SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY Andalucia.pdf · Central Andalusia: Karst,...

SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY

CENTRAL ANDALUSIA: KARST, PALEOCLIMATE AND NEOSEISMOTECTONICS

J. J. Durán, B. Andreo, F. Carrasco and J. López-Martínez

FIELD TRIP GUIDE - A6

SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY

CENTRAL ANDALUSIA: KARST, PALEOCLIMATE AND NEOSEISMOTECTONICS J. J. Durán (1) , B. Andreo (2), F. Carrasco (2), J. López-Martínez (3) (1) Instituto Geológico y Minero de España., Ríos Rosas, 23. 28003 Madrid (Spain) e-mail:[email protected] (Fax: 913495742) (2) Universidad de Málaga, Facultad de Ciencias, Departamento de Geología. 29071 Málaga (Spain) e-mail:[email protected]; [email protected] (3) Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Q.A., Geología y Geoquímica. 28049 Madrid (Spain) e-mail: jeró[email protected] 1. Introduction This excursion takes place mainly in the provinces of Granada and Málaga, in southern Spain. From a geological standpoint, it is a visit to the central sector of the Betic Cordillera, one of the great peri-Mediterranean Alpine mountain ranges. The fundamental goal of this trip is to observe the basic features of the karst in central Andalusia, concerning exokarstic geomorphology, the present-day hydrogeological functioning and active and fossil endokarstic forms. The quantity and variety of karst in this region is outstanding, because of the multiple lithologic, structural and climatic differences to be found. Climate variability is very significant, especially regarding mean annual precipitation; there are areas where rainfall is limited to a few hundred mm per year, while in others it exceeds 2000 mm. The route of the excursion will enable us to observe, too, the severe effects on the karst of neoseismotectonic factors, both ancient and subactual, as well as the regional palaeoclimatic evolution that has taken place since the Late Miocene, the period in which the relief of the landscape began to be structured and when karstification became widely developed in this region. The most significant opportunities for observations will be available with stops at the following sites:

• Alhama de Granada, the site of the great earthquake in Andalusia • Los Baños (Alhama de Granada) • Zafarraya polje • The Nerja Cave • El Torcal de Antequera • Fuentedepiedra Lake • Sierra de Líbar (Los Caballeros dam, Pileta Cave and Gato Cave)

1. The region of Alhama de Granada and the Andalusian earthquake The Granada Basin is an intramontane depression, filled by Neogene and Quaternary sediments, situated at the contact point of the Internal Zone, to the south, and the External Zone, to the north, of the central sector of the Betic cordillera (Fig.1). The southern and south-western sectors of the Granada Basin, where the town of Alhama de Granada lies, has been a tectonically active zone since the Late Miocene (Sanz de Galdeano, 1985). There exist morphotectonic indications of important seismic activity during the Holocene, with at least three palaeoseismic events of magnitude equal to or greater than 6.5 having been detected (Reicherter et al., 1999; Reicherter, 2001; Reicherter et al., 2002, 2003).

Central Andalusia: Karst, Paleoclimate and Neoseismotectonics

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Figure 1. Geographic-geologic situation of the area of Alhama de Granada (from Sanz de Galdeano, 1985). Legend: a, Pliocene and Quaternary; b, Late-Middle Miocene; c, Outer Zone and Betic Dorsal; d, Flysch; e, Inner Zone; 1, Cádiz-Alicante fault zone; 2, fractures, showing sinking; 3, directions of Quaternary compression. On 25 December 1884, near Alhama de Granada, there occurred the greatest known earthquake in the Iberian peninsula, since termed the Andalusian Earthquake. Its epicentre was situated about six kilometres south of Alhama de Granada (Muñoz and Udías, 1984). The seismic movement lasted some 20 seconds. In the epicentral zone, an intensity of X was reached, while the isosist of VI included a large part of the provinces of Granada and Málaga, with a surface area of about 15,000 km2. Its effects on towns and villages and on local populations were devastating: 800 people were killed, 1,500 injured, 4,400 houses were destroyed and another 13,000 damaged. The dwellings in Tajo de Marchán, in Alhama de Granada, were the most severely affected (Figs. 2,3,4 and 5). Reicherter (2001) estimated the magnitude of the Andalusian Earthquake to have been between 6.5 and 7.0, basing his calculation on the length of the surface rupture (some 15 km) and on the vertical displacement of some of the largest faults affected by the earthquake (for example, the Ventas de Zafarraya fault).

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Figure 2. Effects of the Andalusian Earthquake on the houses at Río Marchán, in Alhama de Granada (photo taken in 1885)

Figure 3. Houses destroyed in the centre of Alhama de Granada (photo taken in 1885)


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Figure 4. View of the houses destroyed in Tajos de Alhama de Granada (photo taken in 1885)

Figure 5. View of the houses destroyed in Tajos de Alhama de Granada (continuation) (photo taken in 1885) Sanz de Galdeano (1985) believed the earthquake to be related to the existence of an east-west striking axis of subsidence, aligned with which are the faults that delimit the southern border of the Granada Basin, in contact with Sierra Tejeda (Fig.6). Muñoz and Udías (1980) established that the movement, some 20 km long, and in an east-west direction, occurred between the villages of Arenas del Rey (south east of Alhama de Granada) and Ventas de Zafarraya (to the south west).

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Figure 6. Fracturing of the geological landscape by the Andalusian Earthquake (from Sanz de Galdeano, 1985). Legend: 1, Pliocene and Quaternary; 2, Late Miocene; 3, Lignites; 4, Flysch; 5, Outer Zone and Betic Dorsal; 6 and 7, Inner Zone (Malaguide and Alpujarride Complex, respectively); 8, Contact between the Outer and Inner Zones; 9, Dipping; 10, Tilting of the erosive surface; 11, 12, 13 and 14: Fractures (normal, overthrusting, horizontal, probable); 15: Subsidence axis; 16, Possible site of the epicentre of the Andalusian Earthquake; 17, Geologic cross sections; 18, Landslides ; 19, Discordant contacts; 20, Former situation of the village of Arenas del Rey The possible mechanism underlying the earthquake is unclear. Sanz de Galdeano (1985), without opting definitively for a particular mechanism, suggested as the most probable one a vertical or dextral movement. According to Reicherter (2001), the kinematic data found in some planes of the faults are indicative of a multiple reactivation, with normal vertical movements before and after an intermediate dextral transtensive period. The Andalusian earthquake produced numerous important geomorphological changes in a wide sector of its zone of influence (Orueta and Duarte, 1885). There were many landslides, some of which caused severe damage to entire villages. There were also rockfalls, enormous fractures in the ground and very significant changes in the flow and water-chemistry characteristics of many springs. One such case was that of the thermomineral springs known as Los Baños, at Alhama de Granada. 2. Thermomineral springs at Los Baños, at Alhama de Granada The springs at Los Baños (Alhama de Granada) form part of a group of springs, located about three kilometres north of Alhama de Granada, with special physico-chemical characteristics (Fig.7). There are three main springs (López Chicano and Pulido, 1996), two of which are exploited for a health spa and are known as Baños Viejos and Baños Nuevos, while the third,


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called Huerta Rodero, is smaller and used for irrigation purposes. The largest spring is Baños Viejos, and has been known to man since antiquity, as evidenced by the abundant archaeological remains found in the surroundings, showing, for example, that this spring was exploited by the Romans (1st century A.D.) and by the Muslims (12th century).

Figure 7. Hydrogeologic sketch of the springs at Baños de Alhama (from López Chicano and Pulido, 1996). Legend: A: Betic Dorsal limestones and marls, Mesozoic; B: Outer Zone Limestones, Liass; C: Granada Basin marls and silts, Tortonian-Turolian; D: Granada Basin conglomerates and calcarenites, Tortonian; E. Travertines, Quaternary; F: Alluvial detritic sediments, Quaternary; G: Thermomineral springs (size of circle in proportion to mean water flow): 1, Baños Viejos; 2, Baños Nuevos; 3, Huerta Rodero; H: Productive borehole; I: Negative borehole; J. Other, cold water, springs. In modern times, the relation between these thermal springs and local and remote tectonic activity has been made apparent on several occasions. For example, Baños Viejos was affected by the Lisbon Earthquake of 1775, despite its great distance from the epicentre. In addition to the damage caused to the spa installations, the spring water was seriously affected by turbidity for several days. However, the real scale of the relation between these springs and seismogenetic factors was made clear in the Andalusian Earthquake, on Christmas Day 1884. On that occasion, in addition to changes in the flow, turbidity and water temperature at Baños Viejos, a new spring was uncovered nearby; this has since been known as Baños Nuevos, and is also used for the spa.

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Figure 8. Baños Nuevos spring, in 1885

Figure 9. Detail of Baños Nuevos spring, in 1885


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3.1. Characteristics of the water at Los Baños The joint flow volume of the springs exploited by the spa has not been calculated exactly. According to López Chicano and Pulido (1996), the mean joint flow exceeds 35 litres/second, while the company running the two spa installations states the flow to be 80 litres/second at Baños Viejos and about 8 litres/second at Baños Nuevos. There are also differences concerning the water temperature. For López Chicano and Pulido (1996), the three springs present a sequence from south to north, from higher to lower altitudes and from higher to lower temperatures (44-45º C at Baños Viejos, 40-41º C at Baños Nuevos and 26-28º C at Huerta Rodero; the electrical conductivity of the emergent water follows an opposite pattern, increasing from around 900 µS/cm up to almost 1200 µS/cm. However, according to recent data made available by the spa company, the emergent temperature at Baños Viejos is 47º C, while at Baños Nuevos it is 52º C.

Figure 10. Hydrochemical evolution of the waters at Baños Viejos spring, between 1987 and 1988 (from López Chicano and Pulido, 1996) The principal hydrochemical facies of the water in both the main springs is calcium-magnesium sulphate-bicarbonate. The waters are only slightly mineralised, present an important gaseous phase and the mineralisation characteristics vary little over time (López Chicano and Pulido, 1996). 3.2. Hydrogeologic context The hydrogeologic and geologic environment of Los Baños de Alhama is complex. In terms of tectonics, the springs emerge close to the main regional contact point, at the boundary between the Internal Zone (to the south) and the External Zone (to the north) of the Betic Cordillera. Mesozoic carbonate rocks are severely folded and fractured in the area of the springs within the Betic Dorsal, the palaeogeographic unit corresponding to the contact between the two zones. These Mesozoic materials outcrop within a limited surface area, beneath the Miocene sediments of the Granada Basin, which lie discordantly above. The results obtained from analyses of stable

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isotopes of carbon and of oxygen, together with the virtual absence of tritium from the emergent waters, led López Chicano and Pulido (1996) to situate the recharge areas of these springs in the carbonate heights of Sierra Tejeda, over 10 km south of Alhama de Granada. These authors also estimated the waters to be extremely old (adventuring a possible mean age of 4500 years), although recent, superficial water input might also exist, forming part of a deep-level hydrogeologic circuit with base temperatures of 60-70º C, at a depth of 1500-2000 metres. 4. The Zafarraya polje The Zafarraya polje (Fig.11) is one of the largest karstic depressions in Spain. It is situated at an altitude of 800 m a.s.l., between the provinces of Granada and Málaga, in the heart of the Betic cordillera. Considerable structural influences shaped its origin, and the morphological evolution and present-day hydrogeologic functioning are also strongly affected by regional tectonics. To the NE of the Zafarraya polje there are two depressions at a slightly higher altitude, the Llanos de la Dona at 930-940 m a.s.l. and the Pilas Dedil polje at 940-950 m a.s.l. (Fig. 11). Both are of tectonic origin, are delimited by faults and are filled by Miocene and Quaternary sediments. At the base of the limestone cliffs there are tectonically-shaped breccia.

