A mid-Miocene age for the Slanci Formation near Belgrade (Serbia), based on a record of the primitive antelope Eotragus cf. clavatus from Vi{njica

In a borhole at Veliko Selo near Belgrade in the Miocene lacustrine sediments Slanci, which are locally known as the Slana~ka Serija, a mammal tooth was found. The age of these deposits is under discussion. The fossil is here described and attributed with a query to the primitive antelope Eotragus clavatus (GERVAIS, 1850), which is suggestive of a Early Serravallian (“upper Badenian”) or Early Middle Miocene age for these deposits, whereas an Aquitalian or Eggenburgian (“Egerian” or “Eggenburgian”) (Early Miocene) age can be ruled out.


Introduction
The Danube Klju~ area near Belgrade is situated on the borderline of the Balkan Mountains and the Pannonian lowlands on the south bank of the River Danube, comprising the villages of Grocka, Vi{njica and Veliko Selo.Recent studies into the construction of a canalization basin near Vi{njica-Veliko Selo have yielded new data on the geological structure of this area, as well as the first fossil mammal molar from Miocene lacustrine sediments (Slana~ka serija, "formation" sensu PAVLOVI] (1922).This tooth enables an age assignement for strata from which it was recovered.PAVLOVI] (1922) described a new lithostratigraphic unit ("formation" sensu PAVLOVI] 1922) at Veliko Selo and Slanci, east of the city centre of Belgrade, where sandy clays and marly clays with floral imprints were found.He assumed a "First Mediterranean Age" (the old name for Aquitanian and Burdigalian age used localy) for these lacustrine sediments.These strata referred to of the "Slana~ka serija".On the basis of fauna collected from stratigrafically younger transgressive marine sediments, for example ostracods, foraminifera and fish teeth.According to F. Rögl (pers. comm.to KRSTI] 2007), the benthic species Spiroplectinella carinata (D'ORBIGNY) and planctonic Globigerinidae are present.The age of these younger strata deposited in the Danube Klju~ area is estimated to be between 13.25 and 12.9 Ma.
Rich macrofloral remains from the village of Slanci were described by MILAKOVI] (1956,1959) and MIHAJ-LOVI] (1978).These fossils, found in grey marls at a few localities in the village, include forms suggestive of a subtropical Cinnamomum, Myrica, Engelhartia and Libocedrus or a warm-temperate climate Populus, Salix, Zelkova and ferns.Species characteristic of drier and warm habitats include Quercus, Pinus, Celtis and Eleagnus or Eucalyptus, while Metrosideros and Sapindos are also represented.In general, these floral remains are typical of Mediterranean and steppe-savanna associations.Away from the lake, species abundant in a dry and warm climate occur (MIHAJLOVI] 1978).OBRADOVI] (1979) described a sedimentary series of "Burdigalian-Helvetian" age and concluded that these were deposited in a shallow-water, lacustrine environment.The size of the lake and its marginal swamps was estimated to have been about ten square kilometres.The maximum depth was assessed to have been 150 m and preservation of organic material suggested anaerobic and stagnant conditions.The rich fossil flora shows that a humid climate existed in this area.
In the G-1 borehole in the village of Grocka, close to Veliko Selo and Slanci, the stratigraphically oldest lacustrine sediments are found at depths between 1300 and 1100 m (KNE@EVI] et al. 1994).These are older than the overlying marine Paratethys sediments of Badenian age.DOLI] (1997) described the strata of "Slana~ka serija" as part of the "Lake group of the Danube Klju~".In strata exposed between the villages of Vi{njica, Slanci and Veliko Selo, he recognised three formations which represent lacustrine sediments.From bottom to top these are (Fig. 2): 1) the Veliko Selo Formation, consisting of sandstone, conglomerate, tuff and tuffite, with an overal thickness between 150 and 200 m (not figured).
2) the Slanci Formation, with a coal horizon of 30 m thickness and lacustrine pelites with laminated shale, marlstone with tuff and tuffite some 50 to 70 m in thickness.
3) the Bu~var Formation, consisting of conglomerate, breccia, laminated shale and marlstone, with a thickness of 100 m.DOLI] (1997) assumed the lake sediments to be of Aquitanian-Early Burdigalian ("Egerian-Eggenburgian" or Early Miocene) age.The contact between the "Lake group of the Danube Klju~" (Veliko Selo, Slanci and Bu~var formations sensu DOLI]) and the marine sediments of Badenian (Middle Miocene) age, he considered to be discordant.
Thus, the ages proposed for the Slana~ka serija vary between Egerian (some 24 to 20.5 Ma; ages according to STEININGER 1999) or Eggenburgian (20.5 to 18 Ma), Ottnangian (18 to 17.2 Ma), Karpathian (17.2 to 16.5 Ma) (all Early Miocene) and  or "Helvetian" (Middle Miocene).The antelope molar, found in a borehole core and described herein, permits a more precise indication of the age of the sediments in which yielded it.

