Changes in the Early Miocene palynoflora and

N. Jb. Geol. Palaont. Abh.

242 (2/31

171- 204

Stuttaart, Dezernber 2006

Changes in the Early Miocene palynoflora and vegetation in the east of the Rubielos de Mora Basin (SE Iberian Ranges, Spain) Eduardo Barron, Luis Lassaletta and Cristina Alcalde-Olivares, Madrid With 12 figures and 2 tables

B A R R ~ NE., , LASSALETTA, L. & ALCALDE-OLIVARES, C. (2006): Changes in the Early Miocene palynoflora and vegetation in the east of the Rubielos de Mora Basin (SE Iberian Ranges, Spain). -N. Jb. Geol. Palaont. Abh., 242: 171-204; Stxttgart.

Abstract: This paper reports on a palynological study of Early Miocene (Ramblianlower Aragonian) miospores from the eastern part of the Rubielos de Mora Basin (eastern Spain). Analysis of the palynological assemblages in the area's facies associations (fluvial and fluvio-lacustrine, terrigenous and carbonate lacustrine, and anoxic-carbonate lacustrine) allowed the identification of 86 taxa (bryophytes, pteridophytes, gymnosperms and angiosperms). The climate of the region was influenced by its mountainous nature, and the landscape was characterized by coniferous forests. However, a close relationship was observed between the palaeogeographic development of the basin, which had different depositional environments, and the palynological assemblages examined. The fluvial sediments showed higher percentages of pollen belonging to hydro-hygrophytic and riparian taxa than the lacustrine sediments, which mainly contained mesophytic and thermal taxa. A humid subtropical climate was inferred using the so-called "coexistence approach'?. The palynological results obtained were contrasted with the megafloral assemblage of the Rio Rubielos outcrop and compared to Early and Middle Miocene pollen data from the Western Mediterranean Region and the Iberian Peninsula. Zusammenfassung: An der Ostseite des Beckens von Rubielos de Mora (OstSpanien) wurde eine palynologische Studie im Unteren Miozan (Ramblian-Unteres Aragonien) durchgefiihrt. Die Analyse der Palynomorpha ermoglichte die Bestimmung von insgesamt 86 Taxa: Bryophyten, Pteridophyten, Gymnospermen und Angiospermen. Die Auswertungen zeigen, dass enge Zusamrnenhange zwischen den verschiedenen Ablagerungsraumen und den palynologischen Gruppierungen bestehen. So enthalten fluviatile Sedimente prozentual hohere hydro-hygrophytische und uferbegleitendeTaxa als die Sedimente, die prirnar durch mesophytische und w h n e -

0077-774910610242-0171 $8.50 O 2006 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart

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liebende Taxa charakterisiert sind. Um palaookologische Parameter zu berechnen, wurde der sogenannte ,,Koexistenz-Ansatz" angewandt. Die Ergebnisse dieser Analyse lassen auf ein subtropisch-feuchtes Klima schlieRen. Die palynologischen Resultate werden mit den Makrofloren-Assoziationen von Rio Rubielos sowie mit den palynologischen Daten des unteren und mittleren Miozans der westlichen mediterranen Gebiete und der Iberischen Halbinsel verglichen.

1. Introduction Little paleoecological information exists on the terrestrial vegetation present in the eastern Iberian Peninsula during the Early Miocene (BESSEDIK 1981, 1984, 1985; BESSEDIK et al. 1984; Suc et al. 1992, 1999). Indeed, the plant life that reigned in this part of the Mediterranean area during this period is almost completely unknown. The existence of the Rubielos de Mora Basin (Teruel Province, eastern Spain) has been known since the early twentieth century; the area contains bituminous shales and was exploited for oil resources (FERN~DEZ-NAVARRO 1914; GAVALA1921). The presence of plant remains in this basin was first recorded by HERNANDEZ-SMELAYO & CINC~JNEGUI (1926), but the study of these began in the late 1980s (FERNANDEZ-MARRON & ALVAREZ-RAMIS 1988). These fossils, which occur in finely laminated sediments deposited in a meromictic lake (ANADON et al. 1988a, 1988b, 1989), are accompanied by a very abundant paleoentomological fauna (PERALVER 1998, 2002) together with some mammalian fossil assemblages that date these Early Miocene materials as Ramblian-Lower Aragonian (MONTOYA et al. 1996). The first pollen studies performed on the Rubielos de Mora Basin began in the last decade and involved the Rio Rubielos outcrop, where fossil insects and plant megaremains occur abundantly (BALTUILLE et al., 1992; ALVAREZ-RAMIS & F E R N ~ E Z - M A R R1994; O N ALCALA1997; ROIRONet al. 1999; Rmro et al. 1999; BARRON& DE SANTISTEBAN 1999). The importance of the Rubielos de Mora Basin to the knowledge of the vegetation of the Early Miocene of the western Mediterranean is documented by these authors. The aim of the present study was: (1) to provide a detailed palynological description of the Early Miocene assemblages for the entire sedimentary succession of the eastern Rubielos de Mora Basin, (2) to reconstruct the paleoenvironmental conditions of the area by studying the changes that occurred in its vegetation, and (3) to compare these results with palaeobotanical data from neighbouring areas.

Early Miocene palynoflora in the east of the Rubielos de Mora Basin

173

Fig. 1. Main structural units in NE Spain and the Neogene fault-related basins. The Rubielos de Mora Basin is located in the SE of the Iberian Ranges (modified from ANADON et al. 1988b).

2. Geological setting The Rubielos de Mora Basin is an Early Miocene half-graben that developed in an extensional context (GUIMERA1990). It is located in the southernmost part of the Linking Zone (SE Iberian Ranges, Teruel Province, Fig. l), which is made up of a Hercynian basement unconformably overlain by a thick Mesozoic and Cenozoic cover (ANADONet al. 1991). Mesozoic layers beneath the basin are synclinally folded and Miocene beds are found in the core of the fold. The basin, which shows structural asymmetry, is bound ENE-WSW to NE-SW by striking faults, and in the south it shows a steep fault-bound margin related to the ENE-WSW fault (ANADON et al. 1989).

