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Author's personal copy Review of Palaeobotany and Palynology 162 (2010) 382–402

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Review of Palaeobotany and Palynology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / r ev p a l b o

The Cenozoic vegetation of the Iberian Peninsula: A synthesis Eduardo Barrón a,⁎, Rosario Rivas-Carballo b, José María Postigo-Mijarra c, Cristina Alcalde-Olivares c, Manuel Vieira d, Lígia Castro e, João Pais e, María Valle-Hernández b a

Instituto Geológico y Minero de España (IGME), Ríos Rosas 23, 28003 Madrid, Spain Dpto. de Geología, Área de Paleontología, Facultad de Ciencias, Universidad de Salamanca, Plaza de la Merced, 37008 Salamanca, Spain Dpto. de Silvopascicultura, Unidad de Botánica, Escuela Técnica Superior de Ingenieros de Montes, Universidad Politécnica, Ciudad Universitaria, 28040 Madrid, Spain d Centro de Geologia da Universidade do Porto/Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal e Centro de Investigação em Ciência e Engenharia Geológica, Dpto. de Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal b c

a r t i c l e

i n f o

Article history: Received 18 May 2009 Received in revised form 26 October 2009 Accepted 23 November 2009 Available online 2 December 2009 Keywords: Cenozoic palaeobotany palaeovegetation history palaeoclimatology Iberian Peninsula

a b s t r a c t The aim of this work is to provide a first approach to the evolution of Iberia's vegetation during the Cenozoic (with the exclusion of the Quaternary). The Palaeogene was floristically defined by Palaeotropical elements forming tropical/subtropical rainforests, mangrove swamps, edaphically-mediated laurophyllous forests and leguminous-sclerophyllous communities. During the Miocene, Iberian landscapes were drastically modified due to geographic and climatic changes (mainly cooling and aridification) changes. Open, steppe-like environments developed towards the interior of the peninsula and Arctotertiary elements invaded mountainous and riparian ecosystems, coexisting with or becoming part of evergreen, broadleaved forests of Palaeotropical species. From the Late Miocene onwards these forests suffered changes due to the extinction of taxa, the impact of environmental change on the survivors, and the perturbations caused by the arrival of further Arctotertiary elements. However, several Palaeotropical taxa overcame the environmental and climatic changes of the Miocene and Pliocene to form a part of the modern flora of the Iberian Peninsula. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Currently, the Iberian Peninsula can be said (at least in simple terms) to be formed by two large phytogeographic territories: damp Iberia, with a Eurosiberian nature, dominated by deciduous forests, and dry Iberia, with a Mediterranean nature, where the most successful plants include evergreens and xerophytes (Costa Tenorio et al., 2005). An analysis of the different plant taxa in each of these territories, taking into account their palaeophytogeographic origins in agreement with Mai (1989, 1991), shows that most of the species inhabiting damp Iberia are of Arctotertiary origin, while over large areas of dry Iberia the most dominant plants are Palaeotropical in origin (Barrón and Peyrot, 2006). This situation is the result of the long process of evolution of the Euroasiatic Cenozoic flora, and is the outcome of local geological, geographic and climatic events. From a physiographic point of view, some 40% of the Iberian Peninsula is occupied by Cenozoic basins, the stratigraphic records of deposition being mostly complete and commonly covering the entire Palaeogene to Neogene period (Calvo, 2004). Despite this,

⁎ Corresponding author. Fax: + 34 91 349 58 30. E-mail address: [email protected] (E. Barrón). 0034-6667/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.revpalbo.2009.11.007

they are still to receive exhaustive palaeobotanical examination; the information currently available is therefore fragmentary. Nevertheless, those studies that have been undertaken have been of great interest with respect to the evolution of the flora and vegetation of southwestern Europe, showing a local trend for clearly tropical communities dominated by Palaeotropical elements during the Palaeogene, and for subtropical or warm-temperate communities dominated by a mixture of Arctotertiary and Palaeotropical elements during the Neogene (Postigo-Mijarra et al., 2009). Using the evidence provided by the palaeobotanical record, the aim of the present work is to describe the different plant landscapes that existed in Iberia and their evolution over the last 65 million years.

2. The major paleogeographic and geological features of the Cenozoic in the Iberian Peninsula In the Upper Cretaceous, Iberia behaved as a plate independent from Eurasia and Gondwana that was surrounded by continental sedimentary and transition environments. The relative absence of mountain ranges left the entire territory relatively uniform. During the Late Cretaceous–Lower Eocene interval (70–50 Ma), the only

Author's personal copy E. Barrón et al. / Review of Palaeobotany and Palynology 162 (2010) 382–402

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Fig. 1. Distribution of emerged areas during the late Cretaceous–Lower Eocene interval (modified from López-Martínez, 1989): (a) Areas with no deposits (erosion), (b) continental detritic deposits, (c) non-emerged areas with coastal, external platform and oceanic basin deposits, (d) current coastline. Graphic scale: 100 km.

emergent areas were the Hesperic, Catalonian-Provençal and Ebro Massifs (Fig. 1) (López-Martínez, 1989). The folding of the Pyrenees began during the Palaeocene; compressive phases occurred during the Eocene from east to west, giving rise to the Pyrenean axial zone. At the end of the Oligocene (Fig. 2a), both the western Pyrenees and the Basque–Cantabrian regions became definitively emerged (López-Martínez, 1989; AlonsoZarza et al., 2002). During the Miocene, Pyrenean tectonic structures experienced reactivation, and a new compressive phase took place that completed the raising of the Pyrenees as well as the Cantabrian and Iberian Ranges. The large Cenozoic basins of the peninsula occupy interior and epicontinental positions either isolated from or in connection with the Mediterranean or Atlantic. Their geographic and geological characteristics strongly reflect their processes of formation and later change (Civis, 2004). The formation of the Ebro Basin began in the Upper Palaeocene–Eocene coinciding with the folding of the Pyrenees. Sedimentation was generally endorheic. The margins of the basin were characterised by alluvial fans and fluvial deposits, while the centre of the basin was home to a lacustrine system that produced carbonated and evaporitic successions (Pardo et al., 2004). Endorheic conditions ended at the end of the Vallesian (∼ 8.5 Ma), when erosive evacuation towards the Mediterranean took place (García-Castellanos et al., 2003). According Vázquez-Urbez et al. (2003), the first evidence of exorheism in this basin can be inferred from deposits of Turolian age (8.7–5.332 Ma). At the same time, the convergence of Africa and Eurasia led to deformations in the Iberian plate with consequences for the formation of the Duero and Tagus Basins, which came into existence through the raising of the Central system, most likely during the Upper Eocene (Portero and Aznar, 1984). During the Palaeocene–Eocene interval, the compression to the north of what is today the Duero Basin generated a system of faults that contributed to the formation of sub-basins, in which alluvial fans developed (Alonso-Zarza et al., 2004). After the Late Oligocene and throughout the Miocene, endorheic lacustrine systems became established in the Duero Basin, generating large carbonate, siliciclastic and evaporite lacustrine sediments within its centre and in the Almazán Sub-basin. These endorheic

conditions ceased between the Upper Miocene and the Lower Pleistocene (Alonso-Zarza et al., 2002). In the Tagus Basin during the Oligocene–Lower Miocene, the Madrid and Loranca Sub-basins were formed, bringing about the deposition of shallow lacustrine and fluvio-lacustrine facies (AlonsoZarza et al., 2004). At the end of the Miocene, the palaeogeographic configuration of the north of the Iberian Peninsula was very similar to the present day. The southern half, however, underwent some notable change. The palaeogeographic history of the Guadalquivir Basin shows its eminently Neogene development. Although sedimentary infilling began in the Serravalian, most of its sediments are Upper Miocene or Pliocene in age (Alonso-Zarza et al., 2002). During the Lower–Middle Tortonian, the Guadalquivir Basin still formed part of an older, elongated east northeast to west southwest trending feature–the North Betic Straits–which connected the Atlantic and Mediterranean domains (Fig. 2b). These straits, along with the so-called South-Rif Straits, compensated for the water deficit of the Mediterranean by allowing communication between the Atlantic and Neotethys-Mediterranean Sea. In the Middle–Upper Tortonian, most of the olistostromes were deposited, coinciding with the raising of the eastern mountain ranges that interrupted communication via the North Betic Straits and generated the Guadalquivir Basin (Alonso-Zarza et al., 2002). The closure of both the above straits led, about 5.96–5.6 Ma, to the salinity crisis of the Messinian (CIESM, 2008). For European flora and fauna, this geological event may have led to the creation of important routes of species migration with Africa and Asia. Finally, in the Lower Pliocene (Fig. 2c), the Straits of Gibraltar opened, and the connection between the Atlantic and the Mediterranean was restored (AlonsoZarza et al., 2002). Elongated depressions running northeast–southwest began to form on the Atlantic face of the western Iberian Peninsula around the middle of the Eocene. These led to the formation of the Mondego and Lower Tagus Basins. The latter, which was formed at the same time as the Spanish Tagus Basin, was endorheic in nature during the Palaeogene, opening to the Atlantic during the Neogene. An extensive alluvial plane developed in the interior of the Lower Tagus Basin during the Lower and Middle Miocene, and during the Upper Miocene there were large swampy areas. Until