Description of the section penetrated in borehole VI-4i
During the geological research for a construction of the future canalization interceptor, a molar was collected from the core of well VI-4i (Fig. 2).The core was drilled north of Veliko Selo on the elevated right bank of the River Danube at elevation 98 m, in the easterly side of the pit where this canalization interceptor is to be constructed.
The uppermost 1.7 m of the core comprise Quaternary colluvial deposits, while the reminder consists of Miocene sediments of the Slanci Formation.Between 1.7 to 2.7 m, occur clays with coal bands and a number amount of gypsum crystals, while between 2.7 to 8 m, there first are red clays on top with "rusty" siltstone clays with occasional gypsum crystals, and tuff and tuffite below.From 8 to 23.2 m, there are grey clays and yellowish silty clays with intercalations of sandstones of 2 to 3 cm in thickness.Gradually, to the lowest part of this section, sediments are represented by hard marly siltstone and clays.The molar was found at a depth of 8.8 m.In the lowermost portion of the core, at a depth of 23.8-23.2m, there are grey siltstone sands with intersections of clays and a bed of sand with gravel.
Core lithology and correlation with other drillhole sections in the vicinity and sediments exposed suggests that the core covers the older portion of the Slana~ka serija (see Fig. 1).The appearance of coal and coaly clays, as between 2.7 and 1.7 m, is characteristic of the lower part of the Slanci Formation in the eastern area of the Danube Klju~.The multicoloured sediments found at the base of the core probably represent the transition between the Slanci Formation and the underlying Veliko Selo Formation.

Palaeontology Material and methods
The single molar from Vi{njica, is kept in the collection of the Institute for Regional Geology and Paleontology, Faculty of Mining and Geology, University of Belgrade (RGF).It is here compared with Eotragus teeth from other localities, as housed at in the following collections: IPS, Institut de Paleontologia, Sabadell; IPUW, Institut für Paläontologie der Universität Wien; MHNT, Muséum d'Histoire Naturelle, Toulouse; MNHN, Muséum National d'Histoire Naturelle, Paris; NMB, Naturhistorisches Museum, Basel; SLJG, Steiermärkisches Landesmuseum Joanneum, Graz.
Measurements are taken as indicated by VAN DER MADE (1989) and descriptive tooth morphology follows VAN DER MADE (1996).