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m

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Lower Miocene fluvial and fluviolacustrine facies -. - .- .- Unconfonnity

m

upper Miocene [.-..-_A vj Quaternary

Lower Miocene terrigenous and carbonate lacustrine facies Normal fault

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Lower Miocene anoxic-carbonate lacustrine facies

Fig. 2. Geological map of the Rubielos de Mora Basin based on B m 6 &~ DE SANTISTEBAN (1999). 1. Aguarroya outcrop. 2. Alto de Ballester outcrop. 3. Rio Rubielos outcrop.

The Miocene basin sequence is made up of over 800 meter of terrigenous and minor carbonate deposits of alluvial and lacustrine origin which cover some 15 km2. These deposits were attributed firstly by MOISSENET & GAUTIER (1971), CRUSAFONT et al. (1966) and GODOY& A N A D ~(1986) N to the Lower-Middle Miocene. More recently, a micromammal assemblage allowed MONTOYA et al. (1996) to date the laminated levels of the Alto de Ballester outcrop as Ramblian. The stratigraphy of the basin was established by studying the laterally extensive and well developed outcrops in the eastern and western parts of the basin. A N A D ~etNal. (1988a, 1988b, 1989, 1991,2003) described three main depositional units, while B A R R ~& N DE SANTISTEBAN (1999) defined three different associations of depositional facies (Fig. 2). Both studies


175

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Unit C

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Earlv Miocene ~alvnoflorain the east of the Rubielos de Mora Basin

177

record successive stages of basin infilling. Nevertheless, the units are only partly equivalent in their depositional facies. The Rubielos de Mora Basin shows a clear eastern zone where a lacustrine carbonate and lignite depocentre developed, and a western zone with a predominance of subaerial alluvial red beds interbedded with minor lacustrine carbonate deposits lacking lignites (ANADONet al. 1991). The carbonate and lignitiferous sediments of the eastern zone show a more continuous succession of palynological assemblages than those of the western zone. The present study therefore focuses on the outcrops of Aguarroya, Alto de Ballester and Rio Rubielos, all of which are located in the eastern part of the basin (Fig. 2). The Aguasroya outcrop is located in the northeast (see Fig. 2). The stratigraphic succession of this outcrop (Fig. 3) is characterized by grey clay, mar1 and sandstone deposits which alternate or interleave carbonate packets and small coal seams (ANADON et al. 1988b). The sediments of this outcrop may be related to the Lower and Middle units of ANADONet al. (1988b, 1991) since they are dominated largely by sliallow lacustrine sediments. The levels from the base and the top of the succession belong to the fluvial and fluvio-lacustrine facies association of BARRON& DE SANTISTEBAN (1999). Materials from the terrigenous and carbonate lacustrine facies association can be seen in the middle of the succession (Fig. 3). Although no biostratigraphically significant fossils have been found in the Aguarroya outcrop, a possible Ramblian age may be postulated for its sediments on the basis of micromammal fossils present above these deposits. MONT~YA et al. (1996) determined the stratigsaphy of the Alto de Ballester succession using data from the Alto de Ballester and Rio Rubielos outcrops (Fig. 4). This succession is located next to the village of Rubielos de Mora in the southeast of the basin (Fig. 2), and may be related to the laminated mudstones of the Upper Unit (C1) of ANALIONet al. (1988a). Its sediments show the establishment of a permanently stratified lake with anoxic bottom-water conditions (BARR~N & DE SANTISTEBAN 1999). From the bottom to the top, three units can be distinguished in this succession (PERALVER et al. 1999): The lower unit (A) is formed by breccias and coarse grained conglomerates and grey clays. The top of this unit is formed by clays, shales and sandstones with mud cracks. The micromammal site of the Alto de Ballester outcrop is located within the grey clays. A Ramblian age was indicated from a micromammal assemblage and is characterized by the presence of Pseudotheridomys feifari ALVAREZ-SIERRA & DAMS and the lack of modern cricetida (MONTOYA et al. 1996). The sediments of Unit A form part of the terrigenous and carbonate lacustrine facies association and are related to a shallow lake. The middle unit (B) is formed by 80 m of grey and ochre clays which include two olistolitic levels of Cretaceous carbonates and sandstones.

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Finally, the upper unit (C) is a 16 m thick interval mainly formed by marls, including layers of black shales. The well known Rio Rubielos paleontological site, where insect and plant fossils have been found (PERALVER 1998, 2002; B A R R ~& N D ~ ~ G U2001), E Z belongs to this last unit. A RamblianLower Aragonian age is postulated in the present work for the sediments of the Rio Rubielos outcrop due to the lack of biostratigraphically significant fossils above the sediments of the Alto de Ballester outcrop. The sediments of unit C correspond to the anoxic-carbonate lacustrine facies association of BARRON& DE SANTISTEBAN (1999). These sediments were deposited in a deep-water meromictic lake characterized a permanently anoxic bottomwater conditions.

3. Material and methods Sixteen sediment samples were collected from the Aguarroya, Alto de Ballester and Rio Rubielos outcrops for the examination of their pollen contents (Figs. 3-4). All samples were prepared in accordance with the method of PHIPPS& PLAYFORD (1984) using various acids at high temperatures (HCI, HF, HN03). Slides were prepared by mounting the palynomorphs in glycerine jelly. Twelve samples with 500-1,000 miospores were finally examined (samples Agl, Aglo, AB1, and AB2 had no palynological contents). As a total, we have identified 44,393 miospores. In this study, we applied the botanical taxonomy to identify the broad spectrum of miospores. This allows us to infer the palaeovegetation, the palaeoecology and palaeoclimate and to compare the results to present-day floras and vegetations (Suc & BESSEDIK 1981; SUC 1987). It has already been applied successfully for the Miocene and the Pliocene (Suc et al. 1992, 1999; JIM~NEZ-MORENO et al. 2005) knowing that all the living plant genera have been represented since the Eocene (MULLERl98 l). The identifications are primarily on genus level because of the high variability in miospore morphology and the possible presence of extinct species (Suc 1987). Miospores that exhibit morphologies typical for several genera were identified to family level only (i.e. the inaperturate pollen grains with a single prominent papilla were identified as Taxodiaceae or inaperturate pollen grains with papilla obscured or absent were classified as Taxodiaceae-Cupressaceae because these features can be observed in both families, see Moom et al. 1991: 96, pl. 9). Pollen diagrams were constructed using Tilia and Tilia Graph 2.0.b4 softwares (Illinois State Museum, Springfield, USA) to determine the quantitative variation of taxa or groups of taxa over the succession (Figs. 5, 11). Particularly, Pinus and Group D were excluded from the total pollen sum


179

Fig. 5. Pollen diagram for the Lower Miocene of the eastern Rubielos de Mora Basin.

