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The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin)
Palaeogeography, Palaeoclimatology, Palaeoecology 238 (2006) 179 – 189 www.elsevier.com/locate/palaeo
The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin) Jordi Agustí a,⁎, Oriol Oms b , Marc Furió d , María-Jesús Pérez-Vila d , Eduard Roca c a
c
ICREA, Institut de Paleoecología Humana, Universitat Rovira i Virgili, Pl. Imperial Tarraco, 1, 43005-Tarragona, Spain b Universitat Autònoma de Barcelona, Departament de Geologia, 08193-Bellaterra, Spain Dept. Geodinàmica i Geofísica, Faculty of Geology, University of Barcelona, C/ Martí Franquès s/n. 08028-Barcelona, Spain d Institut de Paleontología M. Crusafont. Escola Industrial, 23.08201-Sabadell, Spain Received 11 October 2003; accepted 7 March 2006
Abstract In this paper, a survey on the Messinian section of Can Vilella, in the intramontane basin of La Cerdanya (Pyrenees) is presented. The mammalian association, composed of insectivores, rodents and lagomorphs, is a very atypical one compared to other late Turolian (Messinian) assemblages from Spain and Western Europe, including Central European taxa such as Epimeriones aff. austriacus, which are very rare or absent in the late Miocene from Spain and, even, from Western Europe. The palynological record indicates a riparian forest with abundance of marshy herbs. A magnetostratigraphic study reveals a reverse polarity span for most of the section, whereas in the upper part normal polarities are found. According to the magnetobiostratigraphic correlation established in other basins, the normal geomagnetic episode at the top of the section should correspond either to chron C3An.2n or C3An.1n. In any case, the Can Vilella association clearly predates the onset of the Messinian Salinity Crisis (MSC) in the Mediterranean. This means that the set of climatic and palaeogeographic events associated with the MSC cannot account for the anomalous association from Can Vilella. A discussion as to whether an altitudinal component could be responsible for such an anomaly is undertaken. © 2006 Elsevier B.V. All rights reserved. Keywords: Messinian; Pyrenees; Mammals; Pollen; Dispersals; Cerdanya Basin
1. Introduction The sequence of events associated with the Messinian Stage has been a major topic of research in the last decades, and our understanding of the involved processes has improved considerably in the last years, especially in the marine domain (Clauzon et al., 1996; Krijgsman et al., 1999, and references therein). However, the terres⁎ Corresponding author. Tel.: +34 977558848; fax: +34 977559597. E-mail address: [email protected] (J. Agustí). 0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.03.024
trial response to such events is still poorly understood, especially in the case of the continental mammalian faunas. Dispersal mammalian events associated with the Messinian Salinity Crisis have been a major topic of research among paleontologists for many years (Bruijn, 1974; Aguilar et al., 1984; Agustí and Llenas, 1996), but until very recently accurately calibrated data dealing with dispersal and migration throughout the Mediterranean have been lacking. Fortunately, the work carried out in a number of marginal basins in Southern Spain and Morocco have shed considerable light on this topic
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(Benammi et al., 1996; Garcés et al., 1998, 2001; Agustí et al., 2006-this volume). However, we are still lacking data on the European continental interior, in order to test a possible differential response with respect to the lowland coastal localities. This is because of the scarcity of continental fossiliferous sections in the interior basins which would be suitable for a magnetostratigraphic and biostratigraphic framework. In this respect, the Can Vilella section in the Cerdanya Basin plays a determinant role in reconstruction of the European dispersion of continental mammalian faunas during the Messinian as well as the paleoenvironmental evolution of this intramountainous basin located in the eastern Pyrenees. Previous paleoenvironmental studies carried out in the Cerdanya Basin have been restricted to the Tortonian (Vallesian) when a lake developed in that basin and analyses of macroflora (Sanz de Siria, 1994; MartínClosas, 1995, among others), pollen (Bessedik, 1985; Suc, 1989; Fauquette et al., 2006-this volume) and mammals (see summary in Agustí and Roca, 1987) have been undertaken. Our work is focused on the study of micromammals, pollen and magnetostratigraphic dating of sediments that were deposited during the latter stages of basin infill when the lake was completely filled. An integrated geodynamic and paleoenvironmental revision is also carried out. 2. Geological setting The intramontane Cerdanya Basin is a small (25– 35 km long and up to 7 km wide) basin located in the
eastern part of the Pyrenean Axial Zone (Fig. 1). This zone belongs to the core of the chain where the highest mountains are found. In its eastern part, it is characterised by an ENE–WSW lineation of wide valleys and depressions (Cerdanya, Conflent, Roselló and Seu d'Urgell) which cut the Pyrenees from the Mediterranean to the La Seu d'Urgell Basin in the WSW. The origin of such lineation of valleys and depressions is related to the extensional to strike-slip motion of the La Tet fault during the Neogene (see Roca, 1996 and references therein). This major fault is formed by a set of NE–SW right-stepping en echelon faults and E–W oriented faults that developed mainly in the western block at its southwestern termination. The Cerdanya Basin (see Fig. 2) is located in this termination where today it forms a high plain 1100 m above sea level surrounded by mountains which raise over 2500 m. The structure of the basin is characterized by a set of E–W oriented normal faults that, dipping to the south, are bounded eastwards by the near vertical NE–SW La Tet fault and southwards by a major E–W oriented fault dipping towards the north. As a result, the basin is clearly asymmetrical, with a sharp and more subsiding SE margin constituted by major faults and a NW margin more irregular, where the contact between the basin fill and the basement is basically an unconformity controlled by E–W faults. The Neogene sediments of the basin are from 400 to 1000 m thick (see Pous et al., 1976; Cabrera et al., 1988) and are composed of two depositional units separated by a surface that could be an angular unconformity or a paraconformity.
Fig. 1. Geologial sketch map of the Pyrenees, with location of the Cerdanya basin. Note also it's lineation with Neogene basins in the eastern axial (Paleozoic) zone.
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Fig. 2. Geological map of the Cerdanya basin, slightly modified from Roca (1996) and location of the Can Vilella (Bellver).
The Lower Unit is Vallesian in age (early Late Miocene; Agustí and Roca, 1987) and constitutes most of the Neogene that nowadays outcrops in the Cerdanya Basin. It is formed by a 400 to 800 m thick succession of siliciclastic rocks deposited in an alluvial and fluviolacustrine system (Fig. 3). In general, the alluvial fan environments developed largely along the northwestern basin margin and graded distally (to the southeast) into a broad palustrine-deltaic belt and finally into a lake (Cabrera et al., 1988). The development of this lake, located in the western part of the basin, is recorded by finely laminated organic-rich mud and diatomites which indicate a deep, meromictic and eutrophic lacustrine environment (Margalef, 1957; Haworth and Sabaté, 1993). The Upper Neogene Unit is late Turolian in age (Agustí and Roca, 1987) and is only preserved at the southern edge of the basin. It is integrated by an up to 250 m thick sequence of alluvial red-beds (conglomerates, sandstones and mudstones) that interfinger towards the north (central basin areas) with massive grey clays and minor lignite seams. The studied Can Vilella section includes several of these grey clay levels which contain large plant remains as well as abundant charophytes (Soulié-Märsche and Martín-Closas, 2003) that record the development of minor oligotrophic lakes between the alluvial fans. Unlike the Lower Neogene Unit, the detrital clasts of the Upper Neogene Unit are essentially carbonatic. This drastic lithological change between the units denotes a shift in the main source area of sediments filling the basin. While the Lower Unit is mainly made up of detritical components derived from the erosion of the
Paleozoic granites and slates cropping north of the basin, the Upper Unit records the erosion of source areas located south of the basin. This shift indicates a fall in the production and/or transport of detrital components in the areas located north of the Cerdanya Basin and a relative increase of those coming from the south. The relative increase of the sediments coming from this south faulted margin could be explained by maintenance of the initial sediment input but decreasing the basin subsidence or increasing the initial input by the enlargement or relief rejuvenation of the catchments areas. The less deformation shown by the Upper Unit rocks in relation to the Lower Unit ones points to an attenuation of the fault activity and, therefore, to a scenario in which the sudden progradation of the alluvial fans along the southern basin margin is due both to: a) a drop in the rate of the basin subsidence and b) an enlargement of the catchment areas probably related to a decrease of the isostatic rebound of the footwall block of the faults that bound the Cerdanya Basin to the south. The up to 20° tilting towards the south of the Upper Unit strata as well as their growth geometry close to these faults indicates, however, that these major faults, although attenuated, were still active during this Turolian. According to this interpretation, the Neogene evolution of the La Cerdanya Basin could be divided into two stages. The first, Vallesian in age, is characterised by strong fault activity which led to the basin formation (Roca and Santanach, 1986; Cabrera et al., 1988). During this stage, tectonic subsidence predominated over sedimentation giving rise to the development of a lake
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Fig. 3. Left margin: general schematic section of the Cerdanya basin, with sedimentary units and environments (from Roca, 1996). Left-center: detailed sedimentary successions at Can Vilella (see text), with labelling of pollen, paleomagnetic and mammal sites. Half right: paleomagnetic results and polarity (P).
