Stratigraphy revision of Upper Badenian of Rakovica stream near Belgrade (Central Paratethys, Serbia)

. Belgrade area is a region of high paleobiodiversity, being ranked among the best knovvn m Serbia. The prominent position among a number of middle Miocene (Badenian) fossiliferous sites in the vicinity of Belgrade (southern Pannonian Basin, Centrale Paratethys] are occupied with sediments of Rakovica stream, also known as "Rakovica sands”. Here, the integrated evidence based on new fossil findings of calcareous nannoplankton, foraminifera and molluscs assemblages, allows the stratigraphic revision of the clastic facies of the Rakovica succession. Based on the studies of lithological composition, high paleodiversity molluscs fauna and local palaeogeographical setting, it can be concluded with reasonable certainty that deposits of Rakovica stream en-titled "Rakovica sand” represents a sandstone of the shallow marine (littoral) environment during lower Badenian time. Large benthic foraminifera Ammonia viennensis (d ’O rb ig n y ), and Borelis haueri (d ’O rb ig n y ) as well as zone marker NN5 Sphaenolithus heteromorphus D e f la n d r e correspond to this biostratigraphic level. During the late Early Miocene and Middle Miocene (Badenian), the climate in the Central Paratehys was mainly subtropical. This is supported at its southern margin by the presence of thermophilous mollusc taxa, as well as the Conidae, Strombidae, Xenophoridae, Pleurotomidae, Turridae, Muricidae, etc. Consequently, the investigated deposit can be ascribed to the Early Badenian which biostratigraphically corresponds to the NN5 nannozone by correlation with successions in theirs type-areas to the Central Paratethys, and defines preciously the time of the marine transgression in this area.


Introduction
The shallow marine deposits are famous for a long time for their highly diverse and excellently preserved foraminifers and mollusc assemblages. In Serbia, the largest spatial distribution of Badenian sediments exposed on the surface can be found in Belgrade and its vicinity, where they have been best studied due to the rich mollusc fauna. Also, the bryozoa, spongia, corals, ostracods, along with the crabs and fish remains are present. Since the first discovery of fossils fauna at Rakovica stream (Žujović, 1886;Pavlović, 1890) and later on, this site have been the subject of interest of many researchers (Luković, 1922;Petrović, 1962;Eremija, 1977;Ganić et al. 2016, etc.). The chronostratigraphical framework of the sedimentary succession from Rakovica stream (the Upper Badenian age,Ammonia beccarii Zone) was based on studies of the foraminifera assemblages (Petrović, 1962;, however, these important microfauna collections are not available. As a consequence, it often happens that many local-ities are assumed to belong to the Upper Badenian age (Jovanović, 2018), pointing to the need to reassess the age of some classical Badenian localities. Later, Rundić et al. (2019) published a summary review of several Miocene sites near Belgrade, but they did not add new stratigraphic records for socalled "Rakovica sand".
For the southern margin of Central Paratethys, some independent age constraints were established by working in the last decade (Ćorić et al. 2009;Pezelj et al. 2013;Sant et al. 2018;Jovanović et al. 2019a, Jovanović et al. 2019a; Mandic et al. 2019). These regions of the Pannonian basin were flooded later than the northern and western regions during the early Badenian (Ćorić et al. 2009;Sant et al. 2017;Jovanović, 2018). However, the chronostratigraphic correlations of marine Middle Miocene deposits of the Serbian Neogene are still considered problematic. The facies distribution, stratigraphy, and tectonic structure of the Belgrade area which comprises early and middle Miocene sediments have not been studied in great detail. The precise chronological analysis w as largely im proved for the several sites in Serbia (Sant etal. 2018;Mandic etal. 2019), but chronology o fth e oldest units o fth e Belgrade area are still largely speculative. The outcropping rocks exposed on the Rakovica valley are p art of the Upper Badenian with m ost authors (Ganić et al. 2016, Mandic et al. 2019, Rundić et al. 2019). Recently, the latest discovery in Serbia (Jovanović et al. 2019a) modified previous biostratigraphical results o f som e localities and indicated the n ecessity of stratigraphic revision of Rakovica and som e other localities in the region.
