Vegetation and palaeoclimatic reconstruction of the Sousaki Basin (eastern Gulf of Corinth, Greece) during the Early Pleistocene

Quaternary International 476 (2018) 110e119

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Vegetation and palaeoclimatic reconstruction of the Sousaki Basin (eastern Gulf of Corinth, Greece) during the Early Pleistocene Penelope Papadopoulou*, George Iliopoulos, Ioannis Zidianakis, Maria Tsoni, Ioannis Koukouvelas University of Patras, Geology Department, 26504, Rio Patras, Greece

a r t i c l e i n f o

a b s t r a c t

Article history: Received 25 October 2017 Received in revised form 7 February 2018 Accepted 8 February 2018 Available online 21 February 2018

Pollen analysis was performed on a Lower Pleistocene lacustrine sedimentary sequence outcropping in Sousaki Basin, eastern Gulf of Corinth, Greece for the first time. The palynological assemblages revealed a stable climate, with regard to the glacial/interglacial climate variability timescale, with minor fluctuations in humidity, expressed as a relatively wet phase between 13.1 and 19.3 m and some transient increased aridity and humidity events. A Mediterranean type of vegetation presenting altitudinal zonation was evidenced for the first time in this region. Pinus and Quercus dominate, accompanied by other arboreal and non arboreal plants. The presence of rare taxa such as Taxodiaceae, Engelhardia, Liquidambar, Tsuga and Cedrus in very low percentages shows that these taxa remained in the area as relicts sometime between 2.8 and 1.5Ma. Palaeovegetation patterns from the Balkan Peninsula are lacking, especially during the Early Pleistocene. Thus, in this study a palaeoclimate reconstruction of the Early Pleistocene Sousaki Basin based on palynological data, is presented accentuating the effect of global climate changes in an area where no other similar records exist. © 2018 Elsevier Ltd and INQUA. All rights reserved.

Keywords: Pollen analysis Palaeovegetation Palaeoclimate Lower Pleistocene Greece

1. Introduction Little is known about the Mediterranean flora vegetation history during the Pliocene and Early Pleistocene, mostly because of the incompletely developed palynological record in circusMediterranean regions. During the Tertiary the Mediterranean Basin was mostly covered with evergreen vegetation types. During the Pleistocene, deciduous forests (Querqus and Fagus) emerged in the mountainous belts and at the same time steppe-like vegetation developed along the coasts. Climate was the main driving factor for these changes. (Pignatti, 1978). Mediterranean climate is characterized by a seasonal change with dry summers and mild, moist winters (Jalut et al., 2009). This type of climate is considered to have been originated at the end of the Miocene, was established at the beginning of the Pliocene and developed throughout the Quaternary, at a time when global climate became gradually much more arid (Axelrod, 1975, 1977;

* Corresponding author. Panepistimioupoli Patron 265 04, Rio Patras, Greece. E-mail addresses: [email protected] (P. Papadopoulou), iliopoulosg@ upatras.gr (G. Iliopoulos), [email protected] (I. Zidianakis), [email protected] (M. Tsoni), [email protected] (I. Koukouvelas). https://doi.org/10.1016/j.quaint.2018.02.011 1040-6182/© 2018 Elsevier Ltd and INQUA. All rights reserved.

Spect, 1979; Vallente-Banuet et al., 2006; Sadori et al., 2013; Naidina and Richards, 2016). The dry summer conditions, combined with the climate fluctuations during Pleistocene, probably eliminated Tertiary mesophytic taxa, and thus contributed to the establishment of the Mediterranean type flora (Coleman et al., 2003). In mesic habitats, Mediterranean vegetation corresponds to evergreen sclerophyllous forests and shrubs (Coleman et al., 2003). A certain number of these species (sclerophyllous vegetation mainly) consists of relicts of the former Neogene palaeoflora that remained in the Mediterranean region, while grassland, steppe and desert biotopes/ecosystems expanded. Moreover, the development of orogenic belts across the region as a result of the collision of the African and Eurasian plates is also inferred as a factor for the high species diversity and/or endemism of the Mediterranean flora (Axelrod and Raven, 1978; Goldblatt, 1978; Quezel, 1978; Loidi et al., 2015; Sciandrello et al., 2015; Kadereit, 2017). Large foredeep basins and wetland areas extend along the rising orogenes and allow the development of altitudinal vegetation zonations (KovarEder, 2003). Pollen records have long been used to infer past climate changes across Europe (Lona, 1950; Zagwijn, 1960, 1975; Menke, 1975; Suc and Zagwijn, 1983; Wijmstra and Groenhart, 1983; Suc, 1984; Okuda et al., 2002; Tzedakis et al., 2006; Popescu et al., 2010;

