Palaeoaltitude of the Sila Massif (Southern Apennines, Italy) and distribution of the vegetation belts at ca. 2.4 Ma (Early Pleistocene)

Review of Palaeobotany and Palynology 189 (2013) 1–7

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Research paper

Palaeoaltitude of the Sila Massif (Southern Apennines, Italy) and distribution of the vegetation belts at ca. 2.4 Ma (Early Pleistocene) Séverine Fauquette a,⁎, Nathalie Combourieu-Nebout b a b

Institut des Sciences de l'Evolution (UM2-CNRS 5554), CC 061, Université de Montpellier 2, Place Eugène Bataillon, 34095 Montpellier cedex 5, France Laboratoire des Sciences du Climat et de l'Environnement, CNRS/CEA UMR 8212, Domaine du CNRS, Avenue de la Terrasse, 91198 Gif-sur-Yvette cedex, France

a r t i c l e

i n f o

Article history: Received 3 July 2012 Received in revised form 15 October 2012 Accepted 23 October 2012 Available online 13 November 2012 Keywords: Early Pleistocene Southern Italy palaeoaltitudes interglacial refugia pollen vegetation

a b s t r a c t Palynological studies are considered as an excellent tool for palaeoaltitude estimates as sedimentary basins receive abundant pollen grains from surrounding uplands, especially through riverine detritic inputs. Here, we provide new evidence for estimating the palaeoaltitude of the Sila Massif (southern Apennines, Italy) ca. 2.4 Ma, based on vegetation data derived from pollen analysis of the Semaforo succession. The past vegetation changes reflect shifts in the vegetation belts on the Sila Massif in Calabria, 30 km north of Semaforo. Changes from subtropical forests to open-herbaceous formations indicate climate variability ranging from warm and humid interglacial to cold and/or dry glacial conditions. The climate reconstruction for Calabria, at sea-level, infers that mean annual temperatures were ~4 °C higher than today during the interglacial period, while mean annual temperatures were similar to the present-day during the glacial period. Therefore, pollen-based altitude estimates provide evidence that during the lower Pleistocene the southern part of the Apennines reached between 1600 and 2100 m above sea-level while the Crotone region was 500 m below sea-level. Although the Crotone Basin has been uplifted approximately 650 m since 2.4 Ma, it is not possible to calculate accurately to what extent the Sila Massif has been submitted to the same uplift, as this basin is a fault-bounded basin. Nevertheless, as the southern Apennines did not attain high elevations, the interglacial refugia for microthermic arboreal species such as Abies or Picea were certainly situated northward in the Apennines at higher altitudes, or on the northern slopes of the Sila Massif exposed to cooler and more humid conditions. © 2012 Elsevier B.V. All rights reserved.

1. Introduction The Earth's relief is the mirror of complex coupling between internal and external forcing, such as climate, as well as long-term (> thousands years) and short-term (b thousands years) processes. The main phases of the relief's uplift in Europe are now quite well known and relatively accurately chronologically calibrated. However, the quantification of palaeoaltitudes remains essential for estimating the exhumation rates of mountain belts and for evaluating denudation rates in relation to terrigenous sediments being accumulated in sedimentary basins, as well as for improving palaeoclimatic models (Ramstein et al., 1997; Sepulchre et al., 2009). Many approaches have been used, particularly relating to geomorphology and apatite fission-track thermochronology, which provide evidence about denudation as a consequence of erosion, and thus indications about past altitudes of mountains (Gunnell, 2000). However, none of these methods alone recovers the accurate palaeoaltitude change of the earth's surface.