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the mid Tortonian their evolution was marked by the erosion of the Hesperic massif. After this time, coincidental with the raising of the Betic Ranges, the Central Portuguese range and the Western Mountains began to rise. In the Upper Miocene and during the Zanclean the basin one again showed endorheic features. In the Upper Pliocene the climate of the region became increasingly humid and an exorheic hydrographic network developed, the precursor of what is seen today (Pais, 2004; Pais et al., 2009).

3. Materials and methods

Fig. 2. Palaeogeographical maps of the Iberian Peninsula during the (a) Oligocene (29 Ma), (b) Middle Miocene (13 Ma) and (c) Pliocene (4 Ma). Black colour: oceanic areas, white colour: marine platform, pale grey colour: emerged lands, dark grey colour: main continental basins. The current Iberian coastline and the main tectonic structures are indicated. Graphic scale: 300 km. Modified from Paleogeological maps, Project IGCP 369 PeriTethyan Rift Basins, http:// www-sst.unil.ch/igcp_369/369_text/igcp369_iberia.htm.

All the published palynological and macrofloristic studies that focus on the Cenozoic of the Iberian Peninsula (not including the Quaternary) were taken into account. However, special attention was given to a series of locaties (Fig. 3) since the analyses of the palaeobotanical information they provide allows the floristic characterisation of the different periods of the Palaeogene and Neogene, and permits inferences regarding the composition of their most representative plant communities. This information also provides insight into certain landscapes of the Cenozoic and their evolution. The proposals of the International Commission on Stratigraphy (ICS) and the International Union of Geological Sciences (IUGS) regarding time scales are used throughout this work. The dates proposed by the consulted authors were respected. For the construction of the chronogram (Figs. 4 and 5), the scale proposed by Gradstein et al. (2004) was used, correlating the data from Neogene continental scales using the proposal of Calvo et al. (1993) and Daams et al. (1998). Also included in this synthesis are unpublished palynological data from Neogene outcrops chosen for their pollen richness, their age, and their geographic location (Figs. 6–9). Palynological samples were prepared using standard techniques (Batten, 1999). Some 500–1000 palynomorphs (on up to four slides) were identified per sample to determine the species ratios. Pollen diagrams were constructed using Tilia 1.0.1. software (Grimm, 2008) to determine the quantitative variation of taxa or groups of taxa through the successions examined. Aquatic taxa were grouped in all pollen diagrams and are summarized in Table 1. The pollen sum was calculated using all taxa, except for the Zaratán pollen diagram in which Pinus was excluded owing to its overrepresentation (Fig. 7a). In the pollen diagrams, taxa providing less than 1% of the pollen were not included, although these are shown in Appendix A. The climate was determined using the coexistence approach method (Mosbrugger and Utescher, 1997). This involved the use of ClimStat software and the Paleoflora database, which contains the nearest living relatives of more than 3500 Palaeogene and Neogene plant taxa, together with their climatic requirements (derived from meteorological station records located within their areas of distribution). The climatic variables taken into consideration (Table 2) were: mean annual temperature (MAT), mean temperature of the coldest month (CMT), mean temperature of the warmest month (WMT), and mean annual precipitation (MAP). However, the main aim of the calculations undertaken was not to infer climatic trends but to obtain information on the types of vegetation that existed in Iberia. For this, comparisons with dates for fossil plant associations were made, and with the findings of current climate-vegetation studies (Wolfe, 1978, 1979; Pais, 1986; Fauquette et al., 1998, 1999; Suc et al., 1999; Kvaček, 2005, 2007). Generally, the climatic intervals calculated from pollen and spore information were larger than those derived from megaremains, a consequence of the presence of regional and extra-regional elements within the pollen assemblages studied (see the data


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Fig. 3. Selected outcrops mentioned in the text. Star: Oligocene, 1) Cervera (Lleida province, NE Spain), 2) As Pontes lignite mine (A Coruña province, NW Spain). Circle: Miocene, 3) Izarra (Álava province, N Spain), 4) Lisbon area and S141 Borehole (Vale do Tejo region, Estremadura, W Portugal), 5) Ribesalbes (Castellón province, E Spain), 6) Rubielos de Mora (Teruel province, E Spain), 7) Puente de Toledo (Madrid province, Central Spain), 8) Zaratán (Valladolid province, Central Spain), 9) Belorado (Burgos province, N Spain), 10) La Cerdaña (Lleida province, NE Spain), 11) Gibraleón (Huelva province, S Spain). Triangle: Pliocene, 12) Apostiça (Sesimbra region, Setúbal Peninsula, W Portugal), 13) Casa del Pino (Huelva province, S Spain), 14) Can Albareda (Barcelona province, NE Spain), 15) Les Torrenteres (Papiol, Barcelona province, NE Spain), 16) Rio Maior (Santarém region, Ribatejo, W Portugal), 17) Vale do Freixo (Pombal region, Beira Litoral, W Portugal).

provided by miospores and leaves from Rubielos de Mora and La Cerdaña basins in Table 2). 4. Results and discussion 4.1. Early Palaeogene tropical vegetation (65.5–48.6 Ma) The floras of the early Palaeogene developed in the so-called “greenhouse world”, in which trees were found all around the globe. The Palaeocene initially saw a continuation of the climatic conditions characteristic of the Mesozoic; there was even a small increase in the mean annual temperature from the Middle Palaeocene (59 Ma) until the early Eocene (53 Ma), with a maximum in the Early Eocene climatic optimum (Zachos et al., 2001). Evidence provided by the fossil fauna and sediments of the Iberian Peninsula confirms the tropical nature of the climate; this is in agreement with its position in the European archipelago flanked by the warm Tethys Sea (LópezMartínez, 1989; López-Martínez et al., 1999; Tiffney and Manchester, 2001). The lack of continuous section in the scarce sites that have been found, and the absence of a precise chronostratigraphic framework, only allows a sketch to be drawn of the landscapes of the Palaeocene and Early Eocene. From a floristic standpoint the most valuable data are those provided by palynological studies undertaken in the Catalonian–Aragonese regions of the Pyrenees and the Betic Ranges. According to Knobloch et al. (1993), the palaeobotanical record of Central Europe suggests that the floristic changes of the Late Cretaceous and Palaeocene were gradual but continuous, with the number of modern pollen forms slowly increasing. In this way, the Iberian Paleocene palynological assemblages (Haseldonckx, 1973; Médus, 1977; Médus et al., 1988, 1992; López-Martínez et al., 1999)

present higher modern floristic affinities and diversity than the Maastrichtian ones (Médus, 1970, 1972; Solé de Porta and de Porta, 1984; de Porta et al., 1985), what also was recorded in China and is related to Early–Late Maastrichtian climatic changes (López-Martínez et al., 1999). Contrarily, in North America a loss of pollen and spore diversity is detected during the K/T boundary (Wolfe and Upchurch, 1986; Nichols et al., 1990). During the Palaeogene, the vegetation that developed in Iberia belonged to that of the Palaeotropical belt, and, according to Batten (1981), to the Normapolles province (which already existed in the Late Cretaceous). The Palaeocene forests were home to the first representatives of many genera that exist today (Nichols and Johnson, 2008). During this period, plants that produced Normapolles pollen grains plus Arecaceae, Ebenaceae, Engelhardia, Ericales, Fagaceae, Magnoliaceae, Myricaceae, Nyssa, Sciadopityaceae, Symplocaceae and taxodioid conifers, grew close to swampy areas, along with a great abundance and diversity of ferns (Haseldonckx, 1973; Médus, 1977; Médus et al., 1992; Fernández-Marrón et al., 2004). The importance of conifers in these plant communities should also be highlighted. This was also patent in the Maastrichtian of Iberia (Médus, 1970, 1972; Solé de Porta and de Porta, 1984; de Porta et al., 1985). The few macrofloristic data available (López-Martínez et al., 1999) appear to suggest the existence of evergreen laurophyllous forests that could tolerate seasonal dryness. The floras of the Lower Eocene suggest associations very similar to those inferred for the Palaeocene (Médus, 1977; Médus and Colombo, 1991), and can be considered strongly thermophilous and evergreen (Collinson and Hooker, 2003). One novelty was the appearance of palaeomangrove swamps with Nypa (Fig. 4), the pollen grains of which are abundant (Haseldonckx, 1973). These ecosystems ranged wide across the European archipelago, suggesting a warm, wet climate for this time. Finally, for the Lower Eocene in the Iberian



Fig. 4. Chronostratigraphic scale chart of the Paleogene according the International Geological Time Scale proposed by Gradstein et al. (2004). The most important events concerning the Paleogene Iberian vegetation have been indicated.


