1664105x

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Sedimentary patterns in perched spring travertines near Granada

(Spain) as indicators of the paleohydrological and

paleoclimatological evolution of a karst massif

Agustı´n Martı´n-Algarra

a,b,

*, Manuel Martı´n-Martı´n

a

, Bartolome´ Andreo

c

,

Ramo´n Julia`

d

, Cecilio Gonza´lez-Go´mez

b

a_{Departamento de Estratigrafı´a y Paleontologı´a, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain} b_{Instituto Andaluz de Ciencias de la Tierra, C.S.I.C., Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain}

c

Departamento de Geologı´a, Facultad de Ciencias, Universidad de Ma´laga, 29071 Ma´laga, Spain

d

Institut Jaume Almera, C/Martı´ i Franque´s, s/nj_{, 08028 Barcelona, Spain}

Received 15 May 2002; accepted 27 February 2003

Abstract

Perched spring travertines of the Granada basin (South Spain) constitute a perched system with four well-defined steps, which are formed by several facies associations deposited in different sub-environments (travertine pools, dams and cascades). These perched travertines are considered as a freshwater reef system with a facies zonation and stratigraphic architecture closely resembling that of marine reef terraces and prograding carbonate platforms. The travertine deposits have been dated by

230

Th/234U and14C methods. As in other Mediterranean areas, the travertine deposition occurred episodically during warm and wet interglacial periods coinciding with isotopic stages 9, 7 and 5, and with the transition between isotopic stages 2/1. During these periods, underground dissolution, large outflow in the springs and subsequent calcium carbonate precipitation occurred. In the same way that evolution of reef systems indicates sea level changes, the geomorphology, age and architecture of perched spring travertine systems may be used to interpret former climatically controlled changes in outflow, in base level marked by the altitude of springs and in the chemistry of spring waters. Thus, aggradation or climbing progradation may indicate an increase of outflow at the spring, progradation with toplap is due to a stable base level and, conversely, dowlapping progradation may signify that the base level was gradually dropping. Therefore, the travertines can be considered semiquantitative indicators of the paleohydrological evolution of karstic massifs and used as an important terrestrial proxy climate record.

Keywords:Travertine; Continental reefs;230_Th/234_{U and}14_{C dating; Mediterranean karst}

1. Introduction

Karstic springs on semiarid Mediterranean envi-ronments are sensitive ecotops to paleohydrological changes. Morphologically complex, perched traver-tine bodies very rich in plant remains are usually formed there. The geomorphology, sedimentology and

* Corresponding author. Departamento de Estratigrafı´a y Paleon-tologı´a, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain. Tel.: +34-95-8243337; fax: +34-95-8243203.

E-mail address:[email protected] (A. Martı´n-Algarra).

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dating of these perched spring travertines can provide paleohydrological data to help establish recent cli-matic evolution(Henning et al., 1983; Magnin et al., 1991; Torres et al., 1996; Braum et al., 2000). In Southern Spain, a region representing a very critical climatic and biogeographical border, Quaternary spring travertine deposits are very common, but they

are discontinuous both in space and time (Dura´n, 1996; Torres et al., 1996).

Although travertines are formed by carbonate pre-cipitation, evidence of biological mediation can be found in many cases (Casanova, 1982; Chafetz and Folk, 1984; Chafetz et al., 1991; Pedley et al., 1996; Freytet and Verrechia, 1998; Janssen et al., 1999).

Fig. 1. (A) Location and geological sketch of the study area. (B) Simplified cross-section with indication of the position of the travertine steps and of dated samples.

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Further, the growth and the development of the vegetation itself trigger the location of stream chan-nels and the flow characteristics, and determine the migration of the active sites of carbonate precipitation

(Julia`, 1983; Pedley, 1992).

In this paper, we report upon travertines and asso-ciated spring outcropping in the Granada basin, one of the main post-orogenic basins in Southern Spain(Fig. 1), in order to compare their facies, stratigraphic architecture and the factors controlling their genesis and evolutionary development with those of marine reefs, and to propose a sedimentary pattern for the study area which could be applicable to other traver-tine deposits. The other aim of the paper is, through radiometric dating (230Th/234U and14C) of the traver-tine deposits, to elucidate the paleohydrological evo-lution of Southern Spain, and to increase knowledge on European Quaternary paleoclimatology.