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Fletcher et al., 2013; Pross et al., 2015; Sadori et al., 2016). The major vegetation changes that occurred during the Pleistocene have been imprinted in sedimentary sequences throughout the Northeastern Mediterranean region (e.g. Bertini, 2010; Bertini et al., 2015 and Combourieu-Nebout et al., 2015 and references therein for Italian sites, Okuda et al., 2002; Joannin et al., 2007a; Pross et al., 2015 for Greek sites). However, especially for the Early Pleistocene there are a limited number of Mediterranean palynological records, which are essential for the completion of the Pleistocene vegetation history. The study area is located at the northwesternmost end of the South Aegean volcanic arc, within the eastern prolongation of the Gulf of Corinth. The Gulf of Corinth as a rift zone has been established during the post Alpine evolution of Greece (Kokkalas et al., 2006) and the Sousaki Basin has been developed among other basins in the area (Collier and Dart, 1991). Sousaki volcanic rocks constitute the basement of the Basin and can provide a lower age constrain for the long sedimentary sequences of the Basin (Pe-Piper and Piper, 2005). Moreover, the study area lies between wellknown palaeovegetation study sites in Italy and Turkey (Biltekin, 2010; Biltekin et al., 2015; Magri et al., 2017) and thus covers the passage from the European to the Anatolian provinces. For all the above reasons Sousaki Basin is considered a hot spot for palaeovegetation studies. In this study, pollen analysis has been carried out on a Lower Pleistocene sedimentary sequence in the Sousaki Basin. The scope of this study is the reconstruction of the local palaeovegetation and palaeoclimate history during the Early Pleistocene, in an area affected by global climate changes and orogeny and where similar studies have not been implemented until now. 1.1. Geological setting and stratigraphy of the wider study area Sousaki volcano comprises the northwesternmost end of the South Aegean Volcanic arc (Piper and Perissoratis, 2003; Francalanci et al., 2005; Calvo et al., 2012) (Fig. 1). It is located about 15 km east of Corinth Canal, Central Greece. All that remains from this low-standing volcanic center are some limited volcanic outcrops, in an area 10-km-long and in an E-W direction (see also Francalanci et al., 2005). Even if it presents minor volcanic appearances, Sousaki plays an important role on the evolution of the South Aegean Volcanic arc, as it constitutes the most westerly exposed Late Cenozoic volcanic activity in the arc (Pe-Piper and Piper, 2005) and separates isolated second order basins bounded by volcanic outcrops (Collier and Dart, 1991). Furthermore our study area is located in the eastward prolongation of the Gulf of Corinth, one of the most tectonically and seismically active areas in Europe (Pavlides et al., 2004; Leeder et al., 2008). In particular the Sousaki low-standing volcano is characterized by the presence of a thicker crust than the other volcanic centers of the arc (Pe-Piper and Hatzipanagiotou, 1997). Based on radiometric ages, the volcanic outcrops in the eastern Sousaki area bear an age of 2.8e2.3 Ma. The outcrops of the volcanics in the area are located next to the studied section providing a lower age constrain for it (Pe-Piper and Piper, 2005 and references therein) (Fig. 1). The distribution of the volcanic outcrops is controlled primarily by extensional tectonics. E-W trending faults and secondary SE-NW tectonic lineaments are found as an array of discontinuities throughout the area (Schroeder, 1976; Collier and Dart, 1991; Stiros, 1995; Pe-Piper and Hatzipanagiotou, 1997; Galanopoulos et al., 1998; Francalanci et al., 2005; Tsatsanifos et al., 2007). This tectonic regime has possibly affected the basin since the Pliocene (Francalanci et al., 2005; Papadopoulou, 2016). Consequently, the volcanic rocks interfinger with severely tectonized sedimentary strata. These strata are primarily marly sediments up to 400 m thick, laterally changing into sandy-