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due to the over-representation present in samples such as Ag4, Ag6, Ag7, Ag9, AB1, and ABlb. In addition to the construction of pollen diagrams, the obtained data were subjected to multivariate statistical analysis. Cluster analysis is an explorative technique for identifying groups and subgroups and is based on a given distance or similarity measures. It has been successfully applied in data exploration and visualization and was shown to be particularly useful for palaeoecological studies (HAMMER & HARPER2006). Cluster analysis may reveal potential hidden groups structures that give an approximation of ecological similarities of the samples or taxa (BRUCH& MOSBRUGGER 2002). The outcome of cluster analysis is a two-dimensional dendrogram where clusters may be interpreted as representation of communities, biofacics or fauna1 provinces (SHI 1993). This representation allows an easy and visual understanding and classification of the data. The distance and ordination of the levels in the dendrogram (Q-mode analysis) is not based on a stratigraphical order but on the CO-variationof the miospore abundance (taxa). Otherwise, the situation of the taxa (R-mode analysis) in the same cluster means a similar distribution in the profile. Cluster analysis methods have previously been used in palynology to classify environmental information (BOULTER & HUBBARD 1982; HUBBARD & BOULTER1983, 1997; BRUCH& MOSBRUGGER 2002). A matrix was designed according to RIVAS-CARBALLO et al. (1994), choosing the most representative taxa (the quantitatively most important) that showed recognisable ecological characteristics. Taxa with similar ecological requirements were included under the generic designations of "Pteridophyta" (spores of ferns of families Polypodiaceae and Schizaeaceae), "hydro-hygrophytic plants" (Potamogeton, Sparganium, Nymphaeaceae, Cyperaceae) and "riparian trees and shrubs" (Alnus, Salix, Myrica, Liquidambac Pterocarya, Nyssa, Sambucus, Clethraceae-Cyrillaceae). The Ulmus-Zelkova pollen type was not included in "riparian trees and shrubs" since nowadays the genus Ulmus is often a member of riparian communities and also lives in places with high moisture contents such as fluvial plains and mixed mesophytic forests (FOWELLS1965; WOLFE1979; BL,ANCO CASTROet al. 2005). In addition, the genus Zelkova is now found in the humid, nonriparian, mixed mesophytic forests of northern Anatolia, western Iran and East Asia (WOLFE 1979; QUEZEL et al. 1980; ASSADOLLAHI et al. 1982). R-mode and Q-mode hierarchical cluster analysis was performed using Ward's method (WARD1963) as an amalgamation rule. The Ward's method is an efficient tool that employs the analysis of variance to evaluate distances between clusters. To establish the initial distance matrix, the Pearson product-moment correlation coefficient (BOULTER& HUBBARD1982; HUBBARD & BOULTER 1983, 1997; WILLARD et al. 2001) and the Spearman

Earlv Miocene walvnoflora in the east of the Rubielos de Mora Basin

181

Rank Order Correlation Coefficient (KOVACH l 988, 1989; RIVAS-CARBALLO et al. 1994) are commonly used. Although these coefficients are robust, there is always the chance that several correlations will introduce background noise. Therefore, the Chi-Squared Distance Matrix was used, which avoids this problem. Thus, two taxa are closer in a cluster if their frequencies change proportionally from one sample to another. All calculations were performed using PC-ORD T4.0 software (MjM Software, Gleneden Beach, Oregon, U.S.A.). The change in climate was determined using the coexistence approach (MOSBRUGGER & UTESCHER 1997) employing the dates provided by the 12 assemblages under consideration. This involved the use of the ClimStat software and the PaleoJora database, which contains the nearest living relatives of more than 3,500 Tertiary plant taxa, together with their climatic requirements (derived from meteorological station records located within their areas of distribution). The coexistence approach does not use the relative abundance of fossil taxa as palaeoclimate proxy, and only uses the presence of fossil taxa in a fossil flora. The relative abundance is not considered by this method because of the potential taphonomic bias (MOSBRUGGER & UTESCHER, op. cit.). All 12 palynological assemblages were analysed in this way. In order to calculate the coexistence intervals, this method determines the climatic interval for every taxon identified at specifies, generic or even familiy level (e.g. see BRUCH1998; FIGUEIRAL et al. 1999; ALCALDE-OLIVARES et al. 2004). The climatic variables taken into consideration include: mean annual temperature ("C), mean temperature of the coldest month ('C), mean temperature of the warmest month ("C), and mean annual precipitation (mm). Several taxa were excluded from this analysis. For instance, Sciadopitys and Cathaya were excluded because nowadays both are represented by only a single species with very small distributions (PAGE1990; Lru et al. 1997). In Tertiary times, these two genera were represented by a larger number of species and had a broad distribution across the northern hemisphere. 4. Results 4.1. Pollen analysis

A total of 12 spore and 74 pollen taxa were identified (Table 1). Generally, the miospores studied were in an excellent state of preservation. The percentage variation of the major floral components is shown in the pollen diagram in Fig. 5. Conifer pollen made up over 80% of the pollen content in all samples. A group formed by the genera Carya, Engelhardia, Myrica, Alnus (Fig. 6 I), Rumex (Fig. 6E), Salix, Ilex, Acer (Fig. 6H) and Potamoge-

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TabIe 1. List of spores and pollen grains recorded in the Lower Miocene of the eastern Rubielos de Mora Basin, indicating the levels where they were found. Primary miospore dispersion mechanism: winds (W), insects (I), waters (H).