close the major faults. The second stage, Turolian in age, records an attenuation of the fault activity and tectonic subsidence that results in the final filling of the basin from the predominance of sedimentation processes. Located near the bottom of the Upper Neogene Unit, the studied Can Vilella section records, therefore, the first stages of this second stage of fault activity attenuation. The Can Vilella section here studied (south of Bellver, Fig. 2) is 35 m thick outcropping 20–25 m above the base of the Upper Neogene Unit (Fig. 3). This gap is recorded by a main 27 m thick section and a 5 msection located some 200 m to the southwest. The relative position of this small outcrop is likely to be slightly below the main section, but overlap with the base of the latter cannot be completely excluded. 3. Mammalian record The Can Vilella sites here studied are scattered along the 35 m section and are labelled CV-0B, CV-1 (or Can
Vilella 1), CV-01B, CV-2, CV-04B, CV-03A, CV-03B, CV-3D and CV3F (see Fig. 3). The mammalian record from the level of Can Vilella 1 (the most rich one) includes the following species (Fig. 4): Amblycoptus jessiae Doukas, 1995 Soricini indet. Petenyia dubia Bachmayer and Wilson, 1970 Desmanella dubia Rümke, 1976 Talpa cf. minuta Talpa sp. Archaeodesmana sp. Galericini indet. Epimeriones aff. austriacus Daxner-Hock Kowalskia aff. lavocati (Hugueney and Mein, 1965) Apodemus gudrunae Weerd, 1976 Eozapus aff. intermedius (Bachmayer and Wilson, 1970) Muscardinus aff. vireti Hugueney and Mein, 1965 Glirulus aff. lissiensis Hugueney and Mein, 1965 Prolagus michauxi Lopez
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Fig. 4. Characteristically small mammals from Can Vilella 1. Epimeriones aff. austriacus: 1. Left upper M 1; 2. Left lower m 1. Amblycoptus jessiae: 3. Right upper M 1; 4. Right articular condyle (posterior view).
Other levels having revealed small mammals are CV0B (E. aff. austriacus) and CV-3B (A. gudrunae). The most common element in Can Vilella 1 is the gerbil E. aff. austriacus, which contributes 48% of the teeth. E. austriacus Daxner-Hock, the type-species of the genus, was established in the locality of Eichkogel to designate a gerbil-like muroid with longitudinal spur in the lower molars, labial anterolophid and slightly developed posterosenid (Daxner-Hock, 1972). Despite the difference in age (Eichkogel is an early Turolian locality), the material from Can Vilella fits quite well the type-species in a number of features, such as its broad anteroconid, separated from the protoconid/metaconid complex, and the presence of anterolophid in the lower m 2. However, the Iberian population presents more hypsodont and simplified molars than those of Eichkogel. Close in age to Can Vilella is Epimeriones progressus Kowalski (1974), from the early Pliocene of Podlesice (Poland; Kowalski, 1974). This species is more hypsodont than
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E. austriacus and lacks anterolophids and posterolophids in the lower m 1. Although closer in age, E. aff. austriacus from Can Vilella do not fit the Polish species, since E. progressus presents a peculiar lower m 1, with an enlarged anteroconid which is largely confluent with the protoconid/metaconid complex. The presence of a member of Epimeriones in Can Vilella is surprising, since this genus has been so far recorded only in Eastern and Central Europe: Eichkogel, Podlesice, Mala cave and others (Daxner-Hock, 1972; Kowalski, 1974). In Western Europe, only two teeth can be quoted in the late Turolian of Lissieu (Rhone Valley, France; Mein, 1999). However, in Can Vilella 1 E. aff. austriacus represents 48% of the rodent sample. The rodent association from Can Vilella is very different from that found in other late Turolian localities from Spain and, particularly, from the well calibrated, coeval levels in the Fortuna Basin (SE Spain, Garcés et al., 1998). These levels are characterized by the large dominance of murids, particularly Stephanomys, only sharing with Can Vilella 1 A. gudrunae and M. aff. vireti (Agustí and Llenas, 1996). The cricetid composition is also different, Ruscinomys and Apocricetus being common elements of the late Turolian faunas of Spain, replaced in the case of Can Vilella by a Kowalskia species (K. aff. lavocati). The association of Can Vilella seems in fact closer to that of the fissure infilling of Lissieu (Rhone Valley, France; Mein, 1999), sharing a number of elements such as E. aff. austriacus, Eozapus cf. intermedius, Paraglirulus aff. lissiensis and others. However, as stated, Epimeriones is extremely rare in Lissieu. Again in this respect Can Vilella looks much more “eastern” than any other site from Western Europe. The peculiar character of Can Vilella is confirmed also by the insectivore community. The assemblage from this site is quite similar to that of other Turolian and early Ruscinian localities from the Eastern Mediterranean and Central Europe. Special attention must be paid to the joint distribution of Desmanella and Amblycoptus, since these genera have been rarely quoted together from the same locality. For instance, both genera are common elements in the Central European region, but they never appear associated in the same locality. In Eastern Europe, such an association has been only reported from the Mediterranean Region: Maramena (Greece; Doukas et al., 1995), Kavurca and Amasya (Turkey; Engesser, 1980). In Spain, both genera appear associated in few Turolian localities from the Teruel Basin in Spain, such as Villastar (Mein et al., 1990). Again, the joint occurrence of a Galericini, a Talpinae, a Desmaninae and a Blarinellini is a rare association only seen in Villastar and Can Vilella. In contrast, the late Turolian successions in Southern Spain,
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Fig. 5. Detailed pollen diagram of Can Vilella.