In order to check the stratigraphic position of sediments from the Rakovica stream, several samples have been analysed in respect to nannoplankton, foraminifers, and molluscs. The research was based on these fossil assem blages in order to revise the Upper Badenian deposits of Rakovica stream, and in order to provide a thorough scientific background for future study. New research clarified the stratigraphic position of the deposits of the socalled "Rakovica sand". Micropaleontological and m acropaleontological studies on the outcropping rocks exposed on the Rakovica valley showed the existence of a rich fauna, foraminifera and molluscs being the m ost important component of assem bly of the fossil invertebrate. The combination of biostratigraphic analyses based on studies of some rare calcareous nannoplankton, foraminifera and rich molluscs assem blages, allows the revision of the clastic facies of the Rakovica succession. The studied outcrop is located on the left bank of Rakovica stream, on the southern flanks of Torlak Hill near Belgrade (Fig. 1).

Methods and materials
New bulk samples were taken in 2018 for analyses of fossil materials. Authors have collected stratigraphically and taxonomically important microfossils and macrofossils. A total of 12 samples for the analysis were analysed, collected from two outcrops and from one well. Also, old collections of the Natural History Museum in Belgrade, comprising 3000 specim ens from the Rakovica deposits, were investigated. For stratigraphic revision of these deposits and for explaining the real vertical ranges of studied fossil assem blages, we used calcareous nannoplankton, benthic foraminifera and some termophilic molluscs, in particular those considered of stratigraphic importance to the Badenian. Sediment sam ples were processed by using standard micropaleontological and palaeontological methods of preparation technique. A total of 3 sam ples for the analysis of nannoplankton assem blages were prepared partly at the Vienna Smear slides, following standard procedure described by Perch-Nielsen (1985). For the foraminifera and small mollusc extraction, 9 sam ples were prepared and washed at the laboratory and allowed to dry. Laboratory methods were employed for disintegrating soft sandstone using hydrogen peroxide. Samples were washed and the foraminifera and molluscs were recovered from the over a 0,1 mm fraction-sieve and picked under the microscope. The stratigraphical analysis of the nannoplankton zonation is based on Martini (1971], while the foraminifera zonation is based on Grill (1943). The photos of the molluscs were made with PANASONIC DMC-FZ50.
The preservation of the m ost foraminifera and molluscs specimens is quite good. Collected materials are stored in the collections of Natural History Museum in Belgrade (Serbia). The collectors include: Petar Pavlović, at the end of the 19th century, Petar Stevanović around the mid-20th century, as well as the authors of this paper. As old Museum documentation does not contain all information on the location of some fossils, on the basis of the sediment stored on the fossils, we tried to identify the locality where they came from. The part ofstudied specimens of foraminifera are housed in the University of Tuzla (Bosnia and Herzegovina), while the samples of nannoplankton assem blages are stored in the collection ofthe Geological Survey of Austria in Vienna.

Geological setting
In the Middle Miocene (Badenian) the investigated area was located in the southeastern margin of the Pannonian Basin (Central Paratethys). The deposition of marine sedim ents during the Early Badenian of Central Serbia resulted from the transgression of the Central Paratethys Sea, which initiated the development of several basins, subbasins and bays with a corresponding sedimentation (Anđelković et al. 1989). In that time, the surrounding of Belgrade was a complex network of shallow marine basins. The Slovenian Trans-Tethyan corridor probably functioned as the connecting sea strait with Mediterranean Sea, according to Bistričić & Jenko (1985). Connections are recorded also between the Pannonian and the Transylvanian basins, through the Mures passagew ay and Faget Basin in Transylvania (Rom ania), (Chira & Marunteanu, 1999;Chaix et al. 2018), (Fig. 2B).
M ost of the Belgrade area is covered by mid-Miocene sedim ents, lying transgressively over wellform ed paleo-relief. The Miocene deposition in the Belgrade area begins with continental alluvial and lacustrine sedim entation, which occurred during the Early Miocene time and at the beginning of the Early Badenian, before the first sea transgression. The Belgrade basin is filled with sedim ents com posed of conglom erates, m arls, clays, sand, san d ston es and limestones of different thickness at different sites, because tectonic movements separated these rocks into distinctblocks (Petković, 1912) lifted or plunged, during the Neoalpine tectonic events (Marović et al. 2007;Toljić et al. 2016). Paleogeography, tectonic movements and connections with other basins and sub-basins across the gulf or open-w ater channels (Anđelković et al. 1989;Matencko & Radivojević, 2012;Jovanović, 2018) were the main factors influencing the diversity of m olluscs in Serbia during the Middle Miocene (Badenian), which resulted in the formation of different facies with diverse fauna.