⁎ Corresponding author. E-mail address: [email protected] (S. Fauquette). 0034-6667/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.revpalbo.2012.10.003

It has been assumed for a long time that vegetation is modified according to latitude and altitude, with an almost regular adjustment in respect to decreasing temperatures from south to north in the Northern Hemisphere (Troll, 1966, 1973). As a consequence, plant remains have been used better to estimate palaeoaltitudes than classical geological methods. The first attempts to estimate altitudes from palaeofloras used macroremains (Axelrod, 1965, 1968; Axelrod and Bailey, 1976; Meyer, 1992). Unfortunately, the palaeoaltitude estimates that were obtained remain difficult to calculate as vegetal macroremains only provide a fragmentary and very circumscribed idea of the vegetation. In addition, they do not use a calculated standard thermic gradient (Meyer, 1992). In contrast, palynological studies are considered as an excellent tool for palaeoaltitude estimates. Indeed, sedimentary basins receive, along with detritic inputs from rivers, a high amount of pollen grains; these are representative of all vegetation belts from the catchment area, as demonstrated on modern sediments of the Rhone River (Beaudouin et al., 2005, 2007). In particular, the higher vegetation belts, such as the belt with fir and spruce, appear useful for estimating the minimal altitude of surrounding mountains. Employing this approach, Fauquette et al. (1999a) have successfully reconstructed palaeoaltitudes using Zanclean pollen spectra validated by geomorphology from the Mercantour Massif (southeastern France), from Mount Canigou in the

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Pyrenees in Southern France (Suc and Fauquette, 2012) and for Miocene pollen spectra from the Alpine Foreland and Vienna basins in Central Europe (Jiménez-Moreno et al., 2008). Here we propose to provide palaeoaltitude estimates for the Sila Massif in southern Italy, for the time slice around 2.4 Ma, using vegetation data derived from pollen analysis of the Semaforo succession (Combourieu-Nebout, 1993; Combourieu-Nebout et al., 2000). This is a new landmark for mapping the landscape of Calabria during the lower Pleistocene.

2. Regional setting 2.1. Geological context The complex tectonic evolution of southern Italy makes it difficult to do palaeogeographical reconstructions. Southernmost Italy, Calabria, is located at the margin of an upper plate associated with the active subduction zone of the eastern Mediterranean towards the West. During the Pliocene and Pleistocene, a mountain chain emerged along the modern axis of the Apennines (Meulenkamp and Sissingh, 2003; Khondkarian et al., 2004) (Fig. 1). Thus, Westaway and Bridgland (2007) referred to the Sila Massif as a “palaeo-island” emerging during the Early Pleistocene in Central Calabria, between Cosenza and Crotone. The intense uplift that affected this region resulted in the emersion of marine sediment deposits from below 500 m water depth (Landini and Menesini, 1978) to between 0 and 400 m above sea level around Semaforo today. This uplift phase began during the middle Pleistocene and extended to the Holocene. In southern Italy, it has been assumed that the Sila Massif, about 30 km from the coastal section, was the source area of the pollen grains buried in the lower Pleistocene marine sediments of Crotone (Combourieu-Nebout et al., 2000), especially as the eastern part of the Sila Massif is drained by many short rivers that flow eastward into the Ionian Sea (Westaway and Bridgland, 2007).

2.2. Modern climate and vegetation on the Sila Massif Northwest of Crotone (39°N, 16°42′E; Fig. 2), the Sila Massif culminates at 1928 m a.s.l. at Monte Botte Donato. This massif induces an altitudinal zonation of the vegetation from the coast to the summit in relation to climate and exposure. Mean annual temperatures and precipitation vary respectively from around 16 °C and about 680 mm near the coast, to around 3 °C and about 1400 mm at high altitude. Descriptions and phyto-sociological interpretations of the modern vegetation from southern Italy have been developed in a number of papers (e.g., Ozenda, 1975; Bonin et al., 1976; Bonin, 1981; Gentile, 1982). In addition, the vegetation zones, linked to altitudinal changes and climate are covered in a diverse literature (e.g., Bonin, 1981; Gentile, 1982; Quézel and Médail, 2003): – a thermo-Mediterranean belt with principally Stipa tortilis steppes, Olea, Ceratonia, Pistacia and Pinus halepensis from the littoral to around 500/600 m high depending on local conditions, – a meso-Mediterranean belt with Quercus ilex forests from 500/ 600 m to around 1000 m high, – a supra-Mediterranean belt composed of deciduous Quercus forests (Quercus pubescens, Quercus cerris, Quercus frainetto) with Ostrya carpinifolia, Fraxinus ornus, Carpinus orientalis from around 800/900 to 1200 m high. Locally, Pinus laricio is present. – a mountainous Mediterranean belt from 1100/1200 m to the summit, represented by a Fagus sylvatica forest with, from nearly 1600 m, Abies alba which does not play a prominent role in this region (Bonin, 1981; Gentile, 1982). In the lower part of this belt, Pinus laricio is present on granitic substrates. – an oro-Mediterranean belt with Pinus leucodermis locally. Due to the absence of high mountains (i.e. higher than 2000 m) and to the large amplitude of the mountainous belt (with Fagus) the oro-Mediterranean belt is nearly absent in the Sila Massif. Consequently, the forest reaches the summit.