Figure 11. Sketch of the poljes of Zafarraya, Pilas Dedil and Llanos de la Dona. 4.1. General characteristics of the Zafarraya polje The Zafarraya polje is an elongated depression striking approximately E-W, filled with Quaternary materials (Fig. 12). It has a surface area of approximately 22 km2, is 10 km long and 3.5 km wide. It is located in the southern part of the karstic massif known as Sierra Gorda, receives water from a catchment area of 150 km2 and is traversed lengthwise by the stream called Arroyo de la Madre; this is a seasonally variable watercourse that, under normal rainfall


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conditions, infiltrates the limestones at the entrance to the polje but which in rainy periods and especially after heavy storms, reaches the western sector of the polje, where the main ponors are situated. The infiltration capacity of these ponors can then be exceeded, producing episodic partial or total flooding of the polje. The polje partially seals the contact between the Sierra Gorda Unit and the Zafarraya Unit, both of which are related to the Inner Subbetic domain (Fig. 12). The two Units are fundamentally made up of Upper Triassic and Jurassic carbonate rocks (limestones and dolostones). Upper Cretaceous-Paleogene marls and red marly-limestones outcrop locally (Vera, 1969).

Figure 12. Geological sketch of the Zafarraya polje and its surroundings.1: Limestone materials in Sierra Gorda Unit; 2: Marly materials in Sierra Gorda Unit; 3: Limestone materials in Zafarraya Unit; 4: Marly and marly-limestone materials in Zafarraya Unit; 5: Viñuela Formation, Santana Formation and Colmenar-Periana Complex. Campo de Gibraltar Units; 6: Alpujárride Complex; 7: Marine Upper Miocene of the Granada basin; 8: Undifferentiated Quaternary; 9: Detritic filling of the polje. (Modified from Elorza et al., 1979).

4.2. Quaternary deposits in the polje The Quaternary deposits affecting the polje can be divided into the alluvial-type ones at the bottom of the present-day morphological depression and, on the other hand, the deposits related to the slopes surrounding the polje, which are alluvial fans and debris cones. Data is available on the alluvial fan thanks to a borehole perforated 500 m north of the village of Ventas de Zafarraya, where a mineralogical survey was carried out of the clayey levels (Martín Vivaldi et al., 1971). This borehole made it possible to (partially) determine the thickness of the polje filling, estimated to be 65 m at this site (Fig. 13). Although these rocks have not yet been dated, the above-cited authors, basing their conclusions on the existence of montmorillonite in the bottom layer, of illite and kaolinite in the intermediate levels and on the appearance of chlorite towards the top, interpret the sedimentary sequence as belonging to an initially humid-temperate climate, in transition towards a warmer one and finally, a semi-arid climate. On the basis of this climatic cycle, the authors attribute the filling to the last interglacial period.

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Figure 13. Lithological column of the borehole perforated in the Zafarraya polje and vertical distribution of the minerals in the clay. (Martín Vivaldi et al., 1971)


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Noteworthy among the mineralogical information provided by Martín Vivaldi et al. (1971) is the fact that chlorite is always found to be present in relation to the series in the upper part of the column. Evidence of montmorillonite is restricted to the lower part of what are assumed to be Quaternary deposits in the borehole, and the kaolinite-illite assemblage is distributed, with only slight variations in consistency, throughout the column, from the bottom to the top (Fig. 13). According to Durán and Soria (1989), there seems to be a rhythmicity in the lithological sequence within the borehole, at least in the 22 uppermost metres. Despite the insufficient sedimentological information available, it is possible to distinguish decreasing-grain series made up of two intervals (gravels at the bottom and clayey silts towards the top) that are repeated up to ten times. In each of these series, the lower interval is related to the entry of depositions and the flooding of the polje, the consequence of a reactivation of the drainage systems, while the upper interval results from the settling of fine matter in suspension. The cyclical repetition of this process could be related to climatic variations of as yet unknown range. Other deposits associated with the polje are the alluvial fans and debris cones, which are always found at the base of abrupt heights, when these are sufficiently well drained. The most spectacular examples are situated at the eastern end of the polje, near La Alcaicería. 4.3. Morphological characteristics of the depression One of the aspects that first strikes the attention is the obviously rectilinear nature of the southern border of the polje, unlike the northern border, which has a much more irregular outline (Fig. 14). This longitudinal asymmetry is accentuated by the contrast between the heights on each side of the polje; the jagged forms of the southern mountains, Sierra de Guaro (1456 m), Sierra del Cabrero (1353 m), Morrón de la Cuna (1915 m) and Pico del Puerto (1233 m) versus the more rounded shapes of the northern ones, Malmar (1106 m), El Pollo and Cerro de la Torrecilla (1321 m). The western end of the polje also contrasts strongly with the easternmost part (Fig. 14). In the former, the borders are fairly irregular and do not extend beyond the limits of an ancient fracture oriented N 20º E. On the contrary, at the eastern end, the polje branches along the present-day valleys, and thus its own morphology gradually changes to become that typical of the bottom filling of a fluvial valley. Within the polje, the most important river course is that of Arroyo de la Madre, which extends along its longest axis, westwards, before becoming lost by infiltration into a ponor situated 2 km NW of Zafarraya. Some highly-karstified limestone reliefs outcrop as hums; this is the case of the area containing the village of Zafarraya. Both in the limestone heights within the polje and in those around its northern and western borders, there are a number of stepped, erosive surfaces, the lowest of which are always close to the polje itself or even within it (Fig. 14). These surfaces have been classified, according to their positions with respect to their mean height above the bottom of the polje, into the following families: - Surface I (upper), at 250-300 m. Crowns the uppermost part of El Pollo. Presents abundant

exokarstic forms, most of which are dolines aligned along fractures or mega-diaclases that

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make the whole surface appear highly degraded. This is the oldest surface identified within the study area, and is equivalent to “Mio-Pliocene” surface (Lhènaff ,1968).

Figure 14. Geomorphological sketch of the region of the Zafarraya polje.1: Filling of the polje and alluvials; 2: Hums; 3: Lower surface; 4: Intermediate surface; 5: Degraded intermediate surface; 6: Upper surface with aligned dolines; 7: Travertine plateau; 8: Alluvial cones and fans; 9: Debris slopes; 10: Sinkholes (ponors); 11: Large dolines; 12: Flood areas; 13: Ridges, principal divides; 14: Separations of large blocks; 15: Erosive escarpments; 16: Main fractures; 17: Sima; 18: Cave; 19: Shield; 20: Archaeological and paleontological remains; 21: Thermal spring; 22: Spring. (Durán and Soria, 1989). - Surface II (intermediate), at 100-170 m. Outcrops in Majada de las Vacas, 2 km NE of El

Almendral. This surface is finely-stepped or with a certain degree of slope. Unlike the previous class, it does not present a large number of exokarstic forms, except one well-developed lapiace and a few large dolines, without apparent structural control. Lhènaff (1968) called part of it “Los Morrillos”.

- Surface III (lower), at 0-10 m. This is the surface that is at the same level as most of the hums

in the polje and of the peripheral heights closest to it. A shallow lapiace has formed above it, with abundant decalcification material. According to Lhènaff (1968), this surface is the result of karst corrosion.


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The high land at the southern border of the polje (Sierra del Cabrero-Morrón de la Cuna), which forms a magnificent example of limestone ridge or crest, presents no signs of levelling, and therefore it can be genetically distinguished from the heights of the northern border, in which the above three classes of surfaces are defined. The most noteworthy feature of this area is the appearance of a U-shaped gap, known as Boquete de Zafarraya, that brusquely interrupts the morphological continuity. Some authors (Martín Vivaldi, 1971, Lhènaff, 1998) consider it an ancient surficial drainage of the polje, one that is non-functional today.

4.4. Recent structures As noted above, one of the most characteristic features of the polje is the strongly linear nature of its southern border. This border is made up of a series of rectilinear segments, aligned approximately E-W, that separate it distinctly from the alluvial filling of the carbonate materials of the Zafarraya Unit. From analysis of the morphological features, including the appearance of alluvial fans, the presence of non-degraded escarpments and, taken as a whole, the youthful nature of the high land, in addition to its straight border, it can be assumed to be tectonic in origin (Durán and Soria, 1989). Reicherter et al. (1999, 2002) and Reicherter (2001) have found multiple evidences on this fracture, -the Ventas de Zafarraya fault-, and established their relationship with the Earthquake of Andalusia. The eastward continuation of this structure is a large fracture, oriented N 45º W, to the south of La Alcaicería. This fracture is associated with a large system of superimposed alluvial fans that drain the high ground at the extreme NW of Sierra Tejeda. These fans are tilted and separated eastwards, such that their surface morphology is partially lost. The structure is a very recent one, providing a spectacular example of a tectonically active border. The appearance of hanging valleys to the west of Cortijo de la Alcaicería is a feature that reveals the existence of vertical movements. In this case, at Llanos de Palomeque, the valley is abruptly cut by a fracture aligned N 45 º E, which constitutes the tectonic border of the SE end of the limestone heights of Cerro de las Porras. Within the polje, there are sporadic endorreic areas that are frequently flooded; these could represent zones where differential subsidence currently occurs. In the local toponymy, these are termed “charcones”; one example can be seen immediately west of Ventas de Zafarraya. Coincidentally, this latter case of a presumed subsident zone is related to one of the tectonic southern borders of the polje, which even presents a front of small associated alluvial fans. 5. The Nerja Cave 5.1. Surroundings of the Nerja Cave The Nerja Cave is on the southern slopes of the Sierra Almijara, a range that is characterised by its abrupt, precipitous relief, with high mountains close to the coast divided by deep ravines perpendicular to the coastline. The region is in the Inner Zone of the Betic Cordillera, and contains outcrops of metamorphic rocks belonging to the Alpujarride Complex, together with continental and marine post-orogenic detritic sediments (Fig. 15).

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Figure 15. Geological map of the surroundings of the Nerja Cave (Andreo et al., 1993). The Alpujarride stratigraphic series (Fig. 16) begins with a very thick (up to 1000 m) metapelitic sequence made up of schists that are dark-coloured at the base and lighter towards the top; these are attributed to the Palaeozoic and to the lower Triassic, respectively. This sequence gradually evolves upwards, through transition levels of calcoschists, quartzites, marbles and schists, to a marble series at the base of which are Middle Triassic dolomitic marbles, some 400 m thick, white or grey in colour, medium to coarse grained, highly diaclastic, sometimes with a saccharoid texture that readily disintegrates into sand. Above these is a section of limestone marbles with levels of calcoschists, 30-100 m thick, attributed to the Upper Triassic (Sanz de Galdeano, 1986 and Andreo et al., 1993). The Neogene-Quaternary rocks (Fig. 16) belong to three stratigraphic units (Andreo et al., 1993; Guerra-Merchán and Serrano, 1993): a Lower Pliocene Unit presenting continental assemblages and breccia that evolve laterally southwards to marine assemblages and sands, stacked with a very marked transgressive trend and tilted some 25º towards the sea; an Upper Pliocene Unit with marine and continental sediments but with distinctly regressive characteristics, subhorizontal or slightly tilted southwards; and a Pleistocene Unit fundamentally made up of breccias and assemblages of marble clasts embedded in a reddish matrix. There are also various outcrops of Pleistocene travertines (Durán, 1996).