2. Geological setting

The studied area is located on the NE edge of the Granada basin(Fig. 1A), an intermontane basin in the Betic Cordillera, which originated in the Upper Mio-cene. The bedrocks of the area outcrop widely in the Sierra de la Yedra, which is composed of several alpine thrust sheets of pelitic rocks (Paleozoic slates and Early Triassic sandstones) and carbonate rocks (Triassic dolostones and Jurassic to Lower Miocene limestones). The basin infill is of (1) Tortonian con-glomerates, (2) alluvial deposits interfingering with lacustrine limestones and marls containing gypsum of Messinian age and (3) alluvial conglomerates of Plio – Pleistocene age. Over these materials, travertines were deposited during the Quaternary, which extends from a normal fault that has been neotectonically active, and from large, earthquake-induced landslides that destroyed the villages of Gu¨eve´jar and Nı´var in 1884. This fault separates the infill of the Granada basin from bedrocks.

The Sierra de la Yedra carbonates constitute a 20 km2 karstic massif, in which recharge comes exclu-sively from rainfall while discharge occurs through springs located along the border of the massif (Fig. 1A). Extensive carbonate deposits are not forming today in the springs; but a connection between traver-tine deposition and the ancestors of the modern springs

may be inferred. Hydrochemistry of four spring waters close to travertine deposits distinguished two water types(Andreo et al., 1999):

(a) Waters with low mineralization, from Fuente-grande and Nı´var springs (1 and 2 in Fig. 1), which contain predominantly Ca2 +, Mg2 + and HCO3 ions, and are slightly supersaturated in calcite but they are not precipitating CaCO3today. (b) Highly mineralized waters from Gu¨eve´jar and Pan springs (3 and 4 inFig. 1). They contain higher Ca2 +, Mg2 +and especially SO42 concentrations, indicating the dissolution of gypsum-bearing Mio-cene sediments, and higher calcite saturation index. Some local precipitation of calcite is occurring.

The travertines form a perched system with four regionally well-defined steps in the western edge of the Sierra de la Yedra(Fig. 1B), which can be clearly distinguished because of their erosive bottoms coin-ciding approximately with the slope of the mountain and their flat top which is located at a different altitude: 1110 (Step I), 1095 (Step II), 1060 (Step III) and 1010 m a.s.l. (Step IV).

3. Spring travertines and reef systems

3.1. Travertine architecture and facies

The internal architecture of the travertines is best preserved in Step II NE of Nı´var(Photo 1), where six unconformity-bounded prograding wedges are distin-guished (Fig. 2A). The two wedges located nearer to the mountain side in the lower stratigraphic position (W1– W2 in Fig. 2A) show aggrading relationships between them, whereas the next four are clearly prograding and downlapping, with a toplap surface developed upon wedges W4, W5and W6. Each wedge starts with low-angle clinoforms that become pro-gressively steeper and finally vertical, or nearly so (W4– W6). Subhorizontal beds are visible below the platform formed between the clinoforms and the mountain. The carbonate facies are similar in all platforms, and plants such us those living around the springs today participated in their construction (for terminology see Pedley, 1990, 1992). These

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facies are laterally and vertically organized into three facies associations(Fig. 2B):

(a) Facies Association 1 is mainly found in the ho-rizontally bedded zones (especially in column d,

Fig. 2B). It is dominated by decimeter-scale beds of chalky and peloidal mudstones – wackestones con-taining some gastropods. These alternate with oncolitic ‘gravels’ (Photo 2), bioclastic breccias (rudstone – floatstones) and calcarenites (grain-stones/packstones), sometimes channeled, made of broken stems and leaves ofSalixsp.,Quercussp.