High diversity and excellent preservation of fossil assem b lages are m entioned from a large num ber of Serbian localities, especially m olluscs. The age of these d ep osits should be considered mainly of Middle Miocene (B adenian) which com prises three p arts: Early Badenian (Lagenidae Zone), Middle Badenian (S pirorutilus carinatus Zone), and Late Badenian (A m m onia b e cca rii and E lp h id iu m crispum Zone) (Petrović, 1962;. According to Harzhauser et al. (2018), the Badenian stage can be correlated with the entire Langhian stage and the lower p art of the Serravallian stage of the Standard Global Chronostratigraphic Scale of Gradstein et al. (2012). During the Early Badenian, the first m arine ingression reached Central Serbia area (Eremija, 1977;Jovanović, 2018;Sant etal. 2018;Mandic etal. 2019). On the terrains of the center of Belgrade and its surrounding, like in the Vienna basin, a very pronounced facies differentiation is recorded, when the Early Badenian sea-level rise covered older deposits in Rakovica area (Luković, 1922). Obviously had specific development in terms of facies distribution depending on paleorelief configuration and the tectonic reorganisations in the region. During the Early Badenian, when the sea transgression reaches its biggest extent, from the geotectonic point of view, the Rakovica stream belongs to the western Border of Belgrade basin.

Results
The biostratigraphic analysis is based on the Museum collections and new field research, along with collected materials. The fauna originate from several sites, here described under the names: Rakovica stream section, Rakovica stream -old locality situated at a very short distance (about 100 m), and well cores belonging to the estate of Mr. Šujica. Some specim ens from the Petar Stevanović collection originates from other localities: Clavatula schreibersi (Hoernes) from Rakovica town and Aporrhais dactylifera (Boettger) from Jelen Hill.

Rakovica stream section
The described section of Rakovica stream, with a maximum thickness of 3 m, consists ofyellowish and grey, fine-grained, poorly cemented sandstone and irregularly distributed hard yellowish sandstone lenses. The sediments are composed of a single relatively uniform deposit. A lower part is mainly dominated by the yellow sandstone, Fig. 3 (A a, B a) whereas the central part shows intermixing of grey and yellowish colored sandstone with hard sandstone lenses, Fig. 3 (A b). The contact surfaces between sediments of different color are uneven, Fig. 3

(B).
In its upper part, they are sometimes replaced by yellowish sandstone with hard sandstone lenses. The latest 1.5 m thick unit, Fig. 3 (A c, C), passing into thin and hard layer cemented Leitha sandstone towards top (Fig. 3 d), with poorly preserved nannofossils and well preserved Ascidien spiculae, has been observed. Both are dominated by quartz grains, while the cement is calcite. On their southern side, laterally, two thin wedge-shaped of the grey sandstone layers are exposed (Fig 3 e). Fossils foraminifera come from both yellowish and grey samples, Fig. 3  YeIIowish sandstone Calcareous nannofossils have low abundance and diversity because very shallow sandstones of the Rakovica stream are not very favorable to provide abundant and rich associations of nannofossils. The m ost analysed sam ples from the yellow sandstone were barren in calcareous nannofossils. The rarity of nanofossils made it difficult to establish a biostratigraphic framework. Nevertheless, in two specimens, the few identified species are rather informative and show that NN5 zone of the Middle Miocene is present in the sampled succession. The first manifestation of nannoplankton is noted at the top of section Rakovica stream, Fig. 3 Martini, 1971 w as used). The zone is dated Middle Miocene based on the presence of benthic forms, and corresponds to the M5 zone of Berggren et al. (1995), on the regional scale (Paratethys).