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183

ton, the pollen type Sparganium, and the families Sapotaceae, Oleaceae, Liliaceae and Poaceae, were found in almost every sample (Table 1). The APNAP ratio showed arboreal pollen to be clearly dominant, with values of > 80 % for every level studied (Fig. 5). The spores of ferns such as Leiotriletes, Schizaeaceae and Laevigatosporites (Fig. 6A) always made up < 5 % of the pollen content (except in level ABlb). The fluvial and fluvio-lacustrine facies associations showed palynological contents in two levels of the Aguarroya outcrop @g2-Ag3) (Fig. 3). These were characterised by the predominance of Pinus, the presence of Taxodiaceae-Cupressaceae,Picea, Carya, Engelhardia, Betula (Fig. 6B), riparian and hydro-hygrophytic taxa, and the rare presence of Distylium type and Ligustrum (Fig. 5; Table 1). Terrigenous and carbonate lacustrine facies association occur in the Aguarroya outcrop above the fluvial and fluvio-lacustrine facies. Six consecutive levels showed palynological contents (Ag4-Agg) (Fig. 3). Compared to the lower levels, Ag4 showed a greater content of Cathaya, less Picea and hydro-hygrophytic taxa, and contained Nyctaginaceae (Fig. 5, Table 1). Level Ag5 was characterized by greater amounts of Cauya, Poaceae and hydro-hygrophytic taxa, a smaller presence of Cathaya, Picea and Engelhardia, and the absence of Betula and Oleaceae. The very reduced presence of Riccia, Sphagnum, Cnmarozonosporites, Ulmus-Zelkova, deciduous Quercus, Arecaceae and Juncus was remarkable (Fig. 5; Table 1). The levels above Ag5 were characterized by greater amounts of Taxodiaceae-cupressaceae, Taxodiaceae, Cathaya, Engelhardia and Poaceae, the presence of Polypodium type, Lonicera, Olea, Parthenocissus, Scabiosa, Viburnum and Cyperaceae, reduced amounts of Cay a , and the lack of deciduous Quercus (Fig. 5; Table l). At level Agg, bisaccate pollen grains of Pinus were in great abundance. After a 150 m section containing fluvial, fluvio-lacustrine, terrigenous and carbonate materials (BARR~N& DE SANTISTEBAN 1999), the Alto de Ballester outcrop showed two levels (AB1, and ABlb) with different palynological assemblages (Fig. 5). Compared to the Aguarroya levels, these contained more Ulmus-Zelkova, Carya, deciduous Quercus, Rosaceae, Oleaceae and Pteridophyta, fewer Cathaya, riparian and hydro-hygrophytic taxa, a lack of Betula and Arecaceae (Fig. 5), and a scanty presence of Lycopodium, Bifacialisporites, Polypodiaceoisporites, hteraceae liguliflorae, Plantago and Fabaceae (Table 1). The Rio Rubielos outcrop represents an anoxic-carbonate lacustrine facies, 80 m above the Alto de Ballester outcrop (Fig. 4). The two palynologically productive levels RR1 and RR2 provide fossil plant megaremains and arthropods (MONTOYA et al. 1996; PERALVER1998, 2002; BARRON& DI~GUEZ 2001; POSTIGOet al. 2003). Compared to the Alto de Ballester

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Fig. 6 (Legend see p. 185)


185

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Fig. 7. Dendrogram of the Q-mode cluster analysis using the Ward's method and the Chi-Squared distance matrix for samples.

levels, these contained greater amounts of Taxodiaceae-Cupressaceae, Taxodiaceae and Rosaceae, reduced amounts of Pinus, Cathaya, Picea, Ulmus-Zelkova, Carya and deciduous Quercus (Fig. 5), and contained Bombax (Fig. 6K), Euphorbia, Rhamnus and Sambucus (Fig. 6L and Table 1).

Fig. 6. A - Laevigatosporites, level Ag7. B - Betula, level Ag6. C - Aralia, level Ag9. D - Ericaceae, level Ags. E - Rumex, level Ag6. F - Amaranthaceae-chenopodiaceae, level RR;?. G - Arceuthobium, level RRl. H - Acer, level Ag6. I - Alnus, level Ag7. J - Armeria, level Ag9. K - Bombax, level R . 1 . L - Sambucus, level RRl. All micro-photographs X 1250.

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Group A Pteridophyta

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Fig. 8. Dendrogram of the K-mode cluster analysis using the Ward's method and the

Chi-Squared distance matrix for taxa.

4.2. Cluster analysis

Two cluster diagrams were produced, showing the dendrograms for both the levels and the miospore taxa identified (Figs. 7-8). Analysis of the levels revealed 4 groups (1-4), while analysis of the miospore taxa resulted in five groups (A-E). Groups l and 2 (Fig. 7) were formed by levels from the terrigenous and carbonate lacustrine facies association. Group 1 levels showed a larger deep lacustrine influence compared to Group 2. Group 3


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Pig. 9. Data matrix displayed between the dendrograms for levels and taxa. The levels and group of levels are arranged stratigraphicallyto facilitate interpretation.

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Fig. 10. Reduced data matrix calculated from the main clusters of the dendrograms in Figs. 7 and 8.

included levels from the fluvial and fluvio-lacustrine facies association, and Group 4 was formed by samples from the anoxic-carbonate lacustrine facies association. Group A (Fig. 8) contained only spores of Pteridophyta, Group B was characterized by taxa typical of mesophytic communities, Group C contained taxa with large water requirements plus Picea, Group D reflected mixed coniferous forest communities, and Group E was formed by taxa that required higher temperatures. A data matrix for the two dendrograms was produced (Fig. 9). A second matrix was then calculated using the relative frequencies for each group of taxa in each group of levels (Fig. 10). It was therefore possible to determine the percentage for each group of taxa in every level. The aim was to determine which groups of taxa differentiated among group levels. Group D was predominant in all levels (Fig. 9) although more so in Group 2 and 4 (Fig. 10). Group A, which contained only Pteridophyte spores, showed a sporadic presence in all sample groups (Fig. 9) except for Group l (Fig. 10). Group B was relatively well represented in Group 1and 4 (Figs. 9-10). Group C was unimportant in Group 2, 3 and 4 (Fig. 9) and mainly characterized Group 3 (Fig. 10). Group E distinguished Group 4 from the rest (Fig. 10).