(Photo 3)and other unidentified plant fragments. Thin, planar to undulose stromatolite crusts (micritic to peloidal bindstones) and isolated small patches of mosses are also found. Laminated to pisolitic caliche crusts and corroded surfaces, locally mineralized by Fe-oxyhydroxides, are pre-sent at the top of some sequences (Fig. 2B, column d, Photo 4). This facies association laterally changes to scree deposits (column e inFig. 2B). (b) Facies Association 2 is typical of the clinoform

areas (columns b, c and d inFig. 2B,Photo 5). It consists of alternations between decimeter-scale

beds of allochthonous sediments and thickening upward beds of bioconstructed facies (Photo 6). These typically grow on leaf and stem breccias that include fan-shaped frame-bafflestones of cane-like and reed-like plants or long round stems of rushes. Tubular framestones associated with decimeter-scale mounds and crusts of mosses and domal stromatolites progressively develop up-wards. When the clinostratification is nearly vertical, the main builders are straight branching pipes, the fossil remnants of a bramble-like vegetation, and curved tubes(Photo 7)that appear to be climbing plants. These builders clearly grew in place but hanging from the upper part of the slope, alternating with planar to undulose beds and mounds of mosses and stromatolites. Deci-meter to Deci-meter-size primary framework voids are partially filled with laminated, speleothem-like encrustations of crystalline calcite, stromatolite crusts and channeled bioclastic sediment, although no thick secondary mineralization of sparry calcite has occurred.

(c) Facies Association 3 appears in downlapping zones of the travertine wedges, and is dominated again by

Photographs 1 – 4. (1) Panoramic view of the travertine Step II, located at the NE of the Nı´var village inFig. 1. (2) Oncolitic gravels of a pool environment. (3) Leaves facies. (4) Corroded surface mineralized by Fe-oxyhydroxides.

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Fig. 2. (A) Facies architecture of the travertine Step II around Nı´var, and position of the dated samples; a – e are location of columns reproduced in (B). (B) Measured sections with indication of facies; W1– W6are the unconformity-bounded prograding wedges. (C) Sedimentary patterns of

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allochthonous facies, mainly leaf and stem brec-cias, and oncoidal calcarenites and calcirudites (Fig. 2B, column a). Fallen blocks of the travertine structure are common here(Photo 8). Bedding is laterally discontinuous, irregular and inclined down the general slope of the mountain side, with frequent low-angle cross-bedded sets of strata and common small erosion surfaces and channels. Thin stromatolite crusts, decimeter-sized mounds of mosses and patches of canes and rushes are also abundant. Near the base of the travertine bodies and following the slope of the mountain, especially in W1to W3(Fig. 2A), there is an alternation in facies with features intermediate between Associations 1 and 3, and units of fine- to coarse-grained alluvial siliciclastics.

3.2. Sedimentary patterns

These facies associations are the sub-environments of systems of travertine dams and cascades (Julia`, 1983; Pedley, 1990; Ford and Pedley, 1996); their lithology, morphology, architecture and sedimentary dynamics (Fig. 2C) remind one of terraced reefs located on tectonically rising coastlines and of pro-grading platforms(James, 1983; Pomar, 1991).

The Facies Association 1 is indicative of a pool environment, near the former spring (Fig. 2C). This zone closely resembles back-reef or lagoonal areas where fine-grained carbonate facies, oncolites and stromatolites are common. The corroded and miner-alized surfaces are interpreted as karst and pedogenic features formed during desiccation periods.

Facies Association 2 represents dam and cascade environments, very similar to marine reef front facies

(Fig. 2C). The dam coincides with the upper parts of the clinoforms and was characterized by an active upward growth of vegetation that favored the isolation of the pool and the progressive steepening of the slope, which generated a downstream cascade (Casa-nova, 1982). The dam is quite similar geometrically to a reef crest and the cascade to a reef wall. Even the resulting constructional morphology of the main tra-vertine builders closely resembles those more typical in marine reefs: mounds of mosses are similar to massive domal coral heads; tubular framestones of brambles and climber plants are equivalent to branch-ing corals and pillars; and fan-shaped bafflestones of

rushes and canes look like plate-like corals and iso-lated branching algal and coral patches in the toe of the reef front. Finally, as in a reef front, the cascade zone exhibits porosity with microbial and especially cement encrustations.

Facies Association 3 is typical of the distal parts of the travertine slope, downstream of the cascade (Fig. 2C). Here the water flows over a thick bed of more or less encrusted vegetation debris, and disperses along multiple small watercourses isolated by mounds of mosses and patches of herbaceous vegetation. This channeled slope apron of calcified plant detritus closely resembles the fore reef slope.

4. Geochronology

4.1. Methodological aspects

In order to understand the development of perched travertine terraces in a tectonically uplifting area, a simple chronological framework has been established using some uranium disequilibrium and radiocarbon dates.