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such as those of the Fortuna Basin, had never provided fossil remains of Desmanella or Amblycoptus. Moreover, the insectivore representation in this basin is always less diversified than those of the northern regions. 4. Pollen record Six samples provide a pollen flora. They respectively almost correspond to mammal layers CV-0B (sample 5B), CV-01B (sample 3), CV-2 (sample 8), CV-03A (samples 20 and 21) and CV-3D (sample 27) (Figs. 5 and 6). The pollen flora is more or less dominated by herbs including mostly marshy elements such as Cyperaceae, Typha,
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Alismataceae and Poaceae. Some trees correspond to swamp environments such as the Taxodium type, Myrica and Nyssa, Cephalanthus. Most of them document marginal riparian lake forests (for instance, Alnus, Salix, Ulmus, Zelkova, Populus). The regional forest is underlined by deciduous Quercus, Taxodiaceae p.p., Sapotaceae, Engelhardia, Carya, Carpinus, etc. Some midaltitude elements are present, such as Taxodiaceae p.p., Tsuga, Keteleeria, Cathaya, Picea and Abies. The lowermost part of the section mainly corresponds to swampy–marshy local conditions (samples 5B and 3). The middle part of the section (samples 8 and 20) is dominated by riparian trees. The uppermost pollen spectrum (sample 27) denotes a more open regional vegetation. The Can Vilella pollen record indicates warm climatic conditions in agreement with those provided by Fauquette et al. (2006-this volume) for the Messinian and the Early Zanclean in the Northwestern Mediterranean region. The local humid conditions were related to marshy environments. 5. Paleomagnetism and chronology
Fig. 6. Synthetic pollen diagram of Can Vilella. Taxa have been grouped according to their ecological significance as follows: 1) megamesothermic (= subtropical) elements (Taxodiaceae, Engelhardia, Cyrillaceae–Clethraceae, Myrica, Sapotaceae, Nyssa, Leea), 2) Cathaya, an altitudinal conifer living today in southern China, 3) mesothermic (= warm–temperate) elements (deciduous Quercus, Carya, Pterocarya, Carpinus, Juglans, Zekkova, Ulmus, Acer, Alnus, Salix, Populus, Betula, Fagus), 4) Pinus and poorly preserved Pinaceae pollen grains, 5) high-altitude trees (Abies, Picea), 6) nonsignificant pollen grains (undetermined ones, poorly preserved pollen grains, some cosmopolitan or widely distributed elements such as Rosaceae and Ranunculaceae), 7) Mediterranean xerophytes (Olea), 8) herbs (Poaceae, Erodium, Convolvulus, Asteraceae Asteroideae, Asteraceae Cichorioideae, Apiaceae, Linum, Ericaceae, Amaranthaceae–Chenopodiaceae, Caryophyllaceae, Cyperaceae, Potamogeton, Typha, Alismataceae, etc).
Paleomagnetic sampling was focused on all fine grained lithologies (basically reddish to dark mudstones) that looked to be suitable for magnetostratigraphic studies. In consequence, sampling of conglomerates and coarse grained sandstones (dominant lithologies in the section) was not considered. This allowed a sampling of 11 stratigraphic levels for the entire section. From each considered level three oriented cores were obtained with a portable drilling machine. Laboratory analyses consisted of stepwise thermal demagnetization of one specimen for each core. Bulk susceptibility measures were also made in order to detect the formation of new minerals during heating. A demagnetization procedure of up to 16 steps (ranging from room temperature to 690 °C) was applied to each sample. Measurement of remanence was achieved with a three-axes cryogenic magnetometer at the Paleomagnetism Laboratory of the Institute of Earth Sciences (UB-CSIC, Barcelona). Samples have high values of the Natural Remnant Magnetization (ranging from 0.3 to 10.5 mA/m) and display relative stable demagnetization plots (see Fig. 7). Typically, up to three components can be recognized. First, a viscous component that always got completely demagnetized at temperatures below 150 °C. Second, a low temperature component that became unblocked at temperatures between 150 and around 300 °C. Finally a high temperature component was demagnetized at temperatures generally between 300 and up to 690 °C. A few demagnetization plots were not considered if
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Fig. 7. Representative demagnetization orthogonal plots from the Can Vilella sections. CV 02 and CV3 account for reverse polarities found at the base of the section, whereas CV 11 is an example of normal polarity found at the uppermost levels.
sudden susceptibility variations were observed. Once all high temperatures were obtained (see declination and inclination values in Fig. 3), a mean of the directional values for each site was calculated in order to derive the Virtual Geomagnetic Polarity Latitude. As seen in Fig. 3, the small lower section displays an entirely reverse magnetization. In the largest section reverse polarities can be observed for the lower 18 m, while the upper 8–9 m display normal polarities. Thus, although the stratigraphic record at Can Vilella section is not very thick, a polarity reversal is clearly detected after the occurrence of relatively stable demagnetization of samples. Recent work carried out in the thick late Miocene continental sequences of the Fortuna Basin enables one to identify to some degree the normal geomagnetic event detected at Can Vilella. In this basin, a minimum age for the FAD of A. gudrunae (base of MN 13) has been established within chron C3Ar, that is, close to 6.8 Ma (Garcés et al., 1998; Agustı´ et al., 2001). On the other hand, data from the Cabriel section (Opdyke et al., 1997) provides a minimum age of 4.9 Ma (chron C3n.3r) for the lower boundary of the Promimomys Zone (MN 14; Agustí et al., 2001). Therefore, the normal chron at the top of the Can Vilella section can be identified either as C3An.2n or C3An.1n. In the Fortuna Basin, the FAD of Paraethomys miocaenicus occurs within chron C3An.1n (Agustí et al., 2001, 2006-this volume). However, this species is absent from the record of Can Vilella, so a decision as to whether the normal chron from this section corresponds to C3An.2n or C3An.1n cannot be taken. In any case, the Can Vilella succession can be placed in the Messinian stage, before the onset of the Messinian Salinity Crisis. 6. Biogeographic remarks From a biogeographical point of view, Can Vilella 1 represents a very atypical mammalian association in the
context of the Western European faunal assemblages. Only few elements are shared in common with other late Turolian localities from Spain, such as those of the Teruel and Fortuna basins. The late Turolian sites in these basins are characterized by a highly diversified endemic fauna of murids (Stephanomys, Occitanomys, Huerzelerimys, Paraethomys, Castillomys) and cricetids (Ruscinomys, Apocricetus) (Agustı´ and Llenas, 1996). The closest latest Miocene reference to Can Vilella is the fissure infilling of Lissieu in the Rhone Valley (France), which shares with Can Vilella the absence of the former endemic elements and the presence of Epimeriones and Eozapus (Mein, 1999). However, Epimeriones is represented in Lissieu only by two teeth, while it represents close to 50% in Can Vilella. A possible explanation for the Can Vilella biogeographical anomaly would be that the faunal association from this site represents the extension to the south of a higher-latitude fauna, that is, a “colder” local biotope, linked to a late Neogene uplift of the Pyrenees range. This interpretation is supported by the large populations of the Characeae Lychnothamus barbatus found in the grey mudstones of the same outcrop, which are typical of cold lacustrine waters (Soulié-Märsche and MartínClosas, 2003). However, the pollen data do not support the proposition that the Cerdanya basin was as elevated in the Late Miocene–Early Pliocene as today. Thus, the Messinian Cerdanya pollen flora is not significantly different from the Tortonian one (Bessedik, 1985; Suc, 1989). Some megathermic and mega-mesothermic elements have disappeared (such as Meliaceae, Distylium and Platycarya) while Fagus was more important in the Tortonian flora than in the Messinian one. The Messinian pollen flora from Cerdanya is very similar to the marshy pollen flora from Vivès (Suc, 1989) in the Roussillon coastal basin, which belongs to the earliest Zanclean (5.33 Ma). Similarity between these floras