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Fig. 2. Location map of the Sila and of the Semaforo section in Calabria (southern Italy).

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Fig. 3. Stratigraphic column with chronology, polarity, lithology, pollen samples and biostratigraphy (Combourieu-Nebout, 1993) and MPRS coding (Hilgen, 1991) (from Klotz et al., 2006).

2.3. Lower Pleistocene vegetation and climate in Southern Italy The Crotone Series (south of Crotone, Italy) is certainly one of the best-studied Early Pleistocene successions in Europe (Suc et al., 2010) with biostratigraphic, magnetostratigraphic and cyclostratigraphic analyses. These studies have established that the Crotone Series cover the time interval from 2.47 to 1.21 Ma. The Semaforo marine record (Fig. 2) corresponds to the lower part of the Crotone Series and consists of 180 m of marine clays, including eight sapropel layers (layers 222 to 204, Hilgen, 1991; Lourens, 1993) and three volcanic ash beds (near sapropel layers 222, 208, and 206). The chronology (Fig. 3) is based on successive tie-points according to foraminifera and nannofossil occurrences, palaeomagnetism and correlation with the astronomical sapropel chronology (Combourieu-Nebout, 1993; Lourens, 1993). Thus, the Semaforo section covers a time span from 2.46 Ma to 2.11 Ma and belongs to the Gelasian stage (Suc et al., 2010). With respect to the international agreement for placing the Pliocene–Pleistocene boundary at 2.588 Ma (Gibbard et al., 2010), the Semaforo section covers the Early Pleistocene. The palynological record obtained on this section displays 165 pollen spectra and 110 identified taxa (Combourieu-Nebout, 1993). The pollen flora changes sensitively from the base to the top of the section and reflects palaeoclimate oscillations related to lower Pleistocene interglacial– glacial cycles. Therefore, alternation of the main vegetation groups occurs (Fig. 4) in which plants with similar phytogeographical affinities are gathered together and indicate certain climate variations. Each cycle begins with deciduous forest (composed mainly of Quercus, Acer, Ilex, Carpinus, Buxus, Eucommia, Carya, Juglans, Pterocarya, Ulmus) followed by subtropical humid forest (Cathaya, Engelhardia, Magnolia, Nyssa, Symplocos, “Taxodiaceae” 1) development, then altitudinal forest (Tsuga, Cedrus, Picea, Abies), and finally open herbaceous formation and steppe (Chenopodiaceae, Poaceae, Artemisia, Ephedra, Asteraceae) expand. The Mediterranean forest association although present (Olea, Ceratonia, Pistacia, Quercus ilex, Cistus, Phillyrea, Ligustrum), remains scarce and follows irregularly the deciduous forest and/or the subtropical humid forest pattern. Such vegetation changes undoubtedly reflect shifts in the vegetation belts over the Sila Massif, the main pollen source area. With respect to present-day characteristics of vegetation belts on the Sila Massif, during the lower Pleistocene, open vegetation and Mediterranean associations expanded at the lowermost elevations, subtropical and temperate forests at medium altitude, while forests composed of microthermic plants developed at the height of the Sila Massif (Combourieu-Nebout and 1 Many genera formerly assigned to Taxodiaceae (e.g. Combourieu-Nebout, 1993) are now grouped in subfamilies of Cupressaceae, e.g. Taxodioideae (Taxodium, Glyptostobus, Cryptomeria) and Sequoioideae (Sequoia, Sequoiadendron, Metasequoia).