In spite of their high porosity, travertines can remain closed to radioisotope migration in their inner parts. Some authors have suggested that fossil travertine deposits preserve their isotopic composition, which changes only by radioactive decay, making14C dating possible (Hillarie-Marcel et al., 1986; Torres et al., 1996). Thus, systematic dating of travertine samples has also been undertaken to establish a chronology of travertine deposits(Kronfeld et al., 1988; Horvatincic et al., 2000). Nevertheless, the interpretation of meas-ured14C activity of travertine samples requires knowl-edge of several factors peculiar to travertine formation

(Dandurand et al., 1982). These factors, such as the isotopic composition of the total dissolved inorganic carbon (TDIC) in spring waters, are rarely available. Note that the TDIC depends on: (1) recent atmospheric CO2; (2) old carbon dissolved from fossil carbonate of the aquifers; (3) CO2 of deep origin that may be released along fault systems; and (4) CO2 due to organic matter decay. As a result, the radiocarbon content of inorganically precipitated calcium carbonate in hard-water areas is normally lower than that pre-dicted from consideration of equilibrium with atmos-pheric CO2. Consequently, travertine samples yield

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fictitious14C dates which can be older than the ‘‘real’’ age by thousands of years(Edwards et al., 1986 – 87). The uranium-series disequilibrium dating method has been successfully used for dating travertine depos-its (Bischoff et al., 1988; Eikenberg et al., 2001; Soligo et al., 2002). For this reason, the U/Th method will be concentrated upon here.

Eight samples from the four travertine steps around Nı´var (two samples from Step I, three samples from Step II, one sample from Step III and two samples from Step IV: located inFigs. 1B and 2A) were dated at the Laboratory of the Jaume Almera Institut (Bar-celona) by the230Th/234U method, using alpha spec-trometry. The chemical separation and purification follows the procedure described by Bischoff et al. (1988). The isotope electrodeposition follows the traditional method described by Talvitie (1972) and modified byHallstadius (1984). Age calculations are based on the computer program by Rosenbauer (1991). In addition, one travertine sample from Step IV (equivalent to S8, seeFig. 1B) was dated by the 14

C method in order to compare with the U/Th data. 14

C dating was performed at the University of Gran-ada Radiocarbon Dating Laboratory by benzene syn-thesis and liquid scintillation counting. Calculations and data are processed by a PC computer, using a general program byGonza´lez-Go´mez (1995).

4.2. Age of the travertines

The results obtained for the first analysed sample from Step I (S1 inTable 1) were rejected due to their high degree of contamination (230Th/232Th = 1.9). A second sample from the same step (S2 in Table 1) yielded a nominal age of 291,541 + 25,621/ 20,908

years BP with a slight contamination (230Th/232Th = 16.16). In conclusion, after U/Th radiometric method, Step I was approximately deposited around 290 ky.

Macrovertebrate associations indicating late Mid-dle Pleistocene ages, younger than 490.000 years

(Ruiz-Bustos, 1995), are interlayered within the low-ermost beds of the higher travertine step in Alfacar (PS-1 inFig. 1A), which can be correlated with Step I of Nı´var, and rodent fossils older than 270.000 years also appear as fissure fillings within the same step (PS-2 in Fig. 1A). These data are coherent with the aforementioned radiometric data of travertine Step I, in spite of its contamination by detrital thorium. The same fossil associations are also found within lacus-trine travertines in the Granada basin (Ruiz-Bustos, 1995). So, late Middle Pleistocene was a favorable period for carbonate precipitation, and travertine dep-osition in the region occurred mainly after this age when the Granada basin had already been filled.

The three samples analysed in the travertine Step II (S3, S4 and S5 in Figs. 1B and 2A) provided ages ranging from 200 to 250 ky BP with very low contamination (230Th/232Th ratios greater than 44.5,

Table 1). In spite of the confidence limits of sample S5, the three nominal ages agree with the depositional architecture and, as could be expected, younger depos-its form at the most distal parts of the travertine terrace. Only one sample was analysed from travertine Step III (S6 in Table 1), providing a nominal age of 84,625 + 3463/ 3366 year BP. In spite of their degree of contamination (230Th/232Th = 7.8), it is evident that Step III was deposited after Step II because contami-nation by detrital Th produces older nominal ages.

