SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY Gallocanta.pdf · Gallocanta karst polje and Piedra river valley 2 During the Lower-Middle Miocene the tectonic regime changed gradually

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 1Dpto. 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 Lower-Middle 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

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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).

F.-Javier Gracia and J. Benavente

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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 Cruz-Valdelacasa 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. 14C 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. 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).

a

b


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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


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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.


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Fresh water spring

Well

Drilling

Piezometric flow

Resurgence

Gallocantalake

Zaidalake

Salt water spring

Los Ojos

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).


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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


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Calatayud Graben considered as Late Miocene by Meléndez et al. (1982). The lower surface is locally fossilised by Pliocene alluvial fans.

1400

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Upper Pliocene planation surfaceC1C2

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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


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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.


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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


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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.


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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.


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References

Arenas, C., Auqué, L.F., Elías, M.J., Longares, L.A., Osacar, M.C., Pardo, G., Peña, J.L., Sancho, C. And Vázquez, M. (2004). Depósitos tobáceos actuales y fósiles del río Piedra en el entorno del Monasterio de Piedra (provincia de Zaragoza). Geo-Guías, 1, 10 – 32.

Burjachs, F., Rodó, X. and Comín, F.A. (1996). Gallocanta: ejemplo de secuencia palinológica en una laguna efímera. In: Estudios Palinológicos (Ruiz Zapata, B., ed.), XI Simp. Palinología, Universidad de Alcalá, Alcalá de Henares, 25 – 29.

Campillo, T. del (1915). Documentos históricos de Daroca y su comunidad. Biblioteca de Escritores Aragoneses, Zaragoza.

Cascales, J.C., Doblas, J.G. and Garrido, M. (1979). Hidrogeología de la Laguna de Gallocanta. In: 2º Simp. Nac. Hidrogeología, Asoc. Geol. Esp. M.O.P.U. Pamplona, vol. 4, 431 – 446.

Comín, F.A., Julia, R., Comín, M.P. and Plana, F. (1990). Hydrogeochemistry of Lake Gallocanta (Aragón, NE Spain). Hydrobiologia, 197, 51 – 66.

Davis, B. (1994). Palaeolimnology and Holocene environmental change from endorreic lakes in the Ebro Basin. North-East Spain. PhD Thesis, University of Newcastle Upon Tyne, 317 pp.

Durán, J.J. (1989). Geocronología de los depósitos asociados al karst en España. In: El karst en España (J.J. Durán and J. López, eds.), Sociedad Española de Geomorfología, Monografía 4, 243 – 256.

Fabre, G. and Nicod, J. (1982). Modalités et rôle de la corrosion crypto-karstique dans les karst méditerranéens et tropicaux. Zeitschrift für Geomorphologie. 22, 209 - 224.

Fenero, M. (1988). Hidrogeología de la Cuenca de Gallocanta. XXII Curso de Hidrogeología Noel Llopis, Universidad Autónoma de Madrid, 188 pp.

Ford, D. and Williams, P. (1989). Karst Geomorphology and Hydrology. Chapman & Hall, London, 601 pp.

Gams, I. (1978). The polje: the problem of definition. Zeitschrift für Geomorphologie. 22, 170-181.

García, M.A. and Arqued, V.M. (2000). Evaluación de los recursos subterráneos en el dominio hidrogeológico Alto Jalón – Alto Jiloca. Geotemas, 1(2), 87 – 91.

Gracia, F.J. (1990). Geomorfología de la región de Gallocanta (Cordillera Ibérica central). Ph. D. Thesis. Universidad de Zaragoza, Zaragoza, 660 pp.

Gracia, F.J. (1995). Shoreline forms and deposits in Gallocanta Lake (NE Spain). Geomorphology, 11, 323 – 335.

Gracia, F.J., Gutiérrez, F. and Gutiérrez, M. (2002). Origin and evolution of the Gallocanta polje (Iberian Range, NE Spain). Zeitschrift für Geomorphologie, 46 (2), 245 – 262.