Vergnaud Grazzini, 1991; Combourieu-Nebout, 1993). Furthermore, the cyclic vegetational replacements that occurred mainly during the lower Pleistocene resulted from variations in temperature and moisture (Combourieu-Nebout, 1995; Combourieu-Nebout et al., 2000). The changes from subtropical forests to open-herbaceous formations reflect certainly the shift from warm and humid interglacials to cold and/or dry glacials. A long-term vegetation change is superimposed on the interglacial/glacial cyclic pattern as from the base to the top of the section, subtropical humid forest elements (especially “Taxodiaceae”) are increasingly replaced by deciduous forest elements (especially deciduous Quercus), until the subtropical ecosystems finally disappear in the Mediterranean area at around 1.2 Ma (Combourieu-Nebout, 1995). Simultaneously, a general increase in altitudinal coniferous forest trees and Artemisia indicates the opening up of the vegetation, although arboreal pollen grains always dominate over herbaceous pollen. The regional climatic changes have been reconstructed from pollen data (Klotz et al., 2006) using the “Probability mutual Climatic Spheres” (PCS) described in detail by Klotz (1999) and Klotz et al. (2004). The application of PCS on the Semaforo pollen record provides a detailed view on the lower Pleistocene regional climate in the central Mediterranean and clearly reveals a succession of eight interglacial periods and nine glacial periods (Klotz et al., 2006). The climate reconstruction points to higher temperatures by reference to present day ones of at least 2.8 °C on average annually and 2.2 °C in winter temperatures, and 500 mm in precipitation during the interglacial periods. During the glacial periods, temperatures are generally lower than today, but annual precipitation is equivalent. Along the consecutive interglacial periods, a trend toward a reduction in annual and winter temperatures by more than 2.3 °C, and toward a higher seasonality is observed. Along the consecutive glacial periods, a trend toward a strong reduction in all temperature parameters of at least 1.6 °C is reconstructed. Climatic amplitudes of interglacial–glacial transitions increase from the older to the younger cycles for summer and annual temperatures.

3. Method of palaeoaltitude estimate from pollen data The method to quantify palaeoaltitudes, developed by Fauquette et al. (1999a), besides climatic reconstructions, takes into account pollen floras accumulated near the coastline, providing a regional view of the vegetation from the littoral up to the uppermost altitudinal belts. Altitudinal zonation of plants reflects along the slopes of mountains their latitudinal distribution. As an example, today the upper part of the Fagus vegetation belt is situated at 1200 m high in the Vosges massif (France), while it is situated at about 2000 m high in Calabria (Italy) (Ozenda, 1989) (Fig. 5). Similarly, the distribution of Abies varies in altitude in relation to latitude (Fig. 6) (Ozenda, 1961; Noirfalise et al., 1987;

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Quézel, 1998). Thus, the vertical shift of the vegetation belts in relation to latitude is even more difficult to quantify, as the altitudinal range of plant species is controlled by climatic parameters (decreasing temperature and increasing precipitation with altitude), as well as by local conditions (nature of soils, slope orientation, etc.). Ozenda (1975) attempted to quantify this shift in Europe according to three observations: (i) vegetation belts occur at different altitudes at different latitudes; (ii) in temperate regions, mean annual temperature varies of ≈0.6 °C per degree in latitude (1° in latitude= ca. 110 km); (iii) temperature decreases in relation to the altitude of ≈0.55 °C per 100 m of elevation. Therefore, Ozenda (1989) established that a shift of 1 km to the north corresponds, from a bioclimatic point of view, to a shift of 1 m in altitude. So today, in Europe, vegetation belts move usually 110 m in altitude per degree in latitude. Using such an altitude–latitude relationship together with the vegetation distribution and the climatic estimates, the altitude of the southern Apennine ranges may be assessed for the lower Pleistocene, especially as it has been