The results of the first analysed sample from Step IV (S7 inTable 1) were rejected due to their degree of

Table 1

U-series radiometric data and derived dates for samples from Nı´var travertine Step II

Sample 238_{U (ppm)} 232_{Th (ppm)} 234_U/238_U 230_Th/234_U 230_Th/232_Th _{Nominal date}

(ky BP) S1 0.58 0.93 1.03F0.01 0.96F0.02 1.9 >250 S2 0.45 0.09 1.08F0.01 0.95F0.02 16.2 291F23 S3 0.77 0.01 1.22F0.01 0.94F0.01 195.2 245F13 S4 0.64 0.02 1.35F0.04 0.92F0.04 101.3 218F25 S5 0.75 0.05 1.19F0.01 0.88F0.01 44.5 202F9 S6 0.68 0.21 1.39F0.01 0.56F0.02 7.8 84F3 S7 0.83 0.17 1.48F0.01 0.14F0.01 3.2 16F0.7 S8 0.87 0.03 1.46F0.01 0.10F0.00 12.3 11F0.2

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contamination (230Th/232Th = 3.2). A second sample from the same level (S8 in Fig. 1B and Table 1) provided a more reliable age of 11,888F_{185 year BP,} with low contamination (230Th/232Th = 12.3). The14C method was also applied in the same level, and a radiocarbon age of 13,210F_{110 year BP was} ob-tained (d13

C = 6.869x). Both ages correspond to the Late Glacial (Bølling – Allerød) period.

It is clear that some aforementioned datings pre-sent contamination problems because travertine sam-ples contain a proportion of detrital232Th.Kelly et al. (2000)found the same problem in calcretes from the Sorbas basin (south Spain), and they developed a methodological approach by U/Th using multiple samples to define an isochron. However, in the

Granada basin, we have additional information that corroborates the U/Th datings. Thus, the U/Th dating travertine Step I is coherent with the paleontological data available, the sample dated from Step III is contaminated but anyway younger that Step II, which gives stratigraphically coherent U/Th ages and, finally, ages of travertine Step IV obtained by two different methods (Th/U and 14C) are similar. There-fore, in spite of the contamination problems, the final scenario coming out from results is coherent and it is acceptable that higher travertine steps are older that the lower ones. The travertine deposit took place

(Fig. 3) during oxygen isotope stages 9 (Step I), 7 (Step II) and 5 (Step III), and during the Late Glacial period (Step IV).

Fig. 3. Correlation of the studied travertines with orbitally driven chronostratigraphy of thed18

O record ofMartinson et al. (1987)and with the cycles of travertine formation in Spain(Dura´n, 1996). I, II, III and IV are travertine steps and W1– W6are the wedges of travertine Step II which

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5. Concluding remarks: paleohydrological and paleoclimatic significance

The terraced morphology, the stratigraphic archi-tecture and the deposition of perched travertines are caused by the balance between carbonate productivity, hydrodynamics and changes in the base level of the associated karstic massif(Cruz Sanjulia´n, 1981; Ped-ley, 1990; Chafetz et al., 1991; Pedley et al., 1996; Freytet and Verrechia, 1998), and are similar to that of prograding reefs on carbonate platforms(James, 1983; Tucker and Wright, 1990; Pomar, 1991; Webb, 1996). In marine reef, the base level is the sea level, but in carbonate massifs, the base level is marked by the altitude of the springs, rather than the water table. Travertine deposits will occur at the same altitude or slightly below the spring, while the water table usually is approximately at the same altitude or higher than the point of discharge. Thus, if the water table is very low, then springs and travertine deposits will only occur in the low areas. However, with a high water table, the deposits can form either on the high areas or low areas or anywhere in between, depending on where the readily available conduit intersects the surface.

In Granada basin, travertines were deposited by springs located successively in lower elevation with time and by analogy with reefs on carbonate platforms: (a) aggradation or climbing progradation may indicate an increase of outflow at the spring, with perhaps some rise of the water table; (b) progradation with toplap signifies intense outflow associated with a relatively stable base level; (c) downlapping progradation may imply that the regional base level was gradually drop-ping due to decreasing rainfall or descending erosion and later elevation of outflow; finally (d) the formation of a separate lower step requires periods without travertine deposit, descending karstification and drop-ping of the base level, either due to undersaturation of spring waters in calcium carbonate or to dryness and cessation of outflow.