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Figure 16. Synthetic stratigraphic columns of the Alpujarride Complex (A) and of the Neogene-Quaternary (B) in the surroundings of the Nerja Cave. 1: Limestone marbles with intercalations of calcoschists; 2: Saccharoid dolomitic marbles; 3: Light-coloured schists; 4: Dark-coloured schists; 5: Gravels and sands; 6: Sands and silts; 7: Travertines; 8: Breccias of marble clasts; 9: Sands and microassemblages; 10: Assemblages; 11: Sands and assemblages; 12: Breccias; UIP: Lower Pliocene Unit; USP: Upper Pliocene Unit; UP: Pleistocene Unit; UH: Holocene Unit. (Andreo et al., 1993). The general structure of the Alpujarride rocks corresponds to a group of superimposed, folded and faulted nappes that comprise highly complex forms. The Almijara nappe mainly outcrops in the Nerja sector; its geometry is simple, almost tabular, tilting downwards some 20º southwards. Further east, the structure is complicated by the overthrusting of the schists over the marbles of the same series, these marbles outcropping in various small-scale tectonic windows (Fig. 17). This geological structure is interrupted to the south by WNN-ESE and NW-SE faults, which played an important role in the structuring of the region and were responsible for the uplifting of the Sierra Almijara during the Pliocene and the Quaternary. The Pliocene and Quaternary rocks have been affected by neotectonic activity. An intra-Pliocene tectonic event is evidenced by the angular, erosive discordance that separates the two Pliocene units. During the Pleistocene, tectonic activity and the generalised uplifting of the region led to a

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large volume of deposition and the progressive deepening of the water courses, giving rise to the formation of different generations of alluvial fans (Guerra-Merchán et al., 2004).

Figure 17. Geological cross sections: Guájares nappe (1: Dark-coloured schists; 2: Light-coloured schists; 3: Marbles); Almijara nappe (4: Dark-coloured schists; 5: Light-coloured schists; 6: Base marbles; 7: Marbles with calcoschists); Lower Pliocene Unit (8: Breccias and continental assemblages; 9: Marine microassemblages); Upper Pliocene Unit (10: Breccias and continental assemblages; 11: Marine microassemblages); Pleistocene Unit (12: Breccias of marble clasts; 13: Travertines); 14: Right-lateral strike-slip fault; 15: Normal fault, (Andreo et al., 1993). The locations of the cross-sections are shown in Fig. 1. The Alpujarride marbles form an extensive aquifer (Fig. 18) that is mainly fed by the infiltration of the rain that falls directly onto the outcrops of permeable rocks and, to a lesser extent, by the infiltration of surface runoff, in the middle reaches of the rivers crossing the area. The discharge at the southern edge occurs, visibly, through springs, noteworthy among which is the Maro


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Spring, near the Nerja Cave, and invisibly through diffuse springs in the lower courses of the rivers, towards the Neogene-Quaternary detritic rocks and towards the sea. Water is also extracted by pumping (IGME, 1983 and SGOP, 1991).

Figure 18. Hydrogeological sketch of the surroundings of the Nerja Cave. 1: Triassic carbonate rocks; 2: Paleozoic metapelites; 3: Pliocene and Quaternary deposits; 4: Faults; 5: Groundwater flow; 6 Submarine discharge; 7: Spring; 8: Borehole. 5.2. Geomorphological and geological characteristics of Nerja Cave The Nerja Cave is one of the most outstanding karstic cavities in Andalusia. Its geological, geomorphological and archaeological characteristics explain its geological interest and lend it great importance in the catalogue of the Andalusian natural heritage. Its chambers are spectacular, with abundant, varied speleothems, and contain archaeological remains and ancient cave paintings (Durán et al., 1996 and Carrasco et al., 1998a). All of this, together with its geographic situation, within a world-famed tourist area, make it one of the most visited destinations on the Costa del Sol and, at the same time, an important source of wealth for the local economy. The Nerja Cave is of great scientific interest, with a fossil record providing evidence of millions of years of regional geological history. Especially interesting is the chemical sedimentation that occurred, at least, from the Middle Pleistocene to date. The cave also contains signs of some of the most noteworthy paleoclimatic, neotectonic and paleohydrologic features to be found in the region. Moreover, it has one of the most important prehistoric archaeological sites in the western Mediterranean, with a sedimentary sequence extending from the beginnings of the Upper Paleolithic to the final period of the Copper Age. Additionally, prehistoric cave paintings and carvings cover virtually all the surfaces of the cavity (Sanchidrián, 1994).

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The cave is located on the southern slopes of the Sierra Almijara, at an altitude of 158 m and at a distance of 800 m from the present-day coastline. It presents a horizontal development, being about 750 m long and with a maximum vertical difference of 68 m, between 127 and 195 m a.s.l. It has three entrances, two natural subcircular torcas and, near these, an artificial entrance created in 1960, one year after the cave’s discovery, to enable tourist visits. Its large chambers and galleries have a total volume of some 300,000 m3 and are oriented approximately N-S, in line with the main fracture directions. The cavity complex is divided into two well-differentiated zones (Fig. 19): - The sector prepared for tourist visits, called the Lower Chambers or Tourist Galleries, which correspond to the southernmost third of the cave. These are oriented N 35º E and have a main axis measuring some 250 m. These Galleries are formed of a succession of chambers and spaces, separated by structures of speleothems. - The rest of the cavity, containing the Upper Galleries and the New Galleries, comprising the remaining, innermost two thirds of the cave. This sector is not open to tourist visits. It continues the general N-S orientation, although it is locally labyrinthian, and comprises a succession of large chambers, separated by small segments of rocky matrix, chaotic blocks or large volumes of lithochemical reconstructions.

Figure 19. Sketch of the Nerja Cave


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The cavity develops through the dolomitic marbles of the Almijara nappe. The geological structure of the sector containing the cave is virtually tabular, sinking southwards 15-20º. This structure is bounded to the south by faults oriented NW-SE, which provoked vertical movements during the Pliocene and the Quaternary, raising the carbonate relief in which the cave is located. The cave originated after the nappe structuring of the Betic Cordillera. During the Middle and Upper Miocene, the various nappes covering that of the Almijara were eroded away such that the marbles of Sierra de Almijara were exposed to dissolution by the infiltration water that circulated through the numerous diaclases and stratification surfaces of the rocky matrix. Progressively, the widening of these discontinuities created the large chambers of the Nerja Cave. In the Pliocene, the cave was close to the natural discharge points of the aquifer and was partially flooded. During the Pleistocene, the Nerja area was subject to frequent, severe climatic variations that caused different stages of speleothem growth. During the Pleistocene - Holocene transition, the area of the current-day cave entrance began to fill in with materials transported from the exterior. Chemical activity and detritic sedimentation continued in the Holocene near the cave entrance. The distribution of geomorphological elements and deposits in the tourist sector of the cave have been studied by means of the elaboration of a geomorphological map (Jiménez-Sánchez et al., 2004; Arrese et al., 2005). This map (Fig. 20) shows the variety of geomorphological elements (natural and antropic) and it allows to quantify the distribution of the same ones. The natural elements present in the cave have grouped in four main categories: rock, speleothems, detritic sediments and water. Starting from the geomorphological map, it has been deduced that the spatial distribution of the geomorphological elements is represented for the most part by speleothems, occupying 44% of the total surface; flowstones are the more abundant element. The detritic sediments are the 36% of the studied surface, being the deposits of blocks, sand and gravels the most abundant. The antropic elements, typical from show caves, constitute 19% of the surface, being the pathways the majority constructions. The active points of water, classified as litlle ponds, filtrations and leaks, only constitute 0,6% of surface in the tourist sector, corresponding to a very dry cave, located several meters above the local freatic level. The analysis carried out shows that the study and mapping of the geomorphological elements present into the caves, specially in show caves, constitutes an effective tool to understand the evolution of the cavity, and is also of interest for the management. At present, as a result of neotectonic activity and variations in the base level, the Nerja Cave is situated in the unsaturated zone of the aquifer (Carrasco et al., 1998b). Epiaquatic mineralisations show that the cave was partially flooded and reveal the relative fall in phreatic levels that occurred with the raising of the Sierra de Almijara (Fig. 21).

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Figure 20. Geomorphological map of Nerja Cave (touristic sector). Modified from Jiménez-Sanchez et al.( 2004) and Arrese et al.(2005)


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Figure 21. Sketch of the different generations in the Gallery of the Levels of the Nerja Cave. G1: Ancient generation of subaerial speleothems; G2: Generations of subaquatic speleothems (levels); G3: Generation of recent subaerial speleothems (Durán, 1996). The speleothems of the cave have been dated by ESR and by the uranium series method (Duran et al., 1993 and Durán, 1996). The analysis of the chronological results obtained from the speleothems in the Nerja Cave, for the last million years, is shown in Figure 22. Clearly visible are six generations, or growth phases, of speleothems, corresponding to the following approximate ages and isotopic stages (Durán, 1996): (1) ca. 800,000 B.P., perhaps corresponding to one of the warm periods at the end of the Lower Pleistocene or the beginning of the Middle Pleistocene; (2) ca. 350,000 B.P., clearly indicating isotopic stage 9; (3) ca. 260,000 B.P., isotopic stage 7; (4) a period between ca. 180,000 and 110,000 B.P., with a net maximum at about 155,000 - 150,000 B.P., end of isotopic stage 6 and beginning of isotopic stage 5; (5) a period between 100,000 B.P. and 60,000 B.P., with an absolute maximum at about 85,000 B.P., corresponding to the final episodes of stage 5; and (6) a clearly Holocene period, isotopic stage 1.

Figure 22. Frequency diagram of the speleothems dated in the Nerja Cave, for the last million years (Durán, 1996).

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Samples taken from the Cataclysm Chamber corresponding to two generations of speleothems, in physical continuity but separated by an important deformation phase, reveal the existence of a deformational event ca. 800.000 B.P., possibly related to some type of seismotectonic phenomenon (Fig. 23, Durán et al., 1993).

Figure 23. Location of the samples CNE-3 and CNE-4, representative of two generations of speleothems, separated in time by a deformation phase (Durán et al., 1993). In general, dripwater volumes are very low throughout the cave, with lower values being recorded in winter and spring, and higher ones in summer. The trend varies in months of abundant rainfall, when water levels rise in rapid response to the precipitation. Taking these facts into account, it can be concluded there is a slow circulation of rainfall through the sector of marbles above the cave, thus producing a seasonal lag from the entry of the precipitation until its exit through the dripwater points. The system is, thus, highly inertial, with a long delay before response to rainfall is evident, and therefore one presenting a significant modulating effect on the entry signal (the precipitation). Nevertheless, when heavy rainfall occurs, the dripwater volume increases rapidly. The transit time for rainwater to infiltrate as far as the dripwater points within the cave (6-8 months, except during periods of abundant rainfall, when it is around 2 months) has been determined by chemical and isotopic analyses of the water (Carrasco et al., 1996, Andreo et al., 2002). The dripwater is of a magnesium-calcium bicarbonate facies, arising from the dolomitic nature of the marbles through which the water circulates. Mineralisation levels are medium - low and the mean conductivity varies from 392 to 547 µS/cm, according to the dripwater point taken (Andreo and Carrasco, 1993). The mean temperature of the water is lower in the part of the cave open to tourist visits (18.6-18.9 ºC) than in the restricted area (19.2-20.0 ºC), probably because of the proximity of the former area to the cave’s natural entrances and to the existence of a lesser