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conglomeratic facies up to 250 m thick (Schroeder, 1976). The numerous and frequent changes in the sedimentary facies across the Sousaki Basin provide evidence not only for rapid palaeogeographic changes but also for intense vertical motions. The stratigraphy of the basin is provided in detail by Mettos et al. (1988) and Collier and Dart (1991). The volcano-sedimentary sequence overlies an Upper Triassic-Lower Jurassic limestone and a Post-Upper Jurassic ophiolithic nappe (possibly thicker than 1000 m), which shows intensive hydrothermal alteration (Kaplanis et al., 2013). Finally, Holocene sediments overlie unconformably above the aforementioned sequences (Galanopoulos et al., 1998). 1.2. Lithostratigraphy of the studied section The composite stratigraphic column of the wider study area is shown in Fig. 2. The base of the column consists of the volcanic basement that is exposed southeast of the studied section. It is unconformably overlain by alterations of thick conglomerate layers and interbedded rhythmic deposition of organic rich sediments and marly/sandy layers. This Unit (Conglomerate Unit-Fig. 2) is exposed to an artificial section about 200 m east-southeast of the studied section. It is overlain by marls (Marl Unit-Fig. 2). Between the two units there is a gap in the stratigraphic data caused by the construction of the railway tracks in the area. The studied section is located on the north side of the railway tracks of Athens-Corinth suburban railway, 3.7 km west of Ag. Theodoroi town (E 37
550 23.6500 , N 23
50 42.33’') (Figs. 1 and 2). It is a well-exposed outcrop of marly sediments that lie next to the outcrops of the eastern group of volcanics. The studied section is composed mainly of alterations of white to yellow marls and marly limestones with varying thicknesses (from 0.10 m to 1 m) (Fig. 2). At the base of the section a strongly carbonated conglomerate has been found (more than 5 m thick), overlain by the typical alterations of marly sediments and by some intercalations of thinbedded organic rich shales and gypsum beds. Organic rich shales (beds thicker than 5 cm) occur at 6.04e6.20 m, 8.97e9.31 m, 9.94e9.99 m, 13.11e13.16 m and 15.58e15.67 m. They are tabular to lenticular and extend laterally for a few tens of meters. They contain rootlets and plant debris. Upwards the section consists of alterations of marls and marly limestones, which gradually become more abundant whereas the organic rich shales and gypsum beds almost disappear. The stratigraphy of the studied section is presented in detail in the respective stratigraphic column (Fig. 2; Papadopoulou, 2016). 1.3. Present day climate and vegetation The study area lies on the low hills of Gerania Mountains (1.351 m), in the eastern prolongation of the Gulf of Corinth, Greece. The climate of the wider area is typical Mediterranean as inferred by the Hellenic National Meteorological service. Especially in the plains the climate is semi-arid with very mild winters (mean annual rainfall 409.6 mm, mean annual temperature 18.2
C according to the Hellenic National Meteorological service, Corinth station, 37
560 N, 22
570 Е, altitude:15 m, data mining period:1970e1984). The vegetation type is also typical Mediterranean, presenting high endemism because of the special geological features of the bedrocks (e.g. ophiolites and volcanics) (Konstantinidis, 1997). Above 700 m, forests with Pinus halepensis and Abies cephalonica occur accompanied by Pinus nigra and Querqus. Leathery, broad-leaved evergreen shrubs or small trees (maquis vegetation) coexist (Arbutus andrachne, Arbutus unedo, Capparis spinosa, Cotinus coggygria, Daphne jasmine, Globularia alypum, Myrtus communis, Nerium oleander, Olea europaea, Phillyrea latifolia, Pistacia lentiscus and Pistacia terebinthus amongst others). On the low hills and the

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Fig. 1. a) Detailed (Google) Map of the Sousaki basin indicating the location of the studied section. Upper left, the South Aegean Volcanic Arc and Sousaki volcano. b) Geological map of the eastern part of Susaki Basin (modified from Gaitanakis et al., 1985; Mettos et al., 1988; Pe-Piper and Piper, 2005). The location of the studied section is also indicated.

plains phryganic vegetation occurs together with Caryophyllaceae, Asteraceae, Poaceae etc. (e.g. Ballota acetabulosa, Bufonia stricta, Cistus creticus, Cistus monspeliensis, Cistus parriflorus, Coridothymus capitatus, Hypericum empetrifolium and Hypericum triquetrifolium amongst others). Locally, in places with high humidity Platanus can be found. Finally, azonal vegetation is very common in the area mostly as a result of cultivation. A more detailed list of plant species found in the wider study area can be found in Konstantinidis (1997). 2. Materials and methods Pollen analyses were carried out on twenty two samples collected from the studied section (Fig. 2). Sample processing followed a modified Faegri and Iversen (1989) methodology and included digestion by acids (10% HCl and 40% HF), heavy liquid separation (ΖnCl2, density ¼ 2) and sieving (10 mm). The pollen residue, mounted in glycerol, was prepared on slides. Counting was performed at 400 magnification to a minimum pollen sum of 300

pollen grains (including Pinus). The raw counts were transformed to pollen percentages based on the pollen sum and plotted in Fig. 3 (excluding Pinus, sum of counted pollen grains without Pinus always above 100 depending on the sample). The taxa were grouped according to their vegetation type, and plotted in synthetic pollen diagrams (Fig. 4). Pollen taxa were also grouped according to the phytogeographical affinities of the corresponding plants as mentioned in Combourieu-Nebout (1993); Fletcher et al. (2013) and Sadori et al. (2016). Dinoflaggellates (range 21e93) and algae (range 7e46) were also counted in the same samples. Their percentages were calculated relative to the pollen sum of terrestrial taxa and their nomenclature was based on Marret and Zonneveld (2003). Additionally, the Aridity Pollen Index ((Artemisia þ Amaranthaceae or/and Chenopodiaceae)/Poaceae) (Fowell et al., 2003) and the Humidity index (H index ¼ arboreal pollen excluding Pinus/Steppic taxa, as steppic taxa Artemisia, Amaranthaceae or/and Chenopodiaceae, Asteraceae, Poaceae), (Triantaphyllou et al., 2009) were also calculated and plotted in Fig. 4.