Travertine formation in the study area was pulsat-ing along the Middle – Late Pleistocene(Fig. 3), dur-ing oxygen isotope stages 9, 7 and 5, and the transition of isotopic stages 2 and 1, coinciding with periods of other maximum travertine and speleothem deposition in Spain(Dura´n, 1996; Torres et al., 1996). Travertine deposition occurred especially during warm and wet periods that favored intensified

under-ground dissolution, large outflow in the springs and subsequent calcium carbonate precipitation (Henning et al., 1983; Andreo et al., 1999; Braum et al., 2000). During these periods, the Mediterranean forest in the mountains expanded, and the volume of spring waters in their foothills increased. Forest expansion increased the supply of CO2to soils, thereby increasing carbo-nate dissolution after infiltration, leading to saturation of karst waters in calcite, which precipitated around springs building up the travertine (Pentecost, 1995; Chafetz et al., 1991). Periods without travertine pre-cipitation correspond to colder climate and/or increased aridity that prevented outflow, soil development and underground karstification, but favored steppe-type vegetation, deforestation, erosion and dropping of the base level.

Thus, travertines north of Granada formed prefer-entially during interglacial periods. This picture is similar to that obtained for other Mediterranean (Kron-feld et al., 1988; Bischoff et al., 1988; Torres et al., 1996; Horvatincic et al., 2000), some Northwest Euro-pean (Baker et al., 1993; Braum et al., 2000) and African(Hillarie-Marcel et al., 1986)travertines. The only exception is the travertine Step IV, which was deposited to the transition between isotopic stages 2/1, but radiometric data prove that travertine deposition was occurring during this time in Southern Spain(Fig. 3). This Step IV is coeval with humid periods detected in NW Africa between 11,000 and 14,000 year BP

(Gasse et al., 1990). In these periods, the climate was oceanic, before the change to Mediterranean conditions occurred around 10,000 year BP(Jalut et al., 1997).

In conclusion, in the same way that evolution of reef systems indicates sea level changes, the geo-morphology, architecture and age of the studied perched travertine system reflect climatically con-trolled changes in outflow, in elevation of the base level and in chemistry of spring waters. In spite of local factors such as groundwater chemistry or tec-tonic uplift, the episodic nature of travertine deposi-tion north of Granada shows clear links to changes in the global Quaternary climate: it was associated with wet and warm or mild, Middle and Late Pleistocene interglacial and Late Glacial periods, and ceased during glacial time. Thus, perched travertine systems are semiquantitative indicators of the paleohydrogeo-logical evolution of karstic massifs which can be radiometrically dated and can be successfully used

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to evaluate climatic change on the continent in Med-iterranean areas.

Acknowledgements

This work is a contribution to Projects PB91-0079, PB96-1430, CLI95-1905 and PB97-1267-C03-02 of the DGICYT and IGCP 448 of the UNESCO, as well as to Groups 4089 and RNM-208 and RNM-308 of the Junta de Andalucı´a. We thank G. Monzo´n, F. Valle-Tendero, A. Ruiz-Bustos and M. Berna´rdez for their assistance. We are grateful to Dr. Derek C. Ford (Univ. McMaster, Canada) and Dr. Ce´sar Viseras (Univ. Granada, Spain) for their helpful comments and suggestions. We also thank the interesting criticisms done by Dr. Henry Chafetz and an anonymous referee who contribute to improve this paper.

References

Andreo, B., Martıń-Martıń, M., Martıń-Algarra, A., 1999. Hydro-chemistry of spring water associated with travertines. Examples of the Sierra de la Alfaguara (Granada, southern Spain). Comp-tes Rendus de l’Academie des Sciences Paris, Sciences de la Terre et des Plane`tes 328, 745 – 750.

Baker, A., Smart, P.L., Ford, D., 1993. Northwest European palaeo-climate as indicated by growth frequency variations of secon-dary calcite deposits. Palaeogeography, Palaeoclimatology, Pa-laeoecology 100, 291 – 301.

Bischoff, J.L., Julia`, R., Mora, R., 1988. Uranium-series dating of the Mousterian occupation at Abric Romanı´, Spain. Nature 332, 68 – 70.