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covering of rock above the cave. The dripwater in the visitable area is more highly mineralised, and is clearly influenced by the infiltration water from the irrigation of the gardens above the outermost areas of the cavity. Practically all the samples of dripwater taken from within the cave are supersaturated in calcite and comprise, therefore, encrusting water that produces the precipitation of calcium carbonate that contributes to the growth of the formations, although with the present-day volume of dripwater, this growth is very slow. This water is characteristic of slow infiltration, being subject to a diphasic flow (with water-air exchange taking place through the fissures of the rock) that controls the variations in the components of the calcocarbonic system. For this reason, the karstic activity in the cave derived from infiltration water is limited to the scant, slow formation of speleothems by the precipitation of calcium carbonate. (Andreo and Carrasco, 1993, Carrasco et al., 1995). The current rate of sedimentation is lower than must have existed during certain periods of the Pleistocene. The Nerja Cave is one of the most visited natural monuments in Spain, with an average of around 500,000 visits a year. The monthly distribution features minimum values in the first and last months of the year (11,000-20,000 visits/month) and maximum values during August (90,000-120,000 visits/month). For the study of the environmental parameters of the cave, and to identify the effects produced by the tourist visits, a network of environmental sensors has been installed (Carrasco et al., 1999) and had provided recordings since 1986. Records are kept of the temperature and relative humidity of the air, the temperature of the rock, the atmospheric pressure, the wind speed and the concentrations of CO

2 and of radon. Furthermore, the quantity of pollen in the atmosphere and the

number of visitors to the cave are measured. A fully-equipped meteorological station is sited outside the cave. The evolution of the daily mean air temperatures in the different chambers of the cave is very similar to the pattern of the exterior temperature, with maximum and minimum temperatures being displaced by approximately one month, and with lower ranges and coefficients of variation. The air temperature in the cave, almost throughout the year, increases from the outermost chamber (the Bethlehem Chamber) towards the innermost (the Cataclysm Chamber). The coefficients of variation are low and decrease towards the innermost chambers. The greatest difference in temperature between the three chambers analysed is found during the spring. In summer, when the outside temperature is higher than within the cave, there is an inversion of the heat gradient, with mean temperatures falling towards the innermost chambers. The daily mean relative humidity of the air is very similar in all three chambers in the cave, with the highest values found in the outermost one, where the values of the coefficient of variation are also maximum. There is a dry period during the autumn and winter and a wet one with maximum values in the summer, when water vapour almost becomes saturated in the outermost chamber.

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The daily mean concentrations of CO2 inside the cave present a wide coefficient of variation. Minimum values are registered in autumn and winter, when fewest visitors enter the cave and when the index of ventilation is highest, and maximum CO2 values are recorded in summer, when visitor numbers are highest and the ventilation index is lowest. 6. El Torcal de Antequera El Torcal de Antequera is one of the most spectacular and unusual karstic landscapes in Spain. This massif belongs to the Penibetic domain, forming part of the External Zones but close to the border with the Internal Zones of the Betic Cordillera. El Torcal is about 4 km north of the town of Antequera and is oriented approximately E-W overlooking the depression to the north made up of the Triassic outcrops of Antequera and the Miocene to Quaternary rocks, while to the south it overlooks the outcrops of the Campo de Gibraltar and of the Internal Zones, which extend to the coast (Fig. 24).

Figure 24. Situation of El Torcal de Antequera in the Betic Cordillera (Martín Algarra, 1987) El Torcal de Antequera reaches an altitude of 1,366 m and extends eastwards towards the Sierra de la Chimenea, at an altitude of 1,377 m. The sector known as Torcal Alto contains the most striking karstic forms, which because of their geological interest and special botanical and other features led to El Torcal being declared a Natural Site of National Interest in 1929, this site extending over an area of 1,200 ha. El Torcal de Antequera is still a protected area, and is currently classified as a Natural Landscape by the Regional Government of Andalusia.


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6.1. Lithostratigraphic and structural influences on the relief The relief of El Torcal de Antequera, in terms of both its broad features and the lesser elements that make it geomorphologically unique, are, in part, the consequence of the lithostratigraphy and the structural arrangement of the Mesozoic rocks that constitute the massif. The sheer north and south-facing flanks of the mountain are made up of massive marine limestones, containing oolites, stratified into thick layers, belonging to the Endrinal Formation, from the Lower and Middle Jurassic. At the base of these limestones are the so-called Jarastepar Dolostones, which outcrop in the area of Boca del Asno, forming the nucleus of the anticlinal massif. At the top of the Endrinal Formation there is a stratigraphic discontinuity, with a paleokarst that presents various lapies forms that seem to have been created in a marine-terrestrial interface environment. Above these, and constituting the upper part of the massif, is the so-called Torcal Formation. It is aged from Oxfordian (Malm) to Berriasian (Lower Cretaceous), and two members can be distinguished within it (Martín Algarra, 1987), a lower one that is nodulous and an upper one made up of oolitic limestones. Between the two there are alternating lateral and vertical facies. The series is of variable thickness, up to 200 m, well stratified in layers ranging from a few centimetres to several metres. The alternation of compact oolitic limestones with more erosionable nodulous, breccoid rocks is an essential feature of the morphology of Torcal de Antequera. The general structure of the sierra consists of an anticlinal fold oriented NE-SW, with a broad transfer zone that enables the layers to be subhorizontal in the upper part, while the flanks present greater dipping, becoming subvertical or even inverted, as can be seen at the southern border (Fig. 25). These characteristics lead to the development of the karstic forms of El Torcal Alto and to the sheer slopes at the boundary of the massif.

Figure 25. Geological profile of El Torcal de Antequera (Martín Algarra, 1987).

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Two main tectonic phases have been identified in the massif (Peyre, 1974): the first of these led to the folding of the rocks and to minor fractures, while the second provoked the raising of the massif above the surrounding terrain and the major fractures. The network of fractures affecting the massif is one of the most notable features concerning the geomorphology of El Torcal de Antequera. Various studies (Peyre, 1974; Fernández-Rubio et al., 1981; among others) have distinguished two conjugated systems, oriented N40-60E and N110-120E, which are slightly inflected and are oriented N70-80E and N130-150E, respectively, in the eastern part of the massif. Additionally, in the Torcal Alto area, a second network of smaller fractures has been identified, with an orientation N70E and N135E. Recent tectonic activity has been observed in the zone, for example at the fault in the extreme NE of the massif. The plane of this fault presents well-preserved striae that affect Quaternary slope deposits (Durán and Soria, 1989). 6.2. Exokarstic and endokarstic geomorphology Its exokarstic geomorphology is the most characteristic and spectacular feature of El Torcal de Antequera, and is most highly developed in the upper part of the massif, Torcal Alto, where a flattened plateau coincides with the above-mentioned broad transfer zone (Fig. 25). The relief is very abrupt with a wide range of karstic forms, with particularly abundant dissolution forms related to stratification and to fracturing of the rock. There are different types of lapies, bogaz formations, residual reliefs and closed depressions. In the local toponymy, there are frequent references to these types of forms.

Figure 26. Geomorphological sketch of El Torcal de Antequera (modified from Lhènaff, 1981).


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El Torcal de Antequera is an outstanding example in Spain of a ‘stone-city’ type of morphology. They are not very common in the Mediterranean region, being found more often in relatively humid climates and subject to the influence of snow cover. However, in this case, contributions to creating this phenomenon might have included the climate of the area, with an annual precipitation at the top of the massif of around 800 mm per year, the effects of extreme cold, in particular during the Quaternary glacial periods and, especially, the characteristics and arrangement of the strata, the alternation of layers within the Torcal Formation and the network of fractures that affect the massif. All these factors are relevant to the development of the characteristic morphology of El Torcal de Antequera, where screw-type shapes and the differential erosion of less resistant layers are very characteristic elements (Fig. 26). It has been observed that 64% of the dolines are aligned with the major fractures: N40-70E and N110-135E (Pezzi, 1979). Moreover, numerous karstic corridors and bogaz-type forms, with lengths and depths of several tens of metres, are also aligned with these fractures. The cavities present a development that is mainly vertical, in adaptation to the structure of the massif. Among the most important cavities that have been explored are the following: Sima Rasca (-225 m), Sima de la Unión (-144 m), Sima del Nevazo Verde (-141 m), Sima Azul (-115 m). 6.3. Slope deposits On the slopes of the massif there are flood accumulations of breccoid-type, ordered debris flow, or grèzes-litées, which have been associated with periods of periglacial activity (Pezzi, 1975, 1977). This author has assigned to the Riss-Wurm interglacial stage some reddish, clayey deposits that were located on the southern slopes of the massif, between two accumulations of breccias, although other authors do not share this opinion.

Figure 27. The exokarstic morphology is the most characteristic feature of El Torcal de Antequera.

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6.4. Hydrogeology El Torcal massif presents endorreic drainage, with highly developed absorption forms that receive surface water and channel it towards the endokarstic circulation system. The aquifer has an effective surface area of 35 km2 and its mean resources are estimated to be around 15 hm3 per year. Over 85% of this volume is drained towards the most important spring, called Fuente de la Villa, which is used to supply water to the town of Antequera. This spring, with water of calcium bicarbonate facies, has an estimated mean flow volume of 425 l/s, although the flow is highly variable, from 0 to 2000 l/s. It is currently regulated by means of boreholes. Recharge to the aquifer is exclusively via precipitation, with a value of about 800 mm per year, and the coefficient of infiltration is about 51-55%. A study of precipitation and discharge, carried out using correlatory and spectral analysis (Pulido and Mangin, 1983; Pulido et al., 1987; Pulido, 1993), has revealed the system to be highly inertial, with a response to rains being measured about four weeks later, and to have a high degree of memory, with a regulatory capacity exceeding 70 days. Therefore, the hydrologic functioning of this system presents similarities with that of a porous medium. This peculiar hydrogeologic behaviour pattern contrasts with the extreme development of the exokarstic absorption forms and is probably the result of the characteristics of the endokarst, which are as yet incompletely understood. 7. Fuente de Piedra Lake The Fuente de Piedra lake, a wetland of exceptional interest at regional and national levels, and one of great international importance in the context of protecting biodiversity, is included in the Ramsar International Convention, which was ratified by Spain in 1982. It is a continental, karstic wetland that lies over evaporitic rocks and contains saline water of a sodium chloride facies. 7.1. Situation and general characteristics Fuente de Piedra lake is situated in the north of the province of Málaga, at an altitude of 410 m a.s.l. It is almost elliptical in shape, with longer and shorter axes 6.8 and 2.5 km long, respectively; its perimeter measures 18 km and it has a surface area of 13 km2, measuring the normal extension of the water. Fuente de Piedra is the largest lake in Andalusia and one of the largest salt lakes in Spain. The water rarely exceeds 2 m in depth in conditions of maximum storage. It is a seasonal lake, usually drying out in summer. It lies within an endorreic basin of 153 km2 situated on the Atlantic - Mediterranean divide, between the river basins of the Guadalhorce to the south and the Guadalquivir to the north (Fig. 28). The high points of this divide are located in the mountain ranges of Mollina-La Camorra (798 m a.s.l.) and Humilladero (629 m a.s.l.), which are also the highest land masses in the river catchment area. One of the fundamental characteristics of the lake is the salinity of the water stored in it. The lake water is saline with a high content of sodium chloride and calcium sulphate. The common salt that is precipitated was exploited commercially until relatively recent times. The salt exploitation that took place led to a series of modifications in the bed of the lake that remain, more or less unchanged, to the present day. There is a longitudinal channel crossing the lake along its longest axis, and another one around the perimeter, some 2-3 m wide, that was created to collect the surface runoff waters in order to promote a high saline concentration in the


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water and thus extract salt. The runoff waters were channelled to a drainage tunnel (now destroyed) constructed at the southernmost end. Within the lake, there are various elements forming hummocks, of varying shapes and sizes, including the groynes that are used by nesting pink flamingos (phoenicopterus ruber roseus); the area, thus, is ecologically valuable and has been declared a Nature Reserve. This category represents the highest level of protection in Spain against transformation or alteration.