Foraminifers are unequally distributed in the yellowish sediment and almost exclusively represented by benthic forms, only two planktonic forms of genus Orbulina were found. Foraminifers are more numerous and diverse than those of the sample of grey sandstone. The following foraminifera were determined: Ammonia viennensis ( The mollusc assem blages were already known in the 19th century, when Žujović (1886) and Pavlović (1890) made the list of mollusc species from the Rakovica stream. However, the majority of identified molluscs have a wide chronostratigraphic distribution, making it difficult to divide the Badenian, using them as a basis. Current investigation of the fossil assem blages and recent morphological studies (Atanacković, 1985;     The grey sandsone The grey sandstone contains only foraminifera fauna and mollusc shells. Nannoplankton is absent. Foraminifers are represented alm ost exclusively by benthic forms while the planktonic forms are scarce, only one specimen of Orbulina have been recorded. The follovving foraminifera were determined: Ammonia viennensis (d'Orbigny, 1846), Elphidium crispum (Linnaeus, 1758), Borelis haueri (d'Orbigny, 1846), Dendritina haueri d'Orbigny, 1846, QuinqueIoculina sp. and Orbulina suturalis Bronnimann, 1951. (Fig. 4 A). Amongmolluscs, the following species are identified: Antalis vulgaris (da Costa, 1778);/l/7tofecf. mutabilis (Hornes,

Rakovica stream -old locality
This section is not longer available for fossil sampling, but it might be possible to correlate it to the beds 4, 5, 6 of the section described by Eremija (1977). We represent it by museum collections. The sam ple of yellowish sand from fossils was taken in 1995. The section's length was 10 m, and the yellowish sand and small lense of sandstone could have been recognized. Foraminifera, bryozoa, corals, ostracod shells, echinoid spines, remains of crabs, and rich mollusc communities are also present. These marine assem blages from a highly energetic, normally saline environment were characterized by ex-cellent preservation of foraminiferal tests and mollusc shells.

Discussion and Interpretation
In Serbia and som e other regions of Central Paratethys, the temporal span and boundaries of the Badenian regional stage remain unclear. Generally, in Paratethys area, other biostratigraphic problems were noticed (Kovač et al. 2018). In recent works, Badenian transgression is well documented from Serbia (Sant et al., 2018;Jovanović et al., 2019a;Mandic et al., 2019;Rundić et al., 2019), but the base of the Badenian has not yet been precisely defined. The intense efforts directed at resolving stratigraphic problems have not yet been matched with the latest researches of Badenian sedim ent of Central Paratethys. As pointed out by Jovanović et al. (2019a), a biostratigraphic revision is required for some Badenian localities. In order to check the stratigraphic position of sediments from the Rakovica stream, several sam ples have been analysed in respect to nannoplankton, foraminifers and molluscs. The existing information of the Middle Miocene calcareous nannofossil species from the Serbia sites: Višnjica (near Belgrade) and Koceljeva (Western Serbia) have been published by Mihajlović & Knežević (1989), and Jovanović et al. (2019a). Age of these deposits corresponds to the calcareous nannoplankton Sphenolithus heteromorphus (NN5) zone. A similarity is registered between the nannofossil assem blages of Lower Badenian deposits in Serbia, Transylvania, Slovenia, Bosnia, as reported by several authors (Bartol, 2009;Chira & Vulc (2003); Mihajlović & Knežević (1989), or between the other fauna (Jovanović et al., 2019a;Chaix et al., 2018).
Both Rakovica stream and Rakovica stream -old locality are not significantly different because they contain alm ost the sam e rich fossil assem blages, though the old locality seem s som ewhat more diverse in term s of gastropods. Chronologically, the section Rakovica stream -old locality is stratigraphically slightly older, taking into account the falling angle of the sediments, 30-40° (Petković, 1912;Eremija, 1977). In the investigated area, the identification of the nannoplankton zone NN5 (Martini, 1971), was made based on the presence of Sphenolithus heteromorphus and the absence of Helicosphaera ampliaperta. Sphenolithus heteromorphus was recorded in the sample of the old museum collection. Its LO (Last Occurrence) in the Mediterranean was dated at ~ 13.4 Ma (Abdul Aziz et al., 2008), which points to the fact that these sediments must have been older than 13.4 Ma. This means that these Rakovica sediments correspond to the NN5 calcareous nannoplankton zone (Martini, 1971).