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would suggest that the altitude of the Cerdanya basin did not rise much between ca. 9.6 and ca. 7–6.2 Ma. In contrast, there are a number of geological arguments that during the Messinian the relief was not so different than the present one, with relatively high mountains bounding the basin to the South. Fissiontrack data collected in the Canigó and Mont-Lluis massifs indicate that the topography resulting from the motion of the La Tet fault was generated between the middle Oligocene and the Burdigalian, at least along the French part of the fault (Maurel et al., 2002). Considering that the Cerdanya faults belong to the southwestern prolongation of La Tet fault, they point to the fact that the difference in the topographic height between the basin and the mountains that bound it to the south and southeast is relatively old and surely existed when the Can Vilella sediments were deposited. Paleocurrent analyses carried out in the Cerdanya basin (Cabrera et al., 1988) indicate that the predominant Carboniferous derived clasts in the conglomerates of Can Vilella came from the south, that is, from the footwall block of the Cerdanya fault. In this area the Carboniferous outcrops always below a height of 1900 m. Taking into account that the footwall block in this area (Cadí-Penyes Altes del Moixeró-Tossa d'Alp) attains heights of 2200–2500 m, it implies that during the beginning of the Upper Neogene Unit sedimentation, there was a range bounding the basin to the south with a height at least of 500 m above the basin plain. Moreover, the evolution of the alluvial fans (see description in the geological setting) denotes that most fault activity along the Cerdanya fault took place during the Vallesian and decreased considerably during the Turolian. This indicates that most of the relative uplift of the footwall block of the Cerdanya fault took place during the Vallesian since both isostatic and tectonic vertical motions generated by the motion of a fault have been recognized in models as well as in other regions as coeval to the periods of main fault activity (Tucker and Slingerland, 1994; Watts et al., 2000; Gaspar-Escribano et al., 2004). However, this late Neogene uplift was not an instantaneous event but was associated with a large wavelength change of the topography related to the Pyrenean orogenic evolution. With respect to Pyrenean topography evolution, apatite fission track profiles carried out more to the west across the central Pyrenees, indicate that, since the late Miocene, exhumation of the southern flank of the Pyrenees accelerated with an average erosion of 2–3 km (Fitzgerald et al., 1999). Consequently, a post-Middle Miocene regional uplift of the Pyrenees is required. This uplift could be explained by
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the thermal re-equilibrium of the thick Pyrenean lithosphere which presently shows evidence of lower crustal heating with generation of partial meltings (Pous et al., 1995; Glover et al., 2000). The amount of this lithospheric uplift and its effect in the Cerdanya Basin remain unknown but, considering that the crustal structure of this portion of the Pyrenees is similar to that of the central Pyrenees (Muñoz, 1992; Vergés et al., 1995), we can assume that it is also significant, although less than 2 km. Altogether, these data point to an uplift of at least 500 m above the basin plain at the beginning of the sedimentation of the Upper Neogene Unit and more than 1000 m at the end of the deposition of this unit and support the argument that the relief of the Cerdanya Basin and surrounding areas was similar to the present one, with high chains bounding it both to the north and to the south. Therefore, the higher-latitude small mammalian fauna from Can Vilella can be explained by the association of relatively high reliefs and some of the cold events that punctuate the beginning of the Messinian, prior to the onset of the MSC. In this way, benthic δ18O at Site 982 in the North Atlantic records a latest Miocene glaciation that lasted from ∼ 6.26 to 5.50 Myr and was marked by 18 glacial-to-interglacial oscillations that were controlled by the 41-kyr cycle of obliquity (Hodell et al., 2001). Combination of one these first glacial cycles with relative uplift of the Pyrenees could be responsible for the dominance in the Upper Neogene Unit of La Cerdanya Basin of higher-latitude elements such as E. aff. austriacus. This scenario would also favor placement of Can Vilella in geomagnetic chron C3An.1n. Acknowledgements Magnetostratigraphic measurements were undertaken in the Paleomagnetism Laboratory of the Serveis Científico-Tècnics of the Universitat de BarcelonaCSIC. This study was financed by projects BOS20011044 and PB96-0815 of the Ministry of Science and Technology of Spain and Grup de Recerca de Qualitat SGR2001-00077 of Departament d'Universitats, Recerca i Societat de la Informació (Generalitat de Catalunya). Authors acknowledge the revision by Miguel Garcés and Rosa Domenech (Universitat de Barcelona). M.F. acknowledges the support from the European Science Foundation (EDEEN Exchange Grant) and the comments by L.W. van den Hoek Ostende (Naturalis, Leiden) and J.W.F. Reumer (Natuurmuseum, Rotterdam) on the study of insectivores. The pollen study was supported by the French Program
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“Environnement, Vie et Sociétés” (Institut Français de la Biodiversité). References Aguilar, J.P., Brandy, L.D., Thaler, L., 1984. Les Rongeurs de Salobreña (Sud de l'Espagne) et le problème de la migration messinienne. Paleobiol. Cont., Montpellier 14 (2), 3–17. Agustí, J., Llenas, M., 1996. The Late Turolian Muroid Rodent Succession in Eastern Spain. Acta Zool. Cracov. 39 (1), 47–56 (Kràkow). Agustí, J., Roca, E., 1987. Síntesis bioestratigráfica de la fosa de la Cerdanya (Pirineos). Estud. Geol. 43, 521–529. Agustí, J., Cabrera, L., Garcés, M., Krijgsman, W., Oms, O., Parés, J.M., 2001. A calibrated mammal scale for the Neogene of western Europe. State of the art. Earth Sci. Rev. 52, 247–260. Agustí, J., Garcés, M., Krijgsman, W., 2006. Evidence for African– Iberian exchanges during the Messinian in the Spanish mammalian record. Palaeogeogr., Palaeoclimatol., Paleoecol., vol. 238, pp. 5–14. [this volume]. doi:10.1016/j.palaeo.2006.03.013. Benammi, M., Calvo, M., Prévot, M., Jaeger, J.J., 1996. Magnetostratigraphy and paleontology of Aït Kandoula basin (High Atalas, Morocco) and the African–European late Miocene terrestrial fauna exchanges. Earth Planet. Sci. Lett. 145, 15–29. Bessedik, M., 1985. Reconstitution des environments miocènes des règions nordouest mediterraneennes a partir de la Palynologie. PhD thesis, Univ. Montpellier, 162 pp. de Bruijn, H., 1974. The Ruscinian rodent succession in southern Spain and its implications for the biostratigraphic correlation of Europe and North Africa. Senkenb. Lethaia 55, 435–443. Cabrera, L., Roca, E., Santanach, P., 1988. Basin formation at the end of a strike-slip fault: the Cerdanya Basin (eastern Pyrenees). J. Geol. Soc. (Lond.) 145, 261–268. Clauzon, G., Suc, J.-P., Gautier, F., Berger, A., Loutre, M.-F., 1996. Alternate interpretation of the Messinian salinity crisis: controversy resolved? Geology 24 (4), 363–366. Daxner-Hock, G., 1972. Die Wirbeltierfauna aus dem Alt-Pliozän (Pont) von Eichkogel bei Mödling (Niederösterreich). Ann. Naturhist. Mus. Wien 76, 143–160. Doukas, C.S., van den Hoek Ostende, L.W., Theocharopoulos, C.D., Reumer, J.W.F., 1995. The Vertebrate Locality Maramena (Macedonia, Greece) at the Turolian–Ruscinian boundary (Neogene). 5. Insectivora (Erinaceidae, Talpidae, Soricidae, Mammalia). Münch. Geowiss. Abh., A 28, 43–64. Engesser, B., 1980. Insectivora und Chiroptera (Mammalia) aus dem Neogen der Türkei. Schweiz. Paläontol. Abh. 102, 47–149. Fauquette, S., Suc, J.-P., Bertini, A., Popescu, S.-M., Warny, S., Bachiri Taouiq, N., Perez Villa, M., Chikhi, H., Subally, D., Feddi, N., Clauzon, G., Ferrier, J., 2006. How much I did climate forced the Messinian salinity crisis? Quantified climatic conditions from pollen records in the Mediterranean region. Palaeogeogr., Palaeoclimatol., Palaeoecol., vol. 238, pp. 281–301. [this volume]. doi:10.1016/j.palaeo.2006.03.029. Fitzgerald, P.G., Muñoz, J.A., Coney, P.J., Baldwin, S.L., 1999. Asymmetric exhumation across the Pyrenean orogen: implications for the tectonic evolution of a collisional orogen. Earth Planet. Sci. Lett. 173, 157–170. Garcés, M., Krijgsman, W., Agustí, J., 1998. Chronology of the late Turolian of the Fortuna basin (SE Spain): implications for the Messinian evolution of the eastern Betics. Earth Planet. Sci. Lett. 163, 69–81.