Figure 28. A: Situation of Fuente de Piedra lake. B: Fuente de Piedra lake basin. Main population centres and watercourses (modified from Benavente et al., 1996) The mean annual precipitation is 463 mm, with the most intense rainfall occurring from November to February, while July is the driest month (Linares, 1990). The annual mean daily temperature is 17º C, January being the coldest month with a mean temperature of 9.6º C and August the hottest at 26.2º C. The mean rate of evaporation is 1,689 mm per year (ITGE, 1998).

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As a consequence of the climate affecting the region, the lake is characterised by alternating cycles of flooding and dryness. The salinity of the water stored shows fairly significant seasonal variations and a saline crust is created during the summer. 7.2. Geology The region is in the External Zone of the Betic Cordillera. The geological materials form part of the Subbetic Domain and the Flysch Complex of Campo de Gibraltar, and post-orogenic sediments lie above these materials (Fig. 29, Benavente et al., 1996).

Figure 29. Hydrogeological sketch of Fuente de Piedra Salt Lake basin. 1: Clays and evaporates (Triassic). 2: Carbonates (Jurassic). 3: Marls (Paleogene). 4: Sands and calcareous sandstones (Miocene). 5: Alluvion (Quaternary). From Benavente et al. (1996)

7.2.1 Stratigraphy The Triassic sediments belong to Trias de Antequera; they present a Germano-Andalusian facies, with a higher, Keuper, level constituted of a group of mainly reddish and greenish clays and sandstones that include stratiform or irregular intercalations of gypsum. This layer is normally overlain by a few metres of carniolas, grey or yellowish limestone-dolomitic rocks with a vuggy, brechoid appearance. Irregular masses of ophites are also observed frequently. Gypsum is present in varied forms and colours, both as large arrow-headed crystals and as alabaster-type. Other evaporitic rocks such as halite do not outcrop on the surface, but are assumed to be present at greater depths, as a great many saline pools and springs are associated with Triassic sediments. Jurassic carbonate rocks are found in the mountain ranges in the region, and generally crop out in an isolated way. The Jurassic series begins with a Lower Lias dolomitic formation, estimated to be over 200 m thick. Above this there is a massive, sometimes folded limestone formation, attributed to the Lower and Middle Triassic, which is never less than 200 m thick. The rest of this Jurassic series is made up of a thick, heterogeneous formation of limestones, marly-limestones with silex and marls. The Cretaceous series comprises marls and white marly-limestones.


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The materials corresponding to the Flysch Complex of Campo de Gibraltar form a flyschoid-type group made up of brownish-green clays with layers of detritic limestones with a turbiditic appearance. It has been attributed to the Paleocene era. The post-orogenic sediments begin with a series constituted of calcarenites with intercalations of marls, sands and occasional assemblages. It has been attributed to the Miocene and its thickness is variable, on occasions exceeding 100 m. The Quaternary deposits are fairly heterogeneous, with slope deposits, alluvial deposits and depression fillings. It is not very thick and presents a varied lithology made up of clays, sands and loose gravel that is occasionally cemented, especially on the slopes of significant heights. In the proximity of the lake there are abundant dark-coloured sediments of a clay-sand nature with a high content of organic matter; in this area, too, there is usually a saline crust that is the most recent level of the sedimentation in the zone. The sedimentation in the lake may be considered a typical ‘beach-lake’ deposit; during the summer, it is covered by a salt crust that is sometimes several cm thick. Lateral zoning takes place in the appearance and variety of the various minerals, depending on their distance from the peripheral zones of the lake. Near the edge, there is a predominance of detritic minerals (quartz, feldspar and phylosilicates) and carbonate minerals (mainly calcite), while towards the centre the saline crust develops with a greater variety of salts (halite, gypsum, hexahedrite, mirabilite and polyhalite), the greater part of this being halite, which becomes ever more predominant towards the centre of the lake, where it is the only salt present. There is, moreover, a vertical zoning characterised by the development of intercrystalline growths of gypsum with the formation of large crystals and the dolomitisation of the carbonates (Rodríguez-Jiménez et al., 1993). 7.2.2. Tectonics The materials making up Trias de Antequera are allochthonous and present a highly-deformed internal structure. In large sectors, this terrain has lost its internal coherence and has been transformed into chaotic, brecciated masses that belong to what are termed Subbetic Chaotic Complexes (Vera and Martín-Algarra, 2004). These latter Complexes included masses with no apparent internal structure, in which there is a broad predominance of Triassic rocks of Subbetic origin, but also containing olistolites and post-Triassic blocks and blocks from other Betic units, sometimes included in Langhian-Serravallian sediments (Arias et al., 2004). Its chaotic structure was created during the Middle Miocene by the combined action of rock slides, faulting and diapirism. These are, therefore, tectonic-sedimentary complexes, as the Triassic breccias also contain small and large blocks of post-Triassic and pre-Tortonian terrain (Crespo-Blanc et al., 2004). The relation between the Triassic and its coverage is produced by mechanical contact, such that the Jurassic carbonate outcrops are situated over Triassic materials and represent the remains of a primitive coverage. The internal structure of the Mesozoic rocks is fairly complex. The materials belonging to the Flysch Complex of Campo de Gibraltar are allochthonous and rest upon the Triassic.

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The post-orogenic Miocene materials are deposited within a basin where the main features had already become established and where the surrounding limestone heights had probably already emerged. This fact determined the distribution of the sediments and their variations in thickness. These sediments were affected by movements related to faulting during the post-orogenic phase, which created megastructures related to neotectonics and to small-scale faults (ITGE, 1998). 7.3. Geomorphology The relief of most of the endorreic basin of Fuente de Piedra, made up of Triassic materials and post-orogenic sediments, is smoothly rounded, with a slope that descends gradually to the floor of the basin, where the lake is situated. Jurassic carbonate rocks are outstanding features of the relief and constitute the heights of the eastern part of the basin, where the highest altitudes are attained, where the relief is most abrupt and where slopes are steepest. The relief is little developed; it has suffered virtually no wearing and the drainage network is ill-defined in many sectors. These features, together with the fact that the area lies at the watershed of the Atlantic-Mediterranean divide, favour the endoreism that characterises the zone (MMA, 2000). The basin contains several streams (‘arroyos’), generally small, that flow into the lake. The most important surface watercourse, some 7 km long, is Arroyo de Santillán, which flows into the northern end of the lake. At the eastern edge is Arroyo de Humilladero, while Arroyo de la Arenales and Arroyo de Mari Fernández flow into the western part of the lake. The regimes of these streams are very irregular; they remain dry during most of the year, but the water flow increases considerably during rainy periods. The evaporitic materials, gypsums and salt, found in the Triassic formations present high levels of solubility, which have given rise, in some sectors in the north of the province of Málaga, to different karst morphologies, including dolines, sinkholes, shafts and subterranean conduits (Pezzi, 1977). All this has led to the formation of depressions containing more or less permanent lakes. In these regions, the hydrographic network is little developed and is made up of short, relatively unbranched watercourses. Most of these flow into the lakes or are lost in shafts or sinkholes, and so an endorreic regime has become established over the Triassic rocks and this largely determines the chemical quality of the surface and subterranean waters in the area, as a result of the dissolution of evaporites. The endorreic basin of Fuente de Piedra is a depression formed by progressive sinking of the terrain, which in turn is the result of the dissolution and collapse of the evaporitic materials that developed during the Triassic and which underlie all the materials in the area (Durán et al., 2005). In addition to the karstification of the substrate, this process was also subject to the intervention of groundwater flows towards the lake, which contributed to the dissolution of the evaporitic materials affected by these flows and, thus, to the definitive establishment of an endorreic basin (MMA, 2000). In the basin of Fuente de Piedra itself, and as a consequence of the undeveloped relief, there are numerous small endorreic areas; these are more or less isolated from the hierarchised surface drainage network that flows into the lake, and may give rise to small seasonal or temporary pools, depending on the rainfall during the period in question. Many of these areas have suffered considerable modifications from their original state, produced by drainage works carried out for purposes of agricultural exploitation (MMA, 2000).


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7.4. Hydrogeology The materials of Trias de Antequera, as a whole, constitute a hydrogeologic unit of low permeability. However, there do exist areas in which the development of processes of karstification over evaporitic materials has created areas of greater permeability, where the groundwater can accumulate and circulate freely. The calcareous Jurassic materials constitute highly karstified carbonate aquifers that are recharged by the infiltration of rainfall and that discharge through springs and, invisibly, via subterranean lateral flows towards the aquifers situated within the surrounding Tertiary and Quaternary materials. The largest aquifer (in terms of surface area) in the basin is made up of Miocene calcarenites. This formation is permeable by intergranular porosity; it occupies the lowest parts of the basin and mostly lies above Triassic materials. The area where there seems to be the highest proportion of large-sized materials (where permeability, thus, is highest) is in the NW of the basin, close to the highlands constituted of Jurassic materials, which probably emerged during the Miocene deposition and contributed larger detritic elements. The greatest thicknesses found are related to zones where fractures have created depressions. The Quaternary formations of greatest hydrogeologic interest are the alluvion related to Arroyo de Santillán and the piedmont deposits of Sierra de Humilladero. The above-mentioned aquifers are hydraulically connected and make up a hydrogeologic system whose borders coincide approximately with those of the surface basin. Groundwater circulates from the borders of the system towards the centre of the basin, where the lake constitutes the base level and into which the aquifers discharge (Fig. 30). The intense evaporation that takes place in the lake during most of the year favours the groundwater flow into it (Linares, 1990; ITGE, 1998).

Figure 30. Water table contours (m a.s.l.) for the Fuente de Piedra Salt Lake basin. From Benavente et al. (1996)

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The subterranean flow is towards the interior of the basin, and is accompanied by a generalised increase in salinity of the water from zones of good quality near the watershed (Jurassic carbonate aquifers) to the brines below the lake or immediately adjacent to it. The groundwater corresponding to the basin is, in general, quite highly mineralised, with a predominantly sodium chloride facies. The highest ionic concentrations are found in the areas closest to the lake and to the outcrops of the Triassic substrate that provoke the high degree of mineralisation (DPM, 1988). Electrical conductivity is generally greater than 2000 microS/cm, and in the vicinity of the lake these values exceed 5000 microS/cm. The main hydrochemical facies is chloride-sulphate sodium-calcium. On the whole, an increase in concentration can be detected towards the end of the dry seasons in comparison with sampling made during recharge periods (Benavente et al. 1996). Inside the lake there is a well with sodium-chloride-type waste and TDS of approximately 180 g/l, which was previously used to obtain salt. The existence of brines such as those related to the Triassic evaporitic materials is a relatively frequent phenomenon in this area (Carrasco, 1986). 7.5. Hydrological regime of the lake The entry of water to the lake is constituted of: a) direct precipitation onto the lake bed; b) the surface runoff from the streams flowing into it; c) contributions from the aquifers in the area. The main loss of water is by evaporation from the lake bed. Fig. 31 represents the hydrological balance of the basin (mean values). Its total resources are around 21 hm3/year. There is a wide interannual variation (Benavente et al., 1996).