387

Table 1 Genera and families considered in pollen diagrams (Figs. 6–9) as aquatic taxa. Taxa Alisma Alismataceae Callitriche Cyperaceae Epilobium Hippuris Lythrum Myriophyllum Nuphar Nymphaea Nymphaeaceae Polygonum persicaria type Potamogeton Sparganium Sparganiaceae–Typhaceae Trapa Typha Utricularia

Barranco Casas

Puente de Toledo

Zaratán

Belorado

La Cerdaña

Gibraleón

Casa del Pino

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* * * *

*

*

* *

* *

Les Torrenteres * *

*

*

*

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*

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Can Albareda * *

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*

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*

*

southwest (in the Betic Ranges), Solé de Porta et al. (2007) suggested a tropical–subtropical rainforest vegetation including Arecaceae and pteridophytes. 4.2. Climate-induced modifications in the Palaeotropical vegetation of Iberia From the Late Eocene onwards there was a growing trend towards aridity, which led to the continentalisation of Eurasian climates. This was accompanied by a fall in temperatures around the world (LópezMartínez, 1989; Mai, 1989). From the climatic optimum of the Lower Eocene (Fig. 4) until the beginning of the Oligocene (~ 34 Ma), temperatures continued to fall, culminating in the Eocene–Oligocene transition and its long period of glaciation (400,000 ka; the Oi-1 glaciation; Fig. 4). This glaciation coincided with the appearance of the Antarctic ice cap (Miller et al., 1991; Zachos et al., 2001; Mosbrugger et al., 2005). The observed trend to greater dryness and greater cold from the Late Eocene had notable repercussions for the floras of Central Europe and North America (Collinson, 1992; Wolfe, 1992; Knobloch et al., 1993). According to Mosbrugger et al. (2005), this was a time of marked seasonality with particularly cold winters. In the Iberian Peninsula, the climate changes that culminated in the Eocene– Oligocene Transition were marked by the disappearance of 32 Palaeotropical genera (Postigo-Mijarra et al., 2009). 4.2.1. Changes in vegetation during the Late Eocene Pinus pollen dominates assemblages from the very early Bartonian record of the Pyrenees (Fig. 4). This has been related to a fall in temperatures and an increase in seasonality (Haseldonckx, 1973). The results of palynological studies of Bartonian– Priabonian sediments from the Ebro Basin indicate this period to have been a time when different Palaeotropical plant communities existed, including mangrove swamps, forests associated with swampy areas, and extrapalustrine forests, all of which developed due to the warm, wet climate (Cavagnetto and Anadón, 1994, 1996). These ecosystems were inhabited by taxa such as Alangium, Alchornea, Austrobuxus, Bignoniaceae, Croton, Dissilaria, Paedicalyx and Grewia that today are confined to tropical and subtropical areas. The genera Acrostichum, Avicennia, Aegiceras, Brownlowia, Pelliceria, Heritiera, and especially Nypa, defined the mangroves that existed during the Upper Eocene (Álvarez Ramis, 1982; Cavagnetto and Anadón, 1996). For the Priabonian of the Ebro Basin, taxa such as Acacia, Albizia, Combretum-type and Terminalia–plants associated with open,

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Rio Maior

*

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*

*

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dry environments–have been detected (Cavagnetto and Guinet, 1994; Cavagnetto and Anadón, 1996). These provide the first evidence of the climate change that occurred in the Late Eocene in Iberia, and indicate a change in the landscape as tropical forests became open tropical/subtropical sclerophyllous forests (Fig. 4). Megafossil woods belonging to the Cupressaceae family (CupressiVallin = Tetraclinis sp.?; Plate I, fig. 1) have been recovered in the Mondego Basin, along with the remains of leguminous plants (Leguminoxylon teixeirae Vallin; Plate I, fig. 4), as well as abundant Pinus pollen, all of which indicates the existence of plant formations adapted to dry climates (Pais, 1992). Formations of such xerophytic plants seem to have been restricted to the south of Europe during this period (Utescher and Mosbrugger, 2007), a time when Normapolles plants apparently disappeared. The Iberian final records for the latter are those for the Upper Eocene of the Catalonian Pyrenees (Sitter, 1961).

4.2.2. Evergreen subtropical Oligocene–Miocene vegetation (33.9–13.82 Ma) The fossil record of the Oligocene for Iberia shows that the Ebro Basin during the Rupelian was home to a subtropical flora with 34–49% of its components being megathermal or megamesothermal and well adapted to periods of seasonal drought (Sanz de Siria, 1992; Cavagnetto and Anadón, 1996; Hably and Fernández-Marrón, 1998). Notophyllous species belonging to Lauraceae (Plate I, fig. 2), Myricaceae and Ficus were widespread but linked to areas where the soil water was sufficient and where the topography was favourable (Sanz de Siria, 1996). These lauroids were mixed with species of the genus Quercus and the families Cupressaceae, Fabaceae, Juglandaceae, Myrtaceae, Sapindaceae and Sapotaceae, forming an evergreen, sclerophyllous– laurophyllous forest. In the northwest of the peninsula, the palynoflora reflected in the Rupelian–Chattian transition levels (Cavagnetto, 2002) reveals the existence of Palaeotropical trees and an abundance of ferns and members of the Pinaceae, Podocarpaceae, taxodioid conifers, Cycadaceae, Sapotaceae, Symplocaceae, Malvaceae, Araliaceae, Theaceae, Cyrillaceae, Juglandaceae, Fagaceae and Arecaceae (Fig. 4). These accounted for some 49% of the taxa in the Ebro Basin at this time. Open areas with herbaceous vegetation cannot be inferred from this data, nor is there evidence of sclerophyllous formations (Cavagnetto and Anadón, 1996). The temperature intervals for the Ebro Basin (Cervera outcrop) and Peninsular northwest (As Pontes lignite mine) (Fig. 3)



Fig. 5. Chronostratigraphic scale chart of the Marine Mediterranean Neogene based on the International Geological Time Scale (Gradstein et al., 2004). The Land Neogene Western European Stages have been correlated with the Marine Mediterranean ones according the frameworks proposed by Calvo et al. (1993) and Daams et al. (1998). The most important events concerning the Neogene Iberian vegetation have been indicated.