Garcés, M., Krijgsman, W., Agustí, J., 2001. Chronostratigraphic framework and evolution of the Fortuna basin (eastern Betics) since the Late Miocene. Basin Res. 13, 199–216. Gaspar-Escribano, J., García-Castellanos, D., Roca, E., Cloetingh, S., 2004. Cenozoic vertical motions of the Catalan Coastal Ranges (NE Spain): the role of tectonics, isostasy, and surface transport. Tectonics 23. Glover, P.W.J., Pous, J., Queralt, P., Muñoz, J.A., Liesa, M., Hole, M.J., 2000. Integrated two-dimensional lithospheric conductivity model in the Pyrenees using field-scale and laboratory measurements. Earth Planet. Sci. Lett. 178, 59–72. Haworth, E., Sabaté, S., 1993. A new Miocene Aulacoseira species in diatomite from the ancient lake in La Cerdanya (NE Spain). Nova Hedwig., Beih. 106, 227–242. Hodell, D.A., Curtis, J.H., Sierro, F.J., Raymo, M.E., 2001. Correlation of late Miocene to early Pliocene sequences between the Mediterranean and North Atlantic. Paleoceanography 16, 164–178. Kowalski, K., 1974. Remains of Gerbillinae (Rodentia, Mammalia) from the Pliocene of Poland. Bull. Acad. Pol. Sci. C II 22 (9), 591–595. Krijgsman, W., Hilgen, F.J., Raffi, I., Sierro, F.J., Wilson, D.S., 1999. Chronology, causes and progression of the Messinian salinity crisis. Nature 400, 652–655. Margalef, R., 1957. Paleoecología del lago de la Cerdaña. Publ. Inst. Biol. Apl. 25, 131–137. Martín-Closas, C., 1995. Plant taphonomy of La Cerdanya Basin (Vallesian, eastern Pyrenees). Geobios 18, 287–298. Maurel, O., Brunel, M., Monié, P., 2002. Exhumation cénozoïque des massifs du Canigou et Mont-Louis (Pyrénées orientales, France). C. R. Geosci. 334, 941–948. Mein, P., 1999. The late Miocene small mammal succession from France, with emphasis on the Rhone Valley localities. In: Agustí, J., Rook, L., Andrews, P. (Eds.), The Evolution of Neogene Terrestrial Ecosystems in Europe. Cambridge University Press, pp. 140–164. Mein, P., Moissenet, E., Adrover, R., 1990. Biostratigraphie du Néogène Supérieur du bassin de Teruel. Paleontol. Evol. 23, 121–139. Opdyke, N., Mein, P., Lindsay, E., Pérez-Gonzáles, A., Moissenet, E., Norton, V.L., 1997. Continental deposits, magnetostratigraphy and vertebrate paleontology, late Neogene of eastern Spain. Palaeogeogr. Palaeoclimatol. Palaeoecol. 133, 129–148. Muñoz, J.A., 1992. Evolution of a continental collision belt: ECORSPyrenees crustal balanced cross-section. In: McClay, K. (Ed.), Thrust Tectonics. Chapman & Hall, London, pp. 235–246. Pous, J., Julià, R., Sole Sugrañes, L., 1976. Cerdanya basin geometry and its implication on the Neogene evolution of the eastern Pyrenees. Tectonophysics 129, 355–365. Pous, J., Muñoz, J.A., Ledo, J.J., Liesa, M., 1995. Partial melting of subducted continental lower crust in the Pyrenees. J. Geol. Soc. (Lond.) 152, 217–220. Roca, E., 1996. The Neogene Cerdanya and Seu d´Urgell intramontane basins (eastern Pyrenees). In: Friend, P., Bario, C.J. (Eds.), Tertiary Basins of Spain. The Stratigraphic Record of Crustal Kinematics. Cambridge University Press, Cambridge, pp. 114–118. Roca, E., Santanach, P., 1986. Génesis y evolucion de la Fosa de la Cerdanya (Pirineos orientales). Geogaceta 1, 37–38. Sanz de Siria, A., 1994. La evolución de las paleofloras en las cuencas cenozoicas catalanas. Acta Geol. Hisp. 29, 169–189 (Barcelona). Soulié-Märsche, I., Martín-Closas, C., 2003. Lychnothamnus barbatus (Charophytes) from the Upper Miocene of La Cerdanya
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The Messinian terrestrial record in the Pyrenees: The case of Can Vilella (Cerdanya Basin) Jordi Agustí a,⁎, Oriol Oms b , Marc Furió d , María-Jesús Pérez-Vila d , Eduard Roca c a
c
ICREA, Institut de Paleoecología Humana, Universitat Rovira i Virgili, Pl. Imperial Tarraco, 1, 43005-Tarragona, Spain b Universitat Autònoma de Barcelona, Departament de Geologia, 08193-Bellaterra, Spain Dept. Geodinàmica i Geofísica, Faculty of Geology, University of Barcelona, C/ Martí Franquès s/n. 08028-Barcelona, Spain d Institut de Paleontología M. Crusafont. Escola Industrial, 23.08201-Sabadell, Spain Received 11 October 2003; accepted 7 March 2006
Abstract In this paper, a survey on the Messinian section of Can Vilella, in the intramontane basin of La Cerdanya (Pyrenees) is presented. The mammalian association, composed of insectivores, rodents and lagomorphs, is a very atypical one compared to other late Turolian (Messinian) assemblages from Spain and Western Europe, including Central European taxa such as Epimeriones aff. austriacus, which are very rare or absent in the late Miocene from Spain and, even, from Western Europe. The palynological record indicates a riparian forest with abundance of marshy herbs. A magnetostratigraphic study reveals a reverse polarity span for most of the section, whereas in the upper part normal polarities are found. According to the magnetobiostratigraphic correlation established in other basins, the normal geomagnetic episode at the top of the section should correspond either to chron C3An.2n or C3An.1n. In any case, the Can Vilella association clearly predates the onset of the Messinian Salinity Crisis (MSC) in the Mediterranean. This means that the set of climatic and palaeogeographic events associated with the MSC cannot account for the anomalous association from Can Vilella. A discussion as to whether an altitudinal component could be responsible for such an anomaly is undertaken. © 2006 Elsevier B.V. All rights reserved. Keywords: Messinian; Pyrenees; Mammals; Pollen; Dispersals; Cerdanya Basin
1. Introduction The sequence of events associated with the Messinian Stage has been a major topic of research in the last decades, and our understanding of the involved processes has improved considerably in the last years, especially in the marine domain (Clauzon et al., 1996; Krijgsman et al., 1999, and references therein). However, the terres⁎ Corresponding author. Tel.: +34 977558848; fax: +34 977559597. E-mail address: [email protected] (J. Agustí). 0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.03.024
trial response to such events is still poorly understood, especially in the case of the continental mammalian faunas. Dispersal mammalian events associated with the Messinian Salinity Crisis have been a major topic of research among paleontologists for many years (Bruijn, 1974; Aguilar et al., 1984; Agustí and Llenas, 1996), but until very recently accurately calibrated data dealing with dispersal and migration throughout the Mediterranean have been lacking. Fortunately, the work carried out in a number of marginal basins in Southern Spain and Morocco have shed considerable light on this topic
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(Benammi et al., 1996; Garcés et al., 1998, 2001; Agustí et al., 2006-this volume). However, we are still lacking data on the European continental interior, in order to test a possible differential response with respect to the lowland coastal localities. This is because of the scarcity of continental fossiliferous sections in the interior basins which would be suitable for a magnetostratigraphic and biostratigraphic framework. In this respect, the Can Vilella section in the Cerdanya Basin plays a determinant role in reconstruction of the European dispersion of continental mammalian faunas during the Messinian as well as the paleoenvironmental evolution of this intramountainous basin located in the eastern Pyrenees. Previous paleoenvironmental studies carried out in the Cerdanya Basin have been restricted to the Tortonian (Vallesian) when a lake developed in that basin and analyses of macroflora (Sanz de Siria, 1994; MartínClosas, 1995, among others), pollen (Bessedik, 1985; Suc, 1989; Fauquette et al., 2006-this volume) and mammals (see summary in Agustí and Roca, 1987) have been undertaken. Our work is focused on the study of micromammals, pollen and magnetostratigraphic dating of sediments that were deposited during the latter stages of basin infill when the lake was completely filled. An integrated geodynamic and paleoenvironmental revision is also carried out. 2. Geological setting The intramontane Cerdanya Basin is a small (25– 35 km long and up to 7 km wide) basin located in the
eastern part of the Pyrenean Axial Zone (Fig. 1). This zone belongs to the core of the chain where the highest mountains are found. In its eastern part, it is characterised by an ENE–WSW lineation of wide valleys and depressions (Cerdanya, Conflent, Roselló and Seu d'Urgell) which cut the Pyrenees from the Mediterranean to the La Seu d'Urgell Basin in the WSW. The origin of such lineation of valleys and depressions is related to the extensional to strike-slip motion of the La Tet fault during the Neogene (see Roca, 1996 and references therein). This major fault is formed by a set of NE–SW right-stepping en echelon faults and E–W oriented faults that developed mainly in the western block at its southwestern termination. The Cerdanya Basin (see Fig. 2) is located in this termination where today it forms a high plain 1100 m above sea level surrounded by mountains which raise over 2500 m. The structure of the basin is characterized by a set of E–W oriented normal faults that, dipping to the south, are bounded eastwards by the near vertical NE–SW La Tet fault and southwards by a major E–W oriented fault dipping towards the north. As a result, the basin is clearly asymmetrical, with a sharp and more subsiding SE margin constituted by major faults and a NW margin more irregular, where the contact between the basin fill and the basement is basically an unconformity controlled by E–W faults. The Neogene sediments of the basin are from 400 to 1000 m thick (see Pous et al., 1976; Cabrera et al., 1988) and are composed of two depositional units separated by a surface that could be an angular unconformity or a paraconformity.