Figure 31. Water balance components for the Fuente de Piedra Salt Lake basin. Numbers represent approximate mean values (in hm3/year) for the 1962-1987 period. From Benavente et al. (1996)


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8. Sierra de Líbar 8.1 Location The Sierra de Líbar is situated in Andalusia, southern Spain, at the border of the provinces of Cádiz in the west and Málaga in the east, and is the easternmost part of the Serranía de Grazalema (Fig. 32) and the natural park of the same name (Parque Natural de Sierra de Grazalema). In 1977, the area was declared a Biosphere Reserve by UNESCO. Its declaration as a Natural Park in 1984 was finally confirmed by the regional government of Andalusia in 1989. The Sierra de Líbar covers an area of 85 km2 and basically consists of two NE-SW striking mountain ranges, which enclose a series of poljes known as the Llanos de Líbar (Fig. 32). The eastern, higher, range culminates in the summit of El Palo (1,401 m), and the western range has a maximum altitude of 1,303 m at Hoyo de los Quejigos. The poljes inside the Sierra de Líbar are situated at heights of 950-1000 m a.s.l. In the east, the terrain descends relatively steeply down to less than 400 m a.s.l. at the Guadiaro River, and in the west to the Llanos de Villaluenga (higher, at approximately 800 m a.s.l.). The western ridge of the area is constituted of Sierra de Montalate and Sierra de Líbar s.s. (from north to south), and the eastern ridge comprises Sierra de Juan Diego, Sierra del Palo, Sierra Blanquilla and Sierra de los Pinos (Fig. 32).

Figure 32. Geographical situation of the Sierra de Líbar

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8.2. Climate The average annual temperatures measured at seven climate stations in the surroundings of the Sierra de Líbar and the Sierra de Grazalema range from 13.9 °C in Villaluenga to 18.3 °C in Buitreras (DGOHCA, 1997). While the average temperature is quite regularly distributed, the annual precipitation shows large differences, varying greatly not only between different locations, but also between dry and wet years. Figure 33 shows the average annual precipitation for a dry year, the average year, a wet year and the exceptionally wet hydrological year of 1995/96 (for each of six climate stations in the surroundings of the Sierra de Líbar). It also shows the altitude (in metres above sea level) of each station. The average rainfall in Sierra de Líbar is about 1200 mm.

212

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Figure 33. Annual precipitation and altitude of different climate stations in the surroundings of the Sierra de Líbar (modified from DGOHCA, 1997) There is no direct relation between precipitation and altitude. The position with respect to the prevailing wind direction and the protection offered by mountain ranges seem to be more important. For example the comparably low values in Montejaque probably result from the relatively protected position of the village. 8.3. Geological setting From the geological standpoint, the Sierra de Líbar is located in the Penibetic, the western part of the Internal Subbetic belonging to the External Zone of the Betic Cordillera (Fig. 34). In this area, the rocks cropping out are carbonate rocks of Jurassic age, underlain by Triassic sediments with evaporites (Keuper) and overlain by marls and marly-limestones of Cretaceous age (Fig. 34). The Jurassic stratigraphic series is mainly constituted of the Líbar massif and it is composed, at the bottom (thus, during the Lias), of dark-grey saccharoidal dolomites and white sparitic limestone, which reaches a thickness of over 100 m. The series continues with 200-300 m of white oolitic and pisolitic limestone, of Dogger age. The Malm is formed by nodular, oolitic and pseudo-breccoid limestones, with a thickness of up to 200 m (Martin-Algarra, 1987).


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Clays and sandstones of the Flyschs Complex of the Campo de Gibraltar, aged Paleocene to Miocene, outcrop in the northern part of the Sierra de Líbar, overthrusting the Penibetic. Discordant above all these materials are Quaternary clays, sands and gravels.

Figure 34. Geological map and cross section of the Sierra de Líbar (simplified from Martín Algarra, 1987) The geological structure is characterised by a series of NE-SW oriented anticlines and synclines (Martín-Algarra, 1987), which are several kilometres long and dip slightly to the north-east, which provokes the outcropping of the Lias dolostones in the south-eastern part of the massif (Fig. 32). The anticlinal structures contain outcrops of Jurassic limestones, while outcrops of Cretaceous marls and marly limestones are to be found at the borders or in the upper part of the sierra, aligned with the synclines. Thus, two large anticlines form the karstic ridges of the area: the actual Sierra de Líbar in the west and the ridge consisting of Sierra de los Pinos, Sierra

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Blanquilla, Sierra del Palo and Sierra de Juan Diego in the east, creating the box-fold structure of the area (Fig. 34). Longitudinal faults oriented N40E, associated with a syncline in the centre of the box-fold, delimit a semigraben coinciding with the syncline, in which Cretaceous sediments have been conserved. Superimposed to the folds, intense fracturing by E-W reverse faults and N140-160E normal faults can be observed, especially in the Jurassic materials. The largest reverse fault in this area is located in the anticline of Sierra de los Pinos and Sierra Blanquilla, locally overthrusting the Llanos de Líbar syncline. The Jurassic limestone is highly fractured, not only by faults but also, and especially, by penetrative joints at various scales, from megascopic to microscopic (Durán and Soria, 1989; Durán and López Martínez, 1992). 8.4. Geomorphology The coexistence of soluble lithologies, as is the case of limestones and dolostones, lying subhorizontal in the anticlinal transition zones (plateau relief in the central sector), fracturing and the high rates of precipitation in the area (mean values of 1,500 mm/year) have produced a spectacular development of karst modelling (Delannoy, 1987; Durán, 1996; Gracia et al., 2000). The karstic landforms are abundant, including karren, sinkholes and poljes with swallow holes, where some streams infiltrate directly into the limestones, as well as abundant karstic cavities (Fig. 35).

Polje de Zurraque

Polje de Burfo

Polje de L

íbar

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lo

Polje de BenaojánPolje de

Zurraque

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PoljePaleopoljeDolines FieldDolinesKarren

Cueva del Gato

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Hydric network

Figure 35. Geomorphological map of the Sierra de Líbar (modified from Delannoy, 1987)


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The study area contains exokarstic forms of all types (Fig. 3) from lapies fields to poljes, including lines of various kinds. The lapies and the dolines are more common in the limestone outcrops, which are generally denuded of soil. The larger poljes (such as Llanos de Líbar, Pozuelo and Burfo) are found in the central part of the sierra and are made up of the Cretaceous materials that were preserved from erosion within synclinal structures and in blocks that were sunk by faults. Extensive areas of the Sierra de Líbar are covered by karren fields, with many different kinds of karren (pointed, sharp-edged, meander-type, with dips and channels, pinnacles, etc.). In many places, extensive karstification has created ruin-like karren features (Delannoy, 1999) which are sometimes hard to distinguish from rockfall blocks. Especially in outcrops of the Jurassic limestones, spectacular features (e.g. pinnacles resembling a pile of plates) can be seen. Many of these formations are probably relics of a morphokarst from the last cold periods of the Pleistocene (Delannoy, 1999). Dolines are also very abundant in the outcrops of the Jurassic rocks, with diameters ranging from 3 to 20 m. Some of these dolines are filled with sediment or residual loam, the larger ones often containing smaller dolines, acting as swallow holes. Several poljes exist in this area, including those of Pozuelo, Líbar, el Republicano, Zurraque, el Burfo, the Benaoján semi-polje and some very small poljes in the east (Fig. 35). The majority of the poljes in Sierra de Líbar are tectonic poljes (Delannoy, 1999), and in all of them the Cretaceous rocks have been preserved from erosion and are now surrounded by Jurassic limestone. The most important polje in the area is Polje de Líbar, which is 4.3 km long and 1.5 km wide, and linked to a tectonic semigraben, situated in the axis of the box fold. This polje is drained by a stream which infiltrates into several ponors. All or most of the water of several streams and of one river in the area infiltrates into the karst aquifer. Most of these streams are located in the poljes of Líbar, Pozuelo and El Republicano and end in simas, very deep shafts or swallow holes. Many of these simas, some still active during the rainy season, others no longer so, have been explored by speleologists. A more spectacular case is the sinking of the Gaduares river. This river, collecting the surface runoff of the north-western slopes of the Sierra de Líbar and (to a greater extent) of the flysch areas north-west of the study area, totally sinks into the karst aquifer in the north of the Sierra de Líbar (Hundidero). Apart from the above-mentioned karst features, there are also abundant endokarstic forms (Delannoy, 1987; Durán, 1996; Mayoral, 2004), mainly in the upper part of the sierra. These are cavities with a predominantly vertical development, most of which are the continuation of karstic sinkholes by which water infiltrates. At the north-eastern and eastern borders of the massif are cavities of horizontal development that are related to the discharge from the aquifer, such as the Pileta Cave, a former karstic drain that is more than 2 km long, and the Hundidero-Gato system that constitutes the subterranean continuation of the Gaduares river through the Sierra de Líbar (Fig. 32). 8.5. Hydrogeology The aquifer of the Sierra de Líbar is formed by Jurassic and Lower Cretaceous materials. These limestones and dolomites are severely karstified, with an extremely developed epikarst and an extensive underground drainage system. The development of the karst network is also favoured

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by intense fracturing and abundant faults, along which karst drains develop preferentially. This high secondary porosity results in a very high degree of total permeability. The average recharge of the aquifer is about 90 hm3/year, by direct infiltration (55 hm3/year) of rainfall and by the infiltration of runoff from the Gaduares and Álamos sinking streams (20 and 15 hm3/year respectively), according to the report by IGME (1984).

Figure 36. Hydrogeological sketch of the Sierra de Líbar and flow path deduced from tracer test (Andreo et al., 2004) In the Sierra de Líbar and its surroundings there are about 36 springs (DGOHCA, 1997). Nevertheless, most of these discharge less than 1 l/s. The most important springs are all situated in the east of the Sierra de Líbar (Fig. 36), near the river Guadiaro: these include Cueva del Gato (462 m a.s.l.) with an average flow of 1.5 m3/s, although during flood periods it can surpass 20 m3/s, Benaoján (450 m a.s.l.), with an average flow of 0.88 m3/s, Charco del Moro (223 m a.s.l.) with an approximate average flow of 2 m3/s and Jimera de Líbar (410 m a.s.l.) with an average flow of 0.15 m3/s. All the karst springs except Charco del Moro are located on the NE border of


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Sierra de Líbar. The flow from these springs increases rapidly, from zero to several m3/s after rainfall. Hydrograph analysis reveals that, because of karstification, the decreases in the flow are also rapid (Benavente and Mangin, 1984); depletion of the spring water is characterised by α-coefficient values of around 10-2 days-1 (Jiménez et al., 2004). The chemical quality of the groundwater in the Sierra de Líbar is very homogeneous (calcium bicarbonate hydrochemical facies) and characterised by low mineralisation and rapid chemical variations. The frequency curves of hydrochemical data show a wide range of variation and are predominantly plurimodal. A multitracer test was carried out in the Sierra de Líbar carbonate aquifer to characterise its hydrogeological behaviour and to identify the connection between the swallow holes in recharge areas and the springs (Andreo et al., 2004). The karstic behaviour was determined and flow velocities of more than 100 m/h were calculated. The karstic conduits and, consequently, the groundwater flow are constrained by a NE-SW trending antiform and by NW-SE fractures. Furthermore, the catchment areas of the Cueva del Gato, Benaoján, Jimera de Libar and Charco del Moro springs (Fig. 36) were defined and it was found that the runoff of the Álamos stream infiltrates into the Republicano swallow hole and appears in the Charco del Moro spring, after an underground path flow through the karst conduits, approximately 12 km long. 9. The Pileta Cave The Pileta cave is situated at the eastern edge of the Sierra de Líbar, approximately 3 km south of Benaoján, about 350 m above the talweg of the Guadiaro river. It is the relict of an ancient drainage system that is now disconnected from the karstic water circulation (Delannoy, 1999). It is a dry cavity, 2 km long, in which two interconnected karst paleolevels can be distinguished. The upper level, where the present-day cave entrance is situated, presents a rising longitudinal profile (from 0 to +40 m) ending in a well about 50 m deep (Gran Sima). The other level is located below, at between -15 and -20 m.