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Fig. 2. Synthetic stratigraphic column of the wider study area and stratigraphic column of the studied section. The positions of the collected pollen samples are indicated on the right.

3. Results Out of the twenty two samples, two were barren. The diversity in the remaining samples is considerably high, ranging between 32 and 54 taxa and bears an average of 46 taxa (Fig. 3). According to our analyses, pollen spectra are dominated by arboreal plants with percentages up to 60% of the total assemblages. Non arboreal pollen, Pteridophytes, algae and dinoflagellates were also recognized in smaller percentages. The tree assemblage is dominated by Pinus, with significant percentages of pollen grains per sample (16%e29% of the total pollen sum). Nevertheless, this high abundance should not be overvalued in the interpretations as it is well known that Pinus trees are characterized by very high pollen grain productivity and their adequate dispersion (Seppa, 2007). Quercus type trees appear quite often in all samples (Querqus robur: 10%e23% and Querqus ilex: 6%e14% of the total pollen sum excluding Pinus). Other arboreal plants (e.g. Abies, Acer, Alnus, Betula, Buxus, Carpinus, Cedrus, Corylus, Ephedra, Fagus, Fraxinus, Hedera, Juglans, Ostrya, Taxodiaceae, Tilia, Tsuga and Ulmus), appear less commonly

(percentages 0%e5% of the total pollen sum excluding Pinus). The presence of Platanus, Picea, Engelhardia and Liquidambar is well noted although in very small percentages (0%e2.3% of the total pollen sum excluding Pinus) (Fig. 3). As far as non arboreal pollen is concerned Poaceae, Asteraceae, Amaranthaceae-Chenopodiaceae and Аrtemisia (3.5%e16% of the total pollen sum excluding Pinus) dominate. Other non arboreal pollen appear less often (0%e2.2% of the total pollen sum excluding Pinus e.g. Caryophyllaceae, Cistus, Plantago, Typhaceae). In several samples dinoflagellate cysts were identified in small numbers (percentages of 4.7%e15.8%). Their identification was difficult because they were not well preserved. Nevertheless, the presence of Polysphaeridium zoharyi and Spiniferites delicatus is noted, accompanied by Impagidinium aculeatum, Impagidinium patulum, Impagidinium plicatum, Operculodinium centrocarpum, Spiniferites cruciformis, Gonyaulax digitalis, Gonyaulax spinifera and Lingulodinium machaeroforum (identification following Fauconnier and Masure, 2004). Sporadically, some algae have been also found (e.g., Ovoidites, Zygnema sp., Tetrahedron sp., Pediastrum boryanum and Pediastrum simplex).

P. Papadopoulou et al. / Quaternary International 476 (2018) 110e119 Fig. 3. Detailed pollen records plotted against height of the studied section in Sousaki basin. All percentages of pollen taxa (Pinus is excluded) were calculated using the total sum of pollen. In diagrams of species with percentages less than 10%, exaggeration lines 10, are used in order to make the percentage fluctuations more visible.