The foraminifera associations from the analysed sandstones of the Rakovica stream belong to the lower Badenian, namely the older zone A. viennensis and E. crispum. This finding is supported by several facts. The first is that in the sandstones a species of B. haueri has been designated, which in Central Paratethys is exclusively associated with the Lower Badenian (Cicha et al., 1998). Additionaly, the sandstones contain a rich association of fossils, which is nota feature ofthe upperm ostzone of Upper Badenian in Central Paratethys. Due to the few fossil communities, this zone is also referred to as the "Impoverishment Zone" in the Vienna Basin (Papp & Schmid, 1985). The cause of "Impoverished fauna" is probably the decrease in salinity of the seaw ater at the end of Badenian. Also, this "Impoverishment Zone" is characteristic of the upperm ost zone of Upper Badenian in the area of Northern Bosnia (Vrabac, 1999). Very important difference between the Upper Badenian and Lower-Badenian zones of Ammonia viennensis is that the Upper Badenian zone was formed during the regression, while the Lower Badenian zone is related to the transgression of Central Paratethys. Basal conglomerates and fossilifer-ous san d sto n es o f the Rakovica stream w ere dep osited during the tran sg ressio n o f the low er Badenian Sea, which is a feature ofth e lower Badenian sedim ents of the A. viennensis Zone, both in Serbia (Jovanović et al.,201 9 a) and in Northern Bosnia (Ćorić etal., 2018). Upper Badenian zone sedim ents are highly regressive in the Vienna Basin (Papp & Schmid, 1985). This w as stated in num erous sites of the southern m argin of Central Paratethys (Vrabac et al., 2015). In the Višnjica locality n ear Belgrade (accordin gto Krstić &Mitrović, 1993), sedim ents of the u pper Badenian with Ammonia beccarii (= Ammonia viennensis) lying over the older ones (zone with Spiroplectamina carinata) w ere drilled in the V-26 well. Biostratigraphically, they correspond to the Bolivina dilatata Zone, and their total thickness is about 40 m.
The Badenian fauna from Rakovica is thought to contain a large proportion of m olluscs (Žujović, 1886;Pavlović, 1890;Eremija, 1977Eremija, , 1987Ganić et al. 2016) but understanding the age and general spatiotemporal processes that shaped their distribution are yet unclear, and they are probably older than the Upper Badenian (Jovanović, 2018). In previous literature, the chronostratigraphical framework of the sedimentary succession was based on the foraminifera assem blages and the entire succession is dated as Upper Badenian. In recentyears, the Middle Miocene deposits of the Rakovica area have been studied, as well as the Badenian fauna. However, m ost of these papers refer to the outdated biostratigraphy (Ganić et al., 2016;Rundić et al., 2017) or misidentification of foraminifera (Rundić et al. 2019). For example, in the Fig. 5 (p. 114) according to Rundić et al. (2019), we can clearly identify Borelis haueri.
Our results show approximately 150 mollusc species occurring in the studied sections, thermophile molluscs are common. Gastropods dominated in the sam ples. Molluscan assem blages represent elements common in Early Miocene or early Middle Miocene (Badenian) of the Central Paratethys. The Early Badenian is characterized by a rich fauna that prefers warm water (Harzhauser & Piller, 2007). Many marine molluscs display a peak in diversity during the warm Early Badenian. The high diversity reflects the warm tem perature and indicated Middle Miocene Climatic Optimum, which allowed numerous thermophilic proto-Mediterranean elements to migrate into the Paratethys (Harzhauser et al. 2003). Despite the fact that thermophile taxa play an important role in establishing biostratigraphic and biogeographic correlations (Harzhauser & Piller, 2007), they were poorly used for biostratigraphy of Serbian deposits. Molluscs such as Xenophora deshayesi, Babylonia eburnoides, Semicassis laevigata, Vitularia linguabovis, Persististrombus exbonellii, Persististrombus cf. lapugyensis, Aporrhais dactylifera and Megacardita hoernesi, belong to the Early Miocene or appear at the beginning of the Badenian transgression. Stenohaline, thermophilic species from the investigated area are followed by numerous gastropod cerithiids (over 500 specimens) and Rissoina (over 100), indicative ofthe occurrence of sea-grass meadows in a predominantly shallow water environement. Therefore, the investigated sections correspond to Early Badenian age (nannoplankton zone NN5) and to TB 2.4, the Badenian sequence within the NN5 nannozone.