Fig. 1. Geologial sketch map of the Pyrenees, with location of the Cerdanya basin. Note also it's lineation with Neogene basins in the eastern axial (Paleozoic) zone.
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Fig. 2. Geological map of the Cerdanya basin, slightly modified from Roca (1996) and location of the Can Vilella (Bellver).
The Lower Unit is Vallesian in age (early Late Miocene; Agustí and Roca, 1987) and constitutes most of the Neogene that nowadays outcrops in the Cerdanya Basin. It is formed by a 400 to 800 m thick succession of siliciclastic rocks deposited in an alluvial and fluviolacustrine system (Fig. 3). In general, the alluvial fan environments developed largely along the northwestern basin margin and graded distally (to the southeast) into a broad palustrine-deltaic belt and finally into a lake (Cabrera et al., 1988). The development of this lake, located in the western part of the basin, is recorded by finely laminated organic-rich mud and diatomites which indicate a deep, meromictic and eutrophic lacustrine environment (Margalef, 1957; Haworth and Sabaté, 1993). The Upper Neogene Unit is late Turolian in age (Agustí and Roca, 1987) and is only preserved at the southern edge of the basin. It is integrated by an up to 250 m thick sequence of alluvial red-beds (conglomerates, sandstones and mudstones) that interfinger towards the north (central basin areas) with massive grey clays and minor lignite seams. The studied Can Vilella section includes several of these grey clay levels which contain large plant remains as well as abundant charophytes (Soulié-Märsche and Martín-Closas, 2003) that record the development of minor oligotrophic lakes between the alluvial fans. Unlike the Lower Neogene Unit, the detrital clasts of the Upper Neogene Unit are essentially carbonatic. This drastic lithological change between the units denotes a shift in the main source area of sediments filling the basin. While the Lower Unit is mainly made up of detritical components derived from the erosion of the
Paleozoic granites and slates cropping north of the basin, the Upper Unit records the erosion of source areas located south of the basin. This shift indicates a fall in the production and/or transport of detrital components in the areas located north of the Cerdanya Basin and a relative increase of those coming from the south. The relative increase of the sediments coming from this south faulted margin could be explained by maintenance of the initial sediment input but decreasing the basin subsidence or increasing the initial input by the enlargement or relief rejuvenation of the catchments areas. The less deformation shown by the Upper Unit rocks in relation to the Lower Unit ones points to an attenuation of the fault activity and, therefore, to a scenario in which the sudden progradation of the alluvial fans along the southern basin margin is due both to: a) a drop in the rate of the basin subsidence and b) an enlargement of the catchment areas probably related to a decrease of the isostatic rebound of the footwall block of the faults that bound the Cerdanya Basin to the south. The up to 20° tilting towards the south of the Upper Unit strata as well as their growth geometry close to these faults indicates, however, that these major faults, although attenuated, were still active during this Turolian. According to this interpretation, the Neogene evolution of the La Cerdanya Basin could be divided into two stages. The first, Vallesian in age, is characterised by strong fault activity which led to the basin formation (Roca and Santanach, 1986; Cabrera et al., 1988). During this stage, tectonic subsidence predominated over sedimentation giving rise to the development of a lake
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Fig. 3. Left margin: general schematic section of the Cerdanya basin, with sedimentary units and environments (from Roca, 1996). Left-center: detailed sedimentary successions at Can Vilella (see text), with labelling of pollen, paleomagnetic and mammal sites. Half right: paleomagnetic results and polarity (P).
close the major faults. The second stage, Turolian in age, records an attenuation of the fault activity and tectonic subsidence that results in the final filling of the basin from the predominance of sedimentation processes. Located near the bottom of the Upper Neogene Unit, the studied Can Vilella section records, therefore, the first stages of this second stage of fault activity attenuation. The Can Vilella section here studied (south of Bellver, Fig. 2) is 35 m thick outcropping 20–25 m above the base of the Upper Neogene Unit (Fig. 3). This gap is recorded by a main 27 m thick section and a 5 msection located some 200 m to the southwest. The relative position of this small outcrop is likely to be slightly below the main section, but overlap with the base of the latter cannot be completely excluded. 3. Mammalian record The Can Vilella sites here studied are scattered along the 35 m section and are labelled CV-0B, CV-1 (or Can
Vilella 1), CV-01B, CV-2, CV-04B, CV-03A, CV-03B, CV-3D and CV3F (see Fig. 3). The mammalian record from the level of Can Vilella 1 (the most rich one) includes the following species (Fig. 4): Amblycoptus jessiae Doukas, 1995 Soricini indet. Petenyia dubia Bachmayer and Wilson, 1970 Desmanella dubia Rümke, 1976 Talpa cf. minuta Talpa sp. Archaeodesmana sp. Galericini indet. Epimeriones aff. austriacus Daxner-Hock Kowalskia aff. lavocati (Hugueney and Mein, 1965) Apodemus gudrunae Weerd, 1976 Eozapus aff. intermedius (Bachmayer and Wilson, 1970) Muscardinus aff. vireti Hugueney and Mein, 1965 Glirulus aff. lissiensis Hugueney and Mein, 1965 Prolagus michauxi Lopez
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Fig. 4. Characteristically small mammals from Can Vilella 1. Epimeriones aff. austriacus: 1. Left upper M 1; 2. Left lower m 1. Amblycoptus jessiae: 3. Right upper M 1; 4. Right articular condyle (posterior view).
