.
According to the fluvial morphodynamics and flora associations, Arenas et al. (2004)
distinguished eight different types of sedimentary environments in this sector of the Piedra River.
Taking into account the tufa classification and terminology proposed by Pedley (1990), these
types belong to the Cascade and Fluviatile models and include:
Small cascades and rapids with bryophyte and green algae growths (like Cladophora).
Stepped cascades with important bryophyte accumulations, moss and cyanobacteria growths
and green algae.
Important cascades (> 2 m high) with moss curtains built out from the fall rim.
Channel sectors with rapid flow, up and downstream of important cascades. They include
laminar calcite accumulations with biofilms containing micrite crystals.
Water splash zones near waterfalls, with moderate moss, cyanobacteria and green algae
growths.
21
Barrage lake deposits up and downstream of waterfalls and cascades. They show typical
phytoclast accumulations with oncoids and gastropods.
Caves developed behind cascades. They include stalactites sometimes starting at hanging
stems, bryophytes and other phyto-micro-films.
Low carbonate lakes with algae (Chara hispida) and marginal mosses and ferns.
The Piedra River in this zone presents a calcium bicarbonate alkaline water (average pH = 8.4),
with conductivity values between 630 and 670 mS/cm (Arenas et al., 2004). These authors used
rods and rock slabs for measuring present carbonate precipitation rates at different environments
within the Monastery of Piedra and concluded that precipitation takes place mainly in summer
(when vegetation activity increases, taking CO2 from the water). High rates (3 – 5 cm/year) are
recorded where degassing processes are most effective, especially on tufa curtains (values of up to
10 cm/year during summer). Minimum rates are recorded in pond upstream areas. In the artificial
Mirror Lake, water is in chemical equilibrium with calcite and no carbonate precipitation occurs.
22
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and Gutiérrez, M. (1983b). Memoria y Mapa
Geológico de España, E.1:50,000. Hoja nº 490,
Odón. Instituto Geológico y Minero de España.
Madrid, 76 pp.
Sampietro, F.J. (2002). Las aves. In: Guía de la
naturaleza de Gallocanta (Mañas, J., coord.).
Prames Ed., Zaragoza, 72 – 97.
Pedley, H.M. (1990). Classification and
environmental models of cool freshwater tufas.
Sedimentary Geology, 68, 143 – 154.
Schütt, B. (2000). Holocene paleoenvironments in
Central Spain reconstructed by sedimentological
investigation of playa lake systems. In:
Geomorphology, human activity and global
environmental change (Slaymaker, O., ed.). John
Wiley & Sons, 151 - 184.
Penck, W. (1924). Die Morphologische Analyse:
ein capitel der Physikalischen Geologie.
Englehorns, Stuttgart.
24
Sopeña, A., Gutiérrez-Marco, J.C., Sánchez-Moya,
Y., Gómez, J.J., Mas, R., García, A. and Lago,
M. (Coords.) (2004). Cordilleras Ibérica y
Costero Catalana. In: Geología de España. (Vera,
J.A., ed.). IGME, Madrid, 467-470.
Sweeting, M.M. (1972).
McMillan Press, 362 pp.
Karst
landforms.
Zenkovich, V.P. (1967). Processes of coastal
development. Oliver and Boyd, Edinburgh.
25
ROAD LOG:
Departure from the Conference Hall at 8:30.
0-90 km Road N-330 to Daroca city and then A-211 to Gallocanta village. Stop 1 at Puerto de
Santed (kilometric roadmark 50) to see a panoramic view of the Calatayud and Daroca
grabens.
90-100 km
Road A-211 to Gallocanta village. Stop 2 at a panoramic point in front of
Allucant Hostel to see the main geological and geomorphological features of Gallocanta
basin and lake. Coffee stop at Allucant Hostel.
100-110 km
Road A-1507 to Tornos village. Stop at gravel pits located close to the
secondary road between Tornos and Bello to see lacustrine terrace deposits (stop 3). 10
minutes walk along the road for making a short visit to the Visitors Centre of the Gallocanta
Lake.
110-120 km
Road A-2506 to Cubel. We will stop at a panoramic point to see the main
geomorphological features of La Zaida fresh water lake (stop 4).
120-140 km
Road A-2506 to the next cross and then local road to the left towards Torralba,
Aldehuela and Cimballa villages. At the entrance of Cimballa a path crosses the Piedra
River. After a 5 min. walk we will climb up some meters the slope of the Piedra valley until
reaching enough height for obtaining a general view of the Cimballa karstic springs (stop 5).
140-154 km
We will continue the local road until connecting with road A-202 to Calatayud.
After about 6 km, stop at a panoramic point (La Requijada, 14 km from Cimballa) to see tufa
cascades on the Piedra River (stop 6).
154-156 km
Two kilometers ahead we will stop at another panoramic point (Virgin of La
Blanca hermitage, 4 km South of Nuévalos) to see a general view of the Piedra River canyon
at the Monastery of Piedra (stop 7).
156-157 km
Arrival to the Monastery of Piedra for lunch. Afterwards we will make a short
cultural visit to the remains of the Old Cistercian Monastery and the Wine Museum. The rest
of the trip will be a 2 hours peaceful walk through the Monastery of Piedra Natural Park
(stop 8). Several stops will serve to examine present and fossil tufa sedimentary
environments, including the spectacular fluvial waterfalls of the Piedra River.
157-270 km
Road A-202 to Calatayud and then highway A-2 to Zaragoza (about 1:30 hours).
Expected arrival time to the Conference Hall: 21:00.
26
to
to Hue
sca
Lo
gr
oñ
o
na
to Barcelo
Zaragoza
to
A-2
87
24
La Tranquera
Dam
lló
n
A2
02
Munébrega
ste
N - 330
Calatayud
Jalón
River
Ca
to Teruel an
d Valencia
adrid
to M
Nuévalos
8
7
6
02
Monasterio
de Piedra
21
1
Aldehuela
Santed
La Zaida
Lake
Torralba
1
Val de
San Martín
7
Gallocanta
4
2
Ga
llo
ca
Las Cuerlas
14
N
14
el
r
ve
Ri
15 km
ru
Te
ra
ed
Pi
0
to
5
Daroca
Cimballa
A-
A-2
Llumes
nt
a
Berrueco
14
La
k
e
Tornos
3
Bello
27

gallocanta karst polje and piedra river valley

Transcription

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