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4. Discussion 4.1. Depositional palaeoenvironment reconstruction The presence of dinoflagellate cysts throughout the section and especially the presence of P. zoharyi, imply that the depositional environment was coastal, close to a river mouth (Rossignol, 1962; Zonneveld and Pospelova, 2015). The presence of other typical coastal/lagoonal taxa such as Spiniferites spp. and L. machaeroforum, confirms this assumption (Verleye et al., 2009; Shumilovskikh et al., 2013; Koutsodendris et al., 2017). However, the presence of the fully marine Impagidinium spp. (De Vernal et al., 1997; Thomas et al., 2017), implies a close proximity or even a connection of the depositional environment to the sea. This connection was not permanent in any case, as implied by the very low abundances of marine taxa (e.g. O. centrocarpum, Spiniferites spp.) (Kouli et al., 2009). The percentages of algae (2%e7.8%) are constant throughout the section and reveal the influence of fresh water in the aquatic environment, especially with the presence of Pediastrum boryanum, Zygnema sp. and Ovoidites, which are often found in carbonaceous sediments (Rich et al., 1982). Zygnemataceae algae characterize shallow and stagnant waters (van Geel et al., 19801981). The co-existence of fully marine, coastal/lagoonal and freshwater elements reveals a significant mixing of waters of neighboring environments and possibly a dynamic environment subjected to evolutionary changes. Similar examples have been reported from Holocene study areas in proximity with the studied section (Kouli et al., 2009; Avramidis et al., 2017; Koutsodendris et al., 2017), where similar species composition was recorded. 4.2. Palynostratigraphic age assignment of the Sousaki sequence Generally, mesothermic elements (Fig. 3) dominate the pollen assemblage, while other types of vegetation like megathermic or microthermic elements co-occur in several samples. An important characteristic of the above described pollen assemblage is the presence, even in low percentages, of rare taxa such as Liquidambar, Taxodiaceae, Engelhardia, Cedrus and Tsuga. These taxa provide information for the age of the studied section and also make possible a comparison between Sousaki and other well studied available Pleistocene palynological records of Greece and Southern Italy. Liquidambar is an almost extinct from South Europe taxon, except its presence today in Rhodes Island where it also occurred during the Early Pleistocene according to Joannin et al. (2007a). It was continuously present in S. Italy until 1.3 Ma; afterwards it was recorded sporadically (Magri et al., 2017). In Greece, Liquidambar is present in the E. Pleistocene palynological record of the Southern coast of Corinth (Rohais et al., 2007) but is absent from the E. Pleistocene record of Zakynthos (Subally et al., 1999) as is also the case for the M. Pleistocene record of Megalopolis (Okuda et al., 2002). It is also present in the long Pleistocene palynological record of Tenaghi Philippon (Van der Wiel and Wijmstra, 1987a,b) until 480 ka and this is its last occurrence in Greece. In general, Liquidambar shows a marked decline towards the end of the Early Pleistocene in Southern Europe (Magri et al., 2017). It has been recorded in Sousaki discontinuously and in low percentages but its presence is evident. Taxodiaceae, which were continuously recorded in the studied section (Fig. 3), were present in Southern Italy (Follieri, 2010; Combourieu-Nebout et al., 2015) (even if they are only discontinuously observed in the lacustrine sediments of Camerota by Brenac, 1984), until 600-500ka, when they finally disappeared (Magri et al., 2017). In Greece Taxodiaceae were present in Zakynthos between 2

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Fig. 4. Quantitative abundance plots of selected pollen taxa versus studied section height. All percentages of pollen taxa (except Pinus) were calculated using the total sum of pollen without Pinus. Pinus abundance is normalized to the total pollen sum. The main phases described in the text are indicated on the right. Steppe taxa: Artemisia, Chenopodiaceae, Ephedra, Deciduous temperate trees: Acer, Alnus, Artemisia, Buxus, Carpinus, Corylus, Fraxinus, Hedera, Juglans, Ostrya, Platanus, Quercus robur type, Taxodiaceae-Cupressaceae, Tilia, Ulmus. Altitudinal coniferous trees: Abies, Betula, Cedrus, Fagus, Picea, Herbaceous open vegetation: Apiaceae, Asteraceae, Caryophyllaceae, Cyperaceae, Plantago, Poaceae Mediterranean taxa: Cistus, Oleaceae, Quercus ilex type. Pollen taxa are grouped according to the phytogeographical affinities of the corresponding plants as mentioned in CombourieuNebout (1993); Fletcher et al., 2013 and Sadori et al., 2016. The total algae and dinoflagellate cysts percentages are also plotted. The Aridity and Humidity indexes (following Fowell et al., 2003 and Triantaphyllou et al., 2009, respectively) were also calculated.

and 1,8 Ma (Subally et al., 1999) but absent from other well-known palynological sites of the Balkan Peninsula, such as Tenaghi Philippon (max. age 1,35 Ma) (Van der Wiel and Wijmstra, 1987a,b), lake Ohrid (max. age 500 ka) (Sadori et al., 2016), Ioannina basin (max. age 423 ka) (Tzedakis, 1994) and also from the Lower Pleistocene record of Corinth Basin (Rohais et al., 2007). They have only been recorded in Rhodes Island until 700 ka (Joannin et al., 2007a). Engelhardia has been found in Sousaki in very low percentages but its presence is still notable (Fig. 3). This taxon is an important Early Pleistocene biostratigraphic marker becoming rare in Southern European sites after 1.5 Ma and disappearing after 1 Ma (Magri et al., 2017). In Southern Italy Engelhardia is present in Semaforo section between 2.4 and 2.1 Ma (Combourieu-Nebout, 1993) and its last instantaneous occurrence is recorded between 1.8 and 1.7 Ma in Camerota (Brenac, 1984). In Greece it is reported from Rhodes up to 1.7 Ma (Joannin et al., 2007a) and from Zakynthos up to 1.8 Ma (Subally et al., 1999) but is totally absent from all other Greek sites. However across S. Europe, Engelhardia during the E. Pleistocene has been found in disjunctive populations and many times with modest presence, as it is the case for Semaforo section in S. Italy (Magri et al., 2017). Its overall limited presence may well be a result of unfavorable conditions but it can also be assigned to the lack of information due to the existence of a poor chronostratigraphic framework (especially for Calabrian sites), unpublished detailed data (e.g. Vrica section in S. Italy, Combourieu Nebout and Vergnaud Grazzini, 1991) and a lack of studies in continental records (Magri and Tzedakis, 2000; Magri et al., 2017). The poor constrain of Engelhardia across S. Europe during the E. Pleistocene, implies a degree of uncertainty when determining the age of the studied sediments but it is still considered a powerful tool when other chronostratigraphic markers are lacking. Cedrus, that is currently absent from continental Europe, was continuously recorded in the studied samples. It was abundant in Early Pleistocene sites of Southern Italy and Greece such as Rhodes