T he in v estigated fau n a h as b een frequen tly u se d a s refe re n ce fau n a for th e c o m p a riso n w ith oth er fam e d P arateth y an E arly B ad en ian m o llu sc fau n a from Low er A u stria (G ainfarn an d V oslau), Poland (K orytnica) an d R om ania (L ap u giu de Sus, Costei), an d can be c o rre la te d w ith th e L a g e n id ae Zone (G rill, 1941) o f the B aden ian , a s w ell a s w ith som e classic B ad en ian fo ssilifero u s site s o f Serbia. From the R akovica n e ar B elgrade, the rich m ollusc fo ssils p re se n te d h ere can be co m p a re d w ith th a t o f the G olubac (N o th eastern Serbia), (Mikinčić, 1932;Spajić, 1975;Jovanović, 2018). Both lo calities sh o w high d iversity w ith n u m erou s com m on term op h ile ta x a s (Persististrombus, Xenophora, Lautoconus, Varioconus, Phasmoconus, Kalloconus, Terebra, Clavatula, Babylonia, etc), but Golubac site is m uch m ore abund an t in the n u m b er o f sp e c ie s an d sp e cim e n s (Jovanović, 1996). The n u m e ro u s id en tified m o llu scs from R akovica site s have a w ide geo grap h ic distribution in Central P arateth ys such a s Flabellipecten besseri, Pecten aduncus, Microloripes dentatus (Defrance), Cardites partschi, Athleta rarispina, Paroxystele orientale, Xenophora deschayesi etc (Studencka, 1986; Landau e t al., 2013; Chaix etal., 2018). Incomp a riso n w ith o th er lo calities in Central P arateth ys (Baluk, 2003(Baluk, , 2006Mikuž, 1998) etc, quite the "impoverished" conoidean fauna from the Rakovica stream is observed. Turrids are important marine carnivorous gastropods that are highly diversified in shallovv as well as deep water. Among Turridae and Pleurotomidae, only seven species are identified, thermophile genus Clavatula with three species and more than 110 specimens indicated to warm climate [Clavatulagranulatocincta, C. sophiae, C. schreibersi). Some rare gastropods as well as representatives of family Architectonidae (= Solariidae), etc are noticed. The architectonicids known as "sundials," are a group of worldwide distribution, mainly in subtropical and tropical waters which have an extended veliger stage enabling larvae to live in the plankton for relatively long periods and thus to cover great distances with the ocean currents, ensuring wide distributional ranges (Mauro-Pietro & Cesare, 2016). Heliacus monilifera and Psilaxis cf. simplex have a wide chronostratigraphic distribution (Landau et al., 2013).
A frequent alternation of different facies is the result of inflows into the shallow sea and the characteristic of sea shore. In addition, the Rakovica stream sedim ents w ere deposited in a fairly shallow m arine em baym ent in which the m aterial w as occasionally brought in by stream s or rivers. Coccolithus pelagicus is com m on in close to river m ouths (Ćorić, 20l>3). This type of deposition is indicated by the nature of the layers, such as w edge-sh aped sed im en tary deposits, gradual transitions between sedim ents of different colours and sm all differences in grain size. All d ata indicated th at the com m unications with a d eeper sea w ere establish ed a s early as in Lower Badenian. The Badenian m olluscan biodiversity w as sh aped by a series of events connected with the geodynamic and climatic evolution of the southern margin of Central Paratethys during the early Middle M iocene (Badenian). Palaeogeography, tectonic m ovem ents and connectionb via bayw ays or canals with open se a (Anđelkov'ć et al. 1989;Matenco & Radivojević, 2012) p resen t the m ain factors within the m ollusc community, m aking Serbian diversity during Middle Miocene (Badenian), (Jovanović, 2018).
The lithofacial and biofacial characteristics of the studied deposits ofthe Rakovica stream indicate that they were deposited in a very shallow, coastal part of the infralittoral sea with normal salinity. The cos-mopolitan nanofossil indicates shallowing of the sea. The small reticulofenestrids such as R. minu^a or R. haqii have a wide ecological tolerance and indicate a nutrient-rich, eutrophic, near-shore environment (Auer et al. 2015). The abundant and varied molluscan assem blage signifies subtropicai conditions, favorable substrates, and abundant food supply. Large benthic forms are suggesting a shallow water highenergy environment. Therefore, the mollusc assemblage clearly indicates the infralittoral zone and, thus, the euphotic zone. Shallow marine environments are also dorumented by the numerous trace bioerosion on shell of molluscs (Ganić etal. 2016), as well as in the investigated materials presented here. In sout'iern Topčider river area, sedimentation took place in shallow marine settings, resulting in deposition of coal-bearing clay, probably corresponding to Upper Badenian. This probably documents shallow or estuarine environments and coast vicinity.