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established that an altitude/latitude temperature gradient similar to the present-day existed since the Tortonian (ca. 10 Ma) (Fauquette et al., 2007). High altitude tree taxa represent the best indicators of palaeoaltitude in the fossil pollen spectra. Nevertheless, pollen data do not yet allow to estimate either the altitudinal range of this altitudinal vegetation belt or to know whether alpine herbaceous and perpetual-snow belts existed above. This is due to the difficulty in differentiating alpine from lower elevation herbaceous elements. As a consequence, to estimate the palaeoaltitude, we generally use the tree taxa growing near the summit such as Fagus, Abies, Picea if they are present. In the case of the Semaforo site, Abies constitutes the best indicator. Indeed, in the Pleistocene pollen spectra of this region, Fagus remains poorly represented and the behaviour of its record seems to be closer to that of mesothermic taxa than microthermic taxa. The Pleistocene Fagus from Semaforo may be rather related to Fagus orientalis that lives nowadays in Eastern Europe at low altitude as in the Hyrcanian mountains with Carpinus betulus, Quercus,

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Zelkova, Acer, etc. (Zohary, 1973) and along the rivers (Walter, 1974) or closer to Fagus pliocenica (syn. Fagus pristina, Barron and Diéguez, 1994), a species which no longer exists but is recorded in the Neogene macroflora (e.g. Menendez-Amor, 1955; Roiron, 1981). Denk (1998) compares the European Late Tertiary plant assemblages containing Fagus to a relict area of northern Turkey and western Georgia. Hence, in our study Fagus can not be used as a high altitude marker. Picea can not be used here either as it is no more present in the Sila Massif today. Then, its past lower altitudinal occurrence can not be known in the studied area. We will thus use Abies as the best altitudinal marker. The first climatic reconstruction performed on the Semaforo section integrated the climatic signal from the complete pollen spectra, including high altitude forest elements, giving an estimate of the regional climate (Klotz et al., 2006). However, the palaeoaltitude estimates are based on the mean annual temperature at the low altitude allowing the altitudinal and latitudinal temperature gradients to be used (Fauquette et al., 1999a). In the present study, for low altitude, the climate has been reconstructed from the taxa growing at low to middle-low altitudes and using the “Climatic Amplitude Method” developed by Fauquette et al. (1998). In this method, the past climate is estimated by transposing the climatic requirements of the larger modern taxa set to the fossil data. The most likely climate for a set of taxa is then estimated according to the proper climatic interval for the highest number of taxa. Numerous palynological studies (e.g. Suc et al., 1995a,b, 1999; Jiménez-Moreno, 2005) have shown that the Neogene and Lower Pleistocene vegetation zonation follows a similar latitudinal and altitudinal zonation to that observed in present-day south-eastern China (Wang, 1961), where most of the taxa that had disappeared from Europe by the late Neogene may be found. Therefore, high latitude/altitude taxa were excluded from the reconstruction process and the reconstructed climate estimates correspond here to the climate at low to middle-low altitude (Fauquette et al., 1998).

4. Results: palaeoaltitude of the Sila Massif at ca. 2.4 Ma Our estimates have been performed on the older climatic cycle from the Semaforo succession, which is the most typical. The interglacial climate corresponds there to pollen spectra recorded between 2.418 and 2.423 Ma and the glacial climate by pollen spectra between 2.433 and 2.437 Ma. During the interglacial, the mean annual temperature (Ta) is estimated between 15.5 and 24.5 °C, with a most likely value (MLV) around