(Joannin et al., 2007a), Tenaghi Philippon (Van der Wiel and Wijmstra, 1987a,b) and Zakynthos (Subally et al., 1999) until 1.4 Ma. Rohais et al. (2007) reports it also in the Corinth Basin record until 0.7 Ma. Tsuga appears discontinuously in the Sousaki record but its presence is important because it has not been found in Southern Italian and Greek sites after 0.5 Ma (Magri et al., 2017). More specifically, in Southern Italy it is present in the Early Pleistocene record of Camerota (Brenac, 1984) and in other sites until approximately 0.5 Ma (Magri et al., 2017). In Greek palynological records it appears sparse in Rhodes (Joannin et al., 2007a). In Corinth Basin, it is present only in the samples of 1.8e0.9 Ma age (Rohais et al., 2007). In Tenaghi Philippon (Van der Wiel and Wijmstra, 1987a,b) it is present until 0.7 Ma but is absent from all other younger Greek palynological sites. Sciadopitys and Eucommia are two taxa that are not reported from Southern Italian and Greek sites after 2.1 Ma (Magri et al., 2017) with the exception of Tenaghi Philippon (Van der Wiel and Wijmstra, 1987a,b) where Eucommmia only, is again reported after 1.4 Ma. Their absence from the studied section may imply an age younger than 2.1 Ma, nevertheless this cannot consist a robust argument, because their absence may well be the result of unfavorable local conditions in the Sousaki Basin and/or failure of preservation of their pollen grains. The absence of a number of other important biostratigraphic markers widely used in Pleistocene palynological records, such as Carya, Zelkova, Pterocarya, Cathaya and Parrotia, limits our age considerations, but can be related to their special ecological preferences. A characteristic example can be Pterocarya, which shows uneven behavior in several sites of Southern Europe because of its dependence on the local hydrological regime (Magri et al., 2017). Carya on the other hand, was adequately represented in Early Pleistocene Southern Italian sites such as Camerota (Brenac, 1984), it was present in Tenaghi Philippon (Van der Wiel and Wijmstra,

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1987a,b), Rhodes (Joannin et al., 2007a) and Corinth basin (Rohais et al., 2007) in low percentages, but is absent from other Greek sites such as Zakynthos (Subally et al., 1999) and Ioannina (Tzedakis, 1994). Evidently, its distribution appears patchy throughout Southern Europe (Magri et al., 2017) and for this reason its absence is not a safe biostratigraphic marker. Another typical element of Early Pleistocene age is Cathaya. It was continuously present in Southern Italy (Magri et al., 2017) except Camerota (Brenac, 1984), present in Rhodes (Joannin et al., 2007a) and Zakynthos (Subally et al., 1999) but absent in all other Pleistocene Greek sites including Sousaki. Its absence could be related to its reduction in Southern Europe after 1.5 Ma (Magri et al., 2017) (as proposed for Camerota section by Brenac (1984) but it could also have been caused due to identification difficulties (similarity of its pollen grains with certain species of Pinus as proposed by Magri et al., 2017). Moreover the bad preservation condition of pollen grains from Sousaki record did not allow the separation of some pollen grains that appear similar in structure to each other such as Ulmus and Zelkova (Magri et al., 2017)). According to Tzedakis (2007), the Mediterranean type climate was established in the Mediterranean region after 3.6 Ma, and this favored the strong presence of Mediterranean taxa. The above consideration together with the high percentages of Mediterranean taxa (between 10% and 20%) in most part of the studied section, leads to the conclusion that the studied section bears an age younger than 3.6 Ma. This age can be further delimited by the inferred age of the eastern group of volcanics that serves as the basement of the basin (2.8e2.3 Ma, Pe-Piper and Piper, 2005 and references therein). There are also some further indications for the lower age limit of the studied section. The absence of Sciadopitys and Eucommia can potentially imply an age younger than 2.1Ma. Moreover, because of the absence of Liquidambar from the nearby Zakynthos section and its presence in Sousaki section, the implied age could be even younger than 1.8 Ma, but this is an assumption that needs further evidence. In addition, the described palaeovegetation shows distinct similarities to other known palynological sites of the same age in Greece and Southern Italy, namely Zakynthos (Subally et al., 1999), Corinth Basin (Rohais et al., 2007) and especially with Camerota section in S. Italy (Brenac, 1984) as noted above. However, the latter considerations need further proof and cannot be undoubtedly adopted. According to the synthesis of the palynological assemblage and mostly because of the coexistence of Taxodiaceae and Engelhardia, the upper age limit for the studied section is placed to 1.5 Ma (Fig. 5). Especially Engelhardia does not exist in other studied sites in Southern Italy and Greece after 1.7 Ma. However this age estimation is rather tentative because of Engelhardia‘s poorly constrain through S. Europe during the E. Pleistocene. In conclusion, a safe age estimation for the studied section would be a time span between 2.8 and 1.5Ma. 4.3. Elevation dependent vegetation changes The pollen assemblage reveals a well-diversified flora in which altitudinal coniferous trees, subtropical elements, temperate trees and herbs are found more or less together. This indicates an altitudinal zonation of the vegetation in the bordering lands. From coast to highlands, vegetation was organized in altitudinal belts (Horvat et al., 1974; eFloras, 2008). The exact elevation gradients for the Early Pleistocene altitudinal belts are not known but herein they are inferred to present day altitudinal belts with which they would not differentiate critically. The vegetation of the coastal environment was characterized by the presence of halophytes such as members of the families Amaranthaceae and Chenopodiaceae (mainly herbs) and probably