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Table 2 Climatic variables calculated using the Coexistence Approach method (Mosbrugger and Utescher, 1997) for selected Iberian Cenozoic outcrops. The obtained data are not in accordance with those exposed by Jiménez-Moreno et al. (2009). Site

Age

Cervera (Ebro Basin)

Rupelian (Lower Oligocene) Rupelian/Chattian (Oligocene) Aquitanian (Lower Miocene) Aquitanian (Lower Miocene) Aquitanian (Lower Miocene) Lower Aragonian (Lower Miocene) Lower Aragonian (Lower Miocene) Lower Aragonian (Lower Miocene) Burdigalian (Lower Miocene) Serravallian (Middle Miocene) Aragonian (Middle Miocene) Aragonian–Vallesian (Middle–Upper Miocene) Aragonian–Vallesian (Middle–Upper Miocene) Early Tortonian (Upper Miocene) Vallesian (Upper Miocene) Vallesian (Upper Miocene) Messinian (Upper Miocene) Zanclean (Pliocene)

As Pontes (NW Spain) Izarra Basin (N Spain) Izarra Basin (N Spain) Lisbon area (Lower Tagus Basin, Portugal) Ribesalbes (E Spain) Rubielos de Mora (E Spain) Barranco Casas (Rubielos de Mora, E Spain) S 141 borehole (Lower Tagus Basin, Portugal) Lisbon area (Lower Tagus Basin, Portugal) Puente de Toledo (Madrid Sub-basin, C Spain) Zaratán (Central Duero Basin, C Spain) Belorado (NE Duero Basin, C Spain) Lisbon area (Lower Tagus Basin, Portugal) La Cerdaña Basin (NE Spain) La Cerdaña Basin (NE Spain) Gibraleón (Guadalquivir Basin, SW Spain) Casa del Pino (Guadalquivir Basin, SW Spain) Lower Tagus Basin (Portugal) Can Albareda, base (NE Spain) Can Albareda, top (NE Spain) Les Torrenteres (NE Spain) Rio Maior (Lower Tagus basin, Portugal)

Number of taxa

Material

Reference

MAT

CMT

WMT

MAP

Leaves

Sanz de Siria (1992)

17–18.5 °C

5.6–11.7 °C

27.2–27.8 °C

1255–1355 mm

Miospores

Cavagnetto (2002)

17.2–18.4 °C

6.6–7.0 °C

27.3–27.8 °C

1300–1322 mm

28

Leaves

Barrón et al. (2006a)

15.5–15.6 °C

0–4.8 °C

26.4–26.7 °C

867–1237 mm

87

Miospores

Barrón et al. (2006a)

16.2–18.5 °C

5.5–11 °C

25.8–27.6 °C

956–1349 mm

45

Miospores

Pais (1981)

15.6–21.7 °C

5–13.6 °C

24.7–27.9 °C

1096–1520 mm

32

Leaves

Fernández-Marrón (1979)

13.6–15.8 °C

2.2–4.8 °C

26.5 °C

1000 mm

33

Leaves

Barrón and Diéguez (2001)

12.9–16.1 °C

0.6–2.7 °C

23.8–25.6 °C

1036–1058 mm

94

Miospores

This work

17.2–18.3 °C

7.7–10.2 °C

25.0–26.4 °C

1217–1384 mm

60

Miospores

Pais (1981)

15.7–16.6 °C

5–12.5 °C

26.5–26.6 °C

1122–1355 mm

31

Miospores

Pais (1981)

15.7–21.1 °C

2.9–13.3 °C

25.7–28.3 °C

1096–1355 mm

94

Miospores

This work

16.5–18.5 °C

5.5–13.1 °C

20.3–23.1 °C

887–1167 mm

62

Miospores

Rivas-Carballo (1991)

15.6–17 °C

5–10.3 °C

24.7–26 °C

823–1372 mm

68

Miospores

Valle-Hernández et al. (1995)

15.6–18.4 °C

6.4–12.5 °C

24.7–27.7 °C

823–1167 mm

64

Miospores

Pais (1981)

15.6–17.9 °C

5–11.4 °C

24.7–26.4 °C

828–1167 mm

53

Leaves

Barrón (1996)

14.4–15.8 °C

3.7–5.2 °C

25.7–26.4 °C

1231–1355 mm

78

Miospores

This work

16.5–17 °C

0.9–10.03 °C

23.6–26.3 °C

887–1167 mm

47

Miospores

Peñalba (1985)

15.6–19.5 °C

5–13.5 °C

24.7–26.4 °C

823–1613 mm

49

Miospores

Peñalba (1985)

13.3–18.3 °C

5.6–10.2 °C

23.6–26.4 °C

735–1384 mm

Zanclean (Pliocene)

52

Miospores

Vieira (2009)

15.7–17.4 °C

6.6–8.3 °C

24.7–27 °C

1096–1355 mm

Piacenzian (Pliocene)

40

Miospores

This work

11.4–19.5 °C

0.4–13.3 °C

21.7–26.4 °C

631–1355 mm

Piacenzian (Pliocene)

72

Miospores

This work

15.7–17 °C

5–10.03 °C

24.7–26.4 °C

1096–1372 mm

Piacenzian (Pliocene) Piacenzian–Gelasian (Pliocene)

92 130

Miospores Miospores

This work Vieira (2009)

15.6–17 °C 16.4–17 °C

5.6–9.6 °C 6.6–10.3 °C

21.7–26.4 °C 25–26 °C

1096–1281 mm 1194–1278 mm

77 167

obtained by the coexistence approach method are practically identical (Table 2), with both enjoying subtropical climates. The rainfall for the Peninsular northeast was slightly higher than in the Ebro Basin. The floras of the Lower Miocene in Iberia showed some similarities with those of the Oligocene, although with significant differences due to the extinction of many Palaeotropical genera (Postigo-Mijarra et al., 2009). In fact, the lowermost Miocene outcrops of As Pontes e Izarra (Médus, 1965; Barrón, 1999; Barrón et al., 2006a), the Aquitanian–Serravallian outcrops of the Lower Tagus Basin (Castro, 2006; Pais et al., in press), and the Burdigalian–Langhian outcrops of Catalonia (Bessedik, 1985) are all still characterised by Palaeotropical elements such as Simaroubaceae, aquatic ferns (Plate I, fig. 3), Malvaceae, Sapotaceae, Engelhardia, etc. The results of the calculations for the climate of the Izarra Basin (Fig. 3; Table 2) indicate conditions similar to those in East Asia where broadleaved sclerophyllous subtropical forests are now found (Wolfe, 1979). The mean annual temper-

ature of the Lower Tagus Basin (Lisbon area; Fig. 3) during the Aquitanian appears to have been between 15.6–21.7 °C and the area appears to have enjoyed abundant rainfall (Pais, 1986; Table 2). From the Oligocene onwards, communities of leguminous plants (forests or shrubs) started to dominate the landscape of many Iberian regions (Fig. 4). These communities included species of the genera Acacia, Albizia, Caesalpinia, Cassia, Hylodesmum, Mimosa and Gleditsia, and sclerophyllous taxa such as Paliurus, Ziziphus, Rhamnus and Tetraclinis. These have been recorded in Iberia since the Lower Oligocene (Cavagnetto and Guinet, 1994), and were very well represented in the Lower and Mid Miocene in Catalonia (Sanz de Siria, 1994). The most recent data for these communities come from the late Zanclean of the Guadalquivir Basin (Barrón et al., 2003). Over this long period of time the above plant communities changed in composition depending on the climate. On some occasions they may have made up mixed formations with conifers, along with remnants of the genus Tetraclinis during drier times (Sanz de Siria, 1992; Barrón,



1999), and with Pinaceae when times were comparatively wetter (Fernández-Marrón, 1979). On the shores of the Tethys Sea changes were also underway in the composition of the mangroves, which from the early Aquitanian until the Lower Tortonian were characterised by Avicennia (Bessedik, 1985; Bessedik and Cabrera, 1985; Jiménez-Moreno and Suc, 2007). The tolerance of this genus to grow and reproduce across a broad range of climatic, saline, and tidal conditions and to produce large numbers of buoyant propagules (Duke et al., 1998) allowed it to colonize the western coastlines of the Mediterranean during the Miocene and today may explain its ubiquitous presence in mangrove habitats around the world. Mangroves with Rhizophora survived in southeastern Iberia until the Pliocene (Postigo-Mijarra et al., 2009). 4.3. Laurel forests (notophyllous broadleaved evergreen forests) According to Mai (1989), laurel forests were one of the most important vegetation types making up the Palaeotropical geoflora of the European Palaeogene and Neogene. The first compelling data for Cenozoic laurel forests in Iberia come from the Upper Rupelian of the Ebro Basin (Cervera outcrop; Figs. 3 and 4). In a macrofloristic study Sanz de Siria (1996) indicates the existence of mixed lauroid communities of Lauraceae (Plate I, fig. 2) and Fagaceae plus members of Ebenaceae, Juglandaceae, Myrtaceae, Sapindaceae and Ficus; these developed in humid environments at altitudes of 400–500 m (similar to that of the oak-type laurels of southeastern China). The leaf assemblages examined also showed a high number of sclerophyllous taxa belonging to the families Anacardiaceae, Cupressaceae, Fabaceae and Rhamnaceae, whose presence is confirmed by palynological data (Cavagnetto and Anadón, 1996). Unlike that indicated by Sanz de Siria (1996), this suggests that extremely dry conditions prevailed in the area during this time. However, the strong presence of laurel leaves in associations greater in number than microphyllous associations might indicate that the laurels were found close to water — and therefore in the area where fossilisation was most likely. Thus, the laurel forests that existed during the late Lower Oligocene in the Ebro Basin must have existed for much of the year on the water to be found in the soil, and probably made up riparian communities. Such formations growing in a semi-arid–arid tropical context have no modern-day analogues, and may relate to the edaphically-mediated formation of laurel-conifer forests discussed by Mai (1989). Dry conditions prevailed in many areas of the Peninsula during the Miocene. Thus, although riparian laurel woods persisted in different basins, the plant communities to which they belonged became increasingly characterised by Arctotertiary taxa. Edaphically-mediated laurel forests have been recorded for the Lower Miocene of the Izarra Basin (Barrón, 1999) and for the Lower and Middle Miocene of Catalonia (Sanz de Siria, 1994). According to Utescher et al. (2007), during the Langhian the Peninsular northeast represented the part of Europe with the greatest diversity of tree taxa in this type of forest. From the Aquitanian, laurel forests also appear to be linked to humid sea-influenced or mountainous areas (Fig. 5). This is the case for those which developed in the La Cerdaña Basin (Fig. 3; Barrón, 1996; Barrón and Diéguez, 2005). The growth of these forests in the Vallesian may have been related to the orography of the area and the orientation of its peaks. These forests possessed elements reminiscent of those that exist today in Macaronesia, which include different genera of Lauraceae, Myricaceae and