Figure 37. Speleological sketch of the Pileta cave, based in topographical works of several speleological groups

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In the cavity (Fig. 37) there are abundant, elliptical-section “forced-conduit” galleries, some 3-10 m wide and a great many scallops (Delannoy, 1999). There are also many speleothems, which can be grouped into various generations (Delannoy, 1999; Durán, 1996). One generation consists of thick columns and whitish, senile stalagmite shields, which were subsequently eroded. Another consists of a system of brownish-toned, stratified gours-shields that originally covered the gallery floors and which were also later eroded, in part. A further generation of sinter creation corresponds to stalagmite encrustments, which are still functional during rainy periods, and to stalactites aligned along discontinuities in the rock matrix (stratification and fractures). Geochronological datings with U-Th series have been performed on the stalagmite formations in the cave, and isotopic stages 7, 5 and 1 have been detected (Durán, 1996). The oldest speleothems are aged over 350,000 years. Further precision cannot be obtained with the U-Th method utilised (Delannoy, 1999). The Pileta cave is also famous for its cave paintings, the study of which has enabled various phases of human occupation to be identified. These phases correspond to two major periods, the Upper Paleolithic (Solutrean-Magdalenian) and the Neolithic. The cave was declared a National Monument in June 1924 and a Good of Cultural Interest in June 1985.

Figure 38. Evolution of the Pileta system (Delannoy, 1999). (1) Jurassic limestones; (2) Cretaceous marls; (3) Saturated zone; (4) Unsaturated zone; (5) Rapid infiltration; (6) Karst runoff; (7) Karst drain; (8) Karst paleodrain.


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The speleogenetic evolution of the Pileta cave comprises various stages (Fig. 38). The first of these took place under a regime of inundation; the cave galleries corresponded to ancient karstic drains that must have discharged towards a former talweg of the river Guadiaro at an altitude of 750-800 m a.s.l. Subsequently, the base level marked by this river deepened and the cave ceased to be functional; according to Delannoy (1999), this occurred during the Upper Pleistocene. Under these circumstances, the cave became a place of transit for the water infiltrating from the surface towards the saturated zone, and many of the speleothems that fill the cavity were formed. After several phases of speleothem creation, erosive stream water began to circulate. Finally, prior to the human occupations that took place during the Upper Paleolithic, there occurred the deposition of the third generation of speleothems. 10. Hundidero-Gato System The river Gaduares, in a natural mode, entered the Hundidero shaft and emerged at the Cueva del Gato spring. Since the construction of Los Caballeros (or Montejaque) dam, between 1920 and 1923, water from the Gaduares has infiltrated upstream of the dam into the karstified limestones. The dam was built for hydroelectric purposes, but as the water infiltrates diffusely into the karst, the water level in the dam never rises to more than a few metres. The Hundidero-Gato complex is approximately 8 kilometres long and it is the largest underground karst feature of the Sierra de Líbar (Fig. 39). The first known crossing from Hundidero to Gato was made in 1965 (Mayoral, 2004). In this underground passage, various sectors can be distinguished (Durán, 1994; Delannoy, 1999; Mayoral, 2004). The first one is characterised by the virtual absence of circulation and by its greater difference in altitude, with numerous sheer falls; the points of greatest interest are the Super chamber, in the mouth of the Hundidero, the spectacular gours in the Gours chamber and the residual lakes (Giant’s marmitas). The sector from Plaza de Toros (a large, circular depression) to the Great Stalagmite contains the greatest concentration of springs within the cavity; this water infiltrates from the floor of the reservoir above. Beyond this area, when water levels are high, passage is difficult because of fast-flowing water and numerous waterfalls. In the sector between the Great Stalagmite and the Angel’s Leap there are large lakes at low water levels, although there are losses of runoff towards the lower karstification level in Cabo de las Tormentas that become estavelas when water levels are high. The so-called Chamber of Boredom extends from the Angel’s Leap to Lake 1100; in this chamber, too, there are losses from estavelas, before the chamber meets the New Gallery or Montejaque tributary. From Lake 1100 as far as the Dunas Chamber (where a large body of sand has accumulated), there is a change in the physiognomy of the speleological network and it presents a transversal, keyhole-shaped profile; moreover, there is a shaft in the Dunas Chamber that makes contact with the lower level of karstification. From the Dunas Chamber to Paso de la Olla, water only circulates when levels are extremely high, when the shaft’s capacity to evacuate water from the Dunas Chamber is surpassed. In the final sector of the passage, there is an abrupt change in the cave’s direction, to become W-E, which presents characteristics of a forced conduit; once again, springs are to be found, some permanent and some seasonal, which drain through the Cueva del Gato spring that is situated 20 m above the actual talweg of the river Guadiaro. We see, thus, that the Hundidero-Gato speleological network is an occasional drainage channel that becomes active when water is high in the river Gaduares. When waters are low, the Gaduares feeds an (unknown) lower drainage channel, via the numerous losses through the river bed (Delannoy, 1999).

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Figure 39. Speleological sketch of the Hundidero-Gato system (Durán, 1996) An additional feature characterising the cavity is the scarcity of speleothems, with sporadic signs of lithochemical deposits only being observed in the highest areas. Some of these speleothems, dated by Durán (1996), correspond to isotopic stage 5 and to the transition between stages 3 and 2. The Hundidero-Gato complex presents three levels of karstification (Fig. 40), of which the intermediate one is the most highly developed and through which it is possible to pass from Hundidero to Gato (Durán, 1994). The upper level, which is representative of the primitive stages of the cavity, is preserved in very few sectors, while the lowest level is flooded and functions as a collector and/or transmitter of water, according to the state of hydraulic charge of the system.


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Figure 40. Speleological cross section of the Hundidero-Gato system (Durán and Soria, 1989) The Hundidero-Gato system can be considered an ancient subterranean drainage structure, as it currently constitutes the area through which the runoff from the river Gaduares circulates and, moreover, it lies 20 m above the present-day course of the river Guadiaro. Various stages in its evolution can be distinguished: in an initial one, the morphology of the Hundidero ravine must have been produced by the free, ground-level circulation of the Gaduares river as far as what was then the inundated karstic drain of Cueva del Gato. There then occurred a fall in the base level of the Guadiato and the subterranean drainage system was reorganised (the Gato gallery was left abandoned, above the saturated zone), although the Hundidero-Gato speleological network is still a drainage route for groundwater when levels are high.

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REFERENCES

Andreo, B. and Carrasco, F. (1993). Estudio geoquímico de las aguas de infiltración de la Cueva de Nerja. In: Trabajos sobre la Cueva de Nerja, 3. Geología de la Cueva de Nerja (F. Carrasco Ed.), 299-328

Andreo, B., Carrasco, F. and Sanz de Galdeano, C. (1993). Estudio geológico del entorno de la Cueva de Nerja. In: Trabajos sobre la Cueva de Nerja, 3. Geología de la Cueva de Nerja (F. Carrasco, Ed.), 25-50

Andreo, B., Liñán, C, Carrasco, F. and Vadillo, I. (2002). Funcionamiento hidrodinámico del epikarst de la Cueva de Nerja (Málaga). Geogaceta, 31. 7-10

Andreo, B., Vadillo, I., Carrasco, F., Neukum, C., Jiménez, P., Goldscheider, N., Hötzl, H. Vías, J.M., Pérez I. and Göppert, N. (2004). Precisiones sobre el funcionamiento hidrodinámico y la vulnerabilidad a la contaminación del acuífero kárstico de la Sierra de Líbar (provincias de Málaga y Cádiz, Sur de España) a partir de un ensayo de trazadores. Rev. Soc. Geol. España, 16 (3-4), 187-197.

Arias, C., García-Hernandez, M., López-Garrido, A.C., Martín-Algarra, A., Martín-Chivelet, J., Molina, J.M., Rivas, P., Ruíz-Ortiz, P.A., Sanz de Galdeano, C. y Vilas.L. (2004). Las Zonas Externas Béticas y el Paleomargen Sudibérico, In: Geología de España, SGE-IGME, J.A. Vera (Ed.), 354-361.

Arrese, B., Durán, J.J. and López-Martínez, J. (2005). Geomorphological mapping applied to caves: the example of the touristic sector of Nerja Cave (Málaga, southern Spain). Sixth International Conference on Geomorphology. Zaragoza, Spain.

Benavente, J., Cruz-Sanjulián, J. and Linares, L. (1996). Use of groundwater for the maintenance of a protected wetland (Fuente de Piedra Salt Lake. Andalusia, Spain). In: Wetlands: a multiapproach perspective (J. Cruz-Sanjulián and J. Benavente, Eds.), 13-24.

Benavente, J. and Mangin, A. (1984). Aplicación del análisis de series de tiempo al sistema espeleológico Hundidero-Gato. I Congreso Español de Geología, 3, 541-553.

Carrasco, F. (1986). Contribución al conocimiento de la cuenca alta del río Guadalhorce: El medio físico. Hidrogeoquímica. Tesis Doct. Univ. Granada, 435 p

Carrasco, F., Andreo, B., Benavente, J. and Vadillo, I. (1995). Chemistry of the water in the Nerja Cave System (Andalusia, Spain). Cave and Karst Science, 21. 27-32

Carrasco, F., Andreo, B., Liñán, C. and Vadillo, I. (1996). Consideraciones sobre el funcionamiento hidrogeológico del entorno de la Cueva de Nerja (provincia de Málaga). Recursos hídricos de regiones kársticas, 249-263

Carrasco, F., Andreo, B., Durán, J.J., Vadillo. I. and Liñán, C. (1998a). La Cueva de Nerja como elemento geológico del patrimonio natural andaluz. En: IV Reunión Nacional de Patrimonio Geológico (J.J. Durán and M. Vallejo, Eds.), 51-55

Carrasco, F., Andreo, B., Durán, J.J., Liñán, C and Vadillo. I. (1998b). Consideraciones sobre el karst de Nerja. In: Karst en Andalucía (J.J. Duran and J. López-Martínez, Eds.). 173-181

Carrasco, F., Andreo, B., Vadillo. I., Durán, J.J. and Liñán, C. (1999). El medio ambiente subterráneo de la Cueva de Nerja (Málaga). Modificaciones antrópicas. En: Contribución del estudio científico de las cavidades kársticas al conocimiento geológico (B. Andreo, F. Carrasco y J.J. Durán Eds.), 323-334

Crespo-Blanc, A., Estevéz, A., López-Garrido, A.C., Martín-Algarra, A., Molina, J.M., Sanz de Galdeano, C. y Vera, J.A. (2004). Deformación orogénica de las Zonas Externas Béticas. In: Geología de España, SGE-IGME, J.A. Vera (Ed.), 387-389


48

Delannoy, J.J. (1987). Reconocimiento biofísico de Espacios Naturales de Andalucía. Junta de Andalucía, Casa de Velázquez. Madrid. 50 pp

Delannoy, J.J. (1999). Contribución al conocimiento de los macizos kársticos de las Serranías de Grazalema y de Ronda. En: El Karst en Andalucía (Durán, J.J. y López Martínez, eds.). Instituto Tecnológico Geominero de España, Madrid, 93-129;

Diputación Provincial de Málaga, DPM (1988). Atlas hidrogeológico de la provincia de Málaga. 151 pp

Dirección General de Obras Hidráulicas y Calidad de las Aguas –DGOHCA- (1997). Las unidades hidrogeológicas de las Sierras de Líbar (00.06) y Grazalema (05.64). Secretaría de Estado de Aguas y Costas, Ministerio de Medio Ambiente, 52 pp.