Fig. 5. Stratigraphical setting and schematic pollen biostratigraphy of key taxa of selected Pleistocene records from Southern Italy and Greece (Camerota-Brenac, 1984; Tenaghi-Van der Wiel and Wijmstra, 1987a,b; Semaforo-Combourieu-Nebout, 1993; Ioannina-Tzedakis, 1994; Zakynthos-Subally et al., 1999; Megalopolis-Okuda et al., 2002; Rhodes-Joannin et al., 2007a; Corinth-Rohais et al., 2007, Ohrid-Sadori et al., 2016). Palaeomagnetic polarity reversals were redrawn from Shackleton et al. (1990). Continuous lines suggest continuous presence during the respective time interval. Dashed lines imply discontinuous presence or reduced abundances (Lisiecky and Raymo, 2005).

the sporadic presence of pine trees. The occurrence of coastal marshes covered with members of the family Typhaceae is also considered possible. At the plains and low hills from sea level to an altitude of around 700e1000 m a mixed broad-leaved mesophytic temperate forest predominated consisting mainly of deciduous elements such as Acer, Carpinus, Corylus, Fagus, Juglans, Ostrya, Quercus robur type, Tilia and Ulmus. In protected valleys these temperate elements co-

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occurred with more thermophilous trees and shrubs such as Engelhardia and Taxodiaceae. Especially, the presence of Taxodiaceae implies the presence of swamps in the vicinity of the study area, since Taxodiaceae are typical for such environments (Kovar-Eder, 2003). In less humid regions with infertile soil, pine trees could have developed poor stands or would have co-occurred with deciduous elements in mixed forests. The only climbing plant that has been identified in the pollen spectra is Hedera, which lived in the mixed mesophytic forest. At the ground level fern and fern allies -like Pteridophytes-thrived. In warm, more arid sites in this altitude belt, a Mediterranean-like woodland probably occurred, composed of Quercus ilex type, Oleaceae and Cupressaceae as well as of various xerophilous herbs like Cistus. Above 1000 m it seems that the mixed broad-leaved deciduous forests gradually passed to mixed coniferous forests with Pinus, Cedrus and Tsuga while above 1300 m in altitude (on the nearby mountains) Abies and Picea forests occurred. Betula but mostly Picea, nowadays do not grow or exist in significant populations, south of Rodopi Mountains in Northern Greece (Gerasimidis and Athanasiadis, 1995). This is an interesting indication for their phytogeographical evolution. The azonal (riparian) vegetation across lake and river banks was characterized by Platanus, Liquidambar and Alnus. Below the forest canopy Pteridophytes thrived, while in the shallow and quiet fresh water bodies (lake margins) Typhaceae and Cyperaceae or even Taxodiaceae possibly existed. Open habitats covered by herbaceous plants, such as grasses (Poaceae) and steppe elements (Artemisia, Ephedra), surely had a significant presence in the region during the Early Pleistocene. 4.4. Climate changes The pollen diagrams (Figs. 3 and 4) reveal rather stable climatic conditions during the Early Pleistocene in the Sousaki Basin. The Mediterranean type vegetation elements (Fig. 4) show almost constant percentages around 20% suggesting that a Mediterranean climate had already become well established in the region (Coleman et al., 2003). It was mainly characterized as temperatesubtropical with constant water supply and mild temperatures as implied by the dominance of mesothermic elements and the composition of the arboreal and non arboreal plants (Fig. 4). The increased percentages of herbaceous open vegetation (abundances constantly higher than 15%) reveal the coastal character of the environment (Fig. 4). The presence of Ephedra, Poaceae and Amaranthaceae-Chenopodiaceae in the palynological record could be explained by saline edaphic conditions as opposed to high aridity (Combourieu-Nebout et al., 2015). According to the Aridity Pollen Index the whole section was deposited during moist intervals dominated by meadow or forest steppe (Aridity Pollen Index <5%) (Fowell et al., 2003). The almost stable percentages of the pollen records show no severe climatic oscillations, although in the Early Pleistocene the glacial/interglacial cycles provide the main climatic control also in the Mediterranean region (Joannin et al., 2007a,b; Tzedakis, 2007; Rohling et al., 2015). This is also evident by the very low percentages of steppic taxa, which usually got increased during the cold glacial stages of the Pleistocene (Combourieu-Nebout et al., 2015). Although the palynological record shows no significantly fluctuating percentages, there are some minor changes in the palynofloral distributions suggesting that there was a minor zonation in the record. Between 13.1 and 19.3 m, the H index (Triantaphyllou et al., 2009) shows relatively high values. This time interval represents a wetter phase, which is also pointed out by an increase in the Platanus abundance. Accordingly, Artemisia that usually grows in arid and semi-arid habitats shows lower values during this time