Other levels having revealed small mammals are CV0B (E. aff. austriacus) and CV-3B (A. gudrunae). The most common element in Can Vilella 1 is the gerbil E. aff. austriacus, which contributes 48% of the teeth. E. austriacus Daxner-Hock, the type-species of the genus, was established in the locality of Eichkogel to designate a gerbil-like muroid with longitudinal spur in the lower molars, labial anterolophid and slightly developed posterosenid (Daxner-Hock, 1972). Despite the difference in age (Eichkogel is an early Turolian locality), the material from Can Vilella fits quite well the type-species in a number of features, such as its broad anteroconid, separated from the protoconid/metaconid complex, and the presence of anterolophid in the lower m 2. However, the Iberian population presents more hypsodont and simplified molars than those of Eichkogel. Close in age to Can Vilella is Epimeriones progressus Kowalski (1974), from the early Pliocene of Podlesice (Poland; Kowalski, 1974). This species is more hypsodont than
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E. austriacus and lacks anterolophids and posterolophids in the lower m 1. Although closer in age, E. aff. austriacus from Can Vilella do not fit the Polish species, since E. progressus presents a peculiar lower m 1, with an enlarged anteroconid which is largely confluent with the protoconid/metaconid complex. The presence of a member of Epimeriones in Can Vilella is surprising, since this genus has been so far recorded only in Eastern and Central Europe: Eichkogel, Podlesice, Mala cave and others (Daxner-Hock, 1972; Kowalski, 1974). In Western Europe, only two teeth can be quoted in the late Turolian of Lissieu (Rhone Valley, France; Mein, 1999). However, in Can Vilella 1 E. aff. austriacus represents 48% of the rodent sample. The rodent association from Can Vilella is very different from that found in other late Turolian localities from Spain and, particularly, from the well calibrated, coeval levels in the Fortuna Basin (SE Spain, Garcés et al., 1998). These levels are characterized by the large dominance of murids, particularly Stephanomys, only sharing with Can Vilella 1 A. gudrunae and M. aff. vireti (Agustí and Llenas, 1996). The cricetid composition is also different, Ruscinomys and Apocricetus being common elements of the late Turolian faunas of Spain, replaced in the case of Can Vilella by a Kowalskia species (K. aff. lavocati). The association of Can Vilella seems in fact closer to that of the fissure infilling of Lissieu (Rhone Valley, France; Mein, 1999), sharing a number of elements such as E. aff. austriacus, Eozapus cf. intermedius, Paraglirulus aff. lissiensis and others. However, as stated, Epimeriones is extremely rare in Lissieu. Again in this respect Can Vilella looks much more “eastern” than any other site from Western Europe. The peculiar character of Can Vilella is confirmed also by the insectivore community. The assemblage from this site is quite similar to that of other Turolian and early Ruscinian localities from the Eastern Mediterranean and Central Europe. Special attention must be paid to the joint distribution of Desmanella and Amblycoptus, since these genera have been rarely quoted together from the same locality. For instance, both genera are common elements in the Central European region, but they never appear associated in the same locality. In Eastern Europe, such an association has been only reported from the Mediterranean Region: Maramena (Greece; Doukas et al., 1995), Kavurca and Amasya (Turkey; Engesser, 1980). In Spain, both genera appear associated in few Turolian localities from the Teruel Basin in Spain, such as Villastar (Mein et al., 1990). Again, the joint occurrence of a Galericini, a Talpinae, a Desmaninae and a Blarinellini is a rare association only seen in Villastar and Can Vilella. In contrast, the late Turolian successions in Southern Spain,
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Fig. 5. Detailed pollen diagram of Can Vilella.
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such as those of the Fortuna Basin, had never provided fossil remains of Desmanella or Amblycoptus. Moreover, the insectivore representation in this basin is always less diversified than those of the northern regions. 4. Pollen record Six samples provide a pollen flora. They respectively almost correspond to mammal layers CV-0B (sample 5B), CV-01B (sample 3), CV-2 (sample 8), CV-03A (samples 20 and 21) and CV-3D (sample 27) (Figs. 5 and 6). The pollen flora is more or less dominated by herbs including mostly marshy elements such as Cyperaceae, Typha,
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Alismataceae and Poaceae. Some trees correspond to swamp environments such as the Taxodium type, Myrica and Nyssa, Cephalanthus. Most of them document marginal riparian lake forests (for instance, Alnus, Salix, Ulmus, Zelkova, Populus). The regional forest is underlined by deciduous Quercus, Taxodiaceae p.p., Sapotaceae, Engelhardia, Carya, Carpinus, etc. Some midaltitude elements are present, such as Taxodiaceae p.p., Tsuga, Keteleeria, Cathaya, Picea and Abies. The lowermost part of the section mainly corresponds to swampy–marshy local conditions (samples 5B and 3). The middle part of the section (samples 8 and 20) is dominated by riparian trees. The uppermost pollen spectrum (sample 27) denotes a more open regional vegetation. The Can Vilella pollen record indicates warm climatic conditions in agreement with those provided by Fauquette et al. (2006-this volume) for the Messinian and the Early Zanclean in the Northwestern Mediterranean region. The local humid conditions were related to marshy environments. 5. Paleomagnetism and chronology
Fig. 6. Synthetic pollen diagram of Can Vilella. Taxa have been grouped according to their ecological significance as follows: 1) megamesothermic (= subtropical) elements (Taxodiaceae, Engelhardia, Cyrillaceae–Clethraceae, Myrica, Sapotaceae, Nyssa, Leea), 2) Cathaya, an altitudinal conifer living today in southern China, 3) mesothermic (= warm–temperate) elements (deciduous Quercus, Carya, Pterocarya, Carpinus, Juglans, Zekkova, Ulmus, Acer, Alnus, Salix, Populus, Betula, Fagus), 4) Pinus and poorly preserved Pinaceae pollen grains, 5) high-altitude trees (Abies, Picea), 6) nonsignificant pollen grains (undetermined ones, poorly preserved pollen grains, some cosmopolitan or widely distributed elements such as Rosaceae and Ranunculaceae), 7) Mediterranean xerophytes (Olea), 8) herbs (Poaceae, Erodium, Convolvulus, Asteraceae Asteroideae, Asteraceae Cichorioideae, Apiaceae, Linum, Ericaceae, Amaranthaceae–Chenopodiaceae, Caryophyllaceae, Cyperaceae, Potamogeton, Typha, Alismataceae, etc).
Paleomagnetic sampling was focused on all fine grained lithologies (basically reddish to dark mudstones) that looked to be suitable for magnetostratigraphic studies. In consequence, sampling of conglomerates and coarse grained sandstones (dominant lithologies in the section) was not considered. This allowed a sampling of 11 stratigraphic levels for the entire section. From each considered level three oriented cores were obtained with a portable drilling machine. Laboratory analyses consisted of stepwise thermal demagnetization of one specimen for each core. Bulk susceptibility measures were also made in order to detect the formation of new minerals during heating. A demagnetization procedure of up to 16 steps (ranging from room temperature to 690 °C) was applied to each sample. Measurement of remanence was achieved with a three-axes cryogenic magnetometer at the Paleomagnetism Laboratory of the Institute of Earth Sciences (UB-CSIC, Barcelona). Samples have high values of the Natural Remnant Magnetization (ranging from 0.3 to 10.5 mA/m) and display relative stable demagnetization plots (see Fig. 7). Typically, up to three components can be recognized. First, a viscous component that always got completely demagnetized at temperatures below 150 °C. Second, a low temperature component that became unblocked at temperatures between 150 and around 300 °C. Finally a high temperature component was demagnetized at temperatures generally between 300 and up to 690 °C. A few demagnetization plots were not considered if
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Fig. 7. Representative demagnetization orthogonal plots from the Can Vilella sections. CV 02 and CV3 account for reverse polarities found at the base of the section, whereas CV 11 is an example of normal polarity found at the uppermost levels.