Durán, J.J. (1994). Sistema Hundidero-Gato. In: Mundo Subterráneo (Fernández Rubio, ed.), Enresa, 121-128.

Durán, J.J. (1996). Los sistemas kársticos de la provincia de Málaga y su evolución: Contribución al conocimiento paleoclimático del Cuaternario en el Mediterráneo Occidental. Tesis doctoral. Univ. Complutense. 409 pp

Durán, J.J., Cuenca Rodríguez, J. and López Martínez J. (1996). Un ejemplo de sistematización e inventario del Patrimonio Geológico. El Patrimonio kárstico de la provincia de Málaga (Cordillera Bética). Geogaceta, 19. 224-227

Durán, J.J., García de Domingo, A., López Geta, J.A., Robledo, P.A. y Soria, J.M. (2002). Humedales del Mediterráneo español: modelos geológicos e hidrogeológicos. Serie Hidrogeología nº 3. IGME, 160 pp.

Durán, J.J., Grün, R. and Ford, D. (1993). Dataciones geocronológicas (métodos ESR y series de uranio) en la Cueva de Nerja. Implicaciones evolutivas, paleoclimáticas y

neotectónicas. En: Trabajos sobre la Cueva de Nerja, 3 (F. Carrasco, Ed.), 233-248

Durán, J.J. and Soria, J.M. (1989). Sierra de Líbar. In: II Encuentro de campo sobre Geomorfología, Cuaternario y Tectónica (Durán, J.J. y Soria, J.M., eds.), 122-141

Durán, J.J. and López Martínez, J. (1992). Application of geological, hydrochemical and isotopic methods for hydrogeological investigation of selected Spanish karst regions. International Contributions to Hydrogeology, 13, 43-60.

Durán, J.J. and Soria, J.M. (Eds.). 1989. II Encuentro de campo sobre geomorfología, Cuaternario y Geotectónica. Libro-guía. ITGE y Grupo Andaluz del Cuaternario (AEQUA). Madrid. 168 p.

Elorza, J.J., García-Dueñas, V., Matas, J., Martín, L. y Gómez Prieto, J. (1979). Mapa geológico y memoria explicativa de la hoja nº 1040 (Zafarraya). IGME.

Fernández-Rubio, R., Jorquera, A., Martín, R., Zofio, J., Villalobos, M. and Pulido, A. (1981). Análisis de la fracturación y directrices estructurales en el acuífero kárstico de El Torcal de Antequera (Málaga). SIAGA, 2, 659-673.1981.

Guerra, A. and Serrano, F. (1993). Análisis estratigráfico de los materiales neógeno-cuaternarios de la región de Nerja. En: Trabajos sobre la Cueva de Nerja, 3. Geología de la Cueva de Nerja (F. Carrasco Ed.), 55-90

Guerra-Merchán, A., Serrano, F. and Ramallo, D. (2004). Geomorphic and sedimentary Plio-Pleistocene evolution of the Nerja area (northern Alboran basin, Spain). Geomorphology, 89-105

Gracia, F.J., Benavente, J. and Anfuso, G. (2000). Implicaciones endokársticas de la evolución geomorfológica de los poljes de Zurraque y Burfo (Sierra de Líbar, Málaga). I Congreso Andaluz de Espeleología, 341-351.

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49

IGME (1983). Sistema Acuífero nº 41, calizas y dolomías triásicas de la Sierra Almijara-Sierra de Lújar. Informe técnico nº 10

Instituto Geológico y Minero de España –IGME- (1984). Estudios de investigación hidrogeológica para la regulación de los recursos hídricos subterráneos de la divisoria Guadalete-Guadiaro.

Instituto Tecnológico GeoMinero de España, ITGE (1998). Hidrogeología de la Reserva Natural de la Laguna de Fuente de Piedra (Málaga). 79 pp.

Jiménez, P., Andreo, B. and Carrasco, F. (2004). Análisis de la descarga del sector nororiental de la Sierra de Líbar (provincias de Málaga y Cádiz, Sur de España). In: As Águas Subterráneas no sul da Península Ibérica (Ribeiro et al., eds.), 107-116.

Jiménez-Sánchez, M., Durán, J.J., López-Martínez, J., Martos, E. and Arrese, B. (2004). Estudios geomorfológicos en cavidades kársticas de España. En: Investigaciones en sistemas kársticos españoles. (B. Andreo and J.J. Durán, Eds.). Serie: Hidrogeología y Aguas Subterráneas, nº 12, 333-349. Madrid, Publicaciones del Instituto Geológico y Minero de España.

Lhènaff, R. (1981). Recherches geomorphologiques sur les Cordilleres Bétiques Centro-Occidentales (Espagne). Thèse. Université de Lille III. 713 p.

López Chicano, M. and Pulido, A. Observaciones hidrogeológicas e hidroquímicas sobre los manantiales termominerales de Alhama de Granada (Cordilleras Béticas. España). Geogaceta, 19, 134-137.

Lhènaff, R. (1968). Le Poljé de Zafarraya (Province de Granada). Melanges de la Casa de Velásquez, IV, 3-26.

Lhènaff, R. (1998). Los poljes de Andalucía. En: Karts en Andalucía (J.J. Durán and J. López Mártinez, Eds.) ITGE, 55-58.

Linares, L. (1990). Hidrogeología de la Laguna de Fuente de Piedra (Málaga). Tesis Doct. Univ. Granada, 343 p.

López Chicano, M. and Pulido, A. 1996. Observaciones hidrogeológicas e hidroquímicas sobre los manantiales termominerales de Alhama de Granada (Cordilleras Béticas. España). Geogaceta, 19, 134-137.

Martín-Algarra, A. (1987): Evolución geológica alpina del contacto entre las Zonas Internas y las Zonas Externas de la Cordillera Bétca (Sector Occidental). Tesis Doctoral, Univ. Granada, 1171 pp.

Martín Vivaldi, J.L., Caballero, M.A., Calle, M. y Lhènaff, R. (1971). Estudio mineralógico de los niveles arcillosos del polje de Zafarraya, Granada (España). Estudios Geológicos, XXVII, 137-144.

Mayoral, J. (2004). Investigaciones espeleológicas en Montejaque y Benaoján (Málaga), 153 pp.

Ministerio de Medio Ambiente MMA (2000). Propuestas para la redacción del Plan de Protección Hídrica de la laguna de Fuente de Piedra (Málaga).

Muñoz, D. and Udías, A. 1981. In: El Terremoto de Andalucía del 25 de diciembre de 1884, segunda parte. Instituto Geográfico Nacional, 139 pp. Madrid.

Orueta y Duarte, D. 1885. Informe de los terremotos ocurridos en el Sur de España en diciembre de 1884 y enero de 1885. Tip. De Fausto Muñoz, 51 pp. Málaga.

Peyre, Y. (1974). Geologie d’Antequera et de sa region (Cordilleras Bétiques, Espagne). Thèse Université de Paris. 2 vols., 528+76 p.

Pezzi, M. (1975). Le Torcal d’Antequera (Andalousie): un karst structural retouché par le périglaciarisme. Mediterranée, 2, 23-27.

Pezzi, M. (1977). Morfología kárstica del sector central de la Cordillera Bética. Cuadernos


50

Geográficos de la Universidad de Granada, Serie Monografías, 2, 289 p. Tesis Doctoral. Universidad de Granada.

Pezzi, M. C. (1979). Análisis morfológico del Torcal de Antequera. Jábega, 26, 54-64.

Pulido, A. (1993). The karstic aquifer of the Torcal de Antequera (Málaga). In: Some Spanish karstic aquifers (A. Pulido, ed) 37-50. Universidad de Granada, Granada.

Pulido, A. and Mangin, A. (1983). Aplicación de los análisis de correlación y espectral en el estudio de acuíferos kársticos. Tecniterrae, 51, 53-65.

Pulido, A., Marsily, G. and Benavente, J. (1987). Análisis de la descarga del Torcal de Antequera mediante deconvolución. Hidrogeología, 2.

Reicherter, K.R. 2001. Paleoseismological advances inthe Granada Basin (Betic Cordilleras, southern Spain). Acta Geológica Hispánica, 36, 3-4, 267-281.

Reicherter, K. R., Jabaloy, A., Galindo-Zaldívar, J. and Ruano, P. Active faults in the Granada Depression and Zafarraya areas (Betic Cordilleras). 1999. Geogaceta, 27, 193-196.

Reicherter, K.R., Jabaloy, A., Galindo-Zaldívar, J., Ruano, P., Becker-Heidmann, P., Morales, J. , Reiss, S. and González Lodeiro, F. 2002. Holocene palaeoseismic history of the Ventas de Zafarraya Fault (Central Betic Cordilleras, SE Spain). Primer Centenario del Observatorio de la Cartuja, Cien años de Sismología en Granada. Granada

Reicherter, K.R., Jabaloy, A., Galindo-Zaldívar, J., Ruano, P., Becker-Heidman, P., Morales, J., Reiss, S. and González Lodeiro, F. 2003. Repeated palaeoseismic activity of the Ventas de

Zafarraya Fault (Spain) and its relation with the 1884 Andalusian Earthquake. International Journal of Earth Sciences (Geologische Rundschau), 92, 912-922.

Rodríguez-Jiménez, P., Carrasco, F., Benavente, J. y Almécija, C. (1993). Mineralogía de los sedimentos de la laguna de Fuente de Piedra (Málaga). Geogaceta, 14, 18-20.

Sanchidrián, J.L. (1994). Arte rupestre de la Cueva de Nerja. Trabajos sobre la Cueva de Nerja nº 4, 332 pp

Sanz de Galdeano, C. (1985) La fracturación del borde sur de la Depresión de Granada (discusión acerca del escenario del Terremoto del 25-XII-1884). Estudios Geológicos, 41, 59-68

Sanz de Galdeano, C. (1986). Structure et stratigraphie du secteur oriental de la Sierra Almijara (Zone Alpujarride, Cordillères Bétiques). Estudios Geológicos, 42. 281-289

SGOP (1991). Estudio hidrogeológico de las Sierras Tejeda, Almijara y Guájares (Málaga y Granada). Servicio Geológico de Obras Públicas.

Vera, J.A. (1969). Estudio Geológico de la Zona Subbética en la transversal de Loja y sectores adyacentes. Memorias IGME, 72, 187 pp.

Vera, J.A. and Martín-Algarra A. (2004). Cordillera Bética y Baleares. Rasgos generales. Divisiones mayores y nomenclatura. In: Geología de España, SGE-IGME, J.A. Vera (Ed.), 348-350.

J.J. Duran et al.

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Road-log of the excursion

Route:

September 3, 2005. Granada-Nerja (Málaga)

First stop: Alhama de Granada; road A-335, 300 m north of the bridge over the Alhama River, opposite the cemetery.

Second stop: Alhama de Granada Spa

Third stop: Zafarraya Polje: Waste water treatment plant at Zafarraya

Fourth stop: Nerja Cave

September 4, 2005. Nerja- Ronda

Fifth stop: Torcal de Antequera

Sixth stop: Fuentedepiedra lake, Visitors’ centre

September 5, 2005. Ronda- Sevilla

Seventh stop: Los Caballeros dam, Montejaque (road MA-505)

Eighth stop: Speleology Information Centre, Montejaque

Ninth stop: La Pileta Cave, Benaoján

Tenth stop: Entrance of El Gato Cave, Benaoján (road Benaoján-Ronda).

Transfer Benaoján-Sevilla. End of Excursion.

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