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interval. However, at 13 m and 17.1 m the Aridity index shows instantly high values which could be a result of transient aridity incidents. On the other hand, at 7.7 m and 18.3 m, the Aridity index shows instantly low values corresponding to slightly increased values of H index. These could be considered as episodes of relatively increased humidity. Overall these minor but tangible fluctuations in the humidity reflect also minor oscillations of the climate. In the upper part of the section above 19.3 m both Humidity and Aridity indices decrease. This might be due to the overall low pollen sum and the bad preservation condition of pollen in the samples from this part of the section. The overall prevalence of thermophilous taxa in the whole section with more or less steady percentages and the low percentages of Artemisia which remains below 5% in all studied samples, together with the coexistence of maquis shrub land vegetation and subtropical taxa provides evidence for the prevalence of relatively warm climatic conditions. These data resemble the climate and vegetation in N. Anatolia and N. Aegean Sea (Biltekin, 2010) during the Tiglien warm period (1.75e2.2 Ma, MIS 63e103, according to Leroy, 2007) (Zagwijn, 1960, 1975; Zagwijn and Suc, 1984). 5. Conclusions The pollen analyses of a sediment outcrop section from the Lower Pleistocene of Sousaki Basin, eastern Gulf of Corinth, Greece, provides an insight into the vegetation and climate during Early Pleistocene, in a region where similar studies have not been implemented until now. The palynological assemblage indicates almost stable climatic conditions and a Mediterranean type of vegetation with altitudinal zonation due to the existence of the Gerania Mountains at the north of the basin, around a coastal area. Pinus and Quercus dominate, accompanied by other arboreal and non arboreal plants. Rare taxa, which do not occur nowadays in Southern Europe, such as Taxodiaceae, Engelhardia, Liquidambar, Tsuga and Cedrus were present in Sousaki between 2.8 and 1.5 Ma. The presence of these rare taxa is inferred for the first time for this region. This tentative age is implied by the co-existence of Taxodiaceae and Engelhardia. Moreover the almost stable percentages of the pollen records show no severe climatic oscillations notwithstanding that in the Early Pleistocene the glacial/interglacial cycles comprise the main climatic control. Acknowledgements Authors sincerely thank Dr. C. Ioakim and the Greek Institute of Geology and Mineral Exploration for providing us the ability to analyze in their laboratory the palynological assemblages. We are also indebted to Dr. C. Ioakim and Dr. A. Koutsodendris for their thoughtful remarks on the palynological results. This research did not receive any specific grant from public, commercial, or not-forprofit funding bodies. References Avramidis, P., Iliopoulos, G., Nikolaou, K., Kontopoulos, N., Koutsodendris, A., van Winjngaarden, G.J., 2017. Holocene sedimentology and coastal geomorphology of Zakynthos Island, Ionian Sea: a history of a divided Mediterranean island. Palaeogeogr. Palaeoclimatol. Palaeoecol. 487, 340e354. Axelrod, D.I., 1975. Evolution and biogeography of the Madrean-Tethyan sclerophyll vegetation. Ann. Mo. Bot. Gard. 62, 280e334. Axelrod, D.I., 1977. Outline history of California vegetation. In: Barbour, M.G., Major, J. (Eds.), Terrestrial Vegetation in California. John Wiley and Sons, New York, USA, pp. 139e193. Axelrod, D.I., Raven, P.H., 1978. Late Cretaceous and Tertiary vegetation history of Africa. In: Werger, M.J.A. (Ed.), Biogeography and Ecology of Southern Africa. Dr. W. Junk, The Hague, Netherlands, pp. 77e130. Bertini, A., 2010. Pliocene to Pleistocene palynoflora and vegetation in Italy: state of

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