Myrsinaceae. They must also have included magnolias and oaks such as Quercus drymeja Ung. and Q. neriifolia Al. Braun. The last laurel forest records for the Iberian Peninsula are those of the Piacenzian outcrops at Baix Llobregat (Barcelona), Ciurana (Girona) and around Tortosa (Tarragona) (Sanz de Siria, 1987). They all share the trait that their fossils do not come from mountainous areas but from places close to the Mediterranean coast. In fact, trees with lauroid leaves belonging to the genera Laurus, Persea, Cinnamomum, Benzoin and Quercus represent 47% of the plant remains at the Papiol site. The above data show that laurel forests were of great importance in the landscapes of much of Cenozoic Iberia. In contrast to that indicated by Kovar-Eder et al. (2006), they appear to have occupied more than 30% of its territory from the Tortonian to the Piacenzian, growing everywhere from mountainous to lowlying areas. 4.4. Appearance and spreading of Arctotertiary vegetation During the Upper Eocene, genera of Arctotertiary origin such as Alnus, Castanea, Salix and Ulmus began to be represented (Fig. 4), although they were not very common and were always linked to riparian formations. During the Oligocene the appearance of Arctotertiary elements persisted. The above genera became consolidated and Abies, Acer, Carpinus, Celtis, Cornus, Corylus, Fagus, Fraxinus, Juglans, Liquidambar, Ostrya, Picea, Populus, Sambucus, Tsuga and Zelkova appeared in the assemblages for the first time (Cavagnetto and Anadón, 1996; Cavagnetto, 2002). The Oligocene–Miocene boundary (23 Ma) was characterised by a strong glacial maximum lasting a brief 200 Ka. This was followed by a series of less intense, intermittent glaciations (Miller et al., 1991; Paul et al., 2000; Zachos et al., 2001; Billups et al., 2004) and an accompanying fall in global temperatures. According to Mosbrugger et al. (2005), this cooling was especially noticeable during winter. During this time, the major floral changes in Central Europe involved the coexistence of an interaction between Palaeotropical and Arctotertiary plants, including the substitution of the former by the latter (Mai, 1989). The data available regarding plant extinctions suggests that in the Iberian Peninsula these changes in flora were slower and took place over the Neogene (Postigo-Mijarra et al., 2009). In the Lower Miocene of As Pontes (Fig. 3; Médus, 1965), the transformation of a swampy vegetation with Palaeotropical elements (including Myricaceae, Simaroubaceae, Anacardiaceae, Cyrillaceae and Engelhardia) to one of Arctotertiary genera such as Betula, Corylus, Carpinus and Carya can be clearly seen (Fig. 5). At the beginning of the Burdigalian (~ 19 Ma) in the Lower Tagus Basin (S 141 Borehole; Fig. 3), the deciduous tree flora began to take on more importance than the subtropical evergreen and coniferous flora (Pais, 1986). However, at the beginning of the Miocene climatic optimum, Palaeotropical plants along with conifers once again dominated the subtropical landscapes. According to the available palynological (Pais, 1981) and climatic data (Table 2), they appear to have formed notophyllous broadleaved evergreen forests. At the end of the Burdigalian there was a time of high rainfall (Böhme, 2003) that once again allowed the expansion of Arctotertiary vegetation. From then on until the Tortonian the area seems to have been dominated by a mixed broadleaved evergreen/deciduous vegetation, although humid tropical to subtropical taxa such as Spirematospermum, Toddalia, Malvaceae (Plate I, fig. 3), and Sapotaceae associated with hydro-hygrophytic

Fig. 6. (a) Pollen diagram of Barranco Casas outcrop (western Rubielos de Mora Basin, E Spain). For stratigraphic details see Peñalver (2002); (b) pollen diagram of La Cerdaña Basin (eastern sector of the Sub-basin of Bellver, NE Spain). For stratigraphic details see Barrón and Comas-Rengifo (2007); (c) pollen diagram of Gibraleón outcrop (Guadalquivir Basin, S Spain). For stratigraphic details see Peñalba (1985).


391



genera have been identified for the Serravallian (Pais, 1986; Pais et al., in press.). It may be that mixed broadleaved/deciduous vegetation also existed in the Mid Miocene in the Peninsular northwest, as indicated by the pollen composition of the Xinzo de Limia Basin (Alcalá et al., 1996), where Pinaceae, Alnus, Betula, Quercus, Ericaceae, Poaceae and Pteridophyta are represented in considerable numbers. Unlike in the west of the Peninsula, where the Atlantic had an important impact on the structure of the vegetation during the Miocene, in the rest of the Iberia Arctotertiary vegetation was restricted to damp or mountainous areas. The megafloras of the Lower Miocene basins of Ribesalbes and Rubielos de Mora (which are in close geographical proximity; Fig. 3) suggest the climate of the latter to have been wetter and cooler, but not so drier and cooler as Jiménez-Moreno et al. (2007) indicated; this is confirmed by the results of calculations for their CMT and MAP. However, their inferred MAT are similar (Table 2) and illustrative of a subtropical climate in which notophyllous broadleaved evergreen forests developed. The climatic discrepancy between them is almost certainly conditioned by the fact that the Ribesalbes Basin was closer to sea level during the Early Miocene. Its flora had an Arctotertiary component including Alnus, Celtis, Liquidambar (Plate I, fig. 9), Populus and taxodioid conifers (Fernández-Marrón, 1979) that developed in a shoreline area. In contrast, the Rubielos de Mora Basin was situated at more than 900 m above sea level, and here broadleaved evergreen and coniferous forest including ferns (Plate II, fig. 6), Calocedrus, Carya, Cryptomeria, Picea, Pinus, Quercus, Sequoia, Sorbus (Plate I, fig. 5), Zelkova and diverse herbs (Plate II, fig. 1) grew (Barrón and Diéguez, 2001; Barrón et al., 2006b). The palynological data (Fig. 6A) seem to suggest a better representation of Arctotertiary elements than Palaeotropical elements, with periods of predominance of conifers alternating with others characterised by deciduous angiosperm trees (Barrón et al., 2006b; JiménezMoreno et al., 2007). Similarly, the sites of the La Cerdaña (Fig. 3) and La Bisbal (Catalonia) Basins, both of Upper Miocene age, are geographically very close. The intramontane basin of La Cerdaña developed in the eastern Pyrenees during the Vallesian. Its palaeobotanical record indicates that, in a subtropical climatic context (Table 2) and owed to its altitude and orography, an ecotone involving notophyllous broadleaved evergreen forests and mixed mesophytic forests existed. The latter showed high diversity, containing species of the genera Abies, Acer, Betula, Carpinus, Fagus, Fraxinus (Plate I, fig. 8), Ostrya, Parrotia, Pinus (Plate I, fig. 6), Quercus (Plate II, fig. 7), Tilia and Zelkova, thereby relating them to those that currently exist in the Euxinic and Hyrcan regions (Barrón, 1996). Palynological studies (Fig. 6b; Appendix A) have confirmed the above macrofloristic information, and show that there were times when the presence of conifers diminished (the RIU level). This might have been related to palaeofires or changes in the environment (greater development of lacustrine areas, increase in rainfall etc.). Unlike at La Cerdaña, the record for the La Bisbal outcrop reveals an Arctotertiary vegetation with Alnus, Salix, Platanus, Populus, Ulmus and Pterocarya linked to a riparian environment (Sanz de Siria, 1994). This flora developed under subtropical conditions with mean annual temperatures of around 18 °C, and at low altitude close to the Mediterranean coast. In a manner opposite to that suggested for the laurel forests, the deciduous Arctotertiary vegetation of the Upper Miocene was not so important in the Peninsular northeast — in contrast to that indicated by Kovar-Eder et al. (2006). This

Arctotertiary vegetation would have had to compete with broadleaved evergreen forests, causing it to concentrate in very damp or very cold areas.