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5. Discussion 5.1. Palaeoecological features of the Rubielos de Mora Basin

The presence and number of different miospores in a fossil assemblage reflects the autecology of the plants that controls them, the kind of plant communities to which these belonged, their dispersal mechanisms, and the characteristics of the sedimentary environment. The pollen diagram in Fig. 5 shows a predominance of pollen grains of arboreal plants, which suggests there were forests in the basin during the Early Miocene. The floral composition of these forests changed through time, but they were characterized by conifers (mainly those of the genus Pinus and the families Taxodiaceae and Cupressaceae) and mesophytic taxa such as Cay a , Engelhardia and Ulmaceae. These forest had a diverse undergrowth including shrubs such as Aralia (Fig. 6C), Buxus, Distylium, Ericaceae (Fig. 6D), Ilex, Ligustrum, Mahonia, Rhamnus, Sapotaceae, Viburnum, grasses and vascular cryptogamma such as Lycopodium, Selaginella, Polypodiaceae, Schizaeaceae, Amaranthaceae-Chenopodiaceae (Fig. 6F), Apiaceae, Armeria (Fig. 6 J ) , Asteraceae, Convolvulus, D@sacaceae, Euphorbia, Fabaceae, Lamiaceae, Linum, Rumex (Fig. 6E), Thymelaeaceae, Valeriana, Liliaceae and Poaceae. Climbers such as Lonicera and Parthenocissus and epiphytes such as Arceuthobium (Fig. 6G) were also present. The palynological assemblages suggest a mountainous environment, mainly indicated by the conspicuous amounts of Picea. Nowadays, this genus lives at low altitude and at high latitudes (FARJON1990). The genus Abies, which today lives in mountainous parts of the Mediterranean (BARBERO & QUEZEL1975), was not foun4 although other authors have reported its presence in the Lower Miocene of the Rubielos de Mora Basin (ALCALA1997; ROIRONet al. 1999). With regard to dispersal (Table l), the majority of the miospores identified belong to anemophilous plants (43,493). Smaller numbers of miospores of entomophilous (623), mixed anemophilous and entomophilous (276), and hydrophilous (1) plants were also present. This overrepresentation of anemophilous miospores can be explained by the very high pollen production of taxa such as Pinus, Picea, C a y a or Poaceae. The majority of the entomophilous taxa identified corresponds to grasses or shrubs with smaller pollen production rates and more reduced areas of dispersion. A single spore of Riccia, the only hydrophilous taxon identified in eastern Rubielos de Mora Basin, has been detected in sample Ag5. The cluster analysis provides additional insight into the succession of plant life in the basin during the Early Miocene. Group D was overrepresented in all levels (Fig. 11) in a relatively constant manner (Fig. 9). This suggests that the appearance of these plants at different levels is inde-

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Fig. 11. Pollen diagram taking into account the ecological groups obtained after cluster analysis.

Earlv Miocene walvnoflora in the east of the Rubielos de Mora Basin

191

pendent of the environmental conditions. Because of their pollen dispersal efficiency, the taxa of Group D may therefore be considered to be a regional or allochthonous component appearing alongside the local flora. The basin may have been surrounded by mixed coniferous forests, mainly formed by Pinus, Taxodiaceae and Cupressaceae. It is impossible to distinguish the genera of conifers that produced the pollen type Taxodiaceae-Cupressaceae. However, the megafloral record indicates the existence of two genera of Taxodiaceae and three of Cupressaceae in the basin (BARRON & DIEGUEZ 2001). All pollen produced by the Cupressaceae that lived in the region integrate within Group D whereas those of Taxodiaceae had a fewer representation within this group. The family Taxodiaceae had a wider representation in the plant communities of the basin as indicated by the number of pollen in Group E. The lowermost levels of the Aguarroya outcrop (Group 3) were deposited in a wide flood plain with small ephemeral lakes (PERALVER et al. 1999). Group C plants were the most important in these levels. This environment had enough shallow-water and wetlands to allow the growth of hydro-hygrophytic herbaceous plants such as Potamogeton and Sparganium. In addition, groves of Alnus, Myrica, Salix and possibly Betula covered the riparian and swampy areas. Surprisingly Picea appears in Group 3. This may bc due to the abundance and the dispersal capabilities of its pollen by wind and fluvial transport. A similar situation has been recorded for the Early Pliocene of the Languedoc (Suc & DR~VALIARI 1991). In addition, a female cone of t h s genus has been found in the Rio Rubielos outcrop (BARRON& DIEGUEZ 2001) which must have been transported by water, confirming that Picea was a native of the basin. In the Early Miocene, the non-riparian mesophytic communities (Group B) were characterized by Carya and Engelhardia. The extant representatives of the genus Carya are found in the mesophytic forests of North America and East Asia (in subtropical and tempcrate regions with high rainfall, FOWELLS 1965). Engelhardia now inhabits tropical regions. The latter genus was widespread throughout Eurasia during Tertiary times, growing in mixed mesophytic forests (BRUCH& MOSBRUGGER 2002). Compared to the oldest levels of the Aguarroya outcrop, the youngest (Group 2) showed fewer hydro-hygrophytic and riparian taxa (Group C) and fewer Carya (included in Group B, Figs. 5 , l l ) . The spread of shallow carbonate lacustrine sedimentation in the eastern basin areas which coincide with Group 2, might be in relation with an area1 shrinkage of the terminal alluvial zones andlor with a relative rising of the lacustrine water level (ANADON et al. 1988b). This could be related to the occurrence of a progressive reduction of the wetlands. So, the marginal lacustrine zones were mainly colonized by