Description and comparison
The specimen preserves the buccal half of a right upper molar of selenodont morphology (Fig. 3).In the matrix sample contacting it, there is a root of another molar in front, suggesting it to be a second or third molar.The buccal wall extends much further posteriorly at the occlusal surface than at the base, which suggests that it is not a M 3 , but rather a M 2 .The selenodont morphology and its low crown show the tooth to have belonged to a ruminant, most probably a bovid or cervid.Although the crown is worn, it is visible that the tooth must have been fairly low, suggesting a Middle Miocene bovid or Miocene cervid, because younger members of these families tend to have higher crowns.
The buccal wall is relatively flat, as in early bovids.Early cervids, like Procervulus, Dicroceros and Euprox generally have a more strongly developed paraexocrista and the style in the centre is much more massive than at the base.In these characters, the tooth is closer to that in low-crowned early bovids, such as Eotragus and Pseudoeotragus.Of the protocone, only the protoendocrista can be seen.It is well developed, but at the occlusal level, it is not fused to the tetraprecrista or parapostcrista.In early cervids, the protopostcrista is better developed than the protoendocrista, whereas in later cervids the former crest tends to disappear and the latter becomes well developed.Even the earliest bovids have a well-developed protoendocrista and the protopostcrista is absent.The tetraprecrista and tetrapostcrista do not reach the buccal wall at the occlusal surface, leaving the posterior fossa open at both sides.Thus, the tooth represents an early bovid.
The tooth has a very low crown, much lower than in the Hypsodontinae (KÖHLER 1987), Protragocerus/Miotragocerus and also lower than a bovid from MN5 in Spain (Puente de Vallecas, Arroyo del Olivar, Valde- Although Tethytragus from Pasalar, Çandir and La Grive are relatively low-crowned, they still are slightly higher than the molar from Vi{njica.Pseudoeotragus seegrabensis has a M 2 that is slightly more high-crowned (VAN DER MADE 1989).Eotragus is a bovid having molars with the lowest crowns and thus is comparable in this respect to the molar from Vi{njica.
In Europe, the Eotragus artenensis GINSBURG & HEINTZ, 1968 -E.clavatus (GERVAIS, 1850) (= sansaniensis (LAR-TET, 1851)) lineage is recognised, characterised by size increase, plus the very small E. cristatus (BIEDERMANN, 1873) (VAN DER MADE 1989).The M 2 from Vi{njica has a length (DAPo = occlusal antero-posterior diameter) of 13.5 mm and a basal length (DAPb = basal antero-posterior) of 12.2 mm.In Fig. 3, the size increase in M 2 in the E. artenensis -E.clavatus lineage is shown.Additional measurements of other teeth show a similar picture (MAZO et al. 1998).The large sample from Sansan shows the range of variation.The molar from Vi{njica is large compared to the M 2 of most samples, but is close to the mean value for specimens from Sansan.

Discussion
Morphological features Vi{njica molar best fit Eotragus.Accepting the range of variation as indicated by the Sansan sample, the specimen could be a particularly large individual of the small species E. artenensis.However, assuming that the small samples for Fig. 3 are probably close to the mean of populations which they represent, the tooth from Vi{njica probably belongs to Eotragus clavatus.The use of open nomenclature reflects these uncertainties.

The Eotragus fossil and the age of the Slana~ka serija
As mentioned above, the ages proposed for the Slana~ka serija vary between Aquitanian or Early Burdigalian to Early Serravalien.The molar comes from the lower Slanci Formatioin, below the coal horizon.
As is apparent from the description and comparison, the age it indicates lies between the first and last occurrence of Eotragus, with a greater probability for a date close to Göriach and Sansan.
The more likely age of this molar ranges between Göriach and Sansan and possibly also Manchones I. Göriach was placed in MN6 (MEIN 1975(MEIN , 1977(MEIN , 1990;;DE BRUIJN et al. 1992), but its more likely age is very late in MN5, close to the MN5-6 transition, and time equivalent to zone E of the Aragonian (VAN DER MADE 1998; VAN DER MADE & RIBOT 1999;DAXNER-HÖCK et al. 2004;).The age of the MN5-6 transition has been estimated to be about 15.1 Ma (REICHENBACHER et al. 1998) and13.75 Ma (DAAMS et al. 1999a/b).The age of Sansan is under discussion as well, since its palaeomagnetism has been interpreted in different ways indicating ages of about 15 and 13.6 Ma (SEN, 1997, DAAMS et al. 1999a/b).As stated above, the age of Manchones I is estimated to be 13.25 Ma.The more likely age for deposits at Vi{njica thus is around 15.1-13.25 Ma.This is more in line with the younger age estimates, which places the Slana~ka serija Slanci Sequence in the Middle Miocene.

Fig. 1 .
Fig. 1.In the vicinity of Belgrade on the banks of the River Danube, Vi{njica, Veliko Selo and Slanci are located.The thickness of the deposits referred to as the "Slana~ka serija" in the literature, is estimated to be 350 to 400 m (DOLI] 1977).The Slanci Formation is one unit of this series.In borehole VI-4i (indicated with asterisk) (GPS position data: 20°35'50'' E; 44°49'30'' N) at a depth of 8.8 m in the Slanci Formation, a specimen RGFKS31 was found.

Fig. 2 .
Fig. 2. Section penetrated in well VI-4i at Vi{njica north of Veliko Selo on the elevated right bank of the River Danube (at 98 m) composed to a section of the formations of the Danube Klju~ (according to DOLI], 1997).The position of Eotragus cf.clavatus is indicated.