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20 °C, while during glacial times, Ta is estimated to have been between 9.5 and 21.5 °C, with a most likely value around 15.5 °C. These estimates illustrate that, during this interglacial period, mean annual temperatures reached ca. 4 °C higher than today. Such values are consistent with previous climate reconstructions from other Mediterranean sites (Fauquette et al., 1999b). They confirm those obtained by Combourieu-Nebout et al. (2000) indicating that glacial climate conditions were very similar to present-day ones in Calabria, despite the lower Pleistocene specific flora with no modern analogue in the Mediterranean. During glacial periods, the annual temperature was very similar to the present-day temperature at Crotone. Abies could thus have developed from around 1600 m above sea-level as nowadays. The interglacial temperature estimate (MLV) is recorded today at about 34° north, at Gabès in Tunisia, thus i.e. 5° southward of Crotone. Using the relationship established by Ozenda (1989), a shift of 5° in latitude corresponds to a shift of about 550 m in altitude. Today, the lower altitudinal limit for Abies in the Sila Massif occurs at around 1600 m (Bonin, 1981). Taking into account the shift of 550 m in vegetation belts between the Pleistocene and the present day, Abies would have been present above 2150 m. This value is an estimate of palaeoaltitude of the lower limit of the Abies belt during interglacials. Accordingly, such a result indicates a minimum altitude for the southern part of the Apennines, around 2100 m high above sea-level. However, Abies percentages are very low and even absent during interglacial periods showing that the southern Apennines probably did not attain 2100 m. Our results indicate that the Sila Massif elevation was probably between 1600 and 2100 m high at around 2.4 Ma. The palaeoaltitude estimate was calculated using the most likely value of Ta obtained from pollen data. The MLV is certainly less representative of the climate than the entire reconstructed climatic amplitude (as plants may sometimes support large climatic ranges); however it provides a good idea of the optimum climate where they best develop. MLVs have been statistically tested on modern pollen data and they are considered to give reliable results (Fauquette et al., 1998). Moreover, a validation of the palaeoaltitude reconstruction method on modern pollen data has been realised indicating that, although the reconstructed climatic interval may be large, the MLV gives a reliable estimate for the altitude (Suc and Fauquette, 2012). 5. Discussion Geological studies point out the complex history of the Southern Apennines uplift (e.g. Malinverno and Ryan, 1986; Ferranti et al., 1996; Bartolini et al., 2003; Piedilato and Prosser, 2005). In fact, the Southern Apennines were built up from the late Oligocene-early Miocene to the late Pleistocene and consist of an upper wedge composed of strongly deformed deep marine and carbonate platform successions and a buried thrust and fold belt in the carbonate rocks of the Apulian platform (Piedilato and Prosser, 2005). The present study based on pollen data shows that during the lower Pleistocene (i.e. around 2.4 Ma) the southern part of the Apennines (Sila Massif) reached between 1600 and 2100 m. However, the relatively low percentages of Abies in the pollen spectra covering interglacial periods show that it was certainly at its limit of distribution. The maximum altitude of the Sila Massif was thus more certainly around 1600 m than 2100 m. For what concerns the estimation of the Sila Massif palaeoaltitude, the method is based on the modern distribution of the Abies belt following the latitudinal and altitudinal thermal gradients. However, the distribution of Abies is somewhat crude since it depends on several parameters such as exposure to sun, wind, soil, competition and, of course, human activity. Abies may obviously develop at lower altitudes under favourable environmental conditions. Moreover climate conditions may generate an under-estimation of the paleoaltitudes. Indeed, when the climate at low altitude becomes colder such as in recent