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arboreal vegetation, as its megaremains suggest (BARRON& DIBGUEZ2001). These new conditions with large extensions of shady places could not support prominent communities of heliophytic plants such as Sparganium. The conspicuous increase of Cathaya, Taxodiaceae and Cupressaceae in Group 2 is coincident with the remarkable reduction in Picea (Fig. 5), probably due to its replacement by other conifers. The poor representation of hydro-hygrophytic and riparian taxa (Group C ) in samples from the Alto de Ballester and Rio Rubielos outcrops (Groups 1 and 4; Fig. 11) may be related to the presence of a permanent lake whose existence has been inferred from sedimentological data (MONTOYA et al. 1996).The studied samples were collected from sediments in open lacustrine areas. Their assemblages mainly included pollen grains from non-riparian anemophilous trees. The palynological assemblages of the sediments of the latter outcrops show a taphonomical bias probably caused by the "Neves effect" - a differential distribution of palynomorphs in a paralic or limnic basin depending on their distance to the shore (CHALONER & MUIR 1968). Thus, palynomorphs of riparian or wetland plants mainly accumulated near the shore, whereas those of plants living in more distant areas were deposited offshore in larger amounts. The mesophytic and thermal groups (Groups B and E respectively), mainly represented by non-riparian anemophilous taxa, were consistently predominant during the presence of a meromictic lake (Groups l and 4; Fig. l l). Mesophytic (Group B) and thermal taxa (Group E) may have alternated depending on environmental but not taphonomical factors. Pteridophyta (Group A ) occurred in low numbers over the succession, but were most abundant in periods when mesophytic taxa reigned. Ferns could have grown as part of the undergrowth of these communities, as suggested by the close position in the cluster analysis (Fig. 8). The high percentage of anemophilous trees shown by the assemblages from the Alto de Ballester and Rio Rubielos outcrops suggests that the pollen was deposited in offshore sediments. This is consistent with the existence of riparian and hydro-hygrophytic plant communities, as suggested by megaremains (BARRON& DIEGUEZ 2001). 5.2. Climatic analysis

The calculated coexistence interval suggests a mean annual temperature of 15.6-18.6 "C for the Early Miocene period (Fig. 12). This is higher than the current mean annual temperature of 13.8 "C reported by the Instituto Nacional de Metereologia. The mean temperature of the warmest month was between 26.5 to 27.6 "C (Fig. 12), which is also higher than present-day temperatures. The interval obtained for the mean temperature of the coldest


193

Mean Annual Temperature

I

I

l

1

12 Levels I\;2 A& ~ $ A& 4

A& A& ~ $ A& 8

AB,~ A B < ~ RR ~ ,R ~

14 12

Mean temperature of the coldest month

'C l 0 8 6 4 '

Levels

'c

I

I\;2

I\;3

A&

~

$

-

24

22

~ 5 $ ~6 $ A& 7 ~ 4 AB,* 9 A B ~ ~ R RRRZ ,

Mean temperature

-

-

- of the warmest month

1800 1600 1400

mm 1000 "0°

1

Mean annual precipitation

800

0

Levels

l 1\42

A&

~

$

4A&

~ b I\b7 s A& A& A&. AB..RR~ R&'

Fig. 12. Results of the coexistence approach analyses for each level studied.

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month revealed a range from 4.9 to 13.2 "C (Fig. 12). This could be due to the fact that most of the taxa used to determine this interval such as Picea, Betula and Salix, now live in temperate climates and have a wide distribution in the northern hemisphere. The lowest values were always determined by Engelhardia. Accordingly, periods of frost seem to have been very short or even non-existent. The current mean temperature of the coldest month is lower (l.S°C); days with temperatures below 0 "C usually occur only in winter. Finally, the mean annual precipitation is calculated to have ranged between 1,200 and 1,390 mm (Fig. 12), although great variations may have occurred in some years. All calculated intervals are higher than the current mean annual precipitation rates (533 mm). If the paleoclimatological dates obtained from the palynoflora of the Rubielos de Mora Basin are compared to the classification of present-day forest climates (based on those of Eastern Asia; WOLFE1979), a subtropical and particularly humid climate may be inferred for this region during the Early Miocene. 5.3. Comparison of the results obtained in megaflora and pollen analyses

Previous studies from the Rio Rubielos outcrop (level RR1, Fig. 4) recorded a megafloral assemblage (BARR~N & DIEGUEZ2001; POSTIGO et al. 2003). Some 142 remains were studied, and mainly contained leaves of dicot plants and winged seeds and fruits (Table 2). The indications of FERGUSON (1985) and BURNHAM (1989), the very good preservation of the leaf remains, and the lack of over-representation of leaves of riparian taxa support the following conclusions: (i) the importance of wind dispersal, (ii) the lack of degradation by micro-organisms (due to the anoxic nature of the bottom waters of the lake), and (iii) the deposition of sediments in an open, offshore location. All recorded megafloral assemblages from the Rubielos de Mora Basin constitute a phylocoenosis (BARRON& DIEGUEZ2001). The same occurs in the assemblage from the level RR1. Here, the leaves of dicotyledonous plants were the predominant fossil remains (47.18 %). The best represented families were Lauraceae, Ulmaceae, Salicaceae, Rosaceae and Aceraceae (Table 2). Secondly, remains of conifers were conspicuous (needles, seeds and cones, 31.74 %), with the genus Pinus as the most abundant representative (19.71 %, Table 2). The abundance of Pinus in the phylocoenosis, the occurrence of female and male cones, and the predominance within the pollen record, support the existence of a pine forests in the basin. This genus is also well-represented but not dominant in all studied plant assemblages.


195

Table 2. List of plant megaremains collected from the Rio Rubielos outcrop (according to BARRON & DI&GUEZ 2001 and POSTIGO et al. 2003).