During the late Early Miocene and Middle Miocene (Badenian), the climate in the Central Paratehys was mamly subtropical (Kovać etal., 2007). This is supported at tht southern margin by the abundance of thermoph.lous mollusc taxa as well as in the same interpretations made by other authors engaged in the same fieldwork (Jovanović et al., 2019c;Mandic et al., 2019). The studied mollusc fauna indicates the influence ofthe period of global warming, so called Middle Miocene Climatic Optimum (MMCO initial warming beginning ca. 18 Ma and with peak warming ca. 17-14.75 Ma, according to Zachos et al. (2001Zachos et al. ( ,2008, thatpreceded the Middle Miocene Climatic Transition (global cooling during the interval -15-13 Ma). MMCO event initiated many ecological changes, including the influence on the development of mollusc fauna and their distribution. Literature data from around the world suggest that during the MMCO, many localities were characterized by rich invertebrate remains, containing an abundance of predominant foraminifers, gastropods and bivalves. Numerous taxa are very sensitive to temperature and salinity change. The presence of typical warm-water indicators (e.g., Conidae, Clavatulidae, Strombidae, Xenophoridae, Cypraeidae) within the studied Museum collections, supports the interpretation that studied fauna excisted during the late phase of the Middle Miocene Climatic Optimum. Based on these criteria, we conclude that it is necessary to continue the revision of the Upper Badenian in Serbia, Bosnia and Herzegovina, and Croatia, on the localities where the Upper Badenian has been determined only based on the Rotalia beccarii zone (= Ammonia viennensis).

Conclusion
This paper presents the results of biostratigraphic studies of Badenian (early Middle Miocene) sedim ents of the Rakovica stream near Belgrade (Central Serbia). The Badenian sediments, rich in various fossils, have a w idespread distribution in the area of Belgrade. A review of past works on the early Middle Miocene sedim ents of the Rakovica stream (Petrović, 1962(Petrović, , 1985Ganić et al., 2016;Rundić et al., 2019), together with new fieldwork in that area and the latest research of the vicinity of Koceljeva (Jovanović et al., 2019a), have indicated the necessity of stratigraphic revision of those beds. Micropaleontological and macropaleontological studies of the sediments of Rakovica stream herein attributed to the Lower Badenian showed the existence of a rich fauna where molluscs and foraminifera, as well as some rare nannofossils, allowed accurate dating the age of the researched sediments. The biostratigraphic analysis is based on the old Museum collections and new ressearches. The conducted investigation resulted in defining middle Miocene (lower Badenain, Lagenidae NN5 Zone) age of these sediments.
Our conclusions about the fossil records give new light on the stratigraphy of Rakovica sediments for further studies, providing a useful resource to the future study of fossil assem blage diversity. The results show approximately 150 molluscs species, occurring in the studied sections and Museum collections. Many Middle Miocene species belongingto extinct or extant genera have been recorded in the Paratethyan region. Further research might increase the total number of mollusc taxa indicated above for the Badenian of Rakovica.
During the late Early Miocene and Middle Miocene (Badenian), the climate in the Central Paratehys was mainly subtropical. This is supported at its southern margin by the abundance of thermophilous mollusc taxa as well as Conidae, Strombidae, Cypraeidae, Xenophoridae, Muricidae, Pleurotomidae, etc. Based on the studies of lithological composition, nannofossils, foraminifers and high paleodiversity mollusc fauna and local palaeogeographical setting, it can be concluded with reasonable certainty that the Rakovica deposits represented a shallow marine (sublittoral) environment during Lower Badenian time. The abundant and varied molluscan assemblage and other fossil assem blages indicate favorable substrates, abundant food supply, and warm-temperate to subtropical conditions. Current investigation of the fossil assem blages that are here dated as Lower Badenian will contribute to clarify more accurately the biogeographic pattern of Badenian fauna of the region, and fill in the gaps in the biostratigraphical division of the Badenian sediments of Serbia. It should also contribute to a better knowledge of the paleoecological conditions during early Middle Miocene (Badenian), when the warm climate zone was much wider than today. We conclude that it is necessary to continue the revision of the Upper Badenian in Serbia, Bosnia and Herzegovina, and Croatia, in the localities where it is determined solely based on the Rotalia beccarii zone (= Ammonia viennensis).