sudden susceptibility variations were observed. Once all high temperatures were obtained (see declination and inclination values in Fig. 3), a mean of the directional values for each site was calculated in order to derive the Virtual Geomagnetic Polarity Latitude. As seen in Fig. 3, the small lower section displays an entirely reverse magnetization. In the largest section reverse polarities can be observed for the lower 18 m, while the upper 8–9 m display normal polarities. Thus, although the stratigraphic record at Can Vilella section is not very thick, a polarity reversal is clearly detected after the occurrence of relatively stable demagnetization of samples. Recent work carried out in the thick late Miocene continental sequences of the Fortuna Basin enables one to identify to some degree the normal geomagnetic event detected at Can Vilella. In this basin, a minimum age for the FAD of A. gudrunae (base of MN 13) has been established within chron C3Ar, that is, close to 6.8 Ma (Garcés et al., 1998; Agustı´ et al., 2001). On the other hand, data from the Cabriel section (Opdyke et al., 1997) provides a minimum age of 4.9 Ma (chron C3n.3r) for the lower boundary of the Promimomys Zone (MN 14; Agustí et al., 2001). Therefore, the normal chron at the top of the Can Vilella section can be identified either as C3An.2n or C3An.1n. In the Fortuna Basin, the FAD of Paraethomys miocaenicus occurs within chron C3An.1n (Agustí et al., 2001, 2006-this volume). However, this species is absent from the record of Can Vilella, so a decision as to whether the normal chron from this section corresponds to C3An.2n or C3An.1n cannot be taken. In any case, the Can Vilella succession can be placed in the Messinian stage, before the onset of the Messinian Salinity Crisis. 6. Biogeographic remarks From a biogeographical point of view, Can Vilella 1 represents a very atypical mammalian association in the
context of the Western European faunal assemblages. Only few elements are shared in common with other late Turolian localities from Spain, such as those of the Teruel and Fortuna basins. The late Turolian sites in these basins are characterized by a highly diversified endemic fauna of murids (Stephanomys, Occitanomys, Huerzelerimys, Paraethomys, Castillomys) and cricetids (Ruscinomys, Apocricetus) (Agustı´ and Llenas, 1996). The closest latest Miocene reference to Can Vilella is the fissure infilling of Lissieu in the Rhone Valley (France), which shares with Can Vilella the absence of the former endemic elements and the presence of Epimeriones and Eozapus (Mein, 1999). However, Epimeriones is represented in Lissieu only by two teeth, while it represents close to 50% in Can Vilella. A possible explanation for the Can Vilella biogeographical anomaly would be that the faunal association from this site represents the extension to the south of a higher-latitude fauna, that is, a “colder” local biotope, linked to a late Neogene uplift of the Pyrenees range. This interpretation is supported by the large populations of the Characeae Lychnothamus barbatus found in the grey mudstones of the same outcrop, which are typical of cold lacustrine waters (Soulié-Märsche and MartínClosas, 2003). However, the pollen data do not support the proposition that the Cerdanya basin was as elevated in the Late Miocene–Early Pliocene as today. Thus, the Messinian Cerdanya pollen flora is not significantly different from the Tortonian one (Bessedik, 1985; Suc, 1989). Some megathermic and mega-mesothermic elements have disappeared (such as Meliaceae, Distylium and Platycarya) while Fagus was more important in the Tortonian flora than in the Messinian one. The Messinian pollen flora from Cerdanya is very similar to the marshy pollen flora from Vivès (Suc, 1989) in the Roussillon coastal basin, which belongs to the earliest Zanclean (5.33 Ma). Similarity between these floras
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would suggest that the altitude of the Cerdanya basin did not rise much between ca. 9.6 and ca. 7–6.2 Ma. In contrast, there are a number of geological arguments that during the Messinian the relief was not so different than the present one, with relatively high mountains bounding the basin to the South. Fissiontrack data collected in the Canigó and Mont-Lluis massifs indicate that the topography resulting from the motion of the La Tet fault was generated between the middle Oligocene and the Burdigalian, at least along the French part of the fault (Maurel et al., 2002). Considering that the Cerdanya faults belong to the southwestern prolongation of La Tet fault, they point to the fact that the difference in the topographic height between the basin and the mountains that bound it to the south and southeast is relatively old and surely existed when the Can Vilella sediments were deposited. Paleocurrent analyses carried out in the Cerdanya basin (Cabrera et al., 1988) indicate that the predominant Carboniferous derived clasts in the conglomerates of Can Vilella came from the south, that is, from the footwall block of the Cerdanya fault. In this area the Carboniferous outcrops always below a height of 1900 m. Taking into account that the footwall block in this area (Cadí-Penyes Altes del Moixeró-Tossa d'Alp) attains heights of 2200–2500 m, it implies that during the beginning of the Upper Neogene Unit sedimentation, there was a range bounding the basin to the south with a height at least of 500 m above the basin plain. Moreover, the evolution of the alluvial fans (see description in the geological setting) denotes that most fault activity along the Cerdanya fault took place during the Vallesian and decreased considerably during the Turolian. This indicates that most of the relative uplift of the footwall block of the Cerdanya fault took place during the Vallesian since both isostatic and tectonic vertical motions generated by the motion of a fault have been recognized in models as well as in other regions as coeval to the periods of main fault activity (Tucker and Slingerland, 1994; Watts et al., 2000; Gaspar-Escribano et al., 2004). However, this late Neogene uplift was not an instantaneous event but was associated with a large wavelength change of the topography related to the Pyrenean orogenic evolution. With respect to Pyrenean topography evolution, apatite fission track profiles carried out more to the west across the central Pyrenees, indicate that, since the late Miocene, exhumation of the southern flank of the Pyrenees accelerated with an average erosion of 2–3 km (Fitzgerald et al., 1999). Consequently, a post-Middle Miocene regional uplift of the Pyrenees is required. This uplift could be explained by
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the thermal re-equilibrium of the thick Pyrenean lithosphere which presently shows evidence of lower crustal heating with generation of partial meltings (Pous et al., 1995; Glover et al., 2000). The amount of this lithospheric uplift and its effect in the Cerdanya Basin remain unknown but, considering that the crustal structure of this portion of the Pyrenees is similar to that of the central Pyrenees (Muñoz, 1992; Vergés et al., 1995), we can assume that it is also significant, although less than 2 km. Altogether, these data point to an uplift of at least 500 m above the basin plain at the beginning of the sedimentation of the Upper Neogene Unit and more than 1000 m at the end of the deposition of this unit and support the argument that the relief of the Cerdanya Basin and surrounding areas was similar to the present one, with high chains bounding it both to the north and to the south. Therefore, the higher-latitude small mammalian fauna from Can Vilella can be explained by the association of relatively high reliefs and some of the cold events that punctuate the beginning of the Messinian, prior to the onset of the MSC. In this way, benthic δ18O at Site 982 in the North Atlantic records a latest Miocene glaciation that lasted from ∼ 6.26 to 5.50 Myr and was marked by 18 glacial-to-interglacial oscillations that were controlled by the 41-kyr cycle of obliquity (Hodell et al., 2001). Combination of one these first glacial cycles with relative uplift of the Pyrenees could be responsible for the dominance in the Upper Neogene Unit of La Cerdanya Basin of higher-latitude elements such as E. aff. austriacus. This scenario would also favor placement of Can Vilella in geomagnetic chron C3An.1n. Acknowledgements Magnetostratigraphic measurements were undertaken in the Paleomagnetism Laboratory of the Serveis Científico-Tècnics of the Universitat de BarcelonaCSIC. This study was financed by projects BOS20011044 and PB96-0815 of the Ministry of Science and Technology of Spain and Grup de Recerca de Qualitat SGR2001-00077 of Departament d'Universitats, Recerca i Societat de la Informació (Generalitat de Catalunya). Authors acknowledge the revision by Miguel Garcés and Rosa Domenech (Universitat de Barcelona). M.F. acknowledges the support from the European Science Foundation (EDEEN Exchange Grant) and the comments by L.W. van den Hoek Ostende (Naturalis, Leiden) and J.W.F. Reumer (Natuurmuseum, Rotterdam) on the study of insectivores. The pollen study was supported by the French Program
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