Species Pteridophytes Hypolepidaceae Gymnosperms Taxodiaceae Cupressaceae Pinaceae

Pteridium oeningense (Unger) Hantke

%

1

0.70

1 5

0.70 3.52

4

2.82

1 8 1 6

0.70 5.60 0.70 4.22

5

3.52

142

100

Cryptomeria sp. (female cone) Sequoia abietina (Brongniatt) Knobloch Juniperus sp. (branchlets) gen. et sp. indet. (branchlets) Picea sp. (female cone) Pinus sp. (needles) Pinus sp. (winged seeds) Pinus sp. (male cones) Pinus sp. (female cone)

Angiosperms (Dicotyledones) Aceraceae Acer vindobonensis (Ettingshausen) Berger Acer sp. cf. haselbachensis Walther Acer sp. (winged fruits) gen. et sp. indet. (seeds) Asteraceae Alnus gaudinii (Heer) Knobloch et KvaEek Betulaceae Alnus sp. (female inflorescence) gen. et sp. indet. (leaflet) Caesalpiniaceae Juglandaceae Pterocarya paradisiaca (Unger) lljinskaja Myricaceae Myrica vindobonensis (Ettingshausen) Heer Dahnogene polymorpha (A. Braun) Ettingshausen Lauraceae Neolitsea paleosericeaTakhtajan Laurophyllum sp. Loranthus obovatifolia Givulescu et Olos Loranthaceae Rosaceae Sorbus sp. (composite leaves) gen. et sp. indet. (leaflet) Salicaceae Populus populina (Brongniart) Knobloch Salix lavateri A. Braun sensu Hantke Ulmaceae Celtis begonioides Goeppett Ulmus sp. (leaves) Tremophyllum tenerrimum (Weber) Ruffle Zelkova zelkovifolia (Unger) Biriek et Kotlaba lncertae sedis (leaves) lncertae sedis (flowers and inflorescences) Angiosperms (Monocotyledones) gen. et sp. indet. (flower) Cyperaceae gen. et sp. indet. (flower) Poaceae Potamogetonaceae Potamogeton geniculatum A. Braun Typha latissima A. Braun in Heer Typhaceae lncertae sedis (leaves) Total megaremains

Specimens

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The results of the pollen analysis of the Rio Rubielos outcrop are consistent with a large presence of Pinus, but are only partially consistent with some aspects of the megafossil evidence. Conspicuous amounts of Taxodiaceae-Cupressaceae and Taxodiaceae pollen were present throughout the stratigraphic succession (Fig. 5), although megaremains were rare (Cupressaceae 7.04 % and Taxodiaceae 4.22 %). The pollen of dicots was well represented but not predominant (Fig. 5), with several taxa such as Engelhardia being well represented in terms of pollen but not in terms of megaremains. Similarly, taxa such as members of the Lauraceae and Populus, whose miospores do not fossilize well, were only represented as megaremains (see Tables 1 and 2). The predominance of angiosperm leaves and samaroid seeds and fruits provide information on the energy of the waters in the Lower Miocene lake. Low-energy lacustrine sediments primarily contain angiosperms leaves and samaroid seeds and fruits. High-energy sediments contain different plant organs, wood, heavy seeds and fruits (SPICER& WOLFE1987). Pine needles and female cones are usually abundant in high-energy environments but winged seeds are generally poorly represented. As mentioned above, in the Rio Rubielos outcrop the leaves of dicots are the most abundant remains, including winged seeds and fruits of Pinus, Acer and Asteraceae. To date, no wood nor heavy diaspores have been found, although three female cones of conifers have been collected (Table 2). In general, the megafloral assemblage of the Rio Rubielos outcrop indicates the lake to have had low-energy water. However, this does not mean that forests of angiosperms characterized the vegetation of the basin; it simply means that their leaves were not destroyed when they were deposited in the lake. The occurrence of female cones of conifers could also indicate that the growing area of these plants was not distant from the lake emphasizing the importance of conifers in the vegetation of the basin. The conspicuous representation in the pollen record of taxa such as Engelhardia, which do not appear in the megafloral assemblage, indicates them to have had an extra-basinal or regional origin. This agrees with the results of the statistical analysis (Fig. 9). The physiognomie study of the dicot leaves indicated the presence of mixed broad-leaved evergreen and coniferous forests (sensu WOLFE1979) that developed in a subtropical or warm temperate, frost-free climate. This agrees with the intervals obtained for the mean annual temperature and the mean temperature of the coldest month (Fig. 12). This climate allowed notophyllous evergreen elements such as Lauraceae, Myricaceae and Tremophyllum tenerrimum (WEBER)RCJFFLEto exist. The presence of Lauraceae, and the record for the Taxodiaceae (Cryplomeria sp., Sequoia abietina (BRONGNIART) KNOBLOCH), also indicate a very damp, rainy or misty environment.

:


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5.4 Comparison of the studied pollen with that of neighbouring areas

After the study of just two samples, ROIRONet al. (1999) related the pollen flora of the basin to the Lower Miocene French outcrops of Thkzan-16sBCziers and Lespignan. Unlike the Rubielos de Mora samples, these French outcrops show larger amounts of Engelhardia, as well as a remarkable presence of other taxa that are scarce or absent in the Rubielos de Mora Basin, such as Celastraceae, Olea, Platycaya and Euphorbiaceae (BESSEDIK 1985). The presence of Avicennia in these outcrops indicates the proximity of coastal areas. The pollen flora of the Lower Miocene (Aquitanian-Lowermost Bwdigalian) of the Vence Basin (French-Italian Maritime Alps, ZHENG1990) is the most similar to that of the Rubielos de Mora Basin. The assemblages at Vence include very large amounts of extra-basinal pollen grains, probably transported from the Corsican mountains to the coastal areas. These pollen assemblages are numerically dominated by conifers (Pinus, Cathaya, Taxodiaceae) and mesophytic taxa such as Engelhardia, Cay a , Platycaya, Myrica, Ulmus-Zelkova, Carpinus,Alnus, Quercus and Salix. Pollen analyses of other Early and Middle Miocene locations in the Iberian Peninsula suggest their vegetation to have been different to that of Rubielos de Mora: 1 - In the Bwdigalian-Langhian of Catalonia, an open, semi-arid vegetation mainly composed of herbs and thermal taxa was detected after the study of three sections of the VallBs-PenedBs region (La fierussa, Sant Pau d'Ordal and Vilovi, BESSEDIK 1984, 1985). The presence of Avicennia indicates the existence of mangroves in the area.