Braum, F.N., Hambach, M., Mangini, A., Wagner, G., 2000. Warm period growth of travertine during the Last Interglaciation in Southern Germany. Quaternary Research 54 (1), 38 – 48. Casanova, J., 1982. Morphologie et biolithoge´ne`se des barrages de

travertins. Actes du Colloque de l’A.G.F., Formations carbona-te´es externes, tufs et travertins, 45 – 54.

Chafetz, H.S., Folk, R.L., 1984. Travertines: depositional morphol-ogy and the bacterially constructed constituents. Journal of Sedi-mentary Petrology 54, 289 – 316.

Chafetz, H.S., Rush, P.F., Utech, N.M., 1991. Micro environmental controls on mineralogy and habit of CaCO3 precipitates: an

example from an active travertine system. Sedimentology 38, 107 – 126.

Cruz Sanjuliań, J.J., 1981. Evolucioń geomorfolo´gica e hidrogeo-lo´gica reciente en el sector Teba-Can˜ete la Real (Ma´laga) a la luz de la datacioń de formaciones travertıńicas. Boletıń Geo-lo´gico y Minero 92 (4), 297 – 308.

Dandurand, J.L., Gout, R., Hoefs, J., Menschel, G., Schott, J., Usdowsky, E., 1982. Kinetically controlled variations of major

components and carbon and oxygen isotopes in a calcite-precip-itating spring. Chemical Geology 36, 299 – 315.

Durań, J.J., 1996. Los sistemas ka´rsticos de la provincia de Ma´laga y su evolucioń: Contribucioń al conocimiento paleoclima´tico del Cuaternario en el Mediterrańeo occidental. PhD Thesis, Complutense University of Madrid, Spain.

Edwards, R.L., Chen, J.H., Wasserburg, G.J., 1986 – 87.

238

U –234U –234Th –232Th systematics and the precise measure-ment of time over the past 500,000 years. Earth and Planetary Science Letters 81, 175 – 192.

Eikenberg, J., Vezzu, G., Zumsteg, I., Bajo, S., Ruethi, M., Wys-sling, G., 2001. Precise two chronometer dating of Pleistocene travertine: the230Th/234U and226Ra/226Ra (0) approach. Qua-ternary Science Reviews 20, 1935 – 1953.

Ford, T.D., Pedley, H.M., 1996. A review of tufa deposits of the world. Earth Science Reviews 41, 117 – 175.

Freytet, P., Verrechia, E.P., 1998. Fresh-water organism that build stromatolites. A synopsis of biocrystallization by prokaryotic and eukaryotic algae. Sedimentology 45 (3), 535 – 563. Gasse, F., Te´het, R., Durand, A., Gibert, E., Fontes, J.C., 1990. The

arid – humid transition in the Sahara and the Sahel during the last deglaciation. Nature 346, 141 – 146.

Gonza´lez-Go´mez, C., 1995. A general computer program for radio-carbon dating laboratories. Radioradio-carbon 37 (2), 789 – 790. Hallstadius, L., 1984. A method for the electrodeposition of

acti-nides. Nuclear Instruments and Methods in Physics Research 223, 266 – 267.

Henning, G.J., Gru¨nn, R., Brunacker, K., 1983. Speleothems, tra-vertines and paleoclimates. Quaternary Research 20, 1 – 29. Hillarie-Marcel, C., Carro, O., Casanova, J., 1986.14C and Th/U

dating of Pleistocene and Holocene stromatolites from East African paleolakes. Quaternary Research 25, 312 – 329. Horvatincic, N., Calic, R., Geyh, M.A., 2000. Interglacial growth of

tufa in Croatia. Quaternary Research 53, 185 – 195.

Jalut, G., Esteban-Amat, A., Riera I Mora, S., Fontugne, M., Mook, R., Bonnet, L., Gauquelin, T., 1997. Holocene climatic changes in the western Mediterranean: installation of the Mediterranean climate. Comptes Rendus de l’Academie des Sciences Paris Se´rie IIA 325, 327 – 334.

James, N.P., 1983. Reef environment. In: Scholle, P.A., Bebout, D.G., Moore, C.H. (Eds.), Carbonate Depositional Environ-ments. American Association of Petroleum Geologists, Mem-oir, vol. 33, pp. 347 – 362.