Gracia, F.J., Gutiérrez, F. and Gutiérrez, M. (2003). The Jiloca karst polje-tectonic graben (Iberian Range, NE Spain). Geomorphology, 52, 215-231.

Gutiérrez, M., and Gracia, F.J. (1997). Environmental interpretation and evolution of the Tertiary erosion surfaces in the Iberian Range (Spain). In: Palaeosurfaces: Recognition, Reconstruction and Palaeoenvironmental Interpretation (Widdowson, M., ed.), Geological Society Special Publication 120, 147-158.

Gutiérrez, F. (1998). Fenómenos de subsidencia por disolución de formaciones evaporíticas en las fosas neógenas de Teruel y Calatayud (Cordillera Ibérica). Ph.D. Thesis, Universidad de Zaragoza, Zaragoza, 569 pp. (unpubl.)


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Hart, B.S. and Plint, A.G. (1989). Gravelly shoreface deposits: a comparison of modern and ancient facies sequences. Sedimentology, 36, 551 – 557.

Hernández, A., Olivé, A., Moissenet, E., Pardo, G., Villena, J., Portero, J.M. and Gutiérrez, M. (1983). Memoria y Mapa Geológico de España, E.1:50,000. Hoja nº 491, Calamocha. Instituto Geológico y Minero de España. Madrid, 73 pp.

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Meléndez, A.; Pardo, G.; Pendón, G. and Villena, J. (1982).- Una etapa de comunicación entre las cuencas de Calatayud y Almazán durante el Mioceno superior. 1ª Reun. sobre Geología de la Cuenca del Duero. I.G.M.E., p. 415 - 429.

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Olmo, P.-Del, Portero, J.M. and Gutiérrez, M. (1983a). Memoria y Mapa Geológico de España, E.1:50,000. Hoja nº 464, Used. Instituto Geológico y Minero de España. Madrid, 74 pp.

Olmo, P.-Del, Portero, J.M., Villena, J., Pardo, G. 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.

Pedley, H.M. (1990). Classification and environmental models of cool freshwater tufas. Sedimentary Geology, 68, 143 – 154.

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Peña, J.L., Gutiérrez, M., Ibáñez, M.J., Lozano, M.V., Rodríguez, J., Sánchez, M. Simón, J.L., Soriano, M.A. and Yetano, L.M. (1984). Geomorfología de la provincia de Teruel. Instituto de Estudios Turolenses, Teruel, 149 pp.

Pérez, A., Luzón, A., Roc, A.C., Soria, A.R., Mayayo, M.J. and Sánchez, J.A. (2002). Sedimentary facies distribution and genesis of a recent carbonate-rich saline lake: Gallocanta lake, Iberian Chain, NE Spain. Sedimentary Geology, 148, 185 – 202.

Roc, A.C. (2003). Evolución medioambiental de las lagunas salino-carbonatadas durante el Holoceno en la cuenca de Gallocanta, Aragón, NE España. Estudio sedimentológico y palinológico. PhD Thesis. University of Zaragoza, 452 pp.

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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.

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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.


27

to Logroño toH

ues

ca

to Barcelona

toC

astellón

Zaragoza

toT

eru

elan

dV

ale

nci

a

N-

330

87

to Madrid

A-2Calatayud

24

MunébregaLa Tranquera

Dam

Nuévalos A-2

02

Monasteriode Piedra

A-2

02

8

7

6

5

Llumes

Cimballa

Aldehuela

15 km0

PiedraRiver

Jalón River

TorralbaLa Zaida

Lake

Santed

4

3

2

1

Las Cuerlas

Bello

14

14 Tornos

Gallocan

taLake

Berrueco

Gallocanta

7

Val deSan Martín

14

Daroca

toTeru

el

A-2

11

N

Documents

SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY Gallocanta.pdf · Gallocanta karst polje and Piedra river valley 2 During the Lower-Middle Miocene the tectonic regime changed gradually