,

2 - The pollen assemblages of the Tagus Basin (Portugal) usually show high percentages of bisaccate coniferous pollen grains and thermophilic taxa such as Engelhardia, Myrica, Bombax and Sapotaceae (PAIS 1981, 1986). This vegetation is very different from the Rubielos de Mora Basin, especially in terms of the great abundance of Quercus and Castanea. Similarly, the high diversity of vascular cryptogam spores, the scarcity of mesophylic taxa such as Alnus, Carya, Ulmus-Zelkova, and the lack of microthermal elements, indicates a rather wet climated and much warmer environmental conditions than in the Rubielos de Mora Basin.

3 - In the As Pontes Basin (Galicia, Northwestern Spain) both subtropical swampy vegetation and mesophytic and coniferous forests have been inferred (MEDUS1965). The abundance of Simarubaceae, Rhus, Carpinus/ Corylus, Sparganiaceae-Typhaceae, Cyrillaceae and Engelhardia indicates a climate very different to that of the Rubielos de Mora Basin.

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4 - The presence of Picea, Alnus and Betula in the Xinzo de Limia Basin (Galicia, Northwestern Spain, ALCALA et al. 1996) is similar to that for the Aguarroya outcrop. However, high percentages of Cedrus, Abies, Ostrya, Carpinus and Poaceae indicate the area's vegetation to have been different.

5 - The pollen flora of the Duero Basin indicates the existence of a steppe vegetation (RIVAS-CARBALLO 1991a, 1991b; WAS-CARBALLO et al. 1994), except for the border areas where woods associated with grasses appear to have developed (VALLEet al. 1995). The Belorado area (the northeastern border of the Duero Basin) has some similarities with the Rubielos de Mora Basin (i.e., a high percentage of Picea, Carya, Alnus, Quercus, Taxodiaceae and Oleaceae). These similarities are certainly related to the proximity of mountains and more humid conditions.

6. Conclusions The 12 miospore assemblages from the Early Miocene (Ramblian-lower Aragonian) sediments in the east of the Rubielos de Mora Basin indicate that forests were the dominant vegetation at that time. These were home to the families Pinaceae, Cupressaceae and Taxodiaceae, although mesophytic non-riparian and riparian trees were also common. The conspicuous presence of Picea suggests that the Rubielos de Mora Basin was influence by a mountainous environment. The fluvial-influenced sediments of the Aguarroya outcrop, which were deposited in a flood plain with small, ephemeral lakes, showed high percentages of riparian and hydro-hygrophytic pollen taxa. Later, the pollen of riparian and hydro-hygrophytic taxa were gradually less common as a permanent lake became installed. The analysis of the Alto de Ballester outcrop suggests the area was home to pine forests and non-riparian mesophytic communities with ferns in their undergrowth. The Rio Rubielos outcrop, however, showed fewer non-riparian mesophytic communities and forests with thermal taxa. The climate in the Rubielos de Mora Basin during the Early Miocene was subtropical, and warmer than that of today (TMA: 15.6-18.6 "C). Its winters had very short frost periods, and summers were hot. Rain was abundant (1,200- 1,390 mm) and there was no dry season. The pollen and megaflora analyses of the Rio Rubielos outcrop both suggest the presence of plant communities formed by different conifers, plus mesophytic, riparian and aquatic taxa that developed in a damp, warmtemperate to damp subtropical environment. The comparison of the present palynological assemblages with those of other Early and Middle Miocene basins of the Western Mediterranean


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Region and Iberian Peninsula reveals the exclusive nature of the flora of the Rubielos de Mora Basin. This was probably influenced by the mountainous character of the basin, as well as by its geographical location. The Vence Basin (Early Miocene, French-Italian Maritime Alps) and the Belorado area (Middle Miocene, Duero Basin, Central Spain) show the most similar pollen assemblages.

Acknowledgements This work is a contribution to the International Research Programme NECLIME (Neogene Climate Evolution in Eurasia). We wish to thank M. LANGER (Editor) and the three anonymous referees who provided useful criticism and valuable suggestions for the improvement of the manuscript. We also sincerely thank Dr. E. PE~ALVER, Dr. C. DE SANTISTEBAN and Dr. P. MONTOYA (Valbncia University), Dr. C. DIEGUEZ (National Museum of Natural History (CSIC), Madrid), Dr. A. LOPEZ-SAEZ (Instituto de Historia (CSIC), Madrid), Dr. M. J. COMASand C. ALONSO (Department of Palaeontology, Complutense University of Madrid), Dr. A. BRUCH(Senckenberg Research Institute, Frankfurt), Dr. T. UTESCHER (Geological Institute, Bonn), J. CASTRILLO, R. MANCHE~O, R. CANOand H. WIRZfor their help, criticism and kindness.

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Prof. Dr. EDUARDO BARR~N, Museo Geominero, Institute Geologic0 y Minero de Espafia (IGME), Rios~osas,23,28003 Madrid.(Spain); e-mail: e.barr0naijgne.e.s Dr. Lms LASSALETTA, Departamento Tnteruniversitario de Ecologia, Facultad de Ciencias Biolbgicas, Universidad Complutense de Madrid, JosC Antonio Novais, 2, 28040 Madrid (Spain); e-mail: [email protected] Dr. CRISTINAALCALDE-OLIVARES, Escuela TCcnica Superior de Ingenieros de Montes, Ciudad Universitaria sln, Unidad de Bothnica, E.T.S.I. de Montes, 28040 Madrid (Spain); e-mail: 7ed437saiies.e~