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glacial periods it leads to a lesser shift in altitude for the vegetation belts. The Abies belt is then estimated at lower altitude than during the first glacial/interglacial cycles and ensuing estimation of the minimal altitude of the Sila is then lower than that calculated in our work. This corresponds to an artefact linked to the lowering of the Abies belt. We have to keep in mind these uncertainties, though our results give a good idea about changes in the relief and elevation. Westaway (1993) and Westaway and Bridgland (2007, 2009) studied the Quaternary uplift of southern Italy and in particular of Basilicata and of Calabria (following ancient stratigraphy charts showing the Quaternary beginning at 1.8 Ma, Gibbard et al., 2010). Based on the study of marine terrace formation, they calculated that the uplift was in mean around 1 mm/year from 0.7 million years ago in this region. This uplift rate imposes almost 660 to 900 m of total uplift in the region since 2 Ma. Moreover, as indicated by the fossilized remains of fish, which are related to present species occurring at depth (Landini and Menesini, 1978), the sediments corresponding to the lower Pleistocene (2.4 Ma) of the Semaforo section were deposited at least 500 m under sea level. Currently, these are exposed at 150 m a.s.l which corresponds to an uplift of at least 650 m. This estimate coincides with that of Westaway (1993) and Westaway and Bridgland (2007, 2009). These uplift estimates do not give information concerning the uplift of the Sila Massif since 2.4 Ma as the Crotone Basin is a fault-bounded basin, separated from the Southern Apennines by normal faults. Indeed, the Sila Massif has probably not been submitted to the same uplift rate as the Crotone Basin. Subsequently, Westaway and Bridgland (2007) estimated an uplift over 1 km in southernmost Italy since around 3 Ma based on fluvial and marine terraces. In fact, they indicate the presence of marine terraces between 1000 and 1400 m a.s.l. in some localities in Calabria. The relief history of this region is a complex coupling between tectonic processes and external processes (denudation due to climate). A good reconstruction of the palaeotopography is needed, in particular to quantify the denudation rates with independent data. The erosion processes are considered to be one of the causes of the rapid uplift of the southern Apennines during the Pleistocene (Amato et al., 2003; Westaway and Bridgland, 2007). Numerical modelling undertaken by Westaway and Bridgland (2007) indicates that time-averaged and spatially-averaged erosion rates in this region are around 0.5 mm per year since the last million years. Amato et al. (2003) have calculated for the same period an average erosion rate between 0.22 and 0.3 mm per year, based on the evaluation of rock volumes removed between the present topography and a reconstructed past-topography of their study area. However, these studies both show that the southern Apennines had not reached at that time equilibrium between uplift and erosion. As described by Combourieu-Nebout (1993) and CombourieuNebout et al. (2000), the vegetation was, as today, organised in altitudinal belts on the Sila Massif, following the thermic and precipitation gradients. However these vegetation belts moved and changed with climate change. During interglacials, herbaceous taxa were restricted to the coastal band, “Taxodiaceae”, Cathaya and Quercus developed from the lower to the middle-high elevations and Cedrus developed at higher altitudes. However, Abies occurred sparsely, at its distribution limits. During glacials, an open vegetation developed, mainly composed of Asteraceae (within Artemisia), Amaranthaceae–Chenopodiaceae and Poaceae to the detriment of the forest. Only Abies and Cedrus developed at the top of mountains. Although Fagus is well developed today in the mountainous Mediterranean belt of the Sila Massif (Bonin et al., 1976; Bonin, 1981; Gentile, 1982), it was scarce in the region of Crotone during the Pleistocene and the mountainous belt was dominated by Cedrus, Cathaya and Tsuga. The interglacial refuge areas for Abies and Picea were certainly situated northward in the Apennines at higher altitudes or on the northern slopes of the Sila Massif under particular conditions, especially where exposure to the sun was reduced (Barbero and Bono, 1970).

On the contrary, glacial refuge areas for subtropical plants were confined to the littoral region where humidity provided by the sea allowed their survival. 6. Conclusions The palaeovegetation, palaeoclimatic and palaeoaltitude reconstructions at around 2.4 Ma based on the pollen data of the Semaforo section (Calabria) covering the lower Pleistocene show the following: 1) In Calabria, during the lower Pleistocene interglacial periods, mean annual temperatures were ca. 4 °C higher than today, which is consistent with previous climate reconstructions from other Mediterranean sites, and during glacial periods climate conditions were very similar to the present-day in this region. 2) Based on pollen data, our study shows that during the lower Pleistocene (i.e. at around 2.4 Ma) the southern part of the Apennines (Sila Massif) reached between 1600 and 2100 m above sea-level while the region of Crotone was 500 m below sea-level. 3) The sediments corresponding to the lower Pleistocene of the Semaforo section have been uplifted almost 650 m since 2.4 Ma. However, it is impossible to say here if the Sila Massif has been submitted to the same uplift as this basin is a fault-bounded basin. 4) As the southern Apennines did not attain high elevations, the interglacial refugia for microthermic plants such as Abies and Picea were certainly situated northward in the Apennines at higher altitudes or on the northern slopes of the Sila Massif under particular conditions, taking into account the higher temperatures.

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