4.5. Neogene non-forested lands and steppe-like areas From the Priabonian onwards, herbaceous plants and bushes such as Ephedra, Chenopodiaceae, Combretum, Linum, Plumbaginaceae and Thymelaeaceae characteristic of dry, open lands (Cavagnetto and Anadón, 1996), began to become more important in the Ebro Basin. Grasses were scarce — a situation to date reported only for Rupelian of the Sarral outcrop. Grasses were common in Iberian ecosystems from the Upper Burdigalian (Fig. 5), when Catalonia was home to open lands characterised by these plants, along with Amaranthaceae– Chenopodiaceae and Asteraceae (Bessedik, 1985). From the Langhian onwards, at the very end of the Miocene climatic optimum, droughts lasting six months occurred (Böhme, 2003). This, along with the significant fall in temperatures of the Langhian-Serravallian, allowed the formation of open, steppe-like ecosystems in the Peninsular northeast, south and centre during the Mid and Upper Miocene (Valle-Hernández et al., 2006; JiménezMoreno and Suc, 2007). In general terms, the vegetation of the Aragonian–Vallesian in the central domain of the Duero Basin (Zaratán section; Fig. 3) corresponded to a steppe of Asteraceae, Amaranthaceae–Chenopodiaceae, Poaceae and Plantago with isolated stands of Juniperus, Quercus and Pinus (Fig. 7a) and total absence of Arctotertiary taxa from midaltitude areas such as Betula, Cathaya, Cedrus, Fagus and Tsuga. Fraxinus dominated riparian woods where water was available (RivasCarballo, 1991; Rivas-Carballo et al., 1994). This vegetation changed over the Mid and Upper Miocene. Dry steppeland gave way to thermophilous forests of Juniperus–Quercus, which in turn gave way to prairie land with formations of xerophytic Mediterranean vegetation dominated by evergreen Quercus (Fig. 5). The climate inferred for the area was subtropical (Table 2) variation in the vegetation may therefore have been due to local changes in the climate. In areas close to mountain ranges ecotones developed. In the region of Belorado (Fig. 3), which lies in the Duero Basin where a small depression formed at the foot of a south-facing mountain range, ideal conditions were created for the establishment of a local subtropical microclimate (Table 2). Palynological studies (Valle-Hernández et al., 1995) have revealed the area was home to far fewer Mediterranean taxa than the centre of the basin, the scarcity of Juniperus, Quercus and Asteraceae pointing to a less continental climate (Fig. 7b). In addition, the evidence suggests the existence of prairies, deciduous broadleaved forest with Palaeotropical elements such as Arecaceae, Malvaceae, Sapotaceae and Schizeaceae, forests of conifers such as Abies, Picea, Cedrus and Pinus, and formations of riparian taxa such as Alnus, Clethraceae– Cyrillaceae, Nyssa and Populus (Fig. 7b; Appendix A). In the Aragonian in the Madrid Sub-basin (Puente de Toledo outcrop; Fig. 3), open ecosystems with Asteraceae, Amaranthaceae–Chenopodiaceae, Poaceae and Plumbaginaceae (Fig. 7c) developed, along with open Mediterranean woodland characterised by evergreen Quercus and riparian formations with Pteridophyta, hygrophytic herbs (Plate II, fig. 2), Populus and Ulmaceae (Rivas-Carballo and Valle-Hernández, 2004). Scarcely, other mesophylous taxa such as Betula, Carpinus, Carya (Plate II, fig. 4), Fraxinus and Tilia appear (Appendix A). The climatic

Fig. 7. (a) Pollen diagram of Zaratán section (Centro Duero Basin, Central Spain). For stratigraphic details see Rivas-Carballo (1991) and Rivas-Carballo et al. (1994); (b) pollen diagram of Belorado area (Northeastern Duero Basin, N Spain). For stratigraphic details see Valle-Hernández et al. (1995); (c) pollen diagram of Puente de Toledo outcrop (Madrid Sub-basin, Central Spain). For stratigraphic details see Rivas-Carballo (2007).


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Fig. 8. (a) Pollen diagram of Casa del Pino outcrop (Guadalquivir Basin, S Spain). For stratigraphic details see Peñalba (1985); (b) pollen diagram of Can Albareda section (Catalonia, NE Spain). For stratigraphic details see Civis (1977b) and Valle-Hernández (1983); (c) pollen diagram of Les Torrenteres section (Catalonia, NE Spain). For stratigraphic details see Civis (1977a) and Valle-Hernández (1982).

Fig. 9. Pollen diagram of Rio Maior (F98 Borehole) (Lower Tagus Basin, W Portugal). For stratigraphic details see Vieira (2009).

Author's personal copy

E. Barrón et al. / Review of Palaeobotany and Palynology 162 (2010) 382–402 395




intervals obtained are similar to those calculated for the Duero Basin (Table 2); the two basins may therefore have had similar plant life. On the Atlantic margin of the Peninsula during the Upper Burdigalian– Lower Tortonian (Lisbon area; Fig. 3), herbaceous formations were less important than trees — a consequence of the influence of the ocean. It is possible that their development was linked to coastal zones (Pais, 1986). However, in the Lower Tortonian, the climatic intervals in this area were similar to those of the Madrid Sub-basin and Duero Basin, reflecting the similar climatic conditions to be found over much of the Peninsula at that time (Table 2). The plant life may therefore have been similar in different places. At the end of the Miocene, the process of aridification intensified, extending the area occupied by open ecosystems and encouraging the appearance or expansion of several families of plants adapted to such environments (Singh, 1988). From 9 Ma the Iberian Peninsula began to show conditions of great aridity which intensified during the Messinian. Few data exist for this period, but the aridity seems to have conditioned the existence of prairies and steppe in the centre, east and south of the Peninsula (Solé de Porta and de Porta, 1977; Peñalba, 1985; Van Campo, 1989). In the Iberian southwest (Gibraleón outcrop; Fig. 3), the Messinian vegetation was characterised by prairies or steppe of Asteraceae, Plantago, Poaceae and Rumex which became progressively enriched with Mediterranean-type elements (Arecaceae, Cornus, Oleaceae, Pinus and Quercus) (Fig. 6c). Some subtropical taxa such as Clethraceae–Cyrillaceae, Nyssa and Symplocaceae (Fig. 6c; Appendix A) were also present (Peñalba, 1985).

4.6. The vegetation in the Pliocene (5.332–1.806 Ma) The Pliocene is a key period for understanding the origin of Iberia's current vegetation. This period experienced a profound transformation of its plant landscapes, largely due to climate change. The cooling that occurred over the Zanclean, approximately during MIS TG5-MIS GI1, was progressive, leading to periodic variations in temperature (Lisiecki and Raymo, 2005). Later, in the Piacenzian, a new, brusque cooling occurred about 3.3 Ma. Finally, about 2.7–3.3 Ma, isotopic studies show another acute cooling occurred over a relatively short period of time (Lisiecki and Raymo, 2005, 2007). A progressive reduction in summer rainfall and the development of a dry season coinciding with the warmest period of the year occurred around 3.1–3.2 Ma, thus initiating Mediterranean seasonality (Suc and Cravatte, 1982; Bessais and Cravatte, 1988). These changes led to the disappearance of the subtropical tree vegetation (Fig. 5), giving way to the Mediterranean vegetation that exists today. These climate changes also led to the extinction of many Palaeotropical and Arctotertiary taxa (Postigo-Mijarra et al., 2009).