Janssen, A., Swennen, R., Podoor, N., Keppens, E., 1999. Biolog-ical and diagenetic influence in recent and fossil tufa deposits from Belgium. Sedimentary Geology 126 (1 – 4), 75 – 95. Julia`, R., 1983. Travertines. In: Scholle, P.A., Bebout, D.G.,

Moore, C.H. (Eds.), Carbonate Depositional Environments. American Association of Petroleum Geologists, Memoir, vol. 33, pp. 62 – 72.

Kelly, M., Black, S., Rowan, J.S., 2000. A calcrete-based U/Th chronology for landform evolution in the Sorbas basin, south-east Spain. Quaternary Science Reviews 19, 995 – 1010. Kronfeld, J., Vogel, J.C., Rosenthal, E., Weinstein-Evron, M., 1988.

Age and paleoclimatic implications of bet shean travertines. Quaternary Research 30, 298 – 303.

(12)

travertins: accumulations carbonateés associeés aux syste`mes karstiques, se´quences se´dimentaires et paleó-environnements quaternaires. Bulletin Societe´ Geólogique de France 162 (3), 585 – 594.

Martinson, D.C., Pisias, N.G., Hays, J.D., Imbrie, J., Moore Jr., T.C., Shackleton, N.J., 1987. Age dating and the orbital theory of the ice ages: development of a high-resolution 0 to 300,000 year chronostratigraphy. Quaternary Research 27, 1 – 29.

Pedley, H.M., 1990. Classification and environmental models of cool freshwater tufas. Sedimentary Geology 68, 143 – 154. Pedley, H.M., 1992. Fresh-water (phytoherm) reefs—the role of

biofilms and their bearing on marine reef cementation. Sedimen-tary Geology 79 (1 – 4), 255 – 274.

Pedley, H.M., Andrews, J.E., Ordoń˜ez, S., Garcıá del Cura, M.A., Gonza´lez-Martıń, J.A., Taylor, D., 1996. Does climate control the morphological fabric of freshwater carbonates? A comparative study of Holocene barrage tufas from Spain and Britain. Palaeo-geography, Palaeoclimatology, Palaeoecology 121, 239 – 257. Pentecost, A., 1995. The quaternary travertine deposits of

Eu-rope and Asia minor. Quaternary Science Reviews 14 (10), 1005 – 1028.

Pomar, L., 1991. Reef geometries, erosion surfaces and high-fre-quency sea-level changes, upper Miocene Reef Complex, Mal-lorca, Spain. Sedimentology 38, 243 – 269.

Rosenbauer, R.J., 1991. UDATE1: a computer program for the calculation of uranium-series isotopic ages. Computers and Ge-osciences 17 (1), 45 – 75.

Ruiz-Bustos, A., 1995. Biostratigraphy of continental deposits in the Granada, Guadix and Baza basins (Betic Cordillera). Int. Conf. of Human Palaeontology, Orce, (Spain), pp. 153 – 174. Soligo, M., Tuccimei, P., Barberi, R., Delitala, M.C., Miccadei, E.,

Taddeucci, A., 2002. U/Th dating of freshwater travertine from Middle Velino Valley (Central Italy): paleoclimatic and geolog-ical implications. Palaeogeography, Palaeoclimatology, Palaeo-ecology 184, 147 – 161.

Talvitie, N.A., 1972. Electrodeposition of actinides for alpha spec-trometric determination. Analytical Chemistry 44, 280 – 283. Torres, T., and 20 authors more, 1996. Aportaciones al conocimiento

de la evolucioń paleoclima´tica y paleoambiental en la penıńsula Ibe´rica durante los dos u´ltimos millones de anõs a partir del estudio de travertinos y espeleotemas. Empresa Nacional de Re-siduos Radioactivos, S.A., Publicacioń tećnica nj3/96. 118 pp. Tucker, M.E., Wright, P.V., 1990. Carbonate Sedimentology.

Black-well, London. 482 pp.

Webb, G.E., 1996. Was Phanerozoic reef history controlled by the distribution of the Nonenzymatically secreted reef carbonates (microbial carbonate and biologically induced cement). Sedi-mentology 43 (6), 947 – 971.