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After the crisis of the Messinian, the Iberian Peninsula enjoyed a warm-temperate or subtropical climate that lasted throughout the first part of the Pliocene. The few palaeobotanical data we have for the Zanclean of Iberia come from the Guadalquivir Valley and the Tagus Basin. The results of the palynological studies performed by Peñalba (1985) and Valle-Hernández and Peñalba (1987) show that the Guadalquivir Valley (Casa del Pino outcrop; Fig. 3) was home to a mixed forest vegetation including conifers, deciduous Arctotertiary elements (Alnus, Fraxinus Populus and Salix), certain Palaeotropical elements linked to swampy areas (Taxodiaceae, Clethraceae–Cyrillaceae, Myrica, Nyssa, Sapotaceae, etc.), and a high density of pteridophytes (Fig. 8a; Appendix A). The percentages of evergreen Quercus and Asteraceae at the top of the succession indicate the formation of steppe zones with stands of Mediterranean elements. At the end of the Zanclean, these steppes were characterised by leguminous shrubs (Barrón et al., 2003). The palynological data for the Lower Tagus Basin (Apostiça and Vale do Freixo outcrops; Fig. 3) appear to indicate that in the Upper Zanclean broadleaved notophyllous evergreen forests with Arecaceae, Castanea/Castanopsis, Engelhardia, Magnolia, Sapotaceae, Symplocos and taxodioid conifers existed (Vieira, 2009; Pais et al., in press.), with little in the way of Arctotertiary plants. These forests developed in a subtropical environment with much moisture (the product of rainfall and humidity due to the proximity of the Atlantic) (Table 2). Palaeobotanical studies of the Piacenzian of Catalonia reveal the existence of a diverse vegetation which, depending on soil conditions and altitude, would have been structured as follows (Valle-Hernández, 1982; Sanz de Siria, 1987): halophyte formations close to the coast (Amaranthaceae–Chenopodiaceae, Armeria, Asteraceae, Ephedra, etc.); taxodioid conifers, riparian deciduous trees and hydrohygrophytic elements such as Myriophyllum, Potamogeton, Ranunculaceae and Typha in swampy areas and along rivers; laurel forests with Lauraceae, evergreen oaks, Magnoliaceae, Myrica, Ficus, Ilex and Diospyros close to sources of water; Arctotertiary and Mediterranean elements (Cupressaceae, Pinus, evergreen and deciduous oaks, Acer, Olea, Phillyrea, Carya, Carpinus, Poaceae, Amaranthaceae–Chenopodiaceae, Plantago, etc.) in more or less open plains woodlands; and coniferous forests of Pinus, Picea and Abies in mountainous areas. Evidence also exists that there were moments when the tree component became much reduced, giving way to prairies and steppes characterised by Amaranthaceae–Chenopodiaceae, Poaceae and different Asteraceae, such as Armeria (Suc and Cravatte, 1982; Bessais and Cravatte, 1988). Palynological studies carried out in Can Albareda and Les Torrenteres sections (Fig. 3), have related the sedimentological characteristics of the area's outcrops and the different types of vegetation that existed during the Pliocene. In the sandiest and most detritic levels originating from materials close to the coast (bottom of

Plate I. Selected Cenozoic Iberian megaremains: (1).

Cupressinoxylon lusitanensis Vallin wood (specimen housed in the Dpto. de Ciências da Terra, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa) from the Late Eocene of Sobreda (Mondego Basin, Portugal);

(2).

Lindera stenoloba (Saporta) Laurent (specimen 32.499, Museu de Ciències Naturals de la Ciutadella, Barcelona), upper Rupelian (Oligocene) of Cervera (Catalonia);

(3).

Salvinia sp. (specimen FM-301, Museo de Ciencias Naturales de Álava, Vitoria-Gasteiz), Aquitanian (Lower Miocene) of Izarra outcrop (N Spain);

(4).

Leguminoxylon teixeirae Vallin wood (specimen housed in the Dpto. de Ciências da Terra, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa) from the Late Eocene of Sobreda (Mondego Basin, Portugal);

(5).

Composite leaf of Sorbus sp. (specimen MPV-1797-RM, Museo de Ciènces Naturals de València) from the lower Aragonian (Lower Miocene) of Rubielos de Mora Basin (E Spain);

(6).

Male cones of Pinus sp. (specimen MNCNV-4750, Museo Nacional de Ciencias Naturales, CSIC), Vallesian (Upper Miocene) of La Cerdaña Basin, (NE Spain);

(7).

Acer pseudomonspessulanum Unger (specimen UH-Le-26, Dpto. Geodinámica y Paleontología, Universidad de Huelva), upper Zanclean (Pliocene) of Lepe (Guadalquivir Basin) (S Spain);

(8).

Samara of Fraxinus numana Massalongo (specimen 032, Lladó Collection, Sabadell) from the Vallesian (Upper Miocene) of La Cerdaña Basin, (NE Spain);

(9).

Palmate leaf of Liquidambar pseudoprotensa Andreánszky (specimen Rb-p-54, Museo de la Baronía, Castellón), Ramblian–Aragonian (Lower Miocene) of Ribesalbes Basin (E Spain). Graphic scale: (1) = 150 μm, (4) = 200 μm, (2–3, 5–9) = 1 cm.




the Can Albareda diagram; Fig. 8b) Pinaceae is poorly represented, and taxodioid conifers and Pteridophyta are almost completely absent. However, Alnus, Rhamnus, Olea-Phillyrea, Ericaceae, deciduous Quercus, Plantago and Poaceae appear in much larger numbers. These assemblages stand out because of the importance of Mediterranean-type elements that surely existed in woody formations similar to those that exist now. However, the marly sediments provided by areas further away from the coast are dominated by Pinus and contain a greater amount (and greater diversity) of taxodioid conifers, evergreen Quercus, Cedrus, Tsuga, Engelhardia, Olea-Phillyrea, Alnus, Poaceae and Amaranthaceae–Chenopodiaceae, along with different pteridophytes (Fig. 8b–c). These last assemblages may reflect the existence of extralittoral mixed forests with riparian or swamp elements. The calculations for the climate seem to indicate somewhat drier, colder conditions for the base of the Can Albareda than for its top and Les Torrenteres (Table 2); this agrees with the available palynological and sedimentological data. At the end of the Piacenzian and throughout the Gelasian, between 1.8 and 2.58 Ma, thermal contrasts became ever greater and the progressive cooling underway became more intense (Lisiecki and Raymo, 2005). These falls in temperature have been related to the extinction of many (mainly Palaeotropical) taxa (Postigo-Mijarra et al., 2009). In Catalonia, the vegetation inferred by Gelasian macroremains are characterised by sub-Mediterranean deciduous Arctotertiary elements (Fig. 5), especially Quercus cerris L. and Carpinus suborientalis Sap. (Roiron, 1983). Palynological studies indicate forested environments containing Arctotertiary deciduous elements and conifers plus some residual genera from older periods, such as Engelhardia, Eucommia, Nyssa, Symplocos and Sapotaceae. The latter would have required warmer and wetter conditions than the above sub-Mediterranean elements, and were therefore in decline. During the coldest times steppes with Pinus formed (Leroy, 1997). At Rio Maior (F98 Borehole, Lower Tagus Basin; Fig. 3), during the Piacenzian and Gelasian, a mixed broadleaved evergreen vegetation almost certainly developed, containing mainly Pinus, Quercus, Engelhardia, Myrica and Ericaceae (Diniz, 1984a,b; Vieira, 2009). During the first part of the Piacenzian, this vegetation was characterised by subtropical plants typical of swampy areas (taxodioid conifers, Craigia [Plate II, fig. 5], Nyssa, Leitneria), and abundant Pteridophyta, all living in a subtropical climate (Table 2). Later, coinciding with the climate change of the middle–late Piacenzian, the pollen diagram evidence shows the decreasing of the more thermophilous taxa such as Engelhardia, and an increase in Pinus. Finally, in the Gelasian, the vegetation became more open, and was accompanied by a drastic fall in the number of thermophilous taxa, ferns and Quercus, and an increase in Asteraceae (Fig. 9). 4.7. Xerophytic Mediterranean vegetation Palamarev (1989) proposed that the Mediterranean floras arose out of the subtropical flora living in azonal communities and influenced by dry soil conditions in areas with their own microclimates. This vegetation corresponds to an Eocene association in the Dryophylleto–Daphnogenetum-sempervirentifruticosum-type group. From the Oligocene onwards, coinciding with the start of the

399

formation of arid areas, the pre-Mediterranean elements of this association began to diversify to form subtropical or warm-temperate, broadleaved and deciduous or evergreen communities principally comprising Lauraceae, Fagaceae, Magnoliaceae, Theaceae and certain conifers. A large number of the ancestors of modern-day Mediterranean taxa can be found among Palaeotropical floras which, during the Neogene, had to compete with Arctotertiary elements that gradually became more significant. Some elements of these floras must have adapted to the dry climates throughout the Miocene. As mentioned above, during this period evergreen sclerophyllous–laurophyllous forests were of great importance in the vegetation of Iberia. It may have been in Iberia where species of the genera Pistacia and Ceratonia evolved. The oldest recorded Pistacia are those of the Burdigalian of Catalonia (Bessedik, 1985), while Ceratonia has a first appearance in the Middle Miocene of Madrid Basin (Appendix A) and the south of the Peninsula (Jiménez-Moreno and Suc, 2007). Other pre-Mediterranean elements may have been associated with this evergreen laurophyllous vegetation, e.g., the ancestors of Quercus ilex L. and Q. coccifera L. The former may have its origins in holm oaks associated with lauroid elements such as Q. drymeja Ung. in the Upper Miocene of La Cerdaña (Barrón, 1996), Q. praeilex Sap. in the Upper Miocene of Ardèche (Saporta, 1879), and Q. praecursor Sap. et Mar. in the Pliocene of Meximieux (Saporta and Marion, 1876). The idea that Q. ilex should arise from this set of subtropical oaks is in agreement with the area of distribution of the subspecies ilex in humid and subhumid Mediterranean areas (Pons and Vernet, 1971). Q. coccifera on the other hand appears to be related to fossil species that developed in humid–mesic environments (Kvaček and Walther, 1989) such as Q. mediterranea Ung. During the driest periods of the Neogene, this species most likely sought refuge in lauroid formations. In the Iberian Peninsula, Q. mediterranea has been identified in the Vallesian of the La Cerdaña Basin in association with mesophyllous and notophyllous taxa (Barrón, 1996). Similarly, the genus Nerium was related to lauroid vegetation from the Palaeogene until the Pliocene (Saporta and Marion, 1876; Colom, 1983; Sanz de Siria, 1987). As mentioned earlier, the first data on Mediterranean-type environments in the Iberian Peninsula came from palynological studies of Aragonian materials within the Duero Basin. Here the tree cover was represented by Mediterranean woodland, which would have included both fluvial broadleaved ash and alder woods, and steppeland woods and thickets dominated by Quercus (Rivas-Carballo, 1991). From the Pliocene onwards, the eastern Peninsula saw an expansion of Mediterranean-type taxa, many of which had Palaeotropical ancestors. Arctotertiary taxa that adapted to Mediterranean climatic conditions were also to be found, although in smaller numbers in megafloristic assemblages. Such was the case of Acer pseudomonspessulanum Ung., (Plate I, fig. 7) the remains of which have been found in the south of the Peninsula (Barrón et al., 2003). Despite the disappearance of the laurel forests during the Pliocene, some of the species that belonged to them survived in refugia, and are now found in areas that can provide for their specific temperature and water requirements (Costa Tenorio et al., 2005). Such is the case of Laurus nobilis L., Rhododendron ponticum L., Prunus lusitanica L., Myrica faya Ait. and different types of vascular cryptogams.

Plate II. Selected Neogene Iberian miospores: (1).

Liliaceae gen. et sp. indet., lower Aragonian (Lower Miocene), Barranco Casas outcrop, Rubielos de Mora Basin (E Spain),

(2).

Lithrum sp., Aragonian (Middle Miocene), Puente de Toledo outcrop, Madrid Sub-basin (C Spain);

(3).

Bombacidites lusitanicus Pais, Serravallian (Middle Miocene), Penedo section, Lisbon Area (W Portugal);

(4).

Carya sp., Aragonian (Middle Miocene), Puente de Toledo outcrop, Madrid Sub-basin (C Spain);

(5).

Craigia sp., Piacenzian (Pliocene), F98 Borehole, Rio Maior (W Portugal);

(6).

Polypodiaceoisporites sp., lower Aragonian (Lower Miocene), Barranco Casas outcrop, Rubielos de Mora Basin (E Spain);

(7).

Quercus sp., Vallesian (Upper Miocene), La Cerdaña Basin, (NE Spain).



Fig. 10. Composite range chart of the main types of vegetation in the Iberian Peninsula along the Cenozoic. The appearance and disappearance time of these vegetation types is shown. Abbreviations: Dan — Danian, Se — Selandian, Tha — Thanetian, Y — Ypresian, Lu — Lutetian, Ba — Bartonian, Pri — Priabonian, Ru — Rupelian, Ch — Chattian, Aq — Aquitanian, Bur — Burdigalian, Lan — Langhian, Ser — Serravallian, Tor — Tortonian, Mes — Messinian, Zan — Zanclean, Pia — Piacenzian, Gel — Gelasian, E — Early Pleistocene, M — Middle Pleistocene, L — Late Pleistocene, H — Holocene.

Today, Macaronesia provides refugia for Palaeotropical broadleaved evergreen vegetation. Species of Laurus, Ocotea, Persea, Notholaea, Prunus, Myrica, Myrsinaceae, etc., still co-occur, as they did in the Iberian Peninsula during the Neogene. However, these forests are impoverished with respect to certain typical Palaeotropical components such as the Magnoliaceae, Ebenaceae, the evergreen Quercus and different species of Arecaceae.

5. Conclusions During most of the Cenozoic, the vegetation of the Iberian Peninsula was characterised by Palaeotropical taxa that lived alongside Arctotertiary elements from the Oligocene onwards. The main vegetational types through the Cenozoic were: tropical, evergreen xerophyllous (subtropical and Mediterranean sclerophyllous formations, leguminous communities), coniferous, laurel and deciduous broad leaved forests, mangroves and non-forested lands (steppes or prairies) (Fig. 10). During the Palaeocene and Eocene, tropical evergreen forests developed with Lauraceae, Fagaceae, Juglandaceae and Normapolles producers, with ferns occupying the understory, forming a vegetation style similar to that of the late Cretaceous. From the Eocene onwards, mangroves including Nypa became important along the shores of the Tethys Sea. The cooling that occurred at the end of the Palaeogene led to the development of evergreen sclerophyllous forests, open woodland of leguminous species, edaphically-mediated laurel forests and the appearance of Arctotertiary taxa during the Oligocene. The laurel forests were of great importance in the landscapes of the Cenozoic in Iberia. They may have replaced the territory's tropical forests following the Late Eocene. Showing great ecological tolerance they appeared in mountain ranges and near the sea. These forests were the main generators of the taxa that comprise the modern Iberian Mediterranean flora.

During the Miocene, the Arctotertiary vegetation survived the warm, subtropical climate by retreating to the mountains or riparian areas where water (from the rain or in the ground) was in sufficient supply. It may have competed with laurel forests to form ecotones in mountainous areas, although it was predominant in the Lower Tagus Basin in the Middle and Upper Miocene. Grasses became common from the Upper Burdigalian. Depending on the water available, great prairies or steppes of Amaranthaceae– Chenopodiaceae, Poaceae and Asteraceae developed in the centre of the Peninsula during the Mid and Upper Miocene. The first signs of Mediterranean-type environments are reflected in small Quercus and Cupressaceae woods that dotted the steppe of the Duero Basin during the Vallesian. In Catalonia and Portugal, palynological studies have shown that during the Pliocene there was a progressive extinction of thermophyllous taxa and an increase in Mediterranean elements (evergreen Quercus, Olea, Ericaceae and Cistaceae). In the Lower Tagus Basin, open vegetation became predominant during the Gelasian. Despite all data presented in this paper, the majority of the Cenozoic Iberian basins have been not sufficiently studied from a Palaeobotanical point of view. In addition, there is less knowledge concerning Iberian Paleogene than Neogene. At present, these deficiencies impede a complete reconstruction of the vegetational history during the Iberian Cenozoic.

Acknowledgements This work was performed as part of the PALEODIVERSITAS I (CGL 2006-02,956-BOS) and NECLIME research projects. We wish to thank Dr. José Carrión (Editor) and the two anonymous referees who provided valuable suggestions for the improvement of the manuscript. We also sincerely thank Dr. Nuria Solé de Porta, Dr. Jorge Morales, Dr. Julio Gómez-Alba, Robert Raine and Adrian Burton